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DIE BIBLIOTHEK DER TECHNIK

388

48 Volt Technology For more efficiency and fun to drive

VERLAG MODERNE INDUSTRIE

CONTINENTAL


Volume 388 Die Bibliothek der Technik

48 Volt Technology For more efficiency and fun to drive Bernhard Klein, Oliver Maiwald

verlag moderne industrie


This book was produced with the technical collaboration of Continental.

To the authors of this book: Bernhard Klein is Head of Business Development of the Hybrid Electric Vehicle Business Unit within the Powertrain Division at Continental. Dr. Oliver Maiwald is Senior Vice President for the Powertrain Department Technology & Innovation at Continental.

Editorial assistance: Jörg Christoffel

© 2016 All rights reserved with SZ Scala GmbH, 81677 Munich Illustrations: No. 27 Schaeffler AG; cover, page 1, nos. 2, 4-26, 28-41 Continental, Regensburg Typesetting: JournalMedia GmbH, 85540 Munich-Haar Printing and binding: Kösel GmbH & Co. KG, 87452 Altusried-Krugzell Printed in Germany 236102 ISBN 978-3-86236-102-1


contents

Electric power in the vehicle – a short introduction

4

A race of technologies............................................................................. 5 Downsizing and turbocharging............................................................... 6 Change of paradigm............................................................................... 8 48 volt technology..................................................................................... 11

48 volt components and integration

14

Electric energy........................................................................................... 15 48 volt hardware........................................................................................ 17 Vehicle integration architectures............................................................. 21

Energy harvesting and fuel saving

27

Main strategies.......................................................................................... 27 Diesel hybridization with 48 volt................................................................ 36 Mild hybrid vehicle optimization.............................................................. 37

Energy use in hybrid operating strategies

41

Core electrical strategies.......................................................................... 43 Supporting strategies................................................................................ 52

Outlook – future potential for higher efficiency

56

Connected energy management........................................................... 56 Hybrid electric systems for many use cases ........................................... 64 Conclusion................................................................................................ 65

Sources 68 Abbreviations 69 The company behind this book

71


4  

Electric power in the vehicle

Electric power in the vehicle – a short introduction

One of the first electric cars

While it is often considered a very modern idea to power vehicles with electric energy, the concept has actually been around for quite some time: “(…) while oil-powered engines will journey across the lands at high speeds, and the smooth asphalt surfaces (…) in major cities will be traveled by accumulator-powered electric vehicles.” [1] If one ignores the slightly old-fashioned wording, this statement could have been published in any 21st century newspaper article, book, or TV program on vehicles with an electric motor. Yet the statement was made in 1897 by the Oberbaurat a.D. Adolph Klose during the inaugural meeting of the “Mitteleuropäischer MotorwagenVerein Berlin”. When Klose said this, not even ten years had passed since Andreas Flocken, an engineer based at Coburg, had presented his “Flocken Elektrowagen” in 1888 (Fig. 1) [2]. This vehicle – still looking very much like a horse-drawn carriage – was one of the world’s first electric cars and probably the first in Germany. Obviously Klose was ahead of his time. There was one thing in particular which he had analyzed very clearly: There are different vehicle user profiles, and even today a battery electric vehicle (BEV) which is powered by an electric motor “fueled” by a battery will only have a limited range. Going on a long trip with a BEV requires an electric infrastructure and sufficient time for charging. In Klose’s days, we would have been talking about 40 kilometers or less of electric range instead of several hundred. But then the early “roads” would not have encouraged too much long-distance driving anyway.


 5

Electric power in the vehicle

A race of technologies If it had not been for the still-young lead-acid battery technology of the late 19th century, the electric motor might have won the race with the combustion engine and could have become the preferred propulsion technology in the car. Initially electric vehicles held many speed and distance records. For instance, it was an electric car which first broke the 100 km/h speed barrier. In contrast, early combustion engines were difficult to handle, noisy, dirty, and not very durable. Yet eventually, the internal combustion engine proved to offer the greater level of flexibility and freedom to the driver. Technical progress made it more reliable and less difficult to start. Also, fossil fuel was becoming widely available, plus it was cheap. The road network was constantly being expanded so that longer journeys were becoming possible.

Fig. 1: Reconstruction of the 1888 Flocken electric car

Comeback of the combustion engine


6  

The race for efficiency

Electric power in the vehicle

For many decades it seemed the race between the two propulsion technologies was decided. However, things have begun to change. The availability and price of fossil fuels are increasingly hard to predict. Carbon dioxide (CO2) emissions and engine-out pollutions in particular are becoming an international concern because they contribute to the greenhouse effect and impact the air quality. Still, more nations around the world increase their standard of living, and individual mobility is a part of growing affluence. As a result, the global number of cars is going up all the time. It appears there is only one way out: Every new generation of cars needs to be cleaner and greener than the previous one. A new race is on: It is the race for vehicle efficiency.

Downsizing and turbocharging

Smaller engines with fewer cylinders

Efficiency in this context is a measure for the relation between internal combustion engine design, engine torque and power output, fuel consumption respective CO2 emission, and pollutant emission. Increasingly stringent regulations such as the Euro 6c/6d-TEMP standard in Europe (2017) and the European passenger car fleet average of 95 g of CO2 emission per kilometer (2020/21) define the targets which have to be met. Similar standards are being prepared all around the world (Fig. 2). The constant need to make combustion engines more efficient has generated a trend towards smaller displacement with higher specific power. The number of cylinders is going down. Cars that were traditionally powered by large 8-cylinder engines now tend to be fitted with 6-cylinder engines instead. Models which used to have 6-cylinder engines now offer the same power and torque


 7

CO2 emission, normalized to NEDC [g/km]

Electric power in the vehicle

240

CO2 limits in g/km: EU cars Japan China China US cars only

220 200 180

2020: 2020: 2020: 2025: 2025:

95 g 105 g 117 g 105 g 93 g

Historical performance Enacted targets Proposed target

160 140 120 100 80

2000

2005

2010

2015

with only four cylinders. And in the mass market segment of medium-sized 4-cylinder engines (1.6 to 2.0 liters), highly compact 3-cylinder engines are now gaining credence. However, one cannot reduce the displacement of an internal combustion engine without end. For instance, there is a thermodynamic optimum which is somewhere in the region between 300 and 500 cubic centimeters (ccm) per cylinder. It is therefore no coincidence that the ultimate downsized engine of today has three cylinders and one liter of displacement. The challenge lies in ensuring that it is still fun to drive a 1.5 ton car with a tiny combustion engine of this type. The answer lies in turbocharging. But even then the combustion engine has a drawback which can become tangible in such a small motor. When the engine speed is very low, the turbocharger will hardly react because the exhaust gas flow is not sufficient to accel­ erate the turbine wheel. To a driver, this turbo lag is most unwelcome as he feels rather let down when a car fails to respond to his demand for torque.

2020

2025

Fig. 2: Restrictions on the average fleet CO2 emissions per kilometer will become more severe.


8  

Electric power in the vehicle

Change of paradigm This brings the electric motor back in the race. In fact it is beginning to gain on the combustion engine for two reasons: Firstly, battery technology is making progress which helps to overcome the range anxiety step by step. Secondly, the electric motor is a perfect supplement to a car with a

Fig. 3: Reconstruction of the Lohner-Porsche “Mixte”

downsized turbocharged combustion engine because electric power can dramatically increase the vehicle’s overall efficiency while making it more fun to drive. Therefore, the race between combustion engine and electric motor is taking a different turn. Why compete when one can jointly win? Combining the strengths of the combustion engine with those of an electric motor helps to compensate the downsides of both technologies. Hybrid electric vehicles (hybrid cars for short) offer the combined strength of both engine technologies. It is not a new idea. As early as 1902, Dr. Ferdinand Porsche, who then worked at the


9

electric power in the vehicle

Jacob Lohner & Co company, presented his Lohner-Porsche “Mixte” serial hybrid car, propelled by electric wheel-hub motors (Fig. 3) [3]. The electric energy for the motors was provided by a gasoline engine which ran at a constant speed and drove an electric generator feeding batteries and the wheel-hub motors. Despite the simplicity of the electric motor in comparison to a combustion engine, one must say in all fairness that a complete electric drivetrain is not always quite as simple. If one wishes to propel a family-size passenger car weighing around 1.5 tons or more, for instance, the electric motor for that purpose needs several hundred volts and amps to do the job. Electric currents of this magnitude require many safety features to avoid the risk of electric arc/fire and shock under all circumstances – including maintenance, repair or a severe crash. If one factors electric motor power kw Electric vehicle

vehicle segment a

B

c

D

e

Fig. 4: Market penetration chances for the individual electrification strategies A Subcompact cars B Compact cars C Medium cars D Large cars E Premium cars

co2 saving potential *Saving potential “tank-to-wheel” in NEDC %*

60 - 120

100 High-voltage axle drive

60 - 120

50 - 75

Full hybrid

20 - 40

20 - 30

48 volt mild hybrid

10 - 20

13 - 22

Plug-in hybrid

12 volt micro hybrid

<5

market penetration:

3-4

Excellent

Partly

High-voltage power electronics

48 volt belt starter generator Voltage stabilization system

Less

48 volt DC/DC converter


10

electric power in the vehicle

acceptable cost-benefitratio

Fig. 5: Main components of a 48 volt hybrid system

in the need for a large and powerful traction battery, a high-voltage hybrid drivetrain will add substantial cost to a car. While this can still offer an attractive cost-benefit ratio when it is part of larger vehicle model, the cost of a highvoltage hybrid system tends to be prohibitive in a smaller B-segment (compact) or C-segment (medium) vehicle. Figure 4 provides an overview of electrification strategies plus an assessment of how suitable individual strategies are for specific types of vehicle. Factoring in a realistic cost-benefit ratio of electrification, compact mass-production cars pose a particular challenge as they need electrification more than any other because the economy of scale is so great: If millions of cars were to save upwards of 20% of fuel, for instance, the total saving would be massive indeed. So one is not only looking at the need to have highly efficient cars, they also need to be affordable. The answer to that lies in clarifying a misconception. Electrification should not be an allor-nothing-at-all approach. To be successful on

48 volt belt-driven starter generator

48 volt DC/DC converter

Li-ion battery


11

Electric power in the vehicle

a large scale and soon, electrification needs to be “tailored to fit”. If one is able to increase the fuel efficiency of a C-segment car by a two-digit percentage through adding a compact electric motor, right-sized battery, and compact electronics, then this is a powerful lever to fleet efficiency. 48 volt hybridization offers exactly this (Fig. 5).

48 volt technology 48 volt technology is entering the mass market. The first 48 volt hybrid models manufactured by European OEMs and by international car makers will be available at the end of 2016. Two cardinal virtues of the 48 volt system are paving the way to its future reach: »» 48 volt technology is simple to integrate into a vehicle. Being essentially an intrinsically safe and compact modular system, it can be made part of an existing model but it can just as well be designed in to varying integration depths during vehicle development. The hardware is so compact that it adds only very little mass to the vehicle. »» At the same time the efficiency gain can be massive. Depending on the vehicle architecture and optimization on the total vehicle level, a 48 volt hybridization may save up to 25% of fuel during urban driving when compared to the applicable reference vehicle. In other words: With the exception of purely electric driving, the 48 volt hybrid can exploit most of the efficiency gain that a high-voltage hybrid offers (Fig. 6). Hybrid vehicles offer the full scope of use cases that drivers are accustomed to, e.g. everything from short distances on to daily commuting and right up to long-distance trips. Industry esti-

Two cardinal virtues


12

co2 reduction

Fig. 6: The individual hybrid functions contribute to the total vehicle efficiency.

electric power in the vehicle

recuperation

coasting extended start-stop start-stop hybrid functions

mates predict that by 2025, around 28 million vehicles will have some sort of powertrain electrification (Fig. 7). Of these, nearly every second vehicle is expected to have a 48 volt system on board. Within the remaining share of high-voltage hybrid cars, the plug-in hybrid vehicle (PHEV) will probably play an important role.

Fig. 7: By 2025, nearly every second vehicle with powertrain electrification is expected to have a 48 volt system.

ElectriďŹ cation in million vehicles

60

Electric vehicle Hybrid vehicle 48 volt

50

50 13

40 28

30

12

5 20

9 12

10 0

5 3 2017

1 1

5

25

2 14

5 2020

2025

2030


Electric power in the vehicle

One thing can hardly be overrated: It is fun to drive a 48 volt hybrid car. The system increases the vehicleâ&#x20AC;&#x2122;s drivability despite saving so much fuel. Take the start-stop function which is already popular in cars with a traditional 12 volt system. In a 48 volt hybrid, the automatic engine re-start is much faster and smoother. If the driver changes his mind abruptly because a red light suddenly turns green on him, the 48 volt system will support his request and make the combustion engine available immediately. Real-world road capabilities like this will boost the 48 volt systemâ&#x20AC;&#x2122;s success. The future will be electric. However, vehicle electrification is not a case of all-or-nothing-atall. By its nature electric energy is very versatile, so it is obvious to utilize it in many ways. 48 volt technology is one particularly intelligent, attractive and efficient example.

â&#x20AC;&#x201E;13

Fun to drive is the key to mass acceptance


14  

48 volt components and integration

48 volt components and integration

Harvesting available energy

Electric energy plays a lead role in the modern vehicle. In fact, electric energy is in so much demand that is has become a “scarce commodity”: For many years now, the traditional 12 volt electrical net in the car has been hard put to supply the growing number of electric consumers spread all over the vehicle. The consumption of electric energy is increased by all of the global vehicle mega trends: Greater safety, higher efficiency, lower emissions, more comfort, and vehicle connectivity. As a result, electric/electronic (E/E) components and software account for a constantly growing share of the car value. This trend will continue with vehicle hybridization, adding to its momentum. As electric power is the product of voltage and current, a low voltage level also limits the number of use cases for electric energy. Practically speaking, the performance limit of a traditional 12 volt system is somewhere around 3000 watt total power demand. However, when one quadruples the voltage, one is looking at a totally different picture and can do things with electric power which cannot be done within a 12 volt net. For instance, it is possible to integrate components with a high demand for electric energy into the 48 volt net. Another benefit of 48 volt technology is to install completely new electric consumers which are not an option in a 12 volt system. Still, the most attractive feature of a 48 volt system is to harvest kinetic energy during vehicle deceleration phases by efficiently transforming this kinetic energy into electric energy, which is then stored for later use.


â&#x20AC;&#x201E;15

48 volt components and integration

Electric energy Before diving into the details of a 48 volt hybrid system a brief discourse on the nature of electric energy shall add to the greater picture. It has already been mentioned that electric energy is very versatile. It can be utilized to provide kinetic energy for propulsion or actuation, to generate heat, cold, illumination (not just light but also displays as a part of the cockpit), and to facilitate digital control including everything from sensor technology to data processing and digitalization. In fact there would be no modern vehicle without electric energy. Electric energy is just as much the fuel of the networked vehicle as data is. In comparison, fossil fuel offers only a very limited number of use cases. Burning it will deliver heat and pressure â&#x20AC;&#x201C; and emissions. In a passenger car combustion engine, around 30% of the energy content in the fuel are transformed into kinetic energy for propulsion. Figure 8 shows an overall energy balance from tank-towheel, based on the New European Drive Cycle (NEDC). It is clearly visible how many losses come together to limit the overall efficiency. The

Electric energy is versatile

Fig. 8: Breakdown of the energy use in a vehicle with combustion engine

Exhaust losses Exhaust energy

Exhaust recuperation Heat lost in piston Heat lost in Heat lost in piston cylinder wall

Heat losses

Total heat lost

Heat lost in cylinder head Friction heat

Friction work Indicated engine work

Stored in oil

Friction

Stored in water Underhood dissipation Radiator dissipation

Generator work Effective engine work

Stored in engine masses

Driving work Lost in transmission

Driving resistance Brake work

Aerodynamic work Rolling resistance work


16  

Energy sources are important

Complexity is the price of efficiency

One unique quality

48 volt components and integration

irony of the situation is that a certain percentage of the kinetic energy, which a combustion engine generates, is then required to generate the electric energy, which is needed by many functions and systems in the vehicle. In contrast to that, an electric motor can have an efficiency of greater than 95% if one considers the tank-to-wheel chain. Put another way: 95% of the electric energy which flow into the electric motor are transformed into kinetic energy. This compares to a 30% efficiency of the combustion engine. Admittedly, this equation is neither complete nor is it quite fair: Electric energy needs to be generated first, and depending on the national mix of power plant technologies, a hybrid vehicle may indeed be a greener car than a BEV that gets its electric energy form an electric grid fed by fossil fuel power plants. In all sobriety, the attraction of the combustion engine lies not so much in its functional principle – unless one is a true “petrol head” of course – but in the ease of refueling. The complexity of the combustion engine is the price we are willing to pay for this quick refueling. A clean and efficient combustion engine of today is a highly refined system (with many ancillary components), which requires an ever greater level of digital control over vital functions such as injection/combustion and the air path, for instance. This complex technological masterpiece is part of an equally complex drivetrain including transmission and exhaust gas aftertreatment. An increasing amount of effort goes into making the combustion engine greener and cleaner. An electric motor is simple and efficient in comparison. However, the electric motor offers one unique quality which more than makes up for its present range limitations: In the


17

48 volt components and integration

“motor mode”, an electric motor can push out kinetic energy – and the same electric motor can generate electric energy a second later in the “generator mode”. This energy source can be utilized to increase the fuel efficiency of a hybrid car.

48 volt hardware A 48 volt hybrid system consists of only few core components. The main functional elements of a 48 volt system are an electric motor, an inverter, an energy storage system with high dynamic capability, and a DC/DC converter. The main function of the asynchronous electric motor is to harvest energy during deceleration phases and to support the combustion engine by providing additional torque. Since the electric motor requires a 3-phase alternating current (AC) for its speed variable operation, an inverter is integrated into the electric motor. This inverter changes the 48 volt direct current (DC) coming from the battery into the 3-phase AC for the electric motor (Fig. 9). In a 48 volt hybrid car the electric motor replaces the conventional 12 volt alternator. From the point of view of installation space, the integration of a 48 volt electric motor is therefore DC

12 volt board net

DC

Pel

PDC IBat

R1 + U – 0

RL0

RL1

AC UBat

DC 48 volt battery

Fig. 9: Electric architecture of a dual voltage board net with a 48 volt system AC Alternating current DC Direct current IBat Battery current Iph Phase current L 1, L 2, L 3 Phases L1 – L3 PDC Inverter input power Pel Electrical power of the motor Pme Mechanical power of the motor R1 Battery internal resistance RL0 Resistance on wiring harness RL1, RL2, RL3 Resistance on phases L1 – L3 U0 Battery internal voltage UBat Battery output voltage UL-L Voltage drop between two phases

Inverter

RL2 RL3

Iph

Pme

L1

UL-L

L2

Belt

L3

Inductive motor

Combustion engine


18  

48 volt components and integration

neutral. The 48 volt electric motor and inverter fit into the space of the alternator (Fig. 10). Never­ theless, the asynchronous machine depicted here offers 6 kW nominal power and 15 kW peak Fig. 10: A compact 48 volt belt starter generator

Bidirectional power flow

output. This electric motor can provide up to 60 Nm of torque and add up to 150 Nm of torque at the crankshaft to assist the combustion engine. Figure 11 conveys an idea of how densely packed the motor components need to be to facilitate vehicle integration. The main function of the rechargeable 48 volt battery is to provide electric power to the components which are connected to the 48 volt system. The power flow between battery and electric motor is bidirectional: When the electric motor operates in “motor mode”, the battery is discharged, when it operates in “generator mode”, the battery is re-charged. Lithium-ion technology (Li-ion for short) is particularly suitable for this purpose because it has a higher energy density than other cell types such as lead-acid or nickel-metal hydride (NiMH). Also, Li-ion batteries are better suited to absorb the frequent


19

48 volt components anD integration

Pulley

Housing

Rotor

Stator

and abrupt high energy flows to the battery, which occur during recuperation. In addition to that, Li-ion batteries have a better cyclical strength which is important because there are many more battery charging and discharging events in a hybrid car than in a car with a traditional drivetrain. As the 48 volt battery is comparatively small, it is affordable in comparison to a high-voltage traction battery. The energy content of the 48 volt Li-ion battery currently used in 48 volt demonstrator cars is 500 Wh. Figure 12 shows that the batteryâ&#x20AC;&#x2122;s form factor strongly resembles a conventional lead-acid battery. The 48 volt Li-ion battery is monitored by a battery management system for reasons of safety but also to provide the information needed to calculate the most efficient driving strategy. Battery diagnostics include important

Integrated inverter

Fig. 11: Exploded view of the 48 volt electric motor


20â&#x20AC;&#x201E;â&#x20AC;&#x201E;

48 volt components and integration

Fig. 12: 48 volt lithium-ion battery

Fig 13: 48 volt/12 volt DC/DC converter

key parameters like state of health (SOH), state of function (SOF) and state of charge (SOC). To protect the energy storage system against overcurrent, overcharge, over-discharge, or overload, a fuse and a disconnector unit are integrated in the power path. Cell balancing, current measurement and thermal management are installed to control the cell temperatures. A 48 volt/12 volt DC/DC converter serves to transfer energy from the 48 volt level to the 12â&#x20AC;Żvolt system (Fig. 13). This ensures a stable power supply of the remaining 12 volt power


21

48 volt components and integration

net at any time. The DC/DC converter shown here can deliver up to 3 kW of power. In addition to these core components, some of the possible 48 volt architectures require a belt tensioner, which maintains an even tension of the belt irrespective of the electric motor mode and running direction. Of course, the belt itself is also an important part of the system as it has to meet very tough requirements concerning its mechanical durability. Finally, the system requires a cabling solution to establish the electrical connections. However, the cabling effort is limited in comparison to a high-voltage hybrid. This is owed to the fact that 48 volts fall within the “intrinsically safe-to-touch” DC voltage (≤60 VDC), defined in the ECE-R 100 standard (ECE, Economic Commission for Europe). Bearing in mind that electric power is the product of voltage and current, it becomes obvious that a higher voltage requires a lower current to achieve the same level of power. A lower level of current, however, requires only a smaller cable cross-section because it is the current level which dictates the cable diameter. Smaller crosssections mean lower weight. Therefore 48 volt cabling has a lower mass by definition. An additional benefit of 48 volt hybridization can come from replacing high-current 12 volt applications by 48 volt applications connected by wiring with a smaller diameter. This can take further cost and weight out of the on-board net.

Vehicle integration architectures The components of a 48 volt hybrid system are added to the vehicle’s existing drivetrain architecture and 12 volt electrical network, often

Reduced cabling effort

Lower cabling cost and weight


22

48 volt components anD integration

referred to as the â&#x20AC;&#x153;traditional on-board netâ&#x20AC;?. The components described above form a second electric net, which is connected to the 12 volt on-board net via the 48 volt/12 volt DC/DC converter (Fig. 14).

Combustion engine

Combustion engine

DC

Generator

DC

Belt

12 volt battery

Fig. 14: Transition from 12 volt architecture to dual voltage architecture

12 volt board net

12 volt battery

Inv. BSG 48 volt board net

Belt

48 volt battery

There are at least three possible ways of integrating a 48 volt hybrid system into a vehicle. These three principal architectures make use of the systemâ&#x20AC;&#x2122;s modular nature to address different use cases and desired integration depths. From the viewpoint of a vehicle manufacturer, it is necessary to cover three integration challenges. In the introductory phase of 48 volt hybridization the most pressing challenge is to integrate 48 volt components into existing vehicle models, which were never designed for hybridization. To minimize the integration cost (which is one of two serious cost drivers of a high-voltage hybrid project, the other being a big traction battery), the vehicle and transmission architecture should not be touched at all. The easiest way of achieving this is to integrate the 48 volt electric motor into the already existing engine


23

48 volt components and integration

belt drive by replacing the 12 volt generator. This “P0” architecture is therefore typically referred to as “belt starter generator” (BSG) configuration (Fig. 15a). In the next step of 48 volt hybridization, the components will be designed in during the early vehicle development phase. Again to limit the integration effort, the electric motor can be integrated via a belt. However, in this case the belt drive is located between the transmission and the combustion engine. The electric motor is connected to each side via an actuated clutch. The clutches on both sides are independent from each other and can be opened and closed in any combination. Referring to the position of the electric motor, this solution is called “sideattached”. In Figure 15b, it is shown as the “P2” architecture. Side-attaching the electric motor offers specific advantages, which can be exploited via extended hybrid operating strategies aiming to further increase the system’s efficiency. If required, the electric motor can be fully integrated “in-line” between transmission and combustion engine (Fig. 15c), hence the name “in-line starter generator” (ISG). This “P2 inline” architecture does not require a belt drive at all, which increases the system efficiency because there are no more belt losses. Another benefit of this configuration lies in the interaction between electric motor and transmission. It has a high influence on the savings and the drivability. Optimizing the entire drivetrain on the system level with regard to cost and efficiency can, for instance, mean reducing the number of gears. The electric motor compensates the reduced number of gears, especially if it is moved to the drive side of the trans­ mission.

Different architectures for different use cases


› 48 volt introduction

24

48 volt components anD integration › Integration in existing

belt drive architecture › Enhanced driver comfort (e.g. start /stop, p0 belt starter generator air(Bsg) conditioning)

Fig. 15: 48 volt architecture options

G)

uction

existing itecture

er tart /stop, g)

–13%

a

❯ 48 volt introduction ❯ Integration in existing belt drive architecture Starter

P2 Side-Attached Starter Generator

(e.g. start/stop, › 48 volt introduction

› Adapted Water pump Water Pump BSG performance

air conditioning)

Climate Compressor compressor

› Integration in existing CO2 potential: –13% › CO –13% Improved regeneration belt drive architecture 2 Potential: capability › Enhanced driver b › Electrified auxiliaries comfort (e.g. start /stop, p2 side-attached starter generator (ssg) air conditioning) 48 V Electric Motor

❯ Adapted BSG performance

› Im ca

› El

48volt V Electric 48 electric Motor motor

P0 Belt Generator (BSG) ❯ Enhanced

driver comfort

› Ad BS

P2 Sta

›Elec M Wate ca

›CO El2

› eP as

48 V volt electric 48 Electric motor Motor

❯ Improved recuperation P2 Side-Attached capability Starter Generator ❯ Electrified

Climate auxiliaries Compressor

› Adapted Water Pump BSG performance

P2 Integrated Starter Generator ›Electric MaximumClimate regeneration Climate Electric Waterpump Pump Compressor compressor water capability (less losses)

CO2 potential: –18% › › Improved regeneration Electrified auxiliaries CO CO 2 Potential: –13% 2 Potential: –18 % capability › eParking, eCreeping c › Electrified auxiliaries as option p2 integrated starter generator (isg)

48 V Electric ❯ Maximum Motor

recuperation capability

❯ Electrified auxiliaries

Electric Water Pump

❯ eParking, eCreeping as option

Climate Compressor

volt 48 V electric Electric motor Motor

Electric climate Electric Climate Compressor compressor Electric water Electric Waterpump Pump

CO–18 –22% CO Potential: –22 % 2 potential: CO2 Potential: % 2

E

CO2


25

48 volt components anD integration

potential fuel economy benefits

It is difficult to measure “absolute” fuel savings, which are enabled by a 48 volt hybridization. For instance, a 48 volt mild hybrid vehicle with a BSG configuration, which shows a 13% better fuel economy during the NEDC, may save up to 21% during real-world urban driving, while the same car may only deliver a one-digit percentage fuel saving on the motorway. In other words: The fuel economy of a vehicle is strongly influenced by the driving situation and especially by the number of so-called load changes. The term load-change denotes any situation during which the driver requests either more or less torque at the pedal. It is therefore no big surprise that the driving style is another major influence on fuel efficiency. All percentage figures given for a 48 volt hybrid car need to be seen in the context of the cycle or trip and the type of driver. A cooperative driver, who does not override hybrid operating strategies but makes optimal use of them, will save more fuel than a sporty driver. cost-benefit ratio

It has often been lamented that vehicle electrification is such a slow process despite the initial high hopes. Ignoring the range anxiety angle – because it is of no relevance to a hybrid vehicle – the spoilsport of hybridization is cost and cost alone. 48 volt technology can help to overcome this hurdle because it is a perfect example of the Pareto Principle’s validity. In a modernized form, the principle, defined by the Italian economist Pareto, is used to express that 80% of an achievement typically stem from 20% of the effort one makes. This observation is therefore also called the 80-20 rule or the law of the vital few. It is a good management’s job to identify the 20% of

influencing factors


26  

Comparatively low additional costs

48 volt components and integration

effort because this is the most efficient and profitable part of a business. If one transfers the law of the vital few to vehicle hybridization, the 80-20 split denotes that low-voltage hybridization with a 48 volt system already exploits a large share (≈”80”) of the benefits a high-voltage system can offer. In other words, 48 volt hybridization lowers the initial hurdle of hybridization for the vehicle buyer. The added cost is comparatively low (≈“20”), while the fuel economy benefit potential is great. In order to support the 80-20 rule, 48 volt electrification has to meet a long list of requirements: The components must be compact (easy to integrate), light-weight (to help limit vehicle weight), rugged and reliable (10 years lifetime and more than 200,000 kilometers), they must be modular (ease of integration), and their electric efficiency needs to be high. Many years of development have gone into the optimization of the 48 volt system and have now led to mass market acceptance of the mature components.


Energy harvesting and fuel saving

Energy harvesting and fuel saving In a traditional car, the combustion engine is the sole source of power. Its torque serves to accelerate the car, its drag can be used to gently decelerate. Driving a car is a permanently changing balance between the two. During acceleration, the combustion engine pushes out power which increases the kinetic energy level of the vehicle. When the driver steps off the pedal, the engine is overrun by the kinetic energy stored in the vehicle mass. During overrun, fuel injection is switched off and the moving pistons compress air during their cycle. This combination of pump work and friction losses, occurring between all the moving parts, slows the vehicle down. Experienced drivers use this engine drag effect to avoid unnecessary braking, to drive more smoothly, and to economize on fuel.

Main strategies As a bottom line, it is inefficient to accelerate the vehicle mass if the speed will need to be reduced soon after. Avoiding sudden load changes and braking as little as possible is therefore a key to efficient driving. Applying the wheel brakes transforms the vehicleâ&#x20AC;&#x2122;s kinetic energy into friction work generating heat, which is dissipated to the environment. In other words, applying the wheel brakes causes an immediate energy loss or increase of entropy. A rule of thumb says that a driver can influence the fuel efficiency of his vehicle within a bandwidth of 20% to maybe 30% via his driving style alone, considering factors like anticipatory driving, speed changes and braking behavior.

â&#x20AC;&#x201E;27


28  

Energy harvesting and fuel saving

Obviously some deceleration phases can be avoided, while others cannot. As important as a driver’s influence is on vehicle efficiency, it is also limited. To increase vehicle efficiency further, a technical solution is needed to reduce the amount of dissipated energy. If one looks at the whole picture, there are two things one can do to increase vehicle fuel efficiency: »» The first thing is to avoid unnecessary load changes and braking actions in particular. »» The second thing is to use the combustion engine in the most efficient part of its map – or not at all. In a conventional car this is easier said than done but the driver’s influence on fuel consumption underlines the importance of the driving style. In a hybrid car with a 48 volt electrical motor, both objectives can be fulfilled to a much higher extent. Turning losses into profit

More effective recuperation

Once the combustion engine of a conventional car has converted the energy contained in the fuel into kinetic energy, this energy either propels the car or it is lost during braking or overrun. In the hybrid vehicle the situation is quite different: When the driver steps off the pedal in a hybrid car or activates the brake, the kinetic energy of the vehicle is harvested by the electric motor. Instead of wasting kinetic energy, it is transformed into electricity and stored in the Li-ion battery. In contrast to 12 volt systems, 48 volt recuperation is significantly more effective so there is more energy available for later use. To ensure that recuperation goes unnoticed by the driver, the brake system of a hybrid car needs to be modified. When the driver activates the brake within a limit of 0.2 g deceleration re-


29

Energy harvesting and fuel saving

quest (the value is an example, the threshold can vary according to the vehicle), it will actually not be the wheel brakes which provide the deceleration but the electric motor run in generator mode. Nevertheless, the feel of the brake pedal response must remain unchanged. Therefore the pedal and brake actuation are decoupled. A control algorithm in the electronic braking system ensures a smooth blending between recuperation and wheel braking. If, for instance, the driver demands a higher brake torque beyond 0.2 g, the generator mode will be ramped down while the wheel brake application is ramped up. In a 48 volt hybrid configuration, this brake blending strategy can offer more electric braking power than in a 12 volt system because the 48 volt electric motor has a greater drag in generator mode. Therefore, deceleration phases can be used to a greater extent in the 48 volt hybrid. In order to maximize the kinetic energy recuperated, the combustion engine can be switched off completely and can be decoupled from the drivetrain so that there is no more engine drag and no more fuel injection. A car moving in this state is said to “coast”. Any driver who has ever stepped onto the clutch pedal (so that the engine just idles) and let his vehicle roll along in neutral will agree that a rolling car can maintain its speed for a long time. On a sloping road the car may in fact accelerate. Even if one is overtaking at 120 km/h on an expressway and takes one’s foot off the pedal, the vehicle’s energy may be sufficient to allow one to keep up with the traffic and continue with the overtaking maneuver. Upon reversion, this underlines the amount of energy which is stored in the vehicle mass. Turning the deceleration losses of a conventional car into profit is a key strength of the hybrid car. The icing on the cake is that this energy

Brake blending

Coasting


30â&#x20AC;&#x201E;â&#x20AC;&#x201E;

Energy harvesting and fuel saving

is available for free. No additional fuel needs to be burnt to generate it. 48 volt net as second energy source

Greatest effect during inner-city driving

It is the process of recuperation (or regenerative braking) that delivers the energy to the 48 volt net. The point of the 48 volt net is that it does not require additional energy (e.g. from the grid) but it contributes additional energy to the vehicle. Obviously, the amount of energy recuperation depends on the topography of the road and the traffic situation. If one drives at a constant speed on the motorway, there will only be a very limited number of recuperation phases. During urban driving, on the other hand, the number of load changes and braking activities is much higher so that more kinetic energy can be harvested. As city traffic typically causes the highest level of fuel consumption, it is especially welcome that the 48 volt system shows its greatest effect during inner-city driving. When a 48 volt system was developed and installed for the first time in a demonstrator vehicle, the initial expectations were to save up to 13% of fuel during the NEDC. This compares to a reference vehicle with a 12 volt start-stop system already delivering better fuel economy than the conventional baseline model with no start-stop system. The chosen C-segment vehicle is powered by a 1.2-liter direct injection turbocharged gasoline engine (GDI) and is equipped with a dual clutch transmission. To prove the point that a 48 volt system can actually be integrated into an existing vehicle without touching the engine and drivetrain architecture, the components were added within a P0 BSG configuration (see Fig. 15a, p. 24). During real-world driving, the fuel economy of the 48 volt technology demonstrator vehicle


31

Energy harvesting and fuel saving

CO2 emission

was found to fall within a much wider span than expected (Fig. 16). While the NEDC savings were fully confirmed, the influence of the topography and traffic situation on the savings was also revealed during road testing: Fig. 16: Fuel efficiency results of the 48 volt demonstrator vehicle

NEDC

New European Driving Cycle Recuperation

Real driving

– 13% + coasting

Total CO2 reduction:

– 8% -21%

»» Driving on the country road delivered a fuel efficiency improvement of up to 9% because the number of recuperation phases was lower than in the NEDC. »» However, when tested by the independent editorial staff of a television program, the 48 volt demonstrator car delivered a 21% better fuel efficiency than the reference model during urban driving. [4] Coasting as important fuel-saving strategy

Such massive savings are not the result of recuperation alone, of course. Instead, the 48 volt demonstrator car uses the electric energy harvested during braking for fuel saving operating strategies. The most important one is to switch off the combustion engine when it is not needed to propel the car. Other use cases for the harvested energy include supporting the com­ bustion engine with up to 150 Nm of torque during acceleration (electric boost) and to

Up to 21% fuel savings


32  

Popular 12 volt start-stop system

Energy harvesting and fuel saving

deliver electric energy to the 12 volt net during engine-off. Switch off the combustion engine? In a motor vehicle? Admittedly it may not be the first idea that comes to mind. Drivers are used to the engine running almost permanently, probably with the rather recent exception of 12 volt startstop systems. However, they are a limited exception to the rule and only apply to waiting phases at a red traffic light or at a crossing. Experience has shown that a 12 volt start-stop system, which automatically switches off the engine during standstill and restarts it as soon as the clutch is engaged, can save up to 2% or 3% of fuel during urban driving. This explains why this system (often referred to as a “micro hybrid”, although one could reasonably argue whether this is indeed a hybrid) has become popular. Its system cost is very limited and the gain in fuel efficiency is welcome. Simple as the 12 volt start-stop technology may be, it points the way: Switching off the combustion engine helps to save fuel. Investigation of the engine-off potential and driver acceptance

22% of driving time with engineoff coasting

How often then can the combustion engine be switched off in a mild hybrid with a 48 volt system? Again the answer depends on the road topography, trip and traffic situation. To investigate the engine-off potential during real-world driving, a representative drive cycle was chosen (Fig. 17). It has a length of 92 kilometers, passes through various speed limit zones and includes a cumulated difference in altitude of 180 meters. Various test drivers took the 48 volt demonstrator car through this city cycle during low- and peak-level traffic. The result was quite astounding: During around 22% of the total driving


33

energy harvesting anD Fuel saving

Fig. 17: Driving Time Driving cycle used to test the 48 volt (City) Urban demonstrator Non Urban vehicle

Regensburg

Highway Total hours

Obertraubling

A93

Mild Hybrid Functions Gebelkofen

Engine-off Coasting

Thalmassing

Regeneration Start / Stop

A93

Change of Mind Driver Change Behavio

Dünzling

Load Point Shift

Hausen

› Long engine-off coast

Paring

Großmuß

› 22 % engine-off coasti 10 % fuel saving

A93

› Smooth and fast chang diesel vehicles

Bachl Driving time

Driving distance

Urban (city)

37% Urban (city)

20 km

Non urban

46% Non urban

38 km

Highway

16% Highway

34 km

Total hours

1:35 Total

92 km

Mild hybrid functions Engine-off coasting

Average active time 22%

Recuperation

9%

Start/stop

6%

Change of mind Driver change behavior

6%

Load point shift

5%

time, the engine was switched off for coasting (Fig. 18). In other words, the engine was completely decoupled from the drivetrain to avoid


Active coasting share [% of driving time]

34  

Energy harvesting and fuel saving

35

Average coasting activation: ~12 s

30

Average coasting share: ~22% (without start-stop)

25 20 15 10 5 0

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Speed range [km/h]

Fig. 18: Coasting share during the driving cycle

Fast response during “changeof-mind” situations

any engine drag. On average, a single coasting phase lasted for 12 seconds. Figure 19 shows the extent to which the hybrid function of recuperation was active. Switching off the engine frequently will only be accepted by the driver if it works smoothly. This can be an issue with 12 volt start-stop systems because the limited performance of the electric motor makes 12 volt cranking a longer and more audible process than with a 48 volt electric motor. Whenever the driver responds to a change in the traffic situation by either taking the foot off the accelerator pedal or suddenly applying pressure again, the combustion engine needs to respond immediately. However, this “change-of-mind” situation is a particular challenge to 12 volt technology. Given the performance of the 48 volt electric motor, the combustion engine is re-started in under 0.2 seconds and very smoothly so (therefore this function is referred to as “premium start”). Thus a driver who had to change his mind quickly – and who may be under a


35

Active recuperation share [% of driving time]

Energy harvesting and fuel saving

18 16 14 12 10

Average recuperation share: ~9%

8 6 4 2 0

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Speed range[km/h]

certain level of stress as a result – will get the desired rapid response from the combustion engine. Re-starting the combustion engine silently and fast is also highly instrumental in extending engine-off phases. With the combustion engine available almost immediately, it can already be switched off under a threshold speed of 20 km/h while the car is, for instance, approaching a red traffic light. This prolongs the engine-off phase of a start-stop function to save more fuel. The rapid re-start capability ensures that the driver maintains the full choice of spontaneous decisions. It is one of the many examples how the electrical performance of the 48 volt system helps to build trust and system acceptance. Another example can be found in the availability of the start-stop function at lower temperatures: While a 12 volt start-stop function is usually deactivated under 3 to 5°C ambient temperature, 48 volt start-stop can be available down to –10°C and will thus continue to save fuel during the cold season.

Fig. 19: Share of driving time with active recuperation

Higher start-stop availability


36â&#x20AC;&#x201E;â&#x20AC;&#x201E;

Energy harvesting and fuel saving

Diesel hybridization with 48 volt A lot has been said about adding a 48 volt system to a car with a gasoline engine. So what about the diesel engine? Can it benefit from 48 volt hybridization as well? The answer is a straightforward yes, although the 48 volt benefit to a diesel engine is slightly different from what it offers to a gasoline engine. To demonstrate the effect 48â&#x20AC;Żvolt technology can offer in a diesel car, it has been integrated in a mid-size class model with a 1.6-liter TDI (turbocharged direct injection) drive without any significant change of the existing vehicle architecture (Fig. 20).

Fig. 20: 48 volt diesel demonstrator vehicle

Fundamentally the key operating strategies are no different from the gasoline hybrid: Recuperation and engine-off coasting. Calculations with the diesel 48 volt demonstrator vehicle promise consumption savings of 7% to 9% in the NEDC. Another benefit of 48 volt hybridization is to ensure that the combustion engine operates in an efficient part of its map. In that respect, the mild diesel hybrid works a little


Energy harvesting and fuel saving

differently. While the gasoline engine is more efficient at high loads and needs support in the low-rpm field, the diesel is more efficient at part load and lower to medium rpm. Therefore the electric energy and electric torque can be used to avoid high-rpm situations and high load requests in a diesel engine, in particular in high transient conditions. This strategy is called “phlegmatization”. The term, however, is somewhat misleading. What it translates into is using the diesel engine in the best way by using the electric torque to avoid the inefficient parts of the diesel map and to maintain good drivability. If the diesel engine runs under the most favorable conditions, engine developers can mitigate the buildup of nitrogen oxides (NOx) and soot in certain load ranges. Depending on the engine development objective of the vehicle manufacturer and the exhaust aftertreatment technology in place, there is greater freedom to balance engine efficiency and vehicle emissions. Measurements (in accordance with the NEDC) have shown that this strategy reduces nitrogen oxide emissions from the diesel 48 volt demonstrator vehicle by up to 10% and by up to 20% in the new Worldwide Harmonized Light-duty Vehicle Test Cycle (WLTC).

Mild hybrid vehicle optimization Adding a second source of (propulsion) energy to a vehicle opens up a wide choice of potential optimization paths, some of which extend beyond the drivetrain. While a 48 volt system can be “simply added” to the architecture of an existing vehicle model, the beneficial interaction between combustion engine and electric motor can be exploited to a greater extent by optimizing the complete vehicle on a higher system level.

 37

Using the diesel engine in the best way

More optimization options


38â&#x20AC;&#x201E;â&#x20AC;&#x201E;

Integrated approach

Fig. 21: The highly integrated mild hybrid concept vehicle (Gasoline Technology Car GTC)

Energy harvesting and fuel saving

In practical terms this means adding highly efficient technologies and networking them to achieve an effect which is greater than the sum of the individual parts. By applying this integrated approach to mild hybrid vehicle optimization, even vehicles with a highly efficient drivetrain can achieve significant fuel efficiency increases. To prove this point, a hybrid concept vehicle (Fig. 21) was developed by utilizing a 48 volt system and other key technologies. Already in its first version (2014), it demonstrated how a net-

worked integration of key mild hybrid technologies can cut fuel consumption as well as CO2 emissions by up to 17%. For a moment this may not sound too exciting when considering the fuel economy of the 48 volt demonstrator vehicle. In fact, the publication of this 17% efficiency gain attracted a lot of attention for two reasons:


Energy harvesting and fuel saving

»» The chosen reference model is a highly efficient car with downsized 3-cylinder gasoline engine – the Ford Focus 1.0 l EcoBoost. Its engine has been awarded “International Engine of the Year 2012 and 2013” for its efficiency and performance. To squeeze another 17% of efficiency out of this drivetrain is therefore no small achievement. »» Yet, there is more. While hybrid operating strategies such as coasting normally require an automatic transmission, the highly integrated 48 volt concept car makes use of them with a 6-gear manual transmission. By adding this level of freedom, 48 volt technology is ready to take another step in addressing the world markets and their specific needs. Many technologies contribute to the high efficiency of this hybrid concept vehicle. Among them are an improved injection, an electronic clutch, intelligent split-cooling thermal management, reduced friction, and an electrically heated catalyst (EHC, EMICAT®). With these components and the intelligent operating strategy, the vehicle not only increases fuel efficiency. It also meets the limits set by the upcoming Euro 6c/6dTEMP emissions standard (2017/2018). Much like the 48 volt demonstrator car, the highly integrated mild hybrid concept vehicle makes use of frequent engine-off phases to save fuel. In addition to that the electrically heated catalyst helps to overcome one challenge posed by switching off the combustion engine: An engine that is not running will eventually cool down. Unfortunately, though, it is not just the engine that will cool down but the catalytic converter as well. When its temperature falls below the light-off temperature, the pollutant conversion will not function properly any more. When

 39


40  

Ensuring converter lightoff temperature

Energy harvesting and fuel saving

the engine is restarted, it will take some time until the converter is sufficiently hot again. In the meantime pollutants can slip through. The electrically heated catalyst solves this problem by heating up the converter structure within fractions of a second so that engine-off phases can be fully exploited without any concern about impacting emissions (Fig. 22).

Fig. 22: Electrically heated catalyst (EMICAT®)

Efficient recuperation is the hybrid vehicle’s Archimedean point. This is where the added energy comes from. However, physics still apply of course: The kinetic energy of a moving car can only be utilized once, either by recuperation or by coasting – or by a combination of the two. Deciding about when to apply which operating strategy is the very core of achieving the best hybrid vehicle efficiency.


Energy use in hybrid operating strategies

 41

Energy use in hybrid operating strategies During normal driving, the operating strategy of regenerative braking will eventually lead to a fully charged 48 volt Li-ion battery in a mild hybrid vehicle. It has been demonstrated with a highly integrated hybrid concept car that 48 volt recuperation is so efficient that it can deliver almost twice as much energy as the concept car needs for the on-board power supply. The ultimate goal of recuperation, however, is not just to store this extra energy but to make use of it. In fact, the efficiency of a hybrid car depends mostly on the application of fuel-saving hybrid operating strategies. The 48 volt battery provides the energy for such strategies. Once this energy is available, the biggest question is: What shall be done with it? Simply storing it is not helpful, because once the battery is fully charged, the next deceleration phase – which is certain to come – cannot be exploited via regenerative braking. From the point of view of efficiency, this would be a waste of precious energy. It is therefore necessary to balance energy generation and energy use (Fig. 23). In a 48 volt hybrid many hybrid operating strategies can be utilized to increase the vehicle efficiency. Among these strategies are extended start-stop (engine stop below 20 km/h), recuperation, engine-off coasting, operating point shift of the combustion engine, electric boost, state of charge (SOC) forecast of the 48 volt energy storage (“virtual SOC”), sailing, electric launch, and others. When these strategies are exploited in the best possible combination and to an optimum extent, the efficiency increase can be substantial. When the first highly integrated 48 volt mild

Balancing of energy generation and energy use


42  

Energy use in hybrid operating strategies

Vehicle speed [km/h] 48 volt torque

Transient torque assist

Recuperation Brake light switch

Comfort feature

Engine-off coasting

0

Premium engine start 520

530

Fig. 23: Exemplary combi­ nation of hybrid functions during real driving

Extended engine-off phases

540

550

560 570 Time [s]

580

590

600

610

hybrid concept car was introduced in 2014, it offered 17% better fuel efficiency than the reference vehicle with a highly efficient 3-cylinder gasoline engine. Without touching the 48 volt hardware or the vehicle architecture, the same concept car delivered a 19.4% better fuel efficiency during the NEDC than the reference vehicle by the end of 2015. This progress has been facilitated merely by advancing the operating strategy. Two things were changed: Firstly, the potential for engine-off phases and recuperation was utilized to a greater extent. For instance, a phase of regenerative braking can be extended nearly to vehicle standstill. Thus less fuel is burnt and more kinetic energy is recovered. This results in additional fuel savings, which reduce CO2 emission by another 3 g/km, which brings the second generation concept vehicle’s CO2 emission down to just below 92 g/km. Secondly, the electrically heated catalyst is used more extensively in order to avoid fuel injection as a means to heat up the catalyst. In a car without electrically heated catalyst, the amount of fuel injection needs to be temporarily in-


43

Energy use in hybrid operating strategies

creased when the catalyst temperature drops below the light-off threshold. By injecting more fuel than is burnt in the cylinder (enrichment), the unburnt hydrocarbons in the exhaust gas flow will ignite in the catalyst and heat it up. However, this injection strategy clashes with the overall target of saving fuel and reducing particle number and particle mass. Additionally, it takes comparatively long for the catalyst to heat up this way. Making consistent use of the electrically heated catalyst helps to exploit engine-off phases without losing some of their benefit by unwanted fuel injection. Consistent electrically heated catalyst use makes it possible to switch off the combustion engine again immediately after a cold start, if this is appropriate for the driving situation. On top of saving fuel, this can result in a reduction in particulate emissions of around 60% in the first 200 seconds in the NEDC. Viewed across the entire cycle, this indicates a drop in particulate emissions of about one third. Electrically heated catalyst use is a good example of the level of networking and interdependencies in a hybrid car. Without exaggeration one can say that a 48 volt hybrid is not just a car with an extra electric motor and an additional battery. It is a complete “ecosystem”, with many levers to improve efficiency and drivability. Some hybrid strategies are rather obvious while others may not be. For instance, the additional 48 volt energy source can be used to optimize the combustion engine in a way which would be difficult to achieve with a conventional drivetrain.

Core electrical strategies Improved acceleration characteristics

48 volt technology can be used for many purposes in a hybrid vehicle. This type of mild

Complete “ecosystem”


44  

Energy use in hybrid operating strategies

Fig. 24: Faster acceleration in a 48 volt vehicle

Situation 1 Situation 1

Acceleration from Acceleration from th gear 60 km / hto to80 80km/h km / h 60 km/h inin 4th4gear

85

85

105

80

100

80

75

-15%

70

Vehicle speed [km/h]: STD

60

Vehicle speed [km/h]: 48 V

65 60

20

21

Vehicle [km/h]: 24 Standard25 22 speed 23 Gear

Stand

2280 km23 6021 km / h to /h

th gear 24 25 4

2.7 se

Situation 2

80 km / h to 100 km / h

5th gear

3.8 se

Time [s]

Situation 1 Acceleration Gear Standard 48 V Eco Drive Delta

Acceleration from Acceleration from ththgear gear 80 km / hto to100 100 km/ h /h 60 80 km/h km inin 80 km/h in 54th5 gear

105

22 Time [ s ]

23

100

100 95 75

–15%

90 70 95

24

-11%

90

85 75 55 39 19 80

–11%

Vehicle Vehicle speed speed [km/h] [km/h]:: 48 48 V V Vehicle Vehicle speed speed [km/h] [km/h]:: STD STD

85 65

80 60 25

Situa 105

100 80

Vehicle speed [km/h] : 48 V

39

Acceleration

105 85

ehicle speed [km/h]: STD

75

55 19 20 Situation 1

Situation 2 1 Situation 2

–15%

85 80

Time [ s ]

60 km/h to 80 km/h 4th gear 2.7 s 2.3 s –0.4 s / –15%

ation from h to 80 km / h in 4th gear

90

Vehicle speed [km/h] : 48 V

65

19

95

–15%

70 75

55

Situa

Vehicle speed [km/h]: 48 V 40 20

41 21

42 43 45 Vehicle [km/h]:44 Standard 22 speed 23 24 25 Time Time [[ ss ]]

95 90 85 80 75

39

ation

Gear

Standard

h to 80 km / h

4th gear

th gear 4280 km 43 44 45 39 40 2.360 41 2.7 sec. sec. – 0.4 –15% km / h to / hsec. /4 Situation 1

2.7 se

h to 100 km / h

5th gear

th gear 3.8 sec. 2 3.480 sec. 0.4/ h sec. /5 –11% km / h to 100–km Situation

3.8 se

75

48Acceleration V Eco Drive

Delta

Gear

Time [s]

80 km/h to 100 km/h 5th gear 3.8 s 3.4 s –0.4 s / –11%

Situation 2 Acceleration Gear Standard 48 V Eco Drive Delta

hybridization is by nature versatile. It offers a choice of benefits to all vehicle segments, ranging from the big sports utility vehicle (SUV) to the

Stand


45

Energy use in hybrid operating strategies

sub-compact class. Depending on the vehicle mass and engine type, the mix of applicable hybrid operating strategies can be adapted to the specific vehicle. One prime reason to integrate a 48 volt system into a compact vehicle with a highly efficient, downsized combustion engine is to improve the vehicle’s drivability. It has already been mentioned that highly compact combustion engines tend to have a weakness in the lowrpm field when the turbocharger is not yet setting in on account of the limited exhaust gas flow (turbo lag). This can be relevant during starting up from standstill but it can also apply to accelerating from a medium speed in a higher gear. In either case a “leisurely” acceleration is neither very satisfying nor is it always very safe. If one wishes to merge into fast-moving traffic, for instance, then one wants to exercise a sufficient rate of acceleration to do so. The 48 volt demonstrator vehicle uses the electric energy to meet this requirement. Testing has shown that the electric torque coming from the electric motor during electric boost improved the vehicle acceleration by up to 15% in comparison to the standard model with the same engine. Figure 24 shows the effect. When the driver wants to accelerate in a high gear, the added electric torque coming from the side-mounted starter generator (P2) foreshortens the time lag until the car reaches 100 km/h by nearly half a second when compared to the standard powertrain architecture. Side-attached BSG and electric driving (e-drive)

A lot of load changes during normal driving are hardly tangible because the “delta” value of the torque (the amount of torque increase) that the

Faster acceleration


46â&#x20AC;&#x201E;â&#x20AC;&#x201E;

Low part-load just requires 5 to 15 kW

Sailing becomes possible

Energy use in hybrid operating strategies

driver requests at the accelerator pedal is small. Assuming that one has a regular driving style, a surprising share of driving time will actually only require 5 kW to 15 kW of the available combustion engine power because all one may need to do is sail smoothly and flow with the traffic. Such low torque requests mean that the combustion engine operates at a low speed (low rpm) and delivering low torque. Unfortunately, this is the part of the so-called engine map where the gasoline engine in particular has its lowest thermodynamic efficiency. During coasting, this part of the engine map is avoided by switching off the engine and decoupling it from the drivetrain. As the kinetic energy stored in the vehicle is limited, this strategy can only be applied for a certain time. At some point the driver has to step on the accelerator pedal again to prevent too much deceleration. If 5 kW to 15 kW is all one needs to sail along with the traffic at times, why not use the electric motor to provide this level of propulsion energy? It offers exactly the power span required. In a mild hybrid car with a P0 BSG configuration, the hybrid operating strategy extends as far as coasting. The belt drive at the front of the engine is not suitable to convey enough power to propel the vehicle, due to the engine drag losses. In a P2 configuration with a side-attached BSG, the situation is different. If a vehicle is designed for a 48 volt technology integration from the beginning, electrical sailing becomes possible. Again this has been demonstrated in a second generation highly integrated mild hybrid concept car. A compact module comprising a 48 volt BSG and a belt drive is integrated between the internal combustion engine and transmission of this car (Fig. 25, Fig. 26). Adding a second coupling in front of the BSG means that the electric motor


47

energy use in hyBriD operating strategies

Fig. 25: Second generation highly integrated mild hybrid concept car with P2 BSG architecture Fig. 26: Integration of the 48 volt hybrid components in the P2 BSG architecture of the second generation highly integrated mild hybrid concept car DMF Dual mass flywheel LIVC Late intake valve closing DC

DC

+ – 12 volt battery

+ – 48 volt battery

Connected energy management

p2 hybrid module 48 volt inverter

48 volt E-motor

DMF

LIVC engine

Starter Thermomanagement

RAAX® Turbocharger

Transmission Clutch 0

Belt

Clutch 1

A/Ccompressor

mGap

(modified brake booster)

Electric main water pump

Electric heated catalyst

Electric vacuum pump

can be driven by the belt in recuperation phases without the internal combustion engine having to be dragged along, too. Because no drag losses occur, more power is available for fuel-saving driving strategies.


48  

Energy use in hybrid operating strategies

The P2 BSG module (Fig. 27) designed for side-attaching is very compact to facilitate integration in the limited space available for belt installation between the internal combustion engine and the transmission. In this configuration the combustion engine can be decoupled and the propulsion energy can be delivered by the electric motor. This operating strategy is called “sailing”. It can be applied if the driver only requests a limited amount of torque, which can be proFig. 27: Compact 48 volt P2 BSG module

Prolonged engine-off phases

vided electrically. Of course this operating strategy will only be available if the 48 volt battery is sufficiently charged and if the road topography permits driving electrically. From the point of view of efficiency, sailing can prolong engine-off coasting phases to save more fuel. Electric launch

In principle, a P2 side-attached 48 volt hybrid configuration also permits starting up the vehicle from standstill by using the electric motor alone (Fig. 28). Within the performance span of up to 15 kW, the combustion engine is not needed to launch the vehicle. A use case for this would be an automated start-up function, which supports the driver in stop-and-go traffic. The electric


â&#x20AC;&#x201E;49

Energy use in hybrid operating strategies

Electric motor

Dual mass flywheel

Transmission

Clutch 0

Clutch 1

Combustion engine

clutch can make this hybrid operating strategy available in a car with manual transmission as well. Depending on the clutch system design, an engine stall protection can also be integrated, which ensures that driving off is comfortable. Another mild hybrid pure e-drive function can be based on this capability of electric launching. If the vehicle is equipped with an automated parking function, the 48 volt electric motor can ideally support this because it can be run forward and in reverse without any gear changes. Stabilizing the electrical net

During engine-off periods, electric energy from the 48 volt battery can be used to supply electrical consumers in the vehicle. Even today, many conventional cars with a 12 volt system already have two lead-acid batteries. One of them is typi­ cally reserved to ensure that the car can be started after a longer period of standstill. The other battery provides electric energy to the many consumers. Depending on the ambient conditions, the conventional 12 volt net is often nearly exhausted by the many electrical consumers. Add-

Fig. 28: Energy flow during electrical launching and sailing


50â&#x20AC;&#x201E;â&#x20AC;&#x201E;

Energy use in hybrid operating strategies

Electric motor

Dual mass flywheel

Transmission

Clutch 0

Clutch 1

Combustion engine Air conditioning compressor Fig. 29: Energy flow during electrical HVAC operation

Greater comfort

ing a second electric net with 48 volts can help to significantly improve this situation. In order to stabilize the electrical net, energy can flow from the 48 volt net to the 12 volt net and vice versa. For instance, this option could be used to stabilize the 12 volt side during engine cranking. One benefit of this strategy would be to avoid the deep voltage drops which normally occur during cranking. Depending on the weather conditions, the voltage may drop from 12 volts to as low as 6 volts during engine start. Many consumers are automatically switched off during cranking (e.g. the radio). In a hybrid car with many engine-off and engine re-start events, this would be unacceptable. Within reasonable limits, the 48 volt battery can provide the electrical energy during standstill so that comfort functions such as the air conditioning (heating, ventilation, air conditioning, HVAC) can continue to function as long as the battery status allows it (Fig. 29). Re-defining the electrical architecture

Another potential to increase the energy efficiency of a mild hybrid vehicle lies in changing


â&#x20AC;&#x201E;51

Energy use in hybrid operating strategies

its electrical architecture. If, for instance, highcurrent consumers such as an electrical water pump or the air conditioning compressor are moved from the 12 volt side of the architecture to the 48 volt net they can be run with greater electrical efficiency. Another application of this newly defined electrical net can be roll stabilization, which adds to the driving safety. This function cannot be powered within a 12 volt net, however, roll stabilization with 48 volts works. Electric compressor

Electrical energy, harvested during vehicle deceleration, can be used to bridge the time gap between a torque request of the driver when the engine is running at low speed and the turbocharger response. In this situation, a fast-reacting electric motor can be used for a duration of several seconds to pressurize the intake air. An electric compressor can thus support the exhaust-gas-driven turbine at low-end rpm (Fig. 30).

Improved drivability

Fig. 30: 48 volt electric compressor

In addition, the electric motor of the electric compressor can be run in generator mode (just like the 48 volt electric motor) to harvest energy from the exhaust gas flow at high engine speeds, when a part of the exhaust gas flow is bypassed via the turbocharger wastegate.


52  

Energy use in hybrid operating strategies

Electrically heated catalyst

Faster heating

By using the electrically heated catalyst, the maximum potential for engine-off phases can be utilized in a 48 volt mild hybrid. The electrically heated catalyst makes it unnecessary to inject additional fuel just to bring the catalyst back to its operating temperature after a longer combustion engine standstill or after frequent engine-off phases. Thus the electric heating is faster because it takes a certain time for the air-fuel mix to flow downstream to the catalyst, to ignite and to produce heat (see chapter “Mild hybrid vehicle optimization”, p. 37 ff.).

Supporting strategies Thermal management

Switching off the combustion engine as often as possible reduces the engine temperature. Overly high friction losses and limited availability of the catalyst are potential problems which can arise from a low engine temperature. To limit these effects, the thermal management in a 48 volt mild hybrid car needs to reduce heat losses. In this context, two main requirements have to be met: »» During cold-start, the engine working temperature should be reached as fast as possible. »» During engine-off phases, the heat should be preserved in the engine block as long as possible. Split cooling architecture

Both goals can be achieved via a split cooling architecture. A control valve, which stops coolant circulation during cold-start conditions, ensures that the engine heats up quickly. When the engine is not working during a coasting phase, for instance, a temporary disconnection of the engine from the coolant circuit keeps the heat in the cyl-


Energy use in hybrid operating strategies

 53

inder crankcase for longer. As a result, the engine is still warm at the end of a switched-off phase and starts up again smoothly. This thermal management makes an ideal combination with the electrically heated catalyst, because it reduces the number of electric heating events and thus the consumption of electric energy. Engine optimization

Allowing for the fact that the combustion engine remains the main source of propulsion force in a mild hybrid car, the efficiency of the combustion engine is clearly pivotal for the total vehicle efficiency. Within the “ecosystem” of a hybrid car, both energy sources need to be optimized. By networking both forms of energy, the combustion engine can be optimized in ways which are not equally feasible in a vehicle without a 48 volt system. In the second generation of the highly integrated 48 volt mild hybrid concept car (GTC II), this combustion engine potential has been addressed. A higher compression ratio increases the gasoline engine’s thermodynamic efficiency, which brings down the specific fuel consumption. To avoid the knock tendency caused by the higher compression ratio, an engine cycle with late intake valve closing (LIVC; so-called Atkinson cycle) is applied. This measure reduces the peak temperature and peak pressure toward the end of the compression stroke. During part-load condition, the LIVC strategy also improves the efficiency by reducing the gas exchange work. During full-load operation, however, an LIVC strategy has a downside caused by the reduced volumetric efficiency. To achieve a sufficient gas exchange during low-end-torque and full load, the charge pressure needs to be higher. Therefore a turbocharger with a radial-axial

Better thermodynamic efficiency


54

energy use in hyBriD operating strategies

turbine was adapted to the engine because its specific turbine geometry offers a fast response particularly at low engine speeds, for instance,

Brake mean effective pressure

Reference vehicle

0 1000

1500

2000

2500

3000

3500

4000

Engine speed [rpm]

Brake mean effective pressure

P2 conďŹ guration with LIVC

Fig. 31: Map of the reference engine (top) and of the mild hybrid concept car with improved map (below)

0 1000

1500

2000

2500

3000

3500

4000

Engine speed [rpm] Low BSFC

High BSFC


energy use in hyBriD operating strategies

when a sudden acceleration is requested. In combination, the Atkinson cycle and the adapted turbocharging enlarge the part of the engine map which offers the lowest brake specific fuel consumption (BSFC). Figure 31 depicts the standard engine map of the reference vehicle (top) in comparison to the engine map of the 48 volt car (below). The green part of the map is the area of highest engine efficiency. It is clearly visible to what extent this area could be extended in the mild hybrid vehicle. The black circles indicate the load points which apply to the NEDC, while the diameter of the black circles equals the timebased emphasis of these load points. By adapting the engine operating strategy accordingly and by using electric torque assistance (electric boost), the second generation concept car offers a better fuel efficiency and improved drivability, which also enhances driver acceptance. The P2 side-attached mild hybrid configuration with this optimized engine can lead to fuel efficiency increases of 25% and above.

55

greater overall efficiency


56  

Outlook

Outlook – future potential for higher efficiency

Predictive driving

In the pioneering generation of 48 volt mild hybrid vehicles, the activation and the mix of hybrid operating strategies will be based on impulses provided by the driver. If he steps off the accelerator pedal, for instance, coasting and recuperation or a mix of the two will be initiated. This control principle, based upon a system response to a triggering impulse, is highly effective but is also subject to one limitation: By solely being responsive, some opportunities for saving fuel and harvesting kinetic energy are entirely missed or will only be exploited to a certain extent. One of many conceivable examples would be a speed limit zone to which the driver can only respond as soon as the traffic sign comes into sight. Other examples can be found in an unexpected crossing where the driver has to yield to right, or in a downgrade the driver did not know about. During each of these situations, hybrid operating strategies could contribute to the vehicle efficiency if the event was known in advance. So the bottom line is that the driver’s line of sight is often too short to exploit the full potential of coasting, recuperation, and of electric boost or sailing. In future, this limitation can be eliminated by extending the horizon of the vehicle and adding a predictive element to hybrid control.

Connected energy management Current strategies to minimize energy consumption successfully build on numerous parameters in the vehicle itself. A predictive operating strat-


â&#x20AC;&#x201E;57

Outlook

egy for the powertrain, however, uses data about the surrounding area to allow for proactive action instead of a purely reactive control system. The effect of this improved data basis can be seen in another 48 volt mild hybrid demonstrator vehicle, which is equipped with a connected energy management (cEM) (Fig. 32). The predictive driving strategies of this car employ static map data as a basis of decisionmaking. Take the downgrade that the driver Fig. 32: Connected energy management control unit

does not know about, for instance. If the hybrid controller â&#x20AC;&#x153;knowsâ&#x20AC;? about the oncoming gradient on the chosen route, the electric boost function can be used on the way up to support the combustion engine. Even if this discharges the 48 volt battery to a considerable extent, it will not impact the 48 volt system availability as the downgrade ahead provides a computable potential for recuperation. In fact, it is more efficient to utilize the energy in the battery for electric boost because otherwise the energy harvesting potential on the way down cannot be exploited, simply because a fully charged battery cannot accept more energy.

Better energy use


58  

Recommendations to the driver

Outlook

To make this predictive control possible, the driver needs to be integrated into the process of controlling hybrid operation strategies. Therefore, cEM not only activates the powertrain components optimally but also supports the driver in selecting an energy-optimal speed trajectory. One very effective way of doing this is to provide haptic signals to the driver’s foot. To add this human machine interface, the connected energy management car is equipped with an accelerator force feedback pedal (AFFP®). It can generate discrete signals to the driver, telling him when stepping off the gas would be ideal to save fuel. In an initial step, energy consumption was reduced by 3% during cross-country driving with the 48 volt system by using static map information. After the driver releases the accelerator, the energy-optimum driving profile for the upcoming driving situation is activated. If the driver wishes to override the system suggestion, all he needs to do is step on the gas or the brake. For further energy-based optimization of the speed trajectory, up-to-date dynamic route information is useful, particularly for urban driving where conditions change rapidly. Suitable data can be provided by means of a vehicle connection to an intelligent backend via a dynamic electronic horizon (eHorizon). This algorithm makes information on traffic signs, dynamic speed limits, expected traffic light phases, and current traffic data available. One of the use cases would be to switch the vehicle powertrain to coasting when the car approaches a red traffic light and to use the last bit of the approach to add a deceleration phase with regenerative braking that brings the vehicle to a standstill in front of the traffic light (Fig. 33). Likewise, the coasting phase can begin just before a section of


59

outlook

Speed[ km [km/h] Speed /h]

Coasting Phase Coasting phase

Braking Phase phase

48 volt V System without cEM 48 system without cEM 48 system with cEM 48 volt V System with cEM

Coasting Coasting phase Phase

Braking Braking phase (only Phase (only with withBSG) BSG)

Distance Distance [ m ][m]

road with a speed limit. Depending on the altitude profile of the route as well as any bends, intersections, and traffic signs, this allows the driving strategy to be adapted to suit the route. To analyze the savings potential of cEM, three functions named Smart Traffic Light Assist, Smart Curve Speed Assist, and Intelligent Deceleration Assist were developed and implemented in the demonstrator car. The demonstrator car with the Smart Traffic Light Assist was first demonstrated under real-world driving conditions

Fig. 33: Function of the Smart Traffic Light Assist management

Fig. 34: The Smart Traffic Light Assist was first demonstrated during test driving in Las Vegas.


60  

Outlook

at the 2016 Consumer Electronics Show (CES) in Las Vegas (Fig. 34). To measure potential fuel efficiency benefits of cEM, systematic test drives were carried out. A typically urban driving cycle of 12.5 km length provided a combination of city freeway (80 km/h speed limit), urban traffic (50 km/h speed limit), and 1.3 km at a reduced maximum speed of 30 km/h (Fig. 35). Within this driving cycle, relevant situations such as traffic lights and speed limits were identified. During 29 real

Speed [km/h]

100

Speed limit Vehicle speed

80 60 40 20 0

0 2 4 6 8 10 12 Distance [km]

Fig. 35: An urban driving cycle and its speed profile highlight the importance of deceleration phases.

test drives, the effect of an anticipatory hybrid control system was considerable: »» The Smart Traffic Light Assist accounted for further consumption saving of 2.7% in comparison to the 48 volt demonstrator car without cEM. »» Another 0.7% of additional fuel savings could be attributed to the Intelligent Deceleration Assist in the case of static speed limits. Taking into consideration the dynamic electronic horizon data, hybrid driving strategies can be used more effectively through energy-efficient adjustments to the deceleration trajectory. The test drives revealed a total potential of an additional 3.4% fuel saving compared with the


61

outlook

Fig. 36: Functional principle of the Smart Curve Speed Assist

Coasting

Recuperation

Speed reduction

Re-acceleration

already highly efficient 48 volt demonstrator vehicle. Further potential can be exploited via the Smart Curve Speed Assist. When the driver approaches a curve, its bend radius can necessitate a deceleration. This provides another opportunity for energy harvesting. Based on static map data and/or dynamic data, the vehicle speed can be adjusted to an optimum level from both the driving safety angle and from the angle of energy efficiency (Fig. 36). Input level (sensing)

Driver

Driver assistance systems

Fig. 37: Complexity and interdependencies of cEM on the vehicle level

Body and interior systems

Chassis systems

connected energy management (energy and co2 emissions) Powertrain â&#x20AC;&#x201C; operating strategy and connected driving Mandatory: OBD management, VDA EGAS/ISO 26262, tuning protection Electric energy management

Actuator and subsystem control level (acting)

Component level

eHorizon

Strategy level (planning)

Mechanical energy management

Electric system control

Storage Plug-in Storage system charger system

DC/DC

Electric machine control 3~ AC

Rotor Rotor ďŹ field eld

Thermal energy management

Transmission control

Clutch Clutch

Gear shift

Combustion engine control

Air

Electric energy Mechanical energy Thermal energy

Predictive driving

Fuel

Ignition

Thermal system control Actuator

Actuator Actuator


62  

Outlook

Obviously the efficiency of a 48 volt mild hybrid vehicle – or of any vehicle for that matter – strongly depends on the decisionmaking database and on identifying hybrid driving opportunities. Predictive management and cEM can in future further improve the total efficiency of a mild hybrid car. Figure 37 shows the complexity of a comprehensive

Fig. 38: cEM uses real time traffic information


Outlook

approach to cEM on a vehicle level. It is clearly conceivable that energy management is highly instrumental to hybrid vehicles, given the many energy flows and interdependencies within the car. The decision-making database can be provided via a combination of navigation data, connectivity, and backend information (Fig. 38).

â&#x20AC;&#x201E;63


64â&#x20AC;&#x201E;â&#x20AC;&#x201E;

Outlook

Hybrid electric systems for many use cases It would create a limited picture of mild hybrid technology to look only at the demands made by downsized turbocharged engines in small to compact-size cars. Also the other vehicle classes will benefit from the fuel saving capabilities of the 48 volt system. And there is another valuable benefit available from the 48 volt technology: Energy harvesting within the 48 volt system can provide additional electrical energy to stabilize the on-board net and to power comfort functions. Fig. 39: Innovative pedelec/ ebike drive based on 48 volt technology

Electrification on two wheels

In other world markets, 48 volt technology may play a totally different role yet again. While this technology is one of two core energy sources in a mild hybrid car, it can also be the sole energy source in a two-wheeled vehicle such as an electrified scooter or motorcycle. In this case, it is not a hybrid technology any more. Instead it becomes the core part of a battery electric vehicle (BEV). This can extend right on to pedelecs (pedal electric cycles) or ebikes (electric cycles). The reasons to use 48 volt technology for pedelecs/ebikes or small BEVs are the same as for mild hybrid cars: The technology is compact, powerful, efficient, easily integrated and mature (Fig. 39).


65

Outlook

Transferring automotive 48 volt technology to other areas of mobility is a sensible strategy as the requirements are similarly tough. All system components for an electric scooter or pedelec/ ebike must be optimized for use in rugged surroundings. On top of that, the electric motor needs to run smoothly, must meet stringent electromagnetic compatibility tests, and is always part of a highly integrated total system com­plete with control and transmission. In contrast to high-voltage hybrid technology, 48  volt technology can be used in such different surroundings. Obviously electric motors for micro-mobility solutions will be of a different size, but the principal diversity of 48 volt solutions will make them an important part of future hybridization. A wide application scope like this underlines the idea that electrification should not be an all-ornothing-at-all approach. Most vehicle classes can benefit from 48 volt technology even assuming that the budget for electrification may be very limited.

Conclusion Electrification is the future of mobility. It may come along in various types, though (Fig. 40). 48 volt technology has the potential to become the work horse of mild hybridization. Owing to its simple integration and limited cost, it can be used in the mass volume segments where the scale effect is potentially enormous. If a large share of the world’s vehicles were to save a twodigit percentage of fuel, the global benefit will be highly welcome. Assuming that the integration depth of 48 volt systems and the systematic optimization on the vehicle level will increase, a growing

Wide application scope


CO2 reduction

66  

Outlook

Fuel saving with low voltage technology

Fuel saving and electric driving

100% electric driving Electric vehicle

Plug-in hybrid Full hybrid 48 volt Eco Drive 12 volt start-stop

Electrification

Fig. 40: Electrification tailored to fit: types of vehicle electrification

number of 48 volt vehicles may be able to save upwards of 25% of fuel during urban driving in the future. Considering the global trend towards living in mega cities, this makes a perfect fit between technology and the expected lifestyle of billions of people. Whether the combustion engine is here to stay or whether mild hybridization may “only” be a matter of some decades of transition, 48 volt technology will establish itself as a versatile, modular and affordable contribution to modern individual mobility. This trend may well be accelerated further by the advent of automated driving. Vehicles capable of taking over the driving task for a certain time will not only contribute to driving safety. Automated driving will also help to save fuel by increasing the total efficiency of a trip. In order to achieve this benefit, automated vehicles (Fig. 41) require electric energy to power actuators needed for functions such as automated steering. Providing the elec-


Outlook

tric energy for this new demand is another potential contribution 48 volt technology can make. Once the energy content, weight and cost of high-voltage batteries reach a level that makes them truly mass-suitable, BEVs will develop into a solution not only for “the smooth asphalt surfaces in major cities” but also for “journeying across the land at high speeds” (see the opening quote in chapter “Electric power in the vehicle – a short introduction”, p. 4). The future is going to be electric.

 67

Fig. 41: An optimum hybrid vehicle efficiency requires the data flows leading to and from a networked vehicle.


68  

Sources

Sources [1] Siemens AG: “como – Facts, Trends and Stories on Integrated Mobility.” Issue 13, September 2014, page 15 [2] Franz Haag: “1888 Flocken Elektrowagen Rüsselsheim”, 2013, Creative Commons https://creativecommons.org/licenses/by-sa/3.0/ deed.en [3] Autoviva - Flickr: “Reconstruction of the hybrid vehicle Mixte” Geneva Motor Show, 2011, Creative Commons https://creativecommons.org/licenses/by/2.0/ deed.en [4] VOX TV: “auto mobil – das VOX-Automa­ gazin.” Broadcasted at 5pm on 16th November, 2014


Abbreviations

Abbreviations AC

Alternating Current

AFFP®

Accelerator Force Feedback Pedal

A-segment Subcompact cars BEV

Battery Electric Vehicle

BMEP

Brake Mean Effective Pressure

B-segment Compact cars BSFC

Brake Specific Fuel Consumption

BSG

Belt Starter Generator

C-segment Medium cars cEM

connected Energy Management

DC

Direct Current

DMF

Dual Mass Flywheel

D-segment Large cars ebike

electric cycle

ECE

Economic Commission for Europe

EHC

Electrically Heated Catalyst

E/E Electric/Electronic E-segment

Premium cars

GDI

Gasoline Direct Injection

GTC

Gasoline Technology Car (I + II)

HEV

Hybrid Electric Vehicle

HVAC Heating Ventilation Air Condi-

tioning ICE

Internal Combustion Engine

ISG

In-line Starter Generator

LIVC

Late Intake Valve Closing

Li-ion Lithium-ion mGAP

modified Brake Booster

NEDC

New European Drive Cycle

 69


70  

Abbreviations

NiMH

Nickel-Metal Hydride

OEM Original Equipment Manufac-

turer (i.e. Car Maker) Pedelec

Pedal Electric Cycle (bicycle)

PHEV

Plug-in Hybrid Electric Vehicle

SOC

State Of Charge

SOF

State Of Function

SOH

State Of Health

SSG

Side-attached Starter Generator

SUV

Sports Utility Vehicle

TDI Turbocharged Direct Injection

(Diesel) VDC

Volt DC

WLTC Worldwide Harmonized Light-

duty Vehicle Test Cycle


the company behind this book

Continental Continental develops intelligent technologies for transporting people and their goods. As a reliable partner, the international technology company provides sustainable, safe, comfortable, individual, and affordable solutions. In 2015, the corporation generated sales of €39.2 billion with its five divisions, Chassis & Safety, Powertrain, Interior, Tires, and ContiTech. Continental currently employs approximately 215 ,000 people in 55 countries. Chassis & Safety Division focuses on modern technologies for active and passive safety and for vehicle dynamics. Powertrain Division represents innovative and efficient system solutions for the powertrain of today and of the future for vehicles of all categories. Interior Division combines all activities relating to the presentation and management of information in the vehicle. Tires offers the right tires for every application – from passenger cars through trucks, buses and construction site vehicles to special vehicles, bicycles and motorcycles. ContiTech develops and produces functional parts, components, and systems for the automotive industry and for other key industries.

CONTINENTAL POWERTRAIN DIVISION Continental Automotive GmbH Siemensstrasse 12 93055 Regensburg www.continental-automotive.com


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