WEC – 2015 PORSCHE 919 HYBRID unit was built. However, due to the uncertainty of its performance, the space in the monocoque was still left large enough that the 2014 battery could be accommodated if necessary. ‘The battery is the biggest weight contributor,’ says Hitzinger. ‘We made a big step – we redesigned it again so that it is smaller and lighter, but at the same time we increased the power. This was by far the biggest step in terms of power density increase on the battery side. ‘We had changes to the MGU-H and MGU-K and to the power electronics as well. The whole system has to deliver more energy so it needs to be more powerful. When I saw for sure where we were weight-wise and energy-wise at Le Mans, I said OK, we can’t wait for the new battery in 2016, we do it for 2015. We did in six months what we originally planned to do in a year. We made a new cell, and a completely new battery. Cooling is where we are really good. We have a clever cooling concept that allows us to stress the battery heavily without over-stressing it.’ There were no figures available for the efficiency or power density of the new hybrid system, but it is clear that this is a huge step not only in technology, but also in performance. Over one lap at the Paul Ricard circuit, the Porsche was able to lap almost as fast as the old Peugeot 908 HDI FAPs in all of their V12 glory. Many are expecting that the reduced weight, coupled with the higher MJ category will see the Porsche excel in qualifying, although race pace is still a concern. ‘It is always a trade-off, because you get less fuel amount,’ says Hitzinger of the leap to 8MJ. ‘If you are comfortable in the class in terms of how much you can recuperate, it is always a gain. Then you have to look at 8MJ at Le Mans, it does not mean you can gain that in other tracks because of the braking zones, yes, and more because of the factor 1.55. Pro-rata you can do a lot more. Hypothetically, if you can do just about 8MJ at Le Mans, there is a good chance that you cannot do the maximum allowed on the other tracks. It may still make sense if you can do 7.5MJ. If you can do 7MJ, that is the break-even point. Then it is worse at the other tracks, and it doesn’t make sense anymore.’
TECH SPEC Porsche 919 Hybrid (2015) Le Mans prototype LMP1 class Monocoque: Composite material structure consisting of carbon fibres with an aluminium honeycomb core. The monocoque was developed on the basis of the 2015 LMP regulations and was tested in accordance with the 2015 FIA crash and safety standards. The cockpit is closed. Combustion engine: V4 engine (90 degree cylinder bank angle), turbocharged, 4 valves per cylinder, DOHC, 1 Garrett turbocharger, direct petrol injection, fully load-bearing aluminium cylinder crankcase, dry sump lubrication Max. engine speed: 9000/min Engine management: Bosch MS5 Displacement: 2000 cm3 (V4 engine) Output: Combustion engine: > 500bhp, rear axle MGU: > 400bhp, front axle Hybrid system: KERS with a motor generator unit (MGU) mounted on the front axle; ERS for recuperation of energy from exhaust gases. Energy storage in a liquid-cooled lithiumion battery (with cells from A123 Systems) Drive system: Rear-wheel-drive, traction control (ASR), temporary all-wheel-drive at the front axle via the electric motor when boosted, hydraulically operated sequential 7-speed racing gearbox Chassis: Independent front and rear wheel suspension, push-rod system with adjustable dampers Specifications: Porsche 919 Hybrid 12 Brake system: Hydraulic dual-circuit brake system, monoblock light alloy brake calipers, ventilated carbon fibre brake discs (front and rear), infinitely variable control of braking force distribution by driver Wheels and tyres: Forged magnesium wheel rims from BBS; Michelin Radial tyres, front and rear: 310/710-18 Dimensions/weights: Minimum weight: 870kg Length: 4650mm Width: 1900mm Height: 1050mm Fuel tank capacity: 68.5litres
The two-litre V4 engine powers the rear axle with over 500bhp. When the driver recalls the stored energy from the battery, an extra 400bhp drives the front axle
‘Hypothetically, if you can do just about 8MJ at Le Mans, there is a good chance that you cannot do the maximum allowed on the other tracks’
12 www.racecar-engineering.com JUNE 2015
Stint time
One of the key areas for development for Porsche was improving the stint time for the cars. In 2014 rival teams quickly noticed that the Porsche was not able to compete as well in the races as in qualifying. The team has worked on the suspension kinematics to improve the tyre performance over a longer distance, and the team has undoubtedly learnt more about which of the Michelin tyres to use, and when. However, there are other factors in using the tyres efficiently, including the downforce levels that are run, and how the energy is recuperated and distributed. While Toyota uses both the front and the rear axles, Porsche generates only to the front axle