The fuel injector driver circuit

Fuel Injector Driver Circuit Pravat Kumar Behera Formerly Technical Specialist-Controls, Cummins Technologies India Pvt Ltd B.E (Electronics & Telecommunication), U.C.E,Burla (INDIA) Pbehera1998@gmail.com;

Abstract The function of a fuel injector is to spray atomized fuel into the combustion chamber of an internal combustion engine. The fuel injector is a small nozzle into which liquid fuel is injected at high pressure. The placement of the injector can be in a different part of the engine depending upon the type of fuel injection system is being used. High pressure from the fuel pump feeds the fuel to the fuel injector.

Fig-1: Common rail System

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1. INTRODUCTION The fuel injector driver is an integral part of the electronic fuel injection (EFI) controller. The EFI controls injector timing and pulse width by applying a pulse to the circuit at exactly the right instant. Since a constant supply of battery voltage is already present on the circuit (whenever the ignition is on), this initiates a precise spray of fuel from the pressurized fuel injector. This action occurs for each cylinder in sequential repetition. In addition to controlling the fuel injection system, the electronic fuel injection (EFI) also monitors individual fuel injector circuit feedback resistance for signs of a malfunction. This may allow the EFI to detect a problem . before it is exhibited as a drivability issue. .

Fig-2: Electronic Fuel Injector •

Injector body- Same as the mechanically controlled fuel injector the body of this type of injector is a precisely designed hollow shell inside which all the other components are arranged.

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Plunger- Same as the mechanically controlled fuel injector a plunger is used for the opening and closing of the nozzle but in electronically controlled fuel injector the opening of the nozzle is controlled electronically with the help of electromagnets.

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Spring – Same as the mechanically controlled fuel injector a plunger spring is used to hold the plunger in its position in order to close the nozzle of the fuel injector when required.

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Electromagnets – Unlike mechanically controlled fuel injector this type of injector is equipped with electromagnets just around the plunger which controls the opening of the nozzle by taking the electronic signal from the electronic control unit of the engine through the electronic plug or connection connecting the fuel injector with the electronic control unit of the engine.

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Electronic plug/connection- At the top end of electronically controlled fuel injector a connection/plug is present through which the electronic signal from the electronic control unit of the engine is transferred to the electromagnets which in turn opens the nozzle in order to spray the fuel.

2. DRIVER CIRCUIT

Fig-3: Fuel injector drive circuitry The IC is designed to control an external power NPN Darlington transistor that drives the high current injector solenoid. Current required to open a solenoid is several times greater than the current necessary to merely hold it open.

Normally powered from a 5V± 10% supply, the IC is typically operable over the entire temperature range (−55°C to+125°C ambient) with supplies as low as 3V. This is particularly useful under “cold crank” condition.

Fuel injectors can usually be modeled by a simple RL circuit. Figure1 shows such a model for a typical fuel injector. In actual operation, the value of L1 will depend

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upon the status of the solenoid. In other words, L1 will change depending upon whether the solenoid is open or closed.

Fig-4: Electrical Model of Fuel Injector

The peak and hold currents are determined by the value of the sense resistor RS, the battery voltage and the saturation voltage of Q1.The drop across the sense resistor is created by the solenoid current, and when this drop reaches the peak threshold level, typically 385mV,the IC is tripped from the peak state in to the hold state. The IC now behaves more as an OPAMP and drives Q1 within a closed loop system to maintain the hold reference voltage, typically 94mV, across RS. In order to guarantee injector operation over the life and temperature range of the system, a peak current of approximately 4 amps was chosen. This led to a value of RS of 0.1â„Ś.

The purpose of the timer function is to limit the power dissipated by the injector or solenoid under certain conditions. Specifically, when the battery voltage is low due to engine cranking and there may not be sufficient voltage available for the injector to achieve the peak current. The waveforms under the low battery condition, the injector current can be seen to be leveling out at 3 amps, or 1 amp below the normal threshold. Since continuous operation at 3 amps may over heat the injectors, the timer function on the IC will force the transition into the hold state after one time constant (the time constant is equal to RTx CT), or when the voltage on the TIMER pin(Pin8) is greater than typically VSUPPLY x 63%. The timer is reset at the end of each input pulse. For systems where the timer function is not needed, it can be disabled by grounding the TIMER Pin (Pin8).

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CLASSICAL DRIVER CIRCUIT +5V

BATTERY

2

DRIVER_HS 15.0K,0805 FEEDBACK

VIN

VBB

ST

VOUT

D3

5

ACTUATOR+

0

1

4

GND

U1 BTS432

10K,0805

R12

3

R2

VB20200G R5

R1 150E,1/2W

47K,0805

C1

C2

0.01uF,100V

1000pF,100V D8 V10PM10-M3/H

D4 VS-MBRS1100-M3/5BT 0

0

R6

Chassis Ground

D5

100K,0805

ACTUATOR43V,1W V1FM10HM3/H D7

R4

R3

Chassis Ground

5

U2 LM321 R9

4

ADC

107

C6 1uF,10V

+

1

-

3

2

20K,0805

AGND

R8 1K,0805 C5 1uF,10V

R10

AGND

1000pF,100V

BTS141TC

47E,1206

+5V

C4

0.01uF,100V M1

DRIVER_LS 2K,1206

C3

R7 0.1E,2.5W

15K,0805 R11

AGND

0

1K,0805 AGND

Fig-5: Classical Fuel Injector Drive Circuit

3. REFERENCES 1) https://www.bosch-mobility-solutions.com/en/products-and-services/passengercars-and-light-commercial-vehicles/powertrain-systems/common-rail-systempiezo/ 2) https://www.mechanicalbooster.com/2018/09/what-is-fuel-injector.html 3) https://www.ti.com/product/LM1949

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