Fuel Injector: Notes

The injectors incorporate piezoelectric actuators required for high-speed activation. The higher switching speed allows the intervals between individual fuel injections to be reduced and controlled more precisely. This feature contributes to a quiet and more efficient engine.

The fuel injector drive circuit is arranged in two separate banks. Each bank is controlled by a control integrated circuit, which drives the power stage to activate the piezoelectric actuators. Bank 1 is comprised of injectors 4, 5 and 6, while bank 2 is comprised of injectors 1, 2 and 3. The microprocessor receives information concerning the operation of the control integrated circuits and power stages.

The engine requires a high number of injections during normal operation. At an engine speed of 1000 RPM for example, the ECM may activate the injectors up to 250 times every second. Enough energy needs to be quickly stored to activate the injectors within these time constraints. The piezoelectric actuators also require high-voltage for proper operation. To supply the demand of power, each injector bank contains the following stages:

1. Booster stage
2. Charge/discharge driver stage
3. Piezoelectric-driver stage

The control IC of each bank controls the operation of its corresponding booster stage, charge driver stage and piezoelectric actuator driver stage. The booster stage is controlled via the charge pump. The charge driver stage is controlled via the charge and discharge power transistors. In the piezoelectric actuator driver stage, the control IC controls the power and ground side of each piezoelectric actuator via high-side and low-side power transistors. The high side selects the bank, while the low side selects the individual cylinders. The ECM monitors the current flow throughout the injector drive circuit via the shunt resistors to determine the state of charge of the booster capacitor.

The booster stage contains the following main components:

1. DC-DC Converter-designed to step-up the battery voltage to 200V
2. Charge Pump-transistor that switches the DC-DC transformer to induce the high voltage
3. Booster Capacitor-stores the energy required to activate the piezoelectric actuators

The charge/discharge driver stage contains the following main components:

1. Charge Power Transistor-allows power to flow to the piezoelectric high-side transistor
2. Discharge Power Transistor-short circuits the piezoelectric actuators to ensure the end of injection
3. Stop Power Transistor-short circuits all the piezoelectric actuators in an emergency to end the injection
4. Transfer Coil-produces a smooth rise and fall of current to avoid damage to the piezoelectric actuators

The piezoelectric driver stage contains the following main components:

1. High-Side Power Transistor - directs the high-voltage to the specific cylinder bank for injector activation
2. Low-Side Power Transistors - Grounds the specific piezoelectric actuator for injector activation