Operation

OPERATION




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:

- Booster stage
- Charge/discharge driver stage
- 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:

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

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

- Charge Power Transistor-allows power to flow to the piezoelectric high-side transistor
- Discharge Power Transistor-short circuits the piezoelectric actuators to ensure the end of injection
- Stop Power Transistor-short circuits all the piezoelectric actuators in an emergency to end the injection
- 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:

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

INJECTION STAGES





Depending on the engine requirements, an injection cycle may consist of up to two pilot injections, one main injection and two post injections.

Piezoelectric actuators have a capacitive behavior. When charged at a certain voltage, they will hold this voltage for a long time. Fuel is injected when the piezoelectric actuator is charged, and the rail pressure is sufficiently high. The piezoelectric actuator is then discharged to end the injection of fuel. The piezoelectric actuator is discharged normally by switching a power transistor ON. If the transistor cannot be switched ON, or if the circuit is interrupted, the piezoelectric actuator remains charged and will continue to inject fuel. To avoid this, a bleed resistor is connected in parallel to the piezoelectric actuator, ensuring that the actuator is discharged over a defined period of time.

The charging and discharging phases of a piezoelectric actuator are also similar to that of a capacitor. Injection is performed by charging the piezoelectric actuator to a set voltage and discharging it again when the activation time has elapsed. A current flow is only present during charging and discharging. The travel of the piezoelectric actuator is proportional to the voltage and is transferred to the control valve via the hydraulic coupler. The control valve controls the movement of the nozzle needle.
Pilot Injection:




The purpose of pilot injection is to reduce combustion noise and emission of pollutants. Up to two pilot injections are possible before the main injection. During pilot injection, the pressure in the cylinder is slightly raised. The slight increase in pressure causes a shorter delay in the combustion of the main injection, which reduces combustion pressure peaks. This effect produces a soft combustion while reducing the combustion noise. By shortening the combustion delay, the pilot injection indirectly affects the engine torque. In addition, pilot injection reduces particulate matter in the exhaust gas.

Pilot injection Z has two possible ranges of operation that depend on injection requirements. However, a combination of the two ranges is not possible during an injection event. Pilot injection Z can either occur at an earlier stage if a wider space between injections is required, or right before pilot injection 1.

The ECM controls the amount of fuel injected by adjusting the start of pilot injection and the pilot injection duration. The ECM calculates the start of pilot injection depending on engine load. The last start of main injection and the battery voltage are also taken into account. The ECM calculates the quantity of fuel injected based upon the following inputs:

- Fuel rail pressure
- Boost pressure
- Coolant temperature
- Charge air temperature
- Inlet air pressure
- Engine speed

The ECM uses the coolant temperature, charge air temperature and inlet air pressure inputs to correct the pilot injection quantity. The ECM shuts off pilot injection if one of the following conditions is present:

- Pilot injection time is exceeded
- Quantity of pilot injection is too low
- Detected engine speed is too high
- Quantity of main injection is too low
- Fuel rail pressure is too low
- Engine is switched off

Main Injection:
Main injection takes place following pilot injection. The main injection provides the energy for the performance of the engine. This injection phase is the main factor responsible for supplying the engine torque. The ECM controls the start of main injection (injection timing) and the main injection duration (injection period). The ECM calculates the main injection fuel quantity based upon the following inputs:

- Fuel rail pressure
- Boost pressure
- Coolant temperature
- Charge air temperature
- Inlet air pressure
- Accelerator pedal position
- Engine speed
- Fuel temperature

The ECM shuts off the main injection if one of the following conditions is present:

- Engine speed is above 4500 rpm
- Fuel temperature limit exceeded
- Fuel rail pressure is too low
- External quantity control (ESP)
- Engine in deceleration mode
- Engine is switched off

Post Injection:
Post injection takes place following main injection. The purpose of post injection is to reduce particulates and regenerate the DPF. Up to two post injections are possible after the main injection. With post injection Z, a small amount of fuel is injected while combustion is still in progress. The soot particles are burned off and soot emissions are reduced. The post injection Z also contributes to the generation of torque.

The post injection 1 is the last injection phase and takes place 40º ATDC or later. The post injection 1 brings hydrocarbons to the oxidation catalyst for an exothermic reaction (a chemical reaction that produces heat). The ECM detects the load status of the DPF via the differential pressure sensor and activates post injection 1 if needed. The burning of post injected fuel in the oxidation catalyst further increases the temperature of the exhaust gas and triggers the regeneration process of the DPF. Post injection 1 does not contribute to the generation of torque.

The ECM calculates the post injection quantity based upon the following inputs:

- Fuel rail pressure
- Boost pressure
- Coolant temperature
- Charge air temperature
- Inlet air pressure
- Differential pressure (DPF)

The ECM uses the coolant temperature, charge air temperature and barometric pres-sure inputs to correct the post-injection quantity.

- The ECM shuts off post-injection if one of the following conditions is present:
- Pilot injection time is exceeded
- Detected engine speed is too high
- Quantity of post-injection is too low
- Quantity of main injection is too low
- Fuel rail pressure is too low
- Engine is switched off