FUEL INJECTION CONTROL



Fuel injection volume is regulated to obtain the optimum air-fuel ratio in accordance with the constant minute changes in engine driving conditions. Fuel injection volume is controlled by injector drive time (injection time). There is a prescribed basic drive time that varies according to the engine speed and intake air volume. Engine-ECU adds prescribed compensations to this basic drive time according to conditions such as the intake air temperature and engine coolant temperature to decide injection time. Fuel injection is done separately for each cylinder and is done once in two engine rotations.
System Configuration Diagram


1. INJECTOR ACTUATION (FUEL INJECTION) TIMING


Injector drive time in case of multipoint fuel injection (MPI) is controlled as follows according to driving conditions.
Fuel Injection During Cranking and Normal Operation

Fuel injection to each cylinder is done by driving the injector at optimum timing while it is in exhaust process based on the crankshaft position sensor signal. Engine-ECU compares the crankshaft position sensor output pulse signal and camshaft position sensor output pulse signal to identify the cylinder. Using this as a base, it performs sequential injection in the sequence of cylinders 1, 3, 4, 2.
Additional Fuel Injection During Acceleration

In addition to the synchronizing fuel injection with crankshaft position sensor signal during acceleration, the volume of fuel is injected according to the extent of the acceleration.

2. Fuel injection volume (injector drive time) control


Under normal operating conditions, the figure shows the flow chart of calculating the injection amount during the injector driving time. Basic drive time is decided based on the air flow sensor signal (intake air volume signal) and crankshaft position sensor signal (engine rotation signal). This basic drive time is compensated according to signals from various sensors and optimum injector drive time (fuel injection volume) is calculated according to driving conditions.
Fuel Injection Volume Control Block Diagram (Normal Operation)


[Injector basic drive time]


Fuel injection is performed once per cycle for each cylinder. Basic drive time refers to fuel injection volume (injector drive time) to achieve theoretical air-fuel ratio for the intake air volume of 1 cycle of 1 cylinder. Fuel injection volume changes according to the pressure difference (injected fuel pressure) between manifold pressure and fuel pressure (constant). So, injected fuel pressure compensation is made to injector drive time for theoretical air-fuel ratio to arrive at basic drive time.


Intake air volume of each cycle of 1 cylinder is calculated by engine-ECU based on the airflow sensor signal and crank angle sensor signal. Also, during engine start, the map value prescribed by the coolant temperature sensor signal is used as basic drive time.

[Injector drive time compensation]


After calculating the injector basic drive time, the engine-ECU makes the following compensations to control the optimum fuel injection volume according to driving conditions.

List of main compensations for fuel injection control


Compensations
Content
Linear air-fuel ratio sensor feedback compensation
The linear air-fuel ratio sensor signal is used for making the compensation to get air-fuel ratio with best cleaning efficiency of the 3-way catalytic converter. This compensation might not be made sometimes in order to improve drivability, depending on driving conditions. (Air-fuel ratio compensation is made.) The engine-ECU compensates the output signal of the oxygen sensor (front) using the output signal of the oxygen sensor (rear). This allows the deviation of the output signal, caused by the deterioration of the oxygen sensor (front), to be solved, then the highly accurate exhaust gas control is performed.
Air-fuel ratio compensation
Under driving conditions where oxygen sensor feedback compensation is not performed, compensation is made based on pre-set map values that vary according to engine speed and intake air volume.
Engine coolant temperature compensation
Compensation is made according to the engine coolant temperature. The lower the engine coolant temperature, the greater the fuel injection volume.
Acceleration/ Deceleration compensation
Compensation is made according to change in intake air volume. During acceleration, fuel injection volume is increased. Also, during deceleration, fuel injection volume is decreased.
Fuel injection compensation
Compensation is made according to the pressure difference between atmospheric pressure and manifold absolute pressure. The greater the difference in pressure, the shorter the injector drive time.
Battery voltage compensation
Compensation is made depending on battery voltage. The lower the battery voltage, the greater the injector drive signal time.
Learning value for fuel compensation
Compensation amount is learned to compensate feedback of linear air-fuel ratio sensor. This allows system to compensate in accordance with engine characteristics.

[Fuel-cut control when over-run]


When engine speed exceeds a prescribed limit (4,800 r/min), engine-ECU cuts fuel supply to prevent overrunning and thus protect the engine.