4. Acceleration enrichment
The air-fuel ratio becomes lean, especially during the start of acceleration because a fuel supply lag tends to occur during acceleration against the rapid change of the amount of the intake air when the accelerator pedal is depressed. For this reason, the injection duration is lengthened to increase the fuel injection volume against the intake air to prevent the air-fuel mixture from becoming lean. The acceleration is determined by the speed of the change in the throttle valve opening angle. The correction during acceleration increases greatly during the start of acceleration and is gradually reduced thereafter until the increase has ended. In addition, the more rapid the acceleration is, the larger the fuel injection volume increase.
5. Fuel cut-off
During deceleration, injection operation is stopped according to the deceleration condition in order to reduce the harmful exhaust gases and improve the engine braking effect. Then the fuel cut-off control is activated to cut-off the fuel injection. The state of deceleration is determined from the throttle valve opening and the engine speed. When the throttle valve is closed and the engine speed is high, it is determined that the vehicle is decelerating.
Fuel cut-off control
The fuel cut-off control stops the fuel injection when the engine speed is higher than a determined speed and the throttle valve is closed. Fuel injection will resume when the engine speed slows to a determined speed or the throttle valve is opened. The fuel cut-off engine speed and fuel injection resumption engine speed will increase when the coolant temperature is low. In addition, the fuel cut-off engine speed and fuel injection resumption engine speed are increased when the air conditioner switch is on to prevent the engine speed from falling and an engine from stalling. There are also some engine models in which these engine speeds drop during braking (i.e., when the stop light switch is on).
6. Power enrichment
As there is a large amount of the intake air at heavy loads, such as when climbing a steep hill, it is difficult to sufficiently mix the injected fuel with the intake air. And all of the intake air is not used during combustion, causing some to remain. Therefore, more fuel than for the theoretical air-fuel ratio is injected to use all of the intake air in combustion to increase power. Heavy loads are determined from the throttle position sensor opening, engine speed, and intake air mass (VG or PIM). The greater the intake air mass (VG or PIM) or the higher the engine speed is, the ratio of the increased amount becomes larger. In addition, the amount is further increased when the throttle valve opening angle becomes a certain value or more. The correction of the increased amount is from approx. 10% to 30%.
7. Intake air temperature correction
The air density changes depending on the air temperature. For this reason, a correction must be made to increase or decrease the fuel volume in accordance with the intake air temperature to optimize the mixture ratio required for the current engine conditions. The intake air temperature is detected by the intake air temperature sensor. The engine ECU is set to a standard intake air temperature of 20 C (68 F). The correction amount is determined when the temperature rises above or falls below this temperature. When the intake air temperature is low, the amount is increased because the air density is high. When at high temperature, the amount is decreased because the air density is low. The correction of the increased/decreased amount is approx. 10%.
For hot-wire type air flow meters, the air flow meter itself outputs a corrective signal for the intake air temperature. Therefore, intake air temperature correction is not required.
8. Voltage correction
There is a slight delay between the time where the engine ECU sends an injection signal to the injector, and the time when the injector actually injects the fuel. If there is a severe drop in battery voltage, then this delay will be longer. This means that the time the injector injects the fuel is shorter than the time calculated by the engine ECU. Therefore, the ratio of air becomes higher (in other words, leaner) than the mixture ratio required by the engine. For this reason, the engine ECU adjusts this by making the injector injection duration longer in accordance with the battery voltage drop.
4. Acceleration enrichment