Function of ISC Operation of Rotary Solenoid Type


1. Staring control
When the engine ECU receives a starter signal (STA), it determines that the engine is starting and opens the ISCV to improve startability. The ISCV opening is controlled according to the engine speed signal (NE) and coolant temperature signal (THW).
2. Warm-up (fast-idle) control
After the engine starts, the engine ECU opens the ISCV in accordance with the coolant temperature (THW) to increase the idling speed. As the coolant temperature rises, the engine ECU controls the ISCV toward closing direction to decrease the idle speed. When the engine is cold, the idling speed is unstable due to such factors as the engine oil viscosity being high and poor fuel atomization. For this reason, the idling speed must be made higher than normal to stabilize it. This is called fast idling.
3. Feedback control
For feedback control, the target idling speed stored in the engine ECU and the actual idling speed are compared. Then, the ISCV is controlled to correct the actual idling speed to the target idling speed. When the actual idling speed is lower than the target idling speed: The ISCV is opened to correct the idling speed to the target idling speed. When the actual idling speed is higher than the target idling speed: The ISCV is closed to correct the idling speed to the target idling speed. In addition, the target idling speed varies depending on the engine condition, such as whether the neutral switch is ON or OFF, electric load signal is ON or OFF, or air conditioner switch is ON or OFF.
4. Engine speed change estimate control
The engine speed change estimate control estimates the change in idling speed from the engine load and controls the ISCV accordingly. When the shift lever is changed from D to N or N to D, or when there is a change in engine load immediately after an electrical component, such as the tail lamp relay, defogger relay, or air conditioner switch operates, the idling speed increases or decreases. The feedback control then increases or decreases the idling speed, but the idling speed is unstable until the target idling speed is reached. For this reason, when the engine ECU receives an engine load signal from an electrical component, etc., the ISCV is controlled before the idling speed changes to reduce the amount of idling speed change.
5. Other controls
The engine ECU opens the ISCV when the IDL point of the throttle position sensor is closed (accelerator pedal is released) to prevent a sudden drop in the engine speed.
In vehicles equipped with EHPS (Electro-Hydraulic Power Steering), the electrical load increases when the EHPS operates. Therefore, the engine ECU opens the ISCV to prevent the idling speed from dropping.
Operation of Stepper Motor Type
1. Starting set-up
The starting set-up sets the ISCV in the fully opened position when the engine is stopped (when the engine ECU does not receive the NE signal) to improve startability the next time the engine is started.
Main relay control
The engine ECU instructs that electrical power continued to be supplied to the main relay for a little while even after the ignition switch is turned OFF in order to set the ISCV in the fully opened position. After the ISCV has been set, the engine ECU stops supplying power to the main relay.
2. After-start, warm-up (fast-idle) and feedback control
These controls are basically the same as for the rotary solenoid type. After the engine is started, the valve closes from the fully opened position to the open position determined for the engine speed and coolant temperature, and then the valve gradually closes as the coolant temperature rises. When the coolant temperature reaches 80C (176 F), feedback control is used to maintain the target idling speed.

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