Scheme 3
Restriction on Power Assist Operation
Repeated extreme steering force, such as turning the steering wheel continuously back-and-forth with the vehicle stopped, causes an increase in electrical current draw by the EPS motor. The increase of electric current causes the EPS motor to heat up. Because this heat adversely affects the system, the control unit monitors the electric current draw of the EPS motor.
When the control unit detects heat build-up in the EPS motor, it reduces the electric current to the EPS motor gradually to protect the system, and it restricts the power assist operation. The EPS indicator does not come on during this function.
When steering torque is not applied to the steering wheel, or when the ignition is turned to LOCK (0) and the EPS motor cools, the control unit will restore the power assist gradually until it's fully restored (after about 26 minutes).
System Operation
The EPS control unit controls the EPS motor by these signals
- Vehicle speed signal (from PCM)
- Engine speed signal (from PCM)
- Torque sensor signal
At idle or low vehicle speeds, the EPS control unit sends a signal to the PCM to increase the engine idle speed to prevent the engine from stalling.
When the EPS control unit detects a failure in the system, it stores a DTC and sends a signal to the gauge control module to turn the EPS indicator on.
Scheme 4
EPS motor operation
The EPS uses an efficient DC type motor. The EPS motor control circuit is composed of a system control CPU, the field-effect transistor (FET) drive circuit, the H type FET bridge, the power relay, the fail-safe relay, the electric current sensor, and the EPS motor. From the input sensor signals, the CPU calculates and duty cycles outputs the appropriate current for the FET drive circuit. This operation is duty controlled.
