ELECTRIC POWER STEERING (EPS) CONTROL MODULE CONSTRUCTION AND OPERATION

id061300247100


Construction

•  The EPS control module is installed in the engine compartment on the left side.
•  The module calculates the proper assist current based on the steering force signal from the torque sensor installed on the steering gear and linkage, the motor rotation angle signal from the resolver sensor, and the vehicle and engine speed signals from the PCM via CAN communication, and then outputs the control current to the EPS motor.

Function Table

Control item

Function
Motor current control
•  Calculates the optimum assist current based on the steering force, motor rotation angle, and vehicle and engine speeds, and outputs a control current to the EPS motor.
System overheating prevention control
•  In order to prevent system overheating, motor current is controlled according to the turning limit or motor output control.
On-board diagnostic function
•  The main part of the system control includes the self-diagnosis function. In case a malfunction occurs, the EPS warning light illuminates to alert the driver, and a DTC is stored in the EPS control module at the same time.
•  As a result of the on-board diagnosis, when a malfunction is determined, system control is suspended or limited to assure safety while driving.

am6zzn00000252

Operation


Motor current control

•  The proper assist current is calculated based on the steering force signal from the torque sensor, the motor rotation angle signal from the resolver sensor, and the vehicle and engine speed signals from the PCM, and then the control current is output to the EPS motor.
•  In addition, various control corrections are performed according to vehicle driving conditions.
Base current control
―  The base current is the fundamental current amount for driving the EPS motor and is calculated based on the steering force and vehicle speed signals.
am6zzn00000253
Inertia (static friction) correction control
―  The inertia correction control compensates for the influence caused by the revolution inertia of the motor (insufficient torque when starting, torque continuance when stopping). The correction current to the base current is increased according to vehicle conditions.
am6zzn00000254
Damping (viscosity) correction control
―  The damping correction control reduces slight vibrations transmitted from the road surface (kickback) using the motor control current. The correction current to the base current is either increased or decreased according to vehicle conditions.
―  The damping correction control is calculated based on the vehicle speed signal and the motor speed.


System overheating prevention control

•  To prevent a malfunction of the system caused by overheating (due to motor over-speed or other factors), the steering mechanism turning limit and the cumulative value of the motor current are detected and the current output to the EPS motor is controlled accordingly.
Turning limit control
―  The turning limit control detects the turning limit of the steering mechanism and, when it is determined that the limit has been reached, current output to the EPS motor is reduced by approximately one-half.
am6zzn00000255
―  When it is determined that it is no longer at the turning limit, the motor current is returned to normal.
Motor output restriction control
―  The motor output limit control detects the cumulative value of the current output to the motor, and if the steering mechanism is turned from lock to lock continuously (or similar repetitious operation), current output to the EPS motor is lowered.
―  The motor current will gradually return to normal after the steering torque is detected at 0 N·m or the ignition switch is turned off. A maximum of 58 min is required to return to normal conditions.
am6zzn00000256