Mazda CX-5 Service & Repair Manual: Electric Power Steering (Eps) Control Module

Purpose/ Function

• The EPS control module (CM) calculates the optimum assist current based on the steering torque signal from the torque sensor installed to the steering column and the vehicle speed signal sent via CAN transmission from the PCM.

• The EPS CM controls the following functions:

Block Diagram

NOTE:

• Before the steering angle neutral position auto learning is completed, the EPS CM receives a steering angle signal from the steering angle sensor via the start stop unit and outputs the signal to the other modules through the CAN communication.

• After the steering angle neutral position auto learning is completed, the EPS CM outputs an EPS status signal, which is calculated by EPS CM itself, through the CAN communication.

Construction

• The EPS CM is installed to the steering column and integrated with the EPS motor.

Operation

EPS Motor Current Control

Normal control

• The optimum assist current is calculated based on the steering force signal from the torque sensor and the vehicle and engine speeds signal from the PCM, and then the control current is output to the EPS motor.

System overheating protection control

• The system overheating protection control lowers the current output to the EPS motor if the steering mechanism is turned from lock to lock continuously or the steering rack turning limit is reached repeatedly.

  NOTE:

  • During system overheating protection control, the assist force will feel weaker due to a decrease in the control current. This is normal for the EPS CM to prevent the EPS motor from burning or seizure, and it does not indicate a malfunction.

  • While the assist force weakens during this period of time, steering operation can be performed.

• The system overheating protection control has middle and complete steps, and it can verify current conditions and the history using the PID/data monitor function and snap shot data.

• System overheating protection control (middle): Motor output is 40 % or less (reference)

• System overheating protection control (complete): Motor output is 20 % or less (reference)

• The current output returns to normal if the temperature in the system decreases to the normal operation temperature.

  

  
  

Backup control

• Even if an open circuit malfunction occurs in 1 out of the 3 phases in the EPS motor line, the backup control performs control to maintain steering assist.

• If the EPS CM detects a phase 1 open circuit malfunction in the EPS motor, the EPS CM controls output current to the EPS motor using a calculation method different than during normal EPS CM control. As a result, even with a phase 1 open circuit malfunction, the steering assist can be maintained.

  NOTE:

  • If a phase 1 open circuit malfunction is detected in the EPS motor, the EPS CM stores DTC U2011:72 and illuminates the electric power steering malfunction indicator light/master warning light.

  • If the steering wheel is operated during backup control, the steering wheel operation may feel heavier (resistance).

Fail-safe