EPAS System

The PSCM controls the functions of the EPAS system and communicates with other modules over the HS-CAN2.

To activate, the EPAS system requires battery voltage at the PSCM hot at all times input and ignition voltage at the PSCM ignition run input. In addition, the system must be able to communicate with other modules over the HS-CAN2. The PSCM must also receive the ignition status message from the BCM in order to be set into operation mode.

The main input for calculating the level of EPAS assist is the steering torque sensor signal. Vehicle speed is also taken into consideration in order to achieve the vehicle speed dependent steering assist characteristic.

The EPAS gear uses a reversible motor to apply the steering assist. The motor is connected to the rack of the steering gear by a toothed belt and a pulley and bearing assembly. The motor is used by the PSCM to move the rack inside the steering gear housing.

The PSCM continually monitors and adjusts steering efforts based on the steering torque sensor signal, motor position and HS-CAN2 inputs to enhance the feel of the steering system. As vehicle speed increases, the amount of assist decreases to improve and enhance road feel at the steering wheel. As vehicle speed decreases, the amount of assist increases to ease vehicle maneuvering. Compensation is made to reduce the effect of pull or drift that can be experienced when driving on roads with a high degree of camber. Also the impact of wheel imbalance on steering feel is compensated for up to a predetermined threshold.

The steering torque sensor senses the torque at the steering wheel. It is integrated into the PSCM and works by measuring the relative rotation between an input and output shaft which are connected by a torsion bar. The steering torque sensor sends out 2 PWM signals which allows a channel to channel cross-check and an accurate correction of the neutral point.

The PSCM is self-monitoring and is capable of setting and storing Diagnostic Trouble Codes (DTCs). Depending on the DTC set, the PSCM may enter a failure mode. In addition, the PSCM may send a request to the IPC to display a message in the message center, alerting the driver of a potential EPAS concern. The warning message is sent over the HS-CAN2 to the GWM where it is converted to a HS-CAN3 message and sent to the IPC over the HS-CAN3.