EPAS System

The PSCM  controls the functions of the EPAS  system and communicates with other modules over the High Speed Controller Area Network (HS-CAN).

To activate, the EPAS  system needs to be connected to battery voltage at the hot at all times input and at the ignition/run input to the PSCM  . In addition, the system must communicate with other modules over the High Speed Controller Area Network (HS-CAN). The PSCM  must receive the power mode signal from the BCM  in order to be set into operation mode.

The main input for calculating the level of EPAS  assist is the 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 pulley/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 torque sensor, motor position and High Speed Controller Area Network (HS-CAN) 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 compensation for the impact of wheel imbalance on steering feel is made up to a predetermined threshold.

The steering torque sensor senses the torque at the steering wheel. It is hard wired to the PSCM  and works by measuring the relative rotation between an input and output shaft which are connected by a torsion bar. The 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 High Speed Controller Area Network (HS-CAN) to the BCM  where it is converted to a Medium Speed Controller Area Network (MS-CAN) message and forwarded on to the IPC  over the Medium Speed Controller Area Network (MS-CAN).