Steering: Description and Operation

Power Steering System Description and Operation (with HP5)

Electric Power Steering

The EPS system consists of the following components:

* The power steering control module (PSCM)
* The power steering motor
* The power steering motor rotational sensor
* The torque sensor
* The steering gear (rack and dual-pinion)

The rack & dual-pinion electric power steering (EPS) system reduces the amount of effort needed to steer the vehicle utilizing the power steering control module (PSCM) to control the power steering motor to maneuver the steering gear. The PSCM also uses a combination of the torque sensor, motor rotational sensor, battery voltage circuit and GMLAN serial data circuit to perform the system functions. The PSCM monitors vehicle speed and engine speed from the engine control module (ECM) via the GMLAN serial data circuit to determine the amount of steering assist needed to steer the vehicle. At low speeds more assist is provided for easy turning during parking maneuvers. At higher speeds less assist is provided for improved road feel and directional stability.

The PSCM uses a combination of the torque sensor, motor rotational sensor, vehicle speed, and calculated system temperature inputs to determine the amount of assist needed. The power steering control module (PSCM) continuously monitors the digital torque sensor's torque and index current signals. As the steering wheel is turned and torsional twist is applied to the steering shaft, the steering input and output shafts are monitored via the torque signal circuit and then processed by the PSCM to calculate the steering torque. The voltage signals of the motor position sensor and the digital torque sensor's index current signal are both processed by the PSCM to detect and calculate the steering wheel angle.

The PSCM responds to the change in the digital torque sensor signals as well as the motor rotational sensor's voltage signals by commanding current to the power steering motor. The PSCM controls the pulse width modulated (PWM) motor drive circuit to drive the 3-phase motor. The PSCM & motor assembly is attached to the base of the steering gear housing and assists the steering gear pinion to maneuver the rack from left to right according to turning the steering wheel.

The PSCM has the ability to calculate an internal system temperature to protect the power steering system from damage caused by high temperature. To reduce a high system temperature, the PSCM will reduce the amount of current commanded to the power steering motor, which reduces the amount of steering assist. The PSCM has the ability to detect malfunctions within the electric power steering system. Any malfunction detected that disables steering assist will cause the SERVICE POWER STEERING message to be displayed on the driver information center (DIC).