Power Steering System Description and Operation without HP5

The Electric Power Steering (EPS) system reduces the amount of effort needed to steer the vehicle. The system uses the power steering control module (PSCM), torque sensor, power steering motor rotational sensor, power steering motor, discrete battery voltage supply circuit, and the GMLAN serial data circuit to perform the system functions. The PSCM and power steering motor are each serviced separately from the steering column assembly. However, the motor rotational sensor is serviced as part of the power steering motor, and the torque sensor is serviced as part of the steering column assembly. The PSCM also monitors vehicle speed from the engine control module (ECM) via the GMLAN serial data circuit. 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.

Torque Sensor

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. As the steering wheel is turned and torsional twist is applied to the steering column shaft, the torque sensor's input and output shaft sinusoidal voltage signals are processed by the PSCM to detect and calculate the steering torque. Additionally, the difference between the angle of the steering column output and input shafts detected by the torque sensor and the sinusoidal voltage signals of the motor rotational sensor are both processed by the PSCM to detect and calculate the steering wheel angle.

EPS Motor

The PSCM responds to the change in the sinusoidal voltage signals of the torque and motor rotational sensors by commanding current to the power steering motor. The motor is attached to the base of the steering column housing and assists steering through a worm and reduction gear attached to the steering column shaft. A DC/DC converter is applied to the battery voltage input within the PSCM to boost the pulse width modulated (PWM) motor drive circuit. The motor is a brushless, 3-phase motor with a rated maximum phase current of 35 amps-rms.

Power Steering Control Module (PSCM)

The PSCM uses a combination of commanded motor voltage and current levels to calculate an estimated power steering system temperature. Neither the PSCM nor the power steering motor are designed to handle around 60 amps continuously and will enter into overload protection mode if the system is exposed to exclusive static steering conditions. If the steering wheel is turned to its maximum rotation point and held at this position for an extended period of time, the PSCM will reduce the amount of current commanded to the power steering motor, which reduces the amount of steering assist as well as system temperature. The PSCM has the ability to detect malfunctions within the power steering system. Any malfunction detected will cause the SERVICE POWER STEERING message to be displayed on the driver information center (DIC).

Power Steering System Description and Operation with HP5

The EPS system consists of the following components:

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).