Power Steering System Description and Operation (Electronic
Power Steering)
The power steering system consists of the following
components:
• |
The power steering control
module |
• |
The power steering
motor |
• |
The power steering motor
rotational sensor |
• |
The steering gear (rack and
dual pinion) |
The rack and dual pinion electric power steering system reduces
the amount of effort needed to steer the vehicle utilizing the
power steering control module to control the power steering motor
to maneuver the steering gear. The power steering control module
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 power steering control module
monitors vehicle speed and engine speed from the engine control
module 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 power steering control module 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 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 power steering control module 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
power steering control module to detect and calculate the steering
wheel angle.
The power steering control module 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 power steering control module controls the
pulse width modulated motor drive circuit to drive the 3-phase
motor. The power steering control module and 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 power steering control module 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 power steering control module will reduce the
amount of current commanded to the power steering motor, which
reduces the amount of steering assist. The power steering control
module 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.
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