Steering: Description and Operation

The Variable Assist Power Steering System varies the amount of power assist available to the driver. when vehicle speed and steering wheel rotation rate are low, the system provides a high level of power assist. This allows the driver to turn the steering wheel easily during parking maneuvers. As vehicle speed increases, the amount of power assist decreases. This provides better road "feel" for the driver. If the steering wheel is jerked suddenly, as in an acident avoidance situation, the steering wheel rotation rate increases and the system immediately provides a high level of power assist.

Variable Assist Power Steering is available on vehicles as a separate option or together with the Air suspension System. On vehicles with Air Suspension, the Air Suspension/EVO Steering Module controls both the Air Suspension System and the Variable Assist Power Steering System.

MODULE INPUTS

Steering Wheel Rotation Sensor

The Steering Wheel Rotation Sensor is an optical sensor that provides steering wheel rotation rate (in rpm) to the Air Suspension/EVO Steering Module or EVO Steering Module. With a rotation rate below 15 rpm, the Module uses only the vehicle speed input to determine the amount of power assist. If rotation rate exceeds 15 rpm, the rotation rate input causes the Module to boost power assist. At rotation rates of 100 rpm and above, full power assist is provided, regardless of vehicle speed.

Vehicle Speed Sensor

The Vehicle Speed Sensor provides the Module with vehicle speed information. The Module uses this input to control the EVO Actuator, which controls power assist. With vehicle speed between 0 and 5 mph, full assist is provided. As speed increases from 6 to 80 mph, power assist decreases gradually. Above 80 mph, little power assist is provided.

MODULE OUTPUTS

EVO Actuator

The EVO Actuator is mounted on the power steering pump controls power assist by regulating the flow of power steering fluid in the pump. When maximum assist is required, the Actuator allows full fluid flow. When the Module determines that the power assist level should decrease, it powers the actuator to reduce fluid flow.

The Variable Assist Power Steering System has built-in "fail safe" feature. An electrical malfunction will cause the Actuator to provide full power assist at all times.