Variable Effort Steering Description

The VES steering system has software contained in the Electronic Brake Control Module (EBCM). It processes vehicle speed information from the ABS wheel speed sensors and uses the steering wheel speed sensor to provide a control signal to the power steering pump actuator on the power steering pump.

Component Description
The VES system is made up of the following special power steering components:
- Electronic Brake Control Module (EBCM)
- Power Steering Pump Actuator
- Steering Wheel Speed Sensor
- Power Rack and Pinion
- Power Steering Pump

Power Steering Pump Actuator





The power steering pump actuator assembly at the power steering pump discharge fitting contains an Electronic Variable Orifice (EVO) solenoid-operated pintle valve. Fluid leaving the pump passes through an orifice in the actuator tip. When the solenoid is grounded by the EBCM, it moves the pintle into the orifice, reducing power steering fluid flow. As vehicle speed increases, the pintle restricts the orifice proportional to the speed of the vehicle. Other power steering system components, while specially modified for use with the VES system, are similar to non-VES power steering components.

Steering Wheel Speed Sensor





The steering wheel speed sensor is an input to the EBCM. The sensor monitors the steering shaft position and the rotational speed.

Power Rack and Pinion
Except for differences in valve machining, the design of the VES power rack and pinion assembly is the same as a non-VES system. As with non-VES steering, the steering wheel movement is transferred to the pinion; the pinion moves the rack left or right through meshing pinion and rack teeth; the force is then transmitted through the tie rod ends and steering knuckles to steer the wheels.

The power rack and pinion steering system has a rotary control valve which directs hydraulic fluid (from the power steering pump) to one side or the other side of the rack piston. The piston is attached to the rack, and uses hydraulic pressure in order to assist the rack movement left or right. The rotary control valve regulates the degree of assist by responding to the driver's torque input.

If hydraulic assist is not available, manual control is maintained. However, under this condition, more driver steering effort is required.

Power Steering Pump
The standard vane-type pump, which provides hydraulic pressure for the system, incorporates a special discharge fitting to hold the EVO actuator.