Variable Effort Steering Description
The variable effort steering (VES) system varies the driver effort that is required to steer as the vehicle speed changes. At low speeds, the system provides maximum power assist for easy turning and parking maneuvers. At higher speeds, steering effort is increased in order to provide the driver with firmer steering (road feel) and directional stability. The VES system varies the driver effort by reducing the power steering fluid flow from the pump as vehicle speed increases. When the vehicle is stationary, the system provides maximum flow. As the vehicle speed increases, the fluid flow is decreased.
The VES system consists of the following power steering components:
| • | The speed sensitive power steering (SSPS) control module |
| • | The electronic variable orifice (EVO) actuator |
| • | The steering wheel position sensor |
| • | The power rack and pinion |
| • | The power steering pump |
Speed Sensitive Power Steering (SSPS) Control Module
The variable effort steering (VES) steering system software is contained in the speed sensitive power steering (SSPS) control module. The SSPS control module processes vehicle speed information from the vehicle speed sensor. The SSPS control module uses the steering wheel position sensor in order to provide a control signal to the electronic variable orifice (EVO) actuator located on the power steering pump.
Power Steering Pump Fluid Flow Control Valve Actuator
The power steering pump actuator assembly is located at the power steering pump discharge fitting. The power steering pump actuator assembly contains an electronic variable orifice (EVO) solenoid-operated pintle valve. Fluid leaving the pump passes through an orifice in the actuator tip. When the EVO solenoid is grounded by the speed sensitive power steering (SSPS) control module, the solenoid moves the pintle into the orifice. The movement of the pintle into the orifice reduces the power steering fluid flow. As vehicle speed increases, the pintle blocks more of the orifice.
Variable effort steering (VES) system components are similar to non-VES power steering components.
Steering Wheel Position Sensor
The steering wheel position sensor sends a signal to the speed sensitive power steering (SSPS) control module when abrupt or evasive steering maneuvers occur.
Variable Effort Steering Power Rack and Pinion
The design of the variable effort steering (VES) power rack and pinion assembly is the same as for a non-VES system, except for differences in valve machining.
