Description & Operation

Variable Effort Steering (VES) system, or Electronic Variable Orifice (EVO) steering system, varies the effort required by the driver to turn the steering wheel. Both VES and EVO provide a firmer steering (road) feel and improved directional stability as vehicle speed increases.

System decreases amount of pump pressure applied to steering gear as vehicle speed increases. Reduced pump pressure increases steering effort, improving steering feel. As a safety feature, the system detects when a sudden turn is made (such as in an evasive maneuver), and then increases pump pressure to the steering gear, decreasing steering effort.

System consists of a VES control module (or power steering control module), VES actuator (or EVO actuator), steering wheel rotation sensor and Vehicle Speed Sensor (VSS) module. VES control module receives inputs from steering wheel rotation sensor and VSS module. Based on inputs from these components, VES control module cycles VES actuator on and off.

When VES actuator is off (de-energized), full pump pressure is allowed to flow through pressure line outlet, increasing pump pressure to steering gear. When VES actuator is on (energized), fluid bypasses pressure line outlet and is routed back into pump, decreasing pump pressure to steering gear.

If VES control module detects a fault in steering wheel rotation sensor, VES actuator or related circuits, it will turn VES solenoid off to provide full assist at all speeds.