Variable Assist Steering: EVO
Variable assist steering systems are designed to provide less assist while traveling at highway speeds, giving the driver a tighter feel of the road, while still providing full assist during parking maneuvers and traveling slowly. The system is greatly reliant on vehicle speed. It controls flow, reducing pressure at highway speeds and increasing pressure while parking.
If excessive assist is provided at highway speeds, the variable orifice is not functioning and providing too much pressure. The orifice can become clogged resulting in less assist during parking maneuvers. This system is not to be confused with the standard flow control valve that regulates pressure in a standard power steering system to prevent over pressure and damage to the system. A flow control valve provides a regulated pressure, but does not provide variable pressure like an EVO does.