Description & Operation
The Variable Assist Power Steering (VAPS) control system automatically adjusts power steering fluid pressure to provide light steering effort during low speed driving and firm steering during high speed driving.
The VAPS system consists of a control module, steering angle sensor, vehicle speed sensor, solenoid valve, power steering pump, rack and pinion and interconnecting hoses. The system continuously monitors steering wheel angle and vehicle speed to adjust steering system pressure. See Fig 1 .
The VAPS system controls power steering fluid pressure through solenoid valve, mounted on rack and pinion. Solenoid valve opens to provide full power assist at maneuvers less than 6.2 MPH or when steering wheel is moved more than 45 degrees in either direction.
The control module has a 3-position slide switch. See Figure . Switch may be placed in "H" for steering effort that is 10 percent harder than normal, "N" for normal or "L" for steering effort 10 percent lighter than normal.
Probe uses a one-piece power steering gear unit. Gear and valve housing are combined into an aluminum die casting. Quick connect fittings are used for pressure and return lines. Fittings are designed to swivel and should not be overtightened.
A hydraulic-mechanical unit with an integral piston and rack provides power-assisted steering control. Internal valving directs pump flow and controls pressure. Unit contains a rotary fluid control valve and a boost cylinder integral with gear rack.