Principles of Operation

Steering System








Special Tool(s)





Material

Principles of Operation

Variable Assist Power Steering (VAPS)
Navigator vehicles include a VAPS system that controls the level of power assistance available to the driver based on vehicle speed. Below 3.2 Km/h (2 mph), full power steering assist is provided to lessen steering efforts and increase maneuverability. Between 3.2 Km/h (2 mph) and 191 Km/h (119 mph), steering assist will decrease gradually at a calibrated rate to raise steering efforts for increased directional stability and greater road feel. Above 191 Km/h (119 mph), steering assist is constant.

The air suspension module outputs a Pulse-Width-Modulated (PWM) current to the control valve actuator. The control valve actuator controls the hydraulic valve that determines the amount of hydraulic assist provided to the steering gear. The amount of assistance provided varies with the control valve actuator current, which is based on vehicle speed according to a look-up table internal to the module. The module pulse-width modulates the VAPS actuator current to provide the desired amount of assistance. The amount of hydraulic steering assistance provided by the VAPS subsystem is proportional to the average control valve current.

The vehicle speed is provided to the air suspension module through a transmission mounted Vehicle Speed Sensor (VSS).