General Description
The speed sensitive power steering (SSPS) system consists of the power steering pump, the power steering fluid reservoir and the power steering rack and pinion gear. The power steering pump is a multi-vaned hydraulic pump driven by the accessory drive belt on the engine, and provides hydraulic pressure to the rack and pinion gear. A pressure-relief valve inside the flow control valve limits the pump pressure. The pump draws on the power steering fluid reservoir, a remote reservoir used in order to make more space available in the engine compartment. The reservoir is connected to the rack and pinion gear, which directs hydraulic fluid from the pump to either side of the rack piston. The rack is moved left or right by hydraulic pressure and this force is transmitted to the steering knuckles, which turn the wheels.
| 1. | Steering column |
|---|---|
| 2. | SSPS actuator |
| 3. | Power steering fluid reservoir |
| 4. | Fluid hose |
| 5. | Power steering pump |
| 6. | Rack and pinion assembly |
| 7. | SSPS control module |
Speed Sensitive Power Steering System
The SSPS system varies the effort required by the driver to steer as the vehicle speed changes. At low speeds, the system provides maximum assistance to the steering gear, for full steering power when turning and parking. At higher speeds, steering power is reduced as assistance to the steering gear is decreased, to provide the driver with firmer steering and directional stability.
The SSPS control module uses vehicle speed information from the ABS control module to determine the amount of power steering assistance required. The SSPS control module constantly compares the amount of current flowing through the SSPS actuator to the desired current it has calculated, changing the current by varying the output duty cycle. The SSPS control module sends a signal to the actuator to vary the rate of reaction force to be output to the steering torsion bar by the actuator's magnetic coil. The SSPS control module varies the current supplied to the coil from -3A to 3A.
Steering wheel movement is transferred to the pinion via the intermediate shaft. The pinion moves the rack left or right through meshing of the pinion and the rack teeth. The force is then transmitted through the tie rods and steering knuckles to the wheels.
The SSPS power rack and pinion steering system has a rotary control valve which directs the hydraulic fluid, coming from the pump, to either side of the rack piston. The rack piston is attached to the rack and uses hydraulic pressure to move the rack left or right. The rotary control valve regulates the degree of steering assistance by responding to the driver's torque input.
The SSPS control module has the ability to detect faults within the module itself, the SSPS actuator, or the circuitry to these components. Any fault detected will cause power steering assistance to remain at maximum at all speeds. If, however, hydraulic assistance is not available, manual rack and pinion control is used, requiring more steering effort. Movement of the steering wheel is transferred directly to the pinion. The rotary movement of the pinion is then transferred through the pinion threads, which mesh with teeth on the rack, causing the rack to move in a linear direction.
Power Steering Warning Indicator
When the ignition is turned ON, The SSPS control module will perform a self–test for between 1.5 and 3 seconds. The power steering warning indicator comes on for 3 seconds and then extinguishes.
In the event of a malfunction, the power steering warning indicator illuminates and the SSPS control module shuts off the current to the magnetic coil. More effort will be required to steer the vehicle.
Trouble codes are displayed and cleared using TECH 2.
