Power Steering Pump: Description and Operation
POWER STEERING PUMPThe power steering pump is a CB-series, vane-type positive displacement pump with an integral fluid reservoir. (Pumps used with supercharged engines also have a remote reservoir for checking and adding fluid.) A pressure relief valve limits maximum system pressure, and is located inside the flow control valve in the pump housing; the relief valve is not serviced separately. The power steering pump is driven by the engine via an automatically tensioned drive belt.
TWO FLOW ELECTRONIC SYSTEM
The two flow electronic (TFE) system is a speed-dependent power steering system. The system provides either full power assist, or a preset reduced level of assist. The CB-series pump utilizes a solenoid equipped fitting in place of the standard union fitting. This solenoid is electrically controlled by on-off signals from the multi-function chime module, which serves as the "brain" for the TFE system. The module receives speed-related input signals from the powertrain control module (PCM), decodes them, and signals the TFE solenoid to energize or de-energize.
At vehicle speeds below about 27 to 32 km/h (17 to 20 mph), the solenoid is energized, enabling maximum assist from increased fluid flow through the system. Full assist via full fluid flow is maintained for about 3 minutes when the vehicle is not moving and the engine is idling. However, after this time has passed, the solenoid is de-energized and the TFE system shuts down until the vehicle begins to move again. This de-energization reduces unnecessary heat build up in the solenoid coil.
As the vehicle is accelerating toward 32 km/h (20 mph), the solenoid is energized. Beyond this speed, the solenoid is de-energized again, the fluid flow returns to its "normal" flow, and the steering effort needed is similar to a standard power steering system.