What Does Speed-Sensing Steering Mean?by Craig Woodman
A common complaint about power-assist steering systems in vehicles is that the system provides so much steering assist at higher speeds that the driver cannot feel the road, contributing to an out-of-control feeling. Manual steering systems may require too much effort for drivers with less arm strength when executing parking lot and slow-speed maneuvers. Speed-sensing steering is a way to compromise in these areas and offer better vehicle handling and performance at all speeds.
Speed-sensing steering uses input from various sensors and computer modules to determine how much power assist should be applied to the steering input. The amount of assist required decreases as the vehicle speed increases, and the system responds appropriately. This allows the driver of the vehicle to steer with ease during slow, parking lot speed maneuvers by giving maximum steering assist, while offering a better feel for the road at higher speeds by reducing the amount of power assist provided.
Hydraulic power steering systems use either a hydraulic pump driven by a belt attached to the engine crankshaft or an electric motor to pressurize hydraulic fluid. This pressurized fluid is delivered to the steering gear by hoses, where it helps the driver turn the wheels with less effort. Most hydraulic systems with speed-sensing steering vary the pump output pressure or volume by using electronic controls to rapidly release and re-apply pressure in the system as the vehicle's speed increases. Some systems may also use a variable valve that restricts fluid flow and pressure as the vehicle speed increases.
Electric power-assist steering systems have become more common, starting with GM vehicles around 2006. Electric systems use a specially designed electric motor to provide assistance to the steering gear as it responds to the driver's input from the steering wheel. A control module varies the amount of assistance by restricting the electrical supply to the motor or by applying increased voltage. Electric power-steering systems eliminate the mechanical power-steering pump and the hoses, which may make the system more reliable.
Speed-sensing steering systems are generally reliable, but as with any mechanical system, failures can occur. A computer module failure or wiring problem such as a short circuit or broken wire can make the speed-sensing steering inoperative, as can a failure of a vehicle speed sensor or steering-angle sensor. If a speed-sensing steering system has a failure like this, or the computers in the system are reading inconsistent data as the vehicle operates, the speed-sensing system will usually default to full-power assist at all speeds and warn the driver of the problem by lighting a malfunction indicator light on the dash of the vehicle. Failure of this system will not cause the driver to lose steering control.
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