Power steering reduces the effort required to steer a car by using an external power source to assist in turning the wheels. The system was developed in the 1920s by Francis W. Davis and George Jessup in Waltham, Massachusetts.
Davis was the chief engineer of the truck division of the Pierce Arrow Motor Car Company, and saw first hand how hard it was to steer heavy vehicles. He quit his Job and got work developing the hydraulic steering system that led to power steering. Chrysler introduced the first commercially available power steering system on its 1951 Imperial, under the name "Hydraguide."
Most power-steering systems work by using a belt- driven pump to provide hydraulic pressure to the system. This pressure is generated by a rotary-vane pump driven by the vehicle's engine. As the speed of the engine increases, the pressure in the hydraulic fluid also increases, so a relief valve is needed to allow excess pressure to be bled away.
When the power steering is not being used, for example when driving in a straight line, twin hydraulic lines provide equal pressure to both sides of the steering wheel gear. When the wheel is turned, the hydraulic lines provide unequal pressures and hence assist in turning the wheels in the intended direction.
Electric power steering systems are now starting to replace hydraulic ones. In this system, sensors detect the motion and torque of the steering column and a computer applies assisted power via electric motors. This allows varying amounts of assistance to be applied depending on driving conditions—more at low speed and less at high speed. Electric systems do not require engine power to operate, so are an estimated 3 percent more fuel efficient than the original hydraulic system.
