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Power steering
Power steering works with both rack and pinion and recirculating ball in relatively the same manner. When the steering wheel is turned, a hydraulic pump forces fluid against the steering gears to assist the driver.
At the heart of power steering systems is the rotary valve. This valve typically sits at the base of the steering column, next to the steering gear. It connects to a rotary-vane pump run by pulleys connected to a motor. This pump forces hydraulic fluid in and out of the rotary valve to the steering gear.
The amount of fluid forced into the system is determined by the torsion bar, located inside the rotary valve. The torsion bar is a thin rod of metal that twists when force is applied to it. The top of the bar connects to the steering wheel, while the bottom connects to the pinion or worm gear. When the driver turns the wheel, force - or torque - is applied to the bar. The more torque the driver uses to turn the wheels, the more the bar twists and the greater the hydraulic pressure applied to the steering gears.
How does this system work? When the steering wheel is not being turned, the hydraulic lines running into the rotary valve provide the same amount of pressure to the steering gear. When the wheel is turned one way or the other, ports open up in the rotary valve to send high-pressure fluid rushing to the appropriate lines, which helps turn the wheels in the appropriate direction.
Some rack-and-pinion systems are fitted with electronically controlled power steering, which is designed to regulate the hydraulic steering boost according to vehicle speed. In these systems, electronic controls and an electric motor replace the hydraulic pump, hoses and fluid. The motor features an armature that the rack passes through. A ball nut with thrust bearing, also part of the motor, transfers the rotary motion of the armature to the linear movement of the rack. This extra push on the rack makes steering easier.
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