Recirculating ball

Recirculating ball, also known as recirculating ball and nut or worm and sector, is a steering mechanism commonly found in older cars and some trucks. Most newer cars use rack and pinion steering instead, but some significant manufacturers (including Chrysler and General Motors) still use this technology in some models, e.g. the Jeep Wrangler and the Crossfire.

Mechanism

The recirculating ball steering mechanism contains a worm gear inside a block with a threaded hole in it; this block has gear teeth cut into the outside to engage the sector shaft (also called a sector gear) which moves the pitman arm. The steering wheel connects to a shaft which rotates the worm gear inside of the block. Instead of twisting further into the block, the worm gear is fixed so that when it spins, it moves the block, which transmits the motion through the gear to the pitman arm, causing the wheels to twist.

Ball bearings

The worm gear is similar in design to a ball screw, the threads are filled with ball bearings that recirculate through the gear and rack as it turns. The balls serve to reduce friction and wear in the gear and reduce slop. Slop, when the gears come out of contact with each other, would be felt when changing the direction of the steering wheel; causing the wheel to feel loose. Nice, Karem [http://auto.howstuffworks.com/steering3.htm "How Car Steering Works"] , "HowStuffWorks", Accessed August 13, 2007 ]

Power assistance

Power steering in a recirculating-ball system works similarly to in a rack-and-pinion system. Assistance is provided by supplying higher-pressure fluid to one side of the block.

References