Basics of Variable-ratio, Recirculating-ball and Power Steering

By | May 19, 2014

Variable-ratio steering
Some cars have a variable-ratio steering. They use a rack, whose number of teeth per inch varies over the rack, so that it has a low steering ratio at the center and higher ratio towards the ends. So, the wheel responds quickly at the beginning at the turn, and the steering becomes easier at the limits of the turn.

Recirculating-ball steering
Recirculating-ball steering is used in a lot of off-road vehicles, trucks and SUV’s. Its functions are a little different from a rack and pinion system. The central component in the recirculating ball steering is the worm gear. The gear section has two parts. The steering shaft connects directly to a rod, which has threads like a screw. The threaded rod runs into a block, whose insides are also threaded. The block also has its outside threaded, which connects to another gear and this leads to a device called the pitman arm.

When the steering wheel is turned, the rod is turned along with it. Here, it does not rotate itself into the threaded block that surrounds it. In case of other gear rods, this will be the case. But, since the threaded rod is fixed, it moves the threaded block up and down. This activates the pitman arm and thus the wheels are turned.

Ball bearings
The rod does not directly turn the block. Instead, it is done through a number of ball bearings. The ball bearings are circulated gap between the threads in the rod and the threads on the insides of the block, and this ensures less friction and better hold of the block and the rod. They also reduce a phenomenon called slop. Slop is something that is felt when one changes the direction of turn of the steering gear. The threads of the rod, for a moment will lose contact with the threads of the block, making the turn feel empty. The ball bearings make threads of both the rod and the block engage tightly with each other.

Power steering
A power steering mechanism is a little complicated than the usual rack and pinion or recirculating-ball steering systems. A power steering is a mechanism which helps drivers augmenting their effort of turning the steering wheel. Either hydraulic or electric actuators are added to increase the steering power and so, the driver only has to apply a minimum of effort for a good responsive turn. This helps a lot in turning the wheels while the vehicle has stopped or is moving slowly.

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