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Rack and Pinion Steering System

The mostly used steering system is rack and pinion and mostly 80 percent of commercial vehicles are using this type. And this is the simplest one, fewer parts and easy to design. A rack and pinion is a type of linear actuator that comprises of a pair of gears that convert rotational motion into linear motion. A circular gear called “the pinion” engages teeth on a linear “gear” bar called “the rack”; rotational motion applied to the pinion causes the rack to move relative to the pinion, thereby translating the rotational motion of the pinion into linear motion.

Parts of Rack and pinion steering mechanism

Rack and pinion steering mechanism consists of-
1. Rack
2. Tubular casing
3. Pinion
4. Track rod
5. Ball and socket joint
6. Adjusting screw.

Rack

• Is a toothed bar contained in a metal housing
• The rack is similar to the parallelogram center link in that its sideways movement in the housing is what pulls or pushes the tie-rods to change wheel directions.

Pinion

• It is a toothed or worm gear mounted at the base of the steering column assembly where it is moved by the steering wheel.
• The pinion gear meshes with the teeth in the rack so that the rack is propelled sideways in response to the turning of the pinion.

Construction of the Rack and Pinion Steering System :

In this type of steering gearbox, a pinion is mounted at the end of the steering shaft. The pinion engages with a rack that is provided with ball joint at its each end in order to allow for the rise and fall of the wheel. The rotary motion of the steering wheel is transmitted to the pinion. The circular motion of pinion is converted into the linear rack movement, which further transmitted to tie rods to the stub axle
through the ball joint.
This type of steering gearbox provides sufficiently low gear reduction for car and it is quite suitable even for heavier motor vehicles if assisted with power. It occupies very less space and less number of linkages.

Rack and pinion steering System Diagram :

rack and pinion steering gear mechanism diagram

Working principle of rack and pinion steering gear:

The rack-and-pinion steering box has a pinion, connected to the steering column.
This pinion runs in mesh with a rack that is connected to the steering tie rods. Both the pinion and the rack teeth are helical gears. Helical gearing gives smoother and quieter operation for the driver.
Turning the steering wheel rotates the pinion, and moves the rack from side to side. Ball joints at the end of the rack locate the tie-rods and allow movement in the steering and suspension.
Mechanical advantage is gained by the reduction ratio. The value of this ratio depends on the size of the pinion.
A small pinion gives light steering, but it requires many turns of the steering wheel to travel from the lock, to lock.
A large pinion means the number of turns of the steering column is reduced, but the steering is heavier to turn.

Steering Ratio :

Steering ratio is the main criteria while designing the steering system. It is nothing but the ratio of the number of teeth in the rack rod to the number of teeth in pinion gear.
Steering ratio = no of teeth in the rack rod/no of teeth in the pinion gear
In the normal steering system for example ambassador old model, the driver has to turn the steering wheels 4 or 5 full turns to turn the vehicle from full left to full right, so here the driver has to give more effect to turn the steering wheel but the steering wheel is easy to turn only number of turns are more. it is due to a low number of teeth in rack rod and smaller radius pinion gear. when we use the pinion gear with a higher or greater radius and more no of rack teeth, the driver has no need to turn more rotation of steering wheel, but it is hard to turn at this case.

Applications of rack and pinion steering System

Maruti 800,
Hindustan Ambassador mark ll
Small trucks,
SUV’s
Alto, Wagon R, SweftDezire, i10, etc

Advantages of rack and pinion steering System

Advantages of rack and pinion type steering gear:

1) Rack & pinion steering gearbox is simple in construction
2) Economical & easy to manufacture.
3) It is easy to operate with accuracy.
4) Contact between steering rack & pinion is free from play
5) Internal damping is maintained.
6) Minimal steering elasticity, compact so mostly used in front-engine Front-wheel drive.
7) The idler arm & intermediate rod is not needed
8) Easy to limit steering rack travel and so steering angle