Get familiar with steering mechanisms in automobiles

The steering gear mechanism in an automobile is used for changing the direction of two or more of the wheel axles with reference to the chassis, so as to move the automobile in any desired path. 

Usually, the two back wheels have a common axle, which is fixed in direction with reference to the chassis and the steering is done by means of the front wheels.

There are two types of steering mechanisms:

1.Ackerman steering gear mechanism
2.Davis steering gear mechanism

The Ackerman steering gear mechanism is much simpler than Davis steering gear and hence quite popular. I will be explaining the Ackerman steering mechanism below however the main difference between the Ackerman and Davis steering gear mechanism are given here:-

The whole mechanism of the Ackerman steering gear is mounted at the back of the front wheels, where as in Davis steering gear, it is in the front of the wheel.

The Ackerman steering gear consists of turning pair, whereas Davis steering gear consists of sliding member

Ackerman Steering Mechanism

In the Ackerman steering gear, the mechanism ABCD is a four bar crank chain, as shown in figure below. The shorter links BC and AD are of equal length and are connected by hinge joint with front wheel axles. The longer links AB and CD are of unequal length. 

The following are the only three positions for correct steering.

1. When the vehicle moves along a straight path, the longer links AB and CD are parallel and the shorter links BC and AD are equally inclined to the longitudinal axis of the vehicle, as shown by firm lines in the figure.

2. When the vehicle is steering to the left, the position of the gear is shown by dotted lines in the figure. In this position, the lines of the front wheel axle intersect on the back wheel axle at I , for correct steering

3. When the vehicle is steering to the right, a similar position may be obtained again.

Sometimes incorrect steering condition with a combination of high speed and bad road conditions can lead to over and under steer. These two are the major drawbacks of incorrect steering.

1. Under steer occurs during a turn of a corner, when you try to turn the vehicle but it continues in a straight line, heading off the road. This occurs because the front tyres have reached their adhesion limit and cannot grip the road adequately enough to turn. The best way to correct under steer is to brake, release break, steer in the opposite desired direction and quickly change back to turning in the correct direction. However, you should not brake into a corner as this will cause further under steer, rather try and brake on the straightest line possible. This will ensure the cars slow down enough to regain enough grip to turn.

2. Over steer occurs when turning a corner and the vehicles back slides out as the rear wheels do not have enough grip to complete the turn. To counter such an event do not accelerate further through the corner, but rather very carefully break gently in the straightest manner possible. Full force braking can become more dangerous than helpful. However, braking gently can correct your steering in situations such as over steer.