Car Parts and Accessories

What the Mechanism has to do

All cars are steered by turning the front wheels in the required direction and allowing the rear wheels to follow.

There would be several disadvantages in trying to steer a car by its rear wheels, the main one being that the car would be directionally unstable.

On a bicycle, the steering is controlled directly by the handle-bars. But in a car, the driver would not be strong enough to control the front wheels if they were connected directly to the steering wheel. So the steering must include a gearbox, and sometimes power assistance, to multiply the driver’s effort.

Major requirements in any steering mechanism are that it should be precise and easy to handle, and that the front wheels should have a tendency to return to the straight-ahead position after a turn.

The steering must not ‘kick back’ from road shocks, although there must be some degree of reaction, or `feed-back’, from the road to the driver.

The steering column, which encloses and supports the steering shaft, often carries controls, such as the horn, light and wiper switches.

A combined headlamp-flasher and dip- switch unit is frequently fitted just below the steering wheel, with a direction indicator switch opposite it; or the two functions may be controlled by a single lever.

Some cars have an adjustable steering column. The top part—with the steering wheel—can be moved up and down in telescopic fashion and, in some cases, can be tilted at an angle to suit the driver’s height and driving position.

Considerable research has been carried out in recent years to safeguard the driver against injuries inflicted by the steering wheel (or column) when the car is in a front-end collision.

The steering column can be designed to collapse on impact. For example, in the AC Delco design, the tubular column is made of an ‘expanded-metal’ grid so that, although strong in twist, it collapses and absorbs energy if compressed lengthwise. A telescopic joint is provided in the steering shaft.

Another design divides the steering shaft into sections which are connected by joints, but not placed in line.

The steering wheel is ‘dished’ and provided with a large boss and wide spokes in order to spread the load of impact over the driver’s chest. The wheel or boss can also be designed to collapse when under a pre-determined load.

Different Steering Systems

A CAR is steered through a steering gearbox and a linkage—a system of rods and levers —designed to give the driver directional control with minimal effort.

The steering wheel itself is attached to a shaft which is enclosed in a supporting tube known as the steering column.

The shaft is connected to a steering gearbox, which converts the turning motion of the steering wheel into a to-and-fro movement of the steering linkage and provides the driver with the extra leverage he needs to steer the road wheels without excessive effort.

Various types of steering boxes used over the years include those known as the cam and peg, worm and nut, and recirculating ball; but most cars today use a rack-and-pinion system.

With this design, a toothed rack is moved by a small pinion at the lower end of the steering shaft. When the steering wheel is turned, the rack moves from side to side and causes the stub axles—the two short shafts on which the front wheels are mounted—to swivel.

On earlier designs, the steering box carried a short lever known as a drop-arm, which operated the rest of the linkage.

On old cars fitted with a beam front axle, and on some types of independent front suspension, the stub axles swivel on a spindle called a king-pin. On cars with modern types of independent front suspension, the stub axles swivel on two widely separated hemispherical bearings.

Steering Gearbox reduces Effort needed by Driver

THE AMOUNT of reduction of effort—or leverage—to be provided by the steering box depends on the weight, type and use of the car.

A light sports car requires little reduction, as the driver needs quick control to correct skids or `drifts’; but a heavy car, with ‘fat’ tyres, requires a big reduction and/or some form of power assistance to make low-speed turns.

The steering ‘box and the linkage also pass back to the steering wheel the reaction of the wheels to the road surface.

This reaction gives immediate warning to the driver of changing conditions, but designers have different ideas as to how much reaction there should be.

Some mechanisms are efficient in transmitting the driver’s effort to the road wheels but are less effective in feeding back information about irregularities in the road surface to the driver.

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