Rack and Pinion Steering

A DRIVER steering a car on a twisting road has two distinct tasks: to match the road curvature, and to keep a proper distance from the lane edges. Both are achieved by turning the steering wheel, but it is not clear which part or parts of the road ahead supply the visual information needed, or how it is used. Current models of the behaviour of real drivers1,2 or 'co-driver' simulators3–5 vary greatly in their implementation of these tasks, but all agree that successful steering requires the driver to monitor the angular deviation of the road from the vehicle's present heading at some 'preview' distance ahead, typically about 1 s into the future. Eye movement recordings generally support this view6–9. Here we have used a simple road simulator, in which only certain parts of the road are displayed, to show that at moderate to high speeds accurate driving requires that both a distant and a near region of the road are visible. The former is used to estimate road curvature and the latter to provide position-in-lane feedback. At lower speeds only the near region is necessary. These results support a two-stage model1 of driver behaviour.

Why do some cars respond so well to the driver? Great handling makes you feel safe and in control – and makes panic swerves and steering corrections as effective as possible. The lightest touch of the wheel should direct the steering system effortlessly and precisely. As well as a well-designed suspension parts, it takes a good quality steering system and steering parts to achieve excellent handling. If you’d like to know the anatomy of a steering system and how it supports handling, road holding and driveability, here is an easy overview.

The function of a steering parts

When you rotate the steering wheel, the car responds. But how does this steering system in cars give you a smooth route forward? A group of parts called the steering system transmits the movement of the steering wheel down the steering shaft to move the wheels left and right – although car wheels don’t turn at the same angle. 

The popular rack and pinion steering system 

In most cars, small trucks and SUVs on the road today, there is a rack and pinion steering system. This converts the rotational motion of the steering wheel into the linear motion that turns the wheels and guides your path. The system involves a circular gear (the steering pinion) which locks teeth on a bar (the rack). It also transforms big rotations of the steering wheel into small, accurate turns of the wheels, giving a solid and direct feel to the steering.

How does power steering affect the rack and pinion?

It’s likely that if you drive today, you’re used to power steering. Contemporary cars, and especially trucks and utility vehicles have a power steering system function – also called power-assisted steering. This gives that extra energy (either hydraulic or electric) to help turn the wheels and means parking and manoeuvering requires less effort than with simple manual force. The rack and pinion steering system is slightly different with power steering, with an added engine-driven pump or electric motor to aid the steering assembly.

So is ease the only benefit of power steering? The system allows you to have higher gear steering and means you have to turn the steering wheel less to turn the wheels further (less steering wheel turns lock-to-lock). It therefore sharpens up response times and makes the steering even more precise. With such busy roads and traffic jams, this means drivers can more safely manoeuvre in close proximity to other vehicles. Keeping tight control at all speeds, in any conditions and in critical situations, will help to avoid accidents. 

What are the components of the steering system in cars?

Whatever a car’s make and model, quality auto steering parts support a flawless drive. Premium rack and pinion parts manufactured by MOOG include axial rods, tie rod ends, drag links, centre arms, steering rack gaiter kits, tie rod assemblies and wheel end bearings.

These steering parts are robust and hard wearing enough to provide both strength and durability. Choosing parts which meet OE manufacturer specifications means the whole assembly will be responsive and long-lasting.

The return of four-wheel steering 

Beyond the swivel of the front wheels, some cars have a steering system which affects all four. This has traditionally been exclusive to sporty or luxury models, but there’s a growing trend towards the feature in more affordable cars.

A four-wheel steering control unit sits behind the rear axle of the car and affects the rear wheels as needed. Car wheels turn in opposite directions at low speeds, but at high speeds, turning all four wheels in concert helps to maintain stability and prevent fishtailing.

Stating that automotive literature presents surprisingly little helpful information concerning the faults of the steering-systems used on automotive vehicles and that, in spite of the fact that so many of the faults are self-evident, they frequently are overlooked in actual practice, the author includes with the presentation of his own investigations summaries of the views expressed by numerous well-qualified automotive engineers and discusses these steering-gear faults in some detail. Beginning with the subject of safety, consideration is given successively to the causes of hard steering, the angular position of knuckle-pivots, knuckle-pivot location, the foregather or toe-in of wheels, castering or trailing effect, wheel-wabble, drag-link location, irreversibility, steering-gear type comparisons, tie-rods and tie-rod arms. Numerous drawings illustrative of present-day practice are presented and commented upon, reference being made also to other articles, printed previously, that are pertinent.

Rack and pinion steering systems are not suitable for steering the wheels on rigid front axles, as the axles move in a longitudinal direction during wheel travel as a result of the sliding-block guide. The resulting undesirable relative movement between wheels and steering gear cause unintended steering movements. Therefore only steering gears with a rotational movement are used. The intermediate lever 5 sits on the steering knuckle (Fig. 4.5). The intermediate rod 6 links the steering knuckle and the pitman arm 4. When the wheels are turned to the left, the rod is subject to tension and turns both wheels simultaneously, whereas when they are turned to the right, part 6 is subject to compression. A single tie rod connects the wheels via the steering arm.

Two types of vehicle steering are in general use. The venerable rack-and-pinion system is the simplest and most popular for cars. As the steering wheel is turned, a pinion attached to the base of the steering column moves along a linear-toothed rack to which it is meshed. The arrangement converts the rotary movement of the wheel to a horizontal movement along the transverse axis of the vehicle. The rack is attached at each end to tie rods which transmit the movement to the wheels. This method of steering is positive and provides rapid feedback to the driver. A second steering mechanism, the so-called recirculating-ball system, is used on some heavy trucks and SUVs because of its robustness and greater mechanical advantage. The latter attribute makes turning the wheel easier but, with the advent of power steering, this action is now less of an issue and many heavy vehicles are now adopting rack-and-pinion