Steering Systems Topics covered in this presentation: Basic Steering Systems Linkage Steering Rack-and-Pinion Steering Power Steering

The Steering System When the driver turns the steering wheel, the front and sometimes the rear wheels move and the car turns the corner! From the drivers point of view it is that simple, but many more things have to be taken into consideration. For example – The effect of road surface irregularities Tyre behaviour under cornering stress An efficient mechanical system to give easy turning of the steering wheel Driver fell must be maintained No (or very little) difference between empty and fully loaded The effect of accelerating or braking when the wheels are turned The front wheels should have a natural tendency to return to the straight ahead position

The Steering System Imagine a car driving round a roundabout, the outer wheel has to travel a greater distance than the inner, this is why a differential is required in the transmission, it will be also noticed, that for the steered wheels to maintain true running or rolling motion i.e. the wheels must always be turning exactly end over end, much like a coin rolling across the desk, if this was not the case, there would be a scrubbing action ( the tyres would be dragged across the road surface resulting in considerable wear), the inner wheel has to turn through a sharper corner than the outer. This requirement is met by the steering system through the use of special linkage between the steered wheels, so each wheel is turned a slightly different amount, so true rolling motion is maintained. This is known as the ‘Ackerman Principle’ and is named after the person who invented it. The slight change in the angles between the steered wheels is often referred to as toe out on turns

Terminology The Steering Wheel – The Bit the driver holds on to! It also incorporates the Air Bag. Steering Column – The shaft connecting the steering wheel to the steering box or steering rack. Steering Rack – A combination of a small gear and a toothed rack. This changes the rotation of the steering wheel into a back and forth movement of the rack which in turn moves the road wheels. Steering Box – This does a similar job to the rack but needs extra linkages and rods to connect it to the road wheels. Mostly used on old cars, but still is in use on larger vehicles. Track rod/Tie rod – A rod to connect the left and right steered wheels. The steering rack is also the track rod. Track rod end – A ball joint to allow steering and suspension movement. Ball joint/Swivel joint – Part of the suspension, but these are joints which allow the steered wheels to left and right. PAS – Power assisted steering. An engine driven pump or electric motor, provides extra force to help the driver turn the steering. Tracking – toe in or toe out setting for the steered wheels.

Ackerman Principle Steering assembly at rest, the Axle longer bar represents the front suspension axle, the shorter bar is the steering linkage/mechanism. Axle Ackerman Principle Steering Ackermann stated the principle that when a vehicle travels in a curved path, its wheels should describe circles around the same centre. A wheel which follows a markedly different path will slide to some extent, this would cause excessive tyre wear. The steering mechanism is designed to insure that when the vehicle turns left or right, the inner wheel is turned through a larger angle to prevent tyre wear Steering assembly in operation, as the steering linkage is shorter than the axle, the inner wheel is turned through a larger angle.

Turning Radius (Ackerman Principle) When turning, the inner wheels must turn on a tighter radius than the outer, this helps avoid unnecessary tyre wear. The steering system is designed to compensate for the different radiuses. Toe-out is increased on turns. Small adjustments can be made, but normally any error will result in worn or damaged components being replaced.

Front Wheel Tracking Tracking – A steering adjustment which is used to insure that the steered wheels are pointing straight ahead when the vehicle is moving Toe-in - The wheels point inward, toward each other. This setting is critical for tyre wear. A small amount of Toe-in helps compensate for the effect of rear-wheel drive. Toe-out - The wheels point away from each other. A small amount of Toe-out is normal on front-wheel drive vehicles. Zero “toe” effect is required when the vehicle is moving. This helps reduce tyre wear (scuffing or feathering).

Steering Shafts and Columns Nearly all steering systems use a steering column or shaft to link the driver (steering wheel) to the steering rack or gear/box. Flexible coupling isolates steering wheel from road shocks. Steering wheel Steering rack or gear/box Universal joints allow steering shaft angles to change. Collapsible section Flexible coupling Most steering columns are designed with a collapsible section that helps prevent forces generated in a collision being transferred to the driver. Universal joints Master spline location Bottom of steering column normally has a master spline where it mounts onto the steering rack-and-pinion or steering gear/box. Next >

Basic Steering Systems Two main types of steering: Drop arm Idler arm Track rods Centre link Steering knuckles Steering gear/box Linkage or Conventional type (also known as Parallelogram). Rack-and-pinion type. Linkage type uses a worm gear inside the steering gear/box, this operates the drop arm, then couples to a centre link, idler arm, track rods and the steering knuckles. Track rods Rack-and-pinion Rack-and-pinion type uses track rods to couple the rack to the steering knuckles. Next >

Rack-and-Pinion Type Steering System Rack-and-pinion steering is more precise and compact. Uses less component parts. Steering knuckle Steering column Ball joint Steering rack Track rod Boot More common on modern vehicles. Next >

Rack-and-Pinion Steering Principle Pinion gear is turned by steering shaft. Pinion meshes with rack to move it sideways. Thrust spring holds rack against pinion to prevent backlash. Pinion shaft is normally shimmed to minimize end float (up or down movement) also reducing backlash. Next >

Ball Joints Ball joints are common on most steering systems and provide a controllable link to the other steering components. Ball socket Track rod end Adjusting thread Adjusting lock nut Inner track rod Ball joints allow linkage components to swivel freely. Suspension (vertical) and steering (horizontal) movements. Ball joint Inner track rod Boot Shock damper assembly Nearly all ball joints have some form of adjustment. Most steering rack ends have adjustable ball joints and some incorporate shock dampers. Next >

Drop arm (connected to steering gear/box) Linkage Type Steering System Idler arm Drop arm (connected to steering gear/box) Idler arm bracket Steering damper Track rod assembly Track rod assembly Centre link Linkage type steering has many component parts and is normally found on older vehicles. Next >

Re-circulating ball type Steering Gear/box Principles Most linkage type steering systems require some form of mechanical advantage, this is provided mainly by the gear ratio in the steering gear/box. Three main types of steering gear/box: Worm Gear Re-circulating Ball Worm and roller (older Vehicles) Worm gear type Re-circulating ball type Most common are “Worm Gear” and “Re-circulating Ball”. Drop arm couples to links. Worm drive on steering shaft. Re-circulating ball mechanism. Small number of teeth needed. Next >