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

2. 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

3. 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

4. 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.

5. 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.

6. 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.

7. 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).

8. 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.
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9. 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.
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10. 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.
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11. 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.
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12. 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.
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13. 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.
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14. 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.
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