steering l 1 notes

8/10/2019 Steering l 1 Notes

1/14

Steering Systems

Topics covered in this presentation:

Basic Steering Systems

Linkage Steering

Rack-and-Pinion Steering

Power Steering


2/14

The Steering System

When the driver turns the steering wheel, the front and sometimesthe 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


3/14

The Steering System

Imagine a car driving round a roundabout, the outer wheel has totravel 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 roadsurface 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 AckermanPrinciple 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


4/14

Terminology

The Steering WheelThe Bit the driver holds on to! It alsoincorporates the Air Bag.

Steering ColumnThe shaft connecting the steering wheel to thesteering box or steering rack.

Steering RackA combination of a small gear and a toothed rack.This changes the rotation of the steering wheel into a back and forthmovement of the rack which in turn moves the road wheels.

Steering BoxThis does a similar job to the rack but needs extralinkages and rods to connect it to the road wheels. Mostly used onold cars, but still is in use on larger vehicles.

Track rod/Tie rodA rod to connect the left and right steeredwheels. The steering rack is also the track rod.

Track rod endA ball joint to allow steering and suspension

movement. Ball joint/Swivel jointPart of the suspension, but these are joints

which allow the steered wheels to left and right.

PASPower assisted steering. An engine driven pump or electricmotor, provides extra force to help the driver turn the steering.

Trackingtoe in or toe out setting for the steered wheels.


5/14

Ackerman

Principle

Axle

Steering

Steering assembly at rest, the

longer bar represents the front

suspension axle, the shorter bar

is the steering linkage/mechanism.

Steering assembly

in operation, as the

steering linkage is

shorter than the axle,

the inner wheel isturned through

a larger angle.

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. Thesteering 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


6/14

Turning Radius (Ackerman Principle)

The steering system is designed to compensate for the different radiuses.

When turning, the inner wheels must turn on a tighter radius than the outer,

this helps avoid unnecessary tyre wear.

Toe-out is increased on turns.

Small adjustments can be made, but normally any error will result in worn or

damaged components being replaced.


7/14

Tracking A steering adjustment which is used to insure that the

steered wheels are pointing straight ahead when the vehicle is moving

This setting is critical for tyre

wear. A small amount of Toe-in

helps compensate for theeffect of rear-wheel drive.

Zero toe effect is required when the

vehicle is moving. This helps reduce

tyre wear (scuffing or feathering).

Toe-in- The wheels point inward,

toward each other.

Toe-out- The wheels point

away from each other.

A small amount of Toe-outis normal on front-wheel

drive vehicles.

Front Wheel Tracking


8/14

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.

Bottom of steering column normally

has a master spline where it mounts

onto the steering rack-and-pinion or

steering gear/box.

Universal joints allow steering

shaft angles to change. Flexiblecoupling

Universal

joints

Flexible coupling isolates steering

wheel from road shocks.Steering

wheel

Steering rack

or gear/box

Most steering columns are

designed with a collapsible

section that helps prevent

forces generated in a collisionbeing transferred to the driver.

Collapsible

section

Master spline

location

Next >


9/14

Linkagetype 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.

Basic Steering Systems

Rack-and-piniontype uses track

rods to couple the rack to the

steering knuckles.

Two main types of steering:

Linkageor Conventional

type (also known as

Parallelogram).

Next >

Rack-and-piniontype.

Drop arm Idler arm

Track rods

Centre link

Steering knuckles

Steeringgear/box

Track rods

Rack-and-pinion


10/14

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 >


11/14

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 >


12/14

Ball Joints

Ball joints are common on

most steering systems and

provide a controllable link to

the other steering components.

Suspension (vertical) and

steering (horizontal) movements.

Most steering rack ends have

adjustable ball joints and some

incorporate shock dampers.

Nearly all ball joints have someform of adjustment.

Ball joint

Inner trackrod

Boot

Shock damper

assembly

Ball socket

Track rod

end

Adjusting thread

Adjusting

lock nutInner trackrod

Ball joints allow linkagecomponents to swivel freely.

Next >


13/14

Linkage Type Steering System

Track rodassembly

Track rod

assembly

Idler arm

bracket

Drop arm (connected to steering

gear/box)

Steering

damper

Centre link

Idler arm

Linkage type steering has many component

parts and is normally found on older vehicles.

Next >


14/14

Worm gear type

Small number of teeth needed.

Steering Gear/box Principles

Drop arm couples to links.

Re-circulating ball mechanism.

Worm drive on steering shaft.

Most common are Worm Gear

and Re-circulating Ball.

Worm Gear

Re-circulating Ball Worm and roller (older Vehicles)

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:

Re-circulating

ball type

Next >

steering l 1 notes

Documents