Steering System PPT

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Chapter

Chapter--5

5 Automobile Steering System

Automobile Steering System

Prof. Santosh J. Madki

Course: Automobile Engineering Class: B.E. (Mech. Engg.)

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Functions of Steering System

• To achieve angular motion of •the front wheels to make a turn

•To provide perfect rolling motion of the road wheels at all the time. •To provide directional stability of the

vehicle when going straight ahead.

of the road wheels at all the time.

•Absorb most of the shock going to the steering wheel as the tire hits holes

and bumps in the road. • To facilitate straight ahead recovery after completing a turn

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Functions of Steering System

It helps in swinging the wheels to the left or right.

It helps in turning the vehicle at the will of the driver.

It provides directional stability.

It helps in controlling wear and tear of tyres.

It helps in achieving the self-rightening effect.

It converts the rotary movement of the steering wheel into

an angular turn of the front wheels.

It multiplies the effort of the driver by leverage in order to

make it fairly easy to turn the wheels.

It absorbs a major part of the road shocks thereby

preventing them to get transmitted to the hands of the driver.

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Requirements of good steering system

The steering mechanism should be very accurate and

easy to handle

The effort required to steer should be minimum and

must not be tiresome to the driver

The steering mechanism should also provide the

directional stability. This implies that the vehicle should

have tendency to return to its straight ahead position

after turning

It should provide pure rolling motion to wheel

It should be designed in such a manner that road

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Front Axle

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Stub Axles

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Wheel Alignment

Positioning the steered wheels to achieve the

following :

1. Directional stability during straight ahead position

2. Perfect rolling condition on steering

3. Recovery after completing the turn

Different types of alignments:

1. The front end alignment

2. Thrust angle alignment

3. Four wheel alignment

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Factors of Wheel Alignment

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Factors of Wheel Alignment

Set

back

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Factors of Wheel Alignment

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Steering Geometry

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Camber angles

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King

King P

Pin Inclination

in Inclination

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Combined angle scrub radius

Combined angle is the angle formed between the wheel centre line and the king pin inclination (or steering axis).

Scrub radius is the distance between the wheel contact point through which road resistance acts and the other point where the steering axis touches the road surface.

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Scrub Radius

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Effects of Scrub Radius

If the scrub radius is negative the wheel

tends to toe in.

If the scrub radius is zero, the wheel keep

their straight position without any

tendency to toe in or toe out. It is called

centre point steering.

If the scrub radius is positive, there is

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Amount

Combined angle: 9 to 10 degrees

Scrub radius : upto 12 mm

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Castor angle

The angle between the king pin centre line (or steering axis) and the vertical, in the plane of wheel is called caster angle

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Caster angle

If the king pin centre line meets the ground at a point ahead of the

vertical wheel centre line, it is called positive caster.

Positive caster is preferred in

Automoble Steering System: S J Madki

Positive caster is preferred in automobiles.

If the king pin centre line meets the ground at a point behind the vertical wheel centre line, it is called positive caster.

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Toe

Toe –

–in or Toe out

in or Toe out

Toe-in is the amount by which the front wheels are set closer together at the front when it is stationary.

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CONDITION FOR PERFECT STEERING

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TYPES OF STEERING SYSTEM

(a) Davis steering system,

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DAVIS

DAVIS STEERING SYSTEM

STEERING SYSTEM

The correct steering depends upon a sutable selection of cross arm angle α

Α = b/l where b= AB (dist. between pivots)

L= wheel base (centre distance between front and rear axle)

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ACKERMANN

ACKERMANN STEERING SYSTEM

STEERING SYSTEM

C

D

A B

K

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Ackerman’s Geometry

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Slip Angle & Cornering Force

While taking a turn, the centrifugal force acts on the vehicle which produces a side thrust. To sustain the force, the plane of the wheel must make some angle with the direction of motion of the vehicle. This is achieved by the distortion of the tire which is flexible.

The angle through which the wheel has to tilt to sustain the side force is called the slip angle and the force produced due to this (at right angles to the plane of the wheel) which counters the side thrust, is known as cornering force.

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Slip Angle & Cornering Force

The value of slip angle depends upon

- Amount of side force - Flexibility of tire

- Load carried by the wheel - Camber angle

- Condition of road surface

Magnitude of slip angle is small at low speeds and at less sharp curves It is more, at high speeds and at sharp curves

Automoble Steering System: S J Madki

It is more, at high speeds and at sharp curves For same slip

angle-Cornering force increases for positive camber Cornering force decreases for negative camber

The alteration in the cornering force due to camber is known as camber force

Cornering Power = Side force sustained Slip Angle

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Understeer

Understeer and

and Oversteer

Oversteer

Understeer: When the slip angles of the front wheels are greater than those for the rear wheels, radius of the turn increases. The vehicle turns less sharply than it is expected. Therefore to keep it on right path we have to steer more.

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Understeer

Understeer &

& Oversteer

Oversteer

Oversteering: When slip angles of the front wheels are less than those of the rear wheels, the radius of the turn decreases. The vehicle turns more sharply than it is expected. Therefore to keep it on right path we have to steer a little less than needed.

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Factors affecting

Factors affecting Understeer

Understeer &

& Oversteer

Oversteer

Passive Factors:

1) Weight Distribution

2) Type of Drive

3) Suspension and chassis setup

4) Tire type & Pressure

Active Factors:

1)Cornering Speed

2) Throttle Position

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COMPONENTS OF

COMPONENTS OF STEERING SYSTEM

STEERING SYSTEM

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Steering System

Linkage Steering System (Worm Gear) Parts

•Steering Wheel – used by the driver to rotate a steering shaft that passes through the steering column.

•Steering Shaft – transfers turning motion from the steering wheel to the steering gearbox.

•Steering Column – supports the steering shaft.

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Steering System

Linkage Steering System (Worm Gear) Parts

•Steering Gearbox – changes turning motion into a straight-line motion to the left or right. •Steering gear box ratios range from 15:1 to

24:1 (with 15:1, the worm gear turns 15 times to turn the selector shaft once).

•Steering linkage – connects the steering gearbox to the steering knuckles and wheels.

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Steering Linkage

Pitman Arm transfers gearbox motion to

the steering linkage.

•Pitman arm is splined to the gearbox.

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Steering Linkage for Independent Suspension

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Steering Linkage

Center Link (Relay Rod) steel bar connects the

right and left side of the steering linkage.

•Connects to Pitman arm, Tie rod ends, and Idler arm.

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Steering Linkage

Idler Arm supports the end of the center

link on the passenger side of the vehicle.

•Bolts to the vehicle’s frame.

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STEERING

STEERING GEARS

GEARS

(Steering gear boxes):

•Worm and wheel steering gear

•Cam and roller or worm and roller steering gear

•Worm and nut or screw and nut steering gear

•Recirculating ball steering gear

•Rack and pinion steering gear.

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Worm and wheel steering

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WORM AND ROLLER STEERING GEAR

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SCREW AND NUT TYPE STEERING GEAR

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RECIRCULATING BALL TYPE STEERING GEAR

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RACK AND PINION

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Steering System

Basic Rack-and-Pinion Steering

•Pinion Gear- rotated by the steering wheel and steering shaft; it’s teeth mesh with the teeth on the rack.

•Rack- long steel bar with teeth along one section; slides sideways as the pinion gear turns.

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POWER STEERING SYSTEM

Power Steering

normally use an engine driven pump and a hydraulic system to assist steering action.

Three major types of power steering systems: •Integral-piston linkage system.

•External power steering system. •External power steering system.

•Rack-and-pinion system •Integral power piston.

•External power piston.

Integral Rack-and-pinion system is the most common.

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POWER STEERING

The slight movement of the steering wheel actuates a valve so that the fluid under pressure from the reservoir enters on the appropriate side of the cylinder, thereby applying the pressure on one side of the piston to operate the steering linkage, which steers the wheel in the appropriate direction.