a report on steering of a vehicle

8/22/2019 A Report on Steering of a Vehicle

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Training Guide Mr Jagrit Sharma

STEERING SYSTEMA Summer Training Project Report on steering

system of a car

Sandeep Kumar Mishra

B.tech (Mechanical 2nd year)

JSS ACADEMY OF TECHNICAL EDUCATION, NOIDA


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MSIL Summer Training project Page 1

Content List

Title Page

1. Company at a Glance . 2

2. Introduction . 3

3. Caster . 4

4. Camber ........ 4

5. Toe ... 5

6. Steering axis inclination .. 6

7. Scrub radius .. 6

8. Steering dynamics ... 7

9. Types of steering system .. 8


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1.Company at a Glance

If youve gone from here to there or just about anywhere

in India, chances are youve driven with us. For over 3

decades now, Maruti Suzuki has been going places with

India.

1982. Gurgaon, Haryana. Little did this quiet suburb of

New Delhi know that it was to become the seat of Indias

automobile revolution, at the Maruti Suzuki factory. In

1982, India turned out just 40,000 cars every year. The

Maruti 800 rolled out and a new chapter began.

It was a new story of leadership. Today, Maruti Suzuki alone makes 1.5 million cars

every year. Thats one car every 12 seconds. Head and shoulders above the rest,

this includes every major global auto company.


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2.Introduction to the steering system

The design of the steering system has an influenceon the directional response behaviour of a motorvehicle that is often not fully appreciated. Thefunction of the steering system is to steer the frontwheels in response to driver command inputsin order to provide overall directional control of thevehicle. However, the actual steer angles achievedare modified by the geometry of the suspensionsystem, the geometry and reactions within thesteering system. Steering system can be front

wheel controlled, rear wheel control, all wheelcontrol. Here we will keep our focus on front wheelcontrolled steering system.

3. Caster

Casteris the forward or rearward tilt of the steering axis in reference to a vertical lineas viewed from the side of the vehicle. The steering axis is defined as the line drawn

through the upper and lower steering pivot points. On anSLA suspension system, the upper pivot is the upper balljoint and the lower pivot is the lower ball joint. On aMacPherson strut system, the upper pivot is the centre ofthe upper bearing mount and the lower pivot point is thelower ball joint. Zero caster means that the steering axisis straight up and down, also called 0 degrees orperfectly vertical, as shown in Figure.

3.1Types of caster-

There are three types of caster angle

Positive Caster

Negative Caster

Zero caster.

3.2 Effect of caster angle on steering-

Positive caster - If caster is positive, the vehicle steering will

be very stable (will tend to go straight with little steeringwheel correction needed). This degree of caster helps with


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steering wheel return abilityafter a turn. If the caster is positive, steering effort willincrease with increasing positive caster. Greater road shocks will be felt by the driverwhen driving over rough road surfaces. Vehicles with as many as 11 degrees positivecaster, such as many Mercedes vehicles, usually use a steering dampener to controlpossible shimmy at high speeds and to dampen the snap-back of the spindle after a

turn.

Negative Caster- Negative caster is seldom specified ontodays vehicles because it tends to make vehicle unstableat highway speed. Negative caster is present in old vehiclewhich are not equipped with powered steering to reducesteering effort.

4 Camber

Camberis the inward or outward tilt of the wheels from true vertical as viewed fromthe front or rear of the vehicle.

If the top of the tire is tilted out, then camber is positive.

If the top of the tire is tilted in, then camber is negative.

Camber is zero (0 degrees) if the tilt of the wheel is true vertical.

4.1 Effect of Camber on steering-

Camber can cause pull if it is unequal side-to-side. The vehicle will pull toward theside with the most positive camber. A difference of more than 1/2 degree from oneside to the other will cause the vehicle to pull.Negative camber tilts the tire and form a cone shape that causes the wheel to pullinward.Positive camber tilts the tire and form a cone shape that causes the wheel to roll orpull outward.


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If the camber angles are different from one side to other, the will pulled towards the

side with the more camber angle.

5 Toe-

Toeis the differenceindistance between the front andrear of the tires. Toe is themost important of the alignment angles.

As viewed from the top of the vehicle (abirds eye view), zero toemeans that both wheels on the same axle are parallel, asshown in figure.It is of two types-

Toe in or Positive toe

Toe out or Negative toe

The purpose of the correct toe setting is to provide maximum stability with aminimum of tire wear when the vehicle is being driven.

If the toe is improper by just 3mm the resulting tire wear is equivalent to dragging a

tire side-ways 8.5m for every mile travelled. First figure illustrate toe in and second

one shows toe out.


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6 Steering axis inclinations (SAI)

SAI is also known as kingpin inclination (KPI) and is the imaginary line drawnthrough the kingpin as viewed from the front. SAI is also called ball joint inclination(BJI), if SLA-type suspension is used, or MacPherson strut inclination (MSI). The

purpose of SAI is to provide an upper suspension pivot location that causes thespindle to travel in an arc when turning, which tends to raise the vehicle.

Vehicle weight tends to keep the front wheels in a straight-ahead position whendriving, thereby increasing vehicle stability, directionalcontrol, and steering wheel return ability. The greaterthe SAI, the more stable the vehicle. It also helpscentre the steering wheel after making a turn andreduces the need for excessive positive caster. TheSAI/KPI angle of all vehicles ranges between 2 and 16degrees. Front-wheel-drive vehicles usually have

greater than 9 degrees SAI (typically 12 to 16degrees) for directional stability, whereas rear-wheel-drive vehicles usually have less than 8 degrees ofSAI. The steering axis inclination angle and thecamber angle together are called the included angle.INCLUDED ANGLE

7 Scrub Radius -

Scrub radiusrefers to the distance between the line through the steering axis andthe centreline of the wheel at the contact point with the road surface.Scrub radius is not adjustable and cannot be measured. Scrub radius can be zero,positive, or negative.Zero scrub radius means that the line through the steering axis intersects thecentreline of the tire at the road surface.Positive scrub radius means that the line intersects the centreline of the tire belowthe road surface.Negative scrub radius means that the line intersects the centreline of the tire abovethe road surface. Scrub radius is also called steering offset by some vehiclemanufacturers. If a wheel is permitted to roll rather than pivot, then steering will be

more difficult because a tire can pivot more easily than it can roll while turning thefront wheels.


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8 Steering Dynamics

To maneuver a vehicle we need a steering mechanism to turn wheels. Steeringdynamics which we review in this chapter, introduces new requirements andchallenges.

8.1 Ackerman geometry-

When the vehicle is moving very slowly, there is a kinematic condition between theinner and outer wheels that allows them to turn slip-free. The condition is called theAckerman condition and is expressed by,

cot o cot i = w/l

Where, i is the steer angle of the inner wheel, and o is the steer angleof the outer wheel. The inner and outer wheels are defined based on theturning centre O. The distance between the steer axes of the steerable wheels iscalled the track and is shown by w. The distance between the front and rear axles iscalled the wheelbase and is shown by l. Track w and wheelbase l are considered askinematic width and length of the vehicle. The mass centre of a steered vehicle willturn on a circle with radius R.


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The Ackerman condition is needed when the speed of the vehicle is too small, andslip angles are zero. There is no lateral force and no centrifugal force to balanceeach other. The Ackerman steering condition is also called the kinematic steeringcondition, because it is a static condition at zero velocity.

From above figure,

Above is the desired condition for Ackerman geometry.

9 Steering System

9.1 Rack and Pinion Arrangement

rack-and-pinion steering gearscan be adjusted. Pinion torque is ameasurement of how much turningforce is needed at the input shaft forthe pinion to overcome theresistance of the rack and move it.The measurement gives anindication of how closely meshed the

pinion teeth and the rack teeth are.Like gear mesh preload in astandard steering gear, pinion torqueindicates steering systemresponsiveness. The adjustmentmethod is to thread the rack supportcover farther into the steering gearhousing to reduce gear lash, or thread it out to increase gear lash. Manufacturersspecify an acceptable range of pinion torque in inch pounds or Newton-meters.Because the middle teeth on the rack wear before the teeth at either end.

9.2 Power steering-

Hydraulics is the study of liquids and their use to transmit force and motion.Hydraulic systemstransmit force and motionthrough the use of fluidpressure. The powersteering pump delivers aconstant flow of hydraulicfluid to the power

steering gear or rack. Atypical power steering


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pump requires less than 1/2 horsepower, which is less than 1% of engine powerwhile driving straight ahead. Even while parking at low speed, the power steeringrequires only about 3 horsepower while providing high hydraulic pressures.Typical pressures generated by a power steering system include the following.

Straight ahead less than 150 PSI (1,400 kPa)Cornering about 450 PSI (3,100 kPa)Parking (maximum) 7501,400 PSI (5,20010,0000 kPa)

Hence the above pressure is generate by power steering to turn the vehicle with lessamount of force.

a report on steering of a vehicle

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