Tanishq Kanungo.pdf

CASE STUDY OF BAJA 2019 VEHICLE • DEPARTMENT – STEERING AND SUSPENSION SYSTEM o STEERING SYSTEM Primary function of steering system is to achieve angular motion of the front wheels to negotiate a turn. This is done through linkage and steering gear which convert the rotary motion of the steering wheel into angular motion of the front road wheels. Secondary functions of the steering system are: (i) (ii) (iii) (iv)

To provide directional stability of the vehicle when going straight ahead. To provide perfect steering condition i.e. perfect rolling motion of the road wheels at all times. To facilitate straight ahead recovery after completing a turn. To minimize tire wear.

o Requirements of a good steering system (i) (ii) (iii)

The steering should be very accurate and easy to handle. The effort required to steer should be minimal and must not be tiresome to the driver. The steering mechanism should also provide directional stability. This implies that the vehicle should have a tendency to return to its straight ahead position after turning.

o Types of steering mechanism: (i) (ii)

Rack and pinion Recirculating ball type

Most modern cars use the rack and pinion steering mechanism. The recirulating ball type mechanism has the advantage of a much greater torque multiplication, thus it was originally used on large, heavier vehicles while the rack and pinion was limited to smaller and lighter cars.

o Steering system specifications of baja 2019 vehicle (i) (ii) (iii) (iv) (v) (vi) (vii)

Steering ratio of 4:1 with 0.8 lock to lock turn is selected. A 7⁰ caster is integrated to induce a steer camber which causes lean into corners. Self designed steering wheel of 280 mm diameter. Steering column is manufactured from mild steel rod for optimum torque transfer. Rack and pinion is manufactured from stainless steel. Rack and pinion casing is made up of aluminium 7075 with gunmetal bushing. Tie rods are designed and manufactured from stainless steel.

o Problems faced in baja 2019 vehicle (i)

Heavy steering due to wrong machining of rack and pinion. The hard or heavy steering may also due excessive friction in the steering gearbox which should be lubricated to reduce friction. Proper machining should be done on rack and pinion so that they work properly without any friction.

(ii)

Steering arms were not given the angles from lower pivot points ( i.e. incorrect Ackerman angles) which is necessary for 100% Ackerman geometry. Solution to these is to give correct Ackerman angles.

(iii)

Play between rack and pinion. Usually a steering wheel has only a few millimeters of play in it, but when it gets high it causes wear which ultimately result in loose steering. Solution only to these is to replace them.

(iv)

Bending of rack due its small diameter. Solution is to redesign the rack of large diameter.

(v)

Small length of steering arm due to which leverage was reduced and also they were colliding with the lower wishbone arms. This problem results in vibrations in the vehicle and affects the stability and free rotation of the steering.

Solution to these is to increase the length of the steering arm. (vi)

Shorter rear wheel track because of transmission problems due to which half shaft was continuously failing. Also this causes the problem of more load transfer on the front axle. Solution to these is to increase the rear wheel track by proper designing and analyzing.

o Steering system used in other road cars (i)

Maruti 800 : Rack and pinion Turning circle: 8.8

(ii)

Turn lock to lock: 3.27

Hindustan ambassador: Rack and pinion Turning circle: 10.83 (right) 10.74 (left)

(iii)

Ford motor co. ( Mustang ) : Manual rack and pinion Overall ratio: 24.93:1 to 21.69:1 20.03:1 to 16.05:1 Turn lock to lock: 4.08 3.40

(iv)

Maruti Suzuki ltd. ( Alto ): Rack and pinion Turning diameter: 9.2 Turn lock to lock: 3.3

o Basic suspension system The primary purpose of a suspension system is to support the weight of the vehicle and give a smooth ride It is desirable that it should also allow rapid cornering without body roll when the car leans to one side, keep tire in firm contact with the road at all times and conditions , prevent body squat ( tilting down at rear ) when accelerating, prevent body dive ( tilting down at front ) when braking, allow front wheels to turn for steering, keep the wheels vertical and in correct alignment at all times. The typical suspension components are: (i) (ii)

Coil spring. A control arm that pivots on the vehicle frame.

(iii) (iv)

Shock absorber which dampens the spring vibrations. The steering knuckle which is ball-jointed to the control arm to allow for vertical and horizontal movement.

o Independent suspension system When a vehicle with rigid axle suspension encounter road irregularities, the axle tilts and the wheels no longer remain vertical. This causes the whole of the vehicle to tilt on one side. Such a state of affairs is not desirable. Apart from causing rough side, it cause “wheel wobble”. The road adhesion is also decreased. To avoid this the wheels are sprung independent of each other, so that tilting of one does not affect the other Advantages over rigid axle suspension: (i) (ii) (iii)

Reduced unsprung weight. Coil spring store more energy then semi-elliptic leaf springs. Improved steering precession since wheel movement are not linked. Disadvantages:

(i) (ii)

High cost. Greater maintainence. Types:

(i) Double wishbone. (ii) Macpherson strut. (iii) Semi-trailing arm. • For sae baja buggy suspension, primary conditions are high wheel travel, less unsprung mass and better reliability so almost all the team prefer independent suspension system. • For front we prefer double wishbone geometry because it provides easy tuning of camber, toe, and ground clearance. It also provide compact and reliable design for front wheels. • For rear semi-trailing arm or multi link type can be preferred to avoid track loss ( camber change ) and to optimize the space and complexity. • It does not mean that SLA is not good for rear geometry. • Team nemesis is using SLA geometry since last two years.

In our atv we have used double wishbone suspension system in both front and rear sides.

o Front suspension Short long double wishbone suspension: A short long arms suspension ( SLA ) is also known as unequal length double wishbone suspension. The upper arm is typically on A arm and is shorter than the lower link, which is an A arm or L arm or some times pair of tension and compression arms. The reason for choosing this was to have an optimum roll centre height which gives minimum vehicle roll during cornering and minimum camber gain which gives minimum traction on wheel during bump.

o Specifications used for front suspension are; (I) (II) (III) (IV) (V) (VI) (VII) (VIII)

Static camber Static toe Kingpin inclination Caster Roll centre height Damper Front track Spring

0⁰ -2⁰ +8.2⁰ 9⁰ 226 mm Fox Float 3 Evol R 1220 mm Air

o Rear suspension Short long double wishbone suspension: Suspension arm, in the shape of H are used for rear suspension of the vehicle since they no need to be steered, they can not be used for a front suspension. Parallel H arms were chosen due to their lower unsprung mass and more strength. An optimum geometry to have less camber gain and no toe during wheel travel.

o Specification use for rear suspension are: (i) (ii) (iii) (iv) (v) (vi)

Static camber Static toe Roll centre height Damper Rear track Spring

0⁰ 0⁰ 228 mm Fox Float 3 Evol R 1120 mm Air

o Problems faced in baja 2019 vehicle o

Damper leakage: If there is a leakage in damper then it can be repaired but repaired damper will have a shorter life and also on the road behaviour of the car will also be severely compromised. It is not recommended to repair because of following reasons:

(I) (II) (III)

o

Unequal damping pressure when compared to an original damper, leading to poor handling or uneven tire wear. Sudden premature loss of damping pressure during use. Sudden lock up of damping valves inside the strut ( due to poor quality of damper oil fired by repairers ) causing the damper to become rock solid during use. This can brake mountings.

Incorrect positioning of suspension mounts: This problem induces the vibrations in the vehicle and reduces the free rotation of the steering. Solution to these is to position them correctly after doing proper analysis.

o

Unintentional toe/camber angle of rear wheel: This causes the problem of tire wear, feathered edges and diagonal wipe on tires. For adjustment one mounting of each suspension arm is incorporated with either eccentric adjusters or shims.

o Suspensions generally used in other road vehicles (i)

Honda siel cars india limited: (a) Accord: Front suspension – Independent double wishbone, antiroll Bar. Rear suspension – Independent multi-link antiroll bar. (b) Jazz: Front wheel drive Front suspension – Independent macpherson struts. Rear suspension – Non-independent torsion beam.

(c) Civic: Front wheel drive Front suspension: Independent macpherson strut coil springs. Rear suspension: Independent dual wishbone, coil springs. (ii)

Mahindra & Mahindra LTD: (a) Scorpio mHawk: Rear wheel drive Front suspension: Independent coil spring, Double wishbone, antiroll bar. Rear suspension: Non-independent 5 link, coil springs, antiroll bar. (b) Axe: Rear wheel drive Front suspension: Independent double wishbone with coil springs. Rear suspension: Independent double wishbone with coil springs, stabilizer bar.

Submittted by: Tanishq Kanungo Enroll. No.: EN17ME303093 Branch: ME (B), 2nd year