Automobile Chapter2

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    Suspension system

    The automobile are mounted on the axels, not directly but through some form of

    springs. this is done to isolate the vehicle body from the road shocks. This system for

    comfort riding and transport the goods without damage is called suspension system.

    Objective of suspension system1. To prevent the road shocks from being transmitted to the vehicle component.

    2. To safeguard the occupants from road shocks.

    3. To prevent the stability of the vehicle in pitching or rolling, while in motion.

    Basic load on suspension system1. Vertical loading

    2. Rolling (due to centrifugal force at turning)

    3. Brake dip (weight transfer i.e front of the vehicle suddenly coming down)

    4. Side thrust (due to cross wind, centrifugal force, cambering of the rod etc. )5. Unsprung weight (this is the weight of the components in between suspension &

    road surface. For e.g. rigid front axle, wheels, brake, steering knuckle etc.

    unsprung weight should be less for minimum vibration.)

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    Types of suspension spring

    1. Steel spring

    i. Leaf spring

    ii. Tapered leaf spring

    iii. Coil spring

    iv. Torsion bar

    2. Rubber springs

    3. Plastic spring

    4. Air spring

    5. Hydraulic spring

    6. Magnetic hydraulic spring

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    Leaf spring

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    tapered leaf spring

    Light weight (60% less than conventional spring)

    No inter leaf friction.

    Absence of sharp edges

    Stress distribution is more uniform, thus better life

    Occupy less space.

    No collection of moisture.

    Less damping characteristic due to absence of friction in between plate

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    Coil spring

    Mainly used in independent suspension

    system.

    Energy stored is almost double as

    compared to leaf spring.

    No noise because no friction in between

    like leaf spring.

    Can take shear and bending stress.

    Unable to take torque reaction(at the time

    of sudden acceleration ) & side thrust

    &braking torque.

    Some time use with internal helper spring

    Bad damping characteristic as compared

    to leaf spring.

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    Torsion bar

    Less weight

    Poor in nature to take braking

    &driving torque

    Poor damping due to absence

    in friction

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    Shock absorber

    Coil spring has no damping characteristic, thus

    even if it crossed the bump still vibration is

    continuing. In case of leaf spring again shockedenergy can not dissipate properly.

    So a shock absorber is used along with spring

    which has a good damping characteristic.

    Shock absorbers are basically two types (i)

    friction type, (ii) hydraulic type.

    Friction type is not used now a days because of

    unpredictable damping characteristic.

    Principle of hydraulic shock absorber is when

    piston forces the fluid in cylinder to pass

    through a small hole. Thus due to viscosity

    damping is there.

    The damping is proportional to the square of

    piston speed.

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    Telescopic shock absorber

    Valve A & B (valve B is fixed at the bottom) are two

    way valves. Eye F is connected to the frame of the

    vehicle & eye E is connected to the wheel axel.

    There is a passage on head connected with the gap in

    between cylinder C and tube D , is used to recollect

    the oil which come out on the head by the rod G.

    When the car has come across the bump, the eye E

    moves up, so valve B also moves up. Now the fluid inbetween valve A & B is pressurized. So that, fluid from

    that passage moves to the upper side of valve A.

    Now bump is over. So there is no external force on

    valve B and the pressure above valve A is more than

    the pressure in between fluid of valve A & B, because

    of rod G. now fluid coming back from upper side ofthe valve A to the area in between valve A & B. at the

    same time the oil from the cylinder tube gap enters to

    the passage in between cylinder A & B from the lower

    side of the valve B to upper side.

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    Suspension system1. rigid axel suspension system

    2. independent suspension system

    Independent suspension system

    When a vehicle with rigid axle suspensionencounters road irregularities, the axeltilts & wheels are no longer remainvertical. Which causes the whole vehicleto tilt one side.

    to avoid this independent suspensionsystem is used. Here the separatesuspension system to each wheel isprovided.

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    Advantage of independent suspension system

    Coil spring is used. So spring is lighter

    It gives better riding comfort

    Unsprung weight is reduced

    In this the engine & chassis frame can be placed relatively lower

    position. So more space can be created.

    disadvantage of independent suspension system It is always changing its camber angle. So due to the change of

    scrub radius, toe in & toe out effect may be frequent.

    Difficult to correct the steering geometry.

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    Mac pherson strut type-simpler than Wishbone type-only lower wishbone is used

    -spring carry the stub axel

    -keeping the unsprun weight lower

    -less change in camber angle as compared to wishbone type

    -it gives maximum space for body

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    Front wheel independent suspension system

    Wishbone type or parallel link type

    Mac pherson strut type

    Vertical guide type

    Trailing link type

    Swinging half axel type

    Wishbone type or parallel link type

    - Upper wishbone is shorter- Small change in camber angle takes place,

    so to in and toe out effect may occur.

    - Because of V shape wishbone it is strongand able to take side thrust

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    Vertical guide type

    1. Simplest one2. No change of camber angle at all

    3. Less stable

    Swinging half axel system-large change of camber angle

    -now a days it is absolated

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    Trailing link type suspension

    -maintain constant camber

    -wheel track remain constant

    -the wheel base may changes

    -due to change in wheel base perfect

    roiling action may not obtained

    -very limited use in practical cases

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    Rear wheel independent suspension

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