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8/6/2019 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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