Suspension system in automobiles

BRANCH-MECHANICAL ENGG.

SEMESTER-6^TH SEM

NAME-Er D BEHERA

What is suspension system

• Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels
• Serve a dual purpose – contributing to the car's handling and braking.
• Protects the vehicle itself and any cargo or luggage from damage and wear

SUSPENSION SYSTEM – LAY OUT

Different suspension systems

• Conventional suspension system
• Independent suspension system
• Air suspension system
• Hydro elastic suspension system

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Conventional suspension system

• Two wheels are mounted on either side of the rigid axle
• When one wheel encounters the bump, both the wheel do not execute parallel up and down motion
• So it gives rise to gyroscopic effect and wheel wobble
• Rear driving wheels mounted on live axle suspended by laminated leaf springs and shock absorbers

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Independent suspension system

• Both the front and the rear wheel are utilized
• Design incorporated in the front wheels
• One wheel goes down ,the other wheel does not have much effect
• Basic classification of the design
• MacPherson Strut
• Double Wishbone
• Multi link

• the most widely used front suspension system in cars
• comprises of a strut-type spring and shock absorber combo, which pivots on a ball joint on the single, lower arm.
• The steering gear is either connected directly to the lower shock absorber housing, or to an arm from the front or back of the spindle (in this case
• When you steer, it physically twists the strut and shock absorber housing (and consequently the spring) to turn the wheel

MACPHERSON STRUT

DOUBLE WISHBONE SUSPENSION

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Type of double-A or double wishbone suspension

Wheel spindles are supported by an upper and lower 'A' shaped arm.

The lower arm carries most of the load.

If you look head-on at this type of system, parallelogram system that allows the spindles to travel vertically up and down.

This side-to-side motion is known as scrub

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• Type of double-A arm suspension although the lower arm in these systems can sometimes be replaced with a single solid arm (as in my picture).
• The spring/shock combo is moved from between the arms to above the upper arm.
• This transfers the load-bearing capability of the suspension almost entirely to the upper arm and the spring mounts.
• The lower arm in this instance becomes a control arm.

Multi-link suspension�

• It's currently being used in the Audi A8 and A4 amongst other cars.
• The basic principle of it is the same, but instead of solid upper and lower wishbones, each 'arm' of the wishbone is a separate item.
• These are joined at the top and bottom of the spindle thus forming the wishbone shape.
• The super-weird thing about this is that as the spindle turns for steering, it alters the geometry of the suspension by torquing all four suspension arms.
• Spring is separate from the schock absorber.

Advantages ( independent front )

• Bigger deflection of front wheels, no reaction on steering
• Greater distance for resisting rolling action
• Front axle (small-stub), improves road holding tendency of tyres.
• Minimum vibrations

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DISADVANTAGES

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• Better shock absorber required.
• Expensive
• Tyre wear increases due to transmission of torque.

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Advantages ( independent rear suspension)

• Lesser unsprung weight – improves ride , reduces tyre wear.
• Increased passenger space
• Rear wheels remain stable ..

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DISADVANTAGES

• Increased cost
• Complicated design
• Steering action is not proper

Traverse suspension system

• Normally find on the rear suspension
• Combines independent double wishbone suspension with a leaf spring.
• It involves one leaf spring mounted across the vehicle, connected at each end to the lower wishbone.
• The centre of the spring is connected to the front subframe in the middle of the car.
• There are still two shock absorbers, mounted one to each side on the lower wishbones.

Air suspension

• Comprises of compressor , suppling air to air tank
• Pressure maintained – 5.6 to 7 kg/sq.m
• Air bags – on each wheel
• As load applied , air bags compressed actuating the levelling valve .
• Air from the tank fills the compressrd air bag & hence raise the level of the frame.
• Air from air bag gets released as load on chassis decreases .

Air suspension layout

Advantages of air suspension

• These maintain a constant frequency of vibration whether the vehicle is laden or unladen.
• Constant frame height is maintained.
• It helps to reduce the load while the vehicle in motion i.e. the dynamic loading as the spring rate variation between laden and unladen weight is much less.
• It gives smooth and comfort ride of the vehicle.
• The stiffness of the system increases with the increase of the deflection.��

Common Air Suspension Problems�

• Air bag or air strut failure

- due to old age, or moisture within the air system that damages them from the inside.

• Compressor failure

- Primarily due to leaking air springs or air struts

- Compressor burnout may also be caused by moisture from within the air system coming into contact with its electronic parts.

• Dryer failure

- which functions to remove moisture from the air system eventually becomes saturated and unable to perform that function

Hydrolastic Suspension�

• a system where the front and rear suspension systems were connected together in order to better level the car when driving.
• The front and rear suspension units have Hydrolastic displacers, one per side.
• These are interconnected by a small bore pipe. Each displacer incorporates a rubber spring
• Damping of the system is achieved by rubber valves.

• when the front wheel encounter bumps ,the piston moves upwards pressurising the fluid to enter into the rear unit.
• Hydroelastic was eventually refined into Hydragas suspension....... ���

Hydrogas suspension�

• Known as hydro-pneumatic suspension.
• The difference is in the displacer unit itself.
• In the older systems, fluid was used in the displacer units with a rubber spring cushion built-in.
• With Hydragas, the rubber spring is removed completely.
• The fluid still exists but above the fluid there is now a separating membrane or diaphragm, and above that is a cylinder or sphere which is charged with nitrogen gas.
• The nitrogen section is what has become the spring and damping unit whilst the fluid is still free to run from the front to the rear units and back.

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Difference …

HELPER SPRING

• DIRECTLY MOUNTED ON MAIN SPRINGS
• TAKE CARE OF LARGE VARIATION IN SPRING LOAD
• DURING LIGHT LOADS ,ONLY MAIN SPIRNG IS ACTIVE , AS LOAD INCREASE TO A PARTICULAR FIXED VALUE , BOTH THE SPRINGS ARE ACTIVE

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AIR ASSISTED HELPER SPRING

LEAF HELPER SPRING

THANK YOU !!!