Need of Suspension System
● In order to provide comfortable ride to the passengers and avoid additional stresses in the vehicle frame.
● The vehicle should neither bounce or roll or sway the passengers when cornering nor pitch when accelerating. braking or sudden lifting or dropping of the front wheel with respect to rear wheels.
● Although some of the road irregularities and inequalities are absorbed by large tyres
● It is necessary to provide a suspension system for reducing the shocks to passengers and for comfortable ride also reduce additional stresses in the automobile frame and body.
● All the parts which perform the function of isolating the automobile from the road shock are collectively called as a suspension system.● A good suspension should have springiness and damping.
● The springiness is the elastic resistance to load while damping is ability of absorbing shocks.
Functions:
1) To act as a safeguard for the occupants against road shocks and provide comfort ride.
2) To preserve the stability of the vehicle in rolling, pitching, while in motion.
3) To minimise the effects of stresses due to road shock on mechanism of a vehicle and provide cushioning effect.
4) To provide the required height to body structure as well as bear the torque and braking reaction.
5) To keep the body perfectly in level while travelling over the uneven road.
6) To provide good road holding while driving, comering and braking.
7) It isolate the automobile body from the road shocks which may be in the form of bounce, pitch, roll or sway.
Requirements of Rigid Suspension System :
The basic requirements of suspension system are listed below.
● It must withstand Greater part of the extra weight of passengers and luggage has to be carried.
● There should be have minimum deflection with the loads as well as the torque or turning forces imposed on it.
● It must be maintained wheels in the proper position with respect to road surface.
● It should be position the axle for minimizing bouncing and associated vibrations to which is liable while moving off, braking and comering particularly.
● It should be of low initial weight.
● It Prevent transmission of 'road noise to the vehicle body .
● It requires appropriate isolation in the suspension joints.
Basic Terms Related to Suspension :
1. Jounce: It refers to the bounce or vertical movement of the vehicle suspension upward when it comes across the bump or shock in the road.
2 Rebound : Rebound refers to the movement of the vehicle suspension in the opposite direction of jounce. The downward travel of the tyre and wheel that extends the spring and shock absorber is called rebound, or extension. When the spring is deflected, it stores energy
3. Sprung and Unsprung Masses:
● The total mass of a vehicle, for the purpose of the suspension design, is broken up into two parts-sprung and Unsprung.
● Unsprung weight consists of tyres, wheels and suspension components that attach these items to the main body chassis structure.
● The rest of the vehicle is sprung weight. In dynamic terms, all items that move with the wheel are unsprung.
● This also includes portions of the shock absorber and sway bar which are attached to the suspension. The portions that are attached to the frame and body are sprung.
● Light components can be kept in contact with the ground more easily heavier ones.
● Motion of the wheels and related embly must be stopped before the springs can return the tyre to the surface.
● Therefore, the lighter the components, the less momentum there is to control.
● With greater unsprung weight, the suspension has to work harder and handling deteriorates.
● Low unsprung mass this allows the use of softer springs, which make for a smoother ride.
● With less unsprung weight, more weight can be controlled with springs and shock absorbers, thus giving a better ride quality.
● Resonance due to the sprung and unsprung weight adversely affect ride, handling and steering.
● The higher the unsprung weight, the higher the hop und tramp amplitudes and the lower the ride quality, road holding and stability.
4. Spring rate : It is defined as the amount of force acts on the vehicle during the needy acro dynamic forces to compress or delectu spring. The rate of the spring, however, remains constant at the load is placed onto the spring.
5. Elasticity : It is the measures of the deformation of an vehicle body when force applied (when it come across the bump) In automobile it must be constant for suspension system.
Types of Leaf spring
Following are the different types of leaf springs.
1. Semi Elliptical Spring
● These are usually used in all the vehicle Particularly in trucks, semi-elliptical springs are fitted in front and rear axles. The leaf springs are made of steel plates or flat semi-elliptical plate.
● But in cars, they are fitted on the rear axle only and the independent suspension is fitted on the front axle. Semi elliptical springs are cheaper and require less repairing. They increase the range of spring action and last for a long time.
2. Quarter Elliptical Spring : This type of spring consists only a quarter portion of the full elliptical spring and fitted with the frame by the bolt.
3. Three Quarter Elliptical Spring : Three quarter elliptical spring is the combination of semi elliptical and quarter elliptical spring.
4. Transverse Spring : Transverse spring in just like the semi elliptical spring but inverted in shape. One end of the spring in joined with chassis frame by shackle, and the other end with the axle. It is also fixed with frame by the bolts a the centre.
5. Full Elliptical Spring: Pull elliptical springs are consists of two semi elliptical springs joined together oppositely. They do not maintain correct axle alignment.
6. Platform Type Spring : Platform type springs consist of two semi-elliptical springs. They are fitted with chassis frame by shackle at one side and the other side is fitted with an inverted semi elliptical spring. In this arrangement, the weight of the car is divided into three points
Construction and Working of Leaf Spring:
● Semi elliptical leaf springs are widely used for suspension in light and heavy commercial vehicle. In car these are used for rear suspension.
● The leaf springs are made of steel plates or flat semi-elliptical plate.
● The advantage of leaf spring over helical spring is that the ends of the spring may be guided along the definite path as it deflects to act as a structural member in addition to energy absorbing device.
● Thus leaf spring carry lateral load, brake torque, driving thrust and shocks.
● It consists of number of semi elliptical plates called blade or leaves.
● The leaves are given initially curvature or camber so that they tend to straighten under the load.
● The blades are vary in length and are held together by a bolt passing through the centre acting as a beam of uniform strength.
● The spring is clamped to the axle housing by means of "U bolts.
● The longest leave is known as master leaves has its end formed in the shape of an eye through which the bolts are passed to secure the spring to its support.
● The eyes are attached to shackle provided with bushing of anti-friction material such as bronze or rubber. The other leaves are graduated leaves.
● To prevent digging in the adjacent leaves, the ends of graduated leaves are trimmed in various forms.
● The master leaf has to withstand vertical bending load, side thrust and twisting moment due to presence of stresses caused by these load it is usual to provide two full length leaves and rest graduated leaves.
● Rebound clips are located at intermediate position in the length of the spring so that graduated leaves also shear the stresses induced in the full length leaves when the spring rebound.
● Highly cambered spring provides a soft suspension but they also increase tendency to jaw (movement about vertical axis). Flat spring reduces tendency of the vehicle to dip (pitching), when brake or accelerate suddenly.
● Use of longer spring gives soft suspension.
● Generally rear spring are kept longer than the front spring. This causes them to vibrate at different frequencies, which prevent excessive bounce.
Advantages:
1. It is simple and strong, acting as a linkage that holds the axle in position without the need for separate linkage.
2. Extra weight and costs are reduced because of the rear axle location. This eliminates the need for trailing arms and a pan hard rod.
3. They also control axle damping
4. It support the weight of the chassis
5. The chassis roll can be controlled more efficiently due to the high rear moment centre and wide spring base.
Disadvantages:
● The ride is not so comfortable because of the inter-leaf friction between cach leaf.
● Longer use offspring it tend to lose shape and can say. When the sag is uneven, it can alter the cross vehicle which can affect the handling slightly. This can also change the axle-to-mount angle.
Helper Springs:
● Helper springs are employed on heavy duty vehicle in addition to main leaf springs. These are allow for wide range loading when the vehicle is lightly loaded, they do not come in operation.
● When load on the vehicle increase, they take their share load.
● Generally these are located at rear suspension. Both the ends of this spring is fixed to the bracket attached to the vehic frame.
Functions :
1. It is semi elliptical leaf spring without eye at the end and help to share the heavy load with main leaf spring.
2. It help to cushion the vehicle and passenger.
3. It provide more rigidity to chassis and frame to avoid distortion.
4. It help to store energy on road bump when vehicle in motion.
Components of leaf spring :
1. Spring hanger
● The spring hunger attaches to the vehicle frame. A bolt and rubber bushing attach the spring eye to the hanger
● As the spring bends the spring eye moves back and forth on the bushing. The bushing also dampens vibration spring.
2. Spring Shackle
● As the spring bends, the distance between the two ends changes. The spring shackle is a swinging support that allows this change.
● Function of shackle in leaf spring
1. It allow the leaf spring to accommodate the change in length of leaf spring during suspension articulation as it is a integral part of suspension system of leaf spring.
2. The shackle mount will provide increase leave rage.
3. The axle will move up and down (yawing action so pinion angle increase.
4. The shackle improve vehicle function by providing ground clearance for larger wheel and tyres.
3. Rubber bush:
Rubber bushing permits the shackle to swing back and forth The bushings also absorb vibration and prevent it from reaching the vehicle body or frame,
4. Single-leaf spring:
● The single-leaf or tapered plate leaf spring is made of a single plate.
● The plate is thick at the center and tapers to the two ends.
● The single-leaf spring mounts and works same as the multi-leaf spring. However, there are no additional leaves to slide on one another.
5. Central bolt and rebound clip:
● It hold all the semi elliptical blade together and rebound clip shear the load during braking and shocks.
