Telescopic Shock Absorber:
Function of shock absorber:
The shock absorber is a part of suspension system used as springing device to compromise between flexibility and stiffness. It absorbs the energy of shock converted into the vertical movement of the axle by providing damping and dissipating the same into heat.
Purpose of shock absorber:
(i) To control the vibrations on springs.
(ii) To provide a comfortable ride.
(iii) To act flexible and to be rigid enough.
(iv) To resist the unnecessary motion of the spring.
Construction of Shock Absorber :
The upper eye of the telescopic shock absorber is attached to the axle and the lower eye is attached to the chassis frame as shown in Figure 4.55. A two-way valve V1 is connected to a rod. Another one two-way valve V2 is connected to the lower end of the cylinder. The fluid occupies in the space between above and below the valve VI and also the annular space between the cylinder and tube. A gland is provided on the head. Fluid scrapped out by the rod is brought down into the annular space through the inclined passage.
Working of Shock Absorber :
When the vehicle comes across a bump, the lower eye will move up. So, the fluid follows from the lower side of the valve V1 to the upper side. Due to less volume of the space above valve V1 than the volume of the rod, the pressure is exerted on valve V2 Thus, the damping force is produced by this pressure of the fluid. The fluid will flow from the upper side of the valve V1 to the lower side when the lower eye moves down and from the lower side of the valve V2 to its upper side.
When a car absorbs shocks from the road surface, the suspension springs will compress and expand because the spring has the characteristic of continuing to oscillate for a long time of oscillation to stop. So, a riding comfort will be poor even the damp oscillation is supplied. Shock absorbers provide better road-holding characteristics and improved steering stability to tires.
The stronger is the damping force, the more will be the oscillations of the body. But, the shock from the damping effect becomes greater than the strength of the stronger damping force. The damping force varies with the speed of the piston.
Types of shock absorbers:
1. Mechanical shock absorber (friction type)
2. Hydraulic shock absorber.
Again the hydraulic shock absorbers are further divided into various types.
1. Van type
2. Piston type
b. Double acting
3. Telescopic type.
Twin-Tube or Dual Tube Shock Absorber
It is the type of shock absorber in which 2 hollow tubes named primary tube and secondary tube or shell are used which are merged together in telescope type fashion i.e. primary tube inside secondary tube or shell.
- The primary tube contains the moving piston, compression valve along with other assembly components and is filled with high viscosity index oil.
- The secondary tube or shell contains the primary tube along with low-pressure gas (mostly nitrogen gas).
- This whole assembly of twin-tube is surrounded by a coil spring that provides the stiffness and also helps this assembly to regain its initial position after actuation.
Mono-Tube Shock Absorber
It is the type of shock absorber in which instead of a double tube, a single tube is used inside which the moving piston is placed.
- High viscosity index oil along with the low-pressure gas (nitrogen in most cases) is filled inside a single tube in a particular proportion.
- The oil and gas-filled inside this single tube is separated by a floating piston that is placed airtight inside the tube.
- This whole assembly is surrounded by a coil spring same as a twin-tube shock absorber
Advantages of Mono-shock suspension system
1. Mono-shock suspension system improves handling of the motorcycle while going over potholes or bad roads as all the force is focused at one point.
2. Due to position of mono-shock suspension is placed ahead of the rear axle at the center of the motorcycle, the movement of the swing arm is not directly transferred to the suspension, this allows a more stability
3. motorcycle performance is more constant than using double shock.
4. More stylish suspension system.
Gas-filled mono-tube shocks
To prevent foaming and bubbles in the oil, which degrades shock-absorber performance, a gas-filled mono-tube shock has a chamber of high-pressure nitrogen above the oil chamber. This high-pressure gas makes it difficult for bubbles to form in the oil, even when the shock absorber moves in and out very quickly, as it might while traveling rapidly on a very rough or washboard road.
Gas-filled shocks are expensive since they require strict manufacturing tolerances, but they are very resistant to fade and consequently are popular in off-road racing and rallying. Gas-filled shocks, by the way, are not the same as “air shocks,” which use an air chamber separate from the shock oil. An air shock is actually an air spring that raises or lowers the vehicle when air is added or removed through a valve.
Advantages of Gas-filled shock absorber
Advantages of gas-filled shock absorber used at the rear end
1. The full diameter of the tube can be used as a working chamber and thereby a larger volume of oil becomes available for damping.
2. The larger volume of oil made available in any one stroke because of the adjustments between gas and oil volumes provides a better facility for the damping force.
3. The tolerance to heat in the gas-filled shock absorber is greater.
4. Gas-filled shock absorber gives longer life to tires and other related components in the suspension such as springs, brushes, etc.
5. A gas-filled shock absorber is designed to reduce the foaming of the oil.
6. Provide stability while graduating turns.
Difference between the telescopic shock absorber and gas-filled shock absorber.
|Sr.No.||Telescopic shock absorber||Gas filled shock absorber|
|1.||In this only hydraulic oil is used.||In this, both oil and gas are used.|
|2.||The tolerance to heat is less.||The tolerance to heat in gas-filled shock the absorber is greater.|
|3.||In this foaming of oil may occur.||A gas-filled shock absorber is designed to reduce the foaming of the oil.|
|4.||Atmospheric conditions do not affect the system.||The atmospheric condition affects on the system.|
|5.||The operating cost is lower.||The cost of nitrogen gas is more as compared to hydraulic oil.|
|6.||Maintenance is comparatively easy.||Maintenance is difficult as compared to the hydraulic shock absorber.|
|7.||The damping effect is relatively less.||Better damping is obtained.|
Advantages of telescopic shock absorber:
1. A large amount of energy is dissipated due to a large volume of fluid displaced without causing a high-temperature rise.
2. There is no wear development in the damper with the absence of connecting arm pivots.
3. The applied force is increased when compared to the indirect-acting type. Low fluid pressure due to the fairly large piston area occurs with reduced levers.
4. The leakage is very less due to lower pressure and absence of the rotating shaft entering the reservoir.
5. The cost is less than springs.
6. No need of topping up is necessary for most of the telescopic dampers.
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