Even though usage of shock absorber on a vehicle may be associated by many aspects, one of the prime ones is eliminating vibrations. There have been many studies and researches to find out the effects of amplitude and frequency of vibration on human health. After the need arose for vehicle design ISO establish a standard to define and recommend permissible level of vibration frequency band as 1-80 cps for all types of vehicles.
Vehicles weight is transferred onto the road surface through vehicle's axles and tyres. When the vehicle stands still the reaction force between the road and tyre is static. As soon as the vehicle begins to move these static forces become dynamic depending on quality and smoothness of road surface. When a vehicle hit a bump or go over a hole on the road an impact force is applied from road surface onto vehicle's tyre. The tyre partially eliminates the impact because of its nature and transfers the leftover force onto the coil springs via vehicle's axle. Then the vehicle begins to vibrate on springs due to the impact. That is where shock absorbers come in to minimize this vibration effect. The aim is to limit the number of vibrations between 1 and 1,5 due to comfort and driving handling aspects.
Some of the significant elements of a shock absorber in terms of its performance can be listed as follows;
1. Piston Ring:
It minimizes friction forces on inner cylinder surface between cylinder tube and piston valve group. It also maximizes sealing performance of piston group during rebound stroke. Piston ring has a special coating on outer surface in order to increase wearing-out resistance and in order to lower the friction coefficient.
2. Du-Bush:
It minimizes the damaging effect of side loads on piston rod. Du bush achieves this task by means of its special material composition and surface coating.
3. Valve Groups:
Valve groups are combinations of springs, discs and sinter parts, assembled together in order to give shock absorber its performance. The main idea is to create a resistence force for oil that is supposed to travel from one space to the other, during which kinetic energy of moving piston rod is absorbed by friction forces within oil passing through bottom valve group. Valve group may be disc type or spring type, depending on applications and design aspects. The same principles are applied for both shocks and struts. Low velocity controlled valve configurations are also available
4. Oil Seal:
Oil seal lowers friction forces and keeps the gas inside at extreme temperatures. Single and multilip seals are available various applications
5. Piston Rod:
Piston rod is the part with te longest process route. After various cutting, machining and threading steps piston rod surface is hardened by means of induction hardening and are chrome plated by means of full automatic plating line in order to give piston rod surface ultimate surface quality in terms of smoothness and endurance.
The characteristics dimensions of shock absorbers can be shown as follows depending on product type;
For shocks:
- Dust tube diameter (dust tube may be made of metal or plastic)
- Base shell diameter
- Piston rod diameter
- Mounting type (Eye or stud type) and relevant dimensions.
For struts:
- Piston rod diameter
- Base shell diameter
- Shape and dimensions of Mounting Brackets (Spring seat and Knucle bracket)
- Stud thread dimension