What Is a Shock Absorber?
A shock absorber is a device that reduces vibrations in machinery and buildings.
In addition to suspensions, passenger cars and motorcycles use shock absorbers to reduce the impact from the ground. Springs attached to shock absorbers, absorb the shock and provide a comfortable ride.
If shock absorbers fail due to aging, it is very dangerous because their ability to absorb shock decreases, making it difficult for the brakes to work. It may also make it difficult to turn corners.
Uses of Shock Absorbers
Shock absorbers are mainly used in vehicles.
The following are examples of applications of shock absorbers:
- Passenger vehicles such as cars and buses
- Motorcycles, such as motorcycles and mountain bikes
- Rail vehicles
These vehicles are equipped with shock absorbers to absorb shocks traveling on the ground. Telescopic cylinder shock absorbers are used for passenger cars, while height-adjustable shock absorbers with variable spring positions are sometimes used for motor sports vehicles with low vehicle height.
Shock absorbers called oil dampers or seismic isolation dampers are sometimes used for vibration control of houses and other structures.
Principle of Shock Absorbers
Shock absorbers can be rotary or telescopic, and telescopic shock absorbers are often used in vehicles.
In a telescopic shock absorber, the shock absorber is built inside the spring. The cylinder receives the energy of the spring, which vibrates upon impact, and absorbs the vibration by moving slowly within the hydraulic system.
At this time, the vibration energy is converted into heat energy, which causes the shock absorber to heat up. Telescopic shock absorbers can be further classified into two types: mono-tube and twin-tube.
1. Mono-Tube
Mono-tube shock absorbers are simpler in construction than twin-tube shock absorbers. A piston moves up and down inside a partially oil-filled cylinder by means of a rod that transmits the vibration of a spring. Hydraulic pressure is applied to the piston, which dampens vibration and absorbs shock.
2. Twin-Tube
The mechanism of the twin-tube is almost the same as that of the mono-tube. An additional cylinder with an oil valve is installed outside the mono-tube cylinder, making it a stronger design than the mono-tube. Twin-tube systems are installed in many passenger cars.
Regular maintenance is necessary because oil leakage due to shock absorber deterioration affects the mileage and the rate of deterioration.
How to Select Shock Absorbers
The general procedure for selecting a shock absorber is as follows:
- Confirm the conditions of use
- Tentatively select a shock absorber based on the conditions
- Calculate the total energy of the collision
- Calculate the equivalent mass
- Evaluate the tentatively selected product
The items that must be checked when selecting a shock absorber are the maximum mass, maximum velocity, and maximum thrust of the impacted object. Care should be taken to remember to add this to the total energy, especially if thrust is generated by free fall or cylinders.
Equivalent mass is also known as the weight effect value, and each product has its own allowable range. If it exceeds the allowable range, a high reaction force will be generated at the end of the Shock Absorber’s stroke, resulting in poor shock absorption. If the equivalent mass exceeds the allowable range described in the product catalog, another Shock Absorber should be considered.
Other Information on Shock Absorbers
Shock Absorber Life Span
Shock absorber performance deteriorates with age. As the performance of a car’s shock absorber deteriorates, the tires and brake pads will wear out faster. If the car continues to be driven as it is, the shock absorber itself may break or leak oil.
The durability of a car’s suspension is generally 100,000 km or 10 years. It is also said that the recommended replacement period for shock absorber is 80,000 km. However, the lifespan depends on the roads used and the way of driving.
Highways and mountain roads place a greater load on the car and tend to deteriorate shock absorbers more easily. Unlike tires, for which there is a correlation between mileage and rpm, shock absorbers are also characterized by the fact that it is difficult to determine a definite replacement time. Therefore, it is important to determine the timing and perform regular maintenance.