- What is a shock absorber
- Shock absorber design
- Why do you need shock absorbers
- Types and types of car shock absorbers
- Which shock absorbers are better
- How to check shock absorber struts
- How to replace shock absorbers
The shock absorber is a key element of the vehicle's suspension, designed to compensate for the stresses on the chassis when driving on uneven roads. Consider what a shock absorber is, how it works, what types there are and how to replace it.
What is a shock absorber
A modern shock absorber is a complex mechanism that dampens vibrations, absorbs shocks and ensures constant contact of the wheels with the road surface when the car is moving. It is installed next to the wheel. With the help of a lever system, mechanical loads (shocks and vibrations) are transferred from the rotating wheel to the mechanism.
This part is equipped with a spring, which provides a quick return of the stem after compression when hitting a bump. If this process does not occur quickly, then the car will become uncontrollable off-road.
Shock absorber design
Most shock absorbers consist of the following units:
- Hollow steel tube (cylinder). On the one hand, it is muffled. An eyelet is welded to this part, which allows the strut to be fixed to the wheel hub. The reservoir is filled with a liquid (a mixture of gas and liquid or only gas), which compensates for the load when the piston is compressed. On the open side, a stem gland is installed to prevent fluid from flowing out of the cavity.
- Shock absorber rod. This is a steel bar, the section of which depends on the model of the mechanism. It fits into the tank. On one side, the rod is attached to the thrust bearing, and on the other, a piston is attached to it, placed inside the cylinder.
- Piston. This element moves inside the cylinder, creating pressure on the liquid or gas inside the tube.
- Bypass valve. It is mounted on the piston and has multiple ports with spring-loaded valves. When the piston moves, one group of valves is triggered, providing overflow from the cavity under the piston to the part above it. Smooth running is ensured by resistance due to small holes (the liquid does not have time to quickly move between the cavities). A similar process occurs during the recoil stroke (when the piston rises), only in this case the valves of another group are triggered.
The device of modern damper mechanisms is constantly being improved, which increases their efficiency and reliability. The design of the shock absorbers can vary significantly depending on the modification of the mechanism. However, the principle of operation remains unchanged. When pushed, the rod moves the piston inside the cylinder, in which the liquid or gas is compressed.
Sometimes shock absorbers are confused with gas springs, which are installed on the front of the trunk or on the hood. Although they are similar in appearance, each of them fulfills a different function. Dampers dampen shocks, and gas springs ensure smooth opening and holding in this position of heavy covers.
Why do you need shock absorbers
When designing vehicles, the early developers faced a major challenge. While driving on the road, the driver experienced terrible discomfort from constant shaking. In addition, due to the loads, the chassis parts quickly failed.
To eliminate the problem, rubber hoses were put on the wheels along with them. Then springs appeared, which extinguished irregularities, but the transport lacked stability. the car swayed strongly on the bumps.
The first shock absorbers appeared in 1903, and were made in the form of springs attached to levers near each wheel. They were mainly installed on sports cars, since horse-drawn vehicles did not need such a system due to low speeds. Over the years, this development has been improved, and hydraulic analogues have replaced the friction shock absorbers.
When driving over bumps, the wheels of the machine must be in constant contact with the surface. The handling of the vehicle will also depend on the quality of the shock absorber.
At the moment of acceleration of the car, the body tilts back. Because of this, the front of the car is unloaded, which reduces the grip of the front wheels with the road. During braking, the reverse process occurs - the body tilts forward, and now the contact of the rear wheels with the ground is broken. When cornering, the load moves to the opposite side of the vehicle.
The task of shock absorbers is not only to dampen shocks, providing maximum comfort for the driver, but also to maintain the car body in a stable horizontal position, preventing it from swinging (as it was in cars with a spring suspension), which increases vehicle handling.
Types and types of car shock absorbers
All shock absorbers are divided into three types:
- Hydraulic. The reservoir contains oil, which, under the action of the piston, flows from one plane of the reservoir to another.
- Gas-hydraulic (or gas-oil). In their design, the compensation chamber is filled with gas, which reduces the likelihood of bottom breakdown due to excessive loading.
- Gas. In this modification, the gas that is under pressure in the working cylinder is used as a damper.
In addition, damper mechanisms are divided into:
Each modification has its own design and principle of operation.
Monotube (monotube) shock absorbers
Single-tube modifications are a new generation of damping mechanisms. They have a simple design and consist of:
- a flask partially filled with oil and gas (among one-pipe models there are completely gas ones);
- a rod that moves the main piston inside the cylinder;
- the piston, mounted on the rod, is equipped with bypass valves through which the oil flows from one cavity to another;
- a separating piston separating the oil chamber from the gas (in the case of gas-filled models, this element is absent).
Such modifications work according to the following principle. When the oil in the reservoir is compressed, the piston valves open. The pressure in the bottom of the cylinder is reduced by fluid overflowing through the small holes in the piston. The rod is gradually lowered to compensate for the shock while the vehicle is moving.
The gas cavity is filled with nitrogen. Due to the high pressure (over 20 atm.), The piston does not reach the bottom of the cylinder, which reduces the likelihood of the shock absorber breaking through on large bumps.
Double-tube types of shock absorbers
Today it is the most common shock absorber category. They consist of the following elements:
- The body, inside which one more flask is placed. In the space between the walls of the vessels there is a gas and a compensation cavity.
- The flask (or working cylinder) is completely filled with a shock-absorbing liquid. At the bottom are intake and exhaust valves.
- The rod pushing the piston is the same as in the one-tube version.
- Piston equipped with check valves. Some open when the piston moves down, while others open when it returns up.
Such mechanisms work according to the following principle. The rod presses on the piston, causing oil to flow into the top of the working cylinder. If the pressure increases sharply (the car runs over a bump - a strong jolt occurs), then the bottom valves of the working flask are activated.
Oil seeping into the compensation cavity (the space between the walls of the working cylinder and the housing) compresses the air in the upper part of the chamber. The stabilization of the rebound forces occurs due to the operation of the piston and bottom valves, through which the oil moves back to the working chamber.
Combined (gas-oil) shock absorbers
This type of shock absorbers replaced the previous type. The design of the mechanisms is identical to the hydraulic modifications. Their only difference is that in the combined damper struts the gas is under a pressure of 4-20 atmospheres, and in hydraulic ones - under normal atmospheric pressure.
This is called gas back-up. These upgrades allow automakers to improve vehicle handling. The gas back-up serves as an additional expansion joint that increases the efficiency of the rack. The front and rear damper struts may require different gas pressure in the expansion chamber.
Adjustable shock absorbers
This type of shock absorbers is installed on expensive cars equipped with a road surface selection function. Such mechanisms are identical to two-pipe modifications, only they have an additional reservoir. It can be located next to the post, or it is made in the form of another tube placed inside the body (forms an additional baffle cavity).
Such shock absorbers work in tandem with a pumping station, which changes the pressure in the gas cavity, giving the suspension the desired characteristics. Changes in parameters are monitored by electronics. The adjustment is carried out from the inside of the car using the corresponding control knobs. The most common types of settings are:
- Standard. The shock absorber works normally. The suspension is soft at this setting, which makes the ride more comfortable. In this case, the travel of the shock absorbers is significantly greater than with other settings. Pits on the road in the cabin are practically not felt.
- Comfort. The gas pressure in the compensation chamber increases slightly to increase the rigidity of the rebound. Most drivers use this feature. It is considered the "golden mean" between ride comfort and vehicle handling.
- Highway. The stroke in this mode becomes even shorter. It is turned on for driving on flat roads. Deficiencies in steering clarity (if any) appear at this setting. The machine will behave softer under heavy load.
- Sports. If you drive on normal roads in this mode, the driver may soon need a chiropractor. The body of the car accurately conveys every bump of the road, as if the car had no suspension at all. However, the presence of this mode allows you to check how high-quality the car is made. Steering responsiveness is felt. Minimum body swing ensures maximum traction.
Such shock absorbers are used to equip expensive car models. They are also used for professional tuning. With the help of such a suspension, you can not only change the rigidity of the rebound, but also change the clearance of the car.
More primitive adjustable shock absorbers look like a conventional twin-tube combo. A thread is cut on the rack housing, on which a spring stop is screwed. This modification is called a coilover. The adjustment is done manually with a wrench (by turning the support nut, moving it either up or down).
Watch also a video about the device and classification of shock absorbers:
Which shock absorbers are better
Each type of shock absorber has its own advantages and disadvantages. Ideally, select struts and springs according to the machine manufacturer's recommendations. "Soft" models will provide increased comfort during the trip, but at the same time will reduce the traction of the wheels. With "hard" ones, the opposite effect is observed - the stability of the car is improved by lowering the comfort for the driver and passengers.
1. One-pipe. The advantage of such damper struts is:
- High precision machine control. They prevent the vehicle from swaying and reduce roll when cornering.
- They can be installed upside down. The backpressure and oil are not mixed due to the floating piston.
- The working cylinder is cooled more efficiently because the air blows directly to its walls. Due to the absence of a housing, the size of the piston and the reservoir are increased, due to which the range of the shock absorber is expanded compared to two-pipe counterparts.
Among the disadvantages are the following:
- Vulnerable to damage. Since they are not equipped with a shell, even a slight deformation of the flask leads to the failure of the entire mechanism - the piston can no longer move freely inside the tank. The only solution to this problem is to replace the rack.
- High sensitivity to changes in ambient temperature. The warmer it is outside, the higher the gas pressure, which increases the stiffness of the suspension.
2. Two-pipe. The advantages of this modification are:
- Simple design, which makes it cheaper than previous counterparts.
- The slave cylinder is protected from external damage. The rack body serves as a buffer.
- Belong to the category of "soft" shock absorbers.
The disadvantages include the following factors:
- High oil aeration. The air in the gas cavity is at atmospheric pressure, so it is easier for liquids to mix with it. The problem persists even when replacing normal air with nitrogen.
- Poor cooling. The slave cylinder, in fact, has a double shell, due to which, when the piston frictions, the oil heats up, its fluidity increases, and the shock absorber becomes even softer.
3. Combined. Since gas-oil shock absorbers are an improved version of conventional twin-tube ones, they have the same advantages and disadvantages. Their main difference is the lack of aeration due to the high pressure in the gas backwater.
4. Adjustable. This category of dampers is the next step in the evolution of the adaptive suspension of the car. Their advantages:
- Adjustment of the damper operation to the appropriate road surface. This will allow you to choose the optimal position between vehicle stability and ride comfort.
- Budget coilovers are easy to adjust - just turn the retaining nut to compress or loosen the spring. More expensive automatic models provide fine tuning of the suspension stiffness. In this case, it is sufficient to move the regulator to the appropriate position. Some models allow separate adjustment of the front and rear struts.
If the vehicle has not been fitted from the factory with an adaptive suspension, installing it may damage the strut mount. Changing the factory characteristics of the car can improve the performance of the car, but at the same time, significantly reduce the working life of various suspension and chassis parts.
When choosing between oil and gas-filled type of shock absorbers, you should pay attention to:
- cost - gas is more expensive than oil;
- comfort and durability - the gas version is tougher than the oil version, therefore it is not suitable for driving on country roads, however, they last longer than liquid ones;
- handling of the car - the gas-filled version is ideal for sports driving, as it ensures the stability of the car on bends and small inclines, and also reduces braking distances... Oil-filled models are designed for measured driving, as at high speed, due to swing and roll, traction deteriorates.
Here's another video to help you determine which shock is the best:
How to check shock absorber struts
To determine the malfunction of the racks, you need to follow a simple procedure. At a speed of 20-30 km / h. press the brake sharply. If the shock absorbers have worked out their resource, the car will "bite" forward, or the rear part will noticeably jump.
You can also test the suspension on bumpy and winding roads. If the machine sways more than usual, the racks have reached the end of their life and must be replaced.
Another way to check shock absorbers is on a shaker. Such a procedure will help determine the state of the mechanisms, and how urgently they need to be changed.
The need for replacement appears as a result of natural wear and tear of parts, as well as due to excessive loads on the damper mechanism (frequent overloads and fast driving over bumps).
How to replace shock absorbers
The shock absorbers are replaced in the following sequence.
- Raise the machine on a lift. If it is raised with jacks, then, when changing the front shock absorbers, the car must be put on the handbrake, and when installing the rear ones, the gear must be turned on (in rear-wheel-drive cars, the front wheels must be blocked in another way, for example, use chocks).
- Unscrew the mount on the steering knuckle.
- When replacing the front struts, the steering tip is removed.
- Unscrew the stem fastening on the support bearing.
The rack is installed in the reverse order.
Using the example of a VAZ 2111, it is shown how the procedure is performed:
Recommendations from professionals:
- Before installing a new strut (for a two-pipe modification), the shock absorber must be pumped so that the air leaves the working cylinder. If this is not done, then during driving will appear "dips" of the piston. The pumping is carried out as follows: the shock absorber, inverted with the stem down, is smoothly compressed, fixed for 2-3 seconds, in this state it is turned over and after 3-5 seconds. release smoothly. Then the rack is turned upside down, wait a couple of seconds, and repeat the procedure three to four times. After bleeding, the shock absorber should be stored in an upright position, as it will be installed on the car.
- Do not use a pneumatic wrench to tighten the stem mount. This can cause the stem to twist and damage the oil seal. If this does not happen, overtightening will create tension in the shock absorber rod, which can cause it to break on a large bump.
- It is strictly forbidden to fix the stem with pliers and other clamping tools. This will damage the rod mirror. A special key should be used to fix it.
- Before final tightening of the stem nut, the vehicle must be lowered from a lift or jack. So the rod will be twisted evenly and will not break or break during the ride. silentblock.
Motorists disagree about the complex replacement of shock absorbers. Some believe that everything needs to be changed at once, while others are sure that it is enough to replace the damaged part.
Although each motorist decides for himself how to repair his car, experts insist on a pair replacement - even if one is out of order, then change both on the side (either front or rear). Due to fatigue wear, old parts combined with new ones can significantly reduce the efficiency of the entire assembly. In any case, remember that one defective part can adversely affect other important parts of the suspension or chassis.
When to change
In which cases it is definitely necessary to change the racks:
- as a result of a visual inspection, traces of fluid leakage were revealed on the body;
- deformation of the rack body;
- the stiffness of the suspension has increased - tangible blows to the body occur in the pits;
- the car sagged noticeably (more often one shock absorber fails, so the car will sag on the corresponding side).
The following video shows one of the options for how to diagnose a suspension malfunction yourself:
If a knock appears in the suspension, you must immediately contact a service station. Such changes in the car cannot be ignored, because the safety of not only the owner of the damaged car, but also other road users depends on them.