The content of the article:
- Choice problems
- Types, features and operating principle of boot lid shock absorbers
- Differences in the dynamics of the rod movement
- Seasonal factor
- Important parameters
- Installation features
- Where can I buy
- Manufacturers
- Prices
The boot lid shock absorber (other names: trunk lift, tailgate stop or shock absorber) is designed to smoothly open / close the trunk lid and lock it in the open (upper) position.
Additionally, such "trunk lifts" make it much easier to open (lift) fairly heavy trunk doors. In this matter, the concepts of "trunk lid", "tailgate", "fifth door", "back door" mean the same thing. Therefore, these shock absorbers are installed for both trunk lids and trunk doors.
Although, to call a "cover" a rather large and heavy structure with glass, similar to a door, is hardly correct.
Nowadays, passenger cars without luggage shock absorbers are practically not produced, and there are a large number of types and varieties of shock absorbers themselves. On new cars, each manufacturer installs standard (standard) shock absorbers corresponding to the design of a particular brand and vehicle modification.
But over time, luggage shock absorbers, like other parts, wear out and cease to fulfill their task. And the question arises before motorists - how to choose and where to buy shock absorbers for the trunk door (lid).
Choice problems
At first glance, there should be no problems with the selection of shock absorbers for the trunk. It is enough just to find out the type of the old shock absorber installed earlier and buy exactly the same one. Although you may not even recognize, but simply remove the old shock absorber and show it to the seller in the car dealership to pick up the same one.
However, in practice, many car owners are faced with two problems of lack of the required type of shock absorber on sale or too high a cost. It is these two factors that make car owners look for interchangeable analogs of luggage shock absorbers at an affordable price and suitable for their car modification.
Those car owners who are forced to look for and choose luggage shock absorbers on their own are advised to study the information below.
Types, features and operating principle of boot lid shock absorbers
Presently the most common types of luggage bumpers are:
- Gas (pneumatic).
- Gas-oil (hydropneumatic).
In addition to these two types, there is a third - "oil". However, this type is considered obsolete, very sensitive to temperature extremes and unsafe. There are cases when shock absorbers of this type were heated in the sun and failed, and the tailgate dropped sharply.
In general, both types of "elevators" (gas-oil and gas) function in the same way. The shock absorbers are folded when the trunk is closed. In this case, the gas is compressed by the piston. When the tailgate is opened, the pressure from the compressed gas begins to exceed the pressure from the weight of the door, from which the rod is pushed out of the cylinder. And the rod, in turn, automatically pushes up the tailgate.
Despite the same functionality, each type of luggage damper has its own distinctive features.
Gas ("pneumatics")
In gas (pneumatic) shock absorbers, the buoyancy pressure on the piston and damping is generated by the gas contained in the shock absorber body (cylinder) under pressure.
The design of the gas shock absorber is not particularly complicated - a piston is located on the rod inside the cylinder-shaped body. Gas (usually nitrogen) is pumped into the cylinder and is pressurized there. The tightness of the cylinder in the area of the rod exit is ensured by an oil seal. In the cylinder itself, gas can move between internal cavities, which are separated by a piston.
In gas shock absorbers, the damping process takes place in a dynamic way. When the piston is just starting to move, the above-piston pressure is substantially higher than the rod-side pressure. As a result, the rod is pushed out of the cylinder.
After the piston passes through the channel in the cylinder wall, the gas flow begins to move from the high pressure region to the low pressure region. As a result, the pressure difference is reduced, and the movement of the piston slows down.
At the last stage, the piston closes the air channel at the lowest point and collides with the gas "cushion". The result is a soft stop (dynamic damping). When the tailgate is closed, the whole process is repeated in reverse order, and the damping occurs in the opposite direction.
Gas-oil ("hydropneumatics")
Unlike gas shock absorbers, there is a small amount of oil in the housing of gas-oil shock absorbers, which is located in the area near the outlet of the stem. At the maximum stem exit (when the tailgate is fully opened), the oil dampes (suppresses) the shock-mechanical energy generated when the piston hits the shock absorber housing.
That is, in gas-oil shock absorbers, another type of damping is used - "hydraulic", in which the piston strikes in the cylinder not into the gas "cushion", but into the oil one.
Differences in the dynamics of the rod movement
Dynamic and hydraulic damping methods differ markedly in the dynamics of the rod movement, which, accordingly, also affects the dynamics of the tailgate:
- In the dynamic version of damping, the stem decelerates smoothly and slowly throughout the entire path.
- In the hydraulic version of damping, the braking of the rod on the main section of the path is weaker and increases only at the end of the path, where there is a sharp braking.
From the differences in driving dynamics, it can be concluded that gas shock absorbers provide smooth and even, but slow opening / closing. And hydraulic oil shock absorbers open / close faster, but less evenly and smoothly.
Seasonal factor
As practice has shown, the performance of gas and gas-oil shock absorbers can be seriously affected by the seasonal factor. So, for example, even with low frosts, gas shock absorbers may have a decrease in damping properties due to a decrease in gas pressure due to its cooling.
Gas-oil shock absorbers can continue to operate efficiently with the optimum oil viscosity. However, during severe frosts, their damping properties also decrease due to an increase in the viscosity of the oil, especially with its low quality.
Important parameters
It will be much easier to choose a luggage damper if you know the important parameters:
- Shock absorber length - measured in the center (axes) of the mountings. A deviation (in each direction) that does not affect the performance is allowed - 5 mm. A deviation of the order of 20 mm may already slightly hinder the operation of the shock absorber.
- Working rod length, the shape of the fastening mechanisms and the method of fastening.
- An effort - measurement in newtons. The force indicator is indicated in the marking on the shock absorber body (3-4 digits with the letter N).
In the absence of marking on the installed (old) shock absorbers (or inability to read it) the following calculations can be used:
- To lift the tailgate (lid), a force of 200 to 600 N is required (the specific figure will depend on the weight of the door and the attachment point).
- The tailgate of a large station wagon will require 650 to 800 N of force.
- The permissible deviation in force is up to 100 N downward, and up to 200 N upward.
Installation features
- Gas shock absorbers can be installed in any position.
- Gas dampers are installed with the stem down to keep the oil at the bottom of the cylinder to ensure proper damping.
- It is recommended to replace shock absorbers in pairs (both at once). Therefore, when choosing and buying a luggage shock absorber, it is better to rely on the purchase of two shock absorbers at once.
- For instructions on how to dismantle and install the luggage shock absorbers, refer to your vehicle's service manual. (No special qualifications are required to replace the luggage shock absorbers, but if your vehicle is under warranty, entrust this work to a specialist).
Where can I buy
In addition to the easy way to buy a trunk shock absorber at a car dealership or car market, there are other popular ways. For example, buy (or order) from an online store.
Today, many online stores offer not only a wide range of licensed shock absorbers, but also help to choose the original or select an analogue by VIN number, with which the equipment of a particular car modification is determined.
However, when choosing luggage shock absorbers, remember that they must be of exactly the type recommended by the vehicle manufacturer... For example, you should not buy "lifts" with a dynamic damping method if the manufacturer recommends a hydraulic method. Otherwise, the load on the tailgate and other body elements may change, which will cause problems during further operation.
Manufacturers
There are a lot of manufacturers of shock absorbers for trunk lids (doors). There are both well-known ones - with a world name and a reliable reputation (and high prices), and little-known ones - with an incomprehensible reputation (but with low prices). Of course, given the financial ability and availability of goods, it is better to choose products from a time-tested manufacturer.
But, of course, in the absence of finance or the desired option, you can choose products and a little-known manufacturer, but it is better to do this on the recommendation of friends or specialists or on the basis of truthful reviews on the Internet.
Rates
Today the price range for "baggage lifts" (depending on the type and manufacturer) is quite wide - from several hundred to several thousand rubles per piece. The most expensive are gas-oil (hydropneumatic).
With such a range of prices, you can adhere to an average pricing policy. That is, buying is not very cheap, but also not very expensive. It is strongly discouraged to buy used shock absorbers. It is almost impossible to check and diagnose such devices, so it is also unrealistic to estimate their remaining resource (how long they will last).
Conclusion
Before making the final choice and not wasting time and money, you need to decide exactly what type and size of luggage shock absorbers you need. It should be remembered that in this matter every little thing is important, even the size (pitch) of the thread on the bolts of the fasteners.
