What is an air suspension and what is it for
What is air suspension and what is it for Modern cars are equipped with different types of suspensions, but in the vast majority of cases their varieties are used, which as the main damping elements include telescopic hydraulic shock absorbers and screw springs. Pneumatic designs are not so widely used yet, and if they are installed, they are mainly in the premium class cars and commercial vehicles. In many respects, therefore, many motorists not very sophisticated in the intricacies and peculiarities of the construction of technology, the question arises: what is air suspension and why use it?
What is air suspension Pneumatic suspension is commonly called a car suspension, in which to achieve a certain position of the body relative to the surface of the roadway using special cylinders filled with air and thus are one of the main elements of the design.
With regard to passenger cars, air suspensions are most often used in the design of executive cars, as well as expensive SUVs. Air suspension is much more widely used in trucks, and not only those that have a relatively small carrying capacity, but also in the long-haul and truck tractors.
What is in the air suspension design Air suspension design
An air suspension consists of basic structural parts such as:
Elastic elements or air cushions; Compressor; Receiver; Control system. What is an air suspension and what is it for, image #10 Each of these air suspension components plays a specific role.
Elastic elements. Air suspension systems use air cylinders as elastic elements. They are installed one at each wheel, and their main function is to hold the car body at a certain height relative to the road surface. Pneumatic cylinders are made of dense, multi-layer rubber and filled with compressed air. Most often they are in the form of “pills”, divided into several sections. There are also pneumatic cylinders, mounted directly on the shock absorber struts, and in such cases, they are a substitute for coil springs.
Compressors. Since the suspension is pneumatic, it needs a source of compressed air to perform its functions. Such is the compressor, with which it is pumped into the elastic elements. Structurally, it consists of parts such as an air dryer and an electric motor, as well as several solenoid valves that ensure the compressed gas to follow a certain circuit. Depending on exactly how many of these valves are in the system, the resilient elements can be inflated either individually, individually, or in pairs.
Receiver. The compressed air does not flow directly from the compressor to the resilient elements, but through a so-called receiver. This is a metal cylinder with a capacity of 3 to 10 liters. This is where the air is pumped in and then flows through magnetic valves to the resilient elements. The air reservoir allows you to adjust the suspension characteristics without turning on the compressor, due to the available supply of compressed air in it.
The control system. Any modern air suspension is necessarily equipped with its own control system, which includes sensors:
The current level of the car body over the road surface; Acceleration of the vehicle; Pressure in the system; Compressor temperature. Information from them goes to the electronic control unit, which processes it in real time and generates signals that are transmitted to actuators. The air suspension control unit is almost always in close cooperation with the directional stability system and the engine electronic control unit (ECU). As for the actuators, these are the valves to create, maintain and release pressure, as well as the compressor switching relay.
How does the air suspension work? Buttons for controlling the air suspension
The operation of the modern car air suspension is based on the fact that, depending on the road conditions and the position of the car body relative to the road, the pressure in the pneumatic cushions varies. With its increase the elastic elements become stiffer, and the clearance of the car increases. If the pressure drops, the opposite process occurs.
Usually, there are three modes of operation of air suspensions:
Normal; Increased; and Reduced. In normal mode, air suspensions operate when the vehicles are driving on smooth roads with paved surfaces at speeds not exceeding 100 km/h. If the movement occurs at low speeds, the clearance is increased, and this is done manually by the driver, with the help of a switch installed in the cabin. This mode is most often used when driving off-road. When driving on roads with smooth paved surfaces at speeds above 100 km/h, the reduced mode is used. This is also manually shifted by the driver.
Automatic correction is carried out when the vehicle is cornering. It is done by pumping more air into the adjacent pads in order to reduce lateral roll. After the turn, the “extra” air is bled out through valves.
Types of air suspensions Types of air suspensions
There are three types of air suspension used in modern vehicles:
Single-circuit; Two-circuit; Four-circuit. What is an air suspension and what is it for, image #11 Single-circuit air suspension is essentially auxiliary and is installed on pickups and small trucks in conjunction with the main suspension. It is installed on only one axle, and most often on the rear axle, in order to be able to adjust its rigidity depending on the degree of loading of the vehicle.
Dual-circuit air suspensions may be installed both on the two axles of the truck simultaneously, and on one axle. In the second case, the motorist is able to adjust the position of the wheels independently.
As for the four-circuit air suspensions, they are the most complex and include all those elements described above.
The main advantage of an air suspension is its very high degree of adaptability. It allows you to quickly, easily and accurately adjust parameters such as ground clearance and stiffness.
Vehicles with air suspensions have better handling. It is especially notable when cornering. In addition, air suspension provides greater comfort for the driver and passengers when traveling, since they are better than conventional suspensions damping horizontal vibrations of car bodies, especially when driving on roads with low-quality pavement and off-road.
There are some disadvantages of pneumatic suspensions. The main ones are the complexity of the design and the high cost of maintenance. In addition, air suspensions are quite sensitive to low temperatures, which is especially important in Russian climatic conditions.
What is the purpose of the air suspension in the car?
Despite the sufficiently large number of varieties of suspension types, in the majority of modern cars are used only their subcategories, in which the main damping element act either powerful springs, or shock absorbers of hydraulic type with a telescopic mechanism. Pneumatic devices have not yet become widespread enough. Their primary area of application is commercial vehicles or cars, belonging to the premium class. Not surprisingly, many motorists are simply not familiar with this type of suspension. Our task is to give the reader an idea of what it is, how it works, what advantages and disadvantages it has.
What is an air suspension
The most common definition of air suspension is a device in which the spatial position of the body relative to the road surface is regulated by air-filled cylinders. In this way, damping is accomplished with compressed air. You may ask, why do we need an air suspension? The answer will be approximately the following: with the help of this device it is possible to change the clearance of the car. Roughly speaking, your sedan can be converted into a parkettes at the touch of a button, which will automatically increase its cross-country ability. When driving on the highway clearance can be made minimal, reducing the drag coefficient of the car. And if you need to turn aside, on a ground road, the increased clearance will allow passing the problem areas with a difficult relief without efforts. However, the pneumatic suspension is characterized by the ability to change the rigidity, which can be useful when passing highways with uneven profile. And now let’s look at what an air suspension looks like.
The design of a typical air suspension
Despite the wide variety of design solutions, the standard air suspension consists of a relatively small number of components:
- control unit;
- air receiver;
- air cushion.
Let’s consider how an air suspension is constructed using all the above-mentioned structural elements as an example.
Air bags are a more formal name for the previously mentioned air cylinders. These elastic elements are installed separately on each wheel. Their main task is to keep the car body at a given height from the road surface.
Pneumatic cylinders, as a rule, are made of hollow multi-layer rubber of increased density, which in the working condition is filled with atmospheric air under a certain pressure. Their characteristic appearance is similar to multi-section tablets. However, it is not uncommon to see pneumatic cylinders installed on shock absorber struts. In other words, in this case they are an alternative to the usual coil springs.
The compressor is a necessary component of any pneumatic system. It is the compressor that creates the pressure required for the normal functioning of the pneumatic elastic elements. The compressor, which is an integral part of the air suspension, consists of the following parts:
- electric motor;
- air dryer;
- electromagnetic valves.
The task of the latter is to ensure routing of compressed gas. Depending on the design features of the pneumatic suspension (in particular, the number of valves), the elastic elements are filled with compressed air either in pairs or individually.
The air reservoir is a suspension element that allows you to change the clearance of the vehicle. It occupies an intermediate position between the compressor and the elastic elements. It is a metal cylinder with a capacity of up to 10 liters, from which the air flows under pressure directly to the elastic elements via electromagnetic valves. Due to the presence of the receiver clearance adjustment is carried out without using a compressor, ie by the available in this reservoir of compressed air.
The air suspension control system is a set of sensors that determine the current performance of the vehicle and send this data to the electronic control unit. The number and composition of sensors may be different, but their typical combination looks as follows:
- vehicle acceleration sensor;
- pressure sensor in the pneumatic system, mounted in the compressor.
The ECU receives signals from the sensors in real time, processes them and issues the appropriate commands to the actuators. In the vast majority of cases, the air suspension control unit interacts closely with the directional stability system. Among the additional devices that support the operation of the air suspension, there are valves responsible for generating the necessary pressure in the system, keeping it at a predetermined level and resetting it if necessary. We have understood what an air suspension consists of, and now we move on to the consideration of how it functions.
How a classic air suspension works
Since the task of the air suspension is to change the position of the vehicle body in relation to the road surface, depending on the current conditions of the car, consider how this is achieved. In principle there is nothing difficult here – increasing pressure in the system, we thereby increase a clearance. But we have to sacrifice stiffness. Decreasing pressure leads to the opposite effect – the car sags, the center of gravity is displaced downwards, but the rigidity of suspension also decreases. It becomes softer and the ride is more comfortable. Note that in most cases, the adjustment of the clearance is a discrete process consisting of three modes:
Normal mode is typical for driving the vehicle on a level road at a speed between 50-100 km/h. If the current situation requires driving at a lower speed and on rough roads, it makes sense to engage the increased ground clearance. For quite understandable reasons, all these manipulations are carried out in a manual mode, by pressing the corresponding button. However, there are situations when automatic correction of auto body position is used. It is the passing of turns. If there is a sufficient amount of compressed air in the receiver at such moments, the reduction of lateral roll of the car will be made without the participation of the driver. After completing the maneuver, the excess air is evacuated through the valves.
Types of air suspensions
The air suspension cannot be called an independent element of the vehicle chassis, as in most cases it functions simultaneously with other types of damping devices (McPherson-type suspension, continuous-beam, the so-called multilever suspension). In general, all such systems, installed as standard, can be divided into two categories:
- simple air suspensions, in which the air element is mounted instead of the classic springs;
- Adaptive devices, in which shock absorbers are able to change stiffness dynamically. In this case the degree of the vibration smoothing can be depending on the driver’s preferences or the road conditions.
Since the air suspension is an expensive element of the chassis design, it is installed either on the premium-class cars, or on commercial vehicles, since its presence is a vital necessity. Depending on the method of implementation of air suspensions there are the following varieties:
- Single-circuit, which has a single air duct, through which the simultaneous change of position of all available cushions (usually there are two, both are mounted on the rear axle);
- double-circuit are used to provide the change of position of the rear axle cushions separately);
- four-circuit systems are characterized by separate lines for all four wheels.
Single-circuit systems are most often installed on heavy-duty tractors or trucks with increased capacity, which are equipped with single-axis (front or rear) air suspension. This type is designed to adjust the stiffness of the entire axle, usually the rear one, since it carries the bulk of the load.
Dual-circuit systems are installed on one or both axles. The single axle assembly allows to adjust the left or right wheel individually. In the second case, it is possible to change rear/front axle stiffness, which is equal to the use of two single-circuit suspensions.
Four-circuit systems are quite difficult to implement, but they provide the possibility of individual adjustment of all four wheels. It really is a highly effective suspension, as the degree of clearance increase/decrease is determined by the onboard computer depending on the information coming from the sensors. Especially noticeable is the use of four-circuit pneumatic suspension when cornering, which in this case is almost not felt because of the compensation of roll.
Pros and cons of modern air suspensions
Since air suspensions are installed on a limited number of foreign car models, for many car owners it would be interesting to know what advantages cars equipped with these systems have. And they are quite a few:
- Variable settings, that is, the ability to adjust the amount of clearance in a certain range. Changing the height of the car above the road, we simultaneously adjust the rigidity of the suspension. For cars equipped with conventional spring elements, such an operation is possible, but only by replacing the springs themselves. Agree, this can hardly be called a way out. Let’s note that the use of stiffened shortened springs really gives fine results on a flat well-paved road, appreciably improving steerability. But the comfort becomes of the second plan – getting on a site with a rough surface, you will turn a trip into a torment. Installation of soft and lengthened springs will make driving on lack of roads comfortable, but the car will behave unpredictably on a high-speed highway. When using the air suspension, all the above problems can be avoided. The driver has an opportunity to switch from a rigid to a soft suspension with a light touch of the corresponding button. In other words, the desired compromise is achieved depending on the particular driving situation;
- Excellent handling is one of the main advantages of an air suspension. This is particularly noticeable when cornering at high speeds, when even a small turning radius makes the vehicle roll noticeable. The air suspension is able to compensate for the difference in position of the wheels above the road surface. For a spring suspension, you can only dream about such mode. However, it should be mentioned that the absence of roll does not mean the absence of centrifugal force during cornering;
- the possibility of individual adjustment. As there are no identical people, each driver has his own style of driving, his preferences concerning the controllability of the car. And if you consider that in most cases, in addition to the driver, there are passengers in the car, the change in load will contribute to improving the handling of the car;
- means to achieve exclusivity. For the majority of car owners bravado of the possibility to change clearance is unacceptable, but there is a category of drivers, for whom it is a vital necessity. They will not spare any means for the sake of re-equipment of their four-wheeled friend;
- Air suspension has been used on trucks for quite a long time and is very successful. It is difficult to overestimate the payload opportunities offered by such a system. Characteristically, changing the degree of wheel load has almost no effect on the driving characteristics of commercial vehicles. Recently, both minivans and pickup trucks have been equipped with pneumatic suspensions. In these vehicles, the load level can indeed vary greatly, even within a single trip;
- Last but not least, the excellent performance of the air suspension, demonstrated at sub-zero temperatures, cannot be overlooked. This is achieved through the use of rubber elements in the manufacture of air suspension bellows, which have good elasticity regardless of weather conditions. Thus, it is possible to increase the service life of the air suspension.
Given such an extensive list of advantages, it seems strange that air suspensions have not yet become widespread. This unfortunate fact becomes clear if you know the main disadvantages of pneumatic damping systems:
- Virtually zero repairability. Regardless of what exactly came into disrepair, it is not possible to restore this unit. And the cost of air suspension is an order of magnitude higher than that of other types of systems. So the improved comfort, reached by such high price is unacceptable for the majority of car owners;
- Negative temperatures are another scourge of such systems, though a pneumatic suspension hardly suffers from severe frosts. But other assemblies can easily break down;
- The road reagents, used for anti-icing, may as well make the air suspension inoperable, as it reacts to such chemicals very sensitively.
Having made a comparative analysis of both lists, we can come to the conclusion that the air suspension is the prerogative of only a small number of cars, whose owners are willing to sacrifice significant sums for the sake of achieving maximum comfort. In Russian off-road conditions it would be useful for many drivers, but the high cost and harsh winters is an obvious limiting factor on the way of mass distribution of air suspension.
What cars are equipped with standard pneumatic suspension
It should be noted that the segment of premium car models is not so small, given that in the developed countries, the middle class, though infrequently, can count on the purchase of a fairly expensive and high-end cars. And if it is equipped with an air suspension – to feel all the charms of a comfortable ride, regardless of the state of the road. But if your plans include the purchase of the model, which is equipped with a suspension of this type, the question arises on which cars air suspension is better? Therefore, it would be interesting to study the results of the rating of brands and models with standard air suspension. And there is such a list. Its authors were guided both by the results of special tests and the users’ questionnaire with a standard list of questions about the performance characteristics of specific cars.
The top 3 of such cars are as follows:
- Audi Q7;
- Porsche Cayenne;
- Volkswagen Touareg.
We shall note, that all these cars are equipped with elements of suspension from the same manufacturers, therefore their ranking was made mainly on the basis of estimation of tuning capabilities. In terms of efficiency and especially reliability to the air suspension used on these models, no claims. In the practical absence of serious drawbacks as such can be considered only the work of the pressure valve. In some cases, occurring very rarely, it spontaneously releases air from the receiver, which eventually affects the comfort of travel, creating an additional load on the compressor unit.
Continue the list of car brands with standard air suspension models, the owners of which have more often applied to the car service with complaints related to this structural element of the chassis. All these cars are characterized by the list of vulnerabilities, which lead to the necessity of repair works:
- The Volkswagen Phaeton and Audi A8 have minimal structural differences between the air suspension. The main disadvantage is the weak struts, which should be replaced, according to the regulations, in pairs after the mileage of 130000-160000 kilometers;
- The air suspension of the Lexus LS430/460 is quite reliable. Their weakest link is considered to be the air shock absorbers, which require replacement every 130,000 kilometers on average;
- The same air suspension is installed on a number of Mercedes Benz models: W220/221 in S-class, W211 (E-class), W219 (CLS-class). The struts have a closed design, so air bags are reliably protected from any external influences. However, this does not affect the life of suspension: the front air suspension does not exceed 100 thousand kilometers, the rear ones have 20000 kilometers more;
- Unlike Mercedex cars, Land Rover’s Vogue and Range Rover’s Sport models have the suspension, which air springs are of open type, that is not well protected from the wear. There are also claims to the electronic control unit, which often fails;
- The first-generation Allroad from Audi is still in considerable demand, indicating the good performance properties of this model, including air suspension. The most frequent failure of air bags, and the common practice among the owners of this car is to replace the faulty element with springs;
- At the end of the rating of cars with air suspension models W164 class ML / GL from Mercedes. Users, and owners of car services claim that here the probability of failure is approximately the same for all air suspension units, but the undoubted advantage of the design is its repairability – almost any part can be replaced with a new one.
Let’s note that any unit or component of a car is not eternal, so it is not necessary to be afraid of the failure of an expensive component. And if to take into account that the reliability of pneumatic damping elements increases from year to year, their prospects do not look so gloomy.