Air springs are used in air suspension systems. The installation and configuration of air suspension systems varies across different makes and models, but the underlying principle remains the same. The metal spring (coil or leaf) is removed and an airbag, also known as an air spring, is inserted or fabricated to fit in place of the factory spring. When air pressure is supplied to the airbag, the suspension can be adjusted up or down (raised or lowered).
The pneumatic spring is nothing more than a flexible bellows, usually made of fabric-reinforced rubber, containing compressed air that is used to transport cargo in vehicles. Air pressure inflates the bellows and lifts the chassis off the axle. Air springs have elasticity or “give” when they are compressed. It is used in many heavy trucks, trailers and buses on the roads today.
Also Read: Air Brake System Parts, Working, Diagram, Principle, Advantages
Characteristics of pneumatic springs:
1. They are soft if the vehicle is unloaded, but the stiffness increases when the load increases, increasing the air pressure inside the chamber. Therefore, it provides ideal driving comfort when the vehicle is lightly loaded and fully loaded.
2. The height of the vehicle is kept constant by varying the air pressure whenever the load changes.
3. Air springs increase vehicle stability by absorbing road shocks.
4. Air spring systems are designed to maximize safe load carrying capacity, stability and overall ride quality.
Pneumatic spring types:
Three basic types of air springs are available as follows.
- the complicated double,
- the conical sleeve, a
- the sleeve rolled up.
The complicated double design looks like small tires held on top of each other. This type of air spring generally has more load capacity, a shorter stroke, and a more progressive spring rate, which is best suited for use on most front suspensions where the spring is considerably within the suspension's load point. This has the effect of multiplying the carrying capacity requirements while at the same time dividing the travel requirements.
Air springs with tapered and rolling sleeves have a smaller diameter, longer stroke, and more linear spring rate. They are best suited for most rear applications because they have more displacement requirements and fewer load capacity requirements.
Devices to control air pressure and compressors to compress air are required in air spring suspensions. These systems generally employ small, electric or engine-driven air compressors, which sometimes fill an onboard air receiver tank that stores compressed air for future use without delay. But the suspension system is more complex. Electronically modulated air suspension is incorporated along with air spring in modern vehicles.
Air suspension types:
The following are different types of air suspension systems based on the design of the air spring used.
(i) Bellows-type pneumatic suspension (spring):
This type of spring consists of rubber bellows. The bellows are made in circular sections with two convolutions for proper functioning as shown in the Figure. Therefore, a bellows-type air suspension replaces the coil spring.
bellows type pneumatic spring(ii) Piston-type pneumatic suspension (spring):
This spring has a metal-air container in the shape of an inverted drum. The drum is connected to the frame. A sliding piston is connected to the lower arm. A flexible diaphragm provides sealing. The diaphragm is firmly connected on its outer circumference to the rim of the drum and in the center to the piston, as shown in Figure
piston type pneumatic spring(iii) Elongated bellows pneumatic spring:
When this suspension system is used on the rear axle of the vehicle, elongated bellows are used. These bellows are approximately rectangular in shape, but have semicircular ends and generally have two convolutions. These elbows are arranged between the rear axle and the vehicle frame. To resist torques and thrusts, spoke rods are used on the rear axle.
pneumatic spring with elongated bellowsAir suspension system:
Air suspension system diagram:
Air suspension system diagramAir suspension system components:
The components of the air suspension system are:
Air Suspension Construction:
The layout of an air suspension system has been shown in Fig. The four air springs, which can be bellows type or piston type, are mounted in the same position where coil springs are usually mounted. It also consists of an air compressor, air accumulator, relief valve, lift control valve, leveling valve and piping.
Air suspension work:
An air compressor takes atmospheric air through a filter and compresses it to a pressure of about 240 MPa, the pressure at which the air is maintained in the accumulator tank, which is also provided with a safety relief valve. This high pressure air passes through the lift control valve and leveling valves to the air springs as shown. Each pneumatic spring is filled with compressed air that supports the weight of the vehicle. The air becomes even more compressed and absorbs the shock when the wheel hits a bump in the road.
Difference Between Air Suspension System and Rigid Suspension System
Air suspension system Rigid suspension system 1. In this system, pneumatic springs or pneumatic bellows1 are used. In this system, leaf springs or helical springs or both are used.2. In air suspension system, wheel deflection is controlled by automatic control devices.2 In this system there is no automatic control device.3. Greater driving comfort and reduced noise level.3 Driving comfort is lower compared to the air suspension system.4. The spring rate varies much less between loaded and unloaded conditions compared to conventional springs.4. The spring rate is higher compared to the air suspension system.5. The stiffness of the system increases with increasing deflection.5. The stiffness of the system decreases with increasing deflection.6. Application: Volvo buses, luxury cars6. Application: Heavy and medium vehicles, passenger cars, etc.7. Reduced fatigue for driver and passenger.7. More fatigue for driver and passenger compared to air suspension system.8. It consists of compressor, reservoir, leveling valve, air springs or air bellows, etc.8. It consists of leaf spring, coil spring, shock absorber, shackle joint, bracket, etc.
Advantages of air suspension:
The advantage of air suspension is as follows:
1) A variable space for wheel deflection is optimally utilized due to automatic control devices
2) As the vehicle's altitude is also constant, changes in headlight alignment due to varying loads are avoided.
3) Spring rate varies much less between loaded and unloaded conditions compared to conventional steel spring. Reduces dynamic loading.
4) Enhanced standard of driving comfort and noise reduction with air springs reduces driver and passenger fatigue.
Disadvantages of the air suspension system:
The disadvantages of an air suspension system are as follows
- Higher initial cost
- Takes up more space.
- The maintenance cost is higher.
- Due to the lack of friction, cushioning is necessary due to road shocks.
Air suspension system application:
Air suspension system is used in modern buses, Volvo, passenger cars and trucks for comfortable driving.
