Air Suspension System
Air springs are used in air suspension systems. The installation and configuration of air suspension systems varies for different makes and models but the underlying principle remains the same. The metal spring (coil or leaf) is removed, and an airbag also referred to as an air spring, is inserted or fabricated to fit in the place of the factory spring. When air pressure is supplied to the airbag, the suspension can be adjusted either up or down (lifted or lowered).
Air spring is nothing but flexible bellows, usually made from textile-reinforced rubber, containing compressed air which is used to carry the load on vehicles. The air pressure inflates the bellows and raises the chassis from the axle. Air springs have elasticity or “springiness” when it is compressed. It is used on many heavy-duty trucks, trailers, and buses on the road today.
Characteristics of air springs:
1. They are soft if the vehicle is not loaded but the stiffness increases when the load is increased by increasing the air pressure inside the chamber. So, it gives the optimum riding comfort when the vehicle is lightly loaded and fully loaded conditions.
2. The height of the vehicle is kept constant by varying the air pressure whenever the load variation occurs.
3. Air springs increase vehicle stability by absorbing road shock.
4. Air spring systems are designed to maximize safe load-carrying capacity, stability, and overall ride quality.
Types Of Air Spring :
Three basic types of air springs are available as follows.
- the double-convoluted,
- the tapered-sleeve, an
- the rolling-sleeve.
The double-convoluted design looks like small tyres kept one over the other. These type of air springs 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 sits considerably inboard of the suspension’s load point. This has the effect of multiplying load capacity requirements while dividing travel requirements.
Tapered- and rolling-sleeve air springs are smaller in diameter with a longer stroke and a more linear spring rate. They are best suited for most rear-end applications because there has more travel requirements and fewer load-capacity requirements.
Devices for controlling the air pressure and compressors for compressing air are required in the air spring suspensions. These systems generally employ small, electric, or engine-driven air compressors which sometimes fill an on-board air receiver tank that stores compressed air for use in the future without delay. But the suspension system is more complex. The electronically modulated air suspension is incorporated along with air spring in modern vehicles.
Types of air suspension:
The following are different types of air suspension systems based on the design of air spring used.
- Bellow type air suspension
- Piston type air suspension
- Elongated bellows air suspension
(i) Bellow type air suspension (Spring):
This type of spring consists of rubber bellows. The bellows are made into circular sections having two convolutions for proper functioning as shown in Figure. So, a bellow type air suspension replaces the coil spring.
(ii) Piston type air suspension (Spring):
This spring has a metal-air container in the form of an inverted drum. The drum is connected to the frame. A sliding piston is connected to the lower wishbone. A flexible diaphragm provides a seal. The diaphragm is tightly connected at its outer circumference to the lip of the drum and at the center to the piston as shown in Figure
(iii) Elotlgated bellows air spring:
When this system of suspension is employed to the rear axle of the vehicle, then elongated bellows are used. These bellows are of approximately rectangular in shape but they are with semi-circular ends having generally two convolutions. These elbows are arranged between the rear axle and the frame of the vehicle. To resist the torques and thrusts, the radius rods are used at the rear axle.
Air Suspension System :
Diagram Of Air Suspension System :
Components Of Air Suspension System :
The components of the air suspension system are:
- Air filter
- Air Accumulator
- Relief valve
- Air spring
- Lift control valve
- Return valve
- Supply line
Construction of Air Suspension :
The layout of an air suspension system has been shown in Fig. The four air springs, which may be either the bellows-type or the piston type, are mounted on the same position where generally the coil springs are mounted. It also consists of an air compressor, air accumulator, relief valve, lift control valve, leveling valve, and pipeline.
Working of Air Suspension :
An air compressor takes the atmospheric air through a filter and compresses it to a pressure of about 240 MPa, at which pressure the air in the accumulator tank is maintained, which is also provided with a safety relief valve. This high-pressure air goes through the lift control valve and the leveling valves, to the air springs as shown. Each air spring is filled with compressed air which supports the weight of the vehicle. The air gets further compressed and absorbs the shock when the wheel encounters a bump on the road.
Difference Between Air Suspension System And Rigid Suspension System
Air Suspension System Rigid Suspension System 1. In this system air springs or air bellows are used 1. In this system leaf spring or coil spring 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. Increased riding comfort and decreased noise level. 3 Riding comfort is less as compared to the air suspension system. 4. The springing rate varies much less between the laden and unladen conditions, as compared with that of conventional springs. 4. The springing rate is more as compared to the air suspension system. 5. Stiffness of the system increases with an increase in deflection. 5. Stiffness of the system decreases with an increase in deflection. 6. Application: Volvo bus, Luxury cars 6. Application: Heavy and medium-duty vehicles, passenger cars, etc. 7. Reduced fatigue to the driver and passenger. 7. More fatigue to the driver and passenger as compared to the 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 put to optimum use by virtue of the automatic control devices
2) Because the vehicle altitude is also constant, changes in head lamp alignment due to varying loads are avoided.
3) The spring rate varies much less between the laden and unladen conditions, as compared with that of conventional steel spring. It reduces the dynamic loading.
4) The improved standard of ride comfort and noise reduction attend with air springs reduces both driver and passenger fatigue.
Disadvantages of Air Suspension System :
Disadvantages of an air suspension system are as follows
- Higher initial cost
- Occupies more space.
- The maintenance cost is more.
- Due to lack of friction damping is necessary due to road shocks.
Application of Air suspension System :
The air suspension system is used in Modern Buses, Volvo, passenger cars, and trucks for comfort ride.
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