Installation and Use of Single Axle Lifting Type Semi Trailer Air Suspension(Part 2)

Installation and Use of Single Axle Lifting Type Semi Trailer Air Suspension

－Introduction of main components and maintenance of air suspensions（Part 2）

1. The structure, function and principle of the main components of the air suspension system

1.1 Air spring assembly

As shown in Figure 1 below. The air spring assembly consists of a top plate, a piston, an air bag, and a rubber buffer block.

The inner wall of the airbag is a rubber sealing layer, the outer wall is a rubber protective layer, and the middle is composed of multiple rings of steel wire to improve its strength.

The air spring bears the load in the vertical direction. With the change of load, the compressed air pressure in the airbag changes accordingly, and the stiffness of the airbag also changes, which has good stiffness characteristics.

(Figure 1. Composition of the air spring)

1.2 Shock absorber

As shown in Figure 2 below. The shock absorber mainly consists of the following components:

1. Piston rod

2. Working cylinder

3. Piston

4. Extension valve

5. Oil storage cylinder

6. Compression valve

7. Compensation valve

8. Flow valve

9. Guide seat

10. Dust cover

11. Oil seal

(Figure 2. Structure diagram of the shock absorber)

When the suspension height changes during vehicle driving, the shock absorber plays a damping role.

When the vehicle body height drops, the shock absorber is in the compression stroke and the shock absorber is compressed. Piston 3 now moves downward. The volume of the lower chamber of the piston decreases, the oil pressure increases, and the oil flows through flow valve 8 to the chamber above the piston. The upper chamber is partially occupied by the piston rod 1, so the increased volume of the upper chamber is less than the reduced volume of the lower chamber. A part of the oil then pushes the compression valve 6 and flows back to the oil storage cylinder 5. The oil conservation by these valves forms a damping force for the suspension's motion in compression.

When the body height increases, the shock absorber is in the extension stroke and the shock absorber is stretched. At this time, piston 3 in the shock absorber moves upward. The oil pressure in the upper chamber of the piston increases, the flow valve 8 closes, and the oil in the upper chamber pushes the extension valve 4 into the lower chamber. Due to the existence of the piston rod, the oil flowing from the upper chamber is not enough to fill the increased volume of the lower chamber, which mainly causes the lower chamber to generate a vacuum. At this time, the oil in the oil reservoir pushes the compensation valve 7 to flow into the lower chamber for replenishment. The throttling effect of these valves plays a damping role in the extension movement of the suspension.

1.3 Load sensing valve

As shown in Figure 3 below, the load sensing valve consists of an air inlet port, a valve body, air outlet ports, a piston rod, a piston, an exhaust port and a drive shaft.

The load sensing valve is installed on the vehicle body (trailer chassis), and the adjusting rod seat is installed on the axle.

The air suspension system controls the height of the airbag through the load sensing valve. When the load weight of the vehicle increases, the swing arm swings upward, and the load sensing valve inflates the airbag; when the load weight decreases, the swing arm swings downward, and the load sensing valve deflates to the atmosphere. Therefore, even if the load increases or decreases, the height of the airbag and the vehicle body can be guaranteed to be relatively stable.

(Figure 3. Load Sensing Valve)

2. Warranty of air suspension

Under normal use and maintenance, the quality warranty of the air suspension (since the trailers sold) is usually as follows:

Component Category	Warranty period   (whichever comes first)
	The time since the trailer is sold	Vehicle travel (km)
Air bag	12 months	100000(km)
Shock absorber	6 months	50000(km)
Rubber ball hinge	6 months	100000(km)
Load sensing   valve	12 months	100000(km)
Other main parts	24 months	200000(km)

Remark:

A. Main parts refer to the main structural parts in the suspension system, such as frame brackets （hangers）, air linker , airbag brackets, etc.

B. The warranty from each manufacturer is different, please follow the policy of each manufacturer.

3. Precautions for the use of the air suspension

The air suspension system can only exert its superior performance when it is used correctly. When using it, be sure to do the following:

1) In order to ensure the normal use of the air suspension system, the OEM must provide separate air tanks for the air suspension system, which is not allowed to be shared with the air tanks of the brake system.

2) When the air pipeline leaks or the airbag is accidentally damaged, the rubber buffer block in the airbag assembly can form a rubber pad support. Please ensure that the vehicle was driven to the nearest service station for maintenance at a speed less than 30km/h.

3) Vehicles shall not be overloaded. Even if driving on good roads such as expressways and class I highways, the overload rate shall not be greater than 10%.

4) The air supply pressure of the air suspension system should be maintained between 6.1 and 7.5 Bar.

5) It is forbidden to use lubricating oil and grease for the rubber parts in the air suspension system.

6) Carry out maintenance according to the requirements of the air suspension manual.

7) The ambient temperature range of the vehicle is - 40 ℃ ~ + 70 ℃.

4. Maintenance

4.1 Daily routine inspection

4.1.1 Check whether the body is tilted

Record the height of the vehicle body at several points that are easy to measure before driving the vehicle every day, and compare it with the previous height records to know whether the vehicle body is tilted and lowered.

4.1.2 Check for air leakage

After parking, go to the installation location of the front and rear airbags to listen for air leakage. If you can hear obvious sound of air leakage, you should do further inspection to confirm the air leakage and fix it.

4.2 Regular safety inspections

The air suspension system shall be inspected regularly every 5000 km.

4.2.1 check the fasteners of the air suspension system

Check whether the fasteners of the air suspension system are loose. Focus on checking whether the fasteners of U-bolts, load sensing valves, airbag assemblies, shock absorbers, lateral stabilizer bars and their suspenders are loose. If they are loose, tighten them according to the specified torque.

4.2.2 check the pneumatic circuit for air leakage

Check whether there is air leakage at the airbag top plates, load sensing valves, pneumatic circuit joints and pipeline by listening and wiping soapy water. If there is air leakage, fasten the joint or replace the joint. At the same time, clean the ponding, oil and dirt at the joint.

4.2.3 Check whether the outer surface of the airbag is worn, bulging, bruised or cut

1) If the surface of the airbag is damaged and the PLY is exposed, replace it.

2) Check whether the airbag interferes and collides with the surrounding fixed parts. If so, adjust it in time, because this may be the root cause of airbag damage.

3) Clean the lubricating grease on the surface of the airbag, the deposited dirt on the piston and the foreign matters clamped between the piston and the airbag, which can cause the airbag rubber to be worn.

4) If there is air leakage at the joint between the airbag and the top plate or piston, it is recommended to remove the airbag, check the upper and lower ports of the airbag and whether the conical sealing area of the airbag top plate or piston is deformed. If it is deformed, replace it; at the same time, check whether the rubber stop is damaged. Its damage may be the root cause of the impact damage to the conical sealing area.

5) If two airbags are controlled by a load sensing valve, air leakage in one of them will reduce the air pressure of the other one.

4.2.4 Check the shock absorber for oil leakage

Most of the oil leakage of the shock absorber is caused by external damage, welding at the welding point and oil seal damage. If there are only some oil marks on the surface of the cylinder body, and there is no obvious wet oil film, it is not an oil leakage. Oil marks are mainly caused by the volatilization of grease in the oil seal at high temperature.

4.3 Secondary maintenance

When the vehicle travels every 20,000 kilometers, the air suspension system should be subjected to secondary maintenance.

In addition to the inspection contents specified in Clause 4.2, the secondary maintenance should also include:

4.3.1 Checking the LSV adjusting rod

Check whether the balance position of the adjusting rod of the load sensing valve has changed, if so, adjust it; if the rubber of the connecting rod is aging, brittle, sticky, or loses elasticity, it should be replaced.

4.3.2 Check the shock absorber

Check whether the welding of the suspending ring of the shock absorber is deformed, and whether the rubber bushing is cracked, brittle, sticky, or loses elasticity. If the above problems occur, they should be corrected in time.

After the above inspection, inflate the airbags and adjust it to the design height, check the wheelbase, vehicle body height, and adjust the airbag height if necessary to make the above data meet the design requirements.

Note: The above content is for reference only, please follow the manufacturer's manual.

Compiled by  WONDEE Autoparts

2022-1-21