BMW Maintenance Cases
The automobile chassis suspension system refers to the connection and support system between the vehicle body and the tire. Its most important function is to support the vehicle body. It is mainly composed of the axle and the damping system. It is divided into independent suspension and non independent suspension. In order to improve the driving experience, cars of class B and above generally use independent suspension. The front suspension and rear suspension of the G12 chassis suspension system of BMW's new 7-series car adopt double wishbone independent suspension and multi link independent suspension respectively, and both adopt the air spring equipped with electronic shock absorber control system (EDC) as the suspension shock absorber. Therefore, the BMW G12 chassis suspension system is also called air suspension, as shown in Figure 3.
The double wishbone independent suspension can withstand large lateral acceleration and has fast response speed. When cornering, it has excellent roll support performance without affecting driving comfort. It also has the same support characteristics as the axle spring and linear driving stability. As the rear suspension of G12 chassis system, the five link suspension has strong tracking ability during driving, especially in various driving situations such as the load change period or the transition period from cornering to straight-line driving, it can maintain the vehicle dynamic performance and driving comfort at the same time.
In order to reduce the impact of load on driving comfort, the BMW G12 chassis system is equipped with optimized air spring shock absorbers for the damping systems of the front and rear axles. The body height can be increased by 20mm or decreased by 10mm. The air suspension can automatically adjust the body height (20mm higher) to compensate for the body height required due to vehicle load or for better trafficability when the vehicle is stationary or when the vehicle speed is not higher than 40 km / h. When the vehicle speed exceeds 140 km / h, the air suspension will automatically reduce the body height to the preset movement height (by 10mm).
Compared with the traditional oil damper, air suspension has significant advantages, such as driving safety, driving comfort and fuel economy. However, if the vehicle often runs in the road environment with deviation of pavement, or the vehicle mileage exceeds 100000 km, the defects such as high maintenance cost and short service life of air suspension will be particularly prominent. According to the maintenance documents of BMW's new 7 Series car, since the air suspension uses many flexible pipes with corresponding compressed air interfaces, it is impossible to ensure that the air suspension is 100% sealed, and less specified amount of compressed air loss is allowed. If the vehicle is parked at normal height, the height loss can reach up to 5mm after 24 hours, and not all components will have the same degree of leakage due to tolerance. After parking for a long time, the body posture may have obvious inclination.