Research On Electronically Controlled Air Suspension Theory And Its Key Technology For Vehicle

Suspension system has an important effect on handling stability, ride comfort, tire grounding and other major performance of the vehicle. Although mechanical height adjustment of air suspension system can regulate the suspension stiffness according to load change, so as to improve the vehicle handling stability and ride comfort to a certain extent, it can’t take all factors into consideration according to vehicle handling stability and ride comfort index to adjust the suspension stiffness, damping and ride height, so it’s hard for the vehicle to achieve the expected performance. With the improvement of vehicle ride comfort requirements, the study on Electronically Controlled Air Suspension (ECAS) system becomes an attractive topic. It is very important to study the vehicle handling stability, ride comfort and safety. Based on the present study of domestic and foreign countries, the ECAS system is researched here, the main contents include:The matching method between the ECAS system and the vehicle is established. Based on the theoretical model and working characteristic of air spring, an eight d.o.f mathematical model of air suspension is built for the ride analysis, and the acceleration, suspension dynamic deflection, tire dynamic loading and other performance index are simulated and analyzed. According to the results, the air suspension parameters, including ride height (air spring’s working height), ideal damping area of adjustable shock absorber can be determined. Then, based on the multi-body dynamics virtual prototype software, the multi-body dynamics virtual prototyping model of the air suspension is created for further verification of the match between the ECAS and the vehicle. After the vehicle performance is simulated, the main factors effecting on the handling stability and ride performance is analyzed, which is the foundation for the ride height and damping integrated control.Some ECAS system control strategies are analyzed and built. Considering the internal working characteristic of air spring and solving the uncertainty of system model, the PID control algorithm is proposed to automatically adjust the suspension stiffness and ride height, which will improve the ride comfort and not worsen handling stability. Under the different driving conditions, a variety of combination control mode and control methods of air suspension are put forward to meet the requirements of the body height, stiffness and damping integrated control. Further, the Ride Height-Damped integrated control strategy based on the vehicle speed is proposed for the engineering applications. The simulation result shows that the proposed integrated control system (ride height switching & damping adjustment) can be fully realized, and the suspension performance can be greatly improved.The road information recognition is very important for the suspension control, so the road information identification model of BP neural network is proposed which combine the suspension dynamic flexibility and vehicle speed. According to different road levels,8 subsidiaries neural network sub-domain model are established, through the study of pavement simulation data and the neural network sample training, more precision road information identification can be made. The comparison of simulation results and field tests further verify the effectiveness of BP neural network road information identification model. Integrating road information identification model into ECAS control system, the road information can be effectively analyzed and judged, so as to provide credible information for vehicle air suspension control.The development of the key parts in ECAS system is carried on.①According to the working characteristics of air springs, combining with structural design theory, CAD technology, Finite Element Analysis, a modern design method of air spring is proposed, and the air spring work characteristic is analyzed by FEA method.②According to the requirements of ECAS’s characteristic to shock absorber, based on common passive hydraulic shock absorber, a new type of swing cylinder-type adjustable damper absorber is developed, which achieve a level adjustable by improving shock absorber piston rod and designing throttle valve. Then adjustable damper absorber mathematical model is established, the results of simulation shows that the adjustable damping shock absorber has good performance, and the ride comfort is significantly improved.③ased on Ride Height-Damping integrated control strategy, the air suspension system integrated controller is developed, and system information is connected by CAN bus. The vehicle with integrated controller of the stable control algorithm can reach the best ride comfort, and handling stability.According to the ECAS system various performance requirements, a test rig of the ECAS system and its main parts is designed which is suitable for the air spring characteristic test, adjustable damping shock absorber characteristic test, control system test, etc. On the basis of the above work, ECAS system is installed in a bus, and test of the whole vehicle is carried on. The testing results show that performance of ECAS system and its main components meet the design requirements, and match well with the whole system, which leads to a great improvement to ride comfort, and handling stability.