Abstract
Air suspension systems are widely applied in luxury cars, sport utility vehicles and mini vans as well as heave duty vehicles due to its advantages such as height adjustment and maintenance of constant low ride frequency independent of the load. The performance of air suspension systems is dependent on the characteristics of pneumatic components such as air springs, a compressor, a reservoir and control valves. Specifications of these components are determined by vehicle specifications and control requirements. A method to predict the performance of an air suspension system before building a prototype is needed to help system engineers and hardware engineers to specify the proper properties of the hardware design parameters from required system specifications at the early stage of development process. In this paper, an analytic model of air suspension systems is developed to estimate the influences of design parameters of the system on its performance. Mathematical models of pneumatic components such as air springs, an air compressor, a reservoir tank and valves are derived and implemented using MATLAB/Simulink. Then the models are validated by comparing the simulation results with measured data. An air spring whose diaphragm consists of rubber reinforced with cords has non-linear characteristics due to its material properties, loading conditions, piston shapes and so on. To predict the spring characteristics considering diaphragm properties such as thickness of cords, angle and space between cords, analysis using finite element method is conducted for various conditions. The static characteristics of air springs obtained from simulation results are used to complement the air spring model.
The analytic model of the whole air suspension systems is constructed by integrating the model of each system component. In order to see whether the design meets the levelling requirement, levelling response is simulated using the derived model and compared with rig test results for various conditions. Finally experiments on an air suspended vehicle are carried out to confirm the usefulness and effectiveness of the proposed method in this paper, which uses a simple easy-to-use model, but runs fast and delivers a reliable result.
Keywords:Air suspension, air spring, analysis, modelling, measurement