Research On Handling Stability Of An Air Spring Bus Equipped With Passive Hydraulically Interconnected Suspension

Buses are more likely to topple over when cornering at high speed or sharply steering to avoid obstacles because of having heavy weights and higher centers of mass, thus, it’s particularly important to improve the roll stability of the buses. On the other hand, good ride comfort is also the basic needs of the drivers and passengers for the long-distance buses.The air spring suspension is widely applied to the bus because of its nonlinear performance. The air spring can reduce the dynamic deflection of the suspension system, depress the body vibration frequency and adjust the height of the bus, so the ride comfort of the bus can be improved evidently. But the air spring does not have an apparent effect on the roll stability. To satisfy the requirements of handlin g stability, the air spring suspension is often used in combination with stronger anti-roll bars. However, the stronger anti-roll bars affect the ride comfort and the holding ground performance, which makes the ride comfort discounted.Aimed at such problem, this paper proposed a new hydraulically interconnected suspension system to replace the anti-roll bar. It can greatly improve the handling stability especially the anti-roll performance without influencing the ride comfort. A further study is conducted on the handling stability of the novel bus installed with hydraulically interconnected suspension system. This paper mainly includes the following four contents: Firstly, a coupled mechanical-hydraulic dynamic model is established. This part employs the analysis of the nonlinear elastic characteristic to extract the static stiffness curve of the air spring. And a seven DOF model of the mechanical system which contains the nonlinear stiffness characteristic of the air spring is established. Then combined with the hydraulically sub-system flow-pressure model, the coupled mechanical-hydraulic mathematical model of the bus is built. Secondly, the matching and improved hydraulically interconnected suspension system is devised. The physical parameters and the modal parameters of the vehicle can be obtained by parameter identification method, such as state variable method. Then, all the parameters are used to calculate the key parameters of the hydraulic components of the hydraulically sub-system. The discrete variables are composed of the key parameters of the hydraulically interconnected suspension system, and the best combination of the discrete variables is sought within the target range of suspension performance requirements to achieve the best matching. Thirdly, simulation analysis based on the established dynamics model is carried out, which verifies the correctness of the models and parameters. Through the simulation analysis, the key parameters of the hydraulic compon ents are optimized. The handling stability and ride comfort of the bus are also simulated to study the effect of the new suspension on the bus, and the simulation results show that the hydraulically interconnected suspension system can make the body roll angle stiffness increased by more than 50%, while the vertical stiffness increased by less than 5%, which means the hydraulically interconnected suspension system can greatly improve the handling stability without influencing the ride comfort. Finally, experimental studies on handling stability are carried out according to the requirements of Automobile Controllability and Stability Test Procedure. From the slalom test, the steady static circular test and the double lane change test, the evaluation indexes of handling stability, such as roll angle, yaw rate, steering angle and understeer coefficient are obtained. The results of the tests show that the hydraulically interconnected suspension system can make the body roll angle decreased by more than 50% under the same lateral acceleration, which means the handling stability of the bus is significantly improved.In summary, this paper takes the air spring bus installed with h ydraulically interconnected suspension system as research object, theoretically analyzes the suspension performance by meanings of modeling, matching design and simulation. The results of the real vehicle tests prove that the novel system has significant positive effects on the handling stability of the air spring bus.