Characteristic analysis of pitch-resistant hydraulically interconnected suspensions for two-axle vehicles

This paper proposes a new method to investigate the characteristics of pitch-resistant hydraulically interconnected suspension (HIS) systems for two-axle vehicles in the pitch plane. The equations of motion for the mechanical and hydraulic coupled system are developed, in which the hydraulic strut forces are derived using the impedance transfer matrix method. The stiffness and damping matrices of the coupled systems are described in a manner similar to the generalized form of uncoupled conventional suspension (UCS) systems. The additional properties of HIS systems are explicitly described via hydraulic physical parameters. Based on the generalized form, (1) the accumulators of HIS systems can be functionally equivalent to a combined system with tandem bump and pitch-angular springs; (2) the direction damper valves (DDVs), which are located at the outlets of actuator cylinders, function like uncoupled tandem dampers; (3) the pitch damper valves (PDVs), which are fitted on the hose to connect the accumulators, alter the mode damping similar to the accumulators changing the mode stiffness; (4) the opposite installation corresponding to the schematic of front piston-rod-upward and rear piston-rod-downward produces higher mode stiffness and damping than the other installations. The dynamic responses are studied between the vehicles with HIS and UCS. Moreover, the damping coefficients are evaluated with the modal analysis method. The obtained results indicate that (1) the top and bottom DDVs mainly affect the vehicle body’s pitch motion and bounce vibration, respectively, (2) the PDVs are able to alter the load distribution among wheel stations, and (3) damping parameters can be designed to minimize the vehicle body’s pitch motion.