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This paper presents a comprehensive model of a hydraulic power steering system for predicting the transient responses under various steering inputs. The first principles of multi-body system dynamics and fluid mechanics are applied to model key nonlinear components and in particular, the rotary spool valve, piped fluid lines, the frictional coupling between multiple contacting surfaces with use of the empirical data. The system model, which integrates together all of lump masses, fluid line elements and hydraulic components, is formulated using the state space representation approach. It contains time-variant coefficient matrices resulting from the nonlinearities in the fluids systems. A numerical simulation scheme is developed to obtain the system transient responses and the results are compared with those measured from the tests.

This paper describes vehicle dynamic models that capture the large amplitude transient characteristics of a passive Hydraulically Interconnected Suspension (HIS) system. Accurate mathematical models are developed to represent pressure-flow characteristics, fluid properties, damper valves, accumulators and nonlinear coupling between mechanical and fluid systems. The vehicle is modeled as a lumped mass system with half- and full-car configurations. The transient performance is demonstrated by numerical integration of the second-order nonlinear differential equations. The stiffness and damping characteristics corresponding to vehicle bounce, roll and pitch motions are extracted from the transient simulation. Simulation results clearly demonstrate the superiority of the HIS system during vehicle handling and stability by providing additional roll stiffness and reduced articulation stiffness.

This paper proposes an approach to optimize the economy performance of a two-speed electric vehicle (EV) by combining gear shifting schedule design and gear ratios selection. Mathematic models for the two-speed EV subsystems are developed, including those of the battery module, electric machine, the driver, transmission and vehicle. Then a procedure for obtaining the optimal gear ratio pairs and corresponding shift schedule for the two-speed EV is presented in detail. The optimized EV powertrain parameters can not only ensure that basic requirements in dynamic performance are achieved, but realize the optimal economic performance of the EV as well. In order to investigate the effectiveness of the proposed method for EV design, simulations based on the developed powertrain model is conducted using different test driving cycles, including NEDC and constant speed. Results of these simulations validate the effectiveness of the proposed optimization method.