Steer-by-wire (SBW) systems in a passenger car can improve vehicle steering capability and design flexibility by replacing the mechanical linkage between the steering wheel and front wheels by a control circuit. The steering controller, however, should provide good performance in response to driver's input signal. This includes fast response, absence of overshoot or oscillatory behavior, and good accuracy with minimal steady-state error. In this paper, an optimal control strategy based on observed system states is proposed and implemented on an electrohydraulic SBW system of a passenger car. First, a linear mathematical model is developed using gray-box system identification techniques. A standard input signal, pseudorandom binary sequence (PRBS), is designed to stimulate the system in the concerned bandwidth. Then, a linear-quadratic regulator (LQR) together with a full-state system observer is designed. Based on simulation, the LQR parameters and the observer poles are chosen to satisfy the aforementioned performance criteria for good steering. Finally, the control strategy is applied in a real-time environment to test the tracking capability, where the system is given high-rate reference signals (relative to the human rate of steering). The results show that the steering system tracks the reference signal with high accuracy even in the existence of high external force disturbances.
During taxing, the aircraft can be treated as a three wheeled vehicle. This work deals with the dynamic behavior of this three-wheeled vehicle during the steering mode. Conventionally the hydraulic power steering systems incorporate either hydraulic or electrohydraulic servo-systems. Nevertheless, Part 1 of this paper deals with the dynamic behavior of a steering system incorporating three directional control valves of poppet type in one housing. A nonlinear mathematical model of the directional control valve assembly was developed and used to simulate the valves dynamic behavior. The validity of the simulation program was evaluated in the steady state by comparing simulation results with results of experimental work conducted on the studied valves. The construction of the mechanical parts is explained and the kinematics of the steering system was analyzed and presented. The transient response of the steering system incorporating the directional control valve assembly was calculated, presented and discussed.
The dynamic performance of a turboshaft gas turbine engine is investigated in this paper. The air flows inlet to the engine and to the power turbine, are controlled by means of two guide vanes cascade. The displacement of the inlet guide vanes is controlled by means of two electrohydraulic servo actuators. The fuel flow rate is controlled by another electrohydraulic controller incorporating a series pressure compensated flow control valve. The equation describing the basic system subsystems and controllers were deduced and applied to develop a simulation program. The simulation program of the electrohydraulic servo controllers was validated experimentally. The engine dynamic performance is studied theoretically using the developed computer simulation program. Simulated results are shown for the transient response of the engine air and fuel flow control systems and its effect on the engine performance. The simulation results of engine air flow control show an agreement with the validated experimental results.
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