Modeling, control, and validation of an electro-hydraulic steer-by-wire system for articulated vehicle applications

X-by-wire control systems in automotive applications refer to systems where the input device used by the operator is connected to the actuation power subsystem by electrical wires, as opposed to being connected by mechanical or hydraulic means. The "X" in the X-by-wire is replaced by "steer", "throttle", and "brake" to represent the steer-by-wire, throttle-by-wire, and brake-by-wire systems. Common to all of these subsystems is that the operator control input device (i.e., steering column, acceleration pedal, and brake pedal) is not connected to the actuation devices mechanically. Rather, it is connected to an embedded computer which, in turn, sends the control signals to the actuation devices. Current state of art steering systems used in articulated vehicles are hydro-mechanical type systems, i.e., the steering column motion is transmitted and amplified by the main hydraulic circuit by hydro-mechanical means. This paper presents a new steer-by-wire (SBW) system which we designed, modeled, analyzed, and tested on wheel type loader construction equipment. The simulation results and tests conducted on a prototype development vehicle (a medium size wheel type loader) show very good agreement. The control algorithm is modeled using graphical modeling tools similar to Simulink and StateFlow. A real-time control algorithm is implemented on a Motorola 68332 microprocessor-based embedded controller. The operational performance of the steer-by-wire system has been convincingly demonstrated.