Investigation on Nonlinear Speed Regulating System in a High-Pressure Common-Rail Diesel

Currently, the digital electronic speed regulator and electrical fuel injection system can only achieve independent control on engine speed and common-rail pressure, respectively. Aiming to enhance the control performance, this study proposed an idea of designing a control module to simultaneously control the diesel engine speed and common-rail pressure. Firstly, differential equations of the speed regulating system in a high-pressure common-rail diesel were derived, and a multi-input coupling nonlinear mathematical model was established by quadratic polynomial fitting, in which engine speed and common-rail pressure were used as state variables and fuel injection quantity and pulse width of fuel supply solenoid valve were used as input variables. Then, the established model was treated as an affine nonlinear system for further analysis, and a sliding-mode variable structure controller was developed. Finally, MATLAB simulation and bench test were performed to examine the control performance of the engine speed and common-rail pressure using PID and sliding-mode variable structure control algorithms respectively. Both simulation and bench test results revealed that the sliding-mode variable structure controller exhibited many advantages including small overshoot, fast response and strong resistance to interference.