Design And Nonlinear Control Of Diesel Electro-Hydraulic Camless Variable Valve Actuator

The fully variable valve techonology(FVVT)of diesel engine can adjust the valve lift in real time under all working conditions,optimize the combustion process in the cylinder,and improve the performance of the diesel engine.It is one of the key technologies of the intelligent diesel engine in the future.It is also one of the important technical means to realize the energy conservation and emission reduction of diesel engine.Due to its high power density and flexible structural design scheme,electro-hydraulic fully variable valve techonology is the first choice to realize diesel engine variable valve technology.However,there are still many problems to be solved in the electro-hydraulic variable valve system.Firstly,multi-objective optimization of valve lift parameters for diesel engine performance.Secondly,the complex nonlinear characteristics of friction,valve dynamics of the variable valve actuator which is used to drive the engine valve.Thirdly,to realize flexible gas distribution and controllable combustion,the high-precision valve lift tracking is necessary.To solve the above problems and promote the engineering application of camless variable valve technology,following research work has been carried out in this paper:An electro-hydraulic actuator was innovatively designed with the demand of the fully variable valve in medium and high-speed diesel engines.The valve timing,velocity and maximum lift can be changed flexiblely with the actuator.Aiming at minimizing the driving power,the structural parameters of the driving mechanism and the parameters of oil supply pressure were optimized.To carry out the valve tracking experiments,a variable valve test bench and measurement & control system were developed.Based on the test bench,the working characteristics of the camless variable valve actuator,including control valve dead zone characteristics,hysteresis characteristics,dynamic response characteristics,valve kinematic characteristics,system nonlinear leakage,and nonlinear friction characteristics were studied through experiments.The nonlinear characteristics of the valve motion boundary and parameters obtained from the experiments.Based on the driving characteristics of the electro-hydraulic camless variable valve actuator,a parametric model of valve lift is established.Taking the effective power and NOX emissions of the diesel engine as the optimization goals,the timing phase,the valve velocity and the maximum valve lift were optimized by a multi-objective optimization strategy.Based on the motion characteristics of the electro-hydraulic actuator,the optimization boundary of each parameter was determined.The response surfaces between valve lift parameters and diesel engine performance parameters can be trained by Hardy quadratic basis function.And the optimal valve lift parameters were obtained by NSGA-Ⅱ genetic algorithm and response surfaces.A high-order nonlinear model of the electro-hydraulic camless variable valve valve actuator system was established.The generation mechanism of the actuator friction force was analyzed in detail.And an improved Lu Gre friction model was proposed,which overcomed the shortcomings of the traditional Lu Gre friction model in the modeling of one-way sealed electrohydraulic actuators.The improved friction model can accurately describe the nonlinear friction phenomenon in the electro-hydraulic coupling mechanism under the condition of one-way sealing.A robust backstepping controller with integral flow feedback was proposed to compensate the actuator nonlinear characteristics.The nonlinear hysteresis of valve response was compensated by parameter tuning of the ideal valve lift.For the nonlinear friction force,based on the improved Lu Gre friction model,the friction force obtained by the model was applied to the backstepping procedure to compensate the influence of the nonlinear friction force.For the dead zone of the control valve,a smooth inverse function of dead zone was designed to eliminate the influence of nonlinear dead zone.For the nonlinear disturbance of the system,it was supressed by an extended state observer and a robust controller.The phase delay was lumped into the engine valve response delay,which can be compensate by ideal valve lift tuning.For the control valve amplitude delay,a compensation strategy based on the integral flow feedback was proposed.In backstepping controller,a feedback to integral flow error was added.Finally,the valve lift tracking control experiments of variable valve actuator were carried out.The valve lift tracking experiment results based on different friction models show that the maximum tracking errors based on the improved Lu Gre friction model can be reduced by 50%compared to the traditional Lu Gre model.The experimental results based on different controllers show that the traditional PID control method was ineffectively completely.In the high-frequency and high-speed camless variable valve lift tracking event,the controller without integral flow compensation had a large overshoot at the maximum lift position.The controller with integral flow compensation had obvious advantages.Compared with the controller without integral flow compensation,the experimental results of the controller based on integral flow compensation show that the maximum error of the valve lift can be reduced by 58.45% on average,and the average error of the valve lift can be reduced by 57.11%.The compensation method based on the integral flow feedback provides an effective solution for improving the control accuracy and response speed of the high-frequency and high-speed electro-hydraulic position servo control system.