Research On The Nonlinear Speed Control System Of Diesel Engine With The Variable Structure Control Theory

The diesel engine occupies greater and greater proportion in the engine. As fuel consumption and environment laws and regulations are more and more stringent, attention has been paid to electronic technology applied in the diesel engine. The electronic governor is a very important part in the automatically controlled system. In order to obtain better speed control result, research on the control algorithm must be carried out. So, after analyzing, designing the electronic governor with the sliding variable structure control algorithm is presented and corresponding work has been done. Moreover, relevant researchs have not been found.The concept of the instantaneous speed of the diesel engine has been explained. The measurement method of speed and speed transduction have been introduced. One dimension linear model of the diesel engine is introduced. Based on 4135 diesel engines test data, such as the speed of diesel engine, the mean indicated pressure and the mean effective work etc., and the indicator diagram, the mean indicated pressure and the mean effective pressure can be calculated. Under the environment of MATLAB, utilizing the non-linear relation among speed, fuel injection amount and the mean indicated pressure which is obtained by using a polynomial fitting method, the non-linear model of the diesel engine speed control system is set up.Based on the non-linear model, the non-linear differential equation of speed control system is converted into a high-order differential equation, one imitative non-linear system, linear brief type and discrete-time system form separately. Firstly, the equal control and sliding mode movement equation are obtained. Secondly, to get sliding mode variable structural controller, a suitable convergence law is selected. Thirdly, the sliding mode variable structural controller that uses a non-linear switching surface, non-linear switching surfaces and one-order dynamic sliding mode variable structural controller are designed. Finally, MATLAB simulation of the non-linear approximate model is carried out according to steady and non- steady vehicle road characteristic separately.On MATLAB software platform, according to data of the 4135 type diesel engine test, the working MAP picture of the diesel engine is set up. And under MATLAB simulation environment, the working course simulation of diesel engine speed control system which uses sliding mode variable structural control algorithm is developed according to the linear switching surface, the non-linear switching surface, non-linear switching surfaces and dynamic sliding mode variable structural control separately. Finally, the simulation results of the sliding mode variable structural controller and the PID controller are compared. The conclusions are as follows:1.The non-linear model of the diesel engine speed control system is correct;2.The control result of the sliding mode variable structural control algorithm to a non-linear system is good;3.Comparing the simulation result of the sliding mode variable structural control with the traditional PID control, it shows that the sliding mode variable structure control is able to respond quickly, robust against system parameters and external disturbances, and able to keep the system stable, obtain strong robustness. But shaking is a problem.For speed control system of the 2135 type diesel engine, a step-by-step electrical device which is the executive organization of the electronic governor to decide rack position of the oil pump. First of all, through a large number of experiments, experimental data could be obtained. Then, analyzing experimental data, the speed of the diesel engine- the steps of electrical device- the rack position-the fuel injection amount relation can be obtained. Thirdly, the working course mathematical model of the 2135 type diesel engine speed control system under MATLAB/Simulink environment could be set up; Finally, simulations of the sliding mode variable structure controller, discrete-time system, self-adaptation form, the saturation function form sliding mode variable structure control and variable structure control- PID methods are carried out separately. And the simulation results are compared with traditional PID controller which shows that for the sliding mode variable structure control, overshoot is small and response is fast.Based on simulation results of the sliding mode variable structural control to be correct, the 2135 type diesel engine MATLAB simulation platform of shelf test is put up by using an industry computer and shelf tests of the 2135 diesel engine nonlinear speed control system for the sliding mode variable structure control algorithm which is real-time online control is carried out. Comparing speed data gathered for the sliding mode variable structure control algorithm with data gathered for PID, it can be found out that for the sliding mode variable structure control, the steady state error is small and overshoot is smaller. But shaking exists.