| Tractor is an essential operational tool in agriculture. With the development of society, people require both efficient and energy saving tractor. Hydraulic suspension has a direct impact on operating efficiency of tractor, in china, suspension control based on force-position adjustable in traditional medium and large tractors has realized, but only manual adjustment, and it need more people to support. At abroad, some large tractor factories have partly realized intelligent control, for example, automatic control system based on force and position adjustment hydraulic suspension, multi-signal real-time display system, and so on, greatly improving the operating efficiency of the tractor. In recent years, the study about force-position-slip control system has been aroused, but in China it only exists in the experiment.The main objective of this subject is to carry out slip control system on the basis of hydraulic suspension force-position adjustment system which has been researched for some time in our laboratory. The purpose of the slip control is to change the work resistance of the tractor through the adjustment of the plowing depth and ensure the slip rate stabilized around the setting value, so as to realize acceleration slip regulation and improve the traction efficiency of tractor.The paper introduces the measurement and analyses of tractor’s slip based on Lab VIEW firstly. The main purpose of the slip measurements is to test the accuracy of sensor, and analyze the characteristics of slip in different operating depths and different operating soil, which can provide empirical evidence for the control system. In the measurements, encoder was used to measure RPM (Revolutions per Minute), radar was used to measure the speed of tractor. Actually, the measurement amend the testing program, get a more accurate measurement methods finally, and the characteristic data of the slip.In the paper, the mathematical of the system was built, and its Matlab/Simulink model was set up by computer. PID, Fuzzy, Fuzzy-PID controller were also built for hydraulic suspension based on slip, and then, these three controller were embedded to the Matlab/Simulink model and Simulink the system. These three controllers’ performances were contrasted, including responsiveness, adaptability, anti-interference performance. It is observed that PID controller is sensitive to the variation of parameters, it has a bad robustness. Fuzzy and Fuzzy-PID controller have similar control effect, but Fuzzy-PID needs more variable, so as a result, Fuzzy controller was more suitable for this system.The paper designed a microcontroller-based tractor hydraulic suspension controller, Freescale’s XS128was chosen. Hardware circuit contains the smallest system, signal acquisition circuit, D/A circuits, button circuit, LCD display circuit, amplifier, etc. The software program is based on C language, including the main program, LCD display, D/A converter, slip control, fuzzy PID controller, rise and fall of hydraulic suspension. In summary, the system can display the signals of slip and speed, control the rising and setting of hydraulic suspension, ensure the slip rate stabilized around the setting value in real time and accurately.At last, in the hydraulic bench some experiments were carried out, including responsiveness, adaptability, anti-interference performance, according to the feedback, adjust the control strategy constantly. Ultimately, a more comprehensive control strategy was got. Finally, the control system was tested on hydraulic suspension test-bed in the laboratory, after adjustment, it can realize all the designed features basically. |
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