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proportional directional valve based automatic steering system for tractors

Frontiers of Information Technology & Electronic Engineering 2016年第5期17卷 458-464页

作者： Jin-yi LIU Jing-quan TAN En-rong MAO Zheng-he SONG Zhong-xiang ZHU Beijing Key Laboratory of Optimized Design for Modern Agricultural Equipment China Agricultural University

Most automatic steering systems for large tractors are designed with hydraulic systems that run on either constant flow or constant pressure. Such designs are limited in adaptability and applicability. Moreover, their control valves can unload in the neutral position and eventually lead to serious hydraulic leakage over long operation periods. In response to the problems noted above, a multifunctional automatic hydraulic steering circuit is presented. The system design is composed of a 5-way-3-position proportional directional valve, two pilot-controlled check valves, a pressure-compensated directional valve, a pressurecompensated flow regulator valve, a load shuttle valve, and a check valve, among other components. It is adaptable to most open-center systems with constant flow supply and closed-center systems with load feedback. The design maintains the lowest pressure under load feedback and stays at the neutral position during unloading, thus meeting the requirements for steering. The steering controller is based on proportional-integral-derivative(PID) running on a 51-microcontroller-unit master control chip. An experimental platform is developed to establish the basic characteristics of the system subject to stepwise inputs and sinusoidal tracking. Test results show that the system design demonstrates excellent control accuracy, fast response, and negligible leak during long operation periods.

关键词： Automatic steering system Hydraulic circuit proportional directional valve proportional-integral-derivative(PID) control

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A differential control method for the proportional directional valve

引用

Journal of Zhejiang University-Science C(Computers and Electronics) 2014年第10期15卷 892-902页

作者： Bo JIN Ya-guang ZHU Wei LI De-sheng ZHANG Lu-lu ZHANG Fei-fei CHEN The State Key Laboratory of Fluid Power Transmission and Control Zhejiang University Ningbo HOYEA Machinery Manufacture Co. Ltd.

For the proportional directional valve controlled by two proportional solenoids, the normal control method(NCM) energizes only one solenoid at a time. The performance of the valve is greatly influenced by the nonlinearity of the proportional solenoid, such as dead zone and low force gain with a small current, and this effect cannot be eliminated by a simple dead-zone current compensation. To avoid this disadvantage, we propose the differential control method(DCM). By employing DCM, the controller outputs differential signals to simultaneously energize both solenoids of the proportional valve, and the operating point is found by analyzing the force output of the two solenoids to make a minimum variation of the current force gain. The comparisons of the valve response characteristics are made between NCM and DCM by nonlinear dynamic simulation and experiments. Simulation and experimental results show that by using DCM, the frequency response of the valve is greatly enhanced, especially when the input is small, which means that the dynamic characteristics of the proportional valve are improved.

关键词： Differential control method Frequency response proportional directional valve Spool displacement feedback

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