Research On Fault-Tolerant Steer-by-Wire System Of Wheel Loader

The continuous development of modern science and technology pushed the overlapping and penetrating between different subjects greatly. And due to the application of the microelectronic technique, computer technology and the electromechanical integration to wheel loader, the comprehensive technique of wheel loader leap onto a new step. The integration of electronic technique, micro-computer, sensor, electro-hydraulic servo and control system remakes the traditional wheel loader. The modern wheel loader is more preponderant in work efficiency, task quality, environmental protection, serviceability and automation. And it is moving forward to further intellectualized direction. The steer-by-wire technology replaces the traditional mechanical or hydraulic juncture by connecting and controlling all the component of steering system through micro-electronics technology, using sensors to collect the data of steering , vehicle corner, vehicle speed, turning resistance and transfers them to the controller on the vehicle. Then the controller processes these signals according to the given control algorithm and outputs actuating signals to control the steering degrees of vehicle so as to realize the steering. The steer-by-wire system on wheel loader has advantages in transmission ratio tunable, road sense clever and vehicles assembly simply. Besides, the design of force and angle transfer characteristics becomes freely. It is a significant innovation in the vehicles steering system. But the steer-by-wire system can replace the existing whole hydraulic pressure steering system or not lies on the reliability, stability and system cost of the steer-by-wire system. And the most important is the reliability and stability of the system that lies on the fault-tolerance capability. Fault-tolerance means that the researched object allow system failure and won't be out of control or breakdown for fault, fault-tolerance control is that the closed-loop control system can remain stable and has perfect characteristic when sensors, controllers, actuators or other parts of the system is wrong. The design of fault-tolerance control system mainly includes two parts: fault diagnosis and fault-tolerance controller design. The former checks the kinds and position of fault (failure separation), degrees and occurrence time(failure recognize). Generally speaking, fault diagnosis methods involve: based on mathematical model, based on signal processing and knowledge. The latter includes hardware fault-tolerance design, software fault-tolerance design, and other fault-tolerance design. Among them, the most important and effective method is the hardware fault-tolerance design that rely on adopting multiple hardware. In this paper, the fault-tolerance steer-by-wire system on wheel loader uses hardware redundancy fault-tolerance technology. Steering wheel corner sensors and vehicle corner sensors have triple modular redundancy, controller and its communication adopts duplication redundancy. At the same time, the system takes software fault-tolerance technology and resolution redundancy technology to ensure the fault-tolerance capability and reliability of the system.This Ph.D. dissertation is funded by the project (No.2005083) named "Application of Steer-By-Wire technology in wheel loader" from JILIN Education Department and the project named "Research of Steer-By-Wire technology and Application on Wheel Loader" funded by corporation. Based on domestic technology level and tracking foreign advanced technology, the fault-tolerance steer-by-wire system on wheel loader is researched and designed. The system integrates electro-hydraulic proportion control technology, computer technology and fault-tolerance control technology etc., realized the transform between two steering sensitivity modes in the light of the wheel loader actual operating modes. At the same time the system has a high reliability and safety.This dissertation fulfilled research objective as following: 1,The research achievements of turning technology of wheel loader and steer-by-wire technology domestic and abroad were surveyed and worked up, and the characteristics, operating principle, the feasibility and progress of the technology applied to the articulated wheel loader steering system is analyzed.2,The design proposal of"fault-tolerance steer-by-wire system on wheel loader "was put forward. This system adopted fault-tolerance control technology with high reliability, adjustable steering ratio and steering sensitive.3,Finite state machine (FSM)was used to establish the system dynamic behavior model, and it was applied to fault diagnosis of the system.4,The control algorithms for steer-by-wire system were researched.MATLAB simulation results showed that Fuzzy control algorithm has quick response time, high stability and control precision.5,. Markov state transition diagram was applied to establish the steer-by-wiresystem reliability analysis model which was used to analysis the system reliability and calculated the reliability of the system.6,Embedded controller of the fault-tolerance steer-by-wire on wheel loader was developed, contains hardware design and software design. Because of the complicated operating modes and the bad working conditions, the wheel loader will be influenced by all sorts of disturbances and the system failure will occur, therefore the system anti-jamming design was done to guarantee the system stabability and reliability under the complex working conditions.7,Some experiments were done for the fault-tolerance steer-by-wire system, including fault diagnosis algorithm and fault-tolerant performance verification test ,the control algorithms verification test. Test and simulation results showed that the fault-tolerance steer-by-wire system on wheel loader has high reliability, and it can satisfy the requirements of real-time, stability and accuracy requirements.8,summarized the steer-by-wire technology on wheel loader , and put forward the research expectation in the future.The main innovations of this dissertation are as follows:1,The fault-tolerance control technology was applied to the steer-by-wire system on wheel loader for the first time domestically.Researches on the steer-by-wire technology on vehicles are fewer in our country than others. Especially, the reliability study is almost blank. The fault-tolerance control technology and the steer-by-wire technology were integrated for the first time domestically. The design scheme of the fault-tolerance steer-by-wire system on wheel loader was put forward in this dissertation, and the theory and experiment researches were taken about it. The results showed that the system has high reliability, and can satisfy the requirements of real-time, stability and accuracy requirements.2,The fault-tolerance steer-by-wire system fault diagnosis algorithm was put forward.In this article, the fault state of the fault-tolerant steer-by-wire system were researched and classified in detail. Finite state machine was used to establish the system dynamic behavior model, and according to the model, fault diagnosis algorithm was proposed. Test results verified the correctness of the algorithm.3,Researches on the steering control algorithm of the steer-by-wire system.Fuzzy control algorithm was chosen through MATLAB simulation results compare. Simulation and test results showed that Fuzzy control with faster response time and the strong anti-interference capability can satisfy the requirement of actual steering system. Research expectation of the future is proposed in this dissertation:1,Take more experimental study to verify the performance including real-time, accuracy and stability of the steer-by-wire system in different operating conditions. Set various fault conditions comprehensively by the fault injection method to certify the fault tolerance and reliability of the system.2,Analysis the infection of the speed, tire pressure and bucket height .Make the system control model and the actual operating mode more closer, and improve the system performance further.3,Research the road sense feedback control to enhance the controllability of the vehicle.4,Carry out the integration control study, and take the steer-by-wire as a part of the entire vehicle control system. Prepare for the integration of the engine control, speed changing, steering, braking, remote fault diagnosis, remote machine cluster operating and so on.5,Strengthen the applied research, optimize the system and reduce the cost in order to prepare full for the production.