| With the rapid development of national economy and continuous growth of highway mileages, passengers bus, as the main highway transportation equipment, has increased rapidly in recent years, and its safety, energy consumption are concerned increasingly because of carrying more passengers, longer transportation distances, more fuel consumption. Currently, fixed characteristic of Hydraulic Power Steering system(Abbr. HPS) is used in bus, and steering pump output flow design principle is to meet the maximum steering resistance condition (spin steering or low-speed steering).Steering resistance decreases in high speed, but output power doesn’t decrease, so, collision, rollover and other accidents are caused easily because drivers’"road feel" in high-speed reduces and over-steering appears in curve-way steering, emergent steering condition. In addition, hydraulic pressure often exits and heat is lost not matter steering or not, and it increases invalid energy consumption. Currently, electric power steering and electric pump steering system used in passenger cars and light commercial vehicles can’t meet the actual steering power requirements due to small power. Electric controlled hydraulic steering system has been used in middle and heavy bus with good applications and effects overseas. Some research work is just carried out in recent years and large gap exited compared with the abroad, and some key technologies hadn’t made breakthrough. So, the questions of how to design new electric hydraulic steering system to coordinate the low-speed steering easiness and high-speed handling stability, and reduce energy consumptions are eager to be solved, and that will be of great important.A new type Electro-hydraulic proportional valve Controlled Hydraulic Steering system (Abbr. ECHPS) used in bus can inherit the advantages of HPS by assembling electro-hydraulic proportional valve in it, and adjust proportional valve flow at different vehicle speed to realize variable power characteristics. It can not only improve the safety at high speed effectively, but also reduce energy consumption in no-steering condition. Due to complicated driving conditions, variable power characteristics of new type ECHPS must be of high control precision. In view of the feasibility of engineering application, proportional valve must have good structural integrity and cost performance. In order to solve the key technologies, ECHPS design method, control theory and application, key parts design are eager to make breakthrough. To solve these problems, ideal power characteristics design, the proportional valve structural design, accurate valve core position control based on adaptive dynamic surface control, vehicle performance simulation and experiment with ECHPS, were studied systematically. The main research work are as follows: Firstly, based on analyzing the mechanism and influence factors of vehicle steering resisting moments, the bus AMESim model including steering system, whole vehicle model, and tire model was established, and equivalent steering moments at different speed were simulated and obtained with assembling HPS. Through studying GM, TOYOTA, and JiLin University research work on drivers’preferred steering torque, and considering ECHPS performance requirements and characteristics, drivers’preferred steering torque were obtained for the first time at safe speed through manually on line adjusting steering power in bus road tests, and the resutls filled the test data in this field. Combined with the simulation and test results, the power characteristics of ECHPS were designed and calculated, and the ideal variable power characteristic curve that met the bus’performance requirements was obtained.Secondly, Aiming at the key technologies of that the hydraulic dynamic force and fiction force influence the valve dynamic characteristics obviously, the new type electro-hydraulic proportional valve with integrated structure of armature iron and valve core was designed creatively. Based on proportional valve Ansoft electromagnetic simulation model, the key structure parameters such as copper chamfer and copper position were studied and optimized. The steady-state control characteristics test of the improved and optimized valve were carried out, and the test and simulation results were consistent basically and showed that the new proportional valve had the good horizontal force-displacement characteristics and steady-state control characteristics.Thirdly, Aiming at the characteristics of bus variable driving condition, sensitive electromagnetic and hydraulic parameters to ECHPS, strong external disturbance, proportional valve control strategy based on adaptive dynamic surface control strategy was proposed by using the advantages on processing nonlinear and parameter uncertainty, and proportional valve RBF neural network adaptive dynamic surface control system was designed by constructing Lyapunov function to ensure system stability, designing first-order filter to eliminate high order differential items, using neural network to approach uncertain function, and stability analysis was carried out at last. Displacement output response characteristics under different control methods and different dynamic signal input were carried out, the results showed that, using neural network dynamic surface control can improve the proportional valve valve core position precision, shorten the response time, have strong anti-jamming capability, solve the key problem of the valve core displacement real-time precise control under the whole vehicle condition.Fourthly, new type ECHPS vehicle model and control system model were established, bus handling stability performances simulation under different typical conditions was carried out, the comparison analysis showed that, steering easiness of ECHPS at low speed was fine as well as HPS, and the average steering torque increased at high speed, and better "road feel" was obtained. It means that ECHPS control system of bus can meet the requirements of both low-speed steering easiness and high-speed handling stability. In addition, the current compensation torque control strategy was designed to ensure the safety in case of emergent and rapid steering angular velocity input.Fifthly, The ECHPS controller hardware including speed signal、displacement signal processing unit and proportional valve driving unit based on Infineon XC886were designed as well as the controller software which includes main program of ECHPS speed,displacement signal collection and PWM output subroutine, and This can provide the foundation of both test bench and bus experiments.Finally, new type ECHPS variable power characteristics bench test was carried out, and it is the first time handling to carry out the stability performances road test of SLK6118bus equipped with ECHPS including lemniscates test, no-load and full-load slalom test, on-center handling test. Besides, the energy consumption comparison test was also the first time to be carried out. The results showed that, ECHPS can acquire low-speed steering easiness as well as traditional HPS. Steering torque peak value and standard deviation increased by20.36%and19.15%respectively when70km/h in slalom test, which means drivers’"handling feeling" increased obviously. The steering torque gradient value increased by55.31%on Og lateral acceleration when70Km/h in on-center handling test, which means new ECHPS enhanced high speed "road feel" notably; ECHPS can save100W/min power under the same working condition in energy comparison test.To sum up, The new type bus ECHPS has compact structure and engineering application based on traditional HPS, and can acquire good low-speed steering easiness and high-speed "road feel",and also enhance energy-saving effects obviously. |
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