Continuously Variable Transmission Control System And Hardware In The Loop Simulation

The target of normal transmission test bench is to simulate vehicle's running condition precisely. This kind test bench is characterised by complex, expensive and energy-intensity. To overcome these disadvangages, study on design theory and experiment method of light duty hardware in the loop(HIL) CVT test bench was carried on. The main work as follows:①Novel HIL test bench construction. A new kind HIL structure was presented by involving a real CVT in simulation loop. Compared to normal test bench, engine and load equipment were replaed by double relative small motors, and electric-close-loop bench was established. Accuracy was ensured and while construction cost and power dissipation was reduced dramatically.②CVT main performance test. 1) Experiments on clamping-force static and dynamic performance were carried on. According to the results, system pressure static value was mainly determined by the applied voltage, and has a good linear character in main working range. System pressure has a good dynamic performance which could adapt the transient change of working condition. 2) ratio-shift-rate performance was tested. According to the results, ratio-shift-rate has no relationship with the torque transmitted and the rotate speed except in low speed. A method calculating ratio-shift-rate was presented with on need sampling primary pressure value. 3) Dissipation and efficiency was measured. According to the results, dissipation and efficiency have no relationship with speed, and were mainly determined by ratio and primary torque. When the ratio is less than 1, the torque loss increased rapidly with the decline of ratio. When the ratio is large than 1, the torque loss has no obvious relation with ratio. As a result, it is possible to measure efficency with small poer motor instead larger motor or engine.③Study on control hierarchy and system modeling. 1) CVT control system was devided into driver, control strategy, control algorithm, acturator and transmission system, which correspond to proposing demand, setting target, making solution method, achieve the target, and satisfying the demand. 2) Based on main components models, transmission system model were established. Further more, integrating simulation model and test bench, CVT HIL system was set up.④Study on low hierarchy control algorithm. 1) Clamping-force semi-close loop control algorithm was presented. Control value consisted of basic value and correction value. Basic control value was available by lookuping pressure static character table. Correction value was calculated by close loop control algorithm. Controlled object information was taken full adavantage. Dynamic performance and roubustness were improved. 2) Traditional constant safety factor method and novel slip-control method are extreme different methods of clamping force control strategy. To integrate advantages of both methods, clamping force control strategy base on dynamic safety factor was presented. Study of theoretical clamping force relevant parameters and engine torque wave characteristics was carried on. Safety factor was determined according to engine torque variation trend and range. Target pressure calculating process was described. Simulation and experiment results showed that by adopting dynamic safety factor, transmission reliability was ensured and the performances of clamping-force and fuel efficiency were improved. 3) To enlarge valid ratio shift range of continuously variable transmission, active coupling control strategy was proposed. Utilizing the coupling effect between clamping force and speed ratio, the shift speed is improved by conditioning the pressure of both primary and second pulleys'hydraulic cylinders. System pressure safety must be ensured to satisfy the clamping force which could meet the requirement of torque transmission. As a result, real ratio tracks the target more rapidly and shift speed range is enlarged. Studies on active coupling control strategy was carried on, which included shift speed, clamping force related transmission reliability, fuel economic, dynamic performance, hard condition adaptability, and shift speed related comfortableness. Simulation results showed that by adopting active coupling control strategy, reliability, economic, and comfortableness were ensured while ratio tracking performance and power performance were improved.⑤Study on high hierarchy control strategy. 1) At the aim of highest efficiency of CVT, an optimization algorithm was designed by considering the efficiency of engine and the main dissipation component. Duel-state hydraulic torque converter (TC) was also included in the algorithm. Control strategy based on power demand was designed in order to realize higher efficiency of whole system. The highest efficiency operating condition which satisfies the power demand is set to be the control objective. As a result, the best economical efficiency is available. While the power demand exceeds the maximum output power under the current vehicle speed, the maximum output power condition is set to be the control objective. As a result, the best dynamic performance is available. TC ideal control line was calculated based on which practice operating line was designed. 2) To improve the drivability of CVT vehicle under hard acceleration condition, a compensation control strategy based on effective power was proposed. Different from normal control methods which are dependent on vehicle and road environment information, the novel strategy set CVT input power as the control objective directly. Power compensation mode was ranked to four classes: holding power, zero power, increasing reserve power, and synthesis control. So, quantification criterions for setting transition curve and optimizing transient condition performance are available. Simulations and experiments results showed that power compensation control strategy could eliminate the harmful effect of power decreasing caused by engine-flywheel inertia and too fast ratio shift-rate and drivability was improved under transient condition.The achievement in this paper not only presented a novel solution for CVT performance test and control system study, but also provided a referrence method for other kinds automatic transmissions and gear boxes. Further more, a relative universal HIL simulation method for transmission system was available.