| The application prospects of CVT,especially metal pushing V-belt CVT,are very good.Therefore,the research and development of CVT technique is of great importance.At present both domestic and foreign researches attach no enough significance on the effect of metal pushing V-belt transmission mechanism and the characteristics of the hydraulic control system on traditional effciency and control stategy,and the consideration for the mutral influence of different control systems and different driving condition control strategies is not sufficient.These have restricted further enhancement of the performance of metal pushing V-belt CVT,such as its driveability and fuel consumption,and also keeps the transmission efficiency of metal pushing V-belt CVT to be at a low level.In response to these problems,this study has done the following work:First,the mathematical models of the element compressive force and the ringtensile force are established to analyze the effect of the element compressive force and the ringtensile force on torque transmission under different transmission ratio and load,and to further deduce the mathematical model of torque transmission which forms the push belt transmission.The main reason for the power loss of push belt transmission is examined and the mathematical models for several main kinds of power loss are set up.Through simulation experiments,the change of several kinds of power loss with the change of torque ratio is further explained,and the effective methods to improve the transmission efficiency of metal pushing V-belt transmission are obtained.The mathematical model of the damping force and ratio hydraulic control system is formed,the main units of which are the proportional reducing valve and the inverse-proportional relief valve,The influence of the lagging characteristic of the hydraulic control system on the working effect of CVT,and the major components which cause power loss in the hydraulic control system and some related questions,are studied.The focus is on forming the mathematical model for power loss caused by the match problem of the pump and the proportional reducing valve to analyze the mechanism of power loss.Some improving measures for the above questions are also provided.Different working models for metal pushing V-belt CVT,driveablity model and fuel-economical model,are established according to the needs of drivers.Based on the needs of two different models in actual driving conditions,the best economical working route and the best driveablity working route for engine are stipulated seperately for the preparation of realizing the real-time match of CVT.Next,the comprehensive control strategy is designed on the basis of the working characteristics of the hydraulic control system,the mechanism of metal pushing V-belt transmission,and the match of engine and the pushbelt CVT.The damping force control strategy based on fuzzy PID,the ratio control strategy based on lagging characteristic,the control strategy of CVT clutch starting based on different stages,the torque converter lock-up working strategy based on transmission efficiency,and the velocity control strategy of CVT automobile based on engine brake,are advanced.All control strategies are coordinated together by stipulating the working scope of each strategy.Finally,the original MG-ROVER transmission system test-bed of Nanjing Automotive Engineering Research Institute is reformed,and intergrated with dSPACE/Simulator the CVT test-bed based on HIL which can simulate road test is established.During the later period,to further confirm the above research work,the electronic hydraulic control system is installed in the Fiat Paliol.3L car and tested on road.The analysis of the experiment data shows that the process and the data of the test reflect the main characteristics of metal pushing V-belt CVT and control strategy,and each contral stategy can improve each function of automobile if giving full consideration of the working characteristics of the hydraulic control system.Moreover,all control strategies are coordinated together to meet different needs under different driving conditions and truly put into effect the comprehensive control of metal pushing V-belt CVT.The innovations of this paper are:(1) explaining and quantizing the mechanism of metal pushingâ…¤-belt transmission power loss by mathematical models on the basis of establishing the mathematical models of the element compressive force and the ringtensile force,advancing the biggish effect of the torque ratio on the transmission efficency of metal pushing V-belt CVT.The torque ratio was kept up to a idea state by control the the damping force,the transmission efficency of metal pushingâ…¤-belt CVT was further improved;(2) verifying the effect of the working characteristics of the hydraulic control system on the control performance and transmission efficiency of metal pushingâ…¤-belt CVT by analyzing the mathematical models and proving by tests;(3) advancing the clamping force control strategy based on fuzzy PID, which rationally controls the clamping force to improve the transmission efficency of metal pushingâ…¤-belt CVT;(4) advancing the ratio control strategy based on the lagging characteristic,which improves the driveability of the automobile during fast acceleration and the fuel economy during slow acceleration;(5) advancing the control strategy of CVT clutch starting based on different stage,which improves the starting function of CVT automobiles by pertinent control methods designed according to the working characteristics of different stages;advancing the velocity control strategy of CVT automobile based on engine brake,which futher gives full play of CVT under special driving conditions on long downward slope.
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