| Because of the good drivability and comfort, CVT becomes more and more popular in the market, clamping force control and ratio control is one of the most difficult technologies of CVT. Based on the International Cooperation Project "New generation Continuously Variable Transmission with higher Torque Density", to decrease the CVT power consuming, in this paper some new design ideas and new structures are cited, which are evaluated bv a lot of test. The test results shows that CVT power consuming can be significantly decreased by this control method and also the vehicle economic is improved. The main research content includes:1Hydraulic system is the actuator of CVT, clamping force control and ratio control are realized via it. So, in this paper, to meet the requirements of lower power consuming, higher torque density and higher efficiency, starting from the hydraulic principle, the creative new structure and new strategy is detailed described.(1)the dual-acting pump is used, not only meet the flow requirements under different working conditions, and also can greatly decrease the overflow power loss is decreased.(2)Taken the proportional solenoid as the pilot valve, which satisfies the precondition of control precision, the structure complexity and manufacturing cost are both reduced.(3) The primary pressure is independent, i.e, the primary pressure does not depend on the secondary pressure, so the primary cylinder can be designed more freely and the CVT structure can also be better than the dependent circuit.(4) The primary/secondary pressure can be controlled respectively without depending on each other, which can enable lower system pressure. By this method the control precision of clamping force control and ratio control can be both improved. At last, the mathematic model of hydraulic components are built up, then the dynamic performance of hydraulic system is simulated. Simulation result and test result show good consistency after comparison.In the traditional control strategy, the power loss is mainly caused by the variator because of the1.3safety factor. To guarantee the torque safety and to get rid of belt slip, one control scheme without any sensor added is tested on the clamping force test rig. One importance relation is founded that Fαx|η=max<Fαx|i=imin<Fαx,safe. Based on this formula, the state equation is set up, which takes the clamping force as input and ratio as output. The input conditions can be adjusted to get the max/min output value. This auto extreme value seeking method during slowly changing process is called extreme-seeking control. Based on this principle, one extreme-seeking controller is designed and tested, the test results shows that it is effective for efficiency increasing under stable working condition.3Extreme-seeking controller can reduce the clamping force and increase the transmission efficiency. But for ratio changing process, the dynamic tracing is slower. Consideration to belt safety under dynamic condition and high efficiency under stable condition, in this paper, the comprehensive control of extreme-seeking control and traditional safety factor control is one main research content, i.e, under stable condition the extreme-seeking method will be used, while under unstable condtion the extreme-seeking will be disabled and traditional method will be used. This comprehensive control can not only increase the robustness of ratio control and the ability of anti-shock, also the vehicle economic performance can be improved.4The comprehensive control method needs to be evaluated by fatigue test and reliability test. Starting from the variator failure mechanism, to find the key factor that causes control failure, the fatigue and reliability test rig is developed, then the test method and test data are analyzed. The road test can reflects the CVT status more directly, so the25,000kilo-meter road test is also carried out. The oil inspection result shows that the wear is of the normal level. The reliability of this comprehensive control is proved by rig test and road test.5The embedded control system is one of the key technology in CVT, also is one bottleneck technique. Only after this technology is grasped, the CVT industrialization can be realized. The embedded system includes:the integrated control of power system(i.e, comprehensive control of engine and CVT), starting clutch control, torque convertor control, ratio control, clamping force control, failure diagnosis and the CAN bus communication, Etc. The embedded control system can be divided into hardware and software. In this paper, based on the previous working foundation, the failure diagnosis system is further perfected, which promoting the self-developed software move from test-room towards market. The software is proved can endure the market test. |
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