| Hydro-mechanical variable transmission (HMT) that combines the advantage of highefficiency of mechanical transmission and hydraulic continuously variable feature is fit forheavy-duty vehicles. Shift-controlling is a key point to improve the performance of HMT.During the range changeover, the hydraulic part’s load torque reversed, the high-pressureside and the low-pressure side of closed hydraulic system interconvert. These result tooscillation of the constant displacement hydraulic part, which caused the instantaneouspower breaking and the velocity ratio oscillating along with noises. Thus it can be seenhydraulic oil characteristics is related to the shifting performance.The mathematic model of range changeover is established, the dynamic behavioralong with its affecting factors and control strategy are researched and simulated in thispaper, and the influence of hydraulic oil characteristics on dynamic behavior of HMTduring range changeover is obtained. The main content includes: (1)The speed, torquepower flow and their influence factors in range changeover is analysed, which turns outthat the factors including hydraulic oil, load torque and shift time are related to dynamicbehavior of HMT. (2)The mathematic and simulated model of range changeover isestablished, including the model of variable displacement hydraulic part, constantdisplacement hydraulic part, load torque and hydraulic oil. By simulation inMATLAB/Simulink, the conclusions were drawn that the more air in oil, the bulk modulusis smaller and the rotate speed oscillation of constant displacement hydraulic part is moretempestuous. (3)Based on the research of load torque influence on HMT dynamicbehavior, time overlap control strategy of the clutch separating and combining is proposed,which can reduce the rotate speed oscillation effectively and adjusting the displacementratio of variable displacement hydraulic part can also reduce the rotate speed oscillation. |
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