Torque handover and control of the HMCVT shift clutches under the theoretical shift condition

Hydraulic mechanical continuously variable transmission (HMCVT) has the advantages of low impact, high efficiency and high power, which could suit the requirements of continuously variable transmission for high-power vehicles such as tractors and engineering vehicles. During the HMCVT phase change, the power needs to be transferred from current clutch to target clutch. In this process, the torque of the quantitative motor reverses, which reverses the pressure on the high and low sides of the hydraulic components, resulting in the reverse power of the hydraulic circuit. as a result of which the rotational speed of hydraulic component changes abruptly, causing the fluctuation of output speed as well as vibrations and noises.Aiming at these problems in the process of power shift, a torque handover mechanism of HMCVT clutch under the condition of theoretical shifting segments is proposed based on the dynamic model of HMCVT power shift. For example, HMCVT shifts from HM2 to HM3. When the double clutches of the current range and target range overlapping，torque handover process is divided into two stages for discussion: hydraulic system positive power stage and hydraulic system negative power stage. When the ideal shift timing comes, clutch C3 would be operated. hydraulic system comes to positive power stage, the increase of C3 torque reduces C2 torque and motor torque until the positive power of hydraulic circuit becomes zero when the motor torque decreases to zero. At this stage, the torque transfer characteristics of clutch depend on C3 torque. When clutch C2 is detached, the reduction of C2 torque increases C3 torque, so that the motor torque changes from zero to negative, and the hydraulic circuit power transfers negative power from zero. At this stage, the torque transfer characteristics of the clutch depend on C2 torque. So, a piecewise-continuous function is established with torque change rate and torque change acceleration as parameters to optimize the torque handover trajectory of the two stages. The clutch controller is designed based on the terminal sliding mode control method. The torque tracking control is realized by tracking the oil pressure. The correctness of the torque transfer mechanism and the effectiveness of the controller are verified by simulation and experiment. The simulation and test results show that the clutch torque transfer mechanism is consistent with the theoretical analysis in the process of load changing, and controlling the clutch torque according to the torque transfer mechanism can realize the smooth switching of the segment. The terminal sliding mode controller can realize the tracking control of clutch oil pressure, so as to realize torque control. When the input shaft is 1 000 r/min and the load is 700 N·m, the terminal sliding mode controller is used to control the clutch for segment change. The fluctuation range of output shaft speed is (-20.6-7.4 r/min), the fluctuation range of output shaft torque torque is (-117.4-107.9 N·m), the maximum impact during the segment change is -6.16 m/s3, the maximum sliding friction work of the segment change clutch is 508.45 J, and there is no power interruption during the segment change. This research can provide a reference for the control of HMCVT shifting.