Kinematic analysis of double-flow hydromechanical transmissions

Double-flow hydromechanical transmissions become more and more widely used in designs of modern tractors and automobiles. Double-flow hydromechanical transmission includes a torque converter or a complex hydrodynamic transmission and a differential unit made in form of three-link differential device. The article discusses all of the 12 possible schemes of double-flow hydromechanical transmissions with a differential unit at the input and at the output with mixed type of gear engagement, and also presents the results of their kinematic analysis. For all of the 12 possible schemes, the expressions are given for determining the angular velocity of links of three-link differential device, depending on the gear ratio of double-flow hydromechanical transmission and the characteristics of planetary gear set. The calculation results with the use of these expressions are presented as curves. It is found that in 4 of the 12 schemes, it is very likely that the angular velocity of either sun gear or satellites will exceed the limits admissible for rolling bearings. There is no such problem for other 4 schemes. The other schemes are applicable to a limited range of characteristics of the planetary gear set. It is found that for 6 schemes there is a possibility that when transmission is functioning in the range of variation of gear ratio from infinity to 1, the torque converter can be operated in modes not typical for its normal operation (the turbine wheel rotates faster than the pump wheel; the turbine wheel rotates counter to the rotation of pump wheel; pump wheel rotates in the opposite direction in relation to the reactor). The triggering conditions of such modes are established and variation limits of gear ratio of torque converter are determined for them.

double-flow hydromechanical transmission, torque converter, three-link differential device, operation analysis