Planetary gear assembly, power-split stepless transmission, and transmission structure

An HMT device that works in cooperation with an HST that, between a first HST speed and a second HST speed, steplessly changes a standard rotary speed power operatively input from a drive source to a pump shaft, and outputs an HST output, which is after the speed change, from a motor shaft, the HMT device comprising:

• a drive shaft to which the standard rotary speed power is operatively transmitted from the drive source;
• cylindrical transmission shaft to which the HST output is operatively transmitted from the motor shaft;
• an output shaft, in a state where at least a part of the output shaft extended outward from the transmission shaft, inserted into the transmission shaft with a free relative rotation about a shaft line;
• a first planetary gear mechanism that has three planetary elements including a first sun gear, a first carrier, and a first internal gear, the first sun gear being supported to the transmission shaft without a relative rotation about an axial line, and one of the first carrier and the first internal gear forming a standard rotary speed power input unit to which the standard rotary speed power is input;
• a first transmission gear train including a first drive gear that is supported to the drive shaft without a relative rotation about an axial line, and a first driven gear that, while being directly or indirectly supported to the output shaft with a free relative rotation about an axial line, is operatively meshed with the first drive gear;
• a first clutch mechanism that is placed coaxially with the transmission shaft, and that engages and disengages a power transmission of the standard rotary speed power from the first driven gear to the standard rotary speed power input unit of the first planetary gear mechanism;
• a second planetary gear mechanism that has three planetary elements including a second sun gear, a second carrier, and a second internal gear, the second planetary gear mechanism being so made that the second sun gear is supported to the transmission shaft without a relative rotation about an axial line, and between the second carrier and the second internal gear, a planetary element different from a planetary element that forms the standard rotary speed power input unit in the first planetary mechanism forms a standard rotary speed power input unit to which the standard rotary speed power is input;
• a second transmission gear train including a second drive gear that is supported to the drive shaft without a relative rotation about an axial line, and a second driven gear that, while being directly or indirectly supported to the transmission shaft with a free relative rotation about an axial line, is operatively meshed with the second drive gear;
• a second clutch mechanism that is placed coaxially with the transmission shaft, and that engages and disengages a power transmission of the standard rotary speed power from the second driven gear to the standard rotary speed power input unit of the second planetary gear mechanism,
• a connection member extrapolated to the transmission shaft with a free relative rotation about an axial line,
• wherein the connection member, without a relative rotation around an axial line, connects, among the three planetary elements in the first planetary gear mechanism, the planetary element that forms a composite output unit other than the first sun gear and the planetary element that forms the standard rotary speed power input unit, with, among the three planetary elements in the second planetary gear mechanism, the planetary element that forms a composite output unit other than the second sun gear and the planetary element that forms the standard rotary speed power input unit, and the connection member, meanwhile, is non-rotatable relative to the output shaft about an axial line.