A powertrain for an automotive vehicle comprising a thermal engine (10), a speed variation device (14) including an engine epicyclic gear train (26) with a sun gear (36) and a crown (48) which are each connected to shaft (12) of the thermal engine by a controlled coupling (28, 30) and to a fixed part (46) of the vehicle by a one-way automatic coupling (32, 34). A machine epicyclic gear train (90) is arranged on a machine shaft (92) substantially parallel to engine shaft (12) and connects the epicyclic gear train to a track for motion transmission to a drive axle. The machine epicyclic gear train comprises a sun gear (94) carried by a sun gear shaft (100), a crown (126) and a planet gear carrier (108). A speed variation device (14) comprises an additional epicyclic gear train (138) and an engine toothed wheel (168) carried by the shaft (12) and connects the shaft to a machine toothed wheel carried by additional epicyclic gear train.

A compact hub-embedded multi-stage transmission is provided which is implemented to achieve multi-stage shifting by using a multi-stage planetary gear set having a one stage or two or more stages and a double one-way clutch in order to impart an overrunning function during inertial travel, and at the same time, to allow rapid shifting to be made even with a small force for manipulating a shift lever by means of use of a forced shift function even in a driven travel state. Accordingly, product marketability can be maximized, and rapid shifting can be made even with a small force for manipulating a shift lever by means of use of a forced shift function even in a driven travel state, thereby considerably improving shifting accuracy.

A two-stage speed-change output device includes a main axle, on which a motor assembly and first and second speed-change assemblies are mounted. The first and second speed-change assemblies are mounted inside an output shell by first and second one-way clutching elements, both operating in a forward direction. The motor assembly is operable to rotate backward to drive the first one-way clutching element to drive the output shell to rotate in the forward direction, while the second one-way clutching element idles. The motor assembly is also operable to rotate forward to drive the second one-way clutching element to drive the output shell to rotate in the forward direction, while the first one-way clutching element idles. The device realizes speed change for two stages to drive the output shell in the same direction with forward and backward rotations of the motor assembly.

The present invention discloses a three-speed bicycle transmission structure and the transmission method thereof, aiming at overcoming the drawbacks that the overall structure of the prior art cannot support three-speed transmission in a small space and requires high manufacturing costs. The present invention comprises a central shaft, a three-speed transmission structure and a gearbox housing; wherein, the three-speed transmission structure comprises a centrifugal clutch shifting mechanism, a composite planetary gear ring and a first-level transmission mechanism, a second-level transmission mechanism and a third-level transmission mechanism. The centrifugal clutch shifting mechanism is used for shifting among the above three levels of transmission mechanisms to carry out three-speed transmission, and the composite planetary gear ring is used for cooperating with the centrifugal clutch shifting mechanism to realize partial gear shifting. The present invention realizes simplified structure, compressed structure space, improved transmission efficiency and cost saving.

A power transmission system includes a simple planetary gearset and a compound planetary gearset. A first coupling mechanism associated with the simple planetary gearset selectively couples a component of the simple planetary gearset to ground, and a second coupling mechanism associated with the compound planetary gearset selectively couples a component of the compound planetary gearset to ground.