Transmission for electric vehicle and control method thereof

A transmission for a vehicle, the transmission comprising:

• a first planetary gear set including three rotation elements of a first rotation element, a second rotation element, and a third rotation element;
• a first motor connected to the first rotation element of the first planetary gear set and configured to input power to the first rotation element of the first planetary gear set;
• a differential connected to the second rotation element of the first planetary gear set and configured to receive power output from the second rotation element of the first planetary gear set;
• a second motor configured to selectively provide power to the third rotation element of the first planetary gear set;
• and
• a compound planetary gear set mounted between a differential case of the differential and a selected output shaft to distribute power provided from the second motor to the differential case and the selected output shaft, and to make directions of torques distributed to the differential case and the selected output shaft be opposite to each other, the selected output shaft being one of output shafts of the differential,
• wherein the compound planetary gear set includes:
• a second planetary gear set including a first rotation element which is connected to the differential case, and a second rotation element which is configured to be selectively connectable to the second motor;
• and
• a third planetary gear set including a third rotation element which is connected to a third rotation element of the second planetary gear set, a second rotation element which is fixed to be stationary, and a first rotation element which is connected to the selected output shaft.

A control method of a transmission for a vehicle comprising two or more motors, two or more clutches, and one or more planetary gear sets, and having two or more gears, wherein a first motor of the two or more motors is connected to a first rotation element of a first planetary gear set of the one or more planetary gear sets, wherein the first planetary gear set includes three rotation elements of the first rotation element, a second rotation element and a third rotation element, wherein the third rotation element of the first planetary gear set is selectively connectable to a transmission housing by a first clutch, wherein the second rotation element of the first planetary gear set is connected to an output shaft, wherein a second motor of the two or more motors is connected to the third rotation element of the first planetary gear set, wherein a second clutch selectively connecting two rotation elements among the three rotation elements of the first planetary gear set is provided, and wherein transmission control through the second motor is allowed,

• the control method including:
• releasing, by a controller, the first clutch after controlling the second motor to provide, to the third rotation element of the first planetary gear set, a same torque as a torque by which the first clutch supports the third rotation element of the first planetary gear set, in a first gear driving state in which the first clutch is engaged and the first motor is driven;
• maintaining, by the controller, a torque of the first motor and a torque of the second motor constant while reducing a speed of the first motor and increasing a speed of the second motor to synchronize speeds of the three rotation elements of the first planetary gear set with one another;
• and
• releasing, by the controller, the torque of the second motor while maintaining the speed of the first motor after engaging the second clutch to form a second gear driving state.