Transmission system and speed control method

The invention belongs to the technical field of mechanical transmission, and discloses a transmission system and a speed control method.The transmission system comprises an engine, a clutch, a variable pump, a variable displacement motor, a coupler and a transmission, an output shaft of the engine is connected to a first shaft through the clutch, and the first shaft is in transmission connection with a third shaft and a driving shaft of the variable pump; the third shaft is connected with the first input end of the coupler, an oil inlet of the variable pump is communicated with the oil tank, an oil outlet of the variable pump is communicated with an oil inlet of the variable motor, a driving shaft of the variable motor is connected with the second output end of the coupler through the second shaft, and the output end of the coupler is connected with the input end of the transmission. The speed control method is applied to the transmission system. According to the transmission system, coupling of two paths of