Planetary gear reducer is a type of gearbox composed of a sun gear, planet gears, and a ring gear. Based on the motion relationship between the ring gear, sun gear, and planet gears, it can achieve the disengagement of the input shaft and output shaft from a rigid transmission, as well as forward or reverse transmission and variable transmission ratio between the input and output shafts. 

• When the vehicle's resistance exceeds the maximum traction force, it enters a deceleration mode, and the speed of motor 1 decreases to enter the negative speed range, while motor 2 remains in drive mode, and motor 1 switches to generator mode. The system still outputs a maximum torque of 1600N.m, in conjunction with a 4-speed gearbox, providing a traction force of 192kN in 1st gear. 
• After the reduction of resistance, motor 1 maintains positive torque and gradually accelerates to the normal speed range, transitioning to normal driving mode. 
• Throughout the entire process of shifting and mode transition, both motor 1 and motor 2 maintain a positive torque direction, ensuring a smooth mode switch without any impact. Even in the locked output mode, the system maintains maximum torque output with only energy losses due to motor control efficiency, resulting in high efficiency, low heat generation, and sustainable output.