It was to start with introduced in 1939 for vehicles. It contains the fluid coupling and three planetary gears. They collectively make 3 ahead and 1 reverse velocity. There isn't any clutch for engagement and disengagement in the motor. Bevel gearboxes have spiral and straight teeth designs. These gearboxes https://gearbox87429.blogitright.com/33922582/the-greatest-guide-to-gearbox