Are the terms “travel motor” and “final drive” interchangeable? What about hydraulic motor – is it the same as a final drive? What about “planetary final drive”? In this blog post, we went all the way back to some of the early patents for things like hydrostatic vehicle drive systems to bring you answers. Let’s dive in!
A Final Drive by Any Other Name ...
First, it seems that the term travel motor is used to differentiate the motors for the wheels (or tracks) from the swing motor. In the image below, you can see clearly see the swing motor at the center of the vehicle, and can get a pretty good idea of where its name came from.
The travel motor is one of the key components in a hydraulic drive system, which is summarized conceptually in the figure below.
In a typical hydraulic drive system, you have a power source (usually an internal combustion engine) that powers a hydraulic pump. The hydraulic pump provides the fluid that actuates the travel motor. The travel motor is essentially the hydraulic motor interfaces with the final drive, providing the power that the final drive transforms into torque. That torque is transferred to the sprocket, which then turns the wheel and/or track. By this definition, the final drive is primarily the planetary gear system that converts power to torque.
That said, some people define final drive a bit differently. The final drive is sometimes described as the combination of a hydraulic motor with a speed reducing planetary gear system, which would seem to make the travel motor part of the final drive. When used in that sense, the final drive may be called the planetary gear final drive unit or the planetary final drive.
In the strictest sense, the term final drive and travel motor are not interchangeable. By some definitions, the travel motor may be considered part of the final drive. The final drive either refers to the combined hydraulic motor and planetary gear hub, or to the gear hub only. The travel motor refers to the hydraulic motor.