A Deere excavator swing motor

Every excavator has a swing drive, and a swing motor. But what's the difference?

What's a Swing Drive?

The swing drive is a hydraulically-driven component on an excavator. Usually, they consist of:

  • A hydraulically-powered swing motor
  • A gear box that consists of at least one, but often multiple sets of planetary gears.
  • A pinion gear that moves the house around the swing bearing.

The planetary gears are designed to convert rotational force into torque, and to output that force through a pinion gear which extends from the bottom of the swing drive. The swing drive itself is there to connect the upper (house) components of the excavator to the lower parts of the excavator, called the undercarriage. Right in the dead center of the machine is a big (or small if it's a mini excavator) gear that goes by a great many names, like slew bearing, slew ring, slewing ring, swing bearing, turntable bearing, ring gear, and swing ring. This pivotal gear is what the swing drive interacts with and allows the excavator house to rotate freely of the undercarriage.

So... What's the difference?

Similar to the final drive and travel motor debate, the swing drive and swing motor are two pieces of the same pie. The swing motor is the topmost portion of the entire swing drive. They are able to be separated in case you only need to replace one portion of the whole pie, instead of having to dole out for the whole thing.

An excavator swing bearing

What're the parts of a Swing Drive?

I'm glad you asked!

  1. Swing Motor: The topmost part of the swing drive. It's a hydraulic motor that consists of valves, ports, and bearings. It's the brain behind the control of hydraulic fluid flowing to the attached gearbox.
  2. Swing Gearbox: Consisting of a bunch of planetary gear systems that convert the energy from high speed input to a lower speed, higher torque output. Since the house of the excavator can weigh a ton, with or without carrying a load, high torque is needed to move get it move.
  3. Planetary Gear Systems: Smaller gears (planets) that all revolve around a centralized (sun) gear. With gear reduction, power is transferred into high torque output to move the excavator house.
  4. Gear Shaft: Extending from the bottom of the swing drive, it interlocks it's teeth with that of the swing bearing. This gear and shaft get turned from the gearbox inside the drive, and in turn walk the pinion around the teeth of the swing bearing, turning the excavator house.
  5. Swing Bearing: While technically not a part of the swing drive itself, the bearing is the stationary component that allows the house to spin free of the undercarriage. Without it, the swing drive would not serve a purpose at all!
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