Winch Gearing Types ExplainedWritten by admin | 2 Comments »
Even if you’re an off-road enthusiast with tons of back country experience…in and out of ditches…you may not give much thought to how your winch works. You just want to know it does when it counts. Grab the hook, stretch the cable, wrap a tree, and pull your 4X4 out of the hole. Still; it’s interesting to know how this happens. And here’s a brief overview of the gearing types used in modern winches.
Winch gears are needed to convert a high-speed, low force electric motor output into a low-speed, high torque pulling machine. In other words, you want the strength to pull heavy weights, but you don’t want to jerk ‘em so fast they fall to pieces. So winches use gears with thick, strong “teeth” which pass this test. And there are 3 main types of gearing systems:
- Spur gears
- Worm gears
- Planetary gears
A simple spur gear.
On the “low end” of the gear spectrum you have spur gears. They connect parallel shafts, have internal or external teeth, and cause no external thrust between gears. They’re inexpensive to manufacture and still perform well making them one of the most cost-effective types of gearing.
The speed and change of the force depends on the gear ratio or number of teeth on the gears to be meshed. One gear is on the input axle of the motor, and the other gear is on the output axle of the wheel. With this higher contact ratio they run smoother and quieter which makes for excellent corrosion resistance.
A sample of a simple worm gear setup.
Next up we have the worm gear made of two parts: the pinion and the worm gear. The pinion has a few teeth wrapped around the pitch cylinder. The worm gear has concave faces to fit the curvature of the worm. This provides a “line of contact” instead of point of contact. They’re capable of transmitting high tooth loads for the ultimate power ratio, but the disadvantage is the high sliding velocities across the teeth.
Worm Gears offer the smoothest, quietest form of gearing with high-ratio speed reduction in minimal spaces. This is great when large gear reductions are required. The worm gear can easily turning the gear, but the gear can’t turn the worm. The angle on the worm is shallow so the friction between the two holds the worm in place.
A “driven sprocket” or electric motor applies torque to the input end of the worm causing the friction between the worm gear and the gear being “driven”. This increases wear on the gear teeth and erosion of the restraining surface. Worm gears serve as speed reducers in many different industries.
The planetary gear system.
Finally, we have the planetary gear, which is actually a set of gears on or inside a larger gear. They make drastic gear ratios possible, and they’re used to turn the input in the same direction as the output. It’s called the “planetary gear” because it looks a little like the sun with some revolving planets. The gear in the center of the larger gear engages two or three smaller gears in the same large gear. Planetary gears turn on a movable center and the sun gears turn on a fixed center.
Planetary gears are also used to produce different gear ratios depending on the which gear is used as input, which one as output and which one is held stationary. They’re the most commonly used gear train, and they have some clear advantages…
- Higher gear ratios
- Most popular for automatic transmissions
- Used in bicycles for controlling pedaling power
- Also used for power train between internal combustion engine and an electric motor.
While all of these gear systems do the same job – gearing down a high-speed electric motor to turn a low-speed, high torque winch drum – their efficiency varies. The worm gear has a transfer efficiency of 35-40% causing the winch to be self-breaking even under heavy loads. The spur gear’s transfer efficiency is 75%, and the planetary gear weighs in at 65%. They both have a tendency to “free spool” when loaded; so a braking mechanism is needed. And that’s another story…