Understanding Speed Reducers and Their Purposes

Blog | October 23rd, 2018

Non-engineering types aren’t aware of basic system design issues. And that’s okay, they shouldn’t ever need to know about such things. Instead, they make blanket assumptions. One such assumption imagines a need for high rotational velocities at all times. Speed reducers, a common feature in power transmission linkages, suggest there are applications where lower velocities are desirable. Come on, let’s follow the power transmitting chain.

Speed Reducers: The Principles 

According to the laws of physics, those pesky laws again, machines can’t destroy energy. Try to understand that principle as it drives a series of bearings and gears. There’s a direct relationship between the speed of those parts and the torque they’re delivering. If a mechanism, a speed reducer, cuts system velocity, the available torque experiences a corresponding rise. And that principle works in reverse, so torque reductions can be translated into velocity gains. A speed reducer, therefore, utilizes differently arranged gear trains and spindles, which convert fast input speeds to slower output velocities, all while simultaneously magnifying that same powertrain’s output torque.

Case Study: A Few Speed Reducing Applications 

Simply by altering gear geometry, a working speed reduction architecture takes form. The input wheel is smaller and has fewer teeth on its rim. As for the output gear, it has a larger diameter, which consequently means more rim teeth. When the gears engage, the faster input side drives the output side at a lower speed. It takes more time, more work, to fully rotate the many-toothed, large diameter gear, so it obviously must rotate slower. Imagine a fast but relatively weak electric motor. Just by introducing a power reducer between the motor and the drive output shaft, the speedy input shaft creates copious quantities of output torque. Cars use this principle to climb hills. The constant RPM of the engine varies little, but the speed reduction mechanism converts that radial velocity into additional hill-climbing oomph. Mobile diggers, cranes, production equipment, and much more, they all benefit from this velocity-to-kinetic power conversion feature.

Speed is an easy enough asset to generate, just by adding windings, plus a few sets of high-performance bearings, to an electric motor. Additional poles then go on to increase system torque somewhat. To mechanically augment that effect, though, system engineers incorporate mechanical speed reducers, which use differently sized gears and complex spindle configurations to slow drive shafts down and gain a subsequent increase in system torque. Of course, this is a fundamental guide to what’s really an advanced engineering principle. In practice, there are ratio altering components, intricate gearbox architectures, and numerous other essential sub-assemblies to the design.

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