A torque limiter is a mechanical device that prevents mechanical overload by controlling the amount of torque the drive shaft is subject to. It can completely decouple the load or allow it to slip during overload. There are several designs, including shear pins, synchronous magnets, bawl catch and pawl, friction plates, magnetic particles, and magnetic hysteresis. Disconnect types must be reset, while clutch-based types can be modulated while the machinery is running.
A torque limiter is a mechanical device that controls how much torque the drive shaft of a car is subject to at any given time. It is a protection mechanism and its purpose is to prevent damage to the machine due to so-called mechanical overload. This is a situation where excessive torque is imposed on the drive. For this reason, the limiter is sometimes alternatively referred to as an overload clutch. It can be found on everything from a ship’s propeller to a bottling plant assembly line to a fishing reel.
There are several ways a torque limiter can work. Some completely decouple the load when an overload is detected. These types are known as disconnect types. Others simply allow the load to slip during overload, similar to how a clutch works in a car’s manual transmission. These are known as torque limiting types.
A disconnect torque limiter can come in several designs. These include shear pins, synchronous magnets, bawl catch and pawl and spring. In general, a disconnect type must be reset in some way after it occurs during an overload. Depending on the type, this can be done automatically or manually.
Shaft pin limiters work by inserting a small metal pin into the unit when it is overloaded, forcibly disconnecting it. In the process, the pin is destroyed and must be replaced before it can be used again. Shear pins are often compared to electrical fuses in the sense that they are sacrificed to protect more expensive parts.
A synchronous magnet system, as the name suggests, uses a pair of strong magnets to rapidly disconnect the shaft with a magnetic pulse. Again, just like its name, a ball restraint works with a number of spring-loaded metal balls installed in the unit, which pop open to disconnect the unit when needed. A pawl and spring torque limiter, which basically uses the swing arm section of a ratchet mechanism, activates when needed, with the pawl going down and catching a notch in the unit, forcing it to disconnect.
Types of torque limiting, which work like clutches, include friction plates, magnetic particles, and magnetic hysteresis. Unlike disconnect types, clutch-based torque limiters are not firm in their use and can be modulated while the machinery is running. They are also less catastrophic in the sense that a system reset is not required after each use. Each type of torque limiting design can be turned on and off in a timely manner, usually without damage to mechanical parts.
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