Technical Information - Airflex - #2

A clutch is a device which transfers energy from one rotating shaft to another in order to perform some useful work.

In the simplest terms, a clutch can be thought of as a starting device because that is what happens when a clutch is engaged. But, more importantly, while engaged itis transferring energy. The clutch takes energy from a power source such as an electric motor or engine and transfers it to where it is required. The power source is referred to as the prime mover because it is the pri­mary source of energy. A clutch is engaged for one reason — to perform some useful work.

A clutch consists of two halves: a driving half and a driven half. The driving half is at­tached to the power source and rotates with it. The driven half is attached to the shaft requiring the energy and is started with each engagement. In addition, the clutch must have some means of engaging and disengaging the two halves.

A brake on the other hand, is a device which absorbs energy that is stored in rotat­ing and linear moving components and/or prevents an energy transfer to them.

Again, in simple terms, a brake can be thought of as a stopping device because that is what happens when a brake is engaged. Like a clutch, a brake also consists of two halves: a driven half

and a stationary half. The driven half is attached to the rotating and linear moving bodies from which energy must be removed. The stationary half is reacted so that it cannot move. The brake also has a means of engaging and disengaging the two halves.

Clutch and brake engagement is made by con­necting the two halves. Since one half is rotating and the other is stationary, the halves will slide or slip relative to each other.

When there is no relative motion between clutch halves, the clutch is locked and max­imum energy is transferred to the work shaft. If a relative speed differential is al­lowed to exist between each half, only par­tial energy is transferred, and the device is referred to as a slip clutch.

When there is no relative motion between brake halves, the brake is set and maxi­mum energy has been removed from the driven components and/or prevents an en­ergy transfer to them. The latter situation is referred to as a holding brake. If a relative speed differential is allowed to existbe-tween each half, only partial energy is ab­sorbed, and the device is referred to as a drag or tension brake.

The connection between clutch and brake halves for Airflex products is dependent upon a frictional couple. The product of the resulting frictional force and the distance to its axis of rotation determines the torque capacity of the clutch or brake. The torque magnitude determines the amount of en­ergy that can be transferred by the clutch or absorbed by the brake.

Heat is generated whenever torque is trans­mitted and a speed differential exists be­tween the clutch and brake halves. The ability to absorb and dissipate this heatde-termines the thermal capacity of the clutch and brake.

A clutch or barke must not only have sufficient torque capacity to transfer the required energy, but must also have sufficient thermal capacity to handle the heat generated due to slippage.

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Copyright Eaton Corporation, 1995, All rights reserved.