One-way cam clutches maintain direction

Edited by the Engineeringtalk editorial team Apr 30, 2003

One-way cam clutches are the workhorse of general industry and are also equally applicable to the leisure and white goods markets, expains Bob Young of Tsubaki UK.

One-way mechanical clutches are efficient mechanical devices that use differences in axial rotating direction and speed of rotation to prevent reverse rotary motion and ensure safety.

They are one of the most simple and efficient devices for achieving backstopping and overrunning in all types of applications, from fan and pump drives to conveyors, cranes and hoists, sports equipment and even washing machines.

Such wide usage owes much to the continuing development of clutches, through ratchet and roller types to the latest cam types manufactured by Tsubaki.

These units feature a full complement of cams, providing the maximum number of load transmitting members per given diameter.

This results in greater torque capacity (up to 686kNm), size-for-size, and longer operational life compared to other designs of one way clutches.

The types of applications for which one way cam clutches are used fall into three main categories: general overrunning, indexing and backstopping.

Clutches used in overrunning applications overrun at either the inner or outer race during the majority of the clutch operating time and are occasionally called upon to lock up and drive.

The pump or fan is driven by a dual drive system consisting of a motor and a turbine.

The cam clutches are used for automatic switching between the driving units.

The fan is normally driven through clutch A on the turbine side.

When starting, or when steam pressure to the turbine drops, the motor takes over from the turbine to drive the fan.

With the motor as the prime mover, cam clutch A overruns, while cam clutch B engages - this procedure being reversed when the drive resorts back to the turbine.

The advantage of this system is that both driving devices can be alternated without switching the clutch.

This is because the difference in the speed of rotation between the motor and turbine engages and disengages the cam clutches, and the driving device rotating the fastest is connected automatically to the driven unit.

In the second major mode of operation for cam clutches, indexing, reciprocating motion applied to the driving race of the clutch is transformed into unidirectional intermittent motion at the driven race.

For example, on an automatic stapling machine the reciprocating motion of an eccentric disc is converted by the cam clutch into an intermittent feed motion, which drives the belt conveyor.

As a result, stapling is timed to the intermittent feed motion and stapling is performed at exactly the right pitch.

This same method of indexing is also highly applicable to food and other types of packaging machines.

The final mode of operation, backstopping, is classified into three types depending on the overrunning speed and load conditions.

In backstop (holdback) applications, the clutches are used to prevent reverse rotation of drive shafts and damage to machinery and other expensive equipment.

With the outer race of the clutch anchored to a stationary member, the inner race can overrun freely in one direction of rotation.

Reverse rotation is instantaneously prevented by the automatic engagement of the clutch.

For reasons of safety, belts (and other types of inclined conveyors) must be prevented from moving backwards.

Installing a cam clutch on the main motor shaft of the conveyor drive system is the easiest and most economical method of achieving this.

In other conveyor applications the inner race of the cam clutch is mounted directly onto the conveyor head pulley, or other shaft with a low speed of rotation, and the outer race is anchored to the conveyor frame to prevent reverse rotation.

As reverse rotation is prevented directly by the conveyor shaft without using a drive chain, gears or couplings, this is regarded as the safest, most reliable mounting method - not to mention the most cost effective.

Tsubaki has been manufacturing cam clutches since 1969, and many major and significant additions have been made to the range since that time, such as the introduction of a complete range of European series clutches and the development of complete cam clutch boxes for high-speed continuous applications as well as for inching and turning drive applications.

Tsubaki is now one of the worlds leading manufacturers of cam clutches to industry.