What is Power Transfer?

Power transfer through a clutch or brake is the method by which the energy is transferred from one rotating device to a second non-rotating device. In the case of a clutch, the second non-rotating device is brought up to the same rotational speed as the driving device. In a brake, the second non-rotating device is fixed, and the driving device is gradually brought to a stop. The end result is that both devices are rotating at the same speed (or in the case of a brake are completely stopped). The two common methods of engagement are:

• Friction
• Jaw (or tooth)
  

The friction and the jaw engagement methods are available in any version of actuation method selected. For example Carlyle Johnson offers a spring-engaged clutch. The spring engaged clutch is available with single or multiple disc friction surfaces or a jaw type torque transfer system.

Power Transfer - How it Works

Friction Clutches and Brakes

Friction clutches and brakes utilize friction discs to transfer the energy from one rotating member to a second rotating member. The friction between the discs of the two bodies allows the clutch or brake to transmit torque. The friction discs are flat smooth surfaces that are alternately attached to the rotating and the non-rotating elements. The sequence and type of friction surface, as well as the load presented to the clutch/brake will determine the size and number of friction surfaces that are utilized to transmit the torque.

Friction discs may be made from various materials. Coated and uncoated metals, various alloys, bonded composite friction materials, and combinations of these may be appropriate depending on the application.

Once the torque capacity of the disc friction surfaces is exceeded then the clutch will slip. The clutch will also slip during engagement and disengagement, while the friction discs are being gradually squeezed together by whatever actuation method is used. This allows a smooth transfer of torque from one device to another, allowing gradual starts (for clutches) and controlled stops (for brakes). Carlyle Johnson offers a wide variety of friction surface types, as well as a large selection of friction surface quantities in every size and type of clutch. An in-depth description of the engagement methods of our clutches is available in our product bulletins.

Single vs. Multiple Disc Designs Carlyle Johnson offers both single disc and multiple disc clutches and brakes. In many applications where low cost and only a small torque handling capability is required, a single friction surface will suffice.

Multiple disc clutches and brakes offer the advantage of handling high torque loads in a compact size device. A multiple disc clutch with seven sets of discs provides fourteen friction surfaces. The total area of these fourteen surfaces would require a very large single disc clutch or brake, to provide equal torque capability. The reason is found in elementary trigonometry. A fourteen surface device with a diameter of 9.50” has the same area as a single surface device of 35.5”! In most high-torque applications, the space does not exist to house a single disc device of such great size.

Similarly, at high rotational speeds, the velocity of a large single disc device could become a safety hazard. A 35.5” device rotating at 5,000 RPM has a velocity at its outer edge of almost 775 feet per second. A 9.5” device rotating at the same speed has a velocity of about 200 feet per second. A large single disc design necessitates engineering considerations and complications in bearing design, inertia loads, component size, shielding, etc. These factors can make the multiple disc device an ideal power transmission solution.

Single disc clutches and brakes tend to be larger but less costly than multiple disc clutches and brakes, because they contain fewer parts and are simpler to design, fabricate, and assemble.

Multiple disc clutches and brakes are usually much more compact although at a cost penalty due to their increased complexity.

Advantages of Friction engagement:

• Soft engagement of the two devices to be coupled;
• Engagement speed is not limited.

Carlyle Johnson Models: All Except JEM & JEB

Jaw (or Tooth) Clutches and Brakes

Jaw clutches and brakes utilize a serrated tooth design to transfer or absorb energy from one rotating device to a second rotating device. The friction between the surfaces of the teeth of the rotating and non-rotating device allows the clutch to transmit torque or a brake to hold a device in a stopped condition.

Various tooth forms as well as different physical numbers of teeth are available to the designer, depending on the application. The design of the tooth form will determine the torque capacity of the clutch or the holding capacity of the brake. Using different tooth forms allows the device to slip or disengage at a predetermined point as determined by the application requirements.

Once the torque capacity of the jaw teeth is exceeded then the jaws will disengage dragging the teeth of one device along the surface of the teeth on the second device. However, this is not a recommended use of the jaw type clutch.

A jaw clutch typically transmits higher torque in the same model size as a friction disc design but is limited by engagement speed; slippage is not allowed unless the tooth form is specifically designed for it. The jaw teeth offer an easy method of obtaining a positive registration between the two devices that will be coupled together. Exceeding 100 RPM during engagement is not recommended in a jaw clutch or brake.

Advantages of Jaw or Tooth engagement:

• High torque in a relatively small size;
• Indexing or registration of input to output capable;
• Positive engagement of teeth allowing virtually zero backlash.

Carlyle Johnson Models: JEM, JEB

Power Transfer Summary

Each method of power transfer offers the designer some advantages and disadvantages. It is important to realize what these advantages are when selecting a clutch or a brake.

This is only a general guide and there are always exceptions, which may involve additional cost and engineering effort to obtain the desired results. Carlyle Johnson has the expertise to resolve the most difficult control problems.

Examples of design variations developed by the engineers at Carlyle Johnson include the use of advanced composite friction surfaces for dust free and virtually zero wear usage, as well as complex multiple pressure-angle jaw configurations to assure positive disengagement in very high torque applications.

Some positioning brakes require virtually zero ‘backlash’ – Carlyle Johnson has developed jaw tooth designs for these precision-indexing applications.

Occasionally the requirement for an application with a manual override will result in the use of several different power transmission devices either in tandem or designed within a single housing, permitting continued operation in the event of power or prime mover failure.

Friction-type devices have also been designed to permit bi-directional driving by an electric motor but no back-driving, resulting in a safety brake which prevents the driven load from moving, until power is restored. The locking action during power failure can assure a condition with “no stored energy” reducing risks of accidents and injuries to personnel.

There are thousands of such custom applications where Carlyle Johnson has solved unique and difficult power transmission problems. Constraints such as weight, size, environment, special materials, service life, accessibility, engagement speed, and cost constraints are challenges we can meet with our expertise and long history.

Our clutches and brakes work in outer space and at ocean depths of 15,000 feet. Consult us for further information on your power transmission application.