What is a Clutch?

“A clutch is a frictional device whose primary function is to
transmit power on an intermittent basis.”

A clutch is a device that is used to couple and uncouple two separate bodies of rotation. These two separate bodies may consist of shafts, gears and sprockets, a prime mover or motor, or any combination of these. The driven components are typically pumps, fans, power take-off shafts, compressors, gearboxes and generators. Normally the shaft of the driven or driving component itself is used to transfer power.

Typical clutch applications are as follows:

1. Shaft to Shaft coupling and uncoupling:

2. Shaft to Sprocket or Gear coupling and uncoupling.

Clutches can be classified by their method of actuation. These include:

• Mechanical
• Electric
• Hydraulic
• Pneumatic (Air)

The last two are frequently combined, as many clutch models suitable for hydraulic actuation can also be used in pneumatic (air) applications.

A sub-type of the classification is based on whether the actuation method is used to engage, or disengage the clutch. The sub-types are:

• Spring Applied (Energy Release)
• Energy Applied

A Spring Applied Clutch is said to be “normally engaged”, meaning the clutch is engaged or transmitting torque when at rest. Actuation energy is required to disengage it. This is a useful design when the driven component is only momentarily decoupled.

An Energy Applied Clutch is said to be “normally disengaged” – there is no power transmitted to the driven device until actuation energy is applied. Most clutches in power transmission applications are of the Energy Applied sub-type.

A further breakdown defines the process by which the engagement method transmits the rotating mechanical energy to the driven component, called “Power Transfer”. These include:

• Friction (single or multiple-disc friction plates held together by the force of springs or by the application of energy such as magnetic flux, or by a piston that is pressurized, to transmit torque by friction);
• Positive engagement (jaw or tooth clutches which move into a known position when engaged).

Each of these classifications and sub-types are designed to offer equipment designers a complete range of options, and each option has its unique advantages and disadvantages.

When selecting a clutch for a given application, it is important to understand the advantages, disadvantages, and limitations of each type of device. Carlyle Johnson offers a full line of standard clutches at modest cost, and can provide engineering expertise to help solve the most difficult control problems.

What is a Brake?

“A Brake is a frictional device that absorbs the kinetic energy of moving bodies
and thus controls their motion”

A brake is a frictional device that is used to stop a rotating inertia load or to hold a component in a specific position without motion. The inertia load is usually the result of several rotating components that need to be stopped.

A holding brake is used to hold a component in position once it is stopped. A dynamic brake is used to bring a rotating load to a stop.

Why the distinction between these two types? Consider the brakes on a vehicle. The stopping or dynamic brakes must be sized considerably larger than the parking or holding brake, which need be only large enough to hold the weight of the vehicle when at rest. This example applies to industrial rotating equipment in the same way.

Frequently, applications are encountered where the brake must perform both holding and dynamic braking functions. The brakes are usually attached to a stationary member in the drive line and a shaft passing through the brake is keyed or splined to the brake hub. Typical brake applications are as follows:

1. Brake:

2. Brake with manual release option and cover:

Brakes are generally classified by the method of actuation. These include:

• Mechanical
• Electric
• Hydraulic
• Pneumatic (Air)

The last two are frequently combined when discussing brake actuation, since many brake models suitable for hydraulic actuation can also be used with pneumatic actuation.

In addition there are subtypes of these classifications. The subtypes are:

• Spring Applied (Energy Release)
• Energy Applied

A brake is “engaged” when it is holding or stopping a load. It is “disengaged” when the device is free to rotate.

A Spring Applied brake is said to be “normally engaged”, requiring the application of actuation energy to disengage it.

An Energy Applied brake is “normally disengaged”, and will not act as a dynamic or a holding brake unless actuation energy is applied.

A further breakdown describes the process by which the engagement method arrests the rotating mechanical energy. These “Power Transfer” methods include:

• Friction (single or multi-disc friction plates which are brought together to stop or hold a rotating load by friction);
• Positive Engagement (jaw or tooth brakes which positively lock when engaged).

Generally, dynamic braking is accomplished with friction type devices, since the load can be brought to a controlled stop at a gradual rate defined by the equipment designer, and consistent with the inertia load being arrested. Friction brakes work well as holding brakes, but lack the precise control possible with a positive locking brake. Nevertheless, in many applications where the brake must perform both dynamic and holding functions, accurate positioning can be accomplished through careful design.

Positive Engagement brakes are best suited for holding brakes, particularly where extremely accurate control of the held device is necessary and backlash is not tolerable, as in medical imaging equipment, azimuth and elevation holding brakes for weapon systems, and the like. However a tooth or jaw brake used as a dynamic brake will cause immediate and violent stopping action, and may result in damage to both the brake and the rotating equipment being stopped.

The various classification and sub-types of brakes offers designers a wide array of options. Each type of brake has its unique advantages and disadvantages. Carlyle Johnson can provide a full line of standard products at modest cost. We can also provide engineering expertise to solve the most difficult control problems where specially engineered solutions are required.