In general each method of actuation offers the designer some advantages and disadvantages. It is important to realize these advantages when selecting a clutch or brake. Carlyle Johnson has the expertise to resolve the most difficult control problems.
Circuits Available for:
- Reducing engagement times in electric clutches (over excitation)
- Controlling torque through pulse width modulation
- Reducing coil wattage through step down/up excitation
- Increasing engagement for soft start and timing applications
Compare Clutches and Brakes
- Electric vs. Hydraulically Actuated
- Energy vs. Mechanically Engaged
- Spring Applied vs Energy Applied
Clutch & Brake: Comparison & Summary
The following general guide can assist you with determining which method of actuation will best fit your needs. Please note this information is for reference only - there are always exceptions to the general guidelines. Please contact us for more information on your order and specific needs.
Energy Engaged Clutches and Brakes
Electric vs. Air / Hydraulic Actuation
|Type||Bearing Life||Heat Load||Response Time|
Less Maintenance & Longer Bearing Life
Electrically engaged clutches require electricity to operate. They can typically operate at higher speeds and have longer periods of usage between maintenance cycles. This is a direct result of longer bearing life. The bearing life of an electric clutch is much longer than that of an equivalent size pneumatic or hydraulic clutch operating at the same speed, as a result of reduced forces placed on the bearings.
Reduced bearing forces are possible because of the magnetic force design of our electric clutches. The magnetic force required to squeeze the friction discs together in a Carlyle Johnson Electric Clutch is self-contained. Only a very small portion this force is transmitted to the bearings.
Requires More Ventilation
Electric clutches will operate warmer than the equivalent pneumatic/hydraulic clutch because of the heat generated by the coil. The coil wattage ranges from as little as 5 watts to as much as 150 watts, therefore the clutch must be operated with sufficient ventilation to ensure that overheating does not occur.
Slower Response Time
Pneumatic/Hydraulic clutches require that air or hydraulic pressure be applied to the clutch for operation. The customer normally utilizes a solenoid to turn the pressure on and off. These solenoids typically have much smaller coils than the coil in an electric clutch. Since the smaller coil has less inductance, the clutch will have a much faster response time than an electric clutch. Faster response time also offers more consistent cycling as long as supply pressure is closely regulated.
Mechanically Engaged vs. Energy Engaged Clutches and Brakes
|Mechanical||Manual||Occasionally Needed||Not Needed|
Driven by Manual Forces
Mechanical clutches and brakes are ideal in applications where manual 'on and off' engagement is required, or where manual 'on' and torque sensing is used to turn the clutch 'off'. Mechanical clutches and brakes require an external force to shift the device from the engaged-to-disengaged, or disengaged-to-engaged position.
Require Adjustment for Proper Function
Mechanically engaged units utilize an internal lever mechanism to produce the force that squeezes the friction discs together and thereby transmits torque. Mechanical devices require occasional adjustment to engage or disengage properly, due to friction disc wear.
Permanent Positioning – No Need for Power
The mechanical clutch or brake has no internal bearings and has a positive engagement position. It will remain in a particular state with no risk of turning on or off due to power or hydraulic/air failure.
Spring Applied vs. Energy Applied Clutches and Brakes
|Type||Adjustment||Clutch Features||Brake Features|
|Spring Applied (Energy Release)||Self-Adjusting*||Used where only momentary "off" condition desired||Equipment stopped until power applied|
|Energy||Self-Adjusting*||No torque transmitted until power applied||Dynamic braking to protect equipment up and downstream|
*Clutches and brakes are self-adjusting for their full service life. When maximum allowable wear point is reached, device must be repaired / refurbished to restore self-adjusting capability.
Periodic Adjustment to Compensate for Wear
Energy Applied clutches and brakes transmit torque – that is they are engaged – when power is applied to the device. They are disengaged – unable to transmit or arrest torque – when the power is removed. Energy applied clutches and brakes are self-adjusting for wear.
Spring applied clutches and brakes work in the opposite fashion. The application of power to a spring applied unit will disengage it – overcoming the engagement spring force and preventing the clutch or brake from transmitting or holding torque. The removal of power will allow the internal springs to engage the device, allowing torque to be transmitted. These devices, too, compensate for normal wear.
Over time, the normal wearing of friction surfaces results in the necessity of additional spring "travel" to get full engagement. Proper design will permit sufficient spring force to compensate for normal wear. However, when they are assembled after maintenance is performed, careful attention must be paid to adjustment and setting instructions to be sure the device will properly engage or disengage.
When selecting a spring applied or energy applied device, design engineers must consider the operating conditions of the device being powered. Spring applied clutches and energy applied brakes potentially allow driven mechanisms downstream to retain 'stored energy' when the actuation power fails. That is, they are not safely disengaged or held unless energy (electricity, hydraulic, or pneumatic power) is available for actuation, to disengage or brake the device.
Energy applied clutches and spring applied brakes will remove power or stop a rotating device when actuation power fails. In applications where personnel are likely to be exposed to injury during jams, power failures, and the like, safety concerns dictate the use of clutches and brakes which do not allow stored energy to remain in a system when equipment is not operating.