Mechanical Clutches Information
Image Credit: Mach III Clutch, Inc. | Baldor Electric Company | Berg W.M., Inc.
Mechanical clutches are equipment drive assemblies that contain mechanically actuated components for connecting two shafts so that they can either be locked together and spin at the same speed, or decoupled and spin at different speeds.
What do Clutches Do?
Engaging the clutch transfers power from an engine to devices such as a transmission and drive wheels. Disengaging the clutch stops the power transfer, but allows the engine to continue turning.
Why Mechanical Clutches?
Mechanical clutches are less expensive than pneumatic or hydraulic clutches, but do not provide the same range of torque. They are best suited for vehicles and industrial equipment such as hoists and cranes. Small mechanical clutches are actuated directly with cams or levers, while larger clutches are operated through compound linkages. Usually, mechanical actuation is feasible only when the lever or pedal can be located near the clutch. Some mechanical clutches can be actuated from long distances, but friction losses in the linkage or cable may be high.
Specifications for mechanical clutches include torque rating, power, and rotational speed. Spring-return clutches require power to engage. Spring-actuated clutches require power to disengage. A variety of engagement methods are available
- Non-contact clutches uses methods such as magnetic fields and eddy currents.
- Friction clutches generate friction between contact surfaces.
- Wrap spring clutches transmit torque from the input to the output through a wrapped spring that uncoils to disengage the clutch.
- Oil shear clutches achieve drive engagement through the viscous shear of transmission fluid between the clutch plates.
- Sprags, steel wheels that tip in one direction to wedge between inner and outer races, are clutches that can often transmit more torque than other slip or overrunning devices.
- Ball detent clutches feature a slip mechanism in which, upon overload, seated balls are dislodged and overcome springs or air pressure engagement.
- Pawl clutches overcome spring or air pressure engagement and rotate out of their detent.
- Roller detent clutches, rollers that are held in place by springs wedge between the inner and outer races to engage the clutch.
How to Select the Right Clutch
Selecting mechanical clutches requires an analysis of
- Shaft configurations
- Drive and Load connections
- Special features
- The cross-sectional width of the assembly
- The dimension along the axis of rotation
Shaft configurations can be
- In-line along the axis of the load
- Parallel but offset from the axis
- Perpendicular (right angle) to the axis
Drive and load connections for mechanical clutches use shafts that attach to bores or flanges. With some drive shafts that attach to bores, the output is a drive component such as a pulley, gear, or sprocket. Often, these types of mechanical clutches are designed to accept several different drive components.
Special features for mechanical clutches include
- Adjustable torque,
- Zero backlash,
- Washdown capability
Slip clutches (torque limiters), overrunning clutches, backstop clutches, and freewheeling clutches are also available.
Industrial or general-purpose mechanical clutches are designed for a wide variety of power transmission applications.
Specialized devices are available for
- Heavy transport,
- Marine, military
- Off-road applications
Some electric clutches are designed for use with
- Web tension control,
- Robotics systems.
Other devices are designed for use with conveyor drives and pump motor drives. Power take off clutches (PTO) are typically used with heavy equipment such as dump trucks, snowplows, and tractors.
SAE J373 - HOUSING INTERNAL DIMENSIONS FOR SINGLE- AND TWO-PLATE SPRING-LOADED CLUTCHES
SAE J1073 - SPRING-LOADED CLUTCH SPIN TEST PROCEDURE