Types and Functions of Mechanical Couplings and Clutches
Understanding Mechanical Couplings
Durable Couplings are essential machine components used during power transmission. Their primary functions involve connecting shafts, facilitating mounting, and simplifying maintenance.
Drive Couplings
These couplings provide a direct link between two shafts, typically transmitting rotational motion. They often involve plates or screws connecting the elements, allowing for power transfer but generally not accommodating misalignment unless specifically designed to do so. They are often simple to calculate and implement.
Torque Limiting Couplings
These are rigid couplings designed to transmit power only up to a certain torque value. They often incorporate a shear element, like a shear pin (Kabila), which is designed to break or shear if the transmitted torque exceeds a safe limit, thus protecting the machinery. Once sheared, the security element must typically be replaced after dismantling. They are simple and cost-effective safety devices.
Flexible (Elastomeric) Couplings
These couplings incorporate a flexible element (like a rubber ‘jersey’ or sleeve) that allows for a certain amount of torsional deflection or temporary deformation under load. This flexibility helps absorb shock and vibration, and the element typically returns to its original shape after the load is reduced. They feature a relatively simple construction.
Misalignment Couplings
These couplings allow for power transmission between shafts that are not perfectly aligned (non-coaxial). A well-known example is the Cardan joint (Universal Joint) or the Oldham coupling. The structure of a Cardan joint, with its central cross (gurutzea) and yokes (forks), allows transmission between shafts at a variable angle. Often, Cardan shafts incorporate splined sections (ildokatu) to allow for changes in length (extensible drive), making them suitable for a wide range of applications.
Exploring Mechanical Clutches
Clutches are couplings designed to allow the connection (engagement) or disconnection (disengagement) of power transmission between shafts, enabling motion to be started, stopped, or controlled.
Actuated Clutches
These clutches require an external actuation mechanism to control their engagement or disengagement, providing continuity or non-continuity of motion.
Friction Clutches
Continuity of motion is achieved through friction between surfaces. These clutches can often be engaged or disengaged while the machine is running. Due to potential wear, friction surfaces are made from specialized materials. They are very common in automotive applications. Example: In a car, pressing the clutch pedal (enbrageko pedal) typically uses levers or springs to separate the pressure plate from the friction disc (igurtzimnduzko album), interrupting power transmission. Releasing the pedal allows springs to press the disc against the flywheel, re-establishing continuity.
Toothed (Dog) Clutches
Engagement is achieved by interlocking solid teeth between two elements, providing a positive, non-slip connection. These are often found in conventional machine tool gearboxes for speed changes. When changing speeds, a toothed coupling (horztun portfolio coupling) is engaged. Synchronizing mechanisms (sinkronizagarri igurtzimenduzko cone), often using small friction cones, may be used to match speeds before engagement, reducing wear.
Fluid Couplings
These use a fluid (often oil, not typically gelatinous ‘water’) contained within a housing with two main components: an impeller (driver) and a runner (driven), both equipped with blades. The driving impeller spins, imparting kinetic energy to the fluid, which then drives the runner. The conductive liquid mass transfers momentum (herrestatzen). They provide smooth start-ups and damp torsional vibration.
Automatic Clutches
These clutches engage and disengage automatically based on changes in operating conditions (like speed or torque) without external intervention.
Centrifugal Clutches
Engagement occurs automatically only when a certain rotational speed is exceeded. As engine speed increases, centrifugal force acts on mobile masses (shoes or weights), causing them to move outward and engage the clutch drum, transmitting power. When the speed drops below a certain level, the centrifugal force decreases, and springs retract the masses, disengaging the clutch.
Torque Limiting Clutches
These clutches automatically disengage or slip when the transmitted torque exceeds a specific preset value, protecting the drive train. Once the torque reduces, they may automatically re-engage. Some designs break permanently (like shear pins), while others slip temporarily. A common mechanism involves spring-loaded balls resting in conical slots (artekatik). When excessive torque occurs, the balls are forced out of their slots, causing separation and interrupting power transmission.
Unidirectional (Overrunning) Clutches
These clutches transmit torque in only one direction of rotation and allow freewheeling in the opposite direction. Examples include automatic screwdrivers, socket wrenches (ratchets – trinket), and bicycle freewheels. They can convert reciprocating motion into intermittent rotational motion. They are typically used for low-speed applications.