Clutches, Brakes, Coupling, and Flywheels n Clutches, brakes, couplings, and flywheels are a group of elements usually associated with rotation that have in common the function of storing and/or transferring rotating energy n In analyzing the performance of these devices we shall be interested in: The actuating force The torque transmitted The energy loss The temperature rise
A simplified dynamic representation of a friction clutch or brake is shown in Fig. 16-la n Two inertias, I 1 and I 2 , traveling at the respective angular velocities; ω 1 and ω 2 , one of which may be zero in the case of brakes, are to be brought to the same speed by engaging the clutch or brake. Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation, resulting in a temperature rise.
n The varies types of devices to be studied may be classified as following: Rim types with internal expanding shoes Rim types with external contracting shoes Band types Disk or axial types Cone types Miscellaneous types
n Figure 16 - lb is a mathematical representation of a flywheel. n An input torque T i , corresponding to a coordinate θ i , will cause the flywheel speed to increase. And a load or output torque T 0 , with coordinate θo , will absorb energy from the flywheel and cause it to slow down. n A flywheel is an inertial energy-storage device. n It absorbs mechanical energy by increasing its angular velocity and delivers energy by decreasing its velocity. Figure 16 - lb
Static Analysis of Clutches and Brakes • Estimate, model, or measure the pressure distribution on the friction surfaces. • Find a relationship between the largest pressure and the pressure at any point. • Use the conditions of static equilibrium to find the braking force or torque and the support reactions. Analyzing general procedure: The net force in the y direction: moment about C from the pressure:
sum of moment about the pin located at A: sum of forces in the x-direction : sum of forces in the y-direction : Can F be equal to or less than zero?
4.2 Internal Expanding Rim Clutches and Brakes n The internal-shoe rim clutch as shown in Fig. 16-3 consists essentially of three elements: n The mating frictional surface. n The means of transmitting the torque to and from the surfaces. n The actuating mechanism. n often used in textile machinery , excavators, and machine tools where the clutch may be located within the driving pulley. n Expanding ring clutches benefit from centrifugal effects ; transmit high torque , even at low speeds; and require both positive engagement and ample release force . Fig. 16-3
n To analyze an internal-shoe device, figure 16-4 shows a shoe pivoted at point A, with the actuating force acting at the other end of the shoe.
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- Spring '16
- Siva Krishins