IMAGE COURTESY OF EATON CORP.
clutches & brakes HYDRAULIC CLUTCHES A clutch is a device used to transmit mechanical power from a prime mover (electric motor or internal combustion engine) to a transmission or driven device. As opposed to a mechanical clutch, a hydraulic clutch uses a fluid coupling device to transmit rotational power at variable operating speeds and without problems of shock loads. The fluid coupling device contains a driving turbine, or torus, also known as the pump, which creates flow within the chambers of the fluid coupling enclosure. This flow drives the output turbine, which is connected to the driven member of the transmission system. Clutches have found use in industrial, automotive, railway, airline and agricultural settings. When selecting a hydraulic clutch, important criteria to consider include what applications, performance specifications and compatibility are desired. The performance of a hydraulic clutch can be broadly specified according to its torque rating, power, rotational speed and maximum pressure. The maximum torque is the greatest rated torque the clutch drive can bear, and is typically the limited factor in most applications. The maximum power capacity refers to the operating power of the load the clutch is intended to operate under, which is a factor of torque and speed. Rotary speed is the intended operating speed that the clutch has been designed to rotate at, while the maximum pressure is the greatest pressure that the clutch can withstand. When considering compatibility of the clutch with driving and driven members, the clutch dimensions, clutch shaft geometry and drive connection type are important considerations. Significant clutch shaft dimensions are bore diameter, clutch diameter, length and weight. Clutch shaft geometry can be in-line, parallel, right angle or another arrangement. The connection type of the clutch shaft can be in-line, through shaft or flanged at the ends.
FLUID POWER WORLD
6 â€˘ 2016
HYDRAULIC BRAKES Hydraulic brakes are used to stop or slow rotating mechanical systems by converting kinetic energy into heat energy. When triggered, they transfer pressure through the use of a fluid and this pressure triggers the braking mechanism by pushing on a piston in a brake caliper or slave cylinder. These braking mechanisms consist of brake types such as drum brakes, disk brakes, band brakes and cone brakes. Each of these braking styles have different braking properties, but they are all powered, by way of hydraulic fluid, from the pressure of a master cylinder or pump. The main specifications considered with brakes are speed, power, torque and maximum pressure. When selecting a brake, the style of braking is the first choice an engineer must decide on. Drum brakes work by applying hydraulic pressure, pushing a braking pad or shoe against the rotating surface, creating friction and slowing the spinning surface down. Disk brakes function by squeezing the rotor with calipers to slow it down. Band brakes work by tightening the band material around the rotating drum, similar to older stationary bikes. A cone brake works by forcing two cone-shaped devices toward each other, one of which is the rotor and the other is the friction material. COMBINATION PACKAGES Because hydraulic brake and clutch components both use fluid power, they can be integrated and manufactured for ease of compatibility and installment into the application. When both clutch and brake components are present, braking can be facilitated by the disengagement of the clutch mechanism, which transmits the power needed to apply the brakes.
6/17/16 4:31 PM
Fluid Power World Handbook 2016