This invention relates to an oil-immersed clutch/brake mechanism for a machine requiring start-stop operation, and is particularly useful for mechanical presses.
Many prior art clutch/brake mechanisms mount the components with the actuating mechanism on the driven shaft, which adds considerably to the inertia which must be started and stopped. This wastes energy and generates large amounts of heat which must be dissipated to maintain acceptable operating temperatures. In addition, the brake must be oversized to stop the added inertia within acceptable stopping angles and times.
An exception to the above-described prior art is shown in Matson U.S. Pat. No. 4,633,986, which has an actuating mechanism mounted to rotate with the driving portion. However, in this arrangement, the bearings are loaded dynamically under axial thrust, which requires appropriately sized bearings and also generates additional heat.
To take advantage of a permissible small size and multiplicity of oil-immersed friction surfaces, brake and clutch engagement forces are considerable. Since most units' actuating mechanisms are carried on the driven shaft, a small piston diameter is desirable to generate the clutch engagement force. One way to attain this employs high pressure hydraulics as an actuating medium. However, low pressure pneumatics are ordinarily applied for machine operation. Hydraulic actuation requires an additional power source for hydraulic pressure which is not commonly available in a plant environment.
Some prior art devices have employed pneumatic actuation to overcome the expense and complexity of hydraulic actuation. Because the pneumatic pressures normally available in industrial environments are in the 60-90 PSIG range, the piston area must be increased considerably over that of hydraulic pistons to produce a sufficient actuating force. This requires a piston diameter far in excess of the smallest necessary friction disc diameter. Therefore, current designs usually compromise by reducing the number of friction discs and making them larger in diameter to accommodate the required pneumatic piston diameters. This results in an inefficient design and adds greatly to the driven inertia.