| 摘要 |
825,149. Operating clutches. BLISS CO., E. W. Oct. 9, 1956 [Oct. 10, 1955], No. 30769/56. Class 80 (2). In a fluid-pressure engaged friction clutch for a crank-driven press or the like the fluid-pressure loading is varied automatically throughout each cycle to protect the machine against overloading. The clutch 10 comprises friction discs 21 which are engaged by pressure fluid on a piston 19 through a pipe 17, brake discs 23 being simultaneously released. On release of the fluid pressure the clutch discs 21 are freed and the brake discs 23 engaged by springs 27. Pressure fluid for the clutch is supplied from a tank 12 through a high- and low-pressure valve 20 and a stop and start valve 22 to pipe 17 and is also controlled by a valve 26 and escape orifice 36. These valves 20, 22 are opened and the valve 26 closed against spring loading on energization of electromagnets 32, 46, 56 respectively which are controlled by a start-stop and jog-run panel 42, Fig. 3, and drum switches 44, 52, 50, 54, 56 rotated in synchronism with the crankshaft of the press. With the start valve 22 open and the valve 20 also open full pressure from tank 12 is supplied to pipe 17 to engage the clutch and release the brake and this condition applies during the return stroke of the press crankshaft. At the top position of the crankshaft switches 50, 52 de-energize the solenoid 32 to close valve 20. The clutch pressure is then reduced to a lower value controlled by a relief valve 24 for about 150 degrees of rotation of the downstroke. At this position switch 54 operates solenoid 56 to open valve 26 which progressively releases the clutch pressure through the orifice 36 during the remainder of the working stroke when the mechanical advantage of the crankshaft and the danger of overload is greatest. After bottom dead centre valve 26 is closed and valve 20 opened to apply full pressure for the return stroke again. After starting the valve 22 normally remains open unless closed manually to stop the press or automatically on slip arising from overload occurring. To this end electromagnet 46 is controlled by a rotating switch 44 and a time relay 40 in parallel. The switch normally closes before the time relay opens so that solenoid 46 remains energized. If, however, slip occurs in the clutch due to overload the relay 40 opens before the switch 44 closes so that valve 22 is closed and clutch pressure released through outlet 48 to apply the brake and stop the press. An alternative to the valve 26 and orifice 36 to control the clutch pressure release consists in a spring- loaded relief valve the loading of which is modified by a crankshaft operated cam. The valves 20 and 24 could be dispensed with if single pressure loading of the clutch other than at the critical working period would be sufficient for satisfactory operation. |
