Patent GB-880819-A (GB)
Title: Improvements in or relating to clutches
IPC: F16D27/08
Filed: 1959-04-24
Abstract: 880,819. Positive clutches; clutch control. BENDIX CORPORATION. April 24, 1959 [April 25, 1958], No. 14074/59. Class 80 (2). An electromagnetic, frictionally synchronized positive clutch for machine tools comprises friction discs 16, 17 respectively splined to a driving member 11 housing a winding 12 energized through a slip ring 51, and fingers 20 of a driven member 13 shown connected to a gear-wheel 22, a disc presser plate 28 being adjustably mounted on an armature 27 axially movable with respect to the member 11 and opposed by springs 31, and positive teeth 44, 45 respectively formed on a further armature 35 splined at 41 to the member 11 and opposed by springs 56 and a ring 46 slots 47 of which engage the fingers 20, and sequenced control means effects actuation of the positive clutch armature 35 after the members 11, 13 have been approximately synchronized by actuation of the friction clutch armature 27, the actuation of armature 35 necessitating an electromagnet field of flux density higher than that necessary for actuation of the armature 27. This higher flux density is necessary only for initial attraction of the armature 35, the flux density required for friction clutch actuation sufficing to hold positive clutch engagement. The difference in flux density requirement is achieved by suitable location of the winding 12, a bridge 57 and an air gap 58 being provided on the armature 35 side, and by springs 56 being stronger than springs 31. The bore of the armature 27 is tapered at 29 to avoid sticking. Control.-D.C. obtained from A.C. lines 70, 71 through a transformer 72 tapped at 73 and a full-wave rectifier 75 is fed through a line 80 to the winding 12 through contacts 96<SP>1</SP>, a potentiometer 81 adjusted to half the voltage at the winding 12, and the slip ring 51. The potentiometer 81 may be shunted by closure of contacts 91, for full voltage at the winding 12, by energizing a relay 90 in a line 85 across the A.C. lines 70, 71. A relay 95, in a line 94 also across the A.C. lines 70, 71, is energized for clutch engagement by closure of manual start switch contacts 93 to close contacts 96 of a relay 95 holding circuit 97 and to close the contacts 96<SP>1</SP> and contacts 96<SP>11</SP> in the line 85, the holding circuit 97 being broken for clutch disengagement by opening manual stop switch contacts 98. The line 85 also comprises, in series, a rectifier 86, contacts 101 opened by energizing a relay 100, and a timing control comprising a capacitor 88 shunted by a resistor 87, which control limits the current flow duration in the line 85 to that of the capacitor charging time, the resistor 87 dissipating residual capacitor charge when the line 85 is broken. In Fig. 4, the relay 100 is energized by current from a magnetic pick-up 60 which is mounted in the member 11 so that its exposed core end is adjacent a notched bore of the last disc 17. Upon relative rotation between the members 11, 13 inwardly projecting tangs formed between the notches in the disc 17 induce an alternating current in the pick-up 60. The pick-up current is fed through a slip-ring 52, a voltage doubling rectifier-capacitor network 102 and thence, as D.C., to the relay 100, a capacitor 104 and resistor 105 being shunted across the relay 100 to prevent too-rapid opening and closing of contacts 101. In operation, with the driving member 11 rotating and the manual contacts 93 closed to hold the relay 95 and close contacts 96<SP>1</SP>, 96<SP>11</SP>, the winding 12 will be fed at half voltage, thereby actuating the friction clutch armature 27 only, until, when synchronism is approached, the relative rotation between the members 11, 13 is insufficient to maintain energization of the relay 100, whereupon the contacts 101 close to energize the relay 90, shunt the potentiometer 81 and feed full voltage to the winding 12. Once the capacitor 88 is fully charged current flow via the resistor 87 will be insufficient to maintain energization of the relay 90 and the feed to the winding 12 will revert to half voltage which is sufficient to hold positive clutch engagement. In Fig. 5 (not shown) in place of the pick-up 60 control, the relay 100 is controlled by a time delay clock. Energizing of the relay 95 also closes contacts in the A.C. clock feed circuit to energize the relay 100 and open contacts 101, the clock subsequently de-energizing the relay 100 and closing contacts 101 after the lapse of sufficient time for synchronization of the members 11, 13.