Patent GB-841969-A (GB)
Title: Improvements in or relating to an electric control circuit for an electro-magnetic clutch
IPC: F16D48/06
Filed: 1957-12-18
Abstract: 841,969. Controlling electromagnetic clutches. FRANCAISE DU FERODO S.A. Dec. 18, 1957 [Dec. 19, 1956; Feb. 12, 1957], No. 39404/57. Class 80 (2). In a control circuit for an electromagnetic clutch comprising a first connection for the starting phase and at least a second connection for later phases the supply to the first connection is from a third brush of a vehicle generator and the changeover switching to the second connection is delayed until the clutch can transmit full torque, means being provided to prevent the supply of excess voltage to the clutch circuit. A motor vehicle generator 44 has a first brush 41 supplying a voltage regulator unit 15 connected to a battery B, a second brush 42 being connected to earth and through the generator field 45 to the regulator 15. A third brush 43 of the generator, located between the brushes 41, 42 at an angular position between +15 degrees and - 45 degrees taking the polar axis as the origin and counting the angles positively towards the brush 41 and negatively towards the brush 42, is connected together with the battery to a manual change-over switch 61. The switch 61 is connected to a double changeover relay 65 and provides for battery operation of the electromagnetic clutch 10 for overhaul or repair. The change-over relay 65 has two moving fingers actuated by a solenoid 71 by battery current through a switch 72 controlled by the speed of the gear-box output shaft such that below a predetermined speed the fingers 69, 70 contact 63 and 68 and above that speed the finger 69 contacts 64 to connect a changeover relay 76 to the battery. The switch 72 may alternatively be controlled by gear-box input or intermediate shaft speeds. The finger 70 of the relay 65 is connected to a non-inductive stabilizing resistance 48 and a switch 49 which is only closed when first and reverse gears are engaged or may be controlled by generator voltage. The resistance 48 provides a stabilizing means for the third brush voltage applied to the clutch and makes the increasing voltage with engine speed more gradual. The connection from relay finger 69 to the relay 76 is to a contact 74, a second contact 75 being connected to the main brush 41 through a resistance 77, to facilitate declutching, the relay 76 being operated by the vehicle brake stop-light switch 80 such that when the brakes are applied the clutch 10 can only be supplied from the brush 41. Current from the relay 76 passes through a relay 83 controlled by a gear lever switch 86 to a wearadjusting resistance 27 and to an engine-brake resistance 88 to the clutch 10. The enginebrake resistance 88 is shunted by a switch 89, which closes when the intake manifold depression is below a predetermined figure, to limit the torque capacity of the clutch on overrun and prevent engine stalling or rear-wheel locking. In operation, to start the switch 62 is put in contact with 67; the switch 72 is open such that finger 70 is in contact with 68 and finger 69 with 63; the switch 49 is closed; switch 80 is open such that finger 79 is in contact with 74; switch 86 is open such that finger 84 is in contact with 82; switch 89 is closed. Under these starting conditions the clutch 10 is supplied from the brush 43 with the stabilizing resistance 48 increasing the voltage progression. As speed increases the fingers 69, 70 will change over and the clutch supply will be ensured by the battery. In second or higher gears the switch 49 is opened but the supply is ensured by the brush 43 if the vehicle speed is low. The low speed of change-over results in the prevention of high voltages from brush 43 being applied through the circuit. On application of the vehicle brakes, the relay 76 changes to supply the clutch from the main brush 41 which at idling speed produces insufficient voltage to engage the clutch. In a simplified embodiment (Fig. 1, not shown) the generator 44 and battery B feed to a change-over relay actuated in response to a speed of a gear-box shaft, this relay feeding via a gear-lever switch relay to the clutch 10. In another embodiment (Fig. 2, not shown) the third and main brushes are connected to the change-over relay through a voltage-sensitive reversing relay to prevent excessive voltage in the clutch circuit.