Patent GB-882331-A (GB)
Title: Improvements in or relating to control circuits for electromagnetic clutches
IPC: H02H7/08
Filed: 1958-06-05
Abstract: 882,331. Clutch control. FRANCAISE DU FERODO S.A. June 5, 1958 [June 5, 1957; March 29, 1958], No. 18057/58. Class 80 (2). An electromagnetic clutch E for motor vehicles is energized for at least part of the engagement period by the usual engine-driven generator D, the two-part field winding I 1 , I 2  of which has mixed excitation during speed responsive clutch engagement, the former I 1  excited from a battery B through a resistor R 1  and the latter I 2  from the generator D itself through a resistor R 2  whilst after clutch engagement the field windings are switched by a relay 11 sensitive to generator voltage, or by an output speed responsive governor (Figs. 9 and 10, not shown) to shunt excitation by the generator alone. The mixed excitation giving a parabolic generator voltage-speed characteristic (Fig. 3, not shown) providing progressive drive take-up in the clutch with increased engine speed. The form of the characteristic may be altered by adjusting the resistors R 1  and/or R 2  which may also compensate for clutch wear. In Fig. 14 the relay 11 acts also as the usual battery-charge cut-out and has two voltage windings 11 1  and 11 2 , the former of which is always energized from the generator whilst the latter 11 3  is only energized on actuation of a switch 15 by high engine manifold depression at 16, providing a change-over at a lower speed for small throttle openings. Alternatively (Fig. 8, not shown), a single relay coil is in series with a resistor which is bridged for high engine manifold depression. The switch 15 also bridges a torque limiting resistor R 3  which is inserted in the clutch circuit on high engine manifold depression above change-over, before which it is bridged by the central switch of the switching means 10, to prevent shocks or skidding on closed throttle down-shift. Alternatively (Fig. 9, not shown), the resistor R 3  may be bridged by a switch operated in dependence on accelerator pedal position (e.g. bridged before quarter open). Part of the resistor R 1  and/or R 2  is bridged for second and higher ratios providing a lower change-over speed in these non-starting ratios. An emergency switch 24 is provided for connecting the clutch E to the battery B if the generator D fails and a declutching relay 25 is controlled from a gear shift lever switch 26. The circuit is completed by the usual ignition switch 22, and the usual battery-charging voltage regulator 23 (less cutout) is provided. In Fig. 15 a two-part field winding I 1 , I 2  is excited, below change-over, partly from the battery B, through ignition switch 146 and resistor R 1  and partly from the voltage regulator Re, supplied at 142 from the generator D, through the resistor R 2 . The clutch E is energized by the generator D through the emergency switch 150, line 156, gear shift relay switch 154 and a wear adjustment resistor R 5 . The change-over relay 111 is energized from the generator D through the switch 150, resistor R 4  which is bridged by a switch 115 on high engine manifold depression. When the change-over speed is attained the relay moves the contacts 140, 143 which engage the contacts 148, 149 before breaking their contact at 144, 147, thereby introducing an intermediate condition in which both windings are fed from both the generator and battery. Increased energization of the relay 111 causes the relay contacts 140, 143 to break from 144, 147 and opens the switch 157, whereafter the field winding is supplied directly by the generator only and the clutch is supplied from the contact 150 through the torque limiting resistor R 3  or its bridging switch 115 for low manifold depression. The voltage regulator terminal 152 now supplies a charging current to the battery through a series coil 153 which assists the relay coil 111. In Figs. 9 and 10 (not shown) the change-over relay is operated by a vehicle speed-responsive governor and the clutch is energized above change-over from the battery. An additional resistor is provided in the clutch circuit (Fig. 10) which is bridged on low manifold depression or if the vehicle is on a slope greater than a predetermined value. As a safety factor the change-over speed is normally above the full clutch engagement speed, but in Fig. 13 (not shown) the changeover speed is reduced and a time-delay is introduced before change-over takes place. The time delay comprises a bimetal strip which is heated by a resistor the circuit of which is made by closing a generator relay operated switch when the clutch engagement speed is reached. After a predetermined delay 3-4 seconds, the bimetal strip closes the change-over circuit. The two field windings may be symmetrically arranged on the polepieces or arranged one on one polepiece and the other on another polepiece. Figs. 3 ... 6 and 16 (not shown) are graphs of generator voltage against generator speed; engine and clutch torque against generator speed; time against engine speed at full throttle; generator voltage against generator speed indicating possible change-over points; generator voltage increase (expressed as a percentage of the battery voltage) against engine speed in r.p.m.