Patent GB-854969-A (GB)
Title: Improvements in or relating to electro-magnetic clutch control means
Filed: 1956-12-03
Abstract: 854,969. Clutch control. FRANCAISE DU FERODO S.A. Dec. 3, 1956 [Dec. 3, 1955; April 23, 1956], No. 36961/56. Class 80.(2). An electromagnetic clutch 1 on..a motor vehicle is energized from two different systems, differing by source and/or circuit resistance, either of which becomes operative under control of a relay 23 actuated by, in addition to other factors, the vehicle service brake system 28. The two energizing systems may comprise separate sources such as the usual battery 4 and engine-driven generator 5; or a common source feeding the clutch through either of two circuits having different resistances; or a single generator with or without a resistor in its field circuit. The systems may be such that at engine idle one provides complete declutch, whilst the other provides part clutch engagement to between 5 and 25 and preferably 10% of the full throttle maximum engine torque. Vehicle and engine speed may also control the change-over relay, and together with the brake control, prevent engine stall on deceleration, particularly when braking. A switch 29 sensitive to gear-shift lever movement, causes clutch release during gear-shift. As shown, a generator-fed clutch-energizing circuit provides automatic clutch release at engine idle, and includes a resistor R 1  ... R 4  varied steplessly or in steps by means responsive to engine speed, torque, throttle-setting and time acting alone or in combination to modify any excessive clutch engaging or slip action which might otherwise result from a too rapid or too slow operation of the accelerator by the driver. In Fig. 1, the resistors R 1 , R 2  are shorted in succession with decrease in engine-manifolddepression acting on a diaphragm 10, whilst the resistor R 3  is shorted by speed-responsive oil pressure provided by an engine-driven pump 21. The resistor R 4  is shorted at the same time as the energized relay 23 actuates a switch 21 to change over from clutch-energization by the generator 5 to the battery 4. Such change-over energization of the relay 23 is effected by closure of either a switch 24, closed in response to increase in engine speed above 1800 r.p.m., or by closure of two series switches, one, 25, closed by increase in vehicle speed above 5 or 20 k.p.h. (as by an oil pump or speedometer), and a second, 26, normally closed but opened in response to a predetermined pressure in the service brake system 28. Closure of the vehiclespeed switch 25 above the predetermined speed causes battery energization of the clutch for engine braking, whilst application of the brakes opens the switch 26 to cause a return to generator energization of the clutch, preventing engine stall on sudden deceleration. The usual generator voltage regulator 7 is provided. In Fig. 2, not shown, and Fig. 6, energization of the change-over relay 23 only cuts out the battery circuit 4 at 22, whilst its de-energization leaves the clutch 1 energized by the battery 4 and generator 5 combined. The vehicle speed switch 25 opens with speed increase and is in parallel with only the brake switch 26 which now closes with brake application, the former, 25, being set to open at a very low speed, 5 k.p.h., to maintain battery energization for engine braking above that speed, whilst the brake switch 26 closes on braking to cut out battery energization and leave the clutch under generator control alone, to prevent engine stall. Fig. 3, not shown, has generator energization only, branching to the clutch through two circuits each including different variable resistors, and selected under control of two change-over switches in series and operated by brake-pressure and vehicle speed respectively. In Fig. 4, not shown, the brake and speed switches control shorting of a resistor in the generator field circuit. In Fig. 6, the change-over relay 23 also shorts a portion of the resistor chain R 1 1 ... R 4 <SP>1</SP> in the combined battery and generator energizing position. The resistors R 1 1 ... R 4 <SP>1</SP> are shorted successively by a cam bar G 1 , operated by a piston 35 subject to inlet manifold depression 13 under control of a slide-valve 40 operated jointly with the engine throttle control 42. With released accelerator, position shown, a groove 45 in the slide-valve 40 applies depression to the piston 35, which moves left, inserting all the resistors R 1 <SP>1</SP> &c., so that the clutch remains fully disengaged. Accelerator depression cuts off the manifold connection 13, and applies successively and cumulatively in accordance with the amount of accelerator movement atmospheric bleeds 50 which permit a timed rightward movement of the piston 35 by a spring to cut out the resistors R 1 <SP>1</SP> &c. successively. The rate of engagement of the clutch is thus determined by the degree of accelerator depression. Initially, on accelerating from rest, the vehicle-speed switch 25 is energizing the relay 23, cutting out the battery energizing circuit and inserting the whole resistor chain R 1 <SP>1</SP> ... R 4 1 in the generator energizing circuit of the clutch 1. The latter thus engages under generator speed and accelerator-modulated time control, as described above. On decelerating, the vehicle-speed switch 25 is open, relay 23 de-energized, so that battery energization of the clutch maintains engine braking to the very low closure speed of the switch 25, unless excessive service braking energizes the relay at 26 to change over to generator energization only, which would declutch for preventing engine stall.