596,908. Friction-clutches. HOBBS, H. F. July 5, 1945, No. 13943/44. [Class 80(ii)] To obtain progressive engagement of a friction-clutch, wherein a faced driven disc 20 is gripped between driving and presser-plates 11, 24, by pumped oil-pressure applied to an annular concentric diaphragm 26 clamped at its inner and outer edges, lubricating-oil is supplied under pressure in a limited quantity to the inner peripheries of the frictionsurfaces to escape freely at their outer peripheries, and an inner oil escape-path, such as holes 60, is also provided to prevent at all times oil- . accumulation at that point, the oil supply being cut-off or reduced during take-up and engagement. Engagement is thus initiated at a low friction-coefficient with liberal slip and is completed at a normal high coefficient as the hydraulic engaging pressure squeezes out the oil. To facilitate the latter action the friction-plates are either truly parallel or slightly tapered so as to contact at their inner peripheries first and shut out further oil supply. The clutch may be allowed to slip or disengage automatically at low engine speeds, as by using a speed-responsive engine-driven oilpump or by making the clutch depend partly on centrifugal pressure for engagement, The pump may be the enginelubricating pump in which case the clutch may act as a centrifugal oil-cleaner. Oil may also be circulated continuously behind the presser-plate 24 in the engaged position to cool it and prevent overheating of the diaphragm. In Figs. 1 and 2, oil is picked up from the clutch-housing through a suction-pipe 44 by a separate gear-pump in a stationary housing 40, surrounding the driven shaft 22, the output of the pump being controlled by a two-position selector-valve 47 which, in one position, for clutch-engagement, feeds, through a radial passage 37, a chamber 14, behind the rubberised-fabric diaphragm 26, and when turned to its other position, for clutch-disengagement, cuts off the supply to the diaphragm-chamber 14 and diverts the pump-output through restricted passages 53, 54 to spray into the clutch and pass centrifugally to the inner periphery of the bonded asbestos frictionsurfaces 18, 19, to coat them rapidly with oil, which escapes at their outer peripheries, and passes out through openings 61 in the driving drum 11. In this position the diaphragm-chamber 14 drains through an escape-port 32, Fig. 2, controlled by a valve 34, which, in the absence of pump-pressure in the passage 37, is centrifugally balanced by the oil in the passage 37 and is moved by a spring into the position shown, to communicate the escapeport 32 with a port 30 in the diaphragmchamber 14. When pump-pressure is applied to the passage 37 for clutchengagement, the valve 34 is moved inwards to cut-off the escape-port 32 and communicate the passage 37 with the diaphragm chamber port 30. Additional constant-leak ports 180 may be provided in the diaphragm-chamber 14 and may be controlled by speed and/or pressure-responsive means such as a spring-loaded centrifugallycontrolled ball in a taper escape passage. Springs 23 apply to the presser-plate 24 a permanent disengaging load which is sufficient to cause rapid disengagement of the clutch in opposition to centrifugal pressure in the diaphragm chamber 14 at idling speeds before the chamber has had time to drain. A groove 87 is provided in the diaphragm-chamber 14 at a greater radius than the supply and leak-ports 30, 180 to receive accumulated oil-sludge, thereby cleaning the oil. Between the clutch-engaging diaphragm 26 and the presser-plate 24 is a plate 28 of resinbonded fabric of low thermal conductivity, and this plate has facial grooves 29 to carry away any leakage oil when the clutch is engaged, thereby cooling the presser plate. In the form shown in Fig. 4, which provides for rapid declutching, there are no leak or supply ports at the outer periphery of the diaphragm-chamber 14 which remains permanently filled with oil, the centrifugal pressure of which is balanced by oil in a chamber 94 formed by a plate 71 on the other side of the diaphragm 26, which latter acts on the clutch presser plate 24 through a plate 72 and sliding pins 70. Clutch engagement and disengagement are effected respectively by putting either chamber 14 or 94 into communication with a pump-supplied pressure-source 73 through a two-position selector-valve 74 controlled by a lever 79. A port 188 in the supply passage 96 to the disengaging chamber 94 feeds oil to the friction surfaces 18,19 when the chamber 94 is pressurised for disengagement. A sealing-ring 104 on the presser-plate 24 contacts the plate 71 in the clutch-disengaged position, to prevent oil from by-passing the friction surfaces, and is clear of the plate in the clutch-engaged position to provide an escape path to carry away leakage oil, or oil may be circulated continuously through this path to cool the clutch. A deflector shield 98 is also provided to deflect any leakage from the bearing - surface 85 away from the friction surfaces. A sludge-groove 105 and escapeports 61 are provided in the periphery of the driving drum 13. In a modification of the form shown in Fig. 4, (Fig. 3, not shown), the inner periphery of the plate 71 does not bear on the member 92 but is open and formed as a shield to prevent leakage oil from the bearing 85 from reaching the friction surfaces in the engaged position. The inner periphery of the shield may extend to a greater or less radius than that of the diaphragm so that, in the disengaged position with the chamber 94 full, the centrifugal pressure due to the chamber 94 is less or greater than that due to the chamber 14. Leakage oil into the chamber 94 in the engaged position escapes over the pins 70. A spring- plate acts on the pins 70 to cause rapid disengagement against centrifugal pressure alone at idling speeds. The centrifugal pressure in the engaging chamber may provide the main engaging pressure although a pump is always used. Where the engine-pump is used to supply the clutch, an additional pump may be provided to scavenge the clutch-housing and such pump may be formed by the enginestarter teeth 12. The invention may be applied to multiple - clutches in changespeed gearing. Specifications 191,716 and 224,711, [both in Class 80(ii)], are referred to.