806,184. Friction clutches ; gearing for stopping and starting machinery. DAIMLERBENZ A.G. Feb. 1, 1957 [Feb. 3, 1956], No. 3603/57. Class 80 (2). [Also in Group XXIX] An hydromechanical clutch driving a changespeed gear comprises a pump wheel 16 and a turbine 17 carrying friction clutch rings 21, 22 directly engaged when the hydrodynamic converter is inoperative, and disengaged by the pressure of the liquid within the converter sliding the turbine leftwards of Fig. 1 when the converter is operative. In the form shown, the converter has a reactor 32 which can be stationed by applying a brake 33. The clutch rings 21, 22 are engaged by springs 26 acting between a reaction plate 23 and the turbine 17. A friction clutch 30 in series with the turbine 17 and a driven shaft 14 is engaged by springs 28 acting on the back face of a ring piston 27, the space at the back of the piston being vented to the atmosphere through a conduit 44. Liquid is supplied to the converter through pipes 34, 35, centrifugal force within the rotating converter forcing the turbine 17 leftwards against the bias of the springs 26 to disengage the clutch rings 21, 22. Liquid then leaks out between the clutch rings and passes via a space 36 and passages 37, 38 to a return pipe 39. If the free flow of liquid through the return pipe 39 is obstructed, pressure builds up in the space 36 and acts on the front face of the ring piston 27, which moves rightwards against the bias of the springs 28 to disengage the series clutch 30. In a modification, Fig. 2 (not shown), the springs 26 are omitted and the direct drive friction clutch rings 21, 22 are engaged solely by supplying liquid under reduced pressure to the space 36, this pressure not being sufficient to disengage the series clutch 30. Control of the arrangement is effected by a circuit fed with liquid from a pump 45, Fig. 3. A pipe 46 leads from the pump to a piston valve 47 which, when set to position M, directs liquid through a passage 48 to the pipe 39 and, as already described, the space 36 to engage the direct drive friction rings 21, 22. The torque converter supply pipe 34 is connected through a discharge pipe 49 to a reservoir. When set to position H, as shown, the valve 47 connects the pipe 46 to the supply pipe 34 so that the torque converter is filled and, when rotated, causes the clutch rings 21, 22 to be disengaged. The liquid leaking past the clutch rings to the space 36 discharges through the pipe 39 to a port opened by the valve 47 and then to a conduit 50. The pressure in the conduit 50, and hence in the space 36 &c. is controlled by a pressure relief valve 52 which opens to a discharge port 54. The relief valve 52 is spring- biased to the closed position, and the pressure in the conduit 50 &c. tends to open it against this bias. To disengage the series clutch 30 between the turbine and the driven shaft, a slide valve 59 is moved from the position E shown to a second position A, where it connects a pipe 58 leading from the pump 45 to the cylinder space 60 at the bottom of the pressure relief valve 52. The pressure of the liquid supplied by the pump 45 is then added to the bias of the spring tending to close the pressure relief valve 52, so that the pressure in the conduit 50 &c. builds up until the series clutch 30 is disengaged. The pressure of the liquid in the space 60 is limited by a relief valve 62. To disengage the series clutch 30 when the piston valve 47 is set to position M and the friction clutch rings 21, 22 are engaged by liquid supplied under pressure through the pipe 46 and passages &c. 48, 39, 36, the slide valve 59 is again moved to the position A. The pressure of the liquid supplied by the pump 45 is then applied through the pipe 58 to the space 61 at the bottom of a second pressure relief valve 53 controlling the pressure in the conduits &c. 51, 48, 36. Again the pressure in the space 36 builds up and the series clutch 30 disengages. Opening the valve 59 supplies liquid under pressure through a pipe 63 to a cylinder 64 containing the end 65 of the piston valve 47, which is accordingly restored to its H position for hydrodynamic drive unless it is held in its H position by a lock (not shown).