697,088. Clutches; change-speed gearing. AKTIEBOLAGET LJUNGSTROMS ANGTURBIN. Jan. 20, 1950. [Jan. 20, 1949], No. 1541/50. Class 80 (ii). [Also in Group XXIX] In a power transmission having a hydrodynamic torque converter for providing power transmission from a driving member to a driven member including, for providing an alternative mechanical driving connection between said members, a friction clutch, a ratio regulator, a source of pressure liquid and conduits and valves controlling the flow of the pressure liquid, said liquid produces engagement or disengagement of said clutch, the ratio regulator being rendered inactive when the clutch is engaged. The converter 24 contained within a stationary casing 10 comprises a rotating housing 16 driven from the engine flywheel 18 on the driving shaft 14 and carrying impeller blades 26, a turbine 36 on a shaft 28 carrying blades 38, 42, and a reaction or guide member 48 carrying blades 44. A fluid operated clutch 72 is interposed between the impeller 16 and the turbine shaft 28 to provide direct drive from the engine shaft 14 to the turbine shaft. A brake 402 comprising a drum 406 on the reaction member 48 and shoes 408 supported by a beam 10a on the casing 10 enables the guide blades 44 to be held stationary. A gear 451 on the turbine shaft meshes with gearing 434 to drive a reverse gear 456. The output shaft 436 carries a dog clutch 438 with friction clutches 440, 442 for synchronising in relation to gears 451 and 456, a ring 448 being moved by a lever 450 to engage the gear 451 for forward, and the gear 456 for reverse, drive. The pump 460 driven by a gear 462 meshing with an intermediate gear 464 and the toothed rim 466 of the rotating impeller casing, draws in fluid at 468 and delivers it through piping 470 to control valves 472 and 474 and through piping 476 to the control valve or ratio regulator 478, the latter comprising an axially slidable valve rod rotating with the gear 462 and having a stroke limiter 488 at one end and a threaded portion 486 carrying a member 490 in frictional engagement with a gear 492 driven from the turbine member of the converter. The gears 462 and 492 are so dimensioned as to give gear 492 the same speed as the gear 462 when the ratio between the speeds of the impeller and turbine reaches the value at which torque multiplication of the converter becomes zero, at which point it is desirable to shift to direct drive. At speeds below this shifting point, that is when the speed of gear 492 is less than that of gear 462, the valve rod of the ratio regulator is in its right hand position but at higher speeds the rod is moved by the relative rotation of the screw thread in the member 490 to its left hand position. A sleeve 508 surrounding the ratio regulator has three borings 510, 512, 514, and is moveable axially by a centrifugal regulator 506 mounted on the gear 492. At low vehicle speeds, i.e. with the turbine and gear 492 rotating slowly, the regulator 506 assumes the position 516 holding the sleeve 508 in its extreme left position in which the boring 510 cannot communicate with pipe 504 whatever the position of the ratio regulator 478 so that the latter cannot be instrumental in raising the valve 474 to establish direct drive. At very high speeds the regulator 506 assumes the position 520 in which the sleeve 508 is moved to its right hand position to connect conduit 476 via the sleeve groove 630 and the conduits 628, 568 independently of the position of the ratio regulator, thereby raising the valve 474 to direct drive position. The gear shifting mechanism 664 comprises a member 666 having a projection 672 engaging a fork 676 on the lever 450 and a projection 668 having a cam surface 669, and a lever 662. In its lower position 680 the member 666 moves the lever 450 so that the ring 448 of the complementary gearing engages the gear 451 to give forward drive, while in the upper position. 682 the ring engages the gear 456 to give reverse drive, in both these extreme positions the lever 662 being raised clear of the valve rod 536 whereas during movement from one position to the other the cam surface 669 causes the lever 662 to depress the valve rod 536 to its neutral position in which a disc 633 on the rod assumes the position N. When the member 666 is moved to bring the ring 448 of the complementary gear into neutral position, the cam 669 depresses the lever 662 and holds the valve 474 in position N against any influence of ratio regulator 478, the centrifugal regulator 506, the throttle pedal 606 or the brake pedal 535. Pressure pipe 470a is closed, pipes 552 and conduits 550, 554 are open to outlet 562 thus emptying the servomotor 424 to release the reaction member brake 402 and releasing the clutch 72, whereas pressure fluid is supplied to the converter via pipes 470b and 548. When the complementary gear ring 448 is put in forward or reverse drive with the throttle pedal 606 in its neutral or engine idling position 612, the pedal moves the valve 472 into its lower position, conveying pressure fluid through conduits 470c and 570 to the upper chamber of the servomotor 532 so that the piston 567 holds the valve 474 in, neutral position N, the lower chamber being vented via conduits 568 and 504 and outlet 622 since the centrifugal regulator is in the position 516 holding the sleeve 508 to the left. If, for example due to the vehicle moving downhill, the output shaft and hence the turbine rotates at a speed relative to the impeller so that the shifting point is reached, the gear 492 rotates faster than the gear 462 and the valve rod 478 is moved to its left position, the centrifugal regulator moves towards the position 518 to move the sleeve 508, and communication is established from the pump delivery 476 via borings 510, 514 and conduits 504, 568 to servomotor 532. The piston 567, having a greater effective area on its lower side than on its upper, raises the valve 474 to the position D in which pressure fluid flows via conduits 470, 470b, groove 540, and conduits 554, 550 to engage clutch 72 to give direct drive, i.e. applying engine braking. Pressure in the converter 24 falls due to conduit 548 being connected to conduit 564 and outlet 566. Fluid pressure from conduit 554 moves the guide blade timing valve 556 to connect a pipe 553 with the outlet 558b, thereby releasing the guide blade brake 402. By depressing the brake pedal 535 to move the valve 702 to the left, fluid from pipes 470a and 557 is admitted to pipe 553 to engage the brake 402 so that the engine braking is augmented by hydraulic braking. When the throttle pedal is depressed, at low vehicle speeds the sleeve 508 is in the left position with the ratio regulator 478 to the right and hence conduit 570 opens to outlet 618 and conduit 568 via pipe 504 to outlet 622, no pressure fluid acts on piston 567 which is constrained by its springs to move the valve 536 to position H, hydraulic drive. At higher vehicle speeds the centrifugal regulator moves to position 518 and sleeve 508 and valve rod 478 are positioned as shown in Fig. 8 in which the bore 510 remains closed and hence since no pressure fluid is supplied to the servomotor 532 the control valve 474 remains in hydraulic drive position. If the speed ratio between the impeller and turbine members exceeds the shifting point, the ratio regulator 474 is moved to the left, outlet 622 is closed and bore 510 connected to pipe 504 and servomotor 532 to raise the valve 536 to direct drive position. At higher vehicle speeds the regulator 506 moves to position 520 and takes the sleeve to the right so that pressure fluid is supplied via conduits 628, 568 to maintain direct drive irrespective of the speed ratio. When the clutch 72 is engaged, the impeller and turbine members rotate in unison and the ratio regulator is inoperative. When shifting from hydraulic to direct drive the disc 633 momentarily closes a switch 638 to actuate a solenoid 640 which interrupts the ignition or closes the throttle 644 to interrupt the torque developed by the engine. A hand brake 722 may be applied when the control valve 474 is in neutral position, and is automatically released when the valve shifts to hydraulic drive since pressure fluid is then admitted to the conduit 730 to depress the piston 726 and release the ratchet 718. The invention is also described when used in conjunction with a hydraulic torque converter having a stationary casing. In another embodiment electrically actuated control is utilised in place of fluid pressure actuated control for certain of the control elements.