956,855. Change-speed gear and control. ROLLS-ROYCE Ltd. June 6, 1962 [June 6, 1961], No. 20335/61. Heading F2D. In a hydromechanical change-speed gear of the kind wherein, for at least one ratio, the drive torque is split into two parallel paths, one of which includes a fluid coupling as torque converter, whilst the other is mechanical and which are recombined to form the gear output, a planet reduction train 20, 23, 24 which may be by-passed is provided in the mechanical path. As shown in a gear providing five forward reduced ratios, direct drive and reverse the planet train 20, 23, 24 is provided in a mechanical path between two direct-reduced planet trains 3, 14 in series and a fluid coupling 6, 10 as torque converter in a parallel path between the trains 3, 14 transmits the whole of the torque in reverse first and second ratios, whilst torque spitting occurs in the higher ratios. The front planet train 3 comprises an input driven ring gear 3, a reaction sun 7 held, for reduced drive, by a brake 8 or clutched at 9 to an output planet carrier 4 which is fast with the impeller 6 of the fluid coupling and with the inner and outer members of clutches 16, 21 which respectively connect the planet carrier 4 directly or through the reduction gears 20, 23, 24 to a ring gear 14 of the rear planet train which is completed by a planet carrier 13 fast with the output shaft and a sun gear 12 fast with the turbine of the fluid coupling. The reduction gear comprises a ring gear 20 fast with the inner member of the clutch 21, a planet carrier 23 fast with the ring gear 14 of the rear train and a sun gear 24 which is held against reverse rotation by a oneway brake 25 or an hydraulically-operated brake. A reversing planet train which compounds with the rear train 14 is shown but not described in detail. For first and second ratios the ring gear 14 is held either at 15 for two-way drive or by a one-way detent 18 the outer ring 17 of which is braked at 19. For split torque third and fourth ratios the brake 15 is released and the clutch 21 engaged, thus providing a mechanical path to the ring gear 14 through the reduction gear. For fifth and direct-drive the clutch 21 is released and the clutch 16 which bypasses the reduction gear is engaged. The clutches may, as shown, be hydraulioallyoperated friction clutches or may be fluid couplings which are filled and emptied for engagement and disengagement respectively. The fluid coupling 6, 10 may be replaced by a device which acts as a fluid coupling in one range and as a torque converter in another range. Control of the reduction gear is effected by a valve 26, Fig. 2, which modifies the hydraulic control system shown in Specification 742,552, wherein ratio shift is effected automatically in response to vehicle speed and throttle opening and a manual valve selects the ranges, one providing automatic shifts between all ratios, an intermediate range which excludes fourth ratio except when overridden by an " overspeed " valve and a low range providing automatic shifts between first and second ratios only. The valve 26 is provided in the line 33 from the 2-3 shift valve to the clutch 16 and when the ratios including the reduction gear are required main line pressure is supplied from the manual valve to the port 27 whereupon pistons 29, 30, 31 are moved down against a spring 32. The clutch 16 is thus exhausted at 38 whilst the pressure fluid from the 2-3 shift valve is supplied through line 36 to the clutch 20. When the reduction gear is operative the output speed-responsive pressure G2 is supplied to a piston 39 which acts on the 3-4 shift valve to cause earlier upshift. The pressure G2 also acts on an override valve 41 which, when the vehicle speed exceeds a predetermined value, moves right to supply output speed-responsive pressure G1 through a line 45 to the valve 26, whereupon the pistons 29, 30, 31 move up and exhaust the clutch line 36 at 37 whilst supplying pressure to the clutch 16 engagement of which by-passes the reduction gear. The manual selector valve may have an additional position for the selection of the reduction gear or the reduction gear range may replace the intermediate or low range. Specifications 522,881, 728,461, and 955,691 also are referred to.