Patent GB-967857-A (GB)
Title: New or improved variable-speed vehicle gearbox
Inventor: TAYLOR ALEC
IPC: F16H61/02
Filed: 1961-03-22
Abstract: 967,857. Change-speed control. DAVID BROWN INDUSTRIES Ltd. March 15, 1962 [March 22, 1961], No. 10388/61. Heading F2D. The control means for an hydraulically operated change-speed gear includes two separate hydraulic circuits connected respectively to input and output shaft driven positive displacement pumps. The driving member 13 of an hydraulic coupling is connected through a clutch 14 to a first sun wheel 15, and the driven member 16 to a second sun wheel 17 of a first epicyclic gear set having intermeshing planets 19, 20 and a ring gear 21 which may be held stationary by a brake 22; the sun 15 may be held by a brake 18. The planet carrier 23 of the first set is connected to a ring gear 24 of a three element epicyclic set having a planet carrier 27 connected to the output shaft 28 and a sun gear 26 normally held by a brake 30 but capable of being clutched to the planet carrier 27 by clutch 29. For first gear brakes 18 and 30 are engaged; for second gear brake 18 and clutch 29; for third gear clutch 14 and brake 30; for fourth gear clutch 14 and clutch 29; and for reverse brakes 22 and 30 are engaged. In first and second gear all torque passes through the coupling and in other gears only a proportion of the torque passes through the coupling. Oil pressure, for the operation of the brakes and clutches, is supplied by two pumps 31, 32, respectively driven from the gear input and output shafts to four differential valves 33, 34, 35, 36 opened by pressure on poppet portions 41, such that closing pressure is less than opening pressure. Opening of these valves respectively controls the engagement of the appropriate clutches and brakes for the four forward speeds, the valves opening at four different successively higher pressures; the valve 33 being responsive to the input shaft pump pressure and the three valves 34, 35, 36 being responsive to the output shaft pump pressure. Reverse is engaged by manual control of a valve 52 which is in series with a reverse baulking valve 60 preventing reverse engagement while pressure is developed by the pump 32. A spring relief valve in the supply line from pump 31 ensures a predetermined pressure from pump 31, when the engine is running, sufficiently high to open valve 33, which relief valve may be manually overridden by selection of neutral with a lever providing manual or automatic ratio selection. The manual lever is connected by a lost motion connection to a lever 62 operating an automatic drive selector valve 64 which when open allows oil from the pump 32 to flow through a sharpedged orifice 74 whose area is controlled by a needle valve 75 operated through a lever 76 connected to the engine throttle. This variable restriction ensures that at high road speed and large throttle openings changes are effected slowly and at low speed small throttle openings changes are rapid. On kickdown the orifice is opened rapidly and a fast downshift occurs. In automatic setting, changes, except for engagement of the lowest speed controlled by pump 31, are initiated by the pressure developed by the output shaft pump 32 acting on the differently loaded valves 34, 35, 36. Movement of the hand lever to the manual range closes the passage 72 from the pump 32 to the orifice 74, and opens the passage 71 to a pressure regulating valve 81 whose spring 83 is loaded in accordance with the ratio selected by a cam 78 rotated by the hand lever. Thus the selection of a desired ratio sets the pressure of the regulating valve 81 to that necessary to open the appropriate valve 33, 34, 35 or 36. The exhaust passage 84 from the valve 81 is controlled by a modulator valve 85 biased through a spring 94 and lever 96 according to the position of the cam 78; the modulator valve having different diameter lands 90, 89. The modulator valve 85 prevents the rapid engagement of low ratios at high speed, by restricting the free flow of oil from passage 84 to the sump, by closing and causing the flow to pass through an orifice 104 to produce a slow fall in pressure.