Patent GB-990584-A (GB)
Title: Improvements in or relating to variable speed power transmission systems
Inventor: DENSHAM JOHN RICHARD
IPC: F16H47/04
Filed: 1962-07-04
Abstract: 990,584. Hydromechanical change speed gears. AUTOMOTIVE PRODUCTS CO. Ltd. July 2, 1963 [July 4, 1962], No. 25581/62. Headings F2C and F2D. A hydromechanical variable speed gear for a motor vehicle comprises a driven planet carrier 29, the planets 28 of which mesh an input driven sun 15 and a ring gear 26 which is connected through a radial piston-type fixed displacement hydraulic pump 18 and a variable displacement motor 22 to the input shaft 10. The planet carrier 29 is fast with a sun 73 of a reverse planet train 72 having an output carried ring gear 74 and a planet carrier 76 which may be clutched at 77 to the sun 73 for forward ratio as held by a brake 78 for reverse ratio. Hydraulic transmission.-The pistons 24 of the pump 18 are reciprocal in a cylinder block 17 fast with the input shaft 10 and carry balls 30 which engage an elliptic track 23 fast with the ring gear 26 and the motor cylinder block 21. The pistons 32 of the motor 22 carry balls 30 which engage a variably eccentric track 33 freely rotatable in bearings 34. The pump and motor inlet and outlet ports 46, 50, 53, 54 communicated with a valve 57 controlled in response to engine speed and accelerator pedal position. The track 33 is normally biased to a position of maximum eccentricity and is moved against bias by a servomotor 96 to increase the speed of the cylinder block 21. Make-up fluid is supplied from an input driven pump 81 to the low pressure motor duct 53 or 54 through a shuttle valve 84 responsive to pressure in the ducts 53, 54. The make-up fluid is also supplied through a non-return valve 87 to the pump circuit. A pressure relief valve 88 is provided. Control.-The reverse gear clutch 77 and brake 78 are respectively engaged by liquidpressure motors 98, 99, selectively supplied with pressure liquid through a valve 97 under the control of a manually-operated lever 122. Axial movement of a spool 65 of the valve 57 is effected by a follow-up servomotor 91 in response to axial movement of a rod 106 connected to an input driven centrifugal governor 104 and through a lost-motion spring coupling 111 to the accelerator pedal 113. A lost-motion spring coupling 107 permits movement of the rod 106 in excess of that required to move the valve spool 65 from one extreme position to another, the excess movement acting through an abutment 117 and bell-crank 118 on the follow-up servomotor 96 which controls the eccentricity of the motor track 33. Movement of the lever 122 to the position L moves a stop 123 into the path of an abutment 124 on the rod 106 and thus prevents movement of the valve spool 65 beyond an intermediate position which provides a low gear ratio. A lostmotion spring coupling 119 permits movement of the accelerator pedal 113 after the throttle 114 is fully open. The excess movement acts through springs 115, 116 to move left the rod 106 which causes the valve spool 65 to move to its intermediate " low gear " position. Operation.-In the neutral condition shown in Figs. 6 and 7, both the clutch 77 and brake 78 are disengaged and the valve spool 65 is in its extreme left position permitting free communication between the pump and motor inlet and outlet ports and thus the pump 18, motor 22 and ring gear 26 rotate idly. To start, the lever 122 is moved to the forward or reverse position to engage the clutch 77 or brake 78 and thereafter on depression of the accelerator pedal 113 engine speed increases and the governor 104 moves right the rod 106 which acts on the servo 91 to cause rightward movement of the valve spool 65. In an intermediate position the valve spool 65 blocks the motor inlet and outlet ports 53, 54 whilst permitting communication between the pump inlet and outlet ports 46, 50. The pump 18 thus rotates idly whilst the motor cylinder block 21 and ring gear 26 are held stationary to provide a mechanical reduced drive through the planet train 16. Further increase of engine speed moves the valve spool 65 to its extreme right position wherein it connects the pump inlet and outlet ports to the motor outlet and inlet ports respectively and the ring gear 27 is driven in the same direction as the sun gear 15 to increase the speed of the planet carrier 29. On still further increase of engine speed and rightward movement of the rod 106 the abutment 117 acts through the bell-crank 118 on the servo 96 to reduce the eccentricity of the track 33 which produces increased speed of the ring gear 26. When the track 33 has been moved to a concentric position the pump 18, motor 22 and ring gear 26 rotate at the same speed to provide a direct drive in the planet train 16. An output pump 101 supplies liquid to the system for tow starting.