Patent GB-895452-A (GB)
Title: New or improved change-speed transmission control mechanism for vehicles
Inventor: ASHFIELD HERBERT EDWARD
IPC: F16H61/02
Filed: 1958-09-29
Abstract: 895,452. Change-speed gear. BROWN INDUSTRIES Ltd., DAVID. Oct. 21, 1959 [Sept. 29, 1958], No. 30965/58. Class 80 (2). In a motor vehicle, which may be a tractor, change of ratio of a two-speed overdrive or step-down gear is effected automatically in accordance with variation of the pressure of a vehicle driven gear-pump 16 from which oil is supplied through a pipe 37 to a valve 17 connected by a pipe 39 to the gearing, the valve being closed by a spring 38 which forces a relatively small area seat 36 against a port at the end of the pipe 37 whereby a relatively high pressure is required to open the valve against its spring bias, maintenance of the valve in its open condition being obtained by the pressure in the pipe 37 acting not only upon the small seat 36 but also upon a larger surrounding seat 36a, so that a lower pressure, corresponding to a lower vehicle speed, is required before the valve closes than the pressure (and speed) at which it opened. Accordingly, upshift takes place at a higher vehicle speed than downshift. The vehicle speeds at which upshifts and downshifts take place are adjusted by means of a manuallycontrolled valve 19. As shown in Fig. 1, the pipe 39 leads through ducts 41, 43 to a directdrive multidisc clutch 10 in a planetary gear having a sun gear 12, Fig. 2, carried by a driving- shaft and meshing stepped planets 56, 57 mounted in a carrier 58 restrained from the reverse rotation when the clutch is disengaged by a one-way detent 60, the planet pinions also meshing a sun gear 59 on a driven shaft. When the clutch 10 is disengaged, the planet carrier 58 is held stationary, and a step-down ratio is obtained between the driving and driven shafts, at the same time the pump 16 supplying oil under low pressure through a by-pass pipe 18 and the valve 19 to a pipe 26 leading through ducts 27, 29 to the inner peripheries of the discs of the clutch 10, which are thereby lubricated. The valve 19 comprises a piston 20 having inlet ports 22 connected with the pipe 18 and a number of staggered outlet ports 21 connecting with a space 25 leading to the pipe 26. The piston 20 is biased rightwards by a spring 23 and moved leftwards by adjusting a knurled screw 24. Axial positioning of the piston 20 determines how many of the outlet ports 21 open freely into the space 25, and hence the volume of oil transmitted through the valve 19. By adjustment of the valve 24 to, e.g., increase the number of ports 21 opening into the space 25, the flow of oil therethrough is increased, and accordingly the speed of the vehicle necessary to cause an upshift is correspondingly increased. A pressure relief valve 30 is connected to the pipe 26. When the valve 17 is in its closed position, the pipe 39 leading to the servo engaging the direct-drive clutch 10 is vented to exhaust through a pipe 44, a groove 45 and a hole 46 in the valve, opening of the valve to connect the pipes 37, 39 shutting off this hole 46. The pipe 39 also contains a pressure relief valve 47. As a modification, the control system may be applied to a two-speed gear giving direct drive and a step-up ratio, the direct drive clutch then being replaced by a multidise clutch 66, Fig. 3, biased to engage by springs 68, and disengaged when oil under pressure is admitted to a cylinder containing a ring-shaped piston 70, stepped planet pinions 62, 63 meshing sun gears 61, 65 on driving and driven shafts and being mounted in a carrier 64 which can be stationed by the admission of oil under pressure to act upon a ring-shaped piston 72 against the bias of springs 71 tending to disengage a multidise brake 67. The control circuit of Fig. 1 is connected to both the clutch 66 and the brake 67, application of oil under pressure thereto simultaneously disengaging the clutch and engaging the brake for the step-up ratio.