Patent GB-496828-A (GB)
Title: Control device for the pressure medium of a gear-changing device of gear-wheel change-speed gears particularly in motor vehicles
IPC: F16H61/02
Filed: 1937-08-26
Abstract: 496,828. Change - speed gearing. MAYBACH - MOTORENBAU GES. Aug. 26, 1937, No. 23440. Convention date, Aug. 28, 1936. [Class 80 (ii)] Relates to a fluid-pressure control for change-speed gearing of the kind having several clutch-actuated stages, so arranged that during a change, the driving members of some of the clutches to be engaged require accelerating to produce synchronism, whilst those of others require to be retarded therefor. Such action in the individual clutches is termed " acceleration-change " and retardationchange respectively. According to this invention, the supply of fluid-pressure to produce an acceleration change is prevented by cut-off valves 51, 61, 62, which are opened by movement of the clutch parts producing a retardation change only when such change is completed. Thus, during any particular speed-change, retardation changes precede acceleration changes, so that, after preselection, the operator has only to close and re-open the engine-throttle, which operation may be performed by automatic auxiliary means, which may also brake the driving shaft for assisting retardation-changes, as described in Specification 474,394. The change-speed gear comprises four gear-pairs and a reverse idler, capable of producing eight forward and four reverse speeds, although, with the control described, seven forward speeds and one reverse are provided. Alternatively, only six forward speeds and reverse may be provided, in which case one of the cutoff valves, e.g. 62, may be eliminated. Wheels 7, 11 are fast respectively on a driving shaft 1 and a stub-shaft 4. Wheels 8, 12 are freely mounted and can be clutched on one side to the shafts 1, 4 respectively by splined clutchdogs 17, 18, and on the other side by clutchdogs 19, 20 to shafts 2, 5, fast respectively to wheels 9, 13. A wheel 14, engaging a wheel 10 in all forward speeds, can be slid to the left to engage teeth 30 on a reverse idler when the latter is slid to the right to engage additional teeth 31 thereon, with the wheel 10 for reverse. The wheel 10 is loose on a final driven shaft 3, which carries a splined clutch-dog 25 for clutching either wheel 9 or 10. All the clutchteeth have inclined faces which delay engagement, by causing the clutch to assume a " rejection position " in which the teeth ratchet over one another, until synchronism is produced by acceleration or retardation of the faster or slower moving element, whereupon the engagement is completed. The clutches 17, 18 and 19, 20 are operated in pairs, respectively through levers 21, 23, rock-shafts 22, 24, levers 35, 45, Fig. 2, and pistons 38, 48, the double clutch 25 being operated through a lever 55 by a piston 58. The opposite sides of the pistons are connected to a source of vacuum (or pressure) through conduits 39, 40, 50, 49, 60, 59, leading to a distributing-valve such as that shown in Specification 457,361. Movement of the piston 38 from right to left always produces a retardation-change, since it causes disengagement of the clutch 18 and engagement of the clutch 17. The retardation-change results from the fact that the wheel 8 was running more slowly than the clutch-member 17 when the clutch 18 was engaged, by virtue of the wheel 8 being larger than the wheel 7, so that the driving shaft 1 has to be retarded as by closing the engine-throttle or by braking, to produce engagement of the clutch 17. Similarly, movement of the piston 38 from left to right produces an acceleration change by engaging the clutch 18 ; leftward and rightward movements of the piston 48 produce acceleration- and retardation-changes respectively ; whilst upward and downward movements of the piston 58 produce retardation- and acceleration - changes respectively. In order that, during any gear-change, a retardation-change shall always precede an acceleration-change, the left side of the piston 48 and the lower side of the piston 58 are connected to their respective distributer-ducts 50, 60 through cut-off valves 51 and 61, 62 respectively, actuated by pistons 69, 77, 72, the right faces of which are connected by pipes 66, 74 to spaces behind the pistons 38, 48, governed as follows. When the piston 38 is in its righthand position, the pipe 66 communicates, through a groove 65 in the piston-rod with the space at the left of the piston. When such space is communicated with suction to produce leftward movement of the piston 38 (retardation-change in the clutch 17), the pistons 69, 72 also are energized and move to the right, closing the valves 51, 62 and cutting off the pipes 501, 6011 leading to the sides of the pistons 48, 58 which produce acceleration-changes. When the retardation-change at the clutch 17 has been completed, e.g. by closing the engine throttle and braking the driving shaft, if desired, a bridge 67 on the piston-rod covers the pipe 66, and if desired also vents it. Springs then move the pistons 69, 77 to the left, opening the valves 51, 62, restoring communication between the cylinder-pipes 501, 6011 and their distributer-ducts 50, 60, so that an accelerationchange can now take place if one of these ducts has been communicated to suction through the distributing-valve. The two cut-off valves 61, 62 controlling the cylinder-pipe 60<11> are arranged in series, the former being controlled by a groove and bridge 73, 75 on the rod of the piston 48, in the same way as the valves 51, 62 are controlled by the piston 38. During an upward change from third to fourth speeds, one acceleration change, viz. : at the clutch 18, and one retardation change, viz. : at the clutch 25<1>, are required. Neither piston 48 nor 58 acts on cut-off valves to delay an acceleration-change by the piston 38, which latter is directly energized by the distributer-ducts 39, 40 in both directions. For this particular change, the acceleration-change in the clutch 18 is not delayed and actually precedes the retardation-change in the following manner. Both pistons 38, 58 are energized simultaneously and move their corresponding clutch-elements 18, 25<1> into the rejection position. In this position, both wheel-pairs 8, 12 and 9, 13 are free of both the driving and driven shafts. Due to their low inertia and oil-drag these wheels lose speed more rapidly than the wheelpair 7, 11 connected to the engine, the effect being to produce an acceleration of the clutchelement 18 in relation to the wheel 12, thereby causing the clutch 18 to engage. Further reduction in speed of the driver, slows the wheel 9 and effects the retardation-change at the clutch 25<1>. Use may be made of auxiliary synchronizing devices for accelerating or retarding the clutch-elements, controlled by passages in the piston-rods, as described in Specification 474,934.