Patent GB-816626-A (GB)
Title: Improvements in and relating to control mechanism and applications thereof particularly in change-speed gears
IPC: F16H61/02
Filed: 1957-07-22
Abstract: 816,626. Change - speed control. COMPAGNIE DE PONT-A-MOUSSON. July 22, 1957 [July 26, 1956], No. 23082/57. Class 80 (2). (Also in Group XXIX] Fluid-pressure servomotor control apparatus comprises two single-acting piston servomotors V1, V2, the first working independently of the second and control of the second being obtained by manual actuation of a preselector valve D2 while establishment of the preselected movement in the second servomotor V2 is effected by, manual operation of a valve D1 also controlling the first servomotor V1, a fluid-pressure operated two-position valve 16 in the pipes feeding the second servomotor being under the control of the preselector valve. The fluid under pressure may be oil or other liquid. The apparatus is shown as controlling a Wilson change-speed gear in series with a planetary overdrive gear. A ratio in the Wilson gear is preselected by operation of a cam-shaft a2 and the preselected ratio is established by movement of a bus-bar a1 actuated by a lever a, in known manner. The planetary overdrive gear is controlled by a valve b1 effecting selective engagement of a clutch b2 and a brake b3, movement of the valve b1 being effected by a lever b. To obtain establishment of a preselected ratio in the Wilson gear, the valve D1, which may be operated by depression of the clutch pedal of a motor car in which the apparatus is mounted, is moved to its second position against spring bias to connect a source of fluid pressure R through pipes 6, 9 to the first servomotor V1. The piston of the first servomotor V1 is moved against spring bias by the fluid pressure and acts through the lever a upon the bus-bar a1 to establish the ratio. On release of the clutch pedal, the valve D1 is restored to the position shown and connects the servomotor V1 to an exhaust passage 8, so that the servomotor spring returns the piston of the servomotor to the position shown. With the second servomotor V2 in the position shown, the overdrive gear gives a step-up ratio. To obtain direct drive in the overdrive gear, the preselector valve D2 is moved to its second position to connect pipes 37, 35. On.operation of the clutch pedal and valve D1, fluid pressure is supplied from the source R to the first servomotor V as before, and simultaneously through pipes 36, 37, 35 to the space above a three-stepped differential piston P, which is thereby moved. downwardly against spring bias so that its stem 24 opens the valve 16 against spring bias and allows fluid under pressure from the source R to pass through a pipe 22 to the second servomotor V2. At the same time, pressure fluid passes from the pipe 22 through a pipe 47 to a space above a small diameter portion 31 of the differential piston P and assists its downward movement. The piston of the second servomotor V2 is moved against spring bias by the pressure of the fluid to its second operative position and effects engagement of the direct drive clutch b2 in the planetary overdrive gear. When the clutch pedal is released and the valve D1 restored to the position shown, the pipes 35, 37, 36 are vented through the passage 8, but the piston P is retained in its downward position with the valve 16 open by the pressure of the fluid acting through the pipes 22, 47 upon its upper portion 31. Accordingly the piston of the second servomotor V2 is maintained at the end of its stroke. If the pressure of the fluid supplied from the source R is not sufficient to move the piston of the second servomotor V2 to the end of its stroke, so that the direct drive clutch b2 is not fully engaged with consequent excessive wear, the pressure above the small diameter portion 31 of the differential piston P is insufficient to maintain a valve 42 closed against the bias of its spring 46. Accordingly the valve 42 opens and allows the fluid pressure acting upon the portion 31 of the differential piston to escape through a pipe 50 to the pipes 35, 37, which are vented through the valve D1 when the clutch pedal is released. The servomotor V2 is then restored by its spring bias to the position shown and the clutch b2 is disengaged. To obtain re-engagement of the overdrive ratio in the overdrive gear under normal circumstances, the preselector valve D2 is returned to the position shown, when the pipe 35 is vented through an exhaust pipe 38. The fluid pressure acting downwardly upon the differential piston P is thus released, and the differential piston is moved upwardly by spring bias to release the valve 16, which accordingly closes and shuts off the supply of pressure fluid from the source R to the pipe 22, simultaneously venting the second servomotor V2 through a passage 27 in the piston stem to an exhaust passage 26. As a modification, the overdrive ratio, instead of direct drive, may be established by supplying pressure fluid to the second servomotor V2.