Patent GB-1048595-A (GB)
Title: Change-speed power transmission mechanisms
Inventor: DAYUS CHARLES JAMES
IPC: F16H61/02
Filed: 1964-05-21
Abstract: 1,048,595. Change-speed control. JAMES ARCHDALE & CO. Ltd. April 6, 1965 [May 21, 1964], No. 20987/64. Heading F2D. In a transmission comprising a forward and reverse gear having fluid pressure engaged clutches 3, 4 and preceding a change-speed gear having gear wheels or additional toothed members movable by cylinder units 6 to establish a ratio, the supply of fluid to the forward and reverse clutches is prevented below a first pressure which is sufficient to operate the fluid pressure cylinder units 6 so that the forward and reverse clutches cannot be engaged whilst a gear-shift cylinder unit is moving. A clutch control valve 9 is mechanically or otherwise interlinked with a main control valve 11 having a stop and a start position, the interlinking being such that the valve 9 cannot be moved from its central position in which both clutches 3, 4 are disengaged, unless the main valve 11 is in its start position. A pump 7 supplies liquid to the clutch control valve 9 through a device 25 having a piston 26 cutting- off the supply of liquid to the valve 9 whenever the pressure falls below a first predetermined value, the pressure required to operate the gear-shifting cylinders 6 being below this value. The cylinders 6 are supplied with liquid by a selector valve 8 which may be provided with an hydraulic locking device (not shown) to prevent movement of the valve while fluid is being supplied thereto, the valve 8 being supplied from the main control valve 11 through a selector control valve, 15. In the stop position of the valve 11 liquid is supplied to a brake 5 acting on the input shaft of the change-speed gear, and is supplied to a left-hand control chamber of the valve 15 to,shift it to its righthand. position (shown) so that the line to the selector valve 8 is open to exhaust through the valve 11. Adjusting the valve 8 preselects a gear; on operation of the control valve 11 to .its start position and operation of the clutch control valve 9, the brake 5 is exhausted and liquid is supplied to the selected cylinder 6 to shift a gear, the pressure being insufficient to open the device 25 so that no pressure fluid is supplied to the clutch 3 or 4. If the ends of the gear teeth should abut, the pressure rises until device 25 opens and liquid is supplied to the clutch 3 or 4 and to the left-hand side of a delay unit piston 28 which is shifted towards the right, liquid expelled from the right-hand side of the piston passing to exhaust through a relief valve 30 which opens at a second predetermined pressure giving light engagement of the clutch 3 or 4. The input shaft is thus turned slowly to permit meshing of the teeth. The cylinder 6 is therefore free to move again and the pressure drops so that the device 25 closes. When the gear is fully engaged the pressure rises and device 25 opens so that the clutch 3 or 4 is lightly engaged and liquid is supplied to the left-hand side of the piston 28 which commences its stroke. Liquid from the right-hand side of the delay piston 28 is supplied, at the second pressure, to a right-hand control chamber of the valve 15 which is thereby moved to the left at a speed determined by a restriction 24. When the valve 15 reaches its left-hand position the supply to the selector valve 8 is cut-off so that the valve 8 can be adjusted to preselect the next ratio. When the piston 28 has completed its stroke the pressure rises to a third predetermined value determined by a release valve 31 which gives full engagement of the clutch 3 or 4. In a modification the valves 11, 9 are independently operable and an interlock valve is provided which prevents operation of the delay unit except when the valve 9 is positioned to supply a clutch. In another modification, the reverse clutch is omitted.