Transmission for a stern drive or outboard drive of a watercraft

Abstract

A stern drive unit for incorporation in the drive leg of a stern drive or outboard drive of a watercraft comprises an intermediate drive shaft ( 8 ) mounted for axial translatory movement within an outer housing ( 1 ) and splined at its upper end for driven engagement with an input drive shaft ( 23 ) of the stern or output drive. The intermediate shaft ( 8 ) carries upper and lower gears ( 9, 10 ) that are rotatable relatively to the intermediate shaft ( 8 ) but can be coupled thereto by means of friction clutches recessed within the respective gears. The intermediate shaft ( 8 ) can be driven axially relatively to the housing ( 1 ) in each of two directions by means of a hydraulic piston and cylinder arrangement ( 26 - 33 ). A collar ( 15 ) fixed with respect to the intermediate drive shaft ( 8 ) is arranged to actuate the respective friction clutches in each direction of translatory motion whereby the intermediate shaft ( 8 ) can be directly coupled either to the gear ( 9 ) or the gear ( 10 ). The gear ( 10 ) is adapted to be directly coupled to an output shaft and the gears ( 9, 10 ) are interconnected by an auxiliary gear train ( 4 - 6 ). Thus, axial translatory movement of the intermediate shaft ( 8 ) permitted by the splined connection with the input drive shaft ( 23 ) is effective to select either a direct drive from the input shaft ( 23 ) to the output gear ( 10 ) or to provide a geared drive to an output shaft via the gears ( 9, 10 ) and the auxiliary gear train ( 4 - 6 ). The construction of the transmission is such that it can be accommodated in a compact arrangement of minimum vertical dimension.

1 . An intermediate united, adapted to be incorporated in a stern drive leg of a stern drive or outboard drive of a watercraft, comprising an intermediate drive shaft ( 8 ) which, in use, is arranged with its axis in an upright position and is adapted to be coupled at its upper end to a drive shaft ( 23 ) of the stern or outboard drive, a first, upper gear ( 9 ) arranged coaxially with said intermediate drive shaft ( 8 ), a second, lower gear ( 10 ) arranged coaxially with said intermediate drive shaft ( 8 ), an auxiliary gear train ( 4 - 6 ) providing a drive transmission between said upper and lower gears ( 9 , 10 ), and friction clutch means ( 17 - 20 ) which is selectively actuatable to provide a driven output either via said upper and lower gears ( 9 , 10 ) and said auxiliary gear train ( 4 - 6 ), or directly from said intermediate drive shaft ( 8 ), characterised in that said lower gear ( 10 ) is arranged to be freely rotatable relatively to the intermediate drive shaft ( 8 ) and to provide the drive output from the intermediate unit, that said friction clutch means ( 17 - 20 ) includes a friction clutch having a driving portion ( 19 ) non-rotatably keyed to said intermediate drive shaft and a driven portion ( 20 ) non-rotatably coupled to said lower gear ( 10 ), that the said intermediate drive shaft ( 8 ) is mounted for axial movement relatively to a housing ( 1 ) of the intermediate unit, that an actuating means ( 26 - 33 ) is provided for driving said intermediate drive shaft ( 8 ) axially to cause frictional engagement of said driving and driven portions ( 19 , 20 ) of said friction clutch, and that the upper end of said intermediate drive shaft ( 8 ) is keyed or splined for sliding driven engagement with a coaxial drive shaft ( 23 ) of a stern drive or outboard drive.  
     
     
         2 . An intermediate unit according to  claim 1  wherein said actuating means ( 26 - 33 ) comprises a hydraulically actuated piston ( 29 , 32 ) arranged coaxially with the input drive shaft ( 8 ).  
     
     
         3 . An intermediate unit according to  claim 1  or  2  wherein the said lower gear ( 10 ) is adapted for coupling to a drive shaft at the lower end of a stern drive leg.  
     
     
         4 . An intermediate unit according to  claim 3 , wherein the said lower gear ( 10 ) is axially recessed to accommodate the friction clutch.  
     
     
         5 . A drive transmission according to  claim 4 , wherein the said friction clutch means includes a second friction clutch ( 17 - 18 ) accommodated in a recess of said upper gear ( 9 ) and the intermediate drive shaft ( 8 ) is arranged to be driven axially in each of two opposite directions, by respective hydraulic pistons ( 29 , 32 ), whereby, in each of said directions of axial movement, the drive shaft ( 8 ) is caused to actuate a corresponding one of said friction clutches.  
     
     
         6 . A drive transmission according to  claim 4 , wherein said intermediate drive shaft ( 8 ) is provided with a radially extending collar, oppositely directed radial surfaces ( 21 , 24 ) of which form clutch pressure plates, the recesses of each of said upper and lower gears ( 9 , 10 ) are bounded by radial surfaces ( 22 , 25 ) forming counter pressure plates, and clutch plates ( 17 - 22 ) keyed respectively to said intermediate drive shaft ( 8 ) and said gears ( 9 , 10 ) are accommodated in said recesses.  
     
     
         7 . A drive transmission according to  claim 2  or any one of claims  3 - 6  as appended thereto, wherein said intermediate drive shaft ( 8 ) has a hollow upper end internally keyed or splined to receive said coaxial drive shaft ( 23 ), and wherein said hydraulically actuated piston ( 29 , 32 ) is arranged coaxially around said hollow upper end.