Power transmission system for marine propulsion unit

Abstract

A power transmission system for a marine propulsion unit includes a case arranged to be supported on a hull; a propeller supported at the lower end portion of the case for rotation about an axis extending in a fore-and-aft direction; a transmission housed in the case and having an axis with planetary gear trains extending vertically to receive an output from an engine, and change the speed of the output prior to transmission thereof; and an interlocking device arranged to receive the output from the transmission and transmit the output to the propeller. A speed reduction device is arranged such that it is interposed between the transmission and the interlocking device, receives the output from the transmission, and decelerates the output to transmit it to the interlocking device. This arrangement reduces the weight of a transmission unit in a power transmission system of a marine propulsion unit and decreases an external size of the transmission unit.

1 . A marine propulsion unit having a power transmission system, the power transmission system comprising:
 a case arranged to be supported by a hull;   a propeller supported in a lower portion of the case;   a transmission unit housed in the case and arranged to receive output from an engine, change a speed of the output, and transmit the output;   an interlocking device arranged to receive the output from the transmission unit and transmit the output to the propeller; and   a speed reduction device interposed between the transmission unit and the interlocking device and arranged to receive the output from the transmission unit and decelerate the output before transmitting the output to the interlocking device.   
     
     
         2 . The marine propulsion unit having the power transmission system according to  claim 1 , wherein the case includes:
 an upper case defining an upper side thereof; and   a lower case separate from the upper case and defining a lower side of the case, the lower case housing the interlocking device, and the lower case is detachably secured to the upper case; wherein   the speed reduction device is provided in the case where the upper case is secured to the lower case such that the speed reduction device is surrounded by mating surfaces of the upper case and the lower case.   
     
     
         3 . The marine propulsion unit having the power transmission system according to  claim 2 , further comprising:
 an accommodating chamber arranged in the lower case to cover the interlocking device and accommodate lubricating oil therein; wherein   the interlocking device includes:
 a power transmission shaft accommodated in the accommodating chamber and supported in the lower case; and 
 a paired set of bevel gears accommodated in the accommodating chamber and interlocking the propeller with a lower end portion of the power transmission shaft; wherein 
   an upper end portion of the accommodating chamber is communicated with the inside of the speed reduction device.   
     
     
         4 . The marine propulsion unit having the power transmission system according to  claim 1 , wherein the speed reduction device includes a planetary gear train with a sun gear integrally provided with the lower case. 
     
     
         5 . The marine propulsion unit having the power transmission system according to  claim 1 , wherein the transmission unit includes:
 an upper planetary gear train and a lower planetary train arranged to sequentially transmit the engine output to the speed reduction device; and   a one-way clutch arranged to permit forward rotation of a sun gear of the upper planetary train and inhibit reverse rotation thereof; and   the transmission unit further includes:
 a speed change section defined by the upper planetary train and the one-way clutch to change the speed of the output of the transmission unit to either a low speed or high speed; and 
 a rotational direction switching section in which the lower planetary gear train switches a rotational direction of the output of the transmission unit to either a forward rotation or a reverse rotation. 
   
     
     
         6 . The marine propulsion unit according to  claim 1 , wherein the speed reduction device is disposed below the transmission unit and includes a water cooling system, the water cooling system comprising:
 a cooling water passage arranged to supply cooling water to the transmission unit in accordance with the engine output; and   a cooling device arranged to cool the speed reduction device with the cooling water discharged from the transmission unit after cooling the transmission unit.   
     
     
         7 . The marine propulsion unit having the water cooling system for the power transmission system according to  claim 6 , wherein the cooling device includes a cover body arranged to cover the speed reduction device from the outside, and a water reservoir arranged to temporarily store the cooling water discharged from the transmission unit between an outer surface of the speed reduction device and the cover body. 
     
     
         8 . The marine propulsion unit having the water cooling system for the power transmission system according to  claim 7 , wherein a drain hole is provided on the cover body to communicate an inner bottom portion of the water reservoir with the outside underneath thereof. 
     
     
         9 . The marine propulsion unit having the water cooling system for the power transmission system according to  claim 7 , wherein the cover body is provided with an opening that allows the water reservoir to open upward, and a cutout extending downward is provided on an edge of the opening.