Drive assembly for a marine dual-propeller drive unit

Abstract

A drive assembly for a marine propeller drive unit has two concentric drive shafts for carrying a respective propeller. A space between the drive shafts is lubricated with liquid lubricant pumped into the space by a pump. The outermost drive shaft is provided with at least one protrusion protruding radially inwards from an inner surface of the outer drive shaft. The inlet of the secondary fluid channel is provided in said at least one protrusion at a first radial level offset radially inwards from the inner surface of the outer drive shaft such that liquid lubricant at said first radial level is able to lubricate bearings between the outermost drive shaft and the innermost drive shaft.

1 . A drive assembly for a marine dual-propeller drive unit, said drive assembly comprising:
 a housing,   an outer drive shaft assembly comprising an outer drive shaft comprising an outer end portion for holding a first propeller and an axially opposite inner end portion for connection to a gear or a motor,   an inner drive shaft assembly comprising an inner drive shaft comprising and outer end portion for holding a second propeller and an axially opposite inner end portion for connection to a gear or a motor, and a lubrication system,   said outer drive shaft comprising a through central opening extending along a rotational axis of the outer drive shaft,   said inner drive shaft extending co-axially with the outer drive shaft, through the central opening of the outer drive shaft,   wherein a plurality of primary bearings are mounted in the central opening for rotationally supporting the inner drive shaft in the outer drive shaft such that the inner drive shaft and the outer drive shaft are rotatable relatively each other about the rotational axis,   wherein a plurality of secondary bearings are mounted around the outer drive shaft for rotatably supporting the outer drive shaft in the housing such that the outer drive shaft is rotatable relatively the housing about the rotational axis,   said lubrication system comprising a liquid lubricant pump, and a primary fluid channel comprising a primary inlet fluidly connected to the liquid lubricant pump for receiving pressurized liquid lubricant, and at least one primary outlet emanating in the central opening of the outer drive shaft,   said outer drive shaft comprising at least one secondary fluid channel extending from a secondary inlet facing the central opening to a secondary outlet facing an outer space between the housing and a radial outside of the outer drive shaft,
 said outer drive shaft being provided with at least one protrusion protruding radially inwards from an inner surface of the outer drive shaft, 
   said secondary inlet of the secondary fluid channel being provided in said at least one protrusion at a first radial level offset radially inwards from the inner surface of the outer drive shaft such that liquid lubricant at said first radial level is able to lubricate at least some of the primary bearings.   
     
     
         2 . The drive assembly according to  claim 1 , wherein the housing is provided with a return channel fluidly connecting a lower portion of the outer space to a sump, said sump being vented to atmospheric pressure and said liquid lubricant pump being fluidly connected to the sump to pump liquid lubricant from the sump. 
     
     
         3 . The drive assembly according to  claim 2 , wherein the sump is fluidly connected to ambient air at atmospheric pressure. 
     
     
         4 . The drive assembly according to  claim 1 , wherein the protrusion comprises a ridge extending circumferentially about the rotational axis. 
     
     
         5 . The drive assembly according to  claim 1 , wherein said protrusion is formed by an insert mounted to the outer drive shaft. 
     
     
         6 . The drive assembly according to  claim 1 , wherein the outer drive shaft comprises a plurality of said secondary fluid channels. 
     
     
         7 . The drive assembly according to  claim 1 , wherein the plurality of secondary fluid channels are circumferentially distributed about the rotational axis such that the outer drive shaft is balanced about the rotational axis. 
     
     
         8 . The drive assembly according to  claim 1 , wherein the primary fluid channel extends through the housing to a confined space between the outer drive shaft and the housing, and through one or more fluid channels in the outer drive shaft from the confined space to said one or more primary outlets. 
     
     
         9 . The drive assembly according to  claim 1 , wherein the primary bearings comprise two tapered roller bearings provided at the inner end portion of the inner drive shaft,
 said tapered roller bearings being spaced-apart and oriented to withstand axial force in opposite axial directions, and   said primary fluid channel comprising a primary outlet emanating between the tapered roller bearings of the primary bearings.   
     
     
         10 . The drive assembly according to  claim 1 , wherein the secondary bearings comprise two tapered roller bearings provided at the inner end portion of the outer drive shaft,
 said tapered roller bearings being spaced-apart and oriented to withstand axial force in opposite axial directions, and   said confined space being provided between the tapered roller bearings of the secondary bearings.   
     
     
         11 . The drive assembly according to  claim 1 , wherein the primary bearings further comprise at least one bearing provided at the outer end portion of the inner drive shaft. 
     
     
         12 . The drive assembly according to  claim 1 , wherein the primary bearing provided at the outer end portion of the inner drive shaft is a needle bearing. 
     
     
         13 . The drive assembly according to  claim 1 , wherein a first seal is provided between the inner drive shaft and the outer drive shaft at the outer end portion, and wherein a second seal is provided between the outer drive shaft and the housing at the outer end portion of the outer drive shaft. 
     
     
         14 . A propeller drive unit comprising the drive assembly according to  claim 1 , a motor and a planetary gear, said planetary gear comprising a ring gear, a planetary carrier and a sun gear, said ring gear being connected to the outer drive shaft, and said planetary carrier being connected to the inner drive shaft or integrated with the inner drive shaft, wherein the sun gear is operatively connected to the motor. 
     
     
         15 . A marine vessel comprising a propeller drive unit according to  claim 14 .