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EP-4570643-B1 - A DRIVE ASSEMBLY FOR A MARINE DUAL-PROPELLER DRIVE UNIT

EP4570643B1EP 4570643 B1EP4570643 B1EP 4570643B1EP-4570643-B1

Inventors

  • BRAUER, Samuel
  • TELL, Johan
  • WIK, LARS
  • ABRAHAMSSON, JOHAN
  • Madisetty, Tarun

Dates

Publication Date
20260513
Application Date
20231211

Claims (15)

  1. A drive assembly (1) for a marine dual-propeller drive unit, said drive assembly (1) comprising: a housing (2), an outer drive shaft assembly comprising an outer drive shaft (3) comprising an outer end portion (4) for holding a first propeller and an axially opposite inner end portion (5) for connection to a gear or a motor, an inner drive shaft assembly comprising an inner drive shaft (6) comprising and outer end portion (7) for holding a second propeller and an axially opposite inner end portion (8) for connection to a gear or a motor, and a lubrication system, said outer drive shaft (3) comprising a through central opening (9) extending along a rotational axis (10) of the outer drive shaft (3), said inner drive shaft (6) extending co-axially with the outer drive shaft (3), through the central opening (9) of the outer drive shaft (3), wherein a plurality of primary bearings (11) are mounted in the central opening (9) for rotationally supporting the inner drive shaft (6) in the outer drive shaft (3) such that the inner drive shaft (6) and the outer drive shaft (3) are rotatable relatively each other about the rotational axis (10), wherein a plurality of secondary bearings (22) are mounted around the outer drive shaft (3) for rotatably supporting the outer drive shaft (3) in the housing (2) such that the outer drive shaft (3) is rotatable relatively the housing (2) about the rotational axis (10), said lubrication system comprising a liquid lubricant pump (12), and a primary fluid channel (13) comprising a primary inlet (14) fluidly connected to the liquid lubricant pump (12) for receiving pressurized liquid lubricant, and at least one primary outlet (15) emanating in the central opening (9) of the outer drive shaft (3), said outer drive shaft (3) comprising at least one secondary fluid channel (16) extending from a secondary inlet (17) facing the central opening (9) to a secondary outlet (18) facing an outer space (19) between the housing (2) and a radial outside of the outer drive shaft (3), said outer drive shaft (3) being provided with at least one protrusion (20) protruding radially inwards from an inner surface of the outer drive shaft (3), said secondary inlet (17) of the secondary fluid channel (16) being provided in said at least one protrusion (20) at a first radial level (21) offset radially inwards from the inner surface of the outer drive shaft (3) such that liquid lubricant at said first radial level (21) is able to lubricate at least some of the primary bearings (11).
  2. The drive assembly (1) according to any one of the preceding claims, wherein the housing (2) is provided with a return channel (26) fluidly connecting a lower portion of the outer space to a sump (27), said sump (27) being vented to atmospheric pressure and said liquid lubricant pump (12) being fluidly connected to the sump (27) to pump liquid lubricant from the sump (27).
  3. The drive assembly (1) according to claim 2, wherein the sump (27) is fluidly connected to ambient air at atmospheric pressure.
  4. The drive assembly (1) according to claim 1, wherein the protrusion (20) comprises a ridge (28) extending circumferentially about the rotational axis (10).
  5. The drive assembly (1) according to any one of the preceding claims, wherein said protrusion (20) is formed by an insert mounted to the outer drive shaft (3).
  6. The drive assembly (1) according to any one of the preceding claims, wherein the outer drive shaft (3) comprises a plurality of said secondary fluid channels (16).
  7. The drive assembly (1) according to claim 6, wherein the plurality of secondary fluid channels (16) are circumferentially distributed about the rotational axis (10) such that the outer drive shaft (3) is balanced about the rotational axis (10).
  8. The drive assembly (1) according to any one of the preceding claims, wherein the primary fluid channel (13) extends through the housing (2) to a confined space (25) between the outer drive shaft (3) and the housing (2), and through one or more fluid channels in the outer drive shaft (3) from the confined space (25) to said one or more primary outlets (15).
  9. The drive assembly (1) according to any one of the preceding claims, wherein the primary bearings (11) comprise two tapered roller bearings (23) provided at the inner end portion (8) of the inner drive shaft (6), said tapered roller bearings (23) being spaced-apart and oriented to withstand axial force in opposite axial directions, and said primary fluid channel (13) comprising a primary outlet (15) emanating between the tapered roller bearings (23) of the primary bearings (11).
  10. The drive assembly (1) according to any one of the preceding claims, wherein the secondary bearings (22) comprise two tapered roller bearings (24) provided at the inner end portion (5) of the outer drive shaft (3), said tapered roller bearings (24) being spaced-apart and oriented to withstand axial force in opposite axial directions, and said confined space (25) being provided between the tapered roller bearings (24) of the secondary bearings (22).
  11. The drive assembly (1) according to any one of the preceding claims, wherein the primary bearings (11) further comprise at least one bearing provided at the outer end portion (7) of the inner drive shaft (6).
  12. The drive assembly (1) according to any one of the preceding claims, wherein the primary bearing (11) provided at the outer end portion (7) of the inner drive shaft (6) is a needle bearing.
  13. The drive assembly (1) according to any one of the preceding claims, wherein a first seal (29) is provided between the inner drive shaft (6) and the outer drive shaft (3) at the outer end portion (7), and wherein a second seal (30) is provided between the outer drive shaft (3) and the housing (2) at the outer end portion (4) of the outer drive shaft (3).
  14. A propeller drive unit comprising the drive assembly (1) according to any one of the preceding claims, a motor and a planetary gear, said planetary gear comprising a ring gear (31), a planetary carrier (32) and a sun gear (33), said ring gear being connected to the outer drive shaft (3), and said planetary carrier (32) being connected to the inner drive shaft (6) or integrated with the inner drive shaft (6), wherein the sun gear (33) is operatively connected to the motor.
  15. A marine vessel comprising a propeller drive unit (1) according to claim 14.

Description

TECHNICAL FIELD The present disclosure relates to a drive assembly for a marine dual-propeller drive unit. Specifically, the present disclosure relates to a design of a lubrication system integrated in such drive assemblies. BACKGROUND Marine dual-propeller drive units typically comprise two co-axial drive shafts each configured to carry a respective propeller. In use the propellers are typically counter rotating. The inner drive shaft is supported in the outer drive shaft, typically using bearings. A space between the outer drive shaft and the inner drive shaft is typically filled with liquid lubricant for lubrication of the bearings. An example of such a marine dual-propeller drive unit is described by EP 0 221 536 A2. A general goal of the present disclosure is to reduce friction in the marine dual-propeller drive unit, thereby reducing power consumption. SUMMARY According to a first aspect of the disclosure, the goal is achieved by a drive assembly for a marine dual-propeller drive unit. The drive assembly comprises: 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, anda lubrication system. The outer drive shaft comprises a through central opening extending along a rotational axis of the outer drive shaft. The inner drive shaft extends co-axially with the outer drive shaft, through the central opening of the outer drive shaft. 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. 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. The lubrication system comprises a liquid lubricant pump, and a primary fluid channel comprising a primary inlet fluidly connected to the liquid lubricant pump 12 for receiving pressurized liquid lubricant, and at least one primary outlet emanating in the central opening of the outer drive shaft. The outer drive shaft comprises 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. The outer drive shaft is provided with at least one protrusion protruding radially inwards from an inner surface of the outer drive shaft. The secondary 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 at least some of the primary bearings. In use, liquid lubricant, such as a suitable oil, is forced by the pump into the central opening of the outer drive shaft through the primary fluid channel. Inside the central opening the liquid lubricant is forced radially outwards by centrifugal force thereby spreading the liquid lubricant in the central opening space along the length of the outer drive shaft. As more liquid lubricant is pumped into the central opening, the radial thickness of the layer of liquid lubricant formed inside the central opening increases and eventually the thickness of the layer of liquid lubricant will be enough to provide proper lubrication to the primary bearings. Also, depending on the location(s) at which liquid lubricant emanated from the first fluid channel into the central opening, the liquid lubricant will also be forced though one or more primary bearings. Also, any tapered roller bearings will, depending on their orientation, provide an additional force moving liquid lubricant through the tapered bearing. The pressure of the liquid lubricant may also be used to force liquid lubricant through the secondary bearings supporting the outer drive shaft in the housing. The secondary fluid channel enables liquid lubricant to escape the central opening such that the space between the outer drive shaft and the inner drive shaft is not filled with liquid lubricant, thereby enabling the inner shaft to rotate surrounded by gas rather than liquid, such that friction between the inner drive shaft and the surrounding fluid is mitigated. The provision of the at least one protrusion offset radially inwards from the inner surface of the outer drive shaft establishes a minimum thickness of the layer of liquid lubricant, thus ensuring proper lubrication of primary bearings. Optionally in some examples,