Title:
PROPULSION UNIT FOR MARINE DRIVE
Kind Code:
A1


Abstract:
A marine propulsion unit having an oil circulation system is provided. In the oil circulation system, lubricant is delivered from a bevel gear mechanism adjacent a drive shaft through an oil passage defined in a lower casing to a journal bearing supporting the drive shaft. From the drive shaft journal bearing, the lubricant flows through a gap between the drive shaft and the inner peripheral wall of a drive shaft chamber in the lower casing and then returns to the bevel gear mechanism.



Inventors:
Asakaze, Ken (Shizuoka-ken, JP)
Application Number:
11/771780
Publication Date:
01/17/2008
Filing Date:
06/29/2007
Assignee:
YAMAHA MARINE KABUSHIKI KAISHA (Shizuoka-ken, JP)
Primary Class:
International Classes:
B63H21/38; B63H20/14; F16H57/04
View Patent Images:
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Primary Examiner:
AVILA, STEPHEN P
Attorney, Agent or Firm:
KNOBBE MARTENS OLSON & BEAR LLP (2040 MAIN STREET FOURTEENTH FLOOR, IRVINE, CA, 92614, US)
Claims:
What is claimed is:

1. A marine drive having an engine and a propulsion unit, the propulsion unit comprising a drive shaft driven by the engine, a bevel gear mechanism, a propeller shaft driven by the drive shaft via the bevel gear mechanism, a lower casing adapted to support the propeller shaft, bevel gear mechanism, and drive shaft, the propeller shaft having a projection projecting generally rearward from the lower casing, a drive shaft bearing for rotatably supporting a journal of the drive shaft, the drive shaft having a bevel gear mechanism attachment part, and a lubricant circulating system adapted to circulate lubricant between the bevel gear mechanism attachment part and the drive shaft bearing, the lubricant circulating system comprising a first lubricant passage extending in the lower casing from the bevel gear mechanism attachment part to the drive shaft bearing and a second lubricant passage defined in a gap between the drive shaft and an inner peripheral wall of a drive shaft chamber in the lower casing and extending from the drive shaft bearing to the bevel gear mechanism attachment part, wherein the lubricant circulating system is configured so that lubricant flows from the bevel gear mechanism attachment part to the drive shaft bearing through the first passage, and from the drive shaft bearing to the bevel gear mechanism attachment part through the second passage.

2. A marine drive as in claim 1, wherein the bevel gear mechanism is adapted to function as a pump to urge lubricant into the first lubricant passage upon rotation of the drive shaft.

3. A marine drive as in claim 2, wherein the drive shaft has a spiral groove disposed in the periphery thereof, the spiral grove delivering lubricant downward upon rotation of the drive shaft.

4. A marine drive as in claim 2, wherein the first lubricant passage is at least partially defined by a shift shaft chamber having a shift shaft disposed therein, the shift shaft selectively setting the bevel gear mechanism to a forward drive mode or a reverse drive mode.

5. A marine drive as in claim 2, wherein the marine drive comprises an outboard motor.

6. A marine drive as in claim 1, wherein the drive shaft has a spiral groove disposed in the periphery thereof, the spiral grove delivering lubricant downward upon rotation of the drive shaft.

7. A marine drive as in claim 6, wherein the first lubricant passage is at least partially defined by a shift shaft chamber having a shift shaft disposed therein, the shift shaft selectively setting the bevel gear mechanism to a forward drive mode or a reverse drive mode.

8. A propulsion unit for a marine drive, comprising a drive shaft adapted to be driven by an engine of the marine drive, a bevel gear mechanism chamber enclosing a bevel gear mechanism that connects to a lower portion of the drive shaft and is driven by the drive shaft, a propeller shaft having a forward portion that is connected to the bevel gear mechanism and is driven by the drive shaft via the bevel gear mechanism, a lower casing comprising the bevel gear mechanism chamber, a drive shaft journal bearing disposed above the bevel gear mechanism chamber for rotatably supporting the drive shaft, and a lubricant circulation system adapted to circulate lubricant between the bevel gear mechanism chamber and the drive shaft journal bearing, the lubricant circulation system comprising a first passage extending generally upwardly from the bevel gear mechanism chamber to the drive shaft journal bearing and a second passage defined in a gap between the drive shaft and an inner peripheral wall of a drive shaft chamber in the lower casing and extending from the drive shaft journal bearing to the bevel gear mechanism chamber, wherein the lubricant circulation system is configured so that lubricant flows from the bevel gear mechanism chamber into the first passage to the drive shaft journal bearing and then through the second passage back to the bevel gear mechanism chamber.

9. A propulsion device as in claim 8, wherein the bevel gear mechanism functions as a pump to urge lubricant into the first passage upon rotation of the drive shaft.

10. A propulsion device as in claim 9, wherein the drive shaft has a spiral groove disposed in the periphery thereof, the spiral grove delivering lubricant downward upon rotation of the drive shaft.

11. A propulsion device as in claim 8, wherein the first passage is at least partially defined by a shift shaft chamber having a shift shaft disposed therein, the shift shaft selectively setting the bevel gear mechanism to a forward drive mode or a reverse drive mode.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application Serial No. 2006-193213, filed on Jul. 13, 2006, the entire contents of which are expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a propulsion unit for a marine drive, and more specifically to a lubrication system in a lower casing of such a marine drive.

2. Description of Related Art

In marine drives such as outboard motors designed for small watercrafts or the like, the driving force from an engine is transmitted from a drive shaft to a propeller shaft via a bevel gear mechanism to produce propulsion force.

In this type of outboard motor, a lower casing for holding the drive shaft, bevel gear mechanism and propeller shaft therein is subjected to a reaction force directly from water when the outboard motor is driven in water. Thus, the lateral width of the lower casing is typically kept very small. Accordingly, the bevel gear mechanism and the other parts described above are disposed in a limited space within the lower casing.

To prolong the life of bearings of the drive shaft and meshing parts of the bevel gear mechanism, the lower casing has lubricant filled therein. The lubricant is circulated in the lower casing to cool and lubricate such parts.

According to Japanese Patent Document JP-A-Sho 57-182595, for example, the drive shaft has a spiral groove between upper and lower bearings. The spiral groove and the inner peripheral wall of a drive shaft hole in the lower casing form a slight gap therebetween to provide a screw pump. The screw pump delivers the lubricant upward from a bevel gear mechanism chamber to the upper and lower bearings. From the upper bearing, the lubricant is returned to the bevel gear mechanism chamber through another passage.

SUMMARY OF THE INVENTION

Applicant has noted, however, that in motors as just described, the lubricant may stagnate or flow back. As a result, the temperature of the lubricant may increase, resulting in wear of the meshing parts of the bevel gear mechanism and the bearings of the drive shaft. The life of the parts may therefore be shortened.

Accordingly, there is a need in the art for a propulsion unit for an outboard motor in which stagnation or backflow of lubricant is prevented, therefore improving lubricant circulation and prolonging the life of meshing parts of a bevel gear mechanism and bearings of a drive shaft.

Through study, experimentation, and analysis, Applicant has discovered that as the drive shaft rotates, the bevel gear mechanism rotates to thereby produce a lubricant stirring effect. This effect causes the lubricant to be delivered in a direction opposite to the intended direction of the lubricant flow through the above-described oil circulating channel, or the direction in which the screw pump delivers the lubricant. Applicant thus determined that the stirring effect causes the stagnation or backflow of lubricant. In light of his discovery, Applicant invented principles and structure for constructing a lubricant circulation system that uses the oil stirring effect to aid lubricant circulation, and thus prevent stagnation or backflow of lubricant.

In accordance with one embodiment, the present invention provides a marine drive having an engine and a propulsion unit. The propulsion unit comprises a drive shaft driven by the engine, a bevel gear mechanism, a propeller shaft driven by the drive shaft via the bevel gear mechanism, and a lower casing adapted to support the propeller shaft, bevel gear mechanism, and drive shaft. The propeller shaft has a projection projecting generally rearward from the lower casing. A drive shaft bearing rotatably supports a journal of the drive shaft, and has a bevel gear mechanism attachment part. A lubricant circulating system is adapted to circulate lubricant between the bevel gear mechanism attachment part and the drive shaft bearing. The lubricant circulating system comprises a first lubricant passage extending in the lower casing from the bevel gear mechanism attachment part to the drive shaft bearing and a second lubricant passage defined in a gap between the drive shaft and an inner peripheral wall of a drive shaft chamber in the lower casing and extending from the drive shaft bearing to the bevel gear mechanism attachment part. The lubricant circulating system is configured so that lubricant flows from the bevel gear mechanism attachment part to the drive shaft bearing through the first passage, and from the drive shaft bearing to the bevel gear mechanism attachment part through the second passage.

In one such embodiment the bevel gear mechanism is adapted to function as a pump to urge lubricant into the first lubricant passage upon rotation of the drive shaft. In another embodiment the drive shaft has a spiral groove disposed in the periphery thereof the spiral groove delivering lubricant downward upon rotation of the drive shaft. In still another embodiment the first lubricant passage is at least partially defined by a shift shaft chamber having a shift shaft disposed therein, the shift shaft selectively setting the bevel gear mechanism to a forward drive mode or a reverse drive mode.

In another embodiment the marine drive comprises an outboard motor.

In accordance with another embodiment, the present invention provides a propulsion unit for a marine drive. The propulsion unit comprises a drive shaft adapted to be driven by an engine of the marine drive, a bevel gear mechanism chamber enclosing a bevel gear mechanism that connects to a lower portion of the drive shaft and is driven by the drive shaft, a propeller shaft having a forward portion that is connected to the bevel gear mechanism and is driven by the drive shaft via the bevel gear mechanism, a lower casing comprising the bevel gear mechanism chamber, a drive shaft journal bearing disposed above the bevel gear mechanism chamber for rotatably supporting the drive shaft, and a lubricant circulation system adapted to circulate lubricant between the bevel gear mechanism chamber and the drive shaft journal bearing. The lubricant circulation system comprises a lirst passage extending generally upwardly from the bevel gear mechanism chamber to the drive shaft journal bearing and a second passage defined in a gap between the drive shaft and an inner peripheral wall of a drive shaft chamber in the lower casing and extending from the drive shaft journal bearing to the bevel gear mechanism chamber. The lubricant circulation system is configured so that lubricant flows from the bevel gear mechanism chamber into the first passage to the drive shaft journal bearing and then through the second passage back to the bevel gear mechanism chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an outboard motor in accordance with an embodiment.

FIG. 2 is a side view of a lower casing with a propulsion unit disposed therein for the outboard motor shown in FIG. 1.

FIG. 3 is a cross sectional view of the lower casing shown in FIG. 2.

FIG. 4 is a sectional plan view of the lower casing shown in FIG. 2.

FIG. 5 illustrates a forward bevel gear of the propulsion unit shown in FIG. 2.

FIG. 6 is a cross sectional view of the forward bevel gear shown in FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.

FIGS. 1 to 6 illustrate a propulsion unit for an outboard motor in accordance with an embodiment. FIG. 1 is a side view of an outboard motor on a hull; FIGS. 2 and 3 are respectively a side view and a cross sectional view of a lower casing having a propulsion unit disposed therein; FIG. 4 is a sectional plan view of a lower casing; and FIGS. 5 and 6 are respectively a front view and a cross sectional view of a forward bevel gear of a bevel gear mechanism. This embodiment shows one example illustrating inventive principles. It is to be understood that the principles discussed herein can be employed in outboard motors having other structural configurations and in other marine drive configurations, such as stern drives.

In the figures, an outboard motor 1 is mounted at the stern 2a of a hull 2. The outboard motor 1 has a clamp bracket 3 secured to the stern 2a and includes a swivel arm 4 and a pivot shaft 5. The swivel arm 4 supports the outboard motor 1 for up-and-down pivotal movement. The pivot shaft 5 supports the outboard motor 1 in a manner to steer to the left and right.

The external structure of the outboard motor 1 generally includes a lower casing 7, an upper casing 8, and a cowling 11. The lower casing 7 has a propulsion unit 6 enclosed therein. The upper casing 8 is coupled to the top of the lower casing 7. On the top of the upper casing 8, an engine 10 is mounted. The cowling 11 is attached so as to surround the engine 10. The engine 10 is positioned vertically such that the crankshaft 10a is oriented generally vertically when the watercraft is driven on water.

The propulsion unit 6 includes a drive shaft 12, a propeller shaft 14, the above-described lower casing 7, and a propeller 15. The drive shaft 12 is coaxially coupled to the crankshaft 10a and is rotationally driven by the engine 10. The propeller shaft 14 is positioned generally horizontally to be perpendicular to the drive shaft 12, and is rotationally driven thereby via a bevel gear mechanism 13. The lower casing 7 preferably holds therein the propeller shaft 14 and the drive shaft 12. The propeller 15 is attached to a projection 14a of the propeller shaft 14 that projects rearward from the lower casing 7.

The bevel gear mechanism 13 includes a drive bevel gear 17, a forward bevel gear 18, and a reverse bevel gear 19. The drive bevel gear 17 is attached to a lower end 12a (bevel gear mechanism attachment part) of the drive shaft 12 for rotation therewith. The forward bevel gear 18 and the reverse bevel gear 19 are in constant mesh with the drive bevel gear 17, and are attached to a front end 14b (bevel gear mechanism attachment part) of the propeller shaft 14 for rotation relative thereto.

The forward bevel gear 18 preferably has a structure of a spiral bevel gear. As shown in FIGS. 5 and 6, the illustrated forward bevel gear 18 is made up of a shaft portion 18b and a bevel portion 18c, and is formed as an integral piece. The shaft portion 18b has a shaft bore 18a disposed therein to receive the propeller shaft 14. The bevel portion 18c has a number of curved teeth 18d disposed circumferentially thereon at a certain pitch.

Each curved tooth 18d curves in the forward rotational direction A of the forward bevel gear 18 as it extends from an inner end 18d′ to an outer end 18d″. Accordingly, the pitch between the two adjacent curved teeth 18d will become larger moving from w2 at the inside end toward w1 at the outside end. In the illustrated embodiment, the drive bevel gear 17 and the reverse bevel gear 19 also have a spiral bevel gear structure comparable with the forward bevel gear 18.

As such, the bevel gear mechanism 13 produces a lubricant stirring effect with the rotation of the drive shaft 12, and acts as a gear pump to deliver lubricant that is in a bevel gear mechanism chamber 7b (to be described later) into a shift shaft chamber 7c.

The illustrated bevel gear mechanism 13 includes a forward-reverse switching mechanism 20. The forward-reverse switching mechanism 20 includes a dog clutch 21, a shift sleeve 22, a shift shaft 24, and a shift lever (not shown). The dog clutch 21 is positioned between the forward and reverse bevel gears 18, 19 on the propeller shaft 14, and spline fitted over the propeller shaft 14 to move axially therealong and to rotate together therewith. The shift sleeve 22 is axially slidably inserted into the front end 14b of the propeller shaft 14. The shift shaft 24 is coupled to the shift sleeve 22 via a shift cam 23. The shift lever (not shown) is coupled to the shift shaft 24 and positioned on the hull 2. The dog clutch 21 selectively engages with the forward or reverse bevel gear 18, 19 as it moves back and forth on the propeller shaft 14.

The shift sleeve 22 is coupled to the dog clutch 21 with a pin 25. The pin 25 is disposed through a pin hole 14e formed in the propeller shaft 14 between the forward and reverse bevel gears 18, 19.

The dog clutch 21 is movable between a neutral position and forward and reverse clutch-in positions. In the neutral position, the dog clutch does not engage with the forward bevel gear 18 nor the reverse bevel gear 19. In the forward and reverse clutch-in positions, the dog clutch engages with the forward or reverse bevel gear 18, 19.

As the operator operates the shift lever from the neutral position to the forward or reverse clutch-in position, the shift shaft 24 will rotate to cause the shift cam 23 to convert the rotation of the shift shaft 24 to the axial movement of the shift sleeve 22. Accordingly, the dog clutch 21 will be brought into engagement with the forward or reverse bevel gear 18, 19. As a result, the rotational force of the drive shaft 12 will be transmitted to the propeller shaft 14.

In the illustrated embodiment, the lower casing 7 is generally bullet-shaped as viewed in a cross sectional view perpendicular to the drive shaft 12. In the lower casing 7 at a generally central portion in the fore-and-aft direction, a drive shaft chamber 7a is defined which extends generally vertically and is open upward. In the drive shaft chamber 7a, the drive shaft 12 is enclosed.

The lower casing 7 preferably also has a bevel gear mechanism chamber 7b defined therein which is positioned at the lower end of the drive shaft chamber 7a. The bevel gear mechanism chamber 7b extends in the fore-and-aft direction and is open rearward. In the bevel gear mechanism chamber 7b, the bevel gear mechanism 13 is enclosed.

A cylindrical bearing housing 30 is mounted within an upper end opening of the drive shaft chamber 7a to establish a seal between the drive shaft 12 and the inner peripheral wall of the drive shaft chamber 7a. In the bearing housing 30, there are disposed a pair of upper and lower seals 31, 31 for sealing between the housing 30 and the drive shaft 12 to prevent lubricant from flowing therethrough.

An upper end 12b of the drive shaft 12 in the illustrated lower casing 7 is rotatably supported by the housing 30 via a needle bearing 32. A lower end 12a of the drive shaft 12 is rotatably supported by a needle bearing 33 disposed within a lower end opening of the drive shaft chamber 7a.

In the illustrated bevel gear mechanism chamber 7b at its front end, a conical roller bearing 35 is disposed for rotatably supporting the forward bevel gear 18. Within a rear end opening of the bevel gear mechanism chamber 7b, a ball bearing 37 is disposed for rotatably supporting the reverse bevel gear 19 via a gear housing 36 (to be described later).

The illustrated lower casing 7 also has a shift shaft chamber 7c defined therein. The shift shaft chamber 7c is positioned in front of the drive shaft chamber 7a and extends parallel to the drive shaft chamber 7a. In the shift shaft chamber 7c, the shift shaft 24 is enclosed. A flange 24a is formed at a lower end of the shift shaft 24. The flange 24a supports the shift shaft 24 in sliding contact with the inner periphery of the shift shaft chamber 7c. The flange 24a has an oil passage groove 24b disposed therethrough.

A lower end of the shift shaft chamber 7c communicates with the bevel gear mechanism chamber 7b. A seal 38 is mounted within an upper end opening of the shift shaft chamber 7c to seal between the shift shaft 24 and the inner peripheral wall of the shift shaft chamber 7c.

The illustrated lower casing 7 has a cooling water intake passage 7d defined therein. The cooling water intake passage 7d is positioned in front of the shift shaft chamber 7c and extends parallel to the shift shaft chamber 7c. The cooling water intake passage 7d is designed to make cooling water flow therethrough which enters through inlets 7g formed in left and right sidewalls of the lower casing 7.

The illustrated lower casing 7 has a cooling water jacket 7h defined therein which surrounds the drive shaft chamber 7a. The cooling water flowing through the cooling jacket 7h cools the lubricant in the drive shaft chamber 7a. The lubricant in the shift shaft chamber 7c is also cooled by the cooling water flowing through the cooling water intake passage 7d and the cooling water jacket 7h.

The illustrated lower casing 7 also has an exhaust gas passage 7e defined therein which is positioned behind the drive shaft chamber 7a. The cooling water jacket 7h is positioned between the exhaust gas passage 7e and the drive shaft chamber 7a. The exhaust gas passage 7e communicates with a discharge opening (not shown) formed in the rear end face of the lower casing 7. Exhaust gas from the engine 10 will flow through the upper casing 7 and through the passage 7c to be discharged through the discharge opening into water.

In the bevel gear mechanism chamber 7b of the illustrated lower casing 7, the gear housing 36 described above is inserted so as to extend across the exhaust gas passage 7e. The gear housing 36 defines the exhaust gas passage 7e and the bevel gear mechanism chamber 7b.

The illustrated gear housing 36 includes a cylindrical portion 36b, a large-diameter portion 36c, a plurality of ribs 36d, and a flange 36e. The cylindrical portion 36b has a propeller shaft bore 36a disposed therethrough. The large-diameter portion 36c is cup-shaped and is formed at a front end of the cylindrical portion 36b. The ribs 36d are formed at a rear end of the cylindrical portion 36b to extend radially outward perpendicularly to the axial direction thereof. The flange 36e is formed on peripheral ends of the ribs 36d. The flange 36e is secured to the peripheral edge of the discharge opening in the lower casing 7 with a plurality of bolts 40 inserted from behind.

The outer periphery of the large-diameter portion 36c preferably is mounted within the rear end opening of the bevel gear mechanism chamber. The ball bearing 37 is mounted between the inner periphery of the large-diameter portion 36c and a boss of the reverse bevel gear 19.

The propeller shaft 14 is disposed through the propeller shaft bore 36a of the gear housing 36. The front end 14b of the propeller shaft 14 is inserted through a shaft bore 19a of the reverse bevel gear 19 and into the shaft bore 18a of the forward bevel gear 18. The front end 14b preferably is supported by the forward and reverse bevel gears 18, 19 for rotation relative thereto, via a metal bearing 42 which is disposed within the shaft bore 18a of the forward bevel gear 18. The propeller shaft 14 and the shaft bore 19a of the reverse bevel gear 19 preferably form a gap therebetween.

At a rear end of the propeller shaft bore 36a of the illustrated gear housing 36, there is disposed a pair of front and rear seals 44, 44 for sealing between the propeller shaft 14 and the gear housing 36.

In the propeller shaft bore 36a of the gear housing 36 and just in front of the seals 44, a needle bearing 43 preferably is disposed for rotatably supporting a rear end 14d of the propeller shaft 14.

The illustrated propulsion unit 6 includes an oil circulating system 47 which circulates therein a first part “a” and a second part “b” of the lubricant filled in the lower casing 7. In the oil circulating system 47, the first part “a” and the second part “b” of the lubricant circulate through the drive shaft chamber 7a, the bevel gear mechanism chamber 7b, the shift shaft chamber 7c, and the propeller shaft bore 36a. The oil level of the lubricant is positioned at the upper needle bearing 32 in the drive shaft chamber 7a. The oil level is also positioned at the same height in the shift shaft chamber 7c.

The oil circulating system 47 preferably includes a drive shaft circulating system 48 and a propeller shaft circulating system 49. The drive shaft circulating system 48 circulates the first part “a” of the lubricant therein to flow from the bevel gear mechanism attachment part (lower end) 12a of the drive shaft 12 to the forward-reverse switching mechanism 20 and then to the upper and lower needle bearings 32, 33. The propeller shaft circulating system 49 circulates the second part “b” of the lubricant therein to flow from the bevel gear mechanism attachment part (front end) 14b of the propeller shaft 14 to the needle bearing 43.

The illustrated propeller shaft circulating system 49 includes an oil passage 49c and a return passage 49d. The oil passage 49c includes an axial passage 49a and a vertical passage 49b. The axial passage 49a is disposed in the propeller shaft 14 and extends axially therealong from the bevel gear mechanism attachment part 14b to a position proximate to the needle bearing 43. The vertical passage 49b radially extends from an extended end of the axial passage 49a and communicates with an area proximate to the needle bearing 43. The return passage 49d preferably is formed by a gap between the propeller shaft 14 and the inner peripheral wall of the propeller shaft bore 36a of the gear housing 36.

The axial passage 49a of the oil passage 49c preferably communicates with the pin hole 14e of the propeller shaft 14. The vertical passage 49b preferably communicates with the area proximate to a front part of the needle bearing 43.

As the dog clutch 21 engages with the forward or reverse bevel gear 18, 19 in response to the operator's operation of the shift lever, the propeller shaft 14 will start rotation. At this time, the second part “b” of the lubricant will be forced out through the vertical passage 49b of the oil passage 49c by centrifugal force due to the rotation of the propeller shaft 14. The forced-out second part “b” will lubricate the needle bearing 43 and then flow through the return passage 49d to lubricate the ball bearing 37 and the meshing parts of the bevel gear mechanism 13, and then return to the bevel gear mechanism chamber 7b. The second part “b” of the lubricant in the bevel gear mechanism chamber 7b will enter the axial passage 49a of the oil passage 49c by the rotation of the propeller shaft 14.

The illustrated drive shaft circulating system 48 includes the shift shaft chamber 7c, an oil return passage 48a, a screw pump 48b, and a communication passage 48c. The shift shaft chamber 7c defines an oil passage for the drive shaft circulating system 48. The oil return passage 48a preferably is formed by a gap between the drive shaft 12 and the inner peripheral wall of the drive shaft chamber 7a of the lower casing 7, and extends axially along the drive shaft 12. The screw pump 48b is formed by an axial central portion of the drive shaft 12 in the lower casing 7 and the inner peripheral wall of the drive shaft chamber 7a. The communication passage 48c communicates the shift shaft chamber 7c and a part of the return passage 48a around the needle bearing 32.

The drive shaft 12 in the illustrated lower casing 7 has a spiral groove 12c formed in the periphery thereof which extends downward in a clockwise direction. The screw pump 48b is obtained by providing a slight gap between the spiral groove 12c and the inner peripheral wall of the drive shaft chamber 7a. The screw pump 48b pressurizes and delivers downward the first part “a” of the lubricant in the oil passage 48a.

As the drive shaft 12 rotates, the screw pump 48b will pressurize and help deliver the first part “a” of the lubricant downward through the oil passage 48a. The bevel gear mechanism 13 will also rotate to thereby stir and deliver the first part “a” in the bevel gear mechanism chamber 7b into the shift shaft chamber 7c.

The first part “a” of the lubricant that entered the shift shaft chamber 7c due to the lubricant stirring effect of the bevel gear mechanism 13 will first lubricate the forward-reverse switching mechanism 20 and then flow through the oil passage groove 24b and go upward through the shift shaft chamber 7c. It will then flow from an upper end of the shift shaft chamber 7c through the communication passage 48c into the oil return passage 48a. The first part “a” that entered the return passage 48a will flow to and lubricate the upper needle bearing 32 of the drive shaft 12. It will then be pressurized and delivered downward by the screw pump 48b to lubricate the lower needle bearing 33, the meshing parts of the bevel gear mechanism 13 and the bearings 35, 37, and then returned to the bevel gear mechanism chamber 7b. The first part “a” in the bevel gear mechanism chamber 7b will be delivered again into the shift shaft chamber 7c by the bevel gear mechanism 13.

In the illustrated embodiment, the first part “a” flowing through the shift shaft chamber 7c and the drive shaft chamber 7a will be cooled by the cooling water flowing through the cooling water intake passage 7d and the cooling water jacket 7h.

In this embodiment, the first part “a” of the lubricant in the drive shaft circulating system 48 is delivered from the bevel gear mechanism chamber 7b into the shift shaft chamber 7c due to the lubricant stirring effect of the bevel gear mechanism 13. The first part “a” flows from the shift shaft chamber 7c through the communication passage 48c into the oil return passage 48a to lubricate the needle bearing 32 of the drive shaft 12. The first part “a” that lubricated the bearing 32 is then delivered downward by the screw pump 48b through the return passage 48a to return to the bevel gear mechanism chamber 7b. Accordingly, the first part “a” of the lubricant can circulate in the direction in which the bevel gear mechanism 13 delivers the lubricant due to the lubricant stirring effect (direction of the arrow “a”). This prevents stagnation or backflow of the lubricant. Hence, less wear occurs to the meshing parts of the bevel gear mechanism 13 and the bearings of the drive shaft 12, thereby assuring the prolonged life of the parts.

In this embodiment, the drive shaft 12 has the spiral groove 12c formed in the periphery thereof which delivers the first part “a” of the lubricant downward. Accordingly, the drive shaft 12 acts as a screw pump to deliver the first part “a” in the same direction as the direction in which the bevel gear mechanism 13 delivers the lubricant. This further facilitates the circulation of the first part “a”, thereby helping to maintain it at an appropriate temperature and helping promote prolonged life of the parts. Thus, the life of the parts can be prolonged further.

In this embodiment, the first part “a” is delivered from the bevel gear mechanism chamber 7b into the shift shaft chamber 7c by the bevel gear mechanism 13. Since the bevel gear mechanism 13 acts as a gear pump, the circulation of the first part “a” is facilitated further.

More specifically, the lubricant stirring effect of the bevel gear mechanism 13 is utilized to make the first part “a” flow from the shift shaft chamber 7c to the drive shaft chamber 7a. Accordingly, the direction in which the bevel gear mechanism 13 delivers the lubricant coincides with the direction in which the screw pump 48b delivers the lubricant. This further prevents stagnation or backflow of the lubricant.

In this embodiment, the shift shaft chamber 7c is used as an oil passage. Accordingly, the oil circulating system can be formed by utilizing the existing shift shaft chamber 7c. This prevents the lower casing 7 from increasing in size and effects cost reduction.

The shift shaft chamber 7c, which is used as an oil passage, preferably is surrounded by the cooling water intake passage 7d and the cooling jacket 7h and is disposed apart from the exhaust gas passage 7e. This provides enhanced cooling characteristics of the first part “a” of the lubricant flowing through the shift shaft chamber 7c.

It should be understood that in this embodiment, the shift shaft chamber 7c is used as the oil passage, but the oil passage may be provided separately from the shift shaft chamber.

Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. For example, bearings and gears having other structure, and being used in other types of marine drives such as stern drives or outboard motors having different structure such as having only a forward gear, or other structures and configurations, can employ inventive aspects. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.