Drivetrain and Transmission for Marine Propulsion Device for Preventing Engine Ingestion of Water

Abstract

A drivetrain for a marine propulsion device includes an engine driving a crankshaft in a first direction, and a driveshaft connected in torque-transmitting relationship with the crankshaft and supported for rotation about a driveshaft axis. The drivetrain further includes a propeller shaft rotatable about a propeller shaft axis. A gearset and a selector clutch are configured to couple the propeller shaft and the driveshaft to each other in torque-transmitting relationship. A one-way clutch is disposed along the drivetrain upstream of the gearset. The one-way clutch prevents rotation of the crankshaft in a second, opposite direction so as to prevent ingestion of water by the engine via an engine exhaust system.

Description

FIELD

The present disclosure relates to drivetrains and transmissions for marine propulsion devices, such as for example outboard motors and/or sterndrives.

BACKGROUND

U.S. Pat. No. 6,960,107, incorporated herein by reference, discloses a transmission for a marine propulsion system that uses a cone clutch in such a way that, when in a forward gear position, torque is transmitted from an input shaft, or driving shaft, to an output shaft, or driven shaft, solely through the cone clutch. When in forward gear position, driving torque between the driving and driven shafts is not transmitted through any gear teeth. When in reverse gear position, torque is transmitted through an assembly of the bevel gears.

U.S. Pat. No. 7,297,036, incorporated herein by reference, discloses a marine transmission in which trailing faces of each of a plurality of gear projections extending axially from a forward gear are provided with a rake angle. This rake angle of each trailing face cooperates with an associated surface of each of a plurality of clutch projections to retain a dog clutch in an axial position relative to the forward gear even during periods when a marine vessel is rapidly decelerating and, as a result, the dog clutch moves into driving relation with the forward gear.

SUMMARY

This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In one example of the present disclosure, a drivetrain for a marine propulsion device includes an engine driving a crankshaft in a first direction, and a driveshaft connected in torque-transmitting relationship with the crankshaft and supported for rotation about a driveshaft axis. The drivetrain further comprises a propeller shaft rotatable about a propeller shaft axis. A gearset and a selector clutch are configured to couple the propeller shaft and the driveshaft to each other in torque-transmitting relationship. A one-way clutch is disposed along the drivetrain upstream of the gearset. The one-way clutch prevents rotation of the crankshaft in a second, opposite direction so as to prevent ingestion of water by the engine via an engine exhaust system.

In another example of the present disclosure, a transmission for a marine propulsion device includes a propeller shaft rotatable about a propeller shaft axis, a forward gear disposed for rotation about the propeller shaft axis, and a reverse gear disposed for rotation about the propeller shaft axis. A driveshaft is supported for rotation about a driveshaft axis, the driveshaft axis being generally perpendicular to the propeller shaft axis. A drive gear is attached for rotation with the driveshaft, and the forward and reverse gears are disposed in meshing relation with the drive gear for rotation in opposite directions from each other about the propeller shaft axis. A selector clutch is attached for rotation with the propeller shaft about the propeller shaft axis and is movable between the forward and reverse gears so as to mesh with one of the forward and reverse gears. A one-way clutch is disposed about the driveshaft. The one-way clutch allows rotation of the driveshaft about the driveshaft axis in a first direction by application of torque from an engine coupled to the driveshaft, and prevents rotation of the driveshaft about the driveshaft axis in a second, opposite direction by application of torque transmitted from the propeller shaft to the drive shaft via the selector clutch, one of the forward and reverse gears, and the drive gear.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is described with reference to the following Figures. The same numbers are used throughout the Figures to reference like features and like components.

FIG. 1 illustrates one example of a drivetrain for a marine propulsion device according to the present disclosure.

FIGS. 2-4 illustrate internal workings of the drivetrain of FIG. 1 under varied circumstances.

FIG. 5 illustrates one example of a sterndrive and its associated transmission.

FIG. 6 illustrates one example of a gear case for an outboard motor and its associated transmission.

FIG. 7 illustrates one example of a one-way clutch according to the present disclosure, wherein the one-way clutch is a sprag clutch.

FIG. 8 illustrates a detailed view of a portion of FIG. 7.

FIG. 9 illustrates another example of a one-way clutch according to the present disclosure, wherein the one-way clutch is a roller clutch.

DETAILED DESCRIPTION

In the present description, certain terms have been used for brevity, clarity and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes only and are intended to be broadly construed.

FIG. 1 illustrates one example of a drivetrain 10 for a marine propulsion device, such as an outboard motor or a sterndrive. The drivetrain 10 comprises an engine 12 having a crankshaft 14. The engine 12 drives the crankshaft 14 in a first direction as shown by the arrow 16, which driving relationship is accomplished by combusting a fuel/air mixture in a plurality of cylinders within the engine 12, the piston rods of which cylinders are coupled to the crankshaft 14, as is well known. The drivetrain 10 further includes a driveshaft 18 connected in torque-transmitting relationship with the crankshaft 14, and supported for rotation about a driveshaft axis 20. For example, the driveshaft 18 is connected in torque-transmitting relationship with the crankshaft 14 by way of a splined connection. In the example in which the drivetrain 10 is meant for a sterndrive, the crankshaft 14 is coupled in torque-transmitting relationship with the driveshaft 18 by a beveled gear set 48. See FIG. 5.

Returning to FIG. 1, the drivetrain 10 further comprises a propeller shaft 22 surrounded at one end by a propeller hub 24 having a propeller 27 attached thereto. The propeller shaft 22 is rotatable about a propeller shaft axis 26. A gear set 28 and selector clutch 30 are configured to couple the propeller shaft 22 and the driveshaft 18 to each other in torque-transmitting relationship. Together, the shafts 18, 22, gear set 28, and selector clutch 30 make up a portion of a transmission 50 of the marine propulsion device.

Those having ordinary skill in the art will recognize that after the engine 12 combusts the above-mentioned fuel/air mixture, exhaust from such combustion is expelled from the cylinders through an exhaust manifold of the engine 12 and thereafter routed through an exhaust system 35 to the propeller hub 24, after which the exhaust is expelled from the propeller hub 24 and into the water in which the marine propulsion device is operating, as shown by the arrows. One example of an exhaust system for a sterndrive is found in U.S. Pat. No. 6,022,254, which is hereby incorporated by reference. One example of an exhaust system for an outboard motor is provided in U.S. Pat. No. 8,540,536, which is hereby incorporated by reference. Such exhaust systems will therefore not be discussed further herein.

One example of a conventional gear set 28 is shown in FIGS. 1-3. A drive gear 32 is attached for rotation with the driveshaft 18. A forward gear 34 and a reverse gear 36 are disposed for rotation about the propeller shaft axis 26. (It should be understood that which gear provides forward or reverse movement of the marine vessel to which the marine propulsion device is attached depends on the direction the driveshaft 18 is turning, as well as the pitch of the propeller 27, and the gears have been herein designated as “forward” and “reverse” for purposes of illustration only.) The forward and reverse gears 34, 36 are disposed in meshing relation with the drive gear 32 for rotation in opposite directions from each other about the propeller shaft axis 26. Each of the gears 32, 34, 36 are shown spaced slightly apart for the purpose of clearly distinguishing the components from one another; however, in operation the bevel gears 32, 34, 36 are disposed in continuous meshing association with each other.

It can be seen that rotation of the drive gear 32 by the driveshaft 18 causes continual rotation of both the forward gear 34 and reverse gear 36. The forward and reverse gears 34, 36 rotate in opposite directions, as illustrated by the arrows. A selector clutch 30, shown herein as a dog clutch, but which could be any other type of clutch known to those having ordinary skill in the art for similar purposes, is movable in an axial direction (horizontal in FIGS. 1-3) between the forward and reverse gears 34, 36. The selector clutch 30 is attached for rotation with the propeller shaft 22 about the propeller shaft axis 26 and is movable between the forward and reverse gears 34, 36 so as to mesh with one of the forward and reverse gears 34, 36. The selector clutch 30 may be coupled in threaded association with the propeller shaft 22 through a set of straight splines, in a manner which is well-known to those skilled in the art of marine transmissions. With the selector clutch 30 in the position shown in FIG. 1, neither the forward gear 34 nor the reverse 36 gear is rigidly attached to the propeller shaft 22. As a result, the forward and reverse gears 34, 36 rotate about their axes of rotation without affecting rotation of the propeller shaft 22. FIG. 1 therefore shows the transmission 50 in neutral.

FIG. 2 shows the gear set 28 of FIG. 1, but with the selector clutch 30 moved toward the left to engage its teeth with the teeth of the forward gear 34. This engagement of the clutch teeth causes the selector clutch 30 to rotate in unison with the forward gear 34. Because the selector clutch 30 is associated in threaded engagement with the propeller shaft 22, the propeller shaft 22 rotates in unison with the forward gear 34 and the selector clutch 30. The rotational arrows indicate that the propeller shaft 22 rotates in the same direction as the forward gear 34.

FIG. 3 illustrates the opposite condition, in which the selector clutch 30 is moved to the right and into tooth engagement association with the reverse gear 36. As a result, the selector clutch 30 rotates in unison with the reverse gear 36, and because of the straight spline connection between the selector clutch 30 and the propeller shaft 22, the propeller shaft 22 also rotates in unison with the reverse gear 36.

When an operator of the marine vessel slows down the marine vessel very quickly, water moving by the propeller 27 of the marine propulsion device sometimes causes the propeller 27 to spin at a speed that exceeds the speed of the engine 12. In other words, the propeller 27 and associated propeller shaft 22 spin faster than the crankshaft 14. This is fine under certain circumstances. However, an undesirable situation occurs when the marine propulsion device's transmission 50 is shifted into reverse while the marine vessel is still moving forward in the water. In this case, if the water is moving by the propeller 27 fast enough, torque from the propeller shaft 22 created by the still forward-spinning propeller 27 may cause the driveshaft 18 and crankshaft 14 to slow to a no-rotation condition, and eventually to rotate in an opposite direction than normal, which causes the engine cylinders to act as pumps. The pumping action of the cylinders creates a vacuum, and water is sucked in backwards through the exhaust system 35 via the propeller hub 24. This causes the engine 12 to ingest water, which is very harmful for the engine 12 because it creates a hydrolock of the pistons in the cylinders on the next rotation when the valves are closed. The present inventors have realized that the situation in which the force from the propeller 27 is so great that it slows the crankshaft 14 down, stops it, and turns it the other way can be rectified by addition of a one-way clutch 38 disposed along the drivetrain 10 upstream of the gear set 28. The one-way clutch 38 prevents rotation of the crankshaft 14 in a direction opposite that which is caused by the engine 12 operating under normal conditions, so as to prevent ingestion of water by the engine 12 via the engine exhaust system 35.

An illustration of the above-described situation is discussed with reference to FIG. 4. Assuming that the marine vessel has just been very quickly slowed from a high speed, the propeller 27 and propeller shaft 22 will still be rotating in a forward direction, as shown by the arrow (compare FIG. 2). If the torque from the propeller shaft 22 overcomes the torque produced by the engine 12, this causes the attached selector clutch 30 to rotate in the same direction as the propeller shaft 22. Because the selector clutch 30 has now been meshed with the reverse gear 36 due to the operator's command, this also rotates the reverse gear 36 in the same direction as the propeller shaft 22. The tooth engagement of the reverse gear 36 with the drive gear 32 then causes the drive gear 32 and thus the driveshaft 18 to rotate in a direction opposite than normal. This same opposite rotation is transferred to the crankshaft 14 and back-drives the engine 12.

Prior art systems utilized a ratcheting dog clutch in the position of the selector clutch 30 shown in FIGS. 1-4. The ratcheting dog clutch would provide engagement of the teeth of the clutch with the forward gear 34 in one direction only, and with the reverse gear 36 in the opposite direction only. This allowed transmission of torque from the forward or reverse gear to the clutch, but not from the clutch to the forward or reverse gear: if the propeller shaft and clutch were rotated in an opposite direction, the forward or reverse gear teeth would slide over the angled surfaces of the ratcheting dog clutch with no engagement therebetween. This allowed the propeller 27 to freewheel if it was spinning faster than the forward or reverse gear. However, this sliding action created a loud noise that was undesirable for many marine vessel operators. Further, if the operator of the marine vessel managed to put the transmission 50 into reverse gear while the propeller 27 was still spinning in a forward direction, the ratcheting dog clutch would in fact engage with the reverse gear 36, thus resulting in potential water ingestion. Both of these occurrences are non-issues when using a one-way clutch, as in the present disclosure.

FIGS. 1, 5, and 6 illustrate several examples of where the one-way clutch 38 of the present disclosure could be placed. In one example, the one-way clutch 38 is placed around the crankshaft 14, as shown in FIG. 1. In the examples shown in FIGS. 5 and 6, the one-way clutch 38 is placed around the driveshaft 18 of the marine propulsion device.

FIG. 5 illustrates a sterndrive 40 attached is a transom 42 of a marine vessel. An inboard engine 12 is connected in torque-transmitting relationship with a crankshaft 14, which is in turn connected through a universal joint 44 to a shaft 46 which drives driveshaft 18 via beveled gear set 48. As described above, driveshaft 18 in turn drives propeller shaft 22 to rotate propeller 27. This coupling is provided by a transmission 50 including a selector clutch 30 axially slideable along propeller shaft 22 between counter-rotating gears 34 and 36. The one-way clutch 38 is shown herein as being upstream of the gear set 28 provided in the transmission 50, but downstream of the gear set 48. More specifically, the one-way clutch 38 is located in an upper half of a gearcase 52 of the sterndrive 40. Alternatively, the one-way clutch 38 could be provided further upstream, and even upstream of the gear set 48, for example on shaft 46 between gear set 48 and universal joint 44, or around the crankshaft 14 between universal joint 44 and engine 12.

Now turning to FIG. 6, illustrated therein is a gearcase 52 for an outboard motor, also known as a lower unit. As is known, the gearcase 52 is attached by bolting or other means to a lower end of a driveshaft housing 54 (midsection), of the outboard motor. Like reference numerals are used in FIG. 6 to call out the components that were described herein above with reference to FIGS. 1 and 5, including a portion of the exhaust system 35. Further shown in FIG. 6 is a shift shaft 56 for rotation about a generally vertical axis 58 and operatively associated with a horizontally disposed shaft 60 that allows the selector clutch 30 to be moved axially along the propeller shaft axis 26 when the shift shaft 56 is rotated about its axis 58. The one-way clutch 38 is shown in FIG. 6 as being located upstream of the drive gear 32 and downstream of the engine (not shown, but which is coupled to the top of the driveshaft housing 54 as known). More specifically, the one-way clutch 38 is located in the gearcase 52 of the marine propulsion device. Additionally, the one-way clutch 38 is located in an upper half of the gearcase 52. More specifically, the one-way clutch 38 is located directly below a top surface 62 of the gearcase 52 that is configured to be coupled to the driveshaft housing 54 of the marine propulsion device.

As shown in FIG. 6, the one-way clutch 38 is provided with a set of upper and lower bearings 64 on either side of the one-way clutch 38. These bearings 64 could be provided separately around the driveshaft 18, or could be provided as part of a set with the one-way clutch 38, depending on the one-way clutch selected for use with the transmission 50.

The one-way clutch 38 could be inserted into and coupled to the gearcase 52 in different ways. In one example, the one-way clutch 38 is seated directly within a driveshaft passageway 66 extending through the gearcase 52 along the driveshaft axis 20. This type of system could be used if the driveshaft passageway 66 is defined by a gearcase 52 made of a hard metal, such as steel. In another example, if the gearcase 52 is made of a softer metal such as aluminum, the one-way clutch 38 may comprise an outer raceway that is keyed to an inner surface of the driveshaft passageway 66. Either the inner surface of the driveshaft passageway 66 or the inner diameter of the outer raceway (as the case may be) provides a jamming surface for a component of the one-way clutch 38 that wedges between the jamming surface and the outer surface of the driveshaft 18 in only one direction of rotation but not the other. This jamming action thereby prevents the driveshaft 18 from turning in a direction opposite that which would normally be imposed by the engine 12. Examples will be described with reference to FIGS. 7-9.

Turning to FIG. 7, an example in which the one-way clutch 38 comprises a sprag-type clutch 67 will be described. Shown in cross-section, the driveshaft 18 is surrounded by a plurality of sprags 68, each sprag 68 having a radially inner end 69 that contacts the outer surface of the driveshaft 18. An outer raceway 70 surrounds the plurality of sprags 68, and is keyed to the inner surface of the driveshaft passageway 66 by a key 72. The radially outer ends 71 of each sprag 68 contact an inner diameter of the outer raceway 70. Alternatively, the outer ends of the sprags 68 could directly contact the inner surface of the driveshaft passageway 66. The sprags 68 are held in place by a cage 74 and may be pre-loaded by springs 76, as is known in the art. An example of this type of sprag clutch is provided in U.S. Pat. No. 3,207,278.

Turning to FIG. 8, a brief description of the way in which a sprag prevents rotation of a shaft relative to a surrounding concentric surface will be described. A distance between the outer diameter of the driveshaft 18 and the inner diameter of the outer raceway 70 (or the driveshaft passageway 66 as may be the case) is labeled as A. The sprag 68 is shaped such that its length as denoted by B is greater than the distance A, and its length as denoted by C is less than the distance A. When torque is applied to the driveshaft 18 by the engine 12 in the normal direction of rotation, for example clockwise as shown by the arrow 78, the driveshaft 18 is allowed to rotate relative to the driveshaft passageway 66 or outer raceway 70 as it slips by the shorter dimensioned portion of the sprag 68. However, when torque is applied to the driveshaft 18 in the opposite direction (counterclockwise as shown by arrow 80) for example due to the situation described above with respect to FIG. 4, the driveshaft 18 jams against the sprag 68, which in turn jams against the driveshaft passageway 66 or outer raceway 70 due to the longer dimensioned portion of the sprag 68. No rotation of the driveshaft 18 is permitted due to this jamming effect.

FIG. 9 illustrates one example in which the one-way clutch 38 comprises a roller-type clutch 81. Shown in cross-section, a plurality of rollers 82 are provided in contact with the driveshaft 18. The outer raceway 70 is provided with a plurality of camming surfaces 86, which define spaces 83 between the driveshaft 18 and outer raceway 70. When the driveshaft 18 rotates counterclockwise, rollers 82 move against springs 84 toward the narrower ends 85 of the spaces 83, and the driveshaft 18 is jammed with respect to outer raceway 70. When the driveshaft 18 is rotated in the clockwise direction, the rollers 82 are in the wider ends 87 of the spaces 83, and the driveshaft 18 is allowed to rotate. An example of a roller-type clutch is provided in U.S. Pat. No. 5,695,031. Some examples of roller-type clutches that could be used are clutch numbers HF2016 and HF2520, provided by NTN Corporation of Osaka, Japan. It should be understood that when the driveshaft passageway 66 is provided as the jamming surface for the rollers 82, the camming surfaces 86 could be integrally cast as part of the inner surface of the driveshaft passageway 66. As another alternative, the driveshaft 18 could be fitted with an splined inner race having ramps extending therefrom against which the rollers jam in one direction but not another.

Placement of the one-way clutch 38 in the gearcase 52, as shown in FIGS. 5 and 6 would prevent a wind up of all the driveline components upstream of the one-way clutch 38. However, placement of the one-way clutch 38 around the crankshaft 14 or elsewhere upstream in the driveline would still accomplish the same affect of disallowing engine ingestion of water. Because the lock-up condition of the one-way clutch 38 begins at a no-rotation condition of the drive line, there is not a lot of torque applied to the drive line at the time that the one-way clutch 38 is operating to prevent counter-rotation of the driveline components. This is because in order for the crankshaft 14 to rotate in a direction opposite that which is normal, it must first slow down and stop rotating in its normal direction. Application of the jamming effect of the one-way clutch 38 at a low torque condition ensures that the one-way clutch 38 will not experience extremely large torque forces. Any components to which the one-way clutch 38 is coupled (such as the gearcase 52) will instead take up a large portion of the load from moving water acting on the stopped propeller 27, which load is transferred via the one-way clutch 38.

In the above description, certain terms have been used for brevity, clarity, and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different systems and method steps described herein may be used alone or in combination with other systems and methods. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims.

Claims

1. A drive train for a marine propulsion device, comprising:

an engine driving a crankshaft in a first direction;

a driveshaft connected in torque-transmitting relationship with the crankshaft and supported for rotation about a driveshaft axis;

a propeller shaft rotatable about a propeller shaft axis;

a gear set and a selector clutch configured to couple the propeller shaft and the driveshaft to each other in torque-transmitting relationship; and

a one-way clutch disposed along the drive train upstream of the gear set, the one-way clutch preventing rotation of the crankshaft in a second, opposite direction so as to prevent ingestion of water by the engine via an engine exhaust system;

wherein the one-way clutch is disposed about the driveshaft in a driveshaft passageway that extends through a gearcase of the marine propulsion device;

wherein the gearcase is made of one of steel and aluminum;

wherein, when the gearcase is made of aluminum, the one-way clutch comprises an outer raceway that is keyed to an inner surface of the driveshaft passageway, and an inner surface of the outer raceway provides a jamming surface for a plurality of wedging elements of the one-way clutch; and

wherein, when the gearcase is made of steel, the one way-clutch is seated directly in the driveshaft passageway, and the inner surface of the driveshaft passageway provides the jamming surface for the plurality of wedging elements of the one-way clutch.

2-4. (canceled)

5. The drive train of claim 1, wherein the marine propulsion device is a sterndrive.

6. The drive train of claim 1, wherein the marine propulsion device is an outboard motor.

7. (canceled)

8. The drive train of claim 1, wherein the gear set comprises:

a forward gear disposed for rotation about the propeller shaft axis;

a reverse gear disposed for rotation about the propeller shaft axis; and

a drive gear attached for rotation with the driveshaft, the forward and reverse gears being disposed in meshing relation with the drive gear for rotation in opposite directions from each other about the propeller shaft axis;

wherein the selector clutch is attached for rotation with the propeller shaft about the propeller shaft axis and movable between the forward and reverse gears so as to mesh with one of the forward and reverse gears.

9. The drive train of claim 1, wherein the one-way clutch comprises a sprag-type clutch and the plurality of wedging elements comprises sprags.

10. The drive train of claim 1, wherein the one-way clutch comprises a roller-type clutch and the plurality of wedging elements comprises rollers.

11. A transmission for a marine propulsion device, comprising:

a propeller shaft rotatable about a propeller shaft axis;

a forward gear disposed for rotation about the propeller shaft axis;

a reverse gear disposed for rotation about the propeller shaft axis;

a driveshaft supported for rotation about a driveshaft axis, the driveshaft axis being generally perpendicular to the propeller shaft axis;

a drive gear attached for rotation with the driveshaft, the forward and reverse gears being disposed in meshing relation with the drive gear for rotation in opposite directions from each other about the propeller shaft axis;

a selector clutch attached for rotation with the propeller shaft about the propeller shaft axis and movable between the forward and reverse gears so as to mesh with one of the forward and reverse gears; and

a one-way clutch disposed about the driveshaft in a driveshaft passageway that extends through a gearcase of the marine propulsion device, the one-way clutch allowing rotation of the driveshaft about the driveshaft axis in a first direction by application of torque from an engine coupled to the driveshaft, and preventing rotation of the driveshaft about the driveshaft axis in a second, opposite direction by application of torque transmitted from the propeller shaft to the driveshaft via the selector clutch, one of the forward and reverse gears, and the drive gear;

wherein the gearcase is made of one of steel and aluminum;

wherein, when the gearcase is made of aluminum, the one-way clutch comprises an outer raceway that is keyed to an inner surface of the driveshaft passageway, and an inner surface of the outer raceway provides a jamming surface for a plurality of wedging elements of the one-way clutch; and

wherein, when the gearcase is made of steel, the one way-clutch is seated directly in the driveshaft passageway, and the inner surface of the driveshaft passageway provides the jamming surface for the plurality of wedging elements of the one-way clutch.

12-13. (canceled)

14. The transmission of claim 11, wherein the one-way clutch is located in an upper half of the gearcase.

15. The transmission of claim 14, wherein the one-way clutch is located directly below an upper surface of the gearcase that is configured to be coupled to a driveshaft housing of the marine propulsion device.

16-17. (canceled)

18. The transmission of claim 11, wherein the marine propulsion device is an outboard motor.

19. The transmission of claim 11, wherein the one-way clutch comprises a sprag-type clutch and the plurality of wedging elements comprises sprags.

20. The transmission of claim 11, wherein the one-way clutch comprises a roller-type clutch and the plurality of wedging elements comprises rollers.