OUTBOARD MOTOR

Abstract

An outboard motor includes: an outboard motor body, and a mounting mechanism provided in front of the outboard motor body and mounts the outboard motor body on a boat. The outboard motor body includes: a motor; a drive shaft; a first transmission mechanism transmits rotation of the motor to the drive shaft; a propeller shaft in which a propeller is provided; and a second transmission mechanism transmits rotation of the drive shaft to the propeller shaft. The first transmission mechanism is disposed so that a front part thereof is positioned above a mounting mechanism and a rear part thereof is positioned above the motor.

Claims

1. An outboard motor comprising: an outboard motor body; and a mounting mechanism provided in front of the outboard motor body and configured to mount the outboard motor body on a boat, wherein the outboard motor body includes: a motor; a drive shaft; a first transmission mechanism configured to transmit rotation of the motor to the drive shaft; a propeller shaft in which a propeller is provided; and a second transmission mechanism configured to transmit rotation of the drive shaft to the propeller shaft, and the first transmission mechanism is disposed so that a front part of the first transmission mechanism is positioned above the mounting mechanism and a rear part of the first transmission mechanism is positioned above the motor.

2. The outboard motor according to claim 1, wherein the mounting mechanism includes: a clamp bracket configured to fix the outboard motor body to the boat; and a swivel bracket being connected to the clamp bracket and configured to support the outboard motor body to be pivotable in a left-right direction relative to the boat, and the front part of the first transmission mechanism is positioned above the swivel bracket.

3. The outboard motor according to claim 2, wherein the drive shaft extends in a vertical direction and is disposed in front of the motor, the first transmission mechanism includes: a first rotation transmission element configured to input the rotation of the motor to the first transmission mechanism; and a second rotation transmission element configured to output the rotation of the motor input to the first transmission mechanism from the first transmission mechanism to the drive shaft, and the first rotation transmission element is disposed above the motor and coaxially with an output shaft of the motor, the second rotation transmission element is disposed above the drive shaft and coaxially with the drive shaft, and a portion of the second rotation transmission element is positioned above the swivel bracket.

4. The outboard motor according to claim 1, wherein the first transmission mechanism includes: a drive sprocket configured to input the rotation of the motor to the first transmission mechanism; a driven sprocket configured to output the rotation of the motor input to the first transmission mechanism from the first transmission mechanism to the drive shaft; and a silent chain stretched across the drive sprocket and the driven sprocket.

5. The outboard motor according to claim 1, further comprising: an inverter configured to control driving of the motor, wherein the inverter is disposed above the first transmission mechanism.

6. The outboard motor according to claim 1, wherein the mounting mechanism includes: a clamp bracket configured to fix the outboard motor body to the boat; a pilot shaft that serves as an axis of pivoting of the outboard motor body in a left-right direction; a swivel bracket that is connected to the clamp bracket and configured to support the pilot shaft to be pivotable; an upper mount configured to connect an upper end of the pilot shaft to the outboard motor body; and a lower mount configured to connect a lower end of the pilot shaft to the outboard motor body, and the first transmission mechanism is positioned above the upper mount.

7. The outboard motor according to claim 6, wherein the motor is disposed below the upper mount, and the first transmission mechanism is disposed above the upper mount.

8. The outboard motor according to claim 6, further comprising: a pair of left and right upper mounts, wherein the drive shaft passes between the pair of upper mounts.

9. The outboard motor according to claim 1, further comprising a case configured to accommodate the first transmission mechanism, wherein the case is disposed above the motor, and a shift actuator that controls switching of a rotation direction of the propeller is attached to the case.

10. The outboard motor according to claim 3, wherein each of the first rotation transmission element and the second rotation transmission element is one of a gear, a sprocket, or a pulley.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0015] FIG. 1 is an explanatory diagram illustrating an outboard motor according to an example of the present invention as viewed from the left.

[0016] FIG. 2 is an explanatory diagram illustrating an upper part of the outboard motor according to the example of the present invention as viewed from behind.

[0017] FIG. 3 is a cross-sectional view illustrating the outboard motor cut along a line III-III in FIG. 2 as viewed from the left.

[0018] FIG. 4 is an explanatory diagram illustrating a motor, an upper case, a middle case, a lower case, and an inverter separated from each other in the outboard motor according to the example of the present invention.

[0019] FIG. 5 is a cross-sectional view illustrating the outboard motor cut along a line V-V in FIG. 3 as viewed from above.

[0020] FIG. 6 is a cross-sectional view illustrating the outboard motor cut along a line VI-VI in FIG. 3 as viewed from above.

DESCRIPTION OF EMBODIMENTS

[0021] An outboard motor according to an embodiment of the present invention includes an outboard motor body and a mounting mechanism that is provided in front of the outboard motor body and mounts the outboard motor body on a boat. The outboard motor body also includes a motor, a drive shaft, a first transmission mechanism for transmitting rotation of the motor to the drive shaft, a propeller shaft in which a propeller is provided, and a second transmission mechanism for transmitting rotation of the drive shaft to the propeller shaft. The first transmission mechanism is disposed so that a front part of the first transmission mechanism is positioned above the mounting mechanism and a rear part of the first transmission mechanism is positioned above the motor.

[0022] In the outboard motor of the embodiment, the mounting mechanism is provided in front of the outboard motor body and the outboard motor body includes the motor. According to such configuration, the mounting mechanism and the motor are aligned in a front-rear direction, with the mounting mechanism positioned in front and the motor positioned behind. The first transmission mechanism is disposed above the mounting mechanism and the motor aligned in the front-rear direction as such. As a result, the front part of the first transmission mechanism is positioned above the mounting mechanism and the rear part of the first transmission mechanism is positioned above the motor.

[0023] In such configuration, when the outboard motor is viewed from above, the first transmission mechanism is disposed so that the front part thereof overlaps with the mounting mechanism. As such, by disposing the first transmission mechanism so that the front part thereof overlaps with the mounting mechanism, an arrangement of the first transmission mechanism can be shifted forward to be brought closer to the boat on which the outboard motor is mounted, compared to when the entire first transmission mechanism is disposed behind the mounting mechanism, whereby a distance between the first transmission mechanism and a transom of the boat in the front-rear direction can be reduced.

[0024] The first transmission mechanism is a mechanism for transmitting rotation of the motor to the drive shaft, and the output shaft of the motor is connected to the first transmission mechanism directly or via another shaft. Therefore, the position of the motor needs to be determined considering the position of the first transmission mechanism, and in the outboard motor of the embodiment, the position of the first transmission mechanism can be shifted forward to be brought closer to the boat, whereby the position of the motor can be shifted forward to be brought closer to the boat. Therefore, the distance between the motor and the transom of the boat in the front-rear direction can be reduced.

[0025] As such, in the outboard motor of the embodiment, the motor and the first transmission mechanism that are heavy objects can be brought closer to the boat, whereby a center of gravity of the outboard motor can be brought closer to the boat. By bringing the center of gravity of the outboard motor closer to the boat, a force necessary for tilting up the outboard motor can be reduced. Therefore, when the outboard motor is configured so that tilting up is performed manually, a burden on a user who tilts up the outboard motor can be reduced. When the outboard motor is configured to be tilted up using a hydraulic or electric actuator, an actuator having a lower output can be used for tilting up, whereby manufacturing costs of the outboard motor can be reduced.

[0026] In the outboard motor of the embodiment, the first transmission mechanism is disposed so that, when the outboard motor is viewed from above, the front part of the first transmission mechanism overlaps with the mounting mechanism, and by disposing the first transmission mechanism so that the front part thereof overlaps with the mounting mechanism as such, the position of the motor can be shifted forward to be brought closer to the mounting mechanism. Therefore, according to the outboard motor of the embodiment, a dimension of the outboard motor in the front-rear direction can be reduced.

EXAMPLE

[0027] An outboard motor according to an example of the present invention will be described with reference to the drawings. In the description of the example, directions of up (Ud), down (Dd), front (Fd), back (Bd), left (Ld), and right (Rd) follow arrows drawn at the lower left in each drawing.

[0028] FIG. 1 illustrates an outboard motor 1 according to the example of the present invention as viewed from the left. FIG. 2 illustrates an upper part of the outboard motor 1 as viewed from behind. FIG. 3 illustrates a cross section of the outboard motor 1 cut along a line III-III in FIG. 2 as viewed from the left. FIG. 4 illustrates a motor 3, an upper case 25, a middle case 26, a lower case 27, and an inverter 35 separated from each other. FIG. 5 illustrates a cross section of the outboard motor 1 cut along a line V-V in FIG. 3 as viewed from above. FIG. 6 illustrates a cross section of the outboard motor 1 cut along a line VI-VI in FIG. 3 as viewed from above.

Overall Configuration of Outboard Motor

[0029] The outboard motor 1 is a device for propelling a boat. As illustrated in FIG. 1, the outboard motor 1 is mounted on a transom 101 of the boat. The outboard motor 1 includes an outboard motor body 2 and a mounting mechanism 40 that mounts the outboard motor body 2 on the boat.

[0030] As illustrated in FIG. 3, the outboard motor body 2 includes the motor 3 that serves as a power source for rotating a propeller 20, a drive shaft 8 that transmits power from the motor 3 to the propeller 20, a speed reducer 9 that reduces rotation of an output shaft 4 of the motor 3 and transmits the rotation to the drive shaft 8, a propeller shaft 13, a rotation transmission mechanism 14 that transmits rotation of the drive shaft 8 to the propeller shaft 13, and the propeller 20 that converts the power from the motor 3 into thrust for the boat. The outboard motor body 2 includes a shift device 31 that controls switching of a rotation direction of the propeller 20. The outboard motor body 2 includes the inverter 35 that controls driving of the motor 3. The speed reducer 9 is a specific example of a first transmission mechanism, and the rotation transmission mechanism 14 is a specific example of a second transmission mechanism.

[0031] The motor 3 and the speed reducer 9 are disposed in an upper part of the outboard motor body 2. When the outboard motor 1 is mounted on a boat, the motor 3 and the speed reducer 9 are positioned above the water surface. Meanwhile, the rotation transmission mechanism 14, the propeller shaft 13, and the propeller 20 are disposed in a lower part of the outboard motor body 2. When the outboard motor 1 is mounted on a boat, the rotation transmission mechanism 14, the propeller shaft 13, and the propeller 20 are positioned below the water surface.

[0032] The mounting mechanism 40 is disposed in front of the upper part of the outboard motor body 2. As illustrated in FIG. 1, the mounting mechanism 40 includes a pair of left and right clamp brackets 41 that fix the outboard motor body 2 to the transom 101 of the boat, a pilot shaft 42 that serves as an axis of pivoting of the outboard motor body 2 in a left-right direction, a swivel bracket 43 that is connected to the clamp brackets 41 and supports the pilot shaft 42 to be pivotable, a pair of left and right upper mounts 47 that connect an upper end of the pilot shaft 42 to the outboard motor body 2, and a pair of left and right lower mounts 49 that connect a lower end of the pilot shaft 42 to the outboard motor body 2.

Details of Each Part of Outboard Motor Body

[0033] In the outboard motor body 2, as illustrated in FIG. 3, the motor 3 includes the output shaft 4 that serves as a power output shaft, a rotor 5 provided on an outer periphery of the output shaft 4, a stator 6 provided on an outer periphery of the rotor 5, and a motor case 7 having a substantially cylindrical shape. The output shaft 4 excluding one end, the rotor 5, and the stator 6 are accommodated in the motor case 7. The motor 3 is disposed so that an extension direction of the output shaft 4 is a vertical direction. The motor 3 is disposed so that an end of the output shaft 4 from which power of the motor 3 is taken out faces upward.

[0034] As illustrated in FIG. 3, the speed reducer 9 is disposed above the motor 3. Specifically, the speed reducer 9 is disposed so that a front part of the speed reducer 9 is positioned above the swivel bracket 43 and a rear part of the speed reducer 9 is positioned above the motor 3. When the outboard motor body 2 is viewed from above, the speed reducer 9 is disposed so that the front part thereof overlaps with the swivel bracket 43. The front part of the speed reducer 9 is positioned above the pilot shaft 42. The speed reducer 9 is positioned above the upper mount 47.

[0035] As illustrated in FIGS. 3 and 5, the speed reducer 9 includes a drive sprocket 10 that inputs rotation of the output shaft 4 of the motor 3 to the speed reducer 9, a driven sprocket 11 that reduces rotation input to the speed reducer 9 and outputs the rotation from the speed reducer 9 to the drive shaft 8, and a silent chain 12 stretched between the drive sprocket 10 and the driven sprocket 11. A gear ratio between the drive sprocket 10 and the driven sprocket 11 (the number of teeth of the driven sprocket 11/the number of teeth of the drive sprocket 10) is greater than 1. The drive sprocket 10 is a specific example of a first rotation transmission element, and the driven sprocket 11 is a specific example of a second rotation transmission element.

[0036] The drive sprocket 10 is positioned above the motor 3 and disposed coaxially with the output shaft 4 of the motor 3. A lower end of a boss of the drive sprocket 10 is coupled (for example, by spline coupling) to an upper end of the output shaft 4 of the motor 3 so that the drive sprocket 10 rotates integrally with the output shaft 4.

[0037] The driven sprocket 11 is disposed in front of the drive sprocket 10. The driven sprocket 11 is disposed above the drive shaft 8 and coaxially with the drive shaft 8. A portion of the driven sprocket 11 is positioned above the swivel bracket 43. A lower end of a boss of the driven sprocket 11 is coupled (for example, by spline coupling) to an upper end of the drive shaft 8.

[0038] The speed reducer 9 is accommodated in the upper case 25. As can be seen from FIGS. 1 and 4, the upper case 25 is disposed above the motor 3 and attached to the motor case 7 using a fastening member such as a bolt. The upper case is a specific example of a case.

[0039] The drive shaft 8 extends in the vertical direction from the speed reducer 9 to the rotation transmission mechanism 14. The drive shaft 8 is disposed between the swivel bracket 43 and the motor 3 aligned in the front-rear direction. As described above, the upper end of the drive shaft 8 is coupled to the lower end of the boss of the driven sprocket 11 so that the drive shaft 8 rotates integrally with the driven sprocket 11.

[0040] As can be seen from FIGS. 1 and 4, in the outboard motor 1, the middle case 26 is provided below the motor 3 and the lower case 27 is provided below the middle case 26. The middle case 26 is attached to the motor case 7 using a fastening member such as a bolt, and the lower case is attached to the middle case 26 using a fastening member such as a bolt. As illustrated in FIG. 3, an upper end portion of the drive shaft 8 is covered by the upper case 25. A portion below the upper end portion in an upper part of the drive shaft 8 is positioned in front of the motor 3 and passes outside the motor case 7. A vertical middle portion of the drive shaft 8 passes inside the middle case 26. A lower portion of the drive shaft 8 passes inside the lower case 27.

[0041] The rotation transmission mechanism 14 is accommodated in the lower case 27. The rotation transmission mechanism 14 includes a transmission gear 15, a forward gear 16, a reverse gear 17, a dog clutch 18, and a shift plunger 19. The transmission gear 15, the forward gear 16, and the reverse gear 17 are all bevel gears. A rotation axis of the transmission gear 15 extends in the vertical direction. The transmission gear 15 is coupled to a lower end of the drive shaft 8 and rotates integrally with the drive shaft 8. Rotation axes of the forward gear 16 and the reverse gear 17 extend in the front-rear direction. The forward gear 16 is disposed in front of the transmission gear 15, and the reverse gear 17 is disposed behind the transmission gear 15. The forward gear 16 and the reverse gear 17 are respectively meshed with the transmission gear 15, and upon receiving rotation of the transmission gear 15, the forward gear 16 and the reverse gear 17 rotate in opposite directions to each other. A through hole is formed in each of a center of the forward gear 16 and a center of the reverse gear 17, and a front part of the propeller shaft 13 is inserted into the through holes. The forward gear 16 and the reverse gear 17 are not fixed to the propeller shaft 13 and are rotatable relative to the propeller shaft 13. The dog clutch 18 is disposed between the forward gear 16 and the reverse gear 17. The dog clutch 18 is attached to the front part of the propeller shaft 13 to not be rotatable relative to the propeller shaft 13 but to be movable in the front-rear direction relative to the propeller shaft 13. The shift plunger 19 is attached inside a front end of the propeller shaft 13 to be movable in the front-rear direction relative to the propeller shaft 13. A rear end of the shift plunger 19 is connected to the dog clutch 18 and a front end of the shift plunger 19 is positioned near a lower end of a shift rod 33, so that pivoting of the shift rod 33 is transmitted to the shift plunger 19 via a cam mechanism. When the shift rod 33 pivots due to driving of a shift actuator 32, pivoting of the shift rod 33 is transmitted to the shift plunger 19 via the cam mechanism, causing the shift plunger 19 to move forward or rearward, and in response, the dog clutch 18 moves forward or rearward. When the dog clutch 18 moves forward, the dog clutch 18 and the forward gear 16 engage with each other, thereby transmitting rotation of the forward gear 16 to the propeller shaft 13. Meanwhile, when the dog clutch 18 moves rearward, the dog clutch 18 and the reverse gear 17 engage with each other, thereby transmitting rotation of the reverse gear 17 to the propeller shaft 13.

[0042] The propeller shaft 13 extends in the front-rear direction. The front part of the propeller shaft 13 is positioned in the lower case 27 and extends into the rotation transmission mechanism 14. A rear part of the propeller shaft 13 is positioned outside the lower case 27. The propeller 20 is fixed to the rear part of the propeller shaft 13 and rotates integrally with the propeller shaft 13.

[0043] The shift device 31 includes the shift actuator 32 and the shift rod 33. The shift actuator 32 is an actuator that controls movement of the dog clutch 18, and is, for example, a small motor. The shift actuator 32 is provided in a right front portion in an upper part of the upper case 25. The shift rod 33 is a rod that transmits power from the shift actuator 32 to the shift plunger 19. The shift rod 33 extends in the vertical direction from the shift actuator 32 toward the front end of the shift plunger 19. An upper part of the shift rod 33 penetrates into the pilot shaft 42 formed in a cylindrical shape, and a lower part of the shift rod 33 penetrates into the lower case 27. An upper end of the shift rod 33 is connected to the shift actuator 32, and a lower end of the shift rod 33 is positioned near the front end of the shift plunger 19. The shift rod 33 pivots by driving of the shift actuator 32. Rotational motion of the shift rod 33 is converted into linear motion of the shift plunger 19 in the front-rear direction by a cam mechanism provided between the lower end of the shift rod 33 and the front end of the shift plunger 19. As described above, the dog clutch 18 moves by movement of the shift plunger 19.

[0044] The inverter 35 includes an inverter body 36 provided with electric and electronic circuits that control driving of the motor 3, and an inverter case 37 that accommodates the inverter body 36. The inverter 35 is disposed above the speed reducer 9 and attached to the upper case 25 using a fastening member such as a bolt.

[0045] By control of the inverter 35, the motor 3 is driven and the output shaft 4 of the motor 3 is rotated. Along with rotation of the output shaft 4 of the motor 3, the drive sprocket 10 of the speed reducer 9 rotates, and rotation of the drive sprocket 10 is transmitted to the driven sprocket 11 via the silent chain 12 so that the driven sprocket 11 is rotated. Here, rotation speed of the output shaft 4 of the motor 3 is reduced. Rotation of the driven sprocket 11 is transmitted to the forward gear 16 and the reverse gear 17 via the drive shaft 8 and the transmission gear 15 in this order. When the dog clutch 18 is moved forward by control of the shift actuator 32, rotation of the forward gear 16 is transmitted to the propeller shaft 13 so that the propeller shaft 13 and the propeller 20 are rotated forward. Forward rotation of the propeller 20 generates thrust that moves the boat forward. Meanwhile, when the dog clutch 18 is moved rearward by control of the shift actuator 32, rotation of the reverse gear 17 is transmitted to the propeller shaft 13 so that the propeller shaft 13 and the propeller 20 are rotated reversely. Reverse rotation of the propeller 20 generates thrust that moves the boat rearward.

Details of Each Part of Mounting Mechanism

[0046] In the mounting mechanism 40, the pair of left and right clamp brackets 41 and the swivel bracket 43 are disposed in front of the upper part of the outboard motor body 2. Although not illustrated in detail, the swivel bracket 43 is disposed between the pair of clamp brackets 41. The swivel bracket 43 is coupled to each clamp bracket 41 via a tilt shaft 44.

[0047] The pilot shaft 42 extends in the vertical direction and is supported by the swivel bracket 43 to be pivotable. An upper mount fixing member 46 is coupled to the upper end of the pilot shaft 42, and front parts of the pair of left and right upper mounts 47 are fixed to the upper mount fixing member 46. Rear parts of the pair of upper mounts 47 are inserted into the upper case 25 and attached to the upper case 25 in the upper case 25. A lower mount fixing member 48 is coupled to the lower end of the pilot shaft 42, and front parts of the pair of left and right lower mounts 49 are fixed to the lower mount fixing member 48. Rear parts of the pair of lower mounts 49 are attached to the middle case 26.

[0048] As can be seen from FIGS. 3 and 6, the upper end portion of the drive shaft 8 passes between the pair of upper mounts 47. The vertical middle portion of the drive shaft 8 passes between the pair of lower mounts 49.

[0049] The clamp brackets 41 are fixed to the transom 101 of the boat, thereby fixing the outboard motor body 2 to the boat. However, the outboard motor body 2 can pivot in the left-right direction relative to the boat about the pilot shaft 42 serving as a rotation axis, thereby allowing a direction of the propeller 20 to be changed in the left-right direction.

[0050] The swivel bracket 43 can pivot in the vertical direction relative to each clamp bracket 41 with the tilt shaft 44 serving as a pivot axis. Accordingly, the outboard motor body 2 can pivot (tilt up, tilt down) in the vertical direction relative to the boat. A tilt actuator 45 is provided between the pair of clamp brackets 41. The tilt actuator 45 is, for example, a hydraulic cylinder or an electric cylinder. The outboard motor body 2 can be tilted up and tilted down by power from the tilt actuator 45.

[0051] As described above, in the outboard motor 1 of the example of the present invention, the speed reducer 9 is disposed so that the front part of the speed reducer 9 is positioned above the swivel bracket 43 and the rear part of the speed reducer 9 is positioned above the motor 3, and when the outboard motor 1 is viewed from above, the speed reducer 9 is disposed so that the front part thereof overlaps with the swivel bracket 43. As such, by disposing the speed reducer 9 so that the front part thereof overlaps with the swivel bracket 43, an arrangement of the speed reducer 9 can be shifted forward to be brought closer to the boat on which the outboard motor 1 is mounted, compared to when the entire speed reducer 9 is disposed behind the swivel bracket 43, whereby a distance between the speed reducer 9 and the transom 101 of the boat in the front-rear direction can be reduced.

[0052] The drive sprocket 10 of the speed reducer 9 is coupled to the output shaft 4 of the motor 3. Therefore, the position of the motor 3 needs to be determined considering the position of the speed reducer 9, and in the outboard motor 1 of the example, the position of the speed reducer 9 can be shifted forward to be brought closer to the boat, whereby the position of the motor 3 can be shifted forward to be brought closer to the boat. Therefore, the distance between the motor 3 and the transom 101 of the boat in the front-rear direction can be reduced.

[0053] As such, with the outboard motor 1 of the example, the motor 3 and the speed reducer 9 that are heavy objects can be brought closer to the boat, whereby the center of gravity of the outboard motor 1 can be brought closer to the boat. By bringing the center of gravity of the outboard motor 1 closer to the boat, a force necessary for tilting up the outboard motor body 2 can be reduced. Therefore, it is possible to use an actuator having a lower output as the tilt actuator 45 for tilting up and tilting down the outboard motor body 2, whereby manufacturing costs of the outboard motor 1 can be reduced.

[0054] In the outboard motor 1 of the example, the speed reducer 9 is disposed so that, when the outboard motor 1 is viewed from above, the front part of the speed reducer 9 overlaps with the swivel bracket 43, and by disposing the speed reducer 9 so that the front part thereof overlaps with the swivel bracket 43 as such, the position of the motor 3 can be shifted forward to be brought closer to the swivel bracket 43. Therefore, according to the outboard motor 1 of the example, a dimension of the outboard motor 1 in the front-rear direction can be reduced.

[0055] In the speed reducer 9 of the outboard motor 1 of the example, the drive sprocket 10 is disposed above the motor 3 and coaxially with the output shaft 4 of the motor 3, the driven sprocket 11 is disposed above the drive shaft 8 and coaxially with the drive shaft 8, and a portion of the driven sprocket 11 is positioned above the swivel bracket 43. By such configuration, the motor 3, the drive shaft 8, and the speed reducer 9 can be brought closer to the boat, whereby the center of gravity of the outboard motor 1 can be brought closer to the boat.

[0056] In the outboard motor 1 of the example, the speed reducer 9 includes the drive sprocket 10, the driven sprocket 11, and the silent chain 12 stretched across the drive sprocket 10 and the driven sprocket 11. When the speed reducer is configured of a plurality of gears meshing with each other, noise generated from the speed reducer will become large and it will not be easy to reduce the noise unless shape, precision, surface properties, and the like of each gear are properly managed. In contrast, when the speed reducer has a configuration in which a silent chain is stretched between a plurality of sprockets, the noise generated from the speed reducer can be easily reduced. Therefore, according to the speed reducer 9 of the outboard motor 1 of the example, the noise generated from the speed reducer 9 can be easily reduced.

[0057] In the example, the speed reducer 9 is configured so that the silent chain 12 is stretched between the drive sprocket 10 and the driven sprocket 11, and by changing a length of the silent chain 12, a distance between the drive sprocket 10 and the driven sprocket 11 can be easily changed without changing a gear ratio. Accordingly, it is possible to facilitate design and manufacture of the outboard motor 1. To describe such configuration by way of example, in the outboard motor 1, as illustrated in FIG. 3, the output shaft 4 of the motor 3 and the drive sprocket 10 of the speed reducer 9 are disposed coaxially with each other. The drive shaft 8, the driven sprocket 11 of the speed reducer 9, and the transmission gear 15 of the rotation transmission mechanism 14 are disposed coaxially with each other. Therefore, when designing the outboard motor 1, a distance between an axis of the drive sprocket 10 and an axis of the driven sprocket 11 in the speed reducer 9 needs to match a distance between an axis of the output shaft 4 of the motor 3 and an axis of the transmission gear 15 of the rotation transmission mechanism 14. According to the speed reducer 9, the distance between the axis of the drive sprocket 10 and the axis of the driven sprocket 11 can be easily changed by changing the length of the silent chain 12 without changing the gear ratio. Therefore, the distance between the axis of the drive sprocket 10 and the axis of the driven sprocket 11 can be easily changed to match the distance between the axis of the output shaft 4 of the motor 3 and the axis of the transmission gear 15 of the rotation transmission mechanism 14. In contrast, when the speed reducer has a configuration in which two gears mesh together, it is difficult to change the distance between an axis of one gear and an axis of the other gear without changing a gear ratio, and it may be difficult to match a distance between the axes of the two gears in the speed reducer with the distance between the axis of the output shaft 4 of the motor 3 and the axis of the transmission gear 15 of the rotation transmission mechanism 14. As such, in the outboard motor 1 of the example including the speed reducer 9 provided with the drive sprocket 10, the driven sprocket 11, and the silent chain 12, design and manufacture of the outboard motor can be simplified compared to other outboard motors equipped with a speed reducer having a configuration in which two gears mesh together.

[0058] In the outboard motor 1 of the example, the inverter 35 is disposed above the speed reducer 9. As described above, in the outboard motor 1 of the example, the speed reducer 9 can be shifted forward to be brought closer to the boat. Therefore, by disposing the inverter 35 above the speed reducer 9, the inverter 35 can be shifted forward together with the speed reducer 9 to be brought closer to the boat. Therefore, even when the inverter 35 is provided in the outboard motor 1, the center of gravity of the outboard motor 1 can be brought closer to the boat.

[0059] In the outboard motor 1 of the example, the speed reducer 9 is positioned above the upper mount 47. By positioning the speed reducer 9 above the upper mount 47 disposed at a position close to the boat, the speed reducer 9 and the motor 3 can be brought closer to the boat, whereby the center of gravity of the outboard motor 1 can be brought closer to the boat.

[0060] In the outboard motor 1 of the example, the motor 3 is disposed below the upper mount 47, and the speed reducer 9 is disposed above the upper mount 47. According to such configuration, the motor 3 and the speed reducer 9 that are vibration generating sources can be brought closer to the upper mount 47, whereby vibration of the outboard motor 1 caused by vibrations generated from both sources can be effectively prevented. That is, when the motor 3 and the speed reducer 9 are operating, the vibrations generated by the motor 3 and the speed reducer 9 respectively cause the outboard motor 1 to vibrate and swing about the upper mount 47. Therefore, by placing the motor 3 and the speed reducer 9 close to the upper mount 47, an amplitude of vibration of the outboard motor 1 caused by vibrations generated by the motor 3 and the speed reducer 9 can be reduced.

[0061] In the outboard motor 1 of the example, the drive shaft 8 passes between the pair of left and right upper mounts 47. Accordingly, each upper mount 47 can function as a partition that prevents external objects from colliding with the drive shaft 8, and the drive shaft 8 can be protected by each upper mount 47.

[0062] In the outboard motor 1 of the example, the shift actuator 32 is attached to the upper case 25 that accommodates the speed reducer 9. Accordingly, the shift actuator 32 can be attached to the outboard motor 1 without providing a separate bracket.

[0063] In the above example, the silent chain 12 is used as the chain of the speed reducer 9, but other types of chains such as a roller chain may be used as the chain of the speed reducer 9. The speed reducer 9 may have a configuration including a plurality of pulleys and a belt stretched between the pulleys. The speed reducer 9 may have a configuration including a plurality of gears meshing with each other.

[0064] The present invention can be modified as appropriate without departing from the spirit or the concept of the invention as can be read from the claims and the entire specification, and outboard motors incorporating such modifications are also included in the technical concept of the present invention.