outboard motor

Abstract

To facilitate work to attach a drive gear to a cover member of a lower case via a bearing or work to replace a shim.SOLUTION: An outboard engine 1 comprises a reverse driving gear 13 and a reverse driving gear unit 12, where the reverse driving gear unit has a bearing 25 an inner ring 26 of which is attached in a boss 14 of the reverse driving gear 13, a washer 28 and a circlip 29 to fasten the inner ring 26 of the bearing 25 to the boss 14, and a mounting member 20 provided between the reverse driving gear 13 and the outer ring 27 of the bearing 25. A unit mounting hole 83 is formed on an outer circumference side of a drive shaft inserting hole 82 on the lower surface of a lid member 81 of a lower case 74. The boss 14 of the reverse driving gear 13 and the bearing 25 are inserted into the unit mounting hole 83 via a shim 31, and each fixed part 23 of the mounting member 20 is fixed on the undersurface of the lid member 81, so that the reverse driving gear unit 12 is attached to the undersurface of the lid member 81.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an outboard motor equipped with a drive shaft that rotates upon receiving power from a power source, and a rotation transmission mechanism that transmits the rotation of the drive shaft to a propeller shaft. [Background technology]

[0002] Many outboard motors include a power source, a propeller, a propeller shaft, a drive shaft, and a rotation transmission mechanism. The power source is located at the top of the outboard motor, which is positioned above the waterline. The propeller is attached to the rear end of the propeller shaft, and the propeller and propeller shaft are located at the bottom of the outboard motor, which is positioned below the waterline. The drive shaft extends vertically from the power source toward the propeller shaft to transmit power between the power source and the propeller shaft, which are spaced apart vertically. The drive shaft receives power from the power source and rotates, and the rotation is transmitted to the propeller shaft by the rotation transmission mechanism, which rotates the propeller shaft. The rotation transmission mechanism has multiple gears and a clutch and is configured to change the rotation direction of the propeller shaft based on clutch control. The power source is covered by a cowl, the drive shaft is housed in an upper case, and the front end of the propeller shaft and the rotation transmission mechanism are housed in a lower case.

[0003] In an outboard motor having such a configuration, a drive gear is splined to the lower end of the drive shaft. The drive gear is one of the gears that make up the rotation transmission mechanism and functions to input the rotation of the drive shaft to the rotation transmission mechanism.

[0004] Among outboard motors having the above-described configuration, there are some that use a bevel gear as a drive gear, and this drive gear is attached via a bearing to a lower case cover member provided on the upper part of the lower case.

[0005] The following Patent Document 1 describes a conventional outboard motor having a bevel gear drive gear attached to a cover member of a lower case via a bearing. Paragraph 0038 of the document describes a configuration in which an upper gear (41) of an outboard motor (1) is rotatably supported by a bearing (412) on a cover member (71) of a lower unit housing (103). The same paragraph also describes a configuration in which the upper gear (41) is engaged with the lower end of an upper drive shaft (171) so as to rotate integrally with the upper drive shaft (171). The same paragraph also describes that a bevel gear is used for the upper gear (41). The parenthesized reference numerals are those used in Patent Document 1. In the description of paragraph 0038 of Patent Document 1, the upper gear (41) corresponds to the drive gear, and the lower unit housing (103) corresponds to the lower case.

[0006] Figure 10 shows an example of a conventional outboard motor in which a drive gear, which is a bevel gear, is attached to a cover member of a lower case via a bearing. Note that the example shown in Figure 10 was created based on an existing and well-known outboard motor in which a drive gear, which is a bevel gear, is attached to a cover member of a lower case via a bearing, and the details of the configuration and reference numerals in the figure do not match those described in Patent Document 1.

[0007] In FIG. 10 , a drive gear 131 is attached to a cover member 121 of the lower case via a bearing 141. More specifically, a drive shaft insertion hole 122 for inserting a drive shaft 101 is formed in the cover member 121, and a bearing mounting hole 123 is formed on the outer periphery of the drive shaft insertion hole 122. The bearing mounting hole 123 opens upward, and a bearing 141 is inserted into the bearing mounting hole 123 from above the cover member 121. The outer ring of the bearing 141 is fixed in the bearing mounting hole 123 by a bearing fixing member 151. That is, the bearing fixing member 151 is formed in a cylindrical shape and has a threaded outer periphery at its lower end. The inner periphery of the upper part of the bearing mounting hole 123 is also threaded. The outer ring of the bearing 141 is fixed in the bearing mounting hole 123 by fitting the bearing fixing member 151 into the bearing mounting hole 123 from above the cover member 121 and tightening it.

[0008] The drive gear 131 is a bevel gear having a boss 132, and a thread is formed on the outer peripheral surface of the upper end of the boss 132. The drive gear 131 is fixed to the inner ring of the bearing 141 by inserting the boss 132 into the inner ring of the bearing 141 from below the cover member 121 and then attaching and tightening a nut 152 to the upper end of the boss 132 from above the cover member 121. A shim 154 is provided between the drive gear 131 and the inner ring of the bearing 141. The shim 154 is an annular member used to adjust the meshing (tooth contact, backlash, etc.) between the drive gear 131 and the driven gear 161 that meshes with the drive gear 131. The shim 154 is attached between the drive gear 131 and the inner ring of the bearing 141 when the boss 132 of the drive gear 131 is inserted into the inner ring of the bearing 141. The lower end of the drive shaft 101 is inserted into a shaft hole 133 of the drive gear 131, and the drive gear 131 is spline-connected to the lower end of the drive shaft 101. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-94116 Summary of the Invention [Problem to be solved by the invention]

[0010] In the configuration of the conventional outboard motor shown in Figure 10, the outer ring of the bearing 141 is fixed in the bearing mounting hole 123 of the cover member 121 by fitting a bearing fixing member 151 into the bearing mounting hole 123 from above the cover member 121. The drive gear 131 is fixed to the inner ring of the bearing 141 by inserting a boss 132 into the inside of the inner ring of the bearing 141 from below the cover member 121 and fitting a nut 152 onto the upper end of the boss 132 from above the cover member 121. Therefore, when attaching the drive gear 131 to the lid member 121 via the bearing 141, the outer ring of the bearing 141 must be fixed in the bearing mounting hole 123 of the lid member 121 from above the lid member 121, the boss 132 of the drive gear 131 must be inserted into the inner ring of the bearing 141 from below the lid member 121, and the boss 132 of the drive gear 131 inserted into the inner ring of the bearing 141 must be fixed to the inner ring of the bearing 141 from above the lid member 121. Thus, in the configuration of conventional outboard motors, attaching the drive gear 131 to the lid member 121 via the bearing 141 requires two operations: one from above the lid member 121 and one from below the lid member 121. As a result, the operation of attaching the drive gear 131 to the lid member 121 via the bearing 141 may become complicated or difficult.

[0011] Furthermore, the shim 154 may be replaced with another shim of a different thickness to adjust the meshing between the drive gear 131 and the driven gear 161. In conventional outboard motor configurations, replacing this shim requires two operations: one from above the cover member 121 and one from below the cover member 121 to remove the drive gear 131 from the inner ring of the bearing 141. Furthermore, after replacing the shim, the drive gear 131 must be attached to the inner ring of the bearing 141, one from below the cover member 121 and one from above the cover member 121. As a result, the shim replacement process may become complicated or difficult.

[0012] In order to solve the above problems, the present invention 1stThe outboard motor comprises a lower case provided at the bottom of the outboard motor and having an open top; a cover member attached to the lower case so as to cover at least a portion of the top of the lower case and having a drive shaft insertion hole; a drive shaft extending vertically from a power source provided at the top of the outboard motor toward the lower case, with its lower end inserted into the drive shaft insertion hole and rotated by power from the power source; a propeller shaft extending longitudinally, with its front end rotatably supported within the lower case and with a propeller attached to its rear end; and a rotation transmission mechanism provided within the lower case, having a drive gear unit, a driven gear, and a shim, for transmitting rotation of the drive shaft to the propeller shaft, the drive gear unit being a bevel gear having a boss and being connected to the drive shaft. the drive gear unit has a drive gear coupled to the lower end side of the shaft, a bearing with an inner ring attached to the boss, a fastening member for fastening the inner ring of the bearing to the boss, and an annular plate-shaped mounting member provided between the drive gear and the outer ring of the bearing, the driven gear is a gear that meshes with the drive gear, the shim is an annular member for determining the vertical position of the drive gear relative to the driven gear, thereby setting the meshing between the drive gear and the driven gear, a mounting hole is provided on the underside of the cover member on the outer periphery side of the drive shaft insertion hole, and the drive gear unit is attached to the underside of the cover member by inserting the boss and the bearing into the mounting hole via the shim and fixing the outer periphery side portion of the mounting member to the underside of the cover member The outer peripheral portion of the mounting member is screwed to the outer peripheral portion of the mounting hole on the underside of the lid member from below. It is characterized by: In order to solve the above-mentioned problems, a second outboard motor of the present invention comprises a lower case that is mounted on the lower part of the outboard motor and has an open top; a cover member that is attached to the lower case so as to cover at least a portion of the top of the lower case and has a drive shaft insertion hole; a drive shaft that extends vertically from a power source mounted on the top of the outboard motor toward the lower case, with its lower end inserted into the drive shaft insertion hole and rotated by power from the power source; a propeller shaft that extends longitudinally, has its front end rotatably supported within the lower case, and has a propeller attached to its rear end; and a rotation transmission mechanism that is mounted within the lower case and has a drive gear unit, a driven gear, and a shim, and transmits rotation of the drive shaft to the propeller shaft, wherein the drive gear unit is a bevel gear that has a boss and is coupled to the lower end of the drive shaft, and an inner ring attached to the boss. the drive gear unit has a bearing attached to the boss, a fastening member that fastens the inner ring of the bearing to the boss, and a mounting member formed in the shape of an annular plate and provided between the drive gear and the outer ring of the bearing, the driven gear is a gear that meshes with the drive gear, the shim is an annular member that determines the vertical position of the drive gear relative to the driven gear, thereby setting the meshing between the drive gear and the driven gear, a mounting hole is provided on the underside of the cover member on the outer periphery of the drive shaft insertion hole, the drive gear unit is attached to the underside of the cover member by inserting the boss and the bearing into the mounting hole via the shim and fixing the outer periphery of the mounting member to the underside of the cover member, and the mounting member is formed so that the inner periphery of the mounting member can be displaced in the vertical direction relative to the outer periphery of the mounting member by elastic deformation. In order to solve the above-mentioned problems, a third outboard motor of the present invention comprises a lower case provided at the bottom of the outboard motor and having an open top; a cover member attached to the lower case so as to cover at least a portion of the top of the lower case and having a drive shaft insertion hole; a drive shaft extending vertically from a power source provided at the top of the outboard motor toward the lower case, with its lower end inserted into the drive shaft insertion hole and rotated by power from the power source; a propeller shaft extending longitudinally, with its front end rotatably supported within the lower case and having a propeller attached to its rear end; and a rotation transmission mechanism provided within the lower case, having a drive gear unit, a driven gear, and a shim, for transmitting rotation of the drive shaft to the propeller shaft, wherein the drive gear unit comprises a drive gear which is a bevel gear having a boss and is coupled to the lower end of the drive shaft, a bearing whose inner ring is attached to the boss, and a drive shaft which is coupled to the propeller shaft. the drive gear unit has a fastening member that fastens the inner ring of a ring to the boss, and an attachment member formed in the shape of an annular plate and provided between the drive gear and the outer ring of the bearing, the driven gear is a gear that meshes with the drive gear, the shim is an annular member that sets the meshing between the drive gear and the driven gear by determining the vertical position of the drive gear relative to the driven gear, a attachment hole is provided on the underside of the cover member on the outer side of the drive shaft insertion hole, the drive gear unit is attached to the underside of the cover member by inserting the boss and the bearing into the attachment hole via the shim and fixing the outer peripheral portion of the attachment member to the underside of the cover member, the attachment member has an annular portion having an inner diameter larger than the outer diameter of the outer ring of the bearing, and a plurality of protrusions protruding inward from the annular portion, the upper surface of the protruding end portion of each protrusion contacts the underside of the outer ring of the bearing. [Means for solving the problem]

[0013] In order to achieve the above object, an outboard motor of the present invention comprises a lower case provided at a lower portion of the outboard motor and having an open top; a cover member attached to the lower case so as to cover at least a portion of the top of the lower case and having a drive shaft insertion hole; a drive shaft extending vertically from a power source provided at an upper portion of the outboard motor toward the lower case, with its lower end inserted into the drive shaft insertion hole and rotated by power from the power source; a propeller shaft extending longitudinally, with its front end rotatably supported within the lower case and having a propeller attached to its rear end; and a rotation transmission mechanism provided within the lower case, having a drive gear unit, a driven gear, and a shim, for transmitting rotation of the drive shaft to the propeller shaft, wherein the drive gear unit is a bevel gear having a boss and is connected to the drive shaft. the drive gear unit has a drive gear connected to the lower end of the drive shaft, a bearing whose inner ring is attached to the boss, a fastening member that fastens the inner ring of the bearing to the boss, and a mounting member formed in an annular plate and provided between the drive gear and the outer ring of the bearing, the driven gear is a gear that meshes with the drive gear, the shim is an annular member that sets the meshing between the drive gear and the driven gear by determining the vertical position of the drive gear relative to the driven gear, a mounting hole is provided on the underside of the cover member on the outer periphery of the drive shaft insertion hole, and the drive gear unit is attached to the underside of the cover member by inserting the boss and the bearing into the mounting hole via the shim and fixing the outer periphery of the mounting member to the underside of the cover member. [Effects of the Invention]

[0014] According to the present invention, it is possible to facilitate the work of attaching the drive gear to the cover member of the lower case via a bearing, or the work of replacing a shim for adjusting the meshing between the drive gear and the driven gear. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an explanatory diagram showing an outboard motor according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view of the lower part of the outboard motor according to the embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view showing a reverse gear mechanism and a clutch in FIG. 2. [Figure 4] FIG. 2 is an exploded perspective view showing a cover member, a reverse drive gear unit, a shim, and the like in the outboard motor according to the embodiment of the present invention. [Figure 5] FIG. 4 is an explanatory diagram showing a cover member to which a reverse drive gear unit is attached in the outboard motor according to the embodiment of the present invention. [Figure 6] FIG. 2 is an exploded perspective view of a reverse drive gear unit in the outboard motor according to the embodiment of the present invention. [Figure 7] 1A and 1B are cross-sectional views showing the cover member and the reverse drive gear unit, etc., of an outboard motor according to an embodiment of the present invention, where FIG. 1A shows the state in which the reverse drive gear unit, etc., is attached to the cover member, and FIG. 1B shows the state in which the reverse drive gear unit, etc., is separated from the cover member. [Figure 8] 10A and 10B are explanatory views showing a state in which each protrusion of the mounting member is elastically deformed when a thick shim is used in the outboard motor according to the embodiment of the present invention; [Figure 9] 10A and 10B are explanatory diagrams showing modified examples of the mounting member according to the present invention. [Figure 10] FIG. 10 is an explanatory diagram showing a state in which a drive gear is attached to a cover member via a bearing in a conventional outboard motor. DETAILED DESCRIPTION OF THE INVENTION

[0016] An outboard motor according to an embodiment of the present invention includes a lower case, a cover member, a drive shaft, a propeller shaft, and a rotation transmission mechanism. The lower case is located at the bottom of the outboard motor and has an open top. The cover member is attached to the lower case so as to cover at least a portion of the top of the lower case. The cover member has a drive shaft insertion hole. The drive shaft extends vertically from a power source located at the top of the outboard motor toward the lower case, with its lower end inserted into the drive shaft insertion hole. The drive shaft rotates when powered by the power source. The propeller shaft extends longitudinally, with its front end rotatably supported within the lower case and a propeller attached to its rear end. The rotation transmission mechanism is located within the lower case and transmits rotation of the drive shaft to the propeller shaft. The rotation transmission mechanism includes a drive gear unit, a driven gear, and a shim.

[0017] The drive gear unit has a drive gear, a bearing, a fastening member, and an attachment member. The drive gear is a bevel gear with a boss and is connected to the lower end of the drive shaft. The bearing is a member that supports the drive gear so that it can rotate on the cover member. The inner ring of the bearing is attached to the boss of the drive gear. The fastening member is a member that fastens the inner ring of the bearing to the boss of the drive gear. The attachment member is formed in the shape of an annular plate and is provided between the drive gear and the outer ring of the bearing.

[0018] The driven gear is a gear that meshes with the drive gear, and the shim is an annular member that determines the vertical position of the drive gear relative to the driven gear, thereby setting the meshing between the drive gear and the driven gear.

[0019] The cover has a mounting hole on the underside of the cover, which is located on the outer periphery of the drive shaft insertion hole. The drive gear unit is attached to the underside of the cover by inserting the boss and bearing into the mounting hole via a shim and fastening the outer periphery of the mounting member to the underside of the cover.

[0020] According to this embodiment, the drive gear unit and the shim can be attached to the cover member by inserting the shim and the drive gear unit (the boss and bearing of the drive gear) into the mounting hole of the cover member from below and fixing the outer peripheral portion of the mounting member to the underside of the cover member from below. This allows the worker to attach the drive gear to the cover member via the bearing only by working from below the cover member. This facilitates the work of attaching the drive gear to the cover member via the bearing. Furthermore, the worker can remove the drive gear unit and shim from the cover member, replace the shim, and attach the replaced shim and drive gear unit to the cover member only by working from below the cover member. This facilitates the work of replacing the shim. [Example]

[0021] An embodiment of an outboard motor of the present invention will be described. In the embodiment, directions such as up (Ud), down (Dd), front (Fd), rear (Bd), left (Ld), and right (Rd) are indicated by arrows drawn at the bottom right of Figures 1 to 8.

[0022] (Outboard motor) Figure 1 shows an outboard motor 1 according to an embodiment of the present invention. As shown in Figure 1, the outboard motor 1 is a contra-rotating propeller outboard motor. The outboard motor 1 includes an engine 2 as a power source, a drive shaft 3 that receives power output from the engine 2 and rotates, a front propeller 4, an outer propeller shaft 5 to which the front propeller 4 is attached, a rear propeller 6, an inner propeller shaft 7 to which the rear propeller 6 is attached, and a rotation transmission mechanism 8 that transmits the rotation of the drive shaft 3 to the outer propeller shaft 5 and the inner propeller shaft 7.

[0023] The engine 2 is disposed at the top of the outboard motor 1. The outer propeller shaft 5 and the inner propeller shaft 7 are disposed at the bottom of the outboard motor 1. The drive shaft 3 extends vertically between the engine 2 and the propeller shafts 5 and 7.

[0024] The rotation transmission mechanism 8 has a reverse gear mechanism 11, a clutch 51, a transmission shaft 57, and a main gear mechanism 61. The reverse gear mechanism 11 is a mechanism that uses the rotation of the drive shaft 3 to generate rotation in the opposite direction to the forward rotation of the drive shaft 3. The clutch 51 is a mechanism that switches between transmitting the forward rotation of the drive shaft 3 to the transmission shaft 57 and transmitting the reverse rotation generated by the reverse gear mechanism 11 to the transmission shaft 57. The transmission shaft 57 is a shaft that transmits the forward rotation of the drive shaft 3 or the reverse rotation generated by the reverse gear mechanism 11 to the main gear mechanism 61. The main gear mechanism 61 is a mechanism that transmits the rotation of the transmission shaft 57 to each of the propeller shafts 5, 7.

[0025] The outboard motor 1 also includes a bottom cowling 71 that is mounted on the top of the outboard motor 1 and covers the lower part of the engine 2, a top cowling 72 that is mounted above the bottom cowling 71 and covers the upper part of the engine 2, an upper case 73 that is mounted in the vertical middle of the outboard motor 1 and houses the drive shaft 3, a lower case 74 that is mounted on the bottom of the outboard motor 1 and houses the front end portions of each propeller shaft 5, 7 and the rotation transmission mechanism 8, and a cover member 81 attached to the top of the lower case 74.

[0026] (Lower case, cover parts) FIG. 2 shows a cross section of components provided at the bottom of the outboard motor 1, taken along a plane extending in the longitudinal and vertical directions and including the axes of the drive shaft 3 and the propeller shafts 5, 7.

[0027] 2, lower case 74 is formed in the shape of a box with an open top. An upper gear chamber 75 that houses reverse gear mechanism 11 and clutch 51 is provided in the upper front part of lower case 74. A lower gear chamber 78 that houses main gear mechanism 61 is provided in the lower front part of lower case 74. A transmission shaft insertion hole 79 for arranging transmission shaft 57 is formed in lower case 74 between upper gear chamber 75 and lower gear chamber 78. A propeller shaft insertion hole 80 for arranging the front end portions of each propeller shaft 5, 7 is formed in the rear part of the lower part of lower case 74.

[0028] The cover member 81 is formed in a generally plate-like shape (see FIG. 4) and is attached to the upper part of the lower case 74 via fixing members such as bolts so as to cover at least a portion of the upper part of the lower case 74. The cover member 81 is formed with a drive shaft insertion hole 82 for inserting the drive shaft 3, and a unit mounting hole 83 (see FIG. 7) for mounting the reverse drive gear unit 12 described below. The drive shaft insertion hole 82 passes through the cover member 81 in the vertical direction and communicates with the interior of the upper gear chamber 75. The unit mounting hole 83 is located on the outer periphery of the drive shaft insertion hole 82 on the underside of the cover member 81 and opens into the upper gear chamber 75.

[0029] (reverse gear mechanism, clutch) Fig. 3 shows an enlarged view of the reverse gear mechanism 11 and clutch 51 in Fig. 2. The reverse gear mechanism 11 has a reverse drive gear 13, a bearing 25 for the reverse drive gear, a reverse driven gear 41, an intermediate shaft 43, two bearings 44 for the reverse driven gear, a reverse output gear 45, and a bearing 49 for the reverse output gear.

[0030] The reverse drive gear 13 is a bevel gear having a boss 14. The reverse drive gear 13 functions to input the rotation of the drive shaft 3 to the reverse gear mechanism 11 and to transmit the rotation of the drive shaft 3 to the transmission shaft 57 via the clutch 51. The reverse drive gear 13 is disposed at the top of the upper gear chamber 75 with its teeth facing downward and its boss 14 protruding upward. The reverse drive gear 13 is rotatably mounted in a unit mounting hole 83 of a cover member 81 via a bearing 25. The bearing 25 is a member that rotatably supports the reverse drive gear 13 on the cover member 81, and in this embodiment, a ball bearing is used as the bearing 25. The lower end of the drive shaft 3 is inserted into the shaft hole 15 of the reverse drive gear 13. The reverse drive gear 13 is spline-connected to the lower end of the drive shaft 3 and rotates integrally with the drive shaft 3. The reverse drive gear 13 is a specific example of a "drive gear."

[0031] The reverse driven gear 41 is a bevel gear and meshes with the reverse drive gear 13. The reverse driven gear 41 is disposed in the rear part of the upper gear chamber 75 with its teeth facing forward. The front end part of an intermediate shaft 43 extending in the front-to-rear direction is inserted into a shaft hole 42 of the reverse driven gear 41. The reverse driven gear 41 is spline-coupled to the front end part of the intermediate shaft 43 and rotates integrally with the intermediate shaft 43. The rear end part of the intermediate shaft 43 is rotatably mounted in an intermediate shaft mounting hole 76 formed in the rear wall of the upper gear chamber 75 via two bearings 44. The reverse driven gear 41 is a specific example of a "driven gear."

[0032] The reverse output gear 45 is a bevel gear having a boss 46, and meshes with the reverse driven gear 41. The reverse output gear 45 is disposed in the lower part of the upper gear chamber 75 with its teeth facing upward and its boss 46 protruding downward. The reverse output gear 45 is disposed coaxially with the reverse drive gear 13 and faces the reverse drive gear 13 in the up-down direction. The reverse output gear 45 is rotatably mounted via a bearing 49 in a gear mounting hole 77 formed in the lower wall of the upper gear chamber 75. A through hole 47 is formed in the center of the reverse output gear 45, through which a transmission shaft 57 passes. The transmission shaft 57 passes through the through hole 47, but does not contact the through hole 47.

[0033] In the reverse gear mechanism 11 having such a configuration, when the drive shaft 3 rotates in the forward direction and the reverse drive gear 13 rotates in the forward direction accordingly, this rotation is transmitted to the reverse output gear 45 via the reverse driven gear 41, and the reverse output gear 45 rotates in the opposite direction to the forward rotation of the drive shaft 3.

[0034] The clutch 51 is a dog clutch formed in a cylindrical shape with clutch pawls 52 formed on each of the upper and lower end surfaces. Grooves 53 are formed around the entire circumference of the clutch 51. The clutch 51 is disposed in the upper gear chamber 75 between the reverse drive gear 13 and the reverse output gear 45. Inside the upper gear chamber 75, the upper end portion of the transmission shaft 57 passes through the through-hole 47 of the reverse output gear 45 and enters between the reverse drive gear 13 and the reverse output gear 45. The clutch 51 is coupled to the upper end portion of the transmission shaft 57 so as to be immovable in the circumferential direction relative to the transmission shaft 57 but movable in the axial direction. As a result, the clutch 51 and the transmission shaft 57 rotate integrally, but the clutch 51 can move up and down relative to the transmission shaft 57.

[0035] Further, a clutch pawl 19 is formed on the lower surface of the reverse drive gear 13, and is engageable with a clutch pawl 52 formed on the upper end surface of the clutch 51. Further, a clutch pawl 48 is formed on the upper surface of the reverse output gear 45, and is engageable with a clutch pawl 52 formed on the lower end surface of the clutch 51.

[0036] Furthermore, in the lower case 74, in front of the upper gear chamber 75, a clutch control unit 54 for controlling the clutch 51 is provided. An actuator is provided inside the clutch control unit 54. Furthermore, a shift member 55 is provided between the clutch 51 and the clutch control unit 54. The front end side of the shift member 55 is connected to the actuator of the clutch control unit 54, and the rear end side of the shift member 55 is inserted into the groove 53 of the clutch 51 with a certain amount of play so that the clutch 51 is rotatable relative to the shift member 55.

[0037] The actuator of the clutch control unit 54 can move the shift member 55 upward or downward. As the shift member 55 moves, the clutch 51 moves upward or downward. When the clutch 51 moves upward, the clutch pawl 52 formed on the upper end surface of the clutch 51 engages with the clutch pawl 19 formed on the lower surface of the reverse drive gear 13. This transmits the forward rotation of the drive shaft 3 to the transmission shaft 57, causing the transmission shaft 57 to rotate in the forward direction. On the other hand, when the clutch 51 moves downward, the clutch pawl 52 formed on the lower end surface of the clutch 51 engages with the clutch pawl 48 formed on the upper surface of the reverse output gear 45. This transmits the reverse rotation generated by the reverse gear mechanism 11 to the transmission shaft 57, causing the transmission shaft 57 to rotate in the reverse direction.

[0038] As shown in FIG. 2, the transmission shaft 57 extends vertically within the lower case 74 between the upper gear chamber 75 and the lower gear chamber 78, and is rotatably supported within the transmission shaft insertion hole 79 via bearings 58, 59.

[0039] (main gear mechanism, propeller shaft) As shown in FIG. 2 , the main gear mechanism 61 has a main drive gear 62, a first main driven gear 63, and a second main driven gear 65. The main drive gear 62 is a bevel gear located in an upper portion of the lower gear chamber 78, is splined to the lower end of the transmission shaft 57, and rotates integrally with the transmission shaft 57. The first main driven gear 63 is a bevel gear located in a rear portion of the lower gear chamber 78, and is rotatably attached to the lower case 74 via a bearing 64. The first main driven gear 63 is splined to the front end of the outer propeller shaft 5, and rotates integrally with the outer propeller shaft 5. The second main driven gear 65 is a bevel gear located in a front portion of the lower gear chamber 78, and is rotatably attached to the lower case 74 via a bearing 66. Furthermore, the second main driven gear 65 is splined to the front end of the inner propeller shaft 7 and rotates integrally with the inner propeller shaft 7. The main drive gear 62 is meshed with the first main driven gear 63 and the second main driven gear 65. As a result, the rotation of the transmission shaft 57 is transmitted to the outer propeller shaft 5 via the main drive gear 62 and the first main driven gear 63, and at the same time, is transmitted to the inner propeller shaft 7 via the main drive gear 62 and the second main driven gear 65.

[0040] The outer propeller shaft 5 and the inner propeller shaft 7 each extend in the front-to-rear direction and are arranged coaxially with each other. The outer propeller shaft 5 is formed in a cylindrical shape, and the front end portion of the inner propeller shaft 7 is arranged within the outer propeller shaft 5. The front end portion of the outer propeller shaft 5 is supported in a propeller shaft insertion hole 80 of the lower case 74 so as to be rotatable relative to the lower case 74, and a front propeller 4 is attached to the rear end portion of the outer propeller shaft 5. The front end portion of the inner propeller shaft 7 is supported in the outer propeller shaft 5 so as to be rotatable relative to the outer propeller shaft 5, and a rear propeller 6 is attached to the rear end portion of the inner propeller shaft 7. The rotation of the transmission shaft 57 is transmitted to the outer propeller shaft 5 and the inner propeller shaft 7 via the main gear mechanism 61, causing the outer propeller shaft 5 and the inner propeller shaft 7 to rotate in opposite directions to each other.

[0041] The forward rotation of the drive shaft 3 is transmitted to the outer propeller shaft 5 and the inner propeller shaft 7 via the clutch 51, the transmission shaft 57, the main gear mechanism 61, etc., to generate a propulsive force that moves the boat to which the outboard motor 1 is attached forward. On the other hand, the reverse rotation generated by the reverse gear mechanism 11 is transmitted to the outer propeller shaft 5 and the inner propeller shaft 7 via the clutch 51, the transmission shaft 57, the main gear mechanism 61, etc., to generate a propulsive force that moves the boat to which the outboard motor 1 is attached backward.

[0042] (reverse drive gear unit) Fig. 4 shows the cover member 81, as well as the reverse drive gear unit 12 and shim 31 separated from the cover member 81. Fig. 5 shows the cover member 81 and the reverse drive gear unit 12 attached to the cover member 81 as viewed from below. Fig. 6 shows the reverse drive gear unit 12 in an exploded state. Fig. 7(A) shows a cross section of the cover member 81 and the reverse drive gear unit 12 taken along section line VII-VII in Fig. 5 as viewed from the left front side. Fig. 7(B) shows the reverse drive gear unit 12 and other components in Fig. 7(A) separated from the cover member 81.

[0043] In the outboard motor 1, the reverse drive gear 13, which constitutes part of the reverse gear mechanism 11, and the bearing 25 for the reverse drive gear are unitized (integrated) as a reverse drive gear unit 12, as shown in Fig. 4. As shown in Fig. 6, the reverse drive gear unit 12 has the reverse drive gear 13, a mounting member 20, a bearing 25, a washer 28, and a circlip 29. The reverse drive gear unit 12 is a specific example of a "drive gear unit." The washer 28 and the circlip 29 are also specific examples of a "fastening member."

[0044] In the reverse drive gear 13, a first step 16 is formed around the entire circumference at the bottom of the boss 14, and a second step 17 is formed around the entire circumference at the top of the boss 14. In addition, a recess 18 is formed around the entire circumference above the second step 17 at the top of the boss 14.

[0045] The mounting member 20 is a member for mounting the reverse drive gear unit 12 to the unit mounting hole 83 of the cover member 81, and is formed, for example, in the shape of an annular plate made of a metal material. The mounting member 20 includes an annular portion 21 and a plurality of protruding portions 22. The annular portion 21 is formed in an annular shape and has an inner diameter larger than the outer diameter of the outer ring 27 of the bearing 25. Each of the protruding portions 22 protrudes radially inward from the annular portion 21. The plurality of protruding portions 22 are arranged at equal intervals in the circumferential direction. As shown in FIG. 6 , the diameter of a circle C passing through the protruding end of each of the protruding portions 22 is larger than the outer diameter of the inner ring 26 of the bearing 25 and smaller than the outer diameter of the outer ring 27 of the bearing 25. The mounting member 20 is provided with a plurality of (e.g., two) fixing portions 23 on its outer periphery. Each fixing portion 23 protrudes radially outward from the annular portion 21. A bolt insertion hole 24 is formed in the protruding end portion of each fixing portion 23.

[0046] 7(B), a mounting member 20 is disposed on the outer periphery of the boss 14 of the reverse drive gear 13. An inner ring 26 of a bearing 25 is mounted above the mounting member 20 on the outer periphery of the boss 14. A washer 28 is disposed above the inner ring 26 of the bearing 25 on the outer periphery of the boss 14, and a circlip 29 is mounted above the washer 28.

[0047] The inner ring 26 of the bearing 25 is fastened to the boss 14 by a circlip 29 and a washer 28, and is supported by the boss 14. That is, the circlip 29 fits into a recess 18 formed in the upper part of the boss 14, and is fixed within the recess 18. The washer 28 is supported between the circlip 29 and the second step 17 of the boss 14. The inner ring 26 of the bearing 25 is supported between the washer 28 and the first step 16 of the boss 14.

[0048] Furthermore, the mounting member 20 is positioned between the reverse drive gear 13 and the outer ring 27 of the bearing 25. The diameter of a circle C (see FIG. 6) that passes through the protruding ends of each protrusion 22 is smaller than the outer diameter of the outer ring 27 of the bearing 25 and is also smaller than the outer diameter of the reverse drive gear 13. Therefore, when the inner ring 26 of the bearing 25 is fastened to the boss 14, the mounting member 20 will not slip out from between the reverse drive gear 13 and the outer ring 27 of the bearing 25.

[0049] As shown in FIG. 7(A), the reverse drive gear unit 12 is attached to the underside of the cover member 81 by inserting the boss 14 and bearing 25 of the reverse drive gear 13 into the unit mounting hole 83 of the cover member 81 via the shim 31 and fixing each fixing portion 23 of the mounting member 20 to the underside of the cover member 81. That is, as described above, the unit mounting hole 83 is formed on the underside of the cover member 81 on the outer circumferential side of the drive shaft insertion hole 82. As shown in FIG. 7(B), the unit mounting hole 83 is arranged coaxially with the drive shaft insertion hole 82. The unit mounting hole 83 is open downward and faces the upper gear chamber 75. The unit mounting hole 83 has an outer diameter approximately equal to the outer diameter of the outer ring 27 of the bearing 25 so that the bearing 25 fits snugly. The boss 14 and bearing 25 of the reverse drive gear 13 are inserted into the unit mounting hole 83 via the shim 31.

[0050] The shim 31 is an annular, plate-shaped member that determines the vertical position of the reverse drive gear 13 relative to the reverse driven gear 41, thereby setting the meshing (tooth contact, backlash, etc.) between the reverse drive gear 13 and the reverse driven gear 41. Several shims 31 with different thicknesses are provided, and by appropriately selecting and using one shim from among them, it is possible to adjust the meshing between the reverse drive gear 13 and the reverse driven gear 41. The inner diameter of the shim 31 is set to be approximately equal to the inner diameter of the outer ring 27 of the bearing 25, for example, and the outer diameter of the shim 31 is set to be equal to or smaller than the outer diameter of the outer ring 27 of the bearing 25. The shim 31 is disposed between the outer ring 27 of the bearing 25 and the upper surface (bottom surface) of the unit mounting hole 83.

[0051] 7(B), a plurality of bolt holes 84 are formed on the underside of the cover member 81 on the outer circumferential side of the unit mounting hole 83. The plurality of bolt holes 84 are arranged to correspond to the bolt insertion holes 24 formed in each of the plurality of fixing portions 23 of the mounting member 20. The reverse drive gear unit 12 is fixed (screwed) to the underside of the cover member 81 by passing bolts 32 from below through the bolt insertion holes 24 of each fixing portion 23 of the mounting member 20, and then inserting the bolts 32 from below into the bolt holes 84 and tightening them.

[0052] 7(A), when each fixing portion 23 of the mounting member 20 is fixed to the bolt hole 84 with the bolt 32, the upper surface of the protruding end side portion of each protruding portion 22 of the mounting member 20 comes into contact with the lower surface of the outer ring 27 of the bearing 25. As a result, the outer ring 27 of the bearing 25 is pressed into the unit mounting hole 83 by each protruding portion 22, and the reverse drive gear unit 12 is held on the lower surface of the cover member 81.

[0053] Furthermore, the mounting member 20 is formed so that, by elastic deformation, the inner peripheral portion of the mounting member 20, i.e., each protrusion 22, can be displaced up and down relative to the outer peripheral portion of the mounting member 20, i.e., the annular portion 21. Specifically, each protrusion 22 of the mounting member 20 has a long, narrow plate shape that protrudes inward from the annular portion 21, and can therefore be elastically deformed to bend up and down relative to the annular portion 21. Therefore, the protruding end portion of each protrusion 22 can be displaced up and down relative to the annular portion 21. This allows the reverse drive gear unit 12 to be fixed and held in the unit mounting hole 83 even when a thick shim 31 is used, as shown in FIG. 8 . That is, if a thick shim 31 is placed between the outer ring 27 of the bearing 25 and the upper surface of the unit mounting hole 83 to reduce backlash between the reverse drive gear 13 and the reverse driven gear 41, the lower part of the outer ring 27 of the bearing 25 may protrude downward from the unit mounting hole 83. In this manner, when the lower portion of the outer ring 27 of the bearing 25 projects downward from the unit mounting hole 83, each protrusion 22 of the mounting member 20 elastically deforms and bends downward, pressing the outer ring 27 of the bearing 25 into the unit mounting hole 83. In this manner, with the mounting member 20, by using the thick shim 31, the reverse drive gear unit 12 can be fixed and held in the unit mounting hole 83 even when the lower portion of the outer ring 27 of the bearing 25 projects downward from the unit mounting hole 83.

[0054] When attaching the reverse drive gear unit 12 to the cover member 81 during manufacturing or maintenance of the outboard motor 1, the worker first inserts the shim 31 and the reverse drive gear unit 12 into the unit mounting hole 83 from below the cover member 81. Next, the worker secures each fixing portion 23 of the mounting member 20 to the underside of the cover member 81 using the bolts 32 from below the cover member 81. When adjusting the meshing between the reverse drive gear 13 and the reverse driven gear 41, the worker first removes each bolt 32 from below the cover member 81 and removes the reverse drive gear unit 12 and the shim 31 from the unit mounting hole 83. Next, the worker inserts another shim having a different thickness from the removed shim 31 and the reverse drive gear unit 12 into the unit mounting hole 83 from below the cover member 81. Next, the worker fixes each fixing portion 23 of the mounting member 20 to the underside of the cover member 81 with the bolts 32 from below the cover member 81 .

[0055] As described above, the outboard motor 1 according to the embodiment of the present invention includes the reverse drive gear unit 12 having the reverse drive gear 13, the bearing 25 with its inner ring 26 mounted on the boss 14 of the reverse drive gear 13, the washer 28 and circlip 29 that fasten the inner ring 26 of the bearing 25 to the boss 14, and the mounting member 20 provided between the reverse drive gear 13 and the outer ring 27 of the bearing 25. A unit mounting hole 83 is formed on the underside of the cover member 81 of the lower case 74, outer peripherally of the drive shaft insertion hole 82. The reverse drive gear unit 12 is mounted to the underside of the cover member 81 by inserting the boss 14 and bearing 25 of the reverse drive gear 13 into the unit mounting hole 83 via shims 31 and fastening the fixing portions 23 of the mounting member 20 to the underside of the cover member 81. With this configuration, an operator can mount the reverse drive gear 13 to the cover member 81 via the bearing 25 simply by working from below the cover member 81. This facilitates the work of attaching the reverse drive gear 13 to the cover member 81 via the bearing 25. Furthermore, the above-described configuration allows the worker to replace the shim 31 only by working from below the cover member 81. This facilitates the work of replacing the shim 31.

[0056] Furthermore, in the outboard motor 1 of this embodiment, each fixing portion 23 of the mounting member 20 is fixed by a bolt 32 from below the cover member 81 to each bolt hole 84 formed on the outer periphery of the unit mounting hole 83 in the underside of the cover member 81. With this configuration, an operator can easily attach and detach the reverse drive gear unit 12 to and from the cover member 81 simply by attaching and detaching the bolts 32 from below the cover member 81.

[0057] In the outboard motor 1 of this embodiment, the mounting member 20 is configured so that its inner peripheral portion can be displaced up and down relative to its outer peripheral portion by elastic deformation. Specifically, the mounting member 20 has an annular portion 21 having an inner diameter larger than the outer diameter of the outer ring 27 of the bearing 25, and a plurality of protrusions 22 protruding inward from the annular portion 21, with each protrusion 22 being configured to be displaceable up and down relative to the annular portion 21. The inner peripheral portion of the mounting member 20, specifically the upper surface of the protruding end portion of each protrusion 22, contacts the lower surface of the outer ring 27 of the bearing 25, thereby holding the reverse drive gear unit 12 in the unit mounting hole 83. With this configuration, the reverse drive gear unit 12 can be held in the unit mounting hole 83 even if the lower part of the outer ring 27 of the bearing 25 protrudes downward from the unit mounting hole 83 by using a thick shim 31, as shown in FIG. 8 . Therefore, the range of thickness of the shim 31 used for meshing adjustment can be increased, and the width of gear meshing adjustment can be widened.

[0058] Furthermore, according to the outboard motor 1 of this embodiment, the reverse drive gear 13, bearing 25, and mounting member 20 are integrated into the reverse drive gear unit 12, which reduces the number of parts required when assembling the outboard motor 1 and also makes it easier to manage the parts of the outboard motor 1.

[0059] The shape of the mounting member of the present invention is not limited to that shown in FIG. 6 . For example, a mounting member 91 having the shape shown in FIG. 9(A) or a mounting member 95 having the shape shown in FIG. 9(B) may be used as the mounting member of the present invention. In FIGS. 9(A) and 9(B), the two-dot chain circle indicates the position of the unit mounting hole 83 when the reverse drive gear unit is mounted in the unit mounting hole 83. The mounting member 91 shown in FIG. 9(A) is formed in an annular, plate-like shape and has multiple notches 92 extending radially outward from the inner peripheral edge of the mounting member 91 to just before the outer peripheral edge. The multiple notches 92 allow the inner peripheral portion of the mounting member 91 to elastically deform so as to bend vertically. Therefore, the inner peripheral portion of the mounting member 91 can be displaced vertically relative to the outer peripheral portion of the mounting member 91. The lower surface of the outer ring 27 of the bearing 25 contacts the upper surface of the inner peripheral portion of the mounting member 91. Similar to the mounting member 20, the mounting member 91 also has multiple fixing portions 93. 9(B) is formed in an annular plate shape, with multiple arms 97 extending radially outward from an annular portion 96 on the inner periphery of the mounting member 95, and the tip of each arm 97 forms a fixing portion 98 that is fixed to the underside of the cover member 81. Due to elastic deformation of each arm 97, the annular portion 96 on the inner periphery of the mounting member 95 can be displaced in the vertical direction relative to each fixing portion 98. The lower surface of the outer ring 27 of the bearing 25 contacts the upper surface of the annular portion 96 on the inner periphery of the mounting member 95.

[0060] In the above embodiment, the inner ring 26 of the bearing 25 in the reverse drive gear unit 12 is fastened to the boss 14 of the reverse drive gear 13 using the washer 28 and the circlip 29, but the present invention is not limited to this. For example, the inner ring 26 of the bearing 25 may be fastened to the boss 14 by forming a thread on the outer circumferential surface of the upper end of the boss 14 of the reverse drive gear 13 and screwing a nut onto the upper end of the boss 14.

[0061] In addition, in the present invention, the power source of the outboard motor is not limited to an internal combustion engine but may be an electric motor. Furthermore, the outboard motor of the present invention is not limited to a contra-rotating propeller outboard motor. Furthermore, in the present invention, the drive gear is not limited to a reverse drive gear, and the driven gear is not limited to a reverse driven gear.

[0062] Furthermore, the present invention may be modified as appropriate within the scope of the claims and the spirit or concept of the invention as can be read from the entire specification, and outboard motors incorporating such modifications are also included within the technical concept of the present invention. [Explanation of symbols]

[0063] 1 outboard motor 3 drive shaft 4 Front propeller (propeller) 5 Outer propeller shaft (propeller shaft) 6 Rear propeller (propeller) 7 Inner propeller shaft (propeller shaft) 8 Rotation transmission mechanism 11 Reverse gear mechanism 12 Reverse drive gear unit (drive gear unit) 13 Reverse drive gear (drive gear) 14. Boss 20, 91, 95 Mounting parts 21 Circular section 22 Protrusion 23, 93, 98 Fixed part 25 bearings 26 Inner Circle 27 Outer ring 28 Washer (fastening part) 29 Circlip (fastening part) 31 Sim 32 volts 41 Reverse driven gear (driven gear) 74 Lower case 81 Cover member 82 Drive shaft insertion hole 83 Unit mounting hole

Claims

1. a lower case provided at the bottom of the outboard motor and having an open top; a cover member attached to the lower case so as to cover at least a portion of an upper portion of the lower case, the cover member having a drive shaft insertion hole; a drive shaft extending vertically from a power source provided on an upper portion of the outboard motor toward the lower case, the drive shaft having a lower end inserted into the drive shaft insertion hole and adapted to rotate by receiving power from the power source; a propeller shaft extending in the front-rear direction, with a front end side rotatably supported within the lower case and a rear end side to which a propeller is attached; a rotation transmission mechanism provided in the lower case, the rotation transmission mechanism having a drive gear unit, a driven gear, and a shim, and transmitting rotation of the drive shaft to the propeller shaft; The drive gear unit is a drive gear which is a bevel gear having a boss and is coupled to the lower end side of the drive shaft; a bearing having an inner ring attached to the boss; a fastening member for fastening the inner ring of the bearing to the boss; a mounting member formed in an annular plate shape and provided between the drive gear and the outer ring of the bearing, the driven gear is a gear that meshes with the drive gear, the shim is an annular member for determining the vertical position of the drive gear relative to the driven gear to set the meshing between the drive gear and the driven gear, an attachment hole is provided on the underside of the cover member on the outer circumferential side of the drive shaft insertion hole; the drive gear unit is attached to the underside of the cover member by inserting the boss and the bearing into the mounting hole via the shim and fixing an outer peripheral portion of the mounting member to the underside of the cover member; an outer peripheral portion of the mounting member being screwed from below the cover member to an outer peripheral portion of the mounting hole on the underside of the cover member;

2. A lower case provided at the bottom of the outboard motor and having an open top; a cover member attached to the lower case so as to cover at least a portion of an upper portion of the lower case, the cover member having a drive shaft insertion hole; a drive shaft extending vertically from a power source provided on an upper portion of the outboard motor toward the lower case, the drive shaft having a lower end inserted into the drive shaft insertion hole and adapted to rotate by receiving power from the power source; a propeller shaft extending in the front-rear direction, with a front end side rotatably supported within the lower case and a rear end side to which a propeller is attached; a rotation transmission mechanism provided in the lower case, the rotation transmission mechanism having a drive gear unit, a driven gear, and a shim, and transmitting rotation of the drive shaft to the propeller shaft; The drive gear unit is a drive gear which is a bevel gear having a boss and is coupled to the lower end side of the drive shaft; a bearing having an inner ring attached to the boss; a fastening member for fastening the inner ring of the bearing to the boss; a mounting member formed in an annular plate shape and provided between the drive gear and the outer ring of the bearing, the driven gear is a gear that meshes with the drive gear, the shim is an annular member for determining the vertical position of the drive gear relative to the driven gear to set the meshing between the drive gear and the driven gear, an attachment hole is provided on the underside of the cover member on the outer circumferential side of the drive shaft insertion hole; the drive gear unit is attached to the underside of the cover member by inserting the boss and the bearing into the mounting hole via the shim and fixing an outer peripheral portion of the mounting member to the underside of the cover member; The mounting member is formed so that an inner peripheral portion of the mounting member can be displaced vertically relative to an outer peripheral portion of the mounting member by elastic deformation.

3. A lower case provided at the bottom of the outboard motor and having an open top; a cover member attached to the lower case so as to cover at least a portion of an upper portion of the lower case, the cover member having a drive shaft insertion hole; a drive shaft extending vertically from a power source provided on an upper portion of the outboard motor toward the lower case, the drive shaft having a lower end inserted into the drive shaft insertion hole and adapted to rotate by receiving power from the power source; a propeller shaft extending in the front-rear direction, with a front end side rotatably supported within the lower case and a rear end side to which a propeller is attached; a rotation transmission mechanism provided in the lower case, the rotation transmission mechanism having a drive gear unit, a driven gear, and a shim, and transmitting rotation of the drive shaft to the propeller shaft; The drive gear unit is a drive gear which is a bevel gear having a boss and is coupled to the lower end side of the drive shaft; a bearing having an inner ring attached to the boss; a fastening member for fastening the inner ring of the bearing to the boss; a mounting member formed in an annular plate shape and provided between the drive gear and the outer ring of the bearing, the driven gear is a gear that meshes with the drive gear, the shim is an annular member for determining the vertical position of the drive gear relative to the driven gear to set the meshing between the drive gear and the driven gear, an attachment hole is provided on the underside of the cover member on the outer circumferential side of the drive shaft insertion hole; the drive gear unit is attached to the underside of the cover member by inserting the boss and the bearing into the mounting hole via the shim and fixing an outer peripheral portion of the mounting member to the underside of the cover member; the mounting member has an annular portion having an inner diameter larger than the outer diameter of the outer ring of the bearing, and a plurality of protrusions protruding inward from the annular portion, the upper surface of the protruding end portion of each of the protrusions contacting the lower surface of the outer ring of the bearing.

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