Power transmission mechanism

Abstract

To inhibit the sealing function of a seal member from being degraded by contacting rust generated on a shaft part.SOLUTION: A shaft part 12 has a first shaft portion 31 integrally formed on a gear part 11, and a second shaft portion 32 separate from the gear part 11. A seal member 17 supports an outer peripheral face 32c of the second shaft portion 32, and the second shaft portion 32 has a first end 41 connected to the first shaft portion 31, and a second end 42 located on the opposite side to the first end 41 and connected to an encoder 22. A housing 13 is formed with an insertion hole 13h through which at least one of the second shaft portion 32 and the encoder 22 is inserted. At least an area ranging from the support part 52 supported by the seal member 17 to the second end 42 side, out of the second shaft portion 32, is a rust prevention part 50 having rust preventing property.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a power transmission mechanism.

Background Art

[0002] A power transmission mechanism transmits the input power to a transmission target. The power transmission mechanism includes, for example, a metal gear portion, a metal shaft portion, a housing, and a seal member. The gear portion rotates when power is input. The shaft portion rotates together with the gear portion. The housing accommodates the gear portion and the shaft portion and holds lubricating oil therein. The seal member seals between the housing and the shaft portion.

[0003] Further, Patent Document 1 discloses an encoder. By connecting the shaft portion to the encoder, the encoder detects the rotational speed of the shaft portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When an encoder is employed in a power transmission mechanism, in order to connect the encoder to the shaft portion, an insertion hole through which at least one of the shaft portion and the encoder is inserted is formed in the housing. At this time, if air contacts the shaft portion, water vapor contained in the air may adhere to the shaft portion, which may cause rust on the shaft portion. When rust occurs on the shaft portion, the seal function of the seal member may be reduced due to the seal member contacting the rust.

Means for Solving the Problems

[0006] A power transmission mechanism that solves the above problems is a power transmission mechanism that transmits input power to a transmission target, comprising: a metal gear portion that rotates when power is input; a metal shaft portion that rotates together with the gear portion; an encoder connected to the shaft portion and detecting the rotational speed of the shaft portion; a housing that houses the gear portion and the shaft portion and holds lubricating oil inside; and a sealing member that seals the space between the housing and the shaft portion, wherein the shaft portion has a first shaft portion integrally formed with the gear portion and a second shaft portion separate from the gear portion, the sealing member supports the outer circumferential surface of the second shaft portion, the second shaft portion has a first end portion connected to the first shaft portion and a second end portion located on the opposite side of the first end portion and connected to the encoder, the housing has an insertion hole through which at least one of the second shaft portion and the encoder is inserted, and at least the part of the second shaft portion from the support portion supported by the sealing member to the second end portion is a rust-proof portion having rust-proof properties.

[0007] With the above configuration, rust is less likely to occur in the part of the shaft that comes into contact with air and accumulates water vapor contained in the air. Therefore, it is possible to suppress the deterioration of the sealing function of the sealing member by contact with rust that has formed on the shaft.

[0008] In a power transmission mechanism, one of the first shaft portion and the first end portion may have a press-fit portion, and the other may have a press-fit portion that is press-fitted into the press-fit portion, and the first shaft portion and the first end portion may be connected by the press-fitting of the press-fit portion into the press-fit portion.

[0009] With the above configuration, compared to a case where one of the first shaft portion and the first end portion is fitted together by providing a female thread on one side and a male thread on the other, the first shaft portion and the first end portion are less likely to shift position relative to each other when the shaft portion rotates. Therefore, the first shaft portion and the first end portion can be connected suitably.

[0010] In the power transmission mechanism, the first end may have the press-fit portion, and the first shaft portion may have the press-fit portion. In the power transmission mechanism, the rust-preventive portion is formed by covering the second shaft portion with a plating layer, and the rust-preventive portion does not necessarily include the press-fit portion.

[0011] With the above configuration, if the press-fit portion is covered with a plating layer, there is a risk that the plating layer may peel off from the press-fit portion due to friction with the portion to be pressed in when the press-fit portion is pressed into the portion to be pressed in. However, such peeling of the plating layer does not occur with the above configuration. Therefore, a decrease in the press-fit accuracy between the press-fit portion and the portion to be pressed in can be suppressed.

[0012] In the power transmission mechanism, the rust-preventive portion may be formed by covering the second shaft portion with a plating layer. According to the above configuration, if the shaft portion, including the first shaft portion, is to be covered with a plating layer, it would be necessary to mask the gear portion in order to maintain the meshing accuracy of the gear portion before plating. However, the complex shape of the gear portion makes masking difficult. According to the above configuration, such masking work can be omitted, thus simplifying the plating layer formation process.

[0013] In the power transmission mechanism, a cover member may be provided to cover the insertion hole from the outside of the housing. According to the above configuration, even if water splashes onto the housing from the outside depending on the installation position of the power transmission mechanism, the cover member can prevent such water from entering the inside of the housing through the through-hole. [Effects of the Invention]

[0014] According to this invention, it is possible to suppress the deterioration of the sealing function of the sealing member due to contact with rust that has formed on the shaft. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic diagram showing a power transmission in an embodiment. [Figure 2] Figure 2 is a cross-sectional view showing the power transmission mechanism in an embodiment. [Figure 3] Figure 3 is a cross-sectional view showing the power transmission mechanism in a modified example. [Modes for carrying out the invention]

[0016] Below, an embodiment of the power transmission mechanism implemented in a reduction gear will be described with reference to the drawings. The power transmission mechanism of this embodiment is mounted, for example, on a vehicle. <Basic configuration of the power transmission mechanism> As shown in Figure 1, the power transmission mechanism 10 comprises a gear section 11, a shaft section 12, and a housing 13. The gear section 11 and the shaft section 12 are made of metal. The power transmission mechanism 10 comprises, for example, a plurality of gear sections 11. The plurality of gear sections 11 mesh with each other. The direction in which the axis of the shaft section 12 extends is also called the axial direction X. The shaft section 12 extends from the gear section 11 in the axial direction X. The shaft section 12 rotates together with the gear section 11. An internal space S1 is partitioned inside the housing 13. The gear section 11 and the shaft section 12 are located in the internal space S1. Thus, the housing 13 accommodates the gear section 11 and the shaft section 12. Lubricating oil is held inside the housing 13. The inside of the housing 13 may be filled with lubricating oil.

[0017] Of the multiple gear sections 11, one gear section 11 is connected to an input shaft 14. Of the multiple gear sections 11, the one gear section 11 to which the input shaft 14 is not connected is connected to an output shaft 15. The input shaft 14 and the output shaft 15 extend between the inside and outside of the housing 13.

[0018] Of both ends of the input shaft 14, the end opposite to the end connected to the gear portion 11 is connected to the motor 16. As the motor 16 is driven, the input shaft 14 rotates. That is, power is input from the motor 16 to the gear portion 11 via the input shaft 14. As the input shaft 14 rotates, the gear portion 11 to which the input shaft 14 is connected rotates. By transmitting the rotation of this gear portion 11 to other gear portions 11, the gear portion 11 to which the output shaft 15 is connected rotates. Thereby, the rotation of the gear portion 11 is transmitted to the transmission target via the output shaft 15. Thus, the gear portion 11 rotates by the input of power. The power transmission mechanism 10 transmits the input power to the transmission target. Note that examples of the transmission target include drive wheels of a vehicle not shown in the drawings.

[0019] As shown in FIG. 2, the power transmission mechanism 10 includes a bearing 18. The bearing 18 is, for example, cylindrical. The bearing 18 is located inside the housing 13 and held on the inner surface of the housing 13. The bearing 18 rotatably supports the shaft portion 12.

[0020] <Insertion hole of the housing> An insertion hole 13h is formed in the housing 13. The insertion hole 13h is a hole penetrating the housing 13. The shaft portion 12 is inserted through the insertion hole 13h.

[0021] <Sealing member> The power transmission mechanism 10 includes a sealing member 17. The sealing member 17 is, for example, annular. The sealing member 17 seals between the housing 13 and the shaft portion 12. Specifically, the sealing member 17 contacts a portion of the inner surface of the housing 13 that partitions the insertion hole 13h and the outer surface of the shaft portion 12. The sealing by the sealing member 17 suppresses the leakage of the lubricating oil inside the housing 13 to the outside of the housing 13 through the insertion hole 13h.

[0022] The power transmission mechanism 10 in this embodiment includes a mounting plate 21. The mounting plate 21 is provided along the outer surface of the housing 13. The mounting plate 21 is, for example, a flat plate. The mounting plate 21 is fixed to the housing 13 by a fixing member (not shown). A through hole 21h is formed in the mounting plate 21. The through hole 21h is, for example, smaller than the insertion hole 13h in the housing 13. The mounting plate 21 is attached to the housing 13 such that the through hole 21h and the insertion hole 13h face each other in the axial direction X.

[0023] The shaft portion 12 is inserted through the through hole 21h. The shaft portion 12 extends between the inside and outside of the housing 13 through the insertion hole 13h of the housing 13 and the through hole 21h of the mounting plate 21.

[0024] <Encoder> The power transmission mechanism 10 includes an encoder 22. The encoder 22 is connected to the shaft 12. More specifically, the encoder 22 has a connection portion 23. The connection portion 23 is, for example, a bottomed cylindrical shape that opens in the axial direction X. The ends of the shaft 12 in the axial direction X that are opposite to the gear portion 11 are inserted into the inside of this connection portion 23. A support member 24 passes through the connection portion 23 and the ends of the shaft 12 inserted into the connection portion 23 from the outside of the connection portion 23. This allows the connection portion 23 to rotate integrally with the shaft 12. The encoder 22 detects the rotational speed of the shaft 12. The rotational speed detected by the encoder 22 is output to a control device (not shown). The control device estimates the speed of the vehicle based on the rotational speed.

[0025] <Cover component> The power transmission mechanism 10 includes a cover member 25. The cover member 25 has a bottomed cylindrical cover body 26 that opens in the axial direction X, and a flange portion 27 extending from the open end of the cover body 26. The opening of the cover body 26 is larger than the opening of the through hole 21h. The opening of the cover body 26 faces the through hole 21h of the mounting plate 21 in the axial direction X. The flange portion 27 is a flat plate that forms an annular shape when viewed from the axial direction X. The flange portion 27 extends along the end faces of the mounting plate 21 in the axial direction X that are opposite to the housing 13. The flange portion 27 is attached to the mounting plate 21 by, for example, a plurality of bolt members 28. In this way, the cover member 25 is attached to the mounting plate 21.

[0026] <Accommodation space> The cover member 25 and the mounting plate 21 form a housing space S2 inside the cover member 25. This housing space S2, the through hole 21h in the mounting plate 21, and the insertion hole 13h in the housing 13 are aligned in this order along the axial direction X. The housing space S2 communicates with the internal space S1 of the housing 13 through the through hole 21h and the insertion hole 13h. The cover member 25 covers the through hole 21h in the mounting plate 21 from the outside of the housing 13. In this way, the cover member 25 covers the insertion hole 13h from the outside of the housing 13.

[0027] In this embodiment, the entire encoder 22 is located in the housing space S2. That is, the entire encoder 22 is located outside the housing 13. Of the ends of the shaft portion 12 in the axial direction X, the end opposite to the gear portion 11 extends from the through hole 21h of the mounting plate 21 into the housing space S2. Therefore, in the housing space S2, the end of the shaft portion 12 is inserted into the connecting portion 23.

[0028] <Shaft> The shaft portion 12 has a first shaft portion 31 and a second shaft portion 32. The first shaft portion 31 is integrally formed with the gear portion 11. Therefore, the first shaft portion 31 is made of the same metal as, for example, the gear portion 11. The first shaft portion 31 is substantially cylindrical in shape and extends from the gear portion 11 in the axial direction X. The bearing 18 supports the outer circumferential surface 31c of the first shaft portion 31. The entire first shaft portion 31 is located inside the housing 13. Of the two ends of the first shaft portion 31 in the axial direction X, the end on the gear portion 11 side is also called the first end 31a, and the end opposite to the first end 31a is also called the second end 31b. The first end 31a corresponds to the end of the shaft portion 12 on the gear portion 11 side. The axis of the first shaft portion 31 corresponds to the axis of the shaft portion 12.

[0029] The first shaft portion 31 has a press-fit portion 34. The press-fit portion 34 is a cylindrical hole that opens at the second end 31b of the first shaft portion 31 and is formed inside the first shaft portion 31. The press-fit portion 34 extends in the axial direction X from the second end 31b of the first shaft portion 31 to the portion between the second end 31b and the first end 31a.

[0030] The second shaft portion 32 is separate from the gear portion 11. The second shaft portion 32 is, for example, made of metal. The second shaft portion 32 may be made of the same metal as the gear portion 11 and the first shaft portion 31, or it may be made of a different metal than the gear portion 11 and the first shaft portion 31. The first shaft portion 31 is interposed between the gear portion 11 and the second shaft portion 32 in the axial direction X. The second shaft portion 32 has a first end portion 41 and a second end portion 42. The second end portion 42 is located on the opposite side from the first end portion 41. The first end portion 41 is located at one end of the second shaft portion 32 in the axial direction X, and the second end portion 42 is located at the other end.

[0031] The second shaft portion 32 has a main shaft portion 43. The main shaft portion 43 is located between the first end portion 41 and the second end portion 42 in the axial direction X. The main shaft portion 43 is cylindrical and extends in the axial direction X. The radial dimensions of the main shaft portion 43 are smaller than, for example, the radial dimensions of the through hole 13h of the housing 13 and smaller than the radial dimensions of the through hole 21h of the mounting plate 21.

[0032] The main shaft portion 43 extends between the inside of the housing 13 and the inside of the through hole 21h of the mounting plate 21, through the inside of the insertion hole 13h. That is, the second shaft portion 32 is inserted through the insertion hole 13h. Of the two ends of the main shaft portion 43 in the axial direction X, one end is in contact with the tip of the first shaft portion 31, and the other end is located inside the through hole 21h of the mounting plate 21.

[0033] The first end portion 41 is cylindrical in shape and extends in the axial direction X from the end of the main shaft portion 43 in the axial direction X. The radial dimensions of the first end portion 41 are, for example, smaller than the radial dimensions of the main shaft portion 43 and the same as the radial dimensions of the press-fit portion 34 of the first shaft portion 31.

[0034] The first end portion 41 is connected to the first shaft portion 31. The first end portion 41 is press-fitted into the press-fit portion 34 of the first shaft portion 31. The portion of the first end portion 41 that is press-fitted into the press-fit portion 34 may be a part of the first end portion 41 from the tip in the axial direction X, or it may be the entire portion in the axial direction X. That is, the first end portion 41 has a press-fit portion 44 that is press-fitted into the press-fit portion 34. Therefore, in this embodiment, of the first shaft portion 31 and the first end portion 41, the first shaft portion 31 has a press-fit portion 34, and the other, the first end portion 41, has a press-fit portion 44. The first shaft portion 31 and the first end portion 41 are connected when the press-fit portion 44 is press-fitted into the press-fit portion 34.

[0035] The second end 42 corresponds to the end of the shaft portion 12 opposite to the gear portion 11 in the axial direction X. The second end 42 is cylindrical and extends in the axial direction X from the end of the main shaft portion 43 opposite to the first end 41 in the axial direction X. The radial dimension of the second end 42 is, for example, slightly smaller than the inner diameter of the connection portion 23 of the encoder 22. The second end 42 extends between the inside of the through hole 21h of the mounting plate 21 and the housing space S2. That is, the second end 42 is exposed to the outside of the housing 13.

[0036] At least a portion of the tip of the second end 42 in the axial direction X is inserted into the connector 23. The connector 23 and the second end 42 are rotatable together by the support member 24. As a result, the second end 42 is connected to the encoder 22.

[0037] <Rust-preventive parts and plating layers> At least a portion of the second shaft portion 32 is a rust-preventive portion 50. The rust-preventive portion 50 is formed by covering the second shaft portion 32 with a plating layer 51. Examples of metals that make up the plating layer 51 include nickel, chromium, copper, silver, and gold.

[0038] Of the outer surfaces of the second shaft portion 32, the outer surface of the second end portion 42 and the outer surface of the main shaft portion 43 are covered with a plating layer 51. As a result, the second end portion 42 and the main shaft portion 43 function as rust-preventive parts 50.

[0039] The sealing member 17 is in contact with the plating layer 51. In this way, the sealing member 17 supports the outer circumferential surface 32c of the second shaft portion 32. More specifically, the sealing member 17 is in contact with the plating layer 51 covering the main shaft portion 43 from the radially outer side of the main shaft portion 43. The sealing member 17 supports the portion of the outer circumferential surface 32c of the second shaft portion 32 that is located on the main shaft portion 43, via the plating layer 51. Therefore, the support portion 52 of the second shaft portion 32 that is supported by the sealing member 17 is located on the main shaft portion 43. The support portion 52 is an annular region extending circumferentially along the outer circumferential surface 32c of the second shaft portion 32.

[0040] The support portion 52 is located in the center of the main shaft portion 43 in the axial direction X. Therefore, in this embodiment, the portion of the second shaft portion 32 from the support portion 52 to the second end portion 42 is the rust-preventive portion 50. In this embodiment, the entire main shaft portion 43 is the rust-preventive portion 50. Therefore, a portion of the second shaft portion 32 from the support portion 52 to the first end portion 41 is also the rust-preventive portion 50.

[0041] Of the outer surface of the second shaft portion 32, the outer surface of the first end portion 41 is not covered with the plating layer 51. Therefore, the first end portion 41 does not function as a rust-preventive portion 50. The rust-preventive portion 50 does not include the press-fit portion 44. As a result, the plating layer 51 is not interposed between the press-fit portion 44 and the portion to be press-fitted 34.

[0042] [Effect of the Embodiment] Next, the operation of the embodiment will be described. Air enters the housing space S2 from outside the cover member 25, for example, through the space between the mounting plate 21 and the flange portion 27 of the cover member 25. Air enters the through hole 21h of the housing 13 from the housing space S2 through the through hole 21h of the mounting plate 21. Because the space between the housing 13 and the shaft portion 12 is sealed by the sealing member 17, the portion of the shaft portion 12 that is on the gear portion 11 side of the support portion 52 supported by the sealing member 17 is less likely to be contacted by the air that has entered the through hole 21h. On the other hand, water vapor contained in the air adheres to the portion of the shaft portion 12 that is on the side of the gear portion 11 that is on the side of the support portion 52.

[0043] In the power transmission mechanism 10 of this embodiment, the portion of the shaft 12 opposite the gear portion 11 from the support portion 52 corresponds to the portion of the second shaft 32 that is on the side of the support portion 52 to the second end portion 42. Since this portion is the rust-preventive portion 50, the portion of the shaft 12 that comes into contact with air becomes rust-preventive. As a result, water vapor contained in the air adheres to the rust-preventive portion 50, making it difficult for rust to occur on the shaft 12 due to the adhesion of water vapor.

[0044] [Effects of the Embodiment] The effects of this embodiment will now be explained. (1) The housing 13 has an insertion hole 13h through which the second shaft portion 32 is inserted. Of the second shaft portion 32, at least the portion from the support portion 52 supported by the sealing member 17 to the second end portion 42 is a rust-preventive portion 50 that has rust-preventive properties. As a result, rust due to the adhesion of water vapor is less likely to occur in the part of the shaft portion 12 that comes into contact with air and adheres to water vapor contained in the air. Therefore, it is possible to suppress the deterioration of the sealing function of the sealing member 17 by coming into contact with rust that has formed on the shaft portion 12.

[0045] (2) Of the first shaft portion 31 and the first end portion 41, the first shaft portion 31 has a press-fit portion 34, and the other first end portion 41 has a press-fit portion 44 that is press-fitted into the press-fit portion 34. The first shaft portion 31 and the first end portion 41 are connected when the press-fit portion 44 is press-fitted into the press-fit portion 34. Therefore, compared to the case in which the first shaft portion 31 and the first end portion 41 are fitted together by providing an internal thread on one of the first shaft portion 31 and the first end portion 41 and providing an external thread on the other, the first shaft portion 31 and the first end portion 41 are less likely to shift position relative to each other when the shaft portion 12 rotates. Thus, the first shaft portion 31 and the first end portion 41 can be suitably connected.

[0046] (3) The rust-preventive portion 50 is formed by covering the second shaft portion 32 with a plating layer 51. The rust-preventive portion 50 does not include the press-fit portion 44. Therefore, if the press-fit portion 44 were covered with the plating layer 51, there is a risk that the plating layer 51 would peel off the press-fit portion 44 due to friction with the press-fit portion 34 when the press-fit portion 44 is pressed into the press-fit portion 34, but such peeling of the plating layer 51 does not occur in the above embodiment. Thus, a decrease in the press-fit accuracy between the press-fit portion 44 and the press-fit portion 34 can be suppressed.

[0047] (4) The rust-preventive portion 50 is formed by covering the second shaft portion 32 with the plating layer 51. Therefore, if the shaft portion 12 including the first shaft portion 31 were to be covered with the plating layer 51, it would be necessary to mask the gear portion 11 in order to maintain the meshing accuracy of the gear portion 11, but the gear portion 11 has a complex shape, making masking difficult. According to the above embodiment, such masking work can be omitted, thus simplifying the process of forming the plating layer 51.

[0048] (5) The power transmission mechanism 10 is equipped with a cover member 25 that covers the insertion hole 13h from the outside of the housing 13. Therefore, depending on the installation position of the power transmission mechanism 10, even if water is splashed onto the housing 13 from the outside, the cover member 25 can prevent such water from entering the inside of the housing 13 through the insertion hole 13h.

[0049] [Example of changes] The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0050] ○ As shown in Figure 3, a seal ring 55 may be provided between the cover member 25 and the mounting plate 21. The seal ring 55 is interposed between the flange portion 27 and the mounting plate 21. This makes it difficult for air to enter the inside of the cover member 25 from the outside through the gap between the flange portion 27 and the mounting plate 21. Therefore, water vapor contained in the air is less likely to come into contact with the shaft portion 12, further suppressing the occurrence of rust on the shaft portion 12. In this case, the shaft portion 12 does not need to be distinguished as a first shaft portion 31 and a second shaft portion 32. The gear portion 11 and the shaft portion 12 may be an integrated member.

[0051] ○ The mounting plate 21 may be omitted from the power transmission mechanism 10. In this case, the cover member 25 may be attached to the housing 13. ○ The cover member 25 may be omitted from the power transmission mechanism 10. In this case, a waterproof encoder 22 may be used as the encoder 22.

[0052] ○ The rust-preventive portion 50 may include the press-fit portion 44. For example, the entire second shaft portion 32 may be the rust-preventive portion 50. ○ The rust-preventive portion 50 is not limited to the second shaft portion 32 being covered with the plating layer 51. For example, the second shaft portion 32 may be made into the rust-preventive portion 50 by using a rust-preventive material as the material for the second shaft portion 32.

[0053] ○ The first shaft portion 31 may have a press-fit portion 44, and the first end portion 41 may have a press-fit portion 34. In short, of the first shaft portion 31 and the first end portion 41, one may have a press-fit portion 34, and the other may have a press-fit portion 44 that is press-fitted into the press-fit portion 34.

[0054] ○ The first shaft portion 31 and the first end portion 41 may be connected to each other by means other than press-fitting. For example, means of connecting the first shaft portion 31 and the first end portion 41 include screwing a female thread to a male thread, or fitting a spline shaft to a sleeve.

[0055] ○ The encoder 22 may be inserted through the insertion hole 13h. Both the second shaft portion 32 and the encoder 22 may be inserted through the insertion hole 13h. ○ The bearing 18 may support the second shaft portion 32.

[0056] ○ The power transmission mechanism 10 is not limited to a reduction gear. [Explanation of symbols]

[0057] 10...Power transmission mechanism, 11...Gear section, 12...Shaft section, 13...Housing, 13h...Through hole, 17...Sealing member, 22...Encoder, 25...Cover member, 31...First shaft section, 31c, 32c...Outer surface, 32...Second shaft section, 34...Press-fitted section, 41...First end, 42...Second end, 44...Press-fitted section, 50...Rust prevention section, 51...Plating layer, 52...Support section.

Claims

1. A power transmission mechanism that transmits input power to a target, A metal gear section that rotates when the aforementioned power is input, A metal shaft that rotates together with the gear section, An encoder connected to the shaft portion and used to detect the rotational speed of the shaft portion, A housing that accommodates the gear portion and the shaft portion, and which holds lubricating oil inside, It includes a sealing member that seals the space between the housing and the shaft portion, The shaft portion comprises a first shaft portion integrally formed with the gear portion and a second shaft portion separate from the gear portion. The sealing member supports the outer circumferential surface of the second shaft portion, The second shaft portion has a first end connected to the first shaft portion and a second end located on the opposite side of the first end and connected to the encoder. The housing has an insertion hole through which at least one of the second shaft portion and the encoder is inserted. A power transmission mechanism characterized in that at least the portion of the second shaft that is supported by the sealing member, from the support portion to the second end portion, is a rust-preventive portion having rust-preventive properties.

2. Of the first shaft portion and the first end portion, one has a press-fit portion, and the other has a press-fit portion that is press-fitted into the press-fit portion. The power transmission mechanism according to claim 1, wherein the press-fit portion is press-fitted into the press-fit portion, thereby connecting the first shaft portion and the first end portion.

3. The first end has the press-fit portion, The power transmission mechanism according to claim 2, wherein the first shaft portion has the press-fit portion.

4. The rust-preventive portion is formed by covering the second shaft portion with a plating layer. The power transmission mechanism according to claim 3, wherein the rust-preventive portion does not include the press-fit portion.

5. The power transmission mechanism according to any one of claims 1 to 3, wherein the rust-preventive portion is formed by covering the second shaft portion with a plating layer.

6. The power transmission mechanism according to any one of claims 1 to 4, further comprising a cover member that covers the insertion hole from the outside of the housing.

Images