Gear unit

Abstract

This gear unit is designed to easily transfer more thermal energy to the gas or liquid present inside the shaft member. [Solution] A gear unit comprising a cylindrical shaft member 30 and gear teeth 31 formed on the outer circumferential surface 30a of the shaft member 30, wherein the inner circumferential surface 30b of the shaft member 30 is covered with a porous material 40, the thermal conductivity of the material constituting the porous material 40 is greater than or equal to the thermal conductivity of the material constituting the shaft member 30, and the thickness of the porous material 40 in the radial direction R is defined as the direction perpendicular to the axis C1 of the shaft member 30, and varies depending on the part of the shaft member 30.

Description

Technical Field

[0001] The present invention relates to a gear unit provided with a cylindrical shaft member.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2022-147228 (Patent Document 1) describes a gear unit (1) provided with a cylindrical shaft member (30). In this gear unit (1), gear teeth (21) are formed on the outer peripheral surface of the shaft member (30).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a gear unit, the shaft member may be cooled by transferring thermal energy to a fluid such as gas or liquid existing inside the cylindrical shaft member, or the thermal energy transferred to the fluid may be utilized elsewhere. When utilizing thermal energy elsewhere like this, enhancing the efficiency of transferring the heat generated in the gear unit to the gas or liquid existing inside the shaft member leads to effective utilization of the thermal energy.

[0005] Therefore, it is desired to realize a gear unit that can easily increase the amount of thermal energy transferred to the gas or liquid existing inside the shaft member.

Means for Solving the Problems

[0006] The gear unit according to this disclosure comprises a cylindrical shaft member and gear teeth formed on the outer circumferential surface of the shaft member, wherein the inner circumferential surface of the shaft member is covered with a porous material, the thermal conductivity of the material constituting the porous material is greater than or equal to the thermal conductivity of the material constituting the shaft member, and the thickness of the porous material in the radial direction, with the direction perpendicular to the axis of the shaft member being the radial direction, varies depending on the part of the shaft member.

[0007] With this configuration, since the density of the porous material is lower than that of the shaft member, it is easier to keep the heat capacity of the gear unit low, thus reducing the thermal energy consumed to raise the temperature of the gear unit and increasing the thermal energy transferred to the fluid inside the shaft member. In addition, because the porous material has a large surface area, it can efficiently transfer heat to the fluid in contact with it. With this configuration, since the radial thickness of the porous material differs depending on the part of the shaft member, for example, the radial thickness of the porous material can be changed between parts where heat is easily generated and parts where heat is not easily generated. Therefore, it is easier to increase the thermal energy transferred from parts where heat is easily generated to the fluid inside the shaft member while maintaining the strength of the shaft member.

[0008] Further features and advantages of the technology relating to this disclosure will become clearer from the following description of exemplary and non-limiting embodiments, with reference to the drawings. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows a vehicle drive system on which the gear unit according to this embodiment is mounted. [Figure 2] Figure 1 shows the gear unit. [Modes for carrying out the invention]

[0010] Hereinafter, an embodiment of the gear unit 10 will be described with reference to the drawings.

[0011] Figure 1 is a schematic diagram showing an example of a vehicle drive system 11 on which a gear unit 10 is mounted. The vehicle drive system 11 is a drive system for an electric vehicle equipped with a rotating electric machine 12 as a driving force source for the wheels 18. The rotating electric machine 12 comprises a stator 12s and a rotor 12r. The vehicle drive system 11 includes a rotor gear 13 connected to the rotor 12r of the rotating electric machine 12. The vehicle drive system 11 includes an output differential gear device 17 that distributes the rotation input to the differential input gear 16 to the two left and right wheels 18.

[0012] Figure 2 is a schematic diagram showing an example of a gear unit 10. The gear unit 10 comprises a cylindrical shaft member 30. The cylindrical shaft member 30 is supported by a non-rotating member 23 via a first bearing 21 and a second bearing 22. Examples of non-rotating members 23 include, for example, the case of a vehicle drive unit 11, the case of a rotating electric machine 12, the body of a vehicle, etc. In this embodiment, the gear unit 10 is a vehicle gear unit mounted on a vehicle. Examples of vehicles include battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), fuel cell electric vehicles (FCEVs), etc.

[0013] The gear unit 10 includes first gear teeth 31 formed on the outer circumferential surface 30a of the shaft member 30. In this embodiment, the first gear teeth 31 are helical teeth. The first gear teeth 31 are integrally formed with the shaft member 30. The first gear teeth 31 are composed of irregularities formed on a part of the outer circumferential surface 30a of the shaft member 30. The shaft member 30 is manufactured, for example, by forging, casting, grinding, polishing, etc.

[0014] The gear unit 10 includes a second gear tooth 32. In this embodiment, the second gear tooth 32 is engaged with the shaft member 30 via an engagement portion. The gear unit 10 is arranged such that the first gear tooth 31 meshes with the differential input gear 16 and the second gear tooth 32 meshes with the rotor gear 13.

[0015] Here, the direction along the axis C1 of the shaft member 30 is defined as the axial direction X. One side of the axial direction X is defined as the first axial side X1. The other side of the axial direction X is defined as the second axial side X2. The direction perpendicular to the axis C1 of the shaft member 30 is defined as the radial direction R. In this embodiment, the second gear teeth 32 are positioned on the second axial side X2 relative to the first gear teeth 31.

[0016] The shaft member 30 is provided with an enlarged diameter portion 33 in a part of the axial direction X, where the diameter of the outer circumferential surface 30a is enlarged in relation to the region adjacent to the axial direction X. The diameter of the outer circumferential surface 30a of the enlarged diameter portion 33 is enlarged in relation to the regions adjacent on both sides of the axial direction X. The first gear teeth 31 are formed on the outer circumferential surface 30a of the enlarged diameter portion 33. In this embodiment, the first gear teeth 31 are formed over the entire area of ​​the enlarged diameter portion 33. However, the first gear teeth 31 may be formed only in a part of the enlarged diameter portion 33.

[0017] The cylindrical shaft member 30 has a space E1 surrounded by the inner circumferential surface 30b of the shaft member 30. The cylindrical shaft member 30 may have one of its ends closed, either the first end in the axial direction X1 or the second end in the axial direction X2. Alternatively, a non-cylindrical portion integrally formed with the shaft member 30 may be disposed at the end of the shaft member 30. In this embodiment, the cylindrical shaft member 30 has open ends in the axial direction X.

[0018] In this embodiment, the diameter of the inner circumferential surface 30b of the shaft member 30 is enlarged in a first region D1, which is a region in the axial direction X that overlaps with the enlarged diameter portion 33 in a radial view along the radial direction R. In this embodiment, the first region D1 is located inside both ends of the enlarged diameter portion 33 in the axial direction X. One or the other end of the first region D1 may be located outside the enlarged diameter portion 33 in the axial direction X, and both ends of the first region D1 may be in the same position as both ends of the enlarged diameter portion 33.

[0019] The shaft member 30 includes a supported portion 35 supported by bearings (first bearing 21 and second bearing 22) in a partial region in the axial direction X. In the present embodiment, in the second region D2, which is a region in the axial direction X set so as to overlap the supported portion 35 in a radial view along the radial direction R, the diameter of the inner peripheral surface 30b of the shaft member 30 is enlarged. In the present embodiment, the second region D2 is disposed inside both ends of the supported portion 35 in the axial direction X. Note that one end or the other end of the second region D2 may be located outside the supported portion 35 in the axial direction X, or both ends of the second region D2 may be at the same positions as both ends of the supported portion 35.

[0020] A heat medium 50 is supplied to a space E1 surrounded by the inner peripheral surface 30b of the shaft member 30. Examples of the heat medium 50 include oil, water, cooling gas, air, etc. In the present embodiment, a liquid heat medium 50 is supplied to the space E1. In the present embodiment, the heat medium 50 is oil. In the present embodiment, the heat medium 50 has the function of lubricating oil for the first gear teeth 31.

[0021] In the present embodiment, the heat medium 50 is supplied to the space E1 from an opening at the end of the second side X2 in the axial direction. In the present embodiment, the heat medium 50 is discharged from an opening at the end of the first side X1 in the axial direction. Note that the heat medium 50 may be supplied to the space E1 from an opening at the end of the first side X1 in the axial direction and discharged from an opening at the end of the second side X2 in the axial direction. Also, the heat medium 50 may be supplied to the space E1 from both ends of the shaft member 30 in the axial direction X.

[0022] The shaft member 30 includes a communication hole 38 that communicates the inner peripheral surface 30b and the outer peripheral surface 30a of the shaft member 30 and through which the heat medium 50 passes. The communication hole 38 is a hole through which the heat medium 50 is discharged from the space E1 to the side of the outer peripheral surface 30a of the shaft member 30. In the present embodiment, the heat medium 50 is supplied to the tooth surface of the first gear teeth 31 from the space E1 through the communication hole 38.

[0023] In this embodiment, a communication hole 38 that connects the inner peripheral surface 30b and the outer peripheral surface 30a of the shaft member 30 is formed in a region where the diameter of the inner peripheral surface 30b of the shaft member 30 is enlarged. In this embodiment, the flow rate of the heat medium 50 discharged from the space E1 to the radially outer side of the enlarged diameter portion 33 can be determined by the number and shape of the communication holes 38.

[0024] In this embodiment, the communication hole 38 is formed in the first region D1. In this embodiment, the communication hole 38 is formed in the second region D2. The heat medium 50 that has passed through the communication hole 38 in the second region D2 is flowed to the end of the shaft member 30 through a flow path in the axial direction X (not shown).

[0025] The gear unit 10 includes a porous material 40. The thermal conductivity of the material constituting the porous material 40 is not less than the thermal conductivity of the material constituting the shaft member 30. Here, the thermal conductivity of the material constituting the porous material 40 and the thermal conductivity of the material constituting the shaft member 30 are the thermal conductivities of the metal or non-metal constituting each of them. The thermal conductivity of the material constituting the porous material 40 does not include the thermal conductivity of the gas or liquid flowing through the porous material 40. Examples of the material constituting the porous material 40 include steel, iron, copper, aluminum, carbide, silicide, and the like. In this embodiment, the material constituting the porous material 40 is a metal.

[0026] The material constituting the porous material 40 and the material constituting the shaft member 30 may be the same or different. When the material of the porous material 40 and the material of the shaft member 30 are different, a material having a higher thermal conductivity than the material constituting the shaft member 30 is used as the material constituting the porous material 40. For example, when the material constituting the shaft member 30 is steel, copper, aluminum, or the like is used as the material constituting the porous material 40.

[0027] In this embodiment, the material constituting the porous material 40 is the same material as the material constituting the shaft member 30. In this embodiment, the thermal conductivity of the material constituting the porous material 40 is the same as the thermal conductivity of the material constituting the shaft member 30. The structure of the porous material 40 may be a regular porous structure such as a lattice structure, or it may be an irregular porous structure. In this embodiment, the porous material 40 has a regular porous structure.

[0028] In this embodiment, the inner circumferential surface 30b of the shaft member 30 is covered with a porous material 40. The thickness of the porous material 40 in the radial direction R varies depending on the part of the shaft member 30. In this embodiment, the diameter of the outer circumferential surface 40a of the porous material 40 that is in contact with the inner circumferential surface 30b of the shaft member 30 varies depending on the part of the shaft member 30. In this embodiment, the diameter of the inner circumferential surface 40b of the porous material 40 is constant regardless of the part of the shaft member 30.

[0029] In this embodiment, the porous material 40 covers the entire inner circumferential surface 40b of the shaft member 30. In this embodiment, the diameter of the inner circumferential surface 40b of the porous material 40 is constant over the entire axial direction X of the porous material 40. However, the porous material 40 may cover only a portion of the inner circumferential surface 30b of the shaft member 30. Examples of this portion include the first region D1, the second region D2, the central part of the porous material 40 in the axial direction X, etc. Furthermore, the diameter of the inner circumferential surface 40b of the porous material 40 may differ depending on the part of the shaft member 30.

[0030] In this embodiment, the thickness of the porous material 40 in the radial direction R is increased in the first region D1. In this embodiment, the diameter of the inner circumferential surface 40b of the porous material 40 is constant in the first region D1.

[0031] In this embodiment, the thickness of the porous material 40 in the radial direction R is increased in the second region D2. In this embodiment, the diameter of the inner circumferential surface 40b of the porous material 40 is constant in the second region D2.

[0032] In this embodiment, the thickness of the porous material 40 in the radial direction R varies according to the amount of heat generated in the area of ​​the shaft member 30. Areas of the shaft member 30 that generate a lot of heat have a greater thickness of the porous material 40 in the radial direction R than areas of the shaft member 30 that generate a lot of heat. Examples of areas of the shaft member 30 that generate a lot of heat include the central part of the shaft member 30, the first region D1, the second region D2, the central part of the first region D1, and so on.

[0033] In this embodiment, at least one of the porosity of the porous material 40 and the shape of the voids in the porous material 40 differs depending on the location on the shaft member 30. The porosity of the porous material 40 is changed, for example, by the size of the voids, the density of the voids, etc. Examples of the shape of the voids in the porous material 40 include circular holes, polygonal holes, lattice shapes, etc. The shape of the voids in the porous material 40 may be changed by selecting either a regular shape or an irregular shape depending on the location on the shaft member 30.

[0034] In this embodiment, at least one of the void ratio of the porous material 40 and the void shape of the porous material 40 differs according to the amount of heat generated in the part of the shaft member 30. For example, in parts of the shaft member 30 where high strength is required, a porous material 40 with a regular shape is selected. Examples of parts of the shaft member 30 where high strength is required include the first region D1, the second region D2, the portion that overlaps with the second gear teeth 32 in a radial view along the radial direction R, the spline engagement portion, the end of the first region D1, and so on.

[0035] In this embodiment, at least one of the porosity of the porous material 40 and the shape of the voids in the porous material 40 differs according to the required strength of the part of the shaft member 30. For example, in parts of the shaft member 30 where heat generation is high, a porous material 40 with a high porosity is selected.

[0036] In this embodiment, the diameter of the inner circumferential surface 30b of the shaft member 30 at the axial first side X1 end of the shaft member 30 is smaller than the diameter of the inner circumferential surface 30b of the shaft member 30 in the first region D1 or the second region D2. In this embodiment, the thickness of the porous material 40 in the radial direction R at the axial first side X1 end of the shaft member 30 is smaller than the thickness of the porous material 40 in the radial direction R in the first region D1 or the second region D2. In this embodiment, the diameter of the inner circumferential surface 30b of the shaft member 30 at the axial second side X2 end of the shaft member 30 is smaller than the diameter of the inner circumferential surface 30b of the shaft member 30 in the first region D1 or the second region D2. In this embodiment, the thickness of the porous material 40 in the radial direction R at the axial second side X2 end of the shaft member 30 is smaller than the thickness of the porous material 40 in the radial direction R in the first region D1 or the second region D2.

[0037] In this embodiment, the diameter of the inner circumferential surface 30b of the shaft member 30 in the region that overlaps radially with the second gear teeth 32 is smaller than the diameter of the inner circumferential surface 30b of the shaft member 30 in the first region D1 or the second region D2. In this embodiment, the thickness of the porous material 40 in the radial direction R in the region that overlaps radially with the second gear teeth 32 is smaller than the thickness of the porous material 40 in the radial direction R in the first region D1 or the second region D2.

[0038] In this embodiment, in the first region D1, the diameter of the inner circumferential surface 30b of the shaft member 30 is increased with respect to regions adjacent to one or both of the axial directions X. In this embodiment, in the first region D1, the thickness of the porous material 40 in the radial direction R is increased with respect to regions adjacent to one or both of the axial directions X.

[0039] In this embodiment, in the second region D2, the diameter of the inner circumferential surface 30b of the shaft member 30 is increased with respect to the region adjacent to one or both of the axial directions X. In this embodiment, in the second region D2, the thickness of the porous material 40 in the radial direction R is increased with respect to the region adjacent to one or both of the axial directions X.

[0040] The shaft member 30 and the porous material 40 of the gear unit 10 are manufactured integrally, for example, by a three-dimensional printing machine, and such that the thickness of the porous material 40 in the radial direction R differs depending on the part of the shaft member 30. Alternatively, for example, a gear unit 10 in which the thickness of the porous material 40 in the radial direction R differs depending on the part of the shaft member 30 may be manufactured by filling a shaft member 30, which has different diameters of inner circumferential surfaces 30b depending on the part, with a foaming agent so that the diameter of the inner circumferential surface becomes constant, and then foaming it by heating. Alternatively, for example, a gear unit 10 in which the thickness of the porous material 40 in the radial direction R differs depending on the part of the shaft member 30 may be manufactured by placing the porous material 40 in a part where the diameter of the inner circumferential surface 30b of the shaft member 30 is enlarged, such as a first region D1 or a second region D2, and then fitting a cylindrical porous material 40 onto the shaft member 30.

[0041] In the gear unit 10 of this embodiment, heat from the shaft member 30 and gear teeth is transferred to the porous material 40, and this heat is then transferred from the porous material 40 to the liquid or gas present inside the shaft member 30. In this case, the thermal conductivity of the material constituting the porous material 40 is greater than or equal to the thermal conductivity of the material constituting the shaft member 30, and because the porous material 40 has a large surface area, heat can be efficiently transferred to the heat transfer medium 50. Furthermore, because the porous material 40 has many voids, its density can be lower than that of the shaft member 30. Therefore, it is easier to reduce the weight of the gear unit 10.

[0042] Furthermore, for example, the inner circumferential surface 30b of the shaft member 30 may be formed in a straight line in order to fit a heat pipe into the shaft member 30. However, in a shaft member 30 with a straight inner circumferential surface 30b, it was difficult to increase the amount of thermal energy transferred to the gas or liquid inside the shaft member 30, depending on the location of the shaft member 30. In the gear unit 10 of this embodiment, the diameter of the inner circumferential surface 30b of the shaft member 30 is increased depending on the location of the shaft member 30, and the thickness of the porous material 40 in the radial direction R is increased, making it easier to increase the efficiency of transferring thermal energy to the gas or liquid inside the shaft member 30.

[0043] [Other Embodiments] Next, other embodiments of the gear unit 10 will be described.

[0044] (1) In the above embodiment, a configuration in which the first gear teeth 31 mesh with the differential input gear 16 and the second gear teeth 32 mesh with the rotor gear 13 was described as an example. However, the embodiment of the gear unit 10 is not limited to such a configuration. For example, the first gear teeth 31 mesh with the rotor gear 13 and the second gear teeth 32 mesh with the differential input gear 16. Also, for example, the gear unit 10 may be mounted on a power generation device that is not for a vehicle and does not have a differential input gear 16.

[0045] (2) In the above embodiment, the shaft member 30 was described as having an enlarged diameter portion 33 in which the diameter of the outer circumferential surface 30a is enlarged in areas adjacent to both sides in the axial direction X, and the first gear teeth 31 are formed on the outer circumferential surface 30a of the enlarged diameter portion 33. However, embodiments of the gear unit 10 are not limited to such a configuration. For example, the first gear teeth 31 may be formed on the outer circumferential surface 30a of the shaft member 30 in a portion different from the enlarged diameter portion 33. Also, for example, the shaft member 30 may not have an enlarged diameter portion 33 in a part of the axial direction X, and the diameter of the outer circumferential surface 30a of the shaft member 30 may be constant. Also, for example, the enlarged diameter portion 33 may be formed at the end of the shaft member 30, and the diameter of the outer circumferential surface 30a may be enlarged only in areas adjacent to one side in the axial direction X.

[0046] (3) In the above embodiment, a configuration was described as in which the diameter of the inner circumferential surface 30b of the shaft member 30 is increased in the first region D1 and the second region D2, and the thickness in the radial direction R of the porous material 40 is increased. However, the embodiment of the gear unit 10 is not limited to such a configuration. For example, the diameter of the inner circumferential surface 30b of the shaft member 30 may not be increased in the first region D1 and the second region D2, and the thickness in the radial direction R of the porous material 40 may be increased. Alternatively, for example, the thickness in the radial direction R of the porous material 40 may not be increased in the first region D1 and the second region D2, and the diameter of the inner circumferential surface 30b of the shaft member 30 may be increased.

[0047] (4) In the above embodiment, a configuration in which communication holes 38 are formed in the first region D1 and the second region D2 was described as an example. However, the embodiment of the gear unit 10 is not limited to such a configuration. For example, communication holes 38 do not have to be formed in either one or both of the first region D1 and the second region D2. Also, for example, communication holes 38 do not have to be formed in the shaft member 30 in a region in which the diameter of the inner circumferential surface 30b of the shaft member 30 is enlarged. Also, for example, communication holes 38 may be formed in a region in which the diameter of the inner circumferential surface 30b of the shaft member 30 is not enlarged.

[0048] (5) In the above embodiment, a configuration was described as in which the diameter of the inner circumferential surface 30b of the shaft member 30 is increased in the second region D2 corresponding to the supported portion 35 supported by the first bearing 21 and the supported portion 35 supported by the second bearing 22, and the thickness of the porous material 40 in the radial direction R is increased. However, the embodiment of the gear unit 10 is not limited to such a configuration. For example, in one or both of the second region D2 corresponding to the supported portion 35 supported by the first bearing 21 and the supported portion 35 supported by the second bearing 22, the diameter of the inner circumferential surface 30b of the shaft member 30 is not increased, and the thickness of the porous material 40 in the radial direction R is not increased.

[0049] (6) In the above embodiment, a configuration in which the porous material 40 is made of the same material as the shaft member 30 was described as an example. However, the embodiment of the gear unit 10 is not limited to such a configuration. For example, the material of the porous material 40 may be different from the material of the shaft member 30.

[0050] (7) The configurations disclosed in the embodiments described above can be applied in combination with configurations disclosed in other embodiments, as long as they do not cause any inconsistencies. With regard to other configurations, the embodiments disclosed herein are merely illustrative in all respects. Therefore, various modifications can be made as appropriate without departing from the spirit of this disclosure.

[0051] [Summary of the above embodiments] The gear unit 10 related to this disclosure will be described below.

[0052] In one embodiment, the gear unit (10) comprises a cylindrical shaft member (30) and gear teeth (first gear teeth 31, second gear teeth 32) formed on the outer circumferential surface (30a) of the shaft member (30), wherein the inner circumferential surface (30b) of the shaft member (30) is covered with a porous material (40), the thermal conductivity of the material constituting the porous material (40) is greater than or equal to the thermal conductivity of the material constituting the shaft member (30), and the thickness of the porous material (40) in the radial direction (R) is defined as the direction perpendicular to the axis (C1) of the shaft member (30), and varies depending on the part of the shaft member (30).

[0053] With this configuration, since the density of the porous material (40) is lower than that of the shaft member (30), it is easier to keep the heat capacity of the gear unit (10) low, reduce the thermal energy consumed to raise the temperature of the gear unit (10), and increase the amount of thermal energy transferred to the fluid (heat transfer medium 50) inside the shaft member (30). In addition, because the porous material (40) has a large surface area, it can efficiently transfer heat to the fluid (heat transfer medium 50) that comes into contact with the porous material (40). With this configuration, since the radial (R) thickness of the porous material (40) differs depending on the part of the shaft member (30), for example, the radial (R) thickness of the porous material (40) can be changed between parts where heat is easily generated and parts where heat is not easily generated. Therefore, while maintaining the strength of the shaft member (30), it is easier to increase the amount of thermal energy transferred from parts where heat is easily generated to the gas or liquid inside the shaft member (30).

[0054] With the axis (X) being the direction along the axis (C1) of the shaft member (30), the shaft member (30) is provided with an enlarged diameter portion (33) in a part of the axial direction (X) in which the diameter of the outer circumferential surface (30a) is enlarged in relation to the region adjacent to the axial direction (X). The gear teeth (first gear teeth 31) are formed on the outer circumferential surface (30a) of the enlarged diameter portion (33). In the first region (D1), which is the axial direction (X) region set to overlap with the enlarged diameter portion (33) in a radial view along the radial direction (R), the diameter of the inner circumferential surface (30b) of the shaft member (30) is enlarged, and the thickness of the porous material (40) in the radial direction (R) is enlarged.

[0055] In this configuration, in the first region (D1) which overlaps radially with the enlarged diameter portion (33) where gear teeth (first gear teeth 31) that are prone to generating heat due to meshing are formed, the radial (R) thickness of the porous material (40) is increased, thereby increasing the surface area for heat exchange with the fluid (heat medium 50) in that region. Therefore, the heat generated in the gear teeth (first gear teeth 31) can be efficiently transferred to the fluid (heat medium 50) inside the shaft member 30.

[0056] With the axis (X) being defined as the direction along the axis (C1) of the shaft member (30), the shaft member (30) has a supported portion (35) supported by bearings (first bearing 21, second bearing 22) in a part of the axial direction (X). In a second region (D2), which is the axial direction (X) region set to overlap with the supported portion (35) in a radial view along the radial direction (R), the diameter of the inner circumferential surface (30b) of the shaft member (30) is increased, and the thickness of the porous material (40) in the radial direction (R) is increased.

[0057] In this configuration, in the second region (D2) which overlaps radially with the supported portion (35) where the bearing, which is prone to generating heat due to rotation, is located, the radial (R) thickness of the porous material (40) is increased. This increases the surface area for heat exchange with the fluid (heat transfer medium 50) in that region. Therefore, the heat generated in the supported portion (35) can be efficiently transferred to the fluid (heat transfer medium 50) inside the shaft member (30).

[0058] A liquid heat transfer medium (50) is supplied to the space (E1) surrounded by the inner circumferential surface (30b) of the shaft member (30), and a communication hole (38) is formed in the region where the diameter of the inner circumferential surface (30b) of the shaft member (30) is enlarged, connecting the inner circumferential surface (30b) and the outer circumferential surface (30a) of the shaft member (30).

[0059] In this configuration, the heat transfer medium (50) located inside the shaft member (30) flows more through the region where the radial (R) thickness of the porous material (40) is increased. Therefore, heat transfer to the heat transfer medium (50) can be performed efficiently.

[0060] The gear unit 10 relating to this disclosure only needs to be able to achieve at least one of the effects described above. [Explanation of symbols]

[0061] 10: Gear unit, 21: First bearing, 22: Second bearing, 30: Shaft member, 30a: Outer surface, 30b: Inner surface, 31: First gear tooth, 32: Second gear tooth, 33: Enlarged diameter section, 35: Supported section, 38: Communication hole, 40: Porous material, 40a: Outer surface, 40b: Inner surface, 50: Heat transfer fluid, C1: Axial center, D1: First region, D2: Second region, E1: Space, R: Radial direction, X: Axial direction

Claims

1. A cylindrical shaft member, Gear teeth formed on the outer circumferential surface of the shaft member, A gear unit equipped with, The inner circumferential surface of the shaft member is covered with a porous material. The thermal conductivity of the material constituting the porous material is greater than or equal to the thermal conductivity of the material constituting the shaft member. The direction perpendicular to the axis of the shaft member is defined as the radial direction, A gear unit in which the radial thickness of the porous material differs depending on the location of the shaft member.

2. The direction along the axis of the shaft member is defined as the axial direction, The shaft member is provided with an enlarged diameter portion in a part of the axial region, in which the diameter of the outer surface is increased compared to the adjacent region in the axial direction. The gear teeth are formed on the outer circumferential surface of the enlarged diameter portion, The gear unit according to claim 1, wherein in the first region, which is the axial region set to overlap with the enlarged diameter portion in a radial view along the radial direction, the diameter of the inner circumferential surface of the shaft member is enlarged, and the thickness of the porous material in the radial direction is enlarged.

3. The direction along the axis of the shaft member is defined as the axial direction, The shaft member has a supported portion supported by a bearing in a part of the axial region, The gear unit according to claim 1, wherein in the second region, which is the axial region set to overlap with the supported portion in a radial view along the radial direction, the diameter of the inner circumferential surface of the shaft member is increased and the radial thickness of the porous material is increased.

4. A liquid heat transfer medium is supplied to the space enclosed by the inner circumferential surface of the shaft member. The gear unit according to claim 2 or 3, wherein a communication hole is formed in a region where the diameter of the inner circumferential surface of the shaft member is enlarged, and the inner circumferential surface and the outer circumferential surface of the shaft member are connected.

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