speed reduction device

Abstract

To provide a speed reducer which enables reduction of the weight of a crank shaft.SOLUTION: A speed reducer 10 of an aspect includes a crank shaft 2 having eccentric parts 23, 24, 25 and extending from the input side in an axial direction. The crank shaft 2 has: an insertion hole 3 which is formed from the input side in the axial direction to allow an input shaft to be inserted thereinto; a connection part 4 for connecting with the input shaft; and an extension hole 5 provided closer to the eccentric parts 23, 24, 25 side than the connection part 4. The side opposite to the input side of the extension hole 5 does not communicate with the side opposite to the input side of the crank shaft 2. The extension hole 5 overlaps with the eccentric parts 23, 24, 25 in a radial direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a speed reduction device.

Background Art

[0002] A speed reduction device that reduces the rotation input to an input shaft and outputs it is known. The applicant has disclosed in Patent Document 1 a speed reduction device provided with an input shaft having a hollow portion into which a motor shaft is inserted. Three eccentric bodies are integrally formed on the input shaft of this speed reduction device. Three external gear wheels are swingably incorporated on the outer periphery of the eccentric body via rollers. Each external gear wheel is internally meshed with an internal gear wheel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventor obtained the following new recognition regarding a speed reduction device provided with a crankshaft having an eccentric portion. From the viewpoint of expanding the application range, it is desirable for the speed reduction device to be lightweight, and as a means, it is conceivable to reduce the weight of the crankshaft. Patent Document 1 does not sufficiently disclose the weight reduction of the crankshaft, and there is room for improvement in the speed reduction device described in this document from the viewpoint of weight reduction of the crankshaft.

[0005] The present invention has been made in view of such problems, and one of the objects is to provide a speed reduction device capable of reducing the weight of the crankshaft.

Means for Solving the Problems

[0006] To solve the above problems, a reduction gear according to one aspect of the present invention is a reduction gear having an eccentric portion and a crankshaft extending axially from the input side, wherein the crankshaft has an insertion hole formed axially from the input side for inserting the input shaft, a connecting portion for connecting with the input shaft, and an extension hole provided on the eccentric side of the connecting portion. The side of the extension hole opposite the input side does not communicate with the side of the crankshaft opposite the input side, and the extension hole overlaps with the eccentric portion when viewed radially.

[0007] Furthermore, any combination of the above components, or in which the components or expressions of the present invention are mutually substituted among methods, systems, etc., are also valid embodiments of the present invention. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing a first example of a speed reduction device according to the embodiment. [Figure 2] This is a cross-sectional view showing a second example of a speed reduction device according to the embodiment. [Modes for carrying out the invention]

[0009] The present invention will be described below with reference to the drawings, based on preferred embodiments. In embodiments and modifications, the same or equivalent components and members will be denoted by the same reference numerals, and redundant explanations will be omitted as appropriate. In addition, the dimensions of the members in each drawing will be enlarged or reduced as appropriate for ease of understanding. Furthermore, some members that are not important for explaining the embodiments will be omitted from the drawings.

[0010] Furthermore, while terms including ordinal numbers such as "first" and "second" are used to describe various components, these terms are used solely to distinguish one component from others, and do not limit the components themselves.

[0011] [Embodiment] The configuration of the reduction gear 10 according to the embodiment will be described with reference to Figures 1 and 2. Figure 1 is a side cross-sectional view showing a first example of the reduction gear 10. Figure 2 is a side cross-sectional view showing a second example of the reduction gear 10. The second example differs from the first example in that the shape of the extension hole 5 is different, but the other configurations are the same. The first example will be mainly described below, and the differences from the second example will also be described.

[0012] Refer to Figure 1. The reduction gear 10 of this embodiment is a reduction gear equipped with a crankshaft 2 having eccentric portions 23, 24, and 25. The motor shaft 1 of the motor 12 is connected to the crankshaft 2, and the rotation of the motor shaft 1 is input. Hereinafter, the direction along the central axis La of the crankshaft 2 will be referred to as the "axial direction," the side of the crankshaft 2 to which the motor shaft 1 is connected in the axial direction (right side in the figure) will be referred to as the input side, and the other side (left side in the figure) will be referred to as the anti-input side. In other words, the crankshaft 2 extends from the input side to the anti-input side in the axial direction. Furthermore, the circumferential direction and radial direction of a circle centered on the central axis La will be referred to as the "circumferential direction" and "radial direction," respectively.

[0013] First, the overall configuration of the reduction gear 10 will be explained. The reduction gear 10 reduces the rotation input from the motor shaft 1 and outputs it to the driven member. As for the motor 12, there are no restrictions as long as it is capable of outputting rotation to the reduction gear 10, and motors based on various principles can be used. The motor 12 in this embodiment is a brushless DC motor (sometimes called an AC servo motor). In the example in Figure 1, the motor shaft 1 of the motor 12 transmits rotation using a key.

[0014] There are no restrictions on the reduction gear 10 as long as it is capable of reducing the input rotation and outputting it; various reduction gears can be used. The reduction gear 10 of this embodiment is an eccentric oscillating type reduction gear that generates rotation of one of the internal gears or the external gear by oscillating the external gear that meshes with the internal gear, and outputs the resulting rotation component from the output member to the driven member. The reduction gear 10 of this embodiment is a center crank type in which the central axis La of the crankshaft 2 is provided on the same axis as the central axis of the internal gear.

[0015] The reduction gear 10 mainly consists of a crankshaft 2, external gears 13, 14, and 15, an internal gear 41, carriers 35 and 36, an internal pin 48, eccentric bearings 16, 17, and 18, main bearings 37 and 38, crankshaft bearings 39 and 40, and a casing 71. The casing 71 has a cylindrical shape that surrounds the reduction gear 10, and the internal gear 41 is provided on its inner circumferential surface.

[0016] The crankshaft 2 is rotated around the rotational centerline La by the rotational power input from the motor shaft 1. The outer circumference of the crankshaft 2 is provided with a first shaft portion 22, a first eccentric portion 23, a second eccentric portion 24, a third eccentric portion 25, and a second shaft portion 26, in order from the non-input side to the input side. The first shaft portion 22 and the second shaft portion 26 support the inner rings of the crankshaft bearings 39 and 40. The first eccentric portion 23, the second eccentric portion 24, and the third eccentric portion 25 are cylindrical portions with a larger diameter than the first shaft portion 22 and are eccentric as described later. The second shaft portion 26 is a cylindrical portion with the same diameter as the first shaft portion 22. In this specification, the first eccentric portion 23, which is located furthest to the non-input side among the eccentric portions 23, 24, and 25, is referred to as the specific eccentric portion 23.

[0017] The crankshaft 2 has an insertion hole 3 into which the motor shaft 1 is inserted. In the example shown in Figure 1, the insertion hole 3 is a hole formed axially from the input end face of the crankshaft 2 and is configured to accommodate the motor shaft 1. The insertion hole 3 is a circular hole coaxial with the central axis La of the crankshaft 2. The insertion hole 3 can be formed by rotating either a cutting tool such as a drill bit or a cutting tool, or a workpiece.

[0018] The crankshaft 2 has a connecting portion 4 for connecting the motor shaft 1 and the crankshaft 2. In this example, the connecting portion 4 includes a keyway 29 formed at a predetermined position on the inner circumferential surface of the insertion hole 3. The crankshaft 2 has an extension hole 5 provided on the side of the eccentric portions 23, 24, and 25 (opposite input side) from the connecting portion 4. The extension hole 5 may be a circular hole coaxial with the central axis La of the crankshaft 2. As shown in Figure 1, in the axial direction, the region in which the eccentric portions 23, 24, and 25 of the crankshaft 2 are provided is called the entire axial range 21 of the eccentric portions 23, 24, and 25. The entire axial range 21 is the range from the opposite input end of the eccentric portion 23 to the input end of the eccentric portion 25 in the axial direction. Also, the entire axial range of each eccentric portion is the range from the opposite input end to the input end of each eccentric portion in the axial direction.

[0019] The extension hole 5 can be formed by rotating either a cutting tool such as a drill bit or a cutting tool, or the workpiece. The extension hole 5 can be formed before the insertion hole 3 is formed. In this case, the insertion hole 3 can be formed using the extension hole 5 as a pilot hole, thus reducing the machining time for the insertion hole 3. The extension hole 5 can be formed after the insertion hole 3 is formed. In this case, the machining stroke of the extension hole 5 is shortened, thus reducing the machining time for the extension hole 5.

[0020] The extended hole 5 includes a cylindrical space region 32 formed by the shoulder of the drill bit, but does not include the inner diameter reduction region 31 (conical space) formed by the tip of the drill bit. The cylindrical space region 32 may include a region that has been expanded in diameter by cutting or other means after drilling, in addition to the region formed by the drill bit. The inner diameter reduction region 31 is formed on the tip side (opposite input side) of the extended hole 5, and the cylindrical space region 32 is formed continuously on the input side of the inner diameter reduction region 31. The cylindrical space region 32 can be said to be the region of the formed hole excluding the inner diameter reduction region 31.

[0021] The crankshaft 2 can be subjected to a predetermined heat treatment such as quenching after the insertion hole 3 and the extension hole 5 are formed. In this case, the machining time for hole machining can be shortened compared to the case of forming the holes after quenching, and the frequency of tool wear replacement is reduced. Further, in the embodiment, since the extension hole 5 extends to a position overlapping the eccentric portion, even if heat treatment is performed after the insertion hole 3 and the extension hole 5 are formed, the influence due to the non-uniformity of the wall thickness is reduced and the hardenability can be maintained. The heat treatment can employ a process of heating the crankshaft 2 to a predetermined temperature and then immersing it in a liquid such as water or oil for rapid cooling.

[0022] In the embodiment, the crankshaft 2 is an eccentric shaft having a plurality of eccentric portions 23, 24, 25 for rocking the external gears 13, 14, 15, and may be referred to as an input shaft. The axes of the eccentric portions 23, 24, 25 are eccentric with respect to the rotation center line La of the crankshaft 2. In the present embodiment, three eccentric portions 23, 24, 25 are provided, and the eccentric phases of the adjacent eccentric portions 23, 24, 25 are shifted by 120°.

[0023] The first shaft portion 22 on the anti-input side of the crankshaft 2 is supported by the first carrier 35 via the crankshaft bearing 39. The second shaft portion 26 on the input side of the crankshaft 2 is supported by the second carrier 36 via the second crankshaft bearing 40. That is, the crankshaft 2 is rotatably supported with respect to the first carrier 35 and the second carrier 36.

[0024] The crankshaft bearings 39, 40 are disposed between the carriers 35, 36 and the shaft portions 22, 26 of the crankshaft 2. The crankshaft bearings 39, 40 can employ various known bearing mechanisms. In this example, the crankshaft bearings 39, 40 are ball bearings having spherical rolling elements.

[0025] The external gears 13, 14, and 15 are individually provided, corresponding to each of the multiple eccentric portions 23, 24, and 25. The external gears 13, 14, and 15 are pivotably mounted on the outer circumference of the eccentric portions 23, 24, and 25 via eccentric bearings 16, 17, and 18. In this example, the eccentric bearings 16, 17, and 18 are roller bearings. The external gears 13, 14, and 15 each oscillate and mesh internally with the internal gear 41. The outer circumference of the external gears 13, 14, and 15 has corrugated teeth, and as these teeth move while in contact with the internal gear 41, the external gears 13, 14, and 15 can oscillate in a plane normalized to the central axis.

[0026] The internal gear 41 meshes with the external gears 13, 14, and 15. The internal gear 41 in this embodiment has an internal gear body 42 integrally provided on the inner circumference side of the casing 71, and a plurality of external pins 43 arranged in pin grooves formed at predetermined intervals in the circumferential direction on the inner circumference surface of the internal gear body 42. The external pins 43 are cylindrical pin members that are rotatably supported in the pin grooves of the internal gear body 42. The external pins 43 constitute the internal teeth of the internal gear 41. The number of external pins 43 (number of internal teeth) of the internal gear 41 is slightly greater (only 1 in this example) than the number of external teeth of the external gears 13, 14, and 15.

[0027] Multiple internal pin holes 45, 46, and 47 are formed in the external gears 13, 14, and 15 at positions offset from their axes. An internal pin 48 passes through the internal pin holes 45, 46, and 47. A cylindrical sleeve 49 is positioned around the outer circumference of the internal pin 48. The sleeve 49 functions as a sliding accelerator to facilitate smooth sliding with the internal pin holes 45, 46, and 47. The outer diameter of the sleeve 49 is smaller than the inner diameter of the internal pin holes 45, 46, and 47 by an amount equivalent to twice the eccentricity. A gap is provided between the sleeve 49 and the internal pin 48 to absorb the oscillation component of the external gears 13, 14, and 15, and the internal pin 48 is always in contact with a portion of the internal pin holes 45, 46, and 47 via the sleeve 49. The internal pin 48 revolves around the axis of the crankshaft 2 in synchronization with the rotational component of the external gears 13, 14, and 15, causing the carriers 35 and 36 to rotate around the axis of the crankshaft 2. The internal pin 48 contributes to the transmission of power between the carriers 35 and 36 and the external gears 13, 14, and 15.

[0028] The carriers 35 and 36 have a hollow ring shape. The first carrier 35 is positioned on the side of the external gears 13, 14, and 15 that is not the input side, and the second carrier 36 is positioned on the side of the external gears 13, 14, and 15 that is the input side. The first carrier 35 is rotatably supported by the casing 71 via the first main bearing 37. The second carrier 36 is rotatably supported by the casing 71 via the second main bearing 38. The first carrier 35 rotatably supports the side of the crankshaft 2 that is not the input side via the first crankshaft bearing 39. The second carrier 36 rotatably supports the input side of the crankshaft 2 via the second crankshaft bearing 40.

[0029] The main bearings 37 and 38 are positioned between the casing 71 and the carriers 35 and 36. The main bearings 37 and 38 can employ various known bearing mechanisms; in this example, the main bearings 37 and 38 are angular contact ball bearings. The inner rolling surfaces of the main bearings 37 and 38 are formed in the carriers 35 and 36.

[0030] The internal pin 48 is integrally formed with the first carrier 35 and extends axially from the input side of the first carrier 35 toward the second carrier 36. The carriers 35 and 36 are connected to each other by screwing a bolt B1 through a through hole in the second carrier 36 into a tapped hole at the end of the internal pin 48.

[0031] One of the carriers 35, 36 and the casing 71 becomes an output member that outputs rotational power to a driven member (not shown), and the other becomes a fixed member that is fixed to a mounting member (not shown) for supporting the reduction gear 10. In this example, the first carrier 35 functions as an output member that outputs rotational power to a driven member, and the casing 71 functions as a fixed member that is fixed to the mounting member.

[0032] The operation of the reduction gear 10 will now be explained. When rotational power is transmitted from the motor shaft 1 to the crankshaft 2, the eccentric parts 23, 24, and 25 of the crankshaft 2 rotate around the rotational centerline passing through the crankshaft 2, and the external gears 13, 14, and 15 oscillate due to these eccentric parts 23, 24, and 25. At this time, the external gears 13, 14, and 15 oscillate so that their own axes rotate around the rotational centerline of the crankshaft 2. As the external gears 13, 14, and 15 oscillate, the meshing positions of the external gears 13, 14, and 15 and the external pins 43 of the internal gear 41 shift sequentially. As a result, with each rotation of the crankshaft 2, one of the external gears 13, 14, and 15 and the internal gear 41 rotates by an amount equivalent to the difference between the number of teeth on the external gears 13, 14, and 15 and the number of external pins 43 of the internal gear 41. In this embodiment, the external gears 13, 14, and 15 rotate on their own, and reduced rotation is output from the first carrier 35. As the first carrier 35 rotates, the driven member connected to the first carrier 35 is rotated.

[0033] Next, the characteristic configuration of this disclosure will be described with reference to Figures 1 and 2. From the viewpoint of expanding the range of application, it is desirable that the crankshaft of the reduction gear be lightweight. Also, since the crankshaft rotates at high speed, it is desirable that the inertia be small from the viewpoint of improving responsiveness. Therefore, in the embodiment, the crankshaft 2 has an insertion hole 3 formed axially from the input side for inserting the motor shaft 1, a connecting portion 4 for connecting with the motor shaft 1, and an extension hole 5 provided on the eccentric portion 23, 24, 25 side of the connecting portion 4. The extension hole 5 overlaps with the eccentric portion 23, 24, 25 when viewed radially. In the embodiment, the input side end of the extension hole 5 is located on the input side of the eccentric portion 23, 24, 25. In the example of Figure 1, the non-input side end of the extension hole 5 is located in the middle of the axial range of the eccentric portion 23. In the example of Figure 2, the non-input side end of the extension hole 5 is located on the non-input side of the eccentric portion 23. The motor shaft 1 is an example of an input shaft.

[0034] The presence of the extension hole 5 reduces the mass of the crankshaft 2. Furthermore, the presence of the extension hole 5 reduces the inertia of the crankshaft 2. Additionally, because the extension hole 5 overlaps with the eccentric portions 23, 24, and 25 when viewed radially, the depth of the extension hole 5 increases, increasing the amount of material reduction and further reducing the mass and inertia of the crankshaft 2.

[0035] If the extension hole 5 communicates with the non-input side of the crankshaft 2, there is a risk that lubricant (such as grease) filled in the gear section and crankshaft bearing 39 may leak through the extension hole 5 to the input side of the crankshaft 2. Therefore, in this embodiment, the non-input side of the extension hole 5 does not communicate with the non-input side of the crankshaft 2. In this case, it is possible to prevent lubricant from leaking to the input side through the extension hole 5. In the example shown in Figure 1, the extension hole 5 is a blind hole formed facing the non-input side. Since the bottom of the non-input side of the extension hole 5 is an integral part with the crankshaft 2 body, strength can be easily ensured compared to when they are separate parts. Alternatively, the extension hole may be formed as a through hole, and a member or means for closing the non-input side of the extension hole may be provided.

[0036] When the heated crankshaft 2 is immersed in a liquid, the extension hole 5 and insertion hole 3 can be immersed facing upwards. This is to prevent air bubbles from remaining in the extension hole 5 and insertion hole 3, which would cause slow cooling and uneven hardness in those areas. Therefore, since the surface 20 of the crankshaft 2 opposite to the extension hole 5 is immersed facing downwards, if there is a recess there, air bubbles may remain in the recess, resulting in uneven hardness and potentially reducing hardenability. Accordingly, in this embodiment, the surface 20 of the crankshaft 2 opposite to the extension hole 5 does not have a recess having a depth that overlaps radially with the eccentric portion (e.g., the eccentric portion 23). In this case, the number of air bubbles remaining in the recess is reduced, mitigating uneven hardness caused by air bubbles and maintaining hardenability. The shallower the depth of the recess on the surface 20 of the crankshaft 2, the better, and it is even better if there is no recess at all.

[0037] By increasing the amount of material reduction due to the extension hole 5, the mass and inertia can be further reduced. In this embodiment, the extension hole 5 overlaps radially with a specific eccentric portion 23 located furthest to the anti-input side among the eccentric portions 23, 24, and 25. In this case, the mass and inertia are smaller than when the extension hole 5 does not overlap with the specific eccentric portion 23.

[0038] Refer to Figure 1. From the viewpoint of reducing machining time, it is desirable to have a small cutting allowance when machining the extension hole 5. Therefore, in the example in Figure 1, the inner diameter D5 of the extension hole 5 is smaller than the inner diameter D3 of the insertion hole 3. In this case, because the inner diameter D5 is small, the cutting allowance is small, and the machining time can be reduced.

[0039] Refer to Figure 2. The wall thickness of the crankshaft 2 differs between the parts with and without the extension hole 5. Near the boundary between the parts with and without the extension hole 5, distortion may occur due to heat treatment due to this difference in wall thickness. In particular, when the inner diameter D5 of the extension hole 5 is large, the wall thickness around the hole becomes thinner, making distortion more likely. If distortion occurs in the eccentric parts 23, 24, and 25, the accuracy in these parts will decrease, which may lead to a decrease in the performance of the reduction gear. Therefore, in the example in Figure 2, the extension hole 5 overlaps with the entire axial range 21 of the specific eccentric part 23 when viewed from the radial direction. In this case, the wall thickness around the extension hole 5 corresponding to the entire axial range 21 of the eccentric parts 23, 24, and 25 becomes almost constant, and distortion due to heat treatment in this part can be suppressed.

[0040] Refer to Figure 2. From the viewpoint of maximizing the weight reduction effect, it is desirable that the amount of material reduced by the extension hole 5 is large. Therefore, in the example in Figure 2, the inner diameter D5 of the extension hole 5 is greater than or equal to the inner diameter D3 of the insertion hole 3. In this case, even greater weight reduction can be achieved than when the inner diameter D5 is small. Such an extension hole 5 can be formed by first creating a pilot hole with the same inner diameter as the insertion hole 3, and then cutting the inner circumference of the pilot hole using a key-shaped cutting tool.

[0041] The features of the reduction gear 10 configured as described above will now be explained. The reduction gear 10 of the embodiment is a reduction gear that has eccentric portions 23, 24, and 25 and includes a crankshaft 2 extending axially from the input side. The crankshaft 2 has an insertion hole 3 formed axially from the input side for inserting the input shaft, a connecting portion 4 for connecting with the input shaft, and an extension hole 5 provided on the side of the eccentric portions 23, 24, and 25 that is closer to the connecting portion 4. The side of the extension hole 5 opposite the input side does not communicate with the side of the crankshaft 2 opposite the input side, and the extension hole 5 overlaps with the eccentric portions 23, 24, and 25 when viewed radially.

[0042] With this configuration, the mass of the crankshaft 2 is reduced by having the extension hole 5, making the reduction gear 10 lighter. In addition, the inertia of the high-speed rotating crankshaft 2 is reduced by having the extension hole 5, improving the responsiveness of the reduction gear 10. Furthermore, since the extension hole 5 overlaps with the eccentric portions 23, 24, and 25 when viewed radially, the depth of the extension hole 5 increases, increasing the amount of material reduction, further lightening the reduction gear 10 and further improving its responsiveness.

[0043] The present invention has been described above based on the embodiments. These embodiments are illustrative, and it will be understood by those skilled in the art that various modifications and changes are possible within the scope of the claims of the present invention, and that such modifications and changes are also within the scope of the claims of the present invention. Accordingly, the descriptions and drawings herein should be treated as illustrative rather than limiting.

[0044] (modified version) The following describes modified examples. In the drawings and descriptions of the modified examples, components and parts that are the same as or equivalent to those in the embodiments are denoted by the same reference numerals. Descriptions that overlap with those in the embodiments will be omitted as appropriate, and the descriptions will focus on the configurations that differ from those in the embodiments.

[0045] In the description of the embodiment, an example was shown in which the input shaft inserted into the insertion hole 3 of the crankshaft 2 is the motor shaft 1, but the present invention is not limited to this. For example, the input shaft inserted into the insertion hole of the crankshaft may be the shaft of a gear that meshes with the motor pinion of the motor shaft.

[0046] In the description of the embodiments, an example was shown in which the crankshaft 2 is connected to the motor shaft 1 using a key, but the present invention is not limited thereto. The crankshaft and the motor shaft may be connected by various known coupling methods.

[0047] In the description of the embodiments, an example was shown in which the reduction gear is a so-called center-crank type eccentric oscillating reduction gear, but the present invention is not limited thereto, and various reduction mechanisms can be employed. For example, the reduction gear may be a so-called distribution type eccentric oscillating reduction gear in which multiple crankshafts are arranged at positions offset from the axis of the internal gear.

[0048] Furthermore, for example, the reduction gear may be a flexible meshing type reduction gear (sometimes called a wave reduction gear) having a cylindrical external gear. The reduction gear may also be a cup-shaped or top-hat-shaped flexible meshing type reduction gear. Here, the flexible meshing type reduction gear includes a vibrator shaft having a vibrator that causes the external gear to bend and deform. The outer circumference of the cross-section perpendicular to the axis is elliptical. The axis of the vibrator coincides with the axis of the vibrator shaft and is not eccentric, but because its outer shape is elliptical, it is deformed from a perfect circle. The eccentric part in this invention is a broad concept that includes such a vibrator.

[0049] The description of the embodiment shows an example in which three external gears 13, 14, and 15 are provided, but the present invention is not limited thereto. The reduction gear may be provided with two or fewer external gears or four or more external gears.

[0050] Each of these modifications produces the same functions and effects as the embodiments.

[0051] Any combination of the embodiments and modifications described above is also useful as an embodiment of the present invention. The new embodiments resulting from these combinations possess the combined effects of both the respective embodiments and modifications. [Explanation of Symbols]

[0052] 1 Motor shaft, 2 Crankshaft, 3 Insertion hole, 4 Connecting part, 5 Extension hole, 10 Reduction gear, 21 Full axial range, 23, 24, 25 Eccentric parts.

Claims

1. A reduction gear having an eccentric portion and a crankshaft extending axially from the input side, The crankshaft has an insertion hole formed axially from the input side for inserting the input shaft, a connecting portion for connecting to the input shaft, and an extension hole provided on the eccentric side of the connecting portion. The non-input side of the extension hole is not in communication with the non-input side of the crankshaft. The aforementioned extension hole overlaps with the aforementioned eccentric portion when viewed from the radial direction. A reduction gear in which the inner diameter of the portion of the extension hole that overlaps with the eccentric portion when viewed radially and the inner diameter of the insertion hole are different from each other.

2. The reduction gear according to claim 1, wherein the face of the crankshaft opposite to the extension hole does not have a recess having a depth to a position that overlaps radially with the eccentric portion.

3. The reduction gear according to claim 1 or 2, wherein the extension hole overlaps radially with a specific eccentric portion located furthest to the input side of the eccentric portion, and the insertion hole does not overlap radially with the specific eccentric portion.

4. The reduction gear according to claim 3, wherein the extension hole overlaps with the entire axial range of the specific eccentric portion when viewed from the radial direction.

5. The reduction gear according to any one of claims 1 to 4, wherein the inner diameter of the portion of the extension hole that overlaps with the eccentric portion when viewed radially is smaller than the inner diameter of the insertion hole.

6. The reduction gear according to any one of claims 1 to 4, wherein the inner diameter of the portion of the extension hole that overlaps with the eccentric portion when viewed radially is larger than the inner diameter of the insertion hole.

7. The crankshaft has undergone a predetermined heat treatment. The reduction gear according to any one of claims 1 to 6, wherein the predetermined heat treatment includes immersing the crankshaft in a liquid.

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