Speed reduction device

Abstract

To provide a speed reduction device that can restrain an increase in device size, and increase a speed reduction ratio while keeping strength.SOLUTION: A speed reduction device (2) comprises: a first gear (251); a second gear (252) comprising a larger number of teeth than those of the first gear (251), and engaged with the first gear (251); and following stage gears (253-256) arranged in a stage following the first gear and the second gear, and to which rotary motion of the first gear (251) and the second gear (252) is transmitted. The module of the first gear (251) is larger than the module of the following stage gears (253-256).SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 describes a speed reducer having a multi-stage gear mechanism.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to increase the reduction ratio without increasing the number of stages of the gear mechanism, the tooth number difference between a pair of gears (a small tooth number gear and a large tooth number gear) that mesh with each other at each stage may be increased. However, if the tooth number of the large tooth number gear is increased to increase the tooth number difference, the diameter of the large tooth number gear becomes large, and the size of the speed reducer increases. Conversely, if the tooth number of the small tooth number gear is decreased, the shaft diameter of the small tooth number gear becomes small, and the strength of the small tooth number gear decreases without any measures.

[0005] An object of the present invention is to provide a speed reduction device capable of suppressing an increase in the size of the device and increasing the reduction ratio while maintaining the strength.

Means for Solving the Problems

[0006] The speed reduction device according to the present invention a first gear, a second gear having a larger tooth number than the first gear and meshing with the first gear, a rear-stage gear disposed at a rear stage of the first gear and the second gear and transmitting the rotational motion of the first gear and the second gear, and The module of the first gear is larger than the module of the subsequent-stage gear.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a speed reduction device that can suppress an increase in the size of the device, maintain the strength, and increase the reduction ratio.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0009] Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. In this specification, "front stage" and "subsequent stage" respectively mean the front and rear in the order of transmission of the power when the power is transmitted from the input shaft to the output shaft.

[0010] (Embodiment 1) FIG. 1 is a cross-sectional view showing the speed reduction device according to Embodiment 1 of the present invention. FIG. 2 is a longitudinal sectional view showing the speed reduction device of FIG. 1. FIG. 1 shows a cross-section along the cutting line e0 of FIG. 2.

[0011] The speed reducer 2 according to Embodiment 1 of the present invention includes a drive unit 21 that generates power, a first bevel gear 22 provided on a rotation shaft 21a of the drive unit 21, a parallel shaft speed reduction mechanism 24 that reduces and transmits the rotational motion of the first bevel gear 22, an output shaft 26 that outputs the rotational motion transmitted by the parallel shaft speed reduction mechanism 24 to the outside, and a casing member 27 that surrounds the parallel shaft speed reduction mechanism 24 and the output shaft 26. The rotation shaft 21a corresponds to an input shaft to which rotational power is input. The rotation center axis of the drive unit 21 and the rotation center axis of the output shaft 26 are in an orthogonal or 90-degree twisted relationship.

[0012] The parallel shaft speed reduction mechanism 24 includes a first shaft 241, a second shaft 242, and a third shaft 243 whose axial centers are parallel to each other, and a plurality of gears fixed to these shafts. The above axial centers are also parallel to the axial center of the output shaft 26, and may be regarded as the parallel shaft speed reduction mechanism 24 including the output shaft 26.

[0013] The plurality of gears include a second bevel gear 246 and a first gear 251 fixed to the first shaft 241, a second gear 252 and a third gear 253 fixed to the second shaft 242, a fourth gear 254 and a fifth gear 255 fixed to the third shaft 243, and a sixth gear 256 fixed to the output shaft 26. Here, "a gear is fixed to a shaft" means that the gear is fixed to the shaft with at least an engagement in the rotational direction so as to rotate integrally with the shaft. The fixing of the gear may be performed by connection, engagement, etc., or may be a mode in which the shaft and the gear are integrally formed by a single member. The third gear 253 to the sixth gear 256 correspond to an example of the subsequent-stage gears provided at a subsequent stage than the first gear 251 and the second gear 252.

[0014] Among the plurality of gears, the first bevel gear 22 and the second bevel gear 246 are engaged with each other, the first gear 251 and the second gear 252 are engaged with each other, the third gear 253 and the fourth gear 254 are engaged with each other, and the fifth gear 255 and the sixth gear 256 are engaged with each other.

[0015] The first shaft 241, the second shaft 242, the third shaft 243, and the output shaft 26 are arranged in this order in a direction orthogonal to the axial center in a plan view.

[0016] The first shaft 241 is rotatably supported by the casing member 27 via the first bearing 28. The first bearing 28 has a pair of bearings 28a and 28b. One bearing 28a supports one end of the first shaft 241, and the other bearing 28b supports the other end of the first shaft 241.

[0017] The second shaft 242 is rotatably supported by the casing member 27 via the second bearing 29. The second bearing 29 has a pair of bearings 29a and 29b. One bearing 29a supports one end of the second shaft 242, and the other bearing 29b supports the other end of the second shaft 242.

[0018] The third shaft 243 is rotatably supported by the casing member 27 via the third bearing 30. The third bearing 30 has a pair of bearings 30a and 30b. One bearing 30a supports one end of the third shaft 243, and the other bearing 30b supports the other end of the third shaft 243.

[0019] The output shaft 26 is rotatably supported by the casing member 27 via the fourth bearing 31. The output shaft 26 may have a hollow structure. The fourth bearing 31 has a pair of bearings 31a and 31b. One bearing 31a supports one end of the output shaft 26, and the other bearing 31b supports the other end of the output shaft 26.

[0020] The first gear 251 and the second gear 252 are helical gears, and the tooth portions of the first gear 251 and the second gear 252 have a twist angle. The third gear 253 to the sixth gear 256 are spur gears. The number of teeth of each of the first gear 251 to the sixth gear 256 is set so that the rotational motion is gradually decelerated.

[0021] The drive unit 21 is configured to be capable of forward and reverse driving, but may also be configured to be capable of only forward driving. The drive unit 21 is, for example, an electric motor, but may also be configured to drive the rotating shaft 21a using power other than electric power.

[0022] With the above configuration, when the rotary shaft 21a is rotationally driven by the drive unit 21, the first bevel gear 22 rotates integrally with the rotary shaft 21a, and this rotation is transmitted to the second bevel gear 246 and the first to sixth gears 251 to 256, causing the output shaft 26 to rotate. As a result, the rotational motion of the drive unit 21 is decelerated and output to the output shaft 26.

[0023] The first gear 251 and the second gear 252 are involute gears. An involute gear means that the cross-sectional shape orthogonal to the rotational axis of the tooth surface is an involute curve. However, in this specification, an involute gear is not limited to a configuration in which the cross-sectional shape of the tooth surface exactly matches the involute curve, but includes cases where an error is included between the cross-sectional shape of the tooth and the involute curve as long as a similar or analogous tooth meshing action can be obtained.

[0024] The first gear 251 and the second gear 252 mesh with a face contact ratio of 1 or less. The face contact ratio is defined in JIS (Japanese Industrial Standards) B_0102-1:2013_3.2.3.11. A face contact ratio of 1 or less means that the number of teeth of the first gear 251, which is a small number of teeth gear, is small. The number of teeth of the first gear 251 may be 2 or more and 6 or less. By using such a small number of teeth gear, the reduction ratio can be made larger. The number of teeth of the first gear 251 may be 10 or less, or may be 12 or less. As the number of teeth increases, the reduction ratio decreases, but a sufficiently large reduction ratio can still be obtained with such a number of teeth.

[0025] Each tooth portion of the first gear 251 and the second gear 252 has a twist angle. In FIG. 1, the twist angle of the tooth portion of the first gear 251 is represented by a two-dot chain line on the first gear 251. In FIG. 1, the twist angle of the tooth portion of the second gear 252 is represented by a two-dot chain line on the second gear 252. By having a twist angle, in the first gear 251 and the second gear 252 with a face contact ratio of 1 or less, the contact ratio can be set to an appropriate value of 1 or more.

[0026] <Module of the Gear> The module of the first gear 251 is larger than the module of any one of the third gear 253 to the sixth gear 256 located downstream of the first gear 251 and the second gear 252. The module of the first gear 251 may be larger than the module of any gear among the third gear 253 to the sixth gear 256 located downstream of the first gear 251 and the second gear 252. The module is a value obtained by dividing the diameter of the pitch circle by the number of teeth.

[0027] By reducing the number of teeth of the first gear 251, the reduction ratio between the first gear 251 and the second gear 252 can be increased. On the other hand, if the number of teeth of the first gear 251 becomes small and the shaft diameter becomes small, the tooth surface pressure, the tooth root bending stress, and the tangential force of the pitch circle of the first gear 251 will increase. Therefore, in this embodiment, contrary to the common sense of gradually increasing the module of the gear from the power input side to the output side, the module of the first gear 251 is increased. As a result, even if the number of teeth of the first gear 251 becomes small, the strength of the first gear 251 is improved, and it becomes possible to counter the increase in the tooth surface pressure, the tooth root bending stress, and the tangential force of the pitch circle in the first gear 251. Therefore, according to the speed reduction device 2 of this embodiment, it is possible to obtain a large reduction ratio while suppressing an increase in the size of the speed reduction device 2 and maintaining the strength of the first gear 251.

[0028] <Specific Example of the Number of Teeth> The number of teeth of the first gear 251 is set smaller than the number of teeth of any of the third gear 253 to the sixth gear 256 located downstream of the first gear 251 and the second gear 252. In this way, by reducing the number of teeth of the first gear 251, the reduction ratio of the speed reduction device 2 can be made larger accordingly.

[0029] Specifically, the number of teeth of the first gear 251 is 5, the number of teeth of the second gear 252 is 33, the number of teeth of the third gear 253 is 18, the number of teeth of the fourth gear 254 is 53, the number of teeth of the fifth gear 255 is 19, and the number of teeth of the sixth gear 256 is 58. In this case, the reduction ratio from the first shaft 241 to the output shaft 26 is 59.3.

[0030] Note that the number of teeth of the first gear 251 is 5 to 13. The number of teeth of each of the second gear 252 to the sixth gear 256 may be set arbitrarily.

[0031] <Arrangement of the first gear and the first shaft> The speed reduction device 2 has a first shaft 241, a second shaft 242, a third shaft 243, and an output shaft 26 as a plurality of parallel shafts. These parallel shafts rotate in conjunction with each other by transmitting motion to each other.

[0032] In the speed reduction device 2 of Embodiment 1, the first shaft 241 that rotates integrally with the first gear 251 is located at the forefront among the plurality of parallel shafts.

[0033] By increasing the module, the strength of the first gear 251 can be improved. However, by reducing the number of teeth of the first gear 251, the load on the first gear 251 increases. Therefore, depending on the torque applied to the first gear 251, the first gear 251 may become the bottleneck of the torque allowed by the device. However, as described above, since the first shaft 241 is located at the forefront where the torque is the smallest among the plurality of parallel shafts, it is possible to suppress the first gear 251 from reducing the allowable torque of the entire device and improve the allowable torque of the entire device.

[0034] <Specific example of the first shaft> As shown in FIG. 1, the first gear 251 and the first shaft 241 may be configured to be integrally formed by a single member. In the configuration of FIG. 1, the first shaft 241 and the first gear 251 are formed by forming a gear on the shaft by forging or cutting.

[0035] In the configuration processed in this way, on the first shaft 241, a rising portion 241a that connects to the tooth portion or the tooth root of the first gear 251 in the axial direction is provided. The rising portion 241a corresponds to a portion including a slope extending from the tooth root of the first gear 251 to the outer peripheral surface of the first shaft 241. The slope has an inclination direction in which the diameter increases as it moves away from the first gear 251 in the axial direction. The slope may include a convex portion (an incomplete portion of the tooth portion) that connects to the tooth portion of the first gear 251.

[0036] By allowing the generation of the rising portion 241a, the process of forming the first shaft 241 and the first gear 251 as an integral configuration becomes easier. On the other hand, the rising portion 241a has lower strength compared to other portions of the first shaft 241, and without any special measures, it becomes a factor that reduces the durability of the first shaft 241 against torsional load or bending load, etc.

[0037] Therefore, the first shaft 241 of Embodiment 1 is subjected to a surface hardening treatment at least on the rising portion 241a. As the surface hardening treatment, for example, plastic deformation processing such as shot peening can be applied, but any treatment that forms a hardened layer on the surface may be used.

[0038] By applying the surface hardening treatment, the durability of the first shaft 241 can be improved without increasing the processing difficulty of the first shaft 241 and the first gear 251.

[0039] (Embodiment 2) FIG. 3 is a cross-sectional view showing a part of the speed reduction device according to Embodiment 2 of the present invention. The speed reduction device 2A of Embodiment 2 has a different bearing structure for the first shaft 241A, and other components are the same as those in Embodiment 1. Hereinafter, the different components will be described in detail.

[0040] Similar to Embodiment 1, the reduction gear 2A includes a first shaft 241A that rotates integrally with the first gear 251, a second shaft 242 that rotates integrally with the second gear 252, a first bearing 28A (a pair of bearings 28Aa and 28Ab) that rotatably supports the first shaft 241A, and a second bearing 29 (a pair of bearings 29a and 29b) that rotatably supports the second shaft 242.

[0041] Furthermore, similar to Embodiment 1, the first gear 251 and the second gear 252 have a twist angle.

[0042] The twist angles of the first gear 251 and the second gear 252 generate a thrust reaction force on the first shaft 241A of the first gear 251. The thrust reaction force acts as an axial load on the first bearing 28A. Therefore, without any special measures, the axial load may reduce the life of the first bearing 28A.

[0043] In the reduction gear 2A of Embodiment 2, the first bearing 28A and the second bearing 29 are provided at different positions in the axial direction of the first shaft 241A and the second shaft 242. Specifically, when viewed in a direction perpendicular to the axis from the second shaft 242 toward the first shaft 241A, the first bearing 28A and the second bearing 29 are provided at positions where they do not overlap. If the first bearing 28A has a small-diameter portion, the small-diameter portion and the second bearing 29 may overlap when viewed in the perpendicular direction. Similarly, if the second bearing 29 has a small-diameter portion, the small-diameter portion and the first bearing 28A may overlap when viewed in the perpendicular direction.

[0044] According to this configuration, interference between the first bearing 28A and the second bearing 29 can be reduced, so a large-sized bearing can be adopted as the first bearing 28A. By adopting a large-sized bearing, the durability of the first bearing 28A can be improved, and the shortening of the life of the first bearing 28A can be suppressed.

[0045] Furthermore, the first bearing 28A is configured to support the first shaft 241A at two locations by a pair of bearings 28Aa and 28Ab, and the second bearing 29 is configured to support the second shaft 242 at two locations by a pair of bearings 29a and 29b. And the interval L1 in the axial direction between the pair of bearings 28Aa and 28Ab is shorter than the interval L2 in the axial direction between the pair of bearings 29a and 29b.

[0046] By reducing the number of teeth of the first gear 251, the shaft diameter of the first shaft 241A becomes smaller, and thus the first shaft 241A becomes more flexible. Such deflection inhibits good tooth contact of the first gear 251. Therefore, according to the speed reducer 2A of the second embodiment, since the axial interval L1 of the first bearing 28A is short, the rigidity against the meshing reaction force of the first shaft 241A can be increased. And due to the high rigidity, good tooth contact of the first gear 251 can be maintained. This effect is similarly achieved even when there is no twist angle in the tooth portion of the first gear 251.

[0047] The casing member 27 may adopt a configuration having a lid portion 27a that can be removed when incorporating one of the bearings 29b of the second bearing 29. The lid portion 27a exposes the arrangement portion of the bearing 29b to the outside of the casing member 27 by removing the lid portion 27a, and covers the arrangement portion of the bearing 29b and can press the bearing 29b by attaching the lid portion 27a. The lid portion 27a is connected to the main body portion of the casing member 27 via a connecting member such as a bolt.

[0048] (Embodiment 3) FIG. 4 is a cross-sectional view showing a part of the speed reducer according to the third embodiment of the present invention. The speed reducer 2B of the third embodiment has a different bearing structure for the first shaft 241, and other components are the same as those in the first embodiment. Hereinafter, the different components will be described in detail.

[0049] The reduction gear 2B includes, as in the first embodiment, a first shaft 241 that rotates integrally with the first gear 251, a second shaft 242 that rotates integrally with the second gear 252, a first bearing 28B (a pair of bearings 28Ba and 28Bb) that rotatably supports the first shaft 241A, and a second bearing 29 that rotatably supports the second shaft 242.

[0050] Furthermore, the first gear 251 and the second gear 252 have a twist angle, as in the first embodiment.

[0051] The twist angles of the first gear 251 and the second gear 252 generate a thrust reaction force on the first shaft 241 of the first gear 251. Since the thrust reaction force acts as an axial load on the first bearing 28B, without any special measures, the life of the first bearing 28B may be reduced.

[0052] In the reduction gear 2B of the second embodiment, as the first bearing 28B, a type of bearing capable of supporting an axial load is adopted. In FIG. 4, an example in which a tapered roller bearing is adopted as the first bearing 28B is shown, but other bearings such as angular ball bearings that can support various axial loads may also be adopted.

[0053] With this configuration, it is possible to suppress the reduction of the life of the first bearing 28B due to the above thrust reaction force.

[0054] The casing member 27 may adopt a configuration having lid portions 27b and 27c that can be respectively removed when incorporating the pair of bearings 28Ba and 28Bb of the first bearing 28B. By removing the lid portions 27b and 27c, the arrangement portions of the bearings 28Ba and 28Bb are exposed to the outside of the casing member 27, and by attaching the lid portions 27b and 27c, the arrangement portions of the bearings 28Ba and 28Bb can be covered and the bearings 28Ba and 28Bb can be pressed. The lid portions 27b and 27c are connected to the main body portion of the casing member 27 via a connecting member such as a bolt.

[0055] (Embodiment 4) FIG. 5 is a cross-sectional view showing a part of the speed reducer according to Embodiment 4 of the present invention. The speed reducer 2C according to Embodiment 4 has a different fixed structure of the first gear 251C with respect to the first shaft 241C, and the other components are the same as those in Embodiment 1. Hereinafter, the different components will be described in detail.

[0056] The speed reducer 2C includes a first gear 251C and a first shaft 241C that rotates integrally with the first gear 251C. The relationship between the number of teeth and the module of the first gear 251C and the number of teeth and the module of the other gears (the second gear 252 to the sixth gear 256) is the same as that in Embodiment 1. The torsional angle of the first gear 251C is also the same as that in Embodiment 1.

[0057] In Embodiment 4, the first gear 251C and the first shaft 241C are formed as separate members. And by engaging the first gear 251C and the first shaft 241C, the first gear 251C and the first shaft 241C are configured to rotate integrally. Specifically, the first gear 251C and the first shaft 241C are coupled by a helical type spline connection.

[0058] More specifically, a tooth portion is formed from one end portion e1 to the other end portion e2 in the axial direction of the member of the first gear 251C, and the tooth portion at the one end portion e1 and the tooth portion at the other end portion e2 function as spline teeth. Further, the first shaft 241C has a first portion 241Ca connected to one end portion e1 of the first gear 251C and a second portion 241Cb connected to the other end portion e2. The connecting portion of the first portion 241Ca has a recess into which the one end portion e1 can be inserted, and a helical type spline groove that engages with the above spline teeth is provided on the inner peripheral surface of the recess. The connecting portion of the second portion 241Cb has a recess into which the other end portion e2 can be inserted, and a helical type spline groove that engages with the above spline teeth is provided on the inner peripheral surface of the recess.

[0059] According to this configuration, it is possible to avoid forming the rising portion 241a (see FIG. 1) at the boundary between the first gear 251C and the first shaft 241C. Therefore, even if a torsional load, a bending load, or the like is applied to the first gear 251C and the first shaft 241C, durability sufficient to withstand these loads can be easily imparted to the first shaft 241C and the first gear 251C. Thus, the durability of the speed reduction device 2C can be improved. Further, since the diameter of the first shaft 241C becomes larger, the torsional rigidity and the bending rigidity between the first gear 251C and the first shaft 241C are improved, and good tooth contact of the first gear 251C can be realized.

[0060] Note that the coupling configuration between the first gear 251C and the first shaft 241C in the fourth embodiment can be similarly applied even when the tooth portion of the first gear 251C has no twist angle, and the same operational effects can be obtained. However, in this case, the spline teeth and the spline groove are not of the helical type, but the straight type (a spline shape in which the convex portion and the groove extend along the axis) is applied.

[0061] As described above, each embodiment of the present invention has been described. However, the present invention is not limited to the above embodiments. For example, in the above embodiments, a configuration in which the drive unit is included in the speed reduction device is shown, but the speed reduction device may not include the drive unit. Further, even when the drive unit is included, a configuration in which the rotation axis of the drive unit and the first shaft are arranged in parallel may be used. Further, in the above embodiments, an example in which the speed reduction device has a parallel-axis reduction mechanism is shown, but the speed reduction device of the present invention may have various reduction mechanisms, such as a center crank type eccentric swing type reduction device, a so-called distribution type eccentric swing type reduction device in which two or more eccentric shafts having eccentric bodies are arranged offset from the axis of the speed reduction device, and a configuration in which an orthogonal-axis reduction mechanism or a parallel-axis reduction mechanism is provided at the subsequent stage of the eccentric swing type reduction gear. Further, the features of the above-described plurality of embodiments may be combined with each other as long as no contradiction occurs. In addition, the details shown in the embodiments can be appropriately changed without departing from the gist of the invention.

Explanation of Signs

[0062] 2, 2A to 2C Speed reduction device 21 Driving part 22 First bevel gear 24 Parallel-axis reduction mechanism 28, 28A, 28B First bearing 29 Second bearing 28a~31a, 28b~31b, 28Aa, 28Ba, 28Ab, 28Bb Pair of bearings 241, 241C First shaft 241a Upturned part 241Ca First part 241Cb Second part 242 Second shaft 243 Third shaft 246 Second bevel gear 251, 251C First gear 252 Second gear 253~256 Third gear~Sixth gear 26 Output shaft 27 Casing member L1, L2 Spacing

Claims

1. A first gear, a second gear having a larger number of teeth than the first gear and meshing with the first gear, a rear-stage gear disposed downstream of the first gear and the second gear and receiving the rotational motion of the first gear and the second gear, comprising: wherein a module of the first gear is larger than a module of the rear-stage gear, a speed reduction device.

2. The number of teeth of the first gear is smaller than the number of teeth of any gear located downstream of the first gear, The speed reduction device according to Claim 1.

3. Comprising a plurality of parallel shafts having parallel axes and rotating in conjunction with the first gear by transmission of motion, wherein the plurality of parallel shafts includes a first shaft rotating integrally with the first gear, the first shaft being located at the most upstream among the plurality of parallel shafts, The speed reduction device according to Claim 2.

4. A first shaft rotating integrally with the first gear, a second shaft rotating integrally with the second gear, a first bearing supporting the first shaft, a second bearing supporting the second shaft, further comprising: wherein tooth portions of the first gear and the second gear have a twist angle, the first bearing and the second bearing are arranged at different positions in the axial direction of the first shaft and the second shaft, The speed reduction device according to Claim 1.

5. A first shaft rotating integrally with the first gear, a second shaft rotating integrally with the second gear, a first bearing supporting the first shaft, a second bearing supporting the second shaft, further comprising: wherein the first bearing is a pair of bearings, the second bearing is a pair of bearings, a distance in the axial direction between the pair of bearings of the first bearing is shorter than a distance in the axial direction between the pair of bearings of the second bearing, The speed reduction device according to Claim 1.

6. Comprising a first shaft rotating integrally with the first gear, wherein the first shaft has a rising portion continuous with a tooth portion of the first gear in the axial direction, the rising portion being surface hardened, The speed reduction device according to Claim 1.

7. Comprising a first shaft rotating integrally with the first gear, wherein the first gear and the first shaft are spline-coupled, The speed reduction device according to Claim 1.

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