differential gear mechanism

Abstract

A differential gear mechanism capable of suppressing a decrease in gear strength is provided. [Solution] The gear includes a first internal gear 12 having first internal teeth 12a, a second internal gear 14 having second internal teeth 14a, and an external gear unit 30 having first external teeth 32p and second external teeth 32q. The first internal teeth 12p mesh with a first pair of first external teeth, and the second internal teeth 14a mesh with a second pair of second external gear 32q simultaneously at multiple locations. The external teeth 32p, 32q are helical teeth that helix in opposite directions and have the same number of teeth, normal module, normal normal pitch, and helix angle. The internal teeth 12a, 14a are helical teeth that helix in opposite directions and have different numbers of teeth. The helical teeth in the first pair and / or the second pair differ from each other in helix angle. The normal tooth groove width of the first internal tooth 12a is equal to the normal tooth width of the first external tooth 32p, and the normal tooth groove width of the second internal tooth 14a is equal to the normal tooth width of the second external tooth 32q.

Description

[Technical Field]

[0001] The present invention relates to a differential gear mechanism, and more particularly to a differential gear mechanism in which two internal gears with different numbers of teeth mesh with an external gear. [Background technology]

[0002] Differential gear mechanisms are used in devices that require a large reduction ratio. Known examples of differential gear mechanisms include a strain wave gear mechanism in which a cylindrical strain wave gear with external teeth and radial flexibility is meshed with two internal gears with different numbers of teeth, and a paradox planetary gear mechanism in which the internal gears of two planetary gear mechanisms have different numbers of teeth.

[0003] FIG. 17(A) is a schematic longitudinal cross-sectional view of a differential gear mechanism 1, and FIG. 17(B) is its schematic transverse cross-sectional view. As shown in FIG. 17, the differential gear mechanism 1 includes two internal gears 2, 3 that are coaxially arranged in the axial direction and have different numbers of teeth. A cylindrical wave gear 4 that is radially flexible is disposed inside the wave gear 4, and a wave generator 5 is provided inside the wave gear 4. The wave generator 5 includes a rigid plug 5a that has an elliptical outer peripheral surface 5b and a wave bearing 5c ​​that is attached to the elliptical outer peripheral surface 5b of the rigid plug 5a and is elliptically flexible. One of the internal gears, 2, is fastened and fixed to a device housing 7, which is a fixed member, and the other internal gear, 3, is fastened and fixed to a disk-shaped output shaft 8, which is a rotating member. The output shaft 8 is rotatably supported by the device housing 7 via a bearing 9.

[0004] The wave gear 4 is pushed out by the elliptical radially protruding portion of the wave generator 5 and meshes with the internal gears 2 and 3. When the rigid plug 5a of the wave generator 5 rotates, the meshing position moves circumferentially. Because the internal gears 2 and 3 have different numbers of teeth, the internal gear 3 and output shaft 8 rotate (see, for example, Patent Document 1).

[0005] Other types of wave generator 5 have also been proposed (see, for example, Patent Document 2).

[0006] Figure 18 is a skeleton diagram of a paradox planetary gear mechanism. In Figure 18, symbol A indicates a sun external gear, symbol B indicates a planetary gear, and symbols C and D indicate internal gears. Internal gears C and D, which have different numbers of teeth, mesh with planetary gear B. For example, if the external gear A is set as the drive shaft, one internal gear C as the driven shaft, and the other internal gear D as the fixed shaft, and the numbers of teeth of gears A, B, C, and D are Za = 24, Zb = 25, Zc = 72, and Zd = 75, respectively, the reduction ratio is 100, which is an extremely large reduction ratio (see, for example, Patent Document 3).

[0007] Helical gears with parallel axes mesh with equal helix angles. For example, Non-Patent Document 1 states, "To mesh helical gears with parallel axes, it is necessary to combine gears with equal helix angles but different helix directions." [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 7408262 [Patent Document 2] Japanese Patent Application Publication No. 2024-171085 [Patent Document 3] Patent No. 4012940 [Non-patent literature]

[0009] [Non-Patent Document 1] "KHK Gear Technical Data", Ohara Gear Industry Co., Ltd., First Edition, First Printing, November 8, 2022, p.22 Summary of the Invention [Problem to be solved by the invention]

[0010] The differential gear mechanism 1 shown in FIG. 17 has the following problems.

[0011] Furthermore, the wave bearing 5c ​​is interposed between the wave gear 4 and the elliptical outer peripheral surface 105b of the rigid plug 5a, causing slippage, and the positional relationship between the wave gear 4 and the elliptical outer peripheral surface 105b of the rigid plug 5a cannot be uniquely determined.

[0012] Furthermore, it is extremely difficult to assemble the wave bearing 5c ​​onto the elliptical outer peripheral surface 105b of the rigid plug 5a and to mesh the wave gear 4 with the two internal gears 2 and 3. Furthermore, the bearing 9 provided between the two internal gears 2 and 3 is an expensive bearing such as a cross roller bearing that is free to rotate in the radial direction but fixed in the axial direction.

[0013] Furthermore, the external teeth of the wave gear 4 are spur teeth with tooth traces extending linearly, but the tooth profile is not a typical involute tooth profile but a special tooth profile, which reduces the strength of the gear.

[0014] When the differential gear mechanism 1 is combined with a motor and used in a robot or the like, it is required to have a hollow structure so that wiring such as signal lines and power supply lines can be passed through. However, the differential gear mechanism 1 does not have a hollow structure.

[0015] Another problem with paradoxical planetary gear mechanisms is that they are extremely inefficient. The two internal gears that are arranged coaxially and mesh with the planetary gear have different numbers of teeth, which requires profile shifting, and this reduces the strength of the gears.

[0016] In view of the above circumstances, an object of the present invention is to provide a differential gear mechanism that can suppress a decrease in gear strength. Another object of the present invention is to provide a differential gear mechanism that is easy to assemble, has a simple configuration, and can be made hollow. [Means for solving the problem]

[0017] In order to solve the above problems, the present invention provides a differential gear mechanism configured as follows.

[0018] The differential gear mechanism comprises (a) a first internal gear having first internal teeth, (b) a second internal gear arranged coaxially with the first internal gear and having second internal teeth, and (c) an external gear unit arranged inside the first internal gear and the second internal gear and having first external teeth meshing with the first internal teeth at a plurality of circumferentially spaced locations simultaneously and second external teeth meshing with the second internal teeth, wherein a gear ratio between the first internal teeth and the first external teeth and a gear ratio between the second internal teeth and the second external teeth are different from each other. Furthermore, (i) the first external teeth and the second external teeth include helices that are helical spiraled in opposite directions and have the same number of teeth, normal module, normal normal pitch, and helix angle, (ii) the first internal teeth and the second internal teeth include helices that are helical spiraled in opposite directions and have different numbers of teeth from each other, and (iii) (a) The first inner teeth and the first outer teeth The helix angles of the respective helices are different from each other, or (b) the second inner teeth and the second outer teeth Each of the above The twist angles are different from each other, or (c) the helical helix angles of the first internal teeth and the first external teeth are different from each other, and the helical helix angles of the second internal teeth and the second external teeth are different from each other; (iv) The normal tooth groove width of the helix of the first internal tooth is equal to the normal tooth width of the helix of the first external tooth, and the normal tooth groove width of the helix of the second internal tooth is equal to the normal tooth width of the helix of the second external tooth.

[0019] According to the above configuration, (i) allows the portion where the first external teeth are formed and the portion where the second external teeth are formed to function as helical external gears with the same number of teeth and the same tooth profile. (ii) allows the portion where the first internal teeth are formed and the portion where the second internal teeth are formed to function as helical internal gears with different numbers of teeth. By varying the helix angles of the parallel shaft helices as in (iii), it is possible to make the reference circle diameters of the first internal teeth and the second internal teeth, which have different numbers of teeth, the same even if the first pair and the second pair have the same module. Furthermore, (iv) allows the meshing pitch circle diameters of the first internal teeth and the second internal teeth, which have different numbers of teeth, the same. By making the reference circle diameters and pitch circle diameters of the first internal teeth and the second internal teeth the same, the helices can mesh with each other without adding profile shifting, thereby preventing a decrease in gear strength. By making the reference circle diameter and pitch circle diameter of each of the first internal tooth and the second internal tooth approximately the same value, the amount of addendum shift can be minimized, a decrease in gear strength can be suppressed, and efficiency can be improved.

[0020] Furthermore, (iv) allows the helical teeth of the first external teeth and the first internal teeth to mesh without backlash, and the helical teeth of the second external teeth and the second internal teeth to mesh without backlash.

[0021] In addition, helical gears have more teeth that mesh simultaneously than spur gears, so they rotate more smoothly and can transmit larger loads.

[0022] In the above configuration, each of the first pair and the second pair may include a plurality of helical beams.

[0023] Preferably, the first external teeth and the second external teeth include double helices having the same number of teeth, tooth normal module, tooth normal normal pitch, and helix angle, and the first internal teeth and the second internal teeth include double helices having different numbers of teeth. (a) Within the first Teeth The twist angle of the double helical bar is Teeth The twist angle is different from that of the above-mentioned double helical or (b) the helix angle of the double helical teeth of the second internal teeth is different from the helix angle of the double helical teeth of the second external teeth; or (c) the helix angle of the double helical teeth of the first internal teeth is different from the helix angle of the double helical teeth of the first external teeth, and the helix angle of the double helical teeth of the second internal teeth is different from the helix angle of the double helical teeth of the second external teeth. do.

[0024] In the above configuration, the double helical teeth include right-hand and left-hand helical teeth, so the axial positional relationship between the first internal teeth and the first external teeth is fixed, and the axial positional relationship between the first internal teeth and the first external teeth is fixed. Therefore, the axial positional relationship between the first internal gear and the second internal gear is fixed via the external gear unit that meshes with the first internal gear and the second internal gear. This simplifies the configuration of the bearings provided between the first internal gear and the second internal gear.

[0025] In a preferred embodiment, the external gear unit includes: (a) a wave gear having a cylindrical shape, the first external teeth and the second external teeth formed on its outer peripheral surface, and being radially flexible; and (b) a wave generator disposed inside the wave gear and pressing the wave gear radially outward to simultaneously mesh the first pair and the second pair at multiple locations and move the meshing positions of the first pair and the second pair in the circumferential direction.

[0026] According to the above configuration, a strain wave gear mechanism can be configured.

[0027] Preferably, spur teeth are formed on the inner peripheral surface of the wave gear. The wave generator includes: (i) a plurality of planetary gears that mesh with the spur teeth of the wave gear, and (ii) a sun gear that is disposed coaxially with the first internal gear and the second internal gear and meshes with the planetary gears.

[0028] According to the above configuration, the planet gears and sun gear of the wave generator can be easily assembled inside the wave gear so that the planet gears mesh with the wave gear.

[0029] Preferably, spur teeth are formed on an inner peripheral surface of the wave gear. The wave generator includes a plurality of planetary gears that mesh with the spur teeth of the wave gear, and a sun gear that is disposed coaxially with the first internal gear and the second internal gear and meshes with the planetary gears.

[0030] According to the above configuration, the wave generator can be easily incorporated inside the wave gear.

[0031] More preferably, the gear train further includes an auxiliary planetary gear between adjacent planetary gears, which meshes with the spur teeth of the wave gear and the sun gear.

[0032] According to the above configuration, the load can be shared by the auxiliary gear, and therefore strength is improved against the inertial force that occurs when the rotation input to the differential gear mechanism suddenly stops.

[0033] In another preferred aspect, the external gear unit includes (a) a plurality of planetary gears on which the first external teeth and the second external teeth are formed, and (b) a sun gear arranged coaxially with the first internal gear and the second internal gear and meshing with the planetary gears.

[0034] In this case, since no wave gear is involved, the configuration is simpler than in a differential gear mechanism that uses a wave gear.

[0035] Preferably, the first internal gear and the second internal gear have opposing annular recesses formed on their axially opposing surfaces, with a ring-shaped solid lubricant member disposed in one of the recesses and an O-ring disposed in the other recess, the O-ring abutting against the solid lubricant member.

[0036] According to the above configuration, the configuration of the bearing provided between the first internal gear and the second internal gear can be simplified.

[0037] The present invention also provides an actuator including a differential gear mechanism and a motor, wherein the differential gear has a sun gear having a hollow hole formed therein, and the motor is configured so that the sun gear is an outer rotor of the sun gear in the hollow hole.

[0038] For example, an outer rotor motor can be constructed by attaching a permanent magnet to the inner surface of the hollow hole of the sun gear and placing a stator inside it. Since the sun gear, i.e., the motor's outer rotor, is rotatably supported via the planetary gears, the bearings provided between the motor's stator and rotor can be constructed using planetary gears. A hollow hole can be formed in the motor's stator, which can be used as wiring space. [Effects of the Invention]

[0039] According to the present invention, it is possible to provide a differential gear mechanism that can suppress a decrease in gear strength, and also to provide a differential gear mechanism that is easy to assemble, has a simple configuration, and can be made hollow. [Brief explanation of the drawings]

[0040] [Figure 1] Fig. 1(a) is a cross-sectional view of the strain wave gear mechanism, and Fig. 1(b) is a longitudinal-sectional view thereof. (Example 1-1) [Figure 2] FIG. 2 is a cross-sectional view of the strain wave gear mechanism (Example 1-1). [Figure 3] Fig. 3(a) is a plan view and a longitudinal cross-sectional view of the second internal gear, and Fig. 3(b) is a longitudinal cross-sectional view and a plan view of the first internal gear. (Example 1-1) [Figure 4] 4 is a plan view and a side view of the wave gear (Example 1-1). [Figure 5] 5 is a plan view of the strain wave gear mechanism (Example 1-1). [Figure 6] Fig. 6(a) is a cross-sectional view of the external gear unit, and Fig. 6(b) is an exploded view of the wave generator 40. (Example 1-1) [Figure 7] Fig. 7(a) is a cross-sectional view of the strain wave gear mechanism, and Fig. 7(b) is a longitudinal-sectional view thereof. (Example 1-2) [Figure 8] Fig. 8(a) is a cross-sectional view of the strain wave gear mechanism, and Fig. 8(b) is a longitudinal-sectional view thereof (Examples 1-3). [Figure 9] 9 is a cross-sectional view of the strain wave gear mechanism (Examples 1-4). [Figure 10] Fig. 10(a) is a cross-sectional view of the differential gear mechanism, and Fig. 10(b) is a longitudinal cross-sectional view thereof. (Example 2-1) [Figure 11] FIG. 11 is an explanatory diagram of the auxiliary internal gear and the auxiliary planetary gear (Example 2-1). [Figure 12] 12 is an enlarged cross-sectional view of the main parts of the first internal gear and the second internal gear (Example 2-1). [Figure 13] Figure 13(a) is a cross-sectional view of the assembly, and Figure 13(b) is a longitudinal-sectional view thereof. (Example 3-1) [Figure 14] Figure 14(a) is a cross-sectional view of the assembly, and Figure 14(b) is a longitudinal-sectional view thereof. (Example 3-2) [Figure 15] Figure 15(a) is a cross-sectional view of the assembly, and Figure 15(b) is a longitudinal cross-sectional view thereof. (Example 3-3) [Figure 16] Figure 16(a) is a cross-sectional view of the assembly, and Figure 16(b) is a longitudinal cross-sectional view thereof. (Examples 3-4) [Figure 17] Figure 17(A) is a schematic vertical cross-sectional view of a strain wave gear mechanism, and Figure 17(B) is a schematic horizontal cross-sectional view thereof (Prior Art 1). [Figure 18] FIG. 18 is a skeleton diagram of a paradox planetary gear mechanism (conventional example 2). [Figure 19]FIG. 19 is an explanatory diagram of the meshing of the first internal teeth and second internal teeth with the external teeth. DETAILED DESCRIPTION OF THE INVENTION

[0041] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0042] As a first embodiment, a strain wave gear mechanism will be described with reference to FIGS. 1 to 9. FIG.

[0043] Example 1-1 A three-leaf differential gear mechanism 10 will be described with reference to FIGS. 1 to 5. FIG. 1(a) is a horizontal cross-sectional view of the differential gear mechanism 10, and FIGS. 1(b) and 2 are longitudinal cross-sectional views thereof. FIG. 1(b) shows the first internal gear 12 and the second internal gear 14 in cross section, and FIG. 2 shows the first internal gear 12, the second internal gear 14, and the strain wave gear 32 in cross section. FIG. 3(a) is a plan view and a longitudinal cross-sectional view of the second internal gear 14, and FIG. 3(b) is a longitudinal cross-sectional view and a plan view of the first internal gear 12. FIG. 4(a) is a plan view of the differential gear mechanism 10, and FIG. 4(b) is a plan view and a side view of the strain wave gear 32. FIG. 5 is a plan view of the strain wave gear mechanism. FIG. 6(a) is a cross-sectional view of the external gear unit 30, and FIG. 6(b) is an exploded view of the wave generator 40.

[0044] As shown in Figures 1 to 6, the differential gear mechanism 10 has a first internal gear 12 having first internal teeth 12a and a second internal gear 14 having second internal teeth 14a arranged adjacent to each other and coaxially, and an external gear unit 30 including a wave gear 32 and a wave generator 40 is arranged inside the first internal gear 12 and the second internal gear 14.

[0045] The wave gear 32 is a generally cylindrical member that is flexible and can be elastically deformed into an elliptical shape. First external teeth 32p that mesh with the first internal teeth 12a of the first internal gear 12 and second external teeth 32q that mesh with the second internal teeth 14a of the second internal gear 14 are formed on the outer circumferential surface of the wave gear 32. Internal teeth 32a are formed on the inner circumferential surface of the wave gear 32. The internal teeth 32a are spur teeth.

[0046] The first external teeth 32p and the second external teeth 32q are double-helical external gears that are twisted in opposite directions, and have the same number of teeth, normal module, normal pitch, and helix angle. Therefore, the portion where the first external teeth 32p are formed and the portion where the second external teeth 32q are formed function as double-helical external gears with the same number of teeth and tooth profile.

[0047] The first internal gear 12a and the second internal gear 14a are double-helical internal gears that twist in opposite directions and have different numbers of teeth. The first internal gear 12 and the second internal gear 14 are double-helical internal gears with different numbers of teeth.

[0048] First inner teeth 12a and first outer teeth Tooth 3 2p, the first pair of second inner teeth 14a and the second outer teeth Tooth 3 In either or both of the second pairs of 2q, the helical angles of the parallel-axis helical teeth are different. By making the helical angles of the parallel-axis helical teeth different, it is possible to make the reference circle diameters of the first internal teeth 12a and the second internal teeth 14a, which have different numbers of teeth, the same value, even if the first pair and the second pair have the same module.

[0049] The normal tooth groove width of the first internal teeth 12a is equal to the normal tooth width of the first external teeth 32p, and the normal tooth groove width of the second internal teeth 14a is equal to the normal tooth width of the second external teeth 32q. This makes it possible to make the helical meshing pitch circle diameters of the first internal teeth 12a and the second internal teeth 14a, which have different numbers of teeth, the same value.

[0050] By making the reference circle diameter and pitch circle diameter of each of the first internal teeth 12a and the second internal teeth 14a the same value, the double helices can be meshed without adding profile shift, and a decrease in gear strength can be suppressed.By making the reference circle diameter and pitch circle diameter of each of the first internal teeth 12a and the second internal teeth 14a approximately the same value, the amount of profile shift can be minimized, and a decrease in gear strength can be suppressed.

[0051] The normal tooth space width corresponds to the normal tooth space width, and the normal tooth width corresponds to the normal tooth thickness. The double helical teeth of the first internal teeth 12a and the first external gear 32p mesh without backlash because the normal tooth space width of the first internal teeth 12a is equal to the normal tooth width of the first external teeth 32p. The double helical teeth of the second internal teeth 14a and the second external gear 32q mesh without backlash because the normal tooth space width of the second internal teeth 14a is equal to the normal tooth width of the second external teeth 32q.

[0052] The planetary mechanism 40 has three planetary gears 42 arranged around a sun gear 46, and an auxiliary planetary gear 44 arranged between adjacent planetary gears 42, 42. The planetary gear 42 and the auxiliary planetary gear 44 have external teeth 42p, 44p, respectively, that mesh with the external teeth 46p of the sun gear 46 and the internal teeth 32a of the wave gear 32. The external teeth 44p, 46p of the planetary gear 42 and the auxiliary planetary gear 44 and the external teeth 46p of the sun gear 46 are spur teeth. A hollow hole 47 is formed in the sun gear 46. The sun gear 46 may be solid without having the hollow hole 47 formed therein.

[0053] The three planetary gears 42 push the wave gear 32 radially outward, and simultaneously at three locations spaced circumferentially, the first external teeth 32p of the wave gear 32 mesh with the internal teeth 32a of the first internal gear 32, and the second external teeth 32q of the wave gear 32 mesh with the internal teeth 32a of the first internal gear 32.

[0054] In the differential gear mechanism 10, the gear ratio of a first pair between the first internal teeth 12a of the first internal gear 12 and the first external teeth 32p of the wave gear 32 is different from the gear ratio of a second pair between the second internal teeth 14a of the second internal gear 14 and the second external teeth 32q of the wave gear 32.

[0055] For example, when the first internal gear 12 is fixed and rotation is input to the sun gear 46, the second internal gear 14 rotates. In this case, the rotation speed of the second internal gear 14 is smaller than the rotation speed of the sun gear 46, and the differential gear mechanism 10 functions as a reducer.

[0056] This will be explained in more detail below.

[0057] The number of teeth of the first internal teeth 12a is Z r1= 66, and the number of teeth of the second internal teeth 14a is Z r2 = 63. When the first internal gear 12, which has a larger number of teeth, is fixed and the meshing position between the first internal gear 12a and the external teeth 32p of the wave gear 32 rotates once relative to the first internal gear 12a, the second internal gear 14a has fewer teeth than the first internal gear 1a, so it rotates in the same direction as the movement of the meshing position with the wave gear 32, which is the input, by the difference in the number of teeth. Therefore, the reduction ratio Z1 is Z r2 / (Z r2 -Z r1 )=63 / (66-63)=21.

[0058] Conversely, if the second internal gear 14 with fewer teeth is fixed and the first internal gear 12 with more teeth is set as the output, the first internal gear 12 with more teeth will move in the opposite direction to the movement of the meshing position with the strain wave gear 32, which is the input, and the reduction ratio will be Z r1 / (Z r2 -Z r1 )=66 / (63-663)=-22.

[0059] In this way, the reduction ratio is determined by the number of teeth Z of the first internal teeth 12a, regardless of the number of teeth of the external teeth 32p, 32q of the wave gear 32. r1 and the number of teeth Z of the second internal teeth 14a r2 It is determined by.

[0060] Next, the conditions for the differential gear mechanism 10 to be established will be explained.

[0061] |Z r2 -Z r1 | is the number of leaves, and Z r1 =66, Z r2 In the example of =63, there are 3 leaves.

[0062] The number of teeth of the external teeth 32p and 32q of the strain wave gear 32 is Z r1 ,Z r2 However, to match the meshing state of the three leaves, the number of teeth of the external teeth 32p, 32q of the strain wave gear 32 must be |Z r2 -Z r1 must have the same divisors as |

[0063] The differential gear mechanism 10 has three leaves, which provides a better balance of rotation transmission than the two-leaf configuration described below, and because it meshes at three points, it can be stronger than the two-leaf configuration.

[0064] A flexible wave gear 32 that is radially flexible is extremely effective in eliminating backlash in the meshing of the wave gear 32 with the first internal gear 12 and second internal gear 14. The wave generator 40 causes the wave gear 32 to mesh closely with the first internal teeth 12 a and second internal teeth 14 a, completely eliminating backlash and increasing the strength of the meshing of the teeth.

[0065] The thin, flexible wave gear 32 is manufactured as a cylindrical gear and is then placed inside the internal teeth 12a, 14a and deformed so that the external teeth 32p, 32q mesh with the internal teeth 12a, 14a. To insert the wave gear 32 inside the internal teeth 12a, 14a, the tip diameters of the external teeth 32p, 32q when the wave gear 32 is cylindrical are made smaller than the tip diameters of the internal teeth 12a, 14a. Furthermore, the planetary gear 42 is inserted inside the wave gear 32 and deformed so that the wave gear 32 meshes with the internal teeth 12a, 14a as a three-lobe gear. Therefore, the external teeth 42a, 44a, 46a of the planetary gear 42, auxiliary planetary gear 44, and sun gear 46, as well as the internal teeth 32a of the wave gear 32, are spur teeth.

[0066] The auxiliary planetary gear 44 meshes with the sun gear and the strain wave gear, but does not push out the strain wave gear 32 so that the strain wave gear 32 meshes with the first internal gear 12 and the second internal gear 14. The auxiliary planetary gear 44 can be omitted, but providing it increases the strength of the rotation transmission. In other words, to suddenly stop rotation, the teeth need to be strong enough to withstand inertial forces, and providing the auxiliary planetary gear 44 that meshes with the strain wave gear 32 reinforces the strength of the teeth, making sudden stopping possible.

[0067] Next, a method for designing the gears of the differential gear mechanism 10 will be described.

[0068] The number of teeth on the internal teeth 12a, 14a of the two internal gears 12, 14 is set to 63 and 66, respectively. Of the two internal gears 12, 14, the gear with the greater number of teeth (multiple gear) and the gear with the fewer number of teeth (pinion gear) are designed. The reference pitch circle is set to 51.6. Then, the transverse module is calculated using the reference pitch circle / number of teeth. Next, the normal pressure angle is set to 40 degrees and the helix angle to 30 degrees, and the normal pitch and normal module are calculated. The calculation results are shown in Table 1 below. [Table 1]

[0069] Next, calculate a virtual internal gear with the average transverse module of the two internal gears. The normal facewidth reduction of this virtual internal gear is set to zero. In order for the external gear to mesh with the two internal gears without backlash, the tooth space widths of the two internal gears must be the same value corresponding to the tooth width of the external gear. Determine the normal facewidth reduction of the two internal gears so that the tooth space width of the internal gear matches the tooth width of the external gear.

[0070] Specifically, as shown in Table 2 below, the normal face width reduction amount for the internal gear with the greater number of teeth (multiple gear) is 0.01819, reducing the face width and increasing the tooth space width, while the internal gear with the fewer teeth (minor gear) reduces the tooth space width by -0.01819 to match the tooth space width of the virtual internal gear. The calculation results are shown in Table 2. [Table 2]

[0071] Next, a three-lobe external gear (strain wave gear 32) is designed. To calculate the reference pitch of a three-lobe gear, the circumference must be calculated from the major axis length (a) and minor axis length (b), just as with an ellipse. In this example, the major axis (a) is 25.8, half of the reference pitch circle's 51.6, but the minor axis length (b) is set as follows:

[0072] There are two limitations to setting the minor axis length. First, a three-lobe external gear transforms a circular object into three lobes. Therefore, if the circumferential length of a three-lobe external gear interferes with the tooth addendum of the gear, it cannot be inserted into the internal teeth. Second, if the difference between the major axis length (a) and the minor axis length (b) also interferes with the tooth addendum, it will not become a strain wave gear.

[0073] If the major axis length (a) is 25.8 and the minor axis length (b) is 24.2, the circumference is 157.4813, and the radius of the circular gear before it was made into three lobes is 50.1278. Therefore, the difference from the internal gear 51.6 is 1.7215, which is half the difference, 0.7361. Therefore, the maximum addendum length of the internal and external teeth (external gear with three lobes) is 0.368. Furthermore, the difference between the major axis length of 25.8 and the minor axis length of 24.2 is 1.6, which is greater than 0.368 and does not pose a problem.

[0074] Therefore, the transverse pitch of the three-leaf external gear is 2.4997, which is the circumference of 157.4813 divided by the number of teeth of the fixed gear, 63. The specifications of the designed three-leaf external gear are shown in Table 3 below. [Table 3] These external teeth are meshed with a virtual internal gear. The number of teeth is set to 63, the number of teeth for the smaller internal gear. The transverse pressure angle is the same as for the virtual internal gear and the two internal gears. The normal module is also matched to the virtual internal gear to calculate the helix angle. This makes it possible to calculate the external teeth with the same normal pitch that mesh with the virtual internal gear. Furthermore, by adjusting the normal facewidth reduction amount and reducing it by 0.0521 mm, it is possible to design an external gear that meshes with the tooth spaces of the two internal gears without backlash.

[0075] By increasing the front pressure angle between the outer teeth 32p, 32q and the internal teeth 12a, 14a of the wave gear 32, it is possible to realize a mechanism that can rotate smoothly even without backlash. In other words, because the planetary gear 42 pushes the wave gear 32 from the inside, the wave gear 32 is firmly coupled with the internal gears 12, 14, and backlash can be reduced to zero.

[0076] Furthermore, the first external teeth 32p of the wave gear 32 mesh with the first internal teeth 12a, and the second external teeth 32q mesh with the second internal teeth .

[0077] The internal teeth 12a, 14a and the external teeth 32p, 32q are double-helical meshed, allowing them to rotate in the radial direction but not move in the axial direction. This means that the two internal gears 12, 14 do not need to use expensive bearings such as cross roller bearings that are fixed in the axial direction but rotate freely in the radial direction.

[0078] The wave generator 40 placed inside the wave gear 32 is a spur-tooth planetary mechanism, so by inserting the planetary mechanism inside the wave gear 32 during assembly, the wave gear 32 can be easily transformed into a three-lobe gear.

[0079] The internal teeth 32a of the wave gear 32 are spur teeth, which allows the wave gear 32 to deform more flexibly than helical teeth, etc. Therefore, the number of teeth of the internal teeth 32a and external teeth 32p, 32q of the wave gear 32 can be reduced, and a smaller reduction ratio can be achieved.

[0080] <Example 1-2> A three-leaf differential gear mechanism 10a configured using bearings 41 will be described with reference to Fig. 7. The differential gear mechanism 10a is configured in substantially the same manner as the differential gear mechanism 10 of Example 1. In the following, the same reference numerals are used for the same components as in Example 1-1, and differences from Example 1-1 will be mainly described.

[0081] Fig. 7(a) is a horizontal cross-sectional view of the differential gear mechanism 10a, and Fig. 7(b) is a vertical cross-sectional view of the differential gear mechanism 10a. As shown in Fig. 7, in the differential gear mechanism 10a, similar to the differential gear mechanism 10 of the first embodiment, a wave gear 32a that meshes with the first internal gear 12 and the second internal gear 14 is disposed inside the first internal gear 12 and the second internal gear 14.

[0082] The inner peripheral surface 32s of the wave gear 32a is smooth, and a wave generator 40a including a bearing 41 and a drive shaft 43 is disposed inside the wave gear 32a. The bearing 41 is disposed between the inner peripheral surface 32s of the wave gear 32a and the outer peripheral surface 43s of the drive shaft 43, which has a substantially triangular cross section, and the wave gear 32a deforms along the outer peripheral surface 43s of the drive shaft 43 via the bearing 41. When the drive shaft 43 rotates, the position at which the wave gear 32a meshes with the first internal gear 12 and the second internal gear 14 moves circumferentially. A hollow hole 43k is formed in the drive shaft 43, which is concentric with the center of rotation of the drive shaft 43. The drive shaft 43 may be solid and not have the through hole 43k.

[0083] <Example 1-3> A two-tooth differential gear mechanism 10b will be described with reference to FIG.

[0084] Fig. 8(a) is a cross-sectional view of the differential gear mechanism 10b, and Fig. 8(b) is a longitudinal-sectional view of the differential gear mechanism 10b. As shown in Fig. 8, the differential gear mechanism 10b has a wave generator 40b arranged inside the strain wave gear 32, and the wave generator 40b has two planetary gears 42b arranged around a sun gear 46b.

[0085] Example 1-4 A six-tooth differential gear mechanism 10c will be described with reference to FIG.

[0086] Fig. 9 is a cross-sectional view of the differential gear mechanism 10c. As shown in Fig. 9, the differential gear mechanism 10c has a wave generator 40c arranged inside the wave gear 32, which serves as a wave generator. The wave generator 40c is made up of six planetary gears 42c arranged around a sun gear 46c.

[0087] Next, a paradox planetary gear mechanism as a differential gear mechanism of a second embodiment will be described with reference to FIGS.

[0088] Example 2-1 The differential gear mechanism 11 will be described with reference to FIGS.

[0089] Fig. 10(a) is a cross-sectional view of the differential gear mechanism 11, and Fig. 10(b) is a longitudinal cross-sectional view of the differential gear mechanism 11. Fig. 11 is an explanatory diagram of the auxiliary internal gears 13k, 15k and the auxiliary gear 23. As shown in Figs. 10 and 11, the differential gear mechanism 11 has a first internal gear 13 having first internal teeth 13a and a second internal gear 15 having second internal teeth 15a arranged coaxially adjacent to each other, and an external gear unit 31 having three planetary gears 22 arranged around a sun gear 24 is arranged inside the first internal gear 13 and the second internal gear 15.

[0090] The outer circumferential surface of the planetary gear 22 is formed with first external teeth 22p that mesh with the first internal teeth 13a of the first internal gear 13 and second external teeth 22q that mesh with the second internal teeth 15a of the second internal gear 15. The sun gear 24 is formed with first external teeth 24p that mesh with the first external teeth 22p of the planetary gear 22 and second external teeth 24q that mesh with the second external teeth 22q of the planetary gear 22.

[0091] The first external teeth 22p and the second external teeth 22q are helical gears that twist in opposite directions, and have the same number of teeth, normal module, normal pitch, and helix angle. Therefore, the portion where the first external teeth 22p are formed and the portion where the second external teeth 22q are formed function as helical external gears with the same number of teeth and the same tooth profile.

[0092] The first internal gear 13a and the second internal gear 15a are helical gears that twist in opposite directions and have different numbers of teeth. Therefore, the first internal gear 13 and the second internal gear are helical internal gears with different numbers of teeth.

[0093] First inner teeth 13a and first outer teeth Tooth 2 2p, the first pair of second inner teeth 15a and the second outer teeth Tooth 2 In either one or both of the second pairs of 2q, the helix angles of the parallel shafts are different. By making the helix angles of the parallel shafts different, it is possible to make the reference circle diameters of the first internal teeth 13a and the second internal teeth 15a, which have different numbers of teeth, the same value, even if the first pair and the second pair have the same module.

[0094] The normal tooth groove width of the first internal teeth 13a is equal to the normal tooth width of the first external teeth 22p, and the normal tooth groove width of the second internal teeth 15a is equal to the normal tooth width of the second external teeth 22q. This makes it possible to make the helical meshing pitch circle diameters of the first internal teeth 13a and the second internal teeth 15a, which have different numbers of teeth, the same value.

[0095] By making the reference circle diameter and pitch circle diameter of each of the first internal teeth 13a and the second internal teeth 15a the same value, the helices can be meshed with each other without applying addendum shift, and a decrease in gear strength can be suppressed.By making the reference circle diameter and pitch circle diameter of each of the first internal teeth 13a and the second internal teeth 15a approximately the same value, the amount of addendum can be minimized, and a decrease in gear strength can be suppressed.

[0096] The helical teeth of the first internal teeth 13a and the first external gear 22p mesh without backlash because the normal tooth space width of the first internal teeth 13a is equal to the normal tooth space width of the first external teeth 22p. The helical teeth of the second internal teeth 15a and the second external gear 22q mesh without backlash because the normal tooth space width of the second internal teeth 15a is equal to the normal tooth space width of the second external teeth 22q.

[0097] The planetary gears 42 and the sun gear 44 are double helical gears. Such gears are easy to roll and can be rolled precisely, so they can be manufactured at extremely low cost.

[0098] A first auxiliary internal gear 13k having spur gear internal teeth 13b formed thereon is press-fitted and fixed to the stepped portion 13x of the first internal gear 13. The number of teeth of the internal teeth 13b of the first auxiliary internal gear 13k is equal to the number of teeth of the first internal teeth 13a of the first internal gear 13.

[0099] A second auxiliary internal gear 15k having spur gear internal teeth 15b formed thereon is press-fitted and fixed to the stepped portion 15x of the second internal gear 15. The number of teeth of the internal teeth 15b of the second auxiliary internal gear 15k is equal to the number of teeth of the second internal teeth 15a of the second internal gear 15.

[0100] An auxiliary gear 23 having a hollow hole 23x is fixed by press fitting to shaft ends 22m, 22n of the planetary gear 22. The auxiliary gear 23 has spur teeth with the same number of teeth as the external teeth 22p, 22q of the planetary gear 22, and rotates integrally with the planetary gear 22.

[0101] The auxiliary gear 23 press-fitted onto one shaft end 22m of the planetary gear 22 meshes with the first auxiliary internal gear 13k, and the auxiliary gear 23 press-fitted onto the other shaft end 22n of the planetary gear 22 meshes with the auxiliary internal gear 15k.

[0102] Since the first auxiliary internal gear 13k, the second auxiliary internal gear 15k and the auxiliary gear 23 are made up of spur teeth, the first auxiliary internal gear 13k and the second auxiliary internal gear 15k are meshed with the auxiliary gear 23 which has spur teeth of the same reference pitch, so that the first auxiliary internal gear 13k and the second auxiliary internal gear 15k are shifted like normal paradox gears.

[0103] The first auxiliary internal gear 13k and the second auxiliary internal gear 15k are thin, and the tooth trace length of the first auxiliary internal gear 13k and the second auxiliary internal gear 15k is shorter than the tooth trace length of the first internal gear 13 and the second internal gear 15. Therefore, loss due to meshing between the first auxiliary internal gear 13k and the second auxiliary internal gear 15k and the auxiliary gear 23 can be ignored in practical use.

[0104] Since the position of the planetary gear 22 relative to the sun gear 24 and the internal gears 13 and 15 is uniquely determined, a carrier is basically not required. However, some positioning is required during assembly, so assembly is performed using a temporary carrier. In this case, if the planetary gear 22 is rotatably supported and positioned using the through holes 22x formed in the planetary gear 22, the differential gear mechanism 11 can be easily assembled. Once assembly is complete, the differential gear mechanism 11 can operate even without the carrier. Note that the planetary gear 22 can also be assembled without forming the through holes 22x.

[0105] By eliminating the carrier, the differential gear mechanism 11 can be made smaller. Also, since friction loss caused by the rotation of the carrier is eliminated, higher efficiency can be achieved.

[0106] Fig. 12 is an enlarged cross-sectional view of a main portion of the first internal gear 13 and the second internal gear 15. As shown in Fig. 12, the first internal gear 13 and the second internal gear 15 have opposing annular recesses 13v and 15v formed on opposing surfaces 13s and 15s, respectively, and a ring-shaped solid lubricant member 26 made of a solid lubricant solidified with resin is disposed in one recess 15v, while an O-ring 28 is disposed in the other recess 13v. As the first internal gear 13 and the second internal gear 15 rotate relative to each other, the O-ring 28 slides against the solid lubricant member 26.

[0107] By fitting the solid lubricant 26 while deforming the O-ring 28, the solid lubricant 26 always serves as a sliding bearing between the first internal gear 13 and the second internal gear 15, and even with slight wear, it continues to perform its lubricating and sealing functions. As the solid lubricant wears, its surface becomes mirror-finished, providing a sealing effect, and the O-ring elastically deforms, constantly pressing against the solid lubricant 26 and preventing it from being damaged.

[0108] The configuration shown in FIG. 12 may be provided to the first internal gear 13 and the second internal gear 15 of the differential gear mechanisms 10, 10a, 10b, and 10c of the first embodiment.

[0109] Next, a method for designing the differential gear mechanism 11 will be described.

[0110] (1) Match the shape of the internal tooth grooves. First, the shapes of the tooth spaces of the internal teeth 13a, 15a of the two internal gears 13, 15 are made to match, in order to simultaneously mesh the two internal gears 13, 15 with different numbers of teeth with an external gear with the same number of teeth.

[0111] In this case, the reference pitch diameters are the same but the number of teeth is different, so the transverse modules are different. If the helix angles of the two internal teeth 13a and 15a are equal, the transverse modules and the normal modules calculated from the helix angles will be different.

[0112] To match the shapes of the two tooth spaces, calculate the two tooth space widths using a common reference pitch diameter and the number of teeth of the two internal gears. At this time, adjust the normal face width reduction amount so that the tooth space widths of the two tooth spaces are the same value. The calculation results are shown in Table 4 below. [Table 4]

[0113] Conventional differential gear mechanisms use two internal gears with different meshing pitch circle diameters. In contrast, the differential gear mechanism 11 matches the shapes of the tooth spaces between the two internal teeth 13a and 15a, making the reference pitch circle diameter and meshing pitch circle diameter of the two internal gears 13 and 15 the same value.

[0114] (2) Next, set the tooth profile of the external gear so that it meshes with the tooth space of the average module without backlash.

[0115] There has been a method to mesh two internal gears with different numbers of teeth. In other words, the method meshes them with the same helix angle. With this method, even if the tooth space shape is the same, the pitch circle that meshes with the external teeth is different, so it cannot solve problems such as efficiency.

[0116] Therefore, a new meshing method is applied to the differential gear mechanism 11. The new method is to make the normal pitch equal by matching the normal modules. This method has not been used with parallel-axis helical gears until now.

[0117] The normal module is a function of the helix angle and the transverse module, i.e., "normal module = transverse module x COS (helical angle)". The average module is Transverse module = Reference pitch circle / Number of teeth. However, the helix angle is equal to the two internal teeth. An external tooth equivalent to this tooth normal module is calculated.

[0118] The transverse module is the reference pitch circle / number of teeth. The internal teeth of the aforementioned average module are not gears with an integer number of teeth, so the meshing gears are actual gears, and the number of teeth is different. Therefore, the reference pitch circle is the same, but the calculation of the number of teeth must be different.

[0119] The sun gear 24 and planet gears 22 are calculated in the same way as the paradox planetary gear mechanism.

[0120] The internal teeth that mesh with the reference pitch circle are the number of teeth on the sun gear + the number of teeth on the planet gear x 2, so if there are 17 planet gear teeth and 36 sun gear teeth, there will be 70 teeth. The average module is 1.7029 and the number of teeth is 70.4681. The transverse module of this gear = reference pitch circle / number of teeth, so it is 1.7029.

[0121] Therefore, since the number of teeth is different, the front module can be calculated, but it differs from the average module.

[0122] If the normal modules are equal, then the normal module = transverse module x COS (helix angle), so the helix angles of the gears will be different. The normal pressure angles will also be different.

[0123] The calculation results are shown in Table 5 below. [Table 5] In other words, in the prior art, it was thought that only gears with the same helix angle could mesh, but they can be meshed by making the normal modules equal. Also, in order to rotate and mesh with the next gear, the normal pitch must be equal.

[0124] Next, the external gears, that is, the planet gear 22 and the sun gear 24, will be described.

[0125] 19, the external teeth 22p and 24q of the planetary gear 22, which is an external gear, mesh with two internal teeth 13a and 15a, which have different numbers of teeth, at a reference pitch circle. In other words, when the internal teeth 13a and 15a mesh with the external teeth 22p and 24q, the meshing pitch circle diameter and the reference pitch circle diameter are the same value.

[0126] A design example of the sun gear 24 and the planetary gears 22 is shown in Table 6 below. [Table 6]

[0127] To increase efficiency, meshing is required only near the reference pitch circle. It is also necessary to avoid interference between the external teeth 22p and 24q of the small-diameter planetary gear 22 and the internal teeth 13a and 15a of the large-diameter internal gears 13 and 15. Therefore, the sun gear 24 and planetary gears 22 have low teeth. The front pressure angle is 40 degrees, which is larger than that of a standard gear (20 degrees). Therefore, rotation is possible even with zero backlash.

[0128] By making the tooth space shapes of two internal gears with different numbers of teeth equal by increasing or decreasing the normal face width, and then meshing the external gears that mesh seamlessly with the tooth space with the same normal module and normal normal pitch, it is possible to mesh gears with different helix angles and normal pressure angles at a reference pitch circle.In addition, by making the external teeth and two internal teeth low, meshing occurs only near the reference pitch circle, resulting in high efficiency, and by increasing the transverse pressure angle, the gears can rotate while meshing without backlash.

[0129] The meshing of the differential gear mechanism 11 can be easily verified because it involves meshing of the tooth normal pressure angle and helix angle. The method of setting the tooth profiles of the two internal teeth 13a, 15a with different numbers of teeth and the external teeth 42p, 42q that mesh with them can be applied to differential gear mechanisms such as strain wave gears and paradox planetary gears.

[0130] The meshing in the differential gear mechanism 11 is a three-dimensional meshing technique that changes the torsion angle, and the range of meshing that can be achieved is widened, thereby achieving better performance than conventional techniques.

[0131] Next, as a third embodiment, an assembly combining a strain wave gear mechanism and a motor will be described with reference to FIGS.

[0132] Example 3-1 An assembly 50 in which the differential gear mechanism 10 of the first embodiment is combined with a motor 60 will be described with reference to FIG.

[0133] Fig. 13(a) is a horizontal cross-sectional view of the assembly 50, and Fig. 13(b) is a vertical cross-sectional view of the assembly 50. As shown in Fig. 13, the assembly 50 is configured such that the first internal gear 12 of the differential gear mechanism 10 is coupled to the end face of the motor 60, the rotating rotor 62 of the motor 60 is coupled to the sun gear 46 of the differential gear mechanism 10, and the second internal gear 14 is rotated by the driving of the motor 60. The hollow hole 47 of the sun gear 46 and the hollow hole 63 of the motor 60 are in communication with each other.

[0134] Example 3-2 An assembly 52 in which the differential gear mechanism 11 of the second embodiment is combined with a motor 60 will be described with reference to FIG.

[0135] Fig. 14(a) is a horizontal cross-sectional view of assembly 52, and Fig. 14(b) is a vertical cross-sectional view of assembly 52. ​​As shown in Fig. 14, assembly 52 is configured such that first internal gear 13 of differential gear mechanism 11 is coupled to the end face of motor 60, and rotor 62 of motor 60 is coupled to sun gear 24 of differential gear mechanism 11, so that second internal gear 15 rotates when motor 60 is driven. Hollow hole 25 of sun gear 24 and hollow hole 63 of motor 60 are in communication.

[0136] Example 3-3 An assembly 54 in which a motor 60 is incorporated inside the differential gear mechanism 10 of the first embodiment will be described with reference to FIG.

[0137] Fig. 15(a) is a horizontal cross-sectional view of the assembly 54, and Fig. 15(b) is a vertical cross-sectional view of the assembly 54. As shown in Fig. 15, the components constituting the motor 60 are arranged in the hollow hole 47 of the sun gear 46 so that the sun gear 46 serves as the outer rotor of the motor 70. That is, a stator 62 wound with a winding 64 is arranged inside the hollow hole 47 of the sun gear 46, and the stator 62 and the first internal gear 12 of the differential gear mechanism 10 are fixed to a common base (not shown). A permanent magnet 66 is fixed to the inner peripheral surface of the sun gear 24, and the sun gear 46 is integrated with the rotor of the motor 60, so that the sun gear 46 rotates as the outer rotor of the motor 60.

[0138] Example 3-4 An assembly 56 in which a motor 70 is incorporated inside the differential gear mechanism 11 of the second embodiment will be described with reference to FIG.

[0139] Fig. 16(a) is a horizontal cross-sectional view of the assembly 56, and Fig. 16(b) is a vertical cross-sectional view of the assembly 56. As shown in Fig. 16, the components that make up the motor 70 are arranged in the hollow hole 25 of the sun gear 24 so that the sun gear 24 serves as the outer rotor of the motor 70. That is, a stator 72 wound with a winding 74 is arranged inside the hollow hole 25 of the sun gear 24, and the stator 72 and the first internal gear 13 of the differential gear mechanism 11 are fixed to the common base 58. A permanent magnet 76 is fixed to the inner circumferential surface of the sun gear 24, and the sun gear 24 is integrated with the rotor of the motor 70, so that the sun gear 24 rotates as the outer rotor of the motor 70.

[0140] <Summary> The differential gear mechanism described above can suppress a decrease in gear strength. In addition, it is easy to assemble, has a simple configuration, and can be made into a hollow structure.

[0141] The present invention is not limited to the above-described embodiment, but can be implemented with various modifications.

[0142] For example, the numbers of teeth of the first internal teeth 12a; 13a, the second internal teeth 14a; 15a, and the external teeth 32p, 32q; 22p, 22q are not limited to those in the embodiment and can be selected appropriately. Furthermore, the meshing pitch circle diameters of the first internal teeth 12a; 13a and the second internal teeth 14a; 15a do not need to be completely the same as the reference pitch circle diameter, and may be slightly different values. [Explanation of symbols]

[0143] 10,11 Differential gear mechanism 12,13 First internal gear 12a,13a 1st internal tooth 14,15 Second internal gear 14a, 15a Second inner teeth 20 External gear unit 22 Planetary gear 22p 1st external tooth 22q 2nd external tooth 24 Sun Gear 30,31 External gear unit 32a internal teeth 32 Strain Wave Gear 32p 1st external tooth 32q 2nd external tooth 40,40a Wave Generator 42 Planetary gear 44 Auxiliary planetary gear 46 Sun Gear 50, 52, 54, 56 Assembly 60,70 motor

Claims

1. a first internal gear having first internal teeth; a second internal gear arranged coaxially with the first internal gear and having second internal teeth; an external gear unit disposed inside the first internal gear and the second internal gear, the external gear unit having first external teeth that mesh with the first internal teeth and second external teeth that mesh with the second internal teeth simultaneously at a plurality of circumferentially spaced locations; Equipped with a gear ratio between the first internal teeth and the first external teeth and a gear ratio between the second internal teeth and the second external teeth are different from each other, the first external teeth and the second external teeth include helices that are helical spiraled in opposite directions to each other and have the same number of teeth, tooth normal module, tooth normal normal pitch, and helix angle; The first internal teeth and the second internal teeth include helices that are twisted in opposite directions and have different numbers of teeth, the helical helix angles of the first internal teeth and the first external teeth are different from each other, or the helical helix angles of the second internal teeth and the second external teeth are different from each other, or the helical helix angles of the first internal teeth and the first external teeth are different from each other and the helical helix angles of the second internal teeth and the second external teeth are different from each other, a helical normal tooth gap width of the first internal tooth is equal to a helical normal tooth width of the first external tooth, a helical normal tooth gap width of the second internal tooth is equal to a helical normal tooth width of the second external tooth, The external gear unit is a wave gear having a cylindrical shape, the first external teeth and the second external teeth being formed on an outer circumferential surface thereof, and being flexible in a radial direction; a wave generator that is disposed inside the wave gear and presses the wave gear radially outward to simultaneously mesh the first pair and the second pair at a plurality of locations and moves the meshing positions of the first pair and the second pair in the circumferential direction; a differential gear mechanism including:

2. Spur teeth are formed on the inner peripheral surface of the wave gear, The wave generator comprises: a plurality of planetary gears that mesh with the spur teeth of the strain wave gear; a sun gear that is arranged coaxially with the first internal gear and the second internal gear and meshes with the planetary gear; 2. The differential gear mechanism of claim 1, comprising:

3. 3. The differential gear mechanism according to claim 2, further comprising an auxiliary planetary gear between adjacent planetary gears, the auxiliary planetary gear meshing with the spur teeth of the strain wave gear and the sun gear.

4. The first external teeth and the second external teeth include helical teeth having the same number of teeth, tooth normal module, tooth normal normal pitch, and helix angle, the first internal teeth and the second internal teeth include helical teeth having different numbers of teeth from each other, 4. The differential gear mechanism according to claim 1, wherein a helix angle of the double helices of the first internal teeth is different from a helix angle of the first external teeth, or a helix angle of the second internal teeth is different from a helix angle of the second external teeth, or a helix angle of the double helices of the first internal teeth is different from a helix angle of the first external teeth and a helix angle of the second internal teeth is different from a helix angle of the second external teeth.

5. A first internal gear having a first internal tooth; a second internal gear arranged coaxially with the first internal gear and having second internal teeth; an external gear unit disposed inside the first internal gear and the second internal gear, the external gear unit having first external teeth that mesh with the first internal teeth and second external teeth that mesh with the second internal teeth simultaneously at a plurality of circumferentially spaced locations; Equipped with a gear ratio between the first internal teeth and the first external teeth and a gear ratio between the second internal teeth and the second external teeth are different from each other, the first external teeth and the second external teeth include helices that are helical spiraled in opposite directions to each other and have the same number of teeth, tooth normal module, tooth normal normal pitch, and helix angle; The first internal teeth and the second internal teeth include helices that are twisted in opposite directions and have different numbers of teeth, the helical helix angles of the first internal teeth and the first external teeth are different from each other, or the helical helix angles of the second internal teeth and the second external teeth are different from each other, or the helical helix angles of the first internal teeth and the first external teeth are different from each other and the helical helix angles of the second internal teeth and the second external teeth are different from each other, a helical normal tooth gap width of the first internal tooth is equal to a helical normal tooth width of the first external tooth, a helical normal tooth gap width of the second internal tooth is equal to a helical normal tooth width of the second external tooth, The first internal gear and the second internal gear have annular recesses formed on surfaces that face each other in the axial direction, and A differential gear mechanism, wherein a ring-shaped solid lubricating member is disposed in one of the recesses and an O-ring is disposed in the other recess, the O-ring abutting against the solid lubricating member.

6. The first external teeth and the second external teeth include helical teeth having the same number of teeth, tooth normal module, tooth normal normal pitch, and helix angle, the first internal teeth and the second internal teeth include helical teeth having different numbers of teeth from each other, 6. The differential gear mechanism according to claim 5, wherein a helix angle of the double helices of the first internal teeth is different from a helix angle of the first external teeth, or a helix angle of the second internal teeth is different from a helix angle of the second external teeth, or a helix angle of the double helices of the first internal teeth is different from a helix angle of the first external teeth and a helix angle of the second internal teeth is different from a helix angle of the second external teeth.

7. A differential mechanism and a motor are provided. The differential mechanism includes: a first internal gear having first internal teeth; a second internal gear arranged coaxially with the first internal gear and having second internal teeth; an external gear unit disposed inside the first internal gear and the second internal gear, the external gear unit having first external teeth that mesh with the first internal teeth and second external teeth that mesh with the second internal teeth simultaneously at a plurality of circumferentially spaced locations; Equipped with a gear ratio between the first internal teeth and the first external teeth and a gear ratio between the second internal teeth and the second external teeth are different from each other, the first external teeth and the second external teeth include helices that are helical spiraled in opposite directions to each other and have the same number of teeth, tooth normal module, tooth normal normal pitch, and helix angle; The first internal teeth and the second internal teeth include helices that are twisted in opposite directions and have different numbers of teeth, the helical helix angles of the first internal teeth and the first external teeth are different from each other, or the helical helix angles of the second internal teeth and the second external teeth are different from each other, or the helical helix angles of the first internal teeth and the first external teeth are different from each other and the helical helix angles of the second internal teeth and the second external teeth are different from each other, a helical normal tooth gap width of the first internal tooth is equal to a helical normal tooth width of the first external tooth, a helical normal tooth gap width of the second internal tooth is equal to a helical normal tooth width of the second external tooth, The external gear unit is a plurality of planetary gears on which the first external teeth and the second external teeth are formed; a sun gear that is arranged coaxially with the first internal gear and the second internal gear and meshes with the planetary gears, A hollow hole is formed in the sun gear, The motor is an actuator configured in the hollow hole of the sun gear such that the sun gear is an outer rotor.

8. The first external teeth and the second external teeth include helical teeth having the same number of teeth, tooth normal module, tooth normal normal pitch, and helix angle, the first internal teeth and the second internal teeth include helical teeth having different numbers of teeth from each other, 8. The actuator according to claim 7, wherein a helix angle of the helical teeth of the first internal teeth is different from a helix angle of the helical teeth of the first external teeth, or a helix angle of the helical teeth of the second internal teeth is different from a helix angle of the helical teeth of the second external teeth, or a helix angle of the helical teeth of the first internal teeth is different from a helix angle of the helical teeth of the first external teeth and a helix angle of the helical teeth of the second internal teeth is different from a helix angle of the helical teeth of the second external teeth.

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