Gear mechanism

Abstract

To obtain a gear mechanism which can suppress a velocity variation, and is compact in a size.SOLUTION: A gear mechanism has an outer tooth circular gear having M-pieces of teeth, and rotating at a first center axis, and an outer tooth non-circular gear having N-pieces of teeth, and rotating at a second center axis which is separated from the first center axis by a prescribed distance D. The outer tooth circular gear has a tooth tip part, and a tooth side part located at a side part of the tooth tip part, and having a radius-r circular shape, and non-circular teeth of the outer tooth non-circular gear have tooth tip parts, and tooth side parts located at side parts of the tooth tip parts, and contacting with the circular gear tooth side parts. In the non-circular gear tooth side parts, at least a part of shapes sets a virtual circle having a radius D×N / (M+N) with the second center axis as a center as a fixed circle, and also sets a virtual circle having a radius D×M / (M+N) with the first center axis as a center as a moving circle. An epitrochoid curve which is drawn as a drawing point with the circular gear tooth side part as a center is formed so that the epitrochoid curve becomes an offset epitrochoid curve which is offset by a length r, and the number of teeth of the outer tooth circular gear is equal to or larger than 4, and equal to or smaller than 10.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] The present invention relates to a gear mechanism. [Background technology]

[0002] 2. Description of the Related Art A gear mechanism including an externally toothed gear that rotates about a first central axis and an externally toothed gear that rotates about a second central axis that is spaced a predetermined distance from the first central axis is already well known. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-82893 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the past, such gear mechanisms had a drawback in that while one externally toothed gear rotates at a constant speed, the other externally toothed gear would wobble, causing speed variations (called speed variations). Therefore, there was a demand for a gear mechanism with a new tooth shape that does not have such a drawback.

[0005] Moreover, in view of commercial merit, there has been a demand for a gear mechanism that is free of the above-mentioned drawbacks and is furthermore compact.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide a gear mechanism which suppresses speed variations and is compact, thereby offering great commercial merit. [Means for solving the problem]

[0007] The main invention to achieve the above object is: A gear mechanism having an externally-toothed arc-shaped gear having M arc-shaped teeth and rotating around a first central axis, and an externally-toothed non-circular gear having N non-circular teeth and rotating around a second central axis separated by a predetermined distance D from the first central axis, the arc-shaped tooth of the externally toothed arc-shaped gear has an arc-shaped gear tooth tip portion and an arc-shaped gear tooth side portion located on a side of the arc-shaped gear tooth tip portion and having a radius r, a non-circular tooth of the externally toothed non-circular gear has a non-circular gear tooth tip portion and a non-circular gear tooth side portion located on a side of the non-circular gear tooth tip portion and in contact with the circular gear tooth side portion, The non-circular gear tooth side portion has a shape of at least a part thereof, When a virtual circle of radius D×N / (M+N) centered on the second central axis is defined as a fixed circle, a virtual circle of radius D×M / (M+N) centered on the first central axis is defined as a moving circle, and the center of the circular gear tooth side portion is defined as a drawing point, the epitrochoid curve drawn is offset by a length r to become an offset epitrochoid curve, It is formed, The gear mechanism is characterized in that the number of teeth M of the externally toothed circular gear is 4 or more and 10 or less.

[0008] Other features of the present invention will become apparent from the following detailed description of the present invention and the accompanying drawings. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram for explaining a gear mechanism 1 according to the present embodiment. [Diagram 2] FIG. 2 is an explanatory diagram for explaining a circular tooth 14 of the externally toothed circular gear 10 according to the present embodiment. [Diagram 3] This is a diagram showing how to draw the epitrochoid curve EP. [Figure 4] This figure shows another way of drawing the epitrochoid curve EP. [Diagram 5] 10 is an explanatory diagram for explaining the behavior of a cam mechanism including a cam 60 relating to an epitrochoid curve EP and a cam follower 62a with a radius of 0. FIG. [Figure 6]FIG. 11 is an explanatory diagram for explaining an offset epitrochoid curve OEP. [Figure 7] 11 is an explanatory diagram for explaining the behavior of a cam mechanism including a cam 60 relating to an offset epitrochoid curve OEP and a cam follower 62a relating to a circle of radius r. FIG. [Figure 8] 3 is an explanatory diagram for explaining non-circular teeth 34 of the externally toothed non-circular gear 30 according to the present embodiment. FIG. [Figure 9] FIG. 13 is a diagram showing the correspondence relationship of tooth sides. [Figure 10] 1 is a conceptual diagram showing a state in which an externally toothed circular gear 10 and an externally toothed non-circular gear 30 are in contact at two points. [Figure 11] FIG. 11 is an explanatory diagram for explaining a contact ratio condition. [Figure 12] 1 is a diagram showing the pitch angle θ1 and the straddle angle θ2 for each of three cases. [Figure 13] FIG. 13 is an explanatory diagram for explaining a cut-down limit. [Figure 14] 11 is a diagram showing the relationship between the number of teeth N of the externally toothed non-circular gear 30 and the value of the left side of a conditional expression. [Figure 15] FIG. 4 is an explanatory diagram for explaining a gear mechanism 100 according to a second embodiment. [Figure 16] 4 is a diagram showing the relationship between the number of teeth M of the externally toothed circular gear 10 and the value of the left side of a conditional expression. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] At least the following matters will become apparent from the description of this specification and the accompanying drawings.

[0011] A gear mechanism having an externally-toothed arc-shaped gear having M arc-shaped teeth and rotating around a first central axis, and an externally-toothed non-circular gear having N non-circular teeth and rotating around a second central axis separated by a predetermined distance D from the first central axis, the arc-shaped tooth of the externally toothed arc-shaped gear has an arc-shaped gear tooth tip portion and an arc-shaped gear tooth side portion located on a side of the arc-shaped gear tooth tip portion and having a radius r, a non-circular tooth of the externally toothed non-circular gear has a non-circular gear tooth tip portion and a non-circular gear tooth side portion located on a side of the non-circular gear tooth tip portion and in contact with the circular gear tooth side portion, The non-circular gear tooth side portion has a shape of at least a part thereof, When a virtual circle of radius D×N / (M+N) centered on the second central axis is defined as a fixed circle, a virtual circle of radius D×M / (M+N) centered on the first central axis is defined as a moving circle, and the center of the circular gear tooth side portion is defined as a drawing point, the epitrochoid curve drawn is offset by a length r to become an offset epitrochoid curve, It is formed, The gear mechanism, wherein the number of teeth M of the externally toothed circular gear is 4 or more and 10 or less.

[0012] Such a gear mechanism can suppress speed variations and can also be made compact, making it possible to realize a gear mechanism that has great commercial merit.

[0013] A gear mechanism having an externally-toothed arc-shaped gear having M arc-shaped teeth and rotating around a first central axis, and an externally-toothed non-circular gear having N non-circular teeth and rotating around a second central axis separated by a predetermined distance D from the first central axis, the arc-shaped tooth of the externally toothed arc-shaped gear has an arc-shaped gear tooth tip portion and an arc-shaped gear tooth side portion located on a side of the arc-shaped gear tooth tip portion and having a radius r, a non-circular tooth of the externally toothed non-circular gear has a non-circular gear tooth tip portion and a non-circular gear tooth side portion located on a side of the non-circular gear tooth tip portion and in contact with the circular gear tooth side portion, The non-circular gear tooth side portion has a shape of at least a part thereof, When a virtual circle of radius D×N / (M+N) centered on the second central axis is defined as a fixed circle, a virtual circle of radius D×M / (M+N) centered on the first central axis is defined as a moving circle, and the center of the circular gear tooth side portion is defined as a drawing point, the epitrochoid curve drawn is offset by a length r to become an offset epitrochoid curve, It is formed, The gear mechanism, wherein the number of teeth N of the externally toothed non-circular gear is 3 or more and 10 or less.

[0014] Such a gear mechanism can suppress speed variations and can also be made compact, making it possible to realize a gear mechanism that has great commercial merit.

[0015] ===Gear Mechanism 1 According to the Present Embodiment=== Next, a gear mechanism 1 according to the present embodiment will be described with reference to Fig. 1. Fig. 1 is an explanatory diagram for explaining the gear mechanism 1 according to the present embodiment.

[0016] The gear mechanism 1 includes two externally toothed gears (external gears) that mesh with each other. As will be described in detail later, the teeth of one gear are arc-shaped, while the teeth of the other gear are not. Therefore, for convenience, the former gear is referred to as the externally toothed circular gear 10, and the latter gear is referred to as the externally toothed non-circular gear 30.

[0017] The externally toothed arc gear 10 is a gear that rotates around a first central axis 12 and has M (eight in this embodiment) teeth (for convenience, referred to as arc teeth 14). In other words, the number of teeth M of the externally toothed arc gear 10 is eight.

[0018] The externally toothed non-circular gear 30 is a gear that rotates around a second central axis 32 that is a predetermined distance (i.e., axis distance D) away from the first central axis 12, and has N (16 in this embodiment) teeth (for convenience, referred to as non-circular teeth 34). In other words, the number of teeth N of the externally toothed circular gear 10 is 16.

[0019] The arc-shaped teeth 14 and the non-arc-shaped teeth 34 mesh with each other.

[0020] It should be noted that the number of teeth M and the number of teeth N are not limited to 8 and 16 (the number of teeth M and the number of teeth N may be the same number).

[0021] Moreover, the externally toothed circular gear 10 has M (8) arc-shaped teeth 14, the externally toothed non-circular gear 30 has N (16) arc-shaped teeth 14, and the number of teeth of the externally toothed non-circular gear 30 is N / M (2) times the number of teeth of the externally toothed circular gear 10. Based on this, the size of the externally toothed non-circular gear 30 is twice that of the externally toothed circular gear 10. More specifically, the value M / (M+N) times (1 / 3) the center distance D is used as the pitch radius R1 of the pitch circle PC1 of the externally toothed circular gear 10, and the value N / (M+N) times (2 / 3) the center distance D is used as the pitch radius R2 of the pitch circle PC2 of the externally toothed non-circular gear 30.

[0022] ===About arc tooth 14=== Next, the arc-shaped teeth 14 of the externally toothed arc-shaped gear 10 according to this embodiment will be described with reference to Figures 1 and 2. Figure 2 is an explanatory diagram for explaining the arc-shaped teeth 14 of the externally toothed arc-shaped gear 10 according to this embodiment. Note that in Figure 2, for the sake of ease of understanding, only one arc-shaped tooth 14 is shown, and the other arc-shaped teeth 14 are omitted.

[0023] The arc-shaped tooth 14 has a tooth side portion with an arc curve that differs from the involute curve that is common in gears. That is, the arc-shaped tooth 14 has an arc-shaped gear tooth tip portion 16 and an arc-shaped gear tooth side portion 18 that is located on the side of the arc-shaped gear tooth tip portion 16 and has an arc shape of radius r. Two tooth sides are provided as the arc-shaped gear tooth side portion 18 (referred to as a first arc-shaped gear tooth side portion 18a and a second arc-shaped gear tooth side portion 18b, both of which have the same radius r).

[0024] The second arc-shaped gear tooth side portion 18b is provided on the opposite side to the first arc-shaped gear tooth side portion 18a when viewed from the arc-shaped gear tooth tip portion 16. The center C2 of the second arc-shaped gear tooth side portion 18b is different from the center C1 of the first arc-shaped gear tooth side portion 18a. The distance L from the first central axis 12 to the center C1 is the same as the distance L from the first central axis 12 to the center C2 (this distance L can be set arbitrarily). The radius r and the pitch angle α of the arc shown in FIG. 2 (the face width can be adjusted by adjusting this angle) can also be set arbitrarily.

[0025] The tooth height can also be set arbitrarily, but in this embodiment, a module m (= pitch circle radius R1 × 2 / number of teeth M) is used to define the arc tooth 14 as a circular arc cut at a position -1.25 × m on the inside and a position + m on the outside based on the pitch circle PC1 of radius R1.

[0026] ===Non-circular tooth 34=== Next, a description will be given of the non-circular teeth 34 of the externally toothed non-circular gear 30 according to this embodiment. The shape of the non-circular teeth 34 is an offset epitrochoid curve OEP obtained by offsetting the epitrochoid curve EP, as will be described below.

[0027] <<<About Epitrochoid Curve EP>>> A trochoid curve is defined as a curve traced by fixed points (also called drawing points) inside or outside a circle when the circle is rolled along a curve (circles being a special case of the circle) without slipping. In particular, a curve made up of two circumscribed circles (i.e., a curve traced by drawing points inside or outside the moving circle when the moving circle is rolled along a fixed circle without slipping) is called an epitrochoid curve EP.

[0028] FIG. 3 is a diagram showing how to draw an epitrochoid curve EP. In the upper left diagram, a fixed fixed circle (second friction wheel 52) is located on the left, and a moving moving circle (first friction wheel 50) is located on the right. In this example, the radius of the fixed circle (second friction wheel 52) is twice the radius of the moving circle (first friction wheel 50), and the drawing point P is located within the moving circle (first friction wheel 50) and on the X-axis. From this state, the moving circle (first friction wheel 50) revolves while rotating along the fixed circle (second friction wheel 52) (upper left diagram → upper right diagram → lower left diagram → lower right diagram. θ1 represents the rotation angle, and θ2 represents the revolution angle), and when the revolution angle reaches 360 degrees, the moving circle (first friction wheel 50) returns to its original position. When the moving circle (first friction wheel 50) moves in this way, the trajectory drawn by the drawing point P becomes the epitrochoid curve EP.

[0029] The method of drawing the epitrochoid curve EP shown in Figure 3 above follows the definition of the epitrochoid curve EP, but there are other ways to draw it. Figure 4 shows another way to draw the epitrochoid curve EP.

[0030] In the example of FIG. 3, the second friction wheel 52 is fixed, but in this example, the second friction wheel 52 rotates. Also, in the example of FIG. 3, the first friction wheel 50 revolves while rotating, but in this example, the first friction wheel 50 only rotates and does not revolve. That is, in this example, the first friction wheel 50 and the second friction wheel 52 rotate (rotate) so as not to slip on each other, with the rotation centers of the first friction wheel 50 and the second friction wheel 52 fixed (upper left figure → upper right figure → lower left figure → lower right figure. θ1 represents the rotation angle of the first friction wheel 50, and θ2 represents the rotation angle of the second friction wheel 52). Then, when the first friction wheel 50 moves, the trajectory drawn by the drawing point P (the arrangement of the drawing point P is the same as in the example of FIG. 3) becomes an epitrochoid curve EP, but in this example, the XY coordinate system rotates together with the rotation of the second friction wheel 52 (therefore, the trajectory drawn in the past moves together with the rotation of the XY coordinate system). In this way, in this example, when the second friction wheel 52 is rotated, the first friction wheel 50 rolls without slipping, and the path drawn by the drawing point P is drawn from the XY coordinate system fixed to the second friction wheel 52. The lower right diagram of Fig. 4 shows the state in which the first friction wheel 50 rotates twice (θ1 = 720 degrees), the second friction wheel 52 rotates once (θ2 = 360 degrees), the XY coordinate system returns to the original position, and the epitrochoid curve EP is drawn. As is clear from a comparison with the lower right diagram of Fig. 3, the method of this example can also draw the same epitrochoid curve EP as shown in Fig. 3.

[0031] Next, let us consider the behavior of the cam mechanism when we assume (assume) that the epitrochoid curve EP is a cam 60 and the drawing point P is a cam follower 62a with a radius of 0 (in other words, a diameter infinitely close to 0). Figure 5 is an explanatory diagram for explaining the behavior of a cam mechanism that includes a cam 60 relating to the epitrochoid curve EP and a cam follower 62a with a radius of 0.

[0032] Fig. 5 is basically the same as Fig. 4. However, in Fig. 5, the epitrochoid curve EP drawn in Fig. 4 is shown in its entirety in four full diagrams (the epitrochoid curve EP is shown in its entirety not only in the lower right diagram but also in the upper left diagram, upper right diagram, and lower left diagram), and this is used as the cam 60. In addition to this, the drawn point P in Fig. 4 is set as a cam follower 62a with a radius of 0 (in other words, a diameter infinitely close to 0), and the part from the drawn point P to the center of the first friction wheel 50 is set as an arm 62b, and a follower 62 having the cam follower 62a and the arm 62b is assumed.

[0033] 5, when the epitrochoid curve EP rotates with the rotation of the second friction wheel 52 (upper left diagram → upper right diagram → lower left diagram → lower right diagram), the drawing point P, which moves with the rotation of the first friction wheel 50, moves on the epitrochoid curve EP. In other words, the cam 60 (epitrochoid curve EP) and the cam follower 62a (drawing point P) move in a state of engagement (contact) with each other.

[0034] Furthermore, since the first friction wheel 50 and the second friction wheel 52 rotate without slipping on each other, when the second friction wheel 52 rotates at a constant speed, the first friction wheel 50 also rotates at a constant speed. This relationship also applies to the cam 60 (epitrochoid curve EP) and the cam follower 62a (drawing point P). That is, when the second friction wheel 52 rotates at a constant speed, the cam 60 (epitrochoid curve EP) rotating with the second friction wheel 52 also rotates at a constant speed, and the cam follower 62a (drawing point P) rotating with the first friction wheel 50 rotating at a constant speed also rotates at a constant speed. In this way, the cam 60 (epitrochoid curve EP) and the cam follower 62a (drawing point P) perform a constant speed rotational motion together while engaged (contacted) with each other. That is, even if the cam 60 (epitrochoid curve EP) rotates at a constant speed, the cam follower 62a (drawing point P) is unstable and the speed varies (hereinafter referred to as speed variation). This is appropriately suppressed.

[0035] <<<About the Offset Epitrochoid Curve OEP>>> In the above, the epitrochoid curve EP is assumed to be the cam 60, and the drawing point P is assumed to be the cam follower 62a with a radius of 0 (in other words, a diameter infinitely close to 0). Here, however, an offset epitrochoid curve OEP associated with the epitrochoid curve EP is defined, and the behavior of the cam mechanism is considered when the offset epitrochoid curve OEP is assumed to be the cam 60, and a circle with a radius of r centered on the drawing point P of the epitrochoid curve EP is assumed to be the cam follower 62a. Figure 6 is an explanatory diagram for explaining the offset epitrochoid curve OEP. Figure 7 is an explanatory diagram for explaining the behavior of a cam mechanism including a cam 60 associated with the offset epitrochoid curve OEP and a cam follower 62a associated with a circle of radius r.

[0036] A tangent line TA is drawn at each point on the epitrochoid curve, and a point is taken that is offset inward from each point in the normal direction to the tangent line TA by a certain distance. The curve connecting these points is defined as the offset epitrochoid curve OEP. In other words, as shown in Figure 6, the locus of the inner end 70b of the bar when the bar 70 is moved so that the line LI perpendicular to the bar 70 at the outer end 70a of the bar 70 always becomes the tangent line TA to the epitrochoid curve EP is the offset epitrochoid curve OEP.

[0037] Then, the offset epitrochoid curve OEP with the certain distance as length r (i.e., the offset epitrochoid curve OEP offset by the length r from the epitrochoid curve EP) is assumed to be the cam 60, and the circle with a radius of r centered on the drawing point P of the epitrochoid curve EP is assumed to be the cam follower 62a. That is, in Fig. 7, the offset epitrochoid curve OEP offset by the length r from the epitrochoid curve EP is shown in all four diagrams, and this is assumed to be the cam 60. In addition to this, a circle with a radius of r centered on the drawing point P is assumed to be the cam follower 62a, and an arm 62b is assumed to extend from the drawing point P to the center of the first friction wheel 50, and a follower 62 having the cam follower 62a and the arm 62b is assumed.

[0038] 7, when the offset epitrochoid curve OEP rotates with the rotation of the second friction wheel 52 (epitrochoid curve EP) (upper left → upper right → lower left → lower right), the cam follower 62a, which moves with the rotation of the first friction wheel 50 (drawing point P), operates while maintaining a state of contact with the offset epitrochoid curve OEP. In other words, the cam 60 (offset epitrochoid curve OEP offset by a length r from the epitrochoid curve EP) and the cam follower 62a (circle of radius r) move in a state of engaging (contacting) with each other.

[0039] Furthermore, since the first friction wheel 50 and the second friction wheel 52 rotate without slipping on each other, when the second friction wheel 52 rotates at a constant speed, the first friction wheel 50 also rotates at a constant speed. This relationship also applies to the cam 60 (offset epitrochoid curve OEP obtained by offsetting the epitrochoid curve EP by a length r) and the cam follower 62a (circle with radius r). That is, when the second friction wheel 52 rotates at a constant speed, the cam 60 (offset epitrochoid curve OEP) that rotates with the second friction wheel 52 also rotates at a constant speed, and the cam follower 62a (circle with radius r) that rotates with the first friction wheel 50 that rotates at a constant speed (revolving around the center of the first friction wheel 50) also rotates at a constant speed. In this way, the cam 60 (offset epitrochoid curve OEP) and the cam follower 62a (circle with radius r) perform a constant speed rotational motion together while engaged (contacted) with each other. That is, even though the cam 60 (offset epitrochoid curve OEP) rotates at a constant speed, the cam follower 62a (circle of radius r) is unstable and the speed varies (speed variation) is appropriately suppressed.

[0040] <<<Regarding the shape of the non-circular teeth 34>>> As described above, assuming that the offset epitrochoid curve OEP, which is obtained by offsetting the epitrochoid curve EP by a length r, is the cam 60, and the cam follower 62a is the circle of radius r centered on the drawing point P of the epitrochoid curve EP, this cam mechanism exerts an effect of appropriately suppressing speed variations (hereinafter also referred to as the speed variation suppression effect). Therefore, this matter is applied to the design of the teeth of the gear mechanism 1.

[0041] This point will be described with reference to Figures 1, 2, and 7 to 9. Figure 8 is an explanatory diagram for explaining the non-circular teeth 34 of the externally toothed non-circular gear 30 according to this embodiment. Figure 9 will be described later.

[0042] As described above, the arc-shaped tooth 14 has arc-shaped gear tooth side portions 18 (first arc-shaped gear tooth side portion 18a and second arc-shaped gear tooth side portion 18b) with an arc-shaped curve. Here, since the arc-shaped gear tooth side portions 18 are part of a circle with a radius r, the first arc-shaped gear tooth side portion 18a (for example, the arc-shaped gear tooth side portion 18 indicated by reference symbol TC1) of one arc-shaped tooth 14 can correspond to the cam follower 62a (see the upper diagrams of FIGS. 7 and 8). In this case, a virtual circle of radius R2 (= axis distance D × number of teeth N / (number of teeth M + number of teeth N)) centered on the second central axis 32 is defined as a fixed circle (second friction wheel 52), a virtual circle of radius R1 (= axis distance D × number of teeth M / (number of teeth M + number of teeth N)) centered on the first central axis 12 is defined as a moving circle (first friction wheel 50), and the center C1 of the first circular arc gear tooth side portion TC1 is defined as a drawing point P. The offset epitrochoid curve OEP (see FIG. 7), which is obtained by offsetting the epitrochoid curve EP by a length r, corresponds to the cam 60. Therefore, if the shape of the non-circular gear tooth side portion 38 in contact with the circular arc gear tooth side portion 18 (first circular arc gear tooth side portion 18a) is defined as the offset epitrochoid curve OEP (see the upper diagram in FIG. 8), a gear mechanism 1 having a speed variation suppressing effect can be realized.

[0043] In this way, the shape of at least a part of the non-circular gear tooth side portion 38 in this embodiment is formed so that when a virtual circle of radius R2 (= axis distance D × number of teeth N / (number of teeth M + number of teeth N)) centered on the second central axis 32 is taken as a fixed circle (second friction wheel 52), a virtual circle of radius R1 (= axis distance D × number of teeth M / (number of teeth M + number of teeth N)) centered on the first central axis 12 is taken as a moving circle (first friction wheel 50), and the center C1 of the first circular arc gear tooth side portion 18a is taken as the drawing point P, the epitrochoid curve EP drawn is offset by a length r to form an offset epitrochoid curve OEP (see Figure 7).

[0044] Like the arc-shaped tooth 14, the non-arc gear tooth 34 has a non-arc gear tooth tip portion 36 in addition to a non-arc gear tooth side portion 38. In other words, the non-arc gear tooth 34 has the non-arc gear tooth tip portion 36 and a non-arc gear tooth side portion 38 located on the side of the non-arc gear tooth tip portion 36.

[0045] A specific example of the design of the non-circular tooth 34 according to this embodiment is as follows. First, one first arc-shaped gear tooth side portion 18a (for example, the arc-shaped gear tooth side portion 18 indicated by reference symbol TC1) is selected, and the offset epitrochoid curve OEP corresponding thereto is drawn. Then, as with the arc-shaped tooth 14, a portion of the offset epitrochoid curve OEP that may come into contact with the first arc-shaped gear tooth side portion TC1 is cut at a position -1.25×m on the inside and a position +m on the outside based on the pitch circle PC2 of radius R2, and this is set as the non-circular gear tooth side portion 38 (indicated by reference symbol TN1a) of the non-circular tooth 34 (however, the tooth height can be set arbitrarily, as with the arc-shaped tooth 14).

[0046] In this embodiment, the number of teeth of the externally toothed non-circular gear 30 is twice the number of teeth of the externally toothed arc-shaped gear 10, so that the externally toothed non-circular gear 30 rotates once while the externally toothed arc-shaped gear 10 rotates twice. Therefore, there are two non-circular gear tooth side portions 38 that contact the first arc-shaped gear tooth side portion TC1, so the non-circular gear tooth side portion 38 (indicated by symbol TN1b) is also obtained by cutting the offset epitrochoid curve OEP that is point-symmetrical to the non-circular gear tooth side portion TN1a as viewed from the second center axis 32. Due to the above-mentioned design, the non-circular gear tooth side portions TN1a and TN1b according to this embodiment have an overall shape that is the offset epitrochoid curve OEP, and therefore the non-circular gear tooth side portions TN1a and TN1b are formed so that the shape of all the portions that contact the arc-shaped gear tooth side portion 18 is the offset epitrochoid curve OEP.

[0047] Next, the above-mentioned items (procedures) are also performed on the second arc-circular gear tooth side portion 18b (designated by reference symbol TC2) provided on the opposite side of the first arc-circular gear tooth side portion TC1 as viewed from the arc-circular gear tooth tip portion 16 (see the lower diagram in FIG. 8). That is, the offset epitrochoid curve OEP corresponding to the second arc-circular gear tooth side portion TC2 is drawn. Then, for a portion of the offset epitrochoid curve OEP that may come into contact with the second arc-circular gear tooth side portion TC2, the offset epitrochoid curve OEP is cut at a position of -1.25×m on the inside and a position of +m on the outside based on the pitch circle PC2 of radius R2, and this is defined as the non-circular gear tooth side portion 38 (designated by reference symbol TN2a) of the non-circular tooth 34. Furthermore, the offset epitrochoid curve OEP that is point-symmetrical to the non-circular gear tooth side portion TN2a as viewed from the second center axis 32 is also cut and defined as the non-circular gear tooth side portion 38 (designated by reference symbol TN2b). In addition, the non-arc gear tooth side portion TN2a (non-arc gear tooth side portion TN2b) is a tooth side portion of another (adjacent) non-arc tooth 34 (also called the second non-arc tooth 34b) different from the non-arc tooth 34 (also called the first non-arc tooth 34a) having the non-arc gear tooth side portion TN1a (non-arc gear tooth side portion TN1b).

[0048] Then, by carrying out the above-mentioned items (procedures) for the other seven arc-circular teeth 14, all of the non-arc-circular teeth 34 can be obtained. Fig. 9 is a diagram showing the correspondence of the tooth sides. Non-arc-circular gear tooth side portions 38 obtained by carrying out the above-mentioned procedures for the first arc-circular gear tooth side portion TC1 (TC3, TC5, TC7, TC9, TC11, TC13, TC15) are indicated by symbols TN1a and TN1b (TN3a and TN3b, TN5a and TN5b, TN7a and TN7b, TN9a and TN9b, TN11a and TN11b, TN13a and TN13b, TN15a and TN15b), and The non-circular gear tooth side portions 38 obtained by subjecting the two-circular gear tooth side portions TC2 (TC4, TC6, TC8, TC10, TC12, TC14, TC16) to the above procedure are indicated by the symbols TN2a and TN2b (TN4a and TN4b, TN6a and TN6b, TN8a and TN8b, TN10a and TN10b, TN12a and TN12b, TN14a and TN14b, TN16a and TN16b).

[0049] Like the arc-shaped gear tooth side portion 18, the non-arc gear tooth 34 also has two non-arc gear tooth side portions 38, namely, a first non-arc gear tooth side portion 38a (for example, the non-arc gear tooth side portion 38 indicated by the symbol TN3a) and a second non-arc gear tooth side portion 38b (for example, the non-arc gear tooth side portion 38 indicated by the symbol TN2a) provided on the opposite side of the first non-arc gear tooth side portion 38a when viewed from the non-arc gear tooth tip portion 36.

[0050] In the above description, the externally toothed non-circular gear 30 is formed by carrying out the above steps when the externally toothed arc-shaped gear 10 is in the rotation position shown in Fig. 9, but this rotation position is arbitrary. For example, a similar externally toothed non-circular gear 30 can be formed by carrying out the above steps when the externally toothed arc-shaped gear 10 is in a position slightly rotated from the rotation position shown in Fig. 9.

[0051] === Number of teeth M of externally toothed circular arc gear 10 === Conventional involute gears are manufactured by a conventional method (e.g., hob method) using a dedicated gear processing machine equipped with a dedicated gear cutting tool. It is known that when the number of teeth of the gear to be manufactured is small, it becomes difficult to manufacture a gear mechanism that adequately exerts the above-mentioned speed variation suppression effect using the gear cutting tool (conventional method). In reality, it has been impossible to realize an involute gear that exerts such an effect and has a number of teeth M of 10 or less.

[0052] In contrast, the externally toothed circular gear 10 according to the present embodiment does not have the manufacturing constraints described above for gears with a small number of teeth. This is because the externally toothed circular gear 10 is manufactured using the manufacturing technology for cams (particularly parallel cams) and cam followers, unlike involute gears. Specifically, like cams and cam followers, the externally toothed circular gear 10 is manufactured by end milling or, if small, by wire cutting. In other words, the profiles of the externally toothed circular gear 10 and the externally toothed non-circular gear 30 having the corresponding cam curve are digitally displayed by the analysis method of the cam and cam follower, and these data are simulated on a three-dimensional CAD to check for backlash and tooth interference. After a preliminary check of the three-dimensional data, the externally toothed circular gear 10 and the corresponding externally toothed non-circular gear 30 are manufactured by end milling using an NC machining center or by wire cutting.

[0053] As described above, in the externally toothed circular gear 10 according to this embodiment, there are no manufacturing constraints on gears with a small number of teeth, and it is possible to set the number of teeth M to 10 or less. This makes it possible to realize compact gears, and furthermore, it is commercially advantageous because gears with a single-digit number of teeth can be appealed to potential buyers.

[0054] As described above, in the externally toothed arc gear 10 according to the present embodiment, the number of teeth M can be 10 or less, but the number of teeth M cannot be reduced as much as desired. That is, there is a lower limit of the number of teeth M (a value below which the externally toothed arc gear 10 that adequately exhibits the speed variation suppression effect cannot be realized under any circumstances). In order to realize an externally toothed arc gear 10 that adequately exhibits the speed variation suppression effect, the meshing ratio needs to be 1 or more, and the lower limit is derived from such a condition (the condition that the meshing ratio is 1 or more; hereinafter, referred to as the meshing ratio condition). That is, a lower limit of the number of teeth M that can (may possibly) satisfy the meshing ratio condition is derived. Such matters will be described in detail below.

[0055] <<<Lower limit value of number of teeth M of externally toothed circular gear 10>>> FIG. 10 is a conceptual diagram showing a state where the externally toothed arc-shaped gear 10 and the externally toothed non-circular gear 30 are in contact at two points. FIG. 11 is an explanatory diagram for explaining the mesh ratio condition. The upper diagram shows a case where the mesh ratio is greater than 1, the center diagram shows a case where the mesh ratio is 1, and the lower diagram shows a case where the mesh ratio is less than 1. FIG. 12 is a diagram corresponding to FIG. 11, and shows the pitch angle θ1 and the straddle angle θ2 for each of the three cases. Note that in FIG. 11 and FIG. 12, the arc teeth of the externally toothed arc-shaped gear 10 are shown with an arc radius of 0. That is, in this section, the description will be given assuming that the arc teeth of the externally toothed arc-shaped gear 10 are ones whose arc diameter is infinitesimally close to 0 (that is, a follower having a cam follower and an arm whose arc diameter is infinitesimally close to 0).

[0056] In order to ensure that there is no backlash between the externally toothed circular gear 10 and the externally toothed non-circular gear 30 and that both gears always rotate in unison, the meshing ratio needs to be 1 or more. A "mesh ratio of 1" means that both gears are always in contact at two or more points (see FIG. 10. Contact points are indicated by reference numeral 80), and in reality, the cycle repeats: two points contact (long term) → three points contact (instantaneous) → two points contact (long term) → three points contact (instantaneous) →...

[0057] As shown in Fig. 11, in order for the externally toothed circular gear 10 and the externally toothed non-circular gear 30 to always be in contact at two or more points, when one arc-shaped tooth (designated with reference symbol A1) of the externally toothed circular gear 10 faces the center of the externally toothed non-circular gear 30, the adjacent arc-shaped teeth (designated with reference symbol A2) on both sides (upper and lower) must be in contact with the externally toothed non-circular gear 30. Looking at Fig. 11 while focusing on this condition, it can be seen that the meshing ratio is 1 or more in the upper and central diagrams of Fig. 11, but in the lower diagram, the arc-shaped tooth designated with reference symbol A2 is not in contact with the externally toothed non-circular gear 30 and the meshing ratio is less than 1. Note that the change in the number of contact points in the diagram above is 2 points of contact (long term) → 3 points of contact (long term) → 2 points of contact (long term) → 3 points of contact (long term) → ···, and the change in the number of contact points in the diagram below is 1 point of contact (long term) → 2 points of contact (long term) → 1 point of contact (long term) → 2 points of contact (long term) → ···.

[0058] This condition can be expressed by the magnitude relationship between the pitch angle θ1 of the externally toothed non-circular gear 30 and the angle between the centers of the arcs of the externally toothed non-circular gear 10 as viewed from the center of the externally toothed non-circular gear 30 (for convenience, this angle is called the straddling angle θ2). When comparing these angles, as shown in the upper diagram of FIG. 12, when the straddling angle θ2 is greater than the pitch angle θ1, the externally toothed non-circular gear 30 is sandwiched between the two outer externally toothed non-circular gears 10, and the three-point contact can be maintained for a while even if the rotation proceeds from the three-point contact state shown in the figure, so the meshing ratio exceeds 1. Also, as shown in the center diagram of FIG. 12, when the straddling angle θ2 and the pitch angle θ1 are equal, the apexes of the externally toothed non-circular gear 10 and the externally toothed non-circular gear 30 on both outer sides coincide with each other, so that when the rotation proceeds from the three-point contact state shown in the figure, the contact becomes two-point, and the meshing ratio is 1. Furthermore, as shown in the lower diagram of FIG. 12, when the straddle angle θ2 is smaller than the pitch angle θ1, there is one-point contact, so the meshing ratio is smaller than 1.

[0059] From the above, the condition for the contact ratio is straddle angle θ2 - pitch angle θ1 ≧ 0. Note that θ1 and θ2 are respectively expressed as θ1 = 2π / N and θ2 = 2·tan using the axis distance D, the distance L (the distance from the center of rotation of the externally toothed circular gear 10 to the center of the arc, i.e., the length of the arm of the externally toothed circular gear 10 (follower) in Figs. 11 and 12), the number of teeth M of the externally toothed circular gear 10, and the number of teeth N of the externally toothed non-circular gear 30. -1 (L·sin(2π / M) / (DL·cos(2π / M))). Therefore, the condition is 2·tan -1 (L sin(2π / M) / (DL cos(2π / M)))-2π / N≧0.

[0060] Next, in order to simplify the conditional expression, the distance L is set to a value at the rounding down limit. Here, the rounding down limit will be explained with reference to Fig. 13. Fig. 13 is an explanatory diagram for explaining the rounding down limit.

[0061] The left diagram of FIG. 13 corresponds to the lower right diagram of FIG. 4 (upper left diagram of FIG. 5). That is, the left diagram of FIG. 13 is a diagram in which the epitrochoid curve EP (cam 60) is drawn by moving the drawing point P (the cam follower 62a of the follower 62). The center diagram of FIG. 13 is a diagram in which the epitrochoid curve EP (cam 60) is drawn in a similar manner by making the length of the arm 62b of the follower 62 (i.e., the distance L) longer than that of the left diagram of FIG. 13. More specifically, the epitrochoid curve EP (cam 60) is drawn by making the distance L equal to the radius D×M / (M+N) of the first friction wheel 50 (moving circle) (i.e., the drawing point P is located on the first friction wheel 50 (moving circle)). In addition, the right diagram of Figure 13 shows the epitrochoid curve EP (cam 60) drawn in a similar manner, with the length of the arm 62b of the follower 62 (i.e., the distance L) being longer than in the central diagram of Figure 13.

[0062] Focusing on the right diagram of Figure 13, it can be seen that a looped portion (indicated by the symbol LO) occurs in the epitrochoid curve EP (cam 60). This phenomenon is called undercutting, and if undercutting occurs, it is of course impossible to actually manufacture the cam 60. Therefore, it is necessary to set the distance L to a length that does not cause undercutting.

[0063] The branching point for whether or not a rounding down occurs is actually when the distance L = D x M / (M + N), that is, the state shown in the center diagram of Figure 13. That is, if the distance L is made larger than D x M / (M + N), a rounding down occurs, and if the distance L is made smaller than D x M / (M + N), a rounding down does not occur. Therefore, the state shown in the center diagram of Figure 13 is called the rounding down limit.

[0064] And the above condition 2·tan -1 Substitute D×M / (M+N), which is the value at the limit of rounding down, for L in (L·sin(2π / M) / (DL·cos(2π / M)))-2π / N≧0, and rearrange the equation. Then, the condition becomes tan -1 (sin(2π / M) / ((M+N) / M-cos(2π / M)))-π / N≧0.

[0065] The reason why the value at the cut-down limit is substituted for L in the conditional expression, that is, why the case where L = D × M / (M + N) is used to find the lower limit of the number of teeth M, is limited to this case, is as follows: That is, as is clear from Fig. 11, the shorter the distance L (i.e., the length of the follower arm), the more difficult it is to satisfy the conditional expression (the stricter the condition becomes), so the case where L = D × M / (M + N) (the case at the cut-down limit) is the most lenient condition within which the cam mechanism can be realized (the cam 60 can actually be manufactured without cut-down occurring).

[0066] Meanwhile, the purpose of this study is to find the lower limit of the number of teeth M that can satisfy (possibly satisfy) the contact ratio condition. For that reason, it is desirable to find the lower limit under the loosest conditions (for example, if the true lower limit of the number of teeth M is 4 (i.e., if the contact ratio condition can actually be satisfied when the number of teeth M is 4), if the answer is 5 because the condition is too strict, the study will be inappropriate). For these reasons, when finding the lower limit of the number of teeth M using a conditional formula, the value at the cut-down limit is substituted for L in the conditional formula.

[0067] As described above, the externally toothed arc gear 10 is assumed to have an arc tooth with an arc diameter as close to 0 as possible (i.e., a follower having a cam follower and an arm with an arc diameter as close to 0 as possible), and this is for the same reason. That is, as is clear from Fig. 11, the larger the arc diameter is from 0, the smaller the straddle angle θ2 becomes, making it more difficult to satisfy the above condition (the condition becomes stricter). For this reason, the case in which the arc diameter is as close to 0 as possible (the loosest condition) is examined.

[0068] Let's go back to the conditional expression and continue our discussion. The conditional expression is tan -1 (sin(2π / M) / ((M+N) / M-cos(2π / M)))-π / N≧0, which is a function of the number of teeth M and the number of teeth N.

[0069] Fig. 14 is a diagram showing the relationship between the number of teeth N of the externally toothed non-circular gear 30 and the value of the left side of the conditional equation. In this diagram, the horizontal axis represents the number of teeth N (from 1 to 100) of the externally toothed non-circular gear 30, and the vertical axis represents the value of the left side of the conditional equation. There are six graphs, each corresponding to the number of teeth M ranging from 1 to 6. That is, in Fig. 14, the number of teeth N is changed to find the value of the left side of the conditional equation for each of the number of teeth M ranging from 1 to 6.

[0070] As can be seen from FIG. 14, when the number of teeth M is 1 to 3, the value of the left side of the equation never becomes greater than 0, regardless of the number of teeth N (it has been confirmed that when the number of teeth M is 1 to 3, the value of the left side never becomes greater than 0, even if the number of teeth N is set to infinity). Therefore, when the number of teeth M is 1 to 3, the contact ratio condition is not satisfied, despite the relaxed condition, regardless of the number of teeth N. On the other hand, when the number of teeth M is 4 or more, the value of the left side becomes greater than 0, and there are cases where the contact ratio condition is satisfied. From the above, it can be seen that the lower limit of the number of teeth M (the value below which the externally toothed circular arc gear 10 that adequately exerts the speed variation suppression effect cannot be realized in any case) is 4.

[0071] <<<Effectiveness of the Gear Mechanism 1 According to the Present Embodiment>>> The gear mechanism 1 of this embodiment comprises an externally toothed arc-shaped gear 10 having M arc-shaped teeth 14 and rotating around a first central axis 12, and an externally toothed non-arc gear 30 having N non-arc-shaped teeth 34 and rotating around a second central axis 32 a predetermined distance D away from the first central axis 12, and the arc-shaped teeth 14 of the externally toothed arc-shaped gear 10 have an arc-shaped gear tooth tip portion 16 and an arc-shaped gear tooth side portion 18 (for example, the first arc-shaped gear tooth side portion 18a indicated by the symbol TC1 in Figure 8) that is located on the side of the arc-shaped gear tooth tip portion 16 and has an arc shape of radius r.

[0072] The non-circular tooth 34 of the externally toothed non-circular gear 30 has a non-circular gear tooth tip portion 36 and a non-circular gear tooth side portion 38 (e.g., non-circular gear tooth side portion 38 indicated by reference characters TN1a and TN1b in FIG. 8 ) located on the side of the non-circular gear tooth tip portion 36 and in contact with the arc-gear tooth side portion 18 (e.g., first arc-gear tooth side portion 18a indicated by reference character TC1 in FIG. 8 ). The non-circular gear tooth side portion 38 (e.g., non-circular gear tooth side portion 38 indicated by reference characters TN1a and TN1b in FIG. 8 ) is at least a part of The shape is formed so that when a virtual circle of radius R2 (= axis distance D × number of teeth N / (number of teeth M + number of teeth N)) centered on the second central axis 32 is taken as a fixed circle (second friction wheel 52), a virtual circle of radius R1 (= axis distance D × number of teeth M / (number of teeth M + number of teeth N)) centered on the first central axis 12 is taken as a moving circle (first friction wheel 50), and the center C1 of the first circular arc gear tooth side portion 18a is taken as the drawing point P, the epitrochoid curve EP drawn is offset by a length r to become an offset epitrochoid curve OEP (see Figure 7).

[0073] The number of teeth M of the externally toothed arc gear 10 is 4 or more and 10 or less.

[0074] Therefore, as described above, it is possible to realize a gear mechanism 1 which exhibits the effect of suppressing speed variations and is also compact, thereby providing great commercial merit.

[0075] ===Other embodiments=== Although the gear mechanism according to the present invention has been described above based on the above embodiment, the above embodiment is for the purpose of facilitating understanding of the present invention and does not limit the present invention. The present invention can be modified and improved without departing from the spirit and scope of the present invention, and of course, equivalents thereof are included in the present invention.

[0076] In the above embodiment (also referred to as the first embodiment), an example of a gear mechanism 1 is given, which includes an externally toothed circular gear 10 and an externally toothed non-circular gear 30 having an offset epitrochoid curve OEP, and in which compactness is achieved by reducing the number of teeth M of the externally toothed circular gear 10. However, the present invention is not limited to this, and compactness may also be achieved by reducing the number of teeth N of the externally toothed non-circular gear 30.

[0077] FIG. 15 is a diagram corresponding to FIG. 1 and is an explanatory diagram for explaining a gear mechanism 100 according to a second embodiment.

[0078] The gear mechanism 100 of the second embodiment, like the first embodiment, comprises an externally toothed arc-shaped gear 10 having M (16 in this embodiment) arc-shaped teeth 14 and rotating around a first central axis 12, and an externally toothed non-arc gear 30 having N (8 in this embodiment) non-arc-shaped teeth 34 and rotating around a second central axis 32 a predetermined distance D away from the first central axis 12, and the arc-shaped teeth 14 of the externally toothed arc-shaped gear 10 have an arc-shaped gear tooth tip portion 16 and an arc-shaped gear tooth side portion 18 located on the side of the arc-shaped gear tooth tip portion 16 and having an arc-shaped shape of radius r.

[0079] As in the first embodiment, the non-arc tooth 34 of the externally toothed non-arc gear 30 has a non-arc gear tooth tip portion 36 and a non-arc gear tooth side portion 38 located on the side of the non-arc gear tooth tip portion 36 and in contact with the arc-gear tooth side portion 18. The shape of at least a part of the non-arc gear tooth side portion 38 is formed so that when a virtual circle of radius R2 (= axis distance D × number of teeth N / (number of teeth M + number of teeth N)) centered on the second central axis 32 is taken as a fixed circle, a virtual circle of radius R1 (= axis distance D × number of teeth M / (number of teeth M + number of teeth N)) centered on the first central axis 12 is taken as a moving circle, and the center of the first arc-gear tooth side portion 18a is taken as the drawing point, the epitrochoid curve drawn is an offset epitrochoid curve by a length r.

[0080] The number of teeth N of the externally toothed non-circular gear 30 is as follows: First, the externally toothed non-circular gear 30 is also similar in that there are no manufacturing constraints on gears with a small number of teeth.

[0081] That is, conventional involute gears are manufactured by a conventional method (e.g., hob method) using a dedicated gear processing machine equipped with a dedicated gear cutting tool. It is known that when the number of teeth of the gear to be manufactured is small, it becomes difficult to manufacture a gear mechanism that adequately exerts the above-mentioned speed variation suppression effect by using the gear cutting tool (conventional method). In reality, it has been impossible to realize an involute gear that exerts such an effect and has a number of teeth N of 10 or less.

[0082] In contrast, the externally toothed non-circular gear 30 according to the second embodiment does not have the manufacturing constraints described above for gears with a small number of teeth. This is because the externally toothed non-circular gear 30 is manufactured using the manufacturing technology for cams (particularly parallel cams) and cam followers, unlike involute gears. Specifically, like cams and cam followers, the externally toothed non-circular gear 30 is manufactured by end milling or, if small, by wire cutting. In other words, the profile of the externally toothed circular gear 10 and the externally toothed non-circular gear 30 having the corresponding cam curve are digitally displayed by the analysis method of the cam and cam follower, and these data are simulated on a three-dimensional CAD to check for backlash and tooth interference. After the three-dimensional data is checked in advance, the externally toothed circular gear 10 and the corresponding externally toothed non-circular gear 30 are manufactured by end milling on an NC machining center or by wire cutting.

[0083] As described above, in the externally toothed non-circular gear 30 according to the second embodiment, there are no manufacturing constraints on gears with a small number of teeth, and it is possible to set the number of teeth N to 10 or less. This makes it possible to realize compact gears, and furthermore, it is also commercially advantageous since gears with a single-digit number of teeth can be appealed to potential buyers.

[0084] As described above, in the externally toothed non-circular gear 30 according to the second embodiment, the number of teeth N can be set to 10 or less, but the number of teeth N cannot be reduced as much as desired, which is the same as in the externally toothed arc-shaped gear 10 (first embodiment). That is, there is a lower limit of the number of teeth N (a value below which the externally toothed non-circular gear 30 that adequately exerts the speed variation suppression effect cannot be realized under any circumstances). In order to realize an externally toothed non-circular gear 30 that adequately exerts the speed variation suppression effect, the meshing ratio needs to be 1 or more, and the lower limit is derived from the meshing ratio condition, which is the same as in the externally toothed arc-shaped gear 10 (first embodiment). That is, a lower limit of the number of teeth N that can (may possibly) satisfy the meshing ratio condition is derived. These matters will be described in detail below.

[0085] <<<Lower limit of number of teeth N of externally toothed non-circular gear 30>>> When determining the lower limit of the number of teeth N of the externally toothed non-circular gear 30, the above-mentioned conditional formula tan -1 (sin(2π / M) / ((M+N) / M-cos(2π / M)))-π / N≧0 can be used.

[0086] FIG. 16 is a diagram showing the relationship between the number of teeth M of the externally toothed circular gear 10 and the value of the left side of the conditional equation. In this diagram, the horizontal axis represents the number of teeth M (from 1 to 100) of the externally toothed circular gear 10, and the vertical axis represents the value of the left side of the conditional equation. There are six graphs, each corresponding to the number of teeth N ranging from 1 to 6. That is, in FIG. 16, the number of teeth M is changed to find the value of the left side of the conditional equation for each of the number of teeth N ranging from 1 to 6.

[0087] As can be seen from FIG. 16, when the number of teeth N is 1 to 2, the value of the left side of the equation never becomes greater than 0, regardless of the number of teeth N (it has been confirmed that when the number of teeth N is 1 to 2, the value of the left side never becomes greater than 0, even if the number of teeth M is set to infinity). Therefore, when the number of teeth N is 1 to 2, the contact ratio condition is not satisfied, despite the relaxed condition, regardless of the number of teeth M. On the other hand, when the number of teeth N is 3 or more, the value of the left side becomes greater than 0, and there are cases where the contact ratio condition is satisfied. From the above, it can be seen that the lower limit of the number of teeth M (the value below which the externally toothed circular arc gear 10 that adequately exerts the speed variation suppression effect cannot be realized in any case) is 3.

[0088] <<<Effectiveness of the gear mechanism 100 according to the second embodiment>>> The gear mechanism 100 of the second embodiment comprises an externally toothed arc-shaped gear 10 having M arc-shaped teeth 14 and rotating around a first central axis 12, and an externally toothed non-arc gear 30 having N non-arc-shaped teeth 34 and rotating around a second central axis 32 a predetermined distance D away from the first central axis 12, and the arc-shaped teeth 14 of the externally toothed arc-shaped gear 10 have an arc-shaped gear tooth tip portion 16 and an arc-shaped gear tooth side portion 18 located on the side of the arc-shaped gear tooth tip portion 16 and having an arc shape of radius r.

[0089] As in the first embodiment, the non-arc tooth 34 of the externally toothed non-arc gear 30 has a non-arc gear tooth tip portion 36 and a non-arc gear tooth side portion 38 located on the side of the non-arc gear tooth tip portion 36 and in contact with the arc-gear tooth side portion 18. The shape of at least a part of the non-arc gear tooth side portion 38 is formed so that when a virtual circle of radius R2 (= axis distance D × number of teeth N / (number of teeth M + number of teeth N)) centered on the second central axis 32 is taken as a fixed circle, a virtual circle of radius R1 (= axis distance D × number of teeth M / (number of teeth M + number of teeth N)) centered on the first central axis 12 is taken as a moving circle, and the center of the first arc-gear tooth side portion 18a is taken as the drawing point, the epitrochoid curve drawn is an offset epitrochoid curve by a length r.

[0090] The number of teeth M of the externally toothed non-circular gear 30 is 3 or more and 10 or less.

[0091] Therefore, as described above, it is possible to realize a gear mechanism 1 which exhibits the effect of suppressing speed variations and is also compact, thereby providing great commercial merit. [Explanation of symbols]

[0092] 1 Gear mechanism 10 Externally toothed circular gear 12 First central axis 14 Circular Tooth 16 Circular gear tooth tip 18 Circular gear tooth side 18a First circular gear tooth side 18b Second circular gear tooth side 30 Externally toothed noncircular gear 32 Second central axis 34 Non-circular teeth 34a First non-circular tooth 34b Second non-circular tooth 36 Non-circular gear tooth tip 38 Non-circular gear tooth side 38a First non-circular gear tooth side 38b Second non-circular gear tooth side 50 First friction wheel 52 Second friction wheel 60 Cam 62 Follower 62a Cam follower 62b Arm 70 Bar 70a outer edge 70b inner edge 80 contact points 100 Gear mechanism A1 Circular tooth A2 Circular tooth C1 center C2 center D Center distance EP Epitrochoid curve L distance LI Line LO Looped part OEP Offset Epitrochoid Curve P drawing point PC1 Pitch Circle PC2 Pitch Circle R1 Pitch circle radius R2 Pitch circle radius TA tangent α Arc pitch angle TC1 First circular gear tooth side TC2 Second circular gear tooth side TC3 First circular gear tooth side TC4 Second circular gear tooth side TC5 First circular gear tooth side TC6 Second circular gear tooth side TC7 First circular gear tooth side TC8 Second circular gear tooth side TC9 First circular gear tooth side TC10 Second circular gear tooth side TC11 First circular gear tooth side TC12 Second circular gear tooth side TC13 First circular gear tooth side TC14 Second circular gear tooth side TC15 First circular gear tooth side TC16 Second circular gear tooth side TN1a, TN1b Non-circular gear tooth side TN2a, TN2b Non-circular gear tooth side TN3a, TN3b Non-circular gear tooth side TN4a, TN4b Non-circular gear tooth side TN5a, TN5b Non-circular gear tooth side TN6a, TN6b Non-circular gear tooth side TN7a, TN7b Non-circular gear tooth side TN8a, TN8b Non-circular gear tooth side TN9a, TN9b Non-circular gear tooth side TN10a, TN10b Non-circular gear tooth side TN11a, TN11b Non-circular gear tooth side TN12a, TN12b Non-circular gear tooth side TN13a, TN13b Non-circular gear tooth side TN14a, TN14b Non-circular gear tooth side TN15a, TN15b Non-circular gear tooth side TN16a, TN16b Non-circular gear tooth side

Claims

1. A gear mechanism having an externally-toothed arc-shaped gear having M arc-shaped teeth and rotating around a first central axis, and an externally-toothed non-circular gear having N non-circular teeth and rotating around a second central axis separated by a predetermined distance D from the first central axis, the arc-shaped tooth of the externally toothed arc-shaped gear has an arc-shaped gear tooth tip portion and an arc-shaped gear tooth side portion located on a side of the arc-shaped gear tooth tip portion and having an arc shape of a radius r, a non-circular tooth of the externally toothed non-circular gear has a non-circular gear tooth tip portion and a non-circular gear tooth side portion located on a side of the non-circular gear tooth tip portion and in contact with the circular gear tooth side portion, The non-circular gear tooth side portion has a shape of at least a part thereof, When a virtual circle of radius D×N / (M+N) centered on the second central axis is defined as a fixed circle, a virtual circle of radius D×M / (M+N) centered on the first central axis is defined as a moving circle, and the center of the circular-arc gear tooth side portion is defined as a drawing point, the drawn epitrochoid curve is offset by a length r to become an offset epitrochoid curve. It is formed, A gear mechanism, wherein the number of teeth M of the externally toothed circular gear is 4 or more and 10 or less.

2. A gear mechanism having an externally-toothed arc-shaped gear having M arc-shaped teeth and rotating around a first central axis, and an externally-toothed non-circular gear having N non-circular teeth and rotating around a second central axis separated by a predetermined distance D from the first central axis, the arc-shaped tooth of the externally toothed arc-shaped gear has an arc-shaped gear tooth tip portion and an arc-shaped gear tooth side portion located on a side of the arc-shaped gear tooth tip portion and having an arc shape of a radius r, a non-circular tooth of the externally toothed non-circular gear has a non-circular gear tooth tip portion and a non-circular gear tooth side portion located on a side of the non-circular gear tooth tip portion and in contact with the circular gear tooth side portion, The non-circular gear tooth side portion has a shape of at least a part thereof, When a virtual circle of radius D×N / (M+N) centered on the second central axis is defined as a fixed circle, a virtual circle of radius D×M / (M+N) centered on the first central axis is defined as a moving circle, and the center of the circular-arc gear tooth side portion is defined as a drawing point, the drawn epitrochoid curve is offset by a length r to become an offset epitrochoid curve. It is formed, The gear mechanism according to claim 1, wherein the number of teeth N of the externally toothed non-circular gear is 3 or more and 10 or less.

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