Planetary gear device

Abstract

To provide a planetary gear device which is reduced in the surface pressure of the tooth surface of each planetary pinion and is suppressed in an increase of the size of the planetary gear device.SOLUTION: A planetary gear device 10 comprises a first sun gear 12, a second sun gear 14, and a carrier 16 rotatable around a common axis A. The carrier 16 rotatably supports first pinions 24 meshing with the first sun gear 12 and second pinions 26 meshing with the second sun gear 14. The first pinions 24 and the second pinions 26 are arranged alternately in the peripheral direction, and the first pinion 24 meshes with the two second pinions 26 adjacent to each other and the second pinion 26 meshes with the two first pinions 24 adjacent to each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a planetary gear device, and more particularly to the structure thereof. [Background technology]

[0002] A known planetary gear set includes a sun gear, an internally toothed ring gear coaxially disposed with the sun gear, and a planetary carrier coaxially disposed with the sun gear, rotatably supporting planetary pinions meshing with the sun gear and ring gear. Hereinafter, the planetary pinion will be referred to as the pinion, and the planetary carrier will be referred to as the carrier. Typically, one pinion meshes with both the sun gear and the ring gear, but double-pinion planetary gear sets are also known, which include two pinions that mesh with each other, one pinion meshing with the sun gear and the other with the ring gear. Among double-pinion planetary gear sets, planetary gear sets with two sun gears, in other words, two sun gears, are also known.

[0003] Figure 9 of Patent Document 1 below shows a planetary gear device 60 including a first pinion 62 meshing with a sun gear 12 and a second pinion 64 meshing with a ring gear 16, with the first pinion 62 meshing with the two second pinions 64. Note that the reference numerals in parentheses above are the reference numerals used in Patent Document 1 below and are not related to the reference numerals used in the description of the embodiments of the present application. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-76156 Summary of the Invention [Problem to be solved by the invention]

[0005] In the planetary gear device of Patent Document 1, two second pinions mesh with one first pinion, which increases the number of meshing points and reduces the surface pressure on the gear tooth surfaces between the pinions. On the other hand, the number of second pinions is twice as many as the number of first pinions, which tends to make the device larger.

[0006] An object of the present invention is to reduce the surface pressure on the gear tooth surfaces while making the planetary gear device compact. [Means for solving the problem]

[0007] A planetary gear device according to the present invention includes a first gear, a second gear, and a planetary carrier that rotatably supports planetary pinions, all of which are rotatable about a common axis. The planetary pinions include a first pinion arranged on a first orbit about the common axis and meshing with the first gear, and a second pinion arranged on a second orbit about the common axis and meshing with the second gear. The first pinions and second pinions are arranged alternately in the circumferential direction, with each first pinion meshing with two adjacent second pinions, and each second pinion meshing with two adjacent first pinions.

[0008] By meshing each of the first and second pinions with two adjacent first or second pinions, the surface pressure applied to the tooth surfaces of each pinion can be reduced.In addition, the number of first pinions and second pinions can be made the same, which prevents the device from becoming too large.

[0009] The first gear may be a first sun gear located inside a first pinion arranged on the orbital path, and the second gear may be a second sun gear located inside a second pinion arranged on the orbital path. In addition to these two sun gears, a ring gear may be provided that is rotatable around a common axis and meshes with either the first pinion or the second pinion.

[0010] Furthermore, the first gear may be a sun gear located inside a first pinion arranged on the orbital path, and the second gear may be a ring gear located outside a second pinion arranged on the orbital path. [Effects of the Invention]

[0011] The surface pressure applied to the tooth surfaces of the first and second pinions can be reduced, and the device can be prevented from becoming large in size. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view showing a planetary gear device according to an embodiment of the present invention. [Figure 2] FIG. 1 is a front view showing a planetary gear device according to an embodiment of the present invention. [Figure 3] 3A and 3B are diagrams showing meshing states between a first sun gear and a first pinion, and between a second sun gear and a second pinion of the planetary gear device of the present embodiment. [Figure 4] FIG. 4 is a diagram showing meshing conditions of a first sun gear with first and second pinions. [Figure 5] FIG. 4 is a diagram showing meshing conditions of first and second sun gears and first and second pinions. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described below with reference to the drawings. Figures 1 and 2 are diagrams showing the schematic configuration of a planetary gear device 10, with Figure 1 being a perspective view with a part cut away and Figure 2 being a front view.

[0014] Planetary gear set 10 includes a first sun gear 12, a second sun gear 14, and a planetary carrier 16, which are three elements that can rotate relatively to one another around axis A. Hereinafter, planetary carrier 16 will be referred to as carrier 16. First sun gear 12 is fixed to a first sun gear shaft 18 whose central axis is axis A. First sun gear shaft 18 extends from first sun gear 12 toward the front in FIG. 1. Second sun gear 14 is fixed to a second sun gear shaft 20 whose central axis is axis A. Second sun gear shaft 20 extends from second sun gear 14 toward the back in FIG. 1. Carrier 16 is fixed to a hollow carrier shaft 22 whose central axis is axis A. Second sun gear shaft 20 extends through the hollow space in carrier shaft 22.

[0015] The carrier 16 rotatably supports four first planetary pinions 24 that mesh with the first sun gear 12 and four second planetary pinions 26 that mesh with the second sun gear 14. Hereinafter, the first planetary pinions 24 will be referred to as the first pinions 24, and the second planetary pinions 26 will be referred to as the second pinions 26. The first pinions 24 are rotatably supported by a first pinion support shaft 28 fixed on the carrier 16. The second pinions 26 are rotatably supported by a second pinion support shaft 30 fixed on the carrier 16. The first pinions 24 and the second pinions 26 are arranged alternately in the circumferential direction. The first sun gear 12, the second sun gear 14, the first pinions 24, and the second pinions 26 each have a single row of teeth arranged in the circumferential direction. The fact that these gears and pinions have a single row of teeth means that these gears and pinions are not made up of two or more gears of different sizes lined up in the axial direction and integrated together.

[0016] Each first pinion 24 meshes with two adjacent second pinions 26, i.e., on both sides in the circumferential direction, and each second pinion 26 also meshes with the first pinion 24 on both sides. The first and second pinions 24, 26 revolve as the carrier 16 rotates about axis A, and are also rotatable, i.e., can rotate, about their respective support shafts 28, 30. Figure 2 shows the orbit T1 of the first pinion 24 and the orbit T2 of the second pinion 26. The meshing state between the first sun gear 12 and the first pinion 24 is shown in the right half of Figure 3, and the meshing state between the second sun gear 14 and the second pinion 26 is shown in the left half of Figure 3.

[0017] First sun gear 12 has a smaller diameter than second sun gear 14. The tooth row of first pinion 24 faces the tooth row of meshing first sun gear 12, and preferably, the tooth width of first pinion 24, i.e., the dimension in the direction of axis A, is approximately equal to the tooth width of first sun gear 12. The tooth row of second pinion 26 faces the tooth row of meshing second sun gear 14, and also faces the tooth row of non-mesh-mesh first sun gear 12. Preferably, the tooth width of second pinion 26 is the sum of the tooth widths of first sun gear 12 and second sun gear 14 when there is no gap between first sun gear 12 and second sun gear 14. Because the tooth width of second pinion 26 is large, second pinion 26 meshes with both first pinion 24 and second sun gear 14, which are positioned offset from each other in the direction along axis A. In addition, the difference in diameter between first sun gear 12 and second sun gear 14 prevents second pinion 26 from interfering with first sun gear 12.

[0018] The tooth row of the first pinion 24 meshes with the tooth row of the first sun gear 12 and the tooth row of the second pinion 26, and the tooth row of the second pinion 26 meshes with the tooth row of the second sun gear 14 and the tooth row of the first pinion 24. Therefore, the tooth rows of the first sun gear 12, the second sun gear 14, the first pinion 24, and the second pinion 26 are all composed of teeth of a common module.

[0019] The meshing between one second pinion 26, two first pinions 24 located on both sides of the second pinion 26, and the first sun gear 12 will be described.

[0020] For the meshing of the second pinion 26-1 and the first pinions 24-1 and 24-2 on either side of it with the first sun gear 12 shown in FIG. 4 to occur, the number of teeth on the circular path S1, indicated by the thick dashed line in FIG. 4, must be an integer. This path S1 is hereinafter referred to as the "relay path S1." The relay path S1 is a joint of the paths of movement of the teeth of the gears of interest. First, attention is focused on the teeth of the first sun gear 12 that mesh with the first pinion 24-1 at meshing point C1. The tooth row of the first sun gear 12 at this point is referred to as the starting tooth row. The tooth of interest on the first sun gear 12 moves to meshing point C2 as the first sun gear 12 rotates R. When the meshing point with another gear / pinion is reached, the tooth of interest is transferred to the meshing tooth of the other gear / pinion. That is, from meshing point C2, attention is focused on the tooth of the first pinion 24-2. When this tooth reaches meshing point C3 with the second pinion 26-1 as the first pinion 24-2 rotates, the tooth of interest is shifted to the tooth of the second pinion 26-1. Similarly, from meshing point C4, the tooth of interest is shifted to the tooth of the first pinion 24-1. When this tooth returns to the initial meshing point C1, the imaginary tooth row of the first sun gear 12 that meshes with this tooth is defined as the arrival tooth row. If the arrival tooth row overlaps with the departure tooth row, the tooth of interest can again mesh with the tooth row of the first sun gear 12 when it returns after making one revolution along the relay path S1. However, if the arrival tooth row and the departure tooth row do not overlap, i.e., if the tooth rows are out of phase with each other, the returned tooth of interest cannot mesh with the actual tooth row of the first sun gear 12. For meshing to occur, the number of teeth on the relay path S1 must be an integer, that is, the length of the relay path S1 must be an integer multiple of the pitch of the tooth row.

[0021] Determine the number of teeth on the relay path S1. S1 , the number of teeth of the second sun gear 14 is Z S2 , the number of teeth of the first pinion 24 is Z p1 , the number of teeth of the second pinion 26 is Z p2 The number of teeth at meshing points C1 to C2 is Z S1 θ7 / 360×2, number of teeth at meshing points C2~C3 is Zp1 θ9 / 360, number of teeth at meshing points C3~C4 is Z p1 θ8 / 360×2, number of teeth at meshing points C4~C1 is Z p1 θ9 / 360. The sum of these numbers of teeth must be an integer (see the following formula (1)).

[0022]

number

[0023] A total of eight pinions are arranged at equal angular intervals in the circumferential direction, so the angle θ7 is 45° (θ7=45°). The relationship between the angles θ7, θ8, and θ9 is expressed by the following equation (2).

number

[0024] From equations (1) and (2), the meshing condition is expressed as equation (3) below.

number

[0025] In the planetary gear set 10, the meshing condition must be satisfied for the relay path S2 shown in FIG. 5 as well, similar to the relay path S1 shown in FIG. 4. The number of teeth belonging to the path on the first sun gear 12 is Z S1 θ1 / 360, the number of teeth belonging to the path on the first pinion 24-2 is Z p1 θ3 / 360, the number of teeth belonging to the path on the second pinion 26-1 is Z p2 θ4 / 360, the number of teeth belonging to the path on the second sun gear 14 is Z S2 θ2 / 360, the number of teeth belonging to the path on the second pinion 26-2 is Z p2 θ5 / 360, the number of teeth belonging to the path on the first pinion 24-1 is Z p1 θ6 / 360. The sum of these numbers of teeth must be an integer (see equation (4) below). Equation (4) can be rearranged to obtain equation (5).

[0026]

number

[0027] The angles θ1 and θ2 are 90°, the sum of the angles θ3 and θ6 is 360°, and the sum of the angles θ4 and θ5 is 360° (the following expressions (6) to (8)).

number

[0028] By rearranging equations (4) to (8), we obtain the following equation (9).

number

[0029] From equation (9), the total number of teeth of first sun gear 12 and second sun gear 14 must be a multiple of four.

[0030] When the first and second sun gears 12, 14 and the first and second pinions 24, 26 are standard gears, i.e., gears without profile shifts, the condition of formula (3) is rarely satisfied. For example, if each gear / pinion is a standard gear and the number of teeth of the first sun gear 12 is 31 (Z S1 =31), the number of teeth of the second sun gear 14 is 37 (Z S2 =37), the number of teeth of the first pinion 24 is 22 (Z p1 =22), the number of teeth of the second pinion 26 is 20 (Z p2 = 20), angle θ8 is determined by geometric conditions, and is θ8 = 63.164°. Because angle θ7 is 45°, substituting these angles and the number of teeth of each gear / pinion into the left side of equation (3) gives 49.987. Because this value is not an integer, meshing does not occur. Therefore, some of the first and second sun gears 12, 14 and first and second pinions 24, 26 are shifted to adjust the center distance of each gear / pinion. Note that the sum of the numbers of teeth of first sun gear 12 and second sun gear 14 is 68 (= 31 + 37), so the condition of equation (9) is satisfied.

[0031] By setting the right-hand side of equation (3) to 50, the integer closest to 49.987, and solving for angle θ8, we obtain θ8 = 63.214°. The centerline distance between the first pinion 24 and the second pinion 26 is adjusted by the amount of addendum of the second pinion 26 so that angle θ8 becomes 63.214°. The addendum modification coefficient of the second pinion 26 at this time is -0.0093. Because the centerline distance between the first pinion 24 and the second pinion 26 has changed, the centerline distance between the second pinion 26 and the second sun gear 14 also changes. To accommodate this change in centerline distance, a addendum is applied to the second sun gear 14. The addendum modification coefficient of the second sun gear 14 at this time is -0.2611.

[0032] As described above, it has been shown that a double-pinion planetary gear device can be formed in which each of the first and second pinions 24, 26 arranged circumferentially meshes with the adjacent first and second pinions 24, 26 on both sides.

[0033] Although the gears / pinions of the planetary gear set 10 described above are spur gears, they may be helical gears. Also, while the planetary gear set 10 has four sets of first and second pinions 24, 26, the number of sets may be three, five or more.

[0034] A ring gear with internal teeth that meshes with the first pinion 24 or the second pinion 26 may be added to the planetary gear set 10. The ring gear has a common axis A with the first sun gear 12, the second sun gear 14, and the carrier 16, and is rotatable about this axis A. Also, one of the first sun gear 12 and the second sun gear 14 may be replaced with the ring gear.

[0035] Furthermore, the gear / pinion that provides the shift may be a gear / pinion other than second pinion 26 and second sun gear 14. [Explanation of symbols]

[0036] 10 planetary gear device, 12 first sun gear, 14 second sun gear, 16 planetary carrier (carrier), 18 first sun gear shaft, 20 second sun gear shaft, 22 carrier shaft, 24 first planetary pinion (first pinion), 26 second planetary pinion (second pinion), 28 first pinion support shaft, 30 second pinion support shaft, Z S1 Number of teeth of the first sun gear, Z S2 Number of teeth of second sun gear, Z p1 Number of teeth of first pinion 24, Z p2 Number of teeth of second pinion 26, angles θ1 to θ9, T1 orbital path of first pinion, T2 orbital path of second pinion, S1, S2 relay path.

Claims

1. A planetary gear device including a first gear, a second gear, and a planetary carrier that rotatably supports a planetary pinion, all of which are rotatable about a common axis, the planetary pinions include a first pinion arranged on a first revolution orbit having the common axis as a central axis and meshing with the first gear, and a second pinion arranged on a second revolution orbit having the common axis as a central axis and meshing with the second gear, the first pinions and the second pinions are arranged alternately in a circumferential direction, each of the first pinions meshes with two adjacent second pinions, and each of the second pinions meshes with two adjacent first pinions, Planetary gear device.

2. 2. The planetary gear arrangement of claim 1, wherein said first gear is a first sun gear and said second gear is a second sun gear.

3. 3. The planetary gear device according to claim 2, further comprising a ring gear rotatable about said common axis and meshing with one of said first pinion and said second pinion.

4. 2. The planetary gear arrangement of claim 1, wherein said first gear is a sun gear and said second gear is a ring gear.

Images