Planetary gear device

Abstract

This planetary gear device (10) comprises a first sun gear (12), a second sun gear (14), and a carrier (16) that can rotate around a common axis (A). The carrier (16) rotatably supports a first pinion (24) that meshes with the first sun gear (12) and a second pinion (26) that meshes with the second sun gear (14). The first pinion (24) and the second pinion (26) are alternately arranged in the circumferential direction, the first pinion (24) meshes with two adjacent second pinions (26), and the second pinion (26) meshes with two adjacent first pinions (24).

Description

Planetary gear unit

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

[0002] A known planetary gear device 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. In a typical planetary gear device, one pinion meshes with both the sun gear and the ring gear. However, double-pinion planetary gear devices 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 devices, planetary gear devices 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), and the first pinion (62) meshes with 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.

[0004] Japanese Patent Application Laid-Open No. 2021-76156

[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.

[0007] A planetary gear device according to the present invention includes a first gear, a second gear, and a planetary carrier rotatably supporting planetary pinions, each 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] Each of the first and second pinions meshes with two adjacent first or second pinions, which reduces the surface pressure applied to the tooth surfaces of each pinion. Furthermore, the number of first pinions and second pinions can be made the same, preventing 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 about 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.

[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.

[0012] Fig. 1 is a perspective view showing a planetary gear device of the present embodiment; Fig. 2 is a front view showing the planetary gear device of the present embodiment; Fig. 3 is a diagram showing a meshing state 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; Fig. 4 is a diagram showing meshing conditions between the first sun gear and the first and second pinions; Fig. 5 is a diagram showing meshing conditions between the first and second sun gears and the first and second pinions.

[0013] 1 and 2 are diagrams showing the schematic configuration of a planetary gear device 10, with Fig. 1 being a perspective view with a portion cut away and Fig. 2 being a front view.

[0014] The 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 an axis A. Hereinafter, the planetary carrier 16 will be referred to as the carrier 16. The first sun gear 12 is fixed to a first sun gear shaft 18 having the axis A as its central axis. The first sun gear shaft 18 extends from the first sun gear 12 toward the front in FIG. 1. The second sun gear 14 is fixed to a second sun gear shaft 20 having the axis A as its central axis. The second sun gear shaft 20 extends from the second sun gear 14 toward the back in FIG. 1. The carrier 16 is fixed to a hollow carrier shaft 22 having the axis A as its central axis. The second sun gear shaft 20 extends through the hollow space of the 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 pinions 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] The first sun gear 12 has a smaller diameter than the second sun gear 14. The teeth of the first pinion 24 face the teeth of the meshed first sun gear 12, and preferably the tooth width of the first pinion 24, i.e., the dimension in the direction of the axis A, is approximately equal to the tooth width of the first sun gear 12. The teeth of the second pinion 26 face the teeth of the meshed second sun gear 14 and also face the teeth of the non-meshed first sun gear 12. Preferably, the tooth width of the second pinion 26 is the sum of the tooth widths of the first sun gear 12 and the second sun gear 14 when there is no gap between the first sun gear 12 and the second sun gear 14. Because the tooth width of the second pinion 26 is large, the second pinion 26 meshes with both the first pinion 24 and the second sun gear 14, which are positioned offset from each other in the direction along the axis A. In addition, the difference in diameter between the first sun gear 12 and the second sun gear 14 prevents the second pinion 26 from interfering with the 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 configured with teeth of a common module.

[0019] The meshing of the one second pinion 26, the two first pinions 24 located on both sides thereof, 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 will be referred to as the "relay path S1" below. The relay path S1 is a joint of the movement paths of the teeth of the gears of interest. First, attention will be paid to 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 will be 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 circuit 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. In order 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] The number of teeth on the relay path S1 is calculated. 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, the number of teeth at meshing points C2 to C3 is Z p1 θ9 / 360, the number of teeth at meshing points C3 to C4 is Zp1 θ8 / 360×2, the number of teeth at meshing points C4 to C1 is Z p1 The sum of these numbers of teeth must be an integer (the following formula (1)).

[0022]

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

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

[0025] In the planetary gear set 10, the meshing condition must be satisfied for the relay path S2 shown in FIG. 5 as well as for 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 the following formula (4)). Formula (4) can be rearranged to obtain formula (5).

[0026]

[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° (see the following equations (6) to (8)).

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

[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, when 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°. Since 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. Since 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 the 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, which is 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 offset of the second pinion 26 so that angle θ8 becomes 63.214°. The offset 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 has also changed. To accommodate this change in centerline distance, an offset is applied to the second sun gear 14. The offset 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 the second pinion 26 and the second sun gear 14.

[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 the first pinion 24, Z p2 Number of teeth of second pinion 26, θ1 to θ9 angles, T1 orbital path of first pinion, T2 orbital path of second pinion, S1, S2 relay path.

Claims

1. A planetary gear device comprising a first gear, a second gear, and a planetary carrier rotatably supporting planetary pinions, all rotatable around a common axis, wherein the planetary pinions include a first pinion arranged on a first orbital path having the common axis as its central axis and meshing with the first gear, and a second pinion arranged on a second orbital path having the common axis as its central axis and meshing with the second gear, wherein the first pinions and the second pinions are arranged alternately in the circumferential direction, and each of the first pinions meshes with two adjacent second pinions, and each of the second pinions meshes with two adjacent first pinions.

2. A planetary gear arrangement according to claim 1, wherein said first gear is a first sun gear and said second gear is a second sun gear.

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

4. A planetary gear arrangement according to claim 1, wherein said first gear is a sun gear and said second gear is a ring gear.

Images