Planetary gear mechanism

Abstract

To provide a planetary gear mechanism capable of reducing its sound pressure level as a whole, while dispersing a frequency of sound generated in respective pinion gears.SOLUTION: The ring gears (3) include a plurality of low-rigidity portions (through holes) (10) having a small section modulus in a radial direction of the ring gears (3) at predetermined intervals in a circumferential direction of the ring gears (3), and a plurality of teeth of the ring gears (3) include heat treatment distortion portions (gears) (9) in which accumulated pitch errors based on heat treatment fluctuate.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a planetary gear mechanism including a plurality of pinion gears rotatably held by a carrier, and at least one of a ring gear and a sun gear with which the pinion gears mesh. [Background technology]

[0002] Patent Document 1 describes a ring gear having external teeth that mesh with a pinion gear. To suppress periodic noise and vibration during transmission of torque, this ring gear has a ring-shaped main body with a plurality of differently shaped lightening portions formed at a predetermined circumferential pitch on the ring-shaped main body, and is then heat-treated. By heat-treating a ring gear with different lightening portions formed at a predetermined pitch, heat treatment deformation varies in the circumferential direction, resulting in suppression of periodic noise and vibration in a specific frequency band during transmission of torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-159835 Summary of the Invention [Problem to be solved by the invention]

[0004] Because the ring gear described in Patent Document 1 is configured to mesh with one pinion gear, even if the ring gear is wave-shaped to adjust the rotational balance, the transmitted torque, i.e., the load acting on the tooth surfaces, does not change depending on the meshing position between the ring gear and pinion gear. Because the sound pressure level associated with the meshing of such a pair of gears depends on the load acting on the tooth surfaces, it may not be possible to reduce the sound pressure level itself even if periodic sounds and vibrations in a specific frequency band are suppressed.

[0005] The present invention has been made in light of the above technical problems, and has an object to provide a planetary gear mechanism that can disperse the frequencies of sounds generated by each pinion gear while reducing the overall sound pressure level. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a planetary gear mechanism including a plurality of pinion gears held so as to be able to rotate and revolve, and a target gear meshing with the plurality of pinion gears, wherein the target gear has a plurality of low-rigidity portions spaced at predetermined intervals in the circumferential direction of the target gear, the low-rigidity portions having a small section modulus in the radial direction of the target gear, and a plurality of teeth of the target gear have heat-treated distorted portions in which the cumulative pitch error due to heat treatment has changed.

[0007] In addition, in the present invention, the target gear may include a ring gear having internal teeth formed thereon, the ring gear having a flange portion with a plurality of through holes formed at predetermined intervals in the circumferential direction, and the low rigidity portion may include a portion where the through holes are formed on the radial outside of the ring gear.

[0008] In addition, in the present invention, the target gear may have a base portion and a gear portion formed on an outer peripheral surface or an inner peripheral surface of the base portion, and the low-rigidity portion may include a groove formed on the outer peripheral surface or the inner peripheral surface of the base portion, on the surface opposite to the gear portion.

[0009] In the present invention, the number of the low rigidity portions may be determined in accordance with the number of teeth of the target gear.

[0010] In the present invention, the number of the low rigidity portions may be 10% or more of the number of teeth of the target gear.

[0011] In the present invention, the number of the low rigidity portions may be 15% or less of the number of teeth of the target gear. [Effects of the Invention]

[0012] According to the present invention, a target gear meshing with multiple pinion gears is provided. The target gear has multiple low-rigidity portions spaced at predetermined intervals around the circumferential direction of the target gear, each having a small section modulus in the radial direction of the target gear. Furthermore, multiple teeth of the target gear have heat-treated distortion portions in which the cumulative pitch error due to heat treatment has changed. This allows for the load shared by each pinion gear when the planetary gear mechanism transmits torque to be varied. This allows for the frequencies of noise (sound) caused by the load acting on each pinion gear to be varied, thereby preventing sounds and vibrations at specific frequencies from becoming louder. In other words, abnormal noise (sound pressure level) and vibrations generated by the planetary gear mechanism can be suppressed. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view illustrating an example of a planetary gear mechanism according to an embodiment of the present invention. [Figure 2] FIG. 2 is a front view for explaining the configuration of the ring gear. [Figure 3] FIG. 10 is a diagram showing the cumulative pitch error of a hardened ring gear. [Figure 4] FIG. 10 is a diagram showing the sum of sound pressures for each frequency generated when the planetary gear mechanism is operated. [Figure 5] FIG. 10 is a front view illustrating another example of a ring gear. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described based on the embodiments shown in the drawings. Note that the embodiments described below are merely examples of specific embodiments of the present invention and are not intended to limit the present invention.

[0015] An example of a planetary gear mechanism according to an embodiment of the present invention is shown in Fig. 1. The planetary gear mechanism 1 shown in Fig. 1 is a single-pinion planetary gear mechanism that includes a sun gear 2, a ring gear 3 that is arranged concentrically with the sun gear 2 and has internal teeth, three pinion gears 4 that mesh with the sun gear 2 and the ring gear 3, and a carrier (not shown) that holds the pinion gears 4 rotatably and also holds the pinion gears 4 so that they can revolve around the central axis of the sun gear 2.

[0016] The sun gear 2 is connected to an input shaft 5 to which torque is transmitted from a driving force source (not shown) so as to be rotatable together with the input shaft 5. In the example shown in Fig. 1, the sun gear 2 is formed in a cylindrical shape, and the input shaft 5 is spline-engaged with the sun gear 2. In other words, the sun gear 2 is configured to function as an input element.

[0017] The ring gear 3 is configured to function as a reaction element. In the example shown in Fig. 1, a flange portion 6 is formed at a predetermined position in the axial direction of the ring gear 3, and the flange portion 6 is configured to be fixed to a fixed portion such as a housing (not shown). This ring gear 3 corresponds to the "target gear" in the embodiment of the present invention.

[0018] Each pinion gear 4 is formed in a cylindrical shape, and a pinion shaft 7 is provided to pass through the cylindrical portion so as to be rotatable relative to the pinion gears 4. Both ends of the pinion shafts 7 are connected to carrier plates (not shown) arranged opposite each other. One of the carrier plates is connected to an output-side rotating member or an output shaft (not shown). In other words, the carrier is made up of multiple pinion shafts 7 and two carrier plates.

[0019] In the planetary gear mechanism 1 configured as described above, the ring gear 3 is fixed and functions as a reaction element, and torque is input from the sun gear 2, causing each pinion gear 4 to revolve while rotating on its own axis, resulting in torque being transmitted to the carrier.

[0020] Fig. 2 shows a front view for explaining the configuration of the above-mentioned ring gear 3. The ring gear 3 shown in Fig. 2 is an internal gear made of a magnetic material. Note that the ring gear 3 may be a spur gear or a helical gear.

[0021] The ring gear 3 shown in Fig. 2 is composed of a cylindrical base portion 8 and a gear portion 9 formed inside the base portion 8, and the above-mentioned flange portion 6 is formed on the outer peripheral surface of the base portion 8. A plurality of through holes 10 are formed in the flange portion 6 at predetermined intervals in the circumferential direction. In the example shown in Fig. 2, 16 through holes 10 are formed in the circumferential direction of the flange portion 6. These through holes 10 are formed at the same distance from the central rotation axis of the ring gear 3 and have the same inner diameter.

[0022] The ring gear 3 described above is processed by broaching, gear cutting, chamfering, shaving, and other processes to form the teeth, and a through-hole 10 is formed in the flange portion 6. The gear portion 9 is then heat-treated by induction hardening or other methods. Specifically, a coil is inserted into the hollow portion of the ring gear 3, and an alternating current is passed through the coil. This alternating current generates eddy currents in the ring gear 3, which is made of a magnetic material. Joule heat generated by the eddy currents heats the gear portion 9, resulting in heat treatment. The hardening conditions, such as the induction hardening time and the magnitude of the current passed through the coil, are determined based on the strength required of the gear portion 9. In Figure 2, dots indicate the hardened layer formed by the hardening process.

[0023] As described above, by performing heat treatment, the radius of the ring gear 3 expands from the inside, causing distortion in the ring gear 3. The amount of distortion of the ring gear 3 depends on the rigidity of each part. In other words, the amount of distortion in the radial direction of the ring gear 3 depends on the section modulus in the radial direction. In the example shown in FIG. 2, the part in the circumferential direction of the ring gear 3 where the through holes 10 are formed is the part with a small section modulus in the radial direction of the ring gear 3, and this part corresponds to the "low rigidity part" in the embodiment of the present invention.

[0024] Therefore, the amount of distortion in the radial direction of the ring gear 3 is large in the circumferential portion of the ring gear 3 where the through holes 10 are formed, and the amount of distortion is small in the portion where the through holes 10 are not formed. In other words, distortion occurs in the ring gear 3 such that the portion of the gear portion 9 where the through holes 10 are formed on the outside is more outer in the radial direction of the ring gear 3 than the portion where the through holes 10 are not formed on the outside.

[0025] Therefore, the cumulative pitch error of gear portion 9 after heat treatment of ring gear 3 varies depending on the number of through holes 10 formed in ring gear 3, as shown in Figure 3. Gear portion 9 in which the cumulative pitch error varies as a result of heat treatment corresponds to the "heat treatment-distorted portion" in an embodiment of the present invention. Note that the horizontal axis in Figure 3 represents the tooth number counted in the circumferential direction of ring gear 3 based on a specific tooth of ring gear 3, and the vertical axis represents the cumulative pitch error based on that specific tooth.

[0026] 3, in the portion where the through hole 10 is formed on the outside, the pitch error increases in the negative direction (i.e., the actual pitch becomes smaller than the design value), and therefore, when the pinion gear 4 meshes with a portion where the cumulative pitch error is relatively small (a portion where the cumulative pitch error is large in the negative direction), the load acting on the pinion gear 4 (hereinafter referred to as the shared load) becomes smaller than the shared load when the pinion gear 4 meshes with a portion where the cumulative pitch error is relatively large. In other words, for each pinion gear 4, the shared load increases or decreases as the pinion gear 4 rotates and revolves while meshing with the ring gear 3.

[0027] Furthermore, because the pinion gears 4 revolve in mesh with each other at a predetermined interval in the circumferential direction of the ring gear 3, when the load share of a predetermined pinion gear 4 increases, the load share of either the other two pinion gears 4 or one of the other two pinion gears 4 decreases. In other words, the total value of the load shares of all pinion gears 4 becomes a load corresponding to the torque transmitted from the sun gear 2 to the carrier, and the load is distributed to each pinion gear 4 according to the meshing position with the ring gear 3.

[0028] Therefore, the load acting on a given pinion gear 4 fluctuates in a cycle ranging from a lower order obtained by subtracting a fluctuation order corresponding to the number of through holes 10 from a meshing order corresponding to the number of teeth of the pinion gear 4, to an upper order obtained by adding the fluctuation order to the meshing order.

[0029] The noise level generated between the ring gear 3 and the pinion gears 4 varies in magnitude depending on the load acting on their contact surfaces, so when the shared load is small, the noise level decreases, and when the shared load is large, the noise level increases. Meanwhile, the shared loads of the pinion gears 4 are different, and the timing of their meshing, in other words, the generated frequencies, are also different. Therefore, the noise of the multiple pinion gears 4 does not resonate. As a result, the noise level of the planetary gear mechanism 1 as a whole can be reduced.

[0030] Fig. 4 is a diagram showing the results of measuring the sum of sound pressures when the sun gear 2 is rotated at a predetermined rotation speed and a predetermined torque is input to the sun gear 2. In Fig. 4, the solid line shows the sum of sound pressures when a ring gear 3 with varied cumulative pitch error is used, and the dashed line shows the sum of sound pressures when a ring gear 3 with no cumulative pitch error is used, in other words, a ring gear without through holes 10 formed in the flange portion 6. In Fig. 4, the horizontal axis represents frequency and the vertical axis represents the sum of sound pressures.

[0031] As shown in FIG. 4, in the region below a predetermined frequency f1, the sum of sound pressures when using the ring gear 3 with the cumulative pitch error varied is smaller than the sum of sound pressures when using the ring gear with the cumulative pitch error not varied.

[0032] As described above, by forming the through holes 10 at predetermined intervals in the circumferential direction of the flange portion 6 and employing the ring gear 3 having a heat-treated distorted portion (i.e., gear portion 9) in which the cumulative pitch error has changed due to heat treatment in the planetary gear mechanism 1, it is possible to vary the load shared by each pinion gear 4. Therefore, by varying the noise frequency, it is possible to prevent sounds and vibrations of specific frequencies from increasing. In other words, it is possible to suppress abnormal sounds and vibrations generated by the planetary gear mechanism 1.

[0033] On the other hand, if the difference in frequency between two or more sounds is 50 Hz or less, the sounds may have a buzzing or muddy feel, which may adversely affect the sense of sensation. Furthermore, sounds that cause discomfort to humans have frequencies of 500 Hz or more. Therefore, in order to make the fluctuation order 50 Hz or more, it is preferable to make the fluctuation order 10% or more of the meshing order. Specifically, it is preferable to form through holes 10 that are 10% or more of the number of teeth formed on the ring gear 3.

[0034] Conversely, increasing the degree of fluctuation reduces the fluctuation range of the load shared by the pinion gear 4. For this reason, it is preferable to form through holes 10 whose number is 15% or less of the number of teeth formed on the ring gear 3.

[0035] The planetary gear mechanism in the embodiment of the present invention is not limited to the ring gear 3 having the through holes 10 formed in the flange portion 6 as long as it includes a gear having a low rigidity portion with low rigidity (section modulus) in order to change the amount of distortion during heat treatment. Specifically, as shown in Fig. 5, grooves 11 may be formed in the base portion 8 of the ring gear 3 at predetermined intervals in the circumferential direction. The grooves 11 may have a rectangular cross section or may have another shape such as a triangular cross section.

[0036] Furthermore, the planetary gear mechanism in the embodiments of the present invention is not limited to the single-pinion planetary gear mechanism described above, but may be a double-pinion planetary gear mechanism having multiple pairs of pinion gears, each pair consisting of a first pinion gear that meshes with the sun gear and a second pinion gear that meshes with the first pinion gear and the ring gear, or a stepped-pinion planetary gear mechanism having a first pinion gear that meshes with the sun gear and a second pinion gear that rotates integrally with the first pinion gear, has a different number of teeth than the first pinion gear, and meshes with the ring gear.

[0037] Furthermore, instead of varying the cumulative pitch error of the ring gear by forming a through hole or the like in the ring gear, the cumulative pitch error of the sun gear may be varied by forming a through hole or the like in the sun gear. That is, in a sun gear having a disk-shaped or cylindrical base portion and a gear portion on its outer circumferential surface, a through hole or groove may be formed in the base portion. By varying the cumulative pitch error of the sun gear in this way, it is possible to vary the load shared by the sun gear and the pinion gear, thereby achieving the same effect as above.

[0038] Furthermore, the planetary gear mechanism in the embodiments of the present invention may be a planetary gear mechanism that has only one of a sun gear and a ring gear, such as a planetary gear mechanism that has a first pinion gear that meshes with the first sun gear and a second pinion gear that rotates integrally with the first pinion gear and meshes with the second sun gear, or a planetary gear mechanism that has a first pinion gear that meshes with the first ring gear and a second pinion gear that rotates integrally with the first pinion gear and meshes with the second ring gear.

[0039] Note that some of the plurality of through holes 10 described above may be used as holes into which bolts for fixing the ring gear 3 to a housing or the like are inserted, and some of the plurality of grooves 11 shown in Fig. 5 may be used as grooves for engaging with protrusions or the like formed on the fixing portion. In other words, other parts of the plurality of through holes 10 do not need to have bolts inserted therein, and other parts of the plurality of grooves 11 do not need to be engaged with protrusions or the like of the fixing portion. [Explanation of symbols]

[0040] 1 Planetary gear mechanism 2 Sun gear 3 ring gear 4 pinion gear 6 Flange 8 Base 9 Gear section 10 through holes 11 Groove

Claims

1. A planetary gear mechanism including a plurality of pinion gears held so as to be capable of rotation and revolution, and a target gear meshing with the plurality of pinion gears, the target gear includes a plurality of low-rigidity portions, each having a small section modulus in a radial direction of the target gear, spaced at predetermined intervals in a circumferential direction of the target gear, The plurality of teeth of the target gear have heat treatment distortion portions in which the cumulative pitch error due to the heat treatment has changed. A planetary gear mechanism characterized by:

2. 2. The planetary gear mechanism according to claim 1, the target gear includes a ring gear having internal teeth formed thereon, the ring gear includes a flange portion having a plurality of through holes formed at predetermined intervals in the circumferential direction, The low-rigidity portion includes a portion where the through hole is formed on the outer side in the radial direction of the ring gear. A planetary gear mechanism characterized by:

3. 2. The planetary gear mechanism according to claim 1, the target gear has a base portion and a gear portion formed on an outer circumferential surface or an inner circumferential surface of the base portion, The low-rigidity portion includes a groove formed on the outer circumferential surface or the inner circumferential surface of the base portion, on the surface opposite to the gear portion. A planetary gear mechanism characterized by:

4. 2. The planetary gear mechanism according to claim 1, The number of the low rigidity portions is determined according to the number of teeth of the target gear. A planetary gear mechanism characterized by:

5. 5. The planetary gear mechanism according to claim 4, The number of the low rigidity portions is 10% or more of the number of teeth of the target gear. A planetary gear mechanism characterized by:

6. 6. The planetary gear mechanism according to claim 4 or 5, The number of the low rigidity portions is 15% or less of the number of teeth of the target gear. A planetary gear mechanism characterized by:

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