Planetary gear mechanism

Abstract

A planetary gear mechanism is provided with a plurality of pinions that are held so as to be able to rotate and revolve, and a ring gear that meshes with the plurality of pinions, the ring gear being provided with a plurality of through-holes, which are low-rigidity parts that are separated at predetermined intervals in the circumferential direction of the ring gear and have a small cross-sectional coefficient in the radial direction of the ring gear. The plurality of teeth of the ring gear have heat treatment deformation parts in which the accumulated pitch error due to the heat treatment has varied.

Description

TECHNICAL FIELD

[0001] The present application relates to a planetary gear mechanism having a plurality of pinions held so as to be able to rotate self-rotatably on a carrier, and at least either a ring gear or a sun gear engaged with the pinions. BACKGROUND

[0002] Japanese Patent Application Publication No. 2010-159835 describes a ring gear having external teeth engaged with pinions. In this ring gear, in order to suppress periodic sound and vibration when transmitting a rotational force, a plurality of hollowed-out portions having different shapes from each other are formed at a prescribed interval in the circumferential direction of a ring-shaped main body portion and are subjected to heat treatment. By subjecting the ring gear having the hollowed-out portions having different shapes from each other formed at a prescribed interval to heat treatment, different heat treatment deformations are generated in the circumferential direction, and as a result, periodic sound and vibration in a specific frequency band are suppressed when transmitting a rotational force. SUMMARY

[0003] The ring gear described in Japanese Patent Application Publication No. 2010-159835 is configured to be engaged with one pinion. Therefore, even if the ring gear is in a wave shape and the rotational balance is adjusted, the torque, that is, the load acting on the tooth surface, does not change depending on the engagement position between the ring gear and the pinion. The sound pressure level accompanying the engagement of such a pair of gears is a level corresponding to the load acting on the tooth surface, and therefore even if periodic sound and vibration in a specific frequency band are suppressed, there is a possibility that the sound pressure level itself cannot be reduced.

[0004] The present application was achieved in view of the above-described technical problems, and an object thereof is to provide a planetary gear mechanism capable of reducing the sound pressure level as a whole while dispersing the frequencies of sound generated by the pinions.

[0005] In order to achieve the above-described object, the planetary gear mechanism of the present application has a plurality of pinions held so as to be able to rotate self-rotatably and revolve, and an object gear engaged with the plurality of pinions, characterized in that,

[0006] the object gear has a plurality of low-rigidity portions spaced at a prescribed interval in the circumferential direction of the object gear and having a cross-sectional coefficient in the radial direction of the object gear that is small,

[0007] the plurality of teeth of the object gear have heat treatment deformation portions based on variation in cumulative pitch error by heat treatment.

[0008] Further, in the present application, it can also be that,

[0009] the object gear includes a ring gear having internal teeth,

[0010] The gear ring has a flange portion having a plurality of through holes formed at a predetermined interval in the circumferential direction,

[0011] The low-rigidity portion includes a portion in which the through hole is formed on the outer side in the radial direction of the gear ring.

[0012] Further, in the present application, it can be that,

[0013] The subject gear has a base portion and a gear portion formed on an outer circumferential surface or an inner circumferential surface of the base portion,

[0014] The low-rigidity portion includes a groove formed on a surface opposite to the gear portion among the outer circumferential surface or the inner circumferential surface of the base portion.

[0015] Further, in the present application, it can be that,

[0016] The number of the low-rigidity portions is determined in accordance with the number of teeth of the subject gear.

[0017] Further, in the present application, it can be that,

[0018] The number of the low-rigidity portions is 10% or more of the number of teeth of the subject gear.

[0019] Further, in the present application, it can be that,

[0020] The number of the low-rigidity portions is 15% or less of the number of teeth of the subject gear.

[0021] According to the present application, a subject gear engaged with a plurality of pinions is provided with a plurality of low-rigidity portions spaced at a predetermined interval in the circumferential direction of the subject gear and having a small cross-sectional coefficient in the radial direction of the subject gear. Further, a plurality of teeth of the subject gear have a heat treatment deformation portion based on variation in cumulative pitch error by heat treatment. Therefore, variation in load shared by each pinion when the planetary gear mechanism transmits torque can be made. Therefore, the frequency of noise (sound) based on the load acting on each pinion can be made different, and the sound and vibration at a specific frequency can be suppressed from becoming large. In other words, abnormal noise (sound pressure level) and vibration generated from the planetary gear mechanism can be suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0022] Features, advantages, and technical and industrial significance of exemplary embodiments of the present application will be described below with reference to the accompanying drawings, wherein the same reference numerals in different drawings denote the same element, and wherein:

[0023] Figure 1 is a perspective view for explaining an example of a planetary gear mechanism in an embodiment of the present application.

[0024] Figure 2 is a front view for explaining the structure of the ring gear.

[0025] Figure 3 is a graph showing the cumulative pitch error of the ring gear on which quenching treatment is performed.

[0026] Figure 4 is a line graph showing the sound pressure and of each frequency generated when the planetary gear mechanism is operated.

[0027] Figure 5 is a front view for explaining another example of the ring gear. DETAILED DESCRIPTION

[0028] The present application will be described based on the embodiment shown in the drawings. In addition, the embodiment described below is only one example of a case where the present application is embodied, and does not limit the present application.

[0029] Figure 1 An example of a planetary gear mechanism in the embodiment of the present application is shown. Figure 1 The planetary gear mechanism 1 shown is a single-pinion type planetary gear mechanism, which is composed of a sun gear 2, a ring gear 3, three pinions 4, and a carrier not shown. The ring gear 3 is disposed on a concentric circle with the sun gear 2, and the ring gear 3 is formed with internal teeth. The three pinions 4 mesh with the sun gear 2 and the ring gear 3. The carrier holds these pinions 4 so as to be able to rotate on their own, and holds the pinions 4 so as to be able to revolve around the center axis of the sun gear 2.

[0030] The sun gear 2 is integrally rotatably connected to an input shaft 5, to which torque is transmitted from a driving power source not shown. In Figure 1 In the example shown, the sun gear 2 is formed in a cylindrical shape, and the input shaft 5 is spline-fitted to the sun gear 2. That is, the sun gear 2 is configured to function as an input element.

[0031] The ring gear 3 is configured to function as a reaction force element. In Figure 1 In the example shown, a flange portion 6 is formed at a prescribed position in the axial direction of the ring gear 3, and the flange portion 6 is configured to be fixed to a fixing portion of an outer case or the like not shown. This ring gear 3 corresponds to the "target gear" in the embodiment of the present application.

[0032] Each pinion 4 is formed in a cylindrical shape, and a pinion shaft 7 is provided so as to be able to relatively rotate through the cylindrical portion. Both ends of these pinion shafts 7 are connected to carrier plates not shown that are disposed opposite each other. Furthermore, one of the carrier plates is connected to an output-side rotating member, an output shaft, or the like not shown. That is, the carrier is composed of a plurality of pinion shafts 7 and two carrier plates.

[0033] In the planetary gear mechanism 1 configured as described above, the ring gear 3 is fixed and functions as a reaction force element, so that each pinion 4 rotates on its own axis while revolving around the sun gear 2 by inputting torque. As a result, the torque is transmitted to the planet carrier.

[0034] Figure 2 A front view is shown to illustrate the structure of the gear ring 3 described above. Figure 2 The gear ring 3 shown is an internal gear made of magnetic material. Alternatively, gear ring 3 can be either a spur gear or a helical gear.

[0035] Figure 2 The gear ring 3 shown consists of a cylindrical base 8 and a gear portion 9 formed inside the base 8. A flange portion 6, as described above, is formed on the outer circumferential surface of the base 8. A plurality of through holes 10 are formed at predetermined intervals in the circumferential direction on the flange portion 6. Figure 2 In the example shown, 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 rotation center axis of the gear ring 3 and have the same inner diameter.

[0036] The aforementioned gear ring 3 is shaped by processes such as broaching, cutting, chamfering, and shaving, and a through hole 10 is formed in the flange portion 6. Subsequently, the gear portion 9 is heat-treated by high-frequency quenching or similar methods. Specifically, a coil is inserted into the hollow portion of the gear ring 3, and an alternating current is passed through the coil. By circulating the alternating current in this way, eddy currents are generated in the gear ring 3, which is made of a magnetic material. Then, the gear portion 9 is heated and heat-treated using the Joule heating corresponding to these eddy currents. The quenching conditions, such as the high-frequency quenching time and the magnitude of the current flowing through the coil, are determined based on the required strength of the gear portion 9. Furthermore, in Figure 2 In the middle, spots are attached to the hardened layer obtained by quenching.

[0037] Through the heat treatment described above, the radius of the gear ring 3 expands from the inside, causing deformation of the gear ring 3. This deformation of the gear ring 3 is a quantity corresponding to the stiffness of each part. In other words, the radial deformation of the gear ring 3 is a quantity corresponding to the section modulus in the radial direction. Figure 2 In the example shown, the portion with the through hole 10 formed in the circumferential direction of the gear ring 3 is the portion with a small section modulus in the radial direction of the gear ring 3, which corresponds to the "low-rigidity portion" in the embodiment of the present invention.

[0038] Therefore, the amount of deformation in the radial direction of the ring gear 3 is large at the portion of the ring gear 3 where the through-hole 10 is formed in the circumferential direction of the ring gear 3, and the amount of deformation is small at the portion where the through-hole 10 is not formed. That is, the ring gear 3 is deformed so that the portion of the gear portion 9 where the through-hole 10 is formed on the outer side is located on the outer side in the radial direction of the ring gear 3 than the portion where the through-hole 10 is not formed on the outer side.

[0039] Therefore, as Figure 3 indicated, the cumulative pitch error of the gear portion 9 after the heat treatment of the ring gear 3 varies depending on the number of the through-holes 10 formed in the ring gear 3. The gear portion 9 in which the cumulative pitch error varies based on the heat treatment in this manner corresponds to the "heat treatment deformation portion" in the embodiment of the present application. In addition, Figure 3 indicated, the cumulative pitch error of the gear portion 9 after the heat treatment of the ring gear 3 varies depending on the number of the through-holes 10 formed in the ring gear 3. The gear portion 9 in which the cumulative pitch error varies based on the heat treatment in this manner corresponds to the "heat treatment deformation portion" in the embodiment of the present application. In addition,

[0040] indicated, the cumulative pitch error of the gear portion 9 after the heat treatment of the ring gear 3 varies depending on the number of the through-holes 10 formed in the ring gear 3. The gear portion 9 in which the cumulative pitch error varies based on the heat treatment in this manner corresponds to the "heat treatment deformation portion" in the embodiment of the present application. In addition, Figure 3 indicated, the cumulative pitch error of the gear portion 9 after the heat treatment of the ring gear 3 varies depending on the number of the through-holes 10 formed in the ring gear 3. The gear portion 9 in which the cumulative pitch error varies based on the heat treatment in this manner corresponds to the "heat treatment deformation portion" in the embodiment of the present application. In addition,

[0041] In addition, each of the pinions 4 engages and revolves at a prescribed interval in the circumferential direction of the ring gear 3. Therefore, in the case where the load shared by a prescribed pinion 4 increases, the load shared by another two pinions 4 or one of the other two pinions 4 decreases. That is, the total value of the loads shared by all of the pinions 4 becomes a load corresponding to the torque transmitted from the sun gear 2 to the carrier, and the load is dispersed to each of the pinions 4 depending on the engagement position with the ring gear 3.

[0042] Therefore, the load acting on a prescribed pinion 4 varies in the range between the lower number of times obtained by subtracting the number of variations corresponding to the number of the through-holes 10 from the number of engagements corresponding to the number of teeth of the pinion 4 and the upper number of times obtained by adding the number of variations to the number of engagements.

[0043] The noise level generated between the ring gear 3 and the pinion gears 4 is of a size corresponding to the load acting on the contact surface, and thus the noise level decreases in the case where the load sharing is small, and the noise level increases in the case where the load sharing is large. On the other hand, the load sharing of each pinion gear 4 is different, and in addition, the engagement timing thereof is different, in other words, the frequency generated is different. Thus, the noises of the plurality of pinion gears 4 do not resonate. As a result, it is possible to reduce the noise level of the planetary gear mechanism 1 as a whole.

[0044] Figure 4 is a graph showing the sound pressure and the result obtained when the sun gear 2 is rotated at a prescribed rotational speed and a prescribed torque is input to the sun gear 2. Further, in Figure 4 , the sound pressure and using the ring gear 3 in which the cumulative pitch error is varied is shown by a solid line. Further, in Figure 4 , the sound pressure and using the ring gear 3 in which the cumulative pitch error is not varied, that is, the ring gear in which the through hole 10 is not formed in the flange portion 6 is shown by a broken line. In addition, Figure 4 , the horizontal axis employs the frequency, and the vertical axis employs the sound pressure.

[0045] As shown in Figure 4 , in the region below the prescribed frequency fl, the sound pressure and using the ring gear 3 in which the cumulative pitch error is varied is smaller than the sound pressure and using the ring gear in which the cumulative pitch error is not varied.

[0046] As described above, in the planetary gear mechanism 1, the ring gear 3 in which the through hole 10 is formed at a prescribed interval in the circumferential direction of the flange portion 6 and which has the heat treatment deformation portion (that is, the gear portion 9) in which the cumulative pitch error based on the heat treatment has been varied is employed. Thereby, it is possible to vary the load shared by each pinion gear 4. Thus, by making the frequencies of the noises different, it is possible to suppress the sound and the vibration at a specific frequency from becoming large. In other words, it is possible to suppress the abnormal noise and the vibration generated by the planetary gear mechanism 1.

[0047] On the other hand, in the case where the difference in the frequency of two or more sounds is 50 Hz or less, the sound generates a buzzing feeling or a muffled feeling, and the sensory experience can deteriorate. Further, the frequency of the sound which is unpleasant is 500 Hz or more. Thus, in order to make the variation number 50 Hz or more, it is preferable to make the variation number 10% or more of the number of engagements. Specifically, it is preferable to form the through hole 10 in a number of 10% or more of the number of teeth formed in the ring gear 3.

[0048] On the contrary, when the variation number increases, the variation range of the load sharing of the pinion gear 4 becomes small. Thus, it is preferable to form the through hole 10 in a number of 15% or less of the number of teeth formed in the ring gear 3.

[0049] The planetary gear mechanism in the embodiments of the present invention can include a gear with a low-rigidity portion having low rigidity (section modulus) formed to change the deformation during heat treatment, and is not limited to the gear ring 3 with the through hole 10 formed in the flange portion 6 as described above. Specifically, as Figure 5 As shown, grooves 11 can be formed at predetermined intervals in the circumferential direction at the base 8 of the gear ring 3. The cross-section of the groove 11 can be rectangular, triangular, or other shapes.

[0050] Furthermore, the planetary gear mechanism in the embodiments of the present invention is not limited to the single-pinion type planetary gear mechanism described above, but can also be a double-pinion type planetary gear mechanism having a pair of first pinions and second pinions. In the double-pinion type planetary gear mechanism, the first pinion can mesh with the sun gear, and the second pinion can mesh with both the first pinion and the ring gear. Additionally, the planetary gear mechanism in the embodiments of the present invention can be a stepped-pinion type planetary gear mechanism. A stepped-pinion type planetary gear mechanism may have a first pinion and a second pinion, the first pinion meshing with the sun gear, the second pinion rotating integrally with the first pinion, having a different number of teeth than the first pinion, and meshing with the ring gear.

[0051] Furthermore, instead of using a structure that varies the cumulative pitch error of the gear ring by forming a through hole or the like, the cumulative pitch error of the sun gear can be varied by forming a through hole or the like in the sun gear. That is, in a sun gear having a plate-shaped or cylindrical base and a gear portion on its outer circumferential surface, a through hole or slot can also be formed in that base. By varying the cumulative pitch error of the sun gear in this way, the load-sharing from the sun gear to the pinion can be varied, achieving the same effect as described above.

[0052] Furthermore, in some embodiments of the present invention, the planetary gear mechanism may be a planetary gear mechanism having only one of a sun gear and a ring gear. For example, in some embodiments of the present invention, the planetary gear mechanism may be a planetary gear mechanism having a first pinion and a second pinion, wherein the first pinion meshes with a first sun gear, and the second pinion rotates integrally with the first pinion and meshes with a second sun gear. For example, in some embodiments of the present invention, the planetary gear mechanism may be a planetary gear mechanism having a first pinion and a second pinion, wherein the first pinion meshes with a first ring gear, and the second pinion rotates integrally with the first pinion and meshes with a second ring gear.

[0053] Additionally, some of the aforementioned through holes 10 can be used as holes for bolts to be inserted, which are used to fix the gear ring 3 to the housing, etc. Furthermore, Figure 5Some of the plurality of grooves 11 shown can be used as grooves for engagement with the protruding portion or the like formed in the fixing portion. In other words, the other portions of the plurality of through holes 10 can not be inserted with the bolt, or the other portions of the plurality of grooves 11 can not be engaged with the protruding portion or the like of the fixing portion.

Claims

1. A planetary gear mechanism provided with a plurality of pinions that are held so as to be able to revolve and orbit, and a subject gear that meshes with the plurality of pinions, characterized in that, the subject gear is provided with a plurality of low-rigidity portions that are spaced apart at a prescribed interval in a circumferential direction of the subject gear, and a cross-sectional coefficient in a radial direction of the subject gear is small, and a plurality of teeth of the subject gear have a heat treatment deformation portion that varies based on a cumulative pitch error of heat treatment.

2. The planetary gear mechanism according to claim 1, characterized in that, the subject gear includes a ring gear that is formed with internal teeth, the ring gear is provided with a flange portion that has a plurality of through holes that are formed at a prescribed interval in the circumferential direction, and the low-rigidity portions include portions in which the through holes are formed on an outer side in the radial direction of the ring gear.

3. The planetary gear mechanism according to claim 1, characterized in that, the subject gear has a base portion and a gear portion that is formed on an outer peripheral surface or an inner peripheral surface of the base portion, and the low-rigidity portions include grooves that are formed on a surface of the base portion that is opposite the gear portion, of the outer peripheral surface or the inner peripheral surface.

4. The planetary gear mechanism according to claim 1, characterized in that, a number of the low-rigidity portions is determined in accordance with a number of teeth of the subject gear.

5. The planetary gear mechanism according to claim 4, characterized in that, the number of the low-rigidity portions is 10% or more of the number of teeth of the subject gear.

6. The planetary gear mechanism according to claim 4 or 5, characterized in that, the number of the low-rigidity portions is 15% or less of the number of teeth of the subject gear. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Images