Planetary gear mechanism

Abstract

This invention provides a planetary gear mechanism that can suppress gear meshing errors and the resulting deterioration of NV characteristics by having rigidity corresponding to the direction in which torque is applied. [Solution] A planetary gear mechanism having a sun gear, a ring gear, and a carrier 5 that holds and rotates a pinion gear meshing with these gears, wherein the carrier 5 has a first side wall portion 7 that holds the end of the pinion shaft passing through the pinion gear and a second side wall portion 8 parallel to the first side wall portion 7, a rotating member 6 connected to either the first side wall portion 7 or the second side wall portion 8, a plurality of circumferential wall portions 9 connecting the outer periphery of the first side wall portion 7 and the outer periphery of the second side wall portion 8 are provided at regular intervals in the circumferential direction of the carrier 5, and the circumferential wall portions 9 are provided with reinforcing portions 15 such that the rigidity of the first side wall portion 7 and the second side wall portion 8 with respect to a first torsional direction is greater than the rigidity with respect to a second torsional direction opposite to the first torsional direction.

Description

Technical Field

[0001] The present invention relates to an epicyclic gear mechanism having three elements: a sun gear, a ring gear, and a carrier that holds pinion gears meshing with these gears, and particularly relates to the structure of the carrier.

Background Art

[0002] As an example of this type of epicyclic gear mechanism, a single pinion type epicyclic gear mechanism is described in Patent Document 1. The epicyclic gear mechanism described in Patent Document 1 is configured to eliminate the imbalance of a carrier that holds pinion gears meshing with both a sun gear and a ring gear. According to the description of Patent Document 1, the carrier has a large cylindrical portion and a small cylindrical portion having a smaller diameter than the large cylindrical portion, and these cylindrical portions are integrally formed so as to be located on the same axis, and the small cylindrical portion protrudes in the axial direction from one side surface portion of the large cylindrical portion. The large cylindrical portion is a cylindrical portion in which the sun gear and the pinion gear are arranged inside, and a plurality of through portions or punched hole portions are formed on the outer peripheral wall at regular intervals in the circumferential direction. The portion between these through portions or between the punched hole portions serves as a rib. Further, the portions of the inner surfaces of the through portion or the punched hole portion that face each other in the direction of the rotation center axis are so-called side wall portions, and a pinion shaft is inserted and held in the holes formed in the side wall portions, and the pinion gear is assembled to the carrier by the pinion shaft. In addition, a spline is formed on the inner peripheral surface of the small cylindrical portion in the carrier described in Patent Document 1, and a part of the outer peripheral portion at the tip of the small cylindrical portion is cut away. The above rib is provided at a position that corrects the deviation of the center of gravity where the notch portion is provided.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a planetary gear mechanism, the carrier may be used as either an output or input element, with either the sun gear or the ring gear being a fixed element and the other being used as either an input or output element. In this case, since the carrier rotates, vibration and noise can be avoided or suppressed by eliminating the imbalance as described in Patent Document 1. Furthermore, since the carrier holds multiple pinion gears so that they can rotate on their own and rotates around the sun gear, even a slight tilt of the pinion shaft can cause meshing errors between the gears, potentially worsening noise, vibration, or so-called NV characteristics. For example, as described in Patent Document 1, both ends of the pinion shaft are fitted and held in the carrier by opposing side walls. Also, the small cylindrical part described in Patent Document 1 is a part for connecting to other rotating members and is provided on one side of the carrier. Therefore, in this configuration, the reaction force when torque is applied to the pinion gear is received by one side wall along with the rotating member, resulting in a torsional force acting on the entire carrier such that one side wall and the opposing side wall rotate in opposite directions. When the carrier is thinned to reduce the overall weight of the planetary gear mechanism, such torsional forces can cause slight deformation in the carrier, resulting in tilting of the pinion shaft or pinion gear, which may worsen the NV characteristics.

[0005] If the configuration takes into account the deformation of the carrier or the tilt of the pinion shaft or pinion gear in accordance with the torque applied during normal operation, the meshing of each gear can be optimized by the application of torque. However, if torque is applied in a direction different from that of normal operation, and the magnitude of that torque is also different from that of normal operation, the deformation of the carrier or the tilt of the pinion shaft, etc., will differ from the deformation or tilt that optimizes the meshing of each gear, which may lead to a deterioration of NVH characteristics.

[0006] This invention was made in view of the above technical problems, and aims to provide a planetary gear mechanism that can suppress gear meshing errors and the resulting deterioration of NV characteristics by having rigidity corresponding to the direction in which torque is applied. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides a planetary gear mechanism in which a pinion gear that meshes with a sun gear and a ring gear and revolves around the outer circumference of the sun gear is held rotatably by a carrier, wherein the carrier has a first side wall portion that holds the end of a pinion shaft that passes through the pinion gear and a second side wall portion parallel to the first side wall portion, a torque transmission member is connected to either the first side wall portion or the second side wall portion, a plurality of circumferential wall portions connecting the outer circumference of the first side wall portion and the outer circumference of the second side wall portion are provided at a constant interval in the circumferential direction of the carrier, and the circumferential wall portion is provided with a reinforcing portion such that the rigidity of the first side wall portion and the second side wall portion with respect to a first torsional direction is greater than the rigidity with respect to a second torsional direction opposite to the first torsional direction. [Effects of the Invention]

[0008] According to the present invention, torque is transmitted between the sun gear, ring gear, and carrier via a pinion gear. In this case, the load is applied to approximately the center of the tooth surface of the pinion gear, while the carrier, which supports the pinion gear via the pinion shaft, receives a reaction force at one of its side walls to which the torque transmission member is connected, resulting in a torsional force acting between the first and second side walls. Since the reinforcing portion is provided such that the rigidity against this torsional force is greater in the first torsional direction and smaller in the second torsional direction, by determining the direction of rigidity increase by the reinforcing portion according to the direction of the transmitted torque, the relative torsional force of each side wall or the displacement of the pinion shaft and pinion gear can be kept equal even if the magnitude of the torque differs depending on the direction. In other words, the meshing of the pinion gear with the sun gear and ring gear can be maintained in the correct state regardless of the direction of torque, thereby suppressing vibrations and noise caused by gear meshing and improving so-called NV characteristics. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing an example of a planetary gear mechanism. [Figure 2] This is a perspective view showing a carrier in an embodiment of the present invention. [Figure 3] This is a cross-sectional view of the bridge section and ribs. [Figure 4] Figure 2 shows the rigidity of the carrier against torque during power application and against torque during regeneration. [Modes for carrying out the invention]

[0010] Next, embodiments of the present invention will be described with reference to the attached drawings. Note that the embodiments described below are merely examples of how the present invention can be implemented and do not limit the invention.

[0011] Figure 1 shows a schematic cross-sectional view of an example of a planetary gear mechanism 1. An internal gear, the ring gear 3, is arranged concentrically with an external gear, the sun gear 2. Multiple pinion gears 4, which mesh with the sun gear 2 and the ring gear 3, are arranged at regular intervals in the circumferential direction of the sun gear 2. These pinion gears 4 are rotatably held by a carrier 5, which is arranged on the same axis as the sun gear 2. This planetary gear mechanism 1 is used, for example, as a reduction gear in electric vehicles (BEV, HEV, PHEV, etc.), where the sun gear 2 is connected to a motor (not shown) which is the driving force source and serves as the input element, the ring gear 3 is attached to a casing (not shown) and serves as the fixed element, and a rotating member 6 such as an output shaft is connected to the carrier 5, making the carrier 5 the output element.

[0012] A carrier 5 in an embodiment of the present invention is shown in Figures 2 and 3. The carrier 5 is cylindrical in shape overall and has a first side wall portion 7 and a second side wall portion 8 which are opposite to each other and a circumferential wall portion 9 which connects these side wall portions 7 and 8 at the outer circumference. A through hole 10 is formed in the center of each side wall portion 7 and 8 for passing through a rotating shaft which is integral with the sun gear 2. A shaft hole 12 is formed on the outer circumference side of the through hole 10 for attaching a pinion shaft 11 which supports the pinion gear 4. In the example shown in Figure 2, three shaft holes 12 are formed at regular intervals in the circumferential direction.

[0013] As shown in Figure 1, the pinion shaft 11 is attached to the carrier 5 by fitting both ends into the shaft holes 12 of the side walls 7 and 8. A pinion gear 4 is rotatably mounted on the middle of the pinion shaft 11 via a bearing 13. In order to engage the pinion gear 4 with the ring gear 3, which is located on the outer circumference of the carrier 5, an opening is made in the circumferential wall 9 of the carrier 5 at the location corresponding to the pinion gear 4. In other words, in the configuration shown in Figure 2, the circumferential wall 9 is a so-called bridge section that connects the outer circumference of each side wall 7 and 8 at three points in the circumferential direction, and the length of this bridge section is set to a length that does not interfere with the pinion gear 4, and the part between these bridge sections is an opening 14. Hereafter, the circumferential wall 9 will be referred to as the bridge section 9.

[0014] As shown in Figure 2, each bridge section 9 connects the side walls 7 and 8 in an orientation inclined at a predetermined angle with respect to an axis parallel to the central axis of the carrier 5. In addition, multiple ribs 15 are formed on the outer surface of each bridge section 9 as reinforcing parts, inclined in the same orientation as the bridge section 9. Figure 3 shows a cross-sectional view of a portion of the bridge section 9 and ribs 15 when cut along a plane parallel to the radial direction of the carrier 5.

[0015] When the planetary gear mechanism 1, equipped with the carrier 5 described above, is mounted on an electric vehicle, and torque is input from the motor to the sun gear 2, and torque is output from the carrier 5 towards the drive wheels (not shown), the carrier 5 rotates at a lower speed than the sun gear 2 because the ring gear 3 is fixed. In other words, the planetary gear mechanism 1 functions as a reduction mechanism.

[0016] In this case, when the carrier 5 moves forward (is driven) by the motor, the direction of rotation of the carrier 5 is the direction indicated by arrow A in Figure 2. Therefore, a force acts on the pinion gear 4 and the middle part of the pinion shaft 11 to which it is attached, causing it to revolve in the direction of arrow A in Figure 2. On the other hand, since a rotating member 6 such as an output shaft is connected to one side wall 7 of the carrier 5, a torque acts on that side wall 7 in the direction that stops its rotation (opposite to arrow A in Figure 2). As a result, in the carrier 5, a force acts on one side wall 7 in the direction opposite to arrow A, and a force acts on the other side wall 8 in the direction of arrow A. In other words, a force that causes torsion is applied to the carrier 5.

[0017] On the other hand, in the so-called engine braking state, the motor is rotated by the inertial force of the vehicle, and energy is regenerated by the motor. In this case, the direction of rotation of the carrier 5 is the direction indicated by arrow A in Figure 2, but the direction in which torque (force) is applied is opposite to that during the above-mentioned acceleration. That is, a force is applied to one side wall portion 7 in the direction indicated by arrow A in Figure 2, and a force is applied to the pinion gear 4 and the pinion shaft 11 to which it is attached in the opposite direction to arrow A in Figure 2. Therefore, the direction of torsion of the carrier 5 is a torsion that rotates one side wall portion 7 in the direction of arrow A and the other side wall portion 8 in the opposite direction to arrow A.

[0018] Considering the load on the bridge section 9 when such torsion occurs, the torsion during power application rotates one side wall section 7 in the direction of arrow A in Figure 2, and the other side wall section 8 in the direction opposite to arrow A. This torsion deforms the bridge section 9 and the rib 15 integrated with it so that they become parallel to the central axis by reducing the angle of inclination with respect to the central axis of the carrier 5. Conversely, during regeneration, the torsion deforms the bridge section 9 and the rib 15 integrated with it so that they become parallel to the central axis by increasing the angle of inclination with respect to the central axis of the carrier 5. Therefore, during power application, there is an effect that compresses the bridge section 9 and the rib 15 in the axial direction of the carrier 5, while during regeneration, there is an effect that promotes bending of the bridge section 9 and the rib 15 relative to one side wall section 7. Thus, the rigidity of the bridge section 9 and the rib 15 is greater during power application and smaller during regeneration than during power application.

[0019] Figure 4 is a diagram showing the rigidity of the carrier 5, including the rigidity against axial deformation. Line L1 represents the rigidity in the powered state, and line L2 represents the rigidity in the regenerative state. As shown in Figure 4, the rigidity in the powered state is higher than the rigidity in the regenerative state, and this difference is larger compared to the case where the bridge section 9 is not inclined as described above and the ribs 15 are not provided. In both cases, the rigidity is lower at the location corresponding to the aforementioned opening 14, and higher in the section between these (i.e., the section corresponding to the bridge section 9). Furthermore, the difference between the rigidity at the location corresponding to the opening 14 and the rigidity at the location corresponding to the bridge section 9 is small.

[0020] When the above-described planetary gear mechanism 1 is used as a transmission mechanism of an electric vehicle, during deceleration, not only the regenerative torque of the motor but also the braking torque by the brake is used for deceleration. Therefore, the torque applied to the planetary gear mechanism 1 during regeneration is generally smaller than that during power running. On the other hand, the rigidity of the carrier 5 is smaller in the regenerative state than in the power running state as described above. Therefore, the deformation amount is the same or approximate both during power running and regeneration. By designing each gear 2, 3, 4 assuming the expected deformation amount, the meshing error of each gear 2, 3, 4 can be eliminated or reduced both during power running and regeneration. As a result, a planetary gear mechanism 1 excellent in NV characteristics with small vibration or noise can be obtained.

[0021] Note that the present invention is not limited to the above-described specific configuration. The reinforcement of the peripheral wall portion (bridge portion) in the present invention may be performed by increasing the plate thickness compared to other portions instead of the above-described rib 15. Further, in the present invention, the peripheral wall portion (bridge portion) may be formed parallel to the axial direction of the carrier, and a reinforcing portion such as a rib provided on the peripheral wall portion (bridge portion) may be inclined with respect to the axial direction of the carrier. Furthermore, the present invention may be any planetary gear mechanism provided with a carrier, and is not limited to a single pinion type planetary gear mechanism.

Explanation of Reference Numerals

[0022] ] 1 Planetary gear mechanism 2 Sun gear 3 Ring gear 4 Pinion gear 5 Carrier 6 Rotating member 7, 8 Side wall portion 9 Peripheral wall portion (bridge portion) 10 Through hole 11 Pinion shaft 12 Shaft hole 13 Bearing 14 Opening 15 Reinforcing portion (rib)

Claims

[Claim 1] A planetary gear mechanism in which a pinion gear that meshes with a sun gear and a ring gear and revolves around the outer circumference of the sun gear is held by a carrier so as to be able to rotate, The carrier has a first side wall portion that holds the end of the pinion shaft that passes through the pinion gear, and a second side wall portion parallel to the first side wall portion. A torque-transmitting rotating member is connected to either the first side wall portion or the second side wall portion. A plurality of circumferential wall portions connecting the outer periphery of the first side wall portion and the outer periphery of the second side wall portion are provided at regular intervals in the circumferential direction of the carrier. The peripheral wall portion is provided with a reinforcing portion such that the rigidity of the first side wall portion and the second side wall portion in the first torsional direction is greater than the rigidity in the second torsional direction opposite to the first torsional direction. A planetary gear mechanism characterized by the following features.

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