Planetary gear mechanism

Abstract

To achieve both an increase in capacity of transmittable torque and improvement of NV characteristics.SOLUTION: At least one first pinion gear 6A of the plurality of pinion gears is movable in the axial direction of the pinion pin 11 and is pressed by a resilient force F0 in the axial direction, At least the other second pinion gear is fixed in the axial direction of the pinion pin, the sun gear 2 is movable in the axial direction, and the first pinion gear 6A is configured to move in the axial direction and disengage from the ring gear 4 while maintaining the meshing with the sun gear 2 in a state where the thrust force F1 accompanying the torque transmission between the sun gear 2 and the first pinion gear 6A is smaller than the resilient force.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a planetary gear mechanism in which a plurality of pinion gears are arranged between a sun gear and a ring gear arranged concentrically with the sun gear. [Background technology]

[0002] As is well known, a planetary gear mechanism is a differential gear mechanism consisting of a sun gear, which is an external gear; a ring gear, which is an internal gear, arranged concentrically with the sun gear; and a plurality of pinion gears, which are arranged between the sun gear and the ring gear and mesh with the sun gear and are held by a carrier so that they can rotate and revolve. Torque is transmitted between the sun gear, the ring gear, and the carrier as the pinion gears rotate or rotate while revolving. In this torque transmission state, repeated meshing occurs between the sun gear and the pinion gear, and between the pinion gear and the ring gear. Therefore, vibrations inevitably occur in the planetary gear mechanism as the pinion gears rotate.

[0003] Patent Document 1 describes a planetary gear mechanism configured to minimize vibration resonance occurring in the pinion gears. The planetary gear mechanism described in Patent Document 1 has multiple pinion gears, and is configured so that the resonance frequency of a vibration system formed by the pinion gears and the pinion shafts supporting the pinion gears varies depending on the position of the pinion gears. Since the resonance frequency depends on, for example, the rigidity of the pinion shafts, the planetary gear mechanism of Patent Document 1 varies the mass and diameter of the pinion shafts. This makes it possible to suppress vibration or noise occurring during torque transmission, even if the number of pinion gears is increased to increase the transmittable torque. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-210028 Summary of the Invention [Problem to be solved by the invention]

[0005] The torque that can be transmitted by a planetary gear mechanism (i.e., torque capacity) can be increased as the number of pinion gears increases. However, as described in Patent Document 1, pinion gears vibrate when they rotate, and therefore the greater the number of pinion gears, the greater the excitation force (exciting force), which may deteriorate the NV characteristics of the planetary gear mechanism as a whole. In the planetary gear mechanism described in Patent Document 1, the resonance frequencies of the pinion gears are different from one another, which prevents or suppresses the deterioration of vibration or noise due to resonance. However, increasing the number of pinion gears increases the excitation force, and there is still room for improvement in terms of reducing the vibration or noise of the planetary gear mechanism as a whole and improving the NV characteristics.

[0006] 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 increase the torque capacity by increasing the number of pinion gears and improve the NV characteristics by reducing the vibratory force at the same time. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a planetary gear mechanism having a sun gear which is an external gear, a ring gear which is an internal gear arranged concentrically with the sun gear, and a plurality of pinion gears which are arranged between the sun gear and the ring gear while meshing with the sun gear and the ring gear and which are rotatably held by a carrier, wherein the sun gear, the pinion gears and the ring gear are configured as helical gears, the plurality of pinion gears are attached to the carrier by pinion pins, and at least one first pinion gear among the plurality of pinion gears is movable in the axial direction of the pinion pin and is rotatable along the axial direction of the pinion pin. The pinion gear is pressed in the axial direction by an elastic force, at least one other second pinion gear among the plurality of pinion gears is fixed in the axial direction of the pinion pin, either the sun gear or the ring gear is movable in the axial direction, and when the thrust force associated with the transmission of torque between either the sun gear or the ring gear and the first pinion gear is smaller than the elastic force, the first pinion gear moves in the axial direction of the pinion pin to maintain meshing with either the sun gear or the ring gear while disengaging from the other of the sun gear and the ring gear. [Effects of the Invention]

[0008] According to the present invention, when the torque to be transmitted is small, the first pinion gear, which is movable in the axial direction, moves axially because the thrust force accompanying the torque transmission becomes smaller than the elastic force. In contrast, the second pinion gear, which is fixed in the axial direction, maintains a meshed state with the sun gear and the ring gear. Therefore, by allowing either the sun gear or the ring gear to move in the axial direction, the first pinion gear maintains meshing with the one gear while disengaging from the sun gear and the ring gear. Therefore, the first pinion gear is no longer involved in torque transmission and does not become a source of vibratory force, resulting in improved NV characteristics for the planetary gear mechanism as a whole. In this case, because the torque to be transmitted is small, problems such as excessive wear on the tooth surfaces do not occur. On the other hand, when the torque to be transmitted is large, the first pinion gear moves in the opposite direction against the elastic force, and thus meshes with both the sun gear and the ring gear, just like the second pinion gear. In other words, all of the pinion gears are involved in torque transmission, so the torque or torque capacity that can be transmitted by the planetary gear mechanism as a whole increases. Ultimately, because the number of pinion gears involved in torque transmission increases or decreases depending on the torque to be transmitted, it is possible to achieve both an increase in torque capacity and an improvement in NV characteristics by reducing excitation forces. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a skeleton diagram schematically illustrating an example of a stepped pinion type planetary gear mechanism according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram for explaining the arrangement of the pinion gears. [Figure 3] 5A and 5B are schematic cross-sectional views for explaining the position of a first pinion gear, where FIG. 5A shows a state at low torque and FIG. 5B shows a state at high torque. [Figure 4] FIG. 10 is a diagram showing the measurement results of sound pressure when the number of pinion gears is three and when the number of pinion gears is two. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the embodiment described below is merely an example of how the present invention can be implemented, and is not intended to limit the present invention.

[0011] The planetary gear mechanism in the embodiment of the present invention is a gear mechanism in which multiple pinion gears held by a carrier are arranged between a sun gear and a ring gear arranged concentrically with the sun gear and meshed with the sun gear and is a differential gear mechanism in which the carrier, sun gear, and ring gear form three rotating elements. Figure 1 shows a skeleton diagram of an example planetary gear mechanism 1, known as a stepped pinion planetary gear mechanism.

[0012] The sun gear 2 is an external gear that is integrated with a predetermined rotation shaft 3. A ring gear 4, which is an internal gear, is provided concentrically with the sun gear 2, and in the example shown in FIG. 1, the ring gear 4 is integrated with a predetermined fixed part 5 such as a casing, thereby serving as a fixed element. The pinion gear 6 is rotatably held by a carrier 7. The sun gear 2, ring gear 4, and pinion gear 6 are all helical gears.

[0013] Each pinion gear 6 has a large-diameter portion 8 that meshes with the sun gear 2 and a small-diameter portion 9 that is smaller in diameter than the large-diameter portion 8 and meshes with the ring gear 4, which are aligned on the same axis and integrated into one unit. The carrier 7 is connected to another rotating shaft 10, so that the pinion gear 6 can rotate and revolve. One of the sun gear 2 and the carrier 7 serves as the input element, and the other serves as the output element. The planetary gear mechanism 1 described here has three pinion gears 6, which are arranged at equal intervals in the circumferential direction as shown in Figure 2. In Figure 2, the pinion gear 6, which has a large-diameter portion 8 and a small-diameter portion 9, is represented by a single circle. The sun gear 2 can move axially by a small amount to accommodate processing and assembly errors. Therefore, the sun gear 2 corresponds to "either the sun gear or the ring gear" in the embodiment of the present invention, and the ring gear 4 corresponds to "the other of the sun gear or the ring gear."

[0014] The pinion gear 6 includes a first pinion gear 6A that is movable in the axial direction and a second pinion gear 6B that is fixed in the axial direction. These pinion gears 6A, 6B are held by the carrier 7 via pinion pins attached to the carrier 7. As shown in FIG. 3, the first pinion gear 6A is fitted onto a pinion pin 11 so as to be movable in the axial direction. In addition, a spring 12 is provided between the first pinion gear 6A and the pinion pin 11 to apply an elastic force to the first pinion gear 6A in the axial direction (leftward in FIG. 3). The acting direction of this elastic force is opposite to the direction of the axial meshing reaction force generated between the tooth surfaces of the large diameter portion 8 of the pinion gear 6A and the sun gear 2 when torque is transmitted from the sun gear 2 to the carrier 7. Alternatively, conversely, when torque is transmitted from carrier 7 to sun gear 2, the axial meshing reaction force generated between the tooth surfaces of large diameter portion 8 of pinion gear 6A and sun gear 2 may be in the opposite direction.

[0015] Next, the operation of the planetary gear mechanism 1 will be described using an example in which torque is transmitted using the sun gear 2 as the input element and the carrier 7 as the output element. Figures 3(a) and 3(b) are schematic cross-sectional views of the first pinion gear 6A described above, with Figure 3(a) showing a case in which the transmitted torque is small and Figure 3(b) showing a case in which the transmitted torque is large. Because the sun gear 2, ring gear 4, and pinion gear 6 are all helical gears, a thrust force (meshing reaction force) of a magnitude corresponding to the torque is generated at each meshing point.

[0016] When the torque transmitted between the sun gear 2 and the first pinion gear 6A is small, as shown in Fig. 3(a), the meshing reaction force F1 is smaller than the elastic force F0 of the spring 12. In other words, Fig. 3(a) shows a torque transmission state in which the meshing reaction force F1 is smaller than the elastic force F0. In this case, the first pinion gear 6A moves to the left in Fig. 3(a) due to the elastic force of the spring 12.

[0017] The tooth flanks of the first pinion gear 6A and the ring gear 4 are inclined relative to their axial direction, and the ring gear 4 is fixed relative to the axial direction. Therefore, when the first pinion gear 6A moves in the axial direction, the tooth flanks that are in contact to transmit torque move apart, and the tooth flanks on the opposite sides come into contact. In other words, the first pinion gear 6A moves in the axial direction to an extent that eliminates backlash. As a result, torque is no longer transmitted between the ring gear 4 and the first pinion gear 6A. As described above, the sun gear 2 can move in the axial direction to an extent that allows it to absorb errors in processing and assembly, so meshing between the first pinion gear 6A and the sun gear 2 is maintained.

[0018] The first pinion gear 6A, which is no longer involved in torque transmission in this way, is shown by a dashed line in Figure 2. Therefore, when the torque to be transmitted is low, the two other pinion gears 6B, which are the second pinion gears, transmit the torque. As a result, the number of pinion gears 6 that generate the vibratory force Fb due to torque transmission is reduced to two, thereby reducing vibration and noise in the planetary gear mechanism 1 as a whole. In other words, the NV characteristics are improved or their deterioration is suppressed. Furthermore, because the torque to be transmitted by the planetary gear mechanism 1 is small, there are no particular problems such as excessive wear even if the number of pinion gears 6 involved in torque transmission is reduced.

[0019] On the other hand, when the torque to be transmitted is large, the state shown in FIG. 3(b) occurs. In this case, due to the large torque to be transmitted, the meshing reaction force F2 generated on the meshing tooth surface between the sun gear 2 and the first pinion gear 6A becomes larger than the elastic force F0 of the spring 12. As a result, the first pinion gear 6A moves to the right in FIG. 3(b). This position in the axial direction is the same as the position of the second pinion gear 6B, and therefore the small diameter portion 9 of the first pinion gear 6B meshes with the ring gear 4. As a result, all three pinion gears 6 are involved in torque transmission, allowing large torque to be transmitted without hindrance.

[0020] FIG. 4 shows the results of an experiment conducted to confirm the improvement in NV characteristics achieved by an embodiment of the present invention. The sound pressure measurement results shown here were obtained for the stepped-pinion planetary gear mechanism described above, which has three pinion gears and is configured so that the number of pinion gears transmitting torque can be switched between three and two. When torque is transmitted by all three pinion gears, the sum of sound pressures, which represents the overall sound pressure of the planetary gear mechanism, is shown by line L3. In contrast, when torque is transmitted by two pinion gears, the sum of sound pressures is shown by line L2. These measurement results demonstrate that vibration or noise is reduced when the number of pinion gears transmitting torque is reduced, and in particular, resonance of the first-order vibration of rotation can be significantly reduced. This frequency is the lowest frequency at which the sum of sound pressures peaks, and since this is a vibration that is easily felt by vehicle occupants in a vehicle, it can be seen that the improvement in NV characteristics achieved by an embodiment of the present invention is excellent.

[0021] Although the above describes an embodiment of the present invention, the present invention is not limited to the above embodiment and can be modified as appropriate within the scope of the present invention. For example, spring 12 can be any elastic member capable of applying an axial elastic force to first pinion gear 6A. Therefore, any conventionally known spring member, such as a coil spring or a disc spring, can be used. Furthermore, the elastic force does not have to be a pressing force but can be a tensile force. Therefore, the position of the elastic body is not limited to the positions shown in FIGS. 1 and 3 . Furthermore, the number of pinion gears is not limited as long as there are multiple pinion gears. Furthermore, the planetary gear mechanism according to the present invention may be a stepped-pinion planetary gear mechanism or other types of planetary gear mechanisms, such as a single-pinion type, double-pinion type, or Ravigneaux type. Furthermore, in the present invention, any of the sun gear, ring gear, and carrier may serve as the input element, output element, or reaction element, and the reaction element does not have to be fixed. [Explanation of symbols]

[0022] 1 Planetary gear mechanism 2 Sun gear 3 Rotation Axis 4 ring gear 5 Fixed part 6 Pinion gear 6A 1st pinion gear 6B Second pinion gear 7 Carrier 8 Large diameter section 9 Small diameter section 10 Rotation axis 11 Pinion pin 12 Spring

Claims

[Claim 1] A planetary gear mechanism having a sun gear which is an external gear, a ring gear which is an internal gear arranged concentrically with the sun gear, and a plurality of pinion gears which are arranged between the sun gear and the ring gear while meshing with the sun gear and the ring gear and which are rotatably held by a carrier, the sun gear, the pinion gear, and the ring gear are configured as helical gears, The pinion gears are attached to the carrier by pinion pins, At least one first pinion gear among the plurality of pinion gears is movable in an axial direction of the pinion pin and is pressed in the axial direction by an elastic force, At least one other second pinion gear among the plurality of pinion gears is fixed in the axial direction of the pinion pin, One of the sun gear and the ring gear is movable in the axial direction, When a thrust force accompanying torque transmission between either the sun gear or the ring gear and the first pinion gear is smaller than the elastic force, the first pinion gear moves in the axial direction of the pinion pin, maintaining meshing between either the sun gear or the ring gear while disengaging from the other of the sun gear and the ring gear. A planetary gear mechanism characterized by:

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