gear mechanism

Abstract

To provide a gear device in which the radial stiffness of a case lid body is increased and furthermore an increase in the axial stiffness and the weight of the case lid body is suppressed, and therefore the meshing of a large-diameter gear with a small-diameter gear can be properly maintained.SOLUTION: A gear device 1 comprises: a differential case 51 rotating integrally with a ring gear 4 meshed with a pinion gear 21; first and second bearings 61, 62 supporting the differential case 51; a case main body 7 having a first fitting portion 73 fit with the first bearing 61; and a case lid body 8 having a second fitting portion 82 fit with the second bearing 62. The case lid body 8 has a plurality of ribs 87 which are arranged while protruding from a wall portion 83, wherein intervals between the plurality of ribs 87 in a peripheral prescribed range R along the rotation direction of the ring gear 4 are formed shallower than intervals of the plurality of ribs 87 in the other peripheral range, and a direction of a load received by the ring gear by engagement with the pinion gear 21 is overlapped on a prescribed range R in an axial view along a rotation axial line of the ring gear 4.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a gear device in which a large diameter gear and a small diameter gear are meshed within a case. [Background technology]

[0002] Conventionally, in vehicles in which the driving force of a drive source is transmitted to wheels via a propeller shaft, for example, a gear device in which a large-diameter gear and a small-diameter gear are meshed within a case is used in the driving force transmission path (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1 describes a transfer in which a large-diameter ring gear and a small-diameter pinion gear mesh within a transfer case. The transfer case has a case body and a case cover, and the case cover is fastened to the case body with multiple bolts. The ring gear is welded to a flange of a connecting hollow shaft that rotates integrally with the front differential case. The connecting hollow shaft is rotatably supported relative to the transfer case by a pair of bearings held by the case body and the case cover, respectively.

[0004] Patent Document 2 describes a final reduction gear in which a large-diameter ring gear and a small-diameter drive pinion mesh within a casing (differential carrier). The casing has a die-cast main body and a lid, and the lid is fixed to the main body with multiple bolts. The ring gear is a hypoid gear and is fixed to the outer periphery of the differential case. The differential case is rotatably supported relative to the casing by a pair of bearings held in the main body and the lid of the casing, respectively.

[0005] As is clear from the drawings of Patent Documents 1 and 2, the connecting hollow shaft of Patent Document 1 and the differential case of Patent Document 2 are supported by a pair of tapered roller bearings in which multiple partially conical rollers are arranged between the outer and inner rings. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-105282 [Patent Document 2] Japanese Patent Application Publication No. 10-281266 Summary of the Invention [Problem to be solved by the invention]

[0007] In a gear device configured as described above, if the case lid (case cover in Patent Document 1, lid in Patent Document 2), which is less rigid than the case main body (case main body in Patent Document 1, main body in Patent Document 2), elastically deforms due to the radial load applied to the ring gear, the ring gear and the small diameter gear (pinion gear in Patent Document 1, drive pinion in Patent Document 2) will not mesh properly, which could result in reduced driving force transmission efficiency, increased noise and vibration, etc. Furthermore, if the wall thickness of the case lid is increased to increase the rigidity of the case lid, the weight of the case lid will increase and it will become difficult to adjust the preload of the pair of tapered roller bearings.

[0008] To explain this preload adjustment in more detail, if the rigidity of the case cover is low, even if the axial spacing between the pair of tapered roller bearings changes due to, for example, expansion or contraction caused by temperature changes in the case body, this change in spacing is absorbed by the elastic deformation of the case cover, and the magnitude of the preload can easily be kept within an allowable range. However, if the rigidity of the case cover is high, even a slight change in the axial spacing between the pair of tapered roller bearings can cause a large change in preload, making it more likely that problems will occur, such as the preload being released at high temperatures or the rotational resistance of the tapered roller bearings increasing due to an increase in preload at low temperatures.

[0009] The inventors conducted extensive research to solve the above-mentioned conflicting problems, and discovered that if the radial rigidity of the case cover body is increased while the axial rigidity of the case cover body is suppressed, it becomes easier to maintain proper meshing between the large-diameter gear and the small-diameter gear while keeping the bearing preload within an allowable range, even if the gap between the pair of bearings changes due to temperature, for example. That is, the object of the present invention is to provide a gear device that increases the radial rigidity of the case cover body while suppressing increases in the axial rigidity and weight of the case cover, thereby making it possible to maintain proper meshing between the large-diameter gear and the small-diameter gear. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides a gearbox comprising: a large-diameter gear and a small-diameter gear that mesh with each other; a rotating member that rotates integrally with the large-diameter gear; a first bearing that supports the rotating member on one axial side of the large-diameter gear; a second bearing that supports the rotating member on the other axial side of the large-diameter gear; a case body that houses the large-diameter gear and has a cylindrical first fitting portion into which the first bearing is fitted; and a case cover that covers an opening of the case body that opens toward the other axial side and has a cylindrical second fitting portion into which the second bearing is fitted; The case cover has an outer edge portion disposed opposite the open end face of the case body and fastened to the case body at a plurality of locations, a plate-shaped wall portion provided between the outer edge portion and the second fitting portion, and a plurality of ribs provided protruding from the wall portion, and the spacing between the plurality of ribs in a predetermined range in the circumferential direction along the rotation direction of the large-diameter gear is formed to be narrower than the spacing between the plurality of ribs in other circumferential ranges, and the direction of the load received by the large-diameter gear due to meshing with the small-diameter gear overlaps with the predetermined range when viewed in the axial direction along the rotation axis of the large-diameter gear. the law of nature , the thickness of the wall portion in the predetermined range is thinner than the thickness of the wall portion in the other circumferential range; A gearing is provided. [Effects of the Invention]

[0011] According to the gear device of the present invention, it is possible to increase the radial rigidity of the case cover body while suppressing an increase in the axial rigidity and weight of the case cover body, and it is possible to maintain proper meshing between the large diameter gear and the small diameter gear even when the temperature changes, for example. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an external view showing a gear device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view of the gear device taken along line AA in FIG. 1. [Figure 3] 3(a) and 3(b) are enlarged views showing a part of FIG. 2. FIG. [Figure 4] FIG. 2 is a configuration diagram of a hypoid gear pair as viewed from the side wall side of the case body. [Figure 5] 1A is a diagram showing the inside of the case cover, FIG. 1B is a cross-sectional view taken along line BB in FIG. 1A, and FIG. 1C is a cross-sectional view taken along line CC in FIG. 1A. [Figure 6] 1(a) is a perspective view showing the inner surface of the case lid, and FIG. 1(b) is a perspective view showing the outer surface of the case lid. [Figure 7] 10(a) and 10(b) are perspective views showing the inner and outer surfaces of a case lid according to a comparative example. [Figure 8] 10(a) to 10(c) are graphs showing the results of comparison between a case lid according to a comparative example and a case lid according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Embodiment Mode] Embodiments of the present invention will be described with reference to Figures 1 to 6. The embodiments described below are shown as preferred specific examples for carrying out the present invention, and although some of the embodiments specifically exemplify various technically preferred aspects, the technical scope of the present invention is not limited to these specific embodiments.

[0014] FIG. 1 is an external view of a gear device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the gear device taken along line AA in FIG. 1. FIGS. 3(a) and 3(b) are enlarged views of a portion of FIG. 2. This gear device 1 is mounted on a vehicle and is used to distribute the driving force of a driving source, such as an engine or an electric motor, to left and right wheels while allowing differential rotation. In the following description, "left" and "right" refer to the left and right sides relative to the forward direction of the vehicle on which the gear device 1 is mounted. In this embodiment, the gear device 1 is disposed on the rear wheel side, and the left side of FIGS. 1 and 2 corresponds to the front side of the vehicle, and the right side of the drawings corresponds to the rear side of the vehicle. However, the gear device 1 may also be disposed on the front wheel side.

[0015] The gear device 1 includes a pinion gear shaft 2 to which driving force from a drive source is input via a drive shaft such as a propeller shaft, a pair of bearings 31, 32 supporting the pinion gear shaft 2, a ring gear 4 meshing with a pinion gear 21 of the pinion gear shaft 2, a differential device 5 having a differential case 51 rotating integrally with the ring gear 4, first and second bearings 61, 62 supporting the differential case 51, first and second shims 63, 64 in the form of annular plates for adjusting preloads of the first and second bearings 61, 62, and a differential carrier 10 as a case member accommodating these components. The pinion gear 21 is one aspect of the small-diameter gear of the present invention. The ring gear 4 is one aspect of the large-diameter gear of the present invention. The differential case 51 is one aspect of the rotating member of the present invention.

[0016] The differential carrier 10 has a case body 7 and a case lid body 8, and the case lid body 8 is fixed to the case body 7 with a plurality of bolts 11. The case body 7 and the case lid body 8 are made of die-cast aluminum alloy. The ring gear 4 and the differential case 51 rotate relative to the differential carrier 10 around a rotation axis O1 that runs along the left-right direction of the vehicle. Hereinafter, the direction parallel to this rotation axis O1 will be referred to as the axial direction.

[0017] The pinion gear shaft 2 has a pinion gear 21, an input portion 22 to which a driving force is input, and a shaft portion 23 supported by a pair of bearings 31, 32. The pinion gear 21 is provided at one end of the pinion gear shaft 2 and transmits the driving force input to the input portion 22 to the ring gear 4. The input portion 22 is provided at the other end of the pinion gear shaft 2 and has a plurality of spline protrusions 221 formed on its outer periphery. The shaft portion 23 has a male thread 231 formed on the end of the input portion 22 side. The pinion gear shaft 2 rotates relative to the differential carrier 10 about a rotation axis O2 that runs along the vehicle front-rear direction. When the gear device 1 is viewed vertically from above, the rotation axis O2 of the pinion gear shaft 2 is perpendicular to the rotation axis O1 of the ring gear 4 and the differential case 51.

[0018] The pair of bearings 31, 32 are tapered roller bearings and include outer rings 311, 321 and inner rings 312, 322, a plurality of tapered rollers 313, 323 arranged between the outer rings 311, 321 and the inner rings 312, 322, and cages 314, 324 that hold the plurality of tapered rollers 313, 323. The shaft portion 23 of the pinion gear shaft 2 is inserted through the inner rings 312, 322. The outer rings 311, 321 are held by the case body 7. A spacer 33 is arranged between the inner ring 312 of the bearing 31 on the pinion gear 21 side and the inner ring 322 of the bearing 32 on the input portion 22 side. A preload is applied to the pair of bearings 31, 32 by a nut 34 that is threaded onto a male thread 231 formed on the shaft portion 23.

[0019] The ring gear 4 has a larger diameter than the pinion gears 21 and is fixed to a flange portion 511 of the differential case 51. In the present embodiment, the ring gear 4 is fixed to the flange portion 511 of the differential case 51 with a plurality of bolts 50, but the ring gear 4 may also be fixed to the flange portion 511 by welding. The ring gear 4 is a hypoid gear and is formed so that its average pitch diameter is larger than the average pitch diameter of the pinion gears 21. The pinion gear 21 and the ring gear 4 mesh with each other to form a hypoid gear pair 100.

[0020] The differential device 5 includes a differential case 51, a pinion shaft 52 fixed to the differential case 51, a pair of pinion gears 53, 53 journaled on the pinion shaft 52, and right and left side gears 54, 55 meshed with the pair of pinion gears 53, 53. Right and left drive shafts 91, 92, shown by imaginary lines (two-dot chain lines) in FIG. 2, are spline-fitted with the right and left side gears 54, 55.

[0021] The differential case 51 is made of cast steel and integrally includes a flange portion 511 to which the ring gear 4 is fixed, a body portion 512 that houses a pair of pinion gears 53, 53 and right and left side gears 54, 55, a first supported portion 513 provided on one axial side of the body portion 512, and a second supported portion 514 provided on the other axial side of the body portion 512. The first supported portion 513 is supported by a first bearing 61, and the second supported portion 514 is supported by a second bearing 62. In other words, the first bearing 61 supports the differential case 51 on one axial side of the ring gear 4, and the second bearing 62 supports the differential case 51 on the other axial side of the ring gear 4.

[0022] The first and second bearings 61, 62 are tapered roller bearings. As shown in Fig. 3(a), the first bearing 61 has an outer ring 611 held by the case body 7 of the differential carrier 10, an inner ring 612 fitted onto the first supported portion 513 of the differential case 51, a plurality of tapered rollers 613 arranged between the outer ring 611 and the inner ring 612, and a cage 614 that holds the tapered rollers 613. As shown in Fig. 3(b), the second bearing 62 has an outer ring 621 held by the case cover 8 of the differential carrier 10, an inner ring 622 fitted onto the second supported portion 514 of the differential case 51, a plurality of tapered rollers 623 arranged between the outer ring 621 and the inner ring 622, and a cage 624 that holds the tapered rollers 623.

[0023] Axial preload is applied to the first and second bearings 61, 62 by fixing a case cover 8 to the case main body 7 with a plurality of bolts 11. The case cover 8 is elastically deformed by being fixed to the case main body 7 with a plurality of bolts 11, and its restoring force applies preload to the first and second bearings 61, 62. When the differential case 51 rotates, the plurality of tapered rollers 613, 623 of the first and second bearings 61, 62 roll on inner circumferential raceway surfaces 611a, 621a of the outer rings 611, 621 and outer circumferential raceway surfaces 612a, 622a of the inner rings 612, 622. The inner circumferential raceway surfaces 611a, 621a and the outer circumferential raceway surfaces 612a, 622a have a partial conical shape inclined with respect to the axial direction.

[0024] The first shim 63 is disposed adjacent to the outer ring 611 of the first bearing 61, and the second shim 64 is disposed adjacent to the outer ring 621 of the second bearing 62. The thicknesses of the first shim 63 and the second shim 64 are selected based on the results of dimensional measurements of each portion during the manufacture of the gear device 1, so as to ensure appropriate meshing between the pinion gear 21 of the pinion gear shaft 2 and the ring gear 4. This dimensional measurement is performed at room temperature in the factory where the gear device 1 is manufactured.

[0025] First and second sealing mechanisms 93, 94 are arranged between the right drive shaft 91 and the case main body 7, and between the left drive shaft 92 and the case cover 8. The first sealing mechanism 93 has a deflector 931 attached to the right drive shaft 91 and a sealing member 932 attached to the case main body 7. The sealing member 932 has sealing lips 932a, 932b that elastically contact the deflector 931 and the drive shaft 91, respectively. The second sealing mechanism 94 has a deflector 941 attached to the left drive shaft 92 and a sealing member 942 attached to the case cover 8. The sealing member 942 has sealing lips 942a, 942b that elastically contact the deflector 941 and the drive shaft 92, respectively.

[0026] The case body 7 accommodates the pinion gear shaft 2, the ring gear 4, the differential device 5, and the first bearing 61. The case cover 8 accommodates the second bearing 62. The case body 7 integrally includes a peripheral wall 71 on the outer periphery of the ring gear 4 and the differential device 5, a side wall 72 closing one axial side of the peripheral wall 71, a cylindrical first fitting portion 73 into which the first bearing 61 fits, a first annular wall portion 74 accommodating a seal member 932 of the first seal mechanism 93, and a first annular protrusion 75 provided between the first fitting portion 73 and the first annular wall portion 74.

[0027] The first shim 63 is disposed opposite an end face 75a of the first annular protrusion 75 on the first fitting portion 73 side, and is sandwiched between the outer ring 611 of the first bearing 61 and the first annular protrusion 75. The end face 75a of the first annular protrusion 75 is a receiving surface that receives a preload applied to the first and second bearings 61 and 62 via the first shim 63.

[0028] The inside of the first fitting portion 73 and the first annular wall portion 74 forms a through hole 70 into which the drive shaft 91 is inserted. The peripheral wall 71 of the case body 7 has an end opposite to the side wall 72 that opens toward the other axial direction, and this opening 700 of the case body 7 is covered by the case lid 8. The configuration of the case lid 8 will be described in detail later.

[0029] FIG. 4 is a configuration diagram of the hypoid gear pair 100 as viewed from the side wall 72 of the case main body 7. In FIG. 4, the arrow indicates the component of the load F perpendicular to the rotation axis O1 of the load F that the ring gear 4 receives when meshing with the pinion gear 21 during forward vehicle travel. The direction of this load F, when viewed axially from the ring gear 4, is toward the rear of the vehicle and toward the vertically downward direction relative to the rotation axis O1. The second bearing 62 supports the second supported portion 514 of the differential case 51 relative to the case cover 8 while bearing this load F. If the case cover 8 were to lack rigidity, the second bearing 62 would be displaced in the direction of the load F, adversely affecting the meshing between the ring gear 4 and the pinion gear 21. Therefore, to maintain proper meshing between the ring gear 4 and the pinion gear 21, it is desirable for the case cover 8 to have high rigidity.

[0030] However, simply increasing the thickness of case cover 8 to increase its rigidity would result in an increase in the weight of case cover 8, and the difference in the thermal expansion coefficient between differential carrier 10 and differential case 51 would make it difficult to adjust the preload on first and second tapered roller bearings 61, 62. In other words, because the thermal expansion coefficient of differential carrier 10, which is made of an aluminum alloy, is higher than that of differential case 51, which is made of steel, the gap between first tapered roller bearing 61 and second tapered roller bearing 62 increases at high temperatures and decreases at low temperatures. Here, if case cover 8 has high rigidity, a slight change in the gap between first tapered roller bearing 61 and second tapered roller bearing 62 would result in a large change in the preload applied to first and second bearings 61, 62.

[0031] In this embodiment, the configuration of the case cover body 8 described below increases the rigidity of the case cover body 8 in the radial direction (direction perpendicular to the rotation axis O1) while suppressing an increase in the axial rigidity and weight of the case cover body 8, making it possible to maintain an appropriate state of meshing between the ring gear 4 and the pinion gear 21.

[0032] Fig. 5(a) is a configuration diagram showing the inner surface (case main body 7 side) of case lid 8. Fig. 5(b) is a cross-sectional view taken along line BB in Fig. 5(a), and Fig. 5(c) is a cross-sectional view taken along line CC in Fig. 5(a). In Figs. 5(b) and 5(c), the left side of the drawings corresponds to the inner surface of case lid 8, and the right side of the drawings corresponds to the outer surface of case lid 8. Fig. 6(a) is a perspective view showing the inner surface of case lid 8, and Fig. 6(b) is a perspective view showing the outer surface of case lid 8.

[0033] The case cover 8 integrally includes an outer edge portion 81 that is arranged opposite the opening end face 71a, which is the end face on the opening side of the peripheral wall 71 of the case main body 7, and is fastened to the case main body 7 at multiple locations, a cylindrical second fitting portion 82 into which the second bearing 62 is fitted, a plate-shaped wall portion 83 that is provided between the outer edge portion 81 and the second fitting portion 82, a second annular wall portion 84 that accommodates the sealing member 942 of the second sealing mechanism 94, a second annular protrusion 85 that is provided between the second fitting portion 82 and the second annular wall portion 84, a plurality of ribs 86 that extend from the outer edge portion 81 toward the second fitting portion 82 on the outside of the case cover 8, and a plurality of ribs 87 that extend from the outer edge portion 81 toward the second fitting portion 82 on the inside of the case cover 8.

[0034] The multiple ribs 86, 87 are protrusions provided to reinforce the wall portion 83, and are formed radially from the rotation axis O1 of the ring gear 4. The multiple ribs 86 are provided to protrude from the wall portion 83 toward the outside of the case cover 8, and the multiple ribs 87 are provided to protrude from the wall portion 83 toward the inside of the case cover 8. The inside of the second fitting portion 82 and the second annular wall portion 84 of the case cover 8 forms a through hole 80 into which the drive shaft 92 is inserted.

[0035] The outer edge portion 81 is formed with a plurality of bolt insertion holes 810 parallel to the rotation axis O1, through which the plurality of bolts 11 are respectively inserted. The opposing surface 81a of the outer edge portion 81 that faces the open end face 71a of the case body 7 is formed in a flat shape. As shown in FIG. 6(b), the periphery of each bolt insertion hole 810 in the outer edge portion 81 forms a boss portion 811 that protrudes outward along the axial direction. The peripheral wall 71 of the case body 7 is formed with a plurality of screw holes 710 that open to the open end face 71a. The outer edge portion 81 of the case lid 8 is fastened to the case body 7 by threading the bolts 11 inserted into the plurality of bolt insertion holes 810 into the screw holes 710.

[0036] The second fitting portion 82 and the second annular wall portion 84 are aligned in the axial direction with the second annular protrusion 85 sandwiched therebetween, and the second fitting portion 82 is provided more inward of the differential carrier 10 than the second annular wall portion 84. As shown in FIG. 3(b), the outer ring 621 of the second bearing 62 is press-fitted into the inner circumferential surface 82a of the second fitting portion 82. The second shim 64 is disposed opposite an end face 85a of the second annular protrusion 85 on the second fitting portion 82 side, and is sandwiched between the outer ring 621 of the second bearing 62 and the second annular protrusion 85. The end face 85a of the second annular protrusion 85 is a receiving surface that receives a preload applied to the first and second bearings 61 and 62 via the second shim 64.

[0037] The wall portion 83 is provided in a disk shape on the outer periphery of the second fitting portion 82 and the second annular wall portion 84. The second fitting portion 82 protrudes from the wall portion 83 toward the inside of the differential carrier 10, and the second annular wall portion 84 protrudes from the wall portion 83 toward the outside of the differential carrier 10. The wall portion 83 is also formed with an injection hole 831 for injecting lubricating oil (differential oil) into the differential carrier 10 and a discharge hole 832 for discharging the lubricating oil. As shown in FIG. 1 , the injection hole 831 is closed by a plug 88, and the discharge hole 832 is closed by a plug 89.

[0038] As shown in Fig. 2, the outer ring 621 of the second bearing 62 is biased in the axial direction with respect to the plurality of bolt insertion holes 810. Specifically, an axial center position C1 of the outer ring 621 of the second bearing 62 and an axial center position C2 of the bolt insertion hole 810 are offset in the axial direction. In Fig. 2, this offset amount is indicated by D. In this embodiment, the outer ring 621 of the second bearing 62 is biased toward the inside of the differential carrier 10 with respect to the bolt insertion hole 810, and the wall portion 83 is inclined so as to be closer to the second fitting portion 82 and toward the inside of the differential carrier 10.

[0039] A plurality of ribs 86 are provided on the outside of the case cover 8 between the outer edge 81 and the second annular wall 84, extending in a radial direction perpendicular to the rotation axis O1. The injection hole 831 and the discharge hole 832 are each provided between two adjacent ribs 86. The axial height of the ribs 86 from the outer surface 83a of the wall 83 increases toward the second annular wall 84.

[0040] As shown in FIG. 5(a), on the inside of the case cover 8, the spacing between the multiple ribs 87 in a predetermined range R in the circumferential direction along the rotation direction of the ring gear 4 is narrower than the spacing between the multiple ribs 87 in other circumferential ranges. In FIG. 5(a), the wall portion 83 in this predetermined range R is indicated by gray shading. When the gear device 1 is viewed axially along the rotation axis O1 of the ring gear 4, the direction of the load that the ring gear 4 receives as a result of meshing with the pinion gear 21 coincides with the predetermined range R. In other words, the case cover 8 receives the load that the ring gear 4 receives as a result of meshing with the pinion gear 21 mainly in the portion of the predetermined range R.

[0041] Hereinafter, of the plurality of ribs 87, the plurality of ribs 87 formed in the predetermined range R will be referred to as narrow-spaced ribs 871, and the plurality of ribs 87 formed in other circumferential ranges outside the predetermined range R will be referred to as wide-spaced ribs 872. In this embodiment, six narrow-spaced ribs 871 and six wide-spaced ribs 872 are provided on the inside of the wall portion 83 of the case lid 8.

[0042] The wide-spaced ribs 872 extend radially perpendicular to the rotation axis O1 from a portion of the outer edge portion 81 where the bolt insertion holes 810 are formed toward the second fitting portion 82. The narrow-spaced ribs 871 are provided at equal circumferential intervals within a predetermined range R and extend radially perpendicular to the rotation axis O1. The narrow-spaced ribs 871 have their outer diameter side ends continuous with the outer edge portion 81 and their inner diameter side ends continuous with the second fitting portion 82. The width W1 of each narrow-spaced rib 871 in a direction perpendicular to the extension direction of the narrow-spaced rib 871 is narrower than the width W2 of each wide-spaced rib 872 in a direction perpendicular to the extension direction of the wide-spaced rib 872. For example, the width W1 of the narrow-spaced rib 871 is equal to or less than half the width W2 of the wide-spaced rib 872.

[0043] As shown in FIG. 5(a), when the angle between two circumferentially adjacent narrow-spaced ribs 871 is θ1 and the angle between the two circumferentially narrowest widely-spaced ribs 872 among the six widely-spaced ribs 872 is θ2, θ1 is smaller than θ2. θ1 is preferably equal to or smaller than half of θ2, and in this embodiment, θ1 is equal to or smaller than one-third of θ2. The intervals between the multiple narrowly-spaced ribs 871 do not necessarily have to be equal. In this case, it is sufficient that the angle between the two circumferentially widest widely-spaced ribs 871 among the multiple narrowly-spaced ribs 871 is smaller than θ2.

[0044] As shown in FIG. 5(b), the wall portion 83 has a thickness T1 in the axial direction within the predetermined range R that is thinner than a thickness T2 in the axial direction within the other circumferential ranges. In this embodiment, the height H1 (maximum height in the axial direction) of the narrow-spaced rib 871 from the inner surface 83b of the wall portion 83 is greater than the height H2 (maximum height in the axial direction) of the wide-spaced rib 872 from the inner surface 83b of the wall portion 83. The height H1 of the narrow-spaced rib 871 from the inner surface 83b of the wall portion 83 may be less than the height H2 of the wide-spaced rib 872 from the inner surface 83b of the wall portion 83. However, by making the height H1 of the narrow-spaced rib 871 greater than the height H2 of the wide-spaced rib 872, the radial rigidity of the case cover 8 within the predetermined range R can be further increased.

[0045] In the predetermined range R of the case cover 8, the narrowly spaced ribs 871 are formed only on the inside of the case cover 8, and no ribs 86 are provided on the outside of the case cover 8. In FIG. 6(b), the reference numeral 800 indicates a blank area where no ribs 86 are provided on the outside of the case cover 8. As shown in FIG. 6(b), one boss portion 811 is present on the outer periphery of this blank area 800, but no ribs 86 are provided extending from the boss portion 811 toward the second annular wall portion 84. That is, in this embodiment, of the inside and outside of the case cover 8 in the predetermined range R, the narrowly spaced ribs 871 are provided only on the inside, which is one side where the outer ring 621 of the second bearing 62 is biased with respect to the bolt insertion holes 810.

[0046] Furthermore, a circumferential rib 873 is provided on the inside of the case cover 8 in the predetermined range R, extending in the circumferential direction and intersecting the multiple narrow-spaced ribs 871. Both circumferential ends 873a, 873b of the circumferential rib 873 in the extending direction are connected to the multiple wide-spaced ribs 872 in other circumferential ranges that are circumferentially adjacent to the predetermined range R. The circumferential rib 873 suppresses circumferential deflection of the case cover 8. Note that, in this embodiment, one circumferential rib 873 is provided in the predetermined range R, but multiple circumferential ribs 873 may be provided, for example, in the form of concentric arcs.

[0047] (Comparative Example) 7(a) and 7(b) are perspective views showing the inner and outer surfaces of a case cover 8A shown as a comparative example. This case cover 8A is provided with a plurality of ribs 86, 87 on the outer and inner sides, extending from the vicinity of each bolt insertion hole 810 in the outer edge portion 81 around the through hole 80 toward the second annular wall portion 84 and the second fitting portion 82, and is not provided with a narrow-spaced rib 871. More specifically, a single rib 87 is provided in place of the plurality of narrow-spaced ribs 871 in a range corresponding to the predetermined range R shown in FIG. 5, and a single rib 86 is provided in a portion corresponding to the blank area 800 shown in FIG. 6(b).

[0048] 8(a) to 8(c) are graphs showing the results of a comparison between a gear device 1 using the case cover 8 according to the above embodiment and a gear device 1 in which the case cover 8 is replaced with a case cover 8A according to a comparative example. FIG. 8(a) shows the results of a comparison of the weights of the case covers 8 and 8A. FIG. 8(b) is a graph showing the amount of displacement of the second fitting portion 82 relative to the outer edge portion 81 due to elastic deformation of the case covers 8 and 8A when a predetermined torque is transmitted from the pinion gear shaft 2 to the drive shafts 91 and 92. FIG. 8(c) is a graph showing the amount of left-right opening, which is the amount of change in dimension between the end face 75a of the first annular protrusion 75 of the case body 7 and the end face 85a of the second annular protrusion 85 of the case cover 8, when a force is applied so as to separate the end face 75a and the end face 85a of the second annular protrusion 85 from each other in the axial direction.

[0049] 8(a), the weight of the case lid 8 according to the embodiment and the weight of the case lid 8A according to the comparative example are equivalent. Even though multiple closely spaced ribs 871 are provided in a predetermined range R on the inside of the case lid 8, the increase in weight is suppressed because the thickness of the wall portion 83 in the predetermined range R is made thinner than the thickness in other circumferential ranges, and ribs 86 are not provided on the outside of the case lid 8 in the predetermined range R.

[0050] 8(b), the amount of displacement of the second fitting portion 82 during torque transmission is reduced by approximately 15% or more when the case cover 8 according to the embodiment is used compared to when the case cover 8A according to the comparative example is used. As a result, when the case cover 8 according to the embodiment is used, the meshing between the pinion gear 21 and the ring gear 4 is maintained better than when the case cover 8A according to the comparative example is used.

[0051] 8(c), the left-right opening amount when the case cover 8 according to the embodiment is used is approximately 14% larger than when the case cover 8A according to the comparative example is used. This shows that the case cover 8 according to the embodiment has higher elasticity so that it can flexibly deform in the axial direction compared to the case cover 8A according to the comparative example. In other words, when the case cover 8 according to the embodiment is used, even if the distance between the first bearing 61 and the second bearing 62 changes due to, for example, a temperature change in the differential carrier 10 or the differential case 51, fluctuations in the magnitude of the preload applied to the first and second bearings 61, 62 are suppressed.

[0052] (Effects of the embodiment) According to the embodiment of the present invention described above, the range in which the multiple narrowly spaced ribs 871 are provided at close intervals in the circumferential direction on the inside of the case cover 8 is limited to the predetermined range R that overlaps with the direction of the load that the ring gear 4 receives when meshed with the pinion gear 21. Therefore, compared to, for example, a case in which multiple ribs are provided at close intervals around the entire circumference of the outer periphery of the second fitting portion 82, the radial rigidity of the case cover 8 can be increased while suppressing an increase in weight of the case cover 8. Note that while the multiple narrowly spaced ribs 871 significantly contribute to increasing the radial rigidity of the case cover 8 in the predetermined range R, they do not significantly contribute to increasing the axial rigidity of the case cover 8. As a result, even if the axial distance between the first bearing 61 and the second bearing 62 changes due to, for example, a temperature change, this change in distance is absorbed by the elastic deformation of the case cover 8, and the magnitude of the preload applied to the first and second bearings 61, 62 can be easily maintained within an appropriate range.

[0053] In addition, in the above embodiment, the thickness of the wall portion 83 in the predetermined range R is formed thinner than the thickness of the wall portion 83 in other circumferential ranges, which prevents an increase in the weight of the case lid body 8 and makes it easier for the case lid body 8 to elastically deform in the axial direction. Furthermore, in the above embodiment, the multiple closely spaced ribs 871 are provided only on the inside of the case lid body 8 in the predetermined range R, and no ribs 86 are provided on the outside of the case lid body 8 in the predetermined range R, which also prevents an increase in the weight of the case lid body 8 and makes it easier for the case lid body 8 to elastically deform in the axial direction.

[0054] Furthermore, in the above embodiment, multiple closely spaced ribs 871 are provided on the inside of the case cover 8, on the side where the outer ring 621 of the second bearing 62 is biased relative to the bolt insertion hole 810. This increases the radial rigidity of the case cover 8 compared to the case where multiple ribs similar to the multiple closely spaced ribs 871 are formed on the outside of the case cover 8.

[0055] Furthermore, in the above embodiment, the circumferential rib 873 suppresses circumferential deflection of the case cover 8. In particular, in the present embodiment, both end portions 873a, 873b of the circumferential rib 873 are connected to the widely spaced ribs 872 in other circumferential ranges, thereby enhancing the deflection suppression effect.

[0056] (Addendum) The present invention has been described above based on the embodiments, but the invention according to the claims is not limited to these embodiments. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. Furthermore, the present invention can be appropriately modified and implemented by omitting some components or adding or substituting components within the scope of the spirit of the invention. For example, the present invention can be modified and implemented as follows.

[0057] In the above embodiment, a case has been described in which the outer ring 621 of the second bearing 62 is biased toward the inside of the differential carrier 10 with respect to the bolt insertion holes 810, but this is not limiting, and the outer ring 621 of the second bearing 62 may be biased toward the outside of the differential carrier 10 with respect to the bolt insertion holes 810. In this case, a plurality of closely spaced ribs are provided at close intervals in a predetermined range R on the outside of the case cover 8 so as to protrude from the outer surface 83a of the wall portion 83, and no ribs are provided on the inner surface 83b of the wall portion 83 in the predetermined range R.

[0058] Furthermore, in the above embodiment, the gear device 1 is described as being disposed between a propeller shaft and a pair of drive shafts in a vehicle, but the use of the gear device of the present invention is not limited to this, and the gear device of the present invention can also be used in industrial machinery, for example. [Explanation of symbols]

[0059] 1...Gear unit 11...Bolt 21...Pinion gear (small diameter gear) 4...Ring gear (large diameter gear) 51...Differential case (rotating member) 61...First bearing 611, 621...Outer ring 62...Second bearing 7...Case body 73...First fitting portion 74...first annular wall portion 8...case lid body 81...Outer edge portion 810...Bolt insertion hole 82... Second fitting portion 85... Second annular protrusion 86,87...Ribs 871...Narrowly spaced ribs 872... Widely spaced ribs 873... Circumferential ribs 873a, 873b...both ends R...predetermined range

Claims

1. a large-diameter gear and a small-diameter gear that mesh with each other; a rotating member that rotates integrally with the large-diameter gear; a first bearing that supports the rotating member on one axial side of the large-diameter gear; a second bearing that supports the rotating member on the other axial side of the large-diameter gear; a case body that houses the large-diameter gear and has a cylindrical first fitting portion into which the first bearing is fitted; and a case cover that covers an opening of the case body that opens toward the other axial side and has a cylindrical second fitting portion into which the second bearing is fitted, the case lid has an outer edge portion disposed opposite to the open end face of the case main body and fastened to the case main body at a plurality of locations, a plate-like wall portion provided between the outer edge portion and the second fitting portion, and a plurality of ribs provided protruding from the wall portion, and the intervals between the plurality of ribs in a predetermined range in a circumferential direction along the rotation direction of the large-diameter gear are formed narrower than the intervals between the plurality of ribs in other circumferential ranges, a direction of a load that the large-diameter gear receives by meshing with the small-diameter gear overlaps with the predetermined range when viewed in an axial direction along a rotation axis of the large-diameter gear, the thickness of the wall portion in the predetermined range is thinner than the thickness of the wall portion in the other circumferential range; Gearing.

2. a width of each of the plurality of ribs in the predetermined range is narrower than a width of each of the plurality of ribs in the other circumferential ranges; 2. The gear device of claim 1.

3. In the predetermined range, the plurality of ribs are provided only on one of the inside and outside of the case lid.

3. A gear device according to claim 1 or 2.

4. A plurality of bolt insertion holes are formed in the outer edge portion parallel to the rotation axis, an outer ring of the second bearing held in the second fitting portion is biased in the axial direction with respect to the plurality of bolt insertion holes, the one side on which the plurality of ribs are provided in the predetermined range is a side on which an outer ring of the second bearing is biased with respect to the plurality of bolt insertion holes; 4. The gearing of claim 3.

5. a height of the plurality of ribs from the surface on the one side of the wall portion in the predetermined range is greater than a height of the plurality of ribs from the surface on the one side of the wall portion in the other circumferential range; 5. The gearing of claim 4.

6. The case cover is provided with a circumferential rib extending in the circumferential direction and intersecting the plurality of ribs in the predetermined range. A gearing according to any one of claims 1 to 5.

7. The circumferential rib has both circumferential ends connected to ribs adjacent to the predetermined range in the circumferential direction among the plurality of ribs in the other circumferential range, 7. The gearing of claim 6.

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