GEARBOX HOUSING

Abstract

Gearbox housing, comprising: a first housing part (6) having a connecting surface (6b) along its outer circumference; a second housing part (7) having along its outer circumference a connecting surface (7a) which is fastened to and abuts the connecting surface (6b) of the first housing part (6) by fastening means (8), and which cooperates with the first housing part (6) to form an accommodation space therebetween which accommodates a transmission (9) with a first gear (17) and a differential with a second gear (21) which is in engagement with the first gear (17), wherein one of the first housing part (6) and the second housing part (7) comprises a side wall (26) having an outer edge (26a) continuously connected to the connecting surface (7a) of the one of the first housing part (6) and the second housing part (7), and a bearing mounting opening (7b) formed in its central region for rotatably supporting the differential (10) via a bearing (24), characterized in that when the portion of the side wall (26) which is subjected to a load (Fc1) acting under a load (Kt1) acting in a tangential direction to the pitch circle of the first gear (17) and the pitch circle of the second gear (21) in a specific direction when the first and second gears (17, 21) meshing with each other move, on the bearing mounting hole (7b) is a first surface portion (33), the first surface portion (33) has a lower rigidity than second surface portions (34, 35) on one and the opposite side in a width direction of the first surface portion (33), thereby distributing the load (Fc1) exerted on the bearing mounting hole (7b) among fastening means on the connecting surface (7a) extending radially outside not only the first surface portion (33) but also the second surface portions (34, 35).

Description

[0001] The present invention relates to a transmission housing and, more particularly, to a transmission housing for a transmission and a differential.

[0002] In general, a transmission case for a wheeled vehicle such as an automobile accommodates a transmission and a differential in its two casings, and the rigidity of that portion of the transmission case surrounding the differential is increased by arranging at least one of the fastening bolts fastening the casings at a position in the direction of which a reaction force from a final drive gear acts during drive of the differential.

[0003] With regard to, for example, the descriptions in JP 3 963 366 B2, the surface at which the two housing parts of a transmission housing meet is remote from a final drive gear due to the design of the transmission housing, and therefore screw attachment parts to which a fastening screw fastens the housing parts are arranged at a location on an axis along which a reaction force originating from the final drive gear acts, in order to absorb the reaction force by this screw. STATE OF THE ART

[0004] In such a conventional transmission case, since the screw attachment parts, to which a fastening screw fastens the case parts, are arranged at a position on an axis along which the force from the final drive gear acts, in JP 3 963 366 B2, the weight of the transmission case increases because a large screw is required as the fastening screw to increase strength, and the number of screws used to fasten the case parts increases in proportion to the number of screws provided at the screw attachment parts. Moreover, the ability to keep the interior of the case parts liquid-tight is reduced due to weakening of the fastening between the fastening screws and the screw attachment parts caused by concentration of the reaction force from the final drive gear at the screw attachment parts.

[0005] Increasing the rigidity of each of the housing parts by increasing the thickness of the housing parts may be effective in preventing a reduction in the ability to keep the interior of the housing parts liquid-tight, but is undesirable because the weight of the transmission housing increases.

[0006] US 2007 / 0 155 572 A1 describes first and second reinforcing ribs formed between the first side connecting surface and the second side connecting surface. The first reinforcing rib extends from a rib connecting portion in a vertical first direction. The second reinforcing rib extends from the rib connecting portion in a horizontal second direction. The first and second reinforcing ribs are provided to surround a drive shaft to transmit the drive force from the transmission mechanism to the transfer case.

[0007] US 2009 / 0 127 954 A1 describes a motor-type drive device in which the rotation of a rotor shaft of an electric motor is transmitted to a differential gear via a reduction gear, and an output shaft of a pair of output shafts of the differential gear is arranged within the rotor shaft. Here, the rigidity of the intermediate housing can be increased by the spindle, thus improving the supporting rigidity of the differential gear and ensuring smooth power transmission. SUMMARY OF THE INVENTION

[0008] The present invention, which has been made in consideration of the problem mentioned above in JP 3 963 366 B2, has an object to provide a transmission case in which a reduction in the ability to keep the interior of case parts liquid-tight is prevented while an increase in the weight of the transmission case is prevented.

[0009] According to a first aspect of the present invention, a transmission housing comprises a first housing part having a connecting surface along its outer circumference, a second housing part having a connecting surface along its outer circumference, which is fastened by fastening means to and abuts the connecting surface of the first housing part, and which cooperates with the first housing part to form an accommodation space therebetween, which accommodation space comprises a transmission having a first gear and a differential having a second gear meshing with the first gear, wherein one of the first housing part and the second housing part comprises a side wall having an outer edge continuously connected to the connecting surface of the one of the first housing part and the second housing part, and a bearing mounting opening formed in its central region for rotatably supporting the differential via a bearing, wherein then,When the portion of the side wall that is subjected to a load acting on the bearing mounting hole under a load tangential to the pitch circle of the first gear and the pitch circle of the second gear in a specific direction when the first and second gears mesh with each other move is a first surface portion, the first surface portion has a lower rigidity than second surface portions on one and the opposite side in a width direction of the first surface portion, thereby enabling distribution of the load acting on the bearing mounting hole among fastening means on the connecting surface that are located radially outside not only the first surface portion but also the second surface portions.

[0010] According to a second aspect of the present invention, when the first surface portion is a first side wall portion and the second surface portions are second side wall portions, the first side wall portion may be bent inwardly with respect to the second side wall portions in a direction orthogonal to the plane of the joining surface of one of the first housing part and the second housing part to form a recessed shape.

[0011] According to a third aspect of the present invention, when the portion of the side wall which is deformed to a maximum extent by a load applied to the bearing mounting hole under a load acting in a tangential direction to the pitch circle of the first gear and the pitch circle of the second gear in a direction opposite to the predetermined direction when the first and second gears meshing with each other move is a third surface portion, the third surface portion may have lower rigidity than fourth surface portions on one and the opposite sides in a width direction of the third surface portion.

[0012] According to a fourth aspect of the present invention, when the third surface portion is a third side wall portion and the fourth surface portions are fourth side wall portions, the third side wall portion may be bent inwardly with respect to the fourth side wall portions in a direction orthogonal to the plane of the joining surface of one of the first housing part and the second housing part to form a recessed shape.

[0013] According to a fifth aspect of the present invention, it is desirable that oil is stored at the bottoms of the first housing part and the second housing part, the third side wall portion is arranged above the bearing mounting hole to form an oil reservoir for oil thrown up by the second gear, and the third side wall portion is formed in its lower region with an oil supply hole to allow oil to drip down onto the bearing mounting hole.

[0014] According to the above-mentioned first aspect, when the portion of the side wall that is deformed to a maximum extent by a load applied to the bearing mounting hole under a load tangential to the pitch circle of the first gear and the pitch circle of the second gear in a certain direction when the first and second gears meshing with each other move is the first surface portion, the first surface portion has lower rigidity than second surface portions on one and the opposite sides in a width direction of the first surface portion. This enables the second surface portions to be deformed after the deformation of the first surface portion under the load applied to the bearing mounting hole.

[0015] Therefore, this enables distribution of the load exerted on the bearing mounting hole between the first surface portion and the second surface portions, thereby enabling distribution of the load exerted on the bearing mounting hole among fasteners on the connecting surface located radially outside not only the first surface portion but also the second surface portions. As a result, it is possible to prevent local deformation of the portion of the connecting surface located radially outside the first surface portion without resorting to increasing the thickness of the sidewall or increasing the number of fasteners.

[0016] This results in preventing the increase in the weight of the transmission case and preventing the fluid tightness of the interior of the transmission case from being reduced.

[0017] According to the above-mentioned second aspect, when the first surface portion is a first side wall portion and the second surface portions are second side wall portions, the first side wall portion may be bent inward with respect to the second side wall portions in a direction orthogonal to the plane of the joining surface of one of the first housing member and the second housing member to form a recessed shape. This makes the deformation of the first side wall portion by the load applied to the bearing mounting hole under the load in the specific direction when the first and second gears mesh with each other move easier than the deformation of the second side wall portions.

[0018] According to the above-mentioned third aspect, when the portion of the side wall which is deformed to a maximum extent by a load applied to the bearing mounting hole under a load acting in a tangential direction to the pitch circle of the first gear and the pitch circle of the second gear in a direction opposite to the predetermined direction when the first and second gears meshing with each other move is the third surface portion, the third surface portion may have a lower rigidity than fourth surface portions on one and the opposite side in a width direction of the third surface portion, and the first surface portion has a lower rigidity than second surface portions on one and the opposite side in a width direction of the first surface portion.This makes it possible for the fourth surface portions to be deformed after the deformation of the third surface portion by the load applied to the bearing mounting hole under the load applied in a tangential direction to the pitch circle of the first gear and the pitch circle of the second gear in a direction opposite to the predetermined direction when the first and second gears meshing with each other move.

[0019] Therefore, this enables distribution of the load exerted on the bearing mounting hole between the third surface portion and the fourth surface portions, thereby enabling distribution of the load exerted on the bearing mounting hole among fasteners on the connecting surface located radially outside not only the third surface portion but also the fourth surface portions. As a result, it is possible to prevent local deformation of that portion of the connecting surface located radially outside the third surface portion without resorting to increasing the thickness of the sidewall or increasing the number of fasteners.

[0020] This results in preventing the increase in the weight of the transmission case and more effectively preventing the fluid tightness of the interior of the transmission case from being reduced.

[0021] According to the fourth aspect mentioned above, when the third surface portion is a third side wall portion and the fourth surface portions are fourth side wall portions, the third side wall portion is bent inward with respect to the fourth side wall portions in a direction orthogonal to the plane of the joining surface of one of the first housing member and the second housing member to form a recessed shape. This makes the deformation of the third side wall portion by the load applied to the bearing mounting hole under the load applied in a direction tangential to the pitch circle of the first gear and the pitch circle of the second gear in a direction opposite to the predetermined direction when the first and second gears mesh with each other move, lighter than the deformation of the fourth side wall portions.

[0022] According to the fifth aspect mentioned above, oil is stored at the bottoms of the first case and the second case, the third sidewall portion is disposed above the bearing mounting hole to form an oil reservoir for oil thrown up by the second gear, and the third sidewall portion is formed with an oil supply hole at its lower portion. This allows oil to drip down onto the bearing mounting hole, allowing oil thrown up by the rotation of the second gear of the differential and stored in the third sidewall portion to drip down onto the bearing of the differential. This improves the lubrication of the bearing. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing an embodiment of a transmission case according to the present invention, which is a plan view of a vehicle having a transmission case including a differential. Fig. 2 is a view showing the embodiment of the transmission case according to the present invention, which is a cross section of a transmission and a differential. Fig. 3 is a view showing the embodiment of the gear case according to the present invention, which is a side view of the gear case seen from an axial end side. Fig. 4 is a view showing the embodiment of the gear case according to the present invention, which is a side view of the gear case seen from the other axial end side. Fig. Fig. 5 is a view showing the embodiment of the gear case according to the present embodiment, which is a cross-sectional view taken along the line V1-V1 in Fig. 4. Fig. Fig. 6 is a view showing the embodiment of the transmission case according to the present embodiment, which is a cross-sectional view taken along the line V2-V2 in Fig. 4. Fig. Fig. 7 is a view showing the embodiment of the gear case according to the present embodiment, which is a cross-sectional view taken along the line V3-V3 in Fig. 4. Fig. 8 is a view showing the embodiment of the gear case according to the present invention, which is a view showing a deformation region of a second case member when the second case member receives a compressive load Fc1. Fig. 9 is a view showing the embodiment of the gear case according to the present invention, which is a view showing a deformation area of ​​the second case member when the second case member receives a compressive load Fc2. DESCRIPTION OF EMBODIMENTS

[0023] With reference to the accompanying drawings, an embodiment of a gear housing according to the present invention will be described below.

[0024] Fig. 1 to 9 show the embodiment of the gear housing according to the present invention.

[0025] First the structure is explained.

[0026] With reference now to Fig. 1, a vehicle 1 has, in a front portion of the vehicle 1, an engine 2 in the form of an internal combustion engine and a power transmission device 3, wherein the power transmission device 3 transmits the power of the engine 2 via respective drive axle shafts 4L, 4R to a left and a right drive wheel 5L, 5R.

[0027] With reference to Fig. 2, the power transmission device 3 comprises a first housing part 6 and a second housing part 7. The first housing part 6 is open at its right end and is formed along the outer circumference of its right end with a connecting surface 6a, to which connecting surface 6a a connecting surface 2a formed along the outer circumference of a left end of an engine block 2A of the engine 2 is fastened by screws not shown.

[0028] Furthermore, the first housing part 6 is open at its left end, and a connecting surface 6b is formed along the outer periphery of its left end. The left housing part 7 is closed at its left end, but is formed with a connecting surface 7a along the outer periphery of its right end at its right end. This connecting surface 7a is fastened to the connecting surface 6b of the first housing part 6 by a plurality of screws 8. The screws 8 are arranged individually separated from each other along a direction in which the connecting surface 6b of the first housing part and the connecting surface 7a of the second housing part extend, and the interiors of the first housing part 6 and the second housing part 7 are held liquid-tight by fastening the connecting surface 6b and the connecting surface 7a to each other by means of the screws 8.

[0029] Furthermore, the engine 2 in the embodiment is a so-called transversely mounted engine, with a crankshaft (not shown) of the engine 2 extending orthogonally to the longitudinal direction of the vehicle. Therefore, the axial ends of the first housing part 6 and the second housing part 7, which are spaced apart in the lateral direction of the vehicle 1, can be referred to as the right end and the left end. In this embodiment, the first housing part 6 and the second housing part 7 cooperate with each other to form a transmission case 31.

[0030] Between the first housing part 6 and the second housing part 7, ie, in the interior of the first housing part 6 and the second housing part 7, a transmission 9 and a differential 10 are arranged, and in other words, the first housing part 6 and the second housing part 7 have a receiving space 11 for receiving the transmission 9 and the differential 10.

[0031] Furthermore, the transmission 9 is accommodated in the front of the receiving space 11 defined by the first housing part 6 and the second housing part 7, while the differential 10 is accommodated in the rear of the receiving space 11 defined by the first housing part 6 and the second housing part 7.

[0032] The transmission 9 is a manual transmission. The transmission 9 includes an input shaft 12 rotatably supported by the first and second housing portions 6, 7 and arranged coaxially with the crankshaft of the engine 2; a countershaft 13 rotatably supported by the first and second housing portions 6, 7 and arranged parallel to the input shaft 12; and a reverse shaft 14 fixed to the first and second housing portions 6, 7 and arranged parallel to the countershaft 13; the input shaft 12 having a gear train 15, and the countershaft 13 having a gear train 16 for providing a selected one of various gears.

[0033] Furthermore, a counter gear 17 (or first gear) is arranged at an output end of the countershaft 13 and this counter gear 17 is in engagement with a final drive gear 21 (or a second gear) of the differential 10.

[0034] In addition, the transmission 9 is designed as a manual transmission in the present embodiment, but the transmission could be a continuously variable transmission (CVT) of the V-belt type or an automatic transmission.

[0035] The differential 10 includes a differential case 20 rotatably supported by a bearing mounting hole 6c of the first case 6 via a bearing 19 and by a bearing mounting hole 7b of the second case 7 via a bearing 24; a final drive gear 21 fixed to the outer periphery of the differential case 20 and meshing with the final drive gear 21; a pair of pinion gears 22 disposed in the differential case 20 and rotatably supported by a shaft or common pin supported by the differential case 20; and a pair of side gears 23 meshing with the pair of pinion gears and supporting inner ends of the drive axle shafts 4L, 4R through a spline coupling.

[0036] The drive axle shafts 4L, 4R are inserted into the differential case 20 through the bearings 19, 24 and coupled to the pair of side gears 23.

[0037] Power from the engine 2 is transmitted from the counter gear 17 to the final drive gear 21 via a power path selected in the transmission 9. As the differential case 20 rotates together with the final drive gear 21, the drive from the transmission 9 is transmitted through the pinion gears 22 and the side gears 23 to the left and right drive wheels 5L, 5R to allow different speeds of the left and right drive wheels 5L, 5R depending on the loads to which the left and right drive wheels 5L, 5R are subjected.

[0038] Moreover, the second housing part 7 is shaped such that its front portion with respect to the vehicle 1 along a width direction of the vehicle 1 has a long length, and its remaining portion at the rear with respect to the vehicle 1 along the width direction of the vehicle 1 has a short length compared to the length of the front portion. Therefore, regarding the volume of the accommodation space 11, the volume of the remaining portion of the space for the differential 10 defined by the first housing part 6 and the second housing part 7 is small compared to the volume of a space portion for the transmission 9 defined by the first housing part 6 and the second housing part 7.

[0039] In other words, on the rear side of the second housing part 7 relative to the vehicle 1, a side wall 26 is formed with an outer edge 26a, which is continuously connected to the connecting surface 7a. Between the side wall 26 and a rear side wall of the first housing part 6 is a differential receiving space 11A for receiving the differential 10, wherein this differential receiving space 11A forms a portion of the receiving space 11.

[0040] Furthermore, a gear housing space 11B is formed between a wall surface on the front side of the first housing 6 with respect to the vehicle 1 and the inner side of a wall surface on the front side of the second housing 6 with respect to the vehicle 1. This gear housing space 11B forms the remaining portion of the housing space 11. This explains why the gear housing space 11B has a larger volume than the differential housing space 11A. Furthermore, the bearing mounting hole 7b is formed in the center of the side wall 26. As used herein, "center" means the center in the radial direction.

[0041] With reference to Fig. 3, screw holes 7c are formed on the connecting surface 7a of the second housing part 7 to allow the insertion of screws 8. These screw holes 7c are individually separated from each other along the direction of the connecting surface 7a. The countershaft 13, indicated by hatching, is rotatably supported at the front of the second housing part 7 with respect to the vehicle 1. In addition, the countershaft gear 17 on the countershaft 13 meshes, as indicated by dashed lines, with the final drive gear 21 attached to the differential case 20. As can be seen from Fig. 3, the differential 10 rotates about a differential axis 25 (ie, a rotation axis of the drive axle shafts 4L, 4R).

[0042] During the power transmission between the transmission 9 and the differential 10, so-called "mesh" loads occur in three directions at a point where the two gears mesh with each other, i.e., a contact point between a pitch circle of the counter gear 17 and a pitch circle of the final drive gear 21.

[0043] The meshing loads are a pitch circle tangential load Kt to the pitch circle of the final drive gear 21, a radial load Kr directed toward the final drive gear 21, and an axial load Ka along the axis of the counter gear 17. When the counter gear 17 rotates counterclockwise when the vehicle 1 moves forward, and when the counter gear 17 rotates clockwise when the vehicle moves backward, the final drive gear 21 is subjected to a pitch circle tangential load Kt1 directed in a certain direction or in Fig. 3 when the vehicle is accelerated during forward movement or decelerated during reverse movement (each of these traveling states will hereinafter be referred to as "at the time of driving the final drive gear 21 by the counter gear 17" or, for short, "during driving"). This pitch circle tangential load Kt1 applied in the specific direction will hereinafter be referred to as "load during driving F1."

[0044] Moreover, the final drive gear 21 is subjected to a pitch circle tangential load Kt2 acting in a direction opposite to the specified direction or in Fig. 3 when the vehicle is accelerated during reverse movement or decelerated during forward movement (each of these traveling states will hereinafter be referred to as "at the time of driving the counter gear 17 by the final drive gear 21" or "when being driven" for short). The direction of this pitch circle tangential load Kt2 is opposite to the direction of the pitch circle tangential load Kt1, so that a unit vector representing the direction of the pitch circle tangential load Kt2 and a unit vector representing the direction of the pitch circle tangential load Kt1 have point symmetry around the point at which the counter gear 17 and the final drive gear 21 mesh with each other. This pitch circle tangential load Kt2, which is applied in the direction opposite to the specified direction, will hereinafter be referred to as "load when being driven F2".

[0045] In addition, at the time when the counter gear 17 drives the final drive gear 21 as mentioned above under the driving load F1 acting on the final drive gear 21, a thrust force Fc1 acts in a direction determined from the countershaft 13 via the bearing 24, that is, downward with respect to the differential axis 25, on the bearing mounting hole 7b of the second case part 7.

[0046] In addition, at the time when the counter gear 17 is driven by the final drive gear 21 as mentioned above under the load F2 acting on the final drive gear 21 when being driven, a thrust load Fc2 acts in a direction determined from the countershaft 13 via the bearing 24, that is, upward with respect to the differential axis 25, on the bearing mounting hole 7b of the second case part 7. The direction of the thrust load Fc2 is generally opposite to the direction of the thrust load Fc1, so that a unit vector representing the direction of the thrust force Fc2 and a unit vector representing the direction of the thrust force Fc1 generally have point symmetry about the differential axis 25.

[0047] With regard to the present embodiment of the transmission case 31, when a first surface portion is the portion of the side wall 26 which is deformed to a maximum extent by the compressive load Fc1 under the driving load F1 exerted in a tangential direction to the pitch circle of the counter gear 17 and the pitch circle of the final drive gear 21 when the counter gear 17 and the final drive gear 21 meshing with each other move, the first surface portion has lower rigidity than second surface portions on one and the opposite side in a width direction of the first surface portion.

[0048] In particular, as in Fig. As shown in Figure 3, the first surface portion is a portion where the compressive load Fc1 is applied and includes the peripheral portions, so that the first surface portion is formed by a first sidewall portion 33. Moreover, the second surface portions on one and the opposite sides in the width direction of the first sidewall portion 33 are formed by second sidewall portions 34, 35.

[0049] With reference to Fig. 3 and Fig. 5, a surface of each of the second side wall portions 34, 35 is formed in a planar shape substantially coplanar with the joint surface 7a, while, compared with the second side wall portions 34, 35, a surface of the first side wall portion 33 is formed in a hollowed shape or bent inward in a direction orthogonal to the plane of the joint surface 7a to form a depressed shape. This makes the rigidity of the first side wall portion 33 against the compressive load Fc1 lower than the rigidity of the second side wall portions 34, 35 in the present embodiment of the gear case 31.

[0050] With regard to the present embodiment of the transmission case 31, when a third surface portion is the portion of the side wall 26 which is deformed to a maximum extent by the compressive load Fc2 under the driving load F2 exerted in a tangential direction to the pitch circle of the counter gear 17 and the pitch circle of the final drive gear 21 when the counter gear 17 and the final drive gear 21 meshing with each other move, the third surface portion has lower rigidity than fourth surface portions on one and the opposite side in a width direction of the second surface portion.

[0051] In particular, as in Fig. As shown in Figure 3, the third surface portion is a portion where the compressive load Fc2 is applied and includes the peripheral portions, so that the third surface portion is formed by a third sidewall portion 36. Furthermore, the fourth surface portions on one and the opposite sides in the width direction of the third sidewall portion 36 are formed by fourth sidewall portions 37, 38. Furthermore, the edge portion of the fourth sidewall portion 37 is coplanar with the edge portion of the second sidewall portion 34.

[0052] With reference to Fig. 3 and Fig. 5 to 7, a surface of each of the fourth sidewall portions 37, 38 is formed in a flat shape. Compared with the fourth sidewall portions 37, 38, a surface of the third sidewall portion 36 is formed in a hollowed shape or bent inward in a direction orthogonal to the plane of the joint surface 7a to form a depressed shape. This makes the rigidity of the third sidewall portion 36 against the compressive load Fc2 lower than the rigidity of the fourth sidewall portions 37, 38 in the present embodiment of the gear case 31.

[0053] At the bottom of the first housing part 6 and that of the second housing part 7, a lubricant for lubricating the transmission 9 and the differential 10 is stored, which is sprayed to the transmission 9 and the differential 10 by being thrown up by the final drive gear 21.

[0054] In Fig. 3, the third sidewall portion 36 is disposed above the bearing mounting hole 7b and forms an oil reservoir for storing the lubricant thrown up by the final drive gear 21. Furthermore, the third sidewall portion 36 is formed in its lower region with an oil supply hole 36a to allow lubricant to drip down to the bearing mounting hole 7b to supply lubricant to the bearing 24 for use in lubricating the bearing 24. An oil discharge hole 39 is formed in the lower region of the bearing mounting hole 7b. This oil discharge hole 39 discharges lubricant supplied to the bearing 24 from the area between the bearing 24 and the bearing mounting hole 7b to the bottom of the first housing part 6 and that of the second housing part 7.

[0055] Next, the operation is explained.

[0056] With reference to Fig. 3 and Fig. 8 occurs at the time of driving the final drive gear 21 by the counter gear 17 while the vehicle 1 is moving as mentioned above, under the load at the drive F1 which is in the certain direction or in Fig. 3, a downward compressive load Fc1 is applied to the final drive gear 21 with respect to the differential axis 25 at the bearing mounting hole 7b of the second housing part 7. The first side wall portion 33 and the second side wall portions 34, 35 of the second housing part 7, which are positioned below a portion surrounded by the bold line "a" with respect to the differential axis 25, are subjected to a compressive force.

[0057] With regard to the present embodiment of the gear housing 31, the first side wall section 33, ie, that portion of the side wall 26 which is deformed to the maximum extent by the compressive load Fc1 under the drive load F1 exerted in a tangential direction to the pitch circle of the counter gear 17 and the pitch circle of the final drive gear 21 when the counter gear 17 and the final drive gear 21, which are meshed with each other, move, is formed in a hollowed shape or bent inward in a direction orthogonal to the plane of the connecting surface 7a to form a depressed shape, while the second side wall portions 34, 35 on one and the opposite side in a width direction of the first side wall portion 33 are formed in a flat shape generally coplanar with the connecting surface 7a, whereby the rigidity of the first side wall portion 33 against the compressive load Fc1 is lower than the rigidity of the second side wall portions 34, 35 is designed.

[0058] This makes it possible for the second side wall portions 34, 35 to deform after the first side wall portion 33 is deformed under the compressive load Fc1 applied to the bearing mounting hole 7b.

[0059] Therefore, this makes it possible to distribute the compressive load Fc1 applied to the bearing mounting hole 7b between the first side wall portion 33 and the second side wall portions 34, 35, which makes it possible to distribute the compressive load Fc1 applied to the bearing mounting hole 7b among the bolts 8 on the connecting surface 7a located radially outside not only the first side wall portion 33 but also the second side wall portions 34, 35. As a result, it is possible to prevent the local deformation of the portion of the connecting surface 7a located radially outside the first side wall portion 33 without resorting to increasing the thickness of the side wall 26 or increasing the number of bolts 8.

[0060] With respect to the compressive load Fc1 exerted on the bearing mounting hole 7b at the time of driving the final drive gear 21 by the counter gear 17, tensile forces Fp1 occur at the third side wall portion 36 and the fourth side wall portions 37, 38. According to the present embodiment of the transmission case 31, the bolts 8 located radially outside the third side wall portion 36 and the fourth side wall portions 37, 38 can bear the compressive load Fc1. This can more effectively suppress the local deformation of the portion of the connecting surface 7a located radially outside the side wall portion 33.

[0061] With reference now to Fig. 3 and Fig. 9 occurs at the time of driving the counter gear 17 by the final drive gear 21 while the vehicle 1 is moving as mentioned above, under the load of being driven F2 which is in a direction opposite to the specific direction or in Fig. 3, a compressive load Fc2 directed upward relative to the differential axis 25 is exerted on the final drive gear 21 at the bearing mounting opening 7b of the second housing part 7. Therefore, the third side wall portion 36 and the fourth side wall portions 37, 38 of the second housing part 7, which are positioned above a portion surrounded by the bold line "b" relative to the differential axis 25, are subjected to a compressive force.

[0062] With regard to the present embodiment of the gear housing 31, the third side wall section 36, ie, that portion of the side wall 26 which is deformed to a maximum extent by the compressive load Fc2 under the driving load F2 exerted in a tangential direction to the pitch circle of the counter gear 17 and the pitch circle of the final drive gear 21 when the counter gear 17 and the final drive gear 21, which mesh with each other, move, is formed in a hollowed shape or bent inward in a direction orthogonal to the plane of the connecting surface 7a to form a depressed shape, while the fourth side wall portions 37, 38 on one and the opposite side in a width direction of the third side wall portion 36 are formed in a flat shape generally coplanar with the connecting surface 7a, whereby the rigidity of the third side wall portion 36 against the compressive load Fc2 is lower than the rigidity of the fourth side wall portions 37, 38 is designed.

[0063] This makes it possible for the fourth side wall portions 37, 38 to deform after the third side wall portion 36 is deformed under the compressive load Fc2 applied to the bearing mounting hole 7b.

[0064] Therefore, this makes it possible to distribute the compressive load Fc2 applied to the bearing mounting hole 7b between the third side wall portion 36 and the fourth side wall portions 37, 38, which makes it possible to distribute the compressive load Fc2 applied to the bearing mounting hole 7b among the bolts 8 on the connecting surface 7a located radially outside not only the third side wall portion 36 but also the fourth side wall portions 37, 38. As a result, it is possible to prevent the local deformation of the portion of the connecting surface 7a located radially outside the third side wall portion 36 without resorting to increasing the thickness of the side wall 26 or increasing the number of bolts 8.

[0065] With respect to the compressive load Fc2 exerted on the bearing mounting hole 7b at the time the counter gear 17 is driven by the final drive gear 21, tensile forces Fp2 occur at the first side wall portion 33 and the second side wall portions 34, 35. According to the present embodiment of the transmission case 31, the bolts 8 located radially outside the first side wall portion 33 and the second side wall portions 34, 35 can bear the compressive load Fc2. This can more effectively suppress the local deformation of the portion of the connecting surface 7a located radially outside the first side wall portion 33.

[0066] This results in preventing the increase in weight of the transmission case 31 and preventing the fluid tightness of the interior of the transmission case 31 from deteriorating. Therefore, it is possible to prevent, for example, oil leakage in the transmission case 31.

[0067] Furthermore, in the present embodiment of the transmission case 31, the third side wall portion 36 forms an oil reservoir, and the third side wall portion 36 is formed with an oil supply port 36a at its lower portion. This allows lubricant, which is thrown up by the rotation of the final drive gear 21 and stored in the third side wall portion 36, to drip down onto the bearing mounting port 7b to supply lubricant to the bearing 24. This improves the lubrication of the bearing 24.

[0068] Moreover, in the gear case 31, the first side wall portion 33 is formed in a hollowed shape to make the rigidity of the first side wall portion 33 lower than the rigidity of the second side wall portions 34, 35, and the third side wall portion 36 is formed in a hollowed shape to make the rigidity of the third side wall portion 36 lower than the rigidity of the fourth side wall portions 37, 38, but the present invention is not limited thereto.

[0069] For example, it is possible to make the rigidity of the first sidewall section 33 less than the rigidity of the second sidewall sections 34, 35 by making the thickness of the first sidewall section 33 less than the thickness of the second sidewall sections 34, 35. Furthermore, it is possible to make the thickness of the third sidewall section 36 less than the thickness of the fourth sidewall sections 37, 38 by making the thickness of the third sidewall section 36 less than the thickness of the fourth sidewall sections 37, 38.

[0070] Furthermore, in the present embodiment of the gear case 31, the first side wall portion 33 and the other side wall portions are formed on the second case 7, but the first side wall portion 33 and the other side wall portions may be formed on the first case 6. The key point is that the first side wall portion 33 and the other side wall portions may be formed on a case having a side wall selected from the first case and the second case.

[0071] Although the present embodiment has been disclosed, it will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the present invention. The following claims are intended to encompass all such modifications and their equivalents. DESCRIPTION OF REFERENCE SYMBOLS:

[0072] 1 ... vehicle, 6 ... first housing part, 6b ... connecting surface, 7 ... second housing part, 7a ... connecting surface, 7b ... bearing mounting opening, 8 ... screw (fastener), 9 ... transmission, 10 ... differential, 11 ... receiving space, 17 ... counter gear (first gear), 21 ... final drive gear (second gear), 24 ... bearing, 26 ... side wall, 26a ... outer edge, 31 ... transmission housing, 33 ... first side wall section (first surface section), 34, 35 ... second side wall section (second surface section), 36 ... third side wall section (third surface section), 36a ... oil supply opening, 37, 38 ... fourth side wall section (fourth surface section), Kt1 ... pitch circle tangential load (load tangential to the pitch circles of the first and second gears, which is exerted in a specific direction), Kt2 ...Pitch circle tangential load (load tangential to the pitch circles of the first and second gears applied in a direction opposite to the specified direction), Fc1, Fc2 ... thrust load (load applied to the bearing mounting hole).

Claims

[1] Gearbox housing, comprising: a first housing part (6) having a connecting surface (6b) along its outer circumference; a second housing part (7) having along its outer circumference a connecting surface (7a) which is fastened to and abuts the connecting surface (6b) of the first housing part (6) by fastening means (8), and which cooperates with the first housing part (6) to form an accommodation space therebetween which accommodates a transmission (9) with a first gear (17) and a differential with a second gear (21) which is in engagement with the first gear (17), wherein one of the first housing part (6) and the second housing part (7) comprises a side wall (26) having an outer edge (26a) continuously connected to the connecting surface (7a) of the one of the first housing part (6) and the second housing part (7), and a bearing mounting opening (7b) formed in its central region for rotatably supporting the differential (10) via a bearing (24), characterized by , that when the portion of the side wall (26) which is subjected to a load (Fc1) acting under a load (Kt1) acting in a tangential direction to the pitch circle of the first gear (17) and the pitch circle of the second gear (21) in a specific direction when the first and second gears (17, 21) meshing with each other move, on the bearing mounting hole (7b) is a first surface portion (33), the first surface portion (33) has a lower rigidity than second surface portions (34, 35) on one and the opposite side in a width direction of the first surface portion (33), thereby distributing the load (Fc1) exerted on the bearing mounting hole (7b) among fastening means on the connecting surface (7a) extending radially outside not only the first surface portion (33) but also the second surface portions (34, 35). [2] A transmission case according to claim 1, wherein when the first surface portion is a first side wall portion (33) and the second surface portions are second side wall portions (34, 35), the first side wall portion (33) is bent inward with respect to the second side wall portions (34, 35) in a direction orthogonal to the plane of the joining surface (7a) of one of the first housing part (6) and the second housing part (7) to form a depressed shape. [3] The gear case according to claim 2, wherein when the portion of the side wall which is deformed to a maximum extent by a load (Fc2) applied to the bearing mounting hole (7b) under a load (Kt2) acting in a tangential direction to the pitch circle of the first gear (17) and the pitch circle of the second gear (21) in a direction opposite to the predetermined direction when the first and second gears (17, 21) meshing with each other move, is a third surface portion (36), the third surface portion (36) has lower rigidity than fourth surface portions (37, 38) on one and the opposite side in a width direction of the third surface portion (36). [4] A transmission case according to claim 3, wherein when the third surface portion (36) is a third side wall portion and the fourth surface portions (37, 38) are fourth side wall portions, the third side wall portion is bent inward with respect to the fourth side wall portions in a direction orthogonal to the plane of the joining surface (7a) of one of the first housing part (6) and the second housing part (7) to form a recessed shape. [5] Gearbox housing according to claim 4, wherein oil is stored at the bottoms of the first housing part (6) and the second housing part (7), the third side wall portion is arranged above the bearing mounting opening (7b) to form an oil reservoir for oil thrown up by the second gear (21), and the third side wall portion is formed in its lower region with an oil supply opening (36a) to allow oil to drip down onto the bearing mounting opening (7b).

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