JPH11287252A - Bearing holding structure in transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bearing holding structure improved in operability or the like of a transmission by making a retainer, holding each bearing for a main shaft and a countershaft on a casing, splittable by means of both holding sections. SOLUTION: A retainer 50 is mounted along the casing of a transmission. Both first and second holding sections 61 and 62 locate a bearing supporting a main shaft or a countershaft free of rotation and prevent this bearing from slipping off. Both these first and second holding sections 61 and 62 are splittable in a part 65 to be weakened by a groove 66 and a loophole 67. When there is only one side at the bearing side where removal is required, since the retainer 50 is split in halves, so that a corresponding holding section alone is removed from the casing, and thus the replacement or the like of the required bearing is made possible to be done in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing holding structure for preventing a bearing provided rotatably supporting a main shaft and a counter shaft provided in a transmission from coming off a casing and positioning the bearing in the front-rear direction. About.

[0002]

2. Description of the Related Art Conventionally, a transmission has a main shaft and a counter shaft arranged in parallel.
A gear stage is provided in which a plurality of gears having different pitch diameters provided on the main shaft and a plurality of gears having different pitch diameters provided on the counter shaft are correspondingly combined. The speed change operation of the transmission is performed by selecting the gear position at which power transmission is to be performed in accordance with the operation of the gear shift operation lever by the driver or the like.

[0003] As a bearing supporting device for a transmission, there is, for example, one disclosed in Japanese Patent Application Laid-Open No. Hei 8-321760. In the transmission bearing support device disclosed in this publication, a taper is provided in a bearing support hole of a transmission case, a taper is provided in an outer diameter of an outer ring of a bearing mounted in the support hole, and an end face of the outer ring is held down by a retainer. It is installed so as to apply preload in the axial direction. The bearing support device of this transmission is designed to correct the outer ring fitting gap and the rolling surface gap caused by the difference in thermal expansion between the case and the bearing.

A retainer 80 as shown in FIGS. 7 and 8 has also been considered. 7 is a front view showing the retainer 80, and FIG. 8 is a cross-sectional view of the retainer shown in FIG. 7 taken along a plane indicated by line ZZ. In the transmission to which the retainer 80 is applied, the main shaft 2 and the counter shaft 3 arranged in parallel are rotatably supported by the bearings 35 and 37 with respect to the rear end wall 9 of the casing 4. The bearings 35 and 37 may be loosely attached to the rear end wall 9 due to mechanical vibration or temperature change. In the worst case, the bearings 35 and 37 may fall out of the rear end wall 9. Therefore, in order to prevent the bearings 35, 37 from slipping out of the rear end wall 9, it is conceivable to press the outer rings of the bearings 35, 37 with a plate-shaped retainer 80. Front transmission section 7 and rear transmission section 8
(See FIG. 1 for the transmission units 7 and 8). When the transmission units 7 and 8 are separated on the left and right sides in FIG. Gears,
For example, the reverse shift speeds Re and 18 are arranged near the rear end wall 9 from the right side in FIG.

The retainer 80 is preferably manufactured as a single metal component as shown in FIG. 7 from the viewpoint of increasing the efficiency of the assembly operation. The retainer 80 has a through hole 51 through which the main shaft 2 penetrates and a through hole 52 through which the counter shaft 3 penetrates. Retainer 80
Has a mounting portion 53 that loops around the outer periphery,
Inside the mounting portion 53, there are provided a pressing portion 55 abutting on the end surface of the outer ring 46 of the bearing 35 and a pressing portion 57 abutting on the end surface of the outer ring 48 of the bearing 37. The mounting portion 53 has a contact surface 54 that contacts the rear end wall 9,
The contact surface 54 is associated in a region where the through hole 51 and the through hole 52 are adjacent to each other. The contact surface 54 of the mounting portion 53, the pressing surface 56 of the pressing portion 55, and the pressing surface 58 of the pressing portion 57 are formed flat. The mounting portion 53 has a bolt hole 5 through which a mounting bolt is inserted at an appropriate position.
9 are formed. The contact surface 54 is a pressing surface 58
A step is provided at the surface position so as to be higher than the above.

[0006] As described above, since the retainer 80 is manufactured as one part, the retainer 80 is mounted on the rear end wall 9 of the casing 4 of the transmission.
The retaining of the bearing 35 that rotatably supports the main shaft 2 and the bearing 37 that rotatably supports the countershaft 3 are simultaneously performed, and the positioning in the axial direction is also performed. Therefore, the assembly work of the transmission can be performed efficiently.

[0007]

However, the retainer 80 having such a structure has the following inconvenience during maintenance of the transmission. Bearing 3
First, it is necessary to remove the bearings 35 and 37 from the casing 4 in order to replace the gears 5 and 37 and to maintain the gears at the main shaft 2 or the counter shaft 3 or at each gear. When removing both the bearing 35 and the bearing 37, it is needless to say that the retainer 80 must be removed. However, since the retainer 80 is a single part, even when only one of the bearing 35 and the bearing 37 is removed. It is necessary to remove the retainer 80 to interrupt the holding of the other bearing. When the transmission is divided into a front transmission section and a rear transmission section by the rear end wall 9, the speed provided in the rear transmission section, for example, the reverse speed Re is close to the rear end wall 9. It is arranged. In this case, if the gear is not removed in advance, the retainer 80 and the bearings 35 and 37 for which the retainer 80 has been prevented from being removed cannot be removed. It will take.

Therefore, there are the following problems with the retainer for preventing the bearing attached to the casing from being pulled out and for positioning in the axial direction. That is, during assembly,
Treating the retainer as a single part improves assembly efficiency,
During maintenance of the components that make up the transmission, the retainer of one of the bearings provided for the main shaft and the countershaft can be maintained while maintaining the retainer of the other bearing while maintaining the retainer in the other position. If it is possible to release the holding by the
An advantageous retainer is obtained.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to prevent each bearing for rotatably supporting a main shaft and a counter shaft of a transmission from coming off a casing, and As a bearing holding structure for positioning the bearing in the axial direction, a retainer capable of separating a portion holding a bearing rotatably supporting a main shaft and a portion holding a bearing rotatably supporting a counter shaft is used. Accordingly, an object of the present invention is to provide a bearing holding structure in a transmission that allows a retainer to be handled as an integral retainer until the retainer is assembled to the casing and both parts to be separately handled when the retainer is removed from the casing.

The present invention has been made in order to solve the above-mentioned object.
It is configured as follows. That is, the present invention provides an input shaft rotatably supported by a casing, a main shaft rotatably supported by a first bearing provided on the casing, and changing and outputting the rotation of the input shaft, and the casing. A transmission that includes a counter shaft rotatably supported by a second bearing provided on the main shaft and arranged side by side with the main shaft, and a retainer holding the first bearing and the second bearing in the casing. The retainer has a first holding part that holds the first bearing in the casing and a second holding part that holds the second bearing in the casing, and the first holding part and the second holding part of the retainer. The retainer is connected to the first holding portion and the first holding portion by dividing the weak portion. About bearing holding structure in the transmission which consists it can be divided into a holding portion.

The bearing holding structure in the transmission according to the present invention is constructed as described above.
When assembling the retainer to the casing, the retainer is assembled as an integral part whose fragile portion is not divided, the first holding portion holds the first bearing in the casing, and the second holding portion holds the second bearing in the casing. After assembling the retainer to the casing, the fragile portion can be easily separated by a tool such as a chisel.
Therefore, it is possible to individually remove one of the first holding portion and the second holding portion from the casing regardless of the assembled state of the other. For reassembly,
Since the divided cross sections match at the mounting position,
The reassembly operation can be performed quickly and easily.

Further, in the bearing holding structure of this transmission, the fragile portion is constituted by a portion in which at least one of a groove and a hole is formed. By forming a groove at the boundary between the first holding portion and the second holding portion, a fragile portion is formed. The depth of the groove and the form of continuous or discontinuous may be appropriately selected as long as it can be easily divided.

In the bearing holding structure of the transmission, a casing provided with the first bearing and the second bearing includes a front gear transmission section having a gear stage for shifting the rotation of an input shaft of the transmission; A rear gear transmission unit provided with the front gear transmission unit and having a gear stage for shifting the rotation of the input shaft, the rear gear transmission unit comprising: an idle shaft mounted on a casing; A reverse gear including a reverse idle gear provided on an idle shaft is provided, and a part of the second holding portion is disposed at a position corresponding to the reverse idle gear.

Further, in the bearing holding structure of this transmission, the rear gear transmission section includes a reverse gear including an idle shaft mounted on a casing and a reverse idle gear provided on the idle shaft, and A part of the holding portion is arranged at a position corresponding to the reverse idle gear, and the second
The holding portion is mounted on the casing by mounting means arranged in a region other than a region corresponding to the reverse idle gear. With such an arrangement,
The retainer can be removed from the casing without removing the reverse idle gear.

Further, in the bearing holding structure of the transmission, the first holding portion of the retainer has a first holding portion formed with a first through hole through which the main shaft passes and holding an outer ring of the first bearing.
And a first attachment portion provided around the first holding portion and attached to the casing, wherein the second holding portion of the retainer is formed with a second through hole through which the counter shaft passes. And the second
It comprises a second holding portion for holding the outer ring of the bearing, and a second attachment portion provided around the second holding portion and attached to the casing.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of a bearing holding structure in a transmission according to the present invention will be described. FIG. 1 is a cross-sectional view of a transmission 1 for a vehicle to which a bearing holding structure according to the present invention is applied, and FIG. 2 is a sectional view of the transmission shown in FIG.
It is sectional drawing which shows the outline seen by X.

The illustrated transmission 1 is a two-axis parallel gear type transmission in which a main shaft 2 and a counter shaft 3 are arranged in parallel. The transmission 1 has a rear end wall serving as a partition partitioning between the front transmission portion 7 housed in a casing 4 (a main casing disposed in the front) and a part of the casing 4 and dividing the front transmission portion 7. 9 and a rear transmission section 8 attached to the rear transmission section 9. The rear transmission 8 is disposed in a rear casing 10 attached to a rear end wall 9. The front transmission 7 has a forward second
Six speed change units (N2 to N7) from the first speed to the seventh speed are arranged, and the first speed (N1) and the reverse speed (R
e) are arranged.

In the transmission 1 shown in FIG.
The main shaft 2 is assembled from the input shaft 6 to a casing 4 having a number of gear stages inside.
Since the extension shaft 42 of the main shaft 2 needs to be able to pass through the inner ring 45 (see FIG. 4) of the bearing 35 provided in the casing 4, the maximum outer diameter of the extension shaft 42 is The diameter is formed smaller than the inner diameter. Similarly, the maximum outer diameter of the extension shaft portion 43 of the counter shaft
7 is formed smaller in diameter than the inner diameter of the inner ring 47 (see FIG. 4).

The main shaft 2 and the counter shaft 3 extend in parallel at the front transmission 7 and the rear transmission 8, respectively. With respect to the main shaft 2, the end on the input shaft 6 side is inside the drive gear 17 of the input shaft 6 rotatably supported via a bearing 34, and the middle portion is a bearing 35.
, And the output end is rotatably supported by the rear casing 10 via a bearing 38. The counter shaft 3 also has a bearing 36 on the input shaft 6 side and a front wall integral with the casing 4, an intermediate portion on the rear end wall 9 via a bearing 37, and an output end on a bearing 39. Are rotatably supported by the rear casing 10 through the respective members. In the rear transmission section 8, an extension shaft 42 integrally extended as a part of the main shaft 2 and a part of the counter shaft 3 are integrally formed in a rear casing 10 attached to the casing 4. And an extension shaft portion 43 extending to the above.

There are three types of transmissions: a selective sliding type, a constant meshing type and a synchronous meshing type.
The illustrated transmission 1 includes a synchromesh mechanism that always meshes a gear provided on a main shaft with a gear provided on a counter shaft, and synchronizes a gear provided on the main shaft with the main shaft. It is a constant mesh transmission. The front transmission unit 7 accommodated in the casing 4 of the transmission 1 is configured to directly connect the drive gear 17 and the main shaft 2 from the second speed (N2) having a large reduction ratio.
Gear speeds (N2 to N7) up to the speed (N7) are provided. On the main shaft 2, each gear speed (N2 to N
Gears 12 to 17 corresponding to 7) are rotatably supported in turn via bearings. The countershaft 3 is provided with gears 22 to 27 fixedly in order corresponding to each gear speed (N2 to N7), and always meshes with the corresponding gears 12 to 17 on the main shaft 2. .

A gear 11 for the first speed (N1) having the largest reduction ratio is rotatably supported on the extension shaft portion 42 of the main shaft 2 in the rear transmission portion 8. The extension shaft 43 of the counter shaft corresponding to the gear 11 has a gear 11
A gear 21 that constantly meshes with the gear 21 is fixedly provided. A gear 18 for a reverse gear stage (Re) is rotatably supported on the extension shaft portion 42 of the main shaft 2 in parallel with the gear 11 by the rear transmission portion 8. The reverse rotation gear 18 always meshes with a reverse idle gear 29 rotatably supported by an idle shaft 40 fixed to the rear casing 10. The reverse idle gear 29 always meshes with the gear 28 formed on the counter shaft 3. Since the reverse idle gear 29 is present, when power is transmitted through the reverse idle gear 29, the rotation direction of the main shaft 2 is opposite to the rotation direction in the case of another forward gear.

The gear 12 provided on the main shaft 2
Between 17 and 11, 18 and the main shaft 2,
Synchromesh mechanisms 30, 31, 32, and 33 are provided. One of the synchromesh mechanisms 30, 31, 3 corresponds to the operation of the shift lever by the driver.
One of the gears 12 to 17 that operates and rotates idle on the main shaft 2 is a corresponding one of the gears 12 to 17.
To be fixed selectively. The illustrated synchromesh mechanism includes a coupling sleeve and a cone-shaped synchronizer ring that can move in the axial direction on the main shaft by operating a shift fork. Since the rotational speeds of the motors are synchronized with each other, the connecting sleeve moves and connects the two by meshing, so that a smooth and quiet connection can be obtained. Since the structure of the synchromesh mechanism itself is well-known, further detailed description will be omitted.

The engine output is input to the input shaft 6 of the transmission 1 via the clutch 5. When the input shaft 6 is rotating, the rotation is performed from the drive gear 17 integrally formed with the input shaft 6 via the gear 27, and the gears 21 to 26 fixedly arranged on the counter shaft 3 and the counter shaft 3. 28, the reverse idle gear 29 and the gears 11 to 18 on the main shaft 2.
By operating one of the synchromesh mechanisms 30, 31, 32, and 33, any one of the gears 12 to 17 and 11, 18 on the main shaft 2 is connected to the main shaft 2. , The output of the selected gear position is obtained on the main shaft 2.

As described above, the main shaft 2 and the counter shaft 3 are connected to the casing 4 and the rear casing 10.
Transmission 1 arranged in parallel in
The main shaft 2 and the countershaft 3 extending over the front transmission section 7 and the rear transmission section 8 are provided with a bearing 3 against a rear end wall 9 of the casing 4 at an intermediate portion therebetween.
5 and 37 rotatably supported. Bearing 3
The bearings 3, 37 are used to prevent them from slipping out of the rear end wall 9 and to position the bearings 35, 37 in the axial direction.
The outer races 5 and 37 are pressed by a plate-shaped retainer 50. FIG. 2 shows an arrangement relationship between the reverse shift speed Re and the retainer 50. The gear 18 rotatably provided on the extension shaft portion 42 of the main shaft 2 constituting the reverse gear Re engages with the reverse idle gear 29 on the idle shaft 40, and the reverse idle gear 29
Meshes with a gear 28 formed on the extension shaft 43 of the counter shaft 3. As will be described later in detail, the retainer 50 includes a first holding portion 61 for preventing the bearing 35 from being pulled out and a second holding portion 62 for preventing the bearing 37 from being pulled out. A part of the second holding portion 62 that holds the bearing 37 occupies a position corresponding to the reverse idle gear 29. That is, the retainer 50 in which the second holding part 62 or the first holding part 61 and the second holding part 62 remain in an integrated state is
As it is, it cannot be removed from the front without interfering with the reverse idle gear 29. Second holding unit 6
A bolt hole 59 for screwing a mounting bolt 64 for attaching 2 to the rear end wall 9 is arranged at a position where it does not interfere with the reverse idle gear 29.

Hereinafter, the structure of the retainer 50 will be described. FIG. 3 is a front view showing an example of a retainer used in the bearing holding structure according to the present invention, and FIG. 4 is a side view of the retainer shown in FIG. The retainer shown in FIGS. 3 and 4 has the same structure as the retainer 80 shown in FIGS. 7 and 8 except that the retainer 80 has a fragile portion. The reference numerals are assigned and duplicate explanations are omitted. In this embodiment, a mounting portion for mounting the retainer 50 to the rear end wall 9 is a through hole 51.
And a second attachment portion 53b along the through hole 52. Both mounting parts 53
A groove 66 is formed at the connection portion where the a and 53b meet so as to extend in the width direction of the retainer 50. Also, holes 67 are formed at appropriate intervals so as to overlap the grooves 66. By forming the groove 66 and the hole 67, the connection portion becomes a weakened portion 65 which is weakened. The portion above the weak portion 65 in FIG. 3 is a first holding portion 61 for preventing the outer ring 46 of the bearing 35 that rotatably supports the main shaft 2 from being removed. The portion below the fragile portion 65 in FIG.
Is formed as a second holding portion 62 for preventing the outer ring 48 of the bearing 37 that rotatably supports the outer ring 48 from coming off. The first holding portion 61 is provided with a bolt hole 59 provided at an appropriate position of the mounting portion 53a.
Is fixed to the rear end wall 9 by screwing the mounting bolt 63 through the rear end wall 9. Also, the second holding unit 6
2 is fixed to the rear end wall 9 by screwing a mounting bolt 64 through a bolt hole 59 provided at an appropriate position of the mounting portion 53b into the rear end wall 9. Vulnerable part 6
In order to form the retainer 5, the retainer 50 is preferably made of a material having a low elongation, such as a die-casting aluminum alloy ADC 10 or 12.

Since the retainer 50 shown in FIGS. 3 and 4 is handled as one part at the time of initial assembly of the transmission 1, the main shaft 2 and the counter shaft 3 and the bearings 35 and 37 for them are mounted on the casing 4. The number of man-hours for assembling work is reduced, and the assembling work is simplified. After assembling the retainer 50,
When it is necessary to remove the bearings 35 and 37 for replacement of the bearings 35 and 37 and maintenance of each transmission mechanism,
When removing both the bearing 35 and the bearing 37, the entire retainer 50 must be removed from the rear end wall 9 of the casing 4. However, when it is sufficient to remove only one of the bearings 35 and 37, the retainer 50 hits the first holding portion 61 and the second holding portion 61 in the weak portion 65 by hitting the weak portion 65 with a tool such as a chisel or a driver. It is easily separated from the holding part 62.

FIG. 5 shows a state in which the retainer 50 is divided into a first holding portion 61 and a second holding portion 62 at the fragile portion 65. To remove a holding portion that needs to be removed, for example, the first holding portion 61, the mounting bolts 63 and 64 that have been inserted into the bolt holes 59 and screwed into the rear end wall 9.
Of these (see FIG. 4), this can be dealt with by removing only the mounting bolt 63. The second holding portion 62 remains attached to the rear end wall 9 by the mounting bolt 64 that is not removed, and the bearing 37 is maintained in the state held by the second holding portion 62. Similarly, when removing only the second holding portion 62, only the mounting bolt 64 is removed.

When the retainer 50 is to be mounted again, the replacement is performed by replacing the retainer 50 with a new one without replacing the retainer 50 with a new one. Since the fracture surface of the fragile portion 65 is basically a fracture surface caused by a single burst, there is no sagging or crushing unlike the fracture surface caused by fusing or fatigue failure. Therefore, the fracture surface of one of the separated holding parts and the other holding part fixed to the rear end wall 9 does not shift when reassembled. In addition, in the case of reassembly, there is no technical reason that both holding portions must be integrated from the viewpoint of the strength of the retainer 50, and the retainer 50 prevents the bearings 35 and 37 from coming off, respectively. What is necessary is just to have the function of positioning in the axial direction. Therefore, after the retainer 50 is divided,
The maintenance is completed by retightening the removed mounting bolt 63 or 64 as it is.

A part of the second holding part 62 occupies a position corresponding to the reverse idle gear 29. A bolt hole 59 into which a mounting bolt 64 for attaching the second holding portion 62 to the rear end wall 9 is screwed is arranged at a position where it does not interfere with the reverse idle gear 29. Therefore, the second holding unit 6
When mounting and removing the mounting bolt 64 for fixing the rear idle gear 29 to the rear end wall 9, there is no need to remove the reverse idle gear 29 from the rear casing 10 in advance, and the reverse idle gear 29 is maintained on the idle shaft 40. The mounting bolt 64 can be mounted and removed.

The fragile portion is not limited to a combination of the groove 66 and the through hole 67 as shown in FIGS. For example, the retainer 70 shown in FIG. 6 forms the weak portion 71 by forming a relatively large number of through holes 72 in a line.
In FIG. 6, elements and portions corresponding to FIG. 3 are denoted by the same reference numerals, and detailed description thereof will not be repeated. Similarly, although not shown, the fragile portion can be constituted only by the groove.

[0031]

Since the present invention is configured as described above, it has the following effects. That is, in the bearing holding structure of the conventional transmission, it was necessary to remove all the mounting bolts and remove the retainer from the casing. However, according to the bearing holding structure of the transmission according to the present invention, the retainer is divided at the fragile portion, and Of the bearings that rotatably support the shaft and counter shaft with respect to the casing,
Only the holding portion holding the bearing to be removed for the purpose of replacement or the like can be removed from the casing. Moreover,
For a bearing that does not need to be removed, the state held by one holding portion can be maintained. Further, even when the reverse gear is disposed close to the rear end wall, even when the reverse idle gear which is originally hindering the removal of the retainer exists, the reverse idle There is no need to remove the gear from the transmission, and the bearing can be removed from the casing.
Since the reverse idle gear is not removed from the reverse shaft, tools, jigs, and man-hours required when the reverse idle gear are removed become unnecessary, and maintenance costs and maintenance time are reduced. Further, the split retainer can be reassembled, and there is no need to replace it with a new retainer.
Further, since the holding portion that has already been removed is used for reassembly as it is, it is also possible to prevent the occurrence of secondary defects such as adhesion of foreign matter and erroneous assembly which are likely to occur due to disassembly and reassembly.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a transmission to which a bearing holding structure in a transmission according to the present invention is applied.

FIG. 2 is a cross-sectional view of the transmission shown in FIG.

FIG. 3 is a front view showing an example of the position of a retainer used in the bearing holding structure of the transmission according to the present invention.

4 is a cross-sectional view of the retainer shown in FIG. 3 taken along a plane indicated by line YY.

FIG. 5 is a perspective view showing a state of the retainer shown in FIG. 3 being divided.

FIG. 6 is a front view showing another example of the retainer used in the bearing holding structure of the transmission according to the present invention.

FIG. 7 is a front view showing an integrated retainer for preventing two bearings from being pulled out.

FIG. 8 is a cross-sectional view of the retainer shown in FIG. 7 taken along a plane indicated by line ZZ.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmission 2 main shaft 3 counter shaft 4 casing 6 input shaft 7 front transmission section 8 rear transmission section 9 rear end wall 10 rear casing 11-18 gear 21-28 gear 29 reverse idle gear 30-33 synchromesh mechanism 34-39 Bearing 40 Idle shaft 46, 48 Outer ring 50 Retainer 51, 52 Through hole 53a First mounting portion 53b Second mounting portion 54 Contact surface 55, 57 Pressing portion 56, 58 Pressing surface 59 Bolt hole 61 First holding portion 62 Second Holding parts 63, 64 Mounting bolts 65 Vulnerable parts 66 Grooves 67 Removal holes 70 Retainers 71 Vulnerable parts 72 Removal holes

Claims (5)

[Claims] 1. An input shaft rotatably supported by a casing, a main shaft rotatably supported by a first bearing provided on the casing, and a speed-changed output of the input shaft, and a main shaft. A counter shaft rotatably supported by a second bearing provided and arranged in parallel with the main shaft;
In a transmission including a retainer for holding a bearing and the second bearing in the casing, the retainer includes a first holding portion for holding the first bearing in the casing and a second holding portion for holding the second bearing in the casing. A retainer, wherein the first retainer and the second retainer of the retainer are connected by a weak portion, and the retainer separates the first retainer and the second retainer by dividing the weak portion. A bearing holding structure in a transmission, which can be divided into two holding parts. 2. The bearing holding structure in a transmission according to claim 1, wherein said weakened portion comprises a portion formed with at least one of a groove and a hole. 3. The casing, in which the first bearing and the second bearing are provided, includes a front gear transmission section having a gear stage for shifting the rotation of the input shaft of the transmission, and the front gear transmission section. 3. A bearing holding structure in a transmission according to claim 1, wherein the partition wall is a partition wall attached to the transmission section and divided into a rear gear transmission section having a gear stage for shifting the rotation of the input shaft. 4. The rear gear transmission section includes a reverse gear including an idle shaft attached to the casing and a reverse idle gear provided on the idle shaft, and a part of the second holding section is provided. The second holding portion is disposed at a position corresponding to the reverse idle gear, and the second holding portion is mounted to the casing by mounting means disposed in a region other than a region corresponding to the reverse idle gear. 4. The bearing holding structure in the transmission according to 3. 5. A first holding portion of the retainer, wherein a first through hole through which the main shaft passes is formed, and a first holding portion for holding an outer ring of the first bearing, and a periphery of the first holding portion. And a first attachment portion attached to the casing, the second holding portion of the retainer is formed with a second through hole through which the counter shaft passes, and the outer ring of the second bearing is formed. The transmission according to any one of claims 1 to 4, further comprising a second holding portion for holding, and a second attachment portion provided around the second holding portion and attached to the casing. Bearing holding structure.