JP5471282B2 - Pinion shaft rotation support device - Google Patents

Description

  The present invention relates to an improvement in a rotation support device for a pinion shaft that constitutes, for example, a differential device for an automobile and a transfer device for a four-wheel drive vehicle.

  A differential device for an automobile and a transfer device for a four-wheel drive vehicle usually include a pinion shaft provided with a pinion gear at one end, and a pair of pinion shafts provided in the housing in an axially separated manner. It has a structure that supports the axial load in both directions in a freely rotatable manner by a rolling bearing.

  FIG. 7 shows one described in Patent Document 1 as an example of a differential apparatus having such a structure. This differential device is provided in the middle of the power transmission system of an automobile to reduce the rotation of the propeller shaft and at the same time to change the rotation direction to a right angle. Is based on the traveling direction of the vehicle, and a pair of annular walls 2a and 2b are provided in the front-rear direction apart from each other in the “front” on the right and “rear” on the left. Inside these annular walls 2a, 2b, a pinion shaft 3 is supported by a pair of single row tapered roller bearings 4a, 4b so as to be rotatable and capable of supporting axial loads in both directions. These single-row tapered roller bearings 4a and 4b have a plurality of tapered rollers between outer rings 5a and 5b fitted inside the annular walls 2a and 2b and inner rings 6a and 6b fitted outside the pinion shaft 3, respectively. The rollers 7a and 7b are provided so as to roll freely. These single-row tapered roller bearings 4a and 4b are installed so that the contact angles are opposite to each other (providing a back-combined contact angle), thereby supporting both axial loads applied to the pinion shaft 3. It is possible.

  An annular body 8 is fixed to the front end portion of the pinion shaft 3. The coupling flange 9 constituting the front end portion of the annular body 8 is disposed at a portion protruding outward from the front end opening of the case 1. A rear end portion of a propeller shaft (not shown) can be connected to the coupling flange 9. A pinion gear 10 is fixed to the rear end portion of the pinion shaft 3, and the pinion gear 10 and the ring gear 11 are engaged with each other. The ring gear 11 is supported at the rear part inside the case 1 so as to be rotatable only.

  Next, FIG. 8 shows a part of the transfer device described in Patent Document 2. This transfer device is mounted on a four-wheel drive vehicle and distributes the output of the transmission to the front and rear wheels. A pinion shaft 3a is provided inside a case 1a, which is a housing, and a pair of single-row tapered roller bearings. By 4c and 4d, the axial load of both directions is supported rotatably. These single-row tapered roller bearings 4c, 4d have a plurality of tapered rollers 7c, 7d between outer rings 5c, 5d fitted in the case 1a and inner rings 6c, 6d fitted on the pinion shaft 3a. Is provided so that it can roll freely. These single-row tapered roller bearings 4c and 4d support the axial loads in both directions applied to the pinion shaft 3a by installing them with their contact angles opposite to each other (with a back combination type contact angle). It is possible.

  An annular body 8a is fixed to the rear end portion of the pinion shaft 3a. The coupling flange 9a constituting the rear end portion of the annular body 8a is disposed at a portion protruding outward from the rear end opening of the case 1a. A front end portion of a propeller shaft (not shown) can be connected to the coupling flange 9a. A pinion gear 10a is fixed to the front end portion of the pinion shaft 3a, and the pinion gear 10a and the ring gear 11a are engaged with each other. The ring gear 11a is supported on the inside of the case 1a so as to be rotatable only.

  By the way, in recent years, there has been a strong demand for saving fuel in automobiles, and power transmission loss is also associated with a pair of rolling bearings incorporated in a pinion shaft rotation support device that constitutes a differential device or a transfer device as described above. In order to keep the torque low, it is required to reduce the rotational torque. However, in the case of each of the conventional structures described above, it cannot be said that the rotational torque is sufficiently small.

  That is, in each of the conventional structures described above, single-row tapered roller bearings 4a and 4b (4c and 4d) are used as a pair of rolling bearings incorporated in the pinion shaft rotation support device. These single row tapered roller bearings 4a, 4b (4c, 4d) include outer rings 5a, 5b (5c, 5d) and inner rings 6a, 6b (6c, 6d) and tapered rollers 7a, 7b (7c, 7d). In addition to the rolling contact, the flanges 34 and 34 existing at the large-diameter end of the outer peripheral surface of the inner rings 6a and 6b (6c and 6d) and the heads of the tapered rollers 7a and 7b (7c and 7d) (large The diameter end face) is always in sliding contact with it, so the torque loss during rotation is large. In particular, the single-row tapered roller bearing 4a (4c) on the pinion gear 10 (10a) side has a larger axial load to be supported than the single-row tapered roller bearing 4b (4d) on the anti-pinion gear 10 (10a) side. The torque loss at that time is also larger than that of the single-row tapered roller bearing 4b (4d) on the anti-pinion gear 10 (10a) side.

  In this case, if a ball bearing is used instead of the single row tapered roller bearing 4a (4c) as the rolling bearing on the pinion gear 10 (10a) side, the rotational torque can be reduced. However, because the installation space is limited, the diameter of each ball (rolling element) constituting the ball bearing cannot be increased too much, and it is difficult to increase the number of each ball sufficiently. There is a concern that the load capacity of the rolling bearing on the pinion gear 10 (10a) side is reduced and the bearing life is reduced.

JP 11-48805 A Japanese Patent Laid-Open No. 10-220468

  In view of the circumstances as described above, the pinion shaft rotation support device of the present invention has been invented to realize a structure that can achieve both a reduction in rotational torque of the rolling bearing on the pinion gear side and securing of load capacity.

The pinion shaft rotation support device of the present invention can be used to configure a differential device for an automobile or a transfer device for a four-wheel drive vehicle. A pinion shaft provided with a pinion gear at one end is disposed inside the housing. A pair of rolling bearings spaced apart in the direction is supported rotatably and capable of supporting axial loads in both directions.

Particularly, in the pinion shaft rotation support device of the present invention, of the two rolling bearings, the pinion gear side rolling bearing can support the axial load acting on the pinion shaft from the pinion gear side toward the non-pinion gear side. A single row ball bearing (for example, a single row deep groove ball bearing or a single row angular ball bearing), and an inner ring raceway constituting the single row ball bearing is formed directly on the outer peripheral surface of the pinion shaft. The diameter of the smallest diameter portion of the track is smaller than the diameter of the smallest diameter portion of the inner ring raceway formed on the outer peripheral surface of the inner ring that is externally fitted and fixed to the pinion shaft constituting the rolling bearing on the anti-pinion gear side.
Further, when carrying out the present invention, as in the invention described in claim 2, for example, the pitch circle diameter of each ball constituting the single row ball bearing is set to each of the rolling bearings on the anti-pinion gear side. It can be made larger than the pitch circle diameter of the rolling elements.
In this case, for example, as in the invention described in claim 3, the diameter of the minimum diameter portion of the inner ring raceway constituting the single row ball bearing is set to the rolling bearing on the anti-pinion gear side of the pinion shaft. Can be made equal to the diameter of the externally fitted portion of the inner ring (not only completely equal, but also substantially equal).

In the case of the rotation support device of the pinion shaft of the present invention configured as described above, a single row ball bearing is used instead of the conventional single row tapered roller bearing as the rolling bearing on the pinion gear side. Torque can be reduced. In addition, this single row ball bearing has an inner ring raceway formed directly on the outer peripheral surface of the pinion shaft, and the diameter of the smallest diameter portion of the inner ring raceway is fixedly fitted to the pinion shaft constituting the rolling bearing on the anti-pinion gear side. Since the diameter of the inner ring raceway formed on the outer peripheral surface of the inner ring is smaller than the diameter of the minimum diameter portion, the diameter of each ball can be increased by that amount, and the load capacity can be increased. As a result, the life of the single row ball bearing can be brought close to that of a conventional single row tapered roller bearing. That is, according to the structure of the present invention, the rolling bearing on the pinion gear side achieves a lower rotational torque than the conventional single row tapered roller bearing while maintaining the same life as the conventional single row tapered roller bearing. Things will be possible. Further, since the single row ball bearing used as the pinion gear side rolling bearing does not have an inner ring separate from the pinion shaft, the rotation support device can be easily assembled.
In addition, when a structure in which the inner ring raceway is formed on the outer peripheral surface of a separate inner ring that is externally fitted and fixed to the pinion shaft is adopted as the single row ball bearing , the minimum diameter portion of the inner ring raceway is reduced. In the inner ring, a portion corresponding to the minimum diameter portion is thinned, which causes a problem that it is difficult to ensure the strength (durability) of the portion. On the other hand, in the case of the present invention , since the structure in which the inner ring raceway of the single row ball bearing is directly formed on the outer peripheral surface of the pinion shaft is employed, such a problem does not occur.

Sectional drawing which shows the 1st example of embodiment of this invention. Sectional drawing which shows the 2nd example. Sectional drawing which shows the 3rd example. Sectional drawing which shows the 4th example. Sectional drawing which shows the 1st example of the reference example relevant to this invention . Sectional drawing which shows the 2nd example . Sectional drawing which shows an example of the differential apparatus incorporating the rotation support apparatus of the conventional pinion shaft. The fragmentary sectional view which shows an example of the transfer apparatus incorporating the rotation support apparatus of the conventional pinion shaft.

[First example of embodiment]
FIG. 1 shows a first example of an embodiment of the present invention . The feature of this example is the structure of the rolling bearing on the pinion gear 10a side (the right side in FIG. 1) among the pair of rolling bearings that support the pinion shaft 3b constituting the transfer device. Since the structure and operation of the other parts are almost the same as those of the conventional structure shown in FIG. 8, the same reference numerals are given to the equivalent parts, and overlapping explanations are omitted or simplified. The description will focus on the features of the example.

In the case of this example, of the pair of rolling bearings that support the pinion shaft 3b, the rolling bearing on the pinion gear 10a side is the pinion shaft 3b from the pinion gear 10a side to the anti-pinion gear 10a side (left side in FIG. 1). The single-row deep groove ball bearing 12 is capable of supporting an axial load acting on the. This single row deep groove ball bearing 12 is formed between a deep groove type outer ring raceway 14 formed on the inner peripheral surface of the outer ring 13 and a deep groove type inner ring raceway 15 formed directly on the front end portion of the outer peripheral surface of the pinion shaft 3b. In addition, a plurality of balls 16, 16 are provided so as to roll freely. Particularly, in the case of this example, by directly forming the inner ring raceway 15 in this manner on the outer peripheral surface of the pinion shaft 3b, and the diameter D _A of the minimum diameter portion of the inner ring raceway 15 (groove bottom), anti-pinion gear 10a The diameter ( _{B A} <D _B ) of the smallest diameter portion (small diameter side end portion) of the inner ring raceway 17 constituting the single-row tapered roller bearing 4d on the side is smaller (D _A <D _B ) {in the illustrated example, the pinion shaft 3b, the diameter D _C of the outer ring of the inner ring 6d constituting the single-row tapered roller bearing 4d on the side opposite to the pinion gear 10a is substantially equal to D _C (D _A ≈D _C )}. The amount of reduced diameter D _A of the minimum diameter portion only of the inner ring raceway 15 constituting the single-row deep groove ball bearing 12 in this manner, is to increase the diameter d of the respective balls 16, 16. The outer ring 13 of such a single row deep groove ball bearing 12 is fitted into the front end of the cylindrical member 18 constituting the case 1b. In this state, the outer ring 13 is positioned in the axial direction by abutting the rear end surface of the outer ring 13 against a step surface 19 formed on the inner peripheral surface of the cylindrical member 18.

  In the case of this example, the outer ring 5d of the single-row tapered roller bearing 4d on the side opposite to the pinion gear 10a is fitted in the portion near the rear end of the cylindrical member 18. Further, in this state, the outer ring 5d is positioned in the axial direction by abutting the front end face of the outer ring 5d against the step surface 20 formed on the inner peripheral surface of the cylindrical member 18. On the other hand, the inner ring 6d of the single row tapered roller bearing 5d is externally fitted to a portion near the rear end of the intermediate portion of the pinion shaft 3b. Further, in this state, a cylindrical spacer 22 in which the cross-sectional shape of the intermediate portion is an arch shape between the front end surface of the inner ring 6d and the stepped surface 21 formed at the intermediate portion of the outer peripheral surface of the pinion shaft 3b. , And the rear end face of the inner ring 6d is held down by an annular body 8a fitted and fixed to the rear end of the pinion shaft 3b. Thereby, the axial internal clearance between the single row deep groove ball bearing 12 and the single row tapered roller bearing 4d is adjusted, and the single row deep groove ball bearing 12 and the single row tapered roller bearing 4d are connected to the cylindrical member 18. Is prevented from falling off between the inner peripheral surface of the pinion shaft and the outer peripheral surface of the pinion shaft 3b.

In the case of the pinion shaft rotation support device of the present example configured as described above, instead of the conventional single row tapered roller bearing 4c (see FIG. 8), a single row deep groove ball bearing is used as the rolling bearing on the pinion gear 10a side. Since 12 is used, rotational torque can be reduced. In addition, the single row deep groove ball bearing 12 is formed by directly forming the inner ring raceway 15 on the outer peripheral surface of the pinion shaft 3b, thereby reducing the diameter D _A of the minimum diameter portion of the inner ring raceway 15 (D _A <D _B , D _A ≈D _C ), the diameter d of each ball 16, 16 is increased, so that the load capacity can be increased. Accordingly, the life of the single row deep groove ball bearing 12 can be made close to the life of the conventional single row tapered roller bearing 4c. That is, according to the structure of this example, the conventional single-row tapered roller bearing with the same life as the conventional single-row tapered roller bearing 4c (see FIG. 8) is maintained for the rolling bearing on the pinion gear 10a side. It becomes possible to realize a rotational torque lower than 4c. In the case of this example, since the single row deep groove ball bearing 12 used as the rolling bearing on the pinion gear 10a side does not have the inner ring separate from the pinion shaft 3b, the rotation support device can be easily assembled. Yes.

  If the inner ring raceway 15 is formed as the single row deep groove ball bearing 12 on the outer peripheral surface of a separate inner ring fitted and fixed to the pinion shaft 3b, the diameter of the minimum diameter portion of the inner ring raceway 15 is reduced. In this case, the portion corresponding to the minimum diameter portion of the inner ring is thinned, which causes a problem that it is difficult to ensure the strength (rolling fatigue life) of the portion. On the other hand, in the case of this example, since the structure in which the inner ring raceway 15 of the single row deep groove ball bearing 12 is directly formed on the outer peripheral surface of the pinion shaft 3b is adopted, such a problem may occur. There is no.

[Second Example of Embodiment]
FIG. 2 shows a second example of the embodiment of the present invention . In this example, an axial load acting on the pinion shaft 3b can be supported from the anti-pinion gear 10a side to the pinion gear 10a side (right side in FIG. 2) as a rolling bearing on the anti-pinion gear 10a side (left side in FIG. 2). The tandem type double-row angular contact ball bearing 23 is used. The tandem double-row angular ball bearings 23 are formed on the inner peripheral surface of the outer ring 24, and are formed on the outer peripheral surface of the double-row outer ring raceways 25 a and 25 b each having an angular shape, and the inner ring 26. Between the double-row inner ring raceways 27a and 27b, which are molds, a plurality of balls 28 and 28 are arranged for each row in a state where contact angles in the same direction are given to each other in both rows, In addition, the pitch circle diameter of the ball row on the anti-pinion gear 10a side is set larger than the pitch circle diameter of the ball row on the pinion gear 10a side. In this example, a tandem double-row angular ball bearing 23 is used as the rolling bearing on the anti-pinion gear 10a side instead of the conventional single-row tapered roller bearing 4d (see FIG. 8). Therefore, rotational torque can be reduced. Other configurations and operations are the same as those in the first example of the embodiment described above.

[Third example of embodiment]
FIG. 3 shows a third example of the embodiment of the present invention . In the case of this example, the axial load acting on the pinion shaft 3b can be supported from the pinion gear 10a side (the right side in FIG. 3) to the anti-pinion gear 10a side (the left side in FIG. 3). The single-row angular contact ball bearing 29 is used. This single-row angular ball bearing 29 is formed between an angular outer ring raceway 14a formed on the inner peripheral surface of the outer ring 13a and an angular inner ring raceway 15a formed directly on the front end portion of the outer peripheral surface of the pinion shaft 3b. In addition, a plurality of balls 16, 16 are provided so as to roll freely with a contact angle applied. In the case of this example, a shoulder 30 is present on the rear end side of the outer ring raceway 14a on the inner peripheral surface of the outer ring 13a, but no shoulder is present on the front end side. For this reason, the single row angular contact ball bearing 29 can be easily assembled. Further, the number of balls 16 and 16 incorporated in the single row angular ball bearing 29 can be increased. That is, in the case of this example, the balls 16, 16 are held around the inner ring raceway 15a (by a retainer, grease, etc., not shown) and the balls 16, 16 are held on the outer ring raceway 14a. The single-row angular ball bearing 29 having a larger number of balls 16 and 16 can be easily assembled by inserting the inner ring in the axial direction from the front end side of the outer ring 13a. Other configurations and operations are the same as those in each example of the above-described embodiment .

[Fourth Example of Embodiment]
FIG. 4 shows a fourth example of the embodiment of the present invention . In the case of this example, regarding the single row angular contact ball bearing 29a which is a rolling bearing on the pinion gear 10a side (right side in FIG. 4), the height H of the shoulder portion 30a existing at the rear end portion of the inner peripheral surface of the outer ring 13b is It is larger than 1/2 of the diameter d of the balls 16 and 16 (H> d / 2). In the case of this example, there is no shoulder portion on the side opposite to the pinion gear 10a (left side in FIG. 4) of the inner ring raceway 15a constituting the single row angular ball bearing 29a. Further, in the case of this example, the inner ring raceway 15a and the end surface of the pinion gear 10a are smoothly continued through the curved surface portion 31, thereby improving the strength and rigidity of the root portion of the pinion gear 10a. . Also in this example, a tandem type double-row angular ball bearing 23 similar to that in the second example of the embodiment shown in FIG. 2 is used as the anti-pinion gear 10a side rolling bearing. Yes.

In the case of the rotation support device for the pinion shaft of this example configured as described above, the outer ring 13b is fitted into the front end portion of the cylindrical member 18 in order to assemble the single row angular ball bearing 29a. With the balls 16, 16 disposed inside the outer ring raceway 14a formed on the inner peripheral surface, the operation of inserting the pinion shaft 3c inside the balls 16, 16 is performed using the front end portion of the cylindrical member 18 as shown in FIG. If it carries out in the state which faced upwards, it can prevent that each said balls 16 and 16 fall out from the inner side of the said outer ring track 14a with the said shoulder part 30a. For this reason, the assembly of the single row angular contact ball bearing 29a can be performed more easily. Note that the above-described spilling of the balls 16 and 16 can be prevented by a cage. However, in the case of the structure of this example, such a prevention function can be exhibited by the shoulder portion 30a. For this reason, what does not have this prevention function can be used as the said retainer, and the freedom degree of design can be raised by that much. Other configurations and operations are the same as those in each example of the above-described embodiment .

[ First example of reference example related to the present invention ]
FIG. 5 shows a first example of a reference example related to the present invention . In the case of this reference example , an axial load acting on the pinion shaft 3b can be supported from the pinion gear 10a side to the non-pinion gear 10a side (left side in FIG. 5) as a rolling bearing on the pinion gear 10a side (right side in FIG. 5). A tandem type double row angular contact ball bearing 23a is used. The tandem double-row angular ball bearings 23a are formed directly on the inner circumferential surface of the outer ring 24a, respectively on the outer circumferential surfaces of the outer circumferential surface of the pinion shaft 3b and the double-row outer ring raceways 25c and 25d each having an angular shape. A state in which a plurality of balls 28 and 28 are provided for each of the rows and the contact angles in the same direction between the rows are formed between the formed double-row inner ring raceways 27c and 27d. And the pitch circle diameter of the ball row on the pinion gear 10a side is larger than the pitch circle diameter of the ball row on the anti-pinion gear 10a side. In the case of this reference example , a tandem double-row angular ball bearing 23 similar to that in the second example of the embodiment shown in FIG. 2 is used as the rolling bearing on the side opposite to the pinion gear 10a. ing.

In the case of the rotation support device for the pinion shaft 3b of the present reference example configured as described above, a tandem type roller bearing 4c (see FIG. 8) is used as a rolling bearing on the pinion gear 10a side instead of the conventional single row tapered roller bearing 4c (see FIG. 8). Since the double-row angular ball bearing 23a is used, the rotational torque can be reduced. The tandem double-row angular contact ball bearing 23a has a sufficiently large load capacity and a sufficiently long life compared to a single-row angular contact ball bearing of the same size. That is, according to the structure of the present reference example , it is possible to realize a rotational torque lower than that of the conventional single row tapered roller bearing 4c while maintaining a sufficient life for the rolling bearing on the pinion gear 10a side. Further, since the tandem double-row angular ball bearing 23a used as the rolling bearing on the pinion gear 10a side does not have a separate inner ring, the rotation support device can be easily assembled. Other configurations and operations are the same as those in each example of the above-described embodiment .

[ Second example of reference example related to the present invention ]
FIG. 6 shows a second example of a reference example related to the present invention . In the case of this reference example , it is possible to support an axial load acting on the pinion shaft 3d from the pinion gear 10a side (the right side in FIG. 6) to the anti-pinion gear 10a side (the left side in FIG. 6). The single-row tapered roller bearing 4e is used. This single-row tapered roller bearing 4e includes a conical concave outer ring raceway 32 formed on the inner peripheral surface of the outer ring 5c, and a conical convex inner ring raceway 33 formed directly on the front end portion of the outer peripheral surface of the pinion shaft 3d. A plurality of tapered rollers 7c, 7c are provided so as to be able to roll therebetween, and the inner ring raceway 33 has no flange on the large diameter side end.

In the case of the rotation support device for the pinion shaft of the present reference example configured as described above, as a rolling bearing on the pinion gear 10a side, a single-row tapered roller bearing 4e that does not have a flange on the large-diameter end of the inner ring raceway 33. Therefore, the conventional single row tapered roller bearing 4c (having the flange 34) (see FIG. 8) has a portion corresponding to the absence of sliding contact between the flange and the head of each tapered roller 7c, 7c. In comparison, the rotational resistance can be reduced. That is, according to the structure of the present reference example , the rolling bearing on the pinion gear 10a side has substantially the same life as that of the conventional single row tapered roller bearing 4c, but more than the conventional single row tapered roller bearing 4c. A low rotational torque can be realized. Further, since the single-row angular contact ball bearing 4e used as the rolling bearing on the pinion gear 10a side does not have a separate inner ring, the rotation support device can be easily assembled. Other configurations and operations are the same as those of the first example of the embodiment shown in FIG.

In each of the embodiments described above, the present invention is applied to the pinion shaft rotation support device constituting the transfer device. However, the present invention is applicable to the pinion shaft constituting the differential device as shown in FIG. It can also be applied to the rotation support device. Similarly, the structure of each reference example described above can also be applied to a pinion shaft rotation support device constituting the differential device as shown in FIG.

DESCRIPTION OF SYMBOLS 1, 1a Case 2a-2d Annular wall 3, 3a-3d Pinion shaft 4a-4e Single row tapered roller bearing 5a-5d Outer ring 6a-6d Inner ring 7a-7d Tapered roller 8, 8a Ring body 9, 9a Coupling flange 10, 10a Pinion gear 11, 11a Ring gear 12 Single row deep groove ball bearing 13, 13a, 13b Outer ring 14, 14a Outer ring raceway 15, 15a Inner ring raceway 16 Ball 17 Inner ring raceway 18 Tubular member 19 Stepped surface 20 Stepped surface 21 Stepped surface 22 Spacer 23, 23a Double-row angular contact ball bearings 24, 24a Outer rings 25a-25d Outer ring raceway 26 Inner rings 27a-27d Inner ring raceway 28 Balls 29, 29a Single row angular contact ball bearings 30, 30a Shoulder part 31 Curved part 32 Outer ring raceway 33 Inner ring raceway 34 buttock

Claims (3)

  A pinion shaft having a pinion gear provided with a pinion gear at one end is rotatably supported by a pair of rolling bearings provided in the housing in the axial direction so as to be capable of supporting an axial load in both directions. In the rotary support device, the rolling bearing on the pinion gear side of the both rolling bearings is a single row ball bearing capable of supporting an axial load acting on the pinion shaft from the pinion gear side toward the anti-pinion gear side. The inner ring raceway constituting the single row ball bearing is directly formed on the outer peripheral surface of the pinion shaft, and the diameter of the minimum diameter portion of the inner ring raceway constitutes the anti-pinion gear side rolling bearing. A pinion shaft rotation support device, characterized in that it is smaller than the diameter of the smallest diameter portion of the inner ring raceway formed on the outer peripheral surface of the inner ring fitted and fixed to the outer ring. The rotation support device for a pinion shaft according to claim 1, wherein a pitch circle diameter of each ball constituting the single row ball bearing is larger than a pitch circle diameter of each rolling element constituting the rolling bearing on the anti-pinion gear side. The diameter of the minimum diameter part of the inner ring raceway that constitutes the single row ball bearing is equal to the diameter of a portion of the pinion shaft that externally fits the inner ring that constitutes the rolling bearing on the anti-pinion gear side. Pinion shaft rotation support device.

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