JP7639593B2 - Rotational Power Transmission Mechanism - Google Patents

Description

The present invention relates to a rotational power transmission mechanism that transmits rotational power by a rotating drive shaft supported by bearings.

Conventionally, for example, a pinion gear shaft that transmits rotational power from a vehicle's propeller shaft to a differential device is supported on a case member by a pair of bearings that are preloaded in the axial direction to suppress the generation of vibration (see, for example, Patent Documents 1 and 2).

In the devices described in Patent Documents 1 and 2, the pinion gear shaft is supported at two axial locations by bearings (tapered roller bearings), and an annular spacer is disposed between these bearings. The spacer is cylindrical at both ends, with the inner and outer diameters of the central portion being larger than those of the two ends. The pinion gear shaft has a male thread formed on part of its outer periphery, and a axial preload is applied to both bearings by tightening a nut that screws onto the male thread.

JP 2013-194765 A JP 2017-144940 A

In the above-mentioned configuration, when the spacer is pressed in the axial direction by the axial force generated by tightening the nut, the cylindrical portions at both ends of the spacer may become eccentric and deformed so that they are misaligned. In this case, one of the cylindrical portions may be strongly pressed against the outer circumferential surface of the shaft in part of the circumferential direction, generating a large frictional force, and there is a risk that an appropriate preload may not be applied to both bearings.

The present invention aims to provide a rotational power transmission mechanism that can properly apply preload to a pair of bearings even if the spacer between the bearings becomes eccentric and deforms when preloading the bearings.

In order to achieve the above object, the present invention provides a rotational power transmission mechanism comprising: first and second bearings each having a plurality of rolling elements disposed between an inner ring and an outer ring; a rotary drive shaft having a shaft portion supported by the first and second bearings; an annular spacer disposed on an outer periphery of the shaft portion between the inner rings of the first and second bearings; and a nut member screwed onto the shaft portion to apply an axial preload to the first and second bearings, the spacer comprising a first cylindrical portion abutting against a side surface of the inner ring of the first bearing, a second cylindrical portion abutting against a side surface of the inner ring of the second bearing, and a nut member screwed onto the first cylindrical portion and a nut member screwed onto the first cylindrical portion. and a deformation portion that is provided between the first cylindrical portion and the second cylindrical portion and deforms so as to be compressed in the axial direction by the preload, wherein the rotary drive shaft has, on an outer periphery of the shaft portion, a first fitting surface into which the inner ring of the first bearing and the first cylindrical portion of the spacer are fitted, and a second fitting surface into which the inner ring of the second bearing is fitted, a small diameter portion having an outer diameter smaller than that of the second fitting surface is formed inside the second cylindrical portion of the spacer on the shaft portion, an inner peripheral surface of the second cylindrical portion and an outer peripheral surface of the small diameter portion face each other via a gap, and the axial width of the small diameter portion is wider than the axial width of the second cylindrical portion .

The rotational power transmission mechanism of the present invention makes it possible to apply appropriate preload to both bearings even if the spacer disposed between the pair of bearings becomes eccentric and deforms.

1 is a schematic diagram showing an example of the schematic configuration of a four-wheel drive vehicle equipped with a rotational power transmission mechanism according to an embodiment of the present invention; 2 is a cross-sectional view showing a driving force transmission device, a rotational power transmission mechanism, a rear differential, and a differential carrier. FIG. FIG. 2 is a cross-sectional view showing a part of the driving force transmission device. FIG. 4 is a configuration diagram showing a support structure for a pinion gear shaft by a first bearing and a second bearing. 5A to 5C are enlarged cross-sectional views showing a spacer together with a portion of the inner ring of a first bearing and a portion of the inner ring of a second bearing.

[Embodiment]
An embodiment of the present invention will be described with reference to Figures 1 to 5. Note that the embodiment described below is shown as a preferred specific example for carrying out the present invention, and while there are some parts that specifically exemplify various technical matters that are technically preferable, the technical scope of the present invention is not limited to this specific embodiment.

(Overall configuration of four-wheel drive vehicle)
1 is a schematic diagram showing an example of the configuration of a four-wheel drive vehicle equipped with a rotational power transmission mechanism according to an embodiment of the present invention. This four-wheel drive vehicle 1 has left and right front wheels 101, 102 as main drive wheels, and left and right rear wheels 103, 104 as auxiliary drive wheels. The drive force (rotational power) of a drive source 11 is changed in speed by a transmission 12 and is constantly transmitted to the front wheels 101, 102, and is also transmitted to the rear wheels 103, 104 depending on the vehicle state. The drive source 11 is, for example, an engine, but may also be an electric motor, or a combination of an engine and an electric motor.

The four-wheel drive vehicle 1 has a driving force transmission system that transmits the driving force of the driving source 11, which has been changed in speed by the transmission 12, to the left and right front wheels 101, 102 and the left and right rear wheels 103, 104, and includes a front differential 13 and a rear differential 14, left and right drive shafts 151, 152 on the front wheel side arranged between the front differential 13 and the left and right front wheels 101, 102, left and right drive shafts 161, 162 on the rear wheel side arranged between the rear differential 14 and the left and right rear wheels 103, 104, a propeller shaft 17 that transmits driving force in the fore-and-aft direction of the vehicle, a gear mechanism 18 between the front differential 13 and the propeller shaft 17, and a driving force transmission device 19 arranged between the propeller shaft 17 and the rear differential 14. The driving force transmission device 19 has a clutch device 2, a rotational power transmission mechanism 3, and a differential carrier 5 as a housing member that houses the clutch device 2 and the rotational power transmission mechanism 3 together with the rear differential 14.

The front differential 13 has a front differential case 131, a pinion pin 132 fixed to the front differential case 131, a pair of pinion gears 133 supported by the pinion pin 132, and a pair of side gears 134 meshing with the pair of pinion gears 133, and left and right drive shafts 151, 152 are fixed to the pair of side gears 134, respectively. The driving force of the drive source 11 is transmitted from the transmission 12 to the front differential case 131. The gear mechanism 18 consists of a ring gear 181 fixed to the front differential case 131, and a pinion gear 182 meshing with the ring gear 181.

The propeller shaft 17 has a front shaft portion 171 and a rear shaft portion 172, a front universal joint 173 that connects the front shaft portion 171 to the pinion gear 182 of the gear mechanism 18, a rear universal joint 174 that connects the rear shaft portion 172 to the front housing 21 (described later) of the clutch device 2, and a sliding constant velocity joint 175 that connects the front shaft portion 171 to the rear shaft portion 172.

The rear differential 14 has a rear differential case 141, a pinion pin 142 fixed to the rear differential case 141, a pair of pinion gears 143 supported on the pinion pin 142, a pair of side gears 144 that mesh with the pair of pinion gears 143, and a ring gear 145 fastened to the outer periphery of the rear differential case 141. Left and right drive shafts 161, 162 are fixed to the pair of side gears 144, respectively.

The clutch device 2 is controlled by the control device 9, and is capable of adjusting the driving force transmitted from the propeller shaft 17 to the rear differential 14 via the rotational power transmission mechanism 3 according to the vehicle state. The control device 9 can obtain the detection values of the rotational speed sensors S1 to S4, which detect the rotational speeds of the left and right front wheels 101, 102 and the left and right rear wheels 103, 104, as well as the detection value of the accelerator pedal sensor S5, which detects the amount of depression of the accelerator pedal 111, and controls the clutch device 2 based on the detection values of these sensors S1 to S5.

Figure 2 is a cross-sectional view showing the clutch device 2, the rotational power transmission mechanism 3, the rear differential 14, and the differential carrier 5. Figure 3 is a cross-sectional view showing a portion of the clutch device 2.

The clutch device 2 includes a cylindrical front housing 21 with a bottom that rotates with the propeller shaft 17, a rear housing 22 fixed to the end of the opening side (rear side of the vehicle) of the front housing 21, a main clutch 23 housed in the front housing 21, a cam mechanism 24 that generates a thrust force that presses the main clutch 22, a pilot clutch 25 that transmits a torque that operates the cam mechanism 24, an armature 26 arranged in line with the pilot clutch 25 in the axial direction, an electromagnetic coil 27 that generates a magnetic force that attracts the armature 26 to the pilot clutch 25, a holder 28 that is integral with the electromagnetic coil 27, and a yoke 29 that supports the electromagnetic coil 27 against the differential carrier 5. An excitation current is supplied to the electromagnetic coil 27 from the control device 9 via a connector pin 281 of a connector portion 280 provided on the holder 28.

The front housing 21 has a cylindrical portion 211 with multiple axially extending spline projections 211a formed on its inner circumference, and a bottom portion 212 with bolt insertion holes 212b for fastening to the rear universal joint 174 of the propeller shaft 17. The flange yoke 171a of the rear universal joint 174 is fixed to the bottom portion 212 of the front housing 21 by bolts 60 inserted through the bolt insertion holes 212b.

As shown in FIG. 3, the rear housing 22 has an outer cylindrical member 221 and an inner cylindrical member 222 made of a magnetic metal that form a magnetic path for the magnetic flux generated by the electromagnetic coil 27, and a non-magnetic ring 223 disposed between the outer cylindrical member 221 and the inner cylindrical member 222. The non-magnetic ring 223 is welded to the outer cylindrical member 221 and the inner cylindrical member 222. The outer cylindrical member 221 is screwed and fixed to the end of the cylindrical portion 211 of the front housing 21 opposite the bottom portion 212 side. The front housing 21 and the rear housing 22 constitute the clutch housing 20 as a rotating body supported by the support portion 34 of the pinion gear shaft 30 described later.

The main clutch 23 is a multi-plate clutch consisting of multiple main outer clutch plates 231 and multiple main inner clutch plates 232 arranged alternately. The multiple main outer clutch plates 231 engage with multiple spline projections 211a of the front housing 21 and are axially movable but non-rotatable relative to the cylindrical portion 211 of the front housing 21.

The cam mechanism 24 has a main cam 241 that faces the main clutch 23, a pilot cam 242 that is aligned with the main cam 241 in the axial direction, and multiple cam balls 243 that are arranged between the main cam 241 and the pilot cam 242. The main cam 241 and the pilot cam 242 are each formed with multiple arc grooves 241a, 242a that are deeper in the axial direction toward the center. When the main clutch 23 and the main cam 241 rotate relative to each other and the cam balls 243 roll in these arc grooves 241a, 242a, the main cam 241 approaches and moves away from the pilot cam 242. The axial movement of the pilot cam 242 away from the main clutch 23 is regulated by a thrust bearing 61 that is arranged between the pilot cam 242 and the inner cylindrical member 222 of the rear housing 22.

The pilot clutch 25 has multiple pilot outer clutch plates 251 spline-engaged to the front housing 21 and multiple pilot inner clutch plates 252 spline-engaged to the pilot cam 242, and the multiple pilot outer clutch plates 251 and multiple pilot inner clutch plates 252 are arranged alternately. The pilot outer clutch plates 251 and the pilot inner clutch plates 252 each have multiple arc-shaped slits 251a, 252a formed in the radial center, preventing short-circuiting of magnetic flux between the outer periphery and the inner periphery.

The armature 26 is spline-engaged with the front housing 21 and can move axially relative to the cylindrical portion 211 of the front housing 21 but cannot rotate relative to it. The pilot clutch 25 is disposed between the armature 26 and the rear housing 22, and when the electromagnetic coil 27 is energized, the armature 26 presses the pilot clutch 25 toward the rear housing 22.

The rotational power transmission mechanism 3 has a pinion gear shaft 30 as a rotational drive shaft, and a bearing portion 4 that rotatably supports the pinion gear shaft 30 relative to the differential carrier 5. The bearing portion 4 has a first bearing 41 and a second bearing 42 aligned in the axial direction, an annular spacer 43 disposed between the first bearing 41 and the second bearing 42, and a nut member 44 screwed onto the pinion gear shaft 30. The nut member 44 applies an axial preload to the first bearing 41 and the second bearing 42.

The pinion gear shaft 30 has an axle portion 31 supported by a first bearing 41 and a second bearing 42, a gear portion 32 having a larger diameter than the axle portion 31, a spline engagement portion 33 having a plurality of spline projections 33a formed on its outer periphery, and a support portion 34 that supports the clutch housing 20 of the clutch device 2. The gear portion 32 is provided at one end of the pinion gear shaft 30 in the axial direction, which corresponds to the rear side of the vehicle, and meshes with the ring gear 145 of the rear differential 14. The support portion 34 is provided at the other end of the pinion gear shaft 30 in the axial direction, which corresponds to the front side of the vehicle. The spline engagement portion 33 is provided between the axle portion 31 and the support portion 34, and the main cam 241 and the plurality of main inner clutch plates 232 are engaged with the plurality of spline projections 33a. The configuration of the pinion gear shaft 30 and the bearing portion 4 will be described in detail later.

The differential carrier 5 is supported by the vehicle body 100 of the four-wheel drive vehicle 1, with a main body 51 at the front of the vehicle and a cover body 52 at the rear of the vehicle fastened by multiple bolts 53. The rear differential case 141 is supported rotatably relative to the differential carrier 5 by a pair of tapered roller bearings 62, 63 arranged between the main body 51 and the cover body 52.

The main body 51 of the differential carrier 5 has a support cylinder 511 that houses the bearing portion 4 and the shaft portion 31 of the pinion gear shaft 30, and an annular protrusion 512 that protrudes inward from the support cylinder 511. A ball bearing 64 is arranged between the end of the support cylinder 511 on the vehicle front side and the inner cylindrical member 222 of the rear housing 22. The ball bearing 64 has an inner ring 641, an outer ring 642, a plurality of rolling elements 643, and a retainer 644. The outer ring 642 is fitted inside the support cylinder 511 and the yoke 29. The inner ring 641 is fitted outside the inner cylindrical member 222, and the rear housing 22 is supported by the support cylinder 511 via the ball bearing 64.

An axial through hole 210 is formed in the bottom 212 of the front housing 21, and a ball bearing 65 is disposed between the inner surface 210a of the through hole 210 and the outer peripheral surface 34a of the support portion 34 of the pinion gear shaft 30. The ball bearing 65 has an inner ring 651, an outer ring 652, multiple rolling elements 653, and a retainer 654, and the inner ring 651 is prevented from coming off the support portion 34 by a retaining ring 66.

A pair of disc springs 671, 672 and a washer 68 are arranged inside the through hole 210 in line with the outer ring 652 in the axial direction, and the washer 68 is engaged with a flange 212a provided on the bottom 212 of the front housing 21. The outer ring 652 is biased in the axial direction by the restoring force of the disc springs 671, 672. The opening of the through hole 210 is closed by a disk-shaped cap 69.

The differential carrier 5 contains differential oil (not shown), and the front housing 21 contains clutch oil, which has a lower viscosity than the differential oil. Leakage of the differential oil is prevented by seal members 71, 72 arranged between the main body 51 and the cover body 52 of the differential carrier 5 and the drive shafts 161, 162, and by a seal member 73 arranged inside the support cylinder portion 511. Leakage of the clutch oil is prevented by a seal member 74 arranged between the inner cylindrical member 222 of the rear housing 22 and the shaft portion 31 of the pinion gear shaft 30, and by a cap 69. In addition, the deflector 75, seal member 76, and slinger 77 prevent foreign matter from entering through the gap between the differential carrier 5 and the front housing 21.

In the clutch device 2 and rotational power transmission mechanism 3 configured as described above, when current is supplied from the control device 9 to the electromagnetic coil 27 during acceleration of the four-wheel drive vehicle 1, the armature 26, which is attracted to the rear housing 22 by magnetic force, presses the pilot clutch 25, and the rotational torque of the front housing 21 is transmitted to the pilot cam 242 by the pilot clutch 25. As a result, the pilot cam 242 rotates relative to the main cam 241, which presses the main clutch 23, and the driving force is transmitted from the front housing 21 to the pinion gear shaft 30 by the main clutch 23. The driving force transmitted to the pinion gear shaft 30 is transmitted from the gear portion 32 to the rear differential 14 and distributed to the left and right rear wheels 103.

Figure 4 is a diagram showing the support structure of the pinion gear shaft 30 by the first bearing 41 and the second bearing 42. The first bearing 41 and the second bearing 42 each have an inner ring 411, 421 fitted onto the shaft portion 31 of the pinion gear shaft 30, an outer ring 412, 422 arranged on the outside of the inner ring 411, 421, a plurality of rolling elements 413, 423 arranged between the inner ring 411, 421 and the outer ring 412, 422, and a retainer 414, 424 that holds the plurality of rolling elements 413, 423.

In this embodiment, as an example, the first bearing 41 is a tapered roller bearing and the second bearing 42 is an angular ball bearing, but this is not limited thereto, and the first bearing 41 may be an angular ball bearing and the second bearing 42 may be a tapered roller bearing.

The first bearing 41 is disposed closer to the gear portion 32 (rearward of the vehicle) than the second bearing 42. The outer ring 412 of the first bearing 41 and the outer ring 422 of the second bearing 42 axially sandwich an annular protrusion 512 provided on the main body 51 of the differential carrier 5. The annular protrusion 512 protrudes inward from the support tube portion 511 toward the shaft portion 31 of the pinion gear shaft 30. The nut member 44 is disposed closer to the support portion 34 (frontward of the vehicle) than the second bearing 42. The spacer 43 is disposed on the outer periphery of the shaft portion 31 of the pinion gear shaft 30 between the inner rings 411, 421 of the first and second bearings 41, 42, respectively.

Hereinafter, of the two side surfaces of the inner ring 411 of the first bearing 41, the side surface on the vehicle front side will be referred to as the first front inner ring side surface 411a, and the side surface on the vehicle rear side will be referred to as the first rear inner ring side surface 411b. Also, of the two side surfaces of the inner ring 421 of the second bearing 42, the side surface on the vehicle front side will be referred to as the second front inner ring side surface 421a, and the side surface on the vehicle rear side will be referred to as the second rear inner ring side surface 421b. A washer 45 is disposed between the first rear inner ring side surface 411b and the rear surface 32a of the gear portion 32. A nut member 44 abuts against the second front inner ring side surface 421a.

The spacer 43 is made of metal and has a first cylindrical portion 431 that abuts against the first front inner race side surface 411a, a second cylindrical portion 432 that abuts against the second rear inner race side surface 421b, and a deformation portion 433 that is provided between the first cylindrical portion 431 and the second cylindrical portion 432 and deforms so as to be compressed in the axial direction by the preload applied by the nut member 44. The deformation portion 433 protrudes radially outward in a mountain shape in a cross section along the axial direction, and its inner and outer diameters are formed larger than those of the first and second cylindrical portions 431, 432. The deformation of the deformation portion 433 due to the preload may be elastic deformation or plastic deformation.

In this embodiment, the inner and outer diameters of the first cylindrical portion 431 and the inner and outer diameters of the second cylindrical portion 432 are equal. In addition, the axial length of the first cylindrical portion 431 and the axial length of the second cylindrical portion 432 are equal. This allows the spacer 43 to be assembled to the pinion gear shaft 30 from either direction, preventing incorrect assembly. In other words, of the two cylindrical portions at both axial ends of the spacer 43, the cylindrical portion located on the first bearing 41 side is the first cylindrical portion 431, and the cylindrical portion located on the second bearing 42 side is the second cylindrical portion 432.

The pinion gear shaft 30 has a first mating surface 31a on the outer periphery of the shaft portion 31, into which the inner ring 411 of the first bearing 41 and the first cylindrical portion 431 of the spacer 43 are mated, and a second mating surface 31b on which the inner ring 421 of the second bearing 42 is mated. The inner ring 411 of the first bearing 41 is press-fitted into the first mating surface 31a. The shaft portion 31 is also formed with a male thread portion 311 into which the nut member 44 is screwed, on the support portion 34 side of the second mating surface 31b. By tightening the nut member 44 that is screwed into the male thread portion 311, an axial preload is applied to the first and second bearings 41, 42.

In this embodiment, the outer diameter _D1 of the first fitting surface 31a and the outer diameter _D2 of the second fitting surface 31b are equal. Here, "equal" means that the difference in diameter between the outer diameter _D1 of the first fitting surface 31a and the outer diameter _D2 of the second fitting surface 31b is 0.5 mm or less. In addition, as described in Patent Documents 1 and 2, for example, the outer diameter of the pinion gear shaft of a typical differential device is formed so that the outer diameter of the portion where the inner ring of one of the pair of bearings on the gear side is fitted is larger than the outer diameter of the portion where the inner ring of the other bearing is fitted. This is in consideration of the fact that the load on the gear side is large when transmitting the driving force. However, in this embodiment, the support portion 34, which is the end opposite to the gear portion 32, supports the clutch housing 20 of the clutch device 2, so that the load received by the support portion 34 is larger than that of the pinion gear shaft of a typical differential device. For this reason, in this embodiment, the outer diameter _D1 of the first fitting surface 31a and the outer diameter D2 of the second fitting surface 31b are set to be equal to _{each other} .

In this embodiment, since the gear portion 32 has a larger diameter than the shaft portion 31, the first bearing 41, the spacer 43, the second bearing 42, and the nut member 44 are arranged in this order on the outer periphery of the shaft portion 31 from the support portion 34 side. Therefore, the outer diameter _D2 of the second fitting surface 31b is set to be equal to or smaller than the outer diameter _D1 of the first fitting surface 31a in consideration of ease of assembly. That is, the inner ring 411 of the first bearing 41 easily passes through the second fitting surface 31b in the axial direction.

In addition, in this embodiment, since the inner ring 411 of the first bearing 41 is press-fitted into the first mating surface 31a as described above, it is desirable that the diameter difference between the first mating surface 31a and the second mating surface 31b is equal to or greater than the press-fit allowance (tightening allowance) of the inner ring 411 of the first bearing 41. If this diameter difference is equal to or greater than the press-fit allowance of the inner ring 411 of the first bearing 41, the load pressing the first bearing 41 when the inner ring 411 of the first bearing 41 passes through the second mating surface 31b can be small, improving the ease of assembly. The press-fit allowance of the inner ring 411 is, for example, 0.03 mm in diameter.

Furthermore, in this embodiment, a small diameter portion 312 having an outer diameter smaller than that of the second fitting surface 31b is formed inside the second cylindrical portion 432 of the spacer 43 in the shaft portion 31 of the pinion gear shaft 30. The inner peripheral surface 432a of the second cylindrical portion 432 and the outer peripheral surface 312a of the small diameter portion 312 face each other through a gap. This small diameter portion 312 is intended to prevent the second cylindrical portion 432 from being strongly pressed against the outer peripheral surface of the shaft portion 31 even if the first cylindrical portion 431 and the second cylindrical portion 432 are deformed eccentrically so as to be misaligned with each other when the spacer 43 is pressed axially by the axial force generated by tightening the nut member 44.

Figures 5(a) to (c) are enlarged cross-sectional views of the spacer 43 together with a portion of the inner ring 411 of the first bearing 41 and the inner ring 421 of the second bearing 42. Figure 5(a) shows the state before the nut member 44 is tightened. Figure 5(b) shows the state in which the spacer 43 is deformed without the first cylindrical portion 431 and the second cylindrical portion 432 becoming misaligned when the nut member 44 is tightened. Figure 5(c) shows an example of the state in which the spacer 43 is deformed due to the first cylindrical portion 431 and the second cylindrical portion 432 becoming misaligned when the nut member 44 is tightened.

The first bearing 41, spacer 43, second bearing 42, and nut member 44 are attached to the pinion gear shaft 30 by positioning the pinion gear shaft 30 vertically so that the gear portion 32 faces downward. The spacer 43 is positioned coaxially with the pinion gear shaft 30 by fitting the first cylindrical portion 431 into the first fitting surface 31a.

As shown in FIG. 5A, the axial width _W1 of the small diameter portion 312 is wider than the axial width _W2 of the second cylindrical portion 432. Here, the axial width _W1 of the small diameter portion 312 is the overall width of the portion having a smaller outer diameter than the second fitting surface 31b. The axial width _W2 of the second cylindrical portion 432 is the width of the portion where the inner circumferential surface 432a of the second cylindrical portion 432 is formed linearly in the cross section of the spacer 43 along the axial direction. The small diameter portion 312 is formed such that the entire range of the width _W2 of the second cylindrical portion 432 is included within the range of the width W1 both before and after the deformation of the spacer 43 by tightening the nut member ₄₄ .

In the state shown in FIG. 5(a), the axial end face 431b of the first cylindrical portion 431 contacts the first front inner race side face 411a, and the axial end face 432b of the second cylindrical portion 432 contacts the second rear inner race side face 421b, but no axial force is generated by tightening the nut member 44, and the spacer 43 is not deformed. When the nut member 44 is tightened from this state, as shown in FIG. 5(b) and FIG. 5(c), the deformed portion 433 of the spacer 43 deforms so as to be compressed in the axial direction, and the second cylindrical portion 432 moves toward the first cylindrical portion 431.

When the spacer 43 deforms in this way, it is ideal for the first cylindrical portion 431 and the second cylindrical portion 432 to deform while maintaining coaxiality, as shown in FIG. 5(b). However, in this embodiment, even if the second cylindrical portion 432 deforms eccentrically relative to the first cylindrical portion 431, as shown in FIG. 5(c), the small diameter portion 312 is formed at the portion corresponding to the inside of the second cylindrical portion 432. For example, the corner between the inner circumferential surface 432a and the axial end surface 432b of the second cylindrical portion 432 is prevented from being strongly pressed against the shaft portion 31, thereby preventing friction from occurring.

The depth D of small diameter portion 312 in shaft portion 31 (the depth of the annular groove formed by the difference between the outer diameter _D2 of second fitting surface 31b and the outer diameter of small diameter portion 312) may be set to a dimension deep enough that the second cylindrical portion 432 does not come into contact with the outer peripheral surface 312a of the small diameter portion 312 even if the second cylindrical portion 432 is significantly displaced in the radial direction. However, even if the second cylindrical portion 432 comes into contact with the outer peripheral surface 312a of the small diameter portion 312, friction when the second cylindrical portion 432 is pressed against the shaft portion 31 can be reduced compared to the case where the small diameter portion 312 is not formed.

(Effects of the embodiment)
According to the embodiment of the present invention described above, when the nut member 44 is tightened to apply a preload to the first and second bearings 41, 42, even if the spacer 43 is eccentrically deformed, the preload can be appropriately applied to the first and second bearings 41, 42. In addition, in this embodiment, the inner diameter of the first cylindrical portion 431 of the spacer 43 is equal to the inner diameter of the second cylindrical portion 432, so that there is no restriction on the assembling direction of the spacer 43, and assembling efficiency is improved. In addition, in this embodiment, the outer diameter _D1 of the first fitting surface 31a of the pinion gear shaft 30 is equal to the outer diameter _D2 of the second fitting surface 31b, so that the clutch housing 20 can be supported by the support portion 34 with high rigidity. Furthermore, according to this embodiment, the axial width _W1 of the small diameter portion 312 is wider than the axial width _W2 of the second cylindrical portion 432 of the spacer 43, so that interference between the second cylindrical portion 432 and the pinion gear shaft 30 can be easily avoided.

(Additional Note)
Although the present invention has been described above based on the embodiment, the invention according to the claims is not limited to the embodiment. It should be noted that not all of the combinations of features described in the embodiment are necessarily essential to the means for solving the problems of the invention. The present invention can be appropriately modified and implemented by omitting some configurations or adding or replacing configurations within the scope of the gist of the invention. For example, in the above embodiment, the rotational power transmission mechanism of the present invention is described as being used to transmit the driving force of a vehicle, but the present invention is not limited to this, and can also be applied to a rotational power transmission mechanism used in, for example, industrial machinery.

3... Rotational power transmission mechanism 30... Pinion gear shaft (rotational drive shaft)
31...Shaft portion 312...Small diameter portion 312a...Outer peripheral surface 314...Support portion 31a...First fitting surface 31b...Second fitting surface 32...Gear portion 34...Support portion 41...First bearing 42...Second bearing 411, 421...Inner ring 412, 422...Outer ring 413, 423...Rolling element 414, 424...Cage 43...Spacer 431...First cylindrical portion 432...Second cylindrical portion 433...Deformation portion 44...Nut member

Claims (4)

A rotational power transmission mechanism comprising: first and second bearings each having a plurality of rolling elements disposed between an inner ring and an outer ring; a rotational drive shaft having a shaft portion supported by the first and second bearings; an annular spacer disposed on an outer periphery of the shaft portion between the inner rings of the first and second bearings; and a nut member screwed onto the shaft portion to apply an axial preload to the first and second bearings, the rotational power transmission mechanism transmitting rotational power by the rotational drive shaft,
the spacer has a first cylindrical portion in contact with a side surface of the inner ring of the first bearing, a second cylindrical portion in contact with a side surface of the inner ring of the second bearing, and a deformation portion provided between the first cylindrical portion and the second cylindrical portion and deformed so as to be compressed in the axial direction by the preload,
the rotation drive shaft has, on an outer periphery of the shaft portion, a first fitting surface into which the inner ring of the first bearing and the first cylindrical portion of the spacer are fitted, and a second fitting surface into which the inner ring of the second bearing is fitted,
a small diameter portion having an outer diameter smaller than that of the second fitting surface is formed inside the second cylindrical portion of the spacer in the shaft portion,
an inner circumferential surface of the second cylindrical portion and an outer circumferential surface of the small diameter portion face each other via a gap,
The axial width of the small diameter portion is greater than the axial width of the second cylindrical portion.
Rotational power transmission mechanism. The spacer has an equal first cylindrical portion and an equal second cylindrical portion, and an outer diameter of the first fitting surface of the rotary drive shaft is equal to an outer diameter of the second fitting surface.
2. The rotary power transmission mechanism according to claim 1. The rotary drive shaft has a gear portion at one end in the axial direction, the gear portion having a larger diameter than the shaft portion, and a support portion at the other end in the axial direction, the support portion supporting a rotor.
3. The rotational power transmission mechanism according to claim 1 or 2 . the first bearing is disposed closer to the gear portion than the second bearing, and the inner ring of the first bearing is press-fitted into the first fitting surface,
The outer diameter of the second mating surface is equal to or smaller than the outer diameter of the first mating surface.
4. The rotary power transmission mechanism according to claim 3 .

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