JP7821064B2 - shaft structure - Google Patents

Description

This disclosure relates to shaft structures.

A known example of a conventional shaft structure is the device disclosed in Patent Document 1. The shaft structure includes a driven gear and a balance shaft. The driven gear meshes with a gear on the crankshaft of the internal combustion engine. The balance shaft is rotatably supported in the housing of the internal combustion engine and rotates in conjunction with the rotation of the driven gear. This shaft structure has an elastic body disposed between the driven gear and the balance shaft. The elastic body functions as a damper to absorb fluctuations in the torque transmitted from the crankshaft.

Japanese Patent Application Laid-Open No. 2022-026420

The elastic body in Patent Document 1 undergoes elastic deformation in response to the load in order to absorb fluctuations in input torque. Repeated elastic deformation gradually fatigues the elastic body, and it will eventually no longer be able to fully function as a damper. Extending the life of such an elastic body will also extend the life of the device.

Therefore, the purpose of this disclosure is to provide a shaft structure that can improve the lifespan of the elastic portion.

The shaft structure disclosed herein comprises a shaft portion that rotates around an axis, a gear portion that is arranged on the outer periphery of the shaft portion, and a gear damper that has an elastically deformable elastic portion and is arranged between the shaft portion and the gear portion. The shaft portion has a flange portion that protrudes from the outer periphery and contacts the gear portion in the axial direction, and the elastic portion presses the gear portion against the flange portion in the axial direction by a biasing force due to its own elastic restoring force.

In the shaft structure, the gear portion is pressed against the flange portion by the elastic portion. As a result, when torque is input to the gear portion, friction is generated between the gear portion and the flange portion. This frictional force acts as a force that tends to rotate the shaft portion. In other words, the torque input to the gear portion is transmitted to the shaft portion not only by the elastic portion, but also by the friction between the gear portion and the flange portion. Compared to when torque from the gear portion to the shaft portion is received only by the elastic portion, the shaft structure disclosed herein can reduce the torque acting on the elastic portion, thereby improving the lifespan of the elastic portion.

FIG. 1 is a perspective cross-sectional view showing a shaft structure according to a first embodiment. FIG. 2 is an enlarged cross-sectional view of a main part showing the shaft structure according to the first embodiment. FIG. 3 is an enlarged cross-sectional view of a further essential part showing the shaft structure according to the first embodiment. FIG. 4 is an enlarged cross-sectional view of a main part of the shaft structure according to the first embodiment, showing a state before the gear damper is assembled.

Description of the embodiments of the present disclosure
A preferred embodiment of the present disclosure is as follows.

The biasing force is preferably an elastic restoring force from a state in which the elastic part is more elongated than its natural state. This configuration allows for a simpler configuration than when the biasing force is an elastic restoring force from a state in which the elastic part is more contracted than its natural state.

The gear damper has an inner ring portion connected to the inner peripheral side of the elastic portion, and an outer ring portion connected to the outer peripheral side of the elastic portion, the inner ring portion having an inner flange that contacts the shaft-side contact surface of the shaft portion facing the axial direction, and the outer ring portion having an outer flange that contacts the gear-side contact surface of the gear portion facing the axial direction. A step is formed between the shaft-side contact surface and the gear-side contact surface, with the shaft-side contact surface recessed in the axial direction from the gear-side contact surface, and the elastic portion is preferably disposed diagonally between the inner ring portion and the outer ring portion in correspondence with the step. This configuration makes it possible to simply press the gear portion against the flange portion using the axial biasing force of the elastic portion.

[Details of the embodiment of the present disclosure]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0014] The present disclosure will be described below with reference to the accompanying drawings. In the following description, the term "annular" used to specify the shape of some components can be replaced with "cylindrical" or "tubular."

Example 1
Example 1 of this embodiment illustrates a balance shaft 10 shown in FIG. 1 as an example of a shaft structure according to the present disclosure. The balance shaft 10 suppresses vibrations of a reciprocating engine serving as an internal combustion engine. The balance shaft 10 receives rotation of a crankshaft (not shown) of the internal combustion engine, rotates in synchronization with the crankshaft, and reduces vibrations of the crankshaft. The balance shaft 10 is rotatably supported by a housing (not shown) of the internal combustion engine.

As shown in Figures 1 to 3, the balance shaft 10 has a shaft portion 20, a gear portion 30, and a gear damper 40. The shaft portion 20 extends along an axis C. The shaft portion 20 rotates around the axis C. The shaft portion 20 has a shaft main body 21, an expanded diameter portion 22, and a flange portion 23. The shaft main body 21 is cylindrical and extends along the axis C. In this embodiment, the axial direction is synonymous with the direction along the axis C, and around the axis is synonymous with around the axis C.

The expanded diameter portion 22 is integrally continuous with the shaft body 21. The expanded diameter portion 22 protrudes radially outward from the shaft body 21 and is disk-shaped with an outer diameter larger than that of the shaft body 21. The outer peripheral surface 22A of the expanded diameter portion 22 is slidable against the inner peripheral surface 30A of the gear portion 30 (described later). As shown in FIG. 4 , the outer peripheral surface 22A of the expanded diameter portion 22 forms a recess 11 between itself and the inner peripheral surface of the large diameter portion 33 of the gear portion 30 (described later). The flange portion 23 is formed in a flange shape protruding radially outward from the outer peripheral surface 22A of the expanded diameter portion 22. The flange portion 23 contacts the gear portion 30 in the axial direction. The flange portion 23 is formed at the other end of the outer peripheral surface 22A of the expanded diameter portion 22 in the direction of axis C. One axial end face 23A of the flange portion 23 contacts the end face 30C (described below) of the gear portion 30.

The shaft portion 20 has an oil passage 24 that runs axially at the center (axial center) of the shaft body 21, and a branch passage 25 that branches radially from the oil passage 24. The lubricating oil flowing through the oil passage 24 is supplied via the branch passage 25 between the outer peripheral surface 22A of the expanded diameter portion 22 and the inner peripheral surface 30A of the gear portion 30. The shaft portion 20 has a weight portion 26. The weight portion 26 is attached to one axial end of the shaft body 21. The weight portion 26 is eccentric with respect to the axial center of the shaft body 21. A weight portion similar to the weight portion 26 (not shown) is attached to the other axial end of the shaft body 21, at a position 180 degrees opposite the weight portion 26 in the circumferential direction.

The shaft portion 20 has a shaft-side contact surface 20A. The shaft-side contact surface 20A is a surface of the expanded diameter portion 22 facing one side in the axial direction C. The shaft-side contact surface 20A comes into contact with the inner flange portion 41A of the inner annular portion 41, which will be described later.

As shown in Figures 1 to 3, the gear portion 30 has an annular shape and is disposed on the outer periphery of the enlarged diameter portion 22 of the shaft portion 20. The gear portion 30 is formed by integrating a synthetic resin tooth portion 31 on the outer periphery with a metal base portion 32 on the inner periphery through insert molding. The gear portion 30 meshes with a drive gear (not shown) of the crankshaft at the tooth portion 31. The inner periphery surface 30A of the gear portion 30 is formed with an inner diameter slightly larger than the outer diameter of the outer periphery surface 22A of the enlarged diameter portion 22 of the shaft portion 20. The gear portion 30 is fitted into the enlarged diameter portion 22 with a loose fit, and is movable circumferentially and axially relative to the shaft portion 20. When the gear portion 30 is properly fitted into the enlarged diameter portion 22, the other axial end face 30C of the gear portion 30 is in contact with the flange portion 23.

The gear portion 30 has a large diameter portion 33. The large diameter portion 33 is provided on the inner circumference of one axial side of the gear portion 30. The large diameter portion 33 is formed with an inner diameter larger than the inner diameter of the inner circumferential surface 30A. The outer ring portion 42 of the gear damper 40, described below, is press-fitted onto the inner circumference of the large diameter portion 33.

The gear portion 30 has a gear-side contact surface 30B. The gear-side contact surface 30B is a surface of the gear portion 30 facing one side in the axial C direction. The gear-side contact surface 30B extends radially outward from one edge of the inner circumferential surface of the large-diameter portion 33 in the axial C direction. The outer flange portion 42A of the outer annular portion 42, described below, contacts the gear-side contact surface 30B. A step 12 is formed between the gear-side contact surface 30B and the shaft-side contact surface 20A. As shown in Figure 4, the step 12 is configured such that the shaft-side contact surface 20A is recessed to the other side in the axial C direction from the gear-side contact surface 30B.

The gear damper 40 is fitted into the recess 11 defined by the outer peripheral surface 22A of the enlarged diameter portion 22 of the shaft portion 20 and the inner peripheral surface of the large diameter portion 33 of the gear portion 30. The gear damper 40 has a damping function. The gear damper 40 serves to absorb (suppress) fluctuations in torque transmitted from the crankshaft to the balance shaft 10. The gear damper 40 also contributes to reducing the rattle noise between the tooth portion 31 of the gear portion 30 and the gear on the crankshaft side (not shown) that meshes with it.

The gear damper 40 has an inner ring portion 41, an outer ring portion 42, and an elastic portion 43. The inner ring portion 41 is a circular metal member. The inner ring portion 41 has an inner flange portion 41A. The inner flange portion 41A expands from one end in the axial C direction toward the inner periphery. This gives the inner ring portion 41 an L-shaped cross section. The inner ring portion 41 is press-fitted onto the outer periphery of the expanded diameter portion 22 of the shaft portion 20. The inner flange portion 41A of the inner ring portion 41 contacts the shaft-side contact surface 20A, which is the surface of the shaft portion 20 facing one side in the axial C direction.

Like the inner ring portion 41, the outer ring portion 42 is a metal annular member. The outer ring portion 42 has an outer flange portion 42A. The outer flange portion 42A is formed by expanding radially outward from one end in the axial C direction. The outer ring portion 42 has an L-shaped cross section that is radially symmetrical to the cross section of the inner ring portion 41. The axial length of the outer ring portion 42 is equal to the axial length of the inner ring portion 41. The outer ring portion 42 is press-fitted onto the inner circumference of the large diameter portion 33 of the gear portion 30. The outer flange portion 42A of the outer ring portion 42 contacts the gear-side contact surface 30B, which is the surface of the gear portion 30 facing one side in the axial C direction.

The elastic portion 43 is disposed between the shaft portion 20 and the gear portion 30 in an elastically deformable manner. In this embodiment, the elastic portion 43 is disposed between the shaft portion 20 and the gear portion 30 via the inner ring portion 41 and the outer ring portion 42. The elastic portion 43 is an annular member made of rubber or elastomer. The elastic portion 43 is disposed in a state where it is sandwiched radially between the inner ring portion 41 and the outer ring portion 42. The elastic portion 43 is vulcanization-bonded to both the inner circumferential surface of the outer ring portion 42 and the outer circumferential surface of the inner ring portion 41.

As shown in FIG. 4 , when the gear damper 40 is in its natural state without elastic deformation, the inner flange portion 41A of the inner annular portion 41 and the outer flange portion 42A of the outer annular portion 42 are radially aligned. When the gear damper 40 is in its natural state without elastic deformation, the axial end faces of the inner annular portion 41 and the outer annular portion 42 are substantially flush with each other. As shown in FIG. 3 , when the gear damper 40 is properly press-fitted and fixed in the recess 11, the inner annular portion 41 and the outer annular portion 42 are positioned corresponding to the step 12. In other words, when the gear damper 40 is properly press-fitted and fixed in the recess 11, the inner annular portion 41 is positioned on the other side of the outer annular portion 42 in the axial direction C. In this state, the elastic portion 43 is diagonally bridged between the inner annular portion 41 and the outer annular portion 42. In this state, the elastic portion 43 is stretched in the direction of axis C more than in its natural state. In this state, the elastic portion 43 exerts a biasing force in the direction of axis C due to its elastic restoring force, pressing the gear portion 30 against the flange portion 23.

The structure of the balance shaft 10 in this first embodiment is as described above. Next, we will explain its functions and effects.

The gear damper 40 is press-fitted into the recess 11 and fixed, integrating the shaft portion 20 and gear portion 30 of the balance shaft 10 via the gear damper 40. When torque from the crankshaft is input to the gear portion 30, the torque is transmitted to the shaft portion 20 via the gear damper 40, causing the balance shaft 10 to rotate. At this time, the gear damper 40 transmits torque from the gear portion 30 to the shaft portion 20 while absorbing torque fluctuations in the elastic portion 43.

In the balance shaft 10, the elastic portion 43 applies a biasing force due to its elastic restoring force, pressing the gear portion 30 against the flange portion 23. When torque is input to the gear portion 30 in this state, a frictional force is generated between the end face 30C of the gear portion 30 and the end face 23A of the flange portion 23. This frictional force bears part of the torque transmission from the gear portion 30 to the shaft portion 20. The elastic portion 43 transmits only the other part of the torque from the gear portion 30 to the shaft portion 20. As a result, the load on the elastic portion 43 is reduced compared to when all of the torque is transmitted from the gear portion 30 to the shaft portion 20, resulting in a longer lifespan.

In the balance shaft 10, the biasing force of the elastic portion 43 is an elastic restoring force from a state in which the elastic portion is more extended than its natural state. Therefore, the configuration can be simplified compared to, for example, cases in which the biasing force is an elastic restoring force from a state in which the elastic portion is more contracted than its natural state.

In the balance shaft 10, the gear damper 40 has an inner annular portion 41 and an outer annular portion 42. The inner annular portion 41 is connected to the inner peripheral side of the elastic portion 43. The outer annular portion 42 is connected to the outer peripheral side of the elastic portion 43. The inner annular portion 41 has an inner flange portion 41A that contacts the shaft-side contact surface 20A of the shaft portion 20. The outer annular portion 42 has an outer flange portion 42A that contacts the gear-side contact surface 30B of the gear portion 30. A step 12 is formed between the shaft-side contact surface 20A and the gear-side contact surface 30B, with the shaft-side contact surface 20A recessed axially from the gear-side contact surface 30B. The elastic portion 43 is disposed diagonally across the step 12 between the inner annular portion 41 and the outer annular portion 42. As a result, the balance shaft 10 can achieve a simple configuration in which the gear portion 30 is pressed against the flange portion 23 by the axial biasing force of the elastic portion 43.

Other Embodiments of the Present Disclosure
The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive.
In the above embodiment, the shaft structure is a balance shaft structure, but in other embodiments, the shaft structure may be a rotating shaft structure other than a balance shaft.
In the above embodiment, the flange portion is provided on the enlarged diameter portion, but in another embodiment, the flange portion may be provided directly on the outer periphery of the shaft body.
In the above embodiment, the elastic portion exerts an elastic restoring force from a state stretched more than the natural state as a biasing force, but it may also exert an elastic restoring force from a state compressed more than the natural state as a biasing force.
In the above embodiment, the step is formed by recessing the shaft side contact surface in the axial direction from the gear side contact surface, but it may also be formed by protruding the gear side contact surface in the axial direction from the shaft side contact surface.
In the above embodiment, the elastic portion is provided between the inner annular portion and the outer annular portion, but in other embodiments, the elastic portion may be in direct contact with at least one of the shaft portion and the gear portion. Furthermore, the elastic portion is not particularly limited as long as it is arranged between the shaft portion and the gear portion in an elastically deformable manner and applies a biasing force due to an elastic restoring force to press the gear portion against the flange portion, and may be, for example, a coil spring, a disc spring, or the like.

10...Balance shaft (shaft structure)
12: Step 20: Shaft portion 20A: Shaft side contact surface 23: Flange portion 30: Gear portion 30B: Gear side contact surface 40: Gear damper 41: Inner ring portion 41A: Inner flange portion 42: Outer ring portion 42A: Outer flange portion 43: Elastic portion C: Shaft

Claims (3)

a shaft portion that rotates around an axis;
a gear portion disposed on an outer periphery of the shaft portion;
a gear damper having an elastically deformable elastic portion , an inner annular portion connected to an inner circumferential side of the elastic portion, and an outer annular portion connected to an outer circumferential side of the elastic portion , the gear damper being disposed between the shaft portion and the gear portion and transmitting torque from the gear portion to the shaft portion while absorbing fluctuations in the elastic portion ;
Equipped with
the shaft portion has a flange portion that protrudes from an outer periphery and contacts the gear portion in the axial direction,
A shaft structure in which the elastic portion presses the gear portion against the flange portion in the axial direction by a biasing force due to its own elastic restoring force. The shaft structure described in claim 1, wherein the biasing force is an elastic restoring force from a state stretched beyond its natural state. the inner annular portion includes an inner flange portion that contacts a shaft-side contact surface of the shaft portion that faces the axial direction,
the outer annular portion includes an outer flange portion that contacts a gear-side contact surface of the gear portion that faces the axial direction,
a step is formed between the shaft-side contact surface and the gear-side contact surface, the step being such that the shaft-side contact surface is recessed in the axial direction from the gear-side contact surface;
The shaft structure according to claim 2 , wherein the elastic portion is disposed diagonally between the inner annular portion and the outer annular portion in correspondence with the step.