CN112334679B

CN112334679B - Low hysteresis cam mechanism with tapered roller

Info

Publication number: CN112334679B
Application number: CN201880094627.4A
Authority: CN
Inventors: 川田和隆
Original assignee: GKN Driveline International GmbH
Current assignee: GKN Driveline International GmbH
Priority date: 2018-06-20
Filing date: 2018-06-20
Publication date: 2023-09-15
Anticipated expiration: 2038-06-20
Also published as: WO2019244268A1; CN112334679A; JPWO2019244268A1; JP6912666B2

Abstract

The cam mechanism for generating axial force in combination with a unit for generating differential motion around an axis comprises: a cam plate rotatable about the shaft and coupled to the unit to receive the differential motion; a pressing plate axially opposed to the cam plate and movable in the axial direction; a pair of cam surfaces formed on the cam plate and the pressure plate, respectively, and facing each other, and inclined in a circumferential direction with respect to a circumferential surface orthogonal to the shaft, respectively; a plurality of tapered rollers interposed between the pair of cam surfaces, rolling on the cam surfaces according to the differential motion, and generating the axial force by the platen, the tapered rollers each having a rolling surface rotationally symmetrical in a radial direction orthogonal to the axis and tapered toward the axis; and a texture formed on one or more of the cam surface and the rolling surface, the texture being resistant to twisting of each tapered roller in the radial direction.

Description

Low hysteresis cam mechanism with tapered roller

Technical Field

The following disclosure relates to a cam mechanism that generates an axial force using a tapered roller, for example, and a power transmission device of a clutch device provided with the cam mechanism.

Background

Typically, vehicles utilize several clutches. For example, for the purpose of switching between a two-wheel drive (2 WD) mode and a four-wheel drive (4 WD) mode, a clutch is sometimes interposed between two shafts, and the actuator controls the on-off connection thereof. Since it is difficult to generate a sufficient axial force required to connect the clutch by a separate mechanism, cam mechanisms are sometimes combined in order to increase the output thereof.

In order to smoothly operate the cam mechanism, balls may be interposed between the cam members. By rolling the balls between the relatively rotating cam surfaces, the balls significantly reduce the sliding resistance. This reduces the load on the actuator, but since the cam surface is in point contact with the balls only, there is a problem in that a large axial force is applied to the cam mechanism. The use of rollers capable of making line contact instead of balls is one of the means for solving this problem. Patent document 1 discloses a related art.

Prior art literature

Patent literature

Patent document 1: international patent application publication WO2017/149829A1

Disclosure of Invention

Depending on the rollers in line contact, greater axial forces can be generated, but the inventors have found other new problems. According to the related art described above, the cam mechanism presses the pressure ring against the clutch according to the current applied to the driver, thereby coupling the clutch to transmit torque thereto. From the standpoint of controllability of torque transmission, it is desirable that the torque transmitted by the applied current is unique. However, as illustrated in FIG. 1 of the present application, curve C of torque T transferred to applied current I _p In the current increasing process (the process of coupling the clutch) P _I With current reduction (to be disconnected) P _D And exhibit a non-negligible hysteresis. Needless to say, hysteresis is a main cause of impaired controllability. The present inventors studied the structure of the cam mechanism for the purpose of reducing hysteresis, and thought the following mechanism or device.

The following disclosure relates to a cam mechanism capable of reducing hysteresis while using tapered rollers, and a power transmission device of a clutch device provided with the cam mechanism.

According to one aspect, a cam mechanism for generating an axial force in combination with a unit for generating a differential motion about an axis includes: a cam plate rotatable about the shaft and coupled to the unit to receive the differential motion; a pressing plate axially opposed to the cam plate and movable in the axial direction; a pair of cam surfaces formed on the cam plate and the pressure plate, respectively, and facing each other, and inclined in a circumferential direction with respect to a circumferential surface orthogonal to the shaft, respectively; a plurality of tapered rollers interposed between the pair of cam surfaces, rolling on the cam surfaces according to the differential motion, and generating the axial force by the platen, the tapered rollers each having a rolling surface rotationally symmetrical in a radial direction orthogonal to the axis and tapered toward the axis; and a texture formed on one or more of the cam surface and the rolling surface, the texture being resistant to twisting of each tapered roller in the radial direction.

According to another aspect, a clutch device for controlling torque transmission between a first rotating body and a second rotating body that are rotatable about axes, respectively, includes: a cam plate rotatable about the shaft; a brake device coupled to the cam plate so as to controllably brake the cam plate against the first rotary body; a pressing plate axially opposed to the cam plate, rotatable together with the second rotating body, and movable in an axial direction; a pair of cam surfaces formed on the cam plate and the pressure plate, respectively, and facing each other, and inclined in a circumferential direction with respect to a circumferential surface orthogonal to the shaft, respectively; a plurality of tapered rollers interposed between the pair of cam surfaces, rolling on the cam surfaces according to the differential motion, and generating the axial force by the platen, the tapered rollers each having a rolling surface rotationally symmetrical in a radial direction orthogonal to the axis and tapered toward the axis; a texture formed on one or more of the cam surface and the rolling surface, the texture being resistant to twisting of each tapered roller in the radial direction; and a clutch that transmits the torque between the first rotating body and the second rotating body when pressed by the pressing plate in the axial direction.

Drawings

Fig. 1 is a graph showing an example of hysteresis in a cam mechanism.

Fig. 2A is a schematic longitudinal cross-sectional view of a cam mechanism illustrating forces applied to tapered rollers.

Fig. 2B is a schematic cross-sectional view of the cam mechanism in a plane orthogonal to the radial direction.

Fig. 2C is a schematic cross-sectional view of the cam mechanism showing a state in which the tapered roller rolls on the rolling surface.

Fig. 3 is a longitudinal sectional view of a clutch device including a cam mechanism according to an embodiment.

Fig. 4 is a partially cut-away perspective view of the cam mechanism.

Fig. 5A is a top view of a textured tapered roller and cam surface.

Fig. 5B is a top view of a tapered roller and cam surface based on other examples.

Fig. 6A is a schematic top view of the development of the texture on the rolling or cam surface into a plane.

Fig. 6B is a schematic top view of a texture based on other examples unfolded into a plane.

Fig. 6C is a schematic top view of a texture based on other examples unfolded into a plane.

Fig. 6D is a schematic top view of a texture based on other examples unfolded into a plane.

Fig. 6E is a schematic top view of a texture based on other examples unfolded into a plane.

Fig. 7 is a schematic cross-sectional view showing a form in which textures on the rolling surface and the cam surface are engaged with each other.

Fig. 8A is a cross-sectional view of the tapered roller and the cam plate in an example in which a part of the cam plate is in contact with the outer peripheral surface of the tapered roller.

Fig. 8B is a cross-sectional view of a tapered roller and cam plate based on another example.

Detailed Description

Several exemplary embodiments are described below with reference to the accompanying drawings. In the following description and the scope of the claims, unless otherwise specified, the axis means the rotation axis of the cam mechanism, the axial direction means a direction parallel thereto, and the radial direction means a direction orthogonal thereto. The rotation axis of the clutch device is generally coincident with the rotation axis of the cam mechanism, but is not necessarily limited thereto.

Referring to fig. 2A and 2B, when the cam mechanism includes the cam plate 5, the platen 9, and the tapered roller 11 interposed therebetween, the rolling surface 11 of the tapered roller 11 _R Is in line contact with the cam surface 5c of the cam plate 5, is also in line contact with the cam surface 9c of the pressure plate 9, and these contact lines are inclined with respect to the radial direction. In this state, when the axial force F is applied to the cam mechanism, a radially outward reaction force is generated in the tapered roller 11 due to the inclination of the contact lineF _R . Radial reaction force F _R The outer peripheral surface 11f of the tapered roller 11 is pressed against the inner peripheral surface 5f of the cam plate 5 and the inner peripheral surface 9f of the pressure plate 9. This becomes a cause of friction that hinders the rolling of the tapered roller 11.

In this state, as shown in FIG. 2C, the cam plate 5 pivots about the shaft relative to the platen 9 to cause a differential M _D When the clutch is to be engaged, a force is generated to twist the tapered roller 11 on the pressed contact surface. The tapered roller 11 causes a rolling M on the cam surfaces 5c, 9c _R While the inclined surface is raised, the pressing plate 9 causes the axial movement Mx, which is generated under the influence of the friction force and the torsion force.

At this time, the axial force F' increases compared to the first, and therefore the radial reaction force pressing the outer peripheral surface 11F against the inner peripheral surfaces 5F, 9F also increases, while the contact area between the outer peripheral surface 11F and the inner peripheral surfaces 5F, 9F decreases because the cam plate 5 and the pressure plate 9 are separated by the axial movement Mx. Here, although the increase in the radial reaction force may prevent rolling, the decrease in the contact area is an element that promotes rolling.

On the other hand, when the state shown in fig. 2B is to be returned from the state shown in fig. 2C (the process of disengaging the clutch), the force of twisting the tapered roller 11 also acts in the opposite direction due to the differential reverse direction, and the axial force F' decreases, but the contact area between the outer peripheral surface 11F and the inner peripheral surfaces 5F and 9F increases.

In curve C of torque T transmitted to applied current I _p The hysteresis that occurs in (a) shows the composite result of these effects. The present inventors considered solving the problem by coping with the force of the torsion tapered roller without increasing the rolling resistance, and therefore conceived the following embodiments.

The cam mechanism 3 of the present embodiment is applied to the clutch device 1 illustrated in fig. 3, for example, but is not necessarily limited thereto. The clutch device 1 is a device that intermittently transmits or controls torque between a first rotating body and a second rotating body that rotate around an axis X, respectively, the first rotating body being a clutch housing 21 in this example, and the second rotating body being a shaft 23.

The clutch 25 is interposed between the clutch housing 21 and the shaft 23 to regulate torque transmission. In this example, the clutch 25 is a multiple plate clutch, but may be another type of friction clutch. The clutch 25 has a plurality of outer plates coupled to the clutch housing 21 by a lug pattern or the like, and a plurality of inner plates alternately arranged with the outer plates coupled to the shaft 23 by a lug pattern or the like. The cam mechanism 3 frictionally couples the outer plate and the inner plate by applying an axial force to the clutch 25, and transmits torque between the clutch housing 21 and the shaft 23. Further, the torque transmitted by increasing or decreasing the axial force increases or decreases.

The clutch device 1 further includes a unit 27 for generating a differential motion for operating the cam mechanism 3, and the unit 27 includes a pilot clutch 29 and a solenoid 31 for operating the pilot clutch. In this example, the unit 27 is a mechanism that generates a differential motion with respect to the platen 39 by braking the cam plate 35, but may be a motor or a gear mechanism that rotates the cam plate 35 with respect to the platen 39 about the axis X.

In this example, the pilot clutch 29 is a multiple plate clutch, but may be another type of friction clutch. The plurality of outer plates of the pilot clutch 29 are coupled to the clutch housing 21 by a lug pattern or the like, and the plurality of inner plates alternately arranged with the outer plates are coupled to the cam plate 35 by a lug pattern or the like.

The solenoid 31 further includes a core 32 that guides the magnetic flux and has a gap, and an armature 33 that is disposed so as to span the gap, and the core 32 and the armature 33 are disposed so as to sandwich the guide clutch 29. When the solenoid 31 is excited, the magnetic flux induces the armature 33 toward the core 32, and friction is generated between the outer plate and the inner plate, thereby braking the cam plate 35. That is, when there is an angular velocity difference between the clutch housing 21 and the shaft 23, a differential motion is generated in the cam plate 35 with respect to the pressure plate 39.

Referring to fig. 4 in combination with fig. 3, the cam mechanism 3 is basically provided with a cam plate 35, a pressing plate 39 and a plurality of tapered rollers 41 interposed therebetween. Although not shown, an annular support member may be interposed between the cam plate 35 and the pressure plate 39, and the support member may support the tapered roller 41 so as to maintain the orientation thereof constant.

The cam plate 35 is rotatable about the axis X, and is coupled to the inner plate of the unit 27 by a lug pattern or the like in order to receive the differential motion, as described above. The cam plate 35 has a rolling surface 41 similar to that of the tapered roller 41, like the cam plates in fig. 2B and 2C _R And the cam surfaces are connected. The cam surface is slightly inclined in the circumferential direction with respect to the circumferential surface orthogonal to the axis X so as to roll the tapered roller 41 to move in the axial direction.

The pressing plate 39 is rotatable about the axis X, axially faces the cam plate 35, and axially faces the clutch 25 and is movable in the axial direction so as to press the clutch 25. Further, the shaft 23 is engaged with the shaft 23 so as to rotate together with the shaft 23. Thus, if braked, cam plate 35 is differentially moved relative to pressure plate 39. The platen 39 is also provided with a rolling surface 41 corresponding to the tapered roller 41, similar to the platens shown in FIGS. 2B and 2C _R The cam surfaces 39c that meet. The cam surface 39c is also slightly inclined in the circumferential direction with respect to the circumferential surface orthogonal to the axis X so as to move the pressing plate 39 in the axial direction by the rolling of the tapered roller 41. Alternatively, the inclination may be imparted to only one of the two cam surfaces.

The plurality of tapered rollers 41 are symmetrically arranged about the axis X. The number of tapered rollers 41 is 3 in the illustrated example, but is not limited to this. Although 3 or more is preferable from the viewpoint of parallelism between the holding plates 35, 39, a large load of axial force is not normally imposed even if many.

Each tapered roller 41 is approximately shaped like a truncated cone, and has a rolling surface 41 approximately shaped like a conical surface _R And an outer peripheral surface 41f and an inner peripheral surface, which are respectively close to the plane. The tapered rollers 41 are oriented radially with respect to the axis X, and the rolling surfaces 41 are the side surfaces thereof _R In contact with and rolling on the cam surface 39c. The rolling surface 41 _R Rotationally symmetrical in the radial direction and tapering towards the axis X.

The inner peripheral surface and the outer peripheral surface 41f of each tapered roller 41 may be flat surfaces parallel to the axis X, or may be curved surfaces or spherical surfaces. If the outer peripheral surface 41f is a curved surface or a spherical surface, as shown in fig. 8A, the contact with the cam plate 35 is limited to a point, and therefore, friction is reduced and torsion is prevented.

Referring back to fig. 3 and 4, the rolling surface 41 is preferable _R With cam surface 39c to roll surface 41 _R Is sized to connect the vertices on axis X. This helps to prevent the rolling surface 41 _R Sliding is generated with the cam surface 39c.

Rolling surface 41 _R The contact with the cam surface 39c is substantially a line contact spanning the entire length, which contributes to the large axial force burden of the cam mechanism 3. Rolling surface 41 _R It may be slightly rounded (referred to as convex or chamfer in some fields of technology) toward the outer peripheral surface 41f and the inner peripheral surface. This enhances contact with the cam surface 39c at its center, weakening the contact toward both ends. Alternatively or additionally, the cam surface 39c may be slightly rounded. They maintain the line contact but prevent the stress from increasing toward the end of the contact, thus helping to prevent the generation of force that twists the tapered roller 41. Since the excessive fillet may prevent the cam mechanism 3 from receiving a large axial force, the inclination due to the fillet is limited to, for example, 1/100, more preferably 1/10000, of the bus bar.

It is known from the knowledge in the art that if the rolling elements and the rolling surfaces supporting the rolling elements are rough, the rolling resistance thereof increases. It is therefore generally accepted that they should be finished as smooth as possible, for example to mirror surfaces. However, in the present embodiment, as illustrated in fig. 5A and 5B, one or both of them has a texture composed of appropriate irregularities. As will be described below, in certain cases, the rolling surface 41 _R And/or the texture on the cam surface 39c becomes a resistance to the force of the torsional tapered roller 41, on the other hand, does not create significant resistance to rolling. I.e. the texture helps to achieve a smooth rolling without twisting.

With reference to fig. 6A to 6E in combination with fig. 5A and 5B, the rolling surface 41 _R Is provided with texture 41 _T . Or may replace the rolling surface 41 _R Texture 41 on _T Alternatively, the cam surface 39c may be provided with a texture 39 _T . Although not shown in the drawings, the cam surface of the cam plate 35 may be textured. Of course, it is also possibleAt both cam surfaces and rolling surface 41 _R Is textured over the entirety of (a).

Texture 41 _T For example a plurality of grooves or protrusions parallel to each other. FIGS. 5A, 6A are texture 41 _T Fig. 5B and 6B show examples of the axis X being substantially parallel in the radial direction. The texture on the rolling surface and the texture on the cam surface preferably run the same or may run differently.

Alternatively, the texture may walk in both radial and circumferential directions as shown in fig. 6C, or may have an inclination with respect to any direction as shown in fig. 6D.

Texture 39 _T 、41 _T The large width and pitch of the grooves or protrusions respectively is effective as resistance against torsion, but small is advantageous from the viewpoint of rolling resistance. Therefore, the width can be in the range of 1 to 500 μm, and the pitch can be in the range of 1 to 3mm. The depth of the groove or the height of the protrusion can be extremely small, and even in the order of 1 μm, for example, the groove can function as resistance against torsion. In contrast, if the depth or the protrusion is excessively large, the rolling resistance can be increased.

These textures can be easily formed by machining. Such a structure can be intentionally formed, or a flaw inevitably generated by machining may be left on the surface locally or entirely. Further, it may be formed by either scanning a laser or an electron beam on a smooth surface, or may be formed by pressing a mold or a texture on the mold onto a surface for transfer.

The texture may not have a structure extending in a specific direction, and may be isotropic and random irregularities, for example, as shown in fig. 6E. The structure may be formed by, for example, localized pickling, or may be formed by a method such as shot peening. In this example, the height or depth of the irregularities can be extremely small, and even in the order of 1 μm, for example, the irregularities can function as resistance against torsion.

These textures can maintain the tapered roller 41 toward the radial direction and become resistance to the tapered roller 41 from twisting in the radial direction.

As shown in fig. 7, the rolling surface 41 _R Texture 41 on _T And texture 39 on cam surface 39c _T It is also possible to dimension in a mutually engaging manner. This further enhances the effect of the texture that is maintained in a manner that keeps the tapered roller 41 from twisting. In addition, in this case, the protrusions and grooves of the texture can be relatively large, and even in this case, the rolling resistance does not increase significantly. The relationship may be in the rolling surface 41 _R And the cam surface of the cam plate 35.

Referring to fig. 8A, one or both of cam plate 35 and pressure plate 39 have a peripheral wall for supporting outer peripheral surface 41f of tapered roller 41. As described above, the outer peripheral surface 41f is in point contact with the peripheral wall. This helps to reduce friction and prevents twisting of the tapered roller 41. The point contact may occur at the edge of the peripheral wall or may occur at any of the inner surfaces of the peripheral wall. The point contact may be substantially the center of the outer peripheral surface 41f as illustrated in fig. 8A, or may be away from the center as illustrated in fig. 8B. The surface of the point contact may also have an angle alpha with respect to the surface orthogonal to the radial direction.

As shown by the dashed line in fig. 1, the current I-torque T curve of each embodiment represents a reduced hysteresis C compared to the prior art _I . The degree of hysteresis is also equivalent to the example based on the ball cam, and is very practical. This is because the tapered roller can smoothly roll without twisting with respect to the shaft.

In addition, in the process P of increasing the current I from the starting point O, compared with the example based on the ball cam _L In the process P, it was confirmed that the rise of the torque T was relatively stopped and the current I was reduced from the vicinity of the end point E _R In this, it was confirmed that the torque T was relatively reduced and stopped, that is, the curve was in an S-shape. However, there is a stagnant process P of the former _L This results in a torque transmission which does not increase immediately and thus contributes to a so-called drag torque reduction. In addition, there is a stagnant process P of the latter _R To help prevent unintended disengagement of the clutch.

In view of the above, the embodiments disclosed provide a cam mechanism or a power transmission mechanism that suppresses hysteresis and has excellent controllability.

Although the embodiments have been described, modifications and variations of the embodiments can be made based on the above disclosure.

Claims

1. A cam mechanism generating an axial force in combination with a unit generating a differential motion around a shaft, comprising:

a cam plate rotatable about the shaft and coupled to the unit to receive the differential motion;

a pressing plate axially opposed to the cam plate and movable in the axial direction;

a pair of cam surfaces formed on the cam plate and the pressure plate, respectively, and facing each other, and inclined in a circumferential direction with respect to a circumferential surface orthogonal to the shaft, respectively;

a plurality of tapered rollers interposed between the pair of cam surfaces and rolling on the cam surfaces according to the differential motion to generate the axial force on the platen, the tapered rollers each having a rolling surface rotationally symmetrical in a radial direction orthogonal to the axis and tapered toward the axis; and

and a texture formed on one or more of the cam surface and the rolling surface, the texture being resistant to twisting of each tapered roller in the radial direction.

2. The cam mechanism of claim 1, wherein the cam mechanism is configured to move the cam member,

the texture includes a plurality of grooves or protrusions having a width of 1 to 500 μm, respectively, and being substantially parallel to each other, and a space between the grooves or protrusions is 1 to 3mm.

3. The cam mechanism of claim 1, wherein the cam mechanism is configured to move the cam member,

the texture includes isotropic irregularities.

4. The cam mechanism of claim 1, wherein the cam mechanism is configured to move the cam member,

the texture is formed on all of the cam surface and the rolling surface.

5. The cam mechanism of claim 4, wherein the cam mechanism is configured to move the cam member,

the texture of the cam surface and the texture of the rolling surface are sized to intermesh.

6. The cam mechanism of claim 1, wherein the cam mechanism is configured to move the cam member,

the plurality of tapered rollers each have an outer peripheral surface facing outward in a radial direction, and any one or more of the cam plate and the pressure plate is in contact with the outer peripheral surface.

7. A clutch device for controlling torque transmission between a first rotating body and a second rotating body that are rotatable about axes, the clutch device comprising:

a cam plate rotatable about the shaft;

a brake device coupled to the cam plate so as to controllably brake the cam plate against the first rotary body;

a pressing plate axially opposed to the cam plate, rotatable together with the second rotating body, and movable in an axial direction;

a plurality of tapered rollers interposed between the pair of cam surfaces and rolling on the cam surfaces in accordance with a differential motion of the cam plate with respect to the platen to generate an axial force on the platen, the tapered rollers each having a rolling surface rotationally symmetrical in a radial direction orthogonal to the axis and tapered toward the axis;

a texture formed on one or more of the cam surface and the rolling surface, the texture being resistant to twisting of each tapered roller in the radial direction; and

and a clutch that transmits the torque between the first rotating body and the second rotating body when pressed by the pressing plate in the axial direction.