CN112334679A

CN112334679A - Low-hysteresis cam mechanism with tapered roller

Info

Publication number: CN112334679A
Application number: CN201880094627.4A
Authority: CN
Inventors: 川田和隆
Original assignee: GKN Automotive Ltd
Current assignee: GKN Automotive Ltd
Priority date: 2018-06-20
Filing date: 2018-06-20
Publication date: 2021-02-05
Anticipated expiration: 2038-06-20
Also published as: JP6912666B2; CN112334679B; WO2019244268A1; JPWO2019244268A1

Abstract

A cam mechanism which generates an axial force in combination with a unit generating a differential motion around an axis includes: a cam plate which is rotatable about the shaft and coupled to the unit to receive the differential; a pressure plate that is axially movable and axially opposed to the cam plate; a pair of cam surfaces formed on the cam plate and the pressure plate, respectively, facing each other, and inclined in a circumferential direction with respect to a circumferential surface orthogonal to the shaft; a plurality of tapered rollers that are interposed between the pair of cam surfaces, roll on the respective cam surfaces in accordance with the differential, and generate the axial force on the pressure plate, and each of the tapered rollers has a rolling surface that is rotationally symmetric in a radial direction orthogonal to the axis and that is tapered toward the axis; and a texture formed on one or more of the cam surface and the rolling surface, the texture serving as resistance to the respective tapered rollers from twisting in the radial direction.

Description

Low-hysteresis cam mechanism with tapered roller

Technical Field

The following disclosure relates to a cam mechanism for generating an axial force by tapered rollers, and a power transmission device including a clutch device having the cam mechanism.

Background

Typically, the vehicle utilizes several clutches. For example, for the purpose of switching between a two-wheel drive (2WD) mode and a four-wheel drive (4WD) mode, a clutch may be interposed between the two shafts, and the drive may control the connection and disconnection. Since it is difficult to generate a sufficient axial force required to couple the clutches by a separate mechanism, a cam mechanism is sometimes combined in order to increase the output thereof.

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

Documents of the prior art

Patent document

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

Disclosure of Invention

Larger axial forces can be generated from the rollers in line contact, but the inventors have discovered other new problems. According to the related art described above, the cam mechanism presses the pressure ring against the clutch in accordance with the current applied to the actuator, thereby coupling the clutch and transmitting the torque thereto. From the viewpoint 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, a curve C of torque T transmitted for an applied current I_pDuring the current increase (during the clutch engagement process) P_IWith current reducing process (process to be disconnected) P_DMedium deviation, presenting a hysteresis that cannot be ignored. Needless to say, hysteresis is a main cause of impairing controllability. The inventionThe following mechanism or device is conceived by studying the structure of the cam mechanism for the purpose of reducing the hysteresis.

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

According to one aspect, a cam mechanism that generates an axial force in combination with a unit that generates a differential motion around an axis includes: a cam plate which is rotatable about the shaft and coupled to the unit to receive the differential; a pressure plate that is axially opposed to the cam plate and is movable in the axial direction; a pair of cam surfaces formed on the cam plate and the pressure plate, respectively, facing each other, and inclined in a circumferential direction with respect to a circumferential surface orthogonal to the shaft; a plurality of tapered rollers that are interposed between the pair of cam surfaces, roll on the respective cam surfaces in accordance with the differential, and generate the axial force on the pressure plate, and each of the tapered rollers has a rolling surface that is rotationally symmetric in a radial direction orthogonal to the axis and that is tapered toward the axis; and a texture formed on one or more of the cam surface and the rolling surface, the texture serving as resistance to the respective tapered rollers from twisting in the radial direction.

According to another aspect, a clutch device for controlling transmission of torque between a first rotating body and a second rotating body that are rotatable around axes, includes: a cam plate rotatable about the shaft; a braking device coupled to the cam plate to controllably brake the cam plate with respect to the first rotating body; a pressing plate that is axially opposed to the cam plate, rotates together with the second rotating body, and is movable in the axial direction; a pair of cam surfaces formed on the cam plate and the pressure plate, respectively, facing each other, and inclined in a circumferential direction with respect to a circumferential surface orthogonal to the shaft; a plurality of tapered rollers that are interposed between the pair of cam surfaces, roll on the respective cam surfaces in accordance with the differential, and generate the axial force on the pressure plate, and each of the tapered rollers has a rolling surface that is rotationally symmetric in a radial direction orthogonal to the axis and that is tapered toward the axis; a texture formed on one or more of the cam surface and the rolling surface and serving as resistance to the respective tapered rollers from twisting 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 pressure plate in the axial direction.

Drawings

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

Fig. 2A is a schematic longitudinal sectional view of the cam mechanism illustrating the force applied to the 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 rollers roll on the rolling surfaces.

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 plan view of a tapered roller and a cam surface according to another example.

Fig. 6A is a schematic top view of the texture on the rolling or cam surface being stretched out to be flat.

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

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

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

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

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

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

Fig. 8B is a sectional view of a tapered roller and a cam plate according to another example.

Detailed Description

Several exemplary embodiments are described below in conjunction with the appended drawings. In the following description and claims, unless otherwise specified, the shaft refers to the rotation axis of the cam mechanism, the axial direction is a direction parallel thereto, and the radial direction is a direction perpendicular thereto. The rotation axis of the clutch device and the rotation axis of the cam mechanism are generally coincident, but not necessarily limited thereto.

Referring to fig. 2A and 2B, when the cam mechanism includes the cam plate 5, the presser plate 9, and the tapered roller 11 interposed therebetween, the rolling surface 11 of the tapered roller 11_RThe cam surfaces 5c of the cam plate 5 and the cam surfaces 9c of the pressure plate 9 are in line contact with each other, and these contact lines are inclined with respect to the radial direction. In this state, if an axial force F is applied to the cam mechanism, a radial reaction force F is generated radially outward in the tapered roller 11 based on the inclination of the contact line_R. Radial reaction force F_RThe outer peripheral surfaces 11f of the tapered rollers 11 are pressed against the inner peripheral surface 5f of the cam plate 5 and the inner peripheral surface 9f of the presser plate 9. This causes a frictional force that hinders rolling of the tapered rollers 11.

In this state, as shown in fig. 2C, the cam plate 5 causes a differential M about the axis with respect to the pressure plate 9_D(process of coupling the clutch), a force to twist the tapered roller 11 is generated on the pressed contact surface. The tapered roller 11 causes rolling M on the cam surfaces 5c, 9c_RThe inclined surface is raised, and the axial movement Mx of the pressure plate 9 is caused by this movement, but this movement is generated by the influence of friction and torsion.

At this time, the axial force F' is increased from the initial force by the cam action, so the radial reaction force pressing the outer peripheral surface 11F against the inner peripheral surfaces 5F, 9F is also increased, and on the other hand, the contact area between the outer peripheral surface 11F and the inner peripheral surfaces 5F, 9F is reduced because the cam plate 5 is separated from the presser plate 9 by the axial movement Mx. Here, although the increase in the radial reaction force hinders rolling, the decrease in the contact area is an element that promotes rolling.

On the other hand, when the state shown in fig. 2C is returned to the state shown in fig. 2B (the process of disengaging the clutch), the force of the twisted tapered rollers 11 acts in the opposite direction due to the reverse differential 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.

Curve C of torque T transmitted for applied current I_pThe hysteresis arising in (a) shows a composite result of these effects. The present inventors have considered solving the problem by coping with the force of twisting the tapered roller without increasing the rolling resistance, and have conceived the following embodiments.

The cam mechanism 3 of the present embodiment can be 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 for interrupting or controlling the transmission of torque between a first rotating body and a second rotating body that rotate about an axis X, and in this example, the first rotating body is a clutch housing 21 and the second rotating body is a shaft 23.

The clutch 25 intervenes 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 a friction clutch of another type. A plurality of outer plates of the clutch 25 are coupled to the clutch housing 21 by a lug or the like, and a plurality of inner plates alternately arranged with the outer plates are coupled to the shaft 23 by a lug or the like. The cam mechanism 3 applies an axial force to the clutch 25, whereby the outer plate and the inner plate are frictionally coupled to each other, and torque is transmitted between the clutch housing 21 and the shaft 23. In addition, 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 operation to operate the cam mechanism 3, and the unit 27 is provided with 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 pressure plate 39 by braking the cam plate 35, but may alternatively be a motor or a gear mechanism that rotates the cam plate 35 about the axis X relative to the pressure plate 39.

In the present example, the pilot clutch 29 is a multiple-plate clutch, but may be a friction clutch of another type. The outer plates of the pilot clutch 29 are coupled to the clutch housing 21 by a lug pattern or the like, and the 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 having a gap for guiding the magnetic flux and an armature 33 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, magnetic flux induces the armature 33 toward the core 32, thereby generating friction between the outer plate and the inner plate to brake 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 on the cam plate 35 with respect to the pressure plate 39 accordingly.

Referring to fig. 4 in conjunction with fig. 3, the cam mechanism 3 is basically provided with a cam plate 35, a pressure 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 to support the tapered rollers 41 so as to keep the orientation of the tapered rollers constant.

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

The pressure plate 39 is also rotatable about the axis X, faces the cam plate 35 in the axial direction, and is movable in the axial direction so as to face the clutch 25 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. Therefore, if braking is performed, the cam plate 35 generates a differential with respect to the pressure plate 39. The presser plate 39 is also provided with a rolling surface 41 similar to that of the tapered roller 41, as in the presser plates of fig. 2B and 2C_RAnd an adjoining cam surface 39 c. The cam surface 39c is also slightly inclined in the circumferential direction with respect to the circumferential surface orthogonal to the axis X so that the pressure plate 39 is moved in the axial direction by the rolling of the tapered rollers 41. Alternatively, the inclination may be given to only one of the two cam surfaces.

The plurality of tapered rollers 41 are arranged symmetrically with respect to the axis X. Although the number of tapered rollers 41 is 3 in the illustrated example, it is needless to say that the number is not limited to this. Although 3 or more is preferable from the viewpoint of parallelism between the holding

plates

35, 39, even a large amount of holding plates usually do not contribute much to the axial force.

Each tapered roller 41 has a substantially truncated cone shape and has a rolling surface 41 having a substantially conical surface_RAnd an outer peripheral surface 41f and an inner peripheral surface which are close to a plane, respectively. Each tapered roller 41 is oriented in the radial direction with respect to the axis X, and is a rolling surface 41 on the side surface thereof_RContacts and rolls on the cam surface 39 c. The rolling surface 41_RRotationally symmetrical in the radial direction and tapering towards the axis X.

Each of the inner circumferential surface and the outer circumferential surface 41f of each tapered roller 41 may be a plane parallel to the axis X, or may be a curved surface or a spherical surface. If the outer peripheral surface 41f is a curved surface or a spherical surface, the contact with the cam plate 35 is limited to a point as shown in fig. 8A, and thus contributes to reduction of friction and prevention of twisting.

Referring back to fig. 3 and 4, the rolling surface 41 is preferably selected_RWith cam surface 39c and rolling surface 41_RIs sized so that the vertex is connected to the axis X. This helps to prevent rolling surface 41_RSliding with the cam surface 39 c.

Rolling surface 41_RThe contact with the cam surface 39c is substantially a line contact over the entire length, which contributes to the cam mechanism 3 being burdened with a large axial force. Rolling surface 41_RIt may be slightly rounded (referred to as a convex surface or a chamfer in some technical fields) toward the outer circumferential surface 41f and the inner circumferential surface. This increases contact with the cam surface 39c at its center, and decreases contact toward both ends. Alternatively or in addition, the cam surface 39c may be slightly rounded. They prevent the stress from increasing toward the end of the contact while maintaining the line contact, and thus contribute to preventing the force that twists the tapered rollers 41 from being generated. Since the fillet is too large and may prevent the cam mechanism 3 from being loaded with a large axial force, the inclination due to the fillet is limited to, for example, 1/100, more preferably 1/10000, with respect to the generatrix.

According to the usual practice in the artIt is known that if the rolling elements and the rolling surfaces supporting the rolling elements are rough, the rolling resistance increases. Therefore, it is generally considered that they should be finished as smoothly as possible, for example, finished as mirror surfaces. However, in the present embodiment, as illustrated in fig. 5A and 5B, one or both of them have a texture formed of appropriate irregularities. As will be described below, the rolling surface 41 is fixed_RAnd/or the texture on the cam surface 39c becomes a resistance against the force of the twisted tapered rollers 41, but does not generate a significant resistance against rolling. I.e. the texture helps to achieve a smooth rolling without twisting.

With reference to fig. 6A to 6E in conjunction with fig. 5A and 5B, rolling surface 41_RHas a texture 41_T. Or may replace the rolling surface 41_R Upper texture 41_TAlternatively, 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, both cam surfaces and rolling surfaces 41 may be provided_RIs textured over all of it.

Texture 41_TFor example a plurality of grooves or protrusions parallel to each other. FIGS. 5A and 6A show textures 41_TFig. 5B and 6B are examples of the axis X being substantially parallel in the radial direction, and are examples of the axis X along the circumferential 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 run in both radial and circumferential directions, as shown in FIG. 6C, or may have a slope with respect to any direction, as shown in FIG. 6D.

Texture 39_T、41_TThe width and pitch of each of the grooves or projections are large, which 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 3 mm. The depth of the groove or the height of the protrusion can be extremely small, and even if it is about 1 μm, for example, it can function as a resistance against torsion. Conversely, if the depth or the protrusion is too large, the rolling resistance can be increased.

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

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

These textures are capable of maintaining the tapered rollers 41 toward the radial direction and act as resistance to twisting of the tapered rollers 41 relative to the radial direction.

As shown in fig. 7, the rolling surface 41_R Upper texture 41_TAnd texture 39 on cam surface 39c_TAnd may be sized to intermesh. This further enhances the effect of the texture that is retained in such a manner that the tapered rollers 41 are not twisted. 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. This relationship can of course also be in the rolling surface 41_RAnd the cam surface of the cam plate 35.

Referring to fig. 8A, one or both of the cam plate 35 and the pressure plate 39 includes a peripheral wall for supporting the outer peripheral surface 41f of the tapered roller 41. As described above, the outer peripheral surface 41f is in point contact with the peripheral wall. This helps reduce friction and prevents twisting of the tapered rollers 41. The point contact may occur at the edge of the peripheral wall or may occur anywhere on the inner surface of the peripheral wall. The point contact may be substantially at 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 be at an angle α with respect to a surface orthogonal to the radial direction.

As shown by the dotted lines in fig. 1, the entitiesThe current I-torque T curve of the embodiment shows a reduced hysteresis C compared to the prior art_I. The degree of hysteresis is also comparable to the example based on a ball cam, and is very practical. This is because the tapered rollers can roll smoothly without twisting with respect to the shaft.

In addition, in the process P of increasing the current I from the starting point O, compared to the example based on the ball cam_LIn the process P, it is confirmed that the rise of the torque T is relatively stagnated, and the current I is reduced from the vicinity of the end point E_RIn (2), it was confirmed that the decrease of the torque T was relatively stagnant, i.e., the curve was in the shape of an S. However, there is a stall process P of the former_LThis results in that the torque transmission does not increase immediately and therefore contributes instead to a reduction of the so-called drag torque. In addition, there is a stall process P of the latter_RHelping to prevent unintended disengagement of the clutch.

In summary, the disclosed embodiments provide a cam mechanism or a power transmission mechanism with good controllability while suppressing hysteresis.

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

Claims

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

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

a pressure plate that is axially opposed to the cam plate and is movable in the axial direction;

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

a plurality of tapered rollers that are interposed between the pair of cam surfaces, roll on the respective cam surfaces in accordance with the differential, and generate the axial force on the pressure plate, and each of the tapered rollers has a rolling surface that is rotationally symmetric in a radial direction orthogonal to the axis and that is tapered toward the axis; and

and a texture formed on one or more of the cam surface and the rolling surface, the texture serving as resistance to the respective tapered rollers from twisting in the radial direction.

2. The cam mechanism of claim 1,

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

3. The cam mechanism of claim 1,

the texture includes isotropic asperities.

4. The cam mechanism of claim 1,

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

5. The cam mechanism of claim 4,

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

6. The cam mechanism of claim 1,

the plurality of tapered rollers each have an outer circumferential surface facing outward in the radial direction, and at least one of the cam plate and the pressure plate is in contact with the outer circumferential surface.

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

a cam plate rotatable about the shaft;

a braking device coupled to the cam plate to controllably brake the cam plate with respect to the first rotating body;

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

a plurality of tapered rollers that are interposed between the pair of cam surfaces, roll on the respective cam surfaces in accordance with the differential, and generate the axial force on the pressure plate, and each of the tapered rollers has a rolling surface that is rotationally symmetric in a radial direction orthogonal to the axis and that is tapered toward the axis;

a texture formed on one or more of the cam surface and the rolling surface and serving as resistance to the respective tapered rollers from twisting in the radial direction; and

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