WO2019171459A1 - Low-hysteresis cam mechanism provided with tapered rollers - Google Patents

Abstract

A cam mechanism which generates an axial force in combination with a means for producing a differential around a shaft is provided with: a cam plate which is rotatable around the shaft and coupled with the means to receive the differential; a pressure plate which is opposed to the cam plate in a shaft direction and moveable in the shaft direction; a plurality of tapered rollers which are interposed between the cam plate and the pressure plate and each of which is rotationally symmetric with respect to a radial axis orthogonal to the shaft, the tapered rollers having a rolling surface forming a conical surface tapering toward the shaft and an outer peripheral surface facing radially outward; and an annular support which contacts the outer peripheral surface so as to support each of the plurality of tapered rollers rotatably around the radial axis and so as to move axially together with the plurality of tapered rollers. Each of the cam plate and the pressure plate includes a cam surface contacting the rolling surface. The cam surfaces are inclined circumferentially with respect to a circumferential surface orthogonal to the shaft so as to generate the axial force in the pressure plate by causing the tapered rollers to roll in accordance with the differential.

Description

Low hysteresis cam mechanism with taper roller

The following disclosure relates to a cam mechanism that generates an axial force using a taper roller, and a power transmission device such as a clutch device including the cam mechanism.

Generally, vehicles use several clutches. For example, a clutch may be interposed between two shafts for the purpose of switching between a two-wheel drive (2WD) mode and a four-wheel drive (4WD) mode, and an actuator may control connection / disconnection of the clutch. Since it is difficult to generate an axial force sufficient to connect the clutch by a single means, a cam mechanism may be combined to increase the output.

∙ Balls may be interposed between cam members for the purpose of smoothly operating the cam mechanism. As the ball rolls between the relatively rotating cam surfaces, the ball significantly reduces sliding resistance. This reduces the burden on the actuator, but the cam surface and the ball are only in point contact, and there is a problem in placing a large axial force on the cam mechanism. Using a roller capable of line contact instead of a ball would be one of the means for solving such a problem. Patent Document 1 discloses a related technique.

International Patent Application Publication WO2017 / 149829A1

Although a larger axial force can be generated by a roller in line contact, the present inventors have found another new problem. 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 connecting the clutch and transmitting torque thereto. From the viewpoint of controllability of torque transmission, it is ideal that the torque transmitted for the applied current is unique. However, as illustrated in FIG. 1, the curve C _{p of the} torque T transmitted with respect to the applied current I has a current increasing process (process for engaging the clutch) P _I and a current decreasing process (demounting). deviate in an attempt linked to the process) and P _D, exhibit not be ignored hysteresis. Needless to say, hysteresis is a factor that impairs controllability. The present inventors have studied the structure of a cam mechanism for the purpose of reducing hysteresis, and have come up with the following mechanism or apparatus.

The following disclosure relates to a cam mechanism that can reduce hysteresis while using a tapered roller, and a power transmission device such as a clutch device including the cam mechanism.

According to one aspect, a cam mechanism for generating an axial force in combination with a means for generating a differential around an axis is rotatable about the axis and coupled to the means for receiving the differential A cam plate, a pressure plate facing the cam plate in the axial direction and movable in the axial direction, and interposed between the cam plate and the pressure plate, each of which is rotationally symmetric with respect to a radial axis perpendicular to the axis. A plurality of tapered rollers each having a rolling surface having a conical surface tapered toward the shaft and an outer circumferential surface facing radially outward, and each of the plurality of tapered rollers is rotated around the radial axis. An annular support that is in contact with the outer peripheral surface so as to be supported and move in the axial direction together with the plurality of taper rollers, and the cam plate and the pressure pressure Each cam surface is in contact with the rolling surface, and each cam surface rolls the taper roller in accordance with the differential to generate the axial force on the pressure plate. It is inclined in the circumferential direction with respect to the surface.

According to another aspect, a clutch device for controlling transmission of torque between a first rotating body and a second rotating body, each rotatable around an axis, is rotatable around the axis A cam plate, a braking device coupled to the cam plate to controllably brake the cam plate with respect to the first rotating body, an axially opposed to the cam plate, together with the second rotating body A pressure plate that is rotated and movable in the axial direction, and is interposed between the cam plate and the pressure plate, each of which is rotationally symmetric with respect to a radial axis orthogonal to the axis, and forms a conical surface tapered toward the axis. A plurality of taper rollers each having a rolling surface and an outer circumferential surface facing radially outward; and each of the plurality of taper rollers rotatably supported around the radial axis and the tape. An annular support that contacts the outer peripheral surface so as to move in the axial direction together with the roller, and the torque between the first rotating body and the second rotating body when pressed in the axial direction by the pressure plate. Each of the cam plate and the pressure plate includes cam surfaces that are in contact with the rolling surfaces, respectively, and the cam plate is braked to generate a differential with respect to the pressure plate. The cam surface is inclined in the circumferential direction with respect to the circumferential surface orthogonal to the shaft so as to generate an axial force that rolls the taper roller according to the differential and presses the pressure plate toward the clutch. .

FIG. 1 is a graph showing an example of hysteresis in the cam mechanism. FIG. 2A is a schematic longitudinal sectional view of a cam mechanism for explaining a force applied to the taper roller. FIG. 2B is a schematic cross-sectional view of the cam mechanism on 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 perspective view of the cam mechanism. FIG. 5A is a cross-sectional view of a pressure plate, a taper roller, and a cam plate cut along a cross section including a radial axis passing through the shaft and the center of the taper roller. FIG. 5B is a partial plan view of the tapered roller and the support when viewed in the axial direction. FIG. 6A is a schematic cross-sectional view showing a relationship between a crowned roller or a chamfered taper roller and a rolling surface. FIG. 6B is a schematic cross-sectional view showing the relationship between the crowned or chamfered rolling surface and the tapered roller. FIG. 7A is a partial plan view of a tapered roller and a support based on an example in which the outer peripheral surface of the tapered roller is a curved surface. FIG. 7B is a partial plan view of the tapered roller and support based on an example in which the partition between the tapered rollers is separate from the support. FIG. 7C is a partial plan view of a tapered roller and support based on the example of a support without partitions. FIG. 8A is a partial plan view of a tapered roller and a support based on an example of a support provided with a protrusion protruding to make point contact with the outer peripheral surface. FIG. 8B is a longitudinal sectional view of a taper roller and a support based on an example of a support having a longitudinal section sharpened so as to be in line contact or point contact with the outer peripheral surface. FIG. 8C is a partial plan view of a tapered roller and support based on an example of a support having a pivot that pivotally supports the tapered roller. FIG. 9A is a cross-sectional view of a pressure plate, a tapered roller, and a cam plate based on an example in which the outer peripheral surface is exposed outward in the radial direction. FIG. 9B is a cross-sectional view of the pressure plate, the taper roller, and the cam plate based on an example in which the pressure plate and the cam plate protrude so as to cover the outer peripheral surface of the taper roller.

Several exemplary embodiments are described below with reference to the accompanying drawings. Throughout the following description and claims, unless otherwise specified, the axis means the rotating shaft of the cam mechanism, the axial direction means a direction parallel to this, and the radial direction means a direction perpendicular thereto. is there. The rotating shaft of the clutch device usually coincides with the rotating shaft of the cam mechanism, but is not necessarily limited thereto.

Figure 2A, a reference to 2B, when the cam mechanism comprises a cam plate 5 and the pressure plate 9, and a tapered roller 11 interposed between the cam surface 5c and the line of the rolling surface 11 _R cam plate 5 of the tapered roller 11 They come into contact with the cam surface 9c of the pressure plate 9, and these contact lines are inclined with respect to the radial direction. When the axial force F is applied to the cam mechanism in such a state, the radial reaction force F _R is generated toward the radially outwardly in tapered roller 11 based on the inclination of the contact line. Radial reaction force F _R is pressed against the outer peripheral surface 11f of the tapered roller 11 on the inner peripheral surface 9f of the inner circumferential surface 5f and the pressure plate 9 of the cam plate 5. This causes a frictional force that prevents the taper roller 11 from rolling.

In this state, as shown in Figure 2C, the cam plate 5 causes the differential M _D about the axis relative to the pressure plate 9 and (the process of trying to connect the clutch), the tapered roller 11 in a contact surface pressed against A twisting force is generated. Tapered roller 11, the cam surface 5c, climb the sloped surface causing the rolling M _R on 9c, the pressure plate 9 I than the cause axial driving Mx, but such movement under the influence of the frictional force and twisting force is there.

At this time, the axial force F ′ has increased from the beginning due to the cam action, so that the radial reaction force that presses the outer peripheral surface 11f against the inner peripheral surfaces 5f and 9f also increases. Are separated, the contact area between the outer peripheral surface 11f and the inner peripheral surfaces 5f, 9f decreases. Here, an increase in the radial reaction force prevents rolling, but a decrease in the contact area is an element that promotes rolling.

On the other hand, when trying to return from the state shown in FIG. 2C to the state shown in FIG. 2B (the process of trying to disengage the clutch), the differential is in the reverse direction, so the force to twist the taper roller 11 also acts in the reverse direction, Although the axial force F ′ decreases, the contact area between the outer peripheral surface 11f and the inner peripheral surfaces 5f and 9f increases.

Hysteresis appearing in the curve C _p of the torque T to be transmitted to the applied current I is expected to result in a composite of these effects. Based on this consideration, the inventors have arrived at the following embodiments.

The cam mechanism 3 according to 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 that intermittently controls torque transmission between a first rotating body and a second rotating body that rotate about an axis X. In this example, the first rotating body is a clutch. The case 21 and the second rotating body is the shaft 23.

The clutch 25 is interposed between the clutch case 21 and the shaft 23 to mediate torque transmission. In this example, the clutch 25 is a multi-plate clutch, but other types of friction clutches may be used. A plurality of outer plates of the clutch 25 are coupled to the clutch case 21 by lugs or the like, and a plurality of inner plates arranged alternately with the outer plates are coupled to the shaft 23 by lugs or the like. When the cam mechanism 3 exerts an axial force on the clutch 25, the outer plate and the inner plate are frictionally connected, and torque is transmitted between the clutch case 21 and the shaft 23. Further, the torque transmitted by increasing / decreasing the axial force increases / decreases.

The clutch device 1 is also provided with a means 27 for generating a differential in order to operate the cam mechanism 3, and the means 27 generally includes a pilot clutch 29 and a solenoid 31 for operating the clutch. In this example, the means 27 is a mechanism that brakes the cam plate 35 to cause a differential with respect to the pressure plate 39. Alternatively, the means 27 rotates the cam plate 35 around the axis X relative to the pressure plate 39. It may be a motor or gear mechanism.

The pilot clutch 29 is also a multi-plate clutch in this example, but may be another type of friction clutch. A plurality of outer plates of the pilot clutch 29 are coupled to the clutch case 21 by lugs or the like, and a plurality of inner plates arranged alternately with the outer plates are coupled to the cam plate 35 by lugs or the like.

The solenoid 31 further includes a core 32 that guides the magnetic flux but includes a gap, and an armature 33 that is disposed so as to straddle the gap. The core 32 and the armature 33 are disposed so as to sandwich the pilot clutch 29. Yes. When the solenoid 31 is excited, the magnetic flux attracts the armature 33 toward the core 32, and friction is generated 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 case 21 and the shaft 23, a differential is generated in the cam plate 35 with respect to the pressure plate 39 accordingly.

Referring to FIG. 4 in combination with FIG. 3, the cam mechanism 3 generally includes a cam plate 35, a pressure plate 39, a plurality of tapered rollers 41 interposed therebetween, and an outer peripheral surface 41f of each of the tapered rollers 41. And an annular support 37 for supporting the.

The cam plate 35 is rotatable about the axis X and is connected to the inner plate of the means 27 by a lug or the like so as to receive the differential as described above. The cam plate 35 is also in the same manner as in FIG. 2B, 2C, comprises a cam surface 35c in contact with the rolling surface 41 _R of the tapered roller 41. The cam surface 35c is slightly inclined in the circumferential direction with respect to the circumferential surface orthogonal to the axis X so that the taper roller 41 rolls and moves in the axial direction.

The pressure plate 39 is also rotatable about the axis X, is opposed to the cam plate 35 in the axial direction, and is also opposed to the clutch 25 in the axial direction so as to press the clutch 25 and is movable in the axial direction. Moreover, it is engaged with the shaft 23 so as to rotate together with the shaft 23. Accordingly, the cam plate 35 is differential with respect to the pressure plate 39 when braked. The pressure plate 39 as well, as in FIG. 2B, 2C, comprises a cam surface 39c in contact with the rolling surface 41 _R of the tapered roller 41. 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 can be moved in the axial direction by the rolling of the taper roller 41. Alternatively, the inclination may be given to only one of the cam surface 35c and the cam surface 39c.

The plurality of taper rollers 41 are arranged symmetrically with respect to the axis X. The number of taper rollers 41 is three in the illustrated example, but is not limited to this. Although 3 or more is preferable from the viewpoint of keeping the parallelism between the plates 35 and 39, too many usually do not contribute to the burden of the axial force.

Referring to FIG. 5A in combination with FIG. 4, each taper roller 41 is directed along a radial axis X _R orthogonal to the axis X, and its side surface is in contact with the cam surfaces 35c and 39c as shown in FIG. 5A. It is a rolling surface 41 _R rolling on it. Such rolling surface 41 _R is rotationally symmetrical with respect to the radiation axis X _R, also forms a tapered such conical surface towards the axis X.

In each taper roller 41, the outer peripheral surface 41f facing outward in the radial direction is separated from the cam plate 35 and the pressure plate 39 and contacts only the support 37. The inner peripheral surface 41 i may be separated from any of the plates 35 and 39, the support 37, and the shaft 23, or may be in contact with the shaft 23.

Referring to FIG. 5B in combination with FIG. 5A, the support 37 is generally annular, and the inner peripheral surface 37f contacts the outer peripheral surface 41f of the taper roller 41, respectively. The support 37 moves in the circumferential direction and the axial direction as the taper roller 41 rolls up and down on the cam surfaces 35c and 39c, and continues to support the outer peripheral surface 41f in a rotatable manner. Since the support 37 is relatively immovable with respect to the taper roller 41 both in the circumferential direction and in the axial direction, this structure reduces the frictional force acting on the outer peripheral surface 41f and prevents the generation of a force for twisting the taper roller 41. To help.

Preferably, as the extension of the rolling contact surface 41 _R is connecting the vertex on the axis X, the rolling surface 41 _R and the cam surface 35c, is dimensioned and 39c. This helps to prevent the rolling surface 41 _R and the cam surface 35c, the sliding between the 39c occurs.

Rolling surface 41 _R and the cam surface 35c, contact with 39c may be substantially its entire length across line contact. This is useful for the cam mechanism 3 to bear a large axial force. Rolling surface 41 _R is as shown in FIG. 6A, slightly rounded towards the outer peripheral surface 41f and the inner peripheral surface 41i may be (called crowning or chamfering in some technical fields). This strengthens the contact with the cam surfaces 35c and 39c at the center and weakens the contact toward both ends. Alternatively, as shown in FIG. 6B, the cam surfaces 35c and 39c may be slightly rounded instead of or in addition to this. While these maintain the line contact, they help to prevent the stress from increasing towards the end of the contact, thus preventing the generation of forces that twist the taper roller 41. In these drawings, the roundness is emphasized, but if the roundness is too large, the cam mechanism 3 may be prevented from bearing a large axial force. Therefore, the inclination due to roundness is limited to, for example, 1/100, more preferably, 1/10000 with respect to the bus.

In the example shown in FIG. 5B, the inner peripheral surface 37f and the outer circumferential surface 41f together but plane parallel to the plane perpendicular to the radial axis X _R, even the outer peripheral surface 41f as shown in FIG. 7A is a curved surface or spherical surface Good. This limits the contact between the two contact points around the radiation axis X _R, reduces friction I hereinafter, also helps to prevent twisting. Instead of or in addition to this, the inner peripheral surface 37f may also be a curved surface.

Support 37 includes a plurality of partitions 37w extending inwardly respectively radial direction between the tapered roller 41, the partition 37w may also be sized to respectively slide on the rolling surface 41 _R. This is useful for preventing the taper roller 41 from being eccentric or precessing.

The plurality of partitions 37w of the support 37 may be slidably fitted to the shaft 23 at the radially inner end. This serves to align the taper roller 41 and the support 37 with respect to the axis X. Such fitting requires a certain amount of play so that the lubricating oil can enter between the partition 37w and the shaft 23 and hold the oil film, but is tightened to such an extent that the support 37 is restricted from moving in the axial direction. Also good. Since this prevents the actuation of the cam in its initial (to significantly stagnant process P _L described later), to prevent operation of unintended cam helps to reduce consequently the drag torque. In particular, when the shear resistance of the lubricating oil is large at a low temperature, the drag torque is likely to increase, but the effect of hindering the initial operation of the cam is also increased. Therefore, this configuration is advantageous in expanding the effective operating temperature range. Instead of or in addition to reducing play, a structure, member or coating that increases friction in the axial direction may be interposed, one example being extending the fitting surface in the axial direction. Separately or in combination with this, a means for reducing friction in the circumferential direction may be applied, and for example, a groove for holding lubricating oil may be interposed.

The plurality of partitions 37w may be integrated with the support 37, but may be separate as shown in FIG. 7B. In this case, the partitions 37w may be connected to each other on the inner peripheral side, and such portions may be slidably fitted to the shaft 23 as described above. Also in this case, the inner peripheral surface 41 i of the taper roller 41 can be separated from the support 37. Alternatively, the inner peripheral surface 41i may be in contact with the support 37, but does not need to be actively supported.

Alternatively, as shown in FIG. 7C, the support 37 may be a simple ring without the partition 37w.

Alternatively, referring to FIG. 8A, the support 37 may include a protrusion 37p that makes point contact with the outer peripheral surface 41f. Correspondingly, the outer peripheral surface 41f, in about the radiation axis X _R, may be provided with a recess receiving the protrusion 37 p. Or conversely, the outer peripheral surface 41f may be provided with a protrusion. Furthermore, as shown in FIG. 8B, the support 37 has a V-shape in its cross section, and may form a protrusion 37p that makes point contact. These structures help reduce friction and prevent twisting.

Alternatively, referring to FIG. 8C, support 37 is provided with arbor 37a, may be rotatably supports the tapered roller 41 around the radial axis X _R Te Tsu. The arbor 37a may be separate from the support 37 or may be integrated. In the case of a separate body, the arbor 37a may be fixed by being press-fitted into a through hole opened in the support 37, or may be by other fixing means. The structure supported by the arbor 37a is useful for preventing the taper roller 41 from being eccentric or precessing.

In any case, the inner peripheral surface 41 i of the taper roller 41 can be separated from the shaft 23.

As already described, the outer peripheral surface 41 f faces outward in the radial direction and is separated from the cam plate 35 and the pressure plate 39. As shown in FIG. 5A, the outer peripheral surface 41f may not be partially covered and may be exposed outward in the radial direction as shown in FIG. 9A. This facilitates the circulation of the lubricating oil and helps to reduce the rolling resistance of the taper roller 41. Further, the taper roller 41 may partially protrude outward from the cam plate 35. Of course, as shown in FIG. 9B, either or both of the cam plate 35 and the pressure plate 39 may cover the outer peripheral surface 41f. If the outer peripheral surface 41f is not in contact with the cam plate 35 and the pressure plate 39, friction and / or twist will not increase.

Figure 3,4,5A, current I- torque T curve according to the embodiment shown in 5B is, as shown in broken lines in FIG. 1, shows a hysteresis _{C I,} which is reduced than the prior art. The degree of hysteresis is not inferior to that of the ball cam example and is sufficiently practical. This is considered to be because the support that moves both in the axial direction and in the circumferential direction supports the tapered roller instead of the cam plate and the pressure plate that perform complicated movement with respect to the tapered roller.

Also when compared with examples according to the ball cam, it is permitted to rise relatively stagnant torque T in the process P _L to increase the current I from the starting point O, also in the process P _R to reduce the current I from the vicinity of the end point E It can be seen that the decrease in torque T is relatively stagnant, ie the curve is S-shaped. But there is the former stagnation processes P _L because immediately torque transmission lead to no increase, help reduce rather so-called drag torque. Also it is the latter stagnation process P _R serves to prevent decoupling of unintended clutch.

In summary, each disclosed embodiment provides a cam mechanism or a power transmission mechanism with good controllability while suppressing hysteresis.

Although several embodiments have been described, the embodiments can be modified or modified based on the above disclosure.

Claims (6)

1. A cam mechanism for generating an axial force in combination with a means for generating a differential around an axis,
   A cam plate rotatable about the axis and coupled to the means for receiving the differential;
   A pressure plate facing the cam plate in the axial direction and movable in the axial direction;
   A rolling surface that is interposed between the cam plate and the pressure plate and is rotationally symmetric with respect to a radial axis orthogonal to the axis and having a tapered conical surface toward the axis; and radially outward A plurality of taper rollers having an outer peripheral surface facing;
   An annular support that contacts the outer peripheral surface so as to rotatably support the plurality of taper rollers around the radial axis and to move in the axial direction together with the plurality of taper rollers, and
   The cam plate and the pressure plate each have a cam surface in contact with the rolling surface, and each cam surface rolls the tapered roller according to the differential to generate the axial force on the pressure plate. A cam mechanism that is inclined in a circumferential direction with respect to a circumferential surface orthogonal to the axis.
2. The cam mechanism according to claim 1, wherein the cam plate and the pressure plate are separated from the outer peripheral surface.
3. The cam mechanism according to claim 1, wherein the cam plate and the pressure plate are dimensioned so that the outer peripheral surface is exposed outward in a radial direction.
4. The support includes one or more partitions extending radially inward between the plurality of taper rollers, and each partition slides on the rolling surface so that each taper roller is separated from each radial axis. The cam mechanism of claim 1, dimensioned to prevent eccentricity.
5. The cam mechanism according to claim 1, wherein the support includes a protrusion that makes line contact or point contact with the outer peripheral surface, or a pivot that rotatably supports the taper roller around the radial axis.
6. A clutch device for controlling transmission of torque between a first rotating body and a second rotating body, each of which can rotate around an axis,
   A cam plate rotatable about the axis;
   A braking device coupled to the cam plate to controllably brake the cam plate relative to the first rotating body;
   A pressure plate facing the cam plate in the axial direction, rotating with the second rotating body and movable in the axial direction;
   A rolling surface that is interposed between the cam plate and the pressure plate and is rotationally symmetric with respect to a radial axis orthogonal to the axis and having a tapered conical surface toward the axis; and radially outward A plurality of taper rollers having an outer peripheral surface facing;
   An annular support in contact with the outer peripheral surface so as to rotatably support the plurality of tapered rollers around the radial axis and to move in the axial direction together with the tapered rollers;
   A clutch that transmits the torque between the first rotating body and the second rotating body when pressed against the pressure plate in the axial direction;
   The cam plate and the pressure plate are respectively provided with cam surfaces that are in contact with the rolling surfaces, and when the cam plate is braked to generate a differential with respect to the pressure plate, each cam surface corresponds to the differential. A clutch device that is inclined in a circumferential direction with respect to a circumferential surface orthogonal to the shaft so as to generate an axial force that rolls the taper roller and presses the pressure plate toward the clutch.

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