JP6912666B2 - Low hysteresis cam mechanism with tapered rollers - Google Patents

Description

The following disclosure relates to a cam mechanism that uses a taper roller to generate an axial force, and a power transmission device such as a clutch device provided with such a cam mechanism.

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

A ball may be interposed between the cam members for the purpose of smoothly operating the cam mechanism. The rolling of the ball between the relatively rotating cam surfaces significantly reduces the sliding resistance of the ball. This reduces the load on the actuator, but since the cam surface and the ball only make point contact, there is a problem in causing the cam mechanism to bear a large axial force. The use of rollers capable of line contact instead of balls would be one of the means to solve such a problem. Patent Document 1 discloses a related technique.

Publication of international patent application WO2017 / 149829A1

Although larger axial forces can be generated by line-contacting rollers, we have found other new problems. According to the related art described above, the cam mechanism presses the pressure ring against the clutch in response to the current applied to the actuator, thereby engaging the clutch and transmitting torque to it. From the viewpoint of torque transmission controllability, it is ideal that the torque transmitted with respect to the applied current is unique. However as illustrated in present FIG 1, curve C _p of the torque T to be transmitted to the applied current I is (process to try to connect the clutch) process of the current increase P _I and the current reduction process (de 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 arrived at the following mechanism or device.

The following disclosure relates to a cam mechanism that enables reduction of hysteresis while utilizing a tapered roller and a power transmission device such as a clutch device including the cam mechanism.

According to one aspect, a cam mechanism that generates an axial force in combination with a means that produces a differential around the shaft is rotatable around the shaft and coupled with the means to receive the differential. A cam plate, a pressure plate that is axially opposed to the cam plate and is movable in the axial direction, and a peripheral surface that is formed on the cam plate and the pressure plate and faces each other and is orthogonal to the axis. A pair of cam surfaces that are inclined in the circumferential direction and the pair of cam surfaces are interposed and roll on each cam surface according to the differential to generate the axial force on the pressure plate. A plurality of tapered rollers, each of which is rotationally symmetric with respect to a radial direction orthogonal to the axis and has a rolling surface forming a conical surface that tapers toward the axis, and the cam surface and the rolling. It includes a texture formed on one or more of the surfaces, which resists twisting of each of the tapered rollers in each of the radial directions.

According to another aspect, the clutch device for controlling the transmission of torque between the first and second rotating bodies, which are rotatable around the shaft, respectively, is rotatable around the shaft. Together with the cam plate, a braking device coupled to the cam plate to controlally brake the cam plate against the first rotating body, and axially facing the cam plate and the second rotating body. A pair of cam surfaces that are formed on the cam plate and the pressure plate and are opposed to each other and are inclined in the circumferential direction with respect to a peripheral surface orthogonal to the axis, respectively, and a pressure plate that is rotated and movable in the axial direction. A plurality of tapered rollers that are interposed between the pair of cam surfaces and roll on each cam surface according to the differential to generate the axial force on the pressure plate, each orthogonal to the axis. A plurality of tapered rollers having a rolling surface that is rotationally symmetric with respect to the radial direction and forms a conical surface that tapers toward the axis, and each of the tapered rollers formed on one or more of the cam surface and the rolling surface. Has a texture that resists twisting in each of the radial directions, and when pressed axially by the pressure plate, the torque is transmitted between the first rotating body and the second rotating body. It is equipped with a clutch to rotate.

FIG. 1 is a graph showing an example of hysteresis in the cam mechanism. FIG. 2A is a schematic vertical sectional view of a cam mechanism for explaining the force applied to the taper roller. 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 a cam mechanism showing a state in which the taper roller rolls on a rolling surface. FIG. 3 is a vertical 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 plan view of the tapered roller having a texture and the cam surface. FIG. 5B is a plan view of the tapered roller and the cam surface according to another example. FIG. 6A is a schematic plan view in which the texture on the rolling surface or the cam surface is developed into a plane. FIG. 6B is a schematic plan view in which the texture according to another example is developed into a plane. FIG. 6C is a schematic plan view in which the texture according to another example is developed into a plane. FIG. 6D is a schematic plan view in which the texture according to another example is developed into a plane. FIG. 6E is a schematic plan view in which the texture according to another example is developed into a plane. FIG. 7 is a schematic cross-sectional view showing a mode in which the textures on the rolling surface and the cam surface mesh with each other. FIG. 8A is a cross-sectional view of the taper roller and the cam plate according to an example in which a part of the cam plate is in contact with the outer peripheral surface of the taper roller. FIG. 8B is a cross-sectional view of a tapered roller and a cam plate according to another example.

Some exemplary embodiments will be described below with reference to the accompanying drawings. Throughout the following description and claims, unless otherwise stated, the axis means the axis of rotation of the cam mechanism, the axial direction means the direction parallel to it, and the radial direction means the direction orthogonal to it. be. The axis of rotation of the clutch device usually coincides with, but is not limited to, the axis of rotation of the cam mechanism.

With reference to FIGS. 2A and 2B, when the cam mechanism includes a cam plate 5 and a pressure plate 9 and a taper roller 11 interposed therein, the rolling surface 11 _R of the taper roller 11 is aligned with the cam surface 5c of the cam plate 5. They are in contact with each other and are in line contact with the cam surface 9c of the pressure plate 9, and these contact lines are inclined in 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 hinders the rolling of the taper roller 11.

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 be.

At this time, the axial force F'is increased by the cam action from the beginning, and therefore the radial reaction force for pressing the outer peripheral surface 11f against the inner peripheral surfaces 5f and 9f is also increased, while the axial motion Mx is the cam plate 5 and the pressure plate 9. The contact area between the outer peripheral surface 11f and the inner peripheral surfaces 5f and 9f is reduced. Here, an increase in radial reaction force hinders rolling, but a decrease in contact area is a factor 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 force for twisting the taper roller 11 also acts in the opposite direction because the differential is in the opposite direction. The axial force F'decreases, but the contact area between the outer peripheral surfaces 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. The present inventors considered to solve the problem by coping with the force of twisting the taper roller without increasing the rolling resistance, and thus came up with each of the following embodiments.

The cam mechanism 3 according to the present embodiment can be applied to, for example, the clutch device 1 illustrated in FIG. 3, but is not necessarily limited to this. The clutch device 1 is a device that intermittently or controls the transmission of torque between a first rotating body and a second rotating body that rotate around the axis X, respectively. In this example, the first rotating body is a clutch. The case 21 and the second rotating body are the shaft 23.

A 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. The plurality of outer plates of the clutch 25 are coupled to the clutch case 21 by a lug or the like, and the plurality of inner plates alternately arranged with the outer plate are coupled to the shaft 23 by a lug 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. In addition, the torque transmitted increases or decreases by increasing or decreasing the axial force.

The clutch device 1 also comprises means 27 that generate a differential to actuate the cam mechanism 3, which generally comprises a pilot clutch 29 and a solenoid 31 that actuates it. Means 27 is, in this example, a mechanism that brakes the cam plate 35 to give it a differential with respect to the pressure plate 39, or rotates the cam plate 35 relative to the pressure plate 39 about an axis X. It may be a motor or a gear mechanism to make it.

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

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

With reference to FIG. 4 in combination with FIG. 3, the cam mechanism 3 generally includes a cam plate 35, a pressure plate 39, and a plurality of tapered rollers 41 interposed therein. Although not shown, an annular support may be further interposed between the cam plate 35 and the pressure plate 39 to support the taper roller 41 so as to keep the orientation constant.

The cam plate 35 is rotatable about the axis X and is coupled to the inner plate of the means 27 by a lug or the like in order to receive the differential as described above. The cam plate 35 also includes a cam surface in contact with _{the rolling surface 41 R} of the taper roller 41, as in FIGS. 2B and 2C. The cam surface is slightly inclined in the circumferential direction with respect to the peripheral surface orthogonal to the axis X so that the taper roller 41 can be rolled and moved in the axial direction.

The pressure plate 39 is also rotatable about the axis X, is axially opposed to the cam plate 35, and is axially movable with the clutch 25 so as to press the clutch 25. It is also engaged with the shaft 23 so that it rotates with the shaft 23. Therefore, the cam plate 35 creates a 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 peripheral 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 both cam surfaces.

The plurality of tapered rollers 41 are arranged symmetrically with respect to the axis X. The number of taper rollers 41 is 3 in the illustrated example, but of course, it is not limited to this. From the viewpoint of maintaining parallelism between the plates 35 and 39, 3 or more is preferable, but even if the number is too large, most of them usually do not contribute to the burden of axial force.

Each tapered roller 41 has a shape generally close to a truncated cone, and has a rolling surface 41 _R forming a substantially conical surface, an outer peripheral surface 41f close to a flat surface, and an inner peripheral surface, respectively. Each taper roller 41 is oriented in the radial direction with respect to the axis X, and the rolling surface 41 _{R, which} is a side surface thereof, comes into contact with the cam surface 39c and rolls on the rolling surface 41 R. The rolling surface 41 _R is rotationally symmetric with respect to the radial direction and tapers toward the axis X.

Both the inner peripheral surface and the outer peripheral surface 41f of each tapered roller 41 may be a flat surface 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 points as shown in FIG. 8A, which is useful for reducing friction and preventing twisting.

Referring back to FIG. 3 and 4, preferably, the extension of the rolling contact surface 41 _R is so as to connect the vertices on the axes X, is dimensioned and rolling surface 41 _R and the cam surface 39c. This helps to prevent the slip between the rolling surface 41 _R and the cam surface 39c is caused.

The contact between the rolling surface 41 _R and the cam surface 39c is substantially a linear contact over its entire length, which helps the cam mechanism 3 bear a large axial force. The rolling surface 41 _R may be slightly rounded (referred to in some technical fields as crowning or chamfering) toward the outer peripheral surface 41f and the inner peripheral surface. This strengthens the contact with the cam surface 39c at its center and weakens the contact towards both ends. Alternatively, or in addition, the cam surface 39c may be slightly rounded. Although they maintain line contact, they help prevent stress from increasing towards the ends of the contact and thus prevent the generation of twisting forces on the taper roller 41. If the roundness is too large, the cam mechanism 3 may hinder the burden of a large axial force. Therefore, the inclination due to the roundness is limited to, for example, 1/100 with respect to the bus, and more preferably 1/10000.

According to common sense in the art, if the rolling element and the rolling surface that supports it are rough, the rolling resistance is increased. Therefore, it is usually considered that these should be finished as smoothly as possible, for example mirror-finished. However, in the present embodiment, as illustrated in FIGS. 5A and 5B, one or both of them have a texture having appropriate unevenness. As described below, in certain cases, the texture on the rolling surface 41 _R and / or the cam surface 39c, while the resistance to the force twisting the tapered roller 41, a remarkable resistance to rolling Does not occur. That is, the texture helps to achieve smooth rolling without twisting.

In reference to FIGS. 6A to 6E in combination with FIGS. 5A and 5B, the rolling surface 41 _R includes a texture 41 _T. Alternatively, or in addition to the texture 41 _T on the rolling surface 41 _R , the cam surface 39c may include a texture 39 _T. Although not shown in the figure, the cam surface of the cam plate 35 may also have a texture. Needless to say, it may be textured is formed in all of the two cam surfaces and rolling surfaces 41 _R.

The texture 41 _T is, for example, a plurality of grooves or protrusions parallel to each other. 5A and 6A are _{examples in which the texture 41 T} is substantially parallel in the radial direction with respect to the axis X, and FIGS. 5B and 6B are examples in which the texture 41 T is along the circumferential direction. The texture on the rolling surface and the texture on the cam surface preferably run in the same direction, but may be in different directions.

Alternatively, as shown in FIG. 6C, the texture may run in both the radial and circumferential directions, or as shown in FIG. 6D, it may have an inclination in either direction.

As for _{the width and pitch of the grooves or protrusions of the textures 39 T} and 41 _T , larger ones may be effective as resistance to twisting, but smaller ones may be advantageous in terms 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 grooves or the height of the protrusions can be very small and can act as resistance to twisting, even to the extent of, for example, 1 μm. Rather, if the depth or protrusions are too large, rolling resistance can be increased.

These textures can be easily formed by machining. Such a structure can be intentionally formed, or scratches unavoidably caused by machining may be left on the surface partially or entirely. Further, it may be formed by scanning a laser or an electron beam on a smooth surface, or the texture on the die or mold may be pressed against the surface and transferred.

Furthermore, the texture does not have to have a structure extending in a particular direction and may be isotropic and random irregularities, for example as shown in FIG. 6E. Such a structure can be formed by, for example, local pickling, or can be formed by a method such as shot peening. Also in such an example, the height and depth of the unevenness can be made very small, and even if it is about 1 μm, for example, it can act as a resistance to twisting.

These textures can maintain the taper roller 41 in the radial direction and resist the taper roller 41 from twisting in the radial direction.

The texture 41 _T on the rolling surface 41 _{R and the texture 39 T} on the cam surface 39c may be dimensioned to mesh with each other, as shown in FIG. This further strengthens the action of the texture that keeps the taper roller 41 from twisting. Further, in this case, the protrusions and grooves of the texture can be made relatively large, and even in that case, the rolling resistance is not significantly increased. Of course, such a relationship may _{also hold between the rolling surface 41 R} and the cam surface of the cam plate 35.

With reference to FIG. 8A, one or both of the cam plate 35 and the pressure plate 39 is provided with a peripheral wall to support the outer peripheral surface 41f of the tapered roller 41. As already described, the outer peripheral surface 41f and the peripheral wall are in point contact. This helps reduce friction and prevent twisting of the taper roller 41. Point contact may occur at the edge of the peripheral wall or at any of the inner surfaces of the peripheral wall. Further, the point contact may be substantially the center of the outer peripheral surface 41f as illustrated in FIG. 8A, or may be separated from the center as illustrated in FIG. 8B. The surfaces that make point contact may have an angle α with respect to a surface that is orthogonal to the radial direction.

Current I- torque T curve of the respective embodiment 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 because the taper roller can roll smoothly without twisting with respect to the shaft.

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 The decrease in torque T is found to be relatively stagnant, i.e. the curve is S-shaped. But there is a former stagnation process P _L, so immediately the torque transmission leads not to increase, help reduce rather so-called drag torque. Also it is the latter stagnation process P _R serves to prevent decoupling of unintended clutch.

Taken together, each of the disclosed embodiments provides a cam mechanism or power transmission mechanism that suppresses hysteresis and has good controllability.

Although some embodiments have been described, it is possible to modify or modify the embodiments based on the above disclosure contents.

Claims (7)

A cam mechanism that generates axial force in combination with means that generate differentials around the shaft.
A cam plate that is rotatable around the axis and coupled with the means to accept the differential.
A pressure plate that faces the cam plate in the axial direction and is movable in the axial direction,
A pair of cam surfaces formed on the cam plate and the pressure plate, which face each other and are inclined in the circumferential direction with respect to the peripheral surfaces orthogonal to the axis, respectively.
A plurality of tapered rollers that are interposed between the pair of cam surfaces and roll on each cam surface according to the differential to generate the axial force on the pressure plate, each having a diameter orthogonal to the axis. A plurality of tapered rollers having a rolling surface that is rotationally symmetric with respect to the direction and forms a conical surface that tapers toward the axis.
A texture formed on one or more of the cam surface and the rolling surface, which resists twisting of each of the tapered rollers in each of the radial directions.
Cam mechanism with. The cam mechanism of claim 1, wherein each texture comprises a plurality of grooves or protrusions each having a width of 1 to 500 μm and substantially parallel to each other, and the pitch between the grooves or the protrusions is 1 to 3 mm. The cam mechanism according to claim 1, wherein the texture includes isotropic irregularities. The cam mechanism according to claim 1, wherein the texture is formed on all of the cam surface and the rolling surface. The cam mechanism according to claim 4, wherein the texture of the cam surface and the texture of the rolling surface are sized so as to mesh with each other. The cam mechanism according to claim 1, wherein each of the plurality of tapered rollers has an outer peripheral surface facing outward in the radial direction, and one or more of the cam plate and the pressure plate is in contact with the outer peripheral surface. A clutch device for controlling the transmission of torque between a first rotating body and a second rotating body that can rotate around an axis, respectively.
With a cam plate that can rotate around the axis,
A braking device coupled to the cam plate to brake the cam plate to the first rotating body in a controllable manner.
A pressure plate that faces the cam plate in the axial direction, rotates 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, which face each other and are inclined in the circumferential direction with respect to the peripheral surfaces orthogonal to the axis, respectively.
A plurality of tapered rollers that are interposed between the pair of cam surfaces and roll on each cam surface according to the differential to generate the axial force on the pressure plate, each having a diameter orthogonal to the axis. A plurality of tapered rollers having a rolling surface that is rotationally symmetric with respect to the direction and forms a conical surface that tapers toward the axis.
A texture formed on one or more of the cam surface and the rolling surface, which resists twisting of each of the tapered rollers in each of the radial directions.
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.
Clutch device equipped with.

Images