ROTATION TRANSMISSION DEVICE

Abstract

A rotation transmission device which can quickly change the direction of rotation. It includes a inner ring formed with cam surfaces on its outer periphery, a outer ring formed with a cylindrical surface on its inner periphery, and a plurality of pairs of rollers, each pair being disposed between one of the cam surfaces and the cylindrical surface so as to be circumferentially opposed to each other. A roller separation spring is disposed between each pair of rollers to bias the rollers away from each other so that the rollers are wedged between the cam surface and the cylindrical surface. The rollers are retained by a roller retainer which can change the distance between each pair of circumferentially opposed rollers. By reducing the distance between each pair of rollers with the roller retainer, it is possible to disengage the rollers from the cam surfaces and the cylindrical surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view of a rotation transmission device according to a first embodiment of the present invention;

FIG. 2 is an enlarged sectional view of the rotation transmission device of FIG. 1, showing its portion including the roller retainer;

FIG. 3 is a developed view of FIG. 2, showing its portion including rollers;

FIG. 4 is a sectional view taken along line IV-IV of FIG. 3;

FIG. 5 is a sectional view taken along line V-V of FIG. 3;

FIG. 6 is an enlarged sectional view similar to FIG. 2 when the electromagnetic coil is deenergized;

FIG. 7 is a developed view of FIG. 6, showing its portion including rollers;

FIG. 8 is a sectional view taken along line VIII-VIII of FIG. 7;

FIG. 9 is a sectional view taken along line IX-IX of FIG. 7;

FIG. 10 is a developed view similar to FIG. 3 showing different roller separation springs;

FIG. 11 is an enlarged sectional view of a rotation transmission device according to a second embodiment of the invention, showing its portion including the roller retainer;

FIG. 12 is a developed view of FIG. 11, showing its portion including rollers;

FIG. 13 is a sectional view taken along line XIII-XIII of FIG. 12;

FIG. 14 is a perspective view of the inner ring and a roller separation spring of FIG. 12;

FIG. 15 is a developed view of the rotation transmission device showing its portion including rollers when the electromagnetic coil of FIG. 11 is deenergized;

FIG. 16 is a sectional view taken along line XVI-XVI of FIG. 15;

FIG. 17 is an enlarged sectional view of a rotation transmission device according to a third embodiment of the invention, showing its portion including the roller retainer;

FIG. 18 is a developed view of FIG. 17 showing rollers;

FIG. 19 is a sectional view taken along line XIX-XIX of FIG. 18;

FIG. 20 is a perspective view of the inner ring, rollers, roller separation springs, and the spring retainer of FIG. 18;

FIG. 21 is a developed view showing rollers when the electromagnetic coil of FIG. 17 is deenergized;

FIG. 22 is a sectional view taken along line XXII-XXII of FIG. 21;

FIG. 23 is a sectional view similar to FIG. 19 showing how a roller separation spring is buckled at its portions in contact with the outer periphery of rollers;

FIG. 24 is a sectional view similar to FIG. 19 showing a different roller separation spring;

FIG. 25 is an enlarged perspective view of the roller separation spring of FIG. 24;

FIG. 26A is a sectional view similar to FIG. 22 showing different protrusions of the annular retainer members;

FIG. 26B shows how the rollers are disengaged by pushing the rollers with the protrusions of FIG. 26A;

FIG. 27 is a developed view similar to FIG. 21 showing different roller retainer and spring retainer;

FIG. 28 is a developed view similar to FIG. 27 showing the state in which the distance between rollers is reduced by moving the annular retainer members of FIG. 27 relative to each other;

FIG. 29 is a enlarged sectional view of a rotation transmission device according to a fourth embodiment of the invention, showing its roller retainer; and

FIG. 30 is an enlarged sectional view similar to FIG. 29 showing a different armature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now referring to FIGS. 1 to 5, the rotation transmission device of the first embodiment includes, as shown in FIGS. 1 and 2, an inner ring 2 and an outer ring 1 which is rotatably supported on the inner ring 2 through a rolling bearing 3 provided around the inner ring 2. As shown in FIG. 4, a cylindrical surface 4 is formed on the inner periphery of the outer ring 1, and cam surfaces 5 are formed on the outer periphery of the inner ring 2 to define wedge spaces in cooperation with the cylindrical surface 4. Each wedge space has a radial width that gradually decreases from its circumferential central portion to circumferential ends.

As shown in FIGS. 3 and 4, a pair of circumferentially opposed rollers 6 are disposed between each cam surface 5 and the cylindrical surface 4. A roller separation spring 7 is disposed between the pair of rollers 6 to bias the rollers 6 circumferentially away from each other. A roller retainer 8 keeps constant the distance between each pair of rollers 6.

The roller retainer 8 comprises a pair of annular retainer members 9A and 9B which are circumferentially and axially movable relative to each other. The annular retainer member 9A comprises a cylindrical portion 10A and a plurality of protrusions 11A axially extending from the cylindrical portion 10A and circumferentially spaced from each other. Similarly, the annular retainer member 9B comprises a cylindrical portion 10B and a plurality of protrusions 11B axially extending from the cylindrical portion 10B and circumferentially spaced from each other. The protrusions 11A each have a side contact surface 12 that is in contact with a side contact surface 12 of the adjacent protrusion 11B. Each pair of rollers 6 are disposed in a space defined by two adjacent protrusions 11A and 11B with one of the pair of rollers 6 supported by the protrusion 11A and the other supported by the protrusion 11B.

The contact surfaces 12 are inclined relative to the axis of the roller retainer 8 so that when the annular retainer members 9A and 9B are moved axially relative to each other, the annular retainer members 9A an 9B also move circumferentially relative to each other with the side contact surfaces 12 of one of the annular retainer members 9A and 9B guided by the side contact surfaces of the other of the annular retainer members 9A and 9B. Thus, by axially moving the annular retainer members 9A and 9B relative to each other, the relative position between the annular retainer members 9A and 9B changes circumferentially in proportion to the relative axial movement of the retainer members 9A and 9B, so that the distance between each pair of rollers 6 also changes.

As shown in FIG. 2, a slide bearing 13 is mounted on the outer periphery of the annular retainer member 9A at its axially outer end to rotatably support an annular armature 14. The armature 14 is prevented from axial movement relative to the annular retainer member 9A by a snap ring 15 fitted on the outer periphery of the annular retainer member 9A.

The armature 14 is made of a magnetic material (such as iron). The armature 14 is axially opposed to a field core 17 fixed to a case 16. A permanent magnet 18 is embedded in the field core 17. Also, an electromagnetic coil 19 is wound on the field core 17. The magnetic field produced by energizing the electromagnetic coil 19 is adapted to cancel the magnetic field produced from the permanent magnet 18. The field core 17 is provided with an armature separation spring 20 biasing the armature 14 away from the field core 17.

A rolling bearing 21 is mounted on the inner periphery of the field core 17 to rotatably support a rotary shaft 22. The rotary shaft 22 is formed with splines on its outer periphery at one end which engage splines formed on the inner periphery of the inner ring 2 so that the inner ring 2 is rotationally fixed to the rotary shaft 22.

The annular retainer member 9B is prevented from axial movement relative to the inner ring 1 by a snap ring 23 fitted on the outer periphery of the inner ring 1. As shown in FIG. 5, the annular retainer member 9B is elastically and circumferentially held in position relative to the inner ring 2 by a switch spring 24. The switch spring 24 comprises a C-shaped annular portion 25 and engaging portions 26 radially outwardly extending from the respective ends of the C-shaped annular portion 25. The engaging portions 26 are in engagement with one and the other of circumferentially opposed end walls of each of a cutout 27 formed in the inner ring 2 and a cutout 28 formed in the annular retainer member 9B, respectively.

The operation of this rotation transmission device is now described. When the electromagnetic coil 19 is deenergized, as shown in FIG. 6, the armature 14 is pulled by the magnetic attraction force of the permanent magnet 18 until the armature 14 abuts the field core 17, so that the annular retainer member 9A is moved in a direction away from the annular retainer member 9B. As a result, as shown in FIG. 7, each pair of rollers 6 are moved away from each other under the force of the roller separation spring 7, so that their distance increases. Thus, the rollers 6 are wedged between the cam surfaces 5 and the cylindrical surface 4 as shown in FIG. 8. Also, because the annular retainer member 9B moves circumferentially relative to the inner ring 2, the switch spring 24 is elastically deformed as shown in FIG. 9.

When the electromagnetic coil 19 is energized, the magnetic field produced from the electromagnetic coil 19 cancel the magnetic field of the permanent magnet 18, thus allowing the armature 14 to move away from the field core 17 under the force of the armature separation spring 20, so that the annular retainer member 9A moves toward the annular retainer member 9B. When the member 9A moves toward the member 9B, the annular retainer members 9A and 9B are circumferentially moved relative to each while being guided along their contact surfaces 12 in such a direction that the spaces between the circumferentially adjacent protrusions 11A and 11B in which the rollers 6 are disposed decreases. The distance between each pair of rollers 6 thus decreases. Also, the annular retainer member 9B is circumferentially moved under the elastic restoring force of the switch spring 24 until the rollers 6 disengage from the cam surfaces 5 and the cylindrical surface 4.

In this arrangement, with both of each pair of circumferentially opposed rollers 6 wedged between the cam surface 5 and the cylindrical surface 4 by increasing the distance therebetween, it is possible to transmit rotation in one direction between the inner and outer rings 2 and 1 through one of each pair of rollers 6 and rotation in the opposite direction through the other of each pair of rollers 6. Thus, it is not necessary to circumferentially move the roller retainer 8 when the direction in which rotation is transmitted between the inner and outer rings changes, so that the direction of transmission of rotation can be changed without a delay in response.

Also, with the rollers 6 disengaged from the cam surfaces 5 and the cylindrical surface 4, a space is reliably left between the rollers 6 and the cylindrical surface 4, so that the rollers are less likely to be untimely wedged between the cam surfaces 5 and the cylindrical surface 4. Therefore, the rotation transmission device according to this invention operates extremely stably.

Because rotation is transmitted between the inner and outer rings 2 and 1 through as many rollers 6 as the cam surfaces 5, a large turning torque can be transmitted between the inner and outer rings.

Also, when compared to the rotation transmission device disclosed in JP patent publication 2003-262238A, this rotation transmission device is less expensive because it is not necessary to provide a rotor that rotates together with the outer ring 1 between the armature 14 and the field core 17.

In this embodiment, as shown in FIG. 3, the roller separation springs 7 are retained by the annular retainer member 9B to stabilize the attitude of the roller separation springs 7. But instead, as shown in FIG. 10, the roller separation springs 7 may be provided separately from the roller retainer 8.

FIGS. 11 to 13 show a rotation transmission device according to the second embodiment of this invention. In this embodiment, the switch spring 24 of the first embodiment is omitted, and instead, the roller separation springs are fixed to the inner ring 2. Thus, elements similar to or identical to those of the first embodiment are denoted by identical numerals and their description is omitted.

As shown in FIGS. 12 and 13, each pair of circumferentially opposed rollers 6 are biased away from each other by a roller separation spring 30 disposed between the pair of rollers 6. The roller separation springs 30 are circumferentially shrinkable corrugated leaf springs. As shown in FIG. 14, each spring 30 includes an extension 31 protruding axially from the circumferential central portion of the spring 30 and having its tip fixed to the inner ring 2 at its portion corresponding to the circumferential central portion of one of the cam surfaces 5.

The operation of this rotation transmission device is now described. When the electromagnetic coil 19 is deenergized, the annular retainer member 9A is pulled by the magnetic attraction force of the permanent magnet 18 away from the annular retainer member 9B. As a result, as shown in FIG. 15, each pair of rollers 6 are moved away from each other under the force of the roller separation spring 30, so that their distance increases. Thus, the rollers 6 are wedged between the cam surfaces 5 and the cylindrical surface 4 as shown in FIG. 16.

When the electromagnetic coil 19 is energized, the annular retainer member 9A is moved toward the annular retainer member 9B under the biasing force of the armature separation spring 20. Thus, the distance between each pair of rollers 6 decreases as shown in FIG. 12. At this time, because the extension 31 of each roller separation spring 30 is fixed to the inner ring 2 at its portion corresponding to the circumferential central portion of the cam surface 5, the distance between each pair of rollers 6 decreases while being positioned so as to be symmetrical with respect to the circumferential center of the cam surface 5. Both of each pair of rollers 6 thus disengage from the cam surfaces 5 and the cylindrical surface 4.

In this arrangement, with both of each pair of circumferentially opposed rollers 6 wedged between the cam surface 5 and the cylindrical surface 4 by increasing the distance therebetween, it is possible to transmit rotation in one direction between the inner and outer rings 2 and 1 through one of each pair of rollers 6 and rotation in the opposite direction through the other of each pair of rollers 6. Thus, it is not necessary to circumferentially move the roller retainer 8 when the direction in which rotation is transmitted between the inner and outer rings changes, so that the direction of transmission of rotation can be changed without a delay in response.

In this embodiment, because the roller separation springs 30 are fixed to the inner ring, it is possible to omit the switch spring 24 used in the first embodiment, so that the rotation transmission device of this embodiment is more economical.

FIGS. 17 to 19 show the rotation transmission device according to the third embodiment of the invention. In this embodiment, elements corresponding to those of the first embodiment are denoted by identical numerals and their description is omitted.

In this embodiment, as shown in FIGS. 18 and 19, a pair of roller separation springs 40 are disposed between each pair of circumferentially opposed rollers 6 to bias the pair of rollers 6 away from each other. The roller separation springs 40 are held in position by a spring retainer 41.

As shown in FIG. 20, the spring retainer 41 includes a flange 42 and bridges 43 axially extending from the flange 42. The flange 42 is fixed to one axial end surface of the inner ring 2 by screws 44. As shown in FIG. 18, the bridges 43 are inserted between the respective pairs of circumferentially opposed rollers 6, thereby supporting the respective roller separation springs 40 on its surfaces 45 opposed to the rollers 6. Each roller separation spring 40 comprises a pair of parallel coil springs having one end of one of the coil springs coupled to one end of the other coil spring, and simultaneously biases one and the other ends of the corresponding roller 6. Each bridge 43 has roller stoppers 46 protruding from the surfaces 45 opposed to the respective rollers 6.

The operation of this rotation transmission device is now described. When the electromagnetic coil 19 is deenergized, the annular retainer member 9A is moved away from the annular retainer member 9B under the magnetic attraction force of the permanent magnet 18, so that each pair of rollers 6 are moved away from each other under the force of the roller separation springs 40 and thus the distance therebetween increases as shown in FIG. 21. Thus, as shown in FIG. 22, the rollers 6 are wedged between the cam surfaces 5 and the cylindrical surface 4.

When the electromagnetic coil 9 is energized, the annular retainer member 9A is moved toward the annular retainer member 9B under the force of the armature separation spring 20. When the member 9A moves toward the member 9B, as shown in FIG. 18, the annular retainer members 9A and 9B are circumferentially moved relative to each while being guided along the contact surfaces 12 of the protrusions 11A and 11B in such a direction that the spaces between the circumferentially adjacent protrusions 11A and 11B in which the rollers 6 are disposed decreases. The distance between each pair of rollers 6 thus decreases. Also, because the roller separation springs 40 are fixed to the inner ring 2 through the spring retainer 41, as shown in FIG. 19, the distance between each pair of rollers 6 decreases while being positioned so as to be symmetrical with respect to the circumferential center of the cam surface 5. The rollers 6 thus disengage from the cam surfaces 5 and the cylindrical surface 4.

At this time, as shown in FIG. 18, the roller stoppers 46 of the bridges 43 engage the respective rollers 6, so that the rollers 6 are always spaced from the respective bridges 43. This prevents breakage of the roller separation springs 40.

In this embodiment too, as in the first embodiment, with both of each pair of circumferentially opposed rollers 6 wedged between the cam surface 5 and the cylindrical surface 4 by increasing the distance therebetween, it is possible to transmit rotation in either direction between the inner and outer rings. Thus, it is not necessary to circumferentially move the roller retainer 8 when the direction in which rotation is transmitted between the inner and outer rings changes, so that the direction of transmission of rotation can be changed without a delay in response.

Generally, coil springs are less likely to suffer permanent strain compared to leaf springs. Thus, roller separation springs 40 of this embodiment, which are coil springs, are more durable than the roller separation springs 7 of the first embodiment, which are leaf springs. But as shown in FIG. 23, the roller separation springs 40 may buckle at their roller contact portions 40A that are in contact with the rollers 6, thus destabilizing the biasing force applied to the rollers 6 from the springs 40. Thus, as shown in FIGS. 24 and 25, the roller contact portions 40A preferably have the shape of a flange having an increased diameter to prevent the buckling of the roller contact portions 40A, thereby stabilizing the biasing force applied to the rollers 6 from the roller separation springs 40.

As shown in FIG. 26A, side walls 47A and 47B of the protrusions 11A and 11B which abut the rollers 6 are preferably inclined radially outwardly toward each other so that the rollers 6 each abut one of the side walls 47A and 47B at its portion that is spaced apart from the cam surface 5 by a greater distance than is its center. With this arrangement, as shown in FIG. 26B, when the rollers 6 are pushed by the protrusions 11A and 11B, the rollers 6 can roll on the cam surfaces 5, so that the rollers 6 can smoothly move on the cam surfaces. This in turn makes it possible to reduce the energy necessary to disengage the rollers 6.

Preferably, as shown in FIG. 27, a retainer stopper 48 is integrally formed on the flange 42 of the spring retainer 41 which are disposed between a pair of circumferentially adjacent and spaced protrusions 11A and 11B with circumferential end surfaces 49A and 49B thereof in abutment with the protrusions 11A and 11B, respectively, so that the annular retainer members 9A and 9B are circumferentially positioned relative to the inner ring 2. With this arrangement, as shown in FIG. 28, when the protrusions 11A and 11B move in such a direction as to shorten the distance between each pair of rollers 6, the pair of protrusions 11A and 11B abut the retainer stopper 48 at a position where each pair of rollers 6 are symmetrical with respect to the circumferential center of the cam surface 5. This prevents the rollers 6 from being untimely wedged between the cam surfaces 5 and the cylindrical surface 4.

In any of the above-described embodiments, by providing the permanent magnet 18 in the field core 17, the armature 14 is attracted to the field core 17 when the electromagnetic coil 19 is deenergized. But the permanent 18 in the field core 17 may be omitted to attract the armature 14 to the field core 17 when the electromagnetic coil 19 is energized.

FIG. 29 shows the rotation transmission device according to the fourth embodiment of the present invention. Elements similar to or identical to those of the third embodiment are denoted by identical numerals and their description is omitted.

At the axially outer end of the annular retainer member 9A, an annular armature 50 made of a magnetic material is integrally provided to axially oppose an annular rotor 51 fixed to the outer periphery of the rotary shaft 22. A permanent magnet 52 is embedded in the rotor 51. A field core 54 on which an electromagnetic coil 53 is wound is provided to axially face the armature 50 with the rotor 51 disposed between. The magnetic field produced by energizing the electromagnetic coil 53 cancels the magnetic field of the permanent magnet 52. An armature separation spring 55 is mounted to the rotor 51 to bias the armature 50 away from the rotor 51.

The operation of this rotation transmission device is now described. When the electromagnetic coil 53 is deenergized, the armature 50 is magnetically attracted by the permanent magnet 52 until it abuts the rotor 51, so that the annular retainer member 9A is moved away from the annular retainer member 9B. Thus, as in the third embodiment, each pair of rollers 6 are both wedged between the cam surface 5 and the cylindrical surface 4.

When the electromagnetic coil 53 is energized, the annular retainer member 9A is moved toward the annular retainer member 9B under the force of the armature separation spring 55. Thus, as in the third embodiment, each pair of rollers 6 both disengage from the cam surface 5 and the cylindrical surface 4.

In this embodiment too, as in the first embodiment, with both of each pair of circumferentially opposed rollers 6 wedged between the cam surface 5 and the cylindrical surface 4 by increasing the distance therebetween, it is possible to transmit rotation in either direction between the inner and outer rings. Thus, the direction of transmission of rotation can be changed without a delay in response.

With this rotation transmission device, even when the armature 50 is moved away from the rotor 51, because the rotor 51 and the armature 50 are rotationally fixed to each other, no frictional resistance is produced therebetween. Thus, when compared to the third embodiment, when the rollers are not wedged between the cam surfaces 5 and the cylindrical surface 4, idling torque transmitted between the inner and outer rings 2 and 1 is small.

In FIG. 29, the armature 50 is in the shape of a radially outwardly extending flange. But instead, the armature 50 may be in the shape of a radially inwardly extending flange as shown in FIG. 30.

In this embodiment, by providing the permanent magnet 52 in the rotor 51, when the electromagnetic coil 53 is deenergized, the armature 50 is attracted to the rotor 51. But the permanent magnet 52 may be omitted to attract the armature 50 to the rotor 51 when the electromagnetic coil 53 is energized.

In any of the above embodiments, an electromagnetic coil is used as an actuator for axially changing the relative position between the annular retainer members 9A and 9B. But a different type of actuator such as an electric motor, a hydraulic actuator or a pneumatic actuator may be used to change the axial relative position between the annular retainer members 9A and 9B.

In any of the embodiments, the cylindrical surface 4 is formed on the inner periphery of the outer ring 1, and the cam surfaces 5 are formed on the outer periphery of the inner ring 2. But instead, the cam surfaces may be formed on the inner periphery of the outer ring 1 and the cylindrical surface may be formed on the outer periphery of the inner ring 2.

Claims

1. A rotation transmission device comprising an inner ring having an outer periphery, an outer ring having an inner periphery, one of said outer periphery and inner periphery being formed with cam surfaces, and the other of said outer periphery and inner periphery being formed with a cylindrical surface, a plurality of pairs of rollers, each pair being disposed between one of said cam surfaces and said cylindrical surface to circumferentially face each other, roller separation springs each disposed between one of said plurality of pairs of rollers to bias said pair of rollers away from each other until wedged between said one of said cam surfaces and said cylindrical surface, and a roller retainer retaining said rollers and capable of changing the distance between each of said plurality of rollers, reducing the distance between each of said plurality of pairs of rollers, whereby said rollers are disengageable from said cam surfaces and said cylindrical surface by reducing the circumferential distance between each of said plurality of pairs of rollers with said roller retainer.

2. The rotation transmission device of claim 1 wherein said roller retainer is elastically retained by one of said inner ring and said outer ring that is formed with said cam surfaces.

3. The rotation transmission device of claim 1 wherein said roller separation springs are fixed to one of said inner ring and said outer ring that is formed with said cam surfaces.

4. The rotation transmission device of claim 3 further comprising a spring retainer for retaining said roller separation springs, said spring retainer being fixed to said one of said inner ring and said outer ring, thereby fixing said roller separation springs in position.

5. The rotation transmission device of claim 1 further comprising stoppers each disposed between one of said plurality of pairs of rollers for restricting the minimum distance between said pair of rollers, thereby preventing breakage of said roller separation springs.

6. The rotation transmission device of claim 1 wherein said roller separation springs comprise coil springs having contact portions that are brought into contact with said respective rollers, said contact portions having an increased diameter.

7. The rotation transmission device of claim 1 wherein said roller retainer comprises first and second annular retainer members that are circumferentially movable relative to each other, said first and second annular retainer members having first axial protrusions and second axial protrusions, respectively, to support each of said plurality of pairs of rollers with one of said first axial protrusions and one of said second axial protrusions that is adjacent to said one of said first axial protrusions, whereby the distance between each of said plurality of pairs of rollers is changeable by circumferentially moving said first and second annular retainer members relative to each other.

8. The rotation transmission device of claim 7 wherein said first and second annular retainer members are axially movable relative to each other, said first and second annular retainer members having first and second contact surfaces, respectively, that are in sliding contact with each other, said first and second contact surfaces being configured such that when said first and second annular retainer members move axially relative to each other with said first and second contact surfaces in sliding contact with each other, said first and second annular retainer members are also circumferentially moved relative to each other.

9. The rotation transmission device of claim 7 wherein said first and second protrusions are in abutment with said respective rollers at portions that are spaced from said respective cam surfaces by a larger distance than are the centers of the respective rollers.

10. The rotation transmission device of claim 7 further comprising a retainer stopper disposed between one of said first axial protrusions and one of said second axial protrusions that is adjacent to said one of said first protrusions and fixed to one of said inner and outer rings that is formed with said cam surfaces, whereby said first and second annular retainer members are retained in position by bringing said first and second annular retainer members into abutment with said retainer stopper.

11. The rotation transmission device of claim 8 further comprising an annular armature made of a magnetic material and rotatably but axially immovably mounted on said first annular retainer member, a field core axially spaced from said armature, and an electromagnetic coil wound on said field core, whereby said first and second annular retainer members can be axially movable relative to each other by energizing said electromagnetic coil.

12. The rotation transmission device of claim 8 further comprising an annular armature made of a magnetic material and integrally formed on said first annular retainer member, an annular rotor rotationally fixed to one of said inner and outer rings that is formed with said cam surfaces and axially facing said armature, a field core axially facing said armature with said rotor disposed between, and an electromagnetic coil wound on said field core, whereby said first and second annular retainer members can be axially movable relative to each other by energizing said electromagnetic coil.