JP3243438B2 - Driving force transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving force transmission device disposed between a rotary shaft and a driven shaft of a vehicle, such as a driven shaft, for transmitting torque between the rotary members.

[0002]

2. Description of the Related Art As one type of a driving force transmitting device, as disclosed in Japanese Utility Model Laid-Open Publication No. 7-14229 under the name of "electromagnetic clutch", both inner and outer rotating members are coaxially and relatively rotatably positioned. A friction clutch arranged between them,
An electromagnetic control means that operates by energization to frictionally engage the friction clutch, the control means comprising: an armature located inside the outer rotating member and facing the friction clutch; An electromagnet is provided on the outer side and opposed to the friction clutch with a side wall of the outer rotating member interposed therebetween, and by energizing the electromagnet, the armature is attracted to frictionally engage the friction clutch, and the friction is applied. There is a driving force transmission device of a type in which the two rotating members are connected so that torque can be transmitted by frictional engagement force of a clutch.

In the driving force transmission device described in the above publication, a rotating case is employed as an outer rotating member and a hub is employed as an inner rotating member, and the electromagnetic control means is a friction clutch. , And an electromagnet located on the front side wall of the rotating case.

[0004] In the driving force transmitting device, a yoke for supporting the electromagnet by energizing the electromagnetic coil of the electromagnet,
A magnetic path circulating through the front side wall of the rotating case, the friction clutch, the armature, the friction clutch, the front side wall and the yoke is formed, and the armature is attracted toward the friction clutch by a magnetic induction action. As a result, the armature presses the friction clutch to frictionally engage, and the friction engagement force directly
Further, the main clutch mechanism is operated to connect the rotating case and the hub so that torque can be transmitted.

[0005]

In the driving force transmission device of the type described above, the front side wall of the rotating case is formed of a magnetic material and functions as a magnetic path forming member. It is preferable that the magnetic permeability is large and the coercive force is as small as possible. The magnetic path forming member having a large magnetic permeability and a small coercive force is formed of a soft magnetic material having a low carbon content.

On the other hand, we do it magnetic path forming member which is rotatably supported by a supporting member provided with a sliding contact portion between the support member, the sliding contact portion is hard and heat resistance and corrosion resistance It is required to be excellent. A member having high hardness and excellent heat resistance and corrosion resistance is formed by heat-treating a metal material such as iron having a high carbon content. However,
A member having a high carbon content has a large coercive force and is not suitable for a magnetic path forming member.

That is, when a member having a large carbon content and a large coercive force is employed as the magnetic path forming member,
Even if the supply of current to the electromagnet is stopped, the magnetic path remains in the magnetic path forming member, causing a response delay in the interruption of the magnetic path. In the operating state, the transmission of torque between the two rotating members may still be continued.

[0008] Therefore, in the magnetic path forming member, the low coercive force and the high hardness are incompatible characteristics, and an object of the present invention is to ensure low coercive force in the magnetic path forming member and at the required site. The purpose is to ensure high hardness.

[0009]

The present invention relates to a driving force transmitting device, and more particularly to a friction clutch disposed between inner and outer rotating members coaxially and rotatably positioned relative to each other, and actuated by energization. And electromagnetic control means for frictionally engaging the friction clutch, wherein the control means includes an armature located inside the outer rotating member and facing the friction clutch, and an armature located outside the outer rotating member. And an electromagnet opposed to the friction clutch with the side wall of the outer rotating member interposed therebetween. The energization of the electromagnet attracts the armature to frictionally engage the friction clutch. The present invention is applied to a driving force transmission device of a type in which the two rotating members are connected so that torque can be transmitted by an engagement force.

A driving force transmitting device according to the present invention is a driving force transmitting device of the above-described type, wherein a magnetic path forming member that forms a magnetic path between the electromagnet and the armature when energizing the electromagnet is provided. It also rotates integrally with the outer rotating member.
A cylindrical sliding contact portion rotatably supported by the
Forming member be composed at a low carbon magnetic material, the <br/> sliding contact portion is characterized in that it comprises a surface of high hardness.

In the driving force transmission device according to the present invention,
The magnetic path forming member is rotatably supported by a part of the vehicle body.
But, the sliding contact portion of the magnetic path forming member is preferably formed on the surface of high hardness by surface hardening treatment, surface hardening treatment applied to the sliding contact portion of the magnetic path forming member is carburized and Only the surface of the sliding contact portion of the magnetic path forming member is carburized and quenched to harden the surface, or the entire surface of the magnetic path forming member is carburized. The carburized surface portion of the magnetic path forming member excluding the sliding contact portion is cut, and the non-cut portion is hardened by surface hardening.

In the driving force transmission device according to the present invention,
The magnetic path forming member is a side wall of the outer rotating member, the outer rotating member is a bottomed cylindrical front housing made of a non-magnetic material, and is screwed into a rear end opening of the front housing to form the rear end. It is preferable that the outer rotating member includes a rear housing made of a magnetic material that covers the opening, and the rear housing forms a side wall of the outer rotating member.

In the above-described driving force transmitting device according to the present invention, a main clutch mechanism for transmitting torque between the two rotating members by frictional engagement between the two rotating members, An electromagnetic pilot clutch mechanism to be engaged, and a cam mechanism located between the main clutch mechanism and the pilot clutch mechanism for converting a frictional engagement force of the pilot clutch mechanism into a pressing force with respect to the main clutch mechanism. It is preferable that a clutch mechanism is constituted by the friction clutch and the control means.

[0014]

In the driving force transmission device according to the present invention, the power is supplied to the electromagnetic coil that constitutes the electromagnet.
A magnetic path circulating through the yoke supporting the electromagnet, the side wall of the outer rotating member, the friction clutch, the armature, the friction clutch, the side wall, and the yoke is formed, and the armature is attracted toward the friction clutch by a magnetic induction action. As a result, the armature presses the friction clutch to cause frictional engagement, thereby bringing both rotating members into a connected state in which torque can be transmitted by the frictional engaging force, and torque transmission is performed between the two rotating members according to the frictional engaging force. You.

Thus, in the driving force transmission device according to the present invention, the magnetic path forming member that forms the magnetic path between the electromagnet and the armature when the electromagnet is energized is made of a low-carbon magnetic material. The sliding portion of the magnetic path forming member has a high hardness surface. For this reason, the magnetic path forming member has a large magnetic permeability as a whole, a small coercive force, and a surface of only the sliding contact portion requiring high hardness is hard and has excellent heat resistance and corrosion resistance.

Therefore, in the driving force transmission device,
When the low coercive force of the magnetic path forming member can be ensured, and the high hardness at the required portion can be ensured, and when the supply of current to the electromagnet is stopped, the magnetic path forming member is formed. The existing magnetic path does not disappear quickly and there is no delay in response to the interruption of the magnetic path. Therefore, when the supply of current to the electromagnet is stopped, the operation of the friction clutch is immediately stopped, and the transmission of torque between the two rotating members is interrupted.

In the magnetic path forming member, the sliding contact portion is formed on the surface of high hardness by a surface hardening process, but the surface hardening process applied to the sliding contact portion of the magnetic path forming member is carburizing and quenching. By carburizing and quenching only the surface of the sliding portion of the magnetic path forming member, or by carburizing the entire surface of the magnetic path forming member, By cutting the carburized surface except for the sliding contact portion and quenching the non-cut portion, the surface can be easily hardened.

In the driving force transmission device according to the present invention,
The magnetic path forming member is a side wall of an outer rotating member. The outer rotating member is a bottomed cylindrical front housing made of a non-magnetic material, and is screwed to a rear end opening of the front housing to form the rear end opening. If the rear housing is formed on the side wall of the outer rotating member, the rear housing can be configured to have a large magnetic permeability and a small coercive force, so that sliding contact can be achieved. Only the part can be easily subjected to a surface hardening treatment.

In each of the above-described driving force transmitting devices according to the present invention, a main clutch mechanism for transmitting torque between the two rotating members by frictional engagement between the two rotating members, An electromagnetic pilot clutch mechanism that engages, and a cam mechanism that is located between the main clutch mechanism and the pilot clutch mechanism and converts the frictional engagement force of the pilot clutch mechanism into a pressing force on the main clutch mechanism, the pilot clutch mechanism comprises: With a configuration formed by the friction clutch and the control means, the frictional engagement force of the pilot clutch mechanism can be smoothly and increased transmitted to the main clutch mechanism via the cam mechanism.

As a result, the main clutch mechanism is strongly frictionally engaged, so that the transmission torque between the two rotating members can be increased, and the driving force transmission characteristics of the driving force transmission device can be improved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 shows an example of a driving force transmission device according to the present invention. As shown in FIG. 3, the driving force transmission device 10 is disposed on a driving force transmission path to a rear wheel of a four-wheel drive vehicle.

In the four-wheel drive vehicle, the transaxle 21 integrally includes a transmission, a transfer, and a front differential, and outputs the driving force of the engine 22 to both axle shafts 23 a via the transaxle 21. Then, the left and right front wheels 23b are driven and output to the propeller shaft 24 side. The propeller shaft 24 is connected to the rear differential 25 via the driving force transmission device 10, and the propeller shaft 24 and the rear differential 2
When the transmission 5 is connected to transmit torque, the driving force is transmitted to the rear differential 25, and is output from the differential 25 to both axle shafts 26a to drive the left and right rear wheels 26b.

The driving force transmission device 10 is accommodated in a differential carrier 27 together with a rear differential 25 and supported by the carrier 27, and is supported by the vehicle body via the carrier 27.

FIG. 1 shows a half portion of the driving force transmission device 10 cut about the axis. The half portion (not shown) is formed substantially symmetrically about the axis. Omitted.

As shown in FIG. 1, the driving force transmitting device 10 includes an outer case 10a, which is an outer rotating member.
An inner shaft 10b, which is an inner rotating member, a main clutch mechanism 10c, a pilot clutch mechanism 10d, and a cam mechanism 10e are provided.

The outer case 10a comprises a front housing 11a having a bottomed cylindrical shape, and a rear housing 11b screwed into a rear end opening of the front housing 11a to cover the opening.
Is formed of an aluminum alloy which is a non-magnetic material, and the rear housing 11b is formed of iron which is a magnetic material. A stainless steel cylinder 11b1, which is a nonmagnetic material, is embedded in a radially intermediate portion of the rear housing 11b, and the cylinder 11b1 forms an annular nonmagnetic portion.

A nut member 11c is screwed on a screw portion formed on the outer periphery of the rear end of the rear housing 11b so as to be able to advance and retreat. The nut member 11c tightens the front housing 11a from the rear end side, and presses the threaded portion of the front housing 11a against the threaded portion of the rear housing 11b to eliminate play between these threaded portions.

The outer case 10a is rotatably supported by a differential carrier 27 at the outer periphery of the front end of the front housing 11a, and is supported by the differential carrier 27 at the outer periphery of the rear end of the rear housing 11b. . A rear end of the propeller shaft 24 is connected to a front end of the front housing 11a so as to transmit torque.

The inner shaft 10b is inserted into the front housing 11a through the center of the rear housing 11b in a liquid-tight manner, and is restricted from moving in the axial direction.
b is rotatably supported. Inner shaft 10b
, The tip of the drive pinion shaft 28 is inserted and connected to transmit torque.

The main clutch mechanism 10c is a wet-type multi-plate type friction clutch, and has a large number of clutch plates (inner clutch plate 12a, outer clutch plate 12b) and is disposed on the back wall side of the front housing 11a. ing. Each inner clutch plate 12a constituting the friction clutch is spline-fitted to the outer periphery of the inner shaft 10b and is assembled so as to be movable in the axial direction, and each outer clutch plate 12b is splined on the inner periphery of the front housing 11a. It is fitted and fitted so as to be movable in the axial direction. The respective inner clutch plates 12a and the respective outer clutch plates 12b are alternately positioned, abut against each other and frictionally engage with each other, and are separated from each other to be in a free state.

The pilot clutch mechanism 10d includes an electromagnet 13, a friction clutch 14, and an armature 15. The electromagnet 13 has an annular shape, and is fitted to the annular recess 11b2 of the rear housing 11b while being fitted to the yoke 16. The yoke 16 is supported by a differential carrier 27 via a conical spring 16a in an axially supported state, and is rotatably supported on the outer periphery of the rear end of the rear housing 11b. Thereby, the rear housing 11b and the yoke 1
6, a predetermined air gap is formed.

The friction clutch 14 is a multi-plate type friction clutch composed of a plurality of clutch plates (an inner clutch plate 14a and an outer clutch plate 14b), and each inner clutch plate 14a constitutes a first cam mechanism 10e described later. Each outer clutch plate 14b is spline-fitted to the inner periphery of the front housing 11a and spline-fitted to the outer periphery of the cam member 17 and is movably assembled in the axial direction. Have been. Each inner clutch plate 14a and each outer clutch plate 14b are located alternately,
They come into contact with each other and frictionally engage with each other, and are separated from each other and become free.

The armature 15 has an annular shape, and is spline-fitted to the inner periphery of the front housing 11a so as to be movable in the axial direction.
And is located on one side of the body.

In the above structure of the pilot clutch mechanism 10d, the outer case 10a corresponds to the outer rotating member of the present invention, and the rear housing 11b corresponds to the side wall of the outer rotating member. The yoke 16, the rear housing 11b,
Friction clutch 14, armature 15, friction clutch 1
4. A magnetic path is formed between the rear housing 11b and the yoke 16.

The power supply to the electromagnetic coil of the electromagnet 13 is turned on and off by a switch operation, so that three drive modes to be described later can be selected. The switch is provided near the driver's seat in the vehicle compartment, so that the driver can easily operate the switch. However, this switch is not always necessary.

The cam mechanism 10e includes a first cam member 17, a second cam member 18, and a cam follower 19. In the first cam member 17 and the second cam member 18, a plurality of cam grooves opposing each other are formed on the opposing surfaces at predetermined intervals in the circumferential direction. The first cam member 17 is
It is rotatably fitted to the outer periphery of the inner shaft 10b,
The inner clutch plate 14a of the friction clutch 14 is spline-fitted to the outer periphery of the rear housing 11b.

The second cam member 18 is connected to the inner shaft 10.
B is spline-fitted to the outer periphery of b and assembled so as to be integrally rotatable, and is located facing the inner clutch plate 12a of the main clutch mechanism 10c. A ball-shaped cam follower 19 is interposed between the opposing cam grooves of the second cam member 18 and the first cam member 17.

Thus, in the driving force transmitting device 10, the armature 15 constituting the pilot clutch mechanism 10d is located on one side of the friction clutch 14 inside the front housing 11a, and 13 is located outside the front housing 11a on the other side of the friction clutch 14 across the rear housing 11b, and the rear housing 11b functions as a magnetic path forming member.

The rear housing 11b is fitted to the outer periphery of the inner shaft 10b in a liquid-tight and rotatable manner, and the front housing 10b is formed at the peripheral portion of the front side wall.
a, and is liquid-tightly and rotatably supported by the differential carrier 27 via an oil seal 27a on the outer periphery of the rear end portion of the rear cylinder portion.

The rear housing 11b is made of a low-carbon magnetic material, for example, an iron material having a carbon content of 0.1% by weight to 0.2% by weight.
The sliding contact portion 11b3 with 7a is subjected to a surface hardening treatment.

The surface hardening treatment of the sliding contact portion 11b3 is both a carburizing treatment and a quenching treatment. Only the surface of the sliding contact portion 11b3 is carburized and the surface is hardened by heat treatment or induction hardening. Alternatively, the entire surface of the rear housing 11b is carburized, and the sliding contact portion 11b3
The carburized surface portion except for the above is cut and the non-cut portion is quenched to harden the surface. Sliding contact part 11b
The carbon content of No. 3 is 0.35% by weight to 2.0% by weight.

In the driving force transmission device 10 having such a configuration, the electromagnet 1 constituting the pilot clutch mechanism 10d is used.
When the power is not supplied to the third electromagnetic coil, no magnetic path is formed, and the friction clutch 14 is in the non-engaged state.
Therefore, the pilot clutch mechanism 10d is in a non-operating state, and the first cam member 1 constituting the cam mechanism 10e is not operated.
7 is rotatable integrally with the second cam member 18 via the cam follower 19, and the main clutch mechanism 10c is in a non-operating state. Thus, the vehicle constitutes a two-wheel drive mode.

On the other hand, when the electromagnetic coil of the electromagnet 13 is energized, a magnetic path is formed in the pilot clutch mechanism 10 d, and the electromagnet 13 attracts the armature 15. For this reason, the armature 15 presses the friction clutch 14 to cause frictional engagement, connects the first cam member 17 of the cam mechanism 10e to the front housing 11a side, and
And a relative rotation is generated between them. As a result, the cam mechanism 1
0e, the cam followers 19 move the two cam members 17, 18
Are pressed away from each other.

As a result, the second cam member 18 is pressed toward the main clutch mechanism 10c, and
0c is frictionally engaged in accordance with the frictional engagement force of the friction clutch 14 to transmit torque between 10a and the inner shaft 10b. Therefore, the vehicle constitutes a four-wheel drive drive mode in which the propeller shaft 24 and the drive pinion shaft 28 are not directly connected. In this drive mode, the driving force distribution ratio between the front and rear wheels can be controlled from 100: 0 (two-wheel drive state) to 50:50 (direct-coupled four-wheel drive state) according to the traveling state.

When the current applied to the electromagnetic coil of the electromagnet 13 is increased to a predetermined value, the armature 15
, The armature 15 is strongly sucked, the frictional engagement force of the friction clutch 14 is increased, and the relative rotation between the cam members 17 and 18 is increased. As a result,
The cam follower 19 increases the pressing force on the second cam member 18 to bring the main clutch mechanism 10c into a connected state. Therefore, the vehicle constitutes a four-wheel drive drive mode in which the propeller shaft 24 and the drive pinion shaft 28 are directly connected.

As described above, in the driving force transmitting device 10, the yoke 16 supporting the electromagnet 13, the rear housing 11 b, the friction clutch 14, the armature 15, the friction clutch 14 A magnetic path circulating between the rear housing 11b and the yoke 16 is formed, and the armature 15 is attracted to the friction clutch 14 by a magnetic induction action. As a result, the armature 15 presses the friction clutch 14 to cause frictional engagement, and the frictional engagement brings the outer case 10a and the inner shaft 10b into a connected state in which torque can be transmitted. In this case, torque is transmitted according to the frictional engagement force.

Thus, in the driving force transmission device 10, when power is supplied to the electromagnetic coil of the electromagnet 13,
Housing 1 that forms a magnetic path between armature and armature 15
1b is made of a low-carbon magnetic material, and a sliding contact portion 11b3 of the rear housing 11b with the oil seal 27a is formed.
Is a high hardness surface. For this reason, the rear housing 11b has a high magnetic permeability as a whole, a small coercive force, and has only the sliding contact portion 11b3, which requires high hardness, having a hard surface and excellent heat resistance and corrosion resistance.

Accordingly, in the driving force transmission device 10, the low coercive force of the rear housing 11b can be ensured, and the high hardness at the required portion can be ensured, so that the electric current to the electromagnetic coil of the electromagnet 13 can be increased. If the supply of
The magnetic path formed in the rear housing 11b disappears quickly, and there is no delay in response to interruption of the magnetic path. Therefore, if the supply of current to the electromagnetic coil is stopped, the friction clutch 14 immediately stops its operation,
The transmission of torque between the outer case 10a and the inner shaft 10b is interrupted.

In the driving force transmitting device 10, the magnetic path forming member is screwed into the rear end opening of the front housing 11a to cover the rear end opening.
b, the rear housing 11b is configured to have a large magnetic permeability and a small coercive force, so that only the sliding contact portion 11b3 can be easily surface hardened.

[0050] In the driving force transmission device 10, between the outer case 10a and the inner shaft 10b,
Outer case 10a and inner shaft 1 by frictional engagement
Main clutch mechanism 10c for transmitting torque between 0b
And an electromagnetic pilot clutch mechanism 10d that is activated by energization and frictionally engages, and a frictional engagement force of the pilot clutch mechanism 10d that is located between the main clutch mechanism 10c and the pilot clutch mechanism 10d.
With the configuration including the cam mechanism 10e that converts the pressing force to 0c, the frictional engagement force of the pilot clutch mechanism 10d can be smoothly transmitted to the main clutch mechanism 10c via the cam mechanism 10e.

As a result, the main clutch mechanism 10c is strongly frictionally engaged, so that the transmission torque between the outer case 10a and the inner shaft 10b can be increased, and the driving force transmission characteristics of the driving force transmission device 10 are improved. be able to.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing a driving force transmission device according to an example of the present invention.

FIG. 2 is a cross-sectional view in which a part of a rear housing 11b which is a magnetic path forming member constituting an outer rotating member of the driving force transmission device is omitted.

FIG. 3 is a skeleton diagram of a vehicle equipped with the driving force transmission device.

[Explanation of symbols]

Reference numeral 10: driving force transmission device, 10a: outer case, 10b
... inner shaft, 10c ... main clutch mechanism, 10
d: pilot clutch mechanism, 10e: cam mechanism, 11
a: front housing, 11b: rear housing, 1
1b1 ... cylindrical body, 11b2 ... annular recess, 11b3 ... sliding contact part,
11c nut member, 12a inner clutch plate, 12b outer clutch plate, 13 electromagnet,
14: friction clutch, 14a: inner clutch plate, 14b: outer clutch plate, 15: armature, 16: yoke, 16a: conical spring, 17
... First cam member, 18 ... Second cam member, 19 ... Cam follower, 21 ... Transaxle, 22 ... Engine, 2
3a ... axle shaft, 23b ... front wheel, 24 ... propeller shaft, 25 ... rear differential, 26a ...
Axle shaft, 26b rear wheel, 27 differential carrier, 27a oil seal, 28 drive pinion shaft.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Kunihiko Suzuki 1-1-1, Asahi-cho, Kariya-shi, Aichi Prefecture Inside Toyota Koki Co., Ltd. (72) Koichi Suzuki 1-1, Toyota-cho, Toyota-shi, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-1-145434 (JP, A) JP-A-61-63383 (JP, A) JP-A-50-42250 (JP, A) JP-A-59-73631 (JP, A) Japanese Utility Model 57-21430 (JP, U) Japanese Utility Model 63-90809 (JP, U) Japanese Utility Model 7-14229 (JP, U) Japanese Utility Model 5-66339 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) F16D 27/10

Claims (7)

(57) [Claims] A friction clutch disposed between inner and outer rotating members coaxially and relatively rotatable with each other, and electromagnetic control means for operating by energization to frictionally engage the friction clutch; An armature located inside the outer rotating member and facing the friction clutch; and an electromagnet located outside the outer rotating member and facing the friction clutch across a side wall of the outer rotating member. The armature is attracted by energizing the electromagnet to frictionally engage the friction clutch, and the two rotating members are brought into a connected state capable of transmitting torque by the frictional engagement force of the friction clutch. A force transmission device, wherein a magnetic path forming member that forms a magnetic path between the electromagnet and the armature when the electromagnet is energized rotates integrally with the outer rotating member.
It has a cylindrical sliding contact part that is rotatably supported by
Road forming member be composed at a low carbon magnetic material, prior
Serial sliding contact portion is the driving force transmission device, characterized in that it comprises a surface of high hardness. 2. A driving force transmitting device according to claim 1, wherein said magnetic path forming member is rotatably supported by a part of a vehicle body.
Wherein the sliding portion of the magnetic path forming member is formed on a surface of high hardness by a surface hardening process. 3. The driving force transmitting device according to claim 2, wherein the surface hardening treatment applied to the sliding contact portion of the magnetic path forming member is both a carburizing treatment and a quenching treatment. A driving force transmission device characterized in that only the surface of the sliding contact portion is carburized and quenched to harden the surface. 4. The driving force transmitting device according to claim 2, wherein the surface hardening treatment applied to the sliding contact portion of the magnetic path forming member is both a carburizing treatment and a quenching treatment. A driving force transmission device characterized in that the entire surface is carburized, the carburized surface portion excluding the sliding contact portion of the magnetic path forming member is cut, and the non-cut portion is hardened to harden the surface. 5. The driving force transmission device according to claim 1, wherein the magnetic path forming member is a side wall of the outer rotating member. 6. A driving force transmission device according to claim 5, wherein said outer rotating member is screwed into a rear end opening of said front housing having a bottomed cylindrical shape made of a non-magnetic material. A driving force transmission device comprising: a rear housing made of a magnetic material that covers a rear end opening, wherein the rear housing forms a side wall of the outer rotating member. 7. A driving force transmitting device according to claim 1, wherein a torque is transmitted between said two rotating members by frictional engagement between said two rotating members. A mechanism, an electromagnetic pilot clutch mechanism that operates by energization and frictionally engages, and a frictional engagement force of the pilot clutch mechanism located between the main clutch mechanism and the pilot clutch mechanism to a pressing force on the main clutch mechanism. A driving force transmission device comprising: a cam mechanism for converting; and the pilot clutch mechanism includes the friction clutch and the control means.