JP2003278799A - Device for transmitting driving force - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the operational responsiveness of a multiple disc type friction clutch 14A by avoiding formation of oil films in a clearance between a clutch plate 14a of the friction clutch 14A and an armature 15 or a rear housing 11a which abuts the clutch plate, in a device for transmitting driving forces in which an outer case 10a with the multiple disc type friction clutch 14A frictionally engaged therewith is connected to an inner shaft 10b by an electromagnetic control means in such a manner that torques can be transmitted therebetween. <P>SOLUTION: The clutch plate 14a is provided with a number of waste oil channels 14a3 on its opposite surfaces 14a1 and 14a2 opposite to the armature 15 and the rear housing 11b, respectively, to assist in discharging oil that may form oil films between the armature 15 and the rear housing 11b. <P>COPYRIGHT: (C)2004,JPO

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 which is disposed between rotary members such as a drive shaft and a driven shaft of a vehicle to transmit torque between the rotary members.

[0002]

2. Description of the Related Art As a type of driving force transmission device, as proposed by the name of "multi-disc clutch", a multi-disc clutch disposed between both inner and outer rotating members coaxially and relatively rotatable with each other. A plate-type friction clutch, and an electromagnetic control unit that is actuated by energization to frictionally engage the friction clutch, the control unit being located inside the outer rotation member and facing the friction clutch. A configuration including an electromagnet located outside the outer rotating member and facing the friction clutch with a side wall of the outer rotating member interposed therebetween,
There is provided a driving force transmission device of a type in which the armature is attracted by energizing the electromagnet to frictionally engage the friction clutch, and the friction engagement force of the friction clutch causes the rotating members to be in a coupled state capable of transmitting torque. There is (see Patent Document 1).

However, in the driving force transmission device (multi-plate clutch) proposed in the above-mentioned Patent Document 1,
The differential case is adopted as the outer rotating member, and the planet carrier hub is adopted as the inner rotating member.
The electromagnetic control means is composed of an armature (pressing ring) located on one side of the friction clutch and an electromagnet located across a part (magnetic material wall section) located on the other side of the friction clutch in the differential case. .

In the driving force transmission device, by energizing the electromagnetic coil of the electromagnet, a magnetic path for circulating the yoke, the magnetic wall of the differential case, the friction clutch, the armature, the friction clutch, the magnetic wall and the yoke is formed. Then, the armature is attracted to the friction clutch side by the magnetic induction action. As a result, the armature presses the friction clutch into frictional engagement, and the frictional engagement force directly or actuates the main clutch mechanism to couple the rotating members so that torque can be transmitted.

[0005]

[Patent Document 1] Utility model registration No. 2525611

[0006]

By the way, in the driving force transmission device of the above-mentioned type, the magnetic wall portion of the differential case and the clutch plate of the friction clutch facing the magnetic wall portion,
Also, since the armature and the clutch plate of the friction clutch that faces the armature are configured so as not to rotate relative to each other, an oil film may be formed in the gap between the magnetic wall and the clutch plate and the gap between the armature and the clutch plate. However, if an oil film is formed in these gaps, there is a problem in that the responsiveness of the operation of the friction clutch is reduced and an operation delay occurs. Therefore, it is an object of the present invention to address such issues.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a driving force transmission device, and more particularly, to a cylindrical outer rotating member whose one end side opening is closed by a side wall, and a state where the outer side rotating member penetrates the side wall. An inner rotating member that is rotatably supported and is coaxially positioned inside the outer rotating member, a multi-plate friction clutch that is arranged between these rotating members, and an electric current that is arranged between these rotating members. The present invention relates to a driving force transmission device that includes an electromagnetic control unit that operates to frictionally engage the friction clutch, and that rotates both the rotating members even when the power supply to the control unit is stopped.

A driving force transmission device to which the present invention is applied is the above-described driving force transmission device, wherein the control means is located inside the side wall of the outer rotating member and faces the friction clutch. An armature and an electromagnet that is positioned outside the side wall of the outer rotating member and faces the friction clutch with the side wall sandwiched therebetween are provided. By energizing the electromagnet, the armature is attracted to the friction clutch. It is a driving force transmission device of a type which is frictionally engaged and is in a connected state capable of transmitting torque by the frictional engagement force of the friction clutch.

Therefore, the first driving force transmitting device according to the present invention is the driving force transmitting device of the above-mentioned type, wherein the clutch plate of the friction clutch facing the armature is rotatable relative to the armature. When the energization of the electromagnet is stopped, the rotation of both the rotating members causes the armature to rotate integrally with the armature. At least one of the opposing surfaces of the clutch plate and the armature is provided with an oil film breakage promoting means. It is characterized by that.

A second driving force transmitting device according to the present invention is the driving force transmitting device of the above-mentioned type, wherein the clutch plate facing the side wall of the outer rotating member in the friction clutch is not the same side wall. Relative rotation is possible, and when the energization of the electromagnet is stopped, it is configured to rotate integrally with the side wall by the rotation of the both rotating members, and at least one of the opposing surfaces of the clutch plate and the side wall is provided with an oil film breakage promoting means. It is characterized by being.

In each of the driving force transmission devices according to the present invention, the oil film breakage promoting means may be the clutch plate, the armature, or a plurality of oil drain grooves formed on the opposing surfaces of the side walls.

Further, in each of the driving force transmission devices according to the present invention, a main clutch mechanism for transmitting torque between the both rotary members by frictional engagement between the both rotary members, and an energized operation mechanism. An electromagnetic pilot clutch mechanism that frictionally engages, and a cam mechanism that is located between the main clutch mechanism and the pilot clutch mechanism and that converts the frictional engagement force of the pilot clutch mechanism into a pressing force for the main clutch mechanism. Further, the pilot clutch mechanism may be configured to include the friction clutch and the control means.

[0013]

In the driving force transmission device according to the present invention, by energizing the electromagnetic coil forming the electromagnet,
A magnetic path that circulates through the yoke that supports 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 to the friction clutch side by the magnetic induction action. As a result, the armature presses the friction clutch for frictional engagement, and the frictional engagement force brings both rotary members into a coupled state capable of transmitting torque, and torque transmission according to the frictional engagement force is performed between both rotary members. It

Therefore, in the first driving force transmitting apparatus according to the present invention, the clutch plate facing the armature in the friction clutch is configured to be rotatable relative to the armature, and the facing surfaces of the clutch plate and the armature are arranged. Although an oil film is formed in the gap between them, the oil film breakage promoting means that is formed on at least one of the opposing surfaces of the clutch plate and the armature accelerates the oil film breakage, so that the response of the friction clutch operation caused by the oil film formation There is no possibility that operation delay will occur due to deterioration of the property.

In this case, the armature can function as one of the clutch plates of the friction clutch,
The friction clutch having the same function can be made compact.

Further, in the second driving force transmission device according to the present invention, the clutch plate facing the side wall of the outer rotating member in the friction clutch is configured to be rotatable relative to the side wall, and the clutch plate and the side wall are provided. Although an oil film is formed in the gap between the opposed surfaces of the friction clutch, the oil film breakage promoting means formed on at least one of the opposed surfaces of the clutch plate and the side wall promotes the oil film breakage. There is no possibility that the responsiveness of the operation is lowered and the operation is delayed.

In this case, the side wall of the outer rotating member can function as one of the clutch plates of the friction clutch, and the friction clutch having the same function can be made compact.

In the driving force transmission device according to the present invention, the clutch plate facing the armature in the friction clutch is configured to be rotatable relative to the armature, and faces the side wall of the outer rotating member in the friction clutch. When the clutch plate to be rotated is configured to be rotatable relative to the side wall, the oil film breakage promoting means is provided on at least one of the facing surfaces of the clutch plate and the armature and at least one of the facing surfaces of the clutch plate and the side wall. And

As a result, it is possible to promote the oil film breakage between the clutch plate and the armature and between the clutch plate and the side wall, and more effectively prevent the reduction in the responsiveness of the operation of the friction clutch due to the formation of the oil film. In addition, the friction clutch can be made more compact.

Further, in each of the above-mentioned driving force transmission devices according to the present invention, a main clutch mechanism for transmitting torque between the rotating members by frictional engagement between the rotating members, and friction by operating by energization. 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 that converts the frictional engagement force of the pilot clutch mechanism into a pressing force for the main clutch mechanism. With the structure formed by the friction clutch and the control means, the friction 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, in the driving force transmission device, the main clutch mechanism is strongly frictionally engaged to increase the transmission torque between both rotary members, and the driving force transmission characteristic of the driving force transmission device is improved. Can be improved.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a driving force transmission device, and FIG. 1 shows a driving force transmission device of the type to which the present invention is applied. As shown in FIG. 4, the drive force transmission device 10 is arranged in the drive force transmission path to the rear wheel side of the vehicle to form 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 23a via the transaxle 21. 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 through the driving force transmission device 10, and when the propeller shaft 24 and the rear differential 25 are connected by the driving force transmission device 10 so that torque can be transmitted. Drive force is transmitted to the rear differential 25, and is output from the differential 25 to both axle shafts 26a, so that the left and right rear wheels 2
6b is driven.

The driving force transmission device 10 includes the differential carrier 2 as well as the rear differential 25.
It is housed in 7 and supported by the carrier 27, and is supported by the vehicle body via the carrier 27. Note that FIG. 1 shows a half part of the driving force transmission device 10 cut along the axis, and the half part not shown is omitted because it is formed substantially symmetrically about the axis. .

As shown in FIG. 1, the driving force transmission 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. Is equipped with.

The outer case 10a comprises a bottomed cylindrical front housing 11a and a rear housing 11b screwed into the 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 cylindrical body 11b1 made of stainless steel, which is a non-magnetic material, is embedded in an intermediate portion in the radial direction of the rear housing 11b, and the cylindrical body 11b1 forms an annular non-magnetic portion.

A nut member 11c is screwed so as to be capable of advancing and retracting to a screw portion formed on the outer peripheral portion of the rear end of the rear housing 11b. The nut member 11c tightens the front housing 11a from the rear end side and presses the screw portion of the front housing 11a against the screw portion of the rear housing 11b to eliminate the looseness between these screw portions.

The outer case 10a is rotatably supported by the 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 portion of the propeller shaft 24 is coupled to the front end portion of the front housing 11a so that torque can be transmitted.

The inner shaft 10b is inserted into the front housing 11a by penetrating the central portion of the rear housing 11b in a liquid-tight manner, and is restricted from moving in the axial direction.
It is rotatably supported by 1b. Inner shaft 10
The tip of the drive pinion shaft 28 is inserted into b and is connected so that torque can be transmitted.

The main clutch mechanism 10c is a wet multi-plate type friction clutch, which is provided with a large number of clutch plates (inner clutch plate 12a, outer clutch plate 12b) and is arranged on the inner wall side of the front housing 11a. ing. Each inner clutch plate 12a constituting the friction clutch is spline-fitted to the outer circumference of the inner shaft 10b and is movably assembled in the axial direction, and each outer clutch plate 12b is splined to the inner circumference of the front housing 11a. It is fitted and assembled so as to be movable in the axial direction. The inner clutch plates 12a and the outer clutch plates 12b are alternately located, abutting against each other for frictional engagement, and 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 in the yoke 16 and fitted in the annular recess 11b2 of the rear housing 11b. The yoke 16 includes a conical spring 16 and a differential carrier 27.
is supported in a state of being axially supported via a,
It is rotatably supported on the outer periphery of the rear end of the rear housing 11b. As a result, a predetermined air gap is formed between the rear housing 11b and the yoke 16.

The friction clutch 14 is a multi-plate friction clutch consisting of a plurality of clutch plates (inner clutch plate 14a, outer clutch plate 14b), and each inner clutch plate 14a constitutes a first cam mechanism 10e which will be described later. The cam member 17 is assembled by spline fitting so as to be movable in the axial direction, and each outer clutch plate 14b is assembled by spline fitting on the inner circumference of the front housing 11a so as to be movable in the axial direction. Has been. The inner clutch plates 14a and the outer clutch plates 14b are alternately located,
They come into contact with each other and frictionally engage with each other, and are separated from each other to be in a free state.

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

In the above construction 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. To the yoke 16, the rear housing 11b, and
Friction clutch 14, armature 15, friction clutch 1
4, a magnetic path is formed between the rear housing 11b and the yoke 16. It should be noted that the energization of the electromagnetic coil of the electromagnet 13 is interrupted by switching the switch, and will be described later.
It is possible to select one drive mode. The switch is arranged near the driver's seat in the vehicle compartment so that the driver can easily operate it. However, this switch is not always necessary.

The cam mechanism 10e comprises a first cam member 17, a second cam member 18, and a cam follower 19. First cam member 17 and second cam member 18
Has a plurality of cam grooves opposed to each other formed on the opposed surface at predetermined intervals in the circumferential direction. First cam member 17
Is rotatably fitted to the outer periphery of the inner shaft 10b and rotatably supported by the rear housing 11b, and the inner clutch plates 14a of the friction clutch 14 are spline-fitted to the outer periphery thereof.

The second cam member 18 serves as the inner shaft 10.
It is spline-fitted to the outer periphery of b and is integrally rotatably assembled, and is located to face the inner clutch plate 12a of the main clutch mechanism 10c. A ball-shaped cam follower 19 is interposed in the cam grooves of the second cam member 18 and the first cam member 17 which face each other.

In the driving force transmission device 10 having such a structure, the electromagnet 1 which constitutes the pilot clutch mechanism 10d.
When the electromagnetic coil 3 is not energized, the magnetic path is not formed and the friction clutch 14 is in the non-engaged state. For this reason, the pilot clutch mechanism 10d is in a non-operating state, and the first cam member 17 constituting the cam mechanism 10e has the second cam member 1 via the cam follower 19.
8 and the main clutch mechanism 10c are in a non-actuated state. Therefore, 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 10d, and the electromagnet 13 attracts the armature 15. Therefore, the armature 15 presses the friction clutch 14 into frictional engagement, connects the first cam member 17 of the cam mechanism 10e to the front housing 11a side, and connects the first cam member 17 to the front cam member 17a.
And the second cam member 18 are caused to rotate relative to each other. As a result, in the cam mechanism 10e, the cam follower 19 presses the two cam members 17, 18 in the direction in which they are separated from each other.

As a result, the second cam member 18 is pressed toward the main clutch mechanism 10c and the main clutch mechanism 1
0c is frictionally engaged according to the frictional engagement force of the friction clutch 14 to transmit torque between the outer case 10a and the inner shaft 10b. Therefore, the vehicle configures a four-wheel drive mode in which the propeller shaft 24 and the drive pinion shaft 28 are not directly connected. In this drive mode, the drive force distribution ratio between the front and rear wheels is set to 10 depending on the running state.
It can be controlled from 0: 0 (two-wheel drive state) to 50:50 (direct-connection four-wheel drive state).

When the current applied to the electromagnetic coil of the electromagnet 13 is increased to a predetermined value, the armature 15 of the electromagnet 13 is increased.
, The armature 15 is strongly attracted to increase the friction engagement force of the friction clutch 14 and increase the relative rotation between the cam members 17 and 18. 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 the engaged state. Therefore, the vehicle constitutes a four-wheel drive mode in which the propeller shaft 24 and the drive pinion shaft 28 are directly connected.

As described above, in the driving force transmission device 10, the yoke 16 that supports the electromagnet 13, the rear housing 11b, the friction clutch 14, the armature 15, and the friction clutch 14 are generated by energizing the electromagnetic coils that form the electromagnet 13. , Rear housing 11b, and yoke 16
A magnetic path that circulates between them is formed, and the armature 15 is attracted to the friction clutch 14 side by the magnetic induction effect. As a result, the armature 15 presses the friction clutch 14 into frictional engagement, and the outer case 10 is engaged by this frictional engagement.
The a and the inner shaft 10b are connected to each other so that torque can be transmitted, and torque is transmitted between the outer case 10a and the inner shaft 10b according to the frictional engagement force.

Therefore, in the driving force transmission device 10 to which the present invention is applied, the friction clutch 14 constituting the pilot clutch mechanism 10d has three inner clutch plates 14a and four outer clutch plates 14b. The inner outer clutch plate 14b faces the armature 15, and the outer outer clutch plate 14b faces the rear housing 11b.

Similar to the armature 15, the armature 15 and the outer clutch plate 14b facing the armature 15 have inner splines 11a1 of the front housing 11a.
Is fitted to the front housing 11a so as to be integrally rotatable with the armature 15.

Further, the outer clutch plate 14b facing the rear housing 11b is the front housing 1
It is spline-fitted to the inner spline 11a1 of 1a and is rotatably assembled to the front housing 11a and is also rotatable integrally with the rear housing 11b.

On the other hand, in the driving force transmission device 10A according to the embodiment of the present invention, the friction clutch 14A constituting the pilot clutch mechanism 10d has the configuration shown in FIG. FIG. 2 is a cross-sectional view showing a portion where the pilot clutch mechanism 10f is provided, which constitutes the driving force transmission device 10A according to the embodiment of the present invention.

The pilot clutch mechanism 10f includes the electromagnet 13, the friction clutch 14A, and the armature 1.
5 is that the pilot clutch mechanism 10d
It has the same configuration as. However, in the driving force transmission device 10A, the friction clutch 14A is composed of three inner clutch plates 14a and two outer clutch plates 14b, and
The inner inner clutch plate 14a has an armature 15
Is assembled to the first cam member 17 so as to face the rear inner housing and the outer inner clutch plate 14a is attached to the rear housing 11
It is different from the pilot clutch mechanism 10d in that it is assembled to the first cam member 17 so as to face b.

Therefore, in the friction clutch 10A, the inner inner clutch plate 14a and the armature 15 rotate relative to each other, and the outer inner clutch plate 14a and the rear housing 11b rotate relative to each other.

In the friction clutch 10A having such a structure, the opposing surface 14a1 of the inner inner clutch plate 14a facing the armature 15 and the opposing surface 14a2 of the outer inner clutch plate 14a facing the rear housing 11b are shown in FIG. As shown in FIG. 5, the oil drain groove 14a is formed on the entire surface thereof. Further, the facing surface 15a of the armature 15 facing the inner inner clutch plate 14a and the facing surface 11b3 of the rear housing 11b facing the outer inner clutch plate 14a are nitrided. 15a and the facing surface 11b3 are provided with high hardening property, wear resistance and corrosion resistance.

Pilot clutch mechanism 10 having such a structure
The driving force transmission device 10A including the f operates in the same manner as the driving force transmission device 10 including the pilot clutch mechanism 10d, and has the same effects and advantages.
In particular, the following operational effects are exhibited.

That is, the pilot clutch mechanism 10f
, The armature 1 in the friction clutch 14A
The inner clutch plate 14a facing 5 is rotatable relative to the armature 15 and the rear housing 11b.
The inner clutch plate 14a facing each other is rotatable relative to the rear housing 11b, and the armature 15 and the rear housing 11 of each inner clutch plate 14a are rotatable.
The oil drain groove 14a3 is formed on the facing surfaces 14a1 and 14a2 facing b.
Are formed.

The oil drain groove 14a3 accelerates the oil film breakage between the inner clutch plate 14a and the armature 15 and between the inner clutch plate 14a and the rear housing 11b, and responds to the operation of the friction clutch 14A due to the formation of the oil film. In the driving force transmission device 10A, the oil drain grooves 14a3 are formed in the facing surfaces 14a1 and 14a2 of each inner clutch plate 14a, but the armature 15 facing the inner clutch plate 14a is not formed. Opposed surface 15a and opposed surface 1 of rear housing 11b opposed to inner clutch plate 14a.
An oil drain groove may be formed in 1b3.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a driving force transmission device of a type to which the present invention is applied.

FIG. 2 is a partial cross-sectional view showing an arrangement portion of a pilot clutch mechanism that constitutes the driving force transmission device according to the embodiment of the present invention.

FIG. 3 is a front view of an inner clutch plate that constitutes the pilot clutch mechanism.

FIG. 4 is a skeleton diagram of a vehicle equipped with the driving force transmission device.

[Explanation of symbols]

10, 10A ... Driving force transmission device, 10a ... Outer case, 10b ... Inner shaft, 10c ... Main clutch mechanism, 10d, 10f ... Pilot clutch mechanism, 10
e ... Cam mechanism, 11a ... Front housing, 11a1
… Inner spline, 11b… Rear housing, 11b1…
Cylindrical body, 11b2 ... annular recess, 11b3 ... facing surface, 11c ...
Nut member, 12a ... Inner clutch plate, 12b
... Outer clutch plate, 13 ... Electromagnet, 14, 14
A ... Friction clutch, 14a ... Inner clutch plate,
14a1, 14a2 ... Opposing surface, 14a3 ... Oil drain groove, 14b
Outer clutch plate, 15 Armature, 15a
... facing surface, 16 ... yoke, 16a ... conical spring, 17 ... first cam member, 18 ... second cam member, 19 ...
Cam follower, 21 ... Transaxle, 22 ... Engine, 23a ... Axle shaft, 23b ... Front wheel, 24
… Propeller shaft, 25… Rear differential,
26a ... axle shaft, 26b ... rear wheel, 27 ... differential carrier, 28 ... drive pinion shaft.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koichi Suzuki             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Akihiko Ikeda             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd.

Claims (4)

[Claims] 1. A cylindrical outer rotating member whose one end side opening is closed by a side wall, and an inner side which is rotatably supported in a state of penetrating the side wall and is coaxially positioned inside the outer rotating member. A rotary member, a multi-plate friction clutch arranged between the rotary members, and an electromagnetic control unit arranged between the rotary members and operated by energization to frictionally engage the friction clutch. A driving force transmission device in which both the rotating members rotate together even when the energization to the control means is stopped, the control means being located inside the side wall of the outer rotation member and facing the friction clutch. And an electromagnet that is located outside the side wall of the outer rotating member and faces the friction clutch with the side wall interposed therebetween. The armature is attracted by energizing the electromagnet. In a drive force transmission device that frictionally engages the friction clutch and brings the rotating members into a coupled state capable of transmitting torque by the friction engagement force of the friction clutch, the clutch plate facing the armature in the friction clutch is the same. The armature is relatively rotatable, and is configured to rotate integrally with the armature by the rotation of both the rotating members when the energization of the electromagnet is stopped,
A driving force transmission device characterized in that oil film breakage promoting means is provided on at least one of the opposing surfaces of the clutch plate and the armature. 2. A cylindrical outer rotating member whose one end side opening is closed by a side wall, and an inner side which is rotatably supported while penetrating the side wall and is coaxially positioned inside the outer rotating member. A rotary member, a multi-plate friction clutch arranged between the rotary members, and an electromagnetic control unit arranged between the rotary members and operated by energization to frictionally engage the friction clutch. A driving force transmission device in which both the rotating members rotate together even when the energization to the control means is stopped, the control means being located inside the side wall of the outer rotation member and facing the friction clutch. And an electromagnet that is located outside the side wall of the outer rotating member and faces the friction clutch with the side wall interposed therebetween. The armature is attracted by energizing the electromagnet. In a driving force transmission device that frictionally engages the friction clutch and brings the rotating members into a coupled state capable of transmitting torque by the friction engagement force of the friction clutch, the driving force transmitting device faces a side wall of the outer rotating member of the friction clutch. The clutch plate is rotatable relative to the side wall, and is configured to rotate integrally with the side wall by the rotation of the rotating members when the energization of the electromagnet is stopped, and at least one of the opposing surfaces of the clutch plate and the side wall. A driving force transmission device characterized in that an oil film breakage promoting means is provided in the. 3. The driving force transmission device according to claim 1 or 2, wherein the oil film breakage promoting means is a plurality of oil drain grooves formed on the opposing surfaces of the clutch plate, the armature, or the side wall. Characteristic driving force transmission device. 4. The driving force transmission device according to claim 1, 2 or 3, wherein a main clutch mechanism for transmitting torque between the rotating members by frictional engagement between the rotating members, and an energized operation. And an electromagnetic pilot clutch mechanism that frictionally engages with each other, and a cam mechanism that is located between the main clutch mechanism and the pilot clutch mechanism and that converts the frictional engagement force of the pilot clutch mechanism into a pressing force for the main clutch mechanism. The driving force transmission device, wherein the pilot clutch mechanism is composed of the friction clutch and the control means.