JP2000346099A - Power transmission mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate backlash. SOLUTION: When an input side member 1 receives an input rotating power from a driving source to rotate, a part of the input rotating power is converted into an axial force by the fit between a nearly V shaped recessed cam 5a and a projected cam 5b, and an intermediate member 3 is axially displaced to the output side against a spring 4. As the intermediate member 3 is axially displaced to the output side, a friction clutch 7 is released, and the intermediate member 3 can rotate in relation to a stationary side member 6. On the other hand, when the driving source is stopped, the intermediate member 3 is axially displaced to the input side against pressing energizing force of the spring 4, and the friction clutch 7 is operated to restrict the intermediate member 3 in the direction of rotation with respect to the stationary side member 6 without causing backlash.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transmission mechanism used for a drive device such as a power seat and a power window of an automobile.

[0002]

2. Description of the Related Art FIG. 12 conceptually shows a slide driving device for a power seat of an automobile. The seat 21 includes a seat 22 and a backrest seat 23. The seat 22 is slidably mounted on a slide rail (not shown) provided on the floor of the vehicle body, and the backrest 23 is attached to the seat 22 so as to be tiltable. A rack 24 is disposed on the floor of the vehicle body in parallel with the slide rails, and a driving device mainly including a pinion 25 meshing with the rack 24, a power transmission mechanism 26, and a driving motor 27 is disposed on the seat 22 side. Is done.

When the drive motor 27 is operated, its rotational power is transmitted to the pinion 25 via the power transmission mechanism 26, and the pinion 25 moves on the rack 24 while rotating, so that the seat 22 is moved to the slide rail. Slide along. When the drive motor 27 is stopped when the seat 22 has moved to the desired position, the rotation of the pinion 25 due to the reverse input from the seat 21 is restrained by the power transmission mechanism 26, and the seat 22 is Is held in that position.

As described above, the power transmission mechanism in this type of drive device transmits the input rotational power from the drive source to the driven side (the seat 22 in the above example) and also when the drive source is stopped. In addition, a function of restraining the reverse input rotational power from the driven side and holding the driven side member (the seat 22) in that position is required. Conventionally, as a power transmission mechanism having such a function, a mechanical clutch utilizing a meshing action of uneven teeth and a wedge action by an engaging element such as a roller, a ball, and a sprag has been used.

[0005]

The mechanical clutch as described above has a backlash caused by a mesh gap between the uneven teeth and a time lag of engaging and disengaging the wedge of the engaging element.
Therefore, when the drive source is stopped, a phenomenon (rattle) occurs in which the driven member slightly moves due to reverse input. This phenomenon is
For example, in a power seat of an automobile, the seating comfort is affected.

Accordingly, the present invention is to solve the problem of backlash in this type of power transmission mechanism.

[0007]

SUMMARY OF THE INVENTION To solve the above problems, the present invention provides an input member rotatable about an axis, and an output member coaxially arranged with the input member and rotatable about the axis. An intermediate member provided non-rotatably and axially movable with respect to the output-side member, an elastic member that presses and biases the intermediate member toward the input side, and is provided between the input-side member and the intermediate member, By the cam fitting, the rotational power from the input side member is transmitted to the intermediate member, and at the same time, the propulsion cam means for axially displacing the intermediate member toward the output side against the elastic member, and between the intermediate member and the stationary side member. The intermediate member is normally restrained without backlash in the rotational direction with respect to the stationary member, and when the intermediate member is axially displaced toward the output side against the elastic member, the restrained state is released. The member can be rotated with respect to the stationary member The input rotation power from the input member is transmitted to the output member through the propulsion cam means and the intermediate member, and the reverse input rotation power from the output member is transmitted through the clutch means to the intermediate rotation power. A power transmission mechanism for restraining between a member and a stationary side member is provided. Since the reverse input rotational power from the output side member is restrained between the intermediate member and the stationary side member via the clutch means without backlash, the output side member does not rattle when the drive source is stopped. .

From the same viewpoint, an input member rotatable about an axis, an output member coaxially disposed with the input member and rotatable about an axis, and an input member between the input member and the output member. An intermediate member provided so as to be movable in the axial direction,
An elastic member that presses and biases the intermediate member toward the input side, and is provided between the input side member and the intermediate member. By cam fitting, rotational power is transmitted between the input side member and the intermediate member, and at the same time, between the two members. The input side propulsion cam means that generates an axial force on the output side member and the intermediate member are provided between the output side member and the intermediate member by cam fitting. Output side propulsion cam means for generating an axial force, provided between the intermediate member and the stationary side member,
A restrained state in which the intermediate member is restrained without backlash in the rotational direction with respect to the stationary member, and a released state in which the intermediate member is rotatable with respect to the stationary member by axial displacement to the output side of the intermediate member. Switchable clutch means, and when transmitting power from the input side, the intermediate member is axially displaced to the output side by an axial force generated by the input side propulsion cam means, and the clutch means is released, and Provided is a power transmission mechanism that, when power is transmitted from an output side, presses an intermediate member toward an input side by an axial force generated by an output-side propulsion cam means to place a clutch means in a restrained state. As a result, power transmission independent of the restraining force of the friction clutch 70 is possible.

In this case, if the axial force generated by the input-side propulsion cam means is set to be larger than the resultant force of the elastic force of the elastic member and the axial reaction force generated by the output-side propulsion cam means, the intermediate member is moved to the output side. Can be easily displaced in the axial direction.
Also, if a gap is provided between the cam surfaces of the input-side propulsion cam means when the clutch means is in the restrained state, the operation of the input-side propulsion cam means at the time of reverse input from the output side (rotation of the input-side member) Can be reliably prevented.

[0010] As the clutch means in the above configuration, a friction clutch having friction surfaces which can be pressed against each other can be adopted. In that case, the friction surface may be an inclined surface that is inclined in a direction to decrease toward the input side. Further, in order to increase the restraining force on the intermediate member, the friction surface can be subjected to a surface treatment for increasing a friction coefficient. As the surface treatment, specifically, application of a lubricant, chemical surface treatment, or surface roughening by machining can be employed. These surface treatments can be performed alone or in combination of two or more.

Further, as the clutch means in the above configuration, it is possible to employ a meshing clutch having uneven teeth which mesh with each other without backlash in the rotational direction. In that case, the circumferential wall surfaces of the uneven teeth can be pressed into a wedge shape with each other at the time of meshing. More specifically, the circumferential cross section of the uneven tooth can be trapezoidal or triangular.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a power transmission mechanism A according to an embodiment.
Is shown. The power transmission mechanism A includes an input-side member 1 rotatable about an axis X and an output-side member 2 disposed coaxially with the input side member 1 and rotatable about the axis X.
And an intermediate member 3 attached to the output side member 2, an elastic member such as a spring 4 interposed between the intermediate member 3 and the output side member 2, and between the input side member 1 and the intermediate member 3. , And a clutch means, for example, a friction clutch 7 provided between the intermediate member 3 and a stationary member 6 such as a housing. In this embodiment, the propulsion cam means 5 includes the input side member 1.
And a convex cam 5b provided on the end face of the intermediate member 3 facing the concave cam 5a.

As shown in FIG. 2, the input side member 1 has a boss hole 1a on the inner periphery for connecting another shaft member (not shown). Also, on one end surface of the input-side member 1,
For example, three substantially V-shaped concave cams 5a are provided at equal circumferential intervals. In this embodiment, the concave cam 5a is formed integrally with the input side member 1. However, a separate cam member having the concave cam 5a may be fixed to the end face of the input side member 1 so as to be relatively non-rotatable.

As shown in FIG. 3, the intermediate member 3 has, for example, a slide spline hole 3a on the inner periphery thereof, and the slide spline hole 3a is fitted into a slide spline 2a formed on the outer periphery of the output side member 2. By this, the output side member 2
It is mounted so that it cannot rotate and can move in the axial direction. On one end surface of the intermediate member 3, for example, three substantially V-shaped convex cams 5b are provided at equal circumferential intervals. Each of the convex cams 5b is fitted with each of the concave cams 5a of the input side member 1 to form the propulsion cam means 5. In this embodiment, the convex cam 5b is formed separately from the intermediate member 3 and is fixed to one end surface of the intermediate member 3 so as not to rotate relatively. However, the convex cam 5b is formed integrally with the intermediate member 3. You may. On the outer periphery of the intermediate member 3, a conical friction surface 7a having a slight inclination angle θ with respect to the axis X is formed.
The direction of the inclination of the friction surface 7a is a direction in which the diameter decreases toward the input side (the right side in the figure).

As shown in FIG. 1, a conical friction surface 7b which is adapted to the friction surface 7a of the intermediate member 3 is formed on the inner periphery of the stationary-side member 6, and friction between the friction surface 7a and the friction surface 7b. The clutch 7 is configured.

The spring 4 is housed in an annular recess 3 b provided in the intermediate member 3, and is compressed and interposed between the spring 4 and a flange 2 b provided in the output side member 2.

The intermediate member 3 is always urged in the axial direction by the elastic force of the spring 4 toward the input side (the right side in the figure). Therefore, the friction surface 7a of the intermediate member 3 comes into pressure contact with the friction surface 7b of the stationary member 6 to operate the friction clutch 7, whereby the intermediate member 3 is restrained against the stationary member 6 without backlash in the rotational direction. Is done.

The binding force (braking force) of the friction clutch 7 is mainly determined by the elastic force F of the spring 4, the inclination angle θ of the friction surface 7a and the friction surface 7b, and the friction coefficient μ in the operation principle shown in FIG. The inclination angle θ is preferably set to, for example, about 3 to 5 °. Further, in order to increase the binding force (braking force) of the friction clutch 7, the friction surface 7a and / or the friction surface 7b can be subjected to a surface treatment for increasing the friction coefficient μ. As the surface treatment, for example, application of a lubricant, chemical surface treatment, and surface roughening by machining (knurling or the like) can be adopted. These surface treatments can be performed alone or in combination of two or more.

In FIG. 1, when the input side member 1 is rotated by receiving input rotational power from a drive source (not shown),
A part of the input rotational power is converted into an axial force by fitting a substantially V-shaped concave cam 5a and a convex cam 5b. The inclined side wall (cam surface) of the concave cam 5a and the convex cam 5b And the side walls (cam surface) of the
An axial force is generated as a component of the rotational force. The axial force causes the concave cam 5a and the convex cam 5b to slide with each other {the inclined side wall (cam surface) of the concave cam 5a. When slippage occurs between the inclined side wall (cam surface) of the convex cam 5b, the intermediate member 3 is axially displaced toward the output side (the left side in the figure) against the spring 4. Then, due to the axial displacement of the intermediate member 3 toward the output side, the friction surface 7a of the intermediate member 3 is separated from the friction surface 7b of the stationary side member 6, and the friction clutch 7 is released. It becomes rotatable with respect to the member 6. Accordingly, the input rotational power from the drive source is transmitted to the output side member 2 via the path of the input side member 1 → the propulsion cam means 5 → the intermediate member 3, and the output side member 2 rotates.

On the other hand, when the driving source is stopped and the input rotational power is lost, the axial force by the propulsion cam means 5 disappears, and the intermediate member 3 is axially displaced toward the input side by the urging force of the spring 4. , Return to the original position. And
In the manner described above, the friction clutch 7 is operated, and the intermediate member 3 is restrained to the stationary member 6 without backlash in the rotational direction. In this state, even if the rotational power is reversely input from the output side member 2, the reverse input rotational power is restrained between the intermediate member 3 and the stationary side member 6 via the friction clutch 7. Both the input member 2 and the input member 1 do not rotate, and the output member 2 does not rattle.

FIG. 5 shows a power transmission mechanism B according to another embodiment. In the power transmission mechanism B of this embodiment, a meshing clutch 7 'is employed as the clutch means instead of the friction clutch 7 described above. The dog clutch 7 ′ includes, for example, a concave tooth 7 a ′ (see FIG. 6) provided on the end face of the intermediate member 3 ′ and a convex tooth 7 b ′ provided on the end face of the stationary side member 6 ′ opposed thereto. Consists of
The concave teeth 7a 'and the convex teeth 7b' mesh with each other without backlash in the rotational direction.

FIG. 7 {circumferential section of the meshing clutch 7 ': FIG. 7 (a) is enlarged and FIG. 7 (b) is enlarged when actuated. As shown in FIG. In order to engage the teeth 7a 'and the convex teeth 7b' in the rotational direction without backlash, the circumferential cross sections of the concave teeth 7a 'and the convex teeth 7b' are each trapezoidal. Circumferential wall surface 7a1 'of concave tooth 7a', circumferential wall surface 7b of convex tooth 7b '
It is preferable that the inclination angle of 1 ′ is set to, for example, about 3 to 5 °.

As shown in FIG. 7 (b), when the intermediate member 3 'is pressed and urged toward the input side by the spring 4' and the concave teeth 7a 'mesh with the convex teeth 7b', the inclined wall surfaces of the two. 7a1 'and the wall surface 7b1' are pressed against each other in a wedge shape, and the meshing gap between them is eliminated. Therefore, when the drive source is stopped, the reverse input rotational power from the output side member 2 ′ is restrained without backlash via the meshing clutch 7 ′, thereby preventing the output side member 2 from rattling (rattle).

The structure of the meshing clutch 7 'is not limited to the above embodiment. For example, the concave teeth 7a' and the convex teeth 7a '
The circumferential cross section of b 'may be triangular (V-shaped), or may be cam-shaped in pressure contact with each other in a wedge shape. Further, convex teeth may be provided on the intermediate member 3 'and concave teeth may be provided on the stationary member 6'. Other items are the same as those of the power transmission mechanism A shown in FIG. 1, and corresponding members and portions are denoted by the same reference numerals (with suffixes), and redundant description will be omitted.

FIG. 8 shows a power transmission mechanism C according to another embodiment. This power transmission mechanism C is provided with the propulsion cam means 5 shown in FIG. 1 at two places (an input side 51 and an output side 52), and an input side member 1 rotatable about an axis X.
0, an output member 20 arranged coaxially with the input member 10 and rotatable about the axis X;
0 and the intermediate member 30 disposed between the output side member 20
And an elastic member such as a spring 40 interposed between the intermediate member 30 and the output member 20, between the input member 10 and the intermediate member 30, and between the intermediate member 30 and the output member 2.
0, propulsion cam means 51, 52 provided respectively.
And a clutch means provided between the intermediate member 30 and a stationary member 60 such as a housing, for example, a friction clutch 70
And are configured as main elements.

The intermediate member 30 includes an outer diameter side member 31 having a cylindrical inner peripheral surface, and an inner diameter side member 3 fitted to the inner diameter portion.
And 2. The outer diameter side member 31 and the inner diameter side member 32 are engaged with each other in the axial direction via the radial surface 30b, and follow the axial movement of the outer diameter side member 31 to the output side. The member 32 follows the axial movement of the inner member 32 to the input side, and the outer member 31 moves in the axial direction. The intermediate member 30 is sandwiched between the input member 10 and the output member 20 so as to be movable in the axial direction.
Unlike the embodiment (power transmission mechanism A) shown in FIG. 1, the output side member 20 (also for the input side member 10) is not spline-coupled. On the outer periphery of the outer diameter side member 31, a conical friction surface 70a having a slight inclination angle θ with respect to the axis X (see FIG. 10) is formed.

On the inner periphery of the stationary side member 60, an outer diameter side member 31 is provided.
A frictional surface 70b having a conical shape is formed that is compatible with the frictional surface 70a. The frictional clutch 70 is formed by the two frictional surfaces 70a and 70b. The inclination angle θ, the direction of the inclination, the surface treatment, and the like of the friction surfaces 70a and 70b are handled in the same manner as in the embodiment shown in FIG.

The springs 40 are provided with concave portions 30 provided on the opposed portions of the inner diameter side member 32 and the output side member 20, respectively.
a and 20a are stored in a compressed state. This spring 4
The outer diameter side member 31 and the inner diameter side member 3
The two intermediate members 30 are integrally pressed and urged toward the input side in the axial direction at all times.

The input-side propulsion cam means 51 and the output-side propulsion cam means 52 are the propulsion cam means 5 of the embodiment shown in FIG.
Similarly, the concave cams 51a and 52a and the convex cam 51
b, 52b. Among them, the concave cam 51a of the input-side propulsion cam means 51 is provided, for example, on the end face of the input-side member 10, as shown in FIG.
As shown in FIGS. 10A and 10B, a portion of the outer diameter side member 31 facing the concave cam 51a (an input side end face in the present embodiment).
Is provided. Further, as shown in FIG. 11, the convex cam 52b of the output side propulsion cam means 52 is, for example,
The concave cam 52a is provided on a portion (the output side end surface in the present embodiment) of the outer diameter side member 31 opposed to the convex cam 52b as shown in FIG. The basic structure of the concave cams 51a and 52a and the convex cams 51b and 52b is the same as that of the embodiment shown in FIG. ), The convex cams 51b, 52b are formed to protrude in a V-shape in the axial direction, and the concave cams 51a, 52a are formed to mesh with the corresponding convex cams 51b, 52b, respectively.

As shown in FIG. 8, when the friction surface of the outer diameter side member 31 is in pressure contact with the friction surface of the stationary side member 60, the concave cams 51a of the input side propulsion cam means 51 and the output side propulsion cam means 52, 52a and convex cams 51b and 52b
The axial gaps S1 and S2 are provided between the respective cam surfaces.

In FIG. 8, when the input-side member 10 is rotated by receiving the input rotational power from a drive source (not shown), a part of the input rotational power is input to the input-side propulsion cam means 51.
Is converted to an axial force by this axial force,
The intermediate member 30 is axially displaced integrally to the output side against the spring 40 while sliding between the concave cam 51a and the convex cam 51b. Since this axial displacement is absorbed by the axial clearance S2 of the output-side propulsion cam means 52, the position of the output-side member 20 does not change. Due to the axial displacement of the intermediate member 30, the friction clutch 70 is released in the above-described manner, and the outer-diameter-side member 31 becomes rotatable with respect to the stationary-side member 60. Further, the engagement between the concave cam 52a and the convex cam 52b of the output side propulsion cam means 52 transmits the rotational power of the outer diameter side member 31 to the output side member 20, and the output side member 20 rotates. At this time, the input side propulsion cam means 5
The cam dimensions and the cam shape of the input-side propulsion cam means 51 are designed such that the axial force generated at 1 is larger than the resultant force of the elastic force of the spring 40 and the axial reaction force generated at the output-side propulsion cam means 52. You. In the present embodiment, as an example, a structure that satisfies the above conditions by adjusting the rising angle of the cam surface is illustrated. In detail, the rising angle φ ₁ of the cam surface of the input-side propulsion cam unit 51 (FIG. b))
Of the cam surface of the output side propulsion cam means 52 (φ ₂ : FIG. 1)
1) to increase the axial force generated by the input-side propulsion cam means 51.

[0033] On the other hand, when the drive source stops,
Since the axial force of the system means 51 disappears, the outer diameter side member 31
And the inner diameter side member 32 is
To the input side and return to the original position,
The friction surface 70a of the member 31 is
b is pressed to the extent corresponding to the elastic force. Due to this elastic force
By the pressure contact, switching of the friction clutch 70 at the time of reverse input is stopped.
Performed in a mood. In this state, it rotates from the output side member 20.
When the power is reversely input, the output-side propulsion cam means 52 inputs the power.
Since the axial force to the side is generated, the outer diameter side member 31 is
Is pressed. Thereby, the friction surface 7 of the outer diameter side member 31 is
0a is strongly pressed against the friction surface 70b of the stationary side member 60
Therefore, the friction clutch 70 is in the restrained state, and the outer diameter side member is
30 is a rotational backlash with respect to the stationary side member 60
The output side member 20 and the input side member 1
Zero rotation is constrained. At this time, the input side propulsion cam
Since the means 51 has the axial gap S1, the output side member 2
The cams 51a and 51b mesh with each other with the reverse input rotational power from 0.
The input-side member 10 does not rotate accordingly.

[0034] With the power transmission mechanism C described above,
Unlike the embodiment described above, the binding force of the friction clutch 70
Independent power transmission becomes possible. That is, as shown in FIG.
In the power transmission mechanism A, the binding force of the friction clutch 70 is
Determined by the magnitude of the elastic force of the spring 40,
On the other hand, the rotational power from the input side is the elastic force of the spring 40.
It must generate the above axial force. Toes
If the binding force of the friction clutch 70 is set large,
The required rotational power on the power side also increases, while the input side
If the rotational power is set small, the friction clutch 70
There is a relationship that the binding force decreases.

[0035] On the other hand, in the power transmission mechanism C, the friction
The restraining force of the friction clutch 70 is controlled by the output-side propulsion cam 52.
Depending on the axial force that occurs,
Force generated by the friction clutch 70 in proportion to the rotational power
You. Therefore, the rotational power on the input side is
And the axial force generated by the output-side propulsion cam means 52.
It is only necessary to overcome the force.
The degree of freedom at the time of setting can be increased.

[0036] The power transmission shown in FIGS.
The friction clutch 70 is exemplified as the clutch means of the mechanism C.
However, it has the uneven teeth 7a ', 7b' shown in FIGS.
It is also possible to employ a meshing clutch 7 'that performs the following.

[0037]

As described above, according to the present invention,
The input rotational power from the input side member is transmitted to the output side member via the propulsion cam means and the intermediate member, and the reverse input rotational power from the output side member is transmitted to the intermediate member and the stationary side via the clutch means without backlash. Since the configuration is such that the output side member is restrained between the members when the drive source is stopped, there is no slight movement (rattle), and the position holding function of the output side member is improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a power transmission mechanism A according to an embodiment.

FIG. 2 is a front view {FIG. 2 (a)} and a side view {FIG. 2 (b)} of an input side member.

FIG. 3 is a side view {FIG. 3 (a)} and a front view {FIG. 3 (b)} of an intermediate member.

FIG. 4 is an operation principle diagram of a friction clutch.

FIG. 5 is a longitudinal sectional view showing a power transmission mechanism B according to another embodiment.

FIG. 6 is a side view {FIG. 6 (a)} and a front view {FIG. 6 (b)} of the intermediate member.

7 is a view showing a circumferential cross section of the dog clutch (FIG. 7 (a) is at the time of disengagement, and FIG. 7 (b) is at the time of operation).

FIG. 8 is a longitudinal sectional view showing a power transmission mechanism C according to another embodiment.

FIG. 9 is a front view of the input side member (FIG. 9A), and FIG.
It is sectional drawing {FIG. 9 (b)} in the direction of the arrow.

FIG. 10 is a sectional view of the outer diameter side member as viewed in the direction of arrow a.
(A)} and a front view {FIG. 10 (b)}.

FIG. 11 is a sectional view of the output side member in the direction of arrow a.
(A)} and a front view {FIG. 11 (b)}.

FIG. 12 is a conceptual diagram of a slide driving device for a power seat of an automobile.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input side member 2 Output side member 3 Intermediate member 4 Spring 5 Propulsion cam means 6 Stationary side member 7 Friction clutch 7a Friction surface 7b Friction surface 7 'Mesh clutch 7a' Concave tooth 7b 'Convex tooth 10 Input side member 20 Output Side member 30 Intermediate member 40 Spring 51 Input-side propulsion cam means 52 Output-side propulsion cam means 60 Stationary-side member 70 Friction clutch 70a Friction surface 70b Friction surface S1 Gap S2 Gap

Claims (11)

[Claims] An input member rotatable about an axis, an output member coaxially arranged with the input member and rotatable about an axis, and a non-rotatable and axially movable member relative to the output member. An intermediate member provided on the intermediate member; an elastic member for pressing and biasing the intermediate member toward the input side; and an intermediate member provided between the input side member and the intermediate member. And a propulsion cam means for displacing the intermediate member in the axial direction toward the output side against the elastic member at the same time as the intermediate member and the stationary member. Clutch means that restrains the intermediate member without backlash in the rotational direction, releases the restrained state when the intermediate member is axially displaced toward the output side against the elastic member, and enables the intermediate member to rotate with respect to the stationary member; Input from the input side member Rotational power is transmitted to the output side member via the propulsion cam means and the intermediate member, and reverse input rotational power from the output side member is transmitted via the clutch means to restrict power between the intermediate member and the stationary side member. mechanism. 2. An input member rotatable about an axis, an output member disposed coaxially with the input member and rotatable about an axis, and an axial member movable between the input member and the output member. An intermediate member provided on the input member; an elastic member pressing the intermediate member toward the input side; and an intermediate member provided between the input side member and the intermediate member. At the same time as the input side propulsion cam means that generates an axial force between the two members, and is provided between the output side member and the intermediate member. An output-side propulsion cam means that generates an axial force between both members at the same time as the transmission, and is provided between the intermediate member and the stationary member, and restrains the intermediate member to the stationary member without backlash in the rotational direction. Constrained state and extension of intermediate members Clutch means capable of switching between an unlocked state in which the intermediate member is rotatable with respect to the stationary side member by an axial displacement to the force side, and when the power is transmitted from the input side, the input side propulsion cam means The intermediate member is axially displaced to the output side by the generated axial force to disengage the clutch means, and the input of the intermediate member is performed by the axial force generated by the output-side propulsion cam means during power transmission from the output side. A power transmission mechanism that pushes the clutch to the side to put the clutch means in a restrained state. 3. The power transmission mechanism according to claim 2, wherein the axial force generated by the input-side propulsion cam means is set to be larger than the resultant force of the elastic force of the elastic member and the axial reaction force generated by the output-side propulsion cam means. . 4. The power transmission mechanism according to claim 2, wherein a gap is provided between the cam surfaces of the input-side propulsion cam means when the clutch means is in a restrained state. 5. The power transmission mechanism according to claim 1, wherein the clutch means is a friction clutch having friction surfaces that can be pressed against each other. 6. The power transmission mechanism according to claim 5, wherein the friction surface is an inclined surface inclined in a direction to decrease toward the input side. 7. The power transmission mechanism according to claim 5, wherein the friction surface has been subjected to a surface treatment for increasing a friction coefficient. 8. The power transmission according to claim 7, wherein the surface treatment is at least one selected from application of a lubricant, chemical surface treatment, and surface roughening by machining. mechanism. 9. The power transmission mechanism according to claim 1, wherein said clutch means is a meshing clutch having uneven teeth meshing with each other without backlash in the rotating direction. 10. The power transmission mechanism according to claim 9, wherein the circumferential wall surfaces of the uneven teeth have a shape in which they come into pressure contact with each other in a wedge shape at the time of meshing. 11. The power transmission mechanism according to claim 10, wherein a circumferential cross section of the uneven teeth is trapezoidal or triangular.