JP2017133520A - Power transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power transmission device which can simplify the whole structure, and can suppress an increase in size in an axial direction.SOLUTION: A power transmission device includes a first rotating shaft 10 having a first gear 20, a second gear 21 meshed with the first gear 20, a second rotating shaft 11 having an outer periphery on which the second gear 21 is arranged to be relatively rotatable, an axial moving part 15 for relatively moving the second gear 21 to the second rotating shaft 11 in an axial direction during rotation of the first and the second gears 20 and 21, and elastic members 14A and 14B held in the axial direction between the second gear 21 and the second rotating shaft 11 and transmitting torque of the first rotating shaft 10 to the second rotating shat 11 by compression force in the axial direction imparted through the second gear 21 relatively moved by the axial moving part 15.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power transmission device that transmits a rotational force of a first rotating shaft to a second rotating shaft.

  Patent Document 1 discloses a crankshaft (first rotation shaft) having a drive gear (first gear), a driven gear (second gear) meshing with the drive gear, and a balance shaft in which the driven gear is disposed on the outer periphery so as to be relatively rotatable. (A second rotating shaft), a rotating member fixed to the axial end portion of the balance shaft, and a stopper rubber that is accommodated in the rotating member at intervals in the circumferential direction. Is disclosed.

  Collision protrusions protrude from the axial end surface of the driven gear, and elastic deformation portions that collide with the collision protrusions when the drive gear and the driven gear rotate are provided at both circumferential ends of the stopper rubber. Further, a friction damper that generates a frictional damping force between the driven gear and the balance shaft is provided on the opposite side of the driven gear in the axial direction from the side where the stopper rubber is located.

  When the drive gear and the driven gear are rotated by the drive of the reciprocating engine, the impact projection is idled while the driven gear is damped by the friction damper. Power is granted. As a result, the rotational force of the driven gear is attenuated and transmitted to the balance shaft so that the balance shaft rotates.

JP 2009-204057 A

  In the above case, the driven gear is provided with a collision protrusion protruding in the axial direction, provided with elastic deformation portions for receiving the collision protrusion at both ends in the circumferential direction of the stopper rubber, and further provided with a stopper rubber at the axial end of the balance shaft. In addition to the provision of a rotating member that accommodates the friction rubber, a friction damper is required in addition to the stopper rubber, so that the overall structure tends to be complicated and the size tends to increase in the axial direction.

  The present invention has been completed based on the above-described circumstances, and an object thereof is to provide a power transmission device that can simplify the entire structure and suppress an increase in axial size. And

  The power transmission device of the present invention includes a first rotating shaft having a first gear, a second gear meshing with the first gear, a second rotating shaft on the outer periphery of which the second gear is disposed so as to be relatively rotatable, An axial movement unit that moves the second gear relative to the second rotation shaft in the axial direction when the first and second gears rotate, and between the second gear and the second rotation shaft Elasticity that transmits the rotational force of the first rotating shaft to the second rotating shaft by the compressive force in the axial direction that is sandwiched in the axial direction and applied through the second gear that is relatively moved by the axial moving portion. And a member.

  When the second gear is moved in the axial direction relative to the second rotation shaft by the axial movement unit, the elastic member is given a compressive force in the axial direction between the second gear and the second rotation shaft. Therefore, the rotational force of the first rotating shaft is attenuated and transmitted to the second rotating shaft. In this case, it is not necessary to provide the second gear corresponding to the collision projection (see Background Art) protruding in the axial direction, and the elastic member receives the projection corresponding to the collision projection in the circumferential direction. It is not necessary to provide a portion, and it is not necessary to provide a structure such as a rotating member (see the background art) that houses an elastic member at the end of the second rotating shaft. Since the entire structure can be simplified, an increase in size in the axial direction can be suppressed.

It is a schematic side view of the balancer device as the power transmission device according to the first embodiment of the present invention. It is sectional drawing which shows the structure of the damping mechanism of a balancer apparatus. It is a front view of an elastic member. In the balancer device as the power transmission device according to the second embodiment, it is a main part sectional view showing the structure of the damping mechanism.

Preferred embodiments of the present invention are shown below.
The axial direction moving part is provided to be able to engage with the second gear and the second rotating shaft, and the rotational movement of the first and second gears is performed between the second gear and the second rotating shaft. Has a conversion mechanism for converting the relative movement in the axial direction. According to this, since the second gear automatically moves in the axial direction with respect to the second rotating shaft when the first and second gears rotate, there is no need to forcibly move the second gear in the axial direction. Can be simplified.

  The second rotating shaft projects radially from the outer peripheral surface of the second rotating shaft and has opposing walls facing each other in the axial direction, and an inner peripheral portion of the second gear is disposed between the opposing walls. The elastic member is sandwiched between both ends in the axial direction and the opposing walls. According to this, unlike the conventional rotating member (see the background art), the elastic member can be received with a simple structure such as an opposing wall, and the structure can be further simplified. Moreover, since the opposing wall has a form that projects in the radial direction from the outer peripheral surface of the rotating member, it is possible to more reliably suppress the axial enlargement.

  Of each of the opposing walls, the opposing wall on the side away from one axial end of the second rotating shaft is provided integrally with the second rotating shaft and is close to one axial end of the second rotating shaft. The opposing wall on the side is provided separately from the second rotation shaft. Since the opposing wall on the side away from one axial end of the second rotating shaft is provided integrally with the second rotating shaft, the number of parts is larger than when the opposing wall is provided separately from the second rotating shaft. Can be reduced. Further, the opposing wall on the side away from the one axial end of the second rotating shaft is used as a stopper wall, and the opposing wall on the side near the one axial end of the elastic member, the second gear, the elastic member and the second rotating shaft is Since it can be assembled sequentially from one end side in the direction, it is possible to ensure good assembly.

  The elastic member has a ring shape surrounding the second rotating shaft. According to this, since the elastic member is not divided into a plurality in the circumferential direction, the number of parts is not increased.

<Example 1>
Embodiment 1 of the present invention will be described below with reference to FIGS. The power transmission device according to the first embodiment is an example applied to a balancer device of an in-line four-cylinder reciprocating engine, and is arranged in parallel with the first rotating shaft 10 as a crankshaft and the first rotating shaft 10. A second rotating shaft 11 as a balance shaft and a third rotating shaft 12 as a balance shaft different from the second rotating shaft 11 arranged in parallel with the first and second rotating shafts 10 and 11 are provided. . The first rotating shaft 10 is rotatably supported by a crankcase (not shown), and the second and third rotating shafts 11 and 12 are rotatably supported by a housing 13 positioned below the crankcase. The rotational force of the first rotating shaft 10 is transmitted to the second rotating shaft 11 via an elastic member 14A, 14B, which will be described later, and a damping mechanism by the axial direction moving unit 15. In the following description, the axial direction is the left-right direction in FIG. 1, the left side indicates one side in the axial direction, and the right side indicates the other side in the axial direction.

First, the overall structure of the balancer device will be described.
As shown in FIG. 1, the first rotating shaft 10 is provided with a crank arm 16, and a piston 18 is connected to the crank arm 16 via a connecting rod 17. The first rotary shaft 10 is provided with a total of eight first balance weights 19 for each piston 18, and among these, the first gear 20 is provided between the two first balance weights 19 on the end side. Is provided. The first gear 20 is made of metal and is fixed to the first rotation shaft 10 so as to be integrally rotatable.

  A second gear 21 that meshes with the first gear 20 is disposed on the outer periphery of the second rotating shaft 11. The second gear 21 is rotatable relative to the second rotating shaft 11, and an outer peripheral portion having a tooth surface is made of resin in order to reduce gear noise caused by meshing with the first gear 20. . In the case of the first embodiment, the entire second gear 21 is made of resin. However, only the outer peripheral portion may be made of resin, and the inner peripheral portion having the axial movement portion 15 may be made of metal. The first and second gears 20 and 21 are helical gears having helical tooth surfaces. The number of teeth of the second gear 21 is set to half the number of teeth of the first gear 20. For this reason, the second rotating shaft 11 rotates at a rotational speed twice that of the first rotating shaft 10.

  The second rotating shaft 11 is provided with a counter gear 22 on the right side of the second gear 21. The third rotating shaft 12 is provided with a driven gear 23 that meshes with the counter gear 22. The counter gear 22 and the driven gear 23 are fixed to the second rotating shaft 11 and the third rotating shaft 12 so as to be integrally rotatable, respectively, and are set to have the same number of teeth. Furthermore, second and third balance weights 24 and 25 are provided at positions on the right side of the second and third rotation shafts 11 and 12, respectively.

  When the first rotating shaft 10 rotates, the second and third rotating shafts 11 and 12 rotate at a rotational speed twice that of the first rotating shaft 10 via the damping mechanism, and the second and third balance weights 24, Thus, it is possible to reduce the vibration such as the secondary vibration of the reciprocating engine.

Next, the damping mechanism will be described.
As shown in FIG. 2, the second gear 21 is rotatable relative to the second rotation shaft 11 and is movable relative to the axial direction. The shaft 11 includes an axial movement unit 15 that allows relative movement of the second gear 21 in the axial direction.

  The axially moving portion 15 has an inner engaging portion 26 provided on the inner peripheral portion of the second gear 21 and an outer engaging portion 27 provided on the outer peripheral portion of the second rotating shaft 11. A flange portion 28 is provided on the inner peripheral portion of the second gear 21 so as to project to both sides in the axial direction.

  The inner engaging portion 26 is formed on the inner peripheral surface of the flange portion 28 by a groove and a protrusion that circulate in a spiral shape (screw shape) in the axial direction. The outer engaging portion 27 is formed on the outer peripheral surface of the second rotating shaft 11 with a groove and a ridge that similarly circulate in a spiral shape (screw shape) in the axial direction. The projection of the outer engagement portion 27 is fitted into the groove of the inner engagement portion 26, and the groove of the outer engagement portion 27 is fitted to the projection of the inner engagement portion 26. In this state, the second gear 21 rotates relative to the second rotating shaft 11, so that the inner engaging portion 26 and the outer engaging portion 27 slide against each other, so that the second gear 21 rotates relative to the second rotating shaft 11. It moves relative to the direction. That is, the inner engagement portion 26 and the outer engagement portion 27 constitute a conversion mechanism that converts the rotational movement of the second gear 21 relative to the second rotation shaft 11 into a linear movement in the axial direction.

  Further, the damping mechanism includes elastic members 14A and 14B that are disposed at positions facing the second gear 21 that moves in the axial direction by the conversion mechanism and are pressed in the axial direction by the second gear 21.

  Specifically, the elastic members 14 </ b> A and 14 </ b> B are made of rubber and have a ring shape as a whole. The elastic members 14 </ b> A and 14 </ b> B surround the second rotating shaft 11 and are arranged in pairs on the left and right sides with the second gear 21 interposed therebetween. Is done. The pair of elastic members 14A and 14B have the same shape as each other. However, in the following description, when it is necessary to distinguish between the two, the one located on the right side is referred to as one elastic member 14A and Those located are referred to as other elastic members 14B.

  Both end surfaces in the axial direction of the elastic members 14A and 14B are flat pressed surfaces 29 that come into surface contact with the end surface of the second gear 21 and the wall surfaces of opposing walls 31 and 32 described later. Of these, the pressed surface 29 that faces the wall surfaces of the opposing walls 31 and 32 is provided with a bottomed oil passage groove 30 that extends in the radial direction and opens on both the inner and outer surfaces, as shown in FIG. Yes. The oil passage grooves 30 are provided at a plurality of locations at intervals (preferably at equal intervals) in the circumferential direction on the pressed surface 29.

  As shown in FIG. 2, a pair of opposing walls 31 and 32 are provided on the outer periphery of the second rotating shaft 11 on both sides in the axial direction with the outer engagement portion 27 interposed therebetween. The opposing walls 31, 32 are integrated with the second rotating shaft 11, and the rear opposing wall 31 that projects from the outer peripheral surface of the second rotating shaft 11 to the outer side in the radial direction over the entire circumference, and the second rotating shaft 11 are It consists of a front side opposing wall 32 that is separate and projects from the position on the outer peripheral surface of the second rotating shaft 11 to the left side of the far side opposing wall 31 radially outward. The near side and the far side mean the near side and the far side in the assembling direction of the elastic members 14A and 14B, the second gear 21 and the near side facing wall 32, respectively.

  The back side opposing wall 31 has an annular plate shape, and a back side wall part 33 arranged with the plate surface (wall surface) directed in the axial direction, and the back side wall part 33 provided integrally around the second rotating shaft 11. The peripheral step portion 34 protrudes to the left from the inner periphery. The near-side facing wall 32 is also in the shape of an annular plate, and has a front side wall portion 35 arranged with the plate surface (wall surface) directed in the axial direction, and a cylindrical shape protruding rightward from the inner periphery of the front side wall portion 35. It consists of a heel part 36.

  Further, the outer peripheral surface of the second rotating shaft 11 includes a large-diameter moving surface portion 37 provided with the outer engaging portion 27 and the back-side facing wall 31, and a small-diameter mounting surface portion orthogonal to the left end surface of the second rotating shaft 11. 38, and a stepped surface portion 39 along the radial direction connecting the mounting surface portion 38 and the moving surface portion 37. The front facing wall 32 is attached to the mounting surface portion 38 of the second rotating shaft 11 from the left side by press-fitting. The front side wall portion 35 is press-fitted into the mounting surface portion 38, stopped against the step surface portion 39, and positioned on the second rotating shaft 11. Further, when the front side opposing wall 32 is press-fitted into the mounting surface portion 38 of the second rotating shaft 11, the front side wall portion 35 and the back side wall portion 33 are arranged to face each other in the axial direction with the second gear 21 interposed therebetween, The outer peripheral surface of the flange portion 36 and the outer peripheral surface of the circumferential step portion 34 are arranged with the same concentric diameter.

  Between the right end surface of the second gear 21 and the back side wall portion 33 and outside the peripheral step portion 34, between the left end surface of the second gear 21 and the front side wall portion 35 and outside the flange portion 36. In each region, one elastic member 14A and another elastic member 14B are accommodated in a tightly fitted state.

  The second rotating shaft 11 has an oil supply passage 40 extending in the axial direction at the shaft center portion, and a branch oil passage 41 penetrating in a radial direction from the oil supply passage 40 to the outer engagement portion 27 of the moving surface portion 37. have.

  The above is the structure of the balancer device according to the first embodiment. Next, a method for assembling and operating the balancer device will be described.

  At the time of assembly, one elastic member 14 </ b> A is extrapolated from the left side to the second rotation shaft 11, and the pressed surface 29 on the right side of the elastic member 14 </ b> A is abutted against the left wall surface of the back side wall portion 33. Next, the second gear 21 is extrapolated from the left side to the second rotating shaft 11, and the second gear 21 is rotated around the axis while the inner engaging portion 26 is engaged with the outer engaging portion 27, so that the axial direction ( Right side) and the right end surface of the second gear 21 is stopped against the pressed surface 29 on the left side of the elastic member 14A. Next, another elastic member 14 </ b> B is extrapolated from the left side to the second rotating shaft 11, and the pressed surface 29 on the right side of the elastic member 14 </ b> B is abutted against the left end surface of the second gear 21. Further, the front facing wall 32 is extrapolated from the left side to the second rotating shaft 11, and the flange portion 36 is fitted in a press-fitted state between the mounting surface portion 38 and the step surface portion 39. Is pressed against the pressed surface 29 on the left side of the elastic member 14B. Thus, the back-side facing wall 31, the one elastic member 14A, the second gear 21, the other elastic member 14B, and the front-side facing wall 32 are sequentially arranged in the axial direction, and the one elastic member 14A is the back-side facing wall. 31 and the second gear 21, and another elastic member 14 </ b> B is sandwiched between the near-side facing wall 32 and the second gear 21. One elastic member 14 </ b> A is fitted on the right flange portion 28 of the second gear 21, and the other elastic member 14 </ b> B is fitted on the left flange portion 28 of the second gear 21.

  When the reciprocating engine accelerates, the rotational speed of the first gear 20 gradually increases, and the second gear 21 that meshes with the first gear 20 also rotates according to the rotational speed of the first gear 20. Thus, the second gear 21 rotates and the outer engagement portion 27 slides on the inner engagement portion 26, whereby the conversion mechanism of the axial movement portion 15 acts, and the rotational movement of the second gear 21 moves in the axial direction. The second gear 21 moves relative to the second rotating shaft 11 in the axial direction, for example, the left side. Then, the second gear 21 presses the pressed surface 29 on the right side of the other elastic member 14B located on the left side, and the elastic member 14B is elastic in the axial direction between the second gear 21 and the front facing wall 32. To be compressed.

  At the start of acceleration of the reciprocating engine, since the pressure acting on the elastic member 14B from the second gear 21 is small, the pressure acting on the near-side facing wall 32 from the elastic member 14B is also small. For this reason, when the rotational movement of the second gear 21 is transmitted to the elastic member 14B, the elastic member 14B frictionally slides on the right wall surface of the front side wall portion 35 in the circumferential direction, and the rotational movement of the second rotating shaft 11 is caused. Slow and start slowly.

  During maximum acceleration of the reciprocating engine, the pressure acting on the elastic member 14B from the second gear 21 is large, so the pressure acting on the near-side facing wall 32 from the elastic member 14B is also large. For this reason, when the rotational motion of the second gear 21 is transmitted to the elastic member 14B, the elastic member 14B rotates substantially integrally with the near-side facing wall 32, and the rotational motion of the second rotational shaft 11 is the first rotational shaft. Proceed according to the rotation speed of 10. During this period, that is, in the acceleration process from the start of acceleration to the maximum acceleration, the damping force of the damping mechanism is gradually reduced and transmitted to the second rotating shaft 11.

  Further, when the reciprocating engine decelerates by engine brake and brake operation control, etc., the first and second gears 20 and 21 rotate in the opposite direction, and the second gear 21 passes through the conversion mechanism to the second rotating shaft. 11 relative to the right side. For this reason, the second gear 21 presses the left pressed surface 29 of the one elastic member 14 </ b> A located on the right side, and the elastic member 14 </ b> A is elastic between the second gear 21 and the rear facing wall 31 in the axial direction. Compressed. Therefore, the rotational force of the second gear 21 is attenuated and transmitted to the second rotating shaft 11 through the one elastic member 14A. As a result of using both elastic members 14A and 14B in accordance with the state of the reciprocating engine, it is possible to prevent only one of the elastic members 14A and 14B from deteriorating at an early stage.

  By the way, while the reciprocating engine is driven, the hydraulic oil reaches the moving surface portion 37 from the oil supply passage 40 of the second rotating shaft 11 through the branch oil passage 41 and lubricates between the outer engagement portion 27 and the inner engagement portion 26. After that, the oil is discharged to the outer peripheral side of the elastic members 14A and 14B through the oil passage groove 30. Therefore, the outer engagement portion 27 and the inner engagement portion 26 slide smoothly. Further, a particularly complicated structure is not required as a path for supplying hydraulic oil between the outer engagement portion 27 and the inner engagement portion 26.

  As described above, according to the first embodiment, the second gear 21 is moved relative to the second rotation shaft 11 in the axial direction by the axial movement unit 15, so that the elastic members 14 </ b> A and 14 </ b> B are moved in the first direction. Since the compression force is applied in the axial direction between the second gear 21 and the second rotation shaft 11, the rotation force of the first rotation shaft 10 is attenuated and transmitted to the second rotation shaft 11. In this case, the second gear 21 does not need to be provided with a structure that protrudes in the axial direction, and the elastic members 14A and 14B do not need to be provided with a structure that receives the protruding portion of the second gear 21. Since it is not necessary to provide a housing structure for the elastic members 14A and 14B at the left end of the rotary shaft 11 and the conventional friction damper can be omitted, the overall structure can be simplified and a large axial size can be achieved. Can be suppressed.

  Moreover, the axial direction movement part 15 has the conversion mechanism which can mutually engage with the 2nd gear 21 and the 2nd rotating shaft 11, and the rotational motion of the 1st, 2nd gears 20 and 21 is 2nd gear by the conversion mechanism. Therefore, it is not necessary to forcibly move the second gear 21 in the axial direction, and the structure can be simplified. In particular, since the conversion mechanism is constituted by the inner engagement portion 26 of the second gear 21 and the outer engagement portion 27 of the second rotating shaft 11, the number of parts is not increased.

  In addition, a pair of opposed walls 31 and 32 projecting in the radial direction and opposed in the axial direction are provided on the outer circumference of the second rotating shaft 11, and the inner circumferential portion of the second gear 21 is interposed between the opposed walls 31 and 32. Is disposed, and the elastic members 14A and 14B are sandwiched between the axial ends of the second gear 21 and the opposing walls 31 and 32, respectively. It is only necessary to provide the walls 31 and 32, and a complicated structure such as a housing structure or a cup structure which is easily increased in size is not required. As a result, the structure can be further simplified, and an increase in axial size can be suppressed more favorably.

  Further, of the opposing walls 31, 32, the far-side opposing wall 31 that is separated from the left end of the second rotating shaft 11 is provided integrally with the second rotating shaft 11, and on the near side of the second rotating shaft 11 near the left end. Since the side facing wall 32 is provided as a separate body from the second rotating shaft 11, the elastic member 14 </ b> A, the second gear 21, the other elastic member 14 </ b> B, and the near side are used with the back facing wall 31 as a stopper wall. The opposing wall 32 can be sequentially assembled to the second rotating shaft 11, and good assemblability can be ensured. In addition, the number of parts can be reduced as compared with the case where the rear-side facing wall 31 is provided separately from the second rotating shaft 11.

  Furthermore, since the elastic members 14A and 14B form a ring shape that surrounds the second rotation shaft 11 and are not divided into a plurality of parts in the circumferential direction, the number of parts can be further reduced.

<Example 2>
FIG. 4 shows a main part of the second embodiment. The second embodiment is the same as the first embodiment except for the axial movement unit 15E, although the structure of the axial movement unit 15E is different from that of the first embodiment. In the following description, the same reference numerals are given to the same structures as those in the first embodiment, and duplicate descriptions are omitted.

  The axial direction moving part 15E includes an inner engaging part 26 provided on the inner peripheral part of the second gear 21, an outer engaging part 27 provided on the outer peripheral part of the second rotating shaft 11, and an inner engaging part 26. A plurality of spherical balls 43 (only one is shown) disposed between the outer engagement portions 27.

  The inner engagement portion 26 is formed of a concave groove provided around the inner peripheral surface of the flange portion 28 of the second gear 21 in a spiral shape (screw shape). Similarly, the outer engaging portion 27 is formed of a concave groove that is provided in a spiral (screw shape) around the moving surface portion 37 of the second rotating shaft 11 so as to face the concave groove. The plurality of balls 43 are tightly held so as to be able to roll (slidably) between both concave grooves.

  This axial direction movement part 15E converts the rotational movement of the 2nd gear 21 into a rectilinear movement by the said structure based on a ball screw. When the second gear 21 rotates relative to the second rotating shaft 11, the balls 43 roll between the inner engaging portion 26 and the outer engaging portion 27, and the second gear 21 moves to the second rotating shaft 11. The elastic members 14A and 14B are moved between the second gear 21 and the opposing walls 31 and 32 in the same manner as in the first embodiment. Elastically compressed. According to the second embodiment, since each ball 43 rolls, the friction between the second gear 21 and the second rotating shaft 11 is relieved, so that the smooth movement of the second gear 21 in the axial direction is achieved. Secured.

<Other embodiments>
Other embodiments will be briefly described below.
(1) The axial movement unit does not have a conversion mechanism, and the second gear receives mechanical power from an external device relative to the second rotation shaft in the axial direction when the first and second gears rotate. The structure which moves may be sufficient.
(2) The elastic member is not limited to a rubber member, and may be made of a spring material such as a coil spring or a leaf spring.
(3) The pair of opposing walls may be provided separately from the second rotation shaft.
(4) The front facing wall may be fixed to the second rotating shaft by screws, or may be fixed to the second rotating shaft via a fixing member such as a fixing pin. Further, it may be fixed to the second rotating shaft by fixing means such as welding.
(5) Before driving the reciprocating engine, the elastic member may be disposed with a clearance in the axial direction between the second gear and the opposing wall.
(6) The present invention does not necessarily deny the use of a friction damper. If necessary, an elastic member and a friction damper may be used together as a damping mechanism.
(7) The present invention is not limited to the balancer device and can be widely applied to an internal combustion engine including a power transmission mechanism.

DESCRIPTION OF SYMBOLS 10 ... 1st rotating shaft 11 ... 2nd rotating shaft 14A, 14B ... Elastic member 15, 15E ... Axial direction moving part 20 ... 1st gear 21 ... 2nd gear 31, 32 ... Opposite wall

Claims (5)

A first rotating shaft having a first gear;
A second gear meshing with the first gear;
A second rotating shaft on the outer periphery of which the second gear is disposed so as to be relatively rotatable;
An axial movement unit that moves the second gear relative to the second rotation shaft in the axial direction when the first and second gears rotate;
The first rotation is caused by an axial compression force applied via the second gear that is sandwiched in the axial direction between the second gear and the second rotating shaft and is relatively moved by the axial moving portion. And a resilient member for transmitting the rotational force of the shaft to the second rotational shaft.   The axial direction moving part is provided to be able to engage with the second gear and the second rotating shaft, and the rotational movement of the first and second gears is performed between the second gear and the second rotating shaft. The power transmission device according to claim 1, further comprising a conversion mechanism that converts the relative movement in the axial direction.   The second rotating shaft projects radially from the outer peripheral surface of the second rotating shaft and has opposing walls facing each other in the axial direction, and an inner peripheral portion of the second gear is disposed between the opposing walls. The power transmission device according to claim 1, wherein the elastic member is sandwiched between both ends in the axial direction and the opposing walls.   Of each of the opposing walls, the opposing wall on the side away from one axial end of the second rotating shaft is provided integrally with the second rotating shaft and is close to one axial end of the second rotating shaft. The power transmission device according to claim 3, wherein a facing wall on the side is provided separately from the second rotation shaft.   5. The power transmission device according to claim 1, wherein the elastic member has a ring shape surrounding the periphery of the second rotation shaft.

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