JP2010019424A - Power transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent vibration and a noise from being generated caused by the looseness of a chain arranged laterally, and to restrain a chain life from getting short. <P>SOLUTION: This power transmission includes a driving shaft 43 supported directed vertically in one end side of a support member (offset frame) 5, a driven shaft 41 supported directed vertically in the other end side of the support member 5, a driving sprocket 45 provided in the driving shaft 43, a driven sprocket 47 provided in the driven shaft 41, and a chain 49 wound within a plane orthogonal vertically between both sprockets 45, 47, and has an inside guide 51 arranged in a widthwise inside of a loosened side chain 49b, out of the chain 49, and contacting with an inside face thereof, and an outside guide part 61 arranged in a widthwise outer side of the loosened side chain 49b, out of the chain 49, and contacting with an outside face thereof, and an upper face of the inside guide 51 is positioned in an upper side of at least anyone out of the an upper face of the driving sprocket 45 and an upper face of the driven sprocket 47. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power transmission device, and more particularly, to a power transmission device in which a chain is hung in a lateral direction between sprockets provided on a drive shaft and a driven shaft.

  There is a power transmission device using a chain as means for transmitting a driving force from a driving shaft to a driven shaft. This power transmission device is configured by hanging a chain between a drive shaft and a driven shaft. However, since the chain may sag due to its own weight, it is preferably used with the chain extended in the vertical direction. However, there is also a power transmission device that is used in a state where the chain extends in the lateral direction due to the positional relationship between the drive shaft and the driven shaft.

  Such a power transmission device in which the chain extends in the lateral direction is also used in, for example, agricultural machinery (see Patent Document 1). This agricultural machine is a ditcher that excavates vertical grooves in a farm field, a fixed machine frame that is attached to the rear part of the tractor, a movable machine frame that is detachably attached to the fixed machine frame and extends laterally, A cylindrical support portion that is fixed to the distal end portion of the movable machine frame and extends downward, a groove digging portion provided at a lower portion of the support portion, and an input case that is provided on the fixed machine frame and receives a driving force from the tractor. The chain transmission mechanism is configured to transmit the driving force from the tractor transmitted to the input case to the groove portion through the fixing machine frame and the support portion.

  In the support portion, a driven shaft extending in the vertical direction connected to the groove portion is incorporated. The upper end portion of the driven shaft protrudes from the support portion, and a driven sprocket that constitutes a chain transmission mechanism is mounted on the protruding driven shaft. In the input case, a drive shaft that rotates by receiving a driving force from the tractor extends in the vertical direction. The chain transmission mechanism includes the above-described driven shaft, driven sprocket, drive shaft, drive sprocket mounted on the drive shaft, and a chain wound around these sprockets.

  According to this agricultural machine, the driving force from the tractor is transmitted to the input case to drive the drive shaft to rotate. When the drive shaft is driven to rotate, the driving force is transmitted to the driven shaft via the drive sprocket, chain, and driven sprocket, and the driven shaft rotates. As a result, power is transmitted to the grooving portion, and the grooving portion is rotationally driven to perform the grooving operation.

Japanese Patent Publication No. 5-87201 (page 2-3, FIG. 5)

Here, since the chain is hung in a state extending laterally between the drive sprocket and the driven sprocket, when the drive force is transmitted to the drive shaft and the chain rotates, the side on the side that transmits power to the driven shaft A large tension is applied to the tension side chain, and the chain becomes tense.
On the other hand, the slack side chain disposed opposite to the tension side chain is in a non-tensioned state due to a small tension. As a result, if the chain stretches due to wear or the like, the slack of the slack side chain increases, and as the chain rotates, the slack side chain swells in the lateral direction and vibration occurs, or the slack chain causes the power transmission device to There arises a problem that noise is generated by contact with the cover member to be covered and the life of the chain is shortened.

  The present invention has been made in view of such a problem, and in a power transmission device in which a chain is disposed in a lateral direction, generation of vibration and noise due to slack in the chain is prevented, and reduction in chain life is suppressed. An object of the present invention is to provide a power transmission device that can perform the above operation.

In order to achieve the above object, a power transmission device according to the present invention is provided on one end side of a support member (for example, the offset frame 5 in the embodiment) and extends in the vertical direction and is rotatably supported. And a driven shaft disposed on the other end side of the support member and extending in the vertical direction and rotatably supported, a drive sprocket provided on the drive shaft, a driven sprocket provided on the driven shaft, and a drive It has a chain hung in a plane perpendicular to the vertical direction between the sprocket and the driven sprocket, and when the drive shaft is rotated, the driving force of the drive shaft is transmitted to the driven shaft through the chain. In the power transmission device,
The chain is disposed on the inner side in the width direction of the slack side chain disposed opposite to the tension side chain that transmits the driving force of the drive shaft to the driven shaft, and contacts the inner surface of the slack side chain. An inner guide,
The slack side chain is arranged on the outside in the width direction of the slack side chain, contacts the outside surface of the slack side chain, and moves along the slack side chain so that the movement path of the slack side chain along with the inside guide part curves toward the tight side chain. An outer guide for guiding the movement of the chain;
The upper surface of the inner guide portion on the loose chain side is positioned above at least one of the upper surface of the drive sprocket and the upper surface of the driven sprocket and contacts the lower surface of the upper plate constituting the loose chain. The plate is pushed upward.
There may be a gap between the lower surface of the inner guide portion and the upper surface of the lower plate constituting the loose chain (Claim 2).

According to the power transmission device of the above configuration (Claim 1 or Claim 2), the slackening of the slack side chain is curved so that the movement trajectory of the slack side chain is curved toward the tension side chain side. By having the inner guide portion and the outer guide portion that guide the movement of the side chain, the loose side chain passes between the inner guide portion and the outer guide portion, curves to the tension side chain side, and moves to the driven shaft side. .
For this reason, the moving distance when the slack side chain moves from the drive shaft side to the driven shaft side can be lengthened, and slackness of the slack side chain can be suppressed even when the chain is extended. As a result, it is possible to prevent the occurrence of vibrations due to the slack of the chain or the occurrence of noise due to the slack chain coming into contact with the cover covering the power transmission device, etc. Can be suppressed.

  According to the power transmission device of the above configuration (claim 1 or claim 2), the upper surface of the inner guide portion is positioned above at least one of the upper surface of the drive sprocket and the upper surface of the driven sprocket, The slack of the chain can be reduced, and as a result, noise generated when the chain comes into contact with and contacts the upper surface of the drive sprocket and the upper surface of the driven sprocket can be suppressed.

In the power transmission device having the above configuration (claim 1 or claim 2), at least one of the inner guide portion and the outer guide portion is disposed below the loose side chain and intersects the loose side chain in plan view. And a lower sag restricting portion that restricts the slack of the slack side chain downward (Claim 3).
In this case, a gap may be secured between the upper surface of the lower sag restricting portion and the lower end of the slack side chain (claim 4).

  According to the power transmission device having the above configuration (Claim 3 or Claim 4), at least one of the inner guide portion and the outer guide portion is disposed below the loose side chain and intersects the loose side chain in plan view. By having the lower sag restricting portion extending in the direction of the sag, it is possible to suppress sag of the slack side chain downward. For this reason, it is possible to prevent the chain engaging with the drive sprocket and the driven sprocket from coming off from these sprockets.

  In the power transmission device having the above-described configuration (claims 1 to 4), the outer guide portion is provided so as to be able to move toward and away from the slack side chain, and is biased toward the slack side chain so that the slack side chain is moved. You may have the chain biasing means biased to the tension side chain side (Claim 5).

  According to the power transmission device having the above configuration (claim 5), the outer guide portion is urged by the chain urging means to urge the slack side chain toward the tension side chain, thereby increasing the slack of the slack side chain. Regardless of this, this slack can be surely eliminated.

  In the power transmission device having the above-described configuration (claim 5), the outer guide portion may be supported by the tip portion of the chain urging means so as to be rotatable in the lateral direction (claim 6).

  According to the power transmission device of the above configuration (Claim 6), the outer guide portion is supported by the tip end portion of the chain urging means so as to be pivotable in the lateral direction, so that the slack of the slack side chain can be accommodated. The outer guide portion rotates in the lateral direction with respect to the tip end portion of the chain biasing means. For this reason, according to the slackness of the slack side chain, the outer side guide part can be rotated and the slack side chain can be in a tensioned state. For this reason, the slack of the chain can be reliably prevented.

  In the power transmission device having the above-described configuration (claim 5), the outer guide portion is supported by the tip portion of the chain biasing means so as to be pivotable in the lateral direction, and the outer guide portion itself is against the chain biasing means. And may be rotatable (claim 7).

  According to the power transmission device of the above configuration (claim 7), the outer guide portion is supported on the tip portion of the chain biasing means so as to be pivotable in the lateral direction, and the outer guide portion itself is also supported with respect to the chain biasing means. The outer guide part rotates laterally with respect to the tip of the chain urging means according to the slackness of the loose chain, and the outer guide part itself also rotates. To do.

For this reason, the outer side guide part can urge the slack side chain toward the tension side chain side without changing the posture. As a result, the loose side chain can be urged over the entire side surface of the outer guide portion, and the loose side chain can be urged over a wide area. Therefore, it is possible to prevent a situation in which an excessive load acts on a part of the slack side chain to reduce the chain life.
In addition, since the slack side chain is urged over a wide area, the amount of deformation of the slack side chain that curves toward the tension side chain due to the urging can be reduced. For this reason, the situation where the slack side chain contacts the tension side chain can be prevented in advance.

As described above, according to the power transmission device according to the present invention, the slack side chain has a movement trajectory curved toward the tension side chain on the outer side and the inner side in the width direction of the slack side chain. By providing the inner guide portion and the outer guide portion that guide the movement, the slack side chain passes between the inner guide portion and the outer guide portion, curves to the tension side chain side, and moves to the driven shaft side. For this reason, the moving distance when the slack side chain moves from the drive shaft side to the driven shaft side can be lengthened, and slackness of the slack side chain can be suppressed even when the chain is extended.
As a result, it is possible to prevent the occurrence of vibration due to the slack of the chain or the occurrence of noise due to the slack chain coming into contact with the cover that covers the power transmission device, etc. Can do.

1 is a perspective view of a wrinkle coater equipped with a power transmission device according to an embodiment of the present invention. A plan view of this wrinkle coater is shown. The offset frame is shown, in which (a) is a plan view of the offset frame, and (b) is a cross-sectional view of the offset frame corresponding to II-II in FIG. The internal plan view of a power transmission device is shown. It is a front view of the part corresponded to IV arrow of Fig.4 (a). The enlarged view of the part corresponded to the III arrow view of FIG.3 (b) is shown. The internal plan view of a power transmission device is shown.

Hereinafter, a preferred embodiment of the present invention will be described with reference to FIGS. The present embodiment will be described below by taking an example of a basket coater for agricultural machinery. For convenience of explanation, the directions of arrows shown in FIG. 1 (perspective view) will be described below as the front-rear direction and the left-right direction. First, before describing the power transmission device according to the present invention, an outline of a coater equipped with the power transmission device will be outlined. As shown in FIG. 1, the scissor coater 1 is connected to a three-point link connecting mechanism (not shown) provided at the rear portion of the traveling machine body (not shown), and the scissors are applied according to the forward movement of the traveling machine body. A painting operation is performed.
The hull coater 1 is attached to the front side of a hitch frame 2 extending in the left-right direction, and can be connected to a hull frame side connecting frame 3 that can be connected to a three-point link connecting mechanism. The offset frame 5 is attached and the rear end side is turnable in the left-right direction, and the working unit 10 is connected to the rear end portion of the offset frame 5 so as to be turnable in the left-right direction.

As shown in FIG. 3B (cross-sectional view), a gear box 4 is provided at the lower center of the hitch frame 2 in the left-right direction. Power is transmitted to the input shaft 4a of the gear box 4 from the PTO shaft (not shown) of the traveling machine body via the transmission shaft (not shown) of the coater side connection frame 3 shown in FIG. The offset frame 5 is a hollow box-shaped member, and a power transmission device 40 described later is provided in the offset frame 5.
As shown in FIG. 1, the offset frame 5 can swing in the left-right direction by the expansion and contraction of a swing cylinder 6 pivotally connected between the offset frame 5 and the hitch frame 2.

  A driven shaft 41 shown in FIG. 3 (b) extending in the vertical direction is provided in the rear end portion of the offset frame 5, and a rotation center shaft 7 shown in FIG. 3 (b) extending downwardly below the driven shaft 41. Are connected. A rotating shaft case 8 extending downward is rotatably attached to the rear end portion of the offset frame 5. The rotating shaft case 8 can be rotated by an expansion / contraction operation of a rotating cylinder 9 that is pivotally connected between the side portion of the offset frame 5 and the side portion of the rotating shaft case 8.

  As shown in FIG. 2 (plan view), the above-described working unit 10 is attached to the lower part of the rotating shaft case 8. The working unit 10 includes a heaven field processing unit 11 that cuts the upper part of the old fence formed along the periphery of the field, a pre-processing unit 21 that piles up the cut soil, and the old soil that has been cut off It has a trimming part 31 to be applied on the collar.

  The celestial processing unit 11 has a celestial processing rotor (not shown) that is rotatable. The celestial processing rotor is connected to and supported by the rotary shaft case 8 shown in FIG. A power transmission mechanism (not shown) is built in the heaven power transmission case 22 so that the driving force from the rotation center shaft 7 shown in FIG. 3B is transmitted to the heaven processing rotor via this power transmission mechanism. It has become.

  The pre-processing unit 21 has a tilling rotor (not shown) that can freely rotate. The tilling rotor is connected to and supported by the rotary shaft case 8 shown in FIG. 1 through a preprocessing power transmission case (not shown). A power transmission mechanism (not shown) is built in the pretreatment power transmission case, and the driving force from the rotation center shaft 7 shown in FIG. 3B is transmitted to the tilling rotor via this power transmission mechanism. Yes.

  The trimming unit 31 extends in the left-right direction and is attached to a rotating shaft (not shown) that is rotatably supported, and a cylinder that is attached to the right end of the polyhedron drum 32 and extends in the lateral direction. Part 33. The trimming unit 31 is connected to and supported by the rotary shaft case 8 via the trimming power transmission case 35. A power transmission mechanism (not shown) is built in the trimming power transmission case 35 so that the driving force from the rotation center shaft 7 shown in FIG. 3B is transmitted to the trimming section 31 via this power transmission mechanism. It has become.

  Next, the power transmission device according to the present invention will be described. As shown in FIG. 3 (b), the power transmission device 40 is disposed in the front end portion of the offset frame 5 and extends in the vertical direction so as to be rotatable, and in the middle portion in the vertical direction of the drive shaft 43. The fixed drive sprocket 45, the aforementioned driven shaft 41, the driven sprocket 47 fixed to the intermediate portion in the vertical direction of the driven shaft 41, the chain 49 hung between the drive sprocket 45 and the driven sprocket 47, and the chain 49, to prevent the slack of the slack side chain 49b shown in FIG. 4 (a) disposed opposite to the tension side chain 49a shown in FIG. 4 (a) that transmits the driving force of the drive shaft 43 to the driven shaft 41. The inner side guide part 51 and the outer side guide part 61 which guide the movement of the loose side chain 49b are provided.

  The drive shaft 43 receives the drive force from the input shaft 4a via bevel gears 37 and 38 disposed in the gear box 4. For this reason, the driving force from the traveling machine body is transmitted to the driven shaft 41 via the input shaft 4 a, the driving shaft 43, the driving sprocket 45, the chain 49 and the driven sprocket 47. Note that the drive sprocket 45 and the driven sprocket 47 are arranged so that each of them has substantially the same height when the offset frame 5 extends in the horizontal direction.

  The inner side guide part 51 and the outer side guide part 61 are arrange | positioned in the approximate center part in the offset flame | frame 5, as shown to Fig.4 (a) (plan view). The inner guide 51 is a block-like member installed on the inner side of the loose side chain 49b extending between the drive sprocket 45 and the driven sprocket 47. The inner side guide portion 51 is in sliding contact with the inner surface of the loose side chain 49b on the loose side chain 49b side. A slidable contact surface 51a that extends in the front-rear direction and curves in a convex shape toward the loose side chain 49b is formed. The position of the sliding contact surface 51a is a position in the vicinity of the inner surface of the slack side chain 49b when the slack side chain 49b extends linearly between the drive sprocket 45 and the driven sprocket 47.

In order to restrict the slack side chain 49b from sagging downward in the inner guide portion 51, a lower side slack is arranged below the slack side chain 49b and extends in a direction substantially perpendicular to the slack side chain 49b in plan view. A restricting portion 52 is provided. Note that the extending direction of the lower sag restricting portion 52 may be a direction that intersects the loose side chain 49b in a plan view, and is not limited to a direction that intersects at right angles.
As shown in FIG. 5, the lower sag restricting portion 52 is a rod-like member, and a tip portion thereof is bent upward and extends upward on the outside of the loose side chain 49b. For this reason, as shown in FIG. 4A, when the drive shaft 43 is rotationally driven in the direction of the arrow A, the loose side chain 49b is guided by the inner side of the loose side chain 49b slidably contacting the sliding contact surface 51a. Move to the shaft 41 side.
Further, the slack side chain 49b is restricted from slacking downward by the bottom slack regulating part 52. For this reason, the vertical positional relationship between the loose side chain 49b, the drive sprocket 45 and the driven sprocket 47 is maintained in a substantially constant positional relationship. For this reason, it is possible to prevent the chain 49 from coming off the sprockets 45 and 47 in advance.

  The outer guide part 61 is disposed closer to the driven shaft 41 than the inner guide part 51. The outer guide portion 61 is a block-like member disposed outside the loose side chain 49b. The loose side chain 49b side slides on the outer side surface of the loose side chain 49b and extends in the front-rear direction so as to be on the loose side chain 49b side. A slidable contact surface 61a curved in a convex shape is formed. The outer guide portion 61 is provided with a chain urging means 63 that urges the outer guide portion 61 toward the loose side chain 49b.

The chain urging means 63 includes a tension adjusting member 65 attached to the side surface 5a of the offset frame 5, a tension spring 67 that is hooked on the tension adjusting member 65 at one end side and extends along the side surface 5a, and the tension spring 67. It has a link portion 69 that is hooked on the end side and is pivotable in the front-rear direction.
The link portion 69 engages the other end side of the tension spring 67 and is connected to the first link member 70 supported to be rotatable in the front-rear direction and the base side of the first link member 70 to be driven shaft 41. It has the 2nd link member 71 which extends to the side and fixes the outer side guide part 61 so that attachment or detachment is possible. The tension adjusting member 65 is attached by screwing to the tip end portion of a bracket 68 protruding from the side surface 5 a of the offset frame 5.
For this reason, by adjusting the protrusion amount L of the tension adjusting member 65 with respect to the bracket 68, the magnitude of the force with which the outer guide portion 61 biases the loose side chain 49b can be adjusted. That is, the smaller the protruding amount L of the tension adjusting member 65 is, the larger the extension amount of the tension spring 67 is, and the urging force of the loose side chain 49b through the outer guide portion 61 can be increased.

For this reason, even when the chain 49 is stretched due to wear or the like and the slack side chain 49b is slack, the outer guide 61 projects the tension adjusting member 65 so that the slack side chain 49b is always urged toward the tension side chain 49a. When the amount L is adjusted, as shown in FIG. 4B (plan view), the outer guide portion 61 has a lateral direction (in FIG. 4B) with the rotation fulcrum 70a of the first link member 70 as the rotation center. The slack side chain 49b is urged by the outer guide portion 61 to be bent toward the tension side chain 49a.
For this reason, the slack slack side chain 49b can be put in a tensioned state. As a result, it is possible to prevent the occurrence of vibration due to the slack of the chain 49 or the occurrence of noise due to the slack of the chain 49 coming into contact with the offset frame 5 and reducing the chain life. Can be suppressed.

The tension adjusting member 65 and the tension spring 67 are covered with a cover member 75 installed on the side of the offset frame 5 as shown in FIG. Here, the tension spring 67 and the tension adjusting member 65 that constitute a part of the chain urging means 63 are arranged along the offset frame 5 at a lateral position of the offset frame 5.
For this reason, the protrusion amount from the offset frame 5 of the cover member 75 which covers these can be made small, and as a result, the enlargement of the offset frame 5 can be suppressed.

As shown in FIG. 6 (partially enlarged view), the upper surface 51 b of the inner guide portion 51 is disposed at a position slightly shifted upward from the upper surface 45 a where the drive sprocket 45 contacts the chain 49. For this reason, the slack of the chain 49 can be reduced, and as a result, generation of noise can be suppressed.
Note that the upper surface 51b of the inner guide portion 51 is disposed slightly above the upper surface 47a of the driven sprocket 47 shown in FIG. 3B, or the upper surface of the outer guide portion 61 shown in FIG. The upper surface 45a of the drive sprocket 45 and the upper surface 47a of the drive sprocket 45 may be disposed slightly above.

Further, as shown in FIG. 7A (plan view), the outer guide portion 61 is supported by the distal end portion of the second link member 71 of the link portion 69 so that the outer guide portion 61 itself can be rotated in the lateral direction. Also good. When the outer guide portion 61 is also provided so as to be pivotable in the lateral direction as described above, when the slack is generated in the slack side chain 49b, as shown in FIG. 7B (plan view), the outer guide portion 61 The first link member 70 rotates in the lateral direction (downward in FIG. 7B) about the rotation fulcrum 70a of the link member 70, and the outer guide portion 61 itself also rotates at the tip end portion of the second link member 71. The slack side chain 49b is urged toward the tension side chain 49a while pivoting in the lateral direction around 71a. For this reason, the outer side guide part 61 can urge | bias the slack side chain 49b, without changing an attitude | position.
Accordingly, the sliding contact surface 61a of the outer guide portion 61 is maintained in a state extending in the front-rear direction, so that the loose side chain 49b can be urged in a wide area, and an excessive load is applied to a part of the loose side chain 49b. It is possible to prevent a situation in which the chain life is reduced due to the action of. Further, since the slack side chain 49b is urged over a wide area, the amount of deformation of the slack side chain 49b that bends toward the tension side chain 49a by urging can be reduced. For this reason, the situation where the slack side chain 49b contacts the tension side chain 49a can be prevented in advance.

In the above-described embodiment, the example in which the outer guide portion 61 is provided so as to be movable toward and away from the loose side chain 49b is shown. However, the outer guide portion 61 is fixed to the offset frame 5. May be installed. In this case, the sliding contact surface 61 a of the outer guide portion 61 is arranged closer to the tension chain 49 a side than the sliding contact surface 51 a of the inner guide portion 51.
In this way, the slack side chain 49b passes between the inner side guide part 51 and the outer side guide part 61, so that the slack side chain 49b can be bent, and as a result, the slack side chain 49b sags. Even if this occurs, a part or all of this slack can be absorbed by bending the loose side chain 49b.

5 Offset frame (support member)
40 power transmission device 41 driven shaft 43 drive shaft 45 drive sprocket 45a upper surface 47 driven sprocket 47a upper surface 49 chain 49a tension side chain 49b slack side chain 51 inner guide portion 51a upper surface 52 lower slack regulating portion 61 outer guide portion 63 chain biasing Means 65 Tension adjusting member 67 Tension spring 69 Link portion

Claims (7)

A drive shaft disposed on one end side of the support member and extending in the vertical direction and supported rotatably;
A driven shaft disposed on the other end side of the support member and extending in the vertical direction and supported rotatably;
A drive sprocket provided on the drive shaft;
A driven sprocket provided on the driven shaft;
A chain hung in a plane perpendicular to the vertical direction between the drive sprocket and the driven sprocket;
In the power transmission device for transmitting the driving force of the driving shaft to the driven shaft via the chain when the driving shaft is rotated,
The chain is disposed on the inner side in the width direction of the slack side chain disposed opposite to the tension side chain that transmits the driving force of the drive shaft to the driven shaft, and contacts the inner surface of the slack side chain. An inner guide,
The slack side chain is arranged on the outside in the width direction of the slack side chain, contacts the outside surface of the slack side chain, and moves along the slack side chain so that the movement path of the slack side chain along with the inside guide part curves toward the tight side chain. An outer guide for guiding the movement of the chain;
The upper surface of the inner guide portion on the loose chain side is positioned above at least one of the upper surface of the drive sprocket and the upper surface of the driven sprocket and contacts the lower surface of the upper plate constituting the loose chain. The power transmission device is characterized in that the plate is pushed upward.   2. The power transmission device according to claim 1, wherein a gap exists between a lower surface of the inner guide portion and an upper surface of a lower plate constituting the slack side chain.   At least one of the inner guide portion and the outer guide portion is disposed below the slack side chain, and extends in a direction intersecting the slack side chain in a plan view to restrict slack of the slack side chain. The power transmission device according to claim 1, further comprising a lower sag restricting portion.   The power transmission device according to claim 3, wherein a gap is secured between an upper surface of the lower sag restricting portion and a lower end of the slack side chain.   The outer guide portion is provided so as to be movable toward and away from the slack side chain, and is also urged toward the slack side chain to urge the slack side chain toward the tension side chain. The power transmission device according to any one of claims 1 to 4, wherein the power transmission device is provided.   The power transmission device according to claim 5, wherein the outer guide portion is supported by a tip portion of the chain urging means so as to be pivotable in a lateral direction. The outer guide portion is supported by a tip end portion of the chain urging means so as to be rotatable in a lateral direction, and the outer guide portion itself is rotatable with respect to the chain urging means. The power transmission device according to claim 5.

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