WO2016028196A1

WO2016028196A1 - Vibration absorber and work equipment having the same

Info

Publication number: WO2016028196A1
Application number: PCT/SE2014/050946
Authority: WO
Inventors: Masanori Kobayashi; Takayuki Kimura
Original assignee: Husqvarna AB
Current assignee: Husqvarna AB
Priority date: 2014-08-18
Filing date: 2014-08-18
Publication date: 2016-02-25
Anticipated expiration: 2017-02-18
Also published as: JP6426830B2; JP2017526357A

Abstract

A vibration absorber (10) is provided in a transmission path of a rotary driving force from an engine to a cutter blade and includes: an input-side transmission shaft (11) that receives the rotary driving force from the engine; an output-side transmission shaft (12) that is disposed on the same axis (AX) as that of the input-side transmission shaft (11) and is rotatable relative to the input-side transmission shaft (11) to output the rotary driving force to the cutter blade; a bushing (13) provided on the axis (AX) and is rotatable relative to the input-side transmission shaft (11) and the output-side transmission shaft (12); a helical torsion coil spring (14) disposed on the axis (AX) and having a first end attached to the bushing (13) and a second end attached to the output-side transmission shaft (12); and a power transmission switching unit (20) that switches a transmission state of the rotary driving force between the input-side transmission shaft (11) and the bushing (13) between a first state and a second state, the first state allowing the transmission of the rotary driving force so that the helical torsion coil spring (14) is deformed in a diameter-reducing range, the second state restricting the transmission of the rotary driving force through the helical torsion coil spring (14).

Description

VIBRATION ABSORBER AND WORK EQUIPMENT HAVING THE SAME

DESCRIPTION TECHNICAL FIELD

[0001]

The present invention relates to a vibration absorber and work equipment having the vibration absorber.

BACKGROUND ART

[0002]

In work equipment such as a portable brushcutter, torsional vibration is disadvantageously generated to a shaft connecting an engine and a cutter blade due to torque fluctuation during acceleration/deceleration of the drive source, fluctuation of the rotation speed, or fluctuation of a load applied to a cutter blade. In order to reduce the torsional vibration, it is known to attach a vibration absorber having a helical torsion coil spring between a driveshaft of an engine and a shaft to absorb the torsional vibration with the helical torsion coil spring (e.g. Patent Literature 1). The vibration absorber includes a rotation restricting unit that keeps the helical torsion coil spring from being twisted by a predetermined angle or more.

[0003]

Another typical vibration absorber includes an engagement step to be engaged with the helical torsion coil spring. Due to the presence of the engagement step, the helical torsion coil spring is deformed toward a diameter-enlarging side (i.e. in a direction for the diameter of the spring to be enlarged from an original state) when a torsion in a predetermined direction is generated, thereby absorbing the torsional vibration (e.g. Patent Literature 2). The vibration absorber disclosed in Patent Literature 2 is configured so that, when a torsion in a direction opposite to the predetermined direction is generated, the helical torsion coil spring is out of engagement with the engagement step.

CITATION LIST

PATENT LITERATURE(S)

[0004]

Patent Literature 1 JP-A-2007-061029

Patent Literature 2 WO 2011/048697 SUMMARY OF THE INVENTION

PROBLEM(S) TO BE SOLVED BY THE INVENTION

[0005]

However, since the deformation of the helical torsion coil spring occurs in both diameter- enlarging and diameter-reducing directions in the vibration absorber disclosed in Patent Literature 1 , a simple harmonic motion of the helical torsion coil spring is generated, so that the torsional vibration is not easily converged.

In the vibration absorber disclosed in Patent Literature 2, since the deformation of the helical torsion coil spring occurs only in a diameter-enlarging range (i.e. a range of the diameter-enlarging side), the toughness of the helical torsion coil spring is rapidly impaired, resulting in poor durability.

[0006]

An object of the invention is to provide a vibration absorber that is capable of reliably absorbing torsional vibration and is excellent in durability, and work equipment provided with the vibration absorber.

MEANS FOR SOLVING THE PROBLEM(S)

[0007]

A vibration absorber according to an aspect of the invention is provided in a transmission path of a rotary driving force from a drive source to a driven object, the vibration absorber including: an input-side transmission shaft that is configured to receive the rotary driving force from the drive source; an output-side transmission shaft that is disposed coaxially with the input-side transmission shaft, the output-side transmission shaft being rotatable relative to the input-side transmission shaft to output the rotary driving force to the driven object; a bushing that is disposed coaxially with the input- side and output-side transmission shafts, the bushing being rotatable relative to the input-side and output-side transmission shafts; a helical torsion coil spring that is disposed coaxially with the input- side and output-side transmission shafts, a first end of the helical torsion coil spring being attached to the bushing and a second end of the helical torsion coil spring being attached to one of the input-side and output-side transmission shafts; and a power transmission switching unit that is configured to switch a transmission state of the rotary driving force between the other of the input-side and output- side transmission shafts and the bushing between a first state and a second state, the first state allowing a transmission of the rotary driving force while the helical torsion coil spring is deformed within a diameter-reducing range, the second state restricting the transmission of the rotary driving force through the helical torsion coil spring.

[0008]

According to the above aspect of the invention, when the rotary driving force is transmitted from the input-side transmission shaft to the output-side transmission shaft, the power transmission switching unit switches the transmission state of the rotary driving force to the first state, so that the helical torsion coil spring is deformed within the diameter-reducing range (i.e. a range in which the diameter of the helical torsion coil spring is reduced from an original state). Accordingly, the torsional vibration caused during the transmission of the rotary driving force due to the torque fluctuation during acceleration/deceleration of the drive source, fluctuation of the rotation speed, or fluctuation of a load applied to the driven object can be absorbed by the deformation of the helical torsion coil spring within the diameter-reducing range. Further, when the rotation speed of the output-side transmission shaft becomes greater than the rotation speed of the input-side transmission shaft and thus the output-side transmission shaft tends to apply a rotary force to the input-side transmission shaft, the power transmission switching unit switches the transmission state of the rotary driving force to the second state, so that the rotary driving force is not transmitted between the other of the input-side and the output-side transmission shafts and the bushing within a predetermined rotation range. Accordingly, the torsional vibration caused due to the difference between rotation speeds between the transmission shafts can be reliably absorbed between the other of the input-side and output-side transmission shafts and the bushing. Further, in the above second state, no rotary driving force is transmitted to the helical torsion coil spring attached to the bushing and thus the helical torsion coil spring is kept from being deformed to the diameter-enlarging side. In other words, the helical torsion coil spring only deforms within the diameter-reducing range, so that the durability of the helical torsion coil spring and, consequently, the vibration absorber can be enhanced.

[0009]

In the vibration absorber according to the above aspect of the invention, the power transmission switching unit preferably includes a first contact portion provided to the other of the input- side and output-side transmission shafts and a second contact portion provided to the bushing, and the power transmission switching unit restricting the transmission of the rotary driving force between the other of the input-side and output-side transmission shafts and the bushing within a rotation range until the first contact portion and the second contact portion contact with each other.

According to the above arrangement, when the first contact portion provided to the other of the input-side and the output-side transmission shafts is not in contact with the second contact portion provided to the bushing, the input-side and output-side transmission shafts are independently and separately rotatable while no rotary driving force is transmitted between the input-side and output-side transmission shafts, thereby reliably achieving the second state.

[0010]

The vibration absorber according to the above aspect of the invention preferably includes a rotation restricting unit that is configured to restrict a mutual rotation range of the one of the input-side and output-side transmission shafts and the bushing so that a deformation of the helical torsion coil spring occurs only within the diameter-reducing range.

According to the above arrangement, the rotation range of the bushing relative to the one of the input-side and output-side transmission shafts is restricted by the rotation restricting unit so that the helical torsion coil spring deforms within the diameter-reducing range. Accordingly, the helical torsion coil spring is reliably kept from being deformed in the diameter-enlarging range, thereby further reliably enhancing the durability of the vibration absorber.

[0011]

In the vibration absorber according to the above aspect of the invention, the rotation restricting unit preferably includes a third contact portion provided to the bushing and a fourth contact portion provided to the one of the input-side and output-side transmission shafts, the third contact portion and the fourth contact portion being adapted to contact with each other to define the rotation range of the one of the input-side and output-side transmission shafts and the bushing.

According to the above arrangement, with the simple arrangement of the mutual contact between the third contact portion provided to the bushing and the fourth contact portion provided to the one of the input-side and output-side transmission shafts, the deformation of the helical torsion coil spring to the diameter-enlarging side can be further reliably prevented.

[0012] Work equipment according to another aspect of the invention includes the above vibration absorber.

According to the above aspect of the invention, since the work equipment includes the above- described vibration absorber, the torsional vibration can be reliably absorbed and the durability of the work equipment can be enhanced.

BRIEF DESCRIPTION OF DRAWING(S)

[0013]

Fig. 1 is an overall view showing a brushcutter according to an exemplary embodiment of the invention.

Fig. 2 is a cross sectional view showing a relevant part of the brushcutter.

Fig. 3 is an exploded perspective view showing a vibration absorber.

Fig. 4 is a sectional side elevational view showing the vibration absorber.

Fig. 5 is a cross sectional view taken along V-V lines in Fig. 4.

Fig. 6 is a cross sectional view taken along VI- VI lines in Fig. 4.

DESCRIPTION OF EMBODIMENT(S)

[0014]

Description of Components

A vibration absorber 10 according to an exemplary embodiment and work equipment provided with the vibration absorber 10 in a form of a brushcutter 1 will be described below with reference to Figs. 1 to 6. The brushcutter 1 includes an outer pipe 2, a power section 3 provided to a first end of the outer pipe 2, and a cutter blade 4 (driven object) provided to a second end of the outer pipe 2 and adapted to be rotated by the power section 3.

[0015]

The power section 3 includes an engine 3A (drive source). A housing 5 that supports the outer pipe 2 is fixed on the power section 3. As shown in Fig. 2, a driveshaft of the engine 3A is connected through a centrifugal clutch 3B and a vibration absorber 10 housed in the housing 5 to a first end of a shaft 6 that is rotatably inserted into the outer pipe 2. In this exemplary embodiment, the driveshaft of the engine 3A rotates counterclockwise when viewed from a side attached with the shaft 6. The cutter blade 4 is attached to a second end of the shaft 6. [0016]

Fig. 3 is an exploded perspective view of the vibration absorber 10. Fig. 4 is a sectional side elevational view of the vibration absorber 10. The vibration absorber 10 includes: an input-side transmission shaft 11 to which a rotary driving force of the engine 3 A is transmitted; an output-side transmission shaft 12 that is rotatable relative to the input-side transmission shaft 11 and adapted to transmit the rotary driving force to the cutter blade 4; a bushing 13 that is rotatable relative to the input- side transmission shaft 11 and the output-side transmission shaft 12; and a left-handed helical torsion coil spring 14.

[0017]

These components are disposed on a common axis AX and each rotate around the axis AX.

The input-side transmission shaft 11, the output-side transmission shaft 12, and the bushing 13 are made of a steel material having sufficient hardness and strength (e.g. chrome molybdenum steel). The helical torsion coil spring 14 is made of a material such as a piano wire. It should be noted that, in the following description, a side near the engine 3A on the axis AX will be referred to as a "proximal side" and a side near the cutter blade 4 on the axis AX will be referred to as a "distal side" of each of the components.

[0018]

The input-side transmission shaft 11 is defined substantially in a form of a rod extending along the axis AX and integrally provided with a large -diameter first flange 111 substantially in the middle thereof along the axis AX. An outer diameter of the first flange 111 is substantially equal to an outer diameter of the helical torsion coil spring 14. The proximal side of the input-side transmission shaft 11 relative to the first flange 111 defines a connector portion 112 provided with a spline grooves used when being connected with the centrifugal clutch 3B, whereas the distal side of the input-side transmission shaft 11 relative to the first flange 111 defines an insert portion 113 that is adapted to be inserted into the output-side transmission shaft 12.

[0019]

The outer diameter of the insert portion 113 is substantially equal to the inner diameter of the output-side transmission shaft 12, so that the input-side transmission shaft 11 is smoothly rotatable relative to the output-side transmission shaft 12. A groove 114 to which a circlip 15 is attachable is provided on the insert portion 113 (see Fig. 4). The circlip 15 engages with a groove 125 (see Fig. 4) provided on an inner circumference of the output-side transmission shaft 12. Thus, the insert portion 113 is kept from being detached from the output-side transmission shaft 12.

[0020]

A pair of first projections 115 (first contact portion) protrude from a face of the first flange

111 facing the distal side (see Fig. 5). As shown in Fig. 5, the first projections 115 are disposed in a point-symmetric manner and are defined each in a sector shape around a point through which the axis AX passes. A center angle a each of the first projections 115 is not limited to a specific value but is 32 degrees in the exemplary embodiment.

[0021]

As shown in Figs. 3 and 4, the output-side transmission shaft 12 is a substantially cylindrical member extending in the direction of the axis AX. The output-side transmission shaft 12 integrally includes a second flange 121 near a distal end thereof. The outer diameter of the second flange 121 is substantially equal to those of the first flange 111 and the helical torsion coil spring 14. As shown in Fig. 4, a first engagement groove 122 is provided to the second flange 121 from the proximal side thereof. One of engagement portions 141 (one at the distal side) of the helical torsion coil spring 14 is engaged with the first engagement groove 122.

[0022]

The output-side transmission shaft 12 is inserted into the helical torsion coil spring 14 from the proximal side of the output-side transmission shaft 12. The outer diameter of a part of the output- side transmission shaft 12 near the proximal side relative to the second flange 121 is slightly smaller than the inner diameter of the helical torsion coil spring 14. Thus, a clearance is provided between the outer circumference of the output-side transmission shaft 12 and the helical torsion coil spring 14. The clearance and a later-described rotation restricting unit 30 keep the helical torsion coil spring 14 from being in contact with the outer circumference of the output-side transmission shaft 12 when a diameter- reducing deformation of the output-side transmission shaft 12 occurs.

[0023]

A connector portion 123 (see Fig. 4) in a form of spline teeth used when being connected with the shaft 6 protrudes from an inner circumference of a middle section of the output-side transmission shaft 12. A circumferential part of a proximal end of the output-side transmission shaft 12 protrude in the direction of the axis AX to define a pair of claws 124 (see Fig. 3) serving as a fourth contact portion. As shown in Fig 6, the claws 124 are disposed in a point symmetric manner around a point through which the axis AX passes. A center angle β of each of the claws 124 is not limited to a specific value but is 77 degrees in the exemplary embodiment.

[0024]

The bushing 13 is a cylindrical member having substantially the same outer diameter as those of the above-described first flange 111 and the second flange 121, and includes a hole 131 at a center thereof penetrating in the direction of the axis AX (see Fig. 3). The insert portion 113 of the distal end of the input-side transmission shaft 11 is inserted into the hole 131 from the proximal side of the bushing 13. The inner diameter of the hole 131 is substantially equal to the outer diameter of the input- side transmission shaft 11, so that the bushing 13 is smoothly rotatable relative to the input-side transmission shaft 11.

[0025]

A pair of second projections 132 that serve as a second contact portion protrude from a face of the bushing 13 facing the proximal side (see Figs. 3 and 5). As shown in Fig. 5, the second projections 132 are disposed in a point-symmetric manner and are defined each in a sector shape, around the point through which the axis AX passes. A center angle γ of each of the second projections 132 is not limited to a specific value but is 38 degrees in the exemplary embodiment.

[0026]

A pair of third projections 134 that serve as a third contact portion protrude from a face of the bushing 13 facing the distal side (see Figs. 3 and 6). As shown in Fig. 6, the third projections 134 are disposed in a point-symmetric manner and are defined each in a sector shape, around the point through which the axis AX passes. A center angle δ of each of the third projections 134 is not limited to a specific value but is 63 degrees in the exemplary embodiment.

[0027]

Further, a second engagement groove 133 is provided to the face facing the distal side of the bushing 13 at a position not overlapping with the third projections 134 from the distal side (see Figs. 4 and 6). The other of the engagement portions 141 (one at the proximal side) of the helical torsion coil spring 14 is engaged with the second engagement groove 133.

[0028]

Both ends of the helical torsion coil spring 14 extend substantially parallel to the axis AX (see Figs. 3 and 4). The extended portions define the above -described engagement portions 141. The helical torsion coil spring 14 is engaged with the first engagement groove 122 and the second engagement groove 133 so that the helical torsion coil spring 14 is slightly deformed to reduce the diameter thereof when no torque is applied to the vibration absorber 10. Further, as will be described below with reference to Fig. 6, a counterclockwise face 124B (i.e. a face facing a counterclockwise direction in the figure) of each of the claws 124 provided to the output-side transmission shaft 12 is in contact with a clockwise face 134A (i.e. a face facing a clockwise direction in the figure) of each of the third projections 134 provided on the bushing 13.

[0029]

Fig. 5 is a cross sectional view of the vibration absorber 10 taken along V-V lines in Fig. 4, where no torque is applied to the vibration absorber 10. The first projections 115 of the input-side transmission shaft 11 are located in the clearances 136 between the pair of second projections 132 of the bushing 13. It should be noted that, though the clockwise face 115 A of each of the first projections 115 is illustrated to be in contact with the counterclockwise face 132B of each of the second projections 132 in Fig. 5, since the vibration absorber 10 does not include a mechanism for determining an original position of the first projections 115, the first projections 115 are not necessarily disposed as illustrated in Fig. 5. For instance, the first projections 115 may be separated from the second projections 132.

[0030]

When the first projections 115 are rotated within the clearances 136 without being in contact with the second projections 132, the input-side transmission shaft 11 merely freely rotates relative to the bushing 13 and the output-side transmission shaft 12, thereby causing no deformation on the helical torsion coil spring 14. On the other hand, when the counterclockwise face 115B of each of the first projections 115 is in contact with the clockwise face 132A of each of the second projections 132, the input-side transmission shaft 11 rotates together with the bushing 13 and the output-side transmission shaft 12, thereby causing a deformation of the helical torsion coil spring 14 within a diameter-reducing range (i.e. a range in which the diameter of the helical torsion coil spring 14 is reduced). [0031]

As described above, the first projections 115 of the input-side transmission shaft 11 and the second projections 132 of the bushing 13 define a power transmission switching unit 20 that switches a transmission state of the rotary driving force between the input-side transmission shaft 11 and the bushing 13, between: (i) a first state, in which the transmission of the rotary driving force is permitted while the helical torsion coil spring 14 is deformed in the diameter-reducing range; and (ii) a second state, in which the transmission of the rotary driving force is restricted.

[0032]

Fig. 6 is a cross sectional view of the vibration absorber 10 taken along VI- VI lines in Fig. 4, where no torque is applied to the vibration absorber 10. Each of the claws 124 of the output-side transmission shaft 12 is disposed in clearances 135 defined between the third projections 134 of the bushing 13. The output-side transmission shaft 12 is biased counterclockwise in Fig. 6 by a biasing force of the helical torsion coil spring 14 that is disposed in a manner slightly deformed in a diameter- reducing direction. Accordingly, the counterclockwise face 124B of each of the claws 124 presses the clockwise face 134A of each of the second projections 132.

[0033]

The rotation range of the output-side transmission shaft 12 relative to the bushing 13 is restricted by the third projections 134 of the bushing 13 and the claws 124 of the output-side transmission shaft 12. As described above, the third projections 134 of the bushing 13 and the claws 124 of the output-side transmission shaft 12 define the rotation restricting unit 30 for restricting the mutual rotation range of the output-side transmission shaft 12 and the bushing 13. Within the rotation range, the deformation of the helical torsion coil spring 14 occurs only within the diameter-reducing range.

[0034]

Description of Vibration-Absorbing Operation

A vibration-absorbing operation by the vibration absorber 10 will be described below with reference to Figs. 5 and 6.

Initially, when the engine 3A is started, the centrifugal clutch 3B is connected to start the rotation of the input-side transmission shaft 11 of the vibration absorber 10 in a counterclockwise direction in Fig. 5, whereby a relative displacement is caused between the input-side transmission shaft 11 and the bushing 13.

[0035]

Specifically, the first projections 115 of the input-side transmission shaft 11 rotate counterclockwise in Fig. 5 (illustrated by arrows AR1), so that the clockwise face 115A of each of the first projections 115 separates from the counterclockwise face 132B of each of the second projections 132 of the bushing 13. The counterclockwise face 115B of each of the first projections 115 then comes into contact with the clockwise face 132A of each of the second projections 132. Thus, the input-side transmission shaft 11 starts rotating integrally with the bushing 13.

[0036]

In this state, the rotation speed of the driveshaft of the engine 3A becomes substantially equal to the rotation speed of the cutter blade 4.

During an actual operation in which a load applied to the cutter blade 4 is extremely small (e.g. only a small amount of grass is mowed or the grass is of a type that can be easily mowed), the helical torsion coil spring 14 hardly deforms to reduce the diameter thereof (i.e. to the diameter- reducing side), so that the rotary driving force of the engine 3A is transmitted to the cutter blade 4 through the vibration absorber 10, thereby performing the mowing operation.

[0037]

When the load applied to the cutter blade 4 gradually increases (e.g. when the amount of the grass to be mowed increases), a relative displacement occurs between the bushing 13 and the output- side transmission shaft 12. Specifically, the counterclockwise face 134B of each of the third projections 134 of the bushing 13 comes close to the clockwise face 124A of each of the claws 124 provided to the output-side transmission shaft 12, thereby reducing the distance between the faces 124A and 134B. At this time, the helical torsion coil spring 14 deforms to reduce the diameter thereof while absorbing the torsional vibration.

[0038]

When the load applied to the cutter blade 4 exceeds a predetermined level, the counterclockwise face 134B of each of the third projections 134 of the bushing 13 contacts with the clockwise face 124A of each of the claws 124 provided on the output-side transmission shaft 12. At this time, the deformation of the helical torsion coil spring 14 towards the diameter-reducing side is maximized. When the third projections 134 are in contact with the claws 124, the input-side transmission shaft 11, the output-side transmission shaft 12, the bushing 13 and the helical torsion coil spring 14 are directly connected, so that the rotary driving force of the engine 3 A is directly transmitted to the cutter blade 4.

[0039]

In contrast, when the load applied to the cutter blade 4 is gradually decreased (i.e. from a great load to a smaller load), the clockwise face 124A of each of the claws 124 is separated from the counterclockwise face 134B of each of the third projections 134, so that the helical torsion coil spring 14 is untwisted (i.e. reduce the diameter-reduction degree thereof) while absorbing the torsional vibration due to load fluctuation or the like. In this state, the helical torsion coil spring 14 transmits the rotary driving force of the engine 3 A to the output-side transmission shaft 12. When the load fluctuation occurs (e.g. when the load is again increased), the above -described operations are repeated.

[0040]

On the other hand, when the engine 3 A is decelerated from when the cutter blade 4 is rotated at a predetermined speed, the rotation speed of the output-side transmission shaft 12 becomes higher than the rotation speed of the input-side transmission shaft 11 while the rotary driving force from the engine 3 A is not transmitted to the vibration absorber 10. At this time, a resilience of the helical torsion coil spring 14 instantaneously brings the counterclockwise face 124B of each of the claws 124 into contact with the clockwise face 134A of each of the third projections 134, thereby restoring the disposition illustrated in Fig. 6.

[0041]

Then, the helical torsion coil spring 14 is not further untwisted but the output-side transmission shaft 12 and the bushing 13 integrally rotate at a speed higher than that of the input-side transmission shaft 11, so that the clockwise face 132A of each of the second projections 132 is separated from the counterclockwise face 115B of each of the first projections 115. The separation absorbs the torsional vibration occurred when the output-side transmission shaft 12 is rotated at a speed higher than that of the input-side transmission shaft 11 without deforming the helical torsion coil spring 14 toward the diameter-enlarging side. [0042]

Modification(s)

It should be noted that the scope of the invention is not limited to the above -described exemplary embodiment but includes modification(s), improvement(s) and the like as long as an object of the invention can be achieved.

For instance, though the bushing 13 is disposed near the input-side transmission shaft 11, the helical torsion coil spring 14 is disposed near the output-side transmission shaft 12 and the bushing 13 and the output-side transmission shaft 12 are connected by the helical torsion coil spring 14 in the above exemplary embodiment, the bushing 13 may be disposed near the output-side transmission shaft 12, the helical torsion coil spring 14 may be disposed near the input-side transmission shaft 11 and the input-side transmission shaft 11 and the bushing 13 may be connected by the helical torsion coil spring 14.

[0043]

In the above exemplary embodiment, the first projections 115, the second projections 132 and the third projections 134 each defining the first contact portion, the second contact portion and the third contact portion are provided in a sector shape. However, the first projections 115, the second projections 132 and the third projections 134 may alternatively provided in a shape of claws. Further, each of the claws 124 defining the fourth contact portion may be provided in a sector shape.

[0044]

Though the work equipment in the above exemplary embodiment is the brushcutter 1, the work equipment may alternatively be a handheld edger, a long reach trimmer, a short reach trimmer, a pole saw and the like. The driven object of the invention may be suitably selected in accordance with the type of the work equipment.

The drive source of the invention is not limited to an engine but may alternatively be an electric motor.

EXPLANATION OF CODE(S)

[0045]

1... brushcutter (work equipment), 3A...engine (drive source), 4...cutter blade (driven object), 10... vibration absorber, 11... input-side transmission shaft, 12... output-side transmission shaft, 13... bushing, 14... helical torsion coil spring, 20... power transmission switching unit, 30... rotation restricting unit, 115...first projection (first contact portion), 124...claw (fourth contact portion), 132...second projection (second contact portion), 134...third projection (third contact portion), AX...axis.

Claims

CLAIM(S)

1. A vibration absorber (10) provided in a transmission path of a rotary driving force from a drive source (3A) to a driven object (4), the vibration absorber (10) comprising:

an input-side transmission shaft (11) that is configured to receive the rotary driving force from the drive source (3A);

an output-side transmission shaft (12) that is disposed coaxially with the input-side transmission shaft (11), the output-side transmission shaft (12) being rotatable relative to the input-side transmission shaft (11) to output the rotary driving force to the driven object (4);

a bushing (13) that is disposed coaxially with the input-side and output-side transmission shafts (11, 12), the bushing (13) being rotatable relative to the input-side and output-side transmission shafts (11, 12);

a helical torsion coil spring (14) that is disposed coaxially with the input-side and output-side transmission shafts (11, 12), a first end of the helical torsion coil spring (14) being attached to the bushing (13) and a second end of the helical torsion coil spring (14) being attached to one of the input- side and output-side transmission shafts (11, 12); and

a power transmission switching unit (20) that is configured to switch a transmission state of the rotary driving force between the other of the input-side and output-side transmission shafts (11, 12) and the bushing (13) between a first state and a second state, the first state allowing a transmission of the rotary driving force while the helical torsion coil spring (14) is deformed within a diameter- reducing range, the second state restricting the transmission of the rotary driving force through the helical torsion coil spring (14).

2. The vibration absorber (10) according to claim 1, wherein

the power transmission switching unit (20) includes a first contact portion (115) provided to the other of the input-side and output-side transmission shafts (11, 12) and a second contact portion (132) provided to the bushing (13), and the power transmission switching unit (20) restricting the transmission of the rotary driving force between the other of the input-side and output-side transmission shafts (11, 12) and the bushing (13) within a rotation range until the first contact portion (115) and the second contact portion (132) contact with each other.

3. The vibration absorber (10) according to claim 1 or 2, further comprising: a rotation restricting unit (30) that is configured to restrict a mutual rotation range of the one of the input-side and output-side transmission shafts (11, 12) and the bushing (13) so that a deformation of the helical torsion coil spring (14) occurs only within the diameter-reducing range.

4. The vibration absorber (10) according to claim 3, wherein

the rotation restricting unit (30) includes a third contact portion (134) provided to the bushing

(13) and a fourth contact portion (124) provided to the one of the input-side and output-side transmission shafts (11, 12), the third contact portion (134) and the fourth contact portion (124) being adapted to contact with each other to define the rotation range of the one of the input-side and output- side transmission shafts (11, 12) and the bushing (13).

5. Work equipment (1) comprising the vibration absorber (10) according to any one of claims 1 to 4.