PORTABLE WORK MACHINE

Abstract

Portable work machine (10), comprising: a drive unit (12); a working unit (14) driven by power from the drive unit (12); a shaft (16) configured to transmit the power of the drive unit (12) to the working unit (14); a tubular portion (18) arranged between the drive unit (12) and the working unit (14) and into which the shaft (16) is inserted; a plurality of bearing elements (20) configured to support the shaft (16) within the tubular portion (18); a handle support portion (22) connected to an outer peripheral surface of the tubular portion (18); and a handle (26) supported by the handle support portion (22) and gripped by an operator, wherein the shaft (16) comprises a first region (50) along a longitudinal direction of the shaft (16) facing the handle support portion (22) and corresponding to a belly of a first oscillation generated in the shaft (16), and the plurality of bearing elements (20) are arranged within the tubular portion (18) at locations other than the first region (50) and at irregular intervals along a longitudinal direction of the shaft (16).

Description

TECHNICAL AREA

[0001] The present invention relates to a portable working machine in which a handle is supported by a tubular portion via a handle support portion and power of a drive unit is transmitted to a working unit via a shaft supported by a plurality of bearing members within the tubular portion. STATE OF THE ART

[0002] JP S53-062627 A, JP H11-257335 A, and JP 5297646 B2, for example, disclose portable work machines. When a handle gripped by an operator is supported by the outer peripheral surface of a tubular portion via a handle support portion, the portable work machine transmits power from a drive unit, such as an internal combustion engine, to a working unit, such as a cutting blade, via a shaft inserted into the tubular portion and supported by a plurality of bearing elements. DE 603 ​​07 535 T2 describes a portable work machine comprising a drive unit, a working unit, and a drive shaft housed in a tube, as well as a handle and a handle support portion. A plurality of bearing bushes, which support the shaft within the tube, are provided at regular intervals along the drive shaft at positions corresponding to nodes of vibration of the drive shaft. OVERVIEW OF THE INVENTION

[0003] When the power of the drive unit is transmitted to the working unit via the shaft and the working unit performs a predetermined work, the shaft, the plurality of bearing elements, and the tubular portion vibrate as a unit due to the vibration of the drive unit or the working unit serving as the vibration source. Accordingly, the vibration of a structure formed by the shaft, the plurality of bearing elements, and the tubular portion is transmitted to the handle via the handle support portion.

[0004] The present invention has been made in consideration of the above problem, and an object thereof is to provide a portable working machine capable of reducing vibration transmitted to a handle.

[0005] According to a first aspect of the present invention, there is provided a portable work machine according to claim 1, comprising: a drive unit; a working unit driven by power from the drive unit; a shaft configured to transmit the power of the drive unit to the working unit; a tubular portion disposed between the drive unit and the working unit, and into which the shaft is inserted; a plurality of bearing members configured to support the shaft within the tubular portion; a handle support portion connected to an outer peripheral surface of the tubular portion;and a handle supported by the handle support portion and gripped by an operator, wherein the shaft includes a first region along a longitudinal direction of the shaft facing the handle support portion and corresponding to an antinode of a first vibration generated in the shaft, and the plurality of bearing elements are arranged within the tubular portion at locations other than the first region and at irregular intervals along a longitudinal direction of the shaft.;

[0006] According to a second aspect of the present invention, there is provided a portable work machine comprising: a drive unit; a working unit driven by power from the drive unit; a shaft configured to transmit the power of the drive unit to the working unit; a tubular portion disposed between the drive unit and the working unit and into which the shaft is inserted; a plurality of bearing members configured to support the shaft within the tubular portion; a handle support portion connected to an outer peripheral surface of the tubular portion;and a handle supported by the handle support portion and gripped by an operator, wherein the shaft includes a first region along a longitudinal direction of the shaft facing the handle support portion and corresponding to an antinode of a first vibration generated in the shaft, wherein two first bearing members are arranged among the plurality of bearing members so as to sandwich the first region, and wherein a distance between the two first bearing members is greater than a distance between each of the two first bearing members and another bearing member adjacent to each other on an outer side of the first region along a longitudinal direction of the shaft;

[0007] According to the present invention, the plurality of bearing members are arranged to avoid the first region, which corresponds to the antinode of a first vibration generated in the shaft and faces the handle support portion. Therefore, the first region vibrates freely independently of the tubular portion. Accordingly, when vibration of the shaft occurs due to vibration of the drive unit or working unit serving as a vibration source, excitation energy flows to the first region, and the first region vibrates strongly due to the excitation energy. As a result, it is possible to prevent the excitation energy from flowing to the tubular portion via the plurality of bearing members and suppress the vibration of the tubular portion.As described above, in the present invention, it is possible to reduce vibrations transmitted from the shaft to the handle via the plurality of bearing members, the tubular portion and the handle support portion. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a work machine according to a present embodiment; Fig. 2 is a side view of the interior of the working machine of Fig. 1 ; Fig. 3 is a cross-sectional view along the line III-III of Fig. 2; Fig. 4 is an explanatory view showing vibration reduction by a first region (first example); Fig. 5 is an explanatory view showing vibration reduction by a second region (second example); Fig. 6 is a graph showing the relationship between frequency and vibration acceleration in the first example; Fig. 7 is a graph showing the relationship between frequency, displacement, and phase in a comparative example; Fig. Fig. 8 is a diagram showing the relationship between frequency, displacement, and phase in the first example; Fig. 9 is a graph showing the relationship between frequency and vibration acceleration in the second example; and Fig. Figure 10 is a graph showing the relationship between frequency and vibration acceleration in the first example. DESCRIPTION OF THE INVENTION

[0008] A preferred embodiment of a portable work machine according to the present invention will now be illustrated and described by way of example with reference to the accompanying drawings. [1. Schematic configuration of the present embodiment]

[0009] As in Fig. 1 and Fig. 2, a portable work machine 10 according to the present embodiment (hereinafter also referred to as a work machine 10 according to the present embodiment) is a portable brush cutter and includes a power unit 12, a work unit 14 driven by power from the power unit 12, a shaft 16 that transmits the power from the power unit 12 to the work unit 14, a tubular portion 18 that is disposed between the power unit 12 and the work unit 14 and into which the shaft 16 is inserted, and a plurality of bearing members 20 that support the shaft 16 inside the tubular portion 18. A floating box 24 having a handle support portion 22 is provided on the outer peripheral surface of the tubular portion 18 on the power unit 12 side. A handle 26 gripped by an operator is supported by the handle support portion 22.

[0010] The drive unit 12 is provided on the base end side of the shaft 16 and the tubular portion 18 and uses, for example, an internal combustion engine as a drive source thereof. The shaft 16 is, for example, a rod-shaped shaft made of steel and has a base end connected to the drive source of the drive unit 12 via a coupling 28 and a distal end connected to the work unit 14 via a gear 29. Therefore, power (rotational force) of the drive unit 12 is transmitted to the work unit 14 via the coupling 28, the shaft 16, and the gear 29. Therefore, the drive unit 12 and the work unit 14 may vibrate at different frequencies due to the gear 29. In addition, when the work machine 10 is actually used, the work unit 14 performs predetermined work at a frequency of about 120 Hz.The tubular portion 18 is, for example, an aluminum tube and has a base end connected to the drive unit 12 and a distal end connected to the working unit 14.

[0011] As in Fig. 2 and Fig. 3, the plurality of bearing members 20 rotatably support the shaft 16 such that the shaft 16 and the tubular portion 18 within the tubular portion 18 are substantially coaxial with each other. Each of the bearing members 20 is formed of a bushing 20a and an elastic member 20b. The bushing 20a is made of an oil-impregnated tubular metal member and is in contact with the outer peripheral surface of the shaft 16. The elastic member 20b is made of an oil-resistant tubular rubber member and is disposed between the outer peripheral surface of the bushing 20a and the inner peripheral surface of the tubular portion 18. The arrangement positions of the plurality of bearing members 20 within the tubular portion 18 will be described later.

[0012] The working unit 14 is, for example, a rotating cutting blade connected to the distal end of the shaft 16 and performs a predetermined work by being driven by power (by being rotated by a rotational force) transmitted from the drive unit 12 via the clutch 28 and the shaft 16. The handle 26 is provided with a pair of left and right grips 30 that are gripped by the operator during work. One grip 30 is provided with a throttle lever 32 that adjusts the power of the drive unit 12.

[0013] A first holding portion 34 is provided at the base end of the tubular portion 18. The first holding portion 34 is connected to the drive unit 12 and covers the coupling 28 and the base end of the tubular portion 18. In addition, a second holding portion 36 is provided at a position separated by a predetermined distance from the base end of the tubular portion 18 toward the working unit 14 along the longitudinal direction of the shaft 16. The second holding portion 36 surrounds the outer peripheral surface of the tubular portion 18. The floating box 24 is arranged on the base end side of the tubular portion 18 so as to be sandwiched between the first holding portion 34 and the second holding portion 36.

[0014] A base end of the floating box 24 is connected to the first support portion 34 via a first vibration absorbing member 38. A distal end of the floating box 24 is connected to the second support portion 36 via a second vibration absorbing member 40. The handle support portion 22 is attached to the distal end of the floating box 24 on the second support portion 36 side. The first vibration absorbing member 38 and the second vibration absorbing member 40 are elastic bodies such as rubber and are provided to suppress vibration transmitted from the base end side of the tubular portion 18 to the handle 26 via the handle support portion 22. [2. Characteristic configuration of the present embodiment]

[0015] Next, a characteristic configuration of the work machine 10 according to the present embodiment will be described. The characteristic configuration relates to the arrangement of the plurality of bearing elements 20 within the tubular portion 18. Fig. 4 and Fig. 5, the configuration of the working machine 10 is shown schematically to highlight the arrangement positions of the plurality of bearing elements 20 with respect to the shaft 16.

[0016] In the prior art, the plurality of bearing elements 20 are arranged at equal intervals along the longitudinal direction of the shaft 16 within the tubular portion 18 (see Fig. 1 to 3). On the other hand, in the present embodiment, as shown in Fig. 4 and Fig. 5, the plurality of bearing elements 20 are arranged at uneven intervals along the longitudinal direction of the shaft 16 within the tubular portion 18. The reason for the uneven arrangement is as follows.

[0017] Also in the prior art, the shaft 16 and the tubular portion 18 are connected to each other via the plurality of bearing elements 20. Further, the base end of the shaft 16 is connected to the drive unit 12. The distal end of the shaft 16 is connected to the work unit 14. Therefore, when vibration is generated in the drive unit 12 or work unit 14 serving as a vibration source, the shaft 16, the plurality of bearing elements 20, and the tubular portion 18 vibrate as a unit due to the vibration. In this case, when the natural frequency of a structure 44 formed by the shaft 16, the plurality of bearing elements 20, and the tubular portion 18 is close to the vibration frequency of the drive unit 12 or work unit 14, the vibration of the structure 44 resonates and becomes larger.The handle support portion 22 is disposed on the outer peripheral surface of the tubular portion 18 via the second support portion 36 and the second vibration-absorbing member 40, and the handle 26 is supported by the handle support portion 22. Therefore, the vibration of the structure 44 is transmitted from the second support portion 36 to the handle 26 via the second vibration-absorbing member 40 and the handle support portion 22.

[0018] As described above, in the prior art, the vibration mode (flexural vibration mode) generated in the structure 44 is not considered at all, and a plurality of bearing members 20 are evenly arranged along the longitudinal direction of the shaft 16. Therefore, for example, if one of the bearing members 20 is arranged at a position of the antinode, the vibration is transmitted in resonance from the shaft 16 to the tubular portion 18 via the bearing member 20. As a result, a larger vibration is transmitted to the handle 26.

[0019] As in Fig. 4 (first example), therefore, in the present embodiment, a portion of the shaft 16 facing the second holding portion 36, that is, the portion obtained by projecting the second holding portion 36 onto the shaft 16, is defined as an area A, and the area A is designed to correspond to an antinode of a first vibration generated in the shaft 16. Then, the plurality of bearing members 20 are arranged inside the tubular portion 18 at positions other than the area A along the longitudinal direction of the shaft 16. Specifically, among the plurality of bearing members 20, two bearing members 20 (first bearing members) are arranged on both sides of the area A along the longitudinal direction of the shaft 16.A region including the region A and extending along the longitudinal direction of the shaft 16 so as to correspond to the distance between the two bearing elements 20 (a region of the shaft 16 enclosed between the two bearing elements 20) is defined as a first region 50. That is, the two bearing elements 20 are arranged so as to enclose the first region 50 (region A) between them. A distance between the two bearing elements 20 is wider than a distance between each of the two bearing elements 20 and another bearing element 20 that are adjacent to each other on the outside of the first region 50 along the longitudinal direction of the shaft 16.

[0020] Since the antinode is a portion where the first vibration is large, the first region 50 is set as an antinode portion that vibrates freely independently of the tubular portion 18. Accordingly, when a first vibration is generated in the shaft 16 due to the vibration of the drive unit 12 or the working unit 14, excitation energy caused by the vibration of the drive unit 12 or the working unit 14 flows to the first region 50, and the first region 50 vibrates greatly due to the excitation energy. Therefore, it is possible to prevent the excitation energy from flowing to the tubular portion 18 via the plurality of bearing members 20. As a result, vibration of the tubular portion 18 is suppressed, and vibration transmitted to the handle 26 via the handle support portion 22 is reduced.

[0021] In this way, the two bearing elements 20 are arranged to sandwich the first region 50, and the distance between the two bearing elements 20 is set to a length corresponding to the frequency of the first vibration generated in the shaft 16. For example, if the distance between the two bearing elements 20 is set to a length corresponding to the frequency of the vibration of the working unit 14, the excitation energy caused by the vibration of the working unit 14 flows to the first region 50, and the first region 50 vibrates strongly due to the excitation energy.

[0022] In Fig. 4, when the vibration frequency of the working unit 14 is 120 Hz, a first vibration generated in the shaft 16 is schematically represented by a thin line, and a vibration generated in the tubular portion 18 is schematically represented by a thick line. By providing the first region 50, the first region 50 vibrates strongly, and the vibration of the tubular portion 18 can be reduced.

[0023] Furthermore, in the present embodiment, as shown in Fig. 5 (second example), a second region 52 may be provided in the shaft 16 separately from the first region 50. In this case, the second region 52 is configured to correspond to an antinode of a second vibration having a different frequency than the frequency of the first vibration corresponding to the first region 50. Then, among the plurality of bearing elements 20, two bearing elements 20 (second bearing elements) are arranged to sandwich both ends of the second region 52.

[0024] The second region 52 is set as an antinode portion that vibrates freely independently of the tubular portion 18. Accordingly, when a second vibration is generated in the shaft 16 due to vibration of the drive unit 12 or the working unit 14, excitation energy caused by the vibration of the drive unit 12 or the working unit 14 flows to the second region 52, and the excitation energy causes the second region 52 to vibrate greatly. In this case too, it is possible to prevent the excitation energy from flowing to the tubular portion 18 via the plurality of support members 20 and prevent the tubular portion 18 from vibrating. As a result, vibration transmitted to the handle 26 via the second support portion 36, the second vibration-absorbing member 40, and the handle support portion 22 can be reduced.

[0025] Furthermore, the distance between the two bearing elements 20 corresponds to the length of the second region 52. In this case, for example, if the distance between the two bearing elements 20 is set to a length corresponding to the frequency of the vibration of the drive unit 12, the excitation energy caused by the vibration of the drive unit 12 flows to the second region 52, and the second region 52 vibrates strongly due to the excitation energy.

[0026] In Fig. 5, when the vibration frequency of the drive unit 12 is 155 Hz, a second vibration generated in the shaft 16 is schematically represented by a thin line, and a vibration generated in the tubular portion 18 is schematically represented by a thick line. By providing the second region 52, a strong vibration is generated in the second region 52 in the shaft 16, and vibration of the tubular portion 18 can be reduced.

[0027] It should be noted that Fig. 4 and Fig. 5 illustrates a case where two regions, namely the first region 50 and the second region 52, are formed in a shaft 16. In the present embodiment, at least one of the first region 50 and the second region 52 may be formed in a shaft 16.

[0028] Fig. 6 shows changes in the vibration acceleration of the tubular portion 18 when the position of the second holding portion 36 is set as a response point in a case where the distance between the two support members 20 sandwiching both ends of the first region 50 is appropriately set to reduce vibration caused by the vibration frequency of the working unit 14 in the first example. The solid line indicates a result in a case where the distance between the two support members 20 sandwiching both ends of the first region 50 is set so that the natural frequency of the shaft 16 in the first region 50 becomes 122 Hz. The broken line indicates a result in a case where the distance between the two support members 20 is set so that the natural frequency of the shaft 16 in the first region 50 becomes 110 Hz.The alternating long and short dashed line indicates a result in a case where the distance between the two bearing elements 20 is set so that the natural frequency of the shaft 16 in the first range becomes 50 135 Hz.

[0029] In this way, the distance between the two support elements 20 sandwiching both ends of the first region 50 is appropriately adjusted according to the frequency of the vibration to be reduced. This allows the first region 50 to vibrate independently of the tubular portion 18 and in synchronization with the vibration frequency of the working unit 14. Accordingly, the excitation energy caused by the vibration of the working unit 14 flows to the first region 50. Therefore, vibration of the tubular portion 18 at the position of the second support portion 36 (response point) is suppressed. As a result, the vibration transmitted to the handle 26 can be reduced. Therefore, by using the method of the present embodiment, it is possible to optimize vibration reduction.For example, even if the design of the reduction ratio of the gear box 29 for driving the working unit 14 is changed and the vibration frequency of the working unit 14 is changed, the vibration reduction can be optimized by appropriately adjusting the distance between the two bearing elements 20 that sandwich the first region 50 between them.

[0030] More specifically, in the method described above, vibration is reduced by effectively utilizing an anti-resonance phenomenon (anti-resonance frequency). Here, the anti-resonance frequency refers to a frequency at which vibration existing between adjacent resonance frequencies is suppressed at a certain response point (the position of the second holding portion 36 in Fig. 4 and Fig. 5) has a minimum value.

[0031] Fig. Fig. 7 (comparative example) shows changes in phase and displacement of the shaft 16 (dashed line) and the tubular portion 18 (solid line) with respect to the frequency when the position of the second holding portion 36 is set as the response point in a case where the plurality of bearing elements 20 are arranged at equal intervals along the longitudinal direction of the shaft 16. Further, Fig. 8 Changes in phase and displacement of the shaft 16 (dashed line) and the tubular portion 18 (solid line) with respect to frequency when the position of the second holding portion 36 is set as the response point in the first example.

[0032] In the comparison example of Fig. 7, the shaft 16 and the tubular portion 18 oscillate as a unit, and resonance occurs at a natural frequency of 120 Hz. Furthermore, the shaft 16 and the tubular portion 18 change in phase with respect to frequency.

[0033] On the other hand, in the first example of Fig. 8 by adjusting the arrangement of the plurality of bearing elements 20, the shaft 16 and the tubular portion 18 on the low frequency side (110 Hz) and the high frequency side (140 Hz) with a frequency of 120 Hz therebetween to resonate. That is, in the first example, the resonance at 120 Hz in the comparative example of Fig. 7 into resonance at two natural frequencies of 110 Hz and 140 Hz. In this case, on the low-frequency side of 110 Hz, the shaft 16 and the tubular section 18 change in phase. Furthermore, on the high-frequency side of 140 Hz, the shaft 16 and the tubular section 18 change in antiphase.

[0034] Therefore, in the first example, the natural frequency is separated into two natural frequencies on the low-frequency side and the high-frequency side, and the phase of the tubular portion 18 is inverted to the phase of the shaft 16 on the high-frequency side. As a result, an antiresonance can be generated at 120 Hz with respect to the displacement of the vibration of the tubular portion 18. That is, it is possible to create a frequency range in which the displacement of the vibration has the minimum value between the two separated natural frequencies.

[0035] If the natural frequency of the first region 50 is set to 120 Hz, a frequency range is created in which the vibration is minimized, and it is possible to effectively reduce the vibration with respect to the excitation frequency of the working unit 14, for example, 120 Hz. The vibration can be reduced based on the same principle for other natural frequencies (110 Hz, 135 Hz) in Fig. 6 can be reduced.

[0036] Fig. 9 shows changes in the vibration acceleration of the tubular portion 18 in a case where the distance between the two support members 20 sandwiching both ends of the second region 52 is appropriately adjusted to reduce vibration caused by the vibration frequency of the drive unit 12 in the second example. In this case, when the natural frequency of the shaft 16 in the second region 52 is changed to 86 Hz, 114 Hz, 128 Hz, 142 Hz, and 161 Hz according to the distance between the two support members 20 sandwiching both ends of the second region 52, the resonance peak of the tubular portion 18 is shifted to the high-frequency side.Accordingly, even if the target frequency of the vibration of the drive unit 12 to be reduced is 155 Hz, the vibration at 155 Hz is suppressed by appropriately adjusting the distance between the two support members 20 sandwiching both ends of the second region 52. Accordingly, vibration transmitted to the handle 26 can be reduced.

[0037] It should be noted that, as exemplified by the second region 52, when the region in which the shaft 16 vibrates independently of the tubular portion 18 is provided at a location shifted from the response point (the position of the second support portion 36 in the tubular portion 18) where vibration is to be reduced, a shift occurs between the natural frequency of the second region 52, determined based on the distance between the two support members 20, and the frequency range in which vibration is most reduced at the response point. In this case, by using CAE (Computer Aided Engineering) analysis or the like, the optimal arrangement of the support members 20 for reducing vibration can be investigated while confirming the frequency response at the response point.

[0038] Fig.10 shows changes in vibration acceleration with respect to frequency in a low-frequency range equal to or lower than 110 Hz when the distance between the two support members 20 sandwiching both ends of the first region 50 is changed in the first example. The solid line indicates the result of the first example. The broken line shows the result of the comparative example. In a case where the frequency of the vibration to be reduced is equal to or higher than 110 Hz, even if the distance between the two support members 20 is changed according to the frequency of the vibration to be reduced, it is possible to suppress an influence on the low-frequency range equal to or lower than 110 Hz.This is because the effect of separating the vibration modes of the tubular portion 18 and the shaft 16 due to the arrangement adjustment of the bearing members 20 is particularly apparent in third-order or higher bending modes of the tubular portion 18, and therefore, the effect of separating the vibration modes of the tubular portion 18 and the shaft 16 in a low-frequency range where the bending order is low is small even when the arrangement adjustment of the bearing members 20 is performed. Therefore, in the present embodiment, it is possible to reduce the vibration at the frequency to be reduced in the high-frequency range where the usage frequency is practically high, without affecting the frequency range of other practical speed ranges. [3. Effects of the present embodiment]

[0039] As described above, the work machine 10 according to the present embodiment includes the drive unit 12, the work unit 14 driven by the power of the drive unit 12, the shaft 16 that transmits the power of the drive unit 12 to the work unit 14, the tubular portion 18 that is arranged between the drive unit 12 and the work unit 14 and into which the shaft 16 is inserted, the plurality of bearing members 20 that support the shaft 16 within the tubular portion 18, the handle support portion 22 that is connected to the outer peripheral surface of the tubular portion 18, and the handle 26 that is supported by the handle support portion 22 and gripped by the operator.In this case, the first region 50 of the shaft 16 facing the handle support portion 22 corresponds to the antinode of a first vibration generated in the shaft 16, and the plurality of bearing elements 20 are arranged within the tubular portion 18 at uneven intervals and at different locations along the longitudinal direction of the shaft 16 than the first region 50.

[0040] Furthermore, in the work machine 10 according to the present embodiment, the first region 50 of the shaft 16 facing the handle support portion 22 corresponds to the antinode of the first vibration generated in the shaft 16, two first bearing members 20 among the plurality of bearing members 20 are arranged to sandwich the first region 50 therebetween, and the distance between the two bearing members 20 is wider than a distance between each of the two bearing members 20 and another bearing member 20 adjacent to each other on the outer side of the first region 50 along the longitudinal direction of the shaft 16.

[0041] In this way, the plurality of bearing members 20 are arranged to avoid the first region 50, which corresponds to the antinode of the first vibration generated in the shaft 16 and faces the handle support portion 22. Therefore, the first region 50 vibrates freely independently of the tubular portion 18. Accordingly, when a first vibration of the shaft 16 occurs due to vibration of the drive unit 12 or working unit 14 serving as a vibration source, excitation energy flows to the first region 50, and the first region 50 vibrates strongly due to the excitation energy. As a result, it is possible to prevent the excitation energy from flowing to the tubular portion 18 via the plurality of bearing members 20 and suppress the vibration of the tubular portion 18.As described above, in the present embodiment, it is possible to reduce vibration transmitted from the shaft 16 to the handle 26 via the plurality of bearing members 20, the tubular portion 18, and the handle support portion 22.

[0042] More specifically, in the present embodiment, the plurality of bearing elements 20 are arranged near the vibration node in a region of the shaft 16 near the handle support portion 22. Accordingly, the first region 50 is formed as a free region in which the shaft 16 can vibrate freely independently of the tubular portion 18 without being restricted by the bearing elements 20. Accordingly, since the natural frequency (resonance frequency) of the structure 44 is shifted, the first region 50 vibrates substantially synchronously with the frequency (excitation frequency) of the drive unit 12 or the working unit 14. As a result, the excitation energy flowing to a portion of the tubular portion 18 where the tubular portion 18 is connected to the handle support portion 22 is reduced, and the vibration of the handle 26 is therefore greatly suppressed.

[0043] In this case, among the plurality of bearing elements 20, two bearing elements 20 (first bearing elements) are arranged to sandwich the first region 50, and the distance between the two bearing elements 20 is set to a length corresponding to the frequency of the first vibration. This makes it possible to reduce vibration at each frequency. That is, if the distance between the two bearing elements 20 is set so that the frequency (resonance frequency) corresponding to the first region 50 matches the excitation frequency, it is possible to reduce vibration at the excitation frequency.

[0044] Therefore, vibration can be effectively reduced compared to the case where the bearing elements 20 are simply arranged at the positions of the nodes of the bending vibration mode. Furthermore, even if the arrangement of the bearing elements 20 is changed, it is not necessary to consider the influence of other frequency ranges (for example, an idle speed range of several tens of Hz).

[0045] In addition, vibrations of multiple different frequencies are generated in the shaft 16 and the tubular portion 18, and in order to cope with the vibrations at the multiple frequencies, the second region 52 is provided in the shaft 16 along the longitudinal direction of the shaft 16 separately from the first region 50. The second region 52 corresponds to an antinode of a second vibration different from the first vibration corresponding to the first region 50. Two bearing members 20 (second bearing members) are arranged to sandwich both ends of the second region 52, and the distance between the two bearing members 20 is set to a length corresponding to the frequency of the second vibration corresponding to the second region 52. As a result, it is possible to take measures to reduce vibrations at multiple frequencies independently.

[0046] Specifically, the frequency of the first vibration corresponding to the first region 50 corresponds to the vibration frequency of the working unit 14, and the frequency of the second vibration corresponding to the second region 52 corresponds to the vibration frequency of the drive unit 12. Accordingly, it is possible to appropriately reduce any vibration caused by the vibration source of the working machine 10.

[0047] Specifically, free areas (the first area 50 and the second area 52) are formed at multiple locations on the shaft 16, and the lengths of these free areas are adjusted by adjusting the distance between the bearing members 20, making it possible to simultaneously and independently reduce vibrations at multiple excitation frequencies. For example, in a case where the excitation frequency of the internal combustion engine serving as the drive unit 12 is set to 155 Hz and the excitation frequency of the cutting blade serving as the working unit 14 is set to 120 Hz, it is possible to take measures to reduce vibrations at the two excitation frequencies independently of each other by providing two free areas of different lengths in the shaft 16.

[0048] Furthermore, with prior art vibration reduction measures, if resonance at one excitation frequency is to be avoided, there is a possibility that the vibration at the other excitation frequency will become quite large. On the other hand, in the present embodiment, as described above, it is possible to reduce vibrations at respective excitation frequencies by providing a plurality of free regions in the shaft 16. [4. Other configurations, etc.]

[0049] In the work machine 10 according to the present embodiment, the plurality of bearing members 20 are arranged at uneven intervals along the longitudinal direction of the shaft 16 within the tubular portion 18. That is, the plurality of bearing members 20 are arranged on the nodal side of the vibration generated in the shaft 16 or the tubular portion 18. Since the vibration node is a portion where the vibration is small, the transmission of vibration between the shaft 16 and the tubular portion 18 is suppressed. That is, the plurality of bearing members 20 function as elements that separate the vibration of the shaft 16 and the vibration of the tubular portion 18, and reduce the vibration transmissibility between the shaft 16 and the tubular portion 18. As a result, the shaft 16 and the tubular portion 18 vibrate in independent modes (flexural vibration modes).As a result, the occurrence of resonance is suppressed and the structure 44 can be prevented from vibrating as a unit.

[0050] Furthermore, by making the arrangement uneven, the natural frequency of the structure 44 can be changed to any desired frequency. Accordingly, the natural frequency of the structure 44 changes within a frequency range different from the vibration frequency of the drive unit 12 or the working unit 14. As a result, the occurrence of resonance in the structure 44 can be avoided. Specifically, two or three bearing members 20 are collectively arranged at each of a plurality of vibration nodes in the structure 44. Thus, the vibration frequency of the drive unit 12 or the working unit 14 is shifted from the natural frequency of the structure 44. As a result, the vibration acceleration of the tubular portion 18 is suppressed, and the vibration acceleration of the handle 26 is also suppressed.

[0051] Furthermore, in the present embodiment, the plurality of bearing elements 20 are arranged on the vibration node side. Accordingly, the vibration transmissibility between the shaft 16 and the tubular portion 18 is reduced, and it is possible to appropriately reduce the vibration transmitted to the handle 26.

[0052] It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various configurations could be adopted therein based on the descriptive content of the present specification.

Claims

[1] Portable work machine (10), comprising: a drive unit (12); a working unit (14) driven by power from the drive unit (12); a shaft (16) configured to transmit the power of the drive unit (12) to the working unit (14); a tubular portion (18) arranged between the drive unit (12) and the working unit (14) and into which the shaft (16) is inserted; a plurality of bearing elements (20) configured to support the shaft (16) within the tubular portion (18); a handle support portion (22) connected to an outer peripheral surface of the tubular portion (18); and a handle (26) supported by the handle support portion (22) and gripped by an operator, wherein the shaft (16) comprises a first region (50) along a longitudinal direction of the shaft (16) facing the handle support portion (22) and corresponding to a belly of a first oscillation generated in the shaft (16), and the plurality of bearing elements (20) are arranged within the tubular portion (18) at locations other than the first region (50) and at irregular intervals along a longitudinal direction of the shaft (16). [2] Portable work machine (10), comprising: a drive unit (12); a working unit (14) driven by power from the drive unit (12); a shaft (16) configured to transmit the power of the drive unit (12) to the working unit (14); a tubular portion (18) arranged between the drive unit (12) and the working unit (14) and into which the shaft (16) is inserted; a plurality of bearing elements (20) configured to support the shaft (16) within the tubular portion (18); a handle support portion (22) connected to an outer peripheral surface of the tubular portion (18); and a handle (26) supported by the handle support portion (22) and gripped by an operator, wherein the shaft (16) comprises a first region (50) along a longitudinal direction of the shaft (16) facing the handle support portion (22) and corresponding to a belly of a vibration generated in the shaft (16), two first bearing elements (20) from the plurality of bearing elements (20) are arranged so that they enclose the first region (50) between them, and a distance between the two first bearing elements (20) is wider than a distance between each of the two first bearing elements (20) and another bearing element (20) which are adjacent to each other along a longitudinal direction of the shaft (16) outside the first region (50). [3] The portable work machine (10) according to claim 1 or 2, wherein two first bearing members (20) of the plurality of bearing members are arranged to sandwich the first region (50) therebetween, and a distance between the two first bearing members (20) is set to a length corresponding to a frequency of the first vibration. [4] Portable work machine (10) according to claim 3, wherein several vibrations with different frequencies are generated in the shaft (16) and the tubular section (18), a second region (52) is provided in the shaft (16) along the longitudinal direction separately from the first region (50) to cope with the vibrations, the second region (52) corresponds to an antinode of a second vibration having a frequency different from a frequency of the first vibration, two second bearing elements (20) are arranged to sandwich the second region (52) between them, and a distance between the two second bearing elements (20) is set to a length corresponding to a frequency of the second oscillation. [5] Portable work machine (10) according to claim 4, wherein the frequency of the first oscillation corresponds to an oscillation frequency of the working unit (14), and the frequency of the second oscillation corresponds to an oscillation frequency of the drive unit (12).

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