WO2012140687A1

WO2012140687A1 - Choke structure of handheld work tool

Info

Publication number: WO2012140687A1
Application number: PCT/JP2011/002128
Authority: WO
Inventors: Ryou Ono
Original assignee: Husqvarna AB
Current assignee: Husqvarna AB
Priority date: 2011-04-11
Filing date: 2011-04-11
Publication date: 2012-10-18
Anticipated expiration: 2013-10-11

Abstract

A choke structure of a handheld work tool, includes: an engine; a carburetor (5) attached to the engine; an air cleaner (6) attached to the carburetor (5); a choke valve (52) rotatably provided in the carburetor (5); a rotary piece (53) provided to a rotary shaft of the choke valve (52); and a pull knob (80) for choke control provided on the air cleaner (6) in such a manner as to be pulled and pushed, in which the rotary piece (53) is provided with a first converter (55) and the pull knob (80) is provided with a second converter (85), when the pull knob (80) is pushed or pulled, a linear movement of the pull knob (80) is converted into a rotary movement of the choke valve (52) through the first and second converters (55, 85), and the first and second converters (55, 85) directly contact with each other.

Description

CHOKE STRUCTURE OF HANDHELD WORK TOOL

The present invention relates to a choke structure of a handheld work tool that is usable, for instance, in a brushcutter, a chain saw or the like.

Conventionally, some types of brushcutter, an example of handheld work tools, employ a pull-knob-type choke structure in consideration of their appearance designs or the like. In a choke structure, by pulling out the pull knob, a choke valve inside a carburetor is rotated to apply choke, and by pushing in the pull knob, a normal-drive mode is on. In the normal-drive mode, an operating portion of the pushed pull knob, i.e., a portion on which the finger of a user is put, is flushed or leveled with a cleaner cover of an air cleaner. Thus, an exterior cover and the pull knob are unified, resulting in an improved design. Patent Literature 1 does not disclose the use of a pull knob, but disclose a main part of a typical choke structure.

Patent Literature 1: JP-A-60-56154

In a typical choke structure using a pull knob, a pull knob is coupled to a choke valve inside a carburetor via a plurality of linking members or the like, which makes the structure complicated (the arrangement of such a linking portion is similar to that of Patent Literature 1). Thus, in order to remove an air cleaner and the carburetor for maintenance, these linking members also need to be detached. Time-consuming attachment and detachment of the linking members prevents facilitation of the maintenance.

An object of the invention is to provide a choke structure of a handheld work tool that is simplified to facilitate maintenance. Further, such a simple structure contributes to reduction in the number of parts, the weight and the cost.

According to an aspect of the invention, a choke structure of a handheld work tool, includes: an engine; a carburetor attached to the engine; an air cleaner attached to the carburetor; a choke valve rotatably provided in the carburetor; a rotary piece provided to a rotary shaft of the choke valve; and a pull knob for choke control provided on the air cleaner in such a manner as to be pulled and pushed, in which the rotary piece is provided with a first converter and the pull knob is provided with a second converter, when the pull knob is pushed or pulled, a linear movement of the pull knob is converted into a rotary movement of the choke valve through the first and second converters, and the first and second converters directly contact with each other.

In the above arrangement, the rotary piece of the choke valve and the pull knob are directly coupled to each other via the first and second converters without any linking member or the like therebetween as in a typical arrangement, resulting in a simplified structure. In addition, since it is unnecessary to handle such a linking member in assembly or disassembly, maintenance can be facilitated.

In the choke structure, it is preferable that one of the first and second converters is an engagement pin provided to one of the rotary piece and the pull knob, and the other of the first and second converters is an engagement portion provided to the other of the rotary piece and the pull knob and engaged with the engagement pin.
In the above arrangement, the first and second converters are provided by simple components, i.e., the engagement pin and the engagement portion, which only need to be engaged with each other to allow choke control. The arrangement does not require a high accuracy in dimensions such as the projecting length of the engagement pin and the dimension of the engagement portion, so that production and assembly can be facilitated.

In the choke structure, it is preferable that an engagement/disengagement direction of the engagement pin and the engagement portion coincides with an attachment/detachment direction of the air cleaner relative to the carburetor.
In the above arrangement, the engagement pin and the engagement portion can be engaged or disengaged at the same time as the air cleaner is attached or detached relative to the carburetor, so that assembly and disassembly can be further facilitated.

In the choke structure, it is preferable that the air cleaner includes: a cleaner case attached to the carburetor to accommodate an element; and a cleaner cover removably attached to the cleaner case to cover the cleaner case, and the pull knob is attached to the cleaner case.
In the above arrangement, the pull knob is attached to the cleaner case, which is the closest to the carburetor in the air cleaner. Thus, it is unnecessary that the pull knob is extended to be close to the rotary piece or the rotary piece is extended to be close to the pull knob, so that the structure can be further simplified.

In the choke structure, it is preferable that the pull knob includes an operating portion, and when the pull knob is pushed in, the operating portion is fitted in a cutout provided to the cleaner cover such that a surface of the operating portion and a surface of the cleaner cover are flushed to be continuous as a whole.
In the above arrangement, the surface of the cleaner cover and the surface of the operating portion of the pull knob are flushed to be continuous. Thus, the operation state of the pull knob can be recognized at a glance, or can be easily and reliably recognized by touching the pull knob even without visual check.

In the choke structure, it is preferable that the cleaner cover is attached to the cleaner case with a screw, and one of the cleaner case and the cleaner cover is provided with a projection that projects toward the other of the cleaner case and the cleaner cover, and the other of the cleaner case and the cleaner cover is provided with an insertion hole in which the projection is inserted.

When the cleaner cover is attached to the cleaner case with a screw, as the screw is tightened, the position of the cleaner cover is deviated in a rotation direction of the screw due to friction between the screw head and the cleaner cover. In view of the above, in the above arrangement, the through hole and the projection are engaged with each other to prevent a deviation in the relative positions of the cleaner case and the cleaner cover in the rotation direction. Thus, a clearance between the cleaner cover and the operating portion is kept enough for the cleaner cover not to contact and interfere with the operating portion of the pull knob fitted in the cutout of the cleaner cover. Thus, the operating portion can be reliably operated to push and pull the pull knob.

In the choke structure, it is preferable that the pull knob includes a slidable portion configured to be attachable or detachable relative to an inside of an accommodating portion provided in the cleaner case, the slidable portion accommodated inside the accommodating portion in a slidable manner along a direction of the linear movement, and the slidable portion includes a contact piece elastically deformed in attachment or detachment relative to the accommodating portion, the contact piece coming into contact with a predetermined position in the accommodating portion to define a sliding amount of the slidable portion.
In the above arrangement, when maintenances are required, the elastic deformation of the contact piece of the pull knob allows the attachment or detachment of the slidable portion of the pull knob relative to the accommodating portion of the cleaner case. Further, the contact piece comes into contact with the predetermined position in the accommodating portion, thereby preventing the pull knob from accidentally coming out of the accommodating portion as well as defining the sliding amount of the slidable portion.

Fig. 1 is an exploded perspective view showing a main body of a brushcutter according to an exemplary embodiment of the invention. Fig. 2 is an exploded perspective view showing a primary part of the exemplary embodiment. Fig. 3 is a perspective view showing a primary part of a cleaner case according to the exemplary embodiment. Fig. 4 is a perspective view showing a state where a pull knob is pushed in according to the exemplary embodiment. Fig. 5 is a perspective view showing a state where the pull knob is pulled out according to the exemplary embodiment.

Referring to Figs. 1 to 3, a brushcutter 1 (handheld work tool) includes a main body 2 that includes a single-cylinder two-stroke engine 4 as a primary element, an operating rod 3 that is coupled to the main body 2 at a base end thereof, an attachment such as a tip saw or a nylon cutter that is attached to a distal end of the operating rod 3, and a handle that is attached in the middle of the operating rod 3. The engine 4 may be provided by a four-stroke engine.

In the main body 2, a carburetor 5 is attached to the engine 4 via an insulator 5A made of synthetic resin, and an air cleaner 6 is attached to the carburetor 5. An exhaust muffler 7 is attached to the engine 4 on the side opposite to the carburetor 5. A fuel tank 8 is attached to the lower side of the engine 4. A fuel in the fuel tank 8 is sucked up into the carburetor 5.

Attached to one end of a crankshaft of the engine 4 (not shown) is a recoil starter 9 having an operating knob 91 with a pull string. Attached to the other end of the crankshaft are a cooling fan 10 having a plurality of vanes 11 and a clutch-shoe assembly of a centrifugal clutch 20.

The centrifugal clutch 20 is attached to the outer side of the cooling fan 10. The centrifugal clutch 20 includes, in addition to the clutch-shoe assembly including a clutch shoe, a clutch drum 21 that is frictionally engaged with the clutch shoe centrifugally rotated outward in a radial direction. A coupling shaft 22 is attached to the clutch drum 21. A drive shaft 31 rotatably housed in the operating rod 3 is splined to the coupling shaft 22.

A clutch housing 23 made of synthetic resin covers the cooling fan 10 and the centrifugal clutch 20. The clutch housing 23 is screwed onto a fan housing 41 integrally formed with a crankcase of the engine 4. The clutch housing 23 is shaped as a trumpet opened wider at a position closer to the main body 2. Inside the clutch housing 23, a bearing on which the coupling shaft 22 of the clutch drum 21 is supported is held with insert mold or the like.

In the brushcutter 1, a driving force of the engine 4 is transferred from the crankshaft to the drive shaft 31 via the centrifugal clutch 20, and is transferred to the attachment from the drive shaft 31 via an appropriate gear provided to a distal end of the drive shaft 31. At this time, after flowing between the engine 4 and the fuel tank 8, a cooling air is sucked through an opening 43, which is provided to an opposed surface 42 of the fan housing 41, with the assistance of the cooling fan 10 rotated along with the crankshaft. The sucked air is then directed toward a cylinder 4A of the engine 4 (see arrow A1).

In Fig. 2, the insulator 5A is attached with three screws 5B. The insulator 5A corresponds to an intake port provided to the cylinder 4A of the engine 4. The carburetor 5 is attached to the insulator 5A via a gasket 5C with a pair of screws 5D. The screws 5D are also used to attach the air cleaner 6 to the carburetor 5.

Specifically, the air cleaner 6 includes a cleaner case 61 that is screwed onto the carburetor 5 with the screws 5D, a sponge element 62 that is housed in the cleaner case 61, and a cleaner cover 64 that is attached to the cleaner case 61 with an operating screw 63. A gasket (not shown) is also interposed between the cleaner case 61 and the carburetor 5.

Description will be made below on features of this exemplary embodiment along with the arrangement of the carburetor 5.
The carburetor 5 includes a bore 51 through which intake air passes, a choke valve 52 rotatably housed in the bore 51 at an upstream position, and a throttle valve (not shown) housed in the bore 51 at a downstream side. In this exemplary embodiment, a butterfly valve is employed as each of the choke valve 52 and the throttle valve, but, instead of that, a rotary valve or the like may alternatively be employed.

The rotary shaft of the choke valve 52 and the rotary shaft of the throttle valve extend from the external surface of the carburetor 5.

Rotary pieces

53 and 54 are attached to these rotary shafts in an externally-operable manner, respectively.

The respective positions of the choke valve 52 and the rotary piece 53 shown in Fig. 2 are related to a state where the engine is in a normal-drive mode and choke is not applied. In this state, while the rotary piece 53 and the rotary piece 54 are not in contact with each other, the rotary piece 54 and the throttle valve are biased to an idling position. A biasing unit for the rotary piece 54 or the like (not shown in Fig. 2) is attached to the rotary shaft of the throttle valve at the end opposite to the rotary piece 54.

In contrast, when choke is applied, the choke valve 52 and the rotary piece 53 are rotated in a direction shown by an arrow, so that the bore 51 is closed by the choke valve 52. Simultaneously, a contact end surface 53B of the rotary piece 53 comes into contact with the rotary piece 54, whereby the throttle valve is slightly rotated to an opening side. As a result, a relatively rich air-fuel mixture is supplied to the engine 4. When the rotary piece 53 is rotated back and a normal-drive mode is set, the contact between the

rotary pieces

53 and 54 are cancelled and the throttle valve and the rotary piece 54 are returned to the idling position by the biasing unit.

Such a rotary operation of the choke valve 52 is effected by an engagement pin 55 that projects from the rotary piece 53 and an engagement portion of a pull knob 80 for choke control that is engaged with the engagement pin 55.
The pull knob 80 includes an operating portion 82 having a recess 81 in which a finger of a user or the like can be inserted, and a slidable portion 83 with a predetermined length that is integrally formed with the operating portion 82. A choke mark 84 is provided on a surface of the operating portion 82. An engagement portion 85 that is shaped as a cutout and is opened toward the engagement portion 55 is formed in a lengthwise middle of the slidable portion 83. A contact piece 86 laterally projects from the slidable portion 83 on a base-end side relative to the engagement portion 85.

The slidable portion 83 of the pull knob 80 is housed in an accommodating portion 65 with a predetermined length provided to one side (right side in Fig. 2, in this exemplary embodiment) of the cleaner case 61. The accommodating portion 65 is formed as a groove having a U-shaped cross section that is opened at a lengthwise end and at a side near the engagement pin 55. The accommodating portion 65 includes an opposed wall 66 opposed to the engagement portion 55, and

lateral walls

67 and 68 provided on both sides of the opposed wall 66.

The lateral wall 67 on the inner side has a cut portion 67A formed by cutting the lateral wall 67 in the lengthwise direction over a predetermined length. The cut portion 67A is continuous with a groove-like portion 69 provided to the inner portion of the cleaner case 61. When the slidable portion 83 of the pull knob 80 is housed in the accommodating portion 65 and the cleaner case 61 is attached to the carburetor 5, the rotary piece 53 is inserted in the groove-like portion 69 and the engagement pin 55 projecting from the rotary piece 53 is inserted in the engagement portion 85 via the cut portion 67A. In other words, the cut portion 67A and the groove-like portion 69 are provided so that the rotary piece 53 and the engagement pin 55 are prevented from interfering with the cleaner case 61.

The lateral wall 68 on the outer side has an opening 68A opened along the lengthwise direction over a predetermined length. When the slidable portion 83 is housed in the accommodating portion 65, the contact piece 86 of the slidable portion 83 is set in the opening 68A. The length of the opening 68A is larger than the length of the contact piece 86 by a dimension S. The dimension S corresponds to a stroke amount of the pull knob 80. At a position shown in Fig. 3, the lower side of the contact piece 86 is in contact with a bottom 68B of the opening 68A. When the pull knob 80 is upwardly pulled out, the upper side of the contact piece 86 is slid by the dimension S to come into contact with a top 68C of the opening 68A.

Thus, the pull knob 80 is slidable in the lengthwise direction of the slidable portion 83 by a stroke corresponding to the dimension S. The contact piece 86 and the opening 68A define the stroke amount and the contact piece 86 is retained within the stroke. Such a linear movement of the pull knob 80 is converted into a rotary movement via the engagement portion 85 and the engagement pin 55, and the choke valve 52 is rotated by a resulting rotary amount, so that the choke valve 52 is opened or closed. In other words, the engagement pin 55 and the engagement portion 85 serve as first and second converters according to the invention.

Fig. 3 shows a state where the pull knob 80 is pushed in. In this state, the contact piece 86 is in contact with the bottom 68B and the choke valve 52 is opened, so that choke is not applied. When the contact piece 86 is in contact with the top 68C, the choke valve is closed and, thus, choke is applied.

The contact piece 86 of the slidable portion 83 is formed as a cantilever with elasticity. Since the contact piece 86 is in an elastically deformable manner, it is possible to attach the slidable portion 83 to the accommodating portion 65 or detach from it by pushing the contact piece 86 for condensing the projecting amount when maintenances are required. When being housed in the opening 68A, the contact piece 86 is elastically recovered to contact the bottom 68B or the top 68C of the opening 68A. The distal end of the slidable portion 83 is shaped like a wedge, so that the slidable portion 83 can be smoothly inserted into the accommodating portion 65.

As described above, the rotary piece 53 of the carburetor 5 can be rotated by linearly pushing and pulling the pull knob 80 engaged with the engagement pin 55. Such an arrangement is simple and easy to operate. Further, the engagement portion 85 of the pull knob 80 is opened toward the engagement pin 55, and an attachment/detachment direction of the cleaner case 61 coincides with an engagement/disengagement direction of the engagement portion 85 and the engagement pin 55. Thus, when the cleaner case 61 with the pull knob 80 attached thereon is attached to the carburetor 5 of the engine 4, the engagement pin 55 can be engaged with the engagement portion 85 substantially at the same time as the cleaner case 61 is attached. On the other hand, in disassembly, the engagement pin 55 and the engagement portion 85 can be disengaged substantially at the same time as the cleaner case 61 is detached. Thus, assembly and disassembly can be facilitated, providing a favorable maintenance efficiency.

A cutout 64A is formed in the cleaner cover 64. The cutout 64A corresponds to the operating portion 82 of the pull knob 80 attached to the cleaner case 61. When the cleaner cover 64 is attached to the cleaner case 61, the operating portion 82 is fitted in the cutout 64.
Insertion holes 61B penetrating in the attachment/detachment direction are provided to the outer edges of the cleaner case 61 opposed to each other at a distance. In attachment of the cleaner cover 64 to the cleaner case 61, projections 64B projecting from the cleaner cover 64 are inserted in the insertion holes 61B.

When the projections 64B are inserted in the insertion holes 61B, the relative positions of the cleaner case 61 and the cleaner cover 64 are not deviated from each other in a rotation direction of the operating screw 63. Thus, a clearance between the cleaner cover 64 and the operating portion 82 is kept enough for the cleaner cover 64 not to contact and interfere with the operating portion 82 of the pull knob 80, so that the operability of the pull knob 80 is not deteriorated.

Fig. 4 shows that the cleaner cover 64 is attached to the cleaner case 61, and the pull knob 80 is pushed in to set the normal-drive mode where choke is not applied. In this state, the surface of the operating portion 82 and the surface of the cleaner cover 64 are flushed to be continuous as a whole. In contrast, when choke is applied, the pull knob 80 is upwardly pulled out as shown in Fig. 5, so that a large step is defined between the surface of the operating portion 82 and the surface of the cleaner cover 64.

In view of the above, only by looking at or touching the pull knob 80 of the air cleaner 6, it is possible to immediately recognize whether the pull knob 80 is pushed in (i.e., choke is not applied under the normal-drive mode), or the pull knob 80 is pulled out (i.e., choke is applied).

It should be understood that the scope of the invention is not limited to the above-described embodiment but includes the following modifications.
For instance, in the above exemplary embodiment, the rotary piece 53 of the choke valve 52 is provided with the engagement pin 55, and the pull knob 80 is provided with the engagement portion 85 shaped as a cutout that is engaged with the engagement pin 55. However, the choke valve 52 may alternatively be provided with a pinion gear and the pull knob 80 may alternatively be provided with a rack gear engageable with the pinion gear.

In such a rack-and-pinion structure, however, not only the dimensional accuracy of each component itself but also the assembling accuracy of the components needs to be high. Otherwise, the rack gear and the pinion gear may not be preferably engaged with each other, resulting in a failure in a reliable transmission of the movement of the pull knob 80 to the choke valve 52.
In contrast, the engagement between the engagement pin 55 and the engagement portion 85 shaped as a cutout as in the above exemplary embodiment does not require such a high dimensional accuracy, so that component costs and assembly errors can be reduced.

Though the accommodating portion 65 is provided on the right side of the cleaner case 61 in the above exemplary embodiment, the accommodating portion 65 may be provided on the left side, the upper side or the lower side. In other words, where the accommodating portion 62 should be provided may be determined in consideration of a direction of attaching the engagement pin 55 to the carburetor 5 or the like.
The accommodating portion 65 is provided to the cleaner case 61 in the above exemplary embodiment. Alternatively, such an accommodating portion 65 may be provided to the cleaner cover 64, which also falls within the scope of the invention.

Though the rotary piece 53 is provided with the engagement pin 55 and the pull knob 80 is provided with the engagement portion 85 in the above exemplary embodiment, the rotary piece 53 may be provided with an engagement portion and the pull knob 80 may be provided with an engagement pin.
Though the cleaner case 61 is provided with the insertion holes 61B and the cleaner cover 64 is provided with the projections 64B, the cleaner case 61 may be provided with a projection(s) and the cleaner cover 64 may be provided with an insertion hole(s).

The invention is usable not only in a brushcutter but also in an engine-driven handheld work tool such as a chain saw or an engine blower.

Reference Sings List

1...brushcutter (handheld work tool)
4...engine
5...carburetor
6...air cleaner
52...choke valve
53...rotary piece
55...engagement pin (one of first and second converters)
61...cleaner case
61B...insertion hole
62...element
63...operating screw (screw)
64...cleaner cover
64B...projection
80...pull knob
85...engagement portion (the other of first and second converters)

Claims

A choke structure of a handheld work tool, comprising:
an engine;
a carburetor attached to the engine;
an air cleaner attached to the carburetor;
a choke valve rotatably provided in the carburetor;
a rotary piece provided to a rotary shaft of the choke valve; and
a pull knob for choke control provided on the air cleaner in such a manner as to be pulled and pushed, characterized in that
the rotary piece is provided with a first converter and the pull knob is provided with a second converter,
when the pull knob is pushed or pulled, a linear movement of the pull knob is converted into a rotary movement of the choke valve through the first and second converters, and
the first and second converters directly contact with each other.
The choke structure according to claim 1, wherein
one of the first and second converters is an engagement pin provided to one of the rotary piece and the pull knob, and the other of the first and second converters is an engagement portion provided to the other of the rotary piece and the pull knob and engaged with the engagement pin.
The choke structure according to claim 2, wherein
an engagement/disengagement direction of the engagement pin and the engagement portion coincides with an attachment/detachment direction of the air cleaner relative to the carburetor.
The choke structure according to any one of claims 1 to 3, wherein
the air cleaner comprises:
a cleaner case attached to the carburetor to accommodate an element; and
a cleaner cover removably attached to the cleaner case to cover the cleaner case, and
the pull knob is attached to the cleaner case.
The choke structure according to claim 4, wherein
the pull knob comprises an operating portion, and
when the pull knob is pushed in, the operating portion is fitted in a cutout provided to the cleaner cover such that a surface of the operating portion and a surface of the cleaner cover are flushed to be continuous as a whole.
The choke structure according to claim 4 or 5, wherein
the cleaner cover is attached to the cleaner case with a screw, and
one of the cleaner case and the cleaner cover is provided with a projection that projects toward the other of the cleaner case and the cleaner cover, and the other of the cleaner case and the cleaner cover is provided with an insertion hole in which the projection is inserted.
The choke structure according to any one of claims 4 to 6, wherein
the pull knob comprises a slidable portion configured to be attachable or detachable relative to an inside of an accommodating portion provided in the cleaner case, the slidable portion accommodated inside the accommodating portion in a slidable manner along a direction of the linear movement, and
the slidable portion comprises a contact piece elastically deformed in attachment or detachment relative to the accommodating portion, the contact piece coming into contact with a predetermined position in the accommodating portion to define a sliding amount of the slidable portion.