WO2012176940A1

WO2012176940A1 - Engine working machine

Info

Publication number: WO2012176940A1
Application number: PCT/JP2012/066635
Authority: WO
Inventors: Naoto Ichihashi
Original assignee: Hitachi Koki Co., Ltd.
Priority date: 2011-06-24
Filing date: 2012-06-22
Publication date: 2012-12-27
Also published as: JP2013007317A

Abstract

To provide an engine working machine which is capable of reducing an exhaust sound while maintaining a compact size and a sufficient engine output and is also capable of reducing a vibration sound generated by a vibration of a wall surface of a muffler. An engine (36) is configured such that: a driving shaft direction of the engine (Y-direction), an opening direction of an exhaust port (Z-direction), and an operation direction of a piston (X-direction) are substantially perpendicular to each other; a muffler (4) is fastened to a proximity of an exhaust port (24) of the engine (36); the muffler (4) has a shape extending in a vertical direction and is extended toward a downward direction lower than a vertical plane (72) passing a lower end portion of a cylinder; and the muffler (4) has a protrusion portion (32) protruding towards a center direction of the engine (36) so as to obtain a volume corresponding to a space (64). Since the muffler (4) is largely extended in a downward direction, a fuel tank (22) is provided to be offset to a left side (- Z-direction), and a left end portion of the fuel tank is extended upward like an arrow (80) so as to obtain a volume corresponding to a space (68).

Description

DESCRIPTION

Title of Invention

ENGINE WORKING MACHINE

Technical Field

The invention relates to an improvement of an engine used as a power source for an engine working machine, and more particularly, to an engine working machine including an improved muffler.

Background Art

Portable engine working machines, such as brush cutters, blowers, hedge trimmers, chain saws, or cutter, are usually used outdoors. For this reason, suppression of noise becomes an issue in areas that are heavily populated, for example, an urban area. Thus, reduction of the noise is highly demanded by users. At the same time, since it is a portable engine working machine, reducing the size thereof is also highly demanded. An engine used as a power source of the engine working machine includes a driving shaft (crank shaft) provided with driven devices, such as a fan for cooling a tip tool or a manual starter device. Thus, the engine is generally made in a high density design with a plurality of components being disposed around the engine. For this reason, for example, PTL 1 discloses a structure suitable for a muffler or an exhaust port for exhaust gas so that the engine is compatible with the compact size and the reduced noise.

Citation List Patent Literature

PTL 1 : JP-A-H11-156802

Summary of Invention

Technical Problem

In PTL 1 , the muffler is provided with a plurality of exhaust ports for exhaust gas which are spaced apart from each other by a predetermined distance or more, to reduce an exhaust sound. However, in the muffler, in addition to the exhaust sound which is generated by high-temperate and high-pressure gas that is instantaneously emitted to the muffler from the engine, a vibration sound is generated from the muffler by a side wall thereof which is vibrated when pressure pulsation is caused by the emission of the high-temperature and high-pressure gas. Thus, it is difficult to further reduce the exhaust sound from the related art. Further, since a back pressure of the exhaust gas is necessarily prevented from being increased so as to permit the output of the engine to be equivalent to that of the related art, the exhaust port should have an opening area of a predetermined level or more. In general, since a noise source of the exhaust sound in the muffler is the exhaust port, the exhaust noise is preferably reduced by decreasing the opening area of the exhaust port. However, for the above reason, it is difficult to decrease the opening area of the exhaust port, so that it is also difficult to obtain an effect of reducing the exhaust sound.

In connection with the above-described problem, it has been required for the engine working machine to have a muffler capable of reducing the exhaust sound while maintaining a compact size and a sufficient engine output. In addition, it is required to reduce the vibration sound generated by the vibration of the wall surface of the muffler. If only the volume of the muffler is increased to deal with the above problems, for example, the volume of the muffler is required to be equal to or more than two times to reduce the noise of 1 dB. Thus, there is a problem in that the effect on reducing the noise is small as compared to increase in design difficulty for the engine working machine, for which the compact size is required. On the other hand, if an area of a tail pipe is reduced to deal with the above problems, for example, the area of the tail pipe must be reduced by a half or less to reduce the noise of 1 dB. However, in such a case, the engine output is decreased due to the reduction of the area of the tail pipe. Thus, the compact size is hardly compatible with the engine output.

The present invention has been made to solve the above-described problems occurring in the related art, and one object of the present invention is to provide an engine working machine capable of further reducing a noise generated from a muffler.

Another object of the present invention is to provide an engine working machine including a muffler, which is capable of increasing a size of the muffler while making the whole size of the engine working machine compact. Still another object of the present invention is to provide an engine working machine which optimizes a relationship between the volume of a muffler and the area of the tail pipe so as to achieve a balance between a high output of an engine and a reduction of the noise.

Solution to Problem Illustrative aspects of the invention disclosed in this application will be describes as follows.

According to a first illustrative aspect of the invention, there is provided an engine working machine comprising: an engine; a fuel tank configured to store fuel to be supplied to the engine; and a muffler configured to suppress an exhaust noise discharged from the engine, wherein: a driving shaft direction of the engine, an opening direction of an exhaust port, and an operation direction of a piston are substantially perpendicular to one another; the muffler is fastened to an exhaust port of the engine such that one of expansion chambers in the muffler is connected to the exhaust port of the engine; and the muffler comprises a protrusion portion extending towards an engine side rather than a fastening plane, which is parallel to a moving direction of the position at the fastening position, wherein the protrusion portion is disposed near an end portion, which is away from an ignition plug in the moving direction of the piston in the engine, of the muffler. According to a second illustrative aspect of the invention, a side of the muffler opposite to the exhaust port is substantially parallel to the fastening plane. According to a third illustrative aspect of the invention, the fuel tank is provided below a lower portion of a crankcase of the engine, and is provided at a lateral side of the protrusion portion of the muffler. According to a fourth illustrative aspect of the invention, the muffler comprises a concave portion between the protrusion portion and the connecting portion with the engine such that the concave portion is away from the fastening plane with respect to the engine.

According to a fifth illustrative aspect of the invention, a volume of the muffler is set to be 17 times or more of a displacement of the engine, and an opening area of a tail pipe provided on the discharge port of the muffler is set to be 0.3 times and more and 0.8 times or less of the displacement. According to a sixth illustrative aspect of the invention, the engine is disposed so that the piston reciprocates in a vertical direction, a cross section of the exhaust port of the engine is positioned in a substantially vertical direction, and a size of the muffler is formed to be extended in a vertical direction to have a relationship of thickness direction < horizontal direction < vertical direction. According to a seventh illustrative aspect of the invention, the size of the muffler is set so that a ratio of vertical direction/horizontal direction is 1.5 or more.

According to an eighth illustrative aspect of the invention, the muffler comprises a rigidity increasing member for increasing rigidity of a lateral surface of the muffler, fastened to the engine by a fastening member and disposed at a position spaced apart from the fastening member in the moving direction of the piston on a lateral surface of the muffler facing the engine and a lateral surface of the muffler opposite to the exhaust port of the engine. According to a ninth illustrative aspect of the invention, the rigidity increasing member comprises a screw and a pipe penetrating the screw, and the pipe is fixed to the lateral surface of the muffler facing the engine and the lateral surface of the muffler opposite to the exhaust port of the engine. According to a tenth illustrative aspect of the invention, the muffler includes therein: a first expansion chamber communicating with the exhaust port of the engine; a second expansion chamber having a discharge port for discharging exhaust gas to an atmosphere; and a third expansion chamber connecting the first expansion chamber and the second expansion chamber, and a catalyst configured to purify an exhaust gas component is disposed in the third expansion chamber. According to an eleventh illustrative aspect of the invention, the third expansion chamber is disposed to include an internal space of the protrusion portion.

Advantageous Effects of Invention

According to the first to foruth illustrative aspects of the invention, the protrusion portion is provided on a portion of the muffler to extend towards the engine side, and the fuel tank is provided below the lower portion of the crankcase of the engine and is provided to be offset to lateral side of the protrusion portion of the muffler. Therefore, the volume of the muffler can be effectively increased with little effect on each portion of both end portions of a driving shaft, with little hindrance to exchange work of an ignition plug, and without enlarging the whole length of the engine in the opening direction of the exhaust port. Accordingly, it is easy to reduce a back pressure and improve the output with the compact configuration, and it is also possible to obtain an effect of reducing the exhaust sound.

According to the fifth illustrative aspect of the invention, the volume of the muffler is set to be 17 times or more of the displacement of the engine, and the opening area of a tail pipe provided on the discharge port of the muffler is set to be 0.3 times and more and 0.8 times or less of the displacement. Therefore, it is possible to reliably reduce the noise without lowering the output of the engine. Further, as compared to the increase in design difficulty of increasing the size of the muffler in the limited space, it is possible to obtain the effect of significantly reducing the noise and maintaining the output, which fits for the difficulty. According to the sixth illustrative aspect of the invention, the size of the muffler is formed to be extended in the vertical direction to have the relationship of thickness direction < horizontal direction < vertical direction. Therefore, it is possible to prevent the increase in size in the thickness direction which is directly linked to the increase the whole length of the engine. Accordingly, the whole length of the engine is minimized, and thus the engine becomes compact.

According to the seventh illustrative aspect of the invention, the size of the muffler is set so that the ratio of vertical direction/horizontal direction is 1.5 or more. Therefore, additional compacting of the engine working machine can be realized by adjusting the engine, which is likely to be longest in the moving direction of the piston, and the layout of the muffler.

According to the eighth illustrative aspect of the invention, the member configured to increase the rigidity of the lateral surface of the muffler is disposed at the position spaced apart from the fastening member in the moving direction of the piston on the lateral surface of the muffler facing the engine and the lateral surface of the muffler opposite to the exhaust port of the engine. Therefore, it is possible to improve the rigidity of the lateral surface of the muffler over the wider range. Accordingly, amplitude of the membrane vibration at the lateral surface of the muffler can be further suppressed, thereby reducing vibration sound.

According to the ninth illustrative aspect of the invention, the rigidity increasing member is the screw and the pipe penetrating the screw, and the pipe is fixed to the lateral surface of the muffler facing the engine and the lateral surface of the muffler opposite to the exhaust port of the engine. According thereto, it is possible to improve the rigidity of the lateral surface of the muffier more effectively. Therefore, the amplitude of the membrane vibration at the lateral surface of the muffler is further suppressed, thereby reducing the vibration sound. Incidentally, in the case where the muffler is fastened to only the proximity of the exhaust port of the engine, there is a concern that the muffler is in a cantilever state and thus the vibration of the muffler is increased. However, the configuration according to the ninth illustrative aspect can suppress the concern, and also suppress metal fatigue caused by the vibration, thereby improving its durability.

According to the tenth illustrative aspect of the invention, the muffler includes therein the first expansion chamber communicating with the exhaust port of the engine, the second expansion chamber having the discharge port for discharging exhaust gas to the atmosphere, and the third expansion chamber connecting the first expansion chamber and the second expansion chamber, and the catalyst is disposed in the third expansion chamber to purify the exhaust gas component. Therefore, the exhaust gas component is combusted by the catalyst, thereby achieving cleaning of the exhaust gas.

According to the eleventh illustrative aspect of the invention, the third expansion chamber is disposed to include the internal space of the protrusion portion. Therefore, by disposing the catalyst on the protrusion portion which easily obtains the large volume, it is possible to cope with the case of changing the catalyst in a large size. Further, in the case of enlarging the catalyst in size, since it is easy to obtain a gap between the lateral surface of the muffler and the catalyst, the heat of the catalyst is suppressed from being transferred to the lateral surface of the muffler. The above and other objects and the features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings.

Brief Description of Drawings

[Fig. 1] Fig. 1 is a perspective view illustrating an appearance of an engine working machine according to one embodiment of the present invention.

[Fig. 2] Fig. 2 is a right side view of the engine working machine according to one embodiment of the present invention.

[Fig. 3] Fig. 3 is a cross-sectional view taken along the line A-A in Fig. 2.

[Fig. 4] Fig. 4 a top plan view of the engine working machine according to one embodiment of the present invention with partially showing a cross-sectional view taken along the line B-B in Fig. 2.

[Fig. 5] Fig. 5 is a cross-sectional view taken along the line C-C in Fig. 2.

[Fig. 6] Fig. 6 is a view illustrating a relationship between a size and an arrangement of a muffler and a fuel tank in the engine working machine according to one embodiment of the present invention.

[Fig. 7] Fig. 7 is a side view illustrating the size of the muffler and an engine in the engine working machine according to one embodiment of the present invention.

[Fig. 8] Fig. 8 is a view illustrating a relationship between an area of a tail pipe and an engine output per a unit of displacement in a case where a volume of the muffler is constant.

[Fig. 9] Fig. 9 is a view illustrating a relationship between the volume of the muffler and a noise per a unit of displacement in a case where the area of a tail pipe is constant. [Fig. 10] Fig. 10 is a view illustrating a relationship between the area of the tail pipe and the noise per a unit of displacement in the case where the volume of the muffler is constant.

[Fig. 11] Fig. 11 is a view illustrating a relationship between the volume of the muffler and area of the tail pipe per a unit of displacement.

[Fig. 12] Fig. 12 is a cross-sectional view of an engine working machine according to a second embodiment of the present invention, in which cross-sectional position corresponds to the line A-A in Fig. 2. Description of Embodiments

First Embodiment

Hereinafter, embodiments of the present invention will now be described with reference to the accompanying drawings. Throughout the description, the same reference numerals refer to the same elements throughout the various figures and embodiments of the present invention, and the repeated description thereof will be omitted. In addition, the terms 'leftward and rightward direction (X-direction),' 'front and rear direction (Y-direction),' and 'upward and downward direction (Z- direction)' are used on a basis of the directions shown in each drawing. Further, the directions seen from a muffler itself are described herein by referring a widthwise direction to as the Y-direction, a thickness direction to as the X-direction, and a vertical direction to as the Z-direction.

Fig. 1 is a perspective view illustrating an appearance of an example in which an engine working machine 1 according to one embodiment of the present invention is applied to a brush cutter. The engine working machine 1 includes an engine accommodated in a cylinder cover 3 made of a resin material. At a lateral portion of the engine working machine 1 , an air cleaner 2 is installed in a left side (- Z-direction) of the engine to cover a carburetor and filter air to be sucked. A muffler 4 is installed at a right side (+ Z-direction) of the engine. The engine to be accommodated in the cylinder cover 3 of the engine working machine 1 is disposed in a so-called vertical direction, and a reciprocating direction of a piston, which will be described later, of the engine is referred to as an X-direction. A plug cap 34 is disposed on an upper portion of the engine. A second volute case 9 is attached to an output shaft of the engine working machine 1 at a front side thereof to cover an output transmission mechanism. The second volute case 9 is provided at a front end (+ Y-direction) thereof with an insertion portion 39 for holding a driving shaft (not illustrated) to be mounted therein. The second volute case 9 is provided at a lower portion thereof with a leg member 9A. The second volute case 9 serves as a support when the engine working machine 1 is placed on a ground or the like. A first volute case 8 is interposed between an engine body and the second volute case 9.

The muffler 4 according to this embodiment has a basic shape of a substantially rectangle, and is disposed such that a longitudinal direction thereof is a vertical direction (X-direction). The reason is that the volume is obtained as large as possible by enlarging the muffler 4 in the vertical direction to effectively reduce an exhaust sound in a limited space. The muffler 4 is directly fixed to the engine by three bolts, that is, muffler fastening bolts 5 A and 5B and a muffler fastening bolt 6. The muffler 4 is provided at the lateral portion thereof with a pipeline, that is, an air intake passage 7, for feeding air from the air intake port 29 of the first volute case 8 accommodating a cooling fan that will be described later. Ribs are provided on an outer surface 27 of the muffler (lateral surface of the muffler which is spaced apart from the engine) disposed in a substantially vertical direction in order to increase the rigidity over a wide range and to reduce a vibration sound which is caused by membrane vibration of the wall surface of the muffler.

Fig. 2 is a right side view of the engine working machine 1 when seen from the right side. The muffler fastening bolts 5A and 5B are disposed at portions (upper side of a cross section B-B) close to an ignition plug connected to the plug cap 34 rather than a crank shaft (positioned on the cross section B-B) of the engine in the vertical direction (X-direction) of the muffler 4. The muffler fastening bolt 6 is disposed at a position which divides a lower end portion 4B of the muffler 4, spaced from the muffler fastening bolts 5 A and 5B and the ignition plug 12, on the outer surface 27 of the muffler into two substantially equal parts, and divides the muffler 2 into two substantially equal parts in a driving shaft direction Y (horizontal direction of the muffler element) perpendicular to a moving direction X of the piston. In this embodiment, the muffler fastening bolt 6 is disposed at a position which is substantially identical to an axis (e.g., driving axis) of the driving shaft in the vertical direction (see Fig. 3). According to this arrangement, the rigidity of the outer surface 27 of the muffler is increased over the wide range, and the amplitude of membrane vibration can be effectively suppressed on the lateral surface of the muffler to reduce the vibration sound.

A manual type starter 10 is attached to the rear portion of the engine. The manual type starter 10 includes a reel, which is connected to the driving shaft of the engine and is wound with a pulling rope, with a clutch being interposed between the reel and the driving shaft, and a starter knob 11 connected to the pulling rope. The engine is started when the pulling rope is pulled by the starter knob 11. Although the internal structure of the starter 10 is not illustrated in Fig. 2, the engine can utilize not only the above manual type starter 10 but also a starter device widely known in the art, such as a recoil starter or an electric motor driven by a battery.

In this embodiment, a distance L between the muffler fastening bolts 5A and 5B and the muffler fastening bolt 6 and a distance L2 between the muffler fastening bolt 6 and the lower end portion 4B of the muffler 4 are approximately set at a ratio of LI :L2 = 4:6 in the moving direction (± X-direction) of the piston. Further, a distance L3 between the muffler fastening bolt 6 and a front end portion of the muffler 4 and a distance L4 between the muffler fastening bolt 6 and a rear end portion of the muffler 4 are approximately set at a ratio of L3:L4 = 4:6 in the driving shaft direction (Y- direction). According to the above configuration, the muffler fastening bolt 6 can increase the rigidity of the outer surface 27 of the muffler, and thus reduce the vibration sound caused by the membrane vibration of the outer surface 27 of the muffler. Further, since the muffler 4 is strongly fastened and fixed to a cylinder 30 of the engine, the vibration of the whole muffler 4 can be reduced, and thus metal fatigue of the fastening portion caused by the vibration can be reduced, thereby improving its durability.

A tail pipe 17 for discharging exhaust gas from the muffler 4 is disposed at a position close to the ignition plug 12 rather than the cross section B-B (horizontal plane passing through the driving shaft of the engine) when seen from the X-direction, and is configured so that an outflow direction EX1 of the exhaust gas is the same (parallel with the cross section B-B) as the driving shaft in the tail pipe 17. An opening area opened to the atmosphere is formed by the tail pipe 17. The muffler 4 according to this embodiment has one opening portion. In this embodiment, the opening area of the exhaust port of the muffler 4 is set to be 3% or less of the area of a cylinder bore. In this way, by taking the sufficient opening area of the tail pipe 17 to the area of the cylinder bore, an effect of suppressing the exhaust sound can be obtained without decreasing the output.

When the engine is to be started, the starting operation is performed by pulling the starter knob 11 of the starter 10, while the engine working machine 1 is put on the ground. In this embodiment, the position of the tail pipe 17 can ensure a predetermined height from the ground in the moving direction X of the piston. Therefore, it is possible to secure the position higher than obstacles such as stones or grass on the ground in a direction of gravity. As such, since there is no obstacle, such as stones or grass, around the exhaust port of the muffler, the starting operation can be smoothly performed. Further, even in the case where an engine speed is increased for the purpose of warming-up or the like while the engine working machine is put on the ground, the structure of the engine working machine 1 can suppress the dust on the ground from being soared up by the exhaust gas, thereby lessening annoyance caused by the dust soared up around the worker. In addition, it is possible to suppress an air filter provided in the air cleaner 2 from being clogged due to the soared dust to be sucked in the engine.

Since the engine working machine 1 is one manually handled by a worker, the engine working machine 1 is generally positioned at a position lower than worker's ears in the direction of gravity while working. For this reason, in the case where the moving direction of the piston in the engine 36 is substantially consistent with the direction of gravity, the exhaust sound generated from the tail pipe 17 is not at least discharged upward towards the worker's ears in the direction of gravity. Therefore, the exhaust sound experienced by the worker can be reduced. Preferably, if an intersection angle of the outflow direction of the exhaust gas and the parallel line of the driving shaft is set to be 0° to 60° in the exhaust port of the muffler, the outflow direction EXl of the exhaust gas is suppressed from facing upward in the direction of gravity which is closer to the worker's ears in the direction of gravity, thereby reducing the exhaust sound to be experienced by the worker.

Incidentally, the above-described ratios or exhaust direction is not limited thereto. For example, the ratio L1 :L2 is preferably set in the range of 4:6 to 6:4, and the ratio L3:L4 is preferably set in the range of 4:6 to 6:4. Further, the tail pipe 17 may be arranged at an angle to be oriented towards a direction away from the ignition plug 12, as the outflow direction EX2 of the exhaust gas, that is, to intersect with the cross section B-B. An intersection angle Θ of EXl and EX2 may be set in the range of 0° to 60°.

Fig. 3 is a cross-sectional view taken along the line A- A in Fig. 2. The engine 36 is a small two-cycle single-cylinder engine of 21 cc displacement. In the engine 36, a driving shaft 20 is connected to a piston 19 by a connecting rod, and the piston 19 is configured to reciprocate up and down in the cylinder 30. The moving direction X of the piston 19, the driving shaft direction Y, and the opening direction Z of the exhaust port are substantially perpendicular to one another. The cylinder 30 of the engine 36 is provided with an exhaust port 24 for discharging the exhaust gas outward from the engine 36. Intake, compression, power, and exhaust strokes of the engine are the same as those of a two-cycle engine of the related art, so that the detailed description thereof will be omitted herein. In this embodiment, the cylinder 30 includes a cylinder body, a head portion, and heat radiation fins which are made of, for example, aluminum alloy by monoblock casting. The ignition plug 12 is attached to the upper portion of the cylinder 30. A high- voltage current is fed to the ignition plug 12 via the plug cap 34 from an ignition device (not illustrated) at a predetermined timing.

The cylinder cover 3 is a cover made of, for example, a plastic material. The cylinder cover 3 is configured to cover the cylinder 30 to be heated at a high temperature at driving, so as to prevent the worker from directly contacting components such as the cylinder 30. For this reason, the cylinder cover 3 is provided a plurality of vent holes. The engine 36 is provided with a carburetor 23, and an air cleaner 2 is provided on the left side (- Z-direction) of the carburetor 23.

A fuel tank 22 is disposed below a bottom side (- Z-direction) of the crankcase 21. A heat shield plate 38 is interposed between the engine 36 and the muffler 4, and between the fuel tank 22 and the muffler 4. By virtue of the heat shield plate 38, the heat of the muffler 4 does not have an effect on the cooling of the engine 36. Further, the heat shield plate 38 blocks radiant heat generated from the muffler 4 to suppress the increase in temperature of the fuel tank 22. The heat shield plate 38 is formed by adhering a heat insulation material to a thin aluminum plate. In the related-art engine working machine, the fuel tank 22 is generally disposed below the bottom side of the crankcase 21 to be symmetrical vertically on a basis of a center plane of the engine 36 in a left-right direction. The reason is to prevent the weight balance of the engine working machine 1 in the left-right direction from being collapsed due to the weight of the fuel, such as mixed gasoline, stored in the fuel tank 22. In this embodiment, however, the size of the muffler 4 is increased in an upward and downward direction, as compared to the muffler for the related-art engine working machine, and has a protrusion portion extending towards the portion on which the fuel tank of the related art is positioned. Thus, in this embodiment, by offsetting the position of the fuel tank 22 in the left side (- Z-direction), the space occupied by the muffler 4 extending to the lower side is reserved, and the weight balance is adjusted. The arrangement relationship between the muffler 4 and the fuel tank 22 will be described below.

The muffler 4 is disposed at the right side of the engine 36. The muffler 4 is provided with a communication portion 31 which communicates with the exhaust port 24. The muffler 4 is fastened to a portion near the exhaust port 24 of the cylinder 30 by the muffler fastening bolts 5A and 5B which are disposed near communication portion 31, with the heat shield plate 38 being interposed therebetween to secure sealing. The muffler 4 is fastened to the crankcase 21 by the muffler fastening bolt 6. The muffler 4 is fixed to the crankcase 21 by the muffler fastening bolt 6 penetrating a circular collar 16 or the muffler 4. The collar 16 and the fastening bolt 6 serve as a rigidity increasing member for increasing the rigidity of the outer surface 27 of the muffler opposite to the exhaust port 24 of the engine 36. An inner surface 26 of the muffler 4 facing the engine 36 including the cylinder 30 and the crankcase 21 has a protrusion portion 32, at the position in which the exhaust port 24 is fastened to the muffler 4, extending toward the engine 36 side more than a fastening plane M which is parallel to the moving direction X of the piston. The protrusion portion 32 is disposed near the lower end portion 4B, which is away from the ignition plug 12 in the moving direction X of the piston, of the muffler 4. An outer surface 27 of the muffler 4 opposite to the exhaust port 24 is configured to be substantially parallel to the fastening plane M. Incidentally, the minimum value LA and the maximum value LB of the distance between the outer surface 27 of the muffler and the fastening plane M are set in the range of LA/LB = 0.7 to 1.0. For example, the range of LA/LB = 0.75 may be set.

The muffler 4 is provided with a partition 37 therein to separate a first expansion chamber 13A having the communication portion 31 from a second expansion chamber 13B having the tail pipe 17 of the exhaust gas. A third expansion chamber 13C, which is an additional expansion chamber disposed near the protrusion portion 32, is disposed between the first expansion 13A and the second expansion chamber 13B. The third expansion chamber 13C is formed by sheet metal working, and is made by expansion chamber cases 15A and 15B made from iron which is fixed to the partition 37 by welding. The third expansion chamber 13C is provided therein with a catalyst 14 for purifying exhaust gas components by combustion. The expansion chamber cases 15A and 15B are respectively provided with expansion chamber opening portions 25A and 25B communicating with the first expansion chamber 13A and the second expansion chamber 13B. The catalyst 14 is disposed to be near the protrusion portion 32. The effect of reducing the exhaust sound can be increased by disposing the third expansion chamber 13C in the above-described way. Further, since -the ; catalyst 14 is involved in the third expansion chamber 13C,_; the exposed area of the catalyst 14 to the sidewall of the muffler 4 can be effectively reduced, so that it is possible to effectively suppress the increase in temperature of the wall surface of the muffler 4 in the case where the catalyst 14 is inserted. The catalyst 14 is an oxidation catalyst for oxidizing HC, CO or the like, the oxidation catalyst including a stainless steel foil of a honeycomb shape which is deposited with palladium, rhodium or the like and is inserted and fixed to a cylinder made from stainless steel. The catalyst 14 is disposed in the internal space of the protrusion portion 32 and is positioned below the lateral portion of the crank case 21 in the Y- direction of the driving shaft of the piston 19. Since the catalyst 14 is provided to be spaced apart from the cylinder 30 which is a heat source, it is possible to prevent the heat sources from being concentrated on one portion, thereby suppressing the increase in temperature of the whole engine working machine.

The first expansion chamber 13 A is provided with an air intake port 18 which communicates with the air intake passage 7. The air intake port 18, which is means for feeding the air, serves as an opening of the air intake passage 7 at the muffler 4 side, which is illustrated in Figs. 1 and 2. The opening area of the tail pipe 17 is set to be about 3% of the area of a bore D of the cylinder 30. The opening area of the opening portions 25A and 25B of the expansion chamber is set to be 5 times or less, for example, about 4 times, of the opening area of the tail pipe 17. For example, when the cylinder bore D is 31 mm, the opening area is about 755 mm², so that the tail pipe 17 has an opening area of 24 mm² corresponding to a circle of φ5.5 in diameter, and the opening portions 25A and 25B of the expansion chamber have an opening area of 97 mm² corresponding to a circle of φ 11 in diameter. The opening area of the communication portion (opening portions 25 A and 25B of the expansion chamber) is secured to a value equal to or more than a predetermined minimum value with respect to the opening area of the exhaust port of the muffler and is limited to a value equal to or less than a predetermined maximum value with respect thereto. According thereto, exhaust resistance in the communication portion is not excessive, and the exhaust sound is reduced. According to this configuration of the engine working machine 1 , the fuel and air are sucked in the engine 36 via the air cleaner 2 and the carburetor 23, and after the fuel and air are combusted, the fuel and air are discharged through the exhaust port 24 as the exhaust gas. In this instance, the reciprocating movement of the piston 19 is converted into the rotational movement of the driving shaft 20.

The exhaust gas flows in the third expansion chamber 13C via the opening portion 25A of the expansion chamber together with the flow AIR2 of the air flowing in the first expansion chamber 13 A via the air intake port 18, like the flow EX of the exhaust gas. After that, the exhaust gas passes through the catalyst 14 and the opening portion 25B of the expansion chamber, and is discharged to the atmosphere through the tail pipe 17. The muffler 4 is formed such that the outer surface 27 of the muffler is in substantially parallel to the fastening plane M. Further, since the protrusion portion 32 is formed near the lower end portion 4B such that the inner surface 26 of the muffler protrudes in the - Z-direction rather than the fastening plane M, the volume of the muffler can be significantly increased without extending the whole length of the exhaust port in the opening direction Z. In this way, the back pressure of the muffler 4 is decreased, so that the output of the engine 36 is easily improved, and the exhaust sound is reduced. Accordingly, since the output is hardly to decreased even though the opening area, which is the noise source of the exhaust sound in the muffler 4, of the tail pipe 17 is set to be relatively smaller than that of the related art, it is possible to effectively reduce the exhaust noise while maintaining the output. In this embodiment, the third expansion chamber 13C is additionally disposed near the protrusion portion 32, so that the volume of the third expansion chamber 13C can be larger than the case where the third expansion chamber 13C is installed at other position. Therefore, even though the opening area of the opening portions 25 A and 25B of the third expansion chamber 13C is set to be relatively small, the output is hardly to decrease. For these reasons, the exhaust sound radiated from the first expansion chamber 13 A to the third expansion chamber 13C is reduced by making the opening area, which is the noise source of the third expansion chamber 13C, of the opening portion 25A of the expansion chamber relatively smaller than that of the related art. In a similar manner, the exhaust sound radiated from the third expansion chamber 13C to the second expansion chamber 13B is also reduced by making the opening portion 25B of the expansion chamber relatively smaller than that of the related art.

In addition, in the case of changing the design in which the catalyst 14 is more increased in size, since the volume of the third expansion chamber 13C is sufficiently secured by the protrusion portion 32 and there is enough room for the dimension, it is possible to easily cope with the design change without carrying out the significant change. Further, since the oxygen required when the exhaust gas components are burned by the catalyst 14 can be supplied by feeding the air to the first expansion chamber 13a through the air intake port 18, the purifying performance of the catalyst is improved. In addition, the volume of the first expansion chamber 13A is significantly increased by the protrusion portion 32, and the back pressure of the first expansion chamber 13 A is decreased. Therefore, pumping power required to feed the air can be decreased, and thus the air can be easily fed to the first expansion chamber 13A.

Fig. 4 a top plan view of the engine working machine 1 with partially showing a cross-sectional view taken along the line B-B in Fig. 2. In the engine working machine 1, the starter 10 and the starter knob 11 are disposed on one end of the driving shaft 20, and a cooling fan 28 is disposed on the other end. The cooling fan 28 generates air flow to cool the cylinder 30, and serves as a flywheel. Further, a magnet (not illustrated) is disposed at a predetermined position of the cooling fan 28 in a circumferential direction thereof to determine a timing of supplying a high-voltage current to the ignition plug 12 and transmit the determined timing to an ignition device (not illustrated). The cooling fan 28 is disposed in the first volute case 8 and the second volute case 9 which are a portion of the crankcase 21. The first volute case 8 is provided with the air intake port 29 of the air intake passage 7. A check valve 35 is installed to the air intake port 29 to prevent backward flow of the exhaust gas from the first expansion chamber 13 A.

As described above, since the driving shaft 20 is rotated by starting the engine 36, the cooling fan 28 sucks the air in the direction AIR1, and feed the air to the vicinity of the cylinder 30 of the engine 36 to cool the engine 36. In this instance, by taking out a fraction, like AIR2, from the air generated by the cooling fan 28 at the air intake port 29, it is possible to feed the air into the first expansion chamber 13a of the muffler 4 through the air intake passage 7.

By disposing the air intake port 29 at the first volute case 8, a thermal path reaching to the air intake port 29 from the first expansion chamber 13A through the air intake passage 7 can be extended. As a result, the heat of the muffler is transferred to the air intake port 29 so that the increase in temperate can be suppressed, and the durability of the check valve 35 which is disposed near the air intake port 29 can be improved. Further, since separate components or shape change is not required to dispose the air intake port 29, the air intake port 29 can be disposed compactly. In addition, since wind is always generated by the cooling fan 28 in the first volute case 8 and the second volute case 9, the air intake port 29 and the check valve 35 are sufficiently cooled by the wind. In this way, a fraction of the wind generated by the cooling fan 28 which is disposed to cool the engine 36 is fed into the muffler 4, so that it is not necessary to separately dispose a pump, a blower fan or the other for feeding the air into the muffler 4. Accordingly, while minimizing the increase in cost, weight and size of the product, a means for feeding the air into the muffler 4 can be realized in a low cost and a compact size, and the performance of the catalyst for purifying the exhaust gas components can be improved. Fig. 5 is a cross-sectional view taken along the line C-C in Fig. 2. The air intake port 29 is disposed at the position, which is the substantially minimum distance from the center N of the cooling fan 28, on the inner peripheral wall portion of the first volute case 8 covering the outer circumference of the cooling fan 28. The first volute case 8 is configured such that the distance from the center N to the inner peripheral wall is gradually increased in a counterclockwise direction according to the rotational direction H of the cooling fan 28 at the center N. The cylinder 3 is smoothly connected to a discharge portion 33 of the first volute case 8 near the portion in which the distance becomes the maximum. With the above configuration, when the cooling fan 28 is rotated, the wind, like AIR3, which flows along the inner peripheral wall of the first volute case 8 and then is discharged from the discharge portion 33, is guided to each portion of the cylinder 30 by the cylinder cover 3 to cool the cylinder 30. Meanwhile, a fraction of the wind, like AIR2, reaches the air intake port 18 of the first expansion chamber 13A through the air intake passage 7 from the air intake port 29, and then is fed into the first expansion chamber 13 A.

In this way, by disposing the air intake means using the first volute case 8 of the related art, it is not necessary to configure separate components or shape for arrangement of the air intake port 29. Accordingly, the air intake port can be disposed compactly. Further, since the inner wall forming the air intake port 29 is disposed at the position which is the substantially minimum distance from the center N in the first volute case 8, the decrease in air quantity guided to the cylinder cover 3 from the discharge portion 33 can be suppressed to the minimum. Therefore, while the decrease in air quantity from the discharge portion 33 used for the purpose of cooling or blowing is suppressed to the minimum, the air can be taken out from so as to be fed into the first expansion chamber 13 A of the muffler 4. In addition, in this embodiment, since the volume of the muffler 4 is formed to be larger than that of the related art, the performance of the pump for feeding the air into the first expansion chamber 13A is decreased, and thus the air can be effectively fed into the first expansion chamber 13 A. Furthermore, since the wind always flows in the first volute case 8 by the cooling fan 28, in the case where the heat of the muffler 4 is transferred from the connection portion between the muffler 4 and the air intake passage 7, it is possible to prevent the temperature of the air intake port 29 from being increased, thereby improving its durability. Fig. 6 is a view explaining the size of the muffler 4 of the engine working machine 1 according to the embodiment of the present invention. As will be understood from Fig. 6, the muffler 4 is attached to the right side (+ Z side) of the engine 36. For the muffler of the related art, since the communication portion 31 is connected to the exhaust port 24 of the engine 36, the upper end portion 4 A of the muffler is positioned near the arrow 41 in the X-direction. In the related-art engine working machine, the muffler is generally configured by the size of a space 61, which is located in an upper side (X-direction) of an exhaust port plane 71, and a space 62, which is located in a lower side (- X-direction) of the exhaust port plane 71, only. In this embodiment, however, to increase the volume of the muffler 4, the portion of the space 63 is secured by extending the muffler 4 in the direction of arrow 76 to a side (- X-direction) lower than a lower end face 72 of the cylinder chamber. Further, to further enlarge the secured space 63, the portion of the space 64 is secured by protruding the side wall surface of the muffler 4 from the space 63 to the left side (- Z- direction) in the direction of arrow 77. The portion, in which the space 64 is positioned, is the protrusion portion 32 protruding to the left side more than the fastening plane M which is a plane passing through the opening of the exhaust port 24. By devising the shape of the muffler 4 in this way, it is possible to obtain the volume of the muffler significantly larger than that of the related art. On the other hand, if the muffler 4 is increased in size, a space for installing a fuel tank which is disposed under the muffler of the related art is reduced. In this embodiment, since the muffler 4 extends in a downward direction more than the lower end face 72 of the cylinder chamber and in the left direction more than the fastening plane M, the right space 65 is decreased and becomes smaller, like an arrow 78, than a center plane 75b of the cylinder of the fuel tank 22. This means that fuel which can be filled is decreased, which is not desirable. Therefore, in this embodiment, the space 67 is secured by extending the left end of the fuel tank 22 in a left direction (- Z-direction) more than the left end face 75 a of the cylinder cover, like an arrow 79, and extending the left end in an upward direction (+ X-direction), like an arrow 80, and an upper end face 22 A of the fuel tank 22 reaches the almost same position as the lower end face 72 of the cylinder chamber. By securing the spaces 67 and 68 in this way, the almost same tank capacity as that of the related art is obtained. Further, even though the shape of the fuel tank 22 is changed in this way, the muffler 4 is positioned at the position in which the spaces 67 and 68 are in face symmetry with respect to a center plane 74 in the left and right directions. Incidentally, since the heat shield plate 38 serving as a heat shielding plate is interposed between the engine 36, the fuel tank 22 and the muffler 4, it is possible to significantly reduce the transfer of the high temperature of the muffler 4 to the fuel tank 22. Even though the space 65 of the fuel tank 22 is decreased, like the arrow 78, it is preferable that the right end thereof is disposed at the right side more than the center plane 75b of the cylinder.

Fig. 7 is a side view explaining the size of the muffler 4 of the engine working machine 1 according to one embodiment of the present invention. In Fig. 7, the engine 36 is shown in a dotted line to compare the muffler 4 and the engine 36. A dimension of the muffler 4 is set in the ratio of vertical direction: horizontal direction: thickness direction = 2.4: 1.2: 1.0. Herein, the muffler volume (cc) of the muffler 4 is set to be about 17 times or more of the displacement (CC) of the engine 36, and the area (mm²) of the tail pipe is set to be about 0.8 times or less of the displacement (cc), preferably, 0.3 times or more and 0.8 times or less. By the above-described setting, it is possible to significantly reduce the noise, while obtaining the output of the engine 36 to a certain extent.

Furthermore, if the moving direction of the piston is the vertical direction of the muffler, the direction of the driving shaft is the horizontal direction of the muffler, and the direction of the exhaust opening is the thickness direction of the muffler, the muffler 4 illustrated in Fig. 7 is set to be thickness < horizontal < vertical (e.g., a size of the muffler 4 is configured to have a relationship of "thickness < length in the horizontal direction < length in the vertical direction"), and a vertical/horizontal ratio is set to be 1.5 or more. Since the horizontal direction (front and back direction when seen from the engine working machine) of the muffler 4 is directly linked to the increase in whole length of the engine 36, the engine working machine can become compact by minimizing the horizontal dimension thereof. Also, since the engine 36 is likely to be longest in the moving direction, the engine working machine can become further compact by combining it with the layout of the muffler 4.

Next, the relationship between the volume of the muffler 4, the area of the tail pipe, and the noise will now be described with reference to Figs. 8 to 11. Herein, a two-cycle engine having an engine of 21 cc displacement is utilized. Fig. 8 illustrates a relationship between the area of the tail pipe and the output (Kw) of the engine output per a unit of displacement. The volume of the muffler is constant as 388.5 cc, and a ratio of the volume of the muffler/displacement is 18.5. In this instance, five mufflers with an area of each tail pipe being changed were prepared and measured. It was determined that when the ratio of the volume of tail pipe/displacement was about 1.3 or more, the maximum output of the engine 36 was 0.75 Kw, and when the ratio of the volume of tail pipe/displacement was 0.9, the output of the engine 36 was lowered by about 5% less than the maximum output. In general, if the area of the tail pipe is small, the noise level is reduced, but the output of the engine is lowered. If the volume of the muffler is set so that the ratio of the volume of tail pipe/displacement is about 0.9 or more, the engine can obtain the almost maximum output while reducing the noise level.

Fig. 9 is a view illustrating a relationship between the volume of the muffler and the noise (dBA) per a unit of displacement. Herein, the area of the tail pipe was 9.45 cm2, and the ratio of the area of tail pipe/displacement was 0.45. It could be known from the above experiment that if the volume of the muffler is increased, the noise level is generally reduced.

Fig. 10 is a view illustrating a relationship between the area of the tail pipe and the noise (dBA) per a unit of displacement. Herein, the volume of the muffler was constant as 388.5 cc, and the ratio of the volume of muffler/displacement was 18.5. It would be known from the above experiment that if the area of the tail pipe is increased, the noise level is also generally reduced. Supposing the practical minimum noise value of the engine is 70 dBA, it could be understood that the area of the tail pipe is set such that the ratio of the volume of tail pipe/displacement is 0.9 or less, an effect of reducing the noise to 1 dB or more is obtained. Fig. 11 is a view illustrating a relationship between the volume of the muffler and the area of the tail pipe per a unit of displacement. On the examination of the relationship when the output of the engine is maintained as 0.7 Kw, it could be understood that if the volume of the muffler is larger while the area of the tail pipe is smaller, the good result is obtained. Further, it could be understood that if the area of the tail pipe is smaller while the volume of the muffler is the same, the output of the engine is lowered to about 20 to 30%. According to the result illustrated in Fig. 10, it is preferable that the ratio of the area of tail pipe/displacement is 0.9 or less to keep the noise level low. On the other hand, in order to improve the output of the engine, the volume of the muffler is preferably increased. As the result of the experiment, it could be understood that the volume (cc) of the muffler to the displacement (cc) is preferably set to be about 17 times or more, and the area (mm²) of the tail pipe to the displacement (cc) is preferably set to be about 0.8 times or less. Incidentally, if the area (mm²) of the tail pipe is too small, the output of the engine is too small. As a result, it is preferable that the ratio of the area of tail pipe/displacement is set to be about 0.3 times or more, which decreases the output to an extent of 20 to 30%.

As described above, since the muffler 4 is increased in size and the arrangement of the fuel tank is changed in this embodiment, the structure of the muffler capable of significantly reducing the noise while maintaining the output can be realized, in the state in which the appearance of the engine working machine 1 is substantially not changed. Second Embodiment Next, an engine working machine according to a second embodiment will now be described with reference to Fig. 12. Fig. 12 is a cross-sectional view corresponding to the line A-A in Fig. 2. A collar 87 is provided therein with a muffler fastening bolt 86 as means for increasing the rigidity in an outer surface of the muffler 84. The collar 87 is adhered to any one of contact surfaces between the inner surface 88 of the muffler and the outer surface 89 of the muffler. With the configuration in which the muffler fastening bolt 86 is shortened, the same effect as that of the first embodiment can be obtained. Incidentally, even though the muffler fastening bolts 5A and 5B are shortened to be inserted in the collar, the same effect can be obtained.

As described above, the prevent invention has been described based on the embodiments, but is not limited thereto. Various modifications can be made without departing from the spirit or scope of the invention. For example, an example, in which the present invention applied to the brush cutter in which the moving direction of the piston 19 is perpendicular to the ground, has been described in the description, but may be applied to a engine working machine (for example, a hedge trimmer or cultivator) in which the moving direction of the piston 19 is horizontally disposed while the layout of the above-described engine working machine is maintained.

This application claims the benefit of Japanese Patent Application No. 2011- 140152 filed on June 24, 2011, the disclosure of which is incorporated herein in its entirety by reference. Industrial Applicability As described above, an engine working machine according to the invention has advantages of capable of reducing an exhaust sound while maintaining a compact size and a sufficient engine output and is also capable of reducing a vibration sound generated by a vibration of a wall surface of a muffler. The invention is useful for the engine working machine, for example.

Reference Signs List

1 Engine working machine

2 Air cleaner

3 Cylinder cover

4 Muffler

4A Upper end portion

4B Lower end portion

5A, 5B, 6 Muffler fastening bolt

7 Air intake passage

8 First volute case

9 Second volute case

9A Leg member

10 Starter

11 Starter knob

12 Ignition plug

13 A First expansion chamber

13B Second expansion chamber

13C Third expansion chamber

14 Catalyst A Expansion chamber case

B Expansion chamber case

Collar

Tail pipe

Air intake port

Piston

Driving shaft

Crankcase

Fuel tank

Carburetor

Exhaust port

A Opening portion of expansion chamberB Opening portion of expansion chamber Inner surface of muffler

Outer surface of muffler

Cooling fan

Air intake port

Cylinder

Communication portion

Protrusion portion

Discharge portion

Plug cap

Check valve

Engine

Partition 38 Heat shield plate

39 Insertion portion

61, 62, 63, 64, 67, 68 Space

71 Exhaust port plane

72 Lower end face of a cylinder chamber

74 Center plane in left and right directions

75 a Left end face of a cylinder cover

75b Center plane of a cylinder

76 to 80 Arrow

84 Muffler

86 Muffler fastening bolt

87 Collar

88 Inner surface of a muffler

89 Outer surface of a muffler

D Inner diameter of a bore

M Fastening plane

N Center of a cooling fan

H Rotational direction of a cooling fan

AIR1 Cooling air

AIR2 Intake air

AIR3 Cooling air

EX Exhaust gas

EX1 Outflow direction of exhaust gas

EX2 Outflow direction of exhaust gas

LA Minimum value of a distance from a fastening plane to a lateral side of a muffler

LB Maximum value of a distance from a fastening plane to a lateral side of a muffler

Claims

[Claim 1]

An engine working machine comprising:

an engine;

a fuel tank configured to store fuel to be supplied to the engine; and

a muffler configured to suppress an exhaust noise discharged from the engine, wherein:

a driving shaft direction of the engine, an opening direction of an exhaust port, and an operation direction of a piston are substantially perpendicular to one another; the muffler is fastened to an exhaust port of the engine such that one of expansion chambers in the muffler is connected to the exhaust port of the engine; and the muffler comprises a protrusion portion extending towards an engine side rather than a fastening plane, which is parallel to a moving direction of the position at the fastening position, wherein the protrusion portion is disposed near an end portion, which is away from an ignition plug in the moving direction of the piston in the engine, of the muffler.

[Claim 2]

The engine working machine according to claim 1, wherein a side of the muffler opposite to the exhaust port is substantially parallel to the fastening plane.

[Claim 3]

The engine working machine according to claim 1 or 2, wherein the fuel tank is provided below a lower portion of a crankcase of the engine, and is provided at a lateral side of the protrusion portion of the muffler.

[Claim 4]

The engine working machine according to any one of claims 1 to 3, wherein the muffler comprises a concave portion between the protrusion portion and the connecting portion with the engine such that the concave portion is away from the fastening plane with respect to the engine.

[Claim 5]

The engine working machine according to any one of claims 1 to 4, wherein a volume of the muffler is set to be 17 times or more of a displacement of the engine, and an opening area of a tail pipe provided on the discharge port of the muffler is set to be 0.3 times and more and 0.8 times or less of the displacement.

[Claim 6]

The engine working machine according to any one of claims 1 to 5, wherein: the engine is disposed so that the piston reciprocates in a vertical direction; a cross section of the exhaust port of the engine is positioned in a substantially vertical direction; and

a size of the muffler is formed to be extended in a vertical direction to have a relationship of thickness direction < horizontal direction < vertical direction.

[Claim 7]

The engine working machine according to claim 6, wherein the size of the muffler is set so that a ratio of vertical direction/horizontal direction is 1.5 or more.

[Claim 8]

The engine working machine according to claim 7, wherein the muffler comprises a rigidity increasing member for increasing rigidity of a lateral surface of the muffler, fastened to the engine by a fastening member and disposed at a position spaced apart from the fastening member in the moving direction of the piston on a lateral surface of the muffler facing the engine and a lateral surface of the muffler opposite to the exhaust port of the engine.

[Claim 9]

The engine working machine according to any one of claims 5 to 8, wherein: the rigidity increasing member comprises a screw and a pipe penetrating the screw; and

the pipe is fixed to the lateral surface of the muffler facing the engine and the lateral surface of the muffler opposite to the exhaust port of the engine.

[Claim 10]

The engine working machine according to claim 9, wherein:

the muffler includes therein:

a first expansion chamber communicating with the exhaust port of the engine;

a second expansion chamber having a discharge port for discharging exhaust gas to an atmosphere; and

a third expansion chamber connecting the first expansion chamber and the second expansion chamber; and

a catalyst configured to purify an exhaust gas component is disposed in the third expansion chamber.

[Claim 11]

The engine working machine according to claim 10, wherein the third expansion chamber is disposed to include an internal space of the protrusion portion.