JP2013007317A - Engine working machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine working machine, which is capable of reducing an exhaust sound while maintaining product dimensions and an engine output comparable to those of a conventional machine, and which is also capable of reducing a vibration sound generated by vibration of a muffler side face.SOLUTION: An engine 36 is configured in such a manner that: a driving shaft direction of the engine 36 (Y direction), an opening direction of an exhaust port (Z direction), and an operation direction of a piston (X direction) are substantially perpendicular to one another; a muffler 4 is fastened to a proximity of an exhaust port 24 of the engine 36; the muffler 4 has a vertically long shape extended downward lower than a plane 72 passing on a lower end of a cylinder; and the muffler is provided with a protrusion 32 protruding in a direction toward the center of the engine 36, which secures a volume corresponding to a space 64. Since the muffler 4 is greatly extended downward, a fuel tank 22 is placed offset to a left side (-Z direction) and extended in a left end upward as shown by an arrow 80, which secures a volume corresponding to a space 68.

Description

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

  Portable engine working machines such as brush cutters, blowers, hedge trimmers, chain saws, and cutters are often used outdoors. For this reason, noise suppression is often a problem particularly in densely populated areas such as urban areas, and there is a high demand for noise reduction from users. However, since it is an engine working machine, there is a high demand for downsizing. The engine used as the power source of the engine working machine has a high-density design in which a driven device such as a tip tool, a cooling fan, and a manual starter is installed on the drive shaft (crankshaft), and many parts are adjacent to the engine. It is common that For this reason, in order to achieve both a small size and low noise, for example, Patent Document 1 proposes a device on the internal structure and the structure of the exhaust gas discharge port in the muffler.

Japanese Patent Laid-Open No. 11-156802

  For Patent Document 1, a plurality of exhaust gas exhaust ports are provided and separated by a predetermined distance or more to reduce exhaust noise. However, in the muffler, in addition to the exhaust sound due to the high temperature and high pressure gas being instantaneously ejected from the engine to the muffler, the noise generated by the vibration of the muffler side due to the pressure pulsation caused by the high temperature and high pressure gas ejection Therefore, it has been difficult to obtain further reduction of exhaust noise than before. Furthermore, in order to make the engine output equal to that of the conventional engine, it is necessary to prevent an increase in the back pressure of the exhaust gas. Normally, in a muffler, the noise source of the exhaust sound is the exhaust port, so it is desirable to reduce the opening area of this exhaust port in order to reduce the exhaust noise. However, it was difficult to obtain a further exhaust noise reduction effect.

  In response to this problem, a muffler capable of reducing exhaust noise while maintaining a small product size and sufficient engine output is desired as an engine working machine. It is also desired to reduce vibration noise caused by the vibration of the muffler wall. If it is attempted to deal with these problems only by increasing the muffler volume, for example, to reduce noise by 1 dB, it is necessary to double the muffler volume. There was a problem that the effect on the rise of was small. Further, in order to cope with the reduction of the tail pipe area, for example, in order to reduce the noise by 1 dB, the tail pipe area needs to be halved or less, and it is difficult to achieve compatibility with the engine output.

  The present invention has been made in view of the above background, and an object thereof is to provide an engine work machine capable of further reducing noise generated from a muffler.

  Another object of the present invention is to provide an engine working machine in which the size of the whole is made compact while the size of the muffler is increased.

  Still another object of the present invention is to provide an engine working machine in which the relationship between the volume of the muffler and the tail pipe area is optimally configured in order to achieve both high engine output and low noise.

  The characteristics of representative ones of the inventions disclosed in the present application will be described as follows.

  According to one aspect of the present invention, an engine, a fuel tank that stores fuel supplied to the engine, and a muffler that suppresses exhaust noise discharged from the engine are provided. The engine working machine is configured so that the opening direction and the piston operating direction are substantially orthogonal to each other, and the muffler is fastened to the engine outlet so that one of the internal expansion chambers is connected to the engine outlet. The projecting portion extending to the engine side from the fastening plane parallel to the moving direction of the piston at the fastening position, and the projecting portion is disposed near the end portion on the side far from the spark plug in the moving direction of the piston of the engine, The muffler side surface facing the exhaust port was arranged so as to be substantially parallel to the fastening plane. In addition, the fuel tank is offset from the lower part of the crankcase of the engine and to the side of the muffler protrusion.

  According to another feature of the present invention, the volume of the muffler is 17 times or more the engine displacement, and the opening area of the tail pipe formed at the exhaust port of the muffler is 0.3 times the displacement. It was set to be twice or more and 0.8 times or less. This engine is arranged so that the piston reciprocates in the vertical direction, and the cross section of the exhaust port of the engine is positioned substantially vertical, and the size of the muffler is as follows: thickness direction <lateral direction <vertical direction It has a vertically long shape. The ratio of the muffler dimension in the vertical direction / horizontal direction is preferably 1.5 or more.

  According to still another feature of the present invention, the muffler is fastened to the engine by the fastening means, and is separated from the fastening means in the moving direction of the piston on the side of the muffler on the side away from the engine and on the side of the muffler facing the engine exhaust port. A means for increasing the rigidity of the muffler side surface was arranged at the position. The means for increasing the rigidity is a screw and a pipe through which the screw passes, and the pipe is fixed to the side of the muffler remote from the engine and the side of the muffler facing the engine exhaust port. The muffler has a first expansion chamber that communicates with the engine exhaust port and a second expansion chamber that has an exhaust port for discharging exhaust gas into the atmosphere, and connects the first expansion chamber and the second expansion chamber. A third expansion chamber was provided, and a catalyst for purifying exhaust gas components was disposed in the third expansion chamber. This third expansion chamber is preferably arranged so as to include the internal space of the protrusion.

  According to the first aspect of the present invention, the projecting portion extending to the engine side is provided in a part of the muffler, and the fuel tank is provided at the lower portion of the crankcase of the engine and offset to the side of the projecting portion of the muffler. Therefore, it hardly affects each part at both ends of the drive shaft, hardly disturbs the replacement work of the spark plug, etc., and effectively increases the muffler volume without increasing the total engine length in the opening direction of the exhaust port. Can be increased. Therefore, it is easy to reduce the back pressure and improve the output with a compact configuration, and further, it is possible to obtain the effect of reducing the exhaust noise.

  According to the second aspect of the present invention, the volume of the muffler is 17 times or more with respect to the engine displacement, and the opening area of the tail pipe formed at the exhaust port of the muffler is 0.3 times or more with respect to the displacement. Since it is 8 times or less, it is possible to reliably reduce noise without reducing the engine output. Moreover, with respect to the increase in the design difficulty of increasing the size of the muffler in a limited space, an effect commensurate with the difficulty of maintaining a significant low noise effect and output can be obtained.

  According to the third aspect of the present invention, the muffler has a vertically long shape such that the thickness direction <the horizontal direction <the vertical direction, so that the increase in the thickness direction directly connected to the increase in the total length of the engine can be prevented. It can be made compact by minimizing.

  According to the fourth aspect of the present invention, since the ratio of the muffler in the vertical direction / horizontal direction is 1.5 or more, the engine work machine can be renewed by combining the engine and the muffler layout which are generally the longest in the piston operation direction. A compact size can be realized.

  According to the fifth aspect, since the muffler side facing away from the engine and the muffler side facing the engine exhaust port, the means for increasing the rigidity of the muffler side is disposed at a position separated from the fastening means in the moving direction of the piston. Since the rigidity of the muffler side surface can be increased over a wider range, the amplitude of the membrane vibration on the muffler side surface can be further suppressed, and vibration noise can be reduced.

  According to claim 6, the means for increasing the rigidity is a screw and a pipe that penetrates the screw, and the pipe is fixed to the muffler side surface on the side away from the engine and the muffler side surface facing the engine exhaust port. Since the rigidity of the muffler side surface can be effectively increased, the amplitude of the membrane vibration on the muffler side surface can be further suppressed, and the vibration noise can be reduced. Furthermore, when the muffler is fastened only in the vicinity of the engine exhaust port, there is a concern that the muffler will be in a cantilever state and vibration of the muffler may increase, but this configuration can suppress this and suppress metal fatigue due to vibration. And durability can be improved.

  According to claim 7, the first expansion chamber communicated with the engine exhaust port, the second expansion chamber having a discharge port for discharging the exhaust gas into the atmosphere, the first expansion chamber and the second expansion chamber. Since the third expansion chamber for connecting the gas and the catalyst for purifying the exhaust gas component is disposed in the third expansion chamber, the exhaust gas component can be burned by the catalyst to achieve the exhaust gas cleaning.

  According to the eighth aspect, since the third expansion chamber is arranged so as to include the internal space of the protruding portion, even when the catalyst is changed by enlarging the catalyst by arranging the catalyst in the protruding portion that easily secures a large volume. Yes. Further, even when the catalyst is enlarged, it is easy to ensure a gap with the muffler side surface, so that the heat of the catalyst can be prevented from being transmitted to the muffler side surface.

  The above and other objects and novel features of the present invention will become apparent from the following description and drawings.

It is a perspective view which shows the external appearance of the engine working machine which concerns on the Example of this invention. It is a right view of the engine working machine which concerns on the Example of this invention. It is sectional drawing of the AA part of FIG. It is a top view of the engine working machine which concerns on the Example of this invention, Comprising: The cross section of the BB part of FIG. 2 is shown in part. It is sectional drawing of the CC section of FIG. It is a figure for demonstrating the magnitude | size and arrangement | positioning relationship of the muffler 4 and the fuel tank 22 of the engine working machine 1 which concern on the Example of this invention. It is a side view for demonstrating the magnitude | size of the muffler 4 and the engine 36 of the engine working machine 1 which concerns on the Example of this invention. It is a figure which shows the relationship between the tail pipe area per unit displacement and engine output in case a muffler volume is constant. It is a figure which shows the relationship between the muffler volume per unit displacement and the noise when the tail pipe area is constant. It is a figure which shows the relationship between the tail pipe area per unit displacement and noise in case a muffler volume is constant. It is a figure which shows the relationship between the muffler volume per unit displacement and tail pipe area. It is sectional drawing which concerns on 2nd Example of this invention (a cross-sectional position is equivalent to the AA part of FIG. 2).

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same portions are denoted by the same reference numerals, and repeated description is omitted. Further, in this specification, the description will be made assuming that the left-right direction (X direction), the front-rear direction (Y direction), and the up-down direction (Z direction) are directions shown in the drawings. In addition, the direction when the muffler is viewed as a single unit will be described assuming that the width direction is the Y direction, the thickness direction is the X direction, and the vertical direction is the Z direction.

  FIG. 1 is a perspective view showing an appearance of an example in which an engine working machine 1 according to an embodiment of the present invention is applied to a brush cutter. The engine working machine 1 has an engine housed in a plastic cylinder cover 3, and on the left side (−Z direction) of the engine, an air cleaner 2 that covers the vaporizer and filters the intake air is provided on the side. The muffler 4 is provided on the right side (+ Z direction) of the engine. The accommodated engine is arranged in a so-called vertical position, and the reciprocating direction of a piston, which will be described later, is the X direction, and the plug cap 34 is located in the upper part of the engine. A second volute case 9 that covers the output transmission mechanism is attached to the output shaft side in front of the engine working machine 1. An insertion portion 39 that holds a drive shaft (not shown) to be mounted is provided on the distal end (+ Y direction) side of the second volute case 9. Below the second volute case 9, a leg portion 9 </ b> A is provided that serves as a support when the engine work machine 1 is placed on the floor or the like. A first volute case 8 is provided between the engine body and the second volute case 9.

  The muffler 4 of the present embodiment has a substantially rectangular parallelepiped basic shape, and is arranged such that its longitudinal direction is the vertical direction (X direction). This is because the muffler 4 is enlarged in the vertical direction to ensure the volume as large as possible in order to effectively reduce the exhaust noise in a limited space. The muffler 4 is directly fixed to the engine by three bolts of the muffler fastening bolts 5A and 5B and the muffler fastening bolt 6. On the side of the muffler 4, a pipe line for introducing air from the air intake port 29 of the first volute case 8 that houses a cooling fan described later, that is, an air introduction path 7 is provided. A muffler outer surface (muffler side surface away from the engine) 27 arranged in a substantially vertical direction is provided with ribs for increasing rigidity over a wide range and reducing vibration noise due to membrane vibration of the wall surface.

  FIG. 2 is a side view of the engine work machine 1 as viewed from the right side. In the longitudinal direction (X direction) of the muffler 4, the muffler fastening bolts 5 </ b> A and 5 </ b> B are closer to the spark plug connected to the plug cap 34 (BB) than the engine crankshaft (located on the BB cross section). Arranged on the upper side of the cross section The muffler fastening bolt 6 divides the muffler fastening bolts 5A, 5B and the lower end 4B of the muffler on the side far from the spark plug 12 in the muffler outer surface 27 into approximately two equal parts, and the drive shaft direction orthogonal to the moving direction X of the piston With respect to Y (the horizontal direction of the muffler alone), the muffler is arranged at a position that bisects the frame. In the present embodiment, the muffler fastening bolt 6 is disposed at substantially the same position as the axis (drive axis) of the drive shaft in the vertical direction. With such an arrangement, the rigidity of the muffler outer surface 27 can be increased over a wide range, so that the amplitude of the membrane vibration on the muffler side surface can be effectively suppressed and vibration noise can be reduced.

  A manual starter 10 is mounted on the rear side of the engine. The starter 10 is connected to a drive shaft of the engine via a clutch, and a starter 10 that starts the engine by pulling the traction string by a starter knob 11. Although the description of the internal structure is omitted in FIG. 2, the starter 10 is not limited to a manual starter, but a known starter such as a recoil starter or an electric motor driven by a battery is used. be able to.

  In this embodiment, the distance L1 between the muffler fastening bolts 5A and 5B and the muffler fastening bolt 6 and the distance L2 between the muffler fastening bolt 6 and the lower end portion 4B are approximately L1: L2 = 4 with respect to the moving direction (± X direction) of the piston. : 6. Further, with respect to the drive shaft direction (Y direction), the distances L3 and L4 from the muffler fastening bolt 6 and the front and rear end portions of the muffler are approximately L3: L4 = 4: 6. With such a configuration, the muffler outer surface 27 can be increased in rigidity over a wide range by the muffler fastening bolt 6, and vibration noise caused by membrane vibration of the muffler outer surface 27 can be reduced. Further, since the muffler 4 can be strongly tightened and fixed to the cylinder 30, vibration of the entire muffler 4 can be reduced, metal fatigue of the fastening portion due to vibration can be reduced, and durability can be improved.

  The tail tube 17 for discharging the exhaust gas from the muffler 4 is disposed closer to the spark plug 12 than the BB cross section (a horizontal surface passing through the engine drive shaft) when viewed in the X direction. The direction is configured to be the same direction as the drive shaft (parallel to the BB cross section) in the tail tube 17 as in EX1. An opening area that opens to the atmosphere is formed by the tail tube 17. The muffler 4 of the present embodiment has one opening. In this embodiment, the opening area of the tail pipe 17, in other words, the opening area of the exhaust port of the muffler 4 is set to 3% or less of the area of the cylinder bore. Thus, by taking a sufficient opening area of the tail tube 17 with respect to the area of the cylinder bore, it is possible to obtain an exhaust noise suppressing effect without causing a decrease in output.

  When starting the engine, the engine work machine 1 is usually placed on the ground and the starter knob 11 of the starter 10 is pulled to start the engine. In this embodiment, since the position of the tail tube 17 can ensure a predetermined height from the ground in the moving direction X of the piston, it is easier to secure a position above the obstacle in the gravity direction than an obstacle such as a stone or grass on the ground, Since the structure is such that there is no obstacle such as stone or grass in the vicinity of the muffler discharge port, the starting operation can be performed smoothly. Even when the engine work machine 1 is placed on the ground and the engine speed is increased to warm up the engine, the dust or dirt on the ground is rarely raised by the exhaust gas. It can alleviate the annoyance of dust and soaring around. Furthermore, it is also possible to suppress the dust and dust that have risen from being sucked into the engine and causing the air filter contained in the air cleaner 2 to clog.

  Since the engine work machine 1 is a work machine that is handled by a worker by hand, the engine work machine 1 is often positioned below the ear of the worker in the direction of gravity during work. Therefore, when the movement direction of the piston of the engine 36 and the gravity direction substantially coincide with each other, the operator feels that the exhaust sound generated from the tail tube 17 is not emitted at least upward in the gravity direction where the worker's ear is located. Exhaust noise can be reduced. Preferably, if the intersection angle between the exhaust gas outflow direction and the parallel line of the drive shaft is set to 0 ° to 60 ° at the muffler exhaust port, the exhaust gas outflow direction EX1 is at least in the gravity direction of the operator's ear. Since it can suppress going upwards in the direction of gravity, which is the approaching direction, the exhaust sound felt by the operator can be reduced.

  The ratios and discard directions described above are not limited to those described above. For example, L1: L2 is preferably set in the range of 4: 6 to 6: 4, and L3: L4 is preferably set in the range of 4: 6 to 6: 4. Further, in the tail pipe 17, the direction of the tail pipe 17 may be inclined so as to go away from the spark plug 12 as in the exhaust gas outflow direction EX2, that is, to cross the BB cross section, and EX1 and EX2 intersect. The angle θ is preferably set to 0 ° to 60 °.

  3 is a cross-sectional view taken along a line AA in FIG. The engine 36 is a two-cycle small single cylinder engine with a displacement of 21 cc. A piston 19 is connected to the drive shaft 20 via a connecting rod, and the piston 19 reciprocates up and down inside the cylinder 30. The operation direction X of the piston 19, the drive shaft direction Y, and the opening direction Z of the exhaust port are substantially orthogonal to each other. The cylinder 30 is formed with an exhaust port 24 for discharging exhaust gas to the outside of the engine 36. Since the engine intake-compression-explosion-exhaust stroke is the same as that of a known two-cycle engine, a detailed description thereof will be omitted. In the present embodiment, the cylinder 30 is formed by integrally casting a cylinder main body, a head portion, and a heat radiation fin, for example, with an aluminum alloy, and an ignition plug 12 is attached to the upper portion of the cylinder 30. A high voltage current is supplied to the spark plug 12 from the ignition device (not shown) through the plug cap 34 at a predetermined timing.

  The cylinder cover 3 is a plastic cover, for example, and covers the cylinder 30 that becomes high temperature during operation so that an operator does not directly touch them. Therefore, a large number of ventilation openings are formed in the cylinder cover 3. The engine 36 is provided with a vaporizer 23, and the air cleaner 2 is provided on the left side (−Z direction) of the vaporizer 23.

  A fuel tank 22 is disposed below the crankcase 21 (−Z direction). A heat shield 38 is interposed between the engine 36 and the muffler 4 and between the fuel tank 22 and the muffler 4 so that the heat of the muffler 4 does not affect the cooling of the engine 36 and the radiant heat of the muffler 4. The temperature rise of the fuel tank 22 is suppressed by shutting off. The heat shield plate 38 is configured, for example, by attaching a heat insulating material to a thin aluminum plate. In the conventional engine working machine, the fuel tank 22 is disposed below the crankcase 21 so as to be symmetrical with respect to the left and right center plane of the engine 36. This is to prevent the left and right weight balance of the engine work machine 1 from being lost due to the weight of fuel such as mixed gasoline stored in the fuel tank 22. However, in this embodiment, the muffler 4 is made larger in the vertical direction than the muffler of the conventional engine working machine, and the protruding portion is also provided so as to extend to the portion where the conventional fuel tank is located. It was. Therefore, in this embodiment, the position of the fuel tank 22 is offset to the left side (−Z direction) to secure the space occupied by the muffler 4 extending downward and adjust the weight balance. The arrangement relationship between the muffler 4 and the fuel tank 22 will be described later.

  A muffler 4 is disposed on the right side of the engine 36. The muffler 4 is provided with a communication portion 31 with the exhaust port 24, and a muffler fastening bolt 5A, 5B disposed in the vicinity of the communication portion 31 interposes a heat shield plate 38 for ensuring sealing performance, thereby It is fastened near 30 exhaust ports 24. The muffler 4 is fastened to the crankcase 21 by the muffler fastening bolt 6. The muffler 4 is further fixed to the crankcase 21 by a muffler fastening bolt 6 that passes through the cylindrical collar 16. The collar 16 and the muffler fastening bolt 6 function as means for increasing the rigidity of the muffler outer surface 27 facing the exhaust port 24 of the engine 36.

  A muffler inner side surface 26 facing the engine 36 composed of the cylinder 30 and the crankcase 21 is a projecting portion extending toward the engine 36 from a fastening plane M parallel to the moving direction X of the piston at a fastening position of the exhaust port 24 and the muffler 4. 32. The protrusion 32 is disposed in the vicinity of the lower end 4B far from the spark plug 12 with respect to the moving direction X of the piston. Further, the muffler outer surface 27 facing the exhaust port 24 is configured to be substantially parallel to the fastening plane M. Note that the minimum value LA and the maximum value LB of the distance between the muffler outer surface 27 and the fastening plane M (thickness direction distance of the muffler 4) are approximately LA / LB = 0.75, but LA / LB It is good to set in the range of 0.7-1.0.

  A partition plate 37 is provided inside the muffler 4 and separates the first expansion chamber 13A having the communication portion 31 and the second expansion chamber 13B having the tail pipe 17 for the exhaust gas. Between the first expansion chamber 13A and the second expansion chamber 13B, a third expansion chamber 13C, which is an additional expansion chamber disposed in the vicinity of the protruding portion 32, is disposed. The third expansion chamber 13C is formed by iron expansion chamber cases 15A and 15B which are molded of sheet metal and fixed to the partition plate 37 by welding. Inside the third expansion chamber 13C, a catalyst 14 for purifying exhaust gas components by combustion is provided, and expansion chamber cases 15A and 15B have expansion chamber openings communicating with the first expansion chamber 13A and the second expansion chamber 13B, respectively. Portions 25A and 25B are provided. Here, the catalyst 14 is disposed in the vicinity of the protrusion 32. By arranging the third expansion chamber 13C in this way, the exhaust noise reduction effect can be enhanced. Further, since the catalyst 14 is included in the third expansion chamber 13C, the exposed area of the catalyst 14 with respect to the side wall of the muffler 4 can be effectively reduced. Therefore, even when the catalyst 14 is inserted, the temperature of the wall surface of the muffler 4 The rise can be effectively suppressed. The catalyst 14 is an oxidation catalyst that oxidizes HC, CO, etc., which are fixed by inserting and fixing a honeycomb-like stainless steel foil in which palladium, rhodium, etc. are vapor-deposited, inside a stainless steel cylinder. The catalyst 14 is disposed in the internal space of the projecting portion 32, and is located at the lower side of the crankcase 21 in the direction of the drive shaft Y of the piston 19. Thus, since the catalyst 14 is provided apart from the cylinder 30 as the heat source, it is possible to avoid the heat source from being concentrated in one place, and thus it is possible to suppress the temperature increase of the engine work machine 1 as a whole. .

In the first expansion chamber 13A, an air introduction port 18 communicating with the air introduction passage 7 is provided. The air introduction port 18 serving as a means for introducing air serves as an opening on the muffler 4 side of the air introduction passage 7 shown in FIGS. 1 and 2. The opening area of the tail pipe 17 is set to be about 3% with respect to the area of the bore D of the cylinder 30. Further, the opening areas of the expansion chamber openings 25A and 25B are set with respect to the opening area of the tail pipe 17. Is set to 5 times or less, for example, about 4 times. For example, when the cylinder bore D is 31 mm, the opening area is about 755 mm ² , so that the tail tube 17 has an opening area of about 24 mm ² corresponding to a circle with a diameter of φ5.5, and the expansion chamber openings 25A and 25B have a circle with a diameter of φ11. The opening area corresponding to is about 97 mm ² . In this way, by limiting the opening area in the communication part (expansion chamber opening parts 25A and 25B) to a predetermined value or more while ensuring a predetermined value or more with respect to the opening area of the muffler discharge port, the exhaust resistance in the communication part is excessive. In addition, an exhaust noise reduction effect can be obtained. In this configuration, the engine working machine 1 sucks fuel and air into the engine 36 through the air cleaner 2 and the carburetor 23, burns the fuel and air, and then discharges them as exhaust gas from the exhaust port 24. At this time, the reciprocating motion of the piston 19 is changed to the rotational motion of the drive shaft 20.

  The exhaust gas passes through the expansion chamber opening 25A and flows into the third expansion chamber 13C as the exhaust gas flow EX together with the air flow AIR2 flowing into the first expansion chamber 13A from the air introduction port 18. After that, after passing through the catalyst 14 and the expansion chamber opening 25B, it is discharged from the tail tube 17 into the atmosphere. Here, the muffler 4 is formed so that the muffler outer surface 27 is substantially parallel to the fastening plane M. Further, in the vicinity of the lower end portion 4B, the muffler inner side surface 26 is formed with a protruding portion 32 that protrudes in the −Z direction from the fastening plane M, so that the muffler volume can be increased without increasing the overall length in the opening direction Z of the exhaust port. Can be greatly increased. Thereby, since the back pressure of the muffler 4 is reduced, the output of the engine 36 can be easily improved, and at the same time, an effect of reducing the exhaust noise can be obtained. Therefore, even if the opening area of the tail pipe 17 that is the noise source of the exhaust sound in the muffler 4 is set to be relatively smaller than the conventional one, the output is not easily lowered, so that the exhaust sound is effectively reduced while maintaining the output. It becomes possible.

  In the present embodiment, since the third expansion chamber 13C is further arranged in the vicinity of the protruding portion 32, the volume of the third expansion chamber 13C can be made larger than that at other positions. Even if the opening areas of the expansion chamber openings 25A and 25B are set to be relatively small, the output is unlikely to decrease. From these, the exhaust sound emitted from the first expansion chamber 13A to the third expansion chamber 13C is obtained by making the opening area of the expansion chamber opening 25A, which is a noise source for the third expansion chamber 13C, relatively smaller than before. Similarly, the exhaust noise released from the third expansion chamber 13C to the second expansion chamber 13B is also reduced by making the expansion chamber opening 25B relatively smaller than before.

  Furthermore, even when a design change is performed to increase the size of the catalyst 14, the volume of the third expansion chamber 13 </ b> C is sufficiently secured by the projecting portion 32, and there is room in the dimensions, so it is easy to make without making a big change. It is possible to cope with design changes. Further, by introducing air from the air inlet 18 into the first expansion chamber 13A, oxygen necessary for burning the exhaust gas component by the catalyst 14 can be supplied, so that the purification performance of the catalyst is improved. Can do. Furthermore, since the volume of the first expansion chamber 13A is formed by the protrusion 32 and the back pressure in the first expansion chamber 13A is reduced, the pumping capacity necessary for air introduction can be reduced. It becomes possible to introduce air into the first expansion chamber 13A.

  FIG. 4 is a top view of the engine working machine 1, and a part of the cross section taken along the line BB in FIG. 2 is shown. In the engine working machine 1, a starter 10 and a starter knob 11 are disposed at one end of the drive shaft 20, and a cooling fan 28 is disposed at the other end. The cooling fan 28 generates an air flow for cooling to the cylinder 30 and also serves as a flywheel. Further, a magnet (not shown) is arranged at a predetermined position in the circumferential direction of the cooling fan 28 for determining the timing for supplying a high-voltage current to the spark plug 12 and transmitting it to the ignition device (not shown). Is done. The cooling fan 28 is disposed inside the first volute case 8 and the second volute case 9 that are part of the crankcase 21. An air intake port 29 of the air introduction passage 7 is disposed in the first volute case 8. The air intake port 29 is provided with a check valve 35 that prevents the backflow of exhaust gas from the first expansion chamber 13A.

  Since the drive shaft 20 rotates when the engine 36 is started as described above, the cooling fan 28 sucks air in the direction of AIR1 and sends it to the vicinity of the cylinder 30 of the engine 36 to cool the engine 36. . At this time, a part of the wind generated by the cooling fan 28 is taken out as AIR2 at the air intake 29, so that air can be introduced into the first expansion chamber 13A of the muffler 4 through the air introduction passage 7. .

  By arranging the air intake 29 in the first volute case 8 in this way, the heat transfer path from the first expansion chamber 13A to the air intake 29 via the air introduction passage 7 can be lengthened, and the air intake It is possible to suppress the temperature rise due to the heat of the muffler transmitted to the inlet 29, and the durability of the check valve 35 disposed in the vicinity of the air intake 29 can be improved. In addition, it is not necessary to separately add additional parts or change the shape in order to arrange the air intake 29, and the air intake 29 can be arranged in a compact manner. Furthermore, since air is always generated by the cooling fan 28 inside the first volute case 8 and the second volute case 9, the air intake 29 and the check valve 35 are sufficiently cooled by this air. As described above, since a part of the wind of the cooling fan 28 arranged for cooling the engine 36 is introduced into the muffler 4, another pump or a blower fan for sending air to the muffler 4. There is no need to arrange etc. Therefore, the means for introducing air into the muffler 4 can be realized at low cost and in a compact manner while minimizing the increase in cost, weight, and product dimensions, and the exhaust gas component purification performance of the catalyst can be improved.

  FIG. 5 is a cross-sectional view taken along the line CC in FIG. An air intake 29 is disposed at a position where the distance from the center N of the cooling fan 28 is substantially minimum on the inner peripheral wall portion of the first volute case 8 that covers the outer peripheral portion of the cooling fan 28. The first volute case 8 is formed in such a manner that the distance from the center N to the inner peripheral wall is increased in the counterclockwise direction in accordance with the rotation direction H of the cooling fan 28 with respect to the center N, and the vicinity where the distance is maximum. Thus, the discharge portion 33 and the cylinder cover 3 are formed so as to be smoothly connected. In such a configuration, when the cooling fan 28 rotates, wind flows along the wall surface on the inner peripheral side of the first volute case 8 as shown by AIR 3, and the wind that flows out from the discharge portion 33 is caused by the cylinder cover 3 in each part of the cylinder 30. Then, the cylinder 30 is cooled. On the other hand, as in AIR2, part of the wind reaches the air inlet 18 of the first expansion chamber 13A from the air intake 29 via the air introduction passage 7 and is introduced into the first expansion chamber 13A.

  Thus, by arranging the air introduction means using the existing first volute case 8, it is not necessary to configure separate parts and shapes for the arrangement of the air intake port 29. Therefore, the air intake port can be arranged in a compact manner. Further, since the inner wall portion where the air intake port 29 is formed is disposed at a position where the distance from the center N is almost the minimum in the first volute case 8, the reduction in the amount of air guided from the discharge portion 33 to the cylinder cover 3 is minimized. It can be suppressed to the limit. Therefore, it is possible to take out air to be introduced into the first expansion chamber 13A of the muffler 4 while minimizing a decrease in the air volume of the discharge unit 33 used for cooling or blowing. Further, in this embodiment, the muffler 4 is formed so that the volume thereof is relatively larger than the conventional one, so that the pumping capacity for introducing air into the first expansion chamber 13A is reduced, so that the air is efficiently supplied to the first. It can be introduced into the expansion chamber 13A. Further, since the wind from the cooling fan 28 always flows inside the first volute case 8, even if the heat of the muffler 4 is transmitted from the connection part of the muffler 4 and the air introduction passage 7, the temperature of the air intake 29 is increased. Can be prevented and durability can be improved.

  FIG. 6 is a side view for explaining the size of the muffler 4 of the engine working machine 1 according to the embodiment of the present invention. As can be understood from FIG. 6, the muffler 4 is attached to the right side (+ Z side) of the engine 36. In the conventional muffler, since the communication portion 31 is connected to the exhaust port 24 of the engine 36, the upper end portion of the muffler is located near the arrow 41 in the X direction. The muffler in the conventional engine working machine is mainly configured by the size of the space 61 and the space 62. However, in this embodiment, in order to increase the volume of the muffler 4, the muffler 4 is extended to the lower side (−X direction) of the cylinder chamber lower end surface 72 in the direction of the arrow 76 to secure the space 63. Further, in order to further expand the secured space 63, a portion of the space 64 was secured by extending the side wall surface of the muffler 4 in the direction of the arrow 77 from the space 63 to the left side (−Z direction). A portion where the space 64 is located is a protruding portion 32 that protrudes to the left side of the fastening plane M that is a surface passing through the opening of the exhaust port 24. Thus, by devising the shape of the muffler 4, it was possible to secure a sufficiently large muffler volume compared to the conventional example.

  On the other hand, when the size of the muffler 4 is increased, the installation space for the fuel tank that has been conventionally disposed on the lower side of the muffler is reduced. In this embodiment, the muffler 4 extends downward from the cylinder chamber lower end surface 72 and leftward from the fastening plane M, so that the space 65 on the right side of the cylinder center surface 75b of the fuel tank 22 is indicated by an arrow 78. It was compressed and became smaller. This means that the amount of fuel that can be stored is reduced, which is not preferable. Therefore, in this embodiment, the left end of the fuel tank 22 is extended leftward (−Z direction) from the cylinder cover left end surface 75a as indicated by an arrow 79 to secure a space 67, and further upward (+ X) as indicated by an arrow 80. The upper end surface 22A is configured to reach almost the same position as the cylinder chamber lower end surface 72. By securing the spaces 67 and 68 in this way, the same tank capacity as that of the prior art was secured. Even if the shape of the fuel tank 22 is changed in this way, the muffler 4 is located in the vicinity of the space 67 and the space 68 and the left and right center plane 74, so that the right and left are good in terms of weight. Balance can be ensured. In addition, since the heat shield plate 38 functioning as a heat shield plate is provided between the engine 36 and the fuel tank 22 and the muffler 4, the high temperature of the muffler 4 can be greatly reduced from being transmitted to the fuel tank 22. Even if the space 65 of the fuel tank 22 is compressed as shown by the arrow 78, it is preferable that the right end of the space 65 be located on the right side of the cylinder center plane 75b.

  FIG. 7 is a side view for explaining the size of the muffler 4 of the engine working machine 1 according to the embodiment of the present invention. In FIG. 7, the engine 36 is indicated by a dotted line so that the sizes of the muffler 4 and the engine 36 can be compared. Each dimensional ratio of the muffler 4 was set to be longitudinal direction: lateral direction: thickness direction = 2.4: 1.2: 1.0. Here, the muffler volume (cc) of the muffler 4 is approximately 17 times or more than the displacement (cc) of the engine 36, and the tail pipe area (mm2) is approximately 0. 0 relative to the displacement (cc). It was set to 8 times or less, particularly preferably 0.3 times to 0.8 times. By setting in this way, it is possible to significantly reduce the noise while securing the output of the engine 36 to some extent.

  The muffler 4 in FIG. 7 is set so that the thickness is smaller than the horizontal when the piston moving direction is the vertical direction of the muffler, the drive shaft direction is the horizontal direction of the muffler, and the exhaust opening direction is the thickness direction of the muffler. The aspect ratio is set to 1.5 or more. Since the horizontal direction of the muffler 4 (the front-rear direction when viewed with the engine working machine) is directly linked to the increase in the overall length of the engine 36, it can be made compact by minimizing this. Further, the engine 36 generally tends to be the longest in the moving direction of the piston 19 and can be made more compact by combining this 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 be described with reference to FIGS. Here, a two-cycle engine having an engine displacement of 21 cc is used. FIG. 8 shows the relationship between the tail pipe area per displacement and the engine output (Kw). Here, the muffler volume is a constant 388.5 cc, and the muffler volume / displacement is 18.5. Under these conditions, five mufflers with different tail pipe areas were prepared and measured. As a result, the maximum output of the engine 36 was 0.75 Kw when the tail pipe area / displacement amount was approximately 1.3 or more, and the tail pipe area / It has been found that when the displacement becomes 0.9, the output decreases by about 5% from the maximum output. Normally, reducing the tailpipe area will reduce the noise level, but at the same time the engine output will drop. If the muffler volume is set so that at least the tailpipe area / displacement is approximately 0.9 or more, the noise engine The maximum output can be obtained.

FIG. 9 shows the relationship between the muffler volume per displacement and the noise (dBA). Here, the tail tube area is 9.45 cm ² , and the tail tube area / displacement amount is 0.45. As can be seen from this experiment, increasing the muffler volume usually reduces the noise level.

  FIG. 10 shows the relationship between the tail tube area per displacement and the noise (dBA). Here, the muffler volume is a constant 388.5 cc, and the muffler volume / displacement is 18.5. As can be seen from this experiment, increasing the tail pipe area / displacement usually increases the noise level. If the practical minimum noise value of this engine is 70 dBA, it can be understood that there is a noise reduction effect of 1 dB or more when the tail pipe area is 0.9 or less.

FIG. 11 is a diagram showing the relationship between the muffler volume per unit displacement and the tail tube area. As a result of investigating the relationship when maintaining 0.7 Kw as the engine output, it was found that the muffler volume should be increased even if the tail tube area is reduced. Further, it can be understood that if the tail pipe area is reduced with the same muffler volume, the engine output is reduced by about 20 to 30%. From the result of FIG. 10, in order to keep the noise level low, it is preferable to set the tail pipe area / displacement to 0.9 or less. On the other hand, in order to increase the output of the engine, the volume of the muffler may be increased. As a result of this experiment, the volume of the muffler (cc) is approximately 17 times or more the displacement (cc) and the tail pipe area is increased. It can be understood that (mm ² ) should be set to about 0.8 times or less of the displacement (cc). If the tail pipe area (mm ² ) is made too small, the engine output becomes too small. Therefore, the tail pipe area / displacement amount at which the output is reduced by 20 to 30% is preferably about 0.3 times or more.

  As described above, in the present embodiment, since the muffler 4 is enlarged and the arrangement of the fuel tank 22 is changed, the external shape of the engine work machine 1 remains substantially the same, and a significant low noise effect and output are achieved. A muffler structure designed to maintain the

  Next, the engine working machine according to the second embodiment will be described with reference to FIG. FIG. 12 is a cross-sectional view corresponding to the AA cross-sectional position of FIG. As a means for increasing the rigidity of the muffler outer surface 89 of the muffler 84, a muffler fastening bolt 86 is formed inside the collar 87. The collar 87 is joined by welding on a contact surface of either the muffler inner side surface 88 or the muffler outer side surface 89. Thus, even in the configuration in which the muffler fastening bolt 86 is shortened, the same effect as that of the first embodiment can be obtained. The same effect can be obtained even if the muffler fastening bolts 5A and 5B are formed short so as to be housed in the collar.

  As mentioned above, although this invention was demonstrated based on the Example, this invention is not limited to the above-mentioned Example, A various change is possible within the range which does not deviate from the meaning. For example, in the present specification, an example in which the present invention is applied to a brush cutter in which the moving direction of the piston 19 is perpendicular to the ground has been described, but the piston 19 is maintained while maintaining the layout of the engine working machine 1 described above. It is also possible to apply to a working machine (for example, a hedge trimmer, a cultivator, etc.) having a horizontal movement direction.

DESCRIPTION OF SYMBOLS 1 Engine working machine 2 Air cleaner 3 Cylinder cover 4 Muffler 4A Upper end part 4B Lower end part 5A, 5B, 6 Muffler fastening bolt 7 Air introduction passage 8 First volute case 9 Second volute case 9A Leg part 10 Starter 11 Starter knob 12 Ignition Plug 13A First expansion chamber 13B Second expansion chamber 13C Third expansion chamber 14 Catalyst 15A Expansion chamber case 15B Expansion chamber case 16 Collar 17 Tail 18 Air inlet 19 Piston 20 Drive shaft 21 Crankcase 22 Fuel tank 23 Vaporizer 24 Exhaust port 25A Expansion chamber opening 25B Expansion chamber opening 26 Muffler inner surface 27 Muffler outer surface 28 Cooling fan 29 Air intake 30 Cylinder 31 Communication portion 32 Projection portion 33 Discharge portion 34 Plug cap 35 Check valve 36 Engine 37 Partition plate 38 Hot plate 39 Insertion part 61, 62, 63, 64, 67, 68 Space 71 Exhaust port surface 72 Cylinder chamber lower end surface 74 Left and right center surface 75a Cylinder cover left end surface 75b Cylinder center surface 76 to 80 Arrow 84 Muffler 86 Muffler fastening bolt 87 Color 88 Muffler inner surface 89 Muffler outer surface D Bore inner diameter M Fastening plane N Cooling fan center H Cooling fan rotation direction AIR1 Cooling air AIR2 Inlet air AIR3 Cooling air EX Exhaust gas EX1 Exhaust gas outflow direction EX2 Exhaust gas outflow direction LA Fastening Minimum value of the distance from the plane to the side of the muffler LB Maximum value of the distance from the fastening plane to the side of the muffler

Claims (8)

An engine, a fuel tank that stores fuel supplied to the engine, and a muffler that suppresses exhaust noise discharged from the engine; a driving shaft direction of the engine, an opening direction of an exhaust port, and an operating direction of a piston Are engine working machines configured to be substantially orthogonal to each other,
The muffler
One of the internal expansion chambers is fastened to the exhaust port of the engine so as to be connected to the exhaust port of the engine,
It has a protrusion that extends to the engine side with respect to the fastening plane parallel to the moving direction of the piston at the fastening position, and the protruding part is disposed near the end portion on the side far from the spark plug in the moving direction of the piston of the engine. ,
The muffler side surface facing the exhaust port is substantially parallel to the fastening plane,
The engine working machine according to claim 1, wherein the fuel tank is provided at a lower portion of a crankcase of the engine and on a side of the projecting portion of the muffler.   The volume of the muffler is 17 times or more with respect to the displacement of the engine, and the opening area of the tail tube formed at the exhaust port of the muffler is 0.3 to 0.8 times with respect to the displacement. The engine working machine according to claim 1, wherein: The engine is arranged such that the piston reciprocates in the vertical direction,
The cross section of the exhaust port of the engine is positioned so as to be substantially vertical,
3. The engine work machine according to claim 1, wherein a dimension of the muffler is a vertically long shape such that a thickness direction <a horizontal direction <a vertical direction. 4.   The engine working machine according to claim 3, wherein a ratio of a longitudinal direction / a lateral direction of a dimension of the muffler is 1.5 or more.   The muffler is fastened to the engine by fastening means, and on the side of the muffler away from the engine and the side of the muffler facing the engine exhaust port, the rigidity of the side of the muffler is separated from the fastening means in the direction of movement of the piston. The engine working machine according to claim 4, wherein means for increasing the pressure is arranged. The means for increasing the rigidity is a screw and a tube passing through the screw,
The engine work machine according to any one of claims 2 to 5, wherein the pipe is fixed to a muffler side surface on a side away from the engine and the muffler side surface facing the engine exhaust port. Inside the muffler, there is a first expansion chamber communicating with the engine exhaust port, and a second expansion chamber having a discharge port for discharging exhaust gas into the atmosphere,
Providing a third expansion chamber connecting the first expansion chamber and the second expansion chamber;
The engine working machine according to claim 6, wherein a catalyst for purifying an exhaust gas component is disposed in the third expansion chamber.   The engine working machine according to claim 7, wherein the third expansion chamber is disposed so as to include an internal space of the protruding portion.

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