WO2010061974A1

WO2010061974A1 - Engine and engine-powered tool equipped with same

Info

Publication number: WO2010061974A1
Application number: PCT/JP2009/070369
Authority: WO
Inventors: Toshinori Yasutomi; Shinki Ohtsu; Junichi Kamimura; Mitsuhiro Sunaoshi
Original assignee: Hitachi Koki Co., Ltd.
Priority date: 2008-11-28
Filing date: 2009-11-27
Publication date: 2010-06-03
Also published as: JP2010151114A

Abstract

The engine (1) has a combustion chamber (4) defined by wall surfaces (5 and 20) of the cylinder bore (3) and the top surface (24) of a piston (9) that reciprocates in the cylinder bore (3) between an upper dead point and a lower dead point. A plurality of protuberances (6) are integrally formed in the upper wall surface (5) of the cylinder bore (3) facing the top surface (24) of the piston (9).

Description

DESCRIPTION

Title of the Invention ENGINE AND ENGINE-POWERED TOOL EQUIPPED WITH SAME

Technical Field

[0001] The present invention relates to an engine especially suitable for a hand-held engine-powered tool such as a weed whacker, chainsaw, blower or the like, and to an engine-powered tool equipped with same.

Background Art

[0002] Patent Literature 1 discloses an engine provided with three scavenging paths in order to improve engine performance. These engine scavenging paths are formed so that the scavenging flow direction into the cylinder from each scavenging path forms a tangent to a circle centered on the cylinder axis, hi addition, a valve for altering the path area is provided in one of the scavenging paths. By controlling this valve, the scavenging flow speed into the cylinder is controlled, so that a swirl centered on the cylinder axis in a prescribed direction is effectively generated. [0003] Patent Literature 1 : Unexamined Japanese Patent Application KOKlAI Publication No. H9-291827.

[0004] Users want engines for engine-powered tools to be compact and lightweight. In contrast, when the above-described a mechanism that generates the swirl is provided in order to improve engine performance, the engine tends to become larger, weight increases, and cost rises as well.

Summary of Invention [0005] The present invention is invented in view of the above problem and the purpose of the present invention is to provide an engine that can realize higher engine output and lower emission, and an engine-powered tool provided with this engine, while curtailing increases in engine size, weight, and cost. [0006] In order to achieve the above purpose, the engine according to the present invention is an engine, provided with a combustion chamber formed by a wall surface of a cylinder and a top surface of a piston that reciprocates between an upper dead point and a lower dead point in the cylinder, this engine being characterized by: a plurality of different levels being integrally provided in the upper wall surface of the cylinder facing the piston top surface.

[0007] Possibly, a sparkplug is provided in the cylinder such that the electrode part of the sparkplug protrudes into the combustion chamber from the cylinder's upper wall surface; and a plurality of different levels are arranged with respect to the position of the electrode part.

[0008] Possibly, the plurality of different levels are arranged in a rotationally symmetrical manner when viewed in the cylinder axis direction; and the electrode part is positioned substantially in a central position of the rotational symmetry of the different levels.

[0009] For example, the plurality of different levels may be formed by the cylinder's upper wall surface and a plurality of protuberances protruding from this cylinder's upper wall surface.

[0010] Possibly, a squish area is formed between the piston top surface and the cylinder's upper wall surface.

[0011] Possibly, the plurality of protuberances are provided near the squish area.

[0012] Possibly, concave areas are formed in the piston top surface such that the ends of the plurality of protuberances are positioned in these concave areas when the piston is positioned near the upper dead point.

[0013] For example, the plurality of protuberances may protrude in directions normal to the cylinder's upper wall surface. [0014] For example, the plurality of protuberances may protrude in the direction of the cylinder axis.

[0015] For example, the plurality of different levels may be formed by the cylinder' s upper wall surface and a plurality of grooves formed in this cylinder's upper wall surface.

[0016] Possibly, the plurality of grooves extend toward the electrode part from near the outer edge of the cylinder's upper wall surface when viewed in the cylinder axis direction.

[0017] Possibly, the plurality of grooves extend to near the electrode part when viewed in the cylinder axis direction.

[0018] Possibly, the plurality of grooves are formed in arc shapes when viewed in the cylinder axis direction. [0019] Possibly, the plurality of grooves are formed so as to become deeper with distance from the two ends in a cross-section parallel to the cylinder axis direction.

[0020] Possibly, a squish area is formed between the piston top surface and the cylinder's upper wall surface.

[0021] In addition, to resolve the problem described above, the engine-powered tool according to the present invention is an engine-powered tool equipped with the engine described above.

[0022] The engine according to the present invention has the plurality of different levels integrally formed in the cylinder's upper wall surface, facing the top surface of the piston.

Therefore, when the piston rises, the fuel-air mixture flowing along cylinder's upper wall surface creates flow in directions different from the compression/expansion direction because of the different levels, so that the flow of the fuel-air mixture becomes turbulent.

Accordingly, when the fuel-air mixture is ignited by the sparkplug and combusts, propagation of the flame is accelerated and combustion speed of the fuel-air mixture is increased. Furthermore, accompanying combustion, the fuel-air mixture expanding toward the outer edge of the combustion chamber again creates flow in directions different from the compression/expansion direction because of the different levels, so that the flow of the fuel-air mixture becomes turbulent. Accordingly, propagation of the flame is further accelerated and combustion speed is further increased. For these reasons, the pressure in the combustion chamber can be raised and engine output can be increased. In addition, the volume of uncombusted gas exhausted from the exhaust port is decreased, so low emission performance can be improved. Thus, it is possible to improve engine performance while curtailing increases in engine size, weight, and cost.

Brief Description of Drawings

[0023] Fig. 1 is a cross-sectional view of the engine according to the First Embodiment of the present invention; Fig. 2 is a cross-sectional view of the combustion chamber of the engine shown in Fig. 1 , with the piston near the upper dead point;

Fig. 3 is a bottom view showing the cylinder block and the sparkplug of the engine shown in Fig. 1;

Fig. 4 is a cross-sectional view of the combustion chamber of the engine according to the Second Embodiment of the present invention, with the piston near the upper dead point;

Fig. 5 is bottom view showing the cylinder block and the sparkplug of the engine shown in Fig. 4;

Fig. 6 is a cross-sectional view of a variation on the engine shown in Fig. 4; Fig. 7 is a cross-sectional view of the engine according to the Third Embodiment of the present invention;

Fig. 8 is a cross-sectional view of the combustion chamber of the engine shown in Fig. 7, with the piston near the upper dead point;

Fig. 9 is a bottom view showing the cylinder block and the sparkplug of the engine shown in Fig. 7; and

Fig. 10 is a perspective view of a weed whacker equipped with the engine according to the Embodiments of the present invention.

Best Mode for Carrying Out the Invention

[0024] The best mode for carrying out the invention will be described hereafter with reference to the drawings. [0025] Fig. 1 is a cross-sectional view of a stratified scavenging two-cycle engine

(hereinafter, the engine) according to the First Embodiment, the cross-section taken along a cylinder axis 7 so that an exhaust port 8 is evenly divided. Fig. 2 is a cross-sectional view of a combustion chamber 4. Fig. 3 is a bottom view of a cylinder block 10 and a sparkplug 2 mounted in the cylinder block 10. In addition, Fig. 10 is an perspective view of a weed whacker 1001 powered by the engine 1 shown in Figs. 1 to 3.

[0026] As shown in Fig. 10, the weed whacker 1001 consists of an operation pole 1002; a rotating blade 1003 provided on the front end of the operation pole 1002; and the engine 1 provided on the back end of the operation pole 1002. The output of the engine 1 is transmitted to the rotating blade 1003 via a drive shaft, not shown, passed through the inside of the operation pole 1002. The operator grips a handle 1004 mounted on the operation pole 1002 to operate the weed whacker 1001.

[0027] As shown in Fig. 1, the engine 1 is equipped with a cylinder block 10 and a crankcase 13. A cylinder bore 3 is formed in the cylinder block 10. A piston 9 is housed inside the cylinder bore 3 so as to be capable of reciprocating between an upper dead point and a lower dead point in the direction of the cylinder axis 7, that is to say, up-and-down movement in Fig. 1. Unless otherwise noted, the direction from the lower dead point toward the upper dead point shall be upward and the direction from the upper dead point toward the lower dead point shall be downward. Fig. 1 shows the piston 9 at the lower dead point. In addition, an exhaust port 8, an intake port 15, and four scavenging ports 16 (as shown in Fig. 3, these are arranged with two pairs of scavenging ports 16 mutually facing each other) are opened in the inner surface of the cylinder bore 3. The exhaust port 8, the intake port 15 and the four scavenging ports 16 open and close in accordance with the up-and-down movement of the piston 9. The scavenging ports 16 are connected to a crank chamber 19 via scavenging paths 26 formed in the cylinder block 10. [0028] The crankcase 13 is mounted on the downward end of the cylinder block 10. The piston 9 is connected to a crankshaft 14, housed in and supported by the crankcase 13 so as to be capable of rotation, via a connecting rod 12. A crank weight 11 is mounted on the crankshaft 14. A squish-dome-type combustion chamber 4 provided with a dome part 21 shown in Fig. 2 and a squish area 17 shown in Fig. 2 is defined by the substantially flat top surface 24 of the piston 9 (hereinafter, the piston top surface), the inner wall surface 20 of the cylinder bore 3, and an upper wall surface 5 of the cylinder bore 3 facing the piston top surface 24. The sparkplug 2 is mounted on the upper end of the cylinder block 10, and an electrode part 18 of the sparkplug 2 is positioned on the cylinder axis 7 near the top of the dome part 21 of the combustion chamber 4. [0029] The combustion chamber 4 will be described in detail next. As shown in Fig. 2 and Fig. 3, the dome part 21 of the combustion chamber 4 is defined by an oblique surface 22 of the upper wall surface 5 of the cylinder bore 3 and has a substantially circular truncated cone shape with the inner diameter becoming larger toward the lower dead point. In addition, the edge of the oblique surface 22 extends to a rim surface 23 that is substantially orthogonal to the cylinder axis 7 and faces the piston top surface 24 substantially parallel thereto. The squish area 17 of the combustion chamber 4 is defined in a ring shape downward of the dome part 21 by the rim surface 23, the inner wall surface 20 of the cylinder bore 3, and the piston top surface 24. In addition, when the piston 9 is at the upper dead point, the piston top surface 24 and the rim surface 23 of the squish area 17 face each other with a predetermined squish clearance in the direction of the cylinder axis 7. Moreover, a plurality of protuberances 6 constituting different levels are integrally formed on the oblique surface 22 of the cylinder block 10. The protuberances 6 are arranged with equidistance spacing on a circle centered on the electrode part 18 and the cylinder axis 7, that is to say in a rotationally symmetrical manner about the electrode part 18 and the cylinder axis 7, when viewed in the direction of the cylinder axis 7. In addition, the protuberances are substantially cylindrical and protrude in directions normal to the oblique surface 22. When the piston 9 is at the upper dead point, sufficient clearance is provided between the piston top surface 24 and the bottom edge of the protuberances 6. In addition, the protuberances 6 are arranged shifted toward the outer edge side of the oblique surface 22 (the boundary with the rim surface 23) from the midpoint between the electrode part 18 and the outer edge of the oblique surface 22, and the bottom edges of the protuberances 6 are positioned near the squish area 17. In Fig. 2, the bottom edges of the protuberances 6 are positioned between the rim surface 23 and the piston top surface 24 at the upper dead point, but the bottom edges of the protuberances 6 may also be positioned upward of the rim surface 23. [0030] The behavior of the engine 1 will be described hereafter with reference to Fig. 1. When the piston 9 rises from the lower dead point to the upper dead point, the fuel-air mixture enters the crank chamber 19 from the intake port 15, and the fuel-air mixture in the combustion chamber 4 is compressed. When the piston 9 reaches near the upper dead point, the fuel-air mixture in the combustion chamber 4 is ignited by the sparkplug 2 and combusts, so that the piston 9 which has reached the upper dead point is forced toward the lower dead point. When the piston 9 falls from the upper dead point toward the lower dead point, first the exhaust port 8 connects to the combustion chamber 4 and the combustion gas is exhausted from the combustion chamber 4. Then, the scavenging ports 16 connect to the combustion chamber 4 and the fuel-air mixture in the crank chamber 19 compressed by the piston 9 flows into the combustion chamber 4. The fuel-air mixture that flows into the combustion chamber 4 expels the combustion gas remaining in the combustion chamber 4.

[0031] The flow of the fuel-air mixture in the combustion chamber 4 will be described hereafter with reference to Figs. 1 to 3. When the piston 9 moves toward the upper dead point, an upward flow is created in the fuel-air mixture in the combustion chamber 4. Immediately before the piston 9 reaches the upper dead point, the fuel-air mixture in the squish area 17 is forced toward the center of the cylinder bore 3 (the cylinder axis 7) and flows upward along the oblique surface 22, as indicated by the arrows in Figs. 2 and 3. At this time, the fuel-air mixture collides with the protuberances 6 and flows around the protuberances 6, creating flow in directions differing from the compression/expansion direction. Through this, the flow of fuel-air mixture becomes turbulent. When the sparkplug 2 ignites, the fuel-air mixture around the electrode part 18 combusts and the flame is propagated. Because the flow of the fuel-air mixture is turbulent at this time, propagation of the flame is accelerated and the combustion speed of the fuel-air mixture is increased. Furthermore, the fuel-air mixture expanding toward the outer edge of the combustion chamber 4 accompanying combustion again collides with the protuberances 6, flows around the protuberances, and creates flow in directions different from the compression/expansion direction. Through this, the flow of the fuel-air mixture becomes turbulent. Consequently, propagation of the flame is further accelerated and the combustion speed of the fuel-air mixture is further increased. As a result, the pressure in the combustion chamber 4 is raised, so the engine output can be increased. In addition, the volume of fuel-air mixture exhausted from the exhaust port 8 without being combusted is decreased, so low emission performance can be improved. Furthermore, because the bottom edges of the protuberances 6 are positioned near the squish area 17, the fuel-air mixture collides with the protuberances 6 near the squish area 17, where flow speed is high. Accordingly, it is possible to effectively generate turbulence in the fuel-air mixture. In addition, because the protuberances 6 are arranged with rotational symmetry about the electrode part 18 and the cylinder axis 7 when viewed in the direction of the cylinder axis 7, uniformly strong turbulence is generated near the electrode part 18 and the cylinder axis 7. Accordingly, it is possible to prevent deformation, etc., of the piston 9 and the cylinder block 10 caused by biased combustion. [0032] As explained above, with the engine 1 having the composition described above, it is possible to increase engine output and improve low emission performance while maintaining size and weight by employing the relatively simple composition of having protuberances 6 in the combustion chamber 4, without needing a complex composition that would be accompanied by increases in the size, weight, and cost of the engine 1. The number, the amount of protrusion, and the arrangement on the oblique surface 22 of protuberances 6 can be appropriately selected on the basis of experiments, simulations, etc., so as to obtain the desired engine output and low emission performance. In addition, in order to effectively generate turbulence of the fuel-air mixture and raise the combustion speed of the fuel-air mixture, a squish area 17 which increases the flow speed of the fuel-air mixture colliding with the protuberances 6 is provided in the engine 1, but the squish area 17 is not a necessary composition. The present invention can be applied even to engines in which no rim surface 23 is formed in the cylinder block 10. [0033] An engine according to the Second Embodiment of the present invention will be described hereafter with reference to Figs. 4 and 5. In the First Embodiment above, the protuberances 6 protrude in directions normal to the oblique surface 22, but the protrusion directions of the protuberances 6 are not limited to this. For example, as shown in Figs. 4 and 5, protuberances 106 may protrude in the direction of the cylinder axis 7. In this case, the protuberances 106 are arranged shifted toward the outer edge side of the oblique surface 22 (the boundary with the rim surface 23) from the midpoint between the electrode part 18 and the outer edge of the oblique surface 22, and the bottom edges of the protuberances 106 are positioned near the squish area 17. In Fig. 4, the bottom edges of the protuberances 106 are positioned between the rim surface 23 and the piston top surface 24 at the upper dead point, but the bottom edges of the protuberances 106 may also be positioned upward of the rim surface 23. In this case, the protuberances 106 are positioned closer to the squish area 17 than the protuberances 6 of the First Embodiment. For this reason, the fuel-air mixture collides with the protuberances 106 closer to the squish area 17 where flow speeds are higher. Accordingly, it is possible to more effectively generate fuel-air mixture turbulence. Through this, propagation of the flame is accelerated and the combustion speed of the fuel-air mixture is raised. Accordingly, it is possible to increase engine output and also improve low emission performance, the same as in the First Embodiment. Additionally, because the protuberances 106 protrude in the direction of the cylinder axis 7, casting of the cylinder block 10 is easy, which can further help reduce manufacturing costs.

[0034] In the First and the Second Embodiments above, the piston top surface 24 was substantially flat, but the shape of the piston top surface 24 is not limited to this. For example, as shown in Fig. 6, a plurality of concave areas 225 may be formed in the piston top surface 224 such that the bottom edges of the protuberances 106 go into the concave areas 225 when the piston 9 reaches the upper dead point. In this case, it is possible to reduce the squish clearance compared to the case that the piston top surface 24 is flat, so the squish flow (flow of fuel-air mixture from the squish area) becomes stronger and the turbulence generated in the combustion chamber 4 becomes stronger. Accordingly, propagation of the flame is further accelerated and combustion efficiency is further improved. Furthermore, the protuberances are not limited to protruding in the direction of the cylinder axis 7. For example, the protuberances 106 may protrude in directions normal to the oblique surface 22, as in the First Embodiment. In this case, the concave areas 225 on the piston top surface 224 may be processed in accordance with the shape of the bottom edges of the protuberances 106. [0035] In addition, the shape of the protuberances 6 and 106 is not limited to a cylindrical shape, and may be, for example, in the shape of a hemisphere, a circular truncated cone, a triangular prism, a quadrangular prism, etc, In addition, the shape of the combustion chamber 4 is not limited to a squish-dome-type, and may be a variety of types, for example, hemispherical-type, wedge-type, etc., and may even be a type with no squish area 17. Furthermore, in the First and the Second Embodiments above, the cylinder block 10 and the so-called cylinder head are integrally formed, but the cylinder block 10 and the cylinder head may be formed as separate parts. Furthermore, the engine 1 is not limited to a two-cycle engine, and may be a four-cycle engine, etc. In addition, in the First and the Second Embodiments above, the protuberances 6 and 106 are arranged with equidistant spacing on a circle centered on the electrode part 18 and the cylinder axis 7, but the protuberances 6 and 106 are not limited to this, for while it is preferable for the protuberances 6 and 106 to be arranged in rotationally symmetrical manner about the electrode part 18 and the cylinder axis 1, they may also be arranged with non-equidistant spacing. [0036] An engine according to the Third Embodiment of the present invention will be described hereafter with reference to Figs. 7 to 9. The engine 1 according to this Embodiment is provided with grooves 206 in the oblique surface 22 of the upper wall surface 5 of the cylinder bore 3 instead of the protuberances 6 and 106 of the First and the Second Embodiments. Fig. 7 is a cross-sectional view of the engine 1 according to this Embodiment, the cross-section taken along the cylinder axis 7 so that the exhaust port 8 is evenly divided. Fig. 8 is a cross-sectional view of the combustion chamber 4. Fig. 9 is a bottom view of the cylinder block 10 and the sparkplug 2 mounted in the cylinder block 10. The same reference numbers are attached to parts that are the same as parts shown in Figs.1-6, and explanation of such is omitted here. [0037] As shown in Figs. 7 and 8, a plurality of grooves 206 constituting different levels are formed in the oblique surface 22 of the cylinder bore 3. The grooves 206 extend to near the electrode part 18 of the sparkplug 2 from the rim surface 23 of the cylinder bore 3 that defines the squish area 17, when viewed in the direction of the cylinder axis 7, as shown in Fig. 9. In addition, the grooves 206 are arranged with equidistant spacing on a circle centered on the electrode part 18 and the cylinder axis 7, that is to say in a rotationally symmetrical manner about the electrode part 18 and the cylinder axis 7. Furthermore, each of the grooves 206 has an arc shape and is positioned so that an extension of the end 206b on the sparkplug 2 side goes toward the electrode part 18. In addition, each of the grooves 206 has a depth with respect to the oblique surface 22 that is shallow at the end 206a on the rim surface 23 side and the end 206b on the sparkplug 2 side, and deepens gradually in accordance with distance from the two ends 206a and 206b, as shown in Figs. 7 and 8.

[0038] The flow of the fuel-air mixture in the combustion chamber 4 in the engine 1 of this Embodiment is described hereafter with reference to Figs. 7 to 9. When the piston 9 moves toward the upper dead point, an upward flow is created in the fuel-air mixture in the combustion chamber 4. Immediately before the piston 9 reaches the upper dead point, the fuel-air mixture in the squish area 17 is forced toward the center of the cylinder bore 3 (the cylinder axis 7) and flows upward along the oblique surface 22, as indicated by the solid arrows in Figs. 8 and 9. At this time, a portion of the fuel-air mixture enters the grooves 206 formed in the oblique surface 22, creating flow in directions differing from the compression/expansion direction, that is to say in the directions of depth of the grooves 206. Because the ends 206a on the squish area 17 side (the rim surface 23 side) of the grooves 206 are shallow, it is easy for the fuel-air mixture to enter the grooves 206. Furthermore, the fuel-air mixture that has entered the grooves 206 flows along the arc-shaped grooves 206, as indicated by the dashed arrows in Fig. 9, and is discharged toward the electrode part 18 of the sparkplug 2. At this time, there is a difference in speed between the fuel-air mixture flowing along the grooves 206 and the fuel-air mixture flowing along the oblique surface 22, so the flow of the fuel-air mixture at the boundary between the grooves 206 and the oblique surface 22 becomes turbulent. In addition, the fuel-air mixture flowing along the oblique surface 22 and the fuel-air mixture discharged from the ends 206b of the grooves 206 on the sparkplug 2 side, that is to say the fuel-air mixtures having differing flow directions, collide, creating turbulence near the electrode part 18. Furthermore, the fuel-air mixture that has entered the arc-shaped grooves 206 flows along the grooves 206 while creating vortexes. Consequently, the fuel-air mixture that has passed through the grooves 206 takes in the fuel-air mixture that has flowed along the oblique surface 22, creating turbulence around the electrode part 18. When the sparkplug 2 ignites, the fuel-air mixture near the electrode part 18 combusts and the flame is propagated. Because the flow of the fuel-air mixture is turbulent at this time, propagation of the flame is accelerated and the combustion speed of the fuel-air mixture is increased. Furthermore, a portion of the fuel-air mixture that expands along the outer edge of the combustion chamber 4 accompanying combustion again enters the grooves 206, creating a turbulent state at the ends 206b of the grooves 206 on the sparkplug 2 side and the boundary between the grooves 206 and the oblique surface 22. In addition, the fuel-air mixture that has entered the grooves 206 flows along the arc-shaped grooves 206 and collides with the fuel-air mixture flowing along the oblique surface 22, creating a turbulent state at the ends 206a of the grooves 206 on the rim surface 23 side. Consequently, propagation of the flame is further accelerated and the combustion speed of the fuel-air mixture is further increased. As a result, the pressure in the combustion chamber 4 is raised, so the engine output can be increased. In addition, the volume of fuel-air mixture exhausted from the exhaust port 8 without being combusted is decreased, so low emission performance can be improved.

[0039] The shape of the grooves 206 is not limited to an arc shape as viewed in the direction of the cylinder axis 7, and may for example be linear as the end 206b of the grooves 206 on the sparkplug 2 side approaches the electrode part 18, or may have corners. In addition, the number, depth and shape of the grooves 206 as viewed in the direction of the cylinder axis 7 can be appropriately determined on the basis of testing, simulations or the like so as to obtain the desired engine output and low emission performance.

[0040] The engine 1 according to the first to the third Embodiments above can be broadly applied to a variety of engine-powered tools, and in particular is suitable for portable engine-powered tools such as weed whackers, chainsaws, blowers, etc.

[0041] Having described and illustrated the principles of this application by reference to one or more preferred embodiments, it should be apparent that the preferred embodiments may be modified in arrangement and detail without departing from the principles disclosed herein and that it is intended that the application be construed as including all such modifications and variations insofar as they come within the spirit and scope of the subject matter disclosed herein.

[0042] This application claims the benefit of Japanese Patent Application 2008-305168, filed November 28, 2008, and Japanese Patent Application 2009-062342, filed March 16, 2009, the entire disclosures of which are incorporated by reference herein.

Claims

Claim 1. An engine, provided with a combustion chamber defined by a wall surface of a cylinder and a top surface of a piston that reciprocates between an upper dead point and a lower dead point in the cylinder, this engine being characterized by: a plurality of different levels being integrally provided in the upper wall surface of the cylinder facing the piston top surface.

Claim 2. The engine according to Claim 1, characterized in that: a sparkplug is provided in the cylinder such that the electrode part of the sparkplug protrudes into the combustion chamber from the cylinder's upper wall surface; and a plurality of different levels are arranged with respect to the position of the electrode part.

Claim 3. The engine according to Claim 2, characterized in that: the plurality of different levels are arranged in a rotationally symmetrical manner when viewed in the cylinder axis direction; and the electrode part is positioned substantially in a central position of the rotational symmetry of the different levels.

Claim 4. The engine according to Claim 1, characterized in that: the plurality of different levels are formed by the cylinder's upper wall surface and a plurality of protuberances protruding from this cylinder's upper wall surface.

Claim 5. The engine according to Claim 4, characterized in that: a squish area is formed between the piston top surface and the cylinder's upper wall surface.

Claim 6. The engine according to Claim 5, characterized in that: the plurality of protuberances are provided near the squish area.

Claim 7. The engine according to Claim 5, characterized in that: concave areas are formed in the piston top surface such that the ends of the plurality of protuberances are positioned in these concave areas when the piston is positioned near the upper dead point.

Claim 8. The engine according to Claim 4, characterized in that: the plurality of protuberances protrude in directions normal to the cylinder's upper wall surface.

Claim 9. The engine according to Claim 4, characterized in that: the plurality of protuberances protrude in the direction of the cylinder axis.

Claim 10. The engine according to Claim 1, characterized in that: the plurality of different levels are formed by the cylinder's upper wall surface and a plurality of grooves formed in this cylinder's upper wall surface.

Claim 11. The engine according to Claim 2, characterized in that: the plurality of different levels are formed by the cylinder's upper wall surface and a plurality of grooves formed in this cylinder's upper wall surface.

Claim 12. The engine according to Claim 11, characterized in that: the plurality of grooves extend toward the electrode part from near the outer edge of the cylinder's upper wall surface when viewed in the cylinder axis direction.

Claim 13. The engine according to Claim 12, characterized in that: the plurality of grooves extend to near the electrode part when viewed in the cylinder axis direction.

Claim 14. The engine according to Claim 10, characterized in that: the plurality of grooves are formed in arc shapes when viewed in the cylinder axis direction.

Claim 15. The engine according to Claim 10, characterized in that: the plurality of grooves are formed so as to become deeper with distance from the two ends in a cross-section parallel to the cylinder axis direction.

Claim 16. The engine according to Claim 10, characterized in that: a squish area is formed between the piston top surface and the cylinder's upper wall surface.

Claim 17. An engine-powered tool equipped with the engine according to Claim 1.