Hand-held work tool with an air-cooled combustion engine

Abstract

Hand-held work device with a housing (2) in which an air-cooled internal combustion engine (8) is arranged, wherein the internal combustion engine (8) has a cylinder (38) arranged in a cylinder chamber (15) formed in the housing (2), wherein a combustion chamber (39) is formed in the cylinder (38) which is bounded by a piston (40) mounted to reciprocate in the direction of a longitudinal axis (11) of the cylinder, wherein a spark plug (49) projects into the combustion chamber (39), wherein the piston (40) drives a crankshaft (42) rotatably mounted in a crankcase (43) about a crankshaft axis of rotation (50), wherein a fan wheel (12) is fixed to the crankshaft (42) to deliver a cooling airflow (57) for the internal combustion engine (8), wherein the internal combustion engine (8) has a median plane (51) which contains the longitudinal axis (11) of the cylinder and which is perpendicular to the crankshaft axis of rotation (50) is positioned, with the side of the median plane (51),on which the fan wheel (12) is arranged, a fan wheel side (52) of the working device is, and wherein the opposite side is the outflow side (53), wherein the cylinder (38) has at least one cooling fin (18 to 27), wherein the internal combustion engine (8) has a transverse plane (54) which contains the cylinder longitudinal axis (11) and the crankshaft rotation axis (50), and wherein the working device has at least one spark plug side (55), wherein a spark plug side (55) of the working device is a side of the transverse plane (54) on which the spark plug (49) is at least partially arranged, characterized in that on at least one spark plug side (55) at least one cooling fin (26, 27) has a recess (63, 64), and that a guide wall (65) of the housing (2) projects into the recess (63, 64) of the cooling fin (26, 27) and at least one first partial airflow (58) of the cooling airflow (57) is deflected in the direction of the transverse plane (54).

Description

[0001] The invention relates to a hand-held working device of the type specified in the preamble of claim 1.

[0002] US Patent No. 8,800,505 B2 discloses a chainsaw with air guide fins arranged on its hood that extend into the cooling air stream flowing along the cylinder. The air guide fins are connected to cooling air openings in the hood.

[0003] DE 10 2011 120 471 A1 discloses a working device in which the cylinder and the fuel pump are arranged in different cooling zones, between which a buffer zone is formed.

[0004] DE 10 2011 120 464 A1 discloses a tool with an internal combustion engine that has an injection valve. The injection valve is arranged in a cooling area into which cooling air flows, conveyed to the fan wheel via a connecting opening in the fan housing.

[0005] DE 197 52 798 A1 discloses a working device in which combustion air is sucked in through a combustion air duct which is delimited by the housing base and a duct wall of the fan housing which covers the housing base as a double floor.

[0006] WO 2014 / 072817 A1 discloses an internal combustion engine with a heat shield that extends downwards from a cover and separates a space above the engine and a space above the exhaust silencer.

[0007] The invention is based on the object of creating a hand-held working device of the generic type in which the cooling of the cylinder is improved.

[0008] This object is achieved by a hand-held working device having the features of claim 1.

[0009] To improve cylinder cooling, a large number of cooling fins are usually arranged on the cylinder. A large cooling fin surface area enables a large amount of heat to be dissipated into the cooling air flowing along the cooling fins. However, cooling fins with a large surface area require a lot of installation space and, due to their mass, increase the weight of the tool. It has now been shown that an improved cooling effect on the spark plug can be achieved if at least one cooling fin has a recess on the spark plug side. A spark plug side is a side of the transverse plane on which the spark plug is at least partially arranged. The spark plug can extend on both sides of the transverse plane, so that both sides of the transverse plane are spark plug sides. The recess advantageously extends on the side of the transverse plane on which the largest part of the spark plug is arranged.However, recesses on both sides of the transverse plane can also be advantageous. It is particularly advantageous if the spark plug extends only on one side of the transverse plane, which forms the spark plug side. The recess is a cutout, i.e., an area of ​​the cooling fin in which the course of the outer contour of the cooling fin is altered. In the recess, the outer contour of the cooling fin is preferably at least partially concave, particularly preferably approximately rectangular.

[0010] A guide wall of the housing protrudes into the recess of the cooling fin and deflects at least a first partial air flow of the cooling air stream towards the transverse plane of the internal combustion engine. Because the guide wall protrudes into a recess in the cooling fin, the guide wall can be arranged relatively close to the spark plug. By deflecting the first partial air flow towards the transverse plane, improved cooling of the spark plug is achieved, even though the effective cooling fin area is reduced. Deflecting the partial air flow towards the transverse plane extends the path of the partial air flow along the cylinder and thus improves the heat transfer from the internal combustion engine to the partial air flow. Because the partial air flow is deflected towards the transverse plane, the partial air flow is guided along the cylinder in the area of ​​the spark plug and can thus actively cool the area of ​​the spark plug, which is subject to high thermal stress during operation.It has been shown that this allows for a simple and improved cooling of the combustion engine while reducing the weight and size of the implement. If the spark plug extends on both sides of the transverse plane and a recess is arranged in at least one cooling fin on both sides of the transverse plane, guide walls of the housing can extend into both recesses.

[0011] The hand-held tool can be, for example, a chainsaw, a brush cutter, a blower, a hedge trimmer, a lawn mower or the like.

[0012] The recess is advantageously arranged at least partially, in particular entirely, on the downstream side. The guide wall can prevent the cooling air flow, which has already partially flowed past the cylinder, from exiting the housing of the working device unhindered. The at least one cooling fin, which has the recess, advantageously extends to the spark plug. This ensures direct cooling of the spark plug via the cooling fin having the recess.

[0013] Good cooling of the cylinder of the internal combustion engine is achieved when the first partial air flow flows past the spark plug on the spark plug side and a second partial air flow flows past the spark plug on the opposite side of the spark plug. Particularly in the case of a tool in which the spark plug is intersected by the transverse plane, it is advantageously provided that the first partial air flow flows past the spark plug on the side of the spark plug facing the rear handle and that the second partial air flow flows past the side of the spark plug that faces the section of the guide rail protruding from the housing. Advantageously, the first partial air flow flows past the spark plug on the side facing away from the transverse plane, and the second partial air flow flows past the spark plug on the side facing the transverse plane.The cooling air flow therefore comprises at least two partial air flows that flow past the spark plug and the region of the cylinder bordering the combustion chamber on opposite sides of the spark plug. The second partial air flow can advantageously flow entirely on one exhaust side of the internal combustion engine or partially on the spark plug side and partially on the exhaust side. A flow path for the first and second partial air flows is advantageously formed on the fan wheel side, through which flow path the partial air flows flow from the fan wheel towards the top of the cylinder facing away from the crankcase. Guiding the first and second partial air flows through the flow path ensures good distribution of the cooling air. The cooling air is directed to areas of the implement that are subject to high thermal stress. The flow path is advantageously designed such that a sufficient amount of cooling air is available for the first and second partial air flows.Advantageously, at least one cooling fin has a cutout in the area of ​​the flow path. The flow path is preferably formed by cutouts in several cooling fins arranged one above the other and by at least one wall of the housing.

[0014] On the downstream side, an outflow opening of the housing is advantageously provided through which the cooling air flows out. The cylinder is in particular arranged in a cylinder chamber of the housing, and the cooling air leaves the cylinder chamber through the outflow opening. The first partial air flow and the second partial air flow are advantageously at least partially separated from one another on the downstream side upstream of the outflow opening. The separation of the first partial air flow from the second partial air flow prevents turbulence between these two partial air flows. The partial air flows are advantageously at least partially separated from one another on the downstream side. It has been shown that the partial air flows can have different volume flows and pressures depending on the operating state of the internal combustion engine. In particular, the second partial air flow has a higher pressure and higher volume flow than the first partial air flow.The partial air flow with the higher pressure and volume flow, in particular the second partial air flow, can push back the other partial air flow, in particular the first partial air flow, whereby already heated cooling air can flow back to the cylinder and in particular back to the guide wall. This would result in a deterioration in cooling, which in unfavorable cases could lead to a failure of the combustion engine. To separate the first and second partial air flows, the housing advantageously has a guide rib which separates the first partial air flow from the second partial air flow at least in the area immediately upstream of the outflow opening. This ensures that no turbulence forms between the first and second partial air flows immediately upstream of the outflow openings.A simple design is achieved if the housing has a cover that defines the cylinder chamber on the side facing away from the crankcase and on which the guide fin and the outlet opening are formed. It can also be provided that the first and second partial air streams are at least partially separated by at least one cooling fin.

[0015] One or more partitions separating the first and second partial air streams from each other can also be advantageous. The at least one partition is advantageously arranged on the cylinder and particularly advantageously extends between adjacent cooling fins of the cylinder. The cooling fin and / or the partition advantageously run approximately parallel to the transverse plane.

[0016] Advantageously, at least one cooling fin is arranged at an angle of 50° to 70° to the cylinder's longitudinal axis. It has been shown that an oblique arrangement of the cooling fins improves the guidance of the cooling air flow from the fan wheel to the cylinder. The at least one cooling fin is advantageously inclined so that the cooling fins run approximately tangentially to the air flow conveyed from the fan wheel to the cylinder. Advantageously, a plurality of cooling fins are provided which enclose an angle of 50° to 70° with the cylinder's longitudinal axis, wherein the angle is measured on the spark plug side and opens towards the fan wheel. Each of the cooling fins is at a distance from the crankshaft's axis of rotation that is measured perpendicular to the plane of the cooling fins through the crankshaft's axis of rotation. At least a first of these cooling fins, which is at the greatest distance from the crankshaft's axis of rotation of all the cooling fins, has the recess.The guide wall advantageously extends at least as far as a second cooling fin, which is second furthest away from the crankshaft rotation axis, with a portion of the first partial air flow flowing between the first cooling fin and the second cooling fin and being deflected by the guide wall. Accordingly, the guide wall not only deflects the partial air flow at the cooling fin furthest away from the crankshaft rotation axis, but also a partial air flow flowing between the cooling fin furthest away and the second furthest away from the crankshaft rotation axis. Advantageously, the second cooling fin also has a recess into which the guide wall extends. As a result, the cooling air flow flowing between the first and second cooling fins can largely be deflected by the guide wall toward the transverse plane.

[0017] Advantageously, a third partial air stream of the cooling air flow is guided along the cylinder on the fan wheel side. To branch off the third partial air stream from the cooling air stream, it is advantageously provided that one of the cooling fins has an outer edge on the fan wheel side, the distance of which from the center plane is greater than the distance of the outer edges of the adjacent cooling fins from the center plane and which branches off the third partial air stream from the cooling air stream. The branching of the third partial air stream is therefore achieved by a cooling fin and not by components of the housing. The housing wall can be arranged closely adjacent to the outer edge of the cooling fin with the increased distance from the center plane, so that the cooling fin largely separates the partial air streams.

[0018] The proposed guide wall, which projects into a recess in at least one cooling fin of the cylinder, is particularly advantageous in a two-stroke engine subject to high thermal loads. An exhaust port controlled by the piston advantageously leads from the combustion chamber. The exhaust port is advantageously arranged on the exhaust side of the transverse plane facing away from the spark plug side. In an internal combustion engine in which the spark plug extends on both sides of the transverse plane, the exhaust side is the side of the transverse plane on which a smaller section of the spark plug extends than on the opposite spark plug side of the transverse plane. The spark plug side is advantageously the side on which a rear handle of the implement is arranged. The exhaust side is advantageously the side of the transverse plane on which a tool of the implement is arranged and extends at least partially outside the housing.The exhaust side can advantageously be the side of the transverse plane facing away from the spark plug side.

[0019] The internal combustion engine advantageously has an inlet window for supplying a fuel / air mixture to the crankcase, which is controlled by the piston. The inlet window is advantageously arranged on the spark plug side. The fact that at least part of the spark plug, in particular the complete spark plug, and the outlet are arranged on opposite sides of the transverse plane results in a favorable arrangement of the spark plug, which enables a small overall size of the working device. At the same time, favorable guidance of the cooling air around the cylinder is enabled. The cylinder advantageously has at least one mounting opening for securing the cylinder to the crankcase. The mounting opening is accessible via openings in the cooling fins. It is provided that the recess encompasses the area of ​​an opening.To secure the cylinder, for example, using a screw connection, a tool, such as a screwdriver, protrudes through the recess. The flow path through which the cooling air flows on the fan wheel side is also advantageously located in the area of ​​openings in the cooling fins. Preferably, openings in the cooling fins in the area of ​​the recesses that form the flow path are completely eliminated.

[0020] Advantageously, at least one cooling fin, which has a recess into which the guide wall projects, borders the combustion chamber. The plane of the at least one cooling fin advantageously intersects the combustion chamber.

[0021] The cylinder advantageously has both cooling fins that form an angle of 50° to 70° with the cylinder's longitudinal axis, as well as at least one cooling fin arranged transversely thereto. For this purpose, at least one further cooling fin is advantageously arranged on the downstream side, forming an angle of 0° to 40° with the cylinder's longitudinal axis. The at least one further cooling fin is advantageously attached to a cooling fin that forms an angle of 50° to 70° with the cylinder's longitudinal axis. Preferably, the at least one further cooling fin extends exclusively on the downstream side of the implement.

[0022] The described designs are advantageous both individually and in virtually any combination. For example, a recess into which a guide wall extends can also be advantageous for a tool in which the cooling air is guided in only one or two partial air streams. The cooling fins of the internal combustion engine can also be aligned perpendicular to the cylinder's longitudinal axis. The internal combustion engine can also be a four-stroke engine. The guidance and distribution of the partial air streams can also be achieved in other ways.

[0023] An embodiment of the invention is explained below with reference to the drawings. They show: Fig. 1 a schematic side view of a chainsaw, Fig. 2 a schematic sectional view of the two-stroke engine of the chainsaw from Fig. 1, Fig. 3 a schematic side view of the cylinder and fan wheel of the implement, illustrating the arrangement of the cooling fins, Fig. 4 a section through the working device on the fan wheel side, Fig. 5 a section along the line VV in Fig. 4, Fig. 6 a section along the line VI-VI in Fig. 4, the spark plug is not shown in section, Fig. 7 a section along the line VII-VII in Fig. 6, Fig. 8 a section along the line VIII-VIII in Fig. 5, Fig. 9 a section along the line IX-IX in Fig. 4, Fig. 10 a perspective view of the cylinder of the two-stroke engine, Fig. 11 a perspective view of the hood of the chainsaw from the side facing the cylinder, Fig. 12 a simplified schematic representation of the guidance of the first and second partial air flow in a plan view of the cylinder.

[0024] Fig. 1 shows a chainsaw 1 as an exemplary embodiment of a hand-held tool. The tool can also be a brush cutter, a blower, a hedge trimmer, a lawnmower, or the like. The chainsaw 1 has a housing 2, on which a rear handle 3 and a handle tube 4 for guiding the chainsaw 1 during operation are arranged. On the side facing away from the rear handle 3, a guide bar 5 projects forward from the housing 2, on which a saw chain 6 is driven in rotation. On the side of the handle tube 4 facing the guide bar 5, a protective bar 7 is held on the housing 2. The protective bar 7 is advantageously pivotally mounted and serves to trigger a chain brake device (not shown). The rear handle 3 and the handle tube 4 are formed on a handle housing 34. The handle housing 34 runs in the Fig. 1, in which the chainsaw 1 is parked on a flat, horizontal support surface 9, with a handle housing section along the underside of the housing 2. The handle housing 34 is connected to a motor housing 10 via three anti-vibration elements 37 in the exemplary embodiment. The housing 2 comprises a hood 14, which in the exemplary embodiment is placed on the motor housing 10. An internal combustion engine 8 is arranged in the motor housing 10, which serves to drive the saw chain 6. In the exemplary embodiment, the internal combustion engine 8 is a two-stroke engine. Instead of the two-stroke engine, another internal combustion engine 8, in particular a four-stroke engine, can also be provided. The internal combustion engine 8 is advantageously a single-cylinder engine. The internal combustion engine 8 has a cylinder longitudinal axis 11, which in the Fig. 1, the position of the chainsaw 1 forms an angle α with the support surface 9 that is less than 90°. The angle α can be, for example, approximately 60° to 80° and, in the exemplary embodiment, opens upward toward the rear side of the chainsaw 1, which encompasses the rear handle 3. The combustion engine 8 is therefore arranged tilted backward in the housing 2.

[0025] Fig. Figure 2 shows the structure of the internal combustion engine 8 schematically. The internal combustion engine 8 has a cylinder 38 in which a combustion chamber 39 is formed. A spark plug 49 projects into the combustion chamber 39. The combustion chamber 39 is defined by a piston 40, which, via a connecting rod 41, drives a crankshaft 42 rotatably mounted in a crankcase 43. The crankshaft 42 is rotatably mounted about a crankshaft rotation axis 50. The crankshaft 42 is in Fig. 2 is shown schematically. In the cylinder 38, a cylinder bore 36 is formed, into which an inlet port 45 opens with an inlet window 46 controlled by the piston 40. An exhaust port 47 leads from the combustion chamber 39, the exhaust window 48 of which is also controlled by the piston 40. In the area of ​​the Fig. At the bottom dead center of the piston 40 shown in Figure 2, the interior of the crankcase 43 is connected to the combustion chamber 39 via transfer ports 44. The transfer ports 86, through which the transfer ports 44 open into the combustion chamber 39, are also controlled by the piston 40.

[0026] During operation, the upwardly moving piston draws in fuel / air mixture or combustion air via the inlet port 45 into the interior of the crankcase 43. During the downward stroke of the piston 40, the mixture is compressed in the crankcase 43 and, as soon as the transfer ports 86 of the transfer ports 44 open, flows into the combustion chamber 39. In the combustion chamber 39, the mixture is compressed by the piston 40 moving upwards towards the spark plug 49. In the region of the top dead center of the piston 40, the spark plug 49 is ignited. Due to the combustion, the piston 40 is accelerated towards the crankcase 43. As soon as the exhaust port 48 opens, the exhaust gases escape from the combustion chamber 39. The fuel can be introduced into the inlet port 45, into the crankcase 43, into one or more of the transfer ports 44, or directly into the combustion chamber 39.

[0027] During operation, a large amount of heat is generated at the cylinder 38. For cooling purposes, a fan wheel 12 is fixed to the crankshaft rotation axis 50, which Fig. 3 is shown schematically and which, during operation, rotates with the crankshaft 42 about the crankshaft rotation axis 50 and thereby conveys cooling air. The fan wheel 12 rotates in a direction of rotation 80. As Fig. 3 shows, the internal combustion engine 8 has a plurality of cooling fins 18 to 27, which are arranged in Fig. 3 are shown schematically. The cooling fins 18 to 27 run to the cylinder longitudinal axis 11 at an angle β which is from 50° to 70°, in particular from 55° to 65°. Advantageously, all cooling fins 18 to 27 are inclined by the same angle β to the cylinder longitudinal axis 11. In the exemplary embodiment, the cooling fins 18 to 27 run at an angle β to a transverse plane 54 of the internal combustion engine 8. The cooling fins 18 to 27 run parallel to the crankshaft axis of rotation 50. The transverse plane 54 is the plane which contains the cylinder longitudinal axis 11 and the crankshaft axis of rotation 50. The cooling fin 27 is at a distance d1 from the crankshaft axis of rotation 50. The distance d1 is measured perpendicular to the plane of the cooling fin 27 up to a reference line 62 which runs parallel to the cooling fin 27 and passes through the crankshaft rotation axis 50.The adjacent cooling fin 26, which is arranged closer to the crankcase 43 of the internal combustion engine 8 than the cooling fin 27, has a distance d2 from the crankshaft rotation axis 50 that is smaller than the distance d1. The distance d3 to d. 10 The cooling fins 18 to 25 further decrease toward the crankshaft rotation axis 50. The distances between the cooling fins 18 to 27 are advantageously approximately constant. The cooling fin 27 is the cooling fin located furthest from the crankshaft rotation axis 50. The cooling fins 18 to 27 can also be inclined to the cylinder longitudinal axis 11 by a different angle β, in particular by an angle β of 90°.

[0028] How Fig. As shown in Figure 4, the cooling fin 27 extends in the area of ​​the spark plug 49. As a result, the cooling fin 27 heats up considerably during operation. The cooling fin 26, which has the second-largest distance from the crankshaft rotation axis 50 of the cooling fins 18 to 27 inclined at an angle β to the cylinder's longitudinal axis 11, is also arranged close to the spark plug 49 and thus heats up considerably during operation.

[0029] The cylinder 38 is arranged in a cylinder chamber 15, which is delimited by the housing 2 of the chainsaw 1. The cylinder chamber 15 refers to the area of ​​the housing interior of the housing 2 in which the cylinder 38 is arranged. The cylinder chamber 15 is partially delimited by the hood 14. As Fig. 4, the hood 14 comprises a front boundary wall 16 which defines the cylinder chamber 15 in the direction of an exhaust silencer and the guide rail 5 ( Fig. 1). In the exemplary embodiment, a rear boundary wall 17 is also provided, which limits the cylinder chamber 15 in the direction of the intake tract of the chainsaw 1 and the rear handle 3 ( Fig. 1). The hood 14 forms an upper boundary wall 61 for the cylinder chamber 15, which defines the cylinder chamber 15 in the Fig. 1. The boundary walls 16, 17, and 61 extend at a short distance from the cooling fins 18 to 27, so that the cooling air flow is directed closely past the cylinder 38. A felling bar 31 is arranged on the hood 14 and is formed as a raised portion on the upper boundary wall 61. With the aid of the felling bar 31, the felling direction can be controlled when cutting a felling notch into a tree.

[0030] How Fig. 4 shows, the fan impeller 12 is arranged in a fan housing 13. The fan housing 13 widens spirally in the direction of rotation 80 of the fan impeller 12. The fan impeller 12 has a plurality of fan impeller blades 81 which, during operation, convey a cooling air flow 57. The cooling air flow 57 flows tangentially from the fan impeller 12. In the exemplary embodiment, the cooling air flow 57 is directed in an arc from the fan housing 13 towards the cylinder 38. There, the cooling air flow 57 flows approximately in the direction of the cooling fins 18 to 27 through the cooling fins 18 to 27. The arrangement is such that the cooling air flow 57 is divided into several partial air flows. In the exemplary embodiment, the cooling air flow 57 is divided into three partial air flows, namely a first partial air flow 58, a second partial air flow 59 and a third partial air flow 60. Partial air flows 58, 59, and 60 are the main cooling air flows. Additional partial air flows may be provided.The cooling air also flows into other areas through gaps between the components that restrict the cooling air flow. These gap air flows account for only a very small proportion of the total cooling air flow and are not considered here.

[0031] The first partial air flow 58 and the second partial air flow 59 initially flow toward the hood 14. The first partial air flow 58 and the second partial air flow 59 flow to the uppermost cooling fins 26 and 27 and, in the region of the cooling fins 26 and 27, onto the side of the cylinder 38 facing away from the fan wheel 12. In the exemplary embodiment, the spark plug 49 is arranged entirely on a spark plug side 55 of the internal combustion engine 8. The spark plug side 55 is the side of the transverse plane 54 on which the spark plug 49 is arranged. In the exemplary embodiment, the spark plug side 55 is the side of the transverse plane 54 on which the inlet channel 45 runs. The internal combustion engine 8 has an exhaust side 56, which is the side of the transverse plane 54 opposite the spark plug side 55 and on which the exhaust port 47 of the internal combustion engine 8 is arranged. In the exemplary embodiment, a Fig. 4 is arranged. The third partial air flow 60 of the cooling air flow 57 flows laterally along the cylinder 38 between the cooling fins 18 to 24. The third partial air flow 60 is directed by the inclined cooling fins 18 to 24 toward the exhaust side 56 facing the exhaust port 47. However, it can also be provided that the spark plug 49 extends on both sides of the transverse plane 54. The spark plug side 55 is, in particular, the side of the transverse plane 54 on which the rear handle 3 is also located.

[0032] Fig. Figure 5 shows the course of the first partial air flow 58, the second partial air flow 59, and the third partial air flow 60 in detail. The cylinder 38 has a center plane 51, which contains the cylinder longitudinal axis 11 and is perpendicular to the crankshaft rotation axis 50 ( Fig. 4). The internal combustion engine 8 has a fan wheel side 52, which is the side of the center plane 51 on which the fan wheel 12 is arranged. The internal combustion engine 8 also has an outflow side 53, which is the opposite side of the center plane 51 and on which the cooling air flows out of the chainsaw 1. On the fan wheel side 52, a flow path 67 is formed on the cylinder 38, which also Fig. 6. The flow path 67 is formed by cutouts 66 in the cooling fins 24 to 27. The flow path 67 is delimited by a side wall 82 of the housing 2 and the rear boundary wall 17 as well as by the cutouts 66, as Fig. 9. The flow path 67 denotes a free space formed between the housing walls 82, 17 and the cylinder 38, through which the first partial air flow 58 and the second partial air flow 59 flow.

[0033] The cutouts 66 in the exemplary embodiment are arranged approximately rectangularly one above the other and are formed as cutouts from the cooling fins 24 to 27. The cutouts 66 each have a longitudinal side 89 running approximately parallel to the center plane 51, which is at a distance c from the center plane 51. The first partial air flow 58 and the second partial air flow 59 can flow through the cutouts 66 on the fan wheel side 52 and on the spark plug side 55 along the cylinder 38. The first partial air flow 58 and the second partial air flow 59 flow from the flow path 67 between the cooling fins 24 to 27 and between the upper cooling fin 27 and the upper boundary wall 61 of the cylinder chamber 15. As Fig. 5 shows, the first partial air flow 58 flows at the Fig. 5 partially in front of the blade plane side along the spark plug 49 to the downstream side 53. The second partial air flow 59 flows at the in Fig. 5 side behind the blade plane along the spark plug 49 to the downstream side 53.

[0034] How Fig. 5 also shows, the cooling fin 24 projects close to a side wall 82 of the hood 14. The cooling fin 24 is wide and projects beyond the adjacent cooling fins 18 to 23 and 25 to 27. As a result, the cooling fin 24 separates the third partial air flow 60 from the partial air flows 58 and 59, so that the third partial air flow 60 is directed between the cooling fins 18 to 24 on the fan wheel side 52 to the outlet side 56 ( Fig. 4) flows.

[0035] The design of the cooling fin 24 is in Fig. 6 in detail. The cooling fin 24 has an outer edge 68, which designates the area of ​​the cooling fin 24 furthest from the center plane 51. The outer edge 68 of the cooling fin 24 has a distance a from the center plane 51. The cooling fin 25 located above it, further away from the crankshaft rotation axis 50 (see Fig. 3) has an outer edge 69, which has a distance b from the center plane 51. The distance b is significantly smaller than the distance a. The distance b is advantageously less than 95%, in particular less than 90% of the distance a. The underlying cooling fins 18 to 24 are also significantly narrower, as Fig. 5. As a result, the cooling fin 24 acts like a flow divider, separating the third partial air flow 60 from the first partial air flow 58 and the second partial air flow 59. The distance c of the longitudinal side 89 from the center plane 51 is significantly smaller than the distance a and the distance b. The distance b is advantageously at least 1.5 times, in particular at least 1.8 times, preferably at least twice the distance c.

[0036] The Fig. 5 and Fig. 6 also show the cooling air flow on the downstream side 53 in detail. The first, uppermost cooling fin 27 has a recess 63 on the downstream side 53, and the second cooling fin 26 located therebelow has a recess 64. The recesses 63 and 64 are completely on the spark plug side 55 ( Fig. 4). It can also be provided that the recesses 63 and / or 64 extend partially onto the fan wheel side 52 and / or partially onto the outlet side 56. Both recesses 63 and 64 are approximately rectangular and arranged approximately congruently one above the other. The recesses 63 and 64 extend on the spark plug side 55 ( Fig. 4). A guide wall 65 projects into the recesses 63 and 64. In the exemplary embodiment, the guide wall 65 is formed on the hood 14. The guide wall 65 causes a deflection of the first partial air flow 58. In the exemplary embodiment, a deflection of the cooling air flowing between the first cooling fin 27 and the upper boundary wall 61 as well as a deflection of the cooling air flowing between the cooling fins 26 and 27 is provided. This cooling air strikes the guide wall 65, which is transverse, in particular approximately perpendicular to the flow direction of the first partial air flow 58, adjacent to the spark plug 49. The extension of the guide wall 65 up to the side of the cooling fin 26 facing the cooling fin 25 is in Fig. 4. How Fig. 4 also shows, the lower edge 87 of the guide wall 65 facing the fan housing 13 runs parallel to the cooling fin 26.

[0037] In further preferred embodiments not shown, three or more cooling fins can have recesses into which a guide wall, preferably guide wall 65, projects. The contour of the recesses advantageously has at least a partially concave shape. The shape of the guide wall is advantageously adapted to the shape of the contour of the recesses. It can also be provided that overlapping recesses have different contours. The guide wall is advantageously adapted to the different contours.

[0038] How Fig. 6, the first partial air flow 58 is deflected by the guide wall 65 toward the exhaust side 56, i.e., toward the transverse plane 54. As a result, the partial air flow 58 is guided for a longer time along the hot areas of the cylinder 38, particularly the areas of the cylinder 38 located directly adjacent to the combustion chamber 39, resulting in improved cooling of these areas. The first partial air flow 58 also flows over a longer distance close to the spark plug 49. As Fig. As also shown in Figure 6, additional cooling fins 28 and 29 are arranged on the first cooling fin 27, which extend approximately perpendicularly from the cooling fin 27 to the side facing away from the cooling fin 26. The cooling fins 28 and 29 are aligned approximately in the direction of the partial air streams 58 and 59. The cooling fins 28 and 29 extend only on the downstream side 53.

[0039] Due to their orientation, the cooling fins 28 and 29 can separate the first partial air flow 58 and the second partial air flow 59. In the exemplary embodiment, the cooling fins 28 and 29 adjoin the spark plug 49 and extend close to the outflow opening 70. The cooling fins 28 and 29 can thus separate the first partial air flow 58 and the second partial air flow 59 downstream of the spark plug 49. Advantageously, in most operating states, in particular at full load, the second partial air flow 59 has a higher pressure and volume flow than the first partial air flow 58. The separation between the first partial air flow 58 and the second partial air flow 59 prevents already heated cooling air from the second cooling air flow 59 from being pushed back into the area of ​​the guide wall 65, which would impair cooling in the area of ​​the spark plug 49.A guide rib 32 is arranged on the hood 14, which also separates the first partial air flow 58 and the second partial air flow 59. The second partial air flow 59 can be completely directed onto the outlet side 56 (. Fig. 4) or partly on the exhaust side 56 and partly on the spark plug side 55.

[0040] In Fig. 6, the flow of the second partial air flow 59 on the opposite side of the spark plug 49 is also visible. The first partial air flow 58 flows past the spark plug 49 on the spark plug side 55. The second partial air flow 59 flows past the spark plug 49 on the opposite side of the spark plug 49. Particularly in the case of a tool in which the spark plug 49 is intersected by the transverse plane 54, it is advantageously provided that the first partial air flow 58 flows past the spark plug 49 on the side of the spark plug 49 facing the rear handle 3 and that the second partial air flow 59 flows past the side of the spark plug 49 that faces the section of the guide rail 8 protruding from the housing 2. In the exemplary embodiment, the first partial air flow 58 flows past the side of the spark plug 49 that faces away from the transverse plane 54. The second partial air flow 59 flows past the side of the spark plug 49 which faces the transverse plane 54.In the exemplary embodiment, the spark plug 49 is arranged entirely on the spark plug side 55 of the chainsaw 1. Cooling air therefore flows around the spark plug 49 on both sides. On the hood 14, as shown. Fig. 6 shows, an outflow opening 70 is provided on the downstream side 53, through which the first partial air flow 58 and the second partial air flow 59 leave the cylinder chamber 15. The third partial air flow 60 is also advantageously guided around the cylinder 38 and exits the cylinder chamber 15 through the outflow opening 70. In Fig. 6 shows a mounting opening 33 on the cylinder 38 for a decompression valve of the internal combustion engine 8.

[0041] The Fig. 5 and Fig. 6 also shows the dimensions of the recesses 63 and 64 and their design in detail. The recess 63 has a longitudinal side 73 which runs approximately parallel to the central plane 51 and which is at a distance e from the central plane 51. The recess 64 has a longitudinal side 75 which runs approximately parallel to the longitudinal side 73 and to the central plane 51 and is at a distance f from the central plane 51. The distances e and f are comparatively small and can, for example, correspond approximately to the cylinder bore. The cooling fin 25 located below the cooling fin 26 is significantly wider in this area and has no recess. The outer side 77 of the cooling fin 25 has a distance g from the central plane 51 which is significantly greater than the distances e and f. The distance g is advantageously at least 1.2 times, in particular at least 1.5 times, preferably at least approximately twice the distances e and f.Outside the recess 63, the first cooling fin 27 has an outer side 88 (. Fig. 6), which is at a distance 1 from the center plane 51. The distance 1 is significantly greater than the distance e and the distance f. The distance 1 is advantageously at least 1.5 times, in particular at least 1.8 times, preferably at least twice the distance e or the distance f. The guide wall 65 runs close to the long sides 73 and 75 and preferably parallel to the long sides 73 and 75. The guide wall 65 is at a distance o from the long sides 73 and 75 which is comparatively small. The distance o is advantageously less than 2 cm, in particular less than 1 cm, preferably less than 0.5 cm. Due to the guide wall 65, despite the comparatively large recesses 63 and 64, good cooling of the cylinder 38 during operation is nevertheless achieved.

[0042] The cutouts 63 and 64 have transverse sides 74 and 76 that run approximately perpendicular to the center plane 51. The cutout 63 has the transverse side 74 that runs parallel to the transverse side 76 of the cutout 64. The transverse sides 74 and 76 run parallel to a wall section 83 of the hood 14, which borders the guide wall 65 at approximately a right angle and directs the partial air flow 58 toward the outlet opening 70. The wall section 83 also extends into the cutouts 63 and 64.

[0043] How Fig. 6 also shows, the cylinder 38 has fastening openings 71 which are used for fixing to the crankcase 43 ( Fig. 2). The recesses 63 and 64 are arranged above a mounting opening 71. The cooling fins 25 and 24 located below have openings 84 for a tool for fixing fastening screws, which protrude through the mounting openings 71. In Fig. 6 also shows a cooling fin 30 which is arranged on the cooling fin 25 and runs transversely thereto.

[0044] How Fig. As shown in Figure 7, the cooling fin 26 extends in a plane 79 that intersects the combustion chamber 39 adjacent to the spark plug 49. This allows for effective heat dissipation, particularly at the second cooling fin 26. The cooling fin 27 extends in a plane above the combustion chamber 39.

[0045] How Fig. 8 shows, the transverse side 74 of the recess 63 has a distance h measured perpendicular to the transverse plane 54 and the transverse side 76 of the recess 64 has a distance i measured perpendicular to the transverse plane 54. The distances h and i are comparatively small. The wall section 83 of the guide wall 65 runs immediately adjacent to the transverse sides 74 and 76. The third cooling fin 25 located underneath has a transverse side 78 which is at a distance k from the transverse plane 54. The distance k is significantly greater than the distances h and i and is advantageously at least 1.1 times, in particular at least 1.2 times, the distances h and i. The transverse side 74 has a distance m from the wall section 83 which is advantageously less than 2 cm, in particular less than 1 cm. The distance m is advantageously measured at the point at which the distance between the transverse side 74 and the wall section 83 is minimal.The transverse side 76 has a minimum distance n from the wall section 83, which advantageously corresponds approximately to the distance m. The distance n is advantageously less than 2 cm, in particular less than 1 cm.

[0046] In Fig. 8 also shows the position of the cooling fins 28 and 29, which are arranged on the cooling fin 27, as well as the cooling fin 30, which is fixed on the cooling fin 25.

[0047] The cooling fins 28, 29 and 30 each extend only on the downstream side 53, as Fig. 6. The cooling fins 28, 29, and 30 form an angle γ with the transverse plane 54, which ranges from 0° to 40°, in particular from 10° to 30°. The cooling fins 28 to 30 are advantageously arranged perpendicular to the cooling fins 18 to 27. The cooling fins 28, 29, and 30 also allow a good cooling effect to be achieved in the upper region of the cylinder chamber 15. Fig. 8 also shows the outflow opening 70, which is formed on the hood 14, in detail. The guide rib 32 is arranged directly upstream of the outflow opening 70 and separates the first partial air flow 58, which flows on the spark plug side 55, from the second partial air flow 59, which flows on the exhaust side 56. This ensures in a simple manner that the two partial air flows 58 and 59 do not impede each other as they flow out of the cylinder chamber 15.

[0048] The outlet opening 70 is also in Fig. 9 in detail. The outlet opening 70 is formed as an opening in the hood 14. In Fig. 9 also shows the path of the third partial air flow 60. The third partial air flow 60 flows along the exhaust side 56 of the cylinder 38 facing away from the spark plug 49. The third partial air flow 60 also flows in the region of the exhaust duct 47 and adjacent to an exhaust silencer (not shown). On the fan wheel side 52, the cooling fins 21 and 23 have only a very small width, i.e., only a short distance from the center plane 51. Advantageously, the cooling fins 21 and 23 are set back relative to the cooling fins 20, 22, and 24. This widens the two channels formed between the cooling fins 20, 22, and 24, and improves the removal of contaminants.

[0049] Fig. Figure 10 shows the design of the recesses 63 and 64 and the cooling fins 28, 29 and 30 in detail. Fig. 10 shows, the cooling fins 26 and 27 extend on the downstream side 53 ( Fig. 5) essentially not on the outlet side 56 ( Fig. 8). This is also the case in Fig. 8, which shows a section on the downstream side 53. How Fig. 10 schematically shows, a partition wall 90 can be arranged between the cooling fins 26 and 27, which in Fig. 10 is shown schematically with a dashed line. Alternatively or additionally, a corresponding partition wall can be provided between the cooling fins 25 and 26. The partition wall 90 separates the first partial air flow 58 from the second partial air flow 59 and thereby prevents turbulence between the first partial air flow 58 and the second partial air flow 59 or the partial air flow 59 from being pushed back. This allows for effective cooling of the cylinder 38 and the spark plug 49.

[0050] Fig. 11 shows the hood 14 in detail. How Fig. 11, the guide rib 32 extends only in the area immediately upstream of the outlet opening 70. The outlet opening 70 is arranged adjacent to an opening 85 for the decompression valve. The opening 85 is also shown in Fig. 8 shown.

[0051] Fig. 12 shows the first partial air flow 58 and the second partial air flow 59 in a highly simplified, schematic representation. The two partial air flows 58 and 59 flow through the flow path 67 into the area of ​​the uppermost cooling fin 27. The first partial air flow 58 flows past the spark plug 49 on the spark plug side 55 of the transverse plane 54. The second partial air flow 59 flows along the spark plug 49 on the outlet side 56. It can also be provided that a portion of the second partial air flow 59 flows on the spark plug side 55. The guide wall 65 extends into the flow path of the first partial air flow 58 and deflects the flow in the direction of the transverse plane 54. As a result, the first partial air flow 58 is guided close to the spark plug 49. The second partial air flow 59 flows on the fan wheel side 52 along the cylinder 38 to the outlet side 56 and on the outlet side 56 from the fan wheel side 52 to the outflow side 53.On the downstream side 53, the first partial air flow 58 and the second partial air flow 59 leave the cylinder chamber 15 through the outflow opening 70. Upstream of the outflow opening 70, the first partial air flow 58 and the second partial air flow 59 are separated from one another by the guide fin 32. The partial air flows 58 and 59 can additionally or alternatively be separated from one another by the cooling fins 28 and 28 and the partition wall 90 of the cylinder 38, as shown in FIGS. Fig. 6 and Fig. 10. The separation of the partial air flows 58 and 59 can take place on the outlet side 56 or on the spark plug side 55 or in the transverse plane 54.

[0052] The terms “above” and “below” each refer to a position of the internal combustion engine 8 with the cylinder longitudinal axis 11 positioned vertically and the cylinder 38 arranged above the crankcase 43.

Claims

[1] Hand-held tool with a housing (2) in which an air-cooled internal combustion engine (8) is arranged, wherein the internal combustion engine (8) has a cylinder (38) which is arranged in a cylinder chamber (15) formed in the housing (2), wherein a combustion chamber (39) is formed in the cylinder (38) and is delimited by a piston (40) mounted to reciprocate in the direction of a cylinder longitudinal axis (11), wherein a spark plug (49) projects into the combustion chamber (39), wherein the piston (40) drives a crankshaft (42) rotatably mounted in a crankcase (43) about a crankshaft rotation axis (50), wherein a fan wheel (12) for conveying a cooling air flow (57) for the internal combustion engine (8) is fixed to the crankshaft (42), wherein the internal combustion engine (8) has a center plane (51) which defines the cylinder longitudinal axis (11) and which is perpendicular to the crankshaft rotation axis (50), wherein the side of the center plane (51),on which the fan wheel (12) is arranged, is a fan wheel side (52) of the working device, and wherein the opposite side is the outflow side (53), wherein the cylinder (38) has at least one cooling fin (18 to 27), wherein the internal combustion engine (8) has a transverse plane (54) which contains the cylinder longitudinal axis (11) and the crankshaft rotation axis (50), and wherein the working device has at least one spark plug side (55), wherein a spark plug side (55) of the working device is a side of the transverse plane (54) on which the spark plug (49) is at least partially arranged, , characterized by that on at least one spark plug side (55) at least one cooling fin (26, 27) has a recess (63, 64), and that a guide wall (65) of the housing (2) projects into the recess (63, 64) of the cooling fin (26, 27) and deflects at least a first partial air flow (58) of the cooling air flow (57) in the direction of the transverse plane (54). [2] Working device according to claim 1, characterized bythat the recess (63, 64) is arranged at least partially on the downstream side (53). [3] Working device according to claim 1 or 2, characterized by that the at least one cooling fin (26, 27) having the recess (63) extends to the spark plug (49). [4] Working device according to one of claims 1 to 3, characterized by that the first partial air flow (58) flows past the spark plug (49) on the spark plug side (55) and that a second partial air flow (59) flows past the spark plug (49) on the opposite side. [5] Working device according to claim 4, characterized by that a flow path (67) for the first and the second partial air flow (58, 59) is formed on the fan wheel side (52), through which the partial air flows (58, 59) flow from the fan wheel (12) to the upper side of the cylinder (38) facing away from the crankcase (43). [6] Working device according to claim 5, characterized bythat at least one cooling fin (24, 25, 26, 27) has a recess (66) in the region of the flow path (67). [7] Working device according to one of claims 4 to 6, characterized by that the housing (2) has an outflow opening (70) on the outflow side (53) through which cooling air flows out. [8] Working device according to claim 7, characterized by that the first partial air flow (58) and the second partial air flow (59) are at least partially separated from one another on the downstream side (53) upstream of the outflow opening (70). [9] Working device according to claim 8, characterized by that the housing (2) has a guide rib (32) which separates the first partial air flow (58) from the second partial air flow (59) at least in the region immediately upstream of the outlet opening (70). [10] Working device according to claim 9, characterized bythat the housing (2) has a hood (14) which delimits the cylinder chamber (15) on the side facing away from the crankcase (43) and on which the guide rib (32) and the outflow opening (70) are formed. [11] Working device according to one of claims 1 to 10, characterized by that a plurality of cooling fins (18 to 27) are provided, which enclose an angle (β) of 50° to 70° with the cylinder longitudinal axis (11), wherein the angle (β) is measured on the spark plug side (55) and opens towards the fan wheel (12), wherein each of the cooling fins (18 to 27) is at a distance (d1, d2, d3, d4, d5, d6, d7, d8, d9, d 10 ), and wherein at least one first cooling fin (27) which has the greatest distance (d1) from the crankshaft rotation axis (50) has the recess (63). [12] Working device according to claim 11, characterized bythat the guide wall (65) extends at least to a second cooling fin (26) which has the second greatest distance (d2) from the crankshaft rotation axis (50), and that a part of the first partial air flow (58) flows between the first cooling fin (27) and the second cooling fin (26) and is deflected by the guide wall (65). [13] Working device according to one of claims 1 to 12, characterized by that a third partial air flow (60) is guided along the cylinder (38) on the fan wheel side (52). [14] Working device according to claim 13, characterized by that one of the cooling fins (24) has an outer edge (68) on the fan wheel side (52), the distance (a) of which from the center plane (51) is greater than the distance (b) of the outer edges (69) of the adjacent cooling fins (23, 25) from the center plane (51) and which branches off the third partial air flow (60) from the cooling air flow (57). [15] Working device according to one of claims 1 to 14, characterized bythat an outlet window (48) for exhaust gases, controlled by the piston (40), leads from the combustion chamber (39), that the outlet window (48) is arranged on the outlet side (56) of the transverse plane (54) facing away from the spark plug side (55), and that the internal combustion engine (8) has an inlet window (46) for supplying fuel / air mixture into the crankcase (43), which is controlled by the piston (40) and is arranged on the spark plug side (55). [16] Working device according to one of claims 1 to 15, characterized by that the cylinder (38) has at least one fastening opening (71) for fixing the cylinder (38) on the crankcase (43), wherein the fastening opening (71) is accessible via openings (84) in the cooling fins (24, 25) and wherein the recess (63) comprises the area of ​​an opening (84).

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