CYLINDER, SINGLE-STROKE TWO-STROKE ENGINE AND WORKING DEVICE WITH A TWO-STROKE ENGINE

Description

[0001] The invention relates to a cylinder for a two-stroke engine, a two-stroke engine with one cylinder, and a working device with a two-stroke engine.

[0002] From DE 10 2009 059 144 A1, a two-stroke engine is known in which all transfer ports are combined below the exhaust port from the combustion chamber and flow together into the crankcase interior. To enable the cylinder to be manufactured using die casting, it is provided that the transfer ports towards the cylinder interior are limited by a cylinder liner or that the transfer ports are closed off to the outside with covers and that an insert is inserted into the cylinder from the crankcase side to limit the transfer ports.

[0003] From DE 10 2010 045 332 A1, a cylinder of a two-stroke engine is known which has a port projecting into the area of ​​the crankcase. Transfer ports from both sides of the cylinder lead into the crankcase through this port. The transfer ports are closed by covers.

[0004] The JP S60-224936 A reveals a two-stroke engine with a transfer port connected to three transfer ports. The cylinder has a collar that projects into the crankcase. The outlet opening into the crankcase interior is formed in this collar.

[0005] The invention is based on the objective of providing a cylinder for a two-stroke engine of the generic type, which has an advantageous design. A further objective of the invention is to provide a two-stroke engine with an advantageous design. A further objective of the invention is to provide a working device with a two-stroke engine having an advantageous design.

[0006] This problem is solved with respect to the cylinder by a cylinder having the features of claim 1. With respect to the two-stroke engine, the problem is solved by a two-stroke engine having the features of claim 6. With respect to the working device, the problem is solved by a working device having the features of claim 17.

[0007] Favorable emissions values ​​can be achieved with two-stroke engines in which all transfer ports are converged below the exhaust port. In this type of transfer port design, the ports leading to the intake-adjacent transfer ports are longer than those leading to the exhaust-adjacent transfer ports. To ensure that a sufficiently large proportion of air and fuel-air mixture is still supplied to the combustion chamber via the intake-adjacent transfer ports, a uniform deflection of the transfer ports with the largest possible deflection radii is desirable. For this purpose, it is advantageous if the deflection of the flow in the circumferential direction begins as far away from the transfer ports as possible within the crankcase.

[0008] For a cylinder, it is provided that the first section of the overflow channel is formed at least partially on a projection extending beyond the flange plane and that at least one side wall in the projection is convexly curved.

[0009] Because the side wall in the extension is convexly curved, the deflection of the transfer ports to both sides of the cylinder begins below the flange plane. This results in a gradual, slow deflection of the first section of the transfer port. This prevents flow separation in the transfer port and ensures good filling of the transfer ports and favorable flow characteristics into the combustion chamber.

[0010] Advantageously, the first section of the transfer channel has at least one inner wall that delimits the first section towards the cylinder bore. The inner wall is advantageously inclined towards the combustion chamber roof and the longitudinal axis of the cylinder. The transfer channel advantageously opens into the combustion chamber via at least one transfer port. Due to the inclination of the inner wall, the flow in the at least one transfer channel is already directed towards the combustion chamber, and in particular towards the at least one transfer port, as it extends into the combustion chamber.

[0011] In the crankcase, the transfer ports can be demolded using cores that extend longitudinally towards the cylinder connection flange, or – in the case of demolding along the crankshaft's axis of rotation – parallel to the crankshaft's axis of rotation. This is possible if the crankcase is split perpendicular to the crankshaft's axis of rotation. In the area where the crankcase halves separate, or where a slide of the injection mold ends, narrow burrs or irregularities can form on the transfer port wall, which are difficult to remove. It has been shown that even slight wall irregularities can lead to undesirable flow separation in the transfer port.

[0012] To largely avoid irregularities on the walls of the transfer channels or to position them at the greatest possible distance from the transfer windows, the invention provides that the first section of the transfer channel formed in the cylinder is at least partially formed on a projection of the cylinder extending beyond the flange plane. This extends the section of the transfer channel formed in the cylinder beyond the flange plane. Within this projection, the transfer channel is bounded by the cylinder along its entire circumference. This ensures favorable flow guidance. Particularly in the case of a die-cast cylinder, this allows for a largely free shaping of the transfer channels over a very long length in a simple manner.

[0013] The extension is advantageously formed as a single piece with the cylinder body. Preferably, the cylinder is formed as a single piece and has no liner, no inserts for closing the transfer ports to the inside of the cylinder, and no covers for closing the transfer ports to the outside of the cylinder. This results in a simple design, and the transfer ports are formed within the cylinder body over their entire circumference, thus avoiding wall irregularities at the transfer ports. A cylinder formed as a single piece is preferably manufactured by gravity casting. Undercuts can be readily produced using gravity casting.

[0014] The extension shifts the area where the two sections of the transfer port meet towards the inlet opening to the crankcase interior. This lengthens the section of the transfer port formed in the cylinder, thus promoting favorable flow characteristics within the cylinder. Particularly when the cylinder is manufactured using die casting, the transfer ports can be designed with large deflection radii, largely preventing flow separation at the port walls. This is especially advantageous for a cylinder with both intake and exhaust port transfer ports. This allows the proportion of air and fresh air mixture supplied via the intake port transfer ports to be adjusted as desired.

[0015] In an alternative embodiment, the extension is formed at least partially on an insert. This allows for the simple creation of a desired flow path. Advantageously, the insert is designed for placement within a receptacle in the cylinder. The insert projects, in particular, into a receptacle in the crankcase. However, it is also possible for the insert to be arranged entirely within a receptacle in the crankcase. In a particularly advantageous design, the insert is multi-part, especially in two parts. This allows the insert to be manufactured using an injection molding process, particularly without the use of cores. The cylinder can be manufactured using gravity casting or die casting.

[0016] In an advantageous embodiment, the extension has a substantially rectangular cross-section. The extent of the cross-section perpendicular to a central plane of the cylinder is advantageously larger than the extent of the cross-section parallel to the central plane of the cylinder. Other cross-sections of the extension may also be advantageous.

[0017] For a two-stroke engine, it is advantageously provided that the cylinder has a first circumferentially closed section of at least one transfer channel, and that the crankcase has at least a circumferentially closed second section of the at least one transfer channel.

[0018] Because the first section is at least partially formed in the extension, the section of the transfer channel formed in the cylinder is lengthened.

[0019] The crankcase is advantageously designed using die casting or injection molding, making it easy and cost-effective to manufacture.

[0020] Advantageously, the crankcase has a mounting surface for the cylinder. The cylinder connects to the crankcase at this mounting surface, advantageously with a gasket in between. The mounting surface is advantageously flat. It is provided that the mounting surface has a recess for the extension. The extension and the recess can be designed to work together to determine the position of the cylinder relative to the crankcase. The extension thus has a centering function. The extension advantageously sets the position of the cylinder relative to the crankcase without any play. Alternatively, the extension can be designed to project into the recess with some play.

[0021] Preferably, the two-stroke engine has several transfer ports that open into the crankcase through a common inlet. Advantageously, at least two transfer ports, and in particular all transfer ports of the two-stroke engine, run through the extension. This achieves favorable flow characteristics in the transfer ports and results in a simpler crankcase design. Alternatively, it is possible to provide two or more extensions, each carrying one or more transfer ports.

[0022] The crankcase has a crankcase plane that contains the axis of rotation of the crankshaft and runs perpendicular to the longitudinal axis of the cylinder. Advantageously, the inlet port and the cylinder are arranged on opposite sides of the crankcase plane. The inlet port is therefore located in a region of the crankcase furthest from the cylinder. This results in a long transfer port. It has been shown that this leads to advantageous flow conditions in the transfer ports and low exhaust emissions.

[0023] The two-stroke engine advantageously has a central plane that runs perpendicular to the axis of rotation of the crankshaft and contains the longitudinal axis of the cylinder. Advantageously, the crankcase is bounded by at least two partial shells that are connected to each other at a parting plane. The parting plane of the partial shells advantageously runs parallel to the central plane, at least in the section of the partial shells that bounds the crankcase. It is possible for the parting plane to coincide with the central plane of the two-stroke engine. However, it is also possible for the parting plane of the partial shells to be at a distance from the central plane.

[0024] Especially in two-stroke engines used in handheld power tools, a small installation space is desirable, resulting in a compact power tool. For this purpose, it is advantageously provided that the second section of the transfer port is located close to the crankcase interior. Advantageously, the second section of the transfer port has a subsection in which at least one wall of the transfer port runs parallel to the cylinder's longitudinal axis. The wall running parallel to the cylinder's longitudinal axis is, in particular, the inner wall of the transfer port adjacent to the crankcase interior. This achieves a compact design. Due to the extension projecting into the crankcase beyond the flange plane, favorable flow guidance of the transfer port is still possible. Preferably, the distance between the inner and outer walls of the transfer port decreases in this subsection in the direction of flow towards the combustion chamber.

[0025] Advantageously, the cylinder has a collar that projects beyond the flange plane into the crankcase, and the cylinder bore runs along the inside of this collar. Preferably, the collar is spaced at every point from the extension. The collar and the extension are therefore formed separately from each other. It can be provided that the collar and the extension together define the position of the cylinder relative to the crankcase, in particular ensuring a zero-play position.

[0026] For a machine with a two-stroke engine, an exhaust silencer is connected to the exhaust port and is located in a silencer chamber. The crankcase has a wall section that defines the second section of the transfer port and the silencer chamber. The silencer chamber is therefore located directly on the outside of the crankcase. Advantageously, a gap is formed between the exhaust silencer and the wall section to prevent excessive heat transfer from the exhaust silencer into the crankcase. In particular, if the transfer port in the crankcase runs close to the crankcase interior, sufficient installation space can be provided for the exhaust silencer, resulting in a compact overall size for the machine.

[0027] The working device advantageously comprises an engine housing and an oil tank for supplying lubricant to a tool of the working device. The oil tank and the crankcase are advantageously integrated within the engine housing. The engine housing advantageously includes a partition wall that delimits the second section of the transfer channel and the oil tank. If the transfer channel in the crankcase is located close to the crankcase interior, a sufficiently large installation space for the working device's oil tank can be ensured. The working device is, in particular, a chainsaw, and the tool is a saw chain. However, it is also possible for the working device to be another handheld tool. The working device can, in particular, be an angle grinder, a brush cutter, a blower, or a lawnmower.

[0028] Exemplary embodiments of the invention are explained below with reference to the drawing. The drawing shows: Fig. 1 a schematic representation of an embodiment of a two-stroke engine, Fig. 2 a schematic representation of a chainsaw, Fig. 3 a partial view of the cylinder of another embodiment of a two-stroke engine, Fig. 4 a partial side view of a partial shell of a crankcase of the two-stroke engine, Fig. 5 the cylinder made of Fig. 3 and the partial shell of the crankcase made of Fig. 4 In a partial, schematic side view, Fig. 6 shows a schematic sectional view through the cylinder and crankcase from the Figs. 3 to 5 , Fig. 7 a sectional view of the cylinder made of Fig. 6 , Fig. 8 a view of the cylinder from Fig. 7 in the direction of arrow VIII in Fig. 7 , Fig 9 a view of the cylinder from Fig. 7 in the direction of arrow IX in Fig. 7 , Fig. 10 a section through the cylinder made of Fig. 7 along line XX in Fig. 7, where the non-visible course of the overflow channels is shown with a dashed line, Fig. 11 a side view of a cast of the overflow channels, Fig. 12 a side view in the direction of arrow XII in Fig. 11 Fig. 13 a sectional view of an exemplary embodiment of a cylinder, Fig. 14 a partial view of the cylinder in the direction of arrow XIV in Fig. 13 Fig. 15 shows a partial sectional view through the cylinder before the installation of an insert part; Fig. 16 shows a view of the cylinder in the direction of arrow XVI. Fig. 15 , Fig. 17 a perspective view of the insert part made of Fig. 14 and 15 , Fig. 18 an exploded view of the insert part made of Fig. 17 , Fig. 19 a section through the insert part along line XIX-XIX in Fig. 15 , Fig. 20 a section through the insert part along line XX-XX in Fig. 19 , Fig. 21 a view of the insertion part in the direction of arrow XXI in Fig. 20 , Fig. 22 a view of the insertion part in the direction of arrow XXII in Fig. 20 Fig. 23 shows a perspective sectional view of the cylinder and crankcase of a two-stroke engine not according to the invention; Figs. 24 and 25 show perspective views of an upper part of the crankcase of the two-stroke engine made of Fig. 23 .

[0029] Fig. 1Figure 1 schematically shows a first embodiment of a two-stroke engine 1. The two-stroke engine 1 is a single-cylinder engine. In this embodiment, the two-stroke engine 1 is a scavenging engine. The two-stroke engine 1 has one cylinder 2. A cylinder bore 27 is formed in the cylinder 2. The cylinder 2 has a longitudinal axis 24, which is the central axis of the cylinder bore 27. A combustion chamber 3 is formed in the cylinder 2. The combustion chamber 3 is bounded by a piston 5, which is mounted to reciprocate in the cylinder 2 along the longitudinal axis 24. The piston 5 drives a crankshaft 7 via a connecting rod 6. The crankshaft 7 is rotatably mounted in a crankcase interior 9 of a crankcase 4. The crankshaft 7 is rotatably mounted in the crankcase 4 about an axis of rotation 8. The crankshaft 7 serves to drive a tool of a machine.

[0030] The two-stroke engine 1 has several transfer ports 10, 11 that fluidically connect the crankcase interior 9 to the combustion chamber 3 in the region of the piston's bottom dead center 5. Fig. 1The piston 5 is shown at its bottom dead center. The transfer ports 10, 11 open into the cylinder bore 27 via transfer ports 46, 47. In this embodiment, the transfer ports 10, 11 are combined into a common section 45 and open into the crankcase interior 9 through a common inlet 28. The transfer ports 10, 11 have a first section 29, which is bounded by the cylinder 2. The first section 29 is closed over its entire circumference and is fully formed within the cylinder 2. The section 29 comprises a subsection in which the transfer ports 10 and 11 run together, and subsections in which the transfer ports 10 and 11 run separately from each other. In the section 29, the transfer ports 10, 11 are not open at their circumference towards the cylinder bore 27.The transfer ports 10, 11 have a second section 30, which is bounded by the crankcase 4 and is also closed around its entire circumference. In the exemplary embodiment, all transfer ports 10, 11 are guided together in the second section 30. In the exemplary embodiment, the second section 30 forms part of the common section 45 in which the transfer ports 10, 11 are guided together.

[0031] The two-stroke engine 1 has an air filter 23 through which combustion air is drawn in during operation. The two-stroke engine 1 has a mixture channel 12 that opens into a mixture inlet 13 at the cylinder bore 27. In the exemplary embodiment, the mixture inlet 13 is controlled by the piston 5 and is open towards the crankcase interior 9 in the region of the piston 5's top dead center. A section of the mixture channel 12 is formed in a carburetor 16. The carburetor 16 contains a throttle element 17 and, in the exemplary embodiment, additionally a choke element 18. Fuel is supplied to the air drawn in through the air filter 23 in the carburetor 16. In the exemplary embodiment, an additional air channel 14 is provided for supplying scavenging air. An air control element 19 for controlling the quantity of scavenging air supplied is mounted in the air channel 14. In the exemplary embodiment, the elements for controlling the flow cross-section are designed as pivotably mounted flaps.

[0032] Alternatively, a common throttle element can be provided for the mixture channel 12 and the air channel 14. In this embodiment, the throttle element is advantageously arranged in a common intake channel, which is advantageously divided downstream of the carburetor 16 into the air channel 14 and the mixture channel 12.

[0033] The air duct 14 opens with two air inlet openings 15 at the cylinder bore 27, of which in Fig. 1 One is shown. The second air inlet opening 15 is symmetrical to the section plane in Fig. 1 arranged. The air inlet openings 15 are also controlled by the piston 5. The piston 5 has two piston pockets 20, of which in Fig. 1one is visible. The piston pockets 20 connect the air inlet openings 15 in the region of the top dead center of the piston 5 with the transfer ports 46 and 47. Air from the air duct 14 can be pre-ported into the transfer channels 10 and 11 via the piston pockets 20.

[0034] An exhaust port 21 leads from combustion chamber 3 into an exhaust channel 22. The exhaust port 21 is also controlled by piston 5.

[0035] During operation, on the upward stroke of piston 5, after the opening of the mixture intake 13, the mixture is drawn into the crankcase interior 9. At the top dead center of piston 5, air is drawn into the transfer ports 10 and 11 via the air intake openings 15 and the piston pockets 20. On the downward stroke of piston 5, the mixture in the crankcase interior 9 is compressed. As soon as the transfer ports 46 and 47 are opened by piston 5 into the combustion chamber 3, scavenging air flows from the transfer ports 10 and 11 into the combustion chamber 3, purging exhaust gases from the previous engine cycle out of the combustion chamber 3. Fresh mixture then flows from the crankcase interior 9 into the combustion chamber 3. The mixture in the combustion chamber 3 is compressed by the upward-moving piston 5 and ignited by a spark plug (not shown) in the area of ​​the top dead center of the piston 5.Due to the combustion that then takes place, piston 5 is accelerated towards the crankcase 4. As soon as piston 5 opens the exhaust port 21, exhaust gases from combustion chamber 3 flow out through the exhaust port 21 and the exhaust channel 22. As soon as the transfer ports 46 and 47 are opened by piston 5, scavenging air and subsequently fresh air-fuel mixture for the next engine cycle flow into combustion chamber 3.

[0036] The cylinder 2 has a connecting flange 25 for fixing it to the crankcase 4. The cylinder 2 rests on the crankcase 4 with a flange plane 26 formed on the connecting flange 25. Advantageously, a seal is arranged between the cylinder 2 and the crankcase 4. Fig. 1As shown, cylinder 2 has a projection 31 that extends beyond the flange plane 26 into the crankcase 4. Part of section 29 of the transfer ports 10, 11 is guided within this projection 31. This extends the section of the transfer ports 10 and 11 formed in cylinder 2.

[0037] The two-stroke engine 1 is advantageously the drive motor in a hand-held work device. Fig. 2Figure 32 shows a chainsaw 32 as an embodiment of a hand-held power tool. The chainsaw 32 has a guide bar 33 on which a saw chain 34 is arranged circumferentially. The saw chain 34 is the cutting tool of the chainsaw 32. The saw chain 34 is driven by the two-stroke engine 1. For guiding the chainsaw 32 during operation, the chainsaw 32 has a rear handle 35 and a handle 36. Other types of handles may also be provided. A hand guard 37 runs along the side of the handle 36 facing the saw chain 34. The hand guard 37 may be provided for triggering a chain brake (not shown) of the saw chain 34. The chainsaw 32 has an exhaust silencer 41, which is connected to the exhaust port 22 ( Fig. 1The chainsaw 32 has an engine housing 38, which is vibrationally decoupled from the handles 35 and 36 by means of vibration elements (not shown). The engine housing 38 includes an oil tank 39 and a fuel tank 40. The two-stroke engine 1 is arranged on the engine housing 38. Advantageously, the crankcase 4 is at least partially formed as a single unit with parts of the engine housing 38. The oil tank 39 serves to lubricate the saw chain 34. The oil tank 39 is arranged adjacent to the exhaust silencer 41 and the crankcase 4 of the two-stroke engine 1. The fuel tank 40 is arranged adjacent to the rear handle 35.

[0038] Fig. 3 Figure 1 shows a partial illustration of an embodiment of cylinder 2. The same reference numerals denote corresponding components in all embodiments. In the embodiment shown, cylinder 2 is... Fig. 3formed in one piece. The cylinder 2 has a base body 54 on which the transfer ports 10, 11 ( Fig. 1 ), the extension 31 and a collar 42 are formed. Cooling fins 55 are also formed on the cylinder 2. The extension 31 and the collar 42 project beyond the flange plane 26 to the crankcase 4. A section of the cylinder bore 27 is formed in the collar 42, as shown. Fig. 6 shows how Fig. 3As shown, the extension 31 and the collar 42 are spaced a distance b apart. The extension 31 and the collar 42 are therefore formed separately and project from the connecting flange 25 in different areas. The extension 31 has a length a. Length a is measured from the flange plane 26 to an end face 68 of the extension 31. The overflow channels 10, 11 open at the end face 68. The length a is advantageously at least 2.5 mm, particularly at least 5 mm, and preferably at least 10 mm. Preferably, the length a is at most 15 mm. Length a is measured parallel to the longitudinal axis 24 of the cylinder. The collar 42 has a length c. Length c is also measured parallel to the longitudinal axis 24 of the cylinder. In the exemplary embodiment, length c is greater than length a. However, it is also possible for length a to be greater than length c or for lengths a and c to be equal.

[0039] In this embodiment, the crankcase 4 is composed of two partial shells, which are divided perpendicular to the axis of rotation 8 of the crankshaft 7. In this embodiment, the crankcase 4 is formed on the engine housing 38. The partial shells of the engine housing 38 form the partial shells of the crankcase 4 in this embodiment. Fig. 4 shows a partial shell 66 of the motor housing 38. Fig. 4Figure 1 shows a view parallel to the axis of rotation 8 of the crankshaft 7 onto a parting line 50 of the engine housing 38. At the parting line 50, the two partial shells 66 of the engine housing 38 abut each other, particularly with a gasket in between. The engine housing 38 may be made of metal. In this case, the engine housing 38 is advantageously formed from two partial shells 66 produced by die casting. Alternatively, the engine housing 38 may be made of plastic. In this case, the partial shells 66 are advantageously formed as injection-molded parts and joined together at the parting line 50. The partial shells 66 may be joined together, for example, by a welding process, particularly an ultrasonic welding process.

[0040] How Fig. 4As shown, the crankcase 4 has a support surface 56 for the cylinder 2. The connecting flange 25 is to be arranged on the support surface 56, in particular with a gasket in between. A recess 57 for the extension 31 is formed in the support surface 56. A filler piece 59 projects beyond the support surface 56 into the cylinder 2. The filler piece 59 projects as follows: Fig. 6 The figure shows the interior of the cylinder bore 27. A space 67 is formed between the filler piece 59 and the cylinder bore 27, into which the piston 5 plunges at bottom dead center. A wall section 58 is formed between the recess 57 and the filler piece 59, separating the recess 57 from the space 67. How Fig. 6 As shown, the collar 42 protrudes into the space 67.

[0041] Fig. 5Figure 1 shows the engine housing 38 with the cylinder 2 and a schematically depicted exhaust silencer 41 arranged on the cylinder 2. The exhaust silencer 41 is arranged in a silencer chamber 64, which is bounded by the engine housing 38 and the cylinder 2. The extension 31 projects into the recess 57. Fig. 5 As also shown, a wall section 65 runs between the second section 30 of the overflow channel 10, 11 and the silencer chamber 64. The wall section 65 borders both the overflow channel 10, 11 and the silencer chamber 64. The second section 30 of the overflow channel 10, 11 is guided along one side of the wall section 65, and the silencer chamber 64 is formed on the other side of the wall section 65.

[0042] An intermediate wall 49 is formed on the engine housing 38, which forms part of the crankcase 4 and delimits the second section 30 of the transfer channel. The intermediate wall 49 forms part of the wall of the oil tank 39 and delimits the oil tank 39. This allows for a large volume of the oil tank 39.

[0043] The second section 30 of the transfer channel 10, 11 is located close to the crankcase interior 9. This is also shown in Fig. 6The second section 30 has an inner wall 51 facing the crankcase interior 4. The second section 30 also has an outer wall 52 that is located further away from the crankcase interior 9 than the inner wall 51. The second section 30 has a subsection 53 in which the inner wall 51 runs parallel to the cylinder longitudinal axis 24. In the exemplary embodiment, the outer wall 52 is slightly inclined relative to the cylinder longitudinal axis 24. The inclination of the outer wall 52 is selected such that the distance d between the inner wall 51 and the outer wall 52 decreases in the flow direction towards the combustion chamber 3. In the exemplary embodiment, the distance d decreases over the entire subsection 53. However, it is possible for the distance d to decrease only over a portion of the subsection 53. Fig. 6 It also shows the course of the air duct 14 up to the air inlet opening 15.

[0044] Fig. 6Figure 1 also shows the position of the inlet opening 28, through which the transfer ports 10, 11 are connected to the crankcase interior 9. The crankcase 4 has a crankcase plane 60. The crankcase plane 60 runs perpendicular to the longitudinal axis 24 of the cylinder and contains the axis of rotation 8 of the crankshaft 7. In the exemplary embodiment, the inlet opening 28 and the cylinder 2 are arranged on opposite sides of the crankcase plane 60. The inlet opening 28 is therefore located on the side of the crankcase plane 60 that is furthest from the cylinder 2. This allows for a long transfer port length 10, 11 and thus a favorable flow pattern.

[0045] How Fig. 6 As also shown, the collar 42 projects beyond the flange plane 26 to the crankcase 4. The collar 42 projects into the space 67 between the filler piece 59 and the wall section 58.

[0046] Fig. 7Figure 2 shows a section through cylinder 2. As the illustration shows, the transfer window 47 of the transfer channel 11 is located closer to the mixture inlet 13 than the transfer window 46 of the transfer channel 10. The cylinder also has a pulse channel 48, which is connected to a fuel pump (not shown) of the carburetor 16 ( Fig. 1 ) is connected and this is controlled by the fluctuating pressure in the crankcase interior 9 ( Fig. 1 ) drives.

[0047] As the Fig. 6 and 7 As shown, cylinder 2 has an inlet flange 61 to which the air channel 14 and the mixture channel 12 are led. Advantageously, a connecting nozzle is attached to the inlet flange 61, through which combustion air is drawn in.

[0048] Fig. 8 shows a view of the connecting flange 25 in the direction of the cylinder longitudinal axis 24. How Fig. 8As shown, the collar 42 and the extension 31 are formed separately from each other and have a distance b between them. In the extension 31, the transfer channels 10, 11 of the opposite sides of the cylinder 2 are brought together. The cylinder 2 has a median plane 63 that divides the extension 31 in the middle and contains the longitudinal axis 24 of the cylinder. Fig. 8 shows a view of the combustion chamber roof 43 in cylinder 2. How Fig. 8 As also shown, the cylinder flange has 25 screw openings 44, to which the cylinder 2 can be screwed onto the crankcase 4.

[0049] How Fig. 8As shown, section 29 of the transfer channels 10 and 11 in extension 31 has an outer wall 76 located away from the cylinder longitudinal axis 24, an inner wall 77 opposite the outer wall 76, and two side walls 78 connecting the inner wall 77 and the outer wall 76. The side walls 78 delimit the first section 29 of the transfer channels 10 and 11 circumferentially with respect to the cylinder longitudinal axis 24. The inner wall 77 delimits the first section 29 towards the cylinder bore 27. The outer wall 76 delimits the first section 29 on the side facing away from the cylinder bore 27. Fig. 8 As also shown, extension 31 has an elongated, approximately rectangular cross-section.

[0050] The separating plane 50 of the motor housing 38, which is in Fig. 4The drawing plane can coincide with the median plane 63. Alternatively, the separating plane 50 can be arranged at a distance from the median plane 63. The separating plane 50 is advantageously arranged parallel to the median plane 63. The separating plane 50, which is in Fig. 8 which coincides with the central plane 63, divides the extension 31, so that in each partial shell 66 of the crankcase 4 a part of the second section 30 of the transfer channels 10 and 11 is formed.

[0051] Fig. 9 shows a side view of cylinder 2, specifically the inlet flange 61. Fig. 10 Figure 1 shows a section through cylinder 2 in the area of ​​extension 31, with the course of the transfer ports 10 and 11 in cylinder 2 partially shown with a dashed line. As the Figs. 9 and 10As shown, the transfer channels 10 and 11 are bounded by the one-piece base body 54 of the cylinder 2. No separate elements, such as covers or the like, are provided that close off the transfer channels 10 and 11 to the outside of the cylinder 2.

[0052] In Fig. 10 The extension 31 is shown in section. The extension 31 has a width f measured perpendicular to the central plane 63. The width f is smallest at the end face 68. With increasing distance from the end face 68, i.e., in the direction of the combustion chamber roof 43 ( Figs. 7 and 8 The width f of the overflow channels 10 and 11 in the extension 31 increases. As a result, the side walls 78 of the first section 29 in the extension 31 form undercuts towards the end face 68 of the extension 31. Therefore, the section of overflow channels 10 and 11 formed in the extension 31 cannot be molded using a die-casting process with a drawn core.

[0053] How Fig. 10As shown, in the exemplary embodiment, the side walls 78 are curved in the extension 31. The side walls 78 are curved in the direction from the front face 68 towards the combustion chamber roof 43 ( Figs. 7 and 8 The side walls 78 are convexly curved. This causes the flow to be deflected to the opposite sides of the central plane 63 and to the transfer ports 46 and 47 as early as extension 31. This allows for comparatively large bending radii of the flow deflection. A gradual deflection of the flow in the transfer ports 10 and 11 counteracts flow separation in the first section 29 of the transfer ports 10 and 11. This allows a sufficiently high proportion of air to be supplied to the combustion chamber 3 via the transfer ports 11 near the intake. This improves scavenging in the combustion chamber 3 and reduces the proportion of mixture that can enter the exhaust port 22 unburned.

[0054] The course of overflow channels 10 and 11 is also shown in the Figures 11 and 12 The position of the end face 68 and the flange plane 26 is shown in the Figures 11 and 12 schematically represented with dashed lines. In Fig. 11 The curvature of the side walls 78 is visible in the area between the end face 68 and the flange plane 26. This curvature is also visible in cylinder 2, namely from the flange plane 26 to the transfer ports 46 ( Fig. 14 ) and 47, the side walls are 78 arcuate.

[0055] How Fig. 12 As shown, the outer wall 76 of the transfer channels 10 and 11, located furthest from the cylinder's longitudinal axis 24, is inclined to the cylinder's longitudinal axis 24 in the area between the end face 68 and the flange plane 26. The outer wall 76 is inclined towards the cylinder's longitudinal axis 24 in the direction from the end face 68 towards the flange plane 26. Therefore, at the flange plane 26, the outer wall 76 is closer to the cylinder's longitudinal axis 24 than at the end face 68. This is also evident in Fig. 7 shown. The outer wall 76 therefore does not form an undercut in the direction of the front face 68.

[0056] The inner wall 77 of the transfer channels 10 and 11, which is closer to the cylinder longitudinal axis 24, is inclined towards the combustion chamber roof 43, i.e. in the direction from the front face 68 to the flange plane 26, towards the cylinder longitudinal axis 24, as Fig. 7 The inner wall 77, due to its inclination, forms an undercut in a direction parallel to the cylinder longitudinal axis 24 and away from the combustion chamber roof 43. The inner wall 77 is closer to the cylinder longitudinal axis 24 in the flange plane 26 than at the end face 68.

[0057] The Figures 13 and 14Figure 1 shows an embodiment of a multi-part cylinder 2. The same reference numerals denote corresponding elements in all figures. The course of the transfer channels 10 and 11 corresponds to that of the preceding embodiment. The cylinder 2 has a base body 54 into which an insert 70 is inserted. In this embodiment, the insert 70 forms the extension 31. In an alternative embodiment, part of the extension 31 can be formed by the insert 70 and another part of the extension 31 by the base body 54 of the cylinder 2. The insert 70 is arranged in a receptacle 69 of the base body 54. In this embodiment, the receptacle 69 is designed as a recess in the flange plane 26. In this embodiment, the insert 70 has a shoulder 83 that abuts the flange plane 26 and thereby limits the insertion depth of the insert 70.

[0058] Fig. 14 The insert part 70 is shown in the recording 69. How Fig. 14 As shown, the insert part 70 has a widened area 81 which can be arranged flush with the flange plane 26. Advantageously, the widened area 81 does not protrude beyond the flange plane 26 from the receptacle 69.

[0059] Figs. 15 and 16 show the base body 54 of the cylinder 2 in the area of ​​the receptacle 69 without the insert part 70 arranged in the receptacle 69.

[0060] The Figures 17 to 20 The design of the insert part 70 is shown in detail. The insert part 70 has a section 84, which is to be arranged in the receptacle 69. The insert part 70 also has the extension 31. The section 84 comprises the widened area 81. How Figs. 17 and 18As shown, the side walls 78 in the widened area 81 are convexly curved in the direction of flow. The widened area 81 allows for comparatively large bending radii of the side walls 78 in this area. Fig. 17 As shown, the insert 70 has a projection 79 on the side furthest from the extension 31. A flow divider 80 is formed on the projection 79, as well as Fig. 19 The flow divider 80 separates overflow channels 10 and 11, whose overflow windows 46, 47 are arranged on one side of the central plane 63, from the overflow channels 10 and 11, whose overflow windows 46 and 47 are arranged on the other side of the central plane 63.

[0061] As the Figures 17 and 18 As shown, the insert part 70 is composed of two parts 71 and 72, which are joined together at a parting line 73. As the Figures 17, 18 and 20As shown, the parting line 73 is curved. The curvature of the parting line 73 advantageously follows approximately the curvature of the inner wall 77 and / or the curvature of the outer wall 76 of the overflow channels 10 and 11. Fig. 18 As shown, part 71 has positioning projections 75 that protrude into the images 82 of the other part 72. Fig. 20 Image 82 is shown as an example.

[0062] Fig. 19 Figure 1 shows the curvature of the side walls 78 relative to each other. The side walls 78 are curved away from each other, so that the distance f between the side walls 78 increases with increasing distance from the front face 68.

[0063] Fig. 20 Figure 1 shows the curvature of the outer wall 76 and the inner wall 77. The outer wall 76 and the inner wall 77 are advantageously curved in the same direction, so that the distance of the outer wall 76 to the inner wall 77 in the extension 31 is approximately constant.

[0064] The Figures 21 and 22Figures 81 show the widened area and the course of the overflow channels 10 and 11 in the insert section 70. How Fig. 22 As shown, the side walls 78 extend into the widened area 81.

[0065] The design of the overflow channels 10 and 11 in the embodiment according to Figs. 13 to 20 advantageously corresponds to the design of the overflow channels 10 and 11 of the preceding embodiment, so that with regard to further features reference is made to the description of the respective other embodiment.

[0066] The cylinder 2 can also be mounted on a differently designed crankcase 4 to form a two-stroke engine 1. In the exemplary embodiment, the cylinder 2 is mounted on a crankcase 4 in which a second section 30 of the transfer channel 10, 11 is formed. It is also possible to mount the cylinder 2 on a crankcase 4 in which no section of transfer channels 10, 11 is formed.

[0067] The cylinder 2 is advantageously manufactured by gravity casting in all embodiments. In particular, for a cylinder 2 with an insert 70, production by die casting is also possible.

[0068] An independent, separate, non-inventive idea concerns the aspects contained in the Figs. 23 to 25 The illustrated design of a two-stroke engine 1. The same reference symbols denote corresponding elements in all figures. How Fig. 23As shown, the alternative embodiment of the two-stroke engine 1 comprises a cylinder 2 and a crankcase 4. The crankcase 4 is composed of an upper shell 90 and a lower shell 91. The shells 90 and 91 are connected to each other at a dividing plane 92, which contains the axis of rotation 8 of the crankshaft 7. The two-stroke engine 1 includes two transfer ports 10, which are guided in a common section 45. The common section 45 is bounded in the cylinder 2 by a raised portion 93 of the upper shell 90 of the crankcase 4. As the Figs. 24 and 25 As shown, the elevation 93 limits the common section 45 both in the direction towards the cylinder longitudinal axis 24 and in the circumferential direction to the cylinder longitudinal axis 24. The cylinder 2 limits the common section 45 radially outwards with respect to the cylinder longitudinal axis 24.

[0069] In the exemplary embodiment according to Figs. 23 to 25No extension 31 is provided on cylinder 2. Instead, the upper shell 90 of the crankcase 4 has an extension 94 that projects beyond the parting line 92 into the lower shell 91. As the Figs. 24 and 25 As shown, the extension 94 delimits the second section 30 of the overflow channels 10 over their entire circumference. The extension 94 forms an outer wall 76, an inner wall 77, and two side walls 78 that delimit the overflow channels 10. The extension 94 exhibits, as shown in particular Fig. 24 shows an approximately rectangular cross-section. Fig. 23 Figure 1 shows a section through the central plane 63 of cylinder 2. Perpendicular to the central plane 63, the transfer channel 10 in the extension 94 has a significantly greater extent than parallel to the central plane 63, as shown by the Figs. 24 and 25 show how the Figs. 23 to 25 As shown, the common section 45 of the overflow channels 10 is the only section of an overflow channel that extends over the flange plane 26.

[0070] By arranging a raised section 93 and a projection 94 on an upper partial shell 90 of the crankcase 4, simple demolding is possible during production using a die-casting process. The curvature of the side walls 78 and the inner wall 77 can begin directly within the crankcase 4. This facilitates easy manufacturability and favorable flow guidance through the transfer ports.

Claims

1. Cylinder for a two-stroke engine (1), wherein the cylinder (2) has at least one first section (29) of an overflow channel (10, 11), wherein the cylinder (2) has a cylinder longitudinal axis (24), wherein the cylinder (2) has a combustion chamber roof (43) and a flange plane (26) for connection to a crankcase (4), wherein the first section (29) has at least one side wall (78) which delimits the first section (29) in the circumferential direction of the cylinder (2), wherein the first section (29) of the overflow channel (10, 11) is formed at least partially on an extension (31) of the cylinder (2) projecting beyond the flange plane (26), wherein the first section (29) is circumferentially closed in the extension (31), wherein the first section (29) in the extension (31) has an outer wall (76) remote from the cylinder longitudinal axis (24), an inner wall (77) opposite the outer wall (76), and two side walls (78) connecting the inner wall (77) and the outer wall (76), and wherein at least one side wall (78) runs in the extension (31) in a convexly curved manner.

2. Cylinder according to Claim 1, characterized in that the inner wall (77) delimits the first section (29) with respect to the cylinder bore (27) and is inclined towards the cylinder longitudinal axis (24) in the direction of the combustion chamber roof (43).

3. Cylinder according to Claim 1 or 2, characterized in that the extension (31) is formed in one part with a main body (54) of the cylinder (2).

4. Cylinder according to Claim 1 or 2, characterized in that the extension (31) is formed at least partially on an insertion part (70).

5. Cylinder according to one of Claims 1 to 4, characterized in that the extension (31) has a substantially rectangular cross section.

6. Two-stroke engine having a cylinder (2) according to one of Claims 1 to 5 and having a crankcase (4), wherein the two-stroke engine (1) has at least one overflow channel (10, 11), wherein the two-stroke engine (1) has a combustion chamber (3) which is formed in the cylinder (2) and is delimited by a piston (5) which is mounted so as to move in a reciprocating manner in the cylinder (2), wherein the piston (5) drives a crankshaft (7) which is mounted rotatably in a crankcase (4), wherein the at least one overflow channel (10, 11) fluidically connects a crankcase interior (9) of the crankcase (4) to the combustion chamber (3) in at least one position of the piston (5), wherein the overflow channel (10, 11) has the first section (29) and a circumferentially closed second section (30) delimited by the crankcase (4).

7. Two-stroke engine according to Claim 6, characterized in that the crankcase (4) has a bearing surface (56) for the cylinder (2), wherein the bearing surface (56) has a depression (57) for the extension (31).

8. Two-stroke engine according to Claim 7, characterized in that the extension (31) and the depression (57) interact in order to fix the position of the cylinder (2) with respect to the crankcase (4).

9. Two-stroke engine according to one of Claims 6 to 8, characterized in that the two-stroke engine (1) has a plurality of overflow channels (10, 11) which pass into the crankcase interior (9) at a common inlet opening (28).

10. Two-stroke engine according to Claim 9, characterized in that at least two, in particular all, overflow channels (10, 11) of the two-stroke engine (1) run through the extension (31).

11. Two-stroke engine according to one of Claims 6 to 10, characterized in that the crankcase (4) has a crankcase plane (60) which contains the axis of rotation (8) of the crankshaft (7) and runs perpendicularly with respect to the cylinder longitudinal axis (24), and in that the inlet opening (28) and the cylinder (2) are arranged on opposite sides of the crankcase plane (60).

12. Two-stroke engine according to one of Claims 6 to 11, characterized in that the two-stroke engine (1) has a central plane (63) which runs perpendicularly with respect to the axis of rotation (8) of the crankshaft (7) and which contains the cylinder longitudinal axis (24), and in that the crankcase (4) has at least two part shells (66) which are connected to one another at a parting plane (50), wherein the parting plane (50) of the crankcase (4) runs parallel to the central plane (63).

13. Two-stroke engine according to one of Claims 6 to 12, characterized in that the second section (30) of the overflow channel (10, 11) has a subsection (53), in which at least one wall of the overflow channel (10, 11), in particular the inner wall (51) lying adjacent to the crankcase interior (7), runs parallel to the cylinder longitudinal axis (24).

14. Two-stroke engine according to Claim 13, characterized in that the distance (d) between the inner wall (51) and the outer wall (52) of the overflow channel (10, 11) in this subsection (53) decreases in the flow direction towards the combustion chamber (3).

15. Two-stroke engine according to one of Claims 6 to 14, characterized in that the cylinder (2) has a collar (42) which projects beyond the flange plane (26) into the crankcase (4) and on the inner side of which a section of the cylinder bore (27) runs.

16. Two-stroke engine according to Claim 15, characterized in that the collar (42) is at a distance (b) from the extension (31) at each point.

17. Work apparatus having a two-stroke engine according to one of Claims 6 to 16, wherein an outlet channel (22) leads out of the cylinder (2) and is adjoined by an exhaust silencer (41) which is arranged in a silencer space (64), wherein the crankcase (4) has a wall section (65) which delimits the second section (30) of the overflow channel (10, 11) and the silencer space (64).

18. Work apparatus according to Claim 17, characterized in that the work apparatus (32) has a motor housing (38) and an oil tank (39) for supplying a tool of the work apparatus with lubricant, in that the oil tank (39) and the crankcase (4) are formed in the motor housing (38), and in that the motor housing (38) has an intermediate wall (49) which delimits the second section (30) of the overflow channel (10, 11) and the oil tank (39).