Fuel supply device and two-stroke engine having a fuel supply device

Abstract

A fuel supply device (20) has a base body (21) with an intake channel section (22) into which a main fuel inlet (24) opens. A throttle valve (25) is provided for controlling the free flow cross-section of the intake channel section (22), which is pivotably mounted about a pivot axis (45). The fuel supply device (20) has a partition section (27) which extends at least also upstream of the throttle valve (25) in the intake channel section (22) and which divides the intake channel section (22) into a mixture channel (18), into which the fuel inlet (23, 24) supplies fuel, and an air channel (19). The partition section (27) has a recess (48) in which the throttle valve (25) is at least partially located in an end position (52).The partition section (27) has a continuous mixture channel surface (41) facing the mixture channel (18) upstream of the recess (48). This surface has lateral sections (54) adjacent to the intake channel wall (56) and a central section (53) extending between the lateral sections (54). The lateral sections (54) have a separation edge (43) upstream of the throttle valve (25) for the flow in the mixture channel (18). The side (57) of the throttle valve (25) facing the mixture channel (18) in the end position (52) of the throttle valve (25) defines a reference plane (60) that divides the fuel supply device into a first area (71), in which the throttle valve (25) is located, and a second area (72). The lateral sections (54) extend at least directly upstream of the recess (48) into the second area (72) of the fuel supply device.

Description

[0001] The invention relates to a fuel supply device of the type specified in the preamble of claim 1 and to a two-stroke engine with a fuel supply device.

[0002] German patent DE 10 2005 003 559 A1 discloses a fuel supply device, namely a carburetor, in which the intake port is divided into a mixture port and an air port. A partition wall section is provided for this purpose within the carburetor. To prevent an uncontrolled leaning of the fuel / air mixture when the throttle valve pivots from a fully open to a closed position, means are provided for unthrottling the mixture port and / or restricting the air port. For this purpose, the partition wall section can be angled towards the throttle valve.

[0003] In particular, when the throttle valve is fully open, the overflow of fuel into the air duct should be avoided in such fuel supply devices, which are especially intended for two-stroke engines operating with scavenging.

[0004] From DE 10 2005 003 559 A1, it is known to provide the partition section upstream of the throttle valve with a flattening. This ensures that the front face of the throttle valve, located in the direction of flow, is exposed to the flow even when the throttle valve is fully open.

[0005] US patent 2021 / 0095619 A1 describes a fuel supply device in which the partition section upstream of the throttle valve is provided with a flattened section.

[0006] DE 10 2006 032 475 A1 discloses a carburetor in which a flow guide element is arranged upstream of the throttle valve. Instead of one flow guide element, two flow guide elements can be provided, spaced apart from each other.

[0007] DE 103 62 394 B3 discloses a carburetor arrangement in which the partition is designed as a separate component. The partition is flat immediately upstream of the recess.

[0008] DE 10 2010 054 838 A1 discloses a carburetor with a partition section between the throttle valve and the choke valve.

[0009] The invention is based on the objective of creating a fuel supply device with good operating characteristics.

[0010] This problem is solved by a fuel supply device having the features of claim 1.

[0011] Because the central section of the mixture channel surface lies at least directly upstream of the recess in the first region, the upstream face of the throttle valve is exposed to the flow when the throttle valve is open. This means that when the throttle valve is slightly closed from the fully open position, the flow conditions change less drastically at the face of the throttle valve. This prevents an uncontrolled leaning of the mixture when the throttle valve closes. Since the lateral sections lie in the reference plane or in the second region, the mixture is guided over the connecting ports and not towards them.

[0012] This allows the proportion of mixture passing into the air duct when the throttle valve is closed and when the throttle valve is opened to be reduced compared to known designs.

[0013] The lateral sections are particularly preferably located at least directly upstream of the recess in the second area, so that mixture flowing in the mixture channel is directed over the connecting openings.

[0014] To simplify the manufacturing of the intake manifold section and to ensure complete, defined closure of the throttle valve in its first end position, the intake manifold section in the area of ​​the throttle shaft bearings is typically machined. The machining area usually extends beyond the throttle shaft bearing area to prevent jamming and tilting of the throttle valve in areas where it protrudes close to the intake manifold wall, even with unfavorable manufacturing tolerances. In this area, a narrow connecting opening between the intake manifold wall and the throttle valve is formed.If the partition section extends into this area to close the connecting opening, it cannot be formed as a single piece with the base body of the fuel supply unit, as otherwise machining the intake manifold section in the area of ​​the throttle shaft bearing would no longer be possible. With a separately formed partition section inserted into the base body of the fuel supply unit, it must be ensured that the partition section extends both to the throttle shaft and laterally to the intake manifold wall to ensure a good seal, and that the movement of the throttle shaft is not obstructed by the partition section. This makes the manufacturing of the fuel supply unit more complex.

[0015] It has now been shown that a complex seal between the throttle shaft and the partition section running upstream of the throttle shaft can be omitted and good operating behavior can still be achieved if the lateral sections of the partition section extend at least directly upstream of the recess in which the throttle valve is located in the end position into the second area of ​​the fuel supply device.

[0016] The two sections of the fuel supply system are defined by conceptually dividing the fuel supply system into two parts at the reference plane. The throttle valve is located in the first section when it is in its end position. The end position of the throttle valve, in which it is at least partially within the recess, is the open end position. In this end position, the throttle valve advantageously forms part of a partition that divides the intake manifold into the mixture channel and the air channel. In this end position, the throttle valve advantageously opens the flow cross-section in the intake manifold to a large extent. Advantageously, the throttle valve also has a further, closed end position in which it largely closes the flow cross-section in the intake manifold.

[0017] Because the lateral sections extend directly upstream of the recess into the second area, the flow in the mixture channel is diverted away from the connecting openings formed between the partition section and the throttle valve in the area of ​​the lateral sections. This eliminates the need for a complex seal between the partition section and the throttle shaft, and largely prevents fuel from passing into the air channel in the aforementioned end position of the throttle valve.

[0018] The central section of the partition wall will be referred to as the middle section in the following. The side sections of the partition wall will be referred to as the side sections in the following.

[0019] The central section and the side sections are portions of a continuous mixture channel surface of the partition section facing the mixture channel and are located upstream of the recess. The mixture channel surface is therefore uninterrupted. This allows fuel to flow freely from the central section to the side sections. The side sections and the central section are portions of the partition section's surface along which the mixture can flow in the second end position of the throttle valve, i.e., the mixture channel surface. Upstream of the throttle valve, the side sections form a separation edge for the flow in the mixture channel. This allows the flow to be guided from the central section to the side sections and from there across the connecting openings formed in the partition section between the throttle valve, intake manifold wall, and partition section.Due to this design, the flow in the mixture channel advantageously does not flow through the connecting openings into the air duct, but rather flows past the connecting openings and remains within the mixture channel. The connecting openings extend between the throttle valve, the partition, and the intake manifold wall. The connecting openings have a substantially triangular shape, with one side of the triangle being curved.

[0020] The flow in the mixture channel is guided over the throttle valve and does not impinge on the front face of the throttle valve in the lateral sections. This allows the flow in the mixture channel to be effectively guided over the connecting openings. Preferably, the mixture channel surface in the lateral sections does not slope downwards relative to the reference surface in the direction of flow, but rather runs parallel to the reference plane or rises relative to the reference plane. This ensures that the mixture flowing along the mixture channel surface in the lateral sections is guided over the connecting openings.

[0021] The middle section lies at least partially within the first area. As a result, in the second end position of the throttle valve, the flow in the mixture channel at least partially affects the front surface of the throttle valve. When the throttle valve is pivoted from the fully open position, the proportion of the front surface of the throttle valve exposed to the mixture in the mixture channel increases continuously. Because the front surface is also exposed to the mixture in the second end position of the throttle valve, the change in flow when the throttle valve opens is comparatively small, thus preventing disturbances in mixture formation due to abrupt changes in pressure at the fuel inlet, especially at a main fuel inlet.Due to the curvature of the throttle valve's front surface, the mixture flowing towards the side sections and from there across the connecting openings is at least partially directed towards the side sections and from there across the connecting openings.

[0022] Advantageously, the central section, at least immediately upstream of the recess, has a distance of at least 50% of the throttle valve thickness, and in particular at least 80% of the throttle valve thickness, from the reference plane. Advantageously, the central section, immediately upstream of the throttle valve recess, has a shorter distance to a partition plane of the partition than the lateral sections over a length that corresponds to at least 30%, and preferably at least 50%, of the throttle valve diameter. The length of the central section is measured parallel to the longitudinal center axis of the intake manifold section.

[0023] This allows the flow in the mixture channel to be influenced in such a way that no mixture, or only very small amounts of mixture, can enter the air duct via the connecting openings, while simultaneously preventing disturbances in mixture formation when the throttle valve opens from the second end position. In a particularly preferred embodiment, the central section has a smaller distance to the partition plane along its entire length than the lateral sections. This also allows for a comparatively large flow cross-section in the mixture channel. The lateral sections advantageously have a total width of at least 5 mm, and particularly at least 7 mm. The total width of the lateral sections is the sum of the individual widths of the two lateral sections. The total width is measured perpendicular to the longitudinal center axis of the intake duct section.

[0024] Advantageously, the lateral sections have a total width of at least 50% of the smallest width of the mixture channel area of ​​the partition section, and in particular at least 70% of the smallest width of the mixture channel area of ​​the partition section. The total width and the smallest width are measured perpendicular to the longitudinal center axis.

[0025] The central section advantageously has a width that is at least 30%, and preferably at least 50%, of the smallest width of the mixture channel area of ​​the partition section. The widths of the lateral sections and the central section are measured perpendicular to the longitudinal center axis and at the mixture channel area.

[0026] Preferably, the lateral sections are inclined at least immediately upstream of the separation edge towards the reference plane. The lateral sections can be inclined in a cross-sectional plane perpendicular to the longitudinal center axis relative to the reference plane. Alternatively or additionally, it is preferably provided that the lateral sections are inclined in a cross-sectional plane that contains the longitudinal center axis of the intake manifold section and is perpendicular to the pivot axis of the throttle valve, preferably rising in the flow direction relative to the reference plane. This allows the mixture in the mixture channel to be effectively diverted away from the connecting opening. The lateral sections are particularly designed in the form of ramps.

[0027] In an advantageous embodiment, the separation edge extends across the entire width of the mixture channel surface of the partition wall section. In an alternative advantageous design, the mixture channel surface can transition into the bottom of the throttle valve recess. In this area, a transition without a separation edge can be provided.

[0028] In an advantageous embodiment, the central section is formed by a recess in the partition section. Preferably, the recess runs concavely in a cross-sectional plane perpendicular to the longitudinal center axis of the intake manifold section. However, a different recess orientation may also be advantageous. In a preferred embodiment, the bottom of the recess runs parallel to the longitudinal center axis of the intake manifold section. This parallel orientation is particularly advantageous in a cross-sectional plane perpendicular to the pivot axis of the throttle valve and parallel to the longitudinal center axis of the intake manifold section. It may also be possible for the recess to form a portion of the throttle valve opening.

[0029] In an advantageous embodiment, the lateral sections run in a radius perpendicular to the longitudinal center axis of the intake duct section. This radius abuts the intake duct wall and is at least 2 mm, and in particular at least 3 mm. Compared to known designs, the radius at which the partition section transitions into the intake duct wall is thus significantly increased. This increased radius alone is sufficient to direct the flow away from the connecting openings.

[0030] In an advantageous embodiment, the side sections connect to the central section on both sides. In an alternative advantageous embodiment, further sections may extend between the side sections and the central section, which may be located in the first or second region of the fuel supply device.

[0031] Advantageously, a choke element is arranged upstream of the partition section. The choke element is preferably a choke flap. In the open position of the choke flap and the second end position of the throttle valve, the choke flap, partition section, and throttle valve advantageously form an approximately continuous partition between the mixture channel and the air channel.

[0032] The partition wall section is particularly advantageous because it is formed as a single piece with the base body of the fuel supply system. This allows for a simple, uninterrupted transition between the mixture channel surface of the partition wall section and the intake manifold wall. The integral forming of the partition wall section with the base body also facilitates simple manufacturing. Due to the raised lateral sections of the mixture channel surface, the passage of mixture from the mixture channel into the air duct through the connecting openings formed between the intake manifold wall, the partition wall section, and the throttle valve is largely prevented. Simultaneously, a sufficiently long surface area is provided for machining the portion of the intake manifold section where the throttle valve is mounted. This results in both simple manufacturing of the fuel supply system and advantageous operational characteristics.

[0033] The fuel supply device is preferably used with a two-stroke engine, particularly with a two-stroke engine operating with scavenging. The air duct section of the fuel supply device preferably forms part of an air duct of the two-stroke engine, which serves to supply fuel-free air for pre-storage in the transfer ports of the two-stroke engine. The mixture duct section forms part of a mixture duct of the two-stroke engine, through which the mixture is advantageously supplied to the crankcase interior of the two-stroke engine.

[0034] The fuel supply device is provided in particular in a two-stroke engine, preferably in the two-stroke engine of a hand-held, advantageously a hand-carried, power tool. The fuel supply device is in particular a carburetor.

[0035] Exemplary embodiments of the invention are explained below with reference to the drawing. The drawing shows: Fig. 1 a schematic representation of a two-stroke engine operating with a scavenging system, Fig. 2 a schematic sectional view through a fuel supply device according to the invention, Fig. 3 a partial schematic sectional view along line III-III in Fig. 2 , Fig. 3a a partially enlarged view of the area of ​​the connecting openings made of Fig. 3 , Fig. 4 a partial schematic sectional view along line IV-IV in Fig. 2 , Fig. 5 a partial schematic sectional view along line VV in Fig. 2 , Fig. 6 a partial schematic view in the direction of arrow VI in Fig. 2 Figures 7 and 8 are schematic perspective longitudinal section views through the fuel supply system. Fig. 2 Fig. 9 shows a partial sectional view of a variant embodiment of the fuel supply device, Fig. 10 shows a partial view in the direction of arrow X in Fig. 9 , Fig. 11 the representation from Fig. 9 without throttle valve, choke valve, throttle shaft and choke shaft, Fig. 12 a partial view in the direction of arrow XII in Fig. 11 .

[0036] Fig. 1 Figure 1 schematically shows a two-stroke engine 1. The two-stroke engine 1 can advantageously be used as a drive motor in a power tool, particularly in a handheld power tool, for example, a chainsaw, an angle grinder, a blower, a brush cutter, a lawnmower, or the like. The two-stroke engine 1 has a cylinder 2 in which a combustion chamber 3 is formed. A piston 5 is mounted to reciprocate within the cylinder 2. The piston 5 drives a crankshaft 7, which is rotatably mounted about an axis of rotation 8 in a crankcase interior 9, via a connecting rod 6. The crankcase interior 9 is formed within a crankcase 4 and is separated from the combustion chamber 3 by the piston 5. An exhaust port 15 leads from the combustion chamber 3 for exhaust gases. A spark plug 32 projects into the combustion chamber 3.

[0037] A mixture channel 18 opens into cylinder 2, connected to a mixture inlet 10. The mixture inlet 10 opens into the crankcase interior 9 and is fluidically connected to the crankcase interior 9 in the region of the piston's top dead center. The piston 5 preferably has at least one piston pocket 14. The two-stroke engine 1 has transfer ports 12 that fluidly connect the crankcase interior 9 to the combustion chamber 3 in the region of the piston's bottom dead center. The transfer ports 12 open into the cylinder bore via transfer ports 13.

[0038] The two-stroke engine 1 comprises an air duct 19 that opens into an air inlet 11 at the cylinder bore of the cylinder 2. At the bottom dead center of the piston 5, the air inlet 11 is located in the area of ​​the piston pocket 14 and connects the air duct 19 to the transfer ports 13 of the transfer channels 12. In the exemplary embodiment, four transfer channels 12 are provided, of which 4 are shown in the sectional view. Fig. 1 Two are visible. A different number and / or shape of transfer ports 12 may also be advantageous. The transfer ports 12 connect the crankcase interior 9 in the region of bottom dead center 5 with the combustion chamber 3, so that fuel / air mixture can flow from the crankcase interior 9 into the combustion chamber 3 via the transfer ports 12. The transfer windows 13 are controlled by the piston 5 and open towards the combustion chamber 3 in the region of the piston 5's bottom dead center.

[0039] Combustion air is drawn in via an air filter 37. The air filter 37 has filter material 39 that separates a cleanroom 38 of the air filter 37 from the environment. The mixture channel 18 and the air channel 19 are connected to the cleanroom 38. Air is drawn in via an intake channel 16, which opens into the cleanroom 38 of the air filter 37. The intake channel 16 is separated from the air channel 19 and the mixture channel 18 by a partition 17 over at least part of its length.

[0040] A fuel supply device 20 is provided for supplying fuel. The fuel supply device 20 has a base body 21. An intake channel section 22 of the intake channel 16 is formed in the base body 21. The fuel supply device 20 can be a carburetor that supplies fuel depending on the vacuum prevailing in the intake channel section 22. In a preferred embodiment, the fuel supply device 20 is a diaphragm carburetor. In an alternative preferred embodiment, the fuel supply device 20 includes a fuel valve that is opened and closed by a control unit of the two-stroke engine 1. The fuel valve is, in particular, an electromagnetic valve, preferably a normally open valve or a normally closed valve.The fuel metered by the fuel valve is advantageously supplied to the intake duct section 22 due to the vacuum prevailing in the intake duct section 22.

[0041] A throttle valve 25 is arranged in the intake duct section 22. The throttle valve 25 is advantageously pivotably mounted to a throttle shaft 35. The throttle valve 25 has a diameter m. In the exemplary embodiment, the partition 17 has a partition section 27 upstream of the throttle shaft 35 and a partition section 28 downstream of the throttle shaft 35. The intake duct section 22 has a longitudinal center axis 29. The longitudinal center axis 29 is the axis that connects the geometric centers of the intake duct section 22 at the upstream and downstream end faces of the base body 21. During operation, the combustion air and the fuel / air mixture flow in the intake duct 16 essentially in one direction 30 from the air filter 37 to the cylinder 2. In the case of back pulsations, a flow in the opposite direction can also occur. The partition 17 divides the intake duct 16 into the mixture duct 18 and the air duct 19.In the fuel supply device 20, a main fuel opening 23 and several auxiliary fuel openings 24 open into the mixture channel 18. The main fuel opening 23 is arranged in the area of ​​a venturi section 31.

[0042] Fig. 2 Figure 1 shows the fuel supply device 20 schematically in detail in longitudinal section. The throttle valve 25 is pivotally mounted to the throttle shaft 35 about a pivot axis 45. How Fig. 2 As shown, a choke flap 26 is arranged in the intake manifold section 22 upstream of the throttle valve 25 with respect to the flow direction 30. The choke flap 26 is pivotally mounted about a pivot axis 46 by means of a choke shaft 36. In the exemplary embodiment, the longitudinal center axis 29 of the intake manifold section 22 intersects the pivot axes 45 and 46. However, it is also possible for the pivot axes 45 and 46 to be arranged offset from the longitudinal center axis 29 in the intake manifold section 22 and not to intersect the longitudinal center axis 29. The main fuel inlet 23 is formed on a main fuel nozzle 40, which is shown in the sectional view in Fig. 2 is shown partially cut away.

[0043] The intake duct section 22 has a central plane 50. The central plane 50 contains the longitudinal center axis 29 of the intake duct section 22 and runs parallel to the pivot axes 45 and 46. In the exemplary embodiment, the pivot axes 45 and 46 lie in the central plane 50.

[0044] Fig. 2 Figure 1 shows the choke valve 26 in its fully open end position. In this end position, a section of the choke valve 26 projects into a recess 49 of the partition section 27. The partition section 27 has a mixture channel surface 41. The mixture channel surface 41 of the partition section 27 is the surface that, in the illustrated end positions of the throttle valve 25 and choke valve 26, defines the mixture channel 18. The partition section 27 has an air channel surface 42, which, in the illustrated end positions of the throttle valve 25 and choke valve 26, defines the air channel 19. In the exemplary embodiment, the air channel surface 42 is planar and approximately parallel to the central plane 50. In the exemplary embodiment, the choke valve 26, in its fully open position, lies parallel to the central plane 50.

[0045] The throttle valve 25 is pivotable between a first end position 51, shown with a dashed line, and a second end position 52, shown with a solid line. In the first end position 51, the throttle valve 25 largely closes the flow cross-section in the intake manifold section 22. The first end position 51 preferably corresponds to the position of the throttle valve 25 at idle. In the exemplary embodiment, in the first end position 51, the throttle valve 25 is arranged completely downstream of the partition section 27. In the second end position 52, the throttle valve 25 largely opens the flow cross-section in the intake manifold section 22. In the second end position 52, the throttle valve 25 forms an angle α with the median plane 50. In this position, an upstream end face 58 of the throttle valve 25 lies on the side of the median plane 50 on which the mixture channel 18 runs.The downstream end face 62 of the throttle valve 25 lies on the side of the central plane 50 on which the air duct 19 runs. The angle α that the throttle valve 25 forms with the central plane 50 can also be 0°. A slight inclination of the throttle valve 25 in the opposite direction in its second end position 52 can also be provided.

[0046] The partition section 27 has a recess 48 on its side facing the mixture channel 18, into which the throttle valve 25 projects at least partially in its second end position 52. The partition section 27 and the throttle valve 25 overlap in the second end position 52, so that the partition section 27 is not completely upstream of the throttle valve 25 in the second end position 52. The partition section 27 is completely upstream of the throttle shaft 35. In the exemplary embodiment, the partition section 27 has a recess 47 on its side facing the mixture channel 18. Due to the recess 47, the mixture flowing in the mixture channel section 18 flows towards the end face 58 of the throttle valve 25, which is located opposite to the flow direction 30. In the exemplary embodiment, the recess 47 has a bottom 59, which runs parallel to the longitudinal center axis 29.In the exemplary embodiment, the bottom 59 of the recess 47 runs closer to the air duct 19 than the end face 58 in the longitudinal section shown through the longitudinal center axis 29. The recess 47 is advantageously arranged in the central section 43 of the partition wall section 27, which faces the mixture channel 18.

[0047] In the exemplary embodiment, the throttle valve 25 projects from the recess 48 over a circumferential region encompassing its entire thickness d. However, it can also be provided that, in the second end position 52, the end face 58 projects from the recess 48 into the mixture channel 18 only over a portion of the thickness d of the throttle valve 25. Advantageously, the throttle valve 25 projects from the recess 48 over a circumferential region by at least 50%, and in particular by at least 80%, of its thickness d.

[0048] The throttle valve 25 has a side 57 facing the mixture channel 18. Side 57 is a flat surface of the throttle valve 25. In the second end position 52 of the throttle valve 25, the mixture flows along side 57 during operation. In this second end position 52, side 57 limits the mixture channel 18. Side 57 of the throttle valve 25 forms a Fig. 2 Reference plane 60 is shown. In the Fig. 2 In the position of the fuel supply device 20 shown, the reference plane 60, i.e. also the side 57 of the throttle valve 25 facing the mixture channel 18, is arranged horizontally, and the fuel opening 23 formed on the main fuel nozzle 40 ( Fig. 1 ) is arranged above the partition wall section 27. In this position of the fuel supply device 20, the central section 53 of the mixture channel surface 41 runs below the reference plane 60.

[0049] The reference plane 60 divides the fuel supply system into two sections, namely a first section 71 and a second section 72. In the first section 71, the throttle valve 25 is arranged in its second end position 52. In the exemplary embodiment, the partition section 27 extends within the first section 71. The main fuel nozzle 40 is arranged in the second section 72 in the exemplary embodiment. The air duct 19 advantageously extends within the first section 71.

[0050] The central section 53 has a distance e measured perpendicular to the reference plane 60 at the edge of the recess 48. Advantageously, the distance e is at least 50%, and in particular at least 80%, of the thickness d of the throttle valve 25. In a preferred embodiment, the distance e is at least equal to the thickness d. In the exemplary embodiment, the distance e is greater than the thickness d.

[0051] The partition wall 17 has a partition plane 63 that runs centrally within the partition wall 17. Advantageously, the partition plane 63 runs parallel to the central plane 50. In the exemplary embodiment, the partition plane 63 coincides with the central plane 50. The central section 53 ( Fig. 3 ), which is shown in the representation in Fig. 2 The section passing through the cutting plane has a minimum distance f measured perpendicular to the partition plane 63. In the exemplary embodiment, the distance f is measured over the entire length 1 of the middle section 53, which is parallel to the longitudinal center axis 29. Fig. 3 ) less than a distance g of the lateral sections 54 to the partition plane 63. Advantageously, the central section 53, immediately upstream of the recess 48 for the throttle valve 25, has a distance f to the partition plane 63 over a length 1 that is less than a distance g of the lateral sections 54 to the partition plane 63. The length 1 advantageously corresponds to at least 30%, and in particular at least 50%, of the diameter m of the throttle valve 25.

[0052] The distance g of the lateral sections 54 to the partition plane 63 changes in the exemplary embodiment in the flow direction 30, as Fig. 2 The lateral sections 54 are therefore not parallel to the partition plane 63. In the exemplary embodiment, the smallest distance f of the central section 53 to the partition plane 63 is constant in the flow direction 30. The smallest distance f is in each case the smallest distance of the central section 53 to the partition plane 63 in every cross-section perpendicular to the longitudinal center axis 29.

[0053] Fig. 3 Figure 1 shows the detailed design of the partition wall section 27. The recess 47 extends from the side of the partition wall section 27 facing the choke shaft 36 to the throttle valve 25 in its second end position 52. The recess 47 has a width c on the side facing the throttle valve 25, measured perpendicular to the longitudinal center axis 29. The width c is measured at the mixture channel surface 41. Advantageously, the width c is at least 30%, and particularly at least 50%, of the smallest width b of the mixture channel surface 41 of the partition wall section 27, measured in the same direction. The smallest width b of the mixture channel surface is measured at the mixture channel surface 41 from one side to the opposite intake port wall 56 and perpendicular to the longitudinal center axis 29. In the exemplary embodiment, the smallest width b is located in the region of the venturi section 31.The recess 47 has a length 1 which is advantageously at least 30%, and in particular at least 50%, of the diameter m of the throttle valve 25. The length 1 is measured in a top view of the median plane 50 along the longitudinal center axis 29.

[0054] The recess 47 forms a central section 53 of the mixture channel surface 41. Lateral sections 54 extend on both sides of the central section 53 between the intake channel wall 56 and the central section 53. In the exemplary embodiment, the lateral sections 54 connect directly to the central section 53. However, it is also possible for further areas to be arranged between the lateral sections 54 and the central section 53. The lateral sections 54 connect directly and without interruption to the intake channel wall 54.

[0055] At the lateral sections 54, the mixture channel surface 41 ends upstream of the recess 48 at a separation edge 43. The separation edge 43 delimits the recess 48. In the central section 53, the recess 47 extends partially into the area of ​​the throttle valve 25. The length 1 of the recess 47 corresponds to the length of the area of ​​the central section 53 that lies lower than the lateral sections 54 with respect to the reference plane 60. In the exemplary embodiment, the recess 47 extends to the upstream side of the mixture channel surface 41 facing the choke valve 26. The mixture channel surface 41 is the one shown in the Fig. 3 The sectional view shown in top view of the side of the partition 17 facing the mixture channel 18 in the open end position of throttle valve 25 and choke valve 26 shows the visible surface of the partition 17. The area of ​​the partition 17 hidden by the throttle valve 25 in this view is not considered part of the mixture channel surface 41.

[0056] How Fig. 2 As shown, the mixture channel 18 and the air channel 19 are connected via connecting openings 55 in the illustrated second end position 52 of the throttle valve 25. The connecting openings 55 are located downstream of the partition wall section 27, each between the throttle valve 25 and the intake duct wall 56. In the area of ​​the connecting openings 55, the intake duct wall 56 is advantageously machined to prevent the throttle valve 25 from jamming during opening and closing. The design of the connecting openings 55 is also shown in the enlarged illustration in Fig. 3a depicted.

[0057] How Fig. 3 As also shown, the throttle valve 25 is fixed to the throttle shaft 35 by a fastening element 33, and the choke valve 26 is fixed to the choke shaft 36 by a fastening element 34. The fastening elements 33 and 34 are preferably screws.

[0058] Fig. 4 The front face 58 of the throttle valve 25 is shown in the area of ​​the recess 47. As the illustration clarifies, the mixture flows in the mixture channel 18 against the front face 58. As the Fig. 4 bis 6 As shown, the recess 47 runs concavely in longitudinal sections perpendicular to the longitudinal center axis 29 of the intake channel 16.

[0059] In Fig. 6 The course of the lateral sections 54 and the central section 53 is visible. The lateral sections 54 each terminate at a trailing edge 43. The central section 53 extends over a width c, which is advantageously at least 30%, and particularly at least 50%, of the smallest width b of the mixture channel area 41. The lateral sections 54 have a width a1 and a width a2, respectively. The widths a1 and a2 of the two lateral sections 54 can be the same or different. The lateral sections 54 have a total width a, which is the sum of the widths a1 and a2. The total width a is advantageously at least 5 mm. The total width a is advantageously at least 50%, and particularly at least 70%, of the smallest width b of the mixture channel area 41. The throttle valve 25 has a thickness d, which is advantageously between 0.5 mm and 3 mm.

[0060] As the Fig. 7 und 8 As shown, the lateral sections 54 in the area arranged upstream of the throttle valve 25 are planar. The separation edge 43 is located approximately at the same height as the side 57 of the throttle valve 25 facing the mixture channel 18. The separation edge 43 is therefore advantageously located in the reference plane 60.

[0061] The lateral sections 54 run in the reference plane 60 (see Fig. 6 bis 8 ). Fig. 8 The design of the demolition edge 43 on the middle section 53 at a distance from the longitudinal center axis 29 is also shown.

[0062] In the exemplary embodiment according to Fig. 9 A recess 47 is also provided on the partition wall section 27. The same reference numerals denote corresponding elements in all embodiments. Elements not described in detail for one embodiment are advantageously designed according to one of the other embodiments.

[0063] The recess 47 is shown in the exemplary embodiment according to Fig. 9 less deeply formed than in the previous embodiment. The separation edge 43 extends continuously across the entire width of the mixture channel surface 41. The lateral sections 54 extend, as in particular Fig. 11 The main fuel nozzle 40 and the lateral sections 54 are advantageously arranged on the same side of the reference plane 60. The main fuel nozzle 40 and the lateral sections 54 are advantageously arranged in the second region 72. The lateral sections 54 are designed as guide elements 44. The lateral sections 54 extend in the flow direction 30 inclined to the reference plane 60. This ensures that the mixture is guided by the Fig. 3 The flow is directed away from the connecting openings 55 shown. The guide elements 44 are advantageously designed as ramps. In the exemplary embodiment, the lateral sections 54 run approximately parallel to the longitudinal center axis 29 and to the center plane 50. In the exemplary embodiment, the guide elements 44 are inclined to the reference plane 60 at an angle β corresponding to the angle α. Advantageously, the angle β between the guide elements 44 and the reference plane 60 is at least 5°, in particular at least 10°. It can also be provided that the guide elements 44 rise in the flow direction 30. A curved shape of the guide elements 44 can also be advantageous. The guide elements 44 advantageously extend over a length h in the first region 72, which is at least 3 mm, in particular at least 5 mm.

[0064] The guide elements 44 are also in Fig. 12 depicted.

[0065] In all embodiments, the partition wall section 27 is preferably formed integrally with the base body 21 of the fuel supply device 20. The partition wall section 27 and the base body 21 are advantageously formed as a single-piece casting.

[0066] The fuel supply device 20 is advantageously a carburetor, in particular a diaphragm carburetor. Metering of fuel via an electromagnetic valve can also be advantageous.

Claims

1. Fuel feed unit for feeding fuel to a two-stroke engine (1), having a base body (21), in which an intake channel section (22) is formed, having at least one fuel opening (23, 24), which opens into the intake channel section (22), having a throttle flap (25) for controlling the free flow cross section of the intake channel section (22), said throttle flap being mounted pivotably about a pivot axis (45), having a partition wall section (27), which runs in the intake channel section (22) at least also upstream of the throttle flap (25) and which divides the intake channel section (22) into a mixture channel (18), into which the fuel opening (23, 24) feeds fuel, and an air channel (19), the partition wall section (27) having a recess (48), in which the throttle flap (25) at least partially lies in an end position (52), the partition wall section (27) having, upstream of the recess (48), a continuous mixture channel surface (41) which faces the mixture channel (18) and which has lateral sections (54) adjacent to the intake channel wall (56) and a middle section (53) running between the lateral sections (54), the lateral sections (54) having, upstream of the throttle flap (25), a separation edge (43) for the flow in the mixture channel (18), wherein, in the end position (52) of the throttle flap (25), in which the throttle flap (25) lies at least partially in the recess (48), that side (57) of the throttle flap (25) which faces the mixture channel (18) defines a reference plane (60), the reference plane (60) dividing the fuel feed unit into a first region (71), in which the throttle flap (25) is arranged, and a second region (72), the middle section (53) of the mixture channel surface (41) at least directly upstream of the recess (48) lying in the first region (71) such that, in the end position (52) of the throttle flap (25), the flow in the mixture channel (18) at least partially flows against the end face of the throttle flap (25), characterized in that the lateral sections (54) lie in the reference plane (60) or in the second region (72).

2. Fuel feed unit according to Claim 1, characterized in that the lateral sections (54) extend, at least directly upstream of the recess (48), into the second region (72) of the fuel feed unit.

3. Fuel feed unit according to Claim 1 or 2, characterized in that the middle section (53) at least in one region at least directly upstream of the recess (48) is at a distance (e) of at least 50% of the thickness (d) of the throttle flap (25), in particular of at least 80% of the thickness (d) of the throttle flap (25), from the reference plane (60).

4. Fuel feed unit according to one of Claims 1 to 3, characterized in that the middle section (53) over a length (l) which is at least 30% of a diameter (m) of the throttle flap (25) directly upstream of the recess (48) for the throttle flap (25) is at a distance (f) from a partition wall plane (63) which runs centrally in the partition wall (17) and which is smaller than a distance (g) of the lateral sections (54) from the partition wall plane (63), the length (l) being measured parallel to the longitudinal centre axis (29) of the intake channel section (22).

5. Fuel feed unit according to Claim 4, characterized in that the middle section (53) over its entire length (l) is at a smaller distance (f) from the partition wall plane (63) than the lateral sections (54).

6. Fuel feed unit according to one of Claims 1 to 5, characterized in that the lateral sections (54) have an overall width (a) of at least 5 mm, in particular at least 7 mm, the overall width (a) being measured perpendicularly to the longitudinal centre axis (29) of the intake channel section (22).

7. Fuel feed unit according to one of Claims 1 to 6, characterized in that the lateral sections (54) have an overall width (a) of at least 50% of the smallest width (b) of the mixture channel surface (41) of the partition wall section (27), in particular at least 70% of the smallest width (b) of the mixture channel surface (41) of the partition wall section (27), the overall width (a) and the smallest width (b) being measured perpendicularly to the longitudinal centre axis (29).

8. Fuel feed unit according to one of Claims 1 to 7, characterized in that the middle section (53) has a width (c) which is at least 30%, preferably at least 50% of the smallest width (b) of the mixture channel surface (41) of the partition wall section (27), the width (c) being measured perpendicularly to the longitudinal centre axis (29).

9. Fuel feed unit according to one of Claims 1 to 8, characterized in that the lateral sections (54) run at an inclination to the reference plane (60) at least directly upstream of the separation edge (43).

10. Fuel feed unit according to one of Claims 1 to 9, characterized in that the separation edge (43) extends over the entire width of the mixture channel surface (41) of the partition wall section (27).

11. Fuel feed unit according to one of Claims 1 to 10, characterized in that the middle section (53) is formed by a depression (47) of the partition wall section (27), said depression running in particular concavely in a sectional plane perpendicular to the longitudinal centre axis (29) of the intake channel section (22).

12. Fuel feed unit according to one of Claims 1 to 11, characterized in that the base (58) of the depression (47) runs parallel to the longitudinal centre axis (29) of the intake channel section (22).

13. Fuel feed unit according to one of Claims 1 to 12, characterized in that the lateral sections (54) adjoin the middle section (53) on both sides.

14. Fuel feed unit according to one of Claims 1 to 13, characterized in that a choke element is arranged upstream of the partition wall section (27).

15. Fuel feed unit according to one of Claims 1 to 14, characterized in that the partition wall section (27) is formed integrally with the base body (21) of the fuel feed unit (20), in particular is produced as an integral cast part with the base body (21).

16. Two-stroke engine having a fuel feed unit according to one of Claims 1 to 15.

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