FUEL FEED UNIT AND TWO-STROKE ENGINE HAVING A FUEL FEED UNIT

Abstract

A fuel feed unit has a base body with an intake channel section, into which a fuel opening opens. A partition wall section divides the intake channel section into a mixture channel and an air channel. The wall section has a recess in which the throttle flap at least partially lies in an end position. The wall section has, upstream of the recess, a continuous surface facing the mixture channel and which has lateral sections adjacent to the channel wall and a middle section running between the lateral sections. The lateral sections have, upstream of the throttle flap, a separation edge for the flow. In the end position, the side of the throttle flap facing the mixture channel defines a reference plane which divides the unit into a first region and a second region. The lateral sections extend, at least directly upstream of the recess, into the second region.

Claims

1. A fuel feed unit for feeding fuel to a two-stroke engine, the fuel feed unit comprising: a base body having an intake channel section formed therein; at least one fuel opening which opens into said intake channel section; a throttle flap configured to control a free flow cross section of said intake channel section; said throttle flap being mounted pivotably about a pivot axis; a partition wall section extending in said intake channel section at least upstream of said throttle flap; said partition wall section dividing said intake channel section into a mixture channel into which said fuel opening is configured to feed fuel and an air channel; said partition wall section having a recess; said throttle flap having an end position in which said throttle flap at least partially lies in said recess; said partition wall section having, upstream of said recess, a continuous mixture channel surface which faces said mixture channel and which has lateral sections adjacent to said intake channel wall and a middle section running between said lateral sections; said lateral sections having, upstream of the throttle flap, a separation edge for the flow in said mixture channel and, in the end position of said throttle flap, a side of said throttle flap, which faces the mixture channel, defining a reference plane which divides the fuel feed unit into a first region, in which said throttle flap is arranged, and a second region; and, said lateral sections extending, at least directly upstream of said recess, into said second region of the fuel feed unit.

2. The fuel feed unit of claim 1, wherein said mixture channel surface in said middle section lies at least partially in said first region.

3. The fuel feed unit of claim 2, wherein said throttle flap has a thickness (d); said middle section, at least in one region at least directly upstream of said recess, is at a distance (e) from the reference plane; and, said distance (e) is at least 50% of said thickness (d).

4. The fuel feed unit of claim 1, wherein: said throttle flap has a diameter (m); said intake channel defines a longitudinal center axis; said partition wall defines a partition wall plane running centrally in said partition wall; said middle section, over a length (l) directly upstream of the recess for said throttle flap, is at a distance (f) from said partition wall plane; said length (l) is at least 30% of said diameter (m); said lateral section is at a distance (g) from said partition wall plane; said distance (f) is smaller than said distance (g); and, said length (l) is measured parallel to said longitudinal center axis of said intake channel section.

5. The fuel feed unit of claim 4, wherein said middle section has a total middle section length; and, said middle section is, over said total middle section length, at a smaller distance from said partition wall plane than said lateral sections.

6. The fuel feed unit of claim 1, wherein said intake channel defines a longitudinal center axis; and, said lateral portions have an overall width (a) of at least 5 mm, said overall width (a) being measured perpendicularly to said longitudinal center axis of said intake channel section.

7. The fuel feed unit of claim 1, wherein said intake channel defines a longitudinal center axis; said lateral sections have an overall width (a) of at least 50% of a smallest width (b) of said mixture channel surface of said partition wall section; and, said overall width (a) and said smallest width (b) are measured perpendicularly to said longitudinal center axis.

8. The fuel feed unit of claim 1, wherein said intake channel defines a longitudinal center axis; and, said middle section has a width (c) which is at least 30% of a smallest width (b) of said mixture channel surface of said partition wall section, said width (c) being measured perpendicularly to said longitudinal center axis.

9. The fuel feed unit of claim 1, wherein said lateral sections run at an inclination to said reference plane at least directly upstream of said separation edge.

10. The fuel feed unit of claim 1, wherein said separation edge extends over an entire width of said mixture channel surface of said partition wall section.

11. The fuel feed unit of claim 1, wherein said intake channel section defines a longitudinal center axis; and, said middle section is formed by a depression of said partition wall section, said depression running concavely in a sectional plane perpendicular to said longitudinal center axis.

12. The fuel feed unit of claim 11, wherein said depression has a base running parallel to said longitudinal center axis.

13. The fuel feed unit of claim 1, wherein said lateral sections adjoin said middle section on both sides.

14. The fuel feed unit of claim 1 further comprising a choke element arranged upstream of said partition wall section.

15. The fuel feed unit of claim 1, wherein said partition wall section is formed integrally with said base body.

16. The fuel feed unit of claim 1, wherein said partition wall section is an integral cast part with said base body.

17. The fuel feed unit of claim 1, wherein said middle section of said mixture channel surface at least directly upstream of said recess lies in said first region; and, said lateral sections lie in said reference plane or in said second region.

18. The fuel feed unit of claim 1, wherein said lateral sections at least directly upstream of said recess lie in said second region.

19. A fuel feed unit for feeding fuel to a two-stroke engine, the fuel feed unit comprising: a base body having an intake channel section formed therein; at least one fuel opening which opens into said intake channel section; a throttle flap configured to control a free flow cross section of said intake channel section; said throttle flap being mounted pivotably about a pivot axis; a partition wall section extending in said intake channel section at least upstream of said throttle flap; said partition wall section dividing said intake channel section into a mixture channel into which said fuel opening is configured to feed fuel and an air channel; said partition wall section having a recess; said throttle flap having an end position in which said throttle flap at least partially lies in said recess; said partition wall section having, upstream of said recess, a continuous mixture channel surface which faces said mixture channel and which has lateral sections adjacent to said intake channel wall and a middle section running between said lateral sections; said lateral sections having, upstream of the throttle flap, a separation edge for the flow in said mixture channel and, in the end position of said throttle flap, a side of said throttle flap which faces the mixture channel defining a reference plane which divides the fuel feed unit into a first region, in which said throttle flap is arranged, and a second region; and, said middle section, at least directly upstream of said recess, lying in said first region and said lateral sections lying in said reference plane or in said second region.

20. The fuel feed unit of claim 19, wherein said lateral sections at least directly upstream of said recess lie in said second region.

21. A two-stroke engine comprising: a fuel feed unit for feeding fuel to the two-stroke engine, the fuel feed unit including a base body, a throttle flap, and a partition wall section; said base body having an intake channel section formed therein; said fuel feed unit further having at least one fuel opening which opens into said intake channel section; said throttle flap configured to control a free flow cross section of said intake channel section; said throttle flap being mounted pivotably about a pivot axis; said partition wall section extending in said intake channel section at least upstream of said throttle flap; said partition wall section dividing said intake channel section into a mixture channel into which said fuel opening is configured to feed fuel and an air channel; said partition wall section having a recess; said throttle flap having an end position in which said throttle flap at least partially lies in said recess; said partition wall section having, upstream of said recess, a continuous mixture channel surface which faces said mixture channel and which has lateral sections adjacent to said intake channel wall and a middle section running between said lateral sections; said lateral sections having, upstream of the throttle flap, a separation edge for the flow in said mixture channel and, in the end position of said throttle flap, a side of said throttle flap which faces the mixture channel defining a reference plane which divides the fuel feed unit into a first region, in which said throttle flap is arranged, and a second region; and, said lateral sections extending, at least directly upstream of said recess, into said second region of the fuel feed unit.

22. A two-stroke engine comprising: a fuel feed unit for feeding fuel to a two-stroke engine, the fuel feed unit including a base body, a throttle flap, and a partition wall section; said base body having an intake channel section formed therein; said fuel feed unit further having at least one fuel opening which opens into said intake channel section; said throttle flap configured to control a free flow cross section of said intake channel section; said throttle flap being mounted pivotably about a pivot axis; said partition wall section extending in said intake channel section at least upstream of said throttle flap; said partition wall section dividing said intake channel section into a mixture channel into which said fuel opening is configured to feed fuel and an air channel; said partition wall section having a recess; said throttle flap having an end position in which said throttle flap at least partially lies in said recess; said partition wall section having, upstream of said recess, a continuous mixture channel surface which faces said mixture channel and which has lateral sections adjacent to said intake channel wall and a middle section running between said lateral sections; said lateral sections having, upstream of the throttle flap, a separation edge for the flow in said mixture channel and, in the end position of said throttle flap, a side of said throttle flap which faces the mixture channel defining a reference plane which divides the fuel feed unit into a first region, in which said throttle flap is arranged, and a second region; and, said middle section, at least directly upstream of said recess, lying in said first region and said lateral sections lying in said reference plane or in said second region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention will now be described with reference to the drawings wherein:

[0034] FIG. 1 shows a schematic illustration of a two-stroke engine operating with a scavenging gas shield;

[0035] FIG. 2 shows a schematic sectional illustration through a fuel feed unit according to the disclosure;

[0036] FIG. 3 shows a schematic sectional illustration, in detail form, along the line III-III in FIG. 2;

[0037] FIG. 3A shows an enlarged illustration, in detail form, of the region of the connection openings from FIG. 3;

[0038] FIG. 4 shows a schematic sectional illustration, in detail form, along the line IV-IV in FIG. 2;

[0039] FIG. 5 shows a schematic sectional illustration, in detail form, along the line V-V in FIG. 2;

[0040] FIG. 6 shows a schematic view, in detail form, in the direction of the arrow VI in FIG. 2;

[0041] FIG. 7 and FIG. 8 show schematic perspective longitudinal sectional illustrations through the fuel feed unit from FIG. 2;

[0042] FIG. 9 shows a sectional illustration, in detail form, of an embodiment variant of the fuel feed unit;

[0043] FIG. 10 shows a view, in detail form, in the direction of the arrow X in FIG. 9;

[0044] FIG. 11 shows the illustration from FIG. 9 without throttle flap, choke flap, throttle shaft and choke shaft; and,

[0045] FIG. 12 shows a view, in detail form, in the direction of the arrow XII in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] FIG. 1 schematically shows a two-stroke engine 1. The two-stroke engine 1 can advantageously be provided as a drive motor in a work apparatus, in particular in a handheld work apparatus, for example a motorized saw, a cut-off grinder, a blowing apparatus, 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 in a reciprocating manner in the cylinder 2. The piston 5 uses a connecting rod 6 to drive a crankshaft 7, which is mounted in a crankcase interior 9 so as to be rotable about a rotational axis 8. The crankcase interior 9 is formed in a crankcase 4 and separated from the combustion chamber 3 by the piston 5. A discharge opening 15 for exhaust gases leads out of the combustion chamber 3. A spark plug 32 protrudes into the combustion chamber 3.

[0047] A mixture channel 18 with a mixture inlet 10 opens at the cylinder 2. The mixture inlet 10 opens into the crankcase interior 9 and, in the region of the upper dead center of the piston 5, is fluidically connected to the crankcase interior 9. The piston 5 preferably has at least one piston pocket 14. The two-stroke engine 1 has transfer channels 12 which, in the region of the lower dead center of the piston 5, fluidically connect the crankcase interior 9 to the combustion chamber 3. The transfer channels 12 open with transfer windows 13 at the cylinder bore.

[0048] The two-stroke engine 1 includes an air channel 19 which opens with an air inlet 11 at the cylinder bore of the cylinder 2. In the region of the lower dead center of the piston 5, the air inlet 11 is located in the region of the piston pocket 14 and connects the air channel 19 to the transfer windows 13 of the transfer channels 12. In the embodiment, four transfer channels 12 are provided, of which two are visible in the sectional illustration in FIG. 1. A different number and/or a different shape of transfer channels 12 may also be advantageous. The transfer channels 12 connect the crankcase interior 9 in the region of the lower dead center 5 to the combustion chamber 3 such that a fuel/air mixture can flow from the crankcase interior 9 via the transfer channels 12 into the combustion chamber 3. The transfer windows 13 are controlled by the piston 5 and, in the region of the lower dead center of the piston 5, are opened toward the combustion chamber 3.

[0049] The combustion air is sucked via an air filter 37. The air filter 37 has filter material 39 which separates a clean chamber 38 of the air filter 37 from the surroundings. The mixture channel 18 and the air channel 19 are connected to the clean chamber 38. Air is sucked up via an intake channel 16 which opens at the clean chamber 38 of the air filter 37. The intake channel 16 is separated over at least part of its length into the air channel 19 and the mixture channel 18 by a partition wall 17.

[0050] A fuel feed unit 20 is provided for feeding fuel. The fuel feed unit 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 feed unit 20 can be a carburetor which feeds fuel depending on the negative pressure prevailing in the intake channel section 22. In a preferred embodiment variant, the fuel feed unit 20 is a diaphragm-type carburetor. In an alternative preferred embodiment variant, it is provided that the fuel feed unit 20 includes a fuel valve which is opened and closed by a controller of the two-stroke engine 1. The fuel valve is in particular an electromagnetic valve, preferably a currentlessly open valve or a currentlessly closed valve. The fuel metered by the fuel valve is advantageously fed into the intake channel section 22 because of the negative pressure prevailing in the intake channel section 22.

[0051] A throttle flap 25 is arranged in the intake channel section 22. The throttle flap 25 is advantageously mounted pivotably with a throttle shaft 35. The throttle flap 25 has a diameter m. In the embodiment, the partition wall 17 has a partition wall section 27 upstream of the throttle shaft 35 and a partition wall section 28 downstream of the throttle shaft 35. The intake channel section 22 has a longitudinal center axis 29. The longitudinal center axis 29 is the axis which connects the geometric center points of the intake channel section 22 to one another 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 channel 16 substantially in a flow direction 30 from the air filter 37 to the cylinder 2. In the event of return pulsations, a flow in the opposite direction may also take place. The partition wall 17 divides the intake channel 16 into the mixture channel 18 and the air channel 19. A main fuel opening 23 and a plurality of secondary fuel openings 24 in the fuel feed unit 20 open into the mixture channel 18. The main fuel opening 23 is arranged in the region of a venturi section 31.

[0052] FIG. 2 shows the fuel feed unit 20 schematically in detail in longitudinal section. The throttle flap 25 is mounted with the throttle shaft 35 pivotably about a pivot axis 45. As FIG. 2 shows, a choke flap 26 is arranged in the intake channel section 22 upstream of the throttle flap 25, with respect to the flow direction 30. The choke flap 26 is mounted with a choke shaft 36 so as to be pivotable about a pivot axis 46. In the embodiment, the longitudinal center axis 29 of the intake channel section 22 intersects the pivot axes 45 and 46. However, provision may also be made for the pivot axes 45 and 46 to be arranged offset with respect to the longitudinal center axis 29 in the intake channel section 22 and not to intersect the longitudinal center axis 29. The main fuel opening 23 is formed at a main fuel nozzle 40, which is illustrated in partially sectioned form in the sectional illustration in FIG. 2.

[0053] The intake channel section 22 has a center plane 50. The center plane 50 contains the longitudinal center axis 29 of the intake channel section 22 and runs parallel to the pivot axes 45 and 46. In the embodiment, the pivot axes 45 and 46 lie on the center plane 50.

[0054] FIG. 2 shows the choke flap 26 in its fully open end position. In this end position, a section of the choke flap 26 protrudes into a recess 49 of the partition wall section 27. The partition wall section 27 has a mixture channel surface 41. The mixture channel surface 41 of the partition wall section 27 is the surface which, in the illustrated end positions of the throttle flap 25 and choke flap 26, delimits the mixture channel 18. The partition wall section 27 has an air channel surface 42 which, in the illustrated end positions of the throttle flap 25 and choke flap 26, delimits the air channel 19. In the embodiment, the air channel surface 42 runs flat and approximately parallel to the center plane 50. In the embodiment, the choke flap 26 is in its fully open position parallel to the center plane 50.

[0055] The throttle flap 25 is pivotable between a first end position 51, illustrated by a dashed line, and the second end position 52, illustrated by a solid line. In the first end position 21, the throttle flap 25 substantially closes the flow cross section in the intake channel section 22. The first end position 51 preferably corresponds to the position of the throttle flap 25 when idling. In the first end position 51, the throttle flap 25 in the embodiment is arranged completely downstream of the partition wall section 27. In the second end position 52, the throttle flap 25 substantially opens up the flow cross section in the intake channel section 22. In the second end position 52, the throttle flap 25 encloses an angle α with the center plane 50. An upstream end face 58 of the throttle flap 25 lies on that side of the center plane 50 on which the mixture channel 18 runs. The downstream end face 62 of the throttle flap 25 lies on that side of the center plane 50 on which the air channel 19 runs. The angle α which the throttle flap 25 encloses with the center plane 50 may also be 0°. A small inclination of the throttle flap 25 in the opposite direction in its second end position 52 may also be provided.

[0056] On its side facing the mixture channel 18, the partition wall section 27 has a recess 48 into which the throttle flap 25 at least partially protrudes in its second end position 52. The partition wall section 27 and the throttle flap 25 overlap in the second end position 52, and therefore, in the second end position 52, the partition wall section 27 is not arranged completely upstream of the throttle flap 25. The partition wall section 27 is completely arranged upstream of the throttle shaft 35. In the embodiment, the partition wall section 27 has a depression 47 on its side facing the mixture channel 18. Owing to the depression 47, mixture flowing in the mixture channel section 18 flows against that end face 58 of the throttle flap 25 which lies counter to the flow direction 30. In the embodiment, the depression 47 has a base 59 which runs in particular parallel to the longitudinal center axis 29. In the embodiment, the base 59 of the depression 47 runs closer to the air channel 19 than the end face 58, in the illustrated longitudinal section through the longitudinal center axis 29. The depression 47 is advantageously arranged in the middle section 43 of the partition wall section 27, which middle section faces the mixture channel 18.

[0057] In the embodiment, the throttle flap 25 protrudes with a circumferential region over its entire thickness d from the recess 48. However, provision may also be made for the end face 58 to protrude, in the second end position 52, only over part of the thickness d of the throttle flap 25 from the recess 48 into the mixture channel 18. The throttle flap 25 advantageously protrudes in a circumferential region by at least 50%, in particular by at least 80%, of its thickness d, from the recess 48.

[0058] The throttle flap 25 has a side 57 facing the mixture channel 18. The side 57 is a flat side of the throttle flap 25. In the second end position 52 of the throttle flap 25, mixture flows along the side 57 during operation. In the second end position 52, the side 57 delimits the mixture channel 18. The side 57 of the throttle flap 25 forms a reference plane 60, indicated in FIG. 2. In the position of the fuel feed unit 20 that is illustrated in FIG. 2, the reference plane 60, that is, also that side 57 of the throttle flap 25 which faces the mixture channel 18, is arranged horizontally, and the fuel opening 23 (FIG. 1) formed on the main fuel nozzle 40 is arranged above the partition wall section 27. In this position of the fuel feed unit 20, the middle section 53 of the mixture channel surface 41 runs below the reference plane 60.

[0059] The reference plane 60 divides the fuel feed unit into two regions, namely a first region 71 and a second region 72. In the first region 71, the throttle flap 25 is arranged in its second end position 52. In the embodiment, the partition wall section 27 runs in the first region 71. In the embodiment, the main fuel nozzle 40 is arranged in the second region 72. The air channel 19 advantageously runs in the first region 71.

[0060] At the edge of the recess 48, the middle section 53 is at a distance e, measured perpendicularly to the reference plane 60, from the reference plane 60. The distance e is advantageously at least 50%, in particular at least 80%, of the thickness d of the throttle flap 25. In a preferred configuration, the distance e corresponds at least to the thickness d. In the embodiment, the distance e is greater than the thickness d.

[0061] The partition wall 17 has a partition wall plane 63 which runs centrally in the partition wall 17. The partition wall plane 63 advantageously runs parallel to the center plane 50. In the embodiment, the partition wall plane 63 coincides with the center plane 50. The middle section 53 (FIG. 3) which, in the illustration in FIG. 2, runs through the sectional plane is at a smallest distance f, measured perpendicularly to the partition wall plane 63, from the partition wall plane 63. In the embodiment, the distance f over the entire length 1, measured parallel to the longitudinal center axis 29, of the middle section 53 (FIG. 3) is smaller than a distance g of the lateral sections 54 from the partition wall plane 63. The middle section 53 is advantageously at a distance f over a length 1 directly upstream of the recess 48 for the throttle flap 25 from the partition wall plane 63, the distance being smaller than a distance g of the lateral sections 54 from the partition wall plane 63. The length 1 advantageously corresponds to at least 30%, in particular at least 50%, of the diameter m of the throttle flap 25.

[0062] In the embodiment, the distance g of the lateral sections 54 from the partition wall plane 63 changes in the flow direction 30, as FIG. 2 shows. Accordingly, the lateral sections 54 do not run parallel to the partition wall plane 63. In the embodiment, the smallest distance f of the middle section 53 from the partition wall plane 63 is constant in the flow direction 30. The smallest distance f here is in each case the smallest distance of the middle section 53 from the partition wall plane 63 in each cross section perpendicular to the longitudinal center axis 29.

[0063] FIG. 3 shows the configuration of the partition wall section 27 in detail. The depression 47 extends from that side of the partition wall section 27 which faces the choke shaft 36 as far as the throttle flap 25 in its second end position 52. On the side facing the throttle flap 25, the depression 47 has a width c which is measured perpendicularly to the longitudinal center axis 29. The width c is measured on the mixture channel surface 41. The width c is advantageously at least 30%, in particular at least 50% of the smallest width b, measured in the same direction, of the mixture channel surface 41 of the partition wall section 27. The smallest width b of the mixture channel surface is measured on the mixture channel surface 41 from one to the opposite intake channel wall 56 and perpendicularly to the longitudinal center axis 29. In the embodiment, the smallest width b runs in the region of the venturi section 31. The depression 47 has a length 1 which is advantageously at least 30%, in particular at least 50%, of the diameter m of the throttle flap 25. The length 1 is measured here in a top view of the center plane 50 at the longitudinal center axis 29.

[0064] The depression 47 forms a middle section 53 of the mixture channel surface 41. Between the intake channel wall 56 and the middle section 53, lateral sections 54 extend on both sides of the middle section 53. In the embodiment, the lateral sections 54 directly adjoin the middle section 53. However, provision may also be made for further regions to be arranged between the lateral sections 54 and the middle section 53. The lateral sections 54 adjoin the intake channel wall 54 directly and without interruption.

[0065] At the lateral sections 54, the mixture channel surface 41 ends at a separation edge 43 upstream of the recess 48. The separation edge 43 delimits the recess 48. In the middle section 53, the depression 47 partially runs into the region of the throttle flap 25. The length 1 of the depression 47 corresponds to that length of the region of the middle section 53 which lies deeper than the lateral sections 54 with respect to the reference plane 60. In the embodiment, the depression 47 extends as far as the upstream side, facing the choke flap 26, of the mixture channel surface 41. The mixture channel surface 41 here is the surface of the partition wall 17 which is visible in the sectional illustration, shown in FIG. 3, in a top view of the side of the partition wall 17 facing the mixture channel 18 in the open end position of the throttle flap 25 and choke flap 26. The region of the partition wall 17 that is concealed by the throttle flap 25 in this view is not considered here to be part of the mixture channel surface 41.

[0066] As FIG. 2 shows, in the illustrated second end position 52 of the throttle flap 25, the mixture channel 18 and the air channel 19 are connected via connection openings 55. The connection openings 55 are each located between the throttle flap 25 and the intake channel wall 56 downstream of the partition wall section 27. Advantageously, the intake channel wall 56 is machined in the region of the connection openings 55 in order to avoid jamming of the throttle flap 25 during the opening and closing. The configuration of the connection openings 55 is also illustrated in the enlarged illustration in FIG. 3A.

[0067] As FIG. 3 also shows, the throttle flap 25 is fixed with a fastening element 33 to the throttle shaft 35 and the choke flap 26 is fixed with a fastening element 34 to the choke shaft 36. The fastening elements 33 and 34 are preferably screws.

[0068] FIG. 4 shows the end face 58 of the throttle flap 25 in the region of the depression 47. As the illustration clarifies, the mixture in the mixture channel 18 flows against the end face 58. As FIGS. 4 to 6 show, the depression 47 runs concavely in longitudinal sections perpendicularly to the longitudinal center axis 29 of the intake channel 16.

[0069] In FIG. 6, the profile of the lateral sections 54 and of the middle section 53 is visible. The lateral sections 54 each end at a separation edge 43. The middle section 53 extends over the width c which is advantageously at least 30%, in particular at least 50%, of the smallest width b of the mixture channel surface 41. The lateral sections 54 have a width a.sub.l and a width a.sub.2. The widths a.sub.1 and a.sub.2 of the two lateral sections 54 can be identical or different in size. The lateral sections 54 have an overall width a which is the sum of the widths a.sub.1 and a.sub.2. The overall width a is advantageously at least 5 mm. The overall width a is advantageously at least 50%, in particular at least 70%, of the smallest width b of the mixture channel surface 41. The throttle flap 25 has a thickness d which is advantageously 0.5 mm to 3 mm.

[0070] As FIGS. 7 and 8 show, the lateral sections 54 are flat in the region arranged upstream of the throttle flap 25. The separation edge 43 is located approximately at the same height as that side 57 of the throttle flap 25 which faces the mixture channel 18. Accordingly, the separation edge 43 advantageously lies in the reference plane 60.

[0071] The lateral sections 54 run in the reference plane 60 (see FIGS. 6 to 8). FIG. 8 also shows the configuration of the separation edge 43 on the middle section 53 at a distance from the longitudinal center axis 29.

[0072] In the embodiment according to FIG. 9, a depression 47 is likewise provided on the partition wall section 27. The same reference signs denote mutually corresponding elements in all of the embodiments. Elements which are not described individually for an embodiment are advantageously configured in accordance with one of the other embodiments.

[0073] In the embodiment according to FIG. 9, the depression 47 is less deep than in the previous embodiment. The separation edge 43 extends continuously over the entire width of the mixture channel surface 41. The lateral sections 54, as in particular FIG. 11 shows, extend upstream of the separation edge 43 in the second region 72. 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 configured as guide elements 44. The lateral sections 54 run in the flow direction 30 at an inclination to the reference plane 60. As a result, the mixture is conducted away from the connection openings 55 shown in FIG. 3. The guide elements 44 are advantageously configured as ramps. In the embodiment, the lateral sections 54 run approximately parallel to the longitudinal center axis 29 and to the center plane 50. In the embodiment, the guide elements 44 run at an inclination with respect to the reference plane 60 by an angle β which corresponds to the angle α. The angle β between the guide elements 44 and the reference plane 60 is advantageously at least 5°, in particular at least 10°: provision may also be made for the guide elements 44 to rise in the flow direction 30. A curved profile of the guide elements 44 may also be advantageous. The guide elements 44 advantageously extend in the first region 72 over a length h which is at least 3 mm, in particular at least 5 mm.

[0074] The guide elements 44 are also illustrated in FIG. 12.

[0075] The partition wall section 27 can preferably be formed integrally with the base body 21 of the fuel feed unit 20. The partition wall section 27 and the base body 21 are advantageously formed as an integral cast part. The fuel feed unit 20 is advantageously a carburetor, in particular a diaphragm-type carburetor. Metering fuel via an electromagnetic valve may also be advantageous.

[0076] It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.