EP3748151A1 - Mixture forming unit and two-stroke engine having a mixture forming unit - Google Patents

Abstract

A mixture formation unit (13) has a base body (23) in which an intake duct section (11) is formed. The suction channel section (11) extends from a first end face (24) of the base body (23) to a second end face (25) of the base body (23). The mixture formation unit (13) has at least one straight channel (26) which opens into the intake channel section (11). The channel (26) opens on the first end face (24) of the base body (23). The mixture formation unit (13) is preferably provided for a two-stroke engine (1) whose intake duct (10) is divided into a mixture duct (12) and an air duct (14) downstream of the mixture formation unit (13).

Description

The invention relates to a mixture formation unit of the type specified in the preamble of claim 1 and a two-stroke engine with a mixture formation unit.

From the US 2014/0261329 A1 a mixture formation device, namely a carburetor, is known in which the main fuel nozzle is arranged in a straight channel. As a result, the main fuel nozzle can easily be pushed or pressed into the base body of the carburetor from the outside. A cover that holds the regulating membrane and a cover for the fuel pump are arranged on the base body. If the cover that holds the regulating membrane is mounted on the base body, the channel in which the main fuel nozzle is located is only accessible from the intake channel.

The channels of a carburetor are usually at least partially produced using machining processes. After the cover of the control chamber has been fitted, the channel in which the main fuel nozzle is arranged is only accessible from the intake channel. As a result, cleaning the carburetor is only possible to a limited extent after all the components have been assembled. Particles that are located in the fuel-carrying channels can loosen during operation and get stuck in undesired positions, for example on sensitive components such as valves or the like, and thus disrupt the operation of the carburetor.

The invention is based on the object of creating a mixture formation unit of the generic type which is extremely robust in operation and is easy to clean.

Another object of the invention is to provide a two-stroke engine with a mixture formation unit.

With regard to the mixture formation unit, this object is achieved by a mixture formation unit having the features of claim 1. With regard to the two-stroke engine, the object is achieved by a two-stroke engine with the features of claim 16.

It is provided that the channel, which opens into the intake channel, is designed as a straight channel and opens at an end face of the base body of the mixture-forming unit. As a result, both ends of the channel are easily accessible even after attachments such as covers, a fuel pump or the control device of the mixture formation unit have been installed. This allows the sewer to be completely cleaned and flushed. A cleaning line can in particular be connected to the end face of the base body, so that the connection is easily accessible.

A component of the mixture formation unit is preferably arranged in the channel. By arranging the mouth opening of the channel on the first end face of the base body, the channel can easily be cleaned before the component is assembled. The component arranged in the channel can, for example, be easily changed subsequently in the event of malfunctions. The first face at which the channel opens can be both the upstream face of the mixture formation unit and the downstream face of the mixture formation unit. The mixture formation unit advantageously has at least one fuel opening which opens into the intake duct section and which is formed on a fuel nozzle. With fuel nozzle the component is referred to where the constriction is formed, which forms the nozzle cross-section. Other functions can also be implemented in the fuel nozzle. The fuel nozzle is a component that can be assembled from several individual parts. The fuel opening is preferably a main fuel opening and the fuel nozzle is a main fuel nozzle. The component preferably forms an annular gap with the channel, in particular with the channel wall of the channel, which is connected to the fuel opening. Because the channel is designed as a straight channel, it can be manufactured with high accuracy, for example by drilling or milling, so that defined dimensions for the annular gap result.

The component arranged in the channel preferably has a check valve. Particles such as chips or the like, which arise during production and are not removed from the base body of the mixture-forming unit, can impair the sealing function of a valve plate of the check valve and thus considerably impair the function. For a check valve in particular, it is therefore desirable to remove residues from previous machining processes such as chips and the like.

In an alternative embodiment, it is advantageously provided that the component is a fuel valve. The fuel valve preferably has a valve plate which is movable between a stop and a valve seat. Here too, chips or the like can impair the sealing function of the valve plate. The fuel valve is in particular an electrically operated fuel valve, preferably an electromagnetic valve.

In a preferred embodiment, the channel runs comparatively flat in the base body of the mixture formation unit. This results in a favorable arrangement and good utilization of the installation space usually available in the mixture formation unit. The central axis of the channel advantageously closes with the longitudinal axis of the intake channel in a sectional plane which contains the longitudinal axis of the intake duct and runs parallel to the central axis of the duct, an angle of 0 ° to 30 °, in particular 0 ° to 25 °. The central axis of the channel can accordingly lie in one plane with the longitudinal axis of the intake channel or run at an angle to the longitudinal axis of the intake channel. If the central axis of the duct is skewed to the longitudinal axis of the intake duct, the angle in the plane of section between a projection of the central axis of the duct perpendicular to the plane of the section and the longitudinal axis of the intake duct is measured.

The intake channel section preferably has a venturi section. Downstream of the Venturi section, in particular, a throttle element is mounted in the base body. The throttle element is preferably arranged to be adjustable and is used to adjust the free flow cross section of the intake duct section. The throttle element can advantageously be pivoted about an axis of rotation.

The mixture formation unit is in particular a carburetor in which the fuel preparation takes place at least partially in or downstream of the Venturi section. The first face at which the channel opens is preferably the upstream face of the base body. However, it can also be provided that the first end face at which the channel opens is the downstream end face of the base body. The throttle element is preferably a throttle valve. A choke element can advantageously be held in the base body upstream of the throttle element. The choke element is preferably a choke flap. If the choke element is designed as a choke flap, there is sufficient installation space in the intake channel section so that the channel and the choke element can be arranged at least partially in the same cross section of the mixture formation unit. It can be provided that no partition wall section is arranged in the intake channel section upstream of the throttle element. In a preferred embodiment, a partition wall section is arranged in the intake duct section upstream of the throttle element. A simple structure results when the component is pressed into the channel. The component can be pressed directly into the channel. The outer circumference of the component and the channel advantageously form an interference fit and lie to each other. In an alternative design, it can be provided that the component is pressed into the channel with at least one seal in between. Several seals can be advantageous, in particular in order to seal different areas on the outer circumference of the component to one another. If the component has a valve, it can be particularly advantageous to separate the areas downstream and upstream of the valve on the outer circumference of the component by means of at least one seal. The seal can be an O-ring, for example. However, a different design of the seal can also be advantageous.

For a two-stroke engine with a mixture formation unit, it is provided that the two-stroke engine has a cylinder in which a combustion chamber is formed which is delimited by a piston. The piston drives a crankshaft rotatably mounted in a crankcase. A crankcase interior is connected to the combustion chamber in at least one position of the piston via at least one overflow duct. The two-stroke engine has an intake duct which is divided downstream of the intake duct section formed in the mixture formation unit by a partition into a mixture duct for supplying the fuel / air mixture into the combustion chamber and an air duct for supplying scavenging air to the at least one transfer duct. It has been shown that, in particular in a mixture formation unit for a flushing reservoir motor, in which the intake duct section is divided into a mixture duct and an air duct, sufficient installation space is available for the straight duct opening at one end of the base body.

Upstream of the throttle element, a partition wall section can be provided for dividing the intake duct section into the mixture duct and the air duct. However, it can also be provided that no partition wall section is provided upstream of the throttle element for dividing the intake duct section into a mixture duct and an air duct.

The mixture formation device according to the invention can also be provided for a two-stroke engine that does not have an air duct or for a two-stroke engine that has an air duct that is guided separately from the mixture duct. The mixture formation device according to the invention is also advantageous for a four-stroke engine, in particular for a mixture-lubricated four-stroke engine.

Fig. 1

eine schematische Darstellung eines Zweitaktmotors,

Fig. 2

eine Schnittdarstellung eines Ausführungsbeispiels eines Vergasers,

Fig. 3

eine ausschnittsweise Seitenansicht des Vergasers aus Fig. 2 in Richtung des Pfeils III in Fig. 2,

Fig. 4

eine Schnittdarstellung eines weiteren Ausführungsbeispiels eines Vergasers,

Fig. 5

eine ausschnittsweise Schnittdarstellung eines weiteren Ausführungsbeispiels eines Vergasers.

Embodiments of the invention are explained below with reference to the drawing. Show it:

Fig. 1

a schematic representation of a two-stroke engine,

Fig. 2

a sectional view of an embodiment of a carburetor,

Fig. 3

a partial side view of the carburetor Fig. 2 in the direction of arrow III in Fig. 2 ,

Fig. 4

a sectional view of a further embodiment of a carburetor,

Fig. 5

a partial sectional view of a further embodiment of a carburetor.

The in Fig. 1 The two-stroke engine 1 shown schematically has a cylinder 2 and a crankcase 4. A combustion chamber 3 is formed in the cylinder 2 and a crankcase interior 6 is formed in the crankcase 4. The crankcase interior 6 and the combustion chamber 3 are separated by a piston 5 that can move back and forth in the cylinder 2. In predetermined piston positions, for example in the in Fig. 1 The position of the piston 5 shown in the illustration in the area of bottom dead center, the crankcase interior 6 and the combustion chamber 3 are connected to one another via overflow channels 8. The overflow channels 8 open into the combustion chamber 3 with overflow windows 9. The overflow windows 9 become the combustion chamber as a function of the position of the piston 5 3 open or closed. The piston 5 drives a crankshaft 7 rotatably mounted in the crankcase 4 to rotate. The two-stroke engine 1 can, for example, be the drive motor in a hand-held tool such as a power saw, a power cutter, a blower, a hedge trimmer, a sprayer or the like, and the crankshaft 7 can serve to drive a tool of the tool. In the case of a blower or sprayer, the tool is usually a blower that promotes a flow of working air. Instead of a two-stroke engine 1, the drive motor can also be a four-stroke engine, in particular a mixture-lubricated four-stroke engine.

The two-stroke engine 1 has an intake tract with an air filter 49, a mixture formation unit 13 and a connection piece 41 for connecting the mixture formation unit 13 to the cylinder 2. The mixture formation unit 13 is a carburetor in the exemplary embodiment. Instead of the connecting piece 41, one or more arbitrary other parts for the fluidic connection of the mixture formation unit 13 to the cylinder 2 or the crankcase 4 can be provided. The air filter 49 has a filter element 39. Downstream of the filter element 39, a clean room 50 is formed, from which an intake duct 10 leads. An intake passage section 11 is formed in the mixture formation unit 13. A throttle element 17, in the exemplary embodiment a throttle valve, is adjustably supported in the intake duct section 11. In the exemplary embodiment, the throttle element 17 is mounted with a throttle shaft 18. Downstream of the throttle element 17, the intake duct 10 is divided into a mixture duct 12 and an air duct 14. The intake channel 10 has an intake channel longitudinal axis 32 which forms the longitudinal center axis of the intake channel 10. The mixture channel 12 opens with a mixture channel opening 15 at the cylinder bore 55. The mixture channel opening 15 is controlled by the piston 5. The mixture channel opening 15 is open towards the crankcase interior 6 in the region of the top dead center of the piston 15. The air duct 14 opens with at least one air duct opening 16 at the cylinder bore 55. The air duct opening 16 is also controlled by the piston 5. The piston 5 has at least one piston pocket 37, which connects the air duct opening 16 in the area of the top dead center of the piston 5 with the overflow windows 9. Via the air duct 14, the air duct opening 16 and the overflow window 9 is upstream in the overflow channels 8 in the area of the top dead center of the piston 5 scavenging air. The cylinder 2 has an outlet 40 from the combustion chamber 3.

As Fig. 1 also shows, a main fuel opening 27 and a plurality of secondary fuel openings 28 open into the intake duct section 11 in the mixture formation unit 13. The main fuel opening 27 is formed on a main fuel nozzle 29. The main fuel opening 27 opens into the intake duct section 11 in the area of a Venturi section 34. The mixture formation unit 13 has a base body 23 which has a first, upstream face 24 and a second, downstream face 25. The main fuel nozzle 29 is arranged in a straight channel 26 which extends from the first end face 24 into the intake channel section 11. As a result, a hose with cleaning fluid such as air can be connected to the first end face 24 during the production of the mixture formation unit 13 or after the main fuel nozzle 29 has been replaced, and the channel 26 and parts of the fuel system can be cleaned. An orifice on the first end face 24 can also be advantageous for other channels of the mixture formation unit 13. In the exemplary embodiment, the first end face 24 at which the channel 26 opens is the upstream end face. The first end face 24, at which the channel 26 opens, can, however, also be the downstream end face of the base body 23.

The main fuel nozzle 29 is advantageously pressed into the channel 26. The main fuel nozzle 29 can be pressed directly into the channel 26 so that the outer circumference of the main fuel nozzle 29 is in contact with the wall of the channel 26. Alternatively, it can be provided that the main fuel nozzle 29 is pressed into the channel 26 with at least one seal in between. In Fig. 2 For this purpose, a seal 80 is shown schematically with a dashed line. The seal 80 can be, for example, an O-ring. Several seals 80 can also be advantageous.

As Fig. 1 shows, no further elements are provided upstream of the throttle element 17 for subdividing the intake duct section 11 into mixture duct 12 and air duct 14. A choke element is also not provided.

Downstream of the throttle element 17 is in the embodiment according to Fig. 1 the intake duct 10 is divided into the mixture duct 12 and the air duct 14 by a partition 35. On the side facing the throttle element 17, the partition 35 has an abutment 38 against which the throttle element 17 rests in the fully open position. When the throttle element 17 is in the partially closed position, an opening is formed between the throttle shaft 18 and the system 38, through which opening fuel can reach the area upstream of the air duct 14.

During operation of the two-stroke engine 1, on the upward stroke of the piston 5, the fuel / air mixture is sucked from the mixture duct 12 into the crankcase interior 6 as soon as the mixture duct opening 15 opens. As long as the air duct opening 16 is connected to the overflow windows 9 via the piston pocket 37, flushing air is stored upstream in the overflow ducts 8. During the downward stroke of the piston 5, the fuel / air mixture in the crankcase interior 6 is compressed and, as soon as the transfer windows 9 open, scavenging air initially flows from the transfer channels 8 and then the fuel / air mixture from the crankcase interior 6 into the combustion chamber 3. The fuel / air mixture is compressed in the combustion chamber 3 during the upward stroke of the piston 5 and ignited by a spark plug 72 in the region of the top dead center of the piston 5. The spark plug 72 is preferably activated by a control device 61 which also has a fuel valve 60 ( Fig. 4 ) controls. During the downward stroke of the piston 5, the piston 5 first opens the outlet 40 so that exhaust gases can flow out of the combustion chamber 3. Subsequently, the overflow windows 9 are opened and purge air flows into the combustion chamber 3 and flushes the remaining exhaust gases out of the combustion chamber 3 through the outlet 40. Fresh fuel / air mixture then flows into combustion chamber 3 for the next combustion.

Fig. 2 shows a further exemplary embodiment of a mixture formation unit 13. The same reference symbols denote elements that correspond to one another in all exemplary embodiments. The mixture formation unit 13 from Fig. 2 likewise has a base body 23 with a first end face 24 and a second end face 25. During operation, air flows from the first end face 24 to the second end face 25, as indicated by arrow 51 in FIG Fig. 2 is shown schematically. The throttle element 17 is fixed to the throttle shaft 18 via a fastening screw 19. In relation to the flow direction upstream of the throttle element 17, a choke element 20 is arranged in the intake channel section 11. The choke element 20 is designed as a choke flap and is fixed to a choke shaft 21 by means of a fastening screw 22. The throttle element 17 is mounted pivotably about an axis of rotation 76, and the choke element 18 is mounted pivotably about an axis of rotation 77. A partition wall section 36 is arranged in the intake duct section 11 in the direction of flow between the choke shaft 21 and the throttle shaft 18. The partition wall section 36 separates the air duct 14 and the mixture duct 12 from one another.

In the embodiment according to Fig. 2 a contact 56 for the throttle element 17 is formed on the partition wall section 36. The system 56 is arranged on the side of the partition wall section 36 facing the mixture channel 12. On the side facing the air duct 12, a system 57 for the choke element 20 is formed.

Also in the embodiment according to Fig. 2 a channel 26 is provided in the base body 23. The channel 26 is advantageously designed as a straight, continuous bore with a constant diameter. The channel 26 advantageously extends from the end face 24 into the intake channel section 11. In the exemplary embodiment, the channel 26 is not closed over its entire length over its entire circumference, but is open to the intake channel section 11 in the area adjoining the end face 24. It can also be provided that the channel 26 is designed to be open on the circumference in another direction over a portion of its length. It can also be provided that the channel 26 over its entire length in one direction over a partial section its scope is open. Here, the wall delimiting the channel 26 can, for example, have an approximately U-shaped cross section. The channel 26 is advantageously produced by means of drilling or milling or is produced as a cast structure when the base body 23 is cast.

The channel 26 has a central axis 33. In the exemplary embodiment, the central axis 33 forms an angle α with the longitudinal axis 23 of the intake duct which is smaller than 90 °. In the exemplary embodiment, the angle α is greater than 0 °. However, an angle of 0 ° can also be advantageous. The angle α is preferably from 0 ° to 30 °, in particular from 0 ° to 25 °. The angle α is measured in a sectional plane which contains the longitudinal axis 32 of the intake duct and which runs parallel to the central axis 33 of the duct 26. In the exemplary embodiment, the sectional plane contains both the intake duct longitudinal axis 32 and the central axis 33 and corresponds to that in FIG Fig. 2 section plane shown. If the intake channel longitudinal axis 32 and the central axis 33 are skewed to one another, the angle α between the intake channel longitudinal axis 32 and a projection of the central axis 33 into the cutting plane is measured in a projection direction perpendicular to the cutting plane.

The base body 23 of the mixture formation device 13 has a first longitudinal side 58 and a second longitudinal side 59. The longitudinal sides 58 and 59 run approximately parallel to the central axis 32 of the intake duct section 11. A fuel pump 46 is advantageously formed on the first longitudinal side 58. The fuel pump 46 is delimited by the base body 23, a pump cover 47 fixed on the base body 23 and a pump diaphragm (not shown). The pump cover 47 is preferably screwed to the base body 23 via a fastening screw 48. A control chamber 42 and a compensation chamber 43, which are separated by a control membrane 44, are advantageously formed on the opposite longitudinal side 59. The control membrane 44 is of an in Fig. 2 The control chamber cover 62 shown schematically is held on the base body 23. The control chamber 42 is advantageously coupled in the usual way with a spring-loaded lever to an inlet valve that the Regulates fuel flow from fuel pump 46 into control chamber 42. The control chamber 42 is connected to secondary fuel openings 28 via a check valve 45. A fuel channel 64, in which a fixed throttle 63 is arranged in the exemplary embodiment, also leads from the control chamber 42. Instead of the fixed throttle 63, an adjustable throttle can be provided, for example.

The main fuel nozzle 29 is arranged in the channel 26. On the outer circumference of the main fuel nozzle 29, an annular gap 30 is formed, into which the fuel channel 64 opens. The annular gap 30 is delimited by a circumferential groove on the outer circumference of the main fuel nozzle 29 and by the wall of the channel 26. A transverse channel 65 is formed in the main fuel nozzle 29, which in the exemplary embodiment runs perpendicular to the central axis 33, as well as a longitudinal channel 66 which runs centrally through the main fuel nozzle 29 in the direction of the central axis 33. The annular gap 30 is connected to the longitudinal channel 66 via the transverse channel 65. The longitudinal channel 66 ends at a valve plate 52. The valve plate 52 forms a check valve 31 with a valve seat 54. In the closed state of the check valve 31, the valve plate 52 rests against the valve seat 54. If there is excess pressure in the intake channel section 11 compared to the control chamber 42, the check valve 31 is closed. When there is negative pressure in the intake channel section 11, the valve plate 52 is lifted off the valve seat 54. The check valve 31 has a stop 53 which limits the maximum stroke of the valve plate 52. The stroke of the valve plate 52 is preferably as small as possible.

Fig. 3 shows the opening of the channel 26 at the first end face 24. In the exemplary embodiment, the channel 26 is formed completely in the base body 23 and is at least partially closed over its circumference. For this purpose, the base body 23 has a section 67 which protrudes into the intake duct section 11. The section 67 reduces the free flow cross-section in the mixture channel 12. In the exemplary embodiment, the section 67 has a bevel 68 so that the flow cross-section at the section 67 extends in the direction of the arrow 51 ( Fig. 2 ) enlarged. The bevel 68 is also in Fig. 2 shown. The bevel 68 can also be omitted in an alternative embodiment.

Fig. 4 shows an embodiment of a mixture formation device 13, the structure of which is essentially that in the Fig. 2 and 3 mixture formation device 13 shown and described corresponds to. The same reference symbols designate elements that correspond to one another in all figures. At the mixture formation device 13 in Fig. 4 is the channel 26 opposite that in the Figs. 1 and 2 shown version rotated. The channel 26 runs parallel to the intake channel longitudinal axis 32. The central axis 33 of the channel 26 and the intake channel longitudinal axis 32 enclose an angle of 0 °, that is to say run parallel.

Fig. 5 shows an embodiment of a mixture formation unit 13 in which a fuel valve 60 is arranged in the channel 26. The further structure of the mixture formation device 13 corresponds to that in FIG Fig. 2 and 3 mixture formation device 13 shown and described. The fuel valve 60 is an electromagnetic valve, preferably a valve that is open in the de-energized state. It can also be advantageous that the fuel valve 60 is closed in the de-energized state. The fuel valve 60 also has a valve plate 52 which, however, is not acted upon by the prevailing pressure conditions, but by a spring 69 and an electromagnet 70. If current flows through the electromagnet 70, the valve plate 52 is pulled against the force of the spring 69 against an inlet opening 71 and closes it. In the de-energized state, the valve plate 52 is pulled to a stop 53 and in this position releases the inlet opening 71. In order to control the electromagnet 70, the fuel valve 60 is connected to a control device 61. The control device 61 is in particular a control device which also controls the ignition timing of the two-stroke engine 1 or a four-stroke engine.

In the embodiment, a check valve 81 is arranged in the fuel channel 64, which connects the control chamber 42 to the channel 26. The check valve 81 closes in the flow direction from the channel 26 to the control chamber 42. The check valve 81 is arranged downstream of the fixed throttle 63 in the exemplary embodiment. Another arrangement of the check valve 81 can also be advantageous.

Another design of the fuel valve 60 can also be advantageous. Instead of the main fuel nozzle 29 or the fuel valve 60, other components can also be arranged in the channel 26. In particular, a needle valve or a spring-loaded valve, such as is used in a purger, can be arranged in the channel 26.

The mixture formation unit 13 is designed as a carburetor in the exemplary embodiments. A carburetor pumps the fuel into the intake channel due to the negative pressure existing in the intake channel. In an alternative configuration, another mixture formation unit can also be provided. The mixture formation unit can, in particular, have a fuel valve which, due to the excess pressure of the fuel, supplies fuel into the intake duct, in particular injects it into the intake duct.

Claims (18)

Mixture formation unit with a base body (23) in which an intake duct section (11) is formed, the intake duct section (11) extending from a first end face (24) of the base body (23) to a second end face (25) of the base body (23) , wherein the mixture formation unit (13) has at least one straight channel (26) which opens into the intake channel section (11),
characterized in that the channel (26) opens out on the first end face (24) of the base body (23). Mixture formation unit according to claim 1,
characterized in that a component of the mixture formation unit (13) is arranged in the channel (26). Mixture formation unit according to claim 2,
characterized in that the mixture formation unit (13) has at least one fuel opening which opens into the intake duct section (11) and which is formed on a fuel nozzle, the fuel nozzle forming the component arranged in the duct (26). Mixture formation unit according to claim 3,
characterized in that the fuel opening is a main fuel opening (27) and the fuel nozzle is a main fuel nozzle (29). Mixture formation unit according to claim 3 or 4,
characterized in that the component forms an annular gap (30) with the channel (26) which is connected to the fuel opening. Mixture formation unit according to one of claims 2 to 5,
characterized in that the component has a check valve (31). Mixture formation unit according to one of claims 2 to 5,
characterized in that the component is a fuel valve (60). Mixture formation unit according to one of Claims 1 to 7,
characterized in that the central axis (33) of the channel (26) forms an angle (α) with the longitudinal axis (32) of the intake channel in a sectional plane which contains the longitudinal axis (32) of the intake channel and which runs parallel to the central axis (33) of the channel (26) ) from 0 ° to 30 °. Mixture formation unit according to one of claims 1 to 8,
characterized in that the intake duct section (11) has a Venturi section (34) and that a throttle element (17) is mounted in the base body (23) downstream of the Venturi section (34). Mixture formation unit according to claim 9,
characterized in that the first end face (24) of the base body (23) is the upstream end face of the base body (23). Mixture formation unit according to claim 9 or 10,
characterized in that the throttle element (17) is a throttle valve. Mixture formation unit according to claim 11,
characterized in that a choke element (20) is held in the base body (23) upstream of the throttle element (17). Mixture formation unit according to one of claims 9 to 12,
characterized in that no partition wall section is arranged in the intake duct section (11) upstream of the throttle element (17). Mixture formation unit according to one of claims 9 to 12,
characterized in that a partition wall section (36) is arranged in the intake duct section (11) upstream of the throttle element (17). Mixture formation unit according to one of claims 1 to 14,
characterized in that the component is pressed into the channel (26). Two-stroke engine with a mixture formation unit according to one of claims 1 to 15, with a cylinder (2) in which a combustion chamber (3) is formed which is delimited by a piston (5), the piston (5) being a crankcase ( 4) drives a rotatably mounted crankshaft (7), a crankcase interior (6) being connected to the combustion chamber (3) in at least one position of the piston (5) via at least one overflow duct (8), with an intake duct (10) which is downstream of the intake duct section (11) formed in the mixture formation unit (13) through a partition (35) into a mixture duct (12) for supplying the fuel / air mixture to the combustion chamber (3) and an air duct (14) for supplying purge air to the at least one overflow channel (8) is divided. Two-stroke engine according to claim 16,
characterized in that upstream of the throttle element (17) there is no partition section for dividing the intake duct section (11) into the mixture duct (12) and the air duct (14). Two-stroke engine according to claim 16,
characterized in that upstream of the throttle element (17) a partition wall section (36) is provided for dividing the intake duct section (11) into the mixture duct (12) and the air duct (14).

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