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EP3748151B1 - Mixture forming unit and two-stroke engine having a mixture forming unit - Google Patents

Mixture forming unit and two-stroke engine having a mixture forming unit Download PDF

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Publication number
EP3748151B1
EP3748151B1 EP20178313.1A EP20178313A EP3748151B1 EP 3748151 B1 EP3748151 B1 EP 3748151B1 EP 20178313 A EP20178313 A EP 20178313A EP 3748151 B1 EP3748151 B1 EP 3748151B1
Authority
EP
European Patent Office
Prior art keywords
channel
mixture
intake
formation unit
unit according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
EP20178313.1A
Other languages
German (de)
French (fr)
Other versions
EP3748151A1 (en
Inventor
Felix Servatius
Wolfgang Luithardt
Horst Denner
Dr. Martin Christoph Arenz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Andreas Stihl AG and Co KG
Original Assignee
Andreas Stihl AG and Co KG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Andreas Stihl AG and Co KG filed Critical Andreas Stihl AG and Co KG
Publication of EP3748151A1 publication Critical patent/EP3748151A1/en
Application granted granted Critical
Publication of EP3748151B1 publication Critical patent/EP3748151B1/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M17/00—Carburettors having pertinent characteristics not provided for in, or of interest apart from, the apparatus of preceding main groups F02M1/00 - F02M15/00
    • F02M17/10—Carburettors having one or more fuel passages opening in valve-member of air throttle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M17/00—Carburettors having pertinent characteristics not provided for in, or of interest apart from, the apparatus of preceding main groups F02M1/00 - F02M15/00
    • F02M17/36—Carburettors having fitments facilitating their cleaning
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B25/00—Engines characterised by using fresh charge for scavenging cylinders
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B25/00—Engines characterised by using fresh charge for scavenging cylinders
    • F02B25/02—Engines characterised by using fresh charge for scavenging cylinders using unidirectional scavenging
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B25/00—Engines characterised by using fresh charge for scavenging cylinders
    • F02B25/02—Engines characterised by using fresh charge for scavenging cylinders using unidirectional scavenging
    • F02B25/04—Engines having ports both in cylinder head and in cylinder wall near bottom of piston stroke
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B25/00—Engines characterised by using fresh charge for scavenging cylinders
    • F02B25/14—Engines characterised by using fresh charge for scavenging cylinders using reverse-flow scavenging, e.g. with both outlet and inlet ports arranged near bottom of piston stroke
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B75/00—Other engines
    • F02B75/02—Engines characterised by their cycles, e.g. six-stroke
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B77/00—Component parts, details or accessories, not otherwise provided for
    • F02B77/04—Cleaning of, preventing corrosion or erosion in, or preventing unwanted deposits in, combustion engines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D9/00—Controlling engines by throttling air or fuel-and-air induction conduits or exhaust conduits
    • F02D9/08—Throttle valves specially adapted therefor; Arrangements of such valves in conduits
    • F02D9/10—Throttle valves specially adapted therefor; Arrangements of such valves in conduits having pivotally-mounted flaps
    • F02D9/109—Throttle valves specially adapted therefor; Arrangements of such valves in conduits having pivotally-mounted flaps having two or more flaps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M17/00—Carburettors having pertinent characteristics not provided for in, or of interest apart from, the apparatus of preceding main groups F02M1/00 - F02M15/00
    • F02M17/08—Carburettors having one or more fuel passages opening in a valve-seat surrounding combustion-air passage, the valve being opened by passing air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M17/00—Carburettors having pertinent characteristics not provided for in, or of interest apart from, the apparatus of preceding main groups F02M1/00 - F02M15/00
    • F02M17/10—Carburettors having one or more fuel passages opening in valve-member of air throttle
    • F02M17/12—Carburettors having one or more fuel passages opening in valve-member of air throttle the valve member being of butterfly type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M17/00—Carburettors having pertinent characteristics not provided for in, or of interest apart from, the apparatus of preceding main groups F02M1/00 - F02M15/00
    • F02M17/34—Other carburettors combined or associated with other apparatus, e.g. air filters
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M19/00—Details, component parts, or accessories of carburettors, not provided for in, or of interest apart from, the apparatus of groups F02M1/00 - F02M17/00
    • F02M19/08—Venturis
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M29/00—Apparatus for re-atomising condensed fuel or homogenising fuel-air mixture
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M35/00—Combustion-air cleaners, air intakes, intake silencers, or induction systems specially adapted for, or arranged on, internal-combustion engines
    • F02M35/10—Air intakes; Induction systems
    • F02M35/1015—Air intakes; Induction systems characterised by the engine type
    • F02M35/1019—Two-stroke engines; Reverse-flow scavenged or cross scavenged engines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M35/00—Combustion-air cleaners, air intakes, intake silencers, or induction systems specially adapted for, or arranged on, internal-combustion engines
    • F02M35/10—Air intakes; Induction systems
    • F02M35/10209—Fluid connections to the air intake system; their arrangement of pipes, valves or the like
    • F02M35/10216—Fuel injectors; Fuel pipes or rails; Fuel pumps or pressure regulators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M35/00—Combustion-air cleaners, air intakes, intake silencers, or induction systems specially adapted for, or arranged on, internal-combustion engines
    • F02M35/10—Air intakes; Induction systems
    • F02M35/10242—Devices or means connected to or integrated into air intakes; Air intakes combined with other engine or vehicle parts
    • F02M35/10262—Flow guides, obstructions, deflectors or the like
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M7/00—Carburettors with means for influencing, e.g. enriching or keeping constant, fuel/air ratio of charge under varying conditions
    • F02M7/12—Other installations, with moving parts, for influencing fuel/air ratio, e.g. having valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B75/00—Other engines
    • F02B75/02—Engines characterised by their cycles, e.g. six-stroke
    • F02B2075/022—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle
    • F02B2075/025—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle two
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M19/00—Details, component parts, or accessories of carburettors, not provided for in, or of interest apart from, the apparatus of groups F02M1/00 - F02M17/00
    • F02M19/08—Venturis
    • F02M19/088—Whirl devices and other atomising means in or on the venturi walls

Definitions

  • the invention relates to a mixture formation unit of the type specified in the preamble of claim 1 and to a two-stroke engine with a mixture formation unit.
  • a mixture formation device namely a carburettor
  • the main fuel nozzle is arranged in a straight channel. This means that the main fuel nozzle can be easily pushed or pressed into the carburettor's base body from the outside.
  • a cover that holds the control membrane and a cover for the fuel pump are arranged on the base body. If the cover that holds the control membrane is mounted on the base body, the channel in which the main fuel nozzle is arranged is only accessible from the intake channel.
  • a float carburetor which feeds a fuel/air mixture into the intake duct using a nozzle.
  • the nozzle is screwed into a duct that opens into one end of the carburetor and protrudes into the duct at a radial distance. This allows air from the intake duct to be sucked into the fuel and to exit into the intake duct together with the fuel as a fuel/air mixture.
  • a carburetor of this type is known.
  • a value range of 0° to 50° is provided for the angle between the center axis of the main fuel nozzle and a perpendicular to the longitudinal axis of the intake duct.
  • the channels of a carburettor are usually manufactured at least partially using machining processes. After the cover of the control chamber has been fitted, the channel in which the main fuel nozzle is located is only accessible from the intake channel. Therefore, cleaning the carburettor after all components have been assembled is only possible to a limited extent. Particles in the fuel-carrying channels can come loose during operation and become stuck in undesirable positions, for example on sensitive components such as valves or the like, thereby disrupting the operation of the carburettor.
  • the invention is based on the object of creating a mixture formation unit of the generic type which is highly robust in operation and is easy to clean.
  • a further object of the invention is to provide a two-stroke engine with a mixture formation unit.
  • the channel runs relatively flat in the base body of the mixture formation unit. This results in a favorable arrangement and a good use of the installation space usually available in the mixture formation unit.
  • the central axis of the channel advantageously forms an angle of 0° to 30°, in particular 0° to 25°, with the intake channel longitudinal axis in a cutting plane that contains the intake channel longitudinal axis and runs parallel to the central axis of the channel.
  • the central axis of the channel can therefore lie in the same plane as the intake channel longitudinal axis or run skewed to the intake channel longitudinal axis. If the central axis of the channel runs skewed to the intake channel longitudinal axis, the angle in the cutting plane is measured between a projection of the central axis of the channel perpendicular to the cutting plane and the intake channel longitudinal axis.
  • the in Fig. 1 The schematically illustrated two-stroke engine 1 has a cylinder 2 and a crankcase 4.
  • a combustion chamber 3 is formed in the cylinder 2 and a crankcase interior 6 in the crankcase 4.
  • the crankcase interior 6 and the combustion chamber 3 are separated by a piston 5 that moves back and forth in the cylinder 2.
  • 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 via overflow windows 9.
  • the overflow windows 9 are opened or closed depending on the position of the piston 5 in relation to the combustion chamber 3.
  • the piston 5 drives a rotating crankshaft 7 which is rotatably mounted in the crankcase 4.
  • the two-stroke engine 1 can, for example, be the drive motor in a hand-held working device such as a chainsaw, a cut-off machine, a blower, a hedge trimmer, a sprayer or the like, and the crankshaft 7 can serve to drive a tool of the working device.
  • the tool is usually a fan that conveys a working air flow.
  • 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 connecting 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 other desired parts can be provided for the fluidic connection of the mixture formation unit 13 to the cylinder 2 or the crankcase 4.
  • 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 channel 10 leads.
  • An intake channel section 11 is formed in the mixture formation unit 13.
  • a throttle element 17, in the exemplary embodiment a throttle valve, is adjustably mounted in the intake channel section 11. In the exemplary embodiment, the throttle element 17 is mounted with a throttle shaft 18.
  • the cylinder 2 has an outlet 40 from the combustion chamber 3.
  • a main fuel opening 27 and several secondary fuel openings 28 open into the intake channel 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 channel section 11 in the region of a venturi section 34.
  • the mixture formation unit 13 has a base body 23 which has a first, upstream end face 24 and a second, downstream end 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.
  • first end face 24 can also be advantageous for other channels of the mixture formation unit 13.
  • first end face 24, at which the channel 26 opens is the upstream end face.
  • first end face 24, at which the channel 26 opens can also be the downstream end face of the base body 23.
  • the intake duct 10 Downstream of the throttle element 17 in the embodiment according to Fig. 1 the intake duct 10 is divided by a partition 35 into the mixture duct 12 and the air duct 14.
  • the partition 35 On the side facing the throttle element 17, the partition 35 has a system 38 against which the throttle element 17 rests in the fully open position.
  • an opening is formed between the throttle shaft 18 and the system 38, through which fuel can reach the area upstream of the air duct 14.
  • a system 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.
  • a system 57 for the choke element 20 is formed on the side facing the air channel 12.
  • 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 front side 24 into the intake channel section 11.
  • the channel 26 is not closed over its entire length over its entire circumference, but is open in the area adjacent to the front side 24 towards the intake channel section 11.
  • the channel 26 is designed to be open in another direction on the circumference over a portion of its length.
  • the channel 26 is open over its entire length in one direction over a portion its circumference is open.
  • the wall delimiting the channel 26 can, for example, be approximately U-shaped in cross section.
  • the channel 26 is advantageously produced by 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.
  • the central axis 33 forms an angle ⁇ with the intake channel longitudinal axis 23 that is less than 90°.
  • the angle ⁇ is greater than 0°.
  • an angle of 0° can also be advantageous.
  • the angle ⁇ is preferably from 0° to 30°, in particular from 0° to 25°.
  • the angle ⁇ is measured in a cutting plane that contains the intake channel longitudinal axis 32 and that runs parallel to the central axis 33 of the channel 26.
  • the cutting plane contains both the intake channel longitudinal axis 32 and the central axis 33 and corresponds to the Fig. 2 shown cutting plane.
  • the angle ⁇ between the intake duct 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 channel 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 to the base body 23 and a pump membrane (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 are advantageously formed on the opposite longitudinal side 59, which are separated by a control membrane 44.
  • the control membrane 44 is surrounded by a Fig. 2
  • the control chamber 42 is held on the base body 23 by a control chamber cover 62 shown schematically.
  • the control chamber 42 is advantageously coupled in the usual way with a spring-loaded lever to an inlet valve, which Regulates the flow of fuel from the fuel pump 46 into the control chamber 42.
  • the control chamber 42 is connected to secondary fuel openings 28 via a check valve 45.
  • a fuel channel 64 also leads from the control chamber 42, in which a fixed throttle 63 is arranged in the exemplary embodiment. 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.
  • An annular gap 30 is formed on the outer circumference of the main fuel nozzle 29, 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, and 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 opens at a valve plate 52.
  • the valve plate 52 forms a check valve 31 with a valve seat 54.
  • valve plate 52 When the check valve 31 is closed, 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. If 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 on the first end face 24.
  • the channel 26 is formed completely in the base body 23 and is at least partially closed over its circumference.
  • the base body 23 has a section 67 which projects into the intake channel section 11.
  • the section 67 reduces the free flow cross-section in the mixture channel 12.
  • 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 ) is enlarged.
  • the bevel 68 is also in Fig. 2
  • the bevel 68 can also be omitted in an alternative design.
  • Fig. 4 shows an embodiment of a mixture formation device 13, the structure of which essentially corresponds to that shown in the Fig. 2 and 3
  • the same reference numerals designate corresponding elements in all figures.
  • Channel 26 is opposite the one in the Fig. 1 and 2 shown version.
  • 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°, i.e. they run parallel.
  • the mixture formation unit 13 is designed as a carburetor in the exemplary embodiments.
  • a carburetor feeds the fuel into the intake channel due to the negative pressure in the intake channel.
  • another mixture formation unit can also be provided.
  • the mixture formation unit can in particular have a fuel valve that feeds fuel into the intake channel due to the excess pressure of the fuel, in particular injects it into the intake channel.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Control Of The Air-Fuel Ratio Of Carburetors (AREA)
  • Cylinder Crankcases Of Internal Combustion Engines (AREA)
  • Means For Warming Up And Starting Carburetors (AREA)
  • Control Of Throttle Valves Provided In The Intake System Or In The Exhaust System (AREA)

Description

Die Erfindung betrifft eine Gemischbildungseinheit der im Oberbegriff des Anspruchs 1 angegebenen Gattung sowie einen Zweitaktmotor mit einer Gemischbildungseinheit.The invention relates to a mixture formation unit of the type specified in the preamble of claim 1 and to a two-stroke engine with a mixture formation unit.

Aus der US 2014/0261329 A1 ist eine Gemischbildungseinrichtung, nämlich ein Vergaser bekannt, bei dem die Hauptkraftstoffdüse in einem geraden Kanal angeordnet ist. Dadurch kann die Hauptkraftstoffdüse auf einfache Weise von außen in den Grundkörper des Vergasers eingeschoben oder eingepresst werden. Am Grundkörper sind ein Deckel, der die Regelmembran hält, sowie ein Deckel der Kraftstoffpumpe angeordnet. Ist der Deckel, der die Regelmembran hält, am Grundkörper montiert, so ist der Kanal, in dem die Hauptkraftstoffdüse angeordnet ist, nur noch vom Ansaugkanal aus zugänglich.From the US 2014/0261329 A1 A mixture formation device, namely a carburettor, is known in which the main fuel nozzle is arranged in a straight channel. This means that the main fuel nozzle can be easily pushed or pressed into the carburettor's base body from the outside. A cover that holds the control membrane and a cover for the fuel pump are arranged on the base body. If the cover that holds the control membrane is mounted on the base body, the channel in which the main fuel nozzle is arranged is only accessible from the intake channel.

Aus der US 1,061,835 A ist ein Schwimmervergaser bekannt, der ein Kraftstoff/LuftGemisch mittels einer Düse in den Ansaugkanal zuführt. Die Düse ist in einem an einer Stirnseite des Vergasers mündenden Kanal eingeschraubt und ragt mit radialem Abstand in den Kanal. Dadurch kann Luft aus dem Ansaugkanal in den Kraftstoff angesaugt werden und gemeinsam mit dem Kraftstoff als Kraftstoff/Luft-Gemisch in den Ansaugkanal austreten.From the US 1,061,835 A A float carburetor is known which feeds a fuel/air mixture into the intake duct using a nozzle. The nozzle is screwed into a duct that opens into one end of the carburetor and protrudes into the duct at a radial distance. This allows air from the intake duct to be sucked into the fuel and to exit into the intake duct together with the fuel as a fuel/air mixture.

Aus der EP 2 947 305 A1 ist ein gattungsgemäßer Vergaser bekannt. Für den Winkel zwischen der Mittelachse der Hauptkraftstoffdüse und einer Senkrechten zur Ansaugkanallängsachse ist ein Wertebereich von 0° bis 50° vorgesehen.From the EP 2 947 305 A1 A carburetor of this type is known. A value range of 0° to 50° is provided for the angle between the center axis of the main fuel nozzle and a perpendicular to the longitudinal axis of the intake duct.

Die Kanäle eines Vergasers werden üblicherweise zumindest teilweise mit spanenden Herstellverfahren hergestellt. Nach der Montage des Deckels der Regelkammer ist der Kanal, in dem die Hauptkraftstoffdüse angeordnet ist, jedoch lediglich vom Ansaugkanal aus zugänglich. Daher ist das Reinigen des Vergasers nach dem Zusammenbau aller Bauteile nur noch eingeschränkt möglich. Partikel, die sich in den kraftstoffführenden Kanälen befinden, können sich im Betrieb lösen und an unerwünschten Positionen, beispielsweise an sensiblen Bauteilen wie Ventilen oder dergleichen festsetzen und damit den Betrieb des Vergasers stören.The channels of a carburettor are usually manufactured at least partially using machining processes. After the cover of the control chamber has been fitted, the channel in which the main fuel nozzle is located is only accessible from the intake channel. Therefore, cleaning the carburettor after all components have been assembled is only possible to a limited extent. Particles in the fuel-carrying channels can come loose during operation and become stuck in undesirable positions, for example on sensitive components such as valves or the like, thereby disrupting the operation of the carburettor.

Der Erfindung liegt die Aufgabe zugrunde, eine Gemischbildungseinheit der gattungsgemäßen Art zu schaffen, die eine hohe Robustheit im Betrieb aufweist und gut zu reinigen ist.The invention is based on the object of creating a mixture formation unit of the generic type which is highly robust in operation and is easy to clean.

Eine weitere Aufgabe der Erfindung liegt darin, einen Zweitaktmotor mit einer Gemischbildungseinheit anzugeben.A further object of the invention is to provide a two-stroke engine with a mixture formation unit.

Diese Aufgabe wird bezüglich der Gemischbildungseinheit durch eine Gemischbildungseinheit mit den Merkmalen des Anspruchs 1 gelöst. Bezüglich des Zweitaktmotors wird die Aufgabe durch einen Zweitaktmotor mit den Merkmalen des Anspruchs 11 gelöst.This object is achieved with respect to the mixture formation unit by a mixture formation unit having the features of claim 1. With respect to the two-stroke engine, the object is achieved by a two-stroke engine having the features of claim 11.

Es ist vorgesehen, dass der Kanal, der in den Ansaugkanal mündet, als gerade verlaufender Kanal ausgebildet ist und an einer Stirnseite des Grundkörpers der Gemischbildungseinheit mündet. Dadurch sind beide Enden des Kanals auch nach der Montage von Anbauteilen wie Deckeln, einer Kraftstoffpumpe oder der Regeleinrichtung der Gemischbildungseinheit noch ohne weiteres zugänglich. Dadurch kann der Kanal vollständig gereinigt und durchspült werden. Eine Reinigungsleitung kann insbesondere an der Stirnseite des Grundkörpers angeschlossen werden, so dass sich eine gute Zugänglichkeit des Anschlusses ergibt.It is intended that the channel that opens into the intake channel is designed as a straight channel and opens into one end of the base body of the mixture formation unit. This means that both ends of the channel are still easily accessible even after the installation of add-on parts such as covers, a fuel pump or the control device of the mixture formation unit. This means that the channel can be completely cleaned and flushed. A cleaning line can be connected in particular to the end of the base body, so that the connection is easily accessible.

In dem Kanal ist ein Bauteil der Gemischbildungseinheit angeordnet. Durch die Anordnung der Mündungsöffnung des Kanals an der ersten Stirnseite des Grundkörpers kann der Kanal vor der Montage des Bauteils einfach gereinigt werden. Das in dem Kanal angeordnete Bauteil kann beispielsweise bei Funktionsstörungen auf einfache Weise nachträglich gewechselt werden. Die erste Stirnseite, an der der Kanal mündet, kann dabei sowohl die stromauf liegende Stirnseite der Gemischbildungseinheit als auch die stromab liegende Stirnseite der Gemischbildungseinheit sein. Die Gemischbildungseinheit weist mindestens eine Kraftstofföffnung auf, die in den Ansaugkanalabschnitt mündet und die an einer Kraftstoffdüse ausgebildet ist. Mit Kraftstoffdüse wird dabei das Bauteil bezeichnet, an dem die Engstelle ausgebildet ist, die den Düsenquerschnitt bildet. Auch weitere Funktionen können in der Kraftstoffdüse verwirklicht sein. Die Kraftstoffdüse ist eine Komponente, die aus mehreren Einzelteilen zusammengesetzt sein kann. Die Kraftstofföffnung ist eine Hauptkraftstofföffnung und die Kraftstoffdüse eine Hauptkraftstoffdüse. Vorzugsweise bildet das Bauteil mit dem Kanal, insbesondere mit der Kanalwand des Kanals, einen Ringspalt, der mit der Kraftstofföffnung verbunden ist. Dadurch, dass der Kanal als gerader Kanal ausgeführt ist, kann er mit hoher Genauigkeit gefertigt werden, beispielsweise durch Bohren oder Fräsen, so dass sich definierte Abmessungen für den Ringspalt ergeben.A component of the mixture formation unit is arranged in the channel. By arranging the opening of the channel on the first end face of the base body, the channel can be easily cleaned before the component is assembled. The component arranged in the channel can be easily replaced later, for example in the event of malfunctions. The first end face at which the channel opens can be either the upstream end face of the mixture formation unit or the downstream end face of the mixture formation unit. The mixture formation unit has at least one fuel opening that opens into the intake channel section and is formed on a fuel nozzle. The fuel nozzle refers to the component on which 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 made up of several individual parts. The fuel opening is a main fuel opening and the fuel nozzle is a main fuel nozzle. Preferably, the component 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 precision, for example by drilling or milling, so that defined dimensions are obtained for the annular gap.

Das in dem Kanal angeordnete Bauteil weist ein Rückschlagventil auf. Partikel wie Späne oder dergleichen, die bei der Herstellung entstehen und nicht aus dem Grundkörper der Gemischbildungseinheit entfernt werden, können die Dichtfunktion eines Ventilplättchens des Rückschlagventils verschlechtern und so die Funktion erheblich beeinträchtigen. Insbesondere für ein Rückschlagventil ist daher eine Reinigung von Rückständen aus vorangegangenen Bearbeitungsverfahren wie Spänen der dgl. wünschenswert.The component arranged in the channel has a check valve. Particles such as chips or the like that are created during production and are not removed from the base body of the mixture formation unit can impair the sealing function of a valve plate of the check valve and thus significantly impair its function. Cleaning of residues from previous processing methods such as chips or the like is therefore desirable, particularly for a check valve.

Der Kanal verläuft in bevorzugter Ausführung vergleichsweise flach im Grundkörper der Gemischbildungseinheit. Dadurch ergibt sich eine günstige Anordnung und eine gute Ausnutzung des in der Gemischbildungseinheit üblicherweise zur Verfügung stehenden Bauraums. Vorteilhaft schließt die Mittelachse des Kanals mit der Ansaugkanallängsachse in einer Schnittebene, die die Ansaugkanallängsachse enthält und parallel zur Mittelachse des Kanals verläuft, einen Winkel von 0° bis 30°, insbesondere von 0° bis 25° ein. Die Mittelachse des Kanals kann demnach mit der Ansaugkanallängsachse in einer Ebene liegen oder windschief zur Ansaugkanallängsachse verlaufen. Verläuft die Mittelachse des Kanals windschief zur Ansaugkanallängsachse, so wird der Winkel in der Schnittebene zwischen einer Projektion der Mittelachse des Kanals senkrecht auf die Schnittebene und der Ansaugkanallängsachse gemessen.In the preferred embodiment, the channel runs relatively flat in the base body of the mixture formation unit. This results in a favorable arrangement and a good use of the installation space usually available in the mixture formation unit. The central axis of the channel advantageously forms an angle of 0° to 30°, in particular 0° to 25°, with the intake channel longitudinal axis in a cutting plane that contains the intake channel longitudinal axis and runs parallel to the central axis of the channel. The central axis of the channel can therefore lie in the same plane as the intake channel longitudinal axis or run skewed to the intake channel longitudinal axis. If the central axis of the channel runs skewed to the intake channel longitudinal axis, the angle in the cutting plane is measured between a projection of the central axis of the channel perpendicular to the cutting plane and the intake channel longitudinal axis.

Der Ansaugkanalabschnitt weist vorzugsweise einen Venturiabschnitt auf. Stromab des Venturiabschnitts ist insbesondere ein Drosselelement im Grundkörper gelagert. Das Drosselelement ist vorzugsweise verstellbar angeordnet und dient zur Einstellung des freien Strömungsquerschnitts des Ansaugkanalabschnitts. Vorteilhaft ist das Drosselelement um eine Drehachse schwenkbar.The intake duct section preferably has a venturi section. Downstream of the venturi section, a throttle element is mounted in the base body. The throttle element is preferably arranged so as to be adjustable and is used to set the free flow cross-section of the intake duct section. The throttle element is advantageously pivotable about a rotation axis.

Die Gemischbildungseinheit ist insbesondere ein Vergaser, bei dem die Kraftstoffaufbereitung zumindest teilweise im oder stromab des Venturiabschnitts erfolgt. Die erste Stirnseite, an der der Kanal mündet, ist bevorzugt die stromauf liegende Stirnseite des Grundkörpers. Es kann jedoch auch vorgesehen sein, dass die erste Stirnseite, an der der Kanal mündet, die stromab liegende Stirnseite des Grundkörpers ist. Das Drosselelement ist bevorzugt eine Drosselklappe. Stromauf des Drosselelements kann vorteilhaft ein Chokeelement im Grundkörper gehalten sein. Das Chokeelement ist bevorzugt eine Chokeklappe. Bei Gestaltung des Chokeelements als Chokeklappe ist ausreichend Bauraum im Ansaugkanalabschnitt vorhanden, so dass der Kanal und das Chokeelement zumindest teilweise im gleichen Querschnitt der Gemischbildungseinheit angeordnet werden können. Es kann vorgesehen sein, dass stromauf des Drosselelements kein Trennwandabschnitt im Ansaugkanalabschnitt angeordnet ist. In bevorzugter Gestaltung ist stromauf des Drosselelements ein Trennwandabschnitt im Ansaugkanalabschnitt angeordnet. Ein einfacher Aufbau ergibt sich, wenn das Bauteil in den Kanal eingepresst ist. Das Bauteil kann dabei unmittelbar in den Kanal eingepresst sein. Der Außenumfang des Bauteils und der Kanal bilden vorteilhaft einen Pressverband und liegen aneinander an. In alternativer Gestaltung kann vorgesehen sein, dass das Bauteil unter Zwischenlage mindestens einer Dichtung in den Kanal eingepresst ist. Mehrere Dichtungen können vorteilhaft sein, insbesondere, um unterschiedliche Bereiche am Außenumfang des Bauteils zueinander abzudichten. Wenn das Bauteil ein Ventil aufweist, kann es insbesondere vorteilhaft sein, am Außenumfang des Bauteils die Bereiche stromab und stromauf des Ventils mittels mindestens einer Dichtung voneinander zu trennen. Die Dichtung kann beispielsweise ein O-Ring sein. Auch eine andere Gestaltung der Dichtung kann jedoch vorteilhaft sein.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 end face at which the channel opens is preferably the upstream end 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 flap. Upstream of the throttle element, a choke element can advantageously be held in the base body. 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 design, a partition wall section is arranged in the intake channel section upstream of the throttle element. A simple structure results if 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 a press fit and lie against one another. 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 from one another. If the component has a valve, it can be particularly advantageous to separate the areas upstream and downstream of the valve on the outer circumference of the component from one another by means of at least one seal. The seal can be an O-ring, for example. However, another design of the seal can also be advantageous.

Für einen Zweitaktmotor mit einer Gemischbildungseinheit ist vorgesehen, dass der Zweitaktmotor einen Zylinder aufweist, in dem ein Brennraum ausgebildet ist, der von einem Kolben begrenzt ist. Der Kolben treibt eine in einem Kurbelgehäuse drehbar gelagerte Kurbelwelle an. Ein Kurbelgehäuseinnenraum ist in mindestens einer Stellung des Kolbens über mindestens einen Überströmkanal mit dem Brennraum verbunden. Der Zweitaktmotor weist einen Ansaugkanal auf, der stromab des in der Gemischbildungseinheit ausgebildeten Ansaugkanalabschnitts durch eine Trennwand in einen Gemischkanal zur Zufuhr von Kraftstoff/Luft-Gemisch in den Brennraum und einen Luftkanal zur Zufuhr von Spülvorlagenluft zu dem mindestens einen Überströmkanal geteilt ist. Es hat sich gezeigt, dass insbesondere bei einer Gemischbildungseinheit für einen Spülvorlagenmotor, bei der der Ansaugkanalabschnitt in einen Gemischkanal und einen Luftkanal geteilt ist, ausreichend Bauraum für den geraden, an einer Stirnseite des Grundkörpers mündenden Kanal zur Verfügung steht.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. In at least one position of the piston, a crankcase interior is connected to the combustion chamber via at least one overflow channel. The two-stroke engine has an intake channel which, downstream of the intake channel section formed in the mixture formation unit, is divided by a partition wall into a mixture channel for supplying fuel/air mixture to the combustion chamber and an air channel for supplying scavenging air to the at least one overflow channel. It has been shown that, particularly in a mixture formation unit for a scavenging engine in which the intake channel section is divided into a mixture channel and an air channel, there is sufficient installation space available for the straight channel opening out at one end of the base body.

Stromauf des Drosselelements kann ein Trennwandabschnitt zur Unterteilung des Ansaugkanalabschnitts in den Gemischkanal und den Luftkanal vorgesehen sein. Es kann jedoch auch vorgesehen sein, dass stromauf des Drosselelements kein Trennwandabschnitt zur Unterteilung des Ansaugkanalabschnitts in Gemischkanal und Luftkanal vorgesehen ist.Upstream of the throttle element, a partition wall section for dividing the intake duct section into the mixture duct and the air duct can be provided. However, it can also be provided that upstream of the throttle element, no partition wall section for dividing the intake duct section into the mixture duct and the air duct is provided.

Die erfindungsgemäße Gemischbildungseinrichtung kann auch für einen Zweitaktmotor vorgesehen sein, der keinen Luftkanal aufweist oder für einen Zweitaktmotor, der einen vom Gemischkanal getrennt geführten Luftkanal aufweist. Auch für einen Viertaktmotor, insbesondere für einen gemischgeschmierten Viertaktmotor, ist die erfindungsgemäße Gemischbildungseinrichtung vorteilhaft.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 separate 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.

Ausführungsbeispiele der Erfindung werden im Folgenden anhand der Zeichnung erläutert. Es zeigen:

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.
Embodiments of the invention are explained below with reference to the drawing. They show:
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 from Fig. 2 in the direction of arrow III in Fig. 2 ,
Fig. 4
a sectional view of another embodiment of a carburetor.

Der in Fig. 1 schematisch dargestellte Zweitaktmotor 1 weist einen Zylinder 2 und ein Kurbelgehäuse 4 auf. Im Zylinder 2 ist ein Brennraum 3 ausgebildet und im Kurbelgehäuse 4 ein Kurbelgehäuseinnenraum 6. Der Kurbelgehäuseinnenraum 6 und der Brennraum 3 sind von einem im Zylinder 2 hin- und hergehend beweglichen Kolben 5 getrennt. In vorgegebenen Kolbenstellungen, beispielsweise in der in Fig. 1 dargestellten Position des Kolbens 5 im Bereich des unteren Totpunkts, sind der Kurbelgehäuseinnenraum 6 und der Brennraum 3 über Überströmkanäle 8 miteinander verbunden. Die Überströmkanäle 8 münden mit Überströmfenstern 9 in den Brennraum 3. Die Überströmfenster 9 werden in Abhängigkeit von der Position des Kolbens 5 zum Brennraum 3 geöffnet bzw. geschlossen. Der Kolben 5 treibt eine im Kurbelgehäuse 4 drehbar gelagerte Kurbelwelle 7 rotierend an. Der Zweitaktmotor 1 kann beispielsweise der Antriebsmotor in einem handgeführten Arbeitsgerät wie einer Motorsäge, einem Trennschleifer, einem Blasgerät, einer Heckenschere, einem Sprühgerät oder dgl. sein, und die Kurbelwelle 7 kann zum Antrieb eines Werkzeugs des Arbeitsgeräts dienen. Bei einem Blasgerät oder Sprühgerät ist das Werkzeug üblicherweise ein Gebläse, das einen Arbeitsluftstrom fördert. Anstatt eines Zweitaktmotors 1 kann der Antriebsmotor auch ein Viertaktmotor, insbesondere ein gemischgeschmierter Viertaktmotor sein.The in Fig. 1 The schematically illustrated two-stroke engine 1 has a cylinder 2 and a crankcase 4. A combustion chamber 3 is formed in the cylinder 2 and a crankcase interior 6 in the crankcase 4. The crankcase interior 6 and the combustion chamber 3 are separated by a piston 5 that moves back and forth in the cylinder 2. In predetermined piston positions, for example in the position shown in Fig. 1 In the position of the piston 5 shown in the area of the 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 via overflow windows 9. The overflow windows 9 are opened or closed depending on the position of the piston 5 in relation to the combustion chamber 3. The piston 5 drives a rotating crankshaft 7 which is rotatably mounted in the crankcase 4. The two-stroke engine 1 can, for example, be the drive motor in a hand-held working device such as a chainsaw, a cut-off machine, a blower, a hedge trimmer, a sprayer or the like, and the crankshaft 7 can serve to drive a tool of the working device. In a blower or sprayer, the tool is usually a fan that conveys a working air flow. 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.

Der Zweitaktmotor 1 weist einen Ansaugtrakt mit einem Luftfilter 49, einer Gemischbildungseinheit 13 sowie einem Verbindungsstutzen 41 zur Verbindung der Gemischbildungseinheit 13 mit dem Zylinder 2 auf. Die Gemischbildungseinheit 13 ist im Ausführungsbeispiel ein Vergaser. Anstatt des Verbindungsstutzens 41 können ein oder mehrere beliebige andere Teile zur fluidischen Verbindung der Gemischbildungseinheit 13 mit dem Zylinder 2 bzw. dem Kurbelgehäuse 4 vorgesehen sein. Der Luftfilter 49 besitzt ein Filterelement 39. Stromab des Filterelements 39 ist ein Reinraum 50 gebildet, aus dem ein Ansaugkanal 10 führt. In der Gemischbildungseinheit 13 ist ein Ansaugkanalabschnitt 11 ausgebildet. Im Ansaugkanalabschnitt 11 ist ein Drosselelement 17, im Ausführungsbeispiel eine Drosselklappe, verstellbar gelagert. Im Ausführungsbeispiel ist das Drosselelement 17 mit einer Drosselwelle 18 gelagert. Stromab des Drosselelements 17 ist der Ansaugkanal 10 in einen Gemischkanal 12 und einen Luftkanal 14 geteilt. Der Ansaugkanal 10 weist eine Ansaugkanallängsachse 32 auf, die die Längsmittelachse des Ansaugkanals 10 bildet. Der Gemischkanal 12 mündet mit einer Gemischkanalöffnung 15 an der Zylinderbohrung 55. Die Gemischkanalöffnung 15 ist vom Kolben 5 gesteuert. Die Gemischkanalöffnung 15 ist im Bereich des oberen Totpunkts des Kolbens 15 zum Kurbelgehäuseinnenraum 6 hin geöffnet. Der Luftkanal 14 mündet mit mindestens einer Luftkanalöffnung 16 an der Zylinderbohrung 55. Auch die Luftkanalöffnung 16 ist vom Kolben 5 gesteuert. Der Kolben 5 besitzt mindestens eine Kolbentasche 37, die die Luftkanalöffnung 16 im Bereich des oberen Totpunkts des Kolbens 5 mit den Überströmfenstern 9 verbindet. Über den Luftkanal 14, die Luftkanalöffnung 16 und die Überströmfenster 9 wird in den Überströmkanälen 8 im Bereich des oberen Totpunkts des Kolbens 5 Spülvorlagenluft vorgelagert. Der Zylinder 2 weist einen Auslass 40 aus dem Brennraum 3 auf.The two-stroke engine 1 has an intake tract with an air filter 49, a mixture formation unit 13 and a connecting 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 other desired parts can be provided for the fluidic connection of the mixture formation unit 13 to the cylinder 2 or the crankcase 4. 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 channel 10 leads. An intake channel section 11 is formed in the mixture formation unit 13. A throttle element 17, in the exemplary embodiment a throttle valve, is adjustably mounted in the intake channel 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 duct 10 has an intake duct longitudinal axis 32, which forms the longitudinal center axis of the intake duct 10. The mixture duct 12 opens with a mixture duct opening 15 on the cylinder bore 55. The mixture duct opening 15 is controlled by the piston 5. The mixture duct 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 on 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 region of the top dead center of the piston 5 to the transfer windows 9. Via the air duct 14, the air duct opening 16 and the overflow windows 9, the air is fed into the overflow ducts 8 in the area of the top dead center of the piston 5, scavenging air is supplied. The cylinder 2 has an outlet 40 from the combustion chamber 3.

Wie Fig. 1 auch zeigt, münden in den Ansaugkanalabschnitt 11 in der Gemischbildungseinheit 13 eine Hauptkraftstofföffnung 27 sowie mehrere Nebenkraftstofföffnungen 28. Die Hauptkraftstofföffnung 27 ist an einer Hauptkraftstoffdüse 29 ausgebildet. Die Hauptkraftstofföffnung 27 mündet im Bereich eines Venturiabschnitts 34 in den Ansaugkanalabschnitt 11. Die Gemischbildungseinheit 13 weist einen Grundkörper 23 auf, der eine erste, stromauf liegende Stirnseite 24 sowie eine zweite, stromab liegende Stirnseite 25 aufweist. Die Hauptkraftstoffdüse 29 ist in einem geraden Kanal 26 angeordnet, der sich von der ersten Stirnseite 24 in den Ansaugkanalabschnitt 11 erstreckt. Dadurch kann bei der Herstellung der Gemischbildungseinheit 13 oder nach einem Austausch der Hauptkraftstoffdüse 29 an der ersten Stirnseite 24 ein Schlauch mit Reinigungsfluid wie beispielsweise Luft angeschlossen werden, und der Kanal 26 sowie Teile des Kraftstoffsystems können gereinigt werden. Auch für andere Kanäle der Gemischbildungseinheit 13 kann eine Mündung an der ersten Stirnseite 24 vorteilhaft sein. Im Ausführungsbeispiel ist die erste Stirnseite 24, an der der Kanal 26 mündet, die stromauf liegende Stirnseite. Die erste Stirnseite 24, an der der Kanal 26 mündet, kann jedoch auch die stromab liegende Stirnseite des Grundkörpers 23 sein.How Fig. 1 also shows, a main fuel opening 27 and several secondary fuel openings 28 open into the intake channel 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 channel section 11 in the region of a venturi section 34. The mixture formation unit 13 has a base body 23 which has a first, upstream end face 24 and a second, downstream end 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, when producing the mixture formation unit 13 or after replacing the main fuel nozzle 29, a hose with cleaning fluid such as air can be connected to the first end face 24 and the channel 26 and parts of the fuel system can be cleaned. An opening 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. However, the first end face 24, at which the channel 26 opens, can also be the downstream end face of the base body 23.

Vorteilhaft ist die Hauptkraftstoffdüse 29 in den Kanal 26 eingepresst. Die Hauptkraftstoffdüse 29 kann dabei unmittelbar in den Kanal 26 eingepresst sein, so dass der Außenumfang der Hauptkraftstoffdüse 29 in Kontakt mit der Wand des Kanals 26 ist. Alternativ kann vorgesehen sein, dass die Hauptkraftstoffdüse 29 unter Zwischenlage mindestens einer Dichtung in den Kanal 26 eingepresst ist. In Fig. 2 ist hierzu schematisch mit gestrichelter Linie eine Dichtung 80 eingezeichnet. Die Dichtung 80 kann beispielsweise ein O-Ring sein. Auch mehrere Dichtungen 80 können vorteilhaft sein.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 an O-ring, for example. Several seals 80 can also be advantageous.

Wie Fig. 1 zeigt, sind stromauf des Drosselelements 17 keine weiteren Elemente zur Unterteilung des Ansaugkanalabschnitts 11 in Gemischkanal 12 und Luftkanal 14 vorgesehen. Auch ein Chokeelement ist nicht vorgesehen.How Fig. 1 shows, no further elements for dividing the intake duct section 11 into mixture duct 12 and air duct 14 are provided upstream of the throttle element 17. A choke element is also not provided.

Stromab des Drosselelements 17 ist beim Ausführungsbeispiel nach Fig. 1 der Ansaugkanal 10 von einer Trennwand 35 in den Gemischkanal 12 und den Luftkanal 14 geteilt. An der dem Drosselelement 17 zugewandten Seite weist die Trennwand 35 eine Anlage 38 auf, an der das Drosselelement 17 in vollständig geöffneter Stellung anliegt. Bei teilweise geschlossener Stellung des Drosselelements 17 ist zwischen der Drosselwelle 18 und der Anlage 38 eine Öffnung gebildet, über die Kraftstoff in den stromauf des Luftkanals 14 liegenden Bereich gelangen kann.Downstream of the throttle element 17 in the embodiment according to Fig. 1 the intake duct 10 is divided by a partition 35 into the mixture duct 12 and the air duct 14. On the side facing the throttle element 17, the partition 35 has a system 38 against which the throttle element 17 rests in the fully open position. When the throttle element 17 is partially closed, an opening is formed between the throttle shaft 18 and the system 38, through which fuel can reach the area upstream of the air duct 14.

Im Betrieb des Zweitaktmotors 1 wird beim Aufwärtshub des Kolbens 5 Kraftstoff/Luft-Gemisch aus dem Gemischkanal 12 in den Kurbelgehäuseinnenraum 6 angesaugt, sobald die Gemischkanalöffnung 15 öffnet. Solange die Luftkanalöffnung 16 über die Kolbentasche 37 mit den Überströmfenstern 9 verbunden ist, wird in den Überströmkanälen 8 Spülvorlagenluft vorgelagert. Beim Abwärtshub des Kolbens 5 wird das Kraftstoff/Luft-Gemisch im Kurbelgehäuseinnenraum 6 komprimiert und, sobald die Überströmfenster 9 öffnen, strömt zunächst Spülvorlagenluft aus den Überströmkanälen 8 und anschließend Kraftstoff/Luft-Gemisch aus dem Kurbelgehäuseinnenraum 6 in den Brennraum 3 ein. Das Kraftstoff/Luft-Gemisch wird beim Aufwärtshub des Kolbens 5 im Brennraum 3 komprimiert und im Bereich des oberen Totpunkts des Kolbens 5 von einer Zündkerze 72 gezündet. Vorzugsweise ist die Zündkerze 72 von einer Steuereinrichtung 61 angesteuert, die auch ein Kraftstoffventil 60 (Fig. 4) ansteuert. Beim Abwärtshub des Kolbens 5 öffnet der Kolben 5 zunächst den Auslass 40, so dass Abgase aus dem Brennraum 3 ausströmen können. Anschließend werden die Überströmfenster 9 geöffnet und Spülvorlagenluft strömt in den Brennraum 3 ein und spült die restlichen Abgase aus dem Brennraum 3 durch den Auslass 40 aus. Anschließend strömt frisches Kraftstoff/Luft-Gemisch für die nächste Verbrennung in den Brennraum 3 ein.When the two-stroke engine 1 is operating, during the upward stroke of the piston 5, a fuel/air mixture is sucked from the mixture channel 12 into the crankcase interior 6 as soon as the mixture channel opening 15 opens. As long as the air channel opening 16 is connected to the transfer windows 9 via the piston pocket 37, purge air is stored in the transfer channels 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, purge air flows out of 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. Preferably, the spark plug 72 is controlled by a control device 61, which also controls a fuel valve 60 ( Fig. 4 ). 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. The overflow windows 9 are then 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 the combustion chamber 3 for the next combustion.

Fig. 2 zeigt ein weiteres Ausführungsbeispiel einer Gemischbildungseinheit 13. Gleiche Bezugszeichen kennzeichnen in allen Ausführungsbeispielen einander entsprechende Elemente. Die Gemischbildungseinheit 13 aus Fig. 2 weist ebenfalls einen Grundkörper 23 mit einer ersten Stirnseite 24 und einer zweiten Stirnseite 25 auf. Luft strömt im Betrieb von der ersten Stirnseite 24 zur zweiten Stirnseite 25, wie durch den Pfeil 51 in Fig. 2 schematisch dargestellt ist. Das Drosselelement 17 ist an der Drosselwelle 18 über eine Befestigungsschraube 19 fixiert. Bezogen auf die Strömungsrichtung stromauf des Drosselelements 17 ist ein Chokeelement 20 im Ansaugkanalabschnitt 11 angeordnet. Das Chokeelement 20 ist als Chokeklappe ausgebildet und mittels einer Befestigungsschraube 22 an einer Chokewelle 21 fixiert. Das Drosselelement 17 ist um eine Drehachse 76 schwenkbar gelagert, und das Chokeelement 18 ist um eine Drehachse 77 schwenkbar gelagert. In Strömungsrichtung zwischen der Chokewelle 21 und der Drosselwelle 18 ist ein Trennwandabschnitt 36 im Ansaugkanalabschnitt 11 angeordnet. Der Trennwandabschnitt 36 trennt Luftkanal 14 und Gemischkanal 12 voneinander. Fig. 2 shows a further embodiment of a mixture formation unit 13. The same reference numerals identify corresponding elements in all embodiments. The mixture formation unit 13 from Fig. 2 also has a base body 23 with a first end face 24 and a second end face 25. Air flows during operation from the first end face 24 to the second end face 25, as indicated by the arrow 51 in Fig. 2 is shown schematically. The throttle element 17 is fixed to the throttle shaft 18 via a fastening screw 19. Upstream of the throttle element 17 in relation to the flow direction, a choke element 20 is arranged in the intake duct 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 pivotally mounted about an axis of rotation 76, and the choke element 18 is pivotally mounted about an axis of rotation 77. In the flow direction between the choke shaft 21 and the throttle shaft 18, a partition wall section 36 is arranged in the intake duct section 11. The partition wall section 36 separates the air duct 14 and the mixture duct 12 from one another.

Beim Ausführungsbeispiel nach Fig. 2 ist am Trennwandabschnitt 36 eine Anlage 56 für das Drosselelement 17 ausgebildet. Die Anlage 56 ist an der dem Gemischkanal 12 zugewandten Seite des Trennwandabschnitts 36 angeordnet. An der dem Luftkanal 12 zugewandten Seite ist eine Anlage 57 für das Chokeelement 20 ausgebildet.In the embodiment according to Fig. 2 a system 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. A system 57 for the choke element 20 is formed on the side facing the air channel 12.

Auch beim Ausführungsbeispiel nach Fig. 2 ist ein Kanal 26 im Grundkörper 23 vorgesehen. Der Kanal 26 ist vorteilhaft als gerade, durchgehende Bohrung mit konstantem Durchmesser ausgeführt. Der Kanal 26 erstreckt sich vorteilhaft von der Stirnseite 24 bis in den Ansaugkanalabschnitt 11. Der Kanal 26 ist im Ausführungsbeispiel nicht über seine ganze Länge über seinen gesamten Umfang geschlossen, sondern in dem an die Stirnseite 24 angrenzenden Bereich zum Ansaugkanalabschnitt 11 hin offen. Es kann auch vorgesehen sein, dass der Kanal 26 in einer anderen Richtung umfangsseitig über einen Teilabschnitt seiner Länge offen ausgebildet ist. Es kann auch vorgesehen sein, dass der Kanal 26 über seine gesamte Länge in einer Richtung über einen Teilabschnitt seines Umfangs offen ausgebildet ist. Hierbei kann die den Kanal 26 begrenzende Wand im Querschnitt beispielsweise etwa U-förmig ausgebildet sein. Vorteilhaft wird der Kanal 26 mittels Bohren oder Fräsen hergestellt oder wird beim Gießen des Grundkörpers 23 als Gussstruktur hergestellt.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 front side 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 in the area adjacent to the front side 24 towards the intake channel section 11. It can also be provided that the channel 26 is designed to be open in another direction on the circumference over a portion of its length. It can also be provided that the channel 26 is open over its entire length in one direction over a portion its circumference is open. The wall delimiting the channel 26 can, for example, be approximately U-shaped in cross section. The channel 26 is advantageously produced by drilling or milling or is produced as a cast structure when the base body 23 is cast.

Der Kanal 26 weist eine Mittelachse 33 auf. Die Mittelachse 33 schließt im Ausführungsbeispiel mit der Ansaugkanallängsachse 23 einen Winkel α ein, der kleiner als 90° ist. Der Winkel α ist im Ausführungsbeispiel größer als 0°. Auch ein Winkel von 0° kann jedoch vorteilhaft sein. Der Winkel α beträgt vorzugsweise von 0° bis 30°, insbesondere von 0° bis 25°. Der Winkel α ist dabei in einer Schnittebene gemessen, die die Ansaugkanallängsachse 32 enthält und die parallel zur Mittelachse 33 des Kanals 26 verläuft. Im Ausführungsbeispiel enthält die Schnittebene sowohl die Ansaugkanallängsachse 32 als auch die Mittelachse 33 und entspricht der in Fig. 2 dargestellten Schnittebene. Sollten die Ansaugkanallängsachse 32 und die Mittelachse 33 windschief zueinander verlaufen, so ist der Winkel α zwischen der Ansaugkanallängsachse 32 und einer Projektion der Mittelachse 33 in die Schnittebene in einer Projektionsrichtung senkrecht zur Schnittebene gemessen.The channel 26 has a central axis 33. In the exemplary embodiment, the central axis 33 forms an angle α with the intake channel longitudinal axis 23 that is less 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 cutting plane that contains the intake channel longitudinal axis 32 and that runs parallel to the central axis 33 of the channel 26. In the exemplary embodiment, the cutting plane contains both the intake channel longitudinal axis 32 and the central axis 33 and corresponds to the Fig. 2 shown cutting plane. If the intake duct longitudinal axis 32 and the central axis 33 are skewed to one another, the angle α between the intake duct 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.

Der Grundkörper 23 der Gemischbildungseinrichtung 13 weist eine erste Längsseite 58 und eine zweite Längsseite 59 auf. Die Längsseiten 58 und 59 verlaufen näherungsweise parallel zur Mittelachse 32 des Ansaugkanalabschnitts 11. An der ersten Längsseite 58 ist vorteilhaft eine Kraftstoffpumpe 46 ausgebildet. Die Kraftstoffpumpe 46 wird vom Grundkörper 23, einem am Grundkörper 23 fixierten Pumpendeckel 47 sowie einer nicht dargestellten Pumpenmembran begrenzt. Der Pumpendeckel 47 ist bevorzugt über eine Befestigungsschraube 48 am Grundkörper 23 angeschraubt. An der gegenüberliegenden Längsseite 59 sind vorteilhaft eine Regelkammer 42 und eine Kompensationskammer 43 gebildet, die von einer Regelmembran 44 getrennt sind. Die Regelmembran 44 ist von einem in Fig. 2 schematisch dargestellten Regelkammerdeckel 62 am Grundkörper 23 gehalten. Die Regelkammer 42 ist vorteilhaft in üblicher Weise mit einem federbeaufschlagten Hebel an ein Einlassventil gekoppelt, das den Kraftstofffluss von der Kraftstoffpumpe 46 in die Regelkammer 42 regelt. Die Regelkammer 42 ist über ein Rückschlagventil 45 mit Nebenkraftstofföffnungen 28 verbunden. Aus der Regelkammer 42 führt außerdem ein Kraftstoffkanal 64, in dem im Ausführungsbeispiel eine Festdrossel 63 angeordnet ist. Anstatt der Festdrossel 63 kann beispielsweise eine einstellbare Drossel vorgesehen sein.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 channel 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 to the base body 23 and a pump membrane (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 are advantageously formed on the opposite longitudinal side 59, which are separated by a control membrane 44. The control membrane 44 is surrounded by a Fig. 2 The control chamber 42 is held on the base body 23 by a control chamber cover 62 shown schematically. The control chamber 42 is advantageously coupled in the usual way with a spring-loaded lever to an inlet valve, which Regulates the flow of fuel from the fuel pump 46 into the control chamber 42. The control chamber 42 is connected to secondary fuel openings 28 via a check valve 45. A fuel channel 64 also leads from the control chamber 42, in which a fixed throttle 63 is arranged in the exemplary embodiment. Instead of the fixed throttle 63, an adjustable throttle can be provided, for example.

Im Kanal 26 ist die Hauptkraftstoffdüse 29 angeordnet. Am Außenumfang der Hauptkraftstoffdüse 29 ist ein Ringspalt 30 gebildet, in den der Kraftstoffkanal 64 mündet. Der Ringspalt 30 wird von einer umlaufenden Nut am Außenumfang der Hauptkraftstoffdüse 29 sowie von der Wand des Kanals 26 begrenzt. In der Hauptkraftstoffdüse 29 ist ein Querkanal 65 ausgebildet, der im Ausführungsbeispiel senkrecht zur Mittelachse 33 verläuft, sowie ein Längskanal 66, der in Richtung der Mittelachse 33 mittig durch die Hauptkraftstoffdüse 29 verläuft. Über den Querkanal 65 ist der Ringspalt 30 mit dem Längskanal 66 verbunden. Der Längskanal 66 mündet an einem Ventilplättchen 52. Das Ventilplättchen 52 bildet mit einem Ventilsitz 54 ein Rückschlagventil 31. In geschlossenem Zustand des Rückschlagventils 31 liegt das Ventilplättchen 52 an dem Ventilsitz 54 an. Bei Überdruck im Ansaugkanalabschnitt 11 gegenüber der Regelkammer 42 ist das Rückschlagventil 31 geschlossen. Bei Unterdruck im Ansaugkanalabschnitt 11 wird das Ventilplättchen 52 vom Ventilsitz 54 abgehoben. Das Rückschlagventil 31 weist einen Anschlag 53 auf, der den maximalen Hub des Ventilplättchens 52 begrenzt. Der Hub des Ventilplättchens 52 ist vorzugsweise möglichst klein.The main fuel nozzle 29 is arranged in the channel 26. An annular gap 30 is formed on the outer circumference of the main fuel nozzle 29, 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, and 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 opens at a valve plate 52. The valve plate 52 forms a check valve 31 with a valve seat 54. When the check valve 31 is closed, 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. If 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 zeigt die Mündung des Kanals 26 an der ersten Stirnseite 24. Der Kanal 26 ist im Ausführungsbeispiel vollständig im Grundkörper 23 ausgebildet und über seinen Umfang zumindest teilweise geschlossen ausgebildet. Der Grundkörper 23 weist hierzu einen Abschnitt 67 auf, der in den Ansaugkanalabschnitt 11 ragt. Der Abschnitt 67 verringert den freien Strömungsquerschnitt im Gemischkanal 12. Der Abschnitt 67 weist im Ausführungsbeispiel eine Abschrägung 68 auf, so dass sich der Strömungsquerschnitt am Abschnitt 67 in Richtung des Pfeils 51 (Fig. 2) vergrößert. Die Abschrägung 68 ist auch in Fig. 2 dargestellt. Die Abschrägung 68 kann in alternativer Ausführung auch entfallen. Fig. 3 shows the opening of the channel 26 on 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 projects into the intake channel 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 ) is enlarged. The bevel 68 is also in Fig. 2 The bevel 68 can also be omitted in an alternative design.

Fig. 4 zeigt ein Ausführungsbeispiel einer Gemischbildungseinrichtung 13, deren Aufbau im Wesentlichen der in den Fig. 2 und 3 gezeigten und beschriebenen Gemischbildungseinrichtung 13 entspricht. Gleiche Bezugszeichen bezeichnen in allen Figuren einander entsprechende Elemente. Bei der Gemischbildungseinrichtung 13 in Fig. 4 ist der Kanal 26 gegenüber der in den Fig. 1 und 2 gezeigten Ausführung gedreht. Der Kanal 26 verläuft parallel zur Ansaugkanallängsachse 32. Die Mittelachse 33 des Kanals 26 und die Ansaugkanallängsachse 32 schließen einen Winkel von 0° ein, verlaufen also parallel. Fig. 4 shows an embodiment of a mixture formation device 13, the structure of which essentially corresponds to that shown in the Fig. 2 and 3 The same reference numerals designate corresponding elements in all figures. In the mixture formation device 13 in Fig. 4 Channel 26 is opposite the one in the Fig. 1 and 2 shown version. 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°, i.e. they run parallel.

Die Gemischbildungseinheit 13 ist in den Ausführungsbeispielen als Vergaser ausgebildet. Ein Vergaser fördert den Kraftstoff aufgrund des im Ansaugkanal bestehenden Unterdrucks in den Ansaugkanal. In alternativer Gestaltung kann auch eine andere Gemischbildungseinheit vorgesehen sein. Die Gemischbildungseinheit kann insbesondere ein Kraftstoffventil aufweisen, das Kraftstoff aufgrund von Überdruck des Kraftstoffs in den Ansaugkanal zuführt, insbesondere in den Ansaugkanal einspritzt.The mixture formation unit 13 is designed as a carburetor in the exemplary embodiments. A carburetor feeds the fuel into the intake channel due to the negative pressure in the intake channel. In an alternative design, another mixture formation unit can also be provided. The mixture formation unit can in particular have a fuel valve that feeds fuel into the intake channel due to the excess pressure of the fuel, in particular injects it into the intake channel.

Claims (13)

  1. Mixture-formation unit having a main body (23) in which an intake-channel portion (11) is formed, wherein the intake-channel portion (11) extends from a first end face (24) of the main body (23) to a second end face (25) of the main body (23), wherein the mixture-formation unit (13) has at least one channel (26) which opens out into the intake-channel portion (11), and wherein, in the channel (26), a component of the mixture-formation unit (13) is arranged, which component has a check valve (31), wherein the mixture-formation unit (13) has at least one fuel opening which opens out into the intake-channel portion (11) and which is formed on a fuel nozzle, wherein the fuel nozzle forms the component arranged in the channel (26), wherein the fuel opening is a main fuel opening (27) and the fuel nozzle is a main fuel nozzle (29), and wherein the main fuel opening (27) opens out into the intake-channel portion (11) in the region of a venturi portion (34),
    characterized in that the channel (26) extends straight, and in that the channel (26) opens out at the first end face (24) of the main body (23).
  2. Mixture-formation unit according to Claim 1,
    characterized in that the component forms together with the channel (26) an annular gap (30) which is connected to the fuel opening.
  3. Mixture-formation unit according to Claim 1 or 2,
    characterized in that the central axis (33) of the channel (26) includes an angle (α) of 0° to 30° with the intake-channel longitudinal axis (32) in a section plane which contains the intake-channel longitudinal axis (32) and which extends parallel to the central axis (33) of the channel (26).
  4. Mixture-formation unit according to one of Claims 1 to 3,
    characterized in that a throttle element (17) is mounted in the main body (23) downstream of the venturi portion (34).
  5. Mixture-formation unit according to Claim 4,
    characterized in that the first end face (24) of the main body (23) is the upstream end face of the main body (23).
  6. Mixture-formation unit according to Claim 4 or 5,
    characterized in that the throttle element (17) is a throttle flap.
  7. Mixture-formation unit according to Claim 6,
    characterized in that a choke element (20) is held in the main body (23) upstream of the throttle element (17).
  8. Mixture-formation unit according to one of Claims 4 to 7,
    characterized in that no partition-wall portion is arranged in the intake-channel portion (11) upstream of the throttle element (17).
  9. Mixture-formation unit according to one of Claims 4 to 7,
    characterized in that a partition-wall portion (36) is arranged in the intake-channel portion (11) upstream of the throttle element (17).
  10. Mixture-formation unit according to one of Claims 1 to 9,
    characterized in that the component is pressed into the channel (26).
  11. Two-stroke engine having a mixture-formation unit according to one of Claims 1 to 10, having a cylinder (2) in which a combustion chamber (3) is formed, which combustion chamber is delimited by a piston (5), wherein the piston (5) drives a crankshaft (7) which is mounted rotatably in a crankcase (4), wherein, in at least one position of the piston (5), a crankcase interior (6) is connected to the combustion chamber (3) via at least one transfer channel (8), having an intake channel (10) which, downstream of the intake-channel portion (11) formed in the mixture-formation unit (13), is divided by a partition wall (35) into a mixture channel (12), which serves for feeding fuel/air mixture into the combustion chamber (3), and into an air channel (14), which serves for feeding scavenging air to the at least one transfer channel (8).
  12. Two-stroke engine according to Claim 11,
    characterized in that no partition-wall portion for subdividing the intake-channel portion (11) into the mixture channel (12) and the air channel (14) is provided upstream of the throttle element (17).
  13. Two-stroke engine according to Claim 12,
    characterized in that a partition-wall portion (36) for subdividing the intake-channel portion (11) into the mixture channel (12) and the air channel (14) is provided upstream of the throttle element (17).
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EP3748151A1 (en) 2020-12-09
CN112049738A (en) 2020-12-08
CN112049738B (en) 2024-07-26

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