MIXTURE FORMATION UNIT AND TWO-STROKE ENGINE WITH A MIXTURE FORMATION UNIT

Description

[0001] 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.

[0002] US 2014 / 0261329 A1 discloses a mixture formation device, namely a carburetor, in which the main fuel nozzle is arranged in a straight channel. This allows the main fuel nozzle to be easily pushed or pressed into the carburetor's base body from the outside. A cover, which holds the control diaphragm, and a cover for the fuel pump are arranged on the base body. If the cover, which holds the control diaphragm, is mounted on the base body, the channel in which the main fuel nozzle is arranged is only accessible from the intake port.

[0003] US Pat. No. 1,061,835 A discloses a float-type carburetor that feeds a fuel / air mixture into the intake port via a nozzle. The nozzle is screwed into a channel opening into one end of the carburetor and protrudes radially into the channel. This allows air from the intake port to be drawn into the fuel and exit into the intake port together with the fuel as a fuel / air mixture.

[0004] A carburetor of this type is known from EP 2 947 305 A1. 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 port.

[0005] The passages of a carburetor are usually manufactured, at least partially, using machining processes. However, after the control chamber cover is installed, the passage containing the main fuel jet is only accessible from the intake port. Therefore, cleaning the carburetor after all components have been reassembled is only possible to a limited extent. Particles in the fuel-carrying passages can become dislodged during operation and become lodged in undesirable locations, for example, on sensitive components such as valves, thereby disrupting the carburetor's operation.

[0006] The invention is based on the object of creating a mixture formation unit of the generic type which is highly robust in operation and easy to clean.

[0007] A further object of the invention is to provide a two-stroke engine with a mixture formation unit.

[0008] 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.

[0009] The duct that opens into the intake port is designed as a straight duct and opens into one end of the base body of the mixture formation unit. This allows both ends of the duct to remain easily accessible even after the installation of add-on components such as covers, a fuel pump, or the control device of the mixture formation unit. This allows the duct to be completely cleaned and flushed. A cleaning line can be connected, particularly to the end of the base body, ensuring easy access to the connection.

[0010] A component of the mixture formation unit is arranged in the channel. By arranging the channel's outlet opening on the first end face of the base body, the channel can be easily cleaned before the component is installed. 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 term fuel nozzle refers to the component on which the constriction that forms the nozzle cross-section is formed. Other functions can also be implemented in the fuel nozzle.The fuel nozzle is a component that can be composed 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, 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, resulting in defined dimensions for the annular gap.

[0011] The component arranged in the channel has a check valve. Particles such as chips or the like that arise during manufacturing 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. Therefore, cleaning residues from previous machining processes, such as chips or the like, is particularly desirable for a check valve.

[0012] In a preferred embodiment, the duct runs relatively 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. Advantageously, the center axis of the duct forms an angle of 0° to 30°, in particular 0° to 25°, with the intake duct longitudinal axis in a sectional plane that contains the intake duct longitudinal axis and runs parallel to the center axis of the duct. The center axis of the duct can therefore lie in the same plane as the intake duct longitudinal axis or run skew to the intake duct longitudinal axis. If the center axis of the duct runs skew to the intake duct longitudinal axis, the angle in the sectional plane is measured between a projection of the center axis of the duct perpendicular to the sectional plane and the intake duct longitudinal axis.

[0013] The intake duct section preferably has a Venturi section. A throttle element, in particular, is mounted in the base body downstream of the Venturi section. The throttle element is preferably adjustable and serves to adjust the free flow cross-section of the intake duct section. The throttle element is advantageously pivotable about a rotational axis.

[0014] 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 valve. Upstream of the throttle element, a choke element can advantageously be held in the base body. The choke element is preferably a choke valve. If the choke element is designed as a choke valve, sufficient installation space is available 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 upstream of the throttle element in the intake duct section. A simple structure results if the component is pressed into the duct. The component can be pressed directly into the duct. The outer circumference of the component and the duct 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 duct with at least one seal interposed. Multiple 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 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, another design of the seal can also be advantageous.

[0015] 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 transfer 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 transfer channel.It has been shown that, particularly in the case of a mixture formation unit for a scavenging engine 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 face of the base body.

[0016] Upstream of the throttle element, a partition wall section may be provided for dividing the intake duct section into the mixture duct and the air duct. However, it may also be provided that no partition wall section is provided upstream of the throttle element for dividing the intake duct section into the mixture duct and the air duct.

[0017] 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.

[0018] Embodiments of the invention are explained below with reference to the drawings. They show: Fig. 1 a schematic representation of a two-stroke engine, Fig. 2 a sectional view of an embodiment of a carburettor, Fig. 3 a partial side view of the carburettor from Fig. 2 in the direction of arrow III in Fig. 2 , Fig. 4 a sectional view of another embodiment of a carburettor.

[0019] The 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 which can move back and forth in the cylinder 2. In predetermined piston positions, for example in the position shown in Fig. 1 In the illustrated position of the piston 5 in the region of bottom dead center, the crankcase interior 6 and the combustion chamber 3 are connected to one another via transfer channels 8. The transfer channels 8 open into the combustion chamber 3 via transfer windows 9. The transfer windows 9 are opened or closed depending on the position of the piston 5 relative to the combustion chamber 3. The piston 5 drives a rotating crankshaft 7 that is rotatably mounted in the crankcase 4. The two-stroke engine 1 can, for example, be the drive motor in a hand-held tool such as a chainsaw, 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 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.

[0020] 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. In the exemplary embodiment, the mixture formation unit 13 is a carburetor. 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 chamber 50 is formed, from which an intake duct 10 leads. An intake duct 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 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 duct 10 has a longitudinal axis 32, which forms the longitudinal center axis of the intake duct 10. The mixture duct 12 opens into a mixture duct opening 15 at 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 into 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 to the transfer ports 9 in the region of the top dead center of the piston 5. Purge air is supplied to the transfer channels 8 in the area of ​​the top dead center of the piston 5 via the air channel 14, the air channel opening 16 and the transfer windows 9.The cylinder 2 has an outlet 40 from the combustion chamber 3.

[0021] How Fig. 1 also shows, a main fuel opening 27 and a plurality of 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, during manufacture of the mixture formation unit 13 or after replacement of the main fuel nozzle 29, a hose containing 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 at 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.

[0022] Advantageously, the main fuel nozzle 29 is 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 interposed. Fig. 2 For this purpose, a seal 80 is schematically shown in dashed lines. The seal 80 can be an O-ring, for example. Multiple seals 80 can also be advantageous.

[0023] How Fig. 1 As shown, no further elements are provided upstream of the throttle element 17 to divide the intake duct section 11 into the mixture duct 12 and the air duct 14. A choke element is also not provided.

[0024] 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 contact surface 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 contact surface 38, through which fuel can reach the area upstream of the air duct 14.

[0025] During operation of the two-stroke engine 1, during the upward stroke of the piston 5, 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, scavenging 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, scavenging air flows first from the transfer channels 8 and then 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 piston 5, piston 5 first opens outlet 40 so that exhaust gases can flow out of combustion chamber 3. Subsequently, transfer ports 9 are opened, and purge air flows into combustion chamber 3 and purges the remaining exhaust gases from combustion chamber 3 through outlet 40. Fresh fuel / air mixture then flows into combustion chamber 3 for the next combustion.

[0026] 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 of Fig. 2 also 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 the arrow 51 in Fig. 2 is shown schematically. The throttle element 17 is fixed to the throttle shaft 18 by a fastening screw 19. Upstream of the throttle element 17 in the flow direction is a choke element 20 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.

[0027] In the example 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.

[0028] Also in the example 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 and across its entire circumference, but is open in the area adjacent to the end face 24 towards the intake channel section 11. It can also be provided that the channel 26 is open in a different 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 of its circumference. In this case, the wall delimiting the channel 26 can, for example, be approximately U-shaped in cross section.Advantageously, the channel 26 is produced by drilling or milling or is produced as a cast structure during casting of the base body 23.

[0029] 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 sectional plane that contains the intake channel longitudinal axis 32 and runs parallel to the central axis 33 of the channel 26. In the exemplary embodiment, the sectional plane contains both the intake channel longitudinal axis 32 and the central axis 33 and corresponds to the Fig. 2 shown section plane. If the intake duct longitudinal axis 32 and the central axis 33 are skewed to each other, the angle α between the intake duct longitudinal axis 32 and a projection of the central axis 33 into the section plane is measured in a projection direction perpendicular to the section plane.

[0030] 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 to 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. On the opposite longitudinal side 59, a control chamber 42 and a compensation chamber 43 are advantageously formed, which are separated by a control diaphragm 44. The control diaphragm 44 is surrounded by a Fig. 2 The control chamber 42 is held on the base body 23 by a schematically illustrated control chamber cover 62. The control chamber 42 is advantageously coupled in the usual manner with a spring-loaded lever to an inlet valve, which regulates the fuel flow 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.

[0031] 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. Formed in the main fuel nozzle 29 are a transverse channel 65 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 duct section 11 compared to the control chamber 42, the check valve 31 is closed.When negative pressure is present in the intake duct section 11, the valve plate 52 is lifted from the valve seat 54. The check valve 31 has a stop 53 that limits the maximum stroke of the valve plate 52. The stroke of the valve plate 52 is preferably as small as possible.

[0032] Fig. 3 shows the opening of the channel 26 at the first end face 24. In the exemplary embodiment, the channel 26 is formed entirely 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 that 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 shown. The bevel 68 can also be omitted in an alternative design.

[0033] 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 und 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°, thus running parallel.

[0034] In the exemplary embodiments, the mixture formation unit 13 is designed as a carburetor. A carburetor delivers the fuel into the intake port due to the negative pressure existing in the intake port. In an alternative design, a different mixture formation unit can also be provided. The mixture formation unit can, in particular, have a fuel valve that supplies fuel to the intake port due to the excess fuel pressure, in particular injects it into the intake port.

Claims

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).