The instant application should be granted the priority date of Apr. 2, 2005, the filing date of the corresponding German patent application 10 2005 015 164.7.
The present invention relates to a two-cycle engine, especially one in a manually-guided implement such as a power saw, a brush cutter, a cut-off machine, or the like.
U.S. Pat. No. 6,101,991 discloses a two-cycle engine having an intake duct or channel that is divided into an air channel and a mixture channel. The two-cycle engine has a carburetor in which a butterfly valve is pivotably mounted in a portion of the intake channel. In the completely opened position, the butterfly valve rests against the edge of a ring-shaped element. Downstream of the throttle shaft, a partition that divides the intake channel adjoins the ring-shaped element. Opening into the intake channel is a fuel opening that upstream of the butterfly valve is disposed at a level to which the ring-shaped element just reaches.
It has been shown that in particular in full throttle operation, in other words when the butterfly valve is disposed approximately parallel to the direction of flow in the intake channel, fuel can pass into the air channel. Due to the pulsations in the intake channel, the fuel passes into the air channel upstream of the butterfly valve. The air that is supplied to the two-cycle engine via the air channel serves to separate the fuel/air mixture in the crankcase from the exhaust gases in the combustion chamber, and to prevent fresh, non-combusted fuel/air mixture from escaping out of the combustion chamber through the outlet. The fuel that passes into the combustion chamber through the air channel can escape out of the combustion chamber with the exhaust gases, thus impairing the quality of the exhaust gas emissions.
It is an object of the present application to provide a two-cycle engine of the aforementioned general type that has lower emission values and has a straightforward construction.
This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which:
The two-cycle engine of the present application comprises a cylinder having a combustion chamber formed therein; a piston reciprocably mounted in the cylinder, wherein in prescribed positions of the piston the combustion chamber is in communication with a crankcase via at least one transfer channel; an intake channel for supplying fuel/air mixture and combustion air; a carburetor, wherein a portion of the intake channel is formed in the carburetor; a butterfly valve pivotably mounted in the carburetor for controlling the flow cross-section of the intake channel, wherein a fuel opening opens into the intake channel portion, and wherein downstream of the carburetor the intake channel is divided into a mixture channel and an air channel; and means disposed on the butterfly valve for increasing the speed of flow in the carburetor in the vicinity of the fuel opening.
Due to the increase of the speed or velocity of flow in the region of the fuel opening, the fuel is supplied to the two-cycle engine via the mixture channel. A passage of fuel into the air channel can thereby be substantially avoided.
The means for increasing the flow velocity is preferably disposed on that side of the throttle valve that in the completely opened position of the throttle valve faces a section of the intake channel that is disposed upstream of the mixture channel. The means for increasing the flow velocity is, in particular, embodied as a flow-directing element.
A flow-directing element on the butterfly valve leads to an alteration of the flow when the butterfly valve is completely opened. As a result, it is possible to influence the flow in that section of the intake channel that is disposed upstream of the mixture channel and into which the fuel opening opens. The flow-directing element can be embodied in such a way that the flow is accelerated at the fuel opening, thus ensuring an adequate supply of fuel.
The flow-directing element is disposed on a that portion of the butterfly valve that is disposed upstream of the throttle shaft when the butterfly valve is completely opened. As a result, the flow-directing element can influence the flow in the region of the fuel opening, whereas downstream of the throttle shaft there is substantially no influence upon the flow. The flow-directing element preferably reduces the flow cross-section in the intake channel. This results in an acceleration of the flow, which leads to an improved drawing-in of fuel from the fuel opening. However, the flow-directing element can also be disposed on that portion of the butterfly valve that is disposed downstream of the throttle shaft when the butterfly valve is completely opened. The flow-directing element is in particular secured to the butterfly valve. In this connection, the flow-directing element can be clipped onto the butterfly valve or screwed or otherwise secured to the throttle shaft. However, it can also be advantageous to monolithically form the flow-directing element with the butterfly valve. The flow-directing element is preferably made of polymeric material, in which case the surface of the element that influences the flow can have substantially any shape. A flow-directing element made of polymeric material is easy and economical to manufacture, and brings about an only minimal increase in the weight of the two-cycle engine.
A venturi section can be formed in the carburetor in a portion thereof disposed upstream of the mixture channel, and the fuel opening can open into the intake channel in the venturi section. When the butterfly valve is completely opened, the fuel opening is preferably disposed in the intake channel at the level of the flow-directing element. Due to the presence of the flow-directing element, the fuel opening at the venturi section can be offset downstream relative to conventional configurations. Despite the fact that the fuel opening is offset downstream, due to the flow-directing element an adequate flow velocity can be achieved at the fuel opening, thus ensuring a good drawing-in of fuel. Arranging the fuel opening at the level of the flow-directing element, and not upstream of the throttle valve as is the case with conventional configurations, leads to a drawing of the fuel into the mixture channel; the fuel cannot pass into the air channel. The fuel opening preferably opens into the intake channel directly adjacent to the pivot region of the butterfly valve. The fuel opening is accordingly offset downstream as far as possible. However, pivoting of the butterfly valve must not be obstructed by the fuel opening. The fuel opening is a main fuel opening, and at least one secondary fuel opening opens into the intake channel downstream of the main fuel opening. At least one secondary fuel opening is disposed downstream of the butterfly valve when the latter is closed, so that a small quantity of fuel can also be supplied during idling.
A straightforward configuration of the two-cycle engine results if the intake channel is divided by a partition into an air channel and a mixture channel. One end of the partition is disposed at the downstream end face of the carburetor. The partition does not extend into the carburetor housing, but rather ends essentially at the end face of the carburetor. In this way, guide means for the partition in the interior of the carburetor can be eliminated, so that a conventional carburetor can be utilized. To influence the flow distribution between air channel and mixture channel, a narrowed section is formed in the carburetor in a section of the intake channel that is disposed upstream of the air channel. The narrowed section is preferably disposed approximately at the level of the butterfly valve. The narrowed section is in particular formed by the venturi section. However, the venturi section can also extend in the carburetor only in that section of the intake channel that is disposed upstream of the mixture channel, while a narrowed section that is separate from the venturi section is disposed in the carburetor in that section of the intake channel that is disposed upstream of the air channel. In this connection, the narrowed section can also be disposed on the butterfly valve.
Further specific features of the present application will be described in detail subsequently.
Referring now to the drawings in detail, the two-cycle engine 1 shown in
The two-cycle engine 1 is connected via an intake channel 9 with an air filter 24, by means of which the two-cycle engine 1 draws in combustion air. A portion 29 of the intake channel 9 is formed in a carburetor 10 in which fuel is supplied to the drawn-in combustion air via a main fuel opening 22 and auxiliary or secondary fuel openings 23. The main fuel opening 22 is disposed at a venturi section 27, which extends about the entire periphery of the intake channel portion 29. The secondary fuel openings 23 are disposed downstream of the main fuel opening 22. A butterfly valve 25 is pivotably mounted in the carburetor 10 on a throttle shaft 26. In
During operation of the two-cycle engine 1, when the piston 5 is moving upwardly, fuel/air mixture is drawn into the crankcase 4 via the mixture inlet 12. In the vicinity of the upper dead center position of the piston 5, the transfer channels 16 and 18, proceeding from their transfer windows 17 and 19, are flushed by the largely fuel-free air from the air channel 13. During the downward movement of the piston 5, the fuel/air mixture in the crankcase 4 is compressed. As soon as the transfer windows 17 and 19 open toward the combustion chamber 3, first the temporarily collected, largely fuel-free air, and subsequently fuel/air mixture, flow through the transfer channel 16 and 18 and into the combustion chamber 3. During the upward movement of the piston 5, the mixture in the combustion chamber 3 is compressed, and in the vicinity of the upper dead center position of the piston 5 is ignited by a spark plug that projects into the combustion chamber 3. As a consequence of the combustion, the piston 5 is accelerated in a direction toward the crankcase 4. As soon as the outlet 15 is opened by the piston 5, the exhaust gases can escape from the combustion chamber 3. The largely fuel-free air flows through the transfer channels 16 and 18 into the combustion chamber 3 and separates the exhaust gasses that are escaping via the outlet 15 from the following fresh mixture.
In
As shown in
In
In the illustrated embodiments, the venturi section 27 extends about the entire periphery of the intake channel portion 29. However, it can also be advantageous for the venturi section 27 to extend only in that section of the intake channel portion 29 that is disposed upstream of the mixture channel 11, while no venturi section is provided upstream of the air channel 13. The venturi section 27 reduces the flow cross-section in the intake channel portion 29, and thus forms a narrowed section. In addition to, or instead of, the venturi section 27 that is formed upstream of the air channel 13, some other type of narrowed section can be provided upstream of the air channel 13. The narrowed section of the flow cross-section upstream of the air channel 13 influences the distribution of flow in the intake channel 9. By means of a suitable configuration of the narrowed section, it is possible to influence the ratio of fuel/air mixture and combustion air, and to prevent fuel from passing over into the air channel 13. The narrowed section can, for example, be formed by a thickened portion disposed on that side of the butterfly valve that is opposite the flow-directing element.
An embodiment of a carburetor 10 having no venturi section upstream of the air channel 13 is shown in
In the carburetor 10 shown in
The specification incorporates by reference the disclosure of German priority document 10 2005 015 164.7 filed Apr. 2, 2005.
The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.
Number | Date | Country | Kind |
---|---|---|---|
10 2005 015 164.7 | Apr 2005 | DE | national |