The present invention relates to a two-cycle engine, especially in a portable, manually guided implement, such as a chain saw, a cut-off machine, or the like.
WO 00/43650 discloses a two-cycle engine that has an air channel for the supply of air into the transfer channel. The air channel is connected with the transfer channel via a piston window. The fresh air previously collected in the transfer channels is frequently not sufficient for a clean separation of exhaust gases and fresh fuel/air mixture that is flowing in from the crankcase. As a result, increased scavenging losses and hence poor exhaust gas values can occur.
It is therefore an object of the present invention to provide an improved two-cycle engine of the aforementioned general type that, while providing a good scavenging result, minimizes the scavenging losses.
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 invention in which is formed a combustion chamber that is delimited by a reciprocating piston that, via a connecting rod, drives a crankshaft that is rotatably mounted in a crankcase, wherein an inlet is provided for a supply of fuel/air mixture into the crankcase, wherein an outlet is provided for discharge of exhaust gas from the combustion chamber, wherein at least one transfer channel is provided for fluidically connecting the crankcase with the combustion chamber in prescribed positions of the piston, wherein the transfer channel opens into the combustion chamber via an inlet window, wherein a clean air path is provided that includes an air channel, a piston window, and a transfer channel, whereby the air channel serves for conveying essentially fuel-free air and, in prescribed positions of the piston, is fluidically connected via the piston window with the inlet window of the transfer channel, and wherein for a good filling of the transfer channels with fresh air to achieve a good scavenging result, it is provided that the direction of flow in the clean air path extends substantially uniformly from the inlet into the cylinder to the outlet out of the piston window, in at least one position of the piston, and in a plane that extends perpendicular to the longitudinal axis of the cylinder. The avoidance of sharp turns or deflections prevents turbulence and thus enables a good filling of the transfer channels. The direction of flow from the inlet into the cylinder to the outlet out of the piston window expediently extends uniformly in every piston position in which transfer channel and air channel are connected via the piston window.
The change of the direction of flow in the clean air path advantageously extends uniformly from the inlet into the cylinder to the outlet out of the piston window in a plane that extends perpendicular to the longitudinal axis of the cylinder. It has been shown to be advantageous for a good filling of the transfer channels if the clean air path from the inlet into the cylinder to the outlet out of the piston window is curved in one direction in a plane that extends perpendicular to the longitudinal axis of the cylinder. The avoidance of changes of the direction of curvature avoids turbulence and leads to a uniform flow therethrough. In particular, the radius of curvature of the clean air path from the inlet into the cylinder to the outlet out of the piston window is approximately constant in at least one piston position in a plane that extends perpendicular to the longitudinal axis of the cylinder.
The rear wall of the piston window expediently extends parallel to the longitudinal axis of the cylinder. The flow through conditions through the piston window are thus largely the same for all the positions in which the air channel is fluidically connected with the transfer window. Expediently, in at least one piston position, in a plane that extends perpendicular to the longitudinal axis of the cylinder, one wall of the portion of the clean air path that is formed in the cylinder merges tangentially into the rear wall of the piston window. The wall advantageously merges tangentially into the rear wall of the piston window over a wide range of the piston positions in which air channel and transfer channels are fluidically connected with one another. The overall volume of the piston window is advantageously 4 to 14% of the stroke volume or piston displacement of the two-cycle engine. A streamlined arrangement results if the flow resistance from the inlet into the cylinder to the inlet window of the transfer channel or channels is approximately constant in at least one position of the piston. The rear wall of the piston window that is contiguous to the longitudinal axis of the cylinder advantageously has a concave configuration in the circumferential direction of the piston. This allows a favorable flow cross-section to be achieved in the piston window for reducing the flow resistance. At the same time, there results a favorable course of the direction of flow.
For a good deflection of the flow direction in the piston window, it is provided that the radius of curvature of the rear wall of the piston window be at least 70% of the diameter of the piston, and in particular one to nine times the diameter of the piston. As a consequence of the large radius relative to the piston diameter, a sharp deflection of the fluid stream in the piston window is avoided. For a low flow resistance, it is provided that the depth of the piston window be 10 to 40%, especially 13 to 25%, of the piston diameter. The width of the piston window is advantageously 50 to 95%, especially 70 to 85%, of the piston diameter.
For favorable control times, especially a relatively long connection of air channel and transfer channel, it is provided that the height of the piston window, in the region of the air channel window, be two to three times the height of the air channel window. The height of an inlet window is advantageously 10 to 50%, especially 25 to 5%, of the height of the piston window in the region of the air channel window. The entire clean air path is advantageously streamlined, i.e. is embodied with few deflections. For this purpose, advantageously two air channels lead to the cylinder, whereby when viewed in the direction of flow the air channels extend skewed relative to one another at the level of a carburetor. In this way, there results a favorable arrangement by means of which sharp deflections are avoided in the air channels. However, it can also be advantageous that one air channel leads from the air filter to the cylinder, with this air channel being divided into two branches in the region of the cylinder, whereby the direction of flow in each branch extends approximately tangential to the direction of flow in the cooperative section. To form a constant fuel/air mixture, the air channel is expediently provided with a throttle or flow control element, that, when viewed in the direction of flow, is disposed approximately at the level of a carburetor.
Further specific features of the present invention will be described in detail subsequently.
Referring now to the drawings in detail,
As illustrated in the cross-sectional view of
In the perspective view of the two-cycle engine 1 in
In the cross-sectional view of
The piston windows 16 have a concave configuration, whereby the rear wall 23 of the piston window 16, which rear wall faces the longitudinal axis 22 of the cylinder, has a radius of curvature r. The radius of curvature r can be constant over the entire rear wall 23. However, it can also be advantageous for the rear wall 23 to be formed from adjoining partial sections having different radii of curvature, which advantageously merge into one another, whereby the radii of curvature are in particular sequentially arranged in an increasing or decreasing manner. It can also be expedient to have sections with largely the same radii of curvature yet offset center points of the curvature.
The portion 25 of the clean air path 24 formed in the cylinder 2 opens at the air channel window 17 into the interior of the cylinder 2. That wall 31 of the portion 25 that is contiguous to the center plane 26 merges tangentially at the air channel window 17 into the rear wall 23 of the piston window 16. The wall 35 of the transfer channel 11 that is near the outlet, which wall 35 is also near the outlet, adjoins, on the opposite side of the piston window 16, the rear wall 23 in a tangential manner. The wall 35 that is near the outlet is thereby that wall of the transfer channel 11 that extends in an approximately radial direction approximately parallel to the longitudinal axis 22 of the cylinder.
The direction of flow 28 in the clean air path 24 extends uniformly from the inlet 29, where the air channel 15 opens into the portion 25 formed in the cylinder 2, to the outlet 30 in the region below the inlet window 13 of the transfer channel 11. In this connection, the term below denotes displaced in a direction toward the crankcase 6. As illustrated in
The resistance to flow in the clean air path 24 is, in at least one position of the piston, advantageously approximately constant over the entire length of the clean air path from the air filter 21 up to the opening out of the transfer channels 11, 12 into the crankcase 6, at least however from the inlet 29 into the cylinder 2 up to the inlet windows 13,14 into the transfer channels 11, 12. The rear wall 23 of the piston window 16 extends parallel to the longitudinal axis 22 of the cylinder. Favorable flow conditions result if the radius of curvature r of the rear wall 23 of the piston window 16 is at least 70% of the diameter d of the piston 4. In particular, the radius of curvature r is one to nine times the diameter d of the piston 4. As a consequence of the large curvature r, a uniform direction of flow is ensured.
In order to be able to realize a low resistance to flow, it is provided that the depth t of the piston window 16, as measured in a radial direction relative to the longitudinal axis 22 of the cylinder, is 10 to 40%, especially 13 to 25%, of the diameter d of the piston 4. The width b of the piston window is 50 to 95%, especially 70 to 85%, of the diameter d of the piston. The overall volume of the piston window 16 is 4 to 14% of the stroke volume or piston displacement of the two-cycle engine 1, i.e. the difference between the volume of the combustion chamber 3 in the lower dead center position of the piston 4 and the volume of the combustion chamber 3 in the upper dead center position of the piston 4. The volume of the piston window 16 should be selected such that the flow resistance in the piston window 16 is not less than it is in other portions of the clean air path 24. The flow cross-section in the transfer channel 11 that is close to the outlet is greater than the flow cross-section in the transfer channel 12 that is remote from the outlet. The flow cross-sections in the transfer channels 11,12 are approximately constant over the length of the transfer channels.
As illustrated in the developed view of
To establish a sufficiently long fluidic connection between the air channel 15 and the transfer channels 11,12, it is provided that the height e of the piston window 16, as measured in the direction of the longitudinal axis of the cylinder, and in the region of the air channel window 17, and in particular the maximum height of the piston window 16, corresponds approximately to two to three times the height a of the air channel window 17. In this connection, the height is respectively the extension in the direction of the longitudinal axis 22 of the cylinder. In a corresponding manner, the width is the extension in the circumferential direction relative to the longitudinal axis 22 of the cylinder. The height c of the inlet window 14, and the height f of the inlet window 13, are approximately 10 to 50%, especially 25 to 35%, of the height e of the piston window 16 in the region of the air channel window 17. In the vicinity of the piston collar 27, on which the connecting rod 5 is mounted in the piston 4, the piston window 16 has a lesser height, since the piston collar 27 is partially spanned by the piston window 16. The air channel window 17 is expediently displaced below the inlet window 14, i.e. in a direction toward the crankshaft axis 8. This results in particularly short flow paths and favorable flow conditions.
The uniform course of the flow direction from the inlet 29 to the outlet 30 illustrated in
The specification incorporates by reference the disclosure of German priority document DE 102 23 070.6 filed 24 May 2002.
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 |
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102 23 070 | May 2002 | DE | national |
Number | Name | Date | Kind |
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6367432 | Araki | Apr 2002 | B1 |
6497204 | Miyazaki et al. | Dec 2002 | B1 |
6571756 | Rosskamp et al. | Jun 2003 | B1 |
6708958 | Warfel et al. | Mar 2004 | B1 |
20020043227 | Carlsson et al. | Apr 2002 | A1 |
Number | Date | Country |
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1 069 294 | Oct 1999 | EP |
0 992 660 | Apr 2000 | EP |
2001323816 | Nov 2001 | JP |
2001329844 | Nov 2001 | JP |
2001-329844 | Nov 2001 | JP |
WO 0043650 | Jul 2000 | WO |
WO 0151782 | Jul 2001 | WO |
Number | Date | Country | |
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20030217709 A1 | Nov 2003 | US |