Patent Grant
7100550
1. Field of the Invention
The present invention relates to internal combustion engines and, more particularly to a transfer system.
2. Background Art
U.S. Pat. No. 6,367,432 discloses a two-stroke cycle internal combustion engine which has a quaternary Schnurle-type scavenging system that is configured such that the capacity of a pair of second scavenging passageways are made larger than te capacity of a pair of first scavenging passageways, so that during the descending stroke of the piston, air is allowed to be introduced into the combustion actuation chamber from the second scavenging passageways prior to the introduction of the air-fuel mixture and at the same time, a relatively large quantity of air is allowed to be introduced into the combustion actuating chamber from the first scavenging passageways over a longer period of time as compared with the period of time in which air is introduced from the second scavenging passageways.
U.S. Pat. No. 6,223,705 discloses a two-stroke internal combustion engine having a Schnurle scavenging system includes a pair of first scavenging ports and a pair of second scavenging ports. An inner horizontal scavenging angle formed close to an exhaust port and an outer horizontal scavenging angle formed remote from the exhaust port by a pair of scavenging flows blown out of the pair of the first scavenging ports are both set to an angle in the range of from 116 to 124 degrees. An inner horizontal scavenging angle formed close to the exhaust port and an outer horizontal scavenging angle formed remote from the exhaust port by a pair of scavenging flows blown out of the pair of the second scavenging ports are set to angles in the ranges of rom 126 to 135 degrees and from 146 to 154 degrees, respectively.
Because of increasing government pollution emissions standards, there is a continuing need to lower engine emissions in two-stroke engines. One of the sources of emission problems has been the discharge of unburned hydrocarbons due to short circuiting of fuel out of an exhaust port during an upward stroke of the piston before the exhaust port is closed. Thus, there is a need to minimize the loss of fresh, short circuit fuel exiting out of the exhaust. This minimization can result in lower hydrocarbon emissions and higher fuel economy.
In accordance with one of the present invention, a two-stroke internal combustion engine is provided including a cylinder; and a piston movably mounted in the cylinder. The cylinder includes an exhaust port and transfer ports. The transfer ports include a first pari of the transfer ports disposed closer to the exhaust port than a second pair of the transfer ports which are disposed further away from the exhaust port. The first pair of transfer ports are angled relative to each other at a first angle of about 70° to about 85° and the second pair of transfer ports are angled relative to each other at a second angle of about 120° to about 150°. Directional discharge of scavenged air out of the transfer ports establishes a flow path for the scavenged air to minimize losses of fresh unburned fuel into the exhaust port.
In accordance with another aspect of the present invention, a two-stroke internal combustion engine is provided comprising a cylinder; and a piston movably mounted in the cylinder. The cylinder comprises an exhaust port and transfer ports. Two of the transfer ports comprise a common bottom channel extending into a side wall of the cylinder in a bottom portion of the cylinder and separate respective top channels. The cylinder comprises a partition wall extending between the two ports to form the two separate top channels.
In accordance with one method of the present invention, a method of introducing scavenged air into a cylinder of a two-stroke internal combustion engine is provided comprising steps of providing the cylinder with an exhaust port and two pairs of transfer ports being located in closer proximity to the exhaust port than a second one of the pairs of transfer ports; opening the second pair of transfer ports to a combustion chamber of the engine by a piston of the engine as the piston moves towards a bottom dead center position before the piston opens the first pair of transfer ports; and opening the first pair of transfer ports by the piston. The second pair of transfer ports is located further away from the exhaust port is opened into the combustion chamber before the first pair of transfer ports is opened into the combustion chamber.
In accordance with other aspects of the present invention, a two-stroke internal combustion engine is provided having a cylinder and a piston movably mounted therein. The cylinder defines an exhaust port and at least one pair of opposed transfer ports directed inwardly toward a transverse center line generally away from the exhaust port toward an opposed cylinder wall wherein the charge from the at least one pair of transfer ports meets in a compact convergence zone spaced between the cylinder central axis and the front wall. Preferably, the convergence zone is spaced from the cylinder axis more than 0.4 times the cylinder radius and most preferably, 0.5-0.8 times the cylinder radius.
In accordance with other aspects of the present invention, a two-stroke internal combustion engine is provided comprising a cylinder and a piston movably mounted therein. This cylinder includes an exhaust port and at least one pair of transfer ports spaced on opposite sides thereof and directing intake charge inwardly and generally away from the exhaust port, the exhaust port opening is 116°-121° after TDC and most preferably, 117°-120° after TDC.
In accordance with other aspects of the present invention, a two-stroke internal combustion engine is provided comprising a cylinder and a piston movably mounted therein. This cylinder includes an exhaust port and at least one pair of transfer ports spaced on opposite sides thereof and directing intake charge inwardly and generally away from the exhaust port wherein the transfer ports open 8°-15° after the exhaust port opens and preferably, 10°-12° after the exhaust port opens.
In accordance with other aspects of the present invention, a two-stroke internal combustion engine is provided comprising a cylinder and a piston movably mounted therein. This cylinder includes an exhaust port and at least one pair of transfer ports spaced on opposite sides thereof and directing intake charge inwardly and generally away from the exhaust port wherein the exhaust port has a restricted blow down region which opens initially, providing 20%-30% of the total exhaust port area, the blow down region having a circumferential length which is substantially less than the maximum exhaust port circumferential length and preferably, approximately about 50% of the maximum exhaust port length.
Referring to
The engine 10 is a two-stroke engine having a cylinder 12, a piston 15, a crankshaft 16, a crankcase 18, a fuel delivery system 20, and an ignition system 22. One type of specific application for the engine 10 could be in a small high speed two-stroke engine such as utilized in a hand-held power tool, such as a leaf blower, string trimmer, head trimmer, chain saw, etc.
The ignition system 22 generally comprises a spark plug 24 and an electrical generating system 26 connected to the spark plug 24. However, in alternate embodiments, any suitable type of ignition system could be used. The ignition system 22 is generally well known in the art.
The fuel delivery system 20 generally comprises a carburetor 28, an air filter 30, a main air inlet 32 into the cylinder 12, and a fuel and air inlet 33 into the bottom of the cylinder 12. However, in alternate embodiments, any suitable type of fuel delivery system could be used. For example, the fuel delivery system 20 could comprise a conventional fuel delivery system well known in the art. Alternatively, the fuel delivery system could comprise a fuel injection system or a newer type of efficient, fuel delivery system such as disclose din U.S. Pat. Nos. 6,295,957; 6,293,235; 6,286,469; and 6,382,176 which are hereby incorporated by reference in their entireties.
The piston 14 is movably mounted in the cylinder 12 and is operably connected to the crankshaft 16 in a conventional manner. Referring also to
Referring also to
As seen best in
In one type of embodiment, the main internal area 38 of the cylinder 12 has a diameter of about 1.375 in. Flows form the transfer ports 36 can be directed towards an inner most general area 61 of the intersection which is spaced at a distance 66 form the cylinder axis 60. For the diameter of about 1.375 in., the distance 66 can be about 0.3 inch to about 0.412 inch.
The transfer ports 36 are angled towards a front of the cylinder in a direction away from the exhaust port 34. The transfer ports 36 extend upward form the bottom 40 of the cylinder to a middle section of the cylinder. The transfer ports 36 extend outward from the main internal area 38 into the interior side walls of the cylinder 12. The transfer ports 36 are preferably wider at their base, proximate the bottom 40, then at their top ends 56, 58. The top ends 56, 58 are substantially flat. However, in alternate embodiments, the top ends could have any suitable type of shape.
As seen best in
Unlike conventional two-stroke engines, the front and rear pair of transfer ports have a phase difference in timing of their opening. As the piston moves downward towards a bottom dead center position, the piston uncovers the front ports, i.e., the second pair of ports 50 about four to eight degrees sooner than the rear ports, i.e., the first pair of transfer ports 48 are uncovered. During the early scavenging process, the front ports 50, which opened sooner, discharge live charge (fuel and air) into the cylinder, away form the exhaust port 34 due to directional discharge characteristics of the ports. The charge that is discharged furthest away from the exhaust port enters the cylinder first and, also travels the longest distance. The earliest entering charge is also the fraction of the total charge that is most likely to be lost into the exhaust 34. Even though the charge that enters through the second transfer ports 50 enters first, it has to travel the farthest and is the least amount of charge entering from the two sets 44, 46. Thus, the fractional loss is also minimum.
The early opening of the front two 50 of the four transfer ports helps to establish a flow path for the charge that follows in such a way that it may result in a near-perfect displacement scavenging. Thus, flow pattern and staggered discharge of live charge helps minimize the loss of resh fuel into the exhaust, which results in lower emissions and higher fuel economy.
The top ends 58 of the second transfer ports 50 can be located below the top end of the exhaust port 34. The width of the second transfer ports 50 can be smaller than the width of the first transfer ports 48. The use of a tapered shape along the height of the second transfer ports 50 can also reduce the side of the opening of the second transfer ports when the second transfer ports 50 are uncovered by the piston 14. It is believed that narrow opening of the front ports late during the blow-down process can increase the discharge velocity, which helps mixing. Low short circuit loss of fresh charge combined with improved mixing reduces significantly the exhaust emissions.
Referring also to
Tests of an engine incorporating features of the proposed invention has demonstrated emissions below 2004 EPA Phase II emission levels without the use of a catalytic converter. Implementation of the present invention into a conventional engine design is relatively simple and existing hardware (such as pistons, etc.) Can be used with the redesigned cylinder described above. Tooling cost to implement the features of the present invention is minimal. The following table shows results of such a test and variations of port configurations on a 30 cc engine. Similar testing on a 25 cc engine has demonstrated low emission levels.
Referring now to
Pairs of the transfer ports, on each side of the cylinder, comprise a common bottom channel 86 extending into the side wall of the cylinder in a bottom portion of the cylinder, and separate respective top channels which form two of the ports 82, 84. The cylinder 78 comprises a partition wall 88 which extends between the two ports 82, 84 to form the two separate top channels. In the embodiment shown, the partition wall 88 comprises a general triangular cross section. However, in alternate embodiments, the wall 88 could comprise any suitable cross sectional shape. The wall 88 has a height that is about two-thirds the heights of the ports 82, 84. In the embodiment shown, the forward and rearward sides of the bottom channels 86 are angled relative to each other at angles 94 and 96. In one embodiment, the angle 94 is about 80° and the angle 96 is about 130°. However, in alternate embodiments, any suitable angles could be provided. This embodiment can be formed the same angles 52, 54, shown in the embodiment of FIG. 3. The top ends 90, 92 comprise top surfaces which are angled downward in a direction of the exhaust port 34. The second transfer ports 84 each comprise a top surface at the ends 92 which is at least partially higher than a top surface of the first transfer ports 82 at th ends 90 such that the second transfer ports open before th first transfer ports as the piston moves towards a bottom dead center position.
There is provided a progression of discharge angle 98 due to curvature of the piston. The partition walls 88 need not extend all the way to the piston 14. One of the features of this embodiment, is that the pairs of transfer ports 82, 84 can be provided in a relatively compact area. This allows features of the present invention to be used in relatively small size cylinders. In an alternate embodiment, the top ends of the transfer ports could be substantially straight and horizontal, and the top surface of the piston could be angled to allow a stepped progression of entry of a charge into the combustion chamber. In another alternate embodiment, the top surfaces of the transfer ports might not be straight, but could be non-straight.
Referring now also to
Referring now also to
The following tables illustrate the exhaust and transfer port areas as a function of piston position in crank angle degrees with 0 representing piston top dead center (TDC) and 180 representing piston bottom dead center (BDC). Four engines W through Z, ranging in displacement from 25 to 40 cc. have been evaluated having a four transfer port design as generally illustrated in
To better illustrate the relative size and timing of the transfer ports and the exhaust port area of the present invention in contrast to the prior art, a port area versus crank angle timing diagram is provided in FIG. 10. The standard prior art two-stroke engine is represented by exhaust port area curve 120 and transfer port area curve 122. Engine Y, is a comparably sized engine utilizing the present invention. Engine Y has an exhaust port area versus crank angle degree curve 124. Relative to standard exhaust port area curve 120, the present invention is not only slightly lower in maximum area, but is shifted approximately at 10° later in time. Quite subtly, but important, is the shape of the exhaust port area curve 120 as it initially opens. The exhaust port area initially increases more gradually than the prior art due to the chevron shaped exhaust port described previously.
The exhaust port of engine Y has a blow down region which is 20% to 30% of the total port area which has a reduced circumferential length relative to the remaining port region resulting in a more gradual port opening and port closing. This small size blow down region allows for the intake charge to be effectively trapped while still allowing efficient exhaust blow down and discharge so that engine power is not compromised. Preferably, the exhaust blow down region will have a circumferential port length of about 50% of the maximum circumferential length from the remainder of the exhaust port.
As further illustrated in
In addition to delaying exhaust port opening and port opening geometry, engines of the present invention open the transfer ports relatively early. The combined area of the transfer ports result in a more gradual transfer port opening. In
The relative timing of the opening of the first and second transfer ports are likewise illustrated in the
The flow of the intake charge into the cylinder in the four transfer port embodiments initially comes from the second transfer ports which are oriented at an included angle of 120°-150° relative to one another as illustrated in FIG. 3. As the piston moves down and opens the first transfer ports, the additional intake charge is introduced into the cylinder and a more pronounced angle relative to the transfer center line with the included angle between the first transfer ports being in the 70°-85° range as illustrated in FIG. 3. The flow through all four transfer ports converges in a transfer port convergence zone 63. The transfer port convergence zone 63 is located along the transverse centerline between the cylinder axis 60 and the cylinder front wall opposite the exhaust port 34. Ideally, the convergence zone is spaced from the bore axis 60, a distance greater than 0.4 times the cylinder radius, preferably, 0.4-0.9 times the cylinder radius and most preferably, 0.5-0.8 times the cylinder radius in the four point embodiment of
In the alternative embodiments shown in
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
This application claims priority to U.S. application Ser. No. 10/264,939, filed Oct. 4, 2002 and application Ser. No. 10/452,079, filed May 30, 2003.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US03/31470 | 10/6/2003 | WO | 00 | 12/1/2003 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2004/033869 | 4/22/2004 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20040244739 A1 | Dec 2004 | US |
