US 3817227 A
A two-cycle internal combustion engine having an electric ignition system and characterized in that a suitably shaped recess is disposed inside the cylinder head, thereby forming a combustion chamber. A device for controlling the quantity of fuel supply and a device for controlling the flow of exhaust gas are operated relatively to each other in such a way that the flow of exhaust gas is increased or decreased in response to increase or decrease in the supply of fuel.
Claims available in
Description (OCR text may contain errors)
U Umted States Patent 1191 1111 3,817,227 Onishi June 18, 1974  TWO-CYCLE INTERNAL COMBUSTION 3,400,702 9/1968 Watkins 123/65 R ENGINE FOREIGN PATENTS OR APPLICATIONS Inventor: ig i i, 1-1 17,176 5/1956 Germany 123/73 R Higashiyama, 3-chome, Kanazawa, 572,529 2/1924 France 123/73 V Japan 865,233 5/1952 Germany 123/73 A 605,610 7/1948 Great Britain 123/65 R Flledi 1972 67,520 7 10/1957 France 123/65 WA  Appl. No.: 232,325
Primary Examiner-Charles .1. Mlyhre Assistant Examiner-W. Rutledge, Jr.  Forelgn Apphcauon Pnomy Data Attorney, Agent, or FirmBlum Moscovitz Friedman Feb. 25, 1971 Japan ..46-9703 & Kaplan  US. Cl. 123/73 A, 123/65 WA,  ABSTRACT 51 1111.01. F02b 25/20, F02d 9/04, F02d 9/10 A 9'. cmbusfion l having  Field of Search 1213/65 R 65 w 65 W A electric ignltlon system and characterized in that a 123 73 R 73 98 suitably shaped recess is disposed inside the cylinder head, thereby forming a combustion chamber. A de-  References Cited vice for controlling the quantity of fuel supply and a device for controlling the flow of exhaust gas are oper UNITED STATES PATENTS ated relatively to each other in such a way that the 13 5 lsmdefson flow of exhaust gas is increased or decreased in repencer 2 L 5/1936 Harper-m. sponse to Increase or decrease In the supply of fuel 2,064,983 12/1936 Lesage 123/65 A 7 Claims, 7 Drawing; Figures PATENTEDJUH 18 I974 sum 2 or 3 Full Open Exhduat V 1 Contr l VUIVQ Closb v v Full Op'on TWO-CYCLE INTERNAL COMBUSTION ENGINE BACKGROUND OF THE INVENTION This invention relates to two-cycle, piston-typeinternal combustion engines in which the gas mixture provided by carburetor system or injector system is compressed inside the cylinder, and more particularly to a two-cycle internal combustion engine employing a loop or cross-scavenging system.
The conventional two-cycle internal combustion engine of loop or cross-scavenging type, particularly of crank case compression type is structurally simple and can be manufactured at a low cost. On the other hand, however, it has several drawbacks. For example, misfire often takes place even if an easily combustible mixture with a high fuel-air ratio is used in the no-load or part-load operating condition. This results in an irregular combustion state involving unpleasant exhaust sounds and rough vibration. Furthermore the specific fuel consumption is raised and the noxious component in the exhaust gas is increased. Generally, in order to increase the charging efficiency in the prior art, the exhaust pipeline is designed to be suitable as to size and shape so that the negative pressure wave produced in the pipe due to the flow of exhaust gas is reversely introduced into the cylinder. This arrangement is effective during high load operation, while it serves as a significant factor causing misfire, because, at a light load where a small amount of gas mixture is applied, the supplied gas mixture is unnecessarily mixed with the residual gas.
SUMMARY OF THE INVENTION In view of the foregoing, the present invention has, as its principal aim, the provision of an improved twocycle internal combustion engine operable at a high combustion efficiency in each cycle even at a relatively low fuel-air ratio, and capable of preventing misfire irrespective of operating condition, minimizing vibration and noise of engine, decreasing the specific fuel consumption, i.e., increasing the thermal efficiency, and purifying the exhaust gas.
With this aim in view, an object of this invention is to provide a two-cycle internal combustion engine in which a suitably shaped recess is disposed inside the cylinder head, thereby forming a combustion chamber, an exhaust gas control part disposed in the exhaust pipeline and a fuel supply control part are relatively operated in such a way that at a part-load operation the gas mixture flow into the cylinder is reasonably slowed and stratified and the mixture is securely sent in said recess space whereby stable combustion is maintained in each cycle even at a low fuel-air ratio, misfire is prevented, and the exhaust gas is purified.
Another object of this invention is to provide a twocycle internal combustion engine in which the squish effect is brought about in the vicinity of the top dead center whereby a higher ignitability is maintained and combustion is accelerated.
Still another object of this invention is to provide a twofcycle internal combustion engine in which an ingition plug is disposed in a specific position and said recess part whereby a higher ignitability is achieved.
BRIEF DESCRIPTION OF THE DRAWINGS The drawings illustrate an embodiment of the present invention wherein:
FIG. I is a schematic sectional side view showing the overall construction;
FIG. 2 is an enlarged view of the cylinder portion, showing the state of distribution of the fuel particles in the injected mixture gas;
FIG. 3 is a schematic sectional view taken along line 1-1 of FIG. 2 in the direction of the arrows;
FIGS. 4 and 5 are schematic sectional views taken along lines 2-2 and 3-3, respectively, of FIG. 3, in the direction of the arrows and showing the state of squish flow;
FIG. 6 is a graphic representation showing the relationship between the exhaust control valve and the throttle valve with respect to valve opening; and
FIG. 7 is a diagrammatic representation of a valvecontrolling linkage.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is schematically illustrated a Schnuerle scavenging type two-cycle internal com bustion engine having a crank case compression systern, wherein a scavenging port 3 and an exhaust port 4 are opened/closed by the motion of a piston 2 reciprocatively disposed in a cylinder 1.. An exhaust control valve 6 is provided in an exhaust pipe 5 connected to exhaust port 4. This exhaust control valve is located at a small distance from said exhaust port 4 whereby a prechamber 20 is formed.
A carbureter 26 is disposed in an intake pipe 7 communicating with a crank case 12. A control lever 9 of a throttle valve 8 of a fuel-supply control means which is to control the fuel supply and a control lever 10 of exhaust control valve 6 of an exhaust-gas control means are interlocked by way of a link mechanism 11, as shown schematically in FIG. 1. Thus, when the throttle valve 8 is moved in an opening direction, namely in the direction of increasing fuel supply, the exhaust control valve 6 is moved also in an opening direction, so that the exhaust outflow resistance is reduced.
A one-way, flexible, springer leaf valve (not shown) which serves to stop the back flow from the crank case 12 is provided in a part 19 where said intake pipe is connected to the crank case 12. The gas mixture compressed in the crank case 12 by the motion of piston 2 is supplied to the cylinder 1 from the scavenging port 3 by way of scavenging passages 13, which are located opposite to each other on the both sides of the cylinder respectively.
The inside of a cylinder head 14 is shaped as shown in FIGS. 2 and 3 which show a recess 15 formed in the neighborhood of the center of the cylinder head. More specifically, the recess is formed to become gradually deeper in the direction of the gas flow in the cylinder, in which the gas stream turns from the upward to downward direction in the vicinity of the cylinder head. The deepest part of the recess 15 is located on the front side of the direction along which the stream advances, and the space of the recess is wide enough so that the stream turning round in the axial direction of the cylinder makes a swirling motion. The: inside of the recess has no part wider than its open end so that the shape of the recess does not become constricted at its open end.
The inner surface 17 of the cylinder head 14 around the recess 15 is shaped corresponding to the top surface' 18 of the piston, and the gases held between the surface 17 and the top of the cylinder head produce a squish stream near the top dead center. This squish stream can be strengthened or weakened by changing the relative relationship between the surface 17 and the top surface 18. Namely, the strength of the squish stream can be determined by the distance between surfaces 17 and 18 at the point of the top dead center, the shapes of surfaces 17 and 18, etc.
This engine of the invention is operated in the following manner:
The gas mixture sucked into the crank case 12 by the motion of the piston 2 by way of the throttle valve 8 of carbureter 26 and the intake pipe 7 is compressed and pressurized by the down motion of the piston 2. The pressurized gas burnt in the cylinder is expanded by the down motion of the piston. When the exhaust port 4 is opened, the exhaust gas is emitted into prechamber 20 and then is exhausted to the exterior from the exhaust port via the exhaust control valve 6.
During light load operation where the intake air is throttled by the throttle valve 8, the exhaust control valve 6 also is throttled by the interlocking link mechanism l1, and valve 6 becomes nearly closed. As a result, the exhaust gas is subjected to resistance at the valve 6, and the pressure in the prechamber 20 is increased. Therefore, the pressure in the cylinder 1 is not rapidly lowered, and flowing of the scavenged (or supplied) gas into the chamber 1 by the opening of the scavenging port 3 is slowed. In other words, the subsequently supplied gas mixture is mixed and diffused into the residual exhaust gas only to a small extent. Thus, the gas mixture is fed into the recess of the cylinder head without sacrificing the combustibility even if the air-fuel ratio is determined to be larger than the stoichiometric value. In other words, the supplied gas is stratified in the form of an are or sphere in the cylinder as indicated by the dot group in FIG. 2 before the gas is appreciably mixed with the residual burnt gas, and there is formed a pattern of stream of the supplied gas flowing moderately into the recess 15. The purpose of the exhaust valve 6 in its nearly closed position is to reflect the interfering wave reversely propagated from the exhaust passage 5 (positioned after the valve 6) into the cylinder 1, keep the stream in the cylinder 1 from being disturbed, and minimize the disturbing influence which may be introduced into the cylinder from the exhaust pipeline. This function contributes largely to perfecting said stratified gas supply.
It has been experimentally found that it becomes difficult to maintain stable part-load operation when the volume of the prechamber is too small. This is because the pressure drop in the cylinder 1 is slowed, the exhaust gas flows back through the gas supply passage 13 to reach as far as the crank case 12 when the scavenging port 3 is opened, and the cylinder is charged with the gas containing a large amount of exhaust gas in the subsequent cycle of ignition, to result in misfire. If the opening of the exhaust control valve 6 is increased in order to solve the above trouble, this means that the control valve 6 is substantially removed.
While, if the exhaust control valve 6 is positioned too distant from the exhaust port 4, the volume of the prechamber 20 becomes too large, the pressure drop in the cylinder 1 goes as in the case where the valve 6 is not provided, and the pressure wave by the injected gas is sent back as a reflection wave of positive pressure to the cylinder l at certain time intervals, to disturb the stratified gas. In this instance also, the exhaust control valve has no significance. It has been experimentally ascertained that desirable combustion causing no misfire and allowing least bypassed fuel can be obtained when the volume of the prechamber 20 is between l/lO and 3/l0 that of the engine stroke. As for combustion, it was also found that there is relationship between the throttle valve 8 and the exhaust control valve 6 with respect to opening. For example, the mean effective pressure is gradually reduced under the condition that the throttle valve 'is kept opened at a certain opening, the interlocking link 11 is released, and only the opening of the exhaust control valve 6 is gradually reduced from its full opening. A similar result can be obtained under the condition that the exhaust control valve is kept opened at a certain opening, and the throttle valve is closed from its full opening.
For combustion where the specific fuel consumption is reduced without causing misfire, it is desirable to maintain the following relationship between the two valves with respect to valve opening. According to experiments, this relationship is as shown by the curve in FIG. 6 in which the opening of the exhaust control valve 6 is very small in the range of small opening of the throttle valve 8, and the exhaust control valve 6 rapidly reaches its full opening position when the opening of the throttle valve 8 is above a certain value.
Referring to FIG. 7, it will be seen that between the levers 9 and 10 there is a cam 11a having a camming edge 11b and supported for free swinging movement about a pivot pin 11b. An elongated link is pivotally connected at its opposite ends to the lever 9 and the cam 11a. The lever 10 is urged in a counter clockwise direction, as viewed in FIG. 7, toward the cam 110 by a spring 10b, and the lever 10 carries a camfollower roller 10a engaging the camming edge 11b. This is one example of a possible embodiment of the linkage 11 for interconnecting the levers 9 and 10 so as to control the movement of the valves 8 and 6, respectively. The lever 9 can be swung in the opening and closing directions as indicated by the double-headed arrow, and the lever 10 will be correspondingly swung in opening and closing directions through the linkage means 11 of FIG. 7. Because of the shape of the camming edge 11b the extent of opening and closing of the valve 6 by turning of the lever 10 will have with respect to the opening and closing of the valve 8 by the lever 9 the relationship shown in FIG. 6.
The gas supplied to the cylinder 1 relatively slowly and in the stratified form is introduced to the recess 15 of the cylinder head round about the central zone 22 in the cylinder 1. The stream of this gas is in spherical form and subjected to a centrifugal force and, hence,
' the supplied gas mixture whose specific gravity is larger than that of the residual gas is positioned on the outer side. The fuel particles contained in the gas mixture have a large apparent specific gravity. Consequently the fuel particles are located further at the outer side, and the fuel-air ratio distribution becomes higher toward the outermost zone of the supplied mixture gas. This state is schematically shown by the density distribution of dots representing mixture gas supply in FIG. 2.
The recess is shaped to become gradually deeper so that the supplied gas flows therein smoothly. The recess is deepest on the side of the front of the gas stream. in this deepest portion the supplied gas is securely re ceived and temporarily held. A spark plug 16 is mounted in a deep part 21 so that the spark plug is positioned in a quiet atmosphere inside the recess and is beyond the gas stream in the cylinder. This facilitates ignition and spread of the initial flame.
According to this embodiment, a squish stream is produced near the top dead center due to the top 18 of the piston and the inner surface 17 of the cylinder head. Practically, for example, as shown in FIGS. 3, 4 and 5, the squish stream 23 due to the top surface of the shallow portion of the recess 15 and the top of the piston serves to drive the supplied mixture into the deep part of the recess. The squish stream 25 opposite to the squish stream 23 acts to keep the supplied gas mixture from flowing out of the recess. The function of the squish streams from the both sides of the recess is to press and spread the supplied gas mixture over the wall of the recess. As a result, the gas mixture is thickly stagnated in the vicinity of the corners 27 of the recess FIG. 5, rather than in the central portion of the recess. lf, therefore, the spark plug is positioned eccentrically from the center recess line (FIG. 3), more stable ignition can be realized. It has been experimentally ascertained that the above arrangement is effective for stable ignition even when there remains in the recess a swirling stream having a rotating vector in the axial direction of the cylinder.
As has been described above, the engine of this invention can be driven with a thin gas mixture whose airfuel ratio is, for example, 15 to 18, by suitably determining the correlation between the exhaust control valve 6 and the shape of the recess 15 of the cylinder head. Especially under part-load and no-load operating conditions, misfire and irregular cycle are minimized or eliminated. This makes it possible to reduce the number of rotations set for idling and to minize the fuel consumption during idling rotation.
According to the invention, stable combustion is maintained at a large air-fuel ratio. This in turn increases the efficiency of purifying the exhaust gas. The concentration of carbon monoxide (CO) is reduced below 1/10 compared with that in the prior art. The component of unburnt hydrocarbon is also reduced to about half that in the prior art by the use of exhaust control valve 6, thereby preventing ineffective dispersion of fuel gas due to stratification and thus minimizing bypass gas flow out to the exterior. inherently, in the two-cycle engine, there remains a large amount of residual gas component which, however, serves as an inactive gas. This is why only very little nitrogen oxide (NOx) component is produced.
The combustibility at a large air-fuel ratio and the minimized fuel bypass escape contribute to improvement on the specific fuel consumption, i.e., on the thermal efficiency. Thus, stable combustion having a small cycle variation is realized and the engine vibration and noise are reduced.
According to the invention, the peak value of the exhaust jet velocity during idling and part-load operation is suppressed and smoothed by virtue of the exhaust control valve and, hence, the exhaust sound from the end of the exhaust pipe is reduced to permit quiet engine drive.
In the foregoing embodiment, an engine using a carbureter has been described. As the fuel supply means, a suitable injection system may be employed instead of carbureter. For example, an intake pipe injection, crank case injection, injection into the cylinder from the scavenging port, injection into the cylinder from the cylinder or from the cylinder head, etc. may be used. The invention permits use of various fuels, for example, gaseous fuel such as LPG, and low quality fuel such as kerosene oil.
According to the invention, the device for controlling the amount of fuel injection into the cylinder, and the device for controlling the flow of the exhaust gas (such as the exhaust control valve) are relatively operated whereby the flow of the exhaust gas is decreased or increased in response to decrease or increase in the fuel supply. This concept can be applied to Diesel compression ignition engines. ln this case, during no loador part-load operation where a small amount of fuel is injected therein, it is necessary to throttle the exhaust control valve so that a suitable amount of air corresponding to the existing load is supplied to the combustion chamber in the stratified form. By this arrangement, it becomes possible not only to reduce the pump loss for air supply but also to hold a relatively large amount of residual gas. As a result, the compression initial temperature, i.e., the compression end temperature, can be raised, thus making available a sufficient temperature rise necessary for the engine operable at a low compression ratio, and the fuel ignition delay time can be reduced. Namely, it has been experimentally conformed that the Diesel knocking phenomenon can be almost perfectly eliminated. Because the combustion can be maintained at a low compression ratio and there remains inactive residual gas, the component of nitrogen oxide (NOx) which is a typical problem of Diesel engines can be largely reduced to about 200 ppm at the full load. it is apparent that the invention, when applied to Diesel engines, is particularly useful and practical.
What ss aitnss js 1. in a two-cycle internal combustion engine having an electrical ignition system, elongated cylinder means having a cylinder axis and formed in its interior at one end region with a combustion recess which becomes gradually deeper in the direction of gas flow in the cylinder up to a deepest portion of said recess situated at that side of said axis toward which the gas stream flows after crossing said axis, the direction of gas flow changing beyond said deepest portion of said recess and said recess having its maximum cross sectionin a plane normal to said axis at that part of said recess which is most distant from the deepest portion of said recess, so that said recess is not constricted at its entrance end, exhaust port means and scavenging port means communieating with said cylinder means, piston means reciprocating in said cylinder means for opening and closing said exhaust port means and said scavenging port means, a crank case situated beneath said cylinder means and receiving fuel to be compressed by said piston means while the latter moves away from said recess before the gas stream flows into said cylinder means through said scavenging port means, supply port means communicating with said crank case for supplying fuel thereto, angularly adjustable supply valve means and angularly adjustable exhaust valve means respectively located in said supply port means and said exhaust port means for controlling the flow of gases therethrough, and linkage means operatively connected with said supply valve means and said exhaust valve means for automatically opening and closing said exhaust valve means during opening and closing of said supply valve means, respectively, said linkage means transmitting movement from said supply valve means to said exhaust valve means and providing for every angular position of said supply valve means a predetermined angular position for said exhaust valve means, said linkage means including a pair of levers respectively connected with said angularly adjustable supply valve means and said angularly adjustable exhaust valve means for respectively swinging both of the latter valve means, a swingable cam situated between said levers, a link extending between the lever connected to said supply valve means and said cam for swinging said cam in response to angular movement of said supply valve means, a cam follower fixedly carried by said lever which is connected to said angularly adjustable exhaust valve means, said follower engaging a camming surface of said cam, the latter camming surface having a configuration which provides a predetermined angular position of said exhaust valve means for every angular position of said supply valve means, and a spring operatively connected with said lever connected to said exhaust valve means for maintaining said follower in engagement with said camming surface.
2. The combination of claim 1 and wherein said cylinder means has a pair of opposed oppositely inclined surface portions defining part of said combustion recess for producing a squish effect.
3. The combination of claim 1 and wherein a spark plug of said electrical ignition system is situated at said deepest portion of said recess and communicates through said deepest portion of said recess with the interior of said cylinder means.
4. The combination of claim 3 and wherein said spark plug is eccentrically positioned beyond said axis.
5. The combination of claim 1 and wherein said exhaust port means defines upstream of said exhaust valve means a prechamber for receiving gas in said exhaust port means prior to flow of gas past said exhaust valve means.
6. The combination of claim 5 and wherein said prechamber has a volume which is between 1/10 and 3/10 the volume of the stroke of said piston means.
7. In a two-cycle internal combustion engine, fuelsupply control means for controlling the fuel supply and exhaust-gas control means for controlling the flow of exhaust gas, and means interconnecting both of said control means for incrasing and decreasing the amount of exhaust gas flow in response to an increase or decrease, respectively, in the fuel supply, whereby combustion is maintained at a relatively low compression ratio, each of said control means including a duct and a tiltable valve therein, and said means interconnecting both of said control means including a mechanical transmission means extending between and operatively connected to said tiltable valves for providing for each angular position of said tiltable valve for said fuelsupply control means a predetermined angular position for said tiltable valve of said exhaust-gas control means, said mechanical transmission means including a pair of levers respectively connected with said tiltable valves for respectively swinging the latter when said levers turn, a cam swingably mounted between said levers, a link interconnecting the lever which is connected to said tiltable valve of said fuel-supply control means with said cam, a cam follower fixedly carried by the other of said levers and engaging a camming surface of said cam which has a configuration providing for the tiltable valve of said exhaustgas control means said predetermined angular position for each angular position of said tiltable valve of said fuel-supply control means, and a spring operatively connected with the latter lever for maintaining said cam follower in engagement with said camming surface.