Patent Publication Number: US-6701883-B2

Title: Cylinder head for use on a spark-ignition internal combustion engine and such spark-ignition internal combustion engine

Description:
This application claims priority to Japanese Patent Application No. 2002-105269, filed Apr. 8, 2002. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a cylinder head for use on a spark-ignition internal combustion engine with a four-stroke and two-valve system and such spark-ignition internal combustion engine and, more particularly, to such spark-ignition internal combustion engine cylinder head and the spark-ignition internal combustion engine which provide for enhancing the output and the rotational speed of the engine and such spark-ignition internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     The four-stroke and two-valve type spark-ignition internal combustion engine typically comprises a cylinder head joined to a cylinder having a piston mounted therein, the cylinder head including a planar squish surface opposing the outer periphery of the top surface of the piston such that a squish area is defined between the squish surface and the piston top surface. The cylinder head is formed in its wall with a combustion chamber recess adjoining the squish surface such that the combustion chamber recess is cooperative with the piston top surface to define a combustion chamber. In addition, the cylinder head has a set of intake and exhaust ports formed open through the wall of the combustion chamber recess at the apex thereof, the intake and exhaust ports being provided with intake and exhaust valves, respectively. An ignition plug aperture is also formed open through the wall of the recess with an ignition plug protruding into the combustion chamber recess. 
     With the spark-ignition internal combustion engine constructed as described above, as the piston is moved up to a point near its top dead center, the air-fuel mixture is compressed in the squish area defined between the squish surface and the piston top surface whereby there is generated a squish stream swirling in the combustion chamber. The swirling air-fuel mixture moves upwardly in the combustion chamber to be ignited by the ignition plug, and the ignited air-fuel mixture then burns with its flame front propagating in the combustion chamber, so that the piston is moved down toward its bottom dead center by the expansion of the burning air-fuel mixture. 
     However, in the conventional spark-ignition internal combustion engine described above, both of the squish surface of the cylinder head and the piston top surface which together define the squish area are formed planar and the squish area is located below the projecting lower end of the ignition plug. Due to this arrangement, the squish flow as produced by the squish area may not move directly toward the ignition plug located above squish area, but swirls around in the combustion chamber before it is directed to the vicinity of the ignition plug. Consequently, the squish flow was not capable of guiding an adequate amount of the air-fuel mixture to the vicinity of the ignition plug, and therefore had the disadvantage of being unable to enhance the propagation rate of the flame front of the ignited air-fuel mixture (which will be referred to as flame propagation rate hereinafter. As a result, such prior art construction undesirably led to a decrease in the output and the rotational speed of the internal combustion engine. 
     BRIEF SUMMARY OF THE INVENTION 
     In order to overcome the foregoing problems, this invention contemplates to provide a cylinder head for a four-stroke and two-valve spark-ignition internal combustion engine and such spark-ignition internal combustion engine which provides for enhancing the output and the rotational speed of the engine by increasing the flame propagation rate of the ignited and burning air-fuel mixture. 
     In order to accomplish this object, the cylinder head for a spark-ignition internal combustion engine as set forth in claim 1 is designed to be used on a four-stroke and two-valve spark-ignition internal combustion engine, and is adapted to be joined at mating surfaces to a cylinder having a piston mounted therein. The cylinder head includes a generally planar squish surface opposing the outer peripheral portion of the top surface of the piston; a combustion chamber recess formed in the wall of the cylinder head adjacent the squish surface and defining together with the piston top surface a combustion chamber; a set of intake port and exhaust port formed open through the wall of the combustion chamber recess either at the apex thereof or on the lateral side of the combustion chamber recess opposite from the squish surface; an ignition plug aperture formed open through the wall of the combustion chamber recess at a location closer to the squish surface relative to the intake port and exhaust port and adapted to receive an ignition plug extending therethrough into the combustion chamber; and a squish guide groove formed by notching into the wall of the combustion chamber recess so as to extend from the side of the ignition plug aperture to a location of the squish surface adjacent the inner wall of the cylinder. 
     The spark-ignition internal combustion engine as set forth in claim 2 is a four-stroke and two-valve type spark-ignition internal combustion engine and comprises a cylinder having a piston mounted therein; a cylinder head adapted to be joined at mating surfaces to the cylinder; a generally planar squish surface formed on the wall of the cylinder head adjacent the mating surfaces and opposing the outer peripheral portion of the top surface of the piston; a combustion chamber recess formed in the wall of the cylinder head adjacent the squish surface and defining together with the piston top surface a combustion chamber; a set of intake valve and exhaust valve disposed on the wall of the combustion chamber recess either at the apex thereof or on the lateral side of the combustion chamber recess opposite from the squish surface; an ignition plug through the wall of the combustion chamber recess into the combustion chamber at a location closer to the squish surface relative to the intake valve and exhaust valve; and a squish guide groove formed by notching into the wall of the combustion chamber recess so as to extend from the side of the ignition plug to a location of the squish surface adjacent the inner wall of the cylinder. 
     With the spark-ignition internal combustion engine cylinder head or the spark-ignition internal combustion engine according to the present invention, the cylinder head is joined to a cylinder block at mating surfaces. In use, upon the intake port being opened by the intake valve, the piston is lowered toward its bottom dead center as the air-fuel mixture flows into the combustion chamber. When the piston reaches its bottom dead center, the intake port is closed by the intake valve and the piston is moved up toward its top dead center while the air-fuel mixture in the combustion chamber is compressed by the rising piston, whereby squish flow is produced between the outer periphery of the piston top surface and the squish surface with the compression of the air-fuel mixture. 
     The thus created squish flow ensures adequate mixing of the air and fuel of the air-fuel mixture. The air-fuel mixture is ignited by the ignition plug and begins the combustion during the process while the piston rises toward its top dead center. With the piston rising, the air-fuel mixture over the squish surface is caused to pass around the ignition plug aperture (ignition plug) and flow into the central region of the combustion chamber under the guidance of the squish guide groove and ignition is effected on such flowing air-fuel mixture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a vertical, fragmentary, cross-sectional view illustrating one embodiment of the spark-ignition engine including a cylinder head according to the present invention; and 
     FIG. 2 is a transverse cross-sectional view taken along lines II—II of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT 
     A preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a vertical cross-sectional view taken along lines I—I of FIG. 2, illustrating a spark-ignition engine  1  including a cylinder head  2  according to one embodiment of the present invention, and FIG. 2 is a transverse cross-sectional view taken along lines II—II of FIG.  1 . The spark-ignition engine  1  is a four-stroke and two-valve internal combustion engine of the spark-ignition type, and mainly comprises a cylinder head  2 , a cylinder  3 , a piston  4  slidably mounted in the cylinder  3 , an intake valve  5  for drawing an air-fuel mixture into a combustion chamber, an exhaust valve  6  for discharging combustion gases out of the combustion chamber, and an ignition plug  7  having an ignition electrode  7   a  for igniting the air-fuel mixture, as shown in FIGS. 1 and 2. Here, the air-fuel mixture means a mixed gas of air and fuel. 
     As shown in FIG. 1, the cylinder head  2  has a combustion chamber recess  10  formed by being recessed upwardly from the surface mating with the cylinder  3 . The combustion chamber recess  10 , together with the top surface  4   a  of the piston and the inner wall surface  3   a  of the cylinder  3 , defines a combustion chamber. Formed open through the wall of the combustion chamber recess  10  at the apex thereof is an intake port  11  which is adapted to be selectively opened and closed by the intake valve  5 . An ignition plug aperture  12  is formed open through the wall of the recess  10  on the left-hand side of the intake port  11  as viewed in FIG.  1 . The ignition plug  7  is fitted in the ignition plug aperture  12  such that the ignition electrode  7   a  protrudes inwardly into the combustion chamber recess  10 . 
     Further, the cylinder head  2  has a generally planar squish surface  13  formed adjacent the surface mating with the cylinder  3  so as to adjoin the combustion chamber recess  10  and oppose the outer peripheral portion of the piston top surface  4   a . It is to be noted here that the ignition plug aperture  12  (for the ignition plug  7 ) is formed through the wall of the recess  10  on the side thereof toward the squish surface  13  such that the ignition electrode  7   a  of the ignition plug  7  is located close to the squish surface  13 . In addition, a squish area  14  is defined between the opposing surface portions of the squish surface  13  and the piston top surface  4   a . The presence of the squish area  14  makes it possible to produce vortices called squish flow in the combustion chamber as the piston  4  rises toward its top dead center (shown in dotted lines in FIG.  1 ). 
     Further, the wall of the combustion chamber recess  10  is formed with a squish guide groove  15  downwardly inclined from the side of the ignition plug aperture  12  toward the squish surface  13 . More specifically, the squish guide groove  15  is formed by notching into the wall of the combustion chamber recess  10  so as to extend from the side of the ignition plug aperture  12  (the ignition electrode  7   a  of the ignition plug  7 ) to a location of the squish surface  13  adjacent the inner wall  3   a  of the cylinder. Through this squish guide groove  15  communication is established between the squish area  14  and the space in the vicinity of the ignition electrode  7   a.    
     As shown in FIG. 2, the wall of the combustion chamber recess  10  is also provided at the apex thereof with the exhaust valve  6  adapted to selectively open and close an exhaust port  16 , in addition to the intake valve  5 . The squish guide groove  15  extends generally straight from the squish surface  13  formed on the side of the ignition plug aperture  12  (the ignition plug  7 ) of the combustion chamber recess  10  toward the ignition plug aperture  12  (the ignition electrode  7   a  of the ignition plug  7 ) and is notched into the wall of the recess  10  so as to have a cross-sectional shape of V recessed forwardly of the drawing plane of FIG.  2 . It is thus to be appreciated that the squish guide groove  15  may be formed by making a very small notch in that peripheral portion of the wall of the combustion chamber recess  10  which is so located that the distance between the ignition plug aperture  12  (the ignition electrode  7   a  of the ignition plug  7 ) and the squish surface  13  is the shortest, so that an increase in the manufacturing cost of the engine  1  involved with the processing of the squish guide groove  15  may be held down. 
     The operation of the spark-ignition internal combustion engine  1  will now be described. When the piston  4  reaches the top dead center (the position shown in dotted lines in FIG.  1 ), the suction stroke starts with the intake port  11  being opened by the intake valve  5  whereupon the piston  4  begins to be lowered to allow the air-fuel mixture to flow into the combustion chamber recess  10 . Upon the piston  4  reaching the bottom dead center, the intake port  11  is closed by the intake valve  5  whereupon the cycle moves to the compression stroke during which the piston  4  is raised from the bottom dead center toward the top dead center whereby the air-fuel mixture within the combustion chamber is compressed between the piston top surface  4   a  and the combustion chamber recess  10  while the air-fuel mixture within the squish area  14  is also compressed and swirled in the form of a squish stream within the combustion chamber as the piston  4  rises to thereby promote the mixing of the fuel and the air. 
     As the piston  4  moves up toward the top dead center, some of the air-fuel mixture within the squish area  14  is inducted (guided) along the squish guide groove  15  toward the ignition electrode  7   a  of the ignition plug  7  and is then ignited by the ignition electrode  7   a  when the piston  4  approaches the top dead center. It is to be appreciated that when the mixture is ignited by the ignition electrode  7   a , there is a flow of the air-fuel mixture around the ignition electrode  7   a  (the ignition plug aperture  12 ) inducted by the squish guide groove  15  so as to move toward the center of the combustion chamber, so that the flame propagation rate (speed) within the combustion chamber may be enhanced as the ignition is effected on such moving air-fuel mixture. 
     Assuming that the conditions except the timing of ignition by the ignition plug  7  are the same, it will be appreciated that an increase in the flame propagation rate allows for correspondingly delaying the timing of ignition by the ignition plug  7 , so that the ignition may be effected in a position where the piston  4  is moved closer to its top dead center while the occurrence of knocking due to the delay in the ignition timing may also be prevented. If the timing of ignition by the ignition plug  7  is delayed while the knocking is prevented in this manner, it is possible to enhanoe the compression ratio of the air-fuel mixture within the combustion chamber to thereby increase the output and the rotational speed of the engine  1 . 
     After the ignition is effected by the ignition electrode  7   a , the piston  4  reaches the top dead center whereupon the cycle moves from the compression stroke to the expansion stroke. During the expansion stroke, the burning air-fuel mixture expands as the piston  4  lowers toward its bottom dead center. Then, upon the piston  4  reaching its bottom dead center, the cycle moves to the exhaust stroke, during which the piston  4  again starts rising toward its top dead center while the exhaust port  16  is opened by the exhaust valve  6  to discharge the combusted air-fuel mixture out of the combustion chamber. 
     While the present invention has been described with respect to the particular embodiment illustrated herein, it is to be understood by those skilled in the art that various changes, alterations and modifications may be made to the embodiment described above without departing from the spirit and scope of the invention. 
     For instance, while in the illustrated embodiment the intake port  11  and the exhaust port  16  are shown as being formed open through the wall of the combustion chamber recess  10  at the apex thereof and the intake valve  5  and exhaust valve S for selectively opening and closing the intake port  11  and the exhaust port  16 , respectively, are disposed at the apex of the combustion chamber recess  10 , the locations of where these intake and exhaust ports are to be formed and the intake and exhaust valves are to be disposed are not limited to the apex of the combustion chamber recess  10 , but may be on the lateral side of the combustion chamber recess opposite from the side where the ignition plug aperture  12  (squish surface  13 ) is located. Further, while in the illustrated embodiment the present invention has been described with respect to the case where a bathtub type combustion chamber is employed as the combustion chamber, this invention is not limited to the use of such type or combustion chamber, but it is to be understood that the Invention is applicable to any spark-ignition engine in which other types of combustion chambers such as the multiple-sphere type, wedge type, etc. are used. 
     In the cylinder head for use on a spark-ignition internal combustion engine and in the spark-ignition internal combustion engine constructed according to this invention, the squish guide groove is formed in the wall of the combustion chamber recess so as to extend from the side of the ignition plug to a location adjacent the inner wall of the cylinder. This squish guide groove communicates the squish area defined between the squish surface and the piston top surface with the combustion chamber to thereby direct the squish flow produced in the squish area toward the ignition plug aperture (ignition plug). It is thus to be appreciated that there is produced a flow of air-fuel mixture around the ignition plug as directed by the squish guide groove so as to move toward the center of the combustion chamber at the time when the ignition plug is activated as the piston rises to its top dead center, so that the flame propagation rate within the combustion chamber may be advantageously enhanced since the ignition is effected on such flow of air-fuel mixture.