Abstract:
The present invention provides a fuel injector mounted on a side of a combustion chamber and delivers an ovalized fuel spray toward an oblong piston bowl of the chamber. The ovality of the spray is selected in relation to the oblong piston bowl and the motion of the combustion chamber air charge during the piston compression stroke to maintain the fuel charge within the piston bowl volume (including the space above the bowl) during compression and combustion of the fuel charge in the chamber. The shape of the oval spray may be adjusted as desired. In a specific embodiment, the ovality of the fuel spray indicated by the ratio of the major dimension to the minor dimension is in the range of about 2/1 to 4/1 for delivery into an oblong piston bowl with an ovality of about 1.2/1 to 1.5/1.

Description:
TECHNICAL FIELD 
     This invention relates to combustion chambers for use in spark ignition engines having direct-injection fuel systems. 
     BACKGROUND OF THE INVENTION 
     Spark-ignition, direct-injection combustion systems for internal combustion engines have been proposed to improve fuel economy when compared with more typical port fuel-injected combustion systems. The spark-ignition, direct-injection engine is provided with a high pressure fuel injection system that sprays fuel directly into the engine combustion chamber which is formed, at least partially, in the piston. The fuel is directed or transported to a specific region within the combustion chamber. This creates a stratified charge in the combustion chamber resulting in fuel economy benefits, since the throttling requirements are less restrictive and the fuel combustion characteristics are improved. Conventional fuel injectors providing a conical fuel spray may be used in such engines. However, injectors providing a fan shaped fuel spray have also been proposed. 
     U.S. patent application Ser. No. 09/930,707 filed Aug. 13, 2001 and assigned to the assignee of the present invention, discloses an improved combustion chamber for a spark ignition direct injection engine. The piston includes an oblong or oval shaped bowl, forming 50% to 70% of the total combustion chamber volume at piston top center, into which a fuel spray is injected during the piston compression stroke. Various physical and dimensional features of the piston and combustion chamber and the use of a conventional direct injection fuel injector are disclosed. 
     SUMMARY OF THE INVENTION 
     The present invention provides improved combustion chambers including fuel injectors having an oval fuel spray for use with direct injection engine combustion chambers of the type disclosed in the previously mentioned patent application U.S. Ser. No. 09/930,707 as well as in other applications. 
     In a preferred embodiment, a fuel injector is mounted on a side of the combustion chamber and delivers an ovalized fuel spray toward an oblong piston bowl of the associated combustion chamber. The ovality of the spray is selected in relation to the oblong piston bowl and the motion of the combustion chamber air charge during the piston compression stroke to maintain the fuel charge within the piston bowl volume (including the space above the bowl) during compression and combustion of the fuel charge in the chamber. 
     The shape of the oval spray may be adjusted as desired in relation to the shape of the piston bowl, as well as for use in other applications of an oval spray injector. As used in a specific embodiment the ovality of the fuel spray indicated by the ratio of the major axis to the minor axis is in the range of about 2/1 to 4/1 for delivery into an oblong piston bowl with an ovality of about 1.2/1 to 1.5/1. 
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is an isometric view of a portion of an engine containing a piston and a portion of a cylinder head with the intake and exhaust valves, the ignition source and the fuel injector incorporating the present invention; 
     FIG. 2 is an isometric view of the fuel injector delivering an ovalized fuel spray into the piston bowl in accordance with the invention; and 
     FIG. 3 is a partial cross-sectional elevational view of a piston and cylinder head with an ovalized spray injector incorporating the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A portion of an engine  10  includes a piston  12  and a cylinder head  14  closing the end of the cylinder. The cylinder head  14  has a primary inlet port  16 , a secondary inlet port  18 , a pair of outlet ports  20  and  22 , an ignition source or spark plug  24 , a fuel injector  26 , two inlet valves  28  and  30  and two exhaust valves  32  and  34 . The spark plug  24  is a conventional device that supplies an ignition source or spark to the combustion chamber  36  formed between the piston  12 , a cylinder wall or bore  37 , and the cylinder head  14 . The fuel injector  26  is a modified direct injection device that is designed according to the invention to inject an ovalized spray of fuel into the combustion chamber  36  during engine operation. The amount and timing of the fuel injection is controlled by a conventional electronic control unit (ECU) that includes a programmable digital computer. These control devices are well known to those skilled in the art of engine design. 
     The inlet valve  28  controls the flow of air into the combustion chamber  36  through the primary inlet port  16 , and the inlet valve  30  controls the flow of air into the combustion chamber  36  through the secondary inlet port  18 . The exhaust valves  32  and  34  control the flow of exhaust products from the combustion chamber  36  through the exhaust ports  20  and  22 , respectively. The opening and closing of the valves  28 ,  30 ,  32  and  34  is controlled in a conventional manner such as through the employment of a cam mechanism, not shown. 
     As best seen in FIGS. 2 and 3, the piston  12  has a bowl  38  formed therein. The combustion chamber  36  includes a bowl volume  40  and a volume space  42 . The bowl volume  40  consists of the volume of the bowl  38  and the space between the bowl  38  and the cylinder head  14 . The volume space  42  includes the volume between the cylinder head  14  and the piston  12  external to the periphery of the bowl  38 . The bowl  38  has a floor  44 , an inner edge of a rim surface  46 , inner edges of exhaust squish surfaces  48  and  50 , inner edges of inlet squish surfaces  52  and  54 , a transporting surface  55 , and three side surfaces  56 ,  57  and  58  that connect with the transporting surface  55  to surround the bowl and extend upward to the edges of, respectively, the rim surface  46 , the inlet squish surfaces  52  and  54 , and the inner edges of the exhaust squish surfaces  48  and  50 . 
     The transporting surface  55  includes a bowl radius  60 , having a dimension in the range of from 3 to 12 mm, and, optionally, a flat surface  62 . Together, the bowl radius and the flat surface, if provided, extend upward from the floor  44  to a substantially linear edge  63  forming part of the inner edges of exhaust squish surfaces  48  and  50 . The floor  44  and the flat surface  62 , if provided, are tangential to the bowl radius  60 . The flat surface  62  (or the upper edge of the bowl radius  60  if there is no flat surface) intersects the squish surfaces  48  and  50  at a negative draft angle  64  (FIG. 3) in the range of 0 to −20 degrees, relative to the axis  66  of the cylinder bore  37 . This forms the linear edge  63 , which is laterally displaced a distance  68  in the range of 6 to 10 mm from the centerline  70  of the spark plug  24 . The side surface  56  is formed as a radius surface that connects tangentially with the floor  44  and the side surfaces  57  and  58  also connect with the floor by tangential radii, not clearly shown. The rim surface  46  is spaced a distance  74  (3 to 8 mm) from the floor  44 . 
     The exhaust squish surface  48  is positioned opposite the exhaust valve  32  and the exhaust squish surface  50  is positioned opposite the exhaust valve  34 . The intake squish surfaces  52  and  54  are positioned opposite the intake valves  28  and  30 , respectively. When the piston  12  is at top center in the cylinder  37 , as shown in FIG. 3, the squish clearance or distance  76  between the cylinder head  14  and the respective squish surfaces  48 ,  50 ,  52  and  54  is in the range of 2 to 6 mm. The volume ratio (VR) of the bowl volume (VB) to total combustion chamber volume (VT) at top center is also an important design parameter insuring that proper combustion will occur. The total volume of the combustion chamber  36  at top center is the space volume  42  plus the bowl volume  40 . Thus, the volume ratio is the bowl volume  40  divided by space volume  42  plus bowl volume  40  (VR=VB/VT). This volume ratio is maintained in the range 0.50 to 0.70. This means that the bowl volume is 50% to 70% of the total combustion chamber volume at piston top center. A peripheral surface  78  extends around the outer edge of the piston  12  from the inlet squish surface  52  past the exhaust squish surfaces  48  and  50  to the inlet squish surface  54 . The peripheral surface  78  is an extension of the rim surface  46  and has a radial dimension in the range of 0 to 6 mm. The outer edges of the peripheral surface  78  and the rim surface  46  essentially define the outer edge of the piston  12  and, due to the close proximity of the cylinder wall  37 , the outer periphery of the combustion chamber  36 . 
     When the engine is operating in a stratified charge combustion mode, the piston  12  is reciprocated in the cylinder bore  37  such that the combustion chamber  36  expands and contracts during the operating cycle of the engine. During the intake stroke, one or both of the intake valves  28 ,  30  are opened to admit an air mass into the cylinder bore. During the compression stroke, the valves are closed and the air mass is compressed as the piston approaches top center. Also during the compression stroke, fuel is injected directly into the combustion chamber  36  by the fuel injector  26  to mix with the air mass. The amount and timing of fuel injected is controlled by the ECU. The fuel-air mixture is ignited by the spark plug  24  at or slightly before top center. The ignited mixture is rapidly expanded as the piston moves down during the power stroke. At approximately bottom center, the exhaust valves  32  and  34  are opened and the piston  12  again moves upward toward the cylinder head  14  during the exhaust stroke so that the exhaust gases are forced from the cylinder bore. The intake stroke is then repeated. 
     When fuel is injected into the air mass, it is carried across the floor  44  of the bowl  38  toward the transporting surface  55  as it mixes with the air mass. The edge  63  of the transporting surface  55  directs the fuel-air mixture to a spark gap  80  of the spark plug  24  where ignition begins. The ignited fuel-air mixture rapidly expands to encompass the entire combustion chamber  36  and efficiently deliver power from the engine. The dimensional parameters of the piston  12  and the combination of the piston  12  and cylinder head  14  are important factors in the distribution of the fuel-air mixture and the resulting combustion sequence. 
     The engine is operated as described above to create stratified charges in the combustion chamber to permit the ignition of lean fuel-air mixtures under low and intermediate loads. At loads nearer the maximum power of the engine, a homogeneous fuel distribution mode may be used. In this mode, the fuel is injected during the intake stroke to mix with the inlet air prior to interaction with the piston bowl features described, which are provided primarily for stratified charge operation. 
     The forgoing describes, except for the modified fuel injector, the exemplary embodiment of the invention essentially as described in application U.S. Ser No. 09/930,707 noted above. The exemplary embodiment of the present invention differs in that the injector  26  is modified to deliver a unique oval or elliptical spray pattern  82  of fuel into the oblong or oval piston bowl  38 , substantially as shown in FIG. 2 of the drawings. For reference, numerals  84 ,  86  indicate, respectively the major and minor dimensions of the oblong piston bowl  38 . Numerals  88 ,  90  indicate, respectively, the major and minor dimensions of the oval fuel spray pattern  82 . The ovality of the piston bowl is relatively small, preferably having a major/minor dimensional ratio in the range of 1.2/1 to 1.5/1. In contrast, the preferred ovality of the fuel spray pattern is greater, defined by a major/minor dimensional ratio in the range of 2/1 to 4/1. 
     Selection of spray pattern ovality is made in consideration of the flow of the cylinder air charge in the cylinder during the piston compression stroke when the fuel is injected during operation of the engine under stratified charge conditions. Comparative evaluation of operation of the engine with fuel injectors with a conical spray pattern and the elliptical oval spray pattern of the invention showed better engine performance and reduced smoke for the oval spray pattern than for conical spray patterns over a range of cone angles. It is considered that the ovalized spray is better in maintaining the fuel spray and resulting combustible mixture within the area of the piston bowl so that it does not penetrate beyond the bowl and cause increased hydrocarbon emissions and does not excessively impact on the bottom of the bowl and increase smoke. 
     It should be clear that the neither the fuel spray nor the piston bowl needs to be a perfect oval or ellipse in order to operate successfully. It is only necessary that they be oblong or approximately oval shaped with different major and minor dimensions. 
     Thus, while the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.