Patent Document

BACKGROUND OF INVENTION 
     This invention relates to a four cycle internal combustion engine of the direct injected spark ignited type and more particularly to an improved combustion chamber construction for such an engine. 
     In the interest of further improving the efficiency and performance of internal combustion engines, direct cylinder injection is increasingly being resorted to. By utilizing direct cylinder injection it is possible to obtain stratification of the mixture at loads less than full load. That can improve not only performance but also fuel efficiency and exhaust emission control. However, in attempting to inject the fuel directly into a open chamber and achieve stratification, it is necessary to insure some way in which a stoichiometric fuel/air mixture is presented at the spark gap at the time the spark plug is fired. Various arrangements have been proposed to achieve this result. 
     In accordance with one type of methodology, the combustion chamber is formed in part by a recess or bowl formed in the head of piston. The fuel is injected toward this bowl and the induction air is directed so as to cause the fuel to be swept along the surface of the bowl and redirected thereby toward the gap of the spark plug so as to insure that a stoichiometric mixture is present at the time when the spark plug is fired. 
     Also, in order to insure complete combustion, particularly under high speed high load conditions when a homogenous mixture is provided in the combustion chamber, it is desirable to position the spark plug close to or at the center of the combustion chamber. This means that the bowl or recess must be configured so as to direct the fuel toward the spark plug even under low speed low load conditions. 
     One structure that has been proposed for this purpose is shown in published Japanese Application Hei 9-144544, published Jun. 3, 1997. This typifies the type of prior art which has been proposed to achieve this result. 
     The difficulty with this prior art type of construction, however, is that in order to achieve the desired stratification under low speed low load conditions, the bowl in the piston head has had a fairly substantial volume. This means that the compression ratio of the engine is severely limited. This in turn, dictates less then optimal performance. 
     It is, therefore, a principal object to this invention to provide a combustion chamber configuration wherein direct cylinder fuel injection is possible and wherein the piston head recess is made as small as possible while still achieving the desired results of stratification. 
     It is a further object to this invention to provide an improved combustion chamber configuration for a direct injection engine having a high compression ratio, a central spark plug position and a bowl in the head of the piston that permits the fuel to be directed toward the gap of the spark plug without significantly adding to the clearance volume of the engine and thus maintaining a high compression ratio. 
     SUMMARY OF INVENTION 
     This invention is adapted to be embodied in an internal combustion engine and more particularly to a combustion chamber therefore. The combustion chamber is defined by a cylinder bore, a cylinder head that closes one end of the cylinder bore and a piston that reciprocates in the cylinder bore. A head of the piston has a generally circular recess formed therein when viewed toward the direction of the axis of the cylinder bore. A fuel injector injects fuel directly into the combustion chamber. An arrangement is provided for causing the fuel flowing from the fuel injector to pass in a circular swirling direction around the axis of the cylinder bore and within the piston head recess. A spark plug is disposed on a side of the piston head recess that is diametrically opposed to the point where the fuel injector injects fuel into the combustion chamber. The piston head recess has a greater depth from a lower surface thereof to the facing surface of the cylinder head on one side of a diametric line extending between the fuel injector and the spark plug, then on the other side of the diametric line. The arrangement for effecting the flow of fuel in the circular swirling direction causes the fuel to flow first into the deeper side of the piston head recess. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a top plan view of a piston and surrounding cylinder bore constructed in accordance with an embodiment of the invention and with certain components of the cylinder head and related induction and exhaust systems show in phantom. 
     FIG. 2 is a cross sectional view taken though the upper portion of one cylinder of the engine. 
     FIG. 3 is an enlarged view looking in the same general direction as FIG. 2 but taken along a different plane. 
     FIG. 4 is a cross sectional view taken along the line  4 — 4  in FIG.  3 . 
     FIG. 5 is a top plan view, in part similar to FIG. 1, and shows another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now in detail to the drawings and first to the embodiment of FIGS. 1-4, a multi-cylinder internal combustion engine is identified generally by the reference numeral  11 . Since the invention deals primarily with the combustion chamber for the engine, only the upper portion of the engine is shown in the drawings and only one cylinder is depicted. It will be readily apparent to those skilled in the art how the invention can be utilized with engines having varying cylinder numbers and configurations. 
     The engine  11  is comprised of a cylinder block, indicated generally by the reference numeral  12  and which defines one or more cylinder bores  13  in which pistons, indicated generally by the reference numeral  14  reciprocate. The cylinder bore axis is indicated as A. 
     A connecting rod  15  is connected at its small end to the piston  14  via a piston pin  16 . The lower end of the connecting rod  15  is journalled on a throw of a crankshaft, which is not shown for the afore noted reasons. 
     The upper end of the cylinder bore  13  is closed by a cylinder head assembly that is comprised of a main cylinder head member  17 . This cylinder head member  17  has an recess  18  formed in its lower surface which closes the cylinder bore  13 . This recess  18  cooperates with the head of the piston  14 , which will be described in more detail later, to define a combustion chamber which is shown at its top dead center position in FIGS. 2-4, when the clearance volume is at the minimum. It will be seen that the cylinder head recess  18  is very shallow and the piston head is domed so as to maintain as high a compression ratio as possible. 
     In the illustrated embodiment, the engine  11  is of the four valve per cylinder type although the invention is not so limited. To this end, there are provided a pair of intake valve seats  18  that are valved by poppet type intake valves  19  in a well known manner. These intake seats  18  lie substantially on one side of a plane containing the cylinder bore axis A and extending perpendicularly to FIG. 2. A pair of intake passages  21 -P and  21 -S serve the valve seats  18 . 
     A suitable induction system (now shown) is affixed to one side of the cylinder head member  17  for collecting intake air. This induction system may be of any suitable type and can include an air inlet silencer, plenum chamber and filter mechanism. In addition, a throttle valve arrangement is incorporated for controlling the total air flow to the engine  11 . In addition to this, the induction system includes a main throttle valve arrangement for controlling the total air flow into the combustion chambers. The air flow direction is indicated by the arrows A. 
     In addition to this a main flow control throttle valve arrangement, each cylinder of the engine is provided with an individual flow controlling valve  22  is positioned in the secondary intake passage  21 -S of each cylinder. This flow controlling valve controls the volume of air flow through the secondary intake passage  21 -S and is controlled by a suitable mechanism, such as a servo motor  23  or linkage system that is interconnected with the main throttle valve so as to operate in a staged sequence. The control strategy for opening the flow control valve  22  is such that this valve is maintained in a closed a position under idle, low speed and low mid-range running performance and opens as the low and/or speed of the engine increases. The purpose for this will described later. 
     Referring primarily to FIG. 2, each of the intake valves  19  is urged toward its closed position by a coil compression spring  24  that operates against a surface of the cylinder head member  17  and a keeper retainer assembly which is associated with a thimble tappet  25  and which is fixed to upper ends of the stems of each of the intake valves  19 . 
     On the side of the cylinder head member  17  opposite the intake passages  21 , there are provided exhaust passages, indicated generally by the reference numeral  26 . These exhaust passages  26  are of the Siamese type and each branch thereof extends from a respective exhaust valve seat  27  that is disposed on the opposite side of the plane containing the cylinder bore axis A from the intake valve seats  18 . 
     Poppet type exhaust valves  28  control the flow of exhaust gases through these exhaust valve seats  27 . These valves  28  are urged toward their closed position by coil compression springs  29  which act against machined surfaces of the cylinder head member  17  and keeper retainer assemblies that are contained within thimble tappets  31  and which are affixed to the upper ends of the stems of the exhaust valves  28  for urging them to their closed position. 
     The exhaust gases exit the engine through a flow path defined by the valve seats  27  and the intake passages  26  and indicated by the arrows E. These exhaust gases are collected through an exhaust manifold  32  and are discharged to the atmosphere through an associated exhaust system of a suitable type, of which is not illustrated. 
     The intake valves  19  and exhaust valves  28  are operated by a valve actuating mechanism, indicated generally by the reference numeral  33  which is formed in a valve chamber  34  formed in part by the cylinder head member  17  and by a cover  35  affixed to the cylinder head member  17 . This valve actuating mechanism  33  includes an intake camshaft which has lobes that cooperate with the intake thimble tappets  25  for opening them and their associated intake valves  19  against the action of the coil springs  24 . In addition, an exhaust camshaft  36  is journalled in the cylinder head assembly in a suitable manner and has cam lobes that cooperate with the exhaust thimble tappets  31  for opening the exhaust valves  28 . The intake and exhaust cam shafts  36  and  37  are operated so as to rotate at one half crankshaft speed in a manner well known in the art. 
     If desired, this valve actuating mechanism may include a variable valve timing mechanism (VVT) of any known type so as to change the valve timing and/or duration. 
     It has been noted that the combustion chamber of the engine is formed at least in part by the cylinder head recess  18  and the cylinder bore  13 . In addition, the chamber is also formed by the head of the piston and this head is formed with a raised domed part having a generally planar upper surface  38  that lies generally along the plane that separates the intake and exhaust ports  18  and  27  and contains the cylinder bore axis A. An inclined downwardly extending portion  39  of this head is formed on the exhaust side and an inclined downwardly extending portion  41  is formed on the intake side. These inclined portions  39  and  41  and the planar upper portion  38  of the head of the piston are surrounded by a squish area. 
     In addition, a bowl or recess, indicated generally by the reference numeral  42  having a shape which will be defined next, is formed in the piston surfaces  38  and  41 . As best seen in FIG. 1, this recess has a generally circular shape when viewed in the direction of the axis A and defined by a peripheral wall  43  which is eccentrically disposed so as to lie primarily on the intake side of the combustion chamber with its innermost peripheral edge being disposed slightly upwardly of the cylinder bore axis A. 
     This recess  42  has a lower wall surface  44  formed at the lower end of the wall  43 , as best seen in FIGS. 3 and 4 that slopes generally downwardly on one side of a second plane, indicated by the broken line CL 2  that contains the cylinder bore axis. As may be best seen in FIG. 3, the peripheral wall  43  has a relatively shallow curvature on the portion closer to the cylinder bore  13  than at the cylinder bore axis A. In fact, there is a relatively steeply inclined curved wall portion  45  formed on the exhaust side of the cylinder bore  13  and piston head and also toward its central diameter. The lower wall surface  44  is perpendicular to a bowl axis BA (FIG.  4 ). The curved wall surface  45  is generated about the bowl axis BA. 
     In fact, this curved wall portion  45  is disposed adjacent the spark gap  46  of a spark plug  47  that is mounted generally on the cylinder bore axis A. This spark gap  46 , as best seen in FIGS. 1 and 3 and lies over the inner peripheral edge of the bowl  42 . 
     A fuel injector, shown only in phantom and identified generally by the reference numeral  48  is mounted in the cylinder head member  17  in a position that underlies the intake passages  21 -P and  21 -S and which has a discharge nozzle opening  49  that lies substantially on the plane CL 2  diametrically opposed to the piston bowl  42  from the spark gap  46 . Thus, the line CL 2  is a diametric line passing between the center of the injector nozzle opening  49  and the spark gap  46  with the injection nozzle opening  49  being positioned on the outer periphery of the bowl or recess  42 . As best seen in FIG. 4, the piston head portion  41  is formed with a recessed area  51  leading into the bowl  42  so as to clear the injection nozzle so that the fuel can be sprayed in a generally downward direction toward the bottom surface  44  of the bowl or recess  42 . 
     In accordance with the invention, an arrangement is provided for causing the spray of fuel from the injector nozzle  49  to be directed toward the deeper side  44 A of the bowl or recess  42  first and then to swirl around the bowl side surfaces  45  toward the shallower side  44 B so as to direct the burning gases outwardly into the remainder of the combustion chamber but to maintain good stratification at the spark gap  46  at the time it is fired. 
     In this embodiment that result is obtained in two ways. First, the axis of the injector nozzle, indicated by the reference numeral  52 , is disposed at an angle e to the centerline CL 2  as seen in FIG. 1 so as to spray toward this side of the bowl surface  41 , which surface is indicated as  44 A. Thus, as seen in this figure, the initial spray from injector, indicated by the arrows  53  with the initial spray portion indicated at  53 A extends in a direction transversely across the recess  42 . This causes the spray to first flow into the deeper bowl portion  44 A. 
     In addition, the flow control valve  22  is closed under conditions when stratification is desired, normally low and low-mid range performance so that the air flow path A will flow in a circular or swirling direction around the cylinder bore axis A. Thus, the fuel is turned in a direction indicated by the spray pattern  53 B to flow around the edge portion  45  of the bowl and be swept upwardly in the direction  53 C toward the spark gap  46  where it will present a stoichiometric mixture at the time the plug  47  is fired. Thus, the system can operate on a lean burn or stratified charge principal quite effectively. 
     As noted, the embodiment of FIGS. 1 through 4 achieve the desired flow path in the bowl by canting both the fuel injector  48  and by providing the desired swirling motion through the use of the control valve  22 . However, FIG. 5 shows another embodiment wherein this skewed disposition of the fuel injector  48  is not required. In this embodiment, the fuel injector  48  has its spray axis  51  disposed on the line CL 2 . However, the swirling motion of the intake air charge is still sufficient to provide the desired path of fuel flow as seen in this figure. 
     Thus, from the foregoing description, it should be readily apparent that the described embodiment provides the ability to obtain a stratified charge through the use of a bowl in the head of the piston, but the bowl configuration is such that it not only promotes the stoichiometric mixture toward the spark gap, but also promotes the flow out of the bowl into the main combustion chamber because of the slanted lower wall and also does not therefore reduce the compression ratio as with the previous type arrangement. Of course, the foregoing description is that of preferred embodiments of the invention and various changes and modifications may be made without departing from the spirit and scope of the invention, as defined by the appended claims.

Technology Category: f