Abstract:
A number of combustion chamber configurations for direct injected engines wherein the fuel injectors inject at least two fuel patches in circumferentially spaced locations. This fuel is injected into a cavity arrangement formed in the head of the piston, which directs the fuel upwardly toward a pair of circumferentially spaced spark plugs so as to insure complete combustion within the combustion chamber. Embodiments having single and paired cavities in the piston head are disclosed.

Description:
BACKGROUND OF INVENTION 
     This invention relates to an in-cylinder injection gasoline engine and more particularly to a combustion chamber arrangement for such engines. 
     It has been proposed to employ direct cylinder injection to improve the performance and particularly the fuel economy and exhaust emission control of internal combustion engines. By utilizing direct cylinder injection, it is possible to obtain stratification under some running conditions to allow the engine to run on a leaner than stoichiometric mixture. In this way it is not necessary to provide a homogeneous stoichiometric mixture in the entire combustion chamber to initiate combustion and to develop the required power. 
     To accomplish this in an open chamber, the fuel injector must inject fuel in a way to form a fuel patch that will be present at the spark gap at the time it is fired. Although this can be easily accomplished if a pre-chamber is employed, it is difficult to achieve this result in an “open chamber”. Open chambers are preferred for a variety of reasons including the pumping losses generated by the pre-chamber. 
     FIGS. 1 and 2 illustrate a typical type of approach that attempts to produce this result in an open chamber. FIG. 1 is a top plan view of a piston used in the arrangement and the associated fuel injector as mounted in the cylinder head. FIG. 2 is a cross sectional view taken along the line  2 — 2  of FIG.  1 . As seen in these figures, a piston, indicated generally by the reference numeral  11  reciprocates in a cylinder bore, indicated by the reference numeral  12 . The piston  11 , cylinder bore  12  and an associated cylinder head surface  13  define the combustion chamber. 
     The head of the piston  11  is formed with a dome comprised of a pair of angularly related, inclined surfaces  14  and  15  which join a generally flat upper surface  16 . A bowl or recess  17  is formed in the piston head and extends through the inclined surface  15  and the. upper flat surface  16 . This bowl  17  has a generally curved configuration which extends upwardly and terminates at its inner peripheral edge adjacent a spark plug  18 . The spark plug  18  positioned generally on the axis of the cylinder bore  12 . 
     A fuel injector  19  is mounted in the cylinder head surface  13  or cylinder block at one side of the cylinder bore  12 . This fuel injector  19  sprays fuel toward and into the piston bowl  17 . In addition, a swirl is generated in the combustion chamber as indicated by the arrows A. This swirl is generated by the induction system so as to sweep the injected fuel in a path indicated by the arrow B in the bowl  17  and toward the gap of the spark plug  18 . In addition, the inclined surface  14  forms a squish area that drives the air in the direction indicated by the arrows D in FIG.  2 . so as to prevent the fuel from escaping from the bowl  17  beyond the outer periphery of the area bounded by the spark plug  18 . 
     An engine of this type may also be provided with a variable valve timing mechanism for varying the valve timing and/or degree of opening of the valves. Thus, the configuration of the combustion chamber and particularly the head surface of the piston  11  must be such as to afford clearance between the valve heads and the piston surfaces under all timing and lift conditions. This results in the formation of a lower than desired compression ratio. 
     Also, under off idle loads there may be fuel left deposited on the piston bowl  17  after combustion has completed. This increases the problem of hydrocarbon emissions. Furthermore, even though the spark plug  18  is positioned at the center of the combustion chamber, there is a likelihood that fuel may pass beyond the bowl  17  toward the opposite side of the combustion chamber regardless of the swish action indicated by the arrows D. Thus there can be further unburned fuel in the combustion chamber. 
     Furthermore these conditions increase the likelihood of knocking, even though a low compression ratio has been dictated by the bowl configuration. 
     It is, therefore, a principle object to this invention to provide an improved combustion chamber for a direct injected internal combustion engine wherein the compression ratio may be significantly raised without causing problems in clearance for the valves and while insuring rapid flame propagation and complete combustion under all running conditions. 
     It is a further object to this invention to provide an improved high efficiency combustion chamber, fuel injection and ignition arrangement for direct injected engines. 
     SUMMARY OF INVENTION 
     This invention is adapted to be embodied in an internal combustion engine that is comprised of an engine body that defines at least one cylinder bore that is closed at one end by a cylinder head surface and at the other end by the head of a piston that reciprocates in the cylinder bore. A fuel injector is mounted in the engine body contiguous to the axis of the cylinder bore. The fuel injector is configured to spray fuel downwardly toward the piston head and in at least two circumferentially spaced, fuel injection directions. The piston head is formed with a cavity arrangement having at least two circumferentially spaced, concave curved wall portions that curve upwardly toward the cylinder head at their radially outer extent. The circumferential spacing at the fuel injection directions correspond to the circumferential spacing of the piston concave curved wall portions so that fuel sprayed from the fuel injector is directed toward the piston concave curved wall portions. A pair of circumferentially spaced ignition devices are provided in the cylinder head surface in proximity to the upper ends of the piston concave curved wall portions for igniting the fuel sprayed from the fuel injector. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a top plan view of a piston constructed in accordance with a prior art type of construction and which shows the fuel injection nozzle associated therewith and the directions of fuel and air flow in the combustion chamber. 
     FIG. 2 is a cross sectional view taken along the line  2 — 2  of FIG.  1  and again shows the prior art construction. 
     FIG. 3 is a bottom plan view of a cylinder head of a first embodiment of the invention. 
     FIG. 4 is a cross sectional view taken along the line  4 — 4  of FIG.  3 . 
     FIG. 5 is a perspective view showing the piston head of this embodiment and the relationship of the spark plugs to this piston head configuration. 
     FIG. 6 is a view, in part similar to FIG. 5, and shows another embodiment of piston head configuration. 
     FIG. 7 is a perspective view, in part similar to FIGS. 5 and 6, and shows a still further embodiment of the piston head construction. 
    
    
     DETAILED DESCRIPTION 
     Referring first to the first embodiment and initially to FIGS. 3 and 4, they illustrate in detail a cylinder head assembly identified generally by the reference numeral  31 . This cylinder head assembly  31  includes a main cylinder head member  32  that has a lower surface  33  that is adapted to be affixed to an associated cylinder block (not shown) in sealing relationship around a cylinder bore formed therein. 
     Although the construction is described in conjunction with a single cylinder, it should be readily apparent that the invention can be utilized with engines having a wide variety of cylinder numbers and cylinder configuration. Also, since the invention deals primarily with the cylinder head configuration and the associated combustion chamber resulting there from, the illustration of the cylinder block is not believed to be necessary to permit those skilled in the art to practice the invention. However, the cylinder bore has a diameter which supports an outer peripheral surface of a piston, indicated by the reference numeral  34 . The shape of the head portion will be described later in more reference to FIG.  5 . 
     FIG. 3, a bottom plan view of the cylinder head member  32  looking generally upwardly in the direction of FIG. 4, shows the placement of the various valves and other components associated with the engine. These include a pair of intake valves  35  which are disposed generally on one side of a plane containing the cylinder bore axis and which valve the flow through the intake passages  36  formed in the cylinder head member  32 . These intake passages  36  are depicted as being of the Siamese type and are associated with a suitable induction system. Again, since the invention deals primarily with the configuration and layout of the combustion chamber, the detailed description of the induction system and the mechanism for operating the intake valves  35  is not believed to be necessary to permit those skilled in the art to practice the invention. However, for the sake of completeness, this valve operating mechanism includes valve springs  36  that urge the intake valves  35  to their closed position. Rocker arm assemblies  37 , which may include variable lift mechanisms of any known type, are interposed between the lobes of an intake camshaft  38  and the stems of the intake valves  35  for opening these valves against the action of the springs  36 . The intake camshaft  39  is driven at one half crankshaft speed by a suitable drive mechanism and this may include a WT mechanism for varying the phase angle of the opening of the intake valves  35  during engine operation. 
     A pair of exhaust valves  41  are positioned in the cylinder head member  32  on the opposite side of the aforenoted plane from the intake valves  35 . These exhaust valves  41  have stem portions and are urged to their closed position by coil compression springs  42 . A suitable operating mechanism for the exhaust valves can be provided for controlling the flow through Siamese exhaust passages  43  formed in the cylinder head member  32  on the side opposite the intake passages  37 . 
     This valve operating mechanism may, for example, be comprised of variable lift rocker arm assemblies  44  that are operated by the cam lobes of an exhaust camshaft  45 . The exhaust camshaft  45 , like the intake camshaft  39 , is driven at one half crankshaft speed by any suitable timing drive. This may also include a VVT mechanism so as to vary the phase angle of opening and closing of the exhaust valves  41 . 
     While continuing to refer primarily to FIGS. 3 and 4, the cylinder head surface which cooperates for the most part with the head of the piston  34  is comprised of a recessed surface area  46  which forms with the head of the piston  34  and the combustion chambers of the engine. Parts of the cylinder head surface  33  overly portions of the cylinder bore as seen in FIG. 3 where the outer periphery of the piston  34  is illustrated. 
     Positioned generally on the axis of the cylinder bore is provided a fuel injector  47  which is disposed to have a bifurcated fuel injection nozzle having a pair of openings that spray in generally diametrically opposite directions. These directions are generally parallel to or within the aforenoted plane that divides the intake and exhaust sides of the cylinder head member  32 . 
     Positioned at the outer peripheral edges of the same plane are a pair of spark plugs  48  that have their spark gaps disposed in a relationship which is shown best in FIG.  5  and which are fired by a suitable ignition system. 
     Referring now to FIG. 5, it will be seen that the piston head is configured with a generally flat peripheral squish area  49  that surround a dome. This dome is formed in part by pair of upwardly inclined parts  51  and  52  that extend above the squish area  49 . A bowl or cavity, indicated generally by the reference numeral  53  is formed in this dome. The dome area in this embodiment may have a generally flat upper surface  54 , which is intersected by the inclined surfaces  51  and  52 . 
     A pair of concave curved portions  55  and  56  are formed at opposite sides of the bowl  53 . These concave curved portions extend in substantial part through the inclined portions  51  and  52  and extend upwardly from a generally planar annular area  57  at the bottom of the bowl  53 . These concave curved portions  55  and  56  are joined with each other at their peripheral edges by curved surfaces  58 . A raised, generally conical shape projection  59  is encircled by the flat piston head area  57  and extends upwardly toward the cylinder head recess  56 . The upper end of the projection  59  is juxtaposed to the fuel injector  47 . 
     Thus, depending upon the injection timing, which will be described in more detail shortly, the fuel from the two nozzle parts of the fuel injector  46  will be sprayed downwardly toward the inclined parts of the dome portion  59  facing the curved outer wall portions  55  and  56 . The fuel will then be directed downwardly by these inclined parts toward the flat area  57  and then turned upwardly by the curved wall portions  55  and  56  toward the gaps of the spark plug  49 . Thus, the fuel will be spread across the diameter of the cylinder head and piston head, but confined within the area encompassed by the spark plugs  48 . 
     Thus, when the spark plugs  48  are fired, they will be surrounded by a stoichiometric mixture of fuel that is stratified under low speed and mid-range performance running. This mixture will be easily ignited under all of the conditions and total flame propagation will be insured across the complete combustion chamber including the area outside of the piston head recess  53 . Thus all fuel in the combustion chamber will be ignited and can be completed burned. Also, it should be noted that the recess  53  is disposed so that it will extend below the peripheral edges of the intake valves  35  and exhaust valves  41  so that further clearance recesses are not required to be formed in the piston head. In addition, this will insure good valve clearance even though the lift and timing are significantly changed depending upon engine running conditions. Thus, knocking can not only be reduced but substantially eliminated. Furthermore this efficient combustion will decrease NOx emissions and the amount of unburned hydrocarbons present in the exhaust gases. 
     Dealing now specifically with the injection timing, under partial loads, fuel is injected late in the timing schedule. For example, fuel is injected on the latter half of a compression stroke for example beginning on the range of 70° to 50° before top dead center (BTDC). However, as the engine speed and load increases, the fuel injection timing is advanced and in fact can be advanced to the intake stroke, for example, from at top dead center (TDC) to 50° after TDC. Because the fuel is injected toward the head of the piston  34 , however, the piston head will be cooled and knocking will be precluded under high speed, high load conditions. 
     FIG. 6 shows another embodiment of the invention in which the cylinder head and valve arrangement is as shown in FIGS. 3 and 4. However, the head of the piston  34  has a slightly different configuration. This is comprised of a raised dome again formed by inclined side portions  51  and  52  that are joined at their central part by a generally flat area  54 . In this embodiment, however, there is provided a pair of side by side cavities  71  and  72 , each of which have concave, curved outer portions  73  and  74  respectively that curve upwardly from their respective lower planar surfaces  75  and  76  toward the spark plugs  48 . 
     The circumferential spacing of these curved concave portions  73  and  74  is the same as the circumferential spacing of the spark plugs  48  and the spray paths from the associated fuel injector. In this embodiment, however, these curved side portions  73  pass through the side walls  77  and  78  which join the sides of the inclined portions  51  and  52  and hence, permit more open flow to the outer periphery of the cylinder bore in this area. 
     Opposing these concave, curved side portions  73  and  74  are inclined walls  79  and  81 , which receive the fuel that is sprayed by the two ports of the fuel injector (fuel injection nozzle  47  which is not shown in this figure). The flat portion  54  of the piston head tends to separate these charges from each other, but once firing begins the flame will propagate across this area so as to achieve the same results as with the previously described embodiment. The advantages of this embodiment are the same as those previously described and the actual cavity area in the piston head can be less while still providing the clearance for the intake and exhaust valves and accommodating the variable lift and variable valve timing of them. 
     FIG. 7 shows another embodiment of the invention, which, like the embodiment of FIG. 6, employs two cavities formed in the piston head, these cavities being indicated by the reference numerals  101  and  102 , respectively. The shape of the piston head outside of these cavities is the same as that previously described and, therefore, these same components are identified by the same reference numerals. In this embodiment, the concave, curved outer surfaces  103  and  104  of the recesses  101  and  102  do no extend through the side walls  77  and  78 , but nevertheless still terminate at the gaps of the spark plugs  48 . Opposing inclined walls  105  and  106  of the cavities  101  and  102  extend upwardly from flat areas  107  and  108 . These walls  105  and  106  are somewhat triangular shape so as to more closely focus the flow of fuel toward the narrow opposing concave, curved surfaces  103  and  104  so as to further confine the fuel flow toward the spark plugs  48  particularly under conditions when small amounts of fuel are injected. This combustion chamber configuration can also have an injection timing arrangement as set forth in the previous embodiment. 
     Thus, from the foregoing description it should be readily apparent that the described combustion chamber configurations function so as to permit separate fuel patches to be formed on opposite sides of the piston so as to minimize the amount of space taken by these cavities and to more uniformly distribute the fuel over the combustion chamber. Nevertheless, sufficient recesses are provided for the valves so as to permit the use of variable valve lift and variable valve timing mechanism without adversely affecting the compression ratio. 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.