Abstract:
A method for injecting fuel directly into a given combustion chamber of an internal combustion engine with externally supplied ignition in which the supply of air to the combustion chambers may be either throttled or unthrottled. To assure unobjectionable operation both at partial load and under full load, the fuel is introduced during partial-load operation with a large air excess, forming a layered charge, in the vicinity of the ignition location at a time immediately prior to the instant of ignition, while at full-load operation, in order to attain maximum power and soot-free combustion by means of a homogeneous fuel-air mixture, the supply of fuel takes place during the intake stroke of the engine piston defining the combustion chamber. In order to perform this method, a distributor-type fuel injection pump is provided, in which either one distributor opening or another distributor opening of two distributor openings comes into effective operation. The distributor openings are located at a fixed rotational angle spacing from one another, by means of which the advancement of the fuel injection at full load is fixed relative to the instant of injection at partial load.

Description:
BACKGROUND OF THE INVENTION 
     The invention is based on a method for the injection of fuel and fuel injection apparatus for performing the method. In a method of this kind known from German Offenlegungsschrift No. 26 36 659, the combustion chamber of each cylinder of the internal combustion engine to be supplied with fuel is subdivided into a secondary and a primary combustion chamber, the two being connected via a straight channel. In this engine with externally supplied ignition, the fuel is introduced via an injection valve in such a manner that a portion of the injected fuel travels via the straight channel and reaches the secondary combustion chamber, while another portion of the fuel is injected directly into the primary combustion chamber. The apportioning of the fuel quantity to be injected to the primary combustion chamber and the secondary combustion chamber is varied in accordance with load such that a readily ignitable and stoichiometric fuel-air mixture is always formed in the secondary combustion chamber. The purpose of the layered combustion process thus realized is to introduce a relatively lean fuel-air mixture into the primary combustion chamber, so that toxic substances forming during combustion in the primary combustion chamber, predominantly because of the flame-extinguishing effect at the combustion chamber walls and in niches in the combustion chamber can be held to a minimum. If a fuel-rich mixture is located in combustion chamber niches in the vicinity of the combustion chamber walls, then the proportion of the fuel components no longer being combusted completely is greater than if a fuel-poor mixture or if only air is located in such regions. The inflammation of the relatively lean fuel-air mixture in the combustion chamber is enabled by means of a torch ignition means. The igniting torch is the product of the mixture, which has been inflamed in the secondary combustion chamber by means of the spark plug, as it flows out of the connecting channel toward the primary combustion chamber. For a homogeneous mixture formation, in particular in the secondary chamber, the injection of the fuel takes place relatively early, and the end of injection should occur approximately 90° to 120° before top dead center. Especially in the upper load range, however, the injection onset may be retarded until during the beginning of the intake phase, so that a large amount of time is available for mixture formation. 
     This known apparatus is very expensive, however, because of the necessity for a secondary chamber and the specialized fuel injection nozzle. Furthermore the known apparatus relates to a combustion method which operates with highly fissured combustion chambers, which in comparison with an internal combustion engine having a simple combustion chamber is associated in principle with less advantageous fuel consumption. Internal combustion engines having specialized, externally supplied ignition and direct injection into a simple combustion chamber have substantial advantages in terms of fuel consumption. However, they do have the disadvantage that despite external ignition the maximum output theoretically possible with this engine construction cannot be realized, because the injection causes the premature occurrence of elevated soot emission levels, similarly to what may happen in self-ignited engines under full-load operation. This soot emission can be ascribed to the incomplete combustion of the fuel, which could not be prepared well enough in the time between the instant of injection and the instant of inflammation. 
     From SAE Paper No. 78 0699, an internal combustion engine is known in which the fuel is injected directly into a simple combustion chamber, and the mixture thereby formed is ignited with the aid of two spark plugs and the compression ratio increased to 11:1. Fuel injection in an engine of this kind is controlled such that at low load the fuel is introduced into the vicinity of the spark plug immediately prior to the instant of ignition, so that an ignitable mixture is produced there, despite the low fuel injection quantity relative to the total air charge of the combustion chamber. With increasing load, the instant of injection is shifted toward &#34;early&#34;, so that at maximum load the injection is terminated at 70° to 90° prior to top dead center. In this engine, specialized additional provisions are made for fuel preparation; in detail, these are inducing turbulence in the air entering the combustion chamber, a high exhaust gas recirculation rate and a high compression ratio. These provisions again occasion considerable expense, which it would be desirable to reduce. Furthermore only a small crankshaft angle range, and a decreasing period of time as the engine speed increases, are available for mixing the fuel thoroughly with combustion air. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The method according to the invention has the advantage that especially at high loads the fuel is already introduced into the combustion chamber during the intake stroke of the engine and can therefore mix thoroughly with the air present in the combustion chamber by the time the instant of ignition arrives. Premature soot emission in full-load operation is thereby prevented, so that the available output of the engine in terms of its construction can be optimally exploited, while also attaining optimal fuel consumption. In partial-load operation, by contrast, the fuel is injected quite late, immediately prior to the instant of ignition, so that an ignitable mixture can form in layers in the vicinity of the spark plug, and this mixture then, after being inflamed, inflames the rest of the charge in the combustion chamber. The direct injection thereby avoids the above-discussed disadvantages of the known apparatuses, in which the mixture located in combustion chamber niches cannot become inflamed because of the flame-extinguishing effect of the combustion chamber walls and thus contributes to considerable emissions of toxic substances, combined with high fuel consumption. With direct injection it is possible to attain a sufficiently sharply defined layering of a mixture capable of burning through, which also participates completely in the combustion. 
     The characteristics disclosed result in an advantageous apparatus for performing the method. In a structurally simple embodiment, the dwell time of the fuel making up the full-load injection quantity is prolonged by 180° of crankshaft angle as compared with that of the partial-load injection quantity. With the apparatus disclosed, there is the advantage that the dwell time of the fuel during full-load operation can be prolonged still further, and the fuel injection can be advanced as far as the beginning of the intake stroke of the engine piston. 
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a section taken through a fuel injection pump, shown in simplified form, by means of which the fuel can be injected in accordance with the method of the invention; 
     FIG. 2 is a partial section through the distributor of an injection pump according to FIG. 1; 
     FIG. 3 is a diagram showing the injection times attained with the fuel injection pump during one engine cycle; 
     FIG. 4 shows a second exemplary embodiment of a fuel injection apparatus in the form of a radial-piston pump; 
     FIG. 5 shows the pump piston position of the pairs of pump pistons according to FIG. 4 with respect to the circle of rotation; 
     FIG. 6 is a section through the distributor of the injection pump of FIG. 4, showing the rotational position of the distributor openings; and 
     FIG. 7 is a diagram showing the injection ranges which can be adhered to with the aid of the embodiment of FIG. 4 during one engine cycle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a first exemplary embodiment according to FIG. 1, a cylinder 2 closed at one end is provided in a housing 1, and a distributor 4 of a radial-piston distributor pump is rotatably supported in the cylinder 2. The cylinder 2 is contiguous on one end with a cylindrical chamber 5, on the radial outer wall of which an adjustable cam path 6 is disposed. The distributor 4 is continuous inside the chamber 5 with a cylindrical carrier body 7, which has a radial through bore 9, in which two oppositely disposed pump pistons 11 are displaceable. On the ends of the pump pistons 11 protruding out of the carrier body 7, these ends have rollers 12, which roll off on the cam path upon the rotational movement of the carrier body 7. The centrifugal force to which the pump pistons 11 are also exposed acts radially outward upon the rollers 12, as does the force of a compression spring 14 fastened between the inner ends 13 of the pump pistons 11. To drive the mechanism, the carrier body 7 or the distributor 4 has a drive shaft 16, which is driven in synchronism with the rpm of the internal combustion engine supplied with fuel by this fuel injection pump. The drive shaft 16 is supported in a sleeve 17 inserted into the housing 1, the sleeve having a connection to a lubricating-oil line 18 in its middle 17&#39;. A seal 19 is provided near the end of the shaft 16 to prevent leakages of oil. 
     The pump work chamber 20 enclosed on both sides in the through bore 9 communicates with a blind bore 21 extending coaxially with the distributor 4, and at the end of the blind bore 21 a radial bore 21&#39; leads into a first annular groove 23 disposed in the jacket face of the cylinder 2. A fuel conduit 25 leads away from this annular groove 23, leading on one end to a control valve 26 with a line 53 connected thereto which connects to a switchover valve 27. 
     The control valve 26 comprises a control slide 28, which is tightly displaceable in a bore 29 between two threaded bolts 30 and 31 which close off the ends of the bore 29 from the outside, and with which the displacement path of the control slide 28 can be adjusted. The fuel conduit 25 discharges into an annular groove 32 in the jacket face of the bore 29. The control slide 28 likewise has an annular groove 33 in its middle, which communicates continuously with a fuel supply line 34 that discharges into the bore 29. By means of one limiting edge of the annular groove 33, the annular groove 32 is opened up in one extreme position of the control slide 28, and communication is established between the fuel conduit 25 and the fuel supply line 34. In the other position, the annular groove 32 is completely closed by the control slide 28. The position of the control slide 28 is effected hydraulically; by a pressure medium brought via a first control line 36 into the annular chamber 33&#39; between the first threaded bolt and one end of the control slide 28, and via a second control line 37 by a pressure medium brought into the chamber 40 between the second threaded bolt 31 and the other end of the control slide 28. The supply of pressure to the first and the second control lines 36 and 37 is effected by means of a piezohydraulic driver 38 in the manner described in German Patent Application No. P 31 35 494.7. This driver 38 comprises a housing 41, in the interior of which a cylindrical hollow chamber 42 is enclosed. A part 43 of the cylindrical wall of this hollow chamber 42 acts as a guide for a piston 45, which separates a pressure chamber 44 from the cylindrical hollow chamber 42. The pressure chamber 44 communicates continuously with the second control line 37 and is filled completely with hydraulic pressure medium. A driver 46 of the piezohydraulic driver is disposed in the cylindrical hollow chamber 42; it is embodied in columnar form and is connected via a threaded tang 47 with the housing 41. On the other end, the driver 46 is firmly connected with the piston 45. The cylindrical hollow chamber 42 is likewise completely filled with hydraulic pressure fluid and is in continuous communication with the first control line 36. The electrical connection of the driver 46 is effected via a cable 49, which is carried out of the hollow chamber 42 toward the outside passing through a seal 50. The cable 49 leads to a control unit 51, from whence a voltage can be imposed on the driver 46, causing the volumes in the cylindrical hollow space 42 and in the pressure chamber 44 to vary complementarily to one another and simultaneously causing the control slide 28 to be displaced back or forth. Since changes in length occur extremely quickly when a piezoceramic element is subjected to electrical voltage, it is possible to realize very short switching times at the control valve 26. The line 18 connects to a bore in housing 41 in order to supply oil to the movable piston 45 via annular groove 43&#39;. 
     From the fuel conduit 25, a main fuel feed conduit 53 branches off and leads to the switchover valve 27. This valve has a control slide 54, which is tightly displaceably disposed in a bore 55 and is connected via a connecting member 56 with an adjusting magnet 57. The control slide has an annular groove 58 in its middle region which communicates continuously with the main fuel feed conduit 53. By means of the axial limiting edges of the annular groove 58, a first fuel feed line 60 and a second fuel feed line 61 are controlled, in such a manner that in one position of the control slide 54 the first fuel feed line 60 is connected with the main fuel feed conduit 53 and in the other position of the control slide 54, as shown in the drawing, the second fuel feed line 61 is connected with the main feed conduit 53. The first fuel feed line 60 discharges into a second annular groove 62 in the jacket face of the cylinder 2 and the second fuel feed line 61 discharges into a third annular groove 63 in the jacket face of the cylinder 2. 
     A first fuel connecting conduit 64, which extends inside the distributor 4 and leads to a first distributor opening 65, communicates continuously with the second annular groove 62. A second fuel connecting conduit 66 also communicates continously with the third annular groove 63, being likewise disposed in the distributor 4 and leading to a second distributor opening 67 on the jacket face of the distributor 4. In the radial plane in which the first distributor opening 65 and the second distributor opening 67 emerge from the distributor 4, fuel injection lines 68 lead to the cylinder 2; the fuel injection lines 68 are distributed about the circumference of the cylinder in accordance with the number and sequence of the engine cylinders to be supplied with fuel. In FIG. 2, a section in this radial plane is shown. From this section it can be seen that the second distributor opening 67 advances by 90° ahead of the first distributor opening 65. This applies to the form of embodiment shown here for a fuel injection pump intended to supply a four-cylinder internal combustion engine. In each case the relationship between the first distributor opening 65 and the second distributor opening 67 is such that two injection lines each can be supplied with fuel simultaneously from both distributor openings; the switching position of the switchover valve 27 determines from which of the distributor openings fuel will proceed to injection. 
     The supply of fuel to the fuel injection pump is effected from a fuel supply container 69, from which a feed pump 70 pumps fuel into the fuel supply line 34, the pressure being adjusted with the aid of a pressure regulating valve 71. 
     The fuel injection pump described above functions as follows: 
     Upon the rotation of the drive shaft 16, the pump pistons 11 are moved back and forth in accordance with the embodiment of the cam ring 6. During the intake stroke of the pump pistons, that is, their outward movement, fuel is delivered from the pump 70 via the slide control valve 26 and the fuel conduit 25 to the pump work chamber 20. To this end, the control slide 28 is brought via the control unit 51 into its right-hand terminal position, establishing communication with the fuel supply line 34. In order to execute a supply stroke, the rotating pump pistons 11 are moved inward by the stationary cam ring and at a fixed injection onset, the control unit 51 closes the fuel conduit 25. The duration of the closure of the control valve 26 determines the fuel injection quantity or the injection duration. The fuel pumped by the pump pistons 11 is delivered via the fuel conduit 25, the main fuel conduit 53 and the annular groove 58 to either the first fuel feed conduit 60 or the second fuel feed conduit 61. From there, the fuel proceeds to the first distributor opening 65 or the second distributor opening 67. 
     When the control valve 26 switches back over again, the fuel conduit 25 is connected again with the fuel supply line 34, permitting the remaining fuel pumped by the pump pistons 11 to flow out in a pressure-relieved manner and terminating the fuel injection. 
     With the above-described fuel injection pump, the instant at which the fuel proceeds to injection in the various cylinders can be varied. This relationship is shown in the diagram of FIG. 3. In the sector marked I of the crackshaft rotational position or the engine piston position, the fuel is injected via the first distributor opening 65 in the lower load range, that is, in partial-load engine operation. This range is shortly before top dead center, that is, immediately prior to the ignition of the fuel-air mixture in the cylinder of the engine. The precisely diametrically opposite range II of the rotational angle position of the crankshaft or of the engine piston is still within the range of the intake stroke of the piston between top dead center (OT) and bottom dead center (UT). During full-load operation, the fuel is injected in this range II, specifically through the second distributor opening 67. Thus upon the injection of the maximum fuel quantity corresponding to full-load engine operation, the fuel introduced into the combustion chamber of the engine has a substantially longer time to mix with the air located therein and to vaporize, especially during the compression stroke of the piston. At the instant of ignition, a well prepared fuel-air mixture is thus available in the engine combustion chamber, so that it is assured that even the full-load fuel quantity burns unobjectionably during the following working stroke, without forming soot. The substantially lesser fuel quantity introduced into the vicinity of the spark plug in range I is sufficient for maintaining an ignitable mixture in the vicinity of the spark plug until ignition occurs. Divided over the total cylinder charge, however, the resultant mixture would be too lean for inflammation in this combustion method, in which the air for combustion is supplied in an unthrottled manner to the engine cylinders. 
     With the fuel injection pump according to the invention and with the method according to the invention, an internal combustion engine having externally supplied ignition can be driven with carburetor fuel, having the advantages that result in a self-ignition engine as a result of the low-loss, unthrottled delivery of the combustion air into the combustion chambers. 
     The exemplary embodiment according to FIGS. 1-3 relates to the supply of fuel to a four-cylinder internal combustion engine. Naturally other numbers of cylinders can also be supplied with such a fuel injection pump, modified accordingly. The second distributor bore 67 in that case advances ahead of the first distributor opening 65 by the same angle by which the injection lines 68 in sequence are separated one from another. 
     In FIG. 4, a second form of embodiment of the fuel injection pump according to the invention is shown. This pump substantially has the same components as the fuel injection pump of FIG. 1. Here again, a cylinder 2 is provided in a housing 1&#39;, and a distributor 4&#39; is rotatably supported in the cylinder 2. The carrier body 7&#39; adjoining the distributor 4&#39; and protruding into the chamber 5 now has a first pair of pump pistons 11 and a second pair of pump pistons 11&#39;, which are disposed in two different radial planes. As in the exemplary embodiment of FIG. 1, a cam ring 6&#39; serves to drive the pump pistons; upon a rotation of the distributor or of the carrier body 7&#39; the cam ring 6&#39; generates a reciprocating movement on the part of the pairs of pump pistons. The first pair of pump pistons 11 encloses a first work chamber 20 and the second pair of pump pistons 11&#39; encloses a work chamber 20&#39;. The first work chamber 20, as in the exemplary embodiment of FIG. 1, communicates continuously via a first fuel feed conduit 73 in the distributor 4&#39; with a first annular groove 74 in the jacket face of the cylinder 2. The second work chamber 20&#39; is likewise connected via a second main fuel feed conduit 75 with a second annular groove 76 in the jacket face of the cylinder 2. A first fuel line 77 leads from the first annular groove 74 into a cylinder 78 of a switchover valve 27&#39;, and a second fuel line 79 likewise leads from the second annular groove 76 into the cylinder 78. Disposed in this cylinder 78 is a control slide 81 which is displaceable by means of an electromagnet 82. The control slide 81 has an annular groove 83 and has spacer tangs 84 on both its ends, by means of which it is supported in its terminal positions on the end faces of the cylinder 78. 
     Regardless of the position of the control slide 81, the annular groove 83 communicates continuously with a fuel conduit 25&#39; discharging into the cylinder 78; this fuel conduit 25&#39; corresponds to the fuel conduit 25 in the embodiment according to FIG. 1 and its communication with a fuel supply line, not shown here, is controlled in the same manner as in the embodiment of FIG. 1. Branching off from the fuel conduit 25&#39; is a main fuel feed conduit 53&#39;, which discharges into a third annular groove 86 in the jacket face of the cylinder 2. A fuel connecting conduit 87 which enters the distributor 4&#39; in this vicinity communicates continuously with this annular groove 86 and leads both to a first distributor opening 88 in the jacket face of the distributor 4&#39; and to a second distributor opening 89, which is located in the same radial plane as the first distributor opening 88. In the operative range of the distributor openings, fuel injection lines 68 lead away from the cylinder 2, on the circumference of which they are distributed; these lines 68 are provided in accordance with the sequence and number of cylinders of an associated engine which are to be supplied with fuel. 
     The ends of the cylinder 78 are continuously relieved via a fuel relief line 90 with which, depending upon the position of the control slide 81, either the first fuel line 77 or the second fuel line 79 is connected; simultaneously, the other one of these fuel lines then communicates with the annular groove and thus with the main fuel feed conduit 53&#39;. This means that only one of the piston pairs 11 or 11&#39; at a time can effectively pump fuel into the fuel injection lines 68, and which of the two pump piston pairs is involved in pumping fuel at a given time is determined by the position of the control slide 81. 
     The pump piston pairs 11, 11&#39; shown in one plane in FIG. 4 are in actuality offset from one another by 45°, as may be seen from the basic diagram of FIG. 5. In FIG. 5, the pump pistons are shown solely in terms of their spacing. The distributor openings 88, 89 are also in the same angular position relative to one another as are the piston pairs; this is shown in FIG. 6. In the illustrated embodiment, the fuel injection pump supplies four cylinders of one engine, the cylinders coming into operation at regular intervals. In the position shown in FIG. 6, only the first distributor opening 88 is capable of feeding fuel into one of the injection lines 68. The other distributor opening 89 is closed by the wall of the cylinder 2, as long as it is located in an intermediate position between two injection lines 68 departing from the cylinder. 
     The exemplary embodiment of FIG. 4 functions as follows: 
     Driven by the drive shaft 16, the carrier body 7&#39; is brought into rotation, together with the distributor 4&#39;. In the illustrated position of the control slide 81, the work chamber 20&#39; of the second pair of pump pistons 11&#39; has just been connected with the fuel conduit 25&#39;. Via this conduit, the pump work chamber can be supplied with fuel as in the exemplary embodiment of FIG. 1. By means of the switching of the switching valve 26 according to FIG. 1, the time and duration of the injection are also determined during the pumping stroke of the pump piston pair 11&#39;. In the illustrated position of the control slide 81, the pump piston pair 11&#39; then pumps the fuel via the main fuel feed line 53&#39; to the fuel connecting conduit 87 and from there via the distributor opening 88 which is free at that time into one of the fuel injection lines 68. If the first pair of pump pistons 11 effects pumping, in the same position of the control slide 81, then the fuel pumped by this pump piston pair is expelled via the relief line 90. This pair of pump pistons thus does not take part in the injection. It is thus determined with the aid of the control slide which pair of pump pistons will be in use at a given time. 
     The pairs of pump pistons are associated with one another such that their pumping strokes are spaced apart by 135° in the direction of rotation. The outlet positions of the distributor openings 88, 89 are also spaced apart by this same angle. The electromagnet 82 is switched in the same manner, in accordance with load, as in the exemplary embodiment of FIG. 1. At low load, in the partial-load range, the fuel is introduced into the combustion chamber by the first pair of pump pistons 11 in range I of FIG. 7, shortly before top dead center and immediately prior to the instant of ignition. As in the first exemplary embodiment, the fuel is introduced into the vicinity of the spark plug, so that at the instant of ignition an ignitable mixture is present in layered form in the combustion chamber at the spark plug; this mixture can then, after being inflamed, be combusted completely with an air excess. In the upper load range, by contrast, that is, at full-load operation, the fuel is injected substantially earlier into the combustion chamber, specifically in range II at the beginning of the intake stroke of the engine piston. To this end, the pump piston pair 11&#39; is then brought into play, this pair being in advance of the pump piston pair 11 by 135° of rotational angle, which corresponds to 270° of crankshaft angle in FIG. 7. In this case, the second distributor opening 89 comes into play, this opening likewise being in advance by the same angular amount of the first distributor opening 88. The first distributor opening 88 is then closed by the wall of the cylinder. One pair of pump pistons at a time executes four pumping strokes and four intake strokes during a single complete revolution of the drive shaft 16, corresponding to the four fuel injection lines 68 to be supplied. If there are more cylinders, the pumping strokes and intake strokes are correspondingly greater in number. With this embodiment, advancements of the injection of the main fuel quantity by more than merely 180° of crankshaft angle can be attained in the range of the intake stroke. However, it must be noted that only such angles can be established at which, during the pumping stroke through one of the distributor openings, the other distributor opening is located just in the cylinder region between the individual fuel injection lines. This naturally also applies to the case where, as shown in FIG. 4, it is desired that only one simple control valve 26&#39; be used, without having to provide for separate control of the individual distributor openings. The advantage of this form of embodiment is that the fuel introduced at full load can be given more time before the instant of ignition to become optimally prepared than is the case with the first exemplary embodiment described herein. While the exemplary embodiment of FIG. 1 can certainly be realized with a reciprocating-piston distributor injection pump, it is necessary in the exemplary embodiment of FIG. 4 to use a radial-piston injection pump, in order to attain the intersecting, offset supply strokes. 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.