INTERNAL COMBUSTION ENGINE AND METHOD FOR ITS OPERATION

Abstract

A method for operating an internal combustion engine having at least two cylinders and having a single injector for central point injection of fuel into an air intake connected to the cylinders, wherein for each of the cylinders an injection quantity of the fuel and a starting time of the injection are specified and set as a function of the present engine load and the present engine speed. The invention further relates to such an internal combustion engine.

Claims

1. A method for operating an internal combustion engine, the method comprising: providing at least two cylinders and a single injector for central point injection of fuel into an air intake connected to the cylinders; and specifying for each of the at least cylinders, an injection quantity of the fuel and a starting time of the injection and set as a function of the present engine load and/or the present engine speed.

2. The method according to claim 1, wherein an end time of the injection is specified and by means of its injection quantity, a starting time is specified.

3. The method according to claim 1, wherein the injector is a unit injector with a coil for moving a plunger, which upon a stroke movement conveys fuel to an injection nozzle, and wherein the starting time of the injection, an end time and/or an injection quantity are set on the basis of a temporal current profile of the coil of the injector.

4. The method according to claim 3, wherein the starting time of the injection, the end time and/or the injection quantity are set as a function of a plunger return time of the plunger.

5. The method according to claim 4, wherein the plunger return time is reduced by increasing the slope of the current profile of the current induced via the coil after de-energization effecting the stroke movement.

6. An internal combustion engine comprising: at least two cylinders; a single injector for central point injection of fuel into an air intake that is connected to the at least two cylinders; and a control unit for carrying out the method according to claim 1.

7. The internal combustion engine according to claim 6, wherein the injector is a unit injector with a plunger that conveys the fuel to an injection nozzle during a stroke movement, and with a coil that in an energized state causes the stroke movement of the plunger towards the injection nozzle.

8. The internal combustion engine according to claim 7, further comprising a circuit connected in parallel with the injector for increasing the slope of the current profile of the current induced via the coil after de-energization of the coil, and for limiting a voltage at a control unit connection of the injector.

9. The internal combustion engine according to claim 8, wherein the circuit has a freewheeling diode and a Zener diode that is connected in series and in an opposite direction, or a semiconductor switch connected in series to a diode for the dissipation of the energy stored in the coil.

10. The internal combustion engine according to claim 6, further comprising a sensor connected to the control unit to determine a position of a crankshaft and/or an engine speed based on a magnet wheel coupled to the crankshaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0030] FIG. 1 is a schematic view of an internal combustion engine, having two cylinders, an air intake connected to the cylinders and a single injector for the central point injection of fuel into the air intake;

[0031] FIG. 2 is a schematic longitudinal section of the injector designed as a unit injector, having a coil for moving a plunger, wherein at a stroke movement of the plunger towards an injection nozzle, fuel is fed into the air intake;

[0032] FIGS. 3a and 3b illustrate, in each case, a circuit connected in parallel with the unit injector, having a freewheeling diode and having a semiconductor switch or a Zener diode to increase the slope of a current induced by the coil, which is produced after the end of the energization, causing the stroke movement;

[0033] FIG. 4a illustrates a time profile of the current through the coil, wherein the starting times and the end times of the injection are set as a function of the present engine load and the present engine speed, and a stroke position of the plunger corresponding thereto;

[0034] FIG. 4b illustrates a time profile of the pressure in the air intake; and

[0035] FIG. 5 illustrates an energization duration-injection quantity diagram for a unit injector.

DETAILED DESCRIPTION

[0036] FIG. 1 shows a four-stroke internal combustion engine 2. This has two cylinders 4, which are connected in terms of flow technology for supplying fuel to an air intake 6 also referred to as an intake manifold. In the air intake 6, a throttle valve 8 is arranged, by means of which the amount of air supplied to the cylinders is set during operation. Furthermore, the internal combustion engine 2 has a single injector 10, which is designed as a unit injector and which injects the fuel into the air intake 6 at a single (injection) location. This is also known as central point injection.

[0037] Furthermore, the internal combustion engine 2 has an exhaust system 12, which serves to discharge the fuel-air mixture ignited in the cylinders 4.

[0038] Further, a crankshaft 14 of the internal combustion engine 2 is coupled with a magnet wheel 16, wherein the magnet wheel 16 rotates in tandem with the crankshaft 14. In this way, an (angular) position of the crankshaft 14 and/or an engine speed can be specified by means of the magnet wheel 16 and by means of a first sensor 18 designed as a so-called VR sensor.

[0039] The internal combustion engine 2 also has an (engine) control unit 20, which is connected both to the first sensor 18 designed as a VR sensor and to the injector 10. The control unit 20 is connected to a second sensor 22, which is arranged in the air intake 6 and is also referred to as a TMAP sensor, and which detects the pressure and the temperature in the air intake 6 and makes these available as measured values for the control unit 20. By means of the measured values, the control unit 20 determines the present engine load.

[0040] FIG. 2 shows the injector 10 which is designed as a unit injector. This has a plunger 24 and a (solenoid) coil 26. When the coil 26 is energized, the plunger 24 is caused to perform a stroke movement toward an injection nozzle 28. Due to the stroke movement, the fuel received in a fuel chamber 30 arranged between the plunger 24 and the injection nozzle 28 is injected by the injection nozzle 28 into the air intake 6. The fuel feed or the fuel return into or out of the fuel chamber 30 is represented by corresponding arrows. In addition, the injector 10 has a spring element 32, which moves the plunger 24 back to a starting position after the coil 26 has been de-energized, that is to say after the end of the stroke movement. In this case, a current I.sub.s is induced by the coil 26 after de-energization. Because of this, a magnetic force is generated which counteracts the restoring effect of the spring element 32. Consequently, the period of time referred to as the return time d.sub.R, which the plunger 24 requires to return to its starting position after the stroke movement has ended, is extended accordingly. To allow for the current I.sub.s induced in the coil 26 to decay as rapidly as possible, in other words, to increase the slope of the current profile I.sub.s(t) of the current I.sub.s induced by means of the coil after the end of the movement, a circuit 34 is connected in parallel with the injector 10, which is shown in FIG. 3a or in an alternative embodiment shown in FIG. 3b.

[0041] FIGS. 3a and 3b show the control device 20 in sections, wherein it has a voltage source 36, which is connected via a first resistor 38 to a control input designed as a gate of a switch 40 designed as a MOSFET (metal oxide semiconductor field effect transistor).

[0042] The injector 10 has a control unit connection 42, by means of which the injector is connected to the control unit 20, in particular on the drain side to the switch 40 of the control unit 20. In addition to the coil 26, the injector 10 has a second resistor 44 connected in series with said coil and a supply input 46 for a further voltage source 48 designed as a battery.

[0043] The circuit 34 connected in parallel with the injector 10 according to FIGS. 3a and 3b has a freewheeling diode 50 which prevents a current flow from the voltage source 48 constructed as a battery through the circuit 34 connected in parallel with the injector 10 toward the control device 20, but is switched in the forward direction with respect to the current induced by the coil 36.

[0044] According to the embodiment of the circuit 34 shown in FIG. 3a, a semiconductor switch 54 in the form of a MOSFET is connected in series with the freewheeling diode 50 for dissipating the energy stored in the coil and for limiting the voltage applied to the control unit connection 42. In this case, the freewheeling diode 50 is connected on the drain side to the semiconductor switch 54 designed in the form of a MOSFET. On the source side, the semiconductor switch 54 is connected to the supply input 46 of the injector 10.

[0045] A third resistor 56 is connected in a current path running between the source and the gate of the semiconductor switch 54, to which a second diode 58 is in turn connected in parallel. The second diode 58 has a forward direction from the source to the gate of the semiconductor switch 54. A fourth resistor 60 and a third diode 62 with a forward direction from the gate of the semiconductor switch 54 to the freewheeling diode 50 are connected in a current path running between the gate and the freewheeling diode 50.

[0046] According to the alternative embodiment of the circuit 34 shown in FIG. 3b, this also has a Zener diode 52 which is switched in series with the freewheeling diode 50 and directed opposite the freewheeling diode 50 in terms of the forward direction, which Zener diode limits a voltage at the injector and at its control unit connection that is induced by means of the coil 26 after de-energization. Further, the Zener diode 52 serves for the dissipation of the energy stored in the coil.

[0047] FIG. 4a shows a time profile I.sub.s(t) of the current I.sub.s through the coil 26. In this case, the crankshaft position per working cycle is indicated in KW of the crankshaft 14 on the abscissa axis. One working cycle includes 720 KW. For an engine speed, in the present case 3600 revolutions/minute (3600 min.sup.1), this crankshaft position is directly proportional to the time t. The engine speed is expediently specified by means of the first sensor 18 designed as a VR sensor. The engine load here corresponds to an output of 15.5 kW, wherein the engine load is specified by means of the (TMAP sensor) second sensor 22.

[0048] FIG. 4b shows a corresponding time profile of the pressure in the air intake also called intake manifold pressure. In an analogous manner to FIG. 4a, the crankshaft position per working cycle is indicated on the abscissa axis.

[0049] The internal combustion engine 2 is of a V-type construction. This can be seen in particular in that an intake phase of the first of the two cylinders 4, in which the intake manifold pressure is reduced accordingly, lasts from 0 KW to 180 KW, and the intake phase of the second cylinder 4 from 270 KW to 450 KW. In addition, the ignition timing ZP of the first of the two cylinders 4 is 360 KW and of the second cylinder 4 is 630 KW. The so-called ignition point offset (ignition time offset) is therefore 270 KW.

[0050] In particular, due to such a V-type construction of the internal combustion engine 2 and the corresponding time profiles of the intake phases of the cylinders 4, the fuel quantity received in the cylinders 4 would differ despite uniform time intervals of the starting points SOI of the injections, i.e., at a time interval corresponding to 360 KW for the internal combustion engine 2 with two cylinders 4 and a working cycle of 720 KW, as well as despite the same injection quantity EM. As a result, the air-fuel ratios of the two cylinders 4 would also be too rich or too lean.

[0051] To avoid this, as shown in FIG. 4a, the starting time SOI, the end time EOI of the injection, and their injection quantity EM based on the temporal current profile I.sub.s(t) of the coil 26 of the injector 10 are set in accordance with the present engine load and the present engine speed. The starting time SOI of the injection is the point in time at which the coil 26 is energized in order to bring about the stroke movement of the plunger 24. The end time point EOI of injection is the point in time at which the coil 26 is no longer energized, and consequently the stroke motion of the plunger 24 toward the injection nozzle 28 has ended. The injection quantity EM is set using the time interval from the starting time SOI to the end time EOI of the injection.

[0052] For the first cylinder 4, the starting time SOI of the injection is at 645 KW, the end point EOI of the injection is at 60 KW. For the second cylinder 4, the starting time SOI of the injection is at 240 KW and the end time EOI of the injection is at 375 KW.

[0053] The end time EOI of the injection is specified. The starting time SOI of the injection is specified by means of the injection quantity EM. For this purpose, the relationship shown in FIG. 5 between the injection quantity and the injection duration d.sub.s, that is to say the time period between the end time EOI of the injection and its starting time SOI, is used. The injection quantity here is 26 mg of fuel per cylinder 4 per working cycle, which according to FIG. 5 corresponds to an injection duration d.sub.s of 6.3 ms.

[0054] FIG. 4a also shows a schematic view of the time profile H(t) of the stroke position H of the plunger 24 as a dash-dotted line. Here, a stroke position H of zero (H=0) corresponds to the starting position and one (H=1) corresponds to the maximum stroke position. The slope of the current profile I.sub.s(t) is increased by means of the circuit 34 in one of the variants of FIG. 3a or 3b, and the plunger return time d.sub.R is reduced accordingly. In comparison to this, the time profile of the stroke position of the plunger 24 after de-energization of the coil 26 for the injection for the first cylinder 4 until the return to the starting position of the plunger 24 is shown as a dotted line for the event that no circuit 34 is connected in parallel to the injector 10. The plunger return time d.sub.R corresponding thereto is greater than the plunger return time d.sub.R when the circuit 34 is used. Thus, the plunger 24 has returned to its starting position more quickly with the use of the circuit 34.

[0055] During operation, the plunger 24 is preferably moved back to its starting position after the stroke movement. Thus, with the use of the circuit 34, it is possible to set the starting time SOI of the injection closer to the end time EOI of the previous injection. According to the embodiment of FIG. 4a, the starting point SOI of the injection takes place prior to reaching the starting position (H=0) of the plunger 24 when the circuit 34 is not used, which is shown accordingly by the dotted line.

[0056] In summary, the starting time SOI of the injection and the end time EOI or the injection quantity EM thereof are set as a function of a plunger return time d.sub.R of the plunger 24.

[0057] To summarize further, the injection quantity EM of the fuel and the starting time SOI of the injection is specified for each of the cylinders 4 as a function of the present engine load and the present engine speed on the basis of relationships stored in the control unit 20. Subsequently, the injection quantity EM of the fuel and the starting time SOI are set accordingly.

[0058] According to a variant not shown, the injection quantities EM of the cylinders 4 are set such that they are different. Here, the energization duration d.sub.s of the coil 26, i.e., the duration from the starting time SOI of the injection until the end time EOI of the injection, is set according to the relationship shown in FIG. 5.

[0059] FIG. 5 shows a diagram which illustrates the relationship of the injection quantity EM and the duration of energization d.sub.s of the coil 26 for generating the stroke movement of the plunger 24. Here, the injection quantity EM increases steadily with an increasing energization period up to a time period d.sub.max and then drops again. This pattern is based on the fact that from the energization period d.sub.max, the plunger 24 does not have enough time within the time period specified by the engine speed to be returned to its starting position after de-energization of the coil 26 before the coil 26 is energized again for the subsequent stroke movement. Accordingly, the following stroke movement cannot be performed with the maximum possible stroke distance and correspondingly, less fuel is delivered. This relationship is stored on the control unit 20.

[0060] The invention is not limited to the exemplary embodiments described above. Rather, other variants of the invention can also be derived therefrom by a person skilled in the art without departing from the subject matter of the invention. In particular, all of the individual features described in connection with the exemplary embodiments can also be combined with one another in other ways without departing from the subject matter of the invention.

[0061] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.