Method and control system for operating a turbocharged internal combustion engine of a motor vehicle

Abstract

A method for operating an internal combustion engine having a turbocharger, wherein a fuel quantity is supplied to the combustion chamber of the engine in a stationary state, which fuel quantity is determined according to a first predetermined relationship between a load requirement to the engine and a rating determining a fuel quantity to be supplied to the combustion chamber, wherein a second predetermined relationship between the rating and the load requirement is used, wherein according to the second relationship, a given load requirement is assigned a larger quantity of fuel than according to the first relationship. In a transient state of the engine, the fuel quantity supplied to the combustion chamber is determined based on an interpolated value of the rating, which is determined for the rating by an interpolation between a value resulting from the first relationship and a value resulting from the second relationship.

Claims

1. A method for operating an internal combustion engine having at least one turbocharger, comprising: via a central engine control unit, presetting a first predetermined relationship between an engine load requirement and a rated engine operating variable; presetting a second predetermined relationship between a given engine load requirement and a given rated engine operating variable; wherein the quantity of fuel according to the second relationship of the given load requirement is greater than the quantity of fuel according to the first predetermined relationship; in a steady state of the internal combustion engine, injecting a quantity of fuel to a combustion chamber of the internal combustion engine based on the first predetermined relationship; and in a transient state of the internal combustion engine, injecting the quantity of fuel fed to the combustion chamber based on an interpolated value of the rated variable obtained by interpolation between a value for the rated engine operating variable, resulting from the first predetermined relationship, and a value for the rated variable, resulting from the second predetermined relationship; and further including: carrying out the interpolation, via the central engine control unit, as a function of a differential rotational speed; wherein the differential rotational speed is calculated as a difference between a setpoint rotational speed and an instantaneous actual rotational speed.

2. The method according to claim 1, further including: via the central engine control unit, optimizing the first predetermined relationship with respect to reduced emissions of the internal combustion engine.

3. The method according to claim 1, including using a characteristic diagram, in which values for the rated engine operating variable of the first predetermined relationship and the second predetermined relationship are stored as a function of a rotational speed and a torque of the internal combustion engine.

4. The method according to claim 1, including using a lambda setpoint value as the rated engine operating variable for the internal combustion engine.

5. The method according to claim 1, further including: via the central engine control unit, retarding ignition time, in a transient state of the internal combustion engine based on an interpolation between a first predetermined ignition time relationship, given between a load requirement of the internal combustion engine and the ignition time, and a second predetermined ignition time relationship, given between the load requirement and the ignition time; wherein an additional rated engine operating variable is combined with the interpolated value of the rated engine operating variable; wherein the additional rated engine operating variable is calculated based on scaling of a rated engine operating variable differential value; wherein the rated engine operating variable differential value is calculated as a difference between a value of the rated engine operating variable, which results from a third predetermined relationship being given between the rated engine operating variable and the load requirement, and the value of the rated engine operating variable of the second predetermined relationship; and wherein the third relationship represents a knocking limit of the internal combustion engine at the ignition time being/having been retarded.

6. The method according to claim 1, wherein the second relationship represents a knocking limit of the internal combustion engine.

7. An internal combustion engine having at least one turbocharger, comprising: an engine block having a combustion chamber; a fuel injection device; and a control device having computer executable instructions stored on an electronic medium for: presetting a first predetermined relationship between an engine load requirement and a rated engine operating variable; presetting a second predetermined relationship between a given engine load requirement and a given rated engine operating variable; wherein the quantity of fuel according to the second relationship of the given load requirement is greater than the quantity of fuel according to the first predetermined relationship; in a steady state of the internal combustion engine, injecting a quantity of fuel to a combustion chamber of the internal combustion engine based on the first predetermined relationship; and in a transient state of the internal combustion engine, injecting the quantity of fuel fed to the combustion chamber based on an interpolated value of the rated variable obtained by interpolation between a value for the rated engine operating variable, resulting from the first predetermined relationship, and a value for the rated variable, resulting from the second predetermined relationship; and wherein the control device carries out the interpolation as a function of a differential rotational speed; wherein the differential rotational speed is calculated as a difference between a setpoint rotational speed and an instantaneous actual rotational speed.

8. The internal combustion engine according to claim 7, wherein the internal combustion engine is a gas engine.

9. The internal combustion engine according to claim 8, wherein the internal combustion engine is a lean gas engine.

10. A motor vehicle, comprising: an internal combustion engine having at least one turbocharger and including: an engine block with a combustion chamber; a fuel injection device; and a control device having computer executable instructions stored on an electronic medium for: preset/presetting a first predetermined relationship between an engine load requirement and a rated engine operating variable; preset/presetting a second predetermined relationship between a given engine load requirement and a given rated engine operating variable; wherein the quantity of fuel according to the second relationship of the given load requirement is greater than the quantity of fuel according to the first predetermined relationship; in a steady state of the internal combustion engine, injecting a quantity of fuel to a combustion chamber of the internal combustion engine based on the first predetermined relationship; and in a transient state of the internal combustion engine, injecting the quantity of fuel fed to the combustion chamber based on an interpolated value of the rated variable obtained by interpolation between a value for the rated engine operating variable, resulting from the first predetermined relationship, and a value for the rated variable, resulting from the second predetermined relationship; and wherein the control device carries out the interpolation as a function of a differential rotational speed; wherein the differential rotational speed is calculated as a difference between a setpoint rotational speed and an instantaneous actual rotational speed.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be explained in more detail below on the basis of the drawing, in which:

(2) FIG. 1 shows a schematic illustration of an exemplary embodiment of a motor vehicle with an internal combustion engine;

(3) FIG. 2 shows a schematic illustration of a detail of an embodiment of the method, and

(4) FIG. 3 shows a further schematic illustration of a detail of the embodiment of the method according to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows a schematic illustration of an exemplary embodiment of a motor vehicle 1 which has an internal combustion engine 3. The motor vehicle 1 is embodied, for example, as a watercraft, in particular as a ship. The internal combustion engine 3 has here an engine block 5 with at least one combustion chamber 7. The internal combustion engine 3 is preferably embodied as a reciprocating piston engine. In this context it is possible for said engine to have a multiplicity of combustion chambers, in particular four, six, eight, ten, twelve, sixteen, eighteen or twenty cylinders or more cylinders or another number of cylinders. It is possible for the internal combustion engine 3 to be embodied as an in-line engine, as a V-type engine, as a W-type engine or in some other suitable configuration.

(6) The internal combustion engine 3 has a turbocharger 9 which has a turbine 13 which is arranged in an exhaust gas section 11 and is driven by a mass flow of exhaust gas flowing in the exhaust gas section 11, wherein the turbine 13 is operatively connected via a shaft 15 to a compressor 19 which is arranged in a charge air section 17, with the result that the compressor 19 can be driven by the turbine 13 via the shaft 15. An injection device 21 for a fuel which is embodied as combustion gas for operating the internal combustion engine 3 is arranged in the charge air section 17, downstream of the compressor 19 here. The combustion gas is fed to the injection device 21 via a combustion gas line 23. Alternatively it is possible for the injection device 21 to be arranged upstream of the compressor 19, that is to say ahead of the compressor 19. Various possible ways of injecting the combustion gas into the charge air are possible, specifically, in particular, as single point injection, preferably ahead of the compressor 19, as intake manifold injection downstream of the compressor 19, in particular as cylinder-specific multi-point injection in the individual combustion chambers 7, individually assigned intake manifold sections or else in the form of a direct injection into the individual combustion chambers 7.

(7) At any rate, an adjustable, variable quantity of combustion gas can be fed to the combustion air by means of the injection device 21, wherein the injection device 21 can be actuated to prescribe the quantity of fuel which is fed to the combustion chamber 7.

(8) The internal combustion engine 3 has a control device 25 which is preferably embodied as an engine control unit (ECU). The control device 25 is operatively connected to the injection device 25 in order to prescribe a quantity of fuel which is to be fed to the combustion chamber 7. Said control device 25 is also preferably operatively connected to a rotational speed sensor 27 for detecting an instantaneous actual rotational speed of the internal combustion engine 3. Furthermore, the control device 25 is operatively connected to a rotational speed prescription device 29, here a control lever, for prescribing a setpoint rotational speed for the internal combustion engine 3. The control device 25 is configured, in particular, to calculate a differential rotational speed between the setpoint rotational speed predefined by means of the rotational speed prescription device 29 and the actual rotational speed detected by means of the rotational speed sensor 27.

(9) Known control devices are typically configured to permit internal combustion engines of this type which are embodied as gas engines to operate with the lowest possible emissions. It is disadvantageous here that in the case of load shifting no sufficient mass flow of exhaust gas is available to ensure a sufficiently dynamic response behavior of the turbocharger 9. Internal combustion engines of this type are therefore generally extremely slow-reacting and have a transient capability which is in need of improvement.

(10) In order to overcome this disadvantage, the control device 25 illustrated in FIG. 1 is configured to carry out a method according to one of the embodiments described above, in particular an embodiment of the method such as is described below with respect to FIGS. 2 and 3. In this context, the control device 25 is configured, in particular, to actuate the injection device 21 as a function of the obtained differential rotational speed.

(11) FIG. 2 shows a schematic illustration of a detail of an embodiment of a method for operating an internal combustion engine, in particular the internal combustion engine 3 illustrated in FIG. 1. In this context, a first predetermined relationship 31 is provided in the form of a characteristic diagram which has values BG.sub.1 for a rated variable which determines a quantity of fuel to be fed to the combustion chamber 7, as a function of rotational speed 35 and a torque 37 of the internal combustion engine 3. In this context, the first relationship 31 is optimized with respect to the lowest possible emissions of the internal combustion engine 3. In particular in steady states of the internal combustion engine 3, the quantity of fuel which is to be fed to the combustion chamber 7 is preferably determined by the values BG.sub.1 which are determined for the rated variable according to the first relationship 31. The rated variable is here, in particular, a lambda setpoint value.

(12) A second predetermined relationship 39 between the rated variable, that is to say the setpoint air ratio here, and the rotational speed 35 and the torque 37 is also provided in the form of a second characteristic diagram. A value BG.sub.2 for the rated variable results from this second relationship 39 as a function of the rotational speed 35 and the torque 37. In this context, the second relationship 39 represents a knocking limit of the internal combustion engine 3. The values BG.sub.2 of the rated variable according to the second relationship 39 are therefore lambda setpoint values at the knocking limit.

(13) In order to improve the transient behavior of the internal combustion engine 3, in a transient state in which load shifting is present and, in particular, the rotational speed of the internal combustion engine 3 is to be increased, interpolation 41 is carried out between the value BG.sub.1 determined for the rated variable according to the first relationship 31 and the value BG.sub.2 determined for the rated variable according to the second relationship 39. Here, the interpolation takes place as a function of a rotational speed difference 43, wherein an interpolation factor g is read out according to a first characteristic curve 45 as a function of the differential rotational speed 43. The interpolation 41 is preferably carried out according to the equation (1) specified above.

(14) This results in an interpolated value BG.sub.int for the rated variable.

(15) It is possible that this interpolated value BG.sub.int of the rated variable is used per se to determine the quantity of fuel to be fed to the combustion chamber 7.

(16) However, in the embodiment of the method illustrated here there is additionally provision that an additional rated variable term BG is combined with the interpolated value BG.sub.int of the rated variable in a calculation element 47.

(17) It is basically possible here that the additional rated variable term BG is a multiplicative term which is multiplied by the interpolated value BG.sub.int. However, in the exemplary embodiment illustrated here there is preferably provision that the calculation element 47 is embodied as an addition element, wherein the additional rated variable term BG is embodied as an additive term and, in particular, as a summand which, according to the equation (4) specified above, is added to the interpolated rated variable BG.sub.int.

(18) The interpolated value BG.sub.int is preferably a lambda setpoint value. Correspondingly, the additional rated variable term BG is preferably a lambda addition value.

(19) A rated variable setpoint value BG.sub.setp results from the calculation in the calculation element 47. Said setpoint value BG.sub.setp is also a lambda setpoint value.

(20) Since in the transient state the internal combustion engine 3 is not to be operated in a lean fashion, a limiting element 49 is preferably provided which limits the value of the rated variable setpoint value BG.sub.setp and therefore, in particular, the setpoint air ratio to 1, in particular by forming a maximum between the rated variable setpoint value BG.sub.setp and 1.

(21) Furthermore, a conversion function 51 is preferably provided which converts the limited rated variable setpoint value into a value suitable for actuation of the injection device 21, for example into a fuel mass flow or a fuel mass to be injected per stroke of a piston which is assigned to the combustion chamber 7. Finally an actuation value 53 results from the conversion function 51 into which, in particular, a pressure and a temperature of the fuel are preferably input, said actuation value 53 being used for the actuation of the injection device 21 by the control device 25.

(22) FIG. 3 shows a second illustration of a detail of the embodiment of the method according to FIG. 2. Identical and functionally identical elements are provided with the same reference symbols, with the result that in this respect reference is made to the preceding description. FIG. 3 illustrates the calculation of the additional rated variable term BG. Furthermore, the calculation of an interpolated ignition point ZZP.sub.int is illustrated.

(23) There is a first predetermined ignition time relationship 55, embodied here in the form of a characteristic diagram which has values ZZP.sub.1 for the ignition time as a function of the rotational speed 35 and the torque 37. Here, the first ignition time relationship 55 is used with optimization to the lowest possible emissions of the internal combustion engine 3. This first ignition time relationship 55 is used, in particular, in steady states of the internal combustion engine 3. The knocking limit which is represented by the second relationship 39 preferably relates to the first ignition time relationship 55 or the ignition times ZZP.sub.1 which are provided according to this first ignition time relationship 55.

(24) A second predetermined ignition time relationship 57 is provided, specifically again in the form of a characteristic diagram which has values ZZP.sub.2 for the ignition time as a function of the rotational speed 35 and the torque 37. Here, the second ignition time relationship 57 is matched, in particular, to a technical limit of the internal combustion engine 3, preferably to a knocking limit thereof, wherein said ignition time relationship 57 has ignition times ZZP.sub.2 which are the maximum which can be implemented without risk to the internal combustion engine 3. The characteristic diagram for the second ignition time relationship 57 is preferably obtained on a test bench. At any rate, the second ignition time relationship 57 comprises later ignition times, given fixed rotational speed 35 and fixed torque 37, than the first ignition time relationship 55.

(25) Within the scope of the method, in a transient state of the internal combustion engine 3, in particular in the case of load shifting and increasing of the rotational speed, interpolation is carried out in an ignition time interpolation step 59 between the ignition time ZZP.sub.1 according to the first ignition time relationship 55 and the ignition time ZZP.sub.2 according to the second ignition time relationship 57. This is carried out by means of an ignition time interpolation factor h which is read out from a second characteristic curve 61 as a function of the differential rotational speed 43. In this context, the interpolation takes place, in particular, according to the equation (2) specified above. An interpolated value ZZP.sub.int for the ignition time with which the internal combustion engine 3 is actuated in the transient state, results from the ignition time interpolation step 59. In every case this brings about adjustment of the ignition time in the retarded direction, as a result of which the knocking limit of the internal combustion engine 3 is shifted to a relatively rich mixture. It is therefore possible to introduce an additional quantity of fuel into the combustion chamber 7.

(26) For this purpose there is preferably provision that the additional rated variable term BG is calculated by means of a third interpolation step 63, wherein interpolation is carried out here between the value BG.sub.2 which is obtained for the rated variable according to the second relationship 39 and a value BG.sub.3 which is obtained for the rated variable according to a third relationship 65. In this context, the third relationship 65 is also embodied here as a characteristic diagram which has values BG.sub.3 for the rated variable as a function of the rotational speed 35 and the torque 37. In this context, the characteristic diagram 65 represents a knocking limit of the internal combustion engine 3 at the ignition time ZZP.sub.2 which is determined according to the second ignition time relationship 57. The value BG.sub.3 which is determined for the rated variable according to the third relationship 65 is here a value which relates to the knocking limit at the ignition time ZZP.sub.2 which is adjusted in the retarded direction according to the second ignition time relationship 57, preferably by a lambda setpoint value.

(27) For the interpolation in the third interpolation step 63, the ignition time interpolation factor h which is obtained according to the second characteristic curve 61 is used here as a scaling factor k, wherein the interpolation is carried out according to the equation (3) specified above. The equating of the ignition time interpolation factor h with the scaling factor k brings about optimum matching of the rated variable which is ultimately used to actuate the injection device 21 with the currently set ignition time. However, it is also alternatively possible for a scaling factor k which is determined independently, in particular according to a third characteristic curve, to be input into the third interpolation step 63.

(28) The additional rated variable term BG which results from the third interpolation step 63 is fed to the calculation element 47 according to FIG. 2.

(29) Overall it becomes apparent that according to the method proposed here and by means of the proposed control device 25 the internal combustion engine 3 can be operated in a richer fashion in a transient state in the case of load shifting and increasing of the setpoint rotational speed than in a steady state in order to make available an increased mass flow of exhaust gas for the turbocharger. In this context, the ignition time can additionally be adjusted in the retarded direction in order to permit additional enrichment of the mixture in the combustion chamber 7. The interpolation steps which are provided bring about, on the one hand, softer control and, on the other hand, savings of fuel as well as a reduction in emissions. Furthermore, they cause the additional enrichment to be incrementally eliminated again when the actual rotational speed approaches the setpoint rotational speed, wherein the internal combustion engine 3 is then set again in a steady-state fashion to reduced emissions. In this context, it also becomes apparent that the internal combustion engine 3 is operated or configured, in particular, as an internal combustion engine which is controlled on the basis of the rotational speed.