Method for operating an internal combustion engine with storage injection

Abstract

Method for operating an internal combustion engine with a storage injection system, wherein fuel is introduced into a pressure accumulator by means of a high-pressure pump and a pressure in the pressure accumulator is set by means of a metering unit controlling the high-pressure pump, and wherein the fuel stored in the pressure accumulator is introduced into at least one combustion chamber of the internal combustion engine by means of at least one injector and a quantity of fuel leakage from the pressure accumulator into a low-pressure area connected to the pressure accumulator caused by the at least one injector is calculated on the basis of a temperature (200) present in the area of ​​the injector (205, 210, 145, 155) and that the pressure in the pressure accumulator is set by means of the metering unit taking into account the calculated leakage quantity, characterized in that the quantity of leakage is calculated as a function of the fuel temperature in the injector return line.

Description

[0001] The invention relates to a method for operating an internal combustion engine with a storage injection system according to the preamble of claim 1. Furthermore, the invention relates to a computer program that performs all steps of the method according to the invention when it is executed on a computing device or a control unit, and to a computer program product with program code stored on a machine-readable medium for carrying out the method according to the invention when the program is executed on a computing device or a control unit. State of the art

[0002] In internal combustion engines with accumulator injection (e.g., common rail systems), fuel is introduced under pressure into a pressure distributor or accumulator (in common rail systems, the so-called "rail") by means of a high-pressure pump. Fuel in the accumulator is injected into the combustion chambers of the internal combustion engine via injectors, e.g., injection valves. This allows for the separation of pressure generation from the injection process and thus the control of injections using maps in which injection timing and injection quantities are stored.

[0003] To maintain pressure in the accumulator, fuel is continuously or at regular intervals supplied to the accumulator via a high-pressure pump controlled by a metering unit. The metering unit receives a control signal, which is derived from the output of a pressure regulator, which in turn receives a signal from a pressure sensor. Some injection systems also incorporate a pressure regulating valve for pressure control.

[0004] A corresponding pressure control system for a common rail system is described in DE 197 31 994 A1. A high-pressure pump delivers fuel from a low-pressure area to the pressure accumulator. Based on the measured rail pressure, a pressure control valve releases a controlled quantity of fuel from the accumulator into the low-pressure area to regulate the pressure in the accumulator. This controlled quantity is regulated to a setpoint.

[0005] Furthermore, DE 10 2011 076 258 A1 discloses a method for operating an internal combustion engine relevant to this case, in which a metering unit is controlled by means of a control value determined by a feedforward control unit. The feedforward control unit serves to calculate the required fuel flow rate that the high-pressure pump must deliver to the pressure accumulator. The flow rate is determined based on the injection quantity and the engine speed. A control quantity for the injector is calculated from the injection quantity, whereby the injector leakage is measured and stored in the form of a characteristic map in a control unit of the internal combustion engine.

[0006] The legal framework governing permissible exhaust emission levels for internal combustion engines requires precise control of fuel combustion and, consequently, fuel metering. Over time, the injectors mentioned become leaky, allowing fuel to escape uncontrollably, particularly in the low-pressure area, which negatively impacts emission levels.

[0007] Document DE 196 200 38 A1 describes a method for monitoring a fuel metering system of an internal combustion engine, in particular a common rail system, in which a malfunction of the metering system is detected by means of a deviation of the exhaust gas composition from a predeterminable value, thereby ensuring better compliance with the aforementioned legal framework.

[0008] German patent DE 10 2008 000 513 A1 relates to a fuel injection system for internal combustion engines that compensates for individual fluctuations in the control pressure characteristic curve. It recognizes that leakage in the system varies from vehicle to vehicle and negatively affects pressure control. The patent proposes dynamically adjusting the PID control parameters (proportional, integral, and differential terms) of a fuel delivery mechanism. This is achieved by determining the actual fuel leakage and correcting the parameters to maintain stable fuel pressure in the common rail and optimize system performance.

[0009] German patent DE 10 2012 103 139 A1 describes a fuel injection control device. It focuses on the precise determination of the fuel temperature inside the injector (Tij). If the residence time of the fuel in the injector or the temperature difference between the injector body and the fuel at the inlet increases, Tij is estimated. The injection quantity is then corrected based on this estimated Tij to improve injection accuracy.

[0010] Furthermore, DE 10 2004 019 849 A1 is known. Disclosure of the invention

[0011] The invention is based on the understanding that, in the injectors concerned, any fuel leakage flows occurring from a pressure accumulator into a low-pressure area connected to the pressure accumulator, preferably via leakage gaps, the size of which depends significantly on the temperature of the injector, in particular the temperature in the region of a given leakage gap. Therefore, determining the leakage rate requires precise knowledge of the temperature in the region of the leakage gap, e.g., the temperature of the pressure accumulator near the leakage gap. The invention provides for calculating the leakage rate as a function of the fuel temperature in the injector return line.

[0012] The invention enables a more precise determination of the leakage quantities of the injectors affected here and thus a more precise control or pre-control of the fuel pressure in a pressure accumulator affected here.

[0013] The method according to the invention is preferably applicable in a common-rail injection system of a diesel engine of a motor vehicle with the advantages described herein, but can also be applied in a gasoline engine of a motor vehicle equipped with a pressure accumulator as described herein. Furthermore, the invention can also be used in internal combustion engines outside of automotive engineering. In the case of a common-rail injection system, the aforementioned low-pressure area constitutes a low-pressure circuit.

[0014] The leakage rate can additionally be calculated based on a setpoint for the pressure in the pressure accumulator and a current leakage factor, thereby increasing the accuracy of the calculation result. The setpoint for the pressure in the pressure accumulator can be converted into a leakage rate using a first characteristic map, the temperature present in the injector area can be converted into a correction value for the leakage rate using a second characteristic map, and the current leakage factor can be converted into a current leakage rate using a third characteristic map. These characteristic maps enable a particularly simple and cost-effective implementation of the method according to the invention.

[0015] The aforementioned leakage quantities can be multiplicatively linked at connection points to generate a leakage request, which can then be transmitted to a metering unit or control device to adjust the pressure regulation of the pressure accumulator accordingly. This approach also allows for simple and cost-effective implementation.

[0016] When calculating the leakage quantity based on a leakage gap, the accuracy of the calculation can be increased by taking into account the temperature increase due to compression of fuel by the high-pressure pump and the subsequent release of fuel pressure in the area of ​​the leakage gap when calculating the leakage quantity.

[0017] To further increase the accuracy in calculating the leakage quantity, the fuel temperature, the cooling water temperature of the internal combustion engine and / or the installation situation of the injector and / or the pressure accumulator in the internal combustion engine, which depends on the respective type of internal combustion engine, can be taken into account in calculating the leakage quantity.

[0018] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0019] It is understood that the features mentioned above and those to be explained below can be used not only in the respective combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention. Brief description of the drawings Fig. Figure 1 shows a block diagram of a calculation structure for calculating a leakage requirement in a common-rail injection system of an internal combustion engine according to the state of the art. Fig. 2 shows one of the Fig. 1 corresponding block diagram of a calculation structure modified according to the invention. Fig. Figures 3a and b show a comparison of leakage quantities (a) measured at an injector and leakage quantities (b) calculated according to the state of the art. Fig. 4a, b shows one of the Fig. 3a and b corresponding comparison of measured (a) and calculated (b) leakage data according to the invention. Description of exemplary implementations

[0020] The following embodiments describe a common-rail system of a diesel engine in which the rail pressure is regulated by an engine control unit (Electronic Diesel Control = EDC). It should be emphasized that the concepts and physical principles described herein are also applicable to other internal combustion engines, e.g., gasoline engines.

[0021] The in Fig. Figure 1, a simplified calculation structure known in the prior art for illustrative purposes, is based on operating parameters of the internal combustion engine or the injection system, which are already available in a control unit 100, e.g., in an engine control unit of the internal combustion engine or the injection system. These operating parameters are a setpoint 105 for the rail pressure, a current value of the fuel temperature 110, and the current operating time of the common rail system 115, which are converted into a current or currently valid relative leakage factor.

[0022] Based on the known relationship between rail pressure and leakage rate, the target value 105 for the rail pressure is converted into a leakage rate 135 resulting from the rail pressure using a first characteristic map 120. The fuel temperature 110 is converted into a correction value 140 for the leakage rate using a second characteristic map 125. This conversion is based on the known relationship between the leakage rate and the fuel temperature, which is based on the known effect that leakage increases with increasing fuel temperature, essentially due to the corresponding decrease in fuel viscosity. The leakage rate 135 and the correction value 140 for the leakage rate are multiplicatively linked at a first connection point 145.

[0023] The operating time 115 of the common-rail system, provided by the controller 100, is converted into a second corresponding leakage (quantity) correction factor 150 using a third characteristic map 130. The resulting value 150 is then multiplicatively combined with the result from the first linking point 145 at a second linking point 155. The output 160 of the calculation structure shown provides a current value for the leakage requirement, which can be supplied to the aforementioned controller 100, for example, to adjust the setpoints for injection and / or the setpoints for the delivery rate of the aforementioned high-pressure pump accordingly.

[0024] In the Fig. 2 is one of the Fig. 1. A corresponding calculation structure adapted to the method according to the invention is shown. The calculation structure with the Fig. 1 matching calculation paths are in the Fig. 2 only indicated by dashed lines and with the Fig. 1. Provided with corresponding reference numerals, with reference being made to the foregoing regarding the matching features.

[0025] Unlike the one in Fig. In the present embodiment according to the invention, the calculation structure shown in 1 is performed by the controller 100, instead of according to Fig. 1. The fuel temperature 110, the injector temperature 200, is supplied. The present value of the injector temperature 200 is converted into a leakage correction value 210 by means of a second characteristic map 205 modified compared to the second characteristic map 125, and the correction value 210 thus calculated, as in Fig. 1, fed to the first multiplicative linking point 145. At output 160 of the calculation structure, there is again a current value of the leakage requirement, whereby the corresponding leakage quantity is compared to the one in Fig. The calculation structure shown in 1 provides a leakage result that is significantly closer to the actual leakage quantity.

[0026] To determine the temperature-dependent leakage rates for the feedforward control of the rail pressure, the following is used instead of the one in Fig. The fuel or system temperature T_Fuel shown in Figure 1 is derived from an injector temperature model, T_Inj. The injector temperature T_Inj is calculated taking into account, in particular, the coolant temperature, the electrical control of the injector, and the hydraulic relationships described below, e.g., regarding compression, expansion, and flow rates.

[0027] The data for the described second characteristic map 205 is preferably determined based on the fuel temperature in the injector return line. The necessary data is already available in modern engine control units and is determined beforehand through measurements.

[0028] The procedure according to the in Fig. The calculation structure shown in Figure 2, modified according to the invention, takes into account in particular the following physical relationships and technical effects.

[0029] The compression of fuel in the high-pressure pump and the subsequent release of the resulting overpressure in the injector, particularly in the area of ​​a leakage gap, leads to an additional temperature increase, which in turn significantly influences the leakage rate. Furthermore, heat flows within the fuel and ambient conditions cause additional changes in the fuel temperature in the pressure accumulator and the common-rail system's lines.

[0030] Furthermore, the installation situation of the injectors or the pressure accumulator in the internal combustion engine results in temperature conditions or changes that vary depending on the specific engine type. The influence of the cooling water temperature is mentioned here only as an example.

[0031] It should be emphasized that there are also differences between the ambient conditions when measuring leakage quantities on a test bench and the temperature conditions resulting from the operation of the internal combustion engine, particularly due to fluctuations in the coolant temperature caused by the operation of the internal combustion engine or the driving style of the motor vehicle.

[0032] Leakage rates are calculated based on injector measurements. These measurements are determined based on the pump inlet temperature and the injector return temperature. The injector under test is heated to a constant temperature using a heating unit.

[0033] Based on the fuel temperature T_Fuel, the corresponding leakage rates are calculated. To determine the temperature dependence of the leakage rates, the fuel temperature at the location of the temperature sensor, usually in the area of ​​the pump inlet, is used.

[0034] The Fig. Figure 3a shows leakage quantities measured at an injector, which are in Fig. 3b. Leakage quantities calculated according to the state of the art are compared or contrasted with these. In the diagrams shown, the leakage quantity is in mm³. 3The graph shows the pressure in seconds ( / s) plotted against the rail pressure (p_Rail), which is specified in bar. For ease of comparison, the scales of both axes are identical.

[0035] At the in Fig. In the set of curves 300 shown in Figure 3a, the uppermost curve 305 was measured at a fuel temperature of 85 °C and the lowermost curve 310 at a fuel temperature of 35 °C. All intermediate curves decrease successively from top to bottom in 5 °C increments. In the Fig. In the family of curves 315 shown in Figure 3b, derived from data obtained by calculation or simulation, the uppermost curve 320 also corresponds to a fuel temperature of 85 °C and the lowermost curve 325 to a fuel temperature of 35 °C, with the intervening curves corresponding to the Fig. 3a. The fuel temperature decreases successively from top to bottom.

[0036] A comparison of the two sets of curves 300 and 315 shows that the measured leakage data differ considerably from the calculated leakage data with regard to their absolute values.

[0037] In the Fig. 4a and Fig. Figure 4b illustrates the improvement in the accuracy of calculated leakage quantities resulting from the method according to the invention. According to the Fig. 3a and Fig. 3b here also represents the leakage quantity in mm. 3 / s plotted against the rail pressure (p_Rail) specified in bar, with the scales of the two axes being identical.

[0038] The in Fig. Figure 4a shows the set of curves 400, where the uppermost curve 405 was measured at a fuel temperature of 115 °C and the lowermost curve 410 at a fuel temperature of 65 °C. The curves in between decrease successively from top to bottom in 5 °C increments. In the Fig. In the family of curves 415 shown in 4b, which was again obtained by calculation, the uppermost curve 420 corresponds to the stated fuel temperature of 115 °C and the lowermost curve 425 to the stated fuel temperature of 65 °C, with the curves in between corresponding to the fuel temperature. Fig. 4a Remove from top to bottom.

[0039] The comparison of the in the Fig. 4a and Fig. 4b shown families of curves 400, 415 with the two in the Fig. 3a and Fig. The curve families 300, 315 shown in 3b clearly show that the curve family 415 calculated according to the invention agrees much better with the measured curve family 400 with respect to the absolute values.

[0040] The described method can be implemented either in the form of a control program in an existing control unit for controlling an internal combustion engine or in the form of a corresponding control unit.

Claims

[1] Method for operating an internal combustion engine with a storage injection system, wherein fuel is introduced into a pressure accumulator by means of a high-pressure pump and a pressure in the pressure accumulator is set by means of a metering unit controlling the high-pressure pump, and wherein the fuel stored in the pressure accumulator is introduced into at least one combustion chamber of the internal combustion engine by means of at least one injector and a quantity of fuel leakage from the pressure accumulator into a low-pressure area connected with the pressure accumulator caused by the at least one injector is calculated on the basis of a temperature (200) present in the area of ​​the injector (205, 210, 145, 155) and that the pressure in the pressure accumulator is set by means of the metering unit taking into account the calculated leakage quantity, characterized by , that the amount of leakage is calculated depending on the fuel temperature in the injector return line. [2] Method according to claim 1, characterized by , that the leakage quantity is additionally calculated on the basis of a target value (105) for the pressure in the pressure accumulator and an operating time (115) of the accumulator injection. [3] Method according to claim 2, characterized by , that the setpoint (105) for the pressure in the pressure accumulator is converted into a leakage quantity (135) using a first characteristic map (120), that the temperature (200) present in the area of ​​the injector is converted into a correction value (210) for the leakage quantity using a second characteristic map (205), and that the operating time (115) is converted into a current leakage quantity correction value (150) using a third characteristic map (130). [4] Method according to claim 3, characterized by , that the leakage quantity (135) and the correction value (210) are linked multiplicatively at a first linking point (145). [5] Method according to claim 4, characterized by, that the result of the linking (145) and the current leakage quantity correction value (150) are linked multiplicatively at a second linking point (155) and as a result of the second linking (155) a leakage request (160) is issued to the metering unit and / or a control unit (100). [6] Method according to any one of the preceding claims, characterized by , that the leakage quantity is calculated based on a leakage gap of at least one injector. [7] Method according to claim 6, characterized by , that a temperature increase due to compression of fuel by the high-pressure pump and a subsequent relaxation of the fuel pressure in the area of ​​the leakage gap is taken into account when calculating the leakage quantity. [8] Method according to claim 6 or 7, characterized by , that the fuel temperature and / or the coolant temperature of the internal combustion engine are taken into account when calculating the leakage rate. [9] Method according to any one of claims 6 to 8, characterized by , that the installation situation of the at least one injector and / or the pressure accumulator in the internal combustion engine, which depends on the respective type of internal combustion engine, is taken into account when calculating the leakage quantity. [10] Computer program that performs all steps of a method according to any one of claims 1 to 9 when executed on a computing device or a control device (100). [11] Computer program product comprising instructions which, when the program is executed by a computer, cause it to execute the method according to any one of claims 1 to 9.

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