Method for controlling an injection by a fuel injection unit, control device and computer program

Abstract

Method for controlling an injection by a fuel injection unit (3), in which, within the framework of the control, the injection duration (10) and an injection flow rate (11) used for the calculation of the injection duration (10) are calculated, characterized in that the calculation of the injection flow rate (11) is carried out within the framework of a first PID control (21) and that, when a gas fraction in the exhaust gas is determined, an error fraction (13) is calculated and the injection flow rate (11) is determined on the basis of this error fraction (13).

Description

[0001] The present invention relates to a method for controlling an injection by a fuel injection unit in an internal combustion engine. Furthermore, the present invention relates to a control device for implementing the method according to the invention and to a computer program.

[0002] Internal combustion engines with fuel injectors typically exhibit a deviation in the injected fuel quantity from the specified fuel quantity over time. In addition, the deviations occurring between the individual fuel injectors vary. The deviations in the fuel quantities allocated to the individual combustion chambers are primarily due to general aging of the fuel injectors. However, deviations in the fuel quantity can also occur due to an incorrectly adjusted injector flow rate due to manufacturing defects. Both hardware-induced deviations—the deviation due to temporal aging and the deviation due to an initial manufacturing defect—lead to different injected fuel quantities in the respective combustion cylinder for the same injection duration.The calculation of the injection duration, which is typically performed at very short time intervals these days, is based on a multitude of parameters within the engine control unit. Two of the main parameters required for the calculation are the measured air quantity and the injection flow rate stored in the device driver. The injected fuel quantity is specified for each cylinder at a stoichiometric air-to-fuel ratio with a lambda value equal to 1. However, if the injected fuel quantity for each cylinder changes due to aging of the fuel injectors or due to an initial manufacturing defect, the lambda value must be corrected by the lambda control. A correction of the lambda value calculation is typically performed by the lambda control in such a way that the injection duration is corrected.However, this can lead to the problem that the lambda control exceeds its tolerance range, resulting in inaccurate control. This is especially the case if no precise engine mapping has been performed beforehand to create a characteristic map.

[0003] US 5,657,735 A discloses an adaptive controller for calculating a feedback correction coefficient. The fuel metering control system of US 5,657,735 A is designed for an internal combustion engine with a plurality of cylinders. The system comprises an air-fuel ratio sensor and an engine operating condition detecting device for detecting engine operating conditions, including the engine speed and the engine load. The fuel quantity of the fuel injection is determined based on the engine speed and the engine load. Thus, the injected fuel quantity can be corrected using the feedback correction coefficient, so that the detected air-fuel ratio is adjusted to the desired air-fuel ratio.

[0004] US 6,550,465 B2 discloses a cylinder air-fuel ratio estimation system for an internal combustion engine. The internal combustion engine can be operated in one of several selectable operating modes. The estimation system selects a data set from a data set of sampled air-fuel ratios such that the air-fuel ratio can be accurately estimated for each cylinder for the selected operating mode.

[0005] US 5,657,736 A discloses a fuel metering control system for an internal combustion engine with a plurality of cylinders. The system includes an air-fuel ratio sensor and an engine operating condition detector. The injected fuel quantity is determined based on mapped data corresponding to the engine speed and engine load. Feedback correction coefficients are calculated via a control unit to correct the amount of base fuel injections, thereby reducing the deviations between the individual cylinder air-fuel idle rates.

[0006] US 5,915,359 A discloses a method and system for determining and controlling the air-fuel ratio during engine cold-start operation. The desired air-fuel ratio is compared with an estimated air-fuel ratio and used to control the desired air-fuel ratio.

[0007] US 6,698,186 B2 discloses a device for controlling an air-fuel ratio of an internal combustion engine. The desired air-fuel ratio for an exhaust gas located upstream of a catalyst is determined sequentially to converge a sensor value downstream of the catalyst to a target value. Control is performed via the amount of fuel supplied to the internal combustion engine and is based on time series data from a linear deterioration condition evaluation function.

[0008] US Pat. No. 5,781,875 A discloses a system for controlling the fuel quantity of an internal combustion engine. The system comprises three feedback loops, each of which calculates a feedback correction coefficient to correct the fuel injection quantity. Two of the three feedback loops are based on PID control. This minimizes the deviation of the fuel ratios between the cylinders.

[0009] From DE 10 2008 042 714 A1 a device for detecting a fuel injection state is known, with which a characteristic waveform of a fuel injection rate is calculated on the basis of a fluctuation waveform of a pressure detected by means of a fuel pressure sensor and is used for corrections of subsequent injections.

[0010] DE 10 2015 117 516 A1 discloses a fuel injection control device having a correction section that performs an air-fuel ratio correction to correct the fuel injection amount based on an air-fuel ratio detected by an air-fuel ratio sensor. Different air-fuel ratio corrections are performed for a full-lift injection and a partial-lift injection.

[0011] From DE 10 2010 036 485 B3 a method for controlling an internal combustion engine with a fuel injection is known, in which a deviation of a flow of the injection valve from a nominal value is determined on the basis of the exhaust gas composition and the injection valve is controlled with an injection duration adapted to compensate for the determined deviation.

[0012] DE 10 2007 000 211 A1 describes a fuel injection control device for controlling the power of an internal combustion engine in which a multiple fuel injection is performed within a combustion cycle. The control device comprises a device for calculating a predicted value of an oxygen concentration in the exhaust gas of the internal combustion engine and a learning device. The learning device is configured to convert the difference between a detected value and a predicted value of the oxygen concentration into a difference per injection of the multiple injection such that an amount of deviation in the injection characteristic of a fuel injection valve is learned.

[0013] DE 692 00 015 T2 discloses a method for controlling and diagnosing malfunctions in a fuel system of an internal combustion engine. An air-fuel mixture is supplied to the engine, and the air-fuel ratio of the mixture is measured. Furthermore, a control correction value for the mixture is determined as a function of the measured air-fuel ratio. The control correction value contains an integral correction term to return the air-fuel ratio to a desired air-fuel ratio. The integral correction term can be set to an integral limit value. Furthermore, a learning correction term is adjusted as a function of the integral correction term in such a way that the air-fuel ratio is returned to the desired air-fuel ratio. The air-fuel mixture is then adjusted based on the control and learning correction terms.If the learning correction term reaches a predetermined limit and the integral correction term is also at the integral limit, a fault condition is indicated.

[0014] DE 10 2004 015 835 A1 discloses a device for controlling an internal combustion engine with multiple cylinders. The device comprises a first unit in which an adaptation value for adjusting the control of the respective injection valve is determined depending on the output variable of a first controller, whose controlled variable is characteristic of the air / fuel ratio in the respective cylinder. Furthermore, the device comprises a second unit in which an adaptation value for adjusting the control of the respective pulse charging valve is determined depending on the output variable of a second controller, whose controlled variable is a rough running value derived from a measurement signal that is characteristic of the crankshaft speed, or whose controlled variable is the torque generated by the internal combustion engine.The first and second controllers are designed so that the control speed of the first controller is greater than the control speed of the second controller.

[0015] DE 103 37 228 A1 mentions fuel mixture adaptation methods with adaptation routines, which usually consist of slow controllers (I controllers) superimposed on the normal internal lambda control based on LSU (fast loop). The value of the I component of the superimposed adaptation controller corresponds to the learned systematic mixture pre-control error. The systematic error of the mixture pre-control is detected by integrating lambda deviations under selected operating conditions, and the mixture pre-control maps for the fuel quantity are adapted using correction factors or modified map values.

[0016] DE 103 07 004 B3 discloses a method for controlling an internal combustion engine with lambda control, which uses simple means to reduce exhaust emissions before the lambda control is activated. The method is based on the finding that, depending on the starting temperature of the internal combustion engine, the mixture pre-control leads to varying degrees of deviations in the combustion lambda and thus to worse emission values ​​than with a reference system. Therefore, an adaptation value is used to determine the fuel mixture, which takes into account the temperature of the internal combustion engine at start-up. The adaptation value is preferably determined from an integral component of the lambda controller. The integral component can be used to correct the pre-control if necessary.

[0017] It is an object of the present invention to provide an improved method for controlling an injection by a fuel injection unit. Further objects of the present invention are to provide a control device and a computer program suitable for implementing the method according to the invention.

[0018] The first object is achieved by a method according to claim 1. The second object is achieved by a control device according to claim 6. The third object is achieved by a computer program according to claim 10. Further embodiments of the present invention are disclosed in the subclaims.

[0019] A method for controlling an injection by a fuel injection unit is provided. Within this control, an injection duration is calculated. The injection flow rate used to calculate the injection duration is calculated.

[0020] According to the invention, the injection flow rate is calculated within the framework of a first PID control. According to the invention, an error component is also calculated when a gas content in the exhaust gas is determined. The injection flow rate is calculated based on this error component. The injection flow rate calculation is thus dependent on a control unit that measures a gas content in the exhaust gas. This control unit determines an error component, whereby the error component obtained through this calculation influences the injection flow rate calculation. The error component calculated by the measuring unit is therefore also included in the calculation of the injection duration via the injection flow rate calculation.

[0021] In a prior art engine control unit, the injection duration is determined based on an injection flow rate stored in the device driver, so that the injection duration is always based on the same flow rate. Deviations in the injection flow rate are not taken into account in the prior art. A deviation in the injection flow rate can occur, for example, if the fuel injection unit has a manufacturing defect. Furthermore, a deviation in the injection flow rate can occur if, for example, the injection nozzles coke over an extended period of time. This deviation in the injection flow rate is taken into account according to the invention by performing an additional calculation in the engine control unit, in which the injection flow rate used to calculate the injection duration is calculated.In particular, the injection flow rate can be calculated based on an output variable of the lambda control. One advantage of the present invention is therefore that an injection flow rate can be used that may differ from the injection flow rate stored in the device driver. This allows changes in the injection flow rate due to manufacturing errors or coking to be compensated. Furthermore, the calculated injection flow rate reduces the control effort of the lambda control, so that the control target can be achieved more quickly than when using the injection flow rate stored in the device driver. Furthermore, since the invention makes it possible to use injectors for which the exact injection flow rate has not been determined, the manufacturing costs and time for injector production can be reduced.

[0022] According to one embodiment of the present invention, the injection duration can be calculated within the framework of a second PID control.

[0023] According to one embodiment of the present invention, the error component is calculated within the framework of a third PID control. The error component is the I component of the third PID control. By calculating the injection flow rate based on the I error component of the third PID control, deviations in the injection flow rate can be largely corrected. Factory pre-calibration of the fuel injectors is thus unnecessary.

[0024] According to one embodiment of the present invention, an error component is calculated when determining the oxygen content in the exhaust gas, on the basis of which error component the injection flow rate is in turn determined.

[0025] To implement the method according to the invention, the present invention provides a control device for controlling an injection by a fuel injection unit. The control device comprises an injection duration calculation device that calculates an injection duration taking into account an injection flow rate. Furthermore, the control device has an injection flow rate calculation device that calculates the injection flow rate and outputs the calculated injection flow rate to the injection duration calculation device.

[0026] According to the invention, the control device comprises a lambda control device. The lambda control device receives a signal from a lambda probe that measures the oxygen content in the exhaust gas. The lambda control device is further configured to calculate the error component and output this error component to the injection flow rate calculation device. The lambda probe can, in particular, be a broadband probe that measures the oxygen content in the exhaust gas.

[0027] According to the invention, a first PID controller is provided to calculate the injection flow rate. A second PID controller can be provided to calculate the injection duration. According to such an embodiment of the present invention, the injection duration and injection flow rate can be calculated independently of one another. If both a first PID controller and a second PID controller are present, a low-pass filter is preferably provided to separate the first PID controller and the second PID controller. The injection duration calculation takes place on short time scales. The PID control of the injection duration calculation is thus a fast control. The injection flow rate calculation, on the other hand, takes place on longer time scales. The associated PID control is thus a slow control.To prevent mutual interference and oscillation between the PID control for calculating the injection duration and the PID control for calculating the injection flow rate, these two control systems are separated by a low-pass filter. This eliminates feedback, allowing the injection flow rate to be calculated independently of the injection duration.

[0028] According to the invention, a computer program with program code is also provided. When executed in the control device, the program code causes the control device to perform the method according to the invention.

[0029] Further features, properties and advantages of the present invention will become apparent from the following embodiment with reference to the accompanying figures. Fig. 1 shows a motor vehicle with a device according to the invention for applying a method according to the invention. Fig. 2 shows a schematic representation of the components of the device for carrying out the method according to the invention.

[0030] With reference to the figures, an exemplary embodiment of the method according to the invention for controlling an injection by a fuel injection unit 3 and a device according to the invention for implementing the method are described below. Within the scope of the control, the injection duration 10 is calculated. The method according to the invention ensures that a temporal change in the injection flow rate 11, whether due to a manufacturing defect or, for example, due to coking of the fuel injection unit 3, is included in the calculation of the fuel injection duration 10.

[0031] Fig. Figure 2 shows the device for carrying out the method in a schematic representation. The device, which is part of the engine control unit 5, in the present embodiment part of a fuel injection controller 6 (see Fig. 1) of the engine control 5, comprises an injection duration calculation device 20 for calculating an injection duration 10 and an injection flow rate calculation device 21 for calculating an injection flow rate 11. According to the invention, the injection flow rate 11 output by the injection flow rate calculation device 21 is an input parameter of the injection duration calculation device 20, cf. Fig. 2.

[0032] In the present embodiment of the device according to the invention, the injection duration calculation device 20 is part of a PID control system. Furthermore, in the present embodiment, the injection flow rate calculation device 21 is part of another PID control system. Here, the PID control system containing the injection duration calculation device 20 and the PID control system containing the injection flow rate calculation 21 are separated from each other by a low-pass filter 12. The PID control system that performs the injection duration calculation takes place on very short time scales, whereas the PID control system that performs the injection flow rate calculation takes place on long time scales. The low-pass filter 12 separates the two PID control systems from each other, so that feedback between the two PID control systems can be excluded.

[0033] In addition, the device according to the invention in the present embodiment comprises a third PID control, which in the present embodiment controls the fuel-air ratio on the basis of the measurement signal of the measuring unit 4. The measuring unit 4 (see Fig. 1) is therefore a lambda probe 4 in the present embodiment, and the third control is a lambda control. The PID control of the measuring unit 4 calculates several error components, including the I component 13 of the PID control. The I component 13 is an output parameter of the PID control and, according to the invention, is forwarded as an input parameter to the injection flow rate calculation 21. According to the invention, this additional calculation allows injection flow fluctuations in the engine control system to be compensated.

[0034] Within the engine control unit, the lambda correction works with a PID controller 22 (see Fig. 2). If there is a deviation of the measured lambda value from the setpoint, the PID controller 22 of the lambda control outputs an output signal to correct the lambda value. This output signal comprises a proportional component (P component), an incremental component (I component), and a differential component (D component). The incremental component, i.e. the I component 13, is identical to the deviation that occurs when the air flow calculation is incorrect. The air flow calculation unit used to calculate the air flow is a separate section within the engine control unit 5. The value specified by the incremental control component of the third PID controller 22 can also be identical to the deviation that is based on the flow rate characteristics of the injection itself. By doing this, frequently occurring fluctuations in the injection flow rate 11, which for example occur due todue to manufacturing defects or due to aging phenomena occurring over time.

[0035] In the present embodiment, the actual incremental part of the lambda control 22, i.e., the I component 13, is multiplied by the constant value of the lambda control 22. The constant value describes the injector flow rate.

[0036] A particular advantage of the present invention is that, when the injection flow rate 11 for each fuel injection unit 3, in particular for each injection nozzle, is not precisely known, manufacturing costs and time can be saved. Previously, each fuel injection unit 3 had to be calibrated to a precisely metered injection flow rate 11 during injection unit production. This costs a lot of time and money.

[0037] A further advantage of the present invention is that the lambda control 22 does not have to work very hard and the deviation of the measured lambda value from the target value can be reduced more quickly than with current methods.

[0038] The device according to the invention in the present embodiment is part of a motor vehicle. This comprises an internal combustion engine 2, a fuel injection unit 3, and a measuring unit, see. Fig.1. The fuel injection unit 3 is connected upstream of the internal combustion engine 2, and the measuring unit 4 is connected downstream of the internal combustion engine 2. Furthermore, the measuring unit 4 is connected to the engine control unit 5 for signal transmission. In the present exemplary embodiment, the measuring unit 4 measures the oxygen content in the exhaust gas, so that the measuring unit in the present exemplary embodiment is a lambda probe 4. The method according to the invention is carried out by the fuel injection controller 6 in the present exemplary embodiment, but it can also be carried out by other units of the engine control unit 5.

[0039] The lambda sensor 4 is designed to measure the oxygen content in the exhaust gas. The exhaust gas passing the lambda sensor 4 is produced by the combustion of the fuel in the internal combustion engine 2. The lambda sensor 4 compares the residual oxygen content in the exhaust gas with the oxygen content of the atmospheric air surrounding the lambda sensor 4. The combustion air ratio lambda can be determined from this and adjusted based on the determined value. The typical measuring principles of a lambda sensor 4 are measuring the voltage of a solid-state electrolyte, for example, with a Nernst probe, or measuring a change in the resistance of a ceramic, for example, with a resistance probe.

[0040] In the present embodiment, the measuring unit is in particular a broadband probe 4 which measures the oxygen content in the exhaust gas.

[0041] The device according to the invention is typically used to meter the amount of fuel such that the combustion air ratio results in optimal performance of the exhaust gas catalytic converter. The fuel supply is metered indirectly via a throttle valve. The wider the throttle valve, which regulates the intake air to the combustion chamber, is opened, the more fuel must be fed into the combustion chamber via the fuel injection unit 3 in order to set the correct lambda value, i.e., the correct combustion air ratio. For example, during spontaneous acceleration of the motor vehicle 1, the throttle valve is opened more widely so that more intake air can enter the combustion chamber. For this purpose, engine electronics regulate the injection of fuel by the fuel injection unit 3 with the aid of the lambda control 22.

[0042] To increase the efficiency of the internal combustion engine 2 and thus also improve power output and exhaust gas quality, especially when using a three-way catalytic converter, where the precise air / fuel ratio is crucial, gasoline injection is used to take advantage of the aforementioned benefits. A distinction is made between direct injection, in which the fuel is injected directly into the combustion chamber, and intake manifold injection, in which the fuel is injected into a chamber upstream of the combustion chamber, usually the intake manifold.

[0043] Coking of the fuel injection unit 3, which is prevented by the invention, occurs, for example, in a gasoline- or diesel-powered motor vehicle 1 with direct injection. Direct injection, particularly in gasoline engines, causes soot particle emissions, which are related to the inhomogeneity of the fuel-air mixture and occur primarily when the mixture is locally too rich, i.e., too low in oxygen, and / or the ignited mixture has come too close to the combustion chamber wall or the piston wall.

[0044] The present invention has been described in detail using an exemplary embodiment for illustrative purposes. However, one skilled in the art will recognize that deviations from the exemplary embodiment are possible. Therefore, the invention is not intended to be limited to the exemplary embodiment, but only by the appended claims. List of reference symbols 1 motor vehicle 2 combustion engine 3 Fuel injection unit 4 lambda probe / broadband probe 5 Engine control 6 fuel injection regulator 10 Injection duration 11 Injection flow rate 12 low-pass filters 13 Error component / I component 20 Injection duration calculation device 21 Injection flow rate calculation device 22 Lambda control

Claims

[1] Method for controlling an injection by a fuel injection unit (3), in which the injection duration (10) and an injection flow rate (11) used for calculating the injection duration (10) are calculated as part of the control, characterized by that the calculation of the injection flow rate (11) takes place within the framework of a first PID control (21) and that when a gas proportion in the exhaust gas is determined, an error proportion (13) is calculated and the injection flow rate (11) is determined on the basis of this error proportion (13). [2] Method according to claim 1, characterized by that the calculation of the injection duration (10) takes place within the framework of a second PID control (20). [3] Method according to claim 1 or 2, characterized by that the calculation of the error component (13) takes place within the framework of a third PID control (22) and that the error component (13) is the I component (13) of the third PID control (22). [4] Method according to one of claims 1 to 3, characterized by that the injection flow rate (11) is determined on the basis of an error component (13) which is calculated as part of determining an oxygen component in the exhaust gas. [5] Method according to claim 3 or 4, characterized by that the third PID control (22) is a lambda control and the error component (13) is an output variable of the lambda control. [6] Control device for controlling an injection by a fuel injection unit (3) for carrying out a method according to one of claims 1 to 5, comprising an injection duration calculation device (20) which calculates an injection duration (10) taking into account an injection flow rate (11), and an injection flow rate calculation device (21) which calculates the injection flow rate (11) and outputs it to the injection duration calculation device (20) characterized bya lambda control device (22) which calculates an error component (13) of a determination of a gas component in the exhaust gas and outputs it to the injection flow rate calculation device (21), and in that a first PID controller (21) is provided for calculating the injection flow rate (11). [7] Control device according to claim 6, characterized by that the lambda control device (22) is connected to a broadband probe (4) measuring the oxygen content in the exhaust gas for receiving a signal representing the oxygen content in the exhaust gas. [8] Control device according to claim 6 or 7, characterized by that a second PID controller (20) is provided to calculate the injection duration (10). [9] Control device according to claim 8, characterized by that a low-pass filter (12) separates the first PID controller (21) and the second PID controller (22) from each other. [10] Computer program with program code for controlling an injection by a fuel injection unit (3), wherein the program code, when executed in a control device, causes the control device to carry out the method according to one of claims 1 to 5.

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