Method for operating an internal combustion engine, control unit and internal combustion engine

Abstract

Method for operating a diesel engine (10) with a lambda control and with a nitrogen oxide storage catalyst in an exhaust gas section (14) of the diesel engine (10), comprising the steps: - Calculating a system setpoint (22) for lambda for lean operation (I) with lambda greater than one; - Providing a map setpoint (24) for lambda for a rich operation (III) with lambda less than one; - Generating a setpoint trajectory (28) for lambda for a transition (II) between lean operation (I) and rich operation (III); and - Guiding the setpoint (λ soll) for lambda on the target value trajectory (28) during a transition (II) between lean operation (I) and rich operation (III), characterized in that the target value trajectory (28) is determined by a shaping factor, wherein the target value trajectory (28) or the shaping factor is selected such that the course of the lambda target value, during a transition between lean operation and rich operation, is continuous and non-linear, wherein the method is carried out during a regeneration of the nitrogen oxide storage catalyst.

Description

[0001] The invention relates to a method for operating an internal combustion engine, a control unit for operating an internal combustion engine, and an internal combustion engine.

[0002] In lean operation with a lambda value greater than one and rich operation with a lambda value less than one, there is often no defined transition for lambda control. This leads to unnecessary controller excitation.

[0003] DE 102 34 849 A1 discloses a method for operating an internal combustion engine in which maintaining a desired torque takes priority over maintaining a predetermined lambda value. Methods and devices for controlling an internal combustion engine are also disclosed in DE 102 41 505 A1, DE 100 64 665 A1, DE 10 2011 003 493 A1, US 2004 / 0 154 288 A1 and US 2007 / 0 101 701 A1.

[0004] The invention is based on the objective of improving the lambda control for a diesel engine.

[0005] This problem is solved by a method according to claim 1, a control unit according to claim 4 or a diesel engine according to claim 5.

[0006] The inventive method for operating a diesel engine with lambda control comprises: - Calculating a system setpoint for lambda for lean operation with lambda greater than one; - Providing a map target value for lambda for rich operation with lambda less than one; - Generating a setpoint trajectory for lambda for a transition between lean and rich operation; and - Guiding the setpoint for lambda along the setpoint trajectory during a transition between lean and rich operation.

[0007] Furthermore, the method according to the invention comprises determining the target value trajectory by a shaping factor, wherein the target value trajectory or the shaping factor is selected such that the lambda target value is continuous and non-linear during a transition between lean and rich operation. According to the invention, the method is carried out during the regeneration of a nitrogen oxide storage catalyst in the exhaust system of a diesel engine.

[0008] The method according to the invention, through setpoint shaping along a trajectory, offers the advantage of improved lambda control during the transition from the lean to the rich phase and back. This avoids undesirably large control deviations. Furthermore, lambda control is already active during the transition between operating phases. The use of a system setpoint allows for individual calculation. Therefore, the setpoint does not need to be stored in a characteristic map, making it application-independent.

[0009] The system setpoint can be calculated based on the total combustion chamber gas mass, the total exhaust gas recirculation rate, the total torque-generating fuel quantity, and the stoichiometric air-fuel ratio. From these values, which are normally available to this system, the system setpoint can be calculated reliably and quickly.

[0010] The internal combustion engine is a diesel engine. The described method is designed according to the invention for a diesel engine, since, typically, in a diesel engine, changing the fuel quantity during lean operation leads to a greater change in torque.

[0011] The internal combustion engine features active exhaust aftertreatment with a nitrogen oxide storage catalyst. For the regeneration and desulfurization of the nitrogen oxide storage catalyst, it is necessary to switch the exhaust lambda value from lean to rich operation. In rich operation, the exhaust lambda value must then be maintained at a defined target value for a defined period of time at all engine operating points.

[0012] The target value trajectory is determined by a shaping factor. The shaping factor allows the target value trajectory to be adjusted. The target value trajectory is non-linear. The target value trajectory, or shaping factor, is chosen such that the lambda target value remains constant, even during transitions between lean and rich operation. This means that a lambda target value is always defined and that only small changes occur over time, without any abrupt jumps.

[0013] The setpoint trajectory can be monotonically increasing or monotonically decreasing, in particular strictly monotonically increasing or strictly monotonically decreasing. The setpoint trajectory can be differentiable, in particular continuously differentiable. Furthermore, it can be free of maxima or minima. In particular, the values ​​on the setpoint trajectory can lie between the values ​​of the initial and final values ​​of the setpoint trajectory.

[0014] The shaping factor can be a function of the transition time. This can be a simple straight line between the characteristic curve setpoint and the system setpoint, where the slope is given by the time duration. This is a particularly simple implementation of the setpoint trajectory.

[0015] The control unit according to the invention for operating an internal combustion engine is characterized in that it is configured to carry out the method described above. The same advantages and modifications apply as described above.

[0016] The internal combustion engine according to the invention with lambda control comprises a control unit as described above. The same advantages and modifications apply.

[0017] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. These show: Fig. 1 a schematic representation of an internal combustion engine with lambda control, and Fig. 2 a diagram showing the setpoint control of the lambda setpoint.

[0018] Fig. Figure 1 shows the part of an internal combustion engine 10 relevant for explaining the invention. In this embodiment, the internal combustion engine 10 is a diesel engine. In a combustion process 12, the supplied fuel-air mixture is burned and discharged via an exhaust gas section 14. The exhaust gas section 14 typically includes an exhaust aftertreatment system 16, here, for example, in the form of a nitrogen oxide storage catalyst. A lambda probe or lambda sensor 18 measures the lambda value, or the value of the exhaust gas lambda. Here, the lambda value is measured downstream of the exhaust aftertreatment system 16. Alternatively or additionally, the lambda value can also be measured upstream of the exhaust aftertreatment system 16, in the exhaust gas section 14.

[0019] The lambda sensor 18 outputs the measured lambda actual value to a control unit 20. The lambda control for the internal combustion engine 10 is performed in the control unit 20. Accordingly, the control unit 20 generates a lambda setpoint and outputs this to the combustion 12, or rather, controls the combustion 12 with the lambda setpoint.

[0020] Based on Fig. Section 2 now describes in more detail the setpoint control for lambda regulation calculated in control unit 20. The diagram of Fig. 2 is the lambda setpoint λ soll The graph is plotted over time t. Different operating phases of the internal combustion engine 10 are shown. Initially, the internal combustion engine starts in lean operation I. After a subsequent transition II, the internal combustion engine 10 transitions into rich operation III. Rich operation III is followed by another transition II, which then returns to lean operation I.

[0021] For lean operation I, a system setpoint value 22 for lambda is calculated. The system setpoint value is calculated according to the following equation: Lambda system setpoint=gas mass setpoint⋅(1−AGRRate setpoint)14.5⋅fuel quantity setpoint

[0022] Where the gas mass Sollwert which corresponds to the total combustion chamber gas mass, EGR rate Sollwert corresponds to the total exhaust gas recirculation rate, current fuel quantity Sollwert which corresponds to the total amount of fuel generating the moment and 14.5 is the stoichiometric air-fuel ratio for diesel fuel.

[0023] For rich operation III and, if applicable, also for transitions II, a map setpoint value 24 is provided or determined. This serves, for example, for the regeneration and desulfurization of the exhaust aftertreatment system 16. For the continuous control of the lambda setpoint λ SollA setpoint trajectory 26 is generated, which connects the system setpoint 22 with the characteristic map setpoint 24 in transition region II. A linear setpoint trajectory 26, which is not covered by the claimed invention, and a nonlinear setpoint trajectory 28, which is covered by the claimed invention, are shown as examples. The setpoint λ soll One of the two trajectories 26 or 28 will be followed.

[0024] The following equation describes the calculation of the lambda setpoint for the shaped transition from the lambda system setpoint 22 to the lambda map setpoint 24: Lambda setpoint=Lambdasystem setpoint+facforming⋅(Lambda field setpoint−Lambdasystem setpoint

[0025] The following equation describes the calculation of the lambda setpoint λ. soll for the shaped transition from the lambda map target value 24 to the lambda system target value 22: Lambda setpoint=Lambda characteristic field set value+facforming⋅(Lambda system set value−Lambda characteristic field set value)

[0026] The size fac Formung is a shaping factor that determines the target value trajectory 26 or 28. The shaping factor is a function of the time duration for transition II and can be defined for transition II. The shaping factor can take on a value between 0 and 1. The shaping factor follows the following equation: FacFormung=f (ΔtTransition);facFormungε[0;1]

[0027] As can be seen, the target value λ soll at any given time a defined value and the guide curve for the setpoint λ soll has a continuous course, meaning that there are no jumps in the course for the target value λ. soll are available.

[0028] This relieves any downstream PIG controller from a setpoint jump. The setpoint control can also operate in parallel with an existing controller and can support it. Reference symbol list 10 Internal combustion engine 12 Combustion 14 Exhaust system 16 Exhaust gas aftertreatment 18 Lambda sensor 20 Control unit 22 System setpoint 24 Key map setpoint 26 Setpoint trajectory 28 Setpoint trajectory Lean operation II Transition III Fat operation

Claims

[1] Method for operating a diesel engine (10) with a lambda control and with a nitrogen oxide storage catalyst in an exhaust gas section (14) of the diesel engine (10), comprising the steps: - Calculating a system setpoint (22) for lambda for lean operation (I) with lambda greater than one; - Providing a map setpoint (24) for lambda for a rich operation (III) with lambda less than one; - Generating a setpoint trajectory (28) for lambda for a transition (II) between lean operation (I) and rich operation (III); and - Guiding the setpoint (λ soll ) for lambda on the setpoint trajectory (28) during a transition (II) between lean operation (I) and rich operation (III), characterized by, that the target value trajectory (28) is determined by a shaping factor, wherein the target value trajectory (28) or the shaping factor is chosen such that the course of the lambda target value, during a transition between lean and rich operation, is continuous and non-linear, wherein the procedure is carried out during a regeneration of the nitrogen oxide storage catalyst. [2] Method according to claim 1, characterized by , that the system setpoint (22) is calculated as a function of a total combustion chamber gas mass, a total exhaust gas recirculation rate, a total torque-generating fuel quantity and the stoichiometric air ratio for the fuel. [3] Method according to claim 1, characterized by , that the shaping factor is a function of the duration of the transition (II). [4] Control unit for operating a diesel engine, characterized by that it is equipped to carry out the procedure according to one of the preceding claims. [5] Diesel engine with lambda control, characterized by , that the diesel engine comprises a control unit (20) according to claim 4.

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