Method for operating an internal combustion engine with high-pressure and low-pressure exhaust gas recirculation

Description

[0001] The invention relates to a method for operating an internal combustion engine, wherein a turbine of an exhaust gas turbocharger arranged in an exhaust system of the internal combustion engine is driven by exhaust gas from the internal combustion engine, and a compressor of the exhaust gas turbocharger driven by the turbine and arranged in a combustion air system of the internal combustion engine compresses combustion air, wherein in a high-pressure exhaust gas recirculation loop (HP-EGR loop) exhaust gas is diverted upstream of the turbine and mixed with the combustion air downstream of the compressor, wherein in a low-pressure exhaust gas recirculation loop (LP-EGR loop) exhaust gas is diverted downstream of the turbine and mixed with the combustion air upstream of the compressor, wherein in the LP-EGR loop the exhaust gas is cleaned by a low-pressure exhaust gas recirculation filter (LP-EGR filter),wherein, depending on an operating state of the internal combustion engine, a predetermined value for a total exhaust gas recirculation rate (total EGR rate) is determined, according to the preamble of patent claim 1.,

[0002] DE 10 2011 080 291 A1 discloses an internal combustion engine with high-pressure exhaust gas recirculation (HP-EGR) and low-pressure exhaust gas recirculation (LP-EGR). This is based on the realization that a turbocharged engine can have higher combustion and exhaust temperatures than a naturally aspirated engine with equivalent output. Such higher temperatures can increase nitrogen oxide (NOx) emissions and cause accelerated material aging in the engine and its associated exhaust system. Exhaust gas recirculation (EGR) is one approach to counteract these effects. EGR strategies reduce the oxygen content of the intake air charge by diluting it with exhaust gas. Using the diluted air-exhaust mixture instead of regular air to support combustion in the engine results in lower combustion and exhaust temperatures.EGR also improves fuel efficiency in gasoline engines by reducing throttling losses and heat dissipation.

[0003] In a turbocharged engine system equipped with a turbocharger compressor and a turbine, exhaust gas can be recirculated through a high-pressure (HP) EGR loop or a low-pressure (LP) EGR loop. In the HP EGR loop, the exhaust gas is diverted upstream of the turbine and mixed with the intake air downstream of the compressor. In the LP EGR loop, the exhaust gas is diverted downstream of the turbine and mixed with the intake air upstream of the compressor. HP and LP EGR strategies achieve optimal efficiency in different regions of the engine load-speed map. For example, in turbocharged gasoline engines with stoichiometric air-fuel ratios, HP EGR is desirable at low loads where the intake vacuum provides a high flow potential. LP EGR is desirable at higher loads where the LP EGR loop provides the greater flow potential.Various other trade-offs between the two strategies also exist for both gasoline and diesel engines. Such complementarity has motivated mechanical engineers to consider redundant EGR systems that incorporate both an HP EGR loop and an LP EGR loop.

[0004] A low-pressure EGR cooler is located in the low-pressure EGR loop. An upstream filter (low-pressure EGR filter) in the low-pressure EGR loop traps residues from the exhaust system to prevent damage to a compressor of an exhaust gas turbocharger (ATL compressor) downstream of the low-pressure EGR loop. The low-pressure EGR filter is monitored by a differential pressure sensor. If the pressure loss across the low-pressure EGR filter exceeds a predetermined threshold, an engine malfunction is indicated. This leads to an increased number of failures.

[0005] To prevent this, careful manufacturing of the exhaust system and exhaust gas treatment system is currently required to ensure that minimal production residues enter the LP EGR loop. However, further particulate deposits during operation over the engine's lifetime cannot be completely prevented.

[0006] From KR 101 198 811 B1, an internal combustion engine with a low-pressure EGR system and a high-pressure EGR system is known. The low-pressure EGR system comprises: a low-pressure EGR valve arranged in or on a low-pressure EGR line to adjust the amount of recirculated exhaust gas; pressure sensors arranged on a downstream and upstream side of the low-pressure EGR valve to detect a pressure difference between the downstream and upstream sides of the low-pressure EGR valve; and a control section that uses the measured or detected pressure difference to control the opening rate of the low-pressure EGR valve. An emergency filter is arranged adjacent to the low-pressure EGR valve. A turbocharger is connected to an exhaust line and an intake line.The turbocharger includes a turbine that uses hot, high-pressure exhaust gas flowing in the exhaust passage to generate rotational energy. A compressor of the turbocharger is connected to the turbine to compress intake air from the intake passage connected to the internal combustion engine, thereby supplying the (compressed) intake air to the engine. The control section can prevent the backflow of the recirculated exhaust gas by adjusting the opening rate of the low-pressure EGR valve if the pressure difference measured by the pressure sensor is smaller than a predetermined target value. That is, the opening rate of the low-pressure EGR valve is reduced to increase the pressure difference between downstream and upstream of the low-pressure EGR valve.A backflow in a high-pressure EGR line of the high-pressure EGR system can be prevented by disposing additional pressure sensors on a downstream side and on an upstream side of a high-pressure EGR valve to adjust the high-pressure EGR gas amount by means of the high-pressure EGR valve.

[0007] EP 1 808 591 A1 discloses an internal combustion engine with an exhaust gas turbocharger and a low-pressure EGR loop and a high-pressure EGR loop. A filter is arranged downstream of a turbine of the exhaust gas turbocharger. The low-pressure EGR line branches off downstream of the filter. A cooler is arranged within the low-pressure EGR loop. A pressure sensor measures the pressure difference between an inlet and an outlet of the low-pressure EGR loop. If the measured pressure difference is greater than a threshold value, the low-pressure EGR flow is controlled such that the pressure difference drops below the threshold value, with the remaining exhaust gas to be recirculated being routed via the high-pressure EGR loop.

[0008] The invention is based on the object of improving a method of the above-mentioned type in such a way that fewer engine operating malfunctions occur due to a clogged ND-EGR filter, which require undesirable premature maintenance of the internal combustion engine in a specialist workshop.

[0009] This object is achieved according to the invention by a method of the above-mentioned type having the features characterized in claim 1. Advantageous embodiments of the invention are described in the further claims.

[0010] For this purpose, in a method of the above-mentioned type, it is provided according to the invention that at least one operating parameter of the internal combustion engine is determined, wherein a proportion of a low-pressure exhaust gas recirculation rate (LP-EGR rate) in the total EGR rate and a proportion of a high-pressure exhaust gas recirculation rate (HD-EGR rate) are determined as a function of a value of the operating parameter.

[0011] This has the advantage that optimized, emission-neutral operation of the internal combustion engine is guaranteed for every operating state of the internal combustion engine.

[0012] A further reduction of undesirable emissions is achieved by reducing or increasing the proportion of the LP EGR rate in the total EGR rate and increasing or reducing the proportion of the HP EGR rate in the total EGR rate accordingly, depending on the operating parameters of the internal combustion engine, so that the total EGR rate reaches the predetermined value.

[0013] In a particularly advantageous manner, a value of a measure of a pressure difference, in particular a pressure difference between a first predetermined point upstream of the ND-EGR filter and a second predetermined point downstream of the ND-EGR filter, is determined as an operating parameter of the internal combustion engine in the exhaust system, wherein a proportion of a low-pressure exhaust gas recirculation rate (ND-EGR rate) of the total EGR rate and a proportion of a high-pressure exhaust gas recirculation rate (HD-EGR rate) are determined as a function of the value of the measure of the pressure difference, in particular of the pressure difference.

[0014] This has the advantage that the operating time of the internal combustion engine until a necessary maintenance in a specialist workshop can be delayed or postponed due to a clogged LP-EGR filter, resulting in lower operating costs for the internal combustion engine, while at the same time ensuring emission-neutral operation of the internal combustion engine despite this extension of the maintenance interval.

[0015] An effective and functionally reliable reduction of the value of a measure of a pressure difference, in particular of the pressure difference, is achieved by reducing the proportion of the LP EGR rate in the total EGR rate and increasing the proportion of the HP EGR rate in the total EGR rate accordingly as the value of a measure of a pressure difference, in particular of the pressure difference, increases, so that the total EGR rate reaches the predetermined value.

[0016] A targeted extension of the maintenance interval to the maximum possible duration is achieved by reducing the proportion of the LP EGR rate in the total EGR rate in such a way that a value for the pressure difference remains below a predetermined value at which an operating fault is indicated.

[0017] In order to be able to identify any need to change the LP-EGR filter or to carry out measures to reduce filter deposits during a workshop visit that is already taking place, the value of the measure for a pressure difference, in particular the pressure difference, is stored in a retrievable manner.

[0018] A further delay in the indication of an engine malfunction despite a clogged LP-EGR filter by any desired period of time is achieved by setting the LP-EGR rate to zero when the predetermined value of the measure for a pressure difference, in particular for the pressure difference, can no longer be undercut by more than a predetermined value by reducing the LP-EGR rate.

[0019] A problem-free replacement of a portion of the LP EGR rate with a corresponding increase in the HP EGR rate is achieved by cooling the recirculated exhaust gas in the HP EGR loop. This ensures that the temperature of the mixture of HP EGR and charge or combustion air does not exceed the temperature of the mixture of LP EGR and charge or combustion air.

[0020] The method according to the invention can be implemented in a computer-implemented embodiment: A control device according to the invention for an internal combustion engine comprises a computing unit and a memory unit. According to the invention, a computer program is filed or stored in the memory unit. By means of the computer program, when it is at least partially executed on the computing unit, a method for operating an internal combustion engine with features or combinations of features according to this representation is carried out.

[0021] The invention will be explained in more detail below with reference to the description of a preferred embodiment and the drawing. Fig. 1 shows an exemplary embodiment of an internal combustion engine for carrying out the method according to the invention in a schematic block diagram; Fig. 2 shows a graphical representation of exhaust gas recirculation rates according to the prior art; and Fig. 3 shows a graphical representation of exhaust gas recirculation rates according to the present invention.

[0022] The Fig. 1 The internal combustion engine shown by way of example comprises an engine block 10 with working cylinders 12, a combustion air system 14 for supplying combustion air 16 to the working cylinders 12 and an exhaust system 18 for discharging exhaust gas 20 from the working cylinders 12.

[0023] The combustion air system 14 comprises an air filter 22, a compressor 24 of an exhaust gas turbocharger (ATL) 26, a charge air cooler 28, a throttle valve 30, and an intake manifold 32. The exhaust system 18 comprises an exhaust manifold 34, a turbine 36 of the ATL 26, a catalytic converter 38, a relative pressure sensor 40, a particulate filter 42, which is in particular a diesel particulate filter (DPF), and an exhaust flap 44.

[0024] A low-pressure exhaust gas recirculation loop (LP-EGR loop) 46 is provided for exhaust gas recirculation, i.e., for recirculating exhaust gas 20 from the exhaust system 18 into the combustion air system 14. This LP-EGR loop 46 branches off from the exhaust system 18 downstream of the turbine 36 and flows into the combustion air system 14 upstream of the compressor 24. The LP-EGR loop 46 comprises a low-pressure exhaust gas recirculation filter (LP-EGR filter) 48, a low-pressure exhaust gas recirculation cooler (LP-EGR cooler) 50, and a low-pressure exhaust gas recirculation valve (LP-EGR valve) 52.

[0025] Furthermore, a high-pressure exhaust gas recirculation loop (HD-EGR loop) 54 is provided for exhaust gas recirculation, ie for returning exhaust gas 20 from the exhaust system 18 to the combustion air system 14. This HP-EGR loop 54 branches off from the exhaust manifold 34 and flows into the combustion air system 14 downstream of the compressor 24. The HP-EGR loop 54 comprises a high-pressure exhaust gas recirculation valve (HP-EGR valve) 56, a high-pressure exhaust gas recirculation cooler (HP-EGR cooler) 58 and a bypass line 60 for the HP-EGR cooler 58. The HP-EGR valve 56 has a dual function: on the one hand, it sets a desired high-pressure exhaust gas recirculation rate (HP-EGR rate) and, on the other hand, it sets which portion of the high-pressure exhaust gas recirculation (HP-EGR) flows via the HP-EGR cooler 58 and which portion flows uncooled via the bypass line 60.

[0026] To determine a pressure difference upstream and downstream of the LP-EGR filter 48, a first pressure sensor 62 is provided at a first location upstream of the LP-EGR filter 48 and a second pressure sensor 64 is provided at a second location downstream of the LP-EGR filter 48.

[0027] In the Fig. 2 and 3 A differential pressure across the LP EGR filter 48 is plotted on a horizontal axis 66, and an exhaust gas recirculation (EGR) rate is plotted on a vertical axis 68. Reference numeral 70 denotes a predetermined threshold value for the differential pressure 66, at which an engine malfunction is indicated. A first graph 72 illustrates a curve of the LP EGR rate versus the differential pressure 66, and a second graph 74 illustrates the curve of the HP EGR rate versus the differential pressure 66 for an operating state of the internal combustion engine.

[0028] For a given operating state of the internal combustion engine, a total exhaust gas recirculation rate (total EGR rate) is determined, which is composed of a portion of the high-pressure EGR rate and a portion of a low-pressure EGR rate (LP EGR rate). Fig. 2 As can be seen, in the prior art the respective EGR rate 72, 74 is kept constant and an engine malfunction is indicated when the threshold value 70 for the differential pressure 66 is reached.

[0029] According to the invention, as can be seen from Fig. 3As can be seen, the proportions of the LP EGR rate 72 and the HP EGR rate 74 are to be changed depending on the differential pressure 66 across the LP EGR filter 48, so that the differential pressure 66 remains below the threshold value 70. With increasing differential pressure 66, the proportion of the LP EGR rate 72 is reduced and the proportion of the HP EGR rate 74 is increased accordingly, so that the desired total EGR rate is achieved, but at the same time the threshold value 70 for the differential pressure 66 is not exceeded. This is done in such a way that, if necessary, the LP EGR rate is reduced to zero, so that the threshold value 70 for the differential pressure 66 is not reached and thus no engine malfunction needs to be indicated, as can be seen from Fig. 3 visible.

[0030] In other words, the distribution of the EGR rate between HP and LP EGR is determined depending on the pressure loss, if necessary up to the complete shutdown of the LP EGR loop 46.

[0031] If the pressure rises across the LP-EGR filter 48, the LP-EGR rate 72 is reduced and the HP-EGR rate is simultaneously increased to achieve largely emission-neutral operation of the internal combustion engine. In any case, exceeding predetermined OBD (On Board Diagnostic) emission thresholds is prevented. If necessary, the LP-EGR rate is reduced to zero, and the internal combustion engine operates exclusively with HP-EGR. The goal is to prevent a reportable engine malfunction (no so-called "MIL ON"). The pressure increase in the LP-EGR filter 48 is stored, for example, in the engine control unit in order to perform a filter change and possibly other filter deposit-reducing measures during an already scheduled workshop visit.

[0032] The method according to the invention is particularly preferably possible in all turbocharged internal combustion engines, such as diesel or gasoline engines, which have an LP-EGR with an upstream LP-EGR filter 48 and a cooled HP-EGR. List of reference symbols

[0033] 10Engine block 12Working cylinder 14Combustion air system 16Combustion air 18Exhaust system 20Exhaust 22Air filter 24Compressor 26Exhaust turbocharger 28Intercooler 30Throttle valve 32Intake manifold 34Exhaust manifold 36Turbine 38Catalytic converter 40Relative pressure sensor 42Particulate filter 44Exhaust flap 46LPG EGR loop 48LPG EGR filter 50LPG EGR cooler 52LPG EGR valve 54HP EGR loop 56HP EGR valve 58HP EGR cooler 60Bypass line for the HP EGR cooler 58 62First pressure sensor 64Second pressure sensor 66Horizontal axis: Differential pressure across the LP-EGR filter 48 68 vertical axis: EGR rate 70 predetermined threshold for the differential pressure 72 first graph: LP-EGR rate versus differential pressure 66 74 second graph: HP-EGR rate versus differential pressure 66

Claims

1. Method for operating an internal combustion engine, wherein a turbine (36) of an exhaust gas turbocharger (26), which is arranged in an exhaust system (18) of the internal combustion engine, is driven by exhaust gas (20) from the internal combustion engine and a compressor (24) of the exhaust gas turbocharger (26), which is driven by the turbine (36) and arranged in a combustion air system (14) of the internal combustion engine, compresses combustion air (16), wherein, in a high-pressure exhaust gas recirculation loop (HP-EGR loop) (54), exhaust gas (20) is diverted upstream of the turbine (36) and mixed with the combustion air (16) downstream of the compressor (24), wherein, in a low-pressure exhaust gas recirculation loop (LP-EGR loop), (46) exhaust gas (20) is diverted downstream of the turbine (36) and mixed with the combustion air (16) upstream of the compressor (24), wherein, in the LP-EGR loop (46), the exhaust gas (20) is cleaned by a low-pressure exhaust gas recirculation filter (LP-EGR filter) (48), wherein a predetermined value for a total exhaust gas recirculation rate (total EGR rate) is determined depending on an operating state of the internal combustion engine, wherein at least one operating parameter of the internal combustion engine is determined, characterized in that as an operating parameter of the internal combustion engine in the exhaust system (18), a value for a measure of a pressure difference (66) between a first predetermined point upstream of the low-pressure exhaust gas recirculation filter (LP-EGR filter) (48) and a second predetermined point downstream of the low-pressure exhaust gas recirculation filter (LP-EGR filter) (48) is determined, wherein, depending on the value of the measure of the pressure difference (66), a proportion of a low-pressure exhaust gas recirculation rate (LP-EGR rate) to the total exhaust gas recirculation rate (total EGR rate) is reduced or increased and a proportion of a high-pressure exhaust gas recirculation rate (HP-EGR rate) to the total exhaust gas recirculation rate (total EGR rate) is increased or reduced accordingly, so that the total exhaust gas recirculation rate (total EGR rate) reaches the predetermined value.

2. Method according to claim 1, characterized in that depending on the operating parameters of the internal combustion engine, the proportion of the LP-EGR rate (72) to the total EGR rate is reduced and the proportion of the HP-EGR rate (74) to the total EGR rate is increased accordingly, so that the total EGR rate reaches the predetermined value.

3. Method according to claim 1, characterized in that depending on the operating parameters of the internal combustion engine, the proportion of the LP-EGR rate (72) to the total EGR rate is increased and the proportion of the HP-EGR rate (74) to the total EGR rate is reduced accordingly, so that the total EGR rate reaches the predetermined value.

4. Method according to at least one of the preceding claims, characterized in that as the value of the measure of the pressure difference (66) increases, the proportion of the LP-EGR rate (72) to the total EGR rate is reduced and the proportion of the HP-EGR rate (74) to the total EGR rate is increased accordingly, so that the total EGR rate reaches the predetermined value.

5. Method according to claim 4, characterized in that the proportion of the LP-EGR rate (72) to the total EGR rate is reduced such that a value for the measure of the pressure difference (66) remains below a predetermined value (70) at which an operating fault is indicated.

6. Method according to at least one of the preceding claims, characterized in that the value for the value for the measure of the pressure difference (66) is stored in a retrievable manner.

7. Method according to at least one of the preceding claims, characterized in that the LP-EGR rate (72) is set to zero when the predetermined value (70) for the value for the measure of the pressure difference (66) can no longer be undershot by reducing the LP-EGR rate (72) by more than a predetermined value.

8. Method according to at least one of the preceding claims, characterized in that the recirculated exhaust gas is cooled in the HP-EGR loop (54).

9. Control device of an internal combustion engine, having a computing unit and a storage unit, characterized in that a computer program is stored in the memory unit, by means of which computer program, when it is at least partially executed by the computing unit, a method for operating an internal combustion engine is carried out according to any of the preceding claims.