METHOD AND DEVICE FOR THE EXHAUST AFTERTREATMENT OF AN INTERNAL COMBUSTION ENGINE

Abstract

The invention relates to a method for exhaust aftertreatment of an internal combustion engine with at least one combustion chamber and an outlet that is connected to an exhaust system, wherein at least one catalytic converter is arranged in the exhaust system. Furthermore, a secondary-air system is provided with which secondary air can be introduced into an exhaust duct of the exhaust system at an intake point downstream from the outlet of the internal combustion engine and upstream from the catalytic converter, and a first lambda sensor is arranged in the exhaust duct downstream from the intake point and upstream from the catalytic converter. The internal combustion engine is operated immediately after start-up with a substoichiometric combustion air ratio ( E<1), and secondary air is introduced into the exhaust duct of the exhaust system downstream from an outlet of the internal combustion engine and upstream from the first lambda sensor. An exhaust-gas lambda is determined by the first lambda sensor and a stoichiometric exhaust-gas lambda ( m=1) set, with the quantity of secondary air being maintained constant and the quantity of fuel being adjusted such that the stoichiometric exhaust-gas lambda ( m=1) is achieved.

Claims

1. A method for exhaust aftertreatment of an internal combustion engine having at least one combustion chamber and an outlet that is connected to an exhaust system, at least one catalytic converter being arranged in the exhaust system, a secondary-air system with which secondary air can be introduced downstream at an intake point of the outlet and upstream from the catalytic converter in an exhaust duct of the exhaust system, and a first lambda sensor being arranged in the exhaust duct downstream from the intake point and upstream from the catalytic converter, comprising the following steps: starting the internal combustion engine, the internal combustion engine being operated immediately after start-up with a substoichiometric combustion air ratio ( E<1), introducing secondary air into the exhaust duct of the exhaust system downstream from an outlet of the internal combustion engine and upstream from the first lambda sensor, determining an exhaust-gas lambda by means of the first lambda sensor, setting a stoichiometric exhaust-gas lambda ( m=1), with the ratio between the exhaust-gas quantity and secondary-air quantity being maintained constant, and with the amount of fuel introduced into the at least one combustion chamber being adjusted such that the stoichiometric exhaust-gas lambda ( m=1) is achieved.

2. The method as set forth in claim 1, wherein the first lambda sensor is embodied as a wideband lambda sensor, with the residual oxygen content of the exhaust-gas lambda ( m) being determined quantitatively.

3. The method as set forth in claim 1, further comprising electrically heating the first lambda sensor immediately after the starting of the internal combustion engine.

4. The method as set forth in claim 1, further comprising performing a continuous measurement of the residual oxygen content in the mixed exhaust gas downstream from the intake point.

5. The method as set forth in claim 1, wherein the internal combustion engine is operated with a combustion air ratio E that lies between 0.7 and 0.85.

6. The method as set forth in claim 1, further comprising shutting off the secondary-air supply and operating the internal combustion engine with a stoichiometric combustion air ratio ( E=1) if the catalytic converter has reached a threshold temperature.

7. The method as set forth in claim 6, wherein the threshold temperature is a light-off temperature of a three-way catalytically active coating of the catalytic converter.

8. An internal combustion engine, comprising: at least one combustion chamber, an outlet that is connected to an exhaust system, at least one catalytic converter arranged in the exhaust system, a secondary-air system with which secondary air can be introduced at an intake point downstream from the outlet and upstream from the catalytic converter in an exhaust duct of the exhaust system, a first lambda sensor arranged in the exhaust duct downstream from the intake point and upstream from the catalytic converter, and an engine control unit configured to carry out a method as set forth in claim 1 upon execution of a machine-readable program code.

9. The internal combustion engine as set forth in claim 8, wherein the catalytic converter is embodied as a three-way catalytic converter or as a four-way catalytic converter.

10. The internal combustion engine as set forth in claim 8, wherein the internal combustion engine is embodied as an internal combustion engine that is supercharged by means of an exhaust gas turbocharger, and wherein a turbine of the exhaust gas turbocharger is arranged in the exhaust duct downstream from the outlet and upstream from the catalytic converter.

11. The internal combustion engine as set forth in claim 10, wherein the intake point of the secondary-air system is arranged downstream from the outlet and upstream from the turbine and wherein the first lambda sensor is arranged downstream from the turbine of the exhaust gas turbocharger and upstream from the catalytic converter.

12. The internal combustion engine as set forth in claim 8, wherein the secondary-air system comprises an electrically driven secondary-air pump.

13. The internal combustion engine as set forth in claim 12, wherein the secondary-air system has a secondary-air line that connects the secondary-air pump to the intake point, and a secondary-air valve is arranged in the secondary-air line.

14. The internal combustion engine as set forth in claim 8, wherein a second lambda sensor is arranged in the exhaust duct downstream from the catalytic converter.

15. The internal combustion engine as set forth in claim 8, wherein the catalyst is arranged as the first exhaust aftertreatment component in a position near the engine in the exhaust system, and an additional exhaust aftertreatment component is arranged downstream from the first catalyst.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The invention will be explained below in exemplary embodiments with reference to the accompanying drawing. In the drawing:

[0033] FIG. 1 shows a first embodiment of a schematically illustrated internal combustion engine for carrying out a method according to the invention;

[0034] FIG. 2 shows a second embodiment of an internal combustion engine for carrying out a method according to the invention;

[0035] FIG. 3 shows a diagram of the timing of the lambda control of the internal combustion engine in a method according to the invention; and

[0036] FIG. 4 shows a diagram of the timing of the introduction of secondary air in a method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0037] FIG. 1 shows an internal combustion engine 10 with a combustion chamber 12 in which a piston 24 is displaceably arranged. Furthermore, a fuel injector 26 is provided at the combustion chamber 12 in order to inject fuel into the combustion chamber 12. The internal combustion engine 10 is connected at its intake 16 to an air intake system 30. The air intake system 30 comprises an intake line 32 in which a compressor 36 of an exhaust gas turbocharger 28 is arranged. In addition, the internal combustion engine 10 is connected with its outlet 18 to an exhaust system 40. The exhaust system 40 comprises an exhaust duct 42 in which, in the direction of flow of an exhaust gas of the internal combustion engine 10 through the exhaust duct 42, a turbine 44 of the exhaust gas turbocharger 28 is arranged, and, downstream from the turbine 44, at least one catalytic converter 46, preferably a three-way catalytic converter or a particulate filter with a three-way catalytically active coating, which is also referred to as four-way catalytic converter. An intake point 58 is provided downstream from the outlet 18 and upstream from the turbine 44 at which fresh air can be introduced into the exhaust duct 42 by means of a secondary-air system 50. A first lambda sensor 60, which is embodied as a wideband lambda sensor, is arranged downstream from the turbine 44 and upstream from the catalytic converter 46. An additional lambda sensor 62, which is preferably embodied as a two-step sensor, is provided downstream from the catalytic converter 46. The internal combustion engine 10 is also connected to an engine control unit 70 that regulates the fuel injection into the combustion chamber 12 of the internal combustion engine 10 as well as the secondary-air supply.

[0038] In order to enable a gas exchange to occur in the combustion chamber 12 of the internal combustion engine 10, at least one intake valve 20 is provided between the combustion chamber 12 and the intake line 32 that allows fresh air to flow into the combustion chamber 12. In addition, an exhaust valve 22 is provided between the combustion chamber 12 and the exhaust duct 42 that enables the exhaust gases to be expelled from the combustion chamber 12 into the exhaust duct 42.

[0039] FIG. 2 shows another exemplary embodiment of an internal combustion engine 10 according to the invention. The internal combustion engine 10 has a plurality of combustion chambers 12, at each of which a spark plug 14 for igniting an ignitable fuel-air mixture in the combustion chambers 12 of the internal combustion engine 10 is arranged. The internal combustion engine 10 is connected at its intake 16 to an air intake system 30. The air intake system 30 comprises an intake line 32 in which, in the direction of flow of fresh air through the intake line 32, an air filter 34 is arranged downstream from the air filter 34, a compressor 36 of an exhaust gas turbocharger 28 is arranged downstream from the air filter 34, andfurther downstreama throttle valve 38 is arranged. In addition, the internal combustion engine 10 is connected with its outlet 18 to an exhaust system 40, which has an exhaust duct 42. In the exhaust duct 42 in the direction of flow of an exhaust gas through the exhaust duct 42 are arranged a turbine 44 of the exhaust gas turbocharger 28 and, downstream from the turbine 44, a first catalytic converter 46, particularly a three-way catalytic converter or a particulate filter with a three-way catalytically active coating. A second exhaust aftertreatment component 48, particularly an additional catalytic converter or a particulate filter, is arranged downstream from the first catalytic converter 46. The internal combustion engine 10 also has a secondary-air system 50 with a secondary-air pump 52 that is connected via a secondary-air line 54 to an intake point 58. A secondary-air valve 56 for controlling the secondary air is additionally arranged in the secondary-air line 58. The intake point 58 is situated in the exhaust duct 42 downstream from the outlet 18 and upstream from the turbine 44. A first lambda sensor 60, preferably a wideband lambda sensor, is arranged downstream from the turbine 44 and upstream from the first catalytic converter 46. A second lambda sensor 62 is provided downstream from the first catalytic converter and upstream from the second catalytic converter 48. It is also possible for additional sensors, in particular a temperature sensor 64 or an additional exhaust-gas sensor 66, in particular a NOx sensor, to be arranged in the exhaust system. Alternatively, the first lambda sensor 60 can also be arranged downstream from the intake point 58 and upstream from the turbine 44 of the exhaust gas turbocharger 28. Alternatively, the internal combustion engine 10 can also be embodied as a naturally aspirated engine, in which case the turbine 44 is omitted from the exhaust duct 42 but the sequence of the exhaust aftertreatment components 46, 48 and of the intake point 58 and lambda sensors 60, 62 remains the same.

[0040] In order to enable a gas exchange to occur in the combustion chambers 12 of the internal combustion engine 10, intake valves 20 are provided between the combustion chamber 12 and the intake line 32 that allow fresh air to flow into the combustion chambers 12. In addition, exhaust valves 22 are provided between the combustion chamber 12 and the exhaust duct 42 that enable the exhaust gases to be expelled from the combustion chambers 12 into the exhaust duct 42.

[0041] FIG. 3 shows the combustion air ratio E and the exhaust-gas lambda m from the exhaust gas of the internal combustion engine 10. From start-up S, the internal combustion engine 10 is operated with a substoichiometric combustion air ratio in the range of 0.7< E<0.85.

[0042] At the same time, secondary air is blown into the exhaust duct 42 by means of the secondary-air system 50. This results in a stoichiometric exhaust-gas lambda, which can be adjusted with precision during the heating phase of the catalytic converter 46.

[0043] In FIG. 4, the secondary-air mass flow SL is shown from the start S of the internal combustion engine 10 over time t. As can be seen from FIG. 4, the secondary-air quantity is regulated very precisely here, so that a stoichiometric mixed exhaust lambda m is reliably achieved even in dynamic operation with simultaneously high heating power. In the method, the first lambda sensor 60 is made operational prior to or at the beginning of the catalyst heating process. At start-up S of the internal combustion engine 10, a substoichiometric fuel-air mixture is set in the combustion chamber 12. At the same time, a quantity of secondary air designed for the system is introduced downstream from the exhaust valves 22 and upstream from the turbine 44 of the exhaust gas turbocharger 28 by means of the secondary-air system 50. The secondary air is mixed with the exhaust gas from the combustion chambers 12 via the turbine 44 of the exhaust gas turbocharger and guided past the first, already operational lambda sensor 60 downstream from the turbine 44.

[0044] The exhaust gas from the combustion chambers 12 is preferably set such that the greatest possible heating power is achieved but a sufficiently large distance is maintained from the rich combustion limit in order to obtain a suitable control range. The control range is maintained both in the direction of the rich combustion limit in order to avoid misfiring and in the direction of stoichiometric exhaust gas in order to avoid reduced heat output. The detected exhaust-gas lambda m is detected in the control circuit and converted to a correction factor for mixture correction in the combustion chamber 12 on the basis of the air mass ratios of combustion and secondary air. The exhaust-gas lambda m is thus adjusted to the target value of 1.00.

[0045] The central position of the exhaust-gas lambda m is influenced inter alia by the state of health of the secondary-air system 50 or the delivery line of the secondary-air system 50. As the exhaust-gas backpressure increases, the system tends to drift toward a substoichiometric exhaust-gas lambda m<1 and is roped in by the rapid mixture correction. This means that the optimum emissions for the system are achieved at every juncture of the method.

[0046] The process is terminated as soon as the temperature of the catalytic converter 46 provided by a model or temperature sensor 64 has reached or exceeded a threshold value, or if the introduced quantity of secondary air has been reduced due to the selected operating point of the internal combustion engine 10 so far that the heating measure can no longer be effectively implemented.

[0047] In a preferred embodiment, the secondary-air system 50 has a controllable secondary-air pump 52. If the injection of the secondary air can be adjusted by means of a signal of the engine control unit 70 in the volumetric flow delivered, it is possible to adjust not only the metered quantity of fuel but also the quantity of secondary air that is conveyed in the event of a deviation of the exhaust-gas lambda from the optimum position. Constant heating power can be provided by means of this setup as the mileage and aging of the overall system progress. Any sooting or leaks in the secondary-air system 50 can thus be compensated for.

[0048] In order to prevent cooling of the exhaust system 40, particularly of the exhaust aftertreatment components 46, 48, during vehicle operation in a targeted manner, or in order to reheat a cooled exhaust system 40, the method can also be used during operation of a motor vehicle.

[0049] By virtue of the proposed method for exhaust aftertreatment, a regulated supply of secondary air can be provided that is more stable and produces lower emissions over the lifetime of the internal combustion engine than can be achieved by solutions that are known from the prior art. Moreover, corresponding control parameters can be monitored by means of on-board diagnostics and thus offer a possibility for enabling a diagnosis of the exhaust aftertreatment system to be made.

LIST OF REFERENCE SYMBOLS

[0050] 10 combustion engine [0051] 12 combustion chamber [0052] 14 spark plug [0053] 16 inlet [0054] 18 outlet [0055] 20 intake valve [0056] 22 exhaust valve [0057] 24 piston [0058] 26 fuel injector [0059] 28 exhaust gas turbocharger [0060] 30 air intake system [0061] 32 intake line [0062] 34 air filter [0063] 36 compressor [0064] 38 throttle valve [0065] 40 exhaust system [0066] 42 exhaust duct [0067] 44 turbine [0068] 46 catalytic converter [0069] 48 additional exhaust aftertreatment component [0070] 50 secondary-air system [0071] 52 secondary-air pump [0072] 54 secondary-air line [0073] 56 secondary-air valve [0074] 58 inlet point [0075] 60 first lambda sensor/guide probe [0076] 62 second lambda sensor [0077] 64 temperature sensor [0078] 66 additional exhaust-gas sensor [0079] 70 engine control unit [0080] E combustion air ratio of the internal combustion engine [0081] Low rich combustion limit of the internal combustion engine [0082] m exhaust gas air ratio downstream from the secondary-air injection [0083] EG mass flow of the exhaust gas [0084] SL mass flow of secondary air [0085] S start-up of the internal combustion engine [0086] t time