METHOD FOR HEATING AN EXHAUST GAS AFTERTREATMENT COMPONENT, AND INTERNAL COMBUSTION ENGINE

Abstract

A method for heating an exhaust gas aftertreatment component in an exhaust system of an internal combustion engine. At the combustion chamber, a fuel injector for injecting a fuel into the combustion chamber and a spark plug for igniting a flammable fuel-air mixture are arranged. The internal combustion engine has a valve lift curve switching mechanism, which allows for a shift and/or change of the opening times of the exhaust valve. The method includes: intake of fresh air into the combustion chamber, injection of a fuel into the combustion chamber, ignition of an ignitable fuel-air mixture in the combustion chamber when the piston is in a range of 10° KW to 30° KW after the upper ignition dead point, and opening of the exhaust valve when the piston is in a range of 55° KW to 95° KW after the upper ignition dead point.

Claims

1. A method for heating an exhaust gas aftertreatment component in an exhaust system of an internal combustion engine having at least one combustion chamber, wherein the combustion chamber is limited by a movable piston and has an intake port which is connected to an intake tract of the internal combustion engine and is closable by an intake valve, and has an exhaust port, which is connected to an exhaust system and is closable by an exhaust valve, wherein a fuel injector for injecting a fuel into the combustion chamber is arranged on the combustion chamber, and with a spark plug, which is configured to ignite a flammable fuel-air mixture in the combustion chamber, and with a valve lift curve switching mechanism, which allows for a shift and/or change of the opening times of the exhaust valve, the method comprising: intake of fresh air into the combustion chamber; injection of a fuel into the combustion chamber; ignition of an ignitable fuel-air mixture in the combustion chamber when the piston is in a range of 10° KW to 30° KW after the upper ignition dead point; and opening of the exhaust valve when the piston is in a range of 55° KW to 95° KW after the upper ignition dead point.

2. The method according to claim 1, wherein an exhaust camshaft comprises a switchable cam contour or a switchable cam, wherein a first switching position of the switchable cam contour is configured to carry out the method and a second switching position of the switchable cam contour is configured to realize a consumption-optimized normal operation of the combustion engine.

3. The method according to claim 2, wherein the first switching position causes a longer opening time of the exhaust valve than the second switching position.

4. The method according to claim 1, wherein a temperature of the exhaust gas aftertreatment component is determined and the method is initiated when the determined temperature of the exhaust gas aftertreatment component is below a first threshold temperature.

5. The method according to claim 1, wherein the internal combustion engine is designed as an internal combustion engine turbocharged by means of an exhaust gas turbocharger, wherein an exhaust gas temperature upstream of a turbine of the exhaust gas turbocharger or a component temperature of the turbine of the exhaust gas turbocharger is determined and the heating measures are reduced if the exhaust gas temperature upstream of the turbine is above a third threshold temperature or the component temperature of the turbine is above a fourth threshold temperature.

6. The method according to claim 1, wherein the opening times of the exhaust valve are shifted by the valve lift curve switching mechanism towards “late” when the exhaust gas aftertreatment component has reached a defined minimum temperature.

7. The method according to claim 1, wherein the method is carried out at a speed of the internal combustion engine of a maximum of 2500 rpm.

8. The method according to claim 1, wherein the exhaust valve is closed when carrying out the method at an angular range of 300° KW after the upper ignition dead point to 380° KW after the upper ignition dead point.

9. The method according to claim 1, wherein a cam for controlling the exhaust valve has an exhaust valve elevation curve having a control width of 250° KW to 290° KW and wherein the exhaust valve is lifted at least 1 mm from its seat over this control width.

10. An internal combustion engine comprising: at least one combustion chamber limited by a movable piston; an intake port which is connected to an intake tract of the internal combustion engine and is closable by an intake valve; an exhaust port which is connected to an exhaust system and is adapted to be closed by an exhaust valve; a fuel injector arranged for injecting a fuel into the combustion chamber is arranged on the combustion chamber; a spark plug configured to ignite a flammable fuel-air mixture in the combustion chamber; a valve lift curve switching mechanism, which allows for a shift and/or change of the opening times of the exhaust valve; an exhaust gas aftertreatment component arranged in the exhaust system; and a control unit, which is configured to carry out the method according to claim 1 when a machine-readable program code stored in a memory unit of the control unit is executed by a computing unit of the control unit.

11. The internal combustion engine according to claim 10, wherein the internal combustion engine is a direct-injection gasoline engine turbocharged by an exhaust gas turbocharger.

12. The internal combustion engine according to claim 10, wherein the spark plug is a hook spark plug.

13. The internal combustion engine according to claim 10, wherein the exhaust gas aftertreatment component is a three-way catalytic converter.

14. The internal combustion engine according to claim 13, wherein the three-way catalytic converter is arranged in the flow direction of an exhaust gas stream of the internal combustion engine as the first emission-reducing exhaust gas aftertreatment component in the exhaust system in a position close to the engine.

15. The internal combustion engine according to claim 10, wherein the valve lift switching mechanism has a switchable cam, with which the opening times of the exhaust valve in a first switching state of the valve lift switching mechanism allow for an early opening of the exhaust valve for heating the exhaust gas aftertreatment component, and in a second switching state, allow for a late opening of the exhaust valve with for an efficiency-optimized combustion in the combustion chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0034] FIG. 1 shows an internal combustion engine with an exhaust system for carrying out a method according to the invention for heating a catalytic converter in a schematic representation,

[0035] FIG. 2 shows a further schematic representation of an internal combustion engine for carrying out a method according to the invention for heating a catalytic converter,

[0036] FIG. 3 shows an ideal Otto cycle,

[0037] FIG. 4 shows a simplified representation of a combustion chamber of an internal combustion engine for carrying out such a cycle process,

[0038] FIG. 5 shows a curve of combustion chamber pressure and exhaust valve lift in the inventive implementation of a preferred method for heating an exhaust gas aftertreatment component, and

[0039] FIG. 6 shows temperature curves at various points in the exhaust system in an inventive method for heating an exhaust gas aftertreatment component and in a conventional method for heating an exhaust gas aftertreatment component.

DETAILED DESCRIPTION

[0040] FIG. 1 shows an internal combustion engine 10 having at least one combustion chamber 12, preferably as shown in FIG. 1 with at least three combustion chambers 12. The combustion engine 10 is designed as a direct-injection gasoline engine. For this purpose, a spark plug 14, preferably a hook spark plug 34, for igniting an ignitable fuel-air mixture and a fuel injector 30 for injecting a fuel into the respective combustion chamber 12 are arranged at each combustion chamber 12. Each combustion chamber 12 is connected via at least one intake port 16 to an unspecified intake tract and via at least one exhaust port 18 to an exhaust system 40. A fluidic connection from the intake tract into the combustion chamber 12 can be closed by an intake valve 20. A fluidic connection from the combustion chamber 12 to the exhaust system 40 can be closed by an exhaust valve 22.

[0041] The exhaust system 40 comprises an exhaust duct 42, in which in the flow direction of an exhaust gas stream of the internal combustion engine 10 through the exhaust system 40, a turbine 46 of an exhaust gas turbocharger 44, and downstream of the turbine 46, at least one exhaust gas aftertreatment component 48 are arranged. Preferably, as shown in FIG. 1, a first three-way catalytic converter 50 downstream of the turbine and, downstream of the first three-way catalytic converter 50, at least one further exhaust gas aftertreatment component 52, in particular a second three-way catalytic converter 54, an oxidation catalytic converter 58 and/or a particulate filter 56 are arranged. The second three-way catalytic converter 54 and the particulate filter 56 may also be combined in one component as a so-called four-way catalytic converter. Further, one or more exhaust gas sensors 60 may be arranged in the exhaust system 40 for monitoring the functionality of the exhaust gas aftertreatment component 48, 52. A first lambda sensor 64 is preferably arranged upstream of the first three-way catalytic converter 50, and a second lambda sensor 66 and a temperature sensor 62, and optionally a pollutant sensor 68, are preferably arranged downstream of the first three-way catalytic converter 50 in the exhaust system 40.

[0042] The internal combustion engine 10 is operatively connected to a control unit 80, which comprises a memory unit 82 and a computing unit 84. In the memory unit 82, one or more machine-readable program codes 86 for controlling the internal combustion engine 10, in particular for controlling the ignition time of the spark plug 14, the injection quantity and the injection timing of the fuel injector 30 and for controlling the opening times of the valves 20, 22 are stored.

[0043] FIG. 2 shows the combustion engine 10 in a further schematic representation. The opening times of the intake valves 20 are controlled by an intake camshaft 24. The opening times of the exhaust valves 22 are controlled by an exhaust camshaft 26. In this case, a valve lift curve switching mechanism 38 is provided on the exhaust camshaft 26, with which a switchable cam contour 28, which can be activated via a switching mechanism 36, can switch between a first opening curve of the exhaust valves 22 and a second opening curve of the exhaust valves 22.

[0044] FIG. 3 schematically shows an ideal Otto cycle, which provides a theoretical basis for the inventive method. FIG. 4 schematically shows a combustion chamber 12 of an internal combustion engine 10 with a piston 70, which is connected via a connecting rod 74 to a crankshaft 76 for carrying out such an Otto cycle. In this case, the combustion chamber 12 is sealed by piston rings 72, which seal a gap between the piston and a cylinder wall of the combustion chamber 12 and rest against the cylinder wall. Furthermore, in FIG. 4, the compression volume V.sub.K and the displacement V.sub.H are shown. In such an ideal process, no dissipation losses, mechanical friction losses or the like are taken into account. Furthermore, the working gas has the same properties over the entire cycle and flow losses are not taken into account. Furthermore, no mixing of charge mixture with exhaust gas is assumed.

[0045] Preferably, the invention relates to a method for a direct-injection four-stroke gasoline engine charged by means of an exhaust gas turbocharger 44. Each stroke consists of a piston stroke of the piston 70 or half a crankshaft revolution. In the four-stroke gasoline engine, the state changes can be assigned to the working cycles. This is described below using FIG. 3:

[0046] The first stroke, the intake stroke, comprises the intake in which the piston 70 moves downwards in FIG. 4 and the combustion chamber 12 fills with fresh air. This corresponds to the connecting line between points 0 and 1 in the diagram.

[0047] The second stroke, the compression stroke, comprises the compression of the combustion chamber charge, wherein the piston 70 moves to the left in FIG. 4. This corresponds in the diagram to the isentropic connecting line between points 1 and 2 and the isochoric heat input q.sub.zu is carried out by ignition and burning of the gas charge, which corresponds to the connecting line between points 2 and 3 (constant-volume combustion).

[0048] The third stroke, the expansion or working stroke, comprises the isentropic expansion, wherein the piston 70 is moved down again as a result of exothermic combustion. This corresponds to the connecting line between points 3 and 4 in the diagram.

[0049] The fourth stroke is also referred to as the exhaust stroke (heat dissipation), wherein the piston 70 moves again to the left by opening the exhaust valve 22, the exhaust gases in the lower dead point expand outwards without further output (connecting line between points 4 and 1) and the rest of the exhaust gas is pushed outwards by the piston stroke (connecting line between points 1 and 0). The heat q.sub.Ab contained in the exhaust gas is released into the environment. The ideal process does not take into account that the residual amount in the compression chamber does not reach the ambient condition.

[0050] FIG. 5 now shows the curve of combustion chamber pressure and exhaust valve stroke according to a preferred embodiment of the invention and a conventional method for catalytic converter heating.

[0051] The curve with the reference sign 90 here shows the curve of the combustion chamber pressure and the reference sign 92 the curve of the valve lift of the exhaust valve 12 in the conventional catalytic converter heating operation, which is known from the prior art.

[0052] Furthermore, the curve with the reference sign 94 shows the curve of the combustion chamber pressure in the catalytic converter heating operation according to the invention, while the reference sign 96 is directed to a curve which describes the curve of the valve lift of the exhaust valve 12 in the catalytic converter heating operation according to the invention.

[0053] In the known method for heating a catalytic converter of a gasoline internal combustion engine, the ignition 91 of the gas charge in one of the cylinders takes place relatively late after the upper ignition dead point, for example 40° KW after the upper ignition dead point, while the exhaust opening of the exhaust valve 22 of the exhaust of the combustion chamber 12 also takes place late, for example 155° KW-175° KW after the upper ignition dead point.

[0054] In the inventive method for heating an exhaust gas aftertreatment component 48, in particular a three-way catalytic converter 50 in the exhaust system 40 of a direct-injection gas engine 10 with at least one combustion chamber 12, the ignition 95 of the gas charge in the combustion chamber 12 takes place in an angular range of 10° KW after the upper ignition dead point up to 30° KW after the upper ignition dead point, while the opening of the exhaust valve 22 takes place in an angular range of 55° KW to 95° KW after the upper ignition dead point.

[0055] A representation of the early exhaust opening can be made here by the valve lift curve switching mechanism 38, in particular by a switchable cam contour 28.

[0056] Alternatively, switching between heating mode and normal operation can be carried out by an exhaust camshaft phase adjuster with a very wide adjustment range, wherein an adjustment range of at least 120° KW is assumed, and a cam contour which is also used outside the heating mode.

[0057] Preferably, the exhaust camshaft 26 has a switchable cam contour 28, wherein the cam contour, which realizes the heating operation, has a larger opening range than the cam contour for normal operation. Preferably, the cam contour for the heating operation comprises an exhaust valve elevation curve having a control width of 250° to 290° KW, preferably of about 270° KW, based on a valve lift of at least 1 mm.

[0058] The embodiment with a switchable cam contour 28 and a control width of 250° to 290° KW is particularly preferred since this allows for configuring the exhaust port and the closing time at the optimal operating point. Compared to the embodiment with a camshaft adjuster with a large adjustment range, the disadvantages associated therewith can be prevented in such a way that this embodiment has a high residual gas rate in the combustion chamber 12 due to the necessarily very early closure of the exhaust, which is accompanied by a reduced air flow rate and suboptimal ignition conditions in the combustion chamber 12.

[0059] The inventive method results in a significantly increased exhaust gas enthalpy. In order to be able to ensure a safe ignition of the fuel-air mixture located in the combustion chamber 12 even at such a late ignition time, the use of a hook spark plug 34 is preferred over a prechamber spark plug, since a prechamber spark plug may not ensure ignition of the fuel-air mixture at the described opening and ignition times.

[0060] FIG. 6 shows temperature curves in the exhaust system in a method according to the invention for heating the exhaust gas aftertreatment component and in a conventional method for heating an exhaust gas aftertreatment component. In this case, the curve 100 shows the temporal curve of an exhaust gas temperature of the combustion engine 10 before entering the turbine 46 of the exhaust gas turbocharger 44 in an inventive method for heating an exhaust gas aftertreatment component 48. Curve 102 shows the temporal curve of a temperature at the intake of a three-way catalytic converter 50 close to the engine. Curve 104 shows the temporal temperature curve in the center of the close-coupled three-way catalytic converter 50 and curve 106 at the exhaust of the close-coupled three-way catalytic converter 50. The curve 108 represents the temporal curve of an exhaust gas temperature before entering the turbine 46 of the exhaust gas turbocharger 44 in a conventional inner-engine heating method known from the prior art for heating an exhaust gas aftertreatment component. Curve 110 shows the temporal temperature curve in the center of the close-coupled three-way catalytic converter 50 in a conventional inner-engine heating process. From a comparison of curves 104 and 110 it can be seen that the center of the three-way catalytic converter 50 reaches a first threshold temperature T.sub.S1 much faster in the inventive method than in the conventional inner-engine heating process.

[0061] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.