METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE, IN PARTICULAR A DIESEL ENGINE

Abstract

A method for operating an internal combustion engine using an external exhaust-gas recirculation device with a recirculation setting device to set the flow rate of the recirculated exhaust gas and using a closing time setting device to adjust the closing time of the at least one inlet valve of the internal combustion engine. For the reduction of nitrogen oxides emitted by the internal combustion engine, it is possible, by way of the closing time setting device, for a nitrogen oxide reduction cycle to be set in which the at least one inlet valve of the internal combustion engine closes earlier or later than in the basic cycle. If the torque of the internal combustion engine falls below at least a defined torque threshold value, the internal combustion engine is operated in the basic cycle and the recirculation of the exhaust gas is enabled by way of the recirculation setting device, and wherein, if the torque of the internal combustion engine exceeds the defined torque threshold value, the internal combustion engine is operated in the nitrogen oxide reduction cycle and the recirculation of the exhaust gas is blocked by way of the recirculation setting device.

Claims

1. A method for operating an internal combustion engine, wherein the internal combustion engine includes at least one inlet valve, the internal combustion engine being part of an apparatus further including an external exhaust-gas recirculation device configured to feed exhaust gas emitted by the internal combustion engine back to the internal combustion engine, the exhaust-gas recirculation device having a recirculation setting device configured to set the flow rate of the recirculated exhaust gas, and a closing time setting device configured to adjust the closing time of at least one inlet valve of the internal combustion engine, the closing time setting device being configured to set a basic cycle of the internal combustion engine in which the at least one inlet valve of the internal combustion engine closes in a crank angle range from 1 to 40 crank angle after BDC (bottom dead center), wherein, for the reduction of the nitrogen oxides emitted by the internal combustion engine, the closing time setting device is configured to set a nitrogen oxide reduction cycle in which the at least one inlet valve of the internal combustion engine closes earlier or later than in the basic cycle, the method comprising the steps of: controlling, by a control unit of the internal combustion engine, the closing time setting device and the recirculation setting device as a function of the torque of the internal combustion engine; if the torque (M) of the internal combustion engine falls below at least a defined torque threshold value (M.sub.Threshold), operating the internal combustion engine in the basic cycle and enabling the recirculation of the exhaust gas by the recirculation setting device; and if the torque (M) of the internal combustion engine exceeds the defined torque threshold value (M.sub.Threshold), operating the internal combustion engine in the nitrogen oxide reduction cycle and blocking the recirculation of the exhaust gas by the recirculation setting device.

2. The method according to claim 1, wherein the internal combustion engine is a diesel engine.

3. The method according to claim 1, wherein the at least one inlet valve of the internal combustion engine closes in a crank angle range from 10 to 40 crank angle after BDC in the basic cycle.

4. The method according to claim 1, further comprising the step of setting the torque threshold value (M.sub.Threshold) by the control unit as a function of an engine speed (n) of the internal combustion engine

5. The method according to claim 4, wherein the set torque threshold value (M.sub.Threshold) decreases with increasing engine speed of the internal combustion engine.

6. The method according to claim 1, wherein the torque threshold value (M.sub.Threshold) lies in a range from 10% to 60% of a maximum torque of the internal combustion engine.

7. The method according to claim 4, further comprising the step of storing, in the control unit, a characteristic map which records the torque threshold value (M.sub.Threshold) as a function of the engine speed (n) of the internal combustion engine.

8. The method according to claim 1, wherein the apparatus further comprises an exhaust tract with an exhaust-gas aftertreatment system and a temperature detection device so that a temperature (T.sub.meas) of the exhaust gas flowing through the exhaust tract is detected upstream of the exhaust-gas aftertreatment system as viewed in the exhaust-gas flow direction, and the step of controlling further includes controlling the closing time setting device and the recirculation setting device additionally as a function of the temperature (T.sub.meas) detected by the temperature detection device.

9. The method according to claim 8, wherein, if the temperature (T.sub.meas) exceeds at least a defined temperature threshold value (T.sub.Threshold) and the torque (M) of the internal combustion engine exceeds the defined torque threshold value (M.sub.Threshold), then at least one of the internal combustion engine is operated in the basic cycle and the recirculation of the exhaust gas is enabled by the recirculation setting device, and if the temperature (T.sub.meas) falls below the at least one defined temperature threshold value (T.sub.Threshold) and the torque (M) of the internal combustion engine exceeds the defined torque threshold value (M.sub.Threshold), then the internal combustion engine is operated in the nitrogen oxide reduction cycle and the recirculation of the exhaust gas is blocked by the recirculation setting device.

10. The method according to claim 9, wherein the temperature threshold value (T.sub.Threshold) lies in a temperature range from 450 C. to 500 C.

11. The method according to claim 8, wherein the apparatus further includes at least one exhaust-gas turbocharger, the method comprising at least one of: introducing at least some of the exhaust gas flowing through the exhaust tract into a recirculation line of the external exhaust-gas recirculation device upstream of a compressor of at least one exhaust-gas turbocharger as viewed in the exhaust-gas flow direction, or introducing the exhaust gas that is recirculated by the external exhaust-gas recirculation device into an intake tract of the internal combustion engine upstream of a turbine of at least one exhaust-gas turbocharger as viewed in the combustion-air flow direction.

12. The method according to claim 1, wherein the apparatus further includes an exhaust tract having an exhaust-gas aftertreatment system with at least one SCR catalytic converter element configured to reduce nitrogen oxides contained in the exhaust gas using ammonia as reducing agent, wherein the method includes introducing, by a feed device, the ammonia into the exhaust tract upstream of the SCR catalytic converter element as viewed in the exhaust-gas flow direction.

13. The method according to claim 1, wherein the nitrogen oxide reduction cycle is a Miller cycle; and in the nitrogen oxide reduction cycle the at least one inlet valve of the internal combustion engine closes in a crank angle range from 40 to 5 crank angle before BDC.

14. The method according to claim 1, wherein the nitrogen oxide reduction cycle is an Atkinson cycle, and in the nitrogen oxide reduction cycle the at least one inlet valve of the internal combustion engine closes in a crank angle range from 50 to 70 crank angle after BDC.

15. The method according to claim 1, wherein the closing time setting device is one of a cam adjustment device or a camshaft adjustment device.

16. The method according to claim 1, wherein the internal combustion engine includes a first exhaust-gas turbocharger and a second exhaust-gas turbocharger for the compression of the combustion air flowing through an intake tract of the internal combustion engine, the method further comprising cooling the compressed combustion air by a cooling device arranged in the intake tract between a compressor of the first exhaust-gas turbocharger and a compressor of the second exhaust-gas turbocharger, and by another cooling device arranged in the intake tract downstream of the compressor of the second exhaust-gas turbocharger, as viewed in the combustion-air flow direction.

17. An apparatus comprising: an internal combustion engine having at least one inlet valve; an external exhaust-gas recirculation device configured to feed exhaust gas emitted by the internal combustion engine back to the internal combustion engine, the exhaust-gas recirculation device having a recirculation setting device configured to set the flow rate of the recirculated exhaust gas; a closing time setting device configured to adjust a closing time of the at least one inlet valve of the internal combustion engine, wherein the closing time setting device is configured to set a basic cycle of the internal combustion engine in which the at least one inlet valve of the internal combustion engine closes in a crank angle range from 1 to 40 crank angle after BDC (bottom dead center), and for the reduction of the nitrogen oxides emitted by the internal combustion engine, the closing time setting device is configured to set a nitrogen oxide reduction cycle in which the at least one inlet valve of the internal combustion engine closes earlier or later than in the basic cycle; a control unit at least one of controlling or regulating the closing time setting device and the recirculation setting device as a function of a torque of the internal combustion engine, wherein, if the torque (M) of the internal combustion engine falls below at least a defined torque threshold value (M.sub.Threshold). the internal combustion engine is operated in the basic cycle and the recirculation of the exhaust gas is enabled by the recirculation setting device, and if the torque (M) of the internal combustion engine exceeds the defined torque threshold value (M.sub.Threshold), the internal combustion engine is operated in the nitrogen oxide reduction cycle and the recirculation of the exhaust gas is blocked by the recirculation setting device.

18. The apparatus according to claim 17, wherein the internal combustion engine is a diesel engine.

19. The apparatus according to claim 17, wherein the at least one inlet valve of the internal combustion engine closes in a crank angle range from 10 to 40 crank angle after BDC in the basic cycle.

20. A vehicle having an apparatus according to claim 17.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention and its advantageous embodiments and/or refinements, and the advantages thereof, will be discussed in more detail below, merely by an example, on the basis of drawings, in which:

[0030] FIG. 1 shows, in a side view, a heavy goods vehicle having the apparatus according to the invention;

[0031] FIG. 2 is a schematic diagram of an apparatus according to an embodiment of the invention;

[0032] FIG. 3 is a diagram shov ing various value lift cycles;

[0033] FIG. 4 is a flow diagram showing a method according to an embodiment of the invention; and

[0034] FIG. 5 is a diagram showing a characteristic map according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] FIG. 1 shows a vehicle 1, which in this case is, by example, in the form of a heavy goods vehicle, with an apparatus 3 according to the invention (FIG. 2). The construction of the device 3 will be discussed in more detail below on the basis of FIG. 2:

[0036] As shown in FIG. 2, the apparatus 3 has an intake tract 5 by which combustion air 9 can be fed to an internal combustion engine 7 of the apparatus 3. Here, by example, the intake tract 5 has, as viewed in an exhaust-gas flow direction, a compressor 11 of a first exhaust-gas turbocharger 13, a heat-dissipating heat exchanger 15, a compressor 17 of a second exhaust-gas turbocharger 19, and a further heat-dissipating heat exchanger 21.

[0037] By the compressor 11, the combustion air 9 flowing into the intake tract 5 is compressed. Subsequently, the combustion air that has been compressed by the compressor 11 is cooled by the heat-dissipating heat exchanger 15. The heat-dissipating heat exchanger 15 may be formed, for example, by a charge-air cooler. Finally, the combustion air is compressed yet further by the compressor 17 and is cooled again by the heat-dissipating heat exchanger 21. The heat-dissipating heat exchanger 21 may likewise be formed by a charge-air cooler.

[0038] According to FIG. 2, the apparatus 3 furthermore also has an exhaust tract 23 through which the exhaust gas 25 emitted by the internal combustion engine 7 is conducted. Here, by example, the exhaust tract 23 has, as viewed in the exhaust-gas flow direction, a turbine 27 of the second exhaust-gas turbocharger 19, a turbine 29 of the first exhaust-gas turbocharger 13, a temperature sensor 31 and a merely schematically indicated exhaust-gas aftertreatment system 33. Here, by example, the exhaust-gas aftertreatment system 33 has an SCR catalytic converter element 35, by which nitrogen oxides contained in the exhaust gas 9 of the internal combustion engine 7 can be reduced using ammonia as reducing agent. It is also the case here that the exhaust-gas aftertreatment system 33 has a feed device 37 by which the reducing agent, in this case for example in the form of an aqueous urea solution, can be introduced into the exhaust tract 23 upstream of the SCR catalytic converter element 35.

[0039] Furthermore, the exhaust tract 23 also has an external exhaust-gas recirculation device 39, by which the exhaust gas 9 emitted by the internal combustion engine 7 can be fed to the internal combustion engine 7 again. Here, by example, for the exhaust-gas recirculation, the exhaust gas 25 emitted by the internal combustion engine 7 is introduced, upstream of the turbine 27, into a recirculation line 41 of the exhaust-gas recirculation device 39, via which recirculation line the exhaust gas 25 can be introduced into the intake tract 5 downstream of the heat-dissipating heat exchanger 21 as viewed in a combustion-air flow direction. The exhaust-gas recirculation device 39 furthermore also has a recirculation setting device which, in this case, is for example in the form of a straight-way valve 43 and by which the flow rate of the recirculated exhaust gas 25 can be set. Here, by example, the exhaust-gas recirculation device 39 furthermore also has a heat-dissipating heat exchanger 45 by which the recirculated exhaust gas 25 is cooled. Here, by example, the heat-dissipating heat exchanger 45 is arranged in the recirculation line 41 downstream of the straight-way valve 43 as viewed in the exhaust-gas flow direction.

[0040] As per FIG. 2, the apparatus 3 furthermore also has a closing time setting device 47 by which the closing time of the inlet valves of the internal combustion engine 7 can be adjusted. Here, by example, the closing time setting device 47 is formed by a camshaft adjustment device. By the closing time setting device 47, a basic cycle of the internal combustion engine 7 can be set, in which the inlet valves of the internal combustion engine 7 are closed in a crank angle range from 10 to 40 crank angle after BDC (bottom dead centre). Furthermore, by the closing time setting device 47, it is also possible for a nitrogen oxide reduction cycle to be set, in which the inlet valves of the internal combustion engine 7 are closed earlier or later than in the basic cycle. Here, by example, the nitrogen oxide reduction cycle is formed by a Miller cycle. Here, the inlet valves of the internal combustion engine 7 are preferably closed, in the Miller cycle, in a crank angle range from 40 to 5 crank angle before BDC, As an alternative to the Miller cycle, it would for example also be possible for the nitrogen oxide reduction cycle to be formed by an Atkinson cycle.

[0041] FIG. 3 shows a diagram 49 which is intended to illustrate the differences between the basic cycle, the Miller cycle and the Atkinson cycle. In the diagram 49 there is plotted a first curve 51, which shows an exemplary valve lift of the inlet valves of the internal combustion engine 7 as a function of the crank angle of the internal combustion engine 7 in the case of the basic cycle. Also plotted in the diagram 49 is a curve 53 which shows an exemplary valve lift of the inlet valves as a function of the crank angle of the internal combustion engine 7 in the case of a Miller process. Also plotted in the diagram 49 is a curve 55 which shows an exemplary valve lift of the inlet valves as a function of the crank angle of the internal combustion engine 7 in the case of an Atkinson cycle.

[0042] As per FIG. 2, the apparatus 3 furthermore also has a control unit 57 by which the closing time setting device 47 and the straight-way valve 43 are regulated and/or controlled, in this case as a function of the present torque of the internal combustion engine 7 and as a function of the temperature measured by the temperature sensor 31. Said regulation or control will be discussed in more detail below on the basis of FIG. 6:

[0043] Proceeding from an initial state in which, in this case, by example, the exhaust-gas recirculation is enabled by the straight-way valve 43 and in the basic cycle of the internal combustion engine 7 is set, it is firstly checked, by the control unit 57, in a step 58, whether the present torque M or the present mean pressure of the internal combustion engine 7 is higher than a defined torque threshold value M.sub.Threshold. If the present torque M of the internal combustion engine 7 is not higher than the defined torque threshold value M.sub.Threshold, the exhaust-gas recirculation remains enabled and the basic cycle remains set. If the present torque M of the internal combustion engine 7 is higher than the defined torque threshold value M.sub.Threshold; then it is checked, in a step 59, whether the temperature T.sub.meas measured by the temperature sensor 31 is higher than a defined temperature threshold value T.sub.Threshold. If the measured temperature T.sub.meas is higher than the temperature threshold value T.sub.Threshold, it is for example the case here that the recirculation of the exhaust gas 9 remains enabled and the internal combustion engine continues to be operated in the basic cycle. If the measured temperature T.sub.meas is not higher than the temperature threshold value, the exhaust-gas recirculation is blocked by the straight-way valve 43 and the Miller cycle is set, or the internal combustion engine 7 is operated in the Miller cycle.

[0044] It is also the case here, by example, that the torque threshold value M.sub.Threshold is adjusted or changed by the control unit 57 as a function of the engine speed n of the internal combustion engine 7. Said adjustment is performed by a characteristic map 61 which is stored in the control unit 57 (FIG. 5). It is preferably also the case that, in addition to the present torque M of the internal combustion engine 5 and the temperature T.sub.meas measured by the temperature sensor 31, the ambient temperature and/or the ambient pressure are/is also taken into consideration in the regulation and/or control of the closing time setting device 47 and of the straight-way valve 43.

LIST OF REFERENCE DESIGNATIONS

[0045] 1 Vehicle [0046] 3 Apparatus [0047] 5 Intake tract [0048] 7 Internal combustion engine [0049] 9 Combustion air [0050] 11 Compressor [0051] 13 First exhaust-gas turbocharger [0052] 15 Heat-dissipating heat exchanger [0053] 17 Compressor [0054] 19 Second exhaust-gas turbocharger [0055] 21 Heat-dissipat ng heat exchanger [0056] 23 Exhaust tract [0057] 25 Exhaust gas [0058] 27 Turbine [0059] 29 Turbine [0060] 31 Temperature sensor [0061] 33 Exhaust-gas aftertreatment system [0062] 35 SCR catalytic converter element [0063] 37 Feed device [0064] 39 Exhaust-gas recirculation device [0065] 41 Recirculation line [0066] 43 Straight-way valve [0067] 45 Heat-dissipating heat exchanger [0068] 47 Closing time setting device [0069] 49 Diagram [0070] 51 Curve [0071] 53 Curve [0072] 55 Curve [0073] 57 Control unit [0074] 58 Step [0075] 59 Step [0076] 61 Characteristic map [0077] M Torque [0078] M.sub.Threshold Torque threshold value [0079] n Engine speed [0080] T.sub.Threshold Temperature threshold value [0081] T.sub.Meas Temperature measurement value