JP4730336B2 - Exhaust gas recirculation control device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation control device for an internal combustion engine.

  An engine exhaust passage such as an exhaust turbocharger turbine outlet and an engine intake passage such as an exhaust turbocharger compressor inlet are connected to each other by an exhaust recirculation (hereinafter also referred to as EGR) passage, and the exhaust gas is recirculated into the exhaust recirculation passage. An internal combustion engine in which a circulation control valve is arranged is known (see FIG. 4 in Patent Document 1). In this case, the opening degree of the exhaust gas recirculation control valve can be controlled such that the exhaust gas recirculation gas amount supplied to the intake passage matches the target amount.

  On the other hand, for example, a catalyst suitable for reducing NOx in the exhaust gas with ammonia under an excess of oxygen is disposed in the exhaust passage, and a urea supply valve is disposed in the exhaust passage upstream of the catalyst. An exhaust purification device that supplies an aqueous urea solution to a catalyst to reduce NOx in the exhaust gas is also known. Here, considering the case where this exhaust gas purification device is applied to the internal combustion engine described above, for example, a urea supply valve and a catalyst can be arranged in the exhaust passage downstream of the turbine outlet.

Japanese Patent No. 2759375

  However, the temperature of the catalyst when the urea aqueous solution is supplied is usually considerably higher than the boiling point of the urea aqueous solution. Therefore, when the urea aqueous solution is supplied to the catalyst at this time, the urea aqueous solution evaporates all at once, and as a result, the catalyst The pressure in the surrounding exhaust passage, for example, the pressure around the inflow end of the exhaust recirculation passage, may increase significantly. In this case, there is a problem that the pressure difference between the inflow end and the outflow end of the exhaust gas recirculation passage is greatly increased, and thus the exhaust gas recirculation gas amount may be larger than the target amount. This problem can also occur when a hydrocarbon such as light oil is supplied to the catalyst.

  In order to solve the above problems, according to the present invention, an exhaust gas of an internal combustion engine in which an engine exhaust passage and an engine intake passage are connected to each other by an exhaust gas recirculation passage and an exhaust gas recirculation control valve is disposed in the exhaust gas recirculation passage. In the recirculation control device, a catalyst is disposed in the exhaust passage and a supply control valve is disposed in the exhaust passage upstream of the catalyst so that liquid is supplied from the supply control valve into the exhaust passage upstream of the catalyst. Thus, when the liquid is supplied from the supply control valve, the opening degree of the exhaust gas recirculation control valve is corrected to decrease compared to when the liquid is not supplied.

  The exhaust gas recirculation amount can be maintained at the target amount.

  FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a gasoline engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electromagnetically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is sequentially connected to the air flow meter 9 and the air cleaner 10 via the intake introduction pipe 8. Electrically controlled throttle valves 11d and 11u are respectively arranged in the intake duct 6 and the intake introduction pipe 8, and a cooling device 12 for cooling the intake air flowing in the intake duct 6 is arranged around the intake duct 6. Is done. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the exhaust aftertreatment device 20.

  Each fuel injection valve 3 is connected to a common rail 14 via a fuel supply pipe 13, and this common rail 14 is connected to a fuel tank 16 via an electrically controlled fuel pump 15 having a variable discharge amount. The fuel in the fuel tank 16 is supplied into the common rail 14 by the fuel pump 15, and the fuel supplied into the common rail 14 is supplied to the fuel injection valve 3 through each fuel supply pipe 13. A fuel pressure sensor (not shown) for detecting the fuel pressure in the common rail 14 is attached to the common rail 14 so that the fuel pressure in the common rail 14 matches the target pressure based on a signal from the fuel pressure sensor. The fuel discharge amount of the fuel pump 15 is controlled.

  The exhaust aftertreatment device 20 includes an exhaust pipe 21 connected to the outlet of the exhaust turbine 7 b, and the outlet of the exhaust pipe 21 is connected to the inlet of the upstream catalytic converter 22. The outlet of the upstream catalytic converter 22 is connected to the inlet of the downstream catalytic converter 24 via the exhaust pipe 23, and the exhaust pipe 25 is connected to the outlet of the downstream catalytic converter 24. A catalyst 26a having an oxidation function and a particulate filter 26b for collecting particulates in the exhaust gas are disposed in order from the upstream side in the upstream side catalytic converter 22, and the exhaust gas is exhausted by ammonia in the downstream side catalytic converter 24. A NOx selective reduction catalyst 27 suitable for reducing NOx therein is disposed. In the embodiment according to the present invention, the NOx selective reduction catalyst 27 is composed of a catalyst suitable for reducing NOx in the exhaust gas with ammonia under an excess of oxygen. A temperature sensor 28 that detects the temperature of the NOx selective reduction catalyst 27 is attached to the NOx selective reduction catalyst 27. An electrically controlled exhaust throttle valve 29 is disposed in the exhaust pipe 23, and an electromagnetically controlled supply control valve 30 is disposed in the exhaust pipe 23 downstream of the exhaust throttle valve 29. On the other hand, a liquid containing an ammonia generating compound that generates ammonia is stored in the tank 31, and the liquid containing the ammonia generating compound stored in the tank 31 is supplied to the supply control valve 30 via the supply pump 32. The exhaust gas is supplied into the exhaust pipe 23 by the supply control valve 30. In this case, the liquid containing the ammonia generating compound is supplied from the supply control valve 30 in the form of continuous pulses.

  As shown in FIG. 1, the exhaust manifold 5 upstream of the inlet of the turbine 7 b of the exhaust turbocharger 7 and the intake manifold 4 downstream of the outlet of the compressor 7 a of the exhaust turbocharger 7 are connected to each other via a high-pressure EGR passage 40. In the high pressure EGR passage 40, an electrically controlled high pressure EGR control valve 41 is disposed. Further, the exhaust pipe 23 downstream of the outlet of the turbine 7b and the intake introduction pipe 8 upstream of the inlet of the compressor 7a are connected to each other via a low pressure EGR passage 42, and an electrically controlled low pressure EGR control valve is provided in the low pressure EGR passage 42. 43 is arranged. In this case, the inflow end 44 of the low pressure EGR passage 42 is connected to the exhaust pipe 23 downstream of the exhaust throttle valve 29 and upstream of the supply control valve 30, and the outflow end 45 of the low pressure EGR passage 42 is connected to the intake inlet pipe 8 downstream of the throttle valve 11 u. Connected to. Further, a cooling device 46 for cooling the EGR gas flowing in the low pressure EGR passage 42 is disposed around the low pressure EGR passage 42. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 46, and the EGR gas is cooled by the engine cooling water.

  The electronic control unit 50 is composed of a digital computer, and is connected to each other by a bidirectional bus 51. A ROM (read only memory) 52, a RAM (random access memory) 53, a CPU (microprocessor) 54, an input port 55, and an output port 56. It comprises. The air flow meter 9 generates an output voltage proportional to the amount of intake air, the temperature sensor 28 generates an output voltage proportional to the temperature Tc of the NOx selective reduction catalyst 27, and these output voltages are respectively supplied to the corresponding AD converters 57. To the input port 55. A load sensor 60 that generates an output voltage proportional to the amount of depression of the accelerator pedal 59 is connected to the accelerator pedal 59, and the output voltage of the load sensor 60 is input to the input port 55 via the corresponding AD converter 57. The Further, the input port 55 is connected to a crank angle sensor 61 that generates an output pulse every time the crankshaft rotates, for example, 30 °. On the other hand, the output port 56 is connected via a corresponding drive circuit 58 to the fuel injection valve 3, the drive device for the throttle valve 11u, the drive device for the throttle valve 11d, the drive device for the fuel pump 15, the exhaust throttle valve 29, the supply control valve 30, Connected to the supply pump 32, the high pressure EGR control valve 41, and the low pressure EGR control valve 43.

  In the internal combustion engine shown in FIG. 1, EGR gas can be supplied to the engine via the high pressure EGR passage 40 or can be supplied via the low pressure EGR passage 42. In the embodiment according to the present invention, for example, the EGR passage for supplying the EGR gas is selectively switched according to the engine operating state determined by the engine load factor KL and the engine speed Ne. Here, the engine load factor KL is the ratio of the engine load to the total load.

  That is, as shown in FIG. 2, when the engine load factor KL is lower than the predetermined first set load factor KLX, and therefore the engine operating state is in the region I, the EGR gas is transmitted only through the high-pressure EGR passage 40. Is supplied. In this way, good responsiveness can be ensured, and the amount of EGR gas supplied to the engine can be precisely controlled. On the other hand, when the engine load factor KL is higher than the first set load factor KLX and lower than the predetermined second set load factor KLY, and therefore the engine operating state is in the region II, the low pressure EGR passage 42 EGR gas is supplied only through this. This makes it possible to reliably supply EGR gas to the engine even when the engine load factor KL is high. Further, when the engine load factor KL is higher than the second set load factor KLY and therefore the engine operating state is in the region III, the supply of EGR gas is prohibited.

  More specifically, when the engine operating state is within the region I, the low pressure EGR control valve 43 is closed and the high pressure EGR control valve 41 is opened, and when the engine operating state is within the engine operating state region II, the high pressure EGR control valve 41 is opened. Is closed and the low pressure EGR control valve 43 is opened. When the engine operating state is within the region III, the high pressure EGR control valve 41 and the low pressure EGR control valve 43 are closed.

  The opening degree DH of the high pressure EGR control valve 41 when the engine operating state is in the region I is the opening degree necessary for making the actual EGR rate (= EGR gas amount / cylinder gas amount) coincide with the target EGR rate. Be controlled. The opening degree DH of the high pressure EGR control valve 41 is stored in advance in the ROM 52 in the form of a map shown in FIG. 3 as a function of the engine load factor KL and the engine speed Ne.

  On the other hand, the opening degree DL of the low pressure EGR control valve 43 when the engine operating state is in the region II is calculated based on the following equation.

DL = DL0 · k
Here, DL0 represents a basic opening, and k represents a correction coefficient.

  The basic opening DL0 is an opening required to make the actual EGR rate coincide with the target EGR rate when the urea aqueous solution is not supplied from the supply control valve 30, and is a function of the engine load factor KL and the engine speed Ne. It is stored in the ROM 52 in advance in the form of a map shown in FIG.

  On the other hand, the correction coefficient k (0 <k ≦ 1.0) is for correcting the decrease in the basic opening degree DL0 when the liquid containing the ammonia generating compound is supplied from the supply control valve 30, and needs to be corrected. If not, it is held at 1.0.

  In addition, each grid point shown by the black circle in FIG.3 and FIG.4 represents the point in which opening degree DH and DL0 are each set, and opening degree DH and DL0 are each calculated by interpolation between grid points. . Further, the opening degrees DH and DL0 may be set to the opening degrees necessary for making the EGR gas amount actually supplied to the engine coincide with the target amount.

  As described above, the liquid containing the ammonia generating compound is supplied into the exhaust pipe 23 upstream of the NOx selective reduction catalyst 27. There are various types of ammonia generating compounds capable of generating ammonia, and therefore various compounds can be used as the ammonia generating compound. In the embodiment according to the present invention, urea is used as the ammonia generating compound, and an aqueous urea solution is used as the liquid containing the ammonia generating compound. Therefore, hereinafter, the present invention will be described by taking as an example the case of supplying an aqueous urea solution into the exhaust pipe 23 upstream of the NOx selective reduction catalyst 27.

On the other hand, in the embodiment shown in FIG. 1, a catalyst V ₂ O ₅ / TiO ₂ (hereinafter referred to as a vanadium / titania catalyst) in which titania is used as the NOx selective reduction catalyst 27 and vanadium oxide is supported on the support is used. A catalyst Cu / ZSM5 (hereinafter referred to as a copper zeolite catalyst) in which a zeolite is used as a carrier and copper is supported on the carrier is used.

When urea aqueous solution is supplied to exhaust gas containing excess oxygen, NO contained in the exhaust gas is reduced by ammonia NH ₃ generated from urea CO (NH ₂ ) ₂ on the NOx selective reduction catalyst 27 (for example, 2NH ₃ + 2NO + 1 / 2O ₂ → 2N ₂ + 3H ₂ O).

  That is, urea in the supplied aqueous urea solution first adheres to the NOx selective reduction catalyst 27. At this time, if the temperature of the NOx selective reduction catalyst 27 is high, for example, approximately 350 ° C. or higher, urea is thermally decomposed at once and ammonia is generated.

  On the other hand, when the temperature of the NOx selective reduction catalyst 27 is from about 132 ° C. to about 350 ° C., urea is once stored in the NOx selective reduction catalyst 27, and then a little ammonia from the urea stored in the NOx selective reduction catalyst 27. It is generated and released one by one. The generation of ammonia in this case is considered to be due to the change in the form of urea on the NOx selective reduction catalyst 27. That is, urea changes to biuret at approximately 132 ° C., biuret changes to cyanuric acid at approximately 190 ° C., and cyanuric acid changes to cyanic acid or isocyanic acid at approximately 360 ° C. Alternatively, as the elapsed time from storage in the NOx selective reduction catalyst 27 becomes longer, urea changes to biuret, biuret changes to cyanuric acid, and cyanuric acid changes to cyanic acid or isocyanic acid. It is considered that ammonia is generated little by little in the process of such morphological change.

  When the urea aqueous solution is supplied to the NOx selective reduction catalyst 27 when the temperature of the NOx selective reduction catalyst 27 is approximately 132 ° C. or less, which is the thermal decomposition temperature of urea, urea in the urea aqueous solution is stored in the NOx selective reduction catalyst 27, Occasionally ammonia is not generated from the stored urea.

  In the embodiment according to the present invention, the supply control is performed when the temperature of the NOx selective reduction catalyst 27 is within the reduction temperature range (for example, about 200 ° C. to about 500 ° C.) in which the NOx purification rate of the NOx selective reduction catalyst 27 is higher than the allowable lower limit. When the urea aqueous solution is supplied from the valve 30 into the exhaust pipe 23 and the temperature of the NOx selective reduction catalyst 27 is outside this reduction temperature range, the supply of the urea aqueous solution is stopped. Further, even when the temperature of the NOx selective reduction catalyst 27 is outside the reduction temperature range, the urea aqueous solution is supplied when the amount of urea stored in the NOx selective reduction catalyst 27 is smaller than the allowable lower limit.

  However, for example, when the urea aqueous solution is supplied to the NOx selective reduction catalyst 27 when the temperature of the NOx selective reduction catalyst 27 is high, the urea aqueous solution comes into contact with the NOx selective reduction catalyst 27 and vaporizes at a stroke, and as a result, the NOx selective reduction catalyst. There is a possibility that the pressure in the exhaust passage around 27, for example, the pressure in the exhaust pipe 23 between the catalytic converters 22 and 24, will increase significantly. In this case, the pressure around the inflow end 44 of the low pressure EGR passage 42 also increases significantly, however, the pressure around the outflow end 45 of the low pressure EGR passage 42 does not change, and therefore the inflow end 44 and outflow end 45 of the low pressure EGR passage 42 are changed. The pressure difference between them increases significantly. Therefore, if the EGR gas is supplied to the engine via the low pressure EGR passage 42 at this time, a large amount of EGR gas may be supplied to the engine and the actual EGR rate may be higher than the target EGR rate.

  That is, as schematically shown in FIG. 5, when the urea aqueous solution is supplied, the pressure PE in the exhaust pipe 23 is significantly increased compared to the exhaust pipe pressure PE0 when the urea aqueous solution is not supplied. . In this case, if the opening degree DL of the low pressure EGR control valve 43 is set to the basic opening degree DL0, the actual EGR rate will be higher than the target EGR rate.

  Therefore, in the embodiment according to the present invention, when the urea aqueous solution is supplied when the EGR gas is supplied through the low pressure EGR passage 42, the basic opening DL0 is corrected to be decreased by the correction coefficient k. As a result, a large amount of EGR gas is prevented from being supplied to the engine.

  Further, in the embodiment according to the present invention, the basic opening degree DL0 is corrected to decrease by the correction coefficient k so that the actual target EGR rate is maintained at the target EGR rate. The correction coefficient k in this case is stored in advance in the ROM 52 in the form of a map shown in FIG. 6, for example, as a function of the temperature Tc of the NOx selective reduction catalyst 27 and the urea aqueous solution supply amount Qu. The increase ΔPE (FIG. 5) of the exhaust pipe pressure PE generated when the urea aqueous solution is supplied is the temperature Tc of the NOx selective reduction catalyst 27 and the amount Qu of the urea aqueous solution supplied to the NOx selective reduction catalyst 27 per unit time. This is because the deviation of the actual EGR rate from the target EGR rate depends on the catalyst temperature Tc and the urea aqueous solution supply amount Qu.

  When the EGR gas is supplied through the high pressure EGR passage 40, the EGR rate or the EGR amount does not change even when the urea aqueous solution is supplied. At this time, the opening degree DH of the high pressure EGR control valve 41 is corrected. Absent.

  FIG. 7 shows an EGR control routine of an embodiment according to the present invention. This routine is executed by interruption every predetermined time.

  Referring to FIG. 7, first, at step 100, it is judged if the engine operating state is within a region I (FIG. 2). When the engine operating state is within the region I, the routine proceeds to step 101 where the opening degree DH of the high pressure EGR control valve 41 is calculated from the map of FIG. In the subsequent step 102, the opening DL of the low pressure EGR control valve 43 is set to zero. Next, the routine proceeds to step 112.

  On the other hand, when the engine operating state is outside the region I, the routine proceeds from step 100 to step 103, where it is determined whether or not the engine operating state is within the region II (FIG. 2). When the engine operating state is within the region II, the routine proceeds to step 104 where the opening degree DH of the high pressure EGR control valve 41 is set to zero. In the following step 105, the basic opening degree DL0 of the low pressure EGR control valve 43 is calculated from the map of FIG. In the following step 106, it is determined whether or not the urea aqueous solution is currently supplied. When the urea aqueous solution is currently supplied, the routine proceeds to step 107, where the correction coefficient k is calculated from the map of FIG. In the following step 108, the opening degree DL of the low pressure EGR control valve 43 is calculated (DL = DL0 · k). Next, the routine proceeds to step 112. On the other hand, when the urea aqueous solution is not currently supplied, the routine proceeds from step 106 to step 109, the correction coefficient k is set to 1.0, and then the routine proceeds to step 108 where the opening DL of the low pressure EGR control valve 43 is calculated. The Next, the routine proceeds to step 112.

  On the other hand, when the engine operating state is outside the region II, that is, within the region III, the routine proceeds from step 103 to step 110, where the opening degree DH of the high pressure EGR control valve 41 is set to zero. In the subsequent step 111, the opening degree DL of the low pressure EGR control valve 43 is set to zero. Next, the routine proceeds to step 112.

  In step 112, the high pressure EGR control valve 41 and the low pressure EGR control valve 43 are driven so that the opening degrees become DH and DL, respectively.

  FIG. 8 shows another embodiment according to the present invention. The embodiment shown in FIG. 8 is provided with an escape passage 35 for allowing exhaust gas to escape from the exhaust pipe 23 to which the inflow end 44 of the low-pressure EGR passage 42 is connected. 1 is different from the embodiment shown in FIG. 1 in that a control type relief control valve 36 is arranged. In the example shown in FIG. 8, the escape passage 35 is connected to the exhaust pipe 25 downstream of the NOx selective reduction catalyst 27. Further, the relief control valve 36 is normally closed.

  In general, when the opening of the valve becomes considerably small, it becomes difficult to accurately control the amount of gas passing through the valve. Therefore, in another embodiment according to the present invention, when the EGR gas is to be supplied through the low pressure EGR passage 42, the opening degree DL of the low pressure EGR control valve 43 is prevented from becoming smaller than the allowable lower limit DLm.

  In another embodiment according to the present invention, when the urea aqueous solution is supplied, the pressure PE in the exhaust pipe 23 increases, and at this time, the opening DL of the low pressure EGR control valve 43 is corrected to decrease. In this case, the degree of opening DL of the low pressure EGR control valve 43 is reduced as the increase width ΔPE of the exhaust pipe pressure PE is increased.

  Therefore, if the exhaust pipe pressure increase ΔPE is considerably large, the opening DL of the low pressure EGR control valve 43 may need to be decreased beyond the allowable lower limit DLm. Nevertheless, the low pressure EGR control valve The opening degree DL of 43 is corrected to decrease only up to the allowable lower limit DLm. In this case, the actual EGR rate is higher than the target EGR rate.

  On the other hand, if the relief control valve 36 is opened, the pressure PE in the exhaust pipe 23 can be reduced, and therefore the actual EGR amount or EGR rate can be reduced.

  Therefore, in another embodiment according to the present invention, when the opening degree DL of the low pressure EGR control valve 43 should be corrected to decrease beyond the allowable lower limit DLm, the opening degree DL of the low pressure EGR control valve 43 is set to the allowable lower limit DLm and the relief control is performed. The valve 36 is opened. The opening degree DE of the relief control valve 36 in this case is stored in advance in the ROM 52 in the form of a map shown in FIG. 9 as a function of the temperature Tc of the NOx selective reduction catalyst 27 and the urea aqueous solution supply amount Qu.

  That is, as shown in FIG. 10, as the pressure increase width ΔPE in the exhaust pipe 23 increases, the opening DL of the low pressure EGR control valve 43 is corrected to decrease, and the opening DL of the low pressure EGR control valve 43 is allowed. When the lower limit DLm is reached, the opening degree DE of the relief control valve 36 is increased while being maintained at the allowable lower limit DLm.

  FIG. 11 shows an EGR control routine of another embodiment according to the present invention. This routine is executed by interruption every predetermined time.

  Referring to FIG. 11, first, at step 200, it is determined whether or not the engine operating state is within a region I (FIG. 2). When the engine operating state is within the region I, the routine proceeds to step 201, where the opening degree DH of the high pressure EGR control valve 41 is calculated from the map of FIG. In the subsequent step 202, the opening degree DL of the low pressure EGR control valve 43 is set to zero. In the subsequent step 203, the opening degree DE of the relief control valve 36 is set to zero. Next, the routine proceeds to step 218.

  On the other hand, when the engine operating state is outside the region I, the routine proceeds from step 200 to step 204, where it is determined whether or not the engine operating state is within the region II (FIG. 2). When the engine operating state is within the region II, the routine proceeds to step 205 where the opening degree DH of the high pressure EGR control valve 41 is set to zero. At the next step 206, the basic opening degree DL0 of the low pressure EGR control valve 43 is calculated from the map of FIG. In subsequent step 207, it is determined whether or not the urea aqueous solution is currently supplied. When the urea aqueous solution is currently supplied, the routine proceeds to step 208, where the correction coefficient k is calculated from the map of FIG. In the following step 209, the opening degree DL of the low pressure EGR control valve 43 is calculated (DL = DL0 · k). Next, the process proceeds to step 211. On the other hand, when the urea aqueous solution is not currently supplied, the routine proceeds from step 207 to step 210, the correction coefficient k is set to 1.0, and then the routine proceeds to step 209, where the opening DL of the low pressure EGR control valve 43 is calculated. The Next, the process proceeds to step 211. In step 211, it is determined whether or not the opening degree DL of the low pressure EGR control valve 43 calculated in step 209 is smaller than the allowable lower limit DLm. When DL ≧ DLm, the routine proceeds to step 212 where the opening degree DE of the relief control valve 36 is set to zero. Next, the routine proceeds to step 218. On the other hand, when DL <DLm, the routine proceeds from step 211 to step 213, where the opening degree DL of the low pressure EGR control valve 43 is set to the allowable lower limit DLm. At the next step 214, the opening degree DE of the relief control valve 36 is calculated from the map of FIG. Next, the routine proceeds to step 218.

  On the other hand, when the engine operating state is outside the region II, that is, within the region III, the routine proceeds from step 204 to step 215, where the opening degree DH of the high pressure EGR control valve 41 is set to zero. In the subsequent step 216, the opening degree DL of the low pressure EGR control valve 43 is set to zero. In the following step 217, the opening degree DE of the relief control valve 36 is set to zero. Next, the routine proceeds to step 218.

  In step 218, the high pressure EGR control valve 41, the low pressure EGR control valve 43, and the relief control valve 36 are driven so that the opening degrees become DH, DL, and DE, respectively.

  So far, the present invention has been described by taking as an example a case where a urea aqueous solution is supplied to the NOx selective reduction catalyst and NOx is reduced with ammonia generated from the urea aqueous solution. However, the present invention can also be applied to a case where another liquid reducing agent is supplied to another catalyst, or a case where the liquid fuel is supplied to the catalyst to raise the temperature of the catalyst and the catalyst carrier. A particulate filter can be used for this catalyst carrier.

  Further, the inflow end 44 of the low pressure EGR passage 42 can be connected to an exhaust pipe downstream of the catalyst to which the liquid is supplied.

1 is an overall view of an internal combustion engine. It is a diagram which shows the area | regions I, II, and III. It is a map which shows the opening degree DH of a high pressure EGR control valve. It is a map which shows the basic opening degree DL of a low pressure EGR control valve. It is a time chart for demonstrating the Example by this invention. It is a map which shows the correction coefficient k. It is a flowchart which shows an EGR control routine. It is a general view of the internal combustion engine which shows another Example by this invention. It is a map which shows the opening degree DE of a relief control valve. It is a diagram which shows the opening degree of the low pressure EGR control valve and the relief control valve in another Example by this invention. It is a flowchart which shows the EGR control routine of another Example by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine main body 4 Intake manifold 5 Exhaust manifold 27 NOx selective reduction catalyst 30 Supply control valve 42 Low pressure EGR passage 43 Low pressure EGR control valve

Claims (8)

  In an exhaust gas recirculation control apparatus for an internal combustion engine in which an engine exhaust passage and an engine intake passage are connected to each other by an exhaust gas recirculation passage and an exhaust gas recirculation control valve is disposed in the exhaust gas recirculation passage, a catalyst is disposed in the exhaust passage. In addition, a supply control valve is disposed in the exhaust passage upstream of the catalyst so that liquid is supplied from the supply control valve into the exhaust passage upstream of the catalyst, and liquid is supplied from the supply control valve. A recirculation control device that corrects the opening of the exhaust gas recirculation control valve to be reduced when compared to when no liquid is supplied.   2. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein the catalyst and the supply control valve are disposed in an exhaust gas passage downstream of an inflow end of the exhaust gas recirculation passage.   2. The exhaust gas recirculation control apparatus for an internal combustion engine according to claim 1, wherein an exhaust passage downstream of the exhaust turbocharger turbine and an intake passage upstream of the compressor of the exhaust turbocharger are connected to each other by the exhaust recirculation passage.   The exhaust gas recirculation control apparatus for an internal combustion engine according to claim 1, wherein the catalyst is composed of a catalyst suitable for reducing NOx in exhaust gas with ammonia, and the liquid is composed of an aqueous urea solution.   The internal combustion engine according to claim 1, wherein when the liquid is supplied from the supply control valve, the opening degree of the exhaust gas recirculation control valve is corrected so that the exhaust gas recirculation gas amount or the EGR rate is maintained at a target value. Engine exhaust gas recirculation control device.   The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein when the liquid is supplied from the supply control valve, the opening degree of the exhaust gas recirculation control valve is corrected according to the temperature of the catalyst.   The exhaust gas recirculation of an internal combustion engine according to claim 1, wherein when the liquid is supplied from the supply control valve, the opening degree of the exhaust gas recirculation control valve is corrected according to the amount of the liquid supplied from the supply control valve. Circulation control device.   An exhaust passage for escaping exhaust gas from the exhaust passage around the catalyst is provided, and a release control valve is disposed in the escape passage. When the opening degree of the exhaust gas recirculation control valve should be corrected to decrease below an allowable lower limit, exhaust gas is discharged. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, wherein the opening degree of the recirculation control valve is set to the allowable lower limit and the opening degree of the relief control valve is increased.

Images