Engine exhaust emission control device and engine exhaust emission control method

ES 2 393 487 T3

DESCRIPTION

Engine exhaust emission control device and exhaust emission control method

[Technical field]

The present invention relates to an engine exhaust emission control device, and in particular, to technology for purifying nitrogen oxides discharged from a vehicle engine, using ammonia as a reducing agent.

[Background of the invention]

As a device for purifying air pollutants discharged from an engine, in particular nitrogen oxides (hereinafter referred to as "NOx") in exhaust gases, using post-treatment, the SCR (Selective Catalytic Reduction) device is known. ) following. This SCR device is arranged in the exhaust gas passage of an engine, and includes an injection device that injects an aqueous solution of ammonia or a precursor thereof. The ammonia injected by this injection device functions as a reducing agent, and reacts with NOx on a catalyst, to reduce and purify NOx. Furthermore, as an SCR device that facilitates the storage of ammonia in a vehicle, the following device is known. This SCR device is provided with a tank that stores urea water as an ammonia precursor, and at the time of actual operation, injects the urea water supplied from this tank to the exhaust gas passage, to produce ammonia from hydrolysis. of urea using exhaust heat (Patent Document 1). Engine operating conditions, such as engine speed and load, are generally detected and urea water in an amount corresponding to the detected operating conditions is injected into the exhaust gases (Patent Document 2).

[Patent Document 1]

Japanese Unexamined Patent Publication No. 2000-027627 (Paragraph No. 0013)

[Patent Document 2]

Japanese Unexamined Patent Publication No. 2001-020724 (Paragraph No. 0004)

JP 2002-371831 describes an automobile exhaust emission control device by interposing an exhaust emission control means having a selective catalytic reduction catalyst in an exhaust system of an automobile engine and devised to inject the agent solution reducer in a reservoir of reducing agent solution to the selective catalytic reduction catalyst. The control device is formed by providing a liquid level sensor and a concentration sensor in the reducing agent solution tank and by providing a control device to send a working signal to an alarm by receiving a liquid shortage signal from the sensor. level indicator and an abnormal concentration signal from the concentration sensor.

Description of the invention

Problems to solve with the invention

However, the previous SCR device has the following problems. As a parameter related to an engine operation, there is a case where the operating characteristics of an engine part, such as a fuel injection valve, are set in order to specifically reduce a particle emission amount. In such a position, an amount of NOx emission generally increases. If the SCR device is operating normally, the discharged NOx can be purified by a reduction reaction with ammonia. Based on such a position that allows the emission of NOx to a certain degree, a case is assumed where an anomaly has occurred in an engine part, and the composition of the exhaust gases has changed. In this case, if the urea water injection amount is kept at the normal level regardless of an increase in the NOx emission amount, then the ammonia is insufficient relative to the NOx, and unpurified NOx is discharged into the atmosphere. On the other hand, if the urea water injection amount is kept at the normal level regardless of a decrease in the NOx emission amount , then not only will the urea water be consumed unnecessarily, but excessive ammonia will be generated and the Surplus ammonia will be discharged into the atmosphere. Also, it is assumed that an abnormality has occurred in the SCR device, and the amount of urea water injection has changed, or the amount of ammonia content in the urea water (that is, the urea concentration) has changed . In this case, since the amount of ammonia addition to the exhaust gas changes, the ratio of NOx and ammonia deviates from an optimal value, and the reduction reaction does not proceed well, so that the NOx extraction rate will not meet the requirements. When ammonia is added excessively, the excess ammonia is discharged into the atmosphere.

An object of the present invention is to control, by suppression, the discharge of NOx and ammonia to the atmosphere

ES 2 393 487 T3 when an abnormality occurs in a motor part or an SCR device.

[Means to solve problems]

The present invention provides an engine exhaust emission control device. The device according to the present invention is provided with an addition device for adding a reducing agent for NOx to exhaust gases, and uses the reducing agent added by this adding device to promote a reduction of NOx in the exhaust gases. The device according to the present invention can be appropriately applied to a vehicle engine, and ammonia can be used for the NOx reducing agent. In one embodiment of the present invention, an abnormality that occurs in the adding device is detected as a first abnormality. By manipulating an engine control factor that influences the exhaust gas composition at the emission time point of a cylinder (hereinafter simply referred to as "engine control factor"), the amount of NOx emission of the engine under the same operating condition varies in the case where the appearance of the first anomaly is detected, with respect to other cases.

In another embodiment of the present invention, an abnormality that occurs in an engine part to realize the engine control factor is detected as a second abnormality. The amount of the reducing agent to be added by the adding device is made to vary in the case where the second anomaly is detected, with respect to other cases.

In another embodiment of the present invention, the occurrence of the first abnormality is detected, and the occurrence of the second abnormality is detected. Times other than when an occurrence of at least one of the first or the second anomaly is detected are assumed to be normal times. The engine control factor is manipulated at the time of the appearance of the first anomaly where the appearance of the first anomaly is detected, to make the amount of NOx emission from the engine vary with respect to the normal times in the same. engine operating conditions. Furthermore, at the time of the appearance of the second anomaly where the appearance of the second anomaly is detected, the amount of the reducing agent to be added by the adding device is made to vary with respect to the normal times.

Effect of the invention

According to the present invention, when an abnormality occurs in an engine part, and the amount of NOx emission from the engine changes, an amount of the reducing agent to be added by the adding device can be controlled to counteract the actual amount of emission of NOx. Therefore, NOx discharge due to insufficient supply of the reducing agent, and discharge of reducing agent due to excessive supply can be avoided. Furthermore, when an abnormality occurs in the adding device, and the device is unable to add an exact amount of the reducing agent, the engine control factor can be manipulated to suppress the formation of NOx itself. Therefore, NOx discharge can be avoided.

Other objects and aspects relating to the present invention can be understood from the following description with reference to the accompanying drawings.

The entire content of a Japanese patent application (No. 2003-345723), which is the basis for a priority claim, is incorporated as a part of the present application and refers thereto.

Brief description of the drawings

Figure 1 represents a configuration of a motor according to an embodiment of the present invention.

Figure 2 represents a configuration of a control system for the engine and an exhaust emission control device therefor.

Figure 3 is a flow chart of an anomaly detection routine performed by a U / C-SCR.

Figure 4 is a flow chart of a urea water injection control routine.

Fig. 5 is a flow chart of an abnormality detection routine performed by a motor U / C.

Figure 6 is a flow chart of a motor control routine.

Description of reference symbols

1: engine, 11: intake air passage, 12: turbocharger, 13: expansion tank, 21: injector, 22: common rail, 31: exhaust gas passage, 32: oxidation catalyst, 33: purification catalyst NOx, 34: ammonia purification catalyst, 35: EGR tube, 36: EGR valve, 41: tank, 42: urea water supply tube, 43: injection nozzle, 44: feed pump, 45: filter , 46: urea water return pipe,

ES 2 393 487 T3

47: pressure control valve, 48: air supply pipe, 51: engine U / C, 61: U / C-SCR, 71, 72: exhaust gas temperature sensor, 73: NOx sensor , 74: urea sensor, 75: residual quantity sensor, 76: air pressure sensor, 77: urea water pressure sensor, 78: element part voltage sensor.

Best Mode of Carrying Out the Invention

An embodiment of the present invention is described below with reference to the drawings.

Fig. 1 depicts a configuration of a motor vehicle engine (hereinafter referred to as an "engine") according to an embodiment of the present invention. In the present embodiment, a direct injection type diesel engine is used as an engine 1.

An air filter (not shown in the diagram) is mounted in an induction part of an air intake passage 11, and the air filter removes dust from the intake air. A compressor 12a of a variable nozzle type turbocharger 12 (constituting a "supercharger" in the present embodiment) is arranged in the air intake passage 11, and the intake air is compressed and discharged by the compressor 12a. The compressed intake air flows to a buffer tank 13, and is distributed to respective cylinders in a manifold part.

In the main engine body, injectors 21 are installed in the cylinder head for each cylinder. The injectors 21 operate according to signals from an engine control unit 51 (hereinafter referred to as the "engine U / C"). Fuel that has been fed by a fuel pump (not represented in the diagram), is supplied to the injectors 21 through a common rail 22, and is injected into the combustion chambers by the injectors 21.

In an exhaust passage 31, a turbine 12b of the turbocharger 12 is installed downstream of the manifold part. Turbine 12b is driven by exhaust gases to thereby rotate compressor 12a. In the turbine 12b, the variable vane angle 121 is controlled by a VNT control unit 122. The rotational speed of the turbine 12b and the compressor 12a changes according to the angle of the variable vanes 121.

Downstream of the turbine 12b, an oxidation catalyst 32, a NOx purification catalyst 33, and an ammonia purification catalyst 34 are installed in this order from the upward side. The oxidation catalyst 32 oxidizes hydrocarbon and carbon monoxide in the exhaust gases, and converts the nitrogen monoxide (hereinafter referred to as "NO") in the exhaust gases to NOx, which is composed primarily of nitrogen dioxide (later called "NO2"). This has the effect of adjusting a ratio of NO and NO2 contained in the exhaust gases to the optimum ratio for a NOx reduction reaction described later. NOx Purification Catalyst 33 reduces NOx in exhaust gases and purifies it. In order to promote NOx reduction with the NOx purification catalyst 33, in the present embodiment, ammonia is added to the exhaust gases upstream of the NOx purification catalyst 33 as a reducing agent.

In the present embodiment, in order to facilitate storage of ammonia, urea is stored in the state of aqueous solution as an ammonia precursor. By storing ammonia as urea, safety can be ensured.

A urea water supply tube 42 is connected to a reservoir 41 containing urea water, and a urea water injection nozzle 43 is mounted on a tip portion of the urea water supply tube 42. A pump Feed tube 44 and a filter 45 are installed in the urea water supply tube 42 in this order from the upward side. Feed pump 44 is driven by electric motor 441. The speed of the electric motor 441 is controlled by signals from an SCR control unit 61 (hereinafter "U / C-SCR), to regulate the discharge rate of the feed pump 44. In addition, downstream of the filter 45, A urea water return tube 46 is connected to the urea water supply tube 42. The urea water return tube 46 is configured with a pressure control valve 47 installed therein so that excess urea water above a specified pressure returns to the reservoir 41.

The injection nozzle 43 is an air-assisted type injection nozzle, and includes a main body 431, and a nozzle portion 432. The urea water supply pipe 42 is connected to the main body 431, and a Air supply 48 for supplying air to assist injection (the supplied air is hereinafter referred to as "assist air") is also connected to main body 431. Air supply tube 48 is connected to an air reservoir (not shown in the diagram), and assist air is supplied from this air reservoir. The nozzle portion 432 is installed to pass through a box of the NOx purification catalyst 33 and an ammonia purification catalyst 34, upstream of the NOx purification catalyst 33. The injection direction of the nozzle portion 432 is set in a direction parallel with the flow of exhaust gases and facing an end surface of the NOx purification catalyst 33.

When urea water is injected, the urea in the injected urea water is hydrolyzed by the exhaust heat, and ammonia is produced. The ammonia produced acts as a NOx reducing agent in the purification catalyst

ES 2 393 487 T3 of NOx 33, and promotes the reduction of NOx. The ammonia purification catalyst 34 is intended to purify unreacted ammonia that has passed through the NOx purification catalyst 33 without contributing to the reduction of NOx. Since ammonia has an irritating odor, it is preferable not to discharge ammonia that has not been purified. The oxidation reaction of NO in the oxidation catalyst 32, the hydrolysis reaction of urea, the reduction reaction of NOx in the NOx purification catalyst 33, and the oxidation reaction of unreacted ammonia in the purification catalyst of ammonia 34, are expressed by the following expressions (1) to (4). In the present embodiment, the NOx purification catalyst 33 and the ammonia purification catalyst 34 are installed in a housing; however, they can be configured to be respectively installed in separate boxes.

NO + 1 / 2O₂-DO NOT₂(1) (NH₂)₂CO + H₂O ^ 2NH₃+ CO₂(2)

NO + NO₂+ 2NH₃-2N₂+ 3H₂OR (3)

4NH₃+ 3O₂-2N₂+ 6H₂OR (4)

Furthermore, the exhaust gas passage 31 is connected to the air intake passage 11 via an EGR pipe 35. The exhaust gases are recirculated to the air intake passage 11 through this EGR pipe 35. An EGR valve 36 is installed in the EGR tube 35, and this EGR valve 36 controls the flow rate of the recirculating exhaust gases. The opening of the EGR valve 36 is controlled by an EGR control unit 361. The exhaust gas recirculation device in the present embodiment is configured by the EGR tube 35 and the EGR valve 36.

In the exhaust gas passage 31, a temperature sensor 71 for detecting the temperature of the exhaust gases before the addition of urea water is installed between the oxidation catalyst 32 and the NOx purification catalyst 33. A temperature sensor 72 to detect the temperature of the exhaust gases after reduction, and a NOx sensor 73 to detect the concentration of NOx contained in the exhaust gases after reduction, are installed downstream of the purification catalyst. ammonia 34. Furthermore, a urea sensor 74 for detecting the Du concentration (hereinafter "concentration" simply refers to urea concentration) of the urea contained in the stored urea water, and a residual quantity sensor 75 for detecting a Ru quantity of the Stored urea water, are arranged inside the reservoir 41.

Like the urea sensor 74 (corresponding to a "first sensor" in the present embodiment), a sensor of any known way can be used. In the present embodiment, a sensor is used that detects the Du concentration based on a heat transfer rate of the urea water corresponding to the urea concentration. Furthermore, the residual quantity sensor 75 (corresponding to a "second sensor") is configured including a float, and a variable resistor that detects the position of the float (that is, the "level"), and a residual quantity Ru of water. urea is detected based on the level of buoyancy detected. According to the temperature sensitive urea sensor 74 that detects a Du concentration based on the heat transfer rate of urea water, since there is a significant difference in heat transfer rate between urea and air, it is You can use it to determine if the reservoir 41 is empty, instead of using the residual amount Ru, by previously obtaining the output characteristics of the urea sensor 74 for when the urea sensor is in air. As a result, the first and second sensors can be realized with the single urea sensor 74.

In the present embodiment, the U / C-SCR 61 corresponds to a "first controller" and the motor U / C 51 corresponds to a "second controller". Furthermore, the reservoir 41, the urea water supply tube 42, the injection nozzle 43, the feed pump 44, and the air supply tube 48 constitute a reducing agent addition device. The urea sensor 74 can have both a function as the first sensor that detects the concentration, and a function as the second sensor that determines the residual amount.

Figure 2 represents a configuration of an engine control system 1.

The motor U / C 51 and the U / C-SCR 61 are connected in order to allow two-way communication.

An EGR control unit 361 and a VNT control unit 122 are connected to the motor U / C 51 in order to respectively allow bi-directional communication. The EGR control unit 361 has the function of detecting an abnormality that has occurred in the EGR system, and a signal indicating the occurrence of this abnormality is sent to the engine U / C 51. The VNT control unit 122 has the function of detecting an anomaly that has occurred in the VNT system, and a signal indicating the appearance of this anomaly is sent to the motor U / C 51. The motor U / C 51 sends command signals according to the operating conditions of the engine 1 to the EGR control unit 361 and the VNT control unit 122. On the other hand, when the signals that indicate the appearance of anomalies are

ES 2 393 487 T3 received from these control units 361 and 122, an engine-side abnormality signal (corresponding to a "adding device control signal" in the present embodiment) indicating the occurrence of an abnormality in the motor 1 is sent to U / C-SCR 61. Furthermore, an ignition switch, a start switch, a crank angle sensor, a vehicle speed sensor, a throttle sensor, and the like, are installed in the engine 1, and the detection signals from these sensors they are sent to the motor U / C 51. The motor U / C 51 calculates a motor speed Ne based on the signal input from the crank angle sensor. The engine U / C 51 sends information required for the urea water injection control, such as the injection amount, to the U / C-SCR 61.

The U / C-SCR 61 receives detection signals from the temperature sensors 71 and 72, the NOx sensor 73, the urea sensor 74, and the residual quantity sensor 75, and calculation information for the injection quantity and analogs, and receives an assist air pressure Pa, a water pressure of urea Pu, and a sensor voltage of urea Vs. The assist air pressure Pa is the pressure within the air supply tube 48, and is detected by a pressure sensor 76 arranged in the air supply tube 48. The urea water pressure Pu is the pressure within the urea water supply tube 42, and is detected by a pressure sensor 77 arranged in urea water supply tube 43 downstream of feed pump 44. The urea sensor voltage Vs is an output voltage based on the concentration sensed by the urea sensor 74, and is sensed by a voltage sensor 78. The U / C-SCR 61 calculates and sets an optimal amount of water injection based on the input signals and information, and sends a command signal according to the set amount of urea water injection to the injection nozzle 43. In addition, the U / C-SCR 61 detects an abnormality that has occurred in the urea water injection system, as described below, based on the assist air pressure Pa, the urea water pressure Pu , the urea sensor voltage Vs, the concentration Dn, and the residual amount Ru, and sends an anomaly signal from the SCR side (corresponds to the “motor control signal”) that indicates the appearance of this anomaly to the U / C motor 51.

The following describes the operation of the motor U / C 51 and the U / C-SCR 61 using flow charts.

First, the operation of the U / C-SCR 61 is described.

Figure 3 is a flow chart of an anomaly detection routine. This routine is started by turning on the power switch, and then repeats during each predetermined interval. This routine detects an abnormality that has occurred in the urea water injection system.

At S101, the assist air pressure Pa, the urea water pressure Pu, the urea sensor voltage Vs, the concentration Du and the residual amount Ru are read.

At S102, it is determined whether or not the assist air pressure Pa is within a predetermined range between a predetermined upper limit value Pa2 and a lower predetermined limit value Pa1 (<Pa2). If the assist air pressure Pa is within this range, control proceeds to S 103, and if it is not within this range, control proceeds to S 108. When an assist air pressure that is less than the Pa1 value is detected, it can be determined that an assist air leak has occurred in the air supply pipe 42, and when an assist air pressure that is greater than the Pa2 value, it can be determined that clogging has occurred in the injection nozzle 43. Clogging of injection nozzle 43 occurs when urea solidifies within nozzle portion 432, thus blocking the passage.

At S103, it is determined whether the water pressure of urea Pu is greater than or equal to a set predetermined value. If it is greater than or equal to the value Pu1, control passes to S104, and if it is less than the value Pu1, control passes to S108. When a urea water pressure is detected that is less than the Pu1 value, it can be determined that the feed pump 44 has failed and is in a state where it cannot supply urea water with sufficient pressure.

At S104, it is determined whether the urea sensor voltage Vs is less than or equal to a predetermined value Vs1. If it is less than or equal to the value Vs1, control goes to S105, and if it is greater than the value Vs1, control goes to S108. When a urea sensor voltage is detected that is greater than the Vs1 value, it can be determined that a disconnect has occurred in the urea sensor 74.

At S105, it is determined whether the residual amount Ru is greater than or equal to a predetermined value Ru1. If it is greater than or equal to the Ru1 value, the control goes to S 106, and if it is less than the Ru1 value, it is determined that the tank 41 is empty, and the residual quantity is insufficient, and the control goes to S 108. The Ru1 value is set to the minimum residual amount required for injection.

At S106, it is determined whether the concentration Du is greater than or equal to a predetermined value Du1. If it is greater than or equal to the Du1 value, the control goes to S107, and if it is less than the Du1 value, it is determined that the urea water has been excessively diluted, and the control goes to S108. The Du1 value is set to the minimum concentration required for ammonia addition.

In S107, since the supposed abnormality in the urea water injection system has not occurred, a

ES 2 393 487 T3 SCR side abnormality determination flag Fscr is set to 0. In the present embodiment, the assist air leakage, the injection nozzle 43 clogging, the feed pump 44 failure, the disconnection of the urea sensor 74, the insufficient residual amount of urea water, and the dilution of the urea water detected as described above, correspond to the "first anomaly".

At S108, since an abnormality of some kind has occurred in the urea water injection system, the side abnormality determination flag SCR Fscr is set to 1, and a warning lamp is operated to inform the operator of the occurrence of the anomaly.

Figure 4 is a flow chart of a urea water injection control routine. This routine is executed during every predetermined interval.

At S201, the SCR side abnormality determination flag Fscr is read, and it is determined whether the read flag Fscr is 0. If the flag is 0, control passes to S202, and if it is not 0, then it is determined that it is An abnormality has occurred in the urea water injection system, and control passes to S208.

At S202, the injection quantity Qf, the concentration of NOx NOX (the output of the NOx sensor 73), and the concentration Du are read.

In S203, the urea water injection amount Qu is calculated. The calculation of the urea water injection quantity Qu is carried out by calculating a basic injection quantity according to the injection quantity Qf and the NOx NOX concentration, and correcting the calculated basic injection quantity by the Du concentration. When the concentration Du is high, and therefore the amount of urea contained per unit injection amount is large, a decrease correction of the basic injection amount is carried out. Conversely, when the concentration Du is low, and therefore the amount of urea contained per unit injection amount is small, an increase correction of the basic injection amount is carried out.

At S204, the engine side abnormality determination flag Feng is read, and it is determined whether the read flag Feng is 0. If the flag is 0, control passes to S205, and if it is not 0, then it is determined that An abnormality has occurred in motor 1, and control passes to S206.

In S205, the urea water injection amount Qu that has been calculated in S203 is set to an output value Qu.

In S206, correction of the urea water injection amount Qu calculated in S203 is carried out according to the abnormality that occurred in the engine 1, and the corrected urea water injection amount is set to the output value. What The mode of the anomaly produced can be determined by inputting an identification signal corresponding to said mode from the motor U / C 51. The trends of the change of the NOx emission amount for each of the anomalies in the engine 1 are determined in advance experimentally, and in the actual operation, the urea water injection amount is changed according to the increase or decrease of the amount of NOx emission due to the anomaly produced. For example, when the NOx emission amount has increased due to an abnormality, the urea water injection amount is increased by an amount corresponding to the increase amount. In conjunction with the correction of the urea water injection quantity, the control can be carried out in order to switch a map of controlled variables of engine parts from the one used in normal times, in order to suppress the formation of NOx. proper.

At S207, an operation signal corresponding to the set output value Qu is sent to the injection nozzle 43.

At S208, the urea water injection is stopped. This is because, in a state where an abnormality has occurred in the urea water injection system, an exact amount of urea water cannot be injected for the amount of NOx emission, and there is a possibility that NOx non-purified is discharged to the atmosphere when the urea water injection amount is less than the optimal value, and when the urea water injection amount is greater than the optimum value there is a possibility not only that urea water is consumed unnecessarily, but also that the excess produced ammonia will not be completely decomposed by the ammonia purification catalyst 34 , and is discharged into the atmosphere. Furthermore, this is because naturally when the tank 41 is empty, or when the urea water has been excessively diluted, or, instead of the urea water, the tank 41 contains water or a different type of aqueous solution other than the urea water, ammonia cannot be added in an amount required for NOx purification.

The following describes the operation of motor U / C 51.

Figure 5 is a flow chart of an anomaly detection routine. This routine is started by turning on the power switch, and then repeats during each predetermined interval. This routine detects an abnormality that has occurred in motor 1.

ES 2 393 487 T3

In S301, it is determined whether an EGR system abnormality determination flag Fegr is 0. If the flag is 0, control passes to S302, and if it is 1, it is determined that an EGR system abnormality has occurred, and control passes to S304. An abnormality in the EGR system is detected by the EGR control unit 361. The EGR control unit 361 detects the voltage of a command signal sent to the EGR valve 36, and when the detected voltage is greater than a predetermined value, it is determined that a disconnect has occurred in a control line of the EGR system, and the EGR system anomaly determination flag Fegr is set to 1.

At S302, it is determined whether a VNT Fvnt system abnormality determination flag is 0. If the flag is 0, control passes to S303, and if it is 1, it is determined that a VNT system abnormality has occurred, and control passes to S304. An abnormality in the VNT system is detected by the VNT control unit 122. The VNT control unit 122 detects an abnormality that has occurred in the VNT system, based on an intake air pressure detected by a boost sensor, when the detected air pressure deviates from a predetermined range indicating normality. In the present embodiment, the boost sensor is installed in the surge tank 13, and detects the pressure inside the surge tank 13. EGR and VNT system anomalies detected as described above correspond to a “second anomaly”.

At S303, the Feng motor side abnormality determination flag is set to 0.

At S304, the Feng engine side abnormality determination flag is set to 1.

Figure 6 is a flow chart of a motor control routine. This routine is executed during every predetermined interval.

At S401, the engine side abnormality determination flag Feng is read, and it is determined whether the read flag Feng is 0. If the flag is 0, control passes to S402, and if it is not 0, it is determined that An abnormality has occurred in motor 1, and control passes to S407.

In S402, various operating conditions used for the control of engine parts are read, such as engine speed Ne and throttle opening APO.

At S403, the SCR side abnormality determination flag Fscr is read, and it is determined whether the read flag Fscr is 0. If the flag is 0, control passes to S404. And if it is not 0, it is determined that an abnormality has occurred in the urea water injection system, and control passes to S405.

In S404, the normal operation map is selected and the selected map is searched according to the read operating conditions, to calculate the controlled variables of the engine parts. In the present embodiment, the engine parts include the EGR valve 36, and the turbocharger 12, and the controlled variables to be calculated (i.e., the engine control factors) include the opening of the EGR valve 36, and the angle of variable vanes 121 (of turbine 12b).

At S405, a low NOx operation map is selected and the selected map is searched according to the read operating conditions, to calculate the controlled variables of the engine parts. When an abnormality has occurred in the urea water injection system, then as mentioned above, the injection of the urea water is stopped. However, by selecting the low NOx operating map, the formation of NOx itself is prevented in order to suppress the discharge of NOx to the atmosphere. In order to suppress NOx formation, for example, an EGR rate is increased (the opening of the EGR valve 36, and the angle of the variable vanes 121 is changed based on this increase), and the operating conditions are changed. fuel injection. For example, the injection time is delayed relative to the stall angle, and the injection pressure is reduced. Fluctuations in engine torque due to changes in fuel injection conditions are avoided by regulating the injection quantity.

At S406, the calculated controlled variables are sent to the engine part control units 361 and 122.

In S407, an identification signal according to the mode of the anomaly produced in the engine 1 is sent to the U / CSCR 61. For example, when the anomaly produced is related to the EGR system, an identification signal is sent indicating the occurrence of an abnormality in the EGR system. If an abnormality occurs in the EGR system, the exhaust gas recirculation stops, and therefore the amount of NOx emission increases. U / CSCR 61 increases the amount of urea water injection with respect to the amount of NOx emission to avoid the discharge of NOx to the atmosphere.

According to the present embodiment, the following effects can be obtained.

Firstly, when an abnormality occurs in the engine 1, and the NOx emission amount changes, then according to this change, the urea water injection amount is changed. Therefore, the amount of urea water injection can be made to counteract the actual amount of NOx emission, and the

ES 2 393 487 T3 NOx discharge due to insufficient urea water and ammonia discharge due to excessive urea water.

Second, when an abnormality occurs in the urea water injection system, the engine parts, such as the EGR valve 36, are controlled in order to suppress the formation of NOx itself. Therefore, NOx discharge can be avoided. In the present embodiment, in conjunction with the control of engine parts, the injection of the urea water is stopped. Therefore, a situation where urea water is injected in excess due to unstable operation, so that ammonia is discharged, can be avoided.

Third, as an abnormality in urea water injection system, in addition to abnormality of parts such as injection nozzle 43, urea water abnormalities such as insufficient residual amount and dilution are adopted, and when the appearance of these anomalies is detected, a warning lamp lights up. Therefore, the operator can be instructed to properly maintain and manage the urea water.

In the above, ammonia is produced as a result of hydrolyzing urea. However, a catalyst for hydrolyzing urea is not specifically specified. In order to improve the hydrolysis efficiency, a catalyst for hydrolysis upstream of the NOx reduction catalyst (ie, the NOx purification catalyst 33) can be provided.

Also, in the above, the anomalies that take place in the EGR system and the VNT system are considered as the second anomalies. However, in addition to these anomalies, anomalies taking place in the fuel supply injector, or the fuel supply system for supplying fuel to the injector, can be considered. As an abnormality that occurs in the injector, for example, the occurrence of a disconnection of a control line can be determined when weak electric current flows to the injector, and the electric current then actually flows is less than a predetermined value. Also, as an abnormality that occurs in the fuel supply system, it can be determined, for example, the occurrence of a fault in the fuel pump when the pressure inside the common rail 22 is detected, and the detected pressure is lower. than a default value.

As the engine, a diesel engine other than the direct injection type or a gasoline engine can be used.

In the above, the present invention has been described using some preferable embodiments. However, the scope of the present invention is not limited in any way by the foregoing description, and is to be determined based on the description of the claims, in accordance with the applicable text.