JP2009156159A - Device for determining abnormal section of exhaust emission control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for determining an abnormal section of an exhaust emission control system capable of determining even abnormality of each element constructing the exhaust emission control system. <P>SOLUTION: This device for determining the abnormal section of the exhaust emission control system includes a selective reduction type NOx catalyst 34 provided in an exhaust gas passage of an internal combustion engine, an NH<SB>3</SB>oxidation catalyst 36 and an urea water supply means 40 at a downstream thereof. The device is provided with a NOx sensor 52 disposed at a downstream of the NH<SB>3</SB>oxidation catalyst, a NOx concentration increase means increasing NOx concentration of exhaust gas by predetermined quantity during an abnormality determination mode, a first output value change detection means detecting change of output value of the NOx sensor when the NOx concentration is increased by predetermined quantity, an urea water supply quantity increase control means controlling predetermined quantity increase of the urea water supply quantity, a second output value change detection means detecting change of output value of the NOx sensor when urea water supply quantity is controlled to be increased by predetermined quantity, and a first determination means determining if at least the selective reduction type NOx catalyst and the NH<SB>3</SB>oxidation catalyst is normal or abnormal based on change of output value of the NOx sensor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for determining an abnormal part of an exhaust gas purification system of an internal combustion engine, particularly an exhaust gas having a selective reduction type NOx catalyst and an ammonia oxidation catalyst, and having urea water supply means for supplying urea water to an exhaust passage upstream thereof. The present invention relates to an apparatus for determining an abnormal part of a gas purification system.

  In general, as an exhaust purification device disposed in an exhaust system of an internal combustion engine such as a diesel engine, a selective reduction type NOx catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen is known. This is because a necessary amount of reducing agent is added upstream of the selective reduction type NOx catalyst, and the reducing agent is subjected to a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the catalyst, thereby discharging NOx. The concentration can be reduced.

  In the case of automobiles, it is difficult to ensure safety with respect to traveling with ammonia itself as a reducing agent, and therefore it has been proposed to use non-toxic urea water as a reducing agent. That is, if urea water is added to the exhaust gas upstream of the selective reduction type NOx catalyst, the urea water is thermally decomposed into ammonia and carbon dioxide gas in the exhaust gas, and the NOx in the exhaust gas is converted into the selective reduction type NOx catalyst. This is because ammonia is reduced and purified well by ammonia.

  By the way, in such an exhaust purification device that reduces and purifies NOx using urea water as a reducing agent, the selective reduction type NOx catalyst is deteriorated with time due to heat and exhaust gas components, and the NOx reduction performance gradually increases. Therefore, if the addition amount control of the urea water is continued with the initial performance of the selective reduction type NOx catalyst as a reference, an excess amount is generated in the added urea water as the operation time becomes longer. In other words, ammonia may be scrubbed to the rear of the selective reduction NOx catalyst without being used in the NOx reduction and purification reaction. Therefore, as a countermeasure, it has not been used in the downstream of the selective reduction NOx catalyst. An ammonia oxidation catalyst for oxidizing ammonia is provided.

  In the exhaust gas aftertreatment system in which urea water is supplied as a reducing agent to such an exhaust gas aftertreatment system including the selective reduction type NOx catalyst and the ammonia oxidation catalyst, the supply amount of urea water is changed. A method for monitoring an exhaust gas aftertreatment system has been proposed in which it is determined that a defect exists when the signal of a sensor arranged in the exhaust gas system does not change as expected (see, for example, Patent Document 1). ).

JP 2004-176719 A

  By the way, in the monitoring method of the exhaust gas aftertreatment system described in Patent Document 1, whether or not the signal of the sensor arranged in the exhaust gas system changes as expected simply by changing the supply amount of urea water. Therefore, it is possible to determine whether or not there is a defect in the exhaust gas aftertreatment system as a whole, that is, it is possible to determine abnormality in the entire system, but each element constituting the exhaust gas aftertreatment system It was impossible to determine which of these was in an abnormal state, and there was room for improvement in that respect.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for determining an abnormal portion of an exhaust gas purification system that can also determine an abnormality of each element constituting the exhaust gas purification system.

In order to achieve the above object, an embodiment of the apparatus for determining an abnormal part of an exhaust gas purification system according to the present invention includes a selective reduction type NOx catalyst provided in an exhaust passage of an internal combustion engine, an NH ₃ oxidation catalyst downstream thereof, An apparatus for determining an abnormal site in an exhaust gas purification system having urea water supply means for supplying urea water to an exhaust passage upstream of a selective reduction type NOx catalyst, comprising: a NOx sensor disposed downstream of the NH ₃ oxidation catalyst; The NOx concentration increasing means for increasing the NOx concentration of the exhaust gas discharged from the internal combustion engine by a predetermined amount during the abnormality determination mode in the predetermined operating state of the internal combustion engine, and the NOx concentration increasing by a predetermined amount by the NOx concentration increasing means A first output value change detecting means for detecting a change in the output value of the NOx sensor, and a change in the output value by the first output value change detecting means. The urea water supply amount increase control means for controlling the urea water supply amount from the urea water supply means to increase by a predetermined amount in response to the detection of liquefaction, and the urea water supply amount by the urea water supply amount increase control means respectively. Based on a change in the output value of the NOx sensor detected by the second output value change detecting means, a second output value change detecting means for detecting a change in the output value of the NOx sensor when the increase control is performed. And a first determination means for determining normality or abnormality of at least the selective reduction type NOx catalyst and the NH ₃ oxidation catalyst.

According to the embodiment of the apparatus for determining an abnormal part of the exhaust gas purification system according to the present invention, the NOx of the exhaust gas discharged from the internal combustion engine by the NOx concentration increasing means during the abnormality determination mode in a predetermined operation state of the internal combustion engine. The concentration is increased by a predetermined amount, and a change in the output value of the NOx sensor disposed downstream of the NH ₃ oxidation catalyst is detected by the first output value change detecting means.

At this time, if the output value of the NOx sensor by the first output value change detecting means does not change, it means that NOx or NH ₃ has not increased despite the increase in NOx concentration, and at least selective reduction. The type NOx catalyst is estimated to be normal. Corresponding to the detection of the change in output value, the urea water supply amount from the urea water supply means is controlled to increase by a predetermined amount by the urea water supply amount increase control means, at which time the second output value change detection is performed respectively. The change in the output value of the NOx sensor is detected by the means. Then, based on the change in the output value of the NOx sensor detected by the second output value change detection means, the first determination means determines whether at least the selective reduction type NOx catalyst and the NH ₃ oxidation catalyst are normal or abnormal. Is done. That is, when the output value of the NOx sensor does not change, NOx and NH ₃ have not increased despite the increase in the urea water supply amount. In other words, the selective reduction type NOx catalyst and the NH ₃ oxidation catalyst are not operating normally. Since it means that it is functioning, it is determined that both the selective reduction type NOx catalyst and the NH ₃ oxidation catalyst are normal. On the other hand, when the output value of the NOx sensor changes, there is an increase in NH ₃ accompanying an increase in the urea water supply amount, which means that this has not been processed, so the selective reduction type NOx catalyst is normal. However, it is determined that the NH ₃ oxidation catalyst is abnormal (failure).

Further, when the output value of the NOx sensor by the first output value change detecting means described above changes, it means that NOx has increased as the NOx concentration has increased, and at least the selective reduction type NOx catalyst is normal. It is presumed to be abnormal without functioning. Corresponding to the detection of the change in output value, the urea water supply amount from the urea water supply means is controlled to increase by a predetermined amount by the urea water supply amount increase control means, at which time the second output value change detection is performed respectively. The change in the output value of the NOx sensor is detected by the means. When the output value of the NOx sensor by the second output value change detecting means has changed, NH ₃ has increased with the increase in the urea water supply amount, which means that this has not been processed. The first determination means determines that both the selective reduction NOx catalyst and the NH ₃ oxidation catalyst are abnormal (failure).

Therefore, according to this embodiment, it is possible to determine whether at least the selective reduction type NOx catalyst or the NH ₃ oxidation catalyst is normal or abnormal.

Here, in the embodiment, when there is a change in the output value by the first output value change detecting unit and there is no change in the output value by the second output value change detecting unit, the urea water supply unit A urea water supply amount reduction control means for reducing the urea water supply amount, and a change in the output value of the NOx sensor when the urea water supply amount is controlled to be reduced by the urea water supply amount reduction control means. Output value change detecting means 3 and the change in the output value of the NOx sensor detected by the third output value change detecting means, the urea water supply means, the selective reduction type NOx catalyst and the NH ₃ oxidation catalyst It is preferable to further comprise a second determination means for determining normality or abnormality.

According to this aspect, when there is a change in the output value by the first output value change detecting means in the one aspect and there is no change in the output value by the second output value change detecting means, the urea water supply amount The amount of urea solution supplied from the urea solution supply unit is controlled to decrease by the amount reduction control unit, and at this time, the change in the output value of the NOx sensor is detected by the third output value change detection unit. When there is a change in the output value by the first output value change detecting means and there is no change in the output value by the second output value change detecting means, the increase in NH ₃ accompanying the increase in the urea water supply amount However, this means that the NH ₃ oxidation catalyst was normally treated, so it is assumed that the NH ₃ oxidation catalyst is normal. When the output value of the NOx sensor by the third output value change detecting means does not change, the urea water supply amount is controlled to be reduced by the urea water supply amount reduction control means. As a result of the reduced amount of water not being supplied, this means that there is no increase in untreated NOx. Therefore, the urea water supply means is abnormal (failure) by the second determination means, and the NH ₃ oxidation catalyst is normal. It is determined. On the other hand, when the output value of the NOx sensor by the third output value change detecting means changes, it means that the NH ₃ oxidation catalyst is normal but the untreated NOx has increased, and the selective reduction type NOx catalyst is normal. It is determined that the function is abnormal.

Therefore, according to this embodiment, it is possible to determine whether the selective reduction type NOx catalyst or the NH ₃ oxidation catalyst is normal or abnormal, including the urea water supply means.

The first determination means detects the second output value change detection means when there is no change in the output value of the NOx sensor detected by the first output value change detection means. When there is no change in the output value of the NOx sensor, it is determined that both the selective reduction type NOx catalyst and the NH ₃ oxidation catalyst are normal, and the output value of the NOx sensor detected by the second output value change detecting means When there is a change, it may be determined that the selective reduction type NOx catalyst is normal and the NH ₃ oxidation catalyst is abnormal.

Further, the first determination means detects the second output value change detection means when there is a change in the output value of the NOx sensor detected by the first output value change detection means. When there is a change in the output value of the NOx sensor, it may be determined that both the selective reduction type NOx catalyst and the NH ₃ oxidation catalyst are abnormal.

Further, the second determination means determines that the NH ₃ oxidation catalyst is normal and the urea water supply means when there is no change in the output value of the NOx sensor detected by the third output value change detection means. May be determined to be abnormal.

The second determination means determines that the NH ₃ oxidation catalyst is normal and the selective reduction type NOx when there is a change in the output value of the NOx sensor detected by the third output value change detection means. It may be determined that the catalyst is abnormal.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic system diagram of an internal combustion engine according to an embodiment of the present invention. In the figure, 10 is a compression ignition type internal combustion engine or diesel engine for automobiles, 11 is an intake manifold communicated with an intake port, 12 is an exhaust manifold communicated with an exhaust port, and 13 is a combustion chamber. . In the present embodiment, fuel supplied from a fuel tank (not shown) to the high pressure pump 17 is pumped to the common rail 18 by the high pressure pump 17 and accumulated in a high pressure state, and the high pressure fuel in the common rail 18 is transferred from the injector 14 to the combustion chamber. 13 is directly injected and supplied. Exhaust gas from the engine 10 passes from the exhaust manifold 12 through the turbocharger 19 and then flows into the exhaust passage 15 downstream thereof. After being purified as described later, the exhaust gas is discharged to the atmosphere. In addition, as a form of a diesel engine, it is not restricted to the thing provided with such a common rail type fuel injection device. It is also optional to include other exhaust purification devices such as EGR devices.

  On the other hand, the intake air introduced from the air cleaner 20 into the intake passage 21 passes through the air flow meter 22, the turbocharger 19, the intercooler 23, and the throttle valve 24 in order to reach the intake manifold 11. The air flow meter 22 is a sensor for detecting the intake air amount, and specifically outputs a signal corresponding to the flow rate of the intake air. The throttle valve 24 is an electronically controlled type.

  The exhaust passage 15 includes, in order from the upstream side, an oxidation catalyst 30 that oxidizes unburned components contained in the exhaust gas, a DPF catalyst 32 that captures and treats particulates (PM), and is contained in the exhaust gas in the passage. A NOx catalyst 34 for reducing and purifying NOx and an ammonia oxidation catalyst 36 are provided. The NOx catalyst 34 of the present embodiment is a selective reduction type NOx catalyst, and can reduce NOx continuously and purify it when a reducing agent is added.

  An addition valve 40 for selectively adding urea as a reducing agent to the selective reduction NOx catalyst 34 is provided in the exhaust passage 15 downstream of the DPF catalyst 32 and upstream of the selective reduction NOx catalyst 34. . Urea is used in the form of a urea aqueous solution, and is injected and supplied into the exhaust passage 15 from the addition valve 40 toward the selective reduction type NOx catalyst 34 on the downstream side. A urea dispersion plate 41 is provided downstream of the addition valve 40 and upstream of the selective reduction type NOx catalyst 34 to uniformly distribute the injected urea aqueous solution to the selective reduction type NOx catalyst 34. Further, a supply device 42 for supplying a urea aqueous solution is connected to the addition valve 40, and a tank 44 for storing the urea aqueous solution is connected to the supply device 42.

Further, an electronic control unit (hereinafter referred to as ECU) 100 is provided as a control means for controlling the entire engine. The ECU 100 includes a digital computer and includes a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processor Unit), an input port, an output port, a storage device, and the like that are connected to each other via a bidirectional bus. . The ECU 100 controls the injector 14, the high-pressure pump 17, the throttle valve 24, and the like so that desired engine control is executed based on detection values of various sensors. The ECU 100 also controls the addition valve 40 and the supply device 42 to control the urea addition amount. Further, the ECU 100 is configured to be able to execute a failure determination process described later by executing a program stored in the ROM, and the ECU 100 has an abnormality site determination device of the exhaust gas purification system according to the present invention. It is configured to function as an example.

  As sensors connected to the ECU 100, in addition to the air flow meter 22 described above, in the present embodiment, a NOx sensor 52 provided on the downstream side of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36, and an addition valve are also used. 40, a pre-catalyst exhaust temperature sensor 54 and a post-catalyst exhaust temperature sensor 56 provided on the upstream side and the downstream side of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36, respectively. The NOx sensor 52, the pre-catalyst exhaust temperature sensor 54, and the post-catalyst exhaust temperature sensor 56 output a signal corresponding to the NOx concentration and temperature of the exhaust gas at the installation position to the ECU 100, respectively.

Here, a thermistor can be used as the exhaust temperature sensor, and a stabilized zirconia solid electrolyte can be used as the NOx sensor 52. The NOx sensor 52 using the stabilized zirconia as a solid electrolyte decomposes NOx in the exhaust gas into O ₂ and N ₂ to detect the O ₂ partial pressure, thereby detecting the NOx concentration in the exhaust gas. . Further, if NH ₃ is present in the exhaust gas, this NH ₃ is oxidized into NO in the solid electrolyte made of stabilized zirconia of the NOx sensor 52, and NO resulting from the oxidation of NH ₃ is also detected as NOx. The detected output value of the NOx sensor 52 is the sum of both the NOx concentration and the NH ₃ concentration in the exhaust gas.

  As other sensors, a crank angle sensor 26 and an accelerator opening sensor 27 are connected to the ECU 100. The crank angle sensor 26 outputs a crank pulse signal to the ECU 100 when the crank angle rotates, and the ECU 100 detects the crank angle of the engine 10 based on the crank pulse signal and calculates the rotational speed of the engine 10. The accelerator opening sensor 27 outputs a signal corresponding to the accelerator pedal opening (accelerator opening) operated by the user to the ECU 100.

Selective reduction type NOx catalyst (SCR: Selective Catalytic Reduction) 34 is supported by supporting a noble metal such as Pt on the surface of a substrate such as zeolite or alumina, or by supporting a transition metal such as Cu on the surface of the substrate by ion exchange. Examples thereof include those obtained by carrying a titania / vanadium catalyst (V ₂ O ₅ / WO ₃ / TiO ₂ ) on the surface of the substrate. The selective reduction type NOx catalyst 34 reduces and purifies NOx when the catalyst temperature (catalyst bed temperature) is in the active temperature range and urea as a reducing agent is added. When urea water is added to the catalyst, ammonia (NH ₃ ) is generated on the selective reduction type NOx catalyst as typically shown in the following chemical reaction formula and the like, and this ammonia reacts with NOx to react with NOx. Are reduced to produce nitrogen (N ₂ ) and water (H ₂ O).
・ CO (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂
・ 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O
・ 6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O

In this embodiment, the urea addition amount with respect to the selective reduction type NOx catalyst 34 is a basic urea water corresponding to the NOx generation amount to be processed based on the information of the engine operating state (for example, the engine rotation speed and the accelerator opening). The amount of addition is determined by reading from a control map that is obtained and set in advance by experiments. Further, the ECU 100 may control the NOx concentration detected by the NOx sensor 52 provided downstream of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36. Specifically, the urea injection amount from the addition valve 40 is controlled so that the detected value of the NOx concentration is always zero. In this case, the urea injection amount may be set based only on the detected value of the post-catalyst NOx concentration, or basic urea water based on the information on the engine operating state (for example, engine speed and accelerator opening) described above. The addition amount may be read and determined from the control map, and this may be feedback correction controlled based on the detection value of the NOx sensor 52. Since the selective reduction type NOx catalyst 34 can reduce NOx only when urea is added, urea water is usually added constantly. Further, control is performed so that urea is added only in a minimum amount necessary for reducing NOx discharged from the engine. In order to prevent the so-called NH ₃ slip that ammonia is discharged downstream of the catalyst due to excessive addition of urea, the above-described ammonia oxidation catalyst 36 is provided.

  Here, with reference to Table 1, each mode in which normality or abnormality is determined by the abnormality site determination device of the exhaust gas purification system in the present embodiment will be described.

  In Table 1, ◯ means normal and x means abnormal. In the mode “1”, it means that the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 are both functioning normally. Conversely, in the mode “4”, the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 This means that both of the catalysts 36 do not function normally and are in an abnormal state. In modes “2” and “3”, it means that either the selective reduction type NOx catalyst 34 or the ammonia oxidation catalyst 36 is in an abnormal state, and mode “5” is normally set from the urea water supply system. This means that there is an abnormal state in which urea is not supplied. In the following description, the first to fifth output values x “1” to x “5” of the NOx sensor 52 are output values corresponding to the above-described modes “1” to “5”, respectively.

Therefore, the relationship between the modes “1” to “5” and the first to fifth output values x “1” to x “5” of the NOx sensor 52 is represented by the distance from the addition valve 40 as the horizontal axis. The concentration and NH ₃ concentration will be described with reference to FIG.

  First, it is assumed that the output gas having a predetermined NOx concentration flows into the selective reduction type NOx catalyst 34 downstream of the addition valve 40. In mode “5”, which is an abnormal state in which urea is not normally supplied from the urea water supply system, NOx reduction processing is not performed, and the NOx concentration is detected by the NOx sensor 52 as shown by a solid line a in FIG. Is detected as an output value x “5”. On the other hand, in the modes “2” and “4” in which the selective reduction type NOx catalyst 34 is in an abnormal state, the NOx reduction process corresponding to the remaining processing capacity is slightly performed and the NOx concentration is lowered. As indicated by a broken line b in A), the output value x “2” and the output value x “4” which are slightly smaller than the output value x “5” are detected. Further, in the mode “1” and the mode “3” in which the selective reduction type NOx catalyst 34 is in a normal state, the NOx reduction process is performed and the NOx concentration is greatly reduced. As a result, a one-dot chain line c in FIG. As shown, the output value x “1” and the output value x “3”, which are almost zero, are detected.

Assuming that urea is supplied from the urea water supply system, a gas having NH ₃ concentration corresponding to the processing capacity appears downstream of the selective reduction type NOx catalyst 34 and flows into the ammonia oxidation catalyst 36. In mode “2” in which the selective reduction type NOx catalyst 34 is in an abnormal state, the urea water is not consumed so much, resulting in a slightly higher NH ₃ concentration gas, whereas the selective reduction type NOx catalyst 34 is in a normal state. In the mode “1”, urea water is almost consumed and becomes a gas having a lower NH ₃ concentration. In the mode “3” and the mode “4” in which the ammonia oxidation catalyst 36 is in an abnormal state, the NH ₃ oxidation process is not performed, and the NOx sensor 52 is used as shown by the broken line d and the solid line e in FIG. The output value x “3” and the output value x “4” corresponding to the NH ₃ concentration are detected. On the other hand, in the mode “1” and the mode “2” in which the ammonia oxidation catalyst 36 is in the normal state, the NH ₃ oxidation process is performed, and the NOx sensor 52 is almost as shown by the one-dot chain line f in FIG. It is detected as an output value x “1” close to zero or an output value x “2”.

Note that the detection output value of the NOx sensor 52, since the sum of the output values of both corresponding to NOx concentration and the NH ₃ concentration as described above, the output value x corresponding respectively to the NOx concentration and the NH ₃ concentration in the above When “1” to x “5” are added, the first to fifth output values x “1” to x “5” of the NOx sensor 52 are obtained as shown in FIG.

  Next, an example of a processing procedure for executing normality or abnormality determination by the abnormality site determination device of the exhaust gas purification system according to the present embodiment will be described with reference to the time chart of FIG. 4 together with the flowchart of FIG. To do. The illustrated determination routine is executed at a predetermined cycle when a predetermined condition is satisfied by the ECU 100.

  Therefore, before executing the normal or abnormal determination routine, it is determined by a normal control routine by the ECU 100 whether or not a predetermined condition is satisfied. Specifically, the bed temperature of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 is within a predetermined temperature range as described later, whether the NOx sensor 52 has been activated, whether urea water is added It is determined whether control is in progress and whether normal or abnormal determination is incomplete as will be described later. When any one of these predetermined conditions is not satisfied, this routine is not executed. This is because correct determination cannot be made even if the determination is executed when the predetermined condition is not satisfied.

  Here, a method for obtaining the bed temperature Tc of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 will be described. The temperatures of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 can be directly detected by a temperature sensor embedded in the catalyst, but in the present embodiment, they are estimated. Specifically, the ECU 100 estimates the bed temperature based on the pre-catalyst exhaust temperature and the post-catalyst exhaust temperature detected by the pre-catalyst exhaust temperature sensor 54 and the post-catalyst exhaust temperature sensor 56, respectively.

  Now, assume that the temperature of the exhaust gas upstream of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 is Tf (° C.), and the amount of the exhaust gas is Ga (g / s). Here, since the amount of exhaust gas can be considered to be equal to the amount of air taken into the engine, the amount of intake air Ga is defined as the amount of exhaust gas. This amount of exhaust gas is the amount of exhaust gas flowing into the catalyst per unit time (here 1 second). On the other hand, the bed temperature of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 is Tc (° C.), the weight of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 is Mc (g), the selective reduction type NOx catalyst 34 and the ammonia oxidation. The temperature of the exhaust gas on the downstream side of the catalyst discharged from the catalyst 36 is defined as Tr (° C.).

Further, Ef is the thermal energy of the exhaust gas upstream of the catalyst, and Ec is the thermal energy of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36. These thermal energies Ef and Ec can be expressed by the following equations (1) and (2). However, Cg is the specific heat ratio of the exhaust gas, Cc is the specific heat ratio of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36, and both are constant values.
Ef = Ga × Tf × Cg (J / s) (1)
Ec = Mc × Tc × Cc (J) (2)

By the way, considering the thermal equilibrium when the exhaust gas having the thermal energy Ef is supplied to the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 having the thermal energy Ec, a unit time has elapsed since the start of the exhaust gas supply. When it is considered that the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 and the exhaust gas are in a thermal equilibrium state later, and the temperature of both after the thermal equilibrium is Tm, the thermal equilibrium formula is expressed by the following formula (3).
Ef + Ec = Ga * Tm * Cg + Mc * Tm * Cc (3)

  This temperature Tm is a basic value of the estimated temperatures of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36. However, in reality, the exhaust gas and the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 do not reach a complete thermal equilibrium state, and the temperature is set downstream of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36. The exhaust gas of Tr is exhausted and the heat energy escapes. Therefore, the thermal energy Er that has escaped downstream is calculated based on the temperature Tr, and thereby the basic estimated temperature Tm of the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 is feedback-corrected, and the final estimated bed temperature Tc is calculated. Calculated.

  As understood from the above description, in this embodiment, the pre-catalyst exhaust temperature Tf, which is the exhaust gas temperature upstream of the selective reduction type NOx catalyst 34, is detected by the pre-catalyst exhaust temperature sensor 54, and the selective reduction type NOx catalyst. The post-catalyst exhaust temperature Tr, which is the exhaust gas temperature downstream of the gas catalyst 34 and the ammonia oxidation catalyst 36, is detected by the post-catalyst exhaust temperature sensor 56. Then, an intake air amount Ga that can be regarded as equivalent to the exhaust gas amount is detected by the air flow meter 22. Based on these detection values, the ECU 100 estimates the bed temperature Tc of the selective reduction NOx catalyst 34 and the ammonia oxidation catalyst 36.

  Then, before execution of the determination routine, it is determined whether or not the estimated bed temperature Tc is within a predetermined temperature range (for example, 200 to 400 ° C.). At the same time, whether or not the NOx sensor 52 has been activated, for example, whether or not the detected impedance has reached a predetermined value corresponding to the activation temperature of the NOx sensor 52, further controlling the addition of urea water. Is determined, for example, by the presence or absence of a valve opening operation control signal from the ECU 100 to the addition valve 40. As a result of these determinations, the determination routine is executed when a predetermined condition is satisfied.

  Therefore, when the above-mentioned predetermined condition is satisfied, in other words, a routine for determining whether the exhaust gas purification system is normal or abnormal is executed in the abnormality determination mode. When this determination routine is executed, first, in step S301, the amount of exhaust gas discharged from the internal combustion engine (hereinafter referred to as “exhaust gas”) is controlled to be constant or within a predetermined range. For example, the opening degree of the throttle valve 24 may be controlled based on the intake air amount Ga detected by the air flow meter 22 so that the intake air amount Ga is constant or within a predetermined range. As one of the predetermined conditions described above, an operating state in which the amount of exhaust gas (exhaust gas) discharged from the internal combustion engine is constant or within a predetermined range based on the intake air amount Ga detected by the air flow meter 22. You may make it set the condition that it is. In this way, changes in the NOx concentration can be grasped more accurately, so that normality or abnormality can be determined more accurately.

  Then, in the next step S302, control for increasing the NOx concentration in the exhaust gas of the engine 10 is executed. That is, the NOx concentration in the output gas is increased at time t0 in the time chart of FIG. As the control for increasing the NOx concentration, for example, in the case of the engine 10 provided with the exhaust gas recirculation device, the EGR amount is decreased from the reference exhaust gas recirculation amount (EGR amount) that minimizes the generation amount of NOx in a predetermined operation state. As a result, the NOx concentration may be increased by increasing the generated NOx amount per unit output gas amount.

Therefore, in the next step S303 after this NOx concentration increase control is performed, the NOx sensor detection value X1 (this is the above-described first to fifth values) as the first detection value measured this time by the NOx sensor 52. The output value x "1" to x "5" is included) and the above-described NOx sensor output value X0 before the NOx concentration increase control is compared. That is, the amount of change in the NOx sensor output value before and after the NOx concentration increase control is calculated as the difference dNOx1 between the two measurement values by the following equation (4).
dNOx1 = X1−X0 (4)

  As a result of the comparison in step S303, when the difference dNOx1 between the measured values of NOx concentration before and after the NOx concentration increase control is zero, that is, there is no change, in other words, the output value of the NOx sensor 52 is constant (mode “1” in FIG. 4). ”Or“ 3 ”), the process proceeds to step S304, and when there is a change (in the case of the mode“ 2 ”,“ 4 ”, or“ 5 ”in FIG. 3), the process proceeds to step S308. In both step S304 and step S308, as will be described later, urea water supply amount increase control is executed in which the urea water injection supply amount from the addition valve 40 is increased by a predetermined amount (time chart of FIG. 3). At time t1). The urea water supply amount increase control corresponds to the standard urea water supply suitable for purifying the NOx amount corresponding to the NOx concentration in the normal operation state before the NOx concentration increase control in step S302. It is carried out by increasing the urea water supply amount at a predetermined rate with respect to the amount (equivalent ratio: 1).

Therefore, in step S305 following step S304 that proceeds when the output value of the NOx sensor 52 is constant, the NOx sensor detection value X2 (see FIG. 4) as the second detection value newly measured by the NOx sensor 52. Mode (corresponding to mode “1” or “3”) is compared with the NOx sensor detection value X1 before the urea water supply amount increase control in step S304 described above. That is, the amount of change in the NOx concentration before and after the urea water supply amount increase control is calculated as the difference dNOx2 between the two measured values by the following equation (5).
dNOx2 = X2-X1 (5)
In this case, since X1 is equal to X0, it may be replaced with X0.

  As a result of the comparison in step S305, when the difference dNOx2 in the measured value of NOx concentration before and after the urea water supply amount increase control is zero, that is, there is no increase change, in other words, when the output value of the NOx sensor 52 is constant, step The process proceeds to S306, and when there is a change, the process proceeds to Step S307.

  In step S306, the output value of the NOx sensor 52 is constant and does not change both before and after the NOx concentration increase control and before and after the urea water supply amount increase control (corresponding to mode “1” in FIG. 4). Therefore, it means that both the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 are functioning normally, so a determination to that effect is made, and this routine is terminated.

  In step S307, the output value of the NOx sensor 52 is constant and unchanged before and after the NOx concentration increase control, but the output value of the NOx sensor 52 increases and decreases before and after the urea water supply amount increase control ( 4 (3)), the selective reduction type NOx catalyst 34 is functioning normally, but the ammonia oxidation catalyst 36 is not functioning normally, that is, it is abnormal. (Corresponding to the mode “3” described above) is performed, and this routine is terminated.

  On the other hand, as a result of the comparison in step S303 described above, the difference dNOx1 in the measured value of NOx concentration before and after the NOx concentration increase control is not zero, that is, in step S308 that proceeds when there is a change, as described above, the addition valve The urea water supply amount increase control is executed in which the urea water injection supply amount from 40 is increased by a predetermined amount (see time t1 in FIG. 4).

Therefore, in the next step S309, the NOx sensor detection value X3 as the third detection value newly measured by the NOx sensor 52 is the NOx sensor detection value X1 before the urea water supply amount increase control in step S308 described above. To be compared. That is, the change amount of the NOx concentration before and after the urea water supply amount increase control is calculated as the difference dNOx3 between the two measurement values by the following equation (6).
dNOx3 = X3−X1 (6)

  As a result of the comparison in step S309, when the difference dNOx3 between the measured values of the NOx concentration before and after the urea water supply amount increase control is zero, that is, there is no change (mode “2” or “5” in FIG. 4), in other words, When the output value of the NOx sensor 52 is constant, the process proceeds to step S311. When there is an increase change, the process proceeds to step S310.

  In step S310, the output value of the NOx sensor 52 changes before and after the NOx concentration increase control, and the output value of the NOx sensor 52 also changes before and after the urea water supply amount increase control (mode “4 in FIG. 4). Therefore, it means that the selective reduction type NOx catalyst 34 and the ammonia oxidation catalyst 36 are not functioning normally because neither NOx treatment nor ammonia treatment is performed, that is, it is abnormal. (Corresponding to the above-mentioned mode “4”) is performed, and this routine is terminated.

  Further, in step S311 which proceeds when there is a change in the output value of the NOx sensor 52 before and after the NOx concentration increase control and the difference dNOx3 in the measured value of NOx concentration before and after the urea water supply amount increase control is zero, that is, there is no change. Then, urea water supply amount reduction control is executed in which the urea water injection supply amount from the addition valve 40 is reduced by a predetermined amount (see time t2 in FIG. 4). The urea water supply amount decrease control is a reference urea water supply suitable for purifying the NOx amount in accordance with the NOx concentration in the normal operation state before the NOx concentration increase control in step S302. It is carried out by reducing the urea water supply amount at a predetermined rate with respect to the amount (equivalent ratio: 1).

Therefore, in the next step S312, the NOx sensor detection value X4 ("2" or "5" in FIG. 4) as the fourth detection value newly measured by the NOx sensor 52 is the urea water in the above-described step S311. It is compared with the NOx sensor detection value X1 or X3 before the supply amount reduction control. That is, the change amount of the NOx concentration before and after the urea water supply amount reduction control is calculated as the difference dNOx4 between the two measured values by the following equation (7).
dNOx4 = X4−X1 (7)
Here, since X1 is equal to X3 in this case, it may be replaced with X3.

  As a result of the comparison in step S312, when the difference dNOx4 between the measured values of NOx concentration before and after the urea water supply amount reduction control is zero, that is, there is no change (“5” in FIG. 4), in other words, the output of the NOx sensor 52. When the value is constant, the process proceeds to step S313, and when there is a change (“2” in FIG. 3), the process proceeds to step S314.

  In step S313, the output value of the NOx sensor 52 has changed before and after the NOx concentration increase control, but the output value of the NOx sensor 52 has not changed before and after the urea water supply amount increase control. At least the ammonia oxidation catalyst 36 is functioning normally, but since the output value of the NOx sensor 52 has not changed before and after the urea water supply amount reduction control, the supply device 42 including the addition valve 40 is abnormal. Is determined (corresponding to the mode “5” described above), and this routine is terminated.

  On the other hand, in step S314, as in step S313, the output value of the NOx sensor 52 has changed before and after the NOx concentration increase control, but the output value of the NOx sensor 52 has changed before and after the urea water supply amount increase control. Since it did not change, it is determined that at least the ammonia oxidation catalyst 36 is functioning normally. However, since the output value of the NOx sensor 52 has changed before and after the urea water supply amount reduction control, it means that the selective reduction type NOx catalyst 34 is not functioning normally, that is, it is abnormal. (Corresponding to the mode “2” described above) is performed, and this routine is terminated.

  In the embodiment of the present invention, the part that functions to execute step S303 in the flowchart of FIG. 3 is the first output value change detection means, and the part that functions to execute steps S304 and S308 is urea water. The supply amount increase control means, the part functioning to execute step S305 and step S309 is the second output value change detecting means, and the part functioning to execute step S306, step S307 and step S310 is the first. The determination means is configured. Further, the part that functions to execute step S311 performs the urea water supply amount reduction control means, the part that functions to execute step S312 performs the third output value change detection means, and executes steps S313 and S314. The part that functions as much as possible constitutes the second determination means.

  As is clear from the above description, according to the present embodiment, it is possible to determine which of the supply device 42 including the selective reduction NOx catalyst 34, the ammonia oxidation catalyst 36, and the addition valve 40 is abnormal. . Here, when any of them is determined to be abnormal, it is preferable that a warning or the like is appropriately given to the driver by a known method.

  Although not shown in the flowchart of FIG. 3, when it is determined in this routine that the supply device 42 including the selective reduction NOx catalyst 34, the ammonia oxidation catalyst 36, and the addition valve 40 is normal or abnormal, it is normal. Alternatively, a flag indicating that the abnormality determination has been completed is set. When this flag is set, in the above-described determination of whether or not the predetermined condition is satisfied, the determination is already completed and the predetermined condition is not satisfied, and the normal or abnormal determination routine after step S301 is not executed. This is because it is sufficient that the determination of normality or abnormality is executed at least once per trip (trip). Therefore, this flag is preferably reset when the engine 10 is stopped.

  Although one embodiment of the present invention has been described above, the present invention can adopt other embodiments. For example, a pre-catalyst NOx sensor may be provided on the upstream side of the selective reduction type NOx catalyst 34. In this case, the NOx concentration in the output gas is measured as a reference output value by the pre-catalyst NOx sensor, and this is compared with the output value of the above-mentioned NOx sensor 52 to determine whether or not the output value has changed. You may do it.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

It is the schematic which shows the determination apparatus of the abnormal site | part of the exhaust gas purification system which concerns on one Embodiment of this invention. 6 is a graph for explaining the relationship between modes “1” to “5” and first to fifth output values x “1” to x “5” of the NOx sensor 52 in the embodiment of the present invention; A) shows the NOx concentration, and (B) shows the NH ₃ concentration on the vertical axis and the distance from the addition valve 40 on the horizontal axis. (C) shows the first to fifth output values x “1” of the NOx sensor 52, which are obtained by adding the output values x “1” to x “5” respectively corresponding to the NOx concentration and the NH ₃ concentration. Or x “5”. It is a flowchart which shows an example of the determination processing procedure of a normal or abnormality in embodiment of this invention. It is a time chart for demonstrating the operation | movement which concerns on the abnormal region determination process in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 15 Exhaust passage 34 Selective reduction type NOx catalyst 36 Ammonia oxidation catalyst 40 Addition valve 42 Supply apparatus 52 NOx sensor 54 Pre-catalyst exhaust temperature sensor 56 Post-catalyst exhaust temperature sensor 100 Electronic control unit (ECU)

Claims (6)

An exhaust gas purification system comprising a selective reduction type NOx catalyst provided in an exhaust passage of an internal combustion engine, an NH ₃ oxidation catalyst downstream thereof, and urea water supply means for supplying urea water to an exhaust passage upstream of the selective reduction type NOx catalyst An apparatus for determining an abnormal site in
A NOx sensor disposed downstream of the NH ₃ oxidation catalyst;
NOx concentration increasing means for increasing the NOx concentration of the exhaust gas discharged from the internal combustion engine by a predetermined amount during an abnormality determination mode in the predetermined operating state of the internal combustion engine;
A first output value change detecting means for detecting a change in the output value of the NOx sensor when the NOx concentration is increased by a predetermined amount by the NOx concentration increasing means;
Urea water supply amount increase control means for increasing the urea water supply amount from the urea water supply means by a predetermined amount in response to detection of a change in the output value by the first output value change detection means;
Second output value change detection means for detecting a change in the output value of the NOx sensor when the urea water supply amount is controlled to increase by a predetermined amount by the urea water supply amount increase control means;
First determination means for determining whether the selective reduction NOx catalyst and the NH ₃ oxidation catalyst are normal or abnormal based on a change in the output value of the NOx sensor detected by the second output value change detection means;
An apparatus for determining an abnormal part of an exhaust gas purification system comprising: When the output value from the first output value change detecting means is changed and the output value from the second output value change detecting means is not changed, the urea water supply amount from the urea water supply means is reduced. Urea water supply amount reduction control means,
A third output value change detecting means for detecting a change in the output value of the NOx sensor when the urea water supply quantity is controlled to be reduced by the urea water supply quantity reduction control means;
A second determination unit that determines whether the urea water supply unit, the selective reduction type NOx catalyst, and the NH ₃ oxidation catalyst are normal or abnormal based on a change in the output value of the NOx sensor detected by the third output value change detection unit; Determining means,
The apparatus for determining an abnormal portion of the exhaust gas purification system according to claim 1, comprising: The first determining means is the NOx sensor detected by the second output value change detecting means when there is no change in the output value of the NOx sensor detected by the first output value change detecting means. When the output value of the NOx sensor does not change, it is determined that both the selective reduction type NOx catalyst and the NH ₃ oxidation catalyst are normal, and the change in the output value of the NOx sensor detected by the second output value change detecting means is _{3. The} apparatus for determining an abnormal part of an exhaust gas purification system according to claim 1, wherein the selective reduction type NOx catalyst is normal and the NH ₃ oxidation catalyst is abnormal. The first determination means includes the NOx sensor detected by the second output value change detection means when there is a change in the output value of the NOx sensor detected by the first output value change detection means. _{3. The} apparatus for determining an abnormal part of an exhaust gas purification system according to claim 1, wherein both the selective reduction type NOx catalyst and the NH ₃ oxidation catalyst are determined to be abnormal when there is a change in the output value of the exhaust gas purification system. . The second determination means determines that the NH ₃ oxidation catalyst is normal and the urea water supply means is abnormal when there is no change in the output value of the NOx sensor detected by the third output value change detection means. The apparatus for determining an abnormal part of an exhaust gas purification system according to any one of claims 2 to 4, characterized in that The second determination means determines that when the output value of the NOx sensor detected by the third output value change detection means is changed, the NH ₃ oxidation catalyst is normal and the selective reduction NOx catalyst is The apparatus for determining an abnormal part of an exhaust gas purification system according to any one of claims 2 to 4, wherein it is determined that the engine is abnormal.

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