JP2016079903A - Failure determination device of exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately determine which selection reduction type NOx catalyst is abnormal while suppressing a cost increase when a plurality of addition valves cannot be individually controlled.SOLUTION: A first addition valve, a first selection reduction type NOx catalyst, a second addition valve, a second selection reduction type NOx catalyst and a NOx sensor are arranged in an exhaust passage in this order. When the abnormality determination of the catalysts is performed, supply amounts of reductants from the first addition valve and the second addition valve are increased more than a supply amount of a reductant which is decided on the basis of an amount of NOx which flows into the first selection reduction type NOx, and when a NOx concentration rate which is calculated on the basis of a NOx concentration detected by the NOx sensor after the lapse of a prescribed time after a time point at which the supply amounts of the reductants from the first addition valve and the second addition valve are increased is not lower than a determination threshold, it is determined that an abnormality has occurred in the first selection reduction type NOx catalyst, and when the NOx concentration rate is lower than the determination threshold, it is determined that an abnormality has occurred in the second selection reduction type NOx catalyst.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a failure determination device for an exhaust gas purification device for an internal combustion engine.

  A selective reduction type NOx catalyst (hereinafter simply referred to as “NOx catalyst”) that purifies NOx contained in exhaust gas from an internal combustion engine by using ammonia as a reducing agent is known. On the upstream side of the NOx catalyst, an addition valve for supplying ammonia or an ammonia precursor into the exhaust gas is installed. Examples of the ammonia precursor include urea. Hereinafter, the precursor of ammonia or ammonia is also collectively referred to as “reducing agent”.

  Here, it is known that two NOx catalysts are provided in series in the exhaust passage of the internal combustion engine, and an addition valve for adding a reducing agent is provided upstream of each NOx catalyst (see, for example, Patent Document 1). .)

JP 2011-202620 A

  Here, in the case where a plurality of NOx catalysts and addition valves are provided, there is a risk that the control may be complicated if each addition valve is controlled individually. On the other hand, control can be simplified by operating each addition valve by the same control. However, when the addition valves cannot be individually controlled, it is difficult to determine which NOx catalyst is abnormal even if there is an abnormality in one NOx catalyst. That is, no matter which NOx catalyst is abnormal, the NOx purification rate of the entire system is similarly reduced, so it is difficult to determine which NOx catalyst is abnormal based on the NOx purification rate. is there. Further, by providing a NOx sensor downstream of each NOx catalyst, the NOx purification rate in each NOx catalyst can be calculated. In this case, it is possible to determine which NOx catalyst is abnormal. it can. However, in this case, it is necessary to install a plurality of NOx sensors, which increases costs.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to determine which selective reduction type NOx catalyst has an abnormality while suppressing an increase in cost when a plurality of addition valves cannot be individually controlled. It is to determine whether or not there is an accuracy.

In order to solve the above problems, the present invention provides a first addition valve provided in an exhaust passage of an internal combustion engine for supplying a reducing agent into the exhaust passage, and an adsorption passage provided in an exhaust passage downstream of the first addition valve. A first selective reduction type NOx catalyst that selectively reduces NOx by the reducing agent that is being used, and a second addition that is provided in the exhaust passage downstream of the first selective reduction type NOx catalyst and supplies the reducing agent into the exhaust passage A second selective reduction type NOx catalyst that selectively reduces NOx by a reducing agent that is provided in an exhaust passage downstream of the second addition valve and adsorbed, and exhaust gas flowing out of the second selective reduction type NOx catalyst A NOx sensor for detecting the NOx concentration of the catalyst, a supply abnormality determining means for determining whether an abnormality has occurred in the supply of the reducing agent, and the supply of the reducing agent based on the amount of NOx flowing into the first selective reduction type NOx catalyst Determine the quantity A control device that operates the first addition valve and the second addition valve according to the same instruction, and when the supply abnormality determining means determines that there is no abnormality in the supply of the reducing agent, A failure determination device for an exhaust gas purification device for an internal combustion engine that determines whether the selective reduction type NOx catalyst is abnormal or the second selective reduction type NOx catalyst is abnormal, wherein the control device is configured to detect the first selective reduction type NOx. When determining whether or not the catalyst and the second selective reduction type NOx catalyst are normal, the supply amount of the reducing agent determined based on the amount of NOx flowing into the first selective reduction type NOx catalyst is more than When the predetermined amount of time has elapsed from the time when the supply amount of the reducing agent from the first addition valve and the second addition valve is increased and the supply amount of the reducing agent from the first addition valve and the second addition valve is increased. By the NOx sensor If the NOx purification rate calculated based on the emitted NOx concentration is greater than or equal to the determination threshold, the first selective reduction NOx catalyst is abnormal, and if it is less than the determination threshold, the second selective reduction NOx catalyst is abnormal. It is determined that

  The abnormality of the first selective reduction type NOx catalyst (hereinafter also referred to as the first NOx catalyst) or the second selective reduction type NOx catalyst (hereinafter also referred to as the second NOx catalyst) according to the present invention is the first NOx. The NOx purification rate of either one of the catalyst or the second NOx catalyst is less than the allowable value, or either the first NOx catalyst or the second NOx catalyst is removed. Say. The first addition valve and the second addition valve supply, for example, urea water or ammonia as a reducing agent in the exhaust gas.

  Since the first addition valve and the second addition valve are operated according to the same instruction by the controller, the same control is performed on both addition valves. For this reason, each addition valve cannot be controlled individually. The first addition valve and the second addition valve perform normal control (hereinafter referred to as normal control) in which a reducing agent corresponding to the amount of NOx discharged from the internal combustion engine is supplied from the first addition valve and the second addition valve. When the addition valve is operated, the NOx purification rate of the entire system is lowered regardless of which NOx catalyst is abnormal. Note that the amount of reducing agent supplied when performing normal control is such that the NOx purification rate is within the target range based on the amount of reducing agent adsorbed by the first NOx catalyst and the second NOx catalyst when the system is normal. To be determined. When this normal control is performed, even if one NOx catalyst is abnormal, the other NOx catalyst can purify NOx, so the NOx purification rate of the entire system does not become zero. Furthermore, even if the first NOx catalyst is abnormal or the second NOx catalyst is abnormal, the same NOx purification rate can be obtained. Therefore, during normal control, it is difficult to determine which of the first NOx catalyst and the second NOx catalyst is abnormal based on the NOx purification rate.

  In the present invention, in order to determine which of the first NOx catalyst and the second NOx catalyst is abnormal, attention is paid to the NOx purification rate when the reducing agent supply amount is increased from the normal control. The increased reducing agent supply amount is hereinafter referred to as “determination supply amount”. The NOx purification rate at this time is a NOx purification rate calculated based on the NOx concentration detected by the NOx sensor, and refers to the NOx purification rate of the entire system. The NOx purification rate can be calculated based on the NOx concentration in the exhaust gas flowing into the first NOx catalyst and the NOx concentration detected by the NOx sensor.

  Here, when the first NOx catalyst or the second NOx catalyst is abnormal, by supplying a determined supply amount of the reducing agent to the abnormal catalyst, the abnormal catalyst is quickly brought into an equilibrium state with respect to the reducing agent. . The equilibrium state relating to the reducing agent refers to a state where the reducing agent adsorption amount and desorption amount are equal in the catalyst, and refers to a state where the reducing agent adsorption amount does not increase even when the reducing agent is supplied to the catalyst. After an abnormal catalyst reaches an equilibrium state with respect to the reducing agent, even if the reducing agent is supplied, the amount of reducing agent adsorbed does not increase in the abnormal catalyst, and the reducing agent flows out of the catalyst. On the other hand, in a normal catalyst, the amount of reducing agent that can be adsorbed is larger than that in an abnormal catalyst. Therefore, even if the reducing agent supply amount is increased, the time until the effect of the increase appears longer than that in an abnormal catalyst. .

That is, when the first NOx catalyst is abnormal, the reducing agent flows out of the first NOx catalyst at an early stage by supplying the determined supply amount of the reducing agent. However, since the second NOx catalyst is normal, the reducing agent flowing out from the first NOx catalyst and the reducing agent supplied from the second addition valve are adsorbed by the second NOx catalyst. For this reason, it takes a certain amount of time for the reducing agent to flow out of the second NOx catalyst. Here, since the NOx sensor detects ammonia in addition to NOx, the detected value of the NOx sensor increases when ammonia is present in the exhaust gas. If the NOx purification rate is calculated based on the detected value of the NOx sensor, the NOx purification rate is apparently lowered. Therefore, when the reducing agent flows out from the second NOx catalyst, the NOx purification rate calculated based on the detected value of the NOx sensor decreases. If the time until the reducing agent flows out from the second NOx catalyst is relatively long, the time until the NOx purification rate decreases is also relatively long.

  On the other hand, when the second NOx catalyst is abnormal, the reducing agent flows out of the second NOx catalyst at an early stage by supplying the determined supply amount of the reducing agent. The reducing agent flowing out from the second NOx catalyst is detected by the NOx sensor. For this reason, the time until the reducing agent is detected by the NOx sensor is shorter when the second NOx catalyst is abnormal than when the first NOx catalyst is abnormal. Therefore, the time until the NOx purification rate decreases is shorter when the second NOx catalyst is abnormal than when the first NOx catalyst is abnormal.

  As described above, when the predetermined amount of time has elapsed from the time when the supply amount of the reducing agent from the first addition valve and the second addition valve is increased (hereinafter also referred to as the instruction time), the first NOx catalyst is abnormal. There is a difference in the NOx purification rate when the second NOx catalyst is abnormal. Therefore, based on the NOx purification rate at this time, it can be determined which of the first NOx catalyst and the second NOx catalyst is abnormal.

  It should be noted that the predetermined time can be a time from when the instruction is made until a difference occurs in the NOx purification rate between when the first NOx catalyst is abnormal and when the second NOx catalyst is abnormal. For example, the predetermined time may be a time from the indication time until an equilibrium state regarding the reducing agent is reached in the abnormal catalyst. This predetermined time may be changed according to the determination supply amount. For example, the larger the determination supply amount, the shorter the time required to reach the equilibrium state regarding the reducing agent in the abnormal catalyst, so the predetermined time may be shortened.

  Here, when there is an abnormality in the first NOx catalyst, the reducing agent flowing out from the first NOx catalyst is adsorbed to the second NOx catalyst after a predetermined time has elapsed since the reducing agent supply amount is set as the determination supply amount. There is almost no decrease in the NOx purification rate due to the reducing agent flowing out of the second NOx catalyst. Even if there is an abnormality in the first NOx catalyst, excess reducing agent is supplied to the first NOx catalyst and the second NOx catalyst, so that the NOx purification rate in each catalyst can be increased.

  On the other hand, when there is an abnormality in the second NOx catalyst, the reducing agent flowing out from the second NOx catalyst is detected by the NOx sensor after a predetermined time has elapsed after the reducing agent supply amount is set as the determination supply amount. The purification rate decreases. Note that the decrease in the NOx purification rate due to the flow of the reducing agent out of the second NOx catalyst is greater than the increase in the NOx purification rate due to excessive supply of the reducing agent.

As described above, the NOx purification rate after a predetermined time has elapsed since the reducing agent supply amount is set as the determination supply amount is relatively high when the first NOx catalyst is abnormal, and compared when the second NOx catalyst is abnormal. Therefore, if the determination threshold is set as a boundary between the NOx purification rate when the first NOx catalyst is abnormal and the second NOx catalyst is abnormal, the NOx purification rate and the determination threshold are compared. By doing so, it can be determined which catalyst is abnormal. For example, when the first NOx catalyst is abnormal, the NOx purification rate after the elapse of a predetermined time from the instruction time becomes equal to or greater than the determination threshold. On the other hand, when the second NOx catalyst is abnormal, the NOx purification rate after the elapse of a predetermined time from the instruction time becomes less than the determination threshold.

  The determination threshold is a value smaller than the NOx purification rate when the entire system is normal, and can be, for example, the NOx purification rate immediately before the reducing agent supply amount is set as the determination supply amount. That is, when the reducing agent supply amount is set as the determination supply amount, if the second NOx catalyst is abnormal, the reducing agent flows out from the second NOx catalyst and the NOx purification rate decreases. The purification rate can be used as a determination threshold.

  In this way, it is possible to determine which of the first NOx catalyst and the second NOx catalyst is abnormal.

  According to the present invention, when a plurality of addition valves cannot be controlled individually, it is possible to accurately determine which selective reduction type NOx catalyst has an abnormality while suppressing an increase in cost.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, its intake system, and an exhaust system. It is the figure which showed the NOx purification rate at the time of normal control, when the system is normal, when the first NOx catalyst is abnormal, and when the second NOx catalyst is abnormal. FIG. 3 is a diagram showing the relationship between the degree of deterioration of a selective reduction type NOx catalyst and the amount of reducing agent flowing out from the selective reduction type NOx catalyst. When the first NOx catalyst or the second NOx catalyst is abnormal, the first time when the time (predetermined time) until the equilibrium state with respect to the reducing agent in the abnormal catalyst elapses from the indicated time point during the increase control. It is the figure which showed the NOx purification rate in each case of abnormality of a NOx catalyst and abnormality of a 2nd NOx catalyst. It is the time chart which showed an example of transition of the reducing agent outflow from each catalyst in case the first NOx catalyst is abnormal at the time of increase control, and NOx purification rate. It is the time chart which showed an example of transition of the reducing agent outflow from each catalyst in case the 2nd NOx catalyst at the time of increase control is abnormal, and NOx purification rate. It is the flowchart which showed the flow of the abnormality determination which concerns on an Example.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

(Example)
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to the present embodiment and its intake system and exhaust system. The internal combustion engine 1 is a diesel engine for driving a vehicle. An exhaust passage 2 is connected to the internal combustion engine 1. In the exhaust passage 2, a first addition valve 41, a first NOx catalyst 31, a second addition valve 42, and a second NOx catalyst 32 are provided in order from the upstream side in the exhaust flow direction. The first NOx catalyst 31 and the second NOx catalyst 32 are selective reduction type NOx catalysts that selectively reduce NOx in the exhaust gas using ammonia as a reducing agent. In the present embodiment, the first NOx catalyst 31 corresponds to the first selective reduction type NOx catalyst in the present invention. In the present embodiment, the second NOx catalyst 32 corresponds to the second selective reduction type NOx catalyst in the present invention.

The first addition valve 41 and the second addition valve 42 are part of the reducing agent supply device 4. In addition to the first addition valve 41 and the second addition valve 42, the reducing agent supply device 4 includes a urea tank 43, a reducing agent supply passage 44, a pump 45, a reducing agent amount sensor 46, a reducing agent concentration sensor 47, a reducing agent. A flow sensor 48 is provided.

  The urea tank 43 stores urea water. The urea water is hydrolyzed by the heat of exhaust gas or heat from the first NOx catalyst 31 and the second NOx catalyst 32 to become ammonia, and is adsorbed on the first NOx catalyst 31 or the second NOx catalyst 32. This ammonia is used as a reducing agent in the first NOx catalyst 31 or the second NOx catalyst 32. The reducing agent supply passage 44 has one end connected to the urea tank 43 and the other end divided into two and connected to the first addition valve 41 and the second addition valve 42. The reducing agent supply passage 44 supplies urea water to the first addition valve 41 and the second addition valve 42. A pump 45 that discharges urea water toward the first addition valve 41 and the second addition valve 42 in the middle of the reducing agent supply passage 44 closer to the urea tank 43 than the portion where the reducing agent supply passage 44 is divided into two. Provided. The reducing agent amount sensor 46 detects the amount of urea water stored in the urea tank 43. The reducing agent concentration sensor 47 detects the concentration of urea water stored in the urea tank 43. The reducing agent flow rate sensor 48 detects the flow rate of the reducing agent downstream from the pump 45 and upstream from the location where the reducing agent supply passage 44 branches. In this embodiment, ammonia and urea water are called reducing agents.

  Furthermore, a first NOx sensor 11 that detects NOx in the exhaust gas flowing into the first NOx catalyst 31 is provided upstream of the first addition valve 41. A second NOx sensor 12 that detects NOx in the exhaust gas flowing out from the second NOx catalyst 32 is provided downstream of the second NOx catalyst 32. In addition, the 1st NOx sensor 11 and the 2nd NOx sensor 12 will also detect ammonia similarly to NOx. An intake passage 6 is connected to the internal combustion engine 1. An air flow meter 16 that detects the intake air amount of the internal combustion engine 1 is attached midway in the intake passage 6.

  The internal combustion engine 1 is also provided with an ECU 10 that is an electronic control unit. The ECU 10 controls the operating state of the internal combustion engine 1, the exhaust purification device, and the like. In addition to the first NOx sensor 11, the second NOx sensor 12, and the air flow meter 16 described above, the crank position sensor 14 and the accelerator opening sensor 15 are electrically connected to the ECU 10, and the output value of each sensor is passed to the ECU 10. It is. In this embodiment, the ECU 10 corresponds to the control device in the present invention.

  The ECU 10 can grasp the operating state of the internal combustion engine 1 such as the engine speed based on the detection of the crank position sensor 14 and the engine load based on the detection of the accelerator opening sensor 15. In this embodiment, the NOx concentration in the exhaust gas flowing into the first NOx catalyst 31 can be detected by the first NOx sensor 11, but the exhaust gas exhausted from the internal combustion engine 1 (purified by the first NOx catalyst 31). The NOx concentration in the exhaust gas before being exhausted, that is, in the exhaust gas flowing into the first NOx catalyst 31) is related to the operating state of the internal combustion engine 1 and is estimated based on the operating state of the internal combustion engine 1. It is also possible to do.

Further, the ECU 10 sends the same signal to the first addition valve 41 and the second addition valve 42 to control the first addition valve 41 and the second addition valve 42. That is, the ECU 10 gives the same instruction regarding opening and closing of the valve to the first addition valve 41 and the second addition valve 42. Therefore, the first addition valve 41 and the second addition valve 42 supply the reducing agent at the same time. The ECU 10 supplies the reducing agent from the first addition valve 41 and the second addition valve 42 so that the NOx purification rate of the entire system falls within the target range with respect to the amount of NOx flowing into the first NOx catalyst 31. Implement normal control. That is, a reducing agent is supplied from the first addition valve 41 and the second addition valve 42 according to the amount of NOx discharged from the internal combustion engine 1. In the normal control, the reducing agent adsorption amount is estimated for each of the first NOx catalyst 31 and the second NOx catalyst 32. During normal control, the reducing agent may be supplied from the first addition valve 41 and the second addition valve 42 so that the reducing agent adsorption amount of each catalyst becomes constant. The reducing agent adsorption amount of the first NOx catalyst 31 is based on the reducing agent supply amount from the first addition valve 41, the NOx purification rate of the first NOx catalyst 31, and the reducing agent amount flowing out of the first NOx catalyst 31. Is calculated using The reducing agent adsorption amount of the second NOx catalyst 31 includes the reducing agent supply amount from the second addition valve 42, the NOx purification rate of the second NOx catalyst 32, the reducing agent amount flowing out of the second NOx catalyst 32, the first Based on the amount of reducing agent flowing out from the NOx catalyst 32, the calculation is performed using a model. The NOx purification rate of the first NOx catalyst 31, the NOx purification rate of the second NOx catalyst 32, the amount of reducing agent flowing out from the first NOx catalyst 31, and the amount of reducing agent flowing out from the second NOx catalyst 32 are based on temperature and the like. Presumed. At this time, estimation is performed assuming that the system is normal.

  The ECU 10 determines whether an abnormality of the first NOx catalyst 31 or an abnormality of the second NOx catalyst 32 has occurred. In this embodiment, it may be confirmed by a known means that there is no abnormality in other devices. For example, you may confirm beforehand that there is no abnormality in the 1st addition valve 41, the 2nd addition valve 42, and a reducing agent. For example, if the amount of reducing agent stored detected by the reducing agent amount sensor 46 is equal to or greater than a specified amount, it can be determined that there is no shortage of reducing agent. Further, if the concentration of the reducing agent detected by the reducing agent concentration sensor 47 is within the specified range, it can be determined that the concentration of the reducing agent is normal. Furthermore, if the flow rate of the reducing agent detected by the reducing agent flow rate sensor 48 is equal to or higher than the specified flow rate, it can be determined that the first addition valve 41 and the second addition valve 42 are normal. That is, if the first addition valve 41 and the second addition valve 42 are normal, the reducing agent supply is performed when the ECU 10 outputs a valve opening instruction to the first addition valve 41 and the second addition valve 42. A reducing agent flows through the passage 44. Accordingly, if the threshold value of the flow rate of the reducing agent when the first addition valve 41 and the second addition valve 42 are normal is set in advance, the first addition is performed when the detected value of the reducing agent flow rate sensor 48 is equal to or greater than the threshold value. It can be determined that the valve 41 and the second addition valve 42 are normal. In the present embodiment, the first addition valve 41, the second addition valve 42, and the ECU 10 that determines whether or not an abnormality has occurred in the reducing agent corresponds to the supply abnormality determination means in the present invention.

Based on the NOx concentration detected by the first NOx sensor 11 (or the NOx concentration estimated from the operating state of the internal combustion engine 1) and the NOx concentration detected by the second NOx sensor 12, the ECU 10 The NOx purification rate of the entire system including the one NOx catalyst 31 and the second NOx catalyst 32 is calculated. The NOx concentration detected by the first NOx sensor 11 is the NOx concentration (upstream NOx concentration) in the exhaust gas flowing into the first NOx catalyst 31, and the NOx concentration detected by the second NOx sensor 12 is the second NOx concentration. This is the NOx concentration (downstream NOx concentration) in the exhaust gas flowing out from the NOx catalyst 32. Unless otherwise specified below, in the case of the NOx purification rate, the NOx purification rate of the entire system is indicated. The NOx purification rate is the ratio of the NOx concentration that decreases as NOx is purified by the first NOx catalyst 31 and the second NOx catalyst 32 to the NOx concentration in the exhaust gas flowing into the first NOx catalyst 31. It can be calculated by an equation.
NOx purification rate = (upstream NOx concentration−downstream NOx concentration) / upstream NOx concentration However, the upstream NOx concentration is the NOx concentration in the exhaust flowing into the first NOx catalyst 31, and the downstream NOx concentration is This is the NOx concentration in the exhaust gas flowing out from the second NOx catalyst 31.

Here, when the devices other than the first NOx catalyst 31 or the second NOx catalyst 32 and the reducing agent are normal, and the NOx purification rate is lower than the lower limit value (also referred to as a normal threshold) of the normal range. Is considered to be abnormal in one of the first NOx catalyst 31 and the second NOx catalyst 32. However, it is difficult to determine which catalyst is abnormal by looking only at the NOx purification rate during normal control. That is, the NOx purification rate in the case of performing normal control in which a reducing agent corresponding to the amount of NOx discharged from the internal combustion engine 1 is supplied from the first addition valve 41 and the second addition valve 42 is the first NOx catalyst. It can be the same level when 31 is abnormal and when the second NOx catalyst 32 is abnormal. For this reason, in this embodiment, which catalyst is abnormal is distinguished. In this embodiment, it is assumed that the first NOx catalyst 31 and the second NOx catalyst 32 do not become abnormal at the same time.

  Here, FIG. 2 is a diagram showing the NOx purification rate when the system is normal, when the first NOx catalyst 31 is abnormal, and when the second NOx catalyst 32 is abnormal during normal control. The normal threshold in FIG. 2 is a lower limit value of the NOx purification rate when the system is normal. FIG. 2 shows the NOx purification rate when a sufficient time has elapsed from the supply of the reducing agent, but the NOx purification rate is equal to or higher than the normal threshold if the system is normal. As described above, the NOx purification rates of the abnormality of the first NOx catalyst 31 and the abnormality of the second NOx catalyst 32 may be substantially the same, and even if the NOx purification rate at this time is used, It is difficult to determine whether the catalyst is abnormal.

  On the other hand, in the present embodiment, attention is paid to the transition of the NOx purification rate after the reducing agent supply amount is increased to the determination supply amount. The determination supply amount is a reducing agent supply amount that is larger than that during normal control. That is, the determination supply amount is a reducing agent supply amount that is larger than the reducing agent amount required for NOx purification. The determination supply amount may be at least the supply amount of the reducing agent that flows out from the abnormal catalyst. That is, the determination supply amount may be a supply amount of the reducing agent that flows out from the abnormal catalyst. The determination supply amount may be a reducing agent supply amount from which the reducing agent flows out from the first NOx catalyst 31 and the second NOx catalyst 32 when the first NOx catalyst 31 and the second NOx catalyst 32 are normal. The time point when the ECU 10 instructs the first addition valve 41 and the second addition valve 42 so that the reducing agent supply amount becomes the determined supply amount is hereinafter referred to as “instruction time point”. The control instructed by the ECU 10 to the first addition valve 41 and the second addition valve 42 so that the reducing agent supply amount becomes the determination supply amount is hereinafter referred to as “increase control”.

  Since the second NOx sensor 12 detects ammonia in addition to NOx, the detected value of the NOx sensor becomes large if ammonia is present in the exhaust gas. If the NOx purification rate is calculated based on the detection value of the second NOx sensor 12, the NOx purification rate is lowered. Therefore, when the reducing agent flows out from the second NOx catalyst 32, the NOx purification rate calculated based on the detected value of the second NOx sensor 12 decreases. The relationship between the degree of deterioration of the selective reduction type NOx catalyst and the amount of reducing agent flowing out from the selective reduction type NOx catalyst is as shown in FIG. FIG. 3 is a graph showing the relationship between the degree of deterioration of the selective reduction type NOx catalyst and the amount of reducing agent flowing out from the selective reduction type NOx catalyst. Thus, the greater the degree of catalyst degradation, the greater the amount of reducing agent outflow from the catalyst. In this embodiment, it is assumed that the catalyst is abnormal when the degree of deterioration exceeds an allowable range.

<Determination of Abnormality of First NOx Catalyst 31 and Second NOx Catalyst 32>
Here, FIG. 4 shows the time (predetermined time) from the indicated time to the equilibrium state related to the reducing agent in the abnormal catalyst during the increase control when the first NOx catalyst 31 or the second NOx catalyst 32 is abnormal. FIG. 4 is a graph showing the NOx purification rate in each case of abnormality of the first NOx catalyst 31 and abnormality of the second NOx catalyst 32 when lapse of time.

  When the first NOx catalyst 31 is abnormal, the reducing agent flows out of the first NOx catalyst 31 after a predetermined time has elapsed by supplying a determined supply amount of the reducing agent. However, since the second NOx catalyst 32 is normal, the reducing agent flowing out from the first NOx catalyst 31 is adsorbed by the second NOx catalyst 32. For this reason, it takes longer than the predetermined time until the reducing agent flows out of the second NOx catalyst 32. Even if the first NOx catalyst 31 is abnormal, the NOx purification rate in the first NOx catalyst 31 can be increased by supplying a large amount of reducing agent to the first NOx catalyst 31 by the increase control. Therefore, when the first NOx catalyst 31 is abnormal, the NOx purification rate after the elapse of a predetermined time from the start of the increase control becomes equal to or higher than the NOx purification rate before the start of the increase control.

  On the other hand, when the second NOx catalyst 32 is abnormal, the reducing agent flows out of the second NOx catalyst 32 after a predetermined time has elapsed by supplying the determined supply amount of the reducing agent. The reducing agent flowing out from the second NOx catalyst 32 is detected by the second NOx sensor 12. For this reason, the time until the reducing agent is detected by the second NOx sensor 12 is shorter when the second NOx catalyst 32 is abnormal than when the first NOx catalyst 31 is abnormal. Therefore, the time until the NOx purification rate decreases is shorter when the second NOx catalyst 32 is abnormal than when the first NOx catalyst 31 is abnormal. Even before a predetermined time has elapsed since the start of the increase control, the reducing agent gradually flows out from the second NOx catalyst 32. For this reason, when the second NOx catalyst 32 is abnormal, the NOx purification rate after the elapse of a predetermined time from the start of the increase control becomes less than the NOx purification rate before the start of the increase control.

  Therefore, during the increase control, from the point in time until the NOx purification rate when the first NOx catalyst 31 is abnormal to the NOx purification rate when the second NOx catalyst 32 is abnormal, there is a difference that can be distinguished. If this time elapses, it can be distinguished whether the first NOx catalyst 31 is abnormal or the second NOx catalyst 32 is abnormal based on the NOx purification rate at this time. The time until a difference that can be distinguished between the NOx purification rate when the first NOx catalyst 31 is abnormal and the NOx purification rate when the second NOx catalyst 32 is abnormal is reduced in the abnormal catalyst. It can be the time to reach equilibrium for the agent. This time is defined as “predetermined time” in this embodiment.

  Thus, if the NOx purification rate at the time when a predetermined time has elapsed from the instruction point in the increase control is greater than or equal to the determination threshold, the first NOx catalyst 31 is abnormal and the second NOx catalyst 32 is normal. Is determined. On the other hand, if the NOx purification rate when a predetermined time has elapsed from the instruction point in the increase control is less than the determination threshold, it is determined that the first NOx catalyst 31 is normal and the second NOx catalyst 32 is abnormal. To do. During the increase control, the predetermined time has a difference that is distinguishable between the NOx purification rate when the first NOx catalyst 31 is abnormal and the NOx purification rate when the second NOx catalyst 32 is abnormal from the instruction point. The time until the occurrence is obtained in advance by experiments or simulations. It should be noted that the time until the equilibrium state with respect to the reducing agent is the NOx purification rate during normal control (may be the degree of catalyst deterioration), the determination supply amount, the temperature of the first NOx catalyst 31 and the second NOx catalyst 32. Since the second NOx catalyst 31 is related to the amount of reducing agent that can be adsorbed, the predetermined time may be changed depending on these values. Further, these relationships may be obtained in advance by experiments or simulations. Further, the reducing agent adsorption amount of the abnormal catalyst at the start of the increase control is estimated from the temperature of the catalyst, the supply amount of the reducing agent, the NOx purification rate, etc., and further the reducing agent in the abnormal catalyst from the NOx purification rate at the start of the increase control. Estimate the amount of reducing agent adsorbed when the equilibrium state is reached, and estimate the time to reach the equilibrium state for the reducing agent in the abnormal catalyst based on the estimated value and the determined reducing agent amount. It may be a predetermined time.

  Strictly speaking, depending on the distance from the second NOx catalyst 32 to the second NOx sensor 12, the time when the reducing agent flows out from the second NOx catalyst 32 and the time when the reducing agent is detected by the second NOx sensor 12 Deviation occurs. Therefore, the predetermined time may be determined in consideration of this time difference.

The determination threshold value can be set as a lower limit value of the NOx purification rate when the first NOx catalyst 31 is abnormal after a lapse of a predetermined time from the instruction point. In this embodiment, the determination threshold is the NOx purification rate before the increase control. That is, if the first NOx catalyst 31 is abnormal, the NOx purification rate after the predetermined time has elapsed is equal to or higher than the NOx purification rate before the increase control, but if the second NOx catalyst 32 is abnormal, the predetermined time has elapsed. The NOx purification rate is less than the NOx purification rate before the increase control. For this reason, the NOx purification rate before the increase control can be set as the determination threshold value. “Before increase control” may be the start point of increase control or may be immediately before the start of increase control.

<Time chart when judging abnormality>
FIG. 5 is a time chart showing an example of the transition of the reducing agent outflow from each catalyst and the NOx purification rate when the first NOx catalyst 31 is abnormal during the increase control. T1 indicates an instruction time point in the increase control, T2 indicates a time point when a predetermined time has elapsed from T1, and T3 indicates a time point when the second NOx catalyst 32 reaches an equilibrium state with respect to the reducing agent from T1. T2 can also be said to be a point in time when the first NOx catalyst 31 is in an equilibrium state with respect to the reducing agent. The solid line in the reducing agent outflow amount indicates the reducing agent outflow amount from the first NOx catalyst 31, and the alternate long and short dash line indicates the reducing agent outflow amount from the second NOx catalyst 32.

  In FIG. 5, the NOx purification rate before the start of the increase control is used as the determination threshold value. Before starting the increase control, the reducing agent has flowed out of the abnormal first NOx catalyst 31. Further, under the influence of the reducing agent flowing out from the first NOx catalyst 31, the reducing agent also flows out from the second NOx catalyst 32 before the start of the increase control. However, the second NOx catalyst 32 does not reach the equilibrium state with respect to the reducing agent, but can further adsorb the reducing agent. When the first NOx catalyst 31 is abnormal, the reducing agent outflow amount from the first NOx catalyst 31 increases after the increase control is started. However, since the second NOx catalyst 32 is normal, the reducing agent flowing out from the first NOx catalyst 31 and the reducing agent supplied from the second addition valve 42 are adsorbed by the second NOx catalyst 32. Accordingly, the reducing agent hardly flows out from the second NOx catalyst 32 during the period from T1 to T2. For this reason, the second NOx sensor 12 hardly detects the reducing agent. Further, during the period from T1 to T2, the NOx purification rate in each catalyst increases due to excessive supply of the reducing agent. Therefore, the NOx purification rate during the period from T1 to T2 gradually increases.

  When the amount of reducing agent flowing out from the first NOx catalyst 31 further increases, the reducing agent starts flowing out from the second NOx catalyst 32 as well. Since this reducing agent is detected by the second NOx sensor 12, the NOx purification rate apparently decreases. After T3, since the second NOx catalyst 32 is also in an equilibrium state with respect to the reducing agent, the amount of reducing agent flowing out from the second NOx catalyst 32 is constant, and the NOx purification rate is also constant.

  Thus, when the first NOx catalyst 31 is abnormal, the NOx purification rate becomes higher than that before the start of the increase control at the time T2 when a predetermined time has elapsed from the start of the increase control. It becomes.

  FIG. 6 is a time chart showing an example of the transition of the reducing agent outflow amount from each catalyst and the NOx purification rate when the second NOx catalyst 32 is abnormal during the increase control. T1 indicates an instruction time point in the increase control, T2 indicates a time point when a predetermined time has elapsed from T1, and T3 indicates a time point when the first NOx catalyst 31 reaches an equilibrium state with respect to the reducing agent from T1. T2 can also be said to be a point in time when the second NOx catalyst 31 reaches an equilibrium state regarding the reducing agent. The solid line in the reducing agent outflow amount indicates the reducing agent outflow amount from the first NOx catalyst 31, and the alternate long and short dash line indicates the reducing agent outflow amount from the second NOx catalyst 32.

Also in FIG. 6, the NOx purification rate before the increase control is used as the determination threshold. Prior to the start of the increase control, the reducing agent hardly flows out from the normal first NOx catalyst 31, whereas the reducing agent flows out from the abnormal second NOx catalyst 32. When the second NOx catalyst 32 is abnormal, the reducing agent flows out from the second NOx catalyst 32 immediately after the increase control is started. For this reason, during the period from T1 to T2, the reducing agent flows out from the second NOx catalyst 32. For this reason, the reducing agent is detected by the second NOx sensor 12. During the period from T1 to T2, the NOx purification rate of each catalyst increases due to excessive supply of the reducing agent, but the NOx purification rate is reduced by detecting the reducing agent rather than the increase in the NOx purification rate. Since the minute is larger, the NOx purification rate as a whole decreases. Therefore, the NOx purification rate during the period from T1 to T2 gradually decreases. Since the first NOx catalyst 32 is normal, the reducing agent does not immediately flow out of the first NOx catalyst 31 even when the increase control is started. After T3, since the first NOx catalyst 31 is also in an equilibrium state with respect to the reducing agent, the amount of reducing agent flowing out from the first NOx catalyst 31 is constant, and the NOx purification rate is also constant.

  Thus, when the second NOx catalyst 32 is abnormal, the NOx purification rate is lower than that before the start of the increase control at the time T2 when a predetermined time has elapsed from the start of the increase control. It becomes.

  Accordingly, after the increase control is started, if the NOx purification rate at time T2 is equal to or higher than the determination threshold, it can be determined that the first NOx catalyst 31 is abnormal, and if it is less than the determination threshold, the second NOx catalyst 32 is abnormal. It can be determined that there is.

<Flow chart of abnormality determination>
FIG. 7 is a flowchart showing a flow of abnormality determination according to the present embodiment. This flowchart is executed by the ECU 10 at regular time intervals.

  In step S101, it is determined whether or not there is an abnormality in the catalyst. In this embodiment, in step S101, it is determined whether or not the first NOx catalyst 31 or the second NOx catalyst 32 is abnormal. When the first NOx catalyst 31 or the second NOx catalyst 32 is abnormal, the NOx purification rate of the entire system is lowered. Therefore, when the NOx purification rate is less than the normal threshold, it is determined that the catalyst is abnormal. Is done. The normal threshold is obtained in advance by experiments or simulations as a lower limit value of the NOx purification rate when the system is normal. The reducing agent supply amount at this time is the reducing agent supply amount in the normal control before the instruction time in the increase control.

  In addition, you may confirm beforehand that there is no abnormality in the other apparatus including the 1st addition valve 41 and the 2nd addition valve 42, a reducing agent, etc. This confirmation may be performed in this step or may be performed before execution of this flowchart. If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, this flowchart is terminated.

  In step S102, the increase control is started. That is, an instruction is issued so that the reducing agent supply amount becomes the determination supply amount. In this step, when the first NOx catalyst 31 or the second NOx catalyst 32 is abnormal, the abnormal catalyst is in an equilibrium state with respect to the reducing agent, and the reducing agent is further reduced from the first NOx catalyst 31 and the second NOx catalyst 32. The reducing agent supply amount is increased so as to flow out. The reduction agent supply amount can be increased by increasing the supply time of the reduction agent. The increase control is performed by increasing the instruction value for the reducing agent supply amount from the ECU 10. Further, the same instruction is simultaneously given to the first addition valve 41 and the second addition valve 42. When the process of step S102 ends, the process proceeds to step S103.

  In step S103, it is determined whether or not a predetermined time has elapsed from the time point (instructed time point) when the increase control is started in step S102. In this step, it is determined whether or not a time period during which it is possible to determine which of the first NOx catalyst 31 and the second NOx catalyst 32 is abnormal has elapsed. If an affirmative determination is made in step S103, the process proceeds to step S104. On the other hand, if a negative determination is made, step S103 is processed again.

In step S104, it is determined whether or not the current NOx purification rate is equal to or greater than a determination threshold value. That is, it is determined whether or not the NOx purification rate at a time point (T2 in FIG. 5 or FIG. 6) at which a predetermined time has elapsed from the instruction time point in the increase control is equal to or greater than a determination threshold value. When the predetermined time has elapsed, if the first NOx catalyst 31 is abnormal, the NOx purification rate is greater than or equal to the determination threshold, and if the second NOx catalyst 32 is abnormal, the NOx purification rate is less than the determination threshold. Therefore, by processing this step, it can be determined which of the first NOx catalyst 31 and the second NOx catalyst 32 is abnormal. If an affirmative determination is made in step S104, the process proceeds to step S105, where it is determined that the first NOx catalyst 31 is abnormal. On the other hand, if a negative determination is made in step S104, the process proceeds to step S106, and it is determined that the second NOx catalyst 32 is abnormal. When the process of step S105 or step S106 ends, the process proceeds to step S107.

  In step S107, the increase control is terminated. That is, the reducing agent supply amount returns from the determination supply amount to the reducing agent supply amount at the time of normal control. Accordingly, the supply of the reducing agent according to the amount of NOx discharged from the internal combustion engine 1 is started. When the process of step S107 ends, this flowchart is ended.

  As described above, according to this embodiment, when there is an abnormality in the catalyst, it is determined whether an abnormality in the first NOx catalyst 31 or an abnormality in the second NOx catalyst 32 has occurred. Can do.

  In the present embodiment, the predetermined time is, for example, the time until the abnormal catalyst reaches an equilibrium state with respect to the reducing agent. However, the time during which a clear difference in the NOx purification rate between when the first NOx catalyst 31 is abnormal and when the second NOx catalyst 32 is abnormal can be set as the predetermined time. That is, as shown in FIGS. 5 and 6, even before and after the time point T2, there is a difference in the NOx purification rate between when the first NOx catalyst 31 is abnormal and when the second NOx catalyst 32 is abnormal. Therefore, the predetermined time may be set in a range where the difference in the NOx purification rate is generated.

1 Internal combustion engine 2 Exhaust passage 4 Reductant supply device 6 Intake passage 10 ECU
11 First NOx sensor 12 Second NOx sensor 14 Crank position sensor 15 Accelerator opening sensor 16 Air flow meter 31 First selective reduction type NOx catalyst (first NOx catalyst)
32 Second selective reduction type NOx catalyst (second NOx catalyst)
41 First addition valve 42 Second addition valve 43 Urea tank 44 Reducing agent supply passage 45 Pump 46 Reducing agent amount sensor 47 Reducing agent concentration sensor 48 Reducing agent flow rate sensor

Claims (1)

A first addition valve that is provided in an exhaust passage of the internal combustion engine and supplies a reducing agent into the exhaust passage;
A first selective reduction type NOx catalyst that selectively reduces NOx by a reducing agent that is provided in an exhaust passage downstream of the first addition valve and is adsorbed;
A second addition valve that is provided in an exhaust passage downstream of the first selective reduction type NOx catalyst and supplies a reducing agent into the exhaust passage;
A second selective reduction type NOx catalyst that selectively reduces NOx by a reducing agent that is provided in an exhaust passage downstream of the second addition valve and is adsorbed;
A NOx sensor for detecting the NOx concentration in the exhaust gas flowing out from the second selective reduction type NOx catalyst;
Supply abnormality determination means for determining whether an abnormality has occurred in the supply of the reducing agent;
A control device for determining a supply amount of a reducing agent based on an amount of NOx flowing into the first selective reduction type NOx catalyst, and operating the first addition valve and the second addition valve according to the same instruction;
With
When it is determined by the supply abnormality determination means that there is no abnormality in the supply of the reducing agent, it is determined whether the first selective reduction type NOx catalyst is abnormal or the second selective reduction type NOx catalyst is abnormal. A failure determination device for an exhaust purification device of an internal combustion engine,
The control device determines whether the first selective reduction NOx catalyst and the second selective reduction NOx catalyst are normal based on the amount of NOx flowing into the first selective reduction NOx catalyst. The supply amount of the reducing agent from the first addition valve and the second addition valve is increased from the supply amount of the reducing agent determined in the above, and the reducing agent is supplied from the first addition valve and the second addition valve. If the NOx purification rate calculated based on the NOx concentration detected by the NOx sensor when a predetermined time elapses from the time when the amount is increased is greater than or equal to the determination threshold, the first selective reduction type NOx catalyst is abnormal. A failure determination device for an exhaust gas purification device for an internal combustion engine that determines that the second selective reduction type NOx catalyst is abnormal if it is less than the determination threshold value.

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