JP4417732B2 - Exhaust purification device deterioration judgment device - Google Patents

Description

  The present invention relates to an apparatus for determining a deterioration state of an exhaust purification apparatus that is disposed in an exhaust system of an internal combustion engine and reduces nitrogen oxides.

  A diesel engine has a high compression ratio, and since the ratio of oxygen and nitrogen to the fuel in the cylinder is high, it easily generates nitrogen oxides. In lean burn engines, lean combustion is performed, so the ratio of air to fuel is large. Therefore, even in a lean burn engine, nitrogen in the air is easily oxidized by oxygen in the air due to heat during combustion, and nitrogen oxides (NOx) are easily generated.

  A NOx occlusion reduction type catalyst is known as a catalyst for reducing nitrogen oxides in exhaust gas. The NOx occlusion reduction type catalyst absorbs nitrogen oxides in a lean atmosphere. When the exhaust gas entering the catalyst is intermittently rich, the absorbed nitrogen oxides are reduced and purified (Patent Document 1).

Further, Patent Document 2 discloses a technique for detecting deterioration based on the temperature of the lean NOx catalyst when supplying a reducing agent several times the normal amount.
Japanese Patent No. 2845103 JP 2001-59413 A

  However, in the above-described method, it is necessary to supply a larger amount of reducing agent to the engine each time the deterioration of the lean NOx catalyst is detected. Thus, supplying a large amount of the reducing agent at the time of detecting deterioration may cause deterioration of fuel consumption and emission.

  Accordingly, an object of the present invention is to provide a highly accurate exhaust gas purification apparatus deterioration determination device while minimizing the deterioration of emission and fuel consumption.

  According to one aspect of the present invention (claim 1), the deterioration determination device for an exhaust purification apparatus of the present invention absorbs nitrogen oxides when the air-fuel ratio of the exhaust gas is lean, and when the air-fuel ratio of the exhaust gas is rich. A deterioration determination device for an exhaust purification device that reduces nitrogen oxides absorbed in the exhaust purification device, wherein the exhaust purification device detects air / fuel ratio of exhaust gas supplied to the exhaust purification device, and is absorbed by the exhaust purification device. Estimation means for obtaining an estimated amount of nitrogen oxides, temperature detection means for detecting the temperature of the exhaust purification device, the air-fuel ratio when the exhaust gas is rich, and the estimated amount of absorbed nitrogen oxides And a determination means for determining the amount of heat generated by the exhaust purification device, and a determination means for determining deterioration of the exhaust purification device based on the calculated amount of heat generation and the detected temperature. According to this, based on the calorific value of the exhaust gas purification device and the actual temperature of the exhaust gas purification device, the nitrogen oxide reducing ability of the exhaust gas purification device when the exhaust gas is rich is monitored. Therefore, when the amount of temperature rise is small compared to the calorific value obtained, it can be determined that the exhaust gas purification device has deteriorated because the nitrogen oxide absorption capacity and the reduction capacity have fallen, and nitrogen oxidation It is possible to determine the deterioration of the exhaust emission control device that is inexpensive and highly responsive without providing an object sensor.

  In the exhaust gas purification apparatus deterioration determination device according to another aspect of the present invention (Claim 2), the determination means includes a temperature change amount of the exhaust gas purification apparatus estimated from the heat generation amount and the detected temperature. When the difference from the amount of change is greater than a predetermined threshold value, it is determined that the exhaust purification device has deteriorated. According to this, it is possible to determine that the exhaust purification device has deteriorated when there is a large difference between the temperature change amount of the exhaust purification device due to the heat generation amount and the actual temperature change amount of the exhaust purification device. It is possible to determine the deterioration of the exhaust purification device.

1. Configuration An embodiment of a deterioration determination apparatus for an exhaust purification apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a diesel engine and its control device mounted on a vehicle according to an embodiment of the present invention. Here, a diesel engine will be described as an example, but a deterioration determination device for an exhaust gas purification device can be configured similarly for a gasoline engine.

  An electronic control unit (hereinafter referred to as “ECU”) 100 includes an input interface 100b that receives data sent from each part of the vehicle, a CPU 100a that performs operations for controlling each part of the vehicle, and a read-only memory (ROM) And a memory 100d having a random access memory (RAM) and an output interface 100c for sending control signals to various parts of the vehicle. The ROM of the memory 100d stores a program for controlling each part of the vehicle and various data. A program for control according to the present invention is stored in the ROM. The ROM may be a rewritable ROM such as an EPROM. The RAM is provided with a work area for calculation by the CPU 100a. Data sent from each part of the vehicle and control signals sent to each part of the vehicle are temporarily stored in the RAM.

  The signal sent to the ECU 100 is transferred to the input interface 100b and converted from analog to digital. The CPU 100a processes the converted digital signal according to a program stored in the memory 100d, and generates a control signal for sending to each part of the vehicle. The output interface 100c sends these control signals to the throttle 106, the fuel injection device 110, and other parts not shown.

  Further, the ECU 100 has a function of estimating the amount of nitrogen oxides absorbed by the LNC, calculating the predicted heat generation amount of the exhaust purification device, and determining deterioration of the exhaust purification device by executing a process described later.

  A fuel injection device 110 is attached to the diesel engine 101, and the fuel injection timing and the fuel injection amount are controlled by the control of the ECU 100. The fuel injection timing and the fuel injection amount are stored in the memory 100d in advance. The fuel injection device 110 is connected to a common rail (accumulation chamber) (not shown), and injects fuel (main injection) into the cylinder near the top dead center after the compression stroke by a signal from the ECU 100. Further, the fuel injection device 110 can also periodically make the fuel amount rich (rich spike) by controlling the fuel injection amount by a signal from the ECU 100. Furthermore, the fuel injection device 110 can also perform post injection by a signal from the ECU 100. Post injection is fuel injection that is additionally performed in the expansion stroke and the exhaust stroke after the main injection is completed. When post-injection is performed, the energy of the fuel is not converted into engine output, and most of the energy is exhaust energy such as heat energy. Therefore, the exhaust system part such as the NOx catalyst is warmed by the heat of the exhaust gas, and the catalyst poisoned by sulfur can be regenerated. Further, when fuel is injected in the exhaust stroke, a large amount of unburned fuel is released as exhaust gas. When there is an oxidation catalyst in the exhaust system, the unburned fuel is oxidized in the oxidation catalyst and changed to heat. Therefore, at this time as well, the exhaust system part such as the NOx catalyst can be warmed by the exhaust gas.

  The diesel engine 101 is provided with a crank angle sensor 107. The crank angle sensor 107 outputs a CRK signal and a TDC signal, which are pulse signals, to the ECU 100 as the crankshaft rotates. The CRK signal is a pulse signal output at a predetermined crank angle (for example, 30 degrees). ECU 100 calculates engine speed NE of engine 101 in accordance with the CRK signal. Note that a map of engine output and torque value is stored in the memory of the ECU 100, and these can be obtained as appropriate from the calculated engine speed.

The LNC (lean NOx catalyst) 107 is an exhaust purification device that reduces nitrogen oxides and is a NOx occlusion reduction type catalyst. The NOx occlusion reduction type catalyst occludes NOx discharged during lean, and reduces and purifies NOx occluded during rich. In the LNC, NO exhausted at the time of lean is oxidized to NO ₂ on the Pt (platinum) surface and stored as nitrate in the storage component. Next, NOx occluded by gas such as HC, CO, H ₂ is reduced and purified in the rich region. Since the air-fuel ratio needs to be rich when reducing the stored NOx, the ECU 100 does not generate a torque step at this time and optimizes the timing for enrichment according to the stored NOx amount. Controlled by.

  Further, an exhaust gas sensor 108 as air-fuel ratio detection means is attached to the exhaust system. The exhaust gas sensor 108 is a LAF sensor (wide area air-fuel ratio sensor) as an example here, detects an air-fuel ratio in a wide range from lean to rich with respect to the exhaust gas discharged from the engine 101, and the air-fuel ratio detected by the ECU 100 Send.

  The LNC 107 is provided with a temperature sensor 109 as temperature detecting means, and the obtained temperature of the LNC 107 is sent to the ECU 100. In this embodiment, the temperature sensor 109 is attached to the LNC 107. However, it is assumed that the temperature of the LNC 107 and the exhaust gas temperature downstream of the LNC are substantially the same, and the temperature sensor 109 is installed in the exhaust system downstream of the LNC 107. It is good also as detecting the temperature of LNC as attaching.

  An air flow meter 111 is attached upstream of the throttle 110, and the detected intake air amount is sent to the ECU 100.

  A DPF (diesel particulate filter) 102 for collecting particulate matter (particulates) is attached to the diesel engine 102. The DPF 102 is composed of a porous filter wall having heat resistance such as ceramic and metal nonwoven fabric, and has a number of channels that form an exhaust channel in the exhaust flow direction. The porous pore diameter is about 10 microns, and the particulate matter contained in the exhaust gas is collected when the exhaust gas passes through the porous filter wall. Specifically, each of the exhaust flow paths is closed at either the upstream end or the downstream end in the exhaust flow direction. A flow path whose upstream end is closed and a flow path whose downstream end is closed are alternately arranged adjacent to each other. For this reason, the exhaust discharged from the exhaust port of each cylinder flows into the flow path in which the upstream end of each DPF is released (the downstream end is closed), and the porous filter wall separating the flow paths is used. It passes through the flow path that has passed through the downstream end and flows out of the DPF from the downstream end.

  Although not shown, other sensors (water temperature sensor 105, throttle opening sensor 112, intake pipe pressure sensor) necessary for operating the diesel engine 101 and various devices (throttle valve 106) are not shown. The common rail (accumulation chamber) is attached to each part of the engine.

2. LNC Deterioration Detection Process An LNC abnormality / deterioration detection process will be described with reference to the flowchart of FIG.

  When a routine for detecting abnormality / deterioration of the LNC is called from the main program, the ECU 100 determines whether or not the engine 101 is currently in rich spike (S201). Here, the rich spike refers to temporarily increasing the air-fuel ratio by increasing the fuel supply amount. A vehicle equipped with an LNC usually performs a rich spike periodically to regenerate the LNC. In the present embodiment, LNC deterioration is determined using the time when the rich spike is performed. The rich spike period is mainly performed at idling when torque fluctuation does not affect drivability. This air-fuel ratio rich spike is executed by another routine (not shown) on condition that the rich spike flag is set to 1. Therefore, the ECU 100 refers to the rich spike flag in the memory 100d, determines whether or not the rich spike flag is 1 (during rich spike), and ends the process when the rich spike is not being performed. On the other hand, when the rich spike is being performed, the process proceeds to S202.

  In the present embodiment, the same method is repeated twice for the LNC deterioration determination method until it is finally determined that the LNC is deteriorated. This is because even if it is determined that the LNC has once deteriorated, the sulfur compound is simply adhered to the LNC, and the NOx purification performance may simply be lowered. Therefore, in this embodiment, the degradation of the LNC is once determined (S203 to S206). When it is determined that the LNC has deteriorated, it is assumed that the LNC has deteriorated temporarily, and then the LNC regeneration process is performed. Then, the determination of the deterioration of the LNC is performed again (S208 to S211).

  Therefore, in this embodiment, a temporary deterioration flag is provided to determine whether or not it has already been determined that the LNC has already been temporarily deteriorated. When it is determined that the LNC has already deteriorated, 1 is set to the temporary deterioration flag.

  In step S202, the ECU 100 determines whether or not the temporary deterioration flag is 1. Here, since the temporary deterioration flag is not set to 1, the ECU 100 predicts the temperature change amount of the LNC based on the air-fuel ratio in the exhaust system during the rich spike and the adsorption amount of nitrogen oxides in the LNC ( S203).

  The predicted temperature variation of the LNC is calculated as follows using catalyst models based on various maps. First, the ECU 100 reads from the memory 100d the estimated amount of nitrogen oxide that is estimated to be absorbed by the LNC. The estimated amount of absorbed nitrogen oxides is sequentially estimated by the ECU 100 in the background and stored in the memory 100d as follows. The ROM portion of the memory 100d stores a nitrogen oxide emission map that gives an instantaneous nitrogen oxide emission amount per unit time from the fuel injection amount and the engine speed. This map is created in advance by experimentally obtaining the nitrogen oxide emission amount per unit time with respect to the fuel injection amount and the engine speed. Next, the ECU 100 acquires the current fuel injection amount and the engine speed, and refers to the nitrogen oxide emission map to identify the emission amount of nitrogen oxide per unit time at this time. Then, the ECU 100 sequentially accumulates values obtained by multiplying the discharge amount per unit time of the identified nitrogen oxide by a minute time (a calculation cycle for calculating the estimated amount of nitrogen oxide), and the nitrogen absorbed by the LNC. An estimated amount of oxide is calculated.

  The ROM portion of the memory 100d stores a predicted heat value map that gives a predicted heat value from the nitrogen oxide amount and the air-fuel ratio. This map is prepared by experimentally obtaining the predicted calorific value with respect to the nitrogen oxide amount and the air-fuel ratio in advance. The ECU 100 acquires the air-fuel ratio from the LAF sensor 108. Then, based on the air-fuel ratio acquired above and the estimated amount of nitrogen oxides absorbed by the LNC, the predicted heat generation amount is obtained by referring to the predicted heat generation map.

  When the predicted heat generation amount generated by the LNC is obtained as described above, the ECU 100 calculates the temperature change amount of the LNC at a predetermined calculation cycle based on the predicted heat generation amount and the heat capacity of the LNC, and sequentially stores them in the memory 100d. . In step S203, the ECU 100 reads out the temperature change amount in the predetermined period d from the memory 100d and adds them to obtain the temperature change amount Δt ′ in the predetermined period d.

  When the predicted temperature change amount of the LNC is obtained, the ECU 100 next acquires the change amount of the actual temperature of the LNC as follows (S204). As described above, the temperature sensor 109 is attached to the LNC 107. In the background, the ECU 100 acquires the temperature of the LNC 107 at a predetermined sampling rate, and sequentially stores the acquired temperature in the memory 100d. The ECU 100 reads the temperature of the LNC 107 and the current temperature of the LNC 107 at a predetermined time before from the memory 100d. Then, the amount of change Δt in the actual temperature of the LNC in a predetermined period d is obtained by subtracting the temperature before a predetermined time from the current temperature.

  Next, the ECU 100 calculates the difference between the predicted temperature change amount Δt ′ of the LNC and the actual temperature change amount Δt of the LNC, and whether or not this difference exceeds a predetermined threshold value (allowable temperature difference). (S205). If the temperature change amount difference exceeds the allowable temperature difference, it is determined that the LNC is temporarily deteriorated, and the temporary deterioration flag is set to 1 (S206). Here, when the temperature difference is large, it is determined that the LNC has deteriorated. When the temperature difference is large, the degree of the reduction reaction of the LNC is low even though the rich spike is performed. This is because the temperature rise of the result LNC is small. The allowable temperature difference is experimentally obtained in advance as a temperature difference suitable for determining that the LNC has deteriorated, and is stored in the memory 100d.

  On the other hand, when the allowable temperature difference is not exceeded, the ECU 100 ends the process on the assumption that the LNC has not deteriorated.

  Note that the actual temperature change of the LNC is slower in response than the temperature change in the catalyst model, and the temperature change is delayed. Therefore, in S205, instead of comparing the difference in the temperature change amount and the allowable temperature difference in the same period, the temperature change of the catalyst model is different from the actual temperature change of the LNC. It is also possible to compare the difference in temperature change with the allowable temperature difference.

  When the temporary deterioration flag is set to 1, the LNC regeneration process is necessary, so the regeneration process is performed to remove sulfur by another routine (not shown). Specifically, the ECU 100 controls the fuel injection device to execute post injection to increase the temperature of the exhaust gas so that the sulfur compound attached to the LNC is burned by the high temperature exhaust gas. Here, the reason why the LNC regeneration process is performed is that the reducing ability of the LNC may be temporarily lowered due to the influence of the sulfate adhering to the LNC.

  Then, when the reproduction process is performed for a predetermined period and the reproduction process is completed, 1 is set to the sulfur reproduction completed flag by another routine (not shown). On the other hand, when the reproduction process has not ended, 0 is set to the sulfur reproduction completed flag.

  Next, when the LNC abnormality / deterioration detection routine is called again from the main program, the ECU 100 determines whether or not the engine 101 is in rich spike (S201). The determination as to whether or not the rich spike is being performed is the same as described above, and a description thereof will be omitted.

  Next, the ECU 100 determines whether or not the temporary deterioration flag is 1 (S202). Since the temporary deterioration flag is set to 1 in the previous execution of this process, the process proceeds to S207. Next, the ECU 100 determines whether or not the regeneration of the sulfur has been completed with reference to the sulfur regeneration completed flag. Here, when the sulfur regenerated flag is not 1, the ECU 100 ends the present process.

  On the other hand, when the sulfur regeneration flag is 1, the ECU 100 predicts the temperature change amount of the LNC (S208). Next, the ECU 100 acquires the actual temperature change amount of the LNC (S209). Then, it is determined whether or not the difference in temperature change amount exceeds a predetermined value (allowable temperature difference) (S210). Since the routines from S208 to S210 are the same as the routines from S203 to S205, the description thereof will be omitted.

  When the difference in the temperature change amount exceeds the allowable temperature difference, the ECU 100 sets the catalyst deterioration flag to 1 assuming that the LNC has deteriorated (S211). Further, when the catalyst deterioration flag is set to 1, a predetermined lamp in the vehicle may be turned on so as to notify that the LNC has deteriorated.

  On the other hand, when the difference in temperature change amount does not exceed the allowable temperature difference, the ECU 100 advances the process to S212. Then, the temporary deterioration flag set to 1 by this process is reset to 0 (S212). Then, this process ends.

  In this embodiment, it is determined that the LNC is provisionally deteriorated in S206. However, as another embodiment, it may be determined that the LNC is finally deteriorated in S206. In this case, the flow from S202 and S207 to S212 is deleted, and the degradation state of the LNC is determined by a single determination.

  According to this, based on the calculated calorific value of the LNC and the actual LNC temperature, the reduction ability of the nitrogen oxides of the LNC when the exhaust gas is rich is monitored. Therefore, when the temperature rise amount is smaller than the calculated calorific value, it can be determined that the LNC has deteriorated because the nitrogen oxide absorption capacity and the reduction capacity have fallen, and the nitrogen oxide sensor It is possible to determine the deterioration of an LNC with low cost and high responsiveness without arranging In addition, since the deterioration of the LNC is determined using the time when the rich spike is performed, the deterioration determination can be executed without deteriorating the emission and fuel consumption as compared with the conventional case.

1 is a schematic diagram of a diesel engine and its control device according to one embodiment of the present invention. The flowchart of the deterioration detection of LNC according to one Embodiment of this invention.

Claims (2)

A deterioration determination device for an exhaust purification device that absorbs nitrogen oxide when the air-fuel ratio of the exhaust gas is lean and reduces nitrogen oxide absorbed when the air-fuel ratio of the exhaust gas is rich,
Air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas supplied to the exhaust purification device;
Estimating means for obtaining an estimated amount of nitrogen oxides absorbed by the exhaust purification device;
Temperature detecting means for detecting the temperature of the exhaust purification device;
A calculation means for obtaining a predicted calorific value of the exhaust emission control device based on the detected air-fuel ratio of the exhaust gas and the estimated amount of absorbed nitrogen oxide during the rich spike ;
Determining means for determining deterioration of the exhaust purification device based on the calculated predicted heat generation amount and the temperature detected during the rich spike ;
An exhaust gas purification device deterioration determination device comprising: The determination means determines the exhaust purification device when a difference between a temperature change amount of the exhaust purification device estimated from the predicted heat generation amount and the detected change amount of the temperature is larger than a predetermined threshold value. The deterioration determination device for an exhaust emission control device according to claim 1, wherein the deterioration determination device is determined to be deteriorated.

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