JP4849052B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device (EGR device) that recirculates a part of exhaust gas to an intake system, and more particularly to deterioration diagnosis of an EGR cooler for cooling the exhaust gas (EGR gas) to be recirculated.

As a technique for reducing the NOx emission amount of the engine, exhaust gas recirculation (EGR) in which a part of the exhaust gas is recirculated to the intake system is known. In order to further reduce NOx emission, an EGR cooler that cools EGR gas is disclosed in Patent Document 1 and the like.
JP 2004-156585 A

  By the way, the cooling performance of the EGR cooler rapidly decreases from the start of use, and when the cooling performance decreases to some extent, the progress of the deterioration becomes moderate and the stable state continues. And even if it will be in the stable state, cooling performance will fall gradually and eventually a cooling effect will be hardly acquired.

  Such a decrease in the cooling performance of the EGR cooler, that is, deterioration can be easily detected by detecting the temperature difference between the inlet and the outlet of the EGR cooler, but the cost increases if a new temperature sensor is provided.

  Therefore, an object of the present invention is to determine the deterioration of the EGR cooler without providing a new sensor.

  An exhaust gas recirculation device for an internal combustion engine according to the present invention includes an exhaust gas recirculation passage that recirculates a part of exhaust discharged from the internal combustion engine as a recirculation gas to an intake system, and a recirculation gas cooling means (EGR cooler) interposed in the exhaust gas recirculation passage. A bypass passage that bypasses the EGR cooler, a switching means that selectively connects one of the passage or bypass passage that interposes the EGR cooler according to the engine operating state, and target exhaust gas according to the engine operating state Target exhaust gas recirculation rate setting means for setting the recirculation rate, recirculation gas amount adjusting means whose opening degree changes according to the target exhaust gas recirculation rate, and detection for detecting the amount of nitrogen oxides generated in the exhaust discharged from the engine An exhaust gas recirculation device for an internal combustion engine comprising: a means for communicating with a passage where an EGR cooler is interposed and a case where a bypass passage is communicated when the target exhaust gas recirculation rate is constant. It is provided with a nitrogen oxide production amount difference calculating means for calculating a difference between detection values of the knowledge means, and the same target as the state in which the initial value is calculated with the nitrogen oxide generation amount difference when the EGR cooler is in the initial state as an initial value. Deterioration degree calculating means for calculating a difference between the nitrogen oxide generation amount in the operating state of the exhaust gas recirculation rate and the initial value as a deterioration degree, and determining that the EGR cooler has deteriorated when the deterioration degree exceeds a threshold value Deterioration determination means.

  According to the present invention, it is possible to determine the deterioration of the EGR cooler based on the amount of nitrogen oxide produced. That is, it is possible to determine the deterioration of the EGR cooler without providing a new sensor or the like for determining the degree of deterioration of the EGR cooler.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an engine to which the first embodiment is applied. 1 is an engine, 2 is an intake passage, 3 is an exhaust passage, 4 is a fuel injection device, and 5 is an EGR pipe (exhaust gas recirculation passage).

  In the intake passage 2, in order from the upstream side, an air cleaner 9 that removes dust in the air, an air flow meter 8 that measures the amount of air that has passed through the air cleaner 9, a compressor 10 a of a variable capacity supercharger 10 that will be described later, a compressor An intercooler 7 for cooling the air compressed at 10a and a collector tank 6 for distributing the intake air to each cylinder are provided.

  The exhaust passage 3 is provided with a NOx sensor (detection means) 20 for detecting the amount of NOx in the exhaust gas of the engine 1, downstream of the turbine 10b of the variable capacity supercharger 10, and further downstream of the oxidation catalyst. 11. A diesel particulate filter (DPF) 12 is provided.

  The fuel injection device 4 is a so-called common rail type, and has a fuel tank (not shown), a supply pump 13, a common rail (accumulation chamber) 14, and a nozzle 15 provided for each cylinder, and the fuel pressurized by the supply pump 13 is common rail. 14 and then distributed to the nozzles 15 of each cylinder.

  The variable capacity supercharger 10 is coaxially connected to a turbine 10b that converts heat energy of exhaust gas into rotational energy and a compressor 10a that compresses intake air, and is driven by a not-shown actuator at a scroll inlet of the turbine 10b. A variable nozzle 10c (geometry variable mechanism) is provided. The variable nozzle 10c is controlled by a control unit 21 (target exhaust gas recirculation rate setting means, nitrogen oxide generation amount difference calculating means, deterioration degree calculating means, deterioration determining means, correcting means) 21 and a predetermined boost pressure from a low rotational speed range. In order to obtain the above, on the low rotational speed side, the opening degree of the nozzle that increases the flow rate of the exhaust gas introduced into the turbine 10b, that is, the tilted state is controlled. On the other hand, in the high rotational speed region, the opening degree of the nozzle that introduces the exhaust gas into the turbine 10b without resistance, that is, the fully open state is controlled so that more intake air can be introduced into the engine 1.

  The EGR pipe 5 is branched from the exhaust passage 3 and connected to the collector tank 6, and an EGR valve 18 is interposed in the pipe 5. The EGR valve 18 is for adjusting the amount of EGR gas flowing through the EGR pipe 5, and the opening degree is controlled in accordance with a target EGR rate (target exhaust gas recirculation rate) described later.

  An EGR cooler bypass passage that bypasses the EGR cooler 17 by interposing an EGR cooler (reflux gas cooling means) 17 that cools the EGR gas by heat exchange from the EGR valve (reflux gas amount adjusting means) 18 to the exhaust passage 3 side. 16 is provided. A switching valve (switching means) 19 is provided at the junction with the EGR cooler bypass passage 16 on the downstream side of the EGR cooler 17. The switching valve 19 selects either the EGR cooler 17 or the EGR cooler bypass passage 16 as the EGR gas flow path. For example, when the EGR cooler bypass passage 16 is selected to reduce hydrocarbon emissions at low water temperatures or when more EGR gas is introduced, the increase in combustion temperature due to the high temperature EGR gas is suppressed. The EGR cooler 17 is selected.

  The control unit 21 receives signals from an accelerator opening sensor 22, a crank angle sensor 23 for detecting a crank angle (engine speed), a water temperature sensor 24 for detecting a cooling water temperature, a supercharging pressure sensor 25, and an air flow meter 8. Based on these signals, the target EGR rate, the target supercharging pressure, and the like are set, and the opening degree of the EGR valve 18 and the switching valve 19 are controlled accordingly. Further, based on the detection value of the NOx sensor 20, combustion control such as setting of the combustion injection amount and the combustion injection timing is also performed.

  FIG. 2 is a diagram showing the relationship between the usage time of the EGR cooler 17 and the cooling performance. As shown in the figure, when the use is started in a new state, the cooling performance is rapidly lowered. Then, when the cooling performance is lowered to some extent (t1 in the figure), the cooling speed declines gradually and becomes almost stable. Note that t1 is about 20 hours when traveling in a traveling pattern for mode evaluation or the like. That is, the cooling performance rapidly decreases until about 20 hours from the start of use, but thereafter, the cooling performance becomes almost stable and gradually decreases. Therefore, in general, the setting of the target EGR rate and the adaptation of the control of the switching valve 19 are performed using the cooling performance in a stable state after t1. However, if the cooling performance after t1 is adapted in this way, there is a problem such as overcooling before t1 and combustion noise worsening. On the other hand, if a new sensor for detecting the cooling performance is provided in order to meet the cooling performance before t1, there is a problem that the cost increases.

  Therefore, in the present embodiment, by performing the control described below, a decrease in cooling performance, that is, deterioration of the EGR cooler 17 is accurately detected without providing a new sensor.

  FIG. 3 is a flowchart showing a control routine executed by the control unit 21.

  In step S100, it is determined whether the engine operating state is constant. Specifically, the determination is made based on detection signals from the accelerator opening sensor 22, the crank angle sensor 23, and the like. If it is constant, the process proceeds to step S110, and if not, the process ends. The determination as to whether or not the driving state is constant is because the target EGR rate needs to be constant in order to perform the following processing. Therefore, the determination may be made based on whether the target EGR rate calculated by the control unit 21 is constant rather than the detection value of the accelerator opening sensor 22 or the like.

  In step S110, the initial value ΔN1 is calculated by executing the subroutine shown in FIG.

  In step S1000 of FIG. 4, the switching valve 19 is controlled to the side where the EGR cooler 17 is used. In step S1010, the detection signal of the NOx sensor 20 is read, and this is set as the NOx amount Nc. Next, the switching valve 19 is controlled to the use side of the EGR cooler bypass passage 16 in step S1020, and the detection signal of the NOx sensor 20 is read in step S1030, and this is set as the NOx amount Nb.

  In step S1040, the difference between the NOx amount Nb and the NOx amount Nc is calculated. In step S1050, this is stored as the initial value ΔN1, and the process proceeds to step S120 in FIG.

  In step S120 of FIG. 3, it is determined whether or not the engine operation state is constant as it is when step S110 is executed. If it is constant, the process proceeds to step S130, otherwise it is the same engine operation as when step S110 is executed. After entering the state, the process proceeds to step S130. This is because the calculation of deterioration degree D and the deterioration determination in steps S130 and S140, which will be described later, are based on the premise that the target EGR rate is the same as when step S110 is executed.

  In step S130, by executing the subroutine shown in FIG. 5, the degree of deterioration D representing the degree of deterioration in cooling performance is calculated.

  In steps S2000 to S2040 in FIG. 5, the same processing as in steps S1000 to S1040 in FIG. 4 is executed to calculate the difference ΔN2 in the NOx amount between when the EGR cooler 17 is used and when the EGR cooler bypass passage 16 is used. Then, in step S2050, the difference between this ΔN2 and the initial value ΔN1 is obtained, and this is set as the deterioration degree D, and the process proceeds to step S140 in FIG.

  Here, the deterioration degree D will be described with reference to FIG. In FIG. 6, the vertical axis represents the target EGR rate determined from the engine operating state and the like, and the horizontal axis represents the NOx emission amount detected by the NOx sensor 20 when operating at the target EGR rate. Xb1 is when the EGR cooler bypass passage 16 is used. Xc1 indicates a NOx emission amount when the EGR cooler 17 is used in a new state (when new), and Xc2 indicates a NOx emission amount when the EGR cooler 17 is used after a predetermined time has elapsed.

  When the EGR gas is cooled, the in-cylinder combustion temperature is lowered, and the NOx emission amount is further reduced as compared with the case of normal EGR gas introduction. Therefore, the NOx emission amounts Xc1, Xc2 when the EGR cooler 17 is used are smaller than the NOx emission amount Xb1 when the EGR cooler bypass passage 16 is used (when the EGR cooler 17 is not used). However, when the cooling performance of the EGR cooler 17 is reduced, the NOx emission reduction effect is reduced, and therefore, as shown by Xc2 in FIG. 6, the NOx emission becomes larger than the NOx emission Xc1 when new. That is, ΔN2 becomes smaller as the cooling performance of the EGR cooler 17 decreases.

  Therefore, the difference between the NOx emission amount ΔN2 between when the EGR cooler 17 is used and when it is not used in the current operating state, and the difference ΔN1 between the NOx emission amount when the EGR cooler 17 is used and when it is not in use when new. The larger the difference is, the lower the cooling performance of the EGR cooler 17 is. Thus, even if the outlet temperature of the EGR cooler 17 is not measured, the degree of deterioration of the EGR cooler 17 can be known based on the NOx emission amount.

  In step S140 of FIG. 3, it is determined whether or not the deterioration degree D is greater than a preset threshold value m. This determination is to determine whether or not the cooling performance of the EGR cooler 17 has deteriorated to a certain extent. The threshold value m can be set arbitrarily. For example, as shown in FIG. 6, the difference between ΔN1 and ΔN2 when the effect of reducing the NOx emission amount by the EGR cooler 17 is almost eliminated is defined as the threshold value m. Since the target EGR rate and the NOx emission reduction effect by the EGR cooler 17 are different depending on the operation state, the threshold value m is set to a different value for each operation state.

  If the degree of deterioration D is greater than the threshold value m, the process is terminated because the EGR cooler 17 has deteriorated to the extent that it needs to be replaced. If it is smaller, the process returns to step S120 and the process is repeated until it exceeds the threshold value m.

  Since it can be determined whether or not the EGR cooler 17 has deteriorated by this control, when it is determined that the EGR cooler 17 has deteriorated, the user may be prompted to replace the EGR cooler 17 by turning on an indicator or the like.

As described above, according to the present embodiment, the following effects can be obtained.
(1) When the NOx emission amount difference is defined as the difference in NOx emission amount between the case of recirculation through the EGR cooler 17 and the case of recirculation through the EGR cooler bypass passage 16 in an operation state where the target EGR rate is constant. Furthermore, the NOx emission amount difference when the EGR cooler 17 is new (initial state) is set to an initial value ΔN1, and the initial value ΔN1 and the initial value ΔN1 are calculated in the same target EGR rate operation state. The difference from the NOx emission difference ΔN2 is defined as the deterioration degree D, and when the deterioration degree D is greater than the threshold value m, it is determined that the EGR cooler 17 has deteriorated. Therefore, the combustion control of a diesel engine or an engine that performs lean combustion is performed. Therefore, it can be determined whether or not the EGR cooler 17 is deteriorated based on the detected value of the NOx sensor 20 that can be used. That is, it is possible to determine whether or not the EGR cooler 17 has deteriorated without providing a temperature sensor or the like at the outlet of the EGR cooler 17.
(2) Since the magnitude of the threshold value m is changed according to the target EGR rate when the initial value ΔN1 is calculated, the deterioration determination is performed based on the appropriate determination threshold value m according to the magnitude of the target EGR rate. can do.

  A second embodiment will be described.

  In the present embodiment, the degree of deterioration D of the EGR cooler 17 is calculated by the same control as in the first embodiment, and the opening degree of the EGR valve 18 is corrected based on this.

  The inside of the EGR cooler 17 is in a state where deposits or the like are easily attached by condensed water or the like in which high-temperature EGR gas is cooled, and the adhesion of deposits causes a decrease in cooling performance. Further, when deposits are deposited, there is a problem that pressure loss is increased and the EGR rate is lowered due to these, in addition to a decrease in cooling performance.

  That is, when the cooling performance of the EGR cooler 17 is lowered, the actual EGR rate (actual EGR rate) becomes lower than the target EGR rate even if the opening degree of the EGR valve 18 is set according to the target EGR rate. Therefore, the control unit 21 makes the actual EGR rate coincide with the target EGR rate by the control described below.

  FIG. 7 is a flowchart showing a control routine executed by the control unit 21. Steps S200 to S230 are the same as steps S100 to S130 in FIG.

  When the deterioration degree D of the EGR cooler 17 is calculated in step S230, the opening degree of the EGR valve 18 is corrected according to the deterioration degree D in step S240.

  While the deterioration degree determination is being performed, the target EGR rate is constant, but as described above, the actual EGR rate is reduced with the cooling performance and the pressure loss. Therefore, the relationship between the degree of deterioration D and the amount of decrease in the actual EGR rate is mapped in advance, and the amount of decrease in the actual EGR rate is calculated based on the degree of deterioration D obtained by calculation. The opening of the EGR valve 18 is corrected to increase so as to compensate for the amount of decrease.

  Note that the target EGR rate may be increased and corrected so as to compensate for the amount of decrease in the actual EGR rate without directly controlling the opening degree of the EGR valve 18. This is because the opening degree of the EGR valve 18 increases with the increase in the target EGR rate, and as a result, the same effect as that obtained by correcting the opening degree of the EGR valve 18 can be obtained.

  As described above, in the present embodiment, the following effects can be obtained in addition to the same effects as those of the first embodiment.

  Since the opening degree of the EGR valve 18 is corrected according to the degree of deterioration D, the actual EGR rate can be brought close to the target EGR rate even when the cooling performance of the EGR cooler 17 is lowered.

  A third embodiment will be described.

  FIG. 8 is a flowchart showing a control routine executed by the control unit 21.

  Steps S300 to S330 are the same as steps S100 to S130 of FIG.

  In step S340, the rate of change ΔD of the deterioration degree D is calculated from the difference between the deterioration degree D calculated at the previous calculation and the deterioration degree D calculated this time.

  In step S350, as in step S140 of FIG. 3, it is determined whether or not the degree of deterioration D is greater than a predetermined value m. As a result of the determination, if it is larger, the process proceeds to step S360, where it is determined that the EGR cooler 17 has deteriorated to some extent, and the user is prompted to replace it by lighting the indicator. As a result of the determination, if the deterioration degree D is smaller than the predetermined value m, the process proceeds to step S370.

  In step S370, it is determined whether or not the change rate ΔD of the deterioration degree D is smaller than the threshold value b continuously for a predetermined time or more. This determination is for knowing whether the cooling performance of the EGR cooler 17 is in a state of rapid deterioration before t1 in FIG. 2 or whether the progress of deterioration after t1 is moderate. The “time” and the “threshold value b” are set based on the characteristics of the cooling performance degradation of the EGR cooler 17 to be used.

  As a result of the determination, if the change rate ΔD is smaller than the threshold value b for a predetermined time, that is, if the progress of deterioration is in a gradual state, the process proceeds to step S380, otherwise, that is, in a state where deterioration rapidly proceeds. If there is, the process proceeds to step S390.

  In step S390, the opening correction of the EGR valve 18 is performed in the same manner as in step S240 of FIG. 7, and in step S380, the opening correction of the EGR valve 18 is ended.

  The reason why the correction of the opening degree of the EGR valve 18 is terminated in step S380 is that the correction is not necessary because the decrease in cooling performance has converged. Note that it is assumed that the cooling performance after t1 in FIG.

  By the above control, in the present embodiment, the following effects can be obtained in addition to the same effects as those of the first and second embodiments.

  When the rate of change ΔD of the deterioration degree D continues for a predetermined time or more and becomes equal to or less than the predetermined value b, the correction of the opening degree of the EGR valve 18 is stopped, so that the calculation load can be reduced.

  In addition, although the case where the engine 1 was a diesel engine was demonstrated in description of the said embodiment, this invention can be applied similarly also to a gasoline engine.

  The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

1 is a schematic configuration diagram of a system to which a first embodiment is applied. It is a figure showing the relationship between the cooling performance of an EGR cooler, and use time. It is a flowchart showing the control routine of 1st Embodiment. This is a subroutine for initial value ΔN1 calculation. This is a subroutine for deterioration degree D calculation. It is a figure showing the relationship between a target EGR rate and NOx discharge | emission amount. It is a flowchart showing the control routine of 2nd Embodiment. It is a flowchart showing the control routine of 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Intake passage 3 Exhaust passage 4 Fuel injection apparatus 5 EGR piping 6 Collector tank 7 Intercooler 8 Air flow meter 9 Air cleaner 10 Variable capacity supercharger 11 Oxidation catalyst 12 Diesel particulate filter (DPF)
13 Supply pump 14 Common rail 15 Nozzle 16 EGR cooler bypass passage 17 Intercooler 18 EGR valve 19 Switching valve 20 NOx sensor 21 Control unit

Claims (4)

An exhaust gas recirculation passage for recirculating a part of the exhaust gas discharged from the internal combustion engine to the intake system as a recirculation gas;
A reflux gas cooling means interposed in the exhaust gas recirculation passage;
A bypass passage bypassing the reflux gas cooling means;
Switching means for selectively communicating either one of the passage including the reflux gas cooling means or the bypass passage;
Target exhaust gas recirculation rate setting means for setting the target exhaust gas recirculation rate according to the engine operating state;
Recirculation gas amount adjusting means whose opening degree changes according to the target exhaust gas recirculation rate;
Detection means for detecting the amount of nitrogen oxides produced in the exhaust discharged from the engine;
An exhaust gas recirculation device for an internal combustion engine comprising:
Nitrogen oxidation for calculating a difference between detection values of the detection means when the passage including the reflux gas cooling means is communicated with the bypass passage when the target exhaust gas recirculation rate is constant Product difference calculation means,
The difference in nitrogen oxide production amount when the recirculation gas cooling means is in the initial state is set as an initial value, and the difference between the nitrogen oxide production amount and the initial value in the operation state with the same target exhaust gas recirculation rate as the initial value is calculated. A deterioration degree calculating means for calculating the difference between the two as a deterioration degree;
A deterioration determining means for determining that the reflux gas cooling means has deteriorated when the degree of deterioration exceeds a threshold;
An exhaust gas recirculation device for an internal combustion engine, comprising:   2. The exhaust gas recirculation apparatus for an internal combustion engine according to claim 1, wherein the threshold value changes according to a target exhaust gas recirculation rate when the initial value is calculated.   The correction means which correct | amends the opening degree of the said recirculation | reflux gas amount adjustment means so that an actual exhaust gas recirculation rate may approach the said target exhaust gas recirculation rate according to the said deterioration degree is provided. An exhaust gas recirculation device for an internal combustion engine.   The correction means calculates the rate of change of the deterioration degree between the previous calculation and the current calculation, and stops correcting the target exhaust gas recirculation rate when the change rate continues for a predetermined time or more and becomes a predetermined value or less. The exhaust gas recirculation device for an internal combustion engine according to any one of claims 1 to 3, characterized in that:

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