JP4498831B2 - Exhaust circulation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas circulation device for an internal combustion engine.

In order to suppress clogging of the EGR cooler provided in the EGR device of the internal combustion engine, a catalyst having an oxidation ability may be provided on the upstream side (exhaust system side) of the EGR cooler.
If the oxidation capacity of the catalyst decreases due to deterioration, the unburned fuel in the exhaust gas cannot be oxidized. As a result, unburned fuel that has passed through the catalyst adheres to the EGR cooler and reduces the cooling efficiency of the EGR cooler. On the other hand, a technique for determining deterioration of the catalyst provided on the upstream side of the EGR cooler is known. For example, there is known a technique for estimating how much the catalyst activity is reduced as a relationship with a driving state such as a travel distance or travel time of a vehicle (see, for example, Patent Document 1).
JP 2002-371874 A JP 2000-97017 A JP 2003-65162 A

  By the way, even if the travel distance or travel time of the vehicle is the same, the degree of deterioration of the catalyst provided upstream of the EGR cooler may differ depending on the rotational speed of the internal combustion engine and the state of the load. For this reason, there is a risk of erroneous determination of deterioration according to the prior art.

  The present invention has been made in view of the above-described problems, and provides a technique capable of more accurately determining deterioration of a catalyst upstream of an EGR cooler in an exhaust gas circulation device of an internal combustion engine. With the goal.

In order to achieve the above object, an exhaust gas recirculation device for an internal combustion engine according to the present invention employs the following means. That is,
An EGR passage for connecting an exhaust system and an intake system of the internal combustion engine and introducing a part of the exhaust from the exhaust system to the intake system;
A catalyst having oxidation ability provided in the EGR passage;
EGR gas cooling means for lowering the temperature of EGR gas flowing through the EGR passage closer to the intake system than the catalyst;
EGR gas temperature decrease suppressing means for suppressing a decrease in temperature of EGR gas by the EGR gas cooling means;
EGR gas temperature detection means for detecting the temperature of the EGR gas flowing through the EGR passage on the intake system side of the portion where the temperature reduction is suppressed by the EGR gas temperature decrease suppression means;
When the temperature of the EGR gas detected by the EGR gas temperature detection means is lower than the first predetermined temperature when the temperature reduction of the EGR gas is suppressed by the EGR gas temperature reduction suppression means, the catalyst deteriorates. Catalyst deterioration determination means for determining that
It is characterized by comprising.

  The most significant feature of the present invention is that when the temperature of the EGR gas is suppressed by the EGR gas temperature decrease suppression means, and the temperature detected by the EGR gas temperature detection means is less than a first predetermined temperature. Is to determine that the catalyst has deteriorated because the amount of reaction heat generated by unburned fuel in the catalyst is small.

  Here, when EGR gas containing unburned fuel flows into the catalyst, the unburned fuel reacts with the catalyst and the temperature of the EGR gas rises. The rising temperature of the EGR gas at this time has a correlation with the degree of deterioration of the catalyst, and therefore the deterioration of the catalyst can be determined based on this rising temperature. That is, the lower the degree of catalyst deterioration, the higher the catalyst rising temperature.

  At this time, the EGR gas temperature decrease suppression unit suppresses the temperature decrease of the EGR gas by the EGR gas cooling unit. Here, if the temperature drop of the EGR gas in the EGR gas cooling means is larger than the temperature rise of the EGR gas due to oxidation of the unburned fuel, the temperature of the EGR gas is lowered by the EGR gas cooling means. It becomes difficult to determine catalyst deterioration using the reaction heat of fuel. That is, even if the temperature of the EGR gas rises due to the reaction heat of the unburned fuel, if the temperature of the EGR gas is greatly lowered by the EGR gas cooling means, the temperature rise of the EGR gas due to the reaction heat of the unburned fuel is judged. It becomes difficult to do.

  On the other hand, if the temperature reduction of the EGR gas is suppressed by the EGR gas temperature decrease suppression means, it is possible to determine how much unburned fuel is reacting based on the temperature of the EGR gas, and the degree of deterioration of the catalyst can be determined. It becomes possible to judge.

Here, the first predetermined temperature can be a lower limit value of the temperature at which the catalyst can be assumed not to deteriorate.
In the present invention, the EGR gas cooling means is provided in the EGR passage closer to the intake system than the catalyst, and exchanges heat between the EGR gas flowing through the EGR passage and the other heat medium to control the temperature of the EGR gas. Consisting of an EGR cooler to lower,
The EGR gas temperature lowering suppression means includes an EGR bypass connecting the EGR passage between the catalyst and the EGR cooler and an EGR passage closer to the intake system than the EGR cooler, and the EGR bypass and the EGR cooler. The EGR gas temperature decrease suppression means changes the flow rate ratio of the EGR gas passing through the EGR gas, and the EGR gas temperature decrease suppressing means reduces the decrease in the EGR gas temperature and the flow rate ratio of the EGR gas passing through the EGR detour. Can be more.

  Here, as the ratio of the EGR gas passing through the EGR bypass is increased, the ratio of the EGR gas cooled by the EGR cooler is decreased, and the temperature of the EGR gas supplied to the intake system is increased. Thereby, since it becomes easy to detect the temperature rise of the EGR gas at the catalyst, the accuracy of the catalyst deterioration determination can be improved.

When determining catalyst deterioration, the flow rate ratio changing valve may cause the entire amount of EGR gas to flow through the EGR bypass.
In the present invention, the EGR gas cooling means is provided in the EGR passage closer to the intake system than the catalyst, and exchanges heat between the EGR gas flowing through the EGR passage and the other heat medium to control the temperature of the EGR gas. Consisting of an EGR cooler to lower,
The EGR gas temperature decrease suppressing means includes a heat exchange amount changing means for changing the amount of heat exchange between the EGR gas and another heat medium in the EGR cooler, and the EGR gas temperature decrease suppressing means includes a decrease in EGR gas temperature. The smaller the value is, the smaller the amount of heat exchange by the EGR cooler can be made.

  Here, the temperature of the EGR gas can be lowered by exchanging heat between the EGR gas and another heat medium. However, it is not desirable to lower the temperature of the EGR gas when the catalyst deterioration is determined as described above. In that respect, as the amount of heat exchange between the EGR gas and the other heat medium is reduced, the amount of heat taken by the EGR gas to the EGR cooler is reduced, and the temperature of the EGR gas supplied to the intake system is increased. Thereby, it becomes easy to detect the temperature increase of the EGR gas at the catalyst, and the accuracy of the catalyst deterioration determination can be improved.

  When determining the deterioration of the catalyst, the heat exchange amount changing means preferably makes the heat exchange amount in the EGR cooler as small as possible. Examples of the heat medium include air, engine cooling water, and engine lubricating oil.

  In the present invention, it is determined that the catalyst is deteriorated by the catalyst deterioration determining means and the temperature of the exhaust gas detected by the EGR gas temperature detecting means is less than a second predetermined temperature lower than the first predetermined temperature. In some cases, the EGR gas temperature decrease suppressing means can further include an abnormality determining means for determining that there is an abnormality.

  Here, if there is an abnormality in the EGR gas temperature decrease suppressing means, the EGR gas is cooled by the EGR gas cooling means, so the temperature of the EGR gas detected by the EGR gas temperature detecting means becomes a low temperature after cooling. The temperature of the EGR gas detected by the EGR gas temperature detecting means after being cooled by the EGR gas cooling means is lower than the temperature of the EGR gas detected when the catalyst is deteriorated. For this reason, if a temperature lower than the temperature estimated by the EGR gas temperature detecting means is detected when the catalyst is deteriorated, an abnormality occurs in the EGR gas temperature decrease suppressing means. It can be determined that

Here, the second predetermined temperature is a lower limit value of the temperature at which there is no abnormality in the EGR gas temperature decrease suppressing means.
In the present invention, when the catalyst deterioration determining means determines that the catalyst is deteriorated, the amount of EGR gas flowing through the EGR detour by the flow rate ratio changing valve is not deteriorated by the catalyst. The flow rate ratio changing valve control means can be further provided in comparison with the flow rate ratio changing valve control means.

  Here, if the EGR gas is flowed to the EGR cooler when the catalyst is deteriorated, unburned fuel contained in the EGR gas may adhere to the EGR cooler. In that respect, it is possible to prevent unburned fuel from adhering to the EGR cooler by flowing a large amount of exhaust gas to the EGR detour, and to suppress the cooling efficiency of the EGR cooler from being lowered.

In the present invention, engine operating state detecting means for detecting the operating state of the internal combustion engine,
Target fresh air amount setting means for setting a target amount of fresh air sucked into the internal combustion engine;
Unburnt fuel amount determination means for determining whether or not the amount of unburned fuel in the exhaust gas is greater than or equal to a predetermined amount based on the engine operation state detected by the engine operation state detection means;
The catalyst deterioration determining means determines that the catalyst has deteriorated, the unburned fuel amount determining means determines that the amount of unburned fuel in the exhaust gas is less than a predetermined amount, and the EGR gas cooling means cools the EGR gas. The intake fresh air amount increasing means for increasing the target amount of the amount of fresh air sucked into the internal combustion engine compared to when it is determined that the catalyst is not deteriorated,
Can further be provided.

  Here, when the catalyst deteriorates, it becomes difficult to oxidize the unburned fuel in the exhaust gas. Therefore, when the amount of unburned fuel in the exhaust gas is large, the EGR gas cooling means should not cool the EGR gas. To do. Thereby, it can suppress that unburned fuel adheres to an EGR gas cooling means or its vicinity.

  Even if the catalyst has deteriorated, if the amount of unburned fuel in the exhaust gas is small, the amount of unburned fuel adhering to the EGR gas cooling means or its vicinity also decreases, so the EGR gas by the EGR gas cooling means Even when cooling is performed, there is almost no decrease in the cooling efficiency of the EGR gas cooling means due to adhesion of unburned fuel. Therefore, when the amount of unburned fuel in the exhaust gas is small, it is desirable to cool the EGR gas by the EGR gas cooling means.

  However, since the temperature of the EGR gas is different between when the EGR gas is cooled by the EGR gas cooling means and when the temperature reduction of the EGR gas is suppressed by the EGR gas temperature reduction suppressing means, the EGR gas is different. The density is different. In other words, if the EGR gas cooling means cools the EGR gas when the amount of unburned fuel in the exhaust gas is small, the density of the EGR gas increases and more EGR gas is sucked into the internal combustion engine. However, when the target value of the intake air amount of the internal combustion engine is determined with reference to the time when the temperature reduction of the EGR gas is suppressed by the EGR gas temperature decrease suppression means, the EGR that has passed through the EGR gas cooling means When gas is supplied to the internal combustion engine, the amount of EGR gas increases with respect to the intake air amount.

In that respect, if the target value of the intake air amount of the internal combustion engine is increased, it becomes possible to make the ratio of the fresh air sucked into the internal combustion engine and the EGR gas appropriate.
When it is determined that the catalyst has deteriorated and the amount of unburned fuel in the exhaust gas is small, the EGR gas temperature detected by the EGR gas temperature detection means is determined when the catalyst has not deteriorated. You may make it change the suppression degree of the temperature fall by an EGR gas temperature fall suppression means so that it may become equal to the detected temperature, ie, the amount of EGR gas supplied to an intake system may not change. This can be achieved by changing the heat exchange rate (cooler efficiency) of the EGR cooler and the ratio of EGR gas flowing through the EGR cooler and the EGR detour.

In order to achieve the above object, the exhaust circulation device for an internal combustion engine according to the present invention may employ the following means. That is,
An EGR passage for connecting an exhaust system and an intake system of the internal combustion engine and introducing a part of the exhaust from the exhaust system to the intake system;
A catalyst having oxidation ability provided in the EGR passage;
EGR gas cooling means for lowering the temperature of EGR gas flowing through the EGR passage closer to the intake system than the catalyst;
EGR gas temperature detection means for detecting the temperature of EGR gas flowing through the EGR passage closer to the intake system than the catalyst;
Catalyst deterioration determination means for determining that the catalyst has deteriorated when the temperature of the EGR gas detected by the EGR gas temperature detection means is lower than a third predetermined temperature;
It is good also as comprising.

  As described above, when EGR gas containing unburned fuel flows into the catalyst, the unburned fuel reacts with the catalyst and the temperature of the EGR gas rises. The rising temperature of the EGR gas at this time has a correlation with the degree of deterioration of the catalyst, and therefore the deterioration of the catalyst can be determined based on this rising temperature. That is, it is possible to perform the deterioration determination based on the fact that the temperature of the catalyst increases as the degree of catalyst deterioration decreases.

  In the exhaust gas recirculation apparatus for an internal combustion engine according to the present invention, the deterioration of the catalyst upstream of the EGR cooler can be more accurately determined by detecting the temperature of the EGR gas while suppressing the cooling of the EGR gas by the EGR cooler. it can.

  Hereinafter, a specific embodiment of an exhaust gas circulation device for an internal combustion engine according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which the exhaust gas circulation device for an internal combustion engine according to the present embodiment is applied and its intake / exhaust system.
The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

The internal combustion engine 1 is provided with a fuel injection valve 3 that injects fuel light oil into the cylinder 2.
An intake passage 4 is connected to the internal combustion engine 1. The intake passage 4 is provided with an intake throttle valve 5 for adjusting the flow rate of intake air flowing through the intake passage 4. An air flow meter 12 that outputs a signal corresponding to the flow rate of air passing through the intake passage 4 is attached in the middle of the intake passage 4 upstream of the intake throttle valve 5. The intake fresh air amount of the internal combustion engine 1 can be obtained from the output signal of the air flow meter 12.

On the other hand, an exhaust passage 6 is connected to the internal combustion engine 1. The exhaust passage 6 communicates with the atmosphere downstream.
Further, the internal combustion engine 1 is provided with an exhaust gas recirculation device 13 (hereinafter referred to as an EGR device 13). The EGR device 13 includes an exhaust gas recirculation passage 14 (hereinafter referred to as an EGR passage 14), a pre-cooler catalyst 15, an EGR bypass circuit 16, an EGR cooler 17, a flow rate ratio changing valve 18, a flow rate adjusting valve 19 (hereinafter referred to as an EGR valve). 19), and an EGR gas temperature sensor 20. The EGR passage 14 connects the exhaust passage 6 and the intake passage 4. A part of the exhaust gas (hereinafter referred to as EGR gas) flowing through the exhaust passage 6 is recirculated to the intake passage 4 through the EGR passage 14.

  In the EGR passage 14, a pre-cooler catalyst 15, an EGR cooler 17, a flow rate ratio changing valve 18, an EGR gas temperature sensor 20, and an EGR valve 19 are disposed in this order from the exhaust passage 6 side. One end of the EGR bypass 16 is connected to the EGR passage 14 between the pre-cooler catalyst 15 and the EGR cooler 17, and the other end is connected to the flow rate ratio changing valve 18.

  The pre-cooler catalyst 15 may be any catalyst having oxidation ability, and for example, an oxidation catalyst, a three-way catalyst, an occlusion reduction type NOx catalyst, or the like can be employed. The uncooled fuel in the EGR gas can be oxidized by the pre-cooler catalyst 15, and a decrease in the cooling efficiency of the EGR cooler 17 due to the adhesion of unburned fuel can be suppressed. Cooling water for the internal combustion engine circulates in the EGR cooler 17, and heat exchange is performed between the EGR gas and the cooling water for the internal combustion engine in the EGR cooler 17 to cool the EGR gas. The flow rate ratio changing valve 18 is operated by a signal from the ECU 10 described later, and is a valve that changes the ratio of the amount of EGR gas passing through the EGR cooler 17 and the EGR bypass circuit 16 with respect to the total amount of EGR gas. The EGR gas temperature sensor 20 outputs a signal corresponding to the temperature of the EGR gas flowing through the EGR passage 14. The EGR valve 19 is opened and closed by a signal from the ECU 10 described later, and adjusts the flow rate of the EGR gas flowing through the EGR passage 14.

  The internal combustion engine 1 is also provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition to the air flow meter 12 and the EGR gas temperature sensor 20, an accelerator opening sensor 11 that outputs a signal corresponding to the accelerator opening is connected to the ECU 10 through electric wiring, and an output signal from the sensor or the like is input. It is like that. The load applied to the internal combustion engine 1 can be obtained by the accelerator opening sensor 11. A load applied to the internal combustion engine 1 can also be obtained based on the amount of fuel injected from the fuel injection valve 3.

On the other hand, the fuel injection valve 3, the intake throttle valve 5, the flow rate ratio changing valve 18, and the EGR valve 19 are connected to the ECU 10 through electric wiring, and these can be controlled by the ECU 10. The amount of intake air used for engine combustion can be adjusted by opening and closing the intake throttle valve 5.

  By the way, the amount of heat taken by the EGR gas passing through the EGR cooler 17 is larger than the amount of heat generated by the pre-cooler catalyst 15. Therefore, regardless of whether or not the pre-cooler catalyst 15 is deteriorated, the temperature of the EGR gas is greatly lowered when the EGR gas passes through the EGR cooler 17. Therefore, if the EGR gas is allowed to flow to the EGR cooler 17 when determining the deterioration of the pre-cooler catalyst 15, it may be difficult to determine the deterioration of the pre-cooler catalyst 15.

  In this regard, when the deterioration of the pre-cooler catalyst 15 is determined, the EGR gas is allowed to flow through the EGR bypass 16 and the EGR gas is not allowed to flow into the EGR cooler 17. The accuracy of the deterioration determination of the catalyst 15 can be improved.

  In this embodiment, when the deterioration determination of the pre-cooler catalyst 15 is performed, the EGR gas is caused to flow through the entire EGR detour 16 by the flow rate change valve 18. That is, EGR gas is prevented from passing through the EGR cooler 17. At this time, the deterioration determination of the pre-cooler catalyst 15 is performed based on the EGR gas temperature obtained from the EGR gas temperature sensor 20.

  Here, FIG. 2 is a diagram showing the relationship between the EGR gas temperature detected by the EGR gas temperature sensor 20 and the failure portion when the entire amount of EGR gas flows through the EGR detour 16. (A) shows the temperature when both the pre-cooler catalyst 15 and the flow rate change valve 18 are normal, and (B) shows the case where the pre-cooler catalyst 15 is deteriorated and the flow rate change valve 18 is normal. (C) shows the temperature when an abnormality has occurred in the flow rate ratio changing valve 18. Further, (a) shows the part of the EGR gas temperature before flowing into the pre-cooler catalyst 15 among the temperatures detected by the EGR gas temperature sensor 20, and (b) shows the part of the rising temperature in the pre-cooler catalyst 15. Is shown.

  The first reference temperature is a temperature at which both the pre-cooler catalyst 15 and the flow rate change valve 18 can be normal, and the second reference temperature is the flow rate change when the pre-cooler catalyst 15 is abnormal. Valve 18 is at a temperature that can be considered normal. That is, the first reference temperature is lower than the temperature obtained by the EGR gas temperature sensor 20 when the pre-cooler catalyst 15 is not deteriorated and the flow rate ratio changing valve 18 is operating normally. Is over the temperature obtained by the EGR gas temperature sensor 20 when the flow rate ratio changing valve 18 is operating normally. The second reference temperature is lower than the temperature obtained by the EGR gas temperature sensor 20 when the pre-cooler catalyst 15 is deteriorated and the flow rate ratio changing valve 18 is operating normally.

  In (A), since both the pre-cooler catalyst 15 and the flow rate change valve 18 are normal, the amount of EGR gas temperature before flowing into the pre-cooler catalyst 15 (a) and the amount of rising temperature in the pre-cooler catalyst 15 ( The temperature obtained by adding b) is detected by the EGR gas temperature sensor 20, and this temperature is equal to or higher than the first reference temperature.

  In (B), since the pre-cooler catalyst 15 is deteriorated, the temperature of the EGR gas does not increase in the pre-cooler catalyst 15. Therefore, only the portion (a) of the EGR gas temperature before flowing into the pre-cooler catalyst 15 is detected by the EGR gas temperature sensor 20, and this temperature becomes lower than the first reference temperature. However, since there is only a portion (b) of the rising temperature in the pre-cooler catalyst 15, a temperature equal to or higher than the second reference temperature is detected by the EGR gas temperature sensor 20.

In (C), the EGR gas flows through the EGR cooler 17 regardless of whether or not the pre-cooler catalyst 15 is deteriorated, so that the amount (a) of the EGR gas temperature before flowing into the pre-cooler catalyst 15 greatly decreases. The temperature detected by the EGR gas temperature sensor 20 is lower than the second reference temperature.

  As described above, when the temperature detected by the EGR gas temperature sensor 20 is equal to or higher than the first reference temperature, the ECU 10 can determine that both the pre-cooler catalyst 15 and the flow rate change valve 18 are normal. Further, when the temperature is equal to or higher than the second reference temperature and lower than the first reference temperature, the ECU 10 can determine that the pre-cooler catalyst 15 has deteriorated. Furthermore, when the temperature is lower than the second reference temperature, the ECU 10 can determine that an abnormality has occurred in the flow rate ratio changing valve 18.

  The first reference temperature and the second reference temperature are obtained in advance through experiments or the like as values according to the operating state of the internal combustion engine 1 (for example, engine speed, engine load) and stored in the ECU 10.

  Further, in this embodiment, the EGR bypass 16 is provided, and when the deterioration of the pre-cooler catalyst 15 is determined, the EGR gas is caused to flow through the EGR bypass 16 to suppress the temperature drop of the EGR gas. The temperature reduction of the EGR gas in the EGR cooler 17 may be suppressed by reducing the cooling efficiency of the EGR cooler 17. That is, the heat exchange amount between the EGR gas and the cooling water in the EGR cooler 17 may be changed. For example, when the flow rate of the cooling water circulating through the EGR cooler 17 can be changed, the cooling efficiency of the EGR cooler 17 can be changed.

In this case, it can be determined whether or not the cooling efficiency of the EGR cooler 17 is changing normally, instead of determining that an abnormality has occurred in the flow rate ratio changing valve 18.
Further, in the present embodiment, the EGR gas is allowed to flow through the entire EGR bypass 16 when the deterioration of the pre-cooler catalyst 15 is determined. The EGR gas at the ratio may flow through the EGR detour 16. In this case, the EGR gas temperature at which it can be assumed that the catalyst has not deteriorated is determined in correspondence with the ratio of the EGR gas flowing through the EGR bypass route 16. Then, when the temperature detected by the EGR gas temperature sensor 20 is lower than the EGR gas temperature at which the catalyst can be assumed not to deteriorate, it can be determined that the pre-cooler catalyst 15 has deteriorated.

In this embodiment, a process when it is determined that the pre-cooler catalyst 15 has deteriorated will be described. The other hardware is the same as that of the first embodiment, so that the description thereof is omitted.
In this embodiment, the intake air is based on the output value of the air flow meter 12 so that the flow rate of the EGR gas flowing into the internal combustion engine 1 becomes an appropriate amount according to the operating state of the internal combustion engine 1 at that time. Perform feedback control of the amount (hereinafter referred to as intake air amount feedback control). This controls the intake throttle valve 5 and the EGR valve 19 so that the target fresh air amount preset for the operating state of the internal combustion engine 1 and the intake air amount obtained from the air flow meter 12 are equal.

  Here, the EGR gas and fresh air passing through the air flow meter 12 are sucked into the internal combustion engine 1. The amount of fresh air decreases as the amount of EGR gas sucked into the internal combustion engine increases, and the amount of fresh air increases as the amount of EGR gas decreases. When the intake air amount changes by the intake air amount feedback control, the flow rate of the EGR gas also changes.

  By the way, when the pre-cooler catalyst 15 is deteriorated, the unburned fuel in the EGR gas is not oxidized in the pre-cooler catalyst 15. When this EGR gas is allowed to flow to the EGR cooler 17, unburned fuel adheres to the EGR cooler 17 due to condensation.

  In this respect, in this embodiment, it is determined that the pre-cooler catalyst 15 has deteriorated, and when the amount of unburned fuel in the EGR gas is equal to or greater than a predetermined amount, it is other than when the catalyst deterioration is determined. Also, EGR gas is allowed to flow through the EGR bypass 16. Thereby, it can suppress that unburned fuel adheres to the EGR cooler 17, and the cooling efficiency of this EGR cooler 17 falls.

  It should be noted that the greater the amount of unburned fuel contained in the EGR gas, the greater the amount of EGR gas that flows through the EGR bypass 16 may be. However, the entire amount of EGR gas may flow through the EGR bypass 16. More preferred. The predetermined amount of the unburned fuel amount is an unburned fuel amount that may cause the unburned fuel to adhere to the EGR cooler 17 and reduce the cooling efficiency of the EGR cooler 17, and is determined by experiments or the like. The unburned fuel amount contained in the EGR gas can be obtained from the intake fresh air amount of the internal combustion engine 1 and the fuel injection amount from the fuel injection valve 3.

  By the way, when the EGR gas is caused to flow through the EGR bypass route 16, the density of the EGR gas becomes small. Even in this case, EGR feedback control is performed, and the intake fresh air amount of the internal combustion engine 1 becomes substantially equal to the target value. Therefore, the mass ratio of the EGR gas sucked into the cylinder 2 of the internal combustion engine 1 with respect to the fresh air is reduced as compared with when the EGR gas is flowing through the EGR cooler 17. Thereby, the effect of the EGR gas supply of suppressing the generation of NOx becomes small.

  In this regard, in this embodiment, when it is determined that the pre-cooler catalyst 15 has deteriorated, the pre-cooler catalyst 15 having a predetermined target value for the intake fresh air amount in the intake air amount feedback control has deteriorated. Change to the value when

  On the other hand, even when the pre-cooler catalyst 15 is deteriorated, if the EGR gas contains almost no unburned fuel, the EGR cooler 17 can be unburned even if EGR gas is allowed to flow through the EGR cooler 17. Fuel hardly adheres. In this case, NOx emission from the cylinder 2 of NOx can be suppressed by flowing the EGR gas through the EGR cooler 17 and lowering the temperature of the EGR gas.

  However, when the EGR gas passes through the EGR cooler 17, the density of the EGR gas increases. However, since the intake fresh air amount is kept constant by the intake air amount feedback control, the EGR gas is sucked into the cylinder 2 of the internal combustion engine 1. The mass ratio of fresh EGR gas to fresh air increases. That is, the EGR gas is excessively supplied, and the EGR concentration in the cylinder 2 becomes higher than an appropriate value.

  In this regard, in the present embodiment, when it is determined that the pre-cooler catalyst 15 has deteriorated and the amount of unburned fuel in the EGR gas is small, the EGR gas is caused to flow through the EGR cooler 17. Then, the intake fresh air amount of the internal combustion engine 1 which is a target in the intake air amount feedback control is increased. Here, a value such that the mass ratio between the fresh air and the EGR gas is appropriate may be obtained in advance by experiments or the like.

  In order to reduce the EGR concentration, the cooling efficiency of the EGR cooler 17 may be reduced by reducing the flow rate of the cooling water circulating through the EGR cooler 17, for example, and the amount of EGR gas passing through the EGR detour 16 is increased. May be.

  As described above, in this embodiment, when it is determined that the pre-cooler catalyst 15 has deteriorated and the amount of unburned fuel contained in the EGR gas is equal to or greater than a predetermined amount, the EGR bypass 16 When the amount of unburned fuel contained in the EGR gas is less than a predetermined amount, the target fresh air amount of the internal combustion engine 1 is increased while flowing the EGR gas to the EGR cooler 17. Reduction in the cooling efficiency of the cooler 17 and excessive supply of EGR gas to the cylinder 2 can be suppressed, and NOx emission from the cylinder 2 can be suppressed.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust-gas-circulation apparatus of the internal combustion engine which concerns on an Example, and its intake / exhaust system. It is the figure which showed the relationship between the EGR gas temperature detected by an EGR gas temperature sensor, and a failure site | part, when EGR gas is made to flow through the whole EGR detour.

Explanation of symbols

1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Intake passage 5 Intake throttle valve 6 Exhaust passage 10 ECU
11 Accelerator opening sensor 12 Air flow meter 13 Exhaust gas recirculation device (EGR device)
14 Exhaust gas recirculation passage (EGR passage)
15 Pre-cooler catalyst (catalyst having oxidation ability)
16 Detour 17 EGR cooler 18 Flow rate change valve 15 Flow control valve (EGR valve)
20 EGR gas temperature sensor (EGR gas temperature detection means)

Claims (5)

An EGR passage for connecting an exhaust system and an intake system of the internal combustion engine and introducing a part of the exhaust from the exhaust system to the intake system;
A catalyst having oxidation ability provided in the EGR passage;
EGR gas cooling means for lowering the temperature of EGR gas flowing through the EGR passage closer to the intake system than the catalyst;
EGR gas temperature decrease suppressing means for suppressing a decrease in temperature of EGR gas by the EGR gas cooling means;
EGR gas temperature detection means for detecting the temperature of the EGR gas flowing through the EGR passage on the intake system side of the portion where the temperature reduction is suppressed by the EGR gas temperature decrease suppression means;
When the temperature of the EGR gas detected by the EGR gas temperature detection means is lower than the first predetermined temperature when the temperature reduction of the EGR gas is suppressed by the EGR gas temperature reduction suppression means, the catalyst deteriorates. Catalyst deterioration determination means for determining that
Equipped with,
The EGR gas cooling means is provided in an EGR passage closer to the intake system than the catalyst, and from an EGR cooler that lowers the temperature of the EGR gas by exchanging heat between the EGR gas flowing through the EGR passage and another heat medium. Become
The EGR gas temperature lowering suppression means includes an EGR bypass connecting the EGR passage between the catalyst and the EGR cooler and an EGR passage closer to the intake system than the EGR cooler, and the EGR bypass and the EGR cooler. The EGR gas temperature decrease suppression means changes the flow rate ratio of the EGR gas passing through the EGR gas, and the EGR gas temperature decrease suppressing means reduces the decrease in the EGR gas temperature and the flow rate ratio of the EGR gas passing through the EGR detour. An exhaust gas recirculation device for an internal combustion engine characterized in that An EGR passage for connecting an exhaust system and an intake system of the internal combustion engine and introducing a part of the exhaust from the exhaust system to the intake system;
A catalyst having oxidation ability provided in the EGR passage;
E for lowering the temperature of the EGR gas flowing through the EGR passage closer to the intake system than the catalyst
A GR gas cooling means;
EGR gas temperature decrease suppressing means for suppressing a decrease in temperature of EGR gas by the EGR gas cooling means;
EGR gas temperature detection means for detecting the temperature of the EGR gas flowing through the EGR passage on the intake system side of the portion where the temperature reduction is suppressed by the EGR gas temperature decrease suppression means;
When the temperature of the EGR gas detected by the EGR gas temperature detection means is lower than the first predetermined temperature when the temperature reduction of the EGR gas is suppressed by the EGR gas temperature reduction suppression means, the catalyst deteriorates. Catalyst deterioration determination means for determining that
Equipped with,
The EGR gas cooling means is provided in an EGR passage closer to the intake system than the catalyst, and from an EGR cooler that lowers the temperature of the EGR gas by exchanging heat between the EGR gas flowing through the EGR passage and another heat medium. Become
The EGR gas temperature decrease suppressing means includes a heat exchange amount changing means for changing the amount of heat exchange between the EGR gas and another heat medium in the EGR cooler, and the EGR gas temperature decrease suppressing means includes a decrease in EGR gas temperature. The exhaust gas recirculation apparatus for an internal combustion engine is characterized in that the amount of heat exchange by the EGR cooler is reduced as the value is reduced . The EGR gas when the catalyst deterioration determining means determines that the catalyst is deteriorated and the exhaust gas temperature detected by the EGR gas temperature detecting means is lower than a second predetermined temperature lower than the first predetermined temperature. The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2 , further comprising abnormality determining means for determining that the temperature decrease suppressing means is abnormal. When the catalyst deterioration determining means determines that the catalyst is deteriorated, the flow rate ratio change valve increases the amount of EGR gas flowing through the EGR detour as compared to when the catalyst is not deteriorated. The exhaust gas circulation device for an internal combustion engine according to claim 1 , further comprising a ratio change valve control means. Engine operating state detecting means for detecting the operating state of the internal combustion engine;
Target fresh air amount setting means for setting a target amount of fresh air sucked into the internal combustion engine;
Unburnt fuel amount determination means for determining whether or not the amount of unburned fuel in the exhaust gas is greater than or equal to a predetermined amount based on the engine operation state detected by the engine operation state detection means;
The catalyst deterioration determining means determines that the catalyst has deteriorated, the unburned fuel amount determining means determines that the amount of unburned fuel in the exhaust gas is less than a predetermined amount, and the EGR gas cooling means cools the EGR gas. The intake fresh air amount increasing means for increasing the target amount of the amount of fresh air sucked into the internal combustion engine compared to when it is determined that the catalyst is not deteriorated,
Exhaust circulation apparatus for an internal combustion engine according to claim 1 or 2, further comprising a.

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