JP5218132B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine, and more particularly to an exhaust gas recirculation device that diagnoses whether or not a bypass valve for bypassing an EGR gas cooler is stuck.

  In an exhaust gas recirculation apparatus that recirculates part of exhaust gas from an exhaust system of an internal combustion engine to an intake system, it is widely used to provide an EGR gas cooler that exchanges heat with outside air or cooling water in order to lower the temperature of the EGR gas. However, in this configuration including the EGR gas cooler, as disclosed in Patent Documents 1 and 2, etc., in order to avoid overcooling of the EGR gas under specific operating conditions, a bypass is provided in parallel with the EGR gas cooler. In addition to providing a passage, it has been proposed to provide a bypass valve at both branch portions so that EGR gas can be supplied by bypassing the EGR gas cooler. In addition, as this bypass valve, there is a type that opens and closes in a binary manner, that is, ON-OFF, and a type that can continuously and variably control the opening degree.

  In the case where the bypass valve is provided in this way, there is a concern that the bypass valve may be fixed due to foreign matter or contamination in the exhaust gas and become inoperable. A technique for detecting changes is disclosed. Here, when the bypass valve is controlled to be fully closed and when it is controlled to be fully open, if the intake air amount does not change, it is determined that the bypass valve is fixed. In addition, when it is detected that the valve is stuck, the reference intake air amount when the bypass valve is normal determined from the engine rotational speed and the like is compared with the intake air amount at that time, so that it is stuck on the fully open side or the fully closed side. It is determined whether or not it is stuck.

JP 2007-1000068 A Japanese Patent Laid-Open No. 2003-247459

  However, the technique of Patent Document 2 does not take into account any exhaust pressure in the exhaust system. For example, the exhaust system includes a turbocharger or exhaust gas such as an increase in deposits in an exhaust filter or exhaust catalyst. When the pressure increase / decrease is large, the intake air amount increases / decreases due to the exhaust pressure, so that an accurate diagnosis of the fixing position cannot be expected.

  An exhaust gas recirculation device for an internal combustion engine according to the present invention adjusts an EGR passage that recirculates part of exhaust gas from an exhaust system of the internal combustion engine to an intake system, and an EGR amount that is interposed in the EGR passage and recirculates to the intake system. A bypass for adjusting a flow rate ratio between an EGR valve, a gas cooler passage and a bypass passage provided in parallel as part of the EGR passage, an EGR gas cooler interposed in the gas cooler passage, and the gas cooler passage and the bypass passage. And an internal combustion engine having a valve.

  Then, a sticking detection means for detecting sticking of the bypass valve from a change in the intake air amount when the target opening of the bypass valve is changed, and a discharge pressure detecting means for detecting the exhaust pressure directly or indirectly. If the sticking of the bypass valve is detected, the sticking position of the bypass valve is determined based on the intake air amount and the exhaust pressure when the EGR valve is set to a predetermined opening.

  According to the present invention, it is possible to accurately diagnose whether or not the bypass valve is fixed and whether it is fixed on the fully closed side or fixed on the fully open side by eliminating the influence of the exhaust pressure.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows the whole structure of the internal combustion engine to which this invention is applied. The flowchart which shows the flow of the process of the diagnosis of the bypass valve in this Example. The characteristic view which shows the characteristic of a 1st control map. The characteristic view which shows the characteristic of a 2nd control map.

  FIG. 1 shows the overall configuration of a turbocharged diesel engine 1 as an example of an internal combustion engine to which the present invention is applied. The diesel engine 1 includes a common rail type fuel injection device. The diesel engine 1 has a fuel injection nozzle 3 at the upper center of a combustion chamber 2 of each cylinder, and fuel pressurized by a supply pump 4 is stored in a pressure accumulation chamber (common rail). ) After being stored in 5, it is distributed to the fuel injection nozzles 3 of the respective cylinders and injected according to the opening and closing of the respective fuel injection nozzles 3. The pressure accumulating chamber 5 is provided with a fuel pressure sensor 6 for detecting fuel pressure (rail pressure).

  The diesel engine 1 also has a variable nozzle turbocharger 11 that is provided with an exhaust turbine 12 and a compressor 13 coaxially. An intercooler 15 is interposed in the intake passage 14 from the compressor 13 to the combustion chamber 2. An EGR passage 17 for recirculating a part of the exhaust gas to the intake system is branched from the middle of the exhaust passage 16 from the combustion chamber 2 to the exhaust turbine 12, and the tip of the EGR passage 17 is connected to the intake collector 18. Has been. The intermediate portion of the EGR passage 17 is partly divided into two parallel passages, that is, a gas cooler passage 19 and a bypass passage 20, and one of the gas cooler passages 19 is filled with outside air or cooling water or lubricating oil and heat. An EGR gas cooler 21 that cools the EGR gas by replacement is provided. And the bypass valve 22 is interposed in the branch part of the gas cooler channel | path 19 and the bypass channel | path 20 in order to adjust the flow rate ratio of the EGR gas which goes to each channel | path. As the bypass valve 22, for example, a switching valve type configuration in which one of the gas cooler passage 19 and the bypass passage 20 is selectively closed, or the flow rates of the two passages are opened and closed by opening and closing the bypass passage 20 having a relatively small passage resistance. Various types of valves can be used, such as an on-off valve type configuration that changes the ratio. In addition, the present invention can be applied to either a type in which the opening degree can be continuously variably controlled or a type in which a binary ON-OFF operation is performed, but in this embodiment, a type in which a binary ON-OFF operation is performed The EGR gas flows to the bypass passage 20 side when ON, and the EGR gas flows to the gas cooler 21 side when OFF. That is, in this example, the ON state corresponds to the fully open state of the bypass passage 20, and the OFF state corresponds to the fully closed state of the bypass passage 20. The bypass valve 22 may be on the outlet side of the gas cooler passage 19 and the bypass passage 20, or may be in the middle of the passage.

  In addition, an EGR valve 23 of an appropriate type in which the opening degree can be continuously variably controlled to adjust the EGR amount is interposed in a portion of the EGR passage 17 downstream of the gas cooler passage 19 and the bypass passage 20. .

  An air cleaner 24 and an air flow meter 25 are provided upstream of the compressor 13 in the intake passage 14.

  The opening and ON / OFF state of the EGR valve 23 and the bypass valve 22 are controlled by a control unit (not shown) in accordance with the engine operating state including the temperature condition such as the cooling water temperature. When is established, a self-diagnosis is performed to ensure its normal operation.

  FIG. 2 is a flowchart showing a flow of self-diagnosis processing of the bypass valve 22 which is a main part of the present embodiment.

  This is done on condition that the engine is in idle condition, as shown in step 1. In particular, since the EGR gas amount is forcibly increased or decreased for diagnosis, it is desirable that the idle condition is after warm-up in order to avoid deterioration in drivability.

  When the diagnosis is started, in step 2, the EGR valve 23 is forcibly opened and the bypass valve 22 is turned on, and the intake air amount detected by the air flow meter 25 is determined as “bypass valve when the EGR valve is fully opened”. Read as “ON-time air quantity Q_byp_on”. Subsequently, in step 3, the bypass valve 22 is turned OFF, and the intake air amount at that time is read as “EGR valve fully open bypass valve OFF air amount Q_byp_off”. Next, in step 3, the absolute value of the difference (Q_byp_off−Q_byp_on) is compared with a predetermined allowable value ε. If the bypass valve 22 is operating normally, the temperature of the EGR gas flowing into the intake collector 18 changes as the bypass valve 22 is switched on and off, so that fresh air taken in through the air flow meter 25 is taken in. The amount of intake air changes. Therefore, if the difference between them, that is, the amount of change in the intake air amount is smaller than the allowable value ε, it is determined that the bypass valve 22 is fixed, and the process proceeds to step 6 and subsequent steps. On the other hand, if there is a change equal to or greater than the allowable value ε, the bypass valve 22 is considered to be operating normally, and the process proceeds to step 5 to end the diagnosis.

  In step 6 and subsequent steps, a diagnosis is made as to what state is fixed. In steps 6 to 8, the exhaust pressure at that time point, which is a precondition for the diagnosis, is estimated. First, at step 6, the EGR valve 23 is switched to fully closed, and the intake air amount at that time is read as “EGR valve fully closed air amount Qe0”. In Step 6 and subsequent steps, since it is assumed that the bypass valve 22 is fixed at a certain opening, the ON / OFF instruction to the bypass valve 22 does not affect the intake air amount. Therefore, in the processing after step 6, the target opening degree of the bypass valve 22 may be fully open (ON) or fully closed (OFF).

  In step 7, the opening degree of the EGR valve 23 is opened to an appropriate opening degree on the small opening side, for example, 15 degrees (here, 90 degrees is fully opened), and the intake air amount at that time is expressed as “EGR valve opening degree”. It reads as “15 degree hour air quantity Qe15”.

  Next, in step 8, the ratio (Qe15 / Qe0) of the two is obtained, and the value of the exhaust pressure corresponding to this ratio (Qe15 / Qe0) is set in the first control map (MAP1) having the characteristics shown in FIG. Seek to find out. The principle of the measurement of the exhaust pressure is that, first, when the EGR gas recirculates (when the EGR valve 23 is open) compared to when the EGR gas does not recirculate to the intake system (when the EGR valve 23 is fully closed), The amount of intake air decreases accordingly. Second, the amount of recirculation of the EGR gas increases as the exhaust pressure increases if the opening of the EGR valve 23 is constant (for example, 15 degrees). It uses the two relations that the amount decreases. Here, as the EGR gas flow rate is lower as a whole, the sensitivity to the exhaust pressure becomes higher. Therefore, comparing the time when the EGR valve 23 is fully closed and the opening degree of 15 degrees, the exhaust pressure at that time is compared. Can be estimated with sufficient accuracy.

  That is, in this embodiment, it is possible to obtain the value of the exhaust pressure, which is a precondition for diagnosis, without using the exhaust pressure sensor, using the same detection signal of the air flow meter 25. In addition, here, it is not necessary to consider engine operating conditions such as the engine speed, and the exhaust pressure can be estimated directly from the ratio of the two intake air amounts.

  Next, in step 9, using this exhaust pressure value, referring to the second control map (MAP2) having characteristics as shown in FIG. 4, it corresponds to the bypass valve ON side fixing (full open side fixing). The ON-side sticking threshold SL_byp_on and the OFF-side sticking threshold SL_byp_off corresponding to the bypass valve OFF-side sticking (fully closed sticking) are calculated.

  In Step 10, the ratio R_oc (= Q_byp_off / Qe0) between the “EGR valve fully open air amount Q_byp_off” obtained in Step 3 and the “EGR valve fully closed air amount Qe0” obtained in Step 6 is calculated. To do. As described above, at this stage where the bypass valve 22 is already fixed, the ON / OFF of the bypass valve 22 has no particular meaning. Therefore, instead of “the amount of air Q_byp_off when the EGR valve is fully opened, the bypass valve is OFF”. The “air amount Q_byp_on when the bypass valve is ON when the EGR valve is fully open” in step 2 may be used. Although it cannot be specified whether the bypass valve 22 is fixed on the fully open side or on the fully closed side, when the EGR valve is fixed, the “air amount Q_byp_off when the bypass valve is OFF when the EGR valve is fully open” and “when the EGR valve is fully open. This is because the air amount Q_byp_on when the bypass valve is ON is substantially equal.

  Therefore, this ratio (Q_byp_off / Qe0) is larger than the intake air amount (Qe0) when the EGR valve 23 is fully closed in a state where the bypass valve 22 is fixed at a certain opening degree. It shows the ratio of the intake air amount (Q_byp_off) when 23 is fully opened. If the EGR gas recirculates with the EGR valve 23 fully opened, the amount of intake air detected by the air flow meter 25 decreases, but the EGR gas mainly passes through the bypass passage 20 at that time due to the fixation of the bypass valve 22 and remains at a high temperature. If it recirculates, the amount of intake air will decrease so much. That is, the ratio R_oc (= Q_byp_off / Qe0) becomes small. On the other hand, if the EGR gas passes through the EGR gas cooler 21 mainly due to the fixation of the bypass valve 22 and is refluxed at a low temperature, the amount of reduction in the intake air amount is small. That is, the ratio R_oc (= Q_byp_off / Qe0) is relatively large. In the second control map shown in FIG. 4, the ratio R_oc, which is considered that the bypass valve 22 is fixed on the ON (fully open) side, is set to the ON-side fixed threshold SL_byp_on, and the exhaust pressure is set as one parameter. Similarly, the value of the ratio R_oc considered that the bypass valve 22 is fixed on the OFF (fully closed) side is assigned as the OFF-side fixed threshold SL_byp_off.

  In step 11, the ON-side adhesion threshold SL_byp_on corresponding to the exhaust pressure at that time set in step 9 is compared with the ratio R_oc. Similarly, in step 12, the OFF side adhesion threshold SL_byp_off corresponding to the exhaust pressure at that time set in step 9 is compared with the above ratio R_oc. If the ratio R_oc is smaller than the ON-side sticking threshold SL_byp_on, the process proceeds to step 13 and it is determined that the bypass valve 22 is in the ON-side sticking state. If the ratio R_oc is larger than the OFF-side sticking threshold SL_byp_off, the process proceeds to step 14 and it is determined that the bypass valve 22 is in the OFF-side sticking state. Further, if both steps 11 and 12 are NO, that is, if the ratio R_oc is an intermediate value between the two threshold values SL_byp_on and SL_byp_off, the process proceeds to step 15 and it is determined that the bypass valve 22 is in the half-open fixed state.

  In the above embodiment, the present invention is applied to a diesel engine with a turbocharger as an example of an internal combustion engine. However, the present invention is not limited to this, and can be applied to a gasoline engine as well. A similar diagnosis can be performed even if a feeder is not provided.

  In the above embodiment, the exhaust pressure is estimated, but an exhaust pressure sensor may be mounted in the exhaust passage and the output value of the exhaust pressure sensor may be used as it is.

  Further, in the above embodiment, in order to specify the fixing position of the bypass valve 22, the ratio R_oc (= Q_byp_off) between the “EGR valve fully open bypass valve OFF air amount Q_byp_off” and the “EGR valve fully closed air amount Qe0”. / Qe0) is used to determine at which opening the bypass valve 22 is fixed, but diagnosis may be performed using only the air amount when the EGR valve is fully open.

  In this case, how the intake air amount changes in accordance with the opening degree of the bypass valve 22 when the EGR valve is fully opened is obtained in advance by experiments and stored in the control unit as a judgment value. . The influence of the exhaust pressure is taken into consideration as in the above embodiment.

  Further, in all of the above embodiments, the ratio is used, but a difference may be used.

DESCRIPTION OF SYMBOLS 1 ... Diesel engine 11 ... Turbocharger 14 ... Intake passage 17 ... EGR passage 18 ... Intake collector 19 ... Gas cooler passage 20 ... Bypass passage 21 ... EGR gas cooler 22 ... Bypass valve 23 ... EGR valve 25 ... Air flow meter

Claims (7)

An EGR passage that recirculates part of the exhaust gas from the exhaust system of the internal combustion engine to the intake system, an EGR valve that is interposed in the EGR passage and adjusts the amount of EGR that recirculates to the intake system, and a part of the EGR passage An exhaust gas recirculation apparatus for an internal combustion engine, comprising: a gas cooler passage and a bypass passage provided in parallel; an EGR gas cooler interposed in the gas cooler passage; and a bypass valve for adjusting a flow rate ratio between the gas cooler passage and the bypass passage. In
Adhesion detection means for detecting adhering of the bypass valve based on a change in the intake air amount when the opening degree of the bypass valve is changed while the EGR valve is open, and detecting or estimating the exhaust pressure An exhaust pressure detecting means,
When the bypass valve is stuck, a sticking state judging means for judging the sticking position of the bypass valve based on the intake air amount and the exhaust pressure when the EGR valve is set to a predetermined opening degree. An exhaust gas recirculation device for an internal combustion engine, comprising: The adhering state determining means further includes a threshold setting means for setting a fully closed side adhering threshold and a fully opened side adhering threshold according to the exhaust pressure,
When it is determined that the opening is fixed, the first intake air amount when the opening of the EGR valve is a relatively small first opening and the second when the opening is relatively large. The value obtained on the basis of the intake air amount is compared with the fully closed side sticking threshold value and the fully open side sticking threshold value to determine whether or not the fully closed side sticking and the fully open side sticking are determined. An exhaust gas recirculation device for an internal combustion engine as described.   The exhaust gas recirculation apparatus for an internal combustion engine according to claim 1 or 2, wherein the fixed state determination means determines that the fixed state is half-open fixed when neither full-closed fixed nor full-opened fixed.   The internal combustion engine according to any one of claims 1 to 3, wherein the exhaust pressure detecting means estimates the exhaust pressure from a change in the intake air amount with respect to a change in the opening on the small opening side of the EGR valve. Exhaust gas recirculation device.   The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2, wherein the exhaust pressure detection means comprises an exhaust pressure sensor provided in an exhaust system.   A ratio between the intake air amount when the EGR valve is fully closed and the intake air amount when the EGR valve opening is a predetermined small opening is obtained, and this ratio is determined by referring to a predetermined map. 5. The exhaust gas recirculation device for an internal combustion engine according to claim 4, wherein a corresponding exhaust pressure is obtained.   The exhaust gas recirculation apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein a diagnosis of sticking of the bypass valve is executed on condition that the internal combustion engine is in an idle condition.

Images