JP4150649B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention provides a first combustion mode in which combustion is performed at an exhaust gas recirculation rate lower than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak, and an exhaust gas recirculation rate that is higher than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak The present invention relates to an exhaust gas recirculation device applied to an internal combustion engine that selectively switches a combustion mode between a second combustion mode that performs combustion at a rate.

  As an apparatus employed in an internal combustion engine such as a diesel engine, there is an exhaust gas recirculation (EGR) device that recirculates a part of exhaust gas into intake air. On the other hand, in a lean combustion internal combustion engine represented by a diesel engine, it is known that smoke emission increases when the ratio of recirculation exhaust in the intake air introduced into the combustion chamber, that is, the EGR rate exceeds a certain level. In general, combustion is performed at an EGR rate equal to or less than a certain rate that satisfies the smoke emission standard.

  However, in recent years, it was confirmed that when the EGR rate was increased, the smoke emission amount reached a peak at a certain EGR rate, and thereafter the smoke emission amount decreased. Therefore, in recent years, an internal combustion engine that operates in a combustion mode in which combustion is performed at an EGR rate higher than the EGR rate at which the smoke emission amount reaches a peak, that is, a so-called low-temperature combustion mode, has been proposed and put into practical use. In this type of internal combustion engine, an intake throttle valve is provided in the intake passage, and an EGR device that recirculates exhaust gas into the intake passage is provided. The opening degree of the intake throttle valve and the opening degree of the EGR valve provided in the EGR device are adjusted. By coordinated control, a high EGR rate of 65% or more is secured, and the smoke emission amount is reduced.

Conventionally, as can be seen, for example, in Patent Document 1, depending on the engine operating condition between the normal combustion mode in which combustion is performed at an EGR rate lower than the EGR rate at which the smoke emission amount reaches a peak, and the low temperature combustion mode. An internal combustion engine that selectively switches the combustion mode is also known. In this type of internal combustion engine, it is necessary to greatly change the EGR rate when switching the combustion mode, and the balance between the fresh air in the intake air and the recirculated exhaust gas becomes inadequate during the switching, and hydrocarbons (HC), etc. Problems such as increased unburned fuel emissions and misfires may occur. Therefore, in the exhaust gas recirculation device described in Patent Document 1, the opening degree of the intake throttle valve and the EGR valve is feedback controlled while accurately grasping the current EGR rate based on the detection result of the intake air amount and the intake pressure. Thus, the EGR rate during switching of the combustion mode is maintained at an appropriate value so as to suppress the above-described problems.
JP 2003-148221 A

  As described above, in the conventional exhaust gas recirculation device for an internal combustion engine, when the combustion mode is switched, a relatively large EGR rate needs to be changed, and the time required for the change causes a delay in switching the combustion mode. There is. Note that if the feedback gain of the EGR valve opening is set large and the opening changing speed is increased, such a combustion mode switching delay can be reduced. On the other hand, during normal EGR control in which the combustion mode is held in either the normal combustion mode or the low temperature combustion mode, the change in the EGR rate is limited to a relatively small value, and the feedback gain is set to be too large. If so, the controllability of the EGR rate in such a situation will deteriorate. Therefore, there is a limit to shortening the EGR rate change period when switching the combustion mode.

  The problem to be solved by the present invention is to provide an exhaust gas recirculation device for an internal combustion engine capable of speeding up the exhaust gas recirculation rate change at the time of switching the combustion mode while suitably maintaining the controllability of the exhaust gas recirculation rate control. Is to provide.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
The invention according to claim 1 is based on the first combustion mode in which combustion is performed at an exhaust gas recirculation rate lower than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak, and the exhaust gas recirculation rate at which the smoke emission amount reaches a peak. Is applied to an internal combustion engine that selectively switches the combustion mode between the second combustion mode that performs combustion at a higher exhaust gas recirculation rate, and is based on the deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate in the exhaust gas recirculation device for an internal combustion engine to adjust the exhaust gas recirculation rate through the feedback control of the recirculation valve opening, said exhaust re with respect to the deviation in the period up to a certain time from the switching start of the combustion mode has elapsed The gist of the invention is to include an opening rate change rate setting means for setting the rate of change so that the rate of change of the circulation valve aperture is increased as compared to when it is not in the same period .

In the above configuration, on the period until the end of a certain time from the combustion mode switching start, the target EGR rate and the actual EGR ratio and exhaust gas recirculation valve for deviation (EGR valve) opening rate of change, the same period not equal-out, that is, increased in comparison with the normal EGR rate control except the period up to a certain time has elapsed from the combustion mode switching start. Therefore, while maintaining controllability during normal EGR rate control in which a relatively small EGR rate change is performed, the EGR rate can be quickly changed when switching the combustion mode that requires a significant change in the EGR rate. it can.
Further, as in the above configuration, if the period for increasing the change rate of the EGR valve opening is defined by the elapsed time from the start of combustion mode switching, the EGR rate change is accelerated and the transition to normal EGR rate control is performed. Can be performed accurately.
The increase period of the EGR valve opening change rate is a period until the change amount of the EGR valve opening from the start of the combustion mode switching becomes a predetermined value or more, or the target EGR rate and the actual EGR rate after the start of the combustion mode switching. Even if it is set as the period until the deviation becomes below a predetermined value, the same effect can be obtained.

The invention according to claim 2 is based on the first combustion mode in which combustion is performed at an exhaust gas recirculation rate lower than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak, and the exhaust gas recirculation rate at which the smoke emission amount reaches a peak. Is applied to an internal combustion engine that selectively switches the combustion mode between the second combustion mode that performs combustion at a higher exhaust gas recirculation rate, and is based on the deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate In an exhaust gas recirculation apparatus for an internal combustion engine that adjusts an exhaust gas recirculation rate through feedback control of a recirculation valve opening, a predetermined time from the start of switching of the combustion mode from the second combustion mode to the first combustion mode It said exhaust gas recirculation valve opening change rate but with respect to the deviation in the period until the elapsed, the opening change rate setting means for setting said change rate to be increased compared to when not the same period To prepare And of the subject matter.

  If the operation in the first combustion mode is started without sufficiently reducing the EGR rate, the amount of oxygen in the air-fuel mixture may be insufficient, leading to engine torque fluctuations, misfires, and the like. On the other hand, even if the operation in the second combustion mode is started without sufficiently increasing the EGR rate, the amount of oxygen in the air-fuel mixture is affected, although there is an influence on the exhaust emission such as an increase in smoke emission amount. Since there is no concern that the engine will run short, engine torque fluctuations and misfires will not occur, and the adverse effects will be relatively small.

  Also, when the EGR valve opening is increased to increase the EGR rate, there is a delay in the gas flow in the EGR system and the intake system, and thus the improvement in the EGR rate changing speed by increasing the EGR valve opening changing rate is naturally limited. There is. On the other hand, when the EGR valve opening is reduced to reduce the EGR rate, the response delay from the reduction of the EGR valve opening to the actual EGR rate is small, and the EGR valve opening change rate increases. Accordingly, the effect of improving the EGR rate changing speed can be remarkably exhibited.

In that respect, in the above configuration, the target EGR rate is limited to a certain period of time after the start of switching of the combustion mode from the second combustion mode to the first combustion mode that requires a significant reduction in the EGR rate. The change rate of the EGR valve opening with respect to the deviation between the actual EGR rate and the actual EGR rate is increased. Therefore, the adverse effect of the delay in changing the EGR rate is more conspicuous, and the improvement effect of the EGR rate changing speed due to the increase in the changing speed of the EGR valve opening is more pronounced from the second combustion mode to the first combustion mode. With regard to switching to the combustion mode, it is possible to quickly change the EGR rate. Therefore, according to the above configuration, the EGR rate change at the time of switching the combustion mode can be made early.

Further, as in the above configuration, if the period for increasing the change rate of the EGR valve opening is defined by the elapsed time from the start of combustion mode switching, the EGR rate change is accelerated and the transition to normal EGR rate control is performed. Can be performed accurately.

  The increase period of the EGR valve opening change rate is a period until the change amount of the EGR valve opening from the start of the combustion mode switching becomes a predetermined value or more, or the target EGR rate and the actual EGR rate after the start of the combustion mode switching. Even if it is set as the period until the deviation becomes below a predetermined value, the same effect can be obtained.

The invention according to claim 3 is based on the first combustion mode in which combustion is performed at an exhaust gas recirculation rate lower than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak, and the exhaust gas recirculation rate at which the smoke emission amount reaches a peak. Is applied to an internal combustion engine that selectively switches the combustion mode between the second combustion mode that performs combustion at a higher exhaust gas recirculation rate, and is based on the deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate in the exhaust gas recirculation device for an internal combustion engine to adjust the exhaust gas recirculation rate through the feedback control of the recirculation valve opening, said exhaust gas recirculation valve opening change rate with respect to the deviation at the time of switching of the combustion mode, when switching An opening change rate setting means for setting the change rate so that the change rate is increased as compared to when it is not, the opening change rate setting means is a feedback correction of the exhaust gas recirculation valve opening based on the deviation Quantity calculation The flop, by switching between the time does not increase with time to increase the rate of change, and its gist to carry out setting of the rate of change.
In the above configuration, when the combustion mode is switched, the rate of change of the exhaust gas recirculation valve (EGR valve) opening relative to the deviation between the target EGR rate and the actual EGR rate is not, that is, a normal EGR rate other than when the combustion mode is switched. Increased compared to control. Therefore, while maintaining controllability during normal EGR rate control in which a relatively small EGR rate change is performed, the EGR rate can be quickly changed when switching the combustion mode that requires a significant change in the EGR rate. it can.
Further, by switching the feedback correction amount calculation map as in the above configuration, it is possible to easily and accurately increase the EGR opening degree change rate at the time of switching the combustion mode.
The invention according to claim 4 is based on the first combustion mode in which combustion is performed at an exhaust gas recirculation rate lower than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak, and the exhaust gas recirculation rate at which the smoke emission amount reaches a peak. Is applied to an internal combustion engine that selectively switches the combustion mode between the second combustion mode that performs combustion at a higher exhaust gas recirculation rate, and is based on the deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate In an exhaust gas recirculation apparatus for an internal combustion engine that adjusts an exhaust gas recirculation rate through feedback control of a recirculation valve opening, with respect to the deviation at the time of switching the combustion mode from the second combustion mode to the first combustion mode Opening degree change rate setting means for setting the change rate so that the change rate of the exhaust gas recirculation valve opening is increased as compared to when it is not switched , the opening degree change rate setting means, The exclusion based on the deviation. The calculation map of the feedback correction amount of the recirculation valve opening, by switching between the time does not increase with time to increase the rate of change, and its gist to carry out setting of the rate of change.
In the above configuration, the EGR valve opening change with respect to the deviation between the target EGR rate and the actual EGR rate is limited only when the combustion mode is switched from the second combustion mode to the first combustion mode that requires a significant reduction in the EGR rate. I try to increase the rate. Therefore, the adverse effect of the delay in changing the EGR rate is more conspicuous, and the improvement effect of the EGR rate changing speed due to the increase in the changing speed of the EGR valve opening is more pronounced from the second combustion mode to the first combustion mode. With regard to switching to the combustion mode, it is possible to quickly change the EGR rate. Therefore, according to the above configuration, the EGR rate change at the time of switching the combustion mode can be made early.
Further, by switching the feedback correction amount calculation map as in the above configuration, it is possible to easily and accurately increase the EGR opening degree change rate at the time of switching the combustion mode.

According to a fifth aspect of the present invention, in the exhaust gas recirculation device for an internal combustion engine according to the first or second aspect, the opening degree change rate setting means is a feedback correction amount of the exhaust gas recirculation valve opening degree based on the deviation. The gist is to set the rate of change by switching the calculation map between when the rate of change is increased and when it is not increased .

By switching the feedback correction amount calculation map as in the above configuration, it is possible to easily and accurately increase the EGR opening degree change rate when switching the combustion mode.
Invention according to claim 6, in the exhaust gas recirculation device for an internal combustion engine according to claim 1, wherein the opening change rate setting means, before Symbol exhaust gas recirculation valve feedback opening by increasing large gains, as its gist to carry out setting to increase the rate of change.
By changing the feedback gain of the EGR valve opening as in the above configuration, the EGR opening change rate at the time of switching the combustion mode can be easily and accurately increased.

Hereinafter, an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a configuration of an internal combustion engine 10 to which the present embodiment is applied. The internal combustion engine 10 is a diesel engine including a common rail fuel injection device and a turbocharger 11, and mainly includes an intake passage 12, a combustion chamber 13, and an exhaust passage 14.

  In an intake passage 12 constituting the intake system of the internal combustion engine 10, an air flow meter 16, a compressor 17 of the turbocharger 11, an intercooler 18, And an intake throttle valve 19 is provided. The intake passage 12 is branched at an intake manifold 20 provided on the downstream side of the intake throttle valve 19 and connected to the combustion chamber 13 of each cylinder of the internal combustion engine 10 via an intake port 21.

  On the other hand, in the exhaust passage 14 constituting the exhaust system of the internal combustion engine 10, the exhaust port 22 connected to the combustion chamber 13 of each cylinder is connected to the exhaust turbine 24 of the turbocharger 11 via the exhaust manifold 23. Yes. In addition, a NOx catalytic converter 25, a PM filter 26, and an oxidation catalytic converter 27 are disposed downstream from the exhaust turbine 24 in the exhaust passage 14 in order from the upstream side.

  The NOx catalytic converter 25 carries an NOx storage reduction catalyst. The NOx catalyst stores NOx in the exhaust when the oxygen concentration of the exhaust is high, and releases the stored NOx when the oxygen concentration of the exhaust is low. Further, the NOx catalyst reduces and purifies the released NOx if there is sufficient unburned fuel component as a reducing agent at the time of releasing the NOx.

  The PM filter 26 that is an exhaust filter for collecting PM in the exhaust is formed of a porous material. Similar to the NOx catalytic converter 25, the PM filter 26 carries an NOx storage reduction catalyst, and purifies NOx in the exhaust gas. Further, the trapped PM is oxidized and removed by a reaction triggered by the NOx catalyst.

The oxidation catalyst converter 27 carries an oxidation catalyst, and HC and CO in the exhaust are oxidized and purified.
In addition, on the upstream side and the downstream side of the PM filter 26 in the exhaust passage 14, an inlet gas temperature sensor 28 that detects the inlet gas temperature that is the temperature of the exhaust gas flowing into the PM filter 26, and the exhaust gas after passing through the PM filter 26. An outgas temperature sensor 29 for detecting an outgas temperature, which is a temperature, is provided. The exhaust passage 14 is provided with a differential pressure sensor 30 for detecting a differential pressure between the exhaust upstream side of the PM filter 26 and the exhaust downstream side thereof. Further, two oxygen sensors 31 and 32 for detecting the oxygen concentration in the exhaust gas are arranged on the exhaust gas upstream side of the NOx catalytic converter 25 in the exhaust passage 14 and between the PM filter 26 and the oxidation catalytic converter 27, respectively. It is installed.

  Further, the internal combustion engine 10 is provided with an exhaust gas recirculation (hereinafter referred to as EGR) device that recirculates a part of the exhaust gas to the air in the intake passage 12. The EGR device includes an EGR passage 33 that allows the exhaust passage 14 and the intake passage 12 to communicate with each other. The most upstream portion of the EGR passage 33 is connected to the exhaust upstream side of the exhaust turbine 24 in the exhaust passage 14. From the upstream side of the EGR passage 33, there are an EGR catalyst 34 that reforms the exhaust gas that is recirculated, an EGR cooler 35 that cools the exhaust gas, and an exhaust gas recirculation valve (EGR valve) 36 that adjusts the flow rate of the exhaust gas. It is arranged. The most downstream portion of the EGR passage 33 is connected to the downstream side of the intake throttle valve 19 in the intake passage 12.

  On the other hand, a fuel injection valve 40 that injects fuel to be used for combustion in the combustion chamber 13 is disposed in the combustion chamber 13 of each cylinder of the internal combustion engine 10. The fuel injection valve 40 of each cylinder is connected to a common rail 42 via a high pressure fuel supply pipe 41. High pressure fuel is supplied to the common rail 42 through a fuel pump 43. The pressure of the high-pressure fuel in the common rail 42 is detected by a rail pressure sensor 44 attached to the common rail 42. Further, low pressure fuel is supplied from the fuel pump 43 to the addition valve 46 through the low pressure fuel supply pipe 45.

  The electronic control unit 50 that controls various controls of the internal combustion engine 10 includes a CPU that executes various calculation processes related to the control of the internal combustion engine 10, a ROM that stores programs and data necessary for the control, a calculation result of the CPU, and the like. A RAM that is temporarily stored, an input / output port for inputting / outputting signals to / from the outside, and the like are provided. In addition to the sensors described above, the input port of the electronic control unit 50 includes an NE sensor 51 that detects the engine speed, an accelerator sensor 52 that detects the accelerator operation amount, and a throttle valve sensor that detects the opening of the intake throttle valve 19. 53 etc. are connected. The output port of the electronic control unit 50 is connected to drive circuits such as the intake throttle valve 19 and the EGR valve 36.

  The electronic control unit 50 outputs a command signal to the drive circuit of each device connected to the output port according to the engine operating state grasped from the detection signal input from each sensor. Thus, control of the fuel injection amount from the fuel injection valve 40, fuel injection timing, fuel addition control from the addition valve 46, EGR control based on the opening control of the EGR valve 36 and the intake throttle valve 19, and the addition valve Various controls such as fuel addition control from 46 are performed by the electronic control unit 50.

  In a lean combustion internal combustion engine typified by a diesel engine such as the internal combustion engine 10, the amount of oxygen in the air-fuel mixture generally decreases with an increase in the EGR rate, so that the smoke emission amount tends to increase. However, if suitable conditions are set through the adoption of a high-efficiency EGR cooler, introduction of a large amount of EGR, adaptation of the fuel injection timing, etc., the EGR rate is greatly increased, and the smoke emission amount is drastically reduced. .

  FIG. 2 shows the relationship between the air-fuel ratio and EGR rate and smoke emission in such an internal combustion engine. As shown in the figure, when the EGR rate is increased from the lean air-fuel ratio state in which a general lean combustion internal combustion engine is operated to enrich the air-fuel ratio, the smoke emission amount increases as the EGR rate increases. To go. However, if the EGR rate is further increased and the air-fuel ratio is enriched to near the stoichiometric air-fuel ratio, the smoke emission amount once decreases and then rapidly decreases. This is caused by slowing the increase in the combustion temperature of the air-fuel mixture in the combustion chamber 13 by introducing a large amount of EGR, thereby suppressing the combustion temperature below the soot formation temperature. Moreover, since generation of NOx is also suppressed under such conditions, it is possible to simultaneously reduce the smoke emission amount and the NOx emission amount. Further, as shown in the figure, under such conditions, the HC emission amount increases and the oxidation reaction with the NOx catalyst is promoted, so that the NOx catalyst can be activated by raising the catalyst bed temperature. .

  Therefore, in the internal combustion engine 10, the low temperature combustion mode in which combustion is performed at an EGR rate higher than the EGR rate at which the smoke emission amount reaches a peak as in region I of FIG. 2, and the smoke emission amount as in region II of FIG. The operation is performed while selectively switching to the normal combustion mode in which combustion is performed at an EGR rate higher than the EGR rate at which the EGR reaches a peak. Such switching of the combustion mode is performed in accordance with engine operation conditions, exhaust purification control requirements, and the like. The operation in the low-temperature combustion mode of the internal combustion engine 10 is mainly performed in the low load / medium / high rotation operation of the internal combustion engine 10. Running in the region. In the low-temperature combustion mode, the EGR rate is set to a high rate of 65% or more, and in order to prevent misfires and torque fluctuations when a large amount of EGR is introduced, the fuel injection timing is advanced and the fuel injection pressure is increased. Is also performed. Incidentally, in this embodiment, the normal combustion mode corresponds to the first combustion mode, and the low temperature combustion mode corresponds to the second combustion mode.

Next, the EGR rate control in the internal combustion engine 10 that switches the combustion mode will be described.
The EGR rate control in the internal combustion engine 10 is performed by feedback control of the opening degree of the EGR valve 36 (exhaust gas recirculation valve opening degree). In the feedback control of the EGR valve opening degree, the air-fuel ratio of the air-fuel mixture in the combustion chamber 13 is obtained from the oxygen concentration of the exhaust detected by the oxygen sensors 31 and 32, and the obtained air-fuel ratio The actual exhaust gas recirculation rate (actual EGR rate tegr), which is the current EGR rate, is calculated from the intake air amount detected by the air flow meter 16. On the other hand, a target exhaust gas recirculation rate (target EGR rate tegr), which is a control target value of the EGR rate, is calculated according to the current combustion mode and engine operating conditions (engine speed, engine load, etc.). Then, the EGR valve opening is adjusted so that the actual EGR rate egr becomes the target EGR rate tegr.

In the internal combustion engine 10, such feedback control of the EGR valve opening is performed by PID control, and an EGR valve opening command value pego2, which is a control target value of the EGR valve opening, is expressed by the following equation (1). Is required.

pego2 ← pego2p + pego2i + pego2d (1)

Here, pego2p is a feedback proportional term of the EGR valve opening, and its value is set in proportion to the deviation Δegr between the target EGR rate tegr and the actual EGR rate egr. Pego2i is a feedback integral term of the EGR valve opening, and its value is set in proportion to the time integral value of the deviation Δegr. Further, pego2d is a feedback differential term of the EGR valve opening, and its value is set in proportion to the time differential value of the deviation Δegr.

  In the internal combustion engine 10, when the combustion mode is switched between the normal combustion mode and the low-temperature combustion mode, the EGR rate and the EGR valve opening need to be significantly changed. Here, if the change in the EGR valve opening after the combustion mode switching is delayed and the change in the EGR rate to the rate corresponding to the combustion mode is delayed, there is a risk of causing problems such as worsening of fuel symptom pairs and worsening of exhaust emission. . In particular, when switching from the low-temperature combustion mode to the normal combustion mode, if the change in the EGR rate is delayed and the control of the injection system is switched to the normal combustion mode without sufficiently reducing the EGR rate, the amount of oxygen in the mixture Will cause engine torque fluctuations and misfires.

  If the change rate of the EGR rate is simply increased, the rate of change of the feedback proportional term pego2p with respect to the deviation Δegr between the target EGR rate tegr and the actual EGR rate egr, that is, the set value of the proportional gain may be increased. However, in the internal combustion engine 10, during normal EGR rate control other than when the combustion mode is switched, the change in the EGR rate remains within a relatively small range. For this reason, if the proportional gain is simply increased, the controllability of normal EGR rate control deteriorates, and problems such as overshoot and hunting of the EGR rate will occur.

  Therefore, in the present embodiment, the EGR valve opening feedback proportional term pego2p is calculated only during a period from the start of switching from the low-temperature combustion mode to the normal combustion mode until a certain time T (for example, 500 milliseconds) elapses. Such a feedback gain, that is, a proportional gain is increased as compared with the case where it is not. As a result, the EGR rate at the time of switching the combustion mode is changed early while suitably ensuring the controllability during normal EGR rate control. Incidentally, in the present embodiment, the constant time T is changed by changing the EGR valve opening at the increased proportional gain, from the required value in the low-temperature combustion mode to the required value in the normal combustion mode. It is set to a time slightly shorter than the time required for.

  In the present embodiment, the calculation map of the feedback proportional term pegeo2p is switched between the period from the start of switching from the low temperature combustion mode to the normal combustion mode until a certain time T elapses and other times. The proportional gain is increased. That is, in the present embodiment, normally, the feedback proportional term pegeo2p is calculated using the first calculation map MAP1 set to have a smaller proportional gain.

  Further, when the EGR rate is reduced during the above period, that is, when the EGR valve opening is changed to the valve closing side, the second calculation map MAP2 having a larger proportional gain than the first calculation map MAP1 is set. The feedback proportional term pego2p is calculated by using this. These first and second calculation maps MAP1 and MAP2 are stored in advance in the ROM of the electronic control unit 50.

  FIGS. 3A and 3B show examples of setting modes of the first and second calculation maps MAP1 and MAP2. The map values pego2map1 and pego2map2 of these calculation maps indicate the absolute value of the feedback proportional term pego2p. In these calculation maps, the correspondence between the absolute value (| Δegr |) of the deviation Δegr and the map values pego2map1, pego2map2 is stored in advance.

  The correspondence relationship between the absolute value of the deviation Δegr and the map value pego2map1 in the first calculation map MAP1 and the correspondence value between the absolute value of the deviation Δegr and the map value pego2map2 in the second calculation map MAP2. The slope of the straight line L2 shown represents the proportional gain of each calculation map. Incidentally, in FIG. 5B, a straight line L1 indicating the correspondence relationship in the first calculation map is shown together with a broken line for comparison. As is apparent from the comparison of the slopes of these straight lines L1 and L2, when the second calculation map MAP2 is used, the proportional gain with respect to the deviation Δegr is set to be larger than when the first calculation map MAP1 is used. Become.

  FIG. 4 shows a flowchart of the feedback proportional term calculation routine in this embodiment. The process of this routine is periodically executed by the electronic control unit 50 as a scheduled interrupt process. In the present embodiment, the processing of this routine corresponds to the processing of the opening degree change rate setting means.

  When the processing of this routine is started, the electronic control unit 50 first determines in step S100 whether or not the currently selected combustion mode is the low temperature combustion mode. Here, if the low temperature combustion mode is not selected, that is, if the normal combustion mode is selected (NO), the electronic control unit 50 advances the process to step S110 and increments the value of the counter count (count ← count + 1). ). On the other hand, if the low-temperature combustion mode is being selected (YES), the electronic control unit 50 advances the process to step S120 and clears the value of the counter count (count ← 0). Therefore, the value of the counter count is set to 0 at the start of switching from the low-temperature combustion mode to the normal combustion mode, and thereafter, the value is incremented by 1 at every execution timing of this routine while the normal combustion mode is continued. The Rukoto. Therefore, the value of the counter count becomes an index value of the elapsed time from the start of switching from the low temperature combustion mode to the normal combustion mode.

  After operating the counter count, the electronic control unit 50 advances the process to step S200, and thereafter calculates the feedback proportional term pegeo2p in the following manner.

  First, in step S200, the electronic control unit 50 calculates a deviation Δegr between the target EGR rate tegr and the actual EGR rate egr (Δegr ← tegr−egr). Then, in subsequent steps S210 and S220, the electronic control unit 50 determines the magnitude relationship between the target EGR rate tegr and the actual EGR rate egr. Specifically, if the deviation Δegr exceeds a predetermined value EO2UP (for example, 0.01) (S210: YES), it is determined that the actual EGR rate egr is smaller than the target EGR rate tegr. If the deviation Δegr is less than a predetermined value EO2DW (for example, −0.01) (S220: YES), it is determined that the actual EGR rate egr is larger than the target EGR rate tegr. Further, if the deviation Δegr is not less than the predetermined value EO2DW and not more than the predetermined value EO2UP (S210: NO and S220: NO), it is determined that the target EGR rate tegr and the actual EGR rate egr are substantially in agreement. Is done.

  If the target EGR rate tegr and the actual EGR rate egr are substantially in agreement, the electronic control unit 50 advances the process to step S240. In step S240, the electronic control unit 50 sets the feedback proportional term pego2p to the value “0”.

  If the actual EGR rate egr is smaller than the target EGR rate tegr, that is, if the EGR rate needs to be increased, the electronic control unit 50 advances the process to step S230. In step S230, the electronic control unit 50 calculates the feedback proportional term pegeo2p using the first calculation map MAP1 (FIG. 3A) and sets the value. Specifically, the map value pego2map1 calculated based on the absolute value of the deviation Δegr is set as the feedback proportional term pego2p at this time.

  Furthermore, if the actual EGR rate egr is larger than the target EGR rate tegr, that is, if the EGR rate needs to be reduced, the electronic control unit 50 advances the process to step S250. In step S250, the electronic control unit 50 determines whether the value of the counter count exceeds 0 and is equal to or less than a predetermined determination value α. As the determination value α, the value of the counter count corresponding to the certain time is set as the value. Therefore, here, it is determined whether or not a certain time (for example, 500 milliseconds) elapses from the start of switching from the low-temperature combustion mode to the normal combustion mode.

  If a negative determination (NO) is made in step S250, the electronic control unit 50 proceeds to step S270, and in step S270, using the first calculation map MAP1 (FIG. 3A). The feedback proportional term pegeo2p is calculated and the value is set. Specifically, the value obtained by inverting the value of the map value pego2map1 calculated based on the absolute value of the deviation Δegr is set as the value in the feedback proportional term pego2p at this time.

  On the other hand, when an affirmative determination (YES) is made in step S250, that is, when it is determined that the predetermined time T has elapsed from the start of switching from the low-temperature combustion mode to the normal combustion mode, the electronic Control device 50 advances the process to step S260. In step S260, the electronic control unit 50 calculates the feedback proportional term pegeo2p using the second calculation map MAP2 (FIG. 3B) and sets the value. Specifically, the value obtained by inverting the value of the map value pego2map2 calculated based on the absolute value of the deviation Δegr is set as the value in the feedback proportional term pego2p at this time.

  As described above, when the feedback proportional term pegeo2p is set, the electronic control unit 50 once ends the processing of this routine. Thereafter, the electronic control unit 50 calculates the EGR valve opening command value pego2 according to the above equation (1) using the set feedback proportional term pego2p, and adjusts the opening of the EGR valve 36.

  FIG. 5 shows an example of the control mode of the present embodiment when switching from the low temperature combustion mode to the normal combustion mode. In the figure, the transition of the EGR valve opening when the proportional gain of the EGR valve opening with respect to the deviation Δegr is always set uniformly is also shown by a broken line.

  When switching from the low-temperature combustion mode to the normal combustion mode is started at time t1 in the figure, the electronic control unit 50 starts incrementing the counter count from that point. At the time t1, the target EGR rate tegr is significantly reduced from a high EGR rate of 65% or higher in the low temperature combustion mode to a relatively low EGR rate in the normal combustion mode. Further, at time t1, the proportional gain of the EGR opening with respect to the deviation Δegr between the actual EGR rate egr and the target EGR rate tegr is increased.

  After this time t1, the EGR valve opening degree starts to be changed to the valve closing side so that the actual EGR rate egr becomes the reduced target EGR rate tegr. The change of the EGR valve opening to the valve closing side at this time is made promptly as much as the proportional gain is increased, and the actual EGR rate egr is also rapidly reduced accordingly.

  At time t2, when the value of the counter count reaches the determination value α and the fixed time T has elapsed from the start of switching of the combustion mode, the increased proportional gain is returned to the original value, and the EGR valve is opened. The change speed to the valve closing side is also the change speed during normal EGR control. At time t3, the actual EGR rate egr is decreased until it matches the target EGR rate tegr, and the required EGR rate in the normal combustion mode is secured.

  Thus, in this embodiment, when switching from the low temperature combustion mode to the normal combustion mode, the proportional gain of the EGR opening with respect to the deviation Δegr between the target EGR rate tegr and the actual EGR rate egr, that is, the EGR valve opening with respect to the deviation Δegr is opened. The rate of change of degree has been increased. Therefore, it is possible to change the EGR rate at the time of switching the combustion mode at an early stage while favorably maintaining the controllability of normal EGR rate control, and it is possible to suitably prevent engine torque fluctuations and misfires.

In addition, the said embodiment can also be changed and implemented as follows.
The calculation of the feedback proportional term pego2p of the EGR valve opening with respect to the deviation Δegr in the above embodiment is performed using the deviation Δegr and the proportional gain Gp as shown in the following equation (2) without using the calculation maps MAP1 and MAP2. It can also be performed by integration. In this case, if the proportional gain Ga is changed to a value larger than the normal value when switching from the low-temperature combustion mode to the normal combustion mode, the deviation Δegr at the time of switching the combustion mode as in the above embodiment. Thus, the change rate of the EGR valve opening degree with respect to the EGR rate can be increased, so that the EGR rate change can be accelerated.

pego2p ← Gp × Δegr (2)

The increase in the EGR valve opening change rate at the time of switching the combustion mode may be performed by increasing the feedback gain (differential gain) related to the calculation of the feedback differential term pego2d of the EGR valve opening. .

In the above embodiment, the change rate of the EGR valve opening is increased only when the combustion mode is switched from the low temperature combustion mode to the normal combustion mode, but this is changed to the combustion from the normal combustion mode to the low temperature combustion mode. It may also be performed when the mode is switched. The large increase in the EGR rate accompanying the switching of the combustion mode from the normal combustion mode to the low temperature combustion mode also has a certain limit due to a delay in the gas flow in the intake system and the EGR system, but the EGR with respect to the deviation Δegr. The increase in the EGR rate change can be improved through an increase in the change rate of the valve opening.

  In the above embodiment, the EGR valve opening command value pego2 is calculated based on the above equation (1) and feedback control of the EGR valve opening command value is performed. However, the EGR valve opening command value pego2 is calculated. The aspect is not limited to this and may be changed as appropriate. Even in such a case, if the rate of change of the EGR valve opening with respect to the deviation Δegr at the time of switching the combustion mode is increased as compared to when it is not, the controllability of the EGR rate control is suitably maintained. However, the EGR rate change at the time of switching the combustion mode can be accelerated.

  The exhaust gas circulation device of the present invention is not limited to the internal combustion engine 10 exemplified in the above embodiment, and can be applied to any internal combustion engine. In short, any internal combustion engine that switches between combustion modes with greatly different EGR rates, such as between the low-temperature combustion mode and the normal combustion mode, has the same effect as that of the above-described embodiment or an effect similar thereto. be able to.

1 is a schematic diagram showing the overall configuration of an internal combustion engine to which an embodiment of the present invention is applied. The graph which shows the relationship between an air fuel ratio, an EGR rate, smoke emission amount, and HC emission amount. (A) (b) The figure which shows an example of the setting aspect of the 1st and 2nd calculation map. The flowchart of a feedback proportional term calculation routine. The time chart which shows an example of the control aspect of the said embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Turbocharger, 12 ... Intake passage, 13 ... Combustion chamber, 14 ... Exhaust passage, 15 ... Air cleaner, 16 ... Air flow meter, 17 ... Compressor, 18 ... Intercooler, 19 ... Intake throttle valve, 20 DESCRIPTION OF SYMBOLS ... Intake manifold, 21 ... Intake port, 22 ... Exhaust port, 23 ... Exhaust manifold, 24 ... Exhaust turbine, 25 ... NOx catalytic converter, 26 ... PM filter, 27 ... Oxidation catalytic converter, 28 ... Incoming gas temperature sensor, 29 ... Outgas temperature sensor, 30 ... Differential pressure sensor, 31, 32 ... Oxygen sensor, 33 ... EGR passage, 34 ... EGR catalyst, 35 ... EGR cooler, 36 ... EGR valve, 40 ... Fuel injection valve, 41 ... High pressure fuel supply pipe 42 ... Common rail, 43 ... Fuel pump, 44 ... Rail pressure sensor, 45 ... Low pressure fuel supply pipe, 46 ... Addition valve, 0 ... electronic control unit, 51 ... NE sensor 52: accelerator sensor, 53 ... throttle valve sensor.

Claims (6)

The first combustion mode in which combustion is performed at an exhaust gas recirculation rate lower than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak, and combustion is performed at an exhaust gas recirculation rate higher than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak. Applied to an internal combustion engine that selectively switches the combustion mode between the second combustion mode to be performed and through feedback control of the exhaust gas recirculation valve opening based on the deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate In an exhaust gas recirculation device for an internal combustion engine that adjusts the exhaust gas recirculation rate,
It said exhaust gas recirculation valve opening change rate with respect to the deviation in the period up to a certain time from the switching start of the combustion mode has elapsed, the said change rate to be increased compared to when not the same period An exhaust gas recirculation device for an internal combustion engine, comprising an opening change rate setting means for setting. The first combustion mode in which combustion is performed at an exhaust gas recirculation rate lower than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak, and combustion at an exhaust gas recirculation rate higher than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak. Applied to an internal combustion engine that selectively switches the combustion mode between the second combustion mode to be performed and through feedback control of the exhaust gas recirculation valve opening based on the deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate In an exhaust gas recirculation device for an internal combustion engine that adjusts the exhaust gas recirculation rate,
It said exhaust gas recirculation valve opening change rate with respect to the deviation in the period from the second combustion mode until a certain time has elapsed from the switching start of combustion mode to the first combustion mode is not the same period An exhaust gas recirculation device for an internal combustion engine, comprising: an opening rate change rate setting means for setting the rate of change so as to increase as compared with the case. The first combustion mode in which combustion is performed at an exhaust gas recirculation rate lower than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak, and combustion is performed at an exhaust gas recirculation rate higher than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak. Applied to an internal combustion engine that selectively switches the combustion mode between the second combustion mode to be performed and through feedback control of the exhaust gas recirculation valve opening based on the deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate In an exhaust gas recirculation device for an internal combustion engine that adjusts the exhaust gas recirculation rate,
Opening degree change rate setting means for setting the rate of change so that the rate of change of the exhaust gas recirculation valve opening relative to the deviation at the time of switching of the combustion mode is increased as compared to when not at the time of switching; ,
The opening change rate setting means switches the calculation map of the feedback correction amount of the exhaust gas recirculation valve opening based on the deviation between when the change rate is increased and when it is not increased. An exhaust gas recirculation device for an internal combustion engine characterized by: The first combustion mode in which combustion is performed at an exhaust gas recirculation rate lower than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak, and combustion is performed at an exhaust gas recirculation rate higher than the exhaust gas recirculation rate at which the smoke emission amount reaches a peak. Applied to an internal combustion engine that selectively switches the combustion mode between the second combustion mode to be performed and through feedback control of the exhaust gas recirculation valve opening based on the deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate In an exhaust gas recirculation device for an internal combustion engine that adjusts the exhaust gas recirculation rate,
The rate of change of the exhaust gas recirculation valve opening relative to the deviation at the time of switching the combustion mode from the second combustion mode to the first combustion mode is increased compared to when the switching is not at the time of switching. An opening change rate setting means for setting the change rate is provided,
The opening change rate setting means switches the calculation map of the feedback correction amount of the exhaust gas recirculation valve opening based on the deviation between when the change rate is increased and when it is not increased. An exhaust gas recirculation device for an internal combustion engine characterized by: The opening change rate setting means switches the calculation map of the feedback correction amount of the exhaust gas recirculation valve opening based on the deviation between when the change rate is increased and when it is not increased. The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2, wherein the setting is performed. The opening change rate setting means, before Symbol exhaust feedback gain of the recirculation valve opening by increasing size, internal combustion according to any one of claims 1 to 5 for setting to increase the rate of change Engine exhaust gas recirculation device.

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