JP5691914B2 - Control device for exhaust gas recirculation system - Google Patents

Description

  The present invention relates to a control device for an exhaust gas recirculation system, and more particularly to a control device for an exhaust gas recirculation system applied to an in-cylinder injection engine that injects fuel directly into a cylinder.

  Conventionally, in a gasoline engine or a diesel engine, a part of exhaust gas is recirculated (recirculated) to an intake system to lower the combustion temperature of the engine, thereby suppressing generation of NOx due to combustion. Further, in recent years, in a diesel engine, when the ratio of EGR gas (EGR rate) in the intake air introduced into the combustion chamber of the engine is increased, the amount of particulate matter (PM) generated by engine combustion is constant EGR. Various techniques have been proposed that pay attention to the fact that the amount of PM generation decreases with an increase in the EGR rate after a peak in rate (see, for example, Patent Document 1). Patent Document 1 discloses that in a diesel engine, when the EGR rate is set to a high state, the emission amount of PM and NOx can be reduced by low-temperature combustion, and the air-fuel ratio becomes richer than that at the time of normal combustion. Performing a rich spike by is disclosed.

JP 2009-191659 A

  The PM emission characteristics with respect to the EGR rate as described above show the same tendency even in a gasoline direct injection engine, and when the EGR rate is larger than a certain EGR rate, the combustion temperature decreases due to the increase in the EGR rate, It is thought that the amount of PM production can be reduced by the decrease in the combustion temperature. On the other hand, when the EGR rate is increased, the engine temperature (piston temperature) decreases as the combustion temperature decreases, so that the fuel attached to the piston tends to remain in a liquid state, and PM is generated due to the piston wetness. There is a concern that the amount will increase.

  The present invention has been made in view of the above problems, and provides a control device for an exhaust gas recirculation system that can suppress the generation of particulate matter (PM) due to engine combustion when exhaust gas recirculation is performed. The main purpose is to do.

  The present invention employs the following means in order to solve the above problems.

The present invention provides an engine including a fuel injection valve that directly injects fuel into a cylinder, and a part of exhaust gas flowing through the exhaust passage of the engine through the communication passage that connects the exhaust passage and the intake passage to the intake passage. The present invention relates to a control device for an exhaust gas recirculation system applied to an exhaust gas recirculation system including an exhaust gas recirculation device that performs recirculation. The first configuration includes an injection control unit that performs fuel injection by the fuel injection valve in an intake stroke of one combustion cycle, and a fuel injection timing by the injection control unit based on each engine operating state. The recirculation is performed in an operating region where the recirculation of the exhaust gas can be performed by the exhaust gas recirculation device, the injection timing calculating means for calculating the basic injection timing, the temperature detecting means for detecting the temperature of the piston of the engine In this case, an injection timing changing means for changing the basic injection timing calculated by the injection timing calculating means to the retard side based on the piston temperature detected by the temperature detecting means is provided.

  In short, when an exhaust gas recirculation request is generated by the exhaust gas recirculation device, and exhaust gas is recirculated in response to the recirculation request, particulate matter (PM) or NOx discharged from the engine due to a decrease in combustion temperature. The amount can be reduced. On the other hand, as the engine temperature (piston temperature) decreases as the combustion temperature decreases, piston wettability is likely to occur, which may lead to an increase in the amount of particulate matter discharged from the engine. Is done. In this respect, in this configuration, when exhaust gas recirculation is performed by the exhaust gas recirculation device in response to exhaust gas recirculation requests, the fuel injection timing (basic injection timing) is delayed in the intake stroke based on the piston temperature at each time. Change to the corner. In this case, even in a situation where the piston temperature is low and piston wet is likely to occur, the fuel can be prevented from adhering to the piston by changing the fuel injection timing to the retard side in the intake stroke. As a result, when exhaust gas recirculation is performed, it is possible to suitably suppress particulate matter emission.

  Here, as the temperature detection means for detecting the piston temperature, for example, a configuration for obtaining parameters (for example, engine rotation speed, engine load, etc.) relating to the engine operating state and estimating the piston temperature based on the obtained parameters, an engine The structure which estimates piston temperature based on the cooling water temperature of this, combustion temperature, the recirculation rate of exhaust gas, etc., the structure which attaches the sensor which detects piston temperature, and directly detects piston temperature by the sensor, etc. are mentioned. Further, as the fuel injection timing, the injection start timing may be the intake stroke.

In the second configuration , when the piston temperature detected by the temperature detecting means is lower than a predetermined temperature, the injection timing changing means is based on the piston temperature detected by the temperature detecting means by the injection timing calculating means. The calculated basic injection timing is changed to the retard side.

  The amount of the particulate matter generated due to the piston wet does not change so much in the temperature range where the combustion temperature is relatively high, but increases rapidly when the combustion temperature is lowered to some extent (see FIG. 2). On the other hand, when the fuel injection timing is changed to the retard side in accordance with the piston temperature, it is conceivable that the combustion efficiency is lowered because the fuel injection timing is retarded from the optimum injection timing. Therefore, it is desirable to delay the fuel injection timing when necessary. In view of this, as in the present configuration, on the condition that the piston temperature is lower than the predetermined temperature, the basic injection timing is changed to the retard side in the intake stroke based on the piston temperature, so that the exhaust gas is recirculated. Appropriate correction can be performed for the piston wet that occurs.

  Specifically, for example, in a configuration in which the relationship between the piston temperature and the change amount of the basic injection timing is determined in advance and the change amount of the basic injection timing corresponding to the current piston temperature is calculated using the relationship, The change amount is set to a value other than 0 in a region where the piston temperature is lower than the predetermined temperature, and the change amount is set to 0 in a region where the piston temperature is higher than the predetermined temperature. Alternatively, there is a correlation between the recirculation rate and the piston temperature, and in view of the fact that the piston temperature decreases as the recirculation rate increases, the recirculation rate is predetermined when exhaust gas recirculation is performed by the exhaust gas recirculation device. If the recirculation rate is greater than a predetermined recirculation rate, for example, it is determined whether or not the recirculation rate is greater than the recirculation rate at which the amount of particulate matter produced by combustion reaches a peak. The basic injection timing is changed to the retard side based on the piston temperature.

In the third configuration , the injection control means should perform fuel injection a plurality of times at different timings by the fuel injection valve in the intake stroke, and inject in one combustion cycle based on each engine operating state A split ratio calculating means for calculating a basic split ratio that is a ratio of a fuel quantity to be injected in the first fuel injection out of the fuel quantity; and when the exhaust gas recirculation device performs the exhaust gas recirculation, the temperature detecting means And a split ratio changing means for changing the basic split ratio calculated by the split ratio calculating means to a smaller side based on the piston temperature detected by the above.

  When fuel injection is performed a plurality of times in one combustion cycle, the amount of fuel to be injected in one combustion cycle is calculated based on the engine operating state, and the calculated fuel amount is distributed as the fuel injection amount for each injection. At the time of distribution, in this configuration, when exhaust gas recirculation is performed in response to exhaust gas recirculation requests, out of a plurality of fuel injections performed in one combustion cycle according to the piston temperature each time. Since the first injection is changed to the side where the amount of fuel is reduced, it is possible to suppress the fuel from adhering to the piston in a situation where the piston temperature is low and piston wet is likely to occur. Thereby, when exhaust gas recirculation is carried out, it is possible to suitably suppress emission of particulate matter.

In the fourth configuration , the exhaust gas recirculation device restricts the exhaust gas recirculation based on the piston temperature detected by the temperature detecting means.

  Even if exhaust gas recirculation is requested, if the piston temperature is low, the combustion temperature decreases due to exhaust gas recirculation, and the piston temperature further decreases, and particulate matter is easily generated due to piston wetness. Become. In view of this, by adopting the above configuration, it is possible to suppress the combustion temperature from being excessively lowered due to the exhaust gas recirculation, and as a result, it is possible to suppress the generation of particulate matter due to piston wet. Here, examples of the configuration that restricts the implementation of exhaust gas recirculation include a configuration that prohibits or stops the implementation of exhaust gas recirculation, and a configuration that provides an upper limit value of the recirculation rate.

As a second invention in the present invention, as in the fifth configuration , an engine including a fuel injection valve that injects fuel directly into the cylinder, and a part of the exhaust gas flowing through the exhaust passage of the engine is used as the exhaust passage. And an exhaust gas recirculation system that recirculates to the intake air passage through a communication passage that communicates the intake air passage and the intake air passage, and is different depending on the fuel injection valve in the intake stroke of one combustion cycle. An injection control means for performing fuel injection a plurality of times at the timing, and a basic division that is a ratio of the fuel amount to be injected in the first fuel injection out of the fuel amount to be injected in one combustion cycle based on each engine operating state A split ratio calculating means for calculating the rate, a temperature detecting means for detecting the temperature of the piston of the engine, and an operation capable of recirculating the exhaust gas by the exhaust gas recirculation device A split ratio changing means for changing the basic split ratio calculated by the split ratio calculating means to a smaller side based on the piston temperature detected by the temperature detecting means when performing the recirculation in a region; It is characterized by that.

  As described above, when exhaust gas recirculation is performed by an exhaust gas recirculation device in response to exhaust gas recirculation requests, the amount of particulate matter (PM) and NOx discharged from the engine can be reduced due to a decrease in combustion temperature. . On the other hand, as the engine temperature (piston temperature) decreases as the combustion temperature decreases, piston wettability is likely to occur, which may lead to an increase in the amount of particulate matter discharged from the engine. Is done. In this regard, in this configuration, when exhaust gas recirculation is performed by the exhaust gas recirculation device in response to exhaust gas recirculation requests, multiple fuel injections performed in one combustion cycle are performed based on the piston temperature each time. Since it changes to the side which reduces the fuel amount of the first injection among these, it can suppress that a fuel adheres to a piston in the situation where piston temperature is low and piston wet easily occurs. As a result, even when exhaust gas recirculation is performed, particulate matter emission can be suppressed.

1 is an overall schematic configuration diagram of an engine control system. The figure which shows PM production amount at the time of EGR introduction. The flowchart which shows the injection correction process at the time of EGR gas introduction. The figure which shows an example of the map which shows the relationship between piston temperature and a division | segmentation ratio correction amount. The figure which shows an example of the map which shows the relationship between piston temperature and time correction amount. The flowchart which shows the process in the case of changing the upper limit of an EGR rate based on piston temperature.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. In the present embodiment, an engine control system is constructed for an in-cylinder injection and spark ignition engine that is an on-vehicle multi-cylinder four-cycle gasoline engine that is an internal combustion engine. In this control system, an electronic control unit (hereinafter referred to as ECU) is used as a center to control the fuel injection amount, control the ignition timing, and the like. FIG. 1 shows an overall schematic configuration diagram of the engine control system.

  In the engine 10 shown in FIG. 1, an air cleaner 12 is provided at the most upstream portion of the intake pipe 11, and an air flow meter 13 for detecting the intake air amount is provided downstream of the air cleaner 12. A throttle valve 14 whose opening degree is adjusted by a throttle actuator 15 such as a DC motor is provided on the downstream side of the air flow meter 13. The opening degree of the throttle valve 14 (throttle opening degree) is detected by a throttle opening degree sensor built in the throttle actuator 15.

  A surge tank 16 is provided on the downstream side of the throttle valve 14, and an intake pipe pressure sensor 17 for detecting the intake pipe pressure is provided in the surge tank 16. An intake manifold 18 for introducing air into each cylinder of the engine 10 is connected to the surge tank 16. The intake manifold 18 is further connected to the intake port of each cylinder.

  An intake valve 21 and an exhaust valve 22 are provided at an intake port and an exhaust port of the engine 10, respectively. The air in the surge tank 16 is introduced into the combustion chamber 23 by the opening operation of the intake valve 21, and the exhaust gas after combustion is discharged to the exhaust pipe 24 by the opening operation of the exhaust valve 22.

  A fuel injection valve 19 that directly supplies fuel into the combustion chamber 23 is attached to the upper part of each cylinder of the engine 10. In this embodiment, the injected fuel is supplied into the combustion chamber 23 from obliquely above the cylinder. The fuel injection valve 19 is attached to. A fuel tank 38 is connected to the fuel injection valve 19 via a fuel pipe 25, and an electromagnetically driven feed pump 39 is disposed at the most upstream portion of the fuel pipe 25, and downstream of the feed pump 39. A mechanically driven high pressure pump 26 is arranged. The fuel in the fuel tank 38 is pumped up by the feed pump 39 and pressurized to a predetermined feed pressure (for example, 0.3 MPa), and then pumped to the high-pressure pump 26. The feed pressure fuel fed to the high-pressure pump 26 is further increased to a high pressure (for example, 4 to 20 MPa) by the high-pressure pump 26, and then pumped to the delivery pipe 27. The fuel injection valve 19 of each cylinder is delivered from the delivery pipe 27. To be supplied. Thereafter, the fuel is injected into the combustion chamber 23 by the fuel injection valve 19.

  A spark plug 29 is attached to the cylinder head of the engine 10. A high voltage is applied to the spark plug 29 at a desired ignition timing through an ignition device (not shown) including an ignition coil. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 29, and the air-fuel mixture in the combustion chamber 23 is ignited and used for combustion. In addition, the combustion of the air-fuel mixture causes the piston 43 accommodated in the cylinder of the engine 10 to reciprocate, thereby rotating the output shaft (crankshaft) of the engine 10.

  The exhaust pipe 24 is provided with a three-way catalyst 31 as a catalyst for purifying CO, HC, NOx and the like in the exhaust gas. Further, the exhaust pipe 24 is provided with a sensor for detecting the air-fuel ratio (oxygen concentration) of the air-fuel mixture using exhaust as a detection target. Specifically, in the exhaust pipe 24, a wide-area detection type air-fuel ratio sensor 32 that outputs a wide-range air-fuel ratio signal proportional to the oxygen concentration in the exhaust gas is provided upstream of the catalyst 31, and downstream of the catalyst 31. Is provided with an electromotive force output type O2 sensor 33 that generates a binary electromotive force due to a difference in oxygen concentration between the atmosphere and exhaust gas. Further, in this system, a catalyst (three-way catalyst or the like) 34 is further provided on the downstream side of the O 2 sensor 33.

  This system is provided with an EGR device (exhaust gas recirculation device) that introduces a part of the exhaust gas into the intake system as EGR gas. In other words, between the intake pipe 11 and the exhaust pipe 24, one end is connected to the throttle valve downstream side (or upstream side) of the intake pipe 11 and the other end is connected to the catalyst downstream side (upstream side) of the exhaust pipe 24. EGR piping 41 is provided. Further, an electromagnetic EGR valve 42 is provided in the middle of the EGR pipe 41. By adjusting the opening degree of the EGR valve 42, the amount of EGR gas introduced into the intake system can be adjusted. .

  In addition, the engine 10 includes a cooling water temperature sensor 35 that detects the cooling water temperature, a crank angle sensor 36 that outputs a rectangular crank angle signal at every predetermined crank angle of the engine 10 (for example, at a cycle of 10 ° CA), and a delivery pipe. A fuel pressure sensor 37 for detecting the fuel pressure in the fuel tank 27 is attached.

  As is well known, the ECU 50 is mainly composed of a microcomputer (hereinafter referred to as a microcomputer) 51 composed of a CPU, ROM, RAM, etc., and executes various control programs stored in the ROM, so that the engine operation state can be changed each time. In response, various controls of the engine 10 are performed. That is, the microcomputer 51 of the ECU 50 receives detection signals from the various sensors described above, calculates the fuel injection amount, ignition timing, and the like based on the input various detection signals, and controls the fuel injection valve 19 and the ignition device. Controls driving and the like.

  Regarding the fuel injection control, the microcomputer 51 calculates the basic injection timing as the fuel injection start timing by using, for example, a predetermined adaptation map based on the engine operating state (for example, engine speed and engine load). (Injection timing calculation means). Further, the driving of the fuel injection valve 19 is controlled so that fuel injection is started at the calculated injection timing. Specifically, in this embodiment, the fuel injection is started in the intake stroke in one combustion cycle (intake stroke → compression stroke → expansion stroke → exhaust stroke). Fuel injection is started in the compression stroke in some engine operating conditions such as when the catalyst is warmed up.

  Further, in this system, a single injection mode in which fuel injection is performed once in one combustion cycle and a divided injection mode in which fuel injection is performed a plurality of times at different timings within one combustion cycle are switched according to the engine operating state each time. . Specifically, in the present embodiment, the single injection mode is selected when the engine 10 is at a low load or a high rotation, and the divided injection mode is selected when the engine 10 is at a medium / high load and at a medium / low rotation. With regard to split injection, in this embodiment, fuel injection is started in the intake stroke in any of a plurality of fuel injections. At this time, the number of injections in the split injection mode may be different depending on the engine operating state. For example, the number of injections may be increased as the engine load increases.

  In order to calculate the fuel injection amount for each injection in the split injection mode, first, the total fuel amount to be injected in one combustion cycle is calculated based on the engine operating state (for example, engine speed and engine load). The total fuel amount is distributed to each injection time in accordance with the basic division ratio. In this embodiment, the basic division ratio is represented by the ratio of the fuel amount in the first injection when the total fuel amount is 1, and is variably set according to the engine operating state each time.

  Further, the microcomputer 51 adjusts the amount of EGR gas introduced into the intake system by controlling the opening degree of the EGR valve 42 based on the engine operating state at each time. Specifically, the microcomputer 51 calculates an actual EGR rate that is an actual EGR rate from the air-fuel ratio detected by the air-fuel ratio sensor 32 and the intake air amount detected by the air flow meter 13. Further, a target EGR rate that is a control target value of the EGR rate is calculated based on the current engine operating state (engine speed, engine load, etc.). Then, the opening degree of the EGR valve 42 is adjusted so that the actual EGR rate becomes the target EGR rate. In this case, the higher the EGR rate (EGR gas amount / (new air amount + EGR gas amount)) is, the more slowly the combustion temperature rises and the NOx emission amount is suppressed.

  In a gasoline direct injection engine, it is considered that the combustion temperature changes in accordance with the magnitude of the EGR rate, and the amount of PM generated by combustion differs in accordance with the change in the combustion temperature, as in the diesel engine. Specifically, as shown by the line L1 in FIG. 2, in the region where the EGR rate is smaller than the predetermined value e1, the PM generation amount increases with the increase in the EGR rate (with the decrease in the combustion temperature). When the rate exceeds the predetermined value e1, the PM generation amount decreases with the increase in the EGR rate (with the decrease in the combustion temperature). There are various possible causes for this, but, for example, in a region where the EGR rate is smaller than the predetermined value e1, the amount of oxygen in the air-fuel mixture introduced into the combustion chamber 23 decreases, resulting in an increase in the PM generation amount and an EGR rate. In a region where is greater than the predetermined value e1, it is considered that the PM generation amount is reduced by slowing the increase in the combustion temperature to suppress the combustion temperature below the PM generation temperature.

  In consideration of such PM emission characteristics, it can be said that in the region where the EGR rate is larger than the predetermined value e1, the NOx emission amount can be reduced and the PM emission amount can be reduced by increasing the EGR rate. Therefore, in this system, in an engine operation region where a relatively large amount of EGR gas can be introduced (for example, an operation region of medium / low load and medium / high rotation of the engine 10), the EGR rate at which the PM generation amount reaches a peak ( By performing combustion at an EGR rate higher than the predetermined value e1), NOx and PM emissions are suppressed. Note that, in the engine operation region where EGR gas introduction is performed, fuel injection is performed once or a plurality of times during the intake stroke.

  Here, when EGR gas is introduced into the intake system, it is conceivable that the temperature of the engine 10 (piston temperature) decreases due to a decrease in the combustion temperature. Further, when the piston temperature decreases, the fuel (gasoline) injected from the fuel injection valve 19 and attached to the piston tends to remain liquid. That is, the piston wet easily occurs. In such a case, the fuel and air are not properly mixed, and as a result, there is a possibility that PM reduction cannot be performed properly even though the emission amount of NOx and PM is being reduced by introducing EGR gas. Specifically, as shown by a line L2 in FIG. 2, when the EGR rate is increased (the combustion temperature is lowered), the amount of PM generated due to piston wet is increased, and it is easily affected by the decrease in the combustion temperature. Conceivable. In particular, when the EGR rate is larger than the EGR rate (predetermined value e1) at which the PM generation amount reaches a peak, the PM generation amount due to the piston wet tends to increase rapidly.

  Therefore, in the present embodiment, when an exhaust gas recirculation request is generated by the EGR device, and when the exhaust gas recirculation is performed by the EGR device, the fuel injection timing (basic) is determined based on the piston temperature at each time. The injection timing is changed to the retard side in the intake stroke. That is, in a situation where the piston temperature is low and piston wet is likely to occur, the fuel injection timing is changed to the retard side in the intake stroke to suppress the fuel from adhering to the piston. Thereby, even when EGR gas is introduced, PM generation can be suppressed.

  Next, the fuel injection timing correction process (injection correction process) when EGR gas is introduced will be described with reference to the flowchart of FIG. This process is executed at predetermined intervals by the microcomputer 51 of the ECU 50.

  In FIG. 3, in step S101, it is determined whether or not an exhaust gas recirculation request has been made by the EGR device. Here, it is determined whether or not the current engine operating state is an operating point within an operating region in which EGR gas can be introduced (for example, an operating region in which the engine 10 has a medium to low load and a medium to high speed). For example, when the EGR valve 42 is switched from a fully closed state to a valve open state as the engine operation region in which EGR gas introduction can be performed is shifted, or when the EGR gas introduction is being performed, the actual EGR rate and the target EGR rate are An affirmative determination is made when the opening degree of the EGR valve 42 is changed or maintained so as to match.

  When there is a request for recirculation of exhaust gas, the opening degree control of the EGR valve 42 is executed by another routine (not shown) so as to satisfy the recirculation request. Specifically, the target EGR rate is calculated based on the current engine operating state (engine speed, engine load, etc.), and the opening degree of the EGR valve 42 is adjusted so that the actual EGR rate matches the target EGR rate. If there is a recirculation request, the process proceeds to step S102 in FIG. 3 to detect the temperature of the piston 43 (temperature detection means). Here, parameters relating to the engine operating state (for example, engine rotation speed and engine load) are acquired, and the piston temperature is estimated based on the acquired values.

  In addition, the structure which detects the temperature of piston 43 is not limited above, For example, it is good also as a structure which estimates piston temperature based on the cooling water temperature detected by the cooling water temperature sensor 35, combustion temperature, and an EGR rate. Further, a sensor for detecting the piston temperature may be attached, and the piston temperature may be directly detected by the sensor.

  In a succeeding step S103, it is determined whether or not the split injection mode is selected. If the split injection mode is selected, the process proceeds to step S104, and the basic split ratio calculated by another routine (not shown) is read. In step S105, the read basic split ratio is corrected according to the piston temperature (split). Rate change means). In the present embodiment, the basic division ratio correction amount (division ratio correction amount) corresponding to the piston temperature is stored in advance as a map, for example, and the map is used to perform the division ratio correction corresponding to the current piston temperature. The amount is calculated, and the basic division ratio is corrected according to the calculated division ratio correction amount. Here, the basic division ratio is corrected by subtracting the division ratio correction amount from the basic division ratio calculated based on the engine operating state.

  FIG. 4 is an example of a map showing the correspondence between the piston temperature and the division ratio correction amount. According to FIG. 4, a larger value is set as the division ratio correction amount as the piston temperature is lower. More specifically, an upper limit value is provided for the division ratio correction amount. In a low temperature range where the piston temperature reaches the value Te1, an upper limit value α1 is set as the division ratio correction amount, and from the value Te1 to the value Te2. In the middle temperature range, a smaller value is set as the division rate correction amount as the temperature becomes higher, and 0 is set as the division rate correction amount in a higher temperature range than the value Te2. According to the relationship of FIG. 4, the lower the piston temperature, the smaller the ratio of the fuel amount of the first injection to the fuel amount to be injected in one combustion cycle.

  Note that the method of correcting the basic division rate by the division rate correction amount is not limited to the above, and may be performed by, for example, multiplying the basic division rate by the division rate correction amount. In this case, it is preferable that the upper limit value of the division rate correction amount is 1, and the division rate correction amount becomes smaller than 1 as the piston temperature decreases.

  In step S106, the basic injection timing calculated by another routine (not shown) is read. At this time, when the divided injection mode is selected, the basic injection timing of the first injection is read. Note that the read basic injection timing is the fuel injection start timing when the EGR gas introduction is performed, and the intake stroke is the injection start timing. In the subsequent step S107, the read basic injection timing is corrected according to the piston temperature (injection timing changing means). In the present embodiment, the basic injection timing correction amount (timing correction amount) according to the piston temperature is stored in advance as a map, for example, and the map is used to determine the timing correction amount corresponding to the current piston temperature. The basic injection timing is corrected according to the calculated timing correction amount. Here, the basic injection timing is corrected by changing the basic injection timing calculated based on the engine operating state to the retard side in the intake stroke by an amount corresponding to the timing correction amount.

  FIG. 5 is an example of a map showing the correspondence between the piston temperature and the timing correction amount. In FIG. 5, the amount of change when the basic injection timing is changed to the retard side in the intake stroke is shown as the timing correction amount. Therefore, the larger the timing correction amount, the larger the amount of change to the retard side with respect to the basic injection timing. In the present embodiment, as shown in FIG. 5, a larger value is set as the timing correction amount as the piston temperature is lower. More specifically, an upper limit value is provided for the timing correction amount, and an upper limit value β1 (for example, 20 to 40 ° C.) is set as the timing correction amount in a low temperature range where the piston temperature reaches the value Te3. In the intermediate temperature range from the value Te3 to the value Te4, a smaller value is set as the timing correction amount as the temperature becomes higher, and in the temperature range higher than the value Te4, 0 is set as the timing correction amount. According to the relationship of FIG. 5, the lower the piston temperature, the more the fuel injection timing is changed to the retard side with respect to the basic injection timing in the intake stroke.

  The correction value of the division ratio obtained in step S105 and the correction value of the fuel injection timing obtained in step S107 are used in fuel injection control by another routine (not shown), so that fuel injection based on these correction values is performed. The

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  When EGR gas is introduced into the intake system by the EGR device, the fuel injection timing (basic injection timing) is changed to the retard side in the intake stroke based on the piston temperature. When EGR gas is introduced, the piston temperature may decrease as the combustion temperature decreases. However, according to this configuration, the fuel adheres to the piston 43 even in a situation where the piston temperature is low and piston wet is likely to occur. Can be suppressed. Therefore, even when EGR gas is introduced, PM emission can be suppressed.

  In the relationship between the piston temperature and the change amount (timing correction amount) of the basic injection timing (see FIG. 5), when the piston temperature is lower than the predetermined value Te2, the timing correction amount is set to a value other than 0 and the piston temperature is set to a predetermined value. The timing correction amount is set to 0 when higher than Te2. As shown in FIG. 2, the amount of PM generated due to piston wet does not change so much in the temperature range where the combustion temperature is relatively high, but increases rapidly when the combustion temperature is lowered to some extent. On the other hand, if the fuel injection timing is changed to the retarded side according to the piston temperature, the fuel injection timing will be retarded from the optimal injection timing, so the combustion efficiency will decrease. It is desirable that the retardation is minimized. In this respect, according to the present configuration, the piston wet temperature generated by the EGR is performed because the basic injection timing is changed to the retard side in the intake stroke based on the piston temperature on the condition that the piston temperature is lower than the predetermined temperature. Can be corrected appropriately.

  In addition, when split injection is performed, when introducing EGR, based on the piston temperature, a change is made to reduce the amount of fuel of the first injection among a plurality of fuel injections performed within one combustion cycle. It was set as the structure to do. Therefore, it is possible to suppress the fuel from adhering to the piston 43 in a situation where the piston temperature is low and piston wet is likely to occur.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  In the above embodiment, the ECU 50 has a function of correcting the basic division ratio based on the piston temperature and a function of correcting the basic injection timing based on the piston temperature. However, only one of the functions is provided. You may have. That is, the ECU 50 may have only a function of correcting the basic division ratio based on the piston temperature, or may have only a function of correcting the basic injection timing based on the piston temperature.

  In the above embodiment, when the split injection mode is selected at the time of exhaust gas recirculation accompanying the exhaust gas recirculation request, the basic split ratio and basic injection timing are corrected based on the piston temperature. Only one of the correction targets may be based.

  -You may change the correction | amendment object based on piston temperature according to the injection mode at the time of implementation of the exhaust gas recirculation accompanying the exhaust gas recirculation request | requirement. Specifically, when the single injection mode is selected, the basic injection timing is corrected based on the piston temperature, and when the split injection mode is selected, the basic split ratio is corrected based on the piston temperature. The configuration is as follows.

  In the above embodiment, as shown in FIG. 5, the relationship between the piston temperature and the change amount of the basic injection timing (timing correction amount) so that the timing correction amount becomes 0 in the temperature range where the piston temperature is higher than the value Te4. Was predetermined. According to the relationship of FIG. 5, when the piston temperature is lower than the predetermined temperature (value Te4), the basic injection timing is changed to the retard side based on the piston temperature, and when the piston temperature is higher than the predetermined temperature, the piston temperature The basic injection timing based on is not changed to the retard side. On the other hand, in this embodiment, it is determined whether the piston temperature is lower than a predetermined temperature using the EGR rate as a parameter instead of the piston temperature. That is, when exhaust gas recirculation is performed in response to exhaust gas recirculation request by the EGR device, it is determined whether or not the EGR rate is greater than a predetermined value, and the EGR rate is greater than a predetermined value. The basic injection timing is changed based on the piston temperature. Here, the predetermined value may be, for example, a PM peak value (predetermined value e1 in FIG. 2) that is a recirculation rate at which the PM generation amount of the engine 10 reaches a peak. When the EGR rate is made larger than the PM peak value, as shown by the line L1 in FIG. 2, the PM generation amount can be reduced by lowering the combustion temperature. However, as shown by the line L2 in FIG. The amount of PM produced increases rapidly. On the other hand, when the fuel injection timing is changed to the retarded side according to the piston temperature, the combustion efficiency is lowered due to the fuel injection timing deviating from the optimal injection timing, so that the delay of the fuel injection timing is minimized. It is desirable to make it. Therefore, in this embodiment, when the EGR rate is larger than the PM peak value, the basic injection timing is changed based on the piston temperature, and when the EGR rate is equal to or less than the PM peak value, the basic injection timing based on the piston temperature. The configuration is not implemented. Also in this case, the fuel injection timing can be retarded as necessary, and an appropriate correction can be made for the piston wet caused by exhaust gas recirculation.

  -When exhaust gas recirculation is performed in response to exhaust gas recirculation requests by the EGR device, the exhaust gas recirculation by the EGR device is limited based on the piston temperature. Even if there is a recirculation request, when the piston temperature is low, the engine temperature (piston temperature) is further lowered by introducing EGR gas, and as a result, PM generation due to piston wet is likely to occur. Therefore, with the above configuration, it is possible to suitably suppress PM generation due to the introduction of EGR gas. As a configuration for restricting the exhaust gas recirculation based on the engine temperature, for example, when the introduction of EGR gas is started in response to the exhaust gas recirculation request, the piston temperature at the start of the PM It is determined whether or not the generated amount is within a predetermined low temperature range that is equal to or greater than the predetermined amount. Further, if the EGR gas introduction is being performed, the exhaust gas recirculation is stopped when the piston temperature falls within a predetermined low temperature range. Alternatively, when exhaust gas recirculation is performed, the upper limit value of the EGR rate may be variable based on the piston temperature.

  FIG. 6 is a flowchart showing a processing procedure when the upper limit value of the EGR rate is variably set based on the piston temperature. This process is executed at predetermined intervals by the microcomputer 51 of the ECU 50. In the description of FIG. 6, the same processing as in FIG. 3 is denoted by the step number of FIG. 3, and the description thereof is omitted.

  In FIG. 6, in steps S301 and S302, the same processing as in steps S101 and S102 is executed, and in step S303, an upper limit value of the EGR rate is set according to the piston temperature. In this embodiment, the upper limit value of the EGR rate corresponding to the piston temperature is determined and stored in advance as a map, for example, and the upper limit value of the EGR rate corresponding to the current piston temperature is set using the map. About this map, in this embodiment, it is determined that the upper limit value of the EGR rate becomes smaller as the piston temperature is lower. Thereafter, in steps S304 to S308, the same processing as in steps S103 to S107 of FIG. 3 is executed, and this routine is terminated. The upper limit value of the EGR rate set in step S303 is used when setting the target EGR rate by another routine (not shown).

  -The configuration for restricting the exhaust gas recirculation based on the piston temperature is a configuration in which the ECU 50 only has a function of correcting the basic division ratio based on the piston temperature, or the basic injection timing based on the piston temperature. You may apply to the structure which has only the function to correct | amend. In addition, the structure illustrated above is mentioned as a structure which restrict | limits implementation of exhaust gas recirculation in this case.

  -There is an upper limit for the correction amount of the basic injection timing and the basic division ratio (see FIGS. 4 and 5), and in the situation where an upper limit value is set as the correction amount, PM generation due to piston wet can be suitably suppressed. There is a possibility that the piston temperature cannot be lowered to the extent. In view of this, in the present configuration, when the PM amount detection means for detecting the PM amount in the exhaust gas is provided and the exhaust gas recirculation is performed while changing the basic injection timing to the retard side according to the piston temperature, When the PM detection unit detects that the PM amount exceeds the determination value, the exhaust gas recirculation by the EGR device is restricted (stop the exhaust gas recirculation or set the upper limit of the EGR rate). As the PM amount detecting means, a PM sensor for detecting the PM amount in the exhaust gas may be provided, and the PM amount in the exhaust gas may be directly detected by the PM sensor. Or it is good also as a structure which estimates PM amount in exhaust_gas | exhaustion based on piston temperature.

  In the above embodiment, as a configuration for changing the basic injection timing to the retard side based on the piston temperature, the relationship between the piston temperature and the timing correction amount is determined in advance, and the relationship (see FIG. 5) is used. The timing correction amount corresponding to the current piston temperature is calculated. On the other hand, in this embodiment, the relationship between the EGR rate and the timing correction amount is determined in advance, and the timing correction amount corresponding to the current EGR rate is calculated using the relationship. The piston temperature varies depending on the EGR rate, and the higher the EGR rate, the lower the combustion temperature and the lower the piston temperature. Therefore, when the EGR rate and the timing correction amount are associated with each other and the timing correction amount is obtained from the current EGR rate based on the correspondence, the timing correction amount can be obtained according to the piston temperature. As a relationship between the EGR rate and the timing correction amount, it is preferable to increase the timing correction amount as the EGR rate is higher. Specifically, for example, when the EGR rate is less than the value E1, the timing correction amount is set to 0. In E1 to E2 (E2> E1), the EGR rate is increased as the EGR rate is increased. In the region higher than the value E2, the timing correction is performed. The amount may be set to an upper limit value (for example, 20 to 40 ° C. A).

  In the above embodiment, the fuel injection valve 19 is configured to supply fuel directly into the combustion chamber 23 from above the cylinder in the upper part of each cylinder of the engine 10, but the fuel injection valve 19 is arranged in the center of the cylinder. In addition, a center injection type configuration in which fuel is injected vertically toward the piston 43 may be employed. In this case, fuel is likely to adhere to the piston 43, and the effect of correcting the fuel injection timing and the split ratio based on the piston temperature, that is, PM is generated with combustion of the engine 10 when exhaust gas recirculation is performed. The effect of suppressing can be suitably obtained.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 19 ... Fuel injection valve, 29 ... Spark plug, 41 ... EGR piping, 42 ... EGR valve, 43 ... Piston, 50 ... ECU, 51 ... Microcomputer (injection timing calculation means, temperature detection means, injection timing change means) , Split rate calculating means, split rate changing means).

Claims (4)

An engine having a fuel injection valve that directly injects fuel into a cylinder, and an exhaust gas that recirculates a part of the exhaust gas flowing through the exhaust passage of the engine to the intake passage through a communication passage that connects the exhaust passage and the intake passage. And an exhaust gas recirculation system comprising a recirculation device,
Injection control means for performing fuel injection by the fuel injection valve in an intake stroke of one combustion cycle;
Injection timing calculating means for calculating a basic injection timing as fuel injection timing by the injection control means based on the engine operating state each time;
Temperature detecting means for detecting the temperature of the piston of the engine;
When the recirculation is performed in an operation region where the exhaust gas recirculation device can perform the exhaust gas recirculation, the basic calculation calculated by the injection timing calculation means based on the piston temperature detected by the temperature detection means Injection timing changing means for changing the injection timing to the retard side;
Equipped with a,
The injection control means performs fuel injection a plurality of times at different timings by the fuel injection valve in the intake stroke,
A split ratio calculating means for calculating a basic split ratio that is a ratio of the fuel amount to be injected in the first fuel injection out of the fuel amount to be injected in one combustion cycle based on each engine operating state;
A division ratio for changing the basic division ratio calculated by the division ratio calculation means to a smaller side based on the piston temperature detected by the temperature detection means when the exhaust gas recirculation is performed by the exhaust gas recirculation device control device for an exhaust gas recirculation system further comprising said Rukoto and changing means.   The injection timing changing means is a basic injection timing calculated by the injection timing calculating means based on the piston temperature detected by the temperature detecting means when the piston temperature detected by the temperature detecting means is lower than a predetermined temperature. 2. The exhaust gas recirculation system control apparatus according to claim 1, wherein the control is changed to a retard side. The exhaust recirculation system control device according to claim 1 or 2 , wherein execution of exhaust gas recirculation by the exhaust gas recirculation device is restricted based on a piston temperature detected by the temperature detection means. An engine having a fuel injection valve that directly injects fuel into a cylinder, and an exhaust gas that recirculates a part of the exhaust gas flowing through the exhaust passage of the engine to the intake passage through a communication passage that connects the exhaust passage and the intake passage. And an exhaust gas recirculation system comprising a recirculation device,
Injection control means for performing fuel injection a plurality of times at different timings by the fuel injection valve in the intake stroke of one combustion cycle;
A split ratio calculating means for calculating a basic split ratio that is a ratio of the fuel amount to be injected in the first fuel injection out of the fuel amount to be injected in one combustion cycle based on each engine operating state;
Temperature detecting means for detecting the temperature of the piston of the engine;
When the recirculation is performed in an operation region where the exhaust gas recirculation device can perform the exhaust gas recirculation, the basic division calculated by the division ratio calculation unit based on the piston temperature detected by the temperature detection unit A split ratio changing means for changing the ratio to a smaller side;
A control device for an exhaust gas recirculation system.

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