JP6613709B2 - EGR control device - Google Patents

Description

  The present invention relates to an EGR control device.

  There is one that detects the differential pressure across the EGR valve with a differential pressure sensor, and controls the EGR valve opening so that the detected differential pressure before and after the EGR valve matches a predetermined differential pressure before and after the EGR valve (Patent Document 1). reference).

US Patent No. 8091535

  The basic EGR valve opening is set when the actual temperature of the downstream temperature of the EGR extraction portion is the basic temperature. For this reason, when the operating point of the engine shifts from the non-EGR region to the EGR region and the actual temperature of the downstream temperature of the EGR extraction portion shifts from the basic temperature to the basic temperature, the actual temperature The differential pressure across the EGR valve changes by an amount corresponding to the temperature difference between the basic temperature and the basic temperature. If the differential pressure before and after the EGR valve changes compared to the case where the actual temperature matches the basic temperature, the amount of EGR gas passing through the EGR valve changes, so the actual amount of EGR gas flowing into the combustion chamber is less than the target amount of EGR gas. Come off. When the basic ignition timing is set according to the basic EGR rate, if the actual EGR gas amount flowing into the combustion chamber deviates from the target EGR gas amount, knocking occurs or combustion in the combustion chamber is unstable. It becomes.

  In this case, according to the technique disclosed in Patent Document 1, the differential pressure sensor detects the differential pressure across the EGR valve, and the detected differential pressure across the EGR valve matches the predetermined differential pressure before and after the EGR valve. Control the opening. As a result, even if the actual temperature of the downstream temperature of the EGR take-out portion is out of the basic temperature, it is possible to avoid the occurrence of knocking and unstable combustion in the combustion chamber.

  However, when the differential pressure sensor is used as in the technique of Patent Document 1, the differential pressure across the EGR valve detected by the differential pressure sensor is greatly affected by exhaust pulsation. For this reason, it is necessary to add a filter that performs high-precision and high-speed processing in order to separate the influence of exhaust pulsation from the differential pressure across the EGR valve detected by the differential pressure sensor, which increases costs.

  Therefore, the present invention has an inexpensive configuration without using a differential pressure sensor, and even when the actual temperature of the downstream temperature of the EGR take-off portion is deviated from the basic temperature to the EGR region, knocking occurs in the combustion chamber. An object of the present invention is to provide an apparatus capable of avoiding unstable combustion.

The EGR control device of the present invention includes an EGR passage that branches from an exhaust pipe and returns a part of the exhaust to the intake pipe, an EGR valve that opens and closes the EGR passage, an actuator that can adjust the opening degree of the EGR valve, and a predetermined amount. Basic EGR valve opening calculation means for calculating the basic EGR valve opening in the EGR region, and when the engine operating point shifts from the non-EGR region to the EGR region, or when the engine operating point shifts within the EGR region A target EGR valve that calculates the target EGR valve opening by correcting the basic EGR valve opening by the temperature difference correction amount when the actual temperature of the downstream temperature of the EGR extraction portion shifts to a predetermined basic temperature. Opening calculation means and actuator control means for controlling the actuator so that the opening degree of the EGR valve becomes the calculated target EGR valve opening degree. This EGR control device predetermines a reverse flow region in which a reverse flow in which the EGR valve flows from the intake pipe side to the exhaust pipe side in the EGR region on the map using the engine torque and the engine rotation speed as parameters. When the engine operating point determined by the engine rotational speed is in the reverse flow region on the map, the reverse flow region is determined, and when the actual temperature is lower than a predetermined temperature, the reverse flow region is expanded to the high load side.

  In the present invention, knocking occurs or combustion occurs in the combustion chamber even if the EGR take-off section downstream temperature is shifted from the basic temperature to the EGR region with an inexpensive configuration without using a differential pressure sensor. Instability can be avoided.

It is a schematic block diagram of the gasoline engine of 1st Embodiment of this invention. It is a driving | operation area | region figure which shows a supercharging area | region and LP-EGR area | region. It is a characteristic figure of a basic LP-EGR rate. It is a timing chart showing changes when the accelerator pedal is depressed after a long idle state to accelerate and the operating point shifts from the non-LP-EGR region to the LP-EGR region where the basic LP-EGR rate is 10%. FIG. 5 is a timing chart of pressures on the upstream side and the downstream side of the LP-EGR valve at point L shown in FIG. 4. 5 is a timing chart of pressures on the upstream side and the downstream side of the LP-EGR valve at point M shown in FIG. 4. It is a timing chart when the operation point shifts to the LP-EGR region by depressing the accelerator pedal and accelerating from the state that has been in the non-LP-EGR region on the low load side for a long time. FIG. 6 is a timing chart when the operating point shifts to the LP-EGR region by decelerating the accelerator pedal from a state where it has been in the non-LP-EGR region on the high load side for a long time. Target LP-EGR valve opening when the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature of the downstream temperature of the EGR take-out section rises from the lower side and shifts to the basic temperature It is a flowchart for demonstrating calculation of a degree. Target LP-EGR valve opening when the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature of the downstream temperature of the EGR take-out section rises from the lower side and shifts to the basic temperature It is a flowchart for demonstrating calculation of a degree. FIG. 6 is a characteristic diagram of a predetermined value 1; It is an area | region figure which shows the content of a basic backflow area | region map. It is an area | region figure which shows the content of an expansion backflow area | region map. It is an area | region figure which shows the content of the reduced backflow area | region map. Target LP-EGR valve opening when the operating point shifts from the non-LP-EGR region to the LP-EGR region, and when the actual temperature of the downstream temperature of the EGR take-out portion decreases from the higher side and shifts to the basic temperature It is a flowchart for demonstrating calculation of a degree. FIG. 6 is a characteristic diagram of a predetermined value 3; It is a flowchart for demonstrating calculation of an ignition timing command value. It is a flowchart for demonstrating calculation of an ignition timing command value. It is a characteristic view of the basic ignition timing in the LP-EGR region. It is a characteristic view of a temperature difference correction amount. It is a characteristic view of difference LP-EGR valve opening correction amount. Target of the second embodiment when the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature of the downstream temperature of the EGR take-out part rises from the lower side and shifts to the basic temperature It is a flowchart for demonstrating calculation of the LP-EGR valve opening degree. Target of the second embodiment when the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature of the downstream temperature of the EGR take-out part rises from the lower side and shifts to the basic temperature It is a flowchart for demonstrating calculation of the LP-EGR valve opening degree. It is a flowchart for demonstrating calculation of the ignition timing command value of 2nd Embodiment. It is a flowchart for demonstrating calculation of the ignition timing command value of 2nd Embodiment. It is a schematic block diagram of the gasoline engine of 3rd Embodiment. The target of the third embodiment when the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature of the downstream temperature of the EGR take-out part rises from the low side and shifts to the basic temperature It is a flowchart for demonstrating calculation of the LP-EGR valve opening degree. The target of the third embodiment when the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature of the downstream temperature of the EGR take-out part rises from the low side and shifts to the basic temperature It is a flowchart for demonstrating calculation of the LP-EGR valve opening degree. FIG. 6 is a characteristic diagram summarizing what operating points are applied when the basic LP-EGR rate is uniform in each of two LP-EGR regions. FIG. 6 is a characteristic diagram summarizing what operating points are applied when the basic LP-EGR rate is not uniform within each of the two LP-EGR regions. FIG. 6 is a characteristic diagram summarizing what operating points are applied when the basic LP-EGR rate is not uniform within each of the two LP-EGR regions. It is a schematic block diagram of the gasoline engine of 4th Embodiment. It is a characteristic figure of the basic LP-EGR rate of a 4th embodiment. It is a characteristic view of the differential pressure device opening degree with respect to the target air amount of the fourth embodiment when the differential pressure device opening degree is given as a continuous value. It is a characteristic view of the differential pressure device opening with respect to the target air amount of the fourth embodiment when the differential pressure device opening is given as a discrete value. It is a driving | operation area | region figure which shows the image of the equal air quantity in the differential pressure device operation area | region of 4th Embodiment. It is a flowchart for demonstrating calculation of the differential pressure device opening degree of 4th Embodiment. It is a driving | running | working area | region figure which shows the differential pressure device operation area | region of 4th Embodiment. It is a characteristic view of the differential pressure device opening degree of 4th Embodiment. It is a timing chart which shows the change of the LP-EGR rate when the operating point shifts to the differential pressure device operation region on the high load side from the state that has been in the non-LP-EGR region on the low load side. It is a timing chart which shows the change of the LP-EGR rate when an operating point shifts to the low pressure side differential pressure device operation area from the state which was in the non-LP-EGR area on the high load side for a long time. The fourth embodiment in the case where the operating point shifts from the non-LP-EGR region to the differential pressure device operating region and the actual temperature of the EGR take-out portion downstream temperature rises from the lower side and shifts to the basic temperature. It is a flowchart for demonstrating calculation of target LP-EGR valve opening. The fourth embodiment in the case where the operating point shifts from the non-LP-EGR region to the differential pressure device operating region and the actual temperature of the EGR take-out portion downstream temperature rises from the lower side and shifts to the basic temperature. It is a flowchart for demonstrating calculation of target LP-EGR valve opening. It is a characteristic view of the device correction amount 1 of 4th Embodiment when giving a differential pressure device opening degree by a discrete value. It is a characteristic view of the device correction amount 1 of 4th Embodiment in the case of giving a differential pressure device opening degree by a continuous value. Target of the fourth embodiment in the case where the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature of the downstream temperature of the EGR take-out part decreases from the higher side and shifts to the basic temperature It is a flowchart for demonstrating calculation of the LP-EGR valve opening degree. It is a characteristic view of the device correction amount 2 of 4th Embodiment in the case of giving a differential pressure device opening degree by a discrete value. It is a characteristic view of the device correction amount 2 of 4th Embodiment in the case of giving a differential pressure device opening degree by a continuous value.

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

(First embodiment)
FIG. 1 is a schematic configuration diagram of a control device for a gasoline engine according to a first embodiment of the present invention.

  The engine 1 is a gasoline engine (hereinafter also simply referred to as “engine”), and is mounted on a vehicle (not shown). The engine 1 includes an intake passage 4 and an exhaust passage 11. The intake passage 4 includes an intake pipe 4a, an intake collector 4b, and an intake manifold 4c.

  The intake pipe 4a immediately upstream of the intake collector 4b is provided with an electronically controlled throttle device that responds to the amount of depression of the accelerator pedal. The throttle device includes a throttle valve 5 and a motor (rotary electric machine) 6 that drives the throttle valve 5. The intake air is metered by the throttle valve 5 through the intake pipe 4a. The metered air is stored in the intake collector 4b, and is distributed and supplied from the intake collector 4b to the cylinders 7 (combustion chambers) of the respective cylinders via the intake manifold 4c. Although the embodiment is an electronically controlled throttle device, the throttle valve and the accelerator pedal may be connected by a wire.

  A fuel injection valve 8 is provided on the intake manifold 4c and a spark plug 9 is provided directly on the cylinder 7, and fuel is injected from the fuel injection valve 8 into the intake manifold 4c (intake port). The injected fuel is mixed with air metered by the throttle valve 5 to form a gas, which is ignited by the spark plug 9 and burned. The burning gas is discharged into the exhaust passage 11 after performing the work of pushing down the piston 10. The position where the fuel injection valve 8 is provided is not limited to the intake manifold. A fuel injection valve may be provided directly facing the cylinder 7.

  The exhaust passage 11 includes an exhaust manifold 11a into which exhaust from the cylinder 7 of each cylinder flows, and an exhaust pipe 11b connected to a collective portion of the exhaust manifold 11a. Since the exhaust contains harmful three components of HC, CO, and NOx, a manifold catalyst 12 is provided at the assembly portion of the exhaust manifold 11a and a main catalyst 13 is provided at the exhaust pipe 11b downstream of the exhaust manifold 11a in order to purify all of them. Yes. The main catalyst 13 is provided, for example, under the floor of the vehicle. Each of these catalysts 12 and 13 is composed of, for example, a three-way catalyst. A muffler 19 is provided at the end of the exhaust pipe 11b.

  The engine 1 further includes a turbocharger 21. The turbocharger 21 includes a turbine 22 provided in the exhaust pipe 11b, a compressor 23 provided in the intake pipe 4a, and a shaft 24 connecting the turbine 22 and the compressor 23. The turbine 22 is rotated by the energy of the exhaust gas flowing through the exhaust pipe 11b, and drives the compressor 23 coaxial with the turbine 22. The compressor 23 compresses the air sucked through the air cleaner 20. The compressed air that is compressed and exceeds the atmospheric pressure is sent to the intake collector 4b. The target supercharging pressure can be obtained by operating the turbocharger 21.

  The turbocharger 21 includes a bypass passage 24 that bypasses the turbine 22 and a normally closed waste gate valve 25 that opens and closes the bypass passage 24. The waste gate valve 25 is driven by a motor (rotating electric machine) 26. For example, when the actual boost pressure detected by the boost pressure sensor 45 becomes higher than the target boost pressure, the waste gate valve 25 is opened by driving the motor 26 and a part of the exhaust flowing into the turbine 22 is removed. The turbine 22 is bypassed to flow. As a result, the turbine rotational speed is decreased from before the waste gate valve 25 is opened, and the compressor rotational speed coaxial with the turbine 22 is also decreased. When the compressor rotational speed decreases, the actual supercharging pressure decreases and matches the target supercharging pressure. The opening degree of the waste gate valve 25 is held at a timing at which the actual boost pressure coincides with the target boost pressure.

  An intercooler 25 is provided in the intake pipe 4 a on the downstream side of the compressor 23. The intercooler 25 is for cooling the air compressed by the compressor 23. The air whose temperature has been increased by the air compression by the compressor 23 is cooled by the intercooler 25, whereby the supercharging efficiency can be increased.

  Now, even in the gasoline engine 1 provided with the turbocharger 21, there is a demand to perform a large amount of EGR (exhaust gas recirculation) in order to suppress knocking in the supercharging region. In order to meet this requirement, in this embodiment, a ropeless loop EGR device 14 is newly provided. The rope pressure loop EGR device 14 includes an EGR passage 15, an EGR cooler 16 interposed in the EGR passage 15, an EGR valve 17 (for example, a butterfly valve) that opens and closes the EGR passage 15, and a motor (rotary electric machine) that drives the EGR valve 17. 18. Here, the actuator that drives the EGR valve 17 is the motor 18, but the invention is not limited to the motor 18.

  The EGR passage 15 is branched from the exhaust pipe downstream of the turbine 22, specifically, the exhaust pipe 11 b between the manifold catalyst 12 and the main catalyst 13, and merges with the intake pipe 4 a upstream of the compressor 23. Thus, when the EGR passage 15 communicates the exhaust pipe 11b downstream of the turbine 22 and the intake pipe 4a upstream of the compressor 23, the gas is determined by the differential pressure between the exhaust pipe pressure downstream of the turbine and the intake pipe pressure upstream of the compressor. (A part of the exhaust gas) flows through the EGR valve 17. Since the differential pressure between the exhaust pipe pressure downstream of the turbine and the intake pipe pressure upstream of the compressor is as small as about 1 kPa, for example, it is called a ropeless loop EGR (hereinafter referred to as “LP-EGR”) device. Hereinafter, the EGR valve of the LP-EGR device is referred to as “LP-EGR valve”. Further, an operation region in which the LP-EGR valve 17 is opened and LP-EGR is performed is referred to as an “LP-EGR region”, and an operation region in which the LP-EGR valve is fully closed is referred to as a “non-LP-EGR region”. The LP-EGR device itself is known in diesel engines, but in the present embodiment, the LP-EGR device 14 is newly adopted for the gasoline engine 1 provided with the turbocharger 21.

  The EGR cooler 16 is provided in the EGR passage 15 upstream of the LP-EGR valve 17. The EGR cooler 16 cools the gas (a part of the exhaust gas) flowing through the EGR passage 15 until it reaches a certain temperature. For this reason, in the LP-EGR region, the gas cooled to a certain temperature flows through the LP-EGR valve 17.

  Here, the reason why the LP-EGR device 14 is newly adopted in the gasoline engine 1 provided with the turbocharger 21 will be described. There is an EGR device that is applied to a gasoline engine that does not include a turbocharger and that causes a portion of relatively high-temperature exhaust to flow into the intake collector 4b. In this EGR device, the gas flows through the EGR valve with a relatively large differential pressure (negative pressure) between the exhaust passage 11 and the intake collector 4b. Therefore, this EGR device is called a high pressure loop EGR (hereinafter referred to as “HP-EGR”) device. .

  Consider applying the HP-EGR device to a gasoline engine equipped with a turbocharger. First, when not supercharging, a pressure (negative pressure) lower than the atmospheric pressure develops in the intake collector 4b, and the differential pressure from the exhaust pressure increases. Therefore, if the EGR valve is opened, gas (EGR gas) is supplied to the intake collector 4b. Can be inhaled. However, at the start of supercharging by the turbocharger, the pressure of the intake collector 4b increases from negative pressure to atmospheric pressure and from atmospheric pressure to a pressure exceeding atmospheric pressure. When the pressure of the intake collector 4b increases to a pressure exceeding the atmospheric pressure, the differential pressure from the exhaust pressure decreases. The pressure exceeding the atmospheric pressure in the intake collector 4b is a supercharging pressure. The higher the supercharging pressure, the smaller the differential pressure from the exhaust pressure. When the differential pressure from the exhaust pressure becomes small, a large amount of EGR gas cannot be sucked into the intake collector 4b.

  On the other hand, in the LP-EGR device, gas (EGR gas) flows through the LP-EGR valve 17 with a small differential pressure (about 1 kPa) between the relatively low exhaust pipe pressure downstream of the turbine and the intake pipe pressure upstream of the compressor. It is not affected by supercharging pressure. In other words, a configuration in which the LP-EGR device 14 is added to the gasoline engine 1 provided with the turbocharger 21 allows a large amount of EGR gas to be introduced into the intake passage even during supercharging by the turbocharger 21. It became.

  More specifically, FIG. 2 shows the supercharging region and the LP-EGR region of this embodiment in an overlapping manner. In FIG. 2, the case where the pressure of the intake collector 4b is atmospheric pressure is indicated by a broken line. In the present embodiment, a region where the pressure of the intake collector 4b is higher than the atmospheric pressure (region above the broken line) is a supercharging region, and a region where the pressure of the intake collector 4b is equal to or lower than the atmospheric pressure (region below the broken line) is not. It is a supercharged area. On the other hand, the LP-EGR region has a substantially isosceles trapezoidal shape as a whole, and the LP-EGR region is largely generated in the supercharging region in this embodiment.

  For this reason, in this embodiment, the operation region is divided into four regions as follows.

<1> Supercharging region and LP-EGR region (region surrounded by B-C-D-E)
<2> Supercharging region and non-LP-EGR region (region indicated by hatching)
<3> Non-supercharging region and LP-EGR region (region surrounded by ABEF)
<4> Non-supercharging region and non-LP-EGR region Here, in FIG. 2, the corners of the isosceles trapezoid are A, C, D, and F, and the points where the isosceles trapezoid and the broken line intersect are B and E. Further, both ends of the broken line are G and J, and the GH-I line is a line at full load. Note that the LP-EGR region is not limited to a substantially isosceles trapezoidal shape as a whole. If the specifications of the engine, turbocharger, and LP-EGR device 14 are different, the shape of the LP-EGR region may be different.

  As shown in FIG. 1, the present embodiment further includes a bypass passage 31 that bypasses the compressor 23. The bypass passage 31 is provided with a recirculation valve 32 driven by a motor (rotating electric machine) 33. This valve 32 recirculates (recirculates) the pressurized air confined in the intake pipe 4a from the throttle valve 5 to the compressor 23 upstream of the compressor 23 when the throttle valve 5 is closed for vehicle deceleration. It is for making it happen. On the other hand, when turbocharging is performed by the turbocharger 21 in an operating region other than when the vehicle is decelerating, the valve 32 is basically fully closed and air upstream of the compressor 23 (including EGR gas). ) Are all guided to the compressor 23.

  Here, the reason why the recirculation valve 32 is necessary is that the handling of the throttle valve differs between the diesel engine and the gasoline engine. That is, in a diesel engine, the throttle valve is always open and is closed only when necessary. On the other hand, in a gasoline engine, the throttle valve 5 is provided immediately upstream of the intake collector 4b, and its opening changes in response to the amount of depression of the accelerator pedal.

  Due to such a difference, in the gasoline engine, when the accelerator pedal is returned to decelerate the vehicle from the state of being supercharged by the turbocharger 21, the throttle valve opening is increased by a certain amount in response to this. Become smaller. Due to this sudden decrease in the throttle valve opening, there is no place for the pressurized air existing in the intake pipe 4 a from the throttle valve 5 to the compressor 23. In addition, the pressure of the intake pipe 4a from the throttle valve 5 to the compressor 23 further increases due to the operation of the compressor 23 when the vehicle is decelerated. Then, the air whose pressure is increased downstream of the compressor flows backward toward the compressor 23. Then, when the pressurized air that flows backward passes through the compressor 23 and escapes upstream, noise (noise) is generated from the compressor 23. Such noise generated during vehicle deceleration affects the quietness of the vehicle compartment. Therefore, when the vehicle is decelerated from the supercharging region, the valve 32 is switched from the fully closed state to the open state, and the pressurized air upstream of the compressor is bypassed the compressor 23 and released upstream (recirculation). This prevents the generation of noise during vehicle deceleration.

  Next, assuming that the EGR rate in the combustion chamber 7 when performing LP-EGR control using the LP-EGR device 14 is referred to as “LP-EGR rate”, the map characteristics of the basic LP-EGR rate are shown in FIG. It is like that. That is, as shown in FIG. 3, the substantially isosceles trapezoidal LP-EGR region as a whole is roughly divided into two, 10% in the high load region and 20% in the low load region.

  The reason why the basic LP-EGR rate is made smaller in the high load side region than in the low load side region is as follows. That is, if the fresh air can be pushed into the cylinder 7 by the turbocharger even on the high load side, the basic LP-EGR rate can be set to 20% on the high load side as well as on the low load side. However, even if fresh air is actually pushed into the cylinder 7 by the turbocharger, the amount of fresh air that can be pushed is limited. On the other hand, it is necessary to generate a larger engine torque on the high load side than on the low load side. Therefore, by reducing the basic LP-EGR rate in the range where knocking does not occur on the high load side in the range where knocking does not occur, and improving the combustion state in the cylinder 7 by that amount, an engine larger than that on the low load side is obtained. Torque is obtained. In FIG. 3, the basic LP-EGR rate is set in two stages, but is not limited to the case where the basic LP-EGR ratio is set in two stages. The basic LP-EGR rate may be changed in three or more stages or continuously.

  Next, it is necessary to determine the LP-EGR valve opening so that the basic LP-EGR rate, which is the target value of the EGR rate in the combustion chamber 7, is obtained. Here, in this embodiment, the LP-EGR rate [%] is a value defined by the following equation.

LP-EGR rate = Qegrcyl / (Qcyl + Qegr) × 100
... (A)
Qcyl in the equation (A) is a fresh air amount [l] (this fresh air amount is hereinafter referred to as “cylinder fresh air amount”) flowing into the combustion chamber 7 in one intake stroke. The cylinder fresh air amount Qcyl is simply detected by the air flow meter 42. Specifically, since the air flow meter 42 detects a fresh air amount Qa [l / s] per unit time (this fresh air amount is simply referred to as “new air amount” hereinafter), the engine rotational speed Ne [rpm] is If they are different, the cylinder fresh air amount Qcyl is different. Therefore, the new air amount Qa detected by the air flow meter 42 is converted into the cylinder fresh air amount Qcyl using the engine rotational speed Ne.

  Qegrcyl in the equation (A) is the amount of EGR gas [1] flowing into the combustion chamber 7 in one intake stroke (this amount of EGR gas is hereinafter referred to as “cylinder EGR gas amount”). The cylinder EGR gas amount Qegrcyl can be obtained from the EGR gas amount Qegr [l / s] per unit time flowing through the LP-EGR valve 17. Hereinafter, the amount of EGR gas per unit time flowing through the LP-EGR valve 17 is also referred to as “EGR gas amount flowing through the LP-EGR valve 17” or simply “EGR gas amount”. When the engine speed Ne is different, the cylinder EGR gas amount Qegrcyl is different, and therefore, the EGR gas amount Qegr is converted into the cylinder EGR gas amount Qegrcyl using the engine rotational speed Ne. The EGR gas amount Qegr is determined by the differential pressure across the LP-EGR valve 17 (hereinafter also referred to as “LP-EGR differential pressure across the valve”) and the opening area of the LP-EGR valve 17.

  In the LP-EGR device 14, EGR gas flows from the exhaust pipe side upstream of the LP-EGR valve 17 to the intake pipe side downstream of the LP-EGR valve 17 due to the differential pressure across the LP-EGR valve. Here, the pressure on the intake pipe side which is the downstream side of the LP-EGR valve 17 is substantially equal to the pressure of the intake pipe 4a upstream of the compressor 23, that is, the atmospheric pressure. For this reason, the EGR gas is pushed into the intake pipe 4a upstream of the compressor with the pressure on the exhaust pipe side that is upstream of the LP-EGR valve 17.

  However, the branch portion of the EGR passage 15 (hereinafter referred to as “EGR extraction portion”) is not the exhaust pipe 11b upstream of the turbine 22, but the exhaust pipe 11b downstream of the turbine 22, specifically, the manifold catalyst 12 and This is an exhaust pipe 11 b between the main catalysts 13. In the exhaust pipe 11 b downstream of the turbine 22, only the manifold catalyst 12, the main catalyst 13, and the muffler 19 generate pressure. For this reason, the LP-EGR valve front-rear differential pressure is small in the first place, and what causes the LP-EGR valve front-rear differential pressure to change is the EGR gas amount Qegr flowing through the LP-EGR valve 17, that is, the above equation (A). The LP-EGR rate will be moved.

  In addition, since the EGR passage 15 connects the devices that actively change the pressure, for example, the throttle valve 5 and the waste gate valve 25, the new air amount Qa [l / s] entering the engine and The exhaust displacement Qexh [l / s] is proportional. The differential pressure across the LP-EGR valve is basically related to the new air amount Qa, and the differential pressure across the LP-EGR valve is also determined by the new air amount Qa. If the LP-EGR valve opening is set to 30 °, for example, and the basic LP-EGR rate is 10%, for example, even if the fresh air amount Qa changes (even if the throttle valve 5 is moved), the LP-EGR rate Can be made constant.

  Therefore, the LP-EGR valve is opened when the temperature of the exhaust pipe 11b downstream of the EGR extraction section (hereinafter referred to as “EGR extraction section downstream temperature”) is a temperature T0 (for example, 600 ° C.) in a steady state on the high load side. Suppose the degree is suitable. The temperature T0 in the steady state on the high load side, that is, the temperature at the time of adaptation, 600 ° C. is hereinafter referred to as “basic temperature”. Then, the LP-EGR valve opening degree adapted to obtain the basic LP-EGR rate at the basic temperature T0 is defined as “basic LP-EGR valve opening degree”. In the present embodiment, the case where the basic temperature T0 is 600 ° C. will be described, but the present invention is not limited to 600 ° C.

  In the LP-EGR device 14, if the basic LP-EGR rate is uniform at the basic temperature T0, the basic LP-EGR valve opening degree can be set almost the same. Thus, when the basic LP-EGR rate is 10% at the basic temperature T0, for example, the actual LP-EGR rate is also 10%.

  However, since the balance between the fresh air amount Qa and the exhaust amount Qexh is lost during acceleration / deceleration, the cylinder EGR gas amount Qegrcyl is the target EGR gas amount (the EGR gas amount in the combustion chamber corresponding to the basic LP-EGR rate) [l. ]. This is because, for example, when the throttle valve 5 is suddenly opened, the fresh air amount Qa increases with good response, but the exhaust amount Qexh continues the previous state for a while, so the balance between the new air amount Qa and the exhaust amount Qexh is lost. It is. During such acceleration / deceleration, the LP-EGR valve opening is already corrected.

  In the present embodiment, a situation different from instantaneous, such as acceleration / deceleration, is handled. For example, assume that the idle state continues in the non-LP-EGR region. Then, since the fresh air amount Qa is smaller in the idle state than in the high load state, the actual temperature of the downstream temperature of the EGR extraction section (this actual temperature of the EGR extraction section downstream temperature is also simply referred to as “actual temperature” hereinafter) Treal. The temperature is lower than the basic temperature T0. When shifting from the long idle state to the LP-EGR region, the exhaust pipe 11b is not warmed for a moment, so the actual temperature Treal remains lower than the basic temperature T0. If the actual temperature Treal remains low, the ventilation resistance of the exhaust pipe 11b is small and the gas easily passes through the exhaust pipe 11b, so the pressure generated on the upstream side of the LP-EGR valve 17 is small. Since the basic LP-EGR valve opening degree is adapted when the actual temperature Treal is the basic temperature T0, when the pressure on the upstream side of the LP-EGR valve decreases, the differential pressure across the LP-EGR valve decreases. When the differential pressure across the LP-EGR valve becomes smaller, the EGR gas amount Qegr becomes lower than when the basic temperature T0. When the EGR gas amount Qegr is lower than that at the basic temperature T0, the cylinder EGR gas amount Qegrcyl is reduced from the target EGR gas amount.

  This will be further described with reference to FIG. FIG. 4 shows a change when the engine operating point shifts from the non-LP-EGR region to the LP-EGR region by depressing the accelerator pedal and accelerating after a long idle state. However, the LP-EGR region here is an LP-EGR region having a basic LP-EGR rate of 10% of the two LP-EGR regions shown in FIG. In FIG. 4, the change in the basic LP-EGR rate is indicated by a solid line, the change in the actual temperature Treal at the downstream temperature of the EGR take-out part is indicated by a long broken line, and the change in the differential pressure across the LP-EGR valve is indicated by a long dashed line. A change in the LP-EGR rate estimated from the front-rear differential pressure is indicated by a short broken line. In addition, a change in actual LP-EGR rate (abbreviated as “actual LP-EGR rate” in the figure) is indicated by a short dashed line.

  Since the actual temperature Treal of the downstream temperature of the EGR extraction part in the idle state is on the lower side than the basic temperature T0, the actual temperature Treal increases from the lower side to the basic temperature T0 as shown by the long broken line in FIG. Transition. During the period when the actual temperature Treal is less than the basic temperature T0, the LP-EGR valve front-rear differential pressure becomes smaller than the LP-EGR valve front-rear differential pressure at the base temperature, as shown by the long dashed line in FIG. . As a result, the LP-EGR rate estimated from the differential pressure across the LP-EGR valve is lower than the basic LP-EGR rate, as indicated by a short broken line in FIG. While the estimated LP-EGR rate is lower than 10% of the basic LP-EGR rate, it becomes difficult for EGR gas to enter the combustion chamber. This means that the cylinder EGR gas amount Qegrcyl becomes insufficient below the target EGR gas amount.

  On the other hand, in the LP-EGR region, the basic ignition timing ADV0 is set according to the basic LP-EGR rate so that MBT (Minimum advance for the Best Torque) is obtained. The basic ignition timing ADV0 is set so that MBT is basically obtained in the non-LP-EGR region, but MBT is also obtained in the LP-EGR region where EGR gas is introduced into the combustion chamber 7. The basic ignition timing ADV0 is set. The basic ignition timing ADV0 in the LP-EGR region is a value that advances as the basic LP-EGR rate increases.

  As described above, if the cylinder EGR gas amount Qegrcyl is less than the target EGR gas amount and becomes insufficient, the basic ignition timing ADV0 at that time causes an over-advanced angle that deviates from the MBT. It is conceivable that knocking occurs when the over-advance angle deviates from the MBT.

  However, if the accelerator pedal opening is maintained and the same state continues, the exhaust temperature rises. As the exhaust gas temperature rises, the differential pressure across the LP-EGR valve increases, so the actual LP-EGR rate approaches the basic LP-EGR rate of 10%, as shown by the short dashed line in FIG. . However, it takes a long time such as several hundred seconds for the actual LP-EGR rate to approach the basic LP-EGR rate of 10%. In the meantime, knocking occurs, so some kind of treatment is required.

  Although the idle state has been described as the case where the actual temperature Treal of the downstream temperature of the EGR take-out portion before shifting to the LP-EGR region and the basic temperature T0 is on the low side, it is not limited to this case. For example, the following example can be given as a case where the actual temperature Treal of the downstream temperature of the EGR take-out portion before shifting to the LP-EGR region and the basic temperature T0 is on the low side. That is, immediately after the engine is started, before the engine warm-up is completed, the fuel cut is continued, the idle stop is continued, the EV traveling is continued in the hybrid vehicle (engine stopped state), and the like.

  The above is the case where the engine operating point shifts from the non-LP-EGR region to the LP-EGR region, and the actual temperature Treal of the EGR take-out portion downstream temperature rises from the lower side and shifts to the basic temperature T0. Met.

  Next, consider a case where the engine operating point shifts from the non-LP-EGR region to the LP-EGR region by decelerating the vehicle from a state such as high-load traveling. In other words, when the operating point of the engine shifts from the non-LP-EGR region to the LP-EGR region, and when the actual temperature Treal of the downstream temperature of the EGR take-out portion decreases from the higher side and shifts to the basic temperature T0. It is. In this case, the LP-EGR valve front-rear differential pressure becomes higher than the LP-EGR valve front-rear differential pressure when the actual temperature Treal is higher than the basic temperature T0. As a result, the LP-EGR rate estimated from the differential pressure across the LP-EGR valve becomes larger than the basic LP-EGR rate. While the estimated LP-EGR rate is larger than the basic LP-EGR rate, EGR gas easily enters the combustion chamber. The cylinder EGR gas amount Qegrcyl exceeds the target EGR gas amount and becomes excessive.

  If the cylinder EGR gas amount Qegrcyl exceeds the target EGR gas amount and becomes excessive, the basic ignition timing ADV0 at that time becomes an over-retarded angle that deviates from MBT. It is conceivable that the combustion state in the combustion chamber 7 becomes worse when the over-delay angle deviates from the MBT.

  However, if the accelerator pedal opening degree is maintained and the same state is continued, the exhaust temperature decreases. As the exhaust gas temperature decreases, the differential pressure across the LP-EGR valve decreases, so the actual LP-EGR rate approaches the basic LP-EGR rate after the step change. However, it takes a long time such as several hundred seconds for the actual LP-EGR rate to approach the basic LP-EGR rate. In the meantime, the state of combustion in the combustion chamber 7 deteriorates, so some kind of treatment is required. There is a predetermined response delay before the change in the EGR gas amount Qegr passing through the LP-EGR valve 17 appears as the change in the cylinder EGR gas amount Qegrcyl. This response delay is an object to be considered when dealing with moments such as acceleration / deceleration. However, the delay until the actual temperature Treal of the EGR extraction section downstream temperature reaches the basic temperature T0 is as long as several hundred seconds as described above. If the response delay until the change in the EGR gas amount Qegr appears as the change in the cylinder EGR gas amount Qegrcyl is compared with this several hundred seconds, the change in the EGR gas amount Qegr becomes the change in the cylinder EGR gas amount Qegrcyl. The response delay until it appears is very small. Therefore, in the present invention, the response delay until the change in the EGR gas amount Qegr appears as the change in the cylinder EGR gas amount Qegrcyl can be ignored.

  Further, as shown in FIG. 4, in the region where the differential pressure before and after the LP-EGR valve at the initial stage of acceleration is particularly small, the LP-EGR rate estimated from the differential pressure before and after the LP-EGR valve (see the short dashed line in FIG. 4). The actual LP-EGR rate (see the short dashed line in FIG. 4) further decreases. This is because, in a region where the differential pressure across the LP-EGR valve is particularly small, the pressure pulsation of the exhaust is received, and the reverse flow occurs before and after the LP-EGR valve 17 (the LP-EGR valve 17 flows from the intake side toward the exhaust side). This is because a flow occurs. Hereinafter, a region where a back flow occurs because the differential pressure across the LP-EGR valve is particularly small is referred to as a “back flow region”.

  This will be further explained. FIG. 5 shows the pressure measured at the point L shown in FIG. 4, and FIG. 6 shows the pressures measured at the upstream and downstream sides of the LP-EGR valve 17 at the point M shown in FIG. It is. As shown in FIG. 6, when the pressure upstream of the LP-EGR valve 17 is higher than the pressure downstream of the LP-EGR valve 17, EGR gas flows from the upstream side to the downstream side. On the other hand, as shown in FIG. 5, when the pressure upstream of the LP-EGR valve 17 becomes lower than the pressure downstream of the LP-EGR valve 17, the EGR gas flows from the downstream side to the upstream side (reverse flow occurs). . The amount of EGR gas Qegr flowing through the LP-EGR valve 17 from the upstream side to the downstream side at the moment when the reverse flow occurs decreases. When the EGR gas amount Qegr in the case where the backflow is generated is lower than the EGR gas amount Qegr in the case where the backflow is not generated, the cylinder EGR gas amount Qegrcyl is further decreased below the target EGR gas amount by the decrease. Even if knocking does not occur in the cylinder EGR gas amount Qegrcyl when no backflow occurs, the basic ignition timing ADV0 when the cylinder EGR gas amount Qegrcyl decreases due to the decrease in the EGR gas amount Qegr caused by the backflow causes an advance angle. End up. As a result, knocking may occur. For this reason, another allowance is required for the backflow region.

  In this case, the differential pressure across the LP-EGR valve is detected by a differential pressure sensor, and the LP-EGR valve is opened so that the detected differential pressure across the LP-EGR valve matches a predetermined differential pressure across the LP-EGR valve. There are conventional devices that control the degree. According to this conventional apparatus, even if the actual temperature Treal of the EGR extraction section downstream temperature is deviated from the basic temperature T0, occurrence of knocking and instability of combustion in the combustion chamber can be avoided.

  However, when the differential pressure sensor is used as in the conventional apparatus, the LP-EGR valve front-rear differential pressure detected by the differential pressure sensor is greatly affected by the exhaust pulsation and fluctuates. For this reason, in order to separate the influence of exhaust pulsation from the differential pressure across the LP-EGR valve detected by the differential pressure sensor, it is necessary to perform filtering. This filtering requires high accuracy and high speed processing, which increases costs. In addition, a delay occurs in the signal after filtering.

  Therefore, in the first embodiment of the present invention, the downstream temperature of the EGR take-out part is used instead of the differential pressure across the LP-EGR valve. That is, the first correction magnification Rhos1 (temperature difference correction amount) corresponding to the temperature difference between the actual temperature Treal of the EGR extraction section downstream temperature and the basic temperature T0 is introduced. When the operating point of the engine shifts from the non-EGR region to the EGR region and the actual temperature Treal shifts to the basic temperature T0, the basic LP-EGR valve opening is set at the first correction magnification Rhos1. The target EGR valve opening is corrected and corrected.

  Specifically, when the actual temperature Treal increases from the low side and shifts to the basic temperature T0, the basic LP-EGR valve opening is corrected to the increasing side with the first correction magnification Rhos1. On the other hand, when the actual temperature Treal decreases from the higher side and shifts to the basic temperature T0, the basic LP-EGR valve opening is corrected to the decreasing side with the first correction magnification Rhos1.

  The origin of the LP-EGR valve differential pressure is the downstream temperature of the EGR extraction section. Here, the EGR take-out portion downstream temperature is originally slow in response. Moreover, although the subject of this invention is a problem which arises regarding the gas flow of the exhaust pipe 11b, the movement of the gas flow of this exhaust pipe 11b is also slow originally. For this reason, even if the EGR extraction portion downstream temperature, which is originally slow in response, is adopted, there is no delay with respect to the problems that occur with respect to the gas flow in the exhaust pipe 11b, and there are some cases that follow. The image is an image in which pressure is not detected directly but pressure that is not jagged under the influence of exhaust pressure pulsation is indirectly detected.

  Since the actual temperature Treal of the downstream temperature of the EGR take-out portion is detected, an expensive filtering process required when the differential pressure sensor is adopted is not necessary. As a result, the cost can be reduced as compared with the case where a differential pressure sensor is employed. It is possible to avoid knocking and instability of combustion while the actual temperature Treal deviates from the basic temperature T0 with an inexpensive configuration without using a differential pressure sensor.

  Further, in the reverse flow region, although it is the LP-EGR region, a second correction magnification (second correction amount) Rhos2 is introduced, and the basic LP-EGR valve opening is further increased using the second correction magnification Rhos2. to correct. This prevents the cylinder EGR gas amount Qegrcyl from falling short of the target EGR gas amount even in the reverse flow region.

  This embodiment will be further described with reference to FIGS. First, FIG. 7 is a timing chart when the operating point shifts to the high load side LP-EGR region by accelerating by depressing the accelerator pedal from a long state (for example, an idle state) in the low load side non-LP-EGR region. It is. Here, it is assumed that the LP-EGR region of the migration destination is an LP-EGR region having a basic LP-EGR rate of 10% among the two LP-EGR regions shown in FIG. In this case, the operating point of the engine becomes a reverse flow region immediately after shifting to the LP-EGR region, and then shifts to the non-reverse flow region. In FIG. 7, the accelerator opening APO, the LP-EGR valve opening, the correction magnification, the LP-EGR rate, the LP-EGR valve front-rear differential pressure, the EGR outlet downstream temperature, and the LP-EGR valve reverse flow from the top are shown. The model shows how it changes.

  First, the case of the comparative example which is the premise of the present embodiment will be described, and then the case of the present embodiment will be described. Here, the first and second correction magnifications Rhos1 and Rhos2 that are not introduced as in the present embodiment are used as comparative examples.

  When the accelerator pedal is depressed at the timing t1, the accelerator opening increases stepwise from the predetermined value APO1 to the predetermined value APO2 as shown in the first stage of FIG. From the timing of t3, the predetermined value APO2 is constant. The basic LP-EGR rate usually increases stepwise from, for example, zero to 10% simultaneously with the change in the accelerator opening (see the solid line in the fourth stage in FIG. 7). The basic LP-EGR valve opening corresponding to the basic LP-EGR rate also usually increases stepwise simultaneously with the change in the accelerator opening (see the second solid line in FIG. 7).

  The actual temperature Treal of the downstream temperature of the EGR take-out portion does not reach the basic temperature T0 instantly, but gradually increases from the timing t1 toward the basic temperature T0 as shown by the solid line in the sixth stage of FIG. . As the actual temperature Treal increases, the actual differential pressure of the LP-EGR valve front-rear differential pressure gradually increases from the timing t1 toward the target differential pressure, and coincides with the target differential pressure at the timing t6 (FIG. 7 Refer to the solid line on the fifth stage). The target differential pressure is a differential pressure across the LP-EGR valve corresponding to the basic temperature T0.

  In the case of the comparative example, the EGR gas amount Qegr that passes through the LP-EGR valve 17 during the period from t1 to t6 when the actual differential pressure of the LP-EGR valve front-rear differential pressure is lower than the target differential pressure is the basic temperature T0. It is lower than when When the EGR gas amount Qegr is lower than that at the basic temperature T0, the cylinder EGR gas amount Qegrcyl becomes lower than the target EGR gas amount and becomes insufficient. Therefore, as indicated by a two-dot chain line in the fourth row of FIG. 7, the actual LP-EGR rate (abbreviated as “actual LP-EGR rate” in FIG. 7) is a basic LP-EGR rate that changes in steps. It responds late, and approaches the basic LP-EGR rate as time elapses from t1. The actual LP-EGR rate coincides with the basic LP-EGR rate at timing t6 when the basic temperature is reached.

  Thus, even if the actual LP-EGR rate is less than 10% of the basic LP-EGR rate, the engine controller 41 has an EGR gas amount (= target EGR gas amount) with a basic LP-EGR rate of 10%. The basic ignition timing ADV0 is calculated on the assumption that it has been introduced into the combustion chamber 7. The actual LP-EGR rate is less than 10% of the basic LP-EGR rate (that is, EGR gas is insufficiently entered into the combustion chamber 7), and knocking occurs.

  Next, the case of this embodiment will be described. In the present embodiment, first and second correction magnifications Rhos1 and Rhos2 are newly introduced, and a value obtained by multiplying the basic LP-EGR valve opening VOegr0 by the first and second correction magnifications Rhos1 and Rhos2 is set to the target LP−. Calculated as the EGR valve opening tVOegr. Specifically, the first and second correction magnifications Rhos 1 and Rhos 2 are increased stepwise from 1.0 to the predetermined values 1 and 2 from the timing t 1, and thereafter decreased with the passage of time. The predetermined values 1 and 2 are initial values of the first and second correction magnifications Rhos1 and Rhos2.

  Here, the first and second correction magnifications Rhos1 and Rhos2 are both values centered on 1.0. The predetermined value 1 which is an initial value of the first correction magnification Rhos1 is calculated according to a temperature difference ΔT0 (= T0−Treal) obtained by subtracting the actual temperature Treal of the EGR extraction section downstream temperature from the basic temperature T0. The predetermined value 2, which is the initial value of the first correction magnification Rhos1, corresponds to the backflow region and is given as a constant value.

  The first correction magnification Rhos1 increases stepwise from 1.0 to the predetermined value 1 at the timing t2 immediately after the operating point shifts to the LP-EGR region as shown in the third row of FIG. From the timing of t2, it gradually approaches 1.0 as the actual temperature Treal approaches the basic temperature T0, and becomes 1.0 at the timing of t6 that coincides with the basic temperature T0 (see the third stage in FIG. 7). ). The reason why the first correction magnification Rhos1 is given with a value that gradually decreases from the initial value with the predetermined value 1 as an initial value in this way corresponds to the fact that the temperature difference ΔT0 gradually decreases from the timing t1. Because.

  On the other hand, the second correction magnification Rhos2 increases stepwise from 1.0 to a predetermined value 2 at the timing t2 immediately after the operating point shifts to the LP-EGR region as shown in the third row of FIG. . From the timing of t2, it gradually approaches 1.0 and reaches 1.0 at the timing of t4 when the backflow region ends (see the third stage in FIG. 7). The reason why the second correction magnification Rhos2 is given with a value that gradually decreases from the initial value with the predetermined value 2 as the initial value is that the LP-EGR valve reverse flow rate that increases stepwise from the timing of t1 gradually increases. This is to cope with the reduction in size.

  In this case, a value obtained by multiplying the first and second correction magnifications Rhos1 and Rhos2 is again set as a correction magnification Rhos (= Rhos1 × Rhos2). For this reason, the slope of decrease differs between the correction magnification Rhos up to t4 and the correction magnification Rhos after t4, and the slope of decrease in the correction magnification Rhos up to t4 is larger than the slope of decrease in the correction magnification Rhos after t4. Yes. Since the characteristic of the correction magnification Rhos after t4 is also expressed by a broken line, the inclination of the decrease in the correction magnification Rhos up to t5 is larger than the inclination of the decrease in the correction magnification Rhos after t5.

  A target LP-EGR valve opening degree tVOegr, which is a value obtained by multiplying the basic LP-EGR valve opening degree VOegr0 by the correction magnification Rhos, is zero from t1 to t2 as indicated by a one-dot chain line in the second stage of FIG. In a stepwise manner, the value increases to a predetermined value (= predetermined value 1 × predetermined value 2). From the timing of t2, the basic LP-EGR valve opening gradually approaches the basic LP-EGR valve opening as the actual temperature Treal rises to the basic temperature T0 (see the one-dot chain line in the second stage in FIG. 7). The target LP-EGR valve opening degree tVOegr matches the basic LP-EGR valve opening degree VOegr0 at the timing of t6.

  According to the present embodiment, the target LP-EGR valve opening degree tVOegr is made larger than the basic LP-EGR valve opening degree VOegr0 (in the case of the comparative example), so that the EGR gas amount Qegr passing through the LP-EGR valve 17 is More than at the base temperature T0. When the EGR gas amount Qegr increases from that at the basic temperature T0, the cylinder EGR gas amount Qegrcyl matches the target EGR gas amount. Accordingly, in the present embodiment, as indicated by a one-dot chain line in the fourth row in FIG. 7, the actual LP-EGR rate coincides with the basic LP-EGR rate in the period from t1 to t6. The basic LP-EGR rate VOegr0 can be obtained even when the actual temperature Treal is decreased from the basic temperature T0 in the period from t1 to t6.

  Next, FIG. 8 shows the timing when the operating point shifts to the low load side LP-EGR region by decelerating the accelerator pedal from the state that has been in the non-LP-EGR region on the high load side for a long time, such as on an expressway. It is a chart. In other words, when the operating point of the engine shifts from the non-LP-EGR region to the LP-EGR region, and when the actual temperature Treal of the downstream temperature of the EGR take-out portion decreases from the higher side and shifts to the basic temperature T0. It is a timing chart. In this case, a backflow region does not occur. Also in FIG. 8, the accelerator opening APO, the LP-EGR valve opening, the correction magnification, the LP-EGR rate, the LP-EGR valve front-rear differential pressure, the EGR outlet downstream temperature, and the LP-EGR valve reverse from the top as in FIG. The model shows how the flow rate changes.

  First, the case of the comparative example which is the premise of the present embodiment will be described, and then the case of the present embodiment will be described.

  In the highway driving state before t11, the actual temperature Treal is higher than the basic temperature T0. When the accelerator pedal is returned from this state at the timing t11, the accelerator opening decreases stepwise from the predetermined value APO3 to the predetermined value APO4 as shown in the first stage of FIG. The predetermined value APO4 is constant from the timing of t13. The basic LP-EGR rate usually increases stepwise, for example, from zero to 10% simultaneously with the change in the accelerator opening (see the solid line in the fourth stage in FIG. 8). The basic LP-EGR valve opening corresponding to the basic LP-EGR rate also usually increases stepwise simultaneously with the change in the accelerator opening (see the second solid line in FIG. 8).

  The actual temperature Treal does not reach the basic temperature T0 in an instant, and gradually decreases from the timing t11 toward the basic temperature T0 as shown by the solid line in the sixth row of FIG. As the actual temperature Treal decreases, the actual differential pressure of the LP-EGR valve front-rear differential pressure gradually decreases from the timing t11 toward the target differential pressure, and coincides with the target differential pressure at the timing t16 (FIG. 8 FIG. 8). (See the solid line on the fifth row). The target differential pressure is a differential pressure across the LP-EGR valve corresponding to the basic temperature T0.

  In the case of the comparative example, the EGR gas amount Qegr passing through the LP-EGR valve 17 during the period from t11 to t16 when the actual differential pressure of the LP-EGR valve front-rear differential pressure is higher than the target differential pressure is the basic temperature T0. It increases more than When the EGR gas amount Qegr increases from that at the basic temperature T0, the cylinder EGR gas amount Qegrcyl exceeds the target EGR gas amount and becomes excessive. For this reason, as indicated by a two-dot chain line in the fourth row of FIG. 8, the actual LP-EGR rate (abbreviated as “actual LP-EGR rate” in FIG. 7) is changed to the basic LP-EGR rate. Respond late. The actual LP-EGR rate was far from the basic LP-EGR rate at the timing of t11, but the actual LP-EGR rate approached the basic LP-EGR rate as time elapsed from t11, and the basic temperature It coincides with the basic LP-EGR rate at timing t16 when T0 is reached.

  Thus, even if the actual LP-EGR rate exceeds 10% of the basic LP-EGR rate, the engine controller 41 burns the EGR gas amount (target EGR gas amount) with the basic LP-EGR rate of 10%. The basic ignition timing ADV0 is calculated on the assumption that it has been introduced into the chamber 7. The actual LP-EGR rate exceeds 10% of the basic LP-EGR rate (EGR gas enters the combustion chamber 7), and the combustion in the combustion chamber 7 deteriorates.

  Next, the case of this embodiment will be described. In the present embodiment, a first correction magnification Rhos1 is newly introduced, and a value obtained by multiplying the first correction magnification Rhos1 by the basic LP-EGR valve opening VOegr0 is calculated as the target LP-EGR valve opening tVOegr. Specifically, the correction magnification 1 is decreased stepwise from 1.0 to a predetermined value 3 from the timing of t11, and thereafter increased with the passage of time. The predetermined value 3 is an initial value of the first correction magnification Rhos1.

  Here, the first correction magnification Rhos1 is a value centered at 1.0. The predetermined value 3, which is an initial value of the first correction magnification Rhos1, is calculated according to a temperature difference ΔT2 (= Treal−T0) obtained by subtracting the basic temperature T0 from the actual temperature Treal of the EGR extraction section downstream temperature.

  The first correction magnification Rhos1 is stepped from 1.0 to a predetermined value 3 (positive value) at the timing t12 immediately after the operating point shifts to the LP-EGR region as shown in the third row of FIG. Becomes smaller. From the timing of t12, the actual temperature Treal gradually approaches 1.0 as the temperature approaches the basic temperature T0, and becomes 1.0 at the timing of t16 that coincides with the basic temperature T0 (see the third stage in FIG. 8). ). The reason why the first correction magnification Rhos1 is given with a value that gradually increases from the initial value with the predetermined value 3 as an initial value in this way corresponds to the fact that the temperature difference ΔT2 gradually decreases from the timing of t11. Because.

  A target LP-EGR valve opening degree tVOegr, which is a value obtained by multiplying the basic LP-EGR valve opening degree VOegr0 by the first correction magnification Rhos1, increases stepwise from zero from t11 to t12. In this case, since the first correction magnification Rhos1 is a value smaller than 1.0, the target LP-EGR valve opening tVOegr is set to the basic LP-EGR valve opening as shown by the one-dot chain line in the second stage of FIG. It becomes stepwise with a smaller inclination than the degree inclination. From the timing of t13, as the actual temperature Treal decreases to the basic temperature T0, the basic LP-EGR valve opening gradually approaches the basic LP-EGR valve opening degree (refer to the one-dot chain line in the second stage in FIG. 8). The target LP-EGR valve opening degree tVOegr coincides with the basic LP-EGR valve opening degree VOegr0 at the timing of t16.

  According to this embodiment, the target LP-EGR valve opening degree tVOegr is made smaller than the basic LP-EGR valve opening degree VOegr0 (in the case of the comparative example), so that the EGR gas amount Qegr passing through the LP-EGR valve 17 is Lower than at the basic temperature T0. When the EGR gas amount Qegr is lower than that at the basic temperature T0, the cylinder EGR gas amount Qegrcyl matches the target EGR gas amount. Accordingly, in the present embodiment, as indicated by a one-dot chain line in the fourth row of FIG. 8, the actual LP-EGR rate coincides with the basic LP-EGR rate in the period from t11 to t16. The basic LP-EGR rate VOegr0 is obtained even when the actual temperature Treal is rising from the basic temperature T0 in the period from t11 to t16.

  As shown in FIG. 1, in addition to the fuel injection valve 8 and the spark plug 9, an engine controller 41 is provided to control the LP-EGR valve 17, the waste gate valve 25, and the recirculation valve 32. The engine controller 41 is configured as a computer unit including peripheral devices such as a microprocessor, ROM, and RAM. The engine controller 41 receives signals from the air flow meter 42, the accelerator sensor 43, the crank angle sensor 44, the temperature sensor 46, and the knock sensor 47. Here, the air flow meter 42 detects the amount of fresh air Qa (mass flow rate) flowing into the intake pipe 4a. The accelerator sensor 43 detects the amount of accelerator pedal depression (accelerator opening) and the amount of change. The crank angle sensor 44 detects the engine speed Ne. The temperature sensor 46 detects the actual temperature of the downstream temperature of the EGR extraction unit. The knock sensor 47 detects knocking that occurs in the combustion chamber 7.

  The control performed by the engine controller 41 will be described with reference to the following flowchart.

  First, the flowcharts of FIGS. 9A, 9B, and 14 are for calculating the target LP-EGR valve opening. 9A and 9B is a flow in the case where the operating point shifts from the non-LP-EGR region to the LP-EGR region, and the actual temperature Treal increases from the low side and shifts to the basic temperature T0. This is for calculating the target LP-EGR valve opening. 9A, 9B, and 14 are executed at regular intervals (for example, every 10 ms).

  9A and 9B will be described. In step 1, it is determined whether or not the engine operating point is in the LP-EGR region shown in FIG. When the operating point is in the LP-EGR region, the process proceeds to step 2. In step 2, it is checked whether or not the acceleration flag (initially set to zero when the engine is started) = 1. Here, the process proceeds to step 3 assuming that the acceleration flag = 0.

  In step 3, an accelerator opening change amount per predetermined time (hereinafter simply referred to as “accelerator opening change amount”) ΔAPO is calculated based on the accelerator opening APO detected by the accelerator sensor 43.

  For example, the accelerator opening change amount ΔAPO is calculated by subtracting the accelerator opening before a predetermined time from the current accelerator opening, that is, the following expression.

ΔAPO = APO−APOz (1)
Where APOz: accelerator opening before a predetermined time,
ΔAPO in equation (1) is a positive value during acceleration and a negative value during deceleration.

  In step 4, the absolute value | ΔAPO | of the accelerator opening change amount is compared with a predetermined value A. The predetermined value A is set in advance as a value for determining whether or not it is a transition time (acceleration and deceleration). When the absolute value | ΔAPO | of the accelerator opening change amount exceeds the predetermined value A, it is determined that the engine is in transition, and the process proceeds to Step 5.

  In step 5, the accelerator opening change amount ΔAPO is compared with zero. When the accelerator opening change amount ΔAPO exceeds zero, that is, when the accelerator opening change amount ΔAPO is positive, it is determined that the vehicle is accelerating, and the routine proceeds to step 6 to set the acceleration flag = 1. In other words, it is determined from steps 1, 4 and 5 that the vehicle is currently in the LP-EGR region by acceleration, that is, the operating point has shifted from the non-LP-EGR region to the LP-EGR region by acceleration.

  In step 7, a value obtained by subtracting the actual temperature Treal [° C.] of the downstream temperature of the EGR extraction portion detected by the temperature sensor 46 from the basic temperature T 0 [° C.] (for example, about 600 ° C.) is defined as a temperature difference ΔT 0 [° C.] That is, the temperature difference ΔT0 is calculated by the following equation.

ΔT0 = T0−Treal (2)
In step 8, a first correction magnification Rhos1 [anonymous number] is calculated by searching a table having the contents shown in FIG. 10 from the temperature difference ΔT0. More specifically, when the table search value is a predetermined value 1, this predetermined value 1 is entered in the first correction magnification Rhos1. Here, the predetermined value 1 is a value for giving an initial value of the first correction magnification Rhos1. As shown in FIG. 10, the predetermined value 1 is a value centered at 1.0, and is a value that increases as the temperature difference ΔT0 increases.

  Steps 9 to 13 in FIG. 9B are parts for selecting different backflow region maps depending on which of the three temperature ranges the actual temperature Treal detected by the temperature sensor 46 is in. Here, there are the following three temperature ranges of the actual temperature Treal.

[1] When the actual temperature Treal is within the allowable range (T1 ± ε, where the allowable value ε> 0) centered on the predetermined temperature T1,
[2] When the actual temperature Treal is lower than the lower limit (T1-ε) of the allowable range,
[3] When the actual temperature Treal is higher than the upper limit (T1 + ε) of the allowable range,
There are three backflow region maps: the basic backflow region map shown in FIG. 11, the enlarged backflow region map shown in FIG. 12, and the reduced backflow region map shown in FIG.

  If the actual temperature Treal is within the allowable range (T1 ± ε) centered on the predetermined temperature T1 in step 9 of FIG. 9B, the process proceeds to step 10 of FIG. 9B to select a basic backflow region map and backflow. Put in region map. When the actual temperature Treal is not within the allowable range (T1 ± ε) centered on the predetermined temperature T1 in step 9, the process proceeds to step 11 in FIG. 9B. When the actual temperature Treal is lower than the lower limit (T1-ε) of the allowable range in step 11, the process proceeds to step 12 in FIG. 9B, and the enlarged backflow region map is selected and put in the backflow region map. If the actual temperature Treal is not below the lower limit (T1-ε) of the allowable range in step 11, the process proceeds to step 13 in FIG. 9B. If the actual temperature Treal exceeds the upper limit (T1 + ε) of the allowable range in step 13, the process proceeds to step 13 in FIG. 9B, and the reduced backflow area prohibition map is selected and entered into the backflow area map. As shown in FIGS. 11, 12, and 13, each reverse flow region map has a reverse flow in a region where the differential pressure across the LP-EGR valve is particularly small on the map where the horizontal axis is the engine speed Ne and the vertical axis is the engine torque. It is predetermined as an area.

  In FIG. 12, the backflow region is expanded to the high load side and the high rotation speed side compared to the case of FIG. This is due to the following reason. In other words, the reverse flow region is determined on the basic reverse flow region map when the actual temperature Treal is within the allowable range of the predetermined temperature T1 (when the predetermined temperature condition is satisfied). When the actual temperature Treal is lower than the predetermined allowable range of the temperature T1, the region where the EGR valve front-rear differential pressure becomes smaller than the predetermined temperature T1 due to the decrease in the downstream pressure of the EGR take-out portion, and no back flow occurs. But backflow will newly occur. As a result, the region where the reverse flow actually occurs is expanded to the higher load side and higher rotational speed side than the reverse flow region on the map. Therefore, when the actual temperature Treal is lower than the predetermined allowable range of the temperature T1, the backflow region is expanded to the high load side and the high rotation speed side in accordance with the newly generated backflow region. The downstream pressure of the EGR extraction part is the pressure of the intake pipe 11b downstream of the EGR extraction part.

  In FIG. 13, the backflow region is reduced to the low load side and the low rotational speed side as compared with the case of FIG. This is due to the following reason. In other words, the reverse flow region is determined on the basic reverse flow region map when the actual temperature Treal is within the allowable range of the predetermined temperature T1 (when the predetermined temperature condition is satisfied). When the actual temperature Treal is higher than the predetermined allowable range of the temperature T1, the region where the EGR valve downstream pressure becomes larger than the predetermined temperature T1 due to the increase in the downstream pressure of the EGR take-out portion, and the backflow has occurred. But no backflow occurs. As a result, the region where the reverse flow actually occurs is reduced to the lower load side and the lower rotation speed side than the reverse flow region on the map. Therefore, the reverse flow region is reduced to the low load side and the low rotational speed side in accordance with the reverse flow region that does not occur when the actual temperature Treal is higher than the predetermined allowable range of the temperature T1.

  In step 14 of FIG. 9B, the selected backflow region map is checked to determine whether or not the operating point determined from the engine speed Ne and the engine torque belongs to the backflow region. When the operating point belongs to the reverse flow region, the process proceeds to step 15 in FIG. 9B to calculate the second correction magnification Rhos2 [anonymous number]. Specifically, the predetermined value 2 is entered in the second correction magnification Rhos2. Here, the predetermined value 2 is a value for giving an initial value of the second correction magnification Rhos2. Similarly to the predetermined value 1, the predetermined value 2 is a value centered on 1.0, and here, a value exceeding 1.0 is adopted. The predetermined value 2 may be a constant value.

  On the other hand, when the operating point does not belong to the reverse flow region in step 14 of FIG. 9B, it is determined that it is not necessary to correct the basic LP-EGR valve opening degree VOegr0 for the reverse flow. At this time, the process proceeds to step 16 in FIG. 9B, and 1.0 is added to the second correction magnification Rhos2.

  In step 17 of FIG. 9B, a value obtained by multiplying the first correction magnification Rhos1 and the second correction magnification Rhos2 is again set as the correction magnification Rhos, that is, the correction magnification Rhos is calculated by the following equation.

Rhos = Rhos1 × Rhos2 (3)
In step 18 of FIG. 9B, a value obtained by multiplying the basic LP-EGR valve opening VOegr0 by the correction magnification Rhos is set as the target LP-EGR valve opening tVOegr, that is, the target LP-EGR valve opening is calculated by the following equation.

tVOegr = VOegr0 × Rhos (4)
The basic LP-EGR valve opening degree VOegr0 in the equation (4) is proportional to the basic LP-EGR rate, that is, the basic LP-EGR valve opening degree VOegr0 is calculated by the following expression.

VOegr0 = conversion coefficient × basic LP-EGR rate (5)
The conversion coefficient of equation (5) is a coefficient for converting the LP-EGR rate into the LP-EGR valve opening, and is obtained in advance.

  Since the acceleration flag is set to 1 in step 6 in FIG. 9A, the process proceeds from step 2 in FIG. 9A to step 19 in FIG. 9A from the next time. Step 19 in FIG. 9A is a portion for gradually reducing the correction magnification Rhos. That is, a value obtained by subtracting the positive predetermined value K from “Rhos (previous)” that is the previous value of the correction magnification is set as the current correction magnification Rhos, that is, the correction magnification Rhos is updated by the following equation.

Rhos = Rhos (previous) -K (6)
The initial value of “Rhos (previous)” is a predetermined value 1 × predetermined value 2. The predetermined value K in the equation (6) is a value for determining the correction period of the basic LP-EGR valve opening VOegr0 to the extent that the correction magnification Rhos is gradually decreased. As the value of K increases, the correction magnification Rhos decreases rapidly (the correction period decreases), and as the value of K decreases, the correction magnification Rhos decreases gradually (the correction period increases). In the case of the comparative example, the predetermined value K is obtained in advance by adaptation so that the correction magnification Rhos becomes 1.0 when the actual LP-EGR rate coincides with the basic LP-EGR rate.

  In step 20 of FIG. 9A, the correction magnification Rhos is compared with 1.0. After proceeding to step 19 in FIG. 9A for the first time from the acceleration flag = 1.0, the correction magnification Rhos is greater than 1.0, so the process proceeds to step 18 in FIG. 9B. In step 18 in FIG. 9B, a value obtained by multiplying the basic LP-EGR valve opening VOegr0 by the correction magnification Rhos at this time is calculated as the target LP-EGR valve opening tVOegr.

  By repeating the operation in step 19 in FIG. 9A, the correction magnification Rhos gradually decreases to 1.0. As long as the correction magnification Rhos that is gradually reduced does not become less than 1.0, the operation of Step 18 in FIG. 9B is executed.

  By repeating the operation in step 19 in FIG. 9A, the correction magnification Rhos becomes less than 1.0 in step 20 in FIG. 9A. At this time, it is determined that it is time to end the correction of the basic LP-EGR valve opening degree VOegr0, and the process proceeds to step 21 of FIG. 9A to set 1.0 to the correction magnification Rhos. In step 22 of FIG. 9A, the current correction of the basic LP-EGR valve opening is terminated, and the acceleration flag = 0 is set in preparation for the next correction.

  Steps 23 to 27 in FIG. 9B are parts for limiting the target LP-EGR valve opening to the upper limit value VOmax. First, in step 23, an upper limit flag (initially set to zero when the engine is started) is checked. Here, it is assumed that the upper limit flag = 0, and the process proceeds to step 24 in FIG. 9B.

  In step 24, the target LP-EGR valve opening tVOegr is compared with the upper limit value VOmax of the LP-EGR valve opening. When the target LP-EGR valve opening tVOegr exceeds the upper limit value VOmax of the LP-EGR valve opening, the process proceeds to steps 25, 26, and 27 in FIG. 9B. In step 25, the upper limit flag is set to 1, and in step 26, the value of the target LP-EGR valve opening tVOegr is moved to the target LP-EGR valve opening calculated value tVOegr1 and stored.

  In step 27, an upper limit value VOmax is set to the target LP-ER valve opening tVOegr. Here, the above “upper limit value” is an upper limit of the LP-EGR valve opening determined mechanically. The reason why the target LP-EGR valve opening degree tVOegr is limited to the upper limit value VOmax when the target LP-EGR valve opening degree tVOegr exceeds the upper limit value VOmax is as follows. That is, since the target LP-EGR valve opening tVOegr is a calculated value, the calculated target LP-EGR valve opening tVOegr may exceed the upper limit value VOmax. In this case, even if the target LP-EGR valve opening tVOegr is commanded to the motor 18 that is the actuator of the LP-EGR valve 17, the LP-EGR valve opening cannot be increased until the upper limit VOmax is exceeded. Therefore, when the target LP-EGR valve opening degree tVOegr exceeds the upper limit value VOmax, the target LP-EGR valve opening degree tVOegr is limited to the upper limit value VOmax.

  The reason why the calculated value tVOegr1 of the target LP-EGR valve opening is stored when the target LP-EGR valve opening tVOegr is limited to the upper limit value VOmax is as follows. That is, the EGR gas amount Qegr is insufficient by the difference between the upper limit value VOmax and the calculated value tVOegr1, and the cylinder EGR gas amount Qegrcyl is insufficient below the target EGR gas amount. Even when the cylinder EGR gas amount Qegrcyl falls short of the target EGR gas amount, knocking may occur if ignition is performed at the basic ignition timing ADV0. Therefore, the basic ignition timing ADV0 is corrected to the retard side in accordance with the difference between the upper limit value VOmax and the calculated value tVOegr1 (see steps 64 and 65 in FIG. 16B). For this purpose, the calculated value tVOegr1 is stored. This is necessary.

  Since the upper limit flag is set to 1 in step 25 in FIG. 9B, the process proceeds from step 23 in FIG. 9B to step 28 in FIG. 9B from the next time. In step 28, the target LP-EGR valve opening tVOegr is again compared with the upper limit value VOmax. When the target LP-EGR valve opening tVOegr exceeds the upper limit value VOmax, the operations of steps 25, 26 and 27 are executed. As long as the target LP-EGR valve opening tVOegr exceeds the upper limit value VOmax in step 28, the operations of steps 25, 26, and 27 are repeated.

  On the other hand, when the target LP-EGR valve opening tVOegr becomes equal to or lower than the upper limit value VOmax in step 28, it is determined that it is not necessary to limit the target LP-EGR valve opening tVOegr to the upper limit value VOmax. At this time, the process proceeds to step 29 in FIG. 9B and returns to the upper limit flag = 0.

  By setting the upper limit limit flag in this manner, the upper limit limit flag = 1 when the target LP-EGR valve opening tVOegr is limited to the upper limit value VOmax. In other words, the upper limit restriction flag = 1 indicates that the target LP-EGR valve opening tVOegr is restricted to the upper limit value VOmax.

  Next, the flow of FIG. 14 will be described. The flow of FIG. 14 is a target LP-EGR valve when the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature Treal decreases from the higher side and shifts to the basic temperature T0. This is for calculating the opening.

  First, in step 31, it is determined whether or not the engine operating point is in the LP-EGR region shown in FIG. When the operating point is in the LP-EGR region, the process proceeds to step 32. In step 32, it is determined whether or not the deceleration flag (initially set to zero when the engine is started) = 1. Here, assuming that the deceleration flag = 0, the process proceeds to step 33.

  In step 33, the accelerator opening change amount ΔAPO is calculated based on the accelerator opening APO detected by the accelerator sensor 43.

  In step 34, the absolute value | ΔAPO | of the accelerator opening change amount is compared with a predetermined value C. The predetermined value C is set in advance as a value for determining whether or not it is a transition time (acceleration and deceleration). The predetermined value C may be the same value as the predetermined value A in step 4 of FIG. 9A. When the absolute value | ΔAPO | of the accelerator opening change amount exceeds the predetermined value C, it is determined that a transition is in progress, and the process proceeds to step 35.

  In step 35, the accelerator opening change amount ΔAPO is compared with zero. When the accelerator opening change amount ΔAPO is less than zero, that is, when the accelerator opening change amount ΔAPO is negative, it is determined that the vehicle is decelerating, and the routine proceeds to step 36 to set the deceleration flag = 1. In other words, it is determined from steps 31, 34, and 35 that the vehicle is currently in the LP-EGR region due to deceleration, that is, the operating point has shifted from the non-LP-EGR region to the LP-EGR region due to deceleration.

  In step 37, a value obtained by subtracting the basic temperature T0 (for example, about 600 ° C.) from the actual temperature Treal of the EGR take-out portion downstream temperature detected by the temperature sensor 46 is set as the temperature difference ΔT2 [° C.], that is, the temperature difference ΔT2 by the following equation. Is calculated.

ΔT2 = Treal−T0 (7)
In step 38, a first correction magnification Rhos1 [anonymous number] is calculated by searching a table having the contents shown in FIG. 15 from the temperature difference ΔT2. More specifically, if the table search value is a predetermined value 3, this predetermined value 3 is entered in the first correction magnification Rhos1. Here, the predetermined value 3 is a value for giving an initial value of the first correction magnification Rhos1. As shown in FIG. 15, the predetermined value 3 is a value centered at 1.0, and is a positive value that becomes smaller than 1.0 as the temperature difference ΔT2 increases.

  In step 39, the value obtained by multiplying the basic LP-EGR valve opening VOegr0 by the first correction magnification Rhos1 is set as the target LP-EGR valve opening tVOegr, that is, the target LP-EGR valve opening tVOegr is calculated by the following equation.

tVOegr = VOegr0 × Rhos1 (8)
Since the deceleration flag is set to 1 in step 36, the process proceeds from step 32 to step 40 onward from the next time. Step 40 is a portion for gradually decreasing the first correction magnification Rhos1. That is, a value obtained by subtracting the positive predetermined value L from “Rhos1 (previous)”, which is the previous value of the first correction magnification, is used as the first correction magnification Rhos1, that is, the first correction magnification Rhos1 is updated by the following equation. To do.

Rhos1 = Rhos1 (previous) -L (9)
The initial value of “Rhos (previous)” is a value of the predetermined value 1. The predetermined value L in the equation (9) is a value for determining the degree of gradually decreasing the first correction magnification Rhos1 or the correction period of the basic LP-EGR valve opening VOegr0. As the value of L is larger, the first correction magnification Rhos1 is rapidly decreased (the correction period is shortened), and as the value of L is smaller, the correction magnification Rhos1 is gradually decreased (the correction period is lengthened). In the case of the comparative example, the predetermined value L is obtained in advance by adaptation so that the first correction magnification Rhos1 becomes 1.0 at the timing when the actual LP-EGR rate coincides with the basic LP-EGR rate.

  In step 41, the first correction magnification Rhos is compared with 1.0. After the process proceeds to step 40 for the first time from the deceleration flag = 1.0, the first correction magnification Rhos1 is larger than 1.0, so the process proceeds to step 39. In step 39, a value obtained by multiplying the basic LP-EGR valve opening VOegr0 by the first correction magnification Rhos1 at this time is calculated as the target LP-EGR valve opening tVOegr.

  By repeating the operation of step 40, the first correction magnification Rhos1 gradually decreases to 1.0. As long as the first correction magnification Rhos1 gradually decreased in this way does not become less than 1.0, the operation of step 39 is executed.

  By repeating the operation of step 40, the first correction magnification Rhos1 becomes less than 1.0 in step 41. At this time, it is determined that it is time to end the correction of the basic LP-EGR valve opening degree VOegr0, the process proceeds to step 42, and 1.0 is set to the first correction magnification Rhos1. In step 43, the correction of the current basic LP-EGR valve opening is terminated, and the deceleration flag = 0 is set in preparation for the next correction.

  In a flow not shown, the target LP-EGR valve opening tVOegr calculated by the flow of FIGS. 9A, 9B, and 16 is output to the motor 18 that is an actuator of the LP-EGR valve 17.

  Next, the flowcharts of FIGS. 16A and 16B are for calculating the ignition timing command value ADV. The flow of FIG. 16A and FIG. 16B is executed independently of the flow of FIG. 9A, FIG. 9B, and FIG. 14 at regular time intervals (for example, every 10 ms).

  In step 51 of FIG. 16A, the average value of the knock signal from the knock sensor 47 is compared with a predetermined slice level S / L. If the average value of the knock signal exceeds the rice level S / L, it is determined that knocking has occurred, and the routine proceeds to step 52 in FIG. 16A, where it is constant at “FB (previous)” which is the previous value of the feedback amount of the ignition timing. A value obtained by adding the value ΔE [°] is defined as a feedback amount FB [°]. The feedback amount FB is a correction amount for retarding the basic ignition timing ADV0. Here, knocking is avoided by retarding the basic ignition timing ADV0 by a fixed value ΔE. Note that the initial value of “FB (previous)” is zero.

  Due to the retardation of the basic ignition timing ADV0, the average value of the knock signal from the knock sensor 47 will be equal to or lower than the slice level S / L at step 51 in FIG. 16A next time. At this time, it is determined that knocking has not occurred, and the process proceeds to step 53 in FIG. 16A.

  In step 53 of FIG. 16A, a value obtained by subtracting a constant value ΔF [°] from “FB (previous)” which is the previous value of the feedback amount of the ignition timing is set as the feedback amount FB [°]. Since the feedback amount FB is a correction amount for retarding the basic ignition timing ADV0, the operation in step 53 indicates that the basic ignition timing ADV0 is advanced by a fixed value ΔF from the previous ignition timing command value. means. Here, the fixed value ΔF is set to a value smaller than the fixed value ΔE.

  If knocking occurs by the operations in steps 51 to 53 in FIG. 16A, the basic ignition timing ADV0 is retarded stepwise by a constant value ΔE, and if knocking does not occur thereafter, the ignition timing is gradually advanced by a constant value ΔF. Horn. When knocking occurs, the operation of retarding the ignition timing step by step by a constant value ΔE is repeated. As a result, the ignition timing is kept at the basic ignition timing ADV0 as much as possible while avoiding knocking.

  In step 54 of FIG. 9B, it is determined whether or not the engine operating point is in the LP-EGR region shown in FIG. When the operating point is in the non-LP-EGR region, the process proceeds to steps 55 and 56 in FIG. 9B.

  Steps 55 and 56 in FIG. 9B are parts for calculating the ignition timing command value ADV when the operating point is in the non-LP-EGR region. First, at step 55, the basic ignition timing ADV0 [° BTDC] at which MBT is obtained according to the operating point determined from the engine load and the rotational speed Ne is calculated.

  In step 56 of FIG. 9B, a value obtained by subtracting the feedback amount FB from the basic ignition timing ADV0 is used as the ignition timing command value ADV [° BTDC], that is, the ignition timing command value ADV is calculated by the following equation.

ADV = ADV0−FB (10)
Here, since the ignition timing command value ADV is a value measured from the compression top dead center to the advance side, the positive feedback amount FB is a correction amount for retarding the basic ignition timing ADV0.

  On the other hand, when the engine operating point is in the LP-EGR region in step 54 of FIG.

  Steps 57 to 67 in FIG. 9B are parts for calculating the ignition timing command value ADV when the operating point is in the LP-EGR region. First, in step 57 of FIG. 9B, the basic ignition timing ADV0 [° BTDC] is calculated so that MBT is obtained even when the operating point is in the LP-EGR region. However, since the cylinder EGR gas amount Qegrcyl is introduced into the combustion chamber 7 in the LP-EGR region, it is necessary to set the basic ignition timing ADV0 in consideration of the cylinder EGR gas amount Qegrcyl. Therefore, the LP-EGR region is considered to be in the same region in terms of operating point, and the cylinder EGR gas amount Qegrcyl is transferred to the combustion chamber 7 by searching a table having the contents shown in FIG. 17 from the basic LP-EGR rate. The basic ignition timing ADV0 is calculated so that MBT can be obtained even in the introduced state. As shown in FIG. 17, the basic ignition timing ADV0 in the LP-EGR region is a value that increases toward the advance side as the basic LP-EGR rate increases. This is due to the following reason. That is, the combustion state in the combustion chamber becomes worse as the basic LP-EGR rate increases. Therefore, by setting the basic ignition timing ADV0 to the advance side, the worsened combustion is stabilized.

  In step 58 of FIG. 16B, the actual temperature Treal of the downstream temperature of the EGR extraction portion detected by the temperature sensor 46 is compared with the basic temperature T0. When the actual temperature Treal is lower than the basic temperature T0, the process proceeds to steps 59, 60, and 67 in FIG.

  Steps 59, 60, and 67 in FIG. 16B are parts for correcting the basic ignition timing ADV0 to the retard side when the actual temperature Treal is lower than the basic temperature T0. In step 59, a value obtained by subtracting the actual temperature Treal from the basic temperature T0 is set as the temperature difference ΔT0 [° C.], that is, the temperature difference ΔT0 is calculated by the following equation.

ΔT0 = T0−Treal (11)
In step 60 of FIG. 16B, a temperature difference correction amount HOS1 [°] is calculated by searching a table having the contents shown in FIG. 18 from the temperature difference ΔT0.

  The temperature difference correction amount HOS1 is a value for correcting the basic ignition timing ADV0 to the retard side. The reason why the basic ignition timing ADV0 is corrected to the retard side when the actual temperature Treal is lower than the basic temperature T0 is as follows. That is, the basic ignition timing ADV is suitable when the actual temperature Treal is the basic temperature T0. Therefore, when the actual temperature Treal is lower than the basic temperature T0, as described above, the EGR gas amount Qegr passing through the LP-EGR valve 17 decreases, the cylinder EGR gas amount Qegrcyl decreases from the target EGR gas amount, and knocking occurs. Tends to occur. Therefore, when the actual temperature Treal is lower than the basic temperature T0, the occurrence of knocking is avoided by correcting the basic ignition timing ADV0 to the retard side with the temperature difference correction amount HOS1.

  Further, as shown in FIG. 18, the temperature difference correction amount HOS1 is a value that increases as the temperature difference ΔT0 increases. When the temperature difference ΔT0 is relatively large, the temperature difference correction amount HOS1 is made larger than when the temperature difference ΔT0 is relatively small for the following reason. That is, when the temperature difference ΔT0 is relatively large, the shortage of the cylinder EGR gas amount Qegrcyl from the target EGR gas amount is larger than when the temperature difference ΔT0 is relatively small. When the shortage of the cylinder EGR gas amount Qegrcyl from the target EGR gas amount is relatively large, knocking tends to occur compared to the case where the shortage from the target EGR gas amount is relatively small. This is because the timing ADV0 needs to be delayed.

  On the other hand, when the actual temperature Treal is equal to or higher than the basic temperature T0 in step 58 of FIG. 16B, it is determined that knocking does not occur. At this time, the process proceeds to step 61 in FIG. 16B, and zero is added to the temperature difference correction amount HOS1.

  In steps 62 and 63 in FIG. 16B, it is checked whether or not the acceleration flag = 1 and the upper limit restriction flag = 1 (already set by the flow in FIGS. 9A and 9B). When the acceleration flag = 1 and the upper limit limit flag = 1, it is determined that the target LP-EGR valve opening tVOegr is limited to the upper limit value VOmax. At this time, the process proceeds to Steps 64, 65, and 67 in FIG.

  Steps 64, 65, and 67 in FIG. 16B are parts for correcting the basic ignition timing ADV0 to the retard side when the target LP-EGR valve opening tVOegr is limited to the upper limit value VOmax. In step 64, the difference between the target LP-EGR valve opening calculated value tVOegr1 (calculated by the flow of FIGS. 9A and 9B) and the upper limit value VOmax is set as the difference LP-EGR valve opening ΔVOegr, that is, the difference LP-EGR by the following equation. The valve opening degree ΔVOegr is calculated.

ΔVOegr = tVOegr1-VOmax (12)
In step 65 of FIG. 16B, a difference LP-EGR valve opening correction amount HOS2 [°] is calculated by searching a table having the contents shown in FIG. 19 from the difference LP-EGR valve opening ΔVOegr.

  In step 67 of FIG. 16B, the ignition timing command value ADV [° BTDC] is obtained by subtracting the difference LP-EGR valve opening correction amount HOS2, the temperature difference correction amount HOS1 and the feedback correction amount FB from the basic ignition timing ADV0. Calculate as That is, the ignition timing command value ADV is calculated by the following equation.

ADV = ADV0-HOS1-HOS2-FB (13)
Here, since the ignition timing command value ADV is a value measured from the compression top dead center to the advance side, the positive difference LP-EGR valve opening correction amount HOS2 is a correction amount for retarding the ignition timing. It becomes.

  The reason why the basic ignition timing ADV0 is retarded by the differential LP-EGR valve opening correction amount HOS2 when the target LP-EGR valve opening tVOegr is limited to the upper limit value VOmax is as follows. That is, the EGR gas amount Qegr passing through the LP-EGR valve 17 is insufficient by the difference between the target LP-EGR valve opening tVOeggr and the upper limit value VOmax, and the cylinder EGR gas amount Qegrcyl becomes smaller than the target EGR gas amount. End up. When the cylinder EGR gas amount Qegrcyl is smaller than the target EGR gas amount, the combustion state of the working gas in the combustion chamber 7 is improved by the difference (ΔVOegr), and knocking tends to occur. Therefore, at this time, the occurrence of knocking is suppressed by correcting the ignition timing to the retard side with respect to the basic ignition timing ADV0.

  As shown in FIG. 19, the difference LP-EGR valve opening correction amount HOS2 is a value that increases as the difference LP-EGR valve opening ΔVOegr increases. When the difference LP-EGR valve opening degree ΔVOegr is relatively large, the difference LP-EGR valve opening degree correction amount HOS2 is made larger than when the difference LP-EGR valve opening degree ΔVOegr is relatively small for the following reason. . That is, when the differential LP-EGR valve opening degree ΔVOegr is relatively large, the shortage of the cylinder EGR gas amount Qegrcyl from the target EGR gas amount is larger than when the differential LP-EGR valve opening degree ΔVOegr is relatively small. Means. When the shortage of the cylinder EGR gas amount Qegrcyl from the target EGR gas amount is relatively large, knocking is more likely to occur than when the shortage from the target EGR gas amount is relatively small. This is because it is necessary to correct the basic ignition timing ADV0 to the side that makes knocking likely to occur.

  On the other hand, when the acceleration flag = 0 or the upper limit flag = 0 in steps 62 and 63 in FIG. 16B, it is determined that knocking does not occur. At this time, the routine proceeds to step 66 where zero is set to the differential LP-EGR valve opening correction amount HOS2.

  In a flow (not shown) provided in the engine controller 41, the ignition timing command value ADV calculated in this way is output to the power transistor of the ignition device including the ignition plug 9. The power transistor is provided on the primary side of the ignition coil, and spark ignition is performed by the spark plug 9 by cutting off the primary current of the ignition coil at the timing of the ignition timing command value ADV.

  Here, the effect of this embodiment is demonstrated.

  In the present embodiment, an EGR passage 15, an LP-EGR valve 17 (EGR valve), basic EGR valve opening calculation means, target EGR valve opening calculation means, and actuator control means are provided. The EGR passage 15 branches from the exhaust pipe 11b and returns a part of the exhaust to the intake pipe 4a. The LP-EGR valve 17 (EGR valve) opens and closes the EGR passage 15. The motor 18 (actuator) can adjust the opening degree of the LP-EGR valve 17. The basic EGR valve opening calculation means (engine controller 41) calculates a basic LP-EGR valve opening (basic EGR valve opening) in a predetermined LP-EGR region (EGR region). The target EGR valve opening degree calculation means (engine controller 41) is a case where the operating point of the engine shifts from the non-LP-EGR region to the LP-EGR region, and the actual temperature Treal of the EGR take-out portion downstream temperature is predetermined. When shifting to the basic temperature T0, the basic LP-EGR valve opening is corrected by the first correction magnification Rhos1 to calculate the target LP-EGR valve opening. The actuator control means (engine controller 41) controls the motor 18 (actuator) so that the opening degree of the LP-EGR valve 17 (EGR valve) becomes the calculated target LP-EGR valve opening degree. In the present embodiment, knocking occurs even if the actual temperature Treal of the EGR take-out portion downstream temperature deviates from the basic temperature T0 to the LP-EGR region with an inexpensive configuration without using a differential pressure sensor. Instability of combustion in the combustion chamber can be avoided.

  When the temperature difference ΔT0 between the actual temperature Treal and the basic temperature T0 is relatively large, knocking is more likely to occur than when the temperature difference ΔT0 is relatively small, and the instability of combustion in the combustion chamber increases. In the present embodiment, the first correction magnification Rhos1 (temperature difference correction amount) is calculated according to the temperature difference ΔT0 between the actual temperature Treal and the basic temperature T0. Thereby, regardless of the temperature difference ΔT0 between the actual temperature and the Treal basic temperature T0, it is possible to avoid the occurrence of knocking and the instability of combustion in the combustion chamber.

  When the actual temperature Treal rises from the lower side and shifts to the basic temperature T0, the EGR valve front-rear differential pressure becomes smaller than that at the basic temperature T0, and the EGR gas amount Qegr passing through the LP-EGR valve 17 decreases. . When the EGR gas amount Qegr decreases, the cylinder EGR gas amount Qegrcyl falls below the target EGR gas amount, and knocking occurs. In the present embodiment, when the actual temperature rises from the lower Real side and shifts to the basic temperature T0, the basic LP-EGR valve opening (basic EGR valve opening) with the first correction magnification Rhos1 (temperature difference correction amount). ) To the increasing side. Thereby, occurrence of knocking can be avoided.

  When the actual temperature Treal decreases from the higher side and shifts to the basic temperature T0, the EGR valve front-rear differential pressure becomes larger than that at the basic temperature T0, and the EGR gas amount Qegr passing through the LP-EGR valve 17 increases. . When Qegr increases, the cylinder EGR gas amount Qegrcyl exceeds the target EGR gas amount, and combustion in the combustion chamber 7 becomes unstable. In the present embodiment, when the actual temperature Treal decreases from the higher side and shifts to the basic temperature T0, the basic LP-EGR valve opening (basic EGR valve opening) with the first correction magnification Rhos1 (temperature difference correction amount). ) To the decreasing side. Thereby, instability of combustion in the combustion chamber 7 can be avoided.

  In the present embodiment, the basic LP-EGR valve opening degree is passed through the LP-EGR valve 17 by the reverse flow in the reverse flow region using the second correction magnification Rhos2 (second correction amount) in the reverse flow region in the LP-EGR region. It changes to the side which supplements the part which EGR gas Qegr decreases. Thus, it is possible to avoid the cylinder EGR gas amount Qegrcyl from deviating from the target EGR gas amount in the reverse flow region where the reverse flow that flows through the LP-EGR valve 17 from the intake pipe side to the exhaust pipe side occurs.

  In the present embodiment, the basic LP-EGR valve opening (basic EGR valve opening) is further corrected to the increasing side using the second correction magnification Rhos2 (second correction amount) in the backflow region. The cylinder EGR gas amount Qegrcyl can be matched with the target EGR gas amount.

  In the present embodiment, a reverse flow region is determined in advance on a map using the engine torque and the engine rotational speed Ne as parameters, and the engine operating point determined by the engine torque and the engine rotational speed Ne is in the reverse flow region on the map. Sometimes it is determined that the region is a reverse flow region. This makes it possible to easily determine whether or not the region is a backflow region.

  The reverse flow region is determined on the map when the actual temperature Treal is a predetermined temperature T1. When the actual temperature Treal is lower than the predetermined temperature T1, the backflow occurs even in the region where the backflow does not occur. The region where the reverse flow is actually generated expands to the high load side and the high rotation speed side than the reverse flow region on the map. In the present embodiment, when the actual temperature Treal is lower than the predetermined temperature T1, the backflow region is expanded to the high load side and the high rotation speed side. Therefore, even when the actual temperature Treal deviates from the predetermined temperature T1 and is low. It is possible to accurately determine whether or not the region is a backflow region.

  The upper limit value of the LP-EGR valve opening is mechanically determined in advance. On the other hand, since the target LP-EGR valve opening is a calculated value, it may exceed the upper limit value VOmax. When the target LP-EGR valve opening degree calculated value tVOegr1 exceeds the upper limit value VOmax, the actual LP-E is calculated even if the target EGR valve opening degree calculated value tVOegr1 is commanded to the motor 18 that is the actuator of the LP-EGR valve 17. The EGR valve opening remains at the upper limit value VOmax. For this reason, the amount of EGR gas Qegr flowing through the LP-EGR valve 17 is reduced by the amount obtained by subtracting the upper limit value VOmax from the target EGR valve opening calculation value tVOegr1. When the EGR gas amount Qegr decreases, the cylinder EGR gas amount Qegrcyl falls below the target EGR gas amount. This improves the combustion state in the combustion chamber and may cause knocking. On the other hand, in this embodiment, the engine controller 41 includes basic EGR rate setting means, basic ignition timing calculation means, and ignition timing retardation correction means. The basic EGR rate setting means sets a basic LP-EGR rate (basic EGR rate) in the LP-EGR region (EGR region). The basic ignition timing calculation means calculates a basic ignition timing ADV0 corresponding to the basic LP-EGR rate that is set. The ignition timing retard correction means retards the ignition timing from the basic ignition timing ADV0 when the target LP-EGR valve opening calculated value tVOegr1 (the calculated target EGR valve opening) exceeds a predetermined upper limit value VOmax. Correct to the side. Thus, knocking can be avoided even when the target EGR valve opening calculation value exceeds the upper limit value.

  The basic ignition timing ADV is suitable when the actual temperature Treal is the basic temperature T0. For this reason, when the actual temperature Treal is lower than the basic temperature T0, the EGR gas amount Qegr passing through the LP-EGR valve 17 decreases. When the EGR gas amount Qegr decreases, the cylinder EGR gas amount Qegrcyl falls below the target EGR gas amount. This improves the combustion state in the combustion chamber and may cause knocking. On the other hand, in the present embodiment, when the actual temperature Treal is lower than the basic temperature T0, the ignition timing is corrected to the retard side with respect to the basic ignition timing ADV0. Thus, knocking can be avoided even when the actual temperature Treal is lower than the basic temperature T0.

(Second Embodiment)
The flowcharts of FIGS. 20A and 20B show the second case where the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature Treal increases from the lower side and shifts to the basic temperature T0. This is for calculating the target LP-EGR valve opening degree of the embodiment. 20A and 20B are executed at regular intervals (for example, every 10 ms). The same parts as those in the flow of FIGS. 9A and 9B of the first embodiment are denoted by the same reference numerals.

  In the second embodiment, EGR control is prohibited by fully closing the LP-EGR valve 17 in the backflow region. The differences from the flow of FIGS. 9A and 9B of the first embodiment will be mainly described. Step 14 in FIG. 20B looks at the selected reverse flow region map to see whether or not the operating point determined from the engine speed Ne and the engine torque belongs to the reverse flow region. When the operating point belongs to the reverse flow region, the process proceeds to step 71 in FIG. 20B, and zero is set to the second correction magnification Rhos2 [anonymous number] centered at 1.0. In step 71 of FIG. 20B, the reverse flow region flag is set to 1 to indicate that it is a reverse flow region.

  When zero is entered in the second correction magnification Rhos2 in step 71 of FIG. 20B, the correction magnification Rhos that is a value obtained by multiplying the first correction magnification Rhos1 and the second correction magnification Rhos2 in step 17 of FIG. 20B becomes zero. When the correction magnification Rhos becomes zero in step 17, the target LP-EGR valve opening tVOegr, which is a value obtained by multiplying the basic LP-EGR valve opening VOegr0 by the correction magnification Rhos in step 18 of FIG. 20B, becomes zero. The target LP-EGR valve opening tVOegr being zero means that the LP-EGR valve 17 is fully closed. In other words, in the reverse flow region within the LP-EGR region, the EGR control is prohibited (EGR is not performed) by fully closing the LP-EGR valve 17.

  Thus, the EGR control is prohibited by fully closing the LP-EGR valve 17 in the reverse flow region for the following reason. That is, since it is difficult to determine whether or not the engine operating point is in the backflow region, the determination accuracy is reduced, and it may be determined that the engine is in the backflow region although it is not the backflow region. If EGR control is performed based on such erroneous determination, knocking may occur. Therefore, in the backflow region in the EGR region, the EGR control is prohibited by fully closing the LP-EGR valve 17 so that the occurrence of knocking due to the EGR control based on the erroneous determination is avoided. is there.

  On the other hand, when the engine operating point does not belong to the reverse flow region in step 14 of FIG. 20B, the process proceeds to step 72 of FIG. 20B, and 1.0 is added to the second correction magnification Rhos2 as in the first embodiment. In step 72 of FIG. 20B, the backflow region flag is set to 0 to indicate that it is not in the backflow region.

  Next, the flowcharts of FIGS. 21A and 21B are for calculating the ignition timing command value ADV of the second embodiment. The flow of FIGS. 21A and 21B is executed at regular intervals (for example, every 10 ms) independently of the flows of FIGS. 20A, 20B, and 14. The same parts as those in the flow of FIGS. 16A and 16B of the first embodiment are denoted by the same reference numerals.

  The difference from the flow of FIGS. 16A and 16B of the first embodiment will be mainly described. In step 54 of FIG. 21B, it is determined whether or not the engine operating point is in the LP-EGR region shown in FIG. When the operating point is in the LP-EGR region, the process proceeds to step 81 in FIG. 21B. In step 81 in FIG. 21B, it is determined whether or not the region is a backflow region by a backflow region flag (already set by the flow in FIGS. 20A and 20B). When the reverse flow region flag = 1 (that is, the reverse flow region), the process proceeds to steps 55 and 56 in FIG. 21B.

  In step 55 of FIG. 21B, a basic ignition timing ADV0 [° BTDC] at which MBT is obtained according to the operating point determined from the engine load and the rotational speed Ne is calculated. This is because, in the second embodiment, EGR control is prohibited when the region is in the backflow region, so that the backflow region is treated the same as the non-LP-EGR region.

  In step 56 of FIG. 21B, a value obtained by subtracting the feedback amount FB from the basic ignition timing ADV0 is set as an ignition timing command value ADV [° BTDC], that is, the ignition timing command value ADV is calculated by the following equation.

ADV = ADV0−FB (14)
Here, the effect of 2nd Embodiment is demonstrated.

  Since it is difficult to determine whether or not the engine operating point is in the backflow region, the determination accuracy is lowered, and it may be determined that the engine is in the backflow region although it is not the backflow region. If EGR control is performed based on such erroneous determination, knocking may occur. In the second embodiment, since the EGR control is prohibited by fully closing the EGR valve in the backflow region, it is possible to prevent the occurrence of knocking by performing the EGR control based on the erroneous determination.

(Third embodiment)
FIG. 22 is a schematic configuration diagram of a gasoline engine according to the third embodiment. The same parts as those in FIG. 1 of the first embodiment are denoted by the same reference numerals.

  In the first and second embodiments, whether or not the operating point is in the backflow region is determined by looking at the backflow region map and whether or not the operating point determined from the engine rotational speed Ne and the engine torque belongs to the backflow region. On the other hand, in the third embodiment, as shown in FIG. 22, a temperature sensor 48 (temperature detection means) that detects the temperature of the EGR passage 15 downstream of the LP-EGR valve 17 is additionally provided.

  FIG. 23A and FIG. 23B are flowcharts for explaining calculation of the target LP-EGR valve opening degree of the third embodiment, which replaces the flow of FIG. 9A and FIG. 9B of the first embodiment. That is, FIGS. 23A and 23B show a case where the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature Treal increases from the lower side and shifts to the basic temperature T0. is there. The same parts as those in the flow of FIGS. 9A and 9B of the first embodiment are denoted by the same reference numerals.

  In the third embodiment, it is determined whether or not the vehicle is in the reverse flow region based on the temperature Tdf of the EGR passage 15 downstream of the LP-EGR valve detected by the temperature sensor 48. The difference from the first embodiment will be mainly described. After calculating the first correction magnification Rhos1 in step 8 of FIG. 23A, the process proceeds to step 91 of FIG. 23B. In step 91, based on the temperature Tdf [° C.] of the EGR passage 15 downstream of the LP-EGR valve detected by the temperature sensor 48, a temperature change amount ΔTdf [° C.] per control cycle is calculated by the following equation.

ΔTdf = Tdf (previous) −Tdf (15)
Where Tdf (previous): previous value of Tdf,
Since the control cycle here is as short as 10 ms, the temperature change amount ΔTdf per 100 ms, which is 10 times, may be calculated. The amount of temperature change per unit may be determined by conformance.

  In step 92, the temperature change amount ΔTdf is compared with zero. When the temperature change amount ΔTdf is a positive value, it represents a temperature decrease amount, and thus the process proceeds to step 93.

  In step 92, the temperature change amount ΔTdf is compared with a predetermined value ΔT3. The predetermined value ΔT3 is a value (positive value) for determining whether or not the temperature of the EGR passage 15 downstream of the LP-EGR valve is lowered due to the backflow, and is set in advance. When the temperature change amount ΔTdf is equal to or greater than the predetermined value ΔT3, it is determined that the temperature of the EGR passage 15 downstream of the LP-EGR valve is lowered due to the backflow (that is, in the backflow region), and the process proceeds to step 15 in FIG. 2 The correction magnification Rhos2 [anonymous number] is calculated. Specifically, the predetermined value 2 is entered in the second correction magnification Rhos2. Here, the predetermined value 2 is a value for giving an initial value of the second correction magnification Rhos2. Similarly to the predetermined value 1, the predetermined value 2 is a value centered on 1.0, and here, a value exceeding 1.0 is adopted. The predetermined value 2 may be a constant value.

  On the other hand, when the temperature change amount ΔTdf is less than the predetermined value ΔT3 in step 93 of FIG. 23B, it is determined that the temperature of the EGR passage 15 downstream of the LP-EGR valve is not lowered due to the backflow (that is, not in the backflow region). At this time, since it is not necessary to correct the basic LP-EGR valve opening degree VOegr0 regarding the backflow, the process proceeds to step 16 in FIG. 23B, and 1.0 is set to the second correction magnification Rhos2.

  It is determined that the temperature of the EGR passage 15 downstream of the LP-EGR valve is not lowered due to the backflow (that is, not in the backflow region) even when the temperature change amount ΔTdf is equal to or less than zero in Step 92 of FIG. 23B. Also at this time, the process proceeds to step 16 in FIG. 23B, and 1.0 is added to the second correction magnification Rhos2.

  Thus, in the third embodiment, it is determined whether or not the vehicle is in the reverse flow region based on the temperature Tdf of the EGR passage 15 downstream of the LP-EGR valve detected by the temperature sensor 48.

  In the reverse flow region, it is considered that the temperature of the EGR passage 15 downstream of the LP-EGR valve 17 is lowered by the fresh air flowing from the intake pipe side to the exhaust pipe side. In the third embodiment, a temperature sensor 48 (temperature detection means) that detects the temperature downstream of the LP-EGR valve 17 (EGR valve) is provided, and the temperature Tdf of the EGR passage 15 downstream of the LP-EGR valve detected by the temperature sensor 48. Based on the above, it is determined whether or not a backflow occurs. As a result, it is possible to easily determine whether or not a backflow occurs by the temperature sensor 48.

  FIG. 24, FIG. 25, and FIG. 26 are characteristic diagrams summarizing at what operating point transition the present invention is applied. First, FIG. 24 is a characteristic diagram summarizing at which operating point the present invention is applied when the basic LP-EGR rate is uniform in each of the two LP-EGR regions. In FIG. 24, [1] to [4] are as follows.

[1] When the operating point shifts from the non-LP-EGR region to the LP-EGR region where the basic LP-EGR rate is 10% by acceleration (that is, the case shown in FIG. 7 in the first embodiment),
[2] When the operating point shifts from the non-LP-EGR region to the LP-EGR region where the basic LP-EGR rate is 20% due to acceleration,
[3] When shifting from the non-LP-EGR region to the LP-EGR region where the basic LP-EGR rate is 10% by deceleration (that is, the case shown in FIG. 8 in the first embodiment)
[4] When shifting from the non-LP-EGR region to the LP-EGR region where the basic LP-EGR rate is 20% by deceleration,
Here, in FIG. 24, the tendency of the exhaust temperature is shown by being overlapped with a broken line. The exhaust temperature is a characteristic that increases as the engine load increases under a constant engine rotational speed Ne, and increases as the engine rotational speed Ne increases under a constant engine load. In FIG. 24, as indicated by a broken line, a line having the same exhaust temperature is indicated by an arc, but it is not necessarily an arc. The above [1] and [2] consider the case of shifting to the side where the exhaust temperature becomes higher due to acceleration. Similarly, the above [3] and [4] consider the case of shifting to a side where the exhaust temperature becomes lower due to deceleration.

  In particular, the cases [1] and [3] have been described in the first embodiment, but the same applies to the cases [2] and [4]. That is, when the operating point shifts from the non-LP-EGR region to the LP-EGR region and the actual temperature Treal shifts to the basic temperature T0, the temperature depends on the temperature difference between the actual temperature Treal and the basic temperature T0. The differential pressure across the EGR valve changes by the amount. If the differential pressure across the LP-EGR valve changes from the case where the actual temperature Treal matches the basic temperature T0, the EGR gas amount Qegr passing through the LP-EGR valve 17 changes, and the cylinder EGR gas amount Qegrcyl becomes the target EGR gas. Out of quantity. For example, in the case of the above [2], the cylinder EGR gas amount Qegrcyl becomes insufficient below the target EGR gas amount. In the case of the above [4], the cylinder EGR gas amount Qegrcyl exceeds the target EGR gas amount and becomes excessive.

  As described above, the same problems as in the first embodiment also occur in the cases [2] and [4]. Therefore, in the case [2], the first correction magnification Rhos1 and the second correction magnification Rhos2 (second correction magnification). The target LP-EGR valve opening is calculated by correcting the basic LP-EGR valve opening by (amount). In the case of [4] above, the basic LP-EGR valve opening is corrected by the first correction magnification Rhos1 to calculate the target LP-EGR valve opening. Then, the motor 18 that is the actuator of the LP-EGR valve 17 may be controlled so that the LP-EGR valve opening is equal to the calculated target LP-EGR valve opening. Thus, also in the cases [2] and [4], the cylinder EGR gas amount Qegrcyl can be matched with the target EGR gas amount.

  Now, in FIG. 24, the basic LP-EGR rate is considered to be uniform in the two LP-EGR regions having the basic LP-EGR rate of 10% and 20%. On the other hand, FIG. 25 and FIG. 26 are characteristic diagrams summarizing at what operating point transition the present invention is applied when the basic LP-EGR rate is not uniform within each of the two LP-EGR regions. That is, in FIG. 25, the basic LP-EGR rate increases as it goes to the upper right in each of the trapezoidal LP-regions (as the load increases and Ne increases), and as it goes to the lower left (the load decreases). It shows a case where the basic LP-EGR rate is small (as Ne is low). When the basic LP-EGR rates are averaged in the two LP-EGR regions shown in FIG. 25, the average values are 10% and 20%. In FIG. 25, [5] and [6] are as follows.

[5] When the operating point shifts from a small LP-EGR rate to a large one by acceleration in the LP-EGR region where the basic LP-EGR rate is 10%.
[6] When the operating point shifts from a small LP-EGR rate to a large one by acceleration in the LP-EGR region where the basic LP-EGR rate is 20%,
On the other hand, FIG. 26 shows that the basic LP-EGR rate decreases as it goes to the upper right in each of the trapezoidal LP-regions (as the load increases and Ne increases), and as it goes to the lower left (the load decreases). This shows the case where the basic LP-EGR rate increases as Ne decreases. When the basic LP-EGR rates are averaged in the two LP-EGR regions shown in FIG. 26, the average values are 10% and 20%. In FIG. 26, [7] and [8] are as follows.

[7] When the operating point shifts from a small LP-EGR rate to a large one in the LP-EGR region where the basic LP-EGR rate is 10% due to deceleration,
[8] When the operating point shifts from a small LP-EGR rate to a large one in the LP-EGR region where the basic LP-EGR rate is 20% due to deceleration,
In the above cases [5] to [8], that is, when the operating point of the engine shifts in the LP-EGR region and the actual temperature Treal shifts to the basic temperature T0, the actual temperature Treal The differential pressure across the EGR valve changes by an amount corresponding to the temperature difference of the basic temperature T0. If the differential pressure before and after the EGR valve changes compared to the case where the actual temperature Treal is equal to the basic temperature T0, the EGR gas amount Qegr passing through the LP-EGR valve 17 changes, and the cylinder EGR gas amount Qegrcyl is calculated from the target EGR gas amount. Come off. For example, in the case of the above [5] and [6], the cylinder EGR gas amount Qegrcyl becomes insufficient below the target EGR gas amount. In the cases [7] and [8], the cylinder EGR gas amount Qegrcyl exceeds the target EGR gas amount and becomes excessive.

  As described above, the same problems as in the first embodiment also occur in the cases [5] to [8]. Therefore, in the cases [5] to [8], the basic LP-EGR valve is opened at the first correction magnification Rhos1. The target LP-EGR valve opening is calculated by correcting the degree. Then, the motor 18 that is an actuator of the LP-EGR valve 17 may be controlled so that the LP-EGR valve opening is equal to the calculated target LP-EGR valve opening. Thereby, also in the cases [5] to [8], the cylinder EGR gas amount Qegrcyl can be matched with the target EGR gas amount.

(Fourth embodiment)
FIG. 27 is a schematic configuration diagram of the gasoline engine of the fourth embodiment, which replaces FIG. 1 of the first embodiment. The same parts as those in FIG. 1 of the first embodiment are denoted by the same reference numerals. Differences from the first embodiment will be mainly described.

  The intake collector 4b includes a water-cooled intercooler 61. When the intercooler 25 of the first embodiment is air-cooled, the water-cooled type in the fourth embodiment is to reduce the volume of the intake pipe 4a. The air-cooled intercooler 25 needs to be interposed in the intake pipe 4a, and the length of the intake pipe 4a is increased accordingly. On the other hand, since the water-cooled intercooler 61 can be provided inside the intake collector 4b, the length of the intake pipe 4a is not increased.

  The intercooler 61 is for cooling the air compressed by the compressor 23 with the cooling water flowing through the cooling water passage. Specifically, the intercooler 61 includes a cooling water passage and an air passage provided on the outer periphery thereof. The cooling water passage of the intercooler 61 and the air-cooled sub-radiator 62 are connected by cooling water passages 63 and 64. For example, the sub-radiator 62 is arranged in series with a radiator for cooling engine coolant so that traveling wind passes therethrough. The cooling water passage 63 is provided with a pump 65 for circulating the cooling water.

  In the sub-radiator 62, the cooling water carried from the intercooler 61 is cooled by traveling wind. The cooling water cooled by the sub radiator 62 is guided to the intercooler 61. In the intercooler 61, heat is exchanged between the air whose temperature has been increased by the air compression by the compressor 23 and the cooling water flowing through the cooling water passage to cool the air. The air whose temperature has been increased by the air compression by the compressor 23 is cooled by the intercooler 61, whereby the supercharging efficiency can be increased.

  Two manifold catalysts 12A and 12B are arranged in series in the intake pipe 11b.

  Next, in the fourth embodiment, a normally-open differential pressure device 51 is provided in the intake pipe 4a upstream of the merge portion of the EGR passage 15 (hereinafter, this merge portion is referred to as “EGR discharge portion”). The differential pressure device 51 is driven by an actuator (for example, a rotating electrical machine) 52. The differential pressure device 51 is constituted by a butterfly valve, for example. Hereinafter, the symbol N is assigned to the EGR extraction portion, and the symbol P is assigned to the EGR discharge portion.

  Here, the reason why the differential pressure device 51 is provided will be described. Since the EGR extraction portion N is provided in the exhaust pipe 11b downstream of the catalysts 12A and 12B, the pressure of the EGR extraction portion N becomes substantially atmospheric pressure on the low rotational speed and low load side in the LP-EGR region. On the other hand, since the EGR discharge part P is provided in the intake pipe 4a upstream of the compressor 23, the pressure of the EGR discharge part P becomes substantially atmospheric pressure on the low rotation speed and low load side in the LP-EGR region. As described above, when the EGR take-out part N and the EGR discharge part P have substantially the same atmospheric pressure, the EGR gas can be discharged from the EGR discharge part P to the intake pipe 4a even if the LP-EGR valve 17 is opened. Can not.

  In this case, if the differential pressure device 51 is closed, a pressure difference is generated before and after the differential pressure device 51, and the pressure of the intake pipe 4a downstream of the differential pressure device 51, that is, the pressure of the EGR discharge part P is lower than the atmospheric pressure. Become. If the atmospheric pressure is zero, a pressure lower than the atmospheric pressure becomes a negative pressure. The pressure lower than the atmospheric pressure generated in the intake pipe 4a downstream of the differential pressure device 51 by closing the differential pressure device 51 is hereinafter referred to as “negative pressure”. When the pressure of the EGR discharge part P becomes negative, a pressure difference is generated before and after the LP-EGR valve 17 even on the low rotation speed low load side in the LP-EGR region, and the EGR gas is discharged from the EGR discharge part P. Is discharged into the intake pipe 4a. Thus, the differential pressure device 51 is provided in order to secure the differential pressure across the LP-EGR valve 17 on the low rotational speed low load side in the LP-EGR region.

  FIG. 28 is a characteristic diagram of the basic LP-EGR rate of the fourth embodiment. In the first embodiment shown in FIG. 3, the basic LP-EGR rate is set according to only the engine load. On the other hand, in the fourth embodiment, the basic LP-EGR rate is set according to the engine load and the engine rotation speed. That is, in the fourth embodiment, the LP-EGR region is divided into three main regions, a low rotation speed / low load region R1, a medium rotation / medium load region R2, and a high rotation / high load region R3. , R2, R3 are set with a predetermined value a%, a predetermined value b%, and a predetermined value c% as basic LP-EGR rates. Here, the basic LP-EGR rate becomes smaller as the three regions R1, R2, and R3 are at higher rotational speeds and higher loads, that is, a> b> c between three predetermined values a, b, and c. Have a relationship.

  The region where the differential pressure device 51 is closed (that is, the differential pressure device 51 is operated) is only the low rotational speed low load side of the LP-EGR region, that is, the low rotational speed low load region R1. Hereinafter, the low rotational speed low load region R1 in the LP-EGR region is also referred to as a “differential pressure device operating region”. On the other hand, the two regions R2 and R3 and the non-LP-EGR region on the high rotation speed and high load side are non-operating regions of the differential pressure device 51 (hereinafter referred to as “non-differential pressure device operating regions”). In the non-differential pressure device operating range, the differential pressure device 51 is held at a default position close to the fully open position (hereinafter simply referred to as “default position”). The reason why the differential pressure device 51 is not closed in the two regions R2 and R3 on the high rotational speed and high load side is that the differential pressure device 51 is provided upstream of the intake pipe 4a. If the valve 51 is closed, the ventilation resistance is increased, so this is avoided.

  In the present embodiment, the LP-EGR region is divided into three, and only the low rotation speed and low load region R1 is used as the differential pressure device operation region, but this is not a limitation. The number that divides the LP-EGR region and makes the basic LP-EGR rate different is considered to vary depending on the engine specifications. Further, it is conceivable that not only one of the divided regions is set as the differential pressure device region, but two or more regions are set as the differential pressure device operating range. Accordingly, whether one or a plurality of divided areas is set as the differential pressure device operating area is determined by conformance. Furthermore, the reason for dividing the LP-EGR region is to simplify the control of the LP-EGR rate by giving the basic LP-EGR rate as three discrete values. If the basic LP-EGR rate is given as a continuous value, it is not necessary to divide the LP-EGR area. Therefore, when the basic LP-EGR rate is given as a continuous value, the differential pressure device operating region is provided on the low rotational speed low load side in the LP-EGR region. Alternatively, it can be considered that the differential pressure device operating region is not limited to the low rotation speed and low load side in the LP-EGR region. Therefore, it is sufficient that the differential pressure device operation region is provided in at least a part of the LP-EGR region.

  FIG. 29 is a characteristic diagram considered when setting the opening of the differential pressure device 51 (hereinafter referred to as “differential pressure device opening”). The horizontal axis represents the target air amount [g / s], which is the target value of the new air amount, and the vertical axis represents the differential pressure device opening [°]. The target air amount is a value that serves as an index when controlling the throttle valve opening. Here, the differential pressure device opening is a value close to the maximum of 90 ° when the differential pressure device 51 is in the default position (hereinafter, this value is referred to as “default value”). As the differential pressure device 51 is closed from the default position, the differential pressure device opening decreases toward 0 ° and reaches a minimum value (a positive value close to zero). Although the minimum value is not described in FIG. 29, the minimum value is smaller than the predetermined value S1 on the vertical axis.

  As shown in FIG. 29, the differential pressure device opening is a default value until the target air amount increases from zero and reaches a predetermined value Q1. This is because the air amount range below the predetermined value Q1 corresponds to the non-LP-EGR region, and it is not necessary to close the differential pressure device 51 in the non-LP-EGR region. In order to enter the low rotational speed low load range R1 (= differential pressure device operating range) at the timing when the target air amount reaches the predetermined value Q1, the differential pressure device opening is set to the predetermined value S1. From the predetermined value Q1, the differential pressure device opening is increased in proportion to the target air amount, and the differential pressure device opening is set to the predetermined value S2 when the target air amount reaches the predetermined value Q2. When the target air amount exceeds the predetermined value Q2, the medium rotational speed medium load region R2 (non-operating device operating region) is entered. From the middle rotational speed medium load range R2 (abbreviated as “air amount influence range” in FIG. 29), the air flow resistance increases when the differential pressure device 51 is closed. To avoid this, the differential pressure device opening is set to the default value. Return to. Thus, by defining the differential pressure device opening in proportion to the target air amount with the low rotational speed low load region R1 in the LP-EGR region as the differential pressure device operating region, the EGR in the differential pressure device operating region The pressure of the discharge part P is maintained at a constant value as a negative pressure. This is due to the following reason. That is, the amount of fresh air passing through the differential pressure device 51 decreases as the differential pressure device opening is reduced in the differential pressure device operating range. The pressure downstream of the differential pressure device 51 decreases as the amount of fresh air passing through the differential pressure device 51 decreases. The differential pressure device opening degree defines the amount of air passing through the differential pressure device 51. Therefore, by determining the amount of fresh air passing through the differential pressure device 51 in proportion to the target air amount, the pressure in the intake pipe 4a downstream of the differential pressure device 51 (pressure of the EGR discharge part P) is independent of the target air amount. It is a constant value.

  Although FIG. 29 shows a case where the differential pressure device opening is given as a continuous value with respect to the target air amount, the present invention is not limited to this case. For example, if two predetermined values S3 and S4 are taken as representative values between the predetermined value S1 and the predetermined value S2, the differential pressure device opening may be given as a discrete value of three predetermined values S1, S3 and S4. Absent. FIG. 30 shows a characteristic diagram of the differential pressure device opening in this case. In FIG. 30, the target air amount corresponding to the predetermined values S1 and S2 is set to predetermined values Q3 and Q4. At this time, when the target air amount is Q1 or more and less than Q3, the differential pressure device opening becomes the predetermined value S1. The differential pressure device opening is a predetermined value S3 when the target air amount is Q3 or more and less than Q4, and the differential pressure device opening is a predetermined value S4 when the target air amount is Q4 or more and less than Q2. Here, when the differential pressure device opening is given as a discrete value, the number of discrete values is three, but is not limited to the case where the number of discrete values is three.

  FIG. 31 is an operation region diagram showing, in an image, what happens to the equal air amount line in the differential pressure device operation region R1. The horizontal axis represents the engine speed Ne [rpm], and the vertical axis represents the engine load [Nm]. An LP-EGR region is provided in the approximate center of the entire operation region. As shown in FIG. 31, when Ne and load are used as parameters, an equal air amount line can be drawn by an oblique straight line from the upper left to the lower right. For this reason, when the equal air amount lines at the predetermined values S1, S3, S4, and S2 shown in FIGS. 29 and 30 are drawn, parallel lines in the differential pressure device operating region R1 are obtained as shown in FIG. Can be drawn.

  When the differential pressure device opening is given as a continuous value, when the operating point of the engine enters the differential pressure device operating region R1, the differential pressure device 50 opens according to the target air amount between the predetermined values S1 and S2. Is closed. On the other hand, when the differential pressure device opening is given as a discrete value, the differential pressure device 50 is closed to any one of the predetermined values S1, S3, S4. As a result, the pressure of the EGR discharge part P becomes a constant value of negative pressure, which is smaller than when the differential pressure device 51 is in the default position. The differential pressure across the EGR valve 17 is increased by the decrease, and the amount of EGR gas discharged from the EGR discharge part P is increased. This is because the amount of EGR gas discharged from the EGR discharge part P is proportional to the opening area of the EGR valve 17 and the differential pressure across the EGR valve 17, so that when the differential pressure across the EGR valve 17 increases, the EGR correspondingly increases. This is because the amount of EGR gas discharged from the discharge part P increases. Thus, by closing the differential pressure device 51 in the differential pressure device operating range, the differential pressure across the EGR valve 17 is ensured.

  The control of the differential pressure device 51 performed by the engine controller 41 will be described. The flowchart of FIG. 32 is for calculating the differential pressure device opening. The flow in FIG. 32 is executed at regular time intervals (for example, every 10 ms).

  In step 101, it is determined whether or not the engine operating point is in the differential pressure device operating range R1. As shown in FIG. 33, the differential pressure device operating region is set to the region R1 on the lowest rotational speed and low load side among the LP-EGR region divided into three regions R1, R2, and R3. When the operating point of the engine does not belong to the differential pressure device operating range R1 shown in FIG. 33, the current process is terminated as it is.

  On the other hand, when the operating point of the engine belongs to the differential pressure device operating range R1 shown in FIG. 33, the process proceeds from step 101 to step 102, and a differential pressure device opening degree is calculated by searching a map having the contents shown in FIG. To do. As shown in FIG. 34, the differential pressure device operating region R1 is divided into three main regions of a first operating region R11, a second operating region R12, and a third operating region R13, and each of the three operating regions R11, R12, The predetermined values S1, S3, and S4 shown in FIG. 30 are entered in R13. Here, S1 <S3 <S4. That is, the characteristics of the differential pressure device opening degree in FIG. 34 correspond to those in FIG. Corresponding to FIG. 29, the characteristics of the differential pressure device opening degree using the engine load and the rotational speed as parameters may be determined.

  The reason why the differential pressure device opening is reduced to S4, S3, and S1 in the differential pressure device operating region R1 at the lower rotational speed and lower load side is as follows. That is, this is because the pressure of the EGR discharge part P is maintained at a constant value as a negative pressure by decreasing the differential pressure device opening degree toward the lower rotational speed and lower load side.

  In a flow not shown, the differential pressure device opening calculated in this way is converted into a drive signal for the actuator 52 and output.

  Here, as shown in FIG. 34, the reason why the differential pressure device opening is given by a map using the engine load and the rotational speed Ne as parameters will be described. The gasoline engine control device is provided with two parts, a throttle valve 5 and a waste gate valve 25. When there are two parts for controlling the fresh air volume, there is a demand for simplifying the control configuration. For this reason, as described above, torque control is performed with the throttle valve opening under atmospheric pressure conditions, and torque control is performed with the waste gate valve opening in the supercharging region. On the other hand, when the differential pressure device 51 is provided in addition to the LP-EGR valve 17 in the fourth embodiment, the amount of EGR gas discharged from the EGR discharge portion P can be controlled also by the differential pressure device opening. . For example, even if the LP-EGR valve opening is constant, if the differential pressure device opening is decreased, the amount of EGR gas discharged from the EGR discharge part P increases (that is, the LP-EGR rate increases). It will change to the side that becomes). However, if the LP-EGR rate is controlled by the differential pressure device opening, it becomes ambiguous whether the LP-EGR rate is controlled by the LP-EGR valve opening or the differential pressure device opening. . That is, there is a demand for simplifying the control configuration even when there are two parts for controlling the LP-EGR rate, such as when the differential pressure device 51 is provided in addition to the LP-EGR valve 17. Therefore, in the fourth embodiment in which the differential pressure device 51 is provided in addition to the LP-EGR valve 17, the LP-EGR rate is controlled by the LP-EGR valve opening degree in order to simplify the control configuration. The LP-EGR rate is not controlled at the pressure device opening. That is, the differential pressure device 51 is used to hold the pressure of the EGR discharge part P at a constant value as a negative pressure, and the LP-EGR rate is not controlled by the differential pressure device opening. In order to maintain the pressure of the EGR discharge part P at a constant value as a negative pressure, the differential pressure device opening is given by a map using the engine load and the rotational speed Ne as parameters. Thus, even if the differential pressure device 51 is provided in addition to the LP-EGR valve 17 by giving the differential pressure device opening by searching the map using the engine load and the rotational speed as parameters, the LP- Control of the EGR rate is simplified. As a result, it is possible to ensure the functional reliability of the LP-EGR valve 17 and the differential pressure device 51.

  Now, even when the operating point shifts from the long non-LP-EGR region on the low load side to the differential pressure device operating region R1 on the high load side, if the first correction magnification is used as it is, the actual LP -It has been newly found that the EGR rate deviates from the basic LP-EGR rate. This will be described with reference to FIG. 35. FIG. 35 shows the LP-EGR when the operating point shifts from the long non-LP-EGR region on the low load side to the differential pressure device operating region on the high load side. The change in rate is shown in the model. Here, since it is only necessary to know how the actual LP-EGR rate (abbreviated as “actual LP-EGR rate” in FIG. 35) varies depending on the difference in the differential pressure device opening, the reverse flow region in FIG. It is described as not. In FIG. 35, the change in the basic LP-EGR rate is indicated by a solid line, and the actual change in the LP-EGR rate when the differential pressure device 51 is in the default position is indicated by a two-dot chain line. Further, the actual LP-EGR rate when the differential pressure device opening is the predetermined value S4 shown in FIG. 34 is indicated by a long broken line, and the actual when the differential pressure device opening is the predetermined value S1 shown in FIG. The LP-EGR rate is shown by a short broken line.

  A case where the differential pressure device 51 is in the default position will be described. This case is the same as that described with reference to FIGS. 4 and 7 in the first embodiment. That is, since the actual temperature Treal of the EGR take-out portion downstream temperature is lower than the basic temperature T0, the EGR gas amount Qegr passing through the LP-EGR valve 17 is lower than that at the basic temperature T0. As a result, the actual LP-EGR rate becomes smaller than the basic LP-EGR rate until the actual temperature Treal of the downstream temperature of the EGR take-out section matches the basic temperature T0. Since the engine controller 41 calculates the basic ignition timing ADV0 corresponding to the basic LP-EGR rate, the basic ignition timing is advanced from the MBT in a period in which the actual LP-EGR rate is smaller than the basic LP-EGR rate. And knocking may occur. Therefore, in the first embodiment, the target LP-EGR valve opening degree tVOegr is obtained by multiplying the basic LP-EGR valve opening degree VOegr0 by the first correction magnification Rhos1, which is a positive value of 1.0 or more. By correcting the LP-EGR valve opening to the increase side with the first correction magnification Rhos1, the actual LP-EGR rate is made to coincide with the basic LP-EGR rate, and the occurrence of knocking is avoided.

  On the other hand, when the operating point shifts from the low load side to the differential pressure device operating range, the differential pressure device 51 is closed (the differential pressure device opening is S4 and S1), so that the differential pressure device 51 is in the default position. The actual differential pressure of the LP-EGR valve front-rear differential pressure is closer to the target differential pressure than in some cases. The actual LP-EGR rate is closer to the basic LP-EGR rate than when the differential pressure device 51 is in the default position by the amount that the actual differential pressure of the LP-EGR valve front-rear differential pressure approaches the target differential pressure (FIG. 35). Long dashed lines, short dashed lines). Even when the differential pressure device 51 is closed in this way, if the basic LP-EGR valve opening is corrected to the increase side using the first correction magnification Rhos1 having the same value as in the first embodiment as it is, the correction is not performed. It ’s too late. A situation in which the LP-EGR valve opening degree is corrected to the increase side and the actual LP-EGR rate returns to the basic LP-EGR rate after the actual LP-EGR rate exceeds the basic LP-EGR rate. "Overshoot"). During the period when the actual LP-EGR rate overshoots, the actual LP-EGR rate is larger than the basic LP-EGR rate, so that knocking does not occur, but at this time, the basic ignition timing ADV0 is higher than the MBT. It becomes a retarded angle side and can lead to an engine stall.

  Next, even when the operating point shifts from the long non-LP-EGR region on the high load side to the differential pressure device operation region R1 on the low load side, if the first correction magnification is used as it is, It has been newly found that the LP-EGR rate deviates from the basic LP-EGR rate. This will be described with reference to FIG. 36. FIG. 36 shows the LP- when the operating point shifts from the long non-LP-EGR region on the high load side to the differential pressure device operating region R1 on the low load side. A change in the EGR rate is shown by a model. 36, the change in the basic LP-EGR rate is indicated by a solid line, and the change in the actual LP-EGR rate when the differential pressure device 51 is in the default position (also abbreviated as “actual LP-EGR rate” in FIG. 36). It is indicated by a two-dot chain line. Moreover, the actual LP-EGR rate when the differential pressure device opening degree is closed to a predetermined value is indicated by a broken line.

  A case where the differential pressure device 51 is in the default position will be described. This case is the same as that described in FIG. 8 in the first embodiment. That is, since the actual temperature Treal of the downstream temperature of the EGR extraction portion is higher than the basic temperature T0, the EGR gas amount Qegr passing through the LP-EGR valve 17 becomes larger than that at the basic temperature T0. As a result, the actual LP-EGR rate becomes higher than the basic LP-EGR rate until the actual temperature Treal of the downstream temperature of the EGR take-out portion matches the basic temperature T0. Since the engine controller 41 calculates the basic ignition timing ADV0 corresponding to the basic LP-EGR rate, the basic ignition timing is retarded from the MBT in a period in which the actual LP-EGR rate is larger than the basic LP-EGR rate. It becomes too much and the combustion state gets worse. Therefore, in the first embodiment, the target LP-EGR valve opening degree tVOegr is obtained by multiplying the basic LP-EGR valve opening degree VOegr0 by the first correction magnification Rhos1, which is a positive value of 1.0 or less. By correcting the LP-EGR valve opening to the decrease side with the first correction magnification Rhos1, the actual LP-EGR rate is made to coincide with the basic LP-EGR rate, and the deterioration of the combustion state is avoided. is there.

  On the other hand, when the operating point shifts from the high load side to the differential pressure device operating range R1, the operating device 51 is closed to a predetermined value. The actual differential pressure approaches the target differential pressure. The actual LP-EGR rate is closer to the basic LP-EGR rate than when the differential pressure device 51 is in the default position by the amount that the actual differential pressure of the LP-EGR valve front-rear differential pressure approaches the target differential pressure (FIG. 36). (See dashed line). Thus, even when the differential pressure device 51 is closed to a predetermined value, if the basic LP-EGR valve opening is corrected to the decreasing side using the first correction magnification Rhos1 of the same value as in the first embodiment as it is, Too much correction. A situation in which the LP-EGR valve opening is corrected too much to the decrease side, and the actual LP-EGR rate returns to the basic LP-EGR rate after the actual LP-EGR rate becomes smaller than the basic LP-EGR rate. It is called “undershoot”). During the period when the actual LP-EGR rate undershoots, the actual LP-EGR rate is smaller than the basic LP-EGR rate. Therefore, at the basic ignition timing ADV0 at this time, the knocking occurs at the advance side from the MBT. Can occur.

  As described above, even when shifting from the low load side to the differential pressure device operating range R1, if the correction magnification value of the first embodiment is used as it is, the basic LP in the period in which the actual LP-EGR rate overshoots. -Deviation from the EGR rate may occur and engine stall may occur. In addition, when shifting from the high load side to the differential pressure device operating range R1, if the correction magnification value of the first embodiment is used as it is, the basic LP-EGR is in a period in which the actual LP-EGR rate undershoots. Knocking may occur due to a deviation from the rate.

  Here, FIG. 35 shows the actual LP-EGR rate when the differential pressure device opening is the predetermined values S4 and S1. On the other hand, FIG. 36 shows the actual LP-EGR rate when the differential pressure device 51 is closed to a predetermined value. Comparing the two figures, FIG. 36 only describes “when the differential pressure device 51 is closed to a predetermined value”, and “when the differential pressure device opening is the predetermined value S4, S1” shown in FIG. Is not supported. Thus, the differential pressure when the differential pressure device opening degree shifts from the high load side to the differential pressure device operation range R1 (FIG. 36) (FIG. 35). The reason why it does not correspond to the device opening (S4, S1) is due to the difference in operating conditions.

  Therefore, in the fourth embodiment, when the operating point shifts from the long non-LP-EGR region on the low load side to the differential pressure device operating region R1 on the high load side, the first correction magnification is corrected to the decrease side. To do. Similarly, when the operating point shifts from the long non-LP-EGR region on the high load side to the differential pressure device operating region R1 on the low load side, the first correction magnification is corrected to the decrease side. Specifically, a correction amount (hereinafter referred to as “device correction amount”) corresponding to the differential pressure device opening is newly introduced, and the first correction magnification is corrected to the reduction side with this device correction amount. In this case, the device correction amount when the operating point shifts to the high load side differential pressure device operating region R1 from a state that has been in the non-LP-EGR region on the low load side for a long time is referred to as “device correction amount 1”. On the other hand, in order to distinguish the device correction amount from the device correction amount 1 described above when the operating point shifts from the long non-LP-EGR region on the high load side to the differential pressure device operating region R1 on the low load side. “Device correction amount 2”. By correcting the first correction magnification to the decreasing side with the device correction amounts 1 and 2, the overcorrection is eliminated, that is, the actual LP-EGR rate exceeds the basic LP-EGR rate by overcorrection. It is to prevent it from happening.

  In this case, in the fourth embodiment, the change in the differential pressure across the LP-EGR valve when the actual temperature Treal of the downstream temperature of the EGR take-off part is out of the basic temperature T0 is reflected in the first correction magnification. It is not reflected in the device correction amounts 1 and 2 described above.

  On the other hand, a method of reflecting the amount of change in the differential pressure across the LP-EGR valve in the case where the actual temperature Treal of the downstream temperature of the EGR take-off portion is out of the basic temperature T0 (this method is hereinafter referred to as “ "Reference method"). For example, when the actual temperature Treal of the downstream temperature of the EGR take-out part is out of the basic temperature T0, the differential pressure across the LP-EGR valve when the differential pressure device is operating is the same as that when the differential pressure device is operating when the differential pressure device is the basic temperature T0. It varies depending on the differential pressure across the LP-EGR valve. Thus, the device correction amounts 1 and 2 are calculated not only in accordance with the differential pressure device opening but also in accordance with the temperature difference between the actual temperature Treal of the EGR extraction section downstream temperature and the basic temperature T0. However, this reference method cannot be adopted.

  The reason why the reference method cannot be adopted is as follows. That is, particularly when the operating point shifts from the non-LP-EGR region to the differential pressure device operating region R1 and when the actual temperature Treal rises from the lower side and shifts to the basic temperature T0, the actual LP -Correction to increase the EGR rate is necessary. In order to increase the actual LP-EGR rate, it is effective to increase the differential pressure across the LP-EGR valve. For this purpose, the device correction amount 1 is calculated according to the temperature difference between the actual temperature Treal and the basic temperature T0 at the downstream temperature of the EGR extraction section, and the calculated device correction amount 1 is used to reduce the differential pressure device opening. Will be corrected (close the differential pressure device 51). On the other hand, when the operating point shifts from the non-LP-EGR region to the differential pressure device operating region R1, the engine load increases when the actual temperature Treal increases from the lower side and shifts to the basic temperature T0. Therefore, there is an operational requirement to increase the amount of fresh air. Then, even if the actual LP-EGR rate can be increased with the device correction amount 1, the differential pressure device 51 is corrected in the closing direction. Therefore, the fresh air amount is reduced from before correction, and the pumping loss is corrected. It will be bigger than before. In this way, even if one request can be satisfied, another request (operational request) cannot be satisfied. Such a situation has occurred because the device correction amount 1 is calculated according to the temperature difference between the actual temperature Treal of the EGR extraction section downstream temperature and the basic temperature T0 by the reference method. Therefore, in order not to cause the above situation, the reference method is not adopted.

  In order to prevent the above situation from occurring, it is not necessary to calculate the device correction amounts 1 and 2 in accordance with the temperature difference between the actual temperature Treal of the EGR extraction section downstream temperature and the basic temperature T0. Therefore, in the fourth embodiment, device correction amounts 1 and 2 are introduced only in accordance with the differential pressure device opening. When the operating point shifts from the non-LP-EGR region to the differential pressure device operation region R1 due to the device correction amounts 1 and 2, particularly when the actual temperature rises from the low side and shifts to the basic temperature. This satisfies the demand to increase the amount of fresh air while increasing the actual LP-EGR rate.

  The flowcharts of FIGS. 37A and 37B are the fourth embodiment, which replaces the flows of FIGS. 9A and 9B of the first embodiment. That is, the flow of FIGS. 37A and 37B is a case where the operating point shifts from the non-LP-EGR region to the differential pressure device operation region R1, and the actual temperature Treal rises from the low side and shifts to the basic temperature T0. In this case, the target LP-EGR valve opening degree is calculated. The flow in FIGS. 37A and 37B is executed at regular time intervals (for example, every 10 ms). The same parts as those in the flow of FIGS. 9A and 9B of the first embodiment are denoted by the same reference numerals. In addition, since the differential pressure device opening degree is controlled in the fourth embodiment, the flow of FIGS. 37A and 37B is executed after the flow of FIG. 32 is executed.

  A description will be given mainly of portions different from the flow of FIGS. 9A and 9B of the first embodiment. In the fourth embodiment, steps 111 to 113 are additionally provided. That is, after calculating the first correction magnification Rhos1 [anonymous number] in step 8, it is checked in step 111 whether the engine operating point is in the differential pressure device operating range R1 shown in FIG. When the operating point of the engine is not in the differential pressure device operating range R1 shown in FIG. 33, steps 112 and 113 are skipped.

  When the engine operating point is in the differential pressure device operating range R1 shown in FIG. 33 in step 111, the routine proceeds to steps 112 and 113. First, in step 112, a device correction amount 1 [anonymous number] is calculated by searching a table having the contents shown in FIG. 38 from the differential pressure device opening (calculated by the flow of FIG. 32) [°]. As shown in FIG. 38, the device correction amount 1 is zero when the differential pressure device opening is other than the predetermined values S1, S3, S4. The reason why the device correction amount 1 is set to zero when the differential pressure device opening is other than S1, S3, S4 is as follows. That is, when the differential pressure device opening is other than S1, S3, and S4, the differential pressure device 51 is not closed. This is because when the differential pressure device 51 is not closed, even if the first correction magnification having the same value as that of the first embodiment is applied as it is, the correction is not excessive.

  On the other hand, when the device opening is a predetermined value S4, S3, S1, the device correction amount 1 is a value that becomes a predetermined value h, i, j (h <i <j). The reason why the device correction amount 1 is increased to h, i, j as the differential pressure device opening decreases as S4, S3, S1 is as follows. That is, as described above with reference to FIG. 35, as the differential pressure device opening becomes smaller as S4 and S1, the actual LP-EGR rate approaches the basic LP-EGR rate than when the differential pressure device 51 is in the default position. It will be overcorrected as it approaches. Therefore, the excessive correction is offset by increasing the device correction amount 1 to h, i, j as the differential pressure device opening decreases to S4, S3, S1. The actual characteristics of FIG. 38 are finally determined by adaptation.

  The characteristics in FIG. 38 correspond to those in FIG. 30 in which the differential pressure device opening is given as a discrete value. On the other hand, FIG. 39 shows the characteristics of the device correction amount 1 corresponding to FIG. 29 in which the differential pressure device opening is given as a continuous value. When the differential pressure device opening is given as a continuous value, the device correction amount 1 becomes zero when the differential pressure device opening exceeds the predetermined value S2 and is less than the predetermined value S1. Next, the device correction amount 1 increases from zero as the differential pressure device opening decreases when the differential pressure device opening is between the predetermined value S2 and the predetermined value S1 (differential pressure device operating region). When the differential pressure device opening is the predetermined value S1, the device correction amount 1 is the predetermined value j.

  In step 113, a value obtained by subtracting the device correction amount 1 [anonymous number] calculated in this way from the first correction magnification Rhos1 [anonymous number] calculated in step 8 is newly obtained as the first correction magnification Rhos1 [anonymous number]. And Here, the first correction magnification Rhos1 calculated in step 8 has a predetermined value 1. This means that what is done in step 113 means that the value obtained by subtracting the device correction amount 1 from the predetermined value 1 is set to the predetermined value 1 again. Since the predetermined value 1 is a value for giving the initial value of the first correction magnification Rhos1, in steps 111 to 113, the initial value is corrected to decrease by the device correction amount 1 in the differential pressure device operating range. Accordingly, the actual LP-EGR rate is reduced to the basic LP-EGR rate by reducing the first correction magnification by the increase in the differential pressure before and after the LP-EGR valve by closing the differential pressure device 51 in the differential pressure device operating range. Is not exceeded.

  Next, the flowchart of FIG. 40 is a case where the operating point shifts from the non-LP-EGR region to the differential pressure device operation region R1, and the actual temperature Treal decreases from the higher side and shifts to the basic temperature T0. This is for calculating the target LP-EGR valve opening degree of the fourth embodiment. The flow in FIG. 40 is executed at regular time intervals (for example, every 10 ms). The same parts as those in the flow of FIG. 14 of the first embodiment are denoted by the same reference numerals. In the fourth embodiment, since the differential pressure device opening degree is controlled, the flow of FIG. 40 is also executed after the flow of FIG. 32 is executed.

  A description will be given mainly of portions different from the flow of FIG. 14 of the first embodiment. In the fourth embodiment, steps 121 to 123 are additionally provided. That is, after calculating the first correction magnification Rhos1 [anonymous number] in step 38, it is checked in step 121 whether the engine operating point is in the differential pressure device operating range R1 shown in FIG. Steps 122 and 123 are skipped when the engine operating point is not in the differential pressure device operating range R1 shown in FIG.

  When the engine operating point is in the differential pressure device operating range R1 shown in FIG. 33 in step 121, the routine proceeds to steps 122 and 123. First, in step 122, a device correction amount 2 [anonymous number] is calculated by searching a table containing the contents of FIG. 41 from the differential pressure device opening (calculated by the flow of FIG. 32) [°]. As shown in FIG. 41, the device correction amount 2 is zero when the differential pressure device opening is other than the predetermined values S1, S3, S4. The reason why the device correction amount 2 is set to zero when the differential pressure device opening is other than S1, S3, S4 is as follows. That is, when the differential pressure device opening is other than S1, S3, and S4, the differential pressure device 51 is not closed. This is because when the differential pressure device 51 is not closed, even if the first correction magnification having the same value as that of the first embodiment is applied as it is, the correction is not excessive.

  On the other hand, when the device opening is the predetermined value S4, S3, S1, the device correction amount 2 is a value that becomes the predetermined value k, l, m (k <l <m). The reason why the device correction amount 2 is increased to k, l, m as the differential pressure device opening decreases as S4, S3, S1 is as follows. That is, as the differential pressure device opening becomes smaller as S4, S3, and S1, the actual LP-EGR rate approaches the basic LP-EGR rate more than when the differential pressure device 51 is in the default position, and the correction is made by that amount. Too much. Thus, the device correction amount 2 is increased to k, l, m as the differential pressure device opening decreases to S4, S3, and S1, thereby canceling overcorrection. The actual characteristics of FIG. 41 are finally determined by adaptation.

  The characteristics in FIG. 41 correspond to those in FIG. 30 in which the differential pressure device opening is given as a discrete value. On the other hand, FIG. 42 shows the characteristics of the device correction amount 2 corresponding to FIG. 29 in which the differential pressure device opening is given as a continuous value. When the differential pressure device opening is given as a continuous value, the device correction amount 1 becomes zero when the differential pressure device opening exceeds the predetermined value S2 and is less than the predetermined value S1. Next, the device correction amount 2 increases from zero as the differential pressure device opening decreases when the differential pressure device opening is between the predetermined value S2 and the predetermined value S1 (differential pressure device operating range). When the differential pressure device opening is the predetermined value S1, the device correction amount 2 is the predetermined value m. 38 and 39 showing the characteristics of the device correction amount 1 and FIGS. 41 and 42 showing the characteristics of the device correction amount 2 have the same vertical scale, that is, h = k, i = 1, j = M, but in reality it is different (h ≠ k, i ≠ l, j ≠ m).

  In step 123, a value obtained by subtracting the device correction amount 2 [anonymous number] calculated in this way from the first correction magnification Rhos1 [anonymous number] calculated in step 38 is renewed as the first correction magnification Rhos1 [anonymous number]. And Here, the first correction magnification Rhos1 calculated in step 38 has a predetermined value 3. This means that what is done in step 123 means that the value obtained by subtracting the device correction amount 2 from the predetermined value 3 is set to the predetermined value 3 again. Since the predetermined value 3 is a value for giving the initial value of the first correction magnification Rhos1, in steps 121 to 123, the initial value is corrected to decrease by the device correction amount 2 in the differential pressure device operating range. Accordingly, the actual LP-EGR rate is reduced to the basic LP-EGR rate by reducing the first correction magnification by the increase in the differential pressure before and after the LP-EGR valve by closing the differential pressure device 51 in the differential pressure device operating range. Is not exceeded.

  In the fourth embodiment, the differential pressure device 51 is connected to the intake pipe 4a upstream of the EGR discharge part P (confluence part to the intake pipe of the EGR passage), and the low rotational speed low load area R1 (EGR) in the LP-EGR area. At least a part of the area is provided with a differential pressure device operating area. Then, the differential pressure device 51 is closed (controlled in the closing direction) in the differential pressure device operating range R1. Further, when the operating point of the engine shifts from the non-LP-EGR region (non-EGR region) to the operating device operating region, the actual temperature of the downstream temperature of the EGR extraction unit (EGR extraction unit) shifts to the basic temperature. In this case, the first correction magnification (temperature difference correction amount) is corrected to the decrease side. As a result, the actual LP-EGR rate is suppressed from overshooting when shifting from the low load side to the differential pressure device operating range R1, and the engine stall due to deviation from the basic LP-EGR rate during the overshooting period is suppressed. Occurrence can be avoided. When the change in the actual LP-EGR rate of the fourth embodiment in the case of shifting from the low load side to the differential pressure device operating range R1 is additionally shown by a one-dot chain line in FIG. 35, the actual LP-EGR rate is the basic LP. -Follows the EGR rate with good response. In the fourth embodiment, the actual LP-EGR rate is suppressed from undershooting when shifting from the high load side to the differential pressure device operating range R1, and deviates from the basic LP-EGR rate during the undershooting period. It is possible to avoid the occurrence of knocking. When the change in the actual LP-EGR rate of the fourth embodiment in the case of shifting from the high load side to the differential pressure device operating range is additionally shown by a one-dot chain line in FIG. 36, the actual LP-EGR rate is the basic LP- It follows the EGR rate with good response. As described above, even when the differential pressure device operating region R1 is shifted from the low load side or the high load side and the actual temperature of the EGR take-out portion downstream temperature shifts to the basic temperature, the actual LP -The EGR value rate can follow the basic LP-EGR rate with good response. As a result, the fuel efficiency can be improved without sacrificing the drivability of the vehicle when shifting from the low load side or the high load side to the differential pressure device operating range R1.

  In the fourth embodiment, each of the two device correction amounts 1 and 2 (value for correcting the temperature difference correction amount to the decrease side) is set to the EGR extraction unit (EGR extraction unit) downstream temperature actual temperature Treal and a predetermined basic temperature. No correction is made according to the difference from T0. As a result, especially when the operating point shifts from the non-LP-EGR region to the differential pressure device operating region R1, the actual LP-EGR rate can be increased, but the operation is to increase the amount of fresh air. It is possible to avoid a situation in which the demands cannot be satisfied.

  In the fourth embodiment, the pressure of the EGR discharge part P (the pressure of the intake pipe downstream of the differential pressure device) is kept constant at a negative pressure by closing the differential pressure device 51 in the differential pressure device operating range R1 (controlling in the closing direction). To hold. Thereby, even if the differential pressure device 51 is provided, the same torque control as in the case where the differential pressure device 51 is not provided can be performed.

  In the fourth embodiment, the differential pressure device 51 is controlled by an opening degree map set in advance using the engine speed and the engine load as parameters. As a result, even if the differential pressure device 51 is provided, torque control and control of the LP-EGR rate are not complicated, and the functional reliability of the throttle valve 5, the LP-EGR valve 17, and the differential pressure device 51 is improved. Can be secured.

  Although the fourth embodiment has been described in the case where the differential pressure device 51 is provided in the intake pipe 4a upstream from the merge portion of the EGR passage 15, the present invention is not limited to this case. For example, a differential pressure device may be provided in the exhaust pipe 11b downstream from the branch portion of the EGR passage 15. In this case, when the differential pressure device is closed, a pressure difference is generated before and after the differential pressure device, and the pressure of the exhaust pipe 11b upstream of the differential pressure device, that is, the pressure of the EGR extraction portion N becomes higher than the atmospheric pressure. . If the atmospheric pressure is zero, a pressure higher than the atmospheric pressure becomes a positive pressure. When the pressure of the EGR take-out part N becomes a positive pressure, a pressure difference is generated before and after the LP-EGR valve 17 even at the low rotational speed and low load side in the LP-EGR region. Gas is discharged into the intake pipe 4a. Thus, by providing a differential pressure device in the exhaust pipe 11b downstream from the branch portion of the EGR passage 15, the differential pressure across the LP-EGR valve 17 can be reduced on the low rotational speed and low load side in the LP-EGR region. Can be secured.

  In the embodiment, the case where the temperature sensor 46 detects the actual temperature Treal of the downstream temperature of the EGR extraction unit has been described, but the present invention is not limited to this case. For example, the actual temperature Treal of the EGR extraction section downstream temperature may be estimated based on the engine operation history. In addition, the actual temperature of the EGR extraction section upstream temperature (the temperature of the exhaust pipe 11b upstream of the EGR extraction section) is detected by a temperature sensor, and the actual temperature of the EGR extraction section downstream temperature is determined based on the detected actual temperature of the EGR extraction section upstream temperature. It may be to estimate the temperature.

  In the embodiment, the first correction magnification Rhos1 (temperature difference correction amount) is calculated based on the actual temperature Treal of the EGR extraction section downstream temperature detected by the temperature sensor 46. However, the present invention is not limited to this case. The first correction magnification Rhos1 (temperature difference correction amount) may be calculated in combination with the EGR extraction portion downstream pressure detected by the pressure sensor.

  In the embodiment, the case where the LP-EGR device is applied to the gasoline engine has been described. However, the present invention is not limited to this case, and the present invention can be applied to the case where the LP-EGR device is applied to the diesel engine. The present invention is applicable not only to the case where the LP-EGR device is provided but also to the case of a gasoline engine and a diesel engine provided with the HP-EGR device. Because, in the future, in the gasoline engine and diesel engine equipped with the HP-EGR device, it is considered to expand the HP-EGR region. In this case, when the operating point shifts from the non-EGR region to the EGR region or when the operating point of the engine shifts within the EGR region, the actual temperature of the EGR take-out portion downstream temperature reaches a predetermined basic temperature. When shifting, the differential pressure across the EGR valve becomes smaller than at the basic temperature. Therefore, there is still room for application of the present invention in this case.

DESCRIPTION OF SYMBOLS 1 Gasoline engine 4a Intake pipe 4b Intake collector 8 Fuel injection valve 9 Spark plug 11b Exhaust pipe 12 Manifold catalyst 13 Main catalyst 14 LP-EGR device 15 EGR passage 16 EGR cooler 17 LP-EGR valve (EGR valve)
18 Motor (actuator)
41 Engine controller (basic EGR valve opening calculation means, target EGR valve opening calculation means, actuator control means)
46 Temperature sensor (temperature detection means)
48 Temperature sensor (temperature detection means)
51 Differential pressure device

Claims (5)

  An EGR passage branched from the exhaust pipe and returning a part of the exhaust to the intake pipe;
  An EGR valve that opens and closes the EGR passage;
  An actuator capable of adjusting the opening of the EGR valve;
  Basic EGR valve opening calculation means for calculating a basic EGR valve opening in a predetermined EGR region;
  When the engine operating point shifts from the non-EGR region to the EGR region or when the engine operating point shifts within the EGR region, the actual temperature of the EGR take-out portion downstream temperature shifts to a predetermined basic temperature A target EGR valve opening calculation means for correcting the basic EGR valve opening by a temperature difference correction amount and calculating a target EGR valve opening;
  Actuator control means for controlling the actuator so that the opening degree of the EGR valve becomes the calculated target EGR valve opening degree,
  On the map using engine torque and engine speed as parameters, a reverse flow region in which the reverse flow that flows from the intake pipe side to the exhaust pipe side of the EGR valve is determined in advance while being in the EGR region,
  When the engine operating point determined by the engine torque and the engine rotation speed is in the backflow region on the map, it is determined that the backflow region,
  When the actual temperature is lower than a predetermined temperature, the backflow region is expanded to the high load side.
  An EGR control device characterized by that.   An EGR passage branched from the exhaust pipe and returning a part of the exhaust to the intake pipe;
  An EGR valve that opens and closes the EGR passage;
  An actuator capable of adjusting the opening of the EGR valve;
  Basic EGR valve opening calculation means for calculating a basic EGR valve opening in a predetermined EGR region;
  When the engine operating point shifts from the non-EGR region to the EGR region or when the engine operating point shifts within the EGR region, the actual temperature of the EGR take-out portion downstream temperature shifts to a predetermined basic temperature A target EGR valve opening calculation means for correcting the basic EGR valve opening by a temperature difference correction amount and calculating a target EGR valve opening;
  Actuator control means for controlling the actuator so that the opening degree of the EGR valve becomes the calculated target EGR valve opening degree,
  A differential pressure device is provided in an intake pipe upstream from a confluence part of the EGR passage or an exhaust pipe downstream from a branch part of the EGR passage, and a differential pressure device operation region is provided in at least a part of the EGR region;
  Controlling the differential pressure device in the closing direction in the differential pressure device operating range;
  When the engine operating point shifts from the non-EGR region to the differential pressure device operating region, and the actual temperature of the downstream temperature of the EGR extraction unit shifts to the basic temperature, the temperature difference correction amount is Compensate for weight loss
An EGR control device characterized by that.   3. The EGR according to claim 2, wherein a value for correcting the temperature difference correction amount to the decrease side is not corrected according to a difference between an actual temperature of the EGR extraction unit downstream temperature and the basic temperature. Control device.   4. The EGR control apparatus according to claim 2, wherein the pressure in the intake pipe downstream of the differential pressure device is kept constant by controlling the differential pressure device in a closing direction in the differential pressure device operating region. 5. .   The EGR control device according to any one of claims 2 to 4, wherein the differential pressure device is controlled by an opening degree map that is set in advance using an engine speed and an engine load as parameters.

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