JP2009156090A - Exhaust recirculating device of variable cylinder internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique in an exhaust recirculating device of an variable cylinder internal combustion engine for obtaining a proper combustion condition relative to an operating cylinder in a cylinder reducing operation while improving fuel consumption by the cylinder reducing operation, and for reducing an NOx amount generated by the operating cylinder in combustion. <P>SOLUTION: This device has a plurality of cylinders, and can execute a cylinder reducing operation for continuing an operation by stopping fuel injection to some of the cylinders and continuing the operation with the rest of the cylinders under a cylinder reducing operation. The device comprises a low-pressure EGR device and a high-pressure EGR device. In the cylinder reducing operation, a ratio of a low-pressure EGR gas amount at an EGR gas amount combined with a low-pressure EGR gas amount recirculated from the low-pressure EGR device supplied to an internal combustion engine and a high-pressure EGR gas amount recirculated from the high-pressure EGR device is made high. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas recirculation device for a variable cylinder internal combustion engine.

A low-pressure EGR device that takes in a part of exhaust gas as low-pressure EGR gas from the exhaust passage downstream of the turbine of the turbocharger and returns the low-pressure EGR gas to the intake passage upstream of the compressor of the turbocharger, and exhausts from the exhaust passage upstream of the turbine. A high-pressure EGR device that takes in a part of the gas as high-pressure EGR gas and recirculates the high-pressure EGR gas to the intake passage downstream from the compressor. When low-temperature combustion is performed, the low-pressure EGR gas amount and high-pressure A technique for controlling the amount of EGR gas is known (see Patent Document 1).
JP-A-2005-76456 JP 2005-54771 A Japanese Patent No. 3175491

  By the way, there is a variable cylinder internal combustion engine that has a plurality of cylinders and performs a reduced cylinder operation in which fuel injection to some cylinders is stopped under reduced cylinder conditions and operation is continued with the remaining cylinders. When the reduced-cylinder operation is performed, the fuel consumption can be improved by increasing the engine load of the working cylinder. A low pressure EGR device and a high pressure EGR device can also be used for this variable cylinder internal combustion engine. However, during the cylinder reduction operation of the variable cylinder internal combustion engine, since the exhaust components discharged from the working cylinder and the idle cylinder are different, the EGR gas component recirculated to the internal combustion engine changes for each cycle. This change affects the EGR rate of the working cylinder to which EGR gas is supplied, makes the EGR rate of the working cylinder unstable, and makes the combustion state of the working cylinder unstable. Further, since the engine load of the working cylinder is increased during the reduced-cylinder operation, the amount of NOx generated by the working cylinder during combustion increases.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas recirculation device for a variable cylinder internal combustion engine, while improving fuel efficiency by reducing cylinder operation, while reducing the operating cylinder during reduced cylinder operation. It is another object of the present invention to provide a technique for realizing an appropriate combustion state and reducing the amount of NOx generated by a working cylinder during combustion.

In the present invention, the following configuration is adopted. That is, the present invention
An exhaust gas recirculation device for a variable cylinder internal combustion engine having a plurality of cylinders and capable of executing a reduced cylinder operation in which fuel injection to some cylinders is stopped under reduced cylinder conditions and operation is continued in the remaining cylinders. ,
A turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
A low-pressure EGR device that takes in a part of exhaust gas as low-pressure EGR gas from the exhaust passage downstream from the turbine and recirculates the low-pressure EGR gas to the intake passage upstream from the compressor;
A high-pressure EGR device that takes in a part of exhaust gas as high-pressure EGR gas from the exhaust passage upstream of the turbine and recirculates the high-pressure EGR gas to the intake passage downstream of the compressor;
With
In the variable-cylinder internal combustion engine, the ratio of the low-pressure EGR gas amount to the EGR gas amount obtained by combining the low-pressure EGR gas amount and the high-pressure EGR gas amount supplied to the internal combustion engine is increased during the reduced-cylinder operation. Exhaust gas recirculation device.

  When the variable cylinder internal combustion engine is in the reduced cylinder operation, the exhaust components discharged from the working cylinder and the non-operating cylinder are different, so the EGR gas component recirculated to the variable cylinder internal combustion engine changes for each cycle. This change affects the EGR rate of the working cylinder to which EGR gas is supplied, makes the EGR rate of the working cylinder unstable, and makes the combustion state of the working cylinder unstable. This is because the carbon dioxide concentration of the high pressure EGR gas recirculated by the high pressure EGR device changes due to the difference in the carbon dioxide concentration of the exhaust discharged from the working cylinder and the idle cylinder, and the intake oxygen concentration in the working cylinder changes. Due to instability. The high pressure EGR gas is recirculated from the exhaust passage upstream of the turbine to the intake passage downstream of the compressor. Therefore, if the high-pressure EGR gas has different carbon dioxide concentrations in the exhaust gas discharged from the working cylinder and the idle cylinder, the carbon dioxide concentration changes in accordance with the cycle-by-cycle change in the carbon dioxide concentration in the exhaust gas. is there. In addition, since the load on the working cylinder increases during the reduced-cylinder operation, the amount of NOx generated by the working cylinder during combustion increases.

  Therefore, in the present invention, during the reduced-cylinder operation, the ratio of the low-pressure EGR gas amount to the EGR gas amount obtained by combining the low-pressure EGR gas amount and the high-pressure EGR gas amount supplied to the internal combustion engine is increased.

  According to the present invention, the ratio of the low pressure EGR gas amount is increased and the ratio of the high pressure EGR gas amount is decreased during the reduced cylinder operation. The low pressure EGR gas is returned from the exhaust passage downstream of the turbine to the intake passage upstream of the compressor. Therefore, even if the low-pressure EGR gas has different carbon dioxide concentrations in the exhaust gas discharged from the working cylinder and the non-operating cylinder, when the low-pressure EGR gas is recirculated to the intake passage upstream of the compressor, It is mixed and stirred with a compressor. For this reason, the low pressure EGR gas and the fresh air are uniformly mixed, and the oxygen concentration of the intake air is stabilized. Thereby, the EGR rate of the working cylinder is stabilized, and an appropriate combustion state can be realized for the working cylinder.

  Further, during the reduced cylinder operation, since the load is increased in the working cylinder, the exhaust amount increases, and in the idle cylinder, the exhaust amount decreases. Therefore, the exhaust pulsation occurs with a large displacement amount and a large span. With such exhaust pulsation, the turbocharger using exhaust energy as a drive source has a reduced supercharging capability. In addition, if a part of the exhaust gas is taken into the high-pressure EGR device from the exhaust passage upstream of the turbine in order to recirculate the high-pressure EGR gas, the amount of exhaust gas passing through the turbine is reduced, which also reduces the turbocharger's supercharging capability. End up. However, according to the present invention, since the ratio of the high pressure EGR gas amount is reduced, the amount of exhaust gas taken into the high pressure EGR device from the exhaust passage upstream of the turbine is reduced, and the exhaust amount passing through the turbine is increased. It is possible to prevent the charger's supercharging ability from being reduced. Since the supercharging capability is maintained in this way, it is possible to smoothly return to the normal operation in which the operation of the deactivated cylinder is resumed.

  Furthermore, since the load on the working cylinder is increased during the reduced-cylinder operation, the amount of NOx generated by the working cylinder during combustion increases. However, according to the present invention, when the low pressure EGR gas is returned from the exhaust passage downstream from the turbine to the intake passage upstream from the compressor, the low pressure EGR gas is cooled because the return passage is long, so that the intake air can be cooled. Since the ratio of the low-pressure EGR gas amount that can cool the intake air is increased, the intake air can be cooled strongly and the combustion temperature is lowered in the working cylinder. When the combustion temperature decreases, the amount of NOx generated during combustion decreases, so the amount of NOx generated by the working cylinder during combustion can be reduced.

  As described above, while reducing fuel consumption by reducing cylinder operation, it is possible to realize an appropriate combustion state for the operating cylinder during reduced cylinder operation, to suppress a decrease in supercharging capacity, and to reduce NOx generated by the operating cylinder during combustion. it can.

  The low-pressure EGR device may be provided with a cooling means for cooling the low-pressure EGR gas flowing through the low-pressure EGR device.

  According to the present invention, the low pressure EGR gas can be cooled more powerfully, so that the intake air can be cooled more powerfully. Therefore, the combustion temperature is further lowered in the working cylinder. When the combustion temperature decreases, the amount of NOx generated during combustion decreases, so that the amount of NOx generated by the working cylinder during combustion can be further reduced.

  According to the present invention, in an exhaust gas recirculation apparatus for a variable cylinder internal combustion engine, while improving fuel efficiency by reducing cylinder operation, it is possible to realize an appropriate combustion state with respect to the operating cylinder during reduced cylinder operation and to generate the operating cylinder during combustion. The amount of NOx can be reduced.

  Specific examples of the present invention will be described below.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas recirculation apparatus for an internal combustion engine according to this embodiment is applied, and an intake system and an exhaust system thereof. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-stroke cycle diesel engine having four cylinders 2 that form a combustion chamber together with a piston. The internal combustion engine 1 is mounted on a vehicle. Each cylinder 2 is provided with a fuel injection valve 3 that is supplied with light oil as fuel and injects the light oil into the cylinder 2 at an appropriate amount and at an appropriate timing. An intake passage 4 and an exhaust passage 5 are connected to the internal combustion engine 1.

  In the middle of the intake passage 4 connected to the internal combustion engine 1, a compressor 6a of a turbocharger that operates using exhaust energy as a drive source is disposed. A first throttle valve 7 that adjusts the flow rate of intake air flowing through the intake passage 4 is disposed in the intake passage 4 upstream of the compressor 6a. The first throttle valve 7 is opened and closed by an electric actuator. An air flow meter 8 that outputs a signal corresponding to the flow rate of fresh air flowing in the intake passage 4 is disposed in the intake passage 4 upstream of the first throttle valve 7. The air flow meter 8 measures the intake air amount (fresh air amount) taken into the internal combustion engine 1. An intake air temperature sensor 9 that outputs a signal corresponding to the temperature of fresh air flowing through the intake air passage 4 is disposed in the intake air passage 4 upstream of the air flow meter 8. The intake air temperature sensor 9 measures the intake air temperature (fresh air temperature) taken into the internal combustion engine 1.

  An intercooler 10 that performs heat exchange between the intake air and outside air is disposed in the intake passage 4 downstream of the compressor 6a. A second throttle valve 11 that adjusts the flow rate of the intake air flowing through the intake passage 4 is disposed in the intake passage 4 downstream of the intercooler 10. The second throttle valve 11 is opened and closed by an electric actuator. These intake passages 4 and the devices arranged in the intake passages 4 constitute an intake system for taking intake air into the internal combustion engine 1.

  On the other hand, a turbocharger turbine 6 b is disposed in the middle of the exhaust passage 5 connected to the internal combustion engine 1. An exhaust purification device 12 is disposed in the exhaust passage 5 downstream of the turbine 6b. The exhaust emission control device 12 includes an oxidation catalyst and a diesel particulate filter (hereinafter simply referred to as a filter) disposed at the subsequent stage of the oxidation catalyst. The filter carries a NOx storage reduction catalyst (hereinafter simply referred to as NOx catalyst). The exhaust passage 5 and the devices arranged in the exhaust passage 5 constitute an exhaust system for exhausting exhaust gas from the internal combustion engine 1.

The internal combustion engine 1 is provided with a low-pressure EGR device 30 that recirculates (recirculates) a part of the exhaust gas flowing through the exhaust passage 5 to the intake passage 4 at a low pressure. In this embodiment, the exhaust gas recirculated by the low pressure EGR device 30 is referred to as low pressure EGR gas.

  The low pressure EGR device 30 includes a low pressure EGR passage 31 through which the low pressure EGR gas flows, a low pressure EGR valve 32 that adjusts a flow rate of the low pressure EGR gas that flows through the low pressure EGR passage 31, a low pressure EGR cooler 33 that cools the low pressure EGR gas, and Have.

  The low pressure EGR passage 31 connects the exhaust passage 5 downstream of the exhaust purification device 12 and the intake passage 4 upstream of the compressor 6 a and downstream of the first throttle valve 7. Through this low-pressure EGR passage 31, the exhaust is sent to the internal combustion engine 1 at low pressure as low-pressure EGR gas.

  The low-pressure EGR valve 32 is disposed in the low-pressure EGR passage 31 downstream from the low-pressure EGR cooler 33, and adjusts the flow cross-sectional area of the low-pressure EGR passage 31 to adjust the flow rate of the low-pressure EGR gas flowing through the low-pressure EGR passage 31. To do. The low pressure EGR valve 32 is opened and closed by an electric actuator. The low-pressure EGR gas flow rate can be adjusted by a method other than the adjustment of the opening degree of the low-pressure EGR valve 32. For example, by adjusting the opening of the first throttle valve 7 or by adjusting the opening of an exhaust throttle valve (not shown), the differential pressure between the upstream and downstream of the low pressure EGR passage 31 is changed. The flow rate of the low pressure EGR gas can be adjusted.

  The low pressure EGR cooler 33 is disposed in the middle of the low pressure EGR passage 31. The low-pressure EGR cooler 33 exchanges heat between the low-pressure EGR gas passing through the low-pressure EGR cooler 33 and the engine cooling water, and lowers the temperature of the low-pressure EGR gas. The low pressure EGR cooler 33 in this embodiment corresponds to the cooling means of the present invention.

  On the other hand, the internal combustion engine 1 is provided with a high pressure EGR device 40 that recirculates (recirculates) a part of the exhaust gas flowing in the exhaust passage 5 to the intake passage 4 at a high pressure. In the present embodiment, the exhaust gas recirculated by the high pressure EGR device 40 is referred to as high pressure EGR gas.

  The high pressure EGR device 40 includes a high pressure EGR passage 41 through which the high pressure EGR gas flows, and a high pressure EGR valve 42 that adjusts the flow rate of the high pressure EGR gas through the high pressure EGR passage 41.

  The high pressure EGR passage 41 connects the exhaust passage 5 upstream of the turbine 6 b and the intake passage 4 downstream of the second throttle valve 11. Exhaust gas is sent to the internal combustion engine 1 at high pressure as high pressure EGR gas through the high pressure EGR passage 41.

  The high-pressure EGR valve 42 is disposed in the high-pressure EGR passage 41 and adjusts the flow rate of the high-pressure EGR gas flowing through the high-pressure EGR passage 41 by adjusting the passage cross-sectional area of the high-pressure EGR passage 41. The high pressure EGR valve 42 is opened and closed by an electric actuator. The adjustment of the high-pressure EGR gas flow rate can also be performed by a method other than the adjustment of the opening degree of the high-pressure EGR valve 42. For example, by adjusting the opening degree of the second throttle valve 11, the differential pressure between the upstream and downstream of the high pressure EGR passage 41 can be changed, and thereby the flow rate of the high pressure EGR gas can be adjusted. Further, when the turbine 6b of the turbocharger is of a variable capacity type, the amount of high-pressure EGR gas can be adjusted also by adjusting the opening degree of the nozzle vane that changes the flow rate characteristics of the turbine 6b.

  The internal combustion engine 1 configured as described above is provided with an ECU 13 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 13 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  The ECU 13 has an air flow meter 8, an intake air temperature sensor 9, a crank position sensor 14 that detects the engine speed, and an accelerator that can detect the fuel injection amount by outputting an electric signal corresponding to the amount of depression of the accelerator pedal 15 by the driver. An opening sensor 16, a water temperature sensor 17 that detects the temperature of the engine cooling water, an atmospheric pressure sensor 18 that detects atmospheric pressure, and a vehicle speed sensor 19 that detects the vehicle speed of the vehicle are connected via electric wiring, and these various sensors An output signal is input to the ECU 13.

  On the other hand, the actuators of the fuel injection valve 3, the first throttle valve 7, the second throttle valve 11, the low pressure EGR valve 32, and the high pressure EGR valve 42 are connected to the ECU 13 through electric wiring. These devices are controlled.

  The internal combustion engine 1 according to this embodiment stops fuel injection into, for example, No. 1 and No. 2 cylinders under the reduced cylinder condition among No. 1 to No. 4 cylinders, and the remaining Nos. 2 and 3 This is a variable-cylinder internal combustion engine that can perform a reduced-cylinder operation that continues operation with two cylinders. In the following, the case where the operation is performed by injecting fuel in all the cylinders is referred to as the normal operation in contrast to the reduced cylinder operation. The purpose of performing the reduced cylinder operation is that when the engine load is taken along the horizontal axis and the fuel consumption is taken along the vertical axis, as shown in FIG. This is because fuel efficiency is improved by increasing the engine load of the working cylinder while reducing the number of cylinders (hereinafter referred to as working cylinders, here, the second and third cylinders). In the reduced-cylinder operation, only the fuel injection is stopped and the intake and exhaust are performed in the cylinders in which the fuel injection is stopped (hereinafter referred to as the stopped cylinders, here, the first and fourth cylinders).

  Next, switching control between normal operation and reduced-cylinder operation in this embodiment will be described. FIG. 3 is a schematic view exemplifying use areas of normal operation and reduced-cylinder operation according to the operation state of the internal combustion engine 1 in the present embodiment. 3 represents the engine speed Ne of the internal combustion engine 1, and the vertical axis represents the required torque T of the internal combustion engine.

  In FIG. 3, the reduced-cylinder operation region is a region where the operating state of the internal combustion engine 1 is low torque and high rotation, and the reduced-cylinder operation is performed. That is, the reduced cylinder condition is when the operating state of the internal combustion engine 1 is included in the reduced cylinder operating region. For example, in the case of a four-cylinder internal combustion engine as in this embodiment, the reduced-cylinder operation is performed when the engine speed is 1600 with a low gear such as the second speed and a vehicle speed of 30 km. Further, in the case of an 8-cylinder internal combustion engine, it is possible to perform a reduced-cylinder operation including an idle state with low torque and low rotation. For this reason, the reduced-cylinder operation region in FIG. 3 is merely an example, and the region changes depending on the type of the internal combustion engine. On the other hand, the normal operation region is a region other than the reduced-cylinder operation region, and normal operation is performed. By switching between normal operation and reduced-cylinder operation in this way, reduced-cylinder operation is performed as much as possible to improve fuel efficiency.

By the way, during the reduced-cylinder operation, the exhaust components discharged from the working cylinder and the non-operating cylinder are different, so the components of the EGR gas combined with the low-pressure EGR gas and the high-pressure EGR gas recirculated to the internal combustion engine 1 change for each cycle. Resulting in. This change in the EGR gas component affects the EGR rate indicating the ratio of EGR gas in the intake air of the working cylinder to which the EGR gas is supplied, and the EGR rate of the working cylinder becomes unstable, and the combustion state of the working cylinder becomes unstable. become. This is because the carbon dioxide concentration of the high pressure EGR gas recirculated by the high pressure EGR device 40 changes due to the difference in the carbon dioxide concentration of the exhaust discharged from each of the working cylinder and the idle cylinder, and the intake oxygen concentration of the working cylinder changes. Is due to the instability. The high pressure EGR gas is recirculated from the exhaust passage 5 upstream from the turbine 6b to the intake passage 4 downstream from the compressor 6a. Therefore, if the high-pressure EGR gas has a short recirculation path and the high-pressure EGR gas has different carbon dioxide concentrations in the exhaust gas discharged from the working cylinder and the idle cylinder, the carbon dioxide concentration in the exhaust gas varies depending on the cycle. This is because the carbon concentration changes cyclically. Further, since the engine load of the working cylinder is increased during the reduced-cylinder operation, the amount of NOx generated by the working cylinder during combustion increases.

  In this embodiment, therefore, the ratio of the low-pressure EGR gas amount to the EGR gas amount that is the sum of the low-pressure EGR gas amount and the high-pressure EGR gas amount supplied to the internal combustion engine 1 is increased during the reduced-cylinder operation.

  Specifically, the maximum opening degree of the high pressure EGR valve 42 during the reduced cylinder operation is decreased and the maximum opening degree of the low pressure EGR valve 32 is increased as compared with the normal operation, so that the low pressure EGR gas amount and the high pressure EGR gas amount are increased. The ratio of the low-pressure EGR gas amount to the combined EGR gas amount is increased.

  According to this embodiment, the ratio of the low-pressure EGR gas amount is increased during the reduced-cylinder operation and the ratio of the high-pressure EGR gas amount is decreased as compared with the normal operation. The low pressure EGR gas is recirculated from the exhaust passage 5 downstream of the turbine 6b to the intake passage 4 upstream of the compressor 6a. Therefore, even when the low pressure EGR gas is recirculated to the intake passage 4 upstream from the compressor 6a, the low pressure EGR passage 31 in the intake passage 4 and the exhaust gas discharged from the working cylinder and the idle cylinder are different from each other. While flowing through a long path from the connection part to the intake valve, it is mixed with fresh air and further stirred by the compressor 6a. For this reason, the low pressure EGR gas and the fresh air are uniformly mixed, and the oxygen concentration of the intake air is stabilized. Thereby, the EGR rate of the working cylinder is stabilized, and an appropriate combustion state can be realized for the working cylinder.

  Further, during the reduced-cylinder operation, the engine load increases in the second and third working cylinders, so the displacement increases, and the first and fourth idle cylinders simply perform intake and exhaust without combustion. For this reason, the exhaust pulsation was a large displacement when the No. 2 and No. 3 working cylinders burned and a span of 180 ° CA during normal operation where all No. 1 to No. 4 cylinders burned. While the 2nd and 3rd working cylinders are combusted, the range is 360 ° CA and the combustion interval is generated with a large span. When the exhaust pulsation has such a large displacement and a large span, the turbocharger that uses exhaust energy as a drive source has a reduced supercharging capability. In addition, if a part of the exhaust gas is taken into the high-pressure EGR device 40 from the exhaust passage 5 upstream from the turbine 6b in order to recirculate the high-pressure EGR gas, the amount of exhaust gas passing through the turbine 6b is reduced, which also causes excessive turbocharger excess. The salary capacity will drop. However, according to the present embodiment, the ratio of the high-pressure EGR gas amount is decreased during the reduced-cylinder operation, so that the amount of the exhaust gas taken into the high-pressure EGR device 40 from the exhaust passage 5 upstream from the turbine 6b is reduced and passes through the turbine 6b. Since the amount of exhaust gas to be increased increases, it is possible to suppress the turbocharger's supercharging capability from being lowered. Since the supercharging capability is maintained in this way and the supercharging pressure is easily applied, for example, when the vehicle accelerates from the reduced cylinder operation and the operation of the deactivated cylinder is resumed to return to the normal operation, the normal operation is smoothly restored. it can.

  Further, since the engine load of the working cylinder is increased during the reduced-cylinder operation, the amount of NOx generated by the working cylinder during combustion increases. However, according to the present embodiment, when the low-pressure EGR gas is recirculated from the exhaust passage 5 downstream from the turbine 6b to the intake passage 4 upstream from the compressor 6a, the low-pressure EGR gas is cooled because the recirculation path is long, and in addition, the low-pressure EGR cooler 33 Because it is cooled strongly by the, intake air can be cooled strongly. Since the ratio of the low-pressure EGR gas amount that can cool the intake air strongly during the reduced-cylinder operation is increased, the intake air can be strongly cooled and the combustion temperature is lowered in the working cylinder. When the combustion temperature decreases, the amount of NOx generated during combustion decreases, so the amount of NOx generated by the working cylinder during combustion can be reduced.

  As described above, according to this embodiment, while improving fuel efficiency by reducing cylinder operation, it is possible to realize an appropriate combustion state with respect to the operating cylinder at the time of reducing cylinder operation, and to suppress a decrease in supercharging capacity. Can reduce the amount of NOx generated during combustion.

  A control routine for performing the reduced-cylinder operation according to this embodiment will be described. FIG. 4 is a flowchart showing a control routine for performing reduced-cylinder operation according to this embodiment. This routine is repeatedly executed every predetermined time.

  In step S101, the ECU 13 detects the engine speed Ne based on the output signal from the crank position sensor 14.

  In step S102, the ECU 13 detects the fuel injection amount qfin based on the output signal from the accelerator opening sensor 16.

  In step S <b> 103, the ECU 13 calculates an environmental correction amount based on output signals from the water temperature sensor 17, the intake air temperature sensor 9, and the atmospheric pressure sensor 18.

  In step S104, the ECU 13 detects the vehicle speed based on the output signal from the vehicle speed sensor 19.

  In step S105, the ECU 13 calculates the required torque T. Specifically, the required torque T is calculated based on the engine speed Ne detected in step S101, the fuel injection amount qfin detected in step S102, the environmental correction amount calculated in step S103, and the vehicle speed detected in step S104. Is done.

  In step S106, the ECU 13 determines whether or not the reduced cylinder operation is possible. In this determination, whether the engine speed Ne detected in step S101 and the required torque T calculated in step S105 are incorporated in the map shown in FIG. Judge by no.

  If an affirmative determination is made in step S106 that the reduced-cylinder operation is possible, the process proceeds to step S107. If it is determined in step S106 that the reduced-cylinder operation is not possible, this routine is temporarily terminated.

  In step S107, the ECU 13 performs cylinder deactivation setting. Specifically, a setting is made to stop fuel injection from the fuel injection valve 3 for the first and fourth cylinders.

  In step S108, the ECU 13 calculates the fuel injection amount from the fuel injection valve 3 for the second and third cylinders during the reduced cylinder operation. Specifically, it is calculated as “fuel injection amount qtmp = 2 × fuel injection amount qfin + torque step correction term qdm during reduced-cylinder operation”. Here, the fuel injection amount qfin is detected in step S102. Further, the torque step correction term qdm is for correcting the torque step during the reduced-cylinder operation, and is a negative correction term for reducing the “fuel injection amount qtmp during the reduced-cylinder operation” from “2 × fuel injection amount qfin”. is there. That is, the fuel efficiency is improved during the reduced cylinder operation by the torque step correction term qdm.

  In step S109, the ECU 13 calculates various control amounts based on the fuel injection amount qtmp during the reduced cylinder operation. Specifically, various control amounts of the common rail pressure, the supercharging pressure, the fuel injection timing, and the fuel injection pattern are calculated based on the fuel injection amount qtmp during the reduced cylinder operation.

  In step S110, the ECU 13 calculates a target EGR rate during the reduced cylinder operation. In order to improve fuel efficiency during reduced-cylinder operation, the fuel injection amount differs between normal operation and reduced-cylinder operation. For this reason, the exhaust components after combustion are also different. Therefore, in order to fill this difference in exhaust components, the target EGR rate during the reduced-cylinder operation tends to increase the amount of EGR gas compared to the target EGR rate during normal operation (the EGR rate indicating the ratio of EGR gas in the total intake air It tends to be larger).

  In step S111, the ECU 13 calculates the high pressure EGR valve opening and the low pressure EGR valve opening (both EGR valve openings) during the reduced cylinder operation. Specifically, the high-pressure EGR valve opening and the low-pressure EGR valve opening during the reduced-cylinder operation are the engine speed Ne detected in step S101, the fuel injection amount qtmp calculated in step S108, and the target calculated in step S110. Calculated from a three-dimensional map based on the EGR rate. At this time, the maximum opening degree of the high pressure EGR valve 42 is reduced and the maximum opening degree of the low pressure EGR valve 32 is increased as compared with the normal operation, thereby reducing the cylinder operation. Increase the ratio of the low-pressure EGR gas amount to the hourly EGR gas amount.

  FIG. 5A shows the maximum opening degree of the high pressure EGR valve 42 with respect to the engine speed Ne, and FIG. 5B shows the maximum opening degree of the low pressure EGR valve 32 with respect to the engine speed Ne. The solid line in FIGS. 5A and 5B is the maximum opening during the reduced cylinder operation, and the broken line is the maximum opening during the normal operation. As shown in FIG. 5, the maximum opening degree of the high pressure EGR valve 42 during the reduced cylinder operation is reduced and the maximum opening degree of the low pressure EGR valve 32 is increased as compared with the normal operation time with respect to the engine speed Ne. This is also true for the fuel injection amount qtmp, and although not shown, the maximum opening of the high-pressure EGR valve 42 during the reduced cylinder operation is smaller for the fuel injection amount qtmp than during normal operation. In addition, the maximum opening degree of the low pressure EGR valve 32 is increased.

  Thereby, at the time of reduced-cylinder operation, the high-pressure EGR valve opening is set to the closed side and the low-pressure EGR valve opening is set to the open side as compared with the normal operation. Therefore, during the reduced cylinder operation, the ratio of the low pressure EGR gas amount is increased and the ratio of the high pressure EGR gas amount is decreased as compared with the normal operation.

  In the present embodiment, the high-pressure EGR valve opening is set to the closed side and the low-pressure EGR valve opening is set to the open side as compared with the normal operation during the reduced-cylinder operation, thereby reducing the low pressure in the EGR gas amount. Although the ratio of the EGR gas amount is increased, the present invention is not limited to this. For example, the high-pressure EGR valve opening and the low-pressure EGR valve opening remain unchanged during the reduced-cylinder operation and during the reduced-cylinder operation, other devices (for example, the first and second throttle valves 7, 11 and the exhaust throttle) The ratio of the low pressure EGR gas amount to the EGR gas amount may be increased by a valve, a variable displacement turbine 6b, or the like.

  In step S112, the ECU 13 executes control. Specifically, the first and fourth cylinder deactivations are executed in accordance with the cylinder deactivation settings set in step S107, various controls are performed in accordance with the various control amounts calculated in step S109, and set in step S111. Control of the high-pressure EGR valve 42 and the low-pressure EGR valve 32 is executed so that the opening degree is reached. After the processing of this step, this routine is once ended.

  By executing the above control routine, the reduced-cylinder operation in which the ratio of the low-pressure EGR gas amount to the EGR gas amount recirculated to the internal combustion engine 1 can be performed.

  The exhaust gas recirculation device for a variable cylinder internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the present invention.

1 is a diagram illustrating a schematic configuration of an internal combustion engine according to a first embodiment and intake and exhaust systems thereof. The figure which shows the relationship between the engine load and fuel consumption in the normal driving | operation and reduced-cylinder driving which concern on Example 1. FIG. The figure which shows the use area | region of the normal driving | operation according to the driving | running state of the internal combustion engine which concerns on Example 1, and a reduced cylinder driving | operation. 3 is a flowchart showing a control routine for performing reduced-cylinder operation according to the first embodiment. It is a figure which shows the relationship between the engine speed of an internal combustion engine and the maximum opening degree of an EGR valve in the normal driving | operation and reduction-cylinder driving which concern on Example 1, (a) is a case where it is a high pressure EGR valve, (b) is This is the case of the low pressure EGR valve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Intake passage 5 Exhaust passage 6a Compressor 6b Turbine 7 First throttle valve 8 Air flow meter 9 Intake temperature sensor 10 Intercooler 11 Second throttle valve 12 Exhaust purification device 13 ECU
14 Crank position sensor 15 Accelerator pedal 16 Accelerator opening sensor 17 Water temperature sensor 18 Atmospheric pressure sensor 19 Vehicle speed sensor 30 Low pressure EGR device 31 Low pressure EGR passage 32 Low pressure EGR valve 33 Low pressure EGR cooler 40 High pressure EGR device 41 High pressure EGR passage 42 High pressure EGR valve

Claims (2)

An exhaust gas recirculation apparatus for a variable cylinder internal combustion engine having a plurality of cylinders and capable of executing a reduced cylinder operation in which fuel injection to some cylinders is stopped under reduced cylinder conditions and operation is continued in the remaining cylinders. ,
A turbocharger having a turbine disposed in an exhaust passage of the internal combustion engine and a compressor disposed in an intake passage of the internal combustion engine;
A low-pressure EGR device that takes in a part of exhaust gas as low-pressure EGR gas from the exhaust passage downstream from the turbine and recirculates the low-pressure EGR gas to the intake passage upstream from the compressor;
A high-pressure EGR device that takes in a part of exhaust gas as high-pressure EGR gas from the exhaust passage upstream of the turbine and recirculates the high-pressure EGR gas to the intake passage downstream of the compressor;
With
In the variable-cylinder internal combustion engine, the ratio of the low-pressure EGR gas amount to the EGR gas amount obtained by combining the low-pressure EGR gas amount and the high-pressure EGR gas amount supplied to the internal combustion engine is increased during the reduced-cylinder operation. Exhaust gas recirculation device.   2. The exhaust gas recirculation device for a variable cylinder internal combustion engine according to claim 1, wherein the low pressure EGR device is provided with a cooling means for cooling the low pressure EGR gas flowing through the low pressure EGR device.

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