JP2009191644A - Control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for accurately estimating a cylinder intake air amount and calculating an appropriate smoke limit injection amount in a control system of an internal combustion engine, including an EGR system in which an HPLEGR device and an LPLEGR device are juxtaposed, for performing fuel injection control for limiting a fuel injection amount according to the smoke limit injection amount defined based on the cylinder intake air amount. <P>SOLUTION: The control system includes the HPLEGR device, the LPLEGR device, and an air-flow meter. Based on a measurement of an air amount by the air-flow meter, an LPLEGR gas amount, and a volume of an air-intake system area which is an area of an air-intake passage from an LPLEGR gas in-flow port to an HPLEGR gas in-flow port, the control system estimates an air amount inside the air-intake system area. Based on the estimation of the air amount inside the air-intake area, the control system estimates a cylinder intake air amount. The control system calculates a smoke limit injection amount based on the estimation of the cylinder intake air amount and performs control to limit a fuel injection amount so that it does not exceed the calculated smoke limit injection amount. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control system for an internal combustion engine.

  A technique for performing EGR for returning a part of exhaust gas from an internal combustion engine to an intake system is known. For example, in Patent Document 1, in an internal combustion engine equipped with a turbocharger, an HPLEGR device that flows a part of exhaust gas from an exhaust passage upstream of a turbine into an intake passage downstream of a compressor, and a downstream of the turbine. The EPLE is equipped with two systems of EGR devices, an LPLEGR device that allows part of the exhaust gas to flow into the intake passage upstream of the compressor from the exhaust passageway, and the EGR is switched by switching between the HPLEGR device and the LPLEGR device according to the operating state of the internal combustion engine. The technique to be performed is described.

Further, by setting a limit value corresponding to the cylinder intake air amount with respect to the fuel injection amount, and performing control so that fuel injection with a fuel injection amount larger than this limit value (referred to as the smoke limit injection amount) is not executed. A technique for suppressing smoke in exhaust gas is known (see, for example, Patent Document 2).
Japanese Patent Laying-Open No. 2005-076456 JP 2004-278431 A JP 2006-249972 A Japanese Patent Laid-Open No. 2002-227692 Japanese Patent No. 3864671

  When the fuel injection amount control as in Patent Document 2 is performed in an internal combustion engine equipped with an EGR system, it is possible to accurately estimate the influence of the EGR gas amount control on the cylinder intake air amount. Is important in setting.

  By the way, in an internal combustion engine equipped with an EGR system equipped with an HPLEGR device and an LPLEGR device as in Patent Document 1, specifications such as the path length and the passage volume are different between the HPLEGR gas distribution path and the LPLEGR gas distribution path. ing. In addition, a large-capacity component such as an intercooler or a compressor is interposed between the HPLEGR gas inlet and the LPLEGR gas inlet in the intake passage. Therefore, the control responsiveness differs between the control of the HPLEGR gas amount sucked into the cylinder and the control of the LPLEGR gas amount.

  Further, an intake system region including a large-capacity component as described above is interposed between the position where the air flow meter measures the amount of fresh air and the cylinder, and fresh air and LPLEGR gas are included in the intake system region. Therefore, there may be a difference between the measured value of the new air amount by the air flow meter and the actual cylinder intake air amount.

  Due to these circumstances, in the case of an EGR system equipped with an HPLEGR device and an LPLEGR device, the HPLEGR gas amount and the LPLEGR gas amount actually sucked into the cylinder are accurately measured, particularly in a transient state where the control amount of the HPLEGR gas and the LPLEGR gas changes. It is difficult to estimate well, and therefore it is difficult to accurately obtain the cylinder intake air amount that is the basis for setting the smoke limit injection amount.

Therefore, when the fuel injection restriction control is performed with the smoke limit injection amount in an internal combustion engine equipped with an EGR system equipped with the HPLEGR device and the LPLEGR device, the smoke limit injection amount is set to an excessive value so that the smoke in the exhaust gas is sufficient. There is a possibility that the engine cannot be suppressed, or conversely, the smoke limit injection amount is set to an excessively small value, and the engine performance such as the acceleration performance is deteriorated.

  The present invention has been made in view of such circumstances, and includes an EGR system that is provided with an HPLEGR device and an LPLEGR device, and a fuel that limits the fuel injection amount by a smoke limit injection amount that is determined according to the cylinder intake air amount. An object of the present invention is to provide a technique for accurately estimating a cylinder intake air amount and calculating an appropriate smoke limit injection amount in a control system for an internal combustion engine that performs injection control.

In order to achieve this object, the control system for an internal combustion engine of the present invention comprises:
An HPLEGR device that causes a part of exhaust gas from the internal combustion engine to flow into the intake passage from an HPLEGR gas inlet provided in the intake passage of the internal combustion engine;
An LPLEGR device that causes a portion of the exhaust from the internal combustion engine to flow into the intake passage from an LPLEGR gas inlet provided upstream of the HPLEGR gas inlet of the intake passage;
An air flow meter for measuring the amount of air flowing into the intake passage;
The measured value of the air amount by the air flow meter, the amount of LPLEGR gas flowing into the intake passage by the LPLEGR device, and the intake system region that is the region from the LPLEGR gas inlet to the HPLEGR gas inlet in the intake passage An air amount estimation means for estimating an air amount in the intake system region based on the volume of
Cylinder intake air amount estimating means for estimating the amount of air sucked into the cylinder of the internal combustion engine based on the estimated air amount in the intake system region;
Based on the estimated cylinder intake air amount, a smoke limit injection amount calculation that calculates a smoke limit injection amount that is an upper limit value of a fuel injection amount that can reduce the amount of smoke in the exhaust gas to a predetermined allowable limit or less. Means,
Fuel injection control means for performing control to limit the fuel injection amount so as not to exceed the calculated smoke limit injection amount;
It is characterized by providing.

  According to the above configuration, the amount of air flowing into the intake system region and the amount of LPLEGR gas flowing out of the intake system region and reflected in the amount of air and LPLEGR gas that is taken into the cylinder is It can be estimated based on the volume of the system area. Then, the estimated delay with respect to the air amount flowing into the intake system region measured by the air flow meter and the LPLEGR gas amount (measured value or control value) flowing into the intake system region by the LPLEGR device. By reflecting the above, it is possible to accurately estimate the air amount and LPLEGR gas amount in the gas in the intake system region. Therefore, even when a large-capacity component such as an intercooler or a turbocharger compressor exists in the intake system region, the air amount and LPLEGR gas amount in the intake system region gas can be accurately estimated. Can do.

  According to the present invention, since the amount of air sucked into the cylinder is estimated based on the air amount in the intake system region gas thus estimated, even in a system in which an HPLEGR device and an LPLEGR device are provided together, It is possible to accurately estimate the cylinder intake air amount. Since the smoke limit injection amount is calculated based on the cylinder intake air amount estimated in this way, it is possible to calculate an appropriate smoke limit injection amount that is not excessive or insufficient with respect to the actual cylinder intake air amount. it can.

  Therefore, by performing fuel injection control that limits the fuel injection amount by the smoke limit injection amount calculated in this way, it is possible to suppress the fuel injection amount from becoming excessive or too small relative to the cylinder intake air amount. it can. Thereby, in the fuel injection amount restriction control, it is possible to suppress the smoke in the exhaust from exceeding the allowable limit or the engine performance such as the acceleration performance from being deteriorated.

  In the above configuration, based on the volume of the intake system region, the time during which the air and LPLEGR gas flowing into the intake system region are transported through the intake system region is estimated, and based on the estimated time, the air flow meter The amount of air flowing into the intake system region and the amount of LPLEGR gas flowing into the intake system region by the LPLEGR device are reflected in the amount of air in the gas flowing through the intake system region and the amount of LPLEGR gas. Can be estimated.

In the present invention,
The air amount estimation means includes air contained in the gas flowing in the intake system region based on the measured value of the air amount by the air flow meter, the LPLEGR gas amount, and the volume of the intake system region. And the ratio of LPLEGR gas,
The cylinder intake air amount estimation means is based on a mixed state of the gas in the intake system region containing air and LPLEGR gas at the estimated ratio and the HPLEGR gas flowing into the intake passage by the HPLEGR device. Thus, the cylinder intake air amount may be estimated.

  As described above, according to the configuration of the present invention, the amount of air flowing into the intake system region, that is, the measured value of the air amount by the air flow meter, and the LPLEGR gas amount flowing into the intake system region by the LPLEGR device are: The delay until it is reflected in the air amount and the LPLEGR gas amount in the gas in the intake system region can be estimated based on the volume of the intake system region. Therefore, it is possible to estimate the ratio of air in the gas flowing through the intake system region and the ratio of LPLEGR gas.

  The gas sucked into the cylinder can be considered as a mixed gas of the gas sucked into the cylinder from within the intake system region and the HPLEGR gas that flows into the intake passage from the HPLEGR inlet and sucked into the cylinder. Therefore, based on the mixed state of the gas derived from the intake system region and the HPLEGR gas in the cylinder intake gas, the ratio of the air in the gas derived from the intake system region and the ratio of the LPLEGR gas, the amount of air in the cylinder intake gas Can be estimated.

According to the present invention, in a transient state where the ratio of HPLEGR gas in the gas sucked into the cylinder changes,
The cylinder intake air amount estimation means estimates the cylinder intake air amount by replacing a change in the ratio of the HPLEGR gas with a change in the ratio of the gas in the intake system region sucked into the cylinder. can do.

  As described above, since the gas sucked into the HPLEGR gas cylinder in the cylinder intake gas can be considered as a mixed gas of the intake system region gas and the HPLEGR gas, the ratio of the HPLEGR gas in the cylinder intake gas is reduced. In this case, it is considered that the ratio of the gas derived from the intake system region in the cylinder intake gas increases by an amount corresponding to the decrease. Conversely, when the ratio of HPLEGR gas in the cylinder intake gas increases, it is considered that the ratio of gas derived from the intake system region in the cylinder intake gas decreases by an amount corresponding to the increase.

According to the configuration of the present invention, the ratio of the air in the gas derived from the intake system region and LPLEGR based on the volume of the intake system region, the measured value of the air amount by the air flow meter, and the LPLEGR gas amount by the LPLEGR device. The gas ratio can be estimated. Therefore, in a transient state in which the ratio of HPLEGR gas in the cylinder intake gas changes, the change in the ratio of HPLEGR gas is replaced with the ratio of the gas derived from the intake system region as described above, and the intake air for the replaced amount By converting the gas derived from the system region into a change in the ratio of the air in the cylinder intake gas and the change in the ratio of the LPLEGR gas according to the change in the ratio of the HPLEGR gas according to the estimated ratio of the air and the ratio of the LPLEGR gas, It is possible to estimate the cylinder intake gas air amount in the transient state.

  As a result, even in an internal combustion engine equipped with an EGR system equipped with an HPLEGR device and an LPLEGR device, it is possible to accurately estimate the cylinder intake air amount in a transient state in which the HPLEGR gas amount and the LPLEGR gas amount change. . Therefore, an appropriate smoke limit injection amount can be set even in a transient state, and an increase in smoke emission amount and a decrease in engine performance can be suitably suppressed in the fuel injection amount restriction control.

  According to the present invention, in an internal combustion engine control system that includes an EGR system that includes an HPLEGR device and an LPLEGR device, and that performs fuel injection control that limits the fuel injection amount by a smoke limit injection amount that is determined according to the cylinder intake air amount, It is possible to accurately estimate the intake air amount and calculate an appropriate smoke limit injection amount.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention only to those unless otherwise specified.

  FIG. 1 is a conceptual diagram schematically showing a schematic configuration of an internal combustion engine to which the EGR system according to the present embodiment is applied and its intake system and exhaust system. The internal combustion engine 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

  Each cylinder 2 of the internal combustion engine 1 communicates with the intake passage 3 via an intake manifold 17. An HPLEGR passage 41, which will be described later, is connected in the vicinity of the connection portion between the intake manifold 17 and the intake passage 3. A second throttle valve 9 that adjusts the amount of intake air flowing through the intake passage 3 is disposed in the intake passage 3 upstream of the connection point of the HPLEGR passage 41. An intercooler 8 for cooling the intake air is disposed in the intake passage 3 upstream of the second throttle valve 9. A compressor 11 of a turbocharger 13 is disposed in the intake passage 3 upstream from the intercooler 8. An LPLEGR passage 31 to be described later is connected to the intake passage 3 upstream of the compressor 11. A first throttle valve 6 that adjusts the amount of fresh air flowing into the intake passage 3 is disposed in the intake passage 3 upstream from the connection point of the LPLEGR passage 31. An air flow meter 7 that measures the amount of fresh air flowing into the intake passage 3 is provided in the intake passage 3 upstream of the first throttle valve 6.

In the intake system configured as described above, external air flows into the intake passage 3 after dust or dirt is removed by an air cleaner (not shown). Air (fresh air) flowing into the intake passage 3 is mixed with LPLEGR gas (described later) flowing into the intake passage 3 from the LPLEGR passage 31, passes through the compressor 11, is pressurized, and passes through the intercooler 8. And cooled. The gas (mixed gas of fresh air and LPLEGR gas) that has passed through the intercooler 8 is mixed with HPLEGR gas (described later) flowing into the intake passage 3 from the HPLEGR passage 41 and flows into the intake manifold 17. The gas (mixed gas of fresh air, LPLEGR gas, and HPLEGR gas) that flows into the intake manifold 17 is sucked into the cylinder 2 through each branch pipe of the intake manifold 17.

  Each cylinder 2 of the internal combustion engine 1 communicates with the exhaust passage 4 via an exhaust manifold 18. An HPLEGR passage 41 is connected to the exhaust passage 4 immediately downstream of the exhaust manifold 18. A turbine 12 of the turbocharger 13 is disposed in the exhaust passage 4 on the downstream side from the connection point of the HPLEGR passage 41. The turbocharger 13 is a variable capacity turbocharger provided with a nozzle vane 5 that makes the flow area of exhaust gas passing through the turbine 12 variable. An exhaust purification device 10 is disposed in the exhaust passage 4 on the downstream side of the turbine 12. The exhaust purification device 10 stores NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and stores the NOx that has been stored when the oxygen concentration of the exhaust gas becomes low, and reduces and purifies the NOx. And a particulate filter capable of collecting particulate matter (PM) therein and capable of oxidizing and removing the collected PM in a timely manner. The configuration of the exhaust purification device 10 is not limited to this example.

  An exhaust throttle valve 19 that adjusts the amount of exhaust gas flowing through the exhaust passage 4 is disposed in the exhaust passage 4 downstream of the exhaust purification device 10. An LPLEGR passage 31 is connected to the exhaust passage 4 downstream of the exhaust throttle valve 19. The exhaust throttle valve 19 may be arranged in the exhaust passage 4 downstream from the connection point of the LPLEGR passage 31.

  In the exhaust system configured as described above, the burnt gas after combustion in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust manifold 18 and flows into the exhaust passage 4. Part of the exhaust gas flowing through the exhaust passage 4 flows into the HPLEGR passage 41 in accordance with EGR control (described later), and is guided to the intake passage 3 as HPLEGR gas. Exhaust gas other than that flows downstream from the HPLEGR passage 41, and after rotating the turbine 13, passes through the exhaust gas purification device 10 to purify NOx, PM, and the like. Part of the exhaust gas that has passed through the exhaust gas purification device 10 flows into the LPLEGR passage 31 in accordance with EGR control, and is led to the intake passage 3 as LPLEGR gas. The other exhaust flows downstream from the LPLEGR passage 31, passes through a muffler (not shown), etc., and is then discharged into the atmosphere.

  The internal combustion engine 1 includes an HPLEGR device 40 that guides a part of the exhaust gas flowing through the exhaust passage 4 upstream of the turbine 12 to the intake passage 3 downstream of the compressor 11 and returns the exhaust gas to the internal combustion engine 1. The HPLEGR device 40 has an HPLEGR passage 41 that connects the exhaust passage 4 upstream of the turbine 12 and the intake passage 3 downstream of the second throttle valve 9, and a part of the exhaust is taken in via the HPLEGR passage 41. It flows into the passage 3. Exhaust gas returned to the internal combustion engine 1 by the HPLEGR device 40 is referred to as HPLEGR gas.

  An HPLEGR cooler 43 that cools the HPLEGR gas is disposed in the HPLEGR passage 41. An HPLEGR valve 42 that changes the flow area of the HPLEGR passage 41 is disposed in the HPLEGR passage 41 on the downstream side (the intake passage 3 side) of the HPLEGR cooler 43. The amount of HPLEGR gas flowing through the HPLEGR passage 41 is adjusted by adjusting the opening degree of the HPLEGR valve 42. As means for adjusting the HPLEGR gas amount, means for adjusting the back pressure by adjusting the opening of the second throttle valve 9, adjusting the back pressure, or adjusting the opening of the nozzle vane 5 is used. You can also.

  The internal combustion engine 1 is provided with an LPLEGR device 30 that guides a part of the exhaust gas flowing through the exhaust passage 4 downstream of the turbine 12 to the intake passage 3 upstream of the compressor 11 and returns the exhaust gas to the internal combustion engine 1. The LPLEGR device 30 has an LPLEGR passage 31 that connects the exhaust passage 4 downstream of the exhaust throttle valve 19 and the intake passage 3 upstream of the compressor 11, and a part of the exhaust is taken into the intake passage through the LPLEGR passage 31. 3 is allowed to flow. The exhaust gas returned to the internal combustion engine by the LPLEGR device 30 is referred to as LPLEGR gas.

  An LPLEGR cooler 33 that cools the LPLEGR gas is disposed in the LPLEGR passage 31. An LPLEGR valve 32 that changes the flow area of the LPLEGR passage 31 is disposed in the LPLEGR passage 31 on the downstream side (the intake passage 3 side) of the LPLEGR cooler 33. The amount of LPLEGR gas flowing through the LPLEGR passage 31 is adjusted by adjusting the opening degree of the LPLEGR valve 32. As means for adjusting the LPLEGR gas amount, means for adjusting the differential pressure between the upstream and downstream of the LPLEGR passage 31 by adjusting the opening of the first throttle valve 6 may be used.

  The internal combustion engine 1 is provided with an ECU 20 that is a computer that controls the internal combustion engine 1. In addition to the air flow meter 7 described above, the ECU 20 outputs an electric signal corresponding to the depression amount (accelerator opening) of the water temperature sensor 14 that outputs an electric signal corresponding to the temperature of the cooling water of the internal combustion engine 1 and the accelerator pedal. Various sensors such as an accelerator opening sensor 15 and a crank position sensor 16 that outputs a pulse signal each time the crankshaft of the internal combustion engine 1 rotates by a predetermined angle (for example, 10 °) are connected, and output signals from these sensors. Is input to the ECU 20. The ECU 20 is connected to devices such as the first throttle valve 6, the second throttle valve 9, the nozzle vane 5, the exhaust throttle valve 19, the LPLEGR valve 32, and the HPLEGR valve 42, and these devices are output from the ECU 20. These drives are controlled by a control signal.

  The ECU 20 grasps the operating state of the internal combustion engine 1 based on signals input from the sensors and performs control corresponding to the driver's request. For example, the ECU 20 calculates the rotational speed of the internal combustion engine 1 based on a signal input from the crank position sensor 16 and calculates the load of the internal combustion engine 1 based on a signal input from the accelerator opening sensor 15. Fuel injection control and EGR control are performed according to the operating state of the internal combustion engine 1 acquired in this way.

  Next, EGR control performed in the system of the present embodiment will be described.

  FIG. 2 is a diagram showing a map of the target EGR rate determined according to the operating state of the internal combustion engine 1. As shown in FIG. 2, in the system of the present embodiment, EGR control is performed so that the EGR rate becomes smaller as the internal combustion engine 1 is operating at a higher load and higher rotation side. The EGR rate is defined as the ratio of EGR gas in all cylinder intake gas. That is, when the cylinder intake air amount Ga and the cylinder intake EGR gas amount Ge are set, the EGR rate Re = Ge / (Ga + Ge).

  Further, in the system of the present embodiment, a target value of the distribution ratio for distributing all EGR gas with HPLEGR gas and LPLEGR gas is determined. FIG. 3 is a diagram showing a general tendency of the target distribution ratio determined according to the operating state of the internal combustion engine 1. As shown in FIG. 3, when the internal combustion engine 1 is in a low-load low-rotation operation state, the HPLEGR gas ratio is set high, and EGR is performed mainly using the HPLEGR device 40. Further, as the load or the rotational speed of the internal combustion engine 1 becomes higher, the ratio of HPLEGR gas is set lower and the ratio of LPLEGR gas is set higher, and EGR is performed using the HPLEGR device 40 and the LPLEGR device 30 in combination. Further, when the internal combustion engine 1 is in a high-load high-rotation operation state, the ratio of the LPLEGR gas is set high, and EGR is mainly performed using the LPLEGR device 30.

The target values of the EGR rate and the distribution ratio of HPLEGR gas and LPLEGR gas are determined by internal operations such as NOx and smoke so that engine performance such as exhaust characteristics and fuel consumption characteristics can achieve predetermined regulation values and desired target values. It is determined according to the operating state of the engine 1 and stored in the ROM of the ECU 20. Further, the amount of HPLEGR gas and the amount of LPLEGR gas flowing into the intake passage 3 by the HPLEGR device 40 and the LPLEGR device 30 satisfy the target values of the EGR rate and the distribution ratio of HPLEGR gas and LPLEGR gas determined as described above. The target values of the opening degrees of the HPLEGR valve 42 and the LPLEGR valve 32 are determined according to the operating state of the internal combustion engine 1, and are similarly stored in the ROM of the ECU 20.

  The ECU 20 acquires the operating state of the internal combustion engine 1 based on the outputs from the sensors, reads the target valve opening of the HPLEGR valve 42 and the LPLEGR valve 32 from the ROM in accordance with the acquired operating state, and reads the HPLEGR valve 42 and LPLEGR. The valve 32 is controlled. The HPLEGR gas amount and the LPLEGR gas amount can be adjusted by a method other than adjusting the valve opening degree of the HPLEGR valve 42 or the LPLEGR valve 32. For example, the HPLEGR gas amount and the LPLEGR gas amount can be adjusted by adjusting the opening degree of the first throttle valve 6, the second throttle valve 9, the nozzle vane 5, and the exhaust throttle valve 19. Feedback control of the first throttle valve 6, the second throttle valve 9, the nozzle vane 5, or the exhaust throttle valve 19 is performed so that the HPLEGR gas amount and the LPLEGR gas amount coincide with target values according to the operating state of the internal combustion engine 1. You may make it do.

  Next, fuel injection control performed in the system of the present embodiment will be described. When the fuel injection amount is excessive as compared with the air amount in the cylinder intake gas, there is a problem that the amount of smoke generated increases. Therefore, in this embodiment, an upper limit value (smoke limit injection amount) of the fuel injection amount that suppresses the amount of smoke generated to be equal to or less than a predetermined allowable limit is obtained, so that the fuel injection amount does not exceed the smoke limit injection amount. In addition, the fuel injection amount was controlled. Specifically, the air amount in the cylinder intake gas is calculated, and the smoke limit injection amount is calculated according to the calculated cylinder intake air amount. Then, the target fuel injection amount calculated in accordance with the operating state is compared with the smoke limit injection amount. When the target fuel injection amount exceeds the smoke limit injection amount, the smoke limit injection amount is set as a command value for the fuel injection amount. In this way, by performing control to limit the fuel injection amount, it is possible to suppress the amount of smoke generated from increasing beyond the allowable limit.

  Next, transient characteristics of EGR control will be described.

  As shown in FIG. 1, the LPLEGR gas that has passed through the LPLEGR valve 32 circulates through the intake passage 3 including the compressor 11 and the intercooler 8 until the cylinder 2 sucks the LPLEGR gas. Therefore, even if the opening degree of the LPLEGR valve 32 is controlled so that the LPLEGR gas amount in the cylinder intake gas becomes the predetermined target LPLEGR gas amount as described above, the LPLEGR gas amount actually sucked into the cylinder 2 is not increased. Until the target LPLEGR gas amount corresponding to the opening degree of the LPLEGR valve 32 is reached, there is a delay corresponding to the volume of the intake system region as described above through which the LPLEGR gas flows. Between the opening degree control of the HPLEGR valve 42 and the change in the amount of HPLEGR gas actually sucked into the cylinder 2, the HPLEGR gas passes through the HPLEGR valve 42 and is sucked into the cylinder 2. A similar delay occurs depending on the volume of the intake system region.

  Due to such a delay, in the transient state where the target value of the EGR gas amount changes, the air amount in the cylinder intake gas, the EGR gas amount, the EGR rate, etc. The related control could not be performed properly. In this regard, a high-load operation state in which the target HPLEGR gas amount and the target LPLEGR gas amount are both set to 0 from a certain operation state (first operation state) in which EGR is performed by using the HPLEGR device 40 and the LPLEGR device 30 together. A description will be given of an acceleration transient to (second operating state) as an example.

FIG. 4B is a time chart showing temporal changes in the ratio Ra of fresh air in the cylinder intake gas, the ratio Rh of HPLEGR gas, and the ratio Rl of LPLEGR gas during the acceleration transient. The sum Rh + Rl of the ratio of HPLEGR gas (HPLEGR rate) and the ratio of LPLEGR gas (LPLEGR rate) in all cylinders intake gas is equal to the EGR rate Re. As described above, the target value for the distribution ratio when the EGR rate Re is distributed to the HPLEGR rate Rh and the LPLEGR rate Rl is determined according to the operating state according to the map of FIG. The sum of the air ratio (air ratio) Ra, the HPLEGR rate Rh, and the LPLEGR rate Rl in all the cylinder intake gases is 1 (100%).

Until time t ₁ is the first operating state, to at time t ₁ and acceleration transition to the second operating state is initiated. In this example, the target EGR rate Re ₂ = 0 corresponding to the second operating state, and therefore the target HPLEGR rate Rh ₂ = 0 and the target LPLEGR rate Rl ₂ = 0. That is, at time _{t 1,} the opening degree of the opening and the LPLEGR valve 32 of HPLEGR valve 42 are both controlled to fully closed.

FIG. 4A is a time chart showing the change over time of the smoke limit injection amount. The smoke limit injection amount Qc is set according to the cylinder intake air amount Ga (= Gcyl × Ra) calculated based on the air ratio Ra in the cylinder intake gas and the total gas amount Gcyl sucked into the cylinder 2. Is done. The cylinder intake total gas amount Gcyl is calculated based on the operating state of the internal combustion engine 1. The control of the smoke limit injection amount shown in FIG. 4A includes the above-described control of the EGR gas amount (that is, the control of the EGR valve), the change in the EGR gas amount actually sucked into the cylinder 2 according to the control, The case where the delay which arises in between is not considered is shown. That is, the control at time _{t 1} the opening of the opening and the LPLEGR valve 32 of HPLEGR valve 42 when it is controlled fully closed, HPLEGR ratio of the actual cylinder intake gas and LPLEGR rate, corresponding to the second operating state In this example, the target value (target HPLEGR rate Rh ₂ = 0, target LPLEGR rate Rl ₂ = 0) is considered to change without delay. In this case, it is considered that the air ratio in the cylinder intake gas immediately changes to the target air ratio Ra ₂ = 1 corresponding to the second operation state at time t ₁ . Accordingly, the smoke limit injection amount Qc is also set to the target smoke limit injection amount Qc ₂ corresponding to the second operating state at time t ₁ . Here, an acceleration transient state is considered, and supercharging by the turbocharger 13 is performed with acceleration, so that the amount of cylinder intake gas increases. Correspondingly, smoke limit injection amount after time t _1, the value increased from Qc ₂ is set.

However, as described above, there is a delay in the control of the EGR gas amount. That is, at the time just after time _{t 1, the} remaining intercooler 8 within such a LPLEGR gas remaining (LPLEGR gas which has been controlled to the target LPLEGR gas amount corresponding to the first operating state) and the intake passage 3 Since the HPLEGR gas (HPLEGR gas that has been controlled to the target HPLEGR gas amount according to the first operation state) and the like are sucked into the cylinder 2, the LPLEGR gas amount and HPLEGR gas amount in the actual cylinder intake gas are as follows: It is considered that the target values (target LPLEGR gas amount = 0, target HPLEGR gas amount = 0) corresponding to the second operation state are not immediately obtained.

Accordingly, it is considered that the actual air ratio in the cylinder intake gas is smaller than the target air ratio Ra ₂ corresponding to the second operating state at a time point immediately after time t ₁ . Therefore, the results in setting the smoke limit injection amount Qc to the target smoke limit injection amount Qc ₂ corresponding to the second operating state at the time immediately after the timing of time t _1, the excessive smoke limit injection to the actual cylinder intake air quantity The amount is set, and smoke exceeding the allowable limit may be discharged depending on the operation state.

On the other hand, after the target EGR rate of the cylinder intake gas is set to the target EGR rate (Re ₂ = 0) corresponding to the second operation state, the actual EGR rate of the cylinder intake gas depends on the second operation state. was taking into account the delay until the change in the target EGR rate, it is conceivable to delay the setting the smoke limit injection amount to the target smoke limit injection amount Qc ₂ corresponding to the second operating state.

FIG. 5 (A), at time _{t 1} from the opening of HPLEGR valve 42 and LPLEGR valve 32 is controlled to fully closed, until the time _{t 2} it is determined that the actual cylinder EGR rate of the intake gas is zero, It shows an example of delayed setting the smoke limit injection amount to the target value Qc ₂ corresponding to the second operating state.

In this case, for HPLEGR rate and LPLEGR ratio of the cylinder intake gas, as shown in FIG. 5 (B), the degree of opening of HPLEGR valve 42 and LPLEGR valve 32 is controlled to the fully closed at time _{t 1,} the time t _This means that the target HPLEGR rate Rh ₁ and the target LPLEGR rate Rl ₁ corresponding to the first operating state remain unchanged until the EGR rate of the cylinder intake gas becomes 0 in ₂ .

  However, as shown in FIG. 1, in the case of LPLEGR gas and HPLEGR gas, the EGR gas (LPLEGR gas, LPLGRGR gas, LPLGRGR gas, LPLGRGR gas, LPLEGR gas, Since the conditions such as the volume of the intake system region through which (HPLEGR gas) flows are different, the control of the EGR gas amount (that is, the control of the EGR valve opening degree) and the EGR gas amount actually sucked into the cylinder 2 in accordance therewith are controlled. The response characteristic during the change is different between the control of the HPLEGR gas amount and the control of the LPLEGR gas amount. Specifically, in general, the pipe length of the LPLEGR passage 31 tends to be longer than that of the HPLEGR passage 41 due to mounting restrictions, and the compressor 11 and the intercooler 8 are provided in the intake system region where the LPLEGR gas flows. Therefore, the response characteristic of the LPLEGR gas amount control tends to be slower than the response characteristic of the HPLEGR gas amount control.

Thus, in practice, at a time prior to LPLEGR gas amount in the cylinder intake gas at time t ₂ is 0, the response HPLEGR gas amount in the cylinder intake gas is changed to 0 is considered to be completed. Therefore, although the HPLEGR gas amount has actually become 0, the smoke limit set based on the assumption that the HPLEGR gas amount corresponding to the first operating state still exists in the cylinder intake gas. The injection amount is considered to be too small relative to the actual cylinder intake air amount. For this reason, the fuel injection amount is excessively limited in spite of the fact that more fuel can be injected, and the acceleration performance may be impaired.

  Therefore, in a transient state where the control target value of the EGR gas amount changes, considering the difference in response characteristics between the HPLEGR gas amount control and the LPLEGR gas amount control, the HPLEGR gas amount and the LPLEGR gas amount in the cylinder intake gas It is conceivable to estimate the changes in

  FIG. 6 shows a case where changes in the HPLEGR gas amount and the LPLEGR gas amount in the cylinder intake gas are estimated in consideration of the difference in response characteristics between the HPLEGR gas amount control and the LPLEGR gas amount control.

As shown in FIG. 6B, the target HPLEGR rate Rh ₂ = 0 and the target LPLEGR rate Rl ₂ = 0 corresponding to the second operation state are set at the start of the acceleration transient state at time t ₁ , and accordingly, The opening degree of the HPLEGR valve 42 and the LPLEGR valve 32 is controlled to be fully closed. Then, to complete the change to the target HPLEGR ratio _Rh 2 = 0 corresponding to the second operating state at time _{t 1} 'to fast HPLEGR rate relatively response is slightly delayed from the time _{t 1.} Further, it is estimated that the LPLEGR rate having a slower response characteristic compared to the HPLEGR gas amount control is completed at the time t ₂ after the time T ₁ ′, and the change to the target LPLEGR rate Rl ₂ = 0 corresponding to the second operating state is completed at the time t ₂ . .

When estimating in this way, in the transition period (time t ₁ ′ to t ₂ ) in which the change in the HPLEGR rate is completed and the change in the LPLEGR rate is delayed, the gas sucked into the cylinder 2 is the first It is presumed that it is composed of LPLEGR gas having an LPLEGR rate Rl ₁ corresponding to the operating state and the remaining air (fresh air). Accordingly, the air ratio Ra ′ (6) of the cylinder intake gas during the transition period is estimated as Ra ′ (6) = Ra ₁ + Rh ₁ . As shown in FIG. 6B, the air ratio Ra ′ (6) during the transition period is larger than the target air ratio Ra ₁ corresponding to the first operating state, and the target air ratio Ra corresponding to the second operating state. Less than ₂ . Accordingly, the smoke limit injection amount during the transition period is larger than the target smoke limit injection amount Qc ₁ corresponding to the first operating state and smaller than the target smoke limit injection amount Qc ₂ corresponding to the second operating state. '(6) is set. In addition, it is the same as that of the above-mentioned that the smoke limit injection quantity also increases from Qc '(6) with the raise of the supercharging pressure during a transition period.

Incidentally, the cylinder intake gas estimation method during the transition period shown in FIG. 6 is such that all of the cylinder intake gas at a ratio corresponding to the change ΔRh = Rh ₁ −Rh ₂ (= Rh ₁ ) of the HPLEGR rate is replaced by air. The LPLEGR rate is based on the premise that the LPLEGR rate Rl ₁ corresponding to the first operating state is constant. However, the cylinder intake gas includes the HPLEGR gas supplied from the HPLEGR passage 41 to the intake manifold 17 and the gas supplied to the intake manifold 17 from the intake system region upstream from the connection point of the HPLEGR passage 41 (that is, fresh air). And a mixture gas of LPLEGR gas), the cylinder intake gas at a ratio corresponding to the change amount ΔRh of the HPLEGR rate is in the intake system region upstream from the connection point of the HPLEGR passage 41. It can be considered that the gas is supplied by the gas supplied from In this embodiment, the composition of the cylinder intake gas during the transition period is estimated based on such a concept.

  Hereinafter, in the intake passage 3, the region upstream of the connection point of the HPLEGR passage 41 (that is, the HPLEGR gas inlet) and downstream of the connection point of the LPLEGR passage 31 (that is, the LPLEGR gas inlet) is referred to as an “intake system region”. ". As described above, the response characteristic of the LPLEGR gas amount control has a tendency to be slower than the response characteristic of the HPLEGR gas amount control. This is because even if the opening degree of the LPLEGR valve 32 changes, the LPLEGR valve 32 is changed at that time. Until all the gas remaining in the intake system region on the downstream side is scavenged and sucked into the cylinder 2, the change in the opening degree of the LPLEGR valve 32 depends on the LPLEGR gas amount in the actual cylinder suction gas. It is because it is not reflected. In this sense, the gas existing in the intake system region is referred to herein as “residual gas”.

の割合で新気が含まれ、

の割合でＬＰＬＥＧＲガスが含まれると考える。ここで、上記の「一定期間」とは、第１運転状態に対応する空気比率及びＬＰＬＥＧＲ率に制御された空気及びＬＰＬＥＧＲガスが、吸気系領域全域を充填するのに要する期間以上の長さの期間である。 Assuming the composition of the residual gas in the intake system area, a certain period of time until the certain just before acceleration transition condition is initiated at time t ₁ to the second operating state, and constantly the internal combustion engine 1 is a first operating state Then, it is considered that it is determined by the control target value Rl ₁ of the LPLEGR rate corresponding to the first operating state and the control target value Ra ₁ of the air ratio corresponding to the first operating state. That is, residual gas in the intake system region

The rate of freshness is included,

It is considered that LPLEGR gas is contained at a ratio of. Here, the above-mentioned “predetermined period” is longer than the period required for the air and LPLEGR gas controlled to the air ratio and LPLEGR rate corresponding to the first operating state to fill the entire intake system region. It is a period.

  Further, the composition of the residual gas may be estimated based on the measured value of the fresh air amount by the air flow meter 7 and the control target value of the LPLEGR gas amount (or LPLEGR rate). In this case, the air that has flowed into the intake system region through the air flow meter 7 and the LPLEGR gas that has flowed into the intake system region through the LPLEGR valve 32 are sucked into the cylinder 2 through the intake system region. Time (time required for scavenging the residual gas in the intake system region) to the history of the volume of the intake system region, the volume of the cylinder 2, the operating state (rotation speed, load, etc.) of the internal combustion engine 1 and the like Estimate based on. Then, a delay process based on the estimated time is performed on the measured value of the fresh air amount by the air flow meter 7 and the control value of the LPLEGR gas amount, so that the ratio of fresh air in the residual gas in the intake system region The ratio Rl_ic between Ra_ic and LPLEGR gas may be estimated.

という計算により推定することができる。 For example, in the case of a general operating state in which the assumption that steady operation has been performed in the first operating state for a certain period of time before the acceleration transient state is reached, for example, The ratio Ra_ic of air in the gas and the ratio Rl_ic of LPLEGR gas can be estimated. When the measured value Ga_bass (t) by the air flow meter 7 at a certain time t, the control map value Gl (t) of the LPLEGR gas amount, and the scavenging time Δt of the residual gas in the intake system region, the residual gas in the intake system region The fresh air ratio Ra_ic (t) and the LPLEGR gas ratio Rl_ic (t) are

It can be estimated by the calculation.

  In addition, the composition of the residual gas in the intake system region may be different depending on the position in the intake system region. In such a case, the fresh air ratio Ra_ic (x) and the LPLEGR gas ratio Rl_ic (x) in the residual gas at the position x in the intake system region, the operating state history, and the air flow meter measurement as described above. By calculating the value, LPLEGR gas amount control map value, intake system region volume, etc., and calculating the sum or average value thereof, the ratio of fresh air in the residual gas in the intake system region Ra_ic and LPLEGR gas The ratio Rl_ic may be estimated.

In this embodiment, it is considered that the change ΔRh (= Rh ₁ −Rh ₂ , where the HPLEGR rate decreases) of the HPLEGR rate in the cylinder intake gas is replaced by the residual gas. That is, the HPLEGR rate in the cylinder intake gas has completed the change to the HPLEGR rate Rh ₂ corresponding to the second operating state, and the LPLEGR rate still corresponds to the first operating state.
In the transition period such that the rate Rl ₁ , the gas sucked into the cylinder 2 includes the fresh air included at the ratio of the air ratio Ra ₁ corresponding to the first operating state and the HPLEGR rate corresponding to the second operating state. and HPLEGR gas contained in a ratio of Rh _2, and LPLEGR gas contained in a proportion of LPLEGR rate Rl ₁ corresponding to the first operating state, the intake system area residual gas contained in a ratio of variation ΔRh of HPLEGR rate, I think that it is comprised by. The residual gas is considered to contain fresh air at a rate of Ra_ic and LPLEGR gas at a rate of Rl_ic as described above.

となる。このようにして推定される過渡期間中における空気の比率Ｒａ’と、過渡期間中における全シリンダ吸入ガス量Ｇｃｙｌと、に基づいて、過渡期間中におけるシリンダ吸入空気量Ｇａ’は、

によって計算することができる。 Therefore, the air ratio Ra ′ and the LPLEGR rate Rl ′ in the cylinder intake gas during the transition period are

It becomes. Based on the air ratio Ra ′ during the transient period estimated in this way and the total cylinder intake gas amount Gcyl during the transient period, the cylinder intake air amount Ga ′ during the transient period is

Can be calculated by:

によって計算することもできる。 Further, the cylinder intake air amount Ga ′ after the HPLEGR gas amount Gh in the cylinder intake gas has changed corresponds to the cylinder intake air amount Ga and the change ΔGh in the HPLEGR gas amount immediately before the HPLEGR gas amount changes. It can also be considered as the sum of the air amount ΔGa contained in the residual gas in the intake system region of the gas amount. Here, the cylinder intake air amount Ga immediately before the HPLEGR gas amount changes takes into account the delay based on the scavenging time Δt of the residual gas in the intake system region with respect to the measured value Ga_bass of the new air amount by the air flow meter 7. Can be calculated. Further, it is considered that the residual gas contains air at a ratio of Ra_ic as described above. Therefore, the cylinder intake air amount Ga ′ (t) at time t during the transition period is

Can also be calculated.

FIG. 7 is a time chart showing the time change of the cylinder intake gas composition estimated by the estimation method of the embodiment and the time change of the smoke limit injection amount set based on the change. Here, as in the cases described above, in the acceleration transient state, the target values of the HPLEGR rate and the LPLEGR rate are set to the target HPLEGR rate Rh ₂ = 0 and the target LPLEGR rate Rl ₂ = 0 corresponding to the second operating state, respectively. The case where it will be described.

As shown in FIG. 7 (B), at time _{t 1} the opening of HPLEGR valve 42 and LPLEGR valve 32 is controlled to fully closed, at time _{t 1} 'to fast HPLEGR rate response characteristics are slightly delayed from the time _{t 1} The change to the target HPLEGR rate Rh ₂ = 0 is completed. Further, the LPLEGR rate having a response characteristic slower than the HPLEGR rate is delayed from the time t ₁ ′, and the change to the target LPLEGR rate Rl ₂ = 0 is completed at the time t ₂ .

Then, the HPLEGR rate has completed the change to the target value Rh ₂ (= 0) corresponding to the second operation state, and the LPLEGR rate has not completed the change (time t ₁ ′ to t ₂ ). , The cylinder intake gas includes air having an air ratio Ra ₁ corresponding to the first operation state, LPLEGR gas having an LPLEGR rate Rl ₁ corresponding to the first operation state, and a change in HPLEGR rate ΔRh = Rh ₁ −Rh. ₂ (= Rh ₁ ) and a residual gas in the intake system region at a rate corresponding to ₂ (= Rh ₁ ).

の比率で空気を含み、

の比率でＬＰＬＥＧＲガスを含むガスであると考える。 When the composition of the residual gas in the intake system area is the time t ₁ before a certain period the internal combustion engine 1 for simplicity has been a steady operating in a first operating state, as described above, the first operating state It is considered that the gas contains air and LPLEGR gas at a mixing ratio determined by the air ratio Ra ₁ and the LPLEGR ratio Rl ₁ corresponding to. That is, the residual gas in the intake system region is

Contains air in a ratio of

It is considered that the gas contains LPLEGR gas at a ratio of

となる。ここで、過渡期間中の空気比率Ｒａ’とＬＰＬＥＧＲ率Ｒｌ’との比を計算すると、

となる。これは、図７の例では、上記過渡期間（ｔ_１’〜ｔ_２）におけるＨＰＬＥＧＲガス量が０であることから、結局、過渡期間中のシリンダ吸入ガスは全て吸気系領域内のガスによって構成されていることに対応している。 Therefore, the air ratio Ra ′ and the LPLEGR rate Rl ′ in the cylinder intake gas during the transition period are

It becomes. Here, when calculating the ratio of the air ratio Ra ′ and the LPLEGR rate Rl ′ during the transition period,

It becomes. This is because, in the example of FIG. 7, the HPLEGR gas amount in the transition period (t ₁ ′ to t ₂ ) is 0, so that all the cylinder intake gas in the transition period is constituted by the gas in the intake system region. It corresponds to being.

In the estimation method of the cylinder intake air amount illustrated in FIG. 6, it is estimated that all of the gas sucked into the cylinder 2 during the transition period corresponds to the amount of change in the HPLEGR rate, which is air. The smoke limit injection amount Qc ′ (6) set based on this may be an excessive value with respect to the actual cylinder intake air amount, and there is a risk that smoke exceeding the allowable limit may be generated depending on the operating state. was there.

  In this regard, according to the estimation method of the present embodiment described with reference to FIG. 7, the amount of air in the gas sucked into the cylinder 2 and the amount of LPLEGR gas during the transition period are converted into the composition of the residual gas in the intake system region. Based on this, it is possible to estimate with high accuracy. Accordingly, it is possible to accurately estimate the cylinder intake air amount during the transition period, and based on this, as shown in FIG. 7A, an appropriate smoke limit that is not excessive or insufficient with respect to the actual cylinder intake air amount. The injection amount Qc ′ can be set. As a result, the fuel injection amount exceeds the smoke limit injection amount during the transition period, and the amount of smoke generated becomes excessive, or conversely, the fuel injection amount is excessively limited and the acceleration performance and drivability are impaired. This can be suppressed.

  Next, the fuel injection control of this embodiment will be described with reference to FIGS. FIG. 8 is a flowchart showing a routine for performing fuel injection control according to this embodiment. This routine is executed by the ECU 20 at every constant crank angle during operation of the internal combustion engine 1.

  When this routine is executed, first, in step S101, the ECU 20 acquires the operating state of the internal combustion engine 1 based on the outputs from the various sensors described above.

  Next, in step S102, the ECU 20 calculates a basic required injection amount Q based on the operating state of the internal combustion engine 1 acquired in step S101. The basic required injection amount Q is calculated in consideration of the rotational speed of the internal combustion engine 1 so as to output a required torque based on the accelerator opening measured by the accelerator opening sensor 15.

  In step S103, the ECU 20 calculates a smoke limit injection amount Qc described later. The smoke limit injection amount Qc is calculated by executing the routine shown in the flowchart of FIG. A routine for calculating the smoke limit injection amount Qc will be described later.

  In step S104, the basic required injection amount Q calculated in step S102 is compared with the smoke limit injection amount Qc calculated in step S103. If it is determined in step S104 that Q> Qc, the ECU 20 proceeds to step S105, and sets the final fuel injection amount command value Qfin to the smoke limit injection amount Qc calculated in step S103. On the other hand, when it is determined in step S104 that Q ≦ Qc, the ECU 20 proceeds to step S106, and sets the final fuel injection amount command value Qfin to the basic required injection amount Q calculated in step S102.

  In step S107, the ECU 20 performs fuel injection of the fuel injection amount command value Qfin set in step S105 or step S106.

  Next, the smoke limit injection amount calculation routine will be described based on FIG. This routine is executed by the ECU 20 immediately before the fuel injection control routine at the same cycle as the fuel injection control routine shown in FIG.

  When this routine is executed, first, in step S201, the ECU 20 calculates a scavenging time Δt of the residual gas in the intake system region. Specifically, the engine 2 is currently sucked into the cylinder 2 based on the operating state history such as the rotational speed, load, intake pressure, intake temperature, etc. of the internal combustion engine 1, the volume of the intake system region, the volume of the cylinder 2, etc. This is calculated as the time required for the gas derived from the residual gas in the intake system region to pass through the intake system region.

  In step S202, the ECU 20 reads the measured value Ga_bass (t−Δt) of the fresh air amount by the air flow meter 7 before Δt from the current time t.

  In step S203, the ECU 20 reads the control target value Gl (t−Δt) of the LPLEGR gas amount before Δt from the current time t.

  In step S204, the ECU 20 calculates a gas composition derived from the residual gas in the intake system region sucked into the cylinder 2 at the current time t. That is, the ratio Ra_ic (t) of fresh air in the residual gas and the ratio Rl_ic (t) of LPLEGR gas are calculated according to the above-described equations (3) and (4).

  In step S205, the ECU 20 calculates a change ΔRh in the HPLEGR rate of the cylinder intake gas.

  In step S206, the ECU 20 calculates the air ratio Ra 'of the cylinder intake gas according to the above-described equation (5).

  In step S207, the ECU 20 calculates the total cylinder intake gas amount Gcyl '.

  In step S208, the ECU 20 calculates the cylinder intake air amount Ga 'according to the above-described equation (7).

  In step S209, the ECU 20 calculates the smoke limit injection amount Qc 'based on the cylinder intake air amount Ga' calculated in step S208.

  By executing the routine described above, the amount of air in the cylinder intake gas can be accurately estimated, and an appropriate smoke limit injection amount that is not excessive or insufficient with respect to the actual cylinder intake air amount can be set. It becomes possible. Therefore, it is possible to prevent the amount of smoke generated from exceeding an allowable limit, or the fuel injection amount from being excessively limited to reduce acceleration performance and drivability.

  In the first embodiment, a relatively special case where the target values of the HPLEGR rate and the LPLEGR rate are reduced and the target HPLEGR rate and the target LPLEGR rate corresponding to the second operating state are both 0. Although illustratively described, it is needless to say that the idea of the present invention can be applied to estimation of the cylinder intake air amount in a more general transient state.

In the present embodiment, the target value of the HPLEGR rate changes from the HPLEGR rate Rh ₁ corresponding to the first operating state to the HPLEGR rate Rh ₂ (> 0, Rh ₂ <Rh ₁ ) corresponding to the second operating state, and LPLEGR. In a transient state where the target value of the rate changes from the LPLEGR rate Rl ₁ corresponding to the first operating state to the LPLEGR rate Rl ₂ (> 0, Rl ₂ <Rl ₁ ) corresponding to the second operating state, the cylinder intake air amount An example of the estimation will be described with reference to FIG.

As shown in FIG. 10B, after the change to the target value Rh ₂ corresponding to the second operating state of the HPLEGR rate is completed at time t ₁ ′, the second operating state of the LPLEGR rate is reached at time t ₂ . During the transition period until the change to the corresponding target value Rl ₂ is completed, the cylinder intake gas includes air with an air ratio Ra ₁ corresponding to the first operating state and an LPLEGR rate Rl corresponding to the first operating state. ₁ LPLEGR gas and the residual gas in the intake system region at a ratio corresponding to the change in the HPLEGR rate ΔRh = Rh ₁ −Rh ₂ .

The composition of the residual gas in the intake system region is considered to be a gas containing fresh air and LPLEGR gas at a mixing ratio determined by the air ratio R1 and the LPLEGR rate Rl ₁ corresponding to the first operating state. That is, the residual gas in the intake system area _includes a air ratio of _{Ra 1 / (Ra 1 + Rl} 1), considered to be a gas containing LPLEGR gas in a ratio of _{Rl 1 / (Ra 1 + Rl} 1).

となる。ここで、上記Ｒａ’の式を変形すると、

となる。同様に、

となる。これは、過渡期間中においてシリンダ２に吸入されるガスのうち、第２運転状態に対応するＨＰＬＥＧＲ率のＨＰＬＥＧＲガス以外のガスは、第１運転状態に対応する空気比率Ｒａ_１及びＬＰＬＥＧＲ率Ｒｌ_１によって決まる混合比率で空気及びＬＰＬＥＧＲガスに分配されるとしてシリンダ吸入ガスの組成を推定していることに対応する。 Therefore, the air ratio Ra ′ and the LPLEGR rate Rl ′ in the cylinder intake gas during the transition period are

It becomes. Here, when the expression of Ra ′ is modified,

It becomes. Similarly,

It becomes. This is because, among the gases sucked into the cylinder 2 during the transition period, the gas other than the HPLEGR gas having the HPLEGR rate corresponding to the second operating state is the air ratio Ra ₁ and the LPLEGR rate Rl ₁ corresponding to the first operating state. This corresponds to estimating the composition of the cylinder intake gas as being distributed to the air and the LPLEGR gas at a mixing ratio determined by the equation (1).

  Based on the air ratio Ra ′ of the cylinder intake gas during the transient period estimated in this way and the cylinder intake total gas amount Gcyl ′ (calculated based on the operating state of the internal combustion engine 1), during the transient period By calculating the cylinder intake air amount Ga ′ at, and setting the smoke limit injection amount Qc ′ during the transient period as shown in FIG. 10A based on the calculated cylinder intake air amount Ga ′. It is possible to set an appropriate smoke limit injection amount for the cylinder intake air amount during the transition period. As a result, the fuel injection amount during the transition period becomes excessive and the smoke generation amount increases beyond the allowable limit, and conversely, an unnecessary limit is imposed on the fuel injection amount, resulting in a decrease in acceleration performance and drivability. This can be suppressed.

  In the first embodiment and the second embodiment, the transient state in which the HPLEGR rate and the LPLEGR rate decrease is illustrated, but the idea of the present invention is based on the estimation of the cylinder intake air amount in the transient state in which the HPLEGR rate and the LPLEGR rate increase. Can also be applied.

In this embodiment, the target value of the HPLEGR rate changes from the HPLEGR rate Rh ₁ corresponding to the first operating state to the HPLEGR rate Rh ₂ (> Rh ₁ ) corresponding to the second operating state, and the target value of the LPLEGR rate is FIG. 11 shows an example of estimating the cylinder intake air amount in a transient state where the LPLEGR rate Rl ₁ corresponding to the first operating state changes to the LPLEGR rate Rl ₂ (> Rl ₁ ) corresponding to the second operating state. I will explain.

As shown in FIG. 11B, after the change to the target value Rh ₂ corresponding to the second operating state of the HPLEGR rate is completed at time t ₁ ′, the second operating state of the LPLEGR rate is reached at time t ₂ . during the corresponding transitional period until the change in the target value Rl ₂ is completed, the cylinder intake gas, a HPLEGR gas contained in a proportion of HPLEGR rate Rh ₂ corresponding to the second operating state, the first operating state The air in which the amount of air contained in the residual gas in the intake system region at a rate corresponding to the change ΔRh = Rh ₂ −Rh ₁ in the HPLEGR rate from the air at the rate of the corresponding air ratio Ra ₁ has decreased, The LPLEGR gas contained in the residual gas in the intake system region at a rate corresponding to the change ΔRh of the HPLEGR rate from the LPLEGR rate at the rate of LPLEGR rate Rl ₁ corresponding to the operating state. It is thought that it is composed of LPLEGR gas with a reduced amount of gas.

の比率で空気を含み、

の比率でＬＰＬＥＧＲガスを含むガスであると考える。 The composition of the residual gas in the intake system region is considered to be a gas containing fresh air and LPLEGR gas at a mixing ratio determined by the air ratio R1 and the LPLEGR rate Rl ₁ corresponding to the first operating state. That is, the residual gas in the intake system region is

Contains air in a ratio of

It is considered that the gas contains LPLEGR gas at a ratio of

となる。実施例２と同様にＲａ’、Ｒｌ’の式を変形すると、

となり、実施例２と同様の式が得られる。つまり、過渡期間中においてシリンダ２に吸入されるガスのうち、第２運転状態に対応するＨＰＬＥＧＲ率のＨＰＬＥＧＲガス以外のガスは、第１運転状態に対応する空気比率Ｒａ_１及びＬＰＬＥＧＲ率Ｒｌ_１によって決まる混合比率で空気及びＬＰＬＥＧＲガスに分配されるとしてシリンダ吸入ガスの組成を推定していることに対応する。 Therefore, the air ratio Ra ′ and the LPLEGR rate R1 ′ during the transition period are

It becomes. As in the second embodiment, when Ra ′ and Rl ′ are transformed,

Thus, the same formula as in Example 2 is obtained. That is, among the gases sucked into the cylinder 2 during the transition period, the gas other than the HPLEGR gas having the HPLEGR rate corresponding to the second operating state is determined by the air ratio Ra ₁ and the LPLEGR rate Rl ₁ corresponding to the first operating state. This corresponds to estimating the composition of the cylinder intake gas as being distributed to the air and the LPLEGR gas at a determined mixing ratio.

  Based on the air ratio Ra ′ of the cylinder intake gas during the transient period estimated in this way and the cylinder intake total gas amount Gcyl ′ (calculated based on the operating state of the internal combustion engine 1), during the transient period By calculating the cylinder intake air amount Ga ′ at, and setting the smoke limit injection amount Qc ′ during the transition period as shown in FIG. 11A based on the calculated cylinder intake air amount Ga ′. It is possible to set an appropriate smoke limit injection amount for the cylinder intake air amount during the transition period. As a result, the fuel injection amount during the transition period becomes excessive and the smoke generation amount increases beyond the allowable limit, and conversely, an unnecessary limit is imposed on the fuel injection amount, resulting in a decrease in acceleration performance and drivability. This can be suppressed.

  By the way, air may remain in the HPLEGR gas and the LPLEGR gas. In particular, in a diesel engine where the excess air ratio is often controlled to a value greater than 1, the amount of air remaining in the exhaust gas is a non-negligible amount. If the cylinder intake air amount is estimated in consideration of the remaining air amount in the exhaust gas, and therefore the air amount in the EGR gas, the accuracy of estimation of the cylinder intake air amount can be further improved.

  According to each of the above embodiments, the cylinder intake air amount during the transition period can be accurately estimated, but the cylinder intake air amount here corresponds to the amount of fresh air flowing into the intake passage 3 from the atmosphere. According to the above embodiments, not only the cylinder intake fresh air amount but also the HPLEGR gas amount and LPLEGR gas amount sucked into the cylinder can be accurately estimated. Therefore, the amount of residual air contained in the HPLEGR gas and LPLEGR gas sucked into the cylinder is estimated based on the control value of the excess air ratio, the HPLEGR passage volume, the LPLEGR passage volume, the volume of the intake system region, and the like. If the cylinder intake air amount is estimated in consideration of the remaining air amount in the HPLEGR gas and LPLEGR gas sucked into the cylinder, the estimation accuracy of the cylinder intake air amount is increased. This can be further improved.

  In each of the above embodiments, the ratio of fresh air and LPLEGR gas in the residual gas in the intake system region is estimated, and the change in the amount of HPLEGR gas is replaced by the residual gas containing fresh air and LPLEGR gas at the ratio. The cylinder intake air amount in the transient state is estimated based on the idea that the air is contained, but the air amount contained in the residual gas in the intake system region is estimated, and the estimated amount of air in the residual gas is calculated. Any estimation model for estimating the cylinder intake air amount can be used.

It is a figure which shows schematic structure of the internal combustion engine in the Example, its intake system, an exhaust system, an EGR system, and a control system. It is a figure which shows an example of the control target value map of the EGR rate in an Example. It is a figure which shows an example of the switching control map of the HPLEGR apparatus in an Example, and an LPLEGR apparatus. It is a figure which shows the time change of the composition of the gas suck | inhaled by a cylinder, and the smoke limit injection amount in the transient state in which the target value of cylinder intake EGR gas amount changes. It is a figure which shows the time change of the composition of the gas suck | inhaled by a cylinder, and the smoke limit injection amount in the transient state in which the target value of cylinder intake EGR gas amount changes. It is a figure which shows the time change of the composition of the gas suck | inhaled by a cylinder, and the smoke limit injection amount in the transient state in which the target value of cylinder intake EGR gas amount changes. It is a figure which shows the time change of the composition of the gas suck | inhaled by a cylinder, and the smoke limit injection amount in the transient state in which the target value of cylinder intake EGR gas amount changes. It is a flowchart showing the fuel-injection control routine in an Example. It is a flowchart showing the smoke limit injection amount calculation routine in an Example. It is a figure which shows the time change of the composition of the gas suck | inhaled by a cylinder, and the smoke limit injection amount in the transient state in which the target value of cylinder intake EGR gas amount changes. It is a figure which shows the time change of the composition of the gas suck | inhaled by a cylinder, and the smoke limit injection amount in the transient state in which the target value of cylinder intake EGR gas amount changes.

Explanation of symbols

1 Internal combustion engine 2 Cylinder 3 Intake passage 4 Exhaust passage 5 Nozzle vane 6 First throttle valve 7 Air flow meter 8 Intercooler 9 Second throttle valve 10 Exhaust purification device 11 Compressor 12 Turbine 13 Turbocharger 14 Water temperature sensor 15 Accelerator opening sensor 16 Crank Angle sensor 17 Intake manifold 18 Exhaust manifold 19 Exhaust throttle valve 20 ECU
30 LPLEGR device 31 LPLEGR passage 32 LPLEGR valve 33 LPLEGR cooler 40 HPLEGR device 41 HPLEGR passage 42 HPLEGR valve 43 HPLEGR cooler

Claims (4)

An HPLEGR device that causes a part of exhaust gas from the internal combustion engine to flow into the intake passage from an HPLEGR gas inlet provided in the intake passage of the internal combustion engine;
An LPLEGR device that causes a portion of the exhaust from the internal combustion engine to flow into the intake passage from an LPLEGR gas inlet provided upstream of the HPLEGR gas inlet of the intake passage;
An air flow meter for measuring the amount of air flowing into the intake passage;
The measured value of the air amount by the air flow meter, the amount of LPLEGR gas flowing into the intake passage by the LPLEGR device, and the intake system region that is the region from the LPLEGR gas inlet to the HPLEGR gas inlet in the intake passage An air amount estimation means for estimating an air amount in the intake system region based on the volume of
Cylinder intake air amount estimating means for estimating the amount of air sucked into the cylinder of the internal combustion engine based on the estimated air amount in the intake system region;
Based on the estimated cylinder intake air amount, a smoke limit injection amount calculation that calculates a smoke limit injection amount that is an upper limit value of a fuel injection amount that can reduce the amount of smoke in the exhaust gas to a predetermined allowable limit or less. Means,
Fuel injection control means for performing control to limit the fuel injection amount so as not to exceed the calculated smoke limit injection amount;
An internal combustion engine control system comprising: In claim 1,
The air amount estimation means estimates the time during which the air and LPLEGR gas flowing into the intake system region are transported through the intake system region based on the volume of the intake system region, and based on the estimated time An internal combustion engine control system characterized by being means for estimating the amount of air in the intake system region. In claim 1 or 2,
The air amount estimation means includes air contained in the gas flowing in the intake system region based on the measured value of the air amount by the air flow meter, the LPLEGR gas amount, and the volume of the intake system region. And a ratio of the LPLEGR gas.
The cylinder intake air amount estimation means is based on a mixed state of the gas in the intake system region containing air and LPLEGR gas at the estimated ratio and the HPLEGR gas flowing into the intake passage by the HPLEGR device. A control system for an internal combustion engine, wherein the control system is a means for estimating the cylinder intake air amount. In claim 3,
In a transient state where the ratio of HPLEGR gas in the gas sucked into the cylinder changes,
The cylinder intake air amount estimation means estimates the cylinder intake air amount by replacing a change in the ratio of the HPLEGR gas with a change in the ratio of the gas in the intake system region sucked into the cylinder. A control system for an internal combustion engine.

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