Patent Description:
<CIT> and <CIT> disclose an intake device of an internal combustion engine with a supercharger that prevents fresh air containing EGR gas from being blown back to an air flow meter when a recirculation valve is opened. The recirculation valve releases a pressure downstream of a compressor to upstream of the compressor when a throttle valve is closed. <CIT> discloses an engine system, which is provided with an engine. <CIT> discloses a control device of engine with a supercharger which includes a low-pressure loop EGR apparatus. <CIT> discloses a control device and control method for an internal combustion engine.

When the recirculation valve is opened during supercharging, gas may flow back to the vicinity of an air cleaner. Therefore, in this case, it is conceivable to fully close an EGR valve so that the EGR gas does not flow back. However, even if EGR is stopped in this way, the EGR gas already existing in an intake passage flows back in the intake passage and then flows into a cylinder of the internal combustion engine. Therefore, it is desired to understand how the backflow EGR gas flows into the cylinder and estimate a more accurate EGR rate.

The present invention is made in view of such a problem, and an object of the present invention is to estimate a more accurate EGR rate when the recirculation valve is opened and the EGR valve is fully closed during supercharging.

An EGR estimation method for an internal combustion engine according to one embodiment of the present invention is the EGR estimation method for the internal combustion engine according to claim <NUM>.

According to other embodiment of our invention, an EGR estimation device according to claim <NUM> corresponding to the EGR estimation method of claim <NUM> is provided.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

<FIG> is a diagram showing a main part of a vehicle. The vehicle includes an internal combustion engine <NUM>, an intake system <NUM>, an exhaust system <NUM>, a supercharger <NUM>, an EGR device <NUM>, and a controller <NUM>.

The intake system <NUM> includes an intake passage <NUM>, an air cleaner <NUM>, an air flow meter <NUM>, an intake throttle valve <NUM>, an intercooler <NUM>, a throttle valve <NUM>, a collector <NUM>, a compressor <NUM>, an intake bypass passage <NUM>, and a recirculation valve (hereinafter referred to as R/V) <NUM>. The intake passage <NUM> connects the air cleaner <NUM> and the internal combustion engine <NUM> and circulates intake air introduced into the internal combustion engine <NUM>. The intake passage <NUM> is provided with the air cleaner <NUM>, the air flow meter <NUM>, the intake throttle valve <NUM>, the compressor <NUM>, the intercooler <NUM>, the throttle valve <NUM>, and the collector <NUM> in this order from an upstream side.

The air cleaner <NUM> removes foreign matters contained in the intake air. The air flow meter <NUM> measures a flow rate of the intake air. The intake throttle valve <NUM> is provided in a portion of the intake passage <NUM>, which is on an upstream side of an EGR convergence portion 11a to which an EGR passage <NUM> is connected, which will be described later. The intake throttle valve <NUM> increases a recirculation amount of exhaust gas through the EGR passage <NUM> by reducing an opening degree.

The intercooler <NUM> cools the supercharged intake air. The throttle valve <NUM> adjusts an amount of the intake air introduced into the internal combustion engine <NUM>. The collector <NUM> temporarily stores the intake air. The compressor <NUM> is a compressor of the supercharger <NUM> and compresses the intake air.

The exhaust system <NUM> includes an exhaust passage <NUM>, an upstream catalyst <NUM>, a downstream catalyst <NUM>, and a turbine <NUM>. The exhaust passage <NUM> is connected to the internal combustion engine <NUM> and circulates exhaust gas discharged from the internal combustion engine <NUM>. The exhaust passage <NUM> is provided with the turbine <NUM>, the upstream catalyst <NUM>, and the downstream catalyst <NUM> in this order from an upstream side. The upstream catalyst <NUM> and the downstream catalyst <NUM> purify the exhaust gas. The turbine <NUM> is the turbine of the supercharger <NUM> and recovers energy from the exhaust gas.

The supercharger <NUM> compresses the intake air and then supplies to the internal combustion engine <NUM>. The supercharger <NUM> is a turbocharger and includes the compressor <NUM>, the turbine <NUM>, and a shaft <NUM>. The supercharger <NUM> is provided in the intake passage <NUM> and the exhaust passage <NUM> by providing the compressor <NUM> in the intake passage <NUM> and the turbine <NUM> in the exhaust passage <NUM>. In the supercharger <NUM>, when the turbine <NUM> is rotated by the exhaust gas, the compressor <NUM> is rotated via the shaft <NUM> to compress the intake air. In the compressor <NUM>, a pair of compressor wheels arranged in a back-to-back direction are provided on the shaft <NUM>, and the intake air is compressed by the pair of compressor wheels. The turbine <NUM> is provided with an exhaust bypass passage, and the exhaust bypass passage is provided with a waste gate valve (not shown) that adjusts a flow rate of the flowing exhaust gas.

The EGR device <NUM> includes the EGR passage <NUM>, an EGR cooler <NUM>, and an EGR valve <NUM>. The EGR device <NUM> recirculates the exhaust gas from the exhaust passage <NUM> to the intake passage <NUM>.

The EGR passage <NUM> connects the exhaust passage <NUM> and the intake passage <NUM>. The EGR passage <NUM> recirculates a part of the exhaust gas flowing through the exhaust passage <NUM> to the intake passage <NUM> as EGR gas. The EGR passage <NUM> is provided with the EGR cooler <NUM> and the EGR valve <NUM>. The EGR cooler <NUM> cools the EGR gas flowing through the EGR passage <NUM>. The EGR valve <NUM> adjusts a flow rate of the EGR gas flowing through the EGR passage <NUM>.

The EGR device <NUM>, specifically, the EGR passage <NUM> connects a portion downstream of the supercharger <NUM>, that is, the turbine <NUM> in the exhaust passage <NUM>, and a portion upstream of the supercharger <NUM>, that is, the compressor <NUM> in the intake passage <NUM>. In this way, the EGR passage <NUM> connecting the intake passage <NUM> and the exhaust passage <NUM> forms an EGR path of a low pressure loop, that is, an LPL. More specifically, the EGR passage <NUM> connects a portion of the exhaust passage <NUM> between the upstream catalyst <NUM> and the downstream catalyst <NUM> and a portion of the intake passage <NUM> between the intake throttle valve <NUM> and the compressor <NUM>.

The intake bypass passage <NUM> connects an upstream pressure portion and a downstream pressure portion of the supercharger <NUM> in the intake system <NUM>. The upstream pressure portion is a portion of the intake passage <NUM> on an upstream side of the supercharger <NUM> and on a downstream side of the EGR convergence portion 11a. The downstream pressure portion is a portion of the intake passage <NUM> on a downstream side of the supercharger <NUM> and on an upstream side of the intercooler <NUM>. Connecting to the downstream pressure portion of the supercharger <NUM> in the intake system <NUM> includes connecting to the compressor <NUM> so that the compressed intake air can flow into the intake bypass passage <NUM>.

The R/V <NUM> is provided in the intake bypass passage <NUM>. The R/V <NUM> includes an on-off valve. During supercharging, a downstream pressure of the supercharger <NUM> is higher than an upstream pressure thereof. Therefore, when the R/V <NUM> is opened during the supercharging, the intake air compressed by the compressor <NUM> is returned to the intake passage <NUM> on the portion upstream of the supercharger <NUM> via the intake bypass passage <NUM>.

The controller <NUM> is an electronic control device, and in addition to the air flow meter <NUM>, signals from various sensors and switches such as a crank angle sensor <NUM>, an accelerator position sensor <NUM>, a supercharging pressure sensor <NUM>, and an atmospheric pressure sensor <NUM> are input to the controller <NUM>. The crank angle sensor <NUM> generates a crank angle signal for each predetermined crank angle. The crank angle signal is used as a signal representing a rotation speed NE of the internal combustion engine <NUM>. The accelerator position sensor <NUM> detects an amount of depression of an accelerator pedal of the vehicle. The amount of depression of the accelerator pedal is used as a signal representing a load of the internal combustion engine <NUM>. The supercharging pressure sensor <NUM> detects the downstream pressure of the supercharger <NUM> in the intake passage <NUM>, and the atmospheric pressure sensor <NUM> detects atmospheric pressure.

The controller <NUM> controls the intake throttle valve <NUM>, the throttle valve <NUM>, the R/V <NUM>, and the EGR valve <NUM> in addition to the internal combustion engine <NUM> based on the above input signals from the various sensors and switches. The controller <NUM> controls the internal combustion engine <NUM> by controlling an ignition timing and a fuel injection amount according to an engine operating state. The engine operating state is, for example, the rotation speed NE or the load.

When the R/V <NUM> is opened during the supercharging, gas may flow back to the vicinity of the air cleaner <NUM>. Therefore, in this case, it is conceivable to fully close the EGR valve <NUM> so that the EGR gas does not flow back. However, even if EGR is stopped in this way, the EGR gas already existing in the intake passage <NUM> flows back in the intake passage <NUM> and then flows into a cylinder of the internal combustion engine <NUM>.

Therefore, in the present embodiment, it is understood how the backflow EGR gas flows into the cylinder, and an EGR rate (actual EGR rate) is estimated based on an understood inflow mode.

<FIG> are diagrams for explaining a flow mode of the EGR gas. In <FIG>, the air flow meter <NUM>, the R/V <NUM>, and the like are not shown. <FIG> shows a state immediately before opening the R/V <NUM> during the supercharging. At this time, the intake passage <NUM> on a downstream side from the EGR convergence portion 11a is filled with the EGR gas having a target EGR rate consisting of mixed gas with the intake gas.

<FIG> shows a state when the R/V <NUM> is opened and the EGR valve <NUM> is fully closed during the supercharging. At this time, the mixed gas compressed by the compressor <NUM> is returned to the intake passage <NUM> on an upstream side of the compressor <NUM> via the intake bypass passage <NUM>, and further flows back to the air cleaner side, that is, to an upstream side of the EGR convergence portion 11a, and then blows through the air cleaner <NUM>. In this way, in the air cleaner <NUM>, the mixed gas is diluted with air. As a result, the EGR rate decreases stepwise at an outlet position of the air cleaner <NUM>, and further gradually decreases toward the upstream side.

<FIG> shows a state when a flow rate Q2 corresponding to a volume of the intake passage <NUM> from the EGR convergence portion 11a to a connection portion with the air cleaner <NUM> (hereinafter referred to as an upstream pipe volume) is re-inhaled. At this time, as a result of the diluted mixed gas reaching immediately before the EGR convergence portion 11a, a step at which the EGR rate decreases stepwise is located immediately before the EGR convergence portion 11a.

<FIG> shows a state in which the diluted mixed gas passes through the EGR convergence portion 11a and then re-inhaled. At this time, in the EGR convergence portion 11a, the EGR rate gradually decreases due to the diluted mixed gas.

In view of such a flow mode of the mixed gas, in the present embodiment, the EGR rate in the EGR convergence portion 11a is estimated based on an amount of the gas flowing back to the air cleaner <NUM> side (hereinafter referred to as a backflow rate of the EGR gas).

<FIG> is a diagram for explaining a method for estimating the EGR rate. A broken line indicates the target EGR rate.

At a timing T1, the R/V <NUM> is opened. At this time, the EGR valve <NUM> is fully closed and the EGR is stopped, but the mixed gas is blown back as described above with reference to <FIG>. As a result, the EGR rate in the EGR convergence portion 11a does not become zero indicated by the broken line, but remains unchanged at the timing T1.

At a timing T2, the flow rate Q2 corresponding to the upstream pipe volume is re-inhaled. As described above with reference to <FIG>, the EGR rate in the EGR convergence portion 11a remains unchanged until the timing T2 at which the flow rate Q2 corresponding to the upstream pipe volume is re-inhaled.

If the backflow rate of the EGR gas is large, a time until the flow rate Q2 corresponding to the upstream pipe volume is re-inhaled becomes long. Therefore, the timing T2 changes according to the backflow rate of the EGR gas. As a result, a predetermined time α shown as a time between the timing T1 and the timing T2 becomes longer as the backflow rate of the EGR gas increases. The predetermined time α is a time from the R/V <NUM> is opened until the flow rate Q2 corresponding to the upstream pipe volume is re-inhaled, and is changed according to the backflow rate of the EGR gas.

Therefore, in the present embodiment, from the timing T1 to the timing T2, even if the R/V <NUM> is opened and the EGR valve <NUM> is fully closed with the upstream pipe volume as a compliant element, until the predetermined time α elapses, the estimated EGR rate is set by a first profile Prof1 that holds the EGR rate in the EGR convergence portion 11a to the target EGR rate immediately before opening the R/V <NUM>.

As described above with reference to <FIG>, immediately after the timing T2, the EGR rate in the EGR convergence portion 11a is represented by an EGR rate in the air cleaner <NUM> when the EGR gas flows back into the air cleaner <NUM>. Therefore, immediately after the timing T2, the EGR rate in the EGR convergence portion 11a is estimated based on the above EGR rate in the air cleaner <NUM>.

Immediately after the timing T2, the EGR rate in the EGR convergence portion 11a decreases stepwise as described above with reference to <FIG>. The EGR rate at this time is higher since the larger an amount of the mixed gas blown back to the air cleaner <NUM>, the more difficult it is for the mixed gas to be diluted. The amount of the mixed gas blown back to the air cleaner <NUM> increases as the backflow rate of the EGR gas increases. Therefore, the EGR rate at this time increases as the backflow rate of the EGR gas increases.

Therefore, in the present embodiment, the estimated EGR rate is set by a second profile Prof2 that decreases the EGR rate stepwise following the first profile Prof1 and increases the EGR rate that is decreased stepwise as the backflow rate of the EGR gas increases, with the backflow rate of the EGR gas as a compliant element.

After the EGR rate is decreased stepwise, the EGR rate in the EGR convergence portion 11a is gradually decreased by the diluted mixed gas as described above with reference to <FIG>. The amount of decrease in the EGR rate at this time changes according to the flow rate of the re-inhaled gas, and is increased as the flow rate of the re-inhaled gas increases. This is because the larger the flow rate of the re-inhaled gas, the faster the diluted mixed gas passes through the EGR convergence portion 11a, and the faster the EGR rate decrease.

Therefore, in the present embodiment, the estimated EGR rate is set by a third profile Prof3 that decreases the EGR rate with passage of time following the second profile Prof2 and decreases the amount of decrease in the EGR rate according to the flow rate of the re-inhaled gas, with the flow rate of the re-inhaled gas as a compliant element.

The third profile Prof3 is a profile that changes the EGR rate with a temporary response delay according to the flow rate of the re-inhaled gas. The amount of decrease in the EGR rate in the third profile Prof3 can be changed by changing a time constant according to the flow rate of the re-inhaled gas.

<FIG> is a control block diagram showing an EGR rate estimation process performed by the controller <NUM>. A passing amount calculation unit <NUM> calculates a passing amount of gas passing through the R/V <NUM>. The passing amount is calculated by multiplying a passing flow rate of the gas passing through the R/V <NUM> by a JOB period of the estimation process, and is set to a negative value when a blowback occurs. The passing flow rate of the gas passing through the R/V <NUM> can be calculated based on, for example, a supercharging pressure of the compressor <NUM>, an atmospheric pressure, and a cross-sectional area of the intake bypass passage <NUM>. The calculated passing amount of the gas is input to an integrated value calculation unit <NUM>.

The integrated value calculation unit <NUM> calculates a blowback amount integrated value QS. The blowback amount integrated value QS is calculated by adding the input passing amount of the gas and the latest calculated blowback amount integrated value QS of the gas. The calculated blowback amount integrated value QS is input to a first determination unit <NUM>, an integrated value peak value calculation unit <NUM>, and a forward flow rate calculation unit <NUM>.

The first determination unit <NUM> determines whether the input blowback amount integrated value QS is smaller than zero. When the blowback occurs, the blowback amount integrated value QS becomes a negative value, and an affirmative determination is made. In this case, a signal is input from the first determination unit <NUM> to an AND circuit unit <NUM>.

The AND circuit unit <NUM> inputs an AND signal to an EGR rate holding unit <NUM> when a signal is input from each of the first determination unit <NUM> and a second determination unit <NUM>, which will be described later. The signal from the first determination unit <NUM> indicates that a blowback occurs, and the signal from the second determination unit <NUM> indicates that the flow rate Q2 corresponding to the upstream pipe volume is not re-inhaled yet after opening the R/V <NUM>. Therefore, the AND signal indicates that a blowback occurs and the flow rate Q2 corresponding to the upstream pipe volume is not re-inhaled yet.

The EGR rate holding unit <NUM> sets an EGR rate to be held, that is, sets an EGR rate based on the first profile Prof1. The EGR rate holding unit <NUM> selects the target EGR rate when no AND signal is input. As a result, the EGR rate is set to the target EGR rate.

When the AND signal is input, the EGR rate holding unit <NUM> selects the latest set EGR rate and stops the process. As a result, the EGR rate to be held is set. The set EGR rate is input to a step change setting unit <NUM> and an EGR rate selection unit <NUM>.

The integrated value peak value calculation unit <NUM> calculates an integrated value peak value QSmax, which is a peak value of the blowback amount integrated value QS. When the input blowback amount integrated value QS is equal to or less than the latest calculated integrated value peak value QSmax (when an absolute value thereof is equal to or more than that of the integrated value peak value QSmax), the integrated value peak value calculation unit <NUM> selects the input blowback amount integrated value QS. As a result, the selected blowback amount integrated value QS is updated as a new integrated value peak value QSmax, and a provisional integrated value peak value QSmax is calculated.

When the input blowback amount integrated value QS is larger than the latest calculated integrated value peak value QSmax (when an absolute value thereof is smaller than that of the integrated value peak value QSmax), the integrated value peak value calculation unit <NUM> selects the latest calculated integrated value peak value QSmax and stops the process. As a result, the latest calculated integrated value peak value QSmax is calculated and determined as a true integrated value peak value QSmax in calculation. The true integrated value peak value QSmax is, in other words, the backflow rate of the EGR gas, and indicates a total flow rate of the mixed gas blown back. The calculated integrated value peak value QSmax is input to the forward flow rate calculation unit <NUM> and the step change setting unit <NUM>.

The forward flow rate calculation unit <NUM> calculates a forward flow rate Q1 for blowback. The forward flow rate Q1 for blowback is, in other words, the flow rate of the re-inhaled gas, and is calculated based on the integrated value peak value QSmax and the blowback amount integrated value QS. Specifically, the forward flow rate Q1 for blowback is calculated by adding the blowback amount integrated value QS with a positive or negative sign thereof unchanged to the integrated value peak value OSmax with a positive or negative sign thereof reversed. The calculated forward flow rate Q1 for blowback is input to the second determination unit <NUM>.

The second determination unit <NUM> determines whether the forward flow rate Q1 for blowback is equal to or less than the flow rate Q2 corresponding to the upstream pipe volume. The forward flow rate Q1 for blowback is equal to or less than the flow rate Q2 corresponding to the upstream pipe volume when the flow rate Q2 corresponding to the upstream pipe volume is not re-inhaled since the opening of the R/V <NUM>. In a case of affirmative determination, a signal is input from the second determination unit <NUM> to the AND circuit unit <NUM>, the EGR rate selection unit <NUM>, and a response delay calculation unit <NUM>.

The step change setting unit <NUM> calculates a step rate (decrease degree) of the EGR rate based on the integrated value peak value QSmax and the rotation speed NE. The step rate of the EGR rate is calculated to be smaller as the integrated value peak value QSmax is larger, and is calculated to be smaller as the rotation speed NE is smaller. This is because when step change occurs in the EGR rate in the air cleaner <NUM>, the amount of the mixed gas blown back to the air cleaner <NUM> depends on the backflow rate of the EGR gas and the rotation speed NE of the internal combustion engine <NUM> that takes in the gas.

The step change setting unit <NUM> further multiplies the calculated step rate by the EGR rate input from the EGR rate holding unit <NUM>. As a result, a step change is set in the EGR rate, and the EGR rate based on the second profile Prof2 is set. The set EGR rate is input to the EGR rate selection unit <NUM>.

The EGR rate selection unit <NUM> selects the EGR rate input from the EGR rate holding unit <NUM> when a signal is input from the second determination unit <NUM>, that is, when the flow rate Q2 corresponding to the upstream pipe volume is not re-inhaled yet since the R/V <NUM> is opened. Therefore, in this case, the EGR rate based on the first profile Prof1 is selected.

The EGR rate selection unit <NUM> selects the EGR rate input from the step change setting unit <NUM> when no signal is input from the second determination unit <NUM>, that is, when the flow rate Q2 corresponding to the upstream pipe volume is re-inhaled, and stops the process. As a result, the EGR rate based on the second profile Prof2 is selected in a form of switching from the EGR rate based on the first profile Prof1. The selected EGR rate is input to the response delay calculation unit <NUM>.

A response delay filter setting unit <NUM> calculates a time constant of a response delay filter of the EGR rate based on the rotation speed NE and a fresh air flow rate. The fresh air flow rate can be detected based on a signal from the air flow meter <NUM>. Response delay of the EGR rate is set to be smaller as the rotation speed NE is higher and the fresh air flow rate is larger. This is because the higher the rotation speed NE is and the larger the fresh air flow rate is, the larger the flow rate of the re-inhaled gas is, and the diluted mixed gas passes through the EGR convergence portion 11a earlier, so that the EGR rate decreases faster. The calculated time constant of the response delay filter is input to the response delay calculation unit <NUM>.

The response delay calculation unit <NUM> applies the time constant of the response delay filter input from the response delay filter setting unit <NUM> to the EGR rate input from the EGR rate selection unit <NUM> when no signal is input from the second determination unit <NUM>, that is, when the flow rate Q2 corresponding to the upstream pipe volume is re-inhaled. As a result, the response delay of the EGR rate is calculated and reflected in the EGR rate. The EGR rate reflecting the response delay is input to the EGR rate determination unit <NUM>.

When a signal is input from the second determination unit <NUM>, that is, when the flow rate Q2 corresponding to the upstream pipe volume is not re-inhaled yet after the opening of the R/V <NUM>, the response delay calculation unit <NUM> does not calculate the response delay of the EGR rate. In this case, the EGR rate input from the EGR rate selection unit <NUM> is directly input to the EGR rate determination unit <NUM>.

The EGR rate determination unit <NUM> determines the input EGR rate as the EGR rate in the EGR convergence portion 11a. In this way, the EGR rate in the EGR convergence portion 11a when the R/V <NUM> is opened and the EGR valve <NUM> is fully closed during the supercharging is estimated according to the first profile Prof1 to the third profile Prof3.

<FIG> is a flowchart showing the EGR rate estimation process performed by the controller <NUM>. The controller <NUM> includes a control unit by being programmed to execute the process shown in this flowchart.

In step S1, the controller <NUM> calculates the blowback amount integrated value QS. The blowback amount integrated value QS can be calculated as described above with reference to <FIG>.

In step S2, the controller <NUM> determines whether the R/V <NUM> is operating, that is, whether the R/V <NUM> is opened. If a negative determination is made in step S2, the process proceeds to step S6.

In step S6, the controller <NUM> determines whether the blowback amount integrated value QS is smaller than zero. In step S6, it is determined that the blowback occurs when the blowback amount integrated value QS is smaller than zero.

When the R/V <NUM> is closed, no blowback occurs. Therefore, if the process proceeds to step S6 following the negative determination in step S2, a negative determination is made in step S6, and the process proceeds to step S7.

In step S7, the controller <NUM> sets the EGR rate in the EGR convergence portion 11a as the target EGR rate. In this way, the EGR rate in the EGR convergence portion 11a is set as the target EGR rate before the R/V <NUM> is opened. After step S7, the process ends temporarily.

If the R/V <NUM> is opened in a subsequent routine, an affirmative determination is made in step S2, and the process proceeds to step S3.

In step S3 and subsequent step S4, the controller <NUM> calculates the integrated value peak value QSmax and the forward flow rate Q1 for blowback. The integrated value peak value QSmax and the forward flow rate Q1 for blowback can be calculated as described above with reference to <FIG>.

In step S5, the controller <NUM> determines whether the forward flow rate Q1 for blowback is equal to or less than the flow rate Q2 for the upstream pipe volume. If an affirmative determination is made in step S5, it is determined that the flow rate Q2 corresponding to the upstream pipe volume is not re-inhaled yet after the opening of the R/V <NUM>, and the process proceeds to step S6.

When the process proceeds to step S6 following the affirmative determination in step S5, the blowback amount integrated value QS becomes smaller than zero, and an affirmative determination is made in step S6. In this case, the process proceeds to step S8.

In step S8, the controller <NUM> holds the EGR rate in the EGR convergence portion 11a to the latest value. That is, in step S8, the first profile Prof1 is applied in estimating the EGR rate. After step S8, the process ends temporarily.

In the subsequent routine, affirmative determinations are made in steps S2 and S5 until the R/V <NUM> is operating and the forward flow rate Q1 for blowback becomes larger than the flow rate Q2 corresponding to the upstream pipe volume, and an affirmative determination is also made in the following step S6. As a result, the EGR rate in the EGR convergence portion 11a remains held at the latest value.

When the R/V <NUM> is operating and the forward flow rate Q1 for blowback is larger than the flow rate Q2 corresponding to the upstream pipe volume, it is determined that the flow rate Q2 corresponding to the upstream pipe volume is re-inhaled after the R/V <NUM> is opened, and a negative determination is made in step S5. In this case, the process proceeds to step S9.

In step S9, the controller <NUM> determines whether a step change is set in the EGR rate in the latest routine. If a negative determination is made in step S9, the process proceeds to step S10.

In step S10, the controller <NUM> sets a step change in the EGR rate in the EGR convergence portion 11a. That is, in step S10, the second profile Prof2 is applied in estimating the EGR rate. After step S10, the process ends temporarily. In this case, in the next routine after <NUM> JOB of the routine in which the process of step S10 is performed, an affirmative determination is made in step S9, and the process proceeds to step S11.

In step S11, the controller <NUM> decreases the EGR rate with a primary response delay. That is, in step S11, the third profile Prof3 is applied in estimating the EGR rate. After step S11, the process of this flowchart ends temporarily.

Next, main functions and effects of the present embodiment will be described.

In the EGR estimation method for the internal combustion engine <NUM> according to the present embodiment, the EGR rate in the EGR convergence portion 11a in the intake and exhaust system <NUM>, <NUM> of the internal combustion engine <NUM> is estimated. The intake and exhaust system <NUM>, <NUM> of the internal combustion engine <NUM> includes the intake system <NUM> including the air cleaner <NUM> and the intake passage <NUM>, the exhaust system <NUM> including the exhaust passage <NUM>, and the supercharger <NUM>. The intake and exhaust system <NUM>, <NUM> is provided with the EGR device <NUM> including the EGR passage <NUM> and the EGR valve <NUM>, and the intake system <NUM> includes the intake bypass passage <NUM> and the R/V <NUM>. The EGR estimation method for the internal combustion engine <NUM> estimates the EGR rate in the EGR convergence portion 11a based on the backflow rate of the EGR gas flowing back to the air cleaner <NUM> side by opening the R/V <NUM> when opening the R/V <NUM> and fully closing the EGR valve <NUM> during the supercharging.

According to such a method, in light of the flow mode of the EGR gas described above with reference to <FIG>, a more accurate EGR rate can be estimated when the R/V <NUM> is opened and the EGR valve <NUM> is fully closed during the supercharging.

In the EGR estimation method for the internal combustion engine <NUM>, even if the R/V <NUM> is opened and the EGR valve <NUM> is fully closed, the EGR rate is estimated by using the EGR rate before the EGR valve <NUM> is fully closed as the EGR rate in the EGR convergence portion 11a, which is an estimated EGR rate, until the predetermined time α elapses. That is, the first profile Prof1 is applied in estimating the EGR rate.

According to such a method, a more accurate EGR rate can be estimated by holding the EGR rate in light of the flow mode of the EGR gas described above with reference to <FIG>.

In such a method, the predetermined time α is changed according to the backflow rate of the EGR gas.

According to such a method, the EGR rate can be held for an appropriate time, so that a more accurate EGR rate can be estimated.

In the EGR estimation method of the internal combustion engine <NUM>, after the predetermined time α elapses, the EGR rate is estimated based on the EGR rate in the air cleaner <NUM> when the EGR gas flows back into the air cleaner <NUM>. That is, the second profile Prof2 and the third profile Prof3 are applied in estimating the EGR rate.

According to such a method, in light of the flow mode of the EGR gas described above with reference to <FIG>, the EGR rate in the EGR convergence portion 11a can be appropriately estimated, so that a more accurate EGR rate can be estimated.

In such a method, the EGR rate estimated based on the EGR rate in the air cleaner <NUM> is decreased stepwise and increased as the backflow rate of the EGR gas increases. That is, the second profile Prof2 is applied in estimating the EGR rate.

According to such a method, in light of the flow mode of the EGR gas described above with reference to <FIG>, the EGR rate is decreased stepwise, and the step rate of the EGR rate when the EGR rate is decreased stepwise is appropriately set, so that a more accurate EGR rate can be estimated.

Further, in such a method, the EGR rate estimated based on the EGR rate in the air cleaner <NUM> is decreased with the passage of time, and the amount of decrease in the EGR rate is changed according to the flow rate of the re-inhaled gas. That is, the third profile Prof3 is further applied in estimating the EGR rate.

According to such a method, in light of the flow mode of the EGR gas described above with reference to FIG. 2F, the EGR rate when the mixed gas diluted with the air cleaner <NUM> passes through the EGR convergence portion 11a can be appropriately reflected, so that a more accurate EGR rate can be estimated.

Although the embodiment of the present invention has been described above, the above-mentioned embodiment is merely a part of application examples of the present invention, and does not mean that the technical scope of the present invention is limited to the specific configurations of the above-mentioned embodiment.

For example, in the above embodiment, the case of estimating the EGR rate in the EGR convergence portion 11a is described. However, the estimated EGR rate may be an EGR rate at a predetermined position from a portion of the intake passage <NUM> downstream of the EGR convergence portion 11a to the internal combustion engine <NUM>, such as the EGR rate of the gas flowing into the cylinder of the internal combustion engine <NUM>. Such an EGR rate can be estimated by, for example, correcting a timing at which the step change of the EGR rate is achieved according to a distance from the EGR convergence portion 11a and the like.

Claim 1:
An EGR estimation method for an internal combustion engine (<NUM>) that estimates an EGR rate in an intake and exhaust system of an internal combustion engine (<NUM>), the intake and exhaust system of an internal combustion engine which is including: an intake system including an air cleaner (<NUM>) and an intake passage (<NUM>) that connects the air cleaner (<NUM>) and the internal combustion engine (<NUM>), an exhaust system including an exhaust passage (<NUM>) that is connected to the internal combustion engine (<NUM>), and a supercharger (<NUM>) that is provided in the intake passage (<NUM>) and the exhaust passage (<NUM>), the intake and exhaust system being provided with an EGR device(<NUM>) including an EGR passage (<NUM>) that connects a position upstream of the supercharger (<NUM>) in the intake passage (<NUM>) and a position downstream of the supercharger (<NUM>) in the exhaust passage (<NUM>) and an EGR valve (<NUM>) that is provided in the EGR passage (<NUM>), and the intake system including an intake bypass passage (<NUM>) that connects an upstream pressure portion and a downstream pressure portion of the supercharger (<NUM>) in the intake system and a recirculation valve (<NUM>) that is provided in the intake bypass passage (<NUM>), wherein EGR gas is flowing through the intake bypass passage (<NUM>) back to the air cleaner side after having opened the recirculation valve (<NUM>) during supercharging and closed the EGR valve (<NUM>); the EGR estimation method being characterised in that it comprises the following steps:
calculating the passing amount of gas through the recirculation valve (<NUM>),
calculates a blowback amount integrated value (QS) by integrating said passing amount of gas,
determining that the blowback occurs when the blowback amount integrated value (QS) becomes a negative value,
estimating whether the volume of the intake passage upstream of the supercharger (<NUM>) has been re-inhaled or not based on the blowback amount integrated value (QS),
when the blowback has occurred, estimating the EGR rate at a position upstream of the supercharger (<NUM>) in the intake passage (<NUM>) as being equal to the EGR rate in the intake passage (<NUM>) before the blowback occurs until the volume of the intake passage upstream of the supercharger has been reinhaled.