JPH07279774A - Estimating device of internal combustion engine exhaust gas reflux rate - Google Patents

Abstract

PURPOSE:To improve accuracy of controlling fuel injection by determining the basic rate of gas reflux from the engine speed and load, estimating the respective exhaust gas quantities in accordance with the opening area of an exhaust gas reflux valve and an opening area command value, and from the result of such estimation, estimating the net rate of exhaust gas reflux. CONSTITUTION:In controlling an exhaust gas reflux mechanism 25 composed by interposing an exhaust gas reflux valve 19 in the midway of an exhaust gas reflux passage 18 connected to an intake pipe 2 of an exhaust gas pipe 13, a correction factor of a basic rate of exhaust gas reflux is retrieved by retrieving a map from the engine speed and the intake pressure, as well as retrieving a lift command value from the engine speed and the intake pressure. The ratio of intake pressure to atmospheric pressure is found and gas quantity QA is found by retrieving a map from this ratio and a lift command value. Also a gas quantity QC is found by retrieving a map from this ratio and the actual lift quantity. The value obtained by computing the correction factor of the basic rate of exhaust gas reflux from 1 is assumed as the steady reflux rate and the net rate is found by multiplying the ratio of values QA, QC by the steady reflux rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation rate estimating device for an internal combustion engine, and more specifically, it has a simple structure, but it is a net exhaust gas of exhaust gas that may have actually been sucked into an engine combustion chamber. The present invention relates to an exhaust gas recirculation rate estimation device for an internal combustion engine capable of accurately estimating the recirculation rate. Here, the “exhaust gas recirculation ratio” means the volume ratio or the weight ratio of exhaust gas / intake air.

[0002]

2. Description of the Related Art An exhaust gas recirculation passage connecting an exhaust passage and an intake passage of an internal combustion engine is provided to recirculate a part of exhaust gas to the intake passage, and an exhaust gas recirculation valve is provided there to control the amount of recirculation. Exhaust gas recirculation control for reducing NOx and improving fuel economy is well known.

In the exhaust gas recirculation control, the lift command value of the exhaust gas recirculation valve is determined from the engine speed and the engine load, but as shown in FIG. 9, the actual lift has a delay with respect to the command value. The delay time is constant in the electric exhaust gas recirculation valve, but the delay time changes in the negative pressure type exhaust gas recirculation valve according to the operating state. Further, there is a delay before the exhaust gas recirculation gas is sucked into the combustion chamber according to the valve opening operation. Therefore, in order to accurately perform the exhaust gas recirculation control, it is necessary to accurately estimate the recirculation ratio of the exhaust gas actually sucked into the combustion chamber (hereinafter referred to as "net recirculation ratio"). The term "lift" is used here to mean the opening area of the exhaust gas recirculation valve.

Further, this exhaust gas recirculation amount becomes a disturbance when controlling the air-fuel ratio of the internal combustion engine, so that it is disclosed in JP-A-60-169.
It has been proposed that the correction coefficient KEGR be obtained according to the exhaust gas recirculation rate and the basic fuel injection amount be reduced and corrected as in the technique described in Japanese Patent No. 641. In this conventional technique, the switching of the correction coefficient KEGR is delayed for a predetermined time in consideration of the fact that the delay time of the negative pressure type exhaust gas recirculation valve changes according to the operating state, and the delay time is changed according to the operating state. It is set. Further, in the technique described in Japanese Patent Laid-Open No. 59-192838, it is proposed to gradually change the value of the correction coefficient KEGR.

However, since the behavior of the exhaust gas is more complicated, the applicant of the present invention has filed Japanese Patent Application Laid-Open No. 5-118239.
In this issue, we propose a method of modeling the behavior of the exhaust gas recirculation gas by the lift command value and expressing it by a mathematical expression to obtain the net recirculation rate. Specifically, in a certain control cycle n, the ratio of the amount of exhaust gas recirculation gas sucked into the combustion chamber during the control cycle n to the amount of exhaust gas recirculation gas that has passed through the exhaust gas recirculation valve is taken as a direct ratio, and the pre-control is performed. Percentage of the amount of exhaust gas recirculated into the combustion chamber during the control cycle n with respect to the amount of recirculation gas that has accumulated in the space up to the combustion chamber after passing through the exhaust gas recirculation valve before cycle n-1. Are taken away, and they are identified from the lift command value of the exhaust gas recirculation valve.

That is, the net recirculation rate is obtained from the lift command value via the direct rate and the take-away rate. This made it possible to grasp the behavior of the exhaust gas more accurately, but calculate the amount of gas that passes through the exhaust gas recirculation valve from the lift command value, and then from the amount of passing gas, the amount of exhaust gas recirculation gas that is drawn into the combustion chamber. However, it was inevitable that the configuration would become complicated.

[0007]

Further, the applicant of the present invention separately described the net reflux rate in Japanese Patent Application No. 5-296409.
We propose a technique to obtain the net return rate = return rate in steady state x (actual lift / lift command value). In this method, the net recirculation rate is obtained by using the ratio of the actual lift and the lift command value, and therefore the previously proposed Japanese Patent Laid-Open No. 5-11823.
It has a simpler structure than No. 9.

As described above, the method proposed in Japanese Patent Application No. 5-296409 has an advantage that the structure is simple as compared with the previously proposed Japanese Patent Application Laid-Open No. 5-118239, but on the other hand, it passes through the exhaust gas recirculation valve. Since the exhaust gas recirculation gas amount is affected not only by the lift amount but also by the operating state at that time, in other words, even the same lift amount may differ depending on the operating state. The accuracy was not always good. Therefore, even when the fuel injection control is performed, the calculation of the correction coefficient of the fuel injection amount determined based on the net recirculation rate is not always accurate.

Therefore, a first object of the present invention is to accurately estimate the recirculation rate (net recirculation rate) of the exhaust gas that is actually sucked into the combustion chamber, even though it has a simple structure. It is an object of the present invention to provide an exhaust gas recirculation rate estimation device for an internal combustion engine, which is configured to improve the control accuracy of various controls performed according to the recirculation rate (net recirculation rate).

Further, the second object of the present invention is to improve the control accuracy when the fuel injection control is performed by accurately estimating the recirculation rate (net recirculation rate) of the exhaust gas actually sucked into the combustion chamber. Another object of the present invention is to provide an exhaust gas recirculation rate estimation device for an internal combustion engine.

Further, even when the exhaust gas recirculation operation is stopped, even if the lift command value of the exhaust gas recirculation valve becomes zero, the actual lift does not become zero immediately because the valve dynamic characteristics are delayed.
In the meantime, the exhaust gas recirculates slightly. Furthermore,
When the lift command value becomes zero, calculation may be hindered.

Therefore, a third object of the present invention is to estimate the recirculation rate (net recirculation rate) of the exhaust gas that is actually taken into the combustion chamber when the lift command value becomes zero. An object of the present invention is to provide an exhaust gas recirculation rate estimation device for an internal combustion engine that can absorb a delay in dynamic characteristics and that does not hinder the calculation.

Further, a fourth object of the present invention is to provide a structure in which the distance between the exhaust gas recirculation passage, the opening end on the intake passage side, and the engine combustion chamber is relatively long, and the recirculation gas is delayed in transportation. (EN) An exhaust gas recirculation rate estimation device for an internal combustion engine, which accurately estimates the recirculation rate (net recirculation rate) of exhaust gas that is actually taken into a combustion chamber.

Further, a fifth object of the present invention is to provide a structure in which the distance between the exhaust gas recirculation passage, the opening end on the intake passage side, and the engine combustion chamber is relatively long, and when the transportation delay of the recirculation gas occurs. Provided is an exhaust gas recirculation rate estimation device for an internal combustion engine, which accurately estimates the recirculation rate (net recirculation rate) of exhaust gas sucked into a combustion chamber and improves the control accuracy when performing fuel injection control. To do.

[0015]

In order to achieve the first object of the present invention, according to the present invention, the exhaust passage and the intake passage of an internal combustion engine are connected to each other by connecting at least a part of the exhaust gas to the intake air. In an apparatus for estimating the exhaust gas recirculation rate of an internal combustion engine, which comprises an exhaust gas recirculation passage that recirculates into the passage and an exhaust gas recirculation valve that opens and closes the exhaust gas recirculation passage, a basic exhaust gas recirculation rate is calculated from at least the engine speed and the engine load. Basic exhaust gas recirculation rate determining means for determining, first estimating means for estimating the exhaust gas amount QACT passing through the exhaust gas recirculation valve according to the opening area of the exhaust gas recirculation valve based on the flow rate characteristic of the exhaust gas recirculation valve, Second estimating means for estimating the exhaust gas amount QCMD passing through the exhaust gas recirculation valve according to the opening area command value of the exhaust gas recirculation valve based on the flow rate characteristic, and the exhaust gas amount QAC
And a net exhaust gas recirculation rate estimating means for estimating a net exhaust gas recirculation rate actually sucked into the combustion chamber according to T and QCMD.

According to a second aspect of the present invention, the net exhaust gas recirculation rate estimating means obtains a correction coefficient based on the net exhaust gas recirculation rate, and the combustion chamber is based on the correction coefficient. It is configured to include means for correcting the fuel injection amount to be supplied to.

In order to achieve the first and second objects,
More specifically, in the third aspect, the flow rate characteristic is configured to be determined at least from an upstream / downstream pressure ratio of the exhaust gas recirculation valve and an opening area.

More specifically, the pressure ratio is the ratio of the pressure in the intake passage to the atmospheric pressure or the exhaust pressure.

More specifically, in the fifth aspect, the net exhaust gas recirculation rate estimating means is configured to make the exhaust gas amounts QACT, QCM.
The ratio QACT / QCMD of D is calculated to estimate the net exhaust gas recirculation rate.

In order to achieve the third object, in claim 6, the net exhaust gas recirculation rate estimation means compares at least one of the opening area command value and the exhaust gas amount QCMD with a threshold value, When it is judged to be below, at least one of the opening area command value and the exhaust gas amount QCMD and the basic exhaust gas recirculation rate correction coefficient are held at predetermined values.

According to a seventh aspect of the present invention, in order to achieve a fourth object, the net exhaust gas recirculation rate estimating means sets the net exhaust gas recirculation rate estimation means for the exhaust gas amount gt that has passed through the exhaust gas recirculation valve in a certain period t. A direct ratio determining means for determining a direct ratio EA indicating a ratio of the amount of exhaust gas sucked into the combustion chamber within the period t, the period t
Of the exhaust gas that has previously passed through the exhaust gas recirculation valve, with respect to the amount gc (t-1) that has accumulated in a site other than the combustion chamber,
A take-away rate determining means for determining a take-away rate EB indicating a ratio of the amount of exhaust gas sucked into the combustion chamber within the period t, and during the period t from the direct rate EA and the take-away rate EB. The exhaust gas amount gin sucked into the combustion chamber is obtained, and the net exhaust gas recirculation rate is estimated accordingly.

In order to achieve a fifth object, according to the present invention, in claim 8, the net exhaust gas recirculation rate estimating means obtains a correction coefficient based on the net exhaust gas recirculation rate, and the combustion chamber is based on the correction coefficient. It is configured to include means for correcting the fuel injection amount to be supplied to.

[0023]

According to the present invention, the flow rate characteristic of the exhaust gas recirculation valve is determined, and the exhaust gas recirculation valve passes through the exhaust gas recirculation valve according to the opening area and the opening area command value of the exhaust gas recirculation valve based on the flow rate characteristic. Since the exhaust gas amounts QACT and QCMD are estimated and the net exhaust gas recirculation rate actually sucked into the combustion chamber is estimated accordingly, in other words, the behavior of the exhaust gas recirculation gas is grasped from the flow rate characteristics of the exhaust gas recirculation valve. Therefore, the net exhaust gas recirculation rate actually sucked into the combustion chamber can be accurately estimated.

In the second aspect, the net exhaust gas recirculation valve estimating means obtains a correction coefficient based on the net exhaust gas recirculation rate, and corrects the fuel injection amount to be supplied to the combustion chamber based on the correction coefficient. Since it is configured to include the means, the control accuracy when controlling the fuel injection is improved, and no lean spike or rich spike occurs.

In the third aspect, the flow rate characteristic is
Since it is configured to be determined at least from the upstream / downstream pressure ratio of the exhaust gas recirculation valve and the opening area, the same operational effect as in claim 1 or 2 is obtained.

According to the fourth aspect of the present invention, the pressure ratio is the ratio of the pressure in the intake passage to the atmospheric pressure or the exhaust pressure. Therefore, the same effect as that of the first or second aspect. Have.

In the present invention, the net exhaust gas recirculation rate estimating means is configured to calculate the ratio QACT / QCMD of the exhaust gas amounts QACT and QCMD to estimate the net exhaust gas recirculation rate. It has the same effect as the item 1 or 2.

According to a sixth aspect of the present invention, the net exhaust gas recirculation rate estimating means is configured to set the opening area command value and the exhaust gas amount QCM.
At least one of D is compared with a threshold value, and when it is determined that it is less than or equal to the threshold value, the opening area command value and the exhaust gas amount QCM
Since at least one of D and the basic exhaust gas recirculation ratio correction coefficient is held at a predetermined value, the exhaust gas recirculation is stopped and the opening area command value of the exhaust gas recirculation valve or the exhaust gas amount Q
Even if the CMD becomes zero, it is held at a predetermined value, so
Since the delay in the dynamic characteristics of the valve can be absorbed and the inconvenience such as the inability to calculate due to the zero division does not occur, the recirculation rate can be always estimated. When it is determined that the basic exhaust gas recirculation rate correction coefficient is equal to or less than the threshold value, the basic exhaust gas recirculation rate correction coefficient is replaced with a predetermined value. Does not occur and the basic exhaust gas recirculation rate becomes 0. Here, the predetermined value is, for example, the previous value.

According to a seventh aspect of the present invention, the net exhaust gas recirculation rate estimating means is sucked into the combustion chamber within the period t with respect to the exhaust gas amount gt that has passed through the exhaust gas recirculation valve during the period t. Direct rate determining means for determining the direct rate EA indicating the ratio of the exhaust gas amount, the amount gc of the exhaust gas that has passed through the exhaust gas recirculation valve before the period t, and is retained in a portion other than the combustion chamber.
A take-away rate determining means for determining a take-away rate EB indicating a ratio of the amount of exhaust gas sucked into the combustion chamber within the period t, with respect to (t-1), and the direct rate EA and the take-away rate. Rate E
Exhaust gas amount g sucked into the combustion chamber during the period t from B
Since in is calculated and the net exhaust gas recirculation rate is estimated in accordance therewith, the net exhaust gas recirculation rate can be accurately estimated even when the transportation delay of the recirculation gas occurs.
The period t has the same meaning as the control cycle n mentioned in the detailed description.

According to the present invention, the net exhaust gas recirculation rate estimating means obtains a correction coefficient based on the net exhaust gas recirculation rate, and corrects the fuel injection amount to be supplied to the combustion chamber based on the correction coefficient. Since it is configured so as to include the means for controlling, the control accuracy of the fuel injection control can be improved even when the transportation delay of the recirculation gas occurs.

[0031]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram showing a fuel control system including an exhaust gas recirculation rate estimation system for an internal combustion engine according to the present invention. The internal combustion engine is, for example, a 4-cylinder internal combustion engine, and a throttle valve 3 is provided in the middle of an intake pipe (intake passage) 2 of the engine body 1.
Is provided. The throttle valve 3 has a throttle position θT.
Throttle position sensor for detecting H (indicated by θTH) 4
Are connected to the electronic control unit (hereinafter "ECU").
To say 5).

The ECU 5 shapes the input signal waveforms from the throttle position sensor 4 and a sensor group described later, corrects the voltage level to a predetermined level, and converts the analog signal into a digital signal value. CPU
5b, a storage means 5c for storing various calculation programs and calculation results executed by the CPU 5b, an output circuit 5d, etc., and performs a reflux rate estimation and the like as described later.

The fuel injection valve 6 is provided for each cylinder between the engine body 1 and the throttle valve 3 and upstream of the intake port (not shown) of the combustion chamber (not shown). The fuel injection valve 6 is connected to a fuel pump (not shown), and EC
The valve opening time (fuel injection amount) is controlled by being electrically connected to U5. On the other hand, an absolute pressure sensor (indicated by PBA) 7 for detecting the intake pipe internal pressure PBA by absolute pressure is provided downstream of the throttle valve 3, and the intake air temperature TA is provided downstream thereof.
An intake air temperature sensor (indicated by TA) 8 for detecting The outputs of these sensors are also sent to the ECU 5.

Further, the engine body 1 is provided with a water temperature sensor (shown by TW) 9 for detecting the engine cooling water temperature TW, and a crankshaft or a camshaft (both not shown) is provided with T.
A crank angle sensor (denoted by CRK) 10 for detecting a predetermined crank angle CRK including a DC position, and a cylinder discrimination sensor (CY) for detecting a predetermined crank angle CYL of a specific cylinder.
11) is provided. The output of these sensors is also E
It is sent to the CU 5, and the output of the crank angle sensor is counted through a counter (not shown) to detect the engine speed NE.

Further, the exhaust pipe (exhaust passage) 13 of the engine body 1
A catalytic converter 14 is disposed in the exhaust gas, and purifies HC, CO, NOx components, etc. in the exhaust gas. An oxygen concentration sensor (indicated by O ₂ ) 15 that detects the oxygen concentration O ₂ in the exhaust gas is mounted upstream of the catalytic converter 14 and supplies an output to the ECU 5. Further, an atmospheric pressure sensor (indicated by PA) 16 for detecting the atmospheric pressure PA is provided near the engine body 1, and a wall temperature sensor for detecting the wall temperature TC is provided on the wall surface of the intake pipe 2 near the intake port. (Indicated by TC) 1
7 is provided. The outputs of these sensors are also supplied to the ECU 5.

Next, the exhaust gas recirculation mechanism 25 will be described.

The exhaust gas recirculation passage 25 includes an exhaust gas recirculation passage 18 for connecting the exhaust pipe 13 to the intake pipe 2 (reference numeral 18a).
Indicates the open end on the intake pipe side). An exhaust gas recirculation valve (EGR valve) 19 is provided in the exhaust gas recirculation passage 18. The exhaust gas recirculation valve 19 is of a negative pressure responsive type and mainly includes the passage 18
A valve body 19a arranged to open and close the valve body, and a valve body 19a
It is composed of a diaphragm 19b which is connected to a and operates by a negative pressure introduced through a solenoid valve 22 described later, and a spring 19c which biases the diaphragm 19b in a valve closing direction.

A communication passage 20 is connected to the negative pressure chamber 19d defined by the diaphragm 19b, and the negative pressure in the intake pipe 2 is passed through a normally closed solenoid valve 22 provided in the middle of the communication passage 20. Configured to be introduced. The atmosphere chamber 19e is
It communicates with the atmosphere. Further, the communication passage 20 has a solenoid valve 22.
The atmosphere communication passage 23 is connected downstream of the communication passage 23, and atmospheric pressure is introduced into the communication passage 20 and then into the negative pressure chamber 19d through an orifice 21 provided in the communication passage 23.

The solenoid valve 22 is connected to the ECU 5,
It operates by the drive signal from CU5, and exhaust gas recirculation valve 19
The lift operation (valve opening operation) of the valve body 19a and its speed are controlled. The exhaust gas recirculation valve 19 is provided with a lift sensor 24, which detects the operation amount (lift amount) of the valve body 19a and sends the output to the ECU 5.

FIG. 2 is a flow chart for explaining the operation of the exhaust gas recirculation rate estimating apparatus for an internal combustion engine according to the present invention. Before starting the description of the figure, an algorithm of the estimation method according to the present invention will be described with reference to FIG.

The amount of gas passing through the exhaust gas recirculation valve is determined by the valve opening area and the pressure ratio before and after the valve, that is, the flow rate characteristics (design specifications), when viewed as a single valve. That is, it is considered that it is obtained from the opening area of the valve, that is, the ratio of the lift amount and the upstream and downstream pressure of the valve.

Also in the actual machine, as shown in FIG. 3, the recirculation gas amount is obtained by calculating the valve lift amount and the ratio between the atmospheric pressure PA acting through the atmosphere communication passage 23 and the intake pressure PBA of the intake pipe 2. It was thought that it was possible to estimate to a certain degree (actually, the flow rate characteristics slightly change depending on the exhaust pressure and exhaust temperature, but it is possible to absorb that specific change to a considerable extent by using the gas amount ratio as described later. Was). In the present invention, focusing on this point, the reflux rate is obtained based on the flow rate characteristic. The opening area is obtained from the lift amount because the valve having a structure in which the lift amount corresponds to the opening area is used. Therefore, when using another structure such as a linear solenoid, the opening area is obtained from another parameter.

By the way, the return flow rate includes a return flow rate in a steady state and a return flow rate in a transient state. Among them, the return rate in a steady state is a value in a state where the lift command value is equal to the actual lift, The recirculation rate is a value when the lift command value is not equal to the actual lift. Then, in the algorithm according to the present invention, it was considered that the difference at the time of transition was caused by the deviation of the reflux rate from the steady-state reflux rate by the corresponding gas amount ratio, as shown in FIG.

Specifically, in the steady state, the lift command value = actual lift, the gas amount ratio = 1, that is, the recirculation rate = the recirculation rate in the steady state.

In the transient state, the lift command value ≠ actual lift, the gas amount ratio ≠ 1, that is, the reflux ratio = the steady-state reflux ratio (map search value) × gas ratio.

As described above, it was considered that the net reflux rate can be obtained by multiplying the steady-state reflux rate by the ratio of both gas amounts. The formula is as follows. Reflux rate = (recirculation rate in steady state) x (gas amount QACT obtained from actual lift and pressure ratio before and after valve) / (gas amount QCMD obtained from lift command value and pressure ratio before and after valve)

Here, the return rate in the steady state is obtained by obtaining a return rate correction coefficient and subtracting it from 1. That is,
When the constant return rate correction coefficient is called KEGRMAP,
It is determined by the constant reflux rate = (1-KEGRMAP).
In this specification, the steady-state recirculation rate or the steady-state recirculation rate correction coefficient is also referred to as a basic exhaust gas recirculation rate or a basic exhaust gas recirculation rate correction coefficient. In addition, the return rate correction coefficient KEG in the steady state
The RMAP is experimentally obtained from the engine speed NE and the intake pressure PBA in advance and set as a map as shown in FIG. 4, and the map is searched and obtained.

Hereinafter, description will be given according to the flow chart of FIG. The program shown in this flow chart is started every predetermined time such as 10 ms.

First, in S10, the engine speed NE and the intake pressure P
BA, atmospheric pressure PA, actual lift LACT (lift sensor 2
(Output of 4) is read, and the process proceeds to S12 to search for the lift command value LCMD from the engine speed NE and the intake pressure PBA. Here, the lift command value LCMD is obtained by searching a map in which the characteristics are set in advance as shown in FIG. Subsequently, the program proceeds to S14, in which the map shown in FIG. 4 is searched from the engine speed NE and the intake pressure PBA to search the basic exhaust gas recirculation ratio correction coefficient KEGRMAP.

Next, in S16, the actual lift L detected is detected.
Confirm that ACT is not zero, that is, exhaust gas recirculation valve 1
After confirming that the valve 9 is opened, the process proceeds to S18, and the lift command value LCMD retrieved is compared with a predetermined lower limit value LCMDLL (minute value). When it is determined in S18 that the search value is not less than or equal to the lower limit value, the process proceeds to S20, where the intake pressure P
The ratio PBA / PA between BA and atmospheric pressure PA is obtained, and a map (not shown) of the characteristics shown in FIG. 3 is searched from the found lift command value LCMD and the gas amount QCM is searched.
Find D. This is the “gas amount obtained from the lift command value and the pressure ratio before and after the valve” in the above formula.

Then, in S22, the same ratio PBA / P is obtained.
Similarly, a map of the characteristics shown in FIG. 3 is searched from A and the detected actual lift LACT to obtain the gas amount QACT. This corresponds to the “gas amount obtained from the actual lift and the pressure ratio before and after the valve” in the above formula.

Subsequently, the routine proceeds to S24, where the value obtained by subtracting the retrieved basic exhaust gas recirculation ratio correction coefficient KEGRMAP from 1 is set as the steady recirculation ratio (basic exhaust gas recirculation ratio or steady recirculation ratio). Here, the steady-state recirculation rate is, as described above, the recirculation rate when the exhaust gas recirculation operation is stable, that is, the exhaust gas recirculation operation is not in a transient state such as when the exhaust gas recirculation operation is started or stopped. Means the reflux rate at that time. Then, in S26, the steady return rate is multiplied by the ratio QACT / QCMD of the values QACT and QCMD to obtain the net return rate as shown in the figure.

Subsequently, the routine proceeds to S28, where the fuel injection correction coefficient KEGRN is calculated. FIG. 6 is a subroutine flow chart showing the operation. In S100, a value obtained by subtracting the net recirculation rate (obtained in S26 of FIG. 2) from 1 is set as the fuel injection correction coefficient KEGRN. The fuel injection amount is corrected by multiplying the basic fuel injection amount Tim obtained from the engine speed and the engine load by the correction coefficient KEGRN to obtain the output fuel injection amount Tout. Since this is known per se, the description will be limited to this degree.

When it is determined in S16 that the actual lift LACT is zero, exhaust gas recirculation has not been performed, so the program is immediately terminated. Further, at S18, the lift command value LC
When it is determined that MD is less than or equal to the lower limit value LCMDLL, S30
And the lift command value LCMD is the previous value LCMDn-1.
Is kept as it is (for simplification, adding n to the value this time is omitted in this flow chart).

As described above, this means that the lift command value LC is set when the region where exhaust gas recirculation is executed is changed to the region where exhaust gas recirculation is not executed.
Even if MD becomes zero, the actual lift LACT does not immediately become zero because the dynamic characteristics of the exhaust gas recirculation valve 19 are delayed. Therefore, the lift command value LCMD is the lower limit value (threshold value) LCMD.
If it is less than LL, lift command value LCMD is changed to previous value LCM.
Dn-1 (value at the time of n-1 in the previous control cycle) is held. This previous value hold is S16.
The process is repeated until it is confirmed that the actual lift LACT has become zero.

Further, the lift command value LCMD is the lower limit value LC
When it is equal to or lower than MDLL, the lift command value LCMD may be zero, and in that case, the QCMD search value in S20 is also zero, and the operation in S26 is divided by zero, which makes the operation impossible.
However, by holding the previous value as described above,
There is no fear of becoming inoperable. Although the lower limit value LCMDLL is a minute value, it may be zero.

Next, in S32, the map search value of the basic exhaust gas recirculation rate correction coefficient KEGRMAP (search in S14) is replaced with the previous search value KEGRMAPn-1. This is because the basic exhaust gas recirculation ratio correction coefficient KEGRMAP searched in S14 is set to 1 in the characteristic planned in this embodiment in the operating state in which the lift command value LCMD searched in S12 is determined to be less than or equal to the lower limit value. To be done. As a result, S
In the calculation of 24, the steady reflux rate may be zero.
S32 is designed to eliminate the inconvenience.

As described above, this embodiment pays attention to the flow rate characteristic of the exhaust gas recirculation valve, and estimates the net recirculation rate by paying attention to the fact that the difference between the recirculation rate in the transient state and that in the steady state is the gas amount ratio. As a result, the previously proposed Japanese Patent Laid-Open No. 5-11823
Although the configuration is simpler than that of the method of No. 9, the behavior of exhaust gas can be accurately grasped. In addition, the method of Japanese Patent Application No. 5-296049 proposed separately, that is, Even when compared with, the net recirculation rate can be obtained more accurately by expressing the behavior of the exhaust gas from the flow rate characteristic of the exhaust recirculation valve.

Further, since the gas amount ratio is used, the influence of exhaust temperature and exhaust pressure on the gas amount can be absorbed to a considerable extent, and in that sense, the estimation accuracy is improved. Further, even when the exhaust gas recirculation is stopped and the lift command value becomes zero, the previous value is held until the actual lift becomes zero, so the delay in the dynamic characteristics of the valve can be absorbed and the exhaust gas recirculation can be properly performed. The rate can be estimated and no inconvenience occurs in the calculation.

Further, in the subsequent correction of the fuel injection amount, the correction coefficient KEGRN is obtained based on the net recirculation rate that accurately grasps the behavior of the recirculation gas. Therefore, the air-fuel ratio can be accurately controlled to the target value, and the occurrence of lean spikes or rich spikes can be prevented.

FIG. 7 is a flow chart showing a second embodiment of the present invention, which is the aforementioned Japanese Patent Application Laid-Open No. 5-118239.
This is a method that partially uses the method for correcting the transport delay of the reflux gas that was proposed in No. That is, in the previous embodiment, the open end 1 of the exhaust gas recirculation passage 18 on the intake pipe 2 side in FIG.
It is premised that the distance between 8a and the combustion chamber is relatively short and the transport delay of the reflux gas can be ignored, but the transport delay was taken into consideration in the second embodiment. More specifically, the calculation of the fuel injection correction coefficient is made different.

Referring to FIG. 7, the required recirculation gas amount is obtained by multiplying the basic fuel injection amount Tim obtained from the engine speed and the engine load in S200 by the net recirculation rate (obtained in S26 of FIG. 2). (Apparently, the amount of recirculation gas that has passed through the exhaust gas recirculation valve 19) gt (n) is determined. Here, n means a certain control cycle, more specifically, a program activation cycle of the flow chart of FIG. 2 (same as time t described in claim 7). Next, in S202, the true recirculation gas amount gin (n) drawn into the combustion chamber in the control cycle n is estimated as shown in the figure.

Here, although gt has been described above, the others are described in EA. ． ． Direct ratio (a value indicating the ratio of the gas sucked into the combustion chamber during the control cycle n among the recirculation gas gt that has passed through the exhaust gas recirculation valve 19 in a certain control cycle n), EB. ． ． Carry-out rate (of the recirculation gas amount gc (n-1) that has passed through the exhaust gas recirculation valve 19 by the previous control cycle n-1 and has accumulated between the exhaust gas recirculation valve 19 and the combustion chamber, the control cycle n is a value indicating the ratio of the gas sucked into the combustion chamber).

That is, the required recirculation gas amount gt is multiplied by the direct ratio EA to obtain the amount of gas sucked into the combustion chamber through the exhaust gas recirculation valve 19 during the control cycle n, and the retained gas amount gc is taken away. It is presumed that the amount of gas that was previously accumulated from n-1 multiplied by EB and was sucked into the combustion chamber during the control cycle n is summed up, and the two are summed up to be taken into the combustion chamber during the control cycle n. The reflux gas amount gin (n) of is calculated.

Next, in S204, the true recirculation gas amount g
A value obtained by dividing in (n) by the basic fuel injection amount Tim is subtracted from 1 to obtain the fuel injection correction coefficient KEGRN. Then, the process proceeds to S206, and the amount of staying gas gc (n) is updated for the calculation at the next program startup. When the program is started next time, gc (n) obtained in S206 is S20.
2 is replaced with gc (n-1), and the true required gas amount gin (n) is calculated there. The details of this transportation delay compensation are described on page 5 and after of the above-mentioned Japanese Patent Application Laid-Open No. 5-118239, so the description will be limited to this extent.

Since the second embodiment is configured as described above, the fuel injection amount can be accurately corrected even when the transport delay of the reflux gas is hard to ignore.

In the second embodiment, the transportation delay is estimated from the method used in the prior application, but the transportation delay may be simplified to be a primary delay.

Further, in the second embodiment, the parameter relating to the fuel transportation delay may be corrected by the obtained net reflux rate, as proposed in the above-mentioned Japanese Patent Application Laid-Open No. 5-118239.

FIG. 8 shows a third embodiment of the present invention, FIG.
3 is a partial flow chart of FIG. In the case of the third embodiment, S
After confirming that the actual lift LACT is not zero at 16, S1
In step S60, the lift command value QCMD is retrieved, and then in step S162, the lift command value QCMD is compared with a predetermined value (threshold value) QCMDLL (minute value). When it is determined that the value is equal to or less than the predetermined value, the process proceeds to S300 and the previous value QCM
Hold Dn-1. The rest of the configuration is the same as that of the first embodiment, and the effect is not different.

In the first, second and third embodiments described above, the atmospheric pressure is used in S12, S20, S22, etc. of FIG. 2, but the exhaust pressure may be used instead.

In the above, the values LCMD, KEGR
Although MAP, QCMD, and QACT have been set as map values, they may be calculated each time.

In the above description, the exhaust gas recirculation valve is of the negative pressure type, but may be of the electric type.

Further, although the intake pressure is used as the parameter indicating the engine load, the intake air amount, throttle opening, etc. may be used.

[0075]

According to the first aspect of the present invention, the net exhaust gas recirculation rate actually sucked into the combustion chamber can be accurately estimated.

According to the second aspect of the present invention, the control accuracy when controlling the air-fuel ratio is improved, and no lean spike or rich spike occurs.

The third aspect has the same effect as the second aspect.

According to the fourth aspect, the same operation and effect as those of the second to third aspects are obtained.

The fifth aspect has the same operational effect as the first or second aspect.

According to the sixth aspect, it is possible to absorb the delay in the dynamic characteristics of the exhaust gas recirculation valve, and there is no inconvenience such as the inability to calculate.

According to the seventh aspect, the net exhaust gas recirculation rate can be accurately estimated even when the transportation delay of the recirculation gas occurs.

According to the eighth aspect, the control accuracy of the air-fuel ratio can be improved even when the transportation of the recirculated gas is delayed.

[Brief description of drawings]

FIG. 1 is a block diagram generally showing an exhaust gas recirculation rate estimation device for an internal combustion engine according to the present invention.

2 is a flow chart showing the operation of the exhaust gas recirculation rate estimation device for an internal combustion engine of FIG. 1. FIG.

FIG. 3 is an explanatory diagram showing a basic algorithm for estimating an exhaust gas recirculation rate according to the present invention, and is an explanatory diagram showing a characteristic of a gas amount with respect to a lift amount of an exhaust gas recirculation rate used in the calculation of the flow chart of FIG. 2;

FIG. 4 is an explanatory diagram showing map characteristics of an exhaust gas recirculation ratio correction coefficient (basic exhaust gas recirculation ratio correction coefficient) in a steady state used in the calculation of the flow chart of FIG. 2;

FIG. 5 is an explanatory diagram showing a map characteristic of a lift command value used in the calculation of the flow chart of FIG.

FIG. 6 is a subroutine flow chart showing the operation of calculating the fuel injection correction coefficient in the flow chart of FIG.

FIG. 7 is a flow chart showing a second embodiment of the present invention, and is a subroutine flow chart showing the operation of calculating the fuel injection correction coefficient in the flow chart of FIG.

FIG. 8 is a main part flow chart of the flow chart of FIG. 2 showing a third embodiment of the present invention.

FIG. 9 is a timing chart generally showing operating characteristics of exhaust gas recirculation rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine main body 2 Intake pipe 5 Electronic control unit (ECU) 7 Absolute pressure sensor 10 Crank angle sensor 16 Atmospheric pressure sensor 18 Exhaust gas recirculation passage 19 Exhaust gas recirculation valve 25 Exhaust gas recirculation mechanism

Claims (8)

[Claims] 1. An exhaust gas recirculation passage that connects an exhaust passage and an intake passage of an internal combustion engine to recirculate at least a part of exhaust gas to the intake passage, and an exhaust recirculation valve that opens and closes the exhaust recirculation passage. For estimating the exhaust gas recirculation rate of another internal combustion engine, comprising: a. Basic exhaust gas recirculation rate determining means for determining the basic exhaust gas recirculation rate from at least the engine speed and the engine load, b. First estimating means for estimating the exhaust gas amount QACT passing through the exhaust gas recirculation valve according to the opening area of the exhaust gas recirculation valve based on the flow rate characteristic of the exhaust gas recirculation valve, c. Second estimating means for estimating the exhaust gas amount QCMD passing through the exhaust gas recirculation valve according to the opening area command value of the exhaust gas recirculation valve based on the flow rate characteristic; and d. An exhaust gas recirculation rate estimating device for an internal combustion engine, comprising: net exhaust gas recirculation rate estimating means for estimating a net exhaust gas recirculation rate actually sucked into a combustion chamber according to the exhaust gas amounts QACT and QCMD. 2. The net exhaust gas recirculation rate estimating means includes means for obtaining a correction coefficient based on the net exhaust gas recirculation rate and correcting the fuel injection amount to be supplied to the combustion chamber based on the correction coefficient. The exhaust gas recirculation rate estimation device for an internal combustion engine according to claim 1. 3. The exhaust gas recirculation rate estimation of an internal combustion engine according to claim 1, wherein the flow rate characteristic is determined at least from a pressure ratio upstream and downstream of the exhaust gas recirculation valve and an opening area. apparatus. 4. The exhaust gas recirculation rate estimating apparatus for an internal combustion engine according to claim 3, wherein the pressure ratio is a ratio of the pressure in the intake passage to the atmospheric pressure or the exhaust pressure. 5. The net exhaust gas recirculation rate estimating means calculates the ratio QACT / QCMD of the exhaust gas amounts QACT, QCMD to estimate the net exhaust gas recirculation rate. An exhaust gas recirculation rate estimation device for an internal combustion engine according to any one of claims. 6. The net exhaust gas recirculation rate estimating means compares at least one of the opening area command value and the exhaust gas amount QCMD with a threshold value, and when it is determined that the opening area command value and the exhaust gas amount are equal to or less than a threshold value. 6. The exhaust gas recirculation rate estimation device for an internal combustion engine according to claim 1, wherein at least one of the quantity QCMD and the basic exhaust gas recirculation rate correction coefficient are held at predetermined values. 7. The net exhaust gas recirculation rate estimating means comprises: e. A direct rate determining means for determining a direct rate EA indicating a ratio of the exhaust gas amount gt that has passed through the exhaust gas recirculation valve in a certain period t to the exhaust gas amount in the period t, f. Of the exhaust gas that has passed through the exhaust gas recirculation valve before the period t, the amount gc (t
-1), a take-away rate determining means for determining a take-away rate EB indicating a ratio of the amount of exhaust gas sucked into the combustion chamber within the period t, and the direct rate EA and the take-away rate EB. And the exhaust gas amount gin that is taken into the combustion chamber during the period t
7. The exhaust gas recirculation rate estimation device for an internal combustion engine according to claim 1, wherein the net exhaust gas recirculation rate is estimated according to the above equation. 8. The net exhaust gas recirculation rate estimating means includes means for obtaining a correction coefficient based on the net exhaust gas recirculation rate and correcting the fuel injection amount to be supplied to the combustion chamber based on the correction coefficient. The exhaust gas recirculation rate estimation device for an internal combustion engine according to claim 7.