JP3307770B2 - Exhaust gas recirculation rate estimation device for internal combustion engine - Google Patents

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 apparatus for an internal combustion engine, and more specifically, to a net exhaust gas of an exhaust gas which may be actually drawn into an engine combustion chamber while having a simple structure. The present invention relates to an exhaust gas recirculation rate estimating device for an internal combustion engine, which is capable of accurately estimating a recirculation rate. Here, “exhaust gas recirculation rate” means a volume ratio or a 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 therein to control a recirculation amount. Exhaust gas recirculation control for reducing NOx and improving fuel efficiency 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, etc., but as shown in FIG. 9, the actual lift has a delay with respect to the command value. The delay time is constant in a motor-operated exhaust gas recirculation valve, whereas the delay time changes in a negative pressure exhaust gas recirculation valve depending on the operation state. Furthermore, there is a delay before exhaust gas recirculation gas is sucked into the combustion chamber in accordance with the valve opening operation. Therefore, in order to accurately control the exhaust gas recirculation, it is necessary to accurately estimate the recirculation rate of the exhaust gas actually sucked into the combustion chamber (hereinafter referred to as “net recirculation rate”). Here, the term “lift” is used to indicate the opening area of the exhaust gas recirculation valve.

Further, the amount of exhaust gas recirculation causes disturbance when controlling the air-fuel ratio of the internal combustion engine.
As disclosed in Japanese Patent Application Laid-Open No. 641, there has been proposed that a correction coefficient KEGR is obtained in accordance with an exhaust gas recirculation rate and the basic fuel injection amount is reduced and corrected. In this prior art, 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 operation state, and the delay time is set according to the operation state. You have set. In the technique described in Japanese Patent Application Laid-Open No. Sho 59-192838, it is proposed to gradually change the value of the correction coefficient KEGR.

However, because the behavior of exhaust gas is more complicated, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 5-118239.
No. 3 proposes a method of modeling the behavior of the exhaust gas recirculation gas according to 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 the exhaust gas recirculated gas sucked into the combustion chamber during the control cycle n to the amount of the exhaust gas recirculated gas passing through the exhaust gas recirculation valve is defined as a direct ratio. Percentage of the amount of the recirculated gas sucked into the combustion chamber during the control cycle n with respect to the amount of the recirculated gas that has passed through the exhaust gas recirculation valve and stayed in the space to the combustion chamber before cycle n-1 Are taken away rates, 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 carry-out rate. As a result, the behavior of the exhaust gas can be grasped more accurately.However, the amount of gas passing through the exhaust gas recirculation valve is obtained from the lift command value, and the amount of exhaust gas recirculated gas sucked into the combustion chamber is obtained from the amount of gas passing therethrough. Therefore, the configuration was inevitably complicated.

[0007]

Further INVENTION Problem to be Solved] The present applicant separately, Hei 5-296 No. 049 (JP-A 7-12749
No. 4) proposes a technique for calculating the net reflux rate by the following formula: net reflux rate = reflux rate at steady state × (actual lift / lift command value). In this method, the net recirculation rate is obtained by using the ratio between the actual lift and the lift command value, so that the configuration is simpler than that of Japanese Patent Laid-Open No. Hei 5-118239.

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

Accordingly, a first object of the present invention is to accurately estimate the recirculation rate (net recirculation rate) of the exhaust gas actually sucked into the combustion chamber while having a simple configuration, and thus to reduce the exhaust gas. It is an object of the present invention to provide an exhaust gas recirculation rate estimating apparatus for an internal combustion engine, in which the control accuracy of various controls performed according to the recirculation rate (net recirculation rate) is improved.

A second object of the present invention is to improve the control accuracy when performing a fuel injection control by accurately estimating the recirculation rate (net recirculation rate) of the exhaust gas actually sucked into the combustion chamber. It is an object of the present invention to provide an exhaust gas recirculation rate estimating device for an internal combustion engine which is made to perform the above.

Further, even when the exhaust gas recirculation operation is stopped, even if the lift command value of the exhaust gas recirculation valve becomes zero, there is a delay in the dynamic characteristics of the valve. Therefore, the actual lift does not immediately become zero.
During that time, the exhaust gas recirculates, albeit slightly. Furthermore,
If the lift command value becomes zero, the calculation may be hindered in some cases.

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

Further, a fourth object of the present invention is to provide an engine 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 transport of the recirculated gas is delayed. An object of the present invention is to provide an exhaust gas recirculation rate estimating apparatus for an internal combustion engine, which accurately estimates a recirculation rate (net recirculation rate) of exhaust gas actually sucked into a combustion chamber.

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

[0015]

According to a first aspect of the present invention, an exhaust passage and an intake passage of an internal combustion engine are connected and at least a part of exhaust gas is supplied to the intake passage. In an apparatus for estimating an exhaust gas recirculation rate of an internal combustion engine comprising an exhaust gas recirculation passage returning to a passage and an exhaust gas recirculation valve for opening and closing the exhaust gas recirculation passage, a basic exhaust gas recirculation rate is determined from at least an engine speed and an engine load. Means for determining basic exhaust gas recirculation rate to be determined, first estimating means for estimating the amount of exhaust gas QACT passing through the exhaust gas recirculation valve according to the opening area of the exhaust gas recirculation valve, based on the flow characteristics of the exhaust gas recirculation valve; Second estimating means for estimating an exhaust gas amount QCMD passing through the exhaust gas recirculation valve in accordance with an opening area command value of the exhaust gas recirculation valve based on the flow characteristics, and the exhaust gas amounts QACT and QC Net exhaust gas recirculation rate estimating means for estimating a net exhaust gas recirculation rate that is actually drawn into the combustion chamber in accordance with the D
And the net exhaust gas recirculation rate estimating means comprises:
Exhaust gas amount QACT, QCMD ratio QACT / QCMD
Is calculated to estimate the net exhaust gas recirculation rate .

In order to achieve the second object, the present invention is directed to a second aspect of the present invention, wherein the net exhaust gas recirculation rate estimating means determines a correction coefficient based on the net exhaust gas recirculation rate, and based on the correction coefficient, calculates the combustion chamber. And a means for correcting the fuel injection amount to be supplied to the engine.

In order to achieve the first and second objects,
More specifically, the flow rate characteristic is determined so as to be determined at least from the pressure ratio between the upstream and downstream of the exhaust gas recirculation valve and the opening area.

More specifically, the pressure ratio is a ratio between the pressure of the intake passage and the atmospheric pressure or the exhaust pressure.

[0019]

[0020] In order to achieve the third object, the present invention provides the following.
In claim 5 , 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. At least one of the QCMDs and the basic exhaust gas recirculation rate correction coefficient are held at predetermined values.

[0021] To achieve the fourth object, the present invention is claimed in claim 6 wherein, the net exhaust gas recirculation rate estimating means, with respect to the exhaust gas amount gt passing through the exhaust gas recirculation valve in a period of time t, the A direct ratio determining means for determining a direct ratio EA indicating a ratio of an amount of exhaust gas sucked into the combustion chamber during the period t; a portion of the exhaust gas which has passed through the exhaust gas recirculation valve before the period t, other than the combustion chamber; residence to relative amount gc (t-1) are, carry-off ratio determining means for determining a carry-off ratio EB indicating the ratio of the amount of exhaust gas sucked into the combustion chamber within the period t, the
Wherein the door obtains the exhaust gas amount gin drawn into the combustion chamber during the <br/> period t from the said direct ratio EA and carry-off ratio EB, as configured for estimating the net exhaust gas recirculation rate accordingly did.

In order to achieve the fifth object, the present invention is the invention according to claim 7 , wherein the net exhaust gas recirculation rate estimating means obtains a correction coefficient based on the net exhaust gas recirculation rate, and based on the correction coefficient, calculates the combustion chamber. And a means for correcting the fuel injection amount to be supplied to the engine.

[0023]

According to the present invention, the flow 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 based on the flow 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 characteristics of the exhaust gas recirculation valve. Therefore, the net exhaust gas recirculation rate actually sucked into the combustion chamber can be accurately estimated.

According to a second aspect of the present invention, the net exhaust gas recirculation valve estimating means obtains a correction coefficient based on a net exhaust gas recirculation rate, and corrects a fuel injection amount to be supplied to the combustion chamber based on the correction coefficient. Since the configuration includes the means, the control accuracy when controlling the fuel injection is improved, and a lean spike or a rich spike does not occur.

According to a third aspect of the present invention, the flow rate characteristic is:
Since it is configured to be determined at least from the pressure ratio between the upstream and downstream of the exhaust gas recirculation valve and the opening area, the same operation and effect as in claim 1 or 2 are obtained.

According to a fourth aspect of the present invention, the pressure ratio is a ratio of the pressure of the intake passage to the atmospheric pressure or the exhaust pressure. Having.

[0027]

According to a fifth aspect of the present invention, the net exhaust gas recirculation rate estimating means includes an opening area command value and an exhaust gas amount QCM.
D is compared with a threshold value, and when it is determined that the value is equal to or less than the threshold value, the opening area command value and the exhaust gas amount QCM
D and the basic exhaust gas recirculation rate correction coefficient are held at predetermined values, so that 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 CMD becomes zero, it is held at a predetermined value.
Since the delay of the dynamic characteristics of the valve can be absorbed, and there is no inconvenience such as no calculation being impossible without occurrence of division by zero, 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 become 1 and the basic exhaust gas recirculation rate becomes 0. Here, the predetermined value is, for example, a previous value.

[0029] In the claim 6 wherein, the net exhaust gas recirculation rate estimating means, the relative amount of exhaust gas gt passing through the exhaust gas recirculation valve in a period of time t, is drawn into the combustion chamber within the period t A direct ratio determining means for determining a direct ratio EA indicating a ratio of an exhaust gas amount, the amount g of the exhaust gas which has passed through the exhaust gas recirculation valve before the period t and stays in a portion other than the combustion chamber.
to c (t-1), the period t carry-off ratio determining means for determining a carry-off ratio EB indicating the ratio of the amount of exhaust gas sucked into the combustion chamber in the, including the city, have said direct supply ratio EA determine the amount of exhaust gas gin from the left index EB drawn into the combustion chamber during the period t, Owing to this arrangement estimates the net exhaust gas recirculation rate accordingly, even when the transport delay of the recirculated gas has occurred, The net exhaust gas recirculation rate can be accurately estimated. Here, the period t is synonymous with the control cycle n mentioned in the detailed description.

According to a seventh aspect of the present invention, the net exhaust gas recirculation rate estimating means calculates a correction coefficient based on the net exhaust gas recirculation rate, and corrects a fuel injection amount to be supplied to the combustion chamber based on the correction coefficient. Since the configuration includes the means for performing the control, the control accuracy of the fuel injection control can be improved even when the transportation of the recirculated gas is delayed.

[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 device including an exhaust gas recirculation rate estimating device for an internal combustion engine according to the present invention. The internal combustion engine is, for example, a four-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 and the output is controlled by an electronic control unit
5).

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

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

The engine body 1 is provided with a water temperature sensor (indicated by TW) 9 for detecting an engine cooling water temperature TW, and a crankshaft or camshaft (both not shown) is provided with a water temperature sensor (not shown).
A crank angle sensor (indicated 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 are provided. The output of these sensors is also E
It is sent to the CU 5 and counts the output of the crank angle sensor via a counter (not shown) to detect the engine speed NE.

The exhaust pipe (exhaust passage) 13 of the engine body 1
Is provided with a catalytic converter 14 for purifying HC, CO, NOx components and the like in the exhaust gas. An oxygen concentration sensor (indicated by O ₂ ) 15 for detecting 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 (denoted by PA) 16 for detecting an atmospheric pressure PA is provided near the engine body 1, and a wall temperature sensor for detecting a wall temperature TC on a wall surface of the intake pipe 2 near the intake port. 1 (indicated by TC)
7 are 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 connecting the exhaust pipe 13 to the intake pipe 2 (reference numeral 18a).
Indicates an 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 a valve element 19a arranged to open and close the
The diaphragm 19b is connected to a and operates by a negative pressure introduced through an electromagnetic valve 22 described later, and a spring 19c for urging the diaphragm 19b in the 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
Communicates with atmosphere. Further, a solenoid valve 22 is provided in the communication passage 20.
An atmosphere communication passage 23 is connected downstream of the communication passage 23, and the atmospheric pressure is introduced into the communication passage 20 through the orifice 21 provided in the middle of the communication passage 23, and then to the negative pressure chamber 19d.

The solenoid valve 22 is connected to the ECU 5,
The exhaust gas recirculation valve 19 is activated by a drive signal from the CU 5.
The lift operation (valve opening operation) of the valve body 19a and the speed thereof 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 an 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. Prior to the description of the figure, the 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 opening area of the valve and the pressure ratio between the front and rear of the valve, that is, the flow characteristics (design specifications). That is, it is considered that the value is obtained from the opening area of the valve, that is, the ratio between the lift amount and the upstream and downstream pressures of the valve.

As shown in FIG. 3 also in the actual machine, the amount of recirculated gas is obtained by calculating the lift amount of the valve 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. Therefore, it was thought that it could be estimated to a certain extent (actually, the flow rate characteristics slightly changed depending on the exhaust pressure and exhaust temperature, but it was thought that the specific changes could be absorbed to a considerable extent by using the gas amount ratio as described later. Was). The present invention pays attention to this point, and obtains the reflux rate based on the flow characteristics. Note that the opening area is obtained from the lift amount, because a valve having a structure in which the lift amount corresponds to the opening area was used. Therefore, when using another structure such as a linear solenoid, the opening area is obtained from another parameter.

The recirculation rate includes a steady-state recirculation rate and a transient recirculation rate. Among them, the steady-state recirculation rate 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 transient time was caused by the shift 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 reflux rate = the reflux rate in the steady state

In the transient state, the lift command value ≠ the actual lift, the gas amount ratio ≠ 1.

As described above, it was considered that the net reflux rate was obtained by multiplying the ratio of the two gas amounts by the reflux rate in the steady state. The expression is as follows. Recirculation rate = (Reflux rate at steady state) × (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 recirculation rate in the steady state is obtained by obtaining a recirculation rate correction coefficient and subtracting it from 1. That is,
When the steady-state recirculation rate correction coefficient is referred to as 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. Also, the steady-state recirculation rate correction coefficient KEG
The RMAP is determined in advance by an experiment based on the engine speed NE and the intake pressure PBA, and is set as a map as shown in FIG.

The operation will be described below with reference to the flow chart of FIG. Note that the program shown in this flowchart is started every predetermined time such as 10 ms.

First, at S10, the engine speed NE and the intake pressure P
BA, atmospheric pressure PA, actual lift LACT (lift sensor 2
4) is read, and the routine proceeds to S12, where a lift command value LCMD is retrieved from the engine speed NE and the intake pressure PBA. Here, the lift command value LCMD is obtained by searching a map in which characteristics are determined and set in advance as shown in FIG. The program then proceeds to S14 in which the map shown in FIG. 4 is retrieved from the engine speed NE and the intake pressure PBA to retrieve the basic exhaust gas recirculation rate correction coefficient KEGRMAP.

Next, the routine proceeds to S16, where the detected actual lift L
ACT is not zero, that is, the exhaust gas recirculation valve 1
After confirming that the valve 9 is open, the process proceeds to S18, where the retrieved lift command value LCMD is compared with a predetermined lower limit value LCMDLL (small value). If it is determined in S18 that the search value is not lower than the lower limit, the process proceeds to S20, where the intake pressure P
The ratio PBA / PA between BA and the atmospheric pressure PA is obtained, and a map (not shown) of the characteristic shown in FIG. 3 is retrieved from the retrieved lift command value LCMD to obtain the gas amount QCM.
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, the program proceeds to S22, in which the same ratio PBA / P
Similarly, a map of the characteristics shown in FIG. 3 is retrieved from A and the detected actual lift LACT to obtain the gas amount QACT. This is equivalent to the "gas amount obtained from the pressure ratio between the actual lift and the pressure before and after the valve" in the above formula.

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

Then, the program proceeds to S28, in which a fuel injection correction coefficient KEGRN is calculated. FIG. 6 is a subroutine flowchart showing this operation. In S100, a value obtained by subtracting 1 from the net recirculation rate (determined in S26 of FIG. 2) is set as a fuel injection correction coefficient KEGRN. The correction of the fuel injection amount is performed 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 the actual lift LACT is determined to be zero in S16, since the exhaust gas recirculation is not performed, the program is immediately terminated. At S18, the lift command value LC
When the MD is determined to be equal to or less than the lower limit LCMDLL, S30
And the lift command value LCMD becomes the previous value LCMDn-1.
(For the sake of simplicity, the addition of n to the current value in this flowchart is omitted).

As described above, this is because the shift from the region in which the exhaust gas recirculation is performed to the region in which the exhaust gas recirculation is not performed,
Even if MD becomes zero, the actual lift LACT does not immediately become zero because there is a delay in the dynamic characteristics of the exhaust gas recirculation valve 19. Therefore, the lift command value LCMD is set to the lower limit value (threshold value) LCMD.
If LL or less, the lift command value LCMD is changed to the previous value LCM
Dn-1 (the value at the time of n-1 in the previous control cycle) is held. This previous value hold is performed in S16
Is performed until it is confirmed that the actual lift LACT has become zero.

The lift command value LCMD is set to the lower limit value LC.
When MDLL is less than or equal to MDLL, the lift command value LCMD may be zero. In this case, the QCMD search value in S20 also becomes zero, and the calculation in S26 is divided by zero, and the calculation becomes impossible.
However, by holding the previous value as described above,
There is no danger that the calculation will not be possible. Although the lower limit LCMDLL is a minute value, it may be zero.

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

As described above, this embodiment focuses on the flow characteristics of the exhaust gas recirculation valve, and estimates the net recirculation rate by focusing on the fact that the difference between the transient recirculation rate and the steady-state recirculation rate is the gas amount ratio. Therefore, Japanese Patent Application Laid-Open No. 5-118823 proposed above
Although the configuration is simpler than that of the technique of No. 9, the behavior of the exhaust gas can be accurately grasped. In addition, the method of Japanese Patent Application No. 5-296049 proposed separately, that is, Compared with, the net recirculation rate can be more accurately determined by expressing the behavior of the exhaust gas from the flow characteristics of the exhaust recirculation valve.

Further, since the gas amount ratio is used, the effects of the exhaust gas temperature and the 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 that 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.

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 recirculated gas. , The air-fuel ratio can be accurately controlled to the target value, and the occurrence of a lean spike or a rich spike can be prevented.

FIG. 7 is a flow chart showing a second embodiment of the present invention.
This method partially uses the method of correcting the recirculation gas transport delay proposed in the method of No. That is, in the previous embodiment, the opening end 1 of the exhaust gas recirculation passage 18 on the intake pipe 2 side in FIG.
It is assumed that the distance between the combustion chamber 8a and the combustion chamber is relatively short and the transport delay of the recirculated gas is negligible. In the second embodiment, the transport delay is considered. 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 determined in S200 from the engine speed and the engine load by the net recirculation rate (determined in S26 in FIG. 2). (Apparently the amount of recirculated 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 start cycle of the program of the flow chart of FIG. 2 (the same as the time t described in claim 7). Subsequently, the process proceeds to S202, in which the true recirculated gas amount gin (n) sucked into the combustion chamber in the control cycle n is estimated as shown in the figure.

Here, gt has been described above, but the others are described in EA. . . EB. Direct rate (a value indicating the proportion of the recirculated gas gt passed through the exhaust gas recirculation valve 19 in a certain control cycle n and taken into the combustion chamber during the control cycle n), EB. . . The carry-out rate (of the recirculated gas amount gc (n−1) that has passed through the exhaust gas recirculation valve 19 before the previous control cycle n─1 and stays between the exhaust gas recirculation valve 19 and the combustion chamber, n is a value indicating the ratio of gas sucked into the combustion chamber).

That is, the required amount of recirculated gas gt is multiplied by the direct ratio EA to determine the amount of gas sucked into the combustion chamber through the exhaust gas recirculation valve 19 during the control cycle n. By multiplying by EB, the amount of gas which has stayed from n-1 before and has been sucked into the combustion chamber during the control cycle n is obtained, and the sum of the two is estimated to be true which is assumed to have been sucked into the combustion chamber during the control cycle n. Of the recirculated gas gin (n) is determined.

Then, the program proceeds to S204, in which the true reflux gas amount g
A fuel injection correction coefficient KEGRN is determined by subtracting a value obtained by dividing in (n) by the basic fuel injection amount Tim from 1. Subsequently, the process proceeds to S206, where the amount of staying gas gc (n) is updated for the calculation at the time of starting the next program. At the time of the next program startup, gc (n) obtained in S206 is replaced by S20.
2 is replaced with gc (n-1), where the true required gas amount gin (n) is calculated. The details of the transport delay compensation are described in the above-mentioned Japanese Patent Application Laid-Open No. 5-118239, page 5 and thereafter, and 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 recirculated gas is difficult to ignore.

In the second embodiment, the transport delay is estimated from the method used in the earlier application, but the transport delay may be simply simplified as the primary delay.

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

FIG. 8 shows a third embodiment of the present invention.
5 is a partial flow chart. In the case of the third embodiment, S
At S16, it is confirmed that the actual lift LACT is not zero.
The program proceeds to S60, in which the lift command value QCMD is searched, and the program proceeds to S162, where the lift command value QCMD is compared with a predetermined value (threshold value) QCMDLL (small value). If 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 remaining configuration is the same as that of the first embodiment, and the effect is not different.

In the first, second, and third embodiments, the atmospheric pressure is used in S12, S20, S22, and the like in 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 a negative pressure type, but may be of an electric type.

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

[0075]

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

According to the second aspect, the control accuracy when controlling the air-fuel ratio is improved, and a lean spike or a rich spike does not occur.

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

The fourth aspect has the same function and effect as the second and third aspects.

[0079]

According to the fifth aspect , it is possible to absorb the delay of the dynamic characteristics of the exhaust gas recirculation valve, and to prevent the inconvenience that the calculation becomes impossible.

[0081] In the sixth aspect, wherein, even when the transport delay of the recirculated gas is generated, it is possible to accurately estimate the net exhaust gas recirculation rate.

[0082] In the seventh aspect, wherein, even when the transport delay of the recirculated gas is generated, it is possible to improve the control accuracy of the air-fuel ratio.

[Brief description of the drawings]

FIG. 1 is an overall block diagram showing an exhaust gas recirculation rate estimating apparatus for an internal combustion engine according to the present invention.

FIG. 2 is a flowchart showing an operation of the exhaust gas recirculation rate estimating apparatus for an internal combustion engine of FIG. 1;

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

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

FIG. 5 is an explanatory diagram showing map characteristics of a lift command value used for calculation of the flow chart of FIG. 2;

FIG. 6 is a subroutine flowchart showing a calculation operation of a fuel injection correction coefficient in the flowchart of FIG. 2;

FIG. 7 is a flow chart showing a second embodiment of the present invention, and is a subroutine flow chart showing a calculation operation of a fuel injection correction coefficient of the flow chart of FIG. 2;

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 an 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 recirculation passage 19 Exhaust recirculation valve 25 Exhaust recirculation mechanism

Continuation of the front page (56) References JP-A-64-63647 (JP, A) JP-A-59-74364 (JP, A) JP-A-5-118246 (JP, A) JP-A-6-101575 (JP) JP-A-7-127497 (JP, A) JP-A-63-227947 (JP, A) JP-A 1-216065 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) F02M 25/07 550 F02M 25/07 570 F02D 41/02 301

Claims (7)

(57) [Claims] And 1. A exhaust gas recirculation passage for recirculating at least a portion of connecting the exhaust passage and an intake passage of an internal combustion engine exhaust gas into the intake passage, and an exhaust gas recirculation valve for opening and closing the exhaust gas recirculation passage Apparatus for estimating the exhaust gas recirculation rate of an internal combustion engine, comprising: a. Basic exhaust gas recirculation rate determining means for determining a basic exhaust gas recirculation rate from at least the engine speed and the engine load; b. First estimating means for estimating an exhaust gas amount QACT passing through the exhaust gas recirculation valve according to an opening area of the exhaust gas recirculation valve based on a flow characteristic of the exhaust gas recirculation valve; c. Second estimating means for estimating an exhaust gas amount QCMD passing through the exhaust gas recirculation valve in accordance with the opening area command value of the exhaust gas recirculation valve based on the flow characteristics, and d. A net exhaust gas recirculation rate estimating means for estimating a net exhaust gas recirculation rate actually sucked into the combustion chamber according to the exhaust gas amounts QACT and QCMD ;
Exhaust gas amount QACT, QCMD ratio QACT / QCMD
And calculating the net exhaust gas recirculation rate to calculate the exhaust gas recirculation rate of the internal combustion engine. 2. The method according to claim 1, wherein 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. The exhaust gas recirculation rate estimating device for an internal combustion engine according to claim 1, wherein 3. The exhaust gas recirculation rate estimation of an internal combustion engine according to claim 1, wherein the flow characteristic is determined at least from a pressure ratio between an upstream and a downstream of the exhaust gas recirculation valve and an opening area. apparatus. 4. An exhaust gas recirculation rate estimating apparatus for an internal combustion engine according to claim 3, wherein said pressure ratio is a ratio of a pressure of said intake passage to an atmospheric pressure or an exhaust pressure. 5. 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. The exhaust gas recirculation rate estimating device for an internal combustion engine according to any one of claims 1 to 4 , wherein at least one of the quantity QCMD and the basic exhaust gas recirculation rate correction coefficient are held at predetermined values. 6. The net exhaust gas recirculation rate estimating means includes: e. To a period of time t in the exhaust gas recirculation valve exhaust gas amount gt passing through the direct ratio determining means for determining a direct supply ratio EA indicating the ratio of the amount of exhaust gas sucked into the combustion chamber within 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
To -1), carry-off ratio determining means for determining a carry-off ratio EB indicating the ratio of the amount of exhaust gas sucked into the combustion chamber within the period t, include city, the direct ratio EA and carry-off ratio EB the <br/> determine the exhaust gas amount gin drawn into the combustion chamber during t, claim 1, wherein the 5 wherein, characterized in that estimating the net exhaust gas recirculation rate accordingly from the An exhaust gas recirculation rate estimating device for an internal combustion engine according to claim 1. 7. The net exhaust gas recirculation rate estimating means includes a 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 estimating device for an internal combustion engine according to claim 6, wherein