JPH11173218A - Egr rate estimation device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the deviation of the EGR rate due to the change in atmospheric pressure without measuring the atmospheric pressure to exactly estimate the actual EGR rate whatever the environment is changed. SOLUTION: The valve lift amount LFT of an EGR valve is retrieved from the map by means of the engine speed NE and the throttle-opening THR, and when LFT≠O, the basic EGR rate STEGR is retrieved from the map by means of the throttle-opening THR and the valve lift amount LFT. Next, the exhaust pressure correction factor KEGRH is retrieved from the map by means of the engine speed NE and the intake pipe pressure PM, and the EGR rate EGRCAL is calculated by multiplying the basic EGR rate by the exhaust pressure correction factor KEGRH (EGRCAL=STEGR × KEGRH). Thus, the deviation of the EGR rate due to the change in atmospheric pressure can be corrected without measuring the atmospheric pressure, and the actual EGR rate can be exactly estimated whatever the environment is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine EGR rate estimating apparatus for estimating an EGR rate when a part of exhaust gas is recirculated to an intake side.

[0002]

2. Description of the Related Art As is well known, in the combustion process of an engine, when the amount of inactive components in the air-fuel mixture is increased, the combustion temperature is decreased due to an increase in the amount of gas per unit heat value, and the generation of NOx in exhaust gas is increased. Is reduced. For this reason, an exhaust gas recirculation (EGR) for recirculating a part of the exhaust gas to the intake side has conventionally been widely used.
It is possible to reduce NOx in the exhaust gas and reduce fuel consumption.

[0003] In this case, a so-called speed density is obtained by estimating an intake air amount per cycle based on an intake pipe pressure and an engine speed and determining a basic fuel injection amount corresponding to the intake air amount per cycle. In the engine adopting the (D JETRONIC) system, an error occurs in the intake air amount estimated from the intake pipe pressure when EGR is performed,
There is a possibility that the fuel injection amount becomes inappropriate and an air-fuel ratio deviation occurs.

Therefore, when performing EGR, an accurate EGR
It is necessary to correct the fuel injection amount by obtaining the rate, for example,
Japanese Patent Application Laid-Open No. 2-308960 discloses that an EG defined at a standard atmospheric pressure by an intake pipe pressure and an engine rotation speed.
The R rate is mapped, and the map is searched based on the corrected intake pipe pressure corrected by the atmospheric pressure and the engine speed, and the obtained EGR rate is multiplied by a correction coefficient calculated based on the atmospheric pressure. There is disclosed a technique for obtaining a corrected EGR rate.

In Japanese Patent Application Laid-Open No. 7-279774, the steady-state EGR rate is obtained from a map created by experiments in advance, and the steady-state EGR rate is calculated by calculating the actual lift of the exhaust gas recirculation valve and the pressure before and after the valve. Estimate the net EGR rate by correcting by the ratio, ie, the gas amount obtained from the ratio between the intake pressure and the atmospheric pressure) / (the lift ratio and the pressure ratio before and after the valve, ie, the gas amount obtained from the ratio between the intake pressure and the atmospheric pressure). A technique for performing this is disclosed.

[0006]

As disclosed in the above prior art, conventionally, when calculating the EGR rate,
In order to compensate for changes in atmospheric pressure, the atmospheric pressure must be detected, and direct measurement by a dedicated sensor for detecting the atmospheric pressure, or a sensor that detects the intake pipe pressure is also used. It was necessary to take measures such as measuring the atmospheric pressure according to the conditions.

In this case, as disclosed in Japanese Patent Application Laid-Open No. 2-308960, a pressure sensor attached to an intake pipe downstream of the throttle valve is used. In the technology in which the output value of the pressure sensor is set to the atmospheric pressure, in an operation state in which the throttle depression amount is small, such as when descending a long downhill, the EGR rate correction may not be calculated because the atmospheric pressure cannot be measured,
On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 7-279774, the technique using a dedicated sensor for detecting the atmospheric pressure has a problem that the cost is increased.

The present invention has been made in view of the above circumstances, and it is possible to correct a deviation of the EGR rate due to a change in the atmospheric pressure without measuring the atmospheric pressure. It is an object of the present invention to provide an EGR rate estimating device for an engine capable of accurately estimating an EGR rate.

[0009]

According to a first aspect of the present invention, a part of exhaust gas is controlled by controlling an opening of an EGR valve interposed in a passage connecting an exhaust pipe of an engine and an intake pipe downstream of a throttle valve. An EGR rate estimating device for an engine for estimating an EGR rate when recirculating air to an intake side, wherein an exhaust pipe pressure is equal to an atmospheric pressure based on the opening degree of the throttle valve and the opening degree of the EGR valve. Means for setting the EGR rate when it is deemed to exist as a basic EGR rate, and setting a correction coefficient for correcting the basic EGR rate in accordance with a change in the exhaust pipe pressure based on the engine speed and the intake pipe pressure. Means for correcting the basic EGR rate with the correction coefficient,
Means for estimating the actual EGR rate for each operating region.

According to a second aspect of the present invention, in the first aspect, the opening degree of the EGR valve is defined as a valve lift amount of the EGR valve, and the valve lift amount is defined as an engine speed and an opening degree of the throttle valve. And is obtained based on the following.

According to a third aspect of the present invention, in the first or second aspect, the basic EGR rate is set by a map created by approximating an EGR rate characteristic in a low load operation region. And

That is, the EGR of the engine according to the present invention
In the rate estimating device, an EGR rate when the exhaust pipe pressure is considered to be equal to the atmospheric pressure is set as a basic EGR rate based on the opening degree of the throttle valve and the opening degree of the EGR valve. Is corrected in accordance with a change in the exhaust pipe pressure using a correction coefficient set based on the engine speed and the intake pipe pressure, and the actual EGR rate for each operating region is estimated.

In this case, the opening of the EGR valve can be determined based on the engine speed and the opening of the throttle valve as the valve lift of the EGR valve. In addition, as described in claim 3, the basic EGR rate is the EGR rate in the low load operation region.
It is desirable to set by a map created by approximating the rate characteristics.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 relate to an embodiment of the present invention, FIG. 1 is a flowchart of an EGR rate estimation / fuel correction coefficient setting routine, FIG. 2 is a main part configuration diagram of an engine control system, and FIG. 3 is an EGR valve lift instruction. FIG. 4 is an explanatory diagram of a basic EGR rate map, and FIG. 5 is an explanatory diagram of an exhaust pressure correction coefficient map.

In FIG. 2, reference numeral 1 denotes an engine,
A surge tank 3 is provided in the middle of an intake passage 2 communicating with an intake port of the engine 1, and a throttle valve 4 is provided upstream of the surge tank 3. Immediately before the intake port of the intake passage 2, an injector 5 for injecting fuel into the intake port is interposed, and an absolute pressure sensor 6 for measuring an intake pipe pressure is installed in the surge tank 3. . Further, a throttle opening sensor 7 for detecting the throttle opening is connected to the throttle valve 4.

On the other hand, an O2 sensor 9 for detecting the oxygen concentration in the exhaust gas is provided in the middle of the exhaust passage 8 communicating with the exhaust port of the engine 1. A catalytic converter 10 is provided downstream of the O2 sensor 9. Is interposed. The exhaust passage 8 is communicated with the surge tank 3 via an EGR passage 11.
Part of the exhaust gas is recirculated to the intake system according to the valve opening of the EGR valve 12 interposed midway 1, and a mixed gas of fresh air, exhaust gas and fuel is sucked into the combustion chamber of the engine 1. It is rekindled. In this embodiment, the EGR valve 12
Is a type in which the valve opening is determined by the valve lift amount.

The engine 1 having the above configuration is an electronic control unit (ECU) 2 comprising a microcomputer or the like.
Electronically controlled by 0. The ECU 20 includes the absolute pressure sensor 6, the throttle opening sensor 7, the O
2 Sensor 9 and other water temperature sensor 1 for measuring cooling water temperature
3. Various sensors such as a crank angle sensor 14 for detecting a crank angle are connected, and various actuators such as the injector 5 and the EGR valve 12 are connected.

The ECU 20 calculates various control amounts such as a fuel injection amount and an ignition timing by using parameters representing an engine operating state by various sensors, and controls the air-fuel ratio of the engine 1 to always maintain an appropriate air-fuel ratio. However, the engine 1 employs a speed density (D JETRONIC) system, and determines the basic fuel injection amount based on the intake pipe pressure downstream of the throttle valve 4 detected by the absolute pressure sensor 6 and the engine speed. Since EGR is performed, it is necessary to correct the fuel injection amount during EGR to prevent the air-fuel ratio from shifting.

Therefore, the ECU 20 estimates the EGR rate EGRCAL and sets the EGR rate EGRCAL to 1
Is set as a fuel correction coefficient FEGR,
By adding it as a correction term when determining the fuel injection amount injected from the injector 5, an appropriate air-fuel ratio is maintained even during EGR.

That is, the final fuel injection pulse width Ti that determines the fuel injection amount injected from the injector 5
Is the basic fuel injection pulse width Tp that determines the basic fuel injection amount.
Is calculated by various correction terms COE set based on the cooling water temperature detected by the water temperature sensor 13 as shown in the following equation (1).
F, an air-fuel ratio feedback correction coefficient RAMBDA set based on the air-fuel ratio detected by the O2 sensor 9;
It is determined by correcting with the fuel correction coefficient FEGR and the voltage correction coefficient TS for interpolating the invalid injection time of the injector 5 set based on the battery voltage.

Ti = Tp × COEF × FEGR × RAMBDA + TS (1) where FEGR = 1−EGRCAL, and when EGR is not performed, EGRCAL = 0, that is, FEGR
= 1, there is no fuel correction.

Here, the EGR rate EGRCAL is defined as a ratio of the EGR gas amount QEGR to the total gas amount in the intake pipe obtained by adding the intake air amount Q and the EGR gas amount QEGR, and is expressed by the following equation (2). Can be transformed into

EGRCAL = QEGR / (QEGR + Q) = 1 / (1 + Q / QEGR) (2) The intake air amount Q is determined by the opening area of the throttle valve 4 and the pressure difference between upstream and downstream of the throttle valve 4.
The opening area of the throttle valve 4 is the throttle opening TH
Since it can be expressed by the function F1 (THR) of R, the intake air amount Q
Is, as shown in the following equation (3), the throttle opening THR
F1 (THR) and the differential pressure Δ upstream and downstream of the throttle valve 4
It can be expressed by the function G1 (ΔPA) of PA.

Q = F1 (THR) × G1 (ΔPA) (3) Similarly, the EGR gas amount QEGR is determined by the opening area of the EGR valve 12 and the pressure difference between the upstream and downstream of the EGR valve 12. The opening area is a function F of a valve lift LFT representing the valve opening of the EGR valve 12.
2 (LFT), the EGR gas amount QEGR is
As shown in the following equation (4), it can be expressed by a function F2 (LFT) of the valve lift amount LFT of the EGR valve 12 and a function G2 (ΔPE) of the differential pressure ΔPE upstream and downstream of the EGR valve 12. For example, when an EGR valve of a type that opens and closes with a rotary solenoid or the like is used,
The aperture area is represented by a function such as a rotation angle.

QEGR = F2 (LFT) × G2 (ΔPE) (4) The functions G1 (ΔPA) and G2 (ΔPE) of the differential pressure in the above equations (3) and (4)
PE), the differential pressure ΔPA upstream and downstream of the throttle valve 4 is the differential pressure between the atmospheric pressure and the intake pipe pressure.
The differential pressure ΔPE upstream and downstream of the GR valve 12 is a differential pressure between the exhaust pipe pressure and the intake pipe pressure. Therefore, when the exhaust pipe pressure can be considered to be equivalent to the atmospheric pressure, that is, when the exhaust pipe pressure is in a low load operation region very close to the atmospheric pressure, the function G1 (ΔPA) of the differential pressure in the throttle valve 4 and the EGR valve 12 can be considered to be the same as the differential pressure function G2 (ΔPE), and Q / QEGR in the above equation (2)
Is given by the function F1 (THR) of the throttle opening THR and EG
Function F2 (LFT) of valve lift LFT of R valve 12
The EGR rate EGRCAL is replaced by the following (5)
It can be expressed as an expression.

EGRCAL = 1 / (1 + F1 (THR) / F2 (LFT)) (5) According to the above equation (5), in the low load operation region, the throttle opening THR and the EGR valve 12 determined for each operation region. Using two parameters, the valve lift amount LFT and EFT,
The GR rate can be estimated, and the EGR rate estimated using these two parameters is used as the basic EG for the entire operation range.
The R rate is STEGR.

On the other hand, when the exhaust pipe pressure is not equal to the atmospheric pressure, the EGR rate cannot be estimated from only the above two parameters. The exhaust pipe pressure is a pressure generated by the amount of exhaust gas exhausted from the engine. The exhaust pipe pressure increases as the load becomes higher, and the exhaust pipe pressure increases even when the atmospheric pressure changes at a high altitude. Changes.

Since the amount of exhaust gas changes in the operating range and can be expressed as a function of the engine speed NE and the intake pipe pressure PM, the basic EGR rate STEGR is used as a parameter for the engine speed NE and the intake pipe pressure PM. Thus, the EGR rate can be estimated in another operation region of the low-load operation region without measuring the atmospheric pressure.

That is, the EGR rate EGRCAL can be finally obtained by the following equation (6) using the correction amount for the basic EGR rate STEGR as the exhaust pressure correction coefficient KEGRH. Also,
It is possible to accurately estimate the ratio between the amount of exhaust gas that would have been actually sucked and the amount of fresh air intake air.

EGRCAL = STEGR × KEGRH (6) Hereinafter, the processing relating to the EGR rate estimation by the ECU 20 will be described with reference to the flowchart of FIG.

FIG. 1 is a diagram showing the relationship between the predetermined time (for example, 10 ms)
The routine is an EGR rate estimation / fuel correction coefficient setting routine that is interrupted and executed every time.
In step S101, the engine speed NE based on the signal from the crank angle sensor 14, the throttle opening THR based on the signal from the throttle opening sensor 7, and the intake pipe pressure PM based on the signal from the absolute pressure sensor 6 are read, and in step S102. ,
The EGR valve lift instruction value map MLFT is referred to using the engine speed NE and the throttle opening THR as parameters, and the valve lift amount LFT of the EGR valve 12 in the current operation region is searched.

The EGR valve lift instruction value map ML
The FT is created in advance by calculating the valve lift amount that provides the optimal EGR gas amount in each operation region in consideration of the EGR limit and the like in the actual machine, and as shown in FIG. A valve lift amount LFT as an EGR valve opening instruction value is stored for each operating region determined by the NE and the throttle opening THR.
As shown in FIG.
The characteristic is such that the valve lift is increased and the EGR amount is increased in a normal range where the throttle opening is at a medium opening at 00 rpm.

Next, the process proceeds to step S103, where
It is determined whether or not the current operation region is the EGR execution region by checking whether or not the valve lift amount LFT searched in S102 is 0, that is, whether or not the EGR valve opening instruction value is fully closed. Then, when LFT = 0 and the EGR valve opening degree instruction value is fully closed and the EGR valve is not in the EGR execution region, the process exits the routine. When LFT ≠ 0, the process proceeds to step S104.

In step S104, the throttle opening THR
FIG.
A basic EGR rate STEGR is searched with reference to a basic EGR rate map MSTEGR as shown in FIG. The basic EGR rate map MSTEGR is obtained from an approximate expression of the EGR rate using the throttle opening THR and the valve lift amount LFT as parameters from the EGR rate characteristic in the low load operation region obtained by the actual machine, and the EGR obtained by the approximate expression. Figure 4
FIG. 4 is a map stored as a basic EGR rate STEGR having a characteristic as shown in FIG. 4B, and is a map of the EGR rate for the entire operation region on the premise that the exhaust pipe pressure of the engine is equal to the atmospheric pressure.

In the following step S105, the engine speed N
FIG. 5 (a) using E and the intake pipe pressure PM as parameters.
The exhaust pressure correction coefficient KEGRH is searched with reference to the exhaust pressure correction coefficient map MKEGRH as shown in FIG. The exhaust pressure correction coefficient map MKEGRH is a basic EGR rate STEGR for each operating region determined by the engine speed NE and the intake pipe pressure PM.
And a map in which the ratio is stored as a coefficient. Although the actual EGR characteristics vary depending on the engine, the higher the load and the higher the speed, the higher the exhaust pipe pressure and, as a result, the less EGR is applied.
As shown in FIG. 5B, the higher the load and the higher the rotation,
The characteristic is such that the EGR rate is corrected so as to decrease.

Thereafter, the process proceeds to step S106, where the basic EGR
When the EGR rate EGRCAL is calculated by multiplying the rate STEGR by the exhaust pressure correction coefficient KEGRH (EGRCAL = S
(TEGR × KEGRH), and at step S107, a fuel correction coefficient FEGR for correcting a deviation of the fuel injection amount due to the EGR is set (FEGR = 1−EGRCAL),
Exit the routine.

The fuel correction coefficient FEGR is referred to when setting the fuel injection amount, and the final fuel injection pulse width Ti is calculated according to the above-mentioned equation (1). Thereby, EGR
It is possible to prevent a deviation of the air-fuel ratio at the time of implementation, and to always maintain an appropriate air-fuel ratio.

[0038]

As described above, according to the present invention, the EGR rate when the exhaust pipe pressure is considered to be equal to the atmospheric pressure is determined based on the throttle valve opening and the EGR valve opening. Set as the basic EGR rate, this basic EGR
The rate is corrected according to the change in the exhaust pipe pressure using a correction coefficient set based on the engine speed and the intake pipe pressure,
Since the actual EGR rate for each operating region is estimated, the deviation of the EGR rate due to a change in the atmospheric pressure can be corrected without measuring the atmospheric pressure, and the actual EGR rate can be accurately determined for any environmental change. Can be estimated. As a result, an excellent effect can be obtained such that the deviation of the air-fuel ratio at the time of performing the EGR can be prevented and the deterioration of the exhaust gas and the fuel efficiency can be prevented.

[Brief description of the drawings]

FIG. 1 is a flowchart of an EGR rate estimation / fuel correction coefficient setting routine.

FIG. 2 is a configuration diagram of a main part of an engine control system.

FIG. 3 is an explanatory diagram of an EGR valve lift instruction value map;

FIG. 4 is an explanatory diagram of a basic EGR rate map.

FIG. 5 is an explanatory diagram of an exhaust pressure correction coefficient map.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 4 ... Throttle valve 12 ... EGR valve 20 ... ECU THR ... Throttle opening LFT ... Valve lift NE ... Engine rotation speed PM ... Intake pipe pressure STEGR ... Basic EGR rate KEGRH ... Exhaust pressure correction coefficient EGRCAL ... EGR rate

Claims (3)

[Claims] An EGR valve for controlling a degree of opening of an EGR valve interposed in a passage connecting an exhaust pipe of an engine and an intake pipe downstream of a throttle valve to reduce an EGR rate when a part of exhaust gas is recirculated to an intake side. An EGR rate estimating device for an engine for estimating, based on the opening degree of the throttle valve and the opening degree of the EGR valve, an EGR rate when the exhaust pipe pressure is considered to be equal to the atmospheric pressure. Based on the engine speed and the intake pipe pressure.
Means for setting a correction coefficient for correcting the GR rate in accordance with a change in the exhaust pipe pressure, and means for correcting the basic EGR rate with the correction coefficient and estimating an actual EGR rate for each operating region. An EGR rate estimating device for an engine. 2. The method according to claim 1, wherein the opening of the EGR valve is defined as a valve lift of the EGR valve, and the valve lift is obtained based on an engine speed and an opening of the throttle valve. Engine EG
R rate estimation device. 3. The engine EGR rate estimating device according to claim 1, wherein the basic EGR rate is set by a map created by approximating the EGR rate characteristic in a low load operation region.