JP2004092479A - Controller of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the accelerating ability and improve the exhaust gas characteristic on acceleration. <P>SOLUTION: An ECU 8 predicts the concentration of exhaust O<SB>2</SB>at a cylinder position, and controls the opening of an EGR valve 7 corresponding to the difference between a predicted value and a concentration of the desired exhaust O<SB>2</SB>. In this case, the response of the EGR valve 7 can be quickly followed without delay for the sharp fluctuation in the exhaust pressure. Therefore, compared with a conventional EGR control (ex. a method for carrying out F/B control of a valve opening corresponding to the difference between the detected valve and a desired value of an air flow meter 9), the EGR valve 7 quickly responses so that the F/B gain of a VNT 2 can be large without increasing an EGR amount owing to the increase of the exhaust pressure to realize the high response of the VNT 2. Therefore, the accelerating ability is improved and smoke is reduced to improve the exhaust gas characteristic. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for an internal combustion engine that controls both a supercharging pressure and an EGR amount.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an engine having a variable-capacity supercharger (referred to as a VNT) that performs EGR for returning a part of exhaust gas to an intake system is known.
VNT changes the supercharging pressure in accordance with the vane opening (throttle amount). For example, the VNT changes the vane opening so that the actual supercharging pressure detected by the supercharging pressure sensor converges to the target supercharging pressure. One that performs feedback (F / B) control is known.
The EGR has an EGR valve that adjusts an opening ratio of the EGR passage. For example, the opening degree of the EGR valve is set to F / B so that an actual intake air amount measured by an air flow meter converges to a target intake air amount. What controls is known.
[0003]
[Problems to be solved by the invention]
By the way, during acceleration, there is a demand to improve the feeling of acceleration by accelerating the introduction of fresh air flowing into the cylinder. On the other hand, it is conceivable to increase the F / B gain of the VNT to speed up the response.
However, if the response of the VNT is increased during the F / B control of the EGR valve in order to obtain a feeling of acceleration, as shown in FIG. 10A, when the F / B gain of the VNT is small and the response is slow, or when the VNT is opened. As compared with the case where the control is performed (indicated by a thin solid line in the figure), the EGR amount increases with an increase in the exhaust pressure, so that the acceleration performance deteriorates and the amount of generated smoke increases. .
[0004]
This is because there is a distance between the position of the air flow meter and the cylinder position, and the effect of the increase or decrease of the EGR amount due to the exhaust pressure fluctuation is not instantaneously reflected in the detection result of the air flow meter. As a result, even if the response of the VNT is made faster, the smoke is increased because the EGR valve cannot quickly follow the rise in the exhaust pressure.
The present invention has been made on the basis of the above circumstances, and an object of the present invention is to provide a control device for an internal combustion engine capable of improving acceleration performance and improving exhaust gas characteristics during acceleration.
[0005]
[Means for Solving the Problems]
(Invention of claim 1)
The present invention provides a variable-capacity supercharger that varies a supercharging pressure according to a vane opening and an EGR device that varies an exhaust gas amount (EGR amount) recirculated to an intake system according to a valve opening. A control device for controlling a vane opening of a supercharger and a valve opening of an EGR device with respect to an internal combustion engine provided,
EGR control means for feedback-controlling the valve opening of the EGR device in accordance with the deviation between the intake state predicted at the cylinder position and the target value, the actual supercharging pressure (detected value of the intake pressure sensor) and the target supercharging A supercharger control means for feedback-controlling the vane opening of the supercharger in accordance with a deviation from the pressure or a deviation between a parameter correlated with the supercharging pressure and a target value thereof.
[0006]
According to the above configuration, when the response of the supercharger is made faster, the exhaust pressure rises sharply, the EGR amount increases, and the amount of fresh air flowing into the cylinder decreases. It is possible to predict the intake state (for example, fresh air amount) at the cylinder position before the result is reflected on the measurement result. Therefore, by performing feedback control of the valve opening of the EGR device in accordance with the deviation between the predicted intake state and the target value, the EGR valve can quickly follow a rapid change in exhaust pressure.
[0007]
(Invention of claim 2)
The control device for an internal combustion engine according to claim 1,
The parameter that correlates to the boost pressure, intake air amount measured by the air quantity measuring means, or A / F which correlates to the amount of intake air, the intake O ₂ concentration, the exhaust O ₂ concentration, EGR rate, EGR quantity Or the intake state at the cylinder position predicted by the intake state predicting means.
The feedback control of the supercharger is generally performed based on the supercharging pressure. However, the feedback control is not limited to the supercharging pressure, and the feedback control may be performed based on the above-described parameter correlated with the supercharging pressure. It should be noted that the A / F and the exhaust O ₂ concentration can use the detection value of the O ₂ sensor attached to the exhaust passage (may be calculated).
[0008]
(Invention of claim 3)
The control device for an internal combustion engine according to claim 1 or 2,
The intake state is characterized by a fresh air amount flowing into the cylinder, or one of A / F, intake O ₂ concentration, exhaust O ₂ concentration, EGR rate, and EGR amount correlated to the new air amount. [0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a configuration diagram schematically showing an air system of the internal combustion engine.
The internal combustion engine (referred to as engine 1) of the present embodiment includes a variable-capacity supercharger (referred to as VNT2) and an EGR device (described below).
As shown in FIG. 2, an injector 3 is attached to a cylinder head of the engine 1, and high-pressure fuel stored in a common rail (not shown) is injected from the injector 3 into the combustion chamber 1a.
[0010]
The VNT 2 includes an exhaust turbine 2A provided in an exhaust passage 4 of the engine 1 and a compressor 2B provided in an intake passage 5, and varies a supercharging pressure according to a vane opening (throttle amount).
The EGR device is a device for returning a part of the exhaust gas (EGR gas) from the exhaust passage 4 to the intake passage 5, and includes an EGR passage 6 that communicates the exhaust passage 4 with the intake passage 5. An EGR valve 7 that adjusts an opening ratio, and varies the amount of exhaust gas (EGR amount) that recirculates from the exhaust passage 4 to the intake passage 5 according to the degree of opening of the EGR valve 7.
[0011]
The EGR passage 6 is connected to the exhaust passage 4 upstream of the exhaust turbine 2A, and is connected to the intake passage 5 downstream of the compressor 2B.
The EGR valve 7 is, for example, a linear electromagnetic valve having a built-in solenoid, and adjusts the opening ratio of the EGR passage 6 by lifting according to a valve lift command value output from the ECU 8 (see FIG. 1). The EGR valve 7 is provided with a lift sensor for detecting a valve lift (EGR operation amount), converts the detected valve lift into an electric signal, and outputs the signal to the ECU 8 (see FIG. 1).
[0012]
In the intake passage 5, an air cleaner (not shown) for filtering intake air is provided at the most upstream portion, and an air flow meter 9 for measuring the amount of intake air is provided upstream of the compressor 2B. An intake throttle 10 is provided downstream of the compressor 2B. An intake pressure sensor 11 for detecting the intake pressure in the intake passage 5 and an intake air temperature for detecting the temperature of the intake air are provided downstream of the intake throttle 10. A sensor 12 is attached. In this embodiment, the upstream side of the intake throttle 10 in the intake passage 5 is called an intake pipe 5a, and the downstream side of the intake throttle 10 is called a manifold 5b.
An O ₂ sensor 13 that detects exhaust O ₂ concentration is attached to the exhaust passage 4 downstream of the exhaust turbine 2A.
[0013]
Each information detected by the air flow meter 9, the intake pressure sensor 11, intake air temperature sensor 12, and the _{O 2} sensor 13 is output to the respective ECU 8.
ECU8 is an electronic control unit constituted of a microcomputer mainly, as shown in FIG. 1, a computing circuit 8a (in the present embodiment the exhaust O ₂ concentration) intake condition at cylinder position predicting calculates, VNT2 A VNT control circuit 8b for controlling the vane opening of the EGR device and an EGR control circuit 8c for controlling the valve opening of the EGR device (the opening of the EGR valve 7).
[0014]
Next, the control contents of this embodiment will be described.
FIG. 3 is a flowchart showing the processing procedure of the ECU 8.
First, the EGR valve 7 is controlled in Steps 100 to 400.
Step 100 ... predicted calculates the exhaust _{O 2} concentration in the cylinder position (will be described later calculation method).
Step200 ... read the target exhaust _{O 2} concentration. The target exhaust O ₂ concentration is stored in advance in the map 8d (see Fig. 1) in accordance with the operating condition of the engine 1 (e.g., the rotation speed Ne injection amount Q).
[0015]
And exhaust _{O 2} concentration in the cylinder position calculated in Step300 ... Step100, calculated F / B amount (feedback amount) in accordance with a deviation between the target exhaust _{O 2} concentration read in Step 200.
Step 400... The F / B amount calculated in Step 300 is added to the base opening previously stored in the map to determine the valve opening. The base opening is determined in accordance with the operating conditions of the engine 1 (for example, the rotation speed Ne and the injection amount Q).
[0016]
Here, the processing content of Step 100 will be described in detail.
FIG. 4 is a subroutine showing the processing procedure of Step 100.
Step 110: Calculate the amount of gas Mcld flowing into the cylinder.
Step 120: Calculate the fresh air amount MDth flowing into the manifold 5b.
Step 130: Calculate the EGR gas amount MEGR flowing into the manifold 5b.
STEP140 ... _{O 2} amount _{O 2} in the gas flowing into the cylinder  Calculate cld.
Step150 ... predicted exhaust _{O 2} concentration Cex at cylinder position 　 Calculate mdl.
[0017]
Next, the processing contents of Steps 110 to 150 will be described in detail.
FIG. 5 is a subroutine showing the processing procedure of Step 110.
Step 111: The intake pressure Pm is read.
Step 112: Read the intake air temperature Tm.
Step 113: The number of rotations Ne is read.
Step 114: The volume efficiency η is calculated as a function of Ne and Pm.
Step 115: The amount of gas Mcld flowing into the cylinder is calculated from the gas state equation and η.
Note that R used in the gas state equation is a gas constant and may be a constant value.
[0018]
FIG. 6 is a subroutine showing the processing procedure of Step 120.
Step 121: Read the intake air amount MAFM (measured value of the air flow meter 9).
Step 122: The intake pressure Pm is read.
Step 123: Read the intake air temperature Tm.
Step 124: A change ΔP in the intake pressure is calculated.
Step 125: The mass increase in the intake pipe 5a is calculated from the gas state equation, and the fresh air amount MDth flowing into the manifold 5b is calculated from the law of conservation of mass in the intake pipe 5a expressed by the following equation (1).
MAFM × (2 / number of cylinders) −MDth = ΔP · VIN / (Tm · R) (1)
[0019]
FIG. 7 is a subroutine showing the processing procedure of Step 130.
Step 131: The intake pressure Pm is read.
Step 132: Read the intake air temperature Tm.
Step 133: The change ΔP of the intake pressure calculated in Step 124 is read.
Step 134 Reads the fresh air amount MDth calculated in Step 125.
Step 135: The cylinder inflow gas amount Mcld calculated in Step 115 is read.
Step 136: The mass increase in the manifold 5b is calculated from the gas state equation, and the EGR gas amount MEGR flowing into the manifold 5b is calculated from the law of conservation of mass in the manifold 5b expressed by the following equation (2).
MDth + MEGR-Mcld = .DELTA.P.Vm / (Tm.R)......
[0020]
FIG. 8 is a subroutine showing the processing procedure of Step 140.
Step 141: Read in the fresh air amount MDth flowing into the manifold 5b.
Step 142 The EGR gas amount MEGR calculated in Step 136 is read.
Step 143: Corrected exhaust O ₂ concentration Cex calculated in the past cycle 　 Read c (in- ₁ ).
Step144… Cex 　 c a _{(i-n 1)} is stored in the memory as the _{O 2} concentration CEGR in EGR gas. Incidentally, n ₁ is obtained by considering the inflow delay of gas, constant or function of Ne,, a function of the vane opening of VNT2, or the like may be a function of the intake pressure.
[0021]
Step145 ... _{O 2} concentration Cm in the fresh air gas and where the EGR gas are mixed 　 Calculate IN.
Step146 ... _{O 2} concentration Cm in the gas flowing into the cylinder 　 Calculate cld. Note that n ₂ takes into account the delay of gas inflow and may be a constant or a function of Ne.
Step 147: The cylinder inflow gas amount Mcld is read.
Step148 ... Mcld and Cm 　 cld and the cylinder inflow O ₂ amount O ₂ Find cld.
[0022]
FIG. 9 is a subroutine showing the processing procedure of Step 150.
Step 151: The cylinder inflow gas amount Mcld is read.
Step 152... C2 inflow O ₂ amount O ₂ calculated in Step 148  Read cld.
Step 153: Read the command injection amount Qr.
Step154 ... _{O 2} amount _{O 2} consumed by the command injection amount Qr  Calculate qr. Incidentally, K1 (a constant) is consumed _{O 2} mass per unit amount of fuel. However, when the rate of incomplete combustion is large (1% or more) depending on the combustion mode, it is preferable to correct it.
[0023]
Step 155: Predicted exhaust O ₂ concentration Cex 　 Calculate mdl.
Specifically, the O ₂ amount O ₂ flowing into the cylinder  consumption from cld _{O 2} amount of _{O 2} The remaining oxygen amount is calculated by subtracting qr, and is divided by the sum of the gas amount Mcld flowing into the cylinder and the fuel amount K2 × Qr to obtain Cex. 　 mdl can be calculated. K2 is a fuel density and is a constant.
[0024]
Next, VNT2 is controlled in Steps 500 to 700.
Step 500: Calculate the target supercharging pressure. The target supercharging pressure is stored in the map 8e (see FIG. 1) in advance according to the operating conditions of the engine 1 (for example, the rotation speed Ne and the injection amount Q).
Step 600: The F / B amount (feedback amount) is calculated from the deviation between the intake pressure read from the intake pressure sensor 11 and the target supercharging pressure calculated in Step 500.
Step 700... The F / B amount calculated in Step 600 is added to the base opening previously stored in the map to determine the vane opening. The base opening is determined in accordance with the operating conditions of the engine 1 (for example, the rotation speed Ne and the injection amount Q).
[0025]
(Effects of the present embodiment)
In the present embodiment, the intake state at the cylinder position (the exhaust O ₂ concentration in the embodiment) is predicted, and the EGR valve 7 is operated by the F / B in accordance with the deviation between the predicted value and the target value (the target exhaust O ₂ concentration). Since the control is performed, the response of the EGR valve 7 can quickly follow the sudden change in the exhaust pressure without delay.
As a result, as compared with the conventional EGR control (for example, a method of performing F / B control of the valve opening in accordance with the deviation between the detection value of the air flow meter 9 and the target value), as shown in FIG. Even when the F / B gain of the VNT 2 is sometimes increased to make the response faster, the response of the EGR valve 7 is fast, so that an increase in the EGR amount due to an increase in the exhaust pressure can be suppressed. As a result, acceleration characteristics are improved, smoke is reduced, and exhaust gas characteristics are improved.
[0026]
(Modification)
In the above embodiment, the exhaust O ₂ concentration is described as the intake state at the cylinder position. However, in addition to the exhaust O ₂ concentration, for example, a fresh air amount flowing into the cylinder, or an A / F correlated to this new air amount , the intake _{O 2} concentration, the exhaust _{O 2} concentration, EGR ratio, even one of the EGR amount better.
Here, the EGR rate REGR at the cylinder position 　 An operation method for estimating cld will be described with reference to the flowchart shown in FIG.
[0027]
Step 800: The fresh air amount MDth flowing into the manifold 5b is read.
Step 810: The amount of EGR gas MEGR flowing into the manifold 5b is read.
Step 820: The EGR rate REGR at the place where the fresh air gas and the EGR gas are mixed is calculated by the following equation.
REGR = MEGR / (MDth + MEGR)
Step 830: EGR rate REGR at cylinder position from REGR 　 Predict cld.
Note that n2 is a constant or a function of Ne.
[0028]
Subsequently, the fresh air amount Air flowing into the cylinder 　 An operation method for estimating cld will be described with reference to the flowchart shown in FIG.
Step 900: The cylinder inflow gas amount Mcld is read.
Step910: EGR rate REGR at cylinder position 　 Read cld.
Step 920: Cylinder inflow fresh air amount Air from the following equation 　 Calculate cld.
Mair 　 cld = Mcld × (1-REGR 　 cld)
[0029]
Further, in the above-described embodiment, the example in which the supercharging pressure F / B control is performed on the VNT 2 is described. However, in addition to the supercharging pressure, the intake air amount measured by the air flow meter 9 or a correlation with the intake air amount. to a / F, the intake _{O 2} concentration, the exhaust _{O 2} concentration, EGR rate, one of the EGR amount, or may be in the intake state at cylinder position predicted by calculation circuit 8a of the ECU 8.
[Brief description of the drawings]
FIG. 1 is a block diagram of a control system.
FIG. 2 is a configuration diagram schematically showing an air system of an engine.
FIG. 3 is a flowchart showing a processing procedure of an ECU.
4 is a flowchart showing the procedure for obtaining the predicted exhaust O ₂ concentration in the cylinder position.
FIG. 5 is a flowchart illustrating a calculation procedure of a cylinder inflow gas amount.
FIG. 6 is a flowchart showing a procedure for calculating a manifold inflow fresh air amount.
FIG. 7 is a flowchart showing a calculation procedure of a manifold inflow EGR gas amount.
FIG. 8 is a flowchart showing a calculation procedure of a cylinder inflow O ₂ amount.
FIG. 9 is a flowchart showing a procedure for calculating a predicted exhaust O ₂ concentration.
FIG. 10 is a time chart comparing the control method at the time of acceleration between the conventional example and the present embodiment.
FIG. 11 is a flowchart showing a procedure for obtaining a predicted EGR rate at a cylinder position.
FIG. 12 is a flowchart showing a procedure for obtaining a fresh air amount flowing into a cylinder.
[Explanation of symbols]
1 engine (internal combustion engine)
2 VNT (variable capacity type turbocharger)
5 intake passage 6 EGR passage (EGR device)
7 EGR valve (EGR device)
8 ECU (control device)
8a arithmetic circuit (intake state prediction means)
8b VNT control circuit (supercharger control means)
8c EGR control circuit (EGR control means)
9 air flow meter (air volume measuring means)
11 Intake pressure sensor

Claims (3)

A variable-capacity supercharger that varies the supercharging pressure according to the vane opening;
Controlling the vane opening of the supercharger and the valve opening of the EGR device for an internal combustion engine including an EGR device that varies the amount of exhaust gas (EGR amount) recirculated to the intake system according to the valve opening. A control device,
Air amount measuring means for measuring an amount of intake air taken into the intake passage;
An intake pressure sensor that detects intake pressure in the intake passage;
Intake state prediction means for predicting an intake state at a cylinder position using at least the intake air amount and the intake pressure;
EGR control means for feedback-controlling the valve opening of the EGR device according to a deviation between the intake state predicted by the intake state prediction means and a target value thereof;
Vane opening of the supercharger according to a deviation between an actual supercharging pressure (detected value of the intake pressure sensor) and a target supercharging pressure, or a deviation between a parameter correlated with the supercharging pressure and a target value thereof. And a supercharger control means for performing feedback control of the engine. The control device for an internal combustion engine according to claim 1,
Wherein a parameter that correlates to the boost pressure, intake air amount measured by the air quantity measuring means, or A / F which correlates to the amount of intake air, the intake O ₂ concentration, the exhaust O ₂ concentration, EGR rate, A control device for an internal combustion engine, which is an intake state at one of EGR amounts or the cylinder position predicted by the intake state prediction means. The control device for an internal combustion engine according to claim 1 or 2,
The intake state is a fresh air amount flowing into the cylinder, or one of A / F, intake O ₂ concentration, exhaust O ₂ concentration, EGR rate, and EGR amount correlated to the new air amount. A control device for an internal combustion engine, comprising:

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