JP3209067B2 - EGR control 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 EGR of an internal combustion engine that recirculates a part of exhaust gas into intake air through an EGR valve provided in an EGR passage that connects an exhaust system and an intake system of the engine.
(Exhaust gas recirculation) Related to a control device.

[0002]

2. Description of the Related Art As a conventional EGR control device for an internal combustion engine, there is one disclosed in Japanese Patent Application Laid-Open No. 61-215426, for example, assuming a diesel engine as the internal combustion engine. FIG. 16 shows a configuration of a conventional example, in which a cylinder intake air-fuel mixture calculating unit 101, a collector intake fresh air amount detecting unit 102, a predicted EGR rate calculating unit 103, a target EGR rate setting unit 104, a target EGR valve opening degree The calculation unit 105, the EGR valve operation unit 106, and the diesel engine 107 are included.

[0003] The cylinder intake air-fuel mixture calculation unit 101 calculates the amount of air-fuel mixture consisting of fresh air and EGR gas sucked into the cylinder from the operating state of the diesel engine. The collector intake fresh air amount detecting means 102 detects a fresh air amount sucked into the collector. The predicted EGR rate calculation unit 103 calculates the amount of air-fuel mixture sucked into the cylinder, which is the output of the cylinder intake air-fuel mixture calculation unit 101, and the amount of fresh air that is output to the collector, which is the output of the collector intake new air amount detection means 102. Is used to calculate the predicted EGR rate by the following equation.

EGRratio = 100 × (Qo−Qw) /
Qw EGRratio: Predicted EGR rate (%) Qo: Air-fuel mixture intake into cylinder (Kg / sec) Qw: New air intake into collector (Kg / sec) The target EGR rate setting unit 104 is an engine operating state. The target EGR rate is set in accordance with.

[0005] The target EGR valve opening degree calculating section 105 calculates a predicted EG value.
The output of the R rate calculating unit 103 is compared with the output of the target EGR rate setting unit 104, and the target EGR valve opening is calculated so that the predicted EGR rate approaches the target EGR rate. EGR valve operation unit 106
Operates the EGR valve to achieve the target EGR valve opening.

[0006]

However, in such a conventional EGR control device for an internal combustion engine, it is considered that the amount of fresh air taken into the collector is equal to the amount of fresh air taken into the cylinder. Therefore, when the flow rate difference actually occurs in the transient state (for example, when the state changes from the idle state to the acceleration state, the amount of fresh air sucked into the collector suddenly increases. , The amount of fresh air sucked into the cylinder gradually increases).
There is a problem that the accuracy of the rate is reduced, and the control performance of the EGR rate may be reduced.

Therefore, Japanese Patent Application No. 7-249180 (hereinafter referred to as "prior application 1") discloses a collector intake fresh air amount detecting means based on dynamic characteristics from the time when fresh air passes through the intake valve to the intake valve. A cylinder intake new air amount calculation unit for calculating a new air amount sucked into the cylinder from a new air amount sucked into the collector, which is an output of the cylinder, is provided. By calculating the predicted EGR rate from the air quantity and the new air quantity sucked into the cylinder, the prediction accuracy of the EGR rate is improved, and as a result,
It proposes to improve the control performance of the EGR rate.

However, even when the EGR rate is predicted to be substantially equal to the actual value, there are the following problems.
In both the conventional example and the prior application 1, the predicted EGR
The target EGR valve opening is obtained based on the difference between the rate and the target EGR rate. Here, the EGR rate is determined by the fresh air in the cylinder and E
The EGR valve controls the amount of EGR sucked into the collector, whereas the EGR valve has a dynamic characteristic until the gas sucked into the collector is sucked into the cylinder. Occurs. That is, the predicted EGR rate and the target EG
Even if the EGR valve is controlled based on the difference from the R rate, the reflection of the result is delayed by the above dynamic characteristics. Therefore, there is a problem that this delay creates a limit on control performance.

The present invention has been made in view of such circumstances,
Target EG to be drawn into cylinders required to achieve GR rate
Target EGR to be drawn into the collector to obtain the R amount
An object of the present invention is to further improve the control performance of the EGR rate by obtaining the amount and controlling the EGR valve.

[0010]

According to the present invention, a target EGR rate setting section for setting a target EGR rate in accordance with an engine operating state, and a new EGR rate and a new EGR rate sucked into a cylinder. A first target EGR amount calculation unit (target cylinder intake EGR amount calculation unit) for calculating a first target EGR amount desired to be sucked into the cylinder from the air volume; and a phase lead compensation for the first target EGR amount. A second target EG for calculating a second target EGR amount desired to be sucked into the collector.
An R amount calculating unit (a target collector intake EGR amount calculating unit), and the second target EGR amount and E actually sucked into the collector.
A target EGR for calculating a target EGR valve opening degree from the GR amount
A valve opening calculation unit, and E so that the target EGR valve opening is attained.
An EGR valve operation unit for operating the GR valve is provided to constitute an EGR control device for the internal combustion engine.

That is, the target EGR amount (first target EGR amount) to be sucked into the cylinder necessary for achieving the target EGR rate
By performing a predetermined phase advance compensation (advance process) on the target EGR amount (second amount) to be sucked into the collector.
The target EGR valve opening is calculated such that the measured or predicted value of the EGR amount actually sucked into the collector approaches the target EGR amount desired to be sucked into the collector. Manipulate.

According to a second aspect of the present invention, in the first aspect of the present invention, the second target EGR amount calculating section (the target collector intake EGR amount calculating section) includes the first target EGR amount calculating section.
Estimate the output of the cylinder intake EGR amount response characteristic setting unit that sets the response characteristics between the amount and the EGR amount actually sucked into the cylinder, and estimate the dynamic characteristics until the gas sucked into the collector is sucked into the cylinder From the first target EGR amount based on the output of the collector dynamic characteristic estimating unit.
The target EGR amount is calculated.

According to a third aspect of the invention, in the first aspect of the invention, the EGR amount sucked into the collector is:
It is obtained by performing a phase lead compensation on the EGR amount sucked into the cylinder based on the output of the collector dynamic characteristic estimating unit for estimating the dynamic characteristic until the gas sucked into the collector is sucked into the cylinder. And In the invention according to claim 4, in the invention according to claim 2 or 3, the collector dynamic characteristic estimating unit estimates the collector dynamic characteristic from the engine rotation speed, the volumetric efficiency, the collector volume, and the stroke volume. It is characterized by being.

According to a fifth aspect of the present invention, in the third aspect of the invention, the EGR amount sucked into the cylinder is:
It is characterized by being obtained from the amount of air-fuel mixture sucked into the cylinder and the amount of fresh air sucked into the cylinder. In the invention according to claim 6, in the invention according to claim 5, the amount of the air-fuel mixture sucked into the cylinder is a volume efficiency, a stroke volume, an engine speed, an absolute pressure indicating a standard state, and an absolute temperature indicating a standard state. And the density of the gas depending on the collector in the standard state, the pressure in the collector, and the temperature in the collector.

According to a seventh aspect of the present invention, in the fifth aspect of the invention, the amount of fresh air sucked into the cylinder is determined by estimating a dynamic characteristic until gas sucked into the collector is sucked into the cylinder. It is obtained from the amount of fresh air sucked into the collector based on the output of the dynamic characteristic estimator. According to an eighth aspect of the present invention, in the fourth or sixth aspect, the volumetric efficiency is obtained from an engine speed and a collector internal pressure.

According to a ninth aspect of the present invention, in the invention according to the sixth aspect, the collector internal temperature is determined from a fuel injection amount, an EGR amount taken into the cylinder, and a fresh air amount taken into the cylinder. It is characterized by. In the invention according to claim 10, in the invention according to claim 7, the amount of fresh air sucked into the collector is obtained from the intake throttle valve opening area, the pressure in the collector, the atmospheric pressure, and the atmospheric density. I do.

According to an eleventh aspect of the present invention, in the invention according to the sixth aspect, the temperature in the collector is measured using a sensor. In the invention according to claim 12,
The invention according to claim 4 is characterized in that a predetermined constant is used for the volumetric efficiency. The invention according to claim 13 is characterized in that, in the invention according to claim 6, a predetermined constant is used for at least one of the volume efficiency and the gas density depending on the collector in the standard state.

According to a fourteenth aspect, in the tenth aspect, a predetermined constant is used for at least one of the atmospheric pressure and the atmospheric density. still,
A target EGR amount desired to be sucked into the collector is calculated, and the same effect as that of the present invention is aimed at with respect to the conventional example and the prior application 1, as disclosed in Japanese Patent Application No. 7-209527 (hereinafter referred to as "prior application 2"). However, the present invention differs in the following points.

In the prior application 2, the target EGR valve opening degree is calculated using the target EGR amount desired to be sucked into the collector and the differential pressure before and after the EGR valve. Target EGR amount and EG sucked into the collector
The difference is that the calculation is performed using the R amount. As a result, in the prior application 2, when the flow path area in the EGR valve is not ensured due to manufacturing variation of the EGR pipe and the EGR valve, clogging due to exhaustion of the EGR valve, or the other way around, the target EGR valve is opened. There is no feedback mechanism for correcting the degree, which degrades the control performance of the EGR rate. On the other hand, in the present invention, E
Compare the GR amount with the EGR amount that you want the collector to inhale,
Since the target EGR valve opening is corrected, there is an effect that the control performance of the EGR rate does not deteriorate due to the manufacturing variation of the EGR pipe and the EGR valve as described above, and the clogging due to the exhaust of the EGR valve.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of the present invention (corresponding to claim 1). A diesel engine is assumed as the internal combustion engine. In the figure, 1 is a target EG
R ratio setting section, 2 is a target cylinder intake EGR amount calculation section (first target EGR amount calculation section), 3 is target collector intake EG
R amount calculating section (second target EGR amount calculating section), 4 is a target E
A GR valve opening calculating section, 5 is an EGR valve operating section, and 6 is a diesel engine.

The target EGR rate setting section 1 sets a target EGR rate according to the operating state of the engine. Target cylinder suction E
The GR amount calculation unit (first target EGR amount calculation unit) 2 calculates a target EGR rate set by the target EGR rate setting unit 1 and a fresh air amount (measured value or predicted value) sucked into the cylinder. Calculate the target EGR amount to be taken into the cylinder.

The target collector intake EGR amount calculation section (second target EGR amount calculation section) 3 compensates for the phase advance of the target EGR amount calculated by the target cylinder suction EGR amount calculation section 3 which is desired to be taken into the cylinder. Advanced processing)
Calculate the target EGR amount desired to be sucked into the collector. The target EGR valve opening calculating section 4 calculates the target E to be drawn into the collector calculated by the target collector suction EGR amount calculating section 3.
From the GR amount and the EGR amount (measured value or predicted value) actually sucked into the collector, the target EGR valve opening is calculated so as to match them.

The EGR valve operating section 5 operates the EGR valve so as to attain the target EGR valve opening. As mentioned above, target E
Target EG to be drawn into cylinders required to achieve GR rate
By performing a predetermined phase lead compensation on the R amount,
A target EGR amount to be sucked into the collector is obtained, and a target EGR valve opening is calculated so that a measured value or a predicted value of the EGR amount actually sucked into the collector approaches the target EGR amount to be sucked into the collector. Operate the EGR valve.

When the EGR amount sucked into the collector matches the target EGR amount desired to be sucked into the collector, as a phase lead compensation, the amount of the EGR amount from the target EGR amount desired to be sucked into the cylinder to the EGR amount actually sucked into the cylinder is corrected. By using phase lead compensation that can arbitrarily set response characteristics, EG
The control performance of the R rate is further improved. The phase lead compensation will be described with reference to FIGS. Hereinafter, the amount of EGR taken into the collector is Qe, the amount of EGR taken into the cylinder is Qce, and the target EGR amount desired to be taken into the collector is MQ.
e, the target EGR amount desired to be sucked into the cylinder is MQce.

As shown in FIG. 2, the cylinder intake EGR amount Qce has a first-order lag relationship with the collector intake EGR amount Qe. When it is desired to increase the target cylinder intake EGR amount MQce in steps as much as possible as shown in FIG. 3, the target cylinder intake EGR amount Qce is more preferably D than in FIG. In this case, the target collector intake EGR amount MQe
To move in the direction from A to B. However, collector inhalation E
In order for the GR amount Qe to follow the target collector intake EGR amount MQe, a faster operation speed and a larger opening area are required of the EGR valve, and there are limitations in hardware.

At this point, the target cylinder intake EGR amount MQce
The phase lead compensation in the present invention, which calculates the target collector intake EGR amount MQe from the target cylinder intake EGR amount MQe, is performed in accordance with the performance of the EGR valve actually used.
There is a feature that a realistic characteristic of the cylinder intake EGR amount Qce can be set with respect to Qce. FIG. 4 is a block diagram showing a method for estimating the EGR amount sucked into the collector (corresponding to claims 3 to 6, 13).

In the figure, reference numeral 11 denotes a cylinder intake air-fuel mixture calculating unit;
Denotes a cylinder suction EGR amount calculation unit, 13 denotes a collector dynamic characteristic estimating unit, and 14 denotes a collector suction EGR amount calculation unit. The cylinder intake air-fuel mixture calculation unit 11 calculates an air-fuel mixture (total flow rate of gas entering the cylinder) from the volume efficiency, the engine rotation speed, the collector internal pressure, and the collector internal temperature (claim). 6). The stroke volume, the absolute pressure indicating the standard state, and the absolute temperature indicating the standard state are given as constants. Further, the density of the gas present in the collector in the standard state is also given as a constant (corresponding to claim 13).

The cylinder intake EGR amount calculation unit 12 calculates the EGR amount to be taken into the cylinder from the amount of air-fuel mixture taken into the cylinder and the amount of fresh air taken into the cylinder (corresponding to claim 5). . The collector dynamic characteristic estimating unit 13 calculates a dynamic characteristic (hereinafter referred to as “collector dynamic characteristic”) until the gas sucked into the collector is sucked into the cylinder from the engine rotational speed and the volumetric efficiency. Equivalent). still,
The collector volume and the stroke volume are given as constants.

The collector suction EGR amount calculation unit calculates the EGR amount sucked into the collector by performing a phase lead compensation on the EGR amount sucked into the cylinder based on the dynamic characteristics of the collector. Equivalent). Hereinafter, more detailed examples of the present invention will be described. FIG. 5 shows a first embodiment of the present invention (applying claims 1 to 9). A diesel engine is assumed as the internal combustion engine.

In the figure, 1 is a target EGR rate setting section, 2 is a target cylinder intake EGR amount calculating section (first target EGR amount calculating section), 3 is a target collector intake EGR amount calculating section (second target EGR amount calculating section). ), 4 is a target EGR valve opening calculator, 5
Denotes an EGR valve operation unit, and 6 denotes a diesel engine. Also,
11 is a cylinder intake air-fuel mixture calculation unit, and 12 is a cylinder intake E
A GR amount calculator, 13 is a collector dynamic characteristic estimator, and 14 is a collector intake EGR amount calculator.

Further, 15 is a collector intake fresh air amount detecting means,
16 is an engine rotational speed detecting means, 17 is a collector pressure detecting means, 18 is a fuel injection amount detecting means, 19 is a cylinder suction fresh air amount calculating section, 20 is a collector temperature estimating section, 21 is a volume efficiency estimating section, 22 Denotes a response characteristic setting unit (cylinder intake EGR amount response characteristic setting unit). Each element is explained below,
The description will be made assuming a four-cylinder diesel engine.

Note that all subsequent calculations are performed in time synchronization. Z in the formula is an operator of Z conversion,
Z ^-1 represents one operation delay. The collector intake fresh air amount detecting means 15, the engine rotational speed detecting means 16, the collector internal pressure detecting means 19, and the fuel injection amount detecting means 18 each use a sensor or the like to detect fresh air sucked into the collector. Since only the amount, the engine speed, the collector internal pressure, and the fuel injection amount are detected, the description is omitted. [Target EGR Rate Setting Section 1] The target EGR rate setting section 1 sets a target EGR rate according to the engine operating state. [Cylinder suction air-fuel mixture calculation unit 11] The cylinder suction air-fuel mixture calculation unit 11 includes an engine rotation speed output from the engine rotation speed detection means 16, a volume efficiency output from the volume efficiency estimation unit 21, Using the collector internal pressure which is the output of the pressure detecting means 17 and the collector internal temperature which is the output of the collector internal temperature estimating section 20, the mixed air amount Qo sucked into the cylinder is calculated by, for example, equation (1). (Corresponding to claim 6).

Qo = (ηv × Pcol × To × ρcol × Vcyl × Ne) / (30 × Po × Z ^-1 Tcol) (1) Qo: The amount of air-fuel mixture sucked into the cylinder (Kg / sec) Ne: engine rotation speed (rpm) ηv: volumetric efficiency Vcyl: stroke volume (m ³ ) ρcol: density of gas present in the collector in a standard state (Kg / m ³ ) Pcol: collector internal pressure (Pa) Tcol: collector Internal temperature (K) Po: Absolute pressure indicating the standard state (Pa) To: Absolute temperature indicating the standard state (K) Here, stroke volume Vcyl, absolute pressure P indicating the standard state
o, the absolute temperature To indicating the standard state is given as a constant. Gas density ρcol in the collector at standard condition
May be sensed or a standard value may be given. It should be noted that ρcol can be regarded as substantially a constant, and when a standard value is used as ρcol, it corresponds to claim 13. [Collector dynamic characteristic estimation unit 13] Collector dynamic characteristic estimation unit 13
The time constant τa of the dynamic characteristic generated by the collector is calculated by using, for example, equation (2), using the volume efficiency output from the volume efficiency estimating unit 21 and the engine speed output from the engine speed detecting means 16. Calculation (corresponding to claim 4).

Τa = (30 × Vcol) / (Ne × Vcyl × ηv) (2) τa: time constant (sec) of dynamic characteristics generated by the collector Vcol: collector volume (m ³ ) Vcyl: stroke volume ( m ³ ) Ne: engine rotation speed (rpm) ηv: volumetric efficiency Here, the collector volume Vcol and the stroke volume Vcyl are given as constants. The collector volume refers to a volume surrounded by the EGR valve, the intake throttle valve, and the intake valve. [Cylinder suction new air amount calculation unit 19] The cylinder suction new air amount calculation unit 19 includes a new air amount sucked into the collector, which is an output of the collector suction new air amount detection unit 15, and a collector dynamic characteristic estimation unit.
Using the output of 13 and the time constant of the dynamic characteristic generated by the collector, the fresh air amount Qcw drawn into the cylinder is calculated by, for example, equation (3) (corresponding to claim 7).

Equation (3) expresses the relationship of the first-order lag represented by the time constant τa using a discrete system equation. Qcw = exp (−Δt / τa) × (Z ⁻¹ Qcw) + [1−exp (−Δt / τa)] × (Z− ¹ Qw) (3) Qcw: fresh air sucked into the cylinder Amount (Kg / sec) Qw: Amount of fresh air sucked into the collector (Kg / sec) τa: Time constant of dynamic characteristics generated by the collector (sec) Δt: Sampling time (sec) Here, Δt is given as a constant. [Cylinder suction EGR amount calculation unit 12] Cylinder suction EGR
The amount calculation unit 12 calculates the amount of air-fuel mixture sucked into the cylinder, which is the output of the cylinder intake air-fuel mixture calculation unit 11, and the amount of new air that is sucked into the cylinder, which is the output of the cylinder intake new air amount calculation unit 19. Then, the EGR amount Qce sucked into the cylinder is calculated by, for example, equation (4) (corresponding to claim 5).

Qce = Qo−Qcw (4) Qce: EGR amount sucked into cylinder (Kg / sec) Qo: Air-fuel mixture amount sucked into cylinder (Kg / sec) Qcw: Suction into cylinder Fresh air volume (Kg / sec) [Collector temperature estimation unit 20] Collector temperature estimation unit 20
Is calculated from the fresh air amount Qcw drawn into the cylinder, which is the output of the cylinder suction new air amount calculation unit 19, and the EGR amount Qce drawn into the cylinder, which is the output of the cylinder suction EGR amount calculation unit 12. Ratio to EGR gas ratio (%) = Qce / Q
Calculate cw. Then, this ratio ratio and the fuel injection amount Qf (× 10 ⁻⁶ Kg / st) which is the output of the fuel injection amount detecting means 18
Then, the collector internal temperature Tcol is estimated with reference to a map prepared in advance (corresponding to claim 9).

FIG. 6 shows an example of a map for estimating the temperature inside the collector.
Shown in [Collector suction EGR amount calculation unit 14] Collector suction EGR
The amount calculation unit 14 uses the EGR amount sucked into the cylinder, which is the output of the cylinder suction EGR amount calculation unit 12, and the constant of the dynamic characteristic generated by the collector, which is the output of the collector dynamic characteristic estimation unit 13, for example, as ( The EGR amount Qe sucked into the collector is calculated by the formulas (5) and (6) (corresponding to claim 3).

Equations (5) and (6) express the phase lead compensation using a discrete-time equation. Qe = (τa / τc) × Qce− (τa / τc−1) × R (5) where, R = exp (−Δt / τc) × (Z ⁻¹ R) + [1-exp ( −Δt / τc)] × (Z ⁻¹ Qce) (6) Qe: EGR amount sucked into the collector (Kg / sec) Qce: EGR amount sucked into the cylinder (Kg / sec) τa: Collector Τc: Collector intake EGR amount prediction time constant (sec) Δt: Sampling time (sec) Here, Δt is given as a constant.

Τc represents the time constant of the delay of the EGR amount sucked into the collector calculated as the predicted value with respect to the actual value, and is set so as to satisfy the relationship of equation (7). 0 <τc <τa (7) Note that as τc is smaller, the prediction delay is reduced, but the influence of disturbance is more likely.

The relationship between the actual value and the predicted value of the EGR amount sucked into the collector is as shown in FIG. 7 (explanatory diagram of the collector suction EGR amount calculating section) via the EGR amount sucked into the cylinder. FIG. 7 shows an input / output relationship using a continuous-time transfer function, where s represents a Laplace operator.
Originally, the amount of EGR sucked into the cylinder can be approximated by a first-order lag of a time constant τa, as shown in the block at the front stage of FIG. 7, with respect to the amount of EGR sucked into the collector.

The collector suction EGR amount calculation unit 14 calculates the EGR amount sucked into the collector by using the transfer function of the block at the latter stage of FIG. As a result, the predicted value of the EGR amount sucked into the collector becomes a first-order lag of a set time constant of τc with respect to the actual value. [Target Cylinder Intake EGR Amount Calculating Unit 2] The target cylinder intake EGR amount calculating unit 2 draws the target EGR rate which is the output of the target EGR amount setting unit 1 and the cylinder which is the output of the cylinder intake fresh air amount calculating unit 19. The target EGR desired to be sucked into the cylinder by using the new air amount to be taken, for example, by equation (8).
The quantity MQce is calculated (corresponding to claim 1).

MQce = (Megr / 100) × Qcw (8) MQce: target EGR amount to be sucked into the cylinder (Kg / se
c) Megr: Target EGR rate (%) Qcw: New air amount sucked into cylinder [Target collector intake EGR amount calculation unit 3] The target collector suction EGR amount calculation unit 3 is an output of the target cylinder suction EGR amount calculation unit 2. Using the target EGR amount desired to be sucked into the cylinder, the time constant of the dynamic characteristic generated by the collector, which is the output of the collector dynamic characteristic estimating unit 13, and the time constant of the response characteristic, which is the output of the response characteristic setting unit 22. For example, (9),
The target EGR amount MQe to be sucked into the collector is calculated by the equation (10) (corresponding to claims 1 and 2).

Equations (9) and (10) express the phase lead compensation using a discrete-time equation. MQe = (τa / τb) × MQce− (τa / τb−1) × L (9) where L = exp (−Δt / τb) × (Z ⁻¹ L) + [1-exp ( −Δt / τb)] × (Z ⁻¹ MQce) (10) MQe: Target EGR amount desired to be sucked into the collector (Kg / se
c) MQce: target EGR amount (Kg / se) to be sucked into the cylinder
c) τa: Time constant of dynamic characteristics generated by the collector (sec)
) Τb: time constant of response characteristics (sec) Δt: sampling time (sec) Here, Δt is given as a constant. [Response Characteristic Setting Unit 17] The response characteristic setting unit 17 sets the time constant τb of the response characteristic of the EGR amount actually sucked into the cylinder from the target EGR amount desired to be sucked into the cylinder (corresponding to claim 2). .

At this time, a positive number smaller than the time constant τa of the dynamic characteristic generated by the collector, which is the output of the collector dynamic characteristic estimating unit 13, is set as shown in equation (11). 0 <τb <τa (11) τb: Time constant of response characteristics (sec) τa: Time constant of dynamic characteristics generated by the collector (sec) The smaller the τb, the better the response characteristics, but the EGR valve A high operating speed and a large opening area are required. [Volume Efficiency Estimating Unit 21] The volume efficiency estimating unit 21 includes a collector pressure Pcol, which is an output of the collector pressure detecting means 17, and
The engine speed Ne, which is the output of the engine speed detector 16
From the above, referring to a map prepared in advance, the volumetric efficiency η
v is estimated (corresponding to claim 8).

FIG. 8 shows an example of a map for estimating the volumetric efficiency. Note that the output of the volume efficiency estimating unit 21 may be a predetermined constant without using the collector internal pressure and the engine rotation speed (corresponding to claims 12 and 13). [Target EGR Valve Opening Calculation Unit 4] The target EGR valve opening calculation unit 4 calculates the amount of EGR sucked into the collector, which is the output of the collector suction EGR amount calculation unit 14, and the target collector suction EGR.
The target E to be sucked into the collector, which is the output of the quantity calculation unit 3,
The target EGR valve opening Aegr is calculated by using the GR amount and, for example, the equations (12) and (13) (corresponding to claim 1).
PI control is performed by expressing the integral as a difference.

Aegr = Kp × (MQe−Qe) + Y (12) where, Y = Z ⁻¹ Y + Δt × Ki × Z ⁻¹ (MQe−Qe) (13) Aegr: target EGR valve Opening MQe: Target EGR amount (Kg / se
c) Qe: EGR amount sucked into the collector (Kg / sec) Δt: Sampling time (sec) Kp: Proportional gain Ki: Integral gain Here, the proportional gain Kp and the integral gain Ki are set in advance by experiments and simulations. Alternatively, it may be changed according to the engine operating state. [EGR valve operating unit 5] The EGR valve operating unit 5
The EGR valve is operated so as to have the valve opening.

Next, the simulation result will be described. FIG. 9 shows a target EGR rate and an actual EGR according to a conventional example.
2 shows a simulation result of a rate and a predicted EGR rate. FIG. 10 shows simulation results of the target EGR rate, the actual EGR rate, and the predicted EGR rate according to the first embodiment. In both cases, it is assumed that the vehicle accelerates from 7 seconds.

From the comparison between FIG. 9 and FIG. 10, it can be seen that the first embodiment (FIG. 10) has a higher EGR rate prediction accuracy. By improving the prediction accuracy, the target EGR of the actual EGR rate
It can be seen that the ability to follow the ratio is also improved. next,
A second embodiment of the present invention will be described. FIG. 11 shows the second embodiment of the present invention.
(Examples 1 to 10 are applied).

The second embodiment is different from the first embodiment in that the amount of fresh air sucked into the collector is obtained by calculation. Therefore, instead of the collector intake fresh air amount detecting means 15 of the first embodiment, an intake throttle valve opening area detecting means is used.
31 and a collector intake fresh air amount calculation unit 32 are provided. The intake throttle valve opening area detecting means 31 detects the intake throttle valve opening area.

The collector suction fresh air amount calculation unit 32 uses the collector internal pressure, which is the output of the collector internal pressure detection means 17, and the intake throttle valve opening area, which is the output of the intake throttle valve opening area detection means 31. For example, the fresh air amount Qw sucked into the collector is calculated by the equation (14) (corresponding to claim 10).
In equation (14), the pressure upstream of the intake throttle valve is set to the atmospheric pressure, and the pressure downstream of the intake throttle valve is set to the pressure inside the collector. It is what it was.

Qw = [2 × (Pa−Pcol) × ρa] ^1/2 × Stvo (14) Qw: New air volume sucked into the collector (Kg / sec) Pcol: Collector internal pressure (Pa) Pa: Atmospheric pressure (Pa) ρa: Atmospheric density (Kg / m ³ ) Stvo: Opening area of the intake throttle valve (m ² ) The atmospheric pressure Pa and the atmospheric density ρa may be sensed or may be standard values. May be given. When a standard value is used as Pa and ρa, this corresponds to claim 14.

Others are the same. Next, the third aspect of the present invention
An example will be described. FIG. 12 shows a third embodiment of the present invention (claims 1 to 9 and 11 are applied). The third embodiment is different from the first embodiment in that the temperature inside the collector is measured by a sensor.

Accordingly, instead of the fuel injection amount detecting means 18 and the collector temperature estimating section 20 of the first embodiment, a collector temperature detecting means 33 for detecting the collector temperature using a sensor is provided. Others are the same. Next, a fourth embodiment of the present invention will be described.

FIG. 13 shows a fourth embodiment of the present invention (claims 1 to 11 are applied). The fourth embodiment is different from the second embodiment in that the temperature inside the collector is measured by a sensor. Therefore, the fuel injection amount detecting means of the second embodiment
A temperature detecting means in the collector for detecting the temperature in the collector using a sensor instead of the temperature estimating unit 20 in the collector 18
33 are provided.

Others are the same.

[0056]

As described above, the present invention (Claim 1)
According to the invention according to the present invention), the amount of fresh air sucked into the collector,
In addition, by taking into account the delay until the EGR amount is sucked into the cylinder, the EGR control accuracy can be improved, whereby effects such as reduction of NOx and black smoke can be obtained.

The present invention and a conventional example (and prior application 1)
The difference from the prior application 2 is that the target EGR valve opening is calculated from the input as shown in FIG.
In the conventional example (and prior application 1), the predicted EGR of the target EGR rate is
The target EGR valve opening is obtained based on the difference from
The GR rate is the ratio of fresh air in the cylinder to EGR gas, whereas the EGR valve controls the amount of EGR sucked into the collector, so that the gas sucked into the collector is sucked into the cylinder. There is a dynamic characteristic up to and there is a delay. That is, E is calculated based on the difference between the predicted EGR rate and the target EGR rate.
Even when the GR valve is controlled, there is a problem that the reflection of the result is delayed by the amount of the dynamic characteristics, and this delay causes a limitation in control performance.

In this regard, the present invention can solve such a problem. In the earlier application 2, the target E that the collector wants to inhale
Using the GR amount and the differential pressure across the EGR valve, the target EGR
The valve opening is calculated. As a result, if the flow path area in the EGR valve is not ensured due to manufacturing variations of the EGR pipe and the EGR valve or clogging due to exhaustion of the EGR valve, a feedback mechanism for correcting this is provided. Does not exist, the control performance of the EGR rate deteriorates.

In this regard, in the present invention, the target EGR valve opening is corrected by comparing the EGR amount sucked into the collector with the EGR amount desired to be sucked into the collector. In other words, the EGR amount sucked into the collector is corrected. Since the amount is fed back, it is possible to correct for such a change in characteristics as described above. FIG. 15 shows the performance of following the actual EGR rate with respect to the target EGR rate when the actual EGR valve opening degree is 70% of the target EGR valve opening degree and the present invention (first embodiment). 3) shows a comparison simulation with FIG. 9 together
It is assumed that the vehicle accelerates from the second. From FIG.
It can be seen that the present invention has higher tracking performance.

The invention according to claims 2 to 14 further has the following features with respect to the effects of the invention according to claim 1. The invention according to claim 2 specifies the second method of calculating the target EGR amount in the invention according to claim 1. According to the third aspect of the present invention, a measuring unit is not required as compared with the case of measuring the amount of EGR sucked into the collector according to the first aspect of the present invention.

The invention according to claim 4 specifies the collector dynamic characteristic in the invention according to claim 2 or 3. The invention according to claim 5 does not require a measuring unit as compared with the case of measuring the amount of EGR sucked into the cylinder in the invention according to claim 3. The invention according to claim 6 does not require a measuring means as compared with the case of measuring the amount of air-fuel mixture sucked into the cylinder according to the invention according to claim 5.

According to the seventh aspect of the present invention, no measuring means is required as compared with the case of measuring the amount of fresh air sucked into the cylinder according to the fifth aspect of the present invention. The invention according to claim 8 specifies a method for estimating the volume efficiency in the invention according to claim 4 or 6. According to the ninth aspect of the present invention, a measuring unit is not required as compared with the case of measuring the temperature in the collector according to the sixth aspect of the present invention.

According to the tenth aspect of the present invention, no measuring means is required as compared with the case of measuring the amount of fresh air sucked into the collector according to the seventh aspect of the present invention. According to the eleventh aspect of the present invention, an estimating unit is not required as compared with the case of estimating the temperature in the collector according to the sixth aspect of the present invention. According to the twelfth aspect of the present invention, an estimating unit is not required as compared with the case of estimating the volume efficiency in the fourth aspect of the present invention.

According to the thirteenth aspect of the present invention, the estimating means and the measuring means are not required as compared with the case of estimating and measuring the volume efficiency and the density in the collector according to the sixth aspect of the present invention.
The invention according to claim 14 does not require a measuring means as compared with the case of measuring the atmospheric pressure or the atmospheric density according to the invention according to claim 10.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is an explanatory diagram of phase lead compensation (1).

FIG. 3 is an explanatory diagram of phase lead compensation (2).

FIG. 4 is a block diagram of a method of estimating a collector intake EGR amount;

FIG. 5 is a block diagram showing a first embodiment of the present invention.

FIG. 6 is a diagram showing an example of a map for estimating the temperature inside the collector;

FIG. 7 is an explanatory diagram of a collector suction EGR amount calculation unit.

FIG. 8 is a diagram showing an example of a map for volumetric efficiency estimation;

FIG. 9 is a diagram showing a simulation result according to a conventional example.

FIG. 10 is a diagram illustrating a simulation result according to the first embodiment.

FIG. 11 is a block diagram showing a second embodiment of the present invention.

FIG. 12 is a block diagram illustrating a third embodiment of the present invention.

FIG. 13 is a block diagram showing a fourth embodiment of the present invention.

FIG. 14 is an explanatory diagram of a difference between an input of a target EGR valve opening calculating unit between the present invention and a conventional example.

FIG. 15 is a diagram showing a simulation result of comparison between the prior application 2 and the present invention.

FIG. 16 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

1 target EGR rate setting section 2 target cylinder intake EGR amount calculation section (first target EG
R amount calculation unit) 3 target collector intake EGR amount calculation unit (second target EG
4 Target EGR valve opening degree calculation section 5 EGR valve operation section 6 Diesel engine 11 Cylinder intake air-fuel mixture calculation section 12 Cylinder intake EGR amount calculation section 13 Collector dynamic characteristic estimating section 14 Collector suction EGR amount calculation section 15 Collector intake fresh air amount detecting means 16 Engine rotational speed detecting means 17 Collector internal pressure detecting means 18 Fuel injection amount detecting means 19 Cylinder intake new air amount calculating unit 20 Collector internal temperature estimating unit 21 Volume efficiency estimating unit 22 Cylinder intake EGR amount response Characteristic setting unit 31 Intake throttle valve opening area detection means 32 Collector intake fresh air amount calculation unit 33 Collector temperature detection means

Claims (14)

(57) [Claims] An EGR for communicating an exhaust system and an intake system of an engine.
In an EGR control device for an internal combustion engine that recirculates a part of exhaust gas into intake air through an EGR valve provided in a passage, a target EG for setting a target EGR rate according to an engine operating state
An R rate setting unit; a first target EGR amount calculating unit that calculates a first target EGR amount desired to be sucked into the cylinder from the target EGR rate and the fresh air amount sucked into the cylinder; A second calculating means for performing a phase lead compensation on the target EGR amount and calculating a second target EGR amount desired to be sucked into the collector;
A target EGR amount calculating section, and a target EG for calculating a target EGR valve opening degree from the second target EGR amount and the EGR amount actually sucked into the collector.
An EGR control device for an internal combustion engine, comprising: an R valve opening calculation unit; and an EGR valve operation unit that operates an EGR valve so as to achieve the target EGR valve opening. 2. The second target EGR amount calculation section calculates the first target EGR amount and EGR actually sucked into a cylinder.
The output of the cylinder intake EGR amount response characteristic setting unit that sets the response characteristic between the amount and the output of the collector dynamic characteristic estimator that estimates the dynamic characteristic until the gas drawn into the collector is drawn into the cylinder. Based on the first target EGR
2. The EGR control device for an internal combustion engine according to claim 1, wherein the second target EGR amount is calculated from the amount. 3. The EGR amount drawn into the collector is drawn into the cylinder based on the output of a collector dynamic characteristic estimating section for estimating the dynamic characteristic until the gas drawn into the collector is drawn into the cylinder. The EGR control device for an internal combustion engine according to claim 1, wherein the EGR amount is obtained by performing a phase lead compensation on the EGR amount. 4. The collector dynamic characteristic estimating section for estimating a collector dynamic characteristic from an engine rotational speed, a volume efficiency, a collector volume and a stroke volume. EGR control device for an internal combustion engine. 5. The EGR of an internal combustion engine according to claim 3, wherein the amount of EGR taken into the cylinder is obtained from the amount of air-fuel mixture taken into the cylinder and the amount of fresh air taken into the cylinder. Control device. 6. The volume of the gas mixture sucked into the cylinder includes volumetric efficiency, stroke volume, engine rotation speed, absolute pressure indicating a standard state, absolute temperature indicating a standard state, and density of a gas depending on a collector in the standard state. 6. The EGR control device for an internal combustion engine according to claim 5, wherein the EGR control device is obtained from the pressure, the pressure in the collector, and the temperature in the collector. 7. The amount of fresh air drawn into the cylinder is drawn into the collector based on the output of a collector dynamic characteristic estimating section for estimating the dynamic characteristic until the gas drawn into the collector is drawn into the cylinder. The EG of an internal combustion engine according to claim 1 or 5, wherein the EG is obtained from a fresh air amount.
R control device. 8. The EGR control apparatus for an internal combustion engine according to claim 4, wherein said volume efficiency is obtained from an engine rotation speed and a collector internal pressure. 9. The EGR control of an internal combustion engine according to claim 6, wherein the collector internal temperature is obtained from a fuel injection amount, an EGR amount taken into the cylinder, and a fresh air amount taken into the cylinder. apparatus. 10. The EGR control of an internal combustion engine according to claim 7, wherein the amount of fresh air sucked into the collector is obtained from an intake throttle valve opening area, a collector internal pressure, an atmospheric pressure, and an atmospheric density. apparatus. 11. The EG for an internal combustion engine according to claim 6, wherein the temperature inside the collector is measured using a sensor.
R control device. 12. The EGR control device for an internal combustion engine according to claim 4, wherein a predetermined constant is used for the volumetric efficiency. 13. The EGR control device for an internal combustion engine according to claim 6, wherein a predetermined constant is used for at least one of the volume efficiency and the gas density depending on the collector in the standard state. 14. The method according to claim 10, wherein a predetermined constant is used for at least one of the atmospheric pressure and the atmospheric density.
An EGR control device for an internal combustion engine according to claim 1.