JPH1018918A - Exhaust gas reflux control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately obtain target exhaust gas reflux amount as a mass flow rate, despite the variation in an exhaust density. SOLUTION: Target exhaust gas reflux amount tEGRm is set as a mass flow rate based on a target exhaust gas reflux rate tEGRr and a fresh air intake air flow rate Qair detected as the mass flow rate. Next, the target exhaust gas reflux amount tEGRm is converted into target exhaust gas reflux amount tEGRv as a volume flow rate based on exhaust temperature Texh and exhaust pressure Pexh, and the target area tEGRa of an exhaust gas reflux path is determined based on the target exhaust gas reflux amount tEGRv as a volume flow rate and the before and after difference pressure (exhaust pressure Pexh-air intake pressure Pint) of an exhaust gas reflux control valve. Here, the target area tEGRa is converted into the target opening tEGRo of the exhaust gas reflux control valve, to control the exhaust gas reflux control valve so as to become the target opening tEGRo.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation control device for an internal combustion engine, and more particularly to a technique for improving the control accuracy of an exhaust gas recirculation amount.

[0002]

2. Description of the Related Art Conventionally, in automobile internal combustion engines,
BACKGROUND ART As a device for reducing NOx in exhaust gas, an exhaust gas recirculation (EGR) device that reduces NOx by lowering a combustion temperature by recirculating a part of exhaust gas to an intake system is known. In the exhaust gas recirculation device, the opening degree of an exhaust gas recirculation control valve provided in an exhaust gas recirculation path may be electronically controlled in order to obtain a required amount of exhaust gas recirculation in accordance with operating conditions. Specifically, the target area of the exhaust gas recirculation path is determined from the target exhaust gas recirculation amount determined according to the operating conditions and the differential pressure between the exhaust pressure and the intake pressure. There has been a method of controlling the opening of a control valve (see Japanese Patent Application No. 7-209527).

[0003]

Incidentally, the target exhaust gas recirculation amount should be set based on the fresh air intake air flow rate at that time so that a required exhaust gas recirculation rate corresponding to the operating conditions can be obtained. Further, in order to obtain the required exhaust gas recirculation rate with high accuracy, it is desired to set the target exhaust gas recirculation rate, which is the target exhaust gas recirculation rate, as the mass flow rate with respect to the fresh air intake air amount as the mass flow rate.

However, conventionally, in setting the target area (the target opening of the exhaust gas recirculation control valve) from the target exhaust gas recirculation amount, the change in the exhaust gas density due to the exhaust gas temperature and the exhaust gas pressure has not been taken into consideration. However, there is a problem that the target exhaust gas recirculation amount cannot be accurately obtained.
The present invention has been made in view of the above problems, and has as its object to provide an exhaust gas recirculation control device capable of obtaining a target exhaust gas recirculation amount as a mass flow rate with high accuracy.

[0005]

According to the present invention, there is provided an exhaust gas recirculation control device for an internal combustion engine that recirculates a part of exhaust gas to an intake system, wherein an area of an exhaust gas recirculation path is variably controlled. In the exhaust gas recirculation control device for an internal combustion engine configured to control the amount of exhaust gas recirculation, a target amount of exhaust gas recirculation set as a mass flow rate is converted into a volume flow rate, and the exhaust gas recirculation path is set based on the target amount of exhaust gas recirculation as the volume flow rate Was determined.

The invention according to claim 2 is configured as shown in FIG. In FIG. 1, a target mass flow rate setting means sets a target exhaust gas recirculation amount as a mass flow rate according to operating conditions. Further, the flow rate conversion means converts the target exhaust gas recirculation amount as the set mass flow rate into a volume flow rate.

The target area setting means sets a target area of the exhaust gas recirculation path based on the target exhaust gas recirculation amount as the converted volume flow rate. Claim 1 and Claim 2
According to the invention described, since the target exhaust gas recirculation amount is set as the mass flow rate, by controlling to the target exhaust gas recirculation amount,
The target exhaust gas recirculation rate can be accurately obtained. Further, in setting the target area from the target exhaust gas recirculation amount as the mass flow rate, the mass flow rate is converted into a volume flow rate, and the target area is set from the volume flow rate. The target area corresponding to the target exhaust gas recirculation amount with high accuracy can be set.

According to the third aspect of the present invention, the target mass flow rate setting means detects intake air flow rate of the engine as a mass flow rate, and sets a target exhaust gas recirculation rate based on operating conditions. Means for setting a target exhaust gas recirculation rate,
The target exhaust gas recirculation amount is set as a mass flow rate based on the detected fresh air intake air flow rate and the set target exhaust gas recirculation rate.

In this configuration, the target exhaust gas recirculation rate is set based on, for example, operating conditions such as the engine load and the engine speed. Is done. Then, a target exhaust gas recirculation amount corresponding to the target exhaust gas recirculation rate is set as a mass flow rate with respect to the fresh air intake air flow rate as a mass flow rate.

According to a fourth aspect of the present invention, the flow rate converting means includes exhaust gas temperature detecting means for detecting an exhaust gas temperature, and the target exhaust gas recirculation amount as the mass flow rate is at least detected by the detected exhaust gas temperature. Is converted to a volume flow rate based on. That is, the configuration is such that the target exhaust gas recirculation amount as a mass flow rate is converted into a volume flow rate in response to a density change due to a change in exhaust temperature.

According to a fifth aspect of the present invention, the flow rate conversion means includes exhaust gas pressure detection means for detecting exhaust pressure together with the exhaust gas temperature detection means. It is configured to convert to a volume flow rate based on the detected exhaust temperature and exhaust pressure. That is, since the exhaust density is affected by the pressure as well as the temperature, the configuration is such that the mass flow rate is converted into the volume flow rate from the exhaust temperature and the exhaust pressure.

In the invention according to claim 6, the target area setting means includes an intake pressure detecting means for detecting an intake pressure, and an exhaust pressure detecting means for detecting an exhaust pressure. The target area of the exhaust gas recirculation path is set based on the target exhaust gas recirculation amount and the detected differential pressure between the exhaust pressure and the intake pressure. That is, the volume flow rate is
At a constant passage area, the target exhaust gas recirculation amount is calculated based on the target exhaust gas recirculation amount as a volume flow rate and the differential pressure between the intake pressure and the exhaust pressure because it is proportional to the half power of the front-rear differential pressure ΔP. The required target area is determined.

The intake air flow rate detecting means, exhaust temperature detecting means, exhaust pressure detecting means, and intake pressure detecting means may be directly detected by a mass flow meter, a temperature sensor, a pressure sensor, or the like. It may be good, or may be estimated (indirectly detected) from other operating conditions. “Setting” and “conversion” in the target mass flow rate setting means, the flow rate conversion means, the target area setting means, and the target exhaust gas recirculation rate setting means are based on a calculation based on a formula and a search from a map stored in advance. It shall include both.

According to a seventh aspect of the present invention, the exhaust gas recirculation path includes an exhaust gas recirculation control valve, and a target opening of the exhaust gas recirculation control valve is set based on a target area set by the target area setting means. An opening degree setting means and an opening degree control means for controlling an opening degree of the exhaust gas recirculation control valve based on the target opening degree set by the target opening degree setting means are provided.

According to such a configuration, by controlling the opening of the exhaust gas recirculation control valve to the target opening, the target area, and hence the target area,
A target exhaust gas recirculation amount as a mass flow rate is obtained.

[0016]

According to the first and second aspects of the present invention, since the target exhaust gas recirculation amount set as the mass flow rate is converted into the volume flow rate, the target area of the exhaust gas recirculation path is set. In addition, even if there is a change in the exhaust gas density, there is an effect that the target exhaust gas recirculation amount as the mass flow rate can be accurately obtained.

According to the third aspect of the present invention, there is an effect that the exhaust gas recirculation amount as a mass flow rate can be controlled with high accuracy so that the exhaust gas recirculation rate required from the operating conditions is obtained.
According to the fourth aspect of the invention, there is an effect that the exhaust gas recirculation amount can be accurately controlled in response to a change in exhaust gas density due to a change in exhaust gas temperature. According to the fifth aspect of the invention, there is an effect that the exhaust gas recirculation amount can be accurately controlled in response to a change in the exhaust density due to a change in the exhaust temperature and the exhaust pressure.

According to the sixth aspect of the present invention, there is an effect that the target area of the exhaust gas recirculation path corresponding to the target exhaust gas recirculation amount as a volume flow rate can be set with high accuracy. According to the seventh aspect of the invention, by controlling the opening degree of the exhaust gas recirculation control valve provided in the exhaust gas recirculation path to the target opening degree, there is an effect that the target exhaust gas recirculation amount as the mass flow rate can be accurately obtained. .

[0019]

Embodiments of the present invention will be described below. FIG. 2 is a diagram illustrating a system configuration of the internal combustion engine according to the embodiment. In FIG. 2, a fuel injection valve 2 is provided so as to face a combustion chamber of the internal combustion engine 1. The fuel injection valve 2 is driven to open by an injection pulse signal to directly inject and supply fuel into the combustion chamber.

In the engine 1, air adjusted by a throttle valve 4 interposed in an intake passage 3 is sucked, and an air-fuel mixture is formed by the fuel injected from the fuel injection valve 2.
The air-fuel mixture is ignited and burned by spark ignition by the ignition plug 5, and the combustion exhaust is discharged through the exhaust passage 6. still,
The fuel injection valve 2 may be provided at the intake port to supply fuel into the cylinder via the intake valve.

An exhaust gas recirculation passage 7 is provided for connecting the exhaust gas passage 6 and the intake passage 3 downstream of the throttle valve 4. The exhaust gas recirculation passage 7 is provided with an exhaust gas recirculation control valve 8. The exhaust gas recirculation control valve 8 is driven to be opened and closed by an actuator such as an electromagnetic coil or a step motor, and the opening is electronically controlled according to an opening control signal from a control unit 9. .

The control unit 9, which controls the fuel injection by the fuel injection valve 2, the ignition by the spark plug 5, the opening of the exhaust gas recirculation control valve 8, and the like, includes a microcomputer and includes various sensors described later. Various controls are performed based on the signals from The various sensors include an air flow meter 10 (intake air flow rate detecting means) such as a hot wire flow meter for detecting a fresh air intake air quantity Qair of the engine 1 as a mass flow rate, and a crank for generating a unit angle signal and a reference angle signal. Angle sensor 11, cooling water temperature T of engine 1
A water temperature sensor 12 for detecting w, a vehicle speed sensor 13 for detecting a vehicle speed VSP, and the like are provided.

By measuring the number of unit angle signals generated from the crank angle sensor 11 per unit time,
Alternatively, the engine rotation speed Ne can be detected by measuring the generation cycle of the reference angle signal. Here, the state of the exhaust gas recirculation amount control by the control unit 9 will be described.
This will be described with reference to the control function block diagram of FIG.
In the following, exhaust gas recirculation is abbreviated as EGR.

First, in a target EGR rate setting section A (target exhaust gas recirculation rate setting means), a target EGR rate t is set in accordance with operating conditions.
Set EGRr. Specifically, a target EGR rate tEGRr is referred to in advance in accordance with the engine rotational speed Ne and the load state of the engine, and the engine rotational speed NEG at that time is referred to.
e and a target EGR rate tEGRr corresponding to the engine load are retrieved. The load state of the engine can be estimated from a cylinder intake air amount, a throttle valve opening, and the like.

As described above, the operating conditions used for setting the target EGR rate tEGRr correspond to the engine speed and the load of the engine. As means for detecting these operating conditions, the air flow meter 10 or the like is used. Crank angle sensor 11
Will be equivalent. The target EGR rate tEGRr
Is output to the target EGR mass flow rate setting unit B. The target EGR mass flow rate setting unit B is configured to set the target EGR rate tEG.
In addition to Rr, a fresh air intake air amount Qair as a mass flow rate detected by the air flow meter 10 is input, and a target EGR amount as a mass flow rate (a target EGR mass flow rate) according to the following equation.
Calculate tEGRm.

TEGRm = Qair × tEGRr The target EGR rate setting section A and the target EGR mass flow setting section B constitute a target mass flow rate setting means.
The calculated target EGR mass flow rate tEGRm is output to a target EGR volume flow rate setting unit C (flow rate conversion means). The target EGR volume flow rate setting section C includes the target E
In addition to the GR mass flow rate tEGRm, the exhaust temperature Texh (the temperature at the inlet of the recirculated exhaust gas into the intake passage), and the exhaust pressure Pex
h (pressure at the exhaust port) is input, and the target EGR mass flow rate tEGRm is converted into a target EGR amount (target EGR volume flow rate) tEGRv as a volume flow rate according to the following equation.

TEGRv = K1 × tEGRm × Texh ×
1 / Pexh (K1 is a constant) Here, the exhaust temperature Texh and the exhaust pressure Pexh may be directly detected by providing a temperature sensor and a pressure sensor, respectively, or may be estimated from operating conditions (indirectly, respectively). (Exhaust temperature detecting means, exhaust pressure detecting means). Further, for simplicity, a configuration in which only the correction based on the exhaust gas temperature may be performed.

If the configuration is such that the mass flow rate is converted to the volume flow rate by the above equation, the target mass flow rate can be accurately converted to the volume flow rate in response to the change in the exhaust density due to the exhaust temperature and the exhaust pressure. . The calculated target EGR volume flow rate tEGRv is output to a target EGR path area setting unit D (target area setting means). In addition to the target EGR volume flow rate tEGRv, the intake pressure Pint and the exhaust pressure Pexh (pressure at the recirculation exhaust port) are input to the target EGR path area setting section D, and the target EGR path area tEGRa is calculated according to the following equation. .

TEGRa = K2 × tEGRv / (Pexh
−Pint) ^1/2 Here, similarly to the exhaust pressure Pexh, the intake pressure Pint may be directly detected by providing a pressure sensor, or may be estimated from operating conditions (indirectly detected). ) (Intake pressure detection means).
The target EGR path area tEGRa is output to a target opening setting section E (target opening setting means).

The target opening degree setting unit E calculates the target EGR path area tEGRa according to a table set in advance.
Into a target opening tEGRo, and the target opening tEGRo
Is output to the exhaust gas recirculation control valve 8 to control the exhaust gas recirculation control valve 8 to the target opening degree tEGRo (opening degree control means). In the target EGR volume flow rate setting section C and the target EGR path area setting section D,
As shown in FIG. 4, a map for converting the target EGR mass flow rate tEGRm to the target EGR volume flow rate tEGRv, a target E
A map for obtaining the target EGR path area tEGRa from the GR volume flow rate tEGRv and the front-back differential pressure is stored in advance,
The target EGR volume flow rate tE is obtained by searching from the map.
The configuration may be such that GRv and the target EGR path area tEGRa are obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an exhaust gas recirculation control device according to the invention of claim 2;

FIG. 2 is a system configuration diagram of an internal combustion engine in the embodiment.

FIG. 3 is a functional block diagram of exhaust gas recirculation control in the embodiment.

FIG. 4 is a functional block diagram showing another embodiment of the exhaust gas recirculation control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Fuel injection valve 3 Intake passage 4 Throttle valve 5 Spark plug 6 Exhaust passage 7 Exhaust return passage 8 Exhaust return control valve 9 Control unit 10 Air flow meter 11 Crank angle sensor 12 Water temperature sensor 13 Vehicle speed sensor

Claims (7)

[Claims] An exhaust gas recirculation control device for an internal combustion engine that recirculates a part of the exhaust gas to an intake system, wherein the exhaust gas recirculation amount is controlled by variably controlling the area of an exhaust gas recirculation path. An internal combustion engine, wherein a target exhaust gas recirculation amount set as a mass flow rate is converted into a volume flow rate, and a target area of the exhaust gas recirculation path is determined based on the target exhaust gas recirculation amount as the volume flow rate. Exhaust recirculation control device. 2. An exhaust gas recirculation control device for an internal combustion engine that recirculates part of exhaust gas to an intake system, wherein the exhaust gas recirculation amount is controlled by variably controlling the area of an exhaust gas recirculation path. In the recirculation control device, target mass flow rate setting means for setting a target exhaust gas recirculation amount as a mass flow rate according to operating conditions, flow rate conversion means for converting the target exhaust gas recirculation amount as the set mass flow rate to a volume flow rate, A target area setting means for setting a target area of the exhaust gas recirculation path based on the target exhaust gas recirculation amount as the converted volume flow rate, an exhaust gas recirculation control device for an internal combustion engine. 3. The target mass flow rate setting means detects intake air flow rate of an engine as a mass flow rate, and a target exhaust gas recirculation rate setting means sets a target exhaust gas recirculation rate based on operating conditions. Means for setting a target exhaust gas recirculation amount as a mass flow rate based on the detected fresh air intake air flow rate and the set target exhaust gas recirculation rate. An exhaust gas recirculation control device for an internal combustion engine according to the above. 4. The flow rate conversion means includes exhaust gas temperature detection means for detecting an exhaust gas temperature. The target exhaust gas recirculation amount as the mass flow rate is converted into a volume flow rate based on at least the detected exhaust gas temperature. The exhaust gas recirculation control device for an internal combustion engine according to claim 2, wherein the conversion is performed. 5. The exhaust gas pressure detecting means for detecting an exhaust pressure together with the exhaust gas temperature detecting means, wherein the target exhaust gas recirculation amount as the mass flow rate is detected by the detected exhaust gas temperature. 5. The exhaust gas recirculation control device for an internal combustion engine according to claim 4, wherein the volume flow is converted into a volume flow based on the exhaust gas pressure and the exhaust gas pressure. 6. The target area setting means includes: an intake pressure detecting means for detecting an intake pressure; and an exhaust pressure detecting means for detecting an exhaust pressure. Setting a target area of the exhaust gas recirculation path based on the detected differential pressure between the exhaust pressure and the intake pressure.
6. The exhaust gas recirculation control device for an internal combustion engine according to any one of 5. 7. An exhaust gas recirculation control valve provided in the exhaust gas recirculation path, and a target opening degree setting means for setting a target opening degree of the exhaust gas recirculation control valve based on a target area set by the target area setting means; 7. An opening control means for controlling the opening of the exhaust gas recirculation control valve based on the target opening set by the target opening setting means. An exhaust gas recirculation control device for an internal combustion engine according to any one of the first to third aspects.