JPH10122057A - Egr controller for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exhibit NOx reduction effect with EGR to the maximum by restricting EGR ratio so as not to exceed heat resisting upper limit temperature for continuance of EGR in case that an EGR part exceeds heat resisting temperature when the EGR is continued at the EGR ratio suited to the operating condition of an engine. SOLUTION: Intake air amount Qa, engine speed Ne, water temperature Tw, and throttle opening TVO are read (S1) to obtain foundamental fuel injection amount Tp, the first target EGR ratio EGRQ, and present exhaust temperature TEPEX (S2, S3, S4). The balance temperature TMPEGRO of an EGR part is estimated when a present condition is continued (S5), Previously obtained EGR part temperature TMPEGR is read (S6), and present EGR part temperature TMPEGR is estimated (S7). If the present EGR part temperature TMPEGR is compared with heat resisting upper limit temperature TMPEGRH (S8) and it is judged as exceeded, by converting it into the first target EGR ratio EGRQ, the second target EGR ratio which is set so as not to exceed the heat resisting upper limit temperature TMPEGRH is set as EGRQ2 (S11).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an EGR for an engine.
In particular, the present invention relates to a technology that suppresses the temperature of an EGR component including an EGR valve to a temperature equal to or lower than a heat-resistant upper limit temperature and expands a region in which EGR is performed to improve a NOx suppression effect.

[0002]

2. Description of the Related Art Conventionally, in an engine having an electronically controlled EGR control device, for example, Japanese Patent Application Laid-Open No.
As shown in No. 62, when the engine continues at a predetermined rotational speed for a predetermined period of time, it is determined that the temperature of the EGR parts including the EGR valve has exceeded a predetermined value, and the EGR valve is fully closed and the EGR valve is closed.
Protecting parts has been done. In addition, there is an apparatus in which the temperature of the EGR valve is directly measured by a sensor to control the opening and closing of the EGR valve.

[0003]

By the way, in general, the combustion temperature is high at the time of high rotation and high load operation, so that the amount of generated NOx is large. EGR is effective in reducing NOx,
Under the above operating conditions, the exhaust gas temperature is high and the EGR parts may be damaged by overheating.
Whether to stop EGR unavoidably (conventional example 1; see FIG. 11)
, Was executed within a predetermined time limit (Conventional Example 2;
Therefore, the NOx reduction function by the EGR could not be sufficiently exhibited.

[0004] The present invention has been made in view of such a conventional problem. If the EGR is continuously performed at an EGR rate set based on the operating state of the engine, the EGR component may be overheated. , By reducing the EGR rate and continuing the EGR, while suppressing overheating of the EGR parts,
An object of the present invention is to provide an EGR control device for an engine capable of sufficiently exhibiting a NOx reduction function by EGR.

Further, EGR is performed at an EGR rate corresponding to the engine operating state until the temperature reaches a temperature near the upper limit of heat resistance while predicting the actual temperature change of the EGR component, and the temperature exceeds the upper limit temperature. The present invention aims to provide an EGR control device for an engine in which the EGR rate is switched so as to reduce and correct the EGR rate so as not to exceed the heat-resistant upper limit temperature so that the NOx reduction function by EGR can be maximized. I do.

[0006]

According to the first aspect of the present invention, an opening degree of an EGR valve provided in an EGR passage connecting an exhaust system and an intake system is controlled so as to become a target EGR rate. An engine EGR control device that detects an operating state of an engine, sets a target EGR rate based on the operating state, and, when the target EGR rate exceeds a heat resistant upper limit temperature of an EGR component, EGR is continued while limiting the target EGR rate so as not to exceed the temperature.

(Operation / Effect) In this way, when the EGR is continued at the EGR rate corresponding to the operating state of the engine, and when the EGR component exceeds the upper temperature limit, the EGR rate is reduced to the upper temperature limit. Since the EGR is continued while being limited to the extent not exceeding, the NOx reduction effect by the EGR can be sufficiently exhibited.

According to a second aspect of the present invention, there is provided an engine EGR for controlling an opening degree of an EGR valve provided in an EGR passage connecting an exhaust system and an intake system so as to become a target EGR rate.
A control device for detecting an operating condition of an engine, setting a first target EGR rate of an EGR valve based on the operating condition, detecting a temperature of the EGR component, and detecting the detected EGR component. After the temperature of the EGR component reaches near the upper limit temperature of the heat resistance while comparing the temperature with the upper limit temperature of the heat resistance of the EGR component, the first target EGR rate is replaced with the first target EGR rate so as not to exceed the upper limit temperature of the heat resistance. A second target EGR rate smaller than the first target EGR rate is corrected and set to decrease.

(Operation / Effect) In this way, if EGR is continued at an EGR rate based on the operating state of the engine,
Even when the EGR component is in an operating state in which the temperature exceeds the upper limit temperature, the state is transient, and when the temperature of the EGR component has not yet reached near the upper limit temperature, the EGR rate is determined based on the engine operating state. Since the EGR is performed, the highest EGR within the range not exceeding the upper temperature limit of heat resistance
The EGR can be performed at the rate, and the NOx reduction effect by the EGR can be maximized.

According to a third aspect of the present invention, as shown in FIG. 1, the opening of an EGR valve interposed in an EGR passage connecting an exhaust system and an intake system is controlled so as to become a target EGR rate. An engine operating condition detecting means for detecting an operating condition of the engine, and a first target EGR rate of an EGR valve based on the detected operating condition of the engine. Target EGR rate setting means, EGR component temperature detecting means for detecting the temperature of the EGR component, comparing means for comparing the estimated EGR component temperature with the upper temperature limit, and when the EGR component temperature reaches the upper temperature limit. After that, the first target EGR rate is replaced with the first target EGR rate so as not to exceed the heat resistant upper limit temperature.
And a second target EGR rate correction means for setting a second target EGR rate smaller than the GR rate.

(Operation / Effect) In this way, the EGR is continued at the EGR rate set by the first target EGR rate setting means, based on the operating state of the engine detected by the engine operating state detecting means. For example, even when the EGR component is in an operation state in which the temperature exceeds the upper limit temperature, the state is transient, and the temperature of the EGR component detected by the EGR component temperature detecting means has not yet reached near the upper limit temperature. When there is no EGR, the EGR is performed at the first EGR rate, so that the EGR can be performed at the maximum EGR rate within a range not exceeding the heat-resistant upper limit temperature.
The Ox reduction effect can be maximized.

Further, the invention according to claim 4 is characterized in that the EGR
The component temperature is detected by an estimation calculation based on the detected operating state of the engine and the current EGR rate. (Operation / Effect) In this way, the engine speed and load, or the intake air amount, etc., and the EGR rate
The temperature and flow rate of the EGR (exhaust gas) can be obtained, and the temperature of the EGR component can be estimated. This eliminates the need for a sensor for detecting the temperature of the EGR component.
Low cost.

Further, the invention according to claim 5 is characterized in that the EGR
In detecting the component temperature, the exhaust gas temperature is calculated based on the detected engine operating state and the current EGR rate, and the EGR rate is calculated based on the engine operating state and the EGR rate.
Calculate the flow rate, calculate the equilibrium temperature of the EGR component when equilibrated in the current state based on the exhaust gas temperature and the EGR flow rate, and calculate the weighted average of the previously calculated EGR component temperature and the EGR equilibrium temperature In this way, it is characterized by estimation and detection.

As described in the operation and effect of the fourth aspect of the present invention, since the exhaust gas temperature and the EGR flow rate are obtained based on the operating state of the engine and the EGR rate, it corresponds to the amount of heat per unit time currently given to the EGR parts. Thus, the temperature of the EGR component can be estimated, but when the exhaust gas temperature or the EGR flow rate changes in a transient state, the change in the EGR component temperature is delayed with respect to the change in the amount of heat supplied to the EGR component.

Therefore, the weight of the EGR component temperature calculated last time and the equilibrium temperature of the EGR component when the current state is continuously balanced are calculated to estimate the temperature of the EGR component accurately even in a transient state. be able to. Also,
The invention according to claim 6 is characterized in that the weight Wf of the EGR component temperature calculated last time in the weighted average calculation is variably set to a smaller value as the EGR flow rate increases.

(Operation / Effect) The greater the EGR flow rate, the greater the influence of the state change, and the more important the equilibrium temperature determined in the current state, the more the EGR component temperature weight Wf calculated last time. Is set to be a relatively small value. The invention according to claim 7 is characterized in that the initial value of the EGR component temperature calculated last time immediately after the start of the engine is set equal to the engine coolant temperature.

(Operation / Effect) Since the temperature of the EGR parts immediately after the start of the engine is considered to be substantially equal to the temperature of the cooling water of the engine, by setting the temperature of the EGR parts equal to the temperature of the cooling water, the temperature of the engine parts can be accurately measured immediately after the start of the engine. Can be estimated. In the invention according to claim 8, a target opening of the EGR valve in accordance with the target EGR rate is determined based on the target EGR rate, an engine throttle valve opening, an intake air amount, and an exhaust gas temperature. It is characterized by setting.

(Operation / Effect) The negative pressure of the intake air at the portion where the EGR gas flows in is determined by the throttle valve opening and the intake air amount, and the density of the EGR gas is determined by the exhaust gas temperature. The target opening of the EGR valve can be set with high accuracy.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a system configuration according to an embodiment of the present invention. The crank angle sensor 2 for detecting the rotation speed of the engine 1 generates a position signal for each unit crank angle and a reference signal for each cylinder stroke phase difference, and measures the number of the position signals generated per unit time,
Alternatively, by measuring the reference signal generation cycle,
The engine speed can be detected.

In the intake passage 3 of the engine 1, an air cleaner 4, an air flow meter 5 for detecting an intake air amount (an intake air amount per unit time), a throttle valve 6 for restricting and controlling the intake air amount, A throttle sensor 7 for detecting the opening of the valve 6 and a fuel injection valve 8 for supplying fuel to each cylinder are mounted. In the engine body,
An intake valve 9 for opening and closing the intake port, an exhaust valve 10 for opening and closing the exhaust port, and a spark plug 1 for igniting the air-fuel mixture in the combustion chamber 11
2. A water temperature sensor 13 for detecting a cooling water temperature (hereinafter referred to as a water temperature) is mounted.

An exhaust passage 14 of the engine 1 has an air-fuel ratio sensor (O ₂ sensor) 15 for detecting the air-fuel ratio of the air-fuel mixture,
Downstream, a three-way catalyst 16 for purifying HC, CO, and NOx in the exhaust gas by oxidation and reduction reactions is mounted. Further, an EGR connecting the exhaust passage 14 upstream of the three-way catalyst 16 and the intake passage 3 downstream of the throttle valve 6.
A passage 17 is provided, and the EGR passage 17 is provided with an EGR valve 18 for controlling an EGR flow rate.

The crank angle sensor 2, the air flow meter 5, the throttle sensor 7, and the water temperature sensor 13 constitute operating state detecting means for detecting the operating state of the engine. You. The control unit 19 receives the respective detection signals, calculates the fuel injection amount from the fuel injection valve 8, the ignition timing of the ignition plug 12, and the target opening degree according to the target EGR rate of the EGR valve 18, and calculates the target opening degree. The control is performed by outputting a signal corresponding to the calculation result to the corresponding actuator.

As a configuration according to the present invention, the control unit 19 predicts the temperature of the EGR components including the EGR valve 18 based on the exhaust gas temperature from the operating state of the engine 1,
At the time of transition, the temperature at the time of equilibrium in the state at that time is estimated, and the estimated equilibrium temperature is compared with the upper temperature limit of the heat resistance of the EGR component. The EGR is performed as much as possible while controlling, so that the NOx reduction function by the EGR is maximized.

EGR by the control unit 19
The control routine will be described with reference to the flowchart of FIG. In FIG. 3, in step 1, the intake air amount Q per unit time detected by the air flow meter 3 is shown.
a, the engine speed Ne detected by the crank angle sensor 2, the water temperature Tw detected by the water temperature sensor 13, and the throttle valve opening TVO detected by the throttle sensor 7 are read.

In step 2, a basic fuel injection amount Tp (= K.Qa / Ne) proportional to the cylinder intake air amount is calculated. The basic fuel injection amount Tp is used as a value representing the load (torque) of the engine. In step 3,
The first target EGR rate EGRQ is set based on the engine rotation speed Ne and the engine load, for example, a basic fuel injection amount Tp by searching a map as shown in FIG. This first target EGR rate EGRQ is:
It is set in consideration of only NOx reduction and engine performance according to the operating state of the engine, and does not consider the temperature of the EGR parts.

In step 4, the current exhaust gas temperature TMP
EX is calculated based on the engine speed Ne and the basic fuel injection amount T.
Based on p, it is estimated by a search from a map or the like.
The map is set based on the exhaust gas temperature characteristics obtained by an experiment as shown in FIG. In step 5,
Equilibrium temperature TM of EGR parts when current state continues
PEGR0 is calculated based on the exhaust temperature TMPEX and the intake air amount Q.
a, Estimate based on first target EGR rate EGRQ.
More specifically, the intake air amount Qa and the first target EGR
The EGR flow rate is calculated from the product of the EGR rate and the EGR rate.
Based on the flow rate and the exhaust temperature TMPEX, estimation is performed by searching from a map or the like. The map estimates the EGR component equilibrium temperature TMPGR0 based on the EGR component equilibrium temperature characteristics obtained by an experiment or the like as shown in FIG.

In step 6, the EGR component temperature TMPEGRB obtained last time is read. In step 7, the current EGR component temperature TMPGR is compared with the EGR component equilibrium temperature TMPGR0, the intake air amount Qa, and the first target E.
GR rate EGRQ and previous EGR component temperature TMPGR
Estimate based on B. Specifically, the previously estimated E
By calculating a weighted average of the GR component temperature TMPEGRB and the EGR component equilibrium temperature TMPEGR0 when equilibrated in the current state, the current EGR component temperature T
Estimate MPEGR. This means that, as shown in FIG.
This is because the GR component temperature changes in a first-order lag with respect to the equilibrium temperature according to the EGR flow rate. In the weighted average calculation, the weight Wf of the previous EGR component temperature TMPEGRB and the weight of the EGR component equilibrium temperature TMPGR0 are used.
(1-Wf) is variably set according to the EGR flow rate. Specifically, as the EGR flow rate increases, the weight Wf of the previous EGR component temperature TMPEGRB increases,
Weight of EGR component equilibrium temperature TMPEGR0 (1-Wf)
Smaller. The previous EGR component temperature TMPEG
Regarding RB, the initial value immediately after starting the engine is the water temperature Tw.
Set to a value equal to

In step 8, the current EGR component temperature TPEGGR estimated in step 7 is
Compare with the heat resistant upper limit temperature of the part TMPEGRH. When it is determined that the current EGR component temperature TMPGR is equal to or lower than the heat-resistant upper limit temperature vicinity value TMPEGRH, the process proceeds to step 9 and the first target EGR rate EGRQ set in step 3 is set to the target value. The EGR rate is set as the EGR rate EGRQ2, and further proceeds to step 10 where the current EGR component temperature TMP estimated in step 7 is set.
The EGR is set as the previous EGR component temperature TMPEGRB for the next calculation processing.

On the other hand, if it is determined in step 8 that the current EGR component temperature TMPGR is higher than the heat-resistant upper limit temperature TMPEGRH, the process proceeds to step 11, where the first target EGR rate is replaced with the first target EGR rate. Heat resistance upper limit temperature TM
Second target EG set not to exceed PEGRH
Set the R rate as EGRQ2. Specifically, the dashed line in FIG. 8 indicates a boundary line of the upper limit temperature TMPEGRH, and a portion on the left side of the boundary line in the figure is a region apart from the boundary line. 4, the EGR rate is set to be lower than the first target EGR rate in the portion from the portion on the left side to the portion on the right side of the boundary line while considering the characteristics of only the engine operating state. Even if the second target EGR rate is continuously controlled, the temperature is set to be equal to or lower than the upper limit temperature TMPEGRH.

In step 12, for the next arithmetic processing,
EGR component temperature when controlling to the target EGR rate,
For example, when the second target EGR rate is set so as to coincide with the heat resistant upper limit temperature TMPEGRH, the heat resistant upper limit temperature TMPEGRH is set to the previous EGR component temperature TMPEGRB.
Set as In step 13, the target opening degree EGRA of the EGR valve at which the target EGR rate EGRQ2 set in step 10 or step 12 is achieved is determined by the throttle valve opening TV detected by the throttle sensor 7.
O, target EGR rate EGRQ2, current EGR component temperature T
Calculation is performed based on MPEGRB.

In step 14, a drive signal of the EGR valve for setting the EGR valve to the target opening EGRA is output to the EGR valve. FIG. 9 shows the relationship between the EGR rate and the EGR component temperature in the conventional example, in the case where the EGR rate is continued only in the engine operating state without considering the heat-resistant upper limit temperature, and in the embodiment of the present invention. That is, by using the present invention,
As long as the EGR component temperature does not exceed the heat resistant upper limit temperature, the maximum EGR rate can be increased and the EGR can be effectively used.
it is obvious.

FIG. 10 shows the change over time of various state quantities in the embodiment of the present invention.
It is also apparent from this figure that the EGR rate can be effectively used by correcting the EGR rate to decrease when the R component temperature reaches just below the upper limit temperature. As shown above,
In the present embodiment, while the EGR component temperature that changes due to a change in the engine operation state or the like is estimated, the EGR rate is secured to the maximum and the EGR can be effectively used. However, as a simple method, the target EGR is used. It is also possible to adopt a method in which only the equilibrium temperature of the EGR component at the rate is calculated and the EGR rate is set so that the equilibrium temperature does not exceed the upper limit temperature.

In the embodiment of this simple system, the above embodiment is superior in terms of the EGR utilization during the transition, but the amount of calculation is small, and the map of the target EGR rate is also small. There is an advantage that it is sufficient to prepare only one set in consideration of the operating state and the upper temperature limit of heat resistance.
In the embodiment described above, the exhaust temperature is estimated from the operating state of the engine, so that the cost can be reduced as compared with the case where the exhaust temperature sensor is provided. However, it is needless to say that the exhaust temperature sensor may be provided. It is.

In the embodiment described above, a spark ignition engine such as a gasoline engine has been described as an engine, but the present invention is also applicable to a diesel engine.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a system configuration according to an embodiment of the present invention.

FIG. 3 is a flowchart showing EGR control according to the embodiment.

FIG. 4 is a view showing characteristics of a first target EGR rate according to the embodiment.

FIG. 5 is a view showing an exhaust gas temperature characteristic of the embodiment.

FIG. 6 is a view showing characteristics of an EGR component temperature equilibrium temperature of the embodiment.

FIG. 7 is an explanatory diagram for calculating an EGR component temperature equilibrium temperature of the embodiment.

FIG. 8 is a view showing characteristics of a second target EGR rate according to the embodiment.

FIG. 9 compares the relationship between the EGR rate and the EGR component temperature in the same embodiment as the conventional example, the case where the EGR rate is continued only in the engine operating state without considering the heat resistant upper limit temperature, and the embodiment of the present invention. Time chart shown.

FIG. 10 is a time chart showing changes with time of various state quantities in the embodiment.

FIG. 11 is a diagram showing EGR control characteristics in a first conventional example.

FIG. 12 is a diagram showing EGR control characteristics in a second conventional example.

[Explanation of symbols]

 Reference Signs List 1 engine 2 crank angle sensor 3 intake passage 5 air flow meter 14 exhaust passage 15 air-fuel ratio sensor 17 EGR passage 18 EGR valve 19 control unit

Claims (8)

[Claims] An engine EGR control device for controlling an opening degree of an EGR valve interposed in an EGR passage connecting an exhaust system and an intake system to a target EGR rate, wherein an engine operating state is detected. Then, the target EGR rate is set based on the operating state, and the target EGR rate is
When the temperature exceeds the heat resistant upper limit temperature of the GR component, the EGR rate is limited while limiting the target EGR rate so as not to exceed the heat resistant upper limit temperature.
EG of the engine characterized by continuing
R control device. 2. An engine EGR control device for controlling an opening of an EGR valve interposed in an EGR passage connecting an exhaust system and an intake system to a target EGR rate, wherein an engine operating state is detected. And, based on the driving state,
The first target EGR rate of the EGR valve is set, the temperature of the EGR component is detected, and the detected EGR component temperature is compared with the heat-resistant upper limit temperature of the EGR component.
After the R component temperature reaches near the upper limit temperature, the second target EGR smaller than the first target EGR rate is used instead of the first target EGR rate so as not to exceed the upper limit temperature.
An EGR control device for an engine, wherein the EGR control device sets the rate by decreasing and correcting the rate. 3. An engine EGR control device for controlling an opening degree of an EGR valve interposed in an EGR passage connecting an exhaust system and an intake system to a target EGR rate, and detecting an operating state of the engine. Engine operating state detecting means for performing the EGR based on the detected operating state of the engine.
First target EGR rate setting means for setting a first target EGR rate of the valve; EGR component temperature detecting means for detecting a temperature of the EGR component; and comparing the estimated EGR component temperature with a heat-resistant upper limit temperature. After the EGR component temperature reaches near the upper temperature limit of heat resistance,
The first target EG is set so as not to exceed the upper temperature limit.
An EGR control device for an engine, comprising: a second target EGR rate correction means for setting a second target EGR rate smaller than the first target EGR rate instead of the R rate. 4. The method according to claim 1, wherein the detection of the EGR component temperature is performed by an estimation calculation based on the detected operating state of the engine and a current EGR rate. EG of the engine according to any one of the above.
R control device. 5. The detection of the EGR component temperature includes calculating an exhaust gas temperature based on the detected operating condition of the engine and a current EGR rate, and detecting the operating condition of the engine and the EGR component.
The EGR flow rate is calculated based on the R rate and the EGR when the current state is balanced based on the exhaust gas temperature and the EGR flow rate.
5. The EGR control of an engine according to claim 4, wherein the EGR control is performed by calculating an equilibrium temperature of the GR component, and calculating and calculating a weighted average of the EGR component temperature calculated last time and the EGR equilibrium temperature. apparatus. 6. The weight according to claim 5, wherein the weight Wf of the EGR component temperature calculated last time in the weighted average calculation is variably set to a smaller value as the EGR flow rate increases. Engine EGR control device. 7. The EGR of an engine according to claim 5, wherein the initial value of the previously calculated EGR component temperature immediately after the start of the engine is set to be equal to the engine coolant temperature. Control device. 8. A target opening of the EGR valve according to the target EGR rate is set based on the target EGR rate, an opening degree of a throttle valve of the engine, an intake air amount, and an exhaust gas temperature. The engine EGR control device according to any one of claims 1 to 7, wherein