JPH10238413A - Controller for exhaust gas recirculation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate an adverse influence due to the response delay of EGR gas temperature during transition of an engine by providing a correcting means for correcting the opening degree of an EGR valve through a control means according to the temperature of EGR gas recirculated in an inlet system and cancelling the correction by the correcting means during the transition of the engine. SOLUTION: A controller 6 is provided with a control means 11 for controlling the opening degree of an EGR valve 5 depending on the operating state of an engine, a correcting means 12 and a cancel means 13 and desired EGR gas temperature is obtained by the control means 11 so that the concentration of NOx in exhaust gas reaches a desired value based on engine rotating speed Ne and load L and a desired EGR valve opening degree is obtained based on the desired EGR gas temperature. Further, the correcting means 12 corrects the desired EGR valve opening degree so that the temperature of EGR gas recirculated in an inlet pipe 3 corresponds to actual temperature based on it. Further, the cancel means 13 detects whether the engine 1 is in a transition state or not and cancels the correction by the correcting means 12 only at the time of the transition state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas recirculation control device for recirculating a part of exhaust gas to an intake system.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG.
EGR pipe 4 that connects exhaust pipe 2 and intake pipe 3
The valve 5 is provided, and the degree of opening of the EGR valve 5 is controlled according to the operating state of the engine 1 (load L, rotation speed Ne, etc.), so that the NOx concentration in the exhaust gas is set to the target NOx concentration. An exhaust gas recirculation control device is known. In this device, as shown in FIG. 5A, the controller 6 sets the target NOx concentration according to the load L and the rotation speed Ne of the engine 1, and sets the opening of the EGR valve 5 to the target NOx concentration. To operate.

However, the above-described exhaust gas recirculation control device cannot sufficiently cope with the increasingly strict exhaust gas regulations in recent years. Therefore, the present applicant has determined that the actual NOx
A feedback control system for obtaining the concentration and correcting the opening degree of the EGR valve 5 so that the actual NOx concentration matches the target NOx concentration has been developed (Japanese Patent Application No. 8-254849). In this system, the temperature of a gas passing therethrough is detected by a temperature sensor 7 provided in the vicinity of the EGR valve 5, and based on the EGR gas temperature T, the actual N
The Ox concentration is determined.

Specifically, at a constant rotation and a constant load,
If the EGR gas temperature T is high, the opening of the EGR valve 5 is large and the actual NOx concentration is low. If the EGR gas temperature T is low, the opening of the EGR valve 5 is small and the actual NOx concentration is high. Therefore, using this correlation, the EGR gas temperature T
From the actual NOx concentration. Then, FIG.
As shown in the figure, the actual NOx concentration obtained in this way is
The opening degree of the EGR valve 5 determined by the load L and the rotation speed Ne is corrected so as to match the Ox concentration.

In such a system, the actual NOx concentration in the exhaust gas is obtained based on the EGR gas temperature T.
As shown in FIG. 5 (b), the target value is the EGR gas temperature,
Similar results can be obtained by controlling the GR gas temperature. That is, the target EGR gas temperature is set according to the operating state of the engine (load L, rotation speed Ne, etc.), the opening degree of the EGR valve 5 is controlled to correspond to the target EGR gas temperature, and the actual EGR gas is detected by the temperature sensor 7. Find the gas temperature T, and find the actual E
The opening degree of the EGR valve 5 is corrected so that the GR gas temperature T matches the target EGR gas temperature.

More specifically, a map M1 of the target EGR gas temperature as shown in FIG. 2B is created according to the load L and the rotation speed Ne of the engine 1 (the map M1 is merely an example). A virtual target EGR valve opening map M2 as shown in FIG. 2 (a) for determining the opening of the EGR valve 5 at that time corresponding to the target EGR gas temperature map M1 is created. Then, the target E is set according to the load L of the engine 1 and the rotation speed Ne.
A target EGR gas temperature is obtained from a GR gas temperature map M1, and the target EGR gas is obtained from a target EGR valve opening map M2.
The opening degree of the EGR valve 5 corresponding to the gas temperature is set. At the same time, the actual EGR gas temperature T at that time is detected by the temperature sensor 7, and the opening of the EGR valve 5 is adjusted so that the actual EGR gas temperature T matches the target EGR gas temperature based on the target EGR gas temperature map M1. Correct the degree.

[0007]

However, in this case,
The direction of the inclination of the target EGR gas temperature map M1 with respect to the load L and the rotation speed Ne does not necessarily match the direction of the inclination of the target EGR valve opening map M2 with respect to the load L and the rotation speed Ne. That is, in FIGS. 2 (a) and 2 (b), when the operation state changes from point A, which is a low rotation and low load, to point B, which is a medium rotation medium load, the target EGR valve opening degree map M2 shows that the valve opening degree While the throttle is narrowed, the target EGR gas temperature map M1 changes from a low temperature to a high temperature (in the direction in which the EGR valve opens, it opens).

For this reason, at the time of transition from the point A to the point B (during acceleration), the temperature sensor 7 detects the actual EGR gas temperature T and compares it with the target EGR gas temperature to correct the opening of the EGR valve 5. When operated, there is a response delay of the EGR gas temperature T (time lag from exhaust gas passing through the EGR pipe 4 to the temperature sensor 7) and a response delay of the temperature sensor T.
Although the opening of the valve 5 is finally closed based on the target EGR valve opening map M2, the opening of the EGR valve 5 is increased during these time lags to increase the actual EGR gas temperature T based on the target EGR gas temperature map M1. The opening is once opened.

This is illustrated in FIG. That is, the operating state of the engine 1 changes from the point A to the point B, and the accelerator opening (or the rack position of the fuel injection pump) opens as shown in FIGS.
When e increases, the target EGR gas temperature increases (in the direction of opening with the valve opening degree) as shown in FIG.
1), the EGR valve 5 is finally operated in the closing direction because the exhaust gas becomes high pressure and high temperature (see map M2). Therefore, at this time, if the actual EGR gas temperature T is detected by the temperature sensor 7 and the above-described feedback control is performed,
Due to the response delay of the EGR gas temperature T and the response delay of the temperature sensor 7, the opening of the EGR valve 5 is initially corrected in the opening direction to increase the EGR gas temperature T as shown in FIG. As a result, the flow rate of the EGR gas becomes excessive, the combustion temperature decreases, and the particulates increase as shown in FIG. 4 (d).

In FIGS. 2 (a) and 2 (b), the load L of the target EGR gas temperature map M1 is changed from the point B which is a medium rotation medium load to the point C which is a high rotation and high load. And the inclination with respect to the rotation speed Ne, and the target EGR valve opening degree map M
Even when the direction of the inclination with respect to the load L and the rotation speed Ne is the same, if the feedback control based on the EGR gas temperature T detected by the temperature sensor 7 is performed during the transition from the point B to the point C, the EGR gas temperature Response delay of T and temperature sensor 7
, The EGR valve 5 is excessively closed and the correction operation is performed, and NOx increases. Conversely, when the point changes from the point C to the point B, the EGR valve 5 is excessively opened and the correction operation is performed, and the particulates increase.

SUMMARY OF THE INVENTION An object of the present invention, which has been made in view of the above circumstances, is to provide an exhaust gas recirculation control device for correcting the opening of an EGR valve by feeding back the EGR gas temperature. An object of the present invention is to provide an exhaust gas recirculation control device that eliminates adverse effects due to a response delay of a temperature and a response delay of a temperature sensor.

[0012]

In order to achieve the above object, an exhaust gas recirculation control device according to the present invention uses an EGR valve provided in an EGR pipe communicating between an exhaust system and an intake system to determine an opening degree of an engine. Control means for controlling the opening degree of the EGR valve by the control means according to the temperature of the EGR gas recirculated to the intake system, and detecting whether or not the engine is in a transient state. And a canceling means for canceling the correction by the correcting means only in the transient state.

According to the present invention, when the engine is in a transient state, the canceling means cancels the correction based on the EGR gas temperature, so that an adverse effect due to a response delay of the EGR gas temperature can be eliminated. Further, when the engine is in a steady state, the canceling means does not operate, so that the correction is performed based on the temperature of the EGR gas by the correcting means, and the NOx concentration (EGR gas temperature) is accurately controlled.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, an exhaust pipe 2 of an engine 1
Between the (exhaust system) and the intake pipe 3 (intake system), an EGR pipe 4 for communicating these is interposed. An EGR valve 5 is provided in the vicinity of the connection between the EGR pipe 4 and the intake pipe 3, the opening of which is adjusted to make the flow passage area in the pipe variable. EG
In the vicinity of the R valve 5, a temperature sensor 7 for detecting the temperature of the EGR gas passing through the inside of the EGR pipe 4 (hereinafter referred to as EGR gas temperature) is provided.

A temperature sensor 7 and an opening adjustment unit 8 for the EGR valve 5
The (solenoid, etc.) is connected to the controller 6 so that the EGR gas temperature T and the opening of the EGR valve 5 are input to the controller 6. Further, the controller 6 is connected to the engine speed sensor 9 and the load sensor 10 of the engine 1, and receives the engine speed Ne and the load L. The rotation speed sensor 9 is, for example, a sensor that counts the rotation speed of a crankshaft.
For 0, for example, an accelerator opening sensor, a rack position sensor of a fuel injection pump, or the like is used.

In accordance with the operating state of the engine 1, that is, the engine speed Ne and the load L, the controller 6
Control means 11 for controlling the opening of the EGR valve 5 is provided. The control means 11 writes a target EGR gas temperature map in which the target EGR gas temperature is written such that the NOx concentration in the exhaust gas becomes a target value in accordance with the engine speed Ne and the load L as shown in FIG. M1 (the map M1 is merely an example) and an EGR corresponding to the target EGR gas temperature map M1 as shown in FIG.
Target EGR valve opening map M2 in which the opening of valve 5 is written
have.

The target EGR gas temperature map M1 has a target N
The target NOx concentration is determined by the manner of setting the Ox concentration, but cannot be determined unconditionally because the target NOx concentration varies depending on the exhaust gas regulation mode, drivability, fuel efficiency, and the like. The target EGR gas temperature map M1 shown in FIG. 2 (b) shows a general tendency to the last, and is set in a mountain shape with the middle load during rotation at the top. This is because the EGR amount is reduced at a high rotation high load where power is required or at a low rotation low load where the combustion temperature is low and NOx is not a problem, and the EGR amount is increased as a measure against NOx at a medium rotation medium load frequently used in normal driving. That's why. The fact that the EGR gas temperature T detected by the temperature sensor 7 is high means that the EGR gas temperature T is constant at a constant rotation and a constant load.
The opening degree of the valve 5 is large, the EGR amount is large, and the EGR gas temperature T
Is low, it means that the opening of the EGR valve 5 is small and the EGR amount is small.

The target EGR gas temperature map M1 is represented by E
When converted to the opening of the GR valve 5, the target EGR valve opening map M2 shown in FIG. Here, since the EGR gas (exhaust gas) temperature T changes depending on the engine speed Ne and the load L, the high degree of the EGR gas temperature T does not necessarily mean that the opening degree of the EGR valve 5 is large. Also,
The target EGR valve opening degree generally opens in a low-rotation low-load condition with a large excess air ratio and closes in a high-rotation high-load condition with a small excess air ratio in order to prevent particulates and smoke.

The controller 6 includes an intake pipe 3
Correction means 12 is provided for correcting the opening of the EGR valve 5 based on the target EGR valve opening map M2 of the control means 11 in accordance with the temperature T of the EGR gas which is recirculated. That is, the correction unit 12 compares the actual EGR gas temperature T detected by the temperature sensor 7 with the target EGR gas temperature obtained from the target EGR gas temperature map M1, and
In order that the R gas temperature T matches the target EGR gas temperature,
The opening of the EGR valve 5 determined by the target EGR valve opening map M2 is corrected.

Further, the controller 6 detects whether or not the engine 1 is in a transient state and cancels the correction by the correcting means 12 only in the transient state. Is provided. Cancellation means 1
3 calculates the differential value of the engine speed Ne and the load L,
If the differential value exceeds a predetermined threshold value, it is determined to be in a transient state, and if it is less than the threshold value, it is determined to be in a steady state.

More specifically, when the steady state changes to the transient state, the transient state is immediately determined when the differential value of the engine speed Ne and the load L exceeds the threshold value, and the transient state is changed to the steady state. In the case of a change, a predetermined time is provided in consideration of the responsiveness of the EGR gas temperature T and the responsiveness of the temperature sensor 7 described above, and the differential value of the engine speed Ne and the load L becomes equal to or less than the threshold value. Is determined to be in a steady state after a certain period of time has passed. However, when the responsiveness of the EGR gas temperature T and the responsiveness of the temperature sensor 7 are sufficiently fast, it is not necessary to provide the fixed time.

The operation of this embodiment will be described with reference to FIG.

As shown in FIG. 3, first, the operating state of the engine 1 is detected (st1). Specifically, the engine speed Ne is detected by the engine speed sensor 9, and the load L is detected by the load sensor 10. Then, based on the engine speed Ne and the load L, the target EGR in FIG.
The target EGR valve opening is read from the valve opening map M2 (st2). Then, the actual opening of the EGR valve 5 is
It is read by the opening adjustment section 8 of the valve 5 (st3).

Then, based on the magnitude relationship between the engine speed Ne, the differential value of the load L, and the threshold value, the engine 1
It is determined whether or not is in a transient state (st4). If it is not a transient state, that is, if it is a steady state, the target EGR gas temperature is read from the target EGR gas temperature map M1 in FIG. 2B based on the engine speed Ne and the load L.
(st6). Then, the actual EGR detected by the temperature sensor 7
A comparison is made between the gas temperature T and the target EGR gas temperature, and if there is a deviation, how much the opening degree of the EGR valve 5 should be corrected to make the actual EGR gas temperature T match the target EGR gas temperature. The temperature correction amount is calculated (st7).

Then, based on the above temperature correction amount calculation,
The actual operation amount of the EGR valve 5 is calculated (st8).
The manipulated variable is output to the opening adjustment unit 8 of the EGR valve 5 (st
9). Thus, when the engine 1 is in the steady state,
Since the correction using the actual EGR gas temperature T as the feedback amount is performed by the correction means 12, the opening degree of the EGR valve 5 is accurately controlled so as to become the target EGR gas temperature (that is, the target NOx concentration).

If it is determined in st4 that the engine 1 is in the transient state, the temperature correction in st5 to st7 is not performed (st10). As described above, when the engine 1 is in the transient state, the feedback correction based on the actual EGR gas temperature T is cancelled. Excessive opening / closing of the opening of the EGR valve 5 (see FIG. 4D) can be avoided, and its adverse effect (see FIG. 4E) can be prevented.

[0028]

As described above, according to the exhaust gas recirculation control device of the present invention, when the engine is in a steady state, the NOx concentration can be accurately controlled by correcting the EGR valve opening with the EGR gas temperature, and the transient state can be controlled. By canceling the temperature control, it is possible to avoid an excessive opening / closing of the EGR valve opening due to a response delay of the EGR gas temperature or a response delay of the temperature sensor. Thus, an increase in NOx and particulates can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an exhaust gas recirculation control device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a target EGR valve opening map and a target EGR gas temperature map provided in a control means.

FIG. 3 is a flowchart showing a control flow of the exhaust gas recirculation control device.

FIG. 4 shows the accelerator opening, engine speed, target EGR gas temperature, and EGR when changing from a steady state to a transient state.
It is a figure which shows a valve operation amount and a particulate.

FIG. 5 is an explanatory diagram showing a procedure for determining the opening degree of an EGR valve previously proposed by the present applicant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust system 3 Intake system 4 EGR pipe 5 EGR valve 11 Control means 12 Correction means 13 Canceling means T Temperature of EGR gas Ne, L Parameter indicating operation state

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 45/00 360 F02D 45/00 360C

Claims (1)

[Claims] A control means for controlling an opening degree of an EGR valve provided in an EGR pipe communicating between an exhaust system and an intake system in accordance with an operation state of an engine, and an EGR recirculated to the intake system.
Correction means for correcting the degree of opening of the EGR valve by the control means in accordance with the temperature of the gas, and cancellation means for detecting whether or not the engine is in a transient state and canceling the correction by the correction means only in the transient state. An exhaust gas recirculation control device comprising: