JPH07166964A - Egr control device for diesel engine - Google Patents

Abstract

PURPOSE:To enable an EGR ratio to be quickly corrected by providing an exhaust pressure interference device for fluctuating pressure within an exhaust passage, and determining the exhaust pressure end time at which fluctuation of the pressure within the exhaust passage ends as operation of the interference device is finished, and restarting renewal of a correction at the end time. CONSTITUTION:In a device in which the opening of an EGR (exhaust gas recycling) valve 35 is adjusted by an actuator 36, target and measured values of an EGR ratio (= EGRflow rate/intake flow rate) are calculated, 37, 40, according to detected values of operating conditions, and a correction HOS for correcting a control command so that the target and measured values of EGR ratio coincide with each other is calculated 41 and the control command to the actuator 36 is determined 42. An exhaust pressure interference device 43 for fluctuating exhaust pressure is installed in an exhaust passage 31 and the exhaust pressure fluctuation time during which pressure within the exhaust passage 31 is fluctuated by operation of the device 43 is determined 44, and renewal of the learned correction HOS is stopped 45 during the exhaust pressure fluctuation, and the end time of the exhaust pressure fluctuation with the finish of operation of the exhaust pressure interference device 43 is determined 46, and renewal of the correction HOS is restarted 47 at the exhaust pressure end time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an EGR control device that recirculates a part of exhaust gas into intake air in order to reduce NOx emitted from a diesel engine.

[0002]

2. Description of the Related Art The required amount of exhaust gas recirculation varies depending on operating conditions, and depending on the operating conditions, EGR gas impairs the output characteristics of the engine, etc., so engine output performance and exhaust performance are balanced. In this way, the target value of the EGR rate (= EGR flow rate / intake air flow rate) according to the operating condition is set in advance, and the target EGR rate that matches the current operating condition is obtained by referring to the map of this target value, By converting this target EGR rate into a control command value and giving this to each actuator such as the EGR valve and the intake throttle valve,
It controls the opening of the valve and the intake throttle valve.

However, due to a command error with respect to the control command value of the EGR valve actuator or the like, or carbon or the like contained in the EGR gas adheres to the EGR valve, the actual E
The GR rate may deviate from the target value and the exhaust performance may deteriorate.

Therefore, for example, Japanese Patent Publication No. 61-1107
The EGR control device disclosed in Japanese Patent Publication detects the actual intake air flow rate and the opening degree of the EGR valve, compares the measured value of the intake air flow rate with a preset target intake air flow rate, and E
The control command value to the EGR valve actuator is corrected so that the target value of the GR rate and the measured value match. As a result, when the exhaust gas recirculation amount due to carbon deposition decreases, control is performed to increase the opening degree of the EGR valve, and the desired EGR flow rate is obtained.

[0005]

However, in such a conventional diesel engine EGR control device, for example, a filter regenerating device for collecting particulates in the middle of the exhaust passage, an exhaust brake, or a variable muffler. In an operating state in which the exhaust pressure interference device operates, the pressure in the exhaust passage fluctuates rapidly. Therefore, if the control command value to the EGR valve actuator is corrected so that the target value of the EGR rate and the measured value match. However, there is a problem in that sufficient control responsiveness cannot be obtained and the control accuracy is rather lowered.

In view of the above problems, the present invention aims to improve the control accuracy of the EGR rate in an EGR control device for a diesel engine.

[0007]

According to the present invention, an exhaust passage 31 is provided.
And an EGR passage 33 that connects the intake passage 32 with the
The EGR valve 35 that opens and closes the R passage 33, and the EGR valve 3
The actuator 36 capable of variably adjusting the opening degree of No. 5, means 37 for calculating the target value R _ET of the EGR rate according to the detected value of the operating condition, and the measured value R of the EGR rate according to the detected value of the operating condition A means 40 for calculating _E and a target value R _{ET of the} EGR rate
A correction value HOS for correcting the control command value FQ _E to the EGR valve actuator 36 so that the measured value R _E and the measured value R _E match.
EG using the means 41 for calculating
In an EGR control device for a diesel engine, which comprises means 42 for determining a control command value FQ _E to the R valve actuator 36, an exhaust pressure interference device installed in the middle of the exhaust passage 31 for varying the pressure in the exhaust passage 31. 43
And the exhaust passage 3 by the operation of the exhaust pressure interference device 43.
Means 44 for determining when the exhaust pressure fluctuates when the pressure 1 fluctuates
A means 45 for stopping the update of the correction value HOS when the exhaust pressure changes, and a means 46 for determining the exhaust pressure convergence time when the pressure fluctuation of the exhaust passage 31 converges due to the termination of the operation of the exhaust pressure interference device 43, Correction value HOS when exhaust pressure converges
And a means 47 for resuming the update of.

[0008]

In normal operation in which the exhaust pressure interference device 43 does not operate, for example, the filter installed in the exhaust passage 31 is clogged, the air cleaner element installed in the intake passage 32 is clogged, or carbon or the like is deposited on the EGR passage 33. When the actual measurement value R _E of the EGR rate becomes larger than the target value R _{ET due to the} above reasons, the correction value HOS is used to correct the opening degree of the EGR valve 35, and the EGR rate is corrected to the target value R _ET. Can be approached to.

When the pressure in the exhaust passage 31 fluctuates due to the operation of the exhaust pressure interference device 43, the update of the correction value HOS is stopped to stop the exhaust passage 31.
It is possible to prevent the control accuracy of the EGR rate from deteriorating due to the pressure fluctuation.

Before and after the exhaust pressure interference device 43 operates, the correction value HOS is restarted at the time of exhaust pressure convergence when the pressure fluctuation in the exhaust passage 31 converges as the operation of the exhaust pressure interference device 43 ends. The EGR rate can be promptly corrected to an appropriate value in accordance with the change in exhaust pressure that occurs in 1.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a diesel engine mounted on a vehicle will be described below with reference to the accompanying drawings.

As shown in FIG. 2, as an exhaust pressure interference device, two filters 12 for collecting particulates contained in the exhaust gas are installed in parallel in the exhaust passage 1. An on-off valve 13 is provided at the inlet of each filter 12, and is fully opened during normal operation and opened to a predetermined opening when the filter 12 is regenerated through an actuator (not shown) that operates based on a signal from the control unit 11. The valve is closed. When the filters 12 are regenerated, the amount of exhaust gas passing through each filter 12 is selectively reduced, and an electric heater (not shown) is energized to burn the particulate matter deposited on the filters 12.

EGR which connects the exhaust passage 1 and the intake passage 2
An EGR valve 5 is provided in the passage 3. The valve lift of the EGR valve 5 is adjusted by the duty control valve (actuator) 6, and the valve lift increases in proportion to the duty ratio (energization time ratio per constant time period) given to the control valve 6. As the duty ratio increases, the ratio of introducing the constant negative pressure from the vacuum pump 7 becomes higher than the atmospheric pressure, the control negative pressure to the working chamber 5A of the EGR valve increases, and the valve lift increases. A stroke sensor 15 detects the valve lift of the EGR valve 5.

An intake throttle valve 8 is provided in the intake passage 2 upstream of the connection with the EGR passage 3. The intake throttle valve 8 is closed stepwise by adjusting the opening degree of the valve by a duty control valve (actuator) 9 to adjust the control negative pressure to the diaphragm actuator 10. Even if the lift of the EGR valve 5 is the same, the differential pressure across the EGR valve 5 increases. Therefore, if the control negative pressure to the diaphragm actuator 10 is increased and the intake throttle valve 8 is closed, the differential pressure across the EGR valve 5 increases and the EGR flow rate increases. Will increase.

The EGR valve 5 and the actuator 1
Both 0s have a diaphragm, but not limited to this, a step motor or the like may be used. When the step motor is used, the opening degree of the EGR valve 5 with respect to the input is more stable, and thus the frequency of feedback control can be reduced.

A control unit 11 composed of a microcomputer is provided to control each of the control valves 6 and 9 in accordance with the detected value of the operating condition. As shown in FIG. 3, in the control unit 11, the opening degree of the intake throttle valve 8 is set to the engine speed N.
Or the fresh air flow rate Qa detected by the aerometer 17
A map 21 for controlling the TVO1, TVO2, and TVO3 in three stages according to the above is provided. A map 22 in which the basic EGR flow rate Q _E is set according to the opening of the intake throttle valve 8 according to the engine speed N and the engine load Tp represented by the lever opening of the fuel injection pump, for example, is provided. The valve lift of the EGR valve 5 is controlled so that the retrieved basic EGR flow rate Q _E is obtained.

However, since the exhaust pressure rises as the amount of collected particulate matter by the filter 12 increases, the actual EGR rate deviates from the target value as the exhaust pressure rises.

As a countermeasure against this, as shown in FIG.
The EGR valve 5 is temporarily closed in a region where R (exhaust gas recirculation) is performed, the EGR rate R _E is calculated from the amount of change in the fresh air flow rate Qa due to opening and closing of the EGR valve 5, and the calculated actual measured value R _E And E
A learning correction value HOS for correcting the control command value to the EGR valve control valve 6 is calculated so that the target value R _ET of the GR rate coincides, and the valve lift target of the EGR valve 5 is calculated using this learning correction value HOS. The control command value P to the EGR valve control valve 6 according to the value
Determine EDTY.

In calculating the actual measurement value R _E of the EGR rate, as shown in FIG. 4, for example, it is obtained when the EGR valve 5 is opened every time the vehicle travels for a certain distance or for a certain time (for example, 20 minutes). Detected fresh air flow rate Q _ON and E
The detected value Q _OFF of the fresh air flow rate obtained when the EGR is stopped when the GR valve 5 is closed is read, and the deviation ΔQ (=
Q the _OFF -Q _ON) to the measured value R _E of the EGR rate on the basis of R _E =
Calculated as ΔQ / Q _OFF .

At a certain operating point of the engine, the sum of the fresh air flow rate Qa and the EGR flow rate (intake air flow rate) taken by the piston in one stroke is constant regardless of whether the EGR valve 5 is open or closed. Therefore, by temporarily closing the EGR valve 5, the fresh air flow rate Q _OFF after closing the EGR valve 5 is equal to the fresh air flow rate Q _ON before the EGR valve 5 is closed.
Is the value obtained by subtracting the EGR flow rate from. This makes E
Deviation Δ in fresh air flow rate detected before and after the GR valve 5 is closed
EGR flow rate is calculated from Q (= Q _ON -Q _OFF ) and EGR flow rate is calculated.
It is possible to accurately calculate the actual measurement value R _{E of the} rate.

If the measured value R _E of the EGR rate deviates from the target value R _ET due to an increase in exhaust pressure, etc., the learning correction value HOS
The, HOS = HOS '- {( R E / R ET) -1} / 2 ... is calculated as. However, HOS 'is the previous learning correction value, and its initial value is 1.

Subsequently, the learning correction value HOS and the basic EG
Using the R flow rate Q _E , the final EGR flow rate FQ _E is calculated as FQ _E = Q _E / HOS.

The target stroke TST of the EGR valve 5 preset according to the final EGR flow rate FQ _E obtained.
E is searched from the preset map 23, and the basic duty value PEDTY output to the control valve 6 is searched from the preset map 24.

The basic duty value output to the control valve 6 is feedback-controlled based on the basic duty value PEDTY so that the target stroke TSTE of the EGR valve 5 and the detection value of the stroke sensor 15 match. .

When the EGR valve is driven by a step motor, the target step number TSRTE is retrieved from the map 25 preset according to the obtained final EGR flow rate FQ _E and is output. Good.

In this way, for example, the amount of particulates deposited on the filter 12 increases and the exhaust pressure rises, or the air cleaner element is clogged, and so on.
When the measured value R _E of the GR rate is larger than the target value R _ET ,
{(R _E / R _ET ) −1} in the expression becomes a positive value,
By reducing the learning correction value HOS, the final EGR
The flow rate FQ _E is corrected to the decreasing side and brought close to the basic EGR flow rate Q _E.

When the measured value R _E of the EGR rate becomes smaller than the target value R _ET due to insufficient opening of the intake throttle valve 8 or the like, {(R _E / R _ET ) -1} in the equation is It becomes a negative value, and by increasing the learning correction value HOS, the final E
The GR flow rate FQ _E is corrected to the increasing side, and the basic EGR flow rate Q _E
Can be approached to.

However, during regeneration of the filter 12, the pressure in the exhaust passage 1 fluctuates abruptly, so that the learning correction value HO is adjusted so that the target value R _ET of the EGR rate and the actual measurement value R _E match.
If S is updated, sufficient control responsiveness cannot be obtained, and the control accuracy of the EGR rate is rather deteriorated.

In response to this, the control unit 1
1, the learning correction value H when the filter 12 is reproduced.
Control is performed to stop the update of the OS and restart the update of the learning correction value HOS at the end of the reproduction of the filter 12.

The flow chart of FIG. 5 shows this control program executed by the control unit 11, which is executed at regular intervals.

To explain this, first, step 1
If it is determined that the regeneration of the filter 12 is started, the process proceeds to step 2 to regenerate the filter 12.

Until it is determined in step 3 that the regeneration of the filter 12 is completed, the routine proceeds to step 7, where the update of the learning correction value HOS is stopped and 1 / _E of the basic EGR flow rate Q _E is reached.
The valve lift of the EGR valve 5 is controlled so that the value of 2 is obtained.

By stopping the update of the learning correction value HOS during the regeneration of the filter 12 as described above, it is possible to prevent the control accuracy of the EGR rate from being deteriorated due to the exhaust pressure change during the regeneration.

When it is determined in step 3 that the regeneration of the filter 12 is completed, the routine proceeds to step 4, where the EGR flow rate FQ _E is obtained while the learning correction value HOS is updated at every constant distance travel. The valve 5 and the intake throttle valve 8 are controlled.

In this way, by restarting the update of the learning correction value HOS at the end of the regeneration of the filter 12, the EGR rate can be promptly corrected to an appropriate value in response to the exhaust pressure change before and after the regeneration. .

When it is determined in step 5 that the difference between the first learning correction value HOS ₁ and the current learning correction value HOSn exceeds the predetermined value, the process proceeds to step 6 to issue the regeneration permission of the filter 12. ing. The regeneration permission of the filter 12 may be issued every time the vehicle is driven for a predetermined time (for example, one hour).

The flow chart of FIG. 6 shows an example of control of the basic EGR flow rate Q _E performed in the process of changing the opening degree of the intake throttle valve 8 executed in the control unit 11, which is executed at regular intervals. It

To explain this, first, step 1
When it is determined in 1 that the operating condition is such that the opening degree of the intake throttle valve 8 is switched from TVO1 to TVO2, in step 12, counting of the switching delay time TM is started, and in step 1
Until it is determined in 3 that the delay time TM exceeds 400 ms, the routine proceeds to step 13, where the basic EGR flow rate Q _E is Q _E = (TM / 400) .Q _E2 + {1- (TM / 400)}. It is calculated as Q _E1 . However, Q _E2 and Q _E1 are basic EGR flow rates when the opening degree of the air throttle valve 8 is set to TVO2 and TVO1.

On the other hand, when it is determined in step 13 that the delay time TM exceeds 400 ms, the routine proceeds to step 13 where the basic EGR flow rate Q _{E is set} to Q _E2 .

As the exhaust pressure interference device for varying the pressure in the exhaust passage, the device provided with the filter regeneration device has been described above. However, an exhaust brake for narrowing the exhaust passage at the time of braking the vehicle or a passage in the muffler is used. It is conceivable to apply the present invention to a variable muffler that is switched to adjust the exhaust sound pressure and the like. In this case, it is possible to prevent the EGR rate control accuracy from deteriorating at the time of operating the exhaust brake or at the time of switching the flow path of the variable muffler, and to promptly adjust the EGR rate to an appropriate value in response to the exhaust pressure change occurring before and after this operation. It can be corrected to a value.

[0041]

As described above, the EGR control device for the diesel engine of the present invention is provided with the exhaust pressure interference device for changing the pressure of the exhaust passage, and the exhaust pressure interference device for changing the pressure of the exhaust passage by the operation of the exhaust pressure interference device. It determines when the atmospheric pressure fluctuates, stops updating the correction value when the exhaust pressure fluctuates, and determines when the exhaust pressure converges when the pressure fluctuations in the exhaust passage converge due to the end of the operation of the exhaust pressure interference device,
The configuration that restarts the update of the correction value when the exhaust pressure converges prevents the deterioration of the control accuracy of the EGR rate due to the operation of the exhaust pressure interference device, and at the same time reduces the exhaust pressure change that occurs before and after the operation of the exhaust pressure interference device. Correspondingly, the EGR rate can be promptly corrected to an appropriate value to enhance the exhaust performance.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the present invention.

FIG. 2 is a system diagram of an EGR control device showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing the contents of EGR control.

FIG. 4 is a timing chart showing the contents of EGR control.

FIG. 5 is a flowchart showing the details of filter regeneration and EGR control.

FIG. 6 is a flowchart showing the contents of EGR control when the intake throttle valve is activated.

[Explanation of symbols]

 31 Exhaust Passage 32 Intake Passage 33 EGR Passage 35 EGR Valve 36 Actuator 37 EGR Rate Target Value Calculating Means 41 Correction Value Calculating Means 42 Control Command Value Determining Means 43 Exhaust Pressure Interference Device 44 Exhaust Pressure Fluctuation Determining Means 45 Update Stopping Means 46 Exhaust pressure convergence means 47 Update restart means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area F02D 43/00 TK

Claims (1)

[Claims] 1. An EGR passage that connects an exhaust passage and an intake passage, an EGR valve that opens and closes the EGR passage, an actuator that can variably adjust the opening of the EGR valve, and an EGR valve that is responsive to a detected value of an operating condition. A means for calculating a target value of the EGR rate, a means for calculating an actually measured value of the EGR rate according to a detected value of an operating condition, and the EGR valve actuator so that the target value of the EGR rate and the actually measured value match. In the EGR control device for a diesel engine, which comprises a means for calculating a correction value for correcting a control command value to the EGR valve, and a means for determining a control command value for the EGR valve actuator using the correction value, Exhaust pressure interference device that is installed in the middle of the passage to change the pressure of the exhaust passage, and when the exhaust pressure changes when the pressure of the exhaust passage changes due to the operation of the exhaust pressure interference device Means for stopping the update of the correction value when the exhaust pressure fluctuates, a means for determining the exhaust pressure convergence time when the pressure fluctuation of the exhaust passage converges due to the end of the operation of the exhaust pressure interference device, and the exhaust pressure An EGR control device for a diesel engine, comprising: a means for resuming the update of the correction value at the time of convergence.