JPH08144866A - Exhaust gas recirculation control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To improve responsiveness at the time of transition as stability in a steady state is secured by thrusting a drive output limit in the case where the computed result of a target value of exhaust gas recirculation quantity is given for reducing useless time until the computed result of a target opening is reflected on control output. CONSTITUTION: A control unit 11 computes EGR quantity on the outputs of an air flow meter 7 and of a crank angle sensor 14 or the like to control an EGR valve 4. In controlling the EGR valve 4, the opening of the EGR valve 4 is regulated according to the target value of computed exhaust gas recirculation quantity, and the regulation of exhaust gas recirculation is executed in a fixed regulation period (main loop), and moreover in a regulation period shorter than the main loop (minor loop). When the computed result of target value is given, the exhaust gas recirculation regulating process carried out; by a minor loop process means is thrusted at least once into the main loop exhaust gas recirculation regulating process to secure transient stability.

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 (hereinafter referred to as "EGR") control device for an internal combustion engine, and more particularly to a technique for improving stability in a steady state and improving responsiveness in a transient state.

[0002]

2. Description of the Related Art Conventionally, an EGR control device for recirculating a part of exhaust gas to an intake system is known as one of the techniques for reducing the amount of NOx generated in an internal combustion engine (hereinafter referred to as engine). As a conventional EGR control device, for example, there is one shown in FIG.

That is, in the figure, a collector 2A that branches from the exhaust manifold 1 and merges with the intake manifold 2
Is provided with an EGR pipe 3, and an EGR valve 4 for controlling the EGR amount is interposed in the EGR pipe 3.
The EGR valve 4 is composed of a valve body 5 and a step motor 6 as an actuator for driving the valve body.
The valve body driving means is not limited to the step motor 6 described above, but the engine negative pressure is adjusted using, for example, a solenoid, and the engine negative pressure is applied to the diaphragm so that the valve body connected to the diaphragm is used. A so-called negative pressure control type actuator that drives may be used.

The control unit 11 arithmetically determines the EGR amount based on the outputs from the air flow meter 7, the crank angle sensor 14 and the water temperature sensor 15, and outputs a pulse to the EGR valve 4. Here, as shown in FIG. 13, the processing for calculating the target opening degree of the EGR valve 4 and the processing for outputting the drive signal to the EGR valve 4 are configured to be performed in independent time periods, It is general that each has an optimal processing cycle.

That is, the target value of the exhaust gas recirculation amount, that is, EGR
Since the process of calculating the target opening of the valve involves a large amount of processing such as searching the target opening in a table or a map according to the operating state of the engine, calculation is performed according to the limit of the capacity of the central processing unit of the control unit 11. It is processed. On the other hand, the process of adjusting the exhaust gas recirculation amount, that is, the process of outputting the drive signal to the EGR valve 4 (control output process) is output in accordance with the characteristics of the actuator used for driving the valve body.

Therefore, the cycle of processing for calculating the target opening of the EGR valve 4 and the cycle of processing for outputting a drive signal to the EGR valve 4 are generally different.

[0007]

However, in such a conventional EGR control device, the EGR valve 4 is used.
Since the target opening degree of is obtained from the map of the engine rotation speed and the intake air amount, it is likely to be accompanied by a minute fluctuation even during steady operation. For this reason, if the control output processing is performed in a cycle close to the target opening calculation cycle, the driving direction of the step motor 6 of the EGR valve 4 is frequently reversed, which is not only extremely disadvantageous in step-out, but also in steady operation performance. It was also affected.

Therefore, the driving stability of the step motor 6 in the engine steady operation state is utilized by utilizing the structure in which the target opening calculation process and the control output process are independently time-synchronized. Considering the above, as shown in FIG. 16, it is possible to make the control output processing cycle slower than the target opening calculation processing cycle. However, if the control output processing cycle is made slower than the target opening calculation processing cycle in this way, as is clear from the figure, the dead time until the target opening calculation result is reflected in the control output becomes large, and there is a transition time. However, there is a problem that the responsiveness of is deteriorated.

Such a problem is that E
Excessive or insufficient GR amount makes it difficult to secure exhaust performance such as increase in NOx, causes misfire, causes deceleration shock due to misfire, increases catalyst capacity, increases size of EGR valve, etc. The necessity increases cost and deteriorates drivability. In view of the above conventional problems, the present invention executes an exhaust gas recirculation amount adjustment process by interrupting at least once when an exhaust gas recirculation amount target value calculation result is output in an internal combustion engine exhaust gas recirculation control device. Or
Depending on the state of the previous exhaust gas recirculation amount adjustment processing, the interrupt is prohibited so that the response maximum speed of the exhaust gas recirculation amount adjustment means is not exceeded, or the exhaust gas recirculation amount adjustment processing cycle is set to the target value and the current exhaust gas return amount. The purpose of the present invention is to improve the responsiveness at the time of transition while ensuring the stability in the steady state by making it possible to change the cycle to the optimum period according to the difference in the flow rate adjustment amount.

[0010]

Therefore, according to the invention described in claim 1, as shown in FIG. 1, exhaust gas recirculation means for recirculating exhaust gas of an internal combustion engine to an intake system, and engine operation for detecting an engine operating state. State detection means, exhaust gas recirculation amount target value calculation means for calculating a target value of the exhaust gas recirculation amount in time synchronization according to the engine operating state detected by the engine operating state detection means,
The exhaust gas recirculation amount by the exhaust gas recirculation device is adjusted directly or indirectly according to the target value of the exhaust gas recirculation amount calculated by the exhaust gas recirculation amount target value calculation device, and the exhaust gas recirculation amount adjustment is processed in a predetermined adjustment cycle. Main loop exhaust gas recirculation amount adjusting means, minor loop exhaust gas recirculation amount adjusting means for processing the exhaust gas recirculation amount adjustment in a shorter adjustment cycle than the main loop exhaust gas recirculation amount adjusting means, and the exhaust gas recirculation amount target value computing means An interrupt means for interrupting the exhaust gas recirculation amount adjusting process by the minor loop processing device at least once in the exhaust gas recirculating amount adjusting process by the exhaust gas recirculating amount adjusting device of the main loop when the target value calculation result by It was configured to include.

According to a second aspect of the present invention, as shown in FIG. 1, storage means for storing the time of the present and previous exhaust gas recirculation amount adjustment intervals, and the storage value stored by the storage means is a set value or more. 2. Exhaust gas recirculation control for an internal combustion engine according to claim 1, further comprising: a prohibition unit that temporarily prohibits interruption of the exhaust gas recirculation amount adjustment processing by the exhaust gas recirculation amount adjustment unit of the minor loop. apparatus.

According to the third aspect of the present invention, as shown in FIG. 1, a target value deviation amount calculation for calculating a target value deviation amount which is a difference between the current exhaust gas recirculation amount adjustment amount and the present exhaust gas recirculation amount target value. Means, and an exhaust gas recirculation amount adjustment processing cycle changing means for changing the exhaust gas recirculation amount adjustment processing cycle by the exhaust gas recirculation amount adjusting means of the minor loop according to the target value deviation amount calculated by the target value deviation amount calculating means, The exhaust gas recirculation control device for an internal combustion engine according to claim 1 or 2, characterized in that the exhaust gas recirculation control device is included.

[0013]

According to the first aspect of the present invention, the drive output control is interrupted when the target value calculation result of the exhaust gas recirculation amount is output, so that the target opening calculation result is reflected in the control output. The dead time can be reduced, and the stability in the steady state can be secured, and the response in the transient state can be improved.

According to the second aspect of the present invention, the interrupt is prohibited when the current and previous exhaust gas recirculation amount adjustment intervals are short, so that the maximum response speed of the exhaust gas recirculation means may be exceeded. Absent. According to the third aspect of the present invention, when the target value is updated, the adjustment processing cycle corresponding to the exhaust gas recirculation amount target value and the current exhaust gas recirculation amount adjustment amount is immediately given, and the exhaust gas recirculation means performs the exhaust at the maximum response speed. It is possible to continue driving the reflux means. As a result, when there is a large deviation between the current exhaust gas recirculation amount adjustment amount and the exhaust gas recirculation amount target value (for example, during rapid acceleration, sudden deceleration, shift operation, etc.), a minimal response delay due to the exhaust gas recirculation amount adjusting means of the minor loop. Although the target value can be followed by, the stability can be secured by the long cycle of the adjustment timing for the small oscillation of the target value in the steady state.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. In FIG. 2, which shows a common system configuration of an embodiment of the invention described in claims 1 to 3, as described above, an EGR pipe that branches from the exhaust manifold 1 and communicates with a collector 2A where the intake manifold 2 is assembled. 3 is provided, and the EGR pipe 3 is provided with an EGR valve 4 as EGR amount adjusting means for adjusting the EGR amount. This E
The GR valve 4 is composed of a valve body 5 and a step motor 6 as an actuator for driving the valve body. Further, the actuator for driving the valve element is not limited to the step motor 6 described above, but a valve connected to the diaphragm is adjusted by adjusting the engine negative pressure by using a solenoid or the like and applying the engine negative pressure to the diaphragm. A so-called negative pressure control type actuator that drives the body may be used.

The intake pipe 2a is provided with an air flow meter 7 for detecting an intake air flow rate introduced through an air cleaner (not shown) and a throttle valve 8 for controlling the intake air flow rate in cooperation with an accelerator pedal. An electromagnetic fuel injection valve 9 is provided for each cylinder. The throttle valve 8 is provided with a potentiometer-type throttle sensor 10 for detecting the opening of the valve 8.

The fuel injection valve 9 is opened and driven by an injection pulse signal from a control unit 11 containing a microcomputer to inject and supply fuel. An air-fuel ratio sensor (hereinafter, referred to as an O ₂ sensor) 12 is provided in the collection portion of the exhaust manifold 1 as a means for detecting the air-fuel ratio of the intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas.

A three-way catalyst 13 for purifying HC, CO _2, and NOx in the exhaust gas under a stoichiometric air-fuel ratio atmosphere is provided in the exhaust pipe 1a downstream of the O ₂ sensor 12. A crank angle sensor 14 is built in a distributor (not shown), and the crank angle unit angle signal output from the crank angle sensor 14 in synchronization with the engine rotation is counted for a certain period of time or the crank reference angle signal of the crank reference angle signal is output. The engine speed is detected by measuring the cycle. Further, a water temperature sensor 15 for detecting the cooling water temperature is provided.

Reference numeral 16 is a spark plug. The control unit 11 arithmetically determines the fuel injection amount and the ignition timing based on the output signals from the air flow meter 7, the throttle sensor 10, and the crank angle sensor 14, and outputs pulse signals to the fuel injection valve 9 and the ignition plug 16, respectively. Output. At this time, the control unit 11 controls the water temperature sensor 15
And the output from the O ₂ sensor 12 are used to correct the fuel injection amount and the ignition timing.

On the other hand, the control unit 11 includes an air flow meter 7, a crank angle sensor 14 and a water temperature sensor 1.
EGR amount is calculated and determined based on the output from EGR
A pulse is output to the valve 4 and the ignition timing is corrected. Here, the EGR control of the embodiment of the invention according to claims 1 and 2 by the control unit 11 is shown in FIG.
This is executed as shown in the flowchart of FIG. Unless otherwise specified, the condition determination unit of the flowchart branches downward when the determination result is “YES” and laterally when it is “NO”.

The EGR control routine is a control cycle processing routine shown in FIG. 3 for allocating control cycles according to a fixed time or the state of an interrupt flag, and an EGR target shown in FIG. 4 called as a subroutine from the control cycle processing routine. The opening degree calculation processing routine and the routine shown in FIG.
The control cycle processing routine is composed of three routines called an EGR drive control output processing routine called as a subroutine.

These routines are processes of time synchronization. First, the control cycle processing routine shown in FIG.
The job timers of 4 msec and 10 msec are incremented for each sec. When the job timers reach their respective predetermined values, the respective control routines are shuffled according to the timers. At this time, if the interrupt by the "interrupt enable flag" is enabled, the process immediately jumps to the EGR drive control output processing routine in a cycle other than the normal cycle.

The EGR target opening calculation processing routine shown in FIG. 4 exists as a subroutine called every 10 msec from the control cycle processing routine. In this EGR target opening degree calculation processing routine, first, the engine cooling water temperature Tw
It is determined whether or not the condition for performing EGR is satisfied from the operating state such as the state of the engine and the idle switch, and if so, the target opening is searched from the map of the target opening based on the intake air amount Q and the engine speed Ne. To do. At this time, if the current target value is equal to the previous target value, that is, if the target opening does not change, the current value is saved to the previous value, the process is terminated, and the process returns to the main routine. If the current target value is not equal to the previous target value, that is, if the target opening changes, set the "interrupt enable flag" that enables interrupt output and set the current value to the previous value. Save the process to end the process and return to the main routine.

The control output processing routine shown in FIG. 5 also exists as a subroutine called every 4 msec from the control cycle processing routine. In such a control output processing routine, first, it is judged from the interrupt permission flag whether the current processing is a normal processing cycle or an interrupt. As a result, the EGR control timer is decremented in the case of the processing in the normal cycle, and when the value is not 0, the processing is not performed and the process returns to the main routine.

When the EGR control timer is 0,
After that, the interrupt enable timer for monitoring the previous output execution state is cleared, and the EGR control timer is initialized to prepare for the next interrupt. The output is sequentially switched to the step motor 6 of the EGR valve 4 in accordance with the difference between the target opening calculated by the target opening calculation routine and the current opening, and the current opening is updated and the interrupt permission flag is cleared. After that, the current opening (current value) is compared with the target value, and if the results are equal, the EGR output execution flag indicating that the output will be performed next time is cleared (reset).
If not, set and return to the main routine.

At this time, if the current processing is activated by an interrupt, the EGR output in-execution flag is checked, and if the result is not in execution, the interrupt flag is cleared and the above-mentioned operation is performed in preparation for the next interrupt. Do the same. If the above result is being executed, the interrupt enable timer is incremented. Thereafter, the content of the timer is compared with the set value, and if it is larger, it is determined that it has become equal to or lower than the maximum drive frequency of the EGR valve, the timer is cleared in preparation for the next processing, and the same processing as described above is performed.

If the content of the timer is smaller than the set value, EG
It is judged that the driving frequency is higher than the maximum drive frequency of the R valve, and the process returns to the main routine. The output effect of the EGR valve obtained by the above operation is as shown in FIG. 6, and when the drive output control is interrupted when the target value calculation result of the exhaust gas recirculation amount is obtained, the target opening calculation result is obtained. Can be reduced to be reflected in the control output, and it is possible to obtain the effect of improving the responsiveness during transient while ensuring the stability in the steady state, and the previous time monitored by the interrupt enable timer. Since the interruption is prohibited depending on the state of the control output, the maximum response speed of the EGR valve is not exceeded.

Next, another embodiment of the invention described in claims 1 and 2 will be described with reference to FIGS. 7 and 8. In this embodiment, if the difference between the previous output opening and the current target opening exceeds a predetermined value as shown in the flowchart in the figure, the target calculation is performed by interruption until the target value and the current opening match. The processing for continuing to drive the EGR valve is performed in a cycle.

Only the operation different from that of the above embodiment will be described with reference to FIGS. 7 and 8. In the flowchart showing the target opening calculation routine shown in FIG. 7, the target opening amount is determined by the intake air amount Q and the engine speed Ne. The process until the target opening is searched from the map is similar to that of the embodiment of the flowchart of FIG. Then, in this example,
When the difference between the previous output result value and the target value this time exceeds the specified value, that is, when the target opening changes by more than the specified value, the interrupt output is enabled. Set. After that, the current value is saved to the previous value, the process is terminated, and the process returns to the main routine.

The control output processing routine shown in FIG. 8 also exists as a subroutine called every 4 msec from the control cycle processing routine. In this control output processing routine, after the EGR control timer is initialized, the output is sequentially switched to the actuator that drives the EGR valve according to the difference between the target opening calculated by the target opening calculation routine and the current opening, Until the current opening is updated, it is the same as the flowchart in FIG.

Thereafter, in this embodiment, the current opening is compared with the target value, and if the results are equal, the EGR output in-execution flag indicating that the output will be performed next time is cleared and the interrupt enable flag is set. Clear to disable output control by interrupt. If they are not equal, the EGR output in-execution flag is set to limit output control by interruption and return to the main routine.

According to the configuration of the above embodiment, once the target value is updated, the EGR valve is immediately opened at the target calculation cycle or the maximum response speed of the EGR valve by interruption until the target value and the current opening degree match. It is possible to continue driving. That is, when the deviation between the current opening and the target opening is large, it is possible to promptly start driving the valve to the target value while minimizing the dead time, and when the deviation is small (when the opening substantially matches). ) Can perform long-cycle driving with an emphasis on steady stability.

The output timing to the EGR valve according to the above flow chart is as shown in FIG. 9, and if the difference between the previous output opening and the current target opening exceeds a predetermined value, the target value and the present opening are opened. It is clear that the process of continuing to drive the EGR valve at the target calculation cycle is performed by interruption until the degree coincides with the degree. Next, claim 3 based on FIG.
An embodiment of the described invention will be described.

In this embodiment, the drive output process is activated by interruption when the difference between the target value and the current opening exceeds a predetermined value as shown in the flow chart of FIG. This is a process for performing driving for changing the driving cycle according to the difference. That is, in the target opening calculation routine shown in FIG. 10, when the difference between the previous output result value and the current target value exceeds a predetermined value, that is, when the target opening changes by a predetermined value or more. The setting of the "interruption permission flag" for permitting interrupt output is similar to the flowchart of FIG.

In this embodiment, when the difference between the previous output result value and the current target value does not exceed the predetermined value, that is, when the change of the target opening less than the predetermined value occurs, this The control cycle is searched from the control cycle table based on the opening difference, the search value is stored, and the previous target value is read. The output timing to the EGR valve according to the above embodiment is as shown in FIG. 11, and when the target value is updated, the drive output cycle corresponding to the target value and the current opening degree is immediately given, and the response maximum of the EGR valve is increased. It is possible to continue driving the EGR valve at speed. As a result, when the deviation between the current opening and the target opening is large (for example, during sudden acceleration, sudden deceleration, or shift operation), the target can be followed with a minimal response delay due to the minor loop, but the steady-state target value With respect to the minute oscillation of, stability can be secured by the long cycle of the output timing.

FIG. 12 shows the effect of each of the above-described embodiments. In the conventional case, the EGR amount is excessive or insufficient due to the operation delay of the actuator of the EGR valve, and the EGR amount is insufficient due to dead time or the EGR amount is excessive. Although NOx and misfire increase, the present invention can suppress the above NOx increase and misfire increase, reduce NOx emission amount, and reduce deceleration shock due to misfire.

Regarding the above processing, the processing by the program is described, but it goes without saying that the processing may be performed by the signal processing by the electronic circuit, and the same effect is obtained.

[0038]

As described above, according to the first aspect of the invention, the drive output control is interrupted when the target value calculation result of the exhaust gas recirculation amount is obtained, and as a result, the target opening degree calculation is performed. It is possible to reduce the dead time until the result is reflected in the control output, and it is possible to obtain the effect that the responsiveness at the time of transition can be improved while maintaining the steady stability.

According to the second aspect of the present invention, when the exhaust gas recirculation amount adjustment interval between the present time and the previous time is short, the interrupt is prohibited, so that the maximum response speed of the exhaust gas recirculation means may be exceeded. Absent. According to the third aspect of the present invention, when the target value is updated, the adjustment processing cycle corresponding to the exhaust gas recirculation amount target value and the current exhaust gas recirculation amount adjustment amount is immediately given, and the exhaust gas recirculation means performs the exhaust at the maximum response speed. It becomes possible to continue to drive the recirculation means, and as a result, when the deviation between the current exhaust gas recirculation amount adjustment amount and the exhaust gas recirculation amount target value is large (for example, during rapid acceleration, sudden deceleration, shift operation, etc.), the minor loop The target value can be followed with a minimal response delay by the exhaust gas recirculation amount adjusting means, but the stability can be secured by the long cycle of the adjustment timing with respect to the minute oscillation of the target value in the steady state.

[Brief description of drawings]

FIG. 1 is a common configuration diagram of the invention according to claims 1 to 3.

FIG. 2 is a common system diagram of an embodiment of the invention of claims 1 to 3.

FIG. 3 is a flowchart (control cycle processing routine) showing the control contents of an embodiment of the invention described in claims 1 and 2.

FIG. 4 is a flowchart showing the control contents of an embodiment of the invention described in claims 1 and 2 (EGR target opening calculation processing routine).

FIG. 5 is a flowchart (EGR drive control output processing routine) showing the control contents of an embodiment of the invention described in claims 1 and 2.

FIG. 6 is a control time chart of the embodiment.

FIG. 7 is a flowchart showing the control contents of another embodiment of the invention according to claims 1 and 2 (EGR target opening calculation processing routine).

FIG. 8 is a flowchart (EGR drive control output processing routine) showing the control contents of another embodiment of the invention according to claims 1 and 2.

FIG. 9 is a control time chart of the embodiment.

FIG. 10 is a flowchart (EGR target opening degree calculation processing routine) showing a control content of an embodiment of the invention according to claim 3.

FIG. 11 is a control time chart of the above embodiment.

FIG. 12 is a time chart showing the effect of the control of the present invention.

FIG. 13 is a control time chart of a conventional device

[Explanation of symbols]

 1 Exhaust Manifold 2 Intake Manifold 3 EGR Pipe 4 EGR Valve 7 Air Flow Meter 11 Control Unit 14 Crank Angle Sensor 15 Water Temperature Sensor

Claims (3)

[Claims] 1. Exhaust gas recirculation means for recirculating exhaust gas of an internal combustion engine to an intake system, engine operating state detecting means for detecting an engine operating state, and exhaust gas according to the engine operating state detected by the engine operating state detecting means. Exhaust gas recirculation amount target value calculation means for calculating the target value of the recirculation amount in time synchronization, and the exhaust gas recirculation directly or indirectly according to the target value of the exhaust gas recirculation amount calculated by the exhaust gas recirculation amount target value calculation means. Means for adjusting the exhaust gas recirculation amount by the means, and processing the exhaust gas recirculation amount adjustment in a predetermined adjustment cycle; and adjusting the exhaust gas recirculation amount shorter than the exhaust gas recirculation amount adjusting means for the main loop. A minor loop exhaust gas recirculation amount adjusting means, and a main loop exhaust gas recirculation amount adjusting means when a target value calculation result by the exhaust gas recirculation amount target value calculating means is output. Exhaust gas recirculation control system for an internal combustion engine, characterized in that it is configured to include an interruption unit that can be interrupted at least once an exhaust gas recirculation amount adjustment processing by the minor loop processing means exhaust gas recirculation amount adjusting process, the. 2. A storage means for storing the time of the present and previous exhaust gas recirculation amount adjustment intervals, and an exhaust gas recirculation amount by the exhaust gas recirculation amount adjusting means of the minor loop when the memory value stored by the memory device is a set value or more. The exhaust gas recirculation control device for an internal combustion engine according to claim 1, further comprising: a prohibiting unit that temporarily prohibits interruption of the flow rate adjusting process. 3. A target value deviation amount calculating means for calculating a target value deviation amount which is a difference between a current exhaust gas recirculation amount adjusting amount and a current exhaust gas recirculation amount target value, and the target value deviation amount calculating means. An exhaust gas recirculation amount adjusting process cycle changing unit for changing an exhaust gas recirculating amount adjusting process cycle by the exhaust gas recirculating amount adjusting unit of the minor loop according to the target value deviation amount. 3. An exhaust gas recirculation control device for an internal combustion engine according to 1 or 2.