JP2596031B2 - Exhaust gas recirculation device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation device used for an internal combustion engine of an automobile or the like, and more particularly, to an exhaust gas recirculation while improving responsiveness to a change in an engine operating state. This enables learning control of the quantity.

<Conventional technology> An exhaust gas recirculation system (hereinafter referred to as EGR (Exhaust Gas Recir
eulation) device). This EGR device is a device for reducing nitrogen oxides (hereinafter, NOx), which are the most difficult to purify among harmful exhaust gases of automobiles. NOx is generated in the combustion chamber of the engine, and the combustion of the air-fuel mixture becomes close to complete combustion, and the generation amount increases as the combustion temperature increases. Therefore, the EGR device achieves the above-mentioned object by introducing a part of the exhaust gas, which is an inert gas (hereinafter, EGR gas), into the combustion chamber together with the fresh intake air to lower the combustion temperature.

The generation rate of NOx decreases as the mixing ratio of EGR gas to the intake air (hereinafter, EGR rate) increases. However, as a matter of course, the ignitability of the air-fuel mixture and the engine output decrease at the same time, so the EGR rate must be increased or decreased according to the operating state of the engine.

The EGR rate is increased or decreased by opening and closing a recirculation control valve (hereinafter, EGR valve) provided in an EGR gas passage that connects the exhaust system and the intake system. As a method for controlling the opening and closing of the EGR valve, pneumatic control using the negative pressure of the intake pipe and the exhaust pressure has been used in the past. However, due to the inability to perform complicated controls for various engine operating conditions with pneumatic control, the increasing demand for exhaust gas purification, and the development of centralized control systems for engines, electronic control systems have become the mainstream. It has become.

In the electronically controlled EGR device, the GER valve is opened and closed so that the EGR rate is programmed in advance according to the engine speed, load, and the like. In addition to the negative pressure, a pulse motor or the like is used as a drive source of the EGR valve, and feedback control is performed in many cases. Hereinafter, as an example of an electronic control type EGR device, EGR valve lift feedback scheme, and Briefly the construction and operation of the intake pipe O ₂ sensor output feedback scheme.

What is EGR valve Luft feedback system?
As disclosed in JP-A-11214, the system includes a driving unit that drives the opening and closing of the EGR valve and a detection unit that detects the opening amount of the EGR valve, and drives the EGR valve according to the operating state of the engine. The feedback control is performed so that a predetermined valve opening amount is obtained. As the driving means, an intake pipe negative pressure, a pulse motor or the like is used, and as the detecting means, a potentiometer or the like is used.

Also, with the intake pipe O ₂ sensor output feedback method,
As shown in JP-60-138264, a method comprising driving means for opening and closing the EGR valve, and O ₂ sensor disposed in an intake pipe. In this manner drives the EGR valve according to the operating condition of the engine, is performed by detecting the feedback control of the deviation between the O ₂ EGR rate calculated from the oxygen concentration measured by the sensor and the target EGR rate. As the O ₂ sensor, a solid electrolytic chamber oxygen pump type oxygen concentration measuring device or the like is used.

<Problems to be Solved by the Invention> However, each of the above-described methods has the following problems.

In the EGR valve lift feedback system, a large acceleration always acts on the valve opening amount detecting means such as a potentiometer during the operation of the engine, so that there is a problem in durability. In addition, since this method detects the opening amount of the EGR valve instead of the EGR rate, even if the EGR rate changes due to wear of the EGR valve, carbon deposition, or the like, correction for the change cannot be performed.

In the O ₂ sensor output feedback scheme, since there is a distance between the EGR valve and the O ₂ sensor, control delay occurs during acceleration or deceleration. That is, even if the target EGR rate is determined on the basis of the intake air amount or the actual GER rate at a certain time, the intake rate and the like fluctuate until the control based on the target EGR rate is performed. In particular, during deceleration, since the EGR rate temporarily becomes excessively large, it is necessary to take measures such as performing prospective control according to the throttle valve opening, and the control program becomes complicated. Moreover, even if such a prospective control is performed, an appropriate EG
It was difficult to get an R rate.

<Means for Solving the Problems> Accordingly, in the present invention, a part of the exhaust gas of the internal combustion engine is introduced into the intake system to lower the combustion temperature, thereby reducing the nitrogen oxide concentration in the exhaust gas. In the gas recirculation device, an operating state measuring means for measuring an operating state of the internal combustion engine, an acceleration / deceleration determining means for judging an acceleration / deceleration operation state of the internal combustion engine, and an exhaust gas recirculation passage, wherein the passage is opened and closed A recirculation amount control valve for increasing or decreasing the amount of recirculation, and control valve driving means for driving the recirculation amount control valve;
A gas concentration detector provided in the exhaust gas recirculation passage downstream of the recirculation amount control valve for detecting an exhaust gas recirculation rate, and an acceleration / deceleration operation state is determined by the acceleration / deceleration determination means. Sometimes, a target exhaust gas recirculation rate is determined based on the measurement result of the operating state measuring means, and the valve opening amount according to the target exhaust gas recirculation rate and the measurement result of the operating state measuring means. Open loop control of the recirculation amount control valve using the control valve driving means so that when the acceleration / deceleration operation state is not determined by the acceleration / deceleration determination means based on the measurement result of the operation state measurement means A target exhaust gas recirculation rate is determined, and the recirculation amount is set to reduce a deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate detected by the gas concentration detector. System It is obtained and control means for updating the correction amount learning with feedback control of the opening amount of the valve.

<Operation> In the exhaust gas recirculation device of the present invention, the control means includes:
When the acceleration / deceleration determination means determines that the vehicle is in the acceleration / deceleration operation state, the target exhaust gas recirculation rate is determined based on the measurement result of the operation state measurement means, and the target exhaust gas recirculation rate and the operation state measurement are determined. While the open-loop control of the recirculation amount control valve is performed so that the valve opening amount is in accordance with the measurement result of the means, when the acceleration / deceleration operation state is not determined, the target exhaust gas is determined based on the measurement result of the operation state measurement means. The recirculation rate is determined, and the opening amount of the recirculation amount control valve is set to reduce the deviation between the target exhaust gas recirculation rate and the actual exhaust gas recirculation rate detected by the gas concentration detector. The feedback control and the correction amount by learning are updated.

<Examples> Specific examples will be described based on two examples applied to an engine with an electronically controlled fuel injection device (hereinafter, ECI) of the present invention.

In the present embodiment, the open loop type and the feedback type are switched according to the operating state of the engine.
It is an example of feedback switching type EGR control.

FIG. 1 schematically shows the entire centralized control system in the present embodiment, and FIG. 2 shows the hardware configuration of an electronic control unit (hereinafter referred to as an ECU) which is a control center of the centralized control system. 3 and 4 show control flowcharts of the present embodiment. And
FIG. 5 shows a map of the target EGR rate, FIG. 6 shows a flow rate characteristic of the EGR valve with respect to the control negative pressure, and FIG. 7 shows a map of the duty ratio of the solenoid valve.

As shown in FIG. 1, in an engine E, an injector 1 for injecting fuel, a spark plug 2 for ignition, and an EG
The opening of the R valve 3 is all under the control of the ECU 4. E
The CU 4 drives and controls these controlled devices (injector 1, spark plug 2, EGR valve 3) together with various data. The outline of sensors for collecting various data used by the ECU 4 and the operation of the controlled device will be described below along the flow of intake air.

The descent of the piston E ₁ in the engine E, intake air that is negative pressure suction from the air cleaner 5, an air flow meter 6 of Maruman vortex, guided to the intake air temperature sensor 7 and the atmospheric pressure sensor 8, intake air quantity, intake air temperature and atmospheric Atmospheric pressure is detected. The air that has flowed into the intake pipe 9 is a butterfly type throttle valve 10.
The opening of the throttle valve 10 is detected by a throttle sensor 11.

A negative pressure outlet pipe 12 and an EG are provided on the intake pipe wall downstream of the throttle valve 10.
The R gas inlet pipe 13 is connected and opened in order, and the negative pressure outlet pipe 1
Air is sucked into the intake pipe 9 from the EGR gas introduction pipe 13 and EGR gas is sucked into the intake pipe 9 from the EGR gas introduction pipe 13. The intake air is mixed with this EGR gas, and the oxygen concentration is detected by an O ₂ sensor 14 provided downstream. The O ₂ sensor 14 is the same as that described in the section of the related art.

Nearby combustion chamber E ₂ side end portion of the intake pipe 9, the injector 1 for the number of cylinders is provided, opens a command from ECU 4, to inject fuel in an amount each of the cylinders is required.
Fuel is pumped from a fuel tank (not shown) to the injector 1 by a fuel pump (not shown).

In the figure, reference numeral 15 denotes a water temperature sensor, which detects a cooling water temperature.

Fuel is injected from the injector 1, the air becomes air-fuel mixture is ignited by the spark plug 2 near compression top dead center is aspirated into the combustion chamber E _2. Due to space limitations in Figure 1, have been Eka to a remote location, but if appreciated that the ignition plug 2 facing its tip into the combustion chamber E _2. A high voltage is supplied to the ignition plug 2 from the ignition coil 16 by the distributor.
Sent over 17. Power transmission timing (ignition timing)
Is calculated in the ECU 4, and the result of the calculation drives the ignition coil 16 via the power transistor 18. The distributor 17 has a built-in crank angle sensor 19 and a cylinder discrimination sensor 20 for detecting the rotation state of the engine.

After the explosion and expansion strokes, the air-fuel mixture becomes exhaust gas, and most of the air-fuel mixture passes through the exhaust pipe 21 and is catalyzed by the catalyzer 21a.
After the harmful components are burned in the inside, they are released into the atmosphere from a muffler (not shown).

Then, a part of the exhaust gas is guided as an EGR gas to the EGR gas extraction pipe 22, and the amount thereof is controlled by the EGR valve 3, and the above-described E
The gas is introduced from the GR gas introduction pipe 13 into the intake pipe 9. EGR valve 3
Is operated by the negative pressure from the negative pressure extraction pipe 12 described above, and this negative pressure increases and decreases by opening and closing an ON-OFF type solenoid valve 23 provided in the middle of the negative pressure extraction pipe 12. I have. In FIG. 1, reference numeral 24 denotes a communication pipe having a filter 25 attached to an end thereof and an orifice 24a provided in a pipe. This communication pipe 24
Is for gradually communicating the EGR valve 3 with the atmosphere when the passage of the negative pressure extraction pipe 12 is closed by the electromagnetic valve 23. The solenoid valve 23 is opened and closed by a command from the ECU 4, and its control method is a variable duty ratio type.

The ECU 4 changes the duty ratio of the solenoid valve 23 so that the EGR rate according to various operating states of the engine E is changed.
Is controlled. In Fig. 1, 26, 27 and 28 are EC
A battery as a driving power source of U4, a battery sensor for detecting a battery voltage, and an ignition switch;
These are also connected to ECU4.

As described above, various sensors and controlled devices are connected to the ECU 4, but the hardware of the ECU 4 is configured around a CPU (central processing unit) 29 as shown in FIG. Intake air temperature sensor 7, atmospheric pressure sensor 8, throttle sensor 1
The data from the 1, O ₂ sensor 14 and the battery sensor 27
Since it is an analog signal, it is input to the CPU 29 via the interface 30 and the A / D converter 31. The data from the ignition switch 28 is transmitted through the interface 32,
Data from the crank angle sensor 19, the cylinder discrimination sensor 20, and the air flow meter 6 are directly input to the CPU 29, respectively.

The CPU 29 also has a ROM (read only memory) 33, a RAM (rewrite memory) 34, and a battery 26 via a bus line.
As long as is connected, data is exchanged with a BURAM (backup memory) 35 in which the stored contents are stored even when the ignition switch 28 is turned off.

Inside the CPU 29, the fuel injection amount, the ignition timing and the opening of the EGR valve are determined using the above-mentioned various data and the memory.
Then, the injector 1 is connected via the injector driver 36 to the power transistor 18 via the ignition driver 37.
The electromagnetic valves 23 are respectively driven via the EGR driver 38.

Hereinafter, the operation of the present embodiment will be described with reference to FIGS. 3 to 7. Prior to detailed description, an outline of control in the present embodiment will be briefly described.

In the present embodiment, first, the calculation is advanced using the set value on the premise of the open loop control, and then it is determined whether or not the feedback control is possible. If the feedback control is not performed, the solenoid valve 23 is driven to return to the starting point.

On the other hand, in the case of performing the feedback control, based on the output value of the operation result and the O ₂ sensor 14 corrects the duty ratio of the solenoid valve 23, and drives the solenoid valve 23.

Further, after that, it is determined whether or not learning is to be performed. When learning is to be performed, the set value itself is corrected, and then the process returns to the starting point.

Thus, unlike the conventional O ₂ sensor feedback method described above in this embodiment, since the switches to control by the open loop during acceleration and deceleration, the response is enhanced, since Yuku enhance gradually control accuracy by learning function is there.

Next, the control flow will be specifically described with reference to the flowcharts of FIGS.

When the engine E starts and enters a predetermined operating state, the EGR control is started. Note that the predetermined operating state is an idle state,
The operating state is outside the operating range, such as full load and high speed.

When the control is started, the CPU 29 obtains the engine speed Ne and the load A / N from the output signals of the crank angle sensor 19 and the air flow meter 6. Next, a map of the EGR rate (shown in FIG. 5) stored in the ROM 33 is called, and a target EGR rate (EGR) _T is obtained from the rotation speed Ne and the load A / N. Next, a target EGR flow rate (EGR) _Q is determined from the target EGR rate (EGR) _T , the engine speed Ne, and the load A / N. (EGR)
_Q is given by the following equation.

(EGR) _Q = (EGR) _T × A / N × Ne (1) Next, from the target EGR flow rate (EGR) _Q , −200 mm of the EGR valve 3 is obtained.
Determine the target flow rate (EGR) _STD in Hg. This is EGR
This is because the measurement of the flow characteristic of the valve 3 is usually performed by applying a negative pressure of -200 mmHg. (EGR) _STD is exhaust pressure
(. For almost the same as the atmospheric pressure, in the embodiment using the input data of the atmospheric pressure sensor 8) P _exh and the intake pressure P _B (load obtained from the A / N) because the obtained intake pipe negative pressure P _exh - It is given by the following equation using P _B.

In this embodiment, the intake pressure P _B was obtained from the load A / N.
When an intake pressure sensor is provided, the value of the intake pressure sensor is naturally used.

Then, necessary to ensure the conversion target flow rate (EGR) _STD, seek control negative pressure P _E of the EGR valve 3. The flow characteristics of the EGR valve 3 used in this embodiment are as shown in FIG.
It has become a linear line with respect to control negative pressure P _E.
In the figure, the valve opening start negative pressure EGR valve 3 (hereinafter, the valve opening negative pressure) is fully opened negative pressure are each P _E1 and P _E2 fully open when the flow rate is (EG
R) _max . Therefore, when the (EGR) _STD is (EGR) is larger than _max, the control negative pressure P _E may be larger than P _E2, but when fully opened negative pressure P _E2 more negative pressure, the time of closing the valve Since the responsiveness deteriorates, the following equation is used.

(EGR) _STD ≧ (EGR) _max P _E = P _E2 (3) The full-open negative pressure P _E is updated by learning control described later, but at this time, the value in the BURAM 35 is used.

Then, by the following equation if (EGR) _STD is (EGR) _max is less than, obtaining the P _E.

(EGR) _STD <(EGR) _max It should be noted that the constants a and b in this arithmetic expression are stored in the BURAM 35 because they are variable values as described later, but default values are also input into the ROM 33 in consideration of the attachment / detachment of the battery 26 and the like.

Next, the operating state of the engine is monitored to determine whether feedback control is possible. The O ₂ sensor in the intake pipe 9
For performing feedback control using the 14, precise control takes time until the EGR gas reaches the O ₂ sensor 14 is a detecting means from the EGR valve 3 is a means for changing the EGR rate in acceleration and deceleration time, etc. This is because it cannot be done. The criterion is the same operating condition (specifically, engine speed Ne and load A / N
Is maintained for a predetermined time, and if this is not satisfied, the feedback control is not performed and the open loop control is executed.

If you do not feedback control, determine the duty ratio D _O of the solenoid valve 23 from the aforementioned control negative pressure P _E load A / N and the target EGR rate (EGR) _T. The duty ratio D _O is
Searched from the map in the ROM 33, the one shown in FIG. 7 is a map when (EGR) _T is 10%. When the duty ratio _DO is determined, the solenoid valve 23 is driven to return to the starting point.

When performing feedback control, first detects the output voltage value I _P of the O ₂ sensor 14. Then, load the output voltage value I _P
Correct by A / N. This is because the output characteristic of the O ₂ sensor 14 changes according to the intake pressure (proportional to the load A / N). Next, determine the actual EGR rate (EGR) _A from the output voltage value I _P.
This operation, the output voltage (I _{P) O} of the O ₂ sensor 14 when not performing EGR is used, (EGR) _A is given by the following equation.

Next, from the actual EGR rate (EGR) _A , the actual EGR flow rate (EGR) ′ _Q
Ask for. (EGR) ' _Q is given by the following equation.

(EGR) ′ _Q = (EGR) _A × A / N × Ne (6) Next, the target EGR flow rate (EGR) _Q and the actual EGR flow rate (EGR) ′ _Q
Is obtained by the following equation.

_{ΔEGR = (EGR) Q - (} EGR) 'Q is then determined by the following equation the correction amount [Delta] P _E of the control negative pressure.

Here, (ΔEGR) _STD is a converted flow rate of ΔEGR calculated using the above-described equation (2).

Then, by using the correction amount [Delta] P _E, it is corrected by the following equation control negative pressure.

P ′ _E = P _E + ΔP _E (8) Here, P ′ _E is compared with the full-open negative pressure P _E2, and when P ′ _E is larger, the following equation is used.

P ′ _E ≧ P _E2 P ′ _E = P _E2 (9) Then, the P ′ _E , the load A / N, and the target EGR rate (EG
R) Retrieve the drive duty ratio D _O of the solenoid valve from _T from the map. When the duty ratio _DO is determined, the solenoid valve 23 is driven.

When P ′ _E is smaller than P _{E2, the} following equation is used.

In the case of P ′ _E <P _E2 P ′ _E = P _E2 (10) Also in this case, the duty ratio D _O is retrieved from the map and the solenoid valve 23 is driven. Then, the converted actual flow rate (EGR) ′ _{STD with} respect to the actual EGR flow rate (EGR) ′ _Q obtained by equation (6)
Is determined by the following equation.

Here, before learning from the result of the feedback, (EGR) ' _Q is compared with (EGR) _max , and the converted actual flow rate (EG
Check that R) ' _STD is smaller than the flow rate at full open (EGR) _max . This is to check whether an erroneous detection or the like of the O ₂ sensor 14 has occurred. (EGR) ′ _STD > (EGR)
_In the case of _max , the control flow returns to the starting point.

If (EGR) ' _STD ≤ (EGR) _max , the learning control is started on the assumption that the EGR device is functioning normally. Learning control is performed based on the conversion actual flow rate (EGR) _'STD and control the negative pressure P _E in the present embodiment, the equation (4) and a (7)
In this method, the constants a and b in the equation are updated by the least squares method. Specifically, as shown in the flowchart of FIG. 4, when (EGR) ′ _STD ≦ (EGR) _max / 4, the constant b is replaced by (EGR)
R) ' _STD > (EGR) _max / 2, the constant a is corrected, and if (EGR) _max / 4 <(EGR)' _STD ≤ (EGR) _max / 2, no correction is performed. Like that. In the figure, K is a filter coefficient for determining the ratio between the proportion and the integration, and is set as appropriate. Further, a ₁ , a ₂ , b ₁ , and b ₂ are limit values that determine the allowable limit of correction, and are set based on experimental results and the like. EGR
In the valve 3, since the flow rate (EGR) _max at the time of full opening does not change, the valve opening negative pressure P _E1 is naturally changed with the renewal of the constants a and b.
And the fully open negative pressure _PE2 are also updated at the same time.

This concludes the description of the present embodiment, but it goes without saying that the present invention is not limited to this embodiment.
The present invention may be applied to an engine having a carburetor instead of I. Further, the recirculation amount detecting means may be other than the O ₂ sensor, or an EGR valve having a higher-order curve flow rate characteristic or a device driven by a pulse motor or the like instead of the negative pressure may be used. . Further, although the calculation method and the calculation procedure in the control are specifically described in the embodiment, the set value for controlling the EGR valve is corrected by the learning control based on the detection result of the recirculation amount detection means. It should just be.

<Effect of the Invention> According to the exhaust gas recirculation device of the present invention, the target exhaust gas recirculation rate determined based on the measurement result of the operation state measurement means and the measurement result during the acceleration / deceleration operation state While the recirculation amount control valve is open-loop controlled so as to have a corresponding valve opening amount, during the acceleration / deceleration operation state, the target exhaust gas recirculation rate and the gas determined based on the measurement result of the operation state measurement means are set. In order to reduce the deviation from the actual exhaust gas recirculation rate detected by the concentration detector, the opening amount of the recirculation amount control valve is feedback controlled and the correction amount by learning is updated. High-precision EGR control can be performed without delay of control, and EGR control is always performed with an optimal amount regardless of a manufacturing error of the EGR valve, a change with time of the EGR device, and the like. As a result, it becomes possible to supply the EGR gas to the intake system at a high EGR rate without impairing the drivability, and environmental pollution due to harmful exhaust gas is reduced.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are a schematic diagram of a centralized control system and a hardware configuration diagram of an electronic control unit, respectively, in one embodiment of the present invention. FIG. 3 and FIG. 4 are control flowcharts for explaining the operation of the present embodiment. Figures 5 to 7
The figure is a map of the target EGR rate, the flow rate characteristic of the EGR valve, and the duty ratio of the solenoid valve, respectively. In the figure, 3 is the EGR valve, the 4 ECU, 14 is the O ₂ sensor 23 is an electromagnetic valve, 33 is ROM, 34 is RAM, 35 is BURAM.

Claims (1)

(57) [Claims] An exhaust gas recirculation system for reducing the concentration of nitrogen oxides in exhaust gas by reducing a combustion temperature by introducing a part of exhaust gas of the internal combustion engine into an intake system. Operating state measuring means for measuring an operating state; acceleration / deceleration determining means for determining an acceleration / deceleration operation state of the internal combustion engine; and an exhaust gas recirculation passage which is provided in an exhaust gas recirculation passage to increase or decrease a recirculation amount by opening and closing the passage. A recirculation amount control valve; a control valve driving means for driving the recirculation amount control valve; and an exhaust gas recirculation passage provided downstream of the recirculation amount control valve to detect an exhaust gas recirculation rate. A gas concentration detector, and a target exhaust gas recirculation rate is determined based on the measurement result of the operating state measuring means when the acceleration / deceleration determining means determines the acceleration / deceleration operation state. Exhaust gas The recirculation amount control valve is open-loop controlled using the control valve driving means so that the valve opening amount is in accordance with the recirculation rate and the measurement result of the operating state measuring means, while the acceleration / deceleration determining means controls the recirculation amount. When the deceleration operation state is not determined, a target exhaust gas recirculation rate is determined based on the measurement result of the operation state measurement means, and the target exhaust gas recirculation rate and the target exhaust gas recirculation rate are detected by the gas concentration detector. Control means for performing feedback control of the opening amount of the recirculation amount control valve and updating a learning amount to be learned so as to reduce a deviation from an actual exhaust gas recirculation rate. Recirculation device.