JPH1089157A - Exhaust gas reflux quantity control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the EGR rate under the same operating condition constant, and to improve the EGR controllability by properly controlling the weight flow rate of the new air and the EGR gas regardless of the change of the atmo spheric pressure. SOLUTION: The basic control quantity EGRB is set on the basis of the number of revolution of engine Ne and the basic fuel injection pulse width Tp representing the engine load, when the EGR executing condition is filled, and a target intake tube absolute pressure PO as a target value of the intake tube absolute pressure of the downstream of a throttle valve at the operation of EGR is set (S40), so that the basic controlling quantity EGRB is corrected on the basis of a feedback correction value EGRCL set corresponding to the result of the comparison of the target intake tube absolute pressure P0 and the real intake tube absolute pressure P of the downstream of the throttle valve, to set the control quantity EGRS to a EGR valve (S41-S45). By using the intake tube absolute pressure, the EGR gas quantity can be indirectly managed by the weight flow rate, and the weight flow rate of the new air and the EGR gas can be properly controlled regardless of the change of the atmospheric pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust gas recirculation control system for controlling the amount of exhaust gas recirculated to an intake system of an engine in accordance with the operating state of the engine.
More specifically, the present invention relates to an exhaust gas recirculation amount control device for an engine that can set a control amount for an exhaust gas recirculation adjusting valve based on an absolute pressure of an intake pipe downstream of a throttle valve and improve controllability with simple control.

[0002]

2. Description of the Related Art Conventionally, exhaust gas recirculation (hereinafter referred to as "EG
An EGR device that recirculates exhaust gas to an intake system of an engine through a passage (referred to as “R”) and reduces nitrogen oxides (NOx) in the exhaust gas by a combustion suppressing effect is employed.

[0003] In this type of EGR device, the ratio of the recirculation amount of exhaust gas to the total amount of intake air (hereinafter referred to as "EGR device").
As the EGR rate increases, the ignitability of the air-fuel mixture and the engine output decrease. Therefore, an EGR valve that adjusts the amount of exhaust gas recirculation to the EGR passage. The EGR valve is controlled according to the engine operating state to control the EGR amount.

For example, Japanese Patent Laid-Open No. Hei 5-99076 discloses that when the EGR valve is momentarily closed and the recirculation of exhaust gas is stopped, the recirculation amount of exhaust gas no longer supplied (EGR amount)
Paying attention to the fact that the intake pipe pressure decreases in accordance with the above, the amount of change in the intake pipe pressure at this time increases and decreases substantially in proportion to the actual EGR amount. It is determined whether the EGR amount has decreased from the target value due to adhesion or the like, or if the EGR amount has increased from the target value due to wear of the EGR valve, and the opening degree of the EGR valve is increased or decreased accordingly. Thus, a technique is disclosed in which the actual EGR rate is accurately controlled to a target value corresponding to the engine speed and the intake pipe pressure, so that the actual exhaust gas recirculation amount can be accurately controlled.

More specifically, the EG at the time of opening the EGR valve
The intake pipe pressure PmNMSS and the engine speed NeNMS at the time of R operation are read, and then the EGR valve is fully closed and E
The intake pipe pressure PmNMSE at the time of GR stop is read. next,
An intake pipe pressure change amount ΔPmNMS is calculated by subtracting the intake pipe pressure PmNMSE at the time of EGR stop from the intake pipe pressure PmNMSS at the time of EGR operation. A pipe pressure change target value ΔPm0 is set. Then, the target value ΔPm0 and the actual intake pipe pressure change amount Δ
A correction amount EGRG is calculated in accordance with a result of comparison with PmNMS, and the target opening degree EGRS of the EGR valve set based on the engine speed Ne and the intake pipe pressure Pm is corrected by the correction amount EGRG.

[0006]

By the way, the above EGR
The rate α is α = Q ′ / (Q + Q ′), Q: fresh air volume flow rate,
Q ′; expressed by EGR gas volume flow rate, the combustion suppression effect of EGR for reducing NOx is actually
Not the volume flow ratio of fresh air and EGR gas, but fresh air weight and E
It is determined by the relationship with the GR gas weight, that is, the ratio of the fresh air and the EGR gas weight flow rate.

However, in the above prior art, the amount of pressure change between the intake pipe pressure when the EGR is activated and the intake pipe pressure when the EGR is stopped is calculated, and the opening of the EGR valve is adjusted so that this pressure change converges to the target value. By feedback control of the degree,
The EGR gas volume flow rate Q ′ that determines the EGR rate is controlled. Therefore, even under the same engine operating conditions, for example, when the atmospheric pressure changes during high-altitude traveling or the like, the fresh air volume flow Q ′ sucked into the engine changes, and the EGR rate also changes.
The EGR rate cannot be controlled to be constant, and there is a disadvantage that controllability and exhaust emission deteriorate.

To cope with this, an EGR gas volume flow rate Q 'corresponding to the above-described fresh air volume flow rate Q which changes with the atmospheric pressure.
, That is, the intake pipe pressure during EGR operation and the EGR
It is conceivable to correct the pressure change amount with the intake pipe pressure at the time of stoppage. However, in this case, there is a disadvantage that the EGR control is significantly complicated.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides an EGR control by controlling the weight ratio of fresh air and EGR gas properly regardless of changes in atmospheric pressure to thereby keep the EGR rate constant under the same operating conditions. It is an object of the present invention to provide an engine exhaust gas recirculation amount control device capable of improving the performance and realizing with simple control.

[0010]

In order to achieve the above object, the present invention is directed to an exhaust gas recirculation amount adjusting valve disposed in an exhaust gas recirculation passage for recirculating exhaust gas of an engine to an intake system. In an exhaust gas recirculation amount control device for controlling an exhaust gas recirculation amount in accordance with an engine operating state, as shown in a basic configuration diagram of FIG. Target intake pipe absolute pressure setting means for setting a target intake pipe absolute pressure which is a target value of the intake pipe absolute pressure downstream of the throttle valve during gas recirculation, and the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve And control amount setting means for setting a control amount for the exhaust gas recirculation amount adjusting valve in accordance with the comparison result.

According to a second aspect of the present invention, the exhaust gas recirculation amount adjusting valve disposed in the exhaust gas recirculation passage for recirculating the exhaust gas of the engine to the intake system is controlled in accordance with the operating state of the engine. As shown in the basic configuration diagram of FIG. 1B, a basic control amount for the exhaust gas recirculation amount adjusting valve is set on the basis of the engine speed and the engine load in the exhaust gas recirculation amount control device for controlling the engine. Target intake pipe absolute pressure setting means for setting a target intake pipe absolute pressure serving as a target value of the intake pipe absolute pressure downstream of the throttle valve at the time of exhaust gas recirculation based on the engine speed and the engine load. Feedback correction amount setting means for setting a feedback correction amount according to a comparison result between the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve. The basic control amount is characterized in that a control amount setting means for setting a control amount for the exhaust gas recirculation amount adjusting valve is corrected by the feedback correction amount.

According to a third aspect of the present invention, an exhaust gas recirculation amount adjusting valve disposed in an exhaust gas recirculation passage for recirculating exhaust gas of an engine to an intake system is controlled in accordance with an engine operating state, thereby obtaining an exhaust gas recirculation amount. In the exhaust gas recirculation amount control device for controlling the engine, as shown in the basic configuration diagram of FIG. 1C, it is determined whether or not the execution condition of the exhaust gas recirculation for performing the exhaust gas recirculation based on the operating state is satisfied. An exhaust gas recirculation execution condition determining means for judging, and a target intake pipe which becomes a target value of an absolute pressure in the intake pipe downstream of the throttle valve at the time of exhaust gas recirculation based on the engine speed and the engine load when the exhaust gas recirculation execution condition is satisfied. Target intake pipe absolute pressure setting means for setting the absolute pressure, and a comparison result between the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve when the execution condition of the exhaust gas recirculation is satisfied. A control amount setting means for setting a control amount for the exhaust gas recirculation amount adjusting valve in response to the exhaust gas recirculation execution condition, and setting a control amount for fully closing the exhaust gas recirculation adjusting valve when the exhaust gas recirculation execution condition is not satisfied. It is characterized by.

That is, according to the present invention, a target intake pipe absolute pressure which is a target value of the intake pipe absolute pressure downstream of the throttle valve at the time of exhaust gas recirculation is set based on the engine speed and the engine load. The control amount for the exhaust gas recirculation amount adjusting valve disposed in the exhaust gas recirculation passage is set according to the result of comparison between the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve.

According to the second aspect of the present invention, the basic control amount is set based on the engine speed and the engine load, and based on the engine speed and the engine load, the absolute control amount in the intake pipe downstream of the throttle valve during exhaust gas recirculation. Set the target intake pipe absolute pressure to be the target value of pressure, and correct the basic control amount by the feedback correction amount set according to the result of comparison between the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve. Then, the control amount for the exhaust gas recirculation amount adjusting valve is set.

According to the third aspect of the present invention, it is determined whether or not the execution condition of the exhaust gas recirculation for performing the exhaust gas recirculation is satisfied based on the operating state. Based on the engine load, a target intake pipe absolute pressure which is a target value of the intake pipe absolute pressure downstream of the throttle valve during exhaust gas recirculation is set, and the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve are set. The control amount for the exhaust gas recirculation amount adjusting valve is set in accordance with the comparison result, and when the exhaust gas recirculation execution condition is not satisfied, the control amount for fully closing the exhaust gas recirculation adjusting valve is set, To stop.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

First, a schematic configuration of the engine will be described with reference to FIG. In the figure, reference numeral 1 denotes an engine, and in the figure, a horizontally opposed four-cylinder engine is shown. Cylinder heads 2 are provided in both left and right banks of a cylinder block 1a of the engine 1, respectively, and each cylinder head 2 is formed with an intake port 2a and an exhaust port 2b.

In the intake system of the engine 1, an intake manifold 3 is communicated with each intake port 2a, and a throttle chamber 5 is communicated with the intake manifold 3 through an air chamber 4 in which intake passages of respective cylinders are gathered. An air cleaner 7 is attached to the upstream side of the throttle chamber 5 via an intake pipe 6, and the air cleaner 7 is connected to the air intake chamber 8.

The throttle chamber 5 is provided with a throttle valve 5a linked to an accelerator pedal.
A bypass passage 9 for bypassing the throttle valve 5a is connected to the intake pipe 6, and the idle speed is controlled by adjusting the amount of bypass air flowing through the bypass passage 9 according to the valve opening during idling. An idle speed control valve (ISC valve) 10 is provided.

In the exhaust system of the engine 1, an exhaust pipe 12 is communicated with a collection portion of an exhaust manifold 11 which communicates with each exhaust port 2b of the cylinder head 2, and a catalytic converter 13 is interposed in the exhaust pipe 12. And is communicated with the muffler 14.

On the other hand, an exhaust gas recirculation passage (hereinafter referred to as "EGR passage") 15 for recirculating exhaust gas from at least one of the exhaust ports 2b of the cylinder head 2 to the air chamber 4 downstream of the throttle valve 5a is connected. A stepping motor drive type EGR valve 16 driven by a built-in stepping motor is provided in the EGR passage 15 as an example of an exhaust gas recirculation amount adjusting valve. The control amount of the EGR valve 16 is calculated by an electronic control unit 40 (see FIG. 11) described later. Then, the stepping motor operates according to the drive signal output from the electronic control device 40 in accordance with the control amount, and the valve opening of the EGR valve 16 is adjusted by the operation of the stepping motor.

In this embodiment, the control amount is 0
At 0H, the EGR valve 16 is fully closed and the recirculation of exhaust gas, that is, EGR is stopped. When the control amount is FFH, the EGR valve 16 is fully opened. Then, the control amount is set between 00H and FFH, and the valve opening of the EGR valve 16 is adjusted according to the drive signal corresponding to this control amount,
The exhaust gas recirculation amount is controlled.

On the other hand, an injector 17 is located just upstream of the intake port 2a of each cylinder of the intake manifold 3. Further, for each cylinder of the cylinder head 2, a spark plug 1 for exposing a discharge electrode at the tip to a combustion chamber is provided.
An igniter 20 is connected to the ignition plug 18 via an ignition coil 19 provided for each cylinder.

Next, sensors for detecting the operating state of the engine will be described. Reference numeral 21 denotes an absolute pressure sensor, which detects the intake pressure in the intake manifold 3 as an absolute pressure as the actual intake pipe absolute pressure downstream of the throttle valve 5a. A thermal intake air amount sensor 22 using a hot wire or a hot film is interposed immediately downstream of the air cleaner 7 in the intake pipe 6, and a throttle opening sensor 23a and a throttle opening sensor 23a are provided in the throttle valve 5a. Valve 5
A throttle sensor 23 having a built-in idle switch 23b which is turned on when fully closed at a is connected.

A knock sensor 24 is attached to the cylinder block 1a of the engine 1,
A cooling water temperature sensor 26 faces a cooling water passage 25 communicating the left and right banks of the cylinder block 1a, and an O2 sensor 27 is disposed upstream of the catalytic converter 13.

The crankshaft 28 of the engine 1
A crank angle sensor 30 is provided on an outer periphery of a crank rotor 29 which is axially mounted on the cam shaft 31. Further, a cam rotor 32 connected to a cam shaft 31 which makes a half turn with respect to the crank shaft 29 has a cam angle for cylinder discrimination. A sensor 33 is provided opposite.

The crank rotor 29 has a projection formed on the outer periphery thereof at every predetermined crank angle, and a projection for cylinder discrimination is formed on the outer periphery of the cam rotor 32. Then, the crankshaft 28 and the camshaft 31 rotate with the operation of the engine, and accordingly, the crank rotor 29 and the cam rotor 32 rotate, and each projection of the crank rotor 29 is detected by the crank angle sensor 30, and the crank angle A crank pulse corresponding to a predetermined crank angle is output from the sensor 30 to the electronic control unit 40 (see FIG. 11), and a cylinder discriminating projection of the cam rotor 32 is detected by the cam angle sensor 33. A cam pulse is output to the electronic control unit 40.

As will be described later, the electronic control unit 40
An engine speed NE is calculated based on an input interval time of a crank pulse output from the crank angle sensor 30, and a cam pulse from the cam angle sensor 33;
The combustion stroke order of each cylinder (for example, # 1 cylinder → # 3 cylinder → #
Based on the pattern of (2 cylinders → # 4 cylinders), cylinder discrimination of a fuel injection target cylinder and an ignition target cylinder is performed.

Calculation of control amounts for actuators such as the EGR valve 16, injector 17, spark plug 18, ISC valve 10, etc., and output of drive signals corresponding to these control amounts, ie, EGR control, fuel injection control, ignition timing control Engine control such as idle speed control is performed by an electronic control unit (ECU) 40 shown in FIG.

The ECU 40 includes a CPU 41, a ROM 4
2, RAM 43, backup RAM 44, and I / O
An interface 45 is mainly composed of microcomputers connected to each other via a bus line 46, and includes a constant voltage circuit 47 for supplying a stabilized power to each section, and a drive circuit 48 connected to the I / O interface 45.
And peripheral circuits such as an A / D converter 49.

The constant voltage circuit 47 is connected to the battery 51 via a first relay contact of a power relay 50 having two relay contacts, and the battery 51 is connected to a relay coil of the power relay 50 by an ignition switch. 52 are connected. Further, the above constant voltage circuit 4
Reference numeral 7 is directly connected to the battery 51. When the ignition switch 52 is turned on and the contact of the power supply relay 50 is closed, power is supplied to each unit in the ECU 40, while the ignition switch 52 is turned on and off.
Regardless, the backup power is always supplied to the backup RAM 44. Further, the power relay 50
A power supply line for supplying power to each actuator via the second relay contact is connected.

The input port of the I / O interface 45 has an idle switch 23b, a knock sensor 2
4. A crank angle sensor 30, a cam angle sensor 33, a vehicle speed sensor 34, and a starter switch 35 for detecting a starting state are connected. Further, an absolute pressure sensor is connected via the A / D converter 49. 21, intake air amount sensor 2
2, throttle opening sensor 23a, cooling water temperature sensor 2
6 and the O2 sensor 27 are connected, and the battery voltage VB is input and monitored.

On the other hand, to the output port of the I / O interface 45, the ISC valve 10, the EGR valve 16, and the injector 17 are connected via the drive circuit 48, and the igniter 20 is connected.

In accordance with the control program stored in the ROM 42, the CPU 41 processes the detection signals from the sensors and switches input via the I / O interface 45, the battery voltage and the like, and stores them in the RAM 43. Based on various data, various learning value data stored in the backup RAM 44, fixed data stored in the ROM 42, and the like, the control amount for the EGR valve 16, the fuel injection amount, the ignition timing, the duty of the drive signal for the ISC valve 10, Calculate the EGR control,
It performs engine control such as fuel injection control, ignition timing control, and idle speed control.

In this case, in the EGR control, the EGR
Is determined based on the operating state, and when the EGR execution condition is satisfied, a basic control amount is set based on the engine speed and the engine load. Then, based on the engine speed and the engine load, a target intake pipe absolute pressure which is a target value of the intake pipe absolute pressure downstream of the throttle valve 5a during the EGR operation is set, and the target intake pipe absolute pressure and the throttle valve 5a downstream are set. The basic control amount is corrected by the feedback correction amount set in accordance with the result of comparison with the actual intake pipe absolute pressure to set a control amount for the EGR valve 16, and a drive signal corresponding to this control amount is sent to the EGR valve 16. It outputs the output to control the valve opening of the EGR valve 16 and performs feedback control so that the actual intake pipe absolute pressure converges to the target intake pipe absolute pressure. When the EGR execution condition is not satisfied, a control amount for fully closing the EGR valve 16 is set, the EGR valve 16 is fully closed, and the EGR is stopped.

That is, the functions of the exhaust gas recirculation execution condition determining means, the basic control amount setting means, the target intake pipe absolute pressure setting means, the feedback correction amount setting means, and the control amount setting means according to the present invention are realized by the ECU 40. .

Here, as described above, the EGR rate α is α
= Q '/ (Q + Q'), Q; fresh air volume flow, Q '; EG
It is represented by R gas volume flow rate. However, the engine combustion suppression effect by EGR for reducing NOx is not actually the relationship between the volume flow rate of fresh air and EGR gas, but the relationship between fresh air weight and EGR gas weight, that is, fresh air and EGR gas.
It is determined by the ratio of the weight flow rate of the gas.

When the EGR is stopped, for example, the absolute pressure in the intake pipe downstream of the throttle valve during idling (absolute pressure of the intake pipe) is the same both at low altitude and at high altitude, and has the same value irrespective of the change in atmospheric pressure.

Therefore, even during the EGR operation in which the EGR is performed, if the absolute pressure of the intake pipe is the same, the ratio of the weight flow rate of the fresh air to the EGR gas is the same regardless of the atmospheric pressure change due to the difference between the highland and the lowland. The weight flow rate of the EGR gas has a unique relationship with the absolute pressure of the intake pipe. Note that, as the intake pipe pressure, a gauge pressure based on the atmospheric pressure (atmospheric pressure is 0)
In the case of using (the value at the time of), the gauge pressure cannot be adopted because the pressure in the highland decreases due to the difference in the atmospheric pressure.

Therefore, the target intake air which is the target value of the absolute value of the absolute pressure in the intake pipe downstream of the throttle valve 5a at the time of EGR operation to obtain an appropriate EGR amount for each engine operation region based on the engine speed and the engine load using the intake pipe absolute pressure. The pipe absolute pressure is obtained in advance by an experiment or the like, and the target intake pipe absolute pressure is set as a map using the engine speed and the engine load as parameters, and this map is stored in a series of addresses in the ROM 42 as fixed data. And EG
At the time of execution of R, a control amount for the EGR valve 16 is set according to a comparison result between the target intake pipe absolute pressure by referring to the map and the actual intake pipe absolute pressure downstream of the throttle valve 5a, and a drive signal corresponding to this control amount is set. Output to EGR valve 16 and EGR
The valve opening of the valve 16 is controlled, and feedback control is performed so that the actual intake pipe absolute pressure converges to the target intake pipe absolute pressure. As a result, the EGR gas amount can be indirectly managed by the weight flow rate, and the fresh air and the EGR gas can be controlled regardless of the atmospheric pressure change.
The EGR rate under the same operating conditions can be controlled to be constant by appropriately controlling the weight flow ratio with the gas, and the EGR controllability is improved, and the accuracy of the engine combustion suppression effect by the EGR is improved. Can be appropriately suppressed to improve exhaust emissions.

Hereinafter, specific control processing according to the present invention executed by the ECU 40 will be described with reference to flowcharts shown in FIGS.

When the ignition switch 52 is turned on,
When the power is supplied to the ECU 40, the system is initialized, and each flag and each counter are initialized except for data such as various learning values stored in the backup RAM 44. Then, the starter switch 35 is turned on.
When the engine is started, the engine speed Ne is calculated based on the input interval time of the crank pulse for each input of the crank pulse from the crank angle sensor 30, and the cylinder is determined based on the cam pulse input from the cam angle sensor 33. . Although not described in detail here, the cylinder determination result is reflected in fuel injection control, ignition timing control, and the like.

The flowcharts shown in FIGS. 2 to 5 show an EGR control routine that is executed every set time (for example, 16 ms) after system initialization. First, in steps S1 to S6, the cooling water temperature that determines the EGR execution conditions is set. Determine the conditions.

In step S1, the engine warm-up completion state in which the cooling water temperature Tw is equal to or higher than the water temperature determination value TWEGR is determined with reference to a water temperature condition determination flag FTW. That is, at the time of the first execution of the EGR control routine of FTW = 0, or at the time of engine cooling in which the cooling water temperature Tw is lower than the water temperature determination value TWEGR during the execution of the previous routine, the process proceeds to step S2, and the first water temperature set value TWEGRH ( For example, the water temperature determination value TWEGR is set based on 50 ° C.). If FTW = 1 and the cooling water temperature Tw is equal to or higher than the water temperature determination value TWEGR at the time of execution of the previous routine and the engine has been completely warmed up, the process proceeds to step S3, and the water temperature is calculated based on the second water temperature set value TWEGRL (eg, 46 ° C.). Set the judgment value TWEGR.

Then, in step S4, the cooling water temperature sensor 2
6 is compared with the water temperature judgment value TWEGR,
When it is determined that the engine warm-up is completed in Tw ≧ TWEGR, the process proceeds to step S5, a water temperature condition determination flag FTW is set (FTW ← 1), and when it is determined that Tw <TWEGR, the engine is in a cold state, step S6. Then, the water temperature condition determination flag FTW is cleared (FTW ← 0). Thus, as shown in FIG. 6, hysteresis is provided for switching between the operation (Tw ≧ TWEGR) and the stop (Tw <TWEGR) of the EGR based on the cooling water temperature determination, thereby preventing control hunting.

Next, in steps S7 to S12, the lower limit side of the EGR execution due to the engine load is determined. In step S7, a basic fuel injection pulse width Tp (calculated in a fuel injection amount setting routine, not shown) that indicates an engine load and determines a basic fuel injection amount. Tp ← K × Q / Ne; K is an injector characteristic correction constant, and Q is Intake air amount) is the lower limit LE
It is determined whether or not the state is equal to or greater than GRL with reference to the engine load lower limit determination flag FTPL. That is, FTPL =
In the first execution of the routine of 0 or the previous execution of the routine, the basic fuel injection pulse width Tp is set to the lower limit LGERL.
If the EGR stop region is less than the EGR stop region, the process proceeds to step S8,
The lower limit value LEGRL is set by the first lower limit value LEGRLH (for example, 2.0 ms). If FTPL = 1 and the basic fuel injection pulse width Tp is equal to or larger than the lower limit LEGRL at the time of executing the previous routine, the process proceeds to step S9, and the lower limit LEGRL is set by the second lower limit set value LEGLRLL (for example, 1.5 ms). I do.

In step S10, the currently set basic fuel injection pulse width Tp is read and the lower limit value LE is set.
If Tp ≧ LEGRL compared to GRL, step S1
Proceeding to 1, the engine load lower limit determination flag FTPL is set (FTPL ← 1). If it is determined that the EGR stop region is Tp <LEGRL, the process proceeds to step S12, where the engine load lower limit determination flag FTPL is cleared (FTPL ← 0). ).

Then, in steps S13 to S18, the upper limit of the EGR execution due to the engine load is determined. In step S13, the basic fuel injection pulse width Tp is set to the upper limit value LEG.
It is determined by referring to the engine load upper limit determination flag FTPH whether or not the state exceeds RH. That is, FTPH
= 0 when the routine is first executed or when the previous routine is executed, the basic fuel injection pulse width Tp is set to the upper limit LGER.
If it is equal to or less than L, the process proceeds to step S14, and the first upper limit set value LEGRHH (for example, 5.0 ms) is used to set the upper limit L
Set EGRH. Also, when the previous routine is executed with FTPH = 1, the basic fuel injection pulse width Tp is set to the upper limit value LEGR.
When the engine is in the EGR stop region where the engine speed exceeds H, the process proceeds to step S15, and the second upper limit set value LEGRHL (for example, 4.5 m) is set.
The upper limit value LEGRH is set according to s).

Then, in step S16, the current basic fuel injection pulse width Tp is compared with the upper limit value LEGRH, and Tp ≦
In the case of LEGRH, the routine proceeds to step S17, in which the engine load upper limit determination flag FTPH is cleared (FTH ← 0), and Tp>
If it is determined that the engine is in the LEGRH EGR stop region, the process proceeds to step S18, in which an engine load upper limit determination flag FTPH is set (FTPH ← 1).

That is, under engine load conditions,
It is assumed that the EGR condition is satisfied when LEGRL ≦ Tp ≦ LEGRH. Further, by the above processing, as shown in FIG. 7, hysteresis is provided for switching between the operation and the stop of the EGR based on the engine load determination, and control hunting is prevented.

In the following steps S19 to S24, the engine speed condition is determined. In step S19, the engine speed N
It is determined with reference to the engine speed condition determination flag FNE whether or not the engine is in the high engine speed state in which e exceeds the high engine speed determination value NEGR. That is, when the engine speed NE is equal to or less than the high engine speed determination value NEGR at the first execution of the routine of FNE = 0 or at the time of execution of the previous routine, the process proceeds to step S20, and the first engine speed setting value NEGRH (for example,
(4000 rpm) to set a high rotation determination value NEGR. On the other hand, if FNE = 1 and the engine speed Ne is higher than the high speed determination value NEGR and the engine is in the EGR stop region at the time of execution of the previous routine, the process proceeds to step S21, and the second
The high revolution determination value NEGR is set based on the revolution speed set value NEGRL (for example, 3600 rpm).

In step S22, the current engine speed Ne is read and compared with the high engine speed determination value NEGR.
If Ne ≦ NEGR, the routine proceeds to step S23, where the engine speed condition determination flag FNE is cleared (FNE ← 0), and Ne>
When it is determined that the engine is running at the NEGR high speed, the routine proceeds to step S24, where the engine speed condition determination flag FNE
Is set (FNE ← 1). As a result, as shown in FIG. 8, the EGR operation (Ne) based on the engine speed determination is performed.
Hysteresis is provided for switching between ≤ NEGR and stop (Ne> NEGR) to prevent control hunting.

Next, in steps S25 to S30, a vehicle speed condition is determined. That is, in step S25, a high-speed running state in which the vehicle speed VSP exceeds the high vehicle speed determination value VEGR is determined by referring to the vehicle speed condition determination flag FVSP. That is, FVSP
When the vehicle speed VSP is equal to or lower than the high vehicle speed determination value VEGR at the time of the first execution of the routine of = 0 or at the time of the execution of the previous routine, the process proceeds to step S26, and the first vehicle speed set value VEGRH.
(For example, 120 km / h), a high vehicle speed determination value VEGR is set, and the process proceeds to step S28. If FVSP = 1 and the vehicle speed VSP is in the high-speed running state exceeding the high vehicle speed determination value VEGR during the previous routine and the vehicle is in the EGR stop region, step S2
7 and the second vehicle speed set value VEGRL (for example, 116 k
m / h), a high vehicle speed determination value VEGR is set, and step S2
Proceed to 8.

In step S28, the vehicle speed VSP detected by the vehicle speed sensor 34 is compared with a high vehicle speed determination value VEGR, and VSP ≦ VE
If GR, the process proceeds to step S29, and the vehicle speed condition determination flag FV
SP is cleared (FVSP ← 0), and when it is determined that the high-speed running state of VSP> VEGR is established, the process proceeds to step S30, and a vehicle speed condition determination flag FVSP is set (FVSP ← 1). As a result, as shown in FIG. 9, hysteresis is provided for switching between EGR operation (VSP ≦ VEGR) and stop (VSP> VEGR) based on the vehicle speed determination.
Control hunting between R operation and EGR stop is prevented.

Then, in steps S31 to S37, the EGR condition for executing EGR based on the flags FTW, FTPL, FTPH, FNE, and FVSP, the operation state of the starter switch 35, and the operation state of the idle switch 23b is satisfied. Judge.

In step S31, the starter switch 35
Is determined. That is, the starter switch 3
When 5 is ON and the engine is being started, the engine is in an unstable state. At this time, if EGR is performed, engine stall may occur. Therefore, when the starter switch 35 is ON, it is determined that the EGR condition is not satisfied, the process jumps to step S38 to stop the EGR, and the starter switch 35
In the case of FF, the process proceeds to step S32, and in steps S32 to S36, the EGR condition is determined with reference to the above flags.

That is, in step S33, referring to the water temperature condition determination flag FTW, the engine warm-up is completed with FTW = 1, and the engine load lower limit determination flag FTPL and the engine load upper limit determination are performed in steps S33 and S34, respectively. Referring to the flag FTPH, the basic fuel injection pulse width Tp indicating the engine load is between the lower limit value LEGRL and the upper limit value LEGRH, which is a so-called medium engine load state, and the engine speed condition determination flag FNE is set at step S35. Only when FNE = 0 and the engine speed Ne is outside the high speed range, and in step S36, the vehicle speed condition determination flag FVSP is referred to, and only when FVSP = 0 and the vehicle speed VSP is outside the high-speed traveling region, the step is executed. Proceed to S37, and idle switch 23b
Is determined. And the idle switch 23
Only when b is OFF and in the non-idle state, it is determined that the EGR condition is satisfied, the process proceeds to step S39, and the EGR is executed by the processing after step S39.

Here, when the engine is cold with FTW = 0,
The combustion state of the engine is unstable, and if EGR is performed at this time, the flammability deteriorates and the engine operability deteriorates remarkably. Further, when the engine is under low load operation with FTPL = 0, the intake amount of fresh air is small, and when EGR is performed, the combustibility of the engine deteriorates. Also, when the engine is under high load operation with FTPH = 1, the engine output is required, and if EGR is performed at this time, the engine output will decrease despite the output request. Further, when the engine is rotating at high speed with FNE = 1 or at the time of high-speed running with FVSP = 1, an output request is also made. If EGR is performed at this time, the engine output is reduced contrary to the output request.

Therefore, if any of the conditions is not satisfied in steps S32 to S37, it is determined that the EGR execution condition is not satisfied, and the process proceeds from the corresponding step to step S38, where the control amount EGRS for the EGR valve 16 is fully closed. Is set to “00H” indicating the control amount EGRS
Is set to a predetermined address of the RAM 43 in step S45, and the routine exits.

When the control amount EGRS is set in this routine, the ECU 40 outputs a drive signal corresponding to the control amount EGRS to EG by another routine (not shown).
The EGR valve 16 is driven to drive the stepping motor of the EGR valve 16 to control the opening degree of the EGR valve 16 to be fully closed.
Stop R.

On the other hand, when the EGR execution condition in which all of the conditions in steps S31 to S37 are satisfied is satisfied, step S39 is executed.
To execute EGR. In step S39, the basic control amount EGRB for the EGR valve 16 is set by referring to the basic control amount map based on the engine speed Ne and the basic fuel injection pulse width Tp representing the engine load.

The basic control amount map is an appropriate EG for each engine operating region based on the engine speed Ne and the basic fuel injection pulse width Tp representing the engine load under a predetermined environment.
A control amount for the EGR valve 16 for obtaining the R amount is obtained in advance by an experiment or the like, and this control amount is set as a basic control amount EGRB as a map using the engine speed Ne and the basic fuel injection pulse width Tp as parameters. Is stored as fixed data at the address. An example of this basic control amount map is shown in step S39.

In the present embodiment, as shown in step S39, the engine speed Ne and the basic fuel injection pulse width Tp are set to 2000 to 4000 rpm and 3.0 to 4.0 m, respectively.
The basic control amount EGRB of the largest value in the predetermined region of s
Is stored. This is because the generation amount of NOx in this region is high, and the generation of NOx is suppressed by increasing the EGR rate. And the engine speed N
As e or the basic fuel injection pulse width Tp deviates from the above range, the generation amount of NOx decreases. Accordingly, a small basic control amount EGRB is stored to reduce the EGR rate correspondingly.

Next, in step S40, the target intake pipe absolute pressure map is referred to based on the engine speed Ne and the basic fuel injection pulse width Tp, and the target value of the intake pipe absolute pressure downstream of the throttle valve 5a during EGR operation is set. The target intake pipe absolute pressure P0 is set as follows.

Here, the target intake pipe absolute pressure map is a throttle at the time of EGR operation for obtaining an appropriate EGR gas weight flow rate for each engine operation region based on the engine speed Ne and the basic fuel injection pulse width Tp representing the engine load. A target intake pipe absolute pressure, which is a target value of the intake pipe absolute pressure downstream of the valve 5a, is determined in advance by an experiment or the like, and the target intake pipe absolute pressure P0 is a map using the engine speed Ne and the basic fuel injection pulse width Tp as parameters. Set as ROM
42 are stored in a series of addresses.
An example of this map is shown in step S40. As described above, the EGR rate is increased to suppress the generation of NOx in the medium rotational speed and medium load regions, and the EGR gas weight flow rate is increased to the maximum. The difference is the largest. Accordingly, the target intake pipe absolute pressure P0 also partially rises centering on the region.

In step S41, the target intake pipe absolute pressure P0 is compared with the current actual intake pipe absolute pressure P downstream of the throttle valve 5a detected by the absolute pressure sensor 21. As a result, when it is determined that the actual intake pipe absolute pressure P is higher than the target intake pipe absolute pressure P0 and the EGR gas weight flow rate is larger than the specified value when P> P0, the process proceeds to step S42, and the stepping of the EGR valve 16 is performed. EGR by motor
In order to reduce the EGR gas weight flow rate by reducing the valve opening of the valve 16 by a predetermined amount, the feedback control amount EGRCL is reduced by a predetermined amount, in this embodiment, by one bit (EGRCL ← E
GRCL-1), and the process proceeds to step S44. On the other hand, when it is determined that the actual intake pipe absolute pressure P is lower than the target intake pipe absolute pressure P0 and the EGR gas weight flow rate is smaller than the specified value when P <P0, the routine proceeds to step S43, where the EGR valve 16 is opened. The feedback control amount EGRCL is increased by a predetermined amount to increase the EGR gas weight flow rate by increasing the opening degree by a predetermined amount (EGRCL ← EGRCL + 1), and the process proceeds to step S44.

Further, if P = P0 and it is determined that the actual intake pipe absolute pressure P is equal to the target intake pipe absolute pressure P0 and the EGR gas weight flow rate is equal to the specified value, step S4
Jump directly from step 1 to step S44.

Then, in step S44, the basic control amount EGRB is corrected by the feedback correction amount EGRCL to set the final control amount EGRS for the EGR valve 16 (EGRS ← EGRB + EGRCL), and the following step S45
Then, the control amount EGRS is set to a predetermined address in the RAM 43, and the process exits from the routine.

By setting the control amount EGRS, the ECU 40 outputs a drive signal corresponding to the control amount EGRS to the EGR valve 16 by another routine (not shown), and drives the stepping motor of the EGR valve 16 to The valve opening of the EGR valve 16 is feedback controlled so that the actual intake pipe absolute pressure P converges to the target intake pipe absolute pressure P0. As a result, the EGR gas weight flow rate is appropriately controlled to a specified value for obtaining an appropriate EGR rate.

Here, EGR for reducing NOx
The engine combustion suppression effect due to is determined by the ratio of the weight flow rate of fresh air and EGR gas. Also, if the intake pipe absolute pressure is the same at the time of EGR operation, regardless of the change in atmospheric pressure due to the difference between highland and lowland, etc. However, the ratio of the weight flow rate of fresh air to that of the EGR gas is the same, and the weight flow rate of the EGR gas has a unique relationship with the intake pipe absolute pressure. Therefore, the feedback control of the valve opening of the EGR valve 16 using the absolute pressure of the intake pipe as described above makes it possible to indirectly manage the EGR gas amount by the weight flow rate, and to control the weight of the fresh air and the EGR gas. Since the EGR rate can be controlled to be constant under the same operating condition regardless of the change in the atmospheric pressure by appropriately controlling the flow rate ratio, the EGR controllability is improved, and the accuracy of the engine combustion suppression effect by the EGR is improved. Thus, the emission can be improved by appropriately suppressing the generation of NOx, and can be realized with very simple control.

In this embodiment, the basic fuel injection pulse width Tp is used as the engine load.
The present invention is not limited to this as long as it represents the engine load. Further, the EGR valve is not limited to the stepping motor type EGR valve of the present embodiment. For example, a diaphragm actuator type EGR valve is employed to regulate a control pressure for operating the diaphragm actuator type EGR valve. The control amount for the duty solenoid valve is set according to the comparison result between the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve, and the actual intake pipe absolute pressure downstream of the throttle valve is set to the target intake pipe absolute pressure. Feedback control may be performed so as to converge.

Further, in the present embodiment, the feedback correction amount is set by integral control according to the result of comparison between the target intake pipe absolute pressure and the actual intake pipe absolute pressure. However, proportional integral control (PI control) or The feedback correction amount may be set by proportional integral derivative control (PID control).

[0073]

As described above, according to the first aspect of the present invention, the engine speed and the engine load are determined by using the intake pipe absolute pressure downstream of the throttle valve, which has a unique relationship with the EGR gas weight flow rate. A target intake pipe absolute pressure that is a target value of the intake pipe absolute pressure downstream of the throttle valve during exhaust gas recirculation is set based on the comparison result between the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve. Depending on,
The control amount of the exhaust gas recirculation control valve disposed in the exhaust gas recirculation passage is set to control the valve opening of the exhaust gas recirculation control valve so that the actual intake pipe absolute pressure converges to the target intake pipe absolute pressure. Since the feedback control is performed, the EGR gas amount can be indirectly managed by the weight flow rate.
The gas weight flow rate can be appropriately controlled to a specified value for obtaining an appropriate EGR rate. Therefore, fresh air and E, which determine the engine combustion suppression effect of EGR for reducing NOx, are determined.
It becomes possible to appropriately control the weight flow rate ratio with the GR gas, so that the EG under the same operating conditions can be controlled regardless of the atmospheric pressure change.
The R rate can be controlled to be constant, the EGR controllability can be improved, the accuracy of the engine combustion suppression effect by the EGR can be improved, and the generation of NOx can be appropriately suppressed to improve the exhaust emission. In addition, since the EGR rate can be controlled to an appropriate value, an effect of improving fuel efficiency can be obtained.

Further, a target intake pipe absolute pressure which is a target value of an absolute pressure in the intake pipe downstream of the throttle valve at the time of exhaust gas recirculation set based on the engine speed and an engine load, and an intake pipe absolute pressure downstream of the throttle valve Since the control amount for the exhaust gas recirculation amount adjusting valve is set in accordance with the result of comparison with the above, it can be realized with very simple control.

According to the second aspect of the present invention, the basic control amount is set based on the engine speed and the engine load, and the absolute amount in the intake pipe downstream of the throttle valve during exhaust gas recirculation based on the engine speed and the engine load. Set the target intake pipe absolute pressure to be the target value of pressure, and correct the basic control amount by the feedback correction amount set according to the result of comparison between the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve. Then, the control amount for the exhaust gas recirculation amount adjusting valve is set, so that in addition to the effect of the first aspect of the invention, the basic control amount for obtaining the EGR rate corresponding to the engine operating state is feedback-corrected by the feedback correction amount. As a result, the feedback correction amount can be relatively reduced, and the actual intake pipe absolute pressure downstream of the throttle valve can be quickly reduced to the target intake pressure. Can be converged in the tube absolute pressure, it has an advantage of being able to further improve the EGR controllability.

According to the third aspect of the present invention, it is determined whether or not the execution condition of the exhaust gas recirculation for performing the exhaust gas recirculation is satisfied based on the operating state. Based on the engine load, a target intake pipe absolute pressure which is a target value of the intake pipe absolute pressure downstream of the throttle valve during exhaust gas recirculation is set, and the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve are set. The control amount for the exhaust gas recirculation amount adjusting valve is set in accordance with the comparison result, and when the exhaust gas recirculation execution condition is not satisfied, the control amount for fully closing the exhaust gas recirculation adjusting valve is set, Is stopped, in addition to the effect of the invention described in claim 1, EGR is performed only in a required operation region,
When an engine output is requested or in a region where the engine becomes unstable when EGR is performed, the EGR can be stopped, the effect of suppressing the generation of NOx by the EGR, the prevention of a decrease in engine output due to the EGR when the engine output is requested, and the EG.
The prevention of instability of the engine due to deterioration of the ignitability of the air-fuel mixture by R can be reliably achieved.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the present invention.

FIG. 2 is a flowchart of an EGR control routine;

FIG. 3 is a flowchart of an EGR control routine (continued).

FIG. 4 is a flowchart of an EGR control routine (continued).

FIG. 5 is a flowchart of an EGR control routine (continued).

FIG. 6 is an explanatory diagram showing hysteresis for preventing control hunting of EGR operation switching based on cooling water temperature determination;

FIG. 7 is an explanatory diagram showing hysteresis for preventing control hunting of EGR operation switching based on engine load determination.

FIG. 8 is an explanatory diagram showing hysteresis for preventing control hunting of EGR operation switching based on engine speed determination.

FIG. 9 is an explanatory diagram showing hysteresis for preventing control hunting of EGR operation switching based on vehicle speed determination.

FIG. 10 is an overall schematic diagram of an engine.

FIG. 11 is a circuit configuration diagram of an electronic control system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 3 Intake manifold (intake system) 5a Throttle valve 15 EGR passage (exhaust gas recirculation passage) 16 EGR valve (exhaust gas recirculation amount adjustment valve) 21 Absolute pressure sensor 40 Electronic control unit (target intake pipe absolute pressure setting means, control) Amount setting means, basic control amount setting means, feedback correction amount setting means, exhaust gas recirculation execution condition determining means) Ne Engine speed Tp Basic fuel injection pulse width (engine load) P0 Target intake pipe absolute pressure P Actual intake pipe absolute pressure EGRS control amount EGRB basic control amount EGRCL feedback correction amount

Claims (3)

[Claims] An exhaust gas control system for controlling an exhaust gas recirculation amount by controlling an exhaust gas recirculation amount adjusting valve disposed in an exhaust gas recirculation passage for recirculating exhaust gas of the engine to an intake system in accordance with an engine operating state. A target intake pipe absolute pressure setting means for setting a target intake pipe absolute pressure which is a target value of an intake pipe absolute pressure downstream of the throttle valve at the time of exhaust gas recirculation based on an engine speed and an engine load; An engine having control amount setting means for setting a control amount for the exhaust gas recirculation amount adjusting valve in accordance with a comparison result between the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve. Exhaust gas recirculation amount control device. 2. An engine exhaust system for controlling an exhaust gas recirculation amount by controlling an exhaust gas recirculation amount adjusting valve disposed in an exhaust gas recirculation passage for recirculating exhaust gas of the engine to an intake system in accordance with an engine operating state. In the gas recirculation amount control device, basic control amount setting means for setting a basic control amount for the exhaust gas recirculation amount adjusting valve based on the engine speed and the engine load, and exhaust gas recirculation based on the engine speed and the engine load. A target intake pipe absolute pressure setting means for setting a target intake pipe absolute pressure which is a target value of the intake pipe absolute pressure downstream of the throttle valve at the time of; and a target intake pipe absolute pressure and an actual intake pipe absolute pressure downstream of the throttle valve. Feedback correction amount setting means for setting a feedback correction amount according to the comparison result; and correcting the basic control amount with the feedback correction amount. A control amount setting means for setting a control amount for the exhaust gas recirculation amount adjusting valve. 3. An engine exhaust system for controlling an exhaust gas recirculation amount by controlling an exhaust gas recirculation amount adjusting valve disposed in an exhaust gas recirculation passage for recirculating exhaust gas of the engine to an intake system in accordance with an engine operating state. An exhaust gas recirculation execution condition determining unit configured to determine whether an exhaust gas recirculation execution condition for performing exhaust gas recirculation is satisfied based on an operation state; Target intake pipe absolute pressure setting means for setting a target intake pipe absolute pressure which is a target value of the intake pipe absolute pressure downstream of the throttle valve at the time of exhaust gas recirculation based on the engine speed and the engine load; At times, the control amount for the exhaust gas recirculation amount adjusting valve is set according to the result of comparison between the target intake pipe absolute pressure and the actual intake pipe absolute pressure downstream of the throttle valve, and the exhaust gas is set. Non established when the scan reflux execution conditions, exhaust gas recirculation amount control apparatus for an engine is characterized in that a control amount setting means for setting a control amount of the exhaust gas recirculation control valve is fully closed.