JP2001193522A - Egr control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control EGR amount at a suitable value regardless of DPF collecting amount. SOLUTION: The amount of intake air of a diesel engine 1 is detected by an air flow meter 25, and the opening of EGR valve 23 is feedback-controlled to make the actual mount of intake air be a reference intake air amount settled according to an engine operating condition, in a reference state wherein particulate is not collected in a particulate filter (DPF) 43. Under this condition, actual intake pipe pressure PM is detected by an intake air pressure sensor 59. Then, the particulate collecting amount of the DPF is calculated on the basis of the detected PM and intake pipe pressure (reference intake pipe pressure) when the amount of intake air is controlled to be the reference intake air amount in the reference state. The EDR valve opening is feedback-controlled to make engine intake air amount be a target intake air amount settled by correcting the reference intake air amount on the basis of the collecting amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine provided with an EGR device for recirculating a part of exhaust gas from an internal combustion engine to an intake system, and more particularly, to an internal combustion engine for controlling a flow rate of exhaust gas recirculated to the intake system. The present invention relates to an EGR control device.

[0002]

2. Description of the Related Art An EGR passage which connects an exhaust passage and an intake passage of an internal combustion engine and recirculates a part of exhaust gas to an intake system, and an EGR passage.
2. Description of the Related Art An exhaust gas recirculation (EGR) device including an EGR valve for controlling a flow rate of exhaust gas returning to an intake system through a GR passage is known. The exhaust gas of the internal combustion engine has a low oxygen concentration and functions as an inert gas that does not contribute to combustion. Therefore, generation of nitrogen oxides by combustion air excess ratio is lowered combustion engine by supplying the exhaust to the combustion chamber (NO _X) is suppressed.

In general, the amount of exhaust gas (E
_The amount of NO _X generated as GR quantity) increases is reduced, but there is a problem of the lack of oxygen in the combustion chamber and to increase the EGR amount excessively the combustion state deteriorates. In particular, in a diesel engine, when the amount of EGR increases, problems such as an increase in particulates in exhaust gas and generation of exhaust smoke occur.

[0004] Therefore, in the case of suppressing the NO _X in the exhaust gas by the EGR, in the EGR rate (herein to inhibition effects of the NO _X in the range of increase in the degradation and particulate combustion does not occur is maximized It is necessary to accurately control the ratio of the mass of EGR gas to the mass of intake air taken into the engine, that is, EGR mass / (new air mass + EGR amount is referred to as an EGR rate) in accordance with the engine operating state.

As a method of accurately controlling the EGR rate of an engine, for example, an actual engine intake air amount (mass flow rate of fresh air sucked into the engine) is detected by an air flow meter or the like, and the detected intake air amount is used as a value of the engine. A method is conceivable in which the EGR valve opening is feedback-controlled so that a predetermined target intake air amount is obtained according to the engine operation state such as the load and the number of revolutions. The volume flow rate of the intake air (a mixture of fresh air and EGR gas) taken into the engine has a substantially constant value according to the operating state if the operating state of the engine is determined. For this reason, when the engine operation state is constant, the amount of fresh air drawn into the engine decreases when the amount of EGR gas recirculated to the intake system increases, and the amount of fresh air drawn into the engine decreases when the amount of EGR gas decreases. The amount of qi increases. Therefore, the amount of fresh air (mass flow rate) sucked into the engine is detected, and the EGR valve opening is feedback-controlled so that the mass flow rate becomes a target value determined according to the operating state of the engine. An optimal amount of fresh air and EGR gas can be supplied according to the operation state. As a result, the amount of fresh air and the EGR rate in the intake air of the engine are controlled to optimal values according to the operating state, and the amount of particulates in the exhaust gas does not increase and the exhaust gas smoke does not occur. NO _X can be reduced to the maximum.

As an example of an actual EGR device, there is one described in, for example, Japanese Patent Application Laid-Open No. 63-143373. The device disclosed in the publication sets a standard EGR amount based on a predetermined relationship based on an engine operating state, and controls the actual EGR amount to a value obtained by correcting the standard EGR amount based on an actual exhaust gas temperature. is there. That is, the apparatus of the publication sets the standard EGR amount and the standard exhaust temperature from a relationship stored in advance based on the engine speed and the load. The standard EGR amount is corrected based on the difference between the actually detected exhaust gas temperature and the standard exhaust gas temperature to set the target EGR amount, and the EGR valve is opened so that the actual EGR amount becomes the target EGR amount. I try to control the degree. As a result, in the device of the publication, the EGR amount is controlled to an appropriate value according to the engine operating state.

[0007]

However, in an engine provided with a particulate filter (hereinafter referred to as "DPF") for collecting particulates in exhaust gas in the engine exhaust passage, the state of the DPF depends on the particulate collection state. Because of the change in exhaust resistance, E
Even if the GR feedback control is performed, there arises a problem that the EGR rate cannot be maintained at an optimal value according to the engine operating state.

Since the DPF collects particulates in the exhaust gas during operation of the engine, the pressure loss of the DPF increases as the amount of collected particulates increases. For this reason, DP
As the particulate collection amount of F increases, the exhaust back pressure of the engine increases. When the exhaust back pressure of the engine increases, the engine output loss increases due to the increase in exhaust resistance. Therefore, the amount of fuel supplied to the engine increases to compensate for the output loss. Therefore, at the same engine output and external load, the exhaust gas temperature rises as the amount of particulate trapped by the DPF increases, and accordingly the temperature of the EGR gas passing through the EGR valve also rises. Therefore, when the trapping amount of the particulate filter increases, the actual intake air temperature of the engine after mixing with fresh air also increases. As described above, if the operating conditions such as the engine speed are the same, the volume flow rate of the intake air is the same, but if the engine intake temperature rises, the mass flow rate of the intake air decreases even if the volume flow rate is maintained the same. I do. On the other hand, if the EGR feedback control is performed based on the engine intake air amount as described above, the mass flow rate of the intake air (fresh air) will depend on the operating state of the engine even if the mass flow rate of the intake air after mixing decreases. Is maintained at the target value.
For this reason, when the mass flow rate of the intake air after mixing due to the temperature rise of the EGR gas occurs, this decrease appears as a decrease in the mass flow rate of the EGR gas. In other words, when the EGR feedback control based on the engine intake air amount is performed, if the trapping amount of the particulate filter increases, the mass flow rate of the intake air (fresh air) of the engine is maintained constant, As a result, the mass flow rate of the gas decreases, and a problem arises in that a predetermined EGR rate cannot be obtained according to the operating state of the engine.

If the actual exhaust gas temperature of the engine is detected and the opening of the EGR valve is corrected in accordance with the detected exhaust gas temperature, as in the apparatus disclosed in Japanese Patent Application Laid-Open No. 63-143373, or It is also considered possible to correct the effect of the increase in the exhaust gas temperature due to the increase in the DPF collection amount on the EGR amount. However, in practice, the EGR amount is also affected by the engine exhaust pressure, and when the amount of trapped DPF increases, not only the exhaust temperature but also the exhaust pressure rises. If the EGR amount is corrected in this manner, it becomes difficult to accurately control the EGR amount when the amount of collected DPF increases.

In view of the above problems, the present invention corrects the EGR valve opening in accordance with the change in the exhaust gas temperature and the exhaust pressure due to the collection of particulate matter in the DPF, and accurately corrects the engine regardless of the amount of particulate matter collected in the DPF. It is an object of the present invention to provide an EGR control device for an internal combustion engine, which is capable of controlling an EGR gas amount to an appropriate value according to an operation state.

[0011]

According to the present invention, a particulate filter disposed in an exhaust passage of an internal combustion engine for collecting particulates in exhaust gas, an engine exhaust system and an intake system are provided. The EGR passage to be connected and the EGR
An EGR valve disposed in the passage to control the flow rate of exhaust gas returning to the engine intake system through the EGR passage.
A GR control device for detecting an engine intake air amount and controlling the EGR valve opening so that the detected engine intake air amount becomes a target intake air amount; exhaust pressure and exhaust temperature of the engine; An EGR valve opening correction means for correcting the EGR valve opening so that the recirculated exhaust gas flow returning to the engine intake system through the EGR passage becomes an appropriate value in accordance with both of the above. An EGR control device for an engine is provided.

That is, according to the first aspect of the present invention, the EGR valve opening degree is adjusted by the EGR valve opening degree correction means so that the recirculation exhaust gas flow rate (EG
R gas amount) is corrected to an appropriate value according to both the exhaust pressure and the exhaust temperature of the engine. For this reason, even when the exhaust pressure and the exhaust temperature change due to an increase in the particulate collection amount of the particulate filter, it is possible to always obtain an appropriate EGR gas amount.

According to the second aspect of the present invention, the EG
The R-valve opening correction means detects an engine operating state, and in the detected engine operating state, the recirculated exhaust gas flow rate becomes an optimum value in a reference state in which the particulate filter does not collect particulates. Reference value setting means for setting a reference intake air amount and a reference intake pipe pressure, which are an engine intake air amount and an engine intake pipe pressure at the time, and the control by setting the target intake air amount to the reference intake air amount. Means for detecting the actual intake pipe pressure when the EGR valve opening is controlled by the means, and based on the detected intake pipe pressure and the reference intake pipe pressure, in the current particulate collection state of the particulate filter, Air amount correction means for performing a correction operation for correcting the reference intake air amount so that the recirculated exhaust gas flow rate becomes an appropriate value, and correction by the air amount correction means 2. An EGR for an internal combustion engine according to claim 1, further comprising: target intake air amount setting means for setting the target intake air amount to a reference intake air amount corrected by the air amount correction means after completion of the operation. A control device is provided.

That is, according to the second aspect of the invention, the actual engine intake air amount (the amount of fresh air taken into the engine) is detected, and the detected intake air amount is determined according to the engine operating state such as the engine load and the engine speed. EGR so that the reference intake air amount becomes
The valve opening is feedback-controlled. As previously mentioned,
Even when the feedback control of the EGR valve opening based on the actual intake air amount of the engine is performed, if the exhaust gas temperature and the pressure increase due to the increase in the trapping amount of the particulate filter, the EGR rate of the engine can be accurately determined. Can no longer be controlled. According to the present invention, the actual engine intake pipe pressure is detected when the engine intake air amount is controlled to the reference intake air amount by feedback control of the EGR valve opening based on the engine intake air amount, and the detected engine intake pipe By correcting the reference intake air amount based on the pressure, the EGR valve opening is corrected so that the EGR rate becomes an appropriate value. If a change in the exhaust gas temperature and the exhaust pressure occurs, a sensor for detecting the exhaust gas temperature and the exhaust gas pressure is provided, and if the EGR valve opening is corrected based on the actually detected exhaust gas temperature and the pressure, the exhaust gas can be theoretically exhausted. It is also possible to maintain the EGR rate at an appropriate value even when the temperature and the exhaust pressure change. However, installing a temperature sensor and a pressure sensor in the exhaust passage is not preferable because it complicates the apparatus and increases the cost.
According to the present invention, the EGR valve opening degree can be easily and inexpensively reduced by providing the appropriate EGR rate according to both the actual exhaust pressure and the exhaust temperature without providing an exhaust temperature sensor or a pressure sensor. Has been corrected.

The engine intake pipe pressure corresponds to the actual intake mass flow of the engine. That is, at the same rotational speed, if the intake mass flow rate of the engine increases, the intake pipe pressure increases, and if the mass flow rate decreases, the intake pipe pressure decreases. For this reason, when the mass flow rate of the engine intake air amount (fresh air) is kept constant and the EGR gas mass flow rate decreases (that is, the EGR rate decreases) due to an increase in the exhaust gas temperature, etc. , The intake pipe pressure decreases. On the other hand, when the EGR gas mass flow rate increases (ie, the EGR rate increases) due to the increase in the exhaust pressure, the intake pipe pressure increases because the mass flow rate of the entire intake air increases.

According to the present invention, the engine is operated in a reference state in which the particulate filter does not collect particulates in advance, and the engine intake air amount that provides an optimal EGR gas amount and the engine intake pipe pressure at that time (that is, the reference value). The intake air amount and the reference intake pipe pressure are determined. For this reason, when the engine intake air amount is controlled to be the above reference intake air amount during actual engine operation, the intake pipe pressure is set to the reference value if particulates are not collected at all in the particulate filter. Matches intake pipe pressure. However, as described above, since the mass flow rate of the EGR gas decreases as the particulate collection amount of the particulate filter increases, even if the actual engine intake air amount is the reference intake air amount, the As the trapping amount of the curable filter increases, the intake pipe pressure decreases.

That is, when the engine is operated at the reference intake air amount, the magnitude of the deviation of the actual intake pipe pressure from the reference intake pipe pressure depends on the change in the exhaust gas temperature and pressure caused by the increase in the trapped amount of the particulate filter. , The change in the EGR gas mass flow rate. In the present invention, the particulate trapping amount of the particulate filter is changed in advance, and the deviation of the actual intake pipe pressure from the reference intake pipe pressure when the engine is operated with the reference intake air amount in each engine operating state is obtained. It is. The correction means calculates the deviation of the trapped amount in each engine operating state and the reference intake air amount required to obtain an optimal EGR rate in each of the particulate filter collecting states in the particulate filter. The correction amount is stored, and during actual engine operation, a particulate filter is obtained from a deviation between the engine intake pipe pressure when the engine intake air quantity is controlled to the reference intake air quantity and a previously stored reference intake pipe pressure. Is estimated, and the target intake air amount of the engine is set by correcting the reference intake air amount so that an appropriate EGR rate is obtained under the particulate collection amount. By performing the feedback control of the opening degree of the EGR valve based on the engine intake air amount using the corrected target intake air amount, even when the engine exhaust temperature and pressure change due to an increase in the trapping amount of the particulate filter. Accordingly, the EGR gas amount is always controlled to a value that maintains an appropriate EGR rate. For this reason, the exhaust temperature,
Without measuring the pressure, it becomes proper EGR rate EGR valve opening in accordance with a change in the exhaust temperature and pressure is corrected to a value obtained, increasing or particulates of the NO _X due to the change in the EGR rate Increase, generation of smoke, and the like are prevented.

According to the present invention, when the actual engine intake pipe pressure is lower than the target pressure, the air amount correcting means performs a correction for decreasing the target intake air amount, thereby realizing the actual engine intake air. 3. The EGR control device for an internal combustion engine according to claim 2, wherein a correction for increasing the target intake air amount is performed when a pipe pressure is higher than the target pressure.

That is, according to the third aspect of the present invention, the air amount correcting means determines whether the actual intake pipe pressure is lower than the reference intake pipe pressure, that is, the EGR gas mass flow rate is appropriate for the fresh air mass flow rate. If the value is lower than the value that gives, the correction for reducing the reference intake air amount is performed. This allows
The target intake air amount is set to a value smaller than the reference intake air amount, and the EGR valve opening feedback control based on the engine intake air amount increases the EGR amount and reduces the engine intake air amount (new air amount), so that EGR The rate is controlled to an appropriate value. Similarly, when the actual intake pipe pressure is higher than the reference intake pipe pressure, that is, when the mass flow rate of the EGR gas increases with respect to the mass flow rate of the fresh air,
The reference intake air amount is corrected so that the target intake air amount becomes larger than the reference intake air amount. Thus, the engine intake air amount is increased by the EGR valve opening feedback control, and the EGR rate is controlled to an appropriate value.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to an automobile diesel engine. 1, reference numeral 1 denotes a diesel engine main body, 2 denotes an intake passage of the engine 1, and 20 denotes an intake passage 2.
Is an intake branch pipe connecting the surge tank 20 and the intake port of each cylinder. In the present embodiment, the intake passage 2 is provided with an intake throttle valve 27 for reducing the flow rate of intake air flowing through the intake passage 2 and an intercooler 26 for cooling intake air. The intake throttle valve 27 includes an actuator 27a of an appropriate type such as a solenoid or a vacuum actuator, and takes an opening in accordance with a control signal from an electronic control unit (ECU) 30 described later. In the present embodiment, the intake throttle valve 27 reduces the intake pressure, for example, when the engine is running at a low speed, so that an EGR passage
In addition to being used to increase the amount of exhaust gas (EGR gas) recirculated to the surge tank 20 through the fuel tank 3, the intake air is used when burning the particulates collected by the particulate filter 43 (regenerating the particulate filter 43). Is used to raise the exhaust temperature.

In FIG. 1, reference numeral 25 denotes an air flow meter provided near the intake port of the intake passage 2. In the present embodiment, an air flow meter 25 such as a hot-wire flow meter that can directly measure the mass flow rate of the intake air flowing through the intake passage 2 is used. The air flowing into the intake passage 2 passes through an air flow meter 25, is pressurized by a compressor of an exhaust supercharger (turbocharger) 35, is cooled by an intercooler 26 provided in the intake passage 2, and It is sucked into each cylinder via the branch pipe 21.

Reference numeral 111 in FIG. 1 denotes a fuel injection valve for directly injecting fuel into each cylinder. Fuel injection valve 111
Is a common accumulator (common rail) for storing high-pressure fuel
115. The fuel of the engine 1 is pressurized by the high-pressure fuel pump 113 and supplied to the common rail 115, and is directly injected from the common rail 115 into each cylinder via each fuel injection valve 111.

In FIG. 1, reference numeral 31 denotes an exhaust manifold for connecting an exhaust port of each cylinder to the exhaust passage 3;
Indicated by is a turbocharger. The turbocharger 35 includes an exhaust turbine driven by exhaust gas in the exhaust passage 3 and an intake compressor driven by the exhaust turbine. In this embodiment, the turbocharger 3
An exhaust throttle valve 37 for reducing the flow rate of exhaust gas flowing through the exhaust passage 3 is disposed on the exhaust passage 3 on the downstream side 5. The exhaust throttle valve 37 includes an actuator 37a similar to the intake throttle valve 27, and takes an opening degree according to a control signal from the ECU 30. In the present embodiment, the exhaust throttle valve 37 is used when raising the exhaust gas temperature for regeneration of the particulate filter 43.

Further, in this embodiment, an EGR device for recirculating a part of the engine exhaust gas to the intake system is provided. E
The GR device includes an exhaust manifold 31 and an intake surge tank 2
0 and an EGR passage 33 communicating with the EGR passage 33
An EGR valve 23 disposed above and an EGR cooler 45 provided in an EGR passage upstream of the EGR valve 23 are provided. The EGR valve 23 includes an actuator (not shown), and takes an opening degree in accordance with a control signal from the ECU 30.
The flow rate of the EGR gas that flows back to the intake surge tank 20 through the GR passage 33 is controlled. In the present embodiment, a relatively large amount of E in a wide operating range from a low load range to a high load range.
The EGR valve 23 is controlled to recirculate the GR gas. For this reason, in this embodiment, the intake air drawn into each cylinder contains a relatively large amount of EGR gas. E
Since GR gas is high-temperature exhaust gas discharged from a cylinder,
When a large amount of EGR gas is recirculated to the intake air, the intake air temperature rises, and the intake volume efficiency of the engine decreases. In the present embodiment, in order to prevent this, EGR
The EGR passage 33 upstream of the valve 23 has a water-cooled or air-cooled EGR passage.
A GR cooler 45 is provided. In the present embodiment, E
By using the GR cooler 45 to lower the temperature of the EGR gas recirculated to the intake system, it is possible to suppress a decrease in the intake volume efficiency of the engine and recirculate a relatively large amount of EGR gas.

Reference numeral 30 in FIG. 1 denotes an electronic control unit (ECU) of the engine 1. ECU 3 of the present embodiment
Reference numeral 0 denotes a microcomputer having a known configuration, in which a CPU, a RAM, a ROM, an input port, and an output port are mutually connected by a bidirectional bus. E
The CU 30 performs basic control such as fuel injection control and rotation speed control of the engine 1, and in the present embodiment, as described later,
Feedback control of the EGR valve 23 opening based on the engine intake air amount and correction of the target intake air amount based on the intake pipe pressure are performed.

In order to perform these controls, a signal corresponding to the engine speed NE is input to an input port of the ECU 30 from a speed sensor 55 disposed near the crankshaft of the engine 1, and an air flow meter 25 is provided. And a signal corresponding to the driver's accelerator pedal depression amount (accelerator opening) ACCP from the accelerator opening sensor 57 disposed near the engine accelerator pedal and the signal corresponding to the EGR valve 23. A signal VEG representing the EGR valve opening from the disposed EGR valve opening sensor 51 and a signal representing the intake pipe pressure PM from the intake pressure sensor 59 disposed in the intake surge tank 20 are input.

The output port of the ECU 30 is connected to a fuel injection valve 11 of the engine 1 through a fuel injection circuit (not shown).
1 and controls the fuel injection amount and fuel injection timing from the fuel injection valve 111. The output port of the ECU 30 is connected to actuators of the EGR valve 23, the intake throttle valve 27, and the exhaust throttle valve 37 via a drive circuit (not shown), and controls the respective valve openings.

Further, in the present embodiment, a known type of exhaust purification catalyst 41 such as a three-way catalyst and a particulate filter (DPF) 4 are disposed downstream of the exhaust throttle valve in the exhaust passage 3.
3 are arranged. The DPF 43 is formed of, for example, a filter such as a metal mesh or a ceramic porous material, and captures particulates in the exhaust gas. In this embodiment, the DPF
As the 43, a known particulate filter of an appropriate type can be used.

As described above, the particulates in the exhaust gas during the operation of the engine are collected in the DPF 43, and gradually increased.
The pressure loss of the exhaust flowing through the PF 43 increases. For this reason, D
When the amount of particulate matter trapped by the PF increases, the exhaust pressure in the exhaust manifold 31 increases, and an increase in back pressure causes a decrease in engine output, an increase in fuel consumption, and the like. For this reason, in the present embodiment, when the amount of trapped particulates of the DPF 43 increases, the exhaust throttle valve 37 and / or the intake throttle valve 27 are closed to reduce the engine intake air amount and reduce the exhaust gas temperature. The DPF 43 is regenerated by raising it. By the DPF regeneration operation, DPF4
Since the particulates trapped in 3 are burned and removed from the DPF, the pressure loss of the DPF 43 recovers.

However, as described above, the DPF 4
When the regeneration operation of No. 3 is performed, the pressure loss of the DPF 43 gradually increases as the particulates are collected during the operation of the engine, and decreases (recovers) repeatedly as the regeneration operation is performed. As will be described later, in the present embodiment, the ECU 30 adjusts the opening degree of the EGR valve 23 so that the engine intake air amount (mass flow rate of fresh air) detected by the air flow meter 25 becomes a target value determined according to the engine operating state. The feedback control of the EGR valve opening based on the controlled engine intake air amount is performed. Thereby, the EGR gas mass occupying the mass of the intake air (total of the fresh air and the EGR gas) sucked into the engine, that is, the EGR gas mass / (new air mass + EGR) appropriate for the operating state of the engine Gas mass)) is always maintained at an appropriate value, and NO _X in the exhaust gas is reduced while preventing an increase in particulates and generation of smoke.

However, if the trapping amount of the particulate filter increases and the exhaust back pressure of the engine fluctuates, the proper EGR valve opening feedback control based on the engine intake air amount is performed as described above. There is a problem that the rate cannot be maintained. When the exhaust back pressure of the engine increases, the exhaust temperature rises accordingly, so that the temperature of the entire intake of the engine rises and the mass flow rate of the engine intake drops even if the volume flow rate of the engine intake is maintained constant. . On the other hand, E
When the feedback control of the opening degree of the GR valve is performed, the mass flow rate of the engine intake air amount (fresh air) is kept constant, so that the mass flow rate of the EGR gas is reduced by the decrease in the mass flow rate of the intake air. That is, the EGR rate decreases. To prevent this, it is theoretically sufficient to detect the engine exhaust gas temperature and correct the EGR gas amount based on the exhaust gas temperature. However, in practice, when the engine exhaust back pressure increases, the amount of burned gas remaining in the cylinder increases due to the increase of the exhaust manifold pressure, and the internal EGR amount increases. Further, in this embodiment, since the EGR cooler 45 for cooling the EGR gas is provided, the rise in the exhaust gas temperature is not equal to the EGR gas temperature. For this reason, in practice, these factors act in a complicated manner, and the EGR gas amount cannot be appropriately corrected only by detecting the exhaust gas temperature.

In this embodiment, this problem is solved by setting the target intake air amount in the feedback control of the EGR valve opening based on the engine intake pipe pressure detected by the intake pressure sensor 59. When the engine speed is constant, the mass flow rate of the intake air (sum of fresh air and EGR gas) actually taken into the engine has a value corresponding to the intake pipe pressure. That is, in a state where the engine speed is constant, the intake pipe pressure becomes the same if the mass flow rate of the engine intake is the same.
Now, consider a state in which the amount of trapped particulates in the DPF is zero (reference state). In this reference state, parameters such as the engine intake air amount, the intake pipe pressure, the exhaust temperature, and the exhaust back pressure depend on the engine operating conditions (rotational speed NE, accelerator opening ACC).
If P) and the EGR rate are determined, they will be constant values accordingly. Therefore, in the reference state, the engine intake air amount (reference intake air amount) that gives an appropriate EGR rate according to each operating condition is obtained in advance, and the engine intake air amount is set to the reference intake air amount.
If the R valve is feedback controlled, the EGR rate becomes an appropriate constant value according to each operating condition, and the engine intake pipe pressure is a constant value (reference intake pipe pressure) determined according to the rotational speed NE and the accelerator opening ACCP. become.

However, when the amount of trapped particulates in the DPF increases, the EGR rate changes from the optimum value due to changes in exhaust temperature and exhaust back pressure, even if the engine intake air amount is controlled to the reference intake air amount, and the intake air amount is reduced. , The engine intake pipe pressure changes from the reference intake pipe pressure.
The deviation (deviation) of the engine intake pipe pressure from the reference intake pipe pressure when the engine intake air quantity is maintained at the reference intake air quantity is D
Since the value increases as the amount of particulate matter trapped in the PF increases, the deviation can be used as a parameter representing the amount of particulate matter trapped in the DPF. In addition, since the amount of engine intake air that gives an appropriate EGR rate in each operation state also changes according to the amount of particulate matter trapped in the DPF, if the amount of particulate matter trapped in the DPF is determined, the appropriate EGR rate is adjusted accordingly. The amount of engine intake air to be given can be determined.

Therefore, in this embodiment, the EGR valve opening is controlled so that the reference intake air amount according to the current engine operating conditions (NE, ACCP) is obtained at regular intervals during engine operation. An actual intake pipe pressure PM is detected, and a DPF is determined based on a deviation between the detected intake pipe pressure PM and a reference intake pipe pressure PM ₀ under current engine operating conditions.
Is calculated. In the present embodiment, the engine is operated with the reference intake air amount for each engine operating condition with the particulate matter trapping amount MDP of the DPF being different in advance, and the actual intake pipe pressure PM and the reference intake pipe pressure PM at that time are operated. ₀ deviation between the ΔPM (= PM ₀ -PM) leave measure, collection amount MDP and the engine operating conditions (NE, AC
The relationship between CP) and ΔPM is stored in the ROM of the ECU 30. During actual engine operation, the intake pipe pressure deviation Δ when the engine intake air amount is controlled to the reference intake air amount
The particulate trapping amount MDP is calculated from PM, NE, and ACCP based on the above relationship.

In this embodiment, based on the actual particulate matter collection amount MDP calculated as described above, the target intake air amount is calculated by correcting the reference intake air amount under each operating condition so as to give an appropriate EGR rate. I do. In this embodiment, the engine is operated in advance with the particulate matter trapping amount MDP of the DPF being different, and the correction amount of the reference intake air amount is obtained in advance so that an optimum EGR rate can be obtained under each operating condition. , ACCP, MDP, and the correction amount are stored in the ROM of the ECU 30. During actual engine operation, this correction amount is calculated from the particulate trapping amount MDP obtained as described above, and NE and ACCP.

Next, the above-mentioned EGR control in this embodiment will be described in detail with reference to FIGS. FIG.
4 is a flowchart illustrating a feedback control operation of an EGR valve opening based on an engine intake air amount. This operation is performed by a routine executed by the ECU 30 at regular intervals.

In FIG. 2, in step 201, the engine speed NE, the intake air amount Gn, and the accelerator opening ACCP are first read from the rotation speed sensor 55, the air flow meter 25, and the accelerator opening sensor 57. In step 203, NE and A read as described above are read.
From CCP, the reference intake air amount Gnt in the current engine operating state is calculated. The value of the reference intake air amount Gnt is stored in advance in the ROM of the ECU 30 in the form of a two-dimensional numerical map using the engine speed NE and the accelerator opening ACCP.

Next, at step 205, it is determined whether or not the value of the flag X is set to 1. Flag X
Is a flag indicating whether or not a calculation operation (FIG. 3) of the particulate matter trapping amount MDP of the DPF 43 described below is currently being executed. If X ≠ 1 in step 205,
That is, if the operation for calculating the MDP is not currently executed, the value of the particulate trapping amount MDP calculated by the operation in FIG.
In, the value of the correction coefficient α of the reference intake air amount under the current operating conditions (NE, ACCP) is calculated from the values of NE, ACCP and the MDP read as described above. As described above, the value of the correction coefficient α of the reference intake air amount is obtained in advance by an experiment, and NE, ACCP,
It is stored in the form of a three-dimensional numerical map using MDP values.

In step 209, the current operating conditions (NE,
(ACCP) Current particulate collection amount MD
After calculating the value of the correction coefficient α corresponding to P, next, at step 21
In step 1, the reference intake air amount Gn calculated in step 203 is set.
The value of t is multiplied by a correction coefficient α, and the reference intake air amount Gnt
Is corrected to Gnt × α. Thus, in the feedback control operation of the opening degree of the EGR valve 23 after step 213, the corrected value of the reference intake air amount Gnt is used as the target intake air amount.

On the other hand, if the calculation operation of the particulate trapping amount MDP is currently being executed in step 205 (X =
1) includes the reference intake air amount G calculated in step 203.
The correction of the value of nt by the correction coefficient α is not performed. That is, during the operation of calculating the particulate collection amount MDP,
Using the value of the reference intake air amount Gnt calculated in step 203 as it is as the target intake air amount, feedback control of the EGR valve 23 opening degree in step 213 and thereafter is performed.

Steps 213 to 221 show a feedback control operation of the opening degree of the EGR valve 23 based on the engine intake air amount Gn using the target intake air amount Gnt set as described above. That is, in step 213, first, it is determined whether or not the actual intake air amount Gn is larger than the target air amount Gnt by a predetermined positive constant value A or more.
With a target opening VEG ₀ increases set by a predetermined amount ΔV of 3, the actual EGR valve 23 opening VE at step 221
G is feedback controlled to the target opening VEG _0. As a result, the amount of EGR gas returning to the intake system increases, and the amount Gn of fresh air sucked into the engine relatively decreases. On the other hand, if Gn−Gnt ≦ A in step 213, then in step 217, it is determined whether the actual intake air amount Gn is smaller than the target air amount Gnt by A or more (Gn−Gnt <−A). If it is smaller than A, the target opening degree V of the EGR valve 23 is determined at step 219.
EG ₀ is decreased by a fixed amount ΔV, and at step 221 the actual EGR valve 23 opening VEG is reduced to the target opening VE.
A feedback control so that the G _0. As a result, the amount of EGR gas recirculated to the intake system decreases, and the amount Gn of fresh air sucked into the engine relatively increases. That is, by executing steps 213 to 221, the actual intake air amount Gn becomes the target intake air amount Gn.
t is controlled within a range of ± A.

FIG. 3 is a flowchart showing an operation for calculating the particulate trapping amount MDP of the DPF 43. This operation is performed by a routine executed by the ECU 30 at regular intervals. Figure 3, the value of the counter CT at step 301 whether or not has reached a predetermined value CT ₀ is determined. The counter CT is incremented by one each time the operation in FIG. 3 is executed, and is cleared in step 317 after the value of the particulate trapping amount MDP is calculated. Since this operation is performed at regular intervals, the value of the counter CT indicates the elapsed time since the previous calculation of the value of the particulate collection amount MDP was completed by the above operation. That is, step 30
At 1, it is determined whether or not a predetermined time has elapsed since the last time the MDP value calculation operation was completed.

If CT <CT ₀ in step 301, that is, if the predetermined time has not elapsed since the completion of the previous MDP calculation operation, this operation is executed in step 303 and subsequent steps.
The processing ends only by executing step 319 without executing the DP calculation operation. As described above, in order to calculate the value of MDP, it is necessary to perform the feedback control of the opening degree of the EGR valve 23 so that the engine intake air amount becomes the uncorrected reference intake air amount. For this reason, M
At the time of the DP calculation operation, the engine EGR rate may not coincide with the appropriate value.
It is not preferable to perform the P calculation operation. Also, DP
Since the particulate collection amount MDP of F gradually increases, the calculation operation of MDP does not need to be performed at such short intervals. Therefore, in the present embodiment, the value of CT ₀ in step 301 is set to a value corresponding to a relatively long time (for example, several minutes to several tens of minutes).

If the predetermined time has elapsed in step 301 (CT ≧ CT ₀ ), then the MDP calculation operations in steps 303 to 317 are executed. In this case, at step 303, the aforementioned flag X (step 2 in FIG. 2)
05) is set to 1. Thus, in the operation of FIG. 2, the EGR is performed using the uncorrected reference intake air amount Gnt.
The feedback control of the opening degree of the valve 23 is performed, and the engine intake air amount Gn is calculated based on the engine speed NE and the accelerator opening degree ACCP in step 203 of FIG. (Air amount) is controlled within a range of ± A.

Next, at step 305, it is determined whether or not the current engine intake air amount Gn is controlled within a range of ± A with respect to the uncorrected reference intake air amount Gnt by the feedback control of FIG. Only when the value is within the range of ± A, D in steps 307 to 313
The value of the particulate collection amount MDP of the PF 43 is calculated.

That is, in step 307, the actual engine intake air amount pressure PM is read from the intake pressure sensor 59 in addition to the current engine speed NE and the accelerator opening ACCP. Then, the reference intake pipe pressure PM ₀ is calculated using the values of step 309 in NE and ACCP. As described above, when the reference intake pipe pressure PM ₀ is in the reference state (the state in which the particulate matter trapping amount of the DPF is zero), the intake air amount Gn is uncorrected to the reference intake air amount (step 2 in FIG. 2).
03 is the intake pipe pressure when controlled to NE), and NE and A are stored in the ROM of the ECU 30 by experiments.
It is stored in the form of a two-dimensional numerical map using CCP.

Next, in step 309, step 3
A deviation ΔPM is calculated as ΔPM = PM−PM ₀ from the actual intake pipe pressure PM and PM ₀ read at 07. As described above, ΔPM is a value corresponding to the particulate collection amount MDP of the DPF 43. Then, in step 313, the current value of the particulate trapping amount MDP of the DPF 43 is calculated based on the values of NE, ACCP, and ΔPM. The value of the particulate trapping amount MDP is determined by actual measurement, and the RO of the ECU 30 is previously determined in the form of a three-dimensional numerical map using the values of NE, ACCP, and ΔPM.
M. Thus, in the operation of FIG. 2, the next time step 207 is executed, the latest MDP value is read.

When the operation of calculating the value of MDP is completed as described above, the value of the flag X is set to 0 in step 315. Accordingly, in the operation of FIG. 2, the operations of steps 207 to 211 are executed after step 205, and the engine intake air amount Gn is set to a value (corrected after correction) corresponding to the current particulate collection amount of the DPF 43. Gnt), and the engine EGR rate is controlled to an appropriate value. In step 317, the value of the counter CT is cleared, so in step 319, the value of the counter CT indicates the elapsed time after the completion of the MDP calculation operation.

As described above, in this embodiment, the DP is determined based on the intake pipe pressure when the engine is operated at the reference intake air amount.
Since the amount of particulates collected by F is calculated and the target amount of intake air is set by correcting the reference amount of intake air based on the calculated amount of collected particulates, it is always appropriate regardless of the amount of particulates collected by the DPF. It is possible to obtain a high EGR rate.

[0050]

According to the invention described in each of the claims, the engine operation state can be accurately determined irrespective of the particulate matter trapping amount of the DPF by correcting the EGR valve opening in accordance with both the exhaust gas temperature and the exhaust gas pressure. Thus, a common effect is achieved that enables the EGR amount to be controlled to an appropriate value according to the above.

According to the second and third aspects of the present invention, when the EGR valve opening is corrected in accordance with both the exhaust gas temperature and the pressure in addition to the above-mentioned common effects, the exhaust gas is actually exhausted. Since there is no need to provide a temperature sensor or an exhaust pressure sensor, the EGR is easily and inexpensively and appropriately adjusted to an appropriate value according to the engine operating state regardless of the amount of particulate matter collected by the DPF.
This has the effect that the amount can be controlled.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment in which the present invention is applied to a vehicle diesel engine.

FIG. 2 is a flowchart illustrating an EGR valve opening degree feedback control operation of the embodiment of FIG. 1;

FIG. 3 is a flowchart illustrating a DPF particulate collection amount calculation operation of the embodiment of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Diesel engine main body 2 ... Intake passage 3 ... Exhaust passage 23 ... EGR valve 25 ... Air flow meter 43 ... Particulate filter 59 ... Intake pressure sensor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G062 AA01 AA05 BA04 BA06 EA04 ED08 FA05 FA09 GA01 GA02 GA04 GA09 GA21 GA22 3G301 HA02 HA11 HA13 HA14 JA24 JA25 KA24 LA00 LA03 LC07 MA11 NA08 NB02 NC01 NC02 NC08 ND01 NE23 PA04Z PA09 PD11Z PD14Z PD15Z PE01Z PF03Z

Claims (3)

[Claims] 1. A particulate filter disposed in an exhaust passage of an internal combustion engine for collecting particulates in exhaust gas, an EGR passage connecting an engine exhaust system and an intake system, and an EGR passage disposed in the EGR passage. An EGR control device for an internal combustion engine, comprising: an EGR valve that controls an exhaust gas flow rate recirculated to an engine intake system, wherein the engine intake air amount is detected and the detected engine intake air amount is set to a target intake air amount. Control means for controlling the opening degree of the EGR valve so as to obtain the EG according to both the exhaust pressure and the exhaust temperature of the engine.
EGR for correcting the opening degree of the EGR valve so that the recirculated exhaust gas flow returning to the engine intake system through the R passage becomes an appropriate value.
An EGR control device for an internal combustion engine, comprising: a valve opening correction means. 2. The EGR valve opening correction means detects an engine operation state, and in the detected engine operation state, the recirculation exhaust gas flow rate in a reference state in which the particulate filter does not collect particulates. Reference value setting means for setting a reference intake air amount and a reference intake pipe pressure which are an engine intake air amount and an engine intake pipe pressure when the target intake air amount becomes the optimum value; The control means detects the actual intake pipe pressure when the EGR valve opening is controlled by the control means, and based on the detected intake pipe pressure and the reference intake pipe pressure, the current particulate filter Air amount correction means for performing a correction operation for correcting the reference intake air amount so that the recirculated exhaust gas flow rate becomes an appropriate value in the curated collection state; And a target intake air amount setting means for setting the target intake air amount to a reference intake air amount corrected by the air amount correction means after completion of the correction operation by the air amount correction means. An EGR control device for an internal combustion engine according to claim 1. 3. The air amount correction means performs a correction to reduce the reference intake air amount when the actual engine intake pipe pressure is lower than the reference intake pipe pressure, and makes the actual engine intake pipe pressure fall below the target pressure. 3. The EGR control device for an internal combustion engine according to claim 2, wherein a correction for increasing the target intake air amount is performed when the target intake air amount is high.