JP2001271674A - Exhaust emission control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent large fluctuations of exhaust recirculation quantity, caused by an increase in exhaust gas pressure when post-injection is performed, in an engine performing a feedback control for exhaust recirculation quantity, based on a change of intake air quantity. SOLUTION: For a prescribed period immediately after a post-injection control is started, a feedback control based on a change of intake air quantity is switched to a feedback control, based on a change of oxygen concentration in exhaust gas, and the feedback control is prevented from reacting excessively to increase in the exhaust gas pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an engine.

[0002]

2. Description of the Related Art Heretofore, as a catalyst for purifying the exhaust gas of an internal combustion engine, HC in the exhaust gas near the stoichiometric air-fuel ratio has been used.
There are known three-way catalysts that can simultaneously and extremely effectively purify (hydrocarbons), CO and NOx (nitrogen oxides),
In a gasoline engine, it is common practice to use the three-way catalyst and to control the air-fuel ratio to approximately the stoichiometric air-fuel ratio in most of the operating region except the full load region and the like.

However, a diesel engine is in a state where the air-fuel ratio is quite lean (for example, A / F ≧ 18) in all normal operating ranges, so that the three-way catalyst cannot be used. In a lean state, the oxygen concentration in the exhaust gas becomes considerably high, and it is difficult to sufficiently reduce and purify NOx in such an atmosphere.

On the other hand, NOx is absorbed in an oxygen-excess atmosphere where the oxygen concentration in the exhaust gas is equal to or higher than a predetermined value (for example, 4%).
There is a technique that uses a so-called NOx trap catalyst that emits NOx. Since the NOx trap catalyst has a reduced absorption performance when the NOx absorption amount increases, it is necessary to perform a so-called refresh to release the absorbed NOx before the NOx absorption amount increases.

Therefore, as described in Japanese Patent Application Laid-Open No. 6-212961, for example, in a diesel engine, when the above-described refresh is to be performed, a small amount of fuel is supplied from the middle stage of the expansion stroke after the main fuel injection to the exhaust stroke. The post-injection reduces the oxygen concentration in the exhaust gas.

Japanese Patent Application Laid-Open No. Hei 8-200045 discloses an engine provided with an exhaust recirculation means for recirculating a part of exhaust gas from an exhaust passage to an intake system and a NOx trap catalyst in the vicinity of a top dead center of a compression stroke of the engine. By performing a post-injection of injecting fuel from the injection valve at a predetermined timing of an expansion stroke or an exhaust stroke after the main injection of injecting fuel,
It is described that the amount of the reducing agent in the exhaust gas is increased for a predetermined period to release NOx from the NOx trap catalyst, and at that time, exhaust gas recirculation means is prohibited from recirculating exhaust gas. This is because if the post-injected fuel is returned to the intake system without burning and introduced into the combustion chamber, the area around the spark plug becomes excessively rich and misfires, and the post-injected fuel burns and returns. And the possibility that the oxygen concentration around the spark plug would be extremely low and cause a misfire.

[0007]

By the way, in the engine having the exhaust gas recirculation means as described above, when the amount of the reducing agent in the exhaust gas is increased by the post-injection, the pressure of the exhaust gas is increased by the so-called after-burning. That is, even if the opening of the exhaust gas recirculation amount control valve is not changed, the amount of exhaust gas recirculated to the intake system increases. At this time, if a method of performing feedback control of the opening degree of the exhaust gas recirculation amount control valve so that the exhaust gas recirculation amount becomes a target value based on the degree of change of the intake air amount detected by the air flow sensor is employed, the post-injection As the amount of intake air decreases due to the increase in the amount of exhaust gas recirculation, the exhaust gas recirculation amount control valve is controlled in the closing direction. When the reducing agent amount increase control ends, the pressure of the exhaust gas decreases and the exhaust gas recirculation amount decreases, so that the exhaust gas recirculation amount control valve is controlled in the opening direction.

However, in the case of controlling the increase of the reducing agent amount by the post-injection, the opening degree of the exhaust gas recirculation amount control valve must be strictly changed each time by the feedback control. , The fluctuation of the exhaust gas recirculation amount is rather large, or the fluctuation of the exhaust gas recirculation amount does not quickly converge to the target value, and the fluctuation tends to be unnecessarily long.

Further, for example, when it is intended to increase the exhaust gas recirculation amount simultaneously with the increase in the reducing agent amount due to the post-injection,
That tendency is strong.

FIG. 8 is a time chart schematically showing feedback control of the exhaust gas recirculation amount.
When the post-injection for each predetermined cylinder is started at time point 1 and the target value EGRt of the exhaust gas recirculation amount is increased, the difference between the actual exhaust gas recirculation amount EGR and the target value EGRt (that is, the intake air detected by the air flow sensor) is obtained. The feedback control amount EGRF / B corresponding to the difference between the amount and the target intake air amount) rises. Accordingly, the opening of the exhaust gas recirculation amount control valve increases, but the actual exhaust gas recirculation amount EGR rapidly increases to exceed the target value EGRt because of the increase in exhaust gas pressure.
Since the amount of intake air detected by the air flow sensor decreases sharply in response to this rapid increase, the feedback control amount EGRF
/ B decreases and becomes negative, and the opening degree of the valve decreases.

As described above, the exhaust gas recirculation amount sharply increases due to the increase in the exhaust gas pressure due to the post-injection and the increase in the target value of the exhaust gas recirculation amount, and the airflow sensor responds sensitively to this and is reflected in the feedback control amount. Therefore, the fluctuation of the exhaust gas recirculation amount becomes large, and the convergence thereof also deteriorates. In other words, when the target value of the exhaust gas recirculation amount is increased to increase the opening of the valve, the feedback control tends to work in the direction to close the valve due to the increase in the exhaust gas pressure, and hunting occurs. It is something that will be.

The present invention is intended to prevent the feedback controllability of the exhaust gas recirculation amount from deteriorating due to the increase in the exhaust gas pressure caused by such an increase in the reducing agent.

[0013]

For this purpose, the present invention provides:
When the amount of the reducing agent in the exhaust gas is increased by the post-injection, the feedback control of the exhaust gas recirculation amount based on the degree of change of the intake air amount is suppressed.

That is, the present invention provides an injection valve which faces a combustion chamber of an engine and injects fuel into the combustion chamber, and an exhaust which recirculates a part of exhaust gas from an exhaust passage extending from the combustion chamber to an intake system of the engine. Recirculation means, means for detecting an intake air amount, and exhaust gas recirculation amount control means for performing feedback control based on a degree of change in the intake air amount detected by the detection means so that the recirculation amount of exhaust gas becomes a target value. A post-injection for injecting fuel from the injection valve to purify exhaust gas at a predetermined timing of an expansion stroke or an exhaust stroke after a main injection in which the injection valve injects fuel near a top dead center of a compression stroke of the engine. And a reducing agent increasing means for increasing the amount of reducing agent in the exhaust gas for a predetermined period of time, wherein the amount of reducing agent is increased by the reducing agent increasing means. Characterized in that it comprises a suppression means for suppressing the feedback control of the air recirculation amount control means.

Therefore, according to the present invention, even if the exhaust gas pressure increases with an increase in the amount of the reducing agent in the exhaust gas, thereby increasing the exhaust gas recirculation amount and changing the intake air amount, this intake Since the feedback control of the exhaust gas recirculation amount based on the degree of change in the air amount is suppressed, it is possible to avoid a large change in the exhaust gas recirculation amount and deterioration of the convergence to the target value. For this reason, for example, in a diesel engine, it is advantageous in obtaining a desired effect of exhaust gas recirculation such as reducing NOx without increasing the amount of soot generation.

In this case, suppression of feedback control means that feedback control is temporarily prohibited (for example,
The opening degree of the exhaust gas recirculation amount control valve may be fixed at the opening degree immediately before the increase of the reducing agent amount), or the response of control to the degree of change of the intake air amount may be reduced.

According to the present invention, there is provided an exhaust gas purifying apparatus for an engine as described above, further comprising an exhaust gas recirculation amount increasing means for increasing the exhaust gas recirculation amount when the reducing agent amount is increased by the reducing agent increasing means. And

For example, in the case where an intake throttle valve for adjusting the intake air amount is provided in the intake passage, means for reducing the intake air amount simultaneously with increasing the reducing agent amount is to reduce the opening degree of the intake passage by the intake throttle valve. However, doing so increases the pumping loss of the engine. Therefore, in the present invention, by increasing the amount of exhaust gas recirculation, it is possible to reduce the amount of intake air without increasing pumping loss, and to vaporize fuel by introducing high-temperature exhaust gas into the combustion chamber.・ Atomization is promoted to reduce soot generation.

When the exhaust gas recirculation amount is increased when the amount of the reducing agent is increased, the feedback control of the exhaust gas recirculation amount based on the degree of change in the intake air amount is continued as described above. In this case, a large change in the exhaust gas recirculation amount is likely to occur, and the convergence to the target value also deteriorates. However, according to the present invention, the feedback control of the exhaust gas recirculation amount based on the degree of change in the intake air amount is suppressed. Therefore, it is possible to avoid such a problem.

When means for increasing the target value of the exhaust gas recirculation amount feedback control is employed for increasing the exhaust gas recirculation amount, the responsiveness of the feedback control to the degree of change in the intake air amount may be used as the suppression means. What is necessary is just to adopt the thing which lowers.

The present invention also relates to an exhaust gas purifying apparatus for an engine, wherein the exhaust gas recirculation amount is increased when the amount of the reducing agent is increased, wherein when the oxygen concentration in the exhaust gas is high in the exhaust passage, the exhaust gas is exhausted. A NOx trap material that absorbs NOx in the gas and releases NOx when the oxygen concentration is reduced is provided.
It is characterized in that the amount of the reducing agent in the exhaust gas is increased in order to release NOx from the Ox trap material.

That is, when the NOx absorption amount of the NOx trapping material becomes close to the saturation amount, it is necessary to reduce the oxygen concentration in the exhaust gas to release NOx. This is to increase the amount of the reducing agent in the exhaust gas.

According to the present invention, in the exhaust gas purifying apparatus for an engine as described above, the suppression means executes the suppression only for a predetermined period immediately after the increase of the reducing agent amount by the reducing agent increasing means. It is characterized by.

That is, the exhaust gas recirculation amount fluctuates largely due to the feedback control based on the degree of change in the intake air amount immediately after the reducing agent amount is increased. Therefore, the feedback control is performed only for a predetermined period immediately after the increase. If suppressed, such large fluctuations can be avoided, and thereafter, the desired exhaust gas recirculation amount can be obtained by restarting the feedback control.

Further, according to the present invention, in the exhaust gas purifying apparatus for an engine as described above, the first exhaust gas recirculation amount for which the amount of recirculated exhaust gas is feedback-controlled based on the degree of change in the amount of intake air so as to be a target value. In addition to the control means, means for detecting the oxygen concentration in the exhaust gas, and feedback control so that the recirculation amount of the exhaust gas becomes a target value based on the degree of change in the oxygen concentration detected by the oxygen concentration detecting means. A second exhaust gas recirculation amount control means, wherein the suppression means causes the second exhaust gas recirculation amount control means to execute the control of the exhaust gas recirculation amount instead of the first exhaust gas recirculation amount control means. Features.

When the exhaust gas recirculation amount increases, the intake air amount decreases accordingly, the air-fuel ratio changes to the rich side, and the oxygen concentration in the exhaust gas also decreases. Therefore, the exhaust gas recirculation amount can be feedback-controlled based on the degree of change in the oxygen concentration. With such feedback control, even if the exhaust gas recirculation amount increases due to an increase in the exhaust gas pressure due to an increase in the amount of the reducing agent, this does not immediately appear as a change in the oxygen concentration but after a predetermined time. In this case, the feedback control reacts excessively and the fluctuation of the exhaust gas recirculation amount is prevented from increasing, and the feedback control to the target value of the exhaust gas recirculation amount can be continued. Even when the target value is changed with an increase in the reducing agent amount, the exhaust gas recirculation amount can be made closer to the target value.

[0027]

As described above, according to the present invention, when the amount of the reducing agent in the exhaust gas is increased by the post-injection or when the amount of the recirculated exhaust gas is increased together with the amount of the reducing agent, the intake air Since the feedback control of the exhaust gas recirculation amount based on the degree of the change in the amount is suppressed, even if the exhaust gas recirculation amount increases due to an increase in the exhaust gas pressure due to an increase in the reducing agent amount and the intake air amount changes, the change does not In this case, it is possible to prevent the feedback control from excessively reacting and the exhaust gas recirculation amount to fluctuate greatly, and to thereby prevent the convergence to the target value from deteriorating, which is advantageous in controlling the exhaust gas recirculation amount to a desired value.

Further, according to the present invention, since the feedback control is suppressed only for a predetermined period immediately after the reducing agent amount is increased during the increasing period, the exhaust gas recirculation amount is prevented from largely fluctuating. Thereafter, the desired exhaust gas recirculation amount can be obtained by restarting the feedback control.

Further, the present invention is characterized in that, in addition to the first exhaust gas recirculation amount control means for performing feedback control on the exhaust gas recirculation amount based on the degree of change of the intake air amount so as to become a target value, the present invention provides A means for detecting the oxygen concentration; and a second exhaust gas recirculation amount control means for performing feedback control on the recirculation amount of the exhaust gas based on the degree of change in the oxygen concentration so as to be a target value. Since the control of the exhaust gas recirculation amount is performed by the second exhaust gas recirculation amount control means instead of the first exhaust gas recirculation amount control means, the feedback control reacts excessively and the fluctuation of the exhaust gas recirculation amount varies. Can be avoided, and feedback control can be performed so that the exhaust gas recirculation amount approaches the target value.

[0030]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall structure of an exhaust gas purifying apparatus A for a diesel engine according to an embodiment of the present invention. Reference numeral 1 denotes an engine body of a multi-cylinder diesel engine mounted on a vehicle. The engine body 1 has a plurality of cylinders 2 (only one is shown), and a piston 3 is reciprocally fitted into each of the cylinders 2. The combustion chamber 4 is formed. In addition, an injector (fuel injection valve) 5 is disposed substantially at the center of the upper surface of the combustion chamber 4 with the injection hole at the tip end facing the combustion chamber 4.
The injection holes are opened and closed at a predetermined injection timing for each cylinder so that fuel is directly injected into the combustion chamber 4.

Each of the injectors 5 is connected to a common common rail (accumulator) 6 for storing high-pressure fuel.
A high-pressure supply pump 8 driven by a crankshaft 7 is connected to the common rail 6. The high-pressure supply pump 8 operates so that the fuel pressure in the common rail 6 detected by the pressure sensor 6a is maintained at a predetermined value or more. A crank angle sensor 9 for detecting a rotation angle of the crank shaft 7 is provided.
Is composed of a plate to be detected (not shown) provided at the end of the crankshaft 7 and an electromagnetic pickup arranged to face the outer periphery of the plate, and the electromagnetic pickup is provided around the entire periphery of the plate to be detected. A pulse signal is output in response to the passage of the projections formed at predetermined angles.

Reference numeral 10 denotes an intake passage for supplying intake air (air) filtered by an air cleaner (not shown) to the combustion chamber 4 of the engine main body 1. At a downstream end of the intake passage 10, a surge tank (not shown) is provided. Each passage branched from the surge tank is connected to each cylinder 2 by an intake port.
Are connected to the combustion chamber 4. The surge tank is provided with an intake pressure sensor 10a for detecting a supercharging pressure supplied to each cylinder 2. The intake passage 10 includes, in order from the upstream side to the downstream side, a hot film type air flow sensor 11 for detecting a flow rate of intake air taken into the engine body 1, and a blower 12 driven by a turbine 21 to compress intake air. An intercooler 13 for cooling the intake air compressed by the blower 12 and an intake throttle valve (intake air amount adjusting means) 14 for reducing the cross-sectional area of the intake passage 10 are provided. The intake throttle valve 14 is a butterfly valve provided with a notch so that intake air can flow even in a fully closed state. Like the EGR valve 24 described later, the magnitude of the negative pressure acting on the diaphragm 15 is negative pressure. The opening degree of the valve is controlled by being adjusted by the control electromagnetic valve 16. Further, the intake throttle valve 1
4 is provided with a sensor (not shown) for detecting the opening.

An exhaust passage 20 for discharging exhaust gas from the combustion chamber 4 of each cylinder 2 is connected to the combustion chamber 4 of each cylinder 2 via an exhaust manifold. The exhaust passage 20 includes, in order from the upstream side to the downstream side, a linear O2 sensor 17 for detecting the oxygen concentration in the exhaust gas, a turbine 21 rotated by the exhaust flow, and HC and CO in the exhaust gas.
And a catalytic converter 22 capable of purifying NOx. Further, the catalytic converter 22 is provided with a temperature sensor 18 for detecting the temperature of the catalyst.

As shown in FIG. 2, the catalytic converter 22 includes an oxidation catalyst 22a for oxidizing and purifying HC and CO and a NOx trap catalyst 22b in series on the upstream side and the downstream side in the exhaust gas flow direction. They are arranged.

Each of the catalysts 22a and 22b has a structure in which a catalyst layer is formed on the wall of each through-hole of a cordierite carrier having a honeycomb structure having a large number of through-holes extending parallel to the axial direction. The catalyst layer of the oxidation catalyst 22a is formed by supporting a catalyst powder obtained by supporting Pt on alumina and ceria on the carrier with a binder. N
The catalyst layer of the Ox trap catalyst 22b is formed by supporting a catalyst powder obtained by supporting Pt and Ba as a NOx trap material on zeolite with a binder on the carrier. When the oxygen concentration of the exhaust gas is high (for example, when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio (for example, A / F ≧ 18) and the oxygen concentration is 4% or more), the NOx trap catalyst 22 b It has a function of absorbing NOx in gas by Ba and releasing the absorbed NOx and reducing and purifying the NOx by Pt when the oxygen concentration is reduced and, for example, the oxygen excess ratio λ is around 1.

An exhaust gas recirculation passage (hereinafter, referred to as an EGR passage) 23 for recirculating a part of the exhaust gas to the intake side branches from a portion of the exhaust passage 20 upstream of the turbine 21, and a portion downstream of the EGR passage 23. The end is connected to the intake passage 10 downstream of the intake throttle valve 14. Near the downstream end of the EGR passage 23, an exhaust gas recirculation amount control valve (exhaust gas recirculation amount adjusting means: hereinafter referred to as an EGR valve) whose opening degree can be adjusted.
A part of the exhaust gas is recirculated to the intake passage 10 while adjusting the flow rate of the exhaust gas in the exhaust passage 20 by the EGR valve 24.

The EGR valve 24 is of a negative pressure responsive type, and a negative pressure passage 27 is connected to a negative pressure chamber of the valve box. The negative pressure passage 27 is connected to a vacuum pump (negative pressure source) 29 via a negative pressure control electromagnetic valve 28. The negative pressure passage 27 is controlled by a control signal (current) from an ECU 35 described later. By opening and closing 27, the negative pressure for driving the EGR valve in the negative pressure chamber is adjusted, whereby the opening of the EGR passage 23 is linearly adjusted.

The turbocharger 25 is a VGT (Variable Geometry Turbo), to which a diaphragm 30 is attached, and a solenoid valve 3 for negative pressure control.
By adjusting the negative pressure acting on the diaphragm 30 by 1, the cross-sectional area of the exhaust gas passage is adjusted.

Each of the injectors 5, high pressure supply pump 8, intake throttle valve 14, EGR valve 24, turbocharger 25
And the like are configured to be operated by a control signal from a control unit (Engine Control Unit: hereinafter referred to as ECU) 35. On the other hand, the ECU 35 receives an output signal from the pressure sensor 6a, an output signal from the crank angle sensor 9, an output signal from the pressure sensor 10a, an output signal from the air flow sensor 11, and an output signal from the O2 sensor 17. An output signal, an output signal from the temperature sensor 18, an output signal from the lift sensor 26 of the EGR valve 24, and an accelerator opening sensor for detecting an operation amount (accelerator opening) of an accelerator pedal (not shown) by a driver of the vehicle. 3
2 are input at least.

The amount of fuel injected by the injector 5 and the fuel injection timing are controlled in accordance with the operating state of the engine body 1 and the state of the catalysts 22a and 22b. The injection pressure is controlled. In addition to this, the intake air amount is controlled by operating the intake throttle valve 14, the exhaust gas recirculation amount is controlled by operating the EGR valve 24, and the operation control of the turbocharger 25 (VGT Control) is performed.

(Fuel Injection Control) The ECU 35 stores in a memory a fuel injection amount map in which an optimum fuel injection amount Qb experimentally determined according to changes in the target torque and the rotation speed of the engine body 1 is recorded. Electronically stored and provided. Then, based on the target torque obtained based on the output signal from the accelerator opening sensor 32 and the engine speed obtained based on the output signal from the crank angle sensor 9, the main injection amount Qb is obtained from the fuel injection amount map. Is read, and the excitation time (valve opening time) of each injector 5 is determined based on the main injection amount Qb and the common rail pressure detected by the pressure sensor 6a.
By this main fuel injection control, an amount of fuel corresponding to the target torque of the engine body 1 is supplied, and the engine body 1
Is operated in a state where the average air-fuel ratio in the combustion chamber 4 is considerably lean (A / F ≧ 18).

During normal operation (when the change in the accelerator opening is small), when the NOx trap amount of the NOx trap catalyst 22b is equal to or more than a predetermined value, λ = 1 and NOx trap catalyst 22b In order to reduce and purify the exhaust gas, post-injection control for increasing the amount of the reducing agent in the exhaust gas is executed. The post-injection is to inject an appropriate amount of fuel in an expansion stroke or an exhaust stroke after the main injection (main fuel injection).

Hereinafter, the control will be described in detail with reference to the control flow shown in FIG. This control is executed at every predetermined crank angle.

First, in step S1 after the start, a crank angle signal, an air flow sensor output, an accelerator opening, and the like are read. In the following step S2, the NOx trap amount Nx of the NOx trap catalyst 22b is estimated.
The NOx trap amount Nx can be estimated based on the history of the engine speed and the engine load from the engine start or the previous NOx release control, or simply estimated based on the engine operating time. Alternatively, a sensor for detecting the concentration of NOx in the exhaust gas may be arranged in the exhaust passage 20 downstream of the NOx trap catalyst 22b for estimation.

In the subsequent step S3, when it is determined that the NOx trap amount Nx exceeds the predetermined value Nxo,
Proceeding to step S4, the timer T is incremented and N
Even when the Ox trap amount Nx does not exceed the predetermined value Nxo, if it is determined in step S5 that the timer T is counting, the process proceeds to step S4, where the value is incremented. The predetermined value Nxo is N in the NOx trap catalyst 22b.
This is the NOx trap amount near the limit value at which the Ox trap is saturated.

In the following step S6, the timer T is set to a predetermined value To.
When the timer T has reached the predetermined value To, the routine proceeds to step S7, where the routine proceeds to step S7 where the routine proceeds to step S7.
Is set to zero, and the process proceeds to step S8 to set the injection amount and the injection timing for operating the engine with the normal air-fuel ratio lean. When it is determined in step S5 that the timer T is not counting, the process proceeds to step S8. The predetermined value To is a time during which the NOx release control is performed, in other words, a time during which the amount of the reducing agent is increased by the post-injection.
5 seconds.

Step S8 will be described first. Here, the main injection amount Qb and its injection timing Ib are set according to the engine operating state. The main injection amount Qb is read from the fuel injection amount map based on the accelerator opening and the engine speed. The fuel injection amount map records the optimum injection amount Qb experimentally determined according to changes in the accelerator opening and the engine speed. The main injection amount Qb is determined as the accelerator opening increases and the engine The higher the rotation speed,
It is set to increase. The main injection timing Ib is set near the top dead center of the compression stroke.
With reference to (crank angle), the more the injection amount Qb is, the more the advance is made, and the smaller the injection amount Qb is, the more the retard is made.
Further, based on the engine water temperature, when the water temperature is low, the main injection timing Ib is retarded by a predetermined amount and the warm-up operation is performed. Further, the post-injection amount Qp is set to zero.

Next, the injection control for setting λ = 1 (oxygen concentration in the exhaust gas to 0.5% or less) will be described. In step S9, the main injection amount Q for setting λ = 1 is set.
bλ and its injection timing Ibλ, and the post-injection amount Qpλ and its injection timing Ibλ are set. The post-injection is performed after the main injection for all the cylinders, and the main injection amount Qbλ is set to the main injection amount Qb during the normal lean operation in order to prevent the engine output from rising excessively due to the influence of the post-injection.
The post-injection amount Qpλ is set to, for example, 30 to 50% (for example, 40%) of the main injection amount Qbλ. The main injection timing Ibλ can be the same as the injection timing Ib during the lean operation. The post-injection timing Ibλ is set at 10 to 90 ° CA, preferably 10 to 20 ° CA after the compression stroke top dead center (ATDC) (for example, at ATDC 15 ° CA).
Set.

The post-injection may not be performed for all cylinders, but may be performed only for predetermined cylinders that undergo an expansion stroke at predetermined intervals.

In step S10, Qbλ, Ibλ, Qpλ, and Ibλ set as described above are given as the main injection amount Qb, the main injection timing Ib, the post-injection amount Qp, and the post-injection timing Ib. . When the injection amount and the injection timing for the normal lean operation are set in step S8, the process also proceeds to step S11 and subsequent steps. That is, when the main injection timing Ib is reached, the main injection is executed (steps S11 and S12). When the post-injection should be performed for the cylinder that has performed the main injection (step S13), the rear injection is performed at the time when the post-injection timing Ip is reached. The injection is executed, and the process returns (steps S14, S15).

(Example 1 of EGR Control) Next, the characteristic EGR control of the present invention will be described with reference to the flow chart shown in FIG.

In step SA1 after the start, a crank angle signal, an accelerator opening signal, an airflow sensor output, an O2 sensor output, and the like are read. Subsequent step SA2
In step (1), a target fresh air amount (target intake air amount) At corresponding to a target EGR amount according to the operating state of the engine is set by reading from a map which is set and electronically stored in advance. This map corresponds to the engine speed and the accelerator opening so that the target EGR amount decreases as the engine speed increases and the accelerator opening increases, so that the target fresh air amount At increases. Is set to.

In the following step SA3, the timer T
When it is determined that the counting is being performed, the control goes to step SA4.
Then, the target fresh air amount At is changed to the target fresh air amount Atλ for increasing the EGR amount and setting the oxygen excess ratio λ = 1. That is, At> Atλ during the air-fuel ratio lean operation.

In the following step SA5, a difference ΔEGR between the target fresh air amount At and the actual fresh air amount (actual intake air amount) detected by the air flow sensor is determined.
, The EGR feedback control amount based on ΔEGR
EGRF / B is obtained by PID operation.

In step SA7, when it is determined that the timer T is in the initial stage of increasing the reducing agent less than the predetermined value T1 (T1 <To), the feedback control based on the O2 sensor output is performed instead of the feed control based on the airflow sensor output. The flow advances to step SA8 to adopt the target oxygen amount O2xo. In addition, this target oxygen amount O2xo is λ =
The oxygen concentration that becomes 1 is about 0.5%. When feedback control based on the O2 sensor output is performed over the entire period (NOx release control period) in which the amount of the reducing agent is increased by the post-injection, T1 = To.

In the following step SA9, the target oxygen amount O
Actual oxygen concentration detected by 2xo and O2 sensors,
That is, the difference ΔEGRx from the actual oxygen amount O2x is obtained, and the EGR feedback control amount EGRF / Bx is read and set from a map previously set and electronically stored and stored in step SA10.

This map is composed of ΔEGRx and EG as shown in FIG.
The relationship with RF / Bx is defined. When ΔEGRx increases with a positive value, EGRF / Bx decreases with a negative value, and when ΔEGRx is a predetermined positive value or more, EGRF / Bx becomes a negative constant value (−A). EGRF / Bx increases with a positive value as ΔEGRx increases with a negative value, and ΔEGRx
Is greater than or equal to a negative predetermined value, EGRF / Bx becomes a positive constant value (+ B), and A <B.

As described above, the EGR feedback control amount
Since EGRF / Bx adopts a proportional control type that has a high response to a change in ΔEGRx, the reducing agent increasing control is performed to shift from the air-fuel ratio lean operation state to λ = 1 operation,
When ΔEGRx becomes negative, the EGR feedback control amount EGRF / Bx increases in proportion to this, and λ = 1
The transition to operation is quick. Further, since A <B, even if ΔEGRx changes to a positive value, E
The reduction amount of the GR feedback control amount EGRF / Bx is small,
It is possible to avoid a large lean air-fuel ratio.

In the following step SA11, EGRF / Bx based on the output of the O2 sensor is used as an EGR feedback control amount EGR.
Given as F / B. In the next step SA12, EGR
A smoothing process (EGR) in which the previous value EGRF / B (k-1) of the feedback control amount EGRF / B is reflected at a predetermined ratio to the current value EGRF / B (k).
F / B = EGRF / B (k-1) × a + EGRF / B (k) × (1-a) where 0 <a <1) is performed, and the EGR valve is controlled based on the EGR feedback control amount EGRF / B. Is driven (step S
A13).

If the timer T is not counting at step SA3, the control proceeds to step SA5 because the reducing agent increase control is not performed. If the timer T is counting but the timer value T has exceeded T1 in step SA7, the flow proceeds to step SA8 without shifting to EGR feedback control based on the O2 sensor output in step SA8 and below.
Proceed to 2.

The smoothing process in step SA12 is to gradually reduce the difference between the EGR feedback control amount EGRF / B when the EGR feedback control based on the output of the airflow sensor is changed from the EGR feedback control based on the output of the O 2 sensor to the EGR feedback control amount EGRF / B. Work to make it smaller,
A sudden change in the EGR control amount is prevented.

As described above, in the above-described embodiment, the predetermined period immediately after the control of increasing the reducing agent in order to release NOx from the NOx trap catalyst is based on the output of the O2 sensor instead of the EGR feedback control based on the output of the airflow sensor. Since the EGR feedback control is employed, it is possible to prevent the fluctuation of the exhaust gas recirculation amount from increasing and the convergence to the target value from deteriorating.

(Example 2 of EGR control) FIG. 6 shows only a processing part of another example of EGR control which is different from the control example of FIG. That is, the process from the start to step SA7 and the process from step SA12 to return are the same as those in FIG.

In this example, if it is determined in step SA7 that the timer value T is in the range of 0 to T1, the process proceeds to step SB1, and the EGR feedback control amount EGRF / B
Is smaller than a predetermined first minimum value Min1. If it is smaller, the process proceeds to step SB2, the first minimum value Min1 is given as the EGR feedback control amount EGRF / B, and the process proceeds to step SA12.
Proceeding to B3, it is determined whether the EGR feedback control amount EGRF / B is larger than a predetermined first maximum value Max1. If it is larger, the process proceeds to step SB4, where the first maximum value Max1 is given as the EGR feedback control amount EGRF / B, and the process proceeds to step SA12. EGR feedback control amount EGRF
When / B is equal to or more than the first minimum value Min1 and equal to or less than the first maximum value Max1, the process proceeds to step SA12 without changing the control amount.

On the other hand, at step SA7, the timer value T
Is greater than or equal to T1, if it is determined in step SB5
Then, it is determined whether the EGR feedback control amount EGRF / B is smaller than a predetermined second minimum value Min2. If smaller, the process proceeds to Step SB6, where the second minimum value Min2 is given as the EGR feedback control amount EGRF / B, and the process proceeds to Step SA12. If larger, the process proceeds to Step SB7, where the EGR feedback control amount EGRF / B is reduced to a predetermined value. 2 maximum value
Determine whether it is greater than Max2. If it is larger, the process proceeds to step SB8, and the EGR feedback control amount EGRF
At step SA12, the second maximum value Max2 is given as / B.
Proceed to. When the EGR feedback control amount EGRF / B is equal to or more than the second minimum value Min2 and equal to or less than the second maximum value Max2, the process proceeds to step SA12 without changing the control amount.

However, the first minimum value Min1 <the second minimum value Min2, and the first maximum value Max1 <the second maximum value Max2.

Accordingly, in the case of this control example, the EGR feedback control amount EGRF / B is calculated based on the output of the air flow sensor for a predetermined period immediately after the control of increasing the reducing agent in order to release NOx from the NOx trap catalyst. However, the value is restricted to a range from the first minimum value Min1 to the first maximum value Max1. That is, the responsiveness of the feedback control to the change in the intake air amount is reduced. Therefore, it is possible to prevent the fluctuation of the exhaust gas recirculation amount from increasing and the convergence to the target value from deteriorating.

(Example 3 of EGR control) FIG. 7 shows another example of the EGR control, showing only processing portions different from the control example of FIG. That is, the process from the start to step SA7 and the process from step SA12 to return are the same as those in FIG.

In this example, if it is determined in step SA7 that the timer value T is in the range of 0 to T1, the process proceeds to step SC1, and the EGR feedback control amount EGRF / B
Is based on the ΔEGR of step SA4, step SA5
Is calculated by a PID operation having different coefficients. That is, the coefficients P1, I1, and D1 in step SC1 are all smaller than the coefficients P, I, and D in step SA5.

Therefore, in the case of this control example, the responsiveness of the feedback control to the change in the intake air amount is reduced during a predetermined period immediately after the control of increasing the reducing agent in order to release NOx from the NOx trap catalyst. It is possible to prevent the fluctuation of the reflux amount from becoming large and the convergence to the target value from deteriorating.

Although the above embodiment relates to a direct injection diesel engine, the present invention can be applied to a direct injection gasoline engine.

In this embodiment, the fresh air amount is detected by using the air flow sensor. However, the fresh air amount may be detected by the intake negative pressure sensor.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an exhaust gas purification device for a diesel engine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a catalytic converter.

FIG. 3 is a flowchart of fuel injection control.

FIG. 4 is a flowchart of an exhaust gas recirculation control example 1.

FIG. 5 is a graph showing a relationship between an oxygen concentration deviation EGRx and a feedback control amount EGRF / Bx.

FIG. 6 is a flowchart of an exhaust gas recirculation control example 2.

FIG. 7 is a flowchart of an exhaust gas recirculation control example 3.

FIG. 8 is a time chart schematically showing conventional feedback control of the exhaust gas recirculation amount.

[Explanation of symbols]

 A Exhaust gas purifier 1 Diesel engine 2 Cylinder 4 Combustion chamber 5 Injector (fuel injection valve) 11 Air flow sensor 17 Oxygen concentration sensor 20 Exhaust passage 22 Catalytic converter 23 Exhaust recirculation passage (EGR passage) 24 Exhaust recirculation control valve (EGR valve) 35 ECU (control unit)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F01N 3/28 301 F01N 3/28 301E 3/36 3/36 B F02D 41/38 F02D 41/38 B 41/40 41 / 40 D 43/00 301 43/00 301J 301N 45/00 366 45/00 366B F02M 25/07 550 F02M 25/07 550F 550R (72) Inventor Kazushi Kataoka 3-1, Fuchu-cho, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Akihiro Kobayashi 3-1, Fuchu-cho, Aki-gun, Hiroshima Pref. EB08 EB11 EB25 EC02 FA08 FA10 FA11 FA12 FA20 FA29 FA33 FA37 FA38 3G091 AA02 AA10 AA11 AA18 AA28 AB02 AB06 AB09 BA02 BA14 BA15 BA19 CA13 CA18 CB02 CB03 CB07 CB08 DA01 DA02 DA05 DA08 DA10 DB01 DB05 DB06 DB07 DB08 EA07 EA18 EA30 EA31 EA33 EA34 FB10 GA06 GB01X GB03Y GB04X GB06W GB09X GB10X GB17X HA36 HA37 HA47 HB05 HB06 3G092 AA01 AA02 AA13 AA17 AA18 BA04 BA06 BB02 BB06 BB13 DB02 DC09 DC15 EA07 EA09 EA11 EA17 EB01 EC01 EC09 FA18 HE08 HD08 HA01XZ05 HD08 HA02 HA06 HA11 HA13 JA04 JA06 JA24 KA21 LC07 MA12 MA19 MA23 MA27 NA01 NA08 NC02 ND01 NE12 NE15 NE23 PA04Z PA07Z PA16Z PD04A PD04Z PD12Z PD15A PD15Z PE01Z PE03Z PE06Z PE08Z PF03Z

Claims (5)

[Claims] An injection valve that faces a combustion chamber of an engine and injects fuel into the combustion chamber; an exhaust recirculation unit that recirculates a part of exhaust gas from an exhaust passage extending from the combustion chamber to an intake system of the engine; Means for detecting the amount of intake air, exhaust gas recirculation amount control means for performing feedback control so that the recirculation amount of exhaust gas becomes a target value based on the degree of change in the amount of intake air detected by the detection means, and the injection valve At the predetermined time of the expansion stroke or the exhaust stroke after the main injection in which fuel is injected near the top dead center of the compression stroke of the engine, the post-injection of the fuel from the injection valve for purifying the exhaust gas in the exhaust gas purifies the exhaust gas. An exhaust gas purification device for an engine, comprising: means for increasing the amount of reducing agent for a predetermined period of time. Exhaust purification apparatus for an engine, characterized in that it comprises a suppression means for suppressing the feedback control. 2. The exhaust gas purifying apparatus for an engine according to claim 1, further comprising an exhaust gas recirculation amount increasing means for increasing the exhaust gas recirculation amount when the reducing agent amount is increased by the reducing agent increasing means. Engine exhaust purification device. 3. The exhaust gas purifying apparatus for an engine according to claim 2, wherein when the oxygen concentration in the exhaust gas is high in the exhaust passage, the NOx in the exhaust gas is absorbed, and NOx is reduced by the decrease in the oxygen concentration. A NOx trap material to be released is provided, and the reducing agent increasing means includes a NOx trap material from the NOx trap material.
An exhaust gas purifying apparatus for an engine, wherein an amount of a reducing agent in exhaust gas is increased to release x. 4. The exhaust gas purifying apparatus for an engine according to claim 1, wherein said suppressing means is a predetermined period immediately after the reducing agent amount is increased by said reducing agent amount increasing unit. An exhaust gas purification apparatus for an engine, wherein the suppression is performed only. 5. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the feedback control is performed so that the recirculation amount of the exhaust gas becomes a target value based on the degree of change in the intake air amount. Means for detecting the oxygen concentration in the exhaust gas, in addition to the first exhaust gas recirculation amount control means, and a target value for the exhaust gas recirculation amount based on the degree of change in the oxygen concentration detected by the oxygen concentration detection means. A second exhaust gas recirculation amount control means for performing feedback control so that the second exhaust gas recirculation amount control is performed in place of the first exhaust gas recirculation amount control means for controlling the exhaust gas recirculation amount. An exhaust gas purification device for an engine, which is executed by a control unit.