JP2001263130A - Exhaust emission control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent HC in exhaust gas from passing through a catalyst without being oxidized thereby. SOLUTION: An NOx purifying catalyst 22a and an oxidizing catalyst 22b are arranged in an exhaust passage 20 so that the former is on the upstream side, and the latter is on the downstream side. When the HC quantity in exhaust gas supplied to the catalyst 22a by injection is increased after a main fuel injection performed near the top dead center of compression stroke, the injection timing is retarded more when the temperature of the downstream oxidizing catalyst 22a is low than when it is high.

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, Japanese Patent Application Laid-Open No. 9-317524 discloses a first diesel engine suitable for reducing and purifying NOx upstream of an exhaust passage in a low temperature region.
A catalyst device is arranged, a second catalyst device suitable for reducing and purifying NOx in a high temperature region is arranged downstream of the catalyst device, and a main fuel injection for generating engine output is performed near a top dead center of a compression stroke, and expansion is performed. In the exhaust stroke or the exhaust stroke, post-fuel injection is performed to increase the amount of hydrocarbon supplied to the catalyst, and then the amount of fuel injection is controlled in accordance with the catalyst temperature, thereby purifying NOx using HC in the exhaust gas as a reducing agent. Is described as being performed effectively.

That is, in view of the fact that when the amount of HC in the exhaust gas increases due to the post-fuel injection, the catalyst temperature rises due to the heat of the HC oxidation reaction in the catalyst, the NOx purification activity is increased for the first and second catalytic devices. When the temperature is lower than the peak temperature, the post-fuel injection amount is increased and the NO
x purification is performed, and when the temperature is higher than the peak temperature, the amount of post-fuel injection is reduced to suppress a rise in the temperature of the catalyst, and to purify NOx as close to the peak temperature as possible.

Japanese Patent Application Laid-Open No. Hei 8-261502 discloses a fuel injection system in which main injection of fuel is performed near a top dead center of a compression stroke of an engine, and post injection of fuel is performed in an expansion stroke or an exhaust stroke. It describes that when the temperature of the reducing catalyst is high, the post-injection timing is delayed as compared with when the temperature is low. That is, by controlling the post-injection timing, the HC having a small carbon number in the exhaust gas is increased when the catalyst temperature is low, and the HC having a large carbon number in the exhaust gas is increased when the catalyst temperature is high. That is. This is based on the finding that HC having a small carbon number effectively works as a reducing agent in purifying NOx on the low temperature side, and HC having a large carbon number works effectively as a reducing agent in purifying NOx on the high temperature side.

[0007]

The first and second catalysts for NOx reduction described above include, for example, Pt or C
Although it carries u, it can be said that it has an oxidation catalyst function because it oxidizes HC in the exhaust gas to reduce NOx. However, NO
If the amount of HC that is not used for reducing x and blows through it is large, when the downstream catalyst has not reached an active state, the blown HC is discharged to the atmosphere without being oxidized and purified by the downstream catalyst. Will be done. This is the same even when a catalyst having an oxidation catalyst function is disposed alone in the exhaust passage, and it is necessary to avoid an increase in the amount of HC that flows through without being oxidized by the catalyst.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention suppresses blow-by of the reducing agent such as HC by controlling the post-injection timing.

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 upstream valve which is disposed in an exhaust passage extending from the combustion chamber and has an oxidation catalyst function for purifying exhaust gas. Reduction of exhaust gas by post-injection of fuel injected from the injection valve at a predetermined time during an expansion stroke or an exhaust stroke after fuel is injected near the top dead center of the compression stroke of the engine by the side catalyst and the injection valve. Reducing agent increasing means for increasing the amount of agent, a downstream catalyst arranged in the exhaust passage downstream of the upstream catalyst and having an oxidation catalyst function for purifying exhaust gas, and a temperature of the downstream catalyst. An exhaust gas purifying apparatus for an engine, comprising: a catalyst temperature detecting unit that detects the temperature of the downstream catalyst detected by the catalyst temperature detecting unit. When the temperature of lower than a predetermined value, characterized in that as the post injection timing is slower than when the predetermined value or more.

In such an exhaust gas purifying apparatus for an engine, when the downstream catalyst is inactive at a low temperature, it is necessary to increase the amount of the reducing agent so that the oxidation catalyst function of the upstream catalyst is sufficiently exhibited. Since the injection timing is retarded, the amount of the reducing agent flowing through the upstream side catalyst is reduced. Although the reason is not clear, according to the study of the present inventors, the proportion of the reducing agent oxidized by the upstream catalyst is large, and the amount of the reducing agent discharged to the atmosphere without being oxidized is reduced. ing. In addition, the fact that the ratio of the reducing agent oxidized by the upstream catalyst due to the delay of the post-injection timing increases means that the exhaust gas temperature increases due to the reaction heat of the catalyst, and the exhaust gas having the increased temperature has a lower temperature. This means that the catalyst is supplied to the downstream catalyst, which is advantageous for increasing the temperature of the downstream catalyst, that is, early activation.

When the temperature of the downstream catalyst is high, the post-injection timing is advanced, thereby reducing the proportion of the reducing agent oxidized by the upstream catalyst. However, since the activity of the downstream catalyst is high, the amount of the reducing agent discharged to the atmosphere without being oxidized is reduced.

The catalyst having an oxidation catalyst function is a catalyst mainly supporting a noble metal or Cu, and is not only an oxidation catalyst and a three-way catalyst, but also a catalyst in which HC and the like are partially oxidized.
The catalyst may be a NOx purifying catalyst that reduces NOx by reacting with x, or absorbs NOx when the oxygen concentration in the exhaust gas is high (for example, 4% or more), and reduces the oxygen concentration by reducing the oxygen concentration. NOx that releases its NOx when it becomes 2-3% or 0.5% or less, for example.
It may include a trapping material. In addition, a diesel particulate filter supporting an oxidation catalyst may be employed for the downstream catalyst.

When the temperature of the downstream side catalyst is lower than a predetermined value, it is preferable to set the post-injection timing to 70 ° CA or more after the top dead center of the compression stroke in order to prevent the blow-by.

Further, the post-injection when the temperature of the downstream side catalyst is lower than a predetermined value is set at 50 ° CA or more after the top dead center of the compression stroke, and the timing is set to 0.2 to 2 seconds. It is preferable to execute it at intervals. That is, during low load operation in which the engine load is less than the predetermined value (the catalyst temperature is also low at this time), the main injection amount for injecting fuel near the top dead center of the compression stroke is smaller than when the load is high. Also, the amount of post-injection must be reduced to avoid an excessive increase in engine output and deterioration of fuel efficiency. In this case, for example, if the post-injection is performed every time the main injection is performed, the amount of one post-injection becomes very small, and it becomes difficult to control the injection amount. On the other hand, if the post-injection interval is long, for example, the post-injection is executed once every 0.2 to 2 seconds, the amount of one post-injection can be increased, and the post-injection can be performed. Control of the volume becomes easier. Further, according to the study of the present inventor, when the post-injection interval is made longer, the temperature rise of the upstream catalyst becomes larger than when the post-injection interval is shorter, and therefore the temperature of the exhaust gas exiting this upstream catalyst becomes higher. This is advantageous for raising the temperature of the downstream catalyst. If the post-injection interval is longer than 2 seconds, the amount of one post-injection becomes too large, which causes an undesirable fluctuation in the engine output.

Here, performing post-injection at intervals of 0.2 seconds means that, for example, when the engine speed is 1500
In the case of rpm, the main injection is performed once every 10 main injections, and the post-injection performed once every two seconds is performed once every 100 main injections. .

When the engine load is equal to or more than a predetermined value,
The post-injection when the temperature of the downstream side catalyst is lower than a predetermined value is preferably executed at intervals shorter than 0.2 seconds.
According to the study of the present inventor, when the post-injection interval is short in this way, it is known that delaying the post-injection timing results in a higher temperature of the exhaust gas exiting the upstream side catalyst. This is because it is advantageous for temperature. Further, in response to the increase in the main injection amount, the post-injection, which is similarly increased, is executed at a long interval, so that it is possible to prevent an increase or decrease in torque or an increase in soot. In this case, if the post-injection timing is delayed, the increase and decrease of the torque can be further suppressed.

Further, the present invention provides an injection valve which faces a combustion chamber of an engine and injects fuel into the combustion chamber, and a catalyst which is disposed in an exhaust passage extending from the combustion chamber and has an oxidation catalyst function for purifying exhaust gas. And the amount of reducing agent in the exhaust gas by the post-injection of injecting fuel from the injection valve at a predetermined time during an expansion stroke or an exhaust stroke after fuel is injected near the top dead center of the compression stroke of the engine by the injection valve. An exhaust gas purifying apparatus for an engine, comprising: a reducing agent increasing unit that increases the post-injection timing of 50 ° CA after the top dead center of the compression stroke; Seconds to 2
It is characterized in that the post-injection is executed once every second.

Therefore, the amount of the reducing agent flowing through the catalyst without being oxidized by the catalyst is reduced, that is, it is possible to suppress the discharge of the unpurified reducing agent into the atmosphere.

In such an exhaust gas purifying apparatus for an engine, it is preferable to dispose an exhaust gas purifying material whose activity increases with an increase in temperature in the exhaust passage downstream of the catalyst. Since the post-injection interval is long, such as performing the post-injection once every 0.2 to 2 seconds, the temperature of the exhaust gas exiting the upstream catalyst increases, and the downstream exhaust gas purifying material This is because it is advantageous for raising the temperature and the activity.

The exhaust gas purifying material may be, for example, the NOx trap material described above, or may be a catalyst having the above-described oxidation catalytic function.

[0021]

As described above, according to the present invention, an upstream catalyst having an oxidation catalyst function and a downstream catalyst having an oxidation catalyst function are arranged in an exhaust passage of an engine, and reduction in exhaust gas is performed by post-injection. In an exhaust gas purification device for an engine that increases the amount of the agent, based on the temperature of the downstream catalyst,
When the temperature is lower than the predetermined value, the post-injection timing is later than when the temperature is higher than the predetermined value, so that the amount of the reducing agent that blows through the upstream catalyst when the downstream catalyst is inactive is reduced, The amount of the reducing agent discharged into the atmosphere without being oxidized is reduced, and the temperature of the downstream-side catalyst can be raised and the activity can be early.

When the temperature of the downstream side catalyst is lower than a predetermined value, the post-injection timing is set to 50 ° C. after the compression stroke top dead center.
A, the post-injection is performed at intervals of 0.2 to 2 seconds, and the post-injection amount is set to 1 even during low engine load operation where the post-injection amount cannot be increased.
The post-injection amount can be increased, and the post-injection amount can be easily controlled, which is advantageous for the temperature rise and early activation of the downstream catalyst.

Further, according to the present invention, a catalyst having an oxidation catalyst function is disposed in the exhaust passage of the engine, and the post-injection timing is set after the top dead center of the compression stroke in order to increase the amount of reducing agent in the exhaust gas. Set to 50 ゜ CA or later, 1 in 0.2 to 2 seconds
Since the post-injection is performed at intervals of the number of times, the amount of the reducing agent flowing through the catalyst without being oxidized by the catalyst is reduced, which is advantageous in suppressing the discharge of the unpurified reducing agent into the atmosphere. Become.

Further, according to the exhaust gas purifying material whose activity increases with an increase in temperature in the exhaust passage downstream of the catalyst, the temperature of the exhaust gas purifying material can be increased.
Becomes active.

[0025]

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

FIG. 1 shows an overall configuration 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 body 1. A surge tank (not shown) is provided at a downstream end of the intake passage 10. 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. And an intercooler 13 for cooling 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. 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, and is similar to an EGR valve 24 described later.
The magnitude of the negative pressure acting on the diaphragm 15 is adjusted by an electromagnetic valve 16 for negative pressure control, whereby the opening of the valve is controlled. Further, the intake throttle valve 14 is provided with a sensor (not shown) for detecting its opening.

An exhaust passage 20 for exhausting 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, an O2 sensor 17 for detecting the oxygen concentration in the exhaust gas, a turbine 21 rotated by the exhaust gas, HC, CO, and N in the exhaust gas.
A catalytic converter 22 capable of purifying Ox is provided. 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 has a NOx purification catalyst 22a and an oxidation catalyst 22b arranged in series on the upstream and downstream sides in the exhaust gas flow direction. Temperature sensor 1 during 22b
8 are provided.

Each of the catalysts 22a and 22b is formed by forming a catalyst layer on the wall surface 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 NOx purifying catalyst 22a is formed by supporting catalyst powder obtained by supporting Pt on zeolite on the carrier with a binder, and when the air-fuel ratio A / F is leaner than the stoichiometric air-fuel ratio (for example, A /
F ≧ 18), it has a function as a NOx reduction catalyst for reducing and purifying NOx of exhaust gas combusted, and has an oxidation catalyst function for oxidizing HC as a reducing agent in exhaust gas. Also works as a catalyst. The catalyst layer of the oxidation catalyst 22b is formed by supporting a catalyst powder obtained by supporting Pt on alumina and ceria on the carrier with a binder.

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. 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 injector 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 fuel injection amount and the fuel injection timing by the injector 5 are controlled in accordance with the operating state of the engine body 1 and the states 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 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 in a memory. 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), the catalyst 22a of the catalytic converter 22
In order to supply a reducing agent component for promoting reduction purification of Ox, the NOx catalyst 22a is used to retard the main injection timing and to inject a small amount of fuel in an expansion stroke or an exhaust stroke after the main injection (main fuel injection). The temperature is appropriately adjusted according to the temperature.

From start to stop of the engine, monitoring (diagnosis) for checking an abnormality such as deterioration of the upstream side catalyst 22a is performed once or twice. This monitoring is performed during a steady operation, and the upstream side catalyst 2
By supplying a large amount of the reducing agent to 2a and observing the temperature change of the oxidation catalyst at that time, the integrated value of the increased amount of the reducing agent in a predetermined time after starting to supply the large amount of the reducing agent is equal to or more than a predetermined value. In the period up to, if the degree of temperature rise such as temperature change or temperature change speed is a predetermined value or more,
Normal (not deteriorated), if less than a predetermined value, it is determined to be abnormal (deteriorated).

A feature of the present invention resides in post-injection control during non-monitoring, in which the post-injection timing and the post-injection interval are controlled in accordance with the temperature of the downstream catalyst 22b.

Hereinafter, the contents of the control will be specifically described based on 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, a temperature sensor output, and the like are read. Subsequent step S2
Sets the main injection amount Qb and its injection timing Ib. 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 It is set to increase as the rotation speed increases. The main injection timing Ib is set near the top dead center of the compression stroke. For example, with reference to BTDC5 ° CA (crank angle), the injection amount Qb is advanced as the injection amount Qb increases, and conversely, the injection amount Q
The smaller b is, the more the retard is. 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.

In the following step S3, the temperature Tcu of the oxidation catalyst 22a disposed on the upstream side and the NO
The temperature Tcd of the x-purifying catalyst 22b is estimated based on the output of the temperature sensor 18 disposed between the two catalysts. That is,
The temperature of the exhaust gas detected by the temperature sensor 18 is estimated as the temperature Tcu of the upstream catalyst 22a, and a predetermined correction (for example, a correction of giving a coefficient of 1 or less or subtracting a predetermined value) is added to the exhaust gas temperature. The temperature T of the downstream catalyst 22b.
Estimate cd. The temperature Tcd of the downstream side catalyst 22b is detected by detecting a temperature of the exhaust gas by arranging a temperature sensor downstream of the catalyst 22b.
May be estimated as the temperature Tcd.

In the following step S4, it is determined whether or not the engine is in a predetermined steady-state operating state (the change in the accelerator opening is equal to or less than a predetermined value) based on the change in the accelerator opening. During acceleration operation, the air-fuel ratio becomes a value near the stoichiometric air-fuel ratio due to an increase in the fuel injection amount, and no post-injection is performed to prevent a shortage of reducing agent (HC) for NOx purification. During idle operation, the fuel injection amount is reduced, and it is not appropriate to execute post-injection.

If the engine is in a steady operation state, the process proceeds to step S5, in which the downstream catalyst temperature Tcd reaches a predetermined temperature Tcdo (the temperature at which the downstream catalyst 22a shows the catalytic activity for purifying HC as the reducing agent in the exhaust gas). Yes, for example, 150 ° C.), that is, whether the downstream side catalyst 22a is in an inactive state. If the catalyst temperature Tcd is low and the downstream side catalyst 22a is in an inactive state, the process proceeds to step S6 to determine a cylinder to be post-injected at a low temperature.

This means that, until the main injection is performed, for example, 100 times in a predetermined order on a plurality of cylinders of the engine, which cylinder is to be subjected to the post-injection following the main injection in accordance with the operating state of the engine. To decide. Main injection 10
After the zero injection is performed, a post-injection cylinder to be performed during the next 100 main injections is determined based on the engine operating state at that time. Here, when the engine load is low, that is, when the engine load is less than a predetermined value (the accelerator opening is less than a predetermined value), for example, the post-injection is performed so that the post-injection is performed once every 0.2 to 2 seconds. The post-injection cylinder is determined so that it is performed once every 25 times, that is, every 25 main injections. When the engine load is above the specified value,
So that the post-injection is performed at intervals shorter than 0.2 seconds,
For example, the post-injection cylinder is determined so that the post-injection is performed every time. Performing the post-injection every time means performing the post-injection each time the main injection for each cylinder is performed. In this case, all the cylinders are determined as the cylinders to be post-injected.

In the following step S7, the post-injection amount Qp and the post-injection timing Ip for the cylinder determined in step S6 are set. In other words, the post-injection amount Qp is converted into an amount when it is assumed that the post-injection is performed every time, and the one-time main injection amount Qb
0.3 to 5%. Therefore, when the post-injection amount is performed every time, the post-injection amount Qp for one time is 0.3 to 5% of the main injection amount Qb for one time.
When post-injection is performed at intervals of one time, one post-injection amount Qp is 1.5 to 25% of one main injection amount Qb. When the engine is under low load, the main injection amount Qb is small, and when the post-injection is performed every time, the single post-injection amount Qp is very small. Since the post-injection is performed every 25 main injections,
One post-injection amount Qp increases, and post-injection control becomes easy.

The post-injection timing Ip is equal to or greater than 50 ° CA of ATDC (after the top dead center of the compression stroke; hereinafter the same) 240
This is before ゜ CA or before ゜ CA, thereby reducing the amount of reducing agent that flows through the upstream catalyst 22a without being oxidized by the upstream catalyst 22a and increases the temperature of the downstream catalyst 22b. When the engine is under a low load, the ATDC is 90 ° to 240 ° CA (preferably 90 ° CA).
(゜ 150 ° CA), the blow-through of the reducing agent is suppressed and the temperature of the downstream catalyst 22b is increased.

When the main injection timing Ib is reached, the main injection is executed (steps S8 and S9), and when the post-injection should be performed for the cylinder that has performed the main injection (step S8).
10) When the post-injection timing Ip is reached, post-injection is executed (steps S11, S12).

On the other hand, in step S5, the downstream catalyst temperature Tcd
Has reached the predetermined temperature Tcdo, that is, the downstream side catalyst 22
If it is determined that a has reached the temperature indicating the catalytic activity for purifying HC as the reducing agent in the exhaust gas, step S1
3 to determine the cylinder to be subjected to post-injection, and further proceed to step S14 to set the post-injection amount Qp and the post-injection timing Ip according to the temperature Tcu of the upstream side catalyst 22a, and then to step S14.
Proceed to 8. The post-injection timing Ip is set before the ATDC 50 CA (to the advanced side) to allow the reducing agent to flow through the upstream catalyst 22a. The determination and setting contents of steps S13 and S14 will be described later. Step S
If it is determined in step 4 that the operation is not the steady operation, the process proceeds to step S8.

During the post-injection control, EGR feedback control is performed. That is, the operation of the EGR valve 24 is controlled based on the output of the air flow sensor 11 with the target of the air-fuel ratio at which each of the NOx generation amount and the soot generation amount becomes equal to or less than the predetermined value.

FIG. 4 shows the case where the post-injection is performed every time in the engine speed of 1500 rpm and the medium load operation, when the post-injection is performed every five times (at an interval of once every five main injections), and 25 times. Every (at intervals of 25 main injections)
In each case when the post-injection is performed, the post-injection timing, the HC concentration (HC before the catalyst) of the exhaust gas flowing into the upstream side catalyst 22a 10 seconds after the start of the post-injection, and the catalyst 22a
The relationship with the HC concentration (HC after the catalyst) of the exhaust gas flowing out of the engine. FIG. 5 shows the same relationship 30 seconds after the start of the post injection.
FIG. 6 shows the same relationship 90 seconds after the start of post-injection. The exhaust gas temperature at the inlet of the upstream side catalyst 22a is about 270 ° C.

4 to 6 that the post-injection timing is ATDC
It is understood that when the temperature is lower than 50 ° CA, the amount of blow-through HC (amount of reducing agent) passing through the upstream catalyst 22a without being purified by the upstream catalyst 22a increases. Accordingly, in this case, it is understood that setting the post-injection timing to be at or after ATDC 50 CA, and further to be at or after ATDC 70 CA is advantageous in reducing the amount of HC blow-through.

FIG. 7 shows the case where the post-injection is performed every time, the case where the post-injection is performed every 5 times, and the case where the post-injection is performed every 25 times in the engine speed of 1500 rpm and the medium load operation. , The post-injection timing and the upstream catalyst 2 at 10 seconds, 30 seconds and 90 seconds after the start of post-injection
2 shows the relationship between 2a and the HC purification rate.

FIG. 7 shows that when the post-injection timing Ip is set at ATDC 70 ° -210 ° CA, particularly at ATDC 70 ° -150 ° CA, the HC purification rate in the upstream side catalyst 22a increases. Note that the HC purification rate is low at ATDC180 CA.

FIG. 8 shows the case where the post-injection is performed every time, the case where the post-injection is performed every 5 times, and the case where the post-injection is performed every 25 times in the engine speed of 1500 rpm and the medium load operation. 5 shows the relationship between the post-injection timing and the inlet temperature and the outlet temperature of the upstream side catalyst 22a 10 seconds after the start of the post-injection. FIG. 9 shows the same relationship 30 seconds after the start of the post-injection, and FIG. 10 shows the same relationship 90 seconds after the start of the post-injection.

8 to 10, the post-injection timing Ip is set to A
TDC50-210 CA, especially ATDC70-210
When set to ゜ CA, the temperature of the exhaust gas exiting the upstream catalyst 22 significantly increases in every injection, every 5 injections, and every 25 injections.
It turns out that it becomes advantageous to temperature rise of 2b. In particular, it is understood that performing the post-injection every 25 times is advantageous in increasing the temperature of the exhaust gas exiting the upstream catalyst 22a.

Next, the post-injection control after the temperature Tcd of the downstream side catalyst 22b becomes equal to or higher than the predetermined temperature Tcdo (step S1).
3, S14) will be described.

The determination of the post-injection cylinder in step S13 is made based on the main injection amount Qb such that when the amount is large, post-injection is performed every time, and when it is small, post-injection is performed every 5 or 25 times. Post injection quantity Qp in step S14
Is based on the temperature of the upstream catalyst Tcu, and when the NOx purification rate is lower than the temperature at which the NOx purification rate reaches a peak, the main injection amount is 0.3 to 5
%, And when the temperature exceeds the peak temperature, the post-injection amount Qp decreases as the temperature Tcu increases, and the NOx purification rate falls below a predetermined value. When the temperature Tcu rises, the post injection quantity Q
Set so that p becomes zero. As described above, the post-injection timing Ip is set before the ATDC 50 CA (advancing side), that is, after the ATDC 20 CA and before the 50 CA.

FIG. 11 shows an engine speed of 1500 rpm,
In the medium load operation, when the post-injection was performed every time, when the post-injection was performed every five times, and when the post-injection was performed every 25 times, the post-injection timing, 10 seconds after the start of the post-injection, and The relationship with the NOx concentration of the exhaust gas flowing into the upstream side catalyst 22a after 30 seconds is shown. The total amount of the post-injection amount was set to be about 4% of the total amount of the main injection amount in each case.

When the post-injection timing is advanced, the NOx concentration is low every time every 5 times and every 25 times.
Or, when the temperature is around 45 ° CA, the decrease in NOx concentration is remarkable, and it can be seen that this is effective in reducing NOx.

FIG. 12 shows an engine speed of 2000 rpm,
In the operation of Pe = 0.57 MPa (without EGR),
The relationship between the post-injection timing and the amount of smoke (soot) when the post-injection is performed every time (the post-injection amount is 5% of the main injection amount) is shown. According to FIG. 14, it can be seen that advancing the post-injection timing is advantageous for reducing smoke.

In the above embodiment, the catalyst for purifying NOx is arranged on the upstream side and the oxidation catalyst is arranged on the downstream side. However, the present invention can be applied to the case where the oxidation catalyst is arranged alone in the exhaust passage 20. Further, the present invention can be applied to a case where an oxidation catalyst is arranged on the upstream side and a NOx trap catalyst is arranged on the downstream side. The NOx trap catalyst can be formed by supporting a catalyst powder comprising Pt and Ba as a NOx trapping material on zeolite on a carrier with a binder. When the oxygen concentration of the exhaust gas is high (for example, the stoichiometric air-fuel ratio Also has a lean air-fuel ratio (for example, A / F ≧ 1
NOx in the exhaust gas was absorbed by Ba (when the oxygen concentration was increased to 4% or more by burning in 8), and when the oxygen concentration was reduced and, for example, the oxygen excess ratio was about λ = 1, it was absorbed. It has a function of releasing NOx and reducing and purifying the NOx with Pt in the presence of HC.

Accordingly, the downstream NOx trap catalyst is H
When the activation temperature for reducing and purifying C and NOx has not been reached, the post-injection control of steps S6 and S7 in the flow of FIG. 3 is performed to prevent blow-through of HC as a reducing agent and increase the temperature of the NOx trap catalyst. To release NOx by lowering the oxygen concentration in the exhaust gas (assuming λ = 1), the N2 released by the NOx trap catalyst
Ox and HC can be efficiently purified.

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

[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 graph showing a relationship between a post-injection timing, an HC concentration of exhaust gas flowing into an upstream side catalyst 10 seconds after the start of post-injection, and an HC concentration of exhaust gas flowing out of the catalyst.

FIG. 5 is a graph showing the relationship between the post-injection timing, the HC concentration of exhaust gas flowing into the upstream catalyst 30 seconds after the start of post-injection, and the HC concentration of exhaust gas flowing out of the catalyst.

FIG. 6 is a graph showing the relationship between the post-injection timing, the HC concentration of exhaust gas flowing into the upstream catalyst 90 seconds after the start of post-injection, and the HC concentration of exhaust gas flowing out of the catalyst.

FIG. 7 is a graph showing the relationship between the post-injection timing and the HC purification rates of the upstream catalyst at 10 seconds, 30 seconds, and 90 seconds after the start of post-injection.

FIG. 8 is a graph showing a relationship between a post-injection timing and an inlet temperature and an outlet temperature of the upstream side catalyst 10 seconds after the start of the post-injection.

FIG. 9 is a graph showing a relationship between a post-injection timing and an inlet temperature and an outlet temperature of the upstream side catalyst 30 seconds after the start of the post-injection.

FIG. 10 is a graph showing a relationship between a post-injection timing and an inlet temperature and an outlet temperature of the upstream side catalyst 90 seconds after the start of the post-injection.

FIG. 11 shows post-injection timing, 10 seconds after the start of post-injection, and 30 seconds after the start.
FIG. 8 is a graph showing a relationship between the exhaust gas flowing into the upstream side catalyst after a second and the NOx concentration of the exhaust gas.

FIG. 12 is a graph showing a relationship between a post-injection timing and a smoke amount each time post-injection is performed.

[Explanation of symbols]

 A Exhaust gas purification device 1 Diesel engine 2 Cylinder 4 Combustion chamber 5 Injector (fuel injection valve) 18 Temperature sensor 20 Exhaust passage 22 Catalytic converter 22a Upstream catalyst 22b Downstream catalyst 35 ECU (control unit)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) F01N 3/24 F01N 3/24 R 3/28 301 3/28 301D 301E (72) Inventor Hiroshi Hayashibara Hiroshima 3-1, Fuchu-cho, Shinchi, Aki-gun F-term in Mazda Motor Corporation (reference) 3G091 AA02 AA10 AA11 AA17 AA18 AA24 AA28 AB02 AB03 AB05 AB06 BA03 BA14 BA15 BA19 BA32 BA33 CB02 CB03 CB07 CB08 DA01 DA02 DA03 DA05 DB10 DC01 EA00 EA06 EA07 EA16 EA18 EA30 EA31 EA34 FA02 FA04 FA07 FA11 FB10 FC04 FC07 GA06 GB01X GB03Y GB04X GB06W GB09X GB10X GB17X HA09 HA10 HA36 HA38 HA47 HB05 HB06 3G301 HA02 HA04 HA11 HA13 JA21 JA25 JA26 KA06 MA08 JA26 KA04 MA08 PE03Z PF03Z PF04Z

Claims (6)

[Claims] An injection valve that faces a combustion chamber of an engine and injects fuel into the combustion chamber; an upstream catalyst that is disposed in an exhaust passage extending from the combustion chamber and has an oxidation catalyst function for purifying exhaust gas; After injection of fuel near the top dead center of the compression stroke of the engine by the injection valve, the amount of reducing agent in the exhaust gas is increased by post-injection of fuel injected from the injection valve at a predetermined time during an expansion stroke or an exhaust stroke. Reducing agent increasing means for reducing, a downstream catalyst disposed in the exhaust passage downstream of the upstream catalyst and having an oxidation catalyst function for purifying exhaust gas, and a catalyst temperature for detecting a temperature of the downstream catalyst Detecting means, the reducing agent increasing means based on the temperature of the downstream catalyst detected by the catalyst temperature detecting means, when the temperature is lower than a predetermined value, when the temperature is higher than a predetermined value Exhaust gas purification apparatus for an engine, characterized in that remote the post injection timing is set to be slow. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the reducing agent increasing means sets a post-injection timing when the temperature of the downstream side catalyst is lower than a predetermined value after a compression stroke top dead center. 70
エ ン ジ ン An exhaust gas purification device for an engine, which is set to CA or later. 3. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the reducing agent increasing means sets a post-injection timing when the temperature of the downstream side catalyst is lower than a predetermined value after a top dead center of a compression stroke. 50
エ ン ジ ン An exhaust gas purification device for an engine, which is set to be CA or later, and executes post-injection at intervals of 0.2 seconds to 2 seconds. 4. The exhaust gas purifying apparatus for an engine according to claim 1, further comprising: means for detecting an engine load, wherein the reducing agent increasing means includes a post injection when a temperature of the downstream catalyst is lower than a predetermined value. Is executed at intervals shorter than 0.2 seconds when the engine load is equal to or greater than a predetermined value. 5. An injection valve which faces a combustion chamber of an engine and injects fuel into the combustion chamber, a catalyst disposed in an exhaust passage extending from the combustion chamber and having an oxidation catalyst function for purifying exhaust gas, and the injection A reduction in which the amount of the reducing agent in the exhaust gas is increased by post-injection in which fuel is injected from the injection valve at a predetermined time during an expansion stroke or an exhaust stroke after fuel is injected near the top dead center of the compression stroke of the engine by the valve. The reducing agent increasing means sets the post-injection timing to 50 ° CA or more after the top dead center of the compression stroke, and performs post-injection at intervals of 0.2 seconds to 2 seconds. An exhaust gas purification device for an engine, which is executed. 6. The exhaust gas purifying apparatus for an engine according to claim 5, wherein an exhaust gas purifying material whose activity increases with a rise in temperature is arranged in the exhaust passage downstream of the catalyst. Characteristic engine exhaust purification device.