JP2760156B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst (hereinafter, referred to as a catalyst) for reducing NOx in an oxidizing atmosphere in the presence of HC in an exhaust system comprising a transition metal or a noble metal.
More specifically, the present invention relates to an exhaust gas purification device having an improved NOx purification rate of a lean NOx catalyst.

[0002]

2. Description of the Related Art A lean NOx catalyst is disclosed in
735, JP-A-1-135543,
Are known.

[0003]

However, lean NOx
The NOx removal rate of the catalyst is not yet sufficiently high in steady state, and its use must be developed to increase its NOx removal rate.

SUMMARY OF THE INVENTION The present invention relates to an exhaust purification system for an internal combustion engine having a lean NOx catalyst in an exhaust system.
The purpose is to improve the Ox purification rate.

[0005]

In order to achieve the above object, an exhaust gas purifying apparatus for an internal combustion engine according to the present invention comprises the following means. An internal combustion engine, a lean NOx catalyst provided in an exhaust system of the internal combustion engine, operating state detecting means for detecting an operating state of the internal combustion engine, and a fuel when the operating state of the internal combustion engine detected by the operating state detecting means is decelerated. Operating state determining means for determining whether or not the engine is in a cut state, and throttle control means for opening the intake throttle valve to an opening position larger than an idle position when the operating state determining means determines that the fuel is cut off when the engine is decelerated.

[0006]

According to the test conducted by the inventor, it has been found that the NOx purification rate of the lean NOx catalyst rises transiently when the temperature rises. In the present invention, at the time of fuel cut at the time of engine deceleration, the intake throttle valve, which is closed at the time of normal fuel cut, is opened at a predetermined opening, whereby intake air flows through the engine to the lean NOx catalyst to cool the lean NOx catalyst, and the fuel at the time of deceleration is provided. The high NOx purifying ability at the time when the temperature of the lean NOx catalyst rises when the engine is operated again after the cut is completed is used. Then, in the actual operation of the vehicle, the fuel cut at the time of engine deceleration is repeated, so that the NOx purification rate of the lean NOx catalyst is increased as a whole.

[0007]

FIG. 5 shows the overall system of an embodiment of the present invention. In FIG. 5, the exhaust system 4 of the internal combustion engine 2 has a lean N
An Ox catalyst 6 is provided. An oxidation catalyst or a three-way catalyst may be provided downstream of the lean NOx catalyst 6 as necessary. An intake throttle valve 10 is provided in the intake system 8 of the internal combustion engine 2 so as to be openable and closable. Reference numeral 12 denotes an electromagnetically controlled fuel injection valve, which injects fuel directly into the intake system 8 or into the cylinder. When the engine is decelerated, the intake throttle valve 10 is in the idle position, and intake air hardly flows. When the engine is decelerated, the fuel injection of the fuel injection valve 12 is cut, thereby improving the fuel efficiency. As shown in FIG. 3, this fuel cut is performed when the engine speed NE is higher than the predetermined speed NC, and is returned to prevent engine stall when the fuel is cut and the NE becomes smaller than NC. You. Conventionally, the intake throttle valve 10 is at the idle position, that is, the closed position (the position indicated by the broken line in FIG. 5) when the fuel is cut at the time of engine deceleration. The opening is opened (the position indicated by the solid line in FIG. 5). In this state, the fuel is not injected and only the intake air flows, so that the lean NOx catalyst 6 is cooled.

The lean NOx catalyst 6 has a higher NOx purification rate in the temperature rising process than in the steady state and the temperature decreasing process, according to the test and research by the inventor. Cooling the lean NOx catalyst 6 by opening the intake throttle valve 10 at a predetermined opening during fuel cut during engine deceleration can use the lean NOx catalyst 6 in the temperature rise process when returning from fuel cut, and thus actively. In order to make a heating-cooling cycle.

The control of opening the intake throttle valve at the time of fuel cut when the engine is decelerated is controlled by an engine control unit (ECU) 2.
0 (see FIG. 5). The ECU 20 includes a microcomputer, and has an input interface 20a,
Output interface 20b, read only memory (RO
M) 20c, random access memory (RAM) 20
d, a central processor unit (CPU) 20e. The ECU 20 has A / D converters 20f and 20g for converting an analog signal into a digital signal, and has a counter 20h and a drive circuit 20i. The digital signal of the crank angle sensor 22 is directly input to the input interface 20a, and is used as an interrupt angle signal to the fuel injection main routine. Is used to calculate As described later, the fuel injection amount (fuel injection period TAU) is obtained based on the engine speed NE and the signal PM of the intake pressure sensor 24, and the exhaust temperature THE is calculated from the NE and PM. The output signal PM of the intake pressure sensor 24 and the output signal of the accelerator opening sensor 26 are converted into digital signals by A / D converters 20f and 20g, respectively, and input to the input interface 20a. The output interface 20b is connected to the fuel injector 12 via a counter 20h and a drive circuit 20i. In the above description, the crank angle sensor 22, the intake pressure sensor 24, the accelerator opening sensor 26 and the like constitute an operating state detecting means for detecting the engine operating state.

At the time of fuel cut during engine deceleration, intake throttle valve 1
FIG. 6 shows details of the mechanism for opening 0 by a predetermined opening. 6, a throttle wire 14a is wound around a first wheel 14c, and the throttle wire 14a moves right and left in the drawing as the intake throttle valve 10 opens and closes.
4c rotates clockwise and counterclockwise. First wheel 14
c, there is a second wheel 14b coaxial with the second wheel 14b.
Rotates with the first wheel 14c. A stopper pin 14d is fixed to the second wheel 14b.
4d is in contact with the tip of the rod 16a of the diaphragm 16 for adjusting the throttle opening. When the stopper pin 14d is at the position A shown by the broken line, it corresponds to the idle position of the intake throttle valve 10 (the position shown by the broken line in FIG. 6). This corresponds to the position of the degree opening (the position indicated by the solid line in FIG. 6). Therefore,
When the tip of the rod 16a of the diaphragm 16 is at the position A, the intake throttle valve 10 can be closed to the idle position. In this state, the rod 16a of the diaphragm 16 is closed.
Are moved to the position B, the wheels 14b, 14c
Rotates to pull the throttle wire 14a and open the intake throttle valve 10 by a predetermined opening.

The diaphragm chamber 1 located on one side of the diaphragm 16b of the diaphragm 16 for adjusting the throttle opening degree.
An intake negative pressure (which may be a negative pressure of a negative pressure hold tank) and an atmospheric pressure are switchably guided to 6d via a three-way solenoid valve 18, and when a negative pressure is applied, the rod 16a is protruded so as to protrude. Move the throttle valve 10 to the open position. When the pressure is switched to the atmospheric pressure, the rod 16a is returned to the original position by the spring 16c, and the intake throttle valve 10 is set to the idle position. The three-way solenoid valve 18 is connected to an output interface 20b of the ECU 20.

The ROM 20c of the ECU 20 has programs for throttle control shown in FIGS. 1 and 2 (control of opening the intake throttle valve 10 by a predetermined opening from an idle position at the time of fuel cut during engine deceleration) and fuel injection shown in FIG. A control program is stored, and is called by the CPU 20e to execute an operation. The routine of FIG.
°, the engine speed N
E, the intake pipe negative pressure PM is read. Then step 304
Therefore, the basic fuel injection amount T using the map from NE and PM.
Calculate P. Next, at step 306, the water temperature increase FWL
And other various correction values. Next, at step 308, the basic fuel injection amount TP is corrected from the obtained correction values such as FWL to obtain the fuel injection amount and the injection timing, and the fuel injection start time t, the fuel injection period TAU, and t are counted from these. The time to be set to 20h is calculated. Next, at step 310, t and TAU are set in the counter 20h at the time when t should be set in the counter 20h.
The fuel injection valve 12 is excited via the drive circuit 20i when the time t has elapsed from the start of counting by the counter 20h and fuel injection is started. The count is restarted from that time and the fuel injection is started when the time TAU has elapsed. The excitation of the valve 12 is stopped, and the fuel injection is stopped. Thus, the period T
Although only AU of fuel is injected, at the time of engine deceleration, TAU = 0 is set in step 308, and TAU =
Since it is 0, the fuel injection is stopped and the fuel is cut.

The routine of FIG. 2 is a routine for determining whether or not the current engine operating state is a fuel cut state at the time of engine deceleration for throttle control. The routine of FIG. 1 is a routine of FIG. If so, this routine is a routine for turning on the throttle control (increase the intake throttle valve opening) and returning to the original state (setting the intake throttle valve opening to the idle position) unless the fuel is cut off when the engine is decelerated. 1 and 2
Is interrupted, for example, at every crank angle of 30 °.

In FIG. 2, in step 202, it is determined whether or not the accelerator switching flag Faa is 1 (when Faa = 1, the foot is released from the accelerator pedal and the engine is in a decelerating state). move on. In steps 204 and 206, it is determined whether or not the engine speed NE is equal to the fuel cut speed NC (see FIG. 3). If the value of NE is equal to or larger than NC (for example, 1300 rpm) in step 204, it is determined that the engine is at the fuel cut rotation speed, and the routine proceeds to step 208, where the fuel cut flag FCUT is set to 1. Step 2
If NE is smaller than NC at 04, proceed to step 206 and NE
Is smaller than or equal to the return rotation speed NR smaller than NC,
If NE is larger than NR, the flow returns with FCUT being 1. When Faa is not 1 in step 202 and when NE is equal to or less than NR in step 206, it is regarded that the engine speed is not fuel cut, and the routine proceeds to step 210, where FCUT
Is determined to be 1 or not, and if FCUT is not 1, the flow returns as it is because the fuel has not been cut. If FCUT is 1, the flow proceeds to step 212 and the FCUT is set to 0 (the fuel has not been cut). The routine in FIG. 2 constitutes an operating state determining means for determining whether the engine operating state is a fuel cut state at the time of engine deceleration. In FIG. 3, NC and NR are set to different values so that the hysteresis loop is drawn in order to prevent hunting.

Next, in FIG. 1, it is determined in step 102 whether the catalyst bed temperature or the exhaust gas temperature is 300 ° C. or higher. The catalyst bed temperature or the exhaust gas temperature THE is the NE-TA of FIG.
Obtained from U map. When the catalyst bed temperature is lower than 300 ° C., as shown in FIG. 8, the phenomenon that the NOx purification rate of the lean NOx catalyst increases in the temperature rising process from the steady state is not observed, so that the throttle control for cooling the catalyst is performed. It becomes meaningless, and it is better to raise the temperature of the catalyst to the activation temperature early.
FF. This throttle control is turned off by a signal from the output interface 20b of FIG.
Is turned off, the atmospheric pressure is guided to the diaphragm chamber 16d in FIG. 6, and the rod 16a is set to the position A.

If the catalyst bed temperature is equal to or higher than 300 ° C. in step 102, the routine proceeds to step 104, where it is determined whether or not the fuel cut flag is 1. If FCUT is 1, it is time to perform throttle control because the engine operating state is in the fuel cut state at the time of engine deceleration, and the routine proceeds to step 106, where the throttle control flag Ffsc is set to 1 (throttle control is performed).
It is determined whether or not Ffsc is 1, the throttle control is being performed because the throttle control is being performed, and if Ffsc is not 1, the throttle control is not performed yet and the process goes to step 108 to turn on the throttle control. The throttle control is turned on by turning on the three-way solenoid valve 18 by a signal from the output interface 20b in FIG. 5, guiding the intake pipe negative pressure to the diaphragm chamber 16d, and setting the distal end position of the rod 16a to B in FIG. Done. In this state, the intake throttle valve 10 is opened by a predetermined opening. After the throttle control is turned on in step 108, the routine proceeds to step 110, where F
The process returns with the fsc flag set to 1. Step 1
If FCUT is not 1 in 04, that is, if the engine operating state is not the time of fuel cut at the time of engine deceleration, step 11
2 to determine whether the Ffsc flag is 1 or not.
If c is not 1, the throttle control has already been turned off, so the flow returns as it is. If Ffsc is 1, the routine proceeds to step 114, where the throttle control is turned off. After the throttle control is turned off in step 114, the process proceeds to step 116, where the Ffsc flag is set to 0, and the routine returns. The routine of FIG. 1 constitutes throttle control means for setting the intake throttle valve 10 to an opening position larger than the idle position when the operation state judgment means judges that the fuel is cut off when the engine is decelerated.

Next, the operation will be described. Conventionally, at the time of fuel cut at the time of engine deceleration, the intake throttle valve 10 is in the idle position and intake air hardly flows, but in the present invention, since the intake throttle valve 10 is opened from the idle position by a predetermined opening, intake air flows. . This intake air flows into the exhaust system without burning because it is at the time of fuel cut, and lean NOx
When passing through the catalyst 6, the lean NOx catalyst 6 is cooled. Next, when accelerating, the throttle control is turned off.
And the combustion starts again and the hot exhaust gas is lean NO
The catalyst bed temperature of the lean NOx catalyst 6 rises. Thus, the lean NOx catalyst 6 cools down every time the vehicle decelerates in the active temperature range of 300 ° C. or more.
The cycle of temperature rise is repeated, and the high NO
The x purification rate characteristic is obtained repeatedly. Therefore, as a whole, the NOx purification rate of the lean NOx catalyst 6 is greatly improved.

[0018]

According to the present invention, the exhaust system 4 of the internal combustion engine 2 is provided.
A lean NOx catalyst 6 is provided on the
The throttle control means (routine of FIG. 1) is provided to open the intake throttle valve 10 by a predetermined opening at the time of fuel cut during engine deceleration. Therefore, the lean NOx catalyst 6 can be cooled by the intake air at the time of fuel cut during engine deceleration,
The transition of the temperature rise of the lean NOx catalyst bed temperature can be positively and repeatedly created, and the NOx purification rate of the lean NOx catalyst 6 can be increased.

[Brief description of the drawings]

FIG. 1 is a flowchart of a throttle control means of an exhaust gas purification device for an internal combustion engine according to one embodiment of the present invention.

FIG. 2 is a flowchart of an operation state determination means of the exhaust gas purification device for an internal combustion engine according to one embodiment of the present invention.

FIG. 3 is a hysteresis loop diaphragm for fuel cut and return.

FIG. 4 is a flowchart of a fuel injection control routine of the internal combustion engine.

FIG. 5 is a system diagram of an exhaust gas purifying apparatus for an internal combustion engine according to one embodiment of the present invention.

FIG. 6 is a system diagram showing an example of an intake throttle valve opening control mechanism of the exhaust gas purification device for an internal combustion engine according to one embodiment of the present invention.

FIG. 7 shows engine speed NE-fuel injection amount (injection period TA
5 is a map for obtaining the exhaust gas temperature THE from the ratio (proportional to U).

FIG. 8 is a relationship diagram between the catalyst bed temperature or exhaust gas temperature of the lean NOx catalyst and the NOx purification rate of the lean NOx catalyst.

[Explanation of symbols]

 Reference Signs List 2 internal combustion engine 4 exhaust system 6 lean NOx catalyst 8 intake system 10 intake throttle valve 12 fuel injection valve 16 throttle opening adjustment diaphragm 18 three-way solenoid valve 20 ECU 22 crank angle sensor 24 intake pressure sensor 26 accelerator opening sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/24 F01N 3/24 R F02D 9/02 315 F02D 9/02 315B

Claims (1)

(57) [Claims] An internal combustion engine, a catalyst provided in an exhaust system of the internal combustion engine and made of a zeolite carrying a transition metal or a noble metal, for reducing NOx in an oxidizing atmosphere in the presence of HC, and the internal combustion engine Operating state detecting means for detecting an operating state of the engine, operating state determining means for determining whether or not the internal combustion engine operating state detected by the operating state detecting means is a fuel cut state at the time of engine deceleration, and the operating state determining means A throttle control means for opening an intake throttle valve to an opening position larger than an idle position when it is determined that the engine is in a fuel cut state at the time of engine deceleration.