JPH0354343A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To increase HC, which is effective for reduction of NOx, so as to decrease NOx emission by controlling air-fuel ratio to slightly a rich side with introduction of EGR, in the case of exhaust gas at a high temperature. CONSTITUTION:A lean operative condition discriminating means discriminates whether an operation is a lean operative condition or not in accordance with an engine operative condition parameter, for instance, cooling water temperature, while an exhaust gas temperature discriminating means discriminates whether or not an exhaust gas temperature is a predetermined value, for instance, 600 deg.C or more. When an engine is in a lean operative condition with the exhaust gas temperature less than the predetermined value, the first air-fuel ratio adjusting means adjusts air-fuel ratio to the first lean air-fuel ratio, and when the engine is in the lean operative condition with the exhaust gas temperature in not less than the predetermined value, the second lean air-fuel ratio adjusting means adjusts the air-fuel ratio to the second air-fuel ratio in a rich side from the first air-fuel ratio. While when the engine is in the lean operative condition with the exhaust gas temperature not less than the predetermined value, an EGR-on means turns on an EGR valve 11. Thus, NOx emission can be reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention is a lean NO. This article relates to a lean burn system using a catalyst.

[Conventional technology]

The applicant of the present application has proposed that NO8 mainly composed of metal-exchanged zeolite, especially Cu-zeolite, be used in a lean burn system.
We have already proposed a lean No. 1 reduction catalyst that can purify at a high rate (Reference: Japanese Patent Application No. 1983-95026).

[Problem to be solved by the invention]

However, as shown in Figure 2, the above-mentioned lean NO and catalyst No. 8 purification rates have a strong temperature dependence, and in a lean atmosphere where the exhaust gas temperature is high (for example, 450 degrees Celsius or higher) and 02a degrees are high, the NO . Purification rate decreases. Furthermore, NO. In order to clear the regulations, the engine must be operated in a lean region with an air-fuel ratio A/F of around 20 to 22, as shown in FIG. 3A.

The reason why the NOx purification rate decreases when the exhaust gas temperature is high and the engine is operated in a lean region is considered to be as follows. That is, if the exhaust gas temperature is high and the engine is operated in a lean region, NO. The hydrocarbons (HC) used for the reduction of HC are completely oxidized by HC, and the higher the exhaust gas temperature, the higher the degree of oxidation. As a result, NO is not reduced and therefore N
O. There is a problem that the purification rate decreases.

In addition, in a lean atmosphere with a low exhaust gas temperature, HC is thought to change into active species through partial oxidation, and NOx is purified by reacting with this active species (Cu(II) -CO-). It is considered that.

Therefore, an object of the present invention is to
The purpose of the present invention is to provide an IJ inverter system with improved purification rate of O8 emissions.

[Means to solve the problem]

A means for solving the above problem is shown in FIG.

In other words, the lean NO installed in the exhaust passage of the internal combustion engine
In an internal combustion engine equipped with an X catalytic converter 12 and an exhaust gas recirculation device 11 provided between an exhaust passage and an intake passage of the engine, the lean operating condition determining means determines an engine operating condition parameter such as a cooling water temperature TH. 'vV determines whether the engine is in a lean operating condition or not, and the exhaust gas temperature determining means determines whether the engine's exhaust gas temperature is at a predetermined value, for example 600.
Determine whether the temperature is above ℃. As a result, when the engine is under lean operating conditions and the exhaust gas temperature of the engine is less than a predetermined value, the first lean air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine to the first lean air-fuel ratio, so that the engine When the exhaust gas temperature of the engine is higher than a predetermined value under lean operating conditions, the second lean air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine to a second lean air-fuel ratio that is richer than the first lean air-fuel ratio. adjust. Also,
When the engine is under lean operating conditions and the exhaust gas temperature of the engine is above a predetermined value, the EGR-on means turns on the exhaust gas recirculation device.

[For production]

The operation of the measures described above is also illustrated in FIG. That is,
When EGR is introduced under lean operating conditions, the result is as shown in Figure 3B, and as a result, NO. The air-fuel ratio A/F to clear regulations is 17-19, which is a bit rich. In other words, the 02 concentration in the exhaust gas decreases, so the above (1)
Rather than the complete oxidation reaction in equation (2), the partial oxidation reaction shown in equation (2) proceeds, and as a result, the reduction of HC used for reducing NOX emissions is prevented, and the purification rate of NO,l is further improved. Become.

〔Example〕

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 4, a pressure sensor 3 is provided in an intake passage 2 of an engine body l.

The pressure sensor 3 is of a semiconductor type that directly measures the intake air pressure, and generates an analog voltage output signal proportional to the intake air pressure. This output signal is provided to an A/D converter 101 with a built-in multiplexer of the control circuit 10. A distributor (not shown) has a crank angle sensor 4 whose shaft generates a pulse signal for detecting a reference position every 720 degrees in terms of crank angle, and a pulse signal for detecting a reference position every 30 degrees in terms of crank angle. A crank angle sensor 5 is provided that generates. The pulse signals of these crank angle sensors 4 and 5 are supplied to the input/output interface 102 of the control circuit 10, and the output of the crank angle sensor 45 is supplied to the interrupt terminal of CP[l103.

Further, the intake passage 2 is provided with a fuel injection valve 6 for supplying pressurized fuel from a fuel supply system to the intake port for each cylinder.

Further, a water jacket (not shown) of the cylinder block of the engine body 1 is provided with a water temperature sensor 7 for detecting the temperature of cooling water.

The water temperature sensor 7 generates an analog voltage electrical signal according to the temperature THW of the cooling water. This output is also A/D converter Lo
It is supplied to t.

Reference numeral 9 denotes an EGR valve device, which incorporates a step motor controlled by a human output interface 102 of a control circuit 1O.

The exhaust system downstream of the exhaust manifold 11 is provided with a phosphor NOx reduction catalytic converter l1 that purifies No. 8 at a high rate in a lean atmosphere, and an oxidation catalytic converter 12 that purifies HC and Co at a high rate. Lean No8
The reduction catalytic converter 11 is mainly made of the above-mentioned Cu-zeolite.

Note that a three-way catalytic converter may be used instead of the oxidation catalytic converter l2.

Further, 13 is an exhaust gas temperature sensor for detecting the exhaust gas temperature in the lean NO8 reduction catalytic converter 12, and its output is supplied to the A/D converter 101 of the control circuit 10. The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, a human output interface 102, a CPU 103, and an R[
IM104/RAM105, backup RAM106
, a clock generation circuit 107, etc. are provided.

Further, in the control circuit 10, a down counter 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7.

That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection amount TAU is counted down by the down counter 1.
08 and Frisov flop 109
is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, the down counter 108
counts a clock signal (not shown) and finally when its borrow-out terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 110 stops energizing the fuel injection valve 7. . In other words, the above fuel injection amount T
The fuel injection valve 7 is energized by AU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 10.
After the A/D conversion of step 1 is completed, the input/output interface 102
When the controller receives a pulse signal from the crank angle sensor 5, when it receives an interrupt signal from the clock generation circuit 107, etc.

The intake air pressure data PM, cooling water temperature data THW, and exhaust gas temperature of the pressure sensor 3 are taken in by an A/D conversion routine executed at a predetermined time or every predetermined crank angle, and stored in a predetermined area of the RAM 105. In other words,
Data PMTHW and exhaust gas temperature in RAMl05 are updated at predetermined intervals. Further, the rotational speed data Ne is calculated by an interrupt every 30' CA of the crank angle sensor 5, and is stored in a predetermined area of the RAM 105.

The operation of the control circuit shown in FIG. 4 will be explained with reference to FIGS. 5 and 6.

FIG. 5 shows an EGR control routine, which is executed at predetermined intervals. That is, in step 501, the RAM 10
Read the exhaust gas temperature from 5 and set it to a predetermined value, for example 450°C.
Determine whether or not the value is greater than or equal to the value. As a result, the exhaust gas temperature is 45
When the exhaust gas temperature is 0°C or higher, the process proceeds to step 502, and when the exhaust gas temperature is less than 450°C, the process proceeds to step 506, where EGR is turned off and the EGR on flag XEGR is turned off.
is set to “0”.

In step 502, the intake air pressure data PM and rotational speed Ne are read from the RAM 105, and the number of steps of the step motor corresponding to the EGR valve opening is calculated by interpolation using a two-dimensional map stored in the ROM 104.

As shown in step 502, the EGR valve opening is set to 0 since there is no room for EGR operation near full load (large PM), and at light load (small PM), it is set to 0.
Since the concentration is low and the exhaust gas temperature is low, EGR operation is not necessary, so it is set to 0. Therefore, EGR will be activated in the middle load area shown by the diagonal line, but in that case,
Increase the EGR valve opening in the center of the shaded area.

In step 503, E calculated in step 502 is
The GR amount (step amount) is instructed to the EGR valve device 11, and in step 504, it is determined whether the EGR valve is turned on, that is, whether or not the EGR valve opening indicated by the diagonal line in step 502 is not 0. As a result, if the EGR valve 11 is on, the EGR valve on flag XEGR is set to "1" in step 505, and in other cases, the flag XεGR is set to "0" in step 506.

The flag XEGR is used in the injection amount calculation routine shown in FIG. 6, which will be described later.

The routine then ends in step 507.

FIG. 6 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA. Step 60
1, the intake air pressure data PM and rotational speed Ne are read from the RAM 105 and RO! , 1104
The basic injection amount TP is calculated by interpolation using the dimensional map. Next, in step 602, it is determined whether the engine is under lean operating conditions or not, for example, based on whether the water temperature T H ''vV is greater than or equal to a predetermined value.As a result, if the engine is under lean operating conditions, the process proceeds to step 603, Otherwise, the process directly proceeds to step 6H and sets the lean correction coefficient KLEAN to 1.0. Note that KLAN1↓.O is a value equivalent to the stoichiometric air-fuel ratio.

Steps 603 to 609 will be explained. Step 6
In step 03, it is determined whether or not the EGR valve is operating based on the EGR on flag XEGR. As a result, if the EGR valve is in operation (XEGR='“1”), steps 604 to 6
In step 06, the coefficient PMLεAN is calculated, and if the EGR operation is stopped (XEGR="0"), the coefficient P\EAN is calculated in step 607.

In step 604, the intake air pressure PM due to EGR operation is
Calculate the increase in PT. PT depends on the EGR valve opening amount and the rotational speed Ne. For example, PT is approximately proportional to the EGR valve opening degree and approximately inversely proportional to Ne, but exactly P
In order to obtain T, a two-dimensional map is prepared in advance in the ROM 104, and interpolation calculations are performed based on this map. Then, in step 605, EG is calculated from the measured intake air pressure PM.
The increase PT caused by the R valve operation is subtracted, and the fresh air intake air pressure PM' is calculated as PM'←PM-PT. In step 606, step 6 is stored in the ROM 104 based on this intake air pressure PM'.
Using the one-dimensional map shown in 06, the coefficient P M L E
A N is calculated by interpolation.

Further, while the EGR valve is not operating, the intake air pressure PM measured in step 607 is directly used to interpolate and calculate the coefficient P M L EA N using the one-dimensional map shown in step 607 stored in the ROM 106 .

As can be seen by comparing the illustrated curves in steps 606 and 607, the value of PMLEAN is larger during EGR operation (step 606) than when EGR operation is stopped (step 607). That is, during EGR operation, it is considered to be somewhat rich.

In step 608, RA! , 1105 and interpolates the coefficient NELEAN using the one-dimensional map shown in step 608, which is stored in the ROM 104.

In step 609, the above two coefficients PMLEANN
The lean correction coefficient KLEAN is determined by εLEAN, and KLE
It is calculated by AN'-PMLEAN-NELEAN, and guarded by the maximum value 1.0 in steps 610 and 611.

In step 612, the final injection amount TAU is determined as TALI=
TP-KLEAN ・Calculate by α+β. In addition,
α and β are correction amounts determined by other operating state parameters. Next, in step 613, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. The routine then ends at step 614.

As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the borrow-out signal of the down counter 108, and the fuel injection ends.

FIG. 7 is a graph explaining the effects of the present invention.

In other words, when the catalyst entry temperature (exhaust gas temperature) increases, EGRI increases and effective HC (olefin,
NOx emissions are reduced by increasing aroma. As a result, as shown in Figure 3, the air-fuel ratio range used becomes richer, but the fresh air decreases due to the addition of EGR, so the absolute amount of fuel does not change much, and the fuel efficiency remains approximately the same. are the same.

〔Effect of the invention〕

As explained above, according to the present invention, when the exhaust gas temperature is high, by introducing EGR and making the air-fuel ratio slightly richer, it is possible to increase HC, which is effective in reducing NOx, and as a result, NOx Emissions can be reduced.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the basic structure of the present invention, Fig. 2 is a graph showing NoX purification characteristics explaining the problems to be solved by the present invention, and Fig. 3 is a graph showing the problems to be solved by the present invention and FIG. 4 is an overall schematic diagram showing an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention; FIGS. 5 and 6 are graphs explaining the operation of the control circuit shown in FIG. 4. FIG. 7 is a graph explaining the effects of the present invention. 1... Engine body, 3... Pressure sensor, 9
...EGR valve device, 11...Lean NO. Reduction catalytic converter.

Claims (1)

[Claims] 1. A lean NO_K catalytic converter (11) provided in an exhaust passage of an internal combustion engine; an exhaust gas recirculation device (9) provided between an exhaust passage and an intake passage of the engine; Lean operating condition determining means for determining whether the engine is under lean operating conditions according to operating state parameters of the engine; Exhaust gas temperature determining means for determining whether exhaust gas temperature of the engine is equal to or higher than a predetermined value. , when the engine is under lean operating conditions and the exhaust gas temperature of the engine is less than the predetermined value, the air-fuel ratio of the engine is set to a first value.
a first lean air-fuel ratio adjusting means that adjusts the air-fuel ratio of the engine to a first lean air-fuel ratio when the engine is in a lean operating condition and the exhaust gas temperature of the engine is equal to or higher than the predetermined value;
a second lean air-fuel ratio adjusting means that adjusts to a second lean air-fuel ratio that is richer than the lean air-fuel ratio of the engine; An air-fuel ratio control device for an internal combustion engine, comprising: EGR-on means for turning on the exhaust gas recirculation device.