JP3150679B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a lean burn system using a lean NO _x catalyst.

[Conventional technology]

The present applicant has already proposed a lean NO _x reduction catalyst which can purify the NO _x mainly composed of metal-exchanged zeolites especially Cu- zeolites in lean burn system at a high rate (Reference: Japanese Patent Application Sho 63-95026 ).

[Problems to be solved by the invention]

However, _the NO _x purification rate of the aforementioned lean NO _x catalyst,
As shown in FIG. 2, in a lean atmosphere having a high temperature dependency, a high exhaust gas temperature (for example, 450 ° C. or higher) and a high O ₂ concentration, the NO _x purification rate sharply decreases. Furthermore, N
In order to clear the _Ox regulation, the engine must be operated in a lean region where the air-fuel ratio A / F is around 20 to 22, as indicated by the symbol A in FIG.

The reason causing a decrease of the NO _x purification rate when the exhaust gas temperature is obtained by operating the high addition engine at a lean region is considered as follows. That is, when the exhaust gas temperature to operate the high addition engine in a lean region, hydrocarbons (HC) is utilized for reduction of NO _x, , And the degree is higher as the exhaust gas temperature is higher. As a result, NO _x is not reduced, thus, NO _x purification rate is a problem of a decrease.

In the exhaust gas temperature is low lean atmosphere, HC is expected to change to the active species by the partial oxidation, the active species (Cu (II) -CO ^-) is, It is considered that NO _x is purified by reacting with NO.

Therefore, an object of the present invention is to provide a high temperature exhaust gas.
It is an object of the present invention to provide a lean burn system with an improved NO _x emission purification rate.

[Means for solving the problem]

The means for solving the above-mentioned problem is shown in FIG. That is, the lean NOx catalytic converter 12, which is provided in the exhaust passage of the internal combustion engine and reacts HC and NOx in a lean atmosphere, communicates between the exhaust passage and the intake passage of the engine, and the exhaust passage side communication port is connected to the lean exhaust passage. In the internal combustion engine including the exhaust gas recirculation device 11 provided on the upstream side of the NOx catalytic converter 12, the lean operating condition determining means determines whether the engine is in the lean operating condition in accordance with the operating state parameter of the engine, for example, the cooling water temperature THW. The exhaust gas temperature determining means determines whether or not the exhaust gas temperature of the engine is equal to or higher than a predetermined value, for example, 600 ° C. When the gas temperature is equal to or higher than a predetermined value, the exhaust gas recirculation device is turned on.

This air-fuel ratio control device for an internal combustion engine adjusts the air-fuel ratio of the engine to a first lean air-fuel ratio when the engine is in a lean operation condition and the exhaust gas temperature of the engine is less than a predetermined value.
Means for adjusting the air-fuel ratio of the engine to a second lean air-fuel ratio richer than the first lean air-fuel ratio when the engine is in a lean operation condition and the exhaust gas temperature of the engine is equal to or higher than a predetermined value. A second lean air-fuel ratio adjusting means for adjusting the fuel ratio.

(Operation)

The operation of the above means is also shown in FIG. That is, the introduction of EGR during the lean operating condition, becomes as shown by reference numeral B in FIG. 3, as a result, the air-fuel ratio A / F to clear the NO _x regulation becomes 17-19 and rich-. That is, the O ₂ concentration in the exhaust gas is reduced.
The partial oxidation reaction shown in the equation (2) proceeds rather than the complete oxidation reaction in the equation, and as a result, the reduction of HC used for reduction of NO _x emission is prevented, so that the purification rate of NO _x is further improved. .

〔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 1. The pressure sensor 3 is of a semiconductor type that directly measures intake air pressure, and generates an analog voltage output signal proportional to the intake air pressure. This output signal is supplied to the A / D converter 101 with built-in multiplexer of the control circuit 10. A distributor (not shown) includes a crank angle sensor 4 whose axis generates a reference position detection pulse signal every 720 ° in terms of crank angle and a reference position detection pulse signal in every 30 degrees which is converted into crank angle. Is provided. The pulse signals of the crank angle sensors 4 and 5 are supplied to an input / output interface 102 of the control circuit 10, and the outputs of the crank angle sensors 4 and 5 are supplied to an interrupt terminal of the CPU 103.

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

A water temperature sensor 7 for detecting the temperature of the cooling water is provided on a water jacket (not shown) of the cylinder block of the engine body 1. The water temperature sensor 7 generates an analog voltage electric signal corresponding to the cooling water temperature THW. This output is also supplied to the A / D converter 101.

Reference numeral 9 denotes an EGR valve device, which has a built-in step motor controlled by the input / output interface 102 of the control circuit 10.

The exhaust system 8 downstream of the exhaust manifold is provided with a lean NO _x reduction catalytic converter 11 for purifying NO _x at a high rate in a lean atmosphere and an oxidation catalytic converter 12 for purifying HC and CO at a high rate. Lean _the NO _x reduction catalytic converter 11 is mainly composed of the above Cu- zeolites. Note that a three-way catalytic converter may be used instead of the oxidation catalytic converter 12.

Reference numeral 13 denotes an exhaust gas temperature sensor for detecting the temperature of the exhaust gas in the lean NO _x reduction catalytic converter 11, and the output thereof is supplied to the A / D converter 101 of the control circuit 10. The control circuit 10 is configured as, for example, a microcomputer, and includes an A / D converter 101, an input / output interface
102, CPU103, ROM104, RAM105, Backup RAM1
06, a clock generation circuit 107 and the like are provided.

In the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110
Is to control the That is, when the fuel injection amount TAU is calculated in a routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 6. On the other hand, when the down counter 108 counts a clock signal (not shown) and its borrow-out terminal finally becomes “1” level, the flip-flop 109 is set, and the drive circuit 110 Stop energizing. That is, the fuel injection valve 6 is energized by the above-described fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

The CPU 103 generates an interrupt when the input / output interface 102 receives the pulse signal of the crank angle sensor 5 after the A / D conversion of the A / D converter 101 is completed.
When an interrupt signal from 7 is received, and so on.

The intake air pressure data PM of the pressure sensor 3, the cooling water temperature data THW of the water temperature sensor 7, and the exhaust gas temperature of the exhaust gas temperature sensor 13 are taken in by an A / D conversion routine executed for a predetermined time or every predetermined crank angle. It is stored in a predetermined area of the RAM 105. That is, the data PMTH in the RAM 105
W and the exhaust gas temperature are updated every predetermined time. The rotation speed data Ne is calculated by an interruption of the crank angle sensor 5 at every 30 CA, and is stored in a predetermined area of the RAM 105.

The operation of the control circuit of FIG. 4 will be described with reference to FIGS.

FIG. 5 shows an EGR control routine which is executed at predetermined time intervals. That is, in step 501, the exhaust gas temperature is read from the RAM 105, and it is determined whether or not the temperature is equal to or higher than a predetermined value, for example, 450 ° C. As a result, when the exhaust gas temperature is equal to or higher than 450 ° C., the process proceeds to step 502, and when the exhaust gas temperature is lower than 450 ° C., the process proceeds to step 506 to turn off the EGR,
The EGR on flag XEGR is set to “0”.

In step 502, the intake air pressure data PM and the rotation 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 the two-dimensional map stored in the ROM 104. The EGR valve opening is determined in step 5
As shown in Fig. 02, near full load (large PM), EGR
Since there is no room for the actuation and 0, the light load (PM is small), since concentration of NO _x is low and the exhaust gas temperature is low, a 0 since the operation of the EGR is not required, therefore, the load in the shaded In this case, the EGR valve is operated in the portion, and at this time, the EGR valve opening is increased in the central portion of the hatched portion.

In step 503, the EGR amount (step amount) calculated in step 502 is instructed to the EGR valve device 9. In step 504, the EGR valve is turned on, that is, the EGR valve opening indicated by the hatched portion in step 502 is opened. It is determined whether the degree is not 0. As a result, if the EGR valve of the EGR valve device 9 is ON, step 505
In step 506, the flag XEGR is set to "0". Note that the flag X
The EGR is used in the injection amount calculation routine of FIG. 6 described later.

 Then, in step 507, this routine ends.

FIG. 6 shows an injection amount calculation routine which is executed at every predetermined crank angle, for example, every 360 ° CA. In step 601, the intake air pressure data PM and the rotation speed Ne are read from the RAM 105, and the basic injection amount TP is calculated by interpolation using a two-dimensional map stored in the ROM 104. Next, in step 602, it is determined whether or not the engine is in a lean operation condition, for example, based on whether or not the water temperature THW is equal to or higher than a predetermined value. As a result, if the condition is the lean operation condition, the process proceeds to step 603. If the condition is not the lean operation condition, the process directly proceeds to step 611 to set the lean correction coefficient KLEAN to 1.0. Note that KLEAN = 1.0 is a value corresponding to the stoichiometric air-fuel ratio.

Steps 603 to 609 will be described. In step 603, 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 operating (XEGR =
“1”), calculate the coefficient PMLEAN in steps 604 to 606,
If the R operation is stopped (XEGR = "0"), a coefficient PMLEAN is calculated in step 607.

In step 604, a rise PT of the intake air pressure PM due to the EGR operation is calculated. PT depends on the EGR valve opening amount and the rotation speed Ne, for example, PT is almost proportional to the EGR valve opening, and N
It is almost inversely proportional to e, but in order to get PT
A two-dimensional map is prepared at 104, and interpolation calculation is performed based on the two-dimensional map. Then, in step 605, the rise PT due to the operation of the EGR valve is subtracted from the measured intake air pressure PM, and the intake air pressure PM 'for fresh air is calculated by PM' ← PM-PT. In step 606, this intake air pressure P
Based on M ', the coefficient PMLEAN is calculated by interpolation using a one-dimensional map shown by a solid line in step 606 stored in the ROM 104 based on M'.

Further, while the operation of the EGR valve is stopped, the coefficient PMLEAN is calculated by interpolation using the one-dimensional map shown in step 607 stored in the ROM 106 by directly using the intake air pressure PM measured in step 607.

As can be seen by comparing the curves shown in steps 606 and 607, the value of PMLEAN is higher during the EGR operation (step 606).
It is larger than during the R operation stop (step 607). That is, during the EGR operation, it is slightly richer.

In step 608, the rotational speed data Ne is read from the RAM 105, and the coefficient NELEAN is calculated by interpolation using the one-dimensional map shown in step 608 stored in the ROM 104.

In step 609, the lean correction coefficient KLEAN is calculated by KLEAN ← PMLEAN / NELEAN using the above two coefficients PMLEAN and NELEAN, and guarding is performed with the maximum value 1.0 in steps 610 and 611.

In step 612, the final injection amount TAU is set as TAU ← TP · KLMAN
・ Calculate using α + β. Note that α and β are correction amounts determined by other operation 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. Then, in step 614, this routine ends.

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 illustrating the effect of the present invention. In other words, when the catalyst input gas temperature (exhaust gas temperature) increases, the EGR amount is increased to increase the effective HC (olefin, aroma).
Since increasing the NO _x emission is reduced. In addition,
As a result, as shown in FIG. 3, the used air-fuel ratio region becomes richer, but the fresh air decreases by the amount of EGR.
The absolute amount of fuel does not change much, and the fuel efficiency is almost the same.

〔The invention's effect〕

According to the present invention described above, when the exhaust gas temperature is high, by the air-fuel ratio to killingゝrich side with EGR introduction, can increase the effective HC for the reduction of NO _x, as a result, it is possible to reduce the NO _x emissions.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention, and FIG. 2 is a NO _x diagram for explaining a problem to be solved by the present invention.
FIG. 3 is a graph illustrating purification characteristics, FIG. 3 is a graph illustrating problems and actions to be solved by the present invention, FIG. 4 is an overall schematic diagram illustrating an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention, 5 and 6 are flowcharts for explaining the operation of the control circuit in FIG. 4, and FIG. 7 is a graph for explaining the effect of the present invention. 1 ... engine body, 3 ... pressure sensor, 9 ... EGR valve device, 11 ... lean NO _x reduction catalytic converter.

Claims (2)

(57) [Claims] 1. A lean NOx catalytic converter provided in an exhaust passage of an internal combustion engine for reacting HC and NOx in a lean atmosphere, and an exhaust passage side communication port for communicating between an exhaust passage and an intake passage of the engine. An exhaust gas recirculation device provided upstream of the lean NOx catalytic converter, lean operating condition determining means for determining whether or not the engine is in a lean operating condition according to an operating state parameter of the engine, Exhaust gas temperature determining means for determining whether the exhaust gas temperature is equal to or higher than a predetermined value; and 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, the exhaust gas recirculation is performed. EGR on means for turning on the device. An air-fuel ratio control device for an internal combustion engine, comprising: 2. A first lean air-fuel ratio for adjusting an air-fuel ratio of the engine to a first lean air-fuel ratio when the engine is in a lean operating condition and an exhaust gas temperature of the engine is less than the predetermined value. Adjusting means for adjusting the air-fuel ratio of the engine to a second lean air-fuel ratio richer than the first lean air-fuel ratio when the engine is in a lean operation condition and the exhaust gas temperature of the engine is equal to or higher than the predetermined value; 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising: a second lean air-fuel ratio adjusting means for adjusting the fuel ratio.