JP2004132280A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device of an internal combustion engine for enhancing the total performance by combining different advantages with each other. <P>SOLUTION: The air-fuel ratio control device of the internal combustion engine comprises an exhaust emission purifying catalytic converter 11 mounted on an exhaust pipe 3 of an engine 1, and an air-fuel ratio modulating means to forcibly modulate the air-fuel ratio of exhaust gas led to the catalyst converter 11 between lean and rich. The air-fuel ratio modulating means controls modulation characteristics at a plurality of different air-fuel ratios in a successively switching manner for each predetermined time by combining the modulation characteristics at the plurality of different air-fuel ratios with each other. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an air-fuel ratio control device for controlling the ratio of air to fuel in an internal combustion engine such as an engine.
[0002]
[Prior art]
2. Description of the Related Art As an exhaust purification system for an internal combustion engine such as an engine, a technique is disclosed in which air and fuel are controlled to combustion gas having a predetermined air-fuel ratio, and exhaust gas after combustion of the combustion gas flows into a catalyst. Further, when the air-fuel ratio is controlled near the stoichiometric air-fuel ratio (also referred to as stoichiometric ratio), three components of THC (all hydrocarbon compounds), CO (carbon monoxide), and NOx (nitrogen oxide) can be simultaneously purified with high efficiency. Three-way catalysts are known.
[0003]
Also, in controlling the air-fuel ratio, instead of controlling the air-fuel ratio by a feedback signal from an O ₂ sensor or the like, the air-fuel ratio is periodically and forcibly modulated to rich and lean alternately at a stoichiometric air-fuel ratio. A technique for improving the purification performance of a catalyst is disclosed. Further, there is disclosed a technique for improving purification performance by superimposing air-fuel ratio control of a plurality of modulation characteristics (see Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent No. 25651532 (pages 3-7, FIG. 1)
[0005]
[Problems to be solved by the invention]
However, as a result of the test, the catalyst shows that the air-fuel ratio modulation characteristics (period, amplitude, duty (ratio of pulse amplitude time to pulse interval), waveform, etc.) that are advantageous for the purification of THC, and the air-fuel ratio modulation that is advantageous for NOx The property was found to be present. For example, if the modulation period is set to 0.1 second in a catalyst not containing Ce (cerium), NOx can be purified with high efficiency in a wider range of air-fuel ratio, but the range in which THC can be purified with high efficiency is not wide. On the other hand, if the modulation period is set to 0.5 seconds, THC can be purified with a high purification efficiency over a wider range, but the range over which NOx can be purified with a high purification efficiency is narrow.
[0006]
Further, when detecting the deterioration of the catalyst, if the modulation period is lengthened, the fluctuation of the deterioration detection signal downstream of the catalyst becomes large, and the deterioration of the catalyst can be easily determined, but the purification performance of the catalyst may be reduced. On the other hand, if the modulation cycle is shortened, the purification performance of the catalyst is improved, but the fluctuation of the deterioration detection signal downstream of the catalyst is reduced, and it may be difficult to determine the deterioration of the catalyst.
[0007]
In other words, under the same air-fuel ratio modulation characteristic, only one of THC and NOx can secure high purification performance, and it is difficult to achieve both determination of catalyst deterioration and maintenance of purification performance. found. Further, even in the air-fuel ratio control device on which a plurality of modulation characteristics are superimposed, control components having a plurality of modulation characteristics are simultaneously mixed, and there is a possibility that sufficient purification performance may not be obtained due to mutual interference. In addition, since it is affected by the high-frequency component of the modulation characteristics, there is a possibility that the detection of catalyst deterioration does not function sufficiently. Conversely, if the performance of detecting the deterioration of the catalyst is to be ensured, there is a limit in increasing the frequency of modulation. No significant improvement in purification performance can be expected.
[0008]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that improves overall performance by combining different benefits.
[0009]
[Means for Solving the Problems]
The air-fuel ratio control device for an internal combustion engine according to claim 1 of the present invention that solves the above-mentioned problem is characterized in that an air-fuel ratio modulation unit that forcibly modulates an air-fuel ratio of combustion gas guided to a catalyst between lean and rich, By sequentially switching and controlling the modulation characteristics of a plurality of different air-fuel ratios, the modulation characteristics of the plurality of different air-fuel ratios are combined, and the exhaust gas is exhausted by an exhaust purification catalyst provided in an exhaust passage of the internal combustion engine. To purify.
[0010]
An air-fuel ratio control device for an internal combustion engine according to claim 2 of the present invention that solves the above-mentioned problems has a modulation characteristic that is advantageous for purifying THC (total hydrocarbon compounds) such as HC as a modulation characteristic of a plurality of different air-fuel ratios; And modulation characteristics advantageous for purifying NOx (nitrogen oxides) such as NO.
[0011]
According to a third aspect of the present invention, there is provided an air-fuel ratio control apparatus for an internal combustion engine, comprising: a modulation characteristic advantageous for detecting deterioration of a catalyst; and a modulation characteristic advantageous for exhaust purification. And
[0012]
According to a fourth aspect of the present invention, there is provided an air-fuel ratio control apparatus for an internal combustion engine, wherein each predetermined time is set in the modulation characteristics of the plurality of different air-fuel ratios, and The modulation characteristics of the plurality of different air-fuel ratios are sequentially controlled for each time.
[0013]
In the air-fuel ratio control apparatus for an internal combustion engine according to claim 5 of the present invention which solves the above-mentioned problem, the catalyst does not substantially contain an oxygen storage material such as ceria and zirconia. That is, a catalyst having no or little oxygen storage capacity is used.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic diagram of an internal combustion engine controlled by an air-fuel ratio control device according to the present invention.
[0015]
As shown in FIG. 1, an engine 1 that is an internal combustion engine has a plurality of combustion chambers (cylinders) 2, and an intake pipe serving as an intake passage upstream thereof so as to communicate with each combustion chamber 2. 3 are provided. Similarly, an exhaust pipe 4 serving as an exhaust passage is provided downstream thereof so as to communicate with each combustion chamber 2.
[0016]
An air cleaner 5 is provided at the most upstream portion of the intake pipe 3, and cleans external intake air here. An air flow sensor 6, a throttle 7, and a throttle opening sensor 8 are provided downstream of the air cleaner 5, and the opening of the throttle 7 is controlled in accordance with the amount of depression of an accelerator pedal. The flow rate is detected by the air flow sensor 6. Although not shown in FIG. 1, an intake temperature sensor, a pressure sensor, and the like are also provided, and the air-fuel ratio is calculated more accurately using these detected values.
[0017]
An electromagnetic injector 9 for injecting fuel is provided on the intake pipe 3 side immediately before each combustion chamber 2, and is mixed with air immediately before each combustion chamber 2. By opening the intake valve 10 provided therebetween, fuel and air combustion gas are introduced into each combustion chamber 2. In FIG. 1, the injector 9 is provided on the intake pipe 3 side. However, the injector 9 may be provided directly in each combustion chamber 2 to supply fuel by direct injection (direct injection type). Although not shown, fuel pressure control means having a fuel tank is connected to the injector 9 via a fuel pipe. The pressure of the fuel from the fuel tank to the injector 9 is controlled by fuel pressure control means using a fuel pump, a regulator, or the like, whereby the injection pressure is controlled and the injection amount to the combustion chamber 2 can be controlled. it can.
[0018]
Each combustion chamber 2 is provided with a spark plug (not shown), which ignites and burns intake air and fuel introduced from the intake pipe 3 to operate a piston and rotate a crankshaft. , Generating engine torque. The crankshaft is provided with a crank angle sensor 12 for detecting a crank angle.
[0019]
An exhaust valve 11 is provided between each combustion chamber 2 and the exhaust pipe 4, and the combustion gas burned in each combustion chamber 2 is opened as an exhaust gas by opening the exhaust valve 11. Is discharged. On the downstream side of the exhaust pipe 4, a catalytic converter 13 is provided as a catalytic device for purifying exhaust gas, and further, a muffler (not shown) serving as a muffler for exhaust gas is provided. The exhaust gas is purified by the catalytic converter 13 and discharged to the outside via the muffler.
[0020]
An O ₂ sensor 14 for detecting the concentration of O _{2 in} the exhaust gas is provided on the upstream side of the catalytic converter 13, and a catalyst deterioration detecting unit for detecting the state of deterioration of the catalyst also on the downstream side of the catalytic converter 13. O ₂ sensor 15 is provided. Deterioration determination of the catalyst is checked by comparing the detected waveform by the modulation waveform and O ₂ sensor 15 of the air-fuel ratio, if the waveform is equal, to be degraded. Conversely, if the catalyst has not deteriorated, the detected waveform by the O ₂ sensor 15 becomes different.
[0021]
The catalytic converter 13 is a carrier in which a noble metal such as platinum (Pt), palladium (Pd), and rhodium (Rh) is supported on a carrier. We do not have it. For example, the catalyst does not contain ceria (CeO ₂ ), zirconia (ZrO ₂ ), or a complex oxide thereof, or contains only a small amount thereof, and has a low oxygen storage capacity. In a catalyst having a low oxygen storage capacity, the noble metal atmosphere tends to fluctuate, and the difference in catalyst performance with respect to the air-fuel ratio modulation characteristics is further increased.
[0022]
The air-fuel ratio control device according to the present invention is realized by controlling the engine 1 having the above configuration. Note that any engine may be used as long as it is equivalent to the engine 1 having the above configuration.
[0023]
FIG. 2 is a block diagram of an air-fuel ratio control device showing an example of an embodiment according to the present invention.
[0024]
In the air-fuel ratio control device according to the present invention, the engine ECU (Electronic Control Unit) 16 mainly controls the injector 9 that injects fuel, thereby realizing the air-fuel ratio modulation characteristics according to the present invention. Specifically, the modulation characteristic of the air-fuel ratio according to the present invention is controlled by controlling the fuel injection amount and the timing of the injection with respect to the amount of air taken in according to the throttle opening of the throttle 7. . At this time, the fuel injection amount is controlled by the fuel pressure control means 17 for controlling the opening degree of the injector 9 and the fuel pressure applied to the injector 9, and the air-fuel ratio of the modulation characteristic according to the present invention can be controlled. Note that the ECU 16 performs comprehensive control of the engine, including air-fuel ratio control.
[0025]
The engine ECU 16 serving as an air-fuel ratio modulation unit includes, as hardware, a CPU (Central Processing Unit) for performing calculations, a ROM (Read Only Memory) as a storage area for a control program, and a RAM (Random Access) as an operation area for a control program. Memory) and an interface for inputting and outputting various signals, and has a control program as software. The control program of the engine ECU 16 determines its control based on various input signals input from the interface, and outputs a control signal via a driver of a device to be controlled.
[0026]
Various input / output devices are connected to the engine ECU 16. The main input device, an air flow sensor 6 for detecting an intake flow rate, a throttle opening sensor 8 for detecting a throttle opening, a crank angle sensor 12 for detecting the crank angle, O ₂ for detecting the O ₂ concentration And detection information from these sensors.
[0027]
As main output control devices, a throttle 7 for controlling a throttle opening, an injector 9 for controlling a fuel injection amount and a timing, a fuel pressure control means 17 for controlling a fuel pressure to the injector, and the like are connected. A fuel injection amount, a fuel injection timing, and the like calculated based on the detection information from each sensor are output to these control devices, whereby an appropriate amount of fuel is injected from the injector 9 at an appropriate timing.
[0028]
FIG. 3 is a flowchart of the air-fuel ratio control showing an example of the embodiment according to the present invention.
[0029]
As shown in FIG. 3, in the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, the control is started when the purification of the exhaust gas by the catalyst is required or when the catalyst deterioration determination is required (step S1). S1). At this time, the first timer is set to a predetermined time of 1 and the second timer is set to 0 as an initial condition.
[0030]
In step S2, the count time of the second timer is determined. Since the second timer is 0 in the initial state, the process proceeds to step S3.
[0031]
In step S3, a preset first modulation air-fuel ratio control waveform is output, and the air-fuel ratio is controlled based on the output waveform.
[0032]
If the first timer is not 0, step S5 is skipped (step S4), the countdown is performed from a predetermined time 1 of the first timer (step S6), and the control of the first modulation is repeated until the first timer becomes 0. That is, during the predetermined time 1, the waveform of the air-fuel ratio control of the first modulation is continuously output. For example, a waveform of a portion at a predetermined time 1 in FIG. 4A described later is a waveform of the first modulation.
[0033]
When the count time of the first timer becomes 0, a predetermined time 2 is set in the second timer (step S5), and the control of the first modulation is ended. When the predetermined time 2 is set in the second timer, it is determined in step S2 that the count time of the second timer is not 0, and the process proceeds to step S8, that is, the control of the second modulation.
[0034]
In step S8, a preset waveform of the air-fuel ratio control of the second modulation is output, and the air-fuel ratio is controlled based on the output waveform.
[0035]
The countdown is performed from a predetermined time 2 of the second timer (step S10), and the control of the second modulation is repeated until the second timer becomes zero. That is, during the predetermined time 2, the waveform of the air-fuel ratio control of the second modulation is continuously output. For example, the waveform of the portion of the predetermined time 2 in FIG. 4A described later is the waveform of the second modulation.
[0036]
When the count time of the second timer becomes 0, a predetermined time 1 is set in the first timer (step S9), and the control of the second modulation is ended. In this case, since the count time of the second timer is determined to be 0 in step S2, the process proceeds to step S3, that is, the control of the first modulation.
[0037]
As described above, in the air-fuel ratio control device according to the present invention, by performing the control of the above-described procedure, the control is performed by sequentially switching the modulation characteristics of a plurality of different air-fuel ratios by a predetermined time set for each modulation characteristic. It becomes.
[0038]
FIG. 4A is a control waveform of air-fuel ratio modulation showing an example of the embodiment of the present invention. For comparison, FIG. 4B shows a control waveform of the conventional forced air-fuel ratio modulation.
FIG. 5 is a control waveform of air-fuel ratio modulation showing another example of the embodiment of the present invention.
[0039]
FIG. 4A is a control waveform of the periodic composite modulation in which the first modulation and the second modulation having different periods are combined and sequentially switched at the operation times of the predetermined time 1 and the predetermined time 2, respectively. The cycle of the first modulation is set shorter than that of the second modulation. In the control of the first modulation having a shorter cycle, the purification efficiency of NOx is improved as compared with the control of the second modulation. Efficiency decreases. On the other hand, in the control by the second modulation having a long cycle, the purification efficiency of the THC is improved as compared with the control by the first modulation, but the purification efficiency of the NOx is reduced. Therefore, the first modulation is set as a modulation characteristic advantageous for NOx purification, and the second modulation is set as a modulation characteristic advantageous for THC purification. At the same time, the second modulation having a long cycle is also a modulation property advantageous for detecting catalyst deterioration, and in this case, the first modulation having a short cycle has a modulation property advantageous for exhaust gas purification.
[0040]
FIG. 5 shows another example of composite modulation. FIG. 5A shows a composite of the first modulation and the second modulation having different amplitudes from each other in the operation time of the predetermined time 1 and the predetermined time 2 respectively. FIG. 5B shows a control waveform of the amplitude composite modulation which is sequentially switched. FIG. 5B shows a composite waveform of the first modulation and the second modulation having different duties, and sequentially switches the operation times of the predetermined time 1 and the predetermined time 2 respectively. FIG. 5 (c) is a control waveform of duty composite modulation, in which the first modulation and the second modulation having different waveforms are combined and sequentially switched at predetermined time 1 and predetermined time 2 operation time, respectively. FIG. 5D shows control waveforms of the composite modulation. FIG. 5D shows a composite waveform of the first modulation and the second modulation having different amplitudes, periods, and duties, and different center air-fuel ratios. Predetermined modulation It is a control waveform of sequentially switching composite modulated at the operating time of the cycle 2. Further, a composite modulation of the center air-fuel ratio which combines air-fuel ratio modulations having different center air-fuel ratios may be used.
[0041]
As shown in FIGS. 4 and 5, by combining the modulation characteristics, the modulation characteristics (period, amplitude, duty, and waveform) that are advantageous for THC and the modulation characteristics that are advantageous for NOx are combined, and both THC and NOx are combined. Purification performance can be improved. Furthermore, the purification performance can be further improved by combining a modulation characteristic advantageous to CO. Similarly, by combining the modulation characteristic advantageous for catalyst deterioration detection and the modulation characteristic advantageous for catalyst purification performance, it is also possible to easily determine catalyst deterioration while ensuring purification performance.
[0042]
As shown in FIGS. 4 and 5, the first modulation and the second modulation are different from each other in at least one or more of modulation characteristics such as a period, an amplitude, a duty, and a waveform. For example, the period of the first modulation and the period of the second modulation are set to 0.1 seconds and 0.5 seconds, respectively, and an optimum value corresponding to the catalyst is set. Further, the predetermined times 1 and 2 may be the same value or different values, and an optimal value according to the catalyst is set. For example, the predetermined time 1 = 1 second and the predetermined time 2 = 1 second. Also, instead of the predetermined times 1 and 2, the predetermined modulation cycles 1 and 2 may be used, or a combination of the predetermined time and the predetermined modulation cycle may be used. For example, the predetermined time 1 = 15 seconds and the predetermined modulation cycle 2 = 1 cycle. The waveform may be a square wave (rectangular wave, trapezoidal wave, or the like), a triangular wave, a polygonal wave, a sine wave, or the like. Furthermore, rather than a forced modulation waveform, and the output value triggers a conventional O ₂ sensor may be a modulated waveform that inverts rich lean direction.
[0043]
Further, in the present embodiment, the two modulation characteristics of the first modulation and the second modulation are combined, but the present invention is not limited to this, and a third modulation may be added, or a different modulation may be added. Is also good. In addition, modulation characteristics according to operating conditions (eg, throttle opening, engine speed, volumetric efficiency, vehicle speed, manifold pressure, exhaust flow rate, exhaust temperature, catalyst temperature, intake air flow rate, or conditions correlated therewith). May be changed, or under specific conditions, the modulation characteristics may not be changed. Further, the different modulation characteristics are changed in a stepwise manner. For example, the period may be set to 0.1 second, 0.2 second, and 0.3 second, and may be gradually changed. The center air-fuel ratio is not limited to stoichiometric, but may be another air-fuel ratio.
[0044]
【The invention's effect】
According to the first aspect of the invention, since the control of the different modulation characteristics is sequentially switched and executed, the purification characteristics of each modulation characteristic can be combined, and the exhaust gas purification performance can be efficiently improved.
[0045]
According to the second aspect of the invention, the purification performance can be balanced at a high level.
[0046]
According to the third aspect of the invention, it is possible to balance the improvement of the exhaust gas purification performance and the performance of detecting the deterioration of the catalyst at a high level.
[0047]
According to the fourth aspect of the present invention, the optimum operation duration can be set for each modulation characteristic, so that the effect of improving the performance by combining can be effectively generated.
[0048]
According to the fifth aspect of the present invention, a difference in purification characteristics due to a difference in modulation characteristics is likely to occur, and an effect of improving performance by compounding can be effectively generated.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an engine showing an example of an embodiment according to the present invention.
FIG. 2 is a block diagram of air-fuel ratio control showing an example of an embodiment according to the present invention.
FIG. 3 is a flowchart of air-fuel ratio control showing an embodiment of the present invention.
FIG. 4 shows a control waveform of air-fuel ratio modulation and a control waveform of conventional forced air-fuel ratio modulation showing an example of an embodiment according to the present invention.
FIG. 5 is a control waveform of air-fuel ratio modulation showing another example of the embodiment according to the present invention.
[Explanation of symbols]
6 Air flow sensor 7 Throttle 8 Throttle opening sensor 9 Injector 12 Crank angle sensor 14 O2 sensor 16 Engine ECU
17 Fuel pressure control means

Claims (5)

An exhaust gas purification catalyst provided in an exhaust passage of the internal combustion engine;
Air-fuel ratio modulation means for forcibly modulating the air-fuel ratio of the exhaust gas guided to the catalyst between lean and rich,
An air-fuel ratio control device for an internal combustion engine, wherein the air-fuel ratio modulation means controls by sequentially switching modulation characteristics of a plurality of different air-fuel ratios. The air-fuel ratio control device for an internal combustion engine according to claim 1,
The air-fuel ratio control device for an internal combustion engine, wherein the modulation characteristics of the plurality of different air-fuel ratios include a modulation characteristic advantageous for THC purification and a modulation characteristic advantageous for NOx purification. The air-fuel ratio control device for an internal combustion engine according to claim 1 or 2,
The air-fuel ratio control device for an internal combustion engine, wherein the modulation characteristics of the plurality of different air-fuel ratios include a modulation characteristic advantageous for detecting catalyst deterioration and a modulation characteristic advantageous for exhaust gas purification. An air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 3,
Wherein the air-fuel ratio modulation means sequentially controls the modulation characteristics of the plurality of different air-fuel ratios for each predetermined time set for the modulation characteristics of the plurality of different air-fuel ratios. apparatus. An air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 4,
An air-fuel ratio control device for an internal combustion engine, wherein the catalyst does not substantially include an oxygen storage material.

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