JP2004162535A - Air-fuel ratio control system for overall exhaust emission control - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To purify all these three components at a further high purification rate by coping with the fact that self-contradiction originally exists in simultaneously purifying HC and CO requiring an oxidation atmosphere for purification and NOx requiring a reduction atmosphere by a three way catalyst. <P>SOLUTION: An oxygen storage quantity of an exhaust emission control catalyst is estimated when leanly operating an internal combustion engine for restraining exhaust of the HC and the CO, and exhaust of MOx is also restrained by performing engine lean operation until the oxygen storage quantity reaches a prescribed upper limit value. The engine may be richly operated until the oxygen storage quantity of the exhaust emission control catalyst reduces to a prescribed lower limit value in succession to this operation. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an internal combustion engine.
[0002]
[Prior art]
The optimum value of the air-fuel ratio of an internal combustion engine differs depending on the viewpoint of evaluating the performance of the engine, and various proposals have been made to optimally control the air-fuel ratio from each viewpoint. Among them, there is a technique described in the following patent document as a technique aiming at an optimal control of an air-fuel ratio in relation to an exhaust purification performance by an exhaust purification catalyst.
[0003]
The technology described in Patent Literature 1 enriches the air-fuel ratio in order to stabilize combustion at the time of cold start of the engine. As a result, a large amount of HC and CO is discharged from the combustion chamber, so that the upstream side of the exhaust purification catalyst is prevented. In the conventional technique of injecting secondary air at a time, there is a problem that SO2 generated by sulfur contained in fuel is oxidized by oxygen of the secondary air to form a sulfate, and adheres to an exhaust purification catalyst. Focusing on this fact, in an internal combustion engine that performs rich operation at cold temperature, means for performing a leaning process so that the air-fuel ratio at the exhaust purification catalyst inlet becomes lean, and an air-fuel ratio at the exhaust purification catalyst inlet after this leaning process Is provided to perform the enrichment process so as to be rich. Note that rich and lean indicate a state where the air-fuel ratio is lower than the stoichiometric air-fuel ratio and a state where the air-fuel ratio is higher than the stoichiometric air-fuel ratio, respectively.
[0004]
The technology described in Patent Literature 2 is based on the prior art in which the engine is operated lean for a predetermined time for early activation of the exhaust purification catalyst at the time of cold start of the engine. Noting that there is a problem that NOx emission is increased due to lack of fuel or excessive lean operation, when the operation is made lean at the time of engine cold start, when the engine coolant temperature reaches the catalyst activation determination temperature This is to cancel the lean operation.
[0005]
The technique described in Patent Literature 3 performs an increase in the amount of air after the engine is started and a retard correction of the ignition timing in order to accelerate the activation of the exhaust gas purification catalyst and reduce the amount of HC emission at the time of cold start of the engine. , The target air-fuel ratio coefficient is set according to the spontaneous ignition rate, and the target air-fuel ratio coefficient is increased as the exhaust gas temperature increases. This is to restore the air-fuel ratio that has been increased by increasing the amount.
[Patent Document 1]
JP-A-9-242528 [Patent Document 2]
JP-A-9-151759 [Patent Document 3]
Japanese Patent Application Laid-Open No. 2000-232455
[Problems to be solved by the invention]
Regarding the purification of harmful components HC, CO, and NOx related to the operation of the internal combustion engine, since HC and CO require an oxidizing atmosphere for their purification and NOx requires a reducing atmosphere for their purification, these three components are used. There is inherent self-contradiction in purifying simultaneously with a primary catalyst. The present invention addresses this self-contradiction and seeks to purify all three components at a higher purification rate.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention provides an air-fuel ratio control device for an internal combustion engine having a fuel supply unit, an air supply unit, and an exhaust purification catalyst having an oxidation assisting function and a reduction assisting function. Means for setting an air-fuel ratio during operation of the internal combustion engine by acting on at least one of the means and the air supply means, and the exhaust purification catalyst based on the air-fuel ratio setting by the first means. Second means for estimating the amount of accumulated oxygen, wherein the first means estimates by the second means when the air-fuel ratio is set to lean to suppress the emission of unburned components from the internal combustion engine. The present invention is to provide an air-fuel ratio control device wherein the amount of oxygen stored in the exhaust purification catalyst is controlled so as not to exceed a predetermined upper limit.
[0008]
In the air-fuel ratio control device as described above, the first means makes the air-fuel ratio of the engine operation rich when the oxygen storage amount of the exhaust purification catalyst estimated by the second means exceeds the upper limit. It may be set. Further, the first means sets the air-fuel ratio of the engine operation to be rich until the oxygen storage amount of the exhaust purification catalyst estimated by the second means decreases to a predetermined lower limit when the air-fuel ratio of the engine operation is set to be rich. May be set to a rich state. Still further, the first means sets the air-fuel ratio of the engine operation to the stoichiometric air-fuel ratio when the oxygen storage amount of the exhaust gas purification catalyst estimated by the second means decreases to the predetermined lower limit. It may be.
[0009]
In any case, the first means may set the air-fuel ratio of the internal combustion engine to lean when the engine is cold started.
[0010]
In any of the above cases, the second means estimates the amount of oxygen accumulated in the exhaust gas purification catalyst based on the amount of exhaust gas flowing through the exhaust gas purification catalyst and the air-fuel ratio and the temperature of the exhaust gas purification catalyst. It may be like.
[0011]
Function and effect of the present invention
As described above, in the internal combustion engine having the fuel supply means, the air supply means, and the exhaust purification catalyst having the oxidation assisting function and the reduction assisting function, the air-fuel ratio control device for controlling the air-fuel ratio includes the fuel supply means and the air. A first means for acting on at least one of the supply means to set an air-fuel ratio during operation of the internal combustion engine, and an amount of oxygen accumulated in the exhaust purification catalyst based on the setting of the air-fuel ratio by the first means The exhaust gas purification estimated by the second means when the first means sets the air-fuel ratio to lean to suppress emission of unburned components from the internal combustion engine. If the oxygen accumulation amount of the catalyst is set so as not to exceed the predetermined upper limit, the lean operation for suppressing the emission of HC and CO from the internal combustion engine is performed, and the resulting exhaust purification catalyst Oxygen storage By controlling both the purification performance for HC and CO and the purification performance for NOx under control so that the equilibrium between them is controlled to an optimum state, and the purification effect for both is comprehensively controlled. Can be maximized.
[0012]
In this case, the first means sets the air-fuel ratio of the engine operation to be rich when the oxygen storage amount of the exhaust gas purification catalyst estimated by the second means exceeds the upper limit. If the amount of oxygen stored in the exhaust gas purification catalyst exceeds the upper limit, the engine operation is subsequently enriched to remove the oxygen accumulated in the exhaust gas purification catalyst by the unburned portion in the exhaust gas. Then, the amount of oxygen stored in the mounted purification catalyst is restored to the original amount. Further, if the rich operation is performed until the oxygen storage amount of the exhaust purification catalyst estimated by the second means decreases to a predetermined lower limit, the rich operation is performed based on the oxygen storage amount of the exhaust purification catalyst. Is controlled to an optimal degree. If the engine operation is operated at a standard air-fuel ratio through a control process combining the lean operation and the rich operation, the emission of HC and CO is temporarily stopped, such as at the time of a cold start of the engine. Can be comprehensively improved in controlling the emission of HC, CO, and NOx in the process of shifting from the operating state in which the pressure increases to the normal operating state.
[0013]
Further, when the air-fuel ratio control as described above is applied particularly to the cold start of the engine, in the process from the start of the engine to the warm-up, HC and CO contained in the exhaust gas with the rise of the engine temperature are increased. Is gradually reduced, and conversely, NOx is gradually increased. Therefore, in the first half of the control, the engine is operated lean to mainly purify better HC and CO, and at that time, the accumulation of oxygen in the exhaust purification catalyst is performed. In the latter half of the control, a rich operation of the engine is performed to ensure that the oxygen accumulated in the exhaust gas purification catalyst is digested and the operation of suppressing the emission of NOx can be performed. It is possible to improve the overall exhaust purification performance at the time of starting.
[0014]
The amount of oxygen stored in the exhaust gas purification catalyst depends on the amount of exhaust gas flowing therethrough and the temperature of the exhaust gas purification catalyst. If the oxygen storage amount is estimated based on the fuel ratio and the temperature of the exhaust purification catalyst, the estimation of the oxygen storage amount required for the air-fuel ratio control can be achieved with sufficiently high accuracy for the purpose. it can.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic diagram showing a configuration in which an air-fuel ratio control device according to the present invention is incorporated in one standard internal combustion engine. In the figure, 10 is a cylinder of an internal combustion engine, and 12 is a piston. An intake port 14 and an exhaust port 16 are provided at the head of the cylinder, and are opened and closed by an intake valve 18 and an exhaust valve 20, respectively. The intake port 14 is supplied with air introduced through an air cleaner 22 through an intake passage 28 having an intake throttle valve 24 and an exhaust gas recirculation control valve 26. The exhaust gas discharged from the exhaust port 16 is discharged to the atmosphere via an exhaust passage 32 including a three-way catalytic converter 30. From the exhaust passage 32, an exhaust gas recirculation passage 34 communicates with the intake passage 28 via the exhaust gas recirculation control valve 26 from a position before the three-way catalytic converter 30. Fuel is supplied from a fuel injection valve 36, and the air-fuel mixture is ignited by an ignition plug 38.
[0016]
The intake valve 18, the exhaust valve 20, the intake throttle valve 24, the exhaust gas recirculation control valve 26, the fuel injection valve 36, and the spark plug 38 are all microcomputers known in the art in various modes. It is controlled by an electronic control unit (ECU) 40 provided. The electronic control device 40 receives information about the engine temperature from the engine temperature sensor 42, information about the catalyst temperature in the three-way catalytic converter 30 from the catalyst temperature sensor 44, an engine speed sensor and an accelerator opening (not shown). The degree sensor supplies information on the engine speed Ne and the accelerator opening Da, and other information necessary for engine operation control.
[0017]
With the above configuration, the operation of the internal combustion engine is basically performed based on the operation of the driver depressing the accelerator pedal to obtain the desired engine speed, and the intake throttle according to the engine speed Ne and the accelerator opening Da. The opening degree of the valve 24 is controlled to control the amount of intake air, and the fuel injection valve 36 is controlled to supply a corresponding amount of fuel. At this time, one or both of the amount of intake air and the amount of fuel supply are set to the other. On the other hand, the air-fuel ratio is controlled by changing the air-fuel ratio relatively. Therefore, the air-fuel ratio control device according to the present invention is substantially constituted by a combination of the intake throttle valve 24, the fuel injection valve 36, and the electronic control device 40, and is further used for estimating the oxygen storage amount in the exhaust purification catalyst. When the catalyst temperature is taken into consideration, a catalyst temperature sensor 44 is added thereto, or when the catalyst temperature is estimated on the basis of the engine temperature, the engine temperature sensor 42 is added thereto. . When the air-fuel ratio control device according to the present invention is applied to a cold start of an internal combustion engine, an engine temperature sensor for detecting whether or not the temperature at the time of starting the engine is equal to or lower than a predetermined value is required.
[0018]
FIG. 2 is a flowchart showing an operation when the air-fuel ratio control device according to the present invention is incorporated in an engine for improving exhaust gas purification at the time of cold start of the engine. When the operation of the air-fuel ratio control device is started simultaneously with the start of the engine, first, at step 1, it is determined whether or not the engine temperature Te is equal to or higher than a predetermined threshold temperature Tea. If the answer is yes, the operation of the air-fuel ratio control device according to the present invention is not required, and the control proceeds to step 8 described below, where the target air-fuel ratio is set to a predetermined standard value from the beginning, and the control operation according to the present invention is performed. To end.
[0019]
If the answer to step 1 is no, the control proceeds to step 2, where the target air-fuel ratio is set to a predetermined lean value R1 higher than the stoichiometric air-fuel ratio, for example, 15.00. Next, the control proceeds to step 3, where the amount of stored oxygen Go in the exhaust purification catalyst is calculated. This oxygen accumulation amount Go increases with the elapse of the operation time of the engine, and its value is basically determined by the intake air amount every moment of the engine operation and the air-fuel ratio controlled in step 2. For the internal combustion engine of each design, it can be experimentally determined in advance based on the command signal for the intake throttle valve 24 and the fuel injection valve 36 and the operation continuation time. Further, since the oxygen storage amount Go is also affected by the catalyst temperature, the oxygen storage amount Go is corrected by the catalyst temperature detected by the catalyst temperature sensor 44 or the catalyst temperature estimated based on the signal from the engine temperature sensor 42. It is preferred that (At the time of cold start of the engine, the exhaust gas recirculation control valve 26 is normally fully closed.)
[0020]
Computer control of this type of internal combustion engine operation is performed in such a manner that the execution of each step in accordance with a predetermined control flowchart is repeated at a period of usually several tens of milliseconds. In the control according to the flowchart of FIG. 2, when the oxygen storage amount Go in the catalyst is calculated in step 3, the control proceeds to step 4, where the value of Go is a predetermined value indicating the allowable upper limit of the oxygen storage amount. It is determined whether or not the threshold value Go1 has been exceeded. While the answer is no, the control returns to step 3 and the operation of calculating Go again and judging again whether or not Go has exceeded Go1 in step 4 are repeated at intervals of several tens of milliseconds.
[0021]
FIG. 3 is a graph showing the progress of such control as a change in the air-fuel ratio with respect to time. In FIG. 3, T0 is the time when the control by the air-fuel ratio control device according to the present invention is started in association with the cold start of the engine, and the air-fuel ratio R1 is the theoretical air-fuel ratio when the engine is operated after the completion of the cold start. This is a predetermined lean air-fuel ratio value higher than the fuel ratio Rt (15.00 in the above example). If the cold start of the engine continues smoothly and the calculation of Go in step 3 continues smoothly, the answer in step 4 will turn from no to yes. That point is T1.
[0022]
When the answer to step 4 changes from no to yes, the control proceeds to step 5, where the target air-fuel ratio is set to a predetermined rich value R2 lower than the stoichiometric air-fuel ratio Rt, for example, 14.45. Next, the control proceeds to step 6, where the catalyst oxygen storage amount Go in the operating state in which the air-fuel ratio is set to rich in step 5 is calculated in the same manner as in step 3. If the air-fuel ratio is set to be rich, the oxygen stored in the catalyst is gradually digested, so that the value of Go gradually decreases. Also in this case, the value of Go at every moment of the engine operation can be experimentally obtained based on the command signal for the intake throttle valve 24 and the fuel injection valve 36 and the operation continuation time. If the correction is made depending on the temperature, the estimation of the amount of accumulated catalyst oxygen can be obtained with higher accuracy. Then, in each subsequent step 7, it is determined whether or not the obtained calculated value Go has fallen to a predetermined lower limit value Go2 at which the rich operation should be terminated. While the answer is no, the control returns to step 6 and the operation of calculating Go again and determining whether it has fallen below Go2 is repeated at intervals of several tens of milliseconds.
[0023]
Thus, if the lean operation continues smoothly, Go eventually falls below Go2, and the answer to step 7 turns from no to yes. This time is the time T2 in the graph of FIG. Then, the control proceeds to step 8, after which the target air-fuel ratio is set to a predetermined standard value, and the operation of the air-fuel ratio control device according to the present invention ends. Such a standard value may usually be a stoichiometric air-fuel ratio, which is generally 14.5 for fuel of a vehicle internal combustion engine.
[0024]
While the present invention has been described in detail with reference to one embodiment, it will be apparent to those skilled in the art that various modifications can be made to such embodiment within the scope of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration in which an air-fuel ratio control device according to the present invention is incorporated into one standard internal combustion engine.
FIG. 2 is a flowchart showing an example of the operation of the air-fuel ratio control device according to the present invention when applied to cold start of an internal combustion engine.
FIG. 3 is a graph showing the progress of control of the air-fuel ratio control device according to the present invention as a change in air-fuel ratio with respect to time.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Cylinder, 12 ... Piston, 14 ... Intake port, 16 ... Exhaust port, 18 ... Intake valve, 20 ... Exhaust valve, 22 ... Air cleaner, 24 ... Intake throttle valve, 26 ... Exhaust gas recirculation control valve, 28 ... Intake Passages, 30: three-way catalytic converter, 32: exhaust passage, 34: exhaust gas recirculation passage, 36: fuel injection valve, 38: spark plug, 40: electronic control device, 42: engine temperature sensor, 44: catalyst temperature Sensor

Claims (6)

An air-fuel ratio control device for an internal combustion engine having a fuel supply means, an air supply means, and an exhaust purification catalyst having an oxidation assisting function and a reduction assisting function, acting on at least one of the fuel supply means and the air supply means First means for setting an air-fuel ratio in the operation of the internal combustion engine, and second means for estimating the amount of oxygen stored in the exhaust gas purification catalyst based on the setting of the air-fuel ratio by the first means. Wherein the first means has a predetermined amount of oxygen accumulated in the exhaust gas purification catalyst estimated by the second means when the air-fuel ratio is set to lean to suppress the emission of unburned components from the internal combustion engine. An air-fuel ratio control device wherein the control is performed within a range not exceeding an upper limit value. The first means is configured to set the air-fuel ratio of the engine operation to be rich when the oxygen storage amount of the exhaust gas purification catalyst estimated by the second means exceeds the upper limit value. The air-fuel ratio control device according to claim 1, wherein The first means enriches the air-fuel ratio of the engine operation until the oxygen accumulation amount of the exhaust purification catalyst estimated by the second means decreases to a predetermined lower limit when the air-fuel ratio of the engine operation is set to rich. 3. The air-fuel ratio control device according to claim 2, wherein the air-fuel ratio control device is in a state. The first means sets an air-fuel ratio for engine operation to a stoichiometric air-fuel ratio when the oxygen storage amount of the exhaust gas purification catalyst estimated by the second means decreases to the predetermined lower limit. The air-fuel ratio control device according to claim 3, wherein: 5. The air-fuel ratio control device according to claim 1, wherein the first means sets the air-fuel ratio of the internal combustion engine to lean when the engine is cold-started. The second means estimates an amount of oxygen stored in the exhaust gas purification catalyst based on an amount of exhaust gas flowing through the exhaust gas purification catalyst, an air-fuel ratio thereof, and a temperature of the exhaust gas purification catalyst. The air-fuel ratio control device according to any one of claims 1 to 5, wherein

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