JPS6251735A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To rapidly and surely inform occurrence of an abnormal condition in an engine in which O2 sensor is provided upstream and downstream of a catalyst for purifying exhaust gas, by judging whether a predetermined pattern coincides with the output of the downstream side O2 sensor or not. CONSTITUTION:First and second oxygen concentration detector (O2 sensor) S1, S2 are provided upstream and downstream of an exhaust purifying catalyst CT disposed in the exhaust system of an internal combustion engine EG, and the air-fuel ratio is controlled to a desired value in accordance with the result of detection by at least the upstream side O2 sensor S1. In such a device, there is provided a judging means C1 for judging whether a predetermined pattern which indicates variations in the oxygen concentration of residual exhaust gas during feed-back control of air-fuel ratio, coincides with the output of the downstream side O2 sensor S2 or not. Further, there is provided an informing means C2 for informing the result of the judging means C1.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention uses an exhaust gas purification catalyst in order to improve the exhaust gas purification of an internal combustion engine. The present invention relates to an air-fuel ratio control device that controls the air-fuel ratio of an internal combustion engine.

[Prior Art] Conventionally, when using an exhaust gas purifying catalyst, such as a three-way catalyst, to purify the exhaust gas of an internal combustion engine, the mixture air-fuel ratio of the internal combustion engine is controlled to a region where the purification rate of the catalyst is high. . The air-fuel ratio control device executes this air-fuel ratio control, and detects the residual oxygen concentration in the exhaust gas with an oxygen concentration sensor installed in the exhaust system of the internal combustion engine. Based on the detection result, the air-fuel ratio control device Feedback control of the air-fuel ratio is achieved by adjusting the amount of fuel supplied. In order to quickly detect the residual oxygen concentration in the exhaust gas of the internal combustion engine and ensure quick response, the above air-fuel ratio control device installs the oxygen concentration sensor upstream of the exhaust gas purification catalyst near the exhaust manifold of the internal combustion engine. It is usually placed.

Furthermore, in order to improve the control characteristics of the air-fuel ratio control device, it has been proposed to install a separate oxygen concentration sensor not only upstream of the above-mentioned exhaust gas purifying catalyst but also downstream thereof. (Unexamined Japanese Patent Publication No. 52/102934>.

This is because, as shown in Figure 2 (△), due to variations in the output characteristics of each oxygen concentration sensor, even if the output voltage of the sensor installed upstream of the exhaust gas purification catalyst detects exhaust gas with the same stoichiometric air-fuel ratio. This is due to differences. Even if the same oxygen concentration sensor has such variations in output characteristics, if the residual oxygen concentration is detected downstream of the exhaust gas purification catalyst, it will be close to the stoichiometric air-fuel ratio as shown in Figure 2 (B). The output voltages of the sensors show almost the same value. Therefore, depending on the output of the oxygen concentration sensor installed on the downstream side, the comparison voltage of the output of the oxygen concentration sensor installed on the upstream side may be changed, or the integral constant of the air-fuel ratio control signal or the output of the oxygen concentration sensor may be changed. This improves the accuracy of feedback control to the stoichiometric air-fuel ratio by changing the delay time, etc.

[Problems to be Solved by the Invention] Conventionally, even in air-fuel ratio control devices using two oxygen concentration sensors, the aim is to improve the accuracy of air-fuel ratio feedback control. Abnormalities in the internal combustion engine system, including the air-fuel ratio control device, have not been detected. For example, if an abnormality occurs in a fuel injection valve whose fuel injection time is strictly controlled to control the air-fuel ratio, it will no longer be possible to feedback control the air-fuel ratio to the desired value. . However, in the past, in such cases, the only response was to simply stop air-fuel ratio feedback control and shift to open control, and the driver was not properly informed of the abnormality. Therefore, there is a risk that the internal combustion engine system will be operated in the abnormal state as described above.

The present invention has been made in view of the above-mentioned problems, and provides an excellent air-fuel ratio control device that can quickly and accurately notify the abnormality when any abnormality occurs in the internal combustion engine system including the air-fuel ratio control device. Its purpose is to provide.

[Means for solving the problems] The means configured by the present invention to solve the above problems are as follows:
As shown in the basic configuration diagram of FIG. 1, the first oxygen concentration detector S1 is provided upstream of the exhaust gas purifying catalyst C provided in the exhaust system of the internal combustion engine EG; a second oxygen concentration detector S2 provided downstream of gcT, and controls the air-fuel ratio of the internal combustion engine EG to a desired value based on at least the detection result of the first oxygen concentration detector S1. In the air-fuel ratio control I device, a determination means C1 determines whether or not a predetermined pattern matches the output of the second oxygen concentration detector S2, and a determination result of the determination means C1 is notified. Information λ1 means C2
The gist is an air-fuel ratio control device characterized by comprising:

[Operation 1] The air-fuel ratio control device of the present invention also performs feedback control of the air-fuel ratio of the internal combustion engine (EG).As a mode of the air-fuel ratio feedback control, the responsiveness is controlled based only on the output of the first oxygen concentration detector S1. Either fast control may be executed, or control may be executed using the output of the second oxygen concentration detector S2 as described above to further improve the accuracy of air-fuel ratio adjustment.

In addition to the air-fuel ratio control described above, the determination means C1 and the notification means C2 provided in the air-fuel ratio control apparatus of the present invention have the following effects.

First, the determining means C1 determines whether or not a predetermined pattern matches the output of the second oxygen concentration detector S2. Here, the predetermined pattern is a pattern of changes shown by the residual oxygen concentration in the exhaust gas during air-fuel ratio feedback control. For example, during air-fuel ratio feedback control, it is clear that the air-fuel ratio periodically changes toward the rich side and lean side around the target stoichiometric air-fuel ratio. Therefore, the output of the second oxygen concentration detector S2 that detects the residual oxygen concentration in the exhaust gas is as shown in FIG.
), it tends to pulse around the output ■S corresponding to a stoichiometric air-fuel ratio, and always outputs a voltage VS within a certain period. Therefore, a pattern in which the voltage Vs is always output within the period is stored as a pattern, and it is determined whether the actual output of the second oxygen concentration detector S2 conforms to this pattern. Further, the above-mentioned pattern may be in various other forms. For example, during air-fuel ratio feedback control, the air-fuel ratio changes periodically as described above, so the output of the second oxygen concentration detector S2 fluctuates within a range whose upper and lower limits are determined. The second oxygen m degree detection type S, which should not be output if air-fuel ratio feedback control is in progress.
It does not matter whether the upper and lower limits of the two outputs are output or not. Furthermore, instead of directly defining the pattern of the output of the second oxygen concentration detector S2, for example, in a device that performs air-fuel ratio feedback based on the output of the second oxygen concentration detector S2, the delay time of the output of the detector S2, etc. , the second oxygen concentration detector is used to determine whether the delay time, etc. to be changed is a value that is unlikely to occur during normal air-fuel ratio feedback control. The determination may be made based on the processed signal pattern of the S2 output.

The notification means C2 is a determination means C that performs the above determination.
The result of determination No. 1 is notified. The information to be notified is the determination result, which is 21 heart information indicating whether or not it is compatible. Therefore, the notification means C2 can be configured with something as simple as lighting a lamp or sounding a buzzer. Furthermore, current information processing equipment may be utilized to provide voice notification using synthesized sounds, information using text on a CRT screen, and other techniques.

EXAMPLES Hereinafter, in order to explain the present invention more specifically, the present invention will be described in detail by giving examples.

[Embodiment] FIG. 3 is a schematic diagram of an internal combustion engine system equipped with an air-fuel ratio control device according to an embodiment. In the figure, 1 is a four-cylinder engine, and an intake pipe 2 thereof is provided with a fuel injection valve 3 for injecting and supplying fuel for each cylinder. Intake air passing through the intake pipe 2 is metered by an air flow meter 5 after passing through an air filter 4, and its temperature is measured by an intake air temperature sensor 6. Further, the intake air range is adjusted by a throttle valve 7 which is linked to an accelerator pedal (not shown), and the throttle valve opening degree is detected by a throttle sensor 8. A three-way catalyst 10 for purifying exhaust gas is provided in the exhaust pipe 9 of the engine 1 to maintain good emissions. A first oxygen sensor 11 for detecting the residual oxygen concentration in the exhaust gas in the exhaust pipe is installed upstream of the three-way catalyst 10, and a similar second oxygen sensor 12 is installed downstream of the three-way catalyst 10. The output of the igniter 14, which generates a high voltage to be applied to each spark plug of the engine 1, is input to a distributor 16 linked to a crankshaft 15, and is distributed and supplied to each spark plug as appropriate. In this distributor 16, the distributor 16
outputs 24 pulse signals (hereinafter referred to as Ne signal) every 1 rotation of the crankshaft 15, that is, 2 rotations of the crankshaft 15, and 1 pulse signal @ (hereinafter referred to as G signal) per rotation of the rotary table sensor and distributor 16. It is equipped with a cylinder discrimination sensor. Note that 17 is a water temperature sensor that detects the temperature of the cooling water of the engine 1.

The fuel injection valve 3, ignition timing, etc. that determine the operating state of the engine 1 as described above are controlled by the output from the electronic control device 20, and the air flow meter 5, the intake The first part including the temperature sensor 6. The outputs of various sensors such as the second oxygen sensors 11 and 12 are input to the electronic control unit @20. The electronic control device 20 is composed of a logic operation circuit centered on a normal microcomputer, and has an input/output port 21 that serves as a data exchange port with the aforementioned external devices and various sensors, and a logic operation circuit. It has a CPU 22 that executes the program according to the program, a ROM 23 that stores the program, various control constants, maps, etc., and a RAM 24 that temporarily stores data. Reference numeral 30 denotes a battery that serves as a power source for the electronic control unit, etc., and 40 a warning light provided in an indicator panel in front of the driver's seat to notify when an abnormality occurs in the air-fuel ratio control.

The internal combustion engine system configured as described above executes air-fuel ratio feedback control of the engine 1 in the following manner.

Flowchart v-l~, not shown in FIG. 4, is the main routine controlled by ff1lJ. This routine is initialized when the engine 1 is started, and first performs initialization such as clearing the internal registers of the CPU 22 (step 100), then sets initial values of data used to control the engine 1, For example, processing is performed such as setting a flag indicating that a fuel cut is in progress to O (step 105). Next, processing is performed to read the operating state of the engine 1, for example, signals from the air flow meter 52 rotation angle sensor and the water temperature sensor 17 (step 110), and from the various data read in this way, the intake air ff1Q of the engine 1, the rotation speed N, Or load Q
/N, etc., which are the basis of control of the internal combustion engine 1, are calculated (step 120). Below, step 120
Based on the various quantities determined in step 130, well-known ignition timing control is performed (step 130), and then the process moves on to calculation of the fuel m to be injected and supplied to the engine 1. Fuel mW
Therefore, it is first determined whether or not the conditions for feedback control of the fuel amount are met (step 140), and if the conditions are not met, the fuel amount n is controlled in an open loop based on the control most suitable for the operating state of the engine 1 at that time. It is calculated by For example, conventionally implemented fuel increase control at the time of starting the engine 1, power increase control during high load operation, etc. are examples of this. When it is determined in step 140 that the feedback condition is met, that is, when the internal combustion engine 1 is performing stable operation in a normal steady state, normal feedback control is executed (step 170).
. After the optimal control for the operating state of the internal combustion engine 1 is selected in this way and the amount of fuel to be injected and supplied is calculated, the fuel injection control in step 190 is executed to actually supply fuel to the internal combustion engine 1. After this process, the process returns to step 110 and the above process is repeated.

In the processing of the main routine described above, control performed when it is determined that the feedback condition is satisfied in step 140, which is a feature of this embodiment, will be described.

Here, first, the load Q/N calculated in step 120
A fuel injection valve 3 that injects fuel to the engine 1 based on
The basic valve opening time, so-called basic fuel injection time P, is calculated. And the first. Second oxygen sensor 11, 12
From the output, a feedback correction coefficient FAF is extracted to correct the basic fuel injection time TP in order to bring the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio, and the fuel injection time TAU for actually performing fuel injection is calculated using the following formula. It is.

TAU=TP-FAF-f (x) Here, f (x) represents a variable representing various correction coefficients and academic values determined according to the output from other sensors that detect the operating state of the engine 1. FIG. 5 is a diagram illustrating the above-mentioned feedback correction coefficient FAF. As shown in the figure, the output of the first oxygen sensor 11 is compared to see whether it is larger or smaller than the comparison voltage, and the feedback correction coefficient FΔF is integrally changed according to the comparison result. As a result, the fuel monitoring time AU is extended or shortened by a small amount of time, as is clear from the above equation, and it becomes possible to operate the engine 1 near the stoichiometric air-fuel ratio.

Further, as described above with reference to FIG. 2(A), it is assumed that the output of the first oxygen sensor 11 changes as shown by the dashed-dotted line in FIG. 5 due to variations in the first oxygen sensor 11 over time. At this moment,
The fluctuation range of the output can be easily detected because the output of the second oxygen sensor 12 is stable near the stoichiometric air-fuel ratio as described above with reference to FIG. 2(B). Therefore, we changed the comparison voltage in Figure 5 (dotted chain line in the figure) by this fluctuation range (i1
f to improve the accuracy of air-fuel ratio control. Note that this variation in the output horn of the first oxygen sensor 11 is caused by the feedback correction coefficient FA, regardless of the change in the comparison voltage as described above.
The same effect can be obtained by controlling the delay time of F and giving a delay time commensurate with the output fluctuation width at the points where the power changes from rich to lean and from lean to rich, as shown in the delay times TDR and TDL in Fig. 5. There is.

In the air-fuel ratio control device of this embodiment, in addition to the normal air-fuel ratio feedback control as described above, the CPU 22 interrupts the following abnormality diagnosis routine at predetermined intervals.

FIG. 6 is a flowchart of this abnormality diagnosis routine. When a predetermined period of time has elapsed and the processing of this routine is interrupted by the CPU 22, it is first determined whether or not the air-fuel ratio feedback processing described above is being executed (step 2).
00). If the feedback condition is not satisfied here, the open control (step 150) described above in FIG.
If it is determined that is being executed, the counter C is reset (step 210) and this routine ends. On the other hand, during feedback control, the second oxygen sensor 1
2 output V2 (see Figure 5) crosses the predetermined voltage VS, that is, from the state of V2<VS to V2>vS
or from the state of V2>VS to V2<VS (step 220). Here, the predetermined voltage ■S is the output voltage value of the second oxygen sensor 12 at the stoichiometric air-fuel ratio shown in FIGS. 2 and 5. If a change in the output (2) of the second oxygen sensor 12 that crosses the predetermined voltage VS is observed, the above-mentioned step 210 is executed and this routine is completed, and if no such change in V2 is observed, step 230 is performed. Subsequent processing is performed. In step 230, the counter C is incremented by "1", and in step 240, the counter C incremented in this way is incremented by "1".
It is determined whether the content of is greater than or equal to a predetermined value. If C≧, step 250 is executed and the warning light 4
The output for instructing the light to turn on is stored in the RAM 24, and this routine ends. If C<K, this routine ends without executing any other processing.

If the air-fuel ratio feedback control is being executed, the output voltage 2 of the second oxygen sensor 12 is set to the predetermined value y.
It is the value of counter C that indicates a sufficiently long period that is expected to cross s.

Therefore, according to the air-fuel ratio control device of this embodiment configured as described above, the output v2 of the second oxygen sensor 12, which most accurately detects the air-fuel ratio state, will not exceed the theoretical value even once within a predetermined period. When the voltage VS indicating the air-fuel ratio does not change from lean to rich or from rich to lean, that is, even though it is in the feedback control execution mode,
It is possible to detect when the air-fuel ratio remains unchanged on the rich or lean side. When such an abnormality in the air-fuel ratio control is detected, a lighting command for the warning light 40 is issued to the RA.
M24, and through the processing of another table routine (not shown), a warning is issued as appropriate at the same time as abnormality detection or when the driver or the like desires to turn on the light. This results in
Even if some kind of abnormality occurs in the entire system of the engine 1, in which air-fuel ratio control is performed, for which there is normally no method of confirmation, the driver etc. can quickly and accurately grasp the abnormality.

FIG. 7 is a flowchart of an abnormality diagnosis routine of another embodiment, which replaces the abnormality diagnosis routine of the first embodiment described above (see FIG. 6). As shown in the figure, the abnormality diagnosis routine (steps 300 to 350) of this embodiment is almost the same as that described above, with the only difference being the content of step 230 described above. Step 320 is the modification, but this is because when the delay time of the feedback correction coefficient FAF based on the output of the first oxygen sensor 11 is controlled by the output of the second oxygen sensor 12 described above, the delay is too large. The time when the time is calculated is determined to be abnormal. Therefore, according to this embodiment as well, when some abnormality occurs in the system of the engine 1 including the air-fuel ratio control device, it is possible to quickly and accurately give a warning.

Note that the second oxygen sensor 12 is not limited to the above two embodiments.
The fluctuation range of the comparison voltage for the output of the first oxygen sensor 11, which is changed by the output of the first oxygen sensor 11, other integral constants, etc. may be subject to the abnormality determination.

Further, each abnormality judgment may be used in combination. For example, if used in conjunction with a conventionally proposed abnormality detection device for a single oxygen sensor, the abnormality of the entire system of the engine 1 warned in this embodiment can be detected by the engine. This is even more effective because it can be easily determined in which part of the system the problem occurs.

[Effects of the Invention] The above is detailed with examples)1. Similarly, the air-fuel ratio control device of the present invention includes a first oxygen concentration detector provided upstream of an exhaust gas purification catalyst provided in the exhaust system of an internal combustion engine, and a first oxygen concentration detector provided downstream of the exhaust gas purification catalyst. a second oxygen concentration detector, and controls the air-fuel ratio of the internal combustion engine to a desired value based on at least the detection result of the first oxygen concentration detector, in which the air-fuel ratio is controlled in a predetermined pattern. and an output of the second oxygen concentration detector, a determining means for determining whether or not the output of the second oxygen concentration detector matches, a notifying means for notifying the determination result of the determining means, and a notifying means for notifying the determination result of the determining means. It is.

Therefore, when any abnormality occurs in the entire internal combustion engine including the air-fuel ratio control device, it is possible to promptly and accurately notify the abnormality. As a result, system abnormalities that may worsen emissions of the internal combustion engine can be easily confirmed, and it is no longer possible to continue operating the internal combustion engine without noticing the abnormality. It also has significant secondary effects, such as a significant improvement in workability in terms of service and maintenance.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram of the present invention, Fig. 2 is an explanatory diagram of variations in output when oxygen concentration sensors are placed upstream and downstream of an exhaust gas purification catalyst, and Fig. 3 is an air-fuel ratio control device of an embodiment. 4 is a flowchart of the main routine of the embodiment, FIG. 5 is an explanatory diagram of air-fuel ratio feedback correction, and FIG. 6 is a flowchart of the abnormality diagnosis routine of the first embodiment. FIG. 7 shows a flowchart of an abnormality diagnosis routine of another embodiment. EG...Internal combustion engine CT...Exhaust gas purification catalyst Sl...First oxygen concentration detector S2...Second oxygen concentration detector C1...Determination means C2...Notification means 1. ... Engine 9 ... Exhaust pipe 11 ... First oxygen sensor 12 ... Second oxygen sensor 20 ... Electronic control unit 40 ... Warning light

Claims (1)

[Scope of Claims] A first oxygen concentration detector provided upstream of an exhaust gas purification catalyst provided in an exhaust system of an internal combustion engine, and a second oxygen concentration detector provided downstream of the exhaust gas purification catalyst. an air-fuel ratio control device that controls the air-fuel ratio of the internal combustion engine to a desired value based on at least the detection result of the first oxygen concentration detector, comprising: a predetermined pattern and the second oxygen concentration sensor; An air-fuel ratio control device comprising: a determination means for determining whether or not the output of a concentration detector matches; and a notification means for notifying a determination result of the determination means.