JP2683418B2 - Air-fuel ratio control device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air-fuel ratio control device for feedback controlling the air-fuel ratio of an internal combustion engine.

2. Description of the Related Art Conventionally, in order to reduce emissions in exhaust gas of an internal combustion engine, an air-fuel ratio of a fuel mixture supplied to the internal combustion engine has been changed based on an output signal of an oxygen sensor attached to an exhaust system of the internal combustion engine. Is controlled. That is, as shown in FIG. 9, in order to control the air-fuel ratio to the stoichiometric air-fuel ratio point where the exhaust gas purification rate is high, air-fuel ratio feedback control is performed based on the output signal of the oxygen sensor.

When the detection system such as the oxygen sensor used for such control does not function normally, the emission of exhaust gas may worsen.Therefore, when an abnormality occurs in the detection system, normal feedback control is performed. Various techniques for correcting the noise have been proposed (Japanese Patent Laid-Open No. S58-222939,
(See JP-A-59-3137).

[Problems to be Solved by the Invention] However, when the oxygen sensor of the detection system is poisoned by various substances, the sensor output shifts to lean or rich as shown in FIG. May change, and as a result, the air-fuel ratio feedback control based on the output signal of the oxygen sensor may not be performed well, and the emission may deteriorate.

For example, when air-fuel ratio feedback control is performed using an oxygen sensor poisoned by silicon or the like, NO
_If air-fuel ratio feedback control is performed using an oxygen sensor that has increased _{X and} is poisoned by lead, etc.,
There was a problem that CO would increase.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an air-fuel ratio control device capable of suitably controlling the air-fuel ratio even when an abnormality occurs in an oxygen sensor or the like.

[Means for Solving the Problem] An air-fuel ratio control device of the present invention made to solve the above-mentioned problems is, as illustrated in FIG. 1, an oxygen sensor M2 provided in an exhaust system of an internal combustion engine M1. In the air-fuel ratio control device for feedback-controlling the air-fuel ratio of the fuel mixture supplied to the internal combustion engine M1, based on the output signal of the, the abnormality of the oxygen sensor M2 is detected based on the variation of the output signal of the oxygen sensor M2. An abnormality detection means M3, an air-fuel ratio setting means M4 for setting the air-fuel ratio of the fuel mixture supplied to the internal combustion engine M2 to a lean and rich state by open loop control, and an air-fuel ratio lean by the air-fuel ratio setting means M4. And when set to rich, a median value calculating means M5 for obtaining the median value of the lean and rich output signals of the oxygen sensor M2, and oxygen by the abnormality detecting means M3. If the abnormality of the capacitors M2 is detected, the threshold value setting means for setting a central value obtained by the median value calculating means M5 as a threshold for distinguishing the lean air-fuel ratio and rich when the feedback control
The point is to have M6 and.

Here, various detecting means can be adopted as the abnormality detecting means M3. For example, the air-fuel ratio of the fuel mixture supplied to the internal combustion engine M1 is set to a lean or rich state by open loop control, and when the air-fuel ratio is set to lean, the output signal of the oxygen sensor M2 is equal to or greater than a predetermined threshold value. In this case, or when the output signal of the oxygen sensor M2 is equal to or higher than a predetermined threshold value when the air-fuel ratio is set to rich, means for determining that the oxygen sensor M2 is abnormal.

Further, the air-fuel ratio is periodically set to a lean and rich state by open loop control, and the minimum value and the maximum value of the output signal of the oxygen sensor M2 when the air-fuel ratio is set to the lean and rich are detected. If at least one of the minimum value or the maximum value is within the predetermined output value range,
A means for determining that the oxygen sensor M2 is abnormal.

The maximum value and the minimum value may be obtained from the average value of a plurality of times.

Further, the feedback control of the air-fuel ratio is performed based on the output signal of the oxygen sensor M2, and when the feedback control of the air-fuel ratio is being performed, when the output signal of the oxygen sensor M2 is within the predetermined output value range. Is means for determining that the oxygen sensor M2 is abnormal.

Incidentally, the open loop control does not perform feedback control of the air-fuel ratio of the fuel mixture based on the output signal of the oxygen sensor M2, but simply indicates control that switches the air-fuel ratio to a lean or rich state and sets it. There is.

[Operation] The air-fuel ratio control device of the present invention is based on the output signal of the oxygen sensor M2 provided in the exhaust system of the internal combustion engine M1.
An air-fuel ratio control device that feedback-controls the air-fuel ratio of the fuel mixture supplied to M1, and when an abnormality of the oxygen sensor M2 is detected by the abnormality detection means M3, the air-fuel ratio setting means M4 causes the internal combustion engine M2 to The air-fuel ratio of the supplied fuel-air mixture is set to lean and rich states by open loop control, and the median value calculating means M5 obtains the median value of the output signals from the lean and rich output signals of the oxygen sensor M2. Then, the threshold value setting means M6 sets the median value as a threshold value for distinguishing between lean and rich air-fuel ratios during feedback control.

Example An example of the present invention will be described below with reference to the drawings.

FIG. 2 is a system configuration diagram of the air-fuel ratio control device of the first embodiment.

As shown in the figure, the air-fuel ratio control device 1 includes an engine 2
An electronic control unit (hereinafter simply referred to as an ECU) 3 that detects the state of (1) and performs various kinds of control such as abnormality diagnosis processing and air-fuel ratio is provided.

The engine 2 includes a combustion chamber 7 including a cylinder 4, a piston 5, and a cylinder head 6, and an ignition plug 8 is disposed in the combustion chamber 7.

The intake system of the engine 2 has an intake valve 9, an intake port 10,
It comprises an intake pipe 11, a surge tank 12 for absorbing pulsation of intake air, a throttle valve 14 for adjusting the intake air amount, and an air cleaner 15.

The exhaust system of the engine 2 includes an exhaust valve 16, an exhaust port 17,
It comprises an exhaust manifold 18, a catalytic converter 19 filled with a three-way catalyst, and an exhaust pipe 20.

The ignition system of the engine 2 includes an igniter 21 that outputs a high voltage required for ignition and a distributor 22 that distributes and supplies the high voltage generated by the igniter 21 to the ignition plug 8 in conjunction with a crankshaft (not shown).

The fuel system of the engine 2 includes an electromagnetic fuel injection valve 25 that injects fuel from a fuel tank (not shown) to the vicinity of the intake port 10.

Further, as sensors for detecting the operating state of the engine 2, an intake pressure sensor 31 for detecting the pressure of the intake air, an intake temperature sensor 32 for detecting the temperature of the intake air, a throttle valve 1
4, a throttle position sensor 33 for detecting the opening degree, a water temperature sensor 35 for detecting the coolant temperature, and an upstream oxygen sensor (hereinafter simply referred to as an oxygen sensor) for detecting the oxygen concentration in the exhaust gas before flowing into the catalytic converter 19. 36, catalytic converter 1
A downstream oxygen sensor (hereinafter referred to as a sub oxygen sensor, which is attached as necessary) 37 for detecting the oxygen concentration in the exhaust gas flowing out from 9, 37, and outputs a reference signal for each revolution of the camshaft of the distributor 22. A cylinder discrimination sensor 38, a rotation speed sensor 39 that outputs a rotation angle signal every 1/24 rotation of the camshaft of the distributor 22, and the like are provided.

The detection signal of each sensor is input to the ECU 3, and the control of the engine speed, the air-fuel ratio, and the like is performed based on the signal. ECU3 is a well-known CPU3a, ROM3b, RAM3c, backup
It is configured as a logical operation circuit around the RAM 3d and the timer 3e,
It is connected to the input / output port 3g via the common bus 3f and performs input / output with the outside. The CPU 3a includes an intake pressure sensor 31, an intake temperature sensor 32, a throttle position sensor 33, a water temperature sensor 35,
The detection signals from the oxygen sensor 36 and the sub oxygen sensor 37 are input via the A / D converter 3h and the input / output port 3g. Also, the detection signals of the cylinder discrimination sensor 38 and the rotation speed sensor 39 are converted into a waveform shaping circuit 3.
Input via i and input / output port 3g. On the other hand, CPU3a
Controls the drive of the igniter 21, the fuel injection valve 25, the check lamp 40 for notifying the abnormality of the oxygen sensor 36, and the like via the input / output port 3g and the drive circuit 3m.

The backup RAM 3d of the ECU 3 is configured so that electric power is supplied from a path that does not pass through an ignition switch (not shown), and a feedback control threshold value, which will be described later, is retained regardless of the state of the ignition switch. Has been done.

Next, the air-fuel ratio control process executed by the ECU 3 will be sequentially described.

[1] Processing of the first embodiment] First, based on the flow chart of FIG. 3, the air-fuel ratio is kept constant at a lean constant state and further kept at a constant rich state, and the output signal of the oxygen sensor 36 at that time is kept. A process for measuring the median and obtaining the median will be described. The present invention is an engine 2
It is performed with the warm-up performed.

First, processing for stopping the feedback control of the air-fuel ratio is performed (step 100). Next, with the feedback control stopped, that is, by open loop control, the fuel injection valve 25 is drive-controlled to perform a process of setting the air-fuel ratio to a lean (for example, excess air ratio λ = 1.02) state ( Step 110). Then, this state is maintained for a predetermined time, and the output signal D _L of the oxygen sensor 36 at the lean time is detected (step 120).

Further, a process for driving and controlling the fuel injection valve 25 by the open loop control to set the air-fuel ratio to a rich (for example, λ = 0.98) state (step 130). And this state was maintained for a predetermined time, it detects the output signal D _R of the oxygen sensor 36 during the rich (step 140).

Next, if the lean output signal D _L of the oxygen sensor 36 is greater than or equal to a predetermined threshold V _L (for example, 400 mV), it is determined that the oxygen sensor 36 is abnormal (step 150), and the check lamp 4
Lights 0 (step 160). Further, when the rich output signal D _L of the oxygen sensor 36 is less than or equal to a predetermined threshold value V _R (for example, 700 mV), it is determined that the oxygen sensor 36 is abnormal (step 170), and the check lamp 40 is similarly turned on. (Step 160).

Then, in step 150 or 170, the oxygen sensor 36
Is determined to be abnormal, the median value V _TH of the lean output signal D _L and the rich output signal D _{R is} calculated (step 180), and the median value V _TH is used during feedback control. It is set as a threshold value (slice level) for distinguishing between lean and rich (step 190), and this processing is once terminated.

That is, as shown in FIG. 4 (a), for example, the output signal D _L when λ = 1.02 has a voltage of 500 mV, and the output signal D _L when λ = 0.98.
When the voltage of D _R is 900 mV, the median value V _TH is 700 mV. Therefore, if this median value V _TH is adopted as the threshold value during feedback control, the output signal of the oxygen sensor 36 becomes
Even if it is vibrating by shifting to the high voltage side or the low voltage side,
Since the center of the vibration becomes the threshold value, lean or rich of the air-fuel ratio can be reliably classified and converted into a binary signal of 0V and 5V as shown in FIG. 4 (b).

That is, since the optimum threshold value can be set according to the output signal of the oxygen sensor 36, even if the output of the oxygen sensor 36 varies due to poisoning or the like, the lean and rich states of the air-fuel ratio can be reliably detected. The air-fuel ratio can be controlled appropriately.

In the first embodiment, in order to detect the abnormality of the oxygen sensor 36, the air-fuel ratio is changed to the lean or rich state by the open loop control, and the control for keeping the state constant is performed. Other than that, various means for detecting abnormality can be adopted as described later. For example, by open loop control, the air-fuel ratio is switched to a lean and rich state at a predetermined cycle, and if the minimum value or maximum value at that time is not within the predetermined range, the oxygen sensor 36 may be determined to be abnormal. Good. Alternatively, feedback control of the air-fuel ratio may be performed, and if the output signal at that time oscillates within a predetermined range, it may be determined as abnormal. The hardware configuration of the other embodiments described below is the same as that of the above embodiment, and further, in the following description, the description of the abnormality determination processing will be briefly described.

[2] Process of Second Embodiment Next, a process of controlling the air-fuel ratio using the minimum value and the maximum value of the output signal of the oxygen sensor 36 will be described based on the flowchart of FIG.

First, similarly to the above process, a process of stopping the feedback control of the air-fuel ratio is performed (step 200). Next, by open loop control, drive control of the fuel injection valve 25 is performed to periodically switch the air-fuel ratio between rich and lean states (step 210). And the oxygen sensor 3 at this time
The output signal of 6 is detected (step 220), and the processing of obtaining the minimum value and the maximum value of the output signal is performed (step 23).
0). Next, if either the minimum value or the maximum value of the output signal of the oxygen sensor 36 is within the predetermined output value range, it is determined that the oxygen sensor 36 is abnormal (step
240) and the process of turning on the check lamp 40 (step 250).

When the oxygen sensor 36 is abnormal, the median value V _TH of the minimum value V _MIN and the maximum value V _MAX is calculated (step 2
60), this median value V _TH is set as a threshold value for distinguishing between lean and rich of the air-fuel ratio in the actual feedback control (step 270), and this processing is once terminated.

That is, as shown in FIG. 6 (a), for example, an oxygen sensor
If the output signal of 36 oscillates at a voltage higher than a preset threshold value V ₀ , it is judged that the oxygen sensor 36 is abnormal, and the minimum value V _MIN of the output signal and the median value V _MAX of the maximum values V _{MAX. TH} is obtained and this median value V _TH is used as a threshold. As a result, even when the output signal of the oxygen sensor 36 is abnormal, during the actual air-fuel ratio feedback control, the lean or rich state of the air-fuel ratio can be reliably distinguished, and as shown in FIG. 6 (b), It can be converted into a binary signal of 0V and 5V.

Thus, in this embodiment, since the threshold value can be changed according to the output signal of the oxygen sensor 36, even if the output fluctuates to the high voltage side or the low voltage side due to poisoning of the oxygen sensor 36, etc. The air-fuel ratio can be controlled appropriately.

[3] Process of Third Embodiment Next, another process using the median value V _TH of the output signal of the oxygen sensor 36 will be described with reference to the flowchart of FIG. 7.

First, in the same manner as the first or second embodiment,
If an abnormality in the oxygen sensor 36 is detected (step 30
0), processing for _{obtaining the} median value V _TH from the output signal of the oxygen sensor 36 is performed (step 310). Then, based on this median value V _TH , the voltage of the signal output from the oxygen sensor 36 is proportionally distributed during the actual feedback control, and a process of changing to a normal signal with a large amplitude is performed (step 320). This process ends.

That is, as shown in FIG. 8 and Table 1 below, the voltage of the output signal of the oxygen sensor 36 is converted.

For example, when the voltage of the output signal is higher than the preset threshold value V _0, 50 at the lean air-fuel ratio (λ = 1.02) is set.
0mV signal to 0V and 900 at rich (λ = 0.98)
Convert the mV signal to 1V. That is, the center of the amplitude of the abnormal output signal of the oxygen sensor 36 is corrected to a preset threshold V ₀ of 500 mV, and the output signal is proportionally converted so as to have a large amplitude. . In this embodiment, when the measured value of the output signal of the oxygen sensor 36 is X and the converted value is Y, conversion is performed based on the following conversion formula.

Y = 2.5X-1250 Therefore, since the signal is corrected by such processing, even if the output signal of the oxygen sensor 36 is biased toward the high voltage side or the low voltage side or has a small amplitude, It is possible to reliably detect the air-fuel ratio state using the set threshold value V ₀ ,
Thereby, the feedback control of the air-fuel ratio can be suitably performed.

Of course, the present invention is not limited to the above-mentioned embodiments, and can be carried out in various modes within the scope of the present invention.

[Advantages of the Invention] As described above, the air-fuel ratio control device of the present invention sets the air-fuel ratio to the lean or rich state by the open loop control, and changes the median value of the output signals from the output signal of the oxygen sensor at that time. When an abnormality of the oxygen sensor is detected, this median value is set as a threshold value that distinguishes lean and rich of the air-fuel ratio during feedback control, so the oxygen sensor is deteriorated due to poisoning, etc. Thus, even if an abnormal signal is output, the feedback control of the air-fuel ratio can be suitably performed.

[Brief description of the drawings]

FIG. 1 is an exemplary diagram of a basic configuration of the present invention, FIG. 2 is a system configuration diagram of a first embodiment of the present invention, FIG. 3 is a flowchart showing a process of the first embodiment, and FIG. 4 is a first embodiment. 5 is a graph showing the output signal of the example, FIG. 5 is a flowchart showing the processing of the second embodiment, FIG. 6 is a graph showing the output signal of the second embodiment, and FIG. 7 is the processing of the third embodiment. FIG. 8 is a flowchart showing the output signal of the third embodiment, FIG. 9 is a graph showing the relationship between the air-fuel ratio and emission, and FIG. 10 is a graph showing the relationship between the air-fuel ratio and the sensor output. is there. M1 ...... Internal combustion engine M2 ...... Oxygen sensor M3 ...... Abnormality detection means M4 ...... Air-fuel ratio setting means M5 ...... Median value setting means M6 ...... Threshold value setting means 2 ...... Internal combustion engine 3 ...... Electronic control unit (ECU) 25 …… Fuel injection valve 36 …… Oxygen sensor 40 …… Check lamp

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-75737 (JP, A) JP-A-59-3137 (JP, A) JP-A-58-222939 (JP, A) Actual development Sho-61- 5343 (JP, U)

Claims (1)

(57) [Claims] 1. An air-fuel ratio control device for feedback-controlling an air-fuel ratio of a fuel mixture supplied to the internal combustion engine based on an output signal of an oxygen sensor provided in an exhaust system of the internal combustion engine. An abnormality detecting means for detecting an abnormality of the oxygen sensor based on the fluctuation of the signal; an air-fuel ratio setting means for setting the air-fuel ratio of the fuel mixture supplied to the internal combustion engine to a lean and rich state by open loop control; When the air-fuel ratio is set to lean and rich by the air-fuel ratio setting means, a median value calculating means for obtaining the median value of the lean and rich output signals of the oxygen sensor, and the oxygen sensor by the abnormality detecting means When the abnormality is detected, the median value obtained by the median value calculating means is set to the lean and lean air-fuel ratio during the feedback control. An air-fuel ratio control device, comprising: