JPH0833132B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a multi-cylinder internal combustion engine for automobiles, and more particularly to an air-fuel ratio control device for preventing deterioration of exhaust gas.

[Conventional technology]

Various methods have been conventionally used in automobile gasoline engines for purification of exhaust gas. Among them, the multi-point fuel injection device is often used as one of the powerful means of the fuel system. This device has a better fuel distribution characteristic to each cylinder of a multi-cylinder engine than a carburetor or single point injection, and because of the structure, the amount of fuel adhering to the wall in the intake pipe is small, so good exhaust gas performance and responsiveness are obtained. To be These satisfactory performances are exhibited when the fuel supply system of the engine, the ignition system, and the engine body are all normal, but when half or more of the cylinders become misfired due to some abnormality, so-called raw gas is released and exhaust gas is emitted. Deteriorates significantly and the catalytic device overheats. Especially when only one cylinder is misfiring, the output obtained from other normal cylinders does not significantly affect the running of the vehicle. Therefore, it is difficult for the driver to notice, the exhaust gas deteriorates, and it is left as it is. May overheat and become damaged.

In order to solve the above problems, a method of detecting misfire and stopping the fuel supply to the cylinder is disclosed in, for example, JP-A-61-2.
It is proposed in Japanese Patent No. 3876. Such a conventional operation will be described with reference to the configuration diagram of FIG. 2 and the flowchart of FIG.

FIG. 2 shows the structure of a multi-point fuel injection device. 1 is an engine, 2 is an intake pipe, 3 is a throttle valve, 4 is an air flow sensor for detecting the amount of intake air, and 5a to 5d are cylinders. Of the intake pipes 2a to 2d, driven by electric pulses, 6a to 6d are in-cylinder pressure sensors for detecting the in-cylinder pressure of the engine 1, and 7 is the engine 1
, A rotation sensor that generates a crank angle pulse, 8 is an exhaust pipe, 9 is an oxygen sensor that detects an air-fuel ratio from components in exhaust gas, and 10 is required from operating parameters such as an air flow sensor 4, a rotation sensor 7, and an oxygen sensor 9. Calculates the amount of fuel and controls the drive pulse width of the fuel injection valves 5a-5d that are energized in synchronization with the rotation of the engine and processes the signal waveforms of the in-cylinder pressure sensors 6a-6d to determine whether or not there is a misfire in each cylinder. A control device 11 for controlling the exhaust gas is a catalyst device for purifying the exhaust gas. Since there are many known examples of the fuel injection control operation with the above-described configuration, the description thereof is omitted here, and the control device 10 is also input / output to / from a microcomputer including a memory and a calculation unit that have been widely used in the past. Since it is composed of a circuit, the description of its mechanism will be omitted and only the operation will be described with reference to the flowchart of FIG.

After the start, first in step 100, the signals of the air flow sensor and the rotation sensor 7 are read, and in step 101, the drive pulse width of the fuel injection valves 5a to 5d is calculated based on this information. This pulse width is basically proportional to the value obtained by dividing the intake air amount by the engine speed, and the error of the air flow sensor 4 and the fuel injection valves 5a to 5d is obtained from the deviation from the median value of the field back correction amount. Perform learning correction. Fuel proportional to the drive pulse width is injected from the fuel injection valves 5a to 5d to the intake pipes 2a to 2d of each cylinder in every predetermined cycle, and the air-fuel mixture is burned in each cylinder.

Next, in step 102, the in-cylinder pressure sensor 6 installed in each cylinder
The signal waveforms a to 6d are sequentially read in synchronization with the rotation pulse obtained from the rotation sensor 7. As shown in FIG. 4, this signal waveform shows that the pressure increase due to combustion becomes large as shown by the solid line in the figure when the crank angle is near TDC, but it is broken by a broken line when the cylinder concerned misfires or does not burn due to some trouble. It shows a low value as shown. Therefore, a known example (Japanese Patent Laid-Open No.
61-23876), whether or not each cylinder is misfiring by comparing the in-cylinder pressure at two points before or after the TDC, or by comparing the peak values of the in-cylinder pressure. Can be detected, and this determination is made in step 103.

The causes of misfire of the cylinder are failure of ignition system devices such as an ignition coil, an igniter, a high-voltage cord, and a spark plug (not shown here), a contact failure of a connector portion connecting them, and further, a contamination of the spark plug.
There are failures in the circuit units 101a to 101d that drive the fuel injection valve, combustion failure due to water leakage into the cylinder, and the like.

As a cylinder pressure sensor method, a piezoelectric type or a pressure sensor can be put to practical use, and misfire can be detected by using other methods (vibration, combustion light, etc.).

When the misfire is detected, the drive of the fuel injection valve of the cylinder concerned is stopped in step 104, and the other cylinders are subjected to the feedback control of the air-fuel ratio based on the signal of the oxygen sensor 9 as shown in FIG. At this time, since the fuel supply to the misfiring cylinder is stopped, the discharge of raw gas is prevented, but the oxygen sensor is exposed to fresh air from the cylinder, that is, a large amount of oxygen,
Since the air-fuel ratios of the other cylinders cannot be accurately detected, it is judged to be lean as a total. Therefore, the drive pulse width of the fuel injection valve of the normal cylinder shifts to the rich side to operate. As a result, the learning correction amount calculated by the feedback correction amount also operates on the rich side.

[Problems to be Solved by the Invention]

However, if one cylinder misfires and the fuel supply to that cylinder is stopped and feedback correction to other cylinders is performed, the air-fuel ratio of the other normal cylinders shifts to the rich side and Hc, C
As a result, a large amount of oxygen is supplied from the misfiring cylinder, and the reaction heat in the three-way catalyst increases, causing deterioration of the catalyst in the operating region where the exhaust temperature is originally high. In addition, the catalyst is difficult to activate in a region where the exhaust temperature is low, such as in the idle region, and the activation temperature does not reach when low temperature air is discharged from the misfiring cylinder, so the total air-fuel ratio becomes the theoretical air-fuel ratio. However, Hc and Co are discharged to the atmosphere without any reaction by the catalyst. Further, if learning shifts to the rich side during feedback, feedback correction is stopped and the air-fuel ratio is made rich, for example, during warm-up operation when the engine is in a cold state. There was a problem that even a cylinder could lead to misfire.

The present invention has been made to solve the above problems, and in a region where purification by a catalyst is possible when a cylinder misfires, feedback control is performed to purify exhaust gas and damage to an engine and a catalyst. An object of the present invention is to obtain an air-fuel ratio control device for an internal combustion engine that does not give a fuel.

[Means for solving the problem]

The air-fuel ratio control device according to the present invention is a multi-cylinder internal combustion engine having a fuel injection valve in each intake pipe of each cylinder, and a misfire detection means for detecting the presence or absence of misfire in each cylinder, and an air-fuel ratio provided in the exhaust pipe. A detection means, a feedback correction means for feedback-controlling the air-fuel ratio by the output of the air-fuel ratio detection means, and a storage means for storing at least a part of the output of the feedback correction means are provided, and misfire is caused by the output of the misfire detection means. Is detected, the operation of the fuel injection valve to the misfiring cylinder is stopped, the feedback correction is performed by the non-misfiring cylinder, and the operation of the storage means is stopped.

Further, the air-fuel ratio control device according to the present invention is provided with catalyst cleanable region detecting means for determining whether or not the catalyst is cleanable region in response to the output of the misfire detecting means, and the catalyst cleanable region is detected. It is designed such that feedback correction is carried out when it is turned on.

[Action]

According to the present invention, in the operating region where the exhaust gas can be purified without stopping the fuel to the cylinder in which the misfire is detected, the catalyst is not damaged by the intake air amount or the engine parameter corresponding to the intake air amount. By continuing the feedback control by other cylinders, Hc, Co, Nox
Of the air flow sensor and fuel injection valve due to deviation during feedback is prohibited to prevent excessive learning of the air flow sensor and fuel injection valve. It is possible to prevent misfire due to over-rich fuel supply.

Further, in the present invention, only the region where purification by the catalyst can be expected is enriched by feedback correction so that unreacted harmful gas is not discharged into the atmosphere.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flow chart showing the procedure of fuel control to each cylinder in the air-fuel ratio control device according to the present invention.
The transient fuel calculation such as the over-deceleration operation of the engine is the same as that of the conventional example shown in FIG. The same steps as those in FIG. 3 perform the same processing. In the present invention, step 107 is provided between steps 104 and 105 to determine whether or not the area is a catalyst purifying area. For example, the amount of intake air is too small and the exhaust temperature is low, so that it is not possible to expect purification with a catalyst or the amount of intake air is high and the exhaust temperature is high. When the reaction is performed, the temperature of the catalyst becomes high and deterioration or damage may occur, the air-fuel ratio feedback is stopped, and the process returns to step 100. If it is determined in step 107 that the catalyst can be cleaned, the unfired cylinders are made rich by steps 105 and 106 as in FIG. 3 to suppress the generation of Nox, and the excess Hc and Co are catalyzed by the oxygen discharged from the misfired cylinders. The exhaust gas to the atmosphere can be purified by reacting with.

Further, in the present invention, since the calculation of the learning value in step 109 is prohibited during the air-fuel ratio feedback including the misfiring cylinder in step 108, the learning value is the air flow when all the cylinders are normally burning. Values for compensating for machine differences such as sensors and fuel injection valves can be appropriately held, and during rich correction during warm-up operation of calculations not shown in FIGS. 3 and 1, transient engine operation. When the acceleration / deceleration is corrected, the air-fuel ratio will not be excessively rich and misfiring will not occur.

Further, as another embodiment of the present invention, a catalyst temperature sensor is provided as a means for detecting whether purification with a catalyst is possible, and the effect of the present invention is enhanced by making the determination of step 107 based on the output of the sensor. That is clear.

Further, by limiting the correction amount of the air-fuel ratio feedback control within the critical temperature range where the temperature of the catalyst is not damaged, the feedback correction can be performed over a wider operating range, and the exhaust gas can be purified. Is clear.

〔The invention's effect〕

As described above, according to the present invention, when a cylinder misfires, the fuel supply to the cylinder is stopped, a large amount of Hc is prevented from being discharged, and other cylinders are enriched by air-fuel ratio feedback. Since NOx is reduced and Hc and Co are purified by enrichment with a catalyst, the purification rate of exhaust gas to the atmosphere can be significantly improved. Also,
By prohibiting learning during feedback, smooth engine operation can be maintained without enriching the air-fuel ratio in the feedback stopped state due to apologized learning, and a large amount of Hc emission can also be prevented. Further, in the present invention, since it is detected by the temperature sensor or the like whether or not purification by the catalyst is possible, feedback enrichment is performed only in the region where purification by the catalyst can be expected without damaging the catalyst. Hc, C to the atmosphere without reaction with the catalyst
It has the excellent effect that o is not emitted.

[Brief description of drawings]

FIG. 1 is a flow chart showing a procedure of fuel control to each cylinder in an air-fuel ratio control apparatus according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a fuel injection device, and FIG. 3 is a conventional fuel control procedure. 4 is a characteristic diagram of the in-cylinder pressure sensor, and FIG. 5 is a characteristic diagram of air-fuel ratio control. 5a to 5d ... Fuel injection valve, 6 ... In-cylinder pressure sensor, 9 ... Oxygen sensor, 10 ... Control device.

Claims (2)

[Claims] 1. In a multi-cylinder internal combustion engine having a fuel injection valve in each intake pipe of each cylinder, there is provided misfire detection means for detecting the presence or absence of misfire in each cylinder, and air-fuel ratio detection means provided in the exhaust pipe. A misfire cylinder that includes feedback correction means that feedback-controls the air-fuel ratio based on the output of the air-fuel ratio detection means, and storage means that stores at least a portion of the output of the feedback correction means, and detects misfire by the output of the misfire detection means. To stop the operation of the fuel injection valve for the internal combustion engine, perform feedback correction by the non-misfiring cylinder, and stop the operation of the storage means. 2. A catalyst cleanable area detecting means for determining whether or not the catalyst is cleanable area in response to an output of the misfire detecting means, wherein the feedback correction is made when the catalyst cleanable area is detected. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein