JPH0233440A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To aim at improving the purification of exhaust gas to the air considerably by stopping the operation of a fuel injection valve to the air cylinder concerned when an accidental fire is detected and having the feedback correction made by the other air cylinders as well as its learning stopped. CONSTITUTION:The driving pulse widths of fuel injection valves 5a-5d are obtained at a control device 10 from the signals outputted from an air flow sensor 4 and a rotation sensor 7, and the feedback correction and injection are made by the output of an O2 sensor 9 as well as the learning value of the feedback correction quantity is storaged in a memory. When an accidental fire in the air cylinder on the side of an engine 1 is detected, the fuel supply to the air cylinder is stopped so as to prevent the considerable amount of HC emission, the other air cylinders are enriched by the feedback control of the air-fuel ratio so as to aim at decreasing NOx, and the HC, CO enriched is purified by means of a catalyser 11. At the same time, the learning of the feedback correction quantity is inhibited so as to prevent wrong learning. As a result, the purification of exhaust gas can be considerably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multi-cylinder internal combustion engine for automobiles, and particularly to an air-fuel ratio control device for preventing deterioration of exhaust gas.

(Prior Art) Various methods have been used to purify exhaust gas in gasoline engines for automobiles. Among these, multi-point fuel injection devices have been widely used as one of the effective means for fuel systems. This device has better fuel distribution characteristics to each cylinder of a multi-cylinder engine than a carburetor or single point injection, and because of its structure, there is less fuel adhering to the wall inside the intake pipe, resulting in better exhaust gas performance and better performance. These satisfactory performances are achieved when the engine's fuel supply system, misfire system, and engine body are all normal, but if half or more of the cylinders are in a misfire state due to some abnormality, a so-called failure occurs. Gas is released, the exhaust gas deteriorates significantly, and the catalyst device overheats.In particular, if only one cylinder misfires, there is no major problem in running the vehicle due to the output obtained from the other normal cylinders. Not only is it difficult for the driver to notice and the exhaust gas is left unattended, but the catalyst may overheat and be damaged.

In order to solve the above-mentioned problems, a method of detecting a misfire and stopping the fuel supply to the relevant cylinder is proposed, for example, in Japanese Patent Application Laid-Open No.
This is proposed in Japanese Patent No. 23876. Such conventional operation will be explained using the configuration diagram of FIG. 1 and the flowchart of FIG. 2.

Figure 2 shows the configuration of a multi-point fuel injection system, where 1 is the engine, 2 is the intake pipe, 3 is the throttle valve,
4 is an air flow sensor for detecting the amount of intake air; 5
Numerals a to 5d are fuel injection valves installed in the intake pipes 2a to 2d of each cylinder and driven by electric pulses, 6a to 6d are cylinder pressure sensors that detect the cylinder pressure of the engine 1, and 7 is a crank angle of the engine 1. A rotation sensor that generates pulses; 8 an exhaust pipe; 9 an oxygen sensor that detects the air-fuel ratio from components in the exhaust gas; 10 an air flow sensor 4 and a rotation sensor 7;
, calculates the required amount of fuel from operating parameters such as the oxygen sensor 9, controls the drive pulse width of the fuel injection valves 5a to 5d, which are energized in synchronization with engine rotation, and controls the signal waveforms of the cylinder pressure sensors 6a to 6d. A control device processes the exhaust gas and determines whether there is a misfire in each cylinder, and 11 is a catalyst device that purifies the exhaust gas. Since there is no known example of the operation of fuel injection control with the above configuration, it is omitted here.The control device 10 also includes a microcomputer consisting of a memory, arithmetic unit, etc. that has been widely used in the past, and input/output. Since it consists of a circuit, the explanation of its mechanism will be omitted, and only the operation will be explained with reference to the flowchart of FIG. 3.

After starting, first, in step 100, signals from the air flow sensor and rotation sensor 7 are read, and in step 101, the driving pulse widths of the fuel injection valves 5a to 5d are calculated based on these information. This pulse width is basically approximately proportional to the value obtained by dividing the amount of intake air by the engine speed, and the error of the air flow sensor 4 and fuel injection valves 5a to 5d is determined based on the deviation from the median value of the field bank correction amount. The fuel injectors 5a to 5d, which undergo learning correction, inject fuel proportional to the driving pulse width into the intake pipes 2a to 2 of the respective cylinders.
d is injected every predetermined cycle, and the air-fuel mixture is combusted in each cylinder.

Next, in step 102, the signal waveforms of the cylinder pressure sensors 6a to 6d installed in each cylinder are sequentially read in synchronization with the rotation pulse obtained from the rotation sensor 7.This signal waveform is normally used for crankshafts as shown in FIG. When the angle is close to TDC, the pressure increase due to combustion becomes large as shown by the solid line in the figure, but if the cylinder misfires due to some problem, that is, combustion does not occur, the pressure rise becomes low as shown by the broken line. Therefore, the known example (
As shown in Japanese Unexamined Patent Publication No. 61-23876), by comparing the cylinder pressure at two points before and after TDC, or by comparing the peak value of the cylinder pressure, it is possible to determine whether each cylinder has misfired. It is possible to detect whether or not the vehicle is present, and this determination is made in step 103.

Factors that can cause cylinder misfires include malfunctions in ignition system devices (not shown here) such as ignition coils, igniters, high-voltage cords, and misfire plugs, poor contact in the connectors that connect these devices, and failures in the spark plugs. Contamination, failure of the circuit parts 101a to 101d that drive the fuel injection valves,
There may be combustion failure due to water leaking into the cylinder.

Piezoelectric types and pressure sensors can be used as cylinder pressure sensors, and other methods (vibration,
Misfires can also be detected by using combustion light, etc.).

When a misfire is detected, the drive of the fuel injection valve of the relevant cylinder is stopped in step 104, and the air-fuel ratios of the other cylinders are subjected to feedback control as shown in FIG. 5 based on the signal from the oxygen sensor 9. At this time, the fuel supply to the misfiring cylinder is stopped, preventing raw gas from being discharged, but the oxygen sensor is exposed to fresh air, that is, a large amount of oxygen, from the cylinder.
The air-fuel ratio of other cylinders cannot be accurately detected, and the system is determined to be lean overall. Therefore, the driving pulse width of the fuel injection valve of the normal cylinder is shifted to the Lynch side. As a result of the above, the learning correction amount determined by the feedback correction amount also operates on the Lynch side.

[Problem to be solved by the invention]

However, when one cylinder misfires and the fuel supply to that cylinder is stopped and feedback correction is performed to the other cylinders, the air-fuel ratio of the other normal cylinders shifts to the rich side and Hc,
As Co increases and a large amount of oxygen is supplied from the misfiring cylinder, the reaction heat in the three-way catalyst increases, causing deterioration of the catalyst in an operating range where the exhaust gas temperature is originally high. In addition, in areas where the exhaust temperature is low, such as in the idle area, the catalyst is activated and does not reach the activation temperature if low-temperature air is exhausted from the misfiring cylinder, so the total air-fuel ratio becomes the stoichiometric air-fuel ratio. Even if Hc is released into the atmosphere without any reaction with the catalyst,
Co will be discharged. Furthermore, if the learning shifts to the rich side during feedback, for example during warm-up when the engine is cold, feedback correction will be stopped and the air-fuel ratio will be enriched, but this will overlap with the rich learning and result in over-rich, which will cause normal operation. There was a problem that even the cylinders would misfire.

This invention was made to solve the above-mentioned problems, and when a cylinder misfires, in the range where the catalyst can purify the exhaust gas, feedback control is performed to purify the exhaust gas, and it also prevents damage to the engine and 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

[Means to solve the problem]

The air-fuel ratio control device according to the present invention is used in a multi-cylinder internal combustion engine in which each cylinder has a fuel injection valve in its intake pipe. A detection means, a feedback correction means for feedback-controlling the air-fuel ratio based on 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, the misfire being detected by the output of the misfire detection means. When detected, the operation of the fuel injection valve to the misfired cylinder is stopped, feedback correction is performed by the non-misfired cylinder, and the operation of the storage means is stopped.

[For production]

In this invention, after stopping the fuel supply to the cylinder in which a misfire has been detected, the catalyst is prevented from being damaged by the intake air amount or engine parameters corresponding to the intake air amount.
In the operating range where exhaust gas purification is possible, feedback control by other cylinders is continued to reduce Hc, Co, and t.
In addition to preventing the emission of iox into the atmosphere, it also prohibits learning of errors in airflow sensors and fuel injection valves due to deviations during feedback, and prevents misfires from occurring in non-misfired cylinders when air-fuel ratio feedback control is stopped, such as during engine warm-up. It is possible to prevent misfires due to over-rich fuel supply.

(Example) Hereinafter, an example of the present invention will be explained with reference to the drawings.
The figure is a flowchart showing the procedure of fuel control for each cylinder in the air-fuel ratio control device according to the present invention, and transient fuel calculations such as warm-up operation and engine over-deceleration operation are the same as in the conventional example shown in Fig. 3. Therefore, it will be omitted. Further, the same steps as in FIG. 3 perform the same processing. In the present invention, a step 107 is provided between steps 104 and 105 in which it is determined whether or not the catalyst purification is possible. For example, if the amount of intake air is too small and the exhaust temperature is low and purification by the catalyst cannot be expected, or if the amount of intake air is large and the exhaust temperature is high, Hc and C are discharged from the non-misfired cylinder due to air-fuel ratio feedback.
When reacting o with a catalyst, the catalyst becomes high in temperature, and in a region where there is a possibility of deterioration or damage, the air-fuel ratio feedback is stopped and the process returns to step 100. If the determination in step 107 is in the catalyst purification possible range, the non-misfired cylinders are enriched in steps 105 and 106 as in FIG. 3, and the N
In addition to suppressing the generation of ox, the exhaust gas discharged into the atmosphere can be purified by causing excess lc and cobalt to react with the oxygen discharged from the misfiring cylinder using a catalyst.

Furthermore, in this invention, the calculation of the learned value in step 109 is prohibited during the air-fuel ratio feedback including the misfiring cylinder in step 108, so the learned value is based on the air flow when all cylinders are burning normally. Values that compensate for machine differences in sensors, fuel injection valves, etc. can be appropriately held, and during Lynch correction during warm-up operation of calculations not shown in Fig. 3 and Fig. 1, and during transient operation of the engine. This prevents problems such as excessive enrichment of the air-fuel ratio during acceleration/deceleration correction, which may lead to misfires.

Further, as another embodiment of the present invention, a catalyst temperature sensor is provided as a means for detecting whether purification by the catalyst is possible or not, and the determination in step 107 is made based on the output of the sensor, thereby increasing the effect of the present invention. That is clear.

Additionally, by limiting the correction amount of air-fuel ratio feedback control within the critical temperature range where the catalyst temperature is not damaged, feedback correction can be performed over a wider operating range, making it possible to purify exhaust gas. is clear.

〔Effect of the invention〕

As explained above, according to the present invention, when a cylinder misfires, the fuel supply to the cylinder is stopped to prevent a large amount of He from being discharged, and the other cylinders are enriched by air-fuel ratio feedback. Since Nox is reduced and Hc and Co are purified by enrichment using a catalyst, the purification rate of exhaust gas to the atmosphere can be significantly improved. Further, by prohibiting learning during feedback, smooth engine operation can be maintained without enriching the air-fuel ratio in the feedback stopped state due to erroneous learning, and it is also possible to prevent a large amount of He from being discharged.

Furthermore, in this invention, since a temperature sensor or the like is used to detect whether or not purification by the catalyst is possible, the feedback is enriched only in areas where purification by the catalyst can be expected without damaging the catalyst. This has the excellent effect that Hc and Go are not discharged into the atmosphere unreacted by the catalyst.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the procedure for fuel control to each cylinder in an air-fuel ratio control device 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. FIG. 4 is a characteristic diagram of the cylinder pressure sensor, and FIG. 5 is a characteristic diagram of air-fuel ratio control. 5a to 5d... fuel injection valve, 6... cylinder pressure sensor,
9... Oxygen sensor, 10... Control device.

Claims (1)

[Claims] In a multi-cylinder internal combustion engine having a fuel injection valve in each cylinder's intake pipe, there is a misfire detection means for detecting the presence or absence of a misfire in each cylinder, an air-fuel ratio detection means provided in the exhaust pipe, and a misfire detection means for detecting the presence or absence of a misfire in each cylinder. A fuel injection valve for a misfiring cylinder, comprising a feedback correction means for feedback-controlling an air-fuel ratio based on the output, and a storage means for storing at least a part of the output of the feedback correction means, and detecting a misfire based on the output of the misfire detection means. 1. An air-fuel ratio control device for an internal combustion engine, characterized in that the operation of a non-misfire cylinder is stopped, feedback correction is performed using a non-misfire cylinder, and the operation of a storage means is also stopped.