JPH03145538A - Exhaust cleaning system for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve control precision and cleaning performance by detecting the emission state after exhaust cleaning with two oxygen sensors, and correcting the air-fuel ratio feedback control based on one oxygen sensor on the upstream side. CONSTITUTION:An oxygen sensor S1 is located on the exhaust passage B of an engine A and detects the oxygen concentration of engine exhaust. An air-fuel ratio feedback control means C sets the feedback correction quantity based on the detected oxygen concentration and feedback controls the air-fuel ratio of a mixture. A three-way catalyst D cleans the component in the engine exhaust. Two separate oxygen sensors S2 and S3 are arranged in series on the downstream side of the three-way catalyst D. Outputs from both oxygen sensors S2 and S3 on the downstream side are monitored, and the deterioration and abnormality of an oxygen sensor S1 on the upstream side are judged. The proportional portion of the feedback control constant is corrected by a correcting means E according to the judged result.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention provides feedback control of the air-fuel ratio of the air-fuel mixture supplied to the engine, and reduces Co and HC in the exhaust gas using a three-way catalyst installed in the exhaust passage of the engine. The present invention also relates to an improved technology for an exhaust purification system for an internal combustion engine that aims to reduce NOx.

<Prior art> Conventionally, as a measure to purify the exhaust of internal combustion engines, a three-way catalyst was installed in the exhaust passage of the engine to oxidize CO1HC in the exhaust components.
Also, NOx is reduced and converted into other harmless substances.

The conversion efficiency of this three-way catalyst is closely related to the air-fuel ratio of the mixture supplied to the engine, and since the stoichiometric air-fuel ratio provides almost optimal exhaust purification performance overall, An oxygen sensor is provided in the passage, and the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled based on rich/lean signals from the oxygen sensor.

However, NOx reduction is insufficient due to the relationship with the amount of NOx generated, so under operating conditions where the Noxfi degree is high, part of the exhaust gas is recirculated into the intake air to lower the combustion temperature. Exhaust gas recirculation (EGR) control is also used to reduce NOx.

<Problems to be Solved by the Invention> Incidentally, the oxygen sensors in the exhaust purification system as described above deteriorate in different ways depending on the usage conditions.

For example, at low temperatures, the engine becomes lean (lean detection time is long) and NOx in exhaust gas emissions (toxic substances) increases. On the other hand, at high temperatures, the exhaust gas becomes richer (the lean detection time is longer) and the amount of C○ in the exhaust gas emissions (hazardous substances) increases.

For this reason, it is difficult to match emissions when the oxygen sensor is new, and if deterioration progresses, emissions regulations may be exceeded.

Furthermore, if NOx in the emissions increases due to deterioration of the exhaust gas recirculation (EGR) control device (deterioration of the orifice, etc.), there is no means to control it, so the emissions regulations may be violated as well.

Therefore, in view of the above-mentioned conventional problems, the present invention detects the state of emissions after exhaust purification using two oxygen sensors, and controls the air-fuel ratio based on the detection results. An object of the present invention is to provide an exhaust purification system for an internal combustion engine that can cope with deterioration of an oxygen sensor for fuel ratio feedback control.

<Means for Solving the Problems> Therefore, as shown in FIG. 1, the exhaust purification system for an internal combustion engine of the present invention includes an oxygen sensor installed in the exhaust passage of the engine to detect the oxygen concentration of the engine exhaust; A feedback correction amount is set according to the deviation between the air-fuel ratio of the air-fuel mixture supplied to the engine and a target air-fuel ratio based on the exhaust oxygen concentration detected by the oxygen sensor, and the air-fuel mixture is adjusted based on the feedback correction amount. An exhaust purification system for an internal combustion engine, comprising: a control means for feedback controlling the air-fuel ratio; and a three-way catalyst installed downstream of the oxygen sensor in the exhaust passage to purify components in the engine exhaust. Two oxygen sensors other than the oxygen sensor are installed in series on the downstream side of the three-way catalyst in the exhaust passage, and one of the two oxygen sensors is made of an oxygen ion conductor used as a solid electrolyte for a concentration battery. Forming an oxidation catalyst layer on the exhaust side surface further reduces NO
The present invention has a configuration in which an do.

<Operation> In the above configuration, when the air-fuel ratio feed pump control is performed normally, the output values of the two oxygen sensors after exhaust gas purification (reaction) in the three-way catalyst are stabilized.

On the other hand, if NOx increases due to lean conditions due to deterioration of the oxygen sensor for air-fuel ratio feedback control, the output of the oxygen sensor with NOx reduction function among the two oxygen sensors will not change, but the output of the other oxygen sensor will change. The output value becomes constant.

Furthermore, if C○ increases during enrichment due to deterioration of the oxygen sensor for air-fuel ratio feedback control, the output values of both oxygen sensors become constant.

Therefore, it is possible to determine whether the oxygen sensor has deteriorated and become abnormal based on the outputs from both oxygen sensors, and by correcting the proportional portion of the feedback control constant based on this determination result, it is possible to air-fuel ratio feedback control can be executed.

<Example> Embodiments of the present invention will be described below based on the drawings.

In FIG. 2, an air flow meter 13 for detecting the intake air flow rate Q and a throttle valve 14 for controlling the intake air flow rate Q in conjunction with the accelerator pedal are provided in the intake passage 12 of the engine 11.
is provided, and an electromagnetic fuel injection valve 15 is provided for each cylinder in the downstream manifold section. The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 having a built-in microcomputer, and injects and supplies fuel that is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator. Further, a water temperature sensor 17 for detecting the cooling water temperature Tw is provided in the cooling jacket of the engine 11, and the exhaust passage 1
An oxygen sensor 19 is provided to detect the air-fuel ratio of the intake air-fuel mixture by detecting the exhaust oxygen concentration in the air-fuel mixture.
A three-way catalyst 20 is provided that purifies exhaust gas on the downstream side by oxidizing CO and HC and reducing NOx. Further, in a distributor (not shown), the engine rotation speed is detected by counting the crank unit angle signal output from the crank angle sensor 21 in synchronization with the engine rotation for a certain period of time, or by measuring the cycle of the crank reference angle signal. be done.

Next, the fuel injection amount calculation routine by the control unit 16 will be explained according to the flowchart shown in FIG.

This routine is performed at predetermined intervals (for example, every 10 m5).

In step (hereinafter abbreviated as S as in the figure), based on the intake air flow rate Q detected by the air flow meter 13 and the engine rotation speed N calculated from the signal from the crank angle sensor 21, the A basic fuel injection amount Tp corresponding to the intake air flow rate Q is calculated using the following equation.

Tp=KxQ/N (K is a constant) In S2, various correction coefficients C0EF are set based on the cooling water temperature Tw etc. detected by the water temperature sensor 17.

In S3, the feedback correction coefficient α set based on the signal from the oxygen sensor 19 is read.

In S4, the voltage correction numerator s is calculated based on the battery voltage value.
Set. This is to correct changes in the injection flow rate of the fuel injection valve 15 due to battery voltage fluctuations.

In S5, the final fuel injection amount Ti is calculated according to the following equation.

Ti=TpXCOEFXα+Ts In S6, the calculated fuel injection amount Ti is set in the output register.

As a result, at a predetermined fuel injection timing synchronized with the engine rotation, a drive pulse signal having a pulse width of the calculated fuel injection amount Ti is applied to the fuel injection valve 15, and fuel injection is performed.

In the internal combustion engine having the above configuration, the present invention is configured as follows.

That is, two oxygen sensors 22 and 23 other than the oxygen sensor 19 are installed in series on the downstream side of the three-way catalyst 20 in the exhaust passage 18. One of these two oxygen sensors 22
has the following structure.

That is, the present applicant has improved a conventional general oxygen sensor in which an oxidation catalyst layer is formed on the exhaust side surface of an oxygen ion conductor used as a solid electrolyte for concentration batteries, and By forming a NOx reduction catalyst layer surrounding the
We have developed an oxygen sensor that does not have an Ox reduction function and shifts the ratio to the rich side to achieve the true stoichiometric air-fuel ratio, and by using this oxygen sensor to feedback control the air-fuel ratio, we can reduce the amount of NOx even when the NOx concentration increases. We have previously proposed a method that improves the NOx conversion efficiency of the three-way catalyst by controlling the air-fuel ratio to the true stoichiometric air-fuel ratio, thereby achieving a sufficient reduction of N○X (patent application). Showa 62-658
No. 44).

Therefore, one of the two oxygen sensors 22 and 23 mentioned above
2 has a structure in which an oxidation catalyst layer is formed on the exhaust side surface of an oxygen ion conductor used as a solid electrolyte for a concentration battery as described above, and an NOx reduction catalyst layer is further formed.

The control unit 16 is equipped with a correction means for correcting the proportionality of the feedback control constant in the air-fuel ratio feedback control means based on the output levels from the two oxygen sensors 22 and 23, respectively.

Next, the operation of this configuration will be explained.

When the air-fuel ratio feedback control is performed normally, the output waveform of the oxygen sensor 19 for air-fuel ratio feedback control becomes as shown in FIG. The output waveforms of the oxygen sensors 22 and 23 are as shown in FIG. 0) and (C), and the output value stabilizes around approximately 500 mV.

On the other hand, when NOx increases due to deterioration of the oxygen sensor 19 for air-fuel ratio feedback control or during EGR failure, the output of the oxygen sensor 22 does not change, but the output value of the oxygen sensor 23 remains constant at approximately IV. becomes (
(See Figure 5).

Further, when C○ increases during enrichment due to deterioration of the oxygen sensor 19 for air-fuel ratio feedback control, the output values of both oxygen sensors 22 and 23 become constant around l■ (see FIG. 6).

Therefore, by monitoring the outputs from both oxygen sensors 22 and 23, it is possible to determine whether the oxygen sensor 19 has deteriorated and become abnormal, and based on this determination result, the proportional portion of the feedback control constant can be calculated. By correcting
Appropriate air-fuel ratio feedback control can be executed.

This operation will be explained based on the flowchart of FIG. 7.

In step (hereinafter abbreviated as S as in the figure) 1, the output (ESA) of the oxygen sensor 23 is monitored. S2
Now, the output (ESB) of the oxygen sensor 22 is monitored. In S3, it is determined whether the output (ESA) of the oxygen sensor 23 is less than or greater than a predetermined value (for example, 800 mV), and if it is less than the predetermined value, the process returns, and if it is greater than or equal to the predetermined value, the process proceeds to S4.

In S4, the output (ESB) of the oxygen sensor 22 reaches a predetermined value (
For example, it is determined whether the voltage is less than 800 mV) or more than 800 mV, and if it is less than a predetermined value, the process proceeds to S5, and if it is more than the predetermined value, the process proceeds to S6.

In S5, the proportional constant PL of the feedback control constant is subtracted immediately after the air-fuel ratio is reversed from lean to rich.
(See Fig. 8) is increased by 302 to the Lynch side.

Also, in S6, the proportional constant PR of the feedback control constant is added immediately after the air-fuel ratio is reversed from rich to rich.
(See Figure 8) on the lean side by 30! Correct the increase.

To summarize the above effects, when ESA>800 mV and ESB>800 mV,
It is determined that the air-fuel ratio control is becoming richer, and the proportional constant PR of the feedback control constant is corrected so that the air-fuel ratio control becomes leaner.

When ESA>800 mV and ESB<800 mV, it is determined that the air-fuel ratio control is lean, and the proportional constant PL of the feedback control constant is corrected so that the air-fuel ratio control becomes rich.

Further, in cases other than the above, it is determined that there is no abnormality, and the above-mentioned control is not performed.

According to this configuration, even if the oxygen sensor 19 for air-fuel ratio feedback control in the exhaust purification system deteriorates or the exhaust gas recirculation (EC; The emission can be obtained, and the man-hours required for difficult emission matching when the oxygen sensor is new can be reduced.

<Effects of the Invention> As explained above, according to the present invention, the state of emissions after exhaust purification is detected using two oxygen sensors, and the air-fuel ratio is controlled based on the detection results. Therefore, it is possible to cope with the deterioration of the oxygen sensor for air-fuel ratio feedback control, obtain good emissions, and further reduce the labor required for difficult emission matching when the oxygen sensor is new. It is a big thing.

[Brief explanation of the drawing]

FIG. 1 is a complaint correspondence diagram of the exhaust purification system for an internal combustion engine according to the present invention, FIG. 2 is a configuration diagram of an embodiment of the same exhaust purification system, and FIG. 3 is a flowchart showing a fuel injection amount control routine. 4 to 6 are output waveform diagrams of the oxygen sensor in the above embodiment, FIG. 7 is a flowchart showing a correction control routine in the above embodiment, and FIG. 8 is an air-fuel ratio and an air-fuel ratio feedback correction coefficient in the above embodiment. 2 is a time chart showing changes in . 11... Engine 13... Air flow meter. 14... Throttle valve 15... Fuel injection valve 16.
...Control unit 17...Water temperature sensor 1
8...Exhaust passage 19.22t 23...Oxygen sensor 20...Three-way catalyst 21...Crank angle sensor

Claims (1)

[Claims] An oxygen sensor installed in the exhaust passage of an engine that detects the oxygen concentration of the engine exhaust air, and the deviation between the air-fuel ratio of the mixture supplied to the engine based on the oxygen concentration in the exhaust gas detected by the oxygen sensor and the target air-fuel ratio. a control means that sets a feedback correction amount according to the feedback correction amount and feedback-controls the air-fuel ratio of the air-fuel mixture based on the feedback correction amount; and a control means that is installed downstream of the oxygen sensor in the exhaust passage and purifies components in the engine exhaust gas. In an exhaust purification system for an internal combustion engine that includes a three-way catalyst, two oxygen sensors other than the oxygen sensor are installed in series on the downstream side of the three-way catalyst in the exhaust passage, and One of the oxygen sensors has a configuration in which an oxidation catalyst layer is formed on the exhaust side surface of an oxygen ion conductor used as a solid electrolyte for a concentration battery, and an NO_x reduction catalyst layer is further formed on the exhaust side surface. 1. An exhaust gas purification system for an internal combustion engine, comprising a correction means for correcting a proportional portion of a feedback control constant in the air-fuel ratio feedback control means based on an output level from the air-fuel ratio feedback control means.