JP2020026756A - Engine control device and engine control method - Google Patents

Abstract

To provide an engine control device and an engine control method capable of accurately controlling an air-fuel ratio of an engine even under a condition out of a theoretical air-fuel ratio.SOLUTION: In an engine control device 100 including a catalyst device 6 composed of a three-way catalyst or an oxidation catalyst provided in an exhaust system 4 of a gasoline engine 2, a total region air-fuel ratio sensor 10 provided in an upstream-side exhaust system of the catalyst device, a NOx sensor 12 provided in a downstream-side exhaust system of the catalyst device, and engine control means 20 for controlling an air-fuel ratio of an air-fuel mixture supplied to the gasoline engine so that the air-fuel ratio calculated on the basis of an oxygen concentration value detected by the total region air-fuel ratio sensor becomes a prescribed target air-fuel ratio, the engine control means corrects the calculated air-fuel ratio or the target air fuel ratio so that the NOx concentration value becomes the target NOx concentration value when the NOx concentration value detected by the NOx sensor is out of the prescribed target NOx concentration value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an engine control device and an engine control method for controlling an air-fuel ratio of an air-fuel mixture supplied to a gasoline engine.

2. Description of the Related Art A technology for installing an oxygen sensor (λ sensor) in an exhaust system of an internal combustion engine to detect an oxygen concentration in exhaust gas and performing feedback control of an air-fuel ratio of an air-fuel mixture so that the detected value becomes a stoichiometric air-fuel ratio is widely used. Are known.
Further, in order to improve the problem that the accuracy of the air-fuel ratio control is reduced due to the deterioration with time of the oxygen sensor, a second oxygen sensor (λ sensor) is installed downstream of the three-way catalyst installed downstream of the oxygen sensor. In some cases, the output of the deteriorated upstream oxygen sensor is corrected in accordance with the output of the downstream oxygen sensor, and the air-fuel ratio is accurately controlled.
Further, NOx sensors are installed upstream and downstream of the three-way catalyst, respectively, and the degree of deterioration (purification rate) of the catalyst is calculated from the output of each NOx sensor, and the upstream oxygen sensor is set so that the purification rate falls within a predetermined range. A technique has been developed to correct the output and to maintain the air-fuel ratio at the stoichiometric air-fuel ratio to ensure catalyst performance (see Patent Document 1).

Japanese Patent No. 2503391

By the way, since the output of the oxygen sensor (λ sensor) rapidly changes stepwise near the stoichiometric air-fuel ratio, for example, when the internal combustion engine is operated under a condition deviating from the stoichiometric air-fuel ratio such as a lean burn engine, the air-fuel ratio control is performed. There is a problem that it cannot be performed accurately.
On the other hand, a full-range air-fuel ratio sensor capable of detecting a wide range of air-fuel ratio is known, and it is assumed that an air-fuel ratio control is performed by installing a full-range air-fuel ratio sensor instead of the λ sensor on the upstream side of the catalyst. Is done.

Here, as shown in FIG. 5, the full range air-fuel ratio sensor utilizes the fact that the sensor output is proportional to the oxygen concentration. However, when the detected oxygen concentration is converted into an air-fuel ratio, as shown in FIG. 6, there is a problem that the output change becomes small on the lean side, and the resolution and, consequently, the detection accuracy decrease. For this reason, the measurement of the air-fuel ratio tends to be inaccurate.
For example, when the internal combustion engine is operated at a predetermined air-fuel ratio A / F on the lean side, the combustion becomes unstable when the air-fuel ratio deviates from the A / F to the lean side, and when the air-fuel ratio deviates from the A / F to the rich side, the exhaust gas is exhausted. NOx in the gas increases.

  Therefore, an object of the present invention is to provide an engine control device and an engine control method capable of accurately controlling the air-fuel ratio of an engine even under conditions deviating from the stoichiometric air-fuel ratio.

  In order to solve the above problems, an engine control device according to the present invention includes a catalyst device including a three-way catalyst or an oxidation catalyst provided in an exhaust system of a gasoline engine, and an entire region provided in the exhaust system on the upstream side of the catalyst device. An air-fuel ratio sensor, a NOx sensor provided in the exhaust system downstream of the catalyst device, and a calculated air-fuel ratio calculated according to the oxygen concentration value detected by the full-range air-fuel ratio sensor become a predetermined target air-fuel ratio. An engine control means for controlling an air-fuel ratio of an air-fuel mixture supplied to the gasoline engine, wherein the engine control means determines that a NOx concentration value detected by the NOx sensor is a predetermined value. When the target NOx concentration value deviates from the target NOx concentration value, the calculated air-fuel ratio or the target air-fuel ratio is corrected so that the NOx concentration value becomes the target NOx concentration value.

When an oxygen sensor (λ sensor) is attached to an exhaust system of a gasoline engine to perform air-fuel ratio control, air-fuel ratio control cannot be performed with high accuracy due to the characteristics of the λ sensor under conditions deviating from the stoichiometric air-fuel ratio. On the other hand, it is assumed that the air-fuel ratio control is performed by the full-range air-fuel ratio sensor that can detect the air-fuel ratio in a wide range, but when the oxygen concentration detected by the full-range air-fuel ratio sensor is converted into the air-fuel ratio, it is detected on the lean side. Accuracy may be reduced and air-fuel ratio measurement may be inaccurate.
Therefore, according to this engine control device, a reduction in the detection accuracy of the air-fuel ratio sensor in all regions is corrected by the detection value of the NOx sensor using a NOx sensor capable of accurately detecting the NOx concentration regardless of the air-fuel ratio. The air-fuel ratio can be accurately estimated, and the air-fuel ratio of the engine can be accurately controlled even under conditions deviating from the stoichiometric air-fuel ratio. Specifically, when the NOx concentration value detected by the NOx sensor deviates from a predetermined target NOx concentration value, the target air-fuel ratio is corrected so that the NOx concentration value becomes the target NOx concentration value.
Further, since the NOx concentration is monitored downstream of the catalyst device of the gasoline engine, when the air-fuel ratio changes to the rich side and the NOx concentration increases, control is performed to immediately reduce the NOx concentration to the target value. Emissions can be reduced.

In the engine control device of the present invention, the engine control means may adjust the calculated air-fuel ratio such that the NOx concentration value becomes the target NOx concentration value when the NOx concentration value is lower than the target NOx concentration value. The target air-fuel ratio may be corrected to the lean side or to the rich side from the current value.
According to this engine control device, the calculated air-fuel ratio or the target air-fuel ratio can be quickly corrected in accordance with the NOx concentration value, and the air-fuel ratio can be accurately controlled.

In the engine control device of the present invention, the engine control means may adjust the calculated air-fuel ratio such that the NOx concentration value becomes equal to the target NOx concentration value when the NOx concentration value exceeds the target NOx concentration value. The target air-fuel ratio may be corrected to a rich side or a lean side from a current value.
According to this engine control device, the calculated air-fuel ratio or the target air-fuel ratio can be quickly corrected in accordance with the NOx concentration value, and the air-fuel ratio can be accurately controlled.

An engine control method according to the present invention includes a catalyst device including a three-way catalyst or an oxidation catalyst provided in an exhaust system of a gasoline engine; a full-range air-fuel ratio sensor provided in the exhaust system on the upstream side of the catalyst device; A NOx sensor provided in the exhaust system downstream of the device,
A control method for the engine system, comprising: a step of mixing the mixture supplied to the gasoline engine such that a calculated air-fuel ratio calculated according to the oxygen concentration value detected by the full-range air-fuel ratio sensor becomes a predetermined target air-fuel ratio. An engine control step of controlling the air-fuel ratio of the air, wherein the engine control step includes the step of, when the NOx concentration value detected by the NOx sensor deviates from a predetermined target NOx concentration value, setting the NOx concentration value to the target NOx concentration. The calculated air-fuel ratio or the target air-fuel ratio is corrected so as to be a concentration value.

  In the engine control method according to the present invention, the engine control step includes the step of: calculating the calculated air-fuel ratio such that the NOx concentration value becomes the target NOx concentration value when the NOx concentration value is lower than the target NOx concentration value. The target air-fuel ratio may be corrected to the lean side or to the rich side from the current value.

  In the engine control method according to the aspect of the invention, the engine control step may include calculating the calculated air-fuel ratio such that when the NOx concentration value is greater than the target NOx concentration value, the NOx concentration value becomes the target NOx concentration value. The target air-fuel ratio may be corrected to a rich side or a lean side from a current value.

  According to the present invention, the air-fuel ratio of the engine can be accurately controlled even under conditions deviating from the stoichiometric air-fuel ratio.

It is a schematic structure figure showing an example of an engine control device concerning an embodiment of the present invention. It is a schematic diagram which shows the relationship between the output of a NOx sensor and NOx concentration. FIG. 4 is a diagram showing a processing flow by an engine control means. It is a schematic diagram which shows the relationship between NOx concentration and air-fuel ratio. It is a schematic diagram which shows the relationship between the output of the full area air-fuel ratio sensor and the oxygen concentration. It is a schematic diagram which shows the relationship between the output of the full area air-fuel ratio sensor and the air-fuel ratio.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a schematic configuration diagram showing an example of an engine control device 100 according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing output characteristics of a NOx sensor 12, and FIG. It is.
The engine control device 100 is applied to the gasoline engine 2, and includes a catalyst device 6 including a three-way catalyst or an oxidation catalyst provided in an exhaust system (muffler) 4 of the gasoline engine 2, a full-range air-fuel ratio sensor 10, a NOx sensor 12, , An engine control means 20.
Further, a fuel control system 8 is installed in the gasoline engine 2, and the fuel control system 8 adjusts the air-fuel ratio of the air-fuel mixture and supplies the mixture to the gasoline engine 2. The fuel control system 8 can be composed of a throttle valve for adjusting the intake air amount of the engine, an injector (fuel injection valve) for injecting fuel, and the like.
The catalyst device 6 can remove at least carbon monoxide (CO) and unburned hydrocarbons (THC). In the case of a three-way catalyst, NOx may also be removed.

The engine control unit 20 is configured as, for example, a part of an ECU, and the ECU also controls the entire gasoline engine 2. The ECU including the engine control means 20 includes a known CPU, ROM, RAM, and the like. The ROM stores various control programs, maps referred to when the various control programs are executed, and the like. The CPU executes various arithmetic processes based on various control programs and maps stored in the ROM. In addition, the RAM temporarily stores the result of calculation by the CPU, data input from each sensor, and the like.
The ECU executes air-fuel ratio feedback control, which will be described later, in addition to various controls of the gasoline engine 2 based on the detection signals of the various sensors described above. Further, the ECU performs correction described below.

The full-range air-fuel ratio sensor 10 is provided in the exhaust system 4 on the upstream side of the catalyst device 6 and detects an air-fuel ratio not only near the stoichiometric air-fuel ratio (λ = 1) but also in a wide range outside the stoichiometric air-fuel ratio. Can be.
The NOx sensor 12 is provided in the exhaust system 4 on the downstream side of the catalyst device 6, and detects a NOx concentration value.
The “oxygen concentration value, NOx concentration value” in the claims is not limited to the oxygen concentration or the NOx concentration itself, but also includes the output (detection current, detection voltage, etc.) detected by each of the sensors 10 and 12.

  Then, the engine control means 20 calculates the calculated air-fuel ratio (see FIG. 6) according to the oxygen concentration value (see FIG. 5) detected by the full-range air-fuel ratio sensor 10. Further, the engine control means 20 controls the fuel control system 8 to feedback-control the air-fuel ratio of the mixture supplied to the gasoline engine 2 so that the calculated air-fuel ratio becomes a predetermined target air-fuel ratio.

Here, as described above, the full-range air-fuel ratio sensor 10 can detect a wide range of air-fuel ratio. However, since the oxygen concentration output by the sensor is converted into an air-fuel ratio, the output change is reduced particularly on the lean side, and the resolution is reduced. As a result, the detection accuracy decreases.
On the other hand, as shown in FIG. 2, since the sensor output of the NOx sensor 12 is proportional to the NOx concentration, the NOx concentration can be accurately detected regardless of the air-fuel ratio (particularly on the lean side).
Therefore, in the present invention, the air-fuel ratio can be accurately estimated by correcting the decrease in the detection accuracy of the entire region air-fuel ratio sensor 10 used for the air-fuel ratio control with the detection value of the NOx sensor 12, and the stoichiometric air-fuel ratio can be obtained. It is possible to accurately control the air-fuel ratio of the engine even under the off-condition.

Specifically, as shown in FIGS. 1 and 3, the engine control means 20 controls the air-fuel ratio.
Here, consider the case where the gasoline engine 2 is operated on the lean side. At this time, a predetermined lean-side target air-fuel ratio for operating the gasoline engine 2 and a target NOx concentration value assumed to be emitted when the gasoline engine 2 is operated at the target air-fuel ratio are determined in advance.
Now, suppose that the actual air-fuel ratio has changed to the rich side as shown in FIG. At this time, as described above, the full-range air-fuel ratio sensor 10 has a low resolution and cannot accurately detect the air-fuel ratio.
On the other hand, as shown in FIG. 4, when the air-fuel ratio becomes richer, the NOx concentration tends to increase. Therefore, as shown in FIG. 3 (ii), when the actual air-fuel ratio changes to the rich side, the NOx concentration increases and deviates from the target NOx concentration value.

In this case, if the fuel control system 8 is controlled so that the air-fuel ratio becomes lean, the NOx concentration decreases, and as shown in FIG. 3 (iv), the NOx concentration value converges to the target NOx concentration value. Become.
Therefore, as shown in FIG. 3 (iii), the engine control means 20 further corrects the target air-fuel ratio to the lean side.
As a result, the above-described feedback control is performed until the air-fuel ratio calculated by the full-range air-fuel ratio sensor 10 becomes the target air-fuel ratio until the air-fuel ratio becomes leaner. As a result, as shown in FIG. The actual air-fuel ratio converges on the initial target air-fuel ratio.

As described above, when the NOx concentration value detected by the NOx sensor 12 deviates from the predetermined target NOx concentration value, the engine control means 20 corrects the target air-fuel ratio so that the NOx concentration value becomes the target NOx concentration value.
This makes it possible to accurately control the air-fuel ratio of the engine even under conditions deviating from the stoichiometric air-fuel ratio.
Further, since the NOx concentration is monitored downstream of the catalyst device 6 of the gasoline engine 2, when the air-fuel ratio changes to the rich side and the NOx concentration increases, control is performed to immediately reduce the NOx concentration to the target value. NOx emissions can be reduced.

  When the actual air-fuel ratio changes to the lean side, the upper and lower sides of FIGS. 3 (i) to (v) are reversed. For example, in FIG. 3 (iii), the target air-fuel ratio is corrected to the rich side.

It goes without saying that the present invention is not limited to the above embodiments, but extends to various modifications and equivalents included in the spirit and scope of the present invention.
As the above correction, in addition to correcting the target air-fuel ratio, a calculated air-fuel ratio calculated from the oxygen concentration value detected by the full-range air-fuel ratio sensor 10 may be corrected. When correcting the calculated air-fuel ratio, the calculated air-fuel ratio is corrected to the rich side so that the target air-fuel ratio is corrected to the lean side while keeping the initial value.

Further, a post-treatment catalyst for removing NOx may be provided downstream of the NOx sensor 12 in the exhaust system 4. Examples of the post-treatment catalyst include LNT (storage type nitrogen oxide reduction catalyst) and SCR (selective catalyst reduction device). Here, in the present invention, since the NOx concentration is monitored as described above, the emission amount of NOx can be reduced, so that the catalyst amount of these post-treatment catalysts can be reduced, and in some cases, the post-treatment catalyst becomes unnecessary. There is.
Further, a particle (particulate) filter may be provided between the catalyst device 6 and the NOx sensor 12.

2 Gasoline engine 4 Exhaust system 6 Catalyst device 10 Full range air-fuel ratio sensor 12 NOx sensor 20 Engine control means 100 Engine control device

Claims (6)

A catalyst device comprising a three-way catalyst or an oxidation catalyst provided in an exhaust system of a gasoline engine;
An all-area air-fuel ratio sensor provided in the exhaust system on the upstream side of the catalyst device,
A NOx sensor provided in the exhaust system downstream of the catalyst device;
Engine control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the gasoline engine so that the calculated air-fuel ratio calculated according to the oxygen concentration value detected by the full-range air-fuel ratio sensor becomes a predetermined target air-fuel ratio,
An engine control device comprising:
The engine control means is configured to control the calculated air-fuel ratio or the target air-fuel ratio such that the NOx concentration value becomes the target NOx concentration value when the NOx concentration value detected by the NOx sensor deviates from a predetermined target NOx concentration value. Engine control device that corrects fuel ratio.   The engine control means sets the calculated air-fuel ratio to the lean side or sets the target air-fuel ratio so that the NOx concentration value becomes the target NOx concentration value when the NOx concentration value becomes lower than the target NOx concentration value. 2. The engine control device according to claim 1, wherein the air-fuel ratio is corrected to be richer than the current value.   The engine control means sets the calculated air-fuel ratio to a rich side or sets the target air-fuel ratio such that the NOx concentration value becomes the target NOx concentration value when the NOx concentration value is higher than the target NOx concentration value. The engine control device according to claim 1, wherein the air-fuel ratio is corrected to be leaner than the current value. A catalyst device comprising a three-way catalyst or an oxidation catalyst provided in an exhaust system of a gasoline engine;
An all-area air-fuel ratio sensor provided in the exhaust system on the upstream side of the catalyst device,
A NOx sensor provided in the exhaust system downstream of the catalyst device;
An engine system control method comprising:
An engine control step of controlling the air-fuel ratio of the air-fuel mixture supplied to the gasoline engine so that the calculated air-fuel ratio calculated according to the oxygen concentration value detected by the full-range air-fuel ratio sensor becomes a predetermined target air-fuel ratio. And
The engine control process includes the step of calculating the calculated air-fuel ratio or the target air-fuel ratio such that the NOx concentration value becomes the target NOx concentration value when the NOx concentration value detected by the NOx sensor deviates from a predetermined target NOx concentration value. An engine control method that corrects the fuel ratio.   The engine control process may include setting the calculated air-fuel ratio to a lean side or the target value so that the NOx concentration value becomes the target NOx concentration value when the NOx concentration value is lower than the target NOx concentration value. 5. The engine control method according to claim 4, wherein the air-fuel ratio is corrected to be richer than the current value.   The engine control process may include setting the calculated air-fuel ratio to a rich side or the target air-fuel ratio so that the NOx concentration value becomes the target NOx concentration value when the NOx concentration value is higher than the target NOx concentration value. The engine control method according to claim 4, wherein the air-fuel ratio is corrected to be leaner than the current value.

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