JP5593794B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine.

  Engines that use compressed natural gas (hereinafter referred to as CNG) as gas fuel have been developed. The composition of CNG varies depending on the country, region or time of purification.

  Therefore, when new CNG is replenished to the gas fuel tank, it is necessary to correct the control such as the ignition timing and the injection amount. In Patent Document 1, when a change in internal pressure of a high-pressure pipe in a CNG supply system for supplying CNG to a gas fuel injector from a gas fuel tank via a regulator is detected, it is determined that CNG is replenished, and an air-fuel ratio is determined. A technique for updating the learning value of control is described.

JP 2004-092529 A JP 2008-031966 A

CNG may contain CO ₂ that affects combustion. This is due to the fact that CO ₂ is not removed in the refining process, and is due to the fact that the equipment for purification varies depending on the region and time.

In addition, an engine that uses biogas as gas fuel has been developed, but biogas also contains a large amount of CO ₂ . The composition of biogas also varies depending on the region and time.

Since CO ₂ mixed with gas fuel is inactive and affects engine performance and exhaust performance, it is necessary to perform ignition timing control and injection amount control according to the amount of CO ₂ mixed in the gas fuel.

Although Patent Document 1 describes detecting the replenishment of CNG, it does not describe the change in CNG CO ₂ concentration and the change in engine control corresponding thereto. This is due to the fact that it is difficult to attach a sensor for detecting fuel properties because the gas fuel pipe is high pressure.

  The present invention has been made in view of such circumstances, and provides a control device for a gas fuel engine that can suppress deterioration in engine performance and exhaust performance when gas fuel having different inert component concentrations is supplied. The purpose is to provide.

The present invention for solving the above problems is a control device for an internal combustion engine operated by gas fuel,
NOx concentration detecting means for detecting the NOx concentration of the exhaust gas of the internal combustion engine;
And CO ₂ concentration estimation means for estimating the CO ₂ concentration of the gas fuel based on the NOx concentration detected by the NOx concentration detection means,
And correcting means for correcting the control amount of the internal combustion engine based on the CO ₂ concentration estimated by the CO ₂ concentration estimation means,
Control means for controlling the internal combustion engine based on the control amount corrected by the correction means.

When the CO ₂ concentration of the gas fuel is increased, the combustion temperature is lowered, so that the NOx emission amount is reduced. Thus, based on the relationships between the NOx concentration in the exhaust gas and the CO ₂ concentration of the gas fuel, it is possible to estimate the CO ₂ concentration of the gas fuel from the NOx concentration in the exhaust gas.

For example, a gas fuel having a known CO ₂ concentration or a gas fuel not containing CO ₂ is used as the standard gas fuel, and the NOx concentration in the exhaust when the standard gas fuel is burned is examined in advance and detected by the NOx concentration detection means. By comparing with the NOx concentration, the CO ₂ concentration of the gas fuel currently used for combustion can be estimated.

Then, based on the estimated CO ₂ concentration, for example, by correcting the control amount of the internal combustion engine determined on the assumption of the standard gas fuel, the engine performance and the exhaust gas in the gas fuel currently used for combustion are corrected. A control amount capable of optimizing the performance can be obtained.

As a result, it is possible to suppress a decrease in engine performance and exhaust performance regardless of the concentration of the inert component (CO ₂ ) of the gas fuel used for combustion.

In the present invention, the control amount of the internal combustion engine is an injection amount of gas fuel,
The correction means may perform correction to increase the injection amount as the CO ₂ concentration estimated by the CO ₂ concentration estimation means is higher.

As the CO ₂ concentration increases, the concentration of inert components in the gas fuel increases and combustion failure tends to occur. However, by increasing the injection amount, it becomes possible to stabilize the combustion and reduce engine performance and exhaust performance. Can be suppressed.

In the present invention, the internal combustion engine is a spark ignition type internal combustion engine in which an air-fuel mixture containing gas fuel in a cylinder is ignited by an ignition means and burned.
The control amount of the internal combustion engine is an ignition timing by the ignition means,
The correction means may perform correction to advance the ignition timing as the CO ₂ concentration estimated by the CO ₂ concentration estimation means increases.

As the CO ₂ concentration increases, the concentration of inert components in the gas fuel increases and combustion failure tends to occur. However, it is possible to stabilize combustion by advancing the ignition timing, resulting in decreased engine performance and exhaust performance. Can be suppressed.

In the present invention, an EGR device for recirculating a part of the exhaust gas of the internal combustion engine as EGR gas to the intake system of the internal combustion engine,
The control amount of the internal combustion engine is the amount of EGR gas recirculated to the intake system by the EGR device,
It said correction means, the CO ₂ concentration estimated by the CO ₂ concentration estimating means may perform a correction for weight loss higher EGR gas amount.

Since EGR gas contains many inert components, the inert component concentration of the air-fuel mixture used for combustion is suitably maintained at the target value by adjusting the amount of EGR gas according to the CO ₂ concentration of the gas fuel. It is possible to suppress a decrease in engine performance and exhaust performance.

In the present invention, the CO ₂ concentration estimation means estimates the CO ₂ concentration of the gas fuel based on the NOx concentration detected by the NOx concentration detection means when the internal combustion engine is in a steady operation state. good.

Thereby, since the NOx concentration of the exhaust gas in a stable combustion state can be detected, the CO ₂ concentration of the gas fuel can be estimated with higher accuracy.

In the present invention, the CO ₂ concentration estimating means estimates the CO ₂ concentration of the gas fuel based on the NOx concentration detected by the NOx concentration detecting means when the warm-up of the internal combustion engine is completed. Anyway.

Thereby, since the NOx concentration of the exhaust gas in a stable combustion state can be detected, the CO ₂ concentration of the gas fuel can be estimated with higher accuracy.

In the present invention, an EGR device for recirculating a part of the exhaust gas of the internal combustion engine as EGR gas to the intake system of the internal combustion engine,
The CO ₂ concentration estimation means stops the recirculation of EGR gas by the EGR device, and the CO _{2 of the} gas fuel is based on the NOx concentration detected by the NOx concentration detection means in a state where the EGR gas is not recirculated. The concentration may be estimated.

By stopping the recirculation of EGR gas, the main inert components in the mixed gas used for combustion are derived from gas fuel, so the accuracy of CO ₂ concentration estimation of gas fuel based on the NOx concentration of exhaust gas is improved. Can be increased.

In the present invention, provided with an exhaust purification device that is provided in the exhaust passage of the internal combustion engine and purifies harmful substances in the exhaust,
The NOx concentration detection means may detect the NOx concentration of the exhaust upstream of the exhaust purification device.

Thereby, since the NOx concentration in which the property of the gas fuel is reflected more directly can be detected, the accuracy of estimating the CO ₂ concentration of the gas fuel based on the NOx concentration of the exhaust gas can be improved.

In the present invention, comprising a replenishment detection means for detecting that the gas fuel is replenished in the storage means for storing the gas fuel,
The correction means may correct the control amount of the internal combustion engine when the supply of gas fuel is detected by the supply detection means.

According to this configuration, even when gas fuels having different concentrations of inactive components (CO ₂ ) are replenished, the gas fuel is replenished on the basis of the NOx concentration of exhaust exhausted by the combustion of the gas fuel. Since the CO ₂ concentration of the gas fuel can be estimated and the control amount of the internal combustion engine can be corrected based on the estimated CO ₂ concentration, engine performance and exhaust performance when gas fuel having different CO ₂ concentrations are replenished Can be suppressed.

In the present invention, it comprises pressure detection means for detecting the pressure of the gas fuel in the storage means or the pressure of the gas fuel in the gas fuel supply path for supplying the gas fuel from the storage means to the fuel injection valve,
The replenishment detecting means may detect replenishment of gas fuel based on a change in pressure detected by the pressure detecting means.

  As the remaining amount of gas fuel in the storage means decreases, the pressure of the gas fuel in the storage means and the gas fuel supply path gradually decreases. When the gas fuel is replenished to the storage means, this pressure changes greatly and becomes a high pressure corresponding to the replenishment amount of the gas fuel. When such a pressure transition is detected, it can be detected that gas fuel has been replenished.

In the present invention, after the replenishment detecting means detects the replenishment of the gas fuel, the gas fuel before the replenishment remaining in the gas fuel supply path for supplying the gas fuel from the storage means to the fuel injection valve is performed. Has a determination means for determining whether or not
The correction means corrects the control amount of the internal combustion engine after the determination means determines that the gas fuel before replenishment has been consumed when the replenishment detection means detects the replenishment of the gas fuel. You may do it.

  Even when new gas fuel is replenished to the storage means, the gas fuel before replenishment remains in the gas fuel supply path for supplying gas fuel from the storage means to the fuel injection valve. The exhaust gas discharged in the operation of the internal combustion engine immediately after the gas fuel is replenished is a gas obtained by burning the remaining gas fuel.

Therefore, even if the NOx concentration of exhaust discharged in the operation of the internal combustion engine immediately after the gas fuel is replenished is detected, the CO ₂ concentration of the newly replenished gas fuel cannot be accurately estimated based on the detected NOx concentration. There is sex.

According to the above configuration, the CO ₂ concentration of the gas fuel is estimated based on the NOx concentration detected by the NOx concentration detecting means after it is determined that the remaining gas fuel before replenishment has been consumed, and the estimated Since the control amount of the internal combustion engine is corrected based on the CO ₂ concentration, it is possible to more reliably correct the control amount based on the CO ₂ concentration of the replenished gas fuel.

Therefore, it is possible to more reliably suppress the deterioration of the engine performance and the exhaust performance when the fuels having different CO ₂ concentrations are supplied.

  The determination means can determine whether or not the remaining gas fuel is consumed based on the volume of the fuel supply path, the history of operating conditions of the internal combustion engine immediately after the gas fuel is replenished, and the like. The determination can also be made based on the elapsed time from the start of operation of the internal combustion engine immediately after the gas fuel is replenished.

  Alternatively, the transition of the detected value by the NOx concentration detecting means is monitored, and when there is a discontinuous change in the detected value that is not linked to the change in the operating condition, the replenished gas fuel from the pre-replenished gas fuel You may judge that it has changed.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the control apparatus of the gas fuel engine which can suppress the fall of engine performance and exhaust performance when the gas fuel from which an inert component density | concentration differs is replenished.

It is a figure which shows schematic structure of the gas fuel internal combustion engine which concerns on an Example, its fuel system, and an intake / exhaust system. It is a flowchart of a process for correcting the combustion control in accordance with the CO ₂ concentration of CNG supplemented during CNG supply in the examples. It is a diagram showing the relationship between the CO ₂ concentration and the fuel injection quantity of CNG in the correction process of combustion control according to the CO ₂ concentration of the CNG embodiment. It is a diagram showing the relationship between the CO ₂ concentration and the ignition timing advance amount of CNG in the correction process of combustion control according to the CO ₂ concentration of the CNG embodiment. It is a diagram showing the relationship between the CO ₂ concentration and the EGR gas amount of CNG in the correction process of combustion control according to the CO ₂ concentration of the CNG embodiment.

  Hereinafter, embodiments of the present invention will be described in detail. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  In this embodiment, the present invention is applied to a gas fuel engine using compressed natural gas (CNG) as gas fuel. In addition, this invention can also apply this invention to the internal combustion engine which uses the natural gas which is primary fuel, such as liquefied petroleum gas (LPG), and petroleum gas, the coal conversion gas which is secondary fuel, and petroleum conversion gas. .

  FIG. 1 is a diagram showing a schematic configuration of a gas fuel internal combustion engine and its fuel system and intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a vehicle driving engine that uses gasoline and CNG as fuel. The internal combustion engine 1 has four cylinders 2. Each cylinder 2 is provided with a spark plug 3 (ignition means).

  An intake manifold 4 and an exhaust manifold 5 are connected to the internal combustion engine 1. An intake passage 6 is connected to the intake manifold 4. An exhaust passage 7 is connected to the exhaust manifold 5. The four branch pipes of the intake manifold 4 are connected to the respective cylinders 2. Each branch pipe is provided with a gasoline injector 8 for injecting gasoline and a CNG injector 9 for injecting CNG.

  Each gasoline injector 8 is connected to a gasoline delivery pipe 10. One end of a gasoline supply passage 12 is connected to the gasoline delivery pipe 10, and the other end of the gasoline supply passage 12 is connected to a gasoline tank 13.

  A feed pump 14 is installed in the gasoline supply passage 12. Gasoline is supplied from the gasoline tank 13 to the gasoline delivery pipe 10 via the gasoline supply passage 12, and further, gasoline is supplied from the gasoline delivery pipe 10 to each gasoline injector 8.

  Each CNG injector 9 is connected to a CNG delivery pipe 11. One end of a CNG supply passage 15 is connected to the CNG delivery pipe 11 and the other end of the CNG supply passage 15 is connected to a CNG tank 16 (storage means). A regulator 17 is installed in the CNG supply passage 15.

  CNG is supplied from the CNG tank 16 to the CNG delivery pipe 11 via the CNG supply passage 15, and further CNG is supplied from the CNG delivery pipe 11 to each CNG injector 9. The CNG supply path 15 and the CNG delivery pipe 11 function as the “gas fuel supply path” in the present invention.

The CNG delivery pipe 11 is provided with a pressure sensor 23 that detects the pressure of the CNG in the CNG delivery pipe 11 and a temperature sensor 24 that detects the temperature of the CNG. Further, a pressure sensor 25 that detects the pressure of CNG in the CNG supply passage 15 and a temperature sensor 26 that detects the temperature of the CNG are also provided upstream of the regulator 17 in the CNG supply passage 15. The pressure sensor 23 or the pressure sensor 25 is “
It functions as “pressure detection means”.

  In the intake passage 6, an air cleaner 18, an air flow meter 22, and a throttle valve 19 are installed in this order. In the exhaust passage 7, an A / F sensor 27 for detecting the air-fuel ratio of the exhaust, a NOx sensor 31 (NOx concentration detecting means) for detecting the NOx concentration of the exhaust, an exhaust purification catalyst 21 (exhaust gas) constituted by a three-way catalyst and the like. (Purification device) is installed.

  The exhaust manifold 5 and the intake passage 6 downstream of the throttle valve 19 are connected by an EGR passage 30. A part of the exhaust gas flows into the intake passage 6 as EGR gas through the EGR passage 30.

The EGR passage 30 is provided with an EGR valve 29 that adjusts the flow area of the EGR passage 30. By adjusting the opening degree of the EGR valve 29, the amount of EGR gas recirculated to the intake passage 6 can be adjusted. The EGR passage 30 and the EGR valve 29 function as the “EGR device” in the present invention.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 20. The ECU 20 is a unit that controls the operating state of the internal combustion engine 1 and the like. An air flow meter 22, pressure sensors 23 and 25, temperature sensors 24 and 26, an A / F sensor 27, and a NOx sensor 31 are electrically connected to the ECU 20.

  Furthermore, a crank angle sensor 28 that detects the crank angle of the internal combustion engine 1 is also electrically connected to the ECU 20. Output signals from the sensors are input to the ECU 20. The ECU 20 derives the engine speed of the internal combustion engine 1 based on the output signal of the crank angle sensor 28.

  Further, the ECU 20 is electrically connected to the ignition plug 3, each gasoline injector 8, each CNG injector 9, the feed pump 14, the regulator 17, the throttle valve 19, and the EGR valve 29. These are controlled by the ECU 20.

The composition of CNG varies depending on the country, region or time of purification. In addition, CNG may contain CO ₂ that affects combustion. Such variations in fuel properties of CNG are caused by the CNG refining process, and the refining equipment varies depending on the country, region or time.

  When CNG is replenished to the CNG tank 16 when the remaining amount of the CNG tank 16 is reduced due to such variation in the fuel properties of the CNG, the CNG having a different property (composition) from that of the CNG tank 16 is May be supplied.

Of the composition of CNG, particularly CO ₂ is inactive, greatly affects combustion, and affects engine performance and exhaust performance. Therefore, especially after the CNG tank 16 is replenished with CNG, the fuel injection amount, the ignition timing, the EGR gas amount, etc. are combusted so that the predetermined engine performance and exhaust performance can be achieved according to the CNG CO ₂ concentration. It is necessary to correct the related engine control.

However, CNGs such as the CNG tank 16, the CNG supply passage 15, and the CNG delivery pipe 11 are high pressure, and a sensor capable of detecting the CNG component composition is attached under such a high pressure environment to detect the CNG CO ₂ concentration. It is difficult.

Therefore, the system of this embodiment, the higher the NOx concentration of the exhaust gas discharged from the internal combustion engine 1, the CO ₂ concentration which is related to the concentration of CO ₂ CNG supplied for combustion (CNG increases, exhaust NOx focusing on the concentration decreases) points, by estimating the CO ₂ concentration of the CNG from the NOx concentration in the exhaust gas, and so as to obtain a CO ₂ concentration of CNG being subjected to current combustion.

Then, by correcting the combustion control manner according to the CO ₂ concentration of the obtained CNG, aiming to suppress the engine performance and exhaust performance is degraded when supplemented with CNG to CNG tank 16.

FIG. 2 is a flowchart showing a process of correcting the combustion control according to the CNG CO ₂ concentration according to the present embodiment. The process represented by the flowchart of FIG. 2 is executed by the ECU 20 when the ignition is turned on.

When the ignition is turned on in step S101, start control and combustion control based on the fuel property data (CO ₂ concentration) of CNG used in the previous combustion control of the internal combustion engine 1 is performed in step S102. That is, here, starting control and combustion control are started on the assumption that the CNG tank 16 is not replenished between the time when the operation of the internal combustion engine 1 is stopped and the time when the current ignition is turned on. To do.

  In step S103, the ECU 20 determines whether or not CNG is replenished to the CNG tank 16. Here, the detection value obtained by the pressure sensor 25 is acquired and compared with the detection value of the pressure sensor 25 immediately before the previous operation of the internal combustion engine 1 is stopped. When it is high, it is determined that CNG is supplied to the CNG tank 16.

  In this case, the pressure sensor 25 functions as the “pressure detection means” of the present invention, and the ECU 20 that executes the above determination processing based on the detection value by the pressure sensor 25 functions as the “replenishment detection means” of the present invention. ing. If it is determined in step S103 that CNG is replenished to the CNG tank 16, the ECU 20 proceeds to step S104.

  On the other hand, if it is determined that the CNG tank 16 is not replenished with CNG, the ECU 20 proceeds to step S111 and performs fuel injection control based on the fuel injection amount, ignition timing, and EGR gas amount used in the previous operation of the internal combustion engine 1. The ignition control and the EGR control are executed.

  In step S104, the ECU 20 determines whether fuel corresponding to the dead volume has been consumed. Here, the dead volume is the volume of the CNG supply passage 15 and the CNG delivery pipe 11.

  When the internal combustion engine 1 is started, first, CNG remaining in the CNG supply passage 15 and the CNG delivery pipe 11 when the operation of the internal combustion engine 1 was stopped last time is injected by the CNG injector 9. Even when another fuel property CNG is replenished to the CNG tank 16, the CNG used for actual combustion is changed to this new CNG after all the remaining CNG in the dead volume has been injected. .

As described above, in the system of the present embodiment, the CNG CO ₂ concentration is estimated based on the NOx concentration of the exhaust gas. Therefore, in order to accurately estimate the CNG CO ₂ concentration newly supplied to the CNG tank 16, It is desirable to be based on the NOx concentration of the combustion exhaust after the CNG used up to the previous time remaining in the dead volume is consumed.

Therefore, in this control, until the fuel corresponding to the dead volume is consumed, the subsequent NOx concentration detection and CNG CO ₂ concentration estimation processing based on the NOx concentration is not advanced. Whether or not fuel for the dead volume has been consumed can be determined based on the volume of the dead volume, the integrated value of the fuel injection amount after startup, the elapsed time after startup, and the like.

  If it is determined in step S104 that fuel for the dead volume has been consumed, the ECU 20 proceeds to step S105. The ECU 20 that executes the process of step S104 functions as the “determination unit” of the present invention.

In step S105, the ECU 20 determines whether or not the internal combustion engine 1 is in a steady operation state. In order to perform a more stable based on the NOx concentration in the exhaust gas CNG of CO ₂ concentration estimated in the combustion state, in this control, until the internal combustion engine 1 is a steady operating state, based on the NOx concentration detected and NOx concentration after The processing of CNG CO ₂ concentration estimation is not advanced.

  If it is determined in step S105 that the internal combustion engine 1 is in a steady operation state, the ECU 20 proceeds to step S106.

In step S106, the ECU 20 stops the recirculation of the EGR gas. That is, the EGR valve 29 is closed. As a result, the main inert component contained in the mixed gas used for combustion is derived from CNG, and the inert component derived from EGR gas is not included. Therefore, the CNG CO ₂ concentration is estimated with higher accuracy. It becomes possible.

  In step S107, the ECU 20 detects the NOx concentration, the air amount, and the rotational speed of the exhaust. The NOx concentration of the exhaust is acquired based on the value detected by the NOx sensor 31. The amount of air is acquired based on the value detected by the air flow meter 22. The number of revolutions is acquired based on the value detected by the crank angle sensor 28.

  In step S108, the ECU 20 acquires the NOx concentration of the exhaust when the standard fuel is used under the same operating condition as the current operating condition of the internal combustion engine 1. The same operating conditions as the current operating conditions of the internal combustion engine 1 are operating conditions specified by the air amount and the rotational speed detected in step S107.

“When standard fuel is used” is when CNG not containing CO ₂ is used as gas fuel. For various operating conditions (air amount and rotational speed), the exhaust NOx concentration when standard fuel is used is previously determined by experiments and stored in the ECU 20 as a two-dimensional map of the air amount and rotational speed. .

  Then, this two-dimensional map is searched based on the air amount and the rotational speed acquired in step S107, and if necessary, interpolation processing is performed to obtain the exhaust NOx concentration when standard fuel is used under the same operating conditions as the present. calculate.

In step S109, the ECU ₂₀ estimates the CO2 concentration of CNG currently used based on the NOx concentration of the exhaust detected in step S107. Here, the relationship between the difference in exhaust NOx concentration compared to the case where standard fuel is used and the CO ₂ concentration of CNG is obtained for each lattice point of the two-dimensional map of the air amount and the number of revolutions as a one-dimensional map. It memorize | stores in ECU20.

Then, the difference between the NOx concentration of the exhaust gas acquired in step S107 and the NOx concentration of the exhaust gas when using the standard fuel under the same operating conditions acquired in step S108 is obtained, and the difference between the exhaust gas NOx concentration and the step Based on the air amount and the rotation speed detected in S107, the two-dimensional map and the one-dimensional map are searched, and if necessary, interpolation processing is performed to calculate the CO ₂ concentration of CNG currently used. . The ECU 20 that executes the process of step S109 functions as the “CO ₂ concentration estimating means” of the present invention.

In step S110, the ECU ₂₀ corrects the control amount of the combustion control of the internal combustion engine 1 based on the CNG CO ₂ concentration estimated in step S109. Here, the fuel injection amount, the ignition timing, and the EGR gas amount are corrected based on the CO ₂ concentration of CNG.

Examples of correction are shown in FIGS. FIG. 3 is a diagram showing the relationship between CNG CO ₂ concentration and fuel injection amount. As shown in FIG. 3, the higher the CNG CO ₂ concentration, the more the fuel injection amount is corrected. Thus, even when the higher is the CO ₂ concentration of CNG, for the fuel injection amount is increased, it is possible to suppress the combustion becomes unstable.

Figure 4 is a diagram showing the relationship between the CO ₂ concentration and the ignition timing advance amount of CNG. As shown in FIG. 4, the higher the CNG CO ₂ concentration is, the more the ignition timing is advanced. Thus, even when the higher is the CO ₂ concentration of the CNG, since the ignition timing is advanced, it is possible to suppress the combustion becomes unstable.

FIG. 5 is a diagram showing the relationship between the CO ₂ concentration of CNG and the amount of EGR gas. As shown in FIG. 5, correction is performed to decrease the EGR gas amount as the CNG CO ₂ concentration increases. Since EGR gas contains many inert components, the concentration of inert components in the air-fuel mixture used for combustion can be maintained at the target value by decreasing the amount of EGR gas as the CO ₂ concentration of CNG increases. .

  The ECU 20 that executes the process of step S110 functions as the “correction unit” of the present invention.

  In step S111, the ECU 20 executes engine control based on the control amount corrected in step S110. That is, the fuel injection control of the CNG injector 9 is executed based on the fuel injection amount corrected in step S110, the ignition control of the spark plug 3 is executed based on the ignition timing corrected in step S110, and the EGR corrected in step S110. The opening degree control of the EGR valve 29 is executed based on the gas amount. The ECU 20 that executes the process of step S111 functions as the “control unit” of the present invention.

By executing the processing described above, even when CNG having a different CO ₂ concentration is supplied to the CNG tank 16, combustion control according to the CO ₂ concentration of the supplied CNG can be executed. And a reduction in exhaust performance can be suppressed.

The above embodiment has an exhaust NOx concentration map when CNG not containing CO ₂ is used as a standard fuel, and an example of calculating a difference in exhaust NOx concentration compared to the case where standard fuel is used based on this map. As described above, the standard fuel may be CNG containing CO _{2 and} having a known CO ₂ concentration.

In that case, the NOx concentration of the exhaust when the CNG having the known CO ₂ concentration is used is obtained for each operating condition, and the difference in the exhaust NOx concentration between the case where the CNG is used and the case where the focused CNG is used is determined. When, it suffices obtained relation between the CO ₂ concentration of the focused CNG.

  Further, in the above embodiment, the internal combustion engine 1 is in a steady operation state and in a state where the recirculation of the EGR gas is stopped so that the exhaust NOx concentration when using the current CNG can be detected with higher accuracy. Although the example of detecting the NOx concentration in the exhaust gas has been described, it may be added as a condition that the internal combustion engine 1 has been warmed up.

  Thereby, more accurate and stable detection can be performed. The EGR device is not an essential component as an embodiment of the present invention. When the present invention is applied to a system that does not include an EGR device, the process of step S106 is not necessary.

  In the above embodiment, the present invention is applied to a bi-fuel engine that can be operated using both CNG and gasoline. However, the present invention can also be applied to a bi-fuel engine based on a diesel engine.

  The present invention can also be applied to a gas fuel engine using only CNG. In this case, the CNG may be a port injection type as in the present embodiment or an in-cylinder direct injection type. The gas fuel is not limited to CNG but can be applied to an engine using biogas.

In the above embodiment, the CNG CO ₂ concentration is estimated only when it is detected that the CNG tank 16 has been replenished, and the combustion control correction based on this is explained. correction may be performed for ignition-on or periodically estimate of the CO ₂ concentration of CNG and combustion control based on it irrespective of whether or not made. Even if the CO ₂ concentration of the CNG is changed for some reason other than the supply of CNG in doing so, it is possible to suppress the deterioration of combustion.

DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Cylinder 3 ... Spark plug 4 ... Intake manifold 5 ... Exhaust manifold 6 ... Intake passage 7 ... Exhaust passage 8 ... Gasoline injector 9 ... CNG injector 10 .. gasoline delivery pipe 11 .. CNG delivery pipe 12 .. gasoline supply passage 13 .. gasoline tank 14 .. feed pump 15 .. CNG supply passage 16 .. CNG tank 17 .. regulator 18. Air cleaner 19 ・ Throttle valve 20 ・ ・ ECU
21 .. Exhaust purification catalyst 22 .. Air flow meter 23 .. Pressure sensor 24 .. Temperature sensor 25 .. Pressure sensor 26 .. Temperature sensor 27 .. A / F sensor 28 .. Crank angle sensor 29-EGR valve 30・ ・ EGR passage 31 ・ ・ NOx sensor

Claims (10)

A control device for an internal combustion engine operated by gas fuel,
NOx concentration detecting means for detecting the NOx concentration of the exhaust gas of the internal combustion engine;
And CO ₂ concentration estimation means for estimating the CO ₂ concentration of the gas fuel based on the NOx concentration detected by the NOx concentration detection means,
And correcting means for correcting the control amount of the internal combustion engine based on the CO ₂ concentration estimated by the CO ₂ concentration estimation means,
Control means for controlling the internal combustion engine based on the control amount corrected by the correction means ,
The control amount of the internal combustion engine is an injection amount of gas fuel,
The control unit for an internal combustion engine, wherein the correction unit performs correction to increase the injection amount as the CO ₂ concentration estimated by the CO ₂ concentration estimation unit increases . A control device for an internal combustion engine operated by gas fuel,
NOx concentration detecting means for detecting the NOx concentration of the exhaust gas of the internal combustion engine;
And CO ₂ concentration estimation means for estimating the CO ₂ concentration of the gas fuel based on the NOx concentration detected by the NOx concentration detection means,
And correcting means for correcting the control amount of the internal combustion engine based on the CO ₂ concentration estimated by the CO ₂ concentration estimation means,
Control means for controlling the internal combustion engine based on the control amount corrected by the correction means ,
The internal combustion engine is a spark ignition type internal combustion engine in which an air-fuel mixture including gas fuel in a cylinder is ignited by an ignition means and burned.
The control amount of the internal combustion engine is an ignition timing by the ignition means,
The control device for an internal combustion engine, wherein the correction means performs correction to advance the ignition timing as the CO ₂ concentration estimated by the CO ₂ concentration estimation means increases . A control device for an internal combustion engine operated by gas fuel,
NOx concentration detecting means for detecting the NOx concentration of the exhaust gas of the internal combustion engine;
And CO ₂ concentration estimation means for estimating the CO ₂ concentration of the gas fuel based on the NOx concentration detected by the NOx concentration detection means,
And correcting means for correcting the control amount of the internal combustion engine based on the CO ₂ concentration estimated by the CO ₂ concentration estimation means,
Control means for controlling the internal combustion engine based on the control amount corrected by the correction means;
An EGR device that recirculates part of the exhaust gas of the internal combustion engine as EGR gas to the intake system of the internal combustion engine;
With
The control amount of the internal combustion engine is the amount of EGR gas recirculated to the intake system by the EGR device,
The control device for an internal combustion engine, wherein the correction means performs correction to reduce the amount of EGR gas as the CO ₂ concentration estimated by the CO ₂ concentration estimation means increases . In any one of Claim 1 to 3 ,
The CO ₂ concentration estimating means estimates the CO ₂ concentration of gas fuel based on the NOx concentration detected by the NOx concentration detecting means when the internal combustion engine is in a steady operation state. Control device. In any one of Claims 1-4 ,
The CO ₂ concentration estimating means, and estimates the concentration of CO ₂ gas fuel based on the NOx concentration detected by the NOx concentration detection means when the a state in which the warm-up is completed the internal combustion engine Control device for internal combustion engine. In any one of Claim 1 to 5 ,
An EGR device that recirculates a part of the exhaust gas of the internal combustion engine as EGR gas to the intake system of the internal combustion engine;
The CO ₂ concentration estimation means stops the recirculation of EGR gas by the EGR device, and the CO _{2 of the} gas fuel is based on the NOx concentration detected by the NOx concentration detection means in a state where the EGR gas is not recirculated. A control device for an internal combustion engine characterized by estimating a concentration. In any one of Claim 1 to 6 ,
An exhaust gas purification device provided in an exhaust passage of the internal combustion engine for purifying harmful substances in the exhaust gas,
The control device for an internal combustion engine, wherein the NOx concentration detection means detects the NOx concentration of exhaust gas upstream of the exhaust gas purification device. In any one of claims 1 to 7,
Comprising replenishment detection means for detecting that gas fuel is replenished in the storage means for storing the gas fuel;
The control device for an internal combustion engine, wherein the correction means corrects a control amount of the internal combustion engine when the supply of gas fuel is detected by the supply detection means. In claim 8 ,
Pressure detecting means for detecting the pressure of the gas fuel in the storage means or the pressure of the gas fuel in the gas fuel supply path for supplying the gas fuel from the storage means to the fuel injection valve;
The control device for an internal combustion engine, wherein the replenishment detecting means detects replenishment of gaseous fuel based on a change in pressure detected by the pressure detecting means. In claim 8 or 9 ,
After the replenishment detecting means detects the replenishment of the gas fuel, is the gas fuel before the replenishment remaining in the gas fuel supply path for supplying the gas fuel from the storage means to the fuel injection valve consumed? Determination means for determining whether or not,
The correction means corrects the control amount of the internal combustion engine after the determination means determines that the gas fuel before replenishment has been consumed when the replenishment detection means detects the replenishment of the gas fuel. A control device for an internal combustion engine.

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