WO2012147184A1

WO2012147184A1 - Internal combustion engine control system

Info

Publication number: WO2012147184A1
Application number: PCT/JP2011/060304
Authority: WO
Inventors: 裕介中山; 徹木所; 櫻井　健治; 裕澤田
Original assignee: トヨタ自動車株式会社
Priority date: 2011-04-27
Filing date: 2011-04-27
Publication date: 2012-11-01

Abstract

In a control system for an internal combustion engine capable of using multiple types of fuel, this invention purports to reduce exhaust gas emissions by effectively utilizing the NO_X adsorption capacity of a three-way catalyst arranged in the exhaust gas system. To that end, when the temperature of the three-way catalyst arranged in the exhaust gas system is below the activation temperature and the internal combustion engine is operating on a gas fuel, this internal combustion engine control system raises the air-fuel ratio of the exhaust gas as much as possible within the range in which the amount of NO_X flowing from the three-way catalyst decreases.

Description

Internal combustion engine control system

The present invention relates to a control technique for an internal combustion engine that can use a plurality of types of fuel.

In recent years, an internal combustion engine that can be operated with a plurality of types of fuels has been proposed. In such an internal combustion engine, when performing NO _X reduction process storage reduction NO _X catalyst arranged in an exhaust system of the internal combustion engine has also been proposed a technique of using a liquid fuel (for example, Patent Documents 1).

JP 2004-239132 A

By the way, there is a case where exhaust gas emission is reduced by arranging a three-way catalyst in the exhaust system of the internal combustion engine and adsorbing NO _X contained in the exhaust gas to the three-way catalyst when the internal combustion engine is cold.

The invention, and purpose in the control system of the available internal combustion engine a plurality of types of fuel, that reduced exhaust emissions by effectively using the NO _X adsorbing capacity of the three-way catalyst disposed in an exhaust system To do.

In order to solve the above-described problems, the present invention provides a control system for an internal combustion engine that can use liquid fuel and gaseous fuel, in which a three-way catalyst disposed in an exhaust system can adsorb nitrogen oxides in the exhaust. when in, the three-way catalyst has focused on matters of varying _the amount of NO _X that can be adsorbed in accordance with the air-fuel ratio of the exhaust gas flowing into the three-way catalyst.

When the internal combustion engine is operated with gaseous fuel, the nitrogen oxide (NO _x ) in the exhaust gas is more easily adsorbed by the three-way catalyst than when the internal combustion engine is operated with liquid fuel. Further, when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is made lean when the internal combustion engine is operated by the gaseous fuel, compared to the case where the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is stoichiometric, _the amount of NO _X adsorbed in the three-way catalyst increases.

Then, the control system of the internal combustion engine of the present invention is
A supply device for supplying one of liquid fuel and gaseous fuel to the internal combustion engine;
An adjustment unit for adjusting the air-fuel ratio of the exhaust gas flowing into the three-way catalyst disposed in the exhaust system of the internal combustion engine;
A control unit that controls the adjustment unit so that the air-fuel ratio of the exhaust gas flowing into the three-way catalyst becomes lean when the supply device supplies gaseous fuel to the internal combustion engine;
I was prepared to.

According to the control system for an internal combustion engine configured as described above, the amount of NO _x adsorbed on the three-way catalyst can be increased. That is, it is possible to effectively utilize the NO _X adsorbing capacity of the three-way catalyst. As a result, it is possible to reduce the amount of NO _X discharged into the atmosphere.

Here, the amount of NO _{X that} can be adsorbed by the three-way catalyst (hereinafter referred to as “NO _X adsorption capacity”) increases when the temperature of the three-way catalyst is in a temperature range lower than the activation temperature. Therefore, the control system for an internal combustion engine of the present invention makes the air-fuel ratio of the exhaust gas flowing into the three-way catalyst lean even when the three-way catalyst is in an inactive state and the internal combustion engine is operated with gaseous fuel. Good.

For example, the control system for an internal combustion engine of the present invention may further include a temperature acquisition unit that acquires the temperature of the three-way catalyst. In this case, the control unit supplies the empty exhaust gas flowing into the three-way catalyst when the supply device supplies the gaseous fuel to the internal combustion engine and the temperature acquired by the temperature acquisition unit is lower than the activation temperature of the three-way catalyst. The adjustment unit may be controlled so that the fuel ratio becomes lean. According to such a configuration, when the three-way catalyst is in a non-activated state, it is possible to reduce the amount of the NO _X discharged into the atmosphere.

As a method for making the air-fuel ratio of the exhaust gas flowing into the three-way catalyst lean, a method for making the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine lean may be used. That is, the adjustment unit may adjust the amount of gaseous fuel supplied from the supply device to the internal combustion engine so that the air-fuel ratio of the air-fuel mixture becomes lean. When the air-fuel ratio of the mixture is made lean, the air-fuel ratio of the exhaust flowing into the three-way catalyst becomes lean, and the amount of hydrocarbon (HC) and carbon monoxide (CO) discharged from the internal combustion engine decreases. To do. As a result, in addition to the reduction of the NO _X amount exhausted to the atmosphere, it is possible to also reduce the hydrocarbons discharged into the atmosphere (HC) and carbon monoxide (CO).

When the air-fuel ratio of the air-fuel mixture becomes lean, the amount of NO _X discharged from the internal combustion engine (hereinafter referred to as “NO _X emission amount”) is larger than when the air-fuel ratio of the air-fuel mixture becomes stoichiometric. Become. Therefore, when the lean degree of the air-fuel mixture is inadvertently increased, as compared with the increase of the NO _X adsorbing capacity of the three-way catalyst, increase of the NO _X emissions is also possible to increase.

Therefore, when the air-fuel ratio of the mixture lean may be to enhance the air-fuel ratio of the mixture within the range increment of the NO _X emissions relative increase of the NO _X adsorbing capacity does not exceed.

For example, the control system of an internal combustion engine according to the present invention may further comprise a amount of NO _X acquisition unit that acquires _the amount of NO _X flowing out from the three-way catalyst. In that case, the control unit, the air-fuel ratio of the mixture is continuously or stepwise increased, is acquired by _the amount of NO _X acquisition unit when the amount of NO _X acquired by the amount of NO _X acquisition unit indicates decreasing trend When the NO _X amount shows an increasing tendency, the adjustment unit may be controlled so that the air-fuel ratio of the air-fuel mixture decreases to a specified air-fuel ratio. The “specified air-fuel ratio” referred to here is an air-fuel ratio suitable for achieving early activation of the three-way catalyst, for example, stoichiometry.

According to such a configuration, the air-fuel ratio of the air-fuel mixture is gradually increased (leanized) in a range in which the amount of NO _X flowing out from the three-way catalyst decreases. As a result, the amount of NO _X flowing out from the three-way catalyst can be reduced as much as possible. Further, when the air-fuel ratio of the air-fuel mixture is increased as much as possible within a range in which the amount of NO _X flowing out from the three-way catalyst is reduced, the amount of gaseous fuel consumed can be further reduced and exhausted from the internal combustion engine. Hydrocarbon (HC) and carbon monoxide (CO) can be further reduced.

In addition, when the three-way catalyst is in an inactive state, the temperature of the internal combustion engine may be lowered. If the air-fuel mixture is made lean when the temperature of the internal combustion engine is low, there is a concern that the combustion stability of the internal combustion engine is impaired and torque fluctuations increase. However, when the internal combustion engine is operated with gaseous fuel, the deterioration in combustion stability due to lean air-fuel mixture is less than when the internal combustion engine is operated with liquid fuel. Therefore, it is possible to reduce exhaust emissions and gas fuel consumption while suppressing torque fluctuations of the internal combustion engine.

The three-way catalyst according to the present invention may include a first three-way catalyst and a second three-way catalyst arranged in series in the exhaust flow direction. In this case, the adjustment unit may include a secondary air supply device that supplies secondary air to the exhaust passage downstream from the first three-way catalyst and upstream from the second three-way catalyst. In such a configuration, when the internal combustion engine is operated using gaseous fuel, the control unit supplies secondary air to the exhaust passage downstream from the first three-way catalyst and upstream from the second three-way catalyst. The adjustment unit may be controlled as described above.

When secondary air is supplied to the exhaust passage downstream from the first three-way catalyst and upstream from the second three-way catalyst, the air-fuel ratio of the mixture is changed to an air-fuel ratio suitable for early activation of the first three-way catalyst (for example, The air-fuel ratio of the exhaust gas flowing into the second three-way catalyst can be made lean while maintaining the stoichiometry. As a result, while achieving early activation of the first three-way catalyst, it is possible to increase the NO _X adsorbing capacity of the second three-way catalyst. Therefore, exhaust emission can be further reduced.

Since the temperature of the secondary air is lower than that of the exhaust, if the supply amount of the secondary air is inadvertently increased, the temperature increase rate of the second three-way catalyst decreases. As a result, the activation time of the second three-way catalyst may be excessively delayed. When the activation time of the second three-way catalyst is delayed, there is a possibility that the amount of NO _X that is not adsorbed or purified by the second three-way catalyst increases.

In contrast, the control system for an internal combustion engine of the present invention increases the amount of secondary air (exhaust gas flowing into the second three-way catalyst) within a range in which the NO _X amount flowing out from the second three-way catalyst shows a decreasing tendency. May be made lean).

For example, the control system of an internal combustion engine according to the present invention may further comprise a amount of NO _X acquisition unit that acquires _the amount of NO _X flowing out from the second three-way catalyst. In that case, the control unit, NO when _the amount of NO _X obtained by _X amount obtaining section indicates decreasing trend increased secondary air is continuously or stepwise, NO is obtained by _the amount of NO _X acquisition unit _X When the amount shows an increasing tendency, the adjustment unit may be controlled so that the supply of secondary air is stopped.

According to such a configuration, the amount of secondary air is gradually increased in a range in which the amount of NO _X flowing out from the second three-way catalyst decreases. Therefore, it is possible to reduce the NO _X amount flowing out from the second three-way catalyst as much as possible while avoiding a situation where the activation timing of the second three-way catalyst is excessively delayed.

According to the present invention, in the control system for an internal combustion engine that can use liquid and gaseous fuels, by effectively using the NO _X adsorbing capacity of the three-way catalyst, it is possible to reduce exhaust emission.

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied in a first embodiment. It is a diagram showing a relationship between the NO _X adsorbing capacity of the air-fuel ratio and a three-way catalyst of the exhaust gas flowing into the three-way catalyst. It is a figure which shows the relationship between the air fuel ratio of an air-fuel | gaseous mixture, and the magnitude | size of a torque fluctuation. Is a flowchart illustrating the NO _X adsorption treatment routine in the first embodiment. It is a figure which shows schematic structure of the internal combustion engine to which this invention is applied in a 2nd Example. It is a diagram showing a relationship between the NO _X adsorbing capacity of the temperature and the three-way catalyst of the three-way catalyst. Is a flowchart illustrating the NO _X adsorption treatment routine in the second embodiment.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. 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.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a spark ignition internal combustion engine that can use liquid fuel and gaseous fuel. The “liquid fuel” used herein may be a non-methane hydrocarbon fuel such as a petroleum liquid fuel such as gasoline or a mixed liquid fuel in which ethanol or methanol is mixed with a petroleum liquid fuel. Further, as the “gaseous fuel”, compressed natural gas (CNG) can be used.

The piston 3 is slidably loaded in the cylinder 2 of the internal combustion engine 1. The piston 3 is connected to an engine output shaft (crankshaft) via a connecting rod (not shown). The internal combustion engine 1 includes an intake port 4 for introducing fresh air (air) into the cylinder 2 and an exhaust port 5 for discharging burned gas from the cylinder 2. The internal combustion engine 1 includes an intake valve 6 for opening and closing the opening end of the intake port 4 and an exhaust valve 7 for opening and closing the opening end of the exhaust port 5. The intake valve 6 and the exhaust valve 7 are driven to open and close by an intake cam shaft and an exhaust cam shaft (not shown), respectively. Further, the internal combustion engine 1 includes a spark plug 8 for generating a spark as a fire type in the cylinder 2.

An intake passage 9 is connected to the intake port 4. The intake passage 9 is a passage for guiding fresh air (air) taken from the atmosphere to the intake port 4. On the other hand, an exhaust passage 10 is connected to the exhaust port 5. The exhaust passage 10 is a passage for discharging burned gas (exhaust gas) flowing out from the exhaust port 5 to the atmosphere after passing through

exhaust purification devices

15 and 16 described later.

Here, the internal combustion engine 1 is provided with a supply device for selectively supplying liquid fuel and gaseous fuel to the internal combustion engine 1. The supply device includes a first fuel injection valve 11, a first fuel passage 110, a first fuel tank 111, a fuel pump 112, a first cutoff valve 113, a second fuel injection valve 12, and a second fuel passage. 120, a second fuel tank (CNG cylinder) 121, a regulator 122, and a second shut-off valve 123. The first fuel injection valve 11 and the second fuel injection valve 12 are provided for each cylinder.

The first fuel injection valve 11 is attached in the vicinity of the intake port 4 in the internal combustion engine 1 and injects liquid fuel into the intake port 4. The first fuel injection valve 11 communicates with the first fuel tank 111 via the first fuel passage 110. A fuel pump 112 and a first shut-off valve 113 are disposed in the middle of the first fuel passage 110. The fuel pump 112 supplies the liquid fuel stored in the first fuel tank 111 to the first fuel injection valve 11. The first cutoff valve 113 is a device that switches between cutoff and conduction of the first fuel passage 110.

The second fuel injection valve 12 is attached to the intake passage 9 in the vicinity of the intake port 4 and injects gaseous fuel into the intake passage 9. The second fuel injection valve 12 communicates with the second fuel tank 121 via the second fuel passage 120. A regulator 122 and a second shut-off valve 123 are disposed in the middle of the second fuel passage 120. The regulator 122 is a device that depressurizes compressed natural gas (CNG) to a predetermined pressure. The second shutoff valve 123 is a device that switches between shutoff and conduction of the second fuel passage 120. The second fuel tank 121 is provided with a remaining amount sensor 124 that outputs an electrical signal correlated with the amount of gaseous fuel stored in the second fuel tank 121.

Next, a throttle valve 13 is disposed in the intake passage 9 upstream of the second fuel injection valve 12. The throttle valve 13 is a device that adjusts the amount of air introduced into the cylinder 2 by changing the passage cross-sectional area of the intake passage 9. An air flow meter 14 is attached to the intake passage 9 upstream of the throttle valve 13. The air flow meter 14 is a sensor that outputs an electrical signal correlated with the amount of air (mass) flowing through the intake passage 9.

A first exhaust purification device 15 is disposed in the exhaust passage 10. The first exhaust purification device 15 contains a three-way catalyst capable of adsorbing nitrogen oxide (NO _x ) in the exhaust when in a low temperature state. The first exhaust purification device 15 corresponds to a first three-way catalyst according to the present invention.

A second exhaust purification device 16 is disposed in the exhaust passage 10 downstream of the first exhaust purification device 15. Similar to the first exhaust purification device 15, the second exhaust purification device 16 contains a three-way catalyst capable of adsorbing nitrogen oxide (NO _X ) in the exhaust. The second exhaust purification device 16 corresponds to a second three-way catalyst according to the present invention.

An air-fuel ratio sensor 17 is disposed in the exhaust passage 10 upstream of the first exhaust purification device 15. The air-fuel ratio sensor 17 is a sensor that outputs an electrical signal correlated with the air-fuel ratio of the exhaust gas flowing through the exhaust passage 10. The first downstream exhaust gas purification device 15, and the second exhaust gas purification unit upstream exhaust passage 10 than 16, NO _X sensor 21 is arranged. The NO _X sensor 21 is a sensor that outputs an electrical signal correlated with the concentration of nitrogen oxide (NO _X ) contained in the exhaust gas flowing out from the first exhaust purification device 15. The NO _X sensor 21 corresponds to the NO _X amount acquisition unit according to the present invention. An O ₂ sensor 18 and an exhaust temperature sensor 19 are disposed in the exhaust passage 10 downstream from the second exhaust purification device 16. The O ₂ sensor 18 is a sensor that outputs an electrical signal correlated with the concentration of oxygen (O ₂ ) contained in the exhaust gas. The exhaust temperature sensor 19 is a sensor that outputs an electrical signal correlated with the exhaust temperature.

The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20. The ECU 20 is electrically connected to various sensors such as the air flow meter 14, the air-fuel ratio sensor 17, the O ₂ sensor 18, the exhaust temperature sensor 19, the NO _X sensor 21, and the remaining amount sensor 124, and output signals from the various sensors. Is configured to allow input.

Further, the ECU 20 is electrically connected to various devices such as the ignition plug 8, the first fuel injection valve 11, the second fuel injection valve 12, the throttle valve 13, the fuel pump 112, the first cutoff valve 113, and the second cutoff valve 123. Connected to each other, and various devices can be controlled in accordance with the output signals of the various sensors described above.

For example, ECU 20, when the first exhaust gas purification device 15 can not sufficiently purify the NO _X in the exhaust gas (for example, when the first exhaust gas purification device 15 is not active), the NO _X in the exhaust gas A process for causing the first exhaust purification device 15 to perform adsorption (hereinafter referred to as “NO _X adsorption process”) is executed. Hereinafter, we describe how to perform of the NO _X adsorption process in this embodiment.

Three-way catalyst contained in the first exhaust gas purification device 15, when it is lower than the activation temperature cold state, adsorbs NO _X in the exhaust gas. Therefore, as in the case where the internal combustion engine 1 is cold-started, when the first exhaust gas purification device 15 is in the deactivated state, by adsorbing the NO _X in the exhaust gas to the first exhaust gas purification device 15, air it can be suppressed to reduce the NO _X amount exhausted during.

However, if it contains a non-methane hydrocarbon in the exhaust gas, the non-methane hydrocarbons are adsorbed to the first exhaust gas purification device 15 in preference to NO _X. Therefore, when the amount of non-methane hydrocarbons contained in the exhaust gas increases when the first exhaust gas purification device 15 is in a low temperature state, the amount of NO _x adsorbed by the first exhaust gas purification device 15 decreases. As a result, the greater the amount of NO _X discharged into the atmosphere.

Here, the burned gas of the liquid fuel (non-methane hydrocarbon fuel) contains a larger amount of non-methane hydrocarbon than the burned gas of the gaseous fuel (compressed natural gas (CNG)). Therefore, when the internal combustion engine 1 is operated with liquid fuel while the first exhaust purification device 15 is in an inactive state, the amount of NO _{X that} can be adsorbed by the first exhaust purification device 15 (NO _X adsorption capacity) decreases. . As a result, there is a possibility that it is impossible to sufficiently reduce the amount of NO _X discharged into the atmosphere.

In contrast, when the internal combustion engine 1 when the first exhaust gas purification device 15 is in the deactivated state is operated by a gaseous fuel, it is possible to increase the NO _X adsorbing capacity of the first exhaust gas purification device 15. Therefore, it is possible to suppress decrease the amount of NO _X discharged into the atmosphere. Further, the NO _X adsorbing capacity of the three-way catalyst when the internal combustion engine 1 is being operated by a gaseous fuel, as shown in FIG. 2, when the air-fuel ratio of the exhaust gas flowing into the first exhaust gas purification device 15 is stoichiometric More when you are leaner. Furthermore, NO _X adsorbing capacity of the three-way catalyst, there are many tends towards is higher than when low degree of leanness of the exhaust.

Therefore, in the NO _X adsorption process in the present embodiment, the ECU 20 operates the internal combustion engine 1 with the gaseous fuel when the temperature of the first exhaust purification device 15 is low, and the air-fuel mixture burned in the internal combustion engine 1 is empty. The fuel ratio was made leaner than stoichiometric.

Meanwhile, if the air-fuel ratio of the mixture is lean as compared with the case where the air-fuel ratio of the mixture is in stoichiometric, NO _X amount exhausted from the internal combustion engine 1 (NO _X emissions) is increased. Therefore, when the air-fuel ratio of the mixture is excessively high (the degree of leanness of the mixture is excessively high), the possibility of NO _X emissions increase compared to increase of the NO _X adsorbing capacity increases There is also. In that case, the NO _X adsorption ability of the first exhaust purification device 15 is saturated, and the amount of NO _X discharged into the atmosphere may increase instead.

On the other hand, when the NO _X amount (output value of the NO _X sensor 21) discharged from the first exhaust purification device 15 shows a decreasing tendency, the ECU 20 gradually increases the air-fuel ratio of the air-fuel mixture, and the first exhaust purification. When the amount of NO _X discharged from the device 15 shows an increasing tendency, the air-fuel ratio of the air-fuel mixture is reduced to a specified air-fuel ratio.

Specifically, ECU 20 when the output value of the NO _X sensor 21 per unit time indicates the decreasing tendency enhances the air-fuel ratio of the mixture to a predetermined amount, output value increase of the NO _X sensor 21 per unit time When the air-fuel ratio is indicated, the air-fuel ratio of the air-fuel mixture is lowered to the specified air-fuel ratio. The “specified air-fuel ratio” here is an air-fuel ratio suitable for early activation of the first exhaust purification device 15, for example, stoichiometric (theoretical air-fuel ratio).

When the air-fuel ratio of the mixture is controlled such, so that the air-fuel ratio of the mixture to the extent that _the amount of NO _X discharged from the first exhaust gas purification device 15 is decreased it is increased as much as possible. That is, increase of the NO _X adsorbing capacity is larger than the increase of the NO _X emissions, and the difference air-fuel ratio of the mixture to the extent that an enlarged tendency of both is as much as possible increased is that. As a result, it is possible to reduce the amount of NO _X discharged from the first exhaust gas purification device 15 as much as possible.

Further, when the air-fuel ratio of the air-fuel mixture is increased as much as possible within the range in which the amount of NO _X discharged from the first exhaust purification device 15 decreases, the consumption of gaseous fuel can be reduced and the internal combustion engine 1 It is also possible to reduce the amount of hydrocarbon (HC) and carbon monoxide (CO) discharged from the plant.

If the air-fuel ratio of the air-fuel mixture is increased when the internal combustion engine 1 is in a cold state, there is a concern that the combustion stability of the internal combustion engine 1 is impaired and torque fluctuations increase. However, as shown in FIG. 3, when the internal combustion engine 1 is operated with gaseous fuel (solid line in FIG. 3), the internal combustion engine 1 is operated with liquid fuel (broken line in FIG. 3). In comparison, the increase in torque fluctuation due to lean air-fuel mixture becomes smaller. Therefore, even if the air-fuel mixture is made lean when the internal combustion engine 1 is operated with gaseous fuel, an increase in torque fluctuation can be suppressed to a low level.

Hereinafter, the execution procedure of the NO _X adsorption process in the present embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing a NO _X adsorption processing routine. The NO _X adsorption processing routine is a routine stored in advance in the ROM of the ECU 20 or the like, and is periodically executed by the ECU 20.

In the NO _X adsorption processing routine of FIG. 4, the ECU 20 first determines whether or not the NO _X adsorption condition of the first exhaust purification device 15 is satisfied in S101. For example, the ECU 20 determines whether or not the temperature of the first exhaust purification device 15 is lower than the activation temperature. Here, as the temperature of the first exhaust purification device 15, the measured value of the exhaust temperature sensor 19 can be used as an alternative value. In that case, the exhaust temperature sensor 19 corresponds to a temperature acquisition unit according to the present invention. When a temperature sensor is attached to the first exhaust purification device 15, the measured value of the temperature sensor may be used as the temperature of the first exhaust purification device 15.

If a negative determination is made in S101, the ECU 20 once ends the execution of this routine. In that case, the NO _X adsorption process is not executed. On the other hand, if an affirmative determination is made in S101, the ECU 20 proceeds to S102.

In S102, the ECU 20 determines whether or not the value of the NO _X adsorption flag Fnox is “0”. The NO _X adsorption flag Fnox is set to “1” when the NO _X adsorption process is started (for example, when the processes of S103 and S104 described later are executed), and when the NO _X adsorption process is completed ( For example, the flag is reset to “0” when the process of S112 described later is executed).

When the value of the NO _X adsorption flag Fnox is “0”, the NO _X adsorption process has not yet started. For this reason, when an affirmative determination is made in S102 (Fnox = 0), the ECU 20 starts NO _X adsorption processing in S103 and S104.

That is, the ECU 20 first controls the supply device so that the gaseous fuel is supplied to the internal combustion engine 1 in S103. Specifically, the ECU 20 stops the fuel pump 112 and stops the supply of liquid fuel by keeping the first shut-off valve 113 and the first fuel injection valve 11 closed. Furthermore, the ECU 20 supplies the gaseous fuel by keeping the second shut-off valve 123 open and opening / closing the second fuel injection valve 12 at an appropriate timing. In this case, the internal combustion engine 1 is operated using gaseous fuel.

Subsequently, in S104, the ECU 20 sets the target air-fuel ratio A / Ftrg of the air-fuel mixture to a default value A / Fl that is leaner than the stoichiometric value. Check default value A / Fl represents an air-fuel ratio is considered to NO _X emissions increase compared to increase of the NO _X adsorbing capacity is sufficiently small, determined by adaptation processing using an advance experiment The fuel ratio. When the target air-fuel ratio A / Ftrg is lean as the air-fuel ratio of the exhaust gas flowing into the first exhaust gas purification device 15 to become lean, NO _X adsorbing capacity of the first exhaust gas purification device 15 increases.

As NO _X adsorption conditions of the S101, when the first exhaust gas purification device 15 is less than the activation temperature, that and the internal combustion engine 1 is provided that is operated using a gaseous fuel, the S103 Processing may be omitted.

The ECU 20 proceeds to S105 after executing the processes of S103 and S104. In S105, the ECU 20 sets “1” to the above-described NO _X adsorption flag Fnox.

Further, when the ECU20 executes the processing of the S102, if the NO _X adsorption flag value of Fnox is "1", so that the NO _X adsorbing process has already started. That is, the NO _X adsorption treatment is initiated during the last previous execution of the routine. Therefore, if the negative determination is made in S102 (Fnox = 1), the ECU 20 skips the processes of S103 to S105 and proceeds to S106.

In S106, ECU 20 includes, as _the amount of NO _X discharged from the first exhaust gas purification device 15, reads the detection value Dnox of the NO _X sensor 21.

In S107, ECU 20 obtains a change amount of the detection value of the NO _X sensor 21 per unit time. Specifically, the ECU 20 subtracts the previous detection value Dnoxold (the detection value read in S106 during the previous execution of this routine) from the detection value Dnox read in S106, so that the first exhaust purification device. A change amount ΔD (= Dnox−Dnoxold) of the NO _X amount discharged from 15 is calculated.

In S108, the ECU 20 determines whether or not the change amount ΔD calculated in S107 is smaller than zero. That, ECU 20 is, NO _X amount exhausted from the first exhaust gas purification device 15, it is determined whether or not tended to decrease.

If an affirmative determination is made in S108 (ΔD <0), the ECU 20 proceeds to S109. In S109, the ECU 20 calculates a new target air-fuel ratio A / Ftrg (= A / Ftrg + ΔA) by adding a predetermined amount ΔA to the current target air-fuel ratio A / Ftrg. That is, the ECU 20 further increases (leanes) the target air-fuel ratio A / Ftrg in S109.

The ECU 20 returns to S101 after executing the process of S109. At that time, if the NO _X adsorption condition is satisfied, the ECU 20 makes a negative determination in S102 and executes the processing subsequent to S106 again. If an affirmative determination is made in S108, the ECU 20 will further make the air-fuel mixture leaner in S109. That, NO _X amount exhausted from the first exhaust gas purification device 15 so long as they exhibit the decreasing tendency, the target air-fuel ratio A / Ftrg of the mixture will be increased stepwise.

If a negative determination is made in S108 (ΔD ≧ 0), the ECU 20 proceeds to S110. In S110, the ECU 20 determines whether or not the change amount ΔD calculated in S107 is zero. Here, when the amount of change ΔD indicates zero would _the amount of NO _X discharged from the first exhaust gas purification device 15 is decreased to a minimum amount. That is, when the change amount ΔD indicates zero, the increase in the NO _X adsorption capacity is larger than the increase in the NO _X discharge amount, and the difference between the two increases to the maximum value. Therefore, when an affirmative determination is made in S110 (ΔD = 0), the ECU 20 continues to use the current target air-fuel ratio A / Ftrg.

On the other hand, if a negative determination is made in S110 (ΔD> 0), the ECU 20 proceeds to S112. Here, when the change amount ΔD is greater than zero, the NO _X adsorption capacity of the first exhaust purification device 15 is saturated due to factors such as an increase in the NO _X emission amount exceeding an increase in the NO _X adsorption capacity. Will be. Therefore, the ECU 20 ends the NO _X adsorption process in S112. Specifically, the ECU 20 sets the target air-fuel ratio A / Ftrg to the stoichiometric air-fuel ratio A / Fs so as to activate the first exhaust purification device 15 at an early stage. Note that the ECU 20 may execute a process of gradually reducing the target air-fuel ratio A / Ftrg instead of executing the process of S112.

ECU20 proceeds S113 f after executing the processing of S112, is reset to "0" to the NO _X adsorption flag Fnox.

As described above, the ECU 20 executes the NO _X adsorption processing routine of FIG. 4, thereby realizing the adjustment unit and the control unit according to the present invention. As a result, when the first exhaust purification device 15 is in an inactive state, NO _x , HC, and CO discharged to the atmosphere can be reduced without increasing torque fluctuations of the internal combustion engine 1. Furthermore, the consumption of gaseous fuel can also be reduced.

In the present embodiment, the example in which the detected value of the NO _X sensor 21 is used as a method for acquiring the NO _X amount discharged from the first exhaust purification device 15 has been described. However, the temperature of the first exhaust purification device 15 ( The estimation calculation may be performed using a calculation model using parameters such as the detection value of the exhaust temperature sensor 19) and the flow rate of the exhaust gas flowing into the first exhaust purification device 15 (the detection value of the air flow meter 14).

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

In the first embodiment described above, an example in which the NO _X adsorption capability of the first exhaust purification device 15 is increased has been described. In this embodiment, an example in which the NO _X adsorption capability of the second exhaust purification device 16 is increased will be described.

FIG. 5 is a diagram showing a schematic configuration of the internal combustion engine in the present embodiment. In FIG. 5, the same components as those in FIG. 1 of the first embodiment are denoted by the same reference numerals.

A secondary air supply device 23 is disposed in the exhaust passage 10 downstream from the first exhaust purification device 15 and upstream from the second exhaust purification device 16. The secondary air supply device 23 is a device that injects secondary air into the exhaust passage 10 and corresponds to an adjusting unit according to the present invention. In the example shown in FIG. 5, the NO _X sensor 21 is disposed in the exhaust passage 10 downstream of the second exhaust purification device 16.

In the control system for an internal combustion engine configured as described above, the ECU 20 executes the NO _X adsorption process for the second exhaust purification device 16 when the second exhaust purification device 16 is in an inactive state. Specifically, the ECU 20 causes the secondary air to be supplied from the secondary air supply device 23 to the exhaust passage upstream of the second exhaust purification device 16. At this time, the amount of secondary air supplied from the secondary air supply device 23 is determined so that the air-fuel ratio of the exhaust gas flowing into the second exhaust purification device 16 becomes lean.

If NO _X adsorption treatment is performed by the above method, it is possible to make only the air-fuel ratio of the exhaust gas flowing into the second exhaust gas purification unit 16 lean. Therefore, even if the first exhaust gas purification device 15 is NO _X adsorption treatment is executed when in the unactivated state, the air-fuel ratio of the prescribed air-fuel ratio of the exhaust gas flowing into the first exhaust gas purification device 15 (first exhaust gas purification device The air / fuel ratio can be 15).

Note that when the air-fuel ratio of the exhaust gas flowing into the first exhaust purification device 15 is set to a specified air-fuel ratio, the temperature increase rate of the first exhaust purification device 15 is higher than when the air-fuel ratio is made lean. . Here, as shown in FIG. 5, the NO _X adsorption capacity of the three-way catalyst is larger when the temperature of the three-way catalyst is lower than when the temperature is higher. Therefore, when the air-fuel ratio of the exhaust gas flowing into the first exhaust purification device 15 is set to the specified air-fuel ratio, the NO _X amount adsorbed by the first exhaust purification device 15 is increased until the first exhaust purification device 15 is activated. May be less.

Incidentally, the amount of heat received by the second exhaust purification device 16 from the exhaust is less than that of the first exhaust purification device 15. Therefore, the temperature increase rate of the second exhaust purification device 16 is lower than that of the first exhaust purification device 15. Further, when the secondary air is supplied from the secondary air supply device 23 to the exhaust passage 10 downstream from the first exhaust purification device 15 and upstream from the second exhaust purification device 16, it flows into the second exhaust purification device 16. The temperature of the gas (mixed gas of exhaust and secondary air) decreases. When the temperature of the exhaust gas flowing into the second exhaust purification device 16 is lowered, the temperature increase rate of the second exhaust purification device 16 is further reduced. Therefore, the period during which the second exhaust purification device 16 is exposed to a lean and low-temperature atmosphere becomes longer. As a result, the amount of NO _{x that} can be adsorbed by the second exhaust purification device 16 increases during the period until the first exhaust purification device 15 is activated. That is, NO _{X that} is not adsorbed and purified by the first exhaust purification device 15 is adsorbed by the second exhaust purification device 16.

Therefore, according to the NO _X adsorption process of the present embodiment, the first exhaust purification device 15 can be activated early, and the amount of NO _X discharged into the atmosphere can be reduced. As a result, it is possible to reduce exhaust emission during the period until the second exhaust purification device 16 is activated.

Note that if the supply amount of the secondary air is increased unnecessarily, the temperature increase rate of the second exhaust purification device 16 may become excessively low. In that case, together with the NO _X adsorbing capacity of the second exhaust gas purification device 16 before the second exhaust gas purification device 16 becomes active is easily saturated, NO _X adsorbing capacity of the second exhaust gas purification unit 16 is the from saturated There is a possibility that the time until the second exhaust purification device 16 is activated becomes longer. If the time until the second exhaust purification device 16 is activated after the NO _X adsorption ability of the second exhaust purification device 16 is saturated becomes longer, the amount of NO _X flowing out from the second exhaust purification device 16 (to the atmosphere) the amount of the discharged is NO _X) there is a possibility that increases.

On the other hand, the ECU 20 gradually increases the supply amount of the secondary air in a range in which the NO _X amount discharged from the second exhaust purification device 16 (the output value of the NO _X sensor 21) decreases, and the second exhaust purification. when _the amount of NO _X discharged from the apparatus 16 is shown an increasing trend is so as to stop the supply of secondary air.

Specifically, when the output value of the NO _X sensor 21 per unit time shows a decreasing tendency, the ECU 20 increases the supply amount of the secondary air by a predetermined amount, and the output value of the NO _X sensor 21 per unit time is increased. When showing an increasing trend, the supply of secondary air was stopped.

When the amount of the secondary air supply is controlled so that the supply amount of the secondary air is to be increased as much as possible to the extent that _the amount of NO _X discharged from the second exhaust gas purification unit 16 decreases . In other words, the air-fuel ratio of the exhaust gas flowing into the second exhaust gas purification device 16 is increased as much as possible within a range where the amount of NO _X flowing out from the second exhaust gas purification device 16 decreases. As a result, the amount of NO _x discharged from the second exhaust purification device 16 can be reduced as much as possible.

Further, if the supply of secondary air is stopped when the amount of NO _X discharged from the second exhaust purification device 16 shows an increasing tendency, the temperature rise rate of the second exhaust purification device 16 increases, so that the second It is possible to avoid a situation where the activation timing of the exhaust purification device 16 becomes excessively late. As a result, it is possible to avoid a situation in which the time until the second exhaust purification device 16 is activated after the NO _X adsorption ability of the second exhaust purification device 16 is saturated can be avoided.

Hereinafter, the execution procedure of the NO _X adsorption process in the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart showing a NO _X adsorption processing routine. The NO _X adsorption processing routine is a routine stored in advance in the ROM of the ECU 20 or the like, and is periodically executed by the ECU 20.

In the NO _X adsorption processing routine of FIG. 7, the ECU 20 first determines whether or not the NO _X adsorption condition of the second exhaust purification device 16 is satisfied in S201. For example, the ECU 20 determines whether or not the temperature of the second exhaust purification device 16 is lower than the activation temperature. Here, as the temperature of the second exhaust purification device 16, the measured value of the exhaust temperature sensor 19 can be used as an alternative value. In addition, when the temperature sensor is attached to the 2nd exhaust purification apparatus 16, you may use the measured value of this temperature sensor as the temperature of the 2nd exhaust purification apparatus 16.

If a negative determination is made in S201, the ECU 20 once ends the execution of this routine. In this case, the NO _X adsorption process for the second exhaust purification device 16 is not executed. On the other hand, when a positive determination is made in S201, the ECU 20 proceeds to S202.

In S202, the ECU 20 determines whether or not the value of the NO _X adsorption flag Fnox2 is “0”. The NO _X adsorption flag Fnox2 is set to “1” when the NO _X adsorption process is started (for example, when the processes of S203 and S204 described later are executed), and when the NO _X adsorption process is completed ( For example, the flag is reset to “0” when the process of S212 described later is executed).

When the value of the NO _X adsorption flag Fnox2 is “0”, the NO _X adsorption process has not yet started. For this reason, when an affirmative determination is made in S202 (Fnox2 = 0), the ECU 20 starts the NO _X adsorption process in S203 and S204.

That is, the ECU 20 first controls the supply device so that the gaseous fuel is supplied to the internal combustion engine 1 in S203. Subsequently, in S204, the ECU 20 sets a default value Qair0 as the target supply amount Qair of the secondary air. The default value Qair0 is an amount that is sufficiently smaller than the supply amount of secondary air that significantly delays the activation timing of the second exhaust purification device 16, and the supply amount obtained in advance by an adaptation process using experiments or the like. It is.

When the second exhaust purification device 16 is less than the activation temperature and the internal combustion engine 1 is operated using gaseous fuel as the NO _X adsorption condition of S201, Processing may be omitted.

The ECU 20 proceeds to S205 after executing the processes of S203 and S204. In S205, the ECU 20 sets “1” to the aforementioned NO _X adsorption flag Fnox.

If the value of the NO _X adsorption flag Fnox2 is “1” when the ECU 20 executes the process of S202, the NO _X adsorption process has already been started. That is, the NO _X adsorption treatment is initiated during the last previous execution of the routine. Therefore, if the negative determination is made in S202 (Fnox2 = 1), the ECU 20 skips the processing of S203 to S205 and proceeds to S206.

In S206, ECU 20 includes, as _the amount of NO _X discharged from the second exhaust gas purification unit 16 reads the detection value Dnox2 of the NO _X sensor 21.

In S207, ECU 20 obtains a change amount of the detection value of the NO _X sensor 21 per unit time. Specifically, the ECU 20 subtracts the previous detection value Dnox2old (the detection value read in S206 at the previous execution of this routine) from the detection value Dnox2 read in S206, whereby the second exhaust purification device. A change amount ΔD2 (= Dnox2−Dnox2old) of the NO _X amount discharged from 16 is calculated.

In S208, the ECU 20 determines whether or not the change amount ΔD2 calculated in 2107 is smaller than zero. That is, the ECU 20 determines whether or not the NO _X amount discharged from the second exhaust purification device 16 shows a decreasing tendency.

If an affirmative determination is made in S206 (ΔD2 <0), the ECU 20 proceeds to S209. In S209, the ECU 20 calculates a new target supply amount Qair (= Qair + ΔQ) by adding a predetermined amount ΔQ to the current target supply amount Qair. That is, the ECU 20 further increases the target supply amount Qair in S209.

The ECU 20 returns to S201 after executing the process of S209. At this time, if the NO _X adsorption condition is satisfied, the ECU 20 makes a negative determination in S202 and executes the processes subsequent to S206 again. If an affirmative determination is made in S208, the ECU 20 will further increase the target supply amount Qair in S209. That, NO _X amount exhausted from the second exhaust gas purification unit 16 so long as they exhibit the decreasing trend, so that the target supply amount of the secondary air Qair is increased stepwise.

If a negative determination is made in S208 (ΔD2 ≧ 0), the ECU 20 proceeds to S210. In S210, the ECU 20 determines whether or not the change amount ΔD2 calculated in S207 is zero. Here, when the amount of change ΔD2 indicates zero, the amount of NO _x discharged from the second exhaust purification device 15 has decreased to the minimum amount. Therefore, when an affirmative determination is made in S210 (ΔD2 = 0), the ECU 20 continues to use the current target supply amount Qair.

On the other hand, if a negative determination is made in S210 (ΔD2> 0), the ECU 20 proceeds to S212. Here, the variation ΔD2 is when greater than zero, NO _X adsorbing capacity of the second exhaust gas purification device 16 is saturated, or NO _X adsorbed in the second exhaust gas purification unit 16 is starting to desorb It will be. Therefore, the ECU 20 ends the NO _X adsorption process in S212. Specifically, the ECU 20 sets “0” as the target supply amount Qair. When the target supply amount Qair becomes “0”, the secondary air is not supplied from the secondary air supply device 23 to the exhaust passage 10. In that case, the temperature of the exhaust gas flowing into the second exhaust gas purification device 16 becomes higher, and the air-fuel ratio of the exhaust gas flowing into the second exhaust gas purification device 16 becomes equal to the specified air-fuel ratio. As a result, the temperature increase rate of the second exhaust purification device 16 increases.

The ECU 20 advances the operation timing (ignition timing) of the spark plug 8 and increases the opening of the throttle valve 13 (increases the intake air amount) when executing the process of S212. (2) The activity of the exhaust emission control device 16 may be promoted. Further, ECU 20, when executing the processing of the S212, by the air-fuel ratio of the mixture rich, be made to reduce _the amount of NO _X discharged from the internal combustion engine 1 (NO _X emissions) Good.

The ECU 20 proceeds to S213 after executing the process of S212, and resets the NO _X adsorption flag Fnox2 to “0”.

As described above, the ECU 20 executes the NO _X adsorption processing routine of FIG. 7 to reduce NO _X discharged into the atmosphere when the second exhaust purification device 16 is in an inactive state. Early activation of the first exhaust purification device 15 can be achieved.

In the present embodiment has described the example of executing the NO _X adsorption treatment the second exhaust gas purification unit 16 as a target, the period until the first exhaust gas purification device 15 is active in the first embodiment described above run the NO _X adsorption treatment of the first exhaust gas purification device 15 as described as a target, the period from when the first exhaust gas purification device 15 is activated until the second exhaust gas purification unit 16 is activated is described in the example As described above, the NO _X adsorption processing for the second exhaust purification device 16 may be executed.

1 Internal combustion engine 2 Cylinder 3 Piston 4 Intake port 5 Exhaust port 6 Intake valve 7 Exhaust valve 8 Spark plug 9 Intake passage 10 Exhaust passage 11 First fuel injection valve 12 Second fuel injection valve 13 Throttle valve 14 Air flow meter 15 First exhaust Purification device 16 Second exhaust purification device 17 Air-fuel ratio sensor 18 O ₂ sensor 19 Exhaust temperature sensor 20 ECU
21 NO _X sensor 23 Secondary air supply device

Claims

A supply device for supplying one of liquid fuel and gaseous fuel to the internal combustion engine;
An adjustment unit for adjusting the air-fuel ratio of the exhaust gas flowing into the three-way catalyst disposed in the exhaust passage of the internal combustion engine;
A control unit that controls the adjustment unit so that the air-fuel ratio of the exhaust gas flowing into the three-way catalyst becomes lean when the supply device supplies gaseous fuel to the internal combustion engine;
An internal combustion engine control system comprising:
In Claim 1, further comprising a temperature acquisition unit for acquiring the temperature of the three-way catalyst,
The control unit flows into the three-way catalyst when the supply device supplies gaseous fuel to the internal combustion engine and the temperature acquired by the temperature acquisition unit is lower than the activation temperature of the three-way catalyst. A control system for an internal combustion engine that controls the adjusting unit so that an air-fuel ratio of exhaust gas becomes lean.
In Claim 1 or 2, it further has a NO X amount acquisition part which acquires the amount of NO X which flows out from the three-way catalyst,
Wherein the control unit, the NO amount of NO X which is obtained by X amount obtaining unit air-fuel ratio of the exhaust gas is continuously or stepwise increased when showing a decreasing tendency, NO acquired by the amount of NO X acquisition unit A control system for an internal combustion engine that controls the adjustment unit so that the air-fuel ratio of the exhaust gas decreases to a specified air-fuel ratio when the X amount shows an increasing tendency.
4. The air-fuel ratio of the air-fuel mixture used for combustion in the internal combustion engine when the adjustment unit makes the air-fuel ratio of the exhaust gas flowing into the three-way catalyst lean. A control system for an internal combustion engine that adjusts an amount of gaseous fuel supplied from the supply unit to the internal combustion engine so as to be lean.
3. The three-way catalyst according to claim 1, wherein the three-way catalyst includes a first three-way catalyst and a second three-way catalyst arranged in series in a flow direction of the exhaust gas,
The adjustment unit includes a secondary air supply device that supplies secondary air to an exhaust passage downstream from the first three-way catalyst and upstream from the second three-way catalyst;
The control unit supplies secondary air to an exhaust passage downstream from the first three-way catalyst and upstream from the second three-way catalyst when the supply device is supplying gaseous fuel to the internal combustion engine. An internal combustion engine control system for controlling the adjustment unit as described above.
The method of claim 5, further comprising a amount of NO X acquisition unit that acquires the amount of NO X flowing out from the second three-way catalyst,
Wherein, said NO when NO X amount acquired by X amount obtaining section indicates decreasing trend the amount of secondary air is increased continuously or stepwise, NO acquired by the NO X acquisition unit A control system for an internal combustion engine that controls the adjusting section so that the supply of secondary air is stopped when the X amount shows an increasing tendency.