JP4899741B2 - Exhaust gas purification control device for multi-fuel internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for a multi-fuel internal combustion engine that is operated using at least one of at least two types of fuels having different properties.

  Conventionally, in the technical field of an internal combustion engine that performs lean combustion, in order to purify a large amount of nitrogen oxide (NOx) generated during lean combustion, the NOx is stored during lean combustion and reduced to nitrogen in a reducing atmosphere. Catalysts are known. For example, Patent Document 1 below discloses an exhaust purification device that performs rich spike control by switching from a premixed combustion mode to a diffusion combustion mode when reducing NOx stored in a NOx catalyst. In Patent Document 2 below, the combustion temperature is raised by switching from the premixed combustion mode to the diffusion combustion mode, thereby increasing the temperature of the exhaust purification catalyst and the DPF (PM trapping device). The technology is disclosed.

JP 2002-188487A JP 2003-65116 A

  However, in a multi-fuel internal combustion engine that is operated using a plurality of types of fuels having different properties, for example, when the fuel introduced into the combustion chamber is of a property that easily generates PM or smoke, the air-fuel ratio is not changed. If the value is controlled from the above value to the overconcentrated side, PM and smoke may be generated during combustion. Therefore, for example, when the technique disclosed in Patent Document 1 is applied to a multi-fuel internal combustion engine, NOx can be reduced, but on the other hand, depending on the properties of the fuel introduced into the combustion chamber, PM and smoke This is not preferable.

  Therefore, the present invention improves the disadvantages of the conventional example, and can suppress the generation of PM and smoke even if the air-fuel ratio is controlled to be richer than the current state according to the state of the exhaust gas purification means. An object of the present invention is to provide an exhaust purification control device for a multi-fuel internal combustion engine.

In order to achieve the above object, according to the first aspect of the present invention, there is provided an exhaust purification control apparatus for a multi-fuel internal combustion engine operated using at least one of at least two types of fuels having different properties. When controlling the air / fuel ratio at the time of combustion to the richer side than the current state according to the state, the higher the PM / smoke suppression degree of the fuel guided into the combustion chamber according to the operating conditions, the larger the air / fuel ratio control amount to the rich side When the control to the rich side is performed, the content of fuel with a high degree of PM / smoke suppression in the fuel introduced into the combustion chamber is increased, and the amount of PM and smoke collected by the PM collector at that time is increased. If it is less than the predetermined value, the air-fuel ratio control amount to the excessively rich side is further increased.

In an internal combustion engine, even if there is a control instruction to the rich side of the air-fuel ratio depending on the state of the exhaust purification means, PM and smoke are more likely to occur as the air-fuel ratio becomes richer, so that exhaust It is difficult to shift the purification means to the best state. However, in the multifuel internal combustion engine according to the first aspect, the degree of PM / smoke suppression of the fuel guided into the combustion chamber according to the operating condition increases (that is, PM and smoke are less likely to be generated). Since the air-fuel ratio control amount to the rich side is increased, the exhaust purification means can be shifted to the best state while suppressing the generation of PM and smoke. Further, in the multi-fuel internal combustion engine according to claim 1, since it becomes difficult to generate PM and smoke by increasing the content ratio of fuel having a high degree of PM / smoke suppression, while suppressing the generation of PM and smoke Thus, the exhaust gas purification means can be shifted to the best state. Furthermore, in the multifuel internal combustion engine according to claim 1, when the air-fuel ratio control amount to the rich side is increased and the content ratio of fuel with a high degree of PM / smoke suppression is increased, the PM trapping device If the trapped amount of PM and smoke is less than the predetermined amount, the air-fuel ratio control amount to the rich side is further increased, so that the exhaust purification means can easily shift to the best state. At that time, PM and smoke are generated. However, since this PM and smoke are collected by the PM collection device, release to the atmosphere is avoided.

Here, in the invention according to claim 2, when the PM trapping device is regenerated, the higher the degree of PM / smoke suppression of the fuel introduced into the combustion chamber, the more the generation of PM and smoke can be suppressed within the lean air-fuel ratio range. A target air-fuel ratio close to the theoretical air-fuel ratio is set.

In the multi-fuel internal combustion engine according to claim 2 , the PM trapping device is heated by raising the temperature of the exhaust gas while suppressing the generation of PM and smoke, and the PM accumulated in the PM trapping device Can be oxidized.

  Here, the combustion mode when the air-fuel ratio control to the rich side is performed is a compression self-ignition diffusion combustion mode or a premixed spark ignition flame propagation combustion mode, as in the third aspect of the invention.

  Further, the state of the exhaust purification means is a state where a temperature increase request or a reduction request is made for the exhaust purification means, as in the fourth aspect of the invention. That is, the exhaust purification means is in a state where a PM regeneration request is made or a NOx or SOx reduction request is made.

According to the exhaust gas purification control apparatus for a multi-fuel internal combustion engine according to the present invention, even if the air-fuel ratio is controlled to be richer than the current state in accordance with the state of the exhaust gas purification means, the air-fuel ratio is maintained in the operating conditions and the combustion chamber. It is set in consideration of the degree of PM / smoke suppression of the fuel itself led to the fuel , and the content ratio of the fuel with a high degree of PM / smoke suppression is increased, so the suppression of PM and smoke generation and exhaust purification The transition to the best state of the means can be made compatible. Furthermore, according to the exhaust gas purification control apparatus for a multi-fuel internal combustion engine according to the present invention, if the amount of PM or smoke collected by the PM collector at that time is less than a predetermined amount, the air-fuel ratio control amount to the rich side is increased. Therefore, the exhaust gas purifying means can easily shift to the best state while the release of the PM and smoke from the PM collection device is prevented from being released into the atmosphere.

  Embodiments of an exhaust purification control apparatus for a multifuel internal combustion engine according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the embodiments.

  A first embodiment of an exhaust gas purification control apparatus for a multi-fuel internal combustion engine according to the present invention will be described with reference to FIGS. Hereinafter, the exhaust purification control apparatus of the first embodiment will be described in detail while explaining an example of the multi-fuel internal combustion engine to be applied.

  The multi-fuel internal combustion engine exemplified here is an internal combustion engine that is operated by previously mixing fuels having different properties stored in individual fuel tanks and introducing the mixed fuel to a combustion chamber. The electronic control unit (ECU) 1 shown in FIG. 1 executes various control operations such as combustion control. The electronic control unit 1 includes a CPU (Central Processing Unit) (not shown), a ROM (Read Only Memory) that stores a predetermined control program and the like, and a RAM (Random Access Memory) that temporarily stores the calculation result of the CPU. , And a backup RAM for storing information prepared in advance. Although only one cylinder is shown in FIG. 1, the present invention is not limited to this, and can be applied to a multi-cylinder multifuel internal combustion engine. In the first embodiment, description will be made assuming that a plurality of cylinders are provided.

  The multifuel internal combustion engine is provided with a cylinder head 11, a cylinder block 12, and a piston 13 that form a combustion chamber CC. Here, the cylinder head 11 and the cylinder block 12 are fastened with bolts or the like via the head gasket 14 shown in FIG. 1, and the recess 11a on the lower surface of the cylinder head 11 and the cylinder bore 12a of the cylinder block 12 formed thereby. The piston 13 is disposed so as to be capable of reciprocating in the space. And the combustion chamber CC mentioned above is comprised by the space enclosed by the wall surface of the recessed part 11a of the cylinder head 11, the wall surface of the cylinder bore 12a, and the top surface 13a of the piston 13. FIG.

  The multifuel internal combustion engine of the first embodiment sends air and fuel into the combustion chamber CC so as to achieve an air-fuel ratio corresponding to operating conditions such as engine speed and engine load and operating mode, and combustion corresponding to the operating conditions Execute control. Therefore, the electronic control unit 1 according to the first embodiment is provided with air-fuel ratio control means for adjusting the air-fuel ratio at the time of combustion in the combustion chamber CC according to operating conditions and the like.

  For example, in the multi-fuel internal combustion engine of the first embodiment, in the normal operation mode, the air-fuel ratio is controlled to become a lean air-fuel ratio (lean air-fuel ratio) having a concentration corresponding to the operating conditions, and the condition of the lean air-fuel ratio is set. The operation is performed in the compression auto-ignition diffusion combustion mode prepared as the combustion mode below.

  The compression self-ignition diffusion combustion mode is a method in which a part of the fuel is self-ignited by injecting high-pressure fuel into the high-temperature compressed air formed in the combustion chamber CC of the compression stroke, and the fuel and air are It is a combustion mode in which combustion proceeds while being diffusely mixed. Here, since the compressed air and fuel in the combustion chamber CC are difficult to be mixed instantaneously, immediately after the start of fuel injection, the air-fuel ratio varies in some places. On the other hand, it is generally preferable to use a fuel having excellent ignitability as described below when performing diffusion combustion, and such a fuel with good ignitability does not have to wait for the entire injection amount to be injected. It ignites itself at the air-fuel ratio suitable for combustion. For this reason, in this compression self-ignition diffusion combustion mode, the fuel of the air-fuel ratio part suitable for combustion self-ignites first, and the flame formed thereby gradually advances the combustion while entraining the remaining fuel and air. Let

  By the way, in order to operate in this compression self-ignition diffusion combustion mode, a fuel with good ignitability whose ignition point is lower than the compression heat of compressed air is usually required. For example, light oil or dimethyl ether can be considered as the fuel with good ignitability. Further, in recent years, GTL (Gas To Liquids) fuel has attracted attention as an alternative fuel for light oil, and this GTL fuel is easily produced in a desired property. For this reason, the GTL fuel produced | generated in order to improve ignitability can also be used for fuel with good ignitability. Such a fuel with good ignitability not only enables compression auto-ignition diffusion combustion, but also reduces the amount of NOx generated when operating in the compression auto-ignition diffusion combustion mode. Vibration can be suppressed.

  Here, the air fed into the combustion chamber CC is sucked from the outside through the intake passage 21 and the intake port 11b of the cylinder head 11 shown in FIG. On the other hand, the fuel sent to the combustion chamber CC is supplied using the fuel supply device 50 shown in FIG.

  First, the air supply path will be described. On the intake passage 21 of the first embodiment, an air cleaner 22 that removes foreign matters such as dust contained in air introduced from the outside, and an air flow meter 23 that detects the amount of intake air from the outside are provided. . In this multi-fuel internal combustion engine, the detection signal of the air flow meter 23 is sent to the electronic control unit 1, and the electronic control unit 1 calculates the intake air amount, the engine load and the like based on the detection signal.

  A throttle valve 24 that adjusts the amount of intake air into the combustion chamber CC and a throttle valve actuator 25 that opens and closes the throttle valve 24 are disposed downstream of the air flow meter 23 on the intake passage 21. Is provided. The air-fuel ratio control means in the electronic control unit 1 of the first embodiment drives and controls the throttle valve actuator 25 according to the operating conditions and the operating mode, and the valve opening degree (in other words, the intake air amount) according to the operating conditions and the like. ), The valve opening angle of the throttle valve 24 is adjusted. For example, the throttle valve 24 is adjusted so that the intake air amount necessary for achieving the air-fuel ratio according to the operating condition and the operating mode is sucked into the combustion chamber CC. The multifuel internal combustion engine is provided with a throttle opening sensor 26 that detects the valve opening of the throttle valve 24 and transmits the detection signal to the electronic control unit 1.

  Further, one end of the intake port 11b opens to the combustion chamber CC, and an intake valve 31 for opening and closing the opening is disposed at the opening portion. The number of openings may be one or more, and an intake valve 31 is provided for each opening. Therefore, in this multi-fuel internal combustion engine, air is sucked into the combustion chamber CC from the intake port 11b by opening the intake valve 31 and closed in the combustion chamber CC by closing the intake valve 31. Inflow of air to is blocked.

  Here, as the intake valve 31, for example, there is a valve that is driven to open and close in accordance with the rotation of an intake camshaft (not shown) and the elastic force of an elastic member (string spring). In this type of intake valve 31, by interposing a power transmission mechanism such as a chain or a sprocket between the intake side camshaft and the crankshaft 15, the intake side camshaft is interlocked with the rotation of the crankshaft 15, Open / close drive is performed at a preset opening / closing timing. In the multifuel internal combustion engine of the first embodiment, the intake valve 31 that is opened and closed in synchronization with the rotation of the crankshaft 15 is applied.

  However, this multi-fuel internal combustion engine may be provided with a variable valve mechanism such as a so-called variable valve timing & lift mechanism that can change the opening / closing timing and lift amount of the intake valve 31. The opening / closing timing and the lift amount can be changed to suitable ones according to the operation conditions and the operation mode. Furthermore, in this multi-fuel internal combustion engine, a so-called electromagnetically driven valve that opens and closes the intake valve 31 using electromagnetic force may be used in order to obtain the same effect as the variable valve mechanism.

  Next, the fuel supply device 50 will be described. The fuel supply device 50 directly guides at least one of a plurality of types of fuels having different properties according to operating conditions and the like into the combustion chamber CC. In the first embodiment, among the two types of fuels (first fuel F1 in the first fuel tank 41A and second fuel F2 in the second fuel tank 41B) stored in separate fuel tanks and having different properties. One type is selected from the above, or each of the fuels is mixed in advance at a predetermined fuel mixing ratio, and the single fuel or the mixed fuel is directly injected into the combustion chamber CC.

  Specifically, the fuel supply device 50 includes a first feed pump 52A that sucks up the first fuel F1 from the first fuel tank 41A and sends it to the first fuel passage 51A, and a second fuel F2 from the second fuel tank 41B. And a second feed pump 52B that sucks up and sends the fuel to the second fuel passage 51B.

  Further, when the first and second fuels F1 and F2 are sent to the fuel supply device 50 from the first and second fuel passages 51A and 51B, respectively, they are mixed, When only one of the fuels is sent, the fuel mixing means 53 that flows downstream as it is, and the high pressure that pressurizes the mixed fuel or the single fuel in the fuel mixing means 53 and pressurizes it to the high pressure fuel passage 54 The fuel pump 55, the delivery passage 56 for distributing the mixed fuel or the single fuel in the high-pressure fuel passage 54 to the respective cylinders, and the mixed fuel or the single fuel supplied from the delivery passage 56 in the combustion chamber CC And a fuel injection valve 57 for each cylinder for injecting into the cylinder.

  In this fuel supply device 50, the first feed pump 52A, the second feed pump 52B, and the fuel mixing means 53 are driven and controlled by the fuel content ratio control means of the electronic control device 1, so that the operating conditions and the combustion mode are set. The fuel mixing means 53 is configured to generate a mixed fuel having a predetermined fuel mixing ratio. For example, the fuel supply device 50 adjusts the fuel mixing ratio of the mixed fuel by adjusting the discharge amount of the first feed pump 52A and the second feed pump 52B to the fuel content ratio control means of the electronic control device 1. Alternatively, the fuel mixing ratio of the mixed fuel may be adjusted by increasing or decreasing the mixing ratio of the first and second fuels F1 and F2 in the fuel mixing means 53 in accordance with the instruction of the fuel content ratio control means. . Here, when 10 to 0 is selected as the fuel mixture ratio, the fuel content ratio control means drives one of the first feed pump 52A or the second feed pump 52B to control the corresponding fuel. The fuel is mixed with the fuel mixing means 53, and the single fuel is caused to flow downstream as it is. The fuel mixture ratio may be a variable value that varies depending on the operating conditions and the like, but is not limited thereto, and may be a constant value set in advance.

  In addition, the fuel supply device 50 causes the high-pressure fuel pump 55 and the fuel injection valve 57 to be driven and controlled by the fuel injection control means of the electronic control unit 1, so that a desired fuel injection amount, fuel injection timing, and fuel injection period can be obtained. The mixed fuel or the single fuel is configured to be injected under the fuel injection conditions according to the operation conditions such as the above and the combustion mode. For example, the fuel injection control means of the electronic control unit 1 pumps the mixed fuel or a single fuel from the high-pressure fuel pump 55 and supplies it to the fuel injection valve 57 under the fuel injection conditions according to the operating conditions, the combustion mode, etc. Let the jet run.

  In the air-fuel ratio control means of the first embodiment, fuel injection control means is prepared as a part of the control function.

  The mixed fuel or the single fuel thus supplied to the combustion chamber CC is burned by the ignition operation in the ignition mode corresponding to the combustion mode in combination with the air described above. The in-cylinder gas (combustion gas) after the combustion is discharged from the combustion chamber CC to the exhaust port 11c shown in FIG. Here, an exhaust valve 61 that opens and closes an opening between the exhaust port 11c and the combustion chamber CC is disposed. The number of openings may be one or more, and the exhaust valve 61 described above is provided for each opening. Accordingly, in this multi-fuel internal combustion engine, the combustion gas is discharged from the combustion chamber CC to the exhaust port 11c by opening the exhaust valve 61, and the combustion gas exhaust port is closed by closing the exhaust valve 61. The discharge to 11c is blocked.

  Here, as the exhaust valve 61, as in the intake valve 31 described above, a valve with a power transmission mechanism, a valve with a variable valve mechanism such as a so-called variable valve timing & lift mechanism, or a so-called electromagnetically driven valve can be used. Can be applied.

  Further, in the multi-fuel internal combustion engine of the first embodiment, the combustion gas discharged to the exhaust port 11c (hereinafter referred to as “exhaust gas”) is released to the atmosphere via the exhaust passage 71 shown in FIG. . For this reason, an exhaust gas purifying means 72 for purifying harmful components in the exhaust gas is disposed on the exhaust passage 71.

For example, the multifuel internal combustion engine of the first embodiment performs compression autoignition diffusion combustion (hereinafter referred to as “lean compression autoignition diffusion combustion”) under a lean air-fuel ratio as described above in the normal operation mode. As the combustion temperature rises in an oxygen atmosphere, the amount of nitrogen oxide (NOx) produced increases. For this reason, the exhaust gas purification means 72 of the first embodiment has a NOx catalyst 72a for purifying harmful components such as NOx into harmless nitrogen (N ₂ ), water (H ₂ O) and carbon dioxide (CO ₂ ). Is provided.

  As the NOx catalyst 72a, NSR (NOx Storage Reduction) and DPNR (Diesel Particulate-NOx Reduction System) are known, and one of them is applied in the first embodiment.

The NSR is a so-called NOx occlusion reduction type catalyst in which a large amount of NOx generated in a lean combustion is stored in the catalyst in the form of nitrate and the nitrate is reduced to N ₂ under a reducing atmosphere. In this NOx occlusion reduction type catalyst, a small amount of NOx that has not been occluded during lean combustion, and hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas are N ₂ by the redox action of HC and CO. , H ₂ O, CO ₂ .

  On the other hand, DPNR is a system capable of purifying particulate matter (PM) and NOx continuously at the same time. For example, a DPF (Diesel Particulate Filter) serving as a PM collection device has a NOx occlusion reduction type catalyst. Is supported.

  Here, when NSR is applied as the NOx catalyst 72a of the first embodiment, a DPF is provided in the exhaust purification means 72 in order to suppress the release of PM and smoke into the atmosphere.

By the way, in the NOx catalyst 72a of the first embodiment, in order to reduce the NOx occluded during the normal operation to N ₂ , the temperature is increased more than during the normal operation, and the NOx is further oxygenated than during the normal operation. It is necessary to create a reducing atmosphere by placing HC or CO as a reducing agent in a low concentration state.

  Therefore, in the multifuel internal combustion engine of the first embodiment, a reducing atmosphere is formed by so-called rich spike control in which the air-fuel ratio is controlled to be richer than the lean air-fuel ratio and burned. For this reason, in the multifuel internal combustion engine of the first embodiment, a rich spike operation mode in which the rich spike control is performed by switching from the normal operation mode is prepared. Here, specifically, the air-fuel ratio is set to the lean air-fuel ratio. To the stoichiometric air-fuel ratio (stoichiometric air-fuel ratio) or the rich air-fuel ratio (rich air-fuel ratio), and compression self-ignition diffusion combustion is performed.

Here, in this multi-fuel internal combustion engine, as the air-fuel ratio control amount to the rich side increases, the temperature of the exhaust gas increases and the amount of HC and CO generated increases, so the NOx catalyst 72a The amount of NOx occluded to N ₂ can be increased.

By performing rich spike control in this way, NOx occluded in the NOx catalyst 72a can be reduced to N ₂ , but on the other hand, the fuel guided into the combustion chamber CC at this time causes PM and smoke to be reduced. In the case of properties that are easily generated, PM and smoke are likely to occur as the air-fuel ratio is controlled to the rich side, although it depends on the operating conditions (engine speed Ne and engine load Kl) at that time. Become.

  Therefore, in the first embodiment, when the normal operation mode is switched to the rich spike operation mode, the PM / smoke suppression degree S0 of the fuel itself guided into the combustion chamber CC and the operation conditions (engine speed Ne and In accordance with the engine load (Kl), the target air-fuel ratio at the time of rich spike control capable of reducing NOx in the NOx catalyst 72a is set while suppressing the generation of PM and smoke. The PM / smoke suppression degree S0 represents the degree of difficulty of PM or smoke (good evaporability or oxygen content) of the fuel itself guided into the combustion chamber CC.

  Specifically, in the first embodiment, based on the PM / smoke suppression degree S0 of the fuel itself guided into the combustion chamber CC and the operating conditions (the engine speed Ne and the engine load Kl), the operating conditions are determined. It is possible to obtain the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC, and to achieve both the suppression of PM and smoke generation and the NOx reduction effect during rich spike control according to the PM / smoke suppression degree S. A target air / fuel ratio is calculated.

  Here, the PM / smoke suppression degree S according to the operating conditions means that the PM and smoke of the fuel guided into the combustion chamber CC under the operating conditions (the engine speed Ne and the engine load Kl) are less likely to be generated. And is obtained from map data and the like using the operating conditions (engine speed Ne and engine load Kl) and PM / smoke suppression degree S0 of the fuel itself led into the combustion chamber CC as parameters. . For example, even if the fuel itself has the same PM / smoke suppression degree S0, the higher the engine speed Ne or the higher the engine load Kl, the higher the temperature and pressure in the combustion chamber CC. Therefore, even if the PM / smoke suppression degree S0 of the fuel itself is the same, if the engine speed Ne or the engine load Kl is higher than the reference speed or the reference load, the generation of PM and smoke can be suppressed. The PM / smoke suppression degree S corresponding to the operating conditions is set higher than the PM / smoke suppression degree S0 of the fuel itself. On the other hand, if the engine speed Ne or the engine load Kl is lower than the reference speed or the reference load even if the PM / smoke suppression degree S0 of the fuel itself is the same, the temperature and pressure in the combustion chamber CC will decrease. Since PM and smoke are likely to occur, the PM / smoke suppression degree S corresponding to the operating conditions is set lower than the PM / smoke suppression degree S0 of the fuel itself.

Furthermore, when the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating conditions is high (that is, PM and smoke are not easily generated), the air-fuel ratio control amount to the over-rich side is set. Even if it is increased, the generation of PM and smoke can be suppressed. Rather, by controlling the air-fuel ratio to a richer side, more NOx stored in the NOx catalyst 72a as described above is reduced to N ₂ . It becomes possible to purify. On the other hand, when the PM / smoke suppression degree S is low (that is, PM and smoke are likely to be generated), PM and smoke will be generated if the air-fuel ratio control amount to the over-rich side is increased. .

  Therefore, in the first embodiment, as the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC corresponding to the operating condition increases, the target air-fuel ratio that increases the air-fuel ratio control amount to the rich side becomes larger. The target air-fuel ratio setting map data at the time of rich spike control shown in FIG. 2 is prepared based on the results of experiments and simulations performed in advance. Note that FIG. 2 illustrates target air-fuel ratio setting map data set to a rich air-fuel ratio for over-rich combustion at the time of rich spike control, but the target air-fuel ratio setting map data is theoretically The air-fuel ratio may be settable.

  Here, when the PM / smoke suppression degree S0 of the fuel introduced into the combustion chamber CC is too low, PM and smoke are generated regardless of how the target air-fuel ratio at the time of rich spike control is varied. It is almost impossible to suppress this. For example, in the multi-fuel internal combustion engine of the first embodiment, light oil having high ignitability is used as the first fuel F1 in order to operate in the compression auto-ignition diffusion combustion mode. Since the amount of oxygen is also small, the PM / smoke suppression degree S0 is low, which is not useful from the viewpoint of PM and smoke suppression. For this reason, in the first embodiment, for example, fuel having a relatively high PM / smoke suppression degree S0 is stored in the second fuel tank 41B as the second fuel F2.

  As the fuel having a high PM / smoke suppression degree S0, a highly evaporative fuel or a fuel having a high oxygen content is used. For example, as the fuel having a high PM / smoke suppression degree S0 in this case, gasoline or alcohol fuel, GTL (Gas To Liquids) fuel having high evaporability, FAME (fatty acid methyl ester), naphtha, or the like can be considered. In addition, for example, if heavy oil is applied as the first fuel F1, the PM / smoke suppression degree S0 of the light oil increases, so that the light oil may be applied to the second fuel F2.

  An example of the target air-fuel ratio setting operation during rich spike control in the exhaust gas purification control apparatus for the multifuel internal combustion engine of the first embodiment will be described below with reference to the flowchart of FIG. The exhaust purification control device of the first embodiment is configured as one function of the electronic control device 1 described above.

  First, the PM / smoke suppression degree S0 of the fuel itself guided into the combustion chamber CC is input to the electronic control unit 1 of the first embodiment (step ST1).

  The PM / smoke suppression degree S0 is, for example, the PM / smoke suppression degree S1 of the first fuel F1, the PM / smoke suppression degree S2 of the second fuel F2, and the fuel mixture ratio of the first fuel F1 and the second fuel F2. It is a value that can be obtained in response to this, and is obtained from map data or the like using these three elements as parameters.

  Here, the PM / smoke suppression degree S1, S2 of the first and second fuels F1, F2 can be known, for example, at a fueling facility, and the first and second fuels F1, F2 are known. It may be configured so that an operator such as a driver can input to the RAM or the like of the electronic control device 1 every F2, and information can be exchanged between the fueling device of the fueling facility and the vehicle. The oil supply device may be configured to input to the RAM or the like of the electronic control device 1 when refueling. In addition, the fuel mixing ratio of the first fuel F1 and the second fuel F2 here is set in advance as a unique value at the time of rich spike control.

  Further, the current engine speed Ne and the engine load Kl in the multifuel internal combustion engine are input to the electronic control unit 1 of the first embodiment (step ST2).

  Here, the engine speed Ne can be grasped from the detection signal of the crank angle sensor 16 shown in FIG. The crank angle sensor 16 is a sensor that detects the rotation angle of the crankshaft 15. On the other hand, the engine load Kl can be grasped from the detection signal of the air flow meter 23 described above.

  Subsequently, the electronic control unit 1 according to the first embodiment is based on the PM / smoke suppression degree S0 of the fuel itself guided into the combustion chamber CC in steps ST1 and ST2, the engine speed Ne, and the engine load Kl. Then, the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC corresponding to the operation condition is obtained (step ST3).

  Then, the air-fuel ratio control means of the electronic control unit 1 of the first embodiment uses the target air-fuel ratio setting map data described above for the target air-fuel ratio at the time of rich spike control suitable for the PM / smoke suppression degree S according to the operating conditions. Is calculated and set (step ST4).

Thus, exhaust gas purification controller of the multi-fuel internal combustion engine of the first embodiment, by performing the rich spike control of NOx of the NOx catalyst 72a when causing reduced to N _2, the combustion chamber CC according to the operating conditions The higher the PM / smoke suppression degree S of the fuel led to is, the larger the air / fuel ratio control amount to the rich side is set to set the target air / fuel ratio between the stoichiometric air fuel ratio and the rich air / fuel ratio. The compression auto-ignition diffusion combustion mode operation is performed under the target air-fuel ratio. This rich spike control operation is performed, for example, continuously or intermittently for a predetermined extremely short time.

  Therefore, in this multi-fuel internal combustion engine, as the PM / smoke suppression degree S corresponding to the operating conditions increases, it becomes easier to suppress PM and smoke generation, and the NOx occluded in the NOx catalyst 72a becomes more oxygen. Since it is placed in a low concentration state and a large amount of HC or CO as a reducing agent is supplied thereto, more NOx can be reduced. On the other hand, in this multi-fuel internal combustion engine, when the PM / smoke suppression degree S according to the operating conditions is low, the air-fuel ratio control amount to the rich side is small, so while reducing NOx, PM and Smoke generation can be suppressed. For this reason, according to the exhaust gas purification control apparatus for a multi-fuel internal combustion engine, it is possible to obtain a good NOx reduction effect suitable for the PM / smoke suppression degree S while suppressing PM and smoke generation during rich spike control. Can do.

  By the way, here, the PM / smoke suppression degree S0 of the fuel itself guided into the combustion chamber CC and the operating conditions (the engine speed Ne and the engine load Kl) are used to enter the combustion chamber CC according to the operating conditions. Although the PM / smoke suppression degree S of the introduced fuel is obtained, the PM / smoke suppression degree S according to the operating conditions may be calculated by a method different from this. For example, the PM / smoke suppression degree S according to the operating conditions and the amount of smoke generated actually generated can be inferred as having a unique relationship with each other. For this reason, the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating condition is set on the upstream side of the exhaust gas flow direction with respect to the exhaust gas purification means 72 on the exhaust passage 71 as shown in FIG. The sensor 73 is provided, and the calculation can be performed based on the amount of smoke generated during the rich spike control detected by the smoke sensor 73. At this time, PM and smoke are generated until the target air-fuel ratio at the time of rich spike control is set. These are DPF or NOx catalyst provided in the exhaust purification means 72 together with NSR as the NOx catalyst 72a. Since it is collected in the DPF in the DPNR 72a, it is not released to the atmosphere.

In the first embodiment, the fuel content ratio control means can arbitrarily set the fuel mixing ratio of the first fuel F1 and the second fuel F2 between 0:10 and 10: 0. Therefore, in the multi-fuel internal combustion engine of the first embodiment, if it is possible to operate only with the second fuel F2 having a relatively high PM / smoke suppression degree S0 among all the fuels, the mixture of the second fuels F2 is possible. It is also possible to operate with a mixed fuel with an increased ratio. Therefore, when setting the target air-fuel ratio at the time of the rich spike control described above, only the second fuel F2 having a relatively high PM / smoke suppression degree S0 or the content ratio of the second fuel F2 in the combustion chamber CC is increased. The target air-fuel ratio may be calculated as an operation with the spent fuel. Thereby, in this case, the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating condition is increased, so the target air-fuel ratio at the time of rich spike control is set further to the rich side. Thus, more NOx stored in the NOx catalyst 72a can be reduced to N ₂ while suppressing the generation of PM and smoke.

  Here, in order to store a large amount of NOx in the NOx catalyst 72a during normal operation, it is necessary to reduce as much NOx as possible during the rich spike control and to make a large space for storing NOx.

  Therefore, in the multifuel internal combustion engine of the first embodiment, the exhaust gas purification means 72 has a function as a PM trapping device (DPF). Therefore, if the amount of PM trapped in the DPF is less than a predetermined amount, Even if the occurrence of PM or smoke is concealed, it is preferable to further increase the air-fuel ratio control amount to the rich side when setting the target air-fuel ratio during rich spike control.

  For example, as shown in the flowchart of FIG. 4, the electronic control device 1 of the first embodiment in this case, first, as in the case of the flowchart shown in FIG. 3 described above, the degree of PM / smoke suppression according to the operating conditions. The target air-fuel ratio at the time of rich spike control that conforms to S is calculated (steps ST1 to ST4).

  Then, the electronic control unit 1 determines whether or not the amount of PM trapped in the DPF of the exhaust purification unit 72 is smaller than a predetermined value (step ST5).

  Here, regarding the amount of collected PM, for example, pressure sensors 74 and 75 shown in FIG. Can be requested accordingly. For example, in this case, if the pressure difference is small, the amount of collected PM is small, and if the pressure difference is large, the amount of collected PM is large. Therefore, the correlation between them is obtained in advance. Prepare map data. In the case where the exhaust purification means 72 is provided with NSR and DPF, in order to detect a more accurate pressure difference, the respective pressure sensors 74 and 75 are provided on the upstream and downstream sides of the DPF, respectively. Is preferred.

  Moreover, since the amount of PM trapped can be estimated from the history of operation states such as the operation mode and operation conditions so far, it may be obtained using this. That is, the generation amount of PM and smoke changes according to the operation state, and by integrating the PM generation amount according to the operation state that changes every moment, What is necessary is just to estimate PM collection amount.

  On the other hand, the predetermined value to be compared with the amount of PM collected is preferably determined as a value for the total amount of PM that can be collected by the DPF. For example, for the total amount of PM that can be collected What percentage should be determined. The predetermined value may be determined based on the remaining amount that can be collected.

  When the electronic control unit 1 determines that “a predetermined amount or more of PM has been collected” by comparing the amount of collected PM thus obtained with a predetermined value, the electronic control unit 1 obtains in step ST4. The target air-fuel ratio is set as the target air-fuel ratio for rich spike control (step ST6). Thereby, in this case, the same effect as in the flowchart shown in FIG. 3 can be obtained.

  In addition, when the electronic control unit 1 determines that “the amount of trapped PM is less than a predetermined value” by the comparison, the electronic control unit 1 corrects the target air-fuel ratio obtained in step ST4 to the over-concentration side, The target air-fuel ratio is set as the target air-fuel ratio at the time of rich spike control (step ST7).

  For example, here, the corrected target air-fuel ratio corrected to the over-concentration side can be obtained by taking into account the correction amount specified in advance or the variation correction amount according to the remaining amount that can be collected in the DPF. . In step ST7, a preset target air-fuel ratio may be used. For example, the corrected target air-fuel ratio in this case can be set without depending on the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating conditions.

Thereby, in this case, NOx occluded in the NOx catalyst 72a is placed in a state where the oxygen concentration is lower than that in the operation at the target air-fuel ratio in step ST6, and HC and CO as many reducing agents are placed there. Therefore, more NOx can be reduced to N ₂ . At that time, PM and smoke are generated as compared with the case of operating at the target air-fuel ratio in step ST6. However, since this PM and smoke are collected in the DPF of the exhaust gas purification means 72 having sufficient margin, Release from

As indicated above, exhaust gas purification controller of the multi-fuel internal combustion engine of the first embodiment, thereby both reducing effect of the N ₂ of NOx in the PM and smoke generation suppressing the NOx catalyst 72a. Further, even when PM or smoke is generated, it is prevented from being released into the atmosphere by being collected by the DPF of the exhaust gas purification means 72.

  However, since the operation time of rich spike control (hereinafter referred to as “rich spike time”) Trs is not described in detail in the embodiments described so far, if the rich spike time Trs is too short, the NOx catalyst 72a is not used. All of the stored NOx cannot be reduced, and if this rich spike time Trs is too long, excessive NOx is burned out even though all the NOx has been reduced, resulting in wasted fuel consumption. Will be done.

  Therefore, here, a calculation method of the rich spike time Trs that can reduce all NOx in the NOx catalyst 72a without excess or deficiency in each of the modes will be described based on the flowchart of FIG.

  First, the electronic control device 1 at this time is caused to calculate and input various calculation parameters necessary for obtaining the rich spike time Trs (steps ST11 to ST18). Note that these calculations and inputs may be performed in any order.

  For example, first, the stoichiometric air-fuel ratio AFs of the fuel (hereinafter referred to as “rich spike fuel”) introduced into the combustion chamber CC during the rich spike control is input to the electronic control unit 1 (step ST11).

  In general, the stoichiometric air-fuel ratio differs for each fuel. For this reason, for example, if only the second fuel F2 (gasoline) is used as the rich spike fuel, the stoichiometric air-fuel ratio AF2 of the second fuel F2 is input to the electronic control unit 1. The theoretical air-fuel ratio AF2 may be received simultaneously when the PM / smoke suppression degrees S1, S2 of the first and second fuels F1, F2 are provided from the fueling facility, for example. When the mixed fuel of the first fuel F1 (light oil) and the second fuel F2 is rich spike fuel, the stoichiometric air-fuel ratio AFs corresponding to the fuel mixture ratio of the mixed fuel is input. The stoichiometric air-fuel ratio AFs in this case is calculated from, for example, map data using the stoichiometric air-fuel ratios AF1 and AF2 of the first and second fuels F1 and F2 received from the fueling facility and the fuel mixture ratio as parameters. You can do it. The theoretical air-fuel ratio AFs of the rich spike fuel may be detected from an air-fuel ratio sensor (not shown).

  In addition, the electronic control unit 1 performs the rich spike control at the time of rich spike control suitable for the PM / smoke suppression degree S of the rich spike fuel according to the operating conditions in the same manner as in steps ST1 to ST4 of FIGS. The target air-fuel ratio AFr is calculated (steps ST12 to ST15).

  In addition, the electronic control unit 1 receives the fuel injection amount F (cc / s) per unit time of the fuel injection valve 57 (step ST16). Here, if the fuel injection valve 57 performs injection only at a constant fuel injection amount, a fixed fuel injection amount F per unit time unique to the fuel injection valve 57 is input, and the fuel If the injection valve 57 can change the fuel injection amount according to the operating conditions, the fuel injection amount F per unit time set at the time of this calculation is input.

  Furthermore, the NOx reduction amount Rnox (g / cc) per unit capacity in the rich spike fuel is input to the electronic control unit 1 (step ST17).

  The NOx reduction amount Rnox per unit capacity is a specific value corresponding to the rich spike fuel. When the rich spike fuel is operated in a rich spike control using 1 cc of the rich spike fuel, for example, how much NOx catalyst 72a is supplied. It shows whether the stored NOx is reduced. The NOx reduction amount Rnox per unit capacity can be obtained using the NOx reduction amounts Rnox1 and Rnox2 per unit capacity in the first and second fuels F1 and F2. For example, the NOx reduction amounts Rnox1 and Rnox2 per unit capacity may be received simultaneously when the PM / smoke suppression levels S1 and S2 of the first and second fuels F1 and F2 are provided from the fueling facility. .

  Here, when only the second fuel F2 (gasoline) is used as the rich spike fuel, the NOx reduction amount Rnox2 per unit capacity in the second fuel F2 is input. Further, when the mixed fuel of the first fuel F1 and the second fuel F2 is the rich spike fuel, the NOx reduction amount Rnox per unit capacity corresponding to the fuel mixture ratio of the mixed fuel is input. The NOx reduction amount Rnox per unit capacity in this case is, for example, from map data using the NOx reduction amounts Rnox1 and Rnox2 per unit capacity in the first and second fuels F1 and F2 and the fuel mixture ratio as parameters. What is necessary is just to make it calculate.

  Furthermore, the NOx occlusion amount Snox (g) in the NOx catalyst 72a is input to the electronic control unit 1 (step ST18).

  The NOx occlusion amount Snox can be inferred using an operation state history such as an operation mode and operation conditions from the end of the previous rich spike control. In other words, the amount of NOx generated varies depending on the operating state, and the NOx in the operating state corresponding to the moment changes from moment to moment, starting from the end of the previous rich spike control. It can be estimated by accumulating the generation amount.

  The electronic control unit 1 calculates the rich spike time Trs by substituting the various calculation parameters thus obtained into the following equation 1 (step ST19).

As is apparent from Equation 1, the rich spike time Trs is a target at the time of rich spike control that matches the theoretical air-fuel ratio AFs of the rich spike fuel and the PM / smoke suppression degree S of the rich spike fuel according to the operating conditions. This is a time determined in consideration of the air-fuel ratio AFr, the fuel injection amount F per unit time, the NOx reduction amount Rnox per unit capacity in the rich spike fuel, and the NOx occlusion amount Snox in the NOx catalyst 72a. Therefore, by performing rich spike control using the rich spike fuel for the rich spike time Trs, all NOx stored in the NOx catalyst 72a can be reduced to N ₂ without excess or deficiency. Therefore, in this multi-fuel internal combustion engine, by setting such a rich spike time Trs, during the rich spike control, all NOx is reduced while suppressing an increase in useless fuel consumption. In addition, after the rich spike control is completed, NOx can be newly stored by the storage amount unique to the NOx catalyst 72a. Furthermore, since the high temperature state of the NOx catalyst 72a can be suppressed to the necessary minimum duration, the deterioration and breakage of the NOx catalyst 72a can be minimized.

  Next, a second embodiment of the exhaust gas purification control apparatus for a multi-fuel internal combustion engine according to the present invention will be described with reference to FIGS. Also in the second embodiment, the same multi-fuel internal combustion engine to which the exhaust purification control device is applied is exemplified as in the first embodiment.

  In this multi-fuel internal combustion engine, the exhaust gas purifying means 72 is provided with a function as a PM trapping device (DPF), so that it is impossible to collect PM unless the PM trapped in the DPF is removed. It will be released to the atmosphere as it is. For this reason, also in the second embodiment, an operation mode for removing the collected PM (hereinafter, referred to as “PM regeneration operation mode”), like a general internal combustion engine having such a DPF. It is prepared.

  The PM regeneration operation exemplified here is a normal operation in which the combustion temperature is raised by lean combustion (in this case, lean compression auto-ignition diffusion combustion) closer to the stoichiometric air fuel ratio than the lean air fuel ratio in the normal operation mode. This is an operation in which exhaust gas in an oxygen atmosphere having a temperature higher than that of the time flows into the DPF of the exhaust gas purification means 72, and the PM accumulated in the DPF is oxidized and removed under the high-temperature oxygen atmosphere. is there. This PM regeneration operation is executed as one control mode of the exhaust purification control device.

  By performing the PM regeneration operation in this way, it is possible to remove the PM collected in the DPF, but on the other hand, the fuel guided into the combustion chamber CC at that time is likely to generate PM and smoke. If it is, the PM and smoke are more likely to occur as the air-fuel ratio is controlled to the rich side, although it depends on the operating conditions (engine speed Ne and engine load Kl).

  Therefore, in the second embodiment, when switching from the normal operation mode to the PM regeneration operation mode, the PM / smoke suppression degree S0 of the fuel itself guided into the combustion chamber CC and the operation conditions (engine speed Ne and In accordance with the engine load (Kl), the target air-fuel ratio is set in the PM regeneration operation that can remove PM from the DPF while suppressing the generation of PM and smoke.

  Specifically, also in the second embodiment, as in the rich spike control of the first embodiment described above, the PM / smoke suppression degree S0 of the fuel itself guided into the combustion chamber CC and the operating condition (engine speed Ne) And PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating conditions is obtained based on the engine load Kl). Here, the target air-fuel ratio that can achieve both the suppression of PM and smoke generation and the PM regeneration effect of the DPF during the PM regeneration operation is calculated according to the PM / smoke suppression degree S. The PM / smoke suppression levels S0 and S are obtained in the same manner as in the rich spike control of the first embodiment.

  Here, when the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC corresponding to the operating condition is high (that is, PM and smoke are not easily generated), the air-fuel ratio control amount to the rich side is controlled. Even if the air pressure is increased, the generation of PM and smoke can be suppressed, and the exhaust gas temperature can be further increased by controlling the air-fuel ratio to the richer side within the range of the lean air-fuel ratio. The whole can be heated to oxidize the PM of the entire DPF. On the other hand, when the PM / smoke suppression degree S is low (that is, PM and smoke are likely to be generated), PM and smoke will be generated if the air-fuel ratio control amount to the over-rich side is increased. .

  Therefore, in the second embodiment, as the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC corresponding to the operating condition increases, the air-fuel ratio control amount to the rich side within the lean air-fuel ratio range. The target air-fuel ratio setting map data during the PM regeneration operation shown in FIG. 6 is prepared based on the results of experiments and simulations performed in advance.

  Hereinafter, an example of the target air-fuel ratio setting operation during the PM regeneration operation in the exhaust gas purification control apparatus for the multifuel internal combustion engine of the second embodiment will be described with reference to the flowchart of FIG.

  First, the electronic control unit 1 according to the second embodiment obtains the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating conditions in the same manner as in the first embodiment (step ST21). ~ ST23).

  The air-fuel ratio control means of the electronic control unit 1 of the second embodiment uses the target air-fuel ratio in FIG. 6 described above as the target air-fuel ratio in the PM regeneration operation that conforms to the PM / smoke suppression degree S according to the operating conditions. It is calculated from setting map data and set (step ST24).

  The multifuel internal combustion engine of the second embodiment uses the target air-fuel ratio setting map data to perform compression auto-ignition diffusion under the target air-fuel ratio during PM regeneration operation that is set to the rich side within the lean air-fuel ratio range. Operate in combustion mode.

  As a result, in this multi-fuel internal combustion engine, the temperature of the exhaust gas is raised and the entire DPF is heated while suppressing the generation of PM and smoke. Therefore, in this multi-fuel internal combustion engine, it is possible to oxidize PM deposited in a place where it is difficult to be heated by exhaust gas in the DPF.

  Further, in this multi-fuel internal combustion engine, the higher the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating conditions, the closer the air-fuel ratio becomes to the stoichiometric air-fuel ratio in a range in which PM and smoke are not generated. The amount of oxygen in the exhaust gas can be reduced. Therefore, in this multi-fuel internal combustion engine, a local high temperature portion appears in the DPF as the exhaust gas becomes hot. However, excessive oxidation of PM in such a high temperature portion can be suppressed, so that the local DPF Overheating can be suppressed and deterioration or breakage of DPF (or DPNR) can be prevented.

  Thus, according to the exhaust gas purification control apparatus for a multi-fuel internal combustion engine of the second embodiment, the DPF (or DPNR) is prevented from being deteriorated or damaged while suppressing the generation of PM or smoke during the PM regeneration operation. PM regeneration effect can be obtained.

  By the way, also in the second embodiment, the fuel mixing ratio control means can arbitrarily set the fuel mixing ratio of the first fuel F1 and the second fuel F2 between 0:10 and 10: 0. Therefore, in the multifuel internal combustion engine of the second embodiment, as in the first embodiment, only the second fuel F2 (for example, gasoline) having a relatively high PM / smoke suppression degree S0 among all the fuels is operated. Alternatively, it is possible to operate with a mixed fuel in which the mixing ratio of the second fuel F2 is increased. Accordingly, when setting the target air-fuel ratio at the time of the PM regeneration operation described above, only the second fuel F2 having a relatively high PM / smoke suppression degree S0 or a mixed fuel in which the mixing ratio of the second fuel F2 is increased is used. The target air-fuel ratio may be calculated as an operation. Thereby, in this case, since the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating condition is increased, the target air-fuel ratio at the time of the PM regeneration operation is further set to the rich side. As a result, it is possible to remove more PM accumulated in the DPF while preventing the deterioration and breakage of the DPF (or DPNR) while suppressing the generation of PM and smoke.

  Here, in the above-described example, the target air-fuel ratio in the PM regeneration operation suitable for the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating conditions is set. The amount of oxygen is not necessarily reduced to such an extent that the deterioration or breakage of DPF (or DPNR) can be prevented. Therefore, if the amount of oxygen is large, the DPF (or DPNR) may be deteriorated or damaged, and PM or smoke may be released to the atmosphere.

  Therefore, here, the target air-fuel ratio AFpm at the time of the PM regeneration operation that can minimize the oxygen amount in the exhaust gas while setting the oxygen amount in the exhaust gas sufficient for PM regeneration is set. . Hereinafter, a method for calculating the target air-fuel ratio AFpm will be described with reference to the flowchart of FIG.

  First, the electronic control unit 1 at this time is input with the stoichiometric air-fuel ratio AFs of the fuel (hereinafter referred to as “PM regeneration fuel”) introduced into the combustion chamber CC during the PM regeneration operation (step ST31). The current engine speed Ne and engine load Kl are also input (step ST32). Here, the theoretical air-fuel ratio AFs of the PM regeneration fuel is obtained in the same manner as the theoretical air-fuel ratio AFs of the rich spike fuel in the first embodiment.

  Subsequently, the electronic control unit 1 calculates a target oxygen supply rate Ro corresponding to the operating conditions (the engine speed Ne and the engine load Kl) (step ST33).

  Here, the target oxygen supply ratio Ro is a PM regeneration operation in which the PM accumulated in the DPF is oxidized and a minimum oxygen amount that can prevent the deterioration of the DPF (or DPNR) is obtained. The target air-fuel ratio AFpm is set so that the target air-fuel ratio AFpm is slightly leaner than the stoichiometric air-fuel ratio AFs of the PM regeneration fuel according to the operating conditions.

  Here, the higher the engine speed Ne or the higher the engine load Kl, the more air is sucked into the combustion chamber CC per unit time even at the same air-fuel ratio. The target oxygen supply ratio Ro is decreased as the value increases. For example, the target oxygen supply ratio Ro is the target oxygen supply ratio setting map data of FIG. 9 using the operating conditions (engine speed Ne and engine load Kl) set in advance based on the results of experiments and simulations as parameters. Based on the above.

  The electronic control unit 1 calculates the target air-fuel ratio AFpm during the PM regeneration operation by substituting the theoretical air-fuel ratio AFs of the PM regeneration fuel and the target oxygen supply ratio Ro thus obtained into the following formula 2. ST34).

  The target air-fuel ratio AFpm obtained from this equation 2 is an air-fuel ratio obtained by taking into account the theoretical air-fuel ratio AFs of the PM regeneration fuel and the target oxygen supply ratio Ro as described above. Therefore, by performing the PM regeneration operation at the target air-fuel ratio AFpm, the DPF has a minimum oxygen that is necessary and sufficient to oxidize PM and that can prevent deterioration of the DPF (or DPNR). Supplied. For this reason, by setting such a target air-fuel ratio AFpm, the PM accumulated in the DPF is oxidized and the PM is regenerated, and the deterioration or breakage of the DPF (or DPNR) is minimized. Will be able to.

  Next, a third embodiment of the exhaust gas purification control apparatus for a multi-fuel internal combustion engine according to the present invention will be described with reference to FIGS. Also in the third embodiment, the multi-fuel internal combustion engine to which the exhaust purification control device is applied is exemplified by the same ones as in the first and second embodiments.

  In this multi-fuel internal combustion engine, light oil and gasoline are cited as typical examples of the first fuel F1 and the second fuel F2, respectively, and since sulfur (S) is contained in these, the sulfur content Is oxidized with lean combustion during normal operation to produce sulfur oxide (SOx). For this reason, in this multifuel internal combustion engine, when the SOx flows into the NOx catalyst 72a, which is a NOx occlusion reduction type catalyst, together with the exhaust gas, the NOx catalyst 72a is covered with SOx (specifically, the SOx Is stored in the catalyst in the form of a sulfate salt) and the NOx storage capacity is reduced.

  Thus, when this multi-fuel internal combustion engine is operated not only with light oil and gasoline but also with a fuel containing sulfur, there is always a problem that the NOx occlusion capacity is lowered due to sulfur poisoning of the NOx catalyst 72a. Therefore, in general, in an internal combustion engine provided with such a NOx catalyst 72a, it is assumed that sulfur poisoning occurs, and the air-fuel ratio is controlled to be richer than the lean air-fuel ratio for a short time. Rich spike control for combustion is performed to create a high-temperature exhaust gas and a reducing atmosphere to recover the NOx catalyst 72a from the sulfur poisoning state.

  Also in the multifuel internal combustion engine of the third embodiment, a sulfur poisoning regeneration operation mode for performing rich spike control for recovering such a NOx catalyst 72a from the sulfur poisoning state is prepared. When the mode is switched, the compression auto-ignition diffusion combustion is performed by controlling the air-fuel ratio from the lean air-fuel ratio to the stoichiometric air-fuel ratio or the rich air-fuel ratio.

  Here, since the sulfate is in a more stable state than the nitrate, the NOx catalyst 72a can hardly be recovered from the sulfur poisoning state by the rich spike control for a very short time, such as during NOx reduction. For this reason, the SOx stored in the NOx catalyst 72a cannot be removed unless the NOx catalyst 72a is heated to a higher temperature and exposed to a reducing atmosphere. Therefore, in the sulfur poisoning regeneration operation mode of the third embodiment, the exhaust gas temperature is raised by increasing the air-fuel ratio control amount to the over-concentration side and operating at the over-concentration over-concentration air-fuel ratio as much as possible. It is preferable to plan.

  However, if the fuel introduced into the combustion chamber CC is of a nature that easily generates PM or smoke, the air-fuel ratio will depend on the operating conditions (engine speed Ne and engine load Kl) at that time. PM and smoke are more likely to occur as controlled to the over-rich side.

  Therefore, in the third embodiment, when switching from the normal operation mode to the sulfur poisoning regeneration operation mode, the PM / smoke suppression degree S0 of the fuel itself guided into the combustion chamber CC and the operation condition (engine speed) In accordance with Ne and engine load Kl), the target air-fuel ratio at the time of the sulfur poisoning regeneration operation capable of recovering the NOx catalyst 72a from the sulfur poisoning state while suppressing the generation of PM and smoke is set.

  Specifically, also in the third embodiment, similarly to the rich spike control of the first embodiment described above, the PM / smoke suppression degree S0 of the fuel itself guided into the combustion chamber CC and the operating condition (the engine speed Ne). And PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating conditions is obtained based on the engine load Kl). Here, according to the PM / smoke suppression degree S, the target sky that can achieve both suppression of PM and smoke generation and recovery effect from the sulfur poisoning state of the NOx catalyst 72a during the sulfur poisoning regeneration operation. Calculate the fuel ratio. The PM / smoke suppression levels S0 and S are obtained in the same manner as in the rich spike control of the first embodiment.

  Here, when the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC corresponding to the operating condition is high (that is, PM and smoke are not easily generated), the air-fuel ratio control amount to the rich side is controlled. Even if it is increased, the generation of PM and smoke can be suppressed, and rather, the SOx occluded in the NOx catalyst 72a as described above can be easily removed by controlling the air-fuel ratio to a richer side. On the other hand, when the PM / smoke suppression degree S is low (that is, PM and smoke are likely to be generated), PM and smoke will be generated if the air-fuel ratio control amount to the over-rich side is increased. .

  Therefore, in the third embodiment, the target air-fuel ratio, in which the air-fuel ratio control amount to the rich side is increased as the PM Smoke suppression degree S of the fuel guided into the combustion chamber CC corresponding to the operating condition becomes higher, is obtained. The target air-fuel ratio setting map data for the sulfur poisoning regeneration operation shown in FIG. 10 is prepared in advance so as to be set. In FIG. 10, the target air-fuel ratio setting map data set to the rich air-fuel ratio to be overburned during the sulfur poisoning regeneration operation is illustrated, but the target air-fuel ratio setting map data is illustrated. The stoichiometric air-fuel ratio may also be settable.

  Hereinafter, an example of the target air-fuel ratio setting operation during the sulfur poisoning regeneration operation in the exhaust gas purification control apparatus of the multifuel internal combustion engine of the third embodiment will be described based on the flowchart of FIG.

  First, the electronic control unit 1 according to the third embodiment obtains the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating conditions in the same manner as in the first embodiment (step ST41). ~ ST43).

  Then, the air-fuel ratio control means of the electronic control unit 1 of the third embodiment uses the target air-fuel ratio in the sulfur poisoning regeneration operation that matches the PM / smoke suppression degree S according to the operation conditions as described above in FIG. It is calculated and set from the air-fuel ratio setting map data (step ST44).

  As described above, the exhaust gas purification control apparatus for the multi-fuel internal combustion engine according to the third embodiment performs the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operation condition when performing the sulfur poisoning regeneration operation. The higher the air-fuel ratio, the larger the air-fuel ratio control amount to the rich side, and the target air-fuel ratio is set between the stoichiometric air-fuel ratio and the rich air-fuel ratio. Run in mode.

  Therefore, in this multi-fuel internal combustion engine, as the PM / smoke suppression degree S corresponding to the operating conditions increases, it becomes easier to suppress PM and smoke generation, and the SOx occluded in the NOx catalyst 72a becomes higher in temperature. Therefore, a lot of SOx is easily removed. On the other hand, in this multi-fuel internal combustion engine, when the PM / smoke suppression degree S according to the operating conditions is low, the air-fuel ratio control amount to the rich side is small, so while reducing the SOx, Smoke generation can be suppressed. Therefore, according to the exhaust gas purification control device of the multi-fuel internal combustion engine, while suppressing the generation of PM and smoke during the sulfur poisoning regeneration operation, the good sulfur of the NOx catalyst 72a suitable for the PM / smoke suppression degree S is achieved. A recovery effect from the poisoned state can be obtained.

  Incidentally, also in the third embodiment, the fuel mixing ratio control means can arbitrarily set the fuel mixing ratio of the first fuel F1 and the second fuel F2 between 0:10 and 10: 0. For this reason, even in the multifuel internal combustion engine of the third embodiment, if it is possible to operate only with the second fuel F2 (gasoline) having a relatively high PM / smoke suppression degree S0 among all the fuels, It is also possible to operate with a mixed fuel in which the mixing ratio of F2 is increased. Therefore, when setting the target air-fuel ratio during the above-described sulfur poisoning regeneration operation, only the second fuel F2 having a relatively high PM / smoke suppression degree S0 or a mixture in which the mixing ratio of the second fuel F2 is increased is used. The target air-fuel ratio may be calculated as an operation with fuel. As a result, in this case, the PM / smoke suppression degree S of the fuel guided into the combustion chamber CC according to the operating conditions increases, so that the target air-fuel ratio at the time of the sulfur poisoning regeneration operation is further increased to the rich side. Thus, it is possible to remove more SOx occluded in the NOx catalyst 72a while suppressing the generation of PM and smoke.

  As described above, the exhaust gas purification control apparatus for the multi-fuel internal combustion engine of the third embodiment achieves both the suppression of PM and smoke generation and the recovery effect from the sulfur poisoning state of the NOx catalyst 72a.

  However, since the operation time during the sulfur poisoning regeneration operation (hereinafter referred to as “sulfur poisoning regeneration operation time”) is not described in detail in the embodiments described so far, this sulfur poisoning regeneration operation time is not described. If it is too short, all of the SOx stored in the NOx catalyst 72a cannot be removed, and if this sulfur poisoning regeneration operation time is too long, it is excessively concentrated even though all of the SOx has been removed. It is burned and wasteful fuel consumption occurs.

  Therefore, here, an exhaust purification control apparatus capable of removing all the SOx of the NOx catalyst 72a without excess or deficiency in each of the modes will be described with reference to the flowchart of FIG. To do.

  First, in the electronic control unit 1 at this time, the target air-fuel ratio at the time of the sulfur poisoning regeneration operation that conforms to the PM / smoke suppression degree S according to the operation conditions is performed in the same manner as in the flowchart of FIG. Is obtained (steps ST41 to ST44).

  And this electronic control unit 1 calculates | requires and sets the sulfur poisoning reproduction | regeneration operation time according to the target air fuel ratio (step ST45).

  Here, as described above, the effect of recovery from the sulfur poisoning state increases as the air-fuel ratio becomes richer. For this reason, when it is assumed that all SOx of the NOx catalyst 72a is reduced by operating for a reference sulfur poisoning regeneration operation time at a reference rich air-fuel ratio, the storage amount of the SOx is the same and the same. When the sulfur poisoning regeneration operation is performed for a certain amount of time, if the target air-fuel ratio is leaner than the reference over-rich air-fuel ratio, all SOx cannot be removed, and the target air-fuel ratio exceeds the reference over-rich air-fuel ratio. However, if it is on the rich side, fuel is wasted even though all the SOx has been removed.

  Therefore, the sulfur poisoning regeneration operation time is set so as to become shorter as the target air-fuel ratio becomes richer. For example, here, the relationship between the two is obtained by using the sulfur poisoning regeneration operation time setting map data shown in FIG. 13 which has been set in advance based on the results of experiments and simulations.

  As a result, the multi-fuel internal combustion engine performs the sulfur poisoning regeneration operation only for the optimum sulfur poisoning regeneration operation time corresponding to the target air-fuel ratio, so that all the SOx stored in the NOx catalyst 72a can be obtained without excess or deficiency. Can be removed. Therefore, in this multi-fuel internal combustion engine, by setting such a sulfur poisoning regeneration operation time, it becomes possible to remove all SOx while suppressing an increase in wasteful fuel consumption, Since the high temperature state of the NOx catalyst 72a can be suppressed to the necessary minimum duration, deterioration and breakage of the NOx catalyst 72a can be minimized.

  By the way, in each of the above-described first to third embodiments, the multi-fuel internal combustion engine that is operated only in the compression auto-ignition diffusion combustion mode has been illustrated, but each exhaust purification control device in each of the first to third embodiments includes, for example, The present invention can be applied to the following multi-fuel internal combustion engines having other combustion modes, and the same effects as these can be obtained.

  For example, in each of the first to third embodiments, when a fuel having a high PM / smoke suppression degree S0 and a good vaporization property is used, the ignitability of the mixed fuel is deteriorated, so that the combustion chamber corresponding to the operating conditions is used. Depending on the ignitability within the CC, even if the mixed fuel is injected into the compressed air, there is a possibility of causing inconvenience such as inability to self-ignite or misfiring after self-ignition. For this reason, in such a case, it is preferable to perform compression auto-ignition diffusion combustion mode operation by assisting ignition, and the multi-fuel internal combustion engine of each of the first to third embodiments is provided with a spark plug 81 shown in FIG. A multi-fuel internal combustion engine that performs compression auto-ignition diffusion combustion (spark-assisted compression auto-ignition diffusion combustion) while assisting ignition by spark ignition of the spark plug 81 may be used.

  Further, as a typical combustion mode other than the compression auto-ignition diffusion combustion mode, a premixed spark ignition flame propagation combustion mode is known, and a multi-fuel internal combustion engine operated only in this premixed spark ignition flame propagation combustion mode is known. You may apply each exhaust gas purification control apparatus in each Examples 1-3 to an engine.

  In the premixed spark ignition flame propagation combustion mode, the premixed gas in the combustion chamber CC in which fuel and air are mixed in advance is given a spark by spark ignition, and combustion is performed while propagating the flame around the fire type. It is a combustion mode to be advanced, and generally a highly evaporative fuel represented by gasoline or alcohol fuel is suitable. In this premixed spark ignition flame propagation combustion mode, homogeneous combustion for igniting a homogeneously mixed premixed gas or a highly concentrated premixed gas is formed around the ignition means, and further, a lean mixture is formed around the premixed spark ignition flame propagation combustion mode. It includes a combustion mode such as stratified combustion in which a premixed gas is formed and ignition is performed on the rich premixed gas.

  For example, this type of multi-fuel internal combustion engine can also be constituted by components similar to those of the multi-fuel internal combustion engine shown in FIG. The apparatus 50 can be replaced with a fuel supply apparatus 150 shown in FIG. 15, and a spark plug 81 can be provided.

  The fuel supply device 150 shown in FIG. 15 is obtained by changing the fuel supply direction downstream side of the fuel mixing unit 53 of the fuel supply device 50 of each of the first to third embodiments, and is generated by the fuel mixing unit 53. A fuel pump 155 that discharges the mixed fuel to the fuel passage 154, a delivery passage 156 that distributes the mixed fuel in the fuel passage 154 to each cylinder, and an intake port of each cylinder that supplies the mixed fuel supplied from the delivery passage 156 And a fuel injection valve 157 for each cylinder that injects fuel into the cylinder 11b.

  Further, another multi-fuel internal combustion engine may be operated in both the compression auto-ignition diffusion combustion mode and the premixed spark ignition flame propagation combustion mode described above. The exhaust purification control apparatus may be applied.

  For example, in this type of multi-fuel internal combustion engine, in the multi-fuel internal combustion engine of each of the first to third embodiments, the fuel supply device 50 is replaced with a fuel supply device 250 shown in FIG. Can be configured. The fuel supply device 250 shown in FIG. 16 includes a fuel passage 154 and a fuel pump 155 similar to the fuel supply device 150 shown in FIG. 15 described above, in addition to the various components of the fuel supply devices 50 of the first to third embodiments. , A delivery passage 156 and a fuel injection valve 157 are provided.

  Further, as another multi-fuel internal combustion engine, there can be considered a multi-fuel internal combustion engine shown in FIG. 16 provided with a fuel supply path for each fuel. May be applied.

  For example, this type of multi-fuel internal combustion engine can be configured by replacing the fuel supply device 250 with a fuel supply device 350 shown in FIG. 17 in the multi-fuel internal combustion engine shown in FIG.

  The fuel supply device 350 shown in FIG. 17 includes a first fuel supply path that directly injects the first fuel F1 into the combustion chamber CC, and a second fuel supply path that injects the second fuel F2 into the intake port 11b. It is provided. The first fuel supply path includes a first feed pump 352A that sucks up the first fuel F1 from the first fuel tank 41A and delivers it to the first fuel passage 351A, and the first fuel F1 in the first fuel passage 351A as a high-pressure fuel. A high pressure fuel pump 355A for pumping to the passage 354A, a first delivery passage 356A for distributing the first fuel F1 in the high pressure fuel passage 354A to the respective cylinders, and the first fuel F1 supplied from the first delivery passage 356A And a fuel injection valve 357A for each cylinder that injects into the combustion chamber CC. On the other hand, the second fuel supply path sucks the second fuel F2 from the second fuel tank 41B and sends it to the second fuel passage 351B, and the second fuel F2 in the second fuel passage 351B, respectively. And a fuel injection valve 357B for each cylinder that injects the second fuel F2 supplied from the second delivery passage 356B into the intake port 11b.

  As described above, the exhaust gas purification control apparatus for a multi-fuel internal combustion engine according to the present invention suppresses the generation of PM and smoke when the air-fuel ratio is controlled to be richer than the current state according to the state of the exhaust gas purification means. Useful for technology

It is a figure shown about the structure of the multi-fuel internal combustion engine to which the exhaust gas purification control apparatus which concerns on this invention is applied. It is a figure which shows an example of the target air fuel ratio setting map data at the time of rich spike control in Example 1. FIG. 3 is a flowchart for explaining a setting operation of a target air-fuel ratio at the time of rich spike control in the first embodiment. 7 is a flowchart illustrating a modification of the target air-fuel ratio setting operation during rich spike control according to the first embodiment. 5 is a flowchart for explaining a calculation operation of a rich spike time in the first embodiment. It is a figure which shows an example of the target air fuel ratio setting map data at the time of PM reproduction | regeneration driving | operation in Example 2. FIG. 6 is a flowchart illustrating a setting operation of a target air-fuel ratio during PM regeneration operation in Embodiment 2. 12 is a flowchart for explaining a modification example of the target air-fuel ratio setting operation during PM regeneration operation in the second embodiment. It is a figure which shows an example of the target oxygen supply ratio setting map data in Example 2. FIG. It is a figure which shows an example of the target air fuel ratio setting map data at the time of the sulfur poisoning reproduction | regeneration operation | movement in Example 3. FIG. 10 is a flowchart for explaining a setting operation of a target air-fuel ratio at the time of sulfur poisoning regeneration operation in Embodiment 3. 6 is a flowchart for explaining a calculation operation of a sulfur poisoning regeneration operation time in the third embodiment. It is a figure which shows an example of the sulfur poisoning reproduction | regeneration driving | operation time setting map data in Example 3. FIG. It is a figure shown about the structure of the other multi-fuel internal combustion engine to which the exhaust gas purification control apparatus which concerns on this invention is applied. It is a figure shown about the structure of the other multi-fuel internal combustion engine to which the exhaust gas purification control apparatus which concerns on this invention is applied. It is a figure shown about the structure of the other multi-fuel internal combustion engine to which the exhaust gas purification control apparatus which concerns on this invention is applied. It is a figure shown about the structure of the other multi-fuel internal combustion engine to which the exhaust gas purification control apparatus which concerns on this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electronic controller 41A 1st fuel tank 41B 2nd fuel tank 72 Exhaust purification means 72a NOx catalyst 73 Smoke sensor 74,75 Pressure sensor F1 1st fuel F2 2nd fuel

Claims (4)

In an exhaust purification control apparatus for a multi-fuel internal combustion engine operated using at least one of at least two types of fuels having different properties,
When the air-fuel ratio at the time of combustion is controlled to be richer than the current state according to the state of the exhaust gas purification means, the higher the degree of PM / smoke suppression of the fuel guided into the combustion chamber according to the operating conditions, the higher the air-fuel ratio to the richer side. When the control to the rich side is increased , the fuel ratio with a high degree of PM / smoke suppression in the fuel introduced into the combustion chamber is increased during the control to the rich side, and at that time, the PM by the PM trapping device is increased. If the trapped amount of smoke or smoke is less than a predetermined amount, the exhaust gas purification control device for a multi-fuel internal combustion engine further increases the control amount of the air-fuel ratio to the rich side.   The target air-fuel ratio closer to the stoichiometric air-fuel ratio that can suppress the generation of PM and smoke within the range of the lean air-fuel ratio, the higher the degree of PM / smoke suppression of the fuel guided into the combustion chamber during regeneration of the PM trapping device The exhaust gas purification control device for a multi-fuel internal combustion engine according to claim 1, wherein   The multi-fuel internal combustion engine according to claim 1 or 2, wherein a combustion mode when the air-fuel ratio control to the rich side is performed is a compression auto-ignition diffusion combustion mode or a premixed spark ignition flame propagation combustion mode. Engine exhaust purification control device.   The state of the exhaust purification unit is a state in which a temperature increase request is made or a reduction request is made in the exhaust purification unit. An exhaust purification control device for a fuel internal combustion engine.

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