JP2004183626A - Intake-air amount controller of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an intake-air amount controller of an internal combustion engine capable of suppressing damage of a catalyst caused by decrease of injection pressure of fuel. <P>SOLUTION: The internal combustion engine 2 comprises a throttle valve 6 actuated by an actuator 12, and a fuel pressure sensor 22 for detecting fuel injection pressure. An electronic control device 10 sets, as a target suction air amount, the smaller one of a first suction air amount calculated based on a load request of a driver and a second suction air amount where the air-fuel ratio is set at the target air-fuel ratio with respect to the maximum injection amount of the fuel allowed by the injection amount of the fuel at that time. The actuator 12 is controlled so as to adjust an opening of the throttle valve 6 to the opening providing the set target suction air amount. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an intake air amount control device for an internal combustion engine.
[0002]
[Prior art]
In an internal combustion engine using compressed natural gas (CNG), gaseous fuel (methane gas or the like) is stored in a compressed state in a fuel tank, and fuel injection control for injecting fuel in a gaseous state from a fuel injection valve is performed. In this fuel injection control, first, a fuel injection amount is obtained from the intake air amount and the engine speed, and the fuel injection time required to supply the fuel of this fuel injection amount to the combustion chamber, that is, the opening of the fuel injection valve. The valve time is calculated.
[0003]
Here, in an internal combustion engine that uses compressed natural gas as fuel, if the pressure in the fuel tank decreases due to an excessive decrease in gaseous fuel in the fuel tank, the fuel injection pressure also decreases. When the fuel injection pressure decreases in this way, the fuel injection amount per unit time decreases. Therefore, in order to supply the required fuel injection amount into the combustion chamber, it is necessary to increase the fuel injection time as the injection pressure decreases. However, there is a limit to the time during which fuel can be supplied to the combustion chamber, and usually, the fuel injection time cannot take a value longer than the maximum fuel injection time according to the engine speed. Therefore, even if the maximum fuel injection time is reached, if the injection pressure is so low that the required fuel injection amount cannot be injected, the amount of fuel supplied to the combustion chamber becomes insufficient.
[0004]
On the other hand, a recent exhaust system of an internal combustion engine is provided with a catalyst for purifying harmful components in exhaust gas. It is known that this catalyst can be damaged in the shortage of fuel conditions described above.
[0005]
For example, when a misfire occurs due to a shortage of fuel and unburned gas is introduced into the exhaust passage, the unburned gas burns on the hot catalyst, and the catalyst is overheated.
In addition, when the air-fuel ratio of the air-fuel mixture becomes lean due to a shortage of fuel and the oxygen concentration in the exhaust gas becomes high, the deterioration of the high-temperature catalyst proceeds, which may damage the catalyst. It is also known that there are.
[0006]
Therefore, in order to suppress damage to the catalyst due to a decrease in the fuel injection pressure in an internal combustion engine using such compressed natural gas as a fuel, for example, in the device described in Patent Document 1, when the fuel injection pressure is reduced, the device is intermittent. To cut fuel. If the fuel cut is performed in this manner, the generation of unburned gas is suppressed, so that the above-described damage to the catalyst due to the unburned gas can be suppressed.
[0007]
[Patent Document 1]
JP 2000-345921 A
[0008]
[Problems to be solved by the invention]
However, in the device described in Patent Document 1, since the fuel cut is performed intermittently, only air is introduced into the exhaust passage during the fuel cut. Therefore, it is difficult to suppress the deterioration of the catalyst which proceeds in the atmosphere having a high oxygen concentration as described above.
[0009]
Not only the internal combustion engine for compressed natural gas, but also in an internal combustion engine for liquefied natural gas in which fuel in a gas phase or a liquid phase is injected from a fuel injection valve, or in a gasoline engine or a diesel engine, The above problems caused by a decrease in the fuel injection pressure are generally common.
[0010]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an intake air amount control device for an internal combustion engine that can suppress catalyst damage due to a decrease in fuel injection pressure. is there.
[0011]
[Means for Solving the Problems]
The means for achieving the above object and the effects thereof will be described below.
The invention according to claim 1 is an intake air amount control device for an internal combustion engine, which is permitted by a first intake air amount calculated based on a driver's load request and a fuel injection pressure at that time. The gist is to set the smaller one of the second intake air amount for setting the air-fuel ratio to the target air-fuel ratio with respect to the maximum fuel injection amount as the target intake air amount.
[0012]
In this configuration, the intake air amount for setting the air-fuel ratio to the target air-fuel ratio with respect to the maximum injection amount that can be injected with the fuel injection pressure at that time is set as the second intake air amount. Therefore, even if the injection pressure of the fuel is reduced and the required fuel injection amount cannot be completely injected within the fuel injection time, if at least the second intake air amount is set as the target intake air amount, The air-fuel ratio can be set to the target air-fuel ratio.
[0013]
The smaller of the second intake air amount and the first intake air amount calculated based on the driver's load request is set as the target intake air amount. Therefore, an intake air amount equal to or larger than the second intake air amount is not set as the target intake air amount, and the air-fuel ratio can be set to the target air-fuel ratio even when the fuel injection pressure decreases. . At this time, by appropriately setting the target air-fuel ratio, it is possible to suppress the damage to the catalyst due to the decrease in the fuel injection pressure.
[0014]
According to a second aspect of the present invention, in the intake air amount control device for an internal combustion engine according to the first aspect, it is determined whether or not to execute the setting of the target intake air amount based on a fuel injection pressure. Is the gist.
[0015]
If the fuel injection pressure is high, that is, if the injection pressure is such that the fuel injection amount can be ensured in accordance with the driver's load request, the above-described reduction in the fuel injection pressure hardly causes damage to the catalyst. Therefore, in the configuration of the second aspect, it is determined whether or not to execute the setting of the target intake air amount based on the fuel injection pressure. Therefore, when there is no risk of catalyst damage, the setting of the target intake air amount is not performed, and, for example, the load on the control device that performs the setting can be reduced appropriately.
[0016]
According to a third aspect of the present invention, there is provided an intake air amount control device for an internal combustion engine, wherein the fuel injection pressure is lower than an injection pressure capable of securing a fuel injection amount according to a load demand of a driver. The gist is to set the intake air amount for setting the air-fuel ratio to the target air-fuel ratio with respect to the maximum fuel injection amount permitted by the injection pressure at that time as the target intake air amount.
[0017]
According to this configuration, when the injection pressure of the fuel decreases and the required fuel injection amount cannot be completely injected within the fuel injection time, the air-fuel ratio is set to the target air-fuel ratio with respect to the maximum injection amount that can be injected at the fuel injection pressure. The intake air amount for setting the fuel ratio is set as the target intake air amount. Therefore, even when the fuel injection pressure decreases, the air-fuel ratio can be set to the target air-fuel ratio. At this time, if the target air-fuel ratio is appropriately set, it is possible to suppress the damage to the catalyst due to the decrease in the fuel injection pressure.
[0018]
According to a fourth aspect of the present invention, in the intake air amount control device for an internal combustion engine according to any one of the first to third aspects, the gist is that a stoichiometric air-fuel ratio is set as the target air-fuel ratio.
[0019]
According to this configuration, the air-fuel ratio is set to the stoichiometric air-fuel ratio even when the fuel injection pressure decreases. When the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio in this way, the generation of unburned gas due to misfire is suppressed, and the oxygen concentration in the exhaust gas is also kept low. Can be suppressed.
[0020]
According to a fifth aspect of the present invention, in the intake air amount control apparatus for an internal combustion engine according to any one of the first to third aspects, damage to a catalyst provided in an exhaust system of the internal combustion engine is avoided as the target air-fuel ratio. The gist is that the minimum value of the obtained air-fuel ratio is set.
[0021]
Even when the air-fuel ratio of the air-fuel mixture becomes lean, damage to the catalyst can be suppressed unless it is excessively lean. In view of this point, in the configuration according to the fifth aspect, the minimum value of the air-fuel ratio that is set through experiments and the like and that can avoid damage to the catalyst is set as the target air-fuel ratio. Therefore, even if the fuel injection pressure decreases, damage to the catalyst can be reliably suppressed.
[0022]
According to a sixth aspect of the present invention, in the intake air amount control device for an internal combustion engine according to any one of the first to third aspects, the target air-fuel ratio is a minimum value of an air-fuel ratio capable of avoiding occurrence of misfire of the air-fuel mixture. Is set as the gist.
[0023]
Even in the case where the air-fuel ratio of the air-fuel mixture becomes lean, unless the air-fuel ratio is excessively lean, misfire of the air-fuel mixture hardly occurs and damage to the catalyst can be suppressed. Further, in a situation where misfire is unlikely to occur, that is, in a situation where fuel combustion is performed normally, the amount of unburned gas in exhaust gas is also kept low. In view of this point, in the configuration of the sixth aspect, the minimum value of the air-fuel ratio that is set through experiments and the like and that can avoid misfire of the air-fuel mixture is set as the target air-fuel ratio. Therefore, even if the fuel injection pressure decreases, damage to the catalyst can be reliably suppressed.
[0024]
According to a seventh aspect of the present invention, in the intake air amount control device for an internal combustion engine according to any one of the first to sixth aspects, a metering mechanism for adjusting an intake air amount as a parameter representing the intake air amount is provided. The gist is that a controlled variable is used.
[0025]
According to this configuration, the first intake air amount and the second intake air amount are actually secured by the adjustment mechanism that adjusts the intake air amount. Therefore, the actual intake air amount can be adjusted to the target intake air amount.
[0026]
According to an eighth aspect of the present invention, in the intake air amount control apparatus for an internal combustion engine according to the seventh aspect, an opening degree of a throttle valve provided in an intake passage is used as a control amount of the metering mechanism. This is the gist.
[0027]
According to this configuration, the control amount of the throttle valve, that is, the throttle opening is set to an opening that can secure the target air amount, so that the actual intake air amount is reliably adjusted to the target intake air amount. Will be able to do it.
[0028]
According to a ninth aspect of the present invention, in the intake air amount control device for an internal combustion engine according to any one of the first to eighth aspects, the gist is that the internal combustion engine is an internal combustion engine using a gaseous fuel.
[0029]
In an internal combustion engine that uses gaseous fuel, the fuel injection pressure tends to decrease when the fuel in the fuel tank decreases, and the damage to the catalyst due to a decrease in the fuel injection pressure is lower than in internal combustion engines that use other fuels. Easy to happen. In this regard, according to the configuration of the ninth aspect of the present invention, in which the configuration of the first aspect is applied to an internal combustion engine using a gaseous fuel, such a problem is effectively solved. Will be able to do it.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an intake air amount control device for an internal combustion engine according to the present invention will be described in detail with reference to FIGS.
[0031]
FIG. 1 is a schematic configuration diagram showing an internal combustion engine 2 using compressed natural gas as a fuel to which the intake air amount control device is applied, and a fuel supply system thereof.
The internal combustion engine 2 has a plurality of cylinders, and a mixture of air sucked from an intake passage 4 and fuel injected from a fuel injection valve 16 is sucked into a combustion chamber 2c defined by a cylinder 2a and a piston 2b. Is done. Then, the air-fuel mixture is ignited by an ignition plug provided in the combustion chamber 2c and burned, and after combustion, is discharged from the combustion chamber 2c to the exhaust passage 18 as exhaust gas.
[0032]
A throttle valve 6 constituting a mechanism for adjusting the amount of intake air is disposed in the intake passage 4, and the opening of the throttle valve 6 is adjusted by an actuator 12. A catalyst 19 for purifying harmful components in the exhaust gas is provided in the exhaust passage 18.
[0033]
The fuel supply system of the internal combustion engine 2 includes a fuel tank 30, a high-pressure fuel pipe 31, a low-pressure fuel pipe 33, a pressure reducing valve 32, a delivery pipe 34, and a fuel injection valve 16 (see FIG. (Only one is shown).
[0034]
In the fuel tank 30, compressed gaseous fuel (for example, methane gas or the like) is stored in a gaseous state. The high pressure fuel pipe 31 is connected to the inside of the fuel tank 30 and the pressure reducing valve 32.
[0035]
The pressure reducing valve 32 is a valve for reducing the pressure of the gaseous fuel in the fuel tank 30 and supplying it to the fuel injection valve 16. The pressure reducing valve 32 is connected between the pressure reducing valve 32 and the delivery pipe 34 by a low pressure fuel pipe 33. ing.
[0036]
The fuel injection valves 16 provided for the respective cylinders of the internal combustion engine 2 are connected to the delivery pipes 34. The delivery pipes 34 supply the gas fuel supplied from the low-pressure fuel pipe 33 to the fuel injection valves 16. A fuel distribution pipe for supplying to the fuel supply line 16 is provided.
[0037]
The delivery pipe 34 is provided with a fuel pressure sensor 22 for detecting a fuel pressure in the delivery pipe 34, in other words, a fuel injection pressure PF.
On the other hand, the internal combustion engine 2 is provided with various sensors for detecting an engine operating state in addition to the fuel pressure sensor 22. For example, an engine speed sensor 23 provided close to a crankshaft which is an output shaft of the internal combustion engine 2 detects an engine speed NE of the internal combustion engine 2 (crankshaft). Further, an intake air amount sensor 20 provided in the intake passage 4 detects an intake air amount GN. The throttle opening sensor 21 detects the opening of the throttle valve 6, that is, the throttle opening. The accelerator opening sensor 24 detects the amount of depression of an accelerator pedal operated by the driver, that is, the accelerator opening ACCP.
[0038]
Various controls such as the fuel injection control of the internal combustion engine 2 and the throttle valve opening control are performed by the electronic control unit 10. The electronic control device 10 is mainly configured by a microcomputer having a central processing control device (CPU). For example, the electronic control unit 10 is provided with a read-only memory (ROM) in which various programs, maps, and the like are stored in advance, and a random access memory (RAM) in which calculation results of the CPU and the like are temporarily stored. The electronic control unit 10 is also provided with a backup RAM, an input interface, an output interface, and the like for storing calculation results, pre-stored data, and the like even after the engine stops. Output signals from the intake air amount sensor 20, the throttle opening sensor 21, the fuel pressure sensor 22, the engine speed sensor 23, the accelerator opening sensor 24, and the like are input to the input interface. The operating state of the internal combustion engine 2 is detected by these sensors and the like.
[0039]
On the other hand, the output interface is connected to a drive circuit for driving each fuel injection valve 16 of the internal combustion engine 2, a drive circuit for driving the actuator 12, and the like. Then, based on the signals from the sensors and the like, the electronic control unit 10 operates according to the control program and the initial data stored in the ROM to open the fuel injection valves 16, that is, the fuel injection time and the opening time of the throttle valve 6. Control the degree etc.
[0040]
Now, in the electronic control device 10 configured as described above, the throttle opening TA is calculated according to the load request of the driver who drives the vehicle equipped with the internal combustion engine 2, that is, based on the accelerator opening ACCP and the like. You. Then, a driving amount of the actuator 12 is calculated based on the throttle opening TA, and the actuator 12 is driven based on the calculated value, so that the opening of the throttle valve 6 is adjusted according to the load demand of the driver. It is adjusted to. Then, the intake air amount GN changes according to the opening degree adjustment. On the other hand, the electronic control unit 10 calculates a fuel injection amount according to the intake air amount GN so that the air-fuel ratio of the air-fuel mixture composed of the intake air and the fuel injected from the fuel injection valve 16 becomes the stoichiometric air-fuel ratio. The opening time of the fuel injection valve 16, that is, the fuel injection time is determined based on the calculated fuel injection amount.
[0041]
Here, in the internal combustion engine 2 using compressed natural gas, when the pressure in the fuel tank 30 decreases due to an excessive decrease in gaseous fuel in the fuel tank 30, the fuel injection valve 16 is opened for the fuel injection time. Even if the valve is opened, the fuel injection amount calculated according to the intake air amount GN cannot be injected. Therefore, the amount of fuel supplied to the combustion chamber 2c becomes insufficient. In this case, the ratio of fuel to the intake air amount GN decreases, and the air-fuel ratio becomes lean. In such a situation where the air-fuel ratio is lean, unburned gas due to misfire is likely to be generated, and the oxygen concentration in the exhaust gas is also high. Therefore, the catalyst 19 is easily damaged for the above-described reason.
[0042]
Therefore, in the present embodiment, in a situation where the air-fuel ratio becomes lean due to a decrease in the fuel injection pressure, the opening of the throttle valve 6 is set smaller than the throttle opening calculated based on the driver's load request. By reducing the intake air amount to make it smaller, the leaning of the air-fuel ratio is suppressed, and thus the damage of the catalyst 19 is suppressed.
[0043]
More specifically, the throttle opening degree TA is used as a parameter indicating the first intake air amount calculated based on the driver's load request. The maximum allowable throttle is used as a parameter representing the second intake air amount for setting the air-fuel ratio to the stoichiometric air-fuel ratio with respect to the maximum fuel injection amount Qmax allowed by the fuel injection pressure PF detected by the fuel pressure sensor 22. The opening degree TAmax is used. Then, the smaller of the throttle opening TA and the maximum allowable throttle opening TAmax is selected as the target intake air amount, and the final throttle opening TAFIN is selected.
[0044]
Hereinafter, an opening degree calculation process of the throttle valve 6 by the intake air amount control device for the internal combustion engine according to the present embodiment will be described in detail with reference to FIG.
FIG. 2 shows a procedure of the opening degree calculation processing. In the present embodiment, the opening degree calculation process is repeatedly executed by the electronic control unit 10 as an interruption process at predetermined time intervals.
[0045]
When this process is started, first, the throttle opening TA is obtained based on the accelerator opening ACCP and the engine speed NE (S110).
Next, it is determined whether the injection pressure PF detected by the fuel pressure sensor 22 is equal to or less than a predetermined value PFmin (S120). This predetermined value PFmin is a minimum value of the injection pressure that can reliably avoid damage to the catalyst 19, and is set in advance based on experiments and the like. When the injection pressure PF is higher than the predetermined value PFmin (NO in S120), it is determined that the catalyst 19 cannot be damaged, and the throttle opening TA is directly set as the final throttle opening TAFIN (S130). The process ends. Thereafter, the actuator 12 is driven by a control amount corresponding to the final throttle opening TAFIN (in this case, the throttle opening TA), and the opening of the throttle valve 6 is adjusted to an opening according to the load demand of the driver.
[0046]
On the other hand, when the injection pressure PF is equal to or less than the predetermined value PFmin (YES in S120), it is determined that the catalyst 19 may be damaged, and the following processing is continuously performed. First, the maximum allowable throttle opening degree TAmax is determined based on the injection pressure PF and the engine speed NE (S140). The maximum allowable throttle opening TAmax is a throttle opening at which an intake air amount capable of setting the air-fuel ratio to the stoichiometric air-fuel ratio with respect to the maximum fuel injection amount permitted at the injection pressure PF is obtained as follows. Is required.
[0047]
First, the injection time during which fuel injection is possible tends to become shorter as the engine speed NE increases. Therefore, based on such a tendency, the maximum fuel injection time TAUmax at the current engine speed NE is calculated. The amount of fuel injected within the fuel injection time tends to decrease as the injection pressure PF decreases. Therefore, based on such a tendency, the maximum fuel injection amount Qmax that can be injected within the maximum fuel injection time TAUmax at the current injection pressure PF is calculated. That is, the maximum fuel injection amount allowed by the current injection pressure PF is calculated. Then, at this maximum fuel injection amount Qmax, an intake air amount capable of setting the air-fuel ratio to the stoichiometric air-fuel ratio is obtained. As the throttle opening at which the obtained intake air amount is obtained, the maximum allowable throttle opening TAmax is obtained. Desired.
[0048]
Next, the maximum allowable throttle opening TAmax is compared with the throttle opening TA (S150). If the throttle opening TA is equal to or larger than the maximum allowable throttle opening TAmax (YES in S150), the maximum allowable throttle opening TAmax is set to the final throttle opening TAFIN (S160), and the process ends. . Thereafter, the actuator 12 is driven with a control amount corresponding to the final throttle opening TAFIN (in this case, the maximum allowable throttle opening TAmax), and the opening of the throttle valve 6 is adjusted so that the air-fuel ratio can be set to the stoichiometric air-fuel ratio. The throttle opening is adjusted to obtain the amount of air.
[0049]
On the other hand, if the throttle opening TA is less than the maximum allowable throttle opening TAmax (NO in S150), the throttle opening TA is set to the final throttle opening TAFIN (S130), and the process is terminated. Thereafter, the actuator 12 is driven by a control amount corresponding to the final throttle opening TAFIN (in this case, the throttle opening TA), and the opening of the throttle valve 6 is adjusted to the opening in accordance with the load demand of the driver.
[0050]
As described above, in the opening degree calculation process according to the present embodiment, the maximum allowable throttle that can obtain the intake air amount that can set the air-fuel ratio to the stoichiometric air-fuel ratio with respect to the maximum fuel injection amount Qmax allowed at the injection pressure PF. The opening degree TAmax is calculated. Therefore, as long as the opening of the throttle valve 6 does not exceed the maximum allowable throttle opening TAmax, the air-fuel ratio can be set to the stoichiometric air-fuel ratio.
[0051]
When the throttle opening TA is equal to or larger than the maximum allowable throttle opening TAmax set in this way, the intake air amount obtained at the throttle opening TA is the maximum fuel injection amount that can be injected at the injection pressure PF. This is a case where the air-fuel ratio becomes excessive with respect to Qmax, and the air-fuel ratio becomes lean. Therefore, the opening of the throttle valve 6 is set to the maximum allowable throttle opening TAmax smaller than the throttle opening TA, and is adjusted to a throttle opening that can secure the stoichiometric air-fuel ratio.
[0052]
On the other hand, even when the injection pressure PF is equal to or less than the predetermined value PFmin, when the value of the throttle opening TA calculated according to the driver's load request is small and the intake air amount GN is small, the required fuel injection amount is small. The maximum fuel injection amount Qmax may be smaller than the maximum fuel injection amount Qmax. In this case, the air-fuel ratio of the air-fuel mixture can be set to the stoichiometric air-fuel ratio even with the intake air amount obtained at the above-mentioned throttle opening TA. Therefore, it is necessary to intentionally make the throttle opening smaller than the maximum allowable throttle opening TAmax. There is no. Therefore, in the opening degree calculation processing, when the throttle opening degree TA is less than the maximum allowable throttle opening degree TAmax, the throttle opening degree TA is set to the throttle opening degree TA in order to secure an intake air amount according to the load demand of the driver. 6 is adjusted.
[0053]
As described above, in the present embodiment, even when the fuel injection pressure decreases, the air-fuel ratio can be set to the stoichiometric air-fuel ratio. Leaning can be avoided, and damage to the catalyst 19 can be suppressed.
[0054]
As described above, according to the intake air amount control device for an internal combustion engine according to the present embodiment, the following effects can be obtained.
(1) The throttle opening degree at which the intake air amount that can make the air-fuel ratio the stoichiometric air-fuel ratio with respect to the maximum fuel injection amount Qmax that can be injected at the current injection pressure PF is calculated as the maximum allowable throttle opening degree TAmax. I have to.
[0055]
The smaller of the maximum allowable throttle opening TAmax and the throttle opening TA calculated based on the driver's load request is set as the final throttle opening TAFIN. Therefore, the throttle opening is not set to a value equal to or greater than the maximum allowable throttle opening TAmax, and the air-fuel ratio can be set to the stoichiometric air-fuel ratio even when the fuel injection pressure PF decreases. Therefore, leaning of the air-fuel ratio due to a decrease in the fuel injection pressure PF is avoided, and damage to the catalyst 19 can be suppressed.
[0056]
(2) Based on the comparison between the fuel injection pressure PF and the predetermined value PFmin, the calculation of the maximum allowable throttle opening TAmax and the determination of whether to execute the comparison between the maximum allowable throttle opening TAmax and the throttle opening TA are performed. To do. Therefore, when there is no risk of damage to the catalyst 19, the calculation of the maximum allowable throttle opening TAmax and the comparison with the throttle opening TA are not performed, and the load on the electronic control device 10 performing the calculation and comparison is reduced appropriately. Will be able to
[0057]
(3) The throttle opening capable of setting the air-fuel ratio to the stoichiometric air-fuel ratio is calculated as the maximum allowable throttle opening TAmax. Therefore, even when the fuel injection pressure PF decreases and the air-fuel ratio becomes lean, the air-fuel ratio is set to the stoichiometric air-fuel ratio. Therefore, the generation of unburned gas due to the misfire is suppressed, and the oxygen concentration in the exhaust gas is also kept low, so that the damage to the catalyst 19 can be surely suppressed.
[0058]
(4) There is a correlation between the control amount of the throttle valve 6 for adjusting the intake air amount, that is, the opening degree of the throttle valve 6 and the intake air amount. Therefore, the throttle opening degree TA is used as a parameter representing the first intake air amount calculated based on the driver's load request. Further, the maximum allowable throttle opening degree TAmax is set as a parameter representing a second intake air amount that can set the air-fuel ratio to the stoichiometric air-fuel ratio with respect to the maximum fuel injection amount Qmax allowed by the fuel injection pressure PF at that time. I use it. Then, the smaller of the throttle opening TA and the maximum allowable throttle opening TAmax is selected as the target intake air amount, and the final throttle opening TAFIN is selected. Therefore, the actual intake air amount is reduced to the target intake air amount by setting the opening degree of the throttle valve 6 constituting the adjusting mechanism for adjusting the intake air amount to the above-mentioned throttle opening degree TA or the maximum allowable throttle opening degree TAmax. It will be possible to reliably adjust to the amount.
[0059]
(5) In the internal combustion engine 2 using gaseous fuel, when the fuel in the fuel tank 30 decreases, the fuel injection pressure PF tends to decrease. The intake air amount control device according to the present embodiment is applied to such an internal combustion engine 2. Therefore, in the internal combustion engine 2 in which the fuel injection pressure tends to decrease, damage to the catalyst 19 can be suppressed.
[0060]
(6) In the present embodiment, in order to suppress damage to the catalyst 19, a fuel cut as in the apparatus described in the above-mentioned publication is not performed. Therefore, deterioration of drivability due to the fuel cut can be prevented.
[0061]
The above embodiments can be modified and implemented as follows.
In the above embodiment, the minimum value of the injection pressure that can reliably avoid damage to the catalyst 19 is set as the predetermined value PFmin. Instead, when the fuel injection pressure PF is lower than the injection pressure capable of securing the fuel injection amount according to the driver's load request, the maximum allowable throttle opening TAmax is always set as the final throttle opening TAFIN. You may make it set. For example, the maximum value of the injection pressure at which the catalyst 19 is surely damaged is obtained in advance through an experiment or the like, and the value obtained from the experiment is set as the predetermined value PFmin, and the throttle opening TA shown in FIG. The comparison processing (S150) with the allowable throttle opening TAmax may be omitted.
[0062]
In the above embodiment, when the injection pressure PF is equal to or less than the predetermined value PFmin, the calculation of the maximum allowable throttle opening TAmax and the comparison between the maximum allowable throttle opening TAmax and the throttle opening TA are performed. Instead of this, the process of S120 shown in FIG. 2, that is, the process of comparing and determining the injection pressure PF and the predetermined value PFmin may be omitted. In this case, regardless of the injection pressure PF, the calculation of the maximum allowable throttle opening TAmax and the comparison between the maximum allowable throttle opening TAmax and the throttle opening TA are always performed. The function and effect according to the form can be obtained.
[0063]
In the above-described embodiment, the opening degree calculation processing when the target air-fuel ratio is set to the stoichiometric air-fuel ratio has been described. Here, even when the air-fuel ratio of the air-fuel mixture becomes lean, damage to the catalyst 19 can be suppressed unless it is excessively lean. In consideration of this point, the minimum value of the air-fuel ratio that can avoid the damage to the catalyst 19 may be determined by an experiment or the like as the target air-fuel ratio, and the minimum value of the air-fuel ratio may be set as the target air-fuel ratio.
[0064]
Further, even when the air-fuel ratio of the air-fuel mixture becomes lean, misfire of the air-fuel mixture hardly occurs unless the air-fuel ratio is excessively lean, and damage to the catalyst 19 can be suppressed. Furthermore, in a situation where misfire is unlikely to occur, that is, in a situation where fuel combustion is performed normally, the amount of unburned gas in exhaust gas is also kept low. In consideration of this point, the minimum value of the air-fuel ratio that can avoid the occurrence of misfire of the air-fuel mixture may be determined by experiment or the like as the target air-fuel ratio, and the minimum value of the air-fuel ratio may be set as the target air-fuel ratio. Even in these cases, damage to the catalyst 19 due to a decrease in the fuel injection pressure PF can be reliably suppressed.
[0065]
In the above embodiment, the opening degree of the throttle valve 6 is used as a parameter indicating the intake air amount. In addition, in the case of an internal combustion engine having a metering mechanism for adjusting the intake air amount by changing the lift amount of the intake valve or the exhaust valve or the valve timing according to the engine operating state, The lift amount, valve timing, or the like may be used as a parameter representing the air amount.
[0066]
In the above embodiment, the fuel pressure sensor 22 is provided on the delivery pipe 34, but may be provided at any location where the injection pressure PF of the fuel injection valve 16 can be detected.
[0067]
In the above embodiment, the case where the intake air amount control device according to the present invention is applied to an internal combustion engine using compressed natural gas as fuel has been described. However, even in an internal combustion engine for liquefied natural gas in which fuel in a gaseous state or a liquid state is injected from a fuel injection valve, or in a gasoline engine or a diesel engine, if the injection pressure of the fuel is reduced, the above-mentioned reason is considered. Therefore, the catalyst may be damaged, and the present invention can be similarly applied to such internal combustion engines.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an embodiment of an intake air amount control device for an internal combustion engine according to the present invention.
FIG. 2 is a flowchart showing a processing procedure for calculating a throttle valve opening according to the embodiment;
[Explanation of symbols]
2 ... internal combustion engine, 2a ... cylinder, 2b ... piston, 2c ... combustion chamber, 4 ... intake passage, 6 ... throttle valve, 10 ... electronic control unit, 12 ... actuator, 16 ... fuel injection valve, 18 ... exhaust passage, 19 ... catalyst, 20 ... intake air amount sensor, 21 ... throttle opening degree sensor, 22 ... fuel pressure sensor, 23 ... engine speed sensor, 24 ... accelerator opening degree sensor, 30 ... fuel tank, 31 ... high pressure fuel pipe, 32 ... pressure reduction Valve, 33: low pressure fuel pipe, 34: delivery pipe.

Claims (9)

A second air-fuel ratio for setting the air-fuel ratio to the target air-fuel ratio with respect to the first intake air amount calculated based on the load request of the driver and the maximum fuel injection amount allowed by the fuel injection pressure at that time. An intake air amount control device for an internal combustion engine, wherein a smaller one of the intake air amount and the intake air amount is set as a target intake air amount. The intake air amount control device for an internal combustion engine according to claim 1,
An intake air amount control device for an internal combustion engine, wherein whether to execute the setting of the target intake air amount is determined based on a fuel injection pressure. When the fuel injection pressure is lower than the injection pressure that can secure the fuel injection amount according to the driver's load request, the air-fuel ratio is set to the maximum fuel injection amount allowed by the injection pressure at that time. An intake air amount control device for an internal combustion engine, wherein an intake air amount for setting a target air-fuel ratio is set as a target intake air amount. The intake air amount control device for an internal combustion engine according to any one of claims 1 to 3, wherein a stoichiometric air-fuel ratio is set as the target air-fuel ratio. The intake air amount control device for an internal combustion engine according to any one of claims 1 to 3, wherein a minimum value of an air-fuel ratio that can avoid damage to a catalyst provided in an exhaust system of the internal combustion engine is set as the target air-fuel ratio. The intake air amount control device for an internal combustion engine according to any one of claims 1 to 3, wherein a minimum value of an air-fuel ratio capable of avoiding misfire of the air-fuel mixture is set as the target air-fuel ratio. The intake air amount control device for an internal combustion engine according to any one of claims 1 to 6, wherein a control amount of a metering mechanism for adjusting the intake air amount is used as the parameter representing the intake air amount. The intake air amount control device for an internal combustion engine according to claim 7, wherein an opening degree of a throttle valve provided in an intake passage is used as a control amount of the adjustment mechanism. The intake air amount control device for an internal combustion engine according to any one of claims 1 to 8, wherein the internal combustion engine is an internal combustion engine that uses gaseous fuel.

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