JP5792611B2 - Internal combustion engine control system - Google Patents

Description

  The present invention relates to a control system for an internal combustion engine using compressed natural gas (CNG) as fuel.

  2. Description of the Related Art Conventionally, an internal combustion engine using CNG as a fuel is provided with an in-cylinder pressure sensor for measuring the pressure in the cylinder, and fuel properties are specified based on an output signal of the in-cylinder pressure sensor, and fuel injection is performed according to the specified fuel properties. A technique for correcting the amount has been proposed (see, for example, Patent Document 1).

JP 2004-346911 A Japanese Utility Model Publication No. 60-145244 JP 2004-346842 A

  The property of CNG changes mainly when CNG is replenished (filled) into the fuel tank. For example, when CNG having a different property from CNG stored in the fuel tank is replenished, the property of CNG changes.

  By the way, according to the above-described conventional technique, after the CNG is replenished, the fuel injection amount does not match the CNG property until the fuel property specification based on the output signal of the in-cylinder pressure sensor is completed after the internal combustion engine is started. There is a possibility of an appropriate amount.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to control an internal combustion engine when the properties of CNG change in a control system for an internal combustion engine using compressed natural gas (CNG) as a fuel. It is to provide an effective technique for compensating the proper operation of the vehicle.

  In order to solve the above-described problems, the present invention provides that the opening degree of a regulator (that is, the size of the cross-sectional area adjusted by the regulator) disposed in the fuel supply path from the fuel tank to the fuel injection valve is compressed and natural. We paid attention to the fact that it correlates with the concentration of inert gas contained in the gas.

  The above point of interest can be utilized as a system for correcting control parameters related to the combustion state of the air-fuel mixture according to the opening of the regulator. In this case, the present invention can be understood as the following control system for an internal combustion engine.

That is, the control system of the internal combustion engine of the present invention is
A fuel tank for storing compressed natural gas;
A fuel injection valve for injecting compressed natural gas into the intake passage or the cylinder;
It is arranged in the middle of a fuel supply passage for introducing compressed natural gas from the fuel tank to the fuel injection valve, and the pressure of the compressed natural gas supplied to the fuel injection valve is equal to a preset pressure. A regulator for adjusting a cross-sectional area of the fuel supply passage;
Detecting means for detecting the size of the passage cross-sectional area adjusted by the regulator when fuel injection by the fuel injection valve is being performed;
An air-fuel ratio sensor provided in the exhaust passage and outputting a signal correlated with the air-fuel ratio of the air-fuel mixture burned in the cylinder;
Correction means for correcting a control parameter related to the combustion state of the air-fuel mixture based on the size of the passage sectional area detected by the detection means when the air-fuel ratio sensor is not active.

  The nature of the compressed natural gas (CNG) is not necessarily uniform, and may be different for each CNG replenishment place (filling place). When CNG is replenished (filled) into the fuel tank, the CNG remaining in the fuel tank (hereinafter referred to as “residual CNG”) and the filled CNG (hereinafter referred to as “filled CNG”) are mixed. When the properties of the filled CNG and the residual CNG are different, CNG supplied from the fuel tank to the internal combustion engine after filling with the filled fuel (CNG in which filled CNG and residual CNG are mixed (hereinafter referred to as “mixed CNG”)) The properties of are different from those of residual CNG.

The influence of the change in CNG properties on the operating state of the internal combustion engine includes changes in the stoichiometric air-fuel ratio and combustion speed. That is, when the concentration of the inert gas contained in the gaseous fuel (for example, carbon dioxide (CO ₂ ) or nitrogen (N ₂ )) changes, the air-fuel ratio (theoretical air) in which CNG and oxygen in the mixture react without excess or deficiency. As the fuel ratio changes, the combustion speed of the air-fuel mixture changes. For example, when the inert gas concentration of CNG is high, the stoichiometric air-fuel ratio is lowered and the combustion speed of the air-fuel mixture is slow compared to when it is low. Therefore, when the inert gas concentration of CNG changes, it is necessary to adjust the control parameter related to the combustion state of the air-fuel mixture according to the changed inert gas concentration.

  The change in the inert gas concentration of CNG is reflected in the correction value used for air-fuel ratio feedback control. Specifically, when the inert gas concentration of CNG changes, the oxygen concentration of the exhaust gas changes as the stoichiometric air-fuel ratio changes. In an internal combustion engine in which the fuel injection amount is feedback-controlled (air-fuel ratio feedback control) based on the deviation between the output signal of the air-fuel ratio sensor (or oxygen concentration sensor) and the target air-fuel ratio, the inert gas concentration of CNG by replenishing CNG Since the output signal of the air-fuel ratio sensor changes, the correction value by the air-fuel ratio feedback control also changes accordingly.

  For example, when the charged CNG having a higher inert gas concentration than the residual CNG is supplied, the inert gas concentration of the mixed CNG becomes higher than the inert gas concentration of the residual CNG. In that case, the stoichiometric air-fuel ratio of the mixed CNG is lower than the stoichiometric air-fuel ratio of the residual CNG. As a result, the air-fuel ratio specified based on the output signal of the air-fuel ratio sensor is shifted to the lean side from the target air-fuel ratio. Therefore, the correction value by the air-fuel ratio feedback control becomes a value (positive value) that increases the fuel injection amount, and the absolute value is the absolute value of the correction value when the CNG property is constant. Greater than the maximum value you can get.

  When the charged CNG having a lower inert gas concentration than the residual CNG is supplied, the inert gas concentration of the mixed CNG becomes lower than the inert gas concentration of the residual CNG. In that case, the stoichiometric air-fuel ratio of the mixed CNG becomes higher than the stoichiometric air-fuel ratio of the residual CNG. As a result, the air-fuel ratio specified based on the output signal of the air-fuel ratio sensor is shifted to the rich side from the target air-fuel ratio. Therefore, the correction value by the air-fuel ratio feedback control becomes a value (negative value) for reducing the fuel injection amount, and the absolute value is taken by the absolute value of the correction value when the CNG property is constant. Greater than the maximum value you can get.

  Therefore, when the absolute value of the correction value by the air-fuel ratio feedback control becomes equal to or greater than the threshold value, it can be determined that the property of CNG has changed. Note that the “threshold value” here is, for example, a value obtained by adding a margin to the maximum value that can be taken by the absolute value of the correction value by air-fuel ratio feedback control under the condition that the properties of CNG are constant.

  When it is determined that the property of the CNG has changed, if the value of the control parameter related to the combustion of the air-fuel mixture is corrected, the change in the combustion state of the air-fuel mixture due to the property change of the CNG can be suppressed.

  By the way, the air-fuel ratio feedback control is performed on condition that the air-fuel ratio sensor is active. Therefore, when the internal combustion engine is operated for the first time after replenishment of CNG, if the air-fuel ratio sensor is not activated, it becomes difficult to quickly detect a change in the properties of CNG.

  On the other hand, as a result of intensive experiments and verifications by the inventor of the present application, the size of the passage cross-sectional area adjusted by the regulator when fuel injection by the fuel injection valve is performed (in other words, the opening degree of the regulator ) Was found to correlate with the inert gas concentration of CNG. Specifically, when fuel injection by the fuel injection valve is being performed, the size of the passage cross-sectional area adjusted by the regulator is stabilized at a substantially constant size, and the size is the inert gas concentration of CNG. When it is high, it is larger when it is high.

  This is presumably because the density of CNG is higher when the inert gas concentration of CNG is higher than when it is low. In other words, when the opening degree of the regulator is constant, the volumetric flow rate of CNG passing through the regulator decreases as the density of CNG increases. Therefore, when the pressure of CNG supplied to the fuel injection valve is constant, the higher the density of CNG (the higher the inert gas concentration of CNG), the higher the opening of the regulator (the cross-sectional area of the passage adjusted by the regulator). The size) increases.

  Therefore, when the control parameter related to the combustion state of the air-fuel mixture is corrected based on the opening of the regulator when fuel injection by the fuel injection valve is being performed, the combustion state of the air-fuel mixture changes due to the change in the properties of CNG. This can be suppressed. In particular, even if the air-fuel ratio sensor is not activated when the internal combustion engine is operated for the first time after replenishment of CNG, it is possible to suppress changes in the combustion state of the air-fuel mixture accompanying changes in the properties of CNG. As a result, when the property of CNG changes, the control parameter related to the combustion state of the air-fuel mixture can be quickly set to a value suitable for the property of CNG.

  In the control system for an internal combustion engine of the present invention, when the air-fuel ratio sensor is active, the correction means sets the control parameter based on the absolute value of the correction value by the air-fuel ratio feedback control as described above. You may make it correct | amend. According to such a configuration, when the internal combustion engine is operated for the first time after replenishment of CNG, the control parameter can be set to a value suitable for the property of CNG regardless of the active state of the air-fuel ratio sensor. Note that the correction means may correct the control parameter related to the combustion state of the air-fuel mixture based on the opening of the regulator even when the air-fuel ratio sensor is active.

  In the control system for an internal combustion engine of the present invention, the correction means corrects the control parameter based on the magnitude of the pressure of the CNG upstream from the regulator in addition to the magnitude of the passage sectional area detected by the detection means. May be. The “pressure of the CNG upstream from the regulator” here may be the pressure itself or a physical quantity (for example, temperature) correlated with the pressure.

When the density of CNG is constant, the volumetric flow rate of CNG passing through the regulator increases as the pressure of CNG upstream from the regulator increases. Therefore, when the pressure of CNG supplied to the fuel injection valve is constant, the higher the pressure of CNG upstream from the regulator, the smaller the opening of the regulator (the size of the cross-sectional area adjusted by the regulator). .

  Therefore, when the control parameter is corrected in consideration of the pressure of the CNG upstream of the regulator in addition to the size of the passage cross-sectional area detected by the detection means, the corrected control parameter is more suitable for the characteristics of the CNG. Value. As a result, it is possible to more reliably suppress changes in the combustion state of the air-fuel mixture when the properties of CNG change.

  Here, as the control parameters related to the combustion state of the air-fuel mixture, the fuel injection amount, the ignition timing, the valve opening characteristics of the intake valve, the valve opening characteristics of the exhaust valve, or the opening degree of an EGR (Exhaust Gas Recirculation) valve are used. be able to.

  For example, when the CNG inert gas concentration is high, the CNG theoretical air-fuel ratio is lower than when it is low. Therefore, the correction unit may perform correction so that the fuel injection amount increases when the passage cross-sectional area detected by the detection unit is large, compared to when it is small. In that case, it is possible to prevent the air-fuel ratio of the air-fuel mixture from deviating from the target air-fuel ratio due to a change in the properties of CNG.

  When the inert gas concentration of CNG is high, the combustion rate of the air-fuel mixture becomes slower than when the CNG inert gas concentration is low. Therefore, the correction means may perform correction so that the ignition timing is earlier when the passage cross-sectional area detected by the detection means is larger than when it is small. In that case, it is possible to prevent the combustion end timing of the air-fuel mixture from becoming excessively late.

  In order to compensate for the change in the combustion speed of the air-fuel mixture accompanying the change in the inert gas concentration of CNG, the correction means remains in the cylinder when the passage cross-sectional area detected by the detection means is large compared to when it is small. The opening / closing timing of the intake valve and / or the exhaust valve may be corrected so that the amount of burned gas (internal EGR gas) is reduced. The correction means may correct the opening degree of the EGR valve so that the amount of EGR gas introduced into the cylinder is smaller when the passage cross-sectional area detected by the detection means is larger than when the passage sectional area is small. . When the internal EGR gas amount and the EGR gas amount are adjusted in this way, it is possible to suppress an excessive decrease in the combustion rate and combustion temperature of the air-fuel mixture.

  In order to compensate for the change in the combustion speed of the air-fuel mixture accompanying the change in the inert gas concentration of CNG, the correction means has a higher intake flow velocity when the passage cross-sectional area detected by the detection means is larger than when it is small. The valve opening characteristics of the intake valve may be changed so that In that case, since the flame propagation speed when the air-fuel mixture burns is increased, an excessive decrease in the combustion speed of the air-fuel mixture can be suppressed.

  Next, the above-described point of interest can be utilized in a device that detects the inert gas concentration of CNG according to the opening of the regulator. In that case, the present invention can be understood as an inert gas concentration detection device for compressed natural gas as follows.

That is, the compressed natural gas inert gas concentration detection device of the present invention is
A fuel tank for storing compressed natural gas;
A fuel injection valve for injecting compressed natural gas into the intake passage or the cylinder;
The fuel supply passage is arranged in the middle of a fuel supply passage for introducing compressed natural gas from the fuel tank to the fuel injection valve, and the pressure of the compressed natural gas supplied to the fuel injection valve is equal to a set pressure. A regulator for adjusting the cross-sectional area of the passage,
Detecting means for detecting a cross-sectional area of the passage adjusted by the regulator when fuel injection by the fuel injection valve is performed;
An air-fuel ratio sensor provided in the exhaust passage and outputting a signal correlated with the air-fuel ratio of the air-fuel mixture burned in the cylinder;
And a calculation means for calculating the concentration of the inert gas contained in the compressed natural gas based on the size of the passage cross-sectional area detected by the detection means when the air-fuel ratio sensor is not activated.

  According to the inert gas concentration detection device for compressed natural gas configured in this way, even if the air-fuel ratio sensor is not activated when the internal combustion engine is operated for the first time after CNG is replenished, The gas concentration can be detected. Note that the inert gas concentration of CNG detected by the inert gas concentration detection device can be used to compensate for proper operation of the internal combustion engine. For example, by determining the fuel injection amount, ignition timing, intake valve opening characteristics, exhaust valve opening characteristics, or EGR valve opening, the inert gas concentration detected by the device is taken into account. Even when the properties of CNG change, the internal combustion engine can be operated properly.

  As described above, the size of the passage cross-sectional area detected by the detecting means may be influenced by the size of the CNG pressure upstream of the regulator in addition to the inert gas concentration of CNG. Therefore, the calculation means calculates the inert gas concentration of the compressed natural gas based on the magnitude of the CNG pressure in the fuel supply passage upstream from the regulator in addition to the magnitude of the passage cross-sectional area detected by the detection means. May be. In that case, it becomes possible to detect the inert gas concentration of CNG more accurately.

  According to the present invention, in an internal combustion engine control system using compressed natural gas (CNG) as a fuel, a technique effective for compensating for proper operation of the internal combustion engine when the properties of the CNG change is provided. Can do.

It is a figure which shows schematic structure of the vehicle to which this invention is applied. It is a figure which shows the correlation with the inert gas density | concentration of CNG, and a theoretical air fuel ratio. It is sectional drawing which shows schematic structure of a regulator. It is a figure which shows the fully closed state of a regulator. It is a figure which shows operation | movement of the regulator before and behind starting of an internal combustion engine. It is a figure which shows the relationship between the inert gas density | concentration of CNG and the intermediate opening degree (theta) of a regulator when the pressure of a decompression chamber and a downstream fuel supply pipe is constant. It is a figure which shows the correlation with the upstream opening degree when the inert gas density | concentration of CNG and the pressure of a pressure reduction chamber are constant, and the intermediate opening degree (theta) of a regulator. It is a flowchart which shows the fuel injection amount calculating routine in a 1st Example. It is a figure which shows the correlation with the inert gas concentration learning value eknco2 and the inert gas concentration of CNG. It is a figure which shows the correlation with the lift correction coefficient f ((theta)) and the inert gas concentration of CNG. It is a figure which shows the relationship between the inert gas concentration learning value eknco2 and ignition timing. It is a figure which shows the relationship between lift correction coefficient f ((theta)) and ignition timing. It is a figure which shows the relationship between the inert gas concentration learning value eknco2 and the amount of EGR gas. It is a figure which shows the relationship between a lift correction coefficient f ((theta)) and EGR gas amount.

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

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of a vehicle to which the present invention is applied. The vehicle shown in FIG. 1 is a vehicle equipped with an internal combustion engine that uses CNG.

  In FIG. 1, an internal combustion engine 1 and a fuel tank 2 are mounted on a vehicle 100. The internal combustion engine 1 includes a plurality of cylinders 3 and a fuel injection valve 4 that injects fuel into each cylinder 3. An intake passage 5 and an exhaust passage 6 are connected to the internal combustion engine 1.

  The intake passage 5 is a passage for guiding fresh air (air) taken from the atmosphere to the cylinder 3 of the internal combustion engine 1. An intake throttle valve 7 for changing the passage cross-sectional area of the intake passage 5 and an intake temperature sensor 8 for measuring the temperature of fresh air (air) (outside air temperature) are attached in the middle of the intake passage 5. .

  The exhaust passage 6 is a passage for discharging burned gas (exhaust gas) discharged from the cylinder 3 to the atmosphere after passing through an exhaust purification catalyst, a silencer, or the like. An A / F sensor 9 that outputs an electrical signal correlated with the air-fuel ratio is attached in the middle of the exhaust passage 6.

  The fuel tank 2 is a tank that stores compressed natural gas (CNG). A pressure sensor 10 for measuring the pressure in the fuel tank 2 is attached to the fuel tank 2. Further, the fuel tank 2 communicates with the fuel injection valve 4 of the internal combustion engine 1 through the fuel supply pipe 11. The fuel supply pipe 11 is a passage for guiding CNG in the fuel tank 2 to the fuel injection valve 4. The fuel tank 2 is connected to a filling port 12 attached to the vehicle body of the vehicle 100 via an inlet pipe 13. The filling port 12 opens when a filling nozzle disposed in a gas station or the like is inserted, and introduces CNG supplied from the filling nozzle into the inlet pipe 13.

  A shutoff valve 14 and a regulator 15 are disposed in the middle of the fuel supply pipe 11. The shut-off valve 14 is closed while the internal combustion engine 1 is stopped (for example, a period when the ignition switch is off), and is opened while the internal combustion engine 1 is operating (for example, a period when the ignition switch is on). It is a valve device. As the shut-off valve 14, for example, an electromagnetic valve device that opens when drive power is applied and closes when drive power is not applied can be used. The regulator 15 reduces the pressure of CNG supplied from the fuel tank 2 to a preset pressure (set pressure). In other words, in the regulator 15, the fuel pressure in the fuel supply pipe 11 downstream from the regulator 15, in other words, the fuel pressure applied to the fuel injection valve 4 (hereinafter referred to as “fuel injection pressure”) becomes equal to the set pressure. Thus, the valve device adjusts the cross-sectional area of the fuel supply pipe 11. As the regulator 15, for example, a mechanical valve device combining a diaphragm and a spring can be used.

  The vehicle 100 configured in this manner is equipped with an ECU 16. The ECU 16 is an electronic control unit that includes a CPU, a ROM, a RAM, a backup RAM, and the like. Various sensors such as an intake air temperature sensor 8, an A / F sensor 9, and a pressure sensor 10 are electrically connected to the ECU 16. Various devices such as the fuel injection valve 4 and the intake throttle valve 7 are electrically connected to the ECU 16. The ECU 16 controls the various devices based on signals input from the various sensors.

For example, the ECU 16 calculates a fuel injection amount according to the load and rotation speed of the internal combustion engine 1 and controls the fuel injection valve 4 according to the calculated fuel injection amount. Specifically, the ECU 16 calculates the fuel injection amount (the valve opening time of the fuel injection valve 4) etau according to the following equation (1).
etau = etp * ekaf * k (1)

  In the above formula (1), etp is a basic injection amount derived from a map having an intake air amount, an engine speed, etc. as arguments. The map here is obtained in advance by an adaptation process using experiments or the like, and is stored in the ROM of the ECU 16.

The ekaf is a correction coefficient (air-fuel ratio feedback correction coefficient) for eliminating the difference between the target air-fuel ratio and the actual air-fuel ratio (the air-fuel ratio detected by the A / F sensor 9). For example, ekaf is calculated according to the following equation (2).
ekaf = (efaf + efgaf + 100) / 100 (2)

  In the equation (2), efaf is a correction value (air-fuel ratio feedback correction value) determined based on the difference between the target air-fuel ratio and the actual air-fuel ratio. efgaf is an air-fuel ratio learning value for compensating for a constant divergence between the target air-fuel ratio and the actual air-fuel ratio (deviation caused by a change in the injection characteristics of the fuel injection valve 4 over time).

  In addition, k in the said Formula (1) is an increase correction coefficient determined according to a cooling water temperature or an accelerator opening.

  When the fuel injection amount (fuel injection time) is determined according to the above equations (1) and (2), the air-fuel ratio of the air-fuel mixture burned in the cylinder 3 can be matched with the target air-fuel ratio. As a result, the output of the internal combustion engine 1 can be matched with the driver's required output, or the exhaust properties can be made suitable for the purification ability of the exhaust purification device.

By the way, the properties of CNG filled in the fuel tank 2 are not necessarily uniform, and may differ from place to place (filling place) of CNG. Further, the air-fuel ratio (theoretical air-fuel ratio) when CNG and oxygen in the air-fuel mixture react without excess or deficiency varies depending on the properties of CNG. In particular, when the concentrations of the inert gas (carbon dioxide (CO ₂ ) and nitrogen (N ₂ )) contained in CNG are different, the stoichiometric air-fuel ratio is also different.

  Here, the correlation between the concentration of the inert gas contained in CNG and the stoichiometric air-fuel ratio is shown in FIG. The horizontal axis in FIG. 2 indicates the concentration of the inert gas contained in CNG, and the vertical axis indicates the theoretical air-fuel ratio. As shown in FIG. 2, the theoretical air-fuel ratio of CNG decreases as the inert gas concentration of CNG increases. That is, the theoretical air-fuel ratio of CNG is inversely proportional to the inert gas concentration of CNG.

  Therefore, when a CNG (filled CNG) having a different property from the CNG remaining in the fuel tank 2 is filled, the fuel injection amount and the intake air amount after filling the stoichiometric air-fuel ratio of the remaining CNG. The actual air / fuel ratio may differ from the desired target air / fuel ratio.

  For example, when the charged CNG having an inert gas concentration higher than the residual CNG is filled, the theoretical air-fuel ratio of the filled CNG (mixed CNG) becomes lower than the theoretical air-fuel ratio of the residual CNG. Therefore, when the fuel injection amount and the intake air amount after charging of the charged CNG are controlled in accordance with the stoichiometric air-fuel ratio of the residual CNG, the actual air-fuel ratio becomes higher (lean) than the target air-fuel ratio, increasing the exhaust emission and engine output It may cause a decrease in the

  When the charged CNG having an inert gas concentration lower than the residual CNG is filled, the stoichiometric air-fuel ratio of the mixed CNG becomes higher than the stoichiometric air-fuel ratio of the residual CNG. For this reason, when the fuel injection amount and the intake air amount after the filling of CNG are controlled according to the stoichiometric air-fuel ratio of the residual CNG, the actual air-fuel ratio becomes lower (rich) than the target air-fuel ratio. As a result, exhaust emissions may increase, engine output may increase, and misfire may occur.

  Therefore, when the property (inert gas concentration) of CNG changes, it is necessary to correct the control parameter related to the combustion state of the air-fuel mixture in order to compensate for the change in the theoretical air-fuel ratio.

  Hereinafter, an example in which the fuel injection amount is corrected as a control parameter related to the combustion state of the air-fuel mixture when the properties of CNG change will be described.

In this embodiment, the ECU 16 calculates the fuel injection amount (fuel injection time) etau using the following equation (3) instead of the equation (1).
etau = etp * ekaf * ekin * k (3)

  In the formula (3), etp, ekaf, and k are the same as the formula (1) described above. In equation (3), ekin is a correction coefficient (inert gas concentration learning correction coefficient) for compensating for a change in the theoretical air-fuel ratio accompanying a change in CNG properties (inert gas concentration change).

The inert gas concentration learning correction number ekin is calculated based on the following equation (4).
ekin = (eknco2 + 100) / 100 (4)

  In equation (4), eknco2 is a learning value (inert gas concentration learning value) for compensating for a constant divergence between the target air-fuel ratio and the actual air-fuel ratio due to the inert gas concentration of CNG. Hereinafter, a method for determining the inert gas concentration learning value eknco2 in the present embodiment will be described.

  The change in the properties of CNG occurs when CNG is replenished in the fuel tank 2. For example, when the charged CNG having a higher inert gas concentration than the residual CNG is replenished, the inert gas concentration of the mixed CNG becomes higher than the inert gas concentration of the residual CNG. Further, when the charged CNG having a lower inert gas concentration than the residual CNG is replenished, the inert gas concentration of the mixed CNG becomes lower than the inert gas concentration of the residual CNG.

  When the properties of the mixed CNG change due to the replenishment of the filled CNG, the air-fuel ratio feedback correction value efaf changes when the air-fuel ratio feedback control is started after the replenishment of the filled CNG.

  For example, when the charged CNG having an inert gas concentration higher than the residual CNG is supplied, the stoichiometric air-fuel ratio of the mixed CNG becomes lower than the stoichiometric air-fuel ratio of the residual CNG. Therefore, the air-fuel ratio detected by the A / F sensor 9 is shifted to the lean side from the target air-fuel ratio. In this case, the air-fuel ratio feedback correction value efaf becomes a value (positive value) for increasing the fuel injection amount, and the absolute value is taken by the absolute value of the correction value when the CNG property is constant. Greater than the maximum value you can get.

Further, when the charged CNG having a lower inert gas concentration than the residual CNG is supplied, the stoichiometric air-fuel ratio of the mixed CNG becomes higher than the stoichiometric air-fuel ratio of the residual CNG. Therefore, the air-fuel ratio detected by the A / F sensor 9 is shifted to the rich side from the target air-fuel ratio. In this case, the air-fuel ratio feedback correction value efaf becomes a value (negative value) that decreases the fuel injection amount, and the magnitude of the absolute value is determined by the absolute value of the correction value when the CNG property is constant. Greater than the maximum value you can get.

  Therefore, when the air-fuel ratio feedback control is started after the replenishment of the charged CNG, if the absolute value of the air-fuel ratio feedback correction value efaf is greater than or equal to the threshold value, it can be considered that the property of the CNG has changed. The “threshold value” here is, for example, a value obtained by adding a margin to the maximum value that can be taken by the absolute value of the air-fuel ratio feedback correction value efaf under the condition that the CNG property is constant.

  Therefore, when the air-fuel ratio feedback control is started after the internal combustion engine 1 is started, the ECU 16 updates the inert gas concentration learning value eknco2 if the absolute value of the air-fuel ratio feedback correction value efaf is greater than or equal to the threshold value. Specifically, the ECU 16 adds a predetermined value a to the inert gas concentration learning value eknco2. The predetermined value a is set to a positive value when the air-fuel ratio feedback correction value efaf is a positive value, and is set to a negative value when the air-fuel ratio feedback correction value efaf is a negative value. The absolute value of the predetermined value a is determined according to the absolute value of the air-fuel ratio feedback correction value efaf (or the difference between the absolute value of the air-fuel ratio feedback correction value efaf and the threshold value). It may be a variable value, or may be a fixed value determined in advance by an adaptation process using an experiment or the like.

  When the ECU 16 updates the inert gas concentration learned value eknco2, the ECU 16 subtracts the updated amount (predetermined value a) of the inert gas concentration learned value eknco2 from the air-fuel ratio feedback correction value efaf. This is because the correction due to the change in the CNG property is included in both the inert gas concentration learning value eknco2 and the air-fuel ratio feedback correction value efaf.

  It is assumed that the learning process of the inert gas concentration learned value eknco2 is executed with priority over the learning process of the air-fuel ratio learned value efgaf. This is a case where after the replenishment of the charged CNG, if the learning process of the air-fuel ratio learning value efgaf is executed prior to the learning process of the inert gas concentration learning value eknco2, even if the property of the CNG changes. This is because the absolute value of the air-fuel ratio feedback correction value efaf becomes less than the threshold value.

  Further, when the difference between the inert gas concentration of the filled CNG and the inert gas concentration of the residual CNG is small, or when the amount of the filled CNG is small relative to the amount of the residual CNG, the properties of the mixed CNG and the residual CNG The difference can be small. Further, the air-fuel ratio learning value efgaf is set in each of a plurality of operation regions divided according to the magnitude of the load. Therefore, depending on the operating region, there may be a case where the change in the property of CNG does not easily appear in the magnitude of the air-fuel ratio feedback correction value efaf.

  On the other hand, even if the absolute value of the air-fuel ratio feedback correction value efaf does not exceed the threshold value, the ECU 16 determines that if the absolute value of the average value efgafave of the air-fuel ratio learning value efgaf in the entire operation region exceeds the threshold value, The inert gas concentration learning value eknco2 may be updated assuming that the properties of CNG have changed. Specifically, the ECU 16 may add a predetermined value b to the inert gas concentration learning value eknco2 when the absolute value of the average value efgafave is equal to or greater than a threshold value. The predetermined value b is set to a positive value when the average value efgafave is a positive value, and is set to a negative value when the average value efgafave is a negative value. The magnitude of the absolute value of the predetermined value b may be a variable value determined according to the magnitude of the absolute value of the average value efgafave, or a fixed value determined in advance by an adaptation process using experiments or the like. It may be. However, the absolute value of the predetermined value b is set to a value smaller than the absolute value of the predetermined value a.

Further, the threshold value to be compared with the average value efgafave is a value obtained by adding a margin to the maximum value that can be taken by the absolute value of the average value efgafave when the property of the CNG is constant. Hereinafter, a threshold value that is compared with the absolute value of the air-fuel ratio feedback correction value efaf is referred to as a first threshold value, and a threshold value that is compared with the absolute value of the average value of the air-fuel ratio learning value efgaf is referred to as a second threshold value.

  When the inert gas concentration learning value eknco2 is updated on condition that the absolute value of the average value efgafave is equal to or larger than the second threshold value, the ECU 16 calculates the inert gas concentration learning value eknco2 from the air-fuel ratio learning value efgaf. The updated amount (predetermined value b) is subtracted. At that time, the ECU 16 subtracts the updated amount of the inert gas concentration learned value eknco2 from the air-fuel ratio learned value efgaf of the entire operation region.

  When the inert gas concentration learning value eknco2 is determined (updated) by the above-described method, the fuel injection amount (fuel injection time) etau calculated according to the equation (3) is the stoichiometric air-fuel ratio associated with the change in CNG properties. It becomes a value that can compensate for the change of the and the change of the Weppe index. As a result, when the properties of CNG change, the air-fuel ratio of the air-fuel mixture can be quickly converged to the target air-fuel ratio, and the amount of heat energy generated when the air-fuel mixture burns matches the desired amount. Can be made.

  By the way, if the A / F sensor 9 is not activated when the internal combustion engine 1 is started for the first time after replenishing CNG, the air-fuel ratio feedback control cannot be started immediately. For this reason, if the A / F sensor 9 is not activated when the internal combustion engine 1 is operated for the first time after replenishment of CNG, it becomes difficult to quickly reflect the change in the properties of CNG in the fuel injection amount.

  In contrast, if the A / F sensor 9 is not activated when the internal combustion engine 1 is started for the first time after replenishing CNG, the ECU 16 corrects the fuel injection amount based on the opening of the regulator 15. did.

  Here, a schematic configuration of the regulator 15 will be described with reference to FIG. FIG. 3 is a cross-sectional view illustrating a schematic configuration of the regulator 15. A primary chamber 151 and a secondary chamber 152 are formed in the housing 150 of the regulator 15. The primary chamber 151 and the secondary chamber 152 communicate with each other through a communication path 153.

  The primary chamber 151 communicates with an inlet 154 for taking CNG into the primary chamber 151 via a passage 155. The inlet 154 is connected to the fuel supply pipe 11 upstream from the regulator 15 (the fuel supply pipe 11 extending from the fuel tank 2 to the regulator 15).

  The secondary chamber 152 communicates with an outlet 156 for discharging CNG from the secondary chamber 152 through a passage 157. The outlet 156 is connected to the fuel supply pipe 11 downstream from the regulator 15 (the fuel supply pipe 11 extending from the regulator 15 to the fuel injection valve 4).

  Hereinafter, as shown in FIG. 1, the fuel supply pipe 11 extending from the fuel tank 2 to the regulator 15 is referred to as an “upstream fuel supply pipe 11 a”, and the fuel supply pipe 11 extending from the regulator 15 to the fuel injection valve 4 is referred to as “upstream fuel supply pipe 11 a”. This is referred to as “downstream fuel supply pipe 11b”.

The communication passage 153 accommodates a valve stem 160 b of a poppet type valve 160. The distal end side of the valve stem 160b projects into the primary chamber 151, and a conical valve body 160a is attached to the end of the valve stem 160b. The outer diameter of the valve stem 160b is formed smaller than the inner diameter of the communication passage 153, and CNG can flow through an annular gap between the outer peripheral surface of the valve stem 160b and the inner peripheral surface of the communication passage 153. . A valve seat 158 is attached to the open end of the communication passage 153 in the primary chamber 151, and the open end of the communication passage 153 is closed when the valve body 160a is seated on the valve seat 158.

  The base end side of the valve stem 160 b extends to the secondary chamber 152, and the end thereof is connected to the tip of the holder 161. An annular diaphragm 162 is installed between the outer peripheral surface of the holder 161 and the inner peripheral surface of the housing 150. Here, the secondary chamber 152 is divided into two rooms 152 a and 152 b by the diaphragm 162. Hereinafter, of the two rooms 152a and 152b, the room 152a communicating with the outlet 156 is referred to as a decompression room 152a, and the other room 152b is referred to as an atmospheric room 152b.

  A spring retainer 163 is attached to the proximal end of the holder 161. An adjustment bolt 165 that is screwed into the housing 150 is disposed at a portion facing the spring retainer 163. A coil spring 164 is disposed between the spring retainer 163 and the adjustment bolt 165. The coil spring 164 urges the diaphragm 162 and the valve 160 from the secondary chamber 152 side to the primary chamber 151 side via the spring retainer 163 and the holder 161. The urging force acting on the spring retainer 163 from the coil spring 164 is adjusted by an adjusting bolt 165.

  According to the regulator 15 configured as described above, when the pressure in the decompression chamber 152a is smaller than the biasing force (set pressure) of the coil spring 164, the spring retainer 163 and the holder 161 receive the biasing force of the coil spring 164 and 2 The primary chamber 151 is displaced from the secondary chamber 152 side. In that case, the diaphragm 162 and the valve 160 are also displaced from the secondary chamber 152 side to the primary chamber 151 side. As a result, the valve body 160a is separated from the valve seat 158 (the valve 160 is opened), and the primary chamber 151 and the decompression chamber 152a are conducted through the communication path 153.

  The outer diameter of the holder 161 is formed larger than the inner diameter of the open end of the communication path 153 in the decompression chamber 152a. Therefore, when the diaphragm 162 and the valve are displaced from the secondary chamber 152 side to the primary chamber 151 side, the position where the diaphragm 162 and the valve 160 can reach is such that the tip of the holder 161 is in the housing 150 at the periphery of the opening end. It is limited to the position where it abuts. Therefore, as shown in FIG. 3, when the tip of the holder 161 comes into contact with the housing 150 at the periphery of the opening end, the opening degree of the valve 160 (opening area (passage cross-sectional area) of the communication passage 153) is maximized. .

  When the valve 160 is open, the CNG that has flowed into the inlet 154 from the upstream fuel supply pipe 11a flows into the decompression chamber 152a via the passage 155, the primary chamber 151, and the communication passage 153 sequentially. CNG that has flowed into the decompression chamber 152a is supplied to the fuel injection valve 4 via the passage 157, the outlet 156, and the downstream fuel supply pipe 11b.

If CNG is continuously supplied from the primary chamber 151 to the decompression chamber 152a, the pressures in the decompression chamber 152a and the downstream fuel supply pipe 11b increase. When the pressure in the decompression chamber 152a and the downstream fuel supply pipe 11b becomes larger than the biasing force (set pressure) of the coil spring 164, the diaphragm 162 is displaced from the primary chamber 151 side to the secondary chamber 152 side (from the decompression chamber 152a side to the atmosphere). Displacement to the chamber 152b side). When the diaphragm 162 is displaced from the primary chamber 151 side to the secondary chamber 152 side, the valve 160 is also displaced from the primary chamber 151 side to the secondary chamber 152 side, so that the opening degree of the valve 160 (opening area of the communication path 153). Decrease. When the valve body 160a is seated on the valve seat 158 (the valve 160 is closed), as shown in FIG. 4, the valve 160 is fully closed (
The opening area (passage cross-sectional area) of the communication passage 153 becomes zero. In that case, the flow of CNG from the primary chamber 151 to the decompression chamber 152a is blocked.

  Here, the operation of the valve 160 before and after the start of the internal combustion engine 1 is shown in FIG. The horizontal axis in FIG. 5 indicates time, and the vertical axis indicates the opening degree of the valve 160. While the operation of the internal combustion engine 1 is stopped, the shutoff valve 14 is closed and CNG remaining in the downstream fuel supply pipe 11b and the decompression chamber 152a gradually leaks from the fuel injection valve 4. The pressure becomes lower than the urging force (set pressure) of the coil spring 164. As a result, when the internal combustion engine 1 is stopped, the opening of the valve 160 is maximized (fully opened).

  When the ignition switch is turned on (t0 in FIG. 5), the shutoff valve 14 is opened, so that the CNG stored in the fuel tank 2 is supplied to the inlet of the regulator 15 through the upstream fuel supply pipe 11a. Flow into 154. The CNG that has flowed into the inlet 154 sequentially flows into the decompression chamber 152a through the passage 155, the primary chamber 151, and the communication passage 153. As a result, the pressure in the decompression chamber 152a increases, and the opening degree of the valve 160 decreases accordingly. When the pressure in the decompression chamber 152a reaches or exceeds the set pressure (the urging force of the coil spring 164) (t1 in FIG. 5), the opening degree of the valve 160 becomes zero (fully closed).

  Thereafter, when the starter switch is turned on and then fuel injection from the fuel injection valve 4 is started (t2 in FIG. 5), the opening of the valve 160 is a substantially constant intermediate opening (θ in FIG. 5). To stabilize. At that time, the valve 160 of the regulator 15 is opened when the pressure of the decompression chamber 152a drops below the set pressure due to fuel injection from the fuel injection valve 4, and supply of CNG from the primary chamber 151 to the decompression chamber 152a. The operation of closing the valve when the pressure in the decompression chamber 152a rises above the set pressure is repeated. However, since the displacement speed of the diaphragm 162 and the valve 160 cannot follow the fuel injection cycle, the opening degree of the valve 160 is increased. It becomes stable at a substantially constant intermediate opening θ.

  The above-described fixed intermediate opening θ varies depending on the concentration of the inert gas contained in CNG. Here, FIG. 6 shows the correlation between the intermediate opening θ of the valve 160 and the concentration of the inert gas contained in the CNG when the pressure in the decompression chamber 152a and the downstream fuel supply pipe 11b is constant. The horizontal axis in FIG. 6 indicates the concentration of the inert gas contained in CNG, and the vertical axis indicates the intermediate opening θ of the valve 160.

  As shown in FIG. 6, the intermediate opening θ when the pressures in the decompression chamber 152a and the downstream fuel supply pipe 11b are constant increases as the inert gas concentration of CNG increases. That is, the opening degree of the valve 160 is proportional to the inert gas concentration of CNG. As a result, the constant intermediate opening θ described above increases as the inert gas concentration of CNG increases.

  Therefore, if the fuel injection amount is corrected using the correlation between the intermediate opening θ and the inert gas concentration of CNG, the A / F sensor is used when the internal combustion engine 1 is operated for the first time after replenishment of CNG. Even if 9 is not activated, the fuel injection amount can be made an amount suitable for the properties of CNG.

  Here, as a method of detecting the opening degree of the valve 160 of the regulator 15, a method of detecting the lift amount of the valve 160 (the amount by which the valve 160 is displaced from the fully closed position) can be considered. Therefore, the regulator 15 of this embodiment includes a lift sensor 17 for detecting the lift amount of the valve 160. As shown in FIGS. 3 and 4, the lift sensor 17 is attached to a plate-like target 171 attached to a surface of the spring retainer 163 facing the adjustment bolt 165 and a portion of the adjustment bolt 165 facing the spring retainer 163. The gap sensor 170 is provided.

  According to the lift sensor 17, the target 171 is displaced integrally with the valve 160, and the gap sensor 170 outputs an electrical signal correlated with the relative distance between the target 171 and the gap sensor 170. Therefore, the output signal value of the gap sensor 170 when the valve 160 is in the fully closed state is stored in advance, and the deviation between the output signal value and the output signal value of the gap sensor 170 at the present time is calculated, thereby 160 lift amounts (openings) can be specified.

  Therefore, the ECU 16 may correct the fuel injection amount using the output signal (intermediate opening θ) of the lift sensor 17 when the fuel injection by the fuel injection valve 4 is being performed as a parameter. Specifically, the ECU 16 calculates a correction coefficient (hereinafter referred to as “lift correction coefficient”) from the intermediate opening θ, and operates the internal combustion engine 1 (engine speed, intake air amount, accelerator opening, cooling). What is necessary is just to multiply the fuel injection amount (fuel injection time) etau determined according to water temperature etc. by the lift correction coefficient. At this time, the lift correction coefficient is an integer equal to or greater than 1, and may be set to a larger value as the output signal (intermediate opening θ) of the lift sensor 17 increases. The relationship between the lift correction coefficient and the intermediate opening degree θ may be obtained experimentally in advance and stored as a map in the ROM of the ECU 16 or the like.

  The intermediate opening θ varies depending on the CNG pressure upstream of the regulator 15 (hereinafter referred to as “upstream pressure”) in addition to the inert gas concentration of CNG. For example, when the inert gas concentration of CNG is constant, the volumetric flow rate of CNG passing through the regulator increases as the upstream pressure increases. Therefore, when the inert gas concentration of CNG and the pressure in the decompression chamber 152a are constant, the intermediate opening θ decreases as the upstream pressure increases, as shown in FIG.

  Therefore, it is desirable that the ECU 16 corrects the fuel injection amount by utilizing the correlation between the intermediate opening θ and the upstream pressure in addition to the correlation between the intermediate opening θ and the inert gas concentration of CNG. Specifically, the ECU 16 calculates a correction coefficient (hereinafter referred to as “pressure correction coefficient”) from the upstream pressure, and multiplies the fuel injection amount (fuel injection time) etau by the pressure correction coefficient and the lift correction coefficient. do it. Here, the pressure correction coefficient is an integer of 1 or more, and may be set to a larger value as the upstream pressure increases. The relationship between the pressure correction coefficient and the upstream pressure may be obtained experimentally in advance and stored as a map in the ROM of the ECU 16 or the like.

  Note that an output signal of the pressure sensor 10 may be used as the upstream pressure. Further, since the upstream pressure correlates with the temperature of the upstream fuel supply pipe 11a and the temperature of the fuel tank 2, the output signal of the intake air temperature sensor 8 may be used as the correlation value of the upstream pressure.

  As described above, when the fuel injection amount (fuel injection time) etau is corrected based on the intermediate opening θ and the upstream pressure, the corrected fuel injection amount (fuel injection time) etau is This is an amount that can compensate for a change in the stoichiometric air-fuel ratio accompanying a change in properties. As a result, when the internal combustion engine 1 is operated for the first time after the replenishment of CNG, the air-fuel ratio of the air-fuel mixture can be made equal to or approximate to the target air-fuel ratio even if the A / F sensor 9 is not activated.

  Hereinafter, the procedure for determining the fuel injection amount (fuel injection time) etau in the present embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing a fuel injection amount calculation routine. The fuel injection amount calculation routine is stored in advance in the ROM of the ECU 16, and is executed by the ECU 16 when the internal combustion engine 1 is started (when the ignition switch is turned on).

In the fuel injection amount calculation routine, the ECU 16 first determines in S101 whether or not the ignition switch is turned on (IG = ON). If a negative determination is made in S101 (IG = OFF), the ECU 16 ends the execution of this routine. If an affirmative determination is made in S101 (IG = ON), the ECU 16 proceeds to S102.

  In S102, the ECU 16 determines whether or not fuel injection by the fuel injection valve 4 is started. If a negative determination is made in S102, the ECU 16 returns to S101. On the other hand, when a positive determination is made in S102, the ECU 16 proceeds to S103.

  In S103, the ECU 16 determines whether an execution condition for the air-fuel ratio feedback control is satisfied. The execution condition of the air-fuel ratio feedback control is that the A / F sensor 9 is activated. The activity of the A / F sensor 9 is that the temperature of the A / F sensor 9 is equal to or higher than the activation temperature, and the cooling water temperature is a predetermined temperature (cooling water temperature when the temperature of the A / F sensor 9 is equal to or higher than the activation temperature). It is determined on the condition that the exhaust gas temperature downstream from the A / F sensor 9 is equal to or higher than a predetermined temperature (exhaust temperature when the temperature of the A / F sensor 9 is equal to or higher than the activation temperature).

  If an affirmative determination is made in S103, the ECU 16 proceeds to S104. In S104, the ECU 16 executes air-fuel ratio feedback control. Specifically, the ECU 16 executes air-fuel ratio feedback control according to a separately set subroutine. In the subroutine, the ECU 16 first calculates the air-fuel ratio feedback correction value efaf based on the difference between the air-fuel ratio detected by the A / F sensor 9 and the target air-fuel ratio. Next, the ECU 16 calculates the air-fuel ratio feedback correction coefficient ekaf by substituting the air-fuel ratio feedback correction value efaf into the equation (2). Further, the ECU 16 calculates the fuel injection amount (fuel injection time) etau by substituting the air-fuel ratio feedback correction coefficient ekaf into the equation (3). The subroutine is repeatedly executed by the ECU 16 as long as the air-fuel ratio feedback control execution condition is satisfied. Further, the ECU 16 is inactive based on the magnitude of the absolute value (| efaf |) of the air-fuel ratio feedback correction value efaf or the magnitude of the average value efgafave of the air-fuel ratio learning value efgaf in the entire operation region of the internal combustion engine 1. A learning process of the gas concentration learning value eknco2 is executed.

  When the air-fuel ratio feedback control and the learning process of the inert gas concentration learned value eknco2 are performed in this way, the fuel injection amount (fuel) is changed when the property of CNG changes (when the inert gas concentration of CNG changes). The injection time) etau is a fuel injection amount (fuel injection time) suitable for the property after the change. That is, the fuel injection amount (fuel injection time) etau is a fuel injection amount (fuel injection time) in which the air-fuel ratio of the air-fuel mixture matches the target air-fuel ratio. As a result, it is possible to avoid a situation where the air-fuel ratio of the air-fuel mixture deviates from the target air-fuel ratio due to a change in the properties of CNG.

  The ECU 16 proceeds to S105 after executing the process of S104, and determines whether or not the ignition switch is turned off. If an affirmative determination is made in S105, the ECU 16 ends the execution of this routine. On the other hand, if a negative determination is made in S105, the ECU 16 returns to S103.

  If a negative determination is made in S103, the ECU 16 proceeds to S106. In S106, the ECU 16 reads the output signal (intermediate opening) θ of the lift sensor 17 and the output signal (upstream pressure) Pu of the pressure sensor 10. It should be noted that the “detecting means” according to the present invention is realized by the ECU 16 executing the process of S106.

  In S107, the ECU 16 calculates a lift correction coefficient f (θ) and a pressure correction coefficient g (Pu) from the intermediate opening θ and the upstream pressure Pu read in S106.

  In S108, the ECU 16 multiplies the fuel injection amount (fuel injection time) etau determined according to the operating state of the internal combustion engine 1 by the lift correction coefficient f (θ) calculated in S107 and the pressure correction coefficient g (Pu). Thus, the fuel injection amount (fuel injection time) etau is corrected. When the ECU 16 executes the process of S108, the “correction means” according to the present invention is realized.

  When the ECU 16 finishes executing the process of S108, it executes the processes of S103 and subsequent steps again.

  As described above, when the ECU 16 executes the fuel injection amount calculation routine of FIG. 8, the fuel injection amount (fuel injection time) etau is obtained when the CNG property changes (when the CNG inert gas concentration changes). The fuel injection amount (fuel injection time) is suitable for the changed properties. That is, the fuel injection amount (fuel injection time) etau is a fuel injection amount (fuel injection time) in which the air-fuel ratio of the air-fuel mixture matches the target air-fuel ratio. As a result, it is possible to avoid a situation where the air-fuel ratio of the air-fuel mixture deviates from the target air-fuel ratio due to a change in the properties of CNG. Furthermore, even if the A / F sensor 9 is not activated when the internal combustion engine 1 is operated for the first time after replenishing CNG, the fuel injection amount (fuel injection time) etau can be set to an amount suitable for the properties of CNG. it can. Therefore, it is possible to avoid a situation in which the air-fuel ratio of the air-fuel mixture deviates from the target air-fuel ratio during the period from when the internal combustion engine 1 is started until the A / F sensor 9 is activated.

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

  In the first embodiment described above, an example in which the fuel injection amount (fuel injection time) is corrected according to the properties of CNG has been described. However, in this embodiment, an example in which the ignition timing is corrected according to the properties of CNG is described. State.

  When the inert gas concentration of CNG is high, the combustion rate of the air-fuel mixture becomes slower than when the CNG inert gas concentration is low. If the combustion speed of the air-fuel mixture becomes slow, the output of the internal combustion engine 1 may decrease, or the exhaust temperature may become unnecessarily high.

  Thus, in this embodiment, the ECU 16 corrects the ignition timing according to the inert gas concentration of CNG when the properties of CNG change. For example, the ECU 16 performs correction so that the ignition timing is advanced (advanced) when the inert gas concentration of CNG is high compared to when it is low.

  Note that the inert gas concentration of CNG is proportional to the magnitude of the above-described inert gas concentration learned value eknco2 or the magnitude of the lift correction coefficient f (θ). For example, as shown in FIG. 9, the inert gas concentration learned value eknco2 increases as the inert gas concentration of CNG increases. Further, as shown in FIG. 10, the magnitude of the lift correction coefficient f (θ) increases as the inert gas concentration of CNG increases. Therefore, when the A / F sensor 9 is active, the ECU 16 may perform correction so that the ignition timing is earlier as the inert gas concentration learned value eknco2 is larger, as shown in FIG. In addition, when the A / F sensor 9 is not activated, the ECU 16 may perform correction so that the ignition timing becomes earlier as the lift correction coefficient f (θ) increases as shown in FIG.

When the ignition timing is corrected in this manner, the combustion end timing of the air-fuel mixture can be set to a desired timing even when the CNG property changes. As a result, it is possible to avoid a situation in which the output of the internal combustion engine 1 decreases or the temperature of the exhaust gas increases unnecessarily.

  The ECU 16 may correct the EGR gas amount instead of the ignition timing in an internal combustion engine equipped with an EGR system. For example, when the A / F sensor 9 is activated, the ECU 16 increases the opening of the EGR valve so that the EGR gas amount decreases as the inert gas concentration learning value eknco2 increases, as shown in FIG. It may be corrected. Further, when the A / F sensor 9 is not activated, the ECU 16 increases the opening degree of the EGR valve so that the EGR gas amount decreases as the lift correction coefficient f (θ) increases as shown in FIG. It may be corrected.

  In an internal combustion engine having a variable valve mechanism that can change the opening / closing timing of at least one of the intake valve and the exhaust valve, the ECU 16 determines the magnitude of the inert gas concentration learned value eknco2 or the lift correction coefficient f (θ). The opening / closing timing of the intake valve and / or the exhaust valve may be corrected according to the size. For example, when the A / F sensor 9 is active, the ECU 16 variably operates so that the burned gas (internal EGR gas) remaining in the cylinder 3 decreases as the inert gas concentration learning value eknco2 increases. The valve mechanism may be controlled. Further, when the A / F sensor 9 is not activated, the ECU 16 variably operates so that the burned gas (internal EGR gas) remaining in the cylinder 3 decreases as the lift correction coefficient f (θ) increases. The valve mechanism may be controlled.

  When the amount of EGR gas in the cylinder 3 is corrected by the various methods described above, even if the inert gas concentration of CNG changes, the change in the concentration of the inert gas contained in the mixture is suppressed. be able to. As a result, when the inert gas concentration of CNG changes, it can suppress that the combustion rate of an air-fuel mixture changes.

  Next, in the internal combustion engine provided with the variable valve mechanism, the ECU 16 changes the speed at which the intake air flows into the cylinder 3 instead of correcting the ignition timing and the EGR gas amount. May be controlled. For example, when the A / F sensor 9 is active, the ECU 16 may control the variable valve mechanism so that the flow rate of the intake air increases as the learned inert gas concentration value eknco2 increases. Further, when the A / F sensor 9 is not activated, the ECU 16 may control the variable valve mechanism so that the flow rate of intake air increases as the lift correction coefficient f (θ) increases.

  If the flow rate of the intake air is increased when the inert gas concentration of CNG is high, the flame propagation speed when the air-fuel mixture burns can be increased. As a result, when the inert gas concentration of CNG increases, it is possible to suppress a decrease in the combustion rate of the air-fuel mixture.

  As described in the first embodiment, the intermediate opening θ is influenced by the upstream pressure Pu in addition to the inert gas concentration of CNG. Therefore, when the A / F sensor 9 is not activated, the ECU 16 multiplies the lift correction coefficient f (θ) based on the intermediate opening θ and the pressure correction coefficient g (Pu) based on the upstream pressure Pu ( = F (θ) * g (Pu)) may be used as parameters to correct the ignition timing, the opening of the EGR valve, and the intake / exhaust valve opening / closing timing.

  In the first and second embodiments described above, an example in which the present invention is applied to an internal combustion engine in which CNG is injected into a cylinder has been described. However, in an internal combustion engine in which CNG is injected into an intake passage (intake port). Of course, the present invention may be applied. In the first and second embodiments, an example in which the present invention is applied to an internal combustion engine using CNG as fuel has been described. However, an internal combustion engine that selectively uses CNG and liquid fuel (such as gasoline or alcohol fuel). The present invention can also be applied to.

  Further, in the first and second embodiments described above, when the A / F sensor 9 is not activated, the control parameter related to the combustion state of the air-fuel mixture according to the intermediate opening θ of the valve 160 of the regulator 15. Although the system for correcting the fuel injection amount, ignition timing, EGR valve opening, intake / exhaust valve opening / closing timing, etc. has been described, a device for identifying the inert gas concentration of CNG from the intermediate opening θ is configured. You can also. That is, the ECU 16 may calculate the inert gas concentration of CNG using the correlation between the intermediate opening θ and the inert gas concentration as shown in FIG. At this time, the ECU 16 preferably calculates the inert gas concentration of CNG in consideration of the relationship between the upstream pressure Pu and the intermediate opening θ (for example, the relationship shown in FIG. 7 described above). Specifically, the ECU 16 may correct the output signal of the lift sensor 17 in accordance with the upstream pressure Pu, and calculate the inert gas concentration from the corrected value and the relationship shown in FIG. .

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Fuel tank 3 Cylinder 4 Fuel injection valve 5 Intake passage 6 Exhaust passage 7 Intake throttle valve 8 Intake temperature sensor 9 A / F sensor (air-fuel ratio sensor)
DESCRIPTION OF SYMBOLS 10 Pressure sensor 11 Fuel supply pipe 11a Upstream fuel supply pipe 11b Downstream fuel supply pipe 12 Filling port 13 Inlet pipe 14 Shut-off valve 15 Regulator 16 ECU
17 Lift sensor 150 Housing 151 Primary chamber 152 Secondary chamber 152a Decompression chamber 152b Air chamber 153 Communication passage 154 Inlet 155 Passage 156 Outlet 157 Passage 158 Valve seat 160 Valve 160a Valve body 160b Valve stem 161 Holder 162 Diaphragm 163 Spring retainer 164 Coil Spring 165 Adjustment bolt 170 Gap sensor 171 Target

Claims (5)

A fuel tank for storing compressed natural gas;
A fuel injection valve for injecting compressed natural gas into the intake passage or the cylinder;
The fuel supply passage is arranged in the middle of a fuel supply passage for introducing compressed natural gas from the fuel tank to the fuel injection valve, and the pressure of the compressed natural gas supplied to the fuel injection valve is equal to a set pressure. A regulator for adjusting the cross-sectional area of the passage,
Detecting means for detecting the size of the passage cross-sectional area adjusted by the regulator when fuel injection by the fuel injection valve is being performed;
An air-fuel ratio sensor provided in the exhaust passage and outputting a signal correlated with the air-fuel ratio of the air-fuel mixture burned in the cylinder;
Wherein when the air-fuel ratio sensor is not active, based on the size of the cross-sectional area which is detected by said detecting means, Bei example and a correcting means for correcting the control parameter relating to the combustion state of air-fuel mixture,
The control parameter is a fuel injection amount,
Said correction means, wherein when a large passage cross-sectional area which is detected by the detection means than when smaller, the control system of the internal combustion engine for increasing the fuel injection amount. The control unit according to claim 1, further comprising air-fuel ratio feedback control for correcting a fuel injection amount of the fuel injection valve based on a deviation between an output signal of the air-fuel ratio sensor and a target air-fuel ratio.
When the air-fuel ratio sensor is active, the correction means corrects the control parameter based on the absolute value of the correction value by the air-fuel ratio feedback control.   3. The correction unit according to claim 1, wherein the correction unit corrects the control parameter based on a magnitude of a pressure of the compressed natural gas upstream of the regulator in addition to a size of a passage sectional area detected by the detection unit. A control system for an internal combustion engine. A fuel tank for storing compressed natural gas;
A fuel injection valve for injecting compressed natural gas into the intake passage or the cylinder;
The fuel supply passage is arranged in the middle of a fuel supply passage for introducing compressed natural gas from the fuel tank to the fuel injection valve, and the pressure of the compressed natural gas supplied to the fuel injection valve is equal to a set pressure. A regulator for adjusting the cross-sectional area of the passage,
Detecting means for detecting a cross-sectional area of the passage adjusted by the regulator when fuel injection by the fuel injection valve is performed;
An air-fuel ratio sensor provided in the exhaust passage and outputting a signal correlated with the air-fuel ratio of the air-fuel mixture burned in the cylinder;
A compression means comprising: a calculation means for calculating the concentration of the inert gas contained in the compressed natural gas based on the size of the passage sectional area detected by the detection means when the air-fuel ratio sensor is not active. Inert gas concentration detector for natural gas. Oite to claim 4, wherein the calculating means, in addition to the size of the cross-sectional area which is detected by the detection means, based on the magnitude of the pressure of compressed natural gas in the upstream from said regulator, included in the compressed natural gas A device for detecting an inert gas concentration of compressed natural gas that calculates the concentration of the inert gas.

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