JP2015129491A - Internal combustion engine fuel supply controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the influence of a change in the composition of a gas fuel and appropriately execute combustion.SOLUTION: A fuel supply system comprises: a gas tank 42; a first injection valve 21 serving as gas injection means injecting a gas fuel supplied from the gas tank 42 via a fuel passage; and a regulator 43 serving as pressure regulation means regulating a fuel supply pressure that is a pressure of the gas fuel supplied to the first injection valve 21 to be reduced. A control unit 80 learns the composition of the gas fuel supplied to the gas injection means and variably controls the fuel supply pressure by the regulator 43 on the basis of a result of learning after completion of the learning.

Description

  The present invention relates to a fuel supply control device for an internal combustion engine, and more particularly to a fuel supply control device for an internal combustion engine capable of supplying gaseous fuel as a combustion fuel for the internal combustion engine.

  Conventionally, vehicles equipped with an internal combustion engine that is driven by burning gaseous fuel such as compressed natural gas (CNG) have been put into practical use. In such an internal combustion engine, the fuel supply system for supplying the gaseous fuel to the fuel injection valve has a gas tank for storing the gaseous fuel in a high pressure state, and is provided in the middle of the fuel pipe connecting the gas tank and the fuel injection valve. The structure provided with the regulator which pressure-reduces and adjusts the pressure of the gaseous fuel supplied from is known.

  In a fuel supply system for gaseous fuel, a configuration is known in which a variable fuel pressure regulator capable of adjusting the pressure of fuel supplied to a fuel injection valve is disposed (see, for example, Patent Document 1). Patent Document 1 discloses a pilot gas pressure control device in a lean combustion gas engine. In this apparatus, it is disclosed that the pressure of the pilot gas is controlled by a variable fuel pressure type regulator using the differential pressure ΔP between the pressure of the pilot gas and the supply air pressure as an index.

JP-A-10-184462

  By the way, in gaseous fuels, such as CNG, a fuel composition may differ with a production place or a production process. In addition, when gaseous fuel having a different composition is replenished in the tank between the previous engine shutdown and the current engine start, the fuel density may change before and after fuel replenishment due to the difference in fuel composition. At this time, when fuel with a low fuel density is filled, the amount of fuel required for each combustion increases, and the injection time required to supply the required amount of fuel to the engine becomes longer. Therefore, for example, it is conceivable that a required amount of fuel cannot be injected in a high rotation and high load range. In such a case, there is a concern that the air-fuel ratio becomes lean due to a shortage of fuel, which may cause problems such as a shortage of engine output or catalyst melting. In addition, when a fuel having a high fuel density is filled, the amount of fuel required for each combustion is reduced, which may limit the minimum injection time of the fuel injection valve. In this case, there is a concern that the air-fuel ratio becomes rich due to the excessive injection amount, resulting in inconveniences such as emission deterioration and fuel consumption deterioration.

  The present invention has been made in order to solve the above-described problems, and mainly provides a fuel supply control device for an internal combustion engine that can appropriately perform combustion while reducing the influence of changes in the composition of gaseous fuel. Objective.

  The present invention employs the following means in order to solve the above problems.

  The present invention is provided in a fuel tank (42) for storing gaseous fuel in a high pressure state, gas injection means (21) for injecting gaseous fuel supplied from the fuel tank through a fuel passage (41), and the fuel passage. The fuel of the internal combustion engine applied to the fuel supply system (40) of the internal combustion engine (10), comprising pressure adjusting means (43) for reducing the fuel supply pressure that is the pressure of the gaseous fuel supplied to the gas injection means The present invention relates to a supply control device. The invention according to claim 1 is based on a composition learning means for learning a composition of the gaseous fuel supplied to the gas injection means and a result of the learning after the learning of the composition of the gaseous fuel by the composition learning means is completed. And pressure control means for variably controlling the fuel supply pressure by the pressure adjusting means.

  In the above configuration, the fuel pressure of the gaseous fuel supplied to the fuel injection valve is variably controlled based on the learning result of the fuel composition. When the composition of the gaseous fuel that is used for combustion in the internal combustion engine changes, the length of the injection time for injecting the same amount of fuel changes. Therefore, it is conceivable that a required amount of fuel cannot be completely injected within a period during which injection is possible, or an excessive amount of fuel is injected due to the limitation on the minimum injection time. In this respect, by adopting the above-described configuration, it is possible to supply gaseous fuel having a fuel pressure corresponding to the fuel composition to the fuel injection valve, and to supply an amount of gaseous fuel necessary for each combustion within the injectable period. Can be supplied to. Thereby, the influence by the change of the composition of gaseous fuel can be reduced and combustion can be implemented appropriately.

1 is an overall schematic configuration diagram of an engine fuel supply control system. FIG. The figure which shows the mode of the change of the air fuel ratio correction amount FB and injection pulse width when a fuel composition changes. The flowchart which shows the process sequence of the regulator drive control based on the learning result of a fuel composition. The figure which shows the relationship between a fuel density and a pressure correction coefficient. The figure which shows the relationship between an engine driving | running state and a pressure correction coefficient.

  Hereinafter, embodiments will be described with reference to the drawings. The present embodiment is a fuel supply system applied to a so-called bi-fuel type on-vehicle engine (internal combustion engine) that uses compressed natural gas (CNG) as a gaseous fuel and gasoline as a liquid fuel as combustion fuel. It is materialized. An overall schematic diagram of this system is shown in FIG.

  An engine 10 shown in FIG. 1 is a multi-cylinder (for example, in-line three-cylinder) spark ignition engine. An intake pipe 11 is connected to the intake port of the engine 10 via an intake manifold 12, and an exhaust pipe 14 is connected to the exhaust port via an exhaust manifold 13. The intake pipe 11 is provided with a throttle valve 15 as air amount adjusting means. The throttle valve 15 is configured as an electronically controlled throttle valve whose opening is adjusted by a throttle actuator 15a such as a DC motor. The opening degree of the throttle valve 15 (throttle opening degree) is detected by a throttle opening degree sensor 15b built in the throttle actuator 15a.

  The exhaust pipe 14 is provided with an exhaust sensor for detecting exhaust components and a catalyst 19 for purifying the exhaust. As the exhaust sensors, oxygen sensors 18a and 18b that output detection signals corresponding to the oxygen concentration in the exhaust are provided on the upstream side and the downstream side of the catalyst 19, respectively.

  An intake valve 25 and an exhaust valve 26 as engine valves for adjusting the amount of air introduced into the cylinder are respectively provided at the intake port and the exhaust port of the engine 10. When the intake valve 25 is opened, a mixture of air and fuel is introduced into the cylinder, and when the exhaust valve 26 is opened, the exhaust gas after combustion is discharged into the exhaust passage.

  A spark plug 20 is provided in each cylinder of the engine 10. A high voltage is applied to the ignition plug 20 at a desired ignition timing through an ignition device 20a including an ignition coil. By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 20, and the fuel introduced into the cylinder is ignited and used for combustion.

  In this system, as fuel injection means for injecting and supplying fuel to each cylinder of the engine 10, a first injection valve 21 as gas injection means for injecting gaseous fuel, and a liquid injection means for injecting liquid fuel A second injection valve 22 is provided. These injection valves 21 and 22 respectively inject fuel into the intake manifold 12.

  Each of the injection valves 21 and 22 is an open / close type control valve in which the valve body is lifted from the closed position to the open position by electrically driving the electromagnetic drive unit. Each valve is driven to open by a valve opening drive signal. Each of these injection valves 21 and 22 opens by energization and closes by energization interruption, thereby injecting an amount of fuel corresponding to the energization time. In the present embodiment, the injection pipe 23 is connected to the distal end portion of the first injection valve 21, and the gaseous fuel injected from the first injection valve 21 is injected into the intake manifold 12 through the injection pipe 23. It is like that. The second injection valve 22 is a port injection type in the present embodiment, but may be a direct injection type that directly injects fuel into the cylinder of the engine 10.

  Next, the gas fuel supply unit 40 that supplies gas fuel to the first injection valve 21 and the liquid fuel supply unit 70 that supplies liquid fuel to the second injection valve 22 will be described.

  The gaseous fuel supply unit 40 is provided with a gas tank 42 that stores gaseous fuel in a high pressure state, and a gas pipe 41 that connects the gas tank 42 and the first injection valve 21. In the middle of the gas pipe 41, a regulator 43 is provided as pressure adjusting means having a function of adjusting the pressure of the gaseous fuel supplied to the first injection valve 21 under reduced pressure. The regulator 43 is a variable fuel pressure type pressure adjustment mechanism that adjusts the pressure of the gaseous fuel stored in the gas tank 42 in a high-pressure state (for example, a maximum of 20 MPa).

  The regulator 43 of this embodiment is an electromagnetic drive type, and the pressure of the fuel supplied to the first injection valve 21 (fuel supply pressure) is controlled within a predetermined pressure range (for example, 0.2 to 1) by energization control on the electromagnetic drive unit. The control pressure of the regulator 43 (regulator control pressure) is variably adjusted so as to be within the pressure range of 2 MPa. The fuel supply pressure of the first injection valve 21 is adjusted by the regulator 43 so that the injection pressure of the first injection valve 21 is adjusted. The gaseous fuel after the decompression adjustment is supplied to the first injection valve 21 through the gas pipe 41.

  The gas pipe 41 further includes a tank main stop valve 44 disposed near the fuel outlet of the gas tank 42, and a shut-off valve disposed downstream of the tank main stop valve 44 and near the fuel inlet of the regulator 43. 45 is provided. These valves 44 and 45 allow and block the flow of gaseous fuel in the gas pipe 41. Both the tank main stop valve 44 and the shut-off valve 45 are electromagnetic on-off valves, and are normally closed types in which the flow of gaseous fuel is blocked when not energized and the flow of gaseous fuel is allowed when energized. In the gas pipe 41, pressure sensors 46 and 47 for detecting fuel pressure are provided upstream and downstream of the regulator 43, and a temperature sensor 48 for detecting fuel temperature is provided downstream of the regulator 43. Is provided.

  The liquid fuel supply unit 70 is provided with a fuel tank 72 that stores liquid fuel, and the fuel tank 72 is connected to the second injection valve 22 via a fuel pipe 71. The fuel pipe 71 is provided with a fuel pump 73 that feeds the liquid fuel in the fuel tank 72 to the second injection valve 22. The liquid fuel pumped up by the fuel pump 73 is supplied to the second injection valve 22 through the fuel pipe 71.

  The control unit 80 includes a CPU, a ROM, a RAM, a backup RAM, and the like, and executes various control programs stored in the ROM, thereby performing various controls of the engine 10 according to each engine operating state. . Specifically, the control unit 80 is electrically connected to the various sensors described above and other sensors (crank angle sensor 81, intake pipe pressure sensor 82, cooling water temperature sensor 83, vehicle speed sensor, etc.) provided in the system. The outputs (detection signals) from these sensors are input. The control unit 80 is electrically connected to a drive unit such as the ignition device 20a, each injection valve 21, 22 and a starter (not shown) as an engine starter, and directs the drive signal to each drive unit. The drive of each drive part is controlled by outputting.

  The control unit 80 selectively switches the fuel to be used for the operation of the engine 10 according to the engine operating state, the fuel remaining amount in the tank, an input signal from a fuel selection switch (not shown), and the like. Specifically, when the use of gaseous fuel is selected by the fuel selection switch, or when the remaining amount of liquid fuel in the tank 72 falls below a predetermined value, the fuel mode of the engine 10 is set as the gaseous fuel supply unit. A gas fuel mode in which gaseous fuel is supplied to the engine 10 is selected at 40. On the other hand, when the use of the liquid fuel is selected by the fuel selection switch or when the remaining amount of the gaseous fuel in the gas tank 42 falls below a predetermined value, the liquid fuel supply unit 70 sets the liquid mode as the fuel mode of the engine 10. A liquid fuel mode for supplying fuel to the engine 10 is selected.

  Regarding the fuel injection control, the control unit 80 calculates the basic injection amount based on the engine operating state (engine rotation speed and engine load), and calculates the fuel injection amount by performing various corrections on the basic injection amount. Then, the calculated fuel injection amount is converted into an injection time corresponding to the injection pressure of the fuel injection valve (the first injection valve 21 and the second injection valve 22), and the fuel injection valve is opened for the injection time. Thus, a required amount of fuel is supplied to the engine 10 according to the engine operating state each time.

  In the present embodiment, as air-fuel ratio control, feedback control based on the deviation between the actual air-fuel ratio and the target air-fuel ratio is performed. Specifically, the target air-fuel ratio is calculated based on the engine operating state (for example, engine speed and engine load), and the actual air-fuel ratio is calculated based on the detection value of the oxygen sensor 18a provided on the upstream side of the catalyst 19. calculate. Then, an air-fuel ratio feedback correction amount (hereinafter also referred to as “air-fuel ratio correction amount FB”), which is a correction amount of the fuel injection amount, is calculated according to the deviation between the actual air-fuel ratio and the target air-fuel ratio. The actual air-fuel ratio is made to coincide with the target air-fuel ratio by correcting the basic injection amount with the air-fuel ratio correction amount FB.

  The air-fuel ratio correction amount FB is decreased by a predetermined amount while the air-fuel ratio detected by the oxygen sensor 18a is rich, and is increased by a predetermined amount during the lean period. In addition, when the air-fuel ratio detected by the oxygen sensor 18a is switched from rich to lean, or from lean to rich, the air-fuel ratio correction amount FB is increased or decreased (skipped) stepwise. In the air-fuel ratio feedback control of this system, the controllability of the air-fuel ratio control is enhanced by adding correction based on the detection value of the oxygen sensor 18b on the downstream side of the catalyst. The air-fuel ratio feedback control is started after the oxygen sensor 18a is activated after the engine is started.

  Here, the gaseous fuel such as CNG includes a plurality of types of components that contribute to combustion, and also includes an inert gas (impurities) such as nitrogen and CO2. Further, the composition of the gaseous fuel varies depending on the production area and production process, and the fuel density varies depending on the difference in the fuel composition. Therefore, if fuel injection is performed on the assumption that the composition of the gaseous fuel filled in the gas tank 42 is always constant, excess or deficiency of fuel supplied to the engine 10 occurs, causing knocking, misfire, worsening of emissions, and the like. Can be considered. Therefore, in the present embodiment, when the gas fuel is replenished in the gas tank 42, the composition of the gas fuel filled in the gas tank 42 is learned (composition learning means). Specifically, in the present embodiment, it is utilized that the composition (fuel density) of the gaseous fuel is correlated with the fuel injection amount correction amount (air-fuel ratio correction amount FB) calculated by the air-fuel ratio feedback control. Thus, the composition of the gaseous fuel is learned based on the air-fuel ratio correction amount FB.

  For example, the learning of the fuel composition is performed as follows. That is, it is determined whether or not gaseous fuel is replenished in the gas tank 42. If it is determined that the fuel is replenished, the composition of the gaseous fuel is learned at the next engine start using the gaseous fuel. At this time, if the air-fuel ratio correction amount FB exceeds a predetermined control range set in advance, a predetermined update amount fa1 is added to the learned value FA of the fuel composition, and the air-fuel ratio correction amount FB is added along with this addition. The update amount fa1 is subtracted from. The update of the learning value FA and the correction of the air-fuel ratio correction amount FB accompanying the update are sequentially repeated to keep the air-fuel ratio correction amount FB within the control range. As a result, the deviation of the air-fuel ratio correction amount FB due to the change in the fuel composition is reflected in the learning value FA to eliminate the steady deviation of the air-fuel ratio correction amount FB.

  Consider a case where gaseous fuel having a different fuel composition is replenished in the gas tank 42 during the period from the previous engine stop to the current engine start. Here, a case where a fuel having a fuel density lower than that of the gaseous fuel filled in the gas tank 42 is replenished will be considered. In this case, the gaseous fuel injected from the first injection valve 21 has a smaller injection mass per unit injection time, so the actual air-fuel ratio is leaner than the target air-fuel ratio. As a result, the air-fuel ratio correction amount FB increases as shown in FIG. The control unit 80 updates the fuel composition learning value FA and subtracts the air-fuel ratio correction amount FB accompanying this update, thereby storing the change ΔFB in the air-fuel ratio correction amount FB as the fuel composition learning value FA. At the same time, the fuel injection amount of the gaseous fuel is calculated using the learned value FA.

  When fuel with low fuel density is replenished, if the fuel pressure supplied to the first injection valve 21 is constant, the injection time becomes longer to inject the required amount of gaseous fuel into the engine 10, for example, As shown in FIG. 2, the injection time (injection pulse width) of the first injection valve 21 is increased by Δt. At this time, if the composition of the gaseous fuel greatly differs before and after fuel replenishment, the injection pulse becomes excessively long, and there is a possibility that the required fuel cannot be injected in the high engine speed and high load range. In this case, it is conceivable that the air-fuel ratio becomes lean due to the shortage of fuel, resulting in insufficient output of the engine 10, misfire, melting of the catalyst 19, and the like. Conversely, when gaseous fuel having a high fuel density is replenished in the gas tank 42, the minimum injection time (minimum injection pulse) that can be set by the first injection valve 21 is limited and supplied to the engine 10. The amount of fuel may be excessive. In such a case, there is a concern that the air-fuel ratio becomes rich due to excessive fuel, leading to deterioration in emissions and fuel consumption.

  Therefore, in the present embodiment, a learning result of the composition of the gaseous fuel supplied to the first injection valve 21 is acquired, and the regulator control pressure is made variable based on the learning result. More specifically, the fuel supply of the first injection valve 21 is such that the learning value updated by the fuel composition learning is a value indicating that the fuel density of the gaseous fuel filled in the gas tank 42 is currently small. The regulator control pressure is set so that the pressure (injection pressure) is on the high pressure side. For example, when the gas fuel is replenished in the gas tank 42 between the previous engine stop and the current engine start, and the fuel density of the gaseous fuel supplied to the first injection valve 21 becomes smaller than that during the previous operation. By changing the regulator control pressure to the high pressure side, as shown in FIG. 2, the injection pulse width (injection time) is shortened by the amount (Δt) shown by the oblique lines.

  FIG. 3 is a flowchart illustrating a processing procedure of regulator drive control according to the present embodiment. This process is executed by the control unit 80 at predetermined intervals.

  In FIG. 3, in step S <b> 101, it is determined whether or not gaseous fuel is selected as the fuel used for combustion of the engine 10. If the liquid fuel is selected, the process is terminated as it is, and if the gaseous fuel is selected, the process proceeds to step S102. In step S102, it is determined whether or not gaseous fuel is replenished in the gas tank 42 before the current engine start. Here, it is determined whether or not the fuel pressure detected by the pressure sensor 46 is higher than the fuel pressure at the previous engine stop by a predetermined value or more. When it is determined that fuel is refilled in the gas tank 42, the process proceeds to step S103, and when it is determined that fuel is not replenished, the process proceeds to step S106.

  In step S103, it is determined whether or not the fuel learning of the gaseous fuel is completed after the current engine start. If the fuel learning of the gaseous fuel is not completed, the process proceeds to step S106. On the other hand, if the fuel learning of the gaseous fuel has been completed, the process proceeds to step S104, and it is determined whether or not the fuel composition has changed due to fuel replenishment in the gas tank 42. Here, a learning result of the fuel composition executed in another routine (not shown) is acquired, and a determination is made based on the acquired learning result. Specifically, after the engine is started, when the air-fuel ratio correction amount FB changes by a predetermined value or more within a predetermined time after the air-fuel ratio feedback control is started, the fuel composition in the gas tank 42 is changed by fuel replenishment. judge.

  If the fuel composition has not changed, the process proceeds to step S106. On the other hand, if the fuel composition has changed, the process proceeds to step S105, where the fuel pressure supplied to the first injection valve 21, that is, the injection pressure of the first injection valve 21, is determined based on the learning result of the fuel composition and the engine operating state. A pressure correction coefficient Fp for correction is calculated (pressure control means). The pressure correction coefficient Fp is a correction coefficient (> 0) with respect to the reference pressure Po of the regulator control pressure Prg (for example, a predetermined pressure of 0.2 to 0.3 MPa). The larger this value, the more the pressure correction amount with respect to the reference pressure Po. Means high on the high pressure side. Here, the pressure correction coefficient Fp is calculated using the fuel density of the gaseous fuel learned by the fuel composition learning and the engine operating state (engine rotational speed and engine load). For example, the pressure correction coefficient Fp is calculated by multiplying or adding the correction coefficient fp1 related to the fuel density of the gaseous fuel and the correction coefficient fp2 related to the engine operating state.

  FIG. 4 shows the relationship between the fuel density of the gaseous fuel and the correction coefficient fp1. According to FIG. 4, the correction coefficient fp1 is set to a larger value as the fuel density of the gaseous fuel is smaller. Thereby, the regulator control pressure Prg is set to a higher value as the gas density of the gaseous fuel is smaller. The fuel density of the gaseous fuel is calculated based on the rate of change of the air-fuel ratio correction amount FB and the rate of change of the injection pulse width. For example, in FIG. 2, when the injection pulse width before the increase of the air-fuel ratio correction amount FB is 1, and the injection pulse width after the increase of the air-fuel ratio correction amount FB is 1.5, the air-fuel ratio correction amount FB The fuel density can be calculated by converting the fuel density according to the ratio (1.5 / 1) of the injection pulse width before and after the change. At this time, instead of the relationship between the fuel density and the correction coefficient fp1, for example, the relationship between the change rate of the air-fuel ratio correction amount FB and the correction coefficient fp1, or the relationship between the change rate of the injection pulse width and the correction coefficient fp1 is stored in advance. In addition, the correction coefficient fp1 may be calculated using these relationships.

  As for the correction coefficient fp2 related to the engine operating state, as shown in FIG. 5, the relationship among the engine speed, the engine load, and the correction coefficient fp2 is determined in advance as a pressure correction map, and is corrected using this map. The coefficient fp2 is calculated. In the map of FIG. 5, the engine operation region is divided into a plurality of operation regions according to the engine rotation speed and the engine load, and the correction coefficient fp2 is set for each of these operation regions. According to the pressure correction map of FIG. 5, the pressure correction coefficient Fp is calculated to be smaller as the engine speed is lower or the engine load is lower. As a result, the regulator control pressure Prg is set to a lower pressure value as the engine speed is lower or the engine load is lower.

  The reason for making the regulator control pressure variable according to the engine operating state is as follows. Gaseous fuel (CNG fuel in this embodiment) has a larger volume per unit mass than liquid fuel such as gasoline, and the ratio of the fuel injected from the first injection valve 21 in the intake pipe 11 increases. Moreover, both gaseous fuel and air are gas, and both are comparatively hard to mix. Therefore, the fuel injected in the gaseous state from the first injection valve 21 tends to stay in the vicinity of the intake valve 25, for example, as a mass of fuel. Moreover, the localization of the fuel is more likely to appear on the engine low-speed side where the airflow is small. When such localization of gas fuel occurs, mixing of fuel and air becomes insufficient, and as a result of worsening combustion, it is considered that fuel efficiency is deteriorated and output is reduced. Therefore, in the present embodiment, as shown in FIG. 4, the regulator control pressure Prg, that is, the fuel supply pressure of the first injection valve 21 is lowered as the engine speed decreases. As a result, the fuel injection time is prolonged on the low-speed side of the engine 10 and mixing is improved by supplying the fuel little by little to the air. In consideration of the fact that the amount of fuel required for each fuel increases at a high load, and the required amount of fuel may not be able to be injected completely, the regulator control pressure Prg is increased as the load increases.

  In this embodiment, regarding the upper limit value and the lower limit value of the regulator control pressure Prg, in this embodiment, the maximum injection amount that is the maximum value of the fuel amount that can be injected from the first injection valve 21 in one fuel injection, and the minimum that is the minimum value thereof. Each value is set so that the injection with the injection amount can be realized. Thus, the required fuel amount calculated based on the engine operating state can be supplied into the cylinder.

  Returning to FIG. 3, in step S107, the regulator control pressure Prg is calculated based on the pressure correction coefficient Fp. Here, the regulator control pressure Prg is calculated by multiplying the reference pressure Po and the pressure correction coefficient Fp. In subsequent step S108, the energization control of the electromagnetic drive unit of the regulator 43 is performed based on the calculated regulator control pressure Prg.

  On the other hand, when it is determined that the gas fuel is not replenished before the engine is started, it is determined that the fuel composition is not changed even if the gas fuel is replenished, or the fuel composition learning is not completed. If YES, the process proceeds to step S106, and the pressure correction coefficient Fp is calculated based on the engine operating state (engine speed and engine load). At this time, the same map (FIG. 5) as the map for calculating the pressure correction coefficient Fp based on the learning result of the fuel composition may be used, or a map different from the map of FIG. 5 may be used. Then, the process of step S107 and S108 is performed and this routine is complete | finished.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  Based on the learning result of the fuel composition, the fuel pressure of the gaseous fuel supplied to the first injection valve 21 is variably controlled. When the composition of the gaseous fuel used for combustion in the engine 10 changes, the length of the injection time required to inject fuel of the same mass changes, and the required amount of fuel cannot be injected within the injectable period. An excessive amount of fuel may be injected due to the limitation on the minimum injection time. In this regard, by adopting the above-described configuration, gaseous fuel having a fuel pressure corresponding to the fuel composition can be supplied to the first injection valve 21, and an amount of gaseous fuel necessary for each combustion can be supplied within a period during which injection is possible. The engine 10 can be supplied. Thereby, the influence by the change of the composition of gaseous fuel can be decreased and combustion of the engine 10 can be implemented appropriately.

  Specifically, the fuel density of the gaseous fuel is learned by fuel composition learning, and the regulator 43 is driven such that the regulator control pressure Prg becomes higher as the learned fuel density decreases. When fuel with a low fuel density is filled, the injection time becomes long in order to supply the required amount of fuel to the engine. For example, the required amount of fuel cannot be injected in a high rotation and high load range, resulting in insufficient fuel. May occur. In addition, if fuel with a high fuel density is filled, it may limit the minimum injection time of the fuel injection valve, resulting in excessive fuel. In consideration of these points, the above configuration can avoid engine output shortage and catalyst erosion due to fuel shortage, and can also reduce emissions and fuel consumption due to excessive fuel. Occurrence can be avoided.

  By calculating the pressure correction coefficient Fp based on the learning result of the fuel composition and the engine operating state, the regulator control pressure Prg is variably controlled. The gaseous fuel injected from the first injection valve 21 tends to stay locally in the intake pipe 11, and this tendency is more likely to appear on the low engine speed side or low load side where the airflow is small. In consideration of these points, the regulator control pressure Prg is set in consideration of the learning result of the fuel composition and the engine operating state, so that they can be easily mixed even in the operation region where the fuel and air are difficult to mix. It is suitable for improving the combustion state of the engine 10.

  It is determined whether or not a change in the composition of the gaseous fuel has occurred based on the learning result of the fuel composition. When it is determined that a change in the fuel composition has occurred, the regulator control pressure Prg can be varied based on the learning result. It was set as the structure controlled to. According to such a configuration, the fuel composition learning can be completed only when the pressure correction based on the learning result is necessary.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be implemented as follows, for example.

  -It is good also as a structure which sets the correction coefficient fp1 regarding the fuel density of gaseous fuel according to an engine operating state. Specifically, for example, the pressure correction coefficient Fp is set to Fp = (fp1 * fp2) * fp2. At this time, if the amount of change in fuel density after fuel replenishment with respect to the fuel density before fuel replenishment is less than the determination value, the pressure correction coefficient Fp = fp1 * fp2, and if the amount of change is greater than or equal to the determination value. The pressure correction coefficient Fp = (fp1 * fp2) * fp2 may be set. In this case also, it is desirable to set the upper limit value and the lower limit value of the regulator control pressure Prg so that the injection with the maximum injection amount and the minimum injection amount of the first injection valve 21 can be realized.

  In the above embodiment, the fuel density that is the learning result of the fuel composition is used, and the regulator control pressure Prg is variably set according to the fuel density, but the amount of change in the fuel density after fuel replenishment with respect to the fuel density before fuel replenishment Accordingly, the regulator control pressure Prg may be changed from the previous value to the high pressure side or the low pressure side by a predetermined amount.

  In the above embodiment, the composition of the gaseous fuel is learned based on the air-fuel ratio correction amount FB during engine operation using the gaseous fuel, but the method of learning the composition of the gaseous fuel is not limited to this. For example, the air-fuel ratio may be estimated based on the detected value of the O2 sensor 18a, and the composition of the gaseous fuel may be learned based on the estimated air-fuel ratio.

  In the above-described embodiment, the case where it is applied to a bi-fuel type vehicle-mounted engine that uses gaseous fuel and liquid fuel as engine combustion fuel has been described, but only for gas that uses only gaseous fuel as fuel for engine fuel You may apply to the vehicle-mounted engine.

  In the above embodiment, the gaseous fuel is CNG fuel, but other gaseous fuels in a gaseous state can be used in the standard state, for example, a fuel mainly composed of methane, ethane, propane, butane, hydrogen, dimethyl ether, etc. It is good also as a structure to use. Further, liquid fuel is not limited to gasoline fuel. For example, you may apply this invention to the system which mounts the supply system of gaseous fuel with respect to the diesel engine which uses light oil as a fuel for combustion.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 18a ... Oxygen sensor, 21 ... 1st injection valve, 22 ... 2nd injection valve, 40 ... Gas fuel supply part, 42 ... Gas tank, 43 ... Regulator, 70 ... Liquid fuel supply part, 80 ... Control part ( Composition learning means, pressure control means).

Claims (4)

A fuel tank (42) for storing gaseous fuel in a high-pressure state; gas injection means (21) for injecting gaseous fuel supplied from the fuel tank through a fuel passage (41); and the gas injection provided in the fuel passage. Applied to a fuel supply system (40) of an internal combustion engine (10), comprising pressure adjusting means (43) for reducing the fuel supply pressure, which is the pressure of gaseous fuel supplied to the means,
Composition learning means for learning the composition of the gaseous fuel supplied to the gas injection means;
Pressure control means for variably controlling the fuel supply pressure by the pressure adjusting means on the basis of the learning result after completion of learning of the composition of the gaseous fuel by the composition learning means;
A fuel supply control apparatus for an internal combustion engine, comprising: The composition learning means learns the density of the gaseous fuel supplied to the gas injection means,
2. The fuel supply control device for an internal combustion engine according to claim 1, wherein the pressure control means makes the fuel supply pressure higher by the pressure adjusting means as the density of the gaseous fuel learned by the composition learning means is smaller.   The internal combustion engine according to claim 1 or 2, wherein the pressure control means variably controls the fuel supply pressure by the pressure adjusting means based on a learning result of the composition learning means and an operating state of the internal combustion engine. Fuel supply control device.   The internal combustion engine according to any one of claims 1 to 3, wherein the pressure control means sets the fuel supply pressure to a low pressure side by the pressure adjusting means as the internal combustion engine is rotated at a lower speed or a load is lower. Engine fuel supply control device.

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