JP2014196736A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the controllability of an internal combustion engine when the operation of the internal combustion engine is performed by a gas fuel injection.SOLUTION: A suction pipe 11 of an engine 10 includes: a suction pipe pressure sensor 92 to detect a pressure in the suction pipe 11; and a first injection valve 21 to inject a gas fuel into the suction pipe 11. During a period of time that the first injection valve 21 performs the injection of the gas fuel, a control part 80 calculates a mass flow of air in a mixed gas of the air and the gas fuel to be sucked into a cylinder 16 on the basis of the pressure detected by the suction pipe pressure sensor 92. The control part 80 then performs various kinds of controls of the engine 10 using the gas fuel on the basis of the calculated mass flow.

Description

  The present invention relates to an internal combustion engine control device, and more particularly to an internal combustion engine control device that drives an internal combustion engine by combustion of gaseous fuel.

  In recent years, gaseous fuel such as compressed natural gas (CNG) and hydrogen fuel has attracted attention as an alternative fuel to replace liquid fuel such as gasoline, and an internal combustion engine that uses gaseous fuel alone or together with liquid fuel as a fuel for combustion Has been put into practical use (see, for example, Patent Document 1). This patent document 1 discloses that the ratio of air mass / fuel mass is always kept constant throughout the fuel injection period, and gaseous fuel is supplied into the cylinder via the intake pipe. Further, in the control device of Patent Document 1, the flow rate of air supplied to the intake pipe is detected by a flow meter provided in the intake pipe, and the fuel gas flow rate corresponding to the detected air flow rate is determined.

JP 2002-206443 A

  By the way, the gaseous fuel has a large volume per unit mass, and the volume ratio of the gaseous fuel injected from the fuel injection valve in the intake pipe is large. For this reason, in the case of a system that detects the intake air amount of the internal combustion engine by the intake pipe pressure sensor arranged in the intake pipe, the gaseous fuel injected from the fuel injection valve is sensed by the intake pipe pressure sensor. In such a case, ignoring the volume flow of the gaseous fuel, that is, if various parameters of the internal combustion engine are calculated using the detected value of the intake pipe pressure sensor as the volume flow of the air flowing through the intake pipe, it is caused by an error in detecting the intake air quantity. As a result, the controllability of the internal combustion engine may be reduced.

  The present invention has been made to solve the above problems, and provides a control device for an internal combustion engine that can improve the controllability of the internal combustion engine when the internal combustion engine is operated by injection of gaseous fuel. Is the main purpose.

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

  The present invention relates to a control device for an internal combustion engine applied to a fuel injection system including fuel injection means (21) for injecting gaseous fuel into an intake pipe (11) of the internal combustion engine (10). The invention according to claim 1 is detected by the pressure detection means (92) for detecting the pressure in the intake pipe and the pressure detection means in a period during which the gaseous fuel is injected by the fuel injection means. Based on the pressure, the air amount calculating means for calculating the mass flow rate corresponding to the air in the mixture of the air sucked into the cylinder of the internal combustion engine and the gaseous fuel, and the air amount calculating means And control means for operating the internal combustion engine using the gaseous fuel based on the mass flow rate.

  In short, in the above-described configuration, in the system that calculates the intake air amount of the internal combustion engine based on the intake pipe pressure, the detected value of the intake pipe pressure is changed to the air in the mixture of the air sucked into the cylinder and the gaseous fuel. Calculate the corresponding mass flow rate. Further, based on the calculated value, the operation of the internal combustion engine using the gaseous fuel is controlled. When the gaseous fuel is injected, the volume ratio occupied by the gaseous fuel in the intake pipe is large, and the volume flow rate of the gaseous fuel is detected by the pressure detection means. In this regard, in the above configuration, the detection error of the gaseous fuel is excluded from the detected value of the intake pipe pressure by the pressure detecting means, that is, the gaseous fuel is used based on the true amount of air sucked into the cylinder. Since various controls relating to the operation of the internal combustion engine are performed, the controllability of the internal combustion engine during the injection of gaseous fuel can be improved.

1 is an overall schematic configuration diagram of an engine fuel injection system. The functional block diagram which shows schematic structure of the engine control at the time of the injection of gaseous fuel. The flowchart which shows the process sequence of the engine control of 1st Embodiment. The figure for demonstrating the outline of the engine control of 2nd Embodiment. The flowchart which shows the process sequence of the engine control of 2nd Embodiment. The functional block diagram which shows schematic structure of the engine control in the case of using the learning result of fuel composition learning.

(First embodiment)
The first embodiment will be described below with reference to the drawings. The present embodiment is applied to a so-called bi-fuel type on-vehicle multi-cylinder engine (multi-cylinder internal combustion engine) that uses compressed natural gas (CNG) that is gaseous fuel and gasoline that is liquid fuel as combustion fuel. It is embodied as a fuel injection system. 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, and an intake pipe 11 is connected to an intake port via an intake manifold 12, and an exhaust manifold is connected to an exhaust port. An exhaust pipe 14 is connected via 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 degree is adjusted by an actuator 15a such as a DC motor. The opening (throttle opening) of the throttle valve 15 is detected by a throttle opening sensor 15b built in the actuator 15a. A surge tank 17 is provided downstream of the throttle valve 15 in the intake pipe 11, and an intake pipe pressure sensor 92 is provided in the surge tank 17 as pressure detecting means for detecting the pressure in the intake pipe 11. It has been.

  On the downstream side of the surge tank 17 in the intake pipe 11, as fuel injection means for injecting fuel to the engine 10, a first injection valve 21 for injecting gaseous fuel and a second injection valve 22 for injecting liquid fuel. Are provided for each cylinder 16. The gaseous fuel is supplied to the intake port of each cylinder 16 by the injection of the first injection valve 21, and the liquid fuel is supplied to the intake port of each cylinder 16 by the injection of the second injection valve 22.

  The exhaust pipe 14 is provided with an exhaust sensor that outputs a signal corresponding to the oxygen concentration in the exhaust, and a catalyst 19 that purifies the exhaust. As exhaust sensors, O2 sensors 18a and 18b that generate different electromotive forces depending on whether the air-fuel ratio of the engine 10 is rich or lean are provided on the upstream side and the downstream side of the catalyst 19, respectively.

  The intake port and the exhaust port of the engine 10 are respectively provided with an intake valve 25 and an exhaust valve 26 as engine valves for adjusting the amount of air introduced into the cylinder 16. The air-fuel mixture is introduced into the cylinder 16 by the opening operation of the intake valve 25, and the exhaust gas after combustion is discharged into the exhaust passage by the opening operation of the exhaust valve 26.

  Each cylinder 16 of the engine 10 is provided with a spark plug 20. A high voltage is applied to the ignition plug 20 at a desired ignition timing through an ignition circuit unit 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 supplied into the cylinder 16 is ignited and used for combustion.

  In this system, as a fuel supply unit for supplying fuel to each of the injection valves 21 and 22, a gas fuel supply unit 40 for supplying gaseous fuel (CNG fuel) and a liquid fuel supply for supplying liquid fuel (gasoline) Part 70 is provided.

  The gaseous fuel supply unit 40 supplies gaseous fuel to the first injection valve 21. Specifically, in the gaseous fuel supply unit 40, a gas tank 42 is connected to the first injection valve 21 via a gas pipe 41. In the middle of the gas pipe 41, a regulator 43 having a pressure adjustment function for adjusting the pressure of the gaseous fuel supplied to the first injection valve 21 is provided. The regulator 43 adjusts the gas fuel in a high pressure state (for example, a maximum of 20 MPa) stored in the gas tank 42 to a mechanically determined pressure value (for example, 0.3 to 0.4 MPa). The gaseous fuel after the decompression adjustment is supplied to the first injection valve 21 through the gas pipe 41.

  The fuel passage formed by the gas pipe 41 and the like further includes a tank main stop valve 44 disposed in the vicinity of the fuel outlet of the gas tank 42 and a fuel inlet of the regulator 43 that is downstream of the tank main stop valve 44. A shut-off valve 45 disposed in the vicinity 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 shutoff valve 45 are electromagnetic on-off valves, and are normally closed types that shut off the flow of gaseous fuel when not energized and allow the flow of gaseous fuel when energized. The regulator 43 is integrally provided with a pressure sensor 46 that detects the fuel pressure before pressure reduction adjustment. A gas pipe 41 on the downstream side of the regulator 43 includes a pressure sensor 47 that detects an injection pressure, and a gas. A temperature sensor 48 that detects the temperature of the gaseous fuel in the pipe 41 is provided.

  The liquid fuel supply unit 70 supplies liquid fuel to the second injection valve 22. Specifically, in the liquid fuel supply unit 70, a 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 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 91, cooling water temperature sensor 93, intake air temperature sensor 94, vehicle speed sensor, etc.) provided in the system. Connected, and outputs (detection signals) from these sensors are input. Further, the control unit 80 is electrically connected to driving units such as the ignition circuit unit 20a and the injection valves 21 and 22, and drives each driving unit by outputting a driving signal to each driving unit. Control.

  A drive signal is input from the control unit 80 to the drive unit such as the ignition circuit unit 20a and the injection valves 21 and 22, and each drive unit is driven according to the input drive signal. Specifically, the ignition circuit unit 20a outputs a high voltage according to the ignition signal from the control unit 80, and causes the spark plug 20 to generate an ignition spark. The first injection valve 21 injects an amount of gaseous fuel according to the injection signal from the control unit 80 into the intake port, and the second injection valve 22 outputs an amount of liquid fuel according to the injection signal from the control unit 80. Inject into the intake port.

  The control unit 80 selectively switches the fuel to be used according to the engine operating state, the fuel remaining amount in the tank, an input signal from a fuel changeover switch (not shown) operated by the driver, and the like. Specifically, when the remaining amount of gaseous fuel in the gas tank 42 falls below a predetermined value or when the use of the liquid fuel is selected by the fuel changeover switch, the liquid fuel is preferentially used, and the fuel tank When the remaining amount of liquid fuel in 72 falls below a predetermined value or when the use of gaseous fuel is selected by the fuel changeover switch, the gaseous fuel is preferentially used.

  In the air-fuel ratio control of this embodiment, feedback control based on the deviation between the actual value of air-fuel ratio (actual air-fuel ratio) and the target value (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 detected value of the O2 sensor 18a provided on the upstream side of the catalyst 19. calculate. Then, the air-fuel ratio feedback correction amount is calculated according to the deviation between the actual air-fuel ratio and the target air-fuel ratio, and the basic injection amount is corrected by the calculated air-fuel ratio feedback correction amount, so that the actual air-fuel ratio matches the target air-fuel ratio. I try to let them. Here, the basic injection amount is a fuel amount necessary for obtaining the target air-fuel ratio, and is calculated based on the mass flow rate of fresh air sucked into the cylinder 16 and the target air-fuel ratio. In the present embodiment, the intake air amount (mass flow rate) is estimated based on the intake pipe pressure detected by the intake pipe pressure sensor 92 and the engine rotational speed detected by the crank angle sensor 91 in this embodiment. The method is adopted. In the air-fuel ratio feedback control of this system, the controllability of the air-fuel ratio control is improved by adding a correction based on the detection value of the O2 sensor 18b on the downstream side of the catalyst. Hereinafter, “intake air amount” means the mass flow rate of air sucked into the cylinder 16.

  By the way, the gaseous fuel has a larger volume per unit mass than, for example, liquid fuel. Therefore, the volume ratio occupied by the gaseous fuel injected by the first injection valve 21 in the intake pipe 11 is large, so that the gaseous fuel is sensed by the intake pipe pressure sensor 92 disposed in the surge tank 17. That is, the detected value of the intake pipe pressure by the intake pipe pressure sensor 92 is determined by the sum of the volume flow rate of fresh air passing through the intake pipe 11 and the volume flow rate of gaseous fuel injected by the first injection valve 21. On the other hand, the load of the engine 10 is determined in accordance with the mass flow rate of air sucked into the cylinder 16, and the engine load increases as the mass flow rate of air (intake air amount) increases. Therefore, when the gaseous fuel is injected by the first injection valve 21, the intake pipe pressure detected by the intake pipe pressure sensor 92 is used as it is, that is, the detected value of the intake pipe pressure is sucked into the cylinder 16. If this is regarded as a volume flow rate of air and converted into a mass flow rate and used for various controls of the engine 10, it is conceivable that the controllability of the engine 10 is reduced due to detection error of the intake air amount.

  Accordingly, in the present embodiment, during the period in which the engine 10 is being operated by the injection of gaseous fuel from the first injection valve 21, suction is performed into the cylinder 16 based on the detected value of the intake pipe pressure by the intake pipe pressure sensor 92. A mass flow rate corresponding to air in the air-fuel mixture is calculated. Based on the calculated mass flow rate, various controls of the engine 10 using gaseous fuel are performed. As a result, in the system that estimates the intake air amount by the intake pipe pressure sensor 92, the detection error associated with the injection of the gaseous fuel is eliminated, and the engine control is performed based on the true air amount sucked into the cylinder 16. I have to.

  Next, a schematic configuration of engine control when using gaseous fuel will be described with reference to the functional block diagram of FIG. As shown in FIG. 2, the control unit 80 includes a gas density calculation unit 81, a volume ratio calculation unit 82, an intake air amount calculation unit 83, and a control amount calculation unit 84.

Based on the temperature (intake pipe temperature) Tin in the intake pipe 11 and the intake pipe pressure Pin, the gas density calculation unit 81 has a density (fuel density) ρF ′ [kg / m 3] of gaseous fuel in the intake pipe 11 and The air density ρA ′ [kg / m 3] is calculated. Here, the fuel density ρF ′ is calculated using the following formula (1), and the air density ρA ′ is calculated using the following formula (2). As the intake pipe temperature Tin [° C.], a detection value by the intake pipe temperature sensor 94 is input and used. As the intake pipe pressure Pin [kPa], a detection value by the intake pipe pressure sensor 92 is input and used.
ρF´ = ρF × (273 / (273 + Tin)) × (Pin / 101.3)… (1)
ρA´ = ρA × (273 / (273 + Tin)) × (Pin / 101.3)… (2)
(In the formula (1), ρF represents the fuel density [kg / m 3] at 0 ° C. and 1 atm, and ρA represents the air density [kg / m 3] at 0 ° C. and 1 atm.)

The volume ratio calculation unit 82 inputs the fuel density ρF ′ and the air density ρA ′ calculated by the gas density calculation unit 81 and the target air-fuel ratio Ar, and uses these input values in the intake pipe 11 (surge The volume ratio α between the air and the gaseous fuel in the tank 17) is calculated. During engine operation using gaseous fuel, the air flowing through the intake pipe 11 and the gaseous fuel injected by the first injection valve 21 are present in the intake pipe 11, and the intake valve 25 is opened. Along with this, a mixture of air and gaseous fuel is sucked into the cylinder 16. Therefore, the volume ratio α is also the volume ratio between the air sucked into the cylinder 16 and the gaseous fuel. Here, the volume ratio occupied by air in the air-fuel mixture sucked into the cylinder 16 is calculated and used as the volume ratio α. Specifically, the volume ratio α is calculated using the following formula (3), formula (4), and formula (5). In the following equation, V represents a volume flow rate of the air-fuel mixture sucked into the cylinder 16, VA represents a volume flow rate of air, VF represents a flow rate of gaseous fuel, and Ar represents a target air-fuel ratio.
α = VA / V = VA / (VA + VF) (3)
However, VA = Ar / ρA ′ (4)
VF = 1 / ρF´… (5)

The intake air amount calculation unit 83 inputs the intake pipe pressure Pin detected by the intake pipe pressure sensor 92, the volume ratio α calculated by the volume ratio calculation unit 82, and the engine rotation speed Ne detected by the crank angle sensor 91. Further, using these input values, the true intake air amount Q (mass flow rate) when the gaseous fuel is injected by the first injection valve 21 is calculated. Specifically, first, an engine load factor (first engine load factor R) is calculated from the intake pipe pressure Pin and the engine rotational speed Ne, and the actual intake air is calculated based on the first engine load factor R and the volume ratio α. A second engine load factor RA is calculated as a true engine load factor corresponding to the quantity Q. Here, the first engine load factor R is an engine load factor when the intake pipe pressure Pin detected by the intake pipe pressure sensor 92 is regarded as a volume flow rate of air sucked into the cylinder 16. The first engine load factor R corresponds to an engine load factor when the engine is operated by liquid fuel injection by the second injection valve 22. On the other hand, the second engine load factor RA is an engine load factor corresponding to the volume flow rate corresponding to the air amount in the intake pipe pressure Pin detected by the intake pipe pressure sensor 92. The intake air amount calculation unit 83 calculates the second engine load factor RA using the following equation (6).
RA = R × (VA / V) = R × α (6)
The intake air amount calculation unit 83 calculates the intake air amount Q (mass flow rate) using the second engine load factor RA. The intake air amount Q is calculated using, for example, a model of the intake air amount Q corresponding to the volumetric flow rate of air and expressing it as a mathematical expression.

  The control amount calculation unit 84 inputs the intake air amount Q calculated by the intake air amount calculation unit 83, and uses the input value to control various parameters related to the operating state of the engine 10, specifically the throttle opening and The amount of gaseous fuel injection is calculated. The calculation of the throttle opening and the fuel injection amount is performed by reading a value corresponding to the current intake air amount Q using, for example, a predetermined map or mathematical expression. Further, the control amount calculation unit 84 generates a drive signal based on the calculated control amount and outputs it to each drive unit (the first injection valve 21 and the throttle actuator 15a).

  Next, the engine control processing procedure of this embodiment will be described with reference to the flowchart of FIG. This process is repeatedly executed by the CPU of the control unit 80 at a predetermined cycle.

  In FIG. 3, in step S101, the intake pipe pressure Pin detected by the intake pipe pressure sensor 92 and the intake pipe temperature Tin detected by the intake temperature sensor 94 are acquired. In a succeeding step S102, it is determined whether or not it is a period in which the engine is operated by the injection of gaseous fuel by the first injection valve 21.

  If it is a period during which the engine operation is being performed by the liquid fuel injection by the second injection valve 22, the process proceeds to step S103, and the intake pipe pressure Pin detected by the intake pipe pressure sensor 92 is taken into the cylinder 16 as air. The engine load factor (first engine load factor R) is calculated from the intake pipe pressure Pin and the engine rotational speed Ne. In the subsequent step S107, the intake air amount Q is calculated based on the engine load factor. Thereafter, the process proceeds to step S108, and the throttle opening corresponding to the calculated intake air amount Q and the fuel injection amount by the second injection valve 22 are calculated. Moreover, a drive signal is output with respect to each drive part (throttle actuator 15a and the 2nd injection valve 22).

  On the other hand, when it is a period during which engine operation is being performed by injection of gaseous fuel from the first injection valve 21, an affirmative determination is made in step S102 and the process proceeds to step S104. In step S104, using the intake pipe pressure Pin and the intake pipe temperature Tin, the fuel density ρF ′ is calculated by the above equation (1), and the air density ρA ′ is calculated by the above equation (2). In the subsequent step S105, the volume ratio α (= VA / V) between the air sucked into the cylinder 16 and the gaseous fuel is calculated by the above formulas (3) to (5).

  In step S106, the first engine load factor R is calculated from the intake pipe pressure Pin and the engine rotation speed Ne, and the engine load factor ((6)) is calculated using the first engine load factor R and the volume ratio α. A second engine load factor RA) is calculated. In the subsequent step S107, the intake air amount Q is calculated based on the engine load factor (air amount calculating means). Thereafter, the process proceeds to step S108, where the throttle opening corresponding to the intake air amount Q and the fuel injection amount by the first injection valve 21 are calculated, and the drive units (throttle actuator 15a and first injection valve 21) are driven. A signal is output (control means).

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

  In the system for calculating the intake air amount Q by the intake pipe pressure Pin, the air out of the mixture of the air sucked into the cylinder 16 and the gaseous fuel based on the detected value of the intake pipe pressure Pin by the intake pipe pressure sensor 92. The mass flow rate corresponding to is calculated, and this is used as the intake air amount Q to perform various controls of the engine 10. When the gaseous fuel is injected, the volume ratio occupied by the gaseous fuel in the intake pipe 11 is larger than when the liquid fuel is injected, and the volume flow rate of the gaseous fuel is sensed by the intake pipe pressure sensor 92. In view of this point, in the above configuration, the true intake air amount Q excluding the detection error of the gaseous fuel is calculated from the detection value of the intake pipe pressure Pin by the intake pipe pressure sensor 92, and this is used to calculate various kinds of the engine 10 By performing the control, it is possible to improve the controllability of the engine 10 when the gaseous fuel is injected.

  The larger the volume ratio occupied by the gaseous fuel in the intake pipe 11, the smaller the volume ratio occupied by the air, and the smaller the actual intake air amount Q with respect to the detected value of the intake pipe pressure Pin. The volume ratio between the air in the intake pipe 11 and the gaseous fuel is represented by the volume ratio between the air and the gaseous fuel in the air-fuel mixture sucked into the cylinder 16. In view of this point, the intake air amount Q is calculated based on the detected value of the intake pipe pressure Pin and the volume ratio α of the air in the air-fuel mixture sucked into the cylinder 16 and the gaseous fuel. According to this configuration, the intake air amount Q can be accurately obtained according to the volume ratio of air and gaseous fuel in the intake pipe 11.

  Further, the volume ratio α is calculated based on the target air-fuel ratio of the engine 10. According to this configuration, the volume ratio is calculated from the detection value of the existing sensor without attaching a new sensor for detecting the volume ratio of the air in the air-fuel mixture sucked into the cylinder 16 and the gaseous fuel. can do.

(Second Embodiment)
Next, a second embodiment will be described. The first embodiment has been described on the assumption that various controls of the engine 10 are performed using the intake pipe pressure Pin detected by the intake pipe pressure sensor 92 during the injection period of the gaseous fuel by the first injection valve 21. On the other hand, in the present embodiment, various controls of the engine 10 are performed in consideration of the case where the intake pipe pressure sensor 92 detects the intake pipe pressure Pin when the first fuel injection valve 21 is not in the gaseous fuel injection period. To do.

  In other words, in the engine 10, the gas fuel injection timing and the injection period length by the first injection valve 21 differ depending on the engine operating state each time. Further, since the fuel injection timing and the length of the injection period are different each time, whether the intake pipe pressure Pin as the sensor detection value is a value detected during the injection period of the gaseous fuel by the first injection valve 21, or It may be different whether the value is detected when it is not the injection period of the gaseous fuel by the first injection valve 21.

  FIG. 4 is a diagram illustrating a relationship between the detection timing of the intake pipe pressure Pin and the length of the injection period. FIG. 4 shows a case where gaseous fuel is supplied to the engine 10 by exhaust stroke injection. Further, the detection timing of the intake pipe pressure Pin is set to a predetermined detection position A during the exhaust stroke. The intake pipe pressure Pin detected at the detection position A is used when calculating a control amount for the next fuel injection (next combustion).

  In FIG. 4, when the fuel injection amount per injection is large, that is, when the fuel injection period is long, gaseous fuel is injected from the first injection valve 21 at the detection position A ((I) in the figure). ). On the other hand, when the fuel injection amount per injection is small, the fuel injection period is shortened, and no gaseous fuel is injected from the first injection valve 21 at the detection position A ((II) in the figure). ). That is, in the case of (I), the intake pipe pressure sensor 92 senses the volume flow rate of the gaseous fuel, and therefore the detected value of the intake pipe pressure sensor 92 is regarded as the volume flow rate of the air sucked into the cylinder 16. As a result, a calculation error of the intake air amount Q occurs. On the other hand, in the case of (II), it is not necessary to consider the influence of gaseous fuel, and the detected value of the intake pipe pressure sensor 92 can be regarded as the volume flow rate of the air sucked into the cylinder 16.

  Therefore, in the present embodiment, when the intake pipe pressure Pin detected by the intake pipe pressure sensor 92 is the pressure detected during the injection period of the gaseous fuel by the first injection valve 21 in one combustion cycle of the engine 10. Calculates a mass flow rate corresponding to air in the mixture of air and gaseous fuel sucked into the cylinder of the engine 10 based on the detected intake pipe pressure Pin. On the other hand, when the intake pipe pressure Pin detected by the intake pipe pressure sensor 92 is a pressure detected when the gaseous fuel is not being injected by the first injection valve 21 within one combustion cycle of the engine 10, The detected intake pipe pressure Pin is regarded as the pressure corresponding to the air in the air-fuel mixture sucked into the cylinder and the mass flow rate corresponding to the air is calculated.

  Next, the engine control processing procedure of this embodiment will be described with reference to the flowchart of FIG. This process is repeatedly executed by the CPU of the control unit 80 at a predetermined cycle. In the description of FIG. 5, the same processes as those in FIG. 3 are denoted by the step numbers in FIG.

  In FIG. 5, in steps S201 and S202, the same processing as in steps S101 and S102 of FIG. 3 is executed. In the following step S203, it is determined whether or not the acquired intake pipe pressure Pin and intake pipe temperature Tin (sensor value) are detected values during the injection period of gaseous fuel by the first injection valve 21. When the acquired sensor value is a detection value during the gaseous fuel injection period, the processing of steps S204 to S208 is executed. The processing in steps S204 to S208 is the same as the processing in steps S104 to S108 in FIG.

  On the other hand, if the acquired sensor value is not the detected value during the injection period of the gaseous fuel, the process proceeds to step S209, and the intake pipe pressure Pin detected by the intake pipe pressure sensor 92 is used as the volume flow rate of the air sucked into the cylinder 16. Therefore, the engine load factor (first engine load factor R) is calculated from the intake pipe pressure Pin and the engine rotational speed Ne. The processing in step S209 is the same as that in step S103 in FIG.

  According to the second embodiment described above, the intake pipe pressure Pin detected by the intake pipe pressure sensor 92 is detected during the injection period of the gaseous fuel by the first injection valve 21 in one combustion cycle of the engine 10. The method of calculating the intake air amount Q based on the detected value of the intake pipe pressure sensor 92 differs depending on whether the pressure is detected or the pressure detected at a timing not during the gaseous fuel injection period by the first injection valve 21. As a result, the intake air amount Q can be calculated with high accuracy even when the fuel injection status differs every time at the detection timing of the intake pipe pressure Pin.

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

In the above embodiment, the second engine load factor RA is calculated by the above equation (6) using the intake pipe pressure Pin and the volume ratio α, and the first injection valve is based on the calculated second engine load factor RA. The fuel injection amount by 21 was calculated. On the other hand, in the present embodiment, the third engine load factor RF is calculated as the engine load factor corresponding to the volume flow rate of the gaseous fuel using the intake pipe pressure Pin and the volume ratio α, and the calculated third engine load is calculated. The fuel injection amount by the first injection valve 21 is calculated using the rate RF. The third engine load factor RF is expressed by the following formula (7). Further, the method for calculating the fuel injection amount using the third engine load factor RF is not particularly limited. For example, the fuel injection amount corresponding to the third engine load factor RF is modeled and expressed by an equation or the like. The method of calculating by using is mentioned.
RF = R × (VF / V)… (7)

  A composition learning means for learning the composition of the gaseous fuel supplied to the first injection valve 21 is provided, and the mixture of the air sucked into the cylinder of the engine 10 and the gaseous fuel using the learning result by the composition learning means The mass flow rate corresponding to the air is calculated. CNG varies in composition depending on the production area and production process. There are also areas where mined natural gas is used as fuel without purification. In particular, when the gas tank 42 is filled with a gaseous fuel having a high mixing ratio of an inert gas (impurities) such as nitrogen and carbon dioxide, the density of the gaseous fuel changes greatly, and the influence on the calculation accuracy of the intake air amount Q. Is considered to be large. By taking the above configuration into consideration, the intake air amount Q can be accurately calculated while suppressing the influence of variations in fuel composition.

  FIG. 6 is a functional block diagram showing a schematic configuration of engine control at the time of gaseous fuel injection in the present embodiment. 6 is based on the premise that the intake pipe pressure Pin 92 is detected by the intake pipe pressure sensor 92 during the injection period of the gaseous fuel in one combustion cycle of the engine 10.

  As shown in FIG. 6, the control unit 80 of this embodiment includes a gas density calculation unit 81, a volume ratio calculation unit 82, an intake air amount calculation unit 83, and a control amount calculation unit 84. The gas density calculation unit 81 inputs the intake pipe temperature Tin, the intake pipe pressure Pin, and the learned value (composition learned value) of the fuel composition, and the density (fuel density) ρF ′ [kg of gaseous fuel based on these parameters. / m3] and air density ρA ′ [kg / m3]. Specifically, for the fuel density ρF ′, the base value of the fuel density is calculated using the above formula (1), and the base value is corrected with the composition learning value. The air density ρA ′ is calculated using the above formula (2).

  The fuel composition learning method may be arbitrary, but an example is a method of calculating a learning value based on a fuel injection amount correction amount (air-fuel ratio correction amount FB) calculated by air-fuel ratio feedback control. Specifically, when the air fuel ratio correction amount FB exceeds a predetermined control range after the start of the next engine operation when the gas fuel is replenished in the gas tank 42, the fuel composition learning value FA is set. A predetermined update amount fa1 is added, and at the same time, the update amount fa1 is subtracted from the air-fuel ratio correction amount FB. By repeating this, the air-fuel ratio correction amount FB is within the control range, and the deviation of the air-fuel ratio correction amount FB at that time is stored as the learning value FA. In this case, the larger the mixing ratio of the inert gas in the gaseous fuel, the more the increase correction for the basic injection amount and the larger the learning value FA. Except for the gas density calculation unit 81, the description is omitted because it is the same as FIG.

  In the above embodiment, the present invention is applied to a system provided with O2 sensors 18a and 18b as exhaust sensors. However, wide-area detection that outputs a wide-range air-fuel ratio signal proportional to the oxygen concentration in the exhaust to at least the upstream side of the catalyst 19 The present invention may be applied to a system provided with a type of A / F sensor.

  When applied to a system in which an A / F sensor is provided on the upstream side of the catalyst 19 as an exhaust sensor, the volume ratio α may be calculated using the actual air-fuel ratio instead of the target air-fuel ratio. By calculating the volume ratio α based on the actual air-fuel ratio, the volume ratio between the air and the gaseous fuel in the intake pipe 11 can be obtained more accurately in a situation where the actual air-fuel ratio and the target air-fuel ratio do not match. it can. As a result, the calculation accuracy of the intake air amount Q can be further increased.

  -An existing gasoline engine having only a fuel injection valve for gasoline injection as a fuel injection means may be changed to a system capable of injecting two types of fuel by installing a fuel supply unit for gaseous fuel. The present invention can also be applied to such a system. Specifically, an injection pipe is connected to the tip of the first injection valve 21, and this injection pipe is provided in the intake pipe. The gaseous fuel ejected from the first injection valve 21 is injected into the intake port of the engine 10 through the injection pipe.

  In the above embodiment, a case has been described in which the present invention is embodied in a bi-fuel engine that uses gaseous fuel (CNG fuel) and liquid fuel (gasoline fuel) as combustion fuel. The present invention may be embodied in a gas engine that uses only fuel. Alternatively, the present invention may be embodied in an engine that uses a combination of gaseous fuel and liquid fuel.

  In the above embodiment, the gaseous fuel is CNG fuel, but other gaseous fuels that are gaseous in the standard state can also be used, for example, fuels mainly composed of methane, ethane, propane, butane, hydrogen, dimethyl ether, etc. It is good also as a structure. Further, liquid fuel is not limited to gasoline fuel. For example, the present invention may be applied to a configuration in which a fuel injection system for gaseous fuel is mounted on a diesel engine using light oil as a liquid fuel for combustion.

  DESCRIPTION OF SYMBOLS 10 ... Engine (internal combustion engine), 11 ... Intake pipe, 16 ... Cylinder, 18a ... Exhaust sensor, 18b ... Exhaust sensor, 21 ... 1st injection valve, 22 ... 2nd injection valve, 40 ... Gaseous fuel supply part, 43 ... Regulator, 45 ... shutoff valve, 70 ... liquid fuel supply unit, 80 ... control unit (air amount calculation means, control means, composition learning means), 92 ... intake pipe pressure sensor (pressure detection means).

Claims (6)

Applied to a fuel injection system comprising fuel injection means (21) for injecting gaseous fuel into an intake pipe (11) of an internal combustion engine (10);
Pressure detecting means (92) for detecting the pressure in the intake pipe;
Based on the pressure detected by the pressure detection means during the period of injection of the gaseous fuel by the fuel injection means, the mixture of the air sucked into the cylinder of the internal combustion engine and the gaseous fuel An air amount calculating means for calculating a mass flow rate corresponding to air,
Control means for operating the internal combustion engine using the gaseous fuel based on the mass flow rate calculated by the air amount calculating means;
A control device for an internal combustion engine, comprising:   2. The control of the internal combustion engine according to claim 1, wherein the air amount calculation unit calculates the mass flow rate based on a pressure detected by the pressure detection unit and a volume ratio of air to the gaseous fuel in the air-fuel mixture. apparatus.   The control apparatus for an internal combustion engine according to claim 2, wherein the air amount calculation means calculates the volume ratio based on an air-fuel ratio of the internal combustion engine.   The air amount calculation means detects when the pressure detected by the pressure detection means is a pressure detected during an injection period of the gaseous fuel by the fuel injection means within one combustion cycle of the internal combustion engine. The control device for an internal combustion engine according to any one of claims 1 to 3, wherein a mass flow rate corresponding to air in the air-fuel mixture is calculated based on the pressure obtained.   The air amount calculating means is a pressure detected when the pressure detected by the pressure detecting means is not during the injection period of the gaseous fuel by the fuel injection means within one combustion cycle of the internal combustion engine, 5. The mass flow rate corresponding to air in the air-fuel mixture is calculated by regarding the detected pressure as a pressure corresponding to air in the air-fuel mixture. Control device for internal combustion engine. Comprising composition learning means for learning the composition of the gaseous fuel supplied to the fuel injection means;
The internal combustion engine according to any one of claims 1 to 5, wherein the air amount calculation means calculates a mass flow rate corresponding to air in the air-fuel mixture using a learning result obtained by the composition learning means. Control device.

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