Fuel injection control device

Abstract

To provide a fuel injection control device capable of properly injecting a fuel in a gas state with a fuel injection valve, even in an operation region where a fuel is injected at a subsonic speed.SOLUTION: A fuel injection control device 100 includes: an intake air amount sensor 2 provided in an intake air passage of an LP gas engine, and for acquiring a detection value regarding an intake air amount of the LP gas engine; an injector 5 provided in a fuel pipeline, and for injecting a fuel in a gas state; a before injection pressure acquisition part 12 for acquiring a before injection pressure which is a pressure further on the upstream side than an injector 5 of the fuel pipeline; an after injection pressure acquisition part 13 for acquiring an after injection pressure which is a pressure in a space where the fuel is injected by the injector 5; and a fuel control part 14 which allows the injector 5 to inject a fuel with injection time that is long compared with the case where the injector 5 injects the fuel at a sonic speed, in the case where the injector 5 injects the fuel at a subsonic speed, based on the detection value of the intake air amount sensor 2 and the before injection pressure and the after injection pressure.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a fuel injection control device. [Background technology]

[0002] 2. Description of the Related Art As a conventional technique relating to a fuel injection control device, for example, Patent Document 1 describes a control device for an engine equipped with an injector that directly injects gaseous fuel into a combustion chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-345884 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an internal combustion engine in which a fuel injector injects gaseous fuel, there is a certain upper limit to the pressure upstream of the fuel injector because there is a restriction on keeping the fuel in a gaseous state at the position of the fuel injector. Therefore, depending on the relationship between the pressures upstream and downstream of the fuel injector, there may be an operating region in which the fuel injector injects fuel at a subsonic speed, which is slower than the speed of sound. In this case, for example, if fuel is injected for the same injection time, the amount of fuel injected at the subsonic speed will be less than the amount of fuel injected at the sonic speed.

[0005] An object of the present invention is to provide a fuel injection control device that can properly inject gaseous fuel from a fuel injection valve even in an operating region where fuel is injected at subsonic speed. [Means for solving the problem]

[0006] A fuel injection control device according to one embodiment of the present invention is a fuel injection control device that controls the amount of fuel supplied to an internal combustion engine, and includes an intake amount detection unit that is provided in an intake passage of the internal combustion engine and acquires a detection value related to the intake amount of the internal combustion engine, a fuel injection valve that is provided in a fuel supply path and injects fuel in a gaseous state, a pre-injection pressure acquisition unit that acquires a pre-injection pressure, which is the pressure upstream of the fuel injection valve in the supply path, a post-injection pressure acquisition unit that acquires a post-injection pressure, which is the pressure of the space into which fuel is injected by the fuel injection valve, and a fuel control unit that causes the fuel injection valve to inject fuel for a longer injection time when the fuel injection valve injects fuel at subsonic speed based on the detection value of the intake amount detection unit, the pre-injection pressure, and the post-injection pressure.

[0007] In a fuel injection control device according to one aspect of the present invention, when the fuel injection valve injects an amount of fuel corresponding to the intake air amount, the fuel injection valve is caused to inject fuel for a longer injection time when injecting at subsonic speed compared to when injecting at sonic speed based on the pre-injection pressure and the post-injection pressure. This makes it possible to suppress a decrease in the amount of fuel injected at subsonic speed compared to a case where the fuel injection valve is operated for an equal injection time for injection at subsonic speed and injection at sonic speed. Therefore, according to the fuel injection control device according to one aspect of the present invention, the fuel injection valve can appropriately inject gaseous fuel even in an operating range where fuel is injected at subsonic speed.

[0008] In one embodiment, the fuel control unit may calculate a unit injection amount, which is an injection amount of fuel per unit injection number of the fuel injection valve, based on a detection value of the intake amount detection unit, calculate an injection conversion time, which is an injection time for injecting a unit injection amount of fuel, based on a pre-injection pressure and a post-injection pressure, and cause the fuel injection valve to inject fuel based on an injection time obtained by multiplying the unit injection amount and the injection conversion time. In this case, the unit injection amount is calculated based on the detection value of the intake amount detection unit. The injection conversion time is calculated based on the pre-injection pressure and the post-injection pressure. Therefore, by setting the injection conversion time to be longer in an operating region where fuel is injected at subsonic speed than in an operating region where fuel is injected at sonic speed, it is possible to suppress the injection amount of subsonic fuel from decreasing below the injection amount of sonic fuel.

[0009] In one embodiment, the fuel control unit may calculate the unit injection amount based on the detection value of the intake air amount detection unit and the rotation speed of the internal combustion engine. In this case, the unit injection amount corresponding to the detection value of the intake air amount detection unit and the rotation speed of the internal combustion engine can be used.

[0010] In one embodiment, the fuel control unit may calculate a reference injection conversion time, which is an injection conversion time when the pre-injection pressure and the post-injection pressure are in a predetermined reference condition, and calculate a conversion ratio, which is a ratio to the reference injection conversion time and is used to calculate an injection conversion time corresponding to the pre-injection pressure and the post-injection pressure other than the reference condition, based on the mass flow rate of fuel injected by the fuel injector and the pre-injection pressure and the post-injection pressure, and cause the fuel injector to inject fuel for the injection time calculated based on the unit injection amount, the reference injection conversion time, and the conversion ratio. In this case, it is possible to facilitate setting of the injection conversion time, compared to a case where a two-dimensional map defined by the pre-injection pressure and the post-injection pressure is preset without using a conversion ratio according to a predetermined theoretical formula, for example. Effect of the Invention

[0011] According to the present invention, gaseous fuel can be appropriately injected by the fuel injection valve even in an operating region where fuel is injected at subsonic speed. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of an internal combustion engine equipped with a fuel injection control device according to an embodiment; [Diagram 2] FIG. 2 is a block diagram of the fuel injection control device of FIG. [Diagram 3] 3 is a flowchart showing an example of a process of the ECU in FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0014] Fig. 1 is a schematic configuration diagram of a fuel injection control device of a first embodiment. As shown in Fig. 1, the fuel injection control device 100 is a device that controls the amount of fuel supplied to an LP gas engine (internal combustion engine) 20. The fuel injection control device 100 is mounted on, for example, an industrial vehicle or the like.

[0015] The LP gas engine 20 is supplied with gaseous fuel obtained by vaporizing liquid fuel stored in a fuel tank (not shown). For example, liquefied petroleum gas (LPG: [Liquefied Petroleum Gas], LP gas) is used as the fuel. LPG contains propane and butane as main components. As other liquid fuels, fuels having a boiling point in a temperature range (e.g., −45° C. to 0° C.) close to the environmental temperature to which the internal combustion engine is subjected, such as DME (dimethyl ether), may be used. In other words, the LP gas engine 20 is an internal combustion engine that burns a mixture containing liquefied petroleum gas (LP gas) as fuel.

[0016] The LP gas engine 20 has an engine body 23 composed of a cylinder block 21, a cylinder head 22, etc. In the engine body 23, a combustion chamber is defined by the cylinder block 21, the cylinder head 22, and a piston (not shown). An intake passage 24 and an exhaust flow path (not shown) are connected to the cylinder head 22 so as to communicate with the combustion chamber. A throttle valve 25 that adjusts the flow rate of intake air is provided in the intake passage 24.

[0017] In the LP gas engine 20 here, an injector (fuel injection valve) 5 is attached to an intake passage 24 near a cylinder head 22. A fuel pipe (supply path) 26 is connected to the injector 5, through which LP gas in a gaseous state is supplied. At the upstream side of the fuel pipe 26, for example, liquid fuel in a fuel tank is sent to a regulator (not shown) at the tank internal pressure (saturated vapor pressure), and the pressure is reduced from the tank internal pressure to a predetermined pressure. LP gas in a gaseous state at a predetermined pressure is supplied to the fuel pipe 26. The injector 5 injects the LP gas in a gaseous state into the intake passage 24 near the cylinder head 22. The injected LP gas in a gaseous state mixes with the intake air to form an air-fuel mixture. In the engine body 23, the air-fuel mixture supplied from the intake passage 24 to the combustion chamber is compressed by a piston, and is ignited by an ignition plug (not shown) provided in the cylinder head 22 and combusted. The combusted air-fuel mixture is discharged as exhaust gas from the exhaust passage.

[0018] The fuel injection control device 100 includes an ECU [Electronic Control Unit] 10. The ECU 10 is an electronic control unit that controls an LP gas engine 20. The ECU 10 includes a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], a communication circuit, and the like. For example, the ECU 10 loads a program stored in the ROM into the RAM, and executes the program loaded into the RAM by the CPU, thereby achieving various functions. The ECU 10 may be composed of multiple electronic units.

[0019] Fig. 2 is a block diagram of the fuel injection control device of Fig. 1. As shown in Fig. 2, the ECU 10 is electrically connected to an engine revolution sensor 1, an intake air amount sensor (intake air amount detection unit) 2, a pre-injection pressure sensor 3, and a post-injection pressure sensor 4.

[0020] The engine revolution sensor 1 is a detector that detects the engine revolution speed of the LP gas engine 20. The engine revolution sensor 1 outputs a detection signal of the detected engine revolution speed to the ECU .

[0021] The intake air amount sensor 2 is provided in the intake passage 24 of the LP gas engine 20, and is a detector that detects a detection value related to the intake air amount of the LP gas engine 20. In this case, the intake air amount sensor 2 is, for example, an intake air pressure sensor that detects the pressure inside the surge tank 24a as a detection value related to the intake air amount of the LP gas engine 20. The intake air amount sensor 2 outputs a detection signal of the intake air amount of the LP gas engine 20 to the ECU 10.

[0022] The pre-injection pressure sensor 3 is a detector for detecting the pre-injection pressure, which is the pressure upstream of the injector 5 in the fuel pipe 26. The pre-injection pressure sensor 3 is attached to the fuel pipe 26 (rail) on which the multiple injectors 5 are arranged in parallel, for example, and detects the pressure (rail pressure) of the gaseous fuel inside the fuel pipe 26 as the pre-injection pressure. The pre-injection pressure sensor 3 outputs a detection signal of the pre-injection pressure to the ECU 10.

[0023] The post-injection pressure sensor 4 is a detector for detecting the post-injection pressure, which is the pressure of the space into which fuel is injected by the injector 5. The space into which fuel is injected by the injector 5 means the internal space of the intake passage 24. The post-injection pressure sensor 4 is attached, for example, to each of the intake manifolds 24b, which are the intake passages 24 closer to the cylinder head 22 than the surge tank 24a. The post-injection pressure sensor 4 detects the pressure of the intake air inside the intake manifold 24b (hereinafter simply referred to as "intake pipe pressure") as the post-injection pressure. The post-injection pressure sensor 4 outputs a detection signal of the pre-injection pressure to the ECU 10.

[0024] By attaching the post-injection pressure sensor 4 to each of the intake manifolds 24b, the pressure of each cylinder before being largely smoothed by the surge tank 24a can be detected by the post-injection pressure sensor 4. The detected value of the post-injection pressure sensor 4 more directly represents the pressure fluctuation in the space into which fuel is injected by the injector 5, compared to the case where the post-injection pressure sensor 4 is attached to the surge tank 24a.

[0025] Next, the functional configuration of the ECU 10 will be described together with an example of processing in Fig. 3. Fig. 3 is a flowchart showing an example of processing in the ECU in Fig. 2. The processing in Fig. 3 is executed while the LP gas engine 20 is in operation. The ECU 10 has an engine state quantity acquisition unit 11, a pre-injection pressure acquisition unit 12, a post-injection pressure acquisition unit 13, and a fuel control unit 14.

[0026] 3, in S11, the ECU 10 acquires the engine speed and the intake air amount by the engine state quantity acquisition unit 11. The engine state quantity acquisition unit 11 acquires the engine speed based on the detection result of the engine speed sensor 1. The engine state quantity acquisition unit 11 acquires the intake air amount based on the detection result of the intake air amount sensor 2.

[0027] In S12, the ECU 10 acquires the pre-injection pressure using the pre-injection pressure acquisition unit 12. Based on the detection result of the pre-injection pressure sensor 3, the pre-injection pressure acquisition unit 12 acquires, for example, the rail pressure (P1) of the fuel pipe 26 (rail) in which the multiple injectors 5 are arranged side by side as the pre-injection pressure.

[0028] In S13, the ECU 10 acquires the post-injection pressure by the post-injection pressure acquisition unit 13. The post-injection pressure acquisition unit 13 acquires, for example, the intake pipe pressure (P2) inside the intake manifold 24b as the post-injection pressure based on the detection result of the post-injection pressure sensor 4.

[0029] In S14, the ECU 10 calculates the unit injection amount by the fuel control unit 14. The unit injection amount is the amount of fuel injected per unit injection of the injector 5. The unit injection amount corresponds to the number of fuel injections for one combustion (one stroke) in one cylinder. In the case of port injection as in this embodiment, for example, the unit injection amount is one because fuel is usually injected once in one intake stroke and the fuel is sucked into the combustion chamber. When the unit injection amount is one, the amount of fuel injected in one injection corresponds to the unit injection amount.

[0030] The fuel control unit 14 calculates the unit injection amount based on the detection value of the intake amount sensor 2. The fuel control unit 14 calculates the unit injection amount based on, for example, the intake amount and engine speed of the LP gas engine 20. As a specific example, the fuel control unit 14 may calculate the unit injection amount UFnm using a two-dimensional map defined by the intake pipe pressure as the detection value of the intake amount sensor 2 and the engine speed, as shown in Table 1 below. [Table 1]

[0031] In the above Table 1, the rows are engine speeds (Ne), the columns are intake pipe pressures (P2), and the map values ​​are unit injection amounts UFkj. Here, k is an integer between 0 and 5 corresponding to the map points of the engine speeds, and j is an integer between 0 and 9 corresponding to the map points of the intake pipe pressures. The unit injection amount UFkj can be determined by experiment as the amount of fuel required to achieve a desired air-fuel ratio for an intake amount corresponding to one combustion (one stroke) at the engine speed (Ne) corresponding to the integer k and the intake pipe pressure (P2) corresponding to the integer j. The unit of the unit injection amount UFkj may be, for example, mg / stroke.

[0032] In S15, the ECU 10 calculates the injection conversion time by the fuel control unit 14. The injection conversion time is the injection time for injecting a unit injection amount of fuel. More specifically, the injection conversion time corresponds to a coefficient for converting the injection amount of fuel corresponding to one combustion (one stroke) into the injection time (driving time) of the injector 5. The injection conversion time is set to a value larger than the injection conversion time for fuel injection at sonic speed so that the injection time (driving time) is such that the injector 5 injects a unit injection amount of fuel even in the case of fuel injection at subsonic speed.

[0033] The fuel control unit 14 calculates the injection conversion time based on the pre-injection pressure and the post-injection pressure. As a specific example, the fuel control unit 14 may calculate the injection conversion time using a two-dimensional map as shown in the following Table 2. The two-dimensional map shown in the following Table 2 is defined using the rail pressure (P1) as the detection value of the pre-injection pressure sensor 3 and the intake pipe pressure (P2) as the detection value of the post-injection pressure sensor 4 as arguments. [Table 2]

[0034] In the above Table 2, the rows are rail pressure (P1), the columns are intake pipe pressure (P2), and the map value is the injection conversion time TFnm, where n is an integer from 0 to 4 corresponding to the map point of the rail pressure, and m is an integer from 0 to 9 corresponding to the map point of the intake pipe pressure. The unit of the injection conversion time TFnm may be, for example, msec / mg.

[0035] The value of the injection conversion time TFnm can be obtained by an experiment using the injector 5, for example, as a numerical value that causes the injector 5 to inject a unit injection amount of fuel according to the rail pressure (P1) and the intake pipe pressure (P2). More specifically, in the injector 5 that injects fuel in a gaseous state, when the ratio of the intake pipe pressure (P2) / rail pressure (P1) is greater than the critical pressure ratio shown in the following (Equation 1), the fuel is injected at a subsonic speed, and when the ratio of the intake pipe pressure (P2) / rail pressure (P1) is equal to or less than the critical pressure ratio, the fuel is injected at a sonic speed. Here, κ is the specific heat ratio of the fuel in a gaseous state.

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[0036] In the above Table 2, as an example, fuel is injected at subsonic speed in the operating region shaded in gray on the left side (low pressure side of P1 when P2 is equal) of the line indicated by the thick solid line. Also, fuel is injected at sonic speed in the operating region on the right side (high pressure side of P1 when P2 is equal) of the line indicated by the thick solid line. In the operating region where fuel is injected at subsonic speed, the injection conversion time is set to be longer than in the operating region where fuel is injected at sonic speed. In the operating region where fuel is injected at subsonic speed, the lower the rail pressure (P1), the longer the injection conversion time is set. In the operating region where fuel is injected at subsonic speed, the higher the intake pipe pressure (P2), the longer the injection conversion time is set. In other words, in the operating region shaded in gray in Table 2, the injection conversion time becomes larger toward the upper left of the table.

[0037] For example, when the rail pressure (P1) is 120 kPa, TF00-TF03, which belong to the operating region where fuel is injected at subsonic speed, are set to be larger than TF04-TF09, which belong to the operating region where fuel is injected at sonic speed. TF00-TF03 are set to be larger as the intake pipe pressure (P2) becomes higher. TF04-TF09 are set to be equal values ​​to each other.

[0038] For example, when the rail pressure (P1) is 140 kPa, TF10-TF12, which belong to the operating region where fuel is injected at subsonic speed, are set to be larger than TF13-TF19, which belong to the operating region where fuel is injected at sonic speed. TF10-TF12 are set to be larger as the intake pipe pressure (P2) becomes higher. TF13-TF19 are set to be equal to each other.

[0039] For example, when the rail pressure (P1) is 160 kPa, TF20 to TF21, which belong to the operating region where fuel is injected at subsonic speed, are set to be larger than TF22 to TF29, which belong to the operating region where fuel is injected at sonic speed. TF20 is set to be larger than TF21. TF22 to TF29 are set to be equal values.

[0040] When the rail pressure (P1) is 180 kPa, TF30 to TF39 are set to be equal to each other since they belong to the operating region where fuel is injected at the sonic speed. When the rail pressure (P1) is 200 kPa, TF40 to TF49 are set to be equal to each other since they belong to the operating region where fuel is injected at the sonic speed.

[0041] In S16, the ECU 10 injects fuel using the fuel control unit 14. The fuel control unit 14 causes the injector 5 to inject fuel based on the injection time obtained by multiplying the calculated unit injection amount by the injection conversion time. That is, based on the detection value of the intake air amount sensor 2, the pre-injection pressure, and the post-injection pressure, the fuel control unit 14 causes the injector 5 to inject fuel for an injection time longer than that when the injector 5 injects fuel at a sonic speed when the injector 5 injects fuel at a subsonic speed. Note that the fuel control unit 14 may cause the injector 5 to inject fuel by applying environmental correction, such as intake air temperature, which is not directly related to the change in the pre-injection pressure, to the injection time obtained by multiplying the unit injection amount by the injection conversion time. After that, the ECU 10 ends the processing of FIG. 3.

[0042] [Action and Effects] In an internal combustion engine using liquefied petroleum gas or the like having a boiling point in a temperature range close to the temperature of the environment in which the internal combustion engine is used as fuel, if the pre-injection pressure is increased too much to a pressure at which fuel is injected at sonic speed over the entire operating range, the pressure may hinder the vaporization of the fuel, causing problems in the operation of the internal combustion engine. Therefore, the pre-injection pressure is set to a pressure that allows fuel to be injected at subsonic speed in a part of the operating range. However, in the conventional fuel injection control device, there is room for improvement in the calculation of the injection time of the injector 5 in the operating range in which fuel is injected at subsonic speed. For example, in the case of a control method (so-called speed density method) in which the injection time is determined from a map of the engine speed and the intake pipe pressure, the upstream pressure of the injector may fluctuate due to the altitude difference (pressure difference), the variation of the regulator, the pressure in the fuel tank, etc. For example, even if the intake manifold pressure is the same, fluctuations in the upstream pressure of the injector may cause fuel injection at subsonic speed to alternate with fuel injection at sonic speed, which may not be sufficiently corrected by general learning control and environmental correction, etc.

[0043] In this regard, in the fuel injection control device 100 as described above, when the injector 5 injects an amount of fuel corresponding to the intake air amount, the injector 5 is caused to inject fuel at subsonic speed for a longer injection time compared to when the injector 5 injects fuel at sonic speed based on the pre-injection pressure and post-injection pressure. This makes it possible to suppress a decrease in the amount of fuel injected at subsonic speed compared to when the injector 5 is operated at equal injection times for subsonic speed injection and sonic speed injection. Therefore, the fuel injection control device 100 makes it possible to appropriately inject gaseous fuel from the injector 5 even in an operating range in which fuel is injected at subsonic speed.

[0044] In the fuel injection control device 100, the fuel control unit 14 calculates a unit injection amount, which is the amount of fuel injected per unit injection count of the injector 5, based on the detection value of the intake air amount sensor 2, calculates an injection conversion time, which is the injection time for injecting a unit injection amount of fuel, based on the pre-injection pressure and the post-injection pressure, and causes the injector 5 to inject fuel based on the injection time obtained by multiplying the unit injection amount and the injection conversion time. In this way, the unit injection amount is calculated instead of the injection time based on the detection value of the intake air amount sensor 2. The injection conversion time is calculated based on the pre-injection pressure and the post-injection pressure. Therefore, by setting the injection conversion time to be longer in the operating region where fuel is injected at subsonic speed than in the operating region where fuel is injected at sonic speed, it is possible to suppress the injection amount of subsonic fuel from decreasing below the injection amount of sonic fuel.

[0045] Incidentally, since the effect of fluctuations in pre-injection pressure is inherent in the injection conversion time, the injection time obtained by multiplying the unit injection amount by the injection conversion time also reflects the difference between sonic and subsonic injection modes. Therefore, it is possible to omit a separate correction for the fluctuations in pre-injection pressure for the injection time obtained by multiplying the unit injection amount by the injection conversion time.

[0046] In the fuel injection control device 100, the fuel control unit 14 calculates a unit injection amount based on the detection value of the intake air amount sensor 2 and the engine speed (here, using a two-dimensional map defined by the intake pipe pressure and the engine speed). This makes it possible to use a unit injection amount that corresponds to the detection value of the intake air amount sensor 2 and the engine speed.

[0047] [Variations] Although the embodiments according to the present invention have been described above, the present invention is not limited to the above-described embodiments.

[0048] For example, in S15, the ECU 10 may perform the following process by the fuel control unit 14 instead of using a two-dimensional map such as that in Table 2 above. Specifically, the fuel control unit 14 may calculate a reference injection conversion time, which is an injection conversion time when the pre-injection pressure and the post-injection pressure are at a predetermined reference condition. The predetermined reference condition means an operating condition corresponding to one point in the two-dimensional map used as a reference for conversion, and may be a predetermined pre-injection pressure and post-injection pressure condition that is set in advance. The predetermined reference condition may be an operating region in which fuel is injected at subsonic speed, or an operating region in which fuel is injected at sonic speed. As an example, the predetermined reference condition may be an operating condition in which the rail pressure (P1) is 140 kPa and the intake pipe pressure (P2) is 100 kPa, so that the operating condition corresponding to one point in the two-dimensional map in Table 2 above is used as a reference.

[0049] The fuel control unit 14 may calculate a conversion ratio based on the mass flow rate of the fuel injected by the injector 5, the pre-injection pressure, and the post-injection pressure to calculate the injection time under the current operating conditions from the reference injection conversion time. The conversion ratio is a ratio to the reference injection conversion time for calculating the injection conversion time corresponding to the pre-injection pressure and the post-injection pressure other than the reference condition. The conversion ratio may be obtained based on the relationship of the following (Equation 2) and / or the following (Equation 3). The following (Equation 2) shows the relationship between P1 and W in the operating region where the fuel is injected at subsonic speed, and the following (Equation 3) shows the relationship between P1 and W in the operating region where the fuel is injected at sonic speed. Here, each W is the mass flow rate of the gas fuel injected by the injector 5, P1 is the pre-injection pressure, P2 is the post-injection pressure, κ is the specific heat ratio of the gas fuel, and γ is the specific weight of the gas fuel. It should be noted that the following (Equation 2) and (Equation 3) are merely examples, and a partially different theoretical formula may be used depending on the specifications of the injector 5, etc.

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[0050] Using the relationship that γ is proportional to P1 in the above (Equation 2), the following (Equation 4) is obtained. Using the relationship that γ is proportional to P1 and κ is constant in the above (Equation 3), the following (Equation 5) is obtained.

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[0051] Next, by adding the suffix "a" to the parameter corresponding to a predetermined reference condition and the suffix "b" to the parameter corresponding to the current operating condition, and using the proportional relationship of the above (Equation 4) and (Equation 5), the following (Equation 6) and (Equation 7) are obtained. In the following (Equation 6) and (Equation 7), the fractional part corresponds to the conversion ratio. The following (Equation 6) means a conversion formula for the mass flow rate in an operating region where fuel is injected at subsonic speed. The following (Equation 7) means a conversion formula for the mass flow rate in an operating region where fuel is injected at sonic speed. According to the following (Equation 6) and (Equation 7), it is possible to convert the mass flow rate Wa of the gaseous fuel injected by the injector 5 under a predetermined reference condition to the mass flow rate Wb of the gaseous fuel injected by the injector 5 under a current operating condition.

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[0052] If the injection conversion time of the injector 5 for injecting gas fuel with a mass flow rate Wa under specified reference conditions is Ta, and the injection conversion time of the injector 5 for injecting gas fuel with a mass flow rate Wb under the current operating conditions is Tb, Ta and Tb are inversely proportional to Wa and Wb, respectively, and therefore can be expressed as shown below in (Equation 8) and (Equation 9).

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[0053] As shown in the above (Equation 8), when the predetermined reference condition is set to an operating region where fuel is injected at subsonic speed, the injection conversion time Tb other than the predetermined reference condition in the operating region where fuel is injected at subsonic speed can be calculated by multiplying the reference injection conversion time Ta under the predetermined reference condition by the conversion ratio of the fractional part of the above (Equation 8). The injection conversion time in the operating region where fuel is injected at sonic speed may be calculated by a similar calculation using the above (Equation 8) only for the critical point. In the operating region where fuel is injected at sonic speed, map values ​​with the same P1 are equal to each other, so it may be given as a pre-calculated constant.

[0054] 3, the fuel control unit 14 may cause the fuel injection valve to inject fuel based on the injection time obtained by multiplying the unit injection amount by the reference injection conversion time and the conversion ratio. The fuel control unit 14 may cause the injector 5 to inject fuel by applying environmental correction, such as intake air temperature, which is not directly related to the change in pre-injection pressure, to the injection time obtained by multiplying the unit injection amount by the reference injection conversion time and the conversion ratio. That is, the fuel control unit 14 causes the injector 5 to inject fuel for a longer injection time when the injector 5 injects fuel at subsonic speed compared to when the injector 5 injects fuel at sonic speed, based on the detection value of the intake amount sensor 2 and the pre-injection pressure and post-injection pressure. After that, the ECU 10 ends the processing of FIG. 3.

[0055] In the fuel injection control device 100 that performs the above-described process of the modified example of S15 and S16, the fuel control unit 14 calculates a reference injection conversion time Ta, which is an injection conversion time when the pre-injection pressure and the post-injection pressure are at predetermined reference conditions (P1a, P2a), calculates a conversion ratio, which is a ratio to the reference injection conversion time Ta and is used to calculate an injection conversion time Tb corresponding to the pre-injection pressure P1b and the post-injection pressure P2b other than the reference conditions, based on the mass flow rate W of the fuel injected by the injector 5, the pre-injection pressure P1, and the post-injection pressure P2, and makes the injector 5 inject fuel at an injection time obtained by multiplying the reference injection conversion time Ta by the conversion ratio and applying the injection conversion time Tb obtained by the multiplication of the reference injection conversion time Ta and the conversion ratio to a unit injection amount. This makes it possible to simplify the setting of the injection conversion time, compared to a case where a two-dimensional map defined by the pre-injection pressure and the post-injection pressure is preset without using a conversion ratio according to a predetermined theoretical formula, for example.

[0056] As another modification, in the above embodiment, the intake air pressure sensor that detects the pressure inside the surge tank 24a is exemplified as the intake air amount detection unit, but the present invention is not limited to this example. The intake air amount detection unit may be, for example, an air flow sensor that detects the flow rate of intake air as a detection value related to the intake air amount of the LP gas engine 20. In this case, the unit injection amount may be calculated by dividing the intake air amount by the engine speed and multiplying the result by a predetermined constant. Alternatively, a two-dimensional map with the flow rate as the axis may be used instead of the intake pipe pressure P2 in Table 1 above. The air flow sensor may be provided in the intake passage 24 upstream of the surge tank 24a. The air flow sensor may be provided in the intake passage 24 upstream of the throttle valve 25. In addition, the axis in Table 1 above may be the charging efficiency.

[0057] In the above embodiment, the pre-injection pressure sensor 3 attached to the fuel pipe 26 (rail) on which the multiple injectors 5 are arranged side by side has been exemplified as a sensor for detecting the pre-injection pressure, but the present invention is not limited to this. The sensor for detecting the pre-injection pressure may be attached to the fuel pipe 26 subsequent to the regulator. Note that, for example, an estimated value of pressure estimated based on the fuel tank internal pressure and atmospheric pressure may be used as the pre-injection pressure.

[0058] In the above embodiment, the post-injection pressure sensor 4 attached to each of the intake manifolds 24b is exemplified as a sensor for detecting the post-injection pressure, but the present invention is not limited to this. The sensor for detecting the post-injection pressure may be a pressure sensor attached to the surge tank 24a. In this case, the sensor may be used in common with the intake pressure sensor that detects the pressure inside the surge tank 24a. Note that an estimated value of the intake pipe pressure estimated by a known method may be used as the post-injection pressure.

[0059] In the above embodiment, the fuel injection valve is exemplified by the so-called port injection injector 5 provided to inject fuel into the intake manifold 24b, but is not limited thereto. The fuel injection valve may be, for example, a so-called in-cylinder direct injection injector provided to inject fuel into a cylinder. In short, the present invention can be applied to any internal combustion engine in which there is an operating region in which the fuel injection valve injects fuel at a subsonic speed slower than the speed of sound, depending on the relationship between the pressures upstream and downstream of the fuel injection valve.

[0060] In the above embodiment, the injector 5 is not used in combination with a mixer, but the injector 5 may be used in combination with a mixer. In this case, when supplying an amount of fuel corresponding to the intake air amount, the fuel injection valve injects the amount remaining after subtracting the fuel supplied by the mixer from the amount of fuel corresponding to the intake air amount. Therefore, for example, the amount of fuel injection remaining after subtraction may be obtained by experiment or the like, and as for this fuel injection amount, when the injector 5 injects fuel at subsonic speed, as described above, the injector 5 may be made to inject fuel for a longer injection time than when the injector 5 injects fuel at sonic speed.

[0061] In the above embodiment, in Table 2, the map values ​​are read without determining whether the fuel is injected at subsonic speed or sonic speed. However, for example, it may be possible to determine whether the fuel is injected at subsonic speed or sonic speed, and switch the injection time to be used based on the determination result.

[0062] In the above embodiment, the unit injection count is one, but is not limited to this. When multiple fuel injections are performed for one combustion (in one stroke), the unit injection count may be a value of two or more. In this case, the unit injection amount is the amount of fuel injected for one combustion, and therefore may correspond to the total amount of fuel injected in the multiple injections. [Explanation of symbols]

[0063] 2...intake amount sensor (intake amount detection section), 5...injector (fuel injection valve), 12...pre-injection pressure acquisition section, 13...post-injection pressure acquisition section, 14...fuel control section, 20...LP gas engine (internal combustion engine), 24...intake passage, 26...fuel piping (supply path), 100...fuel injection control device.

Claims

1. A fuel injection control device for controlling the fuel supply amount to an internal combustion engine, an intake air amount detection unit provided in the intake passage of the internal combustion engine for obtaining a detection value related to the intake air amount of the internal combustion engine; a fuel injection valve provided in the fuel supply passage for injecting the gaseous fuel; an injection pre-pressure acquisition unit for obtaining an injection pre-pressure which is the pressure upstream of the fuel injection valve in the supply passage; an injection post-pressure acquisition unit for obtaining an injection post-pressure which is the pressure in the space where the fuel is injected by the fuel injection valve; based on the detection value of the intake air amount detection unit, the injection pre-pressure, and the injection post-pressure, when the fuel injection valve injects the fuel at subsonic speed, the fuel injection valve injects the fuel at a longer injection time compared to the case where the fuel injection valve injects the fuel at sonic speed, and a fuel control unit for injecting the fuel into the fuel injection valve, the fuel control unit, calculates a unit injection amount which is the injection amount of the fuel per unit injection number of the fuel injection valve based on the detection value of the intake air amount detection unit, calculates an injection conversion time which is a coefficient for converting the unit injection amount into the injection time and is the injection time for injecting the fuel of unit mass based on the injection pre-pressure and the injection post-pressure, A fuel injection control device for injecting the fuel into the fuel injection valve based on an injection time obtained by multiplying the unit injection amount and the injection conversion time.

2. The fuel injection control device according to claim 1, wherein the fuel control unit calculates the unit injection amount based on the detection value of the intake air amount detection unit and the rotational speed of the internal combustion engine.

3. The fuel control unit, calculates a reference injection conversion time which is the injection conversion time when the injection pre-pressure and the injection post-pressure are in a predetermined reference condition, Calculate a conversion ratio, which is a ratio with respect to the reference injection conversion time, based on the mass flow rate of the fuel injected by the fuel injection valve, the pre-injection pressure, and the post-injection pressure, and which is the ratio for calculating the injection conversion time corresponding to the pre-injection pressure and the post-injection pressure other than the reference conditions. The fuel injection control device according to claim 1 or 2, wherein the fuel is injected into the fuel injection valve at an injection time calculated based on the unit injection amount, the reference injection conversion time, and the conversion ratio.

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