JP5910376B2 - Fuel injection system for internal combustion engine - Google Patents

Description

  The present invention relates to a fuel injection system for an internal combustion engine, and more particularly to a fuel injection system for an internal combustion engine that can inject gas fuel and liquid fuel into a cylinder of the internal combustion engine.

  In recent years, as fuel for engines, gas fuel such as compressed natural gas (CNG fuel) and hydrogen fuel has been attracting attention as an alternative fuel to gasoline, and vehicles using gas fuel alone or with liquid fuel have been put into practical use. ing. In addition, as an engine using gas fuel and liquid fuel, there is one that uses gas fuel as the main fuel of the engine and diesel fuel (light oil fuel) as an ignition fuel for starting combustion. The engine described in Patent Document 1 has been proposed (for example, see Patent Document 1). As a fuel injection means, a needle valve for injecting gas fuel and a needle valve for injecting diesel fuel are concentric. A dual fuel injector. The two needle valves in this dual fuel injector are each electromagnetically driven, and the needle valve for gas fuel is driven by controlling the flow rate of the hydraulic oil by energizing the solenoid valve for gas fuel. The needle valve for diesel fuel is driven by controlling the flow rate of the hydraulic oil by energizing the electromagnetic valve. Further, the dual fuel injector is provided with two separate paths, a gas fuel path and a diesel fuel path, as a distribution path of hydraulic oil for driving the needle valve.

JP-T-2004-501306

  However, in the case of the dual fuel injector of the above-mentioned Patent Document 1, the path of the hydraulic oil for the gas injection valve and the path of the hydraulic oil for the liquid injection valve are separately configured in two systems. The structure is complicated. In addition, it is necessary to control the driving of the gas injection valve and the driving of the liquid injection valve separately, which complicates the fuel injection control.

  The present invention has been made to solve the above problems, and provides a fuel injection system for an internal combustion engine capable of simplifying the system in a fuel injection system capable of injecting gas fuel and liquid 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 gas injection valve that directly injects gas fuel from a gas injection hole into a cylinder of an internal combustion engine, a liquid injection valve that directly injects liquid fuel from a liquid injection hole into the cylinder, and the gas injection valve wherein a gas supply unit for supplying a gas fuel, the liquid fuel to high pressure in the high pressure pump, and the high pressure fuel liquid supply portion for supplying the liquid injection valve is supplied to the liquid injection valve from the liquid supply portion to the A discharge passage (51) for discharging the liquid fuel from the liquid injection valve, and a liquid fuel disposed in the discharge passage and supplied to the liquid injection valve by changing a flow rate of the liquid fuel in the discharge passage. The present invention relates to a fuel injection system for an internal combustion engine comprising a pressure adjusting unit (50) for adjusting pressure . In particular, according to the first aspect of the present invention, the gas injection valve biases the first valve body toward the closed side by introducing a fluid to the first valve body that opens and closes the gas injection hole portion. A back pressure chamber that generates an urging force; and an energization drive unit that shifts the first valve body to an open side against the urging force in the valve closing direction by the back pressure chamber when energized. The injection valve operates with the rotation of the second valve body that opens and closes the liquid nozzle hole, the urging means that urges the second valve body to the closed side, and the output shaft of the internal combustion engine, and the cylinder A mechanical drive unit that shifts the second valve body to the open side against a biasing force in the valve closing direction by the biasing means at a predetermined rotational position for igniting the fuel in the fuel supply unit, and the liquid supply unit Has a high pressure passage connecting the high pressure pump and the liquid injection valve, and the back pressure chamber is disposed in the middle of the high pressure passage, In it characterized in that to produce a biasing force that biases the first valve body to close side by the high pressure fuel.

  In short, in the fuel injection system configured as described above, the gas injection valve is an electric drive type that opens and closes by adjusting the flow rate of the fluid by energization control, and the liquid injection valve opens and closes as the output shaft of the internal combustion engine rotates. It is mechanically driven. The liquid injection valve is supplied with fuel that has been increased in pressure by a high-pressure pump. In the middle of a high-pressure passage connecting the high-pressure pump and the liquid injection valve, the valve body of the gas injection valve is provided. A back pressure chamber that generates a biasing force biasing toward the closing side is disposed. That is, in this configuration, high-pressure liquid fuel is used as the fluid introduced into the back pressure chamber. Therefore, unlike a configuration in which a high-pressure fuel path for the liquid injection valve is separately provided, it is not necessary to provide a dedicated path for introducing the fluid into the back pressure chamber of the gas injection valve and leaking the fluid from the back pressure chamber. . In addition, fuel injection by the gas injection valve can be performed and fuel can be supplied to the liquid injection valve by a single process of energizing the energization drive unit of the gas injection valve. Therefore, it is not necessary to separately control the driving of the gas injection valve and the driving of the liquid injection valve. As described above, according to the above configuration, the system can be simplified in the fuel injection system capable of injecting the gas fuel and the liquid fuel.

1 is an overall schematic configuration diagram of an engine fuel injection system. FIG. The figure which shows schematic structure of a gas injection valve. The figure which shows schematic structure of a light oil injection valve. The figure which shows schematic structure of a pressure regulating valve. (A) shows when the valve is closed, and (b) shows when the valve is opened. The flowchart which shows the treatment procedure of gas injection control. The figure which shows the relationship between an engine speed and fuel supply pressure. The time chart which shows the specific aspect of fuel injection control.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. In the present embodiment, an on-vehicle multi-cylinder engine (in this embodiment, a four-cylinder engine) having two fuel passages in which gas fuel is used as engine output fuel and liquid fuel is used as ignition fuel. It is embodied in the fuel injection system.

  In the engine 10 shown in FIG. 1, the intake passage 11 is provided with a throttle valve 12 as air amount adjusting means whose opening is adjusted by a DC motor or the like. The intake port of the engine 10 is provided with an intake valve 13a, and the exhaust port is provided with an exhaust valve 13b. Air is introduced into the combustion chamber 15 by the opening operation of the intake valve 13a, and the exhaust gas after combustion is discharged into the exhaust passage 16 by the opening operation of the exhaust valve 13b.

  The engine 10 includes a gas injection valve 17 that injects gas fuel and a liquid injection valve 18 that injects liquid fuel as fuel injection means for directly injecting and supplying fuel to each cylinder. Among these, gas fuel is supplied from the gas tank 21 to the gas injection valve 17 and liquid fuel is supplied from the liquid tank 32 to the liquid injection valve 18, thereby constructing two fuel passages. ing. Among these fuel injection valves, the gas injection valve 17 is provided on the side of the center of the opposing wall surface facing the piston 14 in the combustion chamber 15, and the liquid injection valve 18 is provided at the center of the opposing wall surface. Is provided. Below, the fuel supply system of this system is demonstrated in detail using FIGS. 1-4.

  In FIG. 1, the gas tank 21 is filled with gas fuel in a high-pressure state (for example, 30 MPa). In this embodiment, CNG fuel is filled as the gas fuel. The gas tank 21 is connected to the gas injection valve 17 via the gas pipe 19 so that the gas fuel is supplied to the gas injection valve 17 through the gas fuel passage formed in the gas pipe 19. It has become. The gas pipe 19 is provided with a regulator (pressure reducing valve) 22 that adjusts the pressure of the gas fuel to be reduced. In the present embodiment, the regulator 22 is mechanically driven, and the pressure of the gas fuel supplied to the gas injection valve 17 is reduced to a predetermined supply pressure (for example, 10 MPa) by reducing the pressure of the high-pressure gas fuel in the gas tank 21. adjust. The regulator 22 is an electromagnetic drive type in which the pressure of the gas fuel supplied to the gas injection valve 17 can be variably adjusted by energization control, and the pressure of the gas fuel supplied to the gas injection valve 17 is within a predetermined pressure range ( For example, it may be variable within a range of 8 to 20 MPa. In this system, the gas tank 21, the gas pipe 19, and the regulator 22 constitute a gas supply unit that supplies gas fuel to the gas injection valve 17.

  Next, a schematic configuration of the gas injection valve 17 will be described with reference to FIG. The gas injection valve 17 of the present system is an electromagnetically driven needle valve. When the solenoid is energized / de-energized, the needle-like valve body (needle) reciprocates in the axial direction, thereby injecting and injecting gas fuel. A stop is made. Specifically, in the gas injection valve 17 of FIG. 2, a cylinder 23 is provided in the main body, and a needle 24 as a first valve body is accommodated in the cylinder 23 so as to be capable of reciprocating in the axial direction. ing. Further, a nozzle hole 25 for injecting gas fuel is provided at the tip of the gas injection valve 17, and one end of a needle 24 is disposed in the nozzle hole 25. Thereby, the nozzle hole part 25 is opened and closed with the reciprocating motion of the needle 24.

  A gas passage 29 connecting the gas pipe 19 and the injection hole portion 25 is formed in the main body of the gas injection valve 17, and the gas fuel in the gas tank 21 is supplied to the injection hole portion 25 through the gas passage 29. Is done. Further, the back pressure chamber 26 that generates an urging force for urging the needle 24 toward the closed side by the hydraulic oil is provided in the main body portion adjacent to an end portion of the both ends of the needle 24 that is different from the nozzle hole 25 side. Is provided. The pressure in the back pressure chamber 26 is adjusted by adjusting the flow rate of the hydraulic oil, and the flow rate of the hydraulic oil is adjusted by opening / closing an electromagnetic valve 27 (corresponding to an energization drive unit) that is opened by energization of the solenoid. Done. Specifically, when the solenoid of the solenoid valve 27 is not energized, the force in the valve closing direction acting on the needle 24 due to the pressure of the hydraulic oil introduced into the back pressure chamber 26 is the force in the valve opening direction. This keeps the needle 24 in the closed position. In this state, when the solenoid of the solenoid valve 27 is energized, the solenoid valve 27 is opened, and the hydraulic oil in the back pressure chamber 26 is leaked from the back pressure chamber 26 via the leak passage 28. As a result, the pressure in the back pressure chamber 26 is reduced, the needle 24 is shifted to the valve open position by the urging force of the spring 31, and the gas fuel in the gas passage 29 is injected from the injection hole portion 25. Further, when the solenoid of the solenoid valve 27 is de-energized, the solenoid valve 27 is closed and the working oil is introduced into the back pressure chamber 26, thereby increasing the pressure in the back pressure chamber 26. Thereby, the needle 24 is shifted to the valve closing position against the urging force of the spring 31, and fuel injection from the injection hole portion 25 is stopped.

  Returning to FIG. 1, the liquid fuel injection system will be described. The liquid tank 32 is filled with self-ignitable liquid fuel, and in this embodiment, light oil fuel is filled as the liquid fuel. The light oil fuel in the liquid tank 32 is supplied to the high-pressure pump 34 via the low-pressure pipe 33, and the pressure is increased by the high-pressure pump 34. The high-pressure fuel is pumped to the common rail 35 through the high-pressure passage 36a, stored in the common rail 35 in a high-pressure state, and then supplied to the liquid injection valve 18 through the high-pressure passage 36b. The rail pressure Pr that is the fuel pressure in the common rail 35 is variably adjusted within a predetermined range (for example, 20 to 120 MPa) by adjusting the fuel discharge amount from the high-pressure pump 34 to the common rail 35.

  Further, a pipe 35b communicating with the liquid tank 32 is connected to the common rail 35, and an electromagnetically driven relief valve 35a for adjusting the rail pressure Pr is provided in the middle of the pipe 35b. In this system, the rail pressure Pr can be adjusted by opening and closing the relief valve 35a. Although the liquid injection valve 18 of each cylinder is connected to the common rail 35, FIG. 1 shows only the first cylinder (# 1), and the fuel injection system of the other cylinders (# 2 to # 4). Is omitted because it is the same as the first cylinder.

  Here, regarding the high-pressure fuel path, particularly in the present system, the back pressure chamber 26 of the gas injection valve 17 is disposed in the middle of the high-pressure passage connecting the high-pressure pump 34 and the liquid injection valve 18. A high-pressure light oil fuel is introduced into 26. That is, as shown in FIGS. 1 and 2, the light oil fuel that has been increased in pressure by the high-pressure pump 34 is supplied to the common rail 35 through the high-pressure passage 36a and then introduced into the back pressure chamber 26 through the high-pressure passage 36b. Further, the high-pressure light oil fuel introduced into the back pressure chamber 26 is supplied to the liquid injection valve 18 through the leak passage 28 when the electromagnetic valve 27 of the gas injection valve 17 is opened. In this system, the high pressure light oil fuel is used as the hydraulic oil in this way, and the high pressure fuel generates an urging force for urging the needle 24 to the closed side by the high pressure fuel in the back pressure chamber 26. Thus, fuel injection by the gas injection valve 17 is performed. Further, along with the opening of the electromagnetic valve 27, the fuel supply to the liquid injection valve 18 is also performed. That is, in this system, the flow rate adjustment of the hydraulic oil to the gas injection valve 17 and the fuel supply to the liquid injection valve 18 are performed as follows: liquid tank 32 → low pressure pipe 33 → high pressure pump 34 → high pressure passage 36a → common rail 35 → high pressure. The system is implemented by one system of the passage 36b → the leak passage 28, thereby simplifying the system.

  The high-pressure passage 36 a, the high-pressure passage 36 b, and the leak passage 28 correspond to the high-pressure passage that connects the high-pressure pump 34 and the liquid injection valve 18. The liquid tank 32, the low pressure pipe 33, the high pressure pump 34, the common rail 35, the high pressure pipe 36, and the leak passage 28 constitute a liquid supply unit that supplies liquid fuel to the liquid injection valve 18.

  Next, a schematic configuration of the liquid injection valve 18 will be described with reference to FIG. The liquid injection valve 18 of the present system is a mechanically driven needle valve, and light oil fuel is injected and stopped when the needle reciprocates in the axial direction in accordance with the rotation of the output shaft 41 of the engine 10. Specifically, in FIG. 3, a cylinder 43 is provided in the main body portion of the liquid injection valve 18, and a needle 44 as a second valve body is disposed in the cylinder 43 so as to reciprocate in the axial direction. ing. Further, a nozzle hole 45 having a plurality of nozzle holes (for example, eight holes) capable of discharging light oil fuel is provided at the tip of the liquid injection valve 18, and one end of the needle 44 is provided in the nozzle hole 45. Has been placed. Accordingly, each nozzle hole in the nozzle hole portion 45 is opened and closed as the needle 44 reciprocates. Note that the liquid injection valve 18 of the present embodiment is an outward opening valve, and each nozzle hole in the nozzle hole 45 is opened by increasing the amount of protrusion protruding from the tip of the liquid injection valve 18 at the end of the needle 44. It becomes a state.

  A fuel passage 46 that connects the leak passage 28 and the injection hole portion 45 is provided in the main body of the liquid injection valve 18. Through this fuel passage 46, light oil fuel that has been pressurized by the high-pressure pump 34 is an injection hole. Supplied to the unit 45. A cam 47 having one cam peak 47a is disposed adjacent to an end different from the nozzle hole 45 side at both ends of the needle 44. In the liquid injection valve 18, the biasing force of the spring 49 is provided. Thus, the cam 47 is brought into contact with the upper end portion of the needle 44. The cam 47 is attached to a cam shaft 48 that can rotate as the engine output shaft 41 rotates. In this embodiment, the cam shaft 48 is rotated every two rotations of the engine output shaft 41 (every 720 ° C.). Is rotated once. Further, the cam crest 47a is a timing at which the fuel injected into each cylinder is ignited, more specifically, at a compression top dead center of each cylinder or a predetermined range in the vicinity thereof (for example, BTDC 10 ° C. A to ATDC 10 The cam crest 47 a is disposed so as to contact the upper end of the needle 44 (within a predetermined range within the temperature A).

  When the cam 47 rotates with the rotation of the engine output shaft 41, the cam crest 47a contacts the end of the needle 44, and the needle 44 shifts to the valve opening position against the urging force of the spring 49. Thereby, the light oil fuel in the fuel passage 46 is injected from the injection hole portion 45. When the cam 47 rotates and the contact between the cam crest 47a and the needle 44 is released, the needle 44 is shifted to the closing side by the urging force of the spring 49. Thereby, injection of the light oil fuel from the nozzle hole part 45 is stopped. The spring 49 corresponds to an urging means for urging the needle 44 to the closing side, and the cam 47 and the cam shaft 48 open the second valve body against the urging force in the valve closing direction by the urging means. This corresponds to a mechanical drive that shifts to the side.

  Further, in the present system, a part of the light oil fuel supplied to the liquid injection valve 18 is discharged from the liquid injection valve 18 with a high pressure, and is supplied to the liquid injection valve 18 by adjusting the discharge amount. Light oil fuel pressure (fuel supply pressure) is adjusted. Specifically, as shown in FIG. 3, the leak passage 28 is connected to the injection hole portion 45 through a fuel passage 46 formed in the main body portion of the liquid injection valve 18, and the fuel passage 46 further includes a light oil fuel. Is connected to a discharge passage 51 for discharging the liquid from the liquid injection valve 18. As a result, part of the high-pressure gas oil fuel supplied to the liquid injection valve 18 through the leak passage 28 is circulated from the fuel passage 46 to the discharge passage 51 while maintaining the high-pressure state. With this configuration, the fuel pressure on the downstream side of the gas injection valve 17 is made lower than the fuel pressure on the upstream side of the gas injection valve 17, in other words, the fuel pressure in the common rail 35. The backflow from the 18 side to the gas injection valve 17 side is prevented.

  In the present system, a pressure adjustment valve 50 as a pressure adjustment unit is disposed in the middle of the discharge passage 51, and the discharge amount of the liquid fuel from the liquid injection valve 18 is adjusted by the pressure adjustment valve 50. The Here, a schematic configuration of the pressure regulating valve 50 will be described with reference to FIG. In FIG. 4, a discharge passage 51 passes through the main body of the pressure regulating valve 50, and a valve body chamber 53 that is a part of the discharge passage 51 is disposed in the middle of the discharge passage 51. A valve body 52 that is axially displaceable is accommodated in the valve body chamber 53, and the opening area of the discharge passage 51 in the valve seat portion 53 a is changed with the displacement of the valve body 52. Further, an adjustment spring 54 for urging the valve body 52 toward the valve opening side is attached to the valve body 52, and the valving force of the adjustment spring 54 causes the valve body 52 in a state where no force acts on the valve body 52. Shifts to the valve open position. In the present embodiment, the adjustment spring 54 is configured such that the pressure of the high-pressure fuel (fuel supply pressure Pl) supplied to the liquid injection valve 18 is a predetermined pressure Pα than the pressure of the high-pressure fuel in the common rail 35 (rail pressure Pr). The spring force is Pα so as to decrease by (for example, 10 to 20 MPa). Thereby, the pressure of the liquid fuel supplied to the liquid injection valve 18 is adjusted to a pressure lower than the fuel pressure in the common rail 35 by a predetermined value to prevent the backflow of the light oil fuel.

  A pressure chamber 55 is provided in the main body of the pressure adjusting valve 50 as a position adjusting unit that adjusts the shift position of the valve body 52. A piping 56 that connects the pressure chamber 55 and the common rail 35 is connected to the pressure chamber 55, and high-pressure fuel in the common rail 35 is supplied into the pressure chamber 55 through the piping 56. As a result, the fuel pressure in the pressure chamber 55 acts on the valve body 52 as a force in the valve closing direction, and the fuel pressure in the valve body chamber 53 acts on the valve body 52 as the force in the valve opening direction. In this embodiment, in the valve body 52, the pressure receiving area on the pressure chamber 55 side is A0, and the pressure receiving area on the valve body chamber 53 side is A1 smaller than A0.

  In the valve body 52, when (force in the valve closing direction)> (force in the valve opening direction), as shown in FIG. 4A, the valve body 52 is seated and held in the valve closing position. Is done. In this case, the flow of the high-pressure fuel in the discharge passage 51 is blocked, and the high-pressure fuel is not discharged from the liquid injection valve 18. On the other hand, when (force in the valve closing direction) <(force in the valve opening direction), as shown in FIG. 4 (b), the valve body 52 is separated from the valve seat portion 53a to the valve opening position. It is displaced to. In this case, the flow of the high-pressure fuel to the discharge passage 51 is allowed, and the high-pressure fuel is discharged from the liquid injection valve 18. Further, the discharge amount is in accordance with the shift position of the valve body 52. Thus, the fuel supply pressure of the liquid injection valve 18 is adjusted so that it is always lower than the rail pressure Pr by the predetermined pressure Pα.

  Next, fuel injection control of this system will be described. In this system, fuel injection for engine output is performed by the gas injection valve 17, and fuel injection for ignition (fire type) for the fuel in the cylinder is performed by the liquid injection valve 18. In the system, an engine 10 and a fuel supply system of the engine 10 are controlled with an electronic control unit (hereinafter referred to as ECU 60) as a center.

  As is well known, the ECU 60 is mainly composed of a microcomputer (hereinafter referred to as a microcomputer) composed of a CPU, ROM, RAM, and the like, and executes various control programs stored in the ROM, so that the engine operation state can be changed each time. In response, various controls of the engine 10 are executed. Specifically, the microcomputer includes a crank angle sensor 63 that outputs a rectangular crank angle signal for each predetermined crank angle of the engine 10, an air flow meter (not shown) that detects an intake air amount, and a pressure in the common rail 35. Each detection signal is input from various sensors such as the fuel pressure sensor 64 that detects the rail pressure Pr, and the driving of the gas injection valve 17 and the discharge amount of the high-pressure pump 34 are controlled based on these various detection signals. To do.

  The fuel injection control (gas injection control) of the gas injection valve 17 will be described with reference to the flowchart of FIG. This process is executed at predetermined intervals by the microcomputer of the ECU 60.

  In FIG. 5, in step S <b> 11, it is determined whether it is a calculation timing for calculating the injection amount and injection timing of the gas fuel. In the present embodiment, for example, a predetermined rotational position in the intake stroke of the engine 10 is determined as the calculation timing of the injection amount and the injection timing, and an affirmative determination is made when the calculation timing is reached. If it is the calculation timing of the injection amount or the like, the process proceeds to step S12, and parameters relating to the engine operating state (for example, engine speed and engine load) are acquired. In step S13, the gas injection amount Qg and the injection timing injected from the gas injection valve 17 are calculated based on the acquired parameters.

  In calculating the gas injection amount Qg, in this embodiment, the engine operating state is calculated by subtracting the injection amount of the light oil fuel injected for the fire type (light oil injection amount Ql) from the gas fuel amount calculated based on the engine operating state. An amount of fuel corresponding to the above is supplied to the combustion chamber 15. For the light oil injection amount Ql, the fuel supply pressure Pl of the liquid injection valve 18 is calculated based on the rail pressure Pr detected by the fuel pressure sensor 64 and the engine rotational speed detected by the crank angle sensor 63, and the calculation is performed. The light oil injection amount Ql is calculated based on the fuel supply pressure Pl. At this time, as the rail pressure Pr is higher or the engine speed is lower, a larger value is calculated as the light oil injection amount Ql. On the other hand, in this embodiment, the injection timing of gas fuel is set before the compression top dead center of the engine 10 in the present embodiment. Here, the injection start timing as the energization timing for starting energization of the solenoid valve 27 is calculated based on the injection end timing set at the predetermined rotational position before the compression top dead center and the calculated gas injection amount Qg. To do.

  In subsequent step S14, it is determined whether or not it is the energization start timing of the electromagnetic valve 27, that is, whether or not it is the injection timing of gas fuel. If it is the injection timing of the gas fuel, the process proceeds to step S15 and the solenoid valve 27 is energized. As a result, gas fuel is injected from the gas injection valve 17 into the combustion chamber 15.

  Next, the injection amount control of the liquid injection valve 18 will be described. Since the liquid injection valve 18 is a cam drive type that is driven in accordance with the rotation of the engine output shaft 41, the injection amount Ql of light oil fuel injected from the liquid injection valve 18 changes each time according to the engine rotation speed. Specifically, the higher the engine rotation speed, the shorter the valve opening time of the injection hole 45 of the liquid injection valve 18, and as a result, the light oil injection amount Ql tends to decrease. In such a case, in the high rotation region of the engine 10, there is a risk that the amount of fuel for the fire type will be insufficient and the mixture will not be ignited. Therefore, in this system, the fuel pressure on the downstream side of the gas injection valve 17, that is, the fuel supply pressure of the liquid injection valve 18, is changed by changing the rail pressure Pr that is the fuel pressure in the common rail 35 in accordance with the engine speed. Pl is made variable so that the amount of light oil injected from the liquid injection valve 18 into the combustion chamber 15 becomes constant. Specifically, as shown in FIG. 6, the fuel discharge amount of the high-pressure pump 34 is adjusted so that the fuel supply pressure Pl increases as the engine speed increases, that is, the rail pressure Pr increases. The fuel return amount from the common rail 35 to the liquid tank 32 is adjusted by opening and closing the relief valve 35a.

  Next, a specific aspect of the fuel injection control of this system will be described using the time chart of FIG. In FIG. 7, when the injection start timing t11 of the gas injection valve 17 is reached, the solenoid of the solenoid valve 27 is energized. This solenoid energization shifts the needle 24 of the gas injection valve 17 to the valve opening position, and the injection rate of the gas injection valve 17 increases (gas fuel is injected). Further, fuel is supplied from the liquid tank 32 to the liquid injection valve 18 via the back pressure chamber 26 of the gas injection valve 17, so that the fuel pressure on the downstream side of the gas injection valve 17, that is, the liquid injection valve 18. The fuel supply pressure Pl increases.

When the injection end timing t12 of the gas injection valve 17 is reached, energization of the solenoid of the electromagnetic valve 27 is stopped. By stopping energization of the solenoid, the needle 24 of the gas injection valve 17 is shifted to the valve closing position, the injection rate of the gas injection valve 17 is reduced (gas fuel injection is stopped), and the gas injection valve 17 Since the communication between the back pressure chamber 26 and the liquid injection valve 18 is blocked, the fuel supply pressure Pl of the liquid injection valve 18 is kept constant. Thereafter, at timing t13 when the compression top dead center is reached, the needle 44 of the liquid injection valve 18 is shifted to the valve open position as the cam 47 rotates, so that a predetermined injection rate (for example, 3 mm ³ / st) from the liquid injection valve 18 is reached. ) Light oil fuel is injected.

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

  The gas injection valve 17 is an electromagnetic drive type that opens and closes by adjusting the flow rate of fluid by energization control, the liquid injection valve 18 is a mechanical drive type that opens and closes as the engine output shaft 41 rotates, and the liquid injection valve 18 is supplied with fuel whose pressure has been increased by the high-pressure pump 34, and the valve body of the gas injection valve 17 is disposed in the middle of the high-pressure passage connecting the high-pressure pump 34 and the liquid injection valve 18. The back pressure chamber 26 that generates a biasing force biasing to the closing side is arranged. Therefore, according to this configuration, the high-pressure fuel path for the liquid injection valve 18 can be used as a passage that introduces fluid into the back pressure chamber 26 of the gas injection valve 17 and leaks the fluid from the back pressure chamber 26. Further, it is not necessary to provide a dedicated fluid path for making the pressure in the back pressure chamber 26 variable, and the system can be simplified.

  Further, according to the fuel injection system of the present embodiment, the fuel injection by the gas injection valve 17 can be performed by a single process of energizing the electromagnetic valve 27 of the gas injection valve 17 and the fuel to the liquid injection valve 18 can be performed. Supply can be made. Therefore, it is not necessary to control the driving of the gas injection valve 17 and the driving of the liquid injection valve 18 separately, which is preferable for simplifying the system.

  Since the self-ignitable liquid fuel injected from the liquid injection valve 18 is used as an ignition source for igniting the mixture of the gas fuel and the intake air, the liquid fuel is injected from a plurality of injection holes provided in the liquid injection valve 18. With the liquid fuel, the ignition of the air-fuel mixture can be made multi-point ignition. Thereby, compared with the case where ignition devices, such as a spark plug, are used as an ignition source, combustion efficiency can be improved.

  Since the liquid fuel is injected after the gas fuel is injected, combustion can be performed in accordance with the injection timing of the liquid fuel, that is, in the vicinity of the compression top dead center, and combustion stability can be achieved.

  Since light oil fuel is used as the liquid fuel, combustion can be reliably performed by good ignitability of the light oil fuel, and the actuator (gas injection valve 17) is preferably driven by an appropriate viscosity of the light oil fuel. can do.

  A discharge passage 51 is provided as a fuel passage for discharging the high-pressure light oil fuel supplied to the liquid injection valve 18, and a pressure adjustment valve 50 is disposed in the discharge passage 51, and the fuel of the liquid injection valve 18 is provided by the pressure adjustment valve 50. The supply pressure Pl is set to be lower than the pressure in the common rail 35. According to this configuration, the fuel supply pressure Pl of the liquid injection valve 18, that is, the fuel pressure downstream of the gas injection valve 17 can be made lower than the fuel pressure upstream of the gas injection valve 17. Can be prevented from flowing backward.

  Focusing on the fact that the amount of fuel injected from the liquid injector 18 decreases when the engine speed is high, the rail pressure Pr is set so that the fuel pressure downstream of the gas injector 17 increases as the engine speed increases. The configuration is variable. Thereby, it can suppress that the excess and deficiency of the fuel for ignition arises, and can burn the engine 10 suitably.

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

  In step S13 of FIG. 5, the gas injection amount Qg injected from the gas injection valve 17 is calculated by subtracting the light fuel injection amount (light oil injection amount Ql) from the gas fuel amount calculated based on the engine operating state. . On the other hand, in the present embodiment, it is configured to switch whether to calculate the gas injection amount Qg in consideration of the light oil injection amount Ql according to the engine operating state. When the engine 10 is under a low load (for example, in an idling state), the ratio of the light oil injection amount Ql to the entire injection amount within one combustion cycle is large, and the influence of the light oil injection amount Ql is large. Sometimes, the proportion of the light oil injection amount Ql is small, and the influence of the light oil injection amount Ql can be ignored. In view of this point, in this embodiment, when the engine load is lower than the predetermined load, the gas injection amount Qg is calculated by subtracting the light oil injection amount Ql from the gas fuel amount calculated based on the engine operating state, and the calculation The injected gas injection amount Qg is injected from the gas injection valve 17. On the other hand, when the engine load is higher than the predetermined load, the gas fuel amount calculated based on the engine operating state is set as the gas injection amount Qg, and the gas injection amount Qg is injected from the gas injection valve 17.

  In the above embodiment, the liquid injection valve 18 is an outer opening valve, but may be an inner opening valve that opens when the needle 44 is shifted into the main body. Also when it is set as an internal opening valve, it is good to provide a some injection hole in an injection hole part similarly to the said embodiment, and to be able to inject fuel radially. Thereby, multipoint ignition using the liquid fuel as a fire type is possible. Further, the gas injection valve 17 may employ an external opening valve instead of the internal opening valve.

  -The pressure control valve 50 as a pressure control part in the said embodiment is good also as an electromagnetic drive type which opens and closes by electricity supply.

  In the above embodiment, the pressure adjustment valve 50 as the pressure adjustment unit may not be provided on the downstream side of the liquid injection valve 18. In this case, the liquid injection valve 18 may be provided with a throttle (orifice) that holds the liquid fuel in a high pressure state and gradually leaks the liquid fuel. Further, a check valve may be provided in the leak passage 28 between the gas injection valve 17 and the liquid injection valve 18 so as to prevent a back flow from the liquid injection valve 18 to the gas injection valve 17.

  In the above embodiment, the gas injection valve 17 is arranged on the side of the combustion chamber 15 rather than the central portion of the opposing wall surface facing the piston 14, and the liquid injection valve 18 is arranged in the central portion of the opposing wall surface. The arrangement of the valve 17 and the liquid injection valve 18 is not limited to this. For example, you may arrange | position both the gas injection valve 17 and the liquid injection valve 18 in the center part of an opposing wall surface.

  In the above embodiment, the case of using light oil fuel as the liquid fuel has been described, but any fuel that can be used as a fuel for ignition of gas fuel may be used. For example, if the engine 10 has a high compression ratio, it is possible to use liquid fuel such as gasoline. Further, the gas fuel is not particularly limited, and for example, hydrogen fuel, liquefied petroleum gas (LPG), or the like may be used instead of CNG fuel.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 15 ... Combustion chamber, 17 ... Gas injection valve, 18 ... Liquid injection valve, 19 ... Gas piping, 21 ... Gas tank, 22 ... Regulator, 24 ... Needle (1st valve body), 25 ... Injection hole part ( (Gas injection hole part), 26 ... back pressure chamber, 27 ... solenoid valve (energization drive part), 28 ... leak passage (high pressure passage), 31 ... spring, 32 ... liquid tank, 34 ... high pressure pump, 35 ... common rail (accumulation pressure) Chamber), 35b ... piping, 36 ... high pressure piping, 36a ... high pressure passage, 36b ... high pressure passage, 41 ... engine output shaft, 44 ... needle (second valve element), 45 ... injection hole portion (liquid injection hole portion), 46 ... fuel passage, 47 ... cam (mechanical drive), 48 ... camshaft (mechanical drive), 49 ... spring (biasing means), 50 ... pressure regulating valve (pressure regulating portion), 51 ... discharge passage, 60 ... ECU (injection control means, pressure control means)

Claims (6)

A gas injection valve (17) for directly injecting gas fuel from the gas injection hole (25) into the cylinder of the internal combustion engine (10);
A liquid injection valve (18) for directly injecting liquid fuel into the cylinder from the liquid injection hole (45);
A gas supply unit (19, 21, 22) for supplying the gas fuel to the gas injection valve;
A liquid supply unit (28, 32, 33, 35, 36a, 36b) for increasing the pressure of the liquid fuel with a high-pressure pump (34) and supplying the high-pressure fuel to the liquid injection valve;
A discharge passage (51) for discharging the liquid fuel supplied from the liquid supply unit to the liquid injection valve from the liquid injection valve;
A pressure adjusting unit (50) disposed in the discharge passage and adjusting the pressure of the liquid fuel supplied to the liquid injection valve by changing a flow rate of the liquid fuel in the discharge passage ;
The gas injection valve includes a first valve body (24) that opens and closes the gas injection hole, and a back pressure chamber that generates an urging force that urges the first valve body to a closed side when fluid is introduced. (26) and an energization drive unit (27) that shifts the first valve body to the open side against energizing force in the valve closing direction by the back pressure chamber when energized,
The liquid injection valve includes: a second valve body (44) that opens and closes the liquid injection hole; an urging means (49) that urges the second valve body toward a closed side; and an output shaft ( 41) a mechanical drive that operates in accordance with the rotation of 41) and shifts the second valve body to the open side against a biasing force in the valve closing direction by the biasing means at a predetermined rotational position where the fuel in the cylinder is ignited. Part (47, 48), and
The liquid supply unit includes high pressure passages (36a, 36b, 28) connecting the high pressure pump and the liquid injection valve, and the back pressure chamber is disposed in the middle of the high pressure passage. A fuel injection system for an internal combustion engine, characterized in that an urging force for urging the first valve body toward the closing side is generated by the high-pressure fuel. The liquid fuel is a liquid fuel capable of self-ignition,
The gas injection valve performs injection of gas fuel before the compression top dead center of the internal combustion engine,
2. The fuel for an internal combustion engine according to claim 1, wherein the liquid injection valve injects liquid fuel after injection of gas fuel by the gas injection valve and with the compression top dead center or the vicinity thereof as the predetermined rotational position. Injection system. The liquid supply unit includes a pressure accumulating chamber for storing high-pressure fuel between the high-pressure pump and the liquid injection valve,
3. The fuel injection of the internal combustion engine according to claim 1, wherein the pressure adjusting unit adjusts the pressure of the liquid fuel supplied to the liquid injection valve to a pressure lower than a pressure in the pressure accumulating chamber by a predetermined value. system. The fuel injection system for an internal combustion engine according to any one of claims 1 to 3 , further comprising injection control means for energizing the energization drive unit at a fuel injection timing for the internal combustion engine. The liquid injection valve injects liquid fuel with the compression top dead center of the internal combustion engine or the vicinity thereof as the predetermined rotational position,
The fuel injection of the internal combustion engine according to claim 4 , wherein the injection control means energizes the energization drive unit so that gas fuel is injected from the gas injection valve before injection of liquid fuel by the liquid injection valve. system. The liquid supply unit includes a pressure accumulating chamber for storing high-pressure fuel between the high-pressure pump and the liquid injection valve,
The pressure control means for changing the pressure of the liquid fuel downstream of the gas injection valve by changing the fuel pressure in the pressure accumulating chamber according to the engine speed of the internal combustion engine. The fuel injection system for an internal combustion engine according to one item.

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