JP2014118844A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly determine whether or not fuel leakage failure occurs in a cut-off valve and a decompression means provided in a gaseous fuel supply system.SOLUTION: In a fuel passage made of a gas pipe 41 and the like, a decompression part 60 is provided which regulates a pressure of gaseous fuel supplied to a first injection valve 21 to reduce the pressure, and a tank main stop valve 44 and a cut-off valve 45 are provided. A control unit 80 monitors conditions of a change in an injection pressure which is a pressure of the gaseous fuel supplied to the first injection valve 21, and on the basis of the conditions of the change in the injection pressure, determines whether a cause of failure occurrence is gaseous fuel leakage failure in the decompression part 60 or gaseous fuel leakage failure in the cut-off valve 45.

Description

  The present invention relates to a fuel injection control device for an internal combustion engine.

  Conventionally, an internal combustion engine in which gas fuel such as compressed natural gas (CNG) is burned has been put into practical use. In such an internal combustion engine, as a configuration of a gas fuel supply system for supplying gas fuel to the fuel injection valve, a gas tank for storing the gas fuel in a high pressure state and a fuel pipe connecting the gas tank and the fuel injection valve are provided in the middle. A configuration is known that includes a pressure reducing valve that adjusts the pressure of gas fuel supplied from a gas tank, and a shut-off valve that is provided upstream of the pressure reducing valve (that is, on the gas tank side) and blocks the flow of gas fuel to the pressure reducing valve. (See, for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-294222

  In the gas fuel supply system as described above, high-pressure gas fuel is supplied from the upstream side to the pressure reducing valve and the shutoff valve, and there is a concern that the high pressure gas leaks downstream through the pressure reducing valve and the shutoff valve. In spite of such fuel leakage, if the operation of the internal combustion engine is continued without noticing it, various inconveniences such as adverse effects on fuel injection in the fuel injection valve may occur. There is room for improvement in this regard.

  The main object of the present invention is to provide a fuel injection control device for an internal combustion engine that can appropriately determine the presence or absence of fuel leakage abnormality with respect to a shutoff valve and pressure reducing means provided in a gas fuel supply system. .

  Hereinafter, means for solving the above-described problems and the effects thereof will be described.

  The present invention is provided with a gas tank (42) for storing gas fuel in a high-pressure state, gas fuel injection means (21) for injecting gas fuel supplied from the gas tank through a fuel passage (41), and the fuel passage. A decompression means (60) for decompressing and adjusting the pressure of the gas fuel supplied to the gas fuel injection means, and a shut-off function provided on the upstream side of the decompression means in the fuel passage, for shutting off the flow of the gas fuel. A fuel injection control device for an internal combustion engine applied to a fuel injection system including a shutoff valve (45). And a monitoring means for monitoring a change in the injection pressure, which is a pressure of the gas fuel supplied to the gas fuel injection means, and the injection pressure monitored by the monitoring means when an abnormality occurs in the gas fuel supply system. An abnormality determining means for determining whether the cause of the abnormality is due to a gas fuel leakage abnormality in the decompression means or a gas fuel leakage abnormality in the shut-off valve, based on the change mode of And

  Even if the pressure reducing means and the shut-off valve provided in the fuel passage leading to the gas tank are in the closed state, it is considered that abnormal fuel leakage occurs in which the gas fuel leaks downstream. When such a fuel leakage abnormality occurs, the mode of change in the injection pressure (supply gas pressure to the gas fuel injection means) becomes different from that in the normal state. Further, the mode of change in the injection pressure differs depending on whether the fuel leakage abnormality has occurred in the pressure reducing means or the shutoff valve. In the present invention, paying attention to such an event, when an abnormality occurs in the gas fuel supply system, the cause of the abnormality is due to a leakage abnormality in the decompression means or a leakage abnormality in the shut-off valve based on the mode of change in the injection pressure. Determine whether it is due to. As a result, it is possible to appropriately determine whether or not there is a fuel leakage abnormality with respect to the shutoff valve and the pressure reducing means provided in the gas fuel supply system.

The block diagram which shows the outline of the fuel-injection system of an engine. The figure which shows schematic structure of a 1st injection valve. The figure which shows schematic structure of a regulator. The schematic diagram which shows the structure of a gas fuel supply part. The figure which put together the aspect of the change of the injection pressure at the time of normal and abnormality. The flowchart which shows the main routine of an abnormality determination process. The flowchart which shows a 1st abnormality determination process. The flowchart which shows a 2nd abnormality determination process. The flowchart which shows a 3rd abnormality determination process. The flowchart which shows a 4th abnormality determination process. The flowchart which shows the post-judgment process of cutoff valve abnormality. The flowchart which shows the post-judgment process of pressure_reduction | reduced_pressure part abnormality. The time chart for demonstrating the effect | action regarding a 1st abnormality determination process. The time chart for demonstrating the effect | action regarding a 2nd abnormality determination process. The time chart for demonstrating the effect | action regarding a 2nd abnormality determination process. The time chart for demonstrating the effect | action regarding a 3rd abnormality determination process. The time chart for demonstrating the effect | action regarding a 4th abnormality determination process.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described 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) as a gas fuel and gasoline as a liquid fuel as combustion fuel. It is supposed to be 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 an inline three-cylinder spark ignition engine, and an intake system 11 and an exhaust system 12 are connected to an intake port and an exhaust port, respectively. The intake system 11 has an intake manifold 13 and an intake pipe 14. The intake manifold 13 has a plurality of (for the number of cylinders of the engine 10) branch pipe portions 13a connected to the intake port of the engine 10, and a collective portion 13b connected to the intake pipe 14 on the upstream side. ing. The intake pipe 14 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 a throttle actuator 15a such as a DC motor. The opening degree of the throttle valve 15 (throttle opening degree) is a throttle opening degree built in the throttle actuator 15a. It is detected by the degree sensor 15b.

  Further, the exhaust system 12 has an exhaust manifold 16 and an exhaust pipe 17. The exhaust manifold 16 has a plurality of (for the number of cylinders of the engine 10) branch pipe portions 16a connected to the exhaust port of the engine 10 and a collecting portion 16b connected to the exhaust pipe 17 on the downstream side. ing. The exhaust pipe 17 is provided with an exhaust sensor 18 for detecting exhaust components and a catalyst 19 for purifying exhaust. Specifically, an air-fuel ratio sensor that detects the air-fuel ratio from the oxygen concentration in the exhaust is provided as the exhaust sensor 18.

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

  Further, the present system is a fuel injection means for injecting and supplying fuel to the engine 10, a first injection valve 21 for injecting gas fuel (CNG fuel), and a second injection valve 22 for injecting liquid fuel (gasoline). And have. Each of these injection valves 21 and 22 injects fuel into the branch pipe portion 13a of the intake manifold 13 in the intake system 11, and gas fuel is supplied to the intake port of each cylinder by the injection of the first injection valve 21. The liquid fuel is supplied to the intake port of each cylinder by the injection of the second injection valve 22.

  Each of the injection valves 21 and 22 is an open / close type control valve in which the valve body is lifted from the closed position to the open position by electrically driving the electromagnetic drive unit. Each valve is driven to open by a valve opening drive signal. These injection valves 21 and 22 are opened by energization and closed by energization interruption. An amount of fuel (gas fuel, liquid fuel) corresponding to the energization time is injected from each of the injection valves 21 and 22. In this embodiment, the injection pipe 23 is connected to the tip of the first injection valve 21, and the gas fuel injected from the first injection valve 21 is branched through the injection pipe 23. 13a is injected.

  Here, the configuration of the first injection valve 21 for gas injection will be described with reference to FIG. In FIG. 2, (a) shows a non-injection state, and (b) shows an injection state. The first injection valve 21 has a so-called self-seal (self-sealing) structure in which the closing sealability is enhanced by the pressure of the gas fuel supplied to itself.

  A valve body 32 is slidably accommodated in the cylindrical body 31, and the valve body 32 is biased in the valve closing direction by a spring 33 in the body 31. In FIG. 2A, the nozzle hole 34 provided at the tip of the injection valve is closed by the tip of the valve body 32. In the body 31, a first fuel chamber 35 is provided on the rear end side (upstream side) of the valve body 32, and a second fuel chamber 36 is provided on the front end side (downstream side) of the valve body 32. Yes. The valve body 32 is provided with a small-diameter portion 32a on the tip side of the sliding portion, and a second fuel chamber 36 is provided around the small-diameter portion 32a. The first fuel chamber 35 and the second fuel chamber 36 are in communication with each other via a fuel passage 37 provided in the valve body 32. The inlet side of the fuel passage 37 communicates with the first fuel chamber 35, and the outlet side thereof It leads to the second fuel chamber 36. The valve body 32 is displaced to the valve opening position in response to energization to the electromagnetic drive unit 38 composed of a solenoid or the like.

  In the first injection valve 21 configured as described above, gas fuel is supplied from a regulator 43 described later to the first fuel chamber 35, and the gas fuel is also introduced into the second fuel chamber 36 via the fuel passage 37. As shown in FIG. 2B, when the valve body 32 is displaced to the valve opening position against the biasing force of the spring 33 as the electromagnetic drive unit 38 is energized, the nozzle hole 34 is opened, and the gas is discharged. Fuel is injected.

  In the first injection valve 21, the valve body 32 is provided with a small-diameter portion 32 a on the distal end side thereof, so that the pressure receiving area on the first fuel chamber 35 side and the pressure receiving side on the second fuel chamber 36 side in the valve-closed state. The area is “pressure receiving area on the first fuel chamber 35 side> pressure receiving area on the second fuel chamber 36 side” (see FIG. 2A). Therefore, in the valve closing state shown in FIG. 2A, the pressure of the gas fuel supplied from the regulator 43 side (corresponding to the injection pressure) is in the direction in which the valve body 32 is closed (valve closing direction). It comes to act more greatly. 2B, the injection pressure also acts on the end face (the lower end face in the figure) of the small-diameter portion 32a, so that the fuel pressure in the valve closing direction acting on the valve body 32 and the valve opening direction are also applied. The fuel pressure is almost the same.

  Next, returning to the description of FIG. 1, the configuration of the gas fuel supply unit 40 that supplies the gas fuel to the first injection valve 21 and the liquid fuel supply unit 70 that supplies the liquid fuel to the second injection valve 22. Will be described.

  In the gas fuel supply unit 40, a gas tank 42 is connected to the first injection valve 21 via a gas pipe 41, and the pressure of the gas fuel supplied to the first injection valve 21 is in the middle of the gas pipe 41. There is provided a regulator 43 having a pressure adjusting function for adjusting the pressure under pressure. The regulator 43 (a pressure reducing unit 60, which will be described in detail later) is configured to use a predetermined set pressure (for example, 0) as the injection pressure of the first injection valve 21 for gas fuel stored in the gas tank 42 in a high pressure state (for example, a maximum of 20 MPa). .2 to 1.0 MPa), and the gas fuel after the pressure reduction adjustment is supplied to the first injection valve 21 through the gas pipe 41. In the gas pipe 41, the upstream side of the regulator 43 is a high-pressure pipe portion 41a that forms a high-pressure side passage, and the downstream side is a low-pressure pipe portion 41b that forms a low-pressure side passage.

  Further, a gas fuel passage formed by the gas pipe 41 and the like further includes a tank main stop valve 44 (tank outlet valve) disposed in the vicinity of the fuel outlet of the gas tank 42 and a downstream side of the tank main stop valve 44. And a shutoff valve 45 disposed in the vicinity of the fuel inlet of the regulator 43. The valves 44, 45 allow and shut off the flow of gas fuel in the gas pipe 41. Yes. Both the tank main stop valve 44 and the shut-off valve 45 are electromagnetic on-off valves, and are normally closed so that the flow of gas fuel is cut off when not energized and the flow of gas fuel is allowed when energized.

  In the gas piping 41, a pressure sensor 46 for detecting the fuel pressure and a temperature sensor 47 for detecting the fuel temperature are provided in the high pressure piping portion 41a, and a pressure sensor 48 for detecting the fuel pressure in the low pressure piping portion 41b. A temperature sensor 49 for detecting the fuel temperature is provided.

  The shut-off valve 45 and the pressure sensor 46 can be provided integrally with the regulator 43. In this embodiment, a configuration in which the shut-off valve 45 and the pressure sensor 46 are provided integrally with the regulator 43 is adopted. (Details will be described later in FIG. 3).

  Here, a specific configuration of the regulator 43 will be described with reference to FIG. The regulator 43 constitutes a mechanical pressure adjusting device that adjusts the fuel pressure in the low-pressure pipe portion 41b with respect to a mechanically determined set pressure.

  In FIG. 3, the regulator 43 has a high-pressure passage 51 connected to the high-pressure piping portion 41a (that is, the gas tank 42 side) and a low-pressure passage 52 connected to the low-pressure piping portion 41b (that is, the first injection valve 21 side). In the high-pressure passage 51, a shut-off valve 45 and a pressure sensor 46 are provided. The pressure sensor 46 detects the pressure of the gas fuel upstream of the shutoff valve 45. Reference numeral 53 is a filter for removing foreign matter.

  The configuration of the shut-off valve 45 is substantially the same as the configuration of the first injection valve 21, and has a self-seal (self-sealing) structure. The configuration will be briefly described. The shut-off valve 45 has a valve body 55 biased in the valve closing direction by a spring 54, and the valve body 55 is closed against the biasing force of the spring 54 by energizing the electromagnetic drive unit 56. The valve is displaced from the position to the valve opening position. A first fuel chamber 57 is provided on the rear end side (upstream side) of the valve body 55, and a second fuel chamber 58 is provided on the distal end side (downstream side where the small diameter portion is provided) of the valve body 55. Yes. Both the fuel chambers 57 and 58 are communicated with each other through a fuel passage 59 provided in the valve body 55. In this case, high-pressure gas fuel is supplied to both the fuel chambers 57 and 58 from the gas tank 42, and in the closed state of the shutoff valve 45, a closing force is applied to the valve body 55 by the fuel pressure on the gas tank 42 side. . When the valve element 55 is displaced to the valve open position against the biasing force of the spring 54 with the energization of the electromagnetic drive unit 56 (as shown), high-pressure gas fuel flows downstream.

  In the regulator 43, a pressure reducing unit 60 is provided on the downstream side of the shutoff valve 45. As a configuration of the decompression unit 60, a valve body chamber 61 is provided in the high-pressure passage 51, and a valve body 62 is accommodated in the valve body chamber 61. The valve body 62 is an opening / closing member that opens and closes the valve seat portion 63 that is an inlet portion of the low pressure passage 52. If the valve body 62 is in the open position, the valve seat portion 63 is opened and the high pressure passage 51, the low pressure passage 52, Is communicated. If the valve body 62 is in the closed position, the valve seat 63 is closed and the communication between the high pressure passage 51 and the low pressure passage 52 is blocked.

  The valve body 62 is opened and closed according to the fuel pressure (corresponding to the injection pressure) in the low pressure passage 52 and the force in the valve opening direction generated by the valve body actuating portion 65. The valve element actuating portion 65 is a space that is open to the atmosphere, and has an air opening portion 67 in which an adjustment spring 66 is provided, and a diaphragm as a partition member that partitions the air release portion 67 and the low-pressure passage 52. 68. The diaphragm 68 is provided integrally with the valve body 62. Fuel pressure in the low pressure passage 52 acts on the diaphragm 68 as a force in the valve closing direction, and an urging force of the adjustment spring 66 and atmospheric pressure act as a force in the valve opening direction.

  In such a configuration, if “force in the valve closing direction> force in the valve opening direction” is satisfied, the valve body 62 is held in the valve closing position. On the other hand, when the fuel pressure in the low pressure passage 52 decreases due to fuel injection or the like of the first injection valve 21 and becomes “force in the valve closing direction <force in the valve opening direction”, the valve element 62 opens with the displacement of the diaphragm 68. To be spoken. At this time, the opening position (valve lift amount) of the valve body 62 is determined according to the difference between the force in the valve closing direction and the force in the valve opening direction, and the opening area of the valve seat 63 is changed according to the opening position. As a result, the amount of fuel flowing from the high pressure passage 51 into the low pressure passage 52 is adjusted.

  A branch valve 52a branched from the low pressure passage 52 is provided with a relief valve 69 that vents gas when the fuel pressure in the low pressure passage 52 becomes abnormally high.

  In the present embodiment, in the regulator 43, a decompression unit is configured by the decompression unit 60 including components such as the valve body 62 and the valve body operating unit 65. In the configuration of FIG. 3, the shutoff valve 45, the pressure sensor 46, and the pressure reducing unit 60 are integrally provided in the regulator 43. However, this may be changed. For example, the shutoff valve 45 and the pressure sensor 46 may be connected to the regulator 43. It is also possible to provide in the high-pressure piping part 41a as a separate body.

  Returning to the description of FIG. 1, 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 81, a ROM 82, a RAM 83, a backup RAM 84, an interface 85, and a bidirectional bus 86. The CPU 81, ROM 82, RAM 83, backup RAM 84, and interface 85 are connected to each other by a bidirectional bus 86.

  The CPU 81 executes a routine (program) for controlling the operation of each unit in this system. The ROM 82 stores in advance various data such as a routine executed by the CPU 81, maps (including tables, relational expressions, and the like), parameters, and the like referred to when the routine is executed. The RAM 83 temporarily stores data as necessary when the CPU 81 executes a routine. The backup RAM 84 appropriately stores data under the control of the CPU 81 in a state where the power is turned on, and retains the stored data even after the power is shut off.

  The interface 85 includes sensors (crank angle sensor, air flow meter, cooling water temperature sensor, etc.) provided in the present system, including the throttle opening sensor 15b, the exhaust sensor 18, the pressure sensors 46, 48, and the temperature sensors 47, 49 described above. A vehicle speed sensor or the like), and outputs (detection signals) from these sensors to the CPU 81. The interface 85 is electrically connected to driving units such as the throttle actuator 15a, the ignition device 20a, the injection valves 21 and 22, the tank main stop valve 44, the shutoff valve 45, and the like, and drives these driving units. Therefore, the drive signal sent from the CPU 81 is output toward the drive unit. That is, the control unit 80 acquires an operation state based on the output signals of the above-described sensors, and performs the above-described drive unit control based on the operation state.

  The control unit 80 selectively switches the fuel to be used according to the remaining amount of fuel in the tank, an input signal from a fuel selection switch (not shown), and the like. Specifically, when the remaining amount of gas fuel in the gas tank 42 falls below a predetermined value or when the use of liquid fuel is selected by the fuel selection switch, the liquid fuel is used preferentially, and the fuel tank When the remaining amount of liquid fuel in 72 falls below a predetermined value or when the use of gas fuel is selected by the fuel selection switch, the gas fuel is preferentially used. Further, the control unit 80 switches the fuel used according to the engine operating state. The control unit 80 switches the fuel to be used according to the supply gas pressure to the first injection valve 21 and the engine load.

  By the way, when one of the decompression unit 60 and the shutoff valve 45 is in an abnormal state (a state of abnormal gas fuel leakage), the injection pressure that is the pressure of the gas fuel supplied to the first injection valve 21 is It may be changed in a manner different from normal. In this case, the mode of change in the injection pressure (behavior of the injection pressure) differs depending on which of the decompression unit 60 and the shutoff valve 45 is in an abnormal state. Therefore, in the present embodiment, it is specified whether the cause of the abnormality is due to the decompression unit 60 or the shutoff valve 45 based on the aspect of change in the injection pressure.

  Here, in the decompression unit 60, a fuel leakage abnormality (closed) occurs in which a gap in the valve closed state is generated due to a decrease in sealing performance or foreign matter adhering in the valve seat 63, and gas fuel leaks excessively. It is conceivable that leakage abnormality during valve operation will occur. In this case, when a fuel leakage abnormality occurs in the decompression unit 60, the high-pressure gas fuel existing upstream thereof unintentionally flows out to the downstream side of the decompression unit 60. Therefore, the fuel pressure (the injection pressure that is the supply gas pressure to the first injection valve 21) increases on the downstream side of the decompression unit 60.

  In the decompression unit 60, it is considered that liquefaction occurs due to the decompression action when the gas fuel passes through the valve seat 63, and the liquefied substance adheres to the valve seat 63. In this case, since the oil component is contained in the gas fuel, a highly viscous substance (corresponding to a foreign matter) containing the oil component adheres to the valve seat portion 63, resulting in fuel leakage in the decompression portion 60. . Such inconvenience may occur when a filter is provided on the upstream side of the decompression unit 60.

  Further, it is conceivable that a fuel leakage abnormality (leak abnormality at the time of valve closing) also occurs in the shutoff valve 45. That is, if the sealing performance is insufficient or foreign matter adheres to the valve seat portion, a gap in the closed state is generated, and the gas fuel leaks excessively. In this case, when a fuel leak occurs in the shutoff valve 45, the high-pressure gas fuel existing on the upstream side of the shutoff valve 45 flows unintentionally to the downstream side of the shutoff valve 45. Therefore, the fuel pressure increases on the downstream side of the shutoff valve 45.

  When high-pressure gas fuel upstream of the decompression unit 60 leaks downstream of the decompression unit 60, a difference occurs in the amount of high-pressure gas leaked in the decompression unit 60 depending on whether the shutoff valve 45 is normal or abnormal. Accordingly, a difference occurs in the manner of change in the injection pressure. That is, as shown in FIG. 4, when the fuel passage portion to the cutoff valve 45 is “A” and the fuel passage portion to the gas tank 42 is “B” on the upstream side of the decompression unit 60, the cutoff valve 45 is normal. If so (the valve closing leakage abnormality has not occurred), the injection pressure changes as the high pressure gas in the portion A flows downstream through the pressure reducing unit 60. On the other hand, when the valve closing leakage abnormality has occurred in the shutoff valve 45, the injection pressure changes as the high pressure gas in the B portion flows out to the downstream side via the pressure reducing unit 60. In this case, the change speed and the increase amount of the injection pressure differ depending on whether the shutoff valve 45 is normal or abnormal.

  Even when the shut-off valve 45 is normal, depending on whether the shut-off valve 45 is in a closed state or an open state, a difference occurs in the amount of high-pressure gas leaked in the decompression unit 60, as described above. Along with this, a difference occurs in the manner of change in the injection pressure.

  Incidentally, in the vehicle, the regulator 43 (the pressure reducing portion 60 and the shutoff valve 45) is provided in the front portion of the vehicle, and the gas tank 42 is provided in the rear portion of the vehicle. Therefore, the high-pressure passage portion between the shutoff valve 45 and the gas tank 42 has a relatively long overall length.

The following conditions (1) to (4) are conceivable as conditions for enabling the abnormality determination of the decompression unit 60 and the shutoff valve 45 to be performed.
(1) When the shutoff valve 45 is closed and gas fuel injection is performed (2) When the shutoff valve 45 is closed and gas fuel injection is stopped (3) Shutdown When the valve 45 is opened and the injection of gas fuel is performed (4) When the shutoff valve 45 is opened and the injection of gas fuel is stopped In the present embodiment, the above (1 ) In the case of (2), the second abnormality determination process in the case of (2), the third abnormality determination process in the case of (3), In this case, the fourth abnormality determination process is performed. In each of the above cases, the normal state and the abnormal state will be described with reference to FIG. FIG. 5 is a diagram summarizing changes in the injection pressure during normal operation and abnormal operation in the above (1) to (4).

  In the case of the above (1) (when the shut-off valve 45 is closed and the injection is performed), if both the pressure reducing unit 60 and the shut-off valve 45 are normal, the gas fuel is not newly supplied to the downstream side of the shut-off valve 45. The injection pressure gradually decreases with the injection. In this case, the opening degree of the decompression unit 60 is adjusted according to the decrease in the injection pressure. This operation is the same even if a fuel leakage abnormality occurs in the decompression unit 60.

  On the other hand, when a fuel leakage abnormality has occurred in the shutoff valve 45, high pressure gas fuel is supplied downstream of the shutoff valve 45, so that the injection pressure does not decrease or the rate of decrease in the injection pressure is slow. Become.

  In the case of the above (2) (when the shutoff valve 45 is closed and the injection is stopped), if both the pressure reducing part 60 and the shutoff valve 45 are normal, the passage part from the shutoff valve 45 to the pressure reducing part 60 (A in FIG. 4) The high-pressure gas fuel existing in the gas gradually diffuses to the downstream side of the decompression unit 60 through the minute gap (allowable gap) of the seal part. As a result, the injection pressure gradually increases. At this time, even if there is no fuel leakage abnormality (leak abnormality when the valve is closed) in the decompression unit 60 or the shutoff valve 45, it is considered that a slight fuel leakage (fuel leakage within an allowable range) has occurred. The injection pressure gradually increases due to leakage.

  On the other hand, when the fuel leakage abnormality occurs in the decompression unit 60, the high-pressure gas fuel existing in the passage portion (A in FIG. 4) from the shutoff valve 45 to the decompression unit 60 is downstream of the decompression unit 60. Spills relatively quickly. In this case, the increase amount of the injection pressure is the same as that at the normal time, but the change speed of the injection pressure is faster than that at the normal time.

  In addition, when a fuel leakage abnormality has occurred in the shutoff valve 45, the high-pressure gas fuel existing in the passage portion (B in FIG. 4) from the gas tank 42 to the decompression unit 60 flows out downstream of the decompression unit 60. . In this case, since the pressure reducing unit 60 is normal, the change speed of the injection pressure is substantially the same as that at the normal time, but the increase amount of the injection pressure is larger than that at the normal time.

  In the case of the above (3) (when the shutoff valve 45 = open and injection is performed), if both the pressure reducing part 60 and the shutoff valve 45 are normal, the pressure reducing adjustment in the pressure reducing part 60 functions correctly and the injection pressure is set to a constant value. Pressure is maintained (this corresponds to normal operation).

  On the other hand, when the fuel leakage abnormality occurs in the decompression unit 60, the decompression adjustment does not function correctly, so that the injection pressure changes unintentionally in a predetermined load state (for example, a low load state) of the engine 10. That is, the injection pressure cannot be adjusted and the injection pressure rises in a low flow rate region where the required injection amount decreases in the low rotation / low load region of the engine 10, that is, a region where fuel consumption due to injection decreases.

  In the case of the above (3), since it is assumed that the shutoff valve 45 is opened, fuel leakage abnormality (closing valve leakage abnormality) at the shutoff valve 45 is not subject to abnormality determination. (The same applies to the case of (4) below).

  In the case of the above (4) (when the shutoff valve 45 is open and the injection is stopped), if both the pressure reducing part 60 and the shutoff valve 45 are normal, the passage portion (B in FIG. 4) from the gas tank 42 to the pressure reducing part 60 is provided. The existing high-pressure gas fuel gradually diffuses to the downstream side of the decompression section 60 through a minute gap (allowable gap) in the seal section. As a result, the injection pressure gradually increases. Further, when (4) is normal, the amount of increase in the injection pressure is larger than when (2) is normal.

  On the other hand, when the fuel leakage abnormality occurs in the decompression unit 60, the high-pressure gas fuel existing in the passage portion (B in FIG. 4) from the gas tank 42 to the decompression unit 60 is downstream of the decompression unit 60. It flows out relatively quickly. In this case, the increase amount of the injection pressure is the same as that at the normal time, but the change speed of the injection pressure is faster than that at the normal time.

  Next, the abnormality determination process performed in the control unit 80 will be described. FIG. 6 is a flowchart showing the main routine of the abnormality determination process, and this process is repeatedly performed by the CPU 81 of the control unit 80 at a predetermined cycle.

  In FIG. 6, in step S <b> 11, the regulator upstream pressure that is the fuel pressure upstream of the shutoff valve 45 is calculated, and in subsequent step S <b> 12, the injection pressure that is the downstream fuel pressure of the decompression unit 60 is calculated. The regulator upstream pressure is calculated from the detection value of the pressure sensor 46. The injection pressure is calculated from the detection value of the pressure sensor 48.

  Thereafter, in step S13, it is determined whether or not the regulator upstream pressure is equal to or higher than a predetermined determination value K1. The determination value K1 is a threshold value for determining whether or not the pressure change state is clear when the pressure reducing unit 60 or the shutoff valve 45 is abnormal, and is, for example, 10 MPa. If the regulator upstream pressure is less than the determination value K1, the process proceeds to step S14 to prohibit the abnormality determination, and then this process is terminated.

If the regulator upstream pressure is equal to or higher than the determination value K1, the process proceeds to step S15, and a series of processes relating to abnormality determination of the pressure reducing unit 60 and the shutoff valve 45 are performed. Here, which abnormality determination is to be performed is switched according to the current situation, and each determination of steps S15 to S17 is performed as a situation determination process. In particular,
In step S15, a fuel switching request (gas → liquid switching request or liquid → gas switching request) has occurred, a gas fuel mode start request has occurred, and a gas fuel mode stop has occurred. It is determined whether any of the requests has been established.
In step S16, it is determined whether either the engine is stopped or the liquid fuel mode is established.
In step S17, it is determined whether or not gas fuel is being injected in the gas fuel mode.

  And if step S15 is YES, it will progress to step S18, and it will be determined whether injection pressure is more than the predetermined determination value K2. The determination value K2 is a threshold value for determining whether or not the injection amount is insufficient when the shutoff valve 45 is closed, and is, for example, a set pressure −α of the pressure reducing unit 60. If the injection pressure is less than the determination value K2, the process proceeds to step S14 to prohibit abnormality determination. If the injection pressure is greater than or equal to the determination value K2, the process proceeds to step S19. In step S19, a close command for closing the tank main stop valve 44 is output, and in a subsequent step S20, a close command for closing the shutoff valve 45 is output. Thereafter, in step S21, the fuel injection mode is set to the gas fuel mode. If the gas fuel mode is already set, the current mode is maintained.

  In step S22, a first abnormality determination process is performed. This first abnormality determination process is an abnormality determination process performed in a state where the shut-off valve 45 is closed and gas fuel is being injected (the state (1) above). 7 shows. The process of FIG. 7 corresponds to a first monitoring unit.

  In FIG. 7, in step S31, it is determined whether or not the shut-off valve 45 is currently in a closed state and is in a state of performing gas fuel injection. If YES, the process proceeds to the subsequent step S32. In step S32, a determination value dP1 for determining abnormality of the shutoff valve 45 is set. The determination value dP1 is determined as a value larger than that based on the change speed of the injection pressure at the normal time (a value smaller than that at the normal time in terms of the decrease speed). Thereafter, in step S33, the change speed of the injection pressure within the period in which the first abnormality determination process is performed is calculated (change speed = current value of injection pressure−previous value). In step S34, it is determined whether or not the change speed of the injection pressure is larger than the determination value dP1. That the change rate of the injection pressure is larger than the determination value dP1 means that the decrease rate of the injection pressure is not more than a predetermined value (the decrease is slow). It should be noted that the change rate of the injection pressure> dP1 may be determined over a predetermined period. If the change speed> dP1, the routine proceeds to step S35, where it is determined that an abnormality (fuel leakage abnormality) has occurred in the shutoff valve 45. At this time, the shutoff valve abnormality flag is set.

  In FIG. 6, if step S <b> 16 is YES, the process proceeds to step S <b> 23 to output a close command for closing the tank main stop valve 44, and in a subsequent step S <b> 24, a close command for closing the shutoff valve 45 is output.

  In step S25, a second abnormality determination process is performed. This second abnormality determination process is an abnormality determination process performed in a state where the shutoff valve 45 is closed and the injection of gas fuel is stopped (the state (2) above). It is shown in FIG. The process of FIG. 8 corresponds to a second monitoring unit.

  In FIG. 8, in step S41, it is determined whether or not the shutoff valve 45 is currently in a closed state and in a state where gas fuel injection is stopped. If YES, the process proceeds to subsequent step S42. In step S42, a determination value Pi1 for determining the abnormality of the shutoff valve 45 is set. The determination value Pi1 is determined as a value larger than that in consideration of the increase in the injection pressure during normal operation. In step S43, a determination value dP2 for determining abnormality of the decompression unit 60 is set. The determination value dP2 is determined as a value larger than that on the basis of the normal rising speed.

  Thereafter, in step S44, it is determined whether or not the injection pressure is larger than the determination value Pi1, and if the injection pressure> Pi1, the process proceeds to step S45, and an abnormality (fuel leakage abnormality) has occurred in the shutoff valve 45. Determine. At this time, the shutoff valve abnormality flag is set.

  In step S46, the change speed of the injection pressure within the period in which the second abnormality determination process is performed is calculated (change speed = current value of injection pressure−previous value). In step S47, it is determined whether or not the change speed (increase speed) of the injection pressure is larger than the determination value dP2. If the change speed is greater than dP2, the process proceeds to step S48 and an abnormality (fuel leakage) is detected in the decompression unit 60. It is determined that (abnormal) has occurred. At this time, the decompression unit abnormality flag is set.

  Note that the process of FIG. 8 may be configured such that abnormality determination is performed for only one of the shut-off valve 45 and the pressure reducing unit 60.

  In FIG. 6, if step S17 is YES, the process proceeds to step S26, and the third abnormality determination process is performed. This third abnormality determination process is an abnormality determination process performed in a state where the shut-off valve 45 is opened and gas fuel is being injected (state (3) above). 9 shows. The process of FIG. 9 corresponds to a third monitoring unit.

  In FIG. 9, in step S51, it is determined whether or not the shut-off valve 45 is currently in the open state and the gas fuel is being injected. If YES, the process proceeds to the subsequent step S52. In step S52, a determination value Pi2 for determining abnormality of the decompression unit 60 is set. The determination value Pi2 is determined as a value larger than that in consideration of the increase in the injection pressure during normal operation. At this time, Pi2 is a determination value that is variably set according to the engine load, and a larger value is set as the engine load is smaller.

  Thereafter, in step S53, it is determined whether or not the injection pressure is larger than the determination value Pi2, and if injection pressure> Pi2, the process proceeds to step S54, and abnormality (fuel leakage abnormality) has occurred in the pressure reducing unit 60. Determine. At this time, the decompression unit abnormality flag is set.

  In FIG. 6, if step S17 is NO, the process proceeds to step S27, and the fourth abnormality determination process is performed. If step S17 is NO, it means that the fuel is being cut in the gas fuel mode. The fourth abnormality determination process is an abnormality determination process performed in a state where the shut-off valve 45 is opened and the injection of gas fuel is stopped (the state (4) above). Shown in The process of FIG. 10 corresponds to a fourth monitoring unit.

  In FIG. 10, in step S61, it is determined whether or not the shutoff valve 45 is currently in an open state and in a state where gas fuel injection is stopped. If YES, the process proceeds to the subsequent step S62. In step S62, a determination value dP3 for determining abnormality of the decompression unit 60 is set. The determination value dP3 is determined as a value that is larger than the rate of increase in the injection pressure during normal operation.

  In step S63, the change speed of the injection pressure within the period in which the fourth abnormality determination process is performed is calculated (change speed = current value of injection pressure−previous value). Then, in step S64, it is determined whether or not the change speed (increase speed) of the injection pressure is larger than the determination value dP3. If the change speed> dP3, the process proceeds to step S65, and an abnormality (fuel leakage) is detected in the decompression unit 60. It is determined that (abnormal) has occurred. At this time, the decompression unit abnormality flag is set.

  Next, post-determination processing performed after abnormality determination by the above-described abnormality determination processing will be described. FIG. 11 is a flowchart showing post-determination processing related to the shutoff valve abnormality, and this processing is repeatedly performed by the CPU 81 of the control unit 80 at a predetermined cycle. In this process, the regulator upstream pressure is decreased to suppress an excessive increase in the injection pressure caused by the high regulator upstream pressure after the abnormality of the shutoff valve 45 is determined.

  In FIG. 11, it is determined in step S71 whether or not a shutoff valve abnormality flag is set, and in subsequent step S72, it is determined whether or not the engine is not stopped. And if both step S71 and S72 are YES, it will progress to step S73 and will command injection of gas fuel. In the subsequent step S74, a close command for closing the tank main stop valve 44 is output, and in a subsequent step S75, an open command for opening the shutoff valve 45 is output.

  Thereafter, in step S76, it is determined whether or not the regulator upstream pressure is smaller than a predetermined determination value Pr1. This determination value Pr1 is a reference value for reducing the regulator upstream pressure to such an extent that an excessive increase in the injection pressure does not occur when an abnormality occurs in the shutoff valve 45. If the regulator upstream pressure is smaller than Pr1, a close command for closing the shutoff valve 45 is output in step S77, and the injection of gas fuel is stopped in the subsequent step S78. Note that after the shutoff valve 45 is opened (after step S75 is performed), the change in the regulator upstream pressure is monitored in that state, and the regulator upstream pressure is reduced to the determination value Pr1 in the shutoff valve 45 = open state. Then, the shutoff valve 45 is closed (step S77).

  FIG. 12 is a flowchart showing post-determination processing related to the decompression unit abnormality, and this processing is repeatedly performed by the CPU 81 of the control unit 80 at a predetermined cycle. In this process, after the abnormality of the decompression unit 60 is determined, the fuel gas is injected with the shut-off valve 45 closed to reduce the injection pressure to a predetermined level.

  In FIG. 12, in step S81, it is determined whether or not the decompression unit abnormality flag is set, and in subsequent step S82, it is determined whether or not the engine is not stopped. Note that the fact that the decompression unit abnormality flag is set means that an abnormality of the decompression unit 60 has been provisionally determined. And if both step S81 and S82 are YES, it will progress to step S83 and will command injection of gas fuel. In a succeeding step S84, a close command for closing the tank main stop valve 44 is outputted, and in a succeeding step S85, a close command for closing the shutoff valve 45 is outputted.

  Thereafter, in step S86, it is determined whether or not the injection pressure is smaller than a predetermined determination value Pi3. This determination value Pi3 is a reference value for reducing the injection pressure to an allowable level when an abnormality occurs in the decompression unit 60. If the injection pressure is smaller than Pi3, the process proceeds to step S87, and it is determined whether or not the temporary determination of abnormality in the pressure reducing unit has been performed a predetermined number of times.

  If the provisional determination has not been performed a predetermined number of times, the process proceeds to step S88 and returns to the normal control. Further, if the provisional determination has been performed a predetermined number of times, the process proceeds to step S89, and the main determination of the decompression unit abnormality is performed. When this determination is performed, the driver is notified of this by a lamp display or a message display. In the subsequent step S90, the injection of gas fuel is stopped.

  Next, the operation of each abnormality determination process described above will be described more specifically. FIG. 13 is a time chart for explaining the operation related to the first abnormality determination process, and assumes a case where an abnormality (fuel leakage abnormality) has occurred in the shut-off valve 45. In FIG. 13, a timing t1 indicates a timing at which an engine start request with gas fuel is generated. Before the timing t1, the tank main stop valve 44 and the shutoff valve 45 are both closed.

  Now, at timing t1, the engine start request is generated by the gas fuel, and the injection of the gas fuel is started. In this example, at the timing t1, the regulator upstream pressure is K1 or more. At timing t1, the shut-off valve 45 is in the closed state and the gas fuel is being injected, and the first abnormality determination process is performed in this state.

  Here, the drop of the injection pressure is slow due to the abnormality of the shutoff valve 45 (abnormality of fuel leakage), and the change speed of the injection pressure is larger than dP1 (in other words, the drop speed of the injection pressure is below a predetermined value). ). Timing t1 to t2 is a determination period for determining the change speed of the injection pressure> dP1. At timing t2, the cutoff valve abnormality flag is set and the cutoff valve 45 is opened. As the shutoff valve 45 is opened while the tank main stop valve 44 is closed, the regulator upstream pressure starts to decrease and the injection pressure starts to increase.

  Thereafter, at timing t3, the regulator upstream pressure is reduced to Pr1, and the shutoff valve 45 is closed. Also, liquid fuel injection is started instead of gas fuel injection. After timing t3, since the regulator upstream pressure has decreased to Pr1, an excessive increase in the injection pressure is suppressed. In this example, Pr1 = the set pressure of the decompression unit 60, and the injection pressure is held constant after timing t3.

  FIG. 14 is a time chart for explaining the operation related to the second abnormality determination process, and assumes a case where an abnormality (fuel leakage abnormality) occurs in the shutoff valve 45. In FIG. 14, the liquid fuel mode is in the initial period, the injection of gas fuel is stopped, and the tank main stop valve 44 and the shutoff valve 45 are both closed. In such a state, the second abnormality determination process is performed. Note that the regulator upstream pressure is K1 or more.

  Now, after timing t11, the injection pressure rises due to an abnormality of the shutoff valve 45 (abnormal fuel leakage), and at timing t12, the injection pressure rises to Pi1. At timing t12, the shut-off valve abnormality flag is set, and gas fuel injection is started instead of liquid fuel injection. As a result, the regulator upstream pressure starts to decrease, and the injection pressure changes from increasing to decreasing. After timing t12, the shutoff valve 45 is opened. In FIG. 14, it is assumed that the shutoff valve is abnormal and the pressure reducing unit is normal, and the change rate of the injection pressure after timing t11 is smaller than dP2.

  Thereafter, at timing t13, the regulator upstream pressure decreases to Pr1, and the shutoff valve 45 is closed. Also, liquid fuel injection is started instead of gas fuel injection. After timing t13, since the regulator upstream pressure has decreased to Pr1, the excessive increase in the injection pressure is suppressed.

  FIG. 15 is a time chart for explaining the operation relating to the second abnormality determination process, and assumes a case where an abnormality (fuel leakage abnormality) occurs in the decompression unit 60. In FIG. 15, the liquid fuel mode is in the initial period, the injection of gas fuel is stopped, and the tank main stop valve 44 and the shutoff valve 45 are both closed. In such a state, the second abnormality determination process is performed. Note that the regulator upstream pressure is K1 or more.

  After timing t21 when the abnormality of the decompression unit 60 (fuel leakage abnormality) occurs, the injection pressure rises and changes relatively quickly, and the change speed of the injection pressure is greater than dP2. Timing t21 to t22 is a determination period for determining the change speed of the injection pressure> dP2. At timing t22, the decompression unit abnormality flag is set, and gas fuel injection is started instead of liquid fuel injection. At this time, as the fuel gas is injected with the tank main stop valve 44 and the shutoff valve 45 closed, the injection pressure changes from increasing to decreasing. In FIG. 15, it is assumed that the shut-off valve is normal and the pressure reducing unit is abnormal, and it is determined that the change speed> dP2 before the injection pressure increases to Pi1 after timing t21.

  Thereafter, at timing t23, the injection pressure is reduced to Pi3, and liquid fuel injection is started instead of gas fuel injection. In this example, the number of provisional determinations has not reached the predetermined number, and after timing t23, the normal control in the liquid fuel mode is restored. After timing t23, the state of injection pressure = Pi3 is maintained.

  FIG. 16 is a time chart for explaining the operation related to the third abnormality determination process, and assumes a case where an abnormality (fuel leakage abnormality) occurs in the decompression unit 60. In FIG. 16, the gas fuel mode is in the initial period, the gas fuel is being injected, and the tank main stop valve 44 and the shutoff valve 45 are both opened. Then, the third abnormality determination process is performed under such a state. Note that the regulator upstream pressure is K1 or more.

  Now, after timing t31, the injection pressure rises due to an abnormality in the pressure reducing unit 60 (abnormal fuel leakage), and at timing t32, the injection pressure rises to Pi2. At timing t32, the decompression unit abnormality flag is set, and both the tank main stop valve 44 and the shutoff valve 45 are closed. In this case, as the fuel gas is injected while the tank main stop valve 44 and the shutoff valve 45 are closed, the injection pressure changes from increasing to decreasing.

  Thereafter, at timing t33, the injection pressure is reduced to Pi3, and the normal control in the gas fuel mode is restored. As a result, the tank main stop valve 44 and the shutoff valve 45 are returned to the open state (returned to the same state as the timing t31). Then, when the injection pressure rises again due to the abnormality of the decompression unit 60 (fuel leakage abnormality) and the injection pressure rises to Pi2 at timing t34, the decompression unit abnormality flag is set again. At this time, if the number of abnormality determinations has reached a predetermined number, the main determination of abnormality in the decompression unit is performed. Then, both the tank main stop valve 44 and the shut-off valve 45 are closed again, and the injection pressure decreases accordingly.

  After the main determination of the decompression unit abnormality is made, at the timing t35 when the injection pressure is reduced to Pi3, the injection of the gas fuel is stopped and the injection of the liquid fuel is started instead.

  FIG. 17 is a time chart for explaining the operation related to the fourth abnormality determination process, and assumes a case where an abnormality (fuel leakage abnormality) occurs in the decompression unit 60. In FIG. 17, at timing t41, fuel cut is started in the gas fuel mode, and the fuel injection is temporarily stopped while both the tank main stop valve 44 and the shutoff valve 45 are opened. Then, the fourth abnormality determination process is performed under such a state. Note that the regulator upstream pressure is K1 or more.

  After timing t41 when the pressure reducing unit 60 is abnormal (fuel leakage abnormality), the injection pressure rises and changes relatively quickly, and the change speed of the injection pressure is greater than dP3. Timings t41 to t42 are determination periods for determining the change speed of the injection pressure> dP3. At timing t42, the decompression unit abnormality flag is set and a small amount of gas fuel is injected. The injection amount of the gas fuel here may be an amount sufficient to cause a decrease in the injection pressure. At this time, as the fuel gas is injected with the tank main stop valve 44 and the shutoff valve 45 closed, the injection pressure changes from increasing to decreasing.

  Thereafter, at timing t43, the injection pressure is reduced to Pi3, and the normal control in the gas fuel mode (in this case, the normal fuel cut state) is restored. Thereby, the tank main stop valve 44 and the shut-off valve 45 are returned to the open state (returned to the same state as the timing t41). Then, when the injection pressure rises again due to the abnormality of the pressure reducing unit 60 (fuel leakage abnormality) and it is determined at timing t44 that the changing speed of the injection pressure> dP3, the pressure reducing unit abnormality flag is set again. At this time, if the number of abnormality determinations has reached a predetermined number, the main determination of abnormality in the decompression unit is performed. Then, both the tank main stop valve 44 and the shut-off valve 45 are closed again, and the injection pressure decreases accordingly.

  At the timing t45 when the injection pressure has decreased to Pi3 after the main determination of the decompression unit abnormality is made, the injection of the gas fuel is stopped and the injection of the liquid fuel is started instead.

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

  When an abnormality occurs in the gas fuel supply system, it is determined whether the cause of the abnormality is due to an abnormal fuel leak at the decompression unit 60 or an abnormal fuel leak at the shutoff valve 45 based on the mode of change in the injection pressure. I did it. As a result, the presence or absence of fuel leakage abnormality can be properly determined for the decompression unit 60 and the shutoff valve 45 provided in the gas fuel supply system. Therefore, it is possible to suppress inconveniences such as an excessive increase in the injection pressure and an adverse effect on the fuel injection in the first injection valve 21 due to this.

  Whether the decompression unit 60 or the shut-off valve 45 is abnormal is determined according to whether the first injection valve 21 is in an injection execution state or an injection stop state, and whether the shut-off valve 45 is in a closed state or an open state. The standard value (judgment value) for abnormality determination is variably set. In this case, the reference value for the abnormality determination is individually set according to which of the first to fourth abnormality determination processes is performed. Thereby, an appropriate abnormality determination can be implemented according to each situation.

  For example, in both the third abnormality determination process and the fourth abnormality determination process, the shutoff valve 45 is in the open state, and the difference is whether the injection of gas fuel is being performed or stopped. In this case, the criterion (determination value) for abnormality determination is changed according to whether or not fuel injection is performed. Thereby, abnormality of the pressure reduction part 60 can be determined appropriately.

  According to the first abnormality determination process (FIG. 7), when the gas fuel is injected with the shut-off valve 45 closed, based on the rate of decrease in the injection pressure during the fuel injection period, Abnormal fuel leakage of the shut-off valve 45 can be suitably determined.

  According to the second abnormality determination process (FIG. 8), when the injection of gas fuel is stopped with the shut-off valve 45 closed, the injection pressure that has increased and changed within the stop period of the fuel injection, and the stop period On the basis of the rising speed of the injection pressure in the engine, it is possible to suitably determine the fuel leakage abnormality in the shutoff valve 45 and the fuel leakage abnormality in the decompression unit 60.

  According to the third abnormality determination process (FIG. 9), when the gas fuel is injected with the shut-off valve 45 opened, based on the injection pressure that has risen and changed during the fuel injection period, A fuel leakage abnormality in the decompression unit 60 can be suitably determined.

  According to the fourth abnormality determination process (FIG. 10), when the gas fuel injection is stopped with the shut-off valve 45 being opened, based on the rate of increase of the injection pressure within the fuel injection stop period, A fuel leakage abnormality in the decompression unit 60 can be suitably determined.

  As the post-judgment post-determination process (FIG. 12), the gas fuel is injected with the shut-off valve 45 closed to reduce the injection pressure. After the injection pressure is reduced, the cause of the occurrence of the abnormality The determination was made again. When a leakage abnormality occurs in the decompression unit 60, the same abnormality determination can be repeatedly performed after the occurrence of the abnormality is temporarily determined (after provisional determination), if the injection pressure is reduced. In this case, the provisional determination can be canceled if the abnormality in the decompression unit 60 is resolved, and the main determination can be performed with high accuracy if the abnormality in the decompression unit 60 is not resolved.

  As a post-judgment post-determination process (FIG. 12), the gas fuel is injected with the shut-off valve 45 closed to reduce the injection pressure. After the injection pressure is reduced, the gas fuel is injected. Was stopped (the gas fuel mode was terminated). Thereby, it can suppress that an injection pressure rises excessively while the injection of gas fuel stops.

  As a post-determination process (FIG. 11) for the shut-off valve abnormality, gas fuel injection is performed with the tank main stop valve 44 closed and the shut-off valve 45 open, and the regulator upstream pressure (fuel pressure in the high-pressure passage) is set. After the reduction of the regulator upstream pressure, the gas fuel injection is stopped (the gas fuel mode is terminated). Thereby, it can suppress that an injection pressure rises excessively while the injection of gas fuel stops. When a leakage abnormality occurs in the shutoff valve 45, the gas fuel upstream of the shutoff valve 45 tends to flow downstream. Therefore, in order to suppress an excessive increase in the injection pressure, it is effective to lower the regulator upstream pressure.

  When it is determined that the regulator upstream pressure is equal to or higher than K1, the cause of the abnormality is determined based on the mode of change in the injection pressure. If the regulator upstream pressure is low, the difference in the mode of change in the injection pressure when an abnormality occurs becomes small, making it difficult to determine abnormality. In this respect, since the abnormality determination is performed on the condition that the regulator upstream pressure is high, the accuracy of the abnormality determination can be improved.

(Other embodiments)
You may change the said embodiment as follows, for example.

  -It is good also as a structure which sets each determination value for abnormality determination variably in the 1st-4th abnormality determination process. For example, each of these determination values is set based on the regulator upstream pressure. The change (behavior) of the injection pressure is considered to change depending on the regulator upstream pressure. Therefore, if each determination value is set based on the regulator upstream pressure, a more appropriate abnormality determination can be performed.

  It is possible to estimate the remaining fuel amount in the gas tank 42 based on the regulator upstream pressure. In such a case, the estimation of the remaining amount of fuel may be stopped during the period in which the tank main stop valve 44 is closed and the gas fuel is injected. That is, in the post-determination process (FIGS. 11 and 12) that is performed after the shut-off valve abnormality or the decompression unit abnormality is determined, the gas fuel is injected with the tank main stop valve 44 closed. In this case, the estimation of the remaining amount of fuel based on the regulator upstream pressure is stopped.

  As each injection valve 21, 22, an opening adjustment type injection valve whose valve opening (opening opening area) is adjusted continuously or in multiple stages by electrically driving an electromagnetic drive unit (not shown). In this case, the valve opening is adjusted by a duty signal input from the control unit 80. At this time, the fuel flow rate per unit time is adjusted according to the valve opening degree of each injection valve 21, 22, and the fuel (gas fuel, liquid fuel) whose flow rate is adjusted is supplied to the intake port of each cylinder.

  In the above embodiment, the injection valves 21 and 22 are provided for each cylinder of the multi-cylinder engine. However, the injection valves 21 and 22 may be provided in common for a plurality of cylinders. . For example, a configuration in which gas fuel or liquid fuel is injected into a collection portion of the intake system 11 may be employed.

  In the above embodiment, the present invention is embodied in a bi-fuel engine that uses gas fuel (CNG) and liquid fuel (gasoline) as combustion fuel. However, this is changed to a gas that uses only gas fuel. It is also possible to embody the present invention with an engine.

  In the above embodiment, the CNG fuel is used as the gas fuel, but other gas fuels that are gas in the standard state can be used, for example, methane, ethane, propane, butane, hydrogen, DME, etc. as the main component. A configuration using fuel may also be used. Further, the liquid fuel is not limited to gasoline fuel, and for example, light oil or the like may be used.

  DESCRIPTION OF SYMBOLS 10 ... Engine (internal combustion engine), 21 ... 1st injection valve (gas fuel injection means), 41 ... Gas piping (fuel passage), 41a ... High pressure piping part (high pressure passage part), 42 ... Gas tank, 45 ... Shut-off valve, 51 ... High pressure passage (high pressure passage portion), 60 ... Pressure reducing portion (pressure reducing means), 80 ... Control portion (fuel injection control device, monitoring means, abnormality determining means).

Claims (14)

A gas tank (42) for storing gaseous fuel in a high pressure state;
Gas fuel injection means (21) for injecting gas fuel supplied from the gas tank through the fuel passage (41);
A pressure reducing means (60) provided in the fuel passage, for reducing the pressure of the gas fuel supplied to the gas fuel injection means;
A shutoff valve (45) provided on the upstream side of the decompression means in the fuel passage and having a shutoff function for shutting off the flow of gas fuel;
A fuel injection control device for an internal combustion engine applied to a fuel injection system comprising:
Monitoring means for monitoring the mode of change in the injection pressure, which is the pressure of the gas fuel supplied to the gas fuel injection means;
When an abnormality occurs in the gas fuel supply system, based on the change in the injection pressure monitored by the monitoring means, whether the cause of the abnormality is due to abnormal gas fuel leakage in the pressure reducing means or the gas in the shutoff valve An abnormality determining means for determining whether the fuel leak is abnormal,
A fuel injection control device for an internal combustion engine, comprising: When the fuel injection by the gas fuel injection means is performed with the shut-off valve closed, the monitoring means calculates the rate of decrease in the injection pressure during the fuel injection period. Have
2. The internal combustion engine according to claim 1, wherein the abnormality determination unit determines that a leakage abnormality has occurred in the shut-off valve when a rate of decrease in the injection pressure calculated by the first monitoring unit is equal to or less than a predetermined value. Fuel injection control device. In addition to the gas fuel injection means, the present invention is applied to a fuel injection system including a liquid fuel injection means (22) for injecting liquid fuel. Gas fuel injection by the gas fuel injection means and liquid fuel injection by the liquid fuel injection means A fuel injection control device for an internal combustion engine that is implemented by switching between
When a request for switching between an operation state using the gas fuel and an operation state using the liquid fuel occurs, a request for starting the internal combustion engine using the gas fuel occurs, a fuel injection state using the gas fuel In any of the cases where a request to stop the internal combustion engine occurs, a means for outputting a close command to the shut-off valve and performing fuel injection by the gas fuel injection means,
The said 1st monitoring means outputs the closing instruction | command to the said shut-off valve, and calculates the fall speed of the said injection pressure under the state which is implementing the fuel injection by the said gas fuel injection means. A fuel injection control device for an internal combustion engine as described. When the fuel injection by the gas fuel injection means is stopped in a state where the shutoff valve is closed, the monitoring means increases the injection pressure within the fuel injection stop period and the fuel injection within the stop period. A second monitoring means for calculating at least one of the rising speeds of the injection pressure;
The abnormality determining means determines that a leakage abnormality has occurred in the shutoff valve when the injection pressure after the increase change calculated by the second monitoring means is greater than or equal to a predetermined value, and the second monitoring means 4. The fuel injection control device for an internal combustion engine according to claim 1, wherein when the calculated increase rate of the injection pressure is equal to or higher than a predetermined value, it is determined that a leakage abnormality has occurred in the pressure reducing means. 5. In addition to the gas fuel injection means, the present invention is applied to a fuel injection system including a liquid fuel injection means (22) for injecting liquid fuel. Gas fuel injection by the gas fuel injection means and liquid fuel injection by the liquid fuel injection means A fuel injection control device for an internal combustion engine that is implemented by switching between
The second monitoring means calculates an injection pressure after the rise change and an increase speed of the injection pressure in an operation state in which liquid fuel is injected by the liquid fuel injection means or in an operation stop state of the internal combustion engine. The fuel injection control device for an internal combustion engine according to claim 4, wherein The monitoring means, when performing fuel injection by the gas fuel injection means with the shut-off valve open, calculates the injection pressure that has risen and changed during the fuel injection execution period. Have
6. The abnormality determination unit according to claim 1, wherein the abnormality determination unit determines that a leakage abnormality has occurred in the pressure reduction unit when an injection pressure after the increase change calculated by the third monitoring unit is equal to or greater than a predetermined value. A fuel injection control device for an internal combustion engine according to claim 1.   The third monitoring means calculates an injection pressure after the increase change when an operation state of the internal combustion engine is an operation state in which gas fuel is injected by the gas fuel injection means. 6. A fuel injection control device for an internal combustion engine according to claim 6. The monitoring means, when the fuel injection by the gas fuel injection means is stopped with the shut-off valve being open, calculates the rate of increase of the injection pressure within the stop period of the fuel injection. Have
8. The abnormality determination unit according to claim 1, wherein the abnormality determination unit determines that a leakage abnormality has occurred in the decompression unit when the rate of increase of the injection pressure calculated by the fourth monitoring unit is equal to or greater than a predetermined value. A fuel injection control device for an internal combustion engine according to the item. Fuel cutting means for temporarily stopping fuel injection in an operating state in which gas fuel is injected by the gas fuel injection means;
9. The fuel injection control device for an internal combustion engine according to claim 8, wherein the fourth monitoring unit calculates an increase rate of the injection pressure in a state where fuel injection is stopped by the fuel cut unit.   The abnormality determining means is configured to determine whether the pressure reducing means and the cutoff are in accordance with whether the gas fuel injection means is in a fuel injection state or an injection stop state, and whether the cutoff valve is in a closed state or an open state. The fuel injection control device for an internal combustion engine according to any one of claims 1 to 9, wherein which of the valves is to be subjected to abnormality determination is selected, and a reference value for abnormality determination is variably set. When it is determined by the abnormality determining means that a leakage abnormality has occurred in the pressure reducing means, the fuel injection by the gas fuel injection means is performed with the shutoff valve closed to reduce the injection pressure. A first decompression control means;
The internal combustion engine according to any one of claims 1 to 10, wherein the abnormality determination unit performs the determination of the cause of the abnormality again after the injection pressure is reduced by the first pressure reduction control unit. Fuel injection control device. When it is determined by the abnormality determining means that a leakage abnormality has occurred in the pressure reducing means, the fuel injection by the gas fuel injection means is performed with the shutoff valve closed to reduce the injection pressure. First decompression control means;
Means for stopping fuel injection by the gas fuel injection means after the injection pressure is reduced by the first pressure reduction control means;
The fuel injection control device for an internal combustion engine according to any one of claims 1 to 11, further comprising: Applied to a fuel injection system provided with a tank outlet valve (44) provided in the vicinity of the fuel outlet of the gas tank and having a shut-off function for shutting off the flow of gas fuel;
When it is determined by the abnormality determining means that a leakage abnormality has occurred in the shutoff valve, fuel injection by the gas fuel injection means is performed with the tank outlet valve closed and the shutoff valve open. Second pressure reduction control means for lowering the fuel pressure in the high pressure passage (41a, 51) between the gas tank and the pressure reduction means,
Means for stopping fuel injection by the gas fuel injection means after the fuel pressure in the high pressure passage is reduced by the second pressure reduction control means;
A fuel injection control device for an internal combustion engine according to any one of claims 1 to 12. Pressure determining means for determining that the fuel pressure in the high pressure passage (41a, 51) between the gas tank and the pressure reducing means is equal to or greater than a predetermined value;
The abnormality determination means determines a factor of occurrence of an abnormality based on a mode of change in the injection pressure when the pressure determination means determines that the fuel pressure in the high pressure passage portion is equal to or higher than a predetermined value. Item 14. The fuel injection control device for an internal combustion engine according to any one of Items 1 to 13.

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