Abstract:
Provided is a shut-off valve fault diagnosis device that performs fault diagnosis on a shut-off valve having a first valve element which is opened first when the power is turned on, and a second valve element which is opened by the drop in differential pressure between upstream and downstream after the valve has been opened. The device is provided with a diagnosis processing unit that infers the open/close state of the first and second valve elements from the time variation characteristics of the downstream pressure of the valve being diagnosed, and performs fault diagnosis on the valve being diagnosed from the actual measurements of downstream pressure, on the basis of the inference results.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a U.S. national stage of application No. PCT/JP2011/050037, filed on 5 Jan. 2011. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2010-062674, filed 18 Mar. 2010, the disclosure of which are also incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a shut-off valve fault diagnosis device. 
       BACKGROUND ART 
       [0003]    In recent years, as a technology for improving fuel efficiency and the environmental protection performance of a vehicle, introduction of a bi-fuel engine system, which selectively switches between a liquid fuel, such as gasoline, and a gaseous fuel, such as compressed natural gas (CNG) and supplies the fuels to a single engine, has progressed. Generally, in this bi-fuel engine system, in the case of using the gaseous fuel, the highly pressurized gaseous fuel that is filled in a gas tank is decompressed to a predetermined pressure by a regulator and is supplied to a fuel injection valve that is dedicated to the gaseous fuel. 
         [0004]    An electromagnetic type shut-off valve is inserted in a fuel supply path ranging from the gas tank to the regulator, initiation and stop of the gaseous fuel supply may be switched by controlling the open and shut states of the shut-off valve using a control device. A shut-off valve fault may have a significant adverse effect on the entirety of a system, such that various technologies for diagnosing shut-off valve faults have been developed in the related art. For example, PTL 1 discloses a technology in which a shut-off valve downstream pressure at the point in time of switching the shut-off valve from a shut valve state to an open valve state, and a shut-off valve downstream pressure after passage of a predetermined time from that point in time are measured, and the fault diagnosis of the shut-off valve is performed based on a pressure rising rate obtained from both of the pressures. 
       CITATION LIST 
     Patent Literature 
       [0005]    [PTL 1] Japanese Unexamined Patent Application Publication No. 2000-282956 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    A kick pilot structure shown in  FIG. 7  is known as a structure of the shut-off valve. In the shut-off valve having this kick pilot structure, while power is not supplied, a plunger  101  is pressed by a spring  102 , and a pilot valve  103  that is integrally provided in the plunger  101  comes into contact with a pilot valve seat  105  that is provided in a main valve  104 . That is, while power is not supplied, both of the pilot valve  103  and the main valve  104  enter a shut valve state, and thus flow of the gaseous fuel from an upstream (gas tank side) flow path  106  to a downstream (regulator side) flow path  107  is blocked (refer to  FIG. 7(   a )). 
         [0007]    On the other hand, when a suction force stronger than a repulsive force of the spring  102  acts on the plunger  101  due to power supply to the shut-off valve, the pilot valve  103  becomes separated (that is opened) from the pilot valve seat  105  due to movement of the plunger  101  by the suction force, and gaseous fuel starts to flow from the upstream flow path  106  to the downstream flow path  107  (refer to  FIG. 7(   b )). At this point in time, since the differential pressure between the upstream flow path  106  and the downstream flow path  107  is still large, the main valve  104  is kept in a shut valve state (the movement of the plunger  101  is stopped). 
         [0008]    In addition, after the pilot valve  103  is opened, when the differential pressure between the upstream flow path  106  and the downstream flow path  107  becomes small, the plunger  101  again initiates the movement at the point in time when the suction force due to the power supply exceeds the repulsive force. Due to the movement of this plunger  101 , the main valve  104  is opened, and the gaseous fuel starts to flow from the upstream flow path  106  to the downstream flow path  107  with the maximum flow rate (refer to  FIG. 7(   c )). In addition, in a case in which there is no differential pressure between the upstream flow path  106  and the downstream flow path  107  before the pilot valve  103  is opened, the main valve  104  is instantly opened and thus the gaseous fuel flows to the downstream flow path  107 . 
         [0009]    Naturally, it is necessary to perform the fault diagnosis on the shut-off valve having the kick pilot structure, but it is difficult to apply the technology disclosed in PTL 1 on this fault diagnosis. This is because of the following reasons. That is, in the kick pilot structure shut-off valve, a downstream pressure of the shut-off valve increases until the main valve  104  is opened after the pilot valve  103  is opened as described above, such that like PTL 1, in the technology of diagnosing the shut-off valve fault based on the pressure raising rate, only the fault of the pilot valve  103  may be diagnosed and fault diagnosis of the main valve  104  may not be performed. 
         [0010]    The present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide a shut-off valve fault diagnosis device that is capable of appropriately performing the fault diagnosis of the shut-off valve having a so-called kick pilot structure. 
       Solution to Problem 
       [0011]    To solve the above-described problem, according to an embodiment of the present invention, there is provided a shut-off valve fault diagnosis device that performs fault diagnosis of a shut-off valve including a first valve body that is opened in advance during power supply and a second valve body that is opened due to a decrease in a differential pressure between upstream and downstream after the first valve body is opened. The shut-off valve fault diagnosis device includes a diagnosis processing unit that estimates an open and shut state of each of the first and second valve bodies from a time-variable characteristic in a downstream pressure of the shut-off valve, and performs the fault diagnosis of the shut-off valve from an actual measurement value of the downstream pressure based on the estimation result. 
         [0012]    In response to the open and shut state of the first valve body that is opened in advance during power supply and the second valve body that is opened due to a decrease in a differential pressure between upstream and downstream after the first valve body is opened, the time-variable characteristic in the downstream pressure of the shut-off valve having the valve bodies tends to be different in each case. That is, when the open and shut state of each of the first and second valve bodies is estimated in advance from the time-variable characteristic of the downstream pressure of the shut-off valve, the fault diagnosis of the shut-off valve (a so-called shut-off valve of a kick pilot structure) may be appropriately performed from the actual measurement value of the downstream pressure based on the estimation result. 
         [0013]    In addition, in the present invention, the diagnosis processing unit may perform the fault diagnosis of the shut-off valve from the actual measurement value of the downstream pressure based on the estimation result that is different between a case in which the actual measurement value of the downstream pressure is less than or equal to a threshold value before power supply to the shut-off valve (a first case) and a case in which the actual measurement value of the downstream pressure exceeds the threshold value (a second case). 
         [0014]    In the first case (case in which the differential pressure between upstream and downstream of the shut-off valve is large) and the second case (case in which the differential pressure between upstream and downstream of the shut-off valve is small), a corresponding relationship between the time-variable characteristic of the downstream pressure of the shut-off valve and the open and shut state of each of the first and second valve bodies becomes different in each case. Therefore, when the fault diagnosis of the shut-off valve is performed based on the estimation result that is different between the first case and the second case, the fault diagnosis may be performed in an appropriate manner in response to the case. 
         [0015]    In addition, in the present invention, in a case where the actual measurement value of the downstream pressure before the power supply to the shut-off valve is less than or equal to the threshold value (first case), the diagnosis processing unit may determine whether or not the actual measurement value of the downstream pressure exceeds the threshold value after a predetermined time has passed from initiation of the power supply to the shut-off valve, and in a case where it is determined that the actual measurement value does not exceed the threshold value, the diagnosis processing unit may determine that the shut-off valve is in a fault state. 
         [0016]    In the first case, in a case where the actual measurement value of the downstream pressure does not exceed the threshold value after a predetermined time has passed from the initiation of the power supply to the shut-off valve, it is estimated that both of the first valve body and the second valve body are in a shut valve state. That is, in this case, it may be determined that the shut-off valve is in a fault state. 
         [0017]    In addition, in the present invention, in a case where it is determined that the actual measurement value of the downstream pressure exceeds the threshold value after a predetermined time has passed from the initiation of the power supply to the shut-off valve, the diagnosis processing unit may activate a fuel injection valve provided downstream of the shut-off valve, and in a case where the actual measurement value of the downstream pressure becomes less than or equal to the threshold value after the activation of the fuel injection valve, the diagnosis processing unit may determine that the shut-off valve is in a fault state. 
         [0018]    In the first case, in a case where the actual measurement value of the downstream pressure exceeds the threshold value after a predetermined time has passed from the initiation of the power supply to the shut-off valve, it is estimated that at least the first valve body is normally opened. Therefore, consumption of fuel downstream of the shut-off valve is attempted by activating the fuel injection valve. In a case where the actual measurement value of the downstream pressure becomes less than or equal to the threshold value after the activation of this fuel injection valve, since it is considered that fuel supply from upstream is not performed in a timely manner with respect to fuel consumption downstream of the shut-off valve, it is estimated that the second valve body is in a shut valve state. That is, in this case, it may be determined that the shut-off valve is in a fault state. 
         [0019]    In addition, in the present invention, the predetermined time may be set to a time until the downstream pressure becomes a value at which an engine is operable after the first valve body is opened from the initiation of the power supply to the shut-off valve. 
         [0020]    When the predetermined time is set in this manner, the fault of the shut-off valve, which becomes a cause of an open fault in the first valve body, may be detected with high accuracy. 
         [0021]    In addition, in the present invention, in a case where the actual measurement value of the downstream pressure exceeds the threshold value before the power supply to the shut-off valve (second case), the diagnosis processing unit may activate a fuel injection valve provided downstream of the shut-off valve after the initiation of the power supply to the shut-off valve, and in a case where the actual measurement value of the downstream pressure is less than or equal to the threshold value after the activation of the fuel injection valve, the diagnosis processing unit may determine that the shut-off valve is in a fault state. 
         [0022]    In the second case, consumption of fuel downstream of the shut-off valve is attempted by activating the fuel injection valve after the initiation of the power supply to the shut-off valve. In a case where the actual measurement value of the downstream pressure becomes less than or equal to the threshold value after the activation of this fuel injection valve, since it is considered that fuel supply from upstream is not performed in a timely manner with respect to fuel consumption downstream of the shut-off valve, it is estimated that at least the second valve body is in a shut valve state. 
         [0023]    That is, in this case, it may be determined that the shut-off valve is in a fault state. 
       Advantageous Effects of Invention 
       [0024]    According to the present invention, a shut-off valve fault diagnosis device, which is capable of appropriately performing fault diagnosis of a shut-off valve having a so-called kick pilot structure, may be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0025]      FIG. 1  is a schematic configuration diagram of a bi-fuel engine system according to an embodiment. 
           [0026]      FIG. 2  is a block configuration diagram of a 1 st -ECU  5  according to this embodiment. 
           [0027]      FIG. 3  is a block configuration diagram of a 2 nd -ECU  6  (a shut-off valve fault diagnosis device) of this embodiment. 
           [0028]      FIG. 4  is a diagram illustrating a relationship obtained by estimating the open and shut states of a pilot valve  103  and a main valve  104  from a time-variable characteristic in a downstream pressure P of the shut-off valve  41  in a first case. 
           [0029]      FIG. 5  is a diagram illustrating a relationship obtained by estimating the open and shut state of the pilot valve  103  and the main valve  104  from the time-variable characteristic in the downstream pressure P of the shut-off valve  41  in a second case. 
           [0030]      FIG. 6  is a flowchart illustrating a shut-off valve fault diagnosis process that is performed by a CPU  66  so as to realize a shut-off valve fault diagnosis function. 
           [0031]      FIG. 7  is an internal configuration example of a shut-off valve having a kick pilot structure. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0032]    Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. In addition, in the following description, as a shut-off valve fault diagnosis device relating to the present invention, an ECU (Electronic Control Unit), which is used in a bi-fuel engine system that selectively switches between a liquid fuel, such as gasoline, and a gaseous fuel, such as compressed natural gas (CNG), and supplies it to a single engine, will be described as an example. 
         [0033]      FIG. 1  is a schematic configuration diagram of a bi-fuel engine system according to an embodiment. As shown in  FIG. 1 , the bi-fuel engine system in this embodiment is schematically configured by an engine  1 , a liquid fuel supply unit  2 , a gaseous fuel supply unit  3 , a fuel-switching switch  4 , 1 st -ECU  5 , and a 2 nd -ECU  6  (shut-off valve fault diagnosis device). 
         [0034]    The engine  1  is a four-cycle engine that may selectively use a liquid fuel and a gaseous fuel, and includes a cylinder  10 , a piston  11 , a connecting rod  12 , a crankshaft  13 , an intake valve  14 , an exhaust valve  15 , an ignition plug  16 , an ignition coil  17 , an intake pipe  18 , an exhaust pipe  19 , an air cleaner  20 , a throttle valve  21 , a liquid fuel injection valve  22 , a gaseous fuel injection valve  23 , an intake air pressure sensor  24 , an intake air temperature sensor  25 , a throttle opening degree sensor  26 , a cooling water temperature sensor  27 , and a crank angle sensor  28 . 
         [0035]    The cylinder  10  is a hollow cylindrical member that is used to make the piston  11 , which is provided at the inside of the cylinder  10 , undergo a reciprocating motion by repeating four strokes including intake, compression, combustion (i.e., expansion), and exhaust. The cylinder  10  includes an intake port  10   a , a combustion chamber  10   b , and an exhaust port  10   c . The intake port  10   a  is a flow path that is used to supply mixed gas of air and fuel to the combustion chamber  10   b . The combustion chamber  10   b  is a space that is used to store the above-described mixed gas and to cause the mixed gas that has been compressed in the compression stroke to be combusted in the combustion stroke. The exhaust port  10   c  is a flow path that is used to discharge exhaust gas from the combustion chamber  10   b  to the outside in the exhaust stroke. A water cooling path  10   d  that is used to circulate cooling water is provided in an outer wall of the cylinder  10 . 
         [0036]    The crankshaft  13 , which is used to convert the reciprocating motion of the piston  11  into rotational motion, is connected to the piston  11  via the connecting rod  12 . The crankshaft  13  extends in a direction orthogonal to the reciprocation direction of the piston  11  and is connected to a flywheel (not shown), a mission gear, and the like. A rotor  13   a , which is used to detect a crank angle, is co-axially connected to the crankshaft  13 . A plurality of protrusions are provided at an outer circumference of the rotor  13   a  in such a manner that the rear end of each of the protrusions is spaced with an equal angular interval (for example, at an interval of 20°) with respect to a rotational direction. 
         [0037]    The intake valve  14  is a valve member that is used to open and shut an aperture portion on the combustion chamber  10   b  side of the air intake port  10   a  and is connected to a camshaft (not shown). The intake valve  14  is driven to open and shut in response to the respective strokes by this camshaft. 
         [0038]    The exhaust valve  15  is a valve member that is used to open and shut an aperture portion of the air exhaust port  10   c  on the combustion chamber  10   b  side and is connected to a camshaft (not shown). The exhaust valve  15  is driven to open and shut in response to the strokes by this camshaft. 
         [0039]    The ignition plug  16  is provided at an upper portion of the combustion chamber  10   b  in such a manner that electrodes are exposed to the inside of the combustion chamber  10   b  and generates a spark between the electrodes by a high-voltage signal that is supplied from the ignition coil  17 . 
         [0040]    The ignition coil  17  is a transformer that is formed by a primary coil and a secondary coil. The ignition coil  17  boosts an ignition voltage signal that is supplied from the 1 st -ECU  5  to the primary coil and supplies the ignition voltage signal from the secondary coil to the ignition plug  16 . 
         [0041]    The intake pipe  18  is an air supply pipe and is connected to the cylinder  10  in such a manner that an intake flow path  18   a  provided inside the intake pipe  18  communicates with the intake port  10   a.    
         [0042]    The exhaust pipe  19  is a pipe that discharges exhaust gas and is connected to the cylinder  10  in such a manner that an exhaust flow path  19   a  inside the exhaust pipe communicates with the exhaust port  10   c.    
         [0043]    The air cleaner  20  is provided upstream of the intake pipe  18 , purifies air taken in from the outside and supplies the purified air to the intake flow path  18   a.    
         [0044]    The throttle valve  21  is provided inside the intake flow path  18   a  and rotates in response to throttle manipulation (or accelerator manipulation). That is, a cross-sectional area of the intake flow path  18   a  varies by the rotational motion of the throttle valve  21 , and the air intake quantity accordingly varies. 
         [0045]    The liquid fuel injection valve  22  is an electromagnetic valve (for example, a solenoid valve or the like) that is provided in the intake pipe  18  in such a manner that an injection port is exposed to the intake port  10   a . The liquid fuel injection valve  22  injects the liquid fuel (gasoline or the like), which is supplied from the liquid fuel supply unit  2 , from the injection port in response to a fuel injection valve driving signal supplied from the 1 st -ECU  5 . 
         [0046]    The gaseous fuel injection valve  23  is an electromagnetic valve (for example, a solenoid valve or the like) that is provided in the intake pipe  18  in such a manner that an injection port is exposed to the intake port  10   a . The gaseous fuel injection valve  23  injects the gaseous fuel (CNG or the like), which is supplied from the gaseous fuel supply unit  3 , from the injection port in response to a fuel injection valve driving signal supplied from the 2 nd -ECU  6 . 
         [0047]    The intake air pressure sensor  24  is a semiconductor pressure sensor that uses, for example, a piezoresistive effect. The intake air pressure sensor  24  is provided in the intake pipe  18  in such a manner that a sensitive surface thereof is exposed to the intake flow path  18   a  downstream of the throttle valve  21  and outputs an intake air pressure signal corresponding to the intake air pressure inside the intake pipe  18  to the 1 st -ECU  5 . 
         [0048]    The intake air temperature sensor  25  is provided in the intake pipe  18  in such a manner that a sensitive portion thereof is exposed to the intake flow path  18   a  upstream of the throttle valve  21  and outputs the intake air temperature signal corresponding to the intake air temperature inside the intake pipe  18  to the 1 st -ECU  5 . 
         [0049]    The throttle opening degree sensor  26  outputs a throttle opening degree signal corresponding to the opening degree of the throttle valve  21  to the 1 st -ECU  5 . 
         [0050]    The cooling water temperature sensor  27  is provided in the cylinder  10  in such a manner that a sensitive portion of the cooling water temperature sensor  27  is exposed to the cooling water path  10   d  of the cylinder  10  and outputs a cooling water temperature signal corresponding to the temperature of the cooling water that flows through the cooling water path  10   d  to the 1 st -ECU  5 . 
         [0051]    For example, the crank angle sensor  28  is an electromagnetic type pickup sensor. The crank angle sensor  28  outputs a pair of pulse signals having polarities different from each other to the 1 st -ECU  5  whenever each of the protrusions provided at the outer circumference of the rotor  13   a  passes the vicinity of the sensor  28 . More specifically, the crank angle sensor  28  outputs a pulse signal having a negative polarity amplitude when the front end of each of the protrusions goes past in the rotation direction, and outputs a pulse signal having a positive polarity amplitude when the rear end of each of the protrusions goes past in the rotation direction. 
         [0052]    The liquid fuel supply unit  2  includes a liquid fuel tank  30  and a fuel pump  31 . 
         [0053]    The liquid fuel tank  30  is a vessel in which liquid fuel, such as gasoline fuel or alcohol fuel, is stored. 
         [0054]    The fuel pump  31  pumps the liquid fuel out of the liquid fuel tank  30  and pumps out the liquid fuel to a fuel inlet of the liquid fuel injection valve  22  in response to a pump driving signal supplied from the 1 st -ECU  5 . 
         [0055]    The gaseous fuel supply unit  3  includes a gaseous fuel tank  40 , a shut-off valve  41 , a regulator  42 , a filter  43 , a fuel pressure sensor  44 , and a relief valve  45 . 
         [0056]    For example, the gaseous fuel tank  40  is a pressure resistant vessel in which highly pressurized gaseous fuel such as CNG is filled. The shut-off valve  41  is a shut-off valve that has a kick pilot structure and that is interposed in a fuel supply path ranging from the gaseous fuel tank  40  to the regulator  42 . The shut-off valve  41  switches initiation and stop of gaseous fuel supply from the gaseous fuel tank  40  by performing a valve opening operation and a valve shutting operation in response to a shut-off valve driving signal that is supplied from the 2 nd -ECU  6 . In addition, as described with reference to  FIG. 7 , the shut-off valve  41  having this kick pilot structure includes a pilot valve  103  (first valve body) that is opened in advance during power supply and a main valve  104  (second valve body) that is opened due to a decrease in the differential pressure between upstream and downstream after the opening. 
         [0057]    The regulator  42  is a pressure regulating valve that is disposed downstream of the shut-off valve  41 . The regulator  42  decompresses the high-pressure gaseous fuel that is supplied from the gaseous fuel tank  40  at the time of opening the shut-off valve  41  to a desired pressure, and then delivers the decompressed gaseous fuel to the filter  43  that is provided at a downstream side. 
         [0058]    The filter  43  removes foreign materials (for example, foreign materials such as compressor oil in the gaseous fuel) contained in the gaseous fuel delivered from the regulator  42 , and delivers the gaseous fuel from which the foreign materials are removed to a fuel inlet of the gaseous fuel injection valve  23 . 
         [0059]    The fuel pressure sensor  44  is a pressure sensor that is provided in the filter  43 . The fuel pressure sensor  44  detects a pressure of the gaseous fuel that is delivered to the gaseous fuel injection valve  23  and outputs a pressure detection signal representing the detection result to the 2 nd -ECU  6 . 
         [0060]    The relief valve  45  is a safety valve that is interposed in a divergence pipe that communicates with a pipe connecting the regulator  42  and the filter  43 . In a case where the fuel pressure downstream of the regulator  42  exceeds a pressure that is set, the relief valve  45  is opened to discharge (relieve) the gaseous fuel to the outside. 
         [0061]    The fuel-switching switch  4  is a switch to realize fuel-switching by manual operation. The fuel-switching switch  4  outputs a fuel designation signal representing a state of the switch, that is, whether either the liquid fuel or the gaseous fuel is designated as fuel that is used in the engine  1  to the 2 nd -ECU  6 . 
         [0062]    The 1 st -ECU  5  mainly performs operation control of the engine  1  that uses the liquid fuel. As shown in  FIG. 2 , the 1 st -ECU  5  includes a waveform shaping circuit  50 , a rotation number counter  51 , an A/D converter  52 , an ignition circuit  53 , a fuel injection valve driving circuit  54 , a pump driving circuit  55 , a ROM (Read Only Memory)  56 , a RAM (Random Access Memory)  57 , a communication circuit  58 , and a CPU (Central Processing Unit)  59 . 
         [0063]    The waveform shaping circuit  50  performs waveform shaping to change a crank signal that is input from the crank angle sensor  28  into a square-wave pulse signal (for example, to change a negative polarity crank signal into a high level signal, and change a positive polarity crank signal in a ground level into a low level signal), and outputs the waveform-shaped signal to the rotation number counter  51  and the CPU  59 . That is, this square-wave pulse signal is a square-wave pulse signal whose cycle is the length of time that is taken for the crankshaft  13  to rotate 20°. In the following description, the square-wave pulse signal that is output from the waveform shaping circuit  50  is referred to as a crank pulse signal. 
         [0064]    The rotation number counter  51  calculates the engine rotation number based on the crank pulse signal that is input from the above-described waveform shaping circuit  50 , and outputs the calculation result to the CPU  59 . 
         [0065]    The A/D converter  52  converts an intake air pressure signal that is input from the intake air pressure sensor  24 , an intake air temperature signal that is input from the intake air temperature sensor  25 , a throttle opening degree signal that is input from the throttle opening degree sensor  26 , and a cooling water temperature signal that is input from the cooling water temperature sensor  27  into a digital signal (a value of the intake air pressure, a value of the intake air temperature, a value of the throttle opening degree, and a value of the cooling water temperature), and then outputs this digital signal to the CPU  59 . 
         [0066]    The ignition circuit  53  includes a capacitor that accumulates power supply voltage that is supplied from a battery (not shown) and discharges electric charges that have been accumulated in the capacitor to a primary coil of the ignition coil  17  as an ignition voltage signal in accordance with the request from the CPU  59 . 
         [0067]    The fuel injection valve driving circuit  54  generates a fuel injection valve driving signal in accordance with the request from the CPU  59  and outputs this fuel injection valve driving signal to the liquid fuel injection valve  22 . 
         [0068]    The pump driving circuit  55  generates a pump driving signal in accordance with the request from the CPU  59 , and outputs the pump driving signal to the fuel pump  31 . 
         [0069]    The ROM  56  is a non-volatile memory in which an engine control program to realize various functions of the CPU  59  and various types of setting data are stored in advance. The RAM  57  is a volatile working memory that is used to temporarily hold data when the CPU  59  causes the engine control program to execute various operations. The communication circuit  58  is a communication interface that realizes a data communication between the 1 st -ECU  5  and the 2 nd -ECU  6  under the control of the CPU  59 , and is connected to the 2 nd -ECU  6  via a communication cable. 
         [0070]    The CPU  59  performs operation control of the engine  1  by the liquid fuel in accordance with the engine control program that is stored in the ROM  56  based on the crank pulse signal that is input from the waveform shaping circuit  50 , the engine rotation number that may be obtained from the rotation number counter  51 , a value of the intake air pressure, a value of the intake air temperature, a value of the throttle opening degree, and a value of the cooling water temperature, which may be obtained from the A/D converter  52 , and various kinds of information that may be obtained from the 2 nd -ECU  6  via the communication circuit  58 . 
         [0071]    Specifically, the CPU  59  monitors a rotational state of the crankshaft  13  (in other words, a position of the piston  11  in the cylinder  10 ) based on the crank pulse signal that is input from the waveform shaping circuit  50 , and outputs an ignition control signal to the ignition circuit  53  at the point in time at which the piston  11  reaches a position corresponding to an ignition time to cause the ignition plug  16  to spark. 
         [0072]    When receiving an instruction of operation by using the liquid fuel from the 2 nd -ECU  6  via the communication circuit  58 , the CPU  59  outputs a fuel supply control signal to the pump driving circuit  55  so as to drive the fuel pump  31  and initiates supply of the liquid fuel to the liquid fuel injection valve  22 . In addition, the CPU  59  outputs the fuel injection control signal to the fuel injection valve driving circuit  54  at the point in time at which the piston  11  reaches a position corresponding to a fuel injection time so as to perform injection of the liquid fuel by the liquid fuel injection valve  22 . In addition, the CPU  59  also has a function of transmitting the position of the piston  11 , the engine rotation number, the value of the intake air pressure, the value of the intake air temperature, the value of the throttle valve opening degree, and the value of the cooling water temperature, which the CPU  59  itself recognize, to the 2 nd -ECU  6  via the communication circuit  58 . 
         [0073]    The 2 nd -ECU  6  performs operation control of the engine  1  that mainly uses the gaseous fuel. As shown in  FIG. 3 , the 2 nd -ECU  6  includes a communication circuit  60 , an A/D converter  61 , a fuel injection valve driving circuit  62 , a shut-off valve driving circuit  63 , a ROM  64 , a RAM  65 , and a CPU  66 . 
         [0074]    The communication circuit  60  is a communication interface that realizes a data communication between the 1 st -ECU  5  and the 2 nd -ECU  6  under the control of the CPU  66  and is connected to the 1 st -ECU  5  (more specifically, the communication circuit  58 ) via a communication cable. The A/D converter  61  converts a pressure detection signal that is input from the fuel pressure sensor  44  into a digital signal and outputs this converted signal to the CPU  66 . In addition, since the digital signal is a signal representing an actual measurement value of the pressure downstream of the shut-off valve  41 , hereinafter, the digital signal is referred to as a downstream pressure actual measurement value. 
         [0075]    The fuel injection valve driving circuit  62  generates a fuel injection valve driving signal in accordance with the request from the CPU  66  and outputs this fuel injection valve driving signal to the gaseous fuel injection valve  23 . The shut-off valve driving circuit  63  generates a shut-off valve driving signal in accordance with the request from the CPU  66  and outputs this shut-off valve driving signal to the shut-off valve  41 . The ROM  64  is a non-volatile memory in which an engine control program to realize various functions of the CPU  66  and various types of setting data are stored in advance. The RAM  65  is a volatile working memory that is used to temporarily hold data when the CPU  66  causes the engine control program to execute various operations. 
         [0076]    The CPU  66  (diagnosis processing unit) performs operation control of the engine  1  by the gaseous fuel in accordance with the engine control program that is stored in the ROM  64  based on the fuel designation signal that is input from the fuel-switching switch  4 , the position of the piston  11 , the engine rotation number, the value of the intake air pressure, the value of the intake air temperature, the value of the throttle opening degree, and the value of the cooling water, which may be obtained from the 1 st -ECU  5  via the communication circuit  60 , and the downstream pressure actual measurement value that may be obtained from the A/D converter  61 . 
         [0077]    Specifically, in a case where it is determined that the liquid fuel is designated as the fuel that is used in the engine  1  from an analysis result of the fuel designation signal that is input from the fuel-switching switch  4 , the CPU  66  transmits an instruction of operation by using the liquid fuel to the 1 st -ECU  5  (more specifically, the communication circuit  58 ) via the communication circuit  60 . 
         [0078]    On the other hand, in a case where it is determined that the gaseous fuel is designated as the fuel that is used in the engine  1  from the analysis result of the fuel designation signal that is input from the fuel-switching switch  4 , the CPU  66  makes a request of generating a shut-off valve driving signal for the shut-off valve driving circuit  63 . Due to this, the shut-off valve driving signal is supplied from the shut-off valve driving circuit  63  to the shut-off valve  41  (that is, power supply of the shut-off valve  41  begins to start), the shut-off valve  41  enters an open state, and supply of the gaseous fuel from the gaseous fuel tank  40  to the gaseous fuel injection valve  23  begins to start. In addition, the CPU  66  makes a request of generating a fuel injection valve driving signal for the fuel injection valve driving circuit  62  at the point in time at which the piston  11  reaches a position corresponding to a fuel injection time so as to perform injection of the gaseous fuel by the gaseous fuel injection valve  23 . 
         [0079]    Furthermore, as a characteristic function in this embodiment, the CPU  66  has a shut-off valve fault diagnosis function of estimating the open and shut states of each of the pilot valve  103  and the main valve  104  from a time-variable characteristic in a downstream pressure of the shut-off valve  41 , and of performing the fault diagnosis of the shut-off valve  41  from an actual measurement value of the downstream pressure that may be obtained from the A/D converter  61  based on the estimation result. Hereinafter, the shut-off valve fault diagnosis function which the CPU  66  has will be described in detail. 
         [0080]    First, a fault diagnosis principle of the shut-off valve  41  in this embodiment is as follows. Specifically, the time-variable characteristic of the downstream pressure of the shut-off valve  41  including the pilot valve  103  and the main valve  104  tends to vary depending on the open and shut states of each of the pilot valve  103  that is opened in advance during power supply to the shut-off valve  41  and the main valve  104  that is opened due to a decrease in the differential pressure between upstream and downstream after the opening. Therefore, in a case where estimation of the open and shut state of each of the pilot valve  103  and the main valve  104  is made in advance from the time-variable characteristic of the downstream pressure of the shut-off valve  41 , the fault diagnosis of the shut-off valve  41  having the kick pilot structure may be appropriately performed from the downstream pressure actual measurement value based on the estimation result. 
         [0081]    In addition, the estimation result of the time-variable characteristic of the downstream pressure of the shut-off valve  41  and the open and shut state of each of the pilot valve  103  and the main valve  104  is different between a case in which the downstream pressure actual measurement value is less than or equal to the threshold value before the power supply to the shut-off valve  41  (first case: a case in which the differential pressure between upstream and downstream of the shut-off valve  41  is large) and a case in which the downstream pressure actual measurement value exceeds the threshold value (second case: a case in which the differential pressure between upstream and downstream of the shut-off valve  41  is small). Here, a solid difference due to manufacturing or deterioration with the passage of time is present in the fuel pressure sensor  44 , such that an error in a detection value with respect to the actual pressure variation occurs. Therefore, a threshold value Pt is set in advance so that correct determination may be performed even when the maximum error in the detection value of the pressure is anticipated in any one of the first case and the second case. It is preferable that the threshold value Pt be set to a value at which it enters a supply shortage state when the gaseous fuel pressure is less than or equal to the threshold value Pt. Therefore, when the fault diagnosis of the shut-off valve  41  is performed based on the estimation result that is different in each of the first case and the second case, appropriate fault diagnosis in correspondence with each case may be performed. 
         [0082]      FIG. 4  shows a relationship obtained by estimating the open and shut states of the pilot valve  103  and the main valve  104  from a time-variable characteristic in a downstream pressure P of the shut-off valve  41  in a first case.  FIG. 4(   a ) shows each tendency of the time-variable characteristic of the downstream pressure P, and  FIG. 4(   b ) shows the open and shut states (valve state) of the pilot valve  103  and the main valve  104  that correspond to each tendency. In addition, in  FIG. 4(   b ), an open valve state represents that a valve is in a normal state, and a shut valve state represents that the valve is in a fault state. 
         [0083]    As shown in  FIG. 4(   a ), in regard to the first case, in a case where the downstream pressure P does not exceed the threshold value Pt after a predetermined time T has passed from the initiation of the power supply to the shut-off valve  41  (refer to a broken line portion), as shown in  FIG. 4(   b ), it is estimated that both of the pilot valve  103  and the main valve  104  enter a shut valve state (refer to pattern d), or the pilot valve  103  enters a shut valve state and the main valve  104  enters an open valve state (refer to pattern c). That is, in this case, it may be determined that the shut-off valve  41  is in a fault state. 
         [0084]    In addition, as shown in  FIG. 4(   a ), in a case where the downstream pressure P exceeds the threshold value Pt after a predetermined time T has passed from the initiation of the power supply to the shut-off valve  41 , it is estimated that at least the pilot valve  103  is normally opened. Therefore, consumption of fuel downstream of the shut-off valve  41  is attempted by activating the gaseous fuel injection valve  23 . After the activation of the gaseous fuel injection valve  23 , as shown in  FIG. 4(   a ), in a case where the downstream pressure P is less than or equal to the threshold value Pt (refer to an one-dot chain line portion), since it is considered that fuel supply from upstream is not performed in a timely manner with respect to fuel consumption downstream of the shut-off valve  41 , as shown in  FIG. 4(   b ), it is estimated that the main valve  104  is in a shut valve state (refer to pattern b). 
         [0085]    That is, also in this case, it may be determined that the shut-off valve  41  is in a fault state. 
         [0086]    Furthermore, as shown in  FIG. 4(   a ), in a case where the downstream pressure P is not less than or equal to the threshold value Pt after the activation of the gaseous fuel injection valve  23  (refer to a solid line portion), since it is considered that fuel supply from upstream is timely performed with respect to fuel consumption downstream of the shut-off valve  41 , as shown in  FIG. 4(   b ), it is estimated that the main valve  104  is also in an open valve state (refer to pattern a). That is, in this case, it may be determined that the shut-off valve  41  is in a normal state. 
         [0087]    In addition, in the above-described first case, it is preferable that the predetermined time T be set to a time until the downstream pressure P becomes a value at which an engine is operable after the pilot valve  103  is opened from the initiation of the power supply to the shut-off valve  41 . When the predetermined time T is set in this manner, the fault of the shut-off valve  41 , which becomes a cause of an open fault in the pilot valve  103 , may be detected with high accuracy. 
         [0088]      FIG. 5  shows a relationship obtained by estimating the open and shut states of the pilot valve  103  and the main valve  104  from a time-variable characteristic in a downstream pressure P of the shut-off valve  41  in a second case.  FIG. 5(   a ) shows each tendency of the time-variable characteristic of the downstream pressure P, and  FIG. 5(   b ) shows the open and shut states (valve state) of the pilot valve  103  and the main valve  104 , which correspond to tendencies. In addition, in  FIG. 5(   b ), an open valve state represents that a valve is in a normal state, and a shut valve state represents that the valve is in a fault state. 
         [0089]    As shown in  FIG. 5(   a ), in the second case, consumption of fuel downstream of the shut-off valve  41  is attempted by activating the gaseous fuel injection valve  23  after the initiation of the power supply to the shut-off valve  41 . After the activation of the gaseous fuel injection valve  23 , as shown in  FIG. 5(   a ), in a case where the downstream pressure P is less than or equal to the threshold value Pt (refer to a one-dot chain line portion), since it is considered that fuel supply from upstream is not performed in a timely manner with respect to fuel consumption downstream of the shut-off valve  41 , as shown in  FIG. 5(   b ), it is estimated that at least the main valve  104  is in a shut valve state (refer to patterns f and h). That is, also in this case, it may be determined that the shut-off valve  41  is in a fault state. 
         [0090]    Furthermore, as shown in  FIG. 5(   a ), in a case where the downstream pressure P is not less than or equal to the threshold value Pt after the activation of the gaseous fuel injection valve  23  (refer to a solid line portion), since it is considered that fuel supply from upstream is timely performed with respect to fuel consumption downstream of the shut-off valve  41 , as shown in  FIG. 5(   b ), it is estimated that at least the main valve  104  is in an open valve state (refer to patterns e and g). That is, in this case, it may be determined that the shut-off valve  41  is in a normal state. 
         [0091]    Based on the fault diagnosis principle of the shut-off valve  41  in this embodiment as described above, hereinafter, a shut-off valve fault diagnosis process that is performed by the CPU  66  to realize the shut-off valve fault diagnosis function will be described with reference to a flowchart of  FIG. 6 . 
         [0092]    As shown in  FIG. 6 , after initiation of the shut-off valve fault diagnosis process, first, the CPU  66  determines whether or not the downstream pressure actual measurement value P 1  that is obtained from the A/D converter  61  before the power supply of the shut-off valve  41  is less than or equal to the threshold value Pt (step S 1 ). In the case of “Yes” in step Si, that is, in the first case shown in  FIG. 4 , the CPU  66  makes a request of generating the shut-off valve driving signal for the shut-off valve driving circuit  63  to initiate the power supply of the shut-off valve  41  (step S 2 ). 
         [0093]    In addition, the CPU  66  determines whether or not a predetermined time T has passed (step S 3 ). Here, in the case of “Yes”, that is, the predetermined time T has passed, the CPU  66  determines whether or not the downstream pressure actual measurement value P 1 , which is obtained from the A/D converter  61  after the passage of the predetermined time T, exceeds the threshold value Pt (step S 4 ). 
         [0094]    In the case of “Yes” in step S 4 , that is, the downstream pressure actual measurement value P 1  exceeds the threshold value Pt after the passage of the predetermined time T from the initiation of the power supply to the shut-off valve  41 , and thus it is estimated that at least the pilot valve  103  is normally opened, the CPU  66  makes a request of generating a fuel injection valve driving signal for the fuel injection valve driving circuit  62  to activate the gaseous fuel injection valve  23  (step S 5 ). In addition, the downstream pressure actual measurement value P 1  after the activation of the gaseous fuel injection valve  23  is acquired from the A/D converter  61  (step S 6 ). 
         [0095]    In addition, the CPU  66  determines whether or not the acquired downstream pressure actual measurement value P 1  is less than or equal to the threshold value Pt (step S 7 ). Here, in the case of “No”, the process returns to step S 6  and the acquisition of the downstream pressure actual measurement value P 1  is continued. On the other hand, in the case of “Yes”, that is, in a case where it is estimated that the main valve  104  enters the shut valve state (in the case of the pattern b in  FIG. 4(   b )), the CPU  66  determines that the shut-off valve  41  is in a fault state and terminates the shut-off valve fault diagnosis process (step S 8 ). 
         [0096]    On the other hand, in the case of “No” in step S 4 , that is, in a case where the downstream pressure actual measurement value P 1  does not exceed the threshold value Pt after the predetermined time T has passed from the initiation of the power supply to the shut-off valve  41 , and thus it is estimated that both of the pilot valve  103  and the main valve  104  enter the shut valve state (in the case of the patterns c and d of  FIG. 4(   b )), the process transitions to step S 8 , and the CPU  66  determines that the shut-off valve  41  is in a fault state and terminates the shut-off valve fault diagnosis process. 
         [0097]    Furthermore, in the case of “No” in step S 1 , that is, in the case of the second case shown in  FIG. 5 , the CPU  66  makes a request of generating the shut-off valve driving signal for the shut-off valve driving circuit  63  to initiate the power supply of the shut-off valve  41  (step S 9 ). In addition, after the initiation of the power supply to the shut-off valve  41 , the CPU  66  makes a request of generating the fuel injection valve driving signal for the fuel injection valve driving circuit  62  to activate the gaseous fuel injection valve  23  (step S 10 ). In addition, the downstream pressure actual measurement value P 1  after the activation of the gaseous fuel injection valve  23  is acquired from the A/D converter  61  (step S 11 ). 
         [0098]    In addition, the CPU  66  determines whether or not the acquired downstream pressure actual measurement value P 1  is less than or equal to the threshold value Pt (step S 12 ). Here, in the case of “No”, the process returns to step S 11  and the acquisition of the downstream pressure actual measurement value P 1  is continued. On the other hand, in the case of “Yes”, that is, in a case where it is estimated that at least the main valve  104  enters the shut valve state (the case of the patterns f and h of  FIG. 5(   b )), the process transitions to step S 8 , and the CPU  66  determines that the shut-off valve  41  is in a fault state and terminates the shut-off valve fault diagnosis process. 
         [0099]    As described above, according to this embodiment, the fault diagnosis of the shut-off valve  41  having the kick pilot structure may be appropriately performed. In addition, when the fault diagnosis of the shut-off valve  41  is performed using a process sequence that is different in each of the first case (case in which the differential pressure between upstream and downstream of the shut-off valve  41  is large) and the second case (case in which the differential pressure between upstream and downstream of the shut-off valve  41  is small), appropriate fault diagnosis in correspondence with each of the cases may be performed. 
         [0100]    In addition, the present invention is not limited to the above-described embodiment, and the following modifications may be made.
       (1) In the above-described embodiment, the bi-fuel engine system, which includes the 1 st -ECU  5  that carries out an operation control by the liquid fuel and the 2 nd -ECU  6  that carries out an operation control by the gaseous fuel and fault diagnosis of the shut-off valve  41 , separately, is given as an example, but a configuration in which the functions of the two ECUs are integrated in one ECU may be adopted.   (2) In the above-described embodiment, description was made with respect to the bi-fuel engine system as an example, but the present invention is not limited thereto, and the present invention is applicable to a mono fuel engine system that supplies only the gaseous fuel to a single engine.   (3) The kick pilot structure of the shut-off valve  41  shown in  FIG. 7  is illustrative only, and the present invention is applicable to a shut-off valve as a fault diagnosis technology thereof as long as the shut-off valve includes a first valve body that is opened in advance during power supply and a second valve body that is opened due to a decrease in the differential pressure between upstream and downstream after the first valve body is opened.   (4) In the above-described embodiment, a description was made with respect to a case in which the downstream pressure (that is, a pressure of a fuel supply path ranging from the regulator  42  to the gaseous fuel injection valve  23 ) of the regulator  42  is measured as the downstream pressure of the shut-off valve  41 , but as the downstream pressure of the shut-off valve  41 , a pressure in a fuel supply path ranging from the shut-off valve  41  to the regulator  42  may be measured. In addition, in the case of serving both as a pressure sensor and a temperature sensor, it is preferable that a place at which the downstream pressure of the shut-off valve  41  is measured be as close as possible to the gaseous fuel injection valve  23 . This is because the accuracy of the temperature measurement is improved.       
 
       INDUSTRIAL APPLICABILITY 
       [0105]    According to the shut-off valve fault diagnosis device of the present invention, the fault diagnosis of the shut-off valve having a kick pilot structure may be appropriately performed.