Patent Publication Number: US-2023160769-A1

Title: Connection structure for fuel pressure sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is based on and claims priority to Japanese Patent Application No. 2020-023616, filed on Feb. 14, 2020, the disclosure of which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     This disclosure relates to a connection structure for a fuel pressure sensor. 
     BACKGROUND ART 
     A connection structure for a fuel pressure sensor that connects a fuel pressure sensor to a fuel rail, so as to detect a pressure of a fuel stored in the fuel rail is known (see e.g., JP2019-11695A). In this connection structure for the fuel pressure sensor, a male screw formed in the fuel pressure sensor is screwed into a female screw formed in the fuel rail, so as to connect the fuel pressure sensor to the fuel rail. 
     SUMMARY 
     In the conventional connection structure for the fuel pressure sensor, a fuel pressure detection portion and the male screw that is fastened to the fuel rail are integrated, and a conical portion formed in a leading end of the male screw (hereinafter, referred to as leading end of male screw) abuts to an abutting surface formed in a bottom surface of a female screw of the fuel rail, so as to form a sealing surface between the leading end of the male screw and the abutting surface for sealing. At this time, the male screw is screwed until a specified torque is applied, and the leading end of the male screw abuts to the abutting surface in an airtight state by applying an axial force to the leading end of the male screw at a high level, so as to maintain a sealing performance (airtightness, oil-tightness) of the sealing surface, which is metal contact. Herein, the leading end of the male screw contacts the abutting surface before a specified torque is applied, so that the sealing surface is formed before a specified torque is applied. That is, the sealing surface formed between the leading end of the male screw and the abutting surface rotates along the rotation of the male screw until a specified torque is applied to the leading end of the male screw. For this reason, the sealing surface may be shifted in the rotation direction of the male screw, which may deteriorate the sealing performance. 
     It is therefore the present disclosure has been made in view of the above problem. An object of the present disclosure is to provide a connection structure for a fuel pressure sensor that prevents relative rotation between the abutting surface of the fuel rail and the contact surface of the fuel pressure sensor to suppress the deterioration in the sealing performance. 
     To achieve the above object, the present disclosure provides a connection structure for a fuel pressure sensor that connects a fuel pressure sensor for detecting a pressure of a fuel to a fuel rail in which the fuel to be supplied to an internal-combustion engine flows, the connection structure includes a tubular attachment boss that is formed in the fuel rail and includes a first screw portion and an abutting surface, an attachment portion that is provided in a sensor body of the fuel pressure sensor, and includes a contact surface that abuts to the abutting surface and a bearing surface provided behind the contact surface, and a nut including a second screw portion that is screwed on the first screw portion and a pressing portion that presses the bearing surface to the abutting surface by screwing the second screw portion on the first screw portion. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic drawing illustrating a fuel supply system of an internal-combustion engine to which a connection structure for a fuel pressure sensor according to a first embodiment is applied. 
         FIG.  2    is a sectional view illustrating the connection structure for the fuel pressure sensor according to the first embodiment. 
         FIG.  3    is a sectional view illustrating a connection structure for a fuel pressure sensor according to a second embodiment. 
         FIG.  4    is a sectional view illustrating a connection structure for a fuel pressure sensor according to a third embodiment. 
         FIG.  5    is a perspective view illustrating divided collars according to the third embodiment. 
         FIG.  6 A  illustrates a procedure for inserting a head portion in a connection procedure of the fuel pressure sensor according to the third embodiment. 
         FIG.  6 B  illustrates a procedure for inserting a first divided collar in the connection procedure of the fuel pressure sensor according to the third embodiment. 
         FIG.  6 C  illustrates a procedure for inserting a second divided collar in the connection procedure of the fuel pressure sensor according to the third embodiment. 
         FIG.  6 D  is a procedure for covering a nut in the connection procedure of the fuel pressure sensor according to the third embodiment. 
         FIG.  6 E  is a procedure for fixing the nut in the connection procedure of the fuel pressure sensor according to the third embodiment. 
         FIG.  7 A  is a sectional view illustrating a connection structure for a fuel pressure sensor to which divided collars according to a first modified example are adapted. 
         FIG.  7 B  is a sectional view illustrating a connection structure for a fuel pressure sensor to which divided collars according to a second modified example are adapted. 
         FIG.  8    is a sectional view illustrating a connection structure for a fuel pressure sensor according to a fourth embodiment. 
         FIG.  9    is a sectional view illustrating a connection structure for a fuel pressure sensor according to a fifth embodiment. 
         FIG.  10    is a sectional view illustrating a single nut for use in the connection structure for the fuel pressure sensor according to the fifth embodiment. 
         FIG.  11 A  illustrates a procedure for inserting a head portion in a connection procedure of the fuel pressure sensor according to the fifth embodiment. 
         FIG.  11 B  illustrates a procedure for swaging a nut in the connection procedure of the fuel pressure sensor according to the fifth embodiment. 
         FIG.  11 C  illustrates a procedure for covering the nut in the connection procedure of the fuel pressure sensor according to the fifth embodiment. 
         FIG.  11 D  illustrates a procedure for fixing the nut in the connection procedure of the fuel pressure sensor according to the fifth embodiment. 
         FIG.  12 A  is a sectional view illustrating a single nut according to a modified example of the nut of the fifth embodiment. 
         FIG.  12 B  is a sectional view illustrating a connection structure for a fuel pressure sensor using the modified example of the nut according of the fifth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     With respect to the use of plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 
     Hereinafter, embodiments of a connection structure for a fuel pressure sensor according to the present disclosure will be described based on first to fifth embodiments illustrated in the figures. 
     First Embodiment 
     A connection structure  1  for a fuel pressure sensor according to the first embodiment is adapted to a fuel supply system  100  that supplies fuel to a direct injection type engine E (internal-combustion engine) that directly injects fuel (e.g., gasoline) into a cylinder at high pressure. The fuel supply system  100  includes a fuel tank  101 , a high-pressure fuel pump  102 , a fuel rail  103 , and an injector  104 . 
     The fuel tank  101  is a tank in which fuel filled from the outside is stored, and is provided with a low-pressure fuel pump  101   a  that pumps the fuel to be transferred to the high-pressure fuel pump  102 . The high-pressure fuel pump  102  presses the fuel transferred from the low-pressure fuel pump  101   a  with a power generated in the engine E, and supplies the high-pressure (e.g., 15 MPa or more) fuel to the fuel rail  103  through a fuel supply pipe  105 . 
     The fuel rail  103  is a straight pipe that extends in a cylinder arrangement direction of the engine E, and stores the high-pressure fuel discharged from the high-pressure fuel pump  102 . A downstream end of the fuel supply pipe  105  is connected to the fuel rail  103 . The fuel rail  103  is provided with an injector attachment portion  103   a . The number of the injector attachment portions  103   a  corresponds to the number of the cylinders of the engine E. A damper that controls the pulsation of the fuel may be provided inside the fuel rail  103 . 
     The injector  104  is provided according to the number of the cylinders of the engine 
     E, and is connected to the fuel rail  103  through a connection pipe  104   a  connected to the injector attachment portion  103   a . The opening and closing of each injector  104  are controlled in an appropriate timing according to the running state of the engine E. Each injector  104  directly injects the high-pressure fuel in the fuel rail  103  into each cylinder of the engine E. 
     A fuel pressure sensor  106  that detects a fuel pressure in a pipe is connected to the fuel rail  103 . 
     A configuration of the connection structure  1  for the fuel pressure sensor according to the first embodiment that connects the fuel pressure sensor  106  to the fuel rail  103  will be described with reference to  FIG.  2   . 
     The connection structure  1  for the fuel pressure sensor according to the first embodiment includes an attachment boss  10  formed in the fuel rail  103 , an attachment portion  20  provided in a sensor body  106   a  of the fuel pressure sensor  106 , and a nut  30  that fixes the fuel pressure sensor  106  to the attachment boss  10 . 
     The attachment boss  10  includes a boss body  11 , a boss internal flow channel  12 , a male screw portion  13  (first screw portion) formed in an outer peripheral surface of the boss body  11 , and an abutting surface  14  provided in a sensor side opening portion  12   b  of the boss internal flow channel  12 . 
     The boss body  11  is a metal cylindrical member fixed to the outer peripheral surface  103   b  of the fuel rail  103 . A first end surface lla that contacts the fuel rail  103  of the boss body  11  curves along the outer peripheral surface  103   b  of the fuel rail  103 , and a second end surface  11   b  that faces the fuel pressure sensor  106  has a flat surface. The boss body  11  is fixed to face a port  103   c  that penetrates through the peripheral surface of the fuel rail  103 . 
     The boss internal flow channel  12  is a through hole that penetrates through the boss body  11  in the axial direction, and includes a rail side opening portion  12   a  that opens at the first end surface  11   a  of the boss body  11  and the sensor side opening portion  12   b  that opens at the second end surface  11   b . The rail side opening portion  12   a  communicates with the port  103   c  formed in the fuel rail  103 . The fuel inside the fuel rail  103  therefore flows into the boss internal flow channel  12  through the port  103   c  and the rail side opening portion  12   a . The inside of the sensor side opening portion  12   b  has a tapered shape that inclines outside in the diameter direction from the center to the opening edge. The tapered inside of the sensor side opening portion  12   b  is the abutting surface  14  to which the attachment portion  20  abuts. 
     The attachment portion  20  is a metal member that projects from the sensor body  106   a  and abuts to the abutting surface  14  of the attachment boss  10 . The attachment portion  20  includes inside thereof a sensor side flow channel  21  in which the fuel flows, and also includes a head portion  22  formed in a leading end facing the attachment boss  10  and an axial portion  23  that connects the head portion  22  and the sensor body  106   a.    
     The sensor side flow channel  21  is a through hole that penetrates through the attachment portion  20  in the axial direction, and includes an inlet  21   a  that opens at the leading end of the head portion  22  and an outlet  21   b  that faces a not-shown pressure detection portion built in the sensor body  106   a . The leading end of the head portion  22  is inserted into the sensor side opening portion  12   b  of the boss internal flow channel  12 , and the inlet  21   a  and the sensor side opening portion  12   b  face to each other, so that the fuel flows into the sensor side flow channel  21 . The fuel that has flowed into the sensor side flow channel  21  flows to the outlet  21   b , and the pressure of the fuel is detected by the pressure detection portion built in the sensor body  106   a.    
     The head portion  22  substantially has a mushroom shape. A leading end of the head portion  22  directed to the attachment boss  10  curves into a convex circular arc shape, and a rear surface of the head portion  22  facing the sensor body  106   a  is formed into a flange shape that projects in the diameter direction from the outer peripheral surface of the axial portion  23 . The inlet  21   a  of the sensor side flow channel  21  is formed in the center of the leading end of the head portion  22 . A contact surface  22   a  that contacts the abutting surface  14  is formed in the head portion  22  to surround the peripheral of the inlet  21   a . The contact surface  22   a  surrounds the whole periphery of the inlet  21   a . The contact between the contact surface  22   a  and the abutting surface  14  in an airtight state forms an annular sealing surface that surrounds the periphery of the inlet  21   a  between the contact surface  22   a  and the abutting surface  14 , so as to prevent the fuel flowing into the sensor side flow channel  21  from the boss internal flow channel  12  from being leaked. On the other hand, the rear surface of the head portion  22  that faces the sensor body  106   a  is a bearing surface  22   b  provided behind the contact surface  22   a.    
     The axial portion  23  has a cylindrical shape thinner than a maximum outer diameter W 1  of the head portion  22 , and is inserted into the through hole  32  of an after-described nut  30  to penetrate through the through hole  32 . 
     The nut  30  is a bagged nut having width across flats as an external shape. The nut  30  has at a first end thereof an opening portion  31  into which the boss body  11  of the attachment boss  10  is inserted and at a second end thereof a through hole  32  through which the axial portion  23  of the attachment portion  20  penetrates. A female screw portion  33  (second screw portion) that is screwed on the male screw portion  13  of the attachment boss  10  is formed in the inner circumferential surface of the nut  30 . The nut  30  has a hollow cylindrical shape in which the attachment boss  10  is inserted. A pressing portion  34  is formed in the periphery of the through hole  32 . 
     In this case, the measurement of the through hole  32  is set such that an inner diameter W is smaller than the maximum outer diameter W 1  of the head portion  22  and a maximum outer diameter W 2  of the sensor body  106   a , and is larger than a maximum outer diameter W 3  of the axial portion  23 . The pressing portion  34  formed in the periphery of the through hole  32  therefore faces the bearing surface  22   b  projecting in the diameter direction from the peripheral surface of the axial portion  23 . The female screw portion  33  is thereby screwed on the male screw portion  13 , and the nut  30  comes close to the fuel rail  103 , so that the pressing portion  34  presses the bearing surface  22   b  toward the abutting surface  14 . When the attachment portion  20  is assembled to the sensor body  106   a  in the fuel pressure sensor  106 , the nut  30  is assembled between the sensor body  106   a  and the attachment portion  20 . 
     Hereinafter, the operation of the connection structure  1  for the fuel pressure sensor according to the first embodiment will be described. 
     To connect the fuel pressure sensor  106  to the fuel rail  103  in the connection structure  1  for the fuel pressure sensor according to the first embodiment, at first, the nut  30  previously assembled to the fuel pressure sensor  106  is previously put on the attachment boss  10  fixed to the outer peripheral surface  103   b  of the fuel rail  103 . Next, the nut  30  is rotated, and the female screw portion  33  formed in the inner peripheral surface of the nut  30  is screwed on the male screw portion  13  formed in the outer peripheral surface of the boss body  11 , so that the nut  30  is fixed to the boss body  11 . The boss body  11  is thereby inserted into the nut  30  through the opening portion  31 , and the attachment portion  20  comes close to the boss body  11 . 
     When the nut  30  is screwed until the attachment portion  20  provided in the sensor body  106   a  of the fuel pressure sensor  106  abuts to the boss body  11 , the head portion  22  is inserted into the sensor side opening portion  12   b  of the boss internal flow channel  12 , and the contact surface  22   a  contacts the abutting surface  14 . 
     At this time, the pressing portion  34  of the nut  30  faces the bearing surface  22   b  of the attachment portion  20 . Thus, when the nut  30  comes close the fuel rail  109  by screwing the nut  30 , the axial force acts on the bearing surface  22   b  from the pressing portion  34 . The contact surface  22   a  is pressed to the abutting surface  14  by this axial force, so that the sealing surface is formed. When the axial force acting on the bearing surface  22   b  reaches a constant force or more, the contact surface  22   a  is elastically deformed to contact the abutting surface  14  at an airtight state, so that the sealing performance is maintained at a high level between the contact surface  22   a  and the abutting surface  14 . As a result, the fuel pressure sensor  106  is connected to the fuel rail  103  in an airtight state. 
     On the other hand, the axial portion  23  of the attachment portion  20  of the fuel pressure sensor  106  in which the contact surface  22   a  is formed penetrates through the through hole  32  formed in the nut  30 , and the attachment portion  20  is separated from the nut  30 . The nut  30  thereby rotates around the attachment portion  20  and the attachment portion  20  does not rotates when the contact surface  22   a  is pressed to the abutting surface  14 . 
     As described above, in the connection structure  1  for the fuel pressure sensor according to the first embodiment, the attachment portion  20  provided in the fuel pressure sensor  106  is pressed by the nut  30  screwed on the attachment boss  10  provided in the fuel rail  103 . That is, when the sealing performance is maintained by pressing the contact surface  22   a  to the abutting surface  14 , the nut  30  that applies the axial force to the attachment portion  20  is separated from the contact surface  22   a  which is pressed to the abutting surface  14 . With this, the contact surface  22   a  and the abutting surface  14  do not relatively rotate in a contact state when the fuel pressure sensor  106  is connected to the fuel rail  103 . The contact surface  22   a  that has contacted the abutting surface  14  in an airtight state is prevented from moving in the rotation direction, and the deterioration in the sealing performance due the shift of the sealing surface can be suppressed. As a result, a stable airtight performance can be maintained between the fuel pressure sensor  106  and the fuel rail  103 . 
     In the connection structure for the fuel pressure sensor in which the contact surface is formed in the leading end of the male screw, and the contact surface rotates when the male screw is screwed, it is necessary to secure an engagement accuracy at a high level between the male screw and the female screw formed in the fuel rail and on which the male screw is screwed, so as to reduce the relative shift between the abutting surface and the contact surface formed in the fuel rail. That is, when the engagement accuracy between the male screw and the female screw is low, the relative shift between the contact surface and the abutting surface increases, resulting in the deterioration in the sealing performance. It is thus considered that the allowable range of the machining accuracy is reduced. 
     However, in the connection structure  1  for the fuel pressure sensor according to the first embodiment, the attachment portion  20  having the contact surface  22   a  is separated from the nut  30  that applies the axial force to the attachment portion  20 . The contact surface  22   a  thereby does not relatively rotate to the abutting surface  14 . Thus, a high engagement accuracy is not required between the male screw portion  13  and the female screw portion  33 , so that the allowable range of the machining accuracy can be increased. 
     The sealing performance between the contact surface  22   a  and the abutting surface  14  can be adjusted by adjusting the screwing amount of the female screw portion  33  on the male screw portion  13  to change the axial force acting on the bearing surface  22   b  from the pressing portion  34 . The sealing performance between the contact surface  22   a  and the abutting surface  14  can be therefore easily adjusted, and the sealing performance can be also recovered by simply refastening the nut  30 . 
     In the connection structure  1  for the fuel pressure sensor according to the first embodiment, the nut  30  has a hollow cylindrical shape including at one end thereof the opening portion  31  into which the attachment boss  10  is inserted and at the other end thereof the through hole  32  through which the attachment portion  20  penetrates. The pressing portion  34  is also formed in the periphery of the through hole  32 . Further, the male screw portion  13  is formed in the outer peripheral surface of the boss body  11  of the attachment boss  10 , and the female screw portion  33  is formed in the inner peripheral surface of the nut  30 . 
     With this configuration, the attachment portion  20  can be connected to the attachment boss  10  with being covered by the nut  30 . 
     In the connection structure  1  for the fuel pressure sensor according to the first embodiment, as illustrated in  FIG.  2   , while the leading end of the head portion  22  has a curved convex circular arc shape, the abutting surface  14  has a tapered shape that inclines outside in the diameter direction from the center to the opening edge. The narrow linear sealing surface can be formed between the contact surface  22   a  and the abutting surface  14 . 
     Second Embodiment 
     Hereinafter, a configuration of a connection structure  2  for a fuel pressure sensor according to the second embodiment will be described with reference to  FIG.  3   . 
     The connection structure  2  for the fuel pressure sensor according to the second embodiment includes an attachment boss  40  formed in a fuel rail  103 , an attachment portion  50  provided in a sensor body  106   a  of a fuel pressure sensor  106 , and a nut  60  that fixes the fuel pressure sensor  106  to the attachment boss  40 . 
     The attachment boss  40  includes a boss body  41  fixed to an outer peripheral surface  103   b  of the fuel rail  103 , a boss internal flow channel  42  formed inside the boss body  41 , a concave portion  45  formed in the boss body  41 , a female screw portion  43  (first screw portion) formed in an inner peripheral surface of the concave portion  45 , and an abutting surface  44  formed in a bottom surface of the concave portion  45 . 
     In the second embodiment  2 , the boss internal flow channel  42  includes a rail side opening portion  42   a  that opens at a first end surface  41   a  that contacts the fuel rail  103  of the boss body  41 , and a sensor side opening portion  42   b  that opens at the bottom surface of the concave portion  45 . The rail side opening portion  42   a  communicates with a port  103   c  formed in the fuel rail  103 , and the fuel in the fuel rail  103  flows into the boss internal flow channel  42  through a port  103   c  and the rail side opening portion  42   a . The fuel that has flowed into the boss internal flow channel  42  flows to the concave portion  45  from the sensor side opening portion  42   b.    
     The concave portion  45  is a recess that opens at a second end surface  41   b  of the boss body  41  facing the fuel pressure sensor  106 , and extends in the axial direction of the boss body  41 . The female screw portion  43  is formed in the inner peripheral surface of the concave portion  45 . The attachment portion  50  and the nut  60  are inserted into the concave portion  45 , and a contact surface  52   a  of the attachment portion  50  abuts to the bottom surface of the concave portion  45  located inside the boss body  41 . The bottom surface of the concave portion  45  has a tapered shape that inclines outside in the diameter direction from the center to the second end surface  41   b , and the tapered bottom surface is the abutting surface  44 . The sensor side opening portion  42   b  of the boss internal flow channel  42  opens at the bottom surface of the concave portion  45 . The boss internal flow channel  42  thus communicates with the concave portion  45 , and the abutting surface  44  is formed in the periphery of the sensor side opening portion  42   b.    
     The attachment portion  50  is a metal member that projects from the sensor body  106   a , is inserted into the concave portion  45  formed in the boss body  41  of the attachment boss  40 , and abuts to the abutting surface  44 . The attachment portion  50  includes inside thereof a sensor side flow channel  51  in which the fuel flows, and also includes a head portion  52  formed in the leading end facing the attachment boss  40  and an axial portion  53  that connects the head portion  52  and the sensor body  106   a.    
     The sensor side flow channel  51  is a through hole that penetrates through the attachment portion  50  in the axial direction, and includes an inlet  51   a  that opens at the leading end of the head portion  52  and an outlet  51   b  that faces a not-shown pressure detection portion built in the sensor body  106   a . The leading end of the head portion  52  is inserted into the sensor side opening portion  42   b  of the boss internal flow channel  42 , and the fuel flows into the sensor side flow channel  51 . The fuel that has flowed into the sensor side flow channel  51  flows to the outlet  51   b,  and the pressure of the fuel is detected by the pressure detection portion built in the sensor body  106   a.    
     The head portion  52  has a mushroom shape. A leading end of the head portion  52  directed to the attachment boss  40  includes a convex inclined surface, and a rear surface of the head portion  52  facing the sensor body  106   a  has a flange shape that projects in the diameter direction from the outer peripheral surface of the axial portion  53 . The inlet  51   a  of the sensor side flow channel  51  is formed in the center of the leading end of the head portion  52 , and a contact surface  52   a  that contacts the abutting surface  44  is formed in the head portion  52  to surround the periphery of the inlet  51   a . The contact between the contact surface  52   a  and the abutting surface  44  in an airtight state forms an annular sealing surface that surrounds the periphery of the inlet  51   a , and prevents the fuel flowing into the sensor side flow channel  51  from the boss internal flow channel  42  from being leaked. On the other hand, the rear surface of the head portion  52  facing the sensor body  106   a  is a bearing surface  52   b  located behind the contact surface  52   a.    
     The axial portion  53  has a cylindrical shape thinner than the maximum diameter of the head portion  52 , and is inserted into the through hole  62  of the nut  60  to penetrate through the through hole  62 . 
     The nut  60  has a hollow cylindrical shape in which a through hole  62  extending in the axial direction is formed and a male screw portion  63  (second screw portion) is formed in the outer peripheral surface. This nut  60  includes in a leading end thereof a pressing portion  64  that is inserted into the concave portion  45  of the attachment boss  40 . 
     The pressing portion  64  is provided in the periphery of the through hole  62  through which the axial portion  53  of the attachment portion  50  penetrates, and faces the bearing surface  52   b  projecting in the axial direction from the peripheral surface of the axial portion  53 . As the pressing portion  64  faces the bearing surface  52   b , the male screw portion  63  is screwed on the female screw portion  43 , and the nut  60  is inserted into the concave portion  45  of the attachment boss  40 , so that the pressing portion  64  presses the bearing surface  52   b  toward the abutting surface  44 . In the fuel pressure sensor  106 , when the attachment portion  50  is assembled to the sensor body  106   a , the nut  60  is assembled between the sensor body  106   a  and the attachment portion  50 . 
     Hereinafter, the connection structure  2  for the fuel pressure sensor according to the second embodiment will be described. 
     To connect the fuel pressure sensor  106  to the fuel rail  103  in the connection structure  2  for the fuel pressure sensor according to the second embodiment  2 , at first, the head portion  52  of the attachment portion  50  of the fuel pressure sensor  106  faces the concave portion  45  formed in the boss body  41  of the attachment boss  40 . Next, the head portion  52  and the nut  60  previously assembled to the fuel pressure sensor  106  are inserted into the concave portion  45 , and the male screw portion  63  is screwed on the female screw portion  43  formed in the inner peripheral surface of the concave portion  45  by rotating the nut  60 . 
     At this time, the pressing portion  64  of the nut  60  contacts the bearing surface  52   b  of the head portion  52 . The bearing surface  52   b  is therefore pressed by screwing the nut  60 , so that the axial force in the direction toward the fuel rail  103  acts to the bearing surface  52   b  from the pressing portion  64 . The head portion  52  is pushed into the concave portion  45  by this axial force, and the contact surface  52   a  is pressed to the abutting surface  44 . When the axial force acting on the bearing surface  52   b  reaches a constant force or more, the contact surface  52   a  is elastically deformed to contact the abutting surface  44  at an airtight state, and a sealing performance is maintained at a high level between the contact surface  52   a  and the abutting surface  44 . As a result, the fuel pressure sensor  106  is connected to the fuel rail  103  in an airtight state. 
     In the connection structure  2  for the fuel pressure sensor according to the second embodiment, the nut  60  that applies the axial force to the attachment portion  50  is also separated from the contact surface  52   a  that is pressed to the abutting surface  44  With this configuration, when the fuel pressure sensor  106  is connected to the fuel rail  103 , the contact surface  52   a  and the abutting surface  44  do not relatively rotate in a contact state, so that the deterioration in the sealing performance due to the shift of the sealing surface by the movement of the contact surface  52   a  that has contacted the abutting surface  44  in an airtight state can be suppressed. 
     In the connection structure  2  for the fuel pressure sensor according to the second embodiment, the female screw portion  43  is formed in the inner peripheral surface of the attachment boss  40 , and the attachment boss  40  includes the concave portion  45  into which the attachment portion  50  and the nut  60  are inserted, and the attachment boss  40  has in the bottom surface thereof the abutting surface  44 . The boss internal flow channel  42  communicates with the concave portion  45 , and the nut  60  has a hollow cylindrical shape that opens at both ends. The attachment portion  50  penetrates through the nut  60 . The male screw portion  63  is formed in the outer peripheral surface of the nut  60 . The nut  60  includes in the leading end thereof inserted into the concave portion  45  the pressing portion  64 . 
     The attachment portion  50  can be thereby connected to the attachment boss  40  with the nut  60  being inserted into the attachment boss  40 . 
     In the connection structure  2  for the fuel pressure sensor according to the second embodiment, as illustrated in  FIG.  3   , the inclination angle of the abutting surface  44  relative to the pressing direction (vertical direction) of the bearing surface  52   b  by the nut  60  and the inclination angle of the contact surface  52   a  relative the pressing direction (vertical direction) of the bearing surface  52   b  are set to be substantially equal. A radially wide sealing surface can be thereby formed between the contact surface  52   a  and the abutting surface  44 . Third Embodiment 
     Hereinafter, a configuration of a connection structure  3  for a fuel pressure sensor according to the third embodiment will be described with reference to  FIGS.  4 ,  5   . 
     The connection structure  3  for the fuel pressure sensor according to the third embodiment includes an attachment boss  70  formed in a fuel rail  103 , an attachment portion  80  provided in a sensor body  106   a  of a fuel pressure sensor  106 , and a nut  90  that fixes the fuel pressure sensor  106  to the attachment boss  70 . 
     The attachment boss  70  includes a boss body  71  fixed to an outer peripheral surface  103   b  of the fuel rail  103 , a boss internal flow channel  72  formed inside the boss body  71 , a male screw portion  73  (first screw portion) formed in the outer peripheral surface of the boss body  71 , and an abutting surface  74  formed in a sensor side opening portion  72   b  of the boss internal flow channel  72 . 
     In the third embodiment, the boss internal flow channel  72  includes a rail side opening portion  72   a  that opens at a first end surface  71   a  that contacts the fuel rail  103  of the boss body  71 , and a sensor side opening portion  72   b  that opens at a second end surface  71   b  of the boss body  71 . The rail side opening portion  72   a  communicates with a port  103   c  formed in the fuel rail  103 , and the fuel in the fuel rail  103  flows into the boss internal flow channel  72  through a port  103   c  and the rail side opening portion  72   a . The inside of the sensor side opening portion  72   b  has a tapered shape that gradually inclines to the opening edge toward the outside in the diameter direction. The tapered inside of the sensor side opening portion  72   b  is an abutting surface  74 . 
     The attachment portion  80  is a metal member that projects from the sensor body  106   a , and abuts to the abutting surface  74  of the attachment boss  70 . This attachment portion  80  includes inside thereof a sensor side flow channel  81  in which the fuel flows, and also includes a head portion  82  formed in the leading end that faces the attachment boss  70  and an axial portion  83  that connects the head portion  82  and the sensor body  106   a.    
     The sensor side flow channel  81  is a through hole that penetrates through the attachment portion  80  in the axial direction, and includes an inlet  81   a  that opens at the leading end of the head portion  82  and an exit  81   b  that faces a not-shown pressure detection portion built in the sensor body  106   a . The leading end of the head portion  82  is inserted into the sensor side opening portion  72   b  of the boss internal flow channel  72 , and the fuel flows in the sensor side flow channel  81 . The fuel that has flowed in the sensor side flow channel  81  flows to the exit  81   b , and the pressure of the fuel is detected by the pressure detection portion built in the sensor body  106   a.    
     The head portion  82  has a mushroom shape. A leading end of the head portion  82  that faces the attachment boss  70  has a curved convex circular arc shape and a rear surface of the head portion  82  that faces the sensor body  106   a  has a flange shape projecting in the diameter direction from the outer peripheral surface of the axial portion  83 . The inlet  81   a  of the sensor side flow channel  81  is formed in the center of the leading end of the head portion  82 , and a contact surface  82   a  that abuts to the abutting surface  74  is formed in the head portion  82  to surround the peripheral of the inlet  81   a . The contact surface  82   a  surrounds the whole peripheral of the inlet  81   a . The contact between the contact surface  82   a  and the abutting surface  74  in an airtight state forms an annular sealing surface that surrounds the peripheral of the inlet  81   a  between the contact surface  82   a  and the abutting surface  74  to prevent the fuel that flows in the sensor side flow channel  81  from the boss internal flow channel  72  from being leaked. On the other hand, the rear surface of the head portion  82  that faces the sensor body  106   a  is a bearing surface  82   b  provided behind the contact surface  82   a.    
     The axial portion  83  has a cylindrical shape thinner than a maximum outer diameter W 1  of the head portion  82 , and is inserted into the through hole  92  of the nut  90  to penetrate through the through hole  92 . 
     The nut  90  is a bagged nut having width across flats (typically, hexagon) as an external shape. The nut  60  has at one end thereof an opening portion  91  into which the boss body  71  of the attachment boss  70  is inserted and at the other end thereof a through hole  92  through which the axial portion  83  of the attachment portion  80  penetrates. A female screw portion  93  (second screw portion) that screws on a male screw portion  73  of the attachment boss  70  is formed in the inner peripheral surface of the nut  90 . A pressing portion  94  is formed in the periphery of the through hole  92 . 
     The measurement of the through hole  92  is set such that an inner diameter W is smaller than a maximum outer diameter W 2  of the sensor body  106   a  and is larger than a maximum outer diameter W 1  of the head portion  82  and a maximum outer diameter W 3  of the axial portion  83 . The attachment portion  80  can thereby penetrate through the through hole  92 . In the third embodiment, a plurality (herein two) of divided collars  95  arranged side by side without a space are provided between the pressing portion  94  and the bearing surface  82   b  in the peripheral direction of the attachment portion  80 . 
     As illustrated in  FIG.  5   , the two divided collars  95  have a cylindrical shape when end faces arranged side by side in the circumferential direction contact, and surround the periphery of the attachment portion  80 . Each of the divided collars  95  includes a tubular portion  95   a  and a flange portion  95   b.    
     The tubular portion  95   a  curves into a circular arc shape along the outer peripheral surface  83   a  of the axial portion  83  of the attachment portion  80 , and covers the outer peripheral surface  83   a  of the axial portion  83 . The inner diameter of the space surrounded by the two tubular portions  95   a  when the two divided collars  95  contact is slightly larger than the maximum outer diameter W 3  of the axial portion  83 , and the axial portion  83  penetrates through the space surrounded by the two tubular portions  95   a . The cylindrical portion formed by the two divided collars  95  has the maximum outer diameter smaller than the inner diameter W of the through hole  92  and can be inserted into the through hole  92 . 
     The flange portion  95   b  projects in the diameter direction from the end portion of the tubular portion  95   a  on the head portion  82  side, and is sandwiched between the pressing portion  94  and the bearing surface  82   b . The flange portion  95   b  includes a first surface  96   a  that contacts the pressing portion  94  and a second surface  96   b  that contacts the bearing surface  82   b . The first surface  96   a  is formed into a flat surface orthogonal to the tubular portion  95   a , and the second surface  96   b  is formed into a curved surface along the bearing surface  82   b.    
     Hereinafter, a connection procedure of the fuel pressure sensor  106  in the connection structure  3  for the fuel pressure sensor according to the third embodiment will be described with reference to  FIGS.  6 A to  6 E . 
     To connect the fuel pressure sensor  106  to the fuel rail  103  in the connection structure  3  for the fuel pressure sensor according to the third embodiment, at first, as illustrated in  FIG.  6 A , the attachment portion  80  provided in the fuel pressure sensor  106  faces the through hole  92  of the nut  90 . Next, the head portion  82  of the attachment portion  80  is inserted inside the nut  90  through the through hole  92 . 
     The maximum outer diameter W 1  of the head portion  82  is smaller than the inner diameter W of the through hole  92 . The attachment portion  80  can be therefore easily inserted inside the nut  90 . 
     As illustrated in  FIG.  6 B , after the head portion  82  is inserted inside the nut  90 , the attachment portion  80  is offset from the center of the through hole  92 , and a part of the space between the head portion  82  and the inner peripheral surface of the nut  90  is increased. One of the divided collars  95  is inserted inside the nut  90  from the tubular portion  95   a  through the opening portion  91  in the increased space. 
     As illustrated in  FIG.  6 C , after the flange portion  95   b  of one of the divided collars  95  contacts the pressing portion  94 , the attachment portion  80  is moved to the center of the through hole  92 , the flange portion  95   b  is sandwiched between the pressing portion  94  and the bearing surface  82   b , and one of the divided collars  95  is held to prevent from falling from the nut  90 . 
     Next, the other of the divided collars  95  is inserted inside the nut  90  from the tubular portion  95   a  through the opening portion  91  in the space between the head portion  82  and the inner peripheral surface of the nut  90 . At this time, the other of the divided collar  95  is inserted by inclining the nut  90  and the other of the divided collars  95 . The flange portion  95   b  of the other of the divided collars  95  thereby contacts the pressing portion  94 , and the flange portion  95   b  of the other of the divided collars  95  is sandwiched between the pressing portion  94  and the bearing surface  82   b.    
     The two divided collars  95  are housed between the attachment portion  80  and the nut  90 , so that the flange portion  95   b  is sandwiched between the pressing portion  94  and the bearing surface  82   b  to be held in the nut  90 . After the two divided collars  95  are housed in the nut  90 , as illustrated in  FIG.  6 D , the nut  90  is put on the attachment boss  70 . As illustrated in  FIG.  6 E , the female screw portion  93  formed in the inner peripheral surface of the nut  90  is screwed on the male screw portion  73  formed in the outer peripheral surface of the boss body  71 , and the nut  90  is fixed to the boss body  71 . The boss body  71  is thereby inserted into the nut  90  through the opening portion  91 , and the attachment portion  80  comes close to the boss body  71 . 
     When the nut  90  is further screwed until the attachment portion  80  of the fuel pressure sensor  106  abuts to the boss body  71 , the head portion  82  is inserted into the sensor side opening portion  72   b  of the boss internal flow channel  72 , and the contact surface  82   a  contacts the abutting surface  74 . 
     At this time, the pressing portion  94  of the nut  90  faces the first surface  96   a  of the divided collar  95 . Accordingly, when the nut  90  comes close to the fuel rail  103  by screwing the nut  90 , the axial force in the direction toward the fuel rail  103  acts on the first surface  96   a  from the pressing portion  94 . On the other hand, the second surface  96   b  of the divided collar  95  contacts the bearing surface  82   b  of the attachment portion  80 . Accordingly, the axial force acting on the first surface  96   a  from the pressing portion  94  acts on the bearing surface  82   b  through the second surface  96   b  of the divided collar  95 . The contact surface  82   a  is thereby pressed to the abutting surface  74 , and the contact surface  82   a  is elastically deformed to contact the abutting surface  74  in an airtight state when the axial force acting on the bearing surface  82   b  reaches a constant force or more. A sealing performance is thereby secured between the contact surface  82   a  and the abutting surface  74  at a high level. As a result, the fuel pressure sensor  106  is connected to the fuel rail  103  in an airtight state. 
     Hereinafter, the operation in the connection structure  3  for the fuel pressure sensor according to the third embodiment will be described. 
     As described above, in the connection structure  3  for the fuel pressure sensor according to the third embodiment, the attachment portion  80  provided in the fuel pressure sensor  106  is pressed by the nut  90  that is screwed on the attachment boss  70  formed in the fuel pressure rail  103 . That is, when securing the sealing performance by pressing the contact surface  82   a  to the abutting surface  74 , the nut  90  that applies the axial force to the attachment portion  80  is separated from the contact surface  82   a  that is pressed to the abutting surface  74 . With this configuration, when the fuel pressure sensor  106  is connected to the fuel rail  103 , the contact surface  82   a  and the abutting surface  74  do not relatively rotate in a contact state. Thus, the contact surface  82   a  that has contacted the abutting surface  74  is prevented from moving in the rotation direction, so that the deterioration in the sealing performance due to the shift of the sealing surface can be suppressed. As a result, a stable airtight performance can be secured between the fuel pressure sensor  106  and the fuel rail  103 . 
     In the third embodiment, the inner diameter W of the through hole  92  formed in the nut  90  is set to be larger than the maximum outer diameter W 1  of the head portion  82  which is the maximum outer diameter of the attachment portion  80 . As illustrated in  FIG.  6 A , the nut  90  can be thereby post-assembled to the fuel pressure sensor  106 , and the nut  90  can be selected according to the shape of the attachment boss  70 , for example. 
     In the third embodiment, the two divided collars  95  arranged side by side in the circumference direction are provided between the pressing portion  94  of the nut  90  and the bearing surface  82   b  of the attachment portion  80 . With this configuration, the axial force can be applied to the bearing surface  82   b  from the pressing portion  94  while preventing the nut  90  from falling from the attachment portion  80  of the fuel pressure sensor  106 . The contact surface  82   a  can be thereby appropriately pressed to the abutting surface  74 , and a required sealing performance can be maintained. 
     Further, in the third embodiment, the divided collar  95  includes the tubular portion  95   a  that covers the outer peripheral surface  83   a  of the axial portion  83  of the attachment portion  80  and the flange portion  95   b  that projects from the tubular portion  95   a  and is sandwiched between the pressing portion  94  and the bearing surface  82   b . Accordingly, when the divided collar  95  moves in the diameter direction, the tubular portion  95   a  interferes with the axial portion  83  of the attachment portion  80 , so that the movement of the divided collar  95  can be suppressed. Thus, the position of the flange portion  95   b  sandwiched between the pressing portion  94  and the bearing surface  82   b  is stabilized, and the flange portion  95   b  can be prevented from falling between the pressing portion  94  and the bearing surface  82   b.    
     The third embodiment shows the example in which the flange portion  95   b  of the divided collar  95  that is sandwiched between the pressing portion  94  and the bearing surface  82   b  includes the first surface  96   a  formed into a flat surface orthogonal to the tubular portion  95   a  and the second surface  96   b  formed into the curved surface along the bearing surface  52   b . However, the shape of the flange portion  95   b  of the divided collar  95  is not limited thereto. For example, as a flange portion  95   c  of a divided collar  95 A according to a first modified example illustrated in  FIG.  7 A , both of a first surface  96   c  that contacts the pressing portion  94  and a second surface  96   d  that contacts the bearing surface  82   b  may be formed in a flat surface orthogonal to the tubular portion  95   a.    
     Further, as a flange portion  95 d of a divided collar  95 B according to a second modified example illustrated in  FIG.  7 B , the rim portion of the flange portion  95 d may be bent into a crank shape, and the flange portion  95 d may include a peripheral wall portion  96   e  that surrounds the periphery of the head portion  82 . In this case, when the divided collar  95 B moves in the diameter direction, the tubular portion  95   a  interferes with the axial portion  83 , and the peripheral wall portion  96   e  interferes with the head portion  82 . The movement of the divided collar  95 B can be thereby further appropriately suppressed. In addition, in the divided collar  95 B according to the second modified example, both of the first surface  96   c  that contacts the pressing portion  94  and the second surface  96   d  that contacts the bearing surface  82   b  may be formed in a flat surface orthogonal to the tubular portion  95   a , or the second surface  96   d  may be formed in a curved surface along the bearing surface  82   b.    
     Fourth Embodiment 
     Hereinafter, a configuration of a connection structure for a fuel pressure sensor according to the fourth embodiment will be described with reference to  FIG.  8   . 
     The connection structure  4  for a fuel pressure sensor according to the fourth embodiment includes an attachment boss  210  formed in a fuel rail  103 , an attachment portion  202  provided in a sensor body  106   a  of a fuel pressure sensor  106 , and a nut  230  that fixes the fuel pressure sensor  106  to the attachment boss  210 . 
     The attachment boss  210  includes a boss body  211  fixed to an outer peripheral surface  103   b  of the fuel rail  103 , a boss internal flow channel  212  formed inside the boss body  211 , a male screw portion  213  (first screw portion) formed in the outer peripheral surface of the boss body  211 , and an abutting surface  214  formed in a sensor side opening portion  212   b  of the boss internal flow channel  212 . 
     The inside of the sensor side opening portion  212   b  of the boss internal flow channel  212  that opens at a second end surface  211   b  of the boss body  211  has a tapered shape that inclines outside in the diameter direction from the center to the opening edge. The tapered inside of the sensor side opening portion  212   b  is the abutting surface  214 . The rail side opening portion  212   a  of the boss internal flow channel  212  that opens at a first end surface  211   a  of the boss body  211  communicates with a port  103   c  formed in the fuel rail  103 . 
     The attachment portion  220  is a metal member that projects from the sensor body  106   a  and abuts to the abutting surface  214  of the attachment boss  210 . The attachment portion  220  has inside thereof a sensor side flow channel  221  in which the fuel flows, and includes a head portion  222  formed in the leading end facing the attachment boss  210 , and an axial portion  223  that connects the head portion  222  and the sensor body  106   a.    
     The head portion  222  has a mushroom shape. A leading end of the head portion  222  directed to the attachment boss  210  has a convex inclined surface and a rear surface of the head portion  222  that faces the sensor body  106   a  is formed into a flange shape projecting from the outer peripheral surface of the axial portion  223  in the diameter direction. An inlet  221   a  of the sensor side flow channel  221  is formed in the center of the leading end of the head portion  222 . A contact surface  222   a  that is inserted into the sensor side opening portion  212   b  of the boss internal flow channel  212  and contacts the abutting surface  214  is formed in the head portion  222  to surround the periphery of the inlet  221   a.    
     The contact surface  222   a  formed in the leading end of the head portion  222  includes a flat surface  222   c  and an inclined surface  222   d  that surrounds the periphery of the flat surface  222   c . The flat surface  222   c  is a circular plane having the inlet  221   a  of the sensor side flow channel  221  as the center, and faces the boss internal flow channel  212 . The inclined surface  222   d  is a surface that surrounds the whole periphery of the flat surface  222   c  and inclines outside in the diameter direction from the flat surface  222   c  toward the axial portion  223 . The contact between the contact surface  222   a  and the abutting surface  214  in an airtight state forms an annular sealing surface that surrounds the periphery of the inlet  221   a  between the contact surface  222   a  and the abutting surface  214 , which prevents the fuel flowing in the sensor side flow channel  221  from the boss internal flow channel  212  from being leaked. On the other hand, the rear surface facing the sensor body  106   a  of the head portion  222  is a bearing surface  222   b  provided behind the contact surface  222   a.    
     The nut  230  is a bagged nut having width across flats (typically, hexagon) as an external shape. The nut  230  includes at one end thereof an opening portion  231  into which the boss body  211  of the attachment boss  210  is inserted and at the other end thereof a through hole  232  through which the axial portion  223  of the attachment portion  220  penetrates. A female screw portion  233  (second screw portion) that screws on the male screw portion  213  of the attachment boss  210  is formed in the inner peripheral surface of the nut  230 . A pressing portion  234  is formed in the periphery of the through hole  232 . 
     In this fourth embodiment, the abutting surface  214  has a tapered shape that inclines outside in the diameter direction from the center to the opening edge. The inclined surface  222   d  of the contact surface  222   a  formed in the leading end of the head portion  222  has a surface that inclines outside in the diameter direction toward the axial portion  223 . Both of the abutting surface  214  and the inclined surface  222   d  incline in the pressing direction (vertical direction) of the bearing surface  222   b  by the nut  230 . As illustrated in  FIG.  8   , the inclination angle θ 1  of the bearing surface  222   b  relative to the pressing direction (vertical direction) of the abutting surface  214  is larger than an inclination angle θ 2  of the bearing surface  222   b  relative to the pressing direction (vertical direction) of the inclined surface  222   d.    
     Hereinafter, the operation of the connection structure  4  for the fuel pressure sensor according to the fourth embodiment will be described. 
     To connect the fuel pressure sensor  106  to the fuel rail  103  in the connection structure  4  for the fuel pressure sensor according to the fourth embodiment, the nut  230  is screwed to the attachment boss  210  formed in the fuel rail  103 , and the attachment portion  220  provided in the fuel pressure sensor  106  is pressed by the nut  230 . The axial force thereby acts on the bearing surface  222   b  of the attachment portion  220  from the pressing portion  234  of the nut  230 , and the contact surface  222   a  is pressed to the abutting surface  214  by the axial force, so that the sealing surface is formed. As a result, the fuel pressure sensor  106  is connected to the fuel rail  103  in an airtight state. 
     In this fourth embodiment, the contact surface  222   a  that is pressed to the abutting surface  214  includes the flat surface having the inlet  221   a  of the sensor side flow channel  221  as the center and the inclined surface  222   d  that inclines outside in the diameter direction from the flat surface  222   c  to the axial portion  223 . The inclination angle θ 1  of the abutting surface  214  relative to the pressing direction (vertical direction) of the bearing surface  222   b  is larger than the inclination angle θ 2  of the inclined surface  222   d  relative to the pressing direction (vertical direction) of the bearing surface  222   b.    
     The abutting surface  214  therefore has an inclination gentler than that of the inclined surface  222   d . The border line (hereinafter, border portion  222   e ) between the flat surface  222   c  that is the leading end of the inclined surface  222   d  and the inclined surface  222   d  in the contact surface  222   a  contacts the abutting surface  214 . The contact area between the abutting surface  214  and the contact surface  22   a  can be thereby reduced, and the narrow liner sealing surface can be formed between the contact surface  222   a  and the abutting surface  214 . The deterioration in the sealing performance due to the variations in the shapes of the abutting surface  214  and the contact surface  222   a  can be suppressed. The axal force acting on the contact surface  222   a  can be also concentrated in the border portion  222   e , so that the elastic deformation of the contact surface  222   a  is improved, and the sealing performance between the contact surface  222   a  and the abutting surface  214  can be further enhanced. 
     In the connection structure  4  for the fuel pressure sensor according to the fourth embodiment illustrated in  FIG.  8   , the male screw portion  213  is formed in the outer peripheral surface of the boss body  211  of the attachment boss  210 , and the female screw portion  233  is formed in the inner peripheral surface of the bagged nut  230 . However, in the connection structure for the fuel pressure sensor that forms the female screw portion in the inner peripheral surface of the attachment boss having the concave portion, and presses the attachment portion by screwing the nut into the concave portion of the attachment boss as shown in the second embodiment, for example, the inclination angle θ 1  of the abutting surface  214  relative to the pressing direction may be set to be larger than the inclination angle θ 2  of the inclined surface  222   d  relative to the pressing direction. In this case, the border portion  222   e  of the border line between the flat surface  222   c  and the inclined surface  222   d  can also contact the abutting surface, and the deterioration in the sealing performance due to the variations in the shape can be prevented by forming the liner sealing surface. 
     Fifth Embodiment 
     A configuration of a connection structure  5  for a fuel pressure sensor according to the fifth embodiment will be described with reference to  FIG.  9   . 
     The connection structure  5  for the fuel pressure sensor according to the fifth embodiment includes an attachment boss  240  formed in the fuel rail  103 , an attachment portion  250  provided in a sensor body  106   a  of the fuel pressure sensor  106 , and a nut  260  that fixes the fuel pressure sensor  106  to the attachment boss  240 . 
     The attachment boss  240  includes a boss body  241  fixed to an outer peripheral surface  103   b  of the fuel rail  103 , a boss internal flow channel  242  formed inside a boss body  241 , a male screw portion  243  (first screw portion) formed in the outer peripheral surface of the boss body  241 , and an abutting surface  244  formed in the sensor side opening portion  242   b  of the boss internal flow channel  242 . 
     The boss internal flow channel  242  includes a rail side opening portion  242   a  that opens at a first end surface  241   a  that contacts the fuel rail  103  of the boss body  241  and a sensor side opening portion  242   b  that opens at a second end surface  241   b  of the boss body  241 . The inside of the sensor side opening portion  242   b  has a tapered shape that inclines outside in the diameter direction from the center to the opening edge. The tapered inside of the sensor side opening portion  242   b  is an abutting surface  244 . 
     The attachment portion  250  is a metal member that projects from the sensor body  106   a  and abuts to the abutting surface  244  of the attachment boss  240 . The attachment portion  250  includes inside thereof a sensor side flow channel  251  in which the fuel flows, and also includes a head portion  252  formed in the leading end facing the attachment boss  240  and an axial portion  253  that connects the head portion  252  and the sensor body  106   a.    
     The sensor side flow channel  251  is a through hole that penetrates through the attachment portion  250  in the axial direction, and includes an inlet  251   a  that opens at the leading end of the head portion  252  and an outlet  251   b  that faces a not shown pressure detection portion built in the sensor body  106   a . The leading end of the head portion  252  is inserted into the sensor side opening portion  242   b  of the boss internal flow channel  242 . 
     The head portion  252  has a mushroom shape. A leading end of the head portion  252  directed to the attachment boss  240  is curved into a convex circular arc shape, and a rear surface of the head portion  252  facing the sensor body  106   a  has a flange shape that projects from the outer peripheral surface of the axial portion  253  in the diameter direction. An inlet  251   a  of the sensor side flow channel  251  is formed in the center of the leading end of the head portion  252 , and a contact surface  252   a  that contacts the abutting surface  244  is formed in the head portion  252  to surround the periphery of the inlet  251   a . The contact surface  252   a  surrounds the whole periphery of the inlet  251   a . The contact between the contact surface  252   a  and the abutting surface  244  in an airtight state forms an annular sealing surface that surrounds the periphery of the inlet  251   a  between the contact surface  252   a  and the abutting surface  244 , which prevents the fuel flowing in the sensor side flow channel  251  from the boss internal flow channel  242  from being leaked. On the other hand, the rear surface facing the sensor body  106   a  of the head portion  252  is a bearing surface  252   b  provided behind the contact surface  252   a . 
     The axial portion  253  has a cylindrical shape narrower than a maximum outer diameter W 1  of the head portion  252 , and is inserted into the through hole  262  of the nut  260  to penetrate through the through hole  262 . 
     The nut  260  is a bagged nut having width across flats (typically, hexagon) as an external shape, and has at one end thereof an opening portion  261  into which the boss body  241  of the attachment boss  240  is inserted and at the other end thereof a through hole  262  through which the axial portion  253  of the attachment portion  250  penetrates. A female screw portion  263  (second screw portion) that screws on the male screw portion  243  of the attachment boss  240  is formed in the inner peripheral surface of the nut  260 . The nut  260  has a hollow cylindrical shape into which the attachment boss  240  is inserted. A pressing portion  264  is formed in the periphery of the through hole  262 . 
     The female screw portion  263  is formed in a region from the opening portion  261  at one end of the nut  260  to the intermediate position in the axial direction. The region in which the female screw portion  263  is formed is referred to as “screw machined portion X”. On the other hand, the nut  260  has a swaging portion Yin a region near the other end of the nut  260  in which the through hole  262  is formed, and has a thickness portion Z between the screw machined portion X and the swaging portion Y. 
     The swaging portion Y is a region that is elastically deformed in the inner diameter direction in the assembled state to the fuel pressure sensor  106  illustrated in  FIG.  9   . A dent portion  265  in which the inner peripheral surface of the nut  260  is annularly dented is formed in the swaging portion Y. The swaging portion Y has a thickness W 5  thinner than a thickness W 4  of the screw machined portion X when assembled to the fuel pressure sensor  106  illustrated in  FIG.  9    and before being assembled to the fuel pressure sensor  106  illustrated in  FIG.  10    (single nut). 
     The thickness portion Z is an area whose rigidity is increased by setting a thickness W 6  to be thicker than the thickness W 5  of the swaging portion Y, and by the absence of the female screw portion  263 . 
     The through hole  262  has a size that can retain the attachment portion  250 . The through hole  262  has an inner diameter W smaller than the maximum outer diameter W 1  of the head portion  252  and the maximum outer diameter W 2  of the sensor body  106   a , and larger than the maximum outer diameter W 3  of the axial portion  253 . 
     The inner diameter W of the through hole  262  is smaller than the maximum outer diameter W 2  of the sensor body  106   a , and larger than the maximum outer diameter W 1  of the head portion  252  and the maximum outer diameter W 3  of the axial portion  253  in the single nut illustrated in  FIG.  10   . The attachment portion  250  can penetrate through the through hole  262 . That is, the through hole  262  is formed by reducing the opening portion having a size through which the attachment portion  250  penetrates to the size that can retain the attachment portion  250  with the elastic deformation of the swaging portion Y. 
     The pressing portion  264  formed in the periphery of the through hole  262  thereby faces the bearing surface  252   b  projecting in the diameter direction from the peripheral surface of the axial portion  253 . The female screw portion  263  is screwed on the male screw portion  243 , and the nut  260  comes close to the fuel rail  103 , so that the pressing portion  264  presses the bearing surface  252   b  to the abutting surface  244 . 
     Hereinafter, the connection procedure of the fuel pressure sensor  106  in the connection structure  5  for the fuel pressure sensor according to the fifth embodiment will be described with reference to  FIGS.  11 A to  11 D . 
     To connect the fuel pressure sensor  106  to the fuel rail  103  in the connection structure  5  for the fuel pressure sensor according to the fifth embodiment, at first, the attachment portion  250  provided in the fuel pressure sensor  106  faces the through hole  262  of the nut  260 , as illustrated in  FIG.  11 A . Next, the head portion  252  of the attachment portion  250  is inserted into the nut  260  through the through hole  262 . 
     In the single nut before being assembled to the fuel pressure sensor  106 , the inner diameter W of the through hole  262  is larger than the maximum outer diameter W 1  of the head portion  252 . The attachment portion  250  can penetrate through the through hole  262 . With this, the attachment portion  250  can be easily inserted inside the nut  260 . 
     After the head portion  252  is inserted inside the nut  260 , the swaging portion Y of the nut  260  is swaged as illustrated in  FIG.  11 B . In addition, “swaging” is meant to reduce a diameter with the elastic deformation by pressing the swaging portion Y in the inner diameter direction from the periphery. At this time, the through hole  262  is reduced by swaging the swaging portion Y to deform the nut  260  to reach the inner diameter W of the through hole  262  smaller than the maximum outer diameter W 1  of the head portion  252  and a size capable of retaining the attachment portion  250 . As a result, the nut  260  is prevented from falling from the attachment portion  250  through the through hole  262 . At this time, the deformation of the female screw portion  263  in the inner diameter direction is controlled by the thickness portion Z. 
     As illustrated in  FIG.  11 C , after the swaging portion Y of the nut  260  is swaged, the nut  260  is put on the attachment boss  240 . Next, as illustrated in  FIG.  11 D , the nut  260  is rotated, and the female screw portion  263  formed in the inner peripheral surface of the nut  260  is screwed on the male screw portion  243  formed in the outer peripheral surface of the boss body  241 , and the nut  260  is fixed to the boss body  241 . The boss body  241  is thereby inserted into the nut  260  through the opening portion  261 , and the attachment portion  250  abuts to the boss body  241 . 
     At this time, the head portion  252  is inserted into the sensor side opening portion  242   b  of the boss internal flow channel  242 , and the contact surface  252   a  contacts the abutting surface  244 . The pressing portion  264  of the nut  260  contacts the bearing surface  252   b  of the attachment portion  250 , and applies the axial force in the direction toward the fuel rail  103  on the bearing surface  252   b . The contact surface  252   a  is thereby pressed to the abutting surface  244 , and the contact surface  252   a  is elastically deformed to contact the abutting surface  244  in an airtight state when the axial force acting on the bearing surface  252   b  reaches a constant force or more, so that the sealing performance can be maintained between the contact surface  252   a  and the abutting surface  244  at a high level. As a result, the fuel pressure sensor  106  is connected to the fuel rail  103  in an airtight state. 
     Hereinafter, the operation in the connection structure  5  for the fuel pressure sensor according to the fifth embodiment will be described. 
     As described above, in the connection structure  5  for the fuel pressure sensor according to the fifth embodiment, in the single nut  260 , the inner diameter W of the through hole  262  is set to be larger than the maximum outer diameter W 1  of the head portion  252  that is the maximum outer diameter of the attachment portion  250 . As illustrated in  FIG.  11 A , the nut  260  can be thereby post-assembled to the fuel pressure sensor  106 , and the nut  260  can be selected according to the shape of the attachment boss  240 , for example. 
     In the fifth embodiment, the nut  260  includes, in the region from the other end of the nut  260  in which the through hole  262  is formed to the screw machined portion X, the swaging portion Y having the thickness W 5  thinner than the thickness W 4  of the screw machined portion X and elastically deformed in the inner diameter direction. On the other hand, the through hole  262  is formed by reducing the opening portion having a size through which the attachment portion  250  penetrates to the size capable of retaining the attachment portion  250  with the elastic deformation of the swaging portion Y. The nut  260  can be thus prevented from falling from the attachment portion  250 . The axial force can be thereby transferred from the nut  260  to the attachment portion  250  without using the divided collars as the third embodiment, and the increase in the number of components can be prevented. As the thickness W 5  of the swaging portion Y is thinner than the thickness W 4  of the screw machined portion X, the swaging portion Y can be appropriately swaged when swaging the swaging portion Y. 
     As described above, the connection structure for the fuel pressure sensor according to the present disclosure is described with reference to the first to fifth embodiments. However, the embodiment is not limited to thereto. Any change in a design and addition should be allowed as long as they do not depart from the gist of the invention according to each claim. 
     The third embodiment shows the example in which the two divided collars are arranged side by side in the circumference direction between the pressing portion  94  and the bearing surface  82   b  without a space therebetween. However, a plurality of divided collars  95  may be arranged between the pressing portion  94  and the bearing surface  82   b , and the axial force acting in the direction toward the fuel rail  103  from the pressing portion  94  may act on the bearing surface  82   b . In this case, three or more divided collars  95  may be arranged, and a space may be provided between the divided collars  95 . 
     The fifth embodiment shows the example in which the dent portion  265  is formed in the inner peripheral surface of the nut  260 , and the thickness W 5  of the swaging portion is set to be thinner than the thickness W 4  of the screw machined portion X. However, the embodiment is not limited thereto. For example, as a nut  270  illustrated in  FIG.  12 A , the thickness W 5  can set to thinner than the thickness W 4  of the screw machined portion X by forming a recess portion  271  on the outer peripheral surface of the nut  270  in the swaging portion Y. 
     In this case, when the swaging portion Y is swaged, the end surface  273  in which the through hole  272  is formed and the portion between the recess portion  271  and the end surface  273  in the swaging portion Y are gradually elastically deformed. As a result, as illustrated in  FIG.  12 B , the level difference is formed in the peripheral surface of the nut  270 .