Patent Publication Number: US-9897043-B2

Title: Air pump, module, and evaporated fuel processing system

Description:
TECHNICAL FIELD 
     The present invention relates to an air pump used for diagnosing a leak by utilizing a pressure fluctuation of automobile piping, a module configured by the air pump, and an evaporated fuel processing system that uses the air pump. 
     BACKGROUND ART 
     For the purpose of preventing air pollution, an evaporation system (evaporated fuel processing system) for processing evaporated gas is mounted to an automobile to prevent the evaporated gas (evaporated fuel) generated in a fuel tank from being released into the atmosphere. 
     In North America, it is further prescribed by law to check whether or not an abnormality such as breakage, a crack, or a hole is present in piping itself of the evaporation system at a specific frequency. Accordingly, it is necessary to perform a leak diagnosis with the piping of the evaporation system and the following method is generally used: a pressure is applied to the piping of the evaporation system in a sealed state, and a fluctuation of the pressure is monitored. 
     The method in which the pressure is applied to the piping of the evaporation system during the leak diagnosis differs depending on an automobile manufacturer, and the method includes a method that uses an air pump and a method that uses a pressure fluctuation caused by natural heat radiation. 
     While the leak diagnosis in the case of using the natural heat radiation is capable of performing the diagnosis without generating a noise, there are disadvantages that a long diagnosis time increases total power consumption and also that a sufficient diagnosis frequency cannot be secured. 
     On the other hand, the leak diagnosis in the case of using the air pump can be carried out in a short time period to thereby achieve power saving and secure the sufficient diagnosis frequency. However, as described about a configuration for absorbing an operation sound of a leak diagnosis apparatus in Patent Document 1, and a configuration for alleviating a collision inside a leak diagnosis apparatus in Patent Document 2, there occurs a problem that a noise is generated during the diagnosis. Since the leak diagnosis in the case of using the air pump is performed under a quiet condition during stop of an engine, the noise during the diagnosis, in particular, poses a problem as an abnormal noise. 
     Note that Non-Patent Document 1 describes a general sound absorbing structure that absorbs sound, but is not limited to the noise generated during the leak diagnosis. 
     CITATION LIST 
     Patent Documents 
     
         
         Patent Document 1: Japanese Patent Application Laid-open No. 2012-117381 
         Patent Document 2: Japanese Patent Application Laid-open No. 2005-69103 
       
    
     Non-Patent Documents 
     
         
         Non-Patent Document 1: Osamu Mochizuki, Yoshiyuki Maruta “Ryutaionkougaku Nyumon (Introduction of Fluid Sound Engineering)” Asakura Publishing Co., Ltd., Apr. 30, 1996, p. 154-155 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     As described above, the leak diagnosis in the case of using the air pump has the problem of the noise generation during the diagnosis, and there exist various noise generation sources. For example, a check valve provided in the air pump also is one of the generation sources, and a vibration of the check valve during operation of the air pump generates the noise. 
     The present invention has been made in order to solve the above problem, and an object thereof is to reduce the noise generated from the check valve of the air pump during the leak diagnosis. 
     Means for Solving the Problems 
     An air pump according to the invention changes, for a leak diagnosis, an internal pressure of an evaporated fuel processing system that collects evaporated fuel generated in a fuel tank to introduce the collected evaporated fuel into an engine, and includes: a housing provided with an opening portion communicating with the evaporated fuel processing system and an opening portion communicating with an air side; a check valve disposed between the two opening portions of the housing to prevent a backflow of discharged gas; and a partition plate in which a hole serving as a first reducing part is opened and which is disposed at the opening portion from which the gas is discharged out of the two opening portions of the housing, to separate an inside from an outside of the housing, wherein a pipe in which a hole is formed is protrusively provided in the partition plate, and the pipe is extended toward the check valve to constitute a second reducing part with the pipe and the check valve. 
     A module according to the invention includes: an electromagnetic valve that opens and closes a flow path connecting an air side and an evaporated fuel processing system that collects evaporated fuel generated in a fuel tank to introduce the collected evaporated fuel into an engine; an air pump that changes an internal pressure of the evaporated fuel processing system for a leak diagnosis; and a case that contains the electromagnetic valve and the air pump, wherein the air pump has a housing provided with an opening portion communicating with the evaporated fuel processing system and an opening portion communicating with the air side, and a check valve disposed between the two opening portions of the housing to prevent a backflow of discharged gas, and one surface of the case is a partition plate in which a hole serving as a first reducing part is opened and which faces the opening portion from which the gas is discharged out of the two opening portions provided in the housing of the air pump, to separate an inside from an outside of the housing, wherein a pipe in which a hole is formed is protrusively provided in the partition plate, and the pipe is extended toward the check valve to constitute a second reducing part with the pipe and the check valve. 
     An evaporated fuel processing system according to the invention collects evaporated fuel generated in a fuel tank to introduce the collected evaporated fuel into an engine, and includes: an air pump that changes an internal pressure of the evaporated fuel processing system for a leak diagnosis; and an insertion opening into which the air pump is inserted, wherein the air pump has a housing provided with an opening portion communicating with the inside of the evaporated fuel processing system and an opening portion communicating with an air side, and a check valve disposed between the two opening portions of the housing to prevent a backflow of discharged gas, and the insertion opening has a partition plate in which a hole serving as a first reducing part is opened and which faces the opening portion from which the gas is discharged out of the two opening portions provided in the housing of the air pump, to separate an inside from an outside of the housing, wherein a pipe in which a hole is formed is protrusively provided in the partition plate, and the pipe is extended toward the check valve to constitute a second reducing part with the pipe and the check valve. 
     Effect of the Invention 
     According to the invention, the partition plate is adapted to separate the inside from outside of the housing on the side of the opening portion from which the gas is discharged out of the opening portions provided in the housing of the air pump, to thereby form a space for sound reduction on a downstream side of the check valve, and hence it is possible to reduce noise generated from the check valve of the air pump during the leak diagnosis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing a configuration of an air pump according to Embodiment 1 of the invention, a leak diagnosis apparatus that includes the air pump, and an evaporation system that serves as a diagnosis target by the leak diagnosis apparatus; 
         FIG. 2  is a cross-sectional view of the air pump according to Embodiment 1 of the invention; 
         FIG. 3  is a view showing a sound reduction effect in Embodiment 1 of the invention; 
         FIG. 4  is a cross-sectional view showing a modification of the air pump according to Embodiment 1 of the invention; 
         FIGS. 5( a ) to 5( d )  have plan views and cross-sectional views showing modifications of a partition plate in Embodiment 1 of the invention; 
         FIGS. 6( a ) and 6( b )  are a cross-sectional view when an air pump and an electromagnetic valve are integrated into a module in Embodiment 2 of the invention; and 
         FIG. 7  is a cross-sectional view when an air pump is inserted into a canister in Embodiment 3 of the invention. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Hereinbelow, in order to describe the invention in greater detail, the best mode for carrying out the invention will be described according to the accompanying drawings. 
     Embodiment 1 
     An evaporation system shown in  FIG. 1  is configured by a fuel tank  1 , a canister  2  that absorbs and temporarily stores evaporated gas generated in the fuel tank  1 , an inlet manifold  3  that introduces the evaporated gas collected by the canister  2  into an engine, a purge solenoid valve  4  that controls the amount of the evaporated gas, a filter  5  that removes dust from passing gas, and piping that connects them. In addition, a piping system  6  indicated by a thick line in  FIG. 1  is a piping system to be a target of a leak diagnosis. 
     The leak diagnosis of the piping system  6  is performed by using a leak diagnosis apparatus that includes an electromagnetic valve  11  that opens and closes a pipe that provides communication between the piping system  6  and an air side, an air pump  12  that introduces the air into the piping system  6  from the air side to pressurize the inside of the piping system  6 , a pressure gauge  13  that detects a pressure in the piping system  6 , and a temperature gauge  14  that detects a temperature inside the piping system  6 . In addition, a check valve  121  that prevents a backflow of compressed air discharged by the air pump  12  is provided between the air pump  12  and the piping system  6 . In Embodiment 1, the air pump  12  and the check valve  121  are provided by an integrated structure. 
       FIG. 2  shows a cross-sectional view of the air pump  12 . 
     In the air pump  12 , a rotor  123  that rotates a plurality of vanes  122 , a first housing  124  made of resin that accommodates the vanes  122  and the rotor  123 , and a motor  126  that is fixed to the first housing  124  with a metal plate  125  interposed between the motor and the first housing  124  to rotationally drive the rotor  123  are provided. The motor  126  is contained in a case  128  having a connector  127 . In addition, an intake opening portion  129  that communicates with the air side to take in the air is provided in the first housing  124 , and a filter  130  is mounted to the intake opening portion. 
     A bottom surface side of the first housing  124  is covered with a second housing  131  which is a plate-like component made of resin, and a third housing  132  which is a cylindrical component made of resin is further mounted to the second housing. The second housing  131  and third housing  132  are fastened to the metal plate  125  together with the first housing  124  with screws not shown. 
     An opening portion  133  through which the air having entered from the intake opening portion  129  passes is provided in the second housing  131 , and an opening portion  135  through which the air having entered from the opening portion  133  passes is provided in a partition wall  134  of the third housing  132 . A sponge-like filter  136  is provided in a space formed between the second housing  131  and partition wall  134  of the third housing  132 . In addition, an outer side of the partition wall  134 , that is, a lower portion of the third housing  132 , serves as an exhaust opening portion  137  that communicates with the piping system  6 , and a partition plate  139  made of, e.g., resin that separates the inside from outside of the third housing  132  is provided in the exhaust opening portion  137 . A hole  138  is formed in the partition plate  139 , and the hole  138  allows passage of the air having entered from the opening portion  135 . 
     A shaft end portion of the check valve  121  passes through and is engaged with the partition wall  134  of the third housing  132 . In addition, an umbrella-shaped valve body of the check valve  121  is positioned in the exhaust opening portion  137 , and receives the pressure of the air flowing in from the opening portion  133  by the operation of the motor  126  to open the opening portion  135 , and closes the opening portion  135  when receiving the pressure from the piping system  6 . 
     An O-ring  140  is provided on an outer peripheral surface of the third housing  132 , and an O-ring  141  is provided on an outer peripheral surface of the case  128 . When the air pump  12  is used by mounting it to a component other than the air pump  12  such as a pipe that connects the canister  2  and the air side, the O-rings are provided in order to seal such mounting portions to thereby prevent the air discharged to the side of the piping system  6  from the exhaust opening portion  137  from leaking from the mounting portions. 
     A description will be given of a flow during the leak diagnosis by the leak diagnosis apparatus having the air pump  12  configured as described above. The air pump  12  may be mounted to any position as long as the position allows pressurization of the inside of the piping system  6 . For example, the air pump  12  may be mounted to the fuel tank  1 , the canister  2 , the filter  5 , or the pipe of the piping system  6  indicated by a thick line in  FIG. 1 . In this case, as shown in  FIG. 1 , the case where the air pump is mounted to the pipe of the piping system  6  will be described. 
     During the leak diagnosis, the air pump  12  is driven with the purge solenoid valve  4  and the electromagnetic valve  11  closed. In the air pump  12 , the air is sucked from the air side to the intake opening portion  129  by the rotation of the vanes  122  caused by the rotation of the motor  126 , and the air is discharged to the opening portion  133 . When the air having passed through the opening portion  133  further passes through the filter  136 , dust thereof is removed, and the air is discharged from the opening portion  135 . Subsequently, the air is discharged from the hole  138  of the partition plate  139  provided in the exhaust opening portion  137  to the side of the canister  2 , and the inside of the piping system  6  is pressurized. In this manner, the pressure in the piping system  6  is put in a state different from atmospheric pressure. 
     During driving of the air pump  12 , the check valve  121  repeatedly opens and closes the opening portion  135  in a state in which a large pressure difference between front and back of the check valve  121  occurs, and hence a vibration of the check valve  121  caused by flow pulsation is increased, so that a noise is generated. At this point, a space R 1  separated from the outside of the third housing  132  by the partition plate  139  is formed on a downstream side of the check valve  121 , and the noise generated by the vibration of the check valve  121  goes out from the hole  138  with the noise reduced in the space R 1 . Consequently, the noise to be traveled to the outside of the air pump  12  is made smaller as compared with the case where the partition plate  139  is not provided. 
     A frequency f 0  (Hz) of the noise reduced at this point can be calculated by the following Expression (1) on the assumption that the space R 1  separated from the outside of the third housing  132  by the partition plate  139  to be formed on the downstream side of the check valve  121  is in the shape of a rectangular parallelepiped: 
     
       
         
           
             
               
                 
                   
                     f 
                     o 
                   
                   = 
                   
                     a 
                     
                       4 
                       ⁢ 
                       L 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     In Expression (1), L (m) is the distance from the partition wall  134  to the partition plate  139 , and a (m/s) is the velocity of sound. When the position of the partition plate  139 , namely the distance L, is set such that the frequency f 0  matches the frequency exhibiting the peak of the noise generated by the vibration of the check valve  121 , the noise can be reduced effectively. 
     In addition, when an opening area of the hole  138  of the partition plate  139  is set to a proper value, it is possible to generate a pressure difference between the inside and the outside of the third housing  132  with the partition plate  139  serving as the boundary. That is, it is possible to change stepwise the pressure in a path from the downstream side of the check valve  121  to the canister  2 . An opening area S (m 2 ) of the hole  138  capable of generating the pressure difference can be calculated by the following Expression (2): 
     
       
         
           
             
               
                 
                   S 
                   ≤ 
                   
                     
                       Q 
                       
                         6 
                         × 
                         
                           10 
                           4 
                         
                       
                     
                     ⁢ 
                     
                       
                         ρ 
                         100 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     In Expression (2), Q is the flow rate (L/min) of the air discharged by the air pump  12 , and ρ is the density (kg/m 3 ) of the air discharged by the air pump  12 . 
     When the pressure in the path from the downstream side of the check valve  121  to the canister  2  is changed stepwise, the pressure difference between front and back of the check valve  121  can be reduced to thus suppress the vibration of the check valve  121  caused by the flow pulsation. As a result, the noise generated by the vibration can be made smaller. 
     For example, in the case where the generated noise is reduced by a sound absorbing member, the frequency having a sound reduction effect is limited. However, the sound reduction effect is equally obtained irrespective of the frequency when the vibration itself is suppressed with the partition plate  139 . The sound quality of the noise generated by the vibration of the check valve  121  differs depending on, for example, dimensional variations of the check valve  121  and peripheral components of the check valve  121 , an atmosphere temperature, and degradation over time, and hence, in light of such conditions, in addition to the configuration in which the sound reduction effect is exerted in the specific frequency by adjustment of L in Expression (1), the sound reduction effect is enhanced when the following configuration is adopted: the vibration itself is suppressed by adjustment of S in Expression (2), so that the sound reduction effect is equallly obtained, irrespective of the frequency. 
       FIG. 3  shows the sound reduction effect by the provision of the partition plate  139 . A dotted line in  FIG. 3  indicates a measurement result in the case where the partition plate  139  is not provided, while a solid line indicates a measurement result in the case where the partition plate  139  having the hole  138  of 2 mm in diamter is provided. It can be seen that the noise is further suppressed in the case where the partition plate  139  is provided and that, in particular, the peak appearing around 1 kHz is suppressed. 
     In the leak diagnosis, the pressure inside the piping system  6  is monitored by the pressure gauge  13 , and the operation of the air pump  12  is stopped at a point of time when a pressure difference between the pressure and atmospheric pressure is generated up to a state that allows the leak diagnosis. At this point, since the pressure on the side of the exhaust opening portion  137  that communicates with the piping system  6  is higher than the pressure on the side of the space in which the filter  136  is disposed, the check valve  121  closes the opening portion  135  due to the pressure difference and completely seals the piping system  6  to thereby maintain a high-pressure state. A pressure fluctuation in the piping system  6  in the completely sealed state is compared with that serving as a reference in the case where a leak occurs, and it is thereby possible to diagnose presence or absence of the leak occurrence. The pressure fluctuation serving as the reference in the case where the leak occurs is corrected by a pipe volume of the piping system  6 , a fuel amount in the fuel tank  1 , the temperature monitored by the temperature gauge  14 , and so on. 
     As mentioned above, when the partition plate  139  having the hole  138  is provided in the exhaust opening portion  137  to separate the inside from outside of the third housing  132 , it is possible to reduce the noise generated due to the vibration of the check valve  121  caused by the flow pulsation. 
     In addition, when the opening area of the hole  138  provided in the partition plate  139  is set to the proper value, the vibration of the check valve  121  caused by the flow pulsation can be suppressed to thus reduce the noise generated due to the vibration of the check valve  121 . 
     Further, the provision of the partition plate  139  can prevent the dust from the piping system  6  from adhering to the check valve  121 . 
     Furthermore, it is only necessary to provide the partition plate  139 , and hence a noise countermeasure can be implemented inexpensively. 
     Note that, though the configuration in which the hole  138  is provided in the partition plate  139  has been described, as shown in  FIG. 4 , a pipe  142  may also be provided. With this arrangement, it is possible to enhance the sound reduction effect to a level higher than that in the case where the hole  138  is simply provided. In the case where the pipe  142  is provided, the pipe  142  may be protruded to the inner side of the air pump  12 , or may also be protruded to the outer side of the air pump  12 . Alternatively, as shown in a cross-sectional view in  FIG. 5( a ) , the pipe may also be protruded to both of the inner and outer sides of the air pump  12 . However, when the length of the portion protruding to the outer side of the air pump  12  is too long, the size of the entire air pump  12  is increased in an axial direction, and hence the pipe  142  is preferably protruded to the inner side of the air pump  12  to such an extent that the opening and closing operations of the check valve  121  are not inhibited. 
     In addition, as shown in a plan view and a cross-sectional view in  FIG. 5( b ) , a plurality of the holes  138  may also be provided in the partition plate  139 . In this case, in order to generate the pressure difference between the inside and outside of the third housing  132  with the partition plate  139  serving as the boundary, a total opening area of the plurality of the holes  138  is set to satisfy the opening area S of Expression (2). As the number of the holes  138  is increased and the opening area of each of the holes  138  is reduced, the dust from the piping system  6  becomes less likely to adhere to the check valve  121 . 
     Further, as shown in a cross-sectional view in  FIG. 5( c ) , a sound absorbing member  143  may be provided on a surface of the partition plate  139  on the inner side of the air pump  12 . With this arrangement, it is possible to enhance the sound reduction effect to a level higher than that in the case lacking the sound absorbing member  143 . 
     Furthermore, as shown in a plan view and a cross-sectional view in  FIG. 5( d ) , ribs  144  that circularly protrude from the surface of the partition plate  139  on the inner side of the air pump  12  may be provided. With this arrangement, it is possible to enhance the sound reduction effect to a level higher than that in the case lacking the ribs  144 . 
     In the partition plate  139 , the position, size, and shape, and the number of the hole  138 , pipe  142 , and rib  144  are not limited to those shown in  FIGS. 2, 4, and 5 . 
     In addition, as the following configuration is shown in  FIG. 5( c ) : the pipe  142  is provided in the partition plate  139 , and the sound absorbing member  143  is further provided thereto, individual configurations of the provision of the hole  138 , the provision of the pipe  142 , the provision of the plurality of the holes  138 , the provision of the sound absorbing member  143 , the provision of the ribs  144 , and so on may be combined with each other. 
     Further, in each of the configurations shown in  FIG. 5 , a specific frequency at which an especially high sound reduction effect of the noise is obtained is present. When the configuration of the partition plate  139  is set such that the frequency exhibiting the peak of the noise generated by the vibration of the check valve  121  matches the specific frequency, the noise can be reduced effectively. 
     As described above, according to Embodiment 1, the partition plate  139  having the hole  138  is provided in the exhaust opening portion  137  provided in the third housing  132  of the air pump  12  to separate the inside from outside of the third housing  132 , so that the space R 1  is formed on the downstream side of the check valve  121 . Since the noise generated by the vibration of the check valve  121  is reduced in the space R 1 , it is possible to reduce the noise generated from the check valve  121  of the air pump  12  during the leak diagnosis. 
     In addition, it is adapted that the hole  138  of the partition plate  139  has the opening area that generates the pressure difference between the inside and outside of the third housing  132  with the partition plate  139  serving as the boundary. Consequently, the pressure is changed stepwise in the path that passes through the piping system  6  from the downstream side of the check valve  121 , whereby the pressure difference between front and back of the check valve  121  can be reduced to thereby suppress the vibration of the check valve  121  caused by the flow pulsation. As a result, the noise generated by the vibration can be diminished. 
     Further, it is adapted that the plurality of the holes  138  are formed in the partition plate  139 . Consequently, when the opening area of each of the holes  138  is made smaller, it is possible to further make the dust from the piping system  6  less likely to adhere to the check valve  121 . 
     Furthermore, it is adapted that the pipe  142  is protrusively provided in the partition plate  139 . Consequently, it is possible to further enhance the sound reduction effect to the noise generated by the vibration of the check valve  121 . 
     Additionally, it is adapted that the ribs  144  are protrusively provided on the surface of the partition plate  139  that faces the check valve  121 . Consequently, it is possible to further enhance the sound reduction effect to the noise generated by the vibration of the check valve  121 . 
     In addition, it is adapted that the sound absorbing member  143  is provided on the surface of the partition plate  139  that faces the check valve  121 . Consequently, it is possible to further enhance the sound reduction effect to the noise generated by the vibration of the check valve  121 . 
     Embodiment 2 
     Though in Embodiment 1, the case where the leak diagnosis is performed with the air pump  12  singly mounted to another component such as the pipe has been described, the air pump  12  may also be mounted with integrated with the electromagnetic valve  11 . 
       FIG. 6( a )  shows a module  15  in which the electromagnetic valve  11  and air pump  12  are integrated with each other. The module  15  contains the electromagnetic valve  11  and air pump  12  in a case  16 , and the case  16  has a first port  161  that communicates with an air side, and a second port  162  that communicates with the piping system  6 . 
     The electromagnetic valve  11  has a core  111  that is excited when a coil  110  is energized, a plunger  112  that can reciprocate by magnetic attraction of the core  111 , and a rod  113  that is supported in the core  111  and interlocked with the plunger  112 . In addition, in a housing  118  of the electromagnetic valve  11 , a valve seat  114 , a first opening portion  115  that communicates with the first port  161  of the case  16 , a second opening portion  116  that communicates with the second port  162  of the case  16 , and a third opening portion  117  that communicates with an intake opening portion  129  of the air pump  12  are formed. Further, inside the housing  118 , a valve body  119  that is fixed to an end of the rod  113 , a spring  120  that constantly biases the valve body  119  in a valve opening direction, and the like are disposed. 
       FIG. 6( a )  shows a non-energization state, that is, a valve opened state in which communication between the first opening portion  115  and second opening portion  116  is established. 
     At the time of excitation, the valve body  119  moves to the side of the valve seat  114  to establish a valve closed state, and the first opening portion  115  and second opening portion  116  of the housing  118  are blocked from each other. Note that, even when the electromagnetic valve  11  is closed, communication between the first opening portion  115  and third opening portion  117  is established via a space in which the spring  120  is prepared. 
     The air pump  12  is contained in the case  16  when the case  128  shown in  FIG. 2  is removed. In addition, in the exhaust opening portion  137 , a filter  145  is provided instead of the partition plate  139  shown in  FIG. 2 . Note that since it is possible to prevent the dust from the piping system  6  from adhering to the check valve  121  with a wall (partition plate)  163  described later, the filter  145  may be omitted. With regard to the air pump  12  in  FIG. 6( a ) , parts identical or equivalent to those in  FIG. 2  are designated by the same reference numerals, and descriptions thereof will be omitted or simplified. 
       FIG. 6( b )  is a cross-sectional view taken along a line A-A of  FIG. 6( a ) . In the wall  163  of the case  16  that faces the exhaust opening portion  137  of the air pump  12 , a hole  164  that communicates with the second port  162  is formed. 
     A description will be given of a flow during a leak diagnosis by a leak diagnosis apparatus having the module  15  configured as described above. Similarly to the description in Embodiment 1, the module  15  may be mounted to any position as long as the air pump  12  can pressurize the inside of the piping system  6 . 
     During the leak diagnosis, while the electromagnetic valve  11  is closed and the first opening portion  115  and second opening portion  116  are blocked from each other, the air pump  12  sucks from the intake opening portion  129 , the air having passed through the first port  161 , the first opening portion  115 , the space in which the spring  120  is provided, and the third opening portion  117 . 
     The air sucked from the intake opening portion  129  passes through the filter  145  and the hole  164  provided in the wall  163  of the case  16  after passing through the air pump  12  and enters the second port  162 , to pressurize the inside of the piping system  6 . At this point, the wall  163  of the case  16  that faces the exhaust opening portion  137  and the hole  164  that is provided in the wall  163  correspond to the partition plate  139  and hole  138  in Embodiment 1, respectively. That is, similarly to the partition plate  139  and the hole  138 , a space R 2  that is separated from the outside of the third housing  132  by the wall  163  is formed on the downstream side of the check valve  121 , and the noise generated by the vibration of the check valve  121  is reduced in the space R 2 . 
     As described above, according to Embodiment 2, the inside and outside of the third housing  132  of the air pump  12  are separated from each other with the wall  163  of the case  16  of the module  15  in which the electromagneitc valve  11  and air pump  12  are integrated with each other, so that the space R 2  is formed on the downstream side of the check valve  121 . Since the noise generated by the vibration of the check valve  121  is reduced in the space R 2 , similarly to Embodiment 1, it is possible to reduce the noise generated from the check valve  121  of the air pump  12  during the leak diagnosis. 
     In addition, in Embodiment 1, the noise countermeasure has been taken by additionally disposing the partition plate  139  that is the component for the noise countermeasure, but the noise countermeasure can be taken by utilizing the shape of the case  16  in Embodiment 2, and hence it is not necessary to additionally dispose the component for the noise countermeasure intentionally. 
     Embodiment 3 
     Embodiment 2 has described the case where the noise countermesure is taken by utilizing the shape of the case  16  when the electromagnetic valve  11  and air pump  12  are integrated into the module  15 , and the noise countermeasure may be taken by utilizing the shape of another component such as a pipe when the air pump  12  is singly mounted to another component such as the pipe. 
       FIG. 7  shows a cross-sectional view when the air pump  12  is mounted to, e.g., the canister  2 . The canister  2  has an insertion opening  21  for the air pump  12 , an opening portion  22  that communicates with an air side is provided in a side surface of the insertion opening  21 , and a partition wall (partition plate)  24  having a hole  23  is provided on a bottom surface of the insertion opening  21 . 
     The intake opening portion  129  of the air pump  12  faces the opening portion  22  of the canister  2 , and the exhaust opening portion  137  is covered with a filter  145  instead of the partition plate  139  shown in  FIG. 2 . Note that it is possible to prevent the dust from the piping system  6  from adhering to the check valve  121  with the partition wall  24 , and hence the filter  145  may be omitted. With regard to the air pump  12  in  FIG. 7 , parts identical or equivalent to those in  FIGS. 2 and 6  are designated by the same reference numerals, and descriptions thereof will be omitted or simplified. 
     During the leak diagnosis, the air pump  12  sucks the air having passed through the opening portion  22  of the canister  2  from the intake opening portion  129 . 
     The air sucked from the intake opening portion  129  passes through the filter  145  and the hole  23  of the partition wall  24  after passing through the air pump  12  and enters the canister  2 , to pressurize the inside of the piping system  6 . At this point, the partition wall  24  that faces the exhaust opening portion  137  and the hole  23  that is provided in the partition wall  24  correspond to the partition plate  139  and the hole  138  in Embodiment 1, respectively. That is, similarly to the partition plate  139  and the hole  138 , a space R 3  that is separated from the outside of the third housing  132  by the partition wall  24  is formed on the downstream side of the check valve  121 , and the noise generated by the vibration of the check valve  121  is reduced in the space R 3 . 
     As described above, according to Embodiment 3, the inside and outside of the third housing  132  of the air pump  12  are separated from each other with the partition wall  24  provided on the bottom surface of the insertion opening  21  prepared in the canister  2 , so that the space R 3  is formed on the downstream side of the check valve  121 . Since the noise generated by the vibration of the check valve  121  is reduced in the space R 3 , similarly to Embodiment 1, it is possible to reduce the noise generated from the check valve  121  of the air pump  12  during the leak diagnosis. 
     The noise countermeasure has been taken by additionally disposing the partition plate  139  that is the component for the noise countermeasure in Embodiment 1, while in Embodiment 3, it is possible to mold the partition wall  24  and the hole  23  integrally when the canister  2  is molded, and hence it is not necessary to especially produce another member such as the partition plate  139 , and it is possible to reduce the number of steps and time required for component production and assembly. 
     Similarly to the configurations shown in  FIGS. 4 and 5 , a plurality of the holes  23  may be provided, and a pipe, a rib, and a sound absorbing member, and so on may be provided on the partition wall  24 . 
     In addition, also in the case where the air pump  12  shown in  FIG. 7  is mounted to a different component other than the canister  2 , the air pump  12  may be appripriately mounted after the configuration corresponding to the partition plate  139  and the hole  138  in Embodiment 1 is formed in that different component. 
     Note that it is possible to freely combine the embodiments, modify any components of the embodiments, or omit any components in the embodiments within the scope of the invention of the present application. 
     Moreover, though the description has been made based on the assumption that the air pump  12  pressurizes the inside of the piping system  6  during the leak diagnosis, the leak diagnosis may be performed by depressurizing the inside of the piping system  6  with the air pump  12 . 
     For example, in the case of the air pump  12  shown in  FIG. 2 , the intake opening portion  129  is communicated with the air side and the exhaust opening portion  137  separated by the partition plate  139  is communicated with the piping system  6 , whereby the air (gas) is discharged and the inside of the piping system  6  is pressurized. In the case of the depressurization, the intake opening portion  129  is communicated with the piping system  6  and the exhaust opening portion  137  separated by the partition plate  139  is communicated with the air side, and the gas in the piping system  6  (e.g., gas in the canister  2 ) may be appropriately sucked. 
     Further, the air pump  12  may also be, e.g., a turbine-type air one other than the vane-type one, and the check valve  121  may also be, e.g., a spherical ball valve other than the umbrella-shaped one. 
     INDUSTRIAL APPLICABILITY 
     As described above, since the air pump according to the invention is capable of reducing the noise generated from the check valve during driving, the air pump is suitably used as a component of an air pump-type leak diagnosis apparatus. 
     DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
     
         
         
           
               1 : fuel tank 
               2 : canister 
               3 : inlet manifold 
               4 : purge solenoid valve 
               5 : filter 
               6 : piping system 
               11 : electromagnetic valve 
               12 : air pump 
               13 : pressure gauge 
               14 : temperature gauge 
               15 : module 
               16 : case 
               21 : insertion opening 
               22 : opening portion 
               23 : hole 
               24 : partition wall (partition plate) 
               110 : coil 
               111 : core 
               112 : plunger 
               113 : rod 
               114 : valve seat 
               115 : first opening portion 
               116 : second opening portion 
               117 : third opening portion 
               118 : housing 
               119 : valve body 
               120 : spring 
               121 : check valve 
               122 : vane 
               123 : rotor 
               124 : first housing 
               125 : metal plate 
               126 : motor 
               127 : connector 
               128 : case 
               129 : intake opening portion 
               130 : filter 
               131 : second housing 
               132 : third housing 
               133 : opening portion 
               134 : partition wall 
               135 : opening portion 
               136 : filter 
               137 : exhaust opening portion 
               138 : hole 
               139 : partition plate 
               140 ,  141 : O-ring 
               142 : pipe 
               143 : sound absorbing member 
               144 : rib 
               145 : filter 
               161 : first port 
               162 : second port 
               163 : wall (partition plate) 
               164 : hole