Abstract:
An electric pump draws and discharges fluid. When the fluid receives heat from the pump, the fluid has a saturation vapor pressure that can surpass the pressure of fluid that is drawn into the pump and is lower than the pressure of fluid discharged from the pump. The pump includes an electric motor; a pump section that is driven by the electric motor to draw, pressurize, and discharge the fluid; and a housing for accommodating the pump section. The housing defines a motor chamber that accommodates the electric motor. The pressure in the motor chamber is equal to the pressure of fluid that is discharged from the pump section. Therefore, the pump prevents fluid in the motor chamber from vaporizing.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an electric pump in which a motor chamber is defined in a housing that accommodates a pump section, and an electric motor for driving the pump section is accommodated in the motor chamber. Particularly, the present invention pertains to an electric pump in which the saturation vapor pressure of fluid that is drawn and pressurized by a pump section can surpass a suction pressure of the pump section according to a temperature increase in a motor chamber, and in which the saturation vapor pressure has a property of being less than a discharge pressure of the pump section due to heat in the motor chamber.  
           [0002]    A typical electric pump is used in a fuel supply system of an internal combustion engine that uses dimethyl ether (hereinafter, referred to as DME) as the fuel (for example, Japanese Laid-Open Patent Publication No. 2003-83188). Japanese Laid-Open Patent Publication No. 2003-83188 discloses an in-tank pump that includes an electric pump accommodated in a fuel tank. The electric pump has a motor chamber opened to the interior of the fuel tank. Therefore, the electric motor is cooled with DME the temperature of which is relatively low.  
           [0003]    Similar in-tank pumps are disclosed in Japanese Laid-Open Patent Publications No. 1-151765, No. 6-288313, and No. 2002-98018. In each of these prior art systems, a discharge pipe is connected to a lid that forms part of a tank. A rubber flexible hose is connected to the pump. The hose is also connected to the pipe in the tank.  
           [0004]    Since the motor chamber is opened to the interior of the fuel tank, the motor chamber is exposed to a suction pressure of the pump section. In this configuration, a great amount of DME is vaporized in the motor chamber due to the characteristics of DME (heating the motor chamber causes the saturation vapor pressure of DME to surpass the suction pressure). A considerable amount of vaporized DME in the motor chamber reduces the heat exchanger effectiveness between DME and heat producing portions of the electric motor, which results in an insufficient cooling of the electric motor.  
           [0005]    Therefore, the housing of the electric motor needs to have a vent passage that vents vaporized DME from the motor chamber to the fuel tank. When forming a vent passage in the housing, the vent passage needs to be located above a portion of the motor chamber in which vaporized DME collects, so that vaporized DME is effectively vented from the motor chamber. Accordingly, the position and the orientation of the electric pump relative to the fuel tank are limited according to the position of the vent passage formed in the housing. This reduces the versatility of the electric pump.  
           [0006]    Also, the flexible hose, which functions as part of a discharge passage, is connected to the pipe by fitting the pipe into the hose. At the joint of the hose and the pipe, the hose needs to be fastened with a clip. In this manner, a section of the discharge passage corresponding to the pipe and a section of the discharge passage corresponding to the flexible hose are connected. This configuration increases the space in the tank for accommodating the pump, and complicates the connecting process.  
         SUMMARY OF THE INVENTION  
         [0007]    Accordingly, it is an objective of the present invention to provide an improved electric pump that is capable of preventing fluid in a motor chamber from vaporizing.  
           [0008]    To achieve the above-mentioned objective, the present invention provides an electric pump for drawing and discharging fluid. When the fluid receives heat from the pump, the fluid has a saturation vapor pressure that can surpass the pressure of fluid that is drawn into the pump and is lower than the pressure of fluid discharged from the pump. The pump includes an electric motor; a pump section that is driven by the electric motor to draw, pressurize, and discharge the fluid; and a housing for accommodating the pump section. The housing defines a motor chamber that accommodates the electric motor. The pressure in the motor chamber is equal to the pressure of fluid that is discharged from the pump section.  
           [0009]    Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
         [0011]    [0011]FIG. 1 is a cross-sectional view illustrating an electric pump according to a first embodiment of the present invention;  
         [0012]    [0012]FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1;  
         [0013]    [0013]FIG. 3 is a diagrammatic view showing a fuel supply system;  
         [0014]    [0014]FIG. 4 is a graph showing the saturation vapor pressure of DME;  
         [0015]    [0015]FIG. 5 is a cross-sectional view illustrating an electric pump according to a modification of the first embodiment;  
         [0016]    [0016]FIG. 6( a ) is a diagrammatic view showing a fuel supply system according to a second embodiment of the present invention;  
         [0017]    [0017]FIG. 6( b ) is a cross-sectional view illustrating the electric pump of FIG. 6( a );  
         [0018]    [0018]FIG. 7 is an enlarged partial cross-sectional view of the electric pump shown in FIG. 6( b );  
         [0019]    [0019]FIG. 8 is an enlarged partial cross-sectional view of the electric pump shown in FIG. 6( b );  
         [0020]    [0020]FIG. 9 is an enlarged view showing the tension spring of FIG. 6( b );  
         [0021]    [0021]FIG. 10 is a cross-sectional view taken along line A-A in FIG. 6( b );  
         [0022]    [0022]FIG. 11 is a cross-sectional view taken along line B-B in FIG. 6( b );  
         [0023]    [0023]FIG. 12 is a cross-sectional view illustrating a third embodiment of the present invention;  
         [0024]    [0024]FIG. 13( a ) is a cross-sectional view illustrating an electric pump according to a fourth embodiment of the present invention;  
         [0025]    [0025]FIG. 13( b ) is an enlarged partial cross-sectional view of the electric pump shown in FIG. 13( a );  
         [0026]    [0026]FIG. 14( a ) is a cross-sectional view taken along line D-D in FIG. 13( a );  
         [0027]    [0027]FIG. 14( b ) is an enlarged partial cross-sectional view of FIG. 14( a );  
         [0028]    [0028]FIG. 15( a ) is a partial cross-sectional view illustrating a fifth embodiment of the present invention;  
         [0029]    [0029]FIG. 15( b ) is an enlarged partial cross-sectional view of FIG. 15( a );  
         [0030]    [0030]FIG. 16 is an enlarged cross-sectional view illustrating a sixth embodiment of the present invention;  
         [0031]    [0031]FIG. 17 is an enlarged cross-sectional view illustrating a seventh embodiment of the present invention;  
         [0032]    [0032]FIG. 18 is an enlarged cross-sectional view illustrating an eighth embodiment of the present invention;  
         [0033]    [0033]FIG. 19 is an enlarged cross-sectional view illustrating a ninth embodiment of the present invention;  
         [0034]    [0034]FIG. 20( a ) is a partial cross-sectional view illustrating an electric pump according to a tenth embodiment of the present invention; and  
         [0035]    [0035]FIG. 20( b ) is an enlarged partial cross-sectional view of FIG. 20( a ). 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    A first embodiment of the present invention will now be described with reference to FIGS.  1  to  4 .  
         [0037]    As shown in FIG. 3, a diesel type internal combustion engine  34 , which functions as a driving source of a vehicle, has a fuel supply system. The fuel supply system includes an electric pump  2 . The entire electric pump  2  is an in-tank pump that is substantially entirely accommodated in a bottom portion of a tank  10 , in which DME, or fluid (fuel), is stored. A suction side of the electric pump  2  is opened to the interior of the tank  10 . A discharge side of the pump  2  is connected to a fuel injection pump  31  with a discharge pipe  30 . The discharge side of the fuel injection pump  31  is connected to the engine  34 . The fuel injection pump  31  receives pressurized DME from the electric pump  2 , and sends the DME to the engine  34  under a high pressure. Surplus DME in the fuel injection pump  31  is returned to the tank  10  through a return passage  4   a.    
         [0038]    As shown in FIG. 1, the electric pump  2  has a connection member  11  and an accommodation case  8 . In a state where the pump  2  is installed in the tank  10 , the connection member  11  is exposed to the outside of the tank  10 . The accommodation case  8  is fixed with bolts (not shown) to a side of the connection member  11  that faces inward of the tank  10 . An inlet forming ring  9  is formed in a wall  10   a , or a sidewall of the tank  10 . The electric pump  2  is fixed to the inlet forming ring  9 . The electric pump  2  is installed in the tank  10  by securing radially end portions of the connection member  11  to the inlet forming ring  9  with screws  12  such that the accommodation case  8  is located inside the tank  10 .  
         [0039]    The accommodation case  8  includes a lid  16 , a motor housing  15 , and a gear housing  17 , which are arranged in this order from the connection member  11 . In this embodiment, the motor housing  15 , the gear housing  17 , the lid  16  and the connection member  11  form a pump housing  6 , or a housing of the electric pump  2 . The motor housing  15  is fixed to the connection member  11  with bolts (not shown). The lid  16  is held between the proximal end (left end as viewed in FIG. 1) of the motor housing  15  and the connection member  11 . The position of the gear housing  17  is determined by positioning pins  51 . In this state, the gear housing  17  is fixed to the distal end (right end as viewed in FIG. 1) by bolts (not shown).  
         [0040]    A motor chamber  152  is defined inside the motor housing  15 . An electric motor M, which functions as a drive source of the electric pump  2 , is accommodated in the motor chamber  152 . The electric motor M includes a stator  21  and a rotor  22 . The stator  21  has a coil  211  and fixed to the inner surface of the motor housing  15 . The rotor  22  has an iron core and rotates relative to the stator  21 . A space (gap)  57  exists between the stator  21  and the rotor  22 . Recesses  58  are formed on a surface of the stator  21  that faces the motor housing  15 . The recesses  58  are arranged along the circumferential direction.  
         [0041]    A rotary shaft  18  is fixed to the rotor  22  such that the rotary shaft  18  rotates integrally with the rotor  22 . The rotary shaft  18 , which functions as a motor shaft, extends between the lid  16  and the gear housing  17 . A connection hole  161  is formed in the lid  16 . A radial bearing  19  is located in the connection hole  161  and supports a proximal end portion  181  of the rotary shaft  18 . A distal end of the rotary shaft  18  is supported by a needle bearing  20  accommodated in the gear housing  17 . The coil  211  of the stator  21  is connected to terminals  39 ,  40  (wiring of which is not shown in FIG. 1) provided in the connection member  11 . When current is supplied to the coil  211  through the terminals  39 ,  40 , the rotary shaft  18  rotates due to electromagnetic induction between the coil  211  and the iron core.  
         [0042]    A pump section P, which is a gear pump, is located in an interior of a joint of the motor housing  15  and the gear housing  17 . The pump section P includes a gear train  53  that rotates when the rotary shaft  18  rotates. The gear train  53  has a drive gear  23  and a driven gear  24 . The drive gear  23  is fixed to the distal end of the rotary shaft  18 . The driven gear  24  is integrally formed with a support shaft  241  and is meshed with the drive gear  23 . As shown in FIGS. 1 and 2, a key  56  is attached to the distal circumferential surface of the rotary shaft  18 . The key  56  extends along the axis of the rotary shaft  18 . The drive gear  23  is engaged with the key  56 .  
         [0043]    In the interior of the distal portion of the electric pump  2 , a set of pump chambers  27  are defined between the teeth of drive gear  23  and an upper section of the inner circumferential surface of the gear housing  17 . Another set of pump chambers  27  are defined between the teeth of driven gear  24  and a lower section of the inner circumferential surface of the gear housing  17 . The pump chambers  27  function as pressurizing passages for DME. Also, a shaft chamber  60  for accommodating the distal end of the rotary shaft  18  is defined in the interior of the distal portion of the electric pump  2 . The shaft chamber  60  extends through the motor housing  15  and the gear housing  17 .  
         [0044]    The support shaft  241  is arranged parallel to the rotary shaft  18 . One end of the support shaft  241  is supported by the motor housing  15  with a needle bearing  25 , and the other end is supported by the gear housing  17  with a needle bearing  26 . When the rotary shaft  18  rotates, the support shaft  241  rotates following the rotation of the rotary shaft  18  with the drive gear  23  and the driven gear  24 .  
         [0045]    As shown in FIG. 2, spaces exist frontward and rearward of the meshed sections of the drive gear  23  and the driven gear  24  in the gear housing  17 . Accordingly, a suction chamber  271  and a discharge chamber  272 , or a discharge side of the pump section P are defined. DME passes through the suction chamber  271  and the discharge chamber  272 . A suction port  55  is formed in the gear housing  17  to connect the suction chamber  271  with the outside of the pump  2 , or the interior of the tank  10  outside the pump housing  6 . A discharge passage  172  is formed in an end wall  151  of the motor housing  15  that contacts the gear housing  17 . The discharge passage  172  functions as an introducing passage, or a first passage, that connects the discharge chamber  272  with the motor chamber  152 .  
         [0046]    When the rotary shaft  18  rotates in a direction indicated by an arrow (clockwise direction), the support shaft  241  rotates following rotation of the rotary shaft  18 . That is, the support shaft  241  rotates in a direction indicated by a hollow arrow. At this time, DME in the tank  10  flows into the suction chamber  271  from the suction port  55 . The DME then flows through the pump chambers  27 , while being pressurized. After reaching the discharge chamber  272 , the DME flows out to the motor chamber  152  through the discharge passage  172 .  
         [0047]    As shown in FIG. 1, an annular space  59  is defined in the lid  16  at a side of the radial bearing  19  that faces the motor chamber  152 . A connection hole  161  is also formed in the lid  16  at a side of the radial bearing  19  that faces the connection member  11 . The connection hole  161  communicates with the space  59  and is open to the side of the connection member  11 . The connection member  11  has a pipe joint  29  to which the discharge pipe  30  (see FIG. 3) from the fuel injection pump  31  is connected. A discharge port  61  is formed in the connection member  11  and the pipe joint  29 . The discharge port  61  connects the connection hole  161  with the outside of the tank  10 . In this embodiment, the space  59 , the connection hole  161 , and the discharge port  61  form a lead-out passage, or a second passage that connects the motor chamber  152  to the outside of the pump housing  6 , or the outside of the tank  10 . Further, the discharge passage  172 , the space  59 , the connection hole  161 , and the discharge port  61  form a discharge path.  
         [0048]    In the motor chamber  152 , the space  57  between the stator  21  and the rotor  22 , and the recesses  58  of the stator  21  form a discharge channel for DME sent to the motor chamber  152  from the pump section P. The space  59  of the lid  16 , a space between an outer ring  191  and an inner ring  192  of the radial bearing  19 , and the connection hole  161  of the lid  16  form a discharge channel when DME that flows out from the space  57  and the recesses  58  reaches the discharge port  61 . DME in the motor chamber  152  is sent to the fuel injection pump  31  through the discharge port  61  and the discharge pipe  30 . As described above, the motor chamber  152  forms part of the discharge path of DME. Therefore, the motor chamber  152  is exposed to the discharge pressure of the pump section P, or the pressure in the discharge chamber  272 .  
         [0049]    As shown in FIG. 4, DME has a property that, when expressed in a graph with a horizontal axis of temperature (° C.) and a vertical axis of pressure (MPa), the saturation vapor pressure of DME is a quadric curve. When the point defined by the pressure and the temperature of DME is located in an area above the quadric curve, DME is liquid. When the point is below the quadric curve, DME is gas. In the graph of FIG. 4, Pin represents the suction pressure of the electric pump  2  (pump section P), or the pressure in the suction chamber  271 . In this embodiment, Pin is 1 MPa. Pout represents the discharge pressure of the electric pump  2  (pump section P). In this embodiment, Pin is 3 MPa.  
         [0050]    When the electric pump  2  is in a normal operation state that corresponds to a low or intermediate speed of the vehicle, the temperature of DME in the motor chamber  152  is approximately 40° C. to 50° C. at the maximum. In these temperatures, the saturation vapor pressure of DME is in a range from approximately 0.8 MPa to value slightly higher than 1 MPa as shown in the graph of FIG. 4. When the electric pump  2  is in a harsh operation state that corresponds to a high speed or an abrupt acceleration speed of the vehicle, the temperature of DME in the motor chamber  152  is increased to approximately 80° C. at the maximum. When the temperature is increased approximately 80° C., the saturation vapor pressure of DME in the motor chamber  152  surpasses the suction pressure Pin. However, as obvious from the graph of FIG. 4, even if the DME temperature is increased to approximately 80° C., the saturation vapor pressure does not exceed the discharge pressure Pout.  
         [0051]    Accordingly, DME, which is used in the electric pump  2  of this embodiment, has the following property. That is, when DME is heated according to a temperature increase in the motor chamber  152 , the saturation vapor pressure of DME can surpass the suction pressure Pin of the pump section P. At the same time, despite the temperature increase in the motor chamber  152 , the saturation vapor pressure stays below the discharge pressure Pout of the pump section P. Therefore, in this embodiment in which the motor chamber  152  is exposed to the discharge pressure, even if the saturation vapor pressure DME is increased due to a temperature increase, the pressure in the motor chamber  152  does not fall below the saturation vapor pressure. Thus, DME is not vaporized in the motor chamber  152 .  
         [0052]    Accordingly, unlike the system disclosed in Japanese Laid-Open Patent Publication 2003-83188, the present embodiment does not require a vent passage for venting DME from a motor chamber to a tank. Therefore, the position and the orientation of the electric pump  2  relative to the tank  10  are not limited. As a result, the electric pump  2  is versatile (advantage (1)).  
         [0053]    Other than the advantage (1), the above embodiment provides the following advantages.  
         [0054]    (2) The motor chamber  152  forms part of the discharge path of DME from the pump section P to the outside of the pump housing  6 , or the outside of the tank  10 . Therefore, a flow of DME from the pump section P to the outside of the pump housing  6  is generated in the motor chamber  152 . This permits the electric motor M to be effectively cooled with DME.  
         [0055]    (3) The electric pump  2  is of an in-tank type. That is, the motor chamber  152  is located adjacent to the wall  10   a  of the tank  10 , and the pump section P is located on the opposite side of the motor chamber  152  from the wall  10   a . In other words, a portion of the pump housing  6  that defines the motor chamber  152  is attached to the wall  10   a . Since the motor chamber  152  is located close to the wall  10   a  of the tank  10 , the lead-out passage, or the second passage from the motor chamber  152  to the outside of the tank  10  is short and simple. In other words, since the motor chamber  152  is used as the part of the discharge path of DME from the pump section P to the outside of the pump housing  6 , the layout of this embodiment is applied without complicating the routing of the lead-out passage.  
         [0056]    (4) The discharge path of DME from the pump section P to the outside of the pump housing  6  passes through the radial bearing  19 , which rotatably supports the rotary shaft (drive shaft)  18 . Thus, the radial bearing  19  is exposed to a flow of DME and is effectively cooled with DME.  
         [0057]    (5) The passage of DME when passing through the electric motor M in the motor chamber  152  is defined not only by the space  57  between the stator  21  and the rotor  22 , but also the recesses  58  on the circumferential surface of the stator  21 . Thus, compared to the case where the passage is defined only by the space  57 , the discharge path of DME is broadened.  
         [0058]    (6) The shaft chamber  60  is exposed to the discharge pressure. Thus, leakage of DME from the pump chamber  27  to the shaft chamber  60  is suppressed.  
         [0059]    In the above embodiment, the electric pump  2  includes the single-stage pump section P. However, the present invention is not limited to electric pumps having a single-stage pump section, but may be embodied in electric pumps having a multi-stage pump section, such as a two-stage pump section shown in FIG. 5.  
         [0060]    A second embodiment according to the present invention will now be described with reference to FIGS.  6 ( a ) to  11 . As shown in FIG. 6( a ), a connection member  11  is fixed to an upper wall  101  of a tank  10  with screws  12 . As shown in FIG. 6( b ), the connection member  11 , which forms part of the tank  10 , covers an insertion hole  102 .  
         [0061]    In this embodiment, the motor housing  15 , the gear housing  17  and the lid  16  form a pump housing  7 , or a housing of the electric pump  13 . Below the connection member  11 , the pump housing  7  is suspended with tension springs  14 , the number of which is three in this embodiment.  
         [0062]    A suction chamber  271 , which is shown in FIG. 10, is connected to the interior of the tank  10  through a suction passage  171 . A discharge chamber  272  of the pump chamber  27  is connected to the interior of the motor housing  15  (the motor chamber  152 ) through a discharge passage  172 .  
         [0063]    The rotary shaft  18  rotates in a direction indicated by an arrow R in FIG. 10. When the rotary shaft  18  rotates, the drive gear  23  rotates integrally with the rotary shaft  18 . Accordingly, the driven gear  24 , while being meshed with the drive gear  23 , rotates in a direction indicated by an arrow Q in FIG. 10. When the drive gear  23  and the driven gear  24  rotate, fluid F (dimethyl ether) in the tank  10  is drawn into the suction chamber  271  through the suction passage  171 .  
         [0064]    An upper end  141  of each spring  14  is hooked to the connection member  11  as shown in FIG. 9. A lower end  142  of each spring  14  is hooked to a screw  43  in a recess  164  formed in the upper surface of the lid  16 . When transmitted to the connection member  11 , vibration of the electric pump  13 , or vibration of the pump housing  7  generates noise. However, the tension springs  14  function as vibration prevention mechanism (dumper) that prevents vibration of the electric pump  13  from being transmitted to the connection member  11 .  
         [0065]    As shown in FIG. 6( b ), a discharge pipe  28  is integrally formed with and projects from a center of the lower surface of the connection member  11 . A pipe joint  29  is attached to a center of the upper surface of the connection member  11 . A channel  291  in the pipe joint  29  communicates with a discharge passage  281  in the discharge pipe  28 . As shown in FIG. 6( a ), the discharge pipe  30  is connected to the pipe joint  29 . The discharge pipe  30  is connected to the fuel injection pump  31 .  
         [0066]    As shown in FIGS.  6 ( b ) and  7 , the discharge pipe  28  is inserted in the connection hole  161  so that the discharge passage  281  communicates with the connection hole  161 . A sealing member, which is a lip seal  32 , is located between a circumferential surface  162  of the connection hole  161  and an outer circumferential surface  282  of the discharge pipe  28 . The lip seal  32  includes an annular case  321 , a pair of retainer rings  322 ,  323 , and a lip ring  324  held between the retainer rings  322 ,  323 . The lip ring  324  is made of polytetrafluorethylene. The case  321  is fitted in the connection hole  161 . The position of the case  321  is determined by a snap ring  33  fitted to a circumferential surface  162  of the connection hole  161 . The lip ring  324  contacts the outer circumferential surface  282  of the discharge pipe  28 .  
         [0067]    Fluid F in the motor chamber  152  is sent to the discharge passage  281  via space between the outer ring  191  and the inner ring  192  of the radial bearing  19 , and the connection hole  161 . Fluid F in the discharge passage  281  is sent to the fuel injection pump  31  via the channel  291  in the pipe joint  29  and the discharge pipe  30 . The fuel injection pump  31  receives fluid F, and sends the fluid F to the engine  34  shown in FIG. 6( a ).  
         [0068]    As shown in FIG. 6( b ), a surrounding cylinder  35  projects and integrally formed with the lower surface of the connection member  11 . A through hole  163  is formed in the lid  16 , and the surrounding cylinder  35  is inserted in the through hole  163 . A sealing member, which is a lip seal  36 , is located between an outer circumferential surface  352  of the surrounding cylinder  35  and a circumferential surface  166  of the through hole  163 . As shown in FIG. 8, the lip seal  36  includes an annular case  361 , a pair of retainer rings  362 ,  363 , and a lip ring  364  held between the retainer rings  362 ,  363 . The lip ring  364  is made of polytetrafluorethylene. The case  361  is fitted in the through hole  163 . The position of the case  361  is determined by a snap ring  37  fitted to a circumferential surface  166  of the through hole  163 . The lip ring  364  contacts an outer circumferential surface  352  of the surrounding cylinder  35 .  
         [0069]    As shown in FIG. 6( b ), the surrounding cylinder  35  has a wiring hole  351  that passes through the connection member  11 . A cup-shaped shutter  38  is fitted in the wiring hole  351 . The terminals  39 ,  40  pass through and are fixed to the bottom wall of the shutter  38 . The stator  21  and the inner ends of the terminals  39 ,  40  are electrically connected to each other with conductive members, which are lead wires  41 . The outer ends of the terminals  39 ,  40  are electrically connected to a power supply (not shown). The position of the shutter  38  is determined by a snap ring  42  fitted to a circumferential surface of the wiring hole  351 . The shutter  38  disconnects the interior of the motor housing  15  (the motor chamber  152 ) and the outside of the tank  10 .  
         [0070]    The pressure of the interior of the motor housing  15  is higher than the pressure in the tank  10  outside the motor housing  15 . The pressure difference presses the lip ring  324  of the lip seal  32  against the outer circumferential surface  282  of the discharge pipe  28 . The pressure difference also presses the lip ring  364  of the lip seal  36  against the outer circumferential surface  352  of the surrounding cylinder  35 . The interior of the motor housing  15  (the motor chamber  152 ) is disconnected from the interior of the tank  10  outside the pump housing  7  by the lip seals  32 ,  36 .  
         [0071]    The pump housing  7 , or the main body of the electric pump  13  is attached to the connection member  11  before being installed in the tank  10 . Before attaching the pump housing  7  to the connection member  11 , the lead wires  41  are not connected to the terminals  39 ,  40 , and the shutter  38  is not attached to the connection member  11 . The attachment is carried out in the following manner. First, the lead wires  41  are drawn through the wiring hole  351  from the surrounding cylinder  35 . The length of the lead wires  41  are determined such that a sufficient length of each lead wire  41  is drawn from the wiring hole  351 . In this state, the lip seal  32  is fitted in the discharge pipe  28 , and the lip seal  36  is fitted in the surrounding cylinder  35 . In a state where the discharge pipe  28  is fitted in the lip seal  32  and the surrounding cylinder  35  is fitted in the lip seal  36 , the lower ends  142  of the tension springs  14  are inserted in the recesses  164 . Then, each screw  43  is threaded into a threaded hole  165  such that the screw  43  crosses the corresponding recess  164 .  
         [0072]    Next, the lead wires  41 , which have been drawn out of the wiring hole  351 , are soldered to the terminals  39 ,  40 . Thereafter, the shutter  38  is fitted in the wiring hole  351  and fixed with the snap ring  42 . In a state where the shutter  38  is fitted in and fixed to the wiring hole  351 , pressurized fluid F in the motor chamber  152  does not leak to the outside of the tank  10  through the wiring hole  351 .  
         [0073]    In this manner, the pump housing  7  is attached to the connection member  11 . The pump housing  7  is then placed in the tank  10  through the insertion hole  102 . The connection member  11 , to which the pump housing  7  is attached, is fastened to the upper wall  101  of the tank  10  with the screws  12 .  
         [0074]    The second embodiment provides the following advantages besides the advantages (1) to (6) of the first embodiment.  
         [0075]    (2-1) In a state where the pump housing  7  is attached to the connection member  11 , which forms part of the tank  10 , the space between the circumferential surface  162  of the connection hole  161  and the outer circumferential surface  282  of the discharge pipe  28  is sealed with the lip seal  32 , and the space between the circumferential surface  166  of the through hole  163  and the outer circumferential surface  352  of the surrounding cylinder  35  is sealed with the lip seal  36 . That is, the discharge pipe  28  is connected to the connection hole  161 , and the surrounding cylinder  35  is connected to the through hole  163 . In a state where the discharge pipe  28  is connected to the connection hole  161 , pressurized fluid F in the motor chamber  152  does not leak to the interior of the tank  10  through the connection hole  161 . Also, in a state where the surrounding cylinder  35  is connected to the through hole  163 , pressurized fluid F in the motor chamber  152  does not leak to the interior of the tank  10  through the through hole  163 .  
         [0076]    The connection of the discharge pipe  28  and the connection hole  161  and the connection of the surrounding cylinder  35  and the through hole  163  are completed by a simple process in which the discharge pipe  28  is inserted into the connection hole  161  and the surrounding cylinder  35  is inserted in the through hole  163 .  
         [0077]    (2-2) The lip seals  32 ,  36 , which exert sealing performance using pressure differences, are favorable as sealing members for preventing pressurized fluid F in the motor chamber  152  from leaking into the interior of the tank  10 . The lip rings  324 ,  364  of the lip seals  32 ,  36  prevent vibration of the electric pump  13  (the pump housing  7 ) from being transmitted to the connection member  11 . Dimethyl ether damages rubber. That is, the dimethyl ether causes rubber to harden or swell, which can result in breakage. However, since the lip rings  324 ,  364  are made of polytetrafluoroethylene, dimethyl ether does not damage the lip rings  324 ,  364 . Accordingly, the damping property of the lip rings  324 ,  364  does not deteriorate.  
         [0078]    (2-3) The rotary shaft  18  is rotatably supported in the connection hole  161  formed in the lid  16 . That is, a hole for rotatably supporting the rotary shaft  18 , which is the connection hole  161 , is also used as a connection hole for connecting the interior of the motor housing  15  (the motor chamber  152 ) with the discharge passage  281  of the discharge pipe  28 . In this structure where a single hole is used for two purposes, no additional connection hole is required. This simplifies the structure.  
         [0079]    (2-4) The power supply terminals for the motor M, which are the terminals  39 ,  40 , are electrically connected to the stator  21  with the lead wires  41 . The lip seal  36  is located between the lid  16  and the surrounding cylinder  35 , which surrounds the lead wires  41 . This structure is favorable for guaranteeing the sealing property about the lead wires  41 .  
         [0080]    (2-5) Unlike Japanese Laid-Open Patent Publications No. 1-151765, No. 6-288313, No. 2002-98018, no flexible hose is used for connecting a section of the discharge path in the connection member  11  with a section of the discharge path in the pump housing  7  (the motor chamber  152  in this embodiment). A connection structure using a flexible tube enlarges the space occupied by a pump in a tank. However, since no flexible tube is used in this embodiment, such a problem is avoided.  
         [0081]    (2-6) To facilitate the attachment of the pump housing  7  (the main body of the electric pump  13 ) to the connection member  11 , it is preferably that the tension spring  14  be easily attached to either one of the pump housing  7  and the connection member  11  during the attaching process. In this embodiment, after the lower end  142  of each tension spring  14  is inserted in the corresponding recess  164  formed in the lid  16  of the pump housing  7 , the spring  14  is coupled to the pump housing  7  simply by threading the screw  43  in the corresponding threaded hole  165  of the lid  16 . The attachment of the springs  14  is thus simple.  
         [0082]    A third embodiment of the present invention will now be described with reference to FIG. 12. In the third embodiment, like or the same reference numerals are given to those components that are like or the same as the corresponding components of the second embodiment.  
         [0083]    The pump housing  7  is suspended from the connection member  11  with vibration insulators  65  (only one is shown in FIG. 12) in between. The vibration insulators  65 , which function as dampers are located about the axis of the rotary shaft  18 . The vibration insulators  65  are made of polytetrafluorethylene. The vibration insulators  65  are adhered to the upper surface of the lid  16  and to the lower surface of the connection member  11 . The vibration insulators  65  prevent vibration of the pump housing  7  from being transmitted to the connection member  11 .  
         [0084]    When attaching the pump housing  7  (the electric motor M) to the connection member  11 , a face of each vibration insulator  65  is adhered to one of the electric motor M and the connection member  11 . Adhesive is applied to the opposite face of each vibration insulator  65 . Then, the lead wires  41  are drawn out through the wiring hole  351 . In this state, the lip seal  32  is fitted in the discharge pipe  28 , and the lip seal  36  is fitted in the surrounding cylinder  35 . In a state where the discharge pipe  28  is fitted in the lip seal  32  and the surrounding cylinder  35  is fitted in the lip seal  36 , the vibration insulators  65  are adhered to the electric motor M and the connection member  11 . Next, the lead wires  41 , which have been drawn out of the wiring hole  351 , are soldered to the terminals  39 ,  40 . Thereafter, the shutter  38  is fitted in the wiring hole  351  and fixed with the snap ring  42 .  
         [0085]    Alternatively, the shutter  38  may be fitted in the wiring hole  351  in advance. In this case, the lead wires  41  are connected to the terminals  39 ,  40 . Thereafter, the connection member  11  and the electric motor M are brought close to each other such that the vibration insulators  65  are adhered to the connection member  11 .  
         [0086]    The third embodiment has the same advantages as the advantages (2-1) to (2-5) of the second embodiment.  
         [0087]    A fourth embodiment will now be described with reference to FIGS.  13 ( a ),  13 ( b ),  14 ( a ) and  14 ( b ).  
         [0088]    As shown in FIGS.  13 ( a ) and  13 ( b ), vibration insulating mechanism, or a damper  71  having a vibration insulating rubber member  70  is located between the lid  16  of the pump housing  7  and the connection member  11 . As shown in FIG. 13( b ), the damper  71  includes the rubber member  70 , a coupling member  72 , a threaded hole forming member  73 , a pair of first screws  74 , and a second screw  75 . The first screws  74  are used to fasten the coupling member  72 , which functions as a first attachment member, with the lid  16 . The second screw  75  is used to fasten the threaded hole forming member  73 , which functions as a second attachment member, to the connection member  11 . The coupling member  72  contacts and is attached to a first contacting end face  701  of the rubber member  70  that faces the pump housing  7 . The thread hole forming member  73  includes a nut portion  731  having a threaded hole, and a coupling plate portion  732  coupled to the nut portion  731 . The nut portion  731  is embedded in the rubber member  70 . The coupling plate portion  732  is attached to a second contacting end face  702  of the rubber member  70  that faces the connection member  11 .  
         [0089]    The coupling member  72  is fastened to the upper surface of the lid  16  with the first screws  74  threaded to the lid  16 . The threaded hole forming member  73  is fastened to the lower surface of the connection member  11  with the second screw  75 , which is passed through a through hole  113  formed in the connection member  11  and is threaded to the nut portion  731 . That is, the damper  71  is attached to the lid  16  with the coupling member  72 , and is also attached to the connection member  11  with the threaded hole forming member  73 .  
         [0090]    As shown in FIG. 14( a ), two or more sets (three in this embodiment) of the dampers  71  are provided about the discharge pipe  28 . The sets of the dampers  71 , which are attached to the connection member  11 , suspend the pump housing  7 .  
         [0091]    As shown in FIGS.  13 ( b ) and  14 ( b ), a polytetrafluoroethylene coating layer  76  is formed on a surface of each vibration insulating rubber member  70  (a circumferential surface  703  in this embodiment). Also, the coating layer  76  is formed on the surface of each coupling member  72  and the surface of each threaded hole forming member  73 . Each vibration insulating rubber member  70  is covered with the coating layer  76  so that the surface of the rubber member  70  is not exposed.  
         [0092]    The fourth embodiment provides the following advantages.  
         [0093]    (4-1) The rubber members  70  prevent vibration of the pump housing  7  from being transmitted to the connection member  11 . Part of the surface of each vibration insulating rubber member  70  is not covered with the coupling member  72  and the threaded hole forming member  73 . Such part of the surface is covered with the polytetrafluoroethylene coating layer  76 . That is, the surface of each vibration insulating rubber member  70  is not exposed to dimethyl ether, which is a liquefied gas fuel. Therefore, when the pump housing  7  is suspended in the tank  10  storing dimethyl ether by using the damper  71 , the rubber members  70  do not deteriorate.  
         [0094]    (4-2) Each damper  71  is attached to the lid  16  and the connection member  11  in the following manner. First, the first screws  74  are threaded to fasten the coupling member  72  to the lid  16 . Then, the second screw  75  is passed through the through hole  113  and threaded to the nut portion  731  of the threaded hole forming member  73 . That is, each damper  71 , in which the coupling member  72  and the threaded hole forming member  73  are coupled to the rubber member  70 , is easily installed between the pump housing  7  and the connection member  11 .  
         [0095]    A fifth embodiment will now be described with reference to FIGS.  15 ( a ) and  15 ( b ).  
         [0096]    As shown in FIG. 15( a ), dampers  78  having a cylindrical vibration insulating rubber member  77  is located between the lid  16  of the pump housing  7  and the connection member  11 . As shown in FIG. 15( b ), the damper  78  includes the rubber member  77 , a coupling member  79 , a threaded hole forming member  80 , a first screw  81 , and the second screw  75 . The first screw  81  is used to fasten the coupling member  79 , which functions as a first attachment member, to the lid  16 . The second screw  75  is used to fasten the threaded hole forming member  80 , which functions as a second attachment member, to the connection member  11 . The coupling member  79  contacts and is attached to a first contacting end face  771  of the rubber member  77 . The thread hole forming member  80  includes a nut portion  801  having a threaded hole, and a coupling plate portion  802  coupled to the nut portion  801 . The nut portion  801  is fitted in an inner surface  773  of the rubber member  77 . The coupling plate portion  802  is attached to a second contacting end face  772  of the rubber member  77 .  
         [0097]    The coupling member  79  is fastened to the upper surface of the lid  16  with the first screw  81  threaded to the lid  16 . The threaded hole forming member  80  is fastened to the lower surface of the connection member  11  with the second screw  75 , which is passed through a through hole  113  formed in the connection member  11  and is threaded to the nut portion  801 . That is, the damper  78  is attached to the lid  16  with the coupling member  79 , and is also attached to the connection member  11  with the threaded hole forming member  80 .  
         [0098]    The inner diameter of the nut portion  801  of the threaded hole forming member  80  and the inner diameter of the rubber member  77  are greater than the diameter of the head of the first screw  81 . Therefore, the first screw  81  can be threaded to the lid  16  through the nut portion  801  and the rubber member  77 .  
         [0099]    As shown in FIG. 15( b ), a polytetrafluoroethylene coating layer  82  is formed on a surface of the rubber member  77  and on an inner surface  773  of the rubber member  77 . Also, the coating layer  82  is formed on the surface of the coupling member  79  and the surface of the threaded hole forming member  80 . The rubber member  77  is covered with the coating layer  82  so that the surface of the rubber member  77  is not exposed.  
         [0100]    The damper  78  is attached to the lid  16  and the connection member  11  in the following manner. First, the first screw  81  is threaded to fasten the coupling member  79  to the lid  16 . Then, the second screw  75  is passed through the through hole  113  and threaded to the nut portion  801  of the threaded hole forming member  80 . That is, the dampers  78 , in which the coupling member  79  and the threaded hole forming member  80  are coupled to the rubber member  77 , is easily installed between the pump housing  7  and the connection member  11 . The fifth embodiment has the same advantage as the advantage (4-1) of the fourth embodiment.  
         [0101]    A sixth embodiment will now be described with reference to FIG. 16.  
         [0102]    A damper  83  includes a cylindrical vibration insulating rubber member  84 , a cylindrical coupling member  85 , a threaded hole forming member  86 , first screws  87 , and a second screw  75 . The first screws  87  are used to fasten the coupling member  85 , which functions as a first attachment member, to the lid  16 . The second screw  75  is threaded to the threaded hole forming member  86 , which functions as a second attachment member. The thread hole forming member  86  includes a nut portion  861  having a threaded hole, and a flange  862  coupled to the nut portion  861 . The rubber member  84  is fitted in the cylinder of the cylindrical coupling member  85 . An annular plate portion  851  of the coupling member  85  contacts an upper end face  841  of the rubber member  84 . The nut portion  861  is fitted in the cylinder of the rubber member  84 . The flange  862  is contacts a lower end face  842  of the rubber member  84 .  
         [0103]    The flange  852  of the coupling member  85  is fastened to the upper surface of the lid  16  with the first screws  87  threaded to the lid  16 . The second screw  75  is threaded to the nut portion  861  of the threaded hole forming member  86 .  
         [0104]    A polytetrafluoroethylene coating layer  88  is formed on the surface of the rubber member  84 . The rubber member  84  is covered with the coating layer  88  so that the surface of the rubber member  84  is not exposed.  
         [0105]    The sixth embodiment thus provides the same advantages as the fourth embodiment.  
         [0106]    A seventh embodiment will now be described with reference to FIG. 17.  
         [0107]    A damper  89  includes an annular vibration insulating rubber member  90 , an annular holding member  91 , and screws  92 . The screws  92  are used to fastening the rubber member  90  and the holding member  91  to the pump housing  7 . The insertion hole  102 , which is formed with an inlet forming ring  9 , is formed in the upper wall  101  of the tank  10 . A flange  901  of the rubber member  90  is held between the inlet forming ring  9  and the connection member  11 .  
         [0108]    A polytetrafluoroethylene coating layer  94  is formed on the surface of the rubber member  90 . The rubber member  90  is covered with the coating layer  94  so that the surface of the rubber member  90  is not exposed.  
         [0109]    The seventh embodiment provides the same advantage as the advantage (4-1) of the fourth embodiment.  
         [0110]    An eighth embodiment will now be described with reference to FIG. 18. An annular rim portion  931  is formed on the inlet forming ring  9 . An annular vibration insulating rubber member  95  is located between the rim portion  931  and a flange  153  of the motor housing  15 . A vibration insulating rubber member  95  is placed on the rim portion  931 , and the flange  153  is placed on the rubber member  95 . The rubber member  95  functions as damper that prevents vibration of the pump housing  7  from being transmitted to the connection member  11 .  
         [0111]    A polytetrafluoroethylene coating layer  96  is formed on the surface of the rubber member  95 . The rubber member  95  is covered with the coating layer  96  so that the surface of the rubber member  95  is not exposed.  
         [0112]    The eighth embodiment provides the same advantage as the advantage (4-1) of the fourth embodiment.  
         [0113]    A ninth embodiment will now be described with reference to FIG. 19. A head  971  of a bolt  97  and an annular washer  98  are embedded in a vibration insulating rubber member  48 . The threaded portion of the bolt  97  passes through the through hole  113  of the connection member  11  and protrudes to the outside of the tank  10 . A nut  99  is threaded to the projecting portion of the bolt  97 . Screws  74 , a coupling member  72 , the rubber member  48 , the bolt  97 , and the washer  98  form a damper.  
         [0114]    A polytetrafluoroethylene coating layer  100  is formed on the surface of the coupling member  72  and the surface of the rubber member  48 . The rubber member  48  is covered with the coating layer  100  so that the surface of the rubber member  48  is not exposed.  
         [0115]    The ninth embodiment thus provides the same advantages as the fourth embodiment.  
         [0116]    A tenth embodiment will now be described with reference to FIGS.  20 ( a ) and  20 ( b ). In the tenth embodiment, the lip seal  32  and the lip seal  36  of the second embodiment are replaced by damper  103  and damper  104 , respectively.  
         [0117]    The damper  103  includes an annular vibration insulating rubber member  105 , an annular coupling member  106 , an annular thread hole forming member  107 , first screws  74 , and second screws  75 . The first screws  74  are used to fasten the coupling member  106 , which functions as a first attachment member, to the lid  16 . The second screws  75  are used to fasten the threaded hole forming member  107 , which functions as a second attachment member, to the connection member  11 . The discharge pipe  28  is fitted in the annular rubber member  105 . The rubber member  105  has an annular sealing portion  1053 . The sealing portion  1053  is pressed against the circumferential surface  282  of the discharge pipe  28  by the difference between the pressure in the motor housing  15  and the pressure in the tank  10 , so that the inner circumferential surface of the sealing portion  1053  closely contacts the circumferential surface  282  of the discharge pipe  28 .  
         [0118]    The coupling member  106  contacts and is attached to a first contacting end faces  1051  of the rubber member  105 . The threaded hole forming member  107  includes an annular contacting plate portion  1072 , and nut portions  1071  each having a threaded hole. The annular contacting plate portion  1072  surrounds the discharge pipe  28 , and the nut portions  1071  are located about the discharge pipe  28 . The nut portions  1071  are embedded in the rubber member  105 . The contacting plate portion  1072  is attached to a second contacting end face  1052  of the rubber member  105 .  
         [0119]    A polytetrafluoroethylene coating layer  108  is formed on the surface of the rubber member  105 , the coupling member  106 , and the surface of the threaded hole forming member  107 . The rubber member  105  is covered with the coating layer  108  so that the surface of the rubber member  105  is not exposed.  
         [0120]    The coupling member  106  is fastened to the upper surface of the lid  16  with the first screws  74  threaded to the lid  16 . The threaded hole forming member  107  is fastened to the lower surface of the connection member  11  with the second screw  75 , which is passed through a through hole  113  formed in the connection member  11  and is threaded to the nut portion  1071 .  
         [0121]    Except for the inner diameter of the rubber member  105 , the damper  104  has the same configuration as the damper  103 . Thus, like or the same reference numerals are given to those components that are like or the same as the corresponding components of the damper  103 . The sealing portion  1053  of the damper  104  is pressed against the circumferential surface  352  of the surrounding cylinder  35  by the difference between the pressure in the motor housing  15  and the pressure in the tank  10 , so that the inner circumferential surface of the sealing portion  1053  of the damper  104  closely contacts the circumferential surface  352  of the discharge pipe  35 .  
         [0122]    The damper  103 ,  104  are arranged between the lid  16  and the connection member  11  in the following manner. First, the first screws  74  are fastened to secure the coupling member  106  to the lid  16 . Then, the discharge pipe  28  is fitted in the rubber member  105  of the damper  103 , and the surrounding cylinder  35  is fitted in the rubber member  105  of the damper  104 . Subsequently, the second screws  75  are passed through the through holes  113  and threaded to the nut portions  1071  of the through hole forming members  107  of the damper  103 ,  104 . Accordingly, the damper  103 ,  104  are attached to the lid  16  and the connection member  11 .  
         [0123]    In the tenth embodiment, the damper  103 ,  104  also function as the lip seals  32 ,  36  in the first embodiment. The tenth embodiment also provides the same advantage as the advantage (4-1) of the fourth embodiment.  
         [0124]    The invention may be embodied in the following forms.  
         [0125]    The lip rings of the lip seals  32 ,  36  may be made of rubber.  
         [0126]    The lip seals  32 ,  36  may be replaced by O-ring shaped sealing members.  
         [0127]    In the second to tenth embodiment of the present invention, the pump housing  7  may be located on the bottom of a tank with dampers in between.  
         [0128]    The present invention may be applied to a system where a sub tank is connected to the tank  10  through a pipe, and a pump is located in the sub tank.  
         [0129]    In the second embodiment of the present invention, the electric pump may be oriented horizontally and accommodated in the tank  10 . In this case, the connection hole and the through holes are formed in the sidewall of the motor housing  15 .  
         [0130]    The electric pump may be suspended from the connection member  11  with elastic belts. If the belts are made of rubber, it is preferable that the surface of the belts be coated with a layer of polytetrafluorethylene.  
         [0131]    The present invention may be applied to a pump that is used in a cogeneration system (private electric generator), which generates electricity while using exhaust heat to heat water (fluid).  
         [0132]    In the third embodiment, instead of using adhesive, a plate may be welded to each side of the vibration insulator  65 , so that the electric motor M is fastened to one side with screws, and the connection member  11  is fastened to the other side with screws.  
         [0133]    In the illustrated embodiments, the present invention is applied to the electric pump, which uses DME. However, the present invention may be applied to pumps that use other types of fluid. That is, as long as a fluid that has the above described properties (the saturation vapor pressure can surpass the suction pressure of the pump section due to heat of the motor chamber, and the saturation vapor pressure stays below the discharge pressure of the pump section despite the heat in the motor chamber) is used, the present invention may be any electric pump that uses a fluid other than DME.  
         [0134]    In the first embodiment, the electric pump  2  need not be of an in-tank type, but may be of a type that is arranged outside the tank  10 .  
         [0135]    In the illustrated embodiments, the motor chamber  152  need not form part of the discharge path of DME. That is, the gear housing  17  may have a discharge port, so that the motor chamber  152  does not form part of the discharge path. In this case, the discharge port is connected to the motor chamber  152  through the passage  172  so that the motor chamber  152  is exposed to the discharge pressure.  
         [0136]    In the second to tenth embodiments, the pump housing  7  may have the discharge pipe  28  and the connection member  11  may have the connection hole  161 .  
         [0137]    In the illustrated embodiments, the pump section is a gear pump. However, the pump section does not need to be a gear pump. For example, the pump section may be a screw pump or a piston pump.  
         [0138]    The present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.