Patent Publication Number: US-7717091-B2

Title: Fuel supply systems

Description:
This application claims priority to Japanese patent application serial number 2007-166052, the contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to fuel supply systems used mainly for engines of vehicles. 
   2. Description of the Related Art 
   A conventional fuel supply system is shown in Japanese Laid-Open Patent Publication No. 2001-90624.  FIG. 6  is a schematic structural view showing the conventional fuel supply system disclosed in this publication. As shown in  FIG. 6 , fuel supply system  200  includes a fuel tank  201 , from which fuel is drawn and pressurized by a fuel pump  202  and passes through a fuel filter  204  and a supply pipe  203 . Then the fuel is injected from each injection valve  205  into a combustion chamber of an internal combustion engine (hereinafter called “engine”). A fuel pressure regulating device  207  opens and closes a reflux control valve  224  in accordance with control signals from a control unit  229 , and accordingly, pressure of fuel (hereinafter called “fuel pressure”) supplied to each injection valve  205  may be switched between high pressure and low pressure. 
   More specifically, the fuel pressure regulating device  207  opens the reflux control valve  224 , for instance when the engine starts to introduce the fuel into a control pressure chamber  208 B of a pressure regulator  208 , for increasing the pressure inside the control pressure chamber  208  B. Accordingly, the fuel pressure inside a fuel pressure regulating chamber  208 A of the pressure regulator  208  is increased, and fuel pressure inside the supply pipe  203  communicating with the fuel pressure regulating chamber  208 A is increased. Due to this, the fuel pressure supplied to each injection valve  205  becomes high to enhance atomization of the injected fuel, and accordingly, starting performance of the engine is improved. The fuel inside the fuel regulating chamber  208 A is then refluxed into a fuel tank  201  via a delivery pipe path  223 . The reflux control valve  224  is closed after starting the engine so that the pressure inside the pressure control chamber  208 B of the pressure regulator  208  is decreased. Therefore, the fuel pressure inside the fuel regulating chamber  208 A and the supply pipe  203  is decreased. Accordingly, the fuel pressure supplied to each injection valve  205  becomes low, and therefore, load on the fuel pump  202  etc. is reduced. 
   In the conventional fuel supply system (see  FIG. 6 ), the fuel introduced into the fuel pressure regulating chamber  208 A of the pressure regulator  208  during the pressurization, flows into the fuel tank  201  via the delivery pipe path  223 . As a result, the efficiency of pump is decreased due to the large loss of fuel flow volume. 
   Therefore, there has been a need for a fuel supply system that can prevent the loss of fuel flow volume during the pressurization, which can improve the efficiency of the pump. 
   SUMMARY OF THE INVENTION 
   One aspect according to a fuel supply system of the present invention includes a pressure regulator for regulating the pressure of fuel supplied from a fuel pump. A valve device is associated with the pressure regulator for controlling the pressure of the fuel regulated by the pressure regulator. The valve device supplies a part of the fuel as a control fluid to the pressure regulator. The part of the fuel supplied from the valve device as the control fluid is not discharged into a fuel tank when the pressure regulator regulates the pressure of the fuel to have a higher value. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is the schematic structural view showing a fuel supply system according to a first embodiment of the present invention; 
       FIG. 2  is a cross-sectional view showing a fuel pump; 
       FIG. 3  is a cross-sectional view showing the pressure regulator; 
       FIG. 4  is a schematic view showing a fuel supply system of a second embodiment of the present invention; 
       FIG. 5  is a schematic view showing a fuel supply system of a third embodiment of the present invention; and 
       FIG. 6  is a schematic view showing a conventional fuel supply system. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Each of the additional features and teachings disclosed above and below may be utilized separately or in conjunction with other features and teachings to provide improved fuel supply systems. Representative examples of the present invention, which examples utilize many of these additional features and teachings both separately and in conjunction with one another, will now be described in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Moreover, various features of the representative examples and the dependent claims may be combined in ways that are not specifically enumerated in order to provide additional useful embodiments of the present teachings. 
   One embodiment of a fuel supply system of the present invention includes a fuel tank for storing fuel, a fuel pump for supplying the fuel inside the fuel tank to outside of the fuel tank, a fuel pressure regulating chamber and a control pressure chamber being defined by a movable partition wall and each configured for introducing a portion of the fuel discharged from the fuel pump, a pressure regulator for regulating the fuel pressure inside the fuel pressure regulating chamber and for returning surplus fuel to the fuel tank, and a valve device controlled by a control device for changing the fuel pressure supplied to outside of the fuel tank by selectively switching between the introduction of the fuel and the introduction of air into the pressure regulating chamber of the pressure regulator. 
   According to the above fuel supply system, the fuel inside the fuel tank is drawn and pressurized (energized) by the fuel pump, regulated by the pressure regulator to be a pre-determined value, and then supplied to the outside of the fuel tank. The valve device is controlled by the control device and the introduction of the fuel and introduction of air into the pressure regulating chamber of the pressure regulator may be selectively switched. More specifically, the valve device blocks the introduction of the fuel when it introduces the air into the control pressure chamber of the pressure regulator. Whereas, the valve device blocks the introduction of the air when it introduces the fuel into the control pressure chamber of the pressure regulator. Accordingly, the fuel pressure inside the fuel pressure regulating chamber of the pressure regulator (in other words, the fuel pressure supplied to outside of the fuel tank) may be changed. When the fuel is introduced into the control pressure chamber of the pressure regulator, the introduction of the air into the control pressure chamber is blocked by the valve device. When the pressure to a movable partition wall (in the control pressure chamber) is increased due to the fuel introduction into the pressure regulating chamber of the pressure regulator, the flow of the fuel into the atmosphere is prevented. Accordingly, the loss of the fuel flowing inside the control pressure chamber  45  during pressurization is inhibited, and thus, the efficiency of the pump is increased. 
   The fuel introduced into the pressure regulating chamber of the pressure regulator may be a pressurized fuel after pressurization by the fuel pump and before being discharged from the fuel pump. According to this configuration, the pressurized fuel after pressurization by the fuel pump and before being discharged from the fuel pump may be introduced into the control pressure chamber of the pressure regulator. 
   The fuel supply system may include a pressure relief valve for regulating the fuel pressure inside the pressure regulating chamber of the pressure regulator to be below a pre-determined value. According to this configuration, the fuel pressure inside the control pressure regulating chamber of the pressure regulator is controlled to be below the pre-determined pressure by the pressure relief valve. 
   The valve device may be a three way valve. Because the valve device is the three-way valve, the introduction of the fuel and the introduction of the air into the control pressure chamber of the pressure regulator may be selectively switched. Accordingly, compared to utilizing a plural number of valve devices, the construction of the fuel supply system may be simplified 
   In another embodiment of the present invention, a fuel supply system includes a fuel tank constructed to store fuel; a fuel pump constructed to pump the fuel from the fuel tank and supplying the fuel to an engine via a first path; a pressure regulator constructed to adjust a pressure of the fuel supplied to the engine based on a pressure of a control fluid; a control valve associated with the pressure regulator and constructed to control the supply of the control fluid to the pressure regulator; and a second path connecting between the fuel pump and the control valve, so that a par of the fuel supplied from the fuel pump serves as the control fluid. The control valve is operable between a first position and a second position. When the control valve is in the first position, the part of the fluid as the control fluid is discharged from the control valve into the fuel tank without being supplied to the pressure regulator, so that the pressure of the fluid supplied to the engine is controlled to have a first pressure value. When the control valve is in the second position, the part of the fuel as the control fluid is supplied from the control valve to the pressure regulator without being discharged into the fuel tank, so that the pressure of the fluid supplied to the engine is controlled to have a second pressure value that is higher than the first value. 
   Embodiments of the present invention will be described with reference to the drawings. 
   First Embodiment 
   A first embodiment of the present invention will be explained below. This embodiment can be used as a fuel supply system for a vehicle.  FIG. 1  is a schematic structural view showing the fuel supply system. As shown in  FIG. 1 , a fuel supply system  10  is installed on a vehicle, which is not shown in the drawings, and has a fuel tank  12  for storing fuel, a fuel pump  14  located inside the fuel tank  12 , a pressure regulator  16  and a valve device  18 . 
   The fuel pump  14  is supported within the fuel tank  12  via a supporting member (not shown), and supplies the fuel from the fuel tank  12  to outside of the fuel tank  12 .  FIG. 2  is a cross sectional view showing the fuel pump  14 . As shown in  FIG. 2 , the fuel pump  14  is a motor-integrated pump and has an electric motor section  20  and an impeller pump section  21  installed on the bottom end of the motor section  20 . When an impeller  22  rotates due to the drive of the motor section  20 , the pump section  21  draws and pressurizes the fuel inside the fuel tank  12  and then discharges the fuel into the motor section  20 . A fuel intake opening  23  for drawing the fuel is located on the bottom surface of the fuel pump  14 . An intake filter  24  for filtering the fuel drawn from the fuel tank  12  into the fuel pump  14  is connected to the fuel intake opening  23  via a pipe. On the upper surface of the fuel pump  14 , a fuel discharge opening  25  for discharging the fuel passing through the motor section  20  is placed. On the bottom surface of the fuel pump  14 , a vapor jet  26  for ejecting (in other words, discharging) vapor (air bubbles generated due to evaporation of the fuel) contained in the fuel during pressurization inside the pump section  21  is provided. The vapor jet  26  may be also called a “vapor fuel discharging opening.” 
   As shown in  FIG. 1 , the fuel pump  14  (specifically, the fuel discharge opening  25  (see  FIG. 2 )) is connected with one end of a tank interior fuel supply path  28 . A tank exterior fuel supply path  29  located outside of the fuel tank  12  is connected with the other end of the tank interior fuel supply path  28 . The downstream-side end (i.e. the engine-side end of the tank), exterior fuel supply path  29  is connected to a delivery pipe which is not shown in the drawings. The delivery pipe has fuel injection valves, in other words, injectors corresponding to combustion chambers (not shown). Accordingly, the fuel pressurized by the fuel pump  14  is discharged into the tank interior fuel supply path  28 , and then supplied to the tank exterior fuel supply path  29 . The fuel supplied into the tank exterior fuel supply path  29  is injected from each injector into each combustion chamber of the engine via the delivery pipe. 
   A first communicating path  31  and a second communicating path  32  are branched from the tank interior fuel supply path  28 . The downstream-side end of the first communicating path  31  is communicated with a fuel pressure regulating chamber  44  of the pressure regulator  16  (described below). The downstream-side end of the second communicating path  32  is communicated with a first connection port  51  of the valve device  18  (described below). 
   The pressure regulator  16  is supported inside the fuel tank  12  with a supporting member which is not shown in the drawings, and regulates pressure of the fuel, in other words, the fuel pressure supplied to the tank exterior fuel supply path  29 .  FIG. 3  is a cross sectional view showing the pressure regulator. As shown in  FIG. 3 , the pressure regulator  16  has a casing  34 , a diaphragm  35 , and a valve element  36 . The casing  34  constitutes an outer shell of the pressure regulator  16 . The casing  34  is comprised of a case  37  and a case  38  coupled to each other. The case  37  has an opening on the upper surface located on the side of the fuel pressure regulating chamber  44 . The case  38  has an opening on the bottom surface located on the side of the control pressure chamber  45 . On the side wall portion of the case  37  on the side of the fuel pressure regulating chamber  44 , a fuel introduction pipe  40  is provided. On the bottom wall portion of the case  37 , a fuel ejection pipe  41  is provided. On the upper wall portion of the case  38 , a communication opening  42  is provided. 
   The diaphragm  35  is clamped between the case  37  of the fuel pressure regulating chamber side and the case  38  of the control pressure chamber side, and divides the, casing  34  into the fuel pressure regulating chamber  44  and the control pressure chamber  45 . The diaphragm  35  is made of a rubber-like resilient material and thus, has flexibility. The valve element  36  is installed in the center of the diaphragm  35  and faces against the upper end surface of the fuel ejection pipe  41 . The upper open end of the fuel election pipe  41  serves as a valve seat. The valve element  36  opens or closes the upper open end of the fuel ejection pipe  41  due to flexural deformation of the diaphragm  35  for permitting and interrupting communication of the inside of the fuel pressure regulating chamber  44  with the inside of the fuel ejection pipe  41 . The diaphragm  35  may be also called as a “moveable partition wall”. 
   Inside the control pressure chamber  45 , a valve spring  47  configured as a coil spring is interposed between the upper wall portion of the case  38  on the side of the control pressure chamber  45 , and the valve element  36  of the diaphragm  35 . The valve spring  47  always biases the valve element  36  towards the seating direction on the valve seat of the fuel ejection pipe  41 , in other words, the valve closing direction. Therefore, when the fuel pressure inside the pressure regulating chamber  44  for pressing the diaphragm  35  is lower than the force inside the control pressure chamber  45  for pressing the diaphragm  35 , in other words, resilient force of the valve spring  47 , the valve element  36  seats on the fuel ejection pipe  41  due to the resilient force of the valve spring  47 , and the fuel ejection pipe  41  is closed. When the fuel pressure inside the fuel pressure regulating chamber  44  (in other words, the fuel pressure) pressing the diaphragm  35  is higher than the resilient force of the valve spring  47 , due to the flexural deformation of the diaphragm  35 , the valve element  36  moves away from the fuel ejection pipe  41 , and the fuel ejection pipe  41  is opened. Accordingly, the fuel inside the fuel pressure regulating chamber  44  is ejected via the fuel ejection pipe  41 , and the fuel pressure in the fuel pressure regulating chamber  44  is lowered to be a pre-determined value. When the fuel pressure in the fuel pressure regulating chamber  44  has become the pre-determined value, the valve material  36  is closed due to the resilient force of the valve spring  47 . 
   Referring to  FIG. 1 , a valve device  18  is an electromagnetically switchable three way valve and supported inside the fuel tank  12  by the supporting member which is not shown in the drawing. The valve device  18  has a first to a third, altogether three connection ports  51 ,  52  and  53  and is switched on and off based on control signals that are outputted from the electronic control unit  50  (“ECU”). 
   The ECU  50  is a control unit that can include a microcomputer, and is connected with a detecting device such as an ignition switch or a starting switch of an engine at the input side and an injector at the output side. The ECU  50  also is set to perform on and off control depending on the operating condition of the engine. For example, the ECU  50  switches on (ON) the valve device  18  until a pre-determined amount of time passes after starting the engine (from switching on of the ignition switch or the starting switch) and switches off the valve device  18  (OFF) after the pre-determined amount of time passes. When the valve device  18  is switched on, the first connection port  51  and the second connection port  52  are connected with each other, and the third connection port  53  is blocked. When the valve device  18  is switched off, the first connection port  51  is blocked, and the second connection port  52  and the third connection port  53  are connected with each other. The ECU  50  may be called as a “control unit.” 
   As shown in  FIG. 1 , the first communicating path  31  is connected with the fuel introduction pipe  40  (See  FIG. 3 ) of the pressure regulator  16 , and communicates with the fuel pressure regulating chamber  44  of the pressure regulator  16 . The first connecting path  31  may be called as a “communicating path on the fuel pressure regulating chamber side.” As shown in  FIG. 1 , the second connection port  52  of the valve device  18  and the communication port  42  of the pressure regulator  16  (See  FIG. 3 ) communicate via a relay pipe path  55 . 
   The second communicating path  32  is connected with the first connecting port  51  of the valve device  18 . The second communicating path  32  may be called as a “communicating path on the control pressure chamber side.” A fuel discharge pipe  57  is connected with the third connection port  53  of the valve device  18 . The fuel discharge pipe  57  and the fuel ejection pipe  41  of the pressure regulator  16  are open inside the fuel tank  12 . 
   The operation of the fuel supply system  10  will now be explained. When the engine starts the valve device  18  is switched on according to the control signals output from the ECU  50 . The first connecting port  51  and the second connecting port  52  then communicate with each other and the third connecting port  53  is blocked. Under this condition, a portion of the fuel (inside the tank internal fuel supply path  28 ) flows into the control pressure chamber  45  of the pressure regulator  16  via the second communicating path  32  and the relay pipe path  55 . At this time, due to the brokerage of the third connecting port  53 , the fuel inside the control pressure chamber  45  is prevented from flowing into the fuel tank  12  via a fuel effluent pipe  57 . 
   When the portion of the fuel flowing inside of the tank internal fuel supply path  28  flows into the control pressure chamber  45  of the pressure regulator  16 , the fuel pressure inside the control pressure chamber  45  is increased. Accordingly, the diaphragm  35  of the pressure regulator  16  (See  FIG. 3 ) deforms in a flexural manner towards the fuel pressure regulating chamber  44  and the valve element  36  seats on the valve seat of the fuel ejection pipe  41 . As a result, the flow of the fuel inside the fuel pressure regulating chamber  44  into the fuel tank  12  through the fuel ejection pipe  41  is prevented. Accordingly, the fuel pressure inside the fuel pressure regulating chamber  44  is further increased. When the fuel pressure inside the fuel pressure regulating chamber  44  of the pressure regulator  16  becomes higher than the fuel pressure of the control pressure chamber  45 , the diaphragm  35  deforms in a flexural manner towards the control pressure chamber  45  and when the valve element  36  has moved away from the valve seat of the fuel ejection pipe  41 , the fuel inside the fuel regulating chamber  44  is ejected into the fuel tank  12  via the fuel ejection pipe  41 . When the fuel pressure inside the fuel pressure regulating chamber  44  drops again, the diaphragm  35  deforms in flexural manner towards the fuel pressure regulating chamber  44  and the valve element  36  seats on the valve seat of the fuel ejection pipe  41 . In this way, the fuel pressure inside the fuel pressure regulating chamber  44 , in other words, the fuel pressure supplied to outside of the fuel tank  12  (engine) is regulated to a pressure for instance, around 600 kPa which is higher than a normal pressure. 
   As explained above, because the fuel pressure supplied to the outside of the fuel tank  12  (engine) is regulated to a high fuel pressure by the pressure regulator  16 , atomization of the injected fuel from the injector is enhanced, and accordingly, the starting performance of the engine is improved. The valve device  18  remains switched on (a starter switch, such as an ignition switch or a start switch, remains to be switched on (ON)) from the start of the engine until a pre-determined amount of time passes. 
   When the pre-determined amount of time has passed after starting of the engine, the valve device  18  is switched off by the control signals output from the ECU  50 . The first connection port  51  of the valve device  18  is then blocked and the second connection port  52  and the third connection port  53  are communicated. Under this condition, a portion of the fuel flowing inside the tank interior fuel supply path  28  is not able to flow via the relay pipe path  55  from the second communicating path  32  and thus, the fuel is prevented from flowing into the control pressure chamber  45  of the pressure regulator  16 . Due to this, the pressure acting on the diaphragm  35  inside the pressure regulating chamber  45  is only the resilient force of the valve spring  47 . Accordingly, the fuel pressure inside the fuel pressure regulating chamber  44  of the pressure regulator  16  (in other words, the pressure of the fuel supplied to the outside of the fuel tank  12  (engine)) is regulated to a normal pressure, for instance, around 400 kPa. 
   As explained above, because the pressure of the fuel supplied to the outside of the fuel tank  12  (engine) is regulated to the normal pressure by the pressure regulator  16 , the load on the fuel pump  14  etc. may be reduced. The condition that the valve device  18  is switched on may be called as a “high pressure condition.” Whereas, the condition that the valve device is switched off may be called as a “normal pressure condition.” 
   According to the fuel supply system  10  (see  FIG. 1 ), because the ECU  50  controls the valve device  18 , introduction of fuel or air into the control pressure chamber  45  of the pressure regulator  16  may be selectively switched. More specifically, the valve device  18  blocks the introduction of the fuel for introducing air into the pressure control chamber  45  of the pressure regulator  16  (see the above explained normal pressure condition). Whereas, the valve device  18  blocks the introduction of the air for introducing the fuel into the pressure regulating chamber  45  of the pressure regulator  16  (See the above explained high pressure condition). Accordingly, the valve device  18  is operable to change the fuel pressure inside the fuel pressure regulating chamber  44  of the pressure regulator  16 , in other words, the pressure of the fuel supplied to the outside of the fuel tank  12 . 
   When the fuel is to be introduced into the control pressure chamber  45  of the pressure regulator  16  (the high pressure condition), the valve device  18  blocks the introduction of air into the control pressure chamber  45 . Accordingly, when the pressure against the diaphragm  35  (see  FIG. 3 ) inside the control pressure chamber  45  is increased due to the fuel introduction into the control pressure camber  45  of the pressure regulator  16 , the flow of the fuel into the atmosphere is prevented. Accordingly, the loss of the fuel flowing inside the control pressure chamber  45  during pressurization is inhibited, and thus, the efficiency of the pump is increased. 
   The fuel discharged from the fuel discharge opening  25  (see  FIG. 2 ) of the fuel pump  14  (i.e. the fuel pressurized by the fuel pressure pump  14 ) may be introduced into the control pressure chamber  45  of the pressure regulator  16 . Alternatively, the fuel discharged from a second discharge opening (pressurized fuel with the discharged fuel pressure) which is separately installed from the fuel discharge opening  25  of the fuel pump  14  may be introduced into the control pressure chamber  45 . 
   Because the valve device  18  is a three-way valve, one valve device  18  may selectively switch between the introduction of the fuel and the introduction the air into the pressure regulating chamber  45  of the pressure regulator  16 . Accordingly, the construction of the fuel supply system may be simplified compared to utilizing a plural number of valve devices that allow to selectively switch between the introduction of the fuel and the introduction of air into the control pressure chamber  45  of the pressure regulator  16 . 
   In an example of utilizing the plural number of valve devices, the valve device  18  and the relay pipe path  55  is omitted, the second communicating path  32  and a fuel discharge pipe  57  are individually connected with the pressure regulating chamber  45  of the pressure regulator  16 , valve devices (i.e. electromagnetic on-off valves) are respectively installed to the second communicating path  32  and the fuel discharge pipe  57 . Due to the open-close control of the valve devices by the ECU  50 , the introduction of the fuel and the introduction of the air into the control pressure chamber  45  of the pressure regulator may be selectively switched. Therefore, selectively switching the introduction of the fuel and the introduction of the air into the control pressure chamber  45  of the pressure regulator  16  utilizing a plural number of valve devices is also within the scope of the present invention. 
   Second Embodiment 
   A second embodiment of the present invention will be explained below. The second embodiment is a modification of the first embodiment. Therefore, explanation is provided for the modified parts only and explanation for the parts that are the same or similar to the first embodiment will not be repeated.  FIG. 4  shows a schematic structural view of the fuel supply system. As shown in  FIG. 4 , in this embodiment, the second connecting path  32  branched from the tank interior fuel supply path  28  inside the fuel supply system  10  in the first embodiment, is communicated with the vapor jet  26  (see,  FIG. 2 ) of the fuel pump  14  instead of the tank interior fuel supply path  28 . Accordingly, the fuel discharged from the vapor jet  26  of the fuel pump  14  is introduced into the second connecting path  32 . Therefore, when the valve device  18  is switched on by the ECU  50 , the fuel discharged from the vapor jet  26  of the fuel pump  14  flows into the control pressure chamber  45  of the pressure regulator  16  via the second connecting path  32  and the relay pipe path  55 . 
   The same effect with the first embodiment may also be achieved based on this embodiment. The fuel discharged from the vapor jet  26  (see  FIG. 2 ) of the fuel pump  14  (the fuel inside the fuel pump  14  which is on the pressurizing process) may be introduced into the control pressure chamber  45  of the pressure regulator  16 . Further, the fuel discharged from a second vapor jet which is separately disposed from the vapor jet  26  of the fuel pump  14  (the pressurized fuel during pressurizing process) may be introduced inside the control pressure chamber  45  of the pressure regulator  16 . Accordingly, due to the introduced fuel, the pressure inside the control pressure chamber  45  of the pressure regulator  16  may be set at any pressure value. 
   Third Embodiment 
   A third embodiment of the present invention will be explained below. The third embodiment is a modification of the second embodiment. Therefore, explanation is provided for the modified parts only and explanation for the parts that are the same or similar to the second embodiment will not be repeated.  FIG. 5  is a schematic structural view of the fuel supply system. As shown in  FIG. 5 , in this embodiment, a pressure relief valve  60  (also called as a “pressure release valve”) is disposed on the second connecting path  32  in the fuel supply system  10  in the second embodiment (see  FIG. 4 ). The pressure relief valve  60  is supported inside the fuel tank with a supporting member which is not shown in the drawings, and controls the fuel pressure introduced into the control pressure chamber  45  of the pressure regulator  16  to be below the pre-determined pressure. 
   The relief valve  60  has a case  61 , a relief path  62  communicating between the inside and outside of the case  61  and communicating with the a midway of the second communicating path  32 , a valve member  63  that can open and close the relief path  62 , and a spring  64  resiliently pressing the valve member  63  in a closing direction. When the fuel pressure inside the second connecting path  32  becomes higher than the resilient force of the spring  64 , the valve member  63  is opened due to the resiliency of the spring  64 , and the fuel inside the second communicating path  32  is released via the relief path  62  and accordingly, the pressure within the second communicating path  32  is lowered until it becomes a predetermined pressure. When the fuel pressure inside the control pressure chamber  45  becomes a pre-determined value, the valve member  63  is closed due to the resiliency of the spring  64 . 
   The same effect with the first embodiment can be achieved based on this embodiment. The fuel pressure inside the second communicating path  32  (in other words, the fuel pressure inside the control pressure chamber  45  of the pressure regulator  16 ) may be controlled to be below the pre-determined pressure by the pressure relief valve  60 . Further, the relief path  62  of the pressure relief valve  60  may communicate with the control pressure chamber  45  instead of communicating with the fuel path (the second communicating path  32 ), the pressure inside which is the same with the fuel pressure inside the control pressure chamber  45  of the pressure regulator  16 . 
   The present invention is not limited to the embodiments discussed above and may be modified without departing from the scope of the present invention.