Patent Publication Number: US-7909023-B2

Title: Fuel supply systems

Description:
This application claims priority to Japanese patent application serial number 2007-299161, 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 known fuel supply system is disclosed, for example, in Japanese Laid-Open Patent Publication No. 2001-248512. The fuel supply system of this publication includes a fuel pump for supplying fuel stored within a fuel tank to a side of an engine, a pressure regulating valve for regulating the pressure of pressurized fuel supplied from the fuel pump to the side of the engine and for discharging surplus fuel, and a jet pump driven by a flow of the surplus fuel discharged from the pressure regulating valve. Typically, a general fuel pump is provided with a vapor jet (also known as a vapor escape hole or a vapor discharge hole, etc.) formed at a pump housing in order to discharge vapor that is generated within a pump passage due to the rotational movement of an impeller driven by a motor so that fuel vapor generated within the pump passage is discharged trough the vapor jet out of the pump while the fuel is pressurized. 
     However, the conventional fuel supply system disclosed in the above publication does not control discharge of fuel vapor through the vapor jet provided to the fuel pump. According to this construction, even if almost no vapor is generated when the pressure has been increased to a system fuel pressure (system fuel pressure is a fuel pressure within a fuel supply passage and is a normal fuel pressure level within a fuel supply system), i.e., at increasing pressure, pressurized fuel may be discharged through the vapor jet. As a result, a loss of flow of the pressurized fuel may be large and it may cause increase in load applied to the fuel pump. Further, because the jet pump is configured to be driven by the flow of the surplus fuel, it may cause a problem that the amount of fuel pumped by the jet pump may become instable due to the change of an amount of the surplus fuel. 
     Therefore, there is a need for a fuel supply system that can reduce a load applied to a fuel pump during increase of a system fuel pressure and can stabilize the amount of fuel pumped by a jet pump. 
     SUMMARY OF THE INVENTION 
     One aspect according to the present invention includes a fuel supply system that includes a fuel pump, a jet pump, a first device and a second device. The fuel pump has a first port, a second port and a third port. Each of the first and second ports is configured to discharge a pressurized fuel. The third port is configured to discharge a fuel vapor that may be produced within the fuel pump. The first port is coupled to an engine via a fuel supply passage. The first device is coupled between the second port and the jet pump and is operable to permit and prevent the supply of the pressurized fuel to the jet pump. The second device is coupled to the third port and is operable to permit and prevent the discharge of the fuel vapor to the outside of the second device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a fuel supply system according to a first representative embodiment; 
         FIG. 2  is a cross sectional view of a changeover valve; 
         FIG. 3  is a cross sectional view of a fuel pump; 
         FIG. 4  is a cross sectional view of a pressure regulating valve; 
         FIG. 5  is a schematic view of a fuel supply system according to a second embodiment; 
         FIG. 6  is a cross sectional view of a first opening/closing valve; 
         FIG. 7  is a cross sectional view of a second opening/closing valve; 
         FIG. 8  is a schematic view of a fuel supply system according to a third embodiment; and 
         FIG. 9  is a schematic view of a fuel supply system according to a fourth embodiment. 
     
    
    
     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. 
     In one embodiment, a fuel supply system includes a fuel pump configured to supply fuel within a fuel tank to a side of an engine and having a vapor jet configured to discharge fuel vapor. A fuel vapor passage permits the fuel vapor discharged from the vapor jet of the fuel pump to flow therethrough. A pressure regulating valve regulates a fuel pressure within a pressure regulating chamber, into which the pressurized fuel discharged from the fuel pump is introduced, based on a pressure within a back pressure chamber, and to discharge surplus fuel. A surplus fuel passage permits the surplus fuel discharged from the pressure regulating valve to flow therethrough. A throttle portion is provided in the surplus fuel passage. A jet pump is driven by a flow of the pressurized fuel and permits the pressurized fuel discharged from the fuel pump to be introduced therein via a jet pump fuel passage. A valve can open and close the fuel vapor passage and the jet pump fuel passage in a manner opposite to each other based on a pressure of the surplus fuel within an upstream passage portion of the surplus fuel passage. The upstream passage portion is positioned on an upstream side of the throttle portion. The valve is operable to close the jet pump fuel passage and to open the fuel vapor passage when the surplus fuel pressure is less than a threshold value, and the valve is operable to open the jet pump fuel passage and to close the fuel vapor passage when the surplus fuel pressure is equal to or higher than the threshold value. 
     With this arrangement, the valve opens the fuel vapor passage and closes the jet pump fuel passage if surplus fuel pressure within the upstream passage portion positioned on the upstream side of the throttle portion of the surplus fuel passage is less than the threshold value due to generation of vapor. For example, the vapor may tend to be generated during increase of fuel pressure at a low voltage operating condition, for example, directly after starting the engine. 
     Because the jet pump is stopped by blocking the jet pump fuel passage while the fuel vapor is discharged through the fuel vapor passage, an amount of pressurized fuel supplied to a side of the engine can be increased. Accordingly, it is possible to reduce the size of the fuel pump and therefore to reduce the power consumption of the fuel pump because the jet pump is stopped within a driving region that determines the size of the fuel pump. 
     The jet pump fuel passage is opened as the fuel vapor passage is closed by means of the valve if the surplus fuel pressure is equal to or above a threshold value when almost no vapor is generated. For example, almost no vapor may be generated if the fuel pump driven under a normal condition and the pressure has been increased to a system fuel pressure, or if the fuel pump is driven in an operating condition, in which an amount of the surplus fuel pressure is increasing. Therefore, it is possible to reduce a load applied to the fuel pump driven to provide the increased system fuel pressure because the pressurized fuel is prevented from being discharged through the vapor jet as the fuel vapor passage is blocked. In addition, the jet pump can be driven by a flow of the pressurized fuel that is introduced via the jet pump fuel passage. In this way, because an amount of pressurized fuel for driving the jet pump can be maintained substantially uniform by utilizing the pressurized fuel discharged from the fuel pump for driving the jet pump, an amount of fuel pumped by the jet pump can be stabilized. 
     As a result, it is possible to reduce a load applied to the fuel pump that is driven to provide the system fuel pressure. It is also possible to stabilize an amount of fuel pumped by the jet pump. 
     In another embodiment, a first open/close valve can open and close the fuel vapor passage. A second open/close valve can open and close the jet pump fuel passage. The first and the second open/close valves can be opened and closed in a manner opposite to each other based on a pressure of the surplus fuel within an upstream passage portion of the surplus fuel passage. The upstream passage is positioned on an upstream side of the throttle portion. The second open/close valve closes the jet pump fuel passage while the first open/close valve opens the fuel vapor passage when the surplus fuel pressure is less than a threshold value. The second open/close valve opens the jet pump fuel passage while the first open/close valve closes the fuel vapor passage when the surplus fuel pressure is equal to or higher than the threshold value. 
     The fuel pressure within the pressure regulating chamber of the pressure regulating valve, i.e., a pressure of fuel supplied to the side of the engine can be varied by opening and closing a back pressure fuel passage by means of a valve device to change a pressure of a pressurized fuel, which is applied to the back pressure chamber of the pressure regulating valve. Therefore, the atomization of injected fuel injected from an injector(s) of the engine can be promoted by increasing the fuel pressure within the pressure regulating chamber of the pressure regulating valve, for example, at the start of the engine. As a result, it is possible to improve the startability of the engine and to reduce an emission. In addition, a load applied to the fuel pump, etc. can be reduced by reducing the fuel pressure within the pressure regulating chamber of the pressure regulating valve after starting the engine. 
     An upstream throttle portion and a downstream throttle portion may be provided in the back pressure fuel passage. The fuel flowing through an intermediate passage portion defined between the upstream throttle portion and the downstream throttle portion is introduced into the back pressure chamber of the pressure regulating valve. Therefore, it is possible to reduce the pressure of fuel applied to the back pressure chamber of the pressure regulating valve when the pressurized fuel to be supplied to the engine is introduced into the back pressure fuel passage. 
     Although a load applied to a fuel pump may be increased in order to obtain high fuel pressure when the engine is started at a low temperature, the load applied to the fuel pump as well as the size of the fuel pump can be reduced by stopping the fuel supply to the jet pump by means of the valve device. 
     First Embodiment 
     A first representative embodiment will now be described with reference to  FIG. 1 . In this embodiment, a fuel supply system is exemplified that is used for a vehicle engine. As shown in  FIG. 1 , a fuel supply system  10  is mounted on a vehicle (not shown) and is provided within a fuel tank  12  for storing fuel. The fuel tank  12  is formed to have a plurality of tank chambers and the fuel supply system  10  is disposed within a main tank chamber (for example, in a reservoir cup provided within the main tank chamber). 
     The fuel supply system  10  includes a fuel pump  14 , a pressure regulating valve  15 , a jet pump  16 , a changeover valve  17  and a valve device  18 , etc. that serve as the main components of the fuel supply system  10 . As shown in  FIG. 3 , the fuel pump  14  is configured as a motor-integrated in-tank fuel pump and has an electric motor section  20  and an impeller pump section  21  that is disposed at a lower end of the motor section  20 . The fuel pump  14  serves to supply fuel within the fuel tank  12  to the side of an engine. As the motor section  20  is actuated to rotate an impeller  23  within a pump housing  22 , the pump section  21  draws and pressurizes the fuel within the fuel tank  12  and discharges the fuel into the motor section  20 . A pump channel  24  having a C-shaped configuration is formed in the pump housing  22  along an outer circumferential portion of the impeller  23 . A fuel inlet port  25  for drawing fuel is disposed at a lower surface side of the pump housing  22  and communicates with a start end portion of the pump channel  24 . An inlet filter  26  for filtering the fuel is connected to the fuel inlet port  25 . An outflow port  28  that communicates with the start end portion of the pump channel  24  and discharges the fuel into a motor housing  27  of the motor section  20 , is provided on an upper surface side of the pump housing  22 . A fuel discharge port  29  for discharging the fuel that has passed through the motor housing  27  is provided on an upper surface side of the motor housing  27 . 
     A vapor jet  30  is provided on the lower surface side of the pump housing  22  for discharging the fuel during the pressurizing process, i.e., the fuel containing vapor (gas bubbles generated due to evaporation of the fuel) from the pump channel  24  to the outside. A first fuel outlet port  31  and a second fuel outlet port  32  are disposed on the lower surface side of the pump housing  22 . The first fuel outlet port  31  communicates with the pump channel  24  at a position on the downstream side of the vapor jet  30  and serves to discharge thed fuel during the pressurizing process from the pump channel  24  to the outside. The second fuel outlet port  32  communicates with the pump channel  24  at a position on the downstream side of the first fuel outlet port  31  and serves to discharge the fuel during the pressurizing process from the pump channel  24  to the outside. 
     As shown in  FIG. 1 , one end of a fuel supply passage  34  is connected to the fuel discharge port  29  of the fuel pump  14 . The fuel supply passage  34  extends from the side of the fuel tank  12  towards the side of an engine. Although not shown, the other end of the fuel supply passage  34  is connected to a delivery pipe having injectors (fuel injection valves) corresponding to respective combustion chambers of the engine. Therefore, the pressurized fuel discharged from the fuel pump  14  is supplied to the delivery pipe on the side of the engine via the fuel supply passage  34 , and is injected into the combustion chambers of the engine by the corresponding injectors. 
     Further, the pressure regulating valve  15  will be described. The pressure regulating valve  15  serves to regulate the pressure of the fuel that is supplied to the fuel supply passage  34  by the fuel pump  14 . As shown in  FIG. 4 , the pressure regulating valve  15  includes a casing  36 , a diaphragm  37 , a valve body  38  and a valve spring  39 , etc. that serve as the main components of the pressure regulating valve  15 . The casing  36  is formed to have an upper casing portion  41  with a lower opening and a lower casing portion  42  with an upper opening, which is joined to the lower surface side of the upper casing portion  41 . A communication port  43  is positioned at an upper wall portion of the upper casing portion  41 . The lower casing portion  42  has a fuel introducing pipe  44  attached to a side wall portion of the lower casing portion  42  and a fuel discharge pipe  45  attached to a bottom wall portion of the lower casing portion  42 . The fuel introducing pipe  44  communicates with a pressurized fuel introducing passage  47  that is branched from the fuel supply passage  34  within the fuel tank  12  (see  FIG. 1 ). Therefore, a part of the pressurized fuel that flows through the fuel supply passage  34  is introduced into the lower casing portion  42  and the fuel pressure is applied within the lower casing portion  42 . 
     As shown in  FIG. 4 , the diaphragm  37  is clamped between both casing portions  41  and  42  of the casing  36 , and divides an inner space of the casing  36  into an upper back pressure chamber  49  and a lower pressure regulating chamber  50 . The diaphragm  37  is made of rubber-like resilient material having a flexibility. The diaphragm  37  may be also called “a movable partition wall”. 
     The valve body  38  is mounted to a center portion of the diaphragm  37 . Due to the flexural deformation of the diaphragm  37 , the valve body  38  can open and close the fuel discharge pipe  45  while an upper end surface of the fuel discharge pipe  45  serves as a valve seat. 
     The valve spring  39  is interposed between opposing surfaces of the upper casing portion  41  and the valve body  38  and normally biases the valve body  38  in a closing direction. 
     Consequently, the valve body  38  is closed due to the resilient force of the valve spring  39 , if a force applied to the diaphragm  37  due to the fuel pressure within the pressure regulating chamber  50  of the pressure regulating valve  15  is lower than a force applied to the diaphragm  37  within the back pressure chamber  49  due to the resilient force of the valve spring  39  greater than the resilient force of the valve spring  39 , the valve body  38  is opened against the resilient force of the valve spring  39 . As a result, the fuel within the pressure regulating chamber  50  is discharged via the fuel discharge pipe  45  so that the fuel pressure within the pressure regulating chamber  50  is reduced to the predetermined value. When the fuel pressure within the pressure regulating chamber  50  has been reduced to a predetermined value, the valve body  38  is closed due to the resilient force of the valve spring  39 . 
     A surplus fuel passage  52  communicates with the fuel discharge pipe  45  of the pressure regulating valve  15  so that surplus fuel discharged from the fuel discharge pipe  45  can be discharged into the fuel tank  12  via the surplus fuel passage  52  (see  FIG. 1 ). A throttle portion  53  for reducing a flow area is disposed on the way of the surplus fuel passage  52  so that fuel pressure (also called as “surplus fuel pressure”) can be generated within a passage portion  52   a , which is positioned on the upstream side of the throttle portion  53 . 
     The jet pump  16  will be described. As shown in  FIG. 1 , a fuel introducing port  55  for introducing fuel for driving the jet pump  16  communicates with the first fuel outlet port  31  of the fuel pump  14  via a jet pump fuel passage  56 . Accordingly, a part of the pressurized fuel within the pump passage  24  of the fuel pump  14  during the pressurizing process (see  FIG. 3 ) is introduced into the jet pump  16  for dividing the same. The jet pump  16  serves to transfer fuel stored in one of tank chambers (such as a sub-tank chamber) into the other one of the tank chambers (such as a main tank chamber) due to a suction force produced by a negative pressure that may be generated by the flow of the driving fuel. 
     The changeover valve  17  will be described. As shown in  FIG. 2 , the changeover valve  17  includes a casing  58 , a valve member  59 , a diaphragm  60  and a valve spring  61 , etc., that serve as the main components of the changeover valve  17 . The casing  58  has a first casing body  63  and a second casing body  64  that are vertically aligned with each other. The first casing body  63  is formed to have an upper casing portion  66  with a lower surface having an opening and a lower casing portion  67  with an upper opening, which is joined to the lower surface side of the upper casing portion  66 . The second casing portion  64  is formed to have an upper casing portion  68  with a lower opening and a lower casing portion  69  with an upper opening, which is joined to the lower surface side of the upper casing portion  68 . A surplus fuel introducing port  70  is provided on an upper wall portion of the upper casing portion  66  of the first casing body  63 . A fuel vapor discharge port  71  is provided on a side wall portion of the lower casing portion  67  of the first casing body  63 . A pressurized fuel discharge port  72  is provided on a side wall portion of the lower casing portion  69  of the second casing body  64 . 
     A lower wall portion of the lower casing portion  67  of the first casing body  63  and an upper wall portion of the upper casing portion  68  of the second casing body  64  are connected to each other by means of a cylindrical casing portion  74  that is formed to have a hollow cylindrical configuration extending in a vertical direction. The inside of the first casing body  63  and the inside of the second casing body  64  are communicated with each other through the inside of the cylindrical casing portion  74 . Upper and lower end portions of the cylindrical casing portion  74  protrude into casing bodies  63  and  64 , respectively. A fuel vapor introducing port  75  is formed on an upper portion of the side surface of the cylindrical casing portion  74 . A pressurized fuel introducing port  76  is formed on a lower portion of the side surface of the cylindrical casing portion  74 . 
     The valve member  59  includes a valve shaft  78 , a first valve body  79 , a second valve body  80  and a flange-like partition wall portion  81  that are formed integrally with each other. The valve shaft  78  is loosely inserted into the cylindrical casing portion  74 . The first valve body  79  is provided on an upper end portion of the valve shaft  78  and serves to open and close the cylindrical casing portion  74 . An upper end surface of the cylindrical casing portion  74  serves as a valve seat. The second valve body  80  is provided on a lower end portion of the valve shaft  78  and serves to open and close a lower end surface of the cylindrical casing portion  74  as a valve seat. The partition wall portion  81  is provided on a middle portion of the valve shaft  78  and slidably contacts with an inner circumferential surface of the cylindrical casing portion  74 . The partition wall portion  81  divides an annular space formed between the cylindrical casing portion  74  and the valve shaft  78  into an upper communication passage  82  and a lower communication passage  83 . The upper communication passage  82  communicates within the fuel vapor introducing port  75  and the first casing body  63 . The lower communication passage  83  communicates within the pressurized fuel introducing port  76  and the second casing body  64 . 
     The diaphragm  60  is clamped between both casing portions  66 ,  67  of the first casing body  63  and divides an inner space of the casing body  63  into an upper back pressure chamber  84  and a lower fuel vapor chamber  85 . The first valve body  79  of the valve member  59  is joined to a center portion of the diaphragm  60 . The diaphragm  60  is made of a rubber-like resilient material and has a flexibility. The diaphragm  60  may be referred to as “a movable partition wall”. 
     The valve spring  61  is interposed between the opposing surfaces of the upper casing portion  68  of the second casing body  64  and the second valve body  80  of the valve member  59  and normally biases the valve member  59  in an upward direction. Therefore, the second valve body  80  is resiliently maintained in a closing position and the first valve body  79  is maintained in an opening position. 
     As shown in  FIG. 1 , a surplus fuel introducing passage  87  communicates with the surplus fuel introducing port  70 . The surplus fuel introducing passage  87  is branched from the upstream passage portion  52   a  of the surplus fuel passage  52 , which is positioned on the upstream side of the throttle portion  53 . Therefore, a part of surplus fuel flowing within the surplus fuel passage  52  is introduced into the back pressure chamber  84  of the changeover valve  17  and accordingly, the surplus fuel pressure produced within the upstream passage portion  52   a , which is positioned on the upstream side of the throttle portion  53 , is applied within the back pressure chamber  84 . 
     The vapor jet  30  of the fuel pump  14  communicates with the fuel vapor introducing port  75  via a fuel vapor introducing passage  88 . The fuel vapor introducing passage  88 , the upper communication passage  82  (see  FIG. 2 ), the fuel vapor chamber  85  and the fuel vapor discharge port  71  are arranged in series with each other to constitute a fuel vapor passage  89  (see  FIG. 1 ). 
     As shown in  FIG. 1 , the jet pump fuel passage  56  for communicating the first fuel outlet port  31  of the fuel pump  14  with the fuel introducing port  55  for introducing fuel for driving the jet pump  16  is divided into an upstream passage portion  56   a  and a downstream passage portion  56   b . A downstream end of the upstream passage portion  56   a  communicates with the pressurized fuel introducing port  76  and an upstream end of the downstream passage portion  56   b  communicates with the pressurized fuel discharge port  72 . The upstream passage portion  56   a , the lower communication passage  83  (see  FIG. 2 ), an inner space  64   a  of the second casing body  64  and the downstream passage portion  56   b  are arranged in series with each other to constitute the jet pump fuel passage  56  ( FIG. 1 ). In order to eliminate influences of the pressure at the jet pump  16 , which may be a high pressure, an outer diameter of the diaphragm  60  is determined to have a larger diameter than an outer diameter of the partition wall portion  81  of the valve shaft  78 . 
     When the force produced by the surplus fuel pressure applied to the diaphragm  60  within the back pressure chamber  84  of the changeover valve  17  is smaller than the resilient force of the valve spring  61 , the valve member  59  moves upward due to the resilient force of the valve spring  61 . As a result, the fuel vapor passage  89  is opened by the first valve body  79  and the jet pump fuel passage  56  is closed by the second valve body  80 . When the force produced by the surplus fuel pressure within the back pressure chamber  84  is larger than the resilient force of the valve spring  61 , the valve member  59  moves downward against the resilient force of the valve spring  61  so that the fuel vapor passage  89  is closed by the first valve body  79  and the jet pump fuel passage  56  is closed by the second valve body  80 . Accordingly, the changeover valve  17  opens and closes the fuel vapor passage  89  and the jet pump fuel passage  56  in a manner opposite to each other in response to the surplus fuel pressure. 
     The valve device  18  will be described. As shown in  FIG. 1 , the valve device  18  is an electromagnetic three-way changeover valve and has first, second and third connection ports  91 ,  92  and  93 . The first connection port  91  communicates with the second fuel outlet port  32  of the fuel pump  14  via the back pressure fuel passage  95 . The second connection port  92  communicates with the communication port  43  of the pressure regulating valve  15 , i.e., the back pressure chamber  49  via a communication passage  96 . The third connection port  93  communicates with an opening passage  97  that is opened into the fuel tank  12 . The valve device  18  is switched ON/OFF based on control signals that are outputted from the electronic control unit  98  (referred to as “ECU”). When the valve device  18  is switched ON, the first connection port  91  and the second connection port  92  are communicated with each other while the third connection port  93  is blocked. As a result, the pressurized fuel pressure (back pressure) applied to the back pressure fuel passage  95  is applied further to the back pressure chamber  84  of the changeover valve  17 . When the valve device  18  is switched OFF, the second communication port  92  and the third communication opening  93  are communicated with each other while the first connection port  91  is blocked. Consequently, the inside of the back pressure chamber  84  of the changeover valve  17  is opened into the atmosphere, i.e., into the fuel tank  12  via the communication passage  96  and the opening passage  97 . 
     The ECU  98  is a control unit that may include a microcomputer, etc. A detecting device, for detecting the operation of an ignition switch or a starting switch, etc. of an engine, is connected to an input side of the ECU  98 . An injector(s), etc. is/(are) connected to an output side of the ECU  98 . The ECU  98  serves to perform ON/OFF control of the valve device  18  based on the driving condition of an engine. For example, the ECU  98  switches the valve device  18  ON at the start of the engine (at the time of switching ON an ignition switch or a starting switch) and maintains the valve device  18  to be switched ON until a predetermined period of time has passed after the engine has started. The ECU  98  switches the valve device  18  OFF after the predetermined period of time has passed. The ECU  98  may be called a “control unit”. 
     A pressure relief valve  100  is disposed on the way of the back pressure fuel passage  95 . The pressure relief valve  100  serves to control the fuel pressure, which is applied to the back pressure chamber  49  of the pressure regulating valve  15 , to be equal to or less than a predetermined pressure. The pressure relief valve  100  has a case  101 , a relief path  102  extending into and out of the case  101  and communicating with a midway of the back pressure fuel passage  95 , a valve body  103  that can open and close the relief path  102 , and a spring  104  for resiliently biasing the valve body  103  of the pressure relief valve  100  in a closing direction. When the force applied by the fuel pressure within the back pressure fuel passage  95  becomes greater than the resilient force of the spring  104 , the valve body  103  of the pressure relief valve  100  is opened against the resilient force of the spring  104 . Accordingly, the pressurized fuel within the back pressure fuel passage  95  is released into the fuel tank  12  through the relief path  102  and the fuel pressure within the back pressure fuel passage  95  is reduced to a predetermined value. Once the fuel pressure within the back pressure fuel passage  95  has reached the predetermined value, the valve body  103  is closed due to the resilient force of the spring  104 . 
     The fuel pump  14 , the pressure regulating valve  15 , the changeover valve  17 , the valve device  18  and the pressure relief valve  100  are fixedly positioned within the fuel tank  12 . 
     The operation of the fuel supply system  10  will be described. For the convenience of explanation, a switching function for the fuel passages (the jet pump fuel passage  56  and the fuel vapor passage  89 ) by means of the changeover valve  17  will be explained after a function of the valve device  18  for varying the fuel pressure is described. 
     A function of the valve device  18  for varying the fuel pressure will be described. When the engine is started, the valve device  18  is switched ON based on control signals outputted from the ECU  98 . Then the first connection port  91  and the second connection port  92  of the valve device  18  are communicated with each other so that the pressure of the pressurized fuel supplied into the back pressure passage  95  is applied to the inside of the back pressure chamber  49  of the pressure regulating valve  15 . In addition, the fuel stored in the back pressure chamber  49  can be prevented from blowing out of the back pressure chamber  49  because the third connection port  93  of the valve device  18  is blocked. 
     When the pressure of the pressurized fuel is applied to the inside of the back pressure chamber  49  of the pressure regulating valve  15  (see  FIG. 4 ), the diaphragm  37  flexurally deforms towards the side of the pressure regulating chamber  50  due to the increased fuel pressure within the back pressure chamber  49 . As the valve body  38  is closed due to the flexural deformation of the diaphragm  37 , the outflow of fuel stored in the pressure regulating chamber  50  is restricted. As a result, the fuel pressure within the pressure regulating chamber  50  is further increased. If the fuel pressure within the pressure regulating chamber  50  exceeds the total value of the force applied by the fuel pressure within the pressure regulating chamber  50  and the resilient force of the valve spring  39 , the diaphragm  37  flexurally deforms towards the side of the back pressure chamber  49 . Accordingly, the valve body  38  is opened and the fuel within the pressure regulating chamber  50  may be discharged as surplus fuel. When the fuel pressure within the fuel regulating chamber  50  is reduced again, the diaphragm  70  flexurally deforms towards the side of the pressure regulating chamber  50  to close the valve body  38 . In this way, the fuel pressure within the pressure regulating chamber  50 , i.e., the fuel pressure supplied to an engine, is regulated to have a pressure value, for example, around 600 kPa, which is higher than a normal pressure value. Therefore, it is possible to promote the atomization of the fuel injected by the injector, improve startability of an engine and reduce an emission. The valve device  18  is maintained switched ON during an engine start period, more specifically, a period from the beginning of starting an engine (at the time of switching ON, for example, an ignition switch or a starting switch) until a predetermined period of time has passed after the engine has started. 
     The valve device  18  is switched OFF based on control signals outputted from the ECU  98  after a predetermined period of time has passed after starting the engine. Then the first connection port  91  of the valve device  18  is blocked and therefore, the pressure of the pressurized fuel may not be applied to the inside of the back pressure chamber  49 . Further, because the second connection port  92  and the third connection port  93  of the valve device  18  communicate with each other, the back pressure chamber  49  is opened to the atmosphere, i.e., into the fuel tank  12  via the communication passage  96  and the opening passage  97 . Consequently, the force applied to the diaphragm  37  within the back pressure chamber  49  may only be the resilient force of the valve spring  39  so that the fuel pressure within the pressure regulating chamber  50 , more particularly, the fuel pressure supplied to an engine may be regulated to have a normal pressure value, for example, around 400 kPa. In this way, a load, which may be applied to the fuel pump  14 , etc., can be reduced. The ON condition of the valve device  18  may be a “high pressure condition” and the OFF condition of the valve device  18  may be a “normal pressure condition”. 
     A switching function for the fuel passages (the jet pump fuel passage  56  and the fuel vapor passage  89 ) by means of the changeover valve  17  (see  FIG. 2 ) will be described. 
     Surplus fuel is discharged from the pressure regulating valve  15  into the surplus fuel passage  52  via the fuel discharge pipe  45 . The amount of the surplus fuel, which is discharged into the fuel tank  12 , is reduced due to a throttle function of the throttle portion  53 . Consequently, a surplus fuel pressure is generated within the upstream passage portion  52   a . The surplus fuel pressure is introduced into the back pressure chamber  84  of the changeover valve  17  via the surplus pressure introducing passage  87 . 
     The resilient force of the valve spring  61  may be greater than surplus fuel pressure when the vapor is easily generated as in the time especially immediately after starting an engine and when the surplus fuel pressure within the back pressure chamber  84  is less than a predetermined threshold value in an operating area of the fuel pump  14 , in which the pressure within the fuel pump  14  is increasing while the fuel pump is driven by a low voltage. Therefore, the fuel vapor passage  89  is opened by the first valve body  79  as the valve member  59  for the changeover valve  17  moves upward due to the resilient force of the valve spring  61  while the jet pump fuel passage  56  is closed by the second valve body  80 . Consequently, the fuel vapor introduced from the vapor jet  30  of the fuel pump  14  is discharged into the fuel tank  12  via the fuel vapor passage  89 . On the other hand, since the jet pump  16  is stopped as the jet pump fuel passage  56  is closed, the amount of pressurized fuel supplied to the side of the engine can be increased. As a result, it is possible to reduce a size of the pump section of the fuel pump  14  and therefore to reduce a current consumption of the fuel pump  14  by stopping the jet pump  16  within a driving region that may determine a size of the fuel pump  14 . 
     When almost no vapor is generated as in the case where the fuel pump  14  is operated in normal operation mode and the fuel pressure within the fuel supply system has reached a system fuel pressure (i.e., a fuel pressure within the fuel supply passage  34  and provides a normal fuel pressure level within the fuel supply system) that provides a pressure increased condition, the amount of surplus fuel is increased. When the surplus fuel pressure within the back pressure chamber  84  increases to be equal to or above a threshold value, the surplus fuel pressure becomes greater than the resilient force of the valve spring  61 . Therefore, the valve member  59  moves downward against the resilient force of the valve spring  61  due to the downward flexural deformation of the diaphragm  60  caused by the surplus fuel pressure, and therefore, the fuel vapor passage  89  is closed by the first valve body  79  while the jet pump fuel passage  56  is opened by the second valve body  80 . Accordingly, it is possible to limit the outflow of the fuel vapor from the vapor jet  30  of the fuel pump  14  by closing the fuel vapor passage  89 . In addition, as the jet pump fuel passage  56  is opened, a part of pressurized fuel during increase in pressure within the fuel pump passage  24  of the fuel pump  14  is introduced into the jet pump  16  as driving fuel in order to drive the jet pump  16 . Accordingly, fuel stored in one of tank chambers (such as a sub-tank chamber) may be transferred into the other tank chamber (such as a main tank chamber) or fuel stored in one of tank chambers (such as a main tank chamber) may be transferred into the other tank chamber (such as a reservoir cup). Therefore, it is possible to stabilize the amount of fuel pumped by the jet pump  16  since the amount of pressurized fuel for driving the jet pump  16  can be maintained uniform by using fuel discharged from the fuel pump  14 , i.e., fuel during increase in pressure as fuel for driving the jet pump  16 . 
     According to the above mentioned fuel supply system  10  (see  FIG. 1 ), it is possible to reduce a load applied to the fuel pump  14  at the system fuel pressure with the pressure increased and to stabilize the amount of fuel pumped by the jet pump  16 . 
     Further, because the changeover valve  17  (see  FIG. 2 ) has a simple mechanical structure, it is possible to reduce cost due to simplification of the structure. In addition, since the changeover valve  17  is configured to switch by utilizing surplus fuel pressure, it is not necessary to make change to the ECU  98 . 
     The fuel pressure within the pressure regulating chamber  50  of the pressure regulating valve  15 , i.e., the pressure of fuel supplied to the side of an engine, can be changed as the fuel pressure of the pressurized fuel applied to the back pressure chamber  49  of the pressure regulating valve  15  is changed by switching ON/OFF the valve device  18 . Accordingly, the atomization of fuel injected from the injector disposed on the side of an engine can be promoted by increasing the fuel pressure within the pressure regulating chamber  50  of the pressure regulating valve  15  at the start of an engine. Therefore, it is possible to improve startability of an engine and reduce an emission. Further, it is possible to reduce a load applied to the fuel pump  14 , etc., by reducing fuel pressure within the pressure regulating chamber  50  of the pressure regulating valve  15  after starting an engine. 
     Because the valve device  18  is a three-way changeover valve, a single valve device  18  can selectively switch between introduction of the pressurized fuel pressure into the back pressure chamber  49  of the pressure regulating valve  15  and release of the fuel from the back pressure chamber  49  into the atmosphere. Accordingly, the construction of the system may be simplified compared to the construction utilizing a plural number of valve devices. An example of the construction utilizing the plural number of valve devices may be as follows: The valve device  18  and the communication passage  96  in the above embodiment may be omitted so that the back pressure fuel passage  95  and the opening passage  97  may be individually communicated with the back pressure chamber  49  of the pressure regulating valve  15 . At the same time, valve devices, such as electromagnetic ON/OFF valves, may respectively be installed into the back pressure fuel passage  95  and the opening passage  97 . The introduction of fuel into the back pressure chamber  49  of the pressure regulating valve  15  and the release of fuel from the back pressure chamber  49  into the atmosphere may selectively be switched by controlling the valve devices to open and close by means of ECU  98 . It is, therefore, also included within the scope of the present invention to selectively switch the introduction of the fuel into the back pressure chamber  49  of the pressure regulating valve  15  and the release from the back pressure chamber  49  by utilizing a plural number of valve devices. 
     Further, fuel pressure within the back pressure chamber  49  of the pressure regulating valve  15  may be controlled to have a pressure equal to or less than a predetermined pressure level by the pressure relief valve  100  (see  FIG. 1 ). The relief path  102  for the pressure relief valve  100  may be directly communicated with the inside of the back pressure chamber  49  for the pressure regulating valve  15  instead of the back pressure fuel passage  95 . 
     Second Embodiment 
     The second representative embodiment is a modification of a part of the first representative embodiment. Therefore, only the modified part will be explained in order to avoid the repetition. 
     As shown in  FIG. 5 , instead of using the changeover valve  17  (see  FIG. 1 ) for the fuel supply system  10  as described in the first representative embodiment, a first open/close valve  110  for opening and closing the fuel vapor passage  89  is used in combination with a second open/close valve  123  for opening and closing the back pressure fuel passage  95  instead of using the changeover valve  17 . Both open/close valves  110  and  123  are fixedly disposed within the fuel tank  12 . 
     As shown in  FIG. 6 , the first open/close valve  110  includes a casing  111 , a diaphragm  112 , a valve body  113  and a valve spring  114  etc., that serve as main components of the first open/close valve  110 . The casing  111  has an upper casing portion  115  with a lower surface having an opening and a lower casing portion  116  with an upper surface having an opening, which is joined to the lower surface side of the upper casing portion  115 . A surplus fuel introducing port  117  is attached to an upper wall portion of the upper casing portion  115 . A fuel vapor introducing pipe  118  is attached to a bottom wall portion of the lower casing portion  116 . A fuel vapor discharge port  119  is provided to a side wall portion of the lower casing portion  116 . 
     The diaphragm  112  is clamped between the upper casing portion  115  and the lower casing portion  116  of the casing  111  and divides an inner space of the casing  111  into an upper back pressure chamber  120  and a lower fuel vapor chamber  121 . The diaphragm  112  is made of rubber-like resilient material and has a flexibility. The diaphragm  112  may be also referred to as “a movable partition wall”. 
     The valve body  113  is disposed at a center portion of the diaphragm  112  and serves to open and close an upper open end of the fuel vapor introducing pipe  118  due to a flexural deformation of the diaphragm  112 . Therefore, the upper end surface of the fuel vapor introducing pipe serves as a valve seat. 
     The valve spring  114  is interposed between opposing surfaces of the lower casing portion  116  and the valve body  113  and always biases the valve body  113  in a direction away from the upper end surface of the fuel vapor introducing pipe  118 , i.e., in a valve opening direction. 
     An upstream passage portion  52   a , which is positioned on the upstream side of the throttle portion  53  of the surplus fuel passage  52  communicates with the surplus fuel introducing port  117  via the surplus fuel introducing passage  87 . Therefore, a part of surplus fuel passing through the surplus fuel passage  52  is introduced into the back pressure chamber  120 . In addition, the pressure of the surplus fuel supplied into the upstream passage portion  52   a  positioned on the upstream side of the throttle portion  53  is applied into the back pressure chamber  120 . 
     A vapor jet  30  of the fuel pump  14  communicates with the fuel vapor introducing pipe  118  via the fuel vapor introducing passage  88 . The fuel vapor introducing passage  88 , the fuel vapor introducing pipe  118 , the fuel vapor chamber  121  and the fuel vapor discharge port  119  are arranged in series with each other to constitute a fuel vapor passage  89 . 
     When the force to press the diaphragm  117  applied by the surplus fuel pressure within the back pressure chamber  120  of the first open/close valve  110  is smaller than the resilient force of the valve spring  114 , the valve body  113  is moved upward to open the fuel vapor passage  89  due to the resilient force of the valve spring  114 . When the force applied by the surplus pressure within the back pressure chamber  120  is larger than the resilient force of the valve spring  114 , the valve body  113  moves downward to close the fuel vapor passage  89  against the resilient force of the valve spring  114 . 
     As shown in  FIG. 7 , the second open/close valve  123  includes a casing  124 , a valve member  125 , a diaphragm  126  and a valve spring  127 , etc., that serve as main components of the second open/close valve  123 . The casing  124  has a first casing body  128  and a second casing body  129  that are vertically aligned with each other. The first casing body  128  has an upper casing portion  131  with a lower opening and a lower casing portion  132  with an upper opening, which is joined to the lower surface side of the upper casing portion  131 . The second casing body  129  has an upper casing portion  133  with a lower opening and a lower casing portion  134  with an upper opening, which is joined to the lower surface side of the upper casing portion  133 . The first casing body  128  is provided with a surplus fuel introducing port  135  disposed to an upper wall portion of the upper casing portion  133  and an opening hole  136  defined in a side wall portion of the lower casing portion  134 . The second casing body  129  is provided with a pressurized fuel discharge port  137  disposed at a side wall portion of the lower casing portion  134 . 
     A lower wall portion of the lower casing portion  134  of the first casing body  128  and an upper wall portion of the upper casing portion  133  of the second casing body  129  are connected with each other via a tubular casing portion  139  that is formed to have a hollow cylindrical configuration extending in a vertical direction. Consequently, an inside of the first casing body  128  and an inside of the second casing body  129  are communicated with each other through an inside of the tubular casing portion  139 . Upper and lower end portions of the tubular casing portion  139  protrude into the casing bodies  128  and  129 , respectively. A pressurized fuel introducing port  140  is formed at a center portion of the tubular casing portion  139 . 
     The valve member  125  includes a valve shaft  142 , a first valve body  143  and a second valve body  144  that are formed integrally with each other. The valve shaft  142  is inserted into the tubular casing portion  139 . The first valve body  143  is disposed at an upper end portion of the valve shaft  142  and serves to open and close an upper end opening of the tubular casing portion  139 . Thus, the upper end surface of the tubular casing portion  139  serves as a valve seat. The second valve body  144  is disposed at a lower end portion of the valve shaft  142  and serves to open and close a lower end opening of the tubular casing portion  139 . Thus, the lower end surface of the tubular casing portion  139  serves as a valve seat. The valve shaft  142  has a large diameter shaft portion  142   a  and a small diameter shaft portion  142   b . The large diameter shaft portion  142   a  is slidably fitted into an upper portion of the tubular casing portion  139 . The small shaft portion  142   b  protrudes from a lower end surface of the large diameter shaft portion  142   a  coaxially therewith and is loosely fitted into a lower portion of the cylindrical casing portion  139 . An annual space defined between the small diameter shaft portion  142   b  and the tubular casing portion  139  forms a communication path  145  that communicates with the pressurized fuel introducing port  140  and an inside of the second casing body  129 . The large diameter shaft portion  142   a  separates an inner space of the first casing body  128  and an inner space of the communication path  145  from each other and always closes the upper open end of the tubular casing portion  139  independently of the vertical movement of the valve member  125 . The first valve body  143  moves towards or away from the upper end surface of the cylindrical casing portion  139  in accordance with the vertical movement of the valve member  125  and serves substantially as a stopper when the valve member  125  moves downward. 
     The diaphragm  126  is clamped between the upper casing portion  131  and the lower casing portion  132  of the first casing body  128  and divides an inner space of the casing  101  into an upper back pressure chamber  146  and a lower atmosphere chamber  147 . The atmosphere chamber  147  communicates with the atmosphere via the opening hole  136 . The first valve body  143  of the valve member  125  is joined to the center portion of the diaphragm  126 . The diaphragm  126  is made of rubber-like resilient material and has a flexibility. The diaphragm  126  is also referred to as “a movable partition wall”. 
     The valve spring  127  is interposed between opposing surfaces of the upper casing portion  133  of the second casing body  129  and the second valve body  144  of the valve member  125  and always biases the valve member  125  in an upward direction. Therefore, the valve spring  127  resiliently maintains the first valve body  143  and the second valve body at an opening position and a closing position, respectively. 
     As shown in  FIG. 5 , a surplus fuel branch passage  148  communicates with the surplus fuel introducing port  135  of the second open/close valve  123  and is branched from the surplus fuel introducing passage  87 . Therefore, a part of the surplus fuel passing through the surplus fuel passage  52  is introduces into the back pressure chamber  146  of the second open/close valve  123  via the surplus fuel branch passage  148  and a surplus fuel pressure may be applied within the upstream passage portion  52   a , which is positioned on the upstream side of the throttle portion  53 . 
     A downstream end of the upstream passage portion  56   a  of the jet pump fuel passage  56  communicates with the pressurized fuel introducing port  140 . An upstream end of the downstream passage portion  56   b  of the jet pump fuel passage  56  communicates with the pressurized fuel discharge port  137 . The upstream passage portion  56   a , the communication path  145  (see  FIG. 7 ), an inner space  129   a  formed within the second casing body  129  and the downstream passage portion  56   b  are arranged in series with each other to constitute a jet pump fuel passage  56  (see  FIG. 5 ). 
     When the force produced by the pressure applied to the diaphragm  126 , i.e., the surplus fuel pressure, within the back pressure chamber  146  of the second open/close valve  123  (see  FIG. 7 ) is smaller than the resilient force of the valve spring  127 , the valve member  125  moves upward due to the resilient force of the valve spring  127 . As a result, the jet pump fuel passage  56  is closed by the second valve body  144  while the first valve body  143  moves away from the upper end surface of the tubular casing portion  139 . When the force produced by the surplus fuel pressure within the back pressure chamber  146  is larger than the resilient force of the valve spring  127 , the valve member  125  moves downward against the resilient force of the valve spring  127 . As a result, the jet pump fuel passage  56  is opened by the second valve body  144  while the first valve body  143  contacts the upper end surface of the cylindrical casing portion  139 . 
     According to the fuel supply system  10  (see  FIG. 5 ), when the surplus fuel pressure applied to the back pressure chamber  120  of the first open/close valve  110  and the back pressure chamber  146  of the second open/close valve  123  is less than a threshold value, the first open/close valve  110  opens the fuel vapor passage  89  and the second open/close valve  123  closes the jet pump fuel passage  56 , respectively. When the surplus pressure is equal to or higher than the threshold value, the first open/close valve  110  closes the fuel vapor passage  89  and the second open/close valve  123  opens the jet pump fuel passage  56 , respectively. Accordingly, the first open/close valve  110  and the second open/close valve  123  open and close the fuel vapor passage  89  and jet pump fuel passage  56 , respectively, in a manner opposite to each other, based on the surplus fuel pressure. 
     Third Embodiment 
     The third representative embodiment is a modification of a part of the first representative embodiment. Therefore, only the modified part will be explained in order to avoid the repetition. 
     Referring to  FIG. 8 , the third representative embodiment corresponds to a modification in a fuel pressure varying function performed by the valve device  18  of the fuel supply system  10  of the first representative embodiment (see  FIG. 1 ). The valve device  18 , the second fuel outlet port  32  of the fuel pump  14 , the back pressure fuel passage  95  and the pressure relief valve  100  of the first embodiment are not incorporated. 
     A back pressure fuel passage  150  communicates with the fuel supply passage at a position on a downstream side of a branch point where the pressurized fuel introducing passage  47  is branched from the fuel supply passage  34 . A valve device  152  constituted by an electromagnetic open/close valve is disposed on the way of the back pressure fuel passage  150 . The valve device  152  divides the back pressure fuel passage  150  into an upstream passage portion  150   a  and a downstream passage portion  150   b . A downstream end of the downstream passage portion  150   b  is opened into the fuel tank  12 . 
     Two throttle portions, i.e., an upstream throttle portion  154  and a downstream throttle portion  155  are disposed on the way of the downstream passage portion  150   b  for reducing its passage area in a stepwise manner. A communication passage  96 , which communicates with the communication port  43  of the pressure regulating valve  15 , communicates with an intermediate passage portion positioned between the upstream throttle portion  154  and the downstream throttle portion  155 . Consequently, fuel having an intermediate pressure and flowing through the intermediate passage portion between the upstream throttle portion  154  and the downstream throttle portion  155  is introduced into the back pressure chamber  49  of the pressure regulating valve  15  via the communication passage  96 . 
     Similar to the valve device  18  (see  FIG. 1 ) of the first representative embodiment, the valve device  152 , is switched ON/OFF based on the control signals outputted from the ECU  98 . When the valve device  152  is switched ON, the upstream passage portion  150   a  and the downstream passage portion  150   b  of the back pressure fuel passage  150  are communicated with each other so that a part of pressurized fuel flowing through the fuel supply passage  34  is introduced into the back pressure fuel passage  150 . As a result, the fuel having the intermediate pressure and positioned between the throttle portions  154  and  155 , which are disposed at the downstream passage portion  150   b  of the back pressure fuel passage  150 , is introduced into the back pressure chamber  49  of the pressure regulating valve  15  via the communication passage  96 . Therefore, the fuel pressure within the pressure regulating chamber  50  of the pressure regulating valve  15  is regulated to a higher level than a normal pressure level. When the valve device  18  is switched OFF, the back pressure fuel passage  150  is blocked. Therefore, the intermediate fuel pressure may not be applied into the back pressure chamber  49  of the pressure regulating valve  15  so that the fuel pressure within the pressure regulating chamber  50  of the pressure regulating valve  15 , i.e., the fuel pressure supplied to an engine, is regulated to a normal pressure level. Accordingly, the fuel pressure within the pressure regulating chamber  50  of the pressure regulating valve  15  can be varied as the pressure of the pressurized fuel applied to the back pressure chamber  49  of the pressure regulating valve  15  is varied by switching ON/OFF the valve device  152 . 
     Because the fuel flowing through the intermediate passage portion defined between the upstream throttle portion  154  and the downstream throttle portion  155  of the back pressure fuel passage  150  is introduced into the back pressure chamber  49  of the pressure regulating valve  15 , it is possible to lower the pressure that is applied to the back pressure chamber  49  of the pressure regulating valve  15  during introduction of the pressurized fuel, which is adapted to be supplied to the engine, into the back pressure fuel passage  150 . Accordingly, the pressure within the fuel supply passage  34  can be regulated to a predetermined pressure level. 
     Fourth Embodiment 
     The fourth representative embodiment is a modification of a part of the first representative embodiment. Therefore, only the modified part will be explained in order to avoid the repetition. 
     As shown in  FIG. 9 , according the fourth embodiment, a fuel pressure varying function of the valve device  18  of the fuel supply system  10  of the first representative embodiment (see  FIG. 1 ) is not incorporated. Therefore, in addition to the valve device  18 , the second fuel outlet port  32 , the back pressure fuel passage  95 , the communication path  96  and the pressure relief valve  100  for the fuel pump  14  are not incorporated. According to the fourth representative embodiment, the fuel pressure within the fuel supply passage  34  can be maintained at a normal level.