Patent Publication Number: US-10330060-B2

Title: Gasoline fuel supply system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is the U.S. national phase of International Application No. PCT/JP2016/002332 filed May 12, 2016, which designated the U.S. and claims priority to Japanese Patent Application No. 2015-117802 filed on Jun. 10, 2015, the entire contents of each of which are herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a gasoline fuel supply system. 
     BACKGROUND ART 
     A gasoline fuel supply system is conventionally well-known, which pumps up a gasoline fuel from a fuel tank and supplies the gasoline fuel to a fuel injection valve. The fuel injection valve directly injects the gasoline fuel into a cylinder of an internal-combustion engine. 
     Patent literature 1 discloses such a gasoline fuel supply system including a feed pump part and a high-pressure pump part. The feed pump part includes an electric pump, as a main component, which operates by being supplied with electric power, and pumps the gasoline fuel from the fuel tank to discharge at a feed pressure. The high-pressure pump part includes a positive displacement mechanical pump which operates in response to an output of an internal-combustion engine, as a main component. The high-pressure pump part pressurizes the gasoline fuel discharged from the feed pump part, and discharges the gasoline fuel at a supply pressure to a fuel injection valve. The supply pressure to the fuel injection valve can be raised to a pressure required for the direct injection of gasoline fuel, since the gasoline fuel supply system is equipped with both the feed pump part and the high-pressure pump part. 
     PRIOR ART LITERATURES 
     Patent Literature 
     Patent Literature 1 JP 2010-133265 A 
     SUMMARY OF INVENTION 
     However, in Patent Literature 1, there is a possibility of a bad influence on the fuel injection characteristic from the fuel injection valve, since the gasoline fuel is vaporized at the low-pressure side of the high-pressure pump part which receives heat from the internal-combustion engine. If the feed pressure from the electric pump is raised in order to control the vaporization, the power consumption will increase at the time of energizing the electric pump. Such an increase in the power consumption is not desirable in the viewpoint of energy-saving. Moreover, in Patent Literature 1, in case where the electric pump is a positive displacement pump, similarly to the mechanical pump, if the electric pump breaks down, the pumping of gasoline fuel itself becomes difficult. It is not desirable in the viewpoint of fail-safe. 
     It is an object of the present disclosure to provide a gasoline fuel supply system which can secure fuel injection characteristic, energy-saving and fail-safe. 
     According to an aspect of the present disclosure, a gasoline fuel supply system supplies a gasoline fuel to a fuel injection valve by pumping from a fuel tank so as to be directly injected by the fuel injection valve into a cylinder of an internal-combustion engine, and includes a feed pump part, an inline pump part, and a high-pressure pump part. The feed pump part includes a non-positive displacement electric pump which operates in response to receiving electric power, and pumps the gasoline fuel from the fuel tank and discharges at a feed pressure. The inline pump part includes a non-positive displacement mechanical pump which operates in response to receiving an output of the internal-combustion engine, and pressurizes the gasoline fuel discharged from the feed pump part and discharges at a middle pressure. The high-pressure pump part includes a positive displacement mechanical pump which operates in response to receiving the output of the internal-combustion engine. The high-pressure pump part pressurizes the gasoline fuel discharged from the inline pump part, and discharges the gasoline fuel at a supply pressure to the fuel injection valve. 
     The inline pump part pressurizes the gasoline fuel discharged from the feed pump part, and discharges at the middle pressure. Furthermore, the high-pressure pump part pressurizes the gasoline fuel discharged from the inline pump part; and discharges the gasoline fuel at the supply pressure to the fuel injection valve. Therefore, while the feed pressure of the gasoline fuel pumped from the fuel tank is restricted to be low in the feed pump part, the inline pump part can raise the middle pressure discharged to the low-pressure side of the high-pressure pump part. Here, the feed pump part includes the non-positive displacement electric pump which operates in response to a passage of electricity, and the inline pump part includes the non-positive displacement mechanical pump which operates in response to the output of the internal-combustion engine. Thereby, the power consumption can be reduced in the feed pump part in which the feed pressure is restricted low at the time of supplying electric power to the non-positive displacement electric pump, and the vaporization of gasoline fuel can be restricted in the inline pump part, in which the non-positive displacement mechanical pump uses the output of the internal-combustion engine. Therefore, the fuel injection characteristic can be secured while the energy can be saved. 
     If the non-positive displacement electric pump breaks down in the feed pump part, the inline pump part can supply the gasoline fuel to the high-pressure pump part, because the gasoline fuel is pumped from the fuel tank through the non-positive displacement electric pump which breaks down. Conversely, if the non-positive displacement mechanical pump breaks down in the inline pump part, the gasoline fuel discharged out of the fuel tank with the non-positive displacement electric pump in the feed pump part can be supplied to the high-pressure pump part through the non-positive displacement mechanical pump which breaks down. Therefore, the fail-safe system can be secured. 
     As mentioned above, it is possible to secure both the fuel injection characteristic, and the energy-saving and fail-safe properties. 
     Moreover, the inline pump part may have a check valve which regulates an adverse flow of the gasoline fuel discharged from the non-positive displacement mechanical pump. 
     Thereby, in the inline pump part, the adverse current of the gasoline fuel discharged from the non-positive displacement mechanical pump is regulated by the check valve. Therefore, at a time of dead soak when the internal-combustion engine is left in the halt condition, at the low-pressure side of the high-pressure pump part which receives heat from the internal-combustion engine, the vaporization can be controlled by maintaining the fuel pressure of gasoline fuel at the middle pressure. Therefore, the fuel injection characteristic can be secured in the internal-combustion engine when the internal-combustion engine is started after the dead soak. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating an internal-combustion engine and a gasoline fuel supply system according to a first embodiment. 
         FIG. 2  is a characteristics view illustrating characteristics of the gasoline fuel supply system of the first embodiment and the internal-combustion engine. 
         FIG. 3  is a diagram illustrating a gasoline fuel supply system according to a second embodiment. 
         FIG. 4  is a diagram illustrating a modification of  FIG. 1 . 
         FIG. 5  is a diagram illustrating a modification of  FIG. 3 . 
         FIG. 6  is a diagram illustrating a modification of  FIG. 1 . 
         FIG. 7  is a diagram illustrating a modification of  FIG. 1 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present disclosure will be described hereafter referring to drawings. In the embodiments, a part that corresponds to a matter described in a preceding embodiment may be assigned with the same reference numeral, and redundant explanation for the part may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. The parts may be combined even if it is not explicitly described that the parts can be combined. The embodiments may be partially combined even if it is not explicitly described that the embodiments can be combined, provided there is no harm in the combination. 
     First Embodiment 
     As shown in  FIG. 1 , a gasoline fuel supply system  1  according to a first embodiment is disposed in a vehicle, together with an internal-combustion engine  2 . 
     The internal-combustion engine  2  is a gasoline reciprocating engine which outputs power from a crankshaft  2   b  by combusting a gasoline fuel  3  in plural cylinders  2   a . The internal-combustion engine  2  may independently generate an output EP, which is power or horsepower, or may be a hybrid engine which produces the output EP with a motor generator. The gasoline fuel  3  combusted in the internal-combustion engine  2  may be motor gasoline which has a predetermined octane number, or may be motor gasoline mixed with, for example, bioethanol. 
     The internal-combustion engine  2  has plural fuel injection valves  5 , each of which directly injecting the gasoline fuel  3  to the respective cylinder  2   a . Each of the fuel injection valves  5  is operated by electric power, and adjusts the injection quantity of the gasoline fuel  3  according to the operational status of the internal-combustion engine  2 . The gasoline fuel  3  having a supply pressure Ps that is according to the operational status of the internal-combustion engine  2  is supplied to each of the fuel injection valves  5  through a high-pressure rail  6  of a vehicle. Here, as shown in (c) of  FIG. 2 , a demanded value of the supply pressure Ps to each of the fuel injection valves  5  changes according to the rotation speed N of the internal-combustion engine  2 . Specifically, in an operating range lower than or equal to a maximum output EPmax of the internal-combustion engine  2 , the demanded value of the supply pressure Ps is raised, as the rotation speed N is raised. Therefore, if the injection frequency of the gasoline fuel  3  from each of the fuel injection valves  5  is raised in response to the rotation speed N, an expected injection quantity can be secured by each of the fuel injection valves  5 . 
     As shown in  FIG. 1 , the gasoline fuel supply system  1  is applied to the internal-combustion engine  2 . The gasoline fuel supply system  1  pumps up the gasoline fuel  3  from the inside of the fuel tank  7  of the vehicle. Furthermore, the gasoline fuel supply system  1  supplies the pumped-up gasoline fuel  3  to each of the fuel injection valves  5  through the high-pressure rail  6 . The gasoline fuel supply system  1  includes a feed pump part  10 , an inline pump part  20 , a high-pressure pump part  30 , pressure passages  40 - 42 , and an engine ECU (Electronic Control Unit)  50 . 
     The feed pump part  10  includes a non-positive displacement electric pump  11  as a main component. The non-positive displacement electric pump  11  is a turbo type pump having an electric motor  110  to be supplied with electric power, and an impeller  112  rotated by the electric motor  110  in a pump casing  111  to operate the pump. At the operation time, the non-positive displacement electric pump  11  pumps the gasoline fuel  3  from the fuel tank  7  to an internal pump room  115  by suction from a suction port  113 . Furthermore, at the operation time, the non-positive displacement electric pump  11  pressurizes the gasoline fuel  3  drawn to the pump room  115  with the impeller  112 , and discharges the gasoline fuel from a discharge port  114 . At this time, the non-positive displacement electric pump  11  discharges the pumped-up gasoline fuel  3  at the feed pressure Pt. The feed pressure Pf is set variably, for example, within a range of 300 to 500 kPa. 
     The non-positive displacement electric pump  11  is arranged inside the fuel tank  7  as an in-tank pump, and the suction port  113  is always soaked in the gasoline fuel  3  in the tank  7 . Thereby, the self-suction from the suction port  113  is possible in the non-positive displacement electric pump  11  at the operation time when the impeller  112  rotates. Namely, the pumping of the gasoline fuel  3  is possible for the non-positive displacement electric pump  11  in the fuel tank  7 . In contrast, when the impeller  112  is suspended, the gasoline fuel  3  is permitted to flow between the suction port  113  and the discharge port  114  in the non-positive displacement electric pump  11 . A centrifugal pump such as swirl pump or turbine pump (diffuser pump) may be adopted as the non-positive displacement electric pump  11 . In this embodiment, a cascade pump (wesco pump) is adopted, whose pressurization performance is higher than that of the centrifugal pump. 
     The feed pump part  10  has a fuel filter  12  in addition to the non-positive displacement electric pump  11 . The fuel filter  12  is arranged in the fuel tank  7 , and communicates with the discharge port  114  of the non-positive displacement electric pump  11 . The gasoline fuel  3  discharged from the discharge port  114  passes through a filter element  120  such as filter paper or filter cloth, of the fuel filter  12  in the filter casing  121 . Thereby, the filter element  120  catches a foreign substance contained in the gasoline fuel  3 , while filtering the fuel  3 . 
     The inline pump part  20  is communicated with the fuel filter  12  of the feed pump part  10  through the pressure passage  40 . The gasoline fuel  3  discharged from the discharge port  114  of the non-positive displacement electric pump  11  in the feed pump part  10  flows into the inline pump part  20  through the fuel filter  12  and through the pressure passage  40 . 
     The inline pump part  20  includes a non-positive displacement mechanical pump  21  as a main component. The non-positive displacement mechanical pump  21  is a turbo type pump, in which the impeller  212  is rotated in the pump casing  211 , and operates in response to the output EP from the crankshaft  2   b  of the internal-combustion engine  2 . At the operation time, the non-positive displacement mechanical pump  21  draws the gasoline fuel  3  discharged from the feed pump part  10  into the internal pump room  215  from the suction port  213 . Furthermore, at the operation time, the non-positive displacement mechanical pump  21  pressurizes the gasoline fuel  3  drawn to the pump room  215  with the impeller  212 , and discharges the pressurized fuel from the discharge port  214 . At this time, the non-positive displacement mechanical pump  21  discharges the gasoline fuel  3  flowing from the feed pump part  10  at a middle pressure Pm. In this embodiment, as shown in (a) of  FIG. 2 , in the operating range below the maximum output EPmax of the internal-combustion engine  2 , as the rotation speed N is raised, the output EP of the internal-combustion engine  2  increases. Therefore, as shown in (b) of  FIG. 2 , the middle pressure Pm is raised. That is, the middle pressure Pm is increased, as the supply pressure Ps demanded in response to the rotation speed N of the internal-combustion engine  2  becomes high. The middle pressure Pm is variably set within a range of, for example, 500 to 700 kPa, which is higher than the feed pressure Pf and lower enough than the supply pressure Ps. 
     As shown in  FIG. 1 , the non-positive displacement mechanical pump  21  is arranged outside the fuel tank  7 , and the suction port  213  is communicated with the pressure passage  40 . During the operation of the internal-combustion engine  2 , the non-positive displacement mechanical pump  21  operates, and the non-positive displacement electric pump  11  also operates by being supplied with electric power. Therefore, at the operation time, in which the impeller  212  rotates, the non-positive displacement mechanical pump  21  is able to self-suction from the suction port  213 . When the impeller  212  stops, the gasoline fuel  3  is permitted to flow between the suction port  213  and the discharge port  214 , in the non-positive displacement mechanical pump  21 . A centrifugal pump such as swirl pump or turbine pump may be adopted as the non-positive displacement mechanical pump  21 . In this embodiment, a cascade pump whose pressurization performance is higher than that of a centrifugal pump is adopted, similarly to the non-positive displacement electric pump  11 . 
     The inline pump part  20  has a middle relief valve  22  in addition to the non-positive displacement mechanical pump  21 . The middle relief valve  22  is a one-way spring-type valve. The middle relief valve  22  is arranged outside the fuel tank  7 , and communicates with a halfway point of the pressure passage  40  and with a halfway point of the pressure passage  41 . Here, the discharge pressure of the gasoline fuel  3  discharged from the discharge port  214  is controlled to be lower than or equal to an upper limit pressure assumed as the middle pressure Pm, at a normal time, in the pressure passage  41  communicated with the discharge port  214 . So, at a normal time when the discharge pressure from the discharge port  214  is lower than or equal to the upper limit pressure of the middle pressure Pm, the middle relief valve  22  is closed. As a result, the discharge pressure from the discharge port  214  is maintained at the middle pressure Pm in the pressure passage  41 . In contrast, at an abnormal time when the discharge pressure from the discharge port  214  exceeds the upper limit pressure of the middle pressure Pm, the middle relief valve  22  is opened. As a result, the discharge pressure from the discharge port  214  is released to the pressure passage  40  where the pressure is lower than the pressure passage  41 . 
     The high-pressure pump part  30  is communicated with the discharge port  214  of the non-positive displacement mechanical pump  21  of the inline pump part  20  through the pressure passage  41 . The gasoline fuel  3  discharged from the discharge port  214  of the inline pump part  20  is received by the high-pressure pump part  30  through the pressure passage  41 . 
     The high-pressure pump part  30  includes a positive displacement mechanical pump  31  as a main component. The positive displacement mechanical pump  31  is a plunger pump or piston pump which operates in response to receiving the output EP from the crankshaft  2   b  of the internal-combustion engine  2 . A cam  8  receiving the output EP makes a movable component  312  to reciprocate in the pump housing  311 . At the operation time, the positive displacement mechanical pump  31  draws the gasoline fuel  3  discharged from the inline pump part  20  from the suction port  313  to the internal pump room  315 . Furthermore, at the operation time, the positive displacement mechanical pump  31  pressurizes the gasoline fuel  3  drawn to the pump room  315  by the movable component  312 , and discharges the pressurized gasoline fuel from the discharge port  314 . At this time, the positive displacement mechanical pump  31  discharges the gasoline fuel  3  flowing from the inline pump part  20  at the supply pressure Ps. In this embodiment, as shown in (a) of  FIG. 2 , in the operating range lower than or equal to the maximum output EPmax of the internal-combustion engine  2 , as the rotation speed N is raised, the output EP of the internal-combustion engine  2  increases. Therefore, as shown in (c) of  FIG. 2 , the supply pressure Ps is raised to fulfill the demanded value. The supply pressure Ps is variably set within a range of, for example, 15 to 30 MPa, which is higher enough than the feed pressure Pf and the middle pressure Pm. 
     As shown in  FIG. 1 , the positive displacement mechanical pump  31  is arranged outside the fuel tank  7 , and the suction port  313  is communicated with the pressure passage  41 . Further, the discharge port  314  of the positive displacement mechanical pump  31  is communicated with the pressure passage  42 . The pressure passage  42  is communicated with the high-pressure rail  6 . Therefore, at a time of downward operation when the movable component  312  moves downward in the pump room  315 , the positive displacement mechanical pump  31  is able to self-suction from the suction port  313 . At a time of rise operation when the movable component  312  moves upward in the pump room  315 , the positive displacement mechanical pump  31  is able to discharge the high pressure from the discharge port  314 . 
     The high-pressure pump part  30  has a suction damper  32 , a suction valve  33 , and a discharge valve  34  in addition to the positive displacement mechanical pump  31 . The suction damper  32  is a pulsation damper such as a diaphragm type. The suction damper  32  is arranged outside the fuel tank  7 , and is attached, for example, to the positive displacement mechanical pump  31 . The suction damper  32  is communicated with a halfway point of the pressure passage  41 . The suction damper  32  controls fuel pressure pulsation of the gasoline fuel  3  in the pressure passage  41 . 
     The suction valve  33  is a solenoid valve which operates in response to a passage of electricity. The suction valve  33  is attached, for example, to the positive displacement mechanical pump  31 , outside the fuel tank  7 , and is located to be able to intercept the communication between the suction port  313  and the pump room  315 . The suction valve  33  is opened by stopping the power supply when the movable component  312  moves downward. As a result, because the communication is made possible between the suction port  313  and the pump room  315 , the gasoline fuel  3  is drawn from the suction port  313  to the pump room  315 . When the movable component  312  moves upward, the suction valve  33  is closed in response to the power supply. As a result, the gasoline fuel  3  is pressurized in the pump room  315 , because of the interception between the suction port  313  and the pump room  315 . 
     The discharge valve  34  is a one-way spring-type valve. The discharge valve  34  is arranged outside the fuel tank  7 , and is arranged at a halfway point of the pressure passage  42 , or at the discharge port  314  of the positive displacement mechanical pump  31  ( FIG. 1  illustrates an example where the discharge valve  34  is arranged at the halfway point of the pressure passage  42 ). Here, the discharge valve  34  is set to open when a pressure difference between the upstream and the downstream of the discharge valve  34  becomes about 20 kPa. Thereby, when the movable component  312  is moved upward, the gasoline fuel  3  having the supply pressure Ps is pushed out of the pump room  315  to the discharge port  314 , such that the discharge valve  34  is opened. As a result, the gasoline fuel  3  discharged at the supply pressure Ps from the discharge port  314  is supplied to the high-pressure rail  6  through the pressure passage  42 , and is further supplied to each of the fuel injection valves  5 . When the discharge of the gasoline fuel  3  from the discharge port  314  of the positive displacement mechanical pump  31  stops, the discharge valve  34  is closed to regulate the adverse current to the pump room  315  through the port  314 . 
     Components of each of the high-pressure pump part  30  and the inline pump part  20  are configured integrally, in this embodiment, with a part of the pressure passage  40 ,  42 , and whole of the pressure passage  41 . Therefore, the high-pressure pump part  30  and the inline pump part  20  can be easily mounted around the internal-combustion engine  2  in a vehicle. Alternatively, the high-pressure pump part  30  and the inline pump part  20  may be formed separately. 
     Moreover, in this embodiment, a high-pressure relief valve  9  is disposed in the high-pressure rail  6 . The high-pressure relief valve  9  is a one-way spring-type valve. The high-pressure relief valve  9  is arranged outside the fuel tank  7 , and communicates with a halfway point between the high-pressure rail  6  and the pressure passage  41 . At a normal time, the fuel pressure of the gasoline fuel  3  accumulated in the high-pressure rail  6  is controlled to be lower than or equal to an upper limit pressure assumed relative to the supply pressure Ps. So, at the normal time when the fuel pressure in the high-pressure rail  6  is lower than or equal to the upper limit pressure of the supply pressure Ps, the high-pressure relief valve  9  is closed. As a result, the fuel pressure in the high-pressure rail  6  is maintained at the supply pressure Ps. At an abnormal time when the fuel pressure in the high-pressure rail  6  exceeds the upper limit pressure of the supply pressure Ps, the high-pressure relief valve  9  is opened. As a result, the fuel pressure in the high-pressure rail  6  is released to the pressure passage  41  where the pressure is lower than that in the rail  6 . 
     The engine ECU  50  includes, as a main component, a microcomputer, and is arranged outside of the fuel tank  7 . The engine ECU  50  is electrically connected to an electronic part such as the fuel injection valve  5  of the internal-combustion engine  2 . Furthermore, the engine ECU  50  is electrically connected also to the non-positive displacement electric pump  11  and the suction valve  33 . The engine ECU  50  controls the electric power supplied to the electronic part such as the fuel injection valve  5  of the internal-combustion engine  2 , and the non-positive displacement electric pump  11  and the suction valve  33 . 
     In the gasoline fuel supply system  1 , when the power switch of the vehicle is turned ON, the engine ECU  50  starts the control. Then, the non-positive displacement electric pump  11  starts operating, and the internal-combustion engine  2  starts operating such that the non-positive displacement mechanical pump  21  and the positive displacement mechanical pump  31  also start operating. As a result, the gasoline fuel  3  is pumped up from the inside of the fuel tank  7  by the non-positive displacement electric pump  11 , and is pressurized by the non-positive displacement mechanical pump  21  from the feed pressure Pf to the middle pressure Pm. Then, the gasoline fuel  3  is further pressurized by the positive displacement mechanical pump  31  to the supply pressure Ps. In this way, the gasoline fuel  3  in which the fuel pressure is raised to the supply pressure Ps is once accumulated in the high-pressure rail  6 , and is supplied to each of the fuel injection valves  5  at the time of injection to the corresponding cylinder  2   a.    
     Hereafter, the operation and advantage of the first embodiment is explained. 
     According to the first embodiment, the inline pump part  20  pressurizes the gasoline fuel  3  discharged from the feed pump part  10 , and discharges the fuel at the middle pressure Pm. The high-pressure pump part  30  further pressurizes the gasoline fuel  3  discharged from the inline pump part  20 , and discharges the fuel at the supply pressure Ps to each of the fuel injection valves  5 . Therefore, the inline pump part  20  can raise the middle pressure Pm at the low-pressure side of the high-pressure pump part  30 , while the feed pressure Pf of the gasoline fuel  3  pumped from the fuel tank  7  is restricted to be lower in the feed pump part  10 . The feed pump part  10  has the non-positive displacement electric pump  11  which operates in response to receiving electric power, and the inline pump part  20  has the non-positive displacement mechanical pump  21  which operates in response to the output EP of the internal-combustion engine  2 . Therefore, the power consumption can be reduced when supplying electric power to the non-positive displacement electric pump  11  in the feed pump part  10  where the feed pressure Pf is restricted to be lower, and the vaporization of the gasoline fuel  3  can be controlled in the inline pump part  20 , because the non-positive displacement mechanical pump  21  uses the output EP of the internal-combustion engine  2 . Thus, the fuel injection characteristic can be secured while the energy can be saved. 
     Moreover, in the first embodiment, both the non-positive displacement electric pump  11  and the non-positive displacement mechanical pump  21  are cascade pumps. Generally, the sliding resistance is smaller at the non-positive displacement electric pump  11  and the non-positive displacement mechanical pump  21 , compared with a positive displacement pump such as a trochoid pump. Therefore, the power consumption or the output consumption for operating the pumps  11 ,  21  can be reduced. Therefore, high energy-saving property can be demonstrated. 
     If the non-positive displacement electric pump  11  breaks down in the feed pump part  10 , the inline pump part  20  is able to supply the gasoline fuel  3  from the fuel tank  7  through the broken-down non-positive displacement electric pump  11  to the high-pressure pump part  30 . Conversely, if the non-positive displacement mechanical pump  21  breaks down in the inline pump part  20 , the gasoline fuel  3  discharged from the non-positive displacement electric pump  11  in the feed pump part  10  can be supplied to the high-pressure pump part  30  through the broken-down non-positive displacement mechanical pump  21 . Therefore, the fail-safe system can be secured. 
     As mentioned above, in the first embodiment, the fuel injection characteristic, the energy-saving and the fail-safe can be secured. 
     According to the first embodiment, when the discharge pressure of the non-positive displacement mechanical pump  21  exceeds the upper limit pressure set for the middle pressure Pm, the discharge pressure is released by the middle relief valve  22  in the inline pump part  20 . Therefore, during the operation of the internal-combustion engine  2 , in which the non-positive displacement mechanical pump  21  operates, an abnormality that the middle pressure Pm exceeding the upper limit pressure can be restricted from being generated at the low-pressure side of the high-pressure pump part  30 . Moreover, at a time of dead soak when the non-positive displacement mechanical pump  21  and the internal-combustion engine  2  are left in the halt condition, at the low-pressure side of the high-pressure pump part  30  which receives heat from the internal-combustion engine  2 , the fuel pressure may rise due to a rise in temperature of the gasoline fuel  3 . However, at a time of the dead soak, at the low-pressure side of the high-pressure pump part  30 , if the fuel pressure corresponding to the discharge pressure of the non-positive displacement mechanical pump  21  exceeds the upper limit pressure of the middle pressure Pm, the fuel pressure can be released by the middle relief valve  22 . Thus, the resistance to pressure can be secured at a time of the dead soak during operation of the internal-combustion engine  2 . 
     Furthermore, according to the first embodiment, as the supply pressure Ps required in response to the rotation speed N of the internal-combustion engine  2  becomes higher, the middle pressure Pm is raised by the non-positive displacement mechanical pump  21  in the inline pump part  20 . Thereby, the feed pressure Pf can be restricted low in the feed pump part  10  including the non-positive displacement electric pump  11 , and the middle pressure Pm can be raised in the inline pump part  20  including the non-positive displacement mechanical pump  21 , such that the supply pressure Ps required to be higher can be met by the high-pressure pump part  30 . Therefore, when the internal-combustion engine  2  is rotated at high speed, not only the energy-saving can be secured, but also an expected fuel injection characteristic can be secured by the high supply pressure Ps. 
     According to the first embodiment, in the feed pump part  10 , the gasoline fuel  3  is pumped by the non-positive displacement electric pump  11  inside the fuel tank  7 . Since the non-positive displacement electric pump  11  is immersed in the fuel in the fuel tank  7 , it become easy to self-suction the gasoline fuel  3  while the non-positive displacement electric pump  11  is generally low in the self-suction ability. Therefore, the non-positive displacement electric pump  11  can be operated while the fuel injection characteristic, the energy-saving and the fail-safe are secured. 
     According to the first embodiment, the gasoline fuel  3  having the feed pressure Pf and discharged from the non-positive displacement electric pump  11  is filtered with the fuel filter  12  in the feed pump part  10 . At this time, since the feed pressure Pf is restricted low in the feed pump part  10 , the resistance specification to pressure required for the fuel filter  12  can be lowered. 
     Second Embodiment 
     As shown in  FIG. 3 , a second embodiment is a modification of the first embodiment. The inline pump part  2020  of the second embodiment has a check valve  2024  in addition to the non-positive displacement mechanical pump  21  and the middle relief valve  22  which are approximately the same as those in the first embodiment. 
     The check valve  2024  is a one-way springless valve. The check valve  2024  is arranged outside the fuel tank  7 , and is arranged at a halfway point of the pressure passage  41 , or at the discharge port  214  of the non-positive displacement mechanical pump  21  ( FIG. 3  illustrates an example where the check valve  2024  is arranged at the halfway part of the pressure passage  41 ). Here, the check valve  2024  is set to open when a pressure difference between the upstream side and the downstream side becomes about 20 Pa. Thereby, the check valve  2024  is opened by the gasoline fuel  3  having the middle pressure Pm being pushed out of the pump room  215  of the non-positive displacement mechanical pump  21  to the discharge port  214 . As a result, the gasoline fuel  3  discharged at the middle pressure Pm is supplied to the positive displacement mechanical pump  31  of the high-pressure pump part  30  through the pressure passage  41  from the discharge port  214 . Further, in the inline pump part  2020 , the gasoline fuel  3  at the middle pressure Pm is supplied also to the middle relief valve  22  communicated with the pressure passage  41  at the downstream of the check valve  2024 . Therefore, at an abnormal time when the fuel pressure of the gasoline fuel  3  exceeds the upper limit pressure of the middle pressure Pm in the pressure passage  41 , the middle relief valve  22  achieves the releasing function. As the result, when the fuel pressure is lowered, the function will stop. When the discharge of the gasoline fuel  3  stops from the discharge port  214  of the non-positive displacement mechanical pump  21 , the check valve  2024  is closed to regulate the adverse current to the pump room  215  through the port  214 . 
     According to the second embodiment, the adverse current of the gasoline fuel  3  discharged from the non-positive displacement mechanical pump  21  in the inline pump part  2020  is regulated by the check valve  2024 . Therefore, at a time of the dead soak in which the internal-combustion engine  2  and the non-positive displacement mechanical pump  21  are left in the halt condition, the vaporization of the gasoline fuel  3  can be controlled by maintaining the fuel pressure at the middle pressure Pm, at the low-pressure side of the high-pressure pump part  30  which receives heat from the internal-combustion engine  2 . Therefore, the fuel injection characteristic can be secured in the internal-combustion engine  2  which starts operation after the dead soak. 
     According to the second embodiment, similarly to the first embodiment, at a time of the dead soak, if the fuel pressure at the low pressure side of the high-pressure pump part  30  exceeds the upper limit pressure of the middle pressure Pm, the fuel pressure can be released by the middle relief valve  22 . Further, at the low-pressure side of the high-pressure pump part  30 , after the releasing function stops by lowering in the fuel pressure, the fuel pressure can be held at the middle pressure Pm by the adverse current regulation function of the check valve  2024 . Accordingly, the resistance to pressure can be secured at the time of dead soak, and the fuel injection characteristic can be secured at a starting time after the dead soak. 
     Other Embodiment 
     It should be appreciated that the present disclosure is not limited to the embodiments described above and can be applied to various embodiments and the combination within the scope of the present disclosure. 
     Specifically, in a first modification of the first embodiment, as shown in  FIG. 4 , the middle relief valve  22  may be eliminated. Similarly, as shown in  FIG. 5 , in a second modification of the second embodiment, the middle relief valve  22  may be eliminated. 
     In a third modification of the first and the second embodiments, as shown in  FIG. 6 , the non-positive displacement electric pump  11  may be located outside the fuel tank  7 . Moreover, in a fourth modification of the first and second embodiment, as shown in  FIGS. 6 and 7 , the fuel filter  12  may be located outside the fuel tank  7 . In addition,  FIG. 6  illustrates the third modification of the first embodiment, and  FIG. 7  illustrates the fourth modification of the first embodiment. 
     In a fifth modification of the first and second embodiments, the fuel filter  12  may be eliminated. In a sixth modification of the first and second embodiments, an operating range may be defined where the middle pressure Pm is not raised when the supply pressure Ps demanded in response to the rotation speed N of the internal-combustion engine  2  becomes high.