Abstract:
A vehicle fuel system has an integrated fuel rail and fuel pump that supplies high pressure fuel directly to the injectors mounted on the engine. The pump is a double acting single piston pump that has two pumping chambers formed co-axially in a single cavity. One pumping chamber is twice the size of the other pumping chamber thereby producing an output flow equal to one half the volume of the larger pumping chamber during each stroke. The smaller pumping chamber communicates with a co-axial fuel rail portion of the cavity. A plurality of outlet ports, one for each injector, are disposed in fluid communication with the fuel rail portion of the cavity.

Description:
TECHNICAL FIELD 
     This invention relates to fuel systems for supplying fuel at elevated pressures to an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     Some modern vehicles employ a high pressure fuel injection system to improve the efficiency and operation of the engine. These systems include an intank supply pump and a high pressure pump that supplies fuel at an elevated pressure to a fuel rail. The fuel rail distributes the high pressure fuel to fuel injectors mounted either directly at the combustion chamber the. 
     The supply pump is generally located in a fuel tank and the high pressure pump is situated on the engine at a distance from the fuel rail. Thus the high pressure fuel has some distance to travel at an elevated pressure between the high pressure pump and the injectors. Since most fuel pumps displace more fuel than is needed by the engine, a fuel return is necessary. The fuel return may be by way of a regulator valve at the high pressure pump to the engine. 
     In some fuel systems, a continuous flow rotary type pump is used and in other systems, a single acting reciprocating pump is used. The reciprocating pump has a plunger that draws fluid into a cylinder when stroked in one direction and expels fluid from the cylinder when stroked in the other direction. Thus the pump delivers a single charge of fuel during each stroking cycle. Systems using either type of pump still utilize a fuel rail for distributing fuel to the individual injectors on the engine. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved fuel rail and fuel pump in a vehicle fuel supply system having a direct injection engine. 
     In one aspect of the present invention, a fuel pump and a fuel rail are integrated in a single assembly. In another aspect of the present invention, the fuel pump is a double acting single piston pump. In yet another aspect of the present invention, the fuel rail is incorporated into one of the pumping chambers of the double acting pump. 
     In still another aspect of the present invention, the fuel rail portion of the integrated assembly has an outlet port for each fuel injector in the fuel system. In a further aspect of the present invention, the pump has a large cylinder portion and a small cylinder portion with the large cylinder portion being connected with a fuel inlet port and a high pressure regulator having an outlet connected with a return fuel line. In yet a further aspect of the present invention, the pump piston has incorporated therein a valve assembly for controlling the flow of fuel between the cylinder portions and for relieving high pressure in the small cylinder portion. 
     The present invention provides a fuel system that incorporates a fuel pump directly into a fuel rail. The pump is a double acting piston pump having one piston. The pump is disposed in a housing that includes a cylindrical cavity in which the piston is disposed. A piston rod, attached to the piston, is also disposed in the cylindrical cavity. One side of the piston cooperates with the cylinder cavity to establish a first pumping chamber and the other side of the piston cooperates with the cylinder cavity and piston rod to establish a second chamber having a volume equal to one-half of the first chamber. Thus for each stroke of the piston, the pump produces an output flow substantially equal to the volume of the second chamber. 
     The second chamber has connected therewith a plurality of fuel outlet ports equal in number to the number of injectors on the engine. The second chamber, therefore, provides a fuel rail for the fuel system. The piston rod is driven by the engine or by an electric motor, at a speed commensurate with the engine speed, such that the pump output flow is proportional the speed of the engine. 
     The first chamber has an inlet port adapted to receive fuel from a fuel reservoir, and a system pressure regulator adapted to return excess fuel to the fuel reservoir. The piston has disposed thereon a plurality of control valves that control the flow of fuel between the chambers. dr 
     DESCRIPTION OF THE DRAWINGS 
     The drawing is a diagrammatic representation of a fuel system with a sectional elevational view of a fuel rail and pump incorporating the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A fuel system  10  includes a fuel rail and pump  12 , a fuel reservoir  14  and a plurality of fuel injectors  16 . The fuel injectors  16  are adapted to deliver fuel to the cylinders of an engine  18  in a conventional manner. The fuel injectors are conventional fuel feed devices which deliver atomized fuel either directly into the combustion chamber of the engine or into the incoming air stream at the inlet valves of the engine. The fuel injection systems are well known in the art. 
     The fuel rail and pump  12  includes a fuel rail  20  and a fuel pump  22  both of which are enclosed in a housing  24 . The pump  22  has a piston rod  26  that extends through the left end of the housing  24  as viewed in the drawing. A seal and bushing assembly  28  is disposed in the housing  24  surrounding and supporting the piston rod  26  in the housing  24 . The piston rod  26  is driven through a conventional mechanism, such as a gear and cam drive, by the engine  18 . In the alternative, the piston rod  26  can be driven by a variable electric motor in a conventional manner. Other drive mechanisms are also possible and well within the known prior art. 
     The piston rod  26  is secured to a piston  30  that is slidably supported in a cavity  31  defined by an inner cylindrical wall  32  of the housing  24 . The piston  30  is driven reciprocably in the housing  24  by the piston rod  26 . The piston  30  and inner cylindrical wall  32  cooperate to form a pumping chamber  34  which is closed at the right end  36  by a valve assembly  38 . The valve assembly  38  has a cap  40  is which is housed a valve  42  and valve plate  44 . The valve  42  is held against a valve plate  44  by a Belleville spring  45  and a threaded fastener  46 . The valve  42  is an annular member comprised of a solid flexible material. The valve  42  overlaps passages  48  in the plate  44 . The valve  42  is effective to normally close the passages  48  from communication with a fuel return port  50  that is connected to return fuel to the reservoir  14  though a conduit  52 . The chamber  34  has an inlet port  51  that is in controlled fluid communication with the fuel reservoir  14  through a conventional inlet check valve assembly  53  and a conduit  55 . 
     The piston has a plurality of passages  54  that are closed by a valve  56  that is urge to close the passages  54  by a Belleville spring  58  and a fastener  60 . The passages  54  communicate with a chamber  62  formed by the piston  30 , the inner surface  32  and the assembly  28 . The valve  56  controls communication between the chamber  62  and the chamber  34 . When the pressure in the chamber  62  exceeds the pressure set by the valve  56 , fuel will flow through the passages  54  to the chamber  34 . 
     The chamber  62  has one-half the crossectional area of the chamber  34 . This is due to the fact that the rod  26  also has a crossectional area equal to one-half of the area of the chamber  34 . The leftmost end  65  of the chamber  62  is incorporated into the fuel rail  20 . The piston  30  also has a plurality of passages  64  that provide controlled fluid communication between the chambers  34  and  62 . The passages  64  are closed by a valve  66  and a spring  68  that is trapped between a shoulder  70  on the rod  26  and the valve  66 . The valve  66  will open under very slight pressure to permit fuel to flow from the chamber  34  to the chamber  62  but will close to prevent reverse flow of the fuel. However as described above, the valve  56  will permit flow from the chamber  62  to the chamber  34  when the pressure in the chamber  62  exceeds the setting of the valve  56 . 
     The fuel rail  20  has connected therewith a plurality of outlet ports  72 . Each outlet port  72  is connected for fluid communication with respective fuel injectors  16  through conduits  74 . The pressurized fuel in the fuel rail  20  is continuous fluid communication with the fuel injectors  16 . However, as is well-known, the fuel injectors  16  only expel fluid to the engine  18  when commanded by a conventional electronic control module (ECM)  76  which includes a conventional programmable digital computer, not shown. The ECM  76  is connected with each of the fuel injectors  16  by wires or electrical conduits  78 . 
     As the piston  30  is stroked rightward in the housing  24 , the volume of the chamber  34  decreases and the volume of the chamber  62  increases. However, the volume of the chamber  34  decreases at twice the rate at which the volume of the chamber  62  increases. When the piston  30  is stroked rightward, a volume of fuel equal to one-half the volume decrease of the chamber  34  is displaced from the chamber  62  through the fuel rail  20  to the injectors  16 . If the injectors  16  cannot accept all of the displaced fuel, the pressure in the chambers  34  and  62  will increase until the preset pressure limit of the valve  42  is overcome and the excess fuel is returned to the fuel reservoir through the conduit  52 . The fluid in the chamber  34  passes to the chamber  62  through the passages  64  and the valve  66 . 
     The volume of fuel displaced by the piston  30  from the chamber  34  is equal to the product of the area of chamber  34  and the length of the stroke of the piston  30 . The volume of fuel displaced by from the chamber  62  is equal to the product of the area a chamber  62  and the length of the stroke of the piston  30 . Obviously the piston  30  displaces twice as much fuel, from the chamber  34 , during a rightward stroke than the chamber  62  can accommodate. Thus half of the pumped volume must be distributed by the fuel rail  20  or returned to the reservoir  14  through the valve  42 . During a leftward stroke of the piston  30 , the same volume of fuel is displaced by the piston  30  through the fuel rail  20  or the valves  56  and  42 . 
     As the piston  30  is stroked leftward, the displaced volume of fuel in the chamber  62  is delivered from the fuel rail  20  to the injectors  16  and the chamber  34  is filled through the check valve assembly  53  from the reservoir  14 . The valves  66  and  56  prevent the fuel in the chamber  62  from flowing into the chamber  34  unless the injectors are satisfied and the preset pressure limit of the valve  56  is overcome. If the valve  56  opens, due to high pressure, the fuel in excess of what the injectors can use is returned to the chamber through the valve  56 . Since the volume of the chamber  62  is only one-half the volume of the chamber  34 , when the fuel is bypassed through the valve  56  the chamber  34  will still need half the volume made up from the reservoir plus the portion of the other half volume that is distributed by the fuel rail  20  to the injectors  16 . 
     The fuel rail and pump  12  provides a compact and efficient package for delivering fuel to the injectors of a fuel injected engine. the number of outlet ports  72  that are employed by the fuel rail  20  is determined by the number of injectors  16  that are positioned on the engine. Generally there is one injector per cylinder. Thus, is a six cylinder engine is used, six outlet ports  72  will be incorporated at the fuel rail  20 . The outlet ports  72  are shown as being radially positioned about the fuel rail  20 . However, it will be apparent that the end  65  can be enlarged radially to permit axial disposition of the outlet ports  72  without affecting the operation of the fuel rail and pump  12 .