Abstract:
A pump, for supplying high pressure fuel from a fuel tank to an engine via a common rail, includes a motor assembly ( 20 ) mounted on top of the fuel tank, a pump assembly ( 26 ) positioned within the fuel tank, and a support column ( 32 ) rotatably connecting the motor assembly to the pump assembly. A high pressure pump sub-assembly ( 46 ) includes a pump body ( 48 ) having a drive bore ( 50 ) and multiple plunger bores ( 60 ) formed therein. The external profile of a drive member ( 58 ) which is rotatable within the drive bore engages the radially inner end of pumping plungers ( 62 ) disposed in each of the plunger bores for a portion of each revolution to reciprocally move the plungers between radially inner and outer limit positions. Reciprocation towards the inner limit position induces a low pressure in the radially outer end of the plunger bore, thereby drawing fuel via the drive bore without the aid of a low pressure pump.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    A number of potential advantages have led the automotive industry to look with increasing interest toward utilizing common rail high pressure direct injection for gasoline engines. Certain difficulties seem to stand in the way of fully achieving the advantages.  
           [0002]    The pressurization of fuel to high levels (e.g., above 100 bar) requires considerable pumping power, which generates considerable heat. Moreover, the industry is looking to even higher rail pressures, above 200 bar. This heat could be dissipated to a large extent, if all the fuel that is pressurized can be quickly injected into the engine cylinders. This is not possible, however, because the fuel pump flow rate is typically sized for engine cranking, which may be at 20-30 bar pressure at a relatively high quantity flow rate, whereas typical steady state cruising conditions would require much lower quantity flow rates at 100 bar. Therefore, in a conventional pumping scheme, the volume of fuel raised to injection pressure during the course of an hour of typical vehicle use, is much greater than the volume of fuel actually injected during that same hour of use. Although pre-metering and various spill control techniques can be used to some advantage in this regard, none of these techniques satisfactorily regulates the power output of the high pressure pump itself.  
           [0003]    Another difficulty is encountered with high pressure pumps that are driven directly by the engine (e.g., crank shaft, cam shaft, accessory belt). During transients when fuel demand is low (e.g., downhill or during gear shifting), the engine continues to turn and the pump continues to deliver high pressure fuel to a common rail that may already be at maximum pressure.  
         SUMMARY OF THE INVENTION  
         [0004]    In the invention, a high pressure rotary pump is intimately coupled to an electric motor as a packaged unit situated at the vehicle fuel tank, with the speed of the motor and thus the pumping rate of the high pressure pump, being responsive to the rail pressure. Thus, the motor can quickly increase the drive shaft speed and thus provide high pumping volume during cranking, while reducing speed to a low level with, associated low pumping volume when the vehicle is cruising. Similarly, the motor can intermittently increase speed as needed to accommodate load demand during acceleration, or in essence stop the pump drive when the vehicle is coasting. The aspects sought to be protected, concern the manner in which the motor and pump are integrated and function together as a package.  
           [0005]    Briefly stated, the invention in a preferred form is a pump for supplying high pressure fuel from a fuel tank to an engine via a common rail. The pump includes a motor assembly mounted on top of the fuel tank, a pump assembly positioned within the fuel tank, and a support column connecting the motor assembly to the pump assembly. The pump assembly comprises a high pressure pump sub-assembly including a pump body having a drive bore and multiple plunger bores formed therein, where a radially inner end of each plunger bore opens into the drive bore. The external profile of a drive member which is rotatable within the drive bore engages the radially inner end of pumping plungers disposed in each of the plunger bores for a portion of each revolution to reciprocally move the plungers between radially inner and outer limit positions. Reciprocation of each pumping plunger towards the inner limit position induces a low pressure in the outer end of the plunger bore, thereby drawing fuel into the outer end of the plunger bore via the drive bore without the aid of a low pressure pump. Reciprocation of each pumping plunger towards the outer limit position induces a high pressure in the outer end of the plunger bore, thereby discharging fuel from the outer end of the plunger bore into the common rail via the high pressure line.  
           [0006]    The pump assembly also comprises a fine filter sub-assembly mounted to the top end portion of the pump body. The fine filter sub-assembly includes a cannister having an upper sleeve portion, a middle housing portion, a radially extending shoulder connecting the sleeve portion to the housing portion, and a lower mounting portion separated from the housing portion by a circumferential, radially inward extending protrusion. The top end portion of the pump body is received within the cannister mounting portion such that the protrusion rests on the pump body. An O-ring disposed in a circumferential groove in the top end portion of the pump body provides a fluid-tight seal between cannister and the pump body. Fuel vapor is vented from the fine filter sub-assembly via a vent orifice in the shoulder, with a check valve positioned in the vent orifice preventing backflow into the cannister. The outer surface of fine filter element disposed within the cannister housing portion, together with the inner surface of the cannister housing portion, forms an annular column and the inner surface of the fine filter element forms a cavity in fluid communication with the drive bore.  
           [0007]    The pump assembly also comprises a coarse filter sub-assembly a coarse filter sub-assembly mounted to the bottom end portion of the pump body. The coarse filter sub-assembly includes a housing having an inlet in fluid communication with the fuel tank and an outlet in fluid communication with the annular column of the fine filter assembly. A coarse filter screen, is disposed intermediate the inlet and outlet of the housing. The housing further has a plurality of downwardly extending, circumferentially spaced spacers defining a plurality of slots which form the inlet. Each of the spacers has a bottom end which engages the inside surface of the bottom of the fuel tank to position the coarse filter screen at a distance above the fuel tank inner surface.  
           [0008]    According, it is an object of the present invention to provide a high pressure gasoline common rail direct injection fuel supply system, in which the high pressure discharge of the means for raising and maintaining the rail pressure above 100 bar, is responsive to engine demand. The energy imparted to the discharged fuel (e.g., pressure increase) is over time, significantly reduced relative to conventional systems. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawings in which:  
         [0010]    [0010]FIG. 1 is a schematic view of a road vehicle having a direct injection fuel pump in accordance with the invention;  
         [0011]    [0011]FIG. 2 is an enlarged, exploded view, partly in cross section and partly broken away, of the direct injection fuel pump of FIG. 1;  
         [0012]    [0012]FIG. 3 is an enlarged, side view, partly in phantom, of the direct injection fuel pump of FIG. 1; and  
         [0013]    [0013]FIG. 4 is an enlarged, cross section view of the direct injection fuel pump and fuel tank of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    With reference to the drawings wherein like numerals represent like parts throughout the several figures, a direct injection fuel pump in accordance with the present invention is generally designated by the numeral  10 .  
         [0015]    In a preferred embodiment, a direct injection fuel pump  10  in accordance with the invention is a gasoline direct injection (GDI) pump which is mounted on and within a vehicle&#39;s fuel tank  12 . In a typical vehicle, FIG. 1, the engine  14  is disposed in the forward part of the vehicle and the fuel tank  12  is disposed in the rear part of the vehicle. The direct injection fuel pump  10  supplies fuel at high pressure through a supply line  16  to multiple fuel injectors  18  mounted in the engine  14  and includes three main sections: 1) a motor assembly  20  mounted on the exterior surface  22  of the top  24  of the fuel tank  12 ; 2) a high pressure pump assembly  26  resting on the interior surface  28  of the bottom  30  of the fuel tank  12 ; and 3) a support column  32  connecting the motor assembly  20  to the pump assembly  26 .  
         [0016]    With reference to FIGS.  2 - 4 , the motor assembly  20  includes a motor  34 , including integral electronics (not shown). The motor  34  is mounted to the exterior surface  22  at the top  24  of the fuel tank  12  via a mounting plate  38 . Preferably, the motor  34  is a 12 volt DC motor, receiving power from the vehicle electrical system, and has a power rating which is closely matched to the operating requirements of the engine  14 . The motor shaft  40  of the electric motor  34  is sealed by a small low friction radial seal (not shown) to prevent fuel vapors from escaping from the tank  12 .  
         [0017]    The pump assembly  26  includes an upper fine filter sub-assembly  42 , a lower coarse filter sub-assembly  44 , and a pump sub-assembly  46  disposed intermediate the filter sub-assemblies  42 ,  44 . The pump sub-assembly  46  includes a pump body  48  having a drive bore  50  formed therein which includes upper and lower drive shaft portions  52 ,  54  and an intermediate portion  56  in which an eccentric drive member  58  is rotatable. At least one, and preferably multiple equi-angularly spaced plunger bores  60  extend radially from the intermediate portion  56  of the drive bore  50 . A pumping plunger  62  is situated in each plunger bore  60  for reciprocal radial movement therein as a result of the eccentric rotation of the drive member  58 . A pumping chamber  64  is formed at the radially outer end of each plunger bore  60 . As the pumping plunger  62  disposed within the associated plunger bore  60  is urged radially to an inner limit position inward by rotation of the drive member  58 , the pressure within the pumping chamber  64  is reduced, thereby opening an inlet check valve  36  and allowing fuel to be delivered to the pumping chamber  64 . Thereafter, as the pumping plunger  62  is urged radially outward to an outer limit position by further rotation of the drive member  58 , the fuel in the pumping chamber  64  undergoes high pressure thereby opening an outlet check valve  65  and allowing the fuel to flow through a discharge passage into a common rail via a high pressure line  66 . The high pressure line  66  extends upwardly through the top  24  of the fuel tank  12  to an external high-pressure outlet  68  located on the motor mounting plate  38 .  
         [0018]    The eccentric drive member  58  is rigidly connected (preferably integrally) to a drive shaft having an upper segment  70  which extends longitudinally through the upper drive shaft portion  52  of the drive bore  50  to an upper end and a lower segment  72  which extends through the lower drive shaft portion  54  of the drive bore  50  to a lower end. The eccentric drive member  58  is supported in the intermediate portion  56  of the drive bore  50  by substantially identical, self-lubricated upper and lower bushings  74  disposed in the upper and lower drive shaft portions  52 ,  54  of the drive bore  50 , respectively. An impeller  76  is carried on the lower segment  72  of the drive shaft within a lower recess  78  in the pump body  48 . The impeller  76  insures sufficient positive pressure at the pump inlet (sump) at all speeds and temperatures thereby minimizing the formation of vapor cavities.  
         [0019]    It should be understood that, typically, the pumping chamber  64  is formed in a removable plunger plug  80  which penetrates the pump body  48 . For the purposes of the present description, however, it can be assumed that the plunger plug  80  is integral with the pump body  48 . Each pumping plunger  62  is connected to a cam shoe  82 , and retention means urges the cam shoe  82  against the external profile of the eccentric drive member  58 . Preferably, the radially inner end of the pumping plunger  62  has a substantially spherical shape and is carried in a cooperating cradle extending from the shoe  82 , thereby providing a pivotal connection.  
         [0020]    The pump body  48  is mounted on top of the coarse filter sub-assembly  44 . The coarse filter sub-assembly  44  includes a housing  84  having multiple, downwardly extending spacers  86  which rest on the bottom  30  of the fuel tank  12 . A coarse filter screen  88  extends substantially horizontally across the coarse filter housing  84  at a vertical position which is intermediate the bottom of the pump body  48  and the bottom ends of the spacers  86 , thereby insuring a certain minimum distance between the coarse screen  88  and the interior surface  28  of the fuel tank  12 . A series of resilient fingers  90  project downward from the pump body  48  to engage the outer edge of the coarse filter housing  84  biasing the housing towards the bottom  30  of the tank  12  and thereby compensating for any longitudinal tolerances. Preferably, the coarse filter screen  88  is a 150 to 300 micron mesh, which in combination with the extremely coarse filtering action of the spacers  86 , acts to protect the impeller  76  and reduce the rate at which the fine filter element  92  (discussed below) is loaded with particulate matter.  
         [0021]    The fine filter sub-assembly  42  is mounted on top of the pump body  48 . The fine filter sub-assembly  42  includes a cannister  94  having a lower mounting portion  96 , a middle housing portion  98 , and an upper sleeve portion  100 . The outer diameter of the sleeve portion  100  is smaller than the outer diameter of the housing portion  98 , forming an upper shoulder  102 . The mounting portion  96  is separated from the housing portion  98  by a circumferential, radially inward extending protrusion  104 . The mounting portion  96  receives an upper end portion  106  of the pump body  48  such that protrusion  104  rests on the upper surface of the pump body  48 . An O-ring  108  disposed in a circumferential groove  110  in the upper end portion  106  of the pump body  48  provides a fluid-tight seal between the mounting portion  96  of the cannister  94  and the pump body  48 .  
         [0022]    A fine filter element  92  is disposed within the housing portion  98  of the cannister  94 . Preferably, the fine filter element  92  has a 2 to 5 micron element and is sized to store the amount of debris expected to accumulate over the entire life expectancy of the vehicle whereby the fine filter sub-assembly  42  does not require servicing over the lifetime of the vehicle. The fine filter element  92  has upper and lower end caps  112 ,  112 ′, each having an axial opening  114 . An upper sealing grommet  116  extends upwardly from the periphery of the opening  114  in the upper end cap  112  to sealingly engage the inner surface of the canister sleeve portion  100 . A lower sealing grommet  116 ′ extends downwardly from the periphery of the opening  114  in the lower end cap  112 ′ to sealingly engage the inner surface of the upper drive shaft portion  52  of the drive bore  50 . An inner surface  118  of the fine filter element  92  defines a cavity  120  which together with openings  114  and the orifices in the upper and lower sealing grommets  116 , define an axial bore extending through the fine filter element  92 . The upper portion  122  of the filter element housing  123  includes a plurality of holes  124  which complete the flow path through the fine filter element  92 .  
         [0023]    The support column  32  is a cardanic (tubular) drive joint, extending from an upper end portion  128  connected to the motor shaft  40 , through the orifice of the upper sealing grommet  116 , cavity  120 , and the orifice of the lower sealing grommet  116 ′ to a lower end portion  130  connected to the upper segment  70  of the drive shaft within the upper drive shaft portion  52  of the drive bore  50 . Notches  134 ,  135  in the lower and upper end portions  130 ,  128  of the support column  32  receive cross pins  132 ,  133  extending from the upper segment  70  of the drive shaft and the motor shaft  40 , respectively, to key the drive shaft to the support column  32 .  
         [0024]    As soon as the eccentric drive member  58  starts to rotate, a pressure drop induced by the suction of the pumping plungers  62  at low speed or by the impeller  76  at intermediate and high speeds forces fuel upwardly through the lower coarse filter assembly  44 , through a fuel passage  136  in the pump body  48 , and into an annular column  138  formed by the inner surface  140  of the fine filter canister  94  and the outer surface  126  of the fine filter element  92 . The fuel then flows radially inward through holes  124  and the filter medium of the fine filter element  92  and forms a supply column  142  above the sump  144  of the high pressure pump  10 . The height of holes  124  relative to the sump  144  ensures that the sump supply is maintained as a column  142  surrounding the drive joint  32  at a level  146  higher than the fuel level  148  in the tank  12 . This small quantity of fuel in the sump supply column  142  insures the presence of a “solid” volume of fuel in the sump  144  even at low fuel level in the tank  12  and while driving either on a steep hill or in a long curve, when all the fuel is forced to one side of the tank  12  and a substantial air quantity could be ingested through the inlet screen  88 .  
         [0025]    Positive pressure generated by the impeller  76 , proportional to motor speed, insures a sufficient amount of fuel flowing through the fine filter element  92 , even if the filter element  92  is partially obstructed by contaminants. Some of the fuel within the fine filter sub-assembly  42  will evaporate and collect in the top portion of cannister  94 , especially at higher speed and elevated temperature. A small vent orifice  150  located in the upper shoulder  102  of the cannister  94  allows the fuel vapors to be returned to the fuel tank  12 , preventing vapor lock within the fine filter sub-assembly  42 . A mushroom style check valve  152  prevents back flow through the vent orifice  150  and thus prevents contamination by the air when the fuel level is below the vent orifice  150 .  
         [0026]    It should be appreciated that a direct injection fuel pump  10  in accordance with the subject invention has several advantages over conventional fuel delivery systems. The elimination of the low pressure feed pump and high pressure control solenoid of the conventional fuel delivery systems more than offsets the higher cost of the electric motor  34 . The inherent torque limits of the electric motor  34  limits the maximum rail pressure, eliminating the need for the pressure limiting valve of conventional systems. The heat generated by the motor  34  and electronics is dissipated outside of the tank  12 , providing for minimum heat rejection inside of the fuel tank  12 . Internal pump seals are not critical since all leakage paths lead back into the fuel tank  12 . The pump  26  and motor  20  are exposed to minimum vibration, narrower temperature extremes, and the pump  26  is exposed only to fuel and normal fuel additives.  
         [0027]    While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.