Abstract:
An apparatus is provided for equalizing pressure between a lubrication fluid for lubricating a pump and a combustion fluid located at a low pressure side of the pump wherein the pump has a rotatable shaft. The apparatus includes a wall defining a bore within the pump wherein a first end of the bore is configured to receive a lubrication fluid and a second end of the bore is configured to receive combustion fluid. An equalizing element is disposed within the bore for separating the lubrication fluid and the combustion fluid and may be at least partially movable in response to pressure differences caused, e.g., by differences in thermal expansion between the lubrication fluid and the combustion fluid.

Description:
FIELD OF THE INVENTION 
     The present invention relates to pumps and, more particularly, to an apparatus for equalizing pressure between a lubrication fluid and a combustion fluid to be pressurized by a supply pump. 
     BACKGROUND OF THE INVENTION 
     Direct gasoline injection has some distinct advantages over prior art systems with respect to emissions and fuel economy of the engine, mainly because of an increase in the efficiency of the engine. 
     Currently, efforts are underway to develop a reliable and inexpensive pump capable of generating a relatively high pressure (such as 120 bar and higher) required for supplying a common rail system used in direct gasoline injection. One such pump is shown in U.S. patent application Ser. No. 09/031,859, filed Feb. 27, 1998 and entitled “Supply Pump for Gasoline Common Rail” (International Application No. PCT/US99/03830 published under International Publication No. WO 99/43949), which is assigned to the present assignee hereof and the entire contents of which is hereby incorporated herein by reference. This supply pump, as is typical of pumps in general, includes a rotating shaft having bearings that are lubricated by either a lubrication fluid (oil) or a combustion fluid (fuel) disposed on the low pressure side of the pump. The fuel may be pre-pressurized to 3 or 4 bar by a separate feed pump, e.g., remotely located in a fuel tank. Seals, such as lip seals, which extend radially about the rotating shaft, are employed to prevent escape and/or mixing of either fluid. 
     While the supply pump described in the International Publication is suitable for its intended purposes, a problem can occur with the supply pump in that because of the differences in pressure between the oil pressure and fuel pressure within the pump, the lip seals may be canted one way or the other into contact with the rotating shaft resulting in premature wear thereof. 
     Another problem can also arise because of the difference in pressure between the oil and the fuel. In particular, passage by either the oil or the fuel through the seal occurs, due to the canting of the seal and/or other factors, resulting in improper mixing of these fluids. In one direction, mixing of the fuel into the oil may result in a reduction in lubricity of the oil. It will be appreciated that reduced lubricity of the oil can, for example, result in premature wear of the pump and possibly other systems of the engine. Also, potential hazardous waste problems concerning disposal of the oil/fuel mixture may arise. In the opposite direction, the mixing of the oil with the fuel may result in a reduction in engine performance. 
     SUMMARY OF THE INVENTION 
     It is, accordingly, an object of the present invention to provide an apparatus which equalizes pressure within a pump between a lubrication fluid and a combustion fluid disposed at a low pressure side of the pump. 
     It is another object to provide such an apparatus which can adjust the pressure of the lubrication fluid to slightly above that of the combustion fluid. 
     It is a further object of the invention to provide a pump for supplying a common rail gasoline fuel injection system for a multi-cylinder internal combustion engine. 
     According to one aspect of the present invention, an apparatus is provided for equalizing pressure between a first region of lubrication fluid for lubricating a pump and a second region of combustion fluid at a low pressure where the pump has a rotatable shaft. The apparatus comprises a wall defining a bore disposed within the pump where the first end of the bore is configured to receive lubrication fluid from the first region and a second end of the bore is configured to receive combustion fluid from the second region. An equalizing element is also provided which is disposed within the bore for separating the lubrication fluid and the combustion fluid. The shuttle is at least partially moveable in response to pressure differences between the first region and the second region generated by changes in volume caused for example by thermal expansion. 
     In a particular aspect of the invention the equalizing element may comprise either a shuttle or a diaphragm. Means may be provided for biasing the shuttle so as to increase the pressure of the lubrication fluid in the first region relative to the combustion fluid in the second region. The rotating shaft may include a recess which communicates with the bore and the bias means may comprise a coil spring. The coil spring may have an enlarged diameter portion at one end thereof, which may be disposed within the recess of the rotating shaft. 
     In another aspect at least one seal is disposed on the shuttle which may comprise a pair of lip seals disposed at opposing ends of the shuttle. Optionally, the shuttle may include a pair of recesses laterally spaced along a longitudinal axis of the shuttle and the at least one seal may comprise two O-rings, each of which are disposed within a respective recess of the shuttle. The axial length of the bore and the spacing of the recesses of the shuttle may also be dimensioned such that during movement of the shuttle each respective O-ring engages only that portion of the bore in contact with a respective lubrication fluid or combustion fluid. The shuttle may also be generally cylindrical in shape. 
     In a further aspect, the pump may comprise a pump housing and the rotatable shaft may be disposed within a pump cavity of the pump housing. A first bearing and a second bearing may be interposed between the rotatable shaft and the pump housing. The first bearing may be in contact with the lubrication fluid and the second bearing may be in contact with the combustion fluid. The first and second bearings may comprise needle bearings or, optionally, the first bearing may comprise a ball bearing and the second bearing may comprise a wet bushing. 
     In a still further aspect, the rotatable shaft has an external profile and the pump may supply the combustion fluid at a relatively high pressure to a common rail and the pump may further comprise the following. At least one shoe means in sliding engagement with the external profile of the rotatable shaft. Retention means for urging the shoe means against the external profile of the rotatable shaft during rotation thereof. At least one pumping plunger disposed in a plunger bore and being in operative engagement with the shoe means. Each of the plungers having radially outer and inner ends relative to the axis and an internal charging passage which opens toward the cavity at the inner end of the plunger and opens towards the outer end of the plunger bore at the outer end of the plunger. The shoe means sliding on the external profile which is configured for providing reciprocal movement of the plungers. A discharge passage from the outer end of the plunger bore into the housing, and a discharge check valve in the discharge passage for permitting flow only away from the plunger bore. The discharge passage communicating with the common rail such that reciprocation of each plunger includes movement toward an inner limit position for inducing low pressure in the outer end of the plunger bore, thereby drawing combustion fluid in a charging phase of operation from the pump cavity through charging passage into the outer end of the plunger bore, and movement toward an outer limit position for developing a high pressure in the outer end of the plunger bore thereby discharging combustion fluid through the discharge check valve into the common rail in a discharging phase of operation. 
     In a still further aspect the charging passage includes a charging check valve which is normally closed at the inner end, but which opens to permit flow from the inner to the outer end of the plunger during the charging phase of operation. The lubrication fluid may comprise a lubricating oil and the combustion fluid may comprise gasoline. 
     In another aspect of the invention an apparatus is provided for equalizing pressure disposed between a lubrication fluid for lubricating a pump and a combustion fluid disposed at a low pressure side of the pump. The apparatus comprises a wall defining a bore disposed within the pump drive shaft, where the first end of the bore is configured to receive lubrication fluid and a second end of the bore is configured to receive combustion fluid. A shuttle is be disposed within the bore for separating the lubrication fluid and the combustion fluid and being movable, for example, in response to differences in thermal expansion between the lubrication fluid and the combustion fluid. 
     In yet a further aspect of the invention, in a pump for receiving combustion fluid at low pressure and supplying combustion fluid at high pressure, an apparatus is provided for equalizing pressure between a first region of lubrication fluid for lubricating the pump and a second region of combustion fluid at a low pressure where the pump has a rotatable shaft. The apparatus comprises wall means defining a bore disposed within the rotatable shaft, a first end of said bore being configured to receive lubrication fluid from said first region and a second end of said bore being configured to receive combustion fluid from said second region and a shuttle disposed within said bore, said shuttle being configured to equalize pressure between the first region and the second region. 
     In a further aspect of the invention means are provided for biasing said shuttle against the lubrication fluid in the bore so as to increase the pressure of the lubrication fluid in the first region relative to the combustion fluid in the second region. 
     In still a further aspect a seal is disposed about the rotatable shaft, wherein said seal is disposed between the first region and the second region. 
     In another aspect, the first region comprises a chamber defined between the shuttle and a closed end of said bore and a passage communicating with said chamber at one end, passing through the shaft and communicating at the other end with one side of said seal. The second region comprises a main cavity which communicates with a second side of said seal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a pump having a needle bearing scheme and employing a pressure equalizing shuttle in accordance with one embodiment of the present invention; 
     FIG. 2 is a cross sectional view of a pump having a needle bearing scheme and employing a pressure equalizing shuttle in accordance with another embodiment of the present invention; 
     FIG. 3 is a cross sectional view of a pump having a ball bearing scheme and employing a pressure equalizing shuttle in accordance with a further embodiment of the present invention; and 
     FIG. 4 is a cross sectional view of a pump having a ball bearing scheme and employing a diaphragm in accordance with still a further embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a pump in accordance with a first embodiment of the present invention is shown generally at  10 . The pump comprises a housing  12  and a flanged sleeve  14  each of which may be composed of, for example, aluminum or steel and may be cast in a well known manner. The flanged cover  14  includes a flange  15  for mounting to the housing  12  via suitable fasteners  16  (shown in dotted line). O-ring  17  is provided for sealing engagement between the flanged cover  14  and housing  12 . 
     The housing  12  includes fuel inlet connector  18  and an outlet connector  20 . The inlet connector  18  is sealed, e.g., by copper washers  19  and includes a bore  21  which receives a combustion fluid or fuel  22 , such as gasoline from a fuel tank (not shown) pressurized by a low pressure feed pump (also not shown) at a feed pressure in the range of 2-5 bar, preferably in the range of 3-4 bar. The outlet connector  20  is connected to a common rail  23  and passes pressurized fuel thereto for injection into, e.g., an internal combustion engine (not shown). 
     The housing  12  defines a main cavity  24  which is closed by the flanged cover  14 . The main cavity  24  communicates with the bore  21  of the inlet connector  18  and indirectly with the outlet connector  20  for passage of fuel through the pump  10 . 
     The flanged cover  14  includes a central aperture  26  defined by a sleeve  28 . A rotating shaft  30  is supported by the sleeve  28  at a first end  32  and at a second end  34  within a recess  36  of the housing  12 . A first bearing  38  is interposed between the rotating shaft  30  and the sleeve  28 . A second bearing  40  is interposed between the second end  34  of the rotating shaft  30  and the recess  36  of the housing  12 . It will be understood that either or both the first and second bearings  38 ,  40  may comprise any suitable bearing such as a needle bearing as illustrated. The first bearing  38  is provided with seals  42 ,  42 ′ which may comprise lip seals as illustrated where each has a base portion  43 ,  43 ′ and inwardly extending lip portions  44 ,  44 ′. The seals  42 ,  42 ′ function to prevent loss of lubricating fluid such as oil  46  and the mixing of oil  46  and fuel  22  as will be discussed in more detail hereafter. 
     The rotating shaft  30  may be composed of any suitably strong and durable material such as a steel and includes a tang  48 , flange  50  and an eccentric profile  52 . The tang  48  is provided for connection with a suitable device for imparting a rotational force to the rotatable shaft  30 . The flange  50  abuts a thrust washer  54  which in combination with a bottom thrust plate  56  prevents excessive axial movement of the rotatable shaft  30 . 
     The eccentric profile  52  of the rotatable shaft  30  is disposed within the main cavity  24  and defines an outer surface which is eccentric with respect to the longitudinal axis of the rotatable shaft  30 . It will be understood that the rotatable shaft  30  has a portion of the shaft (not shown) which is offset from the longitudinal axis. Further details of a rotatable shaft having an offset portion may be unberstood with reference to U.S. patent application Ser. No. 09/031,859 entitled “Supply Pump for Gasoline Common Rail” filed Feb. 27, 1998, the entire contents of which has previously been incorporated herein by reference. 
     The housing  12  includes at least one bore  60  which communicates at one end with the main cavity  24  and at the other end with the outlet connector  20  via internal discharge passages (not shown). A cover  62  and fasteners  64  are provided to enclose a plunger assembly  66  which is disposed within the bore  60 . The cover  62  may also include a spacer  68  and a suitable seal such as an O-ring  70 . 
     Plunger assembly  66  comprises a sleeve  72 , pumping plunger  74 , pumping chamber  75 , check valve  76  and shoe  78 . The sleeve  72  mates with the bore  60  and is sealed by an O-ring  80  to prevent migration of combustion fluid  22  from a high pressure side of check valve  76  into the main cavity  24 . 
     The check valve  76  comprises a spring  82  and plate  84  which is sealingly engageable with an upper surface (not numbered) of the sleeve  72  and communicates with the outlet connector  20 . 
     The shoe  78  comprises a cradle  86 , engagement shoulders  88  and engagement surface  90 . The cradle  86  is configured to receive the pumping plunger  74  and the engagement surface  90  is configured to mate with the eccentric profile  52  of the rotatable shaft  30 . The engagement shoulders  88  contact an energizing cage  92  which retains the shoe adjacent the rotatable shaft  30   
     The pumping plunger  74  is disposed within the sleeve  72  and comprises an outer end  94  and inner end  96  between which is a charging passage  98  and a check valve  100 . Check valve  100  includes a ball stop  102  and a ball  103 . 
     In operation, as the shaft  30  rotates through one revolution the shoe  78  remains in contact with the eccentric profile  52 , whereby the pumping plunger  74  is reciprocated toward an inner limit position, which produces a low pressure in the pumping chamber  75 , to an outer limit position for developing a high pressure in the pumping chamber. In a somewhat conventional manner, highly pressurized fuel in the pumping chamber  75  is discharged through a discharge check valve  76  into a discharge passage  104  which, in turn, fluidly communicates with the outlet connector  20  and common rail  23 . 
     It will be understood that while a single pumping plunger is illustrated, multiple plungers would typically be employed in the practice of this invention, for example, in the form of a radial multiple chamber pump. 
     For a further detailed discussion of the operation of a supply pump suitable for practice in conjunction with the present invention, reference may be had to U.S. patent application Ser. No. 09/031,859 entitled “Supply Pump for Gasoline Common Rail” filed Feb. 27, 1998, discussed above. 
     In accordance with a feature of the present invention, the rotatable shaft  30  is provided with a longitudinal bore  106  having an equalizing element, in this embodiment, a shuttle  107  disposed therein between a closed end  108  and an open end  110 . The open end  110  fluidly communicates with the main cavity  24  such that fuel  22  may flow therebetween. A transfer passage  112  is disposed in fluid communication with the closed end  108  for supplying oil  46  to/from the bearing  38  from/to a chamber  111  defined between the shuttle  107  and closed end  108 . 
     In the preferred embodiment, the oil  46  is introduced during assembly (discussed in more detail below) of the pump  10  and is not in communication with the engine oil (not shown). However, it will be appreciated that oil  46  may be in communication with the engine oil through a passage (not shown) to the engine. A suitable pressure regulator (not shown) may be employed in order to reduce the pressure variations in the engine oil. It is not preferable that the oil  46  be in communication with the engine oil as, e.g., additives for neutralizing acidity required in engine oil are unnecessary for the pump  10 . In addition, the viscosity of oil  46  may be less than that of engine oil. 
     The shuttle  107  is generally cylindrical in shape and may be composed of any suitably strong and moldable material such as a plastic, preferably a nylon or acetal resin such as that sold under the trademark DELRIN, sold by DuPont de Nemours, E.I., Co. Wilmington, Del. The shuttle may include tapered end portions  113  and at least one seal but preferably comprises a pair of O-rings  114  mounted within recesses  120 . The shuttle  107  is moveably disposed within the longitudinal bore  106  such that the pressure associated with the fuel  22  (approximately 2-5 bar) may be balanced or equalized with the pressure of the lube oil  46 . For example, if the pressure of the lube oil  46  is greater than that of the fuel  22 , the shuttle  107  will be urged toward the fuel  22  and vice versa. The term pressure differences as used herein refers to pressure levels between fluids which arise because of, for example, volumetric changes, in particular, the effects of volume changes due to variations in thermal expansion. 
     As can be seen, seal  42 ′ includes lube oil  46  disposed on one side thereof and fuel  22  disposed on the opposite side. Since the shuttle  107  generally equalizes pressure on either side of the seal  42 ′, the seal  42 ′ is prevented from being canted in one direction (arrow  115 ) or the other (arrow  115 ′) due to a substantial difference in pressure. 
     In accordance with another feature of the present invention, a spring  116  having an enlarged diametrical portion  117  is mounted in a recess  118  of the open end  110  of the longitudinal bore  106 . The spring  116  functions to bias the shuttle in the direction of oil  46 , thereby increasing the pressure of the oil  46  relative to that of the fuel  22 . A suitable force provided by the spring  116  ranges from approximately 0.05 lbs to 0.15 lbs and is preferably approximately 0.1 lbs whereby the pressure difference between the oil  46  and fuel  22  ranges from about 1.0 psi to 3.0 psi and is preferably approximately 2.0 psi. Because of this pressure difference, it is more likely that oil  46  will mix slightly with the fuel  22  through, for example, seal  42 ′ rather than, the opposite occurring. As discussed above, while it is most desirable that no mixing occur between the fluids it is less desirable that fuel mixes with oil rather than vice versa as problems such as the loss in lubricity of the oil may occur. 
     It will be understood that the dimension between the O-rings  114  may be arranged such that neither O-ring passes over the portion of the bore  106  passed over by the other given the amount of travel within the bore  106  that the shuttle  107  undergoes. By limiting contact by the O-rings  114  to only a particular fluid, the sealing of the shuttle is increased while the likelihood of mixing of fuel  22  and lube oil  46  is reduced. 
     In anticipation of assembly of the rotatable shaft  30 , with the pump  10 , the bore  106  is preferably pre-filled with an appropriate quantity of oil  46  and thereafter the shuttle  107  is inserted into the bore. Optionally, spring  116  may then be inserted into bore  106  which, in addition to the function discussed above, also functions to prevent loss of oil  46  through the bore  106 . 
     Another embodiment of a shuttle useable in the practice of the present invention is illustrated generally at  207  in FIG.  2 . In this embodiment the shuttle  207  may be generally cylindrical in shape as the prior embodiment, although rather than employing O-rings the sealing of the shuttle may be arranged at opposing ends  208  and  210  of the shuttle. In order to provide a seal, each end  208 ,  210  are dimpled leaving an outer tapered rim  212  and  214 . Each tapered rim  212 ,  214  provides, as will be appreciated, a sealing characteristic adjacent the inner surface  216  of the bore  206 . The shuttle is composed of a sufficiently durable and flexible material such as a plastic material, for example, nylon. It will be understood that while no bias means for biasing the shuttle is illustrated, one may also be employed in connection with this embodiment. 
     Turning now to FIG. 3, another embodiment of a pump used in practice of the present invention is shown generally at  310 . In this embodiment, the pump  310  comprises a ball bearing and bushing rather than needle bearings as provided in the embodiment of FIG.  1 . In particular, a ball bearing  312  is provided for the rotatable shaft  314  along with a wet bushing  316 . 
     An enlarged tang  318  is provided for covering the outer portion of the bearing  312 . In addition, seals  320  and  322  are separated by an oil reservoir  324 . 
     A shuttle  326  is provided which may be similar to that discussed above, with respect to FIG. 1, although as illustrated only one O-ring  328  is provided. It will be understood that while only one O-ring is illustrated in this embodiment, the shuttle  326  may include a par of O-rings. It will also be understood that while no spring for biasing the shuttle is illustrated, any suitable bias may be employed in connection with this embodiment. It will also be understood that the present bearings scheme of FIG. 3 may be employed in combination with the shuttle  207  illustrated in FIG.  2 . 
     Still another embodiment of a pump in accordance with the present invention is illustrated generally at  410  in FIG.  4 . In this embodiment of the invention, an equalizing element is provided which comprises a flexible diaphragm, discussed in more detail below, instead of a shuttle as described above. As illustrated, the pump  410  comprises a first bearing  412 , a rotatable shaft  414  and a second bearing  416 . A pair of seals  418  and  420  are provided which assist in preventing outward migration of lubricating fluid such as oil  422  disposed in a channel  423  located between the seals and about the rotating shaft  414 . 
     An oil/fuel pressure interface chamber is located at  424 . One end  426  of the interface chamber  424  communicates with a passage  428  which, in turn, communicates with the channel  423 . The other end  430  of the interface chamber  424  communicates with fuel inlet  432  via intermediate passages  434 ,  436 ,  438  and annulus  440 . 
     A flexible diaphragm  442  may be centrally located within the interface chamber  424 . The diaphragm  442  may be composed of any suitably flexible material such as a synthetic rubber and may be mounted within the chamber  424  via a mounting rib  444 . The diaphragm  442  may be dimensioned to be substantially larger than a cross sectional area of the chamber  424  whereby fold  446  may occur. During use, the folds  446  may fold or unfold so that the center (not numbered) of the diaphragm  442  may move within the inside of the chamber  424 . 
     Similar to the shuttles  107  and  207  discussed above in connection with FIGS. 1 and 2, the flexible diaphragm  442  is movable based on, e.g., differences in the coeficient of thermal expansion which creates volume changes and, in turn, pressure variations between the oil  422  and fuel  448  disposed within the pump  410 . Accordingly, the diaphragm  442  equalizes the pressure between the oil  422  and fuel  448  which, e.g., reduces the likelihood of mixing of the two such as by passing seal  420  in a manner similar to that discussed above. 
     While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the present invention is not limited to the disclosed embodiments. Rather, it is intended to cover all of the various modifications and equivalent arrangements included within the spirit and scope of the appended claims.