Abstract:
A drive shaft seal for a gasoline direct injection pump is configured as a solid but flexible barrier separating combustion fluid from lubrication fluid in the pump. Each drive shaft seal is generally disc shaped, defining a central shaft opening surrounded by a flexible corrugated portion that is in turn surrounded by a generally planar outer flange. The outer flange of each shaft seal is retained between pump housing sections and sealed by stationary o-rings. An axially projecting lip retained and sealed between a bushing and a shoe race defines the shaft opening. The bushing, shoe race and associated pump components move reciprocally in response to rotation of a shaft mounted eccentric. The corrugated flexible portion of each drive shaft seal flexes to accommodate relative movement between the inner lip and outer flange. No part of the drive shaft seal is in contact with the rotating shaft.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to pumps and, more particularly, to a seal for maintaining separation of lubricating oil and fuel in a high pressure supply pump for a gasoline direct injection system.  
           [0003]    2. Description of the Related Art  
           [0004]    Pumps capable of generating relatively high pressure (such as 120 bar and higher) required for supplying a common rail used in gasoline direct injection (GDI) systems are well known in the art. One such pump is described in U.S. patent application Ser. No. 09/342,566, filed Jun. 29, 1999 and entitled “Supply Pump for Gasoline Common Rail” which is assigned to the Assignee of the present invention, and the entire contents of which is hereby incorporated by reference. This supply pump includes a rotating drive shaft supported by bearings that are lubricated by a lubrication fluid (oil) as is typical in the art. Oil lubricated drive shaft bearings are typically required due to the poor lubricating properties of gasoline. In this pump configuration, energy transfer from the drive shaft to the pumping plungers, e.g., high speed sliding motion between the drive shaft eccentric and the shoes associated with each pumping plunger driven end, takes place in a bath of gasoline. The gasoline in the low pressure area (sump) of the pump may be pre-pressurized to 4 or 5 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.  
           [0005]    A problem can occur with the typical prior art lip seals in that because of the differences in pressure between the lubricating 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 seal wear. It should be understood that lip and other sliding contact seals are by definition wear items whose seal degrades over time. Additionally, typical elastomeric seal materials become rigid and inflexible in extreme cold conditions, causing the seal to remain deformed as a result of idle periods at cold temperatures. All of these conditions produce gaps through which the pressure differential between the oil and the fuel promotes passage either of oil into the fuel or fuel into the oil, resulting in undesirable 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 engine. Also, potential hazardous waste problems concerning disposal of the oil/fuel mixture can arise. In the opposite direction, the mixing of the oil with the fuel may result in a reduction in engine performance by causing premature ignition (knock) and an undesirable increase in engine emissions.  
           [0006]    Any seal consisting of stationary and rotating components, such as the stationary lip seals and rotating shaft described above, will be inherently very sensitive to contamination during assembly as well as to deterioration by wear or contamination during extended operation. Both scenarios can lead to leakage, with serious adverse consequences to the engine and/or the passengers. In addition, the most sophisticated and durable mechanical seals tend to be very expensive, cumbersome and generate large amounts of friction-related heat.  
           [0007]    There is a need in the art for a more reliable drive shaft seal that overcomes the above-described deficiencies.  
         SUMMARY OF THE INVENTION  
         [0008]    An object of the present invention is to provide a new and improved drive shaft seal for use in conjunction with high pressure gasoline supply pumps that substantially eliminates mixing of lubricating oil with fuel.  
           [0009]    Another object of the present invention is to provide a new and improved drive shaft seal for a high pressure gasoline supply pump that permits construction of the pump with a reduced number of simplified components.  
           [0010]    A further object of the present invention is to provide a new and improved drive shaft seal for a high pressure gasoline supply pump that substantially eliminates seal-related heat generation.  
           [0011]    A yet further object of the present invention is to provide a new and improved drive shaft seal for a high pressure gasoline supply pump that minimizes high speed sliding contact between components bathed in gasoline.  
           [0012]    These and other objects of the invention are achieved in a preferred embodiment of the drive shaft seal comprising a flexible barrier for separation of the fuel from lubricated portions of the pump. One embodiment of the drive shaft seal is generally disk-shaped, defining a central shaft opening surrounded by a flexible corrugated portion which is in turn surrounded by a flat outer flange. The planar outer flange of each shaft seal is sandwiched between pump housing segments and sealed by stationary o-rings. A radially inner, axially projecting cylindrical section defines the shaft opening. The cylindrical section is sandwiched and sealed between a radially inward bushing and a radially outer shoe race and sealed by stationary o-rings disposed in grooves defined by the bushing and shoe race respectively. The drive shaft, or cantilever end of an engine shaft, passes through the bushing and never actually contacts the drive shaft seal. The sliding interface between the rotating shaft and bushing may be executed as a dry lubricated bushing, may be lubricated by engine oil and/or equipped with a needle bearing or the like.  
           [0013]    In a supply pump having its own shaft, the front and rear housing segments support the shaft on lubricated roller and/or needle bearings. Clamping and mounting screws align and tightly clamp the pump housing sections together with the flat, radially outer flanges of the drive shaft seals retained between them.  
           [0014]    In a supply pump driven by a cantilevered extension of an engine shaft, the pump itself will have no bearings because the engine shaft is supported by bearings internal to the engine. The pump will utilize a shortened housing and require only one drive shaft seal (to keep fuel from leaking into the bearing supporting the engine shaft). Mounting hardware for the pump will clamp the radially outer flange of the drive shaft seal between the pump housing and the engine or adapter plate. An eccentric on the end of the engine shaft will rotate within a bushing as described above.  
           [0015]    The pump shaft will have at least one portion defining an external profile that is eccentric with respect to the axis of shaft rotation. In the inventive pump, the external profile of the eccentric is engaged in sliding contact with the interior surface of the bushing. The bushing is preferably stationary with respect to the radially inner cylindrical section of each diaphragm and the shoe race that supports the radially inner end of the pump plungers. Thus, the sealing diaphragms are not subject to the wear that is typical of a lip seal because all sliding contact takes place between the external surface of the eccentric and the bushing.  
           [0016]    The flexible portion of each sealing diaphragm has a folded or corrugated configuration. This corrugated configuration permits the radially inner cylindrical lip to move relative to the radially outer flange in response to reciprocal forces generated by the eccentric. The seal materials and corrugated configuration ideally combine to withstand many millions of reciprocal pump cycles while maintaining a continuous barrier between combustion and lubrication fluids in the pump. The corrugations may be in the form of concentric axial folds or alternatively, may be radial folds. The radial folds of seal material will together provide the seal with an axial component, or cup-like configuration from the radially outer flange to the inner shaft opening.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a sectional view through a supply pump for a gasoline direct injection system including a pair of drive shaft seals in accordance with the present invention;  
         [0018]    [0018]FIG. 2 is an overhead perspective view of one drive shaft seal as shown in FIG. 1;  
         [0019]    [0019]FIG. 3 is an overhead perspective view of an alternative embodiment of a drive shaft seal in accordance with the present invention;  
         [0020]    [0020]FIG. 4 is a sectional view through an alternative supply pump for a gasoline direct injection system incorporating a single drive shaft seal as illustrated in FIG. 2;  
         [0021]    [0021]FIG. 5 is a sectional view through the supply pump of FIG. 4 incorporating the alternative drive shaft seal illustrated in FIG. 3;  
         [0022]    [0022]FIG. 6 is a sectional view through an alternative supply pump for a gasoline direct injection system incorporating an alternative embodiment of a drive shaft seal in accordance with the present invention; and  
         [0023]    [0023]FIG. 7 is a sectional view through the supply pump of FIG. 6 incorporating a further alternative embodiment of a drive shaft seal in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    With reference to the drawings, wherein like numerals represent like parts throughout the several Figures, one preferred embodiment of a drive shaft seal in accordance with the present invention is generally designated by the numeral  10 . FIG. 1 is a sectional view through a supply pump appropriate for use in conjunction with a gasoline direct injection (GDI) system. The illustrated pump is constructed from three primary sections. An adapter plate  40  is configured to mate with a complementary opening on an internal combustion engine (not illustrated). The adapter plate  40  includes a first bearing  46  to support one end of the pump drive shaft  32 . The engine end of the pump drive shaft  32  includes a tang drive which mates with complementary parts of an engine driven shaft (not illustrated) to impart rotational energy to the pump drive shaft  32 . The middle section  42  of the pump contains integral plunger bores  43  and preferably also ducts for transmitting low pressure fuel to the pump plunger bores  43  and providing a passage for high pressure fuel away from the pump plungers  22 . A pump cover  44  encloses the outer end of the pump and includes a second bearing  48  for supporting the outer end of the pump drive shaft  32 . FIGS. 2 and 3 show that the outer flange of each seal defines five through holes  13 ,  15  to permit passage of fasteners. Two assembly fasteners (not illustrated) pass through the pump cover, outer seal holes  15 , pump middle section  42  and inner seal holes  15  to threadably engage the adapter plate to align the pump sections and clamp the pump into an assembled unit. After testing and calibration, the pump is then installed to the engine by three mounting fasteners that pass through all three pump sections and flange through holes  13  to threadably engage the engine block.  
         [0025]    The pump drive shaft  32  has a primary axis of rotation  34  defined by bearings  46  and  48 . As is typical in a radial piston pump, the pump drive shaft includes an eccentric portion  35  having an axis of rotation  36  offset by a distance A from the shaft axis  34 . Rotation of the shaft  32  produces an oscillatory movement of the eccentric  35  relative to the pump housing sections  40 ,  42 ,  44 . In the illustrated embodiment, the oscillatory movement of the eccentric  35  is transmitted to the pump plungers  22  through a bushing  28 , a shoe race  26  surrounding the bushing and plunger shoe  24 . The inward end, or head  21  of the pump plunger  22  is pivotally retained to the shoe  24  in a socket  37 . It should be noted that, although one plunger  22  is illustrated in FIGS. 1, 4 and  5 , the illustrated radial GDI pumps will typically incorporate a plurality of plungers  22  and associated shoes  24  with a preferred number being three. Retention means such as the energizing rings  23  urge the shoes  24  against the exterior of the shoe race  26 . Together the bushing  28 , shoe race  26 , shoes  24  and energizing rings  23  follow the movement of the eccentric  35  to produce reciprocal actuation of the plungers  22  in their bores  43 .  
         [0026]    It will be appreciated by those of skill in the art that two dissimilar fluids are present within the GDI pump. The combustion fluid, in this case gasoline, fills a sump  20  that surrounds the radially inward end, or head  21  of the pumping plungers  22  to be drawn into pumping chambers defined at the radially outward end of each plunger and pressurized by radially outward movement of the plungers  22  induced by the eccentric  35 . The fuel may be drawn into the pumping chambers from the sump  20  through openings and passages in the pumping plungers  22  as described in U.S. patent application Ser. No. 09/342,566, incorporated by reference above. Alternatively, low pressure feed passages  25  may supply fuel to the middle section of the plunger bore  43  as illustrated in FIGS. 4 and 5. In either configuration, it will be understood that fuel, e.g., gasoline surrounds the head  21  of each plunger  22  and fills the sump  20 .  
         [0027]    Lubrication fluid preferably surrounds the drive shaft bearings  46  and  48 . Bearings  46  and  48  may be permanently lubricated by grease or may be provided with a stream of lubrication fluid from the engine lube oil supply. In either case, the presence of gasoline in that area of the pump containing lubrication fluid will dissolve the lubrication fluid resulting in loss of lubrication, overheating and possible catastrophic failure of the pump.  
         [0028]    One critical aspect of the GDI pump addressed by the present invention is realization of a reliable drive shaft seal which will separate the combustion fluid (gasoline) from lubrication fluids (oil, grease) necessarily present in the pump. As previously discussed, the typical prior art GDI pump includes seals consisting of radially projecting lips of elastomeric material arranged to abut the rotating exterior surface of the drive shaft. These so-called lip seals are subject to failure during all stages of assembly and operation of the GDI pump, resulting in unacceptable mixing of combustion and lubrication fluids. The present invention replaces these lip seals with a continuous barrier between the fluids having no contact with the rotating shaft  32 . In a first embodiment shown in FIG. 1, two drive shaft seals  10  arranged to define a sump chamber  20  surrounding the radially inward ends of the pump plungers  22 .  
         [0029]    As best seen in FIG. 2, each drive shaft seal  10  comprises a radially outward flange  12  configured for retention between pump housing components such as the adapter plate  40 , middle section  42  and cover  44 . Each drive shaft seal  10  of this first illustrated embodiment defines an axial opening  18  surrounded by an axially projecting lip  16 . Between the lip  16  and the flange  12  are a series of concentric bellows-type folds in the seal material. Seal material is accumulated in axial folds radially progressing away from the axial opening in concentric rings. These bellows folds permit movement of the lip  16  relative to the flange  12 . With reference to FIG. 1, the flanges  12  of the two drive shaft seals  10  are retained between the adapter plate  40  and middle section  42  and cover  44 , respectively. The lips  16  are arranged to project axially toward each other and be retained between the bushing  28  and the shoe race  26 . Sealing grommets or o-rings  33  are arranged in grooves defined by the pump sections and shoe race  26  to enhance sealing engagement of the drive shaft seals  10  with these pump components.  
         [0030]    It will be apparent that no sliding contact occurs between the rotating drive shaft  32  and the drive shaft seals  10 . The bushing  28  provides a sliding interface  29  with the eccentric  35  of the drive shaft  32 . As the pump drive shaft  32  rotates, the eccentric  35  imparts a reciprocal motion to each pumping plunger  22  as previously described. The flexible portion  14  of each drive shaft seal  10  flexes to permit movement of the lip  16  relative to the flange  12  during each pumping cycle.  
         [0031]    It will be noted that the sliding interface  29  eliminates a sliding interface between the plunger shoe  24  and the eccentric  35  found in previous pumps (see U.S. application Ser. No. 09/342,566, incorporated by reference above). The interface  19  between the shoe race  26  and shoes  24  in the illustrated pump embodiments serves only to transmit reciprocal energy to the pumping plunger  22  and is not a high speed sliding interface. This simplified force-distribution relationship between the shoe race  26  and the shoe  24  may support increased loads on the plunger head  21  and shoe  24  in the form of higher pump output pressure or increased pump output volume.  
         [0032]    [0032]FIG. 1 illustrates the eccentric  35  having just completed the upward reciprocal movement of pumping plunger  22 . The flexible portion  14  of each drive shaft seal  10  is shown to be compressed adjacent the pumping plunger  22 , e.g., above the drive shaft  32 . The flexible portion  14  is expanded at the opposite side of the pump, e.g., below the drive shaft  32 . Appropriate selection of drive shaft seal materials and the configuration of the bellows folds comprising the flexible portion  14  permit construction of a drive shaft seal that can easily withstand millions of such compression/expansion cycles. A metallic barrier such as that described herein also has the advantage of being able to withstand minor pressure differentials that may occur between the combustion fluid in the sump chamber  20  and lubrication fluid outside the sump. The drive shaft seals may be displaced slightly inwardly or outwardly by such pressure differentials without adversely affecting their function or increasing wear. Combustion fluid cannot pass through the impervious barrier presented by drive shaft seals  10 . Meanwhile, lubricating oil is free to move through the bearings  46  and  48  as well as the interface  29  between the bushing  28  and the eccentric  35 , without mixing with the combustion fluid in the sump chamber  20 .  
         [0033]    An alternative embodiment of a GDI pump is illustrated in FIGS. 4 and 5. The alternative embodiment is a GDI pump driven by a cantilevered extension of an engine driven shaft, such as a camshaft  30 . Using a cantilevered extension of an engine shaft simplifies pump design by eliminating the need for an internal pump shaft and its associated bearings. The simplified pump includes an adapter plate  40  and a combined middle section/cover  42   a . An eccentric  35  is preferably an integral part extending from one end of the engine shaft  30 . When the pump is mounted to an engine (not illustrated), the eccentric  35  penetrates through the adapter plate  40  to engage the pump bushing  28 . Rotation of the engine shaft  30  imparts reciprocal movement to the pump plunger  22  in a manner identical to that described above with reference to the pump illustrated in FIG. 1.  
         [0034]    Elimination of the pump shaft and associated bearings simplifies the pump design and permits a single drive shaft seal  10  to separate the combustion fluid in the sump chamber  20  from lubrication fluid in the engine. The radially projecting flange  12  of the drive shaft seal  10  is compressively engaged between the adapter plate  40  and the middle section/cover  42   a . The axially projecting lip  16  is retained between the bushing  28  and an alternative shoe race  26   a . The shoe race  26   a  illustrated in FIG. 4 is configured as a cap which extends over the end of the bushing  28  and eccentric  35  to complete the barrier between engine lubrication fluid and combustion fluid in the sump chamber  20 . Sealing grommet  33  keeps combustion fluid from moving past the drive shaft seal  10  by migrating between the shoe race  26   a  and the bushing  28 . The bushing  28  provides a sliding interface  29  with the eccentric  35 .  
         [0035]    The eccentric in FIG. 4 is illustrated at the completion of its upward movement. Thus, the flexible portion  14  of the drive shaft seal above the drive shaft is compressed to a radial dimension D. A diametrically opposed flexible portion is expanded to a radial dimension C to accommodate upward movement of the lip  16  relative to the flange  12 . Continued rotation of the engine shaft  30  will produce a downward reciprocal movement on the pumping plunger  22  to draw combustion fluid through low pressure input passage  25  and check valve  27  into a pumping chamber (not shown) defined at the radially outward end of the plunger  22 . The next upward movement of the eccentric  35  will close check valve  27  and expel the combustion fluid from the pumping chamber at an elevated pressure.  
         [0036]    [0036]FIG. 5 illustrates the pump of FIG. 4 equipped with an alternative embodiment  10   a  of the drive shaft seal. This embodiment of the drive shaft seal forms a closed cap  17  over the end of the pump bushing  28  and eccentric  35 . This eliminates the need for the special shoe race  26   a  illustrated in FIG. 4. In all other respects the pump and drive shaft seal  10   a  operate as previously described.  
         [0037]    As best seen in FIGS. 2 and 3, each drive shaft seal  10 ,  10   a  defines a central axis B passing through the axially projecting lip  16 ,  16   a . It will be understood that the lips  16 ,  16   a  project substantially perpendicularly to the radially projecting flange  22 . The folded flexible portions  14  can be arranged and configured to comply with pump spatial and/or other design constraints. The illustrated drive shaft seals  10 ,  10   a , are arranged so that the bellows-fold flexible portion  14  projects axially away from the lip  16 ,  16   a . Other configurations are of course possible. The illustrated embodiments  10 ,  10   a  illustrate one and one-half bellows folds surrounding the axially projecting lips  16 ,  16   a . The flexible portion  14  may include greater or fewer numbers of bellows folds having a greater or smaller axial dimension depending on the material used, spatial or other design constraints.  
         [0038]    [0038]FIGS. 6 and 7 illustrate a further alternative embodiment of a GDI pump driven by a cantilevered extension of and engine shaft. This pump embodiment has a pump body  41  formed as a single unit. The pump illustrated in FIGS. 6 and 7 replaces the bushing  28  illustrated in FIGS. 1, 4 and  5  with a needle bearing  48 . A needle bearing  48  changes the relationship between the eccentric  35  and the shoe race  26 ,  26   a  from a sliding interface  29  to a more efficient rolling interface  29   a  capable of sustaining much larger forces over greater periods of time. The needle bearing may be pre-lubricated or supplied with oil mist or flow as is known in the art.  
         [0039]    An alternative shaft seal  10   b  incorporates a flexible portion  14   a  comprising a sequence of radial folds that progress in an axial direction. This embodiment of the shaft seal has a axial dimension extending from the outer flange  21   a  to the inner lip  16 . The outer flange  12   a  projects in an axial direction and is trapped between the pump body  41  and a press fit retention ring  52 . A sealing grommet  33  enhances the seal established between the outer flange  12   a  and the pump body  41 . The inner lip  16  (FIG. 6) is similarly trapped between a retention ring  50  and the cap-shaped shoe race  26   a.    
         [0040]    With continuing reference to FIG. 6, the eccentric is illustrated as just having completed the upward pumping stroke of the plunger  22 . Thus, that portion of the shaft seal  10   b  above the shaft  30  is compressed and the opposite portion is expanded. This is reflected in the angles between consecutive of the radial folds making up the flexible portion  14   a . Above the shaft  30 , the compressed radial folds form a narrow acute angle E. Below the shaft, the expanded radial folds form a larger acute angle F. Finite element analysis indicates that a plurality of radial folds as in embodiment  10   b  permit a greater eccentricity of the eccentric relative to the shaft axis  34  (see FIGS. 1 and 7). This, combined with an improved rolling interface  29   a  between the eccentric  35  and the shoe race  26   a , permit an increased pumping volume and pressure output for the pump embodiment of FIGS. 6 and 7 as compared to the pump illustrated in FIGS. 4 and 5.  
         [0041]    [0041]FIG. 7 illustrates a further alternative embodiment of the shaft seal  10   c  in which the inner lip is eliminated and replaced with a welded interface  60  between the final radial fold and the open end of the cup-shaped shoe race  26   a . This welded interface  60  provides a permanent fluid-tight connection between the seal  10   c  and the shoe race  26   a . FIG. 7 also illustrates the radial eccentricity A′ of the eccentric  35  relative to the shaft axis of rotation  35 . It will be noted that shaft eccentricity A′ in FIG. 7 is greater than shaft eccentricity A in FIG. 1. Needle bearings  48  are provided with an outer race  49  that is closely received within the shoe race  26   a . In the illustrated embodiments, eccentric  35  will be provided with a hardened surface to serve as the inner race for the needle bearings.  
         [0042]    It should be noted that all the illustrated pump embodiments eliminate high speed sliding motion between the shoe  24  and an actuating surface, e.g., the eccentric. Absence of sliding motion reduces loading on the shoe  24  and allows for an increase in pressure produced by the pump and/or an increase in the volume of fuel delivered by the pump.  
         [0043]    Each drive shaft seal is preferably formed from thin and flexible stainless steel, although other materials are of course possible. A preferred embodiment of the drive shaft seal comprises a sheet of 300 or 400 series stainless steel having a thickness of between 0.08 and 0.12 millimeters. The thickness of the seal material will depend in part upon the pressure inside the sump. Thicker material may be necessary to withstand higher sump pressures. It will be understood that the material will be the thinnest appropriate for the given sump pressure because thinner materials will have reduced internal stress, as is known in the art. Alternatively, the seal may be made from Beryllium Copper alloy or, in low sump pressure applications, glass or carbon fiber reinforced plastic or elastomeric materials.  
         [0044]    While preferred embodiments of the foregoing invention have been set forth for purposes of illustration, the foregoing description should not be deemed a limitation of the invention herein. Accordingly, various modifications, adaptations and alternatives may occur to one skilled in the art without departing from the spirit and scope of the present invention.