Abstract:
A clamping and seal loading technique for securing the plunger sleeve to the pump housing of a single plunger fuel pump. This is achieved by providing a load ring between a sleeve retainer and the sleeve, such that the axial force applied by the retainer during installation and attachment to the plunger bore wall of the housing, is distributed more evenly on the sleeve and the sealing surface of the sleeve against the housing adjacent to the pumping chamber. The even distribution of force minimizes misalignment of the sleeve and thus maintains concentricity between the sleeve and the plunger.

Description:
RELATED APPLICATION 
     This application claims priority under 35 U.S.C. 119(e) from U.S. Provisional Application No. 60/879,674 filed Jan. 10, 2007 for “Load Ring Mounting of Pumping Plunger”, the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present disclosure relates generally to fuel pumps, and is more particularly concerned with a new and improved single plunger fuel pump. 
     In a typical high pressure, reciprocating plunger fuel supply pump, the plunger reciprocates within a surrounding sleeve which is secured in the plunger bore hole. The sleeve bears on a shoulder or other mounting surface in the housing. To achieve ideal performance and long life, the plunger OD and the sleeve ID must be precisely sized with close tolerances and installed in a manner that preserves a precise fit. 
     Notwithstanding the precision with which the sleeve and plunger may be fabricated, the installation in the pump housing can produce slight misalignment of the plunger within the sleeve. This misalignment can cause excessive or non-uniform wear on the plunger, and can also affect the fluid seal between the sleeve and the housing, giving rise to excessive leakage. Such misalignment is due to an imbalance or asymmetry in the axial force applied around on the sleeve to bear against the mounting surface of the housing. 
     SUMMARY 
     It is an object to provide an improved clamping and seal loading technique for securing the plunger sleeve to the pump housing of a single plunger fuel pump. 
     This object is achieved by providing a load ring between a sleeve retainer and the sleeve, such that the axial force applied by the retainer during installation is distributed more evenly on the sleeve and the mounting surface of the housing. 
     In a preferred embodiment, the invention is directed to a single plunger fuel pump comprising a housing having an internal pumping chamber and an inlet valve that feeds the pumping chamber, a plunger assembly mounting bore in the housing defining a bore wall and an end wall having an opening in fluid communication with the pumping chamber, and a plunger sleeve in the plunger assembly mounting bore adjacent the pumping chamber. The plunger sleeve has a seal face at one end which bears on and seals against a seal surface at the end wall of the mounting bore. A pumping plunger is reciprocable in the plunger sleeve inwardly toward and outwardly away from the pumping chamber. A plunger sleeve retainer is secured against the mounting bore wall and axially supports the sleeve. A plunger return spring is captured between a spring seat at the outer end of the plunger and a shoulder on the sleeve retainer. A load ring is situated between the sleeve retainer and the sleeve, urging the sleeve inwardly with sufficient force to maintain concentricity of the plunger within the sleeve and sealingly press the sealing face of the sleeve against the sealing surface at the end wall of the bore. 
     In an alternative form, the invention is directed a plunger assembly for a fuel pump comprising, a plunger sleeve having upper and lower ends, a substantially tubular body defining a pumping axis, and a radially extending external shoulder. A substantially tubular sleeve retainer concentrically receives the body of the sleeve, with a first radially extending external shoulder facing the shoulder on the sleeve. A pumping plunger is concentrically disposed in the plunger sleeve and retainer, with an upper end adjacent the upper end of the sleeve and a lower end projecting from the retainer. A plunger return spring is captured between a spring seat at the lower end of the plunger and a second shoulder on the sleeve retainer. A load ring is situated between the sleeve retainer first shoulder and the sleeve shoulder. 
     Preferably, the sleeve floats on the load ring until the sleeve retainer is advanced and secured within the bore a sufficient distance to form a seal between the seal face at one end which bears on and seals against a seal surface at the end wall of the mounting bore. The load ring is situated between the inner end of the sleeve retainer and a shoulder on the sleeve, urging the sleeve inwardly with a substantially constant force to sealingly press the sealing face of the sleeve against the sealing surface at the end wall of the bore. 
     Whether the retainer is advanced against the sleeve by threaded engagement or interference fit, the sleeve is uniformly urged by the retainer against the housing mounting surface, thereby maintaining alignment of the plunger within the sleeve and integrity of the seal between the sleeve and the housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the accompanying drawing, like elements are numbered alike in the several Figures: 
         FIG. 1  is a perspective view of a one plunger fuel pump having a substantially cubic housing or body, with the fuel inlet connector projecting on the right, the single plunger actuation assembly projecting from the left, and the inlet control valve projecting from the top; 
         FIG. 2  is a staggered section view of the pump of  FIG. 1 , through the inlet control valve, pumping plunger, and outlet connection, showing one embodiment of the improved clamping and seal loading technique for securing the plunger sleeve to the pump housing; 
         FIGS. 3A and 3B  are enlarged detailed views of the load ring shown in  FIG. 2 , with  FIG. 3B  taken along section line A-A of  FIG. 3A . 
         FIG. 4  is an enlarged view of an alternative embodiment of the improved clamping and seal loading technique for securing the plunger sleeve to the pump housing; and 
         FIG. 5  is an exploded view of the pump of  FIG. 1 , with the embodiment of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a one plunger fuel pump  10  having a substantially cubic housing or body  12 , with the fuel inlet connector  14  projecting from the right, the single plunger actuation assembly  16  projecting from the left, and the inlet control valve  18  projecting from the top. 
     With reference now to  FIGS. 1 and 2 , it is readily understood that the engine drive shaft carries a lobed cam (not shown) that reciprocates the remote end  20  of the pumping plunger  22  within a pumping sleeve  24  secured to the housing, between fuel charging (intake) and discharging (output) phases. The other, pumping end  26  of the plunger is situated in the pumping chamber  28 , which fills with fuel at a feed pressure of up to about 4 bar during the charging phase and, preferably subject to initial spill control, pressurizes the fuel in the pumping chamber up to about 200 bar for delivery via a discharge fitting  30  to, e.g., the common rail (not shown). The fuel is fed directly to the pumping chamber  28  through a solenoid controlled inlet valve  18 . As used herein, “inner” and “outer” refer to directions toward and away from the pumping chamber, respectively. 
     The substantially cylindrical pumping plunger  22  is carried concentrically in the plunger sleeve  24 , which at one end  32  bears on or is otherwise sealed against the end wall  34  of the plunger assembly mounting bore  36  in the housing, and which must be laterally fixed directly or indirectly to the mounting bore. A plunger sleeve retainer  38  is press fit or threaded against the mounting bore wall  40  for this purpose. The plunger  22  is disposed concentrically in the inner wall  40  of the sleeve  24  and the retainer  38 . A plunger return spring  42  is captured between a spring seat  44  at the driven end  20  of the plunger and a shoulder  46  on the sleeve retainer. The outer end  48  of the plunger sleeve retainer is turned inward to capture a lip seal  50  for sealing fuel within the pump. The upper end of the retainer forms a shoulder  52 . 
     Any leakage around the inner end  32  of the plunger sleeve  24  enters the clearance  54  with the ID of the tubular body of sleeve retainer  38  and is directed back to the lower pressure at the inlet valve  18 , via leak off ports  56  in the retainer and an internal passage  58  through the housing. 
     In the embodiment of  FIGS. 1-3 , the sleeve  24  has an enlarged inner end portion  60  adjacent the pumping chamber  28  and a tubular body portion  62  extending to an outer end  64 . The inner end has a sealing rim or bead  66  that is urged against the sealing surface at the end wall  34  of the bore in the housing that receives the sleeve retainer and sleeve. This sealing surface surrounds the plunger near the pumping chamber and when properly sealed prevents pumped fuel from leaking along the outer surface of the sleeve and sleeve retainer. The body  62  of the sleeve is situated within the cylindrical inner wall  68  of the sleeve retainer, whereas the enlarged portion  60  at the inner end of the sleeve is formed with an integral flange or otherwise defines a downward facing shoulder  70  that axially registers with and is spaced  72  from the inner end  52  of the retainer. 
     A load ring  74  is situated between the inner end  52  of the retainer and the shoulder  70  on the sleeve. The sleeve  24  floats on the load ring  74  until the retainer  38  is advanced within the housing bore  36  a sufficient distance to press the sealing rim or bead  66  of the sleeve against the sealing surface  34  at the end wall of the bore. When this condition is reached during assembly, the retainer is fixed with respect to the bore, as by retainer external shoulder  39  bottoming out as a hard stop against the shoulder  37  on the housing, thereby preventing further inward axial movement. This can be achieved with a threaded connection  41  between the retainer and the bore, or the retainer can be press (interference) fit. The shape of the load ring affords considerable tolerance on the effective positioning of the retainer within the bore. The reason for the load ring as opposed to traditional threaded clamping or press-fit designs is to reduce the sleeve ID distortion at the critical interface with the plunger OD. The load ring applies a very consistent, predictable load. 
       FIG. 3  shows the preferred load ring  74 , and  FIG. 4  shows such ring in an alternative to the integral shoulder flange  70 , which would typically have a machined face for interacting with the load ring. According to the embodiment of  FIG. 4 , the machined face is replaced with a snap ring  76  and washer  80 . The sleeve  24 ′ has a circumferential groove  82  to receive and retain the snap ring. With the latter embodiment, less material is required to fabricate the sleeve. 
     The load ring  74  is preferably a split or C-shaped ring having a cross section (taken parallel to the axis  84 ) that generally resembles the letter “W”. The load ring can, however, be a full ring. Preferably, each outer leg  86 ,  88  (at the axial ends) is substantially perpendicular to the axis  84  with all the corners  90 ,  92 ,  94  contoured rather than sharp. The legs are spaced apart a free height H when the ring is not loaded, but move toward each other during loading by the sleeve retainer  38 , to a shorter, compressed height H′. In a typical application, the load ring can be 20-25 mm across the greatest diameter (at  92 ), and 4 to 5 mm less across the smallest diameter (at  90 ,  94 ), for axially transmitting a target seal load of 750-1500 lbs. across a surface area defined by the legs, in the range of 0.0001 to 0.0002 m 2 . As a representative but not limiting example, the free height H of the load ring can be about 4.0 mm, whereas the compressed height H′ for transmitting the target load can range between about 2.0 to 3.0 mm (i.e., a compression of about 1-2 mm). 
     As noted above with reference to  FIG. 2 , any leakage past the seal at  66  is at a low pressure and passes through ports  56  in the retainer  38  into the passage  58  leading to a low pressure volume such as at the inlet valve. Any other potential leakage is blocked by an O-ring  98  or the like situated between an enlarged diameter portion of the retainer outside the leak off port  56 , and a similarly enlarged portion of the housing bore. 
       FIG. 5  is an exploded view of the embodiment of  FIG. 4 , with like structure indicated by like numerals. The inlet fitting assembly  14  forms no part of the present invention, but preferably has a bellows type inlet pressure attenuator such as described in the priority patent application. The inlet valve assembly  18  may be of any conventional type, preferably solenoid controlled. Additionally to the structure previously described with respect to  FIGS. 1-4 ,  FIG. 5  shows an overpressure check valve assembly  100 . The lip seal  50  at the outer end of the plunger is shown separated from its retainer  102 . It is well within the ordinary skill in the art to select an appropriate check valve assembly between the pumping chamber  28  and the discharge fitting  30 . In the version shown in  FIGS. 2 and 5 , a spring  104  has a cap  106  and a seat  108 , aligned with ball  110  and another seat  112 . Also shown is another O-ring  114  for placement in a groove on the neck of the housing, where the housing is mounted to the engine. 
     While preferred embodiments have been set forth for purposes of illustration, the foregoing description should not be deemed a limitation of the disclosure 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 disclosure.