Abstract:
A high pressure pumping apparatus for of an internal combustion engine includes a pump barrel having a bore with a central axis, and a two-part pumping plunger provided in the bore of the barrel. The two-part plunger includes first and second pumping plunger parts that are separate from one another and arranged substantially coaxial with the central axis of the barrel&#39;s bore. A first distal end portion of the first pumping plunger part abuts a first distal end portion of the second pumping plunger part, and a second distal end portion of the first pumping plunger part in part defines a pumping chamber. The high pressure pumping apparatus includes and a tappet assembly that is operably coupled to the second distal end portion of the second pumping plunger part for operably engaging a rotating camshaft, which causes the first and second plunger parts to move in reciprocal motion.

Description:
FIELD OF THE INVENTION 
       [0001]    An apparatus for pumping fluid is disclosed. 
       BACKGROUND 
       [0002]    Internal combustion engines having common-rail fuel delivery systems utilize high pressure fuel pumps to ensure adequate fuel pressure inside the rail at low engine speeds and to provide good air and fuel mixture at high engine speeds. To meter and pressurize fuel, a high pressure fuel pump typically has a single-piece pumping plunger reciprocating within a bore of a barrel in the pump&#39;s body. 
       SUMMARY 
       [0003]    An improved high pressure fuel pumping apparatus for an internal combustion engine exhibiting increased efficiency and reliability is provided by the invention. 
         [0004]    More particularly, embodiments consistent with the invention relate to a high pressure pumping apparatus including a pump barrel having a bore with a central axis. A pumping plunger is provided in the bore of the barrel and includes a first pumping plunger part and a second plunger part. The first and second pumping plunger parts are separate from one another and arranged substantially coaxial with the central axis of the bore. A first distal end portion of the first pumping plunger part abuts a first distal end portion of the second pumping plunger part, and a pumping chamber is defined in part by a second distal end portion of the first pumping plunger part. The high pressure pumping apparatus includes and a tappet assembly that is operably coupled to a second distal end portion of the second pumping plunger part for operably engaging a rotating camshaft, which causes the first and second pumping plunger parts to move in reciprocal motion. 
         [0005]    In accordance with another aspect consistent with the invention, an embodiments of a high pressure fuel pump comprises a pump barrel including a cylindrically shaped bore, a pumping chamber at one end of the bore, and a first cylindrically shaped plunger part positioned in the bore and including a side surface defining a movable surface of the pumping chamber. A second cylindrically shaped plunger part is positioned in the bore and has a diameter smaller than a diameter of the first plunger part, and is adapted to be reciprocally driven at a first end and to drive the first plunger part in the bore at a second end. 
         [0006]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and exemplary only and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention that together with the description serve to explain the principles of the invention. In the drawings: 
           [0008]      FIG. 1  is a cross-sectional view of a portion of a high pressure fuel assembly in accordance with an exemplary embodiment. 
           [0009]      FIG. 2  is an enlarged cross-sectional view of the pump barrel assembly of  FIG. 1  in accordance with an exemplary embodiment. 
           [0010]      FIG. 3  is a graph depicting fuel delivery performance at constant fuel temperature of 40 C for exemplary two-piece plunger pump assembly apparatus embodiments and a standard single-piece plunger pump configuration operating over different engine speeds and pumping pressures. 
           [0011]      FIG. 4  is a graph depicting fuel delivery performance at constant fuel temperature of 70 C for exemplary two-piece plunger pump assembly apparatus embodiments and a standard single-piece plunger pump configuration operating over different engine speeds and pumping pressures. 
           [0012]      FIG. 5  is a graph depicting fuel delivery performance operating at constant 2600 bar over different engine speeds for exemplary two-piece plunger pump assembly apparatus embodiments and a standard pump configuration, where the fuel temperature of the standard single-piece plunger pump configuration and one of the two-piece plunger pump assembly apparatuses is 40 C, and the remaining two-piece plunger pump assembly apparatus is cooled. 
           [0013]      FIG. 6  is a bar graph depicting fuel delivery performance and volumetric efficiency of exemplary two-piece plunger pump assembly apparatus embodiments and a standard pump configuration operated at 1000 RPM, where the fuel temperature of the standard configuration pump and one of the two-piece plunger pump assembly apparatuses is 40 C, and the remaining two-piece plunger pump assembly apparatus is cooled. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The various aspects are described hereafter in greater detail in connection with a number of exemplary embodiments to facilitate an understanding of the invention. However, the invention should not be construed as being limited to these embodiments. Rather, these embodiments are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
         [0015]      FIG. 1  shows a cross-section view of a portion of a high pressure fuel pump assembly  100  according to an exemplary embodiment. The high pressure fuel pump assembly  100  includes a pump housing  102  provided with bores  104  and  106 , and pump units  108  and  110  provided in the bores  104  and  106 . The fuel pump assembly  100  has a pump head  112  mounted on pump housing  102  to cover and seal the bores  104  and  106 . A rotatably mounted camshaft  124  extends through pump housing  102  and functions to operate pump units  108  and  110  via tappet assemblies  130  and  132 . It will be recognized that because  FIG. 1  depicts a partial cross-section, only portions of some parts, such as the pump housing  102 , pump head  112  and camshaft  124 , are shown. Because the pump units  108  and  110  of fuel pump assembly  100  are structurally the same, only pump unit  108  will be described hereinafter. The camshaft  124  can be part of a drive system including the rotating cam and tappet assemblies  130  and  132 , located in a separate mechanical compartment containing lubricating oil, such as disclosed in U.S. Pat. Nos. 5,775,203 and 5,983,863, each of which is hereby incorporated by reference in their entirety. 
         [0016]    The pump unit  108  includes a pump barrel  136  having a barrel bore  140  in which a two-piece, or “dual” plunger assembly including a lower pumping plunger part  142   a  and an upper pumping plunger part  142   b  are provided substantially coaxial with the barrel bore  140 . The lower pumping plunger part  142   a  and the upper pumping plunger part  142   b  are provided as separate pieces in the barrel bore  140 . “Separate”, as used herein with respect to the upper and lower pumping plunger parts  142   a / 142   b,  means the upper pumping plunger part  142   b  is not integral with or physically connected to the lower pumping plunger part  142   a.  Thus, the upper pumping plunger part  142   b  “floats” in the barrel bore  140  and its movement is a result of forces from pressure differential and/or the lower pumping plunger  142   a  acting on it. During operation of the pump assembly  100 , an upper surface of the plunger part  142   a  can contact a lower surface of the plunger part  142   b  at an interface  143  as they reciprocate in the barrel bore  140 . Further, it is to be understood that the terms “upper” and “lower,” as used herein, refer to the orientation exemplary pump assemblies shown in the figures. In other exemplary embodiments consistent with the invention, the orientation of two-piece plunger parts may be flipped relative to the depicted orientations, or both plunger parts may reside on a same vertical plane, for example. 
         [0017]    Returning to  FIG. 1 , the pumping plunger parts  142   a / 142   b  have respective distal end portions positioned adjacent one another and move together in a reciprocal manner as they are driven by the tappet assembly  130 . The tappet assembly  130  is biased toward the camshaft  126  by a spring  146  positioned in the bore  104  of the housing  102 . The pump barrel  136  can include one or more mechanism, such as groove  147  that communicates with a drain passage  148  that permits low pressure escape for fuel leakage from the plunger parts  142   a / 142   b.  At the top of the pump barrel  136 , a pumping chamber  144  is defined in part by a portion of the barrel bore  140  and a distal end portion of the upper pumping plunger part  142   b.  Because the pumping plunger part  142   b  reciprocates within the bore  140 , the pumping chamber  144  varies in size when the upper pumping plunger part  142   b  operates in a pumping stroke to decrease the size of pumping chamber  144  while pressurizing fuel and in a retraction stroke to increase the size of the chamber  144  while drawing fuel into the chamber  144 . 
         [0018]    The tappet assembly  130  includes a tappet housing  150  adapted for reciprocal motion along tappet guiding surfaces provided in the pump housing by the bore  104 . The tappet assembly  130  includes a cam roller  152  rotatably secured to housing  150  by a pin  153  extending through a bore  154  in tappet housing  150 . Tappet housing  150  also includes an annular skirt  155  extending toward pump head  112  to form a recess  138  having an inner support surface  139 . 
         [0019]    The high pressure fuel pump unit  108  further includes a force transmitting device  156  provided on the support surface  139  between tappet assembly  130  and lower plunger part  142   a  for transmitting axial loads to lower plunger part  142   a.  Force transmitting device  156  includes a spring seating surface  158  for receiving the outer end of the spring  146  and a lateral retaining surface  160  that prevents lateral movement of the spring  146 . The force transmitting device  156  includes a supporting end  162 , which abuts, attaches, or otherwise couples to a distal end portion of the lower plunger part  142   a.  The lower plunger part  142   a  can float in the barrel bore  140  such that it is not physically connected to the force transmitting device  156 , its movement in the bore resulting from forces acting on it from the force transmitting device  156  and/or the upper pumping plunger  142   b.    
         [0020]    The high pressure fuel pump assembly  100  can include a lubricating oil circuit that includes various lubricating transfer passages  170 ,  172 , and  174  provided in the components of tappet assembly  130 . In addition, lubricating oil circuit can include passages  176 ,  178  in the force transmitting device  156 . 
         [0021]    During operation, the spring  146  is positioned in abutment against the force transmitting device  156  at one end and the barrel  136  at its other end. The spring  146  biases tappet assembly  130  via the force transmitting device  156  into engagement with the camshaft  124  at an opposite end. As the camshaft  124  rotates, a lobe  126  of the camshaft  124  displaces the tappet assembly  130  within the bore  104 , and thus also displaces the transmitting device  156 , the lower plunger part  142   a,  and the upper plunger part  142   b.    
         [0022]    To substantially improve pumping efficiency, embodiments include separate pumping plunger to barrel bore clearance requirements for the coaxial pumping plunger parts. Referring to  FIG. 2 , the barrel bore  140  can be cylindrical with a diameter d 1  and house cylindrical lower pumping plunger part  142   a  and a cylindrical upper pumping plunger part  142   b.  The lower pumping plunger part  142   a  can be shaped with a constant diameter d 2  to provide clearance, i.e., d 1 -d 2 , between its outer surface and the surface of the bore  140  that is sufficient to minimize the likelihood of sticking and seizure of the lower pumping plunger part  142   a  in the barrel bore  140 . The upper pumping plunger  142   b  can be shaped with a constant diameter d 3  to provide clearance d 1 -d 3  between its outer surface and the barrel bore  140 , which is smaller than the bore-to-plunger clearance of lower pumping plunger  142   a  to minimize fuel leakage. For example, an embodiment can have a clearance d 1 -d 2  for the lower pumping plunger part  142   a  in a range of about 4 to 6 μm, where the particular value in the range can be selected based on a required common rail pump pressure and robustness to sticking and seizure. The upper pumping plunger part  142   b  can have tighter clearance with the barrel bore  140 , d 1 -d 3 , because fuel pumping pressure acts on the upper end face of the upper plunger part  142   b  and the barrel bore  140  at the pumping chamber  144 , and dilates an upper area of the barrel bore  140  where the upper pumping plunger part  142   b  reciprocates. A tighter bore-to-plunger clearance for the upper pumping plunger part  142   b,  in turn, reduces the amount of fuel leakage from the pumping chamber  144  to provide improved high pressure efficiency and reliability. 
         [0023]    The two-piece plunger assembly comprising two pumping plungers  142   a / 142   b  can be designed to optimally address issues specific to each portion of the seal length of the barrel bore. As shown in  FIG. 2 , the diameter d 3  of the upper pumping plunger part  142   b  is constant along its entire length L 1 . This provides a substantially constant close fit along the length L 1  from one end to the other of the pumping plunger part  142   b.  In addition, the length L 1  of the pumping plunger part  142   b  can be set to extend at least as long as dilation of an upper portion of the barrel bore  140  during a pressurizing stroke of the pump assembly  100 , such as along a substantial portion of the seal length SL of the barrel bore  140 . For example, the upper pumping plunger length L 1  shown in  FIG. 2  extends along the majority of the seal length SL above low pressure escape groove  147 . Additionally, the lower pumping plunger length L 2  can extend along the bore seal length SL continuously from the lower end of the upper pumping plunger part  142   b  to the lower end of the barrel bore  140 . 
         [0024]    In an exemplary embodiment, a plunger-to-bore clearance d 1 -d 3  of the top pumping plunger part  142   b  can be one half to one quarter of the clearance d 1 -d 2  of the lower pumping plunger part  142   a.  Thus, for an exemplary embodiment in which a lower pumping plunger part  142   a  has a clearance of within a range of about 4 to 6 μm, the upper pumping plunger part  142   b  can have a clearance between about 2.0 to 3.0 μm, or between about 1.0 to 1.5 μm for more efficient operation. The limit to which a clearance can be set for the upper plunger can be based on, for example, machining limitations, material limitations, cost, and/or pressure required for a particular fuel system application. 
         [0025]    The two piece plunger can allow for a tighter clearance on the upper pumping plunger part  142   b  only, which provides an efficiency lever because of reduced high pressure leakage during pumping. The pressure developed on the upstroke of the two-piece plunger will open (i.e., dilate) an upper portion of the barrel bore  140  during pressurization unlike a lower portion of the barrel bore  140 , so a tighter the clearance of the upper plunger part  142   b  and the barrel bore  140  provides better pumping efficiency. Because dilation is related to the pressure in the bore, above the pumping plunger part  142   b  would have full dilation because it would have full pressure. The pressure is assumed to drop along the match fit to zero in the drain/leakage low pressure groove  147 , and the majority of dilation has been observed in about the first ⅓ rd  of the match fit clearance. Efficiency improvement can be realized with any upper pumping plunger part match being less than the lower pumping plunger part (or single plunger) clearance. Tight clearances, such as clearances less than 1.0 μm, can be applied with improvements in bore and plunger manufacturing. Hence, the clearance of the pumping plunger part  142   b  could be anything less than the clearance lower pumping plunger part  142   a,  and can approach zero clearance with increasing efficiency to an extent allowed by manufacturing capability. 
         [0026]    The length L 1  of the upper pumping plunger part  142   b  can be related to an upper bore length L 3 , which is shown in  FIG. 2  as a distance measured from the low pressure drain/leakage groove  147  to the top of the upper pumping plunger part  142   b  when the plunger part  142   b  is at top dead center (TDC) in barrel bore  140 , and to the stroke of the reciprocating motion of the tappet assembly  130 . This relation involves configuring L 3  and L 1  such that L 3  is less than or equal to the combined length of L 1  and the stroke of the tappet assembly  130 . This ensures that during the retraction and pumping stroke of the tappet assembly  130 , the groove  147  communicates with the area of the pumping plunger parts  142   a / 142   b  including the interface  143 . As the interface  143  passes the groove  147 , any pressure buildup present at the interface area  143  is released to low pressure to prevent holding of pressure between the plungers during the pumping stroke motion back to zero position (TDC). The length of the barrel bore  140  below the upper pumping plunger part  142   b  could be as short as practically possible for minimizing dilution of fuel from above into the oil, and the length L 2  of the lower pumping plunger  142   a  can be as long as a pump design and engine space will allow. 
         [0027]    Some conventional plunger assembly designs have attempted to reduce leakage and improve efficiency by using a one-piece plunger assembly having a particular profile. For example, one conventional fuel pump includes a single-piece plunger having a gradual taper along the length of the plunger. However, this tapered profile allows a significant amount of fuel leakage compared with the constant tight fit of the upper pumping plunger part  142   b  of the two-piece plunger assembly  142   a / 142   b.  Another conventional one-piece plunger assembly utilizes a profile having an upper pumping section and a lower driving section having different constant diameters. In this type of plunger, the diameter of the lower driving section is often significantly smaller relative to the diameter of the upper pumping section. However, the single-piece two-sectioned plunger is less efficient than the two-piece plunger assembly  142   a / 142   b  because the lower driving section typically does not substantially contribute to sealing a pump bore along a seal length of the bore. Additionally, the single-piece  plunger more susceptible to sticking within the pump&#39;s barrel bore compared with fuel pump embodiments including a two piece plunger. By contrast, the fuel pump assembly embodiments described herein significantly reduce high pressure leakage while maintaining continuous operation. 
         [0028]    During a pumping operation, the lower pumping plunger part  142   a  moves in a pumping stroke as the tappet assembly  130  and the force transmitting part  156  are displaced by the cam lobe  126  in a direction toward the head  112 . The upper plunger part  142   b  can float in the barrel bore  140 , but makes contact with or abuts the lower pumping plunger part  142   a  during the upstroke of the tappet assembly  130  and force transmitting part  156 . The upper plunger part  142   b  compresses the fuel volume in the pumping chamber  144  to a prescribed pressure before being released to a common rail (not shown). For example, when the pressure in the pumping chamber  144  reaches a prescribed pressure level, an outlet check valve (not shown) connected to the pumping chamber  144  can open to provide the pressurized fuel to the common rail. 
         [0029]    On the retraction stroke of the tappet assembly  130  and force transmitting part  156 , which takes place just after cam lobe  126  has reached maximum lift, low pressure fuel from a fuel reservoir, for example fuel fed from a fuel tank by a low pressure pump (not shown), enters the pumping chamber  144  while the outlet to the high pressure rail is blocked. For example, a check valve of an outlet leading to the common rail (not shown) can remain closed when the pumping chamber  144  is at low pressure while another check valve opens to supply fuel from the low pressure pump. While fuel is entering the pumping chamber  144 , the floating upper pumping plunger part  142   b  is forced downward toward the retreating lower pumping plunger part  142   a  because pressure in a region between an upper face of lower pumping plunger part  142   a  and an opposing lower face of upper pumping plunger part  142   b  is lower than pressure in the pumping chamber  144 . 
         [0030]      FIGS. 3 and 4  each include a graph showing fuel delivery rate versus engine RPM for a two-piece plunger pump and a standard single-piece plunger pump operating at various fueling pressures. These data are from a pump built with a single plunger in barrel (i.e., the standard arrangement), and then the single barrel was removed and dual plungers installed in the same barrels and rerun to show the efficiency improvement. So the pump barrels had been processed for both a single plunger and dual (two-piece) plungers so the only parts changed are the plungers for a clear back-to-back comparison. 
         [0031]    The standard plunger pump had a 5.3 μm plunger-to-bore clearance for its single-piece plunger, and the two-piece plunger pump had a clearance of 5.3 μm for the lower plunger part and a clearance of 2.2 μm for the upper plunger part of the coaxial arrangement. The data of  FIG. 3  was obtained by operating the two-piece plunger pump and standard single-piece plunger pump using fuel at a temperature of 40 C, and the data of  FIG. 4  relates to the same pumps operated using fuel at a temperature of 70 C. As can be seen, the two-piece plunger pumps achieved significant improvements in the amount of fuel delivered at pressures over 800 bar compared with a standard single-piece plunger pump operating in the same conditions. For instance,  FIG. 3  shows at least a 10% volumetric efficiency increase for a two-piece plunger pump over a standard single-piece plunger pump at engine speeds between 1000 and 1600 RPM.  FIG. 4  shows similar results obtained with warmer fuel, but overall volumetric efficiency was shown to decrease at the higher 70 C temperature.  FIGS. 3 and 4  also show that increases in volumetric efficiencies are less significant at 800 bar because leakage is less a factor at such lower pressures. 
         [0032]    Greater volumetric efficiencies can be obtained by cooling the two-piece plunger pump, for example, by cooling the barrel of the pump using a cooling fluid or providing a fuel cooling unit upstream from the pump.  FIG. 5  shows data of  FIG. 3  related to fuel delivery rate versus engine RPM for a two-piece plunger pump and the standard single-piece plunger pump delivering fuel at 2600 bar along with data related to a cooled two-piece plunger pump operating under the same pressure and engine speeds. Fuel was passed through a fluid circuit in the pump barrel to cool the barrel and other pump elements by removing heat from those pumping elements. As can be seen from  FIG. 5 , using a cooling circuit to remove heat from the two-piece plunger pump increased volumetric efficiency by about 20% or more from those achievable for the standard single-piece plunger pump supplied with 40 C temperature fuel at the inlet. A novel manner of cooling a pumping barrel and other pump elements using a cooling fuel flow is disclosed in copending U.S. patent application Ser. No. 12/398,570, filed Mar. 5, 2009, which is hereby incorporated by reference in its entirety. 
         [0033]      FIG. 6  is a graph depicting performance test results of exemplary two-piece plunger pump assemblies and a standard single-piece plunger pumping assembly for various pumping pressures at 1000 RPM. The clearances of the two-piece plunger parts and the barrel bore pump were 5.3 μm for the plunger part closest to the tappet assembly and 2.3 μm for the part closest to the pumping chamber. One two-piece plunger pumping assembly was operated using fuel at an inlet temperature of 40 C, and the pump was cooled for the other two-piece pumping assembly. The standard single-piece pump configuration used had a bore-to-plunger clearance of 5.3 μm and an inlet fuel temperature of 40 C. Volumetric efficiencies for a sweep volume of 293.1 PPH are depicted inside each of the bars for the respective pump. As can be seen from the results across pressures of 800, 2000, 2400 and 2600 bar, the two-piece plunger pumps outperformed the standard single-piece plunger pump configuration in fuel delivery in each instance, with the cooled two-piece pumping assembly achieving the best performance of the three tested configurations. Accordingly, a cooling unit or system can optionally be placed in the fuel supply upstream an inlet of the pump barrel, or the pump barrel and other pump elements can be cooled to provide greater volumetric efficiency. 
         [0034]    It will be appreciated that the embodiments described and shown herein may be modified in a number of ways. For instance, while the exemplary embodiments described above include an in-line arrangement of plural pumping units, other embodiments consistent with the invention can include more or less two-piece plunger pumps and/or arrange two-piece plunger pumps in another way, such as a radial arrangement driven by a ring cam. Additionally, the two-piece plunger pumps may be driven by any shaft driven by an internal combustion engine, such as a drive shaft or camshaft, although other mechanisms commonly employed to drive ancillary equipment in an internal combustion engine can be used, such as a belt drive. 
         [0035]    Although a limited number of embodiments is described herein, one of ordinary skill in the art will readily recognize that there could be variations to any of these embodiments and those variations would be within the scope of the appended claims. Thus, it will be apparent to those skilled in the art that various changes and modifications can be made to the high pressure two-piece plunger pump assembly described herein without departing from the scope of the appended claims and their equivalents.