Abstract:
A cryogenic hydraulic reciprocating piston pump includes a casing which defines a piston chamber. The sidewall of the piston chamber includes a retraction spill port as well as a pumping spill port. At the end of a retraction stroke, a retraction spill passageway that extends through the piston becomes aligned with the retraction spill port and fluid is communicated from the pressurized side of the piston to the unpressurized side of the piston to stop the retraction stroke before the piston “bottoms out”. Similarly, at the end of a pumping stroke, a pumping spill passageway that extends through the piston becomes aligned with the pumping spill port which provides communication between the pressurized side of the piston and the unpressurized side of the piston thereby stopping movement of the piston before it “bottoms out”.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to hydraulically controlled cryogenic pumps for supplying a cryogenic fluid, such as a cryogenically stored fuel for an internal combustion engine. 
       BACKGROUND 
       [0002]    Natural gas has been used as a fuel for internal combustion engines, primarily because it produces less pollution than diesel or gasoline. Previously, natural gas was introduced into the cylinders through the intake manifold, mixed with the intake air and fed into the cylinders at relatively low pressures. The fuel supply system for a natural gas powered engine is relatively simple. The natural gas is held in and supplied from a tank with a working pressure just above the engine inlet pressure, or from compressed natural gas cylinders through regulators that reduce the pressure to the engine inlet pressure. 
         [0003]    Compressed natural gas (CNG) is commonly stored at ambient temperatures at pressures up to 3600 psig (24,925 kPa), and may be unsuitable for many conventional trucks and buses due to the limited operating range and the heavy weight of the storage tanks. On the other hand, liquefied natural gas (LNG) is normally stored at temperatures of between about −240° F. and −175° F. (−150° C. and −115° C.) and at pressures of between about 15 and 200 psig (204 and 1477 kPa) in a cryogenic tank, providing an energy density of about four times that of CNG. 
         [0004]    However, better efficiency and emissions can be achieved if the natural gas is injected directly into the engine cylinders under high pressure at the end of the compression stroke of the piston. This requires a fuel supply system that can deliver the natural gas at a pressure of about 3000 psig (20,684 kPa) and above. This makes it impossible to deliver the fuel directly from a conventional LNG tank because it is impractical and uneconomical to build an LNG tank with such a high operating pressure. Equally, it is impossible to deliver the natural gas fuel directly from a conventional CNG tank as the pressure in such a tank is lower than the injection pressure as soon as a small amount of fuel has been withdrawn from the CNG tank. Therefore, in both cases, a booster pump is required to boost the pressure from storage pressure to injection pressure. 
         [0005]    Booster pumps in the form of high pressure cryogenic pumps are known, but it has proven difficult to adapt these pumps to the size and demand of a vehicle pump. In general, cryogenic pumps should have a positive suction pressure. It has therefore been common practice to place the pump directly in the LNG so that the head of the LNG will supply the desired pressure. The problem with this approach is that it introduces a large heat leak into the LNG storage tank. Some designs place the pump outside the storage tank and have reduced the required suction pressure by using a large first stage suction chamber. The excess LNG which is drawn into such a chamber is returned to the LNG tank and again, additional heat is introduced into the LNG, which is undesirable. 
         [0006]    Conventional cryogenic pumps are typically centrifugal pumps, which are placed either in the liquid inside the storage tank, or below the storage tank in a separate chamber with a large suction line leading from the tank, with both the pump and suction line being well insulated. Because a cryogenic liquid is at its boiling temperature when stored, heat is leaked into the suction line and a reduction in pressure will cause vapor to be formed. Thus, if the centrifugal pump is placed outside the tank, vapor is formed and the vapor will cause the pump to cavitate and the flow to stop. Consequently, cryogenic pumps of the centrifugal type require a positive feed pressure to prevent or reduce the tendency to cavitation of the pump. Also, centrifugal pumps cannot easily generate high discharge pressures to properly inject fuel directly into the engine cylinder. 
         [0007]    Reciprocating piston pumps have been used for pumping LNG, but such pumps also require a positive feed pressure to reduce efficiency losses that can arise with a relatively high speed piston pump. Such pumps may have a single chamber in which an induction stroke is followed by a discharge stroke, and thus the inlet flow will be stopped half of the time while the piston executes the discharge stroke. U.S. Pat. No. 6,898,940 discloses a dual chamber reciprocating pump that avoids this issue. 
         [0008]    The reciprocating piston cryogenic pump of U.S. Pat. No. 6,898,940 is hydraulically actuated. During the compression phase, there is a desire to keep the piston from bottoming out and there is a need to know when to begin the retraction of the piston. One conventional solution is to sense the increase in the hydraulic system pressure as a signal that the end of the compression stroke has been reached and that the retraction stroke should be commenced. However, this solution may still result in bottoming out of the piston at high hydraulic pressures. Another approach uses an integration of the estimated piston velocity to indicate when the end of the compression stroke has been reached. However, this approach is not optimum if there are errors in volumetric efficiency (i.e., leakage) or errors in the hydraulic pressure, gas pressure or consumption measurements. Yet another approach involves placing a position sensor to indicate the end of the compression stroke. However, this design is not robust and will not prevent bottoming out of the piston if there is a failure of the position sensor. 
         [0009]    Thus, improved hydraulically activated cryogenic pumps for delivering LNG to internal combustion engines are needed. 
       SUMMARY 
       [0010]    In one aspect, a pumping system is disclosed. The pumping system may include a casing that may include a retraction end and a pumping end with a sidewall disposed between the retraction and pumping ends. The retraction and pumping ends and the sidewall may define a piston chamber. The piston chamber may accommodate a piston. The sidewall may include a retraction spill port that extends into the sidewall and a pumping spill port that also extends into the sidewall. The casing may include a first hydraulic passageway disposed between a retraction spill port and the retraction end of the casing and that is in communication with a hydraulic fluid reservoir. The casing may further include a second hydraulic passageway disposed between the pumping spill port and the pumping end of the casing and that is in communication with the hydraulic fluid reservoir. The piston may include a retraction spill passage that provides communication from a pumping portion of the piston chamber, that is disposed between the piston and the pumping end of the casing, and the retraction spill port. The piston may further include a pumping spill passage that provides communication from a retraction portion of the piston chamber, that is disposed between the piston and the retraction end of the casing, and the pumping spill port. 
         [0011]    In yet another aspect, a hydraulic reciprocating piston pump is disclosed that may include a casing that may include a retraction end and a pumping end with a sidewall disposed therebetween. The retraction and pumping ends and the sidewall may define a piston chamber. The piston chamber may accommodate a piston. The sidewall may include a retraction spill port that extends into the sidewall and a pumping spill port that also extends into the sidewall. The casing may include a first hydraulic passageway disposed between the retraction spill port and the retraction end of the casing. The casing may also include a second hydraulic passageway disposed between the pumping spill port and the pumping end of the casing. The piston may include retraction spill passage that provides communication from a pumping portion of the piston chamber, that is disposed between the piston and the pumping end of the casing, and the retraction spill port. The piston may also include a pumping spill passage that provides communication from a retraction portion of the piston chamber, that is disposed between the piston and the retraction end of the casing, and the pumping spill port. 
         [0012]    In yet another aspect, a machine is disclosed which may include an engine coupled to a pump. The pump may be in communication with a hydraulic fluid reservoir. The pump and hydraulic fluid reservoir may be in communication with a direction control valve. The pump may include a casing that may include a retraction end and a pumping end with a sidewall disposed therebetween. The retraction and pumping ends and the sidewall may define a piston chamber. The piston chamber may accommodate a piston that is connected to a rod that sealably passes through the pumping end of the casing and that is slidably received in a rod chamber. The rod chamber may include an outlet that is in communication with a fuel line that is in communication with the engine. The sidewall of the casing may include a retraction spill port that extends into the sidewall and a pumping spill port that also extends into the sidewall. The casing may include a first hydraulic passageway disposed between the retraction spill port and the retraction end of the casing and that is in communication with the directional control valve. The casing may also include a second hydraulic passageway disposed between the pumping spill port and the pumping end of the casing and that is in communication with the directional control valve. The piston may include a retraction spill passage that provides communication from a pumping portion of the piston chamber, that is disposed between the piston and the pumping end of the casing, and the retraction spill port. The piston may also include a pumping spill passage that provides communication from a retraction portion of the piston chamber, that is disposed between the piston and the retraction end of the casing, and the pumping spill port. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic illustration of a disclosed pump and a disclosed pumping system as incorporated into a disclosed machine. 
           [0014]      FIG. 2  is a sectional view of a disclosed pump in the middle of a-pumping stroke. 
           [0015]      FIG. 3  is a sectional view of the pump shown in  FIG. 2  at the end of a pumping stroke. 
           [0016]      FIG. 4  is a sectional view of the pump shown in  FIGS. 2-3  at the start of the retraction stroke. 
           [0017]      FIG. 5  is a sectional view of the pump shown in  FIGS. 2-4  in the middle of the retraction stroke. 
           [0018]      FIG. 6  is a sectional view of the pump shown in  FIGS. 2-5  at the end of the retraction stroke. 
           [0019]      FIG. 7  is a sectional view of the pump shown in  FIGS. 2-6  at the start of the pumping stroke. 
       
    
    
     DESCRIPTION 
       [0020]      FIG. 1  partially illustrates a machine  10  that may include an engine  11  that may be coupled to a hydraulic pump  12  via a drive shaft  13  or other suitable coupling element. The hydraulic pump  12  receives hydraulic fluid from the hydraulic fluid reservoir  14  via the conduit  15 . The pump  12  may then deliver fluid to a directional control valve  16  via the conduit  17 . A controller  18  may be utilized to control the pump  12  and the actuator  21  of the directional control valve  16 . The controller  18  may also be linked to one or more pressure sensors including the pressure sensor  22  that is in communication with the conduit  17 . The controller  18  may also be linked to the pressure sensor  23  which is in communication with the return conduit  24 . The return conduit  24  provides communication between the directional control valve  16  and the hydraulic reservoir  14 . The controller  18  may also be linked to the pressure sensor  25  that may measure the pressure within the accumulator  26 . 
         [0021]    The directional control valve  16  controls the flow of hydraulic fluid to and from the reciprocating piston pump  27 . As shown in  FIG. 1 , the pump  27  is in the middle of a retraction stroke as the pump  12  delivers fluid through the conduit  17 , through the directional control valve  16  and to the conduit  28  which leads to the hydraulic passageway  29 . When shifted upward in the orientation of  FIG. 1 , the directional control valve  16  connects the conduit  17  with the conduit  31  which leads to the hydraulic passageway  32 . When pressure is being delivered through the conduit  31  and through the hydraulic passageway  32  and into the piston chamber  33 , pressure in the conduit  17  may increase thereby causing a pressure increase in the connecting conduit  34  which causes the normally closed pressure release valve  35  to open thereby providing communication between the hydraulic reservoir  14  and the conduit  17  via the conduits  36 ,  34  as shown in  FIG. 1 . 
         [0022]    The pump  27  may be used to deliver a cryogenic fluid, such as LNG from the tank  37  through the fuel line  38  and vaporizer  41  to the accumulator  26 . As the accumulator  26  is charged and the pressure reaches an appropriate input pressure for the engine  11 , LNG flows through the input line  43  to the engine  11 . Energy may be supplied to the vaporizer  41  by engine coolant that flows from and to the engine  11  via the conduits  44 ,  45 . As will be shown below, only one of the pressure sensors  22 ,  23  is necessary to provide the information needed to effectively shift the directional control valve  16 . 
         [0023]    Still referring to  FIG. 1  as well as  FIGS. 2-7 , the pump  27  may include a casing  46  that may include a retraction end  47  and a pumping end  48 . A sidewall  51  may be disposed between the retraction end  47  and pumping end  48 . The retraction end  47 , pumping end  48  and sidewall  51  may define the piston chamber  33  which, for descriptive purposes, may include a retraction portion  52  and a pumping portion  53 . 
         [0024]    The piston chamber  33  accommodates the piston  54 . The piston chamber  33  may also include a retraction spill port  55  that may be annular as shown in  FIGS. 1-7  and a pumping spill port  56  that may also be annular as shown. Further, the piston  54  may include two spill passages including a retraction spill passage  57  that provides communication between the pumping portion  53  of the piston chamber  33  and the retraction spill port  55 . Further, the piston  54  may include a pumping spill passage  58  that may provide communication between the retraction portion  52  of the piston chamber  33  and the pumping spill port  56 . As best seen in  FIGS. 2-7 , the retraction spill passage  57  may include a check valve  61  so that fluid may flow in only one direction through the retraction spill passage  57 , that is from the pumping portion  53  of the piston chamber  33  to the retraction spill port  55  as best seen in  FIG. 6 , which, as explained below, presents the end of a retraction stroke. Similarly, the pumping spill passage  58  may also include a check valve  62  that permits flow only from the retraction portion  52  of the piston chamber  33  to the pumping spill port  56 , which signals the end of a pumping stroke as shown in  FIG. 3 . 
         [0025]    Turning to the sequence illustrated in  FIGS. 2-7 ,  FIG. 2  illustrates the piston  58  in the middle of the pumping stroke as the piston  54  is moving in the direction of the arrow  63  or downward in the orientation of  FIG. 2  towards the pumping portion  53  of the piston chamber  33 . The piston  58  is sliding along the sidewall  51  between the retraction spill port  55  and the pumping spill port  56 . The piston  54  may be connected to a rod  64  that passes through the pumping end  48  of the casing  46  and into a rod chamber  65 . Movement of the rod  64  through the rod chamber  65  applies pressure to the fuel line  38  which may include check valves  66 ,  67  to ensure flow of the cryogenic fluid or LNG in the direction of the arrow  68 . During the pumping stroke, the directional control valve  65  is shifted upward from its position shown in  FIG. 1  so that the pump  12  and conduit  17  are in communication with the conduit  31  and hydraulic passageway  32  thereby providing pressurized fluid to the retraction portion  52  of the piston chamber  33  as indicated by the arrow  77 . The hydraulic passageway  29  serves as a return line as fluid flows from the pumping portion  53  of the piston chamber  33  through the hydraulic passageway  29  in the direction of the arrow  78 , through the conduit  28  to the return conduit  24  before entering the hydraulic reservoir  14 . It will also be noted that the rod  64  and rod chamber  65  may be disposed within a block  71  through which the fuel line  38  passes. 
         [0026]    Turning to  FIG. 3 , the piston  54  is shown at the end of its pumping stroke as the pumping spill passageway  58  is in communication with the pumping spill port  56  thereby causing fluid to flow from the retraction portion  52  of the piston chamber  33  past the check valve  62  and in the direction of the arrow  72 . The communication between the retraction portion  52  of the piston chamber  33  and the pumping portion  53  of the piston chamber  33  reduces the pressure in the retraction portion  52  of the piston chamber  33  thereby causing the piston  54  and rod  64  to slow down and stop its movement in the direction of the arrow  63  shown in  FIG. 2 . Thus,  FIG. 3  illustrates the end of a pumping stroke. In an embodiment, the reduction in pressure in the retraction portion  52  of the piston chamber  33  may be detected by the pressure sensor  22  and communicated to the controller  18 . The controller  18  may then switch the directional control valve  16  to the retraction position shown in  FIG. 1  (the pumping position of the directional control valve  16  is not shown in  FIG. 1 ). 
         [0027]    In contrast,  FIG. 4  illustrates the pump  27  at the beginning of its retraction stroke. The controller has switched the directional control valve  16  to the position shown in  FIG. 1  and fluid is being delivered through the conduit  28  ( FIG. 1 ) through the hydraulic passageway  29  in the direction of the arrow  75  to the pumping portion  53  of the piston chamber  33 . Thus, pressure is building within the pumping portion  53  of the piston chamber  33  which, as shown in  FIG. 5 , results in the rod  64  and piston  54  moving in the direction of the arrow  73 . As shown in  FIGS. 4-5 , the check valve  62  prevents fluid from flowing from the pumping portion  53  of the chamber  33  and through the pumping spill passageway  58  and into the retraction portion  52  of the chamber  33 . Thus, as shown in  FIG. 5 , with the piston  54  and rod  64  moving in the direction of the arrow  73 , the pump  27  is in the middle of a retraction stroke. During a pumping stroke, fluid is exiting the hydraulic passageway  32  in the direction of the arrow  74  and fluid is being delivered to the hydraulic passageway  29  in the direction of the arrow  75 . Thus, the pumping portion  53  of the chamber  33  is pressurized which causes the piston  54  to move in the direction of the arrow  73 . Further, movement of the rod  64  within the rod chamber  65  and away from the fuel line  38  provides suction in the fuel line  38  thereby causing the LNG to continue to flow in the direction of the arrow  76  past the check valves  66 ,  67 . 
         [0028]    Turning to  FIG. 6 , the piston  54  has reached the end of its retraction stroke as the retraction spill passageway  57  is in communication with the retraction spill port  55  thereby providing communication between the pumping portion  53  of the chamber  33  and the retraction portion  52  of the chamber  33 . As a result, fluid flows in the direction of the arrow  81  and the pressure in the pumping portion  53  of the chamber  33  decreases and this decrease in pressure is sensed by the pressure sensor  22  and communicated to the controller  18 . With the piston  54  at the end of its retraction stroke, the controller  18  sends a signal to the actuator  21  to shift the directional control valve  16  back to the pumping position (not shown in  FIG. 1 ) so that hydraulic fluid flows into the retraction portion  52  of the chamber  33  in the direction of the arrow  77  and fluid begins to exit the pumping portion  53  of the chamber  33  through the hydraulic passageway  29  in the direction of the arrow  78 . 
         [0029]    Thus, as shown in  FIGS. 2-7 , the piston  54  never “bottoms out” or reaches the retraction end  47  of the casing  46  or the pumping end  48  of the casing  46 . The combination of the retraction spill port  55 , retraction spill passageway  57 , pumping spill port  56  and pumping spill passageway  58  prevents these occurrences. Thus, at the end of the pumping stroke as shown in  FIG. 3 , the reduction and pressure in the retraction portion  52  of the chamber  33  may be sensed by the pressure sensor  22 . Use of the pressure sensor  22  in the conduit  17  may be preferable to using the pressure sensor  23  in the return conduit  24  at high hydraulic pressures. Further, the pressure sensor  22  is located outside of the pump  27  and therefore no position sensor is required to be placed within the piston chamber  33 . Locating the sensors  22  or  23  outside of the piston chamber  33  provides for a more robust and more reliable design. Similarly, at the end of a retraction stroke as shown in  FIG. 6 , the reduction in pressure in the pumping portion  53  of the piston chamber  33  may be detected by the sensor  22  and no position sensor within the piston chamber  33  is necessary. 
       INDUSTRIAL APPLICABILITY 
       [0030]    A cryogenic pump  27  is disclosed that may be part of a machine  10  and an overall pumping system  81  which prevents the piston  54  from bottoming out at either the retraction end  47  of the pump casing  46  or at the pumping end  48  of the pump casing  46 . Further, position sensors within the piston chamber  33  are not required and, the use of the retraction spill port  55 , retraction spill passageway  57 , pumping spill port  56  and pumping spill passageway  58  enables a reduction in pressure to be detected by the sensor  22  and such a detected reduction in pressure causes the controller  18  to shift the directional control valve  16  accordingly. Thus, an improved cryogenic pump  27 , an improved cryogenic pumping system  81  and an improved machine  10  incorporating the same are disclosed.