Patent Application
20160298622
The present disclosure relates generally to a pump piston and, more particularly, to a piston having a variable diameter.
Gaseous fuel powered engines are common in many applications. For example, the engine of a locomotive can be powered by natural gas (or another gaseous fuel) alone, or by a mixture of natural gas and diesel fuel. Natural gas may be more abundant and, therefore, less expensive than diesel fuel. In addition, natural gas may burn cleaner in some applications.
Natural gas, when used in a mobile application, may be stored in a liquid state onboard the associated machine. This may require the natural gas to be stored at cold temperatures, typically about −100 to −162° C. The liquefied natural gas (LNG) may then be drawn from the tank by gravity and/or by a boost pump and directed to a high-pressure pump. The high-pressure pump further increases a pressure of the fuel and directs the fuel to the machine's engine. In some applications, the liquid fuel is gasified prior to injection into the engine and/or mixed with diesel fuel (or another fuel) before combustion.
One problem associated with high-pressure pumps involves reducing leakage of fuel past pistons of the pump. Although generally tight tolerances between the pistons and associated barrels can be maintained to reduce leakage, such tolerances can also increase friction between the pistons and barrels. This friction requires more energy to drive the pump. Pumps can also have seals between the pistons and barrels to help reduce leakage. The seals can wear over time, thereby reducing the lifespan of the pump.
One attempt to improve sealing around. a piston of a pump is disclosed in U.S. Pat. No. 4,813,342 (the '342 patent) that issued to Schneider et al, on Mar. 21, 1959. in particular, the '342 patent discloses a piston for a reciprocating pump that pressurizes cryogenic fluids. The piston has a core attached to a push rod of the pump. The core includes a shaft that has flanged ends and is surrounded by a sleeve between the flanged ends. Between the sleeve and each of the flanged ends of the shaft are seal rings and expanding members that have higher coefficients of thermal expansion than the sleeve. When the piston is cooled and the core shrinks axially, the flanged ends of the shaft are drawn into the expanding members, which push outwardly on the seal rings to create a seal between the piston and a barrel cylinder of the pump.
While the piston of the '342 patent may have reduced leakage, it may still exhibit a significant amount of friction. Further, the expanding members of the core may increasingly push the associated rings against the cylinder, which increases wear of the rings.
The disclosed piston is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.
in one aspect, the present disclosure is directed to a pump piston. The pump piston may include a body having an actuating end, a pressurizing end opposite the actuating end, and an outer diameter that is greater at the pressurizing end than at the actuating end, wherein the outer diameter varies between the pressurizing end and the actuating end without increasing to form an outer diameter profile.
In another aspect, the present disclosure is directed to a pump piston. The pump piston may include a body having an actuating end connectable to an actuator, and a pressurizing end opposite the actuating end. The pressurizing end may include an annular wall having a fixed end attached to the body, a free end opposite the fixed end, and a cavity having an opening disposed at the free end of the annular wall. The pressurizing end may further include a head attached to the body and disposed within the cavity, wherein the head occupies a majority of the cavity.
In yet another aspect, the present disclosure is directed to a pump. The pump may include at least one pumping mechanism configured to be fluidly connected to a source of cryogenic fluid. The at least one pumping mechanism may include a barrel configured to receive and discharge cryogenic fluid, and a piston configured to be reciprocally driven within the barrel to pressurize the cryogenic fluid. The piston may include an actuating end connectable to an actuator, and a pressurizing end opposite the actuating end. The pressurizing end may include an annular wall having a fixed end attached to the body, a free end opposite the fixed end, and an inner diameter. The pressurizing end may further include a cavity having an opening disposed at the free end of the annular wall, and a head attached to the body and disposed within the cavity, wherein the head occupies a majority of the cavity. The body may further include an outer diameter that varies along an axial length of the body between the pressurizing end and the actuating end, wherein the outer diameter is greater at the pressurizing end than at the actuating end.
Input end 12 may include a driveshaft 18 rotatably supported within a housing (not shown), and connected at an internal end to a load plate 20. Load plate 20 may be oriented at an oblique angle relative to axis 16, such that an input rotation of driveshaft 18 may be converted into a corresponding undulating motion of load plate 20. A plurality of tappets 21 may slide along a lower face of load plate 20, and a push rod 22 may be associated with each tappet 21. In this way, the undulating motion of load plate 20 may be transferred through the tappets 21 to push rods 22 and used to pressurize the fluid passing through pump 10. A resilient member (not shown), for example a coil spring, may be associated with each push rod 22 and configured to bias the associated tappet 21 into engagement with load plate 20. Each push rod 22 may be a single-piece component or, alternatively, comprised of multiple pieces, as desired. Many different shaft/load plate configurations may be possible, and the oblique angle of load plate 20 may be fixed or variable, as desired. Other configurations of input end 12 may be possible.
Output end 14 may be in fluid communication with a cryogenic fluid source via an inlet 24 and an outlet 26. For example, LNG may be supplied to output end 14 from an associated storage tank storing LNG at temperatures of, e.g., about −100 to −162° C. This continuous supply of cold fluid to output end 14 may cause output end 14 to be significantly cooler than input end 12. Cryogenic fluid may be directed through inlet 24 to a reservoir 28 in output end 14.
Output end 14 may include one or more pumping mechanisms 30 fluidly connected to reservoir 28 to draw cryogenic fluid from reservoir 28. In the exemplary embodiment, output end 14 has five pumping mechanisms 30, but it is understood that there may be any number of pumping mechanisms 30. Pumping mechanisms 30 may be mounted to a manifold 32 disposed in output end 14 and may extend into reservoir 28. Push rods 22 may pass through manifold 32 and connect with each pumping mechanism 30.
As shown in
Barrel assembly 34 may include a generally hollow barrel 40 located at proximal end 36 and a head 42 located at distal end 38. Barrel 40 may be formed from a material that can withstand temperature changes (e.g., from ambient to about −165° C.) without operation disruption. This material may resist cracking or other mechanical failures, and may have a low coefficient of thermal expansion (COE). For example, the material of barrel 40 may be stainless steel or a ceramic that is suitable for operation at such low temperatures. However, it is understood that barrel 40 may be formed of another material, if desired.
Head 42 may be attached to barrel 40 to close off barrel 40. Alternatively, barrel assembly 34, including barrel 40 and head 42, may be formed integrally as a single component. Head 42 may include at least one inlet 44 in fluid communication with reservoir 28 for drawing cryogenic fluid from reservoir 28 into barrel assembly 34. Head 42 may also include at least one outlet 46 in fluid communication with outlet 26 (referring to
A piston bore 48 may extend through barrel 40 and be configured to slidably receive a piston 50. A proximal end of piston bore 48 may align with a corresponding push rod 22, such that push rod 22 may serve as an actuator to push piston 50 through piston bore 48. Alternatively, piston 50 may be permanently connected to push rod 22, and the undulation of load plate 20 may cause push rod 22 to push and pull piston 50 through piston bore 48. During the movement of piston 50, high pressures may be generated within piston bore 48 and head 42.
Piston 50 may include a body 52 that is configured to be reciprocally driven within piston bore 48 to pressurize fluid. Body 52 may have an actuating end 54 and a pressurizing end 56. Actuating end 54 may abut the end of corresponding push rod 22, and may be proximally positioned in piston bore 48 with respect to pressurizing end 56. Pressurizing end 56 may be opposite actuating end and configured to pressurize fluid against head 42 of barrel assembly 34. In the example of
Piston 50 may slide between a Bottom-Dead-Center position (BDC) and a Top-Dead-Center (TDC) position within piston bore 48 of barrel 40. While piston 50 reciprocates between BDC and TDC, distal end 38 of barrel assembly 34 may eventually reach an operating pressure P1 and an operating temperature T1. Operating pressure may force fluid to leak past piston 50 through an annular gap 60 between body 52 and piston bore 48 into proximal end 36 of barrel assembly 34. Fluid pressure in gap 60 may vary (e.g., decrease) from about operating pressure P1 near pressurizing end 56 to a lower pressure P2 near actuating end 54. As fluid travels through gap 60 from pressurizing end 56 to actuating end 54, a temperature of the fluid in gap 60 may increase from about operating temperature T1 to a higher temperature T2. Thus, an axial pressure differential and an axial temperature differential may exist between pressurizing end 56 and actuating end 54 of body 52. Further, since pumping mechanism 30 extends into reservoir 28 that contains a cryogenic. fluid, barrel 40 may be at a lower temperature. TB than T1, thereby creating a radial temperature differential between barrel 40 and piston 50.
Cumulative effects of these pressure and temperature differentials may result in various amounts of deflection (e.g., expansion and/or contraction) of piston bore 48 and body 52. For example, fluid pressure in distal end 38 of barrel assembly 34 may reach high enough values (e.g., about 42 MPa) during pressurizing strokes to generate axial forces on piston 50, causing body 52 to expand radially outward toward a wall of piston bore 48 and reduce the width of gap 60 between them. It is understood, however, that higher or lower pressures may be achieved during operation of pump 10. Further, the temperature differential between barrel 40 and piston 50 may cause body 52 to contract less than barrel 40, moving body 52 even closer to the wall of piston bore 48 and further reducing gap 60. The temperature differential between pressurizing end 56 and actuating end 54 may further reduce contraction of body 52, and thus gap 60, near actuating end 54.
However, fluid that has leaked into gap 60 at an initial pressure of P1 may produce radial forces on piston 50 and piston bore 48 that act to increase the width of gap 60. These radial threes may cause an outward expansion of barrel 40, while opposing the outward expansion of body 52 along piston 50. As the pressure within gap 60 decreases from pressurizing end 56 to actuating end 54, the radial forces may also decrease. This change in pressure and force along body 52 may increase the width of gap 60 more near pressurizing end 56 and less near actuating end 54. The net effects of the temperature and pressure differentials may cause gap 60 to be widest near pressurizing end 56 and narrowest near actuating end 54. These effects may also cause gap 60 to be uneven (i.e., non-uniform) along the axial length of piston 50, which may result in high friction where gap 60 is too narrow and/or leakage where gap 60 is too wide.
To reduce this friction and leakage, piston 50 may have an outer profile that is shaped to accommodate the expansion of piston bore 48 and body 52, while achieving a desired clearance in gap 60 (referring to
As the fluid in gap 60 travels from pressurizing end 56 toward actuating end 54, the volume of gap 60 may allow the fluid to expand and the pressure of the fluid to decrease. The pressure of the fluid may decrease more rapidly between actuating end 54 and an intermediate point 64 than between pressurizing end 56 intermediate point 64 because the net expansion, and hence the width of gap 60, changes less from pressurizing end 56 to intermediate point 64 than from intermediate point 64 to actuating end 54 due to the mechanical properties of the material that firms piston bore 48 and body 52. Intermediate point 64 may be a virtual reference point along the length L of body 52 that divides OD profile 62 into portions having different attributes (e.g., slope, shape of curve, average change per unit length, width of gap 60 between barrel 40, net expansion of body 52 and barrel 40, etc.), Further the temperature of body 52 may decrease more rapidly between intermediate point 64 and actuating end 54 due to the rapid pressure decrease between intermediate point 64 and actuating end 54. That is, the fluid may expand at constant enthalpy as it moves through gap 60 from pressurizing end 56 to actuating end 54, thereby resulting in a temperature rise near actuating end and a temperature differential between pressurizing end 56 and actuating end 54. Accordingly, these rates of change of pressure and temperature may cause the width of gap 60 to change at a first lower rate between pressurizing end 56 and intermediate point 64, and at a second higher rate between intermediate point 64 and actuating end 54. To accommodate these variations in gap 60, OD profile 62 may decrease at a first lower rate from pressurizing end 56 to intermediate point 64, and at a second higher rate from intermediate point 64 to actuating end 54.
For example, as shown in
In other embodiments, OD profile 62 may vary non-linearly between pressurizing end 56 and actuating end 54 to more accurately accommodate complex variations in the width of gap 60 (referring to
Because the net expansion of piston bore 48 and body 52 varies with the pressure in piston bore 48, the effects of expansion may be greatest during pressurizing strokes of pump 10 and least during return strokes. And since the net expansion near pressurizing end 56 may be mostly attributed to the pressure in piston bore 48, the width of gap 60 may vary greatly between pressurizing and retracting strokes as the pressure near pressurizing end 56 varies.
To accommodate the greater fluctuation in the width of gap 60 near pressurizing end 56, body 52 may be configured to flex outwardly and return, thereby expanding and contracting OD profile 62, as the pressure in piston bore 48 increases and decreases, respectively. To achieve this flexibility, as shown in
During pressurizing strokes of pump 10, pressurized fluid may be forced into cavity 76. Pressure in cavity 76 may place an outward force along annular wall 72, thereby expanding OD profile 62 of body 52 and decreasing the clearance within gap 60 (referring to
Annular wall 72 may extend a length L2 from fixed end 74 to free end 80, and partially define cavity 76. Cavity 76 may include a space encompassed by an interior side 86 of annular wall 72 along the length L2 of annular wall 72. Thus, interior wall 86 may partially define an inner diameter (ID) of annular wall 72. L2 may be less than about 75% (e.g., 50%) of the length of L1. In one example, L2 may extend to intermediate point 64. L2 may be longer or shorter, if desired. The ID may vary along a length of annular wall (72) to form an ID profile 88. ID profile 88 may be between about 10% and 90% of OD profile 62. For example, OD profile 62 may be about 32 mm and ID may be about 24 mm at free end 80 of annular wall 72, ID profile 88 may be larger or narrower, if desired.
The length L2 of annular wall 72 may affect the flexibility of body 52. For example, as the length L2 of annular wall 72 increases, fixed end 74 is moved farther from free end 80, and the flexibility of annular wall 72 near pressurizing end 56 of body 52 may increase. Conversely, as the length decreases, the flexibility of annular wall 72 near pressurizing end 56 may decrease. For a given length L2 of annular wall 72, the flexibility of body 52 may decrease from free end 80 toward fixed end 74. That is, for a given outward force along the interior side 86 of annular wall 72, body 52 may flex more near free end 80 of annular wall 72 and flex less near fixed end 74.
Annular wall 72 may have a thickness τ that may partially affect the flexibility of body 52. For example, as the thickness τ of annular wall 72 increases, the flexibility of wall 52 may decrease. Conversely, as the thickness τ of annular wall 72 decreases, the flexibility of wall 52 may increase. In some embodiments, the thickness τ of annular wall 72 may be generally constant between free end 80 and fixed end 74 of annular wall 72. In other embodiments, the thickness τ may vary to provide more or less flexibility along annular wall 72. For example, the thickness τ of annular wall 72 may increase from free end 80 to fixed end 74. In one embodiment, thickness τ may vary between about 5% and 45% of OD profile 62 from free end 80 to fixed end 74.
In one example, OD profile 62 may be about 32 mm, ID profile 88 may be about 24 mm, and the thickness τ of annular wall 72 to be about 4 mm near free end 80 of annular wall 72. ID profile 88 may decrease by about 8 mm from free end 80 to fixed end 74, thereby increasing the thickness τ of annular wall 72 by about 4 mm from free end 80 to fixed end 74. In this way, the flexibility of body 52 may be varied to allow greater expansion of OD profile 62 near free end 80 for accommodating larger variations in gap 60 (referring to
As shown in
Head 58 may extend from fixed end 82 through cavity 76 to free end 84. In the example shown in
Head 58 may occupy a majority of cavity 76 in order to limit the total volume of cavity 76, while ensuring that enough space is available to allow a higher pressure to build within cavity 76 than in gap 60. That is, when the space between interior side 86 and head 58 within cavity 76 is greater than the width of gap 60, cavity 76 is sufficiently large enough to allow pressurized fluid to apply an outward radial force to outwardly expand annular wall 72 in order to reduce the clearance in gap 60. Therefore, to allow higher pressure to build in cavity 76 than in gap 60, the space between interior side 86 and head 58 should be greater than the width of gap 60. The volume of cavity 76 can also add to the total volume of compressed fluid that remains within barrel assembly 34 after a pressurizing stroke and may be minimized. For example, as head 58 occupies more space within cavity 76, the volume of cavity 76 may be reduced, and the total volume of compressed fluid remaining in barrel assembly 34 after a pressurizing stroke may be reduced, thereby improving efficiency of pump 10. For example, head 58 may occupy at least 51-99% of the volume of cavity 76. It is understood, however, that head 58 may occupy less than a majority of cavity 76, if desired.
Head 58 may attach to body 52 by any suitable mechanism, such as by fastening, adhesion, press fitting, welding, material deposition, etc. For example, a fastener, such as a bolt or a screw, may be passed through the center of head 58 and anchored into body 52. In another example, head 58 may have a threaded end or other fastening feature that is received by body 52 to connect head 58 and body 52. In other embodiments, head 58 and body 52 may be a unitary component created during a single forming process, such as by casting, material deposition, machining billet materials, etc.
As shown in
Reducing friction and leakage past piston 50 by accommodating the variations in gap 60 (referring to
In one example, the temperature differential between pressurizing end 56 and actuating end 54 may be reduced by exposing actuating end 54 to a coolant. As shown in
In one embodiment, the coolant may be cryogenic fuel that is diverted from an associated storage tank. The cryogenic fluid expelled through outlet 94 may be returned to the associated storage tank, sent to a fuel consumer, or sent to another storage container. In other embodiments, the coolant may be a different fluid (e.g., air, gaseous or liquid hydrogen, liquid nitrogen, etc.) circulated through a dedicated cooling system or through a pre-existing coolant system of pump 10. It is understood that other coolants may be used.
Expansion of body 52 near actuating end 54 may be alternatively or additionally reduced by forming piston 50 from a material having a low coefficient of thermal expansion (COE). Reducing the COE of piston 50 may reduce overall expansion of body 52 at a wide range of temperatures. The COE of piston 50 may be reduced by forming piston 50 from a material such as a low temperature stainless steel, ceramic, or other material having a low COE. In one embodiment, piston 50 may be formed of the same low-COE material as barrel 40. In other embodiments, piston 50 may be formed of a different material (e.g., a different metal, ceramic, etc) having a lower COE than barrel 40. In this way, body 52 of piston 50 may expand less during operation of pump 10, thereby reducing friction and leakage past piston 50 over a wider range of operating temperatures.
The disclosed piston finds potential application in any fluid pump where maintaining an optimum clearance between a piston and a barrel is desirable for reducing leakage and friction between the piston (and/or its seals) and the barrel. The piston pump finds particular applicability in cryogenic pump applications, for example pumps used in conjunction with power system having engines that burn LNG fuel. One skilled in the art will recognize, however, that the disclosed pump could be utilized in conjunction with other fluid systems that may or may not be associated with a power system, Operation of exemplary pump 10 will now be discussed.
Referring to
During pressurizing strokes, the pressure and temperature within piston bore 48 may cause body 52 of piston 50 and piston bore 48 to expand, thereby increasing or decrease the clearance in gap 60. For example the pressure within piston bore 48 during a pressurizing stroke may cause axial compression and lateral expansion of piston 50. This axial force may cause body 52 to expand radially outward toward piston bore 48, thereby decreasing the clearance within gap 60. Further, the low temperatures of the cryogenic fluid may cause piston 50 and piston bore 48 to contract, but the temperature differential between piston 50 and piston bore 48 may cause body 52 of piston 50 to expand less and further decrease the clearance in gap 60. Actuating end 54 of body 52 may be warmer than actuating end 56 due to leaked fluid that has attained a higher temperature and the heat of friction, which may cause the clearance in gap 60 to be less near actuating end 54 than pressurizing end 56.
However, fluid that has leaked into gap 60 at an initial pressure of P1 may produce radial forces on piston 50 and piston bore 48 that increase the width of gap 60 by expanding piston bore 48 and preventing expansion of body 52 of piston. Due to expansion of the fluids within gap 60 that reduce the pressure of the fluid as it travels from pressurizing end 56 toward actuating end 54, the radial forces may be greatest near pressurizing end 56 and least near actuating end 54. Thus, the net expansion due to pressure and temperature may cause gap 60 to be greatest near pressurizing end 56 and least near actuating end 54.
As piston 50 slides toward distal end 38 of barrel assembly 34, the pressure in piston bore 48 may increase the net expansion near pressurizing end 56 and cause a greater clearance in gap 60. First taper 66 (referring to
The increased pressure during pressurizing strokes may also force pressurized fluid through opening 78 of cavity 76 (referring to
After each pressurizing stroke, piston 50 may retract within piston bore 48 toward proximal end 36 of barrel assembly 40 (referring to
During each pressurizing stroke, a coolant may be introduced through coolant inlet 92 into piston bore 48 near actuating end 54 of piston 50. The coolant may reduce the temperature of actuating end 54, thereby bringing its temperature closer to the temperature of pressurizing end 56 and piston bore 48. By bringing these temperatures closer together, the difference in expansion between piston 50 and piston bore 48 may be reduced, thereby reducing the variations in the clearance of gap 60. As gap 60 is allowed to be more consistent along body 52, friction and leakage past piston 50 may be reduced. The coolant may then be expelled through coolant outlet 94 during the following retraction stroke.
As discussed, the disclosed piston 50 may reduce leakage of fuel through gap 60 between piston 50 and piston bore 48 while also reducing friction between piston 50 and piston bore 48 to improve the overall efficiency of pump 10. Particularly, piston 50 may include body 52 that has OD profile 62 that varies along the length L1 of body 52 to reduce leakage and friction caused by variations in gap 60. Further, body 52 of piston 50 may include ID profile 88 that allows OD profile 62 to expand and contract with pressure in barrel 40 to achieve a smaller clearance in gap 60 during pumping strokes to prevent fuel leakage. ID profile 88 further allows OD profile 62 to achieve a greater clearance during retraction strokes to reduce friction and improve efficiency.
It will be apparent to those skilled in the art that various modifications and variations can be made to the pump piston of the present disclosure. Other embodiments of the pump piston will be apparent to those skilled in the art from consideration of the specification and practice of the pump piston disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
