Safety Hydraulic Dump for a Cryogenic Pump

Abstract

A cryogenic fluid pump includes a drive assembly and a pumping assembly. The drive assembly includes a cylinder. The cylinder includes an annular dump channel formed in and extending about an interior wall of the cylinder. A piston is reciprocatable within the cylinder between a first and second position. A hydraulic pressure chamber is defined by the cylinder and the piston. The piston includes an axial spill passage in communication with the pressure chamber and a transverse spill passage in communication with the axial spill passage. The transverse spill passage includes a piston dump port which is sealed to the cylinder in the first position and in the second position unsealed to the cylinder to permit fluid exit from the pressure chamber. The second position includes an over travel state and the dump area of the piston dump port when unsealed to the cylinder increases as the piston advances.

Claims

1. A cryogenic fluid pump, comprising: a drive assembly and a pumping assembly, the drive assembly including a cylinder, the cylinder including an annular dump channel that is formed in and extends about an interior wall of the cylinder; a piston reciprocatable within the cylinder between a first position and a second position; and a hydraulic pressure chamber defined by the cylinder and the piston; the piston including at least one axial spill passage in communication with the hydraulic pressure chamber and a transverse spill passage in communication with the at least one axial spill passage, the transverse spill passage including a piston dump port, the piston dump port sealed to the cylinder in the first position and in the second position unsealed to the cylinder to permit fluid exit from the hydraulic pressure chamber, wherein the second position includes an over travel state and wherein the dump area of the piston dump port unsealed to the cylinder continues to increase as the piston advances in the over travel state.

2. The cryogenic fluid pump of claim 1, wherein the piston dump port is in communication with the annular dump channel in the second position.

3. The cryogenic fluid pump of claim 2, wherein the at least one axial spill passage extends less than half the axial length of the piston.

4. The cryogenic fluid pump of claim 1, wherein the at least one axial spill passage includes a pair of axial spill passages.

5. The cryogenic fluid pump of claim 1, wherein the piston includes a transverse width and the transverse spill passage extends the entire transverse width of the piston.

6. The cryogenic fluid pump of claim 1, wherein the annular dump channel is a rectangular groove.

7. The cryogenic fluid pump of claim 1, wherein the at least one axial spill passage extends more than half the axial length of the piston.

8. The cryogenic fluid pump of claim 7, wherein the piston dump port clears an end portion of the cylinder in the second position, wherein the second position corresponds to greater than or equal to 100 percent of an end of stroke position.

9. The cryogenic fluid pump of claim 8, wherein a top of the piston clears the annular dump channel permitting fluid to exit from the hydraulic pressure chamber directly into the annular dump channel, wherein the second position includes the over travel state.

10. The cryogenic fluid pump of claim 1, wherein the piston dump port includes one of a triangular cross section and a U-shaped cross section.

11. A pumping system for providing a cryogenic fluid for use as a fuel for an engine, comprising: an electronic controller; a cryogenic pump operably associated with the electronic controller, wherein operation of the cryogenic pump is responsive to pump commands from the electronic controller; the cryogenic pump having a plurality of pumping elements, each of the plurality of pumping elements comprising: a drive assembly and a pumping assembly, the pumping assembly operably responsive to the drive assembly, the drive assembly including a cylinder, the cylinder including an annular dump channel that is formed in and extends about an interior wall of the cylinder; a piston reciprocatable within the cylinder between a first position and a second position; and a hydraulic pressure chamber defined by the cylinder and the piston; the piston including at least one axial spill passage in communication with the hydraulic pressure chamber and a transverse spill passage in communication with the at least one axial spill passage, the transverse spill passage including a piston dump port, the piston dump port sealed to the cylinder in the first position and in the second position unsealed to the cylinder to permit fluid exit from the hydraulic pressure chamber, wherein the second position includes an over travel state and wherein the dump area of the piston dump port unsealed to the cylinder continues to increase as the piston advances in the over travel state.

12. The cryogenic fluid pump of claim 11, wherein the piston dump port is in communication with the annular dump channel in the second position.

13. The cryogenic fluid pump of claim 12, wherein the at least one axial spill passage extends less than half the axial length of the piston.

14. The cryogenic fluid pump of claim 11, wherein the at least one axial spill passage includes a pair of axial spill passages.

15. The cryogenic fluid pump of claim 11, wherein the piston includes a transverse width and the transverse spill passage extends the entire transverse width of the piston.

16. The cryogenic fluid pump of claim 11, wherein the at least one axial spill passage extends more than half the axial length of the piston.

17. The cryogenic fluid pump of claim 16, wherein the piston dump port clears an end portion of the cylinder in the second position, wherein the second position corresponds to greater than or equal to 100 percent end of an end of stroke position.

18. The cryogenic fluid pump of claim 17, wherein a top of the piston clears the annular dump channel permitting fluid to exit from the hydraulic pressure chamber directly into the annular dump channel, wherein the second position includes the over stroke state.

19. The cryogenic fluid pump of claim 11, wherein the piston dump port is includes one of a triangular cross section and a U-shaped cross section.

20. A cryogenic fluid pump, comprising: a plurality of pumping elements in communication with an electronic controller, each of the pumping elements including: a drive assembly including an electromechanical actuator having a pin associated therewith, the pin arranged in a bore having a fluid supply passage, a spool valve supply outlet, and a drain outlet, wherein the pin is moveable between a deactivation position, in which the hydraulic oil supply passage is fluidly connected with the spool valve supply outlet, and an activation position, in which the spool valve supply outlet is fluidly connected with the drain outlet; the drive assembly including a cylinder, the cylinder including an annular dump channel that is formed in and extends about an interior wall of the cylinder, a piston reciprocatable within the cylinder between a first position and a second position, and a hydraulic pressure chamber defined by the cylinder and the piston, the piston including at least one axial spill passage in communication with the hydraulic pressure chamber and a transverse spill passage in communication with the at least one axial spill passage, the transverse spill passage including a piston dump port, the piston dump port sealed to the cylinder in the first position and in the second position unsealed to the cylinder to permit fluid exit from the hydraulic pressure chamber, wherein the second position includes an over travel state and wherein the dump area of the piston dump port unsealed to the cylinder continues to increase as the piston advances in the over travel state; the drive assembly associated with and configured to selectively activate one end of a pushrod in response to a command by the electronic controller; and a pump assembly associated with an opposite end of the pushrod wherein the pump assembly is activated for pumping a fluid by the drive assembly; wherein the electronic controller is configured to selectively activate the drive assembly such that a flow of fluid from the cryogenic fluid pump results from successive activations thereof at selected dwell times between activations.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic diagram of an engine system having a compressed gas fuel system that includes a liquid natural gas cryogenic fuel storage tank and corresponding fuel pump in accordance with the disclosure.

[0011] FIG. 2 is a section view of a cryogenic tank including a cryogenic pump in accordance with the disclosure.

[0012] FIG. 3 is a partial section view of a multi-element pump in accordance with the disclosure.

[0013] FIG. 4 is a section view of a unit hydraulic actuator in accordance with the disclosure.

[0014] FIGS. 5 and 6 are section views of a spool valve in accordance with the disclosure in two operating positions.

[0015] FIG. 7 is a section view of a cryogenic pump hydraulic drive in including a hydraulic piston and pushrod assembly in accordance with the disclosure.

[0016] FIGS. 8A-C is a first embodiment of a hydraulic piston in different positions relative to related dump structures.

[0017] FIGS. 9A-C is a second embodiment of a hydraulic piston in different positions relative to related dump structures.

[0018] FIG. 10 shows different embodiments of dump ports in accordance with the present disclosure.

[0019] FIG. 11 is a graph showing dump port metering area as a function of piston travel.

DETAILED DESCRIPTION

[0020] This disclosure relates to machines with engines using a gaseous fuel (e.g., methane of other hydrocarbon mixtures commonly known as natural gas or petroleum gas) source such as direct injection gas (DIG) or indirect injection gas engines using diesel or spark ignition. More particularly, the disclosure relates to a hydraulic drive system for a cryogenic liquid natural gas (LNG) pump that supplies pressurized natural gas fuel to an engine. A schematic diagram of a DIG, engine system 100, which in the illustrated embodiment uses liquid diesel fuel as the ignition source, is shown in FIG. 1. It should be appreciated that port injection engines, and/or engines using a different ignition mode are also contemplated. The engine system 100 includes an engine 102 having a fuel injector 104 associated with each engine cylinder 103. The fuel injector 104 can be a dual-check injector configured to independently inject predetermined amounts of two separate fuels, in this case, diesel and natural gas, into the engine cylinders.

[0021] The fuel injector 104 is connected to a high-pressure gaseous fuel rail 106 via a high-pressure gaseous fuel supply line 108 and to a high-pressure liquid fuel rail 110 via a liquid fuel supply line 112. In the illustrated embodiment, the gaseous fuel is natural or petroleum gas that is provided through the high-pressure gaseous fuel supply line 108 at a pressure of between about 10-50 MPa, and the liquid fuel is diesel, which is maintained within the high-pressure liquid fuel rail 110 at about 15-100 MPa, but any other pressures or types of fuels may be used depending on the operating conditions of each engine application. The liquid fuel can be any hydrocarbon based fuel; for example DME (Di-methyl Ether), biofuel, MDO (Marine Diesel Oil), or HFO (Heavy Fuel Oil).

[0022] Whether the engine system 100 is installed in a mobile or a stationary application, each of which is contemplated, the gaseous fuel may be stored in a liquid state in a tank 114, which can be a cryogenic storage tank that is pressurized at a relatively low pressure, for example, atmospheric, or at a higher pressure. In the illustrated embodiment, the tank 114 is insulated to store liquefied natural gas (LNG) at a temperature of about 160 C. (256 F.) and a pressure that is between about 100 and 1750 kPa, but other storage conditions may be used. The tank 114 further includes a pressure relief valve 116. In the description that follows, a DIG engine system embodiment is used for illustration, but it should be appreciated that the systems and methods disclosed herein are applicable to any machine, vehicle or application that uses cryogenically stored gas, for example, a locomotive in which the tank 114 may be carried in a tender car.

[0023] Relative to the particular embodiment illustrated, during operation, LNG from the tank is pressurized, still in a liquid phase, in a pump 118, which raises the pressure of the LNG while maintaining the LNG in a liquid phase. The pump 118 is configured to selectively increase the flow of the LNG that can vary in response to a command signal provided to the pump 118 from an electronic controller 120. The pump 118 is shown external to the tank 114 in FIG. 1 for illustration, but it is contemplated that the pump 118 may at least partially be disposed within the tank 114, as is illustrated in the figures that follow, for example, in FIG. 2. Although the LNG is present in a liquid state in the tank, the present disclosure will make reference to compressed or pressurized LNG for simplicity when referring to LNG that is present at a pressure that exceeds storage pressure.

[0024] The pressurized LNG provided by the pump 118 is heated in a heat exchanger 122. The heat exchanger 122 provides heat to the compressed LNG to change the LNG phase to a gaseous/supercritical state which is more suitable for combustion. In one exemplary application, the LNG may enter the heat exchanger 122 at a temperature of about 160 C., a density of about 430 kg/m.sup.3, an enthalpy of about 70 kJ/kg, and a viscosity of about 169 Pa s as a liquid, and exit the heat exchanger at a temperature of about 50 C., a density of about 220 kg/m.sup.3, an enthalpy of about 760 kJ/kg, and a viscosity of about 28 Pa s. It should be appreciated that the values of such representative state parameters may be different depending on the particular composition of the fuel being used. In general, the fuel is expected to enter the heat exchanger in a cryogenic, liquid state, and exit the heat exchanger in a supercritical gas state, which is used herein to describe a state in which the fuel is gaseous but has a density that is between that of its gaseous and liquid phases.

[0025] The heat exchanger 122 may be any known type of heat exchanger or heater for use with LNG. In the illustrated embodiment, the heat exchanger 122 is a jacket water heater that extracts heat from engine coolant. In alternative embodiments, the heat exchanger 122 may be embodied as an active heater, for example, a fuel fired or electrical heater, or may alternatively be a heat exchanger using a different heat source, such as heat recovered from exhaust gases of the engine 102, a different engine belonging to the same system such as what is commonly the case in locomotives, waste heat from an industrial process, and other types of heaters or heat exchangers. In the embodiment shown in FIG. 1, which uses engine coolant as the heat source for the heat exchanger 122, a pair of temperature sensors 121A and 121B are disposed to measure the temperature of engine coolant entering and exiting the heat exchanger 122 and provide corresponding temperature signals 123A/B to the electronic controller 120.

[0026] Liquid fuel, or in the illustrated embodiment diesel fuel, is stored in a fuel reservoir 136. From there, fuel is drawn into a fuel pump 138 through a filter 140. The fuel pump 138 may have a variable flow capability to provide fuel to the engine at a variable rate depending on the operating mode of the engine. The rate of fuel provided by the fuel pump 138 can be controlled in response to a command signal from the electronic controller 120. Pressurized fuel from the fuel pump 138 is provided to the high-pressure liquid fuel rail 110. Similarly, the pump 118 has a variable supply capability that is responsive to a signal from the electronic controller 120.

[0027] Contaminants may be removed from the natural gas exiting the heat exchanger 122 by a filter 124. As can be appreciated, the natural gas passing through the filter 124 may be present in more than one phase such as gas or liquid. An optional natural gas accumulator 126 may collect filtered gas upstream of a pressure regulator 128 that can selectively control the pressure of gas provided to the high-pressure gaseous fuel rail 106 that is connected to the high-pressure gaseous fuel supply line 108. To operate the pump 118, a hydraulic pump 150 having a variable displacement and selectively providing pressurized hydraulic fluid to the pump 118 via a valve system 152 is used. Operation of the hydraulic pump 150 is controlled by an actuator 154 that responds to commands from the electronic controller 120. The valve system 152 also operates in response to commands from the controller 120. It will be appreciated that while system 100 illustrates one or more embodiment, other configurations are contemplated.

[0028] A section view of the tank 114 having the pump 118 at least partially disposed therein is shown in FIG. 2. The tank 114 may include an inner wall 202, which defines a chamber 212 containing the LNG at cryogenic storage temperature and pressure, and an outer wall 204. A layer of insulation 206 may optionally be used, and/or a vacuum may be created along a gap between the inner wall 202 and the outer wall 204. Both the inner wall 202 and the outer wall 204 have a common opening 208 at one end of the tank, which surrounds a cylindrical casing 210 that extends into a tank interior 212. The cylindrical casing 210 is hollow and defines a pump socket 214 therein that extends from a mounting flange 216 into the tank chamber 212 and accommodates the pump 118 therein. A seal 218 may separate the interior of a portion of the pump socket 214 from the tank chamber 212.

[0029] The pump 118 in the illustrated embodiment includes a pump flange 220 that supports the pump 118 on the mounting flange 216 of the tank 114. A partially sectioned view of the pump 118, removed from the tank 114, is also shown in FIG. 3. The pump 118 generally includes a drive assembly 302 that operates to selectively activate one or more pushrods 304, which in the figure are inside guide rods of the pushrods. The pushrods 304 (see FIG. 3) surround a compression tube 306, which may optionally also operate as an outlet passage for the pump 118. The pushrods 304, which are caused to reciprocate during operation by the drive assembly 302, extend from the drive assembly 302 to a pumping assembly 310. During operation, the pumping assembly 310, which may be immersed in cryogenic fluid, operates to pump fluid from the tank interior 212 out of the tank and through an outlet or, in some embodiments, the compression tube 306 to supply the engine with fuel, as previously described. The pumping assembly 310 translates the reciprocal motion of the pushrods 304 into a pumping action that operates the pumping assembly 310. The transmission of the reciprocal motion of the pushrods 304 can be accomplished by any appropriate structures or method including via a solid structure or by another method such as a closed hydraulic or pneumatic volume that can transmit a displacement.

[0030] In the illustrated embodiment, the pushrods 304, shown in cross section in FIG. 4 and also shown in enlarged detail in FIG. 7, are downwards, in the orientation of the pump shown in FIG. 3, by a piston 314 operating in a cylinder 316 by hydraulic fluid provided under pressure behind the piston 314 through an activation passage 318. A return spring 320 returns the pushrod 304 via an upper pushrod portion 312, and thus the piston 314, when pressurization of the hydraulic fluid behind the piston is removed or, stated differently, when the space behind the piston 314 is vented.

[0031] The pressurized hydraulic fluid to activate the piston 314 is provided in the space behind the piston, and is also vented, by the selective positioning of a spool valve 322, which is shown in two operating positions in FIGS. 5, and 6. In FIG. 5, the spool valve 322 is shown in a fill position, which fills the space behind the piston 314 with high pressure oil to cause the piston to extend, and in FIG. 6 the spool valve is shown in a drain position, which vents the space behind the piston 314 to permit the piston 314 to return by force of the return spring 320 (FIG. 7), and thus retract.

[0032] The spool valve 322 in the illustrated embodiment includes a spool valve element 324 that is reciprocally mounted and operates within a bore 326. The bore 326, which accommodates the spool valve element 324, is fluidly connected to a fluid supply passage 328, which supplies pressurized fluid to move the piston 314. For example, as shown in FIG. 1, the pressurized fluid can be hydraulic fluid supplied by a hydraulic pump like the hydraulic pump 150. The flow rate and pressure of the hydraulic fluid can be controlled, for example, by the valve system 152 also shown in FIG. 1, in response to control commands from the electronic controller 120.

[0033] The bore 326 is also fluidly connected to a vent passage 330 (partially shown in FIGS. 5 and 6), which is open to a fluid reservoir in the known fashion for venting pressurized fluid. A piston supply passage 332 fluidly connects the bore 326 to the area behind the piston 314, which in the embodiment shown in FIG. 7 means that the piston supply passage 332 is fluidly open to the activation passage 318. During operation, when the spool valve element 324 is disposed at the fill position shown in FIG. 5, the spool valve element 324 fluid supply passage 328 is placed in fluid communication with the piston supply passage 332 and the vent passage 330 is fluidly isolated from the piston supply passage 332. In this operating position, fluid from the fluid supply passage 328 at a high pressure is routed into the piston supply passage 332, which in turn provides the fluid to the activation passage 318 from where the fluid, by hydraulic pressure, pushes the piston 314 that extends the pushrod 304 to activate a pumping element at the other end of the pump 118, as previously described. At the venting position, as shown in FIG. 6, the spool valve element moves to fluidly block the fluid supply passage 328 and in turn fluidly connect the piston supply passage 332 with the vent passage 330. In this operating position, fluid flows out from behind the piston 314, through the activation passage 318 and the piston supply passage 332 and into the vent passage 330, from where it is vented. These motions are facilitated by the return spring 320 that pushes the upper pushrod portion 312, and thus the piston 314, to retract.

[0034] In the illustrated embodiment, the spool valve element 324 at an energized condition is disposed in the fill position (FIG. 5) and, when de-energized, assumes the drain position (FIG. 6). Activation of the spool valve element 324 requires a displacement of the same along an axis along which the spool valve element 324 reciprocates. The displacement is provided by an actuator 334, which is shown in section view in FIG. 4. The actuator 334 is an electromechanical pilot actuator, but other actuator types such as actuators using piezoelectric elements can be used. The actuator 334 includes a solenoid 336 that, when energized, retracts a pin 338 that is reciprocally disposed at least partially in the solenoid 336 and includes a return spring 340. The spool may include a ferric core 342. The pin 338 includes an armature 344 and reciprocates within a pin guide 346 forming a hollow bore 348. The hollow bore 348 is fluidly isolated from a hydraulic oil supply passage 350, a spool valve supply outlet 352, and a drain outlet 354. The hydraulic oil supply passage 350 may be connected directly or through the valve system 152 with an outlet of the hydraulic pump 150 (FIG. 1). The pin guide 346 forms two poppet valve seats that, depending on the activation state of the solenoid 336, fluidly connect or isolate the various fluid passages.

[0035] More specifically, during operation, depending on the activation state of the solenoid 336, the position of the pin 338 within the pin guide 346 operates between an activation position and a drain position. In the activation position, a lower seat valve 347 opens as the armature 344 moves upward, which places the spool valve supply outlet 352 in fluid communication with the drain outlet 354, which, as shown in FIGS. 5 and 6, is connected to the interior of the bore 326 and pressure is relieved above the spool valve element 324, causing the same to move upwards by hydraulic force within the bore from the drain position (FIG. 6) to the fill position (FIG. 5), and thus activate the piston 314 (FIG. 7) as previously described by supplying pressurized fluid to the activation passage 318 through the piston supply passage 332. Thus, when the pin 338 is in the activated position, the spool valve element 324 is in the fill position. Similarly, when the pin 338 is deactivated, or in a drain position, the spool valve supply outlet 352 is placed in fluid communication with the hydraulic oil supply passage 350, which drains the fluid below the spool valve element 324, causing it to extend in the bore 326 and thus vent the activation passage 318 (FIG. 7). Thus, when the pin 338 is in the deactivated, the spool valve element 324 is in the drain position (FIG. 6). The fluid supply passage 328 may be directly connected to an outlet of the hydraulic pump 150, or may alternatively be connected to the outlet of the hydraulic pump 150 via the valve system 152. In the illustrated embodiment, the fluid supply passage 328 is at all times fluidly connected with the hydraulic oil supply passage 350, but the two passages may be separated at times or operate at different pressures depending on the operating condition of the pump 118 and/or the hydraulic pump 150.

[0036] Operation of the actuator 334 depends on the presence of electrical power, which is selectively provided by the electronic controller 120 (FIG. 1) such that the selective pumping action of the pump 118 can be selectively carried out. The pump 118 advantageously includes six, separately actuatable, pumping elements, two of which are shown at 400A and 400B shown in cross section (FIGS. 3 and 8), but another number of pumping elements can be used, for example, one, two, three, four, five, or more than six, depending on the application of the pump to a particular system. It will be understood that other configurations and methods of supplying hydraulic fluid to the activation passage 318 and the piston 314 are contemplated.

[0037] Turning to FIG. 7, an embodiment of a drive assembly including a piston having an hydraulic dump according to the present disclosure is illustrated that relieves fluid pressure at the end of stroke and/or in an over travel condition. It will be understood that the illustrated hydraulic dump can be used in other suitably configured cryogenic pumps.

[0038] For purposes of the present disclosure, travel of the piston 314 within a specified range, i.e., from 0-100 percent of the designed travel will be considered a normal or specified travel state with 100 percent the end of specified travel. Travel of the piston 314 beyond a specified range, i.e., greater than 100 of the designed travel will be considered an over travel state.

[0039] Specifically, piston 314 reciprocates in cylinder 316 and, in part, defines a hydraulic pressure chamber 410, defined at least in part by the top 412 of the piston, that is provided with fluid from activation passage 318. Piston 314 includes at least one axial spill passage 414, which extends axially through the piston in communication with the hydraulic pressure chamber 410. Two axial spill passages 414 are shown. Each axial spill passage 414 may extend through the piston 314 less than the axial length of the piston. In one embodiment, the axial spill passage 414 may extend through the piston 314 about a fourth of the axial length of the piston. The at least one axial spill passage 414 is in communication with a transverse spill passage 416 that extends transversely to the axis of the piston 314 and opens to a relief pressure area, for example, on the outside of the piston. The transverse spill passage 416 has a piston dump port 418, which forms the opening of the passage to the outside of the piston 314. The transverse spill passage 416 can have any cross-sectional shape to supply sufficient flow of fluid to the piston dump port 418. The piston dump port 418, in the illustrated embodiments, may have a non-round cross-section to meter the flow area therethrough such that flow of fluid is dumped at a higher rate that can be accomplished with a circular port opening. Some examples of piston dump ports 418 are shown in detail in FIG. 10 and discussed below in more detail.

[0040] The cylinder 316 includes an annular dump channel 420. The annular dump channel 420 may be a groove formed in the inward facing inside wall of the cylinder 316. The annular dump channel 420 is in communication with the transverse spill passage 416 through the piston dump port 418 when the piston 314 is at its expected fully-extended travel position illustrated at pumping element example 400B and not in communication with the transverse spill passage when at an intermediate travel position or its fully-retracted position as shown at pumping element example 400A. When the piston dump port 418 and annular dump channel 420 are in fluid communication with the cylinder dump port 422, a passage is provided for fluid to exit the fluid chamber 410. The cross sectional shape of the piston dump port 418 in combination with the annular dump channel 420 permits a relief or dumping of hydraulic pressure from the hydraulic pressure chamber 410.

[0041] FIGS. 8A-C demonstrate three different positions of the piston 314, and in which all of the structural elements are the same. FIG. 8A shows the piston 314 in a first, top or uppermost position in the cylinder 316 with essentially no hydraulic fluid present. The axial spill passages 414 and transverse spill passage 416 are sealed off from fluid exit, i.e., not in communication with the annular dump channel 420 and cylinder dump port 422. FIG. 8B shows the piston 314 in a second or bottom position in the cylinder 316 with hydraulic fluid in the hydraulic pressure chamber 410. The axial spill passages 414 and transverse spill passage 416 are in partial communication with the annular dump channel 420 and cylinder dump port 422 with the transverse spill passage partially aligned with annular dump channel and fluid exit is permitted. FIG. 8C shows the piston 314 in a second, over stroke or over travel position in the cylinder 316, with the piston axially beyond a specified bottom position. For example, the over stroke position of the piston 314 may be 103 percent of a specified bottom position. The axial spill passages 414 and transverse spill passage 416 are in full communication with the annular dump channel 420 and cylinder dump port 422 with the transverse spill passage aligned with annular dump channel permitting fluid exit therefrom. The annular dump channel 420 is formed in interior wall 460 in a middle portion 462 of cylinder wall, i.e., between the ends of the cylinder.

[0042] FIGS. 9A-C show an embodiment of a piston and cylinder configuration that is different than the embodiment shown above, while the related structure of the pump 118 may be the same. FIGS. 9A-C include a piston 514 with at least one axial spill passage 515 (two are shown) formed axially along a majority of the axial length of the piston. The axial spill passage 515 is open to the hydraulic pressure chamber 410. A transverse spill passage 516 is formed transversely through the piston 514 in communication with the at least one axial spill passage 515 and open to the outside of the piston. The piston 514 reciprocates in cylinder 517. The cylinder 517 includes an annular dump channel 520 that is configured positionally to communicate with the hydraulic pressure chamber 410 when the second position of the piston 514 is as shown in FIG. 9C, specifically, an over stroke or over travel position, which permits fluid exit therefrom as described above. In the top position or first position, shown in FIG. 9A, the transverse spill passage 516 is located below the annular dump channel 520. In this position, the piston dump port 518 is also sealed with the interior wall 460 of the cylinder 517. Fluid pressure in hydraulic pressure chamber 410 urges piston 514 to the bottom position shown in FIG. 9B where the transverse spill passage 516 is moved below the cylinder end 464 and the transverse spill passage 516 is open to low pressure space 522, whereby fluid pressure in the hydraulic pressure chamber 410 causes fluid to exit from the hydraulic pressure chamber, through the axial spill passage 515, and through the transverse spill passage 516. If the piston 514 moves past the specified bottom position shown in FIG. 9B to the position shown in FIG. 9C, the top 512 of the piston clears or opens to the annular dump channel 520 and fluid pressure is permitted to exit the hydraulic pressure chamber through the annular dump channel. In this embodiment the annular dump channel 520 is formed in an intermediate portion 462 of the cylinder. The piston dump port 518, in the second position, clears or becomes unsealed to the cylinder when it moves past the end portion 464 of the cylinder 517.

[0043] FIG. 10 shows piston dump ports 418a-e. Referring also to FIGS. 8A-C and 9A-C, each of the piston dump ports 418a-e are shown in cross section to show the area of the piston dump ports. Each of the piston dump ports 418a-e includes an initial portion 550, which is the first part of the piston dump port brought into fluid communication with the annular dump port 420 and whereby fluid is permitted to exit as the piston 314, 514 begins to drop to a bottom position in the cylinder 316, 517. Each of the piston dump ports includes a subsequent portion 552 that is brought into fluid communication after the initial portion 552 when the piston dump port is fully aligned with the annular dump port 420 of the cylinder in the case of the embodiment shown in FIGS. 8A-C and the bottom of cylinder 517 in the case of the embodiment shown in FIGS. 9A-C.

[0044] Embodiment 418a has a triangular configuration such that the cross sectional area of the passage available for fluid to flow through is small at the beginning of fluid exit at 550 with a relatively small or first dump port area shown at 554. The port area increases in a quadratic fashion as the piston dump port 418a includes the port area shown at 556. In contrast to a circular port area, where the port area increases initially at a fast rate and then increases at a decreasing rate (less than linear) describing a sigmoid curve, the area of the piston dump port 418a increases at a greater than linear rate. In particular, the port dump area 554, 556 continues to increase as the piston progresses in an over travel state.

[0045] Embodiment 418b and 418c is a U-shape such that flow through is a small amount at the beginning of fluid exit at 550 with a semicircular dump port area shown at 554. The port area increases as the piston dump port 418a includes the rectangular areas shown at 556. Embodiment 418c has a lesser total throughput at maximum port area of combined port areas 554 and 556. The rectangular area 556 provides a linear rate of fluid exit. The port dump area 554, 556 continues to increase as the piston progresses in an over travel state.

[0046] Embodiment 418d is initially the same as 418c including a U-shape such that flow through is a small amount at the beginning of fluid exit at 550 with a semicircular dump port area shown at 554. The port area increases as the piston dump port 418d includes the rectangular areas shown at 556. The rectangular area 556 provides a linear rate of fluid exit. The area shown at 556 includes a flared portion at the upper end 552 thereof which permits a large expansion of fluid flow at the fully open and maximum dump port area which represents an increased rate of flow beyond the linear rate of portion 556. The port dump area 554, 556 continues to increase as the piston progresses in an over travel state.

[0047] Embodiment 418e is initially the same as 418d including a semicircular shape such that flow through is a small amount at the beginning of fluid exit at 550 with a semicircular dump port area shown at 554. The port area increases as the piston dump port 418d includes the triangular area shown at 556. The triangular area 556 provides more than a linear rate of fluid exit. The port dump area 554, 556 continues to increase as the piston progresses in an over travel state.

[0048] FIG. 11 illustrates a plot of piston travel on the horizontal axis versus dump port area on the vertical axis. The result is dump port metering area as a function of piston travel. The plot shows a generally linear relationship. The plot most closely resembles the embodiment of 418a but if the plot includes an initial curve to the schedule it would encompass the U-shaped ports. If the plot included an upturn with a more steep ending rate, it would encompass 418d. As noted above, a circular port area would have a lesser rate of increase at the end of the schedule than at the beginning and according to the disclosure, in order to reduce the possibility of the piston traveling significantly past a specified end of stroke distance or in an over travel state, it is desirable to dump pressure at a higher overall rate than would be provided by a circular port.

INDUSTRIAL APPLICABILITY

[0049] The present disclosure is applicable to any type of application that involves a hydraulic dump to prevent piston over travel. The present disclosure presents several embodiments of dump port configurations that function to protect a cryogenic pump from over travel states. In particular, the embodiments presented herein provide an increase of dump area vs. piston travel in an over travel state.

[0050] It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated.

[0051] Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.