Retention system

While ceramic materials possess properties that make them suitable for use in fuel system components, they tend to be susceptible to failure when exposed to tensile stresses. The retention system described herein helps to reduce the tensile stresses experienced by a retained member by providing a retained member with an engagement structure, a multi-piece retention ring that engages the engagement structure, a resilient member coupled to the retention ring, and a retainer coupled around at least a portion of the retention ring and resilient member and spaced apart from the retention ring and/or resilient member by a gap. The retained member, retention ring, resilient member, and retainer are configured so that the retention ring is moveable in an axial direction relative to the retained member and so that the movement of the retention ring acts to expand the resilient member against the bias provided by the resilient member.

TECHNICAL FIELD

The present disclosure relates generally to a system for retaining a first element relative to a second element or assembly. More particularly, the present disclosure relates to a system, assembly, and method for holding a ceramic plunger within a retention assembly in a high-pressure pump.

BACKGROUND

Ceramic materials generally possess several advantageous properties. For example, components or parts constructed from ceramic materials generally are very hard, have a relatively high resistance to wear, corrosion, thermal stress, and compressive stress, are generally nonconductive, and may possess other properties that are advantageous for particular applications. However, ceramic components and parts also tend to be brittle and are capable of withstanding only relatively small tensile stresses. Consequently, the use of ceramic parts has been primarily limited to applications where the ceramic part is subjected to little or no tensile loads.

While many different machines and devices could benefit from a part or component that is hard, that exhibits high resistance to wear, corrosion, thermal stress, and compressive stress, and that is nonconductive, ceramic has not been a feasible option for use in these machines and devices because of its relative inability to withstand tensile stresses. For example, in high-pressure fuel pumps, such as the fuel pumps used in common rail fuel injection systems to generate rail pressures up to and even beyond 190 MPa, the use of a plunger or piston that is hard, that has high resistance to wear, corrosion, thermal stress, and compressive stress, and that is nonconductive would be beneficial. However, manufacturers have had difficulty making use of ceramic plungers because the ceramic plungers are exposed to excessive tensile stresses which cause the plungers to prematurely fail.

Various retention assemblies that are used to hold a piston within a retainer assembly in a pump or within a rod in a hydraulic cylinder are known. One example of such a retention assembly is described in U.S. Pat. No. 3,654,839, issued Apr. 11, 1972 (“the '839 patent”). The retention assembly of the '839 patent includes a split retainer that has a rib that engages a grooved portion of a rod and a flange that engages a groove in a piston. A circumferentially interrupted band surrounds the split retainer and serves to hold the retainer in an operative condition prior to the insertion of the rod and piston assembly into a cylinder. The engagement of the rib with the groove in the rod and the engagement of the flange with the groove in the piston serve to retain the rod within the piston. Although the retention assembly described in the '839 patent represents a simple way to retain the rod within the piston, it may not be suitable for applications where it is important to minimize the tensile stress experienced by the member being retained (in this case, the rod) because the retention assembly serves to rigidly couple the piston to the rod and does not provide a stress reduction mechanism.

It would be advantageous to provide a relatively simple, reliable, durable, and inexpensive retention system that could effectively hold a ceramic element or plunger and at the same time reduce the magnitude of tensile stresses experienced by the plunger to extend the life of the plunger.

SUMMARY

According to one exemplary embodiment, a retention system comprises a first element, a retention ring, a resilient member, and a retainer. The first element has a longitudinal axis and may include an engagement structure. The retention ring may be divided into at least two pieces and may be located around at least a portion of the first element. At least a portion of the retention ring may engage the engagement structure of the first element. The resilient member may be coupled to the retention ring and may be configured to resiliently bias each of the at least two pieces of the retention ring toward the first member. The retainer may be coupled around at least a portion of the retention ring and at least a portion of the resilient member. The retainer may have an inner surface that is spaced apart from an outer surface of at least one of the retention ring and the resilient member by a gap. The first element, the retention ring, the resilient member, and the retainer may be configured so that the retention ring is moveable in an axial direction relative to the first element and so that the movement of the retention ring relative to the first element acts to expand the resilient member against the bias provided by the resilient member.

According to another exemplary embodiment, a method of retaining a first element within a second element comprises the steps of providing a first engagement structure on the first element and providing a second engagement structure on the second element. The second engagement structure may be configured to engage the first engagement surface and to move relative to the first engagement structure. The method also includes the step of providing a resilient member to store energy when the second engagement structure moves relative to the first engagement structure.

DETAILED DESCRIPTION

Referring generally toFIG. 1, a fuel system10is shown according to one exemplary embodiment. Fuel system10is a system of components that cooperate to deliver fuel (e.g., diesel, gasoline, heavy fuel, etc.) from a location where fuel is stored to the combustion chamber(s) of an engine12where it will combust and where the energy released by the combustion process will be captured by engine12and used to generate a mechanical source of power. Although depicted inFIG. 1as a fuel system for a diesel engine, fuel system10may be the fuel system of any type of engine (e.g., an internal combustion engine such as a diesel or gasoline engine, a turbine, etc.). According to one exemplary embodiment, fuel system10includes a tank14, a transfer pump16, a high-pressure pump18, a common rail20, fuel injectors22, and an electronic control module (ECM)24.

Tank14is a storage container that stores the fuel that fuel system10will deliver. Transfer pump16pumps fuel from tank14and delivers it at a generally low pressure to high-pressure pump18. High-pressure pump18, in turn, pressurizes the fuel to a high pressure and delivers the fuel to common rail20. Common rail20, which is intended to be maintained at the high pressure generated by high-pressure pump18, serves as the source of high-pressure fuel for each of fuel injectors22. Fuel injectors22are located within engine12in a position that enables fuel injectors22to inject high-pressure fuel into the combustion chambers of engine12(or pre-chamber or ports upstream of the combustion chamber in some cases) and generally serve as metering devices that control when fuel is injected into the combustion chamber, how much fuel is injected, and the manner in which the fuel is injected (e.g., the angle of the injected fuel, the spray pattern, etc.). Each fuel injector22is continuously fed fuel from common rail20such that any fuel injected by a fuel injector22is quickly replaced by additional fuel supplied by common rail20. ECM24is a control module that receives multiple input signals from sensors associated with various systems of engine12(including fuel system10) and indicative of the operating conditions of those various systems (e.g., common rail fuel pressure, fuel temperature, throttle position, engine speed, etc.). ECM24uses those inputs to control, among other engine components, the operation of high-pressure pump18and each of fuel injectors22. The purpose of fuel system10is to ensure that the fuel is constantly being fed to engine12in the appropriate amounts, at the right times, and in the right manner to support the operation of engine12.

Referring now toFIG. 2, high-pressure pump18is configured to increase the pressure of the fuel from a pressure that is sufficient to transfer the fuel from the tank to a pressure that is desirable for the injection of the fuel into the combustion chambers of engine12(or injection elsewhere). Such injection pressures may vary between different applications, but often range between approximately 1500 bar and 2000 bar, and may include pressures that are below 1500 bar or above 2000 bar. According to one exemplary embodiment, pump18includes a housing30, a head32, a camshaft34, two tappet assemblies36, two resilient members40, two control valve assemblies42, and two plunger assemblies43.

Housing30is a rigid structure that generally serves as the base of pump18. Housing30includes a central bore44that is configured to receive camshaft34, as well as two spaced-apart, parallel tappet bores46that are each configured to receive at least a portion of a tappet assembly36, a plunger assembly43, a resilient member40, and head32. The axis of each tappet bore46is arranged perpendicular to the axis of central bore44such that the rotation of camshaft34within central bore44causes tappet assemblies36to translate in a linear, reciprocating manner within tappet bores46. Housing30also includes a face48at the distal ends of tappet bores46that is configured to receive head32.

Head32is coupled to face48of housing30and generally serves, among other things, to enclose tappet bores46, provide a portion of the structure defining pumping chambers63(discussed below), receive control valve assembly42, and provide various ports and ducts to direct the flow of fuel into and out of pumping chambers63. Head32includes a face50that cooperates with face48of housing30(and, optionally, a sealing element such as an o-ring) to provide a sealed interface between head32and housing30. Head32also includes two plunger bores52(e.g., chambers, plunger chambers, pressurization chambers, etc.) that are each configured to receive a portion of the corresponding plunger assembly43. In addition, at the end of each of the plunger bores52that is farthest from housing30, head32includes an aperture54that is configured to receive a portion of control valve assembly42.

Camshaft34is a driven member that is formed from an elongated shaft that includes two sets of cam lobes56that are spaced apart along the length of camshaft34and a gear57on one of its two ends. Gear57is a driven gear that is configured to engage another gear that is driven, either directly or indirectly, by engine12. For example, gear57may be configured to engage a corresponding gear of a camshaft that actuates the intake and/or exhaust valves of engine12. The two sets of cam lobes56are spaced along the length of camshaft34so as to correspond with each of the two tappet assemblies36. According to various exemplary and alternative embodiments, each set of cam lobes56may include a single cam lobe, two cam lobes, three cam lobes, or more than three cam lobes, with each cam lobe representing a complete pumping and filling cycle. According to over various alternative and exemplary embodiments, the two sets of cam lobes may be in phase with one another (such that the cam lobes of the first cam lobe set will pass under head32at the same time as the corresponding cam lobes of the second cam lobe set) or they may be out of phase with one another (such that the cam lobes of the first cam lobe set will pass under head32at different times than the corresponding cam lobes of the second cam lobe set). According to various other alternative and exemplary embodiments, the extent to which the cam lobes of the first cam lobe set may out of phase relative to the cam lobes of the second cam lobe set may vary depending on the application of pump18and other factors.

Referring still toFIG. 2, each tappet assembly36(also sometimes referred to as a lifter assembly) is configured to engage one of the two sets of cam lobes56, transform the rotational movement of the corresponding cam lobes56into linear movement, and transfer such linear movement to the corresponding plunger assembly43. Each tappet assembly36includes a body58that engages and receives a portion of plunger assembly43, a roller60that engages and follows a set of cam lobes56, and a pin62that couples roller60to body58. Body58is received within the corresponding tappet bore46of housing30and translates back and forth within tappet bore46as camshaft34rotates.

Resilient member40, shown as a compression spring, is an element or apparatus that serves to bias the corresponding plunger assembly43and tappet assembly36toward camshaft34. By biasing both the corresponding plunger assembly43and tappet assembly36toward camshaft34, resilient member40helps to ensure that plunger assembly43returns to its lowest position (hereinafter referred to as “bottom dead center”) before camshaft34completes another rotation (or partial rotation) and forces plunger assembly43back up to its highest position (hereinafter referred to as “top dead center”). This helps to ensure that plunger assembly43is performing a complete filling cycle (the cycle where plunger assembly43moves from top dead center to bottom dead center) and a complete pumping cycle (the cycle where plunger assembly43moves from bottom dead center to top dead center) for each cam lobe56in the corresponding cam lobe set of camshaft34.

Control valve assembly42generally serves to control the fluid communication between the fuel being provided by transfer pump16(a low pressure fuel source and part of a low pressure fuel system) and pumping chamber63(discussed below), and therefore is capable of controlling the amount of fuel that enters pumping chamber63during the filling cycle and the amount of fuel that is discharged back into the low pressure fuel system during the pumping cycle. Control valve assembly42includes a valve element64, an armature66coupled to the valve element, a biasing member68, and a solenoid70. Valve element64is moveable between on open position in which the fuel inlet (e.g., low pressure fuel system) is fluidly connected to pumping chamber63and a closed position in which the fuel inlet is not fluidly connected to pumping chamber63. Armature66and solenoid70cooperate with one another such that the activation of solenoid causes armature66to move toward solenoid70. Because armature66is coupled to valve element64, the movement of armature66toward solenoid70causes valve element64to move to the closed position. Biasing member68, shown as a compression spring, urges armature66away from solenoid70and therefore urges valve element64toward the open position when solenoid70is deactivated.

Referring now toFIGS. 2,3, and4, each of the two plunger assemblies43is an assembly of components that is located generally between the corresponding tappet assembly36and head32and that reciprocate with tappet assembly36relative to head32to pressurize the fluid within pumping chamber63. According to one exemplary embodiment, plunger assembly43includes a plunger80and a retention assembly82.

Plunger80is a member (e.g., piston, shaft, rod, element, retained member) that is configured to reciprocate or slide within plunger bore52of head32as the corresponding tappet assembly36reciprocates within tappet bore46of housing30. According to one exemplary embodiment, plunger80includes an elongated, generally cylindrical body83having a side wall85, a first end84that is configured to extend into plunger bore52, and a second end86located near tappet assembly36. Each of the first end84and second end86may be tapered or radiused to facilitate pump operation and/or assembly. First end84, plunger bore52, and a portion of control valve assembly42define pumping chamber63, the volume of which changes as plunger80moves back and forth, or up and down, within plunger bore52. Body83also includes an engagement structure shown as an annular groove88proximate second end86that is configured to receive a portion of retention assembly82. According to one exemplary embodiment, engagement structure or groove88includes a main portion90having a generally semi-circular cross-sectional profile and two ends92and94that form a gradual (e.g., radiused or tapered) transition between main portion90and sidewall85of body83. Stated differently, main portion90of groove88is a concave, curved region whereas each of ends92and94of groove88forms a generally convex and/or substantially flat, transition region. The design of groove88is intended to allow the portion of retention assembly82received within groove88to have the ability to move within groove88in an axial direction relative to body83, but only if the retention assembly82also moves in a radially outward direction. Although the engagement structure may take any one of a variety of different shapes that force retention assembly82to move radially outward as it moves in at least one axial direction relative to plunger80, the generally semi-circular groove88described above is beneficial (as other groove shapes may be) in that it helps to reduce stress concentrations in the area of groove88. According to various alternative and exemplary embodiments, the groove may be provided around the entire circumference of body83or may extend over one or more portions or segments of the circumference. According to other various alternative and exemplary embodiments, the ends of the groove may be configured such that only one of the ends forms a transition region so that the retention assembly may only move in one axial direction within the groove. According to still other alternative and exemplary embodiments the engagement member may be a channel, a bead, a flange, an indentation, a projection, a bump, or other suitable structure that cooperates with a corresponding engagement structure provided on the retention ring.

According to various exemplary and alternative embodiments, plunger80may be made from one or more of a variety of different ceramic materials, such as carbides, pure oxides, nitrides, non-silicate glasses and others. For example, according to one exemplary embodiment, plunger80may be made from zirconia (ZrO2). According to other alternative embodiments, plunger80may be made from one or more of alumina (Al2O3), calcia (CaO), silicon carbide (SiC), and silicon nitride (Si3N4). According to other various alternative and exemplary embodiments, the plunger may be made from any one of a variety of different materials that are suitable for the application in which the plunger will be used. Such materials may include one or more of various metals, alloys, irons, steels, composites, polymers, elastomers, or any other suitable materials.

Retention assembly82is an assembly of components that couple to plunger80and that serve to apply at least a portion of the force provided by resilient member40to plunger80. According to one exemplary embodiment, retention assembly82includes a retention ring100, a resilient member102, and a retainer104.

According to one exemplary embodiment, retention ring100is a generally ring-shaped member that is configured to substantially surround and engage groove88of plunger80. Retention ring100is shown as being diametrically divided into two symmetrical pieces or halves. However, according to various alternative embodiments, the retention ring may be divided into three, four, five, or more than five pieces that cooperate to substantially surround groove88. Retention ring100includes an engagement structure shown as a projection in the form of a ring-shaped bead106having a substantially circular cross-sectional shape and also includes a tube-like skirt108having a substantially rectangular cross-sectional shape and extending from engagement structure or bead106in an axial direction. Bead106includes a convexly curved inner surface110that is configured to engage groove88of plunger80and an outer surface112that may be configured to engage or contact a portion of retainer104. The curved profile of inner surface110is substantially semi-circular and closely corresponds to the curved profile of groove88. Skirt108includes an inner surface114that is configured to be located adjacent the portion of sidewall85of plunger80that is between groove88and end86of plunger80. Skirt108also includes an outer surface116that is configured to be adjacent to, and substantially surrounded by, resilient member102. As shown inFIGS. 3 and 4, the cylindrical skirt108has an axial length that is greater than the radially inward extending annular bead106. According to one exemplary embodiment, each half or piece of retention ring100may be formed through a stamping process from a suitable metal. According to other various alternative and exemplary embodiments, the retention ring may be formed as single piece and then cut or split into the appropriate number of pieces. According to still other various alternative and exemplary embodiments, the retention ring or each half or piece of the retention ring may be machined or formed through any suitable manufacturing process from any one or more of a variety of different materials, including metals, steels, alloys, iron, ceramics, composites, or any other suitable material. According to still other alternative and exemplary embodiments the engagement member of the retention ring may be a channel, a bead, a flange, an indentation, a projection, a bump, or other suitable structure that cooperates with a corresponding engagement structure provided on the plunger.

Resilient member102is intended to act upon retention ring100to maintain the engagement of bead106of retention ring100with groove88of plunger80and is also intended to serve as a temporary energy storage device. According to one exemplary embodiment, resilient member102is a circular band of a resilient material (e.g., metal, spring steel, etc.) that includes a split103along the circumference of the band to provide two ends that move relative to one another when the diameter of the band is increased. For example, according to one exemplary embodiment, resilient member102may be similar to a “Corbin Clamp” that does not have tabs that facilitate the easy expansion of the clamp. According to another exemplary embodiment, resilient member102may be a strip of a resilient material that is formed into a circular band such that the two ends of the strip are located proximate one another and move apart from one another when the diameter of the band is increased. Resilient member102includes an inner surface118that is configured to be located adjacent skirt108of retention ring100and an outer surface120that is configured to be located near a corresponding portion of retainer104. The resilient nature of resilient member102allows the two halves of retention ring100to move away from one another when acted upon by a force that overcomes the biasing force provided by resilient member102. As the two halves of retention ring100move away from one another and overcome the biasing force provided resilient member102, the diameter of resilient member102increases and energy is stored within resilient member102. The resiliency of resilient member (e.g, the bias provided by the resilient member and the force required to expand the resilient member) may be tuned for a particular application by the selection of an appropriate material and/or by adjusting the design of the resilient member (e.g, such as by altering the thickness of the resilient member). According to one exemplary embodiment, resilient member102is formed through a stamping process from a suitable metal. According to various alternative and exemplary embodiments, resilient member may be machined or formed through any suitable manufacturing process from any one or more of a variety of different materials, including metals, steels, spring steels, alloys, composites, polymers, elastomers, or any other suitable materials.

Retainer104is an element that serves to receive resilient element40(e.g., spring) and ultimately transfer the force provided by resilient element40to plunger80. According to one exemplary embodiment, retainer104includes a body portion122and a flange124, one or both or which may be engaged by body58of tappet assembly36. Body portion122includes a central aperture126that defines three concentric regions: a first region128in the upper portion of retainer104, a second region130in the lower portion of retainer104, and a transition region132located between first region128and second region130. First region128has a diameter that is large enough to receive plunger80, but not large enough to allow retention ring100to pass through. Second region130, on the other hand, has a diameter that is large enough to receive both retention ring100and resilient member102. More specifically, the diameter of second region130is large enough that there is a predetermined radial gap200between an inner surface134of second region130and outer surface120of resilient member102, or alternatively, a predetermined radial gap201between inner surface134of second region130and outer surface112of bead106. Radial gap200(or radial gap201as the case may be) provides a space that allows the pieces of retention ring100to move away from plunger80and that allows resilient member102to expand. However, the gap200(or gap G′) is sized such that the pieces of retention ring100are not permitted to move far enough away from plunger80that bead106becomes disengaged with groove88. Transition region132, which is intended to serve as a contact surface for bead106of retention ring100, is defined by a surface that extends between the surface defining first region128and inner surface134of second region130. According to one exemplary embodiment, transition region132is defined by a generally flat surface that is oriented at about a60degree angle relative to a line that is parallel to the longitudinal axis of retainer104. According to various alternative and exemplary embodiments, the transition region may be defined by a surface that is curved, radiused, tapered, flat, or by a surface having one or more portions that are curved, radiused, tapered, and/or flat. That particular configuration of transition region132may be determined based on the particular application in which plunger assembly43will be used, as the contact between transition region132and bead106and the component forces transferred thereby may need to be adjusted for different situations. Flange124of retainer104extends radially outward from body portion122and serves as the portion of retainer104that directly engages spring40. According to one exemplary embodiment, retainer104is formed through a stamping process from a suitable metal. According to various alternative and exemplary embodiments, the retainer may be machined or formed through any suitable manufacturing process from any one or more of a variety of different materials, including metals, steels, alloys, iron, ceramics, composites, polymers, elastomers, or any other suitable material.

Although only one pump configuration was described above, it should be understood that the described pump is only one example of a pump in which the retention assembly may be used. For example, while only an inline plunger or piston pump was described above, the retention assembly could also be used within any one of a variety of different piston or plunger pump configurations (e.g., axial piston pump, radial piston pump, bent axis pump, inlet metered pump, outlet metered pump, etc.) and with any one of a variety of different fluids (e.g., fuel, oil, hydraulic fluid, etc.). It also should be understood that while pump18was described above as including two cylinders or pumping chambers63, and consequently, two corresponding tappet assemblies36, resilient members40, control valve assemblies42, and plunger assemblies43, the pump could also be configured to include one, three, four, or more than four pumping chambers, depending on the particular application in which the pump is intended to be used.

INDUSTRIAL APPLICABILITY

Pump18operates to pressurize a fluid (e.g., fuel) by drawing fuel into one or more pumping chambers63, reducing the size of pumping chambers63, and then forcing the fuel through an outlet to common rail20. The way in which pump18operates will now be more specifically described in connection with one of pumping chambers63. Starting from the beginning of the pumping cycle, plunger80is at bottom dead center and pumping chamber63, which is full of fuel, is at its maximum volume. As one of cam lobes56rotates to a position under tappet assembly36, the cam lobe56forces tappet assembly36, and therefore plunger assembly43, upward. As plunger assembly43moves upward (according to the contour of cam lobe56), plunger80moves upward within plunger bore52of head32thereby reducing the volume of pumping chamber63. When plunger80begins to move upward, control valve assembly42is activated, closing off pumping chamber63from the fuel inlet. As plunger80continues to move upward, the volume of pumping chamber63continues to reduce, which forces fuel out of pumping chamber63to common rail20. The pumping cycle continues until plunger80reaches top dead center, which occurs when the peak of cam lobe56is below tappet assembly36. Once plunger80reaches top dead center, control valve assembly42is deactivated to allow inlet fuel from transfer pump16to enter pumping chamber63. As the peak of cam lobe56rotates past tappet assembly36, the bias provided by resilient element40urges plunger assembly43and tappet assembly36back down. At this point, the backside of cam lobe56is below tappet assembly36, which allows it to move back down. As plunger80moves downward within plunger bore52during the filling cycle, fuel continues to fill pumping chamber63. When plunger80reaches bottom dead center, pumping chamber63is full of fuel and is at its maximum volume. The cycle then starts over again, with the cam lobe56urging tappet assembly36and plunger assembly43back up toward top dead center. Control valve assembly42may be activated and deactivated at different times during the pumping and filling cycles to control how much fuel enters pumping chamber63during the filling cycle and to control whether pumping chamber63is coupled to the low pressure system (which acts like a drain) during all or a portion of the pumping cycle. In this way the output of the pump may be controlled.

In order to return each tappet assembly36and plunger assembly43pair to bottom dead center before lobes56on camshaft34initiate the next pumping stroke, resilient member40must apply a substantial force to tappet assembly36and plunger assembly43. Over thousands of cycles, the repetitive application of a force by camshaft34against the bias of resilient member40to take plunger assembly43through the pumping cycle and then the release of the force provided by camshaft34in combination with the continued biasing force provided by resilient member40to take plunger assembly43through the filling cycle, is difficult for a ceramic plunger to withstand. Reducing the magnitude of the forces experienced by the plunger is believed to help improve the useful life of plungers made of ceramics or other similar materials. Plunger assembly43is believed to accomplish this reduction by temporarily storing energy when the forces applied to plunger80are the greatest and then releasing that energy at a later time when the forces acting on plunger80are less.

In operation, tappet assembly36and plunger assembly43move upward (during a pumping cycle) when a lobe56of camshaft34rotates to a point where it is underneath tappet assembly36. In this position, lobe56applies a force to tappet assembly36, which then applies that force directly to plunger assembly43, in particular, to end86of plunger80. This application of force, which overcomes the biasing force provided by spring40, is generally not problematic with respect to the use of ceramic plungers because the stress experienced by plunger80is a compressive stress, which ceramics are able to withstand relatively well. When tappet assembly36and plunger assembly43reach top dead center, the highest point of lobe56will be under tappet assembly36. As camshaft34continues to turn, tappet assembly36will start to roll down the backside of cam lobe56. At that point in time, camshaft34will stop applying any upward force to tappet assembly36and plunger assembly43. Without the force applied by camshaft34, the force provided by spring40(which is fully compressed at this point) to retainer104will urge plunger assembly43and tappet assembly36back toward bottom dead center. This is the point in the cycle that is normally problematic with respect to previous attempts to retain ceramic plungers because this is where the greatest return force is applied to the plunger (due to the full compression of spring40) and because the force is normally applied to the ceramic plunger at a location other than an end of the plunger. Consequently, this is the point in the cycle at which the ceramic plunger is exposed to the greatest tensile stresses.

The downward force applied by spring40is applied directly to flange124of retainer104, which is then transferred to body portion122of retainer104. As previously described, first region128of body portion122receives plunger80, but is not large enough to receive retention ring100. Second region130of body portion122, on the other hand, receives retention ring100in a chamber defined by transition region132and inner surface134of second region130. Thus, as retainer104is forced downward by spring40, retention ring100is also forced downward because it is unable to pass beyond transition region132of retainer104. Specifically, transition region132of retainer104contacts bead106of retention ring100and applies a force to bead106. Due to the orientation of transition region132, a force is applied to bead106that has an axial component that urges bead106downward and a radial component that urges bead106radially inward. Transition region132may be designed to provide a force to bead106that has a proportion between its axial force component and its radial force component that is appropriate for the particular application. Because bead106is located within groove88of plunger80, bead106is not able to move inward. Bead106is, however, able to move downward within groove88as illustrated inFIG. 4. But due to the configuration of bead106and groove88, the only way for bead106to move downward is either to force plunger80downward so that groove88moves along with bead106or to move both outward and downward, relative to plunger80, within groove88. In order for bead106to move outward, the two halves of retention ring100must move apart from one another. This movement of the two halves of retention ring100apart from one another is done against the bias provided by resilient member102and acts to expand resilient member102as illustrated inFIG. 4. The expansion of resilient member102(which acts as a type of spring) against the bias it provides serves to store energy within resilient member102. The energy stored within resilient member102is then released at a later time, either as plunger80moves downward toward bottom dead center or at the beginning of the subsequent pumping cycle. To ensure that bead106stays within groove88, the extent to which the two halves of retention ring100may expand is limited by 1) the radial gap200between outer surface120of resilient member102and inner surface134of second region130of retainer104, and/or 2) the radial gap201between outer surface112of bead106and inner surface134of second region130of retainer104. The size of the radial gap may be adjusted such that it is suitable for the particular application and circumstances.

The magnitude of the force generated by spring40is the greatest when plunger assembly43is at top dead center because that is the point at which spring40is fully compressed. Thus, the magnitude of the force or stress ultimately applied to plunger80is the greatest when plunger80is at or near top dead center. By storing energy within resilient member102at this point, the peak force that acts upon plunger80at any one time can be reduced. The reduction of the peak force or stress is believed to increase the life of the plunger.

Depending upon the configuration and application of the pump, plunger assembly43may be tuned or adjusted to operate most effectively. According to one exemplary embodiment, plunger assembly43may be tuned such that bead106moves within groove88and expands resilient member102only when plunger80would otherwise be subjected to forces that are large enough to damage plunger80. Characteristics such as pump speed, the desired pressure and flow rates of the pump, the size of the pump, the number of cylinders or pumping chambers of the pump, and/or other potential characteristic may all affect how plunger assembly43should be tuned or adjusted. To tune the plunger assembly, factors such as the size and shape of groove88, the size and shape of bead106, the material from which resilient member102is made, the thickness and width of resilient member102, size of the gap200or gap G′, the configuration and orientation of transition region132of the retainer104, the configuration of camshaft34, and other potential factors may be adjusted.

It is important to note that the construction and arrangement of the elements of the retention system as shown in the exemplary and other alternative embodiments is illustrative only. Although only a few embodiments of the retention system have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of the interfaces (e.g., the groove and bead, etc.) may be reversed or otherwise varied, and/or the length or width of the structures and/or members or connectors or other elements of the system may be varied. It should be noted that the elements and/or assemblies of the retention system may be constructed from any of a wide variety of materials that provide sufficient strength, durability, and other relevant characteristics, from any of a wide variety of different manufacturing processes, and in any of a wide variety of colors, textures and combinations. It should also be noted that the retention system may be used in association with various types of pumps, including a variety of different piston pumps, or with a variety of different mechanisms in a variety of different applications (e.g., various mechanisms in engines, such as intake or exhaust valves, hydraulic cylinders, fuel injectors, etc.). Accordingly, all such modifications are intended to be included within the scope of the present inventions. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary and other alternative embodiments without departing from the spirit of the present inventions.