Patent Grant
10557446
The present disclosure relates generally to inlet metered liquid pumps with output control via an inlet throttle valve, and more particularly to an inlet metered liquid pump having a valve stack designed for cavitation mitigation.
In one class of high pressure liquid pumps, output from the pump is controlled by throttling the inlet with an electronically controlled metering valve. As a consequence, cavitation bubbles are generated when the output of the pump is controlled to be less than the volume displaced with each reciprocation of the pump plunger. One application for such a pump is in a fuel system that utilizes a common rail and a high-pressure fuel pump to pressurize the rail. In this specific example, the pump is driven directly by the engine, and the output from the pump is controlled by changing the inlet flow area via the inlet throttle valve.
When the inlet throttle valve reduces the flow area to the plunger cavity, cavitation bubbles can be generated in the vicinity of the throttle valve, or potentially elsewhere, and travel to the plunger cavity to occupy part of the volume created by the retracting plunger of the pump. When the cavitation bubbles collapse adjacent a surface, cavitation erosion can occur. In some instances, cavitation erosion can occur at undesirable locations, such as the inlet port passage or in the vicinity of valve seats. Depending upon where the cavitation damage occurs, and the extent of that damage, the pump performance can be undermined, and maybe more importantly, the eroded particles can find their way into fuel injectors possibly causing even more serious problems.
U.S. Pat. No. 8,202,064 B2 to Tian et al. is directed to an inlet throttle controlled liquid pump with cavitation damage avoidance feature. Tian et al. propose a specially shaped and sized cavitation flow adjuster extending from a valve member in a passive inlet check valve. A flow pattern is apparently formed by the valve in a way that encourages cavitation bubble collapse away from surfaces that could result in unacceptable cavitation damage to the pump. While Tian et al. appear to have provided advancements over the state of the art, additional developments relating to cavitation mitigation would be welcomed in the industry.
In one aspect, a valve assembly for a liquid pump includes a valve body having each of a fluid inlet and a fluid outlet formed therein. The valve body includes a valve stack forming an inlet valve seat and an outlet valve seat each positioned fluidly between the fluid inlet and the fluid outlet. An inlet check valve is positioned at least partially within the valve stack and movable between a closed position blocking the inlet valve seat, and an open position. An outlet check valve is positioned at least partially within the valve stack and movable between a closed position blocking the outlet valve seat, and an open position. A plunger is movable within the valve body between a retracted position and an advanced position. The inlet check valve, the outlet check valve, and the plunger define a common axis that extends through the valve stack, and the inlet check valve is located axially between the outlet check valve and the plunger. The valve body further has formed therein a pumping chamber receiving the plunger, an inlet chamber within the valve stack, and an outlet chamber within the valve stack. Each of the pumping chamber, the inlet chamber, and the outlet chamber are centered on the common axis. The valve assembly further includes a plurality of flow channels for transitioning a pumped liquid between the fluid inlet and the fluid outlet. The plurality of flow channels are arranged in a first parallel group extending between the inlet chamber and the pumping chamber and having a first circumferential distribution about the common axis, and a second parallel group extending between the inlet chamber and the outlet chamber and having a second circumferential distribution about the common axis.
In another aspect, a valve stack for a liquid pump includes an inlet piece having formed therein each of an inlet valve seat, a fluid inlet, and a plurality of incoming fluid passages extending between the fluid inlet and the inlet valve seat. The valve stack further includes an outlet piece positioned upon a first side of the inlet piece, the outlet piece having formed therein an outlet valve seat, and a fluid outlet. The valve stack further includes a pumping piece positioned upon a second side of the inlet piece such that the inlet piece is sandwiched between the pumping piece and the outlet piece, and an inlet check valve positioned at least partially within the inlet piece. The inlet check valve is movable between a closed position blocking the inlet valve seat, and an open position. The valve stack still further includes an outlet check valve positioned at least partially within the outlet piece, and movable between a closed position blocking the outlet valve seat, and an open position. The inlet piece, the outlet piece, and the pumping piece define a common axis. Each of the inlet check valve and the outlet check valve are movable along the common axis between the corresponding closed position and open position. The valve stack further forms an inlet chamber between the inlet piece and the pumping piece, an outlet chamber between the inlet piece and the outlet piece, a pumping chamber, and a plurality of flow channels. The plurality of flow channels are arranged in a first parallel group extending between the inlet chamber and the pumping chamber and having a first circumferential distribution about the common axis, and the second parallel group extending between the inlet chamber and the outlet chamber and having a second circumferential distribution about the common axis.
In still another aspect, a liquid pump includes a pump housing having each of a pump inlet and a pump outlet formed therein, and an inlet metering valve. A valve assembly is positioned within the pump housing and includes a valve body having a valve stack forming an inlet valve seat and an outlet valve seat. The liquid pump further includes an inlet check valve positioned at least partially within the valve stack and movable between a closed position blocking the inlet valve seat, and an open position. An outlet check valve is positioned at least partially within the valve stack and movable between a closed position blocking the outlet valve seat, and an open position. A plunger is movable within the valve body between a retracted position and an advanced position. The inlet check valve, the outlet check valve, and the plunger define a common axis that extends through the valve stack, and the inlet check valve is located axially between the outlet check valve and the plunger. The valve body further has formed therein a pumping chamber receiving the plunger, an inlet chamber within the valve stack, and an outlet chamber within the valve stack, and each of the pumping chamber, the inlet chamber, and the outlet chamber are centered on the common axis. The liquid pump further includes a plurality of flow channels for transitioning a pumped liquid through the valve stack and being arranged in a first parallel group extending between the inlet chamber and the pumping chamber and having a first circumferential distribution about the common axis, and a second parallel group extending between the inlet chamber and the outlet chamber and having a second circumferential distribution about the common axis.
Referring to
Those skilled in the art will be familiar with the concept of an inlet metered pump as in the present context. Inlet valve 18 might be part of and within pump 20 or potentially positioned fluidly upstream of a pump housing 22 of pump 20. A suitable design for inlet valve 18 is known from commonly owned U.S. Pat. No. 8,202,064 B2 to Tian et al., discussed above, although the present disclosure is not thereby limited. Those skilled in the art will also be familiar with cavitation phenomena associated with inlet metered pumps. As will be further apparent from the following description, pump 20 may be structured according to multiple design concepts, which can be used together or independently of one another, to mitigate cavitation. The design concepts include, but are not limited to, robust and symmetric mechanical design, component positioning and arrangement, vapor distribution, reduced hydraulic stiffness, and biasing of the production and/or collapse of vapor bubbles towards areas within the liquid pump relatively less sensitive to cavitation damage.
Pump 20 includes a rotatable camshaft 24 positioned at least partially within pump housing 22 and structured to be rotated by way of an engine geartrain (not shown) in a generally conventional manner. Rotation of camshaft 24 causes the reciprocation of a plurality of pumping mechanisms 26 each equipped with a cam follower 28 for a plunger 78 in a generally conventional manner. Each of the plurality of pumping mechanisms 26 feeds pressurized fluid to a common fluid pressure space 30 (hereinafter “space 30”) and thenceforth to common rail 12 by way of a pump outlet 34 formed in pump housing 22. A pump inlet 32 may be formed in pump housing 22 and is supplied with fuel at a flow determined according to a flow area of inlet valve 18 as described herein.
In the illustrated embodiment, pump housing 22 includes a plurality of housing pieces, namely, a first housing piece 36 defining space 30 and pump outlet 34, a second housing piece 38, and a third housing piece 39 wherein the plurality of pumping mechanisms 26 are disposed. It will be appreciated that a variety of different housing constructions including number and design of the various housing pieces, number of pumping mechanisms, and design and routing of the various plumbing features can vary from that which is illustrated. Moreover, additional valves such as a one-way valve between transfer pump 16 and inlet valve 18 and/or a one-way valve between pump outlet 34 and common rail 12 might be used, but are omitted from
Pump 20 further includes a valve assembly 40 associated with each pumping mechanism 26. It should be appreciated that descriptions herein of any component or assembly in the singular, such as valve assembly 40 or pumping mechanism 26, is intended to refer analogously to any other of such components as are used in pump 20 or other embodiments contemplated herein. Valve assembly 40 includes a valve body 42 positioned within pump housing 22. Referring also to
An inlet check valve 74 coupled with a biasing spring 75 is positioned at least partially within valve stack 60 and at least partially within inlet piece 62. Inlet check valve 74 is movable against a biasing force of biasing spring 75 between a closed position blocking inlet valve seat 64, and an open position, not blocking inlet valve seat 64. An outlet check valve 76 associated with a biasing spring 77 is positioned at least partially within outlet piece 68, and movable between a closed position blocking outlet valve seat 70, and an open position not blocking outlet valve seat 70. A plunger 78 is movable within valve body 42 between a retracted position and an advanced position to draw liquid from pump inlet 32 into valve stack 60 by way of fluid inlet 46 and the various other fluid passages and connections of pump 20, and to pressurize the liquid and convey the same to space 30 to be conveyed to common rail 12 for injection into an engine cylinder.
It will be appreciated that with inlet valve 18 restricting inlet flow area to pump 20, the drawing in of liquid by way of retraction of plunger 78 will tend to cause the fluid pressure of the liquid to drop to or below a pressure at which vapor bubbles form in the liquid, which bubbles must be collapsed for pressurization to occur. The collapse of these bubbles can be associated with production of high velocity micro-jets of liquid which can impinge upon surfaces inside a pump to cause cavitation damage in the nature of erosion of material forming the surfaces. While cavitation phenomena will still occur during operation of pump 20, damaging cavitation phenomena is expected to be reduced in severity, and biased in terms of location to areas of the pump that are remote from surfaces sensitive to erosive damage, in accordance with the present disclosure.
Inlet piece 62, outlet piece 68, and pumping piece 72 define a common axis 80. Each of inlet check valve 74, outlet check valve 76, and plunger 78, is movable along common axis 80 between the corresponding closed position and open position, or in the case of plunger 78 retracted position and advanced position. It has been discovered that arranging substantially axisymmetric parts substantially coaxially as in valve stack 60 can have a number of beneficial effects, including improved symmetry and uniformity of flows of liquid, the ability to match stiffnesses of contacting parts so as to avoid relative motion and thus reduce or avoid fretting damage during service, and also relative uniformity of deformation of parts over time. For example the phenomenon known in the art as “seat beat-in” can be expected to occur in a relatively uniform pattern compare to alternative designs. It can further be noted that inlet piece 62 being axially sandwiched between outlet piece 68 and pumping piece 72 can position inlet check valve 74 axially between plunger 78 and outlet check valve 76. Arranging the valves as shown can, moreover, create a reduced amount of vapor at or near outlet check valve 76, particularly where inlet check valve 74 is arranged spatially and hydraulically in sequence with outlet check valve 76 in an axial direction away from plunger 78. In the illustrated embodiment, inlet valve seat 64 includes a flat seat, and outlet valve seat 70 includes a conical seat, each centered upon common axis 20. The relationships between the foregoing and other design features and cavitation phenomena are further discussed below.
It can further be noted that in the illustrated embodiment valve body 42 includes an outer valve body piece 50 and an insert piece 52 positioned within outer valve body piece 50. Insert piece 52 defines a central bore 54 and an annulus that forms fluid inlet 44, with piece 50. The terms “fluid inlet” and “inlet annulus” are used interchangeably herein. Insert piece 52 further includes a plurality of inlet orifices 56 formed therein that extend between fluid inlet or inlet annulus 44 and central bore 54. Inlet orifices 56 are generally radially extending and feed an axially extending inlet passage 58 in inlet piece 62. Valve stack 60 is within central bore 54 such that inlet annulus 44 is in fluid communication with inlet orifices 56 and with fluid inlet 46 in inlet piece 62. A plurality of incoming fluid passages 66 in inlet piece 62 extend radially inward from fluid inlet 46 to inlet passage 58.
As noted above, liquid pump 20, and in particular valve stack 60, is structured for reduced hydraulic stiffness, which can reduce the rate of pressure increase during a pumping or pressurization stroke with respect to time or “dp/dt”, as further discussed below. To this end, valve stack 60 further forms an inlet chamber 82 between inlet piece 62 and pumping piece 72, an outlet chamber 84 between inlet piece 62 and outlet piece 68, and a pumping chamber 86 between pumping piece 72 and insert piece 52. As shown in
Valve stack 60 also forms a plurality of flow channels 90. Flow channels 90 may each be circular in shape and arranged in a first parallel group 92 extending between inlet chamber 82 and pumping chamber 86 and having a first circumferential distribution about common axis 80, and a second parallel group 94 extending between inlet chamber 82 and outlet chamber 86 and having a second circumferential distribution about common axis 80. A flow area formed by first parallel group 92 may be less than a flow area formed by inlet check valve seat 64. In an implementation, the flow area may be less by a factor of about 50%. It has been observed that providing the greater downstream flow area during filling can bias the production of vapor bubbles towards pumping chamber 82 instead of towards the valve seats or other regions, such that the collapse of vapor bubbles is less troublesome or more manageable.
Referring also now to
Those skilled in the art will appreciate that all inlet metered pumps will by definition have some vapor generation, and the vapor must be collapsed to enable pressure to rise and pumping of liquid to start. In general terms, to obtain minimal or zero erosion in an inlet metered pump the bubbles must be collapsed at a low enough energy level that the bubble collapse does not produce jets high enough in energy to damage surfaces. Bubble collapse energies tend to be high when bubbles are collapsed in regions of high ambient pressure. Pressure rise from below vapor pressure to significantly above vapor pressure that occurs relatively rapidly can result in bubbles being caught in regions of high ambient pressure. As a result, when these vapor bubbles are collapsed they can be problematic and produce cavitation damage. Relatively rapid pumping rates and relatively large plungers can be associated with a relatively large dp/dt at least at the start of pumping.
As discussed above, dead volume can result in less system stiffness due to fluid bulk modulus that drives down dp/dt. In addition, the even and uniform distribution, identical shape and identical size of flow channels 90 results in fluid pumping through flow channels 90 with minimal production of recirculation zones, eddies, or other uneven or non-laminar flows that can be associated with cavitation. The total number of flow channels being eight, the circular shapes, as well as uniform radial spacing from common axis 80 and uniform circumferential distributions about common axis 80 are believed to impart a tendency for the liquid to behave more as a bulk that moves relatively uniformly during pumping action of pump 20. Moreover, the distributed, uniformly sized and uniformly arranged and uniformly shaped flow channels can uniformly distribute vapor such that no one local region is subject to a particular damage of bubble collapse. The smaller flow area of flow channels 90 relative to the open inlet valve seat 64 can also assist in biasing the location of vapor production and/or collapse toward pumping chamber 86, and thereby avoid collapse at critical valve seats or structural hot spots. These and other approaches described herein can maximize life potential of the pump even if some background level of erosion is unavoidable.
Also, as discussed above, the axial stacking, of substantially axisymmetric parts, allows stiffnesses to be matched, thereby minimizing relative motion of mating components at sealing surfaces and reducing or eliminating fretting wear. Symmetrical, on-center valves tend to deform uniformly in the high pressure and highly cyclic environment of pump 20, around a 360 degree seat, ensuring consistent sealing even after minor breaking in or debris-related wear. It has been observed that ensuring consistent sealing, particularly at outlet valves or delivery valves such as outlet check valve number 76, assists in limiting erosion. Valve seat leakage between pumping events can generate high velocity flows at high cavitation numbers, with the vapor bubbles resulting from such flows collapsed at the start of the next pumping event and causing erosive damage in the vicinity of the leaking seat.
Locating inlet check valve 74 axially between the top of pumping chamber 86 and outlet check valve member 76 provides flow paths further mitigating cavitation. In certain earlier designs, vapor bubbles that do form can be chased to the most remote locations from the prime mover, commonly the delivery valve. Without a design provision to mitigate this phenomenon as set forth herein, vapor bubble collapse can occur at that location. It will also be recalled that inlet valve seat 64 can include a flat seat, minimizing flow area versus lift for a given size of valve. Such a design can cause or enhance restriction downstream of the subject valve seat, and does not rely on a knife edge to seal, making the design more resilient to debris damage.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the fill and fair scope and spirit of the present disclosure. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims. As used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.
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