Mass flow control valve with low gain

Abstract

An exemplary valve assembly generally includes a valve seat and a stem. The valve seat includes an opening formed about a longitudinal axis, and the valve seat defines a boundary plane for the opening. The stem is mounted for movement relative to the valve seat and includes a head that projects into the opening. The head includes an untapered section, a tapered section distal to the untapered section, and a channel extending between the untapered section and the tapered section. The untapered section includes an interrupted section that is interrupted by the channel. The stem has a low-open position in which the boundary plane intersects the interrupted section to thereby permit fluid flow through the opening via the channel. The stem has a high-open position in which the boundary plane intersects the tapered section to thereby permit flow through the opening around the head.

Description

WW Ref: 24-3692- WO MASS FLOW CONTROL VALVE WITH LOW GAINCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to US Provisional Patent Application No.63 / 759,663, filed February 18, 2025, the contents of which are hereby incorporated by reference in their entirety.TECHNICAL FIELD

[0002] The present disclosure generally relates to mass flow control valves, and more particularly but not exclusively relates to mass flow control valves for combustion engines.BACKGROUND

[0003] Mass flow control valves for engines typically use a known flow area vs. position profile to produce accurate fuel flow across a large range of flows for a high turndown ratio. One way this may be accomplished is by creating a valve that has a consistent gain through its operating range. As used herein, gain is defined as the percent change in effective flow area for a 1% position movement. Typically, a major source of flow error is due to position sensor error. For a mass flow control valve, the gain value at a given point is also equal to the amount of error that would be caused by a 1% position sensor error. By maintaining a low flow gain, the effect of position errors on accuracy may be reduced.

[0004] Conventional valve designs typically have a very high gain at low positions, and the gain reduces as the valve opens. This can create relatively large inaccuracies at low open percent and at low flow areas. While some poppet style valves may have high turndown ratio by having a fully closed state, if the initial portion of that range has very high gain, the accuracy cannot be maintained on the low end. This results in the accurate turndown ratio being much less than the total turndown ratio. For these reasons among others, there remains a need for further improvements in this technological field.113202-958 / TSH 197868999WW Ref: 24-3692- WOSUMMARY

[0005] An exemplary valve assembly generally includes a valve seat and a stem. The valve seat includes an opening formed about a longitudinal axis that defines a proximal direction and an opposite distal direction, and the valve seat defines a boundary plane for the opening. The stem is mounted for movement relative to the valve seat and includes a head that projects into the opening. The head includes an untapered section, a tapered section positioned distal to the untapered section, and a channel extending between the untapered section and the tapered section. The untapered section includes an interrupted section that is interrupted by the channel. The stem has a low-open position in which the boundary plane intersects the interrupted section to thereby permit fluid flow through the opening via the channel. The stem has a high-open position in which the boundary plane intersects the tapered section to thereby permit flow through the opening around the head. Further embodiments, forms, features, and aspects of the present application shall become apparent from the description and figures provided herewith.- 2 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOBRIEF DESCRIPTION OF THE FIGURES

[0006] Fig. 1 is a cross-sectional illustration of a valve system according to certain embodiments.

[0007] Fig. 2 is a cross-sectional illustration of a portion of the valve system, and illustrates a mass flow control valve assembly according to certain embodiments in a closed position.

[0008] Fig. 3 is an exploded assembly view of the mass flow control valve assembly, which generally includes a valve seat, a stem, a closing seal, and a seat seal.

[0009] Fig. 4 is a cross-sectional illustration of a portion of the mass flow control valve assembly with the mass flow control valve assembly in a closed position.

[0010] Fig. 5 is a cross-sectional illustration of an uninterrupted or dead section of a head of the stem.

[0011] Fig. 6 is a cross-sectional illustration of an interrupted or low flow section of the stem head.

[0012] Fig. 7 is a graph illustrating an example taper profile for a tapered section of the stem head.

[0013] Fig. 8 is a cutaway illustration of a portion of the mass flow control valve assembly with the stem in a dead position.

[0014] Fig. 9 is a cutaway illustration of a portion of the mass flow control valve assembly with the stem in a low-open position.

[0015] Fig. 10 is a cross-sectional illustration of a portion of the valve system with the stem in a sealing position.

[0016] Fig. 11 is a cross-sectional illustration of a portion of the valve system with the stem in a dead position.

[0017] Fig. 12 is a cross-sectional illustration of a portion of the valve system with the stem in a low-open position.

[0018] Fig. 13 is a cross-sectional illustration of a portion of the valve system with the stem in a high-open position.

[0019] Fig. 14 is a schematic illustration of a conventional poppet valve.

[0020] Fig. 15 is a graph illustrating gain vs. flow area for three mass flow control valves.

[0021] Fig. 16 is a cutaway illustration of a portion of a valve assembly according to certain embodiments.- 3 - 113202-958 / TSH 197868999WW Ref: 24-3692- WODETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0022] Although the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described herein in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives consistent with the present disclosure and the appended claims.

[0023] References in the specification to “one embodiment,” “an embodiment,” “an illustrative embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may or may not necessarily include that particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. It should further be appreciated that although reference to a “preferred” component or feature may indicate the desirability of a particular component or feature with respect to an embodiment, the disclosure is not so limiting with respect to other embodiments, which may omit such a component or feature. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0024] Additionally, it should be appreciated that items included in a list in the form of “at least one of A, B, and C” can mean (A); (B); (C); (A and B); (B and C); (A and C); or (A, B, and C). Similarly, items listed in the form of “at least one of A, B, or C” can mean (A); (B); (C); (A and B); (B and C); (A and C); or (A, B, and C). Items listed in the form of “A, B, and / or C” can also mean (A); (B); (C); (A and B); (B and C); (A and C); or (A, B, and C). Further, with respect to the claims, the use of words and phrases such as “a,” “an,” “at least one,” and / or “at least one portion” should not be interpreted so as to be limiting to only one such element unless specifically stated to the contrary, and the use of phrases such as “at least a portion” and / or “a portion” should be interpreted as encompassing both embodiments including only a portion of such element and embodiments including the entirety of such element unless specifically stated to the contrary.

[0025] In the drawings, some structural or method features may be shown in certain specific arrangements and / or orderings. However, it should be appreciated that such specific- 4 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOarrangements and / or orderings may not necessarily be required. Rather, in some embodiments, such features may be arranged in a different manner and / or order than shown in the illustrative figures unless indicated to the contrary. Additionally, the inclusion of a structural or method feature in a particular figure is not meant to imply that such feature is required in all embodiments and, in some embodiments, may be omitted or may be combined with other features.

[0026] With reference to Fig. 1, illustrated therein is a valve system 100 according to certain embodiments. The valve system 100 generally includes a housing 110, a sliding support assembly 120, an actuator 130, and a mass flow control valve assembly 200 according to certain embodiments. The mass flow control valve assembly 200 generally includes a valve seat 210 mounted in the housing 110, and a stem 220 mounted for reciprocal movement relative to the valve seat 210, and may further include a closing seal member 230 and / or a seat seal member 240. As described herein, the actuator 130 is operable to move the stem 220 along a longitudinal axis 101 that defines a proximal direction (to the left in Fig. 1) and an opposite distal direction (to the right in Fig. 1) such that a head 250 of the stem 220 moves in and out of an opening 215 defined by the valve seat 210. In the illustrated form, the actuator 130 is operable to move the stem 220 distally to close the valve 200 and proximally to open the valve 200.

[0027] The housing 110 includes a chamber 111 in which the actuator 130 is seated, and defines a flow path 112 that extends between an inlet 114 and an outlet 113. A mounting area 115 is disposed about a portion of the flow path 112, and the valve seat 210 is mounted in the mounting area 115. Moreover, the mass flow control valve assembly 200 is disposed in the flow path 112 to modulate flow of fluid from the inlet 114 to the outlet 113. Positioned adjacent the mounting area 115 is a shoulder 116 (Fig. 2) defining a proximal stop that limits movement of the valve seat 210 in the proximal direction. The mounting area 115 is at least partially defined by an inner wall 115' that faces an outer wall 218 of the valve seat 210.

[0028] The sliding support assembly 120 is mounted in the housing 110 and supports the stem 220 for sliding reciprocal movement in the proximal direction and the distal direction while limiting the stem 220 to sliding movement along the longitudinal axis 101. In the illustrated form, the sliding support assembly 120 includes a proximal sliding support 122 positioned proximally of the actuator 130 and a distal sliding support 124 positioned distally of the actuator 130. In the illustrated form, each of the sliding supports 122, 124 is provided in the form of a- 5 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOlinear bearing. Tt is also contemplated that one or both of the supports 122, 124 may take another form, such as that of a bushing.

[0029] The actuator 130 is mounted in the housing 110 and is operable to move the stem 220 along the longitudinal axis 101. While other forms are contemplated, in the illustrated form, the actuator 130 generally includes a spring 132 biasing the stem 220 in the distal direction towards its closed position, and a linear motor 134 operable to move the stem 220 proximally against the force of the spring 132 towards the open position. The illustrated actuator 130 is operable to provide for fine control of the linear position of the stem 220 to thereby enable adjustment of the linear position throughout a continuous range of linear positions between the open position and the closed position. In certain forms, the linear motor 134 may be a rotary -to-linear motor. It is also contemplated that the linear motor 134 may be a direct linear motor.

[0030] With additional reference to Figs. 2-4, the valve seat 210 is seated in the mounting area 115, and in the illustrated form is captured between the shoulder 116 and a retaining clip 106. The example valve seat 210 includes a circumferential channel 217 in which the seat seal member 240 is disposed to form a seal 240' between the valve seat 210 and the housing 110. The valve seat 210 is generally annular and defines an opening 215 into which a head 250 of the stem 220 extends. The opening 215 has a longitudinal axis 211, which may be coincident with the longitudinal axis 101 along which the stem 220 extends. As described herein, the valve assembly 200 may include features that facilitate alignment of the valve seat longitudinal axis 211 with the stem longitudinal axis 101 during reciprocal movement of the stem 220. The valve seat 210 includes a proximal face 212, which faces the shoulder 116 of the housing 110 and a distal face 232 of the closing seal 230. The valve seat 210 also includes an inner wall 214 that defines the opening 215, and an outer wall 218 facing the inner wall 115' of the mounting area 115.

[0031] In the illustrated embodiment, the valve seat 210 and the mounting area 115 are engaged with one another via a clearance fit defining a gap 108 that permits limited radial movement of the valve seat 210 within the mounting area 115. More particularly, the mounting area 115 has an inner diameter dl 15 that is greater than the outer diameter d218 of the valve seat outer wall 218 by an amount sufficient to permit formation of a gap 108 between the mounting area 115 and the outer wall 218. In certain forms, the mounting area inner diameter dl 15 may be greater than the valve seat outer diameter d218 by one hundredth of an inch to one tenth of an inch (i.e.,- 6 - 113202-958 / TSH 197868999WW Ref: 24-3692- WO0.01 inch to 0.1 inch) such that the gap 108 has a gap dimension d 108 between five thousandths of an inch and five hundredths of an inch (i.e., 0.005 inch to 0.05 inch) when the valve seat 210 is centered on the longitudinal axis 101. It is also contemplated that the gap dimension dl08 may be larger in certain embodiments.

[0032] As noted above, the proximal face 212 of the valve seat 210 faces the shoulder 116 of the housing 110. As a result, the shoulder 116 and the proximal face 212 are operable to engage one another via a first sliding interface 203. When the valve 200 is in its sealed condition, the proximal face 212 additionally or alternatively engages a distal face 232 of the closing seal 230 at a second sliding interface 205. Moreover, the inner wall 214 defines the opening 215 and is operable to engage an outer surface 251 of the stem head 250 via a third sliding interface 207. In certain embodiments, the valve 200 may include one or more slide bearings 290 configured to facilitate the sliding engagement of two components via a corresponding sliding interface as described herein.

[0033] In certain forms, the one or more slide bearings 290 may include a radial slide bearing 293 configured to facilitate radial sliding of the valve seat 210 against the shoulder 116 at the first sliding interface 203. For example, the proximal face 212 of the valve seat 210 may include a sliding surface 212' that promotes sliding engagement at the sliding interface 203 and at least partially defines the slide bearing 293. Additionally or alternatively, the shoulder 116 may include a sliding surface 116' that promotes sliding engagement at the sliding interface 203 and at least partially defines the slide bearing 293.

[0034] In certain forms, the one or more slide bearings 290 may include a radial slide bearing 295 configured to facilitate radial sliding of the valve seat 210 against the closing seal 230 at the second sliding interface 205. For example, the proximal face 212 of the valve seat 210 may include a sliding surface 212' that promotes sliding engagement at the sliding interface 205 and at least partially defines the slide bearing 295. Additionally or alternatively, the distal face 232 of the closing seal 230 may include a sliding surface 232' that promotes sliding engagement at the sliding interface 205 and at least partially defines the slide bearing 295. Thus, the radial slide bearing 295 may help to ensure that the valve seat 210 is allowed to float to thereby realign itself with the longitudinal axis 101 without sticking. Without this slide bearing, the seal 230 may be more resistant to movement of the valve seat 210, which may result in additional wear on the closing seal 230.- 7 - 113202-958 / TSH 197868999WW Ref: 24-3692- WO

[0035] In certain forms, the one or more slide bearings 290 may include an axial slide bearing 297 configured to facilitate axial sliding of the stem head 250 against the inner wall 214 at the third sliding interface 207. For example, the inner wall 214 of the valve seat 210 may include a sliding surface 214' that promotes sliding engagement at the sliding interface 207 and at least partially defines the slide bearing 297. Additionally or alternatively, the outer surface 251 of the stem head 250 may include a sliding surface 251 ' that promotes sliding engagement at the sliding interface 207 and at least partially defines the slide bearing 297.

[0036] As set forth above, one or more of the sliding interfaces 203, 205, 207 may include one or more slide bearings 290 that promote the sliding engagement of the components that engage one another at the corresponding interface. These slide bearings 290 may reduce the potential for wear that would ultimately reduce the accuracy of the flow control. In certain forms, a slide bearing provided to a component may be formed of a different material as compared to a remainder of the component. In certain forms, the slide bearings 290 may include polytetrafluoroethylene (PTFE), either alone or in a blend. For example, PTFE or a blend including PTFE may be sprayed onto the corresponding surface or applied as a strip. In certain embodiments, a slide bearing 290 may be a sprayed-on coating such as molybdenum disulfide or tungsten disulfide. In certain embodiments, a slide bearing 290 may be provided as a metallic coating such as one applied via electroless nickel plating. In certain embodiments, a slide bearing 290 may comprise diamond-like carbon. In certain embodiments, a slide bearing 290 may include a lubricious stainless steel material, such as nitronic 60, Inconel, or a similar material.

[0037] The valve seat 210 defines a boundary plane 219 that aligns with a mouth 215' of the opening 215 and defines a proximal boundary for the opening 215. In the illustrated form, the opening 215 has a constant diameter d215 along at least a portion of its length distal to the mouth 215'. In certain embodiments, the boundary plane 219 may be considered to be defined by the proximal face 212 of the valve seat 210. In certain embodiments, the boundary plane 219 may be considered to be defined at the distal terminus of a taper 216 that leads to the opening 215.

[0038] The stem 220 generally includes a body 222 that extends through the actuator 130 and which is slidably supported by the sliding support assembly 120. The stem 220 also includes a head 250 defining a distal end portion of the stem 220, and may further include a closing seal seat 223. In the illustrated form, the closing seal seat 223 is positioned proximally of the head- 8 - 113202-958 / TSH 197868999WW Ref: 24-3692- WO250 and defines a mounting location for the closing seal member 230. The closing seal seat 223 generally includes an annular channel 224 and a shoulder 225 defining a proximal limit of the annular channel 224.

[0039] The closing seal member 230 is mounted to the stem 220, for example at the closing seal seat 223. When the stem 220 is in its closed position (Fig. 2), a distal face 232 of the closing seal member 230 abuts the proximal face 212 of the valve seat 210 and thereby forms a seal 230' that blocks the flow of fluid along the flow path 112. In certain embodiments, the closing seal member 230 may be formed of a compliant material, such as an elastomeric material. Moreover, in certain embodiments, the closing seal member 230 may be compressed between the proximal face 212 of the valve seat 210 and the shoulder 225 of the closing seal seat 223 when the stem 220 is in its fully closed position. Those skilled in the art will readily recognize that such compression of the seal member 230 may result in a more complete seal 230' to more fully close the valve 200 that would be possible with a rigid seal member.

[0040] The seat seal member 240 is mounted to the valve seat 210, for example within the circumferential channel 217, and defines a seal 240' between the valve seat 210 and the housing 110. In the illustrated form, the seal member 240 is interposed between the outer surface 218 of the valve seat 210 and the inner wall 115' of the mounting area 115, and thereby provides the seal 240' as a radial seal. It is also contemplated that a seat seal member may provide an axial seal, for example by being interposed between the proximal face 212 of the valve seat 210 and the shoulder 116 of the mounting area 115. An example of such an axial seal is described herein with reference to Fig. 16. As described herein, the seat seal member 240 is compressible and configured to permit some radial shifting of the valve seat 210 while providing a cushioned limit for the radial shifting. While the illustrated seat seal 240 is a U-cup seal, it is also contemplated that other geometries may be utilized.

[0041] The stem head 250 extends distally from the body 222 and generally includes an exterior surface 251, an untapered or cylindrical proximal section 252, a tapered distal section 255, and a metering channel 256 that extends between the untapered section 252 and the tapered section 255. In the illustrated form, the metering channel 256 has a proximal terminus 256' that is offset from the closing seal seat 223 such that the metering channel 256 does not extend along the entire length of the untapered section 252. Moreover, the illustrated metering channel 256 interrupts the exterior surface 251 of the head 250 along its entire length and extends to a distal- 9 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOface 258 of the head 250. Tt is also contemplated that the metering channel 256 may terminate proximal of the distal face 258.

[0042] With additional reference to Figs. 5 and 6, the untapered section 252 has a constant outer diameter d252 along its axial length, and the outer diameter d252 of the untapered section 252 corresponds to the inner diameter d215 of the valve seat opening 215. In certain forms, the diameters d215, d252 may be related to one another to provide a particular type of fit. In the illustrated form, the relationship between the diameters d215, d252 is selected to provide a sliding fit to thereby allow the stem head 250 to reciprocate relative to the valve seat 210 while reducing flow through the tight annular gap 206 between the outer surface 251 of the untapered section 252 and the inner wall 214 of the opening 215. For example, the inner diameter d215 of the opening 215 may be greater than the outer diameter d252 of the untapered section 252 by one to five thousandths of an inch (i.e., .001 inch to .005 inch) to thereby provide the tight annular gap 206 with an annular clearance dimension d206 of .0005 inch to .0025 inch. It is also contemplated that other types of clearance fits may be utilized, such as a close running fit or a free running fit. Regardless of the precise type of fit utilized, the untapered section 252 may substantially block flow of fluid between the exterior surface 251 of the untapered section 252 and the inner wall 214 of the opening 215.

[0043] With additional reference to Fig. 7, illustrated therein is a graph of an example radiusdistance profile 255' for the tapered section 255. While other embodiments are contemplated, in the illustrated form, the overall taper profile 255' of the tapered section 255 is configured to quickly drive the flow gain down to an acceptably low value (e.g., around 4%), and then to maintain close to that gain value through the rest of the profile 255'. In the illustrated form, the profile 255' is provided as a curvilinear profile. It is also contemplated that the profile 255' may be rectilinear or a combination of curvilinear and rectilinear, and that the profile 255' may include multiple rectilinear sections having different slopes and / or multiple curvilinear sections defining different curves.

[0044] As noted above, in the illustrated form, the metering channel 256 does not extend along the entire axial length of the untapered section 252, and instead terminates distal to the proximal terminus of the untapered section 252. This results in the formation of an uninterrupted dead zone 253 proximal to the terminus 256' of the metering channel 256. The portion of the untapered section 252 that is interrupted by the metering channel 256 may be referred to herein- 10 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOas the interrupted section 254. As described herein, the interrupted section 254, when aligned with the mouth 215' of the opening 215, permits a relatively small amount of flow through the opening 215, and may alternatively be referred to herein as the low flow section 254.

[0045] The metering channel 256 is defined in part by a floor 257. In the illustrated form, the floor 257 is curvilinear and gradually slopes away from the proximal terminus 256' of the metering channel 256. It is also contemplated that the channel 256 may have a different configuration. For example, the floor 257 may instead be provided with a different profile, such as the floor 257' illustrated in Fig. 2. Moreover, the illustrated channel 256 has a constant width dimension w256 along its longitudinal length, which may facilitate manufacturing and / or provide more consistent gain results. However, it is also contemplated that the channel 256 may vary in width along the longitudinal direction.

[0046] With additional reference to Figs. 8 and 9, illustrated therein is a portion of the valve system 100 with the stem 220 in a dead position (Fig. 8) and a low-open position (Fig. 9). The dead position (Fig. 8) is slightly offset from the fully closed position (Fig. 2) such that a gap 202 is defined between the proximal face 212 of the valve seat 210 and the distal face 232 of the closing seal member 230. Moreover, with the stem 220 in the dead position, the proximal boundary plane 219 of the valve seat 210 intersects the dead zone 253 such that the dead zone 253 blocks the mouth 215' of the opening 215. As a result, flow of fluid through the mass flow control valve 200 is substantially prevented (e.g., due to the fit between the untapered section 252 and the inner wall 214). Further proximal movement of the stem 220 from the dead position brings the stem 220 to the low-open position (Fig. 9), in which the proximal boundary plane 219 intersects the interrupted portion 254 of the untapered section 252. As a result, the proximal end portion of the metering channel 256 becomes exposed, thereby permitting fluid flow through the opening 215 via the channel 256.

[0047] With additional reference to Figs. 10-13, during operation of the valve system 100, the mass flow control valve 200 may begin with the stem 220 in its closed position (Fig. 10). The actuator 130 may then be actuated to drive the stem 220 to a dead position (Fig. 11), a low-open position (Fig. 12), and a high-open position (Fig. 13).

[0048] Fig. 10 illustrates the valve 200 with the stem 220 in its fully closed position. In this state, the closing seal member 230 may abut the valve seat 210 and thereby form the seal 230' that prevents fluid flow through the opening 215. In such forms, the fully closed position may- 11 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOalternatively be referred to as the sealing position. The stem 220 may be biased toward the closed position, for example by the spring 132 of the actuator 130. In the illustrated form, the seal member 230 is compressed between the proximal face 212 of the valve seat 210 and the shoulder 225 of the body 222 when the stem 220 is in its closed position. For example, the spring 132 may be sufficiently stiff to cause such compression of the seal member 230. From the closed position, the stem 220 may be moved proximally to the dead position, for example by actuating the actuator 130 in a stem-retracting direction.

[0049] Fig. 11 illustrates the valve assembly 200 with the stem 220 in its dead position. In this state, the distal face 232 of the closing seal member 230 is offset from the proximal face 212 of the valve seat 210 such that the gap 202 is defined between the valve seat proximal face 212 and the seal member distal face 232. Moreover, the boundary plane 219 intersects the dead zone 253 such that the mouth 215' of the opening 215 is blocked by the uninterrupted section 253. As a result, while the opening 215 is not as fully sealed as when the stem 220 is in the sealing position, flow through the opening 215 remains substantially blocked as a result of the close sliding fit between the untapered section 252 and the inner wall 214 of the valve seat 210. When using a flexible closing seal member 230, the dead zone 253 may aid in ensuring that the accurate fuel metering range of the valve 200 does not occur until the valve 200 is sufficiently removed from the variability imparted by the flexible seal 230. In the dead zone 253, changing the axial position of the stem 220 results in little to no change in flow since the annular leakage area about the untapered section 252 remains constant.

[0050] From the foregoing, it should be evident that an absolute position of the stem 220 changes during operation of the system 100. As used herein, the “absolute position” of the stem 220 may be considered as the position of the stem 220 relative to a component with a stationary longitudinal position, such as the actuator 130 or the valve seat 210. In certain forms, the absolute position of the stem 220 may be sensed or determined by a controller 139 that controls operation of the actuator 130. For purposes of illustration, the illustrated stem 220 can be considered to have a range of absolute positions spanning from AP 0 to AP 100, wherein the AP 0 position would cause the valve seat 210 to abut the shoulder 225, and the AP 100 position is a fully open position. In this illustrative example, absolute positions between AP 0 and AP 10 may indicate that the stem 220 is in its sealing position, absolute positions between AP 10 and AP 20 may indicate that the stem 220 is in a dead position, absolute positions between AP 20 and AP- 12 - 113202-958 / TSH 197868999WW Ref: 24-3692- WO40 may indicate that the stem 220 is in a low flow position, and absolute positions between AP 40 and AP 100 may indicate that the stem 220 is in a high-open position.

[0051] Those skilled in the art will readily recognize that the absolute position of the stem 220 corresponding to the sealing position may vary from one instance of the system 100 to the next. As one example, part-to-part manufacturing variability may result in one instance of the system 100 having the sealing position at AP 8 while another instance of the system 100 has the sealing position at AP 9. Similarly, the absolute position of the stem 220 corresponding to the sealing position may vary within an instance of the system 100 over time. By way of illustration, degradation of the seal member 230 may result in the sealing position migrating over time from AP 9 to AP 8. In embodiments that do not include the dead zone 253, this migration may cause uncertainty in the effective flow area of the valve 200. For example, if the controller 139 is programmed to determine AP 9 as the sealing position when the true sealing position is AP 8, the controller 139 may interpret a condition in which the stem 220 is at AP 9 as a sealed condition when there is actually a gap between the seal member 230 and the proximal face 212 of the valve seat 210. Without the dead zone 253, such a gap would result in flow through the opening 215. However, because the dead zone 253 closes the mouth 215', flow remains blocked until the controller 139 causes the actuator 130 to move the stem 220 to a low flow position (e.g., beyond AP 20). As a result, the controller 139 may be programmed with a predefined absolute position beyond which flow will begin (e.g., AP 20), as opposed to needing to account for variations in the sealing position.

[0052] Fig. 12 illustrates the valve 200 with the stem 220 in its low-open position. In this state, the interrupted section 254 is aligned with the mouth 215' such that the boundary plane 219 intersects the interrupted section 254. This results in the exposure of a relatively small flow area defined by the channel 256 (Fig. 9). The sliding engagement between the inner wall 214 and the remainder of the exterior surface 251 of the untapered section 252 substantially blocks flow other than through the channel 256. As a result, the effective flow area of the opening 215 can be controlled more closely than if the entire stem head 250 were tapered. As described herein, the metering channel 256 may also facilitate manufacturing, for example by reducing or eliminating the need for a small taper angle.

[0053] Fig. 13 illustrates the valve 200 with the stem 220 in its high-open position. In this state, the tapered section 255 is aligned with the mouth 215' such that the boundary plane 219- 13 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOintersects the tapered section 255. As a result, the effective flow area of the opening 215 includes not only that provided by the channel 256, but also the gap 204 formed at the mouth 215' between the outer surface 251 of the tapered section 255 and the inner wall 214 of the valve seat 210.

[0054] In certain embodiments, it may be advisable to provide one or more components of the valve assembly 200 with relatively tight tolerances. For example, it may be preferable to provide a tight annular clearance between the outer surface 251 of the untapered section 252 and the inner wall 214 defining the opening 215 to thereby reduce leakage through the annular gap 206 when metering is controlled by the metering channel 256 (e.g., when the stem 220 is in a low flow position). Because the body 222 is supported by two linear bearings 122, 124, even a slight misalignment between the longitudinal axis of the opening 215 defined by the valve seat 210 and the longitudinal axis 101 on which the linear bearings 122, 124 are centered could cause binding and wear during opening and / or closing of the valve 200.

[0055] In order to mitigate the dangers of binding and wear, the illustrated valve seat 210 is given an annular clearance 108 from the mounting area inner wall 115' and is allowed to reposition itself radially to align itself with the axis 101 along which the stem 220 reciprocates. For example, if the alignment is slightly off, the tapered section 255 may engage the mouth 215' as the stem 220 moves in the distal direction to thereby adjust the radial position of the valve seat 210 and align the valve seat longitudinal axis 211 with the longitudinal axis 101 along which the stem 220 reciprocates. While the annular gap 108 could create a leak path that would bypass the stem 220 and result in uncontrolled flow, such risk is mitigated by the seat seal member 240 that is positioned between the valve seat 210 and the housing 110. Although the illustrated seal member 240 provides a radial seal, it is also contemplated that a seat seal member may provide an axial seal, for example as described below with reference to Fig. 16. Moreover, the seal member 240 may have any of a number of cross-sectional geometries, such as round, square, or U-cup. However, when the seal member 240 provides a radial seal, the seal member 240 should remain compressible to allow limited radial shifting of the valve seat 210. In the illustrated form, the seal member 240 is provided as a U-cup seal member, which is advantageously compliant and allows for relatively free movement of the valve seat 210.

[0056] With additional reference to Fig. 14, illustrated therein is a conventional poppet valve 90.The conventional poppet valve 90 includes a housing 92 and a poppet 94 mounted for reciprocal- 14 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOmovement relative to the housing 92. During reciprocation of the poppet 94, the flow area increases linearly with the displacement of the poppet 94. This results in relatively high gain at low flow conditions. If it is desired to provide the poppet valve 90 with low flow gain in the initial opening movement, one may increase the overlap of the poppet 94 and the housing 92, and add taper to the poppet 94. However, to achieve gain values around 5% at low flow areas, this approach would require angles at a small fraction of one degree. Such a configuration would be difficult to manufacture and would have high part to part variability. By contrast, the illustrated valve 200 may utilize a metering channel 256 and an untapered section 252 to provide a relatively small and predictable increase in the starting flow area. During the first portion of the valve stroke (e.g., the first 10% of the valve stroke beyond the sealing position), the only flow area is that produced by the metering channel 256 and the constant annular leakage via the gap 108, the latter of which can be reduced by providing tight tolerances.

[0057] With additional reference to Fig. 15, provided therein is a graph illustrating gain vs. flow area for the conventional poppet valve 90 and an example embodiment of the illustrated valve 200. Here, the difference between the conventional valve 90 and the illustrated valve 200 becomes apparent, as the illustrated mass flow control valve assembly 200 reaches a low enough gain to be accurate at a much lower flow area. While both valves 90, 200 may have similar total turndown ratios (e.g., around 100:1), the current valve 200 may provide for an increased accurate turndown ratio. For example, if the maximum acceptable gain for accurate control is determined to be 5%, the traditional poppet valve 90 would have accurate control between about 15 mm2and 55 mm2, whereas the illustrated valve 200 would have accurate control between about 1.4 mm2and 55 mm2. Thus, the traditional valve 90 would have an accurate turndown ratio of 55 / 15, or only about 3.7:1, whereas the illustrated embodiment of the mass flow control valve assembly 200 would have an accurate turndown ratio of 55 / 1.4, or about 40: 1. It should also be noted that by modifying the width, length, and / or profile of the metering channel 256, this gain vs. area curve can be crafted to match the curve generated by the more complex electrical discharge machining (EDM) machined profiles employed in certain existing mass flow control valves.

[0058] Also illustrated in Fig. 15 is a gain vs. flow area line for a modified version of the illustrated valve. More particularly, the modified valve 200' is substantially identical to the illustrated valve 200, but does not included the metering channel 256. While the gain vs. area curve for this modified valve 200' exhibits an improvement over the traditional valve 90, the- 15 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOillustrated valve 200 nonetheless outperforms the modified valve 200' in the area of accurate turndown ratio. In the illustrated implementation, the gain for the modified valve 200' does not fall below 5% until about 6 mm2, resulting in an accurate turndown ratio of 55 / 6 or about 9.2:1. As noted above, the illustrated valve 200 can have an accurate turndown ratio of about 40: 1, which represents a more than four-fold improvement over the modified valve 200' that does not include a metering channel 256.

[0059] With additional reference to Fig. 16, illustrated therein is a valve 300 according to certain embodiments. The valve 300 is substantially similar to the valve 200 described above, and similar reference characters are used to indicate similar elements and features. For example, the illustrated valve 300 generally includes a valve seat 310, a stem 320, a closing seal member 330, and a seat seal member 340, which respectively correspond to the above-described valve seat 210, stem 220, closing seal member 230, and seat seal member 240. In the interest of conciseness, the following description of the valve 300 focuses primarily on elements and features different from those described above with reference to the valve 200.

[0060] In contrast to the valve 200, in which the seat seal member 240 is a radial seal member that provides a radial seal 240' to prevent fluid flow through the gap 108, the seat seal member 340 of the valve 300 is an axial seal member that provides an axial seal 340' to prevent fluid flow through the gap 108. More particularly, the illustrated seat seal member 340 is disposed between a proximal wall 392 of the valve seat 310 and a distal wall 394 of the mounting area 118.Moreover, while the head 250 of the above-described stem 220 has a tapered section 252 with varying taper angles, the stem 320 has a head 350 in which the tapered section 352 has a relatively constant taper angle.

[0061] Certain embodiments of the present application relate to a mass flow control valve assembly, comprising: a valve seat comprising an opening formed about a longitudinal axis that defines a proximal direction and an opposite distal direction, wherein the valve seat defines a boundary plane for the opening; a stem mounted for movement relative to the valve seat, the stem comprising a head that projects into the opening, wherein the head comprises: an untapered section; a tapered section positioned distal to the untapered section; and a channel extending between the untapered section and the tapered section; wherein the untapered section comprises an interrupted section that is interrupted by the channel; wherein the stem has a low-open position in which the boundary plane intersects the interrupted section to thereby permit fluid- 16 - 113202-958 / TSH 197868999WW Ref: 24-3692- WOflow through the opening via the channel; and wherein the stem has a high-open position in which the boundary plane intersects the tapered section to thereby permit flow through the opening around the head.

[0062] In certain forms, the untapered section further comprises an uninterrupted section that is not interrupted by the channel; and wherein the stem has a dead position in which the boundary plane is aligned with the uninterrupted section.

[0063] In certain forms, a cross-section of the uninterrupted section defines a circle.

[0064] Certain forms further comprise a seal member positioned proximal to the uninterrupted section; wherein the stem has a closed position in which the seal member abuts a proximal face of the valve seat.

[0065] In certain forms, the untapered section and the valve seat define a sliding fit.

[0066] In certain forms, the opening extends from the boundary plane along the longitudinal axis and has a constant diameter along the longitudinal axis.

[0067] Certain embodiments of the present application relate to a mass flow control valve assembly, comprising: a valve seat comprising an opening formed about a longitudinal axis that defines a proximal direction and an opposite distal direction, wherein the valve seat defines a mouth for the opening; a stem mounted for movement relative to the valve seat, the stem comprising a head that projects into the opening, wherein the head comprises: a proximal section comprising a dead zone, the dead zone having a cross-section that matches a cross-section of the opening; and a distal section configured to permit flow of fluid through the opening when the distal section is aligned with the mouth; and a closing seal member mounted to the stem proximal of the dead zone; wherein the stem has a closed position in which the closing seal member abuts a proximal face of the valve seat to thereby seal the opening; wherein the stem has a dead position in which the dead zone is aligned with the mouth and the opening is closed by the dead zone; and wherein the stem has an open position in which the distal section is aligned with the mouth to thereby permit fluid flow through the opening.

[0068] In certain forms, the closing seal member is compressed by the valve seat when the stem is in the closed position.

[0069] In certain forms, the closing seal member is formed of an elastomeric material.

[0070] Certain forms further comprise a slide bearing provided at a sliding interface between the valve seat and another component of the mass flow control valve assembly.- 17 - 113202-958 / TSH 197868999WW Ref: 24-3692- WO

[0071] In certain forms, the proximal face of the valve seat comprises a slide bearing formed of a different material from a body of the valve seat.

[0072] In certain forms, the opening is defined by an inner wall of the valve seat; and wherein the inner wall of the valve seat comprises a slide bearing formed of a different material from a body of the valve seat.

[0073] In certain forms, the proximal section further comprises an interrupted section that is interrupted by a channel extending between the proximal section and the distal section; and wherein the stem has a low-open position in which the interrupted section is aligned with the mouth to thereby permit fluid flow through the opening via the channel.

[0074] Certain embodiments of the present application relate to a mass flow control valve system, comprising: a housing comprising a mounting area formed about a longitudinal axis; a stem mounted for reciprocal movement along the longitudinal axis; a valve seat positioned in the mounting area, wherein the valve seat defines an opening into which the stem extends, and wherein a radial clearance is provided between the valve seat and the mounting area to thereby permit limited radial movement of the valve seat relative to the housing; and a compressible seal member engaged between the mounting area and the valve seat to thereby seal the radial clearance while permitting the limited radial movement of the valve seat.

[0075] In certain forms, the radial clearance is formed about an entire circumference of the valve seat.

[0076] In certain forms, the valve seat comprises a proximal face that engages another component at a sliding interface; and wherein the sliding interface comprises a slide bearing configured to promote sliding of the proximal face along the housing.

[0077] In certain forms, the other component comprises the housing and / or a closing seal member.

[0078] In certain forms, the stem comprises a tapered section configured to align the opening with the longitudinal axis during reciprocal movement of the stem.

[0079] In certain forms, the compressible seal member is positioned radially between an outer wall of the valve seat and an inner wall of the mounting area.

[0080] In certain forms, the compressible seal member is positioned axially between a proximal wall of the valve seat and a distal wall of the mounting area.- 18 - 113202-958 / TSH 197868999WW Ref: 24-3692- WO

[0081] While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the inventions are desired to be protected.

[0082] It should be understood that while the use of words such as preferable, preferably, preferred or more preferred utilized in the description above indicate that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, the scope being defined by the claims that follow. In reading the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language “at least a portion” and / or “a portion” is used the item can include a portion and / or the entire item unless specifically stated to the contrary.- 19 - 113202-958 / TSH 197868999

Claims

WW Ref: 24-3692- WO WHAT TS CLAIMED IS:

1. A mass flow control valve assembly, comprising:a valve seat comprising an opening formed about a longitudinal axis that defines a proximal direction and an opposite distal direction, wherein the valve seat defines a boundary plane for the opening;a stem mounted for movement relative to the valve seat, the stem comprising a head that projects into the opening, wherein the head comprises:an untapered section;a tapered section positioned distal to the untapered section; anda channel extending between the untapered section and the tapered section; wherein the untapered section comprises an interrupted section that is interrupted by the channel;wherein the stem has a low-open position in which the boundary plane intersects the interrupted section to thereby permit fluid flow through the opening via the channel; and wherein the stem has a high-open position in which the boundary plane intersects the tapered section to thereby permit flow through the opening around the head.

2. The mass flow control valve assembly of claim 1, wherein the untapered section further comprises an uninterrupted section that is not interrupted by the channel; andwherein the stem has a dead position in which the boundary plane is aligned with the uninterrupted section.

3. The mass flow control valve assembly of claim 2, wherein a cross-section of the uninterrupted section defines a circle.

4. The mass flow control valve assembly of claim 2, further comprising a seal member positioned proximal to the uninterrupted section;wherein the stem has a closed position in which the seal member abuts a proximal face of the valve seat.

5. The mass flow control valve assembly of claim 1, wherein the untapered section and the valve seat define a sliding fit.- 20 - 113202-958 / TSH 197868999WW Ref: 24-3692- WO6. The mass flow control valve assembly of claim 1 , wherein the opening extends from the boundary plane along the longitudinal axis and has a constant diameter along the longitudinal axis.

7. A mass flow control valve assembly, comprising:a valve seat comprising an opening formed about a longitudinal axis that defines a proximal direction and an opposite distal direction, wherein the valve seat defines a mouth for the opening;a stem mounted for movement relative to the valve seat, the stem comprising a head that projects into the opening, wherein the head comprises:a proximal section comprising a dead zone, the dead zone having a cross-section that matches a cross-section of the opening; anda distal section configured to permit flow of fluid through the opening when the distal section is aligned with the mouth; anda closing seal member mounted to the stem proximal of the dead zone;wherein the stem has a closed position in which the closing seal member abuts a proximal face of the valve seat to thereby seal the opening;wherein the stem has a dead position in which the dead zone is aligned with the mouth and the opening is closed by the dead zone; andwherein the stem has an open position in which the distal section is aligned with the mouth to thereby permit fluid flow through the opening.

8. The mass flow control valve assembly of claim 7, wherein the closing seal member is compressed by the valve seat when the stem is in the closed position.

9. The mass flow control valve assembly of claim 7, wherein the closing seal member is formed of an elastomeric material.

10. The mass flow control valve assembly of claim 7, further comprising a slide bearing provided at a sliding interface between the valve seat and another component of the mass flow control valve assembly.

11. The mass flow control valve assembly of claim 7, wherein the proximal face of the valve seat comprises a slide bearing formed of a different material from a body of the valve seat.- 21 - 113202-958 / TSH 197868999WW Ref: 24-3692- WO12. The mass flow control valve assembly of claim 7, wherein the opening is defined by an inner wall of the valve seat; andwherein the inner wall of the valve seat comprises a slide bearing formed of a different material from a body of the valve seat.

13. The mass flow control valve assembly of claim 7, wherein the proximal section further comprises an interrupted section that is interrupted by a channel extending between the proximal section and the distal section; andwherein the stem has a low-open position in which the interrupted section is aligned with the mouth to thereby permit fluid flow through the opening via the channel.

14. A mass flow control valve system, comprising:a housing comprising a mounting area formed about a longitudinal axis;a stem mounted for reciprocal movement along the longitudinal axis;a valve seat positioned in the mounting area, wherein the valve seat defines an opening into which the stem extends, and wherein a radial clearance is provided between the valve seat and the mounting area to thereby permit limited radial movement of the valve seat relative to the housing; anda compressible seal member engaged between the mounting area and the valve seat to thereby seal the radial clearance while permitting the limited radial movement of the valve seat.

15. The mass flow control valve system of claim 14, wherein the radial clearance is formed about an entire circumference of the valve seat.

16. The mass flow control valve system of claim 14, wherein the valve seat comprises a proximal face that engages another component at a sliding interface; andwherein the sliding interface comprises a slide bearing configured to promote sliding of the proximal face along the housing.

17. The mass flow control valve system of claim 16, wherein the other component comprises the housing and / or a closing seal member.- 22 - 113202-958 / TSH 197868999WW Ref: 24-3692- WO18. The mass flow control valve system of claim 14, wherein the stem comprises a tapered section configured to align the opening with the longitudinal axis during reciprocal movement of the stem.

19. The mass flow control valve system of claim 14, wherein the compressible seal member is positioned radially between an outer wall of the valve seat and an inner wall of the mounting area.

20. The mass flow control valve system of claim 14, wherein the compressible seal member is positioned axially between a proximal wall of the valve seat and a distal wall of the mounting area.- 23 - 113202-958 / TSH 197868999

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