Abstract:
A pilot-operated proportional cartridge valve that has low internal leakage and long life, without requiring close ID/OD spool clearances that add cost to comparable prior art valves. The flow control valve is uniquely characterized by the use of two axially spaced-apart spring energized wiper seals that floatingly support a flow control piston within a cylindrical chamber to allow transaxial shifting movement of the piston for proper alignment with mating components, such as a valve seat. The spring energized wiper seals are preferably oriented in opposite directions for sealing against pressure differentials at opposite ends of the valve piston. In a preferred embodiment, the seals are spring energized cup seals.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/934,872 filed Feb. 3, 2014, which is hereby incorporated herein by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates generally to flow control devices, and more particularly to pilot-operated valves. 
       BACKGROUND 
       [0003]    Conventional spool valves spool generally require close ID/OD clearances. Even with close tolerances, spool valves have a tendency to leak low viscosity liquids and gases. 
       SUMMARY OF INVENTION 
       [0004]    The present invention provides a flow control valve and more particularly a pilot-operated proportional cartridge valve that has low internal leakage and long life, without requiring close ID/OD spool clearances that add cost to comparable prior art valves. According to one aspect of the invention, a flow control valve is uniquely characterized by the use of two axially spaced-apart spring energized wiper seals that floatingly support a flow control piston within a cylindrical chamber to allow transaxial shifting movement of the piston for proper alignment with mating components, such as a valve seat. The spring energized wiper seals are preferably oriented in opposite directions for sealing against pressure differentials at opposite ends of the valve piston. In a preferred embodiment, the seals are spring energized cup seals. 
         [0005]    In a preferred embodiment, the valve is a cartridge valve with high pressure proportional and on/off capability. Included are designs for both normally closed and normally open functionality. The valve family utilizes a pilot operated piston to proportionally or digitally modulate the flow from full off to full on. The piston modulates or moves by virtue of balancing the pressure on both (top and bottom) sides of the piston. The pressure is balanced by modulating the bleed flow on the top side of the piston. The bleed flow is modulated by the positional relationship between a pintle and pintle valve seat. The seat is part of the piston. The pintle is part of a proportional valve operator configured in either “push” or “pull” configurations. The “push” operator is used for normally open valves and the “pull” operator for normally closed valves. 
         [0006]    In both normally closed and normally open valves, the piston exactly tracks the movement of the magnetic operator movement. The sealing of the piston to the valve body controls bleed and bypass media. The piston seals also function as resilient bearings as above described. The seals are spring-energized and arranged in an opposing fashion so they seal pressure differences on both the top and bottom sides of the piston. 
         [0007]    The valves may be powered by a 12 or 24 VDC, 200 Hz Pulse Width Modulated (PWM) square wave. The valve flow increases with increasing duty cycle on a normally closed version and the normally open valve decreases flow by increasing duty cycle. At 0% duty cycle the normally closed valve is off, the normally open valve is full open at 0% duty cycle. 
         [0008]    This valve can be used for waste heat recovery applications. The valve can control the flow of liquid refrigerant in a Rankin Cycle closed loop system. 
         [0009]    Accordingly, a fluid flow control valve according to one aspect of the invention includes a valve body having an inlet port, an outlet port in selective fluid communication with the inlet port by a main passageway through the valve body, and a valve seat surrounding the main passageway. A valve member is mounted in the valve body for axial movement between closed and open positions respectively blocking and permitting flow through the valve seat. The valve member has a piston portion that separates a control chamber upstream of the valve seat from a point downstream of the valve seat and a pilot orifice through the piston portion for bleeding off pressure from the control chamber to the point downstream of the valve seat. The valve further includes a plunger movable between a first position blocking flow through the pilot orifice and a second position allowing flow through the pilot orifice, and axially spaced apart spring energized wiper seals that radially support the piston within the passageway while allowing limited radial movement within the passageway. 
         [0010]    Preferably the spring energized wiper seals are spring-energized cup seals. 
         [0011]    Preferably the spring-energized seals are oppositely oriented for sealing against pressure differentials between the control chamber and a point downstream of the valve seat. 
         [0012]    The valve may also include a bleed orifice in communication with the inlet and the control chamber for allowing pressure from the inlet to build up in the control chamber for urging the valve member toward the first position when the plunger is in the first position. 
         [0013]    The pilot orifice preferably has a cross-sectional area that is greater than a cross-sectional area of the bleed orifice. 
         [0014]    Preferably the wiper seals wipe along an inner diameter surface of the valve body that has been roller burnished. 
         [0015]    In preferred embodiments, the piston is made of a plastic material and in particular a polyetherimide, and the bleed and pilot orifices are machined into steel inserts secured in the plastic material of the piston. 
         [0016]    Preferably a filter is provided in the piston for filtering fluid prior to passage through the bleed orifice, the filter preferably being a multilayered depth screen. 
         [0017]    A resilient member can bias the plunger toward the first position, such that the valve functions as a normally closed valve. 
         [0018]    A resilient member can bias the valve member toward the open position, such that the valve functions as a normally open valve. 
         [0019]    In preferred embodiments, a solenoid coil is provided for moving the plunger. 
         [0020]    The position of the plunger over a stroke thereof may be proportional to the current supplied to the solenoid coil, and preferably the current is pulse-width modulated. 
         [0021]    According to another aspect of the invention, a valve comprises a valve body having an inlet and an outlet and a valve seat; a piston movable relative to the valve body to open and close the valve, the piston having a sealing surface for engaging the valve seat when the piston is in the closed position, a bleed orifice providing fluid communication between the sealing surface and a chamber opposite the sealing surface, and a pilot orifice providing fluid communication between the chamber and the outlet; a plunger assembly having a pintle that is movable to open/close the pilot orifice, wherein when the valve is pressurized the opening and closing of the pilot orifice by the pintle results in a change in pressure of the chamber relative to pressure at the sealing surface thereby effecting movement of the piston to proportionally open or close the valve; and a coil for effecting movement of the plunger assembly. 
         [0022]    A pair of spaced apart seal bearings preferably surround the piston and seal between an outer surface of the piston and an inner annular surface of the valve body. 
         [0023]    The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a top view of an exemplary normally closed pilot-operated valve according to the invention. 
           [0025]      FIG. 2  is an elevational view of the pilot-operated valve. 
           [0026]      FIG. 3  is an exploded view of the pilot-operated valve. 
           [0027]      FIG. 4  is a cross-sectional view of the pilot-operated valve, taken along the line  4 - 4  of  FIG. 2 , showing the valve in a closed state. 
           [0028]      FIG. 5  is a cross-sectional view similar to  FIG. 4 , but showing the valve in an open state. 
           [0029]      FIG. 6  is an enlarged cross-sectional view of a solenoid actuated plunger used in the pilot-operated valve. 
           [0030]      FIG. 7  is a further enlarged view of a valve piston used in the pilot-operated valve. 
           [0031]      FIG. 8  is a cross-sectional view of an exemplary normally open pilot-operated valve, showing the valve in a closed state. 
           [0032]      FIG. 9  is a cross-sectional view of the pilot-operated valve of  FIG. 8 , showing the valve in an open state. 
           [0033]      FIG. 10  is an enlarged cross-sectional view of a plunger used in the pilot-operated valve of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The principles of this present invention have particular application to pilot-operated valves and particularly those used in waste heat recovery applications, such as for controlling the flow of liquid refrigerant in a Rankin-cycle closed loop system. It will of course be appreciated, and also understood, that principles of this invention may be applicable to other types of valves used for various applications. 
         [0035]    Referring to the drawings, and initially to  FIGS. 1-5 , an exemplary pilot-operated valve is illustrated generally at reference numeral  10 . The valve includes a housing  11  having a valve body  12  and cover  14 . The cover  14  may be sealed to the main body  12  by a suitable seal  16 , such as an O-ring. In the art, the cover also is commonly referred to as a closure or a flange. 
         [0036]    As shown, the cover may be externally threaded for threaded receipt in a threaded bore in the top of the valve body  12 . 
         [0037]    Similarly, the valve body  12  may be externally threaded for threading into a bore in a manifold (not shown) and may have seals  17  and  18 , such as an O-rings, for sealing the valve body to the manifold. Consequently, the valve  10  can be considered a cartridge-type valve. 
         [0038]    A solenoid assembly  20  is assembled on the valve body  11 . 
         [0039]    In the illustrated embodiment, the solenoid assembly  20  is composed of three parts, a plunger assembly  22 , a coil assembly  23 , and a sleeve assembly (also more simply referred to herein as a sleeve). The plunger assembly includes a plunger  32  that is movable axially in the sleeve  34  that is secured and sealed to the cover  14 . As shown, the plunger may be radially supported in the sleeve by a pair of bushings  35 . 
         [0040]    The axially inner end of the sleeve  34  may be assembled in a bore in the cover  14  and fixed and sealed therein as by welding or other suitable means. The axially outer end of the sleeve may be externally threaded for attachment of a nut  36  used to fasten the coil assembly  23  to the plunger assembly. 
         [0041]    As shown, the coil assembly  23  includes a solenoid coil  38  that is contained within a coil casing  39 . The solenoid coil surrounds a bobbin  40  that defines an interior tube-like space that allows the coil assembly to be slipped axially over the sleeve  34 , with the threaded end of the sleeve  34  protruding beyond the coil casing. 
         [0042]    The coil assembly  23  further includes a body  42  in which the coil assembly and bobbin are housed. As is typical, the body may be injection molded over the coil winding and bobbin. The body  42  is for the most part enclosed by the coil casing  39 , although a portion protrudes from the case to provide for electrical connection of the coil to an external power source. As shown, the solenoid body may have formed therein a socket  43  into which electrical terminals  44  extend for mating with the terminals of an external connector that may plug into the socket. 
         [0043]    The coil  38  may be powered by suitable means, such as by a 12 or 24 VDC, 200 Hz pulse width modulated (PWM) square wave generated by a suitable power source. As will be appreciated, flow through the valve  10  will proportionally increase with increasing duty cycle on a normally closed version and proportionally decrease with increasing duty cycle on a normally open valve. At 0% duty cycle a normally closed valve is off, and a normally open valve is full open at 0% duty cycle. 
         [0044]    The sleeve  34  may be formed by a central tube  45  to which an axially outer end piece  46  is fixed and sealed by suitable means, such as by laser welding. The axially inner end of the central tube  45  may be fixed in a bore in the cover  14 , as by laser welding or other suitable means. In the illustrated embodiment, the end piece  46  and cover are formed from magnetic stainless steel, for example, and the central tube  45  is a non-magnetic series stainless steel, for example. The end piece and cover co-act with the coil when energized to create a magnetic circuit for producing an attraction between the outer end piece and the plunger  32 . The outer end piece also functions as a stop for the plunger. 
         [0045]    As best seen in  FIGS. 4 and 5 , the valve body  12  has an inlet port  50 , an outlet port  52  in selective fluid communication with the inlet port  50  by a main passageway  54  through the valve, and a valve seat  56  surrounding the main passageway  54 . The valve body  12  includes a wall  57 , an upper portion of which forms the valve seat  56 , which directs the flow from the inlet port  50  through the main passageway  54  upward towards the valve seat  56 . Fluid, such as a refrigerant, will flow through the valve seat  56  along the main passageway  54  to the outlet port  52  when a valve member  58  is moved away from the valve seat  56 . Although described as being part of the valve body  12 , it will be appreciated that the valve seat  56  may be a separate piece within the valve body  12 . As shown, the outlet port may be formed by a plurality of radial passages in the valve body. In addition, the inlet port may be equipped with an optional screen  59 . 
         [0046]    A valve member  58  is mounted in the valve housing  11  between the valve body  12  and cover  14  for movement between a closed position blocking flow through the valve seat  56  ( FIG. 4 ) and an open position permitting flow through the valve seat  56  ( FIG. 5 ). The valve member  58  has a piston portion  60  (or more simply a piston) that separates a control chamber  62  from a point downstream of the valve seat  56 , a pilot orifice  64  through the piston  60 , a bleed orifice  66  in communication with the inlet  60  and the control chamber  62 , and a sealing surface  67  ( FIG. 7 ) that engages the valve seat to close the passage through the valve seat. When the pilot orifice is closed by the plunger  32  (as described in detail below), the bleed orifice  66  allows pressure from the inlet  50  to build up in the control chamber  62  for urging the valve member  58  in the closed position when the coil assembly  23  is de-energized. Although shown as extending through the piston  60 , it will be appreciated that the bleed orifice  66  may be formed in the valve body  12  and/or cover  14 . 
         [0047]    The pilot orifice  64 , which is provided for bleeding off pressure from the control chamber  62  to a point downstream of the valve seat  56 , typically will have a cross-sectional area that is greater than a cross-sectional area of the bleed orifice  66 . 
         [0048]    As seen in  FIGS. 4 and 5 , the piston  60  is sealed to the valve body  12  and radially supported for axial movement in the valve body by a pair of axially spaced apart spring-energized wiper seals  70  and  72  (e.g. lip seals). The wiper seals not only seal and support the piston in relation to the valve body, they also allow limited radial movement within an interior bore  74  in the valve body because the outer diameter of the piston is intentionally designed to be smaller than the diameter of the bore  74  in the valve body, such as by about 0.015 inch. As a result, the piston is supported in a “floating” fashion such that it can shift radially a limited amount to accommodate misalignment between the sealing surface  67  and the valve seat  56  so that the sealing surface will properly engage and seal against the sealing surface. Not only does this provide for better sealing, it also reduces wear on the sealing surface, particularly when the valve member  58  is formed from a plastic material as is preferred. In addition, the valve member can shift radially to accommodate any misalignment between the pilot orifice  64  and the plunger  32  (more particularly the below discussed pintle). 
         [0049]    Preferably the wiper seals  70  and  72  are oppositely oriented as shown to provide sealing in both directions to seal against differential pressures in the control chamber and the point downstream of the valve seat. A preferred wiper seal is a spring energized cup seal, and more preferably one made of PTFE. Particularly preferred seals are Flexiseals available from Parker-Hannifin Corporation of Cleveland, Ohio, USA. 
         [0050]    As will be appreciated, a spring-energized seal includes at least one sealing lip that is resiliently urged radially to bias the lip against the surface in contact therewith. 
         [0051]    This manner of supporting and sealing the piston to the valve body enables one or more following advantages to be achieved:
       provides sealing against possible differential pressures in both directions.   design and material selection provides a low wear bearing surface which self-compensates for wear in non-lubricated applications.   scraper feature provides a high degree of debris tolerance.   The Flexiseal geometry (or more generally the spring-energized lip seal geometry) allows for the piston to float within its radial clearance to ensure that the seat surfaces mate properly when valve is in closed position.   the spring energized dual lip seals (e.g. cup seals) combined with a roller burnished valve body bore (6-8 micro-finish) provides low wear frictional damping. This helps mitigate unwanted oscillations (water hammer) in compressible gas applications.       
 
         [0057]    As just noted, the interior cylindrical surface  74  of the valve body preferably is roller burnished to provide a 6-8 micro-finish, i.e. a surface or micro roughness in the range of 6 to 8 micro inches. 
         [0058]    As above noted, the valve member  56  (in particular the piston  60 ) preferably is made of a plastic material such as a polyetherimide (PEI) and particularly Ultem PEI. This makes the valve particularly suitable for high vibration applications such as those “on-engine” (i.e. where the valve is mounted to an engine). In contrast to other designs where bleed and pilot orifices are machined into the plastic, preferably the valve member is a composite assembly. 
         [0059]    As illustrated in  FIG. 7 , the bleed and pilot orifices  64  and  66  preferably are, respectively, precision machined in metal inserts  80  and  82  preferably made austenitic stainless steel. This choice of material provides long term resistance to erosion which could impact valve performance (diameters change). 
         [0060]    In the case of the pilot orifice, it provides a hard mating seating surface which won&#39;t deform over actuation cycles. The metallic pilot and bleed inserts  80  and  82  preferably have radially outwardly protruding interference ribs  84  and  86  that provide a positive seal and mechanical hold within the polymer piston. 
         [0061]    In applications where there may be debris present, the bleed orifice insert  82  may include a filter  88  such as a multilayered depth screen to protect the small bleed orifice which may be a small as 0.012″. Screened precision orifices can be purchased from the Lee Company of Westbrook, Conn., USA. 
         [0062]    In  FIG. 6 , a preferred plunger  32  is shown in greater detail. The plunger has a pilot orifice sealing surface  90  at is inner end (lower end in  FIG. 6 ). Preferably, this sealing surface is formed by the tapered end of a pintle  91 . The pintle is axially movable in a bore in a plunger body  92 , and is inwardly (downwardly in  FIG. 6 ) by a resilient member  93  such as the spring. The pintle has a flange  94  that will engage against a shoulder on the inner diameter of the plunger bore to determine the extent the pintle protrudes beyond the end of the plunger body. The spring is interposed between the pintle and a plug  95  that closes to the outer end of the plunger bore. The plug, spring and pintle preferably are made of non-magnetic stainless steel while the plunger body preferably is made of magnetic stainless steel. 
         [0063]    With additional reference to  FIGS. 4 and 5 , the plug and tubular wall of the plunger body respectively have vent passages  96  and  97  to allow fluid to flow to and from the chamber formed in the sleeve between the end of the plunger and the outer end piece so axial movement of the plunger will not be impeded. 
         [0064]    The plunger  32  is biased by a resilient member  98 , such as a coil spring, to a first position bringing the sealing surface of the pintle into sealing engagement with the pilot orifice  64 , thereby blocking flow through the pilot orifice  64  when the coil assembly  23  is de-energized. The resiliently biased plunger will also act on the valve member  58 , urging it into engagement with the valve seat  56 . When pressure is applied at the inlet, pressure will bleed through the valve member until the pressure in the control chamber  62  equals the pressure at the inlet. The piston  60  has a larger diameter than the valve seat  56  and the pressure at the point downstream of the valve seat  56  is lower than the inlet pressure, and thus the pressure of the fluid in the control chamber  62  acts on the piston portion  60  to hold the valve member  58  in the first position blocking flow through the valve seat  56 . 
         [0065]    When the coil assembly  23  is energized, the plunger  32  will be drawn away from the pilot orifice  64  to a second position, such position being determined by the duty cycle of the coil. This will allow flow through the pilot orifice  64  to a location downstream of the valve seat. This will reduce the pressure in the control chamber and will result in the inlet pressure forcing the valve member away from the valve seat to allow flow through the valve. The valve member will open until once again the pilot orifice is closed by the plunger, at which point further opening of the valve will cease. The open position of the valve will be determined by the position of the plunger which is determined by the power being supplied to the coil. The higher the power, the more the valve will be open. 
         [0066]    Summarizing, the valve is shown in its normally closed position in  FIG. 4 . With the coil de-energized, the plunger return spring forces the piston downwards in the closed position. When the valve is pressurized, system pressure enters the bleed orifice and pressurizes the volume above the piston. Because the plunger assembly pintle is sealed against the pilot orifice, the pressure on the top and bottom sides of the piston assembly are balanced. Since the piston area is larger than the main orifice area, the net force downward is greater. This creates a positive seal between the piston and the valve body. When the coil is energized the plunger assembly moves proportionally upwards depending on the PWM duty cycle which is provided. 
         [0067]    When the plunger assembly pintle lifts off the pilot orifice, the flow is greater than that of the bleed orifice, therefore the pressure on top of the piston assembly decreases causing it to move upward. The piston assembly will move upwards until it approaches the plunger assembly pintle as seen in  FIG. 5 . 
         [0068]    Though the plunger assembly and piston assembly are independent, their movement is tightly coupled by virtue of the pressure differential and resulting movement created on both sides of the piston assembly. 
         [0069]    Turning now to  FIGS. 8 and 9 , a normally open version of an exemplary valve according to the invention is indicated at  110 . The valve  110  is the same as the valve  10  except as set forth below. Accordingly, like features are denoted by the same reference number but indexed by  100 . 
         [0070]    As seen in  FIGS. 8 and 9 , a resilient member  202  is used to bias the valve member  158  away from the valve seat. In the illustrated embodiment, the resilient member is a tapered coil spring that is interposed between a retaining ring or a screen  159  secured in the valve body  112  and the underside of the valve member. 
         [0071]    While the plunger assembly  22  in the valve  10  is a pull plunger assembly, the plunger assembly  122  in the valve  110  is a push plunger assembly. 
         [0072]    The plunger assembly  122  includes a plunger  132  that is movable axially in a sleeve  134  that is secured and sealed to the cover  114 . In the illustrated embodiment and as best seen in  FIG. 10 , the sleeve has an axially outer portion  208  made of magnetic stainless steel, an intermediate portion  210  made of non-magnetic steel, and an axially inner portion  212  made of magnetic stainless steel. The inner portion may be unitary with the cover  114  that also is made of magnetic stainless steel. 
         [0073]    The outer portion  208  of the sleeve may be closed by an end wall that has a protruding post portion  216 . The post portion may be externally threaded for attachment of a nut  136  used to fasten the coil assembly  123  to the plunger assembly  122 . The end wall may have a bore for receiving and guiding a reduced diameter outer end portion of the plunger. 
         [0074]    The plunger  132  acts on a pintle  191  which is guided for axial movement in an end piece  220  made of magnetic steel. The end piece functions as a stop for the pintle which has a radially outwardly extending flange at its outer end that will engage a shoulder on the end piece to limit the extension of the pintle from the end piece. The end piece can be held stationary in the sleeve, as by means of a radially outwardly extending flange  222  that is trapped between the cover and the valve body  112  as shown in  FIGS. 8 and 9 . The pintle is axially biased outwardly away from valve member  158  by a resilient member  226 , such as a coil spring that is interposed between the pintle flange and the bottom of a counterbore in the end piece  220 . 
         [0075]    Consequently, when no power is being supplied to the coil  138 , the pintle will be retracted into the end piece. The valve member will be held away from the valve seat by the spring  202  to maintain the valve in an open state as seen in  FIG. 9 . When fluid pressure is supplied at the inlet  150 , fluid will flow through the open valve. Fluid pressure at the inlet will be bled to the control chamber  162  and this will cause the valve member to start closing when the pilot orifice  164  is closed by the pintle as shown in  FIG. 9 . As the valve member moves toward its closed position the pilot orifice will move away from the pintle, causing pressure to be released from the control chamber, thereby maintaining the valve member in a full open state. 
         [0076]    To close the valve, the coil is energized to establish a magnetic field that will draw the plunger  132  to the end piece  220 . The plunger will then force the pintle axially inwardly towards the valve member (that is pushed out of the sleeve) such that it will follow the piston  160  as the piston is caused to move toward the valve seat  156  by fluid pressure bled into the control chamber. The extent of this following movement will be dictated by the energy supplied to the coil, and this will in turn dictate the extent of closing movement of the valve member. 
         [0077]    Summarizing, the valve is shown in its normally open position in  FIG. 8 . With the coil de-energized, the plunger return spring forces the plunger upwards. 
         [0078]    The piston assembly return spring forces the piston to the open position. 
         [0079]    When the valve is pressurized, system pressure enters the bleed orifice and pressurizes the volume above the piston. Because the plunger assembly pintle is not sealed against the pilot orifice, the pressure on the top side of the piston assembly is lower, therefore the piston will stay open. 
         [0080]    When the coil is energized, the plunger assembly moves proportionally downwards depending on the PWM duty cycle which is provided. 
         [0081]    When the plunger assembly pintle approaches or touches the pilot orifice, the flow is lesser than that of the bleed orifice, therefore the pressure on top of the piston assembly increases causing it to move downward. The piston assembly will move downwards until it closes against the valve body main orifice. 
         [0082]    Though the plunger and piston assembly are independent, there movement is tightly coupled by virtue of the pressure differential and resulting movement created on both sides of the piston assembly. 
         [0083]    Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.