Abstract:
A pressure regulator is associated with a solenoid-operated valve that is operated by a pulse waveform at a fundamental frequency substantially greater than the frequency response of the valve mechanism. This substantially attenuates solenoid pulsations and applies a predetermined pressure differential across the valve mechanism to accomplish improved flow control accuracy. The invention is especially advantageous for purging fuel vapor to an intake manifold of an internal combustion engine of an automotive vehicle.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to emission control valves for automotive vehicles. In one specific aspect, the invention relates to solenoid-operated fluid valves for purging volatile fuel vapors from fuel tanks and vapor storage canisters to internal combustion engines that power such vehicles.  
         BACKGROUND OF THE INVENTION  
         [0002]    A known on-board evaporative emission control system comprises a vapor collection canister that collects volatile fuel vapors generated in the headspace of the fuel tank by the volatilization of liquid fuel in the tank and a canister purge solenoid (CPS) valve for periodically purging collected vapors to an intake manifold of the engine. The CPS valve comprises a solenoid actuator that is under the control of a microprocessor-based engine management system.  
           [0003]    During conditions conducive to purging as determined by the engine management system on the basis of various inputs to it, evaporative emission space that is cooperatively defined by the tank headspace and the canister is purged to the engine intake manifold through the CPS valve, which is fluid-connected between the canister and the engine intake manifold. The CPS valve is opened by a signal from the engine management computer in an amount that allows intake manifold vacuum to draw volatile fuel vapors from the canister for entrainment with the combustible mixture passing into the engine&#39;s combustion chamber space at a rate consistent with engine operation to provide both acceptable vehicle driveability and an acceptable level of exhaust emissions.  
           [0004]    A known CPS valve comprises a movable valve element that is resiliently biased by a compression spring against a valve seat to close the valve to flow when no electric current is being delivered to the solenoid. As electric current begins to be increasingly applied to the solenoid, increasing electromagnetic force acts in a sense tending to unseat the valve element and thereby open the valve to fluid flow. This electromagnetic force must overcome various forces acting on the mechanical mechanism before the valve element can begin to unseat, including overcoming both whatever static friction (stiction) is present between the valve element and the seat, as well as the opposing spring bias force. Once the valve element has unseated, the valve element/valve seat geometry also plays a role in defining the functional relationship of fluid flow rate through the valve to electric current supplied to the solenoid coil. Furthermore, the extent to which a given valve possesses hysteresis will also be reflected in the functional relationship.  
           [0005]    When the valve element comprises a tapered pintle that is selectively positioned axially within a circular orifice which is circumscribed by the valve seat, a well defined flow rate vs. pintle position characteristic can be obtained. However, certain geometric factors present at the valve element/valve seat interface may prevent this characteristic from becoming effective until the valve element has unseated a certain minimum distance from the valve seat. Accordingly, each graph plot of fluid flow rate through the valve vs. electric current supplied to the solenoid coil may be considered to comprise distinct spans: a short initial span that occurs between valve closed position and a certain minimum valve opening; and a more extensive subsequent span that occurs beyond a certain minimum valve opening.  
           [0006]    One specific type of CPS valve comprises a linear solenoid and a linear compression spring that is increasingly compressed as the valve increasingly opens. It is sometimes referred to as a linear solenoid purge valve, or LSPV for short. Such a valve can provide certain desirable characteristics for flow control. By itself a linear solenoid possesses a force vs. electric current characteristic that is basically linear over a certain range of current. When a linear solenoid is incorporated in an electromechanical device, such as a valve, the overall electromechanical mechanism possesses an output vs. electric current characteristic that is a function of not just the solenoid, but also the mechanical mechanism, such as a valve mechanism, to which the solenoid force is applied. As a consequence then, the output vs. electric current characteristic of the overall device is somewhat modified from that of the linear solenoid alone.  
           [0007]    While a CPS valve that incorporates both a linear solenoid and a tapered pintle valve element which is selectively positionable axially within a circular orifice that is circumscribed by the valve seat can exhibit a desired fluid flow rate vs. pintle position characteristic, such characteristic may not become effective until after the pintle has opened a certain minimum amount because of geometric factors at the pintle/seat interface, as noted earlier. Accordingly, each graph plot of fluid flow rate through the valve vs. electric current applied to the solenoid coil may be considered to comprise the spans referred to above, namely, a short initial span that occurs between valve closed position and a certain minimum valve opening, and a more extensive subsequent span that occurs beyond a certain minimum valve opening.  
           [0008]    Generally speaking, a linear solenoid purge valve may be graphically characterized by a series of graph plots of fluid flow rate vs. electric current, each of which is correlated to a particular pressure differential across the valve. Each graph plot may be characterized by the aforementioned short initial span and the more extensive subsequent span. Within the latter span of each graph plot, one especially desirable attribute is that a substantially constant relationship between incremental change in an electric control current applied to the solenoid and incremental change in fluid flow rate through the valve may be obtained by appropriate design of the valve element/valve seat interface geometry. Within the former span, incremental change in fluid flow rate through the valve may however bear a substantially different relationship to incremental change in an electric control current applied to the solenoid.  
           [0009]    In one such linear solenoid purge valve, a certain minimum electric current is required before the valve begins to open. For a given pressure differential across the valve, a corresponding graph plot of fluid flow rate vs. electric current may be described as comprising a relatively short initial span where a small incremental change in electric current will result in an incremental change in flow that is much different from the incremental change that occurs over an ensuing span where the valve has opened beyond a certain minimum opening and incremental change in flow through the valve bears a substantially constant relationship to incremental change in electric current.  
           [0010]    Electric current to the solenoid coil of any solenoid-operated device can be delivered in various ways. One known way is by applying a pulse width modulated D.C. voltage across the solenoid coil. In choosing the pulse frequency of the applied voltage, consideration may be given to the frequency response characteristic of the combined solenoid and mechanical mechanism operated by the solenoid. If a pulse frequency that is well within the frequency response range of the combined solenoid and mechanism is used, the mechanism will faithfully track the pulse width signal. On the other hand, if a pulse frequency that is well beyond the frequency response range of the combined solenoid and mechanical mechanism is used, the mechanism will be positioned according to the time average of the applied voltage pulses. The latter technique may be preferred over the former because the mechanical mechanism will not reciprocate at the higher frequency pulse width modulated waveform, but rather will assume a position corresponding to the time averaged current flow in the solenoid coil. Under the former technique, the mechanism could, by contrast, experience significant reciprocation as it tracks the lower frequency waveform, and that might create unacceptable characteristics. In the case of a CPS valve, such characteristics may include undesirable pulsations in the purge flow and objectionable noise caused by repeated impacting of the valve element with the valve seat and/or a limit stop that limits maximum valve travel. Such a valve may experience unacceptable variation in the start-to-flow duty cycle.  
           [0011]    In order to address the pulsation issue, it is known to associate a mechanical pressure regulator with a CPS valve. The pressure regulator mechanically damps the purge flow pulses, but does not address the root cause, which is due to the pulsating solenoid.  
           [0012]    Accordingly, a need exists for further improvement in certain aspects of pulse-operated emission control valves such as CPS valves because such valves may be required to perform under diverse vehicle operating conditions. For a CPS valve, purging of volatile fuel vapor to the intake manifold when the engine is idling may be quite difficult to accurately control.  
         SUMMARY OF THE INVENTION  
         [0013]    One general aspect of the invention relates to an electric-operated pressure-regulated fluid flow control valve comprising a valve mechanism that is positioned within a valve body by an electric control signal to control fluid flow through the valve body and that has a frequency response characteristic which renders the valve mechanism incapable of faithfully tracking the fundamental frequency of an electric control signal whose fundamental frequency is greater than a predetermined frequency that, when applied in control of the valve mechanism, positions the valve mechanism to a position corresponding to a most recent time average of the electric control signal free of any significant pulsing of the valve mechanism, and a pressure regulator comprising a flow path having an entrance through which fluid flow that has passed through the valve mechanism enters the pressure regulator flow path and an exit from which fluid flow that has entered the pressure regulator flow path exits the pressure regulator flow path, the pressure regulator comprising a pressure regulating mechanism that regulates the pressure at the entrance of the pressure regulator flow path to a pressure that is essentially independent of pressure at the exit of the pressure regulator flow path.  
           [0014]    Another general aspect relates to an electric-operated pressure-regulated fuel vapor purge valve for purging fuel vapor from a fuel tank to an intake manifold of an internal combustion engine comprising a valve mechanism that is positioned within a valve body by an electric control signal to control flow through the valve body and that has a frequency response characteristic which renders the valve mechanism incapable of faithfully tracking the fundamental frequency of an electric control signal whose fundamental frequency is greater than a predetermined frequency that, when applied in control of the valve mechanism, positions the valve mechanism to a position corresponding to a most recent time average of the electric control signal free of any significant pulsing of the valve mechanism, and a pressure regulator comprising a flow path having an entrance through which flow that has passed through the valve mechanism enters the pressure regulator flow path and an exit for communicating the pressure regulator flow path to an engine intake manifold, the pressure regulator comprising a pressure regulating mechanism that regulates the pressure at the entrance of the pressure regulator flow path to a pressure that is essentially independent of intake manifold vacuum.  
           [0015]    A further aspect relates to an LSPV, including a pressure regulator, that is believed to provide further improvements in purge flow control accuracy over a substantial range of valve operation and under diverse operating conditions.  
           [0016]    A still further aspect relates to the provision of certain constructional features in a pressure regulator that, in association with a CPS valve, are believed to provide improved purge flow control accuracy by significantly attenuating the influence of variations in pressure differential that would otherwise produce variations in the purge for a given valve opening.  
           [0017]    The foregoing, along with additional features, and other advantages and benefits of the invention, will be seen in the ensuing description and claims which are accompanied by drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a schematic diagram of an on-board evaporative emission control system, including an enlarged longitudinal cross-sectional view through a canister purge solenoid valve.  
         [0019]    [0019]FIG. 2 is a representative graph plot related to FIG. 1.  
         [0020]    [0020]FIG. 3 is a longitudinal cross-sectional view through another canister purge solenoid valve.  
         [0021]    [0021]FIG. 4 is a longitudinal cross-sectional view through the canister purge solenoid valve of FIG. 3 and an associated pressure regulator in accordance with the inventive principles.  
         [0022]    [0022]FIG. 5 is a series of graph plots useful in explaining the inventive principles in relation to FIG. 4.  
         [0023]    [0023]FIG. 6 is a longitudinal view, partly in cross-section, through another embodiment in accordance with the inventive principles.  
         [0024]    [0024]FIG. 7 is a longitudinal view of the embodiment of FIG. 6, but having a different portion in cross-section. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    [0025]FIG. 1 shows an evaporative emission control system  10  of a motor vehicle comprising a vapor collection canister (carbon canister)  12  and a canister purge solenoid (CPS) valve  14  connected in series between a fuel tank  16  and an intake manifold  18  of an internal combustion engine  20  in a known fashion. An engine management computer  22  supplies a valve control signal as an input to a pulse width modulation (PWM) circuit  24  to create a pulse width modulated signal which is amplified by a drive circuit  26  and applied to electric terminals  14   et  of valve  14 .  
         [0026]    Valve  14  comprises a housing  28  having an inlet port  14   i  that is fluid-coupled via a conduit  30  with a purge port  12   p  of canister  12  and an outlet port  14   o  that is fluid-coupled via a conduit  32  with intake manifold  18 . A conduit  34  communicates a canister tank port  12   t  to headspace of fuel tank  16 . An operating mechanism comprising a solenoid actuator  14   sa  is disposed within housing  28  for opening and closing an internal passage that extends between ports  14   i  and  14   o . The mechanism includes a bias spring  14   bs  that acts to urge a valve element  14   ve  closed against a valve seat  14   vs  for closing the internal passage to flow. When the solenoid actuator is progressively energized by engine management computer  22 , electromagnetic force is applied to an armature  14   a  in opposition to the bias spring force to unseat valve element  14   ve  from valve seat  14   vs  and thus open the internal passage so that flow can occur between ports  26  and  30 .  
         [0027]    Canister  12  is also seen to comprise a vent port  12   v  via which the evaporative emission space where the fuel vapors are contained is vented to atmosphere. Such venting may be via an atmospheric vent valve (not shown) that is operated closed at certain times, such as during OBDII testing.  
         [0028]    [0028]FIG. 2 depicts a representative control characteristic for valve  14  wherein fluid flow rate through the valve is related to the duty cycle of a pulse width modulated voltage that is applied across terminals  14   et . A certain minimum duty cycle, about 10% in the example, is required before the valve begins to open. As the duty cycle increases beyond 10%, the flow rate bears a generally straight line relationship to duty cycle. At 100% duty cycle a constant D.C. voltage is applied across terminals  14   et . The frequency of the pulse waveform that accomplishes this type of operation is relatively low, a representative frequency being within a range from about 5 Hz to about 20 Hz, but possibly as high as about 50 Hz. For valve mechanisms whose frequency response extends beyond such a range, the mechanism will experience significant reciprocal motion as it follows the pulse waveform.  
         [0029]    Because the valve is not pressure-regulated, flow rate will also be a function of the pressure differential across the valve ports. Temperature and voltage variations may also influence the relationship.  
         [0030]    It is known that the use of a linear solenoid can improve control accuracy, and FIG. 3 shows an example of a linear solenoid purge valve  14 ′, certain parts of which correspond to parts of valve  14  already mentioned, and they will be designated by corresponding primed reference numerals.  
         [0031]    Valve  14 ′ comprises a two-piece body B 1 , B 2  having an inlet port  14   i′  and an outlet port  14   o′ . Valve  14 ′ has a longitudinal axis AX, and body piece B 1  comprises a cylindrical side wall  40  that is coaxial with axis AX and that is open at its upper axial end where it is in assembly with body piece B 2 . Side wall  40  comprises upper and lower side wall-portions  40 A,  40 B joined by a shoulder  42 ; the former side wall portion is fully cylindrical while the latter is cylindrical except in the region where it is radially intercepted by port  14   o ′. Port  14   i ′ is in the shape of an elbow that extends from the lower axial end of side wall  40 . By itself, body piece B 1  is enclosed except for its open upper axial end and the two ports  14   o ′ and  14   i′.    
         [0032]    A linear solenoid S is disposed in body piece B 1 , having been introduced through the open upper end of body piece B 1  during fabrication of the valve. The solenoid comprises a bobbin  44 , magnet wire wound on bobbin  44  to form a bobbin-mounted electromagnetic coil  46 , and stator structure associated with the bobbin-coil. This stator structure comprises an upper stator end piece  48  disposed at the upper end of the bobbin-mounted coil, a cylindrical side stator piece  50  disposed circumferentially around the outside of the bobbin-mounted coil, and a lower stator end piece  52  disposed at the lower end of the bobbin-mounted coil.  
         [0033]    Upper stator end piece  48  includes a flat circular disk portion whose outer perimeter fits to the upper end of side piece  50  and that contains a hole into which a bushing  54  is pressed so as to be coaxial with axis AX. The disk portion also contains another hole to allow for upward passage of a pair of bobbin-mounted electrical terminals  56  to which ends of magnet wire  46  are joined. Piece  48  further comprises a cylindrical neck  58  that extends downward from the disk portion a certain distance into a central through-hole in bobbin  44  that is co-axial with axis AX. The inner surface of neck  58  is cylindrical while its outer surface is frusto-conical so as to provide a radial thickness that has a progressively diminishing taper as the neck extends into the bobbin through-hole.  
         [0034]    Lower stator end piece  52  includes a flat circular disk portion whose outer perimeter fits to the lower end of side piece  50  and that contains a hole into which a bushing  60  is pressed so as to be coaxial with axis AX. Piece  52  further comprises an upper cylindrical neck  62  that extends upwardly from the disk portion a certain distance into the central through-hole in bobbin  44  and that is co-axial with axis AX. Neck  62  has a uniform radial thickness. Piece  52  still further comprises a lower cylindrical neck  64  that extends downward from the disk portion a certain distance so that its lowermost end fits closely within lower side wall portion  40 B. A valve seat element  66  is necked to press-fit into the open lower end of neck  64  and is sealed to the inside of wall portion  40 B by an O-ring  67 . Above the lowermost end that fits to side wall  40 , neck  64  contains several through-holes  68  that provide for communication between port  14   o ′ and the space disposed above seat element  66  and bounded by neck  64 . Side wall  40  allows this communication by not restricting through-holes  68 .  
         [0035]    Bushings  54  and  60  serve to guide a valve shaft  70  for linear travel motion along axis AX. A central region of shaft  70  is slightly enlarged for press-fit of a tubular armature  72  thereto. The lower end of shaft  70  comprises a valve  74  that coacts with valve seat element  66 . Valve  74  comprises a head, integrally formed with shaft  70  and having the general shape of a tapered pintle, comprising a rounded tip  74 A, a frustoconical tapered section  74 B extending from tip  74 A, a grooved cylindrical section  74 C extending from section  74 B, and an integral back-up flange  74 D that in part defines the upper axial end of the groove of section  74 C. An O-ring type seal  76  of suitable fuel-resistant elastomeric material is disposed in the groove of section  74   c.    
         [0036]    Seat element  66  comprises an inwardly directed shoulder  66 A that contains a portion of a through-hole that extends axially through the seat element. This portion of the through-hole comprises a straight cylindrical section  78  and a frustoconical seat surface  80  that extends from the upper end of section  78  and is open to the interior space bounded by neck  64 . The remainder of the through-hole axially below section  78  is designated by the reference numeral  81 .  
         [0037]    The upper end of shaft  70  protrudes a distance above bushing  54  and is shaped to provide for attachment of a spring seat  79  thereto. With piece B 2  being attached to piece B 1  by a clinch ring  82  which grips confronting, mated flanges to sandwich a seal  84  between them, a helical coiled linear compression spring  86  is captured between seat  79  and another spring seat  87  that is received in a suitably shaped pocket of piece B 2 . A calibration screw  88  is threaded into a hole in the end wall of this pocket coaxial with axis AX, and it is externally accessible by a suitable turning tool (not shown) for setting the extent to which spring seat  87  is positioned axially relative to the pocket. Increasingly threading screw  88  into the hole increasingly moves seat  87  toward spring seat  79 , increasingly compressing spring  86  in the process. Terminals  56  are also joined with terminals  90  mounted in piece B 2  to form an electrical connector  92  for mating engagement with another connector (not shown) that connects to drive circuit  26 .  
         [0038]    In the valve closed position shown in FIG. 3, a rounded surface portion of seal  76  has circumferentially continuous sealing contact with seat surface  80  so that the valve closes the flow path between ports  14   o ′ and  14   i ′. In this position the upper portion of armature  72  axially overlaps the air gap that exists between the upper end of neck  62  and the lower end of neck  58 , but slight radial clearance exists so that armature  72  does not actually touch the necks, thereby avoiding magnetic shorting.  
         [0039]    Generally speaking, the degree of valve opening depends on the magnitude of electric current flow through the solenoid coil  46  so that the purge flow through the valve is effectively controlled by controlling the electric current flow through the coil. As the magnitude of electric current flow progressively increases from zero, it reaches a value sufficient to break whatever stiction exists between the seated O-ring  76  and seat surface  80 . At that point the valve mechanism begins to open against the opposing force of spring  86 . Valve opening commences as soon as O-ring seal  76  loses contact with seat surface  80 .  
         [0040]    Depending on the specific geometric relationships that are present between the valve pintle, its O-ring seal, and the angle of the valve seat surface, a certain initial axial travel of the pintle that unseats O-ring seal  76  from seat surface  80  may have to occur before tapered section  74 B can become effective by itself to set the effective flow area through the seat element through-hole. In other words, it is only after the valve has traveled more than some initial minimum travel distance that the tapered section can become effective by itself to control the area open to flow. Beyond this initial minimum, the open area progressively uniformly increases as the pintle is increasingly positioned away from the seat element.  
         [0041]    A representative graph plot of fluid flow rate vs. electric current reveals three distinct spans: a first span where current increases without any valve opening; a second span where the valve begins to open but the tapered section  74 B is not yet fully effective to control the flow by itself; and a third span where the valve has opened sufficiently to allow section  74 B to alone control the flow. The second span may be characterized by a relationship wherein a small incremental change in average electric current in solenoid S causes an incremental change in fluid flow rate that is substantially different from the incremental change results when the valve operates instead within the third span.  
         [0042]    Coil  46  of solenoid S is connected across a source of D.C. voltage pulses, such as a pulse-width modulator circuit operating at a selected frequency. Electric current flow to the coil may be controlled by a solid-state driver in accordance with a control output signal from an engine management computer, and the circuit may include a feedback loop for feeding back a signal representative of electric current flow through the solenoid coil so as to endow the control with the ability to compensate for certain environmentally induced changes that could otherwise impair control accuracy. For example, the feedback loop can automatically regulate the current flow through coil  46  such that the influences of changes in ambient conditions, such as temperature and D.C. supply voltage to the circuit, are essentially negated, thereby enabling the valve to operate to a desired position commanded by the circuit substantially free of such influences.  
         [0043]    [0043]FIG. 4 shows a mechanical pressure regulator  200  opperatively associated with valve  14 ′. Pressure regulator  200  comprises a two-piece body  202  having a base  202   b  and a cover  202   c , both of which are fabricated from suitable material, such as fuel tolerant injection molded plastic. Base  202   b  comprises an inlet port  204  and an outlet port  206  each of which is in the form of a nipple. A conduit  208  fluid connects port  204  with outlet port  14   o ′ of valve  14 ′, and outlet port  206  is fluid connected with engine intake manifold by another conduit that is not specifically illustrated in the Fig.  
         [0044]    The nipple forming outlet port  206  comprises a walled conduit having a radial segment that extends inwardly of body  202  to form an axial segment that is coaxial with an axis  210  of pressure regulator  200 . This walled axial conduit segment terminates as a circular rim forming a seal seat  212 . Base  202   b  further comprises a cylindrical walled cup having a circular annular radial shoulder  214 . This cup terminates in a circular rim  216  that is coaxial with axis  210 .  
         [0045]    Cover  202   c  has a generally circular shape whose outer periphery contains one or more catches  218  that attach the cover to the otherwise open end of the cup of base  202   b  at rim  216  by snapping over a lip of the rim as shown. The beaded outer circular perimeter of an impermeable flexible member  220  is held captured between the outer margin of cover  202   c  and rim  216  in a sealed manner. Centered with member  220  coaxial with axis  210  is a rigid circular disk  222 . Secured centrally to disk  222  in confrontational juxtaposition to rim  216  is a circular seal element  224 . In the illustrated embodiment, element  224  is secured to disk  222  by being molded onto the disk, with a portion of the molded material passing from the element, through a small hole in the center of the disk, to create an interlocking circular formation  226  on the opposite face of the disk.  
         [0046]    It can be seen that the outer margin of disk  222  contains an annular area free of molded material. One end of a helical coiled compression spring  228  bears against this annular area. The opposite end of the spring bears against a wall of base  202   b  that extends circumferentially partially around the axial segment of the outlet port nipple below rim  212 .  
         [0047]    Cover  202   c  is formed with a central depression  230 , and in the condition shown by FIG. 4, spring  228  is seen forcing disk  222  away from rim  212  such that the flat end surface of formation  226  is biased against the flat end surface of depression  230 .  
         [0048]    The assembled parts  220 ,  222 ,  224  form a fluid impermeable wall  232  that divides the interior of body  202  into first and second chamber spaces  234 ,  236 . In the position shown by the Fig., chamber  236  provides free communication between ports  204  and  206 . The flow path thus provided is depicted by the arrows which represent purge flow from valve  14 ′, through inlet port  202 , through chamber space  236 , and through outlet port  204  to the engine intake manifold. Chamber space  234  is communicated directly to atmosphere through an atmospheric vent orifice  238  through the wall of cover  202   c.    
         [0049]    Pressure regulator  200  operates in the following manner. For purposes of explanation, assume that it is in the position illustrated in the Fig., that equal pneumatic pressures exist in the two chamber spaces  234 ,  236 , and that valve  14 ′ is open. The creation of increasing intake manifold vacuum in chamber space  236  will begin to create an increasing pressure differential on wall  232 . At a certain differential, the bias force of spring begins to be overcome, and the central region of wall  232  begins moving toward rim  212 . Atmospheric pressure is maintained in chamber space  234  because air is drawn through vent orifice  238  as wall  232  moves toward rim  212 . When the vacuum has increased to a certain larger magnitude, seal element  224  will be sufficiently close to rim  212  to create a restriction of the purge flow. The seal element may actually close on rim  212 , albeit only momentarily. Such restriction or closure, tends to reduce the pneumatic pressure differential acting on wall  232  so that spring  228  then tends to move the central region of the wall away from rim  212 . Atmospheric pressure is maintained in chamber space  234  because air is forced out through vent orifice  238 .  
         [0050]    The overall effect is such that sealing element  224  will assume an average position that causes the vacuum in chamber space  236  to be regulated to a predetermined magnitude that is substantially independent of the magnitude of intake manifold vacuum. Hence, with the tank headspace at atmospheric pressure, flow through the valve is essentially unaffected by change in intake manifold vacuum because a substantially constant pressure differential is maintained across valve  14 ′. Now as valve  14 ′ operates to different positions as commanded by the signal applied to solenoid S, the commanded positions will produce substantially the correspondingly intended purge flow rate, substantially free of variation in intake manifold vacuum. Because flexible member  220  is provided with a convolution, it imposes no restriction of the movement of the central region of the movable wall relative to the open end of the walled axial conduit segment that contains rim  212 .  
         [0051]    Thus, in distinction to prior uses of pressure regulators in conjunction with pulsating purge valves, the disclosed embodiment does not utilize a pressure regulator for the purpose of dampening purge flow pulsations. Rather, the creation of a predetermined pressure differential acting across valve  14 ′ enables a given command signal to directly provide the intended flow rate, free of manifold vacuum variations. It is believed that this can eliminate the need for the engine management computer to include a map for processing an input representing intake manifold vacuum when it calculates what the command signal to the solenoid coil of the valve should be.  
         [0052]    [0052]FIG. 5 shows a series of representative graph plots of purge flow rate through valve  14 ′ vs. time-averaged D.C. current flow in the solenoid coil. Each graph plot corresponds to a different value of intake manifold vacuum as indicated in FIG. 5, but the important effect of pressure regulator  200  can be seen by the substantial congruence of graph plots for 200, 300, 400, 500, and 600 mm Hg intake manifold vacuum. In the examples of FIG. 5, purge flow commences at about 183 milliamps current for the substantially congruent plots.  
         [0053]    [0053]FIGS. 6 and 7 illustrate another embodiment in which an LSPV and a pressure regulator are integrated into a single assembly. Like reference numerals from the preceding Figs. are used to identify like parts, although from comparison of it can be seen that certain parts differ in certain details of construction. FIGS. 6 and 7 show that pressure regulator  200  has been integrated into the lower end of LSPV  14 ′. The nipples that formed valve outlet port  14   o ′ and regulator inlet port  208  have been eliminated. The portion of the flow path downstream of the valve pintle is communicated to chamber space  236  directly within the body of the assembly.  
         [0054]    Flexible member  220 , seal element  224 , and formation  226  are embodied as a single part that is created by insert molding onto disk  222 . The central region of cover  202   c  comprises a tower  230 ′ which is somewhat different from the depression  230  of the earlier embodiment. Tower  230 ′ comprises a generally cylindrical wall  230   w  having a shoulder  230   s . An orifice member  238   m  is secured in place on cover  202   c  by a short axial wall  238   w  that is press-fit to a portion of wall  230   w . A circular radial flange  238   f  at one axial end of wall  238   w  is disposed against shoulder  230   s  to axially locate orifice member  238   m  on cover  202   c.    
         [0055]    One face of disk  222  comprises several circumferentially spaced formations  222   a  that are arranged in a circular pattern to center one axial end of spring  228  against disk  222 . The opposite disk face comprises several circumferentially spaced formations  222   b  also arranged in a circular formation. Proximate shoulder  230   s , cover  202   c  comprises a circular ridge  202   r  against which formations  222   b  bear when spring  228  is biasing seal element  224  maximally away from rim  212 .  
         [0056]    Orifice member  238   m  contains a central through-orifice  238   o  that corresponds to orifice  238  for communicating chamber space  234  to atmosphere through the interior of tower  230 ′ to openings  202   o  that extend through the wall of the tower. Pressure regulator  200  and valve  14 ′ of the FIGS. 6 and 7 embodiment function in the same manner as described above for the earlier embodiment.  
         [0057]    While the solenoid S shown in FIG. 6 functions in the same manner as the solenoid shown in FIGS. 3 and 4, it differs in certain constructional respects. The coil-containing bobbin  44 ,  46  and stator parts  48  and  52  are encased in an overmolding  300  to form an assemblage that also includes the body part B 2  as part of the overmolding.  
         [0058]    Thus, the overmolding includes features forming the shell of connector  92  and accommodations for acceptance of spring  86  and its associated adjustment mechanism.  
         [0059]    These parts that are to be overmolded are placed in a suitably shaped mold cavity in a machine that forms the overmold around them. As overmold material flows, it passes through holes in flanges of stator parts  48  and  52 , covering the end surfaces and outer edges of the bobbin flanges and covering the exterior of coil  46 . The two stator parts are sealed relative to the central interior through-hole of bobbin  44  such that the overmold material does not intrude into that through-hole. Upon curing of the overmold material, the overmold has a final shape as shown, including a short neck at one end. The neck contains a circular groove for acceptance of an O-ring  302  that, when the overmolded assemblage is assembled into the valve during the fabrication process, serves to seal that end of the overmold to the wall of a single molded plastic part  304  in which valve body part B 1 , base  202   b , and the nipples forming inlet port  14   i ′ and exit  206  are integrated.  
         [0060]    In the particular embodiment of FIG. 6, stator part  50  is not part of the overmold assemblage. Rather, it is a separate tubular walled cylinder that is placed inside a main cylindrical wall  305  of body part B 1  via the open upper end thereof, as seen in FIG. 6, and it is axially captured therein by the overmold assemblage as the latter is inserted to assembled position within space bounded by wall  305 .  
         [0061]    The overmold assemblage is retained in final assembled position shown in FIG. 6 by several catches  306  on the wall of part  304  that snap over radial protrusions  307  extending from the overmold. Prior to insertion of the overmold assemblage into the space bounded by wall  305 , various internal parts such as  54 ,  60 ,  70 ,  72 ,  79 ,  86 ,  87 ,  88  are assembled into the overmold assemblage. Also, the valve seat element  66  is assembled to part  304 , that element having a cylindrical wall fitted in a sealed manner by an O-ring  308  to the open internal end (co-axial with axis AX) of the nipple that forms inlet port  14   i ′. Above its transverse wall that contains the valve through-hole controlled by valve  74 , the valve seat element contains an apertured cylindrical wall that provides for vapor flow that has passed through the seat element through-hole to flow to an internal space of part  304  and thence enter regulator chamber space  236 . The vapor flow path is indicated by the unnumbered arrows in FIGS. 6 and 7.  
         [0062]    Embodiments utilizing the inventive principles may be constructed in diverse ways. Because automotive electronic technology commonly employs electronic processors, the development of the electric control signal for the solenoid may be accomplished by utilizing conventional software programming techniques to develop the desired waveform or waveforms for any specific control strategy.  
         [0063]    While the present invention has been described with reference to a preferred embodiment as currently contemplated, it should be understood that the invention is not intended to be limited to that embodiment. Accordingly, the invention is intended to encompass various modifications and arrangements that are within the scope of the claims.