Patent Abstract:
A pressure control valve serves to regulate the fuel pressure in a fuel system. The pressure control valve includes a valve housing, at least one inlet, at least one outlet, and at least one prestressed, electrically actuatable, and at least regionally ball-shaped valve member. The valve member cooperates with a valve seat structurally connected to the housing. To make it possible to achieve stable closed- and/or open-loop control properties of the pressure control valve, it is proposed that the valve seat widen conically toward the valve member, and the ball diameter of the valve member is selected such that with the valve closed, the valve member touches the valve seat in the vicinity of its farther end.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pressure control valve for a direct-injection fuel system of an internal combustion engine, having a valve housing, at least one inlet, at least one outlet, and at least one prestressed, electrically actuatable, and at least regionally spherical valve member, which cooperates with a valve seat structurally connected to the housing. 
     2. Description of the Prior Art 
     One pressure control valve of the type which the invention is concerned is known from European Patent Disclosure EP 0 267 162. In this known pressure control valve, a valve ball is seated on the end of an inlet conduit that accordingly forms a valve seat. The ball is pressed against this valve seat by a valve tappet that is acted upon by a spring. Fastened to the end of the valve tappet remote from the ball is a magnet armature, which is surrounded by an annular electromagnet. When the magnet coil is not excited, the contact-pressure force of the valve ball is effected solely by the force of the spring. Upon an excitation of the magnet coil, the magnetic force is superimposed on this. The superposition takes place in the direction of the spring force, so that depending on the intensity of the magnetic force, the closing pressure of the valve can be increased beyond what the spring alone can exert. 
     However, in the known pressure control valve it has been found that the quality of the pressure control does not always meet the demands made of it. In particular, it has been demonstrated that the known pressure control valve tends to high-frequency fluttering under some circumstances. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to refine a pressure control valve of the type defined at the outset such that in a simple way, it can be operated reliably and makes stable pressure control possible. 
     In a pressure control valve of the type defined at the outset, this object is attained in that the valve seat widens conically toward the valve member, and the ball diameter of the valve member is selected such that with the valve closed, the valve member touches the valve seat in the vicinity of the further end of the valve seat. 
     According to the invention, it has been recognized that the flow downstream of the point of passage between the valve seat and the valve member can be calmed or stabilized if the flow is carried radially outward through a conical widening of the valve seat. This additionally requires, however, that the narrowest point of the passageway gap between the valve member and the valve seat be located as close as possible to the farther, that is, the downstream, end of the valve seat. In such an embodiment of the valve seat and the valve member, a relatively calm, stable, radially outward-oriented flow downstream of the point of passage through the valve gap is obtained when the valve is open. 
     This in turn makes markedly improved quality of the open- or closed-loop control of the fuel pressure in a fuel system possible. This makes more-accurate metering of the fuel upon injection, for instance into a combustion chamber of the engine, possible, which in turn improves the fuel consumption and emissions properties of the engine. The improvement in the open- and closed-loop control quality is achieved without requiring additional components or complex machining steps. Thus the pressure control valve of the invention can be produced relatively inexpensively. 
     In a first refinement of the invention it is proposed that the prestressing force is adjustable, in particular by means of a spring that can be tensed by a screw. In this way, the mechanical opening pressure for each pressure control valve can be adjusted in an especially simple way. 
     It is also possible that the valve member is embodied as a ball, and a retaining element is provided, in which the ball is retained transversely to the actuation direction. By means of such a retaining element, it is assured that even with the valve open, that is, when the valve member is lifted from the valve seat, the annular gap between the valve member and the valve seat is approximately the same size throughout. This prevents lateral differences in pressure at the annular gap, which under circumstances could cause a lateral oscillating motion of the valve member. 
     It is especially preferred if the retaining element has at least three radially inward-oriented retaining tongues, each with at least one radially inner wall on which the ball rests. With such retaining tongues, an unambiguous centering of the valve member relative to the valve seat is possible, without the passage of fluid being severely impaired by the retaining element. 
     In an especially preferred refinement, the pressure control valve of the invention includes a valve tappet, which acts upon the valve member. In addition, at least two plastic slide bushes are provided, in which the valve tappet is retained in an axially sliding fashion. Because of such minimally frictional or even frictionless bearing support of the valve tappet, the adjustment characteristic of the valve tappet has a slight hysteresis, which contributes to fine pressure adjustment by the pressure control valve. 
     The triggering of the pressure control valve can be effected in an especially simple way by providing that it is actuatable electromagnetically, and at least one magnet armature is retained on the valve tappet via a compression connection. 
     It is also especially preferred if the pressure control valve includes a magnet core, extending coaxially to the valve tappet, on which core one of the plastic slide bushes is secured, and the plastic slide bush, toward the armature, has a shoulder which serves as a spacer between the magnet core and the armature. The shoulder assures that even with the armature attracted, a remanent air gap required for the magnetic action is always available between the magnet core and the armature. Providing a magnet core leads to a boost in the magnetic action, which improves the dynamics of the pressure control valve of the invention. Disposing the plastic slide bush on the magnet core makes a separate retaining part unnecessary, which reduces the production cost for the pressure control valve of the invention. 
     According to the invention, a hydraulic module can also be provided, which includes the valve housing, the inlet, the outlet, the valve member, the valve seat, the prestressing element, the valve tappet, the armature, the magnet core, and the plastic slide bushes, and a coil module can be provided, which includes at least one magnet coil, extending coaxially to the magnet armature, as well as an electrical terminal, and the hydraulic module and coil module form separate component groups from one another. 
     This refinement of the pressure control valve of the invention has the advantage that the hydraulic module and the coil module can be produced separately from one another, which lowers the production costs because of the different production requirements. In the case of a defect, it is possible to replace the individual modules separately. Furthermore, a separate coil module makes it possible for different coil modules, equipped with the terminals to suit customer requirements, each to be combined with the same hydraulic module. Once again, this reduces the production cost for the pressure control valve of the invention, since at least for the hydraulic module, relatively large numbers are manufactured. 
     Connecting the hydraulic module to the coil module is preferably done via a frictional-engagement and/or detent connection. This also creates a means of securing it for shipping, which prevents parts located on the inside from becoming soiled or damaged. The fact that the frictional-engagement and/or detent connection can be disconnected again makes easy replacement of the parts possible. 
     In another refinement, it is proposed that the coil module includes an approximately U-shaped bracket element, which as its base has a fastening portion with at least two laterally protruding retaining flanges and as its legs has at least two striplike encapsulation portions, which fit over the coil from outside. With the U-shaped bracket element, the pressure control valve of the invention can thus be fastened in a simple way to some element of the fuel system. At the same time, the bracket element makes a boost in the magnetic force possible, by a laterally outer encapsulation of at least one region of the magnet coil. 
     It is especially preferred if the bracket element, on the ends of the legs, has fastening portions, in particular detent lugs, to which a cap element can be secured, in particular calked, with which cap element the coil is magnetically encapsulated on its end. The terminal encapsulation of the coil boosts the magnetic force still further, and the retention of the applicable cap is accomplished in a simple way by the bracket element. 
     It is also possible that the valve housing has a laterally outward-pointing shoulder, which rests on the bracket element. In this way, there is no need for separately fastening the hydraulic module to the coil module of the built-in pressure control valve, since in the built-in position, the hydraulic module is pressed with its shoulder against the coil module by the hydraulic pressure. 
     To further increase the magnetic force, it is proposed that there is a gap between the valve housing and the magnet core, and the valve housing is joined to the magnet core via a ring of an antimagnetic material. 
     In another preferred refinement of the pressure control valve of the invention, a receiving part with a stepped bore is provided, into which bore a connection peg of the valve housing is inserted, and an inlet-side line discharges into one portion of the stepped bore while an output-side line discharges into another portion, and the inlet-side line is sealed off from the outlet-side line by a first ring seal, and the outlet-side line is sealed off from environment by a second ring seal, and the second ring seal has a larger diameter than the first ring seal, and in the built-in state, the spacing between the first ring seal and the first step of the stepped bore is less than the spacing between the second ring seal and the second step, leading to the environment, and the fastening of the valve housing to the receiving part is elastic in the axial direction. This refinement of the pressure control valve of the invention is based on the following consideration: 
     Should the valve member become wedged in its closing position because of a defect, this means that the pressure limiting function of the pressure control valve is no longer operative. In that case, because of the axially elastic fastening of the valve housing to the receiving part, the valve housing and as a result the entire pressure control valve can be pushed out of the receiving part or out of the stepped bore as the hydraulic pressure increases. 
     If the inlet and outlet and the corresponding ring seals are embodied as claimed, it is assured that whenever the connection peg moves axially out of the receiving part, first the ring seal between the inlet and the outlet slips over the corresponding step, thus establishing a direct communication between the inlet and the outlet. In this way, virtually the entire pressure control valve acts as a valve element, which with increasing hydraulic pressure is lifted from its valve seat, namely the stepped bore. Thus even if the valve member is blocked, a certain pressure limiting function of the pressure control valve is assured. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawings, in which: 
     FIG. 1 is a basic illustration of a fuel system with a pressure control valve; 
     FIG. 2 shows a longitudinal section through the pressure control valve of FIG. 1; 
     FIG. 3 is a section taken along the line III—III of FIG. 2; 
     FIG. 4 shows a detail of the injection valve in FIG. 2; 
     FIG. 5 is a longitudinal section through a region of the pressure control valve of FIG.  1  and of a receiving part; 
     FIG. 6 shows a retaining element for a valve member of the pressure control valve of FIG. 1 in perspective; 
     FIG. 7 is a plan view on the retaining element of FIG. 6; 
     FIG. 8 is a perspective view of a blank from which a bracket element of the pressure control valve of FIG. 1 is made; and 
     FIG. 9 shows the bracket element made from the blank of FIG.  8 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A fuel system is identified overall in FIG. 1 by reference numeral  10 . It includes a fuel tank  12 , from which fuel is pumped via a fuel line  14  by an electric fuel pump  16  to a filter  18  and from there to a high-pressure pump  20 . The pressure in the fuel line  14  is regulated by a low-pressure regulator  22 , which is disposed in a branch line  24 . 
     From the high-pressure pump  20 , a high-pressure fuel line  26  leads to a fuel collection line  28 , called a “rail”. Connected to the rail, in the present exemplary embodiment, are four high-pressure injection valves  30 . By way of these valves, the fuel is injected directly into a combustion chamber, not shown, of an internal combustion engine, also not shown. The pressure in the rail  28  monitored up by a pressure sensor  32 . 
     The adjustment of the pressure in the rail  28  is effected by a pressure control valve  34 , which communicates on its inlet side with the rail  28  via a fuel line  36  and on the outlet side with the low-pressure fuel line  14  via a fuel line  38 . By means of the pressure control valve  34 , the pressure in the rail  28  can be adjusted within a range of approximately 4 to 130 bar. To that end, the pressure control valve  34  is triggered by an open- and closed-loop control unit, not shown. This unit in turn receives signals from the pressure sensor  32 . Adjusting the pressure in the rail  28  can be done by means of a closed control loop or by simple triggering of the pressure control valve  34 . 
     The pressure control valve  34  will now be described in detail, referring to FIGS. 2-9 (for the sake of simplicity, not all the reference numerals are shown in FIG.  3 ): 
     First, the pressure control valve  34  includes a cylindrical valve housing  40  which in its lower region in FIGS. 2 and 3, together with a valve body  43  forms a connection peg  42 . Extending coaxially in this connection peg  42  is an inlet conduit  44 , embodied as a stepped bore. Above the inlet conduit  44  are two radially extending outlet conduits  46  (in another exemplary embodiment, not shown, there is only one outlet conduit; more than two outlet conduits are equally conceivable). The inlet conduit  44  and the outlet conduits  46  communicates with a flow chamber  48  in the interior of the connection peg  42 . A filter piece is mounted on the free end of the connection peg  42 . Approximately in its center axially, the valve housing  40  has an encompassing, radially outward-pointing annular rib  51 . 
     The stepped bore of the inlet conduit  44  narrows axially from the outside inward. However, a conical widened portion  50  (see FIG. 4) is also present on the upper end of the uppermost portion, in FIG. 2, of the inlet conduit  44 . This widened portion forms a valve seat for a valve ball  52 . The diameter of the valve ball  52  is selected such that whenever the valve ball  52  rests on the valve seat  50 , the valve ball  52  touches the valve seat  50  in the vicinity of its farther or in other words upper end in FIGS. 2-4. 
     The valve ball  52  is retained radially of the connection peg  42  by a retaining element  54 . The retaining element has a triangular outer contour, with rounded corners. An also approximately triangular recess  56 , again with rounded corners, is present in the center of the retaining element  54 . From the centers of the sides of the triangle of the recess  56 , retaining tongues  58  extend radially inward, and the radially inner wall of the retaining tongues in each case is identified by reference numeral  60 . The valve ball  52  rests on these radially inner walls  60  of the retaining tongues  58 . In this way, the valve ball  52  is retained transversely to the actuation direction by the retaining tongues  58 . The retaining element  54  has a generally disklike shape and is inserted into an axial recess in the top side of the valve body  43 . 
     The upper boundary wall of the flow chamber  48  is pierced by a bore  62 , into which a first plastic slide bush  64  is inserted. A valve tappet  66  embodied as a cylindrical pin is supported with little friction in the first plastic slide bush  64 . Above the flow chamber  48  in the valve housing  40 , there is a further coaxial, cylindrical recess  68 , which is open at the top. A cylindrical magnet armature  70  is pressed onto the valve tappet  66 . The lower end face of the magnet armature is spaced apart from the lower end face of the recess  68 . With its upper end, the magnet armature  70  protrudes past the upper end of the valve housing  40 . 
     An annular element  72  made of an antimagnetic material is welded onto the outer jacket face, on the upper end of the valve housing  40 . The annular element  72  likewise protrudes past the upper end of the valve housing  40  and is welded at its upper end to a magnet core  74  that extends coaxially to the valve housing  40 . The outside diameter of the magnet core  74  is approximately equivalent to the outside diameter of the upper portion of the valve housing  40 . 
     The magnet core  74  has a bore  76  that extends over its full length. The through bore  76  is likewise embodied in stepped fashion. A second plastic slide bush  78  is inserted into the lowermost portion of this bore in terms of FIGS. 2 and 3. With a shoulder  79 , the plastic slide bush  78  protrudes somewhat past the base of a countersunk feature  80  in the underside of the magnet core  74 . The diameter of the countersunk feature  80  is somewhat greater than the diameter of the magnet armature  70 . The shoulder  79  forms a spacer for the armature  70 . The upper end, in terms of FIGS. 2 and 3, of the valve tappet  66  is supported with little friction in the second plastic slide bush  78 . 
     A spring holder  82  is fastened to the upper end of the valve tappet  66 . The spring holder, on its end toward the valve tappet  66 , has a head  84 , on which a compression spring  86  is braced. The compression spring  86  extends upward coaxially to the valve tappet  66  and is guided by an upward-extending guide portion  88  of the spring holder  82 . The upper end of the spring  86  is in turn braced on an adjusting screw  90 . This screw is screwed into the magnet core  74  in a threaded portion  92  in the upper region of the through bore  76 . 
     The adjusting screw  90  is sealed off from the through bore  76  by an O-ring seal  94 . By means of the adjusting screw  90 , the prestressing force of the spring  86  can be adjusted. The prestressing force of the spring  86  is transmitted via the valve tappet  66  to the valve ball  52 , and as a result the valve ball is pressed against the valve seat  50 . 
     The valve housing  40 , the valve body  43  with the inlet conduit  44  and the outlet conduits  46 , the valve ball  52  and the associated valve seat  50 , the compression spring  86 , the valve tappet  66 , the plastic slide bushes  64  and  78 , the magnet armature  70 , the magnet core  74 , the spring holder  82  and the adjusting screw  90  together form a hydraulic module  96  that forms a cohesive component group. 
     To generate a magnetic force, first an annular winding holder  98  is provided. This winding holder is disposed coaxially to the valve housing  40  and surrounds the upper region of the valve housing  40  as well as the lower region of the magnet core  74 . Winding wire is wound onto the winding holder  98 , forming a coil  99 . On its lower end, the winding holder  98  has a radially inner collar  100 , which protrudes axially downward and with its edge rests on the bracket element  102  and is spray-coated. 
     The bracket element  102  is shown in detail in FIGS. 8 and 9. It is stamped out as a flat part (FIG. 8) and then, by bending two legs  104  upward, shaped into a U-shaped part. There is a circular recess  108  in a base  106  of the bracket element  102 , the inside diameter of which recess is approximately equivalent to the outside diameter of the upper portion of the valve housing  40 . Two retaining flanges  110  protrude laterally from the base  106 , and in each of the retaining flanges there are respective fastening bores  112 . 
     The legs  104  of the bracket element  102  form striplike encapsulation portions, which fit from outside over the winding holder  98  with the coil  99  wound onto it. Detent lugs  114  are embodied on the ends of the legs  104  and are calked to a platelike cap element  116 . The cap element  116  likewise has a central recess  118 , whose diameter is approximately equivalent to the outside diameter of the magnet core  74 . By means of the bracket element  102  and the cap element  116 , an external encapsulation of the coil  99  on the winding holder  98  is created. 
     The coil  99  on the winding holder  98  is connected to a radially protruding flat plug  120 . The bracket element  102 , cap element  116 , flat plug  120  and winding holder  98  with the coil  99  are entirely sheathed with plastic  122 . The winding holder  98  with the coil  99 , the bracket element  102 , the cap element  116 , the flat plug  120  and the molded plastic sheath  122  together form a coil module  124  embodied as a separate component. 
     The joining of the coil module  124  to the hydraulic module  96  is effected simply by slipping the coil module  124  onto the hydraulic module  96  until the base  106  of the bracket element  102  rests on the annular shoulder  51  of the valve housing  40 . The coil module  124  is prevented from slipping off the hydraulic module  96  by detent lugs  126 , which are embodied in the upper region of the magnet core and dig into the molded plastic sheath  122 . Because the pressure control valve  34  has both a hydraulic module  96 , embodied as a separate component group, and a coil module  124 , also embodied as a separate component group, it is possible to connect the hydraulic module  96  to different coil modules  124 . 
     This in turn makes it possible to produce the hydraulic module  96  in very large numbers, which reduces its production costs. The coil module, which is relatively simple to produce, can in turn be equipped to meet specific customer requirements, for instance being equipped with a special flat plug  120 . In the case of a defect, the coil module  124  can simply be pulled off the hydraulic module  96 , which makes the central components of the hydraulic module  96  easily accessible so they can be checked and if needed repaired. 
     As can be seen from FIG. 5, the pressure control valve  34  can be inserted, with the connection peg  42  of the valve housing  40  leading, into a stepped bore  128  of a receiving part  130 . The receiving part  130  can be disposed at various places in the fuel system  10 . For instance, it is possible for it to be present directly on the rail  28 . However, mounting it directly on the high-pressure pump  20  is also conceivable. 
     The receiving part  130  can be provided as a separate part or can be embodied integrally with the rail  28  or the housing of the high-pressure pump  20 . The fuel line on the input side, embodied in the receiving part  130 , is identified by reference numeral  36  as in FIG. 1, while conversely the fuel line on the output side is identified by reference numeral  38 . The pressure control valve  34  is secured to the receiving part  130  via the retaining flanges  110 , shown only in part in FIG.  5 . The hydraulic module is pressed by the fuel pressure with its annular rib  51  against the bracket element  102 . 
     The pressure control valve  34  functions as follows: If the magnet unit, formed by the coil  99  and the winding holder  98 , is not excited, the opening pressure of the pressure control valve  34  is determined solely by the prestressing force of the spring  86 . If the applicable limit pressure is exceeded, the valve ball  52  is lifted from the valve seat  50  because of the pressure difference between the inlet conduit  44  and the flow chamber  48 . As a result, fuel from the inlet-side line  36  and the inlet conduit  44  passes through the gap between the valve seat  50  and the valve ball  52  to reach the flow chamber  48 , and it can flow out into the outlet-side line  38  via the outlet conduits  46 . 
     Because the valve seat  50  is embodied as a conical widened portion, and the passageway gap for the fuel between the valve ball  52  and the valve seat  50  is located in the region of the farther end of the valve seat  50 , upon opening of the pressure control valve  34  a stable flow state is achieved, making the quality of closed- and open-loop control of the pressure control valve  34  optimal. Lateral oscillating motions of the valve ball  52  are reliably prevented by the retaining element  54  with the retaining tongues  58 . 
     To make a different opening pressure of the pressure control valve  34  possible, electric current is delivered to the coil  99 . Depending on the type and intensity of the current delivered, the magnet core  74  exerts a force on the magnet armature  70 . This force is superimposed on the prestressing force furnished by the spring  86 . Because the magnet core  74  exerts a force of attraction on the magnet armature  70 , the contact pressure exerted by the valve tappet  66  on the valve ball  52  decreases, so that the valve ball  52  is pressed with a lesser force against the valve seat  50 . As a result, the opening pressure of the pressure control valve  34  is lowered. In this way, different pressures in the rail  28  can be established. A lowering of the rail pressure to approximately 4 bar is possible. This is equivalent to the pressure that typically prevails in the fuel line  14 . 
     The shoulder  79 , acting like a spacer, of the plastic slide bush  78  assures that even if the magnet armature  70  is completely attracted, a remanent air gap required for the magnetic action will always be present between the magnet armature  70  and the magnet core  74 . The magnetic decoupling between the valve housing  40  and the magnet core  74  is assured by the antimagnetic ring element  72 . By means of the slide bushes  64  and  78 , the valve tappet is supported with little friction, so that upon actuation it exhibits only slight hysteresis—if any. 
     Yet even if the valve ball  52 , for whatever reasons, is blocked on the valve seat  50 , or in other words opening of the pressure control valve  34  is not possible, the pressure control valve  34  can still provide an “emergency pressure limiting function”. This is accomplished as follows: 
     As seen particular from FIG. 5, the connection peg  42  of the valve housing  40  has two ring seals  132  and  134  on its outside. FIG. 5 also shows that between the portion of the stepped bore  128  of smaller diameter in the receiving part  130  and the portion thereof of larger diameter, there is a step  136 , embodied as an insertion chamfer. The region of larger diameter of the stepped bore  128  likewise has an insertion chamfer  138  on its upper end. The lower ring seal  132  in terms of FIG. 5 assures sealing between the inlet-side line  36  and the outlet-side line  38 , while conversely the upper ring seal  134  in FIG. 5 assures sealing between the outlet-side line  38  and the environment. The lower ring seal  132  has a smaller diameter, adapted to the diameter of the corresponding portion of the stepped bore  128 , than the upper ring seal  134 . 
     If the pressure in the inlet-side line  36  now rises, and if because of a jammed valve ball  52  this pressure increase cannot be diverted via the inlet conduit  44 , flow chamber  48  and outlet conduits  46  to the outlet-side line  38 , then because of the differential pressure between the inlet-side line  36  and the environment, the entire pressure control valve  34  is pushed somewhat out of the stepped bore  128  in the receiving part  130 . This is possible because the retaining flanges  110  of the bracket element  102  have a certain elasticity in the axial direction of the pressure control valve  34 . 
     Since as FIG. 5 shows the spacing between the lower ring seal  132  and the insertion chamfer  136  is less than the spacing between the upper ring seal  134  and the insertion chamfer  138 , when the pressure control valve  34  moves axially upward it is the lower ring seal  132  that first reaches the region of the insertion chamfer  136 , while conversely the upper ring seal  134  still remains in the region of the larger-diameter portion of the stepped bore  128 . 
     However, if the lower ring seal  132  reaches the region of the insertion chamfer  136 , the sealing action between the ring seal  132  and the wall of the stepped bore  128  lessens, so that fuel can flow directly from the inlet-side line  36  past the ring seal  132  to reach the outlet-side line  38 , circumventing the pressure control valve  34 . In that case, the entire pressure control valve  34  together with the lower ring seal  132  accordingly acts as a valve member, and the stepped bore  128  in the receiving part  130  acts as a valve seat. The retaining flanges  110  on the bracket element  102  act as a prestressing element. 
     In this way, pressure from the inlet-side line  36  can be let off into the outlet-side line  38  even whenever the pressure control valve  34  is no longer functioning properly. Thus it remains assured that no fuel will reach the environment. 
     In closing, it should be pointed out that the terms “lower” and “upper” used in the description of the present exemplary embodiment pertain to the disposition of the pressure control valve  34  in FIGS. 1-9. It is understood that the pressure control valve  34  can be installed in an arbitrary position in a fuel system  10 . However, preferably it is installed in a more or less upright position, to avert the problem of soiling and icing up during operation of the pressure control valve. 
     The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.

Technology Classification (CPC): 5