Abstract:
A sealing system for a solenoid valve is provided for accommodation in a recess in an actuating element movable by a coil. The recess proceeds from an end face of the actuating element close to a valve seat. The actuating element is movably mounted in a solenoid valve and designed to clear or close the valve seat ( 30 ). A sealing disk and a spring element biasing the sealing disk are provided, wherein the spring element is arranged on the end face facing away from the valve seat centered with respect to the sealing disk and exerts a force on the sealing disk in direction of the valve seat. The sealing disk is axially shiftably guided in the actuating element. A solenoid valve itself includes such sealing system.

Description:
FIELD OF THE INVENTION 
     This invention relates to a sealing system for a solenoid valve. In addition, this invention relates to a solenoid valve. 
     The sealing system according to the invention in particular is provided for the use of high-viscosity oil in oil burners. 
     BACKGROUND 
     Solenoid valves which are used for dosing oil for oil burners are subject to high requirements. Usual conditions are a medium pressure in the range of 30 bar, coil temperatures of about 165° C. for oils with a viscosity of about 75 cst. 
     At pressures of 30 bar, no media-separated valves with diaphragms can be used. This means that the valve space in which a magnet core is moved on switching the valve is filled with medium and the magnet core as well as the sealing system is surrounded by oil. During the switching operation, when the magnet core is attracted, the same must displace the oil from the valve space. High-viscosity media, however, make moving the magnet core more difficult, and the movement is braked. 
     In these valves for use with high-viscosity media it is problematic in addition that the seal at the moment of attraction, i.e. when it actually should be released from the sealing seat, does not yet detach from the sealing seat, but sticks to the same. 
     It is the object of the invention to create a sealing system and a solenoid valve which allow a safe switching when used in high-viscosity media. 
     SUMMARY 
     The invention provides a sealing system for a solenoid valve for accommodation in a recess in an actuating element movable by a coil, wherein the recess proceeds from an end face of the actuating element close to a valve seat and the actuating element is movably mounted in a solenoid valve and is designed for clearing or closing the valve seat, comprising a sealing disk and a spring element biasing the sealing disk, which is arranged on the end face facing away from the valve seat and centered with respect to the sealing disk and exerts a force on the sealing disk in direction of the valve seat, wherein the sealing disk is axially shiftably guided in the actuating element. 
     To reduce position tolerances in actuating direction, the sealing element is axially biased in direction of the valve seat with a spring which is accommodated inside the actuating element. Only when a certain lift-off force and a certain lift-off path are present, will the sealing element be lifted off from the valve seat. The sealing disk preferably has a multi-part design and comprises a preferably metallic seal holder and a sealing element, wherein the seal holder along with the sealing element is axially shiftably guided in the actuating element and holds the sealing element. 
     In the sealing system according to the invention, the sealing element made e.g. of an elastomeric material does not rub against the wall of the actuating element, when it is moved axially. Rather, a seal holder is present, which is made of a low-friction material, preferably of metal. In this way, the friction combinations can be optimized on the one hand, and on the other hand there is no more wear at the outer circumference of the sealing element. In addition, the outer circumference of the seal holder also always is constant, in contrast to the variable outer circumference of an elastic sealing element which is compressed differently. Gaps hence can be designed very small, which is advantageous for the use with high-viscosity oil. 
     The recess in the actuating element should be circularly cylindrical. 
     The seal holder can be designed substantially ring-shaped, in order to accommodate the sealing element. 
     According to the preferred embodiment, the seal holder has a radially outer circumferential surface which is adjacent to an inner side of the actuating element serving as sliding surface. 
     In addition, the seal holder has an inner surface which surrounds a circumferential edge of the sealing element, which however is the case only optionally. Alternatively, the sealing element also might axially be put onto the seal holder. 
     The seal holder preferably has a closed circumferential bead protruding to the inside, against which the sealing element can strike axially. 
     One embodiment provides that the inner surface adjoins this bead at its end close to the valve seat. 
     The sealing element can rest against a flat abutment surface at the bead and hence ensure a particularly tight connection to the seal holder. 
     At the end remote from the valve seat a protrusion radially protruding to the inside optionally is present at the seal holder, with which the sealing element is held in an axial direction, so that the sealing element is axially positioned, preferably axially clamped between holding protrusion and bead. 
     Bead and/or holding protrusion should be an integral part of the seal holder. 
     The holding protrusion can be formed by a thin, web-like wall of the seal holder, which is flanged around the edge of the sealing element. 
     To keep the contact between the sealing disk (or in the case of the multi-piece formation of the unit of seal holder and sealing element) and an axial stop at the actuating element as small as possible, the sealing disk (the seal holder) on the end face close to the valve seat has a preferably closed circumferential, narrow axial tab which alone is responsible for contacting in an end position of the valve. As an alternative, it can of course also be provided not to provide a closed circumferential tab, but individual tabs circumferentially spaced from each other, for example point-like tabs, in order to even further reduce the contact surface. With a reduced contact surface the adhesive force also is reduced, which is produced by oil between the parts. The size of the abutment surface of the tab is smaller than in a sealing disk formed with a continuous flat end face, i.e. the counter-abutment surface for the sealing disk is not contacted completely owing to the tab. 
     The tab can be formed in that the tab is separated from the rest of the end face by a circumferential groove extending all around. 
     In addition, for reducing the circumferential contact surface between sealing disk and inner surface of the recess in the actuating element the sealing disk is provided with at least one recess, in particular chamfer, on its circumferential edge, which is so high that the contact surface is reduced by at least 25% as compared with a sealing disk which has two continuously flat end faces. 
     A simplified manufacture and a compact construction of the seal holder is provided by an embodiment in which the tab axially ends in a plane in which the abutment surface of the bead for the sealing element is located. 
     It must be ensured that even in the case of an actuation of the valve over several years the sealing element always fully rests against the sealing seat and is not loaded unequally or is plastically deformed in the course of time. For this purpose, one or more metallic washers and the spring element for biasing the sealing disk (the sealing element) in direction of the valve seat are provided on the end face of the sealing disk (the sealing element) remote from the valve seat. The washer is present between spring element and sealing disk (sealing element), so that the spring element does not directly press onto the sealing disk (the sealing element) and produce a permanent deformation. 
     A first washer fully rests against the sealing disk, i.e. ensures a uniform introduction of force. A second washer with a central bulge rests against the first washer and provides a point contact in the center of the sealing disk (the sealing element). 
     When the sealing system in addition also is slightly radially mounted with clearance, a kind of floating bearing is obtained, in which a minimal tilting of the unit of sealing disk or seal holder and sealing element as well as washer about the contact point caused by the bulge can be effected. There is obtained a kind of ball head bearing which allows the sealing element to adapt to the plane defined by the sealing seat. 
     When the sealing disk is designed in one piece, it in particular is made of PTFE, PCTFE or PEEK. 
     The solenoid valve according to the invention comprises an actuating element which is moved by a coil, in order to selectively open and close a valve seat. On the end face close to the valve seat the actuating element has a recess in which the sealing system of the invention is axially movably accommodated. 
     One embodiment of the invention provides that in the recess a retaining ring is attached to the actuating element, which defines an end position of the sealing disk. The sealing disk like the entire sealing system thus is axially pushed into the recess and prevented from falling out by the subsequently inserted retaining ring. 
     The retaining ring should be dimensioned such that in an end position (open position) the seal holder supports on the retaining ring with an axial tab. 
     Alternatively or in addition, in this end position the bead can immerse into a space surrounded by the retaining ring, in order to create a space-saving construction. 
     The recess in the actuating element preferably has two portions merging into each other with different diameters. This allows designing of the recess as small as possible. 
     A first portion of the recess remote from the end face of the actuating element has a smaller diameter than the adjoining portion located closer to the valve seat. The first portion is formed as receiving space for a spring element, in the second portion sealing disk (or seal holder and sealing element), retaining ring and possibly washers or the washer can be accommodated. 
     Transverse bores which end in the recess in the actuating element allow an inflow or outflow of the medium during the movement of the sealing system in the recess, wherein preferably a transverse bore opens into each of the two portions of the recess. 
     The actuating element can be formed as magnet core, rocker or hinged armature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a longitudinal sectional view through a solenoid valve according to the invention for an oil burner, 
         FIG. 2  shows an enlarged sectional view through the solenoid valve according to the invention in the region of the sealing system of the invention with closed valve seat, 
         FIG. 3  shows a detail view enlarged corresponding to  FIG. 2  of the sealing system according to the invention with open valve seat, 
         FIG. 4  shows a perspective view of the magnet core according to the invention as used in the solenoid valve according to the invention, 
         FIG. 5  shows a top view of the magnet core as shown in  FIG. 4 , and 
         FIG. 6  shows a cross-sectional view through a one-piece embodiment of the sealing disk. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a solenoid valve which is traversed by high-viscosity oil and is used for dosing oil in oil burners. 
     The solenoid valve comprises a housing  10  with an electric coil  12  for moving an actuating element  14 , which in the present case is formed as magnet core. In the following, however, the magnet core always will be referred to as actuating element for simplification. Via the coil  12 , the actuating element  14  can be moved in axial direction. 
     In the interior of the housing  10  a cavity is provided, which in part also is surrounded by the coil  12  and which in an axial direction is closed by a plug  16  of ferromagnetic material. When the solenoid valve is operated with alternating voltage, an AC voltage ring  18  made of copper or silver is accommodated in the end face of the plug  16 . 
     The actuating element  14  is seated in a so-called valve space which in part is filled by the actuating element  14 , but which in the closed position of the solenoid valve as shown in  FIG. 1  comprises a gap  20  between the plug  16  and the actuating element  14 . 
     A so-called core guiding tube  22  is provided on the inside of the housing  10  and lines the valve space radially to the outside. The guiding tube  22  serves as sliding guide surface for the actuating element  14  sliding along the same. 
     The oil flows through a valve body  24  on which the housing  10  also is seated. The valve body has a first opening  26  and a second opening  28 , between which a connecting passage with a valve seat  30  is provided, which with a closed valve closes the connecting passage and with an open valve clears the valve seat  30  and hence opens the connecting passage. The valve seat  30  is a ring-shaped surface, preferably a freely ending wall with a through opening  31  surrounded by the valve seat  30  as part of the connecting passage. A sealing element  32  can sit on the valve seat  30  and seal the valve seat  30 . 
     The sealing element  32  is made of an elastomeric material, in particular however of PTFE, PCTFE or PEEK. 
     The sealing element  32  is part of a sealing system which in  FIGS. 2 and 3  is shown more clearly and which comprises a seal holder  34 , a first washer  36 , a second washer  38  and a spring element  40 , all of which are accommodated in a recess  42  in the actuating element  14 . The recess  42  proceeds from an end face  44  of the actuating element  14  close to the valve seat  30  and is designed as blind hole. 
     The seal holder  34  and the sealing element  32  form a pre-mounted unit and a sealing disk. 
     The recess  42  has a first portion  46 , which is remote from the end face  44  and has a small diameter, and a second portion  48  which adjoins the first portion  46  towards the end face  44  and has a larger diameter. 
     The two portions  46 ,  48  merge into each other. 
     In the first portion the spring element  40  is accommodated, so that this portion serves as receiving space for the spring element  40 . 
     In the second portion  48  the seal holder  34 , the sealing element  32  and the two washers  36 ,  38  are accommodated. 
     To prevent the sealing system from axially moving out of the recess  42 , a retaining ring  50  is provided in the region of the recess  42 , which at the same time serves as axial stop for the axially movable seal holder  34 . 
     As shown in  FIG. 2 , the seal holder  34  is formed as ring which slides in the circularly cylindrical recess  42 . The seal holder  34  for this purpose has a radially outer circumferential surface  52  which rests against and slides along an inner side of the actuating element  14  serving as sliding surface in the region of the portion  48 . 
     On its inside, the ring-shaped seal holder  34  has an inner surface  54  which preferably sealingly rests against the circumferential edge of the sealing element  32  and surrounds the sealing element  32 . 
     At its end close to the valve seat  30 , the inner surface  54  ends at a preferably closed circumferential bead  56  radially protruding to the inside. The bead  56  is an integral part of the seal holder  34  and has a preferably flat abutment surface  58  for the axial abutment of the sealing element  32 . 
     The sealing element  32  is clamped between the bead  56  and a holding protrusion  60  of the seal holder  34  radially protruding to the inside. The holding protrusion  60  is formed by a thin, web-like wall of the seal holder  34 , which is flanged around the edge of the sealing element  32 , so that an axial clamping is obtained. 
     On the end face close to the valve seat  30 , the seal holder  34  has a preferably closed circumferential, axially protruding tab  62 , which is extremely narrow and which, as shown in  FIG. 3 , rests against the retaining ring  50  in the open position of the valve. Thus, the tab  62  serves as abutment surface in the so-called second end position (opening position) of the valve. The tab  62  ends in a radial plane in which the abutment surface  58  of the bead  56  also is located. 
     On the end face of the sealing element  32  remote from the sealing seat  30  a first washer  64  (see  FIG. 3 ) fully rests. 
     On the back of the first washer  64  in turn a second washer  66  rests, preferably only with a point contact in essence, since the second washer  66  has a central bulge  68 . This bulge ensures that there is a centric introduction of force by the spring element  40 , which provides for a uniform shifting of the sealing system. The first washer  64  ensures a uniform introduction of force into the sealing element  32  and prevents the sealing element  32  from being deformed on its back by the spring force  40  during its use. 
     The spring element  40 , as mentioned already, biases the sealing element, more exactly the rest of the sealing system, in direction of the valve seat  30 . 
     As shown in  FIGS. 2 and 3 , the valve seat  30  is formed such that in the closed condition of the valve it can be closed by the sealing element  32 , wherein the seal holder  34  radially surrounds the valve seat  30  with a distance, so that only the sealing element  32  rests against the valve seat  30 . 
     The seal holder  34  and/or one or both of the washers  64 ,  66  preferably are made of metal. 
     The radial layers of the bead  56  and the retaining ring  50  are adjusted to each other such that independent of the position of the valve the bead  56  does not get in contact with the retaining ring  50 , but in the open condition (see  FIG. 3 ) immerses into the cavity surrounded by the retaining ring  50  and rests against the retaining ring  50  only with the axial tab  62 . 
     The actuating element  14 , as can also be seen in  FIG. 4 , preferably has two radial transverse bores  70 ,  72  which are axially and preferably in addition also circumferentially spaced from each other and in the present case are designed as through bore. The transverse bore  70 , which is also shown in  FIGS. 2 and 3 , opens into the portion  46  of the recess  42  and the transverse bore  72  in the portion  48 . 
     Preferably, the transverse bore  72  is located such that it always is open towards the receptacle  42  also on the back of the sealing element  32 . 
     Close to its end face  44  opposite the valve seat, the actuating element  14  has a circumferential constriction  74  which ends in a shoulder  76  and which serves the accommodation of a spring  78  (see  FIG. 1 ). The spring on the one hand supports on the shoulder  76  and on the other hand on a shoulder  80  which is formed by an expansion of the tube  22 . 
     The tube  22  is expanded towards the valve seat  30  and ends in a flange wall  82  repeatedly bent into a U-shape (see  FIG. 1 ), wherein inside a “U” a seal  84  is accommodated towards the valve body  24 . 
     Beside the end face  44 , which is referred to as first end face, the actuating element  14 , here the magnet core, possesses an opposite second end face  86 . 
     From the second end face  86 , a plurality of preferably radially extending grooves  88 ,  88 ′ are provided in the actuating element  14 , which extend along the middle axis A of the substantially circularly cylindrical actuating element  14 . 
     The grooves  88 ,  88 ′ however do not reach the second end face  44  and end before the same, in particular in the region of the constriction  74 . 
     The grooves  88 ,  88 ′ form longitudinal grooves whose depth T corresponds to at least 25% of the diameter D of the actuating element  14 , wherein this diameter D and the depth are measured in the region of the coil  12 . 
     There are provided longitudinal grooves with different depths, namely longitudinal grooves  88  with a groove depth t 2  which is smaller than the groove depth t 1  of the grooves  88 ′. The grooves  88 ′ are referred to as first longitudinal grooves and the grooves  88  as second longitudinal grooves. Both grooves  88  and  88 ′ axially extend preferably to equal lengths and both begin at the second end face  86 . 
     The groove depth t 2  also is at least 25% of the magnet core diameter D. 
     The first and second longitudinal grooves  88 ,  88 ′ each alternate in circumferential direction, wherein it would also be possible, however, to provide for example two or more adjacent first longitudinal grooves  88 ′ and a second longitudinal groove  88  between groups of first longitudinal grooves  88 ′. 
     The groove width b preferably is the same for the two longitudinal grooves  88 ,  88 ′ and in addition preferably amounts to not more than 10% of the diameter D. 
     In the illustrated exemplary embodiment the diameter D is 19 mm, and there are provided four longitudinal grooves  88  and four longitudinal grooves  88 ′ in alternation. The depth of the longitudinal grooves on the one hand is 5 mm and on the other hand 6.75 mm, the groove width merely is 1.5 mm. 
     Due to the high number of the grooves  88 ,  88 ′ with high depth, an effective reduction of detrimental turbulent flows can be achieved. 
     The location of the spring  78  in the region of the constriction  74  ensures that very little material must be removed from the actuating element  14 , in order to serve for accommodating the spring  78 . Previous embodiments have provided recesses for accommodating the spring  78  in the region of the second end face  86 , which however have led to a great reduction of the magnetic force. 
     As shown in  FIGS. 1 to 3 , the depth of the longitudinal grooves  88 ′, and also of the longitudinal grooves  88 , decreases in direction towards the second end face  44  and shallows out so to speak in the region of the constriction  74 . 
     The solenoid valve according to the invention and the sealing system have some decisive advantages. 
     On the one hand, the elastic sealing element  32  does not rub against the inside of the recess  42  and hence is not subject to severe wear. Due to the material combination metal/metal between seal holder  34  and actuating element  14  the friction also is reduced. 
     Furthermore, the very small abutment surfaces between the seal holder  34  and the retaining ring  50  serve to prevent sticking of the sealing system, when the same is used after an extended standstill, as in this region viscous oil is present due to the absence of media separation. Moreover, a circumferential protruding tab  90  on the end wall between first and second portion  46 ,  48  of the receptacle  42  also serves this purpose, as the tab  90  serves as stop for the washer  38  (see  FIG. 3 ). 
     When a radial gap in addition is present between the seal holder and the inside of the recess  32 , a kind of floating bearing of the sealing system in the actuating element  14  even can occur. 
     Since the sealing system is axially shiftably accommodated in the actuating element  14 , the medium present in the recess  42  must be able to flow into and out of the recess  42  on the back of the sealing element  32 , which is made possible by the transverse bores  70 ,  72 . Thus, the recess  42  always is filled with oil, and also the regions between the washers  64 ,  66 . 
     In the following, the mode of operation of the solenoid valve will be explained. 
     In the starting position, when the coil  12  is not current-carrying, the spring  78  urges the actuating element  14  in direction of the valve seat  30 , so that the sealing element  32  sealingly rests against the valve seat  30 . 
     Tolerances in longitudinal direction are compensated by the spring element  40 , which provides an additional pressing force. 
     When the coil subsequently becomes current-carrying for opening the valve, the coil  12  attracts the magnet core, here the actuating element  14 . The actuating element  14  first is slightly moved upwards, wherein during this starting movement the spring element  40  still holds the sealing element  32  at the sealing seat  30 . Only when the seal holder  34  rests against the retaining ring  50 , which in this case serves as stop, will the sealing element  32  lift off from the sealing seat  30  (see  FIG. 3 ). Medium then can flow through the through opening  31  and the connecting passage, so that the openings  26 ,  28  are in flow connection with each other. 
     To permit the movement of the actuating element  14  into the coil, the medium, here the viscous oil which is present between the end face  86  and the plug  16 , must be displaced. This displacement of the oil is effected via the longitudinal grooves  88 ,  88 ′, so that the oil flows in direction towards the end face  44 , in the region of the expansion of the tube  22 , where a transition to an annular space  100  ( FIG. 3 ) is present, so to speak, which is located radially outside the valve seat  30  and which in the open condition is in flow connection with the through opening  31 . 
     When the sealing element  32  is moved downwards inside the actuating element  14  relative to the same (i.e. from the closed condition into the open condition), oil is sucked into the recess  72  via the transverse bores  70  due to this movement. 
     When the actuating element  14  is moved into the closed condition, oil is delivered back into the gap  20  via the longitudinal grooves  88 ,  88 ′. 
     In the embodiment of  FIG. 6 , the sealing disk is formed in one piece and consists of PTFE, PCTFE or PEEK. The sealing disk originally has a cylindrical basic shape, but for reduction of the contact surfaces a circumferentially closed circumferential groove  102  and a recess in the form of a chamfer  104  provided at the outer circumference are provided, which decreases the circumferential contact surface in the recess by at least 25%. Due to the circumferential groove  102 , the tab  62  serving as stop is cut off. Otherwise, however, the sealing disk can form an alternative for the unit of seal holder and sealing element, so that reference can be made to the remaining drawings. 
     Even if in the present Figures the actuating element is designed as magnet core, the advantages of the invention, in particular of the sealing system, also can be realized in a rocker or a hinged armature. In this case, the sealing system is accommodated in a corresponding recess in the rocker or in the hinged armature.