Abstract:
An electromagnetic valve comprising casing, a coil and a mobile nucleus, sliding axially across the entire extension of the coil, between two operative positions wherein there is an interface with a powering body and a discharging body. The configuration of the electromagnetic valve guarantees a precise guide of the mobile nucleus free from sticking and enables speed and precision in the assembly of the electromagnetic valve.

Description:
FIELD OF THE INVENTION 
     The present invention concerns a electromagnetic valve, in particular a cartridge electromagnetic valve, and the relative assembly method. 
     BACKGROUND OF THE INVENTION 
     Various types of electromagnetic valves are available, usually comprising a casing, a coil, a fixed nucleus coaxial to the coil and a mobile nucleus subject to the action of the magnetic field generated by the coil; in particular, the mobile nucleus is influenced by an axial force of attraction exchanged with the fixed nucleus and moves between two separate working positions in which it interfaces with pneumatic connections, such as, for example, a powering position and a discharging position. 
     The solutions available present several disadvantages. For example, the mobile nucleus tends to stick inside the coil during its working stroke; moreover, the electromagnetic valves available are complex to assemble and the assembly operations do not always guarantee the necessary precision, with particular reference to the working stroke of the mobile nucleus. 
     SUMMARY OF THE INVENTION 
     The problem of the present invention is to create a electromagnetic valve which solves the problems mentioned with reference to currently used techniques. 
     These problems and restrictions are solved by a electromagnetic valve as described below. 
     As can be seen from the description below, the valve according to the invention makes it possible to overcome the problems of the currently used technique. 
     In particular, the flow lines of the magnetic field generated by the coil cross the nucleus axially, the polar expansion radially, then the casing in an axial direction and then a radial direction until they reach the shoulder in order to exercise an action of attraction on the plate of the mobile nucleus. Therefore, the flow lines are not subject to any interruption; in this way the dispersion of the field is limited as is the consumption of the valve. 
     Advantageously, the mobile nucleus crosses the whole coil in order to prevent the nucleus from sticking. Moreover, the force of friction between the mobile nucleus and the coil is constant and does not depend on the position of the nucleus inside the coil. 
     Advantageously, the grooves on the mobile nucleus link up the openings in the casing; moreover, the passage of air through the ribs favours the dispersion of the heat produced by the electric winding. Moreover, improved cooling of the nucleus prevents the risk of it sticking due to thermal dilatation for example. 
     The use of a flat spring guarantees the exercise of purely axial force, in order to perfectly guide the mobile nucleus, reducing friction inside the coil. 
     Thanks to the radial rigidity of the disc spring, the mobile nucleus guided by it is prevented from coming into contact with the polar expansion, creating points of contact between said two elements of the magnetic circuit which could cause gluing phenomena during the activation of the valve. 
     The spring, being made of ferromagnetic material, reduces the value of total reluctance of the magnetic circuit, directly linking the casing and mobile nucleus; in this way the flow lines can cross the spring and avoid running across the radial air gap between the polar expansion and the mobile nucleus. The guide means, such as the collar, being made of ferromagnetic material, also help reduce the total reluctance of the magnetic circuit. 
     The conical shape of the polar expansion creates a compartment in which the spring is free to deform and supply, together with the powering body, the necessary preload. 
     The electromagnetic valve according to the present invention also presents numerous advantages in terms of assembly. 
     In particular, the configuration of the valve with the mobile nucleus passing through makes it possible, at the end of the first manual assembly phase (with the assembly of the flat spring), to obtain a stable assembly, where the action of the spring, contrasted by the plate at the far end of the passing nucleus, prevents the nucleus from slipping out and guarantees the stability of the whole assembly. 
     Consequently there are further advantage, such as easy storage of goods in progress and the possibility to create, for example, a store, and therefore a production detachment between the first, entirely manual phase and the subsequent phases involving extensive automation. Therefore, the restriction of continuity in the production process and one-piece flow production cease to exist. 
     Moreover, the stability of the semi-assembly enables the performance of intermediate checks in order to identify non-conformant products even before assembly is complete (for example, assuming the rejection of the assemblies for which the stroke cannot be corrected by subsequent calibrated plantings). 
     The electromagnetic valves currently available require the planting of the valve body before carrying out the checks, carrying out all the tests at the end of the assembly process. 
     Moreover, the valves currently available are extremely unstable due to the action of the springs which tend to oust the nucleus and complicate the powering body planting phase, requiring the supervision and intervention of the operator. 
     The configuration of the valve according to the present inventions enables the clear separation in the assembly process between a first entirely annual phase and a subsequent extensively/totally automated phase (where the use of automation is determined by the criticality of the plantings due to the tolerances applied. 
     The clear separation of the two phases makes it possible to minimise the need for staff, reduce labour costs and, therefore, the cost of manufacturing the cartridge: the intervention of the operator in the phases characterised by extensive automation—e.g.: for the position of components—involves the supervision of dedicated staff or staff who operate in accordance with machine times. 
     The stability of the assembly constructed at the end of the first manual phase however enables quick and almost completely independent automation, in the subsequent assembly and automatic test phases. 
     The electromagnetic valve according to the present invention presents a limited number of components. 
     The configuration of the electromagnetic valve enables the control and correction of the nominal stroke according to the geometric and dynamic characteristics of the components through the automatic planting of the powering and discharging bodies. 
     A technician in the sector, in order to meet contingent and specific requirements, may make numerous changes and variations to the electromagnetic valves described above, all of which are contained within the context of the invention as defined by the following claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other embodiments of the electromagnetic valve according to the invention are described in the subsequent claims. 
       Further characteristics and advantages of the present invention shall become clearer in the description of preferable but non-restrictive embodiments, in which: 
         FIG. 1  represents a prospective view in separate parts of a electromagnetic valve in accordance with an embodiment of the present invention; 
         FIG. 2  represents a sectioned view in separate parts of the electromagnetic valve in  FIG. 1 ; 
         FIG. 3   a  represents a sectioned view in a configuration of assembly of the electromagnetic valve in  FIG. 2 ; 
         FIG. 3   b  represents a sectioned view of an example of assembly of electromagnetic valves in accordance with the present invention; 
         FIG. 4  represents a prospective view of pert IV of  FIG. 3   a;    
         FIG. 5  represents a prospective view of part V of  FIG. 3   a;    
         FIG. 6  represents a frontal view of part VI of  FIG. 3   a , according to possible variants of embodiment in accordance with the present invention; 
         FIG. 7  represents a prospective view in separate parts of a electromagnetic valve in accordance with a further embodiment of the present invention; 
         FIGS. 8 and 9  represent sectioned views in configuration of assembly of the electromagnetic valve in  FIG. 7 ; 
         FIGS. 10-17  represent sectioned views of subsequent phases of assembly of a electromagnetic valve in accordance with the present invention: 
         FIG. 18  represents a diagram relating to the progress of the planting force of a spring of the electromagnetic valve depending on the movement during the spring assembly phase. 
     
    
    
     The elements or parts of elements in common between the embodiments described hereinafter shall be indicated with the same numeric references. 
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to said figures,  4  is used to globally indicate a electromagnetic valve. 
     The electromagnetic valve  4  comprises a casing  8 , with a mainly X-X axial extension, suitable for building a supporting structure for the electromagnetic valve  4 . For example, the casing  8  has a tubular structure which identifies a cavity  9  and extends from one powering end  10  to one discharging end  12 ; said ends  10 , 12  are preferably axially open. The term axial direction means a direction parallel to said mainly X-X extension. 
     The casing  8  comprises a shoulder  16  which reduces the passage section of the cavity  9 ; the shoulder  16  preferably divides the cavity into a first and second housing compartment  18 ′, 18 ″ which communicate through a connection hole  20 . The shoulder  16  preferably has a pair of electrical connection holes  22 , 23  passing through the shoulder  16  and arranged, according to one embodiment, in decentralised positions compared with the connection hole  20 ; the electrical connection holes  22 , 23  are preferably arranged in positions which are diametrically opposed to the connection hole  20 . 
     The casing  8 , on the side of the shoulder  16 , comprises means of contrast  24 , such as a circular border  25  positioned inside the casing ( FIG. 4 ). 
     Advantageously, the casing  8  is made of ferromagnetic material, thus forming an integrated part of the magnetic circuit of the electromagnetic valve. 
     According to a possible embodiment, the casing  8  comprises several pneumatic connections  26 , for example, for pneumatic uses of the electromagnetic valve or to construct a powering and/or discharging body for the electromagnetic valve. Said pneumatic connections  26  can be, for example, in the form of openings in the lateral wall of the casing  8  so that pneumatic uses of the electromagnetic valve can be achieved. 
     According to one embodiment, said pneumatic connections  26  are suitable for creating a powering and discharging body for the electromagnetic valve  4 . 
     For example, said pneumatic connections  26  comprise at least one powering hole  28  for the electromagnetic valve and/or one discharging hole  34  for the electromagnetic valve. 
     According to one embodiment, the electromagnetic valve  4  comprises a powering body provided with a powering hole  28  with relative powering nozzle  29 , suitable for sending a flow of power to the electromagnetic valve  4 . 
     For example, the powering body  27  is introduced into the cavity  9  of the casing and in particular in the first housing compartment  18 ′, from the powering end  10 ; the powering body  27  is preferably coupled for interference inside the casing  8 . 
     According to one embodiment, the electromagnetic valve  4  comprises a discharging body  32  provided with a discharging hole  34  with relative discharging nozzle  35 . The discharging body  32  is preferably introduced into the cavity  9  of the casing  8  and in particular in the second housing compartment  18 ″, from the discharging end  12 ; in particular, the discharging nozzle is introduced into the connection hole  20  of the shoulder; to guarantee the seal, an O-ring can be used between the discharging body  32  and the second housing compartment  18 ″. 
     According to possible embodiments of the electromagnetic valve according to the invention, at least either said powering body  27  and/or discharging body  32  is one-piece with the casing  8 . 
     The electromagnetic valve  4  comprises a coil  44  to generate a magnetic field, which has a central seat  48  coaxial to the same coil and to the X-X axial extension. The coil  44  comprises a reel  46 , which has to support the electric winding, and electrical connections  52 , of the ‘pin’ type for example, to power the same coil. The reel is preferably made of non-friction material. 
     Preferably following the introductions of the coil  44  into the casing  8 , the electrical connections  52  pass through the electrical connection holes  22 , 23  of the shoulder  16  and come out of the discharging end  12  of the casing  8 . After introduction into the casing  8 , the coil  44  is placed with a radial gap in the first housing compartment  18 ′ and brought to rest against the means of contrast  24 , 25  of the casing  8 . The term radial gap means a gap compared with a direction perpendicular to the X-X axial extension and incident with the latter. 
     The electromagnetic valve  4  comprises a mobile nucleus  60 , arranged coaxially to the coil  44 , made of ferromagnetic material to be influenced by the magnetic field and mobile between two working position in which it interfaces with the powering hole  28  and the discharging hole  34  respectively. 
     Advantageously the mobile nucleus  60  passes through the whole axial extension of the coil  44  in order to selectively open and close the powering hole  28  and the discharging hole  34 , sliding axially within the seat  48  of the coil  44 . 
     In particular, the mobile nucleus  60  in correspondence with opposite axial ends directly facing the powering and discharging holes  28 , 34  preferably has a pair of rubber inserts  64 , which guarantee the hermetic closure of said holes  28 , 34 . It is possible to create axial seats on the ends of the mobile nucleus and introduce the rubber inserts  64  into them, or to envisage a co-moulding phase of the mobile nucleus  60  with the rubber inserts  84 , perhaps following by the rectification of the contrast surfaces of the rubber inserts on the holes  28 , 34 . 
     According to one embodiment, the mobile nucleus  60  is at least partially counter-shaped in comparison to the seat  48  of the coil  44  so that it is guided axially by the coil  44  in the translational movement thereof inside the seat, between a position in which it comes to rest against the powering nozzle  29  and a position in which it comes to rest against the discharging nozzle  35 . Preferably, the mobile nucleus has a substantially cylindrical shape and is coupled, with a gap, inside the cylindrical seat  48 . 
     Preferably, the mobile nucleus  60  is provided with at least one groove  68  on its lateral wall  70  directly facing the seat  48  in order to identify an opening between the coil  44  and the mobile nucleus  60  which forms a duct to allow the passage of air. 
     According to one embodiment, the groove  68  is substantially parallel to the X-X axial direction. 
     Preferably, the groove  68  extends along the lateral wall  70  of the mobile nucleus  60  in order to create fluidic communication between the powering end  10  and the discharging end  12 ; in particular the axial extension of said grooves  68  is preferably greater than or equal to the axial extension of the coil  44 . 
     Preferably, the mobile nucleus  60  comprises a plurality of grooves  68  arranged angularly at a pitch according to an axialsymmetric configuration compared with the X-X axial direction, along the lateral wall  70 . 
     Advantageously, the mobile nucleus  60  comprises a plate  74  suitable for exchanging a force of attraction with the shoulder  16  of the casing  8 . 
     In particular, the plate  74 , in one configuration of assembly, axially faces the shoulder  16  and is positioned externally compared with the seat  48 , between the coil  44  and the shoulder  16 , inside the first housing compartment  18 ′. 
     Therefore, the plate  74  is positioned in correspondence with an axial end of the mobile nucleus  60  directly facing the shoulder  16  of the casing  8  in order to exchange an axial force between the casing  8  and the nucleus  60 . 
     The plate  74  has a radial size greater than the radial size of the seat  48  of the nucleus so that it cannot pass through the seat  48 . 
     Moreover, the plate  74  has a radial size smaller than the first housing compartment  18 ′ of the casing  8  so that it does not interfere radially with the casing and can slide freely inside it along the axial direction X-X. 
     Preferably, the plate  74  comprises at least one notch  76  to allow the passage of electrical connections  52  of the coil  44 . Preferably the notches  76  are radially aligned with the electrical connection holes  22 , 23  in the casing  8 . 
     The mobile nucleus  60  comprises a recess  78  to allow an axial block for elastic means  82  suitable of elastically influencing the stroke of the mobile nucleus  60 . 
     Preferably, said recess  78  is set in a position axially opposite the plate  74 . 
     The elastic means  82  comprise, for example, a disc spring  84  suitable of exercising a purely axial force on the mobile nucleus  60 . Advantageously, the elastic means  82 , and particularly the disc spring  84 , is made of ferromagnetic material. 
     Advantageously, the disc spring  84  comprises a plurality of through openings  86 , suitable for allowing the fluidic connection between the powering end  10  and the discharging end  12 . 
     Preferably the disc spring  84  is radially restricted by a lateral wall inside the casing  8 . 
     Advantageously, the elastic means  82 , and particularly the spring  84 , radially support the mobile nucleus  60  in order to restrict rubbing between the mobile nucleus  60  and the coil  44  as much as possible. In other words, the spring  84  also has to radially support the mobile nucleus  60  in order to guarantee the coaxial relationship with the coil  44  and prevent possible rubbing against the cavity of the coil  44 . According to a further embodiment of the present invention, the electromagnetic valve comprises radial guide means, suitable of radially guiding the mobile nucleus  60  in order to guarantee the coaxial relationship between the mobile nucleus  60  and the coil  44 . 
     For example, said guide means comprise a collar  87  suitable for being fitted over the mobile nucleus, preferably in a position axially opposed to the elastic means  82 , and for radially restricting the mobile nucleus  60 . In other words, the mobile nucleus  60  is radially guided in correspondence with its axially opposed ends. 
     According to a further embodiment, said guide means comprise a further spring, preferably of the disc type, suitable of exercising a radial guide action as well as an axial action on the mobile nucleus  60 . Preferably, said further spring is provided with a lower preload than the disc spring  84  positioned at the opposite axial end of the mobile nucleus  60 . Preferably, the guide means comprise openings  86  to allow the fluid link between the powering and discharging ends  10 , 12 . For example, the guide means are fastened to the mobile nucleus according to a coupling of shape. 
     Preferably, the guide means are made of ferromagnetic material. 
     Advantageously, the electromagnetic valve  4  comprises a polar expansion  90  coaxial to the coil  44  and positioned in correspondence with one end of the coil  44 , preferably facing the powering body  27 . 
     The polar expansion  90  is made of ferromagnetic material in order to form a guide means for the dissemination of the magnetic field flow lines. 
     For example, the polar expansion  90  has a ring configuration and is counter-shaped compared with the lateral wall inside the casing. The polar expansion comprising an opening  92  to allow the passage of the opposite end of the mobile nucleus  60  compared with the plate  74 . Advantageously, the diameter of the opening  92  of the polar expansion  90  is bigger than the diameter of the central seat  48  of the coil  44 ; this prevents the risk of possible contacts between the mobile nucleus  60  and the polar expansion  90  which could cause sticking. 
     In particular, the polar expansion  90  is directly in contact with the casing in order to guarantee continuity of the flow lines of the magnetic field between the mobile nucleus  80  and the casing  8 . 
     Preferably, the polar expansion is slid with interference into the casing, in order to form an axial block for the coil  44  which, after the introduction of the polar expansion, is axially blocked between the polar expansion  90  and the means of contrast  24 , 25  of the casing  8 . 
     Advantageously, the polar expansion  90  is positioned axially between the coil  44  and the disc spring  84 . 
     The polar expansion  90 , on the opposite side to the coil  44 , comprises a flaring  94 , axially facing the spring  84  and suitable for creating a seat to contain said spring  84  in its axial deformation. 
     Advantageously, the disc spring  84  is fastened in contact with the polar expansion  90 , for example in correspondence with the outer diameter of the spring and of the polar expansion, in order to create continuity for the flow lines from the nucleus to the casing. 
     As can be seen, the electromagnetic valve shown in the figures attached is a cartridge type electromagnetic valve and presents three ways and two positions. Obviously it is possible to envisage a different number of ways, or pneumatic connections, depending on the type of component to which the electromagnetic valve is applied. In other words, the number of ways, positions and pneumatic connections of the electromagnetic valve can be varied to suit the requirements and uses of the component. 
     The method used to assemble a valve according to the invention will now be described. 
     In particular, before assembling the various components of the valve  4 , the rubber seal inserts  64  are fitted in the mobile nucleus  60  for example being planted with a press and subsequently adjusted; according to a possible alternative embodiment it is possible to co-mould the rubber inserts  64  directly in their position on the mobile nucleus  60 . The term planting means forced insertion with interference. 
     After axially aligning the casing  8 , the coil  44  and the mobile nucleus  60  ( FIG. 10 ), the mobile nucleus  60  must be introduced, manually for example. Into the coil ( FIG. 11 ) and these components must then be introduced into the casing ( FIGS. 12-13 ). 
     To facilitate these operations, a piece holder  110  can be used. 
     The procedure continues with the assembly of the polar expansion  90  into the casing  8  by planting with interference, preferably with an automatic press; in this way the pieces assembled so far are locked in place; in other words, the polar expansion  90  closes the components in a pack inside the casing  8 , with the coil blocked axially between the polar expansion  90  and the means of contrast  24 , 25  of the casing  8 . 
     Advantageously, the mobile nucleus  60  can slide inside the coil  44  but cannot come out of the semi-assembly, thanks to the fact that the plate  74  of the mobile nucleus  60  acts as a lock to prevent the extraction of the mobile nucleus  60  from the coil  44 . 
     The flat spring  84  is then fitted to the mobile nucleus  60 , preferably through planting with an automatic electric press ( FIG. 14 ). 
     The shape of the end of the mobile nucleus  60  enables easy planting of the spring  84  elastically deforming it and locking it permanently in the recess  78  on the mobile nucleus  60 . 
     Planting takes place with force control; in other words, when the spring  84  enters the recess  78  there will be a drop in force indicating the end of planting. 
     For example,  FIG. 18  shows the progress of the force of introduction of the press compared with the insertion stroke. The force undergoes a sudden change n gradient in correspondence with the introduction of the spring  84  into the appropriate recess  78 , highlighted in  FIG. 18  with the reference ‘E’. 
     The powering body  27  is then assembled in the casing  8  through planting with an automatic press and calibration ( FIG. 15 ). 
     A feeler pushes on the mobile nucleus  60  and takes the plate  74  of the mobile nucleus  60  to rest against the shoulder  16  of the casing  8  and, as it ascends, measures the stroke travelled. 
     The value of this stroke is transferred to a PC and relative software determines the planting stroke of the powering body  27  on the basis of the nominal stroke and the measurement of the height of the powering nozzle  29  positioned on the powering body  27 . 
     The electric press plants the powering body  27  in the casing  8 , checking that the movement made is equal to the measurement calculated. 
     Advantageously, with these operations it is possible to guarantee the preload of the spring  84 , the stroke of the mobile nucleus  60  and therefore the pulling force and capacity values. 
     The discharging body  32  is then assembled ( FIG. 16 ) onto the casing through planting with an automatic electric press. 
     In this case too, the discharging body  32  and its seat in the casing  8  must be measured in order to calculate the planting stroke. 
     The planting operation of the discharging body  32  can be carried out as a second calibration (or a fine tuning of the first calibration). Finally, it is possible to proceed with the application of resin to the electrical connections  52  (of the ‘pin’ type for example) and to the discharging body  32  in order to guarantee the pneumatic seal of the valve  4 . 
     To speed up the polymerisation of the resin applied. UV-sensitive adhesive (not shown) and a special lamp  62  are used ( FIG. 17 ). 
     Preferably, the assembly operations are followed by an electrical pneumatic test of the electromagnetic valve  4 .