Patent Publication Number: US-2004056230-A1

Title: Cartridge-type especially electromagnetically directly actuated directional seat valve

Description:
[0001] The invention relates to a directional control valve which is operated directly, in particular electromagnetically, is in the form of a valve cartridge and has the features from the preamble of patent claim 1.  
       [0002] Directional control valves of this type are known from practice and from prospectus material from various companies. By way of example, a 3/2 directional control valve of this generic type is described on page 73 of the product information publication “Herion-information 1/87 Hydraulics”, produced by the Herion company. In this control valve, the valve piston is arranged in a valve bore which passes through the valve sleeve such that its piston cone is furthest away from the electromagnet with which the valve sleeve is assembled. Towards the electromagnet, the piston cone is followed by a piston neck along which there is a flow cross section between a seating edge and two or more transverse bores which open into the valve bore. Adjacent to the piston neck is a sealing section which seals the fluid area around the mouth of the transverse bores from the area in front of the mouth of the valve bore on the magnet side. This fluid area is connected via an axial bore, which passes through the valve piston, to a connecting area in front of that front end face of the valve sleeve which faces away from the electromagnet. The same pressure, but in opposite directions, is therefore applied to surface areas of the same size on the valve piston, whose sealing cross section is equal to the seating cross section in the area of the sealing section, thus providing pressure equalization.  
       [0003] The product information publication shows a simplified longitudinal section through the control valves. In the case of the 3/2 directional control valve, the piston cone (whose diameter is larger than the seating diameter) of the valve piston is located between two seating edges which are formed directly on the valve sleeve. The valve piston cannot, of course, be installed in this way. In fact, at least that seating edge which is closer to the front end face of the valve sleeve must be formed on a bush which is inserted into the valve sleeve and is referred to as the valve seat.  
       [0004] In the case of a 2/2 directional control valve having a valve piston which has a piston cone, a piston neck and a sealing section, it is not absolutely necessary, by virtue of the nature of the assembly process, for the seating edge to be located on a separate valve seat, which is inserted into the valve sleeve. In principle, the valve sleeve may also itself have a seating edge. However, this then has the disadvantage that, during assembly, the seal on the sealing section must be pushed over the seating edge. Another disadvantage is that the material for the valve sleeve and the material for the valve seat cannot be chosen and handled optimally in accordance with the various requirements. Overall, it therefore appears to be advantageous for a separate valve seat to be inserted into the valve sleeve, even in the case of a 2/2 directional control valve.  
       [0005] Particularly in the case of directional control valves of this generic type which have small nominal sizes, it is difficult to fit a valve seat into the valve sleeve close to the front end face. The external diameter of the valve sleeve normally decreases in two or more steps from the rear end face to the front end face, so that the valve seat actually has its smallest diameter in the area of the valve sleeve.  
       [0006] The invention is based on the object of further developing a 2/2 or 3/2 directional control valve having the features from the preamble of patent claim 1 such that it can be designed to be physically very small.  
       [0007] The desired aim is achieved according to the invention in that, in a corresponding way to the characterizing part of patent claim 1, the valve seat and the valve piston are arranged such that, of the piston sections, the sealing section is located closest to that end face of the valve sleeve which is at the front in the installation direction. In an arrangement such as this, the valve sleeve holds the valve seat and the piston cone of the valve piston in an area in which it has a relatively large diameter, so that the valve seat or seats can be inserted into the valve sleeve from the rear end face without any problems.  
       [0008] Advantageous refinements of a directional control valve according to the invention and which is operated directly can be found in the dependent claims.  
       [0009] If the valve is a 2/2 directional control valve, then it is sufficient for the valve piston to have only one piston neck, which is located in the valve bore, between the piston cone and the sealing section. In the case of a 3/2 directional control valve, the valve piston preferably has a piston cone which is located between two seating edges that are at a distance from one another, and has a piston neck on both sides of the piston cone.  
       [0010] The sealing section of the valve piston also has a guidance function in the known valves of this generic type. This guidance function is preferably also retained in a valve according to the invention. In the known valves, the sealing and guidance section, which can absorb transverse forces that are exerted by the operating element on the valve piston and can keep them away from the piston cone, is located between the point, at which the operating element acts on the valve piston, and the piston cone. In a valve according to the invention, the sealing section, seen from the point at which the operating element acts on the valve piston, is located beyond the piston cone and a piston neck. As claimed in patent claim 3, the valve piston of a valve according to the invention is now advantageously guided within a piston neck and hence close to the piston cone, so that the piston cone is in each case seated very exactly on the valve seat despite the transverse forces that are exerted. If the valve piston has a piston neck which is located alongside the piston cone towards the rear end face of the valve sleeve, then it is preferable, as claimed in patent claim 4, for the valve piston to be guided in this piston neck, that is to say between the piston cone and the point at which the operating element acts.  
       [0011] The guidance within a piston neck is advantageously provided as claimed in patent claims 5 and 6.  
       [0012] In the case of physically small valves, the radial dimensions of the valve piston, in particular, are very small. The valve piston has a very particularly small diameter in a groove in the sealing and guidance section, and this groove holds a sealing ring and one or two supporting rings. A small valve piston such as this can be drilled through axially only with difficulty. Therefore, as is claimed in patent claim 7, a fluid connection is preferably produced from a connecting area of the valve in front of the front end face of the valve sleeve through the valve sleeve to both end faces of the valve piston, for pressure equalization on the valve piston. This is feasible, in particular, because the area of the valve sleeve with a small diameter is, according to the invention, free of any inserted valve seat, so that there is still sufficient material thickness for drilling even in the area of the valve sleeve that has been mentioned. The fluid connection can advantageously be produced as claimed in patent claim 8. 
     
    
    
     [0013] The drawings illustrate a number of exemplary embodiments, which are each operated electromagnetically, of a directional control valve according to the invention. The invention will now be explained in more detail with reference to the figures in these drawings, in which:  
     [0014]FIG. 1 shows a first exemplary embodiment, illustrating a 2/2 directional control valve which is open when no current is flowing and has a pushing electromagnet,  
     [0015]FIG. 1 a  shows a cross section through the valve piston of the first exemplary embodiment,  
     [0016]FIG. 2 shows a second exemplary embodiment, which illustrates a 2/2 directional control valve which is closed when the current is flowing and has a pulling electromagnet,  
     [0017]FIG. 3 shows a third exemplary embodiment, illustrating a 3/2 directional control valve with a pushing electromagnet, and  
     [0018]FIG. 4 shows a fourth exemplary embodiment, illustrating a 3/2 directional control valve with a pulling electromagnet. 
    
    
     [0019] The 2/2 directional control valves shown in FIGS. 1 and 2 are composed of a hydraulic part  10  and an electromagnet  11 , and are in the form of screw-in cartridges. The hydraulic part  10  essentially comprises a valve sleeve  12  and a moving valve piston  13 . The electromagnet  11  and the valve sleeve  12  are screwed to one another. For this purpose, the valve sleeve  12  has a holding part  14 , which has a large external diameter and is provided with an internal thread over a certain distance in a large holder  15 , which is like a blind hole, with a base  16 . The electromagnet  11  has a pole tube  17  and a coil  18  which is pushed over the pole tube. The pole tube is screwed into the holder  15  of the valve sleeve  12  as far as the base  16 . A seal  19  is located in front of the threads (which engage in one another) of the pole tube and valve sleeve, and between these two parts, which seal  19  provides an external seal, against leakage via the thread, for a fluid area  20  which is bound on one side by the base  16  of the holder  15  and on the other side by the walls of a cutout, which is open towards the base, in the pole tube  17 . The base  16  can be regarded as a rear end face of the valve sleeve, which faces the electromagnet  11  and is at right angles to the axis of the valve sleeve.  
     [0020] In front of the holding part  14 , the valve sleeve  12  has a control part  25  whose radial dimensions are significantly smaller than the external diameter of the holding part. Only the control part  25  is held by the corresponding holding bore after installation of a valve in a housing part. The valve sleeve merges conically from the holding part  14  into the control part  25 . There is a small step  26  just in the corner between the control part and the conical surface, and this comes to rest on a housing part when the cartridge is installed in that housing part.  
     [0021] An annular groove  27  for a seal that is not illustrated is turned externally into the control part  25  at a short distance from the step  26 , and this seal provides an external seal for the holding bore for the installed cartridge. The annular groove is followed by an external thread  28 , which is used for screwing the cartridge into a housing part. After the external thread, the control part  25  continues with an external diameter that is reduced even further as far as a front end face  29 , which projects at right angles to the sleeve axis. A seal can be held in an annular groove  30  shortly behind the end face. Once the cartridge has been installed, this seal subdivides the area surrounding the valve sleeve into an axial connecting area  31 , which is located essentially in front of the end face  29  and thus axially in front of the valve sleeve, and a radial connecting area  32  which is located radially outside the valve sleeve.  
     [0022] The valve sleeve  12  has a valve bore  35  which runs on the axis and opens into the fluid area  20 , while it is closed towards the end face  29 . From its base approximately as far as the transition between the annular groove  27  and the external thread  28 , the valve bore  35  has a first diameter in a first section, then merges into a widened area as a second section, in order finally to return to the first diameter over a certain distance in a third section, and thus to open into the fluid area  20 . This last section of the valve bore  35  is formed by a bush-like valve seat  36 , which is pressed into the valve sleeve  12  from the end face  16 . The end-face inner edge of the valve seat  36  forms the only seating edge  34  of the valve that is fixed to the housing.  
     [0023] The valve piston  13  is held in the valve bore  35  such that it can move axially and is essentially located with a sealing and guidance section  37 , whose diameter is equal to the first diameter of the valve bore  35 , in its first section and, in a groove in it, has a seal  38  which forms a seal between the second, widened section of the valve bore and the area between the valve piston and the base of the valve bore. The section  37  is followed by a piston neck  39 , in which the diameter of the valve piston  13  is smaller than the first diameter of valve bore, and by means of which the valve piston passes through the widened section of the valve bore and through the valve seat  36 . In front of the seating edge  34 , the piston neck is followed by a piston cone  40 , whose diameter is larger than the first diameter of the valve bore and by means of which the valve piston  13  can be seated on the seating edge  34 . The piston cone is followed by a connecting section  41 , which is located in the fluid area  20  and ends in a plate  42 .  
     [0024] Approximately in the center of the piston neck  39  and within the bush-like valve seat  36 , the valve piston  13  has a short guide collar  44 , which is provided with two or more flats  45  which are distributed uniformly over the circumference, and between which circular-cylindrical area elements  46  remain, which rest internally on the valve seat  36 , so that, on the one hand, the valve piston is guided close to the piston cone  40  while, on the other hand, it is also possible for fluid to flow through the valve seat.  
     [0025] An oblique bore  51 , which runs through the valve sleeve  12 , is open on the outside to the radial connecting area  32  and thus for fluid-flow purposes connects this connecting area to the area of the valve bore  35  located between the sealing section  37  of the valve piston  13  and the seating edge  37 , opens into the widened section of the valve bore  35  in front of one face of the valve seat  36 . The fluid area  20  is connected for through-flow purposes to the axial connecting area  31  via an axial bore  52  which originates from the end face  16  of the valve sleeve  12 , and via an oblique bore  53  which originates from the end face  29  and meets this axial bore  52 . The oblique bore  53  intersects the valve bore  35  between its base and the sealing section  37  of the valve piston  13 . Both end faces of the valve piston are thus subject to the same pressure, that is to say the pressure in the axial connecting area. Since, furthermore, the diameter of the sealing section  37  is equal to the diameter of the seating edge  34 , the valve piston is subjected to a pressure-equalization force, that is to say it is not subjected to any force resulting from any of the pressures that are applied.  
     [0026] To the extent described so far, the two exemplary embodiments as shown in FIGS. 1 and 2 are completely identical to one another. The first difference is that, in the exemplary embodiment shown in FIG. 1, what is referred to as a pushing electromagnet is used, whose magnet armature (which is not shown in any more detail) moves in the direction of the end face  16  of the valve sleeve  12  when current flows through the magnet coil, while, in the exemplary embodiment shown in FIG. 2, what is referred to as a pulling electromagnet is used, whose magnet armature  55  moves in the direction away from the end face  16  of the valve sleeve  12  when current flows through the magnet coil. A plunger  54  is mounted on the magnet armature of the pushing electromagnet shown in FIG. 1, and the plate  42  of the valve piston  13  rests on this plunger  54 . To be precise, the valve piston is held on the plunger by a helical compression spring  56 , which is clamped in between the valve piston  13  and the base of the valve bore  35  and exerts a force on the valve piston in the sense of lifting the piston cone  40  off the seating edge  34 . In contrast to the exemplary embodiment shown in FIG. 1, in the exemplary embodiment shown in FIG. 2, the valve piston  13  is hooked by the plate  42  like a bayonet into a cutout in the magnet armature of the pulling electromagnet with a small amount of play in the axial direction. Furthermore, in contrast to the exemplary embodiment shown in FIG. 1, a helical compression spring  56  is arranged within the electromagnet, rather than in the valve bore, in the exemplary embodiment shown in FIG. 2. This helical compression spring loads the magnet armature and hence the valve piston  13  in the sense of the piston cone  40  being seated on the seating edge  34  of the valve seat  36 .  
     [0027] When no voltage is applied to the coil of the electromagnet in the exemplary embodiment shown in FIG. 1, the compression spring  56  raises the valve piston off the seating edge  34  on the valve seat  36 . Hydraulic fluid can flow both from the axial connecting area  31  via the bores  53  and  52 , via the fluid area  20 , via a circumferential through-flow cross section between the seating edge  34  and the piston cone  40 , along the piston neck  39  and via the bore  51  to the radial connecting area  32  and via the same path from the radial connecting area  32  to the axial connecting area  31 .  
     [0028] When voltage is applied to the electromagnet  11 , then the magnet armature moves the valve piston  13  against the compression spring  56  until the piston cone  40  is seated on the seating edge  34 . The fluid connection between the two connecting areas is then blocked in both flow directions.  
     [0029] The valve shown in FIG. 1 is thus an electromagnetically operable 2/2 directional control valve which is open when no current is flowing.  
     [0030] When no voltage is applied to the coil of the electromagnet in the exemplary embodiment shown in FIG. 2, the compression spring  56  presses the piston cone  40  of the valve piston  13  against the seating edge  34  via the magnet armature  55 , so that it is impossible for any hydraulic fluid to flow between the two connecting areas  31  and  32 . When voltage is applied to the electromagnet  11 , then the magnet armature lifts the valve piston  13  off the seating edge  34  against the force of the compression spring  56 . Hydraulic fluid can then flow in both directions between the two connecting areas.  
     [0031] The valve shown in FIG. 2 is thus an electromagnetically operable 2/2 directional control valve which is closed when no current is flowing.  
     [0032] The 3/2 directional control valve shown in FIG. 3 uses the same pushing electromagnet  11  as that for the 2/2 directional control valve shown in FIG. 1, and the 3/2 directional control valve shown in FIG. 4 uses the same pulling magnet  11  as that for the 2/2 directional control valve shown in FIG. 2. The two valves shown in FIGS. 3 and 4 differ only in the configuration of the hydraulic part of the valves shown in FIGS. 1 and 2. The hydraulic parts  60  of the two valves shown in FIGS. 3 and 4 when compared with one another differ only in the arrangement of a helical compression spring  56 .  
     [0033] The valve sleeve  62  of a valve shown in FIGS. 3 and 4 has the same holding part  14  as a valve sleeve  12  shown in FIG. 1 or  2 . The control part  63  of the valve sleeve  62 , on the other hand, is longer than that of a valve sleeve  12 . To be precise, a further section is inserted axially between the section with the annular groove  27  for a seal and with the external thread  28  and the section with the annular groove  30  for a seal, and the size of the external diameter of this further section is between the external diameters of the two other sections, and it has an annular groove  64  for a further seal. The further seal provides a further radial connecting area  88 , between the seal that is located in the annular groove  64  and the external thread  28  as well as the seal in the annular groove  27 , radially outside the valve sleeve, alongside the radial connecting area  32  between the seals which are located in the annular grooves  30  and  64 .  
     [0034] The valve sleeve  62  has a valve bore  65  which runs on the axis and opens into the fluid area  20 , which is once again bounded by the rear end face  16  of the valve sleeve and the pole tube  17 , while it is closed towards the front end face  29 . In a first section from its base as far as the additional section of the control part  25 , the valve bore  65  has a first diameter, then merges into a centric widened area as a second section, is then in a following section, which once again has the first diameter, is formed by a first bush-like valve seat  66 , which is inserted into the valve sleeve  62 , and then has an eccentric widened area  67  in order finally to have the first diameter once again over a certain distance in a final section, and thus to open into the fluid area  20 . This final section of the valve bore  65  is formed by the bush-like valve seat  36  in the same way as in the exemplary embodiments shown in FIGS. 1 and 2, which bush-like valve seat  36  is identical to the valve seat  66  and is separated from it by a distance which corresponds to the width of the widened area  67 . There are therefore now two valve seats, whose inner edges are two seating edges  34  on the end faces which face one another and face the widened area  67 .  
     [0035] A valve piston  70  is held in the valve bore  65  such that it can move axially and has a sealing and guidance section  37  whose diameter is equal to the first diameter of the connecting bore  65 , is essentially located in its first section and has a seal  38  in a groove in it, which seal  38  seals the second widened section of the valve bore and the area between the valve piston and the base of the valve bore from one another. The section  37  is followed by a piston neck  39 , in which the diameter of the valve piston  70  is smaller than the first diameter of the valve bore, and by means of which the valve piston passes through the concentrically widened section of the valve bore, and through the valve seat  66 . In the eccentrically widened area  67 , the piston neck  39  is followed by a piston cone  40 , whose diameter is larger than the first diameter of the valve bore. The piston cone  40  is formed symmetrically with respect to a plane at right angles to the axis of the valve sleeve  62 . The valve piston  13  is seated by this piston cone, with the exception of the switching processes, on the seating edge  34  of either the valve seat  66  or the valve seat  36 . The piston cone  40  is followed by a further piston neck  71 , which projects through the valve seat  36  into the fluid area  20 , and the piston neck  71  is, finally, followed by the connecting section  41 , which is located in the fluid area  20  and ends in a plate  42 . In the exemplary embodiment shown in FIG. 3, the plunger  54  of the pushing electromagnet rests on this plate  42 . In the exemplary embodiment shown in FIG. 4, the valve piston  70  is hooked by means of the plate  42  into the magnet armature  55  of the electromagnet.  
     [0036] In the piston neck  71  and within the bush-like valve seat  36 , the valve piston  70  has a short guide collar  44 , which is provided with two or more flats  45  (see FIG. 1 a ), which are distributed uniformly over the circumference and between which circular-cylindrical surface elements  46  remain, which rest internally on the valve seat  36  so that, on the one hand, the valve piston is guided close to the piston cone  40  while, on the other hand, it is still possible for fluid to flow through the valve seat  36 . Where the valve piston  13  shown in FIGS. 1 and 2 and the valve piston  70  shown in FIGS. 3 and 4 have sections that are comparable to one another, they are provided with the same reference numbers.  
     [0037] A bore  72  which runs through the valve sleeve  62  opens into the concentrically widened section of the valve bore  70  in front of one face of the valve seat  66 , is open on the outside to the radial connecting area  68  and thus, for fluid-flow purposes, connects this connecting area to the area of the valve bore  65  which is located between the sealing section  37  of the valve piston  70  and the seating edge  34  on the valve seat  66 . The radial connecting area  32  is connected for fluid flow purposes to the widened area  67  via an oblique bore  74 , which is introduced from the end surface  16  where it is closed by a pushed-in sphere  73  and which intersects the eccentric widened area  67 , and via a radial bore  75  which intersects it. The fluid area  20  is connected for fluid flow purposes to the axial connecting area  31  via an axial bore  52  which originates from the end face  16  of the valve sleeve  12 , and via an oblique bore  53  which originates from the end face  29  and intersects the axial bore  52 . The oblique bore  53  intersects the valve bore  65  between its base and the sealing section  37  of the valve piston  70 . The pressures are thus also equalized for the valve piston  70  in the valves shown in FIGS. 3 and 4.  
     [0038] To the extent described so far, the hydraulic parts  60  in both exemplary embodiments shown in FIGS. 3 and 4 are completely identical to one another. The difference is that, in the exemplary embodiment shown in FIG. 3, a helical compression spring  56  is clamped in between the valve piston and the base of the valve bore, while there is no such spring in the hydraulic part in the exemplary embodiment shown in FIG. 4. In fact, in this case, the helical compression spring  56  is located in the electromagnet  11 , behind the magnet armature  55 , and acts in the opposite direction.  
     [0039] In the exemplary embodiment shown in FIG. 3, the compression spring  56  pushes the valve piston  70  with the piston cone  40  against the seating edge of the valve seat  36  when no current is flowing through the electromagnet. There is a through-flow cross section between the seating edge of the valve seat  66  and the piston cone  40 . Hydraulic fluid can thus flow from the radial connecting area  32  via the bores  75  and  74 , the eccentric widened area  67 , the through-flow cross section between the piston cone  40  and the valve seat  66 , along the piston neck  39 , via the concentrically widened area of the valve bore on one face of the valve seat  66 , and via the bore  72  to the radial connecting area  68 , and vice versa.  
     [0040] When voltage is applied to the electromagnet, the piston cone  40  of the valve piston  70  is pressed against the valve seat  66 , against the force of the compression spring  56 . Hydraulic fluid can now flow from the radial connecting area  32  via the bores  75  and  74 , the eccentric widened area  67 , the through-flow cross section between the piston cone  40  and the valve seat  36 , along the piston neck  71 , via the fluid area  20  and via the bores  52  and  53  to the axial connecting area  31 , and vice versa.  
     [0041] In the exemplary embodiment shown in FIG. 4, the possible flows when the electromagnet  11  is switched on and off are interchanged with one another in comparison to the exemplary embodiment shown in FIG. 3. This is immediately evident.