Abstract:
An electromagnetically actuable proportional hydraulic valve ( 10 ) is described, which is distinguished in particular by a constant, low-wear operating performance. This is attained by means of a closing member ( 60 ) having an approximately conical sealing body ( 60   c,    70 ) with a curved dome-like face end oriented toward the valve seat ( 58 ). The sealing body ( 60   c,    70 ) together with the valve seat ( 58 ) forms a conical seat valve. The sealing body of the closing member ( 60 ) is provided with a flow separation edge ( 60   d ), which improves the temperature sensitivity of the proportional valve ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to electromagnetically actuable proportional hydraulic valves and, more particularly, to electromagnetically actuable proportional hydraulic valves having a magnetic part comprising an electrically triggerable coil, a stationary core protruding into the interior of the coil, an armature guided displaceably and acted upon by the coil, which armature is coupled with a closing member, and a valve part provided with at least one inflow conduit, at least one return conduit, at least one work conduit and at least one valve seat, the valve seat being in operative communication with the closing member so as to control a pressure-fluid communication between the work conduit and the return conduit. 
     2. Description of the Related Art 
     Among other purposes, electromagnetically actuatable proportional hydraulic valves are used to regulate the pressure in hydraulic circuits, for instance in automatic transmissions of motor vehicles. One such proportional valve is already known as an example from German Utility Model DE-GM 94 10 219. This proportional valve has a magnetic part whose armature acts on a closing member of a valve part and with it forms a flat seat valve. Flat seat valves are distinguished in particular by their insensitivity to errors of alignment between the armature and the closing member; however, because of flow conditions of the closing member, they do tend to vibrate, which over the course of operation can cause leaks and wear. If no counteracting provisions are taken at the closing member, its function is furthermore sharply dependent on the temperature, that is, on the viscosity and hence the viscous friction, of the pressure fluid. This can lead to irregular pressure/current characteristic curves of the proportional valve. Both effects are undesirable, since they impair the functional properties of a hydraulic circuit connected to these valves. 
     It is an object of the present invention to provide an electromagnetically actuable proportion hydraulic valve of the above-described kind, which has improved stability when subjected to temperature variations and under flow conditions that tend to produce vibrations. 
     This object and others, which will be made more apparent hereinafter, are attained in an electromagnetically actuatable proportional hydraulic valve, having a magnetic part comprising an electrically triggerable coil, a stationary core protruding into the interior of the coil, an armature guided displaceably and acted upon by the coil, which is coupled with a closing member and a valve part provided with at least one inflow conduit, at least one return conduit, at least one work conduit and at least one valve seat, the valve seat being in operative communication with the closing member in order to control a pressure-fluid communication between the work conduit and the return conduit. 
     According to the invention the closing member, at least in the region of its end toward the valve seat, has a substantially conical sealing body, whose smaller end face is facing toward the valve seat, and the sealing body has at least one flow separation edge on its end remote from the valve seat. 
     By comparison, the electromagnetically actuable proportional hydraulic valve according to the invention has the advantage that it behaves substantially in a more stable manner in the face of temperature factors and flow-dictated inducements to vibrations. The pressure/current characteristic curves of the proportional valve have a more constant and steadier course as a result, thus minimizing the expense for programming triggering for the proportional valve. The sealing properties and wear behavior of the proportional valve of the invention are improved. Sensors to detect and compensate for temperature factors and hydraulic circuits can be dispensed with. Further advantages or advantageous refinements of the invention will become apparent from the dependent claims and the following description. 
     Two exemplary embodiments with particularly advantageous closing members are defined by the dependent claims. In one embodiment the sealing body has a cup-shaped cross section, with a curved face end oriented toward the valve seat. In this embodiment the closing member is distinguished by its simple form and economical manufacture. In other embodiments the armature acts on the closing member by means of a tappet and the sealing body is connected to a guide region that cooperates with a guide member of the housing by means of a connecting portion. In these other embodiments the closing member is especially insensitive to errors of alignment, because its guidance is uncoupled from the armature. In the other dependent claims, features that are advantageous from a production standpoint are disclosed, along with especially suitable usage areas for the proportional valves of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Two exemplary embodiments of the invention are shown in the drawing and described in further detail below. 
     FIGS. 1 and 2 each show one of the exemplary embodiments in longitudinal section; 
     in FIGS. 3 and 4, the closing member  60  is shown as an individual part, enlarged. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The proportional valves  10  shown in FIGS. 1 and 2 each comprise a magnetic part  12  and a valve part  14 , joined integrally to it, that is disposed coaxially with the magnetic part  12 . The magnetic part  12  includes a coil  18 , wound around a coil body  16 ; the coil can be triggered electrically by means of lines  20  and contacts  22 . The lines  20  are injected into a plastic part  24 , which is integrally joined to the coil body  16  and on whose free end a plug housing  26  that receives the contacts  22  is provided. 
     The coil  18  is hollow-cylindrical, and in its end toward the valve part  14 , it receives a core  28  in stationary fashion; the core protrudes in some portions into the interior of the coil  18 . This core  28  has a central longitudinal bore  30 , which on its end located in the inside of the coil  18  discharges in a sink  32 . A guide sleeve  34  with an encompassing collar  34   a  is braced on the bottom of the sink  32 . The guide sleeve  34  has a neck  34   b,  oriented toward the valve part  14  and extending into the inside of the longitudinal bore  30  of the core  28 ; the inner wall of the neck on the end of the guide sleeve  34  toward the valve part forms an axial guide for a tappet  36 . This tappet is solidly connected to an armature  38 , which is located on the end of the coil  18  remote from the valve part  14 . 
     The armature  38  is in the shape of a T, with a head  38   a  that covers the end face of the coil  18  and a shaft  38   b  that protrudes into the coil  18 . The shaft  38   b  ends in a protrusion  38   c,  which can plunge into the sink  32  of the core  28 . 
     To enable a relative motion of the armature  38  relative to the coil  18 , a secondary air gap  40  exists between the shaft  38   b  and the coil body  16 . A working air gap  41 , which allows a reciprocating motion of the armature  38 , can be seen between the end faces, toward one another, of the armature  38  and core  28 . 
     For restoring and centering the armature  38 , a spring disk  39  on the end of the proportional valve  10  remote from the valve part  14  is used. In the region of its outer circumference, this spring disk  39  is fastened between a step of a housing  42  of the magnetic part  12  and a cap  44  that closes off this housing  42  from the outside. The cap  44  and the housing  42  are calked together. A recess  46  is provided in the center of the spring disk  39 , and it is also calked together with a corresponding protrusion  38   d  of the armature  38 . The housing  42  of the magnetic part  12  is created essentially by spray-coating the individual components that form the magnetic part  12  with plastic. A metal sleeve  48  that surrounds the coil  18  is injected into this housing  42  to form a flux guide element. 
     The housing  42  of the proportional valve  10  merges with the housing  43  of the valve part  14 . In the latter, an inflow conduit  50 , return conduit  52  and work conduit  54  are formed. While the work conduit  54  extends along the longitudinal axis of the proportional valve  10 , the inlet  50  and the return conduit  52  are embodied as radial conduits. They are sealed off from one another and from the outside by means of ring seals  56 . To embody a baffle  57 , the inflow conduit  50  is graduated a single time in its inside diameter in the flow direction and is located remote from the magnetic part  12  and discharges flush into the consumer conduit  50 . By comparison, the return conduit  52  located toward the valve part  14  is embodied as a continuous recess, that is, a recess that penetrates the work conduit  54 . 
     At the transition region from the work conduit  54  to the return conduit  52 , a perforated baffle  55  is injected into the valve part  14 . For the sake of wear protection, this baffle is made of high-alloy material, for instance, and it has a sharp-edged valve seat  58 . A closing member  60  actuated by the armature  38  cooperates with this valve seat. The proportional valve  10  can therefore also be called a single-edge regulating valve. 
     In the exemplary embodiment of FIG.  1  and FIG. 3, the closing member  60  is made of a cylindrical guide region  60   a  toward the magnetic part, a connecting portion  60   b  adjoining the guide region, and a sealing body  60   c  that cooperates with the perforated baffle  55 . The guide region  60   a  and the connecting portion  60   b  have a cylindrical cross section; the sealing body  60   c  is conical, and for fluidic reasons is curved outward in domelike fashion on the face end toward the valve part. In cross section, the connecting portion  60   b  has the form of an annular groove, with walls that for instance extend perpendicular to one another. The result at the transition point from the sealing body  60   c  to the connecting portion  60   b  is a flow separation edge  60   d,  which markedly reduces the temperature sensitivity of the proportional valve  10 . To that end, the flow separation edge  60   d  is dimensioned in such a way that the diameter d of the connecting portion  60   b  is at a ratio of less than or equal to 0.9 to the diameter D of the flow separation edge  60   d.  Furthermore, the length L of the connecting portion  60   b  is greater than or equal to half of the difference between the diameter D of the flow separation edge  60   d  and the diameter d of the connecting portion  60   b.  Both of these requirements can be expressed mathematically by the following relationships F 1  and F 2 : 
     
       
           F   1 :  d/D≦ 0.9; 
       
     
     
       
           F   2 :  L ≧( D−d )/2. 
       
     
     Furthermore, the closing member  60  is equipped with a central blind bore  62 , whose opening is toward the magnetic part  12 . The tappet  36  connected to the armature protrudes into this blind bore  62 , and a radial clearance exists between the tappet  36  and the blind bore  62 . This radial clearance makes it possible to compensate for errors of alignment among the closing member  60 , valve seat  58  and tappet  36 . The tappet thus serves as a centering or stop means for the closing member  60  in the primary axis; the actual guidance of the closing member  60  is done at the circumference of the guide region  60   a,  which cooperates with a guide  64  on the housing. The position of this guide is dictated by the injection molding tool for the housing/valve unit and is therefore very precisely aligned with the valve seat  58  formed by the opening of the perforated baffle  55 . 
     The exemplary embodiment of FIGS. 2 and 4 differs from the exemplary embodiment of FIG. 1 described above in having a simpler and therefore less expensive embodiment of the closing member  60 . This closing member comprises only a cup-shaped sealing body  70  with a conical outer contour, and a face end toward the valve part that is likewise curved in domelike fashion outward. This closing member  60  does not have any connecting portion  60   b  or guide region  60   a.  Unlike the first exemplary embodiment, the sealing body  70  is solidly connected to the tappet  36 , for instance being press-fitted onto the end toward the valve part of the tappet  36 . The upper edge of the sealing body  70 , located remote from the valve seat  58 , forms the flow separation edge  60   d,  whose production, in contrast to the first exemplary embodiment, requires no separate work steps. This flow separation edge  60   d  in its dimenions matches those of the first exemplary embodiment of FIG.  1  and in the same way meets the mathematical relationships F 1  and F 2  explained in the context of that embodiment; given the lack of the connecting portion  60   b  in the second exemplary embodiment, d now designates the diameter of the tappet  36 . 
     The guidance of the closing member  60  is effected via the guides of the tappet  36  and armature  38 ; separate guides  64  as in the first exemplary embodiment are not necessary. 
     The mode of operation of such proportional valves  10  is known per se. In the basic position shown in each case for the proportional valve  10 , the coil  18  receives no electrical current, so that the armature  38  is in a neutral position determined by the spring disk  39 . In this neutral position, the dynamic pressure of the inflowing pressure acting on the closing member  60  causes the valve seat  58  to be open, so that the consumer conduit  54  is pressure-relieved to the return conduit  52 . 
     Supplying current to the coil  18 , because of the armature motion in the direction of the valve part  14 , causes a throttling action at the valve seat  58 , so that a pressure level results in the consumer conduit  54  that can be adjusted by the supply of current to the coil  18  or in other words by the stroke of the armature  38 . At maximum, this pressure level can be adjusted to a value that is determined by the supply pressure, minus the pressure loss at the baffle  57  on the inlet side. 
     Because of the conical shape of the sealing bodies  60   c,    70 , the centering of the closing member  60  in the flow of pressure fluid is improved. The flow separation edge  60   d  embodied in accordance with the relationships F 1  and F 2  has the effect that the flow of pressure fluid along the closing member  60  already ruptures again early, which reduces the effect of temperature on the pressure/current characteristic curves of the proportional valve  10 . As a result, these characteristic curves have a steady course over wide temperature and current ranges. 
     It is understood that alterations or additions to the exemplary embodiment described are possible without departing from the fundamental concept of the invention. This fundamental concept in particular comprises relieving conventionally known flat seat valves with conical seat valves that are insensitive to flow and temperature, so as to create proportional valves  10  with especially stable functional properties regarding tightness, temperature sensitivity, wear resistance and the course of the characteristic curves, without entailing additional expense in terms of production cost. To that end, according to the invention, closing members  60  with conical sealing bodies  60   c,    70  are proposed which have a flow separation edge  60   d.