Abstract:
The invention relates to an electromagnetic valve, comprising a valve tappet, which is arranged in a valve housing and which can open or close a valve passage in the valve housing, a magnet armature, which is provided in order to actuate the valve tappet and through which a hole passes for accommodating the valve tappet, and a restoring spring, which acts on the valve tappet and the spring end of which facing away from the magnet armature is supported on a magnet core in the valve housing. For precise valve adjustment, an adjustment sleeve is fixed in the hole of the magnet armature, in which adjustment sleeve the valve tappet is fastened in some sections at the same time.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Phase Application of PCT International Application No. PCT/EP2013/056020, filed Mar. 22, 2013, which claims priority to German Patent Application No. 10 2012 205 503.7, filed Apr. 4, 2012, the contents of such applications being incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention relates to an electromagnetic valve, in particular for slip-controlled motor vehicle brake systems 
     BACKGROUND OF THE INVENTION 
     WO 03/093083 A1, which is incorporated by reference, has already disclosed an electromagnetic valve of the type stated, the magnet armature of which is penetrated by a hole in order to accommodate a valve tappet. A return spring is supported on the valve tappet, and the valve tappet is moved in the magnet armature in order to set the spring preloading force. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention comprises an electromagnetic valve of the type stated in a low-cost way using means that are as simple as possible and functionally appropriate and to improve it in such a way that simple, precise setting of the residual air gap provided between the magnet armature and the magnet core is possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention will emerge from the following description of a number of illustrative embodiments with reference to  FIGS. 1 to 4 , or of which: 
         FIG. 1  shows a first illustrative embodiment of the invention by means of a longitudinal section through an electromagnetic valve, the adjustment sleeve of which has a collar for improved centering of the magnet armature subassembly within the valve housing, 
         FIG. 2  shows a second illustrative embodiment of the invention by means of a longitudinal section through an electromagnetic valve, the adjustment sleeve of which has a collar which rests in full surface contact and therefore without wear against the magnet core during electromagnetic excitation in the magnet armature, 
         FIG. 3  shows a third illustrative embodiment of the invention by means of a longitudinal section through an electromagnetic valve, the valve tappet of which is guided in the direction of the valve seat by means of a centering washer, 
         FIG. 4  shows a fourth illustrative embodiment of the invention by means of a longitudinal section through an electromagnetic valve, the magnet armature of which has an extended guide section which extends into a valve housing bottom part closed in the shape of a pot. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The common features of all the electromagnetic valves depicted in  FIGS. 1 to 4  will be explained first of all below, said electromagnetic valves preferably being used for slip-controlled motor vehicle brake systems. The electromagnetic valves shown consist of functional elements that are known per se. These include in each case a valve passage  13 , which is arranged in a valve housing  14  and can be closed under the action of a return spring  8  by means of a valve tappet  4  arranged on a magnet armature  2  or can be opened by means of a magnet coil (not depicted). For this purpose, the magnet armature  2  is guided over some sections of the circumferential surface thereof in the valve housing  14  in such a way as to be axially movable over a defined working stroke, wherein the return spring  8  is supported by means of its spring end facing away from the magnet armature  2  on a magnet core  5  which closes the valve housing  14 . In the four illustrative embodiments under consideration, the magnet core  5  is in each case pressed in as a closure plug into an austenitic housing sleeve  15 , which, as part of the valve housing  14 , is welded to a thick-walled rigid tubular body  16  that ensures secure fastening in a valve location hole in a valve locating body. 
     All the electromagnetic valves depicted are closed in the electromagnetically unexcited position, for which purpose the return spring  8  arranged above the magnet armature  2  is in each case supported directly on the valve tappet  4 , a section of which is accommodated within a coaxial hole  1  in the magnet armature  2 . By means of suitable electronic analog control, the valve coil to be mounted on the valve housing  14  can in each case be activated in proportion to a current, providing the prerequisite for continuously variable control of the valve flow rate. 
     In order to ensure precise setting of the electromagnetic valves depicted in  FIGS. 1 to 4 , an adjustment sleeve  3 , in which a section of the valve tappet  4  is secured, is in each case fixed in the hole  1  in the magnet armature  2 . By means of the adjustment sleeve  3 , particularly simple, infinitely variable setting of the residual air gap RLS is ensured. 
     In order to prevent unwanted magnetic flux leakages and also “magnetic adhesion” of the magnet armature  2  to the magnet core  5 , the adjustment sleeve  3  is produced from a material which does not conduct the magnetic flux, in particular an austenitic steel. 
     As is clear from all the figures, the adjustment sleeve  3  has an overhang  6  at the end face of the magnet armature  2  facing the magnet core  5 , the axial extent of said overhang corresponding to the residual air gap RLS between the magnet armature  2  and the magnet core  5 , which is to be precisely maintained during electromagnetic excitation. For this purpose, a section of the adjustment sleeve  3  is adjustable to any desired extent in the hole  1  in the magnet armature  2  by means of a sliding interference fit. 
     The valve tappet  4  is fixed in the adjustment sleeve  3  by the same securing method, wherein the depth to which the valve tappet  4  is pressed into the adjustment sleeve  3  is defined by an installation space  7  required for the return spring  8  in the adjustment sleeve  3 . 
     Both the frictional force acting in the sliding interference fit between the adjustment sleeve  3  and the magnet armature  2  and that acting in the sliding interference fit between the adjustment sleeve  3  and the valve tappet  4  are at least equal in magnitude to the mechanical and hydraulic forces acting on the adjustment sleeve  3  and the valve tappet  4  during valve switching. In this context, the adjustment sleeve  3  has two holding sections  9 ,  10 , of which the first holding section  9  includes the interference joint between the outer circumference of the adjustment sleeve  3  and the hole  1 , while the second holding section  10  is defined by the interference joint between the inner circumference of the adjustment sleeve  3  and the valve tappet  4 . 
     It can furthermore be seen from all the figures that, adjoining the first holding section  9 , in the region of the second holding section  10 , an annular space  23  is provided between the adjustment sleeve  3  and the hole  1  in the magnet armature  2 , with the result that a pressure equalizing hole  11  arranged in the adjustment sleeve  3  in the region of transition between the first and second holding sections  10  is in hydraulically pressure equalizing connection via the annular space  23  with an installation space  7  accommodating the return spring  8  in the adjustment sleeve  3 . The annular space  23  furthermore allows a tolerance-compensating radial expansion of the second holding section  10 , thereby favoring the pressing of the valve tappet  4  into the adjustment sleeve  3 . 
     It is furthermore clear from  FIGS. 1 to 4  that the adjustment sleeve  3  is provided at least at one sleeve end with a collar  12  which, according to  FIGS. 2 to 4 , rests locally either as an axial stop on the magnet core  5  or, according to  FIG. 1 , as an armature- and tappet-centering aid on the inner wall of the valve housing  14 , for which purpose the collar  12  of the adjustment sleeve  3  projects below the magnet armature  2 . The collar  12  has a plurality of circumferentially distributed recesses, which allow unhindered compensation of the liquid volume situated above and below the collar  12  in the valve housing  14 . 
     According to  FIG. 1 , the nonmagnetic properties of the adjustment sleeve  3  and of the collar  12  attached thereto advantageously result in nonmagnetic and therefore friction-minimized guidance for the valve tappet  4  and the magnet armature  2  in the valve housing  14 . Since the valve tappet  4  is pressed directly into the nonmagnetic adjustment sleeve  3 , there is therefore no contact with the magnetic material of the magnet armature  2 , with the result that, irrespective of the material chosen, the valve tappet  4  is not subject to any unwanted magnetization, which could have a disadvantageous effect on valve control, the effect being magnetic decoupling. 
     Individual differences between the illustrative embodiments shown in  FIGS. 1 to 4  will be explained below. 
     As already mentioned briefly at the outset,  FIG. 1  shows an extension of the adjustment sleeve  3  below the magnet armature  2  in order to ensure precise guidance of the magnet armature  2  with the valve tappet  4  in the direction of the valve seat  19  in the valve housing  14  by means of the collar  12  formed at the end of the extension. 
     As a departure from  FIG. 1 ,  FIGS. 2 and 4  show an extension of the magnet armature  2  having a plurality of guide ribs  21 , which are supported on the inner wall of the valve housing  14 , to provide precise guidance of the magnet armature  2  and of the valve tappet  4  in the direction of the valve seat  19 . 
     Another modification for precise guidance of the magnet armature  2  with the valve tappet  4  in the direction of the valve seat  19  is shown in  FIG. 3 , according to which a nonmagnetic centering washer  22 , which is provided with pressure equalizing openings and through which the valve tappet  4  extends with a small running clearance, is fixed below the magnet armature  2  in the valve housing  14 . 
     In respect of the construction of the valve housings  14 , it may be mentioned that the electromagnetic valves depicted in  FIGS. 1 to 3  have a solid tubular body  16 , in which the valve seat  19  is press fitted as a separate component. In  FIGS. 1 to 3 , the valve housing  14  is in each case composed of the tubular body  16  and the housing sleeve  15 , which is welded to the tubular body  16 . As a departure from this, the tubular body  16  in  FIG. 4  is connected at the opposite end from the housing sleeve  15  to a further, thin-walled, pot-shaped housing sleeve  17 , with the special feature that the further housing sleeve  17  has a radially encircling collar which is fixed in a recess  18  on the tubular body  6  by plastic deformation by means of a suitable tool. The further housing sleeve  17  is composed of a hardened ferritic material in order to enable the valve seat  19  to be embodied in as wear-free a manner as possible by deep drawing directly on the bottom of the pot-shaped housing sleeve  1  if desired or required, as an alternative to the illustration in  FIGS. 1 to 3 . The valve passage  13  arranged in the valve seat  19  and the passage  20  arranged in the wall of the further housing sleeve  17  can then be produced jointly in a particularly low-cost manner by punching or stamping. 
     The design features presented thus result in an electromagnetic valve, the residual air gap RLS of which can be set in a simple and precise manner by means of the adjustment sleeve  3  press fitted in the hole  1  in the magnet armature  2  since the adjustment sleeve  3  is simply moved until the desired overhang  6  on the upper side of the magnet armature  2  is achieved, the overhang  6  corresponding to the dimension of the residual air gap RLS. 
     In order to be able to compensate for the tolerances which occur in the manufacture of the return spring  8 , setting of the installation space  7  required for the return spring  8  is accomplished in an equally simple and precise manner since the return spring  4  is supported on the end of the valve tappet  4  while the valve tappet  4  is moved continuously in the second holding section  10  of the adjustment sleeve  3  until a defined spring length is achieved. 
     LIST OF REFERENCE SIGNS 
     
         
           1  hole 
           2  magnet armature 
           3  adjustment sleeve 
           4  valve tappet 
           5  magnet core 
           6  overhang 
           7  installation space 
           8  return spring 
           9  holding section 
           10  holding section 
           11  pressure equalizing hole 
           12  collar 
           13  valve passage 
           14  valve housing 
           15  housing sleeve 
           16  tubular body 
           17  housing sleeve 
           18  recess 
           19  valve seat 
           20  passage 
           21  guide rib 
           22  centering washer 
           23  annular space