Abstract:
A seat valve in a motor vehicle wheel slip control system includes a valve tappet acting as a valve closure member, where the valve tappet is movably guided and aligned with a valve seat member by a centering sleeve that guides the valve tappet. The centering sleeve is articulated at the valve seat member.

Description:
TECHNICAL FIELD 
   The present invention relates to a seat valve, in particular an electromagnetically operated seat valve in a motor vehicle wheel slip control system. 
   BACKGROUND OF THE INVENTION 
   DE 101 00 744 A1 discloses a seat valve of the generic type in the shape of a solenoid valve having a valve tappet arranged between the magnetic armature and the valve seat member that is guided in a centering sleeve, which is press fitted to a hollow cylinder stepped in its outside diameter and, as a component of the valve seat member, facing the valve tappet. 
   The smallest radial clearance necessary between the valve tappet and the centering sleeve is influenced by the eccentricity of the sealing edge at the valve tappet in relation to the outside diameter of the hollow cylinder and by the eccentricity of the centering bore in the centering sleeve in relation to the attachment of the centering sleeve at the outside diameter of the hollow cylinder. The result is the necessity and the disadvantage that the minimum radial clearance required for the self-centering of the valve tappet generally must be selected to be large. With an increasing radial clearance in the centering sleeve, however, the valve noise increases, which is based on the transverse force active at the magnet armature and causing an undesirable armature offset during electromagnetic energization and, thus, an undesirable structure-borne noise. 
   Therefore, an object of the invention is to improve a seat valve of the generic type in such a way that the above-mentioned shortcomings are avoided, while maintaining a design as simple as possible. To this end it is required to diminish the minimum radial clearance in the centering sleeve. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal cross-section taken through a solenoid valve that is closed in its non-energized basic position. 
       FIG. 2  is an enlarged view of the details of the solenoid valve illustrated in  FIG. 1  that are essential for the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a solenoid valve that is closed in its non-energized basic position and whose valve housing  1  exemplarily has a cartridge-type construction. The mid-portion of valve housing  1  is configured as a thin-walled valve sleeve  2 , which is seal-tightly closed by means of a plug-shaped magnet core  3 . 
   When desired or required, the valve sleeve  2  can be closed like a dome, in contrast to  FIG. 1 , so that then the cylindrical magnet core  3  without a sealing function is secured in the dome area. 
   For the purpose of analog operation of the solenoid valve, an annular-disc-shaped spring element  4  is disposed below the magnet core  3  in the present invention and bears loosely against the outside edge of the concavely shaped end surface of the piston-shaped magnet armature  5 . In consideration of the magnet armature stroke, the thickness of the spring element  4  corresponds to the necessary dimensions of the residual air slot of the magnet armature so that in the electromagnetically non-energized valve switching position according to the drawings, the spring element  4  has an axial distance to the convexly shaped end surface of the magnet core  3 . 
   The magnet armature  5  accommodates within a stepped bore  13  a per se known spring  6  which, in its capacity as a compression spring, extends with its one coil end through the opening in the spring element  4  towards the end surface of the magnet core  3 . Consequently, the magnet armature  5  is urged, under the effect of spring  6 , at the opposed magnet armature end surface with the valve tappet  7  against a valve seat member  8  in the valve housing  1 , with the result that a pressure fluid channel  9  that extends through the valve housing  1  in horizontal and vertical directions is interrupted in the electromagnetically non-energized valve position. The valve tappet  7  active in the function of a valve closure member is fixed by means of a press fit in the stepped bore  13  of the magnet armature  5  and centered at its end portion facing the valve seat member  8  in a centering sleeve  10  in the direction towards the sealing seat  20 . Likewise the sleeve-shaped valve seat member  8  is attached by means of a press fit in the pressure fluid channel  9  of the cartridge-like valve housing  1 . The centering sleeve  10  is penetrated by transverse bores  23  above the sealing seat  20  in order to allow in the open position of the valve tappet  7  a simplest possible pressure fluid connection to the pressure fluid channel  9  provided as a valve inlet and outlet channel in the valve housing  1 . Above the transverse bores  23  is the sleeve portion of the centering sleeve  10  envisaged for guiding the valve tappet  7  and having an inside diameter that is adapted to the diameter of the valve tappet  7 . Another objective of the sleeve portion is to accommodate the assembly force exerted by means of an assembly tool  22  for fastening the centering member  10  to the valve seat member  8 , as can be seen in  FIG. 2 . 
   Further, the valve tappet  7  includes a disc-shaped step  15  on which the end of spring  6  remote from magnet core  3  is supported. A guiding pin  16  that extends into the spring  6  designed as a helical spring succeeds the step  15  in the direction of the magnet core  3 . In order to radially support spring  6  so that lateral buckling of spring  6  is prevented, the diameter of the guiding pin  16  is chosen to be only slightly smaller than the inside diameter of the spring  6  designed as a helical spring. 
   Guiding the spring  6  directly at the guiding pin  16  instead of in bore  13  is advantageous in terms of manufacturing technology because the guiding pin  16  is easier to finish than the bore wall, when required. A transition area  17  is provided between the step  15  and the guiding pin  16  for the operative and/or form-locking attachment of the end of spring  6  facing the valve tappet  7 . The transition area  17  is produced by an annular groove into which the one end of spring  6  is snapping. The spring  6  pertaining to the valve tappet  7  is held captive thereby. It forms a pre-assembled and already exactly adjusted subassembly in conjunction with the valve tappet  7  inserted into the magnet armature  5 . 
   The magnetic circuit can be closed by energizing a valve coil  11  fitted to the valve housing  1  and a yoke ring  12  enclosing valve coil  11  so that the magnet armature  5  moves in the direction of the magnet core  3 . The result is that the interposed spring element  4  is elastically deformed and moves to abut on the magnet core  3  where it abuts with its full surface on the inclined end surfaces of the magnet core  3  and the magnet armature  5 . The magnet armature  5  is automatically slowed down due a spring force of spring element  4  that is opposed to the movement of the magnet armature  5 , before it can urge the spring element  4  against the end surface of the magnet core  3 . 
   Designing the spring element  4  as a particularly flat spring washer or also as a cup spring advantageously results in a progressive spring characteristic curve which, in addition to the actual design of the solenoid valve as a two-position valve, permits a functional extension of a two-position valve as a solenoid valve of analog or proportional operation which is surprisingly simple especially in terms of control technique. The progressive spring element  4  quasi effects a linearization of the magnet armature force. 
   Upon termination of the electromagnetic energization, the preloading force of the spring element  4  additionally brings about a quickest possible resetting of the magnet armature  5  out of the end position at the magnet core  3  because the so-called sticking of the magnet armature on the magnet core, which is normally caused by remanence, is omitted due to the resetting tendency of the spring element  4 . 
   Irrespective of the embodiment and mode of operation of the above-mentioned solenoid valve chosen, be it as a two-position valve of binary operation or a valve of analog operation, the invention provides that the centering sleeve  10  is articulated at the valve seat member  8 . 
   According to an enlarged illustration of  FIG. 2 , the valve seat member  8  has a stepped sleeve portion  14  whose peripheral surface has either a concave or a convex shape in the area of contact with the inside wall of the stepped centering sleeve  10  in order to constitute a hinge connection (comparable with a Cardan joint). 
   The centering sleeve  10  along with the sleeve portion  14  establishes a press fit connection in the area of the hinge connection  19 , and the friction force prevailing in the press fit connection is at least as high as a transverse force acting at the valve tappet  7  during the electromagnetically energized valve stroke. The friction force chosen in a corresponding quantity prevents an inadvertent readjustment after the single centering operation of the centering sleeve  10  in relation to the sealing seat  20 . The coaxial alignment of the centering sleeve  10  with respect to the sealing seat  20  is carried out in a simple, yet nevertheless precise manner by means of a plug gauge  21 . 
   To maintain a minimum guiding clearance of the valve tappet  8  in the centering sleeve  10 , the diameter of the plug gauge  21  corresponds to the maximum outside diameter of the valve tappet  1  plus the double maximum eccentricity of the spherical segment in relation to the stem of the valve tappet  7 . 
   The hinge connection  19  is configured as a spherical joint, to what end a spherical part shaped as a spherical segment is formed at the sleeve portion  14  of the valve seat member  8  onto which the centering sleeve  10  is seated. 
   The hinge connection  19  is arranged at the outside periphery of the valve seat member  8 , namely at the level of the funnel-shaped sealing seat  20  which is provided at an end of the valve seat member  8  facing the valve tappet  7 . 
   In  FIG. 2 , the centering sleeve  10  fastened at the valve seat member  8  and provided for the solenoid valve illustrated in  FIG. 1  is shown directly after the completion of the assembly and the adjustment of the centering sleeve  10  by means of the plug gauge  21  that bears against the sealing seat  20  and centers the assembly tool  22  of tubular design. To illustrate the chosen large-size outside diameter of the plug gauge, the smaller-diameter valve tappet  7  is further indicated in sections (however, not in a correct scale) in dotted lines in an eccentric position, the valve tappet&#39;s valve closure member exhibiting the shape of a spherical segment that abuts on the sealing seat  10 . 
   The plug gauge  21  is used to center the centering sleeve  10  in relation to the sealing seat  20 , said plug gauge being aligned coaxially in relation to the sealing seat  20  and being pressed against the spherical sealing seat  20  by means of a spring that is symbolically shown. Subsequently, the centering sleeve  10  is displaced along the plug gauge  21  by means of an assembly tool  22 , and the necessary displacement force of the assembly tool  22  is chosen at such a rate that the desired frictional fixation of the hinge connection  19  to be provided between the centering sleeve  10  and the valve seat member  8  is achieved. Thereafter, the plug gauge  21  with the assembly tool  22  is removed so that the subassembly composed of the valve seat member  8  and the centering sleeve  10  can be inserted into the valve housing  1 . 
   In the present embodiment, the tubular valve seat member  8  includes a spherical or crowned swivel head at the level of the sealing seat  20 . Constructive modifications are also possible without departing from the idea of the invention for designing a hinge connection  19  between the valve seat member  8  and the centering sleeve  10 .