Abstract:
A pressure control valve arrangement is described for controlling the fluid pressure in an ABS brake system of a vehicle in such a manner that, in the event of a tendency of individual wheels of the vehicle to lock, the brake pressure in associated brake cylinders can be adaptively adjusted, at least two diaphragm valves which have diaphragms loaded by spring elements, as well as at least one electromagnetic control valve which can be activated by an electronic control device for the pilot control of the diaphragm valves. Also described is a method for producing the pressure control valve arrangement.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a pressure control valve arrangement for controlling the fluid pressure in an ABS brake system of a vehicle in such a manner that, in the event of a tendency of individual wheels of the vehicle to lock, the brake pressure in associated brake cylinders can be adaptively adjusted, at least two diaphragm valves which have diaphragms loaded by spring elements, as well as at least one electromagnetic control valve which can be activated by an electronic control device for the pilot control of the diaphragm valves, and to a method for producing said pressure control valve arrangement. 
     BACKGROUND INFORMATION 
     ABS (anti-lock system) prevents locking of the wheels and comes into operation when there is a demand for a greater frictional connection between a tire and the road surface than can be transmitted, that is, when the driver over-brakes. In the event of over-braking, the central electronic control unit of the ABS brake system detects the tendency of one or more wheels to lock from rotational speed sensor signals and calculates therefrom the activation of the pressure control valve arrangement acting on the associated brake cylinder. The brake pressure is then adjusted by means of the pressure control valve arrangement to an optimal slip, the brake pressure being reduced, maintained or built up according to the wheel behavior and therefore according to the frictional relationship between tire and road surface. 
     A generic pressure control valve arrangement of an ABS brake system is discussed in German patent document DE 101 56 773 A1. For ABS brake systems of vehicles, single-channel pressure control valves with and without a relay effect are generally used. Pressure control valve arrangements with a relay effect are used in semitrailers and draw-bar trailers. ABS pressure control valve arrangements without a relay effect, to which the present invention relates, find application in all other vehicles, for example in utility vehicles, buses and semitrailer tractors as well as in trailers. Pressure control valve arrangements without a relay effect make use of 3/2-way solenoid valves as pilot control valves of diaphragm valves, an electronic control device activating the 3/2-way solenoid valves in order to be able to execute the functions “maintain pressure”, “reduce pressure” and “build up pressure” necessary for ABS operation. During a braking operation without an ABS response (no tendency of a wheel to lock), the pressure medium, usually air, flows through the pressure control valve arrangements unimpeded in both directions as the brake cylinders are pressurized and vented. It is thereby ensured that the operation of the service brake system is not influenced by the ABS pressure control valve arrangement. 
     SUMMARY OF THE INVENTION 
     It is an object of the exemplary embodiments and/or exemplary methods of the present invention to develop a pressure control valve arrangement of the type mentioned in the introduction in such a manner that it is simpler to produce and assemble. At the same time, a corresponding method for producing such a pressure control valve arrangement is to be specified. 
     This object may be achieved according to the exemplary embodiments and/or exemplary methods of the present invention by the features described herein. 
     The present invention provide for openings for inserting or inlaying diaphragms are provided in a surface of a housing part of the housing, and edges of the diaphragms are held between opening edges of the openings and a further housing part of the housing, the opening edges of the openings lying in a common plane or in parallel planes and the surface normals of the opening edges of the openings being oriented in the same direction. 
     “A” surface should be understood here to mean a single unified surface of the housing component, that is, for example, a lateral surface, an end surface or a bottom surface. 
     A “surface normal” should be understood here to mean a perpendicular erected on the corresponding free surface which is oriented away from or projects away from this free surface. 
     A pressure control valve arrangement having these features can then be at least partially produced and assembled in a simple manner using the following steps:
         a) molding the at least two diaphragms,   b) arranging the one housing part in such a manner that the surface normals of the opening edges of the openings are parallel to an assembly direction,   c) placing the diaphragms of the diaphragm valves, in the assembly direction, into the openings in such a manner that the diaphragm edges rest on the opening edges, and then   d) placing the spring elements on the diaphragms in the assembly direction,   e) placing the further housing part onto the one housing part in the assembly direction in such a manner that, on the one hand, the diaphragm edges are fixed between the one housing part and the further housing part and, on the other hand, the spring elements bear against the diaphragms and the further housing part.       

     The diaphragms may be produced from an elastomer by molding, whereby, after being removed from the mold, they are optionally joined to one another by injected-on seals made of elastomer. 
     Because the openings for the diaphragms are arranged side-by-side on a surface, while the opening edges of the openings lie in a common plane (coplanarly) or in parallel planes and the surface normals of the opening edges of the openings are also oriented in the same direction, the diaphragms, optionally joined by injected-on seals, can be introduced into or inlaid into the openings from a single side, which may be from above. These measures simplify the production and assembly of a pressure control valve arrangement as compared to solutions of the prior art, in which the openings for the diaphragms are arranged on different surfaces of the housing, and assembly of the diaphragms is therefore possible only from several assembly directions, necessitating, for example, a resetting of the housing in the tool and a larger number of assembly steps. 
     Furthermore, no further components are needed to hold the edges of the diaphragms in the housing, as they are fixed between the one housing part and the further housing part, for example by a press fit. 
     The measures set forth herein provide for advantageous developments or improvements of the present invention specified herein. 
     According to an exemplary measure, all the screw connections for the fluid lines connected to the pressure control valve arrangements are formed in the housing part having the openings for the diaphragms, this housing part being formed by a light alloy die casting. Especially, this housing part may consist of a pressure die-cast aluminum component. In that case the strength and stiffness of the material are sufficiently high for threaded connections for fluid lines to be provided directly, that is without the provision of inserts, in the housing part. 
     According to a development, the spring elements which load the diaphragms of the diaphragm valves bear at one end centrally against the diaphragms and at the other against the further housing part, blind bores facing towards the one housing part for at least partially receiving the spring elements being provided in the further housing part. By means of the blind bores, the spring elements are automatically centered on the one housing part and fixed in their assembled position upon installation of the further housing part. 
     Especially, the further housing part may be formed by a plastics injection molding, at least one valve seat of the at least one electromagnetic control valve being formed integrally with the further housing part. After being molded together with the further housing part, this valve seat then no longer needs to be processed, for example machined, as the surface quality or roughness of an injection-molded plastics material meets the sealing demands placed on such a valve seat. Inserts forming the valve seat as additional components therefore become superfluous, resulting in an advantageous reduction in the number of components of the pressure control valve arrangement. 
     According to a development, the further housing part forming the valve seat is arranged between the one housing part having the screw connections and the openings for the diaphragms and another housing part, in which the at least one electromagnetic control valve is at least partially received. 
     This other housing part may also be a plastics injection molding in which at least one magnetic coil of the at least one electromagnetic control valve is molded integrally. 
     This other housing part may be provided with at least one through-bore for inserting components of the at least one electromagnetic control valve, such as an armature or a magnetic core, a central axis of the through-bore being arranged parallel to the surface normals of the opening edges of the openings for the diaphragms in the one housing part. The at least one through-bore of the other housing part may be closed by a cover. 
     The at least one valve seat associated with the electromagnetic control valve is then advantageously formed on a surface of the further housing part facing towards the other housing part. 
     On the basis of the above-described configuration of the components of the pressure control valve arrangement, the method for the production thereof then comprises at least the following further steps:
         f) producing at least one valve seat of the at least one electromagnetic control valve in the further housing part, in a surface which faces towards the other housing part,   g) producing at least one through-bore in the other housing part of the housing for receiving components of the at least one electromagnetic control valve, such as an armature and/or a magnetic core, a central axis of the through-bore being disposed parallel to the surface normals of the opening edges of the openings for the diaphragms in the one housing part, or parallel to the assembly direction,   h) inserting the components of the at least one electromagnetic control valve into the through-bore in the other housing part in the assembly direction,   j) placing the other housing part on the further housing part in the assembly direction in such a manner that the at least one valve seat in the further housing part can cooperate with the components of the at least one electromagnetic control valve arranged in the other housing part.       

     All the essential components of the pressure control valve arrangement, such as the housing parts, the diaphragm valves and the at least one electromagnetic control valve, can then be installed from a single assembly direction, which may be vertically and from above, which has the advantage that resetting in the tool is not necessary during assembly. The assembly direction of the pressure control valve arrangement is therefore defined in particular by the direction of the surface normals of the opening edges of the openings in the one housing part, since the diaphragms are placed in the openings in this direction. 
     Especially, the housing of the pressure control valve arrangement may consists solely or exclusively of the one housing part, the further housing part and the other housing part. This measure also leads to an advantageously low number of components of the inventive pressure control valve arrangement, which may be a single-channel pressure control valve arrangement. 
     Further measures improving the exemplary embodiments and/or exemplary methods of the present invention are set out in more detail below together with the description of an exemplary embodiment of the present invention with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a basic diagram of an ABS brake system as a general schema of a 4S/4K ABS brake system of a vehicle. 
         FIG. 2   a  shows a schematic representation of a pressure control valve arrangement activating a brake cylinder in the open state (pressure build-up). 
         FIG. 2   b  shows a schematic representation of the pressure control valve arrangement of  FIG. 2   a  in the closed state (pressure reduction). 
         FIG. 3  shows a cross-sectional representation of a concrete configuration of the pressure control valve arrangement of  FIG. 2   a  and  FIG. 2   b  according to an exemplary embodiment of the present invention. 
         FIG. 4  shows a cross-sectional representation along the line IV-IV of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIG. 1 , a vehicle equipped with an ABS brake system comprises a front axle  1  and a rear axle  2 . Wheels  3   a  and  3   b  are arranged on the front axle  1 ; the rear axle  2  has, for example, wheels  4   a  and  4   b  each equipped with twin tires. The ABS brake system serving to brake these wheels  3   a ,  3   b  and  4   a ,  4   b  is here in the form of a 4S/4K (four sensors, four channels) system. This means that in this case a total of four rotational speed sensors  5   a - 5   d  and four pressure control valve arrangements  7   a - 7   d  are available. The pressure control valve arrangements  7   a - 7   d  are used to activate respective associated brake cylinders  6   a - 6   d . All the pressure control valve arrangements  7   a - 7   d  are connected to a foot brake valve  9  via a branching pneumatic brake pressure line  8 . 
     Upon actuating the foot brake valve  9 , the driver generates a brake pressure which, via the pneumatic brake pressure line  8  and passing through the pressure control valve arrangements  7   a - 7   d , is transmitted to the brake cylinders  6   a - 6   d  associated with the wheels  3   a ,  3   b  and the wheels  4   a ,  4   b.    
     The pressure control valve arrangements  7   a - 7   d  can be activated via integrated electromagnetic valves  15   a ,  15   b  shown in  FIG. 2   a ,  FIG. 2   b  and  FIG. 4 , and for this purpose are connected electrically to a central electronic control unit  10 . The electronic control unit  10  is connected on the input side to the four rotational speed sensors  5   a - 5   b  which detect the wheel speeds. In the event of locking of a wheel  3   a - 3   d , the brake pressure induced by the driver via the foot brake valve  9  is reduced by the corresponding pressure control valve arrangement  7   a - 7   d  according to an ABS control system as determined by the electronic control unit  10  until the locking is eliminated. The ABS brake system of the present exemplary embodiment further includes an ASR (anti-slip) function which includes an ASR unit  11  for reducing the engine torque, together with an ASR solenoid valve  12  and a shuttle valve  13 . 
     The pressure control valve arrangement  7  as shown in  FIG. 2   a , which is used for the purpose of ABS control in the context of the ABS brake system, is constructed in this case in the manner of a 1-channel pressure control valve arrangement and consists essentially of two integrated diaphragm valves  14   a  and  14   b , and two spring-loaded electromagnetic valves  15   a ,  15   b  activating said diaphragm valves  14   a  and  14   b . The diaphragm valves  14   a  and  14   b  are each loaded in the closing direction by respective spring elements  16   a ,  16   b  and are pilot-controlled by means of the respective associated electromagnetic valves  15   a  and  15   b.    
       FIG. 2   a  shows the pressure control valve arrangement  7  in its open position, in which pressure is built up to the connected brake cylinder  6 . In this case neither of the electromagnetic valves  15   a  and  15   b  is electrically activated. In the position shown, the compressed air coming from the foot brake valve  9  presses the diaphragm valve  14   a  configured as the inlet valve open. The normally closed electromagnetic valve  15   a  prevents the associated diaphragm valve  14   a  from being closed again. Through the normally open second electromagnetic valve  15   b  the brake pressure coming from the foot brake valve  9  closes the second diaphragm valve  14   b  serving as the outlet valve. The compressed air therefore passes through the pressure control valve arrangement  7  unimpeded. The pressure control valve arrangement  7  is also in this state when no ABS control is taking place. 
     In order to keep the brake pressure constant in a brake cylinder  6   a  to  6   d , only the electromagnetic valve  15   a  has to be energized, whereby said electromagnetic valve  15   a  opens and the brake pressure coming from the foot brake valve  9  consequently presses the inlet-side diaphragm valve  14   a  shut. The pressure on the right and left side of the diaphragm valve  14   a  is now equal. But because the effective area on the left-hand side of the diaphragm valve  14   a  is greater, the diaphragm valve  14   a  is closed. The corresponding situation applies to the outlet-side diaphragm valve  14   b  which is activated via the electromagnetic valve  15   b . In order to maintain the pressure constant, therefore, the pressure control valve arrangement  7  closes the pneumatic brake pressure line  8  running from the foot brake valve  9  to the brake cylinder  6 . 
     As shown in  FIG. 2   b , a pressure reduction in a brake cylinder  6   a  to  6   d  is effected in that both electromagnetic valves  15   a  and  15   b  are energized. What was described above regarding the maintaining of pressure applies to the electromagnetic valve  15   a  and the associated inlet-side diaphragm valve  15   a . By contrast, the other electromagnetic valve  15   b  is closed as a result of the energization. The pressure coming from the brake cylinder  6  therefore presses the outlet-side diaphragm valve  14   b  open and the brake cylinder  6  is vented. 
     The above-described operations of the pressure control valve arrangement  7  are executed as determined by the electronic control unit  10  in the context of an ABS/ASR control system of the type described in the introduction. 
       FIG. 3  and  FIG. 4  show the pressure control valve arrangement  7 , represented only schematically in  FIG. 2   a  and  FIG. 2   b , in a concrete embodiment and in the installed position; that is to say that the components shown at the top are located at the top. In this embodiment the two electromagnetic valves  15   a ,  15   b  for pilot control of the diaphragm valves  14   a ,  14   b  are combined in a double solenoid valve, the function of which, however, is analogous to that of single valves  15   a ,  15   b.    
     Two adjacently arranged openings  19   a ,  19   b  for the insertion or inlaying of diaphragms  20   a ,  20   b  of the diaphragm valves  14   a ,  14   b  are provided in an upper surface of a lower housing part  17 , as shown in  FIG. 3  and  FIG. 4 , of a housing  18  of the pressure control valve arrangement  7 . In this case the central axes  21   a ,  21   b  of the openings  19   a ,  19   b  are parallel to one another and aligned vertically. The diaphragms  20   a ,  20   b  each cooperate with a respective diaphragm valve seat  45   a ,  45   b , a flow cross-section of a fluid passage  46   a ,  46   b  being opened or closed by a diaphragm  20   a ,  20   b , depending on whether the diaphragm  20   a ,  20   b  is seated on the diaphragm valve seat  45   a ,  45   b  or lifted therefrom. 
     The diaphragm edges  22   a ,  22   b  of the diaphragms  20   a ,  20   b  are held between opening edges  23   a ,  23   b  of the openings  19   a ,  19   b  and a further housing part  24  of the housing  18  of the pressure control valve arrangement  7 , the opening edges  23   a ,  23   b  of the openings  19   a ,  19   b  which may lay in a common plane and the imaginary surface normals of the opening edges  23   a ,  23   b  of the openings  19   a ,  19   b , the direction of which is represented by the arrow  44  in  FIG. 3  and  FIG. 4 , being oriented in the same direction, here upwardly. Alternatively, the opening edges  23   a ,  23   b  of the openings  19   a ,  19   b  might also lie in parallel planes, which in the present case would mean that they would be arranged with a vertical offset according to  FIG. 3 . 
     The diaphragms  20   a ,  20   b  may be produced by molding from an elastomer such as NBR, and may optionally be joined to one another by injected-on seals. 
     The further housing part  24  consists, for example, of an intermediate plate which is in contact with an upper surface  25 , having the openings  19   a ,  19   b  for the diaphragms  20   a ,  20   b , of the lower housing part  17 , and is fastened to the lower housing part  17 , which may be by being screwed thereto. 
     All of the screw connections for fluid lines to be connected to the pressure control valve arrangement  7  are formed in the housing part  17 , shown at the bottom in  FIG. 3  and  FIG. 4 , which includes the openings  19   a ,  19   b  for the diaphragms  20   a ,  20   b , this lower housing part  17  being formed by a light alloy die casting. Especially, the lower housing part  17  may consist of an aluminum die casting. One of these screw connections  26  is shown as an example in  FIG. 3 . These screw connections  26  may be produced directly—that is, without the provision of threaded inserts—in the lower housing part, for example by tapping. 
     The spring elements  16   a ,  16   b  which load the diaphragms  20   a ,  20   b  of the diaphragm valves  14   a ,  14   b  bear at one end centrally against the diaphragms  20   a ,  20   b , for example by means of centering pegs  28   a ,  28   b  projecting from the diaphragms  20   a ,  20   b , and at the other end against the intermediate plate  24 . In order to receive at least partially the spring elements  16   a ,  16   b , the intermediate plate  24  is provided with blind bores  29   a ,  29   b  facing towards the lower housing part  17 . The spring elements  16   a ,  16   b  are, for example, helical springs with what may be vertical spring central axes, so that the direction of movement or action of the diaphragms  20   a ,  20   b  is parallel to an assembly direction to be explained later. Upon installation of the intermediate plate  24 , therefore, the spring elements  16   a ,  16   b  are automatically centered both on the lower housing part  17  and on the intermediate plate  24  and fixed in their installed position. 
     Especially, the intermediate plate  24  may be formed by a plastics injection molding, for example of polyamide, valve seats  30   a ,  30   b  of the electromagnetic valves  15   a ,  15  being formed integrally with the intermediate plate  24 . As is apparent, in particular, from  FIG. 4 , the valve seats  30   a ,  30   b  have a conical configuration in that the surface  43 , having the valve seats  30   a ,  30   b , of the intermediate plate  24  is provided with annular blind bore recesses  31   a ,  31   b . Vertically disposed fluid passages  32   a ,  32   b  open in the port region in the region of the valve seats  30   a ,  30   b.    
     The intermediate plate  24  which forms the valve seats  30   a ,  30   b  is arranged between the lower housing part  17 , which includes the screw connections  26  and the openings  19   a ,  19   b  for the diaphragms  20   a ,  20   b , and an upper housing part  33 , shown at the top in  FIG. 3  and  FIG. 4 , in which housing part  33  the components of the electromagnetic valves  15   a ,  15  are received, with the exception of the valve seats  30   a ,  30   b  formed in the intermediate plate  24 . The valve seats  30   a ,  30   b  of the two electromagnetic valves  15   a ,  15   b  are formed on the surface  43  of the intermediate plate  24  facing towards the upper housing part  33 . 
     The upper housing part  33  may be provided with two through-bores  34   a ,  34   b  for the insertion of components of the electromagnetic valves  15   a ,  15   b , such as their armatures  35   a ,  35   b  and magnetic cores  40   a ,  40   b , the central axes  36   a ,  36   b  of the through-bores  34   a ,  34   b  being arranged parallel to the surface normals, which are oriented in the direction of the arrow  44 , of the opening edges  23   a ,  23   b  of the openings  19   a ,  19   b  in the lower housing part  17 . Furthermore, the central axes  36   a ,  36   b  of the through-bores  34   a ,  34   b  are disposed coaxially with the valve seats  30   a ,  30   b.    
     The through-bores  34   a ,  34   b  of the upper housing part  33  are closed by a cover  37 , which may be a stamping of sheet steel. Furthermore, the upper housing part  33  is, for example, a plastics injection molding in which the two magnetic coils (not visible in the figures) of the electromagnetic valves  15   a ,  15   b  are molded integrally. The magnetic coils of the electromagnetic valves  15   a ,  15   b  may be activated by the electronic control unit  10  via the plug connector housing  38  arranged on the upper housing part  33 . 
     The armatures  35   a ,  35   b  of the electromagnetic valves  15   a ,  15   b  are guided movably in a vertical direction, that is, parallel to the surface normals  44  of the opening edges  23   a ,  23   b  of the openings  19   a ,  19   b  for the diaphragms  20   a ,  20   b , in the through-bores  34   a ,  34   b  of the upper housing part  33 , closing elements  39   a ,  39   b  made of an elastomer being arranged, for example, on the ends facing towards the valve seats  30   a ,  30   b . Depending on the energizing of the magnetic coils of the electromagnetic valves  15   a ,  15   b , the armatures  35   a ,  35   b  therefore adopt a vertical position in which the closing elements  39   a ,  39   b  contact the valve seats  30   a ,  30   b  and therefore close the corresponding fluid passages  32   a ,  32   b , or in which they are lifted from the valve seats  30   a ,  30   b  and therefore open a flow cross section. The stroke of the armatures  35   a ,  35   b  is limited by the magnetic cores  40   a ,  40   b  which are inserted in the through-bores  34   a ,  34   b  from above and fixed therein. The armatures  35   a ,  35   b  are preloaded in the direction of the valve seats  30   a ,  30   b  by spring elements  41   a ,  41   b  which bear at one end against the armatures  35   a ,  35   b  and at the other against the upper housing  33 . 
     Especially, the housing  18  of the pressure control valve arrangement  7  may consist solely or exclusively of three housing parts, namely the lower housing part  17 , the intermediate plate  24  and the upper housing part  33 . These three housing parts  17 ,  24  and  33  are, for example, screwed to one another, fluid carrying channels being sealed by seals  42  at the parting planes of the housing parts. 
     The pressure control valve arrangement  7  is then assembled, here and which may be from above, using at least the following steps, which are carried out in a single, here vertical, assembly direction, without the need for resetting in the tool:
         a) molding the diaphragms  20   a ,  20   b  of the two diaphragm valves  14   a ,  14   b , the diaphragms  20   a ,  20   b  optionally being connected to one another for production reasons by seals (not shown here) which are injected-on or injection molded integrally,   b) producing the valve seats  30   a ,  30   b  of the electromagnetic valves  15   a ,  15   b  in the intermediate plate  24 , in the surface  43  which faces towards the upper housing part  33 ,   c) producing the through-bores  34   a ,  34   b  in the upper housing part  33  of the housing  18  for receiving components of the electromagnetic valves  15   a ,  15   b , such as the armatures  35   a ,  35   b  and the magnetic cores  40   a ,  40   b , the central axes  36   a ,  36   b  of the through-bores  34   a ,  34   b  being disposed parallel to the surface normals  44  of the opening edges  23   a ,  23   b  of the openings  19   a ,  19   b  in the lower housing part  17 ,   d) arranging or clamping the lower housing part  17  in such a manner that the surface normals  44  of the opening edges  23   a ,  23   b  of the openings  19   a ,  19   b  are oriented upwards,   e) placing the diaphragms  20   a ,  20   b  of the diaphragm valves  14   a ,  14   b  from above in the openings  19   a ,  19   b  of the lower housing part  17  in such a manner that the diaphragm edges  22   a ,  22   b  rest on the opening edges  23   a ,  23   b , and   f) optionally removing the injected-on or integrally injection molded seals connecting the diaphragms  20   a ,  20   b,      g) placing the spring elements  16   a ,  16   b  on the diaphragms  20   a ,  20   b  and inserting the spring elements  16   a ,  16   b  in the blind bores  29   a ,  29   b  of the intermediate plate  24 ,   h) placing the intermediate plate  24  on the lower housing part  17  in such a manner that, on the one hand, the diaphragm edges  22   a ,  22   b  are clamped or fixed between the lower housing part  17  and the intermediate plate  24  and, on the other, the spring elements  16   a ,  16   b  bear against the diaphragms  20   a ,  20   b  and the intermediate plate  24 ,   i) inserting the components of the electromagnetic valves  15   a ,  15   b , such as the armatures  35   a ,  35   b  and the magnetic cores  40   a ,  40   b , from below in the through-bores  34   a ,  34   b  of the upper housing part  33 ,   j) placing the upper housing part  33  from above on the intermediate plate  24 , in such a manner that the valve seats  30   a ,  30   b  in the intermediate plate  24  can cooperate with the armatures  35   a ,  35   b  of the electromagnetic valves  15   a ,  15   b.          

     THE LIST OF REFERENCES IS AS FOLLOWS 
     
         
           1  Front axle 
           2  Rear axle 
           3  Wheel 
           4  Wheel 
           5  Rotational speed sensor 
           6  Brake cylinder 
           7  Pressure control valve arrangement 
           8  Brake pressure line 
           9  Foot brake valve 
           10  Control unit 
           11  ASR unit 
           12  ASR solenoid valve 
           13  Shuttle valve 
           14  Diaphragm valve 
           15  Electromagnetic valve 
           16  Spring element 
           17  Lower housing part 
           18  Housing 
           19  Openings 
           20  Diaphragms 
           21  Central axes 
           22  Diaphragm edges 
           23  Opening edges 
           24  Intermediate plate 
           25  Surface 
           26  Screw connection 
           28  Centering peg 
           29  Blind bore 
           30  Valve seats 
           31  Blind bore recesses 
           32  Fluid passages 
           33  Upper housing part 
           34  Through-bores 
           35  Armature 
           36  Central axis 
           37  Cover 
           38  Plug connector housing 
           39  Closing elements 
           40  Magnetic cores 
           41  Spring elements 
           42  Seals 
           43  Surface 
           44  Surface normal 
           45  Diaphragm valve seat 
           46  Fluid passage