Abstract:
A two-stage solenoid valve for an electropneumatic valve control unit, e.g., a pilot control unit of a pressure modulator, includes a solenoid system to which a first and second current intensity can be applied as well as a solenoid valve device with a primary side connectable to a first compressed-air supply and a secondary side connectable to a second compressed-air supply. A primary valve encompassing an adjustable primary armature biased by a primary armature spring is provided on the primary side, and a secondary valve encompassing an adjustable secondary armature biased by a secondary armature spring is provided on the secondary side. The solenoid valve device can be a valve cartridge insertable from one side. Diameters of a front (in relation to insertion direction) region and a central region of the valve cartridge are smaller than or equal to the diameter of a rear region of the valve cartridge.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a two-stage solenoid valve for an electropneumatic valve control unit, especially, for a pilot control unit of a pressure modulator. 
     BACKGROUND OF THE INVENTION 
     DE 10 2004 035 763 A1 describes a solenoid valve of the general type under consideration, which is provided as the valve control unit for two brake ducts of an electropneumatic brake system. An air admission valve having a primary armature and a vent valve having a secondary armature are provided in one valve unit, the two magnet armatures having a common armature guide arrangement and a common solenoid system and being switched at different current intensities. Thus, air can be admitted to the downstream wheel module, the input pressure can be held and venting can be achieved by means of a common solenoid system. 
     The two-stage solenoid valve of DE 10 2004 035 763 A1 is assembled from both sides into the housing of the pilot control unit. Thus, armatures having an armature spring, armature guide tube with core and valve seat, respectively, are introduced from the primary or secondary side, respectively, into the common coil. The respective cores are pressed together in the middle. Closing elements fix the frame interiors of the solenoid systems of the plurality of valve units. 
     DE 100 09 116 A1 describes a valve device for the pilot control unit of a brake pressure modulator in a trailer having an electronic brake system. The solenoid valves are constructed as cartridge solenoid valves, with the valve cartridge placed in a housing having a solenoid. First, this solenoid is introduced into the housing, and then the valve cartridge is inserted into and joined to the housing. 
     SUMMARY OF THE INVENTION 
     Generally speaking, it is an object of the present invention to provide a two-stage solenoid valve for an electropneumatic control unit, wherein the valve permits safer operation and rapid, simple assembly. 
     A solenoid valve of this type can be provided, in particular, in the pilot control unit of a brake modulator, which, with its solenoid valves, activates an air-flow-boosting relay valve, which, in turn, can activate one or more ducts. For use in an electropneumatic brake system, such as an electronically regulated brake system (EBS) for vehicle trailers, wheel brake modules having brake cylinders for the wheel brakes are activated by the relay valve. 
     In accordance with exemplary embodiments of the present invention, a valve cartridge is provided that, by virtue of its cross section, which tapers to one side, can be introduced from one side. The valve cartridge can be inserted, in particular, as a stepped body into the magnet system, together with housed movable parts, such as, for example, armatures and springs. 
     The present invention offers several advantages. 
     The valve cartridge requires little space, is inexpensive and, advantageously, has low susceptibility to improper assembly. 
     Assembly from one side is possible, with simple options for fastening the magnet internals. Thereby, the receiving housing, such as, for example, a pilot control unit, is simpler. 
     Pre-assembled and pre-tested units can be built in. Thus, repair is also made easier. 
     Thermal expansion of the surrounding housing has no influence on the stroke tolerances and the armature forces. 
     Compared with conventional split cores, the one-piece core has the advantage that the magnetic flux is not hindered by a compression joint. The magnetic behavior remains constant over the number of pieces. 
     Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification. 
     The present invention accordingly comprises the features of construction, combination of elements and arrangement of parts, all as exemplified in the constructions herein set forth, and the scope of the invention will be indicated in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is an axial sectional view taken through a valve cartridge of a solenoid valve in accordance with an embodiment of the present invention; 
         FIG. 2  is an axial sectional view taken through a solenoid valve with valve cartridge and solenoid in accordance with an embodiment of the present invention; and 
         FIG. 3  is a sectional view taken through a pilot control unit containing a solenoid valve in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawing figures, a solenoid valve is provided for introduction into, for example, a pilot control housing  2  illustrated in  FIG. 3 . In pilot control housing  2 , at least one valve bore  4  is provided, which extends in transverse direction from a side face  2   c  and which, according to exemplary embodiments of the present invention, can be formed as a blind bore so that the opposite side face  2   d  can be closed. Alternatively, valve bore  4  can also be formed as a through hole. In accordance with exemplary embodiments of the present invention, a plurality of valve bores  4  can be formed in parallel, and it is in this connection that the illustrated valve bore  4  will be described hereinafter. 
     In a molded pocket  5  formed starting from top side  2   a  of pilot control housing  2 , which can be made of plastic, for example, a solenoid system  6  is introduced such that its central through hole coincides with valve bore  4 . Solenoid system  6  is contacted with an electrical interface. 
     A valve cartridge  8  is introduced from side face  2   c , or in other words, from its primary side, into valve bore  4  and is fastened to side face  2   c . In this way, it fixes solenoid system  6 , which was introduced from above, in vertical direction, meaning that it acts as a splint member; in addition, solenoid system  6  is also fixed by other bearing points in the surrounding housing. From its primary side  8   a , which is shown on the right in  FIG. 1 , valve cartridge  8  is pressurized with compressed air, for example, via a compressed air duct  9  extending in vertical direction through pilot control housing  2 , and at its secondary side  8   b , on the left in  FIG. 1 , it discharges compressed air via at least one further compressed air duct  9  extending in vertical direction through pilot control housing  2 . 
     Valve cartridge  8  is provided with a primary valve  10  and a secondary valve  11 . In this exemplary embodiment, primary valve  10  is designed as a 2/2-way valve having one passing and one blocking position. Secondary valve  11  is designed as a 3/2-way valve, and it has an air admission or control pressure position and a venting position. In the air admission position, the compressed air arriving from primary valve  10  is discharged at an air admission output  12   a , for example, for admission of air to a connected pressure cylinder of a wheel brake. In the venting position, first output  12   a  is in communication with a venting output  12   b.    
     Primary valve  10  has a primary armature  10   a  with a diameter of 8 mm, for example, which is guided in axial direction in a magnetically non-conducting armature guide tube  10   b  made of brass or non-magnetic steel, for example, and is pre-loaded by an armature spring  10   c  into its open position, in which primary armature  10   a  is, therefore, not bearing on its primary valve seat  13 . 
     Analogously, secondary valve  11  has a secondary armature  11   a  with a diameter of 6 mm, for example, which is guided in a magnetically conducting armature guide tube  11   b , which is constructed in one piece together with core  15  and is advantageously joined rigidly to primary armature guide tube  10   b . Secondary armature  11   a  is pre-loaded by an armature spring  11   c , and it cooperates with a first valve seat  14   a  for first output  12   a  and with a second valve seat  14   b  for second output  12   b ; in the exemplary embodiments shown in the drawings, this valve seat  14   a  is always able to be open. 
     The magnetic flux through solenoid system  6  passes through both armatures  10   a ,  11   a  and common core  15  of magnetically conducting material formed between them. Anti-sticking elements  17  can be disposed between core  15  and armatures  10   a ,  11   a , which ensure earlier drop-out at higher currents, for example, by pressing into core  15  or pressing against armatures  10   a ,  11   a . For this purpose, an anti-sticking element  17 , in the form of a bush acting as a spacer, for example, is provided between secondary armature  11   a  and core  15 , while an air gap that diverts the magnetic flux passing through primary armature  10   a  radially outward can be formed between core  15  and primary armature  10   a.    
     Both armatures  10   a ,  11   a  are displaced by common solenoid system  6 , which, for this purpose, can be de-energized or else energized with a first lower current intensity or a second higher current intensity. Consequently, three switched positions are obtained: 
     (i) a de-energized home position in which primary valve  10  is open, air admission port  12   a  of secondary valve  11  is left open and vent port  12   b  is shut off; 
     (ii) a position during energization with the first lower current intensity in which only primary armature  10   a  is displaced and primary valve  10  is therefore closed; the spring force of primary armature spring  10   c  and the response of the rest of the valve system are therefore designed such that this system is already displaced at the first current intensity, whereas secondary armature spring  11   c  still holds secondary armature  11   a ; thus, vent port  12   b  continues to be shut off, and the pressure in air admission port  12   a  is held; and 
     (iii) a position during energization with the second higher current intensity in which primary valve  10  continues to be closed and secondary armature  11   a  is also displaced, such that secondary valve  11  places air admission port  12   a  and vent port  12   b  in communication; in this way, venting can take place between air admission port  12   a  and vent port  12   b.    
     The air therefore flows through an air inlet  19  into the primary valve, past (or through) primary armature  10   a  and, during air admission, or in other words, de-energized condition and open primary valve  10 , past valve seat  13  into a central air bore  22  of core  15 , from there into secondary valve  11 , through secondary armature  11   a , past valve seat  14   a  and into air admission port  12   a.    
     As one example, core  15  is joined to primary armature guide tube  10   b  (e.g., made of brass) by adhesive bonding and flanging, or, as another example, is joined to armature guide tube  10   b  via seals. Secondary valve seats  14   a, b  are joined to core  15  by flanging or by seals, for example. As a result, a valve cartridge  8  containing the housed movable parts is formed. 
     A stepped body  18  is obtained, which houses armatures  10   a ,  11   a  and, on the primary side, has a cylindrical region  18   a  with larger diameter and, toward the left on the secondary side, has a cylindrical region  18   b ,  18   c  with smaller diameter, so that it can be introduced into solenoid system  6  or the through hole thereof, thus fixing it. Primary armature spring  10   c  is housed in larger region  18   a  and secondary armature  11   c  in narrower region  18   b . A middle region  18   c , which is located within solenoid system  5 , is formed continuously with narrower region  18   b  housing secondary armature spring  11   c.    
     According to  FIG. 1  and  FIG. 2 , o-ring seals  20  are disposed externally on valve cartridge  8  in the transition from region  18   a  to region  18   c , externally at the front end on valve seat  14   b  and internally on core  15  or secondary armature guide tube  11   b.    
     Valve cartridge  8  can, therefore, be introduced from side face  2   c  of pilot control housing  2  into valve bore (blind bore)  4 , thus, already fixing solenoid system  6 . 
     Since valve cartridge  8  is inherently matched as regards tolerance, only rough fixation is needed in axial direction, and this is ensured by molded pocket  5 . The force built up when the internal pressure faces are pressurized for the first time pushes valve cartridge  8  against the housing stop, where it remains by virtue of friction due to the diverse o-rings of the static seals. 
     The force and stroke tolerances of valve cartridge  8  can be easily adjusted. 
     For the switching thresholds, the force tolerance of armature springs  10   c ,  11   c , and, especially, of primary armature spring  10   c , is the most important factor. The valve seat and armature guide tube of the primary side are sealingly joined to one another. The position of the joint can be found as a function of force. Thus, the armature spring force can be simply adjusted in the on-going process. 
     Subsequently, the armature guide tube and core  15  are joined to one another, for example, by flanging. 
     In this way, the stroke and force of the primary side are adjusted. 
     On the secondary side, an adjustment can be achieved by an adjustment to a specified spring force, or adjustment of a specified stroke. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.