Abstract:
An electromagnetic adjustment unit of a directional control valve is provided. The individual components of the adjustment unit are to be embodied, arranged, and joined such that the assembly expenditure and the costs during the production are reduced to a minimum.

Description:
BACKGROUND 
     The invention relates to an electromagnetic adjustment unit of a hydraulic directional control valve with a housing, at least one armature and at least one magnet yoke. The magnet yoke has a tubular section adjacent to an annular section having a greater outer diameter in the axial direction. Within the magnet yoke there is a tappet push rod, which can move axially and which can be displaced by means of the armature. The housing has a pot-like shape with a base, in which there is an opening, through which the tubular section extends into the housing, the outer diameter of the tubular section is at least approximately adapted to the diameter of the opening, and the base is supported indirectly or directly on the annular section. 
     Such directional control valves are used in internal combustion engines, for example, for controlling hydraulic camshaft adjusters or switchable cam followers. The directional control valves comprise an electromagnetic adjustment unit and a valve section. The valve section represents the hydraulic section of the directional control valve, wherein at least one supply connection, at least one working connection, and one tank connection are formed on the hydraulic section. By means of the electromagnetic adjustment unit, certain connections of the valve section can be selectively connected to each other hydraulically and in this way the flows of pressurized medium are guided. 
     For the use of a directional control valve to control a camshaft adjuster, in the normal case this valve is formed as a 4/3 proportional directional control valve. Such a proportional valve is disclosed, for example, in DE 199 56 160. In this case, the electromagnetic adjustment unit is composed of a first magnet yoke, a coil, a second magnet yoke, a housing, an armature, and a connection element, which receives an electrical plug connection used for supplying power to the coil. 
     The valve section is composed of a valve housing and a control piston that can be displaced axially therein. The valve housing is arranged within a receptacle opening of the second magnet yoke and is connected to this yoke so that it is fixed in position. On the outer jacket surface of the valve housing, there are four annular grooves, which are used as pressurized medium connections. Openings are formed in the groove bottoms of the annular grooves, whereby pressurized medium can be led into the interior of the valve housing. In the interior of the valve housing, there is a control piston that can be displaced axially, wherein the outer diameter of the control piston is adapted to the inner diameter of the valve housing. In addition, annular grooves are also formed on the control piston. Adjacent pressurized medium connections can be connected to each other via these annular grooves. 
     The coil and the first and second magnet yokes are arranged coaxial relative to each other within the housing of the electromagnetic adjustment unit. The first and the second magnet yoke are offset relative to each other in the axial direction. In the region between the first and the second magnet yoke, there is the armature radially within the magnet yokes, wherein this armature is surrounded by the coil in the radial direction. The armature, the housing, the first and the second magnet yokes form a flow path for the magnetic flux lines, which are generated by sending current through the coil. 
     By sending current through the coil, the armature is forced in the direction of the second magnet yoke, wherein this motion is transferred to the control piston by means of a tappet push rod attached to the armature. This piston is now moved in the axial direction against a spring supported against the valve housing. 
     For the most part, directional control valves for controlling switchable cam followers are embodied as switching valves. Such a switching valve is known in a configuration as a 3/2 switching valve, for example, from DE 102 52 431 A1. The electromagnetic adjustment unit comprises, in turn, a housing, an armature, a connection element, and a first and a second magnet yoke. The function and the configuration of the electromagnetic adjustment unit are in broad parts analogous to that of the proportional valve. 
     In this case, a supply connection, a working connection, and a tank connection are formed on the valve section. The working connection communicates via openings, which are each formed as valve seats, both with the supply connection and also with the tank connection. Furthermore, within the valve housing there is a control piston, on which two closing elements are formed. Each closing element can block or open the pressurized medium flow through one of the valve seats depending on the position of the control piston within the valve housing. Depending on the axial position of the control piston, the working connection can be connected selectively to the supply connection or to the tank connection. The axial position of the control piston is fixed relative to the second magnet yoke, in turn, over the axial position of the armature. 
     The assembly of the electromagnetic adjustment unit produces relatively high assembly expenditure, whereby higher costs arise, due to the plurality of components, which must be positioned and fixed relative to each other. 
     SUMMARY 
     Therefore, the invention is based on the objective of avoiding these disadvantages and thus creating an electromagnetic adjustment unit of a directional control valve, wherein its assembly expenditure is minimized and thus its manufacturing costs are reduced. Here, special attention should be placed on simple positioning of the components and economical fixing of the components. 
     According to the invention, this objective is met in that the base and the tubular section are fixed to each other by means of at least one press-fit section. In this way, the directional control valve can be embodied as a proportional valve or as a switching valve. 
     By shaping the magnet yoke holding the tappet push rod with a tubular section, which engages through an opening formed in a base of the pot-shaped housing, the two components can be easily positioned radially relative to each other. The annular section with a greater outer diameter of the magnet yoke on one end of the tubular section also fixes the position of the housing relative to the magnet yoke in the axial direction. Thus, these two components are fixed in the axial and radial direction during the production of the stationary connection between these two components. The fixing of the two components relative to each other by means of press-fitting represents an economical method. 
     In one advantageous embodiment of the invention, the press-fit section is realized by at least one material mass, which is formed on the tubular section and which at least partially covers one edge of the opening in the radial direction. Here, for forming the press-fit section, material of the tubular section of the magnet yoke can be displaced in the axial direction towards the base. 
     During or after the joining process of the two parts, a tubular swage is inserted into the radial intermediate space between the magnet yoke and the housing, with the inner diameter of the swage being shaped at least in parts smaller than the outer periphery of the tubular section of the magnet yoke. In this way, material is removed from the outer periphery of the tubular section and displaced in a form-fitting way to the joint between the housing and the tubular section. The advantage of this procedure is that the press-fitting process can be realized by a simple method, an exact centering of the housing on the magnet yoke is guaranteed, and the joining and fixing can be performed in one processing step. 
     In addition, the press-fit section can be realized over the entire periphery of the tubular section. 
     In this case, the press-fit section is realized by means of a tubular swage with a round cylindrical inner sleeve surface, whose inner diameter is smaller than the outer diameter of the tubular section of the magnet yoke. In this way, a material bead surrounding the joint between the housing and the tubular section is formed in the peripheral direction, whereby a highly stable connection is generated. 
     Alternatively, the press-fit section can be realized with at least two press-fit points, which are spaced apart in the peripheral direction and which are distributed on the periphery of the tubular section. In this case, the press-fitting tool has a tubular shape with a round cylindrical inner sleeve surface, whose inner diameter corresponds to or is larger than the outer diameter of the tubular section of the magnet yoke. Furthermore, several projections, which extend radially inwards and which are spaced apart in the peripheral direction, are formed on the inner sleeve surface, wherein their radial spacing is smaller than the outer diameter of the tubular section of the magnet yoke. Instead of a bead extending in the peripheral direction, in this case several press-fit points are formed. Through such a procedure, the force necessary for producing the connection can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional features of the invention emerge from the following description and from the drawings, in which embodiments of the invention are shown in a simplified form. Shown are 
         FIG. 1  is a schematic view of a first embodiment of an electromagnetic adjustment unit according to the invention, using the example of a 4/3 directional proportional control valve, 
         FIG. 1   a  is a view of a second embodiment of an electromagnetic adjustment unit according to the invention, 
         FIG. 2  is the detail Z from  FIG. 1 , 
         FIG. 3  is a view of a third embodiment of an electromagnetic adjustment unit according to the invention, using the example of a 3/2 directional switching control valve, 
         FIG. 4  is a top view of the electromagnetic adjustment unit along the arrow V from  FIG. 1   a,    
         FIG. 5  is a top view analogous to  FIG. 4  with a differently shaped press-fit section. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a first embodiment of an electromagnetic adjustment unit  2  according to the invention, using the example of a directional control valve  1  embodied as a 4/3 directional proportional control valve. The directional control valve  1  has an electromagnetic adjustment unit  2  and a valve section  3 . 
     The electromagnetic adjustment unit  2  has a coil body  5  and a connection element  6  formed in one piece with this coil body. The coil body  5  supports a coil  7  comprising several windings of a suitable wire. The radially outer surface of the coil  7  is surrounded by a sleeve-shaped material layer  8 , which comprises a non-magnetizable material. The material layer  8  can comprise, for example, a suitable plastic and can be injection molded onto the wound coil  7 . Within the connection element  6 , an electrical plug connection  9  is held, by means of which the coil  7  can be supplied with current. 
     The coil body  5  is formed with an essentially cylindrical, blind hole-like recess  10 , which is arranged concentric to the coil  7 . In addition, the coil body  5  and the connection element  6  on the base-side end of the recess  10  has a sleeve-shaped first magnet yoke  11 . Within the recess  10  there is a pot-shaped armature guide sleeve  12 , wherein its outer contours are adapted to the inner contours of the recess  10 . The base-side end of the armature guide sleeve  12  is provided with stops  13  extending axially inwards. In addition, the armature guide sleeve  12  extends in the axial direction along the entire recess  10 , wherein this sleeve at least partially surrounds the coil body  5  at its opening in the radial direction. 
     The coil body  5  is arranged within a pot-shaped housing  14 . The open end of the housing  14  projects over the connection element  6  in the axial direction, wherein this element and thus the coil body  5  are fixed by means of an edge connection  15  within the housing  14 . 
     Within the armature guide sleeve  12  there is an armature  16  that is displaceable in the axial direction. Here, the outer diameter of the armature  16  is adapted to the inner diameter of the armature guide sleeve  12 . The displacement path of the armature  16  is limited in one direction by the stops  13  and in the other direction by a second magnet yoke  17 . 
     The second magnet yoke  17  has a tubular section  18  and an annular section  19  adjacent to this tubular section in the axial direction. The tubular section  18  extends through an opening  21  formed in the base  20  of the housing  14  into the armature guide sleeve  12  arranged in the recess  10  of the coil body  5 . Here, the outer diameter of the tubular section  18  is adapted to the diameter of the opening  21  possibly with play. The inner diameter of the axial end of the tubular section  18 , which faces the armature  16 , is larger than the outer diameter of the armature  16 . Thus, the armature can be inserted into this section. In addition, the outer jacket surface of the tubular section  18  is conical in the direction of the armature  16 . 
     The housing  14  is supported by a mounting flange  22  on the annular section  19 . The mounting flange  22  is used for fixing the directional control valve  1  on a surrounding construction (not shown). 
     The second magnet yoke  17  can be formed as a one-piece component in  FIG. 1 . An alternative embodiment is shown in  FIG. 1   a . In this embodiment, the second magnet yoke  17  comprises two components, the pole core  23 , and a sleeve-shaped projection  24  formed in one piece with the mounting flange  22 . 
     In  FIG. 2 , the joint between the housing  14  and the second magnet yoke  17  is shown. This joint involves a press-fit section  25 . This can be realized, for example, in that after the housing  14  is positioned on the second magnet yoke  17 , material is displaced from the outer peripheral surface of the second magnet yoke  17  in the axial direction towards the housing  14  and is brought in a form-fitting way into the joint between these two components. Here, material masses are formed on the tubular section  18  in the region of the joint, which extend in the radial direction outwards over an edge  21   a  of the opening  21 . In this way, a functionally reliable and economical connection is realized between the housing  14  and the second magnet yoke  17 . In addition, the housing  14  is centered by this connection method to the second magnet yoke  17 , in the case that the outer diameter of the tubular section  18  and the diameter of the opening  21  are realized with little play. In this case, the material is forced into the intermediate space between these components during the press-fitting process and thus play is eliminated. 
     Between the tubular section  18  of the second magnet yoke  17 , the base  20  of the housing  14 , and the armature guide sleeve  12 , there is a sealing ring  25   a . This prevents pressurized medium, as a rule, motor oil, which penetrates into the electromagnetic adjustment unit  2 , from reaching the coil body  5  in interaction with the armature guide sleeve  12 , whereby this coil body is protected from damage by the pressurized medium. 
     The production of the press-fit section  25  is realized by means of a tubular swage, which is to be moved along the outer sleeve surface of the second magnet yoke  17  in the axial direction towards the housing  14 . Here, the inner diameter of the swage is smaller than the outer diameter of the second magnet yoke  17 . In this case, the press-fit section  25  is formed as an annular material bead surrounding the second magnet yoke  17 . This is shown schematically in  FIG. 5 .  FIG. 5  shows a top view of the electromagnetic adjustment unit  2  from  FIG. 1   a  along the arrow V, wherein only the housing  14  and the second magnet yoke  17  are shown. 
     An alternative connection method is provided in adapting the inner diameter of the swage to the outer diameter of the second magnet yoke  17  or forming it slightly larger, with bulges extending inwards being provided on the swage in the radial direction. In contrast to the embodiment shown in  FIG. 5 , this does not lead to a bead surrounding the second magnet yoke  17  in the peripheral direction, but instead to discrete press-fit points  26  spaced apart in the peripheral direction, as shown in  FIG. 4 . 
     As shown in  FIG. 1 , the valve section  3  of the directional control valve  1  embodied as a 4/3 directional proportional control valve comprises a valve housing  27  and a control piston  28 . The valve housing  27  can be formed either in one piece with the second magnet yoke  17  (right side of the drawing) or as a separate component (left side of the drawing). In the case of a separate construction of the valve housing  27 , this is connected, for example, by means of a screw, weld, edged, or similarly acting connection method to the second magnet yoke  17 . Several annular grooves  29 , which communicate with the interior of the essentially hollow cylindrical valve housing  27  via recesses  30  formed in the groove bases of the annular grooves  29 , are formed on the outer surface of the valve housing  27 . The annular grooves  29  and the opening facing away from the electromagnetic adjustment unit  2  in the valve housing  27  are used as pressurized medium connections A, B, P, T. The middle annular groove  29 , which is used as supply connection P, communicates via a not-shown pressurized medium line to a similarly not-shown pressurized medium pump. The two outer annular grooves  29 , which are used as working connections A, B, each communicate via similarly not-shown pressurized medium lines with a pressure chamber or with a group of oppositely acting pressure chambers of a similarly not-shown camshaft adjuster. The axial connection (tank connection) T communicates with a similarly not-shown pressurized medium reservoir. 
     A control piston  28  is axially displaceable within the valve housing  27 . Control sections  31  formed as annular connecting pieces are formed on the outer surface of the control piston  28 . The outer diameter of the control sections  31  is adapted to the inner diameter of the valve housing  27 . Through suitable axial positioning of the control piston  28  relative to the valve housing  27 , adjacent pressurized medium connections A, B, P can be connected to each other. Each working connection A, B not connected to the supply connection P is simultaneously connected to the tank connection T. In this way, pressurized medium can be fed to the individual pressure chambers of the camshaft adjuster or can be discharged from these chambers. 
     The control piston  28  is charged on one end with the force of a spring element  32  in the direction of the electromagnetic adjustment unit  2 . On the other axial end of the control piston  28  there is a tappet push rod  33 , which extends through a bore hole of the second magnet yoke  17  and is connected fixed in position to the armature  16 . 
     In the unpowered state of the coil  7 , the control piston  28  is displaced in the direction of the electromagnetic adjustment unit  2  due to the force of the spring element  32 . 
     The housing  14 , the first magnet yoke  11 , the armature  16 , and the second magnet yoke  17  comprise a magnetizable material, while the connection element  6 , the tappet push rod  33 , the coil body  5 , and the armature guide sleeve  12  comprise a non-magnetizable material. In this way, a magnetic flux, which displaces the armature  16  in the direction of the valve section  3 , is established by sending current through the coil  7  within the electromagnetic adjustment unit  2  via the armature  16 , the first magnet yoke  11 , the housing  14 , the second magnet yoke  17 , and an air gap  34  located between the armature  16  and the second magnet yoke  17 . Therefore, the control piston  28  is displaced in the axial direction by means of the tappet push rod  33  against the force of the spring element  32 . Through suitable control of the current flowing in the coil  7 , the control piston  28  can be set relative to the valve housing  27  at any arbitrary position between two end stops and thus the flows of pressurized medium to or from the pressure chambers of the camshaft adjuster can be regulated. 
     In the following, the assembly of the electromagnetic adjustment unit  2  is explained. First, the housing  14  is positioned on the first magnet yoke  17 . Therefore, because the outer diameter of the tubular section  18  is adapted to the diameter of the opening  21 , these components are centered relative to each other. The axial position is fixed by the base  20  and the annular section  19 . Subsequent to or in the same processing step, the press-fit section  25  between the base  20  and the second magnet yoke  17  is formed. If there is play between the outer jacket surface of the tubular section  18  and the edge  21   a  of the opening  21 , then in this processing step, the housing  14  is centered relative to the second magnet yoke  17  through material filling. Then the sealing ring  25   a  is inserted, the armature  16  is placed on the second magnet yoke  17 , and the coil body  5  with the connection element  6  and the armature guide sleeve  12  is positioned between the housing  14  and the tubular section  18 . The armature  16  is centered by the tappet push rod  33  connected rigidly to it and its outer surface, which interacts with an inner surface of the tubular section  18 . The coil body  5  is centered by means of the housing  14  and the tubular section  18 . For this purpose, the outer diameter of the coil body  5  and the material layer  8  are adapted to the inner diameter of the housing  14 . Furthermore, the inner diameter of the coil body  5  is adapted to the outer diameter of the tubular section  18 . 
     Then the edge connection  15  between the housing  14  and the connection element  6  is created and, for a separate construction of the valve housing  27 , the valve section  3  is mounted. 
       FIG. 3  shows another embodiment of an electromagnetic adjustment unit  2  according to the invention, using the example of a directional control valve  1  embodied as a 3/2 directional switching control valve. Such valves are used, for example, for controlling a locking mechanism of switchable cam followers. This directional control valve  1  comprises, in turn, an electromagnetic adjustment unit  2  and a valve section  3 . The electromagnetic adjustment unit  2  is in general terms identical to the adjustment unit  2  shown in  FIG. 1  or  1   a . In contrast to these embodiments, there is no conical section on the axial end of the second magnet yoke  17 , which is facing the armature  16 . This is used in the first two embodiments for representing an electromagnetic adjustment unit  2  with a linear characteristic line. In the embodiment shown in  FIG. 3 , such a linear connection is not necessary, because this directional control valve  1  uses only two control states, namely an unpowered state and a maximum powered state. 
     The valve section  3  comprises, in turn, a valve housing  27  and a control piston  28 , which is displaceable axially therein. In contrast to the embodiment shown in  FIG. 1 , there are only three pressurized medium connections A, B, T on the valve housing  27  in this embodiment. Within the valve housing  27  there are two valve seats  35 , with each valve seat  35  able to interact with a closing body  36  formed on the control piston  28 . 
     In  FIG. 3 , the directional control valve  1  is shown in the powered state. Due to the magnetic flux generated by the coil  7 , the armature  16  and thus the control piston  28  is shifted downwards axially in the figure. Consequently, the upper closing body  36  closes the upper valve seat  35 , whereby the connection between the working connection A and the tank connection T is blocked, while pressurized medium can flow from the supply connection P via the open lower valve seat  35  to the working connection A. In the unpowered state of coil  7 , there is no magnetic force on the armature  16 , whereby the control piston  28  is shifted upwards in the axial direction by the force of the pressurized medium flow on the supply connection P. In this way, the lower closing body  36  contacts the lower valve seat  35 , whereby the connection between the supply connection P and the working connection A is disrupted and simultaneously the connection between the working connection A and the discharge connection T is created via the upper valve seat  35 . 
     In this embodiment, the connection between the housing  14  and the second magnet yoke  17  is created using the same means and methods as in the embodiments shown in  FIG. 1  or  1   a.    
     Naturally, the configuration of an electromagnetic adjustment unit  2  according to the invention can also be used in directional control valves  1 , in which the valve section  3  is not connected rigidly to the adjustment unit  2 , but instead the components are arranged without a fixed connection in the axial direction relative to each other. Such directional control valves  1  are used, for example, as a central valve for camshaft adjuster, in which the valve section  3  is arranged within a camshaft and rotates with the camshaft, while the adjustment unit  2  is arranged in the axial direction relative to the camshaft and fixed to a cylinder head or to a cylinder head cap. 
     REFERENCE SYMBOLS 
     
         
           1  Directional control valve 
           2  Adjustment unit 
           3  Valve section 
           5  Coil body 
           6  Connection element 
           7  Coil 
           8  Material layer 
           9  Plug connection 
           10  Recess 
           11  First magnet yoke 
           12  Armature guide sleeve 
           13  Stop 
           14  Housing 
           15  Edged connection 
           16  Armature 
           17  Second magnet yoke 
           18  Tubular section 
           19  Annular section 
           20  Base 
           21  Opening 
           21   a  Edge 
           22  Mounting flange 
           23  Pole core 
           24  Projection 
           25  Press-fit section 
           25   a  Sealing ring 
           26  Press-fit point 
           27  Valve housing 
           28  Control piston 
           29  Annular groove 
           30  Recesses 
           31  Control section 
           32  Spring element 
           33  Tappet push rod 
           34  Air gap 
           35  Valve seat 
           36  Closing body 
         P Supply connection 
         T Tank connection 
         A First working connection 
         B Second working connection