Abstract:
The invention relates to an electromagnetic actuating device ( 1 ) for a camshaft adjustment device of an internal combustion engine of a motor vehicle, with an elongated actuating element ( 2 ) forming an engagement region on the end side and movable by the force of a coil device ( 29 ) provided in a stationary manner, which actuating element preferably has in parts a cylindrical covering contour and penetrates a cut-out ( 8 ) in permanent magnet means ( 6 ) arranged on the shell side, which are constructed for cooperating with a stationary core region ( 5 ) comprising a core body ( 15 ), and which actuating element lies in a switching position with a contact surface ( 11 ), on the end side on the actuating element side, against a contact surface ( 10 ) on the core region side. Provision is made that the contact surface ( 11 ) on the core region side is formed at least in part by a contact element ( 16 ) fixed in the core body ( 15 ), which contact element is constructed from a material which has a greater hardness than the material of the core body ( 15 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an electromagnetic actuating device and a camshaft adjustment device with such an electromagnetic actuating device as actuator. 
     In known electromagnetic actuating devices for adjusting the camshaft, the problem exists that owing to the geometry of the core region and of the armature, due to magnet technology, in the currentless state, an adhesion force acts between the core region of the actuating member of the armature. This adhesion force is intensified by the oil, situated in the adjustment unit, which collects between the contact surfaces of core region and actuating member. The adhesion force which thereby arises acts in particular in the low- and deep temperature range (+10° C. to −40° C.) negatively on the switching times of the electromagnetic adjustment unit. A lengthy idle time of the vehicle can also lead to an intensification of the adhesion force. 
     In order to reduce the above-mentioned disadvantages, an improved electromagnetic actuating device for adjusting a camshaft in a motor vehicle, described in WO 2008/014996 A1, was developed by the applicant. From the publication, it is known to reduce the adhesion force between the actuating member and the core region, caused by lubricant, in that a slit-shaped recess and/or notch, i.e. depression, is provided in the end face of the actuating member. 
     The reduction of the contact surfaces between actuating member and core region, proposed by the applicant, involves a distinctly increased surface pressure and hence an increased material stress of the core body of the core region. Attempts exist to improve the wear resistance of the actuating device with, at the same time, a reduced adhesion force. Preferably, at the same time, the efficiency of the actuating device is to be improved. 
     From DE 20 2007 010 814 U1 and DE 20 2009 001 187 U1 electromagnetic actuating devices are known, which comprise an actuating element which forms an engagement region on the end side and which penetrates a cut-out in permanent magnet means which are arranged on the shell side. 
     From EP 0 428 728 A1 an electromagnetic actuating device is known, which has an actuating element without permanent magnet means, wherein the actuating device is equipped with a contact element. 
     DE 20 2007 005 133 U1 and DE 199 00 995 A1 are additionally named with respect to the prior art. 
     SUMMARY OF THE INVENTION 
     Proceeding from the above-mentioned prior art, the invention is therefore based on the problem of indicating an improved electromagnetic actuating device, optimized with regard to adhesion force, which is distinguished by an increased wear resistance and which preferably manages with a comparatively small—i.e. optimized with regard to installation space—, stationary coil device. The object further consists in indicating a camshaft adjustment device with a correspondingly improved electromagnetic actuating device. 
     This problem is solved with regard to the electromagnetic actuating device by the features disclosed herein and also with regard to the camshaft adjustment device by the features disclosed herein. Advantageous further developments of the invention are also indicated. All combinations of at least two of the features disclosed in the description, the claims and/or the figures fall within the scope of the invention. 
     The invention has identified that the wear resistance can be increased by a suitable choice of material of the core region, wherein initially the problem still exists that harder core region material is generally poorly magnetically flux-conducting, which with a construction of the core body from a hardened material would lead to extremely poor efficiencies up to the point of the electromagnetic actuating device being incapable of functioning. The configuration or respectively improvement according to the invention of an electromagnetic actuating device according to the invention has a way out from this dilemma, in which the core region is not constructed in one part, as in the prior art, by rather in several parts and has a core body which is preferably readily conductive magnetically, and a contact element fixed in this core body, preferably projecting over the core body in the direction of the armature, which contact element is distinguished by an increased hardness compared with the core body, preferably measured in HRC. In other words, the invention initially accepts a construction of the core region in several parts, which at first sight is disadvantageous, and can hereby surprisingly achieve a number of advantages. On the one hand, in a comparatively simple manner the abutment surface or respectively the contact surface encumbered with oil between the core region and the actuating member can be influenced by a corresponding adaptation of the contact element geometry, without it being necessary for this to additionally adapt the core body geometrically. At the same time, on the other hand, despite increased surface pressure owing to the reduction in contact area to avoid the adhesion force, the wear resistance of the core region is increased, because the actuating member rests in a switching position against the contact element, which is harder compared with the core body. In particular when a hardened material, in particular a hardened steel, such as for example 16MnCr5, is used as material for the construction of the contact element, the field line course of the magnetic field lines in the core body surrounding the contact element in sections is influenced in a targeted manner, in particular bundled in a preferably annular region adjacent to the contact element, whereby the efficiency of the electromagnetic actuating device is increased, whereby in turn a smaller dimensioned coil device (optimized with regard to installation space) can come into use. 
     The air gap which is preferably constructed between the permanent magnet means, preferably present as part of a disc pack, or a pole disc on the armature side, and the core body, can be set by means of the, preferably pressed in, contact element with a defined overlap over the core body to effect a force maximum (apex), i.e. the air gap can be set or respectively optimized with regard to a maximum repulsion force, whereby minimal switching times are able to be achieved. 
     Basically it is possible that the actuating member in the above-mentioned switching position in addition to the contact element fixed in the core body rests against the core body, i.e. that the contact surface on the core region side is formed only in sections or respectively partially by the contact element. However, an embodiment is preferred in which the contact surface on the core region side is formed exclusively by the contact element, in order on the one hand to achieve as small a contact surface as possible and hence as low adhesion forces as possible, and in order on the other hand to optimize the wear resistance of the electromagnetic actuating device, in particular the core region, as a whole. It is particularly preferred if the contact surface formed by the contact element is arranged concentrically with respect to a longitudinal centre line of the actuating member. Advantageously, the contact element projects here over the pole surface of the core body facing the permanent magnet means. 
     Basically, it is possible to construct the contact element from a material which offers the magnetic flux the same, or even a lower resistance, as the material of the core body. However, it is preferred, as explained in the introduction, if the magnetic conductivity of the contact element is poorer than that of the core body surrounding it, in order to bundle the field lines in a targeted manner. By means of the preferably pressed in contact element, therefore a bundling of the magnetic field lines is achieved, which brings it about that the field lines are “steered” in a more targeted manner to the oppositely directed field lines from the permanent magnet means. Therefore, an optimization of the repulsion force and hence a minimal switching time can be achieved. 
     It is particularly expedient if the hardness of the material of the contact element, preferably indicated in HRC, is at least twice as great, preferably at least three times as great, still further preferably at least four times as great as the hardness of the core body material. This can be achieved for example in that the core body is constructed from the steel alloy 11SMn30 and the, preferably pin-shaped, contact element is constructed from the alloy 16MnCr5. In this case, the core body has a hardness of approximately 10 HRC and the contact element a hardness of approximately 60 HRC. 
     In order to reduce or respectively optimize the adhesion forces between the contact surface on the core region side and the contact surface on the actuating member side, provision is made in a further development of the invention that the contact surface on the core region side is smaller than a surface (cross-sectional area) of the actuating member extending radially to the longitudinal extent of the actuating member, in particular than the end side (end face) of the actuating member facing the core region and/or the cross-sectional area of the actuating member surrounded by the permanent magnet means. It is especially preferred if the contact surface on the core region side, which is preferably formed exclusively by the contact element, corresponds to only maximally 70%, preferably maximally 60%, more preferably maximally 50%, still more preferably maximally 40% of this area. Particularly good results can be achieved here when the diameter of the preferably cylindrical contact surface on the core region side, formed by the contact element, is selected from a range of values between 2 mm and 8 mm, preferably between 4 mm and 7 mm, particularly preferably approximately 5.2 mm. 
     In order to be able to precisely set the air gap, defined by the contact element, between the core body and the actuating member and/or the permanent magnet means and/or a pole disc arranged on the permanent magnet means, provision is advantageously made in a further development of the invention that a, preferably annular, axial stop surface is provided on the contact element, by which the contact element, fixed in the core body, rests axially against the core body. In an embodiment without an axial stop surface on the contact element, the air gap can be set for example via the setting of a (then variable) axial pressing-in depth of the contact element, wherein in this case it is to be ensured that the press fit between contact element and core body is selected so that also during operation an axial travel of the contact element into the core body and an air gap reduction related thereto during the operation is avoided. Additionally or alternatively to a press fit, the contact element can be fixed to the core body via an axial and/or radial deformation of the core body material (peening). 
     It is especially expedient if the contact element is received in an end-side bore of the core body and is fixed there preferably by means of a press fit. In other words, in a further development of the invention the contact element is introduced into a bore of the core body. 
     It is particularly expedient here if the bore is not realized as a continuous cylinder bore (which is alternatively possible), but rather as a stepped bore with at least one annular shoulder, which preferably forms an axial counter stop surface for an axial stop surface of the contact element. It is still further preferred here if the press fit is realized in a rear or respectively lower bore section in relation to the actuating member. An axial pin pressing of approximately 2 mm to 4 mm, preferably of 3 mm is preferably realized here. 
     It has been found to be particularly expedient if the contact surface formed by the contact element is smaller than the maximum bore diameter of the bore, i.e. in the case of the construction of the bore as a stepped bore is smaller than a front bore diameter or respectively is smaller than an external diameter of an annular axial stop surface. Particularly preferably, the contact surface formed by the contact element corresponds to a cross-sectional area of the contact element in the pressing-in region. It is especially preferred if the free end of the contact element is constructed so as to be convex—in other words, a convexity of the contact surface offered by the contact element is advantageous, because the actuating element as part of the armature assembly in the drawn-in state by a radial preferred position occurring owing to the convexity can become jammed less on the edge of the contact element. 
     As already mentioned in the introduction, it is particularly preferred if the contact element projects over the core body in axial direction, i.e. in the direction of the actuating element. In a further development of the invention, provision is now made that this axial overlap is selected so that with a given current feed of the coil winding a force maximum of the repulsion force results between core body and permanent magnet means. If the axial overlap is selected to be too great, this leads to a loss of force in the effective magnetic forces—if the axial overlap is selected to be too small, this means increased adhesion forces and hence a loss of force in the resulting repulsion force. Preferably, the axial overlap is selected here so that the resulting air gap leads to a maximum repulsion force plus/minus 20%, preferably plus/minus 10%, still further preferably plus/minus 5%. 
     The invention also specifies a camshaft adjustment device with an electromagnetic actuating device, constructed according to the concept of the invention, as actuator for realizing the adjustment movement of the camshaft or respectively of its cams. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, features and details of the invention will emerge from the following description of preferred example embodiments and with the aid of the drawings. 
       These show in: 
         FIG. 1 : a view, partially in section, of a possible embodiment of an electromagnetic actuating device constructed according to the concept of the invention, in which the contact surface on the core region side is formed by a contact element fixed in a core body, 
         FIG. 2 : a detail illustration of a possible embodiment of a combination of core region and armature, 
         FIG. 3 : an illustration of the optimized field line course by the use of a magnetically more poorly conducting contact element, 
         FIG. 4 : a diagram which can be consulted for the design of the air gap and hence of the axial overlap of the contact element over the core body, in order to ensure a maximum repulsion force, and 
         FIG. 5 : the illustration of an example embodiment with convex contact surface on the contact element side. 
     
    
    
     DETAILED DESCRIPTION 
     In the figures, identical elements and elements with the same function are marked by the same reference numbers. 
       FIG. 1  shows the realization of an electromagnetic actuating device for a camshaft adjustment device which is otherwise not illustrated in further detail. A possible variant configuration of the combination of core region and armature is illustrated in  FIGS. 2 and 3 . 
     The camshaft, which is not illustrated, is actuated directly or indirectly with the aid of a continuously elongated, bolt-shaped actuating member  2 , which in addition to permanent magnet means  6 , which are to be further explained later, is a component part of the armature. The actuating member  2  is guided adjustably in axial direction in a sleeve-shaped bearing element  3 , which undertakes at the same time the function of a magnetic yoke. The electromagnetic actuating device  1  comprises, within a cup-shaped housing  4 , a coil device, known per se, not illustrated in  FIG. 1 , to which a magnetic core region  5  is associated. With the aid of the coil device, the actuating member  2  with the permanent magnet means  6  fixed thereon can be adjusted in the axial direction, wherein on the end side of the actuating member  2 , facing away from the core region  5 , an engagement region is constructed, in order to cooperate with a counterpart, in particular with the camshaft. Alternatively, the engagement region can also be provided on the shell side. 
     As previously indicated, permanent magnet means  6  are associated with the actuating member  2 , which in the example embodiment shown according to  FIG. 1  have the form of a cylinder disc. These sit on the shell surface  7 , i.e. on the shell side, of a front cylindrical section of the actuating member  2 . The latter penetrates a cylindrically contoured, central cut-out  8  of the permanent magnet means  6 . These are fixed to the actuating member  2  in a materially connected and/or form-fitting manner, for example by welding. The permanent magnet means  6 , with a coil device not fed with current, serve to keep the actuating member  2  in the illustrated switching position (on the left in the plane of the drawing), in which the actuating member rests with an end side  9 , more precisely with a contact surface  10  constructed thereon on the actuating member side, on a contact surface  11  parallel thereto on the core region side. By feeding the coil device with current, the permanent magnet means  6  are repelled and the actuating member  2  together with these are adjusted into a second switching position, to the right in the plane of the drawing. 
     As can be seen in  FIG. 1 , the electromagnetic actuating device  1  is held in an engine block  12 , which is only shown in part. Here, an inlet- and/or discharge duct  13  for liquid lubricant, here engine oil, is formed in the bearing element  3 . A further duct  14  for the lubricant is situated radially offset to the inlet- and discharge duct  1  within the engine block  12 . 
     As indicated in  FIG. 1  and will be explained by way of example by means of  FIGS. 2 and 3 , the core region  5  is constructed in several parts and comprises a core body  15  of material with good conductivity magnetically, in the actual example embodiment of a steel alloy 11SMn30 with a hardness of 10 HRC. A contact element  16 , forming the contact surface  11  on the core region side, is fixed in this core body  15  by pressing, wherein the contact element  16  is constructed from a material, here the steel alloy 16MnCr5, which has a distinctly greater hardness of 60 HRC here than the core body  15 . 
     In  FIG. 2  the combination of armature  17  with elongated actuating member  2  and core region  5  is illustrated in accordance with a preferred variant embodiment. The construction in multiple parts can be seen, here in two parts, of the core region  5 , which comprises the core body  15  with contact element  16  fixed therein, which forms the contact surface  11  on the core region side, which cooperates with a contact surface  10  of corresponding size on the actuating member side in the illustrated switching position, i.e. lies against it. 
     The structure of the armature  17  can be seen from  FIG. 2 . Permanent magnet means  6  in the form of two permanent magnet discs are fixed on the cylindrical actuating element  2  (actuating member) of the armature  17 . Associated with the permanent magnet means  6  is a pole disc  18  which is also penetrated by the actuating member  2 . The pole disc  18  is oriented parallel to a corresponding opposite pole surface  19  of the core body  15 . A working air gap  20 , partially or completely filled with oil, is formed between pole disc  18  and pole surface  19 . The width of this working air gap  20  is substantially defined by the extent by which the contact element  16  projects over the pole surface  19  of the core body  15  in the direction of the actuating member  2 . In addition, the working air gap  20  is determined by the axial distance between the annular pole surface of the pole disc  18 , facing the pole surface  19 , and the end side  9  of the actuating member  2 . 
     As can be seen from  FIG. 2 , on the end side in the core body  15  a bore  21  is introduced, constructed as a stepped bore, which is divided into a rear, cylindrical section  22  with reduced diameter (press-in section) and a front section  23  with widened diameter, the base of which forms a counter stop surface  24  for an annular axial stop surface  25  of the contact element  16 . The actual press fit between the contact element  16  and the bore  21  is realized (exclusively) in the section  22  with reduced diameter, whereas the section  23  with widened diameter substantially only has as a function the formation of the counter stop surface  24  (i.e. a radial play is possible there). 
     For the form-fitting receiving of the contact element in the bore  21 , embodied as a stepped bore, the contact element  16  according to the illustrated preferred variant embodiment has a lower cylinder section  26  with reduced diameter and a cylinder section  27  with widened diameter axially adjoining thereto, which projects over the cylinder section  26  with reduced diameter by means of a peripheral collar, on which the axial stop surface  25  is constructed on the side facing away from the actuating member  2 . In the example embodiment which is shown, a cylindrical contact surface section  28  adjoins the cylinder section  27  with widened diameter, which cylindrical contact surface section  28  in the example embodiment which is shown has a diameter which corresponds to the diameter of the section  26  with reduced diameter, but if required can, however, also deviate herefrom. A variant embodiment is also conceivable in which the contact surface section  28  is formed by an axially extended cylinder section  27  with widened diameter. 
     It is also able to be realized, for the case where an axial stop surface  25  is to be dispensed with, to construct the contact element in pin form, for example in the form of a circular cylinder, wherein then preferably the bore  21  is not embodied as a stepped bore, but rather as a continuously cylindrical bore. 
     As can be seen from  FIG. 2 , in the example embodiment which is shown the contact surface  11  on the core region side is substantially smaller than the end side  9  of the actuating member. In the example embodiment which is shown, the surface extent of the end face  9  corresponds, at least approximately, to the surface extent of the cross-sectional area of the actuating member  2 , which is surrounded by the permanent magnet means  6 . 
     In  FIG. 3  there is an alternative representation of a cut-out of an electromagnetic actuating device illustrated by way of example in  FIG. 1 . The core body  15  can be seen, in which the contact element  16  is fixed, and namely as in the example embodiment according to  FIG. 2  in a cylinder bore  21 , which provides a counter stop surface  24  for the contact element. In the example embodiment according to  FIG. 3 , the cross-sectional area of the cylindrical contact surface section  28  is smaller than that of the cylinder  26  with reduced diameter, which in turn is smaller than that of the cylinder section  27  with widened diameter, on which the axial stop surface  25  is constructed for the cooperation of the counter stop surface  24  of the core body  15 . 
     As can be further seen from  FIG. 3 , the core body  15  is surrounded by a coil device  29 , illustrated only diagrammatically, for generating the magnetic field  30  which is illustrated partially in the form of field lines. It can be seen that the bore  21  with the contact element  16  received therein displaces the field lines radially outwards and therefore bundles in a region  31  of the core body  15  radially adjacent to the contact element  16 , in order to thus intensify the magnetic force between core body  15  and pole disc  18  in this region. 
     In  FIG. 4  a diagram is shown, which shows the correlation between the repulsion force acting on the armature assembly and the width of the air gap, shown in  FIG. 2 , between the core body  15  and the pole disc  18  (alternatively the permanent magnet means directly). Here, on the vertical axis the repulsion force is indicated in Newtons and on the horizontal axis the width of the air gap is indicated in millimetres. The repulsion force is the difference between the magnetic repulsion force and the adhesion force. It can be seen that in the example a repulsion force maximum exists with an air gap width of approximately 0.4 mm. When the air gap is selected to be smaller, the adhesion forces increase in an extreme manner, so that despite increasing magnetic forces the repulsion force decreases. On the other hand, the magnetic repulsion force and hence the resulting repulsion force likewise decreases with a further increasing air gap width. The axial overlap of the contact element  16  over the core body  15  is therefore preferably selected in the example embodiment shown so that the resulting air gap has a width of at least approximately 0.4 mm in the switching position in which the actuating element  2  lies against the contact element. 
       FIG. 5  shows an example embodiment of a core region  5 , preferably coming into use. The contact element  16 , provided in the core body  15 , can be seen, which contact element projects over the core body  15  in axial direction. It can further be seen that the contact surface  11  on the core region side is embodied so as to be slightly convex, wherein the radius determining the convexity corresponds to a multiple of the diameter of the front contact surface section  28 , which is preferred. 
     Through this convexity, a radial preferred position of the actuating element  2  can occur on the contact element, whereby a jamming on a contact element edge is reliably prevented.