Abstract:
The invention relates to an actuator of an electrohydraulic gas exchange valve drive of an internal combustion engine, comprising an actuator housing ( 4 ), which can be fixed in the internal combustion engine and which comprises a bore ( 9 ); a valve play compensation element ( 8 ) which is received in said bore in an axially movable manner and which comprises a compensating housing ( 12 ) for actuating the gas exchange valve ( 1 ); and an axial stop which limits the extending movement of the compensation housing out of the bore ( 9 ) and which comprises stopes ( 14, 15 ) that overlap each other radially. The stop ( 14 ) on the compensation housing-side is a collar of a sleeve ( 18 ) that surrounds the outer casing of the compensation housing said collar extending outwards in a radial manner.

Description:
BACKGROUND 
       [0001]    The invention concerns an actuator of an electrohydraulic gas exchange valve train of an internal combustion engine, said actuator comprising an actuator housing which can be fixed in the internal combustion engine, said actuator housing comprising a bore, a valve lash adjuster being received axially displaceable in said bore, said lash adjuster comprising a compensating housing for operating the gas exchange valve and further comprising an axial stop for limiting an outward travel of the compensating housing out of said bore and said axial stop comprising radially overlapping stops which are fixed in axial direction on said bore and on said compensating housing. 
         [0002]    It is known that the variability of the opening and closing times of gas exchange valves and of the maximum valve lift is achieved in electrohydraulic valve trains in that a so-called hydraulic linkage together with a pressure chamber is arranged between a cam of a camshaft and the gas exchange valve, wherein the volume of the pressure chamber can be continuously reduced through an electromagnetic hydraulic valve into a pressure relief chamber. Depending on the reduction volume of the hydraulic medium, the cam lift produced by the camshaft is converted fully, partially or not at all into a lift of the gas exchange valve. 
         [0003]    The present invention relates to that part of the valve train actuating system that is situated on the gas exchange valve side and whose movement corresponds to the lift of the gas exchange valve. An actuator of the pre-cited type is known, for example, from DE 10 2007 030 215 A1. The actuator housing in this case is a bushing that is screwed into a hydraulic unit that is fixed in the cylinder head of the internal combustion engine and in whose bore a hydraulically loaded slave cylinder and, adjoining this, a hydraulic valve lash adjuster of a known type are mounted for axial movement. In the disassembled state of the actuator or of the hydraulic unit, the compensating housing of the valve lash adjuster is not seated on the gas exchange valve, and the compensating housing is prevented from falling out of the bore of the actuator housing through the axial stop that is then active. The stops of the axial stop on the compensating housing are made in the form of a polygonal snap ring that is inserted into an annular groove on the outer peripheral wall of the compensating housing to protrude in radial direction therefrom, and the stops on the bore are constituted by a shoulder that is formed by a bore opening with a reduced diameter. 
       SUMMARY 
       [0004]    The object of the present invention is to improve the structure of an actuator of the pre-cited type such that, with differently configured gas exchange valve trains that, in particular, create differently large maximum lifts on the gas exchange valve, appropriately adapted actuators comprising the largest possible number of identical parts (low-cost manufacture) can be used. 
         [0005]    The above object is achieved by implementing one or more of the features of the invention, whereas advantageous developments and configurations of the invention are the subject matter of the dependent claims. According to the invention, the stop on the compensating housing is a radially outwards extending collar of a bushing that surrounds the outer peripheral wall of the compensating housing. In contrast to the cited prior art, in which the stop on compensating housing is made in the form of a snap ring which is always situated at the same axial position relative to the compensating housing, the bushing of the invention serves as a simple to adapt bushing collar with a variable-positioning upper vertical stop in the form of the bushing collar. As a result, the axial movability of the compensating housing within the bore can be varied through the axial dimensioning of the bushing and can be adapted to differently configured gas exchange valve trains, while the compensating housings and, given the case, also the actuator housings always remain identical. 
         [0006]    According to a further development of the invention, the stop surface on the collar extends in a gas exchange valve distal direction outside of the axial dimension of the outer peripheral wall of the compensating housing. Through this configuration, it becomes possible to always use large series compensating housings with a uniform standard length even if the maximum lift to be transmitted by the actuator to the gas exchange valve is relatively high. 
         [0007]    The axial fixing of the bushing on the compensating housing can be realized on the one hand through positive engagement. For this purpose, the inner peripheral wall of the bushing, for instance, can comprise at least one bead that engages into an annular groove on the outer peripheral wall of the compensating housing. Alternatively, the bushing may engage behind the outer peripheral wall of the compensating housing on a radially tapering end section of the compensating housing near the gas exchange valve. 
         [0008]    On the other hand, the axial fixing of the bushing on the compensating housing can also be realized through force locking which creates an interference fit between the inner peripheral wall of the bushing and the outer peripheral wall of the compensating housing. The interference fit enables the bushing to be fixed on the compensating housing at largely variable axial positions of the stop. 
         [0009]    Further, the stop on the bore is a radially inwards extending collar of a further bushing that surrounds an outer peripheral wall of the actuator housing. In contrast to the cited prior art, it is not necessary to make the bore with a stepped configuration which necessitates a relatively complex undercut. In an alternative to this embodiment, the further bushing does not surround the outer peripheral wall of the actuator housing but is fixed on the inner peripheral wall of the bore. 
         [0010]    The axial fixing of the further bushing can be realized through force locking which creates an interference fit between the inner peripheral wall of the bushing and the outer peripheral wall of the actuator housing (or, according to the aforesaid alternative comprising a further bushing that lines the bore between the outer peripheral wall of the further bushing and the inner peripheral wall of the bore). The interference fit further enables the further bushing to be fixed on the actuator housing at largely variable axial positions of the stop on the bore. 
         [0011]    The stop on the bore may also be in the form of a ring, for instance an elastomer O-ring or likewise a snap ring that is inserted into an annular groove extending in the bore and protruding radially out of the annular groove. 
         [0012]    The bushings of the invention can be made particularly as thin-walled, drawn parts out of a sheet metal material or as injection molded parts out of a plastic material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Further features result from the following description and the appended drawings in which parts or details of examples of embodiment of an actuator are illustrated that are important for a better understanding of the invention. If not otherwise mentioned, identical or functionally identical features or components bear identical reference numerals. The figures show: 
           [0014]      FIG. 1   a , a first example of embodiment of the invention, in a longitudinal section; 
           [0015]      FIG. 1   b , the first example of embodiment of the invention in a non-sectional representation; 
           [0016]      FIG. 2   a , the compensating housing including a bushing of a second example of embodiment of the invention, in a longitudinal section; 
           [0017]      FIG. 2   b , the compensating housing including the bushing of  FIG. 2   a , in a perspective representation; 
           [0018]      FIG. 3 , the valve lash adjuster of a third example of embodiment of the invention, in a longitudinal section; 
           [0019]      FIG. 4   a , a fourth example of embodiment of the invention, in a longitudinal section; 
           [0020]      FIG. 4   b , the compensating housing including the bushing of  FIG. 4   a , as a detail; 
           [0021]      FIG. 5 , the compensating housing including a bushing of a fifth example of embodiment of the invention, as a detail; 
           [0022]      FIG. 6 , the compensating housing including a bushing of a sixth example of embodiment of the invention, as a detail; 
           [0023]      FIG. 7   a , a prior art actuator, in the operable assembled state, and 
           [0024]      FIG. 7   b , the actuator of  FIG. 7   a  in the disassembled state 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    For the sake of a better understanding, the invention may be described with reference to  FIG. 7   a  which discloses a section of a prior art electrohydraulic gas exchange valve train for a variable operation of a gas exchange valve  1  that is spring-loaded in closing direction. The section shows an actuator  702  that is fixed in a hydraulic unit  3  that in its turn is arranged in a cylinder head (not shown) of an internal combustion engine between a camshaft and the gas exchange valves and serves for a variable-lift transmission of a cam lift to the respective gas exchange valve  1 . 
         [0026]    The actuator  702  comprises a hollow cylindrical actuator housing  704  that is fixed through a screw connection  5  in a reception  6  of the hydraulic unit  3 , and further comprises a slave piston  7  and a hydraulic valve lash adjuster  708 , both of which are received axially movable in the central bore  709  under a choking valve  10  which serves as a hydraulic brake. The slave piston  7  which is loaded through hydraulic pressure in its turn actuates a pressure piston  711  of a known type that, through a compensating housing  712  which contacts the gas exchange valve  1 , forms a variable-height pressure chamber  13  of the valve lash adjuster  708 . 
         [0027]    In the operational state illustrated, the gas exchange valve  1  is closed and the slave piston  7  and the valve lash adjuster  708  are accordingly fully retracted into the actuator housing  704 . In contrast,  FIG. 7   b  shows the actuator  702  in the disassembled state of the hydraulic unit  3  in which the valve lash adjuster  708  is extended out of the bore  709  up to the limitation formed by an axial stop. The stops  714  and  715  constituting the axial stop are a snap ring disposed on the compensating housing  712  and a shoulder of the bore  709  arranged on the opening of the bore  709  that is made with an undercut. The snap ring  714  is inserted into an annular groove  716  which extends in the outer peripheral wall of the compensating housing  712 , and, due its polygonal shape, the snap ring  714  protrudes at points so far out of the annular groove  716  as to overlap the shoulder  715  in radial direction, and thus prevents the compensating housing  712  from falling out of the bore  709  in the shown stop position. In this stop position, the compensating housing  712  is extended slightly further outwards than during an operational maximum lift on the gas exchange valve  1 . Thus, if the compensating housing  712  remains unchanged but the maximum lift increases, it would be necessary to shift the shoulder which constitutes the stop  715  on the bore in direction of the spring collar  17 . However, this modification is subject to narrow limits because a minimum free axial motion of the actuator housing  704  relative to the spring collar  17  must be preserved. In addition, such a modification would not be compatible with the principle of using identical parts. 
         [0028]    Examples of embodiment of the inventive actuators of electrohydraulic gas exchange valve trains which, in particular, enable the use of identical valve lash adjusters  8  with different maximum lifts of the gas exchange valves are described in the following with reference to the appended  FIGS. 1 to 6 . All embodiments comprise a bushing  18  that is made out of sheet metal material by deep drawing and surrounds the outer peripheral wall of the compensating housing  12 , wherein the stop  14  on the compensating housing is constituted by a radially outwards extending collar of the bushing  18 . 
         [0029]      FIGS. 1   a  and  1   b  show a first example of embodiment. The compensating housing  112  is taken from a construction kit for conventional standard valve trains with hydraulic valve lash adjustment and it accordingly comprises an annular groove  116  for a snap ring. In this case, however, the annular groove  116  has no function because the bushing  118  is fixed on the compensating housing  112  between the inner peripheral wall of the bushing  118  and the outer peripheral wall of the compensating housing  112  through force locking, i.e. through a longitudinal interference fit. To enable the manufacturing of the bore  109  without undercuts and at comparatively low costs, the stop  115  on the bore  109  is formed by a collar of a further deep drawn bushing  19  that surrounds the outer peripheral wall of the actuator housing  104 . The axial fixing of the further bushing  19 , too, is achieved through force locking in that, between the inner peripheral wall of the bushing  19  and the six circular arc-shaped surfaces  20  of the hexagon  21  that serves to screw in the actuator housing  104 , is formed an interference fit in which the radially inwards extending collar  115  bears against the gas exchange valve side front end surface of the actuator housing  104 . As an alternative to this, the dotted-line contour shown in  FIG. 1   b  is meant to indicate that the further bushing  19  can be pressed onto the front end surface of the actuator  104  up to a certain pre-determined axial position even without a stop in order to vary the position of the axial stop as required. 
         [0030]      FIGS. 2   a  and  2   b  show a second example of embodiment. The axial fixing of the bushing  218  on the compensating housing  212  is realized in this case by positive engagement in that the inner peripheral wall of the bushing  218  comprises three beads  222  that are uniformly distributed in peripheral direction, and said beads engage into an annular groove  216  that is modified with respect to  FIG. 1 . 
         [0031]    In the third example of embodiment shown in  FIG. 3 , the axial fixing of the bushing  318  on the compensating housing  312  is realized both through force locking and through positive engagement. The positive engagement is realized in that a diameter constriction  23  of the bushing  318  engages behind the radially tapering gas exchange valve proximate end section of the outer peripheral wall of the compensating housing  312 . Accordingly, in this case too, the annular groove  316  of the compensating housing  312  taken from the construction kit for conventional standard valve trains has no function. Force locking is realized through a comparatively light longitudinal interference fit between the inner peripheral wall of the bushing  318  and the outer peripheral wall of the compensating housing  312 . 
         [0032]    The stop  415  on the bore  409  in the fourth example of embodiment shown in  FIG. 4   a  is constituted by a snap ring that is inserted into an annular groove  24  that is worked into the bore  409 , and said snap ring protrudes radially out of the annular groove  24 . The axial fixing of the bushing  418  on the compensating housing  412  is realized through positive engagement of a circumferential bead  422  of the bushing  418  engaging into the annular groove  416 , said bushing  418  being optionally slit in axial direction for facilitating its mounting on the compensating housing  412 . 
         [0033]      FIG. 4   b  is a detail view of the example of embodiment shown in  FIG. 4   a , and  FIGS. 5 and 6  disclose, as mentioned above, further structural design alternatives for the bushing  18  which serves as a stop adapter. As shown in  FIG. 7   b , the symbolically illustrated stop  15  on the bore determines the extended position of the compensating housing  12  that is limited by the respective axial stop. 
         [0034]    The fifth example of embodiment shown in  FIG. 5  corresponds to the first example of embodiment in  FIG. 1   a , wherein, in place of the interference fit on the inner peripheral wall of the bushing  518 , a bead  522  in positive engagement with the annular groove  516  is used. 
         [0035]    The sixth example of embodiment shown in  FIG. 6  likewise corresponds to the first example of embodiment, wherein, however, the compensating housing  612  does not comprise an annular groove. In these examples of embodiment, too, the stop surface  614  of the collar always extends in a gas exchange valve distal direction outside of the axial dimension of the outer peripheral wall of the compensating housing  612 . Or, to put it more simply, the stop  614  extends spaced by an axial dimension H from the gas exchange valve distal front end surface of the compensating housing  612 . This means that, in the case of both the compensating housings  412  and  512  comprising annular grooves  416  and  516  respectively, the maximum lift on the gas exchange valve with an unmodified compensating housing  12  can be enlarged by the dimension L relative to the example of prior art shown in  FIG. 10 . In the case of the compensating housing  612  without an annular groove, the maximum lift on the gas exchange valve depends on the bushing dimension L and on the pressing dimension P of the bushing  618  on the compensating housing  612 . 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  Gas exchange valve 
           2  Actuator 
           3  Hydraulic unit 
           4  Actuator housing 
           5  Screw connection 
           6  Reception 
           7  Slave piston 
           8  Valve lash adjuster 
           9  Bore of the actuator housing 
           10  Choking valve 
           11  Pressure piston 
           12  Compensating housing 
           13  Pressure chamber 
           14  Stop on the compensating housing 
           15  Stop on the bore 
           16  Annular groove 
           17  Spring collar 
           18  Bushing 
           19  Further bushing 
           20  Circular arc-shaped surface 
           21  Hexagon 
           22  Bead 
           23  Diameter constriction 
           24  Annular groove