Abstract:
A camshaft adjusting device ( 19 ) having a camshaft adjuster ( 4 ), including a stator ( 36 ), a rotor ( 38 ) which can be rotated relative to the stator ( 36 ) about a rotational axis ( 74 ), and a hub ( 52 ) which is arranged on the rotor ( 38 ) or on the stator ( 36 ) and has a receiving cup ( 62 ), and having a camshaft ( 12 ) which is received in the receiving cup ( 62 ). It is provided here that the camshaft ( 12 ) is fixed radially in the receiving cup ( 62 ) via at least three spacer elements ( 64 ). A camshaft adjusting device ( 19 ) of this type can be produced simply and inexpensively.

Description:
[0001]    The present invention relates to a camshaft adjusting device having a camshaft adjuster, which includes a stator, a rotor which is rotatable relative to the stator around a rotation axis, and a hub situated on the rotor or on the stator and having a receiving bushing, as well as a camshaft accommodated in the receiving bushing. In particular, the present invention deals with the problem of centering the camshaft adjuster on the camshaft. 
       BACKGROUND 
       [0002]    Via the hub, the camshaft adjuster of a camshaft adjusting device of the type mentioned at the outset is rotatably fixedly connected to the crankshaft of an internal combustion engine. The phase angle between the crankshaft and the camshaft may be set with the aid of the relative rotatability of the rotor relative to the stator. 
         [0003]    A camshaft adjusting device is known from DE 101 617 01 A1, in which the camshaft is accommodated in a receiving bushing in the rotor of the camshaft adjuster for the purpose of centering with the aid of the camshaft adjuster. The receiving bushing of the hub is designed as a centering opening having an uninterrupted circular surface. The centering opening additionally has an area which is reduced in diameter for the purpose of centering. The camshaft is fixed on the rotor with the aid of a central screw. 
       SUMMARY OF THE INVENTION 
       [0004]    It is an object of the present invention to provide a camshaft adjusting device which is easy and economical to manufacture and which permits a preferably secure centering of the camshaft or the camshaft adjuster on the camshaft. 
         [0005]    The present invention provides a camshaft adjusting device of the type mentioned at the outset in which the camshaft is radially fixed in the receiving bushing with the aid of at least three spacer elements. 
         [0006]    In a first step, the present invention is based on the consideration that a receiving bushing of the hub, into which the camshaft is centrically inserted, must be manufactured or machined within very narrow tolerances, so that the inserted camshaft does not generate an imbalance with respect to the rotation axis of the camshaft adjuster. The required low tolerances are achieved in terms of manufacturing by complex manufacturing or machining. For example, the receiving bushing must be rotated to achieve the necessary low tolerances on the circumferential line. This disadvantageously increases the costs and the cycle times for manufacturing. 
         [0007]    In a second step, the present invention recognizes that, if the camshaft is to be centrically accommodated on the camshaft adjuster, a rotation may be dispensed with according to the operating principle of a chuck. If the camshaft is fixed radially in the receiving bushing with the aid of at least three spacer elements, the receiving bushing as such no longer has to be manufactured with the required low tolerances. Instead, the spacer elements establish the radial position of the camshaft. In other words, an interrupted centering surface is provided, so that a rotation of the receiving bushing is no longer needed for manufacturing. Only the small number of spacer elements must be manufactured in a defined manner with respect to their radial contact surfaces or contact points. 
         [0008]    In particular, the present invention makes it possible to manufacture the hub including the receiving bushing or the rotor or the stator including the receiving bushing without machining or with the aid of a cost-effective sintering. The corresponding individual parts are initially powder-metallurgically pressed into mold parts to form a green compact and subsequently sintered. Only the tolerances of the interrupted centering surface, i.e., of the radial contact surfaces or contact points of the spacer elements as well as, if necessary, the base of the receiving bushing are subsequently set with the aid of a form tool. The form tool may be, for example, a mandrel, a stamp or a die. This setting of the tolerances is also known under the term “calibration.” 
         [0009]    In other words, the present invention also provides a method for manufacturing a camshaft adjusting device of the type mentioned at the outset, a rotor and a stator being provided and assembled, rotatable relative to one another, to form a camshaft adjuster, and the camshaft adjuster being centered on a camshaft. According to the present invention, it is provided that a hub, which includes a receiving bushing and at least three spacer elements, is powder-metallurgically manufactured for the rotor or for the stator, that the radial tolerances of the spacer elements are set with the aid of calibration and that the camshaft is introduced into the receiving bushing and fixed radially with the aid of the spacer elements. 
         [0010]    The rotor or the stator itself, or only the corresponding hub parts, may be powder-metallurgically manufactured. The spacer elements are preferably manufactured together with the receiving bushing, and the radial tolerances of the spacer elements manufactured together with the receiving bushing are set with the aid of calibration. However, it is also possible to manufacture the spacer elements separately and to subsequently insert them into the receiving bushing. The spacer elements may also be mounted on or manufactured together with the camshaft. The spacer elements may be mounted, for example, on a support or the like, which may be inserted into the receiving bushing as a component independent of the camshaft adjuster. In this way, a centering having an accuracy which is independent of the remaining components of the camshaft adjuster may be achieved. It is also possible to introduce the spacer elements radially between the wall of the receiving bushing and the camshaft entirely without fastening. After the radial tolerances of the spacer elements are set, the camshaft is introduced into the receiving bushing and fixed radially. 
         [0011]    In one preferred embodiment of the present invention, at least two of the spacer elements are situated offset from each other in the axial direction. Due to this measure, the camshaft is definitively fixed in its axial alignment, in particular aligned along the rotation axis without a tilt. In the case of a punctiform support of the camshaft on spacer elements situated in an axial plane, mechanical deformation may possibly cause an indeterminacy in the axial direction of the camshaft. 
         [0012]    In one advantageous refinement, the spacer elements extend in the axial direction. This permits a concrete fixing of the camshaft in the axial direction, since, in the axial direction, the camshaft is guided along the spacer element, for example at multiple points or on a surface or an edge. 
         [0013]    The spacer elements advantageously taper toward the camshaft in the radial direction for the purpose of minimizing the active contact surface between the spacer elements and the camshaft, so that multiple contact points with the camshaft, which over-determine the centering of the camshaft, do not occur on the individual spacer elements themselves. The thickness of the spacer elements preferably tapers on a plane perpendicular to the axial direction, while retaining a certain axial extension, so that an axial contact line toward the camshaft results on each of the spacer elements. 
         [0014]    In an additional refinement, the spacer elements extend in the axial direction to a base of the receiving bushing, indentations being introduced into the base, which surround each of the spacer elements. In other words, the indentations are situated directly in the root area of the spacer elements. The indentations in the root area of the spacer elements may also be provided by sintering and/or pressing. The indentations facilitate a flat contact of the front side of the camshaft on the base of the receiving bushing, without an edge-carrying outer rim of the camshaft striking in the radial transition in the root area. Upon finally tightening a camshaft mounted on an edge seat in the root area, for example with the aid of a central screw, the camshaft may undesirably tilt or twist later on, which may result in serious subsequent damages. 
         [0015]    At least one form-fitting element is furthermore advantageously situated on a base of the receiving bushing, which is rotatably fixedly coupled with a complementary form-fitting element on the front of the camshaft. Due to the additional form fit between the front and the base of the receiving bushing, higher torques may be transmitted than in the case of a flat support. A form fit of this type also permits an angle-coded installation of the camshaft. For this purpose, the form-fitting elements are designed in such a way that the camshaft may be inserted into the receiving bushing all the way to the base only in one single, defined angular position. The phase angle of the camshaft on the camshaft adjuster may be predefined thereby, for example during assembly. 
         [0016]    The form-fitting elements situated on the base may, in particular, also taper in the axial direction, so that, when the camshaft is tightened on the camshaft adjuster, for example with the aid of a central screw, they bore, dig or cut into the front side, thereby compensating for any tolerances that may exist. 
         [0017]    In one refinement of the present invention, the spacer elements are situated on an inner lining of the receiving bushing and may particularly preferably be provided as a single piece with the inner lining. In this way, the rotor or the stator may be manufactured using a simple sintering process, the individual spacer elements being brought to the tolerances necessary for centering the camshaft after the sintering process with the aid of calibration. 
         [0018]    In one advantageous embodiment, the receiving bushing is situated on a rotor of the camshaft adjuster. In this case, the camshaft adjuster is mounted together with the rotor on the camshaft, the latter being accommodated in a centered manner in the receiving bushing of the rotor. The stator is then driven by the crankshaft, in particular using a chain drive. The angle between the camshaft and the crankshaft is set with the aid of the phase angle of the rotor relative to the stator. Alternatively, the receiving bushing may be situated in a stator if the stator must be accommodated centrally or centered relative to the camshaft. The stator is then joined directly to the camshaft or supported on it radially. This is the case, in particular, in a camshaft which surrounds an inner shaft and an outer shaft concentric thereto, the stator being connected to the inner shaft and the rotor to the outer shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Exemplary embodiments of the present invention are explained in greater detail below on the basis of a drawing. 
           [0020]      FIG. 1  shows a schematic representation of an internal combustion engine including camshaft adjusters; 
           [0021]      FIG. 2  shows a radial sectional view of one camshaft adjuster from  FIG. 1 ; 
           [0022]      FIG. 3  shows an axial sectional view of the camshaft adjuster from  FIG. 2 ; 
           [0023]      FIG. 4  shows an axial top view of a hub of an alternative rotor of the camshaft adjuster from  FIG. 2 ; 
           [0024]      FIG. 5  shows a perspective view of the hub from  FIG. 4 ; and 
           [0025]      FIG. 6  shows a broken open perspective view of the hub from  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    In the figures, the same elements are provided with the same reference numerals and described only once. 
         [0027]    Reference is hereby made to  FIG. 1 , which shows a schematic representation of an internal combustion engine  2 , including camshaft adjusters  4 . 
         [0028]    In a manner which is known per se, internal combustion engine  2  includes a combustion chamber  6 , which may be opened and closed with the aid of valves  8 . The valves are activated by cams  10  on corresponding camshafts  12 . A reciprocating piston  14 , which drives a crankshaft  16 , is accommodated in combustion chamber  6 . The rotation of crankshaft  16  is transmitted on its axial end to camshaft adjusters  4  via driving means  18 . In the present example, the driving means may be a chain or a belt. 
         [0029]    Camshaft adjusters  4  are each mounted axially on camshafts  12 , absorb the rotation energy of driving means  18  and transfer it to camshafts  12 . Camshaft adjusters  4  are thus able to temporarily decelerate or accelerate the rotation of camshafts  12  with respect to crankshaft  16  for the purpose of changing the phase angle of camshafts  12  with respect to crankshaft  16 . 
         [0030]    Reference is hereby made to  FIGS. 2 and 3 , which show a radial and axial sectional view of one of camshaft adjusters  4  from  FIG. 1 . 
         [0031]    Camshaft adjuster  4  is mounted on camshaft  12 . Camshaft adjuster  4  and camshaft  12  together form camshaft adjusting device  19 . In the present description, the axial end of camshaft  12 , on which camshaft adjuster  4  is mounted, is defined as the “front” and the end opposite this axial end is defined as the “rear.” 
         [0032]    Camshaft  12  has multiple A supply connections  20  and one B supply connection, which is not illustrated, in the form of radial bores guided through the camshaft. The two supply connections  20  may be connected to a pressure port, which is not illustrated, and to a tank connection, which is not illustrated, in a manner which is known to those skilled in the art, for example via a 4/3-way valve. An axial stop  22  is furthermore provided axially upstream from A supply connections  20 , via which the camshaft may be counter-supported in a bearing block, which is not illustrated. 
         [0033]    Camshaft  12  furthermore has a stepped, axial central bore  24 , one step  26  of stepped central bore  24  being provided axially between A supply connections  20  and the B supply connection, which is not illustrated. An inner thread  28 , into which a central screw or a central valve body  30  having an outer thread  31  is screwed, is provided behind step  26  in central bore  24 . Camshaft adjuster  4  is fastened to camshaft  12  in a manner which is still to be described via the central screw or central valve body  30 . 
         [0034]    An annular gap  32  is provided axially in front of step  26  between central screw  30  and a wall of central bore  24 . The B supply connection, which is not illustrated, is inserted into this annular gap  32  in a manner which is not shown. 
         [0035]    Furthermore, four axial bores  34 , which are spaced equidistantly apart in the circumferential direction of camshaft  12  and which are each connected on their front axial end to one of A supply connections  20 , penetrate camshaft  12  radially via central bore  24 . 
         [0036]    Camshaft adjuster  4  has a stator  36  and a rotor  38 , which is rotatably accommodated in stator  36 . 
         [0037]    Stator  36  has an annular outer part  40 , from which multiple separating elements  42  project radially to the inside. Only one of these separating elements  42  is shown in  FIG. 2 . Screws  44 , which are provided to fasten a front cover  46  on the front of stator  36  and a sealing cover  48  on the back of stator  36 , axially penetrate separating elements  42 . An inner chamber surrounded by the annular outer part is axially closed in this way. Teeth  50  are provided on the radial outside of annular outer part  40 , which are able to engage with driving means  18 . 
         [0038]    As mentioned above, rotor  38  is accommodated in stator  36  and rotatably fixedly connected to camshaft  12  with the aid of the central screw or central valve body  30 . Rotor  38  has a hub  52 , from which vanes  54  project radially and which engages between separating elements  42  of stator  36 , viewed in the circumferential direction of camshaft adjuster  4 . Pressure chambers are formed in this way, via which rotor  38  may be adjusted with respect to stator  36  by pumping in hydraulic fluid. Viewed in the direction of rotation of camshaft adjuster  4 , a pressure chamber upstream from a vane  54  is referred to as a retarding chamber, and a pressure chamber downstream from a vane  54  is referred to as an advancing chamber.  FIG. 2  shows a pressure chamber, which is to be assumed to be retarding chamber  56 . 
         [0039]    Gap  32  is continued in rotor  38 . Radial retarding bores  58 , which lead into retarding chambers  56 , penetrate hub  52  from the gap. Only two of these retarding bores  58  are shown in  FIG. 2 . Some of axial bores  34  through camshaft  12  are also continued into rotor  38   36 . Radial advancing bores  60 , which lead into the advancing chambers, penetrate hub  52  from axial bores  34 . Only one of advancing bores  60  is shown in  FIG. 2 . If hydraulic fluid is thereby pumped into camshaft adjuster  4  via A supply connections  20 , the advancing chambers, which are not illustrated, are pressurized, and camshaft  12  is accelerated with respect to crankshaft  16 , which is connected to stator  36  via driving means  18 . In contrast, camshaft  12  is decelerated when hydraulic fluid is pumped into retarding chambers  56  via the B supply port, which is not illustrated. 
         [0040]    To avoid camshaft adjuster  4  generating imbalances during the rotation of camshaft  12 , camshaft adjuster  4  must be mounted on camshaft  12  centrically to rotation axis  74 . For this purpose, hub  52  of rotor  38  has a receiving bushing  62 , which is axially indented from the back of camshaft adjuster  4  and into which camshaft  12  is inserted. Within receiving bushing  62 , camshaft  12  is supported by three spacer elements  64 , which radially fix camshaft  12  with respect to rotor  38  and thus to camshaft adjuster  4 . Hub  52  with receiving bushing  62  and spacer elements  64  situated on the inner wall of receiving bushing  62  is manufactured by sintering. The radial dimensions of spacer elements  64  are set by calibration after the sintering process. 
         [0041]    Spacer elements  64  will be discussed in greater detail on the basis of  FIGS. 4 through 6 . 
         [0042]      FIGS. 4 through 6  show another example of a hub  52  of rotor  38  of camshaft adjuster  4  in an axial top view, in a perspective view and in a broken open perspective view. 
         [0043]    In  FIGS. 4 through 6 , hub  52  has five vane grooves  66 , into which vanes  54  may be inserted. In this way, five advancing chambers and five retarding chambers  56  may be formed by a corresponding stator  36 , which has five separating elements  42 . These adjusting chambers are supplied with hydraulic fluid through five advancing bores  60  and five retarding bores  58 . Correspondingly, five axial bores  34 , which are connectable to A supply connection  20  in the manner described in  FIG. 2 , lead to five advancing bores  60 . Five retarding bores  58  lead into gap  32  described in  FIG. 2 , which is connectable to the B supply connection. 
         [0044]    An axial locking pin bore  68  is furthermore provided in hub  52 , in which a locking pin, which is not illustrated, may be guided, which is able to secure a certain rotational position of stator  36  with respect to rotor  38  in a manner which is known to those skilled in the art. 
         [0045]    In the present embodiment, spacer elements  64  are designed to taper radially to the inside and be spaced a distance apart at a 120° angle  70 . Spacer elements  64  extend in the axial direction. An axially running line results for each spacer element  64  as the contact surface for an essentially cylindrical camshaft  12 . The radial position and angular position of camshaft  12  are definitively established via the three spacer elements  64 . Radial height  72  of spacer elements  64  may decrease in the axial direction counter to the joining direction of camshaft  12  in a manner which is not illustrated. In this way, spacer elements  64  may grip camshaft  12  during insertion into receiving bushing  62  and center it with respect to a center point  74  or a rotation axis  74 . 
         [0046]    Axial indentations  76  are introduced around the bottom or root area of spacer elements  64 , which rest on base  63  of receiving bushing  62 . These axial indentations  76  facilitate a flat support of the front of camshaft  12  on base  63 . An undesirable impact of an outer edge of camshaft  12  on the radial transition in the root area of spacer elements  64  is avoided. 
         [0047]    According to  FIG. 5 , a form-fitting element  65  is provided on base  63  of receiving bushing  62 , which forms a form fit with a complementary form-fitting element on the front of camshaft  12  when camshaft  12  is inserted. The form fit formed hereby on the front of inserted camshaft  12  permits the transmission of higher torques. Due to single form-fitting element  65 , the mounting of camshaft  12  in receiving bushing  62  is possible in only one specific rotational position. 
         [0048]    To manufacture illustrated hub  52 , hub  52  may initially be sintered with spacer elements  64 . Radial height  72  of spacer elements  64  may then be calibrated, for example using a noncutting machining method with the aid of a suitable form tool. To finish rotor  38 , vanes  54  may be inserted into vane grooves  66  in hub  52 . After mounting rotor  38  in a stator  36  (see  FIG. 2 ), camshaft  12  may be introduced into receiving bushing  62  and fixed radially. Camshaft  12  may then be tightened axially with the aid of a central screw or a central valve body  30 . 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           2  Internal combustion engine 
           4  Camshaft adjuster 
           6  Combustion chamber 
           8  Valve 
           10  Cam 
           12  Camshaft 
           14  Reciprocating piston 
           16  Crankshaft 
           18  Driving means 
           19  Camshaft adjusting device 
           20  A supply connection 
           22  Axial stop 
           24  Central bore 
           26  Axial step 
           28  Inner thread 
           30  Central screw 
           31  Outer thread 
           32  Gap 
           34  Axial bore 
           36  Stator 
           38  Rotor 
           40  Outer part 
           42  Separating element 
           44  Screw 
           46  Front cover 
           48  Sealing cover 
           50  Tooth 
           52  Hub 
           54  Vane 
           56  Retarding chamber 
           58  Retarding bore 
           60  Advancing bore 
           62  Receiving bushing 
           63  Base 
           64  Spacer elements 
           65  Form-fitting element 
           66  Vane groove 
           68  Axial locking pin bore 
           70  Angle 
           72  Radial height 
           74  Rotation axis 
           76  Axial indentation