Abstract:
A camshaft adjuster ( 1 ) for an internal combustion engine is provided, wherein the relative angle between a drive wheel ( 2 ) and an inner rotor associated with a camshaft can be adjusted via hydraulic loading of pressure spaces ( 9, 10 ) between an outer rotor ( 3 ) and the inner rotor ( 6 ), wherein the drive wheel ( 2 ) is made of plastic and the outer rotor ( 3 ) associated with the drive wheel ( 2 ) is made of metal. Particularly good linkage can be obtained and mounting complexity can be reduced by having at least one bearing surface between the outer rotor ( 3 ) and the inner rotor ( 6 ) that is connected with a firmly bonded material or positive fit in the drive wheel that is made from plastic.

Description:
BACKGROUND 
       [0001]    The invention relates to a camshaft adjuster for an internal combustion engine according to the preamble of Claim  1 . 
         [0002]    From DE 102 11 607 A1, a camshaft adjuster for adjusting and fixing the relative rotational angle position of a camshaft relative to the crankshaft of an internal combustion engine is known. A hydraulic adjustment device here consists of an external rotor, which is allocated to a drive wheel, and also an internal rotor, which is connected to a camshaft via a driven element. Pressure chambers are formed between the external rotor and the internal rotor. Charging these chambers hydraulically can change the angular relationship between the drive wheel and driven element. 
         [0003]    In the mentioned publication, it is proposed to produce the drive wheel and at least one of the other functional parts integrally from a high load capacity plastic. According to a first embodiment, the drive wheel and the external rotor and also two other components are produced integrally from plastic. For an alternative construction, the external rotor is produced as a separate component from plastic or from a conventional material, such as metal, and is set in a cover formed integrally 
       SUMMARY 
       [0004]    The invention is based on the objective of creating a camshaft adjuster, which is functionally ready or optimized for good production possibilities, a small number of required components, and low weight. 
         [0005]    According to the invention, the objective is met by the features of the independent Claim  1 . 
         [0006]    The invention is based on the knowledge that for the embodiment of DE 102 11 607 A1 named above, a bearing surface is formed with plastic, which is not optimum, under some circumstances, both for a contact partner made from metal and also for such an element made from plastic in terms of bearing properties, sliding properties, and wear as well as operational strength. For example, if a plastic in the form of a duroplastic is used for an external rotor, then it has been shown that such duroplastics can contain minerals. These minerals lead to increased wear and increased friction on sliding surfaces, also those made from steel, and in the worst case to failure of the camshaft adjuster. On the other hand, it has been shown for the second embodiment named above from DE 102 11 607 A1 that a use of a metallic bearing surface requires an additional mounting step, in some circumstances unnecessarily, in a surrounding plastic body. Furthermore, through such a placement, under some circumstances another degree of freedom or play and production inaccuracy for the bearing surface is produced, which can negatively affect the operation of the camshaft adjuster. 
         [0007]    Therefore, according to the invention the bearing surface of the external rotor is formed with a metallic insert body, which is held with a firmly bonded material fit in a carrier body made from plastic. Through this firmly bonded material hold, the undesired degrees of freedom, play, and unnecessary mounting steps can be avoided. Nevertheless, according to the invention a metallic insert body can be used, so that a metallic bearing surface is given, whereby the increased wear and increased friction on the sliding surfaces can be avoided. The carrier body according to the invention can involve either the drive wheel itself or another component, such as a flange, which is connected to the drive wheel via corresponding attachment elements with a friction, positive, and/or firmly bonded material fit, possibly through the intermediate connection of additional components. 
         [0008]    According to one improvement of the invention, the insert body is constructed extending in the peripheral direction and also forms a limit for the pressure spaces in addition to the bearing surface. Accordingly, the insert body has a multifunction construction with the function of the bearing and the operating-fixed shape of the pressure spaces. Here, the insert body can limit the pressure spaces radially outwardly and/or in the peripheral direction and, under some circumstances, can form limits or stops for the internal rotor. Through the formation of the insert body extending in the peripheral direction, a rigid, closed ring structure is formed. In addition, the insert body thus correlates the position and orientation of several pressure spaces distributed over the periphery. 
         [0009]    For improving the positive-fit connection between the external rotor and the carrier body, at least one of the previously mentioned components can have connection elements. Such connection elements can involve ribs, radial projections, or radial recesses, in which a connection means, such as an adhesive, molten material, or injection molded parts of one of the previously mentioned components can be inserted or supported. In this way, the surface of the contact points between the non-positive connection means and the external rotor and carrier body can be increased. Simultaneously, a force to be transmitted between the external rotor and carrier body is supported due to the connection elements by means of larger surfaces. The transmitted forces can be transmitted by the connection elements for suitable shaping between shearing forces in the area of a casing surface and also normal forces through the radial projections and also recesses. 
         [0010]    In one preferred camshaft adjuster according to the invention, the drive wheel is produced from a composite material or a fiber composite material. Examples here can be thermoplastics or duroplastics or materials made from thermoplastics and duroplastics together. In this way, according to the material selection and material combination, the mechanical properties of the drive wheel can be influenced in a suitable way. 
         [0011]    According to another aspect of the invention, the internal rotor is (also) formed with plastic. The internal rotor has at least one bearing surface made from metal connected to this rotor with a firmly bonded material fit. Accordingly, advantages known for a construction made from plastic and named, for example, in DE 102 11 607 A1 can be used for the rotor. In addition, both the internal rotor and also the external rotor have bearing surfaces made from metal, which has proven advantageous in terms of sliding properties and operating strength. 
         [0012]    According to an improvement of the invention, the drive wheel is formed with a belt wheel or a chain wheel from plastic and connected by means of attachment elements to the carrier body formed as a flange made from plastic, which is attached, in turn, to the insert body with a positive fit. Accordingly, a production of the drive wheel, which requires, for example, a formation of teeth with complex teeth structures is allowed separate from a production of the flange with insert bodies, wherein the same or different production methods and the same or different material can be used according to requirements. An operating-fixed connection can be created equally, however, by means of the attachment elements between the drive wheel and flange and also the positive fit or firmly bonded material connection between the flange and insert body. 
         [0013]    For the case that the attachment elements are not to interact with the material of the drive wheel or the flange otherwise used, it is advantageous when the attachment elements interact with reinforcement inserts of the drive wheel and/or the flange. Such reinforcement inserts can involve, for example, metal intermediate layers such as inserts, which are supported, for example, with their casing surface opposite the other material of the drive wheel or the flange while guaranteeing a good force introduction. Possible receptacle recesses of the reinforcement inserts can be shaped selectively for connecting to the attachment elements. For example, they can be inserted into the threading, with which the attachment elements are screwed. In this way, an especially compact construction of the camshaft adjuster is allowed for simultaneously good force introduction and transmission. 
         [0014]    According to another construction of the invention, the connection between the flange and chain wheel or belt wheel is realized radially inwardly from the teeth of the chain wheel or belt wheel. Here, the axial dimension of the chain or belt wheel or its teeth is dependent and given by the force to be transmitted from the drive means, such as a chain or a belt, whereby a minimum of the axial installation length of the camshaft adjuster is given. The installation space can be used optimally according to the invention, because the already present inner space of a chain or belt wheel is used for an arrangement of the connection point between the flange and chain wheel. Here, for example, the chain or belt wheel can have a radially inwardly directed connecting piece, which is screwed to the flange. Another advantage according to the invention is that forces transmitted by the drive means, like the belts, to the drive wheel are not transmitted with a large tilting moment on the internal rotor and additional components of the camshaft adjuster. An optimal solution is produced when the connecting piece, the flange, or the connection point between these is arranged approximately in the axial direction approximately centrally in the drive wheel. 
         [0015]    An even more compact construction of the camshaft adjuster according to the invention is produced when the attachment elements act on a radius that is less than an outer diameter of the pressure chamber. Here, on one hand a radial installation size of the camshaft adjuster can be reduced, because unnecessary, unused installation spaces are avoided, especially between the pressure chamber and belt wheel. On the other hand, for a given size of the drive wheel, the outer diameter of the pressure chamber can be increased, which, under some circumstances, has the result of improved actuation while changing the hydraulic effect. 
         [0016]    For a further improved camshaft adjuster, insert bodies and carrier bodies are connected to each other with a firmly bonded material fit by means of an injection molding process. Accordingly, the insert bodies can be used in addition to their functions in operation during the production as shaping surfaces for an injection molding process, in that injection molding is performed on this material. The injection molding process simultaneously guarantees an especially good positive-fit connection between the contact body and carrier body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Additional features of the invention emerge from the following description and the associated drawings, in which embodiments of the invention are shown schematically. Shown are: 
           [0018]      FIG. 1  a cross-sectional view of a part of a camshaft adjuster according to the invention with an external rotor and a carrier body made from plastic with an insert body attached with a firmly bonded material fit and also an internal rotor that can rotate in the external rotor; 
           [0019]      FIG. 2  half of a longitudinal cross-sectional view of a camshaft adjuster according to the invention in which the drive wheel made from plastic is attached to a flange by means of an attachment element; 
           [0020]      FIG. 3  a view of a drive gearwheel made from plastic according to the invention with radially inwardly pointing brackets for receiving attachment elements; 
           [0021]      FIG. 4  half of a longitudinal cross-sectional view of a drive wheel with a connecting piece or a bracket and inserts inserted into the connecting piece or the bracket; 
           [0022]      FIG. 5  a partial cross-sectional view of a drive gearwheel with radially inwards directed brackets and inserts arranged therein; 
           [0023]      FIG. 6  a partial cross-sectional view of camshaft adjuster according to the invention, wherein attachment elements are pulled radially inwards, so that their distance from the longitudinal axis of the camshaft adjuster is smaller than the outer diameter of the pressure chambers, and 
           [0024]      FIG. 7  a view of a drive gearwheel made from plastic, which is attached by means of a carrier to a housing of the camshaft adjuster. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    The invention relates to a hydraulic camshaft adjuster  1  in a known construction. The camshaft adjuster has a drive wheel  2 , which is constructed in the shown embodiments as a belt wheel. An external rotor  3 , which is arranged radially inside of the drive wheel  2 , is connected rigidly to the drive wheel  2 . The external rotor  3  is formed with bearing surfaces  4 , which correspond to segments of a casing surface of a cylinder, as well as radial bulges for pressure chambers  5 . According to the embodiment shown in  FIG. 1 , four bearing surfaces  4  and also four pressure chambers  5  are provided, which are distributed equally over the periphery. In the external rotor  3 , an internal rotor  6 , which can be connected or is connected locked in rotation with the camshaft, is arranged so that it can rotate relative to the external rotor about a longitudinal axis of the camshaft adjuster  1 . The internal rotor  6  has bearing surfaces  7  formed corresponding to the bearing surfaces  4  of the external rotor  3  and also vane-like radial projections  8 , wherein four bearing surfaces  7  and four projections  8 , which are distributed arbitrarily or equally over the periphery of the internal rotor, are provided according to the embodiment shown in  FIG. 1 . The bearing surfaces  4  and  7  form a seal in the peripheral direction and the end surfaces of the projections  8  extend radially outwardly forming a seal on the associated pressure chambers  5 , so that pressure spaces  9 ,  10  are formed in the peripheral direction on both sides of the projections. Through suitable charging of the pressure chambers  9 ,  10 , the relative angular position between the external rotor  3  and the internal rotor  6  can be changed, whereby the angular relationship between the drive wheel  2  and a camshaft can be changed for adjusting the opening times of valves. 
         [0026]    According to  FIG. 1 , both the pressure chambers  5  and also the bearing surfaces  4  are formed with a metallic insert body  11  extending in the peripheral direction, which has an approximately constant wall thickness. The insert body  11  is held with a firmly bonded material fit in a carrier body  12 , which is formed in the embodiment shown in  FIG. 1  integrated with the drive wheel  2  or is formed as a separate component, which can be connected rigidly to the drive wheel  2 . 
         [0027]      FIG. 2  shows a camshaft adjuster  1 ′ in longitudinal section. In this camshaft adjuster, the drive wheel  2 ′ is formed integrally with inwardly projecting, axial, approximately centrally arranged brackets  13 , which extend in the direction of a longitudinal axis X-X of the camshaft adjuster  1 ′ by one-third up to one-fourth of the width of the running teeth of the drive wheel  2 ′ and which are distributed arbitrarily or equally over the periphery, cf.  FIG. 3 . A flange  14 , which is formed integrally with the external rotor  3 ′, contacts one end of the bracket  13 . The brackets  13  and  14  are connected to each other with a friction, positive, and/or firmly bonded material fit and/or by means of attachment elements  15 , which are formed as screws according to  FIG. 2 . Here, the brackets  13  and also the flange  14  have suitable bores  16  with or without threads. The bores  16  with or without threads can here be formed directly in the material forming the drive wheel or can be provided according to  FIG. 4  by reinforcement intermediate layers  17 , especially inserts, for example, made from metal, which are attached preferably with a positive fit to the additional integral elements of the drive wheel  2 . 
         [0028]    With reference to the drive wheel  2 , the external rotor  3 , the bearing surface  4 , the internal rotor  6 , the bearing surface  7 , the projections  8 , the insert body  11 , the carrier body  12 , the brackets  13 , and/or the flange  14  there are the following shaping possibilities:
       The previously mentioned component can be made from any plastic or from a fiber composite material. In particular, a thermoplastic or a duroplastic of any composition can be used.   Furthermore, any composite can be used, for example, a plastic with an iron metal or a non-iron metal. In terms of the coefficient of thermal expansion, these can be adapted to each other, so that, for example, plastic, fiber composite materials, or composite materials have equal coefficients of thermal expansion, such as adjacent components made from different materials. In particular, components arranged on the driven side, that is, components connected rigidly to the camshaft, have a greater coefficient of thermal expansion than components arranged on the drive side.   The previously mentioned components can be assembled to form one or two-piece units. For example, the drive wheel  2 , the external rotor  3 , the bearing surface  4  with insert body  11 , brackets  13 , and carrier body  12 , as well as flange  14  are constructed as an integral, installation space-optimized component made from one or more materials or composite materials.   For lowering the weight and for improving the assembly possibilities, pockets can be provided in the previously mentioned components.   Drive wheel  2  and insert body  11  can be connected to each other, possibly under the intermediate connection of additional (sub) bodies with a non-positive fit, for example, by screws, with a positive fit, for example, by rivets, or with a firmly bonded material fit, for example, by bonding, injection molding, or one-piece production, wherein combinations of the previously mentioned connection possibilities are also conceivable.   Non-plastic elements can be used as auxiliary agents for screw connections, for example, on the basis of a “mold-in” or “after-molding” technique. One “mold-in” technique involves, for example, a metal bushing with threads, which is molded in a die, while as an example for an “after-mold” technique, a metal bushing with threads is conceivable, which is inserted into a plastic part after the molding process.   Metallic elements or sub-parts can be formed as reinforcement material in other material, for example, for homogenizing the expansion and/or for reinforcing, for forming support material, and for increasing the component stiffness.   A selection of the materials and their orientation can be used as thermal construction parameters, in which a desired target size is set according to the element and its volume percentage of the coefficient of expansion.   The use of reinforcement intermediate layers or inserts can be used especially for minimizing setting force losses and for permitting direct screw connection.   According to  FIG. 1 , the external rotor can be embedded directly in a plastic material. This plastic material can be joined with the external rotor directly, for example, in an injection molding process or else by means of later mounting.       
 
         [0039]      FIG. 6  shows a partial cross section allocated to the embodiment according to  FIG. 2 . From this it is visible that the flange  14  has no circular outer contours, but instead projects radially outwards in the attachment region to the brackets  13 . It is to be seen further that the external rotor  3  has sub-areas with the pressure chambers  5 , which project radially outwards and the attachment elements  15  are connected in the area of recesses  18  or radially inwards oriented pockets with the external rotor  3 . In this way, the attachment elements  15  can be “pulled down” to form small radii, so that the attachment elements  15  act at a radius that lies in the area of the outer diameter of the pressure chamber  5  or is less than this area. Here, the attachment elements  15 , the brackets  13 , and any flange  14  are provided axially between the end faces of the drive wheel  2 ′, so that a small axial installation size is produced. 
         [0040]      FIG. 7  shows an example construction for a drive wheel  2 ″ with associated components, here a toothed ring  19 , a carrier  20 , and a housing  21 . 
         [0041]    The housing  21  is formed especially as a sheet part with an approximately cylindrical casing surface  22  and includes additional components of the camshaft adjuster  1 ″. The carrier  20  is rigidly supported on the casing surface  22 , especially by a positive-fit connection. Here, the carrier  20  has a hollow cylindrical contact connecting piece  23 , which contacts the casing surface  22  on the inside radially and is connected with a positive fit on at least one axial end face with housing  21 . The contact connecting piece  23  transitions, especially under an intermediate connection of a transmission radius, into a circular ring plate-shaped carrier body  24 , which is oriented coaxially relative to the longitudinal axis X-X and which in turn transitions into a hollow cylindrical outer body  25  with a projection  26  or collar running in the end area opposite the carrier body  24 . 
         [0042]    The toothed ring  19  contacts the projection  26  in the area of an axial end face, while the opposite end of the toothed ring  19  has a radially inwards projecting projection  27 , which contacts the carrier body  24  or the transition region between the carrier body  24  and the outer body  25 . On the inside radially, especially approximately centrally, the toothed ring  19  has a connecting area  28  extending around or provided across partial extents of the periphery, which extends approximately over half the width of the toothed ring  19 . The connecting area  28  is connected to the outer casing surface of the outer body  25  with a positive, friction, or firmly bonded material fit. 
         [0043]    All of the previously mentioned materials or material combinations can be used for the toothed ring  19 , the carrier  20 , and the housing  21 . As an exemplary embodiment, a production of the toothed ring  19  from plastic, especially a duroplastic, is conceivable, while the carrier  20  and the housing  21  are produced from a metal. 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           1  Camshaft adjuster 
           2  Drive wheel 
           3  External rotor 
           4  Bearing surface of external rotor 
           5  Pressure chamber 
           6  Internal rotor 
           7  Bearing surface of internal rotor 
           8  Projections 
           9  Pressure space 
           10  Pressure space 
           11  Insert body 
           12  Carrier body 
           13  Bracket 
           14  Flange 
           15  Attachment element 
           16  Bore 
           17  Reinforcement insert 
           18  Recess 
           19  Toothed ring 
           20  Carrier 
           21  Housing 
           22  Casing surface 
           23  Contact connecting piece 
           24  Carrier body 
           25  Outer body 
           26  Projection 
           27  Collar 
           28  Connecting area