Abstract:
A camshaft adjuster ( 1 ) for an internal combustion engine is provided, in which the relative angular position between a driving gear ( 2 ) and an output element that is allocated to the camshaft can be adjusted by hydraulically impinging pressure chambers located between an inner and outer rotor. The outer rotor and the gear ring of the driving gear ( 2 ) are joined to each other via fastening elements ( 15 ). In order to create a particularly compact camshaft adjuster ( 1 ), the fastening elements are located at least in part at a distance from the longitudinal axis of the camshaft adjuster ( 1 ) which is smaller than the external radius ( 35 ) of the pressure chambers.

Description:
BACKGROUND 
   The invention relates to a camshaft adjuster for an internal combustion engine according to the preamble of claim  1 . 
   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. 
   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 with the drive wheel. 
   The outer rotor, which forms the radially outer boundaries, as well as boundaries in the peripheral direction of the pressure spaces, is screwed to a cover, which surrounds the outer rotor with a hollow cylindrical peripheral surface and which has brackets projecting radially outwardly from the peripheral surface and connected to the toothed ring by means of screws passing through the brackets. 
   The invention is based on the objective of providing a camshaft adjuster, which is improved in terms of radial installation size and/or the hydraulic pressure charge. 
   SUMMARY 
   According to the invention, the objective is met by the features of the independent claim  1 . 
   The invention is based on the knowledge that for a camshaft adjuster according to DE 102 11 607 A1, the radial installation size of the camshaft adjuster depends on the sum of the following dimensions:
         The radial installation size of the outer rotor or the radius of the radial boundary of the pressure spaces,   The required radial installation space for the attachment elements and also the brackets of the outer rotor and optionally allocated brackets or flanges, which extend radially inwardly from the toothed ring, and also   The radial dimension of the toothed ring and the associated components.       

   According to the invention, the mentioned sum is reduced in that the attachment elements are arranged at least partially at a distance from a longitudinal axis of the camshaft adjuster, which is smaller than an outer radius of the pressure spaces. In this way, the dimensions according to b) and c) are not summed. Instead, the dimensions related to b) and c) overlap, so that the total radial installation size is reduced. 
   The use of the knowledge according to the invention produces new shaping possibilities:
         For a given outer radius of the drive wheel required, for example, as a result of the gear transmission of the camshaft gearing, according to the invention the outer radius of the pressure spaces can be enlarged. For an unmodified hydraulic design, an inner radius of the pressure spaces can be enlarged, so that open installation space is produced in the camshaft adjuster radially on the inside. On the other hand, for a constant inner radius of the pressure spaces, the active surface for a hydraulic charge can be enlarged, whereby an improved adjustment effect and/or a reduced design of additional hydraulic components can be produced.   For a constant outer diameter of the pressure spaces, the outer radius of the drive wheel can be reduced, whereby the radial installation size of the drive wheel and the camshaft adjuster can be reduced.   Mixtures of the two mentioned alternatives are also possible, which produces expanded structural design possibilities and new installation space possibilities.       

   In the sense of the invention, attachment elements are understood to be attachment elements themselves, such as screws, rivet connections, or other positive or non-positive attachment elements, and also associated regions of the components to be connected, such as the flanges, brackets, or the like. According to the teaching according to the invention, the previously mentioned attachment elements are arranged at least partially in the radial direction at the height of the pressure spaces. Here, the attachment elements can be arranged at any position in the longitudinal direction of the camshaft adjuster and can be arranged arbitrarily over the peripheral direction. 
   According to a special construction of the invention, the attachment elements are arranged in the peripheral direction between pressure spaces and also in the direction of the longitudinal axis of the camshaft adjuster between axial boundaries of the pressure spaces. This construction is based on the knowledge that material clusters, which represent unused installation space and which cause additional weight in the outer rotor, are provided in the outer rotor between the pressure spaces in the peripheral direction according to the state of the art, whereby the mass moment of inertia of the camshaft adjuster is increased. According to the invention, this installation space can be advantageously used, in that the attachment elements are arranged within this space. 
   For this purpose, it can be advantageous according to an improvement of the invention if the outer rotor has radial bulges between adjacent pressure spaces, wherein the radial bulges mean material savings for the outer rotor and simultaneously create the installation space for the attachment elements. Radially inwardly oriented brackets, which can be connected rigidly to the toothed ring of the drive wheel, project into the radial bulges. 
   The invention is further based on the knowledge that for an embodiment of DE 102 11 607 A1, between the outer rotor and inner rotor, a bearing surface is formed with plastic, which is not optimum 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 a second embodiment of 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. 
   Therefore, according to the invention the bearing surface of the external rotor is formed with a metallic insert body, which is held with a non-positive fit in a carrier body made from plastic. Through this non-positive 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 fit, possibly under the intermediate connection of additional components. 
   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 outwards 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 running 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. 
   In one preferred camshaft adjuster according to the invention, the drive wheel is produced from a composite material. In the sense of the invention, a composite material is understood to be a material containing several sub-materials. These sub-materials can be formed, for example, as a carrier material with reinforcement elements arranged in the carrier material. The material can involve a fiber-composite material or a body formed from different layers of different materials. 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. 
   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 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. 
   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 good a 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. 
   For a further improved camshaft adjuster, insert bodies and carrier bodies are connected to each other with a positive 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. 
   Furthermore, the toothed ring can be formed in one piece with the brackets and with a composite material, wherein a reinforcing material of the composite material is arranged in the region of the brackets. In this way, the mechanical properties of the brackets can be improved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional features of the invention emerge from the following description and the associated drawings, in which embodiments of the invention are presented schematically. Shown are: 
       FIG. 1  a cross-sectional view of a part of a camshaft adjuster with an outer rotor and a carrier body made from plastic with a firmly bonded fit connected insert body and also an inner rotor supported rotatably in the outer rotor; 
       FIG. 2  a half longitudinal cross-sectional view of a camshaft adjuster in which the drive wheel made from plastic or an attachment element is attached to a flange; 
       FIG. 3  a view of a drive gearwheel made from plastic with radially inwardly pointing brackets for receiving attachment elements; 
       FIG. 4  a half longitudinal cross-sectional view of a drive wheel with a connecting piece or a bracket and inserts inserted into the connecting piece or bracket; 
       FIG. 5  a partial cross-sectional view of a drive gearwheel with radially inwardly pointing brackets and inserts arranged in these brackets; 
       FIG. 6  a cross-sectional view of a camshaft adjuster, wherein attachment elements are drawn radially inwardly, so that their spacing from the longitudinal axis of the camshaft adjuster is smaller than the outer diameter of the pressure chambers, and 
       FIG. 7  a view of a drive gearwheel made from plastic, which is attached to a housing of the camshaft adjuster via a carrier element. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The invention relates to a hydraulic camshaft adjuster  1  in a known construction. The camshaft adjuster has a drive wheel  2 , which is formed as a pulley in the shown embodiments. An outer rotor  3 , which is arranged, in particular, radially inwardly from the drive wheel  2 , is connected rigidly to the drive wheel  2 . The outer rotor  3  is formed with bearing surfaces  4 , which correspond to segments of a casing surface of a cylinder, and also 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 uniformly over the periphery. An inner rotor  6 , which can be locked or is locked in rotation with the camshaft, is arranged in the outer rotor  3  so that it can rotate relative to this outer rotor about a longitudinal axis of the camshaft adjuster  1 . The inner rotor  6  has bearing surfaces  7  formed corresponding to the bearing surfaces  4  of the outer rotor  3  and also has vane-like radial projections  8 , wherein four bearing surfaces  7  and four projections  8  are provided, which are distributed uniformly across the periphery of the inner rotor, according to the embodiment shown in  FIG. 1 . The bearing surfaces  4  and  7  form a seal in the peripheral direction and the end faces of the projections  8  contact the associated pressure chambers  5  forming a seal radially on the outside, so that in the peripheral direction pressure spaces  9 ,  10  are formed on both sides of the projections. Through suitable charging of the pressure spaces  9 ,  10 , the relative angular position between the outer rotor  3  and the inner 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. 
   According to  FIG. 1 , both the pressure chambers  5  and also the bearing surfaces  4  are both formed with a metallic insert body  11 , which extends in the peripheral direction and which has an approximately constant wall thickness. The insert body  11  is held with a firmly bonded fit in a carrier body  12 , which according to the embodiment shown in  FIG. 1  is formed integrally with the drive wheel  2  or is formed as a separate component, which can be connected rigidly to the drive wheel  2 . 
     FIG. 2  shows a camshaft adjuster  1 ′ in longitudinal section. For this camshaft adjuster, the drive wheel  2 ′ is formed integrally with inwardly projecting brackets  13 , which are arranged approximately in the middle in the axial direction, which extend in the direction of a longitudinal axis X-X of the camshaft adjuster  1 ′ over one third to one fourth of a width of the running gearing of the drive wheel  2 ′, and which are distributed uniformly over the periphery, cf.  FIG. 3 . A flange  14 , which is formed integrally with the outer rotor  3 ′, contacts an end of the brackets  13 . The brackets  13  and the flange  14  are connected to each other with a friction, positive, and/or firmly bonded fit and/or via 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 threading. The bores  16  with or without threading can here be formed directly in the material forming the drive wheel or are prepared according to  FIG. 4  by reinforcement intermediate layers  17 , especially inserts, for example, made from metal, which are attached preferably with a firmly bonded fit to the other integral elements of the drive wheel  2 . 
   In terms of the drive wheel  2 , the outer rotor  3 , the bearing surface  4 , the inner 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 components named above 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 material can be provided, for example, a plastic with an iron metal or a non-iron metal. In terms of the thermal expansion coefficients, these can be adapted to each other mutually, so that, for example, plastic, fiber composite materials, or composite materials have equal thermal expansion coefficients, such as adjacent components made from different materials. In particular, components arranged on the driven side, that is, components connected rigidly to the camshaft, can have a greater thermal expansion coefficient than components arranged on the drive side.   The components named above can be joined to form units in one or more pieces. For example, the drive wheel  2 , the outer rotor  3 , the bearing surface  4  with insert body  11 , bracket  13 , and carrier body  12 , as well as flange  14  are formed as an integral, installation space-optimized component made from one or more materials or composite materials.   For weight reduction and for improving the mounting possibilities, pockets can be provided in the components named above.   The drive wheel  2  and insert body  11  can be connected to each other optionally through the intermediate connection of additional (sub) bodies with a positive fit, for example, by screws, with a form fit, for example, by rivets, or with a firmly bonded fit, for example, by adhesive, injection molding, or integral production, wherein combinations of the connection possibilities named above are conceivable.   Non-plastic elements can be used as aids for the screw connection, for example, based on a “mold-in” or “after-molding” technology. A “mold-in” technology involves, for example, a metal bushing with threading, which is injection molded in a die, while as an example for an “after-mold” technique, a metal bushing with threading is conceivable, which is inserted in a plastic part after the injection-molding process.   Metallic elements or sub-bodies can be formed as reinforcement material in other materials, for example, for homogenizing the expansion and/or for bracing, for forming support material, and for increasing the component stiffness.   A selection of materials and their orientation can be used as thermal construction parameters, in which the expansion coefficient can be set to a desired target according to the element and its volume percentage.   The use of reinforcement intermediate layers or inserts can be used, in particular, for minimizing setting force losses and for permitting direct screw connections.   According to  FIG. 1 , the outer rotor can be embedded directly into a plastic material. Assembling this plastic material with the outer rotor can be realized directly, for example, in an injection molding process or else by means of a later assembly.       

     FIG. 6  shows a partial cross section allocated to the embodiment according to  FIG. 2 . Here, the casing surface of the outer rotor  3  with the pressure spaces  5  has a back-and-forth or meander-shaped construction with different radii, wherein, in the region of the pressure spaces  5 , the outer radius is at a maximum and the radius is reduced in the peripheral region between adjacent pressure spaces  5  through radial bulges or recesses  18 . The brackets  13 , which are connected to the toothed ring  19  rigidly or with a firmly bonded fit, project into the recesses  18  and are connected to the outer rotor  3  in the region of the recesses  18 . In this way, the attachment elements  15  can be “pulled down” to smaller radii, so that the attachment elements  15  act at a radius that lies in the region of the outer diameter  35  of the pressure chamber  5  or that is smaller than this. Here, the attachment elements  15 , the brackets  13 , an optional flange  14 , and the recesses  18  are provided preferably axially between the end faces  33 ,  34  of the drive wheel  2  or corresponding end faces of the pressure spaces  5 , so that a small axial installation size is also produced. 
     FIG. 7  shows an example construction for a drive wheel  2 ″ with allocated components, here a toothed ring  19 , a carrier element  20 , and a housing  21 . 
   The housing  21  is formed especially as a sheet-metal part with an approximately cylindrical casing surface  22  and includes additional components of the camshaft adjuster  1 ″. The carrier element  20  is supported rigidly on the casing surface  22 , especially by a firmly bonded connection. Here, the carrier element  20  has a hollow cylindrical contact connecting piece  23 , which contacts the casing surface  22  radially at the inside and is connected to the housing  21  with a firmly bonded fit on at least one axial end face. The contact connecting piece  23  transitions, especially under the intermediate connection of a transition radius, into a circular disk-shaped carrier body  24 , which is oriented coaxial to the longitudinal axis X-X and which, in turn, transitions in a hollow cylindrical outer body  25  with a surrounding shoulder  26  or collar in the end region opposite the carrier body  24 . 
   The toothed ring  19  contacts the shoulder  26  in the region of an axial end face, while the opposite end of the toothed ring  19  has a radially inwardly projecting radial projection  27 , which contacts the carrier body  24  or the transition region between the carrier body  24  and outer body  25 . The toothed ring  19  has radially on the inside, especially approximately in the middle, a surrounding projection or connection region  29  provided across sub-peripheries, which extends approximately over half the width of the toothed ring  19 . The connection region  29  is connected to the outer casing surface of the outer body  25  with a firmly bonded fit. 
   For the toothed ring  19 , the carrier element  20 , and the housing  21 , all of the previously mentioned materials or material combinations can be used. As an example embodiment, a production of the toothed ring  19  from plastic, especially a duroplastic, is conceivable, while the carrier element  20  and the housing  21  are produced from a metal. 
   The shoulder  26  can be used alternatively or additionally for simplifying the mounting of a guide of a drive element like a toothed belt or a control chain in the direction of the longitudinal axis X-X. 
   The outer body  25  has on its outer casing surface preferably recesses  31  or depressions or grooves, which can be formed as pockets in the outer body or can pass through this body. For the shown embodiment, the recesses  31  are formed with an approximately rectangular cross section. Radially inwardly oriented projections  32  or a surrounding collar extend radially inwardly from the toothed ring  19 , especially from the projection  30 . These projections are held with a positive fit at least in the longitudinal direction X-X and/or in the peripheral direction in the recess  31 , depression, or groove. In the radial direction, the toothed ring  19  can be guided opposite the carrier element  20  through the projection  30  and/or projection  32 . 
   LIST OF REFERENCE SYMBOLS 
   
       
         1  Camshaft adjuster 
         2  Drive wheel 
         3  Outer rotor 
         4  Bearing surface of outer rotor 
         5  Pressure chamber 
         6  Inner rotor 
         7  Bearing surface of inner 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 element 
         21  Housing 
         22  Casing surface 
         23  Contact connecting piece 
         24  Carrier body 
         25  Outer body 
         26  Shoulder 
         27  Projection 
         28  First connection region 
         29  Second connection region 
         30  Projection 
         31  Recess 
         32  Projection 
         33  Axial end face 
         34  Axial end face 
         35  Outer radius of pressure chamber