Abstract:
A camshaft adjusting device including a stator which is connectable to a crankshaft of an internal combustion engine and a rotor which is connectable to a camshaft and rotatably supported with respect to the stator and a locking device for locking the rotor with respect to the stator with a locking slide ( 2 ) fixed to the stator or fixed to the rotor and produced by a powder metallurgy process and at least one locking pin lockable in the locking slide ( 2 ), in at least one section of a surface edge zone ( 3 ) the locking slide ( 2 ) having a higher density compared to the density of the base material of the locking slide ( 2 ).

Description:
[0001]    The present invention relates to a camshaft adjusting. 
       BACKGROUND 
       [0002]    Camshaft adjusting devices are generally used in valve-train assemblies of internal combustion engines in order to change the valve opening and closing times, as the result of which the fuel consumption values of the internal combustion engine and the operating characteristics in general may be improved. 
         [0003]    One specific embodiment of the camshaft adjusting device which has proven satisfactory in practice includes a vane-type adjuster with a stator and a rotor which delimit an annular space that is divided by protrusions and vanes into multiple working chambers. The working chambers may be selectively acted on by a pressure medium which in a pressure medium circuit is supplied from a pressure medium reservoir, via a pressure medium pump, into the working chambers on one side of the vanes of the rotor, and is returned from the working chambers at the respective other side of the vanes into the pressure medium reservoir. The working chambers whose volume is thereby increased have an effective direction which is opposite the effective direction of the working chambers whose volume is decreased. Accordingly, the effective direction means that a pressure medium action on the particular group of working chambers causes a rotation of the rotor relative to the stator in either the clockwise or counterclockwise direction. The control of the pressure medium flow, and thus of the displacement motion of the camshaft adjusting device, takes place, for example, with the aid of a central valve having a complex structure of flow openings and control edges, and a valve body which is displaceable in the central valve and which closes or opens the flow openings as a function of its position. 
         [0004]    One problem with such a camshaft adjusting device is that in a starting phase, it is not yet completely filled with pressure medium or may have even run dry, so that, due to the alternating torques exerted by the camshaft, the rotor may undergo uncontrolled movements relative to the stator which may result in increased wear and undesirable noise levels. To avoid this problem, it is known to provide a locking device between the rotor and the stator which locks the rotor in a rotation angle position with respect to the stator which is favorable for starting when the internal combustion engine is switched off. However, in exceptional cases, for example during stalling of the internal combustion engine, it is possible that the locking device does not lock the rotor as intended, and the camshaft adjuster must be operated in the subsequent starting phase with the rotor unlocked. However, since some internal combustion engines have a very poor starting behavior when the rotor is not locked in the favorable rotation angle position, in the starting phase the rotor must then be automatically rotated into the locking position and locked. 
         [0005]    Such automatic rotation and locking of the rotor with respect to the stator is known from DE 10 2008 011 915 A1, for example. The locking device described therein includes a plurality of spring-loaded locking pins which successively lock in one or multiple locking slide(s), fixed to the stator or fixed to the rotor, when the rotor is rotated. 
         [0006]    One option for the design of the locking slide is a locking cover which is connected to the stator in a rotatably fixed manner and which has one or multiple depressions or recesses in which the locking pin(s) engage(s) for locking the rotor. Alternatively, the locking slide may also be provided directly in the stator, provided that the stator is designed in such a way that it is possible for pressure medium to act on the locking slide(s) in the stator. Alternatively, the locking pin(s) may also be associated with the stator, and the locking slide(s) may also be associated with the rotor, it only being important that the rotor is lockable via the locking device in a certain rotation angle position with respect to the stator. 
         [0007]    With regard to structure, the locking slides may be implemented in multiple components of the camshaft adjusting device and from various materials; from a manufacturing standpoint, slides which are produced and formed preferably by a melt metallurgy process have proven satisfactory, and for cost reasons and a flexibly designable geometry, locking slides produced by a powder metallurgy process (sintered locking slides) are also used. 
       SUMMARY OF THE INVENTION 
       [0008]    In comparison to locking slides which are produced and formed by a melt metallurgy process, locking slides produced by a powder metallurgy process have lower stability values, so that there is the risk of plastic deformation of the locking slide under high stress on the locking slide. The locking play may be increased due to this plastic deformation of the locking slide, which in turn may result in rattling noises. In addition, there is the risk that increased crack propagation, ruptures, and in the extreme case, functional failure of the locking, may occur due to the high surface pressure in the locked state and process-related material irregularities such as pores, cracks, or squeeze folds. 
         [0009]    It is an object of the present invention to provide a camshaft adjusting device which includes a locking slide produced by a powder metallurgy process, having improved functional reliability, in particular under increased stresses. 
         [0010]    The present invention provides that the locking slide has an increased density compared to the density of the base material of the locking slide in at least one section of a surface edge zone. Due to the increased density, the likelihood of a plastic deformation of the locking slide in the area of the denser surface edge zone may be reduced, in particular under high surface pressure. Due to the higher density, the locking slide has increased stability and therefore also increased strength in the area of the surface edge zone. In addition, the crack formation, the crack propagation, and the crack propagation speed may be prevented or reduced as a result of the higher density. It is of particular importance that the locking slide already has fewer and smaller microcracks in the structure due to the increased density in the area of the surface edge zone, which may be regarded as the starting point for development of larger cracks. Furthermore, the surface has fewer irregularities; i.e., the surface is denser and more homogeneous, so that the stress on the locking slide during the locking of the rotor is distributed over a larger surface area, and as a result the local maximum stresses on components may be reduced. In addition, the dimensional tolerance and shape tolerance may also be limited during the manufacture due to the increased density (i.e., stability, strength). 
         [0011]    It is further provided that the entire surface edge zone of the locking slide has an increased density compared to the density of the base material of the locking slide. The manufacture of the compressed surface edge zone may thus be simplified by subjecting the entire locking slide to a surface treatment, for example. In addition, the likelihood of damage is thus naturally reduced, since the locking slide is thereby compressed also in areas in which the locking pin comes to rest only in exceptional cases. 
         [0012]    Alternatively, however, the machining effort may also be reduced by providing the surface edge zone having the increased density only in an area of the locking slide in which the locking pin is likely to come to rest, in particular in the stop positions of the rotor. These may be, for example, the edge sides which limit the movement of the rotor, i.e., the stop surfaces of the locking slide. 
         [0013]    In addition, it has been found that the likelihood of damage, and at the same time a preferably low machining effort, may be reduced when the surface edge zone with the increased density has a thickness of 0.01 mm to 100 mm. 
         [0014]    The increased density of the surface edge zone may be achieved, for example, by overpressing, shot peening, rolling, laser blasting, impregnation, laser hardening, or by heat treatment, coating, or hard coating of the locking slide. In this case, the component is produced in a first step, using a preform or also using the final form of the locking slide, while the compression of the surface edge zone takes place afterwards by a second machining operation on the locking slide. The compression then takes place, for example, by pressing in a punch tool having intentionally larger dimensions, and at the same time supporting the component via a matrix (overpressing) by shot blasting, laser blasting, or rolling, or by impregnation, i.e., by subsequently introducing a pore filling material into the surface edge zone, by laser hardening, or by heat treatment, coating, or hard coating in a second machining step. In the process, the locking contour may be slightly expanded from the preform to the final form, providing that the machining takes place, for example, by overpressing, rolling, or ball shot blasting, i.e., by mechanical compression of the material by an external application of force. 
         [0015]    Alternatively or additionally, the density in the surface edge zone may be increased by providing in the locking slide a press-in or insert bush, insert part, or a composite material having a higher density than the base material of the locking slide. In this case, the locking slide, at least in a basic shape, is formed in a first manufacturing step during the powder metallurgy process, and is then provided with the surface edge zone, having the higher density, via the insert or press-in bush or via the composite material. The basic shape of the locking slide created in the first step is virtually lined by the insert bush or press-in bush, by the insert part, or by the composite material having the higher density. 
         [0016]    It is further provided that the increased density of the surface edge zone is achieved by a finishing or quenching/tempering process, a heat treatment method, or a coating method, or by a combined mechanical and thermal method. 
         [0017]    By use of the heat treatment, for example laser hardening, the material in the surface edge zone is intentionally warmed or heated until the structural condition is able to change to a denser structural condition. For the coating, an additional material which itself has an increased density, or which increases the density of the material of the locking slide in the area of the surface edge zone by penetration into the surface edge zone, is intentionally applied to the surface edge zone. 
         [0018]    Mechanical compression, and at the same time a change in the structural condition, may be achieved by the combined mechanical and thermal method, for example flowdrilling. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The present invention is explained in greater detail below with reference to one preferred exemplary embodiment. In particular, 
           [0020]      FIGS. 1 a  through 1 j    show in detail various locking slides which include a compressed high-strength surface edge zone having increased stability and/or strength. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Various components  1  fixed to the stator, for example a locking cover or also the stator itself, together with a schematically illustrated locking slide  2  which may be designed, for example, as a circular, ring segment-shaped, oval, conical triangular, or polygonal recess, are apparent in  FIGS. 1 a    through  1   j.  Locking slide  2  may also be situated on a rotor of the camshaft adjusting device or on a component of the camshaft adjusting device fixed to the rotor. In the various exemplary embodiments, locking slides  2  in each case include a surface edge zone  3  which has increased density or stability compared to the density of component  1 , and which may be implemented in various ways, as described in greater detail below. 
         [0022]    In the exemplary embodiment shown in  FIG. 1   a,  the increased density of surface edge zone  3  is achieved by shot peening device  4  with a ball, peening, or cuboidal shot blast directed onto surface edge zone  3 . Due to the striking blast bodies or particles of shot peening device  4 , the material of component  1  is locally compressed and strengthened, and at the same time, the surface of surface edge zone  3  is smoothed and brought to the final or finished part quality. 
         [0023]      FIG. 1 b    shows one exemplary embodiment in which a punch tool  5 , which is oversized in comparison to the dimensions of locking slide  2  produced in a prior shaping process, is pressed into locking slide  2 . At the same time, two additional punch tools  14  and  15  are pressed against a corresponding mating contour of component  1 , so that the material in surface edge zone  3  is not able to yield laterally between punch tools  14 ,  15 , and  5 , and is therefore compressed. At the same time, a tool matrix  6  is pressed against component  1  on the respective other side of component  1 , against the pressing direction of punch tools  14 ,  15 , and  5 , for support. The stability, durability, strength, and maintenance of the dimensional tolerance and shape tolerance may be improved by compressing locking slide  2  in the area of surface edge zone  3 . 
         [0024]      FIG. 1 c    shows one exemplary embodiment in which surface edge zone  3  having the increased density is produced by a roller tool  7  which is driven to rotation, in which at least two oppositely situated rollers are pressed radially outwardly against surface edge zone  3 , thus compressing the material in this area. 
         [0025]      FIG. 1 d    through  FIG. 1 f    each show one exemplary embodiment in which an insert part  8 , a press-in bush  9 , or an insert bush  12 , respectively, is inserted into locking slide  2 . Insert part  8 , press-in bush  9 , and insert bush  12  have a higher density and/or stability than component  1 , and are held in locking slide  2  in a displaceably and rotatably fixed manner. This may be achieved by pressing in, for example, as the result of which the density of the area of locking slide  2  adjoining the particular parts may also be further compressed. Alternatively, instead of pressing in, screwing in via a thread or welding of insert part  8  may be implemented. Insert part  8 , press-in bush  9 , and insert bush  12  may preferably be made of a steel part of higher stability or higher density than component  1 , thus selectively strengthening component  1  in the area of locking slide  2 . In particular, the forces resulting from the surface pressure of the locking pin are thus absorbed by these parts and transmitted over a larger surface area on component  1 , so that the stress on component  1 , and thus the likelihood of damage, is decreased. 
         [0026]    Insert part  8  is designed as a ring, and is oversized in relation to the dimensions of the preform of locking slide  2 , and is pressed, screwed, or welded into locking slide  2 . Press-in bush  9  is additionally secured in locking slide  2  by a knurl  11 . Due to knurl  11 , a material displacement  10  into a recess in press-in bush  9  is effectuated during the pressing-in operation of press-in bush  9 , so that press-in bush  9  is subsequently secured tightly in a rotatably fixed manner, and in particular captively, in preformed locking slide  2 . Insert bush  12  in  FIG. 1 f    is formed in the shape of a cup with a collar, and is pressed into the preform of locking slide  2 , which in this case is designed as an opening. All three exemplary embodiments share the common feature that locking slides  2  in component  1 , produced by the powder metallurgy process, are present as a type of preform which is then completed by insert part  8 , press-in bush  9 , or insert bush  12  to form final locking slide  2 . In this case, the shape of final locking slide  2  is determined by insert part  8 , press-in bush  9 , or insert bush  12 . Since insert part  8 , press-in bush  9 , or insert bush  12  each have a higher density or stability than component  1 , these parts preferably undergo little or no deformation during the insertion or pressing-in operation, while component  1  is compressed. Thus, the shape of final locking slide  2  corresponds, with a preferably high degree of dimensional accuracy, to the predefined shape of locking slide  2 , or to the shape of the inserted part, which preferably undergoes little or no deformation. It is preferred that insert part  8 , press-in bush  9 , or insert bush  12  is formed by a closed ring, a cup, or a sleeve which, due to its shape and its material, may absorb particularly well the radially inwardly directed tensions which act during the pressing in, without itself being deformed. 
         [0027]    In  FIG. 1   g,  locking slide  2  is formed by a high-strength composite material  13  which is joined to component  1 . Such high-strength composite materials  13  may be ceramics or the like, for example. 
         [0028]      FIG. 1 h    shows another exemplary embodiment of the present invention, in which an oversized punch tool  5  is likewise pressed into locking slide  2 , the punch tool having a diameter L 2  which is greater than diameter LO of locking slide  2 . As a result, locking slide  2  is preferably expanded radially outwardly, and the material in outer surface edge zone  3  is radially compressed. 
         [0029]      FIG. 1 i    shows one exemplary embodiment of the present invention, in which locking slide  2  is locally strengthened and compressed by a laser beam generated by a laser  16 . Local thermal energy may be additionally introduced into component  1  by the laser beam, as the result of which the material of component  1  is locally melted, and possible pores or cracks are closed to form a compressed and strengthened surface edge zone  3 . In addition, surface edge zone  3  may be hardened due to the introduced thermal energy, thus further increasing the stability. 
         [0030]      FIG. 1 j    shows another exemplary embodiment of the present invention, in which a pore filling material  17  is introduced into the material of component  1 , so that component  1  has an increased density and stability in comparison to the density of its base material. 
         [0031]    Overall, locking slide  2  has an increased density, strength, and stability in the area of compressed surface edge zone  3 , as the result of which crack formation and propagation, and thus the likelihood of damage, may be reduced. In addition, the surface of surface edge zone  3  preferably has fewer irregularities, i.e., the roughness depth is less, so that the surface load results in lower local stresses due to the fact that the load is more uniformly distributed in component  1  or more uniformly introduced into locking slide  2 . The likelihood of damage may thus be additionally reduced. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1  component 
           2  locking slide 
           3  surface edge zone 
           4  peening device 
           5  punch tool 
           6  tool matrix 
           7  roller tool 
           8  insert part 
           9  press-in bush 
           10  material displacement 
           11  knurl 
           12  insert bush 
           13  high-strength composite material 
           14  punch tool 
           15  punch tool 
           16  laser 
           17  pore filling material