Patent Publication Number: US-8978605-B2

Title: Phase-adjusting device of a camshaft for an internal combustion engine

Description:
The present invention relates to a camshaft adjusting device of an internal combustion engine, including two camshafts which are supported concentrically to each other, the axial position of the outer camshaft being determined by an axial bearing and having an active relationship with a sealing cover of an adjusting device, a first cam being rotatably fixedly mounted on the outer camshaft, and a second cam being rotatably fixedly connected to the inner camshaft, the inner camshaft furthermore being able to rotate relative to the outer camshaft with the aid of the adjusting device. 
     BACKGROUND 
     Camshaft adjusting devices are used for particularly accurate and fine control of the combustion in an internal combustion engine. 
     For this reason, one or multiple inlet valves is/are adjusted relative to a driving element, such as a crank wheel, which is driven via the crankshaft with the aid of a traction means drive. However, the outlet cams may also be adjusted. 
     The use of two camshafts is known from the prior art, for example DE 4226798 A1, the outer camshaft completely encompassing the inner camshaft, at least in sections. The inner camshaft is supported within the outer camshaft. 
     DE 4226798 A1 discloses a reciprocating internal combustion engine which has two gas exchange valves per cylinder. Two inlet valves of an internal combustion engine cylinder system are actuated by two cams which are adjustable in relation to each other with regard to their phase angle. In addition, the phase position of both cams is variable in relation to the internal combustion engine crankshaft. The charge exchange dynamics of the internal combustion engine may be determined by the so-called variable cam phasing and the variable spread. 
     DE 4226798 A1 discloses a structural specific embodiment having a single, longitudinally movable positioning bolt which has at least two inclined toothed areas, with the aid of whose shifting movement both the phase position of both cams and their mutual phase angles are changed. 
     In conventional designs, a sealing cover of this adjusting device is fixedly connected, in particular rotatably fixedly connected, to the outer camshaft or an integral part of the outer camshaft, in an adjusting device, in particular a hydraulically active adjusting device. Pressing elements are usually used for this purpose 
     Due to the fact that the adjusting device frequently has a central screw which is screwed into the inner camshaft and axially fixes a rotor, which acts as the adjuster, relative to the inner camshaft with the aid of an outer shoulder of the central screw, the overall configuration having the inner and outer camshafts is axially fixed with the aid of the adjusting device. 
     In some specific embodiments of camshaft adjusting devices, however, it is not desirable to have a fixed connection between the sealing cover of the adjusting device and the outer camshaft. However, it is nevertheless still desirable to fix the inner camshaft in a rotatable yet axially determined manner. 
     It should be noted that a wide range of specific embodiments of phase adjusters exists. 
     Driving a concentrically situated camshaft with the aid of a vane is less common, since the design is particularly complex. 
     As mentioned above, the rotor is frequently rotatably fixedly connected to the inner camshaft via a central screw. With the aid of the axial bearing clearance, this rotor determines the axial position of a stator, which is axially shiftably supported on the outer shaft. 
     SUMMARY OF THE INVENTION 
     The axial bearing clearance of the outer camshaft is usually determined by abutment surfaces at the bearing points. The axial bearing clearance of the inner shaft, however, is present, limited only by the clearance of an elongated hole connection between the outer shaft and a connecting bolt of the corresponding cam of the inner shaft. This clearance may be several tens of a millimeter, which has an unfavorable effect on the necessary tappet lift of a piston in the central screw and thus on the overall length of the central magnet. 
     It is an object of the present invention to eliminate the disadvantages from the prior art, in particular to determine the axial position of the inner camshaft and to minimize the necessary installation space. 
     The present invention provides that the inner camshaft has a locking contour on at least one section of its outside, which engages in a form-fitting manner with a mating contour on at least one section of the inside of the outer camshaft to axially fix the position of the inner camshaft relative to the outer camshaft. 
     It is thus advantageous if an axial sliding seat is provided between a sealing cover and the outer camshaft. 
     It is also advantageous if the locking contour, together with the mating contour, is designed in the manner of a bayonet joint connection, preferably without axial clamping. The function of an axial bearing between the inner camshaft and the outer camshaft is particularly efficiently implemented thereby. 
     To make it easier to insert the inner camshaft into the outer camshaft, it is advantageous if the locking contour is designed as at least one projection which is located on a circumferential section of the inner camshaft, the circumferential section extending over more than 10 degrees but no more than 180 degrees of the circumference of the inner camshaft. 
     It has proven to be particularly advantageous if the projection is designed as a 180-degree segment. The axial clearance is limited by an additional axial bearing of this type which is implemented by a 180-degree segment of this type, which engages with a corresponding mating contour. The 180-degree segment has an outer diameter which is bigger than the rest of the inner camshaft. The inner camshaft is also understood to be the combination of a tubular element having a sleeve-like end component when it is non-detachably connected thereto or detachable only with difficulty. 
     If the mating contour is designed as a groove, the insertability is particularly easy to implement, since the inner camshaft having the 180-degree segment is insertable into the outer camshaft in a twisted manner, may then be twisted further, and the corresponding cam may finally be pegged to the inner or outer camshaft. The corresponding segment rotates into the axially limiting groove of the outlet shaft and thus determines the positions of the two shafts in relation to each other. 
     It is furthermore advantageous if multiple projections are distributed on the outside of the inner camshaft, and multiple grooves or grooves segments parallel to the projections are distributed on the inside of the outer camshaft, permitting an undercut for a form fit. It is, of course, also possible to provide multiple projections but only one groove, which has the corresponding undercut areas for blocking an axial movement of the projections. It is furthermore advantageous if the first and/or second cam(s) is/are designed as inlet cams or as outlet cams. This makes it possible to adjust the corresponding phase position of the desired cam. 
     Assembly is facilitated if the projection is provided on an originally separate shaft component which is non-detachably connected to the inner camshaft, and/or if the sliding seat is implemented by a sliding toothed area on an originally separate component which is non-detachably connected to the outer camshaft. 
     The present invention also relates to an internal combustion engine having a camshaft adjusting device designed according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is explained in greater detail below with the aid of a drawing. A first exemplary embodiment is illustrated in the figures of the drawing. 
         FIG. 1  shows a section of a cross section of a camshaft adjusting device according to the present invention; 
         FIG. 2  shows a schematic perspective view of selected elements of the camshaft adjusting device from  FIG. 1 ; 
         FIG. 3  shows a representation of the camshaft adjusting device from  FIG. 2 , reduced by a number of components; and 
         FIG. 4  shows a detailed representation of the locking contour on a section of the outside of the inner camshaft. 
     
    
    
     DETAILED DESCRIPTION 
     The figures are only schematic and are used only for the sake of understanding the present invention. Identical elements are provided with identical reference numerals. 
     A first specific embodiment of a camshaft adjusting device  1  according to the present invention is illustrated in  FIG. 1 . A camshaft adjusting device  1  of this type is provided for use in an internal combustion engine. Camshaft adjusting device  1  has two camshafts  2  and  3  which are supported concentrically to each other. The outer camshaft has reference numeral  2  and the inner camshaft has reference numeral  3 . The outer camshaft is fixed in its axial position by an axial bearing  4 . 
     An adjusting device  5  for adjusting the angular position between the two camshafts  2  and  3 , which has a sealing cover  6 , is provided on the left side between the two camshafts  2  and  3 . Sealing cover  6  has a sliding toothed area  7  on a section of its inside. Outer camshaft  2  also has a sliding toothed area  7  of this type on a shoulder component  8  which is non-detachably connected to outer camshaft  2 . These two sliding toothed areas  7  are in active contact with each other. 
     A first cam  9  is rotatably fixedly situated on outer camshaft  2 . A second cam  10  is not illustrated in  FIG. 1  but is nevertheless apparent in  FIGS. 2 and 3 . 
     However, a central screw  11  having a piston  12  situated therein is apparent in  FIG. 1 . 
     Sealing cover  6  is connected to a stator  14  via a screw connection  13 . A rotor, which acts as an adjuster, is provided with reference numeral  15 . Screw connection  13  also secures a locking cover  16 . 
     Inner camshaft  3  has a locking contour  17  on at least one section of its outside  18 . Locking contour  17  is designed as a 180-degree segment  19 . Locking contour  17  is provided on a shaft end component  20  of inner camshaft  3 , shaft end component  20  being welded to the rest of inner camshaft  3 . 
     Alternatively, is it possible to implement the projecting section of locking contour  17  on the inside of outer camshaft  2  and to provide a diametrically opposed groove which is open to the outside on the outside of inner camshaft  3 . 
     Engaging with a mating contour  22 , which is diametrically opposed to locking contour  17  and is designed as a groove, is 180-degree segment  19 , which is also referred to as projection  21 . The groove has reference numeral  23 . 
     Projection  21  is also readily apparent in  FIGS. 2 and 3 . The connection of second cam  10  via a bolt  24 , which engages with an elongated hole (not illustrated) of outer camshaft  2 , is also visualized therein. 
       FIG. 4 , in turn, visualizes the embodiment of projection  21  as a 180-degree segment  19 . 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Camshaft adjusting device 
           2  Outer camshaft 
           3  Inner camshaft 
           4  Axial bearing 
           5  Adjusting device 
           6  Sealing cover 
           7  Sliding toothed area 
           8  Shoulder component 
           9  First cam 
           10  Second cam 
           11  Central screw 
           12  Piston 
           13  Screw connection 
           14  Stator 
           15  Rotor/adjuster 
           16  Locking cover 
           17  Locking contour 
           18  Outside 
           19  180-degree segment 
           20  Shaft end component 
           21  Projection 
           22  Mating contour 
           23  Groove 
           24  Bolt