Patent Publication Number: US-9835059-B2

Title: Camshaft for an internal combustion engine and use therefore

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application No. DE 10 2014 116 450.4, filed Nov. 11, 2014, which is incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a camshaft for an internal combustion engine, with a drivable basic shaft and a cam piece which is mounted in the basic shaft, wherein the basic shaft passes through a passage in the cam piece, and the cam piece is mounted in the basic shaft in a rotationally fixed and axially displaceable manner. The invention furthermore relates to a particular use of a camshaft of this type. 
     BACKGROUND OF THE INVENTION 
     A camshaft of the type mentioned is known from DE 10 2011 103 544 A1, which is incorporated by reference herein. In said camshaft, the basic shaft is provided with an external toothing and the cam piece interacting with the basic shaft is provided with a complementary internal toothing. The torque introduced into the basic shaft is introduced by the latter via said toothings into the cam piece, in order to actuate one or more valves of the internal combustion engine. In the case of multi-tooth connection of this type, the basic shaft has a relatively low fatigue strength. 
     In DE 10 2011 000 248 A1, which is incorporated by reference herein, a camshaft with displaceable cam pieces is provided with connecting elements which are arranged spaced apart in an axial direction of the camshaft and serve for connecting a basic shaft to the cam piece. The connecting elements or individual elements of the connecting elements are designed as a sliding spring, four-groove profile or spline shaft section, serration profile, toothed shaft section, four-cornered profile, multi-cornered profile, polygonal profile and/or the like. 
     SUMMARY OF THE INVENTION 
     Described herein is a camshaft, and use therefore, of the type mentioned previously that is designed in such a manner that the basic shaft has a particularly high fatigue strength. 
     The basic shaft has a polygonal profile, and the passage in the cam piece has a complementary polygonal profile for receiving the basic shaft. 
     One particular advantage of the use of a basic shaft with a polygonal profile in the region of the torque transmission between basic shaft and cam piece can be seen in the fact that polygonal profiles do not have any stress concentration and therefore also the moments of inertia do not change. The basic shaft having the polygonal profile is therefore only subjected to a torsional stress. The basic shaft has a substantially higher fatigue strength in comparison to conventional basic shaft profiles, in particular spline shaft profiles of equivalent size. 
     According to a development of the invention, it is provided that the polygonal profiles of basic shaft and passage have an identical shape, wherein the cross section of the polygonal profile of the basic shaft is slightly smaller than the cross section of the polygonal profile of the passage. The basic shaft and the passage of the cam piece are therefore co-ordinated with each other in the region of the polygonal profiles in such a manner that the cam piece is mounted with play in the basic shaft and can be displaced axially with respect to the basic shaft with low adjustment forces. 
     It is provided preferably and in particular from the aspect of simple production that the polygonal profile is of substantially four-cornered, in particular square, design. Moreover, according to a development, it is provided that the polygonal profile has rounded corners. Furthermore, it is considered advantageous if the polygonal profile has an outwardly curved contour in the region connecting respective adjacent corners. 
     A camshaft for an internal combustion engine is therefore proposed, in which the cam piece can be displaced, under torque, longitudinally with respect to the basic shaft. The cam piece is self-centering with respect to the basic shaft. The mounting of the cam piece in the basic shaft is distinguished by little backlash. Alternating torques are minimal. 
     The basic shaft is preferably designed structurally in such a manner that it is connected in the region of one end to an externally driveable drive element. The torque is introduced into the basic shaft via said drive element. The cam piece preferably has a slotted guide element with at least one cam part. In particular, it is provided that the cam piece has two cam parts, wherein two valves are activatable by means of each cam part. 
     The camshaft is preferably used in a motorcycle, for example. The latter in particular has an internal combustion engine with two cylinders. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Further features of the invention emerge from the dependent claims, the attached drawing and the description of the exemplary embodiment reproduced in the drawing, without being limited thereto. In the drawing: 
         FIG. 1  shows a three-dimensional view of the camshaft according to aspects of the invention, 
         FIG. 2  shows a three-dimensional view of the basic shaft used in the camshaft according to  FIG. 1 , 
         FIG. 3  shows a three-dimensional view of the cam piece used in the camshaft according to  FIG. 1 , 
         FIG. 4  shows a section through the cam piece, shown in  FIG. 3 , in a section perpendicular to the axis of rotation of the cam piece. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a camshaft  1  for an internal combustion engine, this preferably being an internal combustion engine with two cylinders for use in a motorcycle. 
     The camshaft  1  has a driveable basic shaft  2  and a cam piece  3  which is mounted in the basic shaft  2 . The basic shaft  2  passes through a passage  4  in the cam piece  3 . The cam piece  3  is mounted in the basic shaft  2  in a rotationally fixed and axially displaceable manner. In order to drive the basic shaft  2 , the latter is connected in the region of one end to an externally driveable drive element  5 . The cam piece  3  has, according to FIG.  3 , two cam parts  6  and a slotted guide element  7  between the latter. Each cam part  6  is provided with two cam pairs  8 . Each cam pair  8  has two cams  9 ,  10 , wherein, as a consequence of axial displacement of the cam piece  3 , the one cam  9  or the other cam  10  can be brought into engagement with an inlet valve or outlet valve of the internal combustion engine. 
     According to  FIG. 2 , the basic shaft  2  has a polygonal profile  11 , and the passage  4  in the cam piece  3 , has, according to  FIG. 4 , a complementary polygonal profile  12  for receiving the basic shaft  2 . The polygonal profiles  11  and  12  are of identical configuration with respect to the cross-sectional design thereof, namely are of square design with rounded corners. That region of the polygonal profile  11  or  12  which connects respective adjacent corners has a slightly outwardly curved contour. The cross section of the polygonal profile  11  for the basic shaft  2  is somewhat smaller in size than the cross section of the polygonal profile  12  for the passage  4  of the cam piece  3 . Accordingly, the cam piece  3  can be displaced with respect to the basic shaft  2  in the longitudinal extent thereof with play. The displacement of the cam piece  3  takes place in a known manner by means of slotted guide pins which can be brought into engagement with the slotted guide part  7 . 
     LIST OF REFERENCE NUMBERS 
     
         
           1  Camshaft 
           2  Basic shaft 
           3  Cam piece 
           4  Passage 
           5  Drive element 
           6  Cam part 
           7  Slotted guide element 
           8  Cam pair 
           9  Cam 
           10  Cam 
           11  Polygonal profile 
           12  Polygonal profile