Patent Publication Number: US-2005115529-A1

Title: Device for adjusting the relative angular position of two rotating elements

Description:
This is a Continuation-In-Part Application PCT/EP03/04105 filed Apr. 19, 2003 and claiming the priority of German application 102 24 446.4 filed Jun. 1, 2002. 
    
    
     BACKGROUND OF THE INVENTION  
      The invention related to a device for adjusting a relative angular position of two rotating elements which are connected to a drive by a transmission element.  
      Devices of this type are used for example in internal combustion engines and are provided there for effecting a relative angular adjustment of the camshaft with respect to the crank-shaft driving the camshaft. The adjustments in the kinematics of the valve drive influences within limits the phase angle of the valve opening, the opening period and the valve stroke in a variable fashion.  
      DE 100 36 375 A1 discloses such a device for effecting a relative angular adjustment between a camshaft and a crank-shaft of an internal combustion engine. A chain wheel is mounted on the camshaft so as to be driven by the crankshaft, the chain wheel driving the camshaft via a transmission element. The transmission element makes it possible to change the relative angular position of the two rotating elements, that is, the chain wheel and the camshaft. This change is brought about by an electric actuating drive whose rotor acts on an actuating shaft of the transmission element and which also rotates in each operating state of the drive.  
      When inertia forces which are triggered by oscillations act on the rotor of the actuating element or the actuating shaft of the transmission element, undesired adjustments of the relative angular position may take place. This has to be compensated for by the actuating drive and requires a continuous application of energy. When the actuating drive fails, this function is no longer effective and uncontrolled adjustments occur which may make the operation of the internal combustion engine difficult and possibly damage the internal combustion engine. Since the actuating drive must also continuously rotate, it may also heat up during normal operation in an unacceptable way. In such a case, the internal combustion engine would have to be shut down in order to prevent damage to the actuating drive.  
      With respect to the general technical background, reference is made also to DE 100 38 354 A1 and DE 41 10 195 A1.  
      It is the object of the present invention to provide a device in which the actuating drive has a low electrical energy consumption and the device has a reliable emergency operating mode.  
     SUMMARY OF THE INVENTION  
      In a device for adjusting the relative angular position of two rotating elements which are connected to a drive and, via a transmission element, to an actuating shaft by means of which a rotor of an electric actuating drive and the relative angular position of the rotating elements can be changed, the actuating shaft is operatively connected to at least one of the rotating elements and normally locked for a safe emergency operating mode.  
      A significant advantage of the invention is that during normal operation, the transmission element can be blocked in a set relative angular position of the two rotating elements and the actuating drive does not require any energy to maintain this setting. This leads to an overall lower energy consumption and thus to a lower application of heat to the actuating drive. If, nevertheless, inadmissible heating of the actuating drive should occur, it can be deactivated for the purpose of cooling when the internal combustion engine is operating without uncontrolled adjustment of the relative angular position of the two rotating elements.  
      In one particular embodiment of the invention, in which the rotor of the actuating drive is operatively connected to at least one of the rotating elements in the state in which the actuating drive is not energized, the transmission element is blocked automatically when the actuating drive fails, thus ensuring a set emergency operating mode.  
      The invention will become more readily apparent from the following description of a preferred embodiment thereof on the basis of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      The sole FIGURE is a schematic, partially sectional, illustration showing a detail of a camshaft drive of an internal combustion engine with a device according to the invention. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT  
      In the schematic illustration of the camshaft drive of an internal combustion engine, a rotating element which is embodied as a camshaft is designated by the reference numeral  1 . A further rotating element  2 , which is embodied as a chain wheel, is mounted on the rotating element  1  in the drive structure of a crankshaft of the internal combustion engine. The chain wheel  2  drives the camshaft  1  via a transmission element  3  so that the camshaft  1  and the chain wheel  2  have the same rotational speed. The chain wheel  2  which is fitted with a chain on its circumference is arranged concentrically with respect to the camshaft  1  and rotatably supported thereon, the transmission element  3  being located operatively between the camshaft  1  and the chain wheel  2 . The transmission element  3  (not illustrated in detail) may be embodied, for example, as a planetary gear mechanism, a swash plate mechanism or the like and has an actuating shaft  4  which is acted on by a rotor  5   a  of an electric actuating drive  5 . The drive torque which is necessary for the position adjustment is generated between the rotor  5   a  and a stator  5   b  of the actuating drive  5 .  
      By means of a relative rotation of the actuating drive  4 , the relative angular position of the two rotating elements  1 ,  2  with respect to one another can be changed. The relative rotation of the actuating shaft  4  is brought about by means of the rotor  5   a  of the actuating drive  5 .  
      In order to bring about low energy consumption and a reliable emergency operating function, the actuating shaft  4  can, according to the invention, be operatively connected to one of the camshaft  1  and the chain gear  2 , the operative connection between the actuating shaft  4  and the chain gear  2  being illustrated in the exemplary embodiment. The operative connection between the actuating shaft  4  and the chain gear  2  is established by means of the rotor  5   a  of the actuating drive  5 , which is connected to the actuating shaft  4  in an axially displaceable fashion. The operative connection of the actuating shaft  4  to the chain gear  2  causes the transmission element  3  to be blocked, as a result of which the relative angular position bof the camshaft  1  and the chain gear  2  remains constant.  
      When the actuating drive  5  is not energized, the rotor  5   a  is operatively connected to the chain gear  2 . The operative connection between the rotor  5   a  and chain gear  2  is made by means of an application of an axial force F A1  to the rotor  5   a , the force being generated by a disc spring  6 . Other devices can also be used to generate the axial force F A1 .  
      Only when the actuating drive is energized, the operative connection between the rotor  5   a  and chain gear  2  is released in order to keep the electrical drive power of the actuating drive  5  low. When the actuating drive  5  is energized, an axial force component F A2  is advantageously established between the stator  5   b  and rotor  5   a  of the actuating drive  5 . Such a force may be generated, for example, by means of an axial offset  7  between the stator  5   b  and rotor  5   a  since, as a result of such an offset  7 , such an axial force component F A2  is provided.  
      In the arrangement shown in the FIGURE the rotor  5   a  is not mounted rotatably on the housing, but on the rotating element  1  thus avoiding friction losses, it being also conceivable to mount it on another rotating element, for example, the actuating shaft  4 .  
      The operative connection between the actuating shaft  4  and one of the rotating elements  1 ,  2  can also be effected by means of a component (not illustrated here) which can be actuated separately. The component may be embodied as a frictionally locking connecting element such as a brake structure and/or a non-positively locking connecting element such as a clutch and/or a positively locking connecting element such as a magnetic clutch.  
      Each of the operative connecting possibilities described above can advantageously be carried out in a frictionally locking fashion.