Abstract:
A triple shaft adjusting gear including a driving part ( 01 ) that can be connected rotationally fast to a drive shaft, a driven part that can be connected rotationally fast to a driven shaft and an adjusting member that can be connected to an adjusting shaft. A mechanical stop for limiting an adjusting angle between the drive shaft and the driven shaft is arranged between two of the three shafts. According to the invention, the stop is an elastic coupling member for damping an impingement in case of a stop.

Description:
BACKGROUND 
     The invention concerns a triple shaft adjusting gear comprising a driving part that can be connected rotationally fast to a drive shaft, a driven part that can be connected rotationally fast to a driven shaft and an adjusting member that can be connected rotationally fast to an adjusting shaft. 
     Triple shaft adjusting gears are used for instance in internal combustion engines for adjusting phase angles, predominantly for adjusting the opening and closing times of the gas exchange valves (camshaft adjusters, phase adjusters for actuator shafts in variable valve trains). The phase adjuster is arranged as an adjusting member in a triple shaft system. Primarily, the driving power is supplied to the triple shaft system through the drive shaft (e.g. chain sprocket), and this driving power is then delivered through the driven shaft (e.g. camshaft). The adjusting member is arranged within the power flow as a connecting member between the drive shaft and the shaft to be driven. The adjusting member, superimposed by a third shaft (adjusting shaft), enables an additional transfer of mechanical power into the shaft system or a withdrawal of this power out of the system. In this way, it is possible to vary the moving function (phase angle) defined by the drive shaft relative to the driven shaft. 
     Examples of such triple shaft adjusting gears are wobble plate mechanisms and internal eccentric mechanisms which are described, for instance in WO 2006/018080. This category further includes the shaft mechanisms disclosed in WO 2005/080757 and the mechanisms known from US 2007/0051332 A1 and US2003/0226534 A1. 
     A variety of phase adjusters are known from the prior art. For example, DE 10 2004 009 128 A1, DE 10 2005 059884 A1 and DE 10 2004 038 681 A1 describe electromechanical camshaft adjusters. 
     DE 102 48 351 A1 discloses an electromechanical camshaft adjuster in which the adjusting motor is connected to the adjusting gear through a disengageable clutch. Through an adequate design of the clutch, it is possible to limit the torque that can be transmitted to the adjusting shaft. This clutch then acts as a safety clutch. 
     A special case of a triple shaft adjusting gear is a double shaft arrangement in adjusting drives in which the drive shaft is fixed to the housing, i.e. power is transmitted only between the adjusting shaft and the driven shaft. A device of this type serves to convert a driving power of an adjusting element delivered at a high speed and low load into an output power at a low speed and high load, and is used, for instance in reducing gear devices for adjusting drives in the automotive field as well as in industrial application e.g. robotics. 
     In order to protect the peripheral components from undesired collisions of components in case of control errors in the actuating system, the adjusting range and the drive power range are limited by a limitation of the rotational angle of one of the three shafts relative to a second shaft or relative to the housing. For this purpose, a mechanical stop made as an integral part of the device is used. In the known prior art of camshaft adjusters, this stop is arranged between the driven shaft and the drive shaft because, as a rule, the adjusting shaft traverses an angle of more than 360°. 
     In such a configuration, the adjusting shaft, which is not limited directly in the adjusting or drive angle, is decelerated in case of a stop through the transmission kinematics and the rigidity of the transmission components as soon as the power take-off side reaches the limit of the rotational angle. During this event, as a result of the extremely high loads, transmission components can get so strongly deformed that they collide with each other and cause the adjusting member to clamp. Moreover, the transmission components can suffer prematurely from fatigue, or they must be oversized for the normal operation to resist the high loads in case of a non-decelerated stop. 
     SUMMARY 
     The object of the invention is to design a triple shaft adjusting gear such that the action of pulsed loads occurring in the adjusting member when a stop is reached is damped. 
     The above object is achieved with a triple shaft adjusting gear including one or more features of the invention. 
     Advantageous features and developments of the invention are described below and in the claims. 
     The triple shaft adjusting gear comprises a driving part that can be connected rotationally fast to a drive shaft, a driven part that can be connected rotationally fast to a driven shaft and an adjusting member that can be connected to an adjusting shaft, and a mechanical stop for limiting an adjusting angle between the drive shaft and the driven shaft being arranged between two of the three said shafts. According to the invention, the stop comprises an elastic coupling member for damping an impingement in case of a stop. 
     The invention will be described in the following with reference to a camshaft adjuster but the invention can also be applied to other triple shaft adjusting gears and double shaft arrangements (driving part fixed on housing). 
     In a preferred form of embodiment of the invention, the elastic coupling member is used in an electromechanical camshaft adjuster in which the stop is arranged between the driving part and the driven part. The stop is formed on the drive side by a stop ring comprising a stop lug and on the driven side by a stop disk comprising a shift gate. Each of the shift gate and the stop lug guided in the shift gate comprise respectively at least one (in the normal case, two) stop surfaces, and these stop surfaces come into contact with each other in case of a stop. The coupling member is preferably disposed between the stop surfaces. 
     The advantages of the invention are to be seen particularly in the fact that an effective internal partial uncoupling of the external load can be achieved with simple constructional measures. From a particular load moment on, the elastic coupling member assures a higher yielding capacity (i.e. lower rigidity) in the force flow between the corresponding stop surfaces when the stop position has been reached. A large part of the kinetic energy of the rotating shafts (drive shaft and adjusting shaft) is thus converted into deformation energy upon impact against the stop. Due to the longer path, work is performed so that, as a result, energy of movement is quasi “destroyed”. Due to the inevitable inner and outer friction, energy is likewise discharged in the form of heat. 
     The dimensioning of the elastic coupling member must be based on the maximum energy that is created in case of a stop. The elastic coupling member can be configured as a mechanical, pneumatic or hydraulic coupling member, or as a combination out of these. Suitable as a mechanical coupling member, for example, is an elastic bed on one or both of the stop surfaces, or a spring mechanism that can be configured either between the stop surfaces or in a rotationally elastic mounting. If, instead, the elastic coupling member is configured as a pneumatic or hydraulic coupling member, it is possible to use a pressure-loaded piston that is disposed, for instance, between the stop surfaces and is displaced in tangential direction or, with help of a ramp or a knuckle joint in radial direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will be described more closely in the following with reference to the figures. 
         FIG. 1  shows a principle sketch of a mechanical stop of a camshaft adjuster comprising a coupling member; 
         FIG. 2  shows a principle sketch of a mechanical stop of a camshaft adjuster comprising two coupling members; 
         FIG. 3  shows three elementary sketches of different coupling members in a camshaft adjuster; 
         FIG. 4  shows a secondary preferred form of embodiment of a camshaft adjuster in three different views; 
         FIG. 5  shows a principle sketch of a radially displaceable piston as coupling member; 
         FIG. 6  shows a preferred form of embodiment of a camshaft adjuster comprising a spring washer; 
         FIG. 7  shows a detail representation of the camshaft adjuster of  FIG. 6 ; 
         FIG. 8  shows a detail representation of the camshaft adjuster comprising modified shaped elements; and 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a principle sketch of a stop of an electromechanical camshaft adjuster. The driving part of the camshaft adjuster is a chain sprocket  01 . The chain sprocket is operatively connected to a crankshaft through a chain (not illustrated). The chain sprocket  01  carries a stop ring  02  comprising a stop lug  03 . Within the stop ring  02  is arranged a stop disk  04  that comprises a shift gate  05  and is firmly connected to a camshaft pinion (driven part). The stop lug  03  is guided in the shift gate  05  for movement relative to the stop disk. The shift gate  05  of the stop disk is limited by stop surfaces  06 . 
     Stop surfaces in the form of an advance stop  07  and a retard stop  08  (drive side) are arranged on the stop ring  02 . In cooperation with the stop surfaces  06  of the stop disk  04 , these stop surfaces limit the angle of adjustment between the crankshaft and the camshaft. 
     In the form of embodiment illustrated, an elastic coupling member, in the present case a spring  09 , is disposed on the retard stop  08 . This creates a soft stop with high elasticity when the retard stop  08  is reached. The advance stop  07  is configured as a rigid stop. 
     The form of embodiment shown in  FIG. 2  differs from the embodiment shown in  FIG. 1  only by the fact that both the advance stop  07  and the retard stop  08  are configured as elastic coupling members. 
       FIG. 3  shows detail views of three different forms of embodiment for coupling members with reference to an example of the retard stop  08 , in schematic representations. The coupling members can be formed by the above-mentioned spring  09 , by a hydraulic or a pneumatic piston  11  or by a combination of the spring  09  and the piston  11 . The practical designing of these forms of embodiment will not confront a person in the art with any problems. 
     In the variants illustrated, the coupling members are all arranged in respective stop surfaces  06  of the stop disk  04  and comprise a buffer  12  which, in case of a stop, comes to abut against the retard stop  08 . For a person skilled in the art, it is very simple to translate these symbolic illustrations of the coupling member into technical forms of embodiment. It is understood that these forms of embodiment can also apply to the advance stop  07  ( FIGS. 1 ,  2 ). 
       FIG. 4  shows a preferred form of embodiment of a triple shaft adjusting gear of the invention. In this figure, the left-hand drawing shows a longitudinal sectional view of a camshaft adjuster, the central drawing shows a cross-sectional view of the camshaft adjuster and the right-hand drawing shows a top view of the camshaft adjuster seen from the side of the camshaft. 
     The camshaft mounted stop disk comprises a primary stop disk  13  and a secondary stop disk  14 . The secondary stop disk  14  is fixed on the camshaft in a clamping fit of a central screw (not shown). The primary stop disk  13  is mounted for rotation on the secondary stop disk  14 . Torsion springs  16  bias the primary stop  17  elastically by a measure of a damping angle α against the secondary stop  18 . In case of a stop, the stop surface  7  or  08  of the stop ring comes to abut at first against the primary stop  17 . Depending on the energy available, said stop surface presses said stop further against the torsion springs  16  and, in doing this, loses energy. The damping properties are guaranteed until the primary stop  13  comes to abut against the secondary stop  14 . This characterizes the mechanically maximum permissible end position. It is understood that the damping function can also be configured alternatively on the driven side without departing from the concept of the invention. 
       FIG. 5  shows an alternative form of embodiment of a coupling member in an elementary sketch. A radially oriented coupling member  19  is arranged on the stop lug  03 . The coupling member  19  comprises a radially displaceable piston  21  that comprises a contour  22  or ramp on its inward directed end. A spring-damper element  23  damps the radial movability of the piston  21 , i.e. the radial movement of the piston is damped. 
     When the stop surface  06  comes into contact with the stop surface  08 , the stop surface  06  at first abuts against the contour  22  of the piston  21  which is thus pushed, against the action of the spring-damper element  23 , in a damped manner in radial direction. In this way, the impact of the stop surface  06  against the stop surface  08  is decelerated as desired. The deceleration function can be dimensioned through the shape of the contour  22 . It is understood that a hydraulic or a pneumatic coupling member may also be used in place of the spring-damper element. 
       FIG. 6  shows a particularly preferred form of embodiment of the inventive cam shaft adjuster comprising an elastic coupling member in form of a spring ring  24 . The spring ring  24  is open after the manner of a circlip and comprises two radially inward directed spring ends comprising primary stop surfaces  28 ,  29 . The angle of opening β and the spring rate of the spring ring  24  must be designed such that a damping of the stop of the stop lug is achieved through a work travel distance w ( FIG. 7 ). The stop lug  03  with the stop surfaces  07 ,  08  is indicated in broken lines. 
     The spring ring  24  is mounted in a spring housing  26  in the chain sprocket  01  and is centered and guided through shaped elements  27 . 1 ,  27 . 2 ,  27 . 3  that are arranged on the chain sprocket  01 . The stop surface  06  of the stop disk  04  comes to abut at first against a primary stop surface  28  of the spring ring  24 . A spring torque results out of the energy of abutment and the spring rigidity and compresses the spring ring through the work travel distance of 1° to 6° depending on the design. At this stage, the spring length remains constant; the angle of opening β becomes smaller. Support of the spring torque is effected through the other end of the spring  29  in the associated shaped element  27 . 3 . At the end of the work travel, the stop surface  06  comes to abut against the stop surface  08  of the stop lug  03  in the chain sprocket  01  and thus reaches the actual end of the displacement range. 
       FIG. 7  is a detail representation of the state described just above. 
     It is understood that alternative forms of embodiment and arrangements are possible as long as the described principle of work is retained. For example,  FIG. 8  shows a modified arrangement of the shaped elements and of the guidance of the spring ring  24  through the pins  29  that are fixed on the chain sprocket (as shaped elements) and guided in corresponding apertures  31  of the spring ring  24 . 
     LIST OF REFERENCE NUMERALS 
     
         
           01  Chain sprocket 
           02  Stop ring 
           03  Stop lug 
           04  Stop disk 
           05  Shift gate 
           06  Stop surface 
           07  Advance stop surface 
           08  Retard stop surface 
           09  Spring 
           10  — 
           11  Pneumatic piston 
           12  Buffer 
           13  Primary stop disk 
           14  Secondary stop disk 
           15  — 
           16  Torsion spring 
           17  Primary stop 
           18  Secondary stop 
           19  Coupling member 
           20  — 
           21  Piston 
           22  Contour 
           23  Spring damper element