Abstract:
A clamping element freewheel including an inner ring and an outer ring that can be rotated relative to the inner ring in at least one rotational direction. A cage for clamping elements is between the inner ring and the outer ring, with a plurality of clamping elements. The clamping elements are pivotable between a clamping position, in which they prevent relative rotation between the inner and outer rings, and a release position, in which they enable relative rotation between the inner and outer rings. A clamping element preload is provided to preload the clamping element radially inwardly and in the clamping position direction. The clamping element preloading is provided by springs that are configured separately for each clamping element.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a clamping element freewheel, in particular a damped clamping element freewheel with a cage, wherein the freewheel is useable, e.g., on an output side of a crank continuously variable transmission. The invention also relates to a crank continuously variable transmission (CVT) with a freewheel of this type. 
     2. Description of the Related Art 
     A crank CVT is known, e.g., from EP 1 650 071 A2. An input shaft that is drivable by an engine, and which forms an input shaft for a transmission, is provided with an adjustable eccentric drive arrangement with eccentric components. The drive arrangement is connected to a driven shaft through a rod shaped connection elements, wherein the driven shaft forms an output shaft for the transmission. The driven shaft is driven to rotate by transferring the stroke of the connection elements through freewheel devices to the driven shaft, and thus the output side of the transmission. The freewheel devices are provided between the rod shaped connection elements and the driven shaft. 
     In that crank CVT, the driving crankshaft and the output shaft, or the driven shaft, are aligned parallel to one another and rotatably supported in a transmission housing. When torque is introduced by an internal combustion engine into the crankshaft, the torque is transmitted through the crank CVT to the output shaft. Depending on the position of the eccentric components with respect to the rotation axis of the drive shaft, the eccentricity of the eccentric components, and thus their rotation axis relative to the drive shaft, is changed, which facilitates adjusting the stroke transferred from the connecting rod shaped connecting element to the drive shaft, and thus the transmission ratio of the transmission. At the output shaft the torque can be captured, e.g., for driving wheels of a vehicle. Typically, plural eccentric units are arranged in the crank CVT in the axial direction of the crankshaft behind one another, at which respective connecting rod shaped connection elements are attached, and which are connected with a respective number of freewheel units on the output side of the transmission, wherein the freewheel units on the output shaft are also arranged behind one another in the axial direction. 
     Two basic types of freewheels are known, namely shiftable freewheels that selectively block a relative rotation of an outer ring and an inner ring in one of the two directions of relative rotation as a function of a shifting position, and freewheels that have a fixed and not variable blocking device, in which they prevent a relative rotation between an outer ring and an inner ring, while a relative rotation of the outer ring and the inner ring is facilitated in another direction of relative rotation. In shiftable freewheels, e.g., in order to implement a reverse gear no additional transmission and no separate engine has to be provided since shifting the freewheels facilitates changing the rotation direction of the output shaft relative to the rotation direction of the input shaft of the transmission. For non-shiftable freewheels, either a separate motor, e.g., an electric motor, is provided, or another transmission is coupled subsequent to the output shaft of the transmission, e.g., a planetary transmission that is part of the load transfer path in the transmission when required, namely when a reverse driving function is to be provided and which is otherwise decoupled. 
     Shiftable freewheels are typically configured as roller freewheels in which rollers roll off between an inner ring and an outer ring, and are pressed through suitable spring loading into a clamping gap in one or another relative direction of rotation. Thus, at least one of the inner ring or the outer ring has a profile so that the clamping gap is generated. 
     As an alternative to the rolling element freewheels, clamping element freewheels are known that are more compact and lighter than rolling element freewheels. In the clamping element freewheels the clamping elements are profiled, e.g., so that they block the relative rotation of the inner ring or outer ring in one position, wherein the inner ring and the outer ring can have circular cross sections and block the relative rotation in another position. 
     In freewheels, the position of the clamping or rolling elements in which the clamping or rolling elements block the inner ring and the outer ring relative to one another is designated as the clamping or blocking position, in which the rolling or clamping elements are disposed in a clamping gap formed between the inner ring and the outer ring. The position in which they facilitate a rotation of the inner ring and the outer ring relative to one another is designated as the freewheeling position. This language is used in the instant description also for clamping element freewheels, in which the blocking or release is a function of a currently effective diameter of the clamping elements and not of a position of the clamping elements along the circumferential direction. 
     Thus, it is an object of the present invention to provide a clamping element freewheel, in particular for a crank CVT, which has a robust configuration and operates reliably. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a freewheel with clamping elements that are configured through their profile in a cross section perpendicular to the axial direction of the freewheel, so that they can assume a clamping position or a freewheeling position depending on their pivot position through rolling on the inner ring. The particular clamping elements are retained and supported in a cage that is provided between the inner ring and the outer ring, and a clamping element spring loading is provided at the cage separately for each clamping element. The pivot position thus defines an effective diameter of the clamping elements, which changes as a function of the tilt position. The separate clamping element spring loading facilitates selecting a direction and size of the force by a suitable selection of a spring constant and an effective direction of the force, so that geometrical tolerances hardly affect the size of the effective force. In addition to a basic contact pressure for each clamping element, which facilitates a quick reset for the movement into the clamping gap, a portion of the energy resulting from the movement out of the clamping gap can be dissipated through friction, or it can be stored in the spring preloadings for the clamping elements in order to provide a quick back rotation of the clamping elements at the end of the damping process, that means back into the clamping gap. Thus, reliable operations for the freewheel can be provided through the particular clamping element spring preloadings for each clamping element. Furthermore, a contact of the clamping element at the inner ring can be provided in any operating condition by an effective direction of the force, which has a radially inward component through the particular spring preloadings of the clamping elements. 
     According to a preferred embodiment, the inner ring and the outer ring are respectively circular in a sectional view perpendicular to the axial direction of the freewheel. Thus, producing the inner ring and the outer ring is simple. That is facilitated by using clamping elements with a profile in a sectional view perpendicular to the axial direction, wherein the profile of the clamping elements is configured so that they facilitate a relative rotation of the inner ring and the outer ring in a pivoted position of the clamping element. That means there is a clearance between the clamping element and, e.g., the outer ring when the clamping element contacts the inner ring. In other pivot positions, the rotation of the inner ring and the outer ring relative to one another is blocked, which is the case when a clamping element is simultaneously clamped at the inner ring and the outer ring. 
     Preferably, the cage is rotatable on the inner ring. Additionally preferably, a cage spring loading is provided which preloads the cage against the inner ring and/or a component permanently connected with the inner ring. That means that friction energy is generated during a rotation of the cage relative to the inner ring, so that the movement of the clamping element out of the clamping gap and the movement of the cage relative to the inner ring are dampened and the energy is dissipated. 
     Thus, for example, the outer ring can also be supported on the inner ring by a straight bearing or a roller bearing, and the straight bearing or roller bearing can be fixed to the inner ring, preferably pressed on. The cage spring loading can then preload the cage in the axial direction against one of the bearing rings of the straight bearing or roller bearing. 
     According to a preferred embodiment, the cage spring preloading is formed by a disc spring, which provides a simple configuration. 
     Preferably, the springs for the clamping element spring preloading are supported at the cage, which in turn provides advantages during assembly since the cage with the clamping element preloading springs can be configured as a unit in advance, and can then be mounted with inner rings and outer rings and the clamping elements. 
     The springs for the clamping element spring preloading are configured as arm—or leaf springs, preferably with a relatively small spring constant. That facilitates on the one hand adjusting the direction of the contact pressure of the springs or the effective direction of the springs, and on the other hand dimensional tolerances hardly affect the amount of force actually imparted upon the clamping elements due to the small spring constant. 
     The clamping element spring preloading force is preferably selected so that the radial component of the clamping element spring preloading force, that means the component of the force that is effective in a radial direction of the freewheel, is greater than a maximum centrifugal force of the respective clamping element. Thus, the clamping element can be reliably pressed against the inner ring in any operating condition, so that lifting the clamping element from the inner ring is reliably prevented in any operating condition. 
     Preferably, the center of gravity of the particular clamping elements is arranged in the radial direction radially outside a support portion for the clamping elements, wherein the support portion is provided at the cage. Thus, the pivoting or rolling movement of the clamping elements can be reliably and simply performed, and is hardly influenced by support portions at the cage. 
     According to a preferred embodiment the cage is configured so that a stop is provided for each clamping element at the cage. The stop can interact with a portion of the clamping element that is configured accordingly, so that a movement path of the clamping element is limited for its movement out of the clamping position into the freewheeling position, which prevents the clamping elements from moving out of the cage or too far away from the clamping gap. That helps to prevent a failure of the freewheel and provides a reliable and quick shift between a clamping position and a freewheel position. 
     Preferably, the clamping elements are supported in the cage with such clearance, and are shaped with respect to the inner ring, so that the clamping elements can roll on the inner ring without the inner ring moving or the clamping element having to slide on the inner ring or cage. Thus, the contours of the cage and the sliding element are preferably matched, so that the contour of the cage includes a shape in the support portion, wherein the shape corresponds to the roll curve of the profile. That means the shape is identical to the roll curve, but moved in parallel by a particular small clearance. Thus, the clamping element always has the same small clearance relative to the cage. That provides that no excessive energy is dissipated in the freewheel which creates friction and thus heat, which may have to be removed. 
     According to a preferred embodiment, the outer ring of the freewheel is configured with a connecting rod eye for connection with a connecting rod shaped connection element of a crank—CVT. The rod shaped connection element establishes a connection to the drive side of the transmission. 
     According to a preferred embodiment, one or plural stress reduction pass-through openings, or load relief pass-through openings, are provided adjacent to the connecting rod eye. That helps to prevent a fracture or tearing of the outer ring in the portion of the connecting rod eye, since load relief openings of that type significantly reduce the stresses in the portion of the connecting rod eye. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is subsequently described with reference to the accompanying drawing figures, wherein: 
         FIG. 1  illustrates a cross-sectional view of a freewheel according to an embodiment of the invention in a direction perpendicular to the axial direction of the freewheel; 
         FIG. 2  illustrates a cross-sectional view in an axial direction through the freewheel according to  FIG. 1 ; 
         FIG. 3  illustrates a detail of the freewheel according to  FIG. 1 , wherein the freewheel is not loaded; 
         FIG. 4  illustrates a view according to  FIG. 3 , wherein the freewheel, however, is loaded; 
         FIG. 5  illustrates a view according to  FIGS. 3 and 4  describing the damping process; 
         FIG. 6  illustrates an enlargement of the view according to  FIG. 2 ; 
         FIG. 7  illustrates a first embodiment of the outer ring; and 
         FIG. 8  illustrates a second embodiment of the outer ring. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a clamping element freewheel  10  according to an embodiment of the invention in a cross-sectional view in a direction perpendicular to the axial direction, and  FIG. 2  illustrates a cross-sectional view in the axial direction. Details of the views according to  FIGS. 1 and 2  are illustrated in  FIGS. 3 through 5 or 6 . 
     The damped clamping element freewheel  10  includes an inner ring  12  and an outer ring  14  having a common axis of rotation A, and which are concentric relative to one another. The inner ring  12  has a circular outer surface  13  in the cross-sectional view illustrated in  FIG. 1 . The outer ring  14  has a circular inner surface  15  in the cross-sectional view illustrated in  FIG. 1 . 
     The inner ring  12  can be, e.g., identical to the output shaft of a crank CVT, or it can be non-rotatably connected with the output shaft, e.g., through a transmission, as required. The outer ring  14  is provided as a circular ring with a bulge  16  in a radially outward direction, wherein a connecting rod eye  18  is integrated in the portion of the bulge  16 . A connection to the input side of the crank CVT can be provided through the connecting rod eye  18 , e.g., through connecting rod shaped connection elements (not shown), so that the stroke generated by the eccentric units at the connecting rod shaped connection elements is transferred to the outer ring  14  and causes a rotation of the outer ring  14 . 
       FIG. 1  furthermore illustrates a stress reduction pass-through opening  19  at the portion of the connecting rod eye  18 , that means adjacent thereto. The stress reduction pass-through opening  19  in the embodiment illustrated in  FIG. 1  is configured essentially as an elongated opening extending in the tangential direction relative to the rod eye  18  or the inner surface  15  of the outer ring  14 . The side of the opening oriented toward the connecting rod eye  18  follows the shape of the connecting rod eye, so that the tension reduction pass-through opening  19  is tapered in a center portion, when viewed in the tangential direction relative to the edge portions. 
       FIG. 7  illustrates the outer ring  14  of  FIGS. 1 and 2  in detail.  FIG. 8  illustrates an alternative embodiment of the outer ring  14 , in particular of the stress reduction pass-through openings  19 ′, wherein two separate stress reduction pass-through openings  19 ′ are provided in the portion adjacent to the bulge  16  of the outer ring  14 . The stress reduction pass-through openings  19  or  19 ′ unload the bulge  16  so that stresses are reduced in that portion. Thus, the stress reduction openings are preferably configured overall as pass-through openings, or stress relief openings, wherein however blind bores are also feasible in principle. 
     As apparent best from  FIGS. 2 and 6 , the outer ring  14  is supported on the inner ring  12  through a straight bearing  20 . The straight bearing  20  is pressed onto the inner ring  12  or the output shaft. Thus, the outer ring  14  is rotatably supported relative to the inner ring  12 . Thus, an annular gap  21  is formed between the inner surface  15  of the outer ring and the outer surface  13  of the inner ring  12 . Clamping elements  22  are inserted into the annular gap  21 , wherein the clamping elements are supported through a cage  24 . The cage  24  is also rotatably supported on the inner ring and can be in contact therewith. Furthermore, cage  24  is axially preloaded through a disc spring  26 , as evident from  FIG. 6 . Thus, the disc spring  26  forms a cage spring preloading. Thus, the cage  24  is pressed against the left bearing ring of the straight bearing  20  through the disc spring  26 . Since the bearing rings of the straight bearing  20  are fixed so that they cannot rotate relative to the inner ring  12 , friction is generated when the cage  24  is rotated relative to the inner ring  12 , or relative to the straight bearing  20 , so that friction energy is dissipated when the cage  24  is rotated. 
     As can be derived from  FIG. 6 , a bearing ring of the straight bearing  20  can be respectively used together at axially adjacent ends of outer ring  14  when the support surface of the straight bearing  20  towards the outer ring  14  is formed. Thus, two support surfaces  23  are formed on a bearing ring of the straight bearing  20 , as is apparent in  FIG. 6 , respectively for one of two adjacent outer rings. 
     Subsequently, the cage  24  and the spring preloading for the clamping elements  22  are described in detail, wherein reference is made in particular to  FIGS. 3 through 5 . 
     The clamping elements  22  respectively include a roll surface  30  through which they can roll on the inner ring  12  without sliding thereon. By rolling on the inner ring  12 , in particular on an outer circumferential surface  13  of the inner ring  12 , the roll surface  30  facilitates a movement of the clamping elements between the non-loaded position of the freewheel  10  illustrated in  FIG. 3  and the loaded position of the freewheel  10  illustrated in  FIG. 4 . 
     Thus, the cage  24  is provided with support surfaces  40  and  41 , which are formed so that a uniform clearance is always provided between the contour surface of the clamping elements  22  and the support surfaces  40  and  41  of the cage  24  when the clamping elements  22  move between the non-loaded position and the loaded position of the freewheel, so that the cage  24  is not moved or influenced. That means that the support surfaces  40 ,  41  substantially correspond to the rolling contour of the lug-shaped clamping element portions  31 ,  32  but are moved parallel thereto, so that the same clearance between the cage  24  and the clamping element  22  is always provided. In the non-loaded position of the freewheel illustrated in  FIG. 3 , in which the clamping elements  22  are pivoted to the right (clockwise) with reference to a tangent at the inner ring  12  at the contact point of the clamping elements  22 , the clamping elements  22  are provided with a clearance relative to the inner surface  15  of the outer ring  14 . 
     The cage  24  furthermore includes a stop  42 , configured as a stop lug for each clamping element, wherein the lug shaped portion  31  of the clamping element  22  can contact the stop lug when the clamping element  22  moves from the loaded position into a release position and can thus limit the movement of the clamping element  22 , which means to limit excessive pivoting of clamping element  22 . 
     The cage  24  respectively includes particular arm springs  50  for a clamping element spring preloading for each clamping element  22 . The arm springs  50  impart a basic contact force F G  upon the clamping element  22 , wherein the basic contact force is oriented in the radially inward direction, and in a direction toward the clamping position (to the left in  FIG. 3 ). Thus, the basic contact force F G  acts at an inclined angle in a direction toward the gap  21  and in the radially inward direction. The tangential component F GT  of the basic contact force F G  is selected so that it provides the basic spring loading toward the clamping position or clamping gap. That means a sufficient basic spring loading is provided for the clamping element  22  in a direction toward the clamping gap. The radial component F GR  of the basic contact force F G  is preferably selected so that it is greater than the maximum operational centrifugal force acting upon the clamping element  22 , and thus it prevents a lift-off of the clamping element  22  from the inner ring  12 . The arm spring  50  preferably has a relatively small spring constant, so that dimensional tolerances, e.g., when installing the arm springs  50  at the cage  24  or the clamping elements  22 , hardly influence the basic contact force F G . 
     In the clamping position illustrated in  FIG. 4 , which is schematically illustrated by an overlap of the outer ring  14  and the clamping element  22 , the clamping element  22  is pivoted to the left, counterclockwise relative to the position illustrated in  FIG. 3 , and thus clamps the inner ring  12  and the outer ring  14  relative to one another. Thus, the inner and the outer ring  12  or  14  can only be rotated together in a counterclockwise direction of rotation in  FIG. 4 . 
     When the freewheel is rotated at high speed, clamping element  22  rotates out of the clamping gap, as illustrated in  FIG. 5 , and pivots in the clockwise direction, so that the arm spring  50  flexes under load and an air gap  52  is created between the inner surface  15  of the outer ring  14  and the clamping element  22 . Thus, the arm spring  50  absorbs a small portion of the energy which is created when the clamping element  22  rotates out of the clamping gap. The stored energy in the arm spring  50  is used at the end of the damping process for turning the clamping element  22  back in a counterclockwise direction toward the clamping gap, and thus into the position illustrated in  FIG. 3 . 
     When moving out of the clamping position into the freewheeling position the clamping element  22  furthermore rolls on the outer surface  13  of the inner ring  12  with its rolling surface  30  until the lug-shaped portion  31  of the clamping element  22  comes in contact with the stop  42  at the cage  24 . That generates an impulse force F J  upon the cage, which can lead to a movement of the cage  24  relative to the inner ring  12  or the straight bearing  20  connected with the inner ring  12 . Such cage movement is dampened by the friction between the straight bearing  20  and the cage  24  by dissipating energy through friction. The reactive force F JR  generated at the clamping element  22  generates a braking force F JRB  in the form of a friction force, and thus also dissipates energy from the system. Thus, the movement of the clamping element  22  out of the clamping gap is limited by contact at the stop  42  of the cage  24 , and respective vibrations are dampened by the friction forces so that clamping element  22  can return quickly and reliably into the start position illustrated in  FIG. 3 , and can be brought from there into the clamping position in a reliable manner. The movement of the cage  24  furthermore also generates a friction force F K  between the other lug-shaped clamping element portion  32  of the clamping element  22  and the respective support surface  41  at the cage, wherein the friction force dampens the oscillating movement of the clamping element  22 .