Abstract:
An actuating device for exerting a force that causes two components arranged to be rotatable relative to each other about an axis of rotation to be urged axially away from each other comprising a radial support element forming a first hydraulic pressure chamber and a second hydraulic pressure chamber, each of the pressure chambers surrounding the axis of rotation and the first pressure chamber being in fluid connection with the second pressure chamber. The actuating device further comprises a first piston axially supported on the first component for sealing the first pressure chamber in an axially displaceable way and a second piston axially supported on the second component for sealing the second pressure chamber in an axially displaceable way.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent claims priority of German Patent Application No. 10 2011 087 873.4 filed Dec. 7, 2011, which application is hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     The invention relates to an axial actuating device. More particularly, the invention relates to an axial actuating device for a friction disc clutch. 
     BACKGROUND OF THE INVENTION 
     In a drive train of a motor vehicle, a friction disc clutch is used between a drive motor and a transmission. The friction disc clutch in general comprises at least one friction disc and a pressure plate. The friction disc and the pressure plate are both arranged to rotate about a common axis of rotation. The friction disc is connected to the drive motor in a force-locking way and the pressure plate is connected to the transmission in a force-locking way. A reverse arrangement is likewise possible. When an axial force is applied to press the friction disc axially against the pressure plate, a transmission of power is established between the drive motor and the transmission due to a friction-fitting connection by the clutch. 
     BRIEF SUMMARY OF THE INVENTION 
     An actuating device that generates the axial force is supported both on the friction disc and on the plate. When the friction disc and the pressure plate are axially separated from each other, they rotate at different rotational speeds. As a consequence, the actuating device needs to be capable of maintaining the axial force even while the pressure plate rotates relative to the friction disc. The pressure chamber is supported on the friction disc by an axial bearing, which is usually a rolling bearing. In general, the actuating device is a hydraulic actuating device including a pressure chamber and a piston that seals the pressure chamber in an axially displaceable way. The piston is axially supported on the pressure plate and the pressure chamber is axially supported on the friction disc. 
     During operation of the clutch, the rolling bearing may be subject to great loads. Therefore, it is of relatively large dimension. 
     In accordance with the invention, an actuating device for exerting a force that causes two components that are arranged to be rotatable relative to each other about an axis of rotation to be urged axially away from each other comprises a radial support element forming a first hydraulic pressure chamber and a second hydraulic pressure chamber, each pressure chamber surrounding the axis of rotation and the first pressure chamber being in fluid connection with the second pressure chamber. The actuating device further comprises a first piston axially supported on the first component for sealing the first pressure chamber in an axially displaceable way, and a second piston axially supported on the second component for sealing the second pressure chamber in an axially displaceable way. 
     Thus, it is possible in part or in total to deflect a portion of a supporting force that acts between the second component and the support element via the second piston. Consequently, the mechanical effort for an axial bearing that supports the support element relative to the second component may be of smaller dimensions. This may contribute to reducing manufacturing costs. In addition, the actuating device may be of more compact design, potentially reducing the installation space on the friction disc clutch. This offers greater freedom in terms of the design and construction of the actuating device. 
     The pressure chambers may be arranged to be radially offset against each other. Thus, the support element may be of simpler shape and may contribute even further to reducing the manufacturing costs of the actuating device. 
     In particular, the second pressure chamber may be located radially inward relative to the first pressure chamber. The first pressure chamber may thus be part of a known actuating device and the second pressure chamber may be provided at a location where additional installation space for the second pressure chamber may be provided in a constructionally simple way. 
     A hydraulically effective surface of the second piston may be smaller than a hydraulically effective surface of the first piston. Since the two pressure chambers are in fluid connection with each other, there will always be an identical pressure in the two pressure chambers. The ratio of the forces acting on the two pistons can easily be adjusted in a constructional way by means of the ratio between the hydraulically effective surfaces of the two pistons. If the surface of the second piston is smaller than the surface of the first piston, the force acting between the support element and the second component is reduced but remains greater than zero. Thereby the axial position of the support element may be defined in an improved way. 
     The invention is based on the object of providing an actuating device that provides improved support of the occurring axial forces in order to be able to use a rolling bearing of smaller dimensions. In accordance with a preferred embodiment, a bearing for axially supporting the support element is provided on the second component. The bearing may in particular be received in the second pressure chamber. This allows a more compact arrangement of the second pressure chamber and of the bearing, while at the same time the bearing is surrounded by the fluid present in the second pressure chamber, which may contribute to cooling and lubricating the bearing. 
     In accordance with one embodiment, the bearing comprises a rolling bearing. The rolling bearing may be of relatively light dimensions and may contribute to reducing a rotational resistance between the second component and the support element. 
     In accordance with another embodiment, the bearing comprises a journal bearing. The journal bearing may in particular comprise a contact plate. Using a journal bearing instead of a rolling bearing may reduce the manufacturing costs of the actuating device. 
     In accordance with yet a further embodiment, the second piston is rigidly fixed to the support element in a radially to the inside or radially to the outside. The axial movability of the second piston relative to the support element is implemented by an axial deformability of the support element. This allows a reduction of the number of seals, which may increase the reliability and useful life of the actuating device. Moreover, the rigid attachment may be advantageous in terms of the assembly of the components. 
     In accordance with yet another embodiment, the second piston is embodied to be integrated with the second component. Such an arrangement may contribute to even further reducing the costs of the actuating device. 
     The invention will be described in more detail with reference to the appended FIGURE. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The FIGURE shows a diagrammatic representation illustrating the upper half of a longitudinal section along an axis of rotation of a friction disc clutch including an axial actuating device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Friction disc clutch  100  is provided to selectively establish a nonpositive connection between component  115  and pressure plate support  120 , which are arranged to rotate about axis of rotation  110 . Component  115  may, in particular, comprise a cover or housing of friction disc clutch  100  shown in the FIGURE. To establish the nonpositive connection, friction facing  125 , pressure plate  130 , and friction facing  135  are arranged axially adjacent to each other at a radial distance to axis of rotation  110 . Friction facings  125  and  135  are arranged in a torque-locking manner but are axially displaceable relative to component  115 . Pressure plate  130  is located axially between friction facings  125  and  135  and is fixed to pressure plate support  120  in a torque-locking but axially displaceable way. 
     The illustrated design of friction disc clutch  100  in terms of component  115 , friction facings  125 ,  135 , and pressure plate  130  is only described by way of example. Other embodiments may include more or fewer friction facings  125 ,  135  and/or a larger number of pressure plates  130 . In some embodiments, friction facings  125 ,  135  and/or pressure plate  130  are axially immovable relative to component  115 ,  120  to which they are connected in a torque-locking way. 
     Friction disc clutch  100  establishes a transmission of power between component  115  and pressure plate support  120  when friction facing  125  is pressed axially to the right against pressure plate  130 , which is pressed against friction facing  135 , which, in turn, is pressed against component  115 . Conversely, the transmission of power between component  115  and pressure plate support  120  may be disrupted by removing the axial force that acts on friction facing  125 . 
     In a non-illustrated further embodiment friction facings  125 ,  135  and pressure plate  130  are axially pressed together by a spring and when actuated, actuating device  105  removes the axial compression, i.e., it compensates the axial force of the spring to reduce the axial compressing force on friction facings  125 ,  135  and pressure plate  130  and to open clutch  100 . 
     Actuating device  105  is provided to press friction facing  125  axially to the right towards component  115 . Actuating device  105  is supported on component  140 , which may, in particular, be embodied as a hub and is arranged to rotate relative to component  115  about axis of rotation  110 . The actual rotatability of components  115 ,  140  relative to each other is usually dependent on whether or not a nonpositive connection is established between component  115  and friction disc support  120 . 
     Actuating device  105  comprises radial support element  145 , which may, in particular, be a flange extending in a radial direction from component  140 , piston  150 , and piston  155 . In the illustrated embodiment, piston  155  is designed to be integrated with component  140 , i.e., to be formed by the latter. In any case, piston  155  is supported on component  140  and piston  150  is supported on component  115 . In the illustrated embodiment, as piston  150  is supported on component  115 , friction facings  125 ,  135  and pressure plate  130  are under compression. 
     In the illustrated sectional view, support element  145  is essentially bent into an S-shape in the radial direction to form hydraulic pressure chamber  160  and hydraulic pressure chamber  165 . Pressure chamber  160  is located radially outside pressure chamber  165 . In an alternative embodiment, two pressure chambers  160 ,  165  may be provided in reverse radial arrangement. 
     Hydraulic pressure chamber  160  is sealed by piston  150  and hydraulic pressure chamber  165  is sealed by piston  155 . Each piston  150 ,  155  is radially displaceable relative to the respective associated pressure chamber  160 ,  165 . 
     In the illustrated embodiment, both piston  150  and piston  155  are embodied as a shoulder piston so that in addition to limiting pressure chamber  160  to the right in an axial direction, piston  150  also acts to limit the pressure chamber radially to the outside. In a corresponding way, in addition to limiting pressure chamber  165  to the left in an axial direction via the axial deformability of support element  145 , piston  155  also acts to limit pressure chamber  165  radially to the inside. 
     Pressure chambers  160 ,  165  are hydraulically connected to each other by aperture  170  formed in support element  145 . Furthermore, pressure chamber  165  is connected to fluid line  175 , which is embodied as a radial bore formed in component  140 . Through fluid line  175 , a hydraulic fluid may enter pressure chamber  165  and pass into pressure chamber  160  through aperture  170 . Due to the exchange of fluid, there will always be an identical pressure in pressure chambers  160 ,  165 . 
     Respective seals  180  are preferably provided between support element  145  and piston  150  and between piston  155  and component  140 . These seals are provided to seal pressure chambers  160  and  165  in a fluid-tight way while allowing pistons  150 ,  155  to move in an axial direction relative to pressure chambers  160 ,  165 , respectively. The axial deformability of support element  145  provides the axial movement of piston  155 . 
     Optionally, bearing  185  may be arranged between component  140  and support element  145 . Bearing  185  is an axial bearing, usually embodied as a rolling bearing. Since the axial load on bearing  185  may be kept relatively small, bearing  185  may also be embodied as a journal bearing, in particular as a contact plate. In yet another embodiment, bearing  185  may even be dispensed with. In the illustrated embodiment, bearing  185  is located inside hydraulic pressure chamber  165 . In alternative embodiments, bearing  185  may be arranged in any other desired location to ensure low-friction axial transmission of power between support element  145  and component  140 . 
     The following is a brief description of the functioning of actuating device  105 . To establish or disrupt a transmission of power between component  115  and pressure plate support  120 , piston  150  is to be moved axially to the right. For this purpose, ignoring the functioning of hydraulic pressure chamber  165 , a hydraulic fluid flows into hydraulic pressure chamber  160  through fluid line  175  and aperture  170 . If pressure inside pressure chamber  160  is higher than outside pressure chamber  160 , piston  150  is pushed to the right against friction facing  125  and a transmission of power is established between friction elements  125 ,  135  and pressure plate  130 . The force acting on piston  150  towards the right needs to be supported by a force of equal magnitude acting on support element  145  towards the left. This force acting towards the left is transmitted to component  140  via bearing  185 . 
     A portion of this force acting on support element  145  towards the left is compensated by the function of pressure chamber  165 . Due to aperture  170 , pressure in pressure chamber  165  is always the same as in pressure chamber  160 . The pressure present in pressure chamber  165  results in a force that urges support element  145  to the right and piston  155  and component  140  to the left. 
     In the process, the force acting on support element  145  in pressure chamber  165  towards the right compensates a portion of the force acting on support element  145  in pressure chamber  160  towards the left. A portion of the opposing forces may be absorbed by a bending of support element  145 . The resultant force acting on support element  145  towards the left will substantially be reduced by a superposition of the individual forces and by their at least partial compensation. 
     As a result, the axial forces that act on bearing  185  decrease so that less load is applied to bearing  185 . The extent of the decrease of the axial load on bearing  185  is defined by a ratio between hydraulically effective surface  190  of piston  150  and hydraulically effective surface  195  of piston  155 . If effective surface  195  of piston  155  is of the same size as surface  190  of piston  150 , the forces may neutralize each other completely, allowing bearing  185  to be dispensed with or to be replaced by a contact plate. If effective surface  195  of piston  155  is smaller than effective surface  190  of piston  150 , a residual force remains and needs to be transmitted between support element  145  and component  140  while friction disc clutch  100  is actuated and hydraulic pressure chambers  160 ,  165  are under pressure to close or open friction disc clutch  100 . 
     In accordance with a further embodiment, radially innermost seal  180  provided between support element  145  and component  140  may be dispensed with and support element  145  may be rigidly connected to component  140  in a fluid-tight way at this point. For example, support element  145  may be connected to component  140  by riveting or welding. In this case, movability of piston  155  relative to support element  145  is ensured by the fact that support element  145  is deformable, in particular, elastically bendable in the axial direction. For this embodiment, hydraulically effective surfaces  190 ,  195  of pistons  150 ,  155  preferably are of similar or equal size so that the axially opposing forces that act on support element  145  approximately cancel each other so that support element  145  only needs a relatively low degree of deformability. 
     REFERENCE NUMERALS 
     
         
           100  friction disc clutch 
           105  actuating device 
           110  axis of rotation 
           115  first component 
           120  pressure plate support 
           125  first friction facing 
           130  pressure plate 
           135  second friction facing 
           140  second component 
           145  support element 
           150  first piston 
           155  second piston 
           160  first hydraulic pressure chamber 
           165  second hydraulic pressure chamber 
           170  aperture 
           175  fluid line 
           180  seal 
           185  bearing 
           190  hydraulically effective surface of the first piston 
           195  hydraulically effective surface of the second piston