Abstract:
To reduce the attainable actuation times of an electrically actuated friction brake and simultaneously keep the friction brake inexpensive, an electrically actuated friction brake with a brake pad ( 3 ) actuated by an actuation device ( 10 ) is proposed, wherein for braking the actuation device ( 10 ) is driven by a spring and is held open by an electrical actuator ( 12 ), so that the spring actuates the friction brake ( 1 ) in case of a power loss, wherein a first transmission element ( 5 ), that is connected to the brake pad ( 3 ), and a second transmission element ( 8 ) with an elevation curve ( 17 ) are provided and a coupling element ( 15 ) is provided on the first transmission element ( 5 ), wherein a follower element ( 14 ) is arranged on the coupling element ( 15 ) that follows the elevation curve ( 17 ) under the action of the spring for actuating the first transmission element ( 5 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a Continuation-in-Part of International Patent Application No. PCT/EP2014/054531 filed Mar. 10, 2014, which claims priority of Austrian Patent Application No. A50165/2013 filed Mar. 11, 2013. Moreover, the disclosure of International Patent Application No. PCT/EP2014/054531 is expressly incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention relate to an electrically actuated friction brake with a brake pad actuated by an actuation device. 
         [0004]    Embodiments of the present invention relate to electrically actuated brakes, thus to brakes in which an electrical actuator such as an electric motor, via transmission parts such as levers, screws, ball screws, cams, eccentrics, fluids, gases, etc., presses on the brake pad, such as a brake disc for example, on the friction surface, such as a brake disc or brake drum, for example. The design of the force characteristics over the actuation travel in electrically actuated brakes is important for the actuation time and the energy expenditure for applying the braking torque. 
         [0005]    2. Discussion of Background Information 
         [0006]    Especially for electrically actuated service brakes of vehicles, there are high standards with regard to short actuation times and pressing force requirement. For example, today&#39;s vehicles demand an actuation time for full braking of around 200 ms. At the same time, in modern vehicle front wheel disc brakes, brake pad pressing forces of 30 to 40 kN can arise, in many cases even significantly more. Since actuation travel*pad pressing force is the energy requirement for actuation of the brake and leads to the required actuation power for a given actuation time, it is apparent that the electrical actuators require accordingly high levels of electrical power. If an actuation travel of 2 mm is covered for full braking for 40 kN of pad pressing force, the energy requirement is roughly 40 Ws. If the braking process here takes 0.2 s, an average mechanical power of at least 200 W per brake is required, which must be provided by the electrical actuator. Available mounting space, weight, costs, and current requirement for the electrical actuator require that the motor power be kept low, which is why an optionally large electrical actuator cannot be used. 
         [0007]    For a linear electrically actuated brake, i.e., for linear transmission elements such as screws, ball screws, and fluids with a linear relationship between the actuation travel and actuator (force, torque), a pad pressing force rising linearly from zero to a maximal value is necessary, under the assumption of a constant coefficient of friction. The necessary transmission ratio of the linear brake is determined here by the required maximal force (full braking), as this must be guaranteed, and remains constant for all lower pad pressing forces. That is disadvantageous, however, because, in all other, generally more frequent cases, the electrical actuator cannot be optimally utilized and is over-dimensioned. For such a linear brake, the electrical actuator is thus operated, up to design full braking, with a smaller than possible load, while the transmission ratio and thus also the attainable actuation time are determined by the constantly high transmission specified for the case of full braking. As a result, optimal and/or short-as-possible actuation times cannot be achieved for linear brakes for braking that does not correspond to the case of full braking. 
         [0008]    In addition, the cost pressure on electrically actuated brakes is also high, because they have to compete with relatively simple hydraulic brakes. Therefore, any possible cost optimization of the electrical actuator is important. It is understood here that the smaller the electrical actuator can be kept, the more advantageous it will be. 
         [0009]    Non-linear electrically actuated brakes such as those described in WO 2010/133463 A1, in which a non-linear transmission element, such as a cam, eccentric, non-linear ramp, etc., is provided between the actuator and brake pad, offer an improvement over linear brakes. In WO 2010/133463 A1, for example, a shaft with an eccentric pin, or a cam to which the brake pad is secured, is turned by an actuation device. Here the torque of an electric motor is transmitted via a linkage and lever to the non-linear transmission element of the brake. Due to the eccentricity of the pin or cam, the brake pad is pressed against the friction surface, and a non-linear relationship arises between the actuation travel or angle of rotation of the shaft and the pad pressing force or the arising braking torque. Due to the eccentric or cam, a force transmission also arises (a small travel effects a high force), whereby the electrical actuator can be dimensioned so as to be smaller. This also makes it possible to shorten the actuation times in comparison with a linear electrically actuated brake. 
         [0010]    As a rule, the installation conditions of the brake, in particular for vehicle brakes, are such that only a very limited mounting space is available to receive the brake, so that electrical motors of small size have to be used. The very high pressing force of the brake pad must be produced from the high speed of the preferably small electric motor. Instead of the linkage and lever of WO 2010/133463 A1, this can be also be achieved, for example, by a transmission driven by an electric motor. For example, the output stage of the transmission rotates the shaft that is integrated in the transmission and has the eccentric or cam, while the non-linear transmission element again acts on the brake pad. With such a transmission, even transmissions of 1:40 can be implemented in a tiny mounting space, whereby small electric motors can be used. The actuation time can thus be reduced even further. But such transmissions are very complex and therefore also expensive. 
         [0011]    A parking brake is known from WO 01/90595 A1 in which a brake actuating linkage is actuated by an electrically driven drive connection. The drive connection is embodied in the form of a cam disc that is rotated by the electric motor and an adjusting element guided along a surface of the cam disc. The cam disc can be embodied such that a constant torque is set on the electric motor in order to shorten the braking time and to achieve a particularly rapid translational movement of the brake actuating linkage. 
         [0012]    For release of a friction brake, often a return spring is tensioned, which is released during release of the friction brake, and opens the friction brake by the energy released thereby. For example, DE 10 2006 012 076 A1 shows an electrically actuated friction brake in which a return spring is tensioned during actuation, and is released for release. The electrical drive must therefore supply energy for tensioning the release spring during the entire actuation of the friction brake. 
       SUMMARY OF THE EMBODIMENTS 
       [0013]    Embodiments of the present invention seek to reduce the attainable actuation times of an electrically actuated friction brake and simultaneously to keep the friction brake inexpensive. 
         [0014]    According to embodiments of the invention, for braking, the actuation device is driven by a spring and is held open by an electrical actuator, so that the spring actuates the friction brake in case of a power loss, wherein a first transmission element, that is connected to the brake pad, and a second transmission element with an elevation curve are provided and a coupling element is provided on the first transmission element, wherein a follower element is arranged on the coupling element that follows the elevation curve under the action of the spring for actuating the first transmission element. The second transmission element can supply much of the transmission required in the actuation device, whereby the electrical actuator is relieved. Due to the additional transmission of the second transmission element, however, the actuation time of the friction brake is also reduced. 
         [0015]    The connection of the coupling element and of the first transmission element is done in a mechanically very simple manner if a first end of a lever in the coupling element is rotatably mounted and a second end of the lever is connected to the first transmission element. 
         [0016]    A very especially simple and advantageous embodiment results if the second transmission element is embodied as a cam disc or as a sliding guide with an elevation curve and the spring rotates the cam disc or the sliding guide. In this way, the actuation device can be implemented by simple and robust device and in a very compact manner. 
         [0017]    If two first transmission elements are provided, it is advantageous if they each be connected via a lever to the coupling element for formation of a parallelogram drive. By way of the parallelogram, a forced synchronization of the two transmission elements is effected in a simple and inexpensive manner. 
         [0018]    In an alternative embodiment, the coupling element is designed as a rocker lever, whose knee joint is guided by a follower element along the elevation curve, wherein the spring acts on the first leg of the rocker lever, and the other leg of the rocker lever is connected to the first transmission element. By way of the rocker lever, especially high transmissions can be implemented in the second transmission element. 
         [0019]    A very simple parking brake function can be implemented if an indentation is provided in the elevation curve, in which the follower element assumes a stable position. The actuation device can thus be fixed in a specific position (parking brake) and can no longer be released except by an outside force. 
         [0020]    The first transmission element is preferably embodied as an eccentric drive or a cam drive, since high transmissions can thereby be implemented with short actuation travels. 
         [0021]    It is very especially advantageous if the elevation curve is formed according to the path translation characteristic of the first transmission element. 
         [0022]    Advantageously, the spring acts on a spring cam arranged on the first transmission element. Thereby it is advantageous when a spring lever is provided on which the spring acts, wherein a first end of the spring lever is rotatably mounted and a spring follower element, that follows the spring cam, is arranged on the other end of the spring lever. 
         [0023]    Further effects and advantages of the of the present friction brake follow from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
           [0025]      FIG. 1  shows a representation of a friction brake according to the invention; 
           [0026]      FIG. 2  shows an alternative embodiment of the actuation device; 
           [0027]      FIG. 3  shows the pad pressing force over the actuation range of the first transmission element; 
           [0028]      FIG. 4  shows the input torque in the first transmission element over its actuation range; 
           [0029]      FIG. 5  shows the arising torque and path transmission characteristic of the second transmission element; 
           [0030]      FIG. 6  shows a representation of an inventive friction brake with release spring; 
           [0031]      FIG. 7  shows the torque from the internal pad pressing force over the actuation range of the electrical actuator; 
           [0032]      FIG. 8  shows the reset torque of the release spring over the actuation range; and 
           [0033]      FIG. 9  shows the torque of the electrical actuator of a friction brake according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0034]    The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice. 
         [0035]      FIG. 1  shows schematically an advantageous exemplary embodiment of a friction brake  1  according to the invention, here in the form of a disc brake with a brake disc as a friction surface  2  and a brake pad  3 , which is pressed by an actuation device  10  on the friction surface  2  for braking. The friction brake  1  could also be embodied as a drum brake, however, and could of course also brake linear movements, i.e., a flatiron as a friction surface instead of a brake disc, for example. Like here, the brake pad  3  can also be arranged on a brake pad carrier  4 . The friction brake  1  can be designed as a sufficiently known floating caliper brake, for example. Components of such a friction brake  1  known per se are not shown here for reasons of clarity, or are only suggested. 
         [0036]    A first transmission element  5  connected to the brake pad  3  (or the pad carrier  4 ) and interacting with same acts on the brake pad  3  or the pad carrier  4 . The first transmission element  5  is embodied here, for example, as an actuation shaft  6 , on which an eccentric journal  7  is provided (suggested by the displaced rotational axes). For example, an eccentric journal  7  can be formed on the actuation shaft  6 , or an eccentric, axial borehole, into which a journal  7  is inserted, can be provided in the actuation shaft  6 . The actuation shaft  6  is rotatably mounted on a fixed part, for example on the brake caliper, or quasi-fixed part, for example on a wear adjuster, of the friction brake  1 . The brake pad  3  or the pad carrier  4  is arranged on the journal  7 . If the actuation shaft  6  is pivoted by a rotational angle α, the brake pad  3  moves the actuation travel s toward the friction surface  2  or away from same (suggested by the double arrow), depending on the direction of rotation. Instead of an eccentric journal  7 , a cam can also be provided as the transmission element  5 . For example, a rotational angle α of 90° from non-braking to full braking can be provided, and the eccentric or the cam can be geometrically designed in order to ensure the actuation travel s necessary for braking. This type of actuation of a friction brake  1  is described in WO 2010/133463 A1. 
         [0037]    Moving the brake pad  2  against the friction surface  2  by a first transmission element  5  produces, starting with contact, a normal force (pad pressing force F N ) that effects the braking force or the braking torque. The normal force is thereby produced by the first transmission element  5  and is also received in full by the latter. That is, the normal force is fully supported by the transmission element  5 . Even an increased normal force due to potentially arising self-reinforcement effects is supported by the transmission element  5 . 
         [0038]    In principle, the pressing of the brake pad  3  against the friction surface  2  can be implemented with any geometry and method that brings a “height gain,” i.e., a travel in the direction of the brake pad  3 . The first transmission element  5  is preferably non-linear. This means that there is no linear relationship between the input (here the rotational angle α, for example) and the output (here the actuation travel s, for example). It is also conceivable for the first transmission element  5  to be linear, however, for example as a cam with a linear elevation curve. The first transmission element  5  is also conceivable as a ball ramp or as rolling movement with thread turns. A cam is a rolled oblique plane, whereby it also being possible for the rolled plane to be rolling or in an any curve or surface in a plane or space, for example also as a helix or multiple helix, such as a ball ramp, thread turns, or rolling pitch, for example. Likewise, the first transmission element  5  can also comprise a hydraulic or pneumatic cylinder with pistons that is actuated for example by an eccentric or cam. 
         [0039]    According to the invention, a second transmission element  8  is now provided in the friction brake  1  which interacts with the first transmission element  5  as described below. 
         [0040]    Here, the second transmission element  8  comprises a cam disc  11  rotatably mounted on a center of rotation  9  and having an elevation curve  17 , which is driven by an electrical actuator  12 , here for example an electric motor of a transmission motor. The cam disc  11  or the electrical actuator  12  is supported on a fixed part  13  of the friction brake  1 , such as for example a brake caliper or a not shown, sufficiently known wear adjuster (regarded as quasi fixed), as suggested in  FIG. 1 . A follower element  14 , for example a needle bearing, rolls on the cam disc  11 , whereas the follower element  14  being rotatably mounted on a coupling element  15 . Depending on the shape of the elevation curve  17 , the second transmission element  8  is thus linear or non-linear. Furthermore, the ends of two levers  16  are rotatably mounted on the coupling element  15 . In each case, the opposing ends of the levers  16  are secured to the actuation shaft  6 . From a mechanical standpoint, the coupling element  15  is a roller cam follower that is simultaneously part of a parallelogram drive. Of course, only one first transmission element  5  could be provided, in which case also only one lever  16  would be necessary. Likewise, more than two first transmission elements  5  could also be provided, and thus also more than two levers  16 . 
         [0041]    If the curve disc  11  is rotated for example by the electrical actuator  12  clockwise, the follower element  14  rolls on the cam disc  11 , whereby the coupling element  15  is moved up or down according to the curve shape of the cam disk  11 . Due to the movement of the coupling element  15 , the actuation shaft  6  is simultaneously rotated via the lever  16 , and the brake pad  3  is pressed against the friction surface  2 . To raise the brake pad  3  from the friction surface  2 , the cam disc  11  is rotated in the opposite direction. 
         [0042]    The kinematics of the actuation device  10  of the friction brake  1  thus consist of the path translation ratio (or equivalently the force- or torque transmission ratio) of the first transmission element  5  and the second transmission element  10 . 
         [0043]    The elevation curve  17  of the second transmission element  10  can also be implemented by a sliding guide instead of a cam disc  11 . The elevation curve  17  can thus also be repeatedly rolled or spatially formed, thus enabling a range of rotation of more than 360° between the initial and end position. For example, the cam disc  11  can be formed as a helix, and the cam disc  11  can always be correctly positioned by a feed device, for example a thread. A sliding guide could also be formed in a spiral shape. 
         [0044]    The elevation curve  17  of the cam disk  11  or a sliding guide or, more generally, any desired elevation curve  17  in space or in a plane can naturally be followed in any mechanically reasonable manner, i.e., apart from the described roller cam follower, a rocker lever or other guide of the follower element  14  as well. Following can naturally also be implemented differently than with a roller hearing, for example by a roller, a sliding contact, or a ball. Consequently, following is understood as rolling or sliding of the follower element  14  on the elevation curve  17 . 
         [0045]    The coupling element  15  can also be embodied in multiple parts, for example several elements or levers connected in an articulated manner. 
         [0046]    The elevation curve  17  of the cam disc  11  (or of the sliding guide) can also have a range that is shaped such that the follower element  14  in this range assumes a stable or energy-favorable position, so that the second transmission element  8  therefore cannot independently return, without external forces, in the direction of the unbraked position. This is provided in  FIG. 1 , for example, at the end of the elevation curve  17  of the cam disc  11  in the form of an indentation  20 . If the follower element  14  comes to rest in this indentation, the follower element  14  cannot advance on its own from this position without the action of an external force, for example the electrical actuator  12 , a wire rope, or the like. This can be used for a parking brake function, for example. 
         [0047]    A parking brake function can also be implemented by a detent latch. If, due to actuation of the actuation device  10 , a detent latch passes a specific position and engages, the actuator position (parking position) is likewise fixed. For unlatching, for example in order to release the parking brake, the detent latch must be released again, for example by a wire rope. An electromagnet can also be used to push the detent latch against a spring. The detent latch then remains locked in the parking position without magnetic action due to friction. For release, the actuation device  12  can be moved somewhat further along, whereby the friction is reduced and the spring releases the detent latch. 
         [0048]    In an alternative embodiment of the inventive friction brake  1  according to  FIG. 2 , a follower element  14  is again rotatably mounted on the coupling element  15 , and again rolls on an elevation curve  17  of the second transmission element  8 . The coupling element  15  is embodied here as a rocker lever, whereby the knee joint is rolling on the elevation curve  17  by the follower element  14 . On one leg of the coupling element  15  is again hinged one end of the lever  16 , by which a cam is rotated. An actuation lever  18 , which is actuated by a motor lever  19  driven by the electrical actuator  12 , acts on the other leg of the coupling element  15 . However, a linear drive could also act on the actuation lever  18 . The elevation curve  17  is arranged in a fixed position. 
         [0049]    Other rolling guides are also conceivable. For example, the follower element  14 , which rolls on the elevation curve  17 , could also be guided with a sliding guide or a journal, which slides in a borehole. 
         [0050]    The starting point for the design of a friction brake  1  according to the invention can for example be a predetermined pad pressing force F N —actuation travel s diagram or a pad pressing force F N —rotational angle α diagram, as shown in  FIG. 3 . The diagram can reflect a linear or non-linear (as in  FIG. 3 ) relationship. Such a diagram arises for example from the fundamental brake design, which considers the stiffnesses of the brake parts and the geometry of the first non-linear transmission element  5 , i.e. for example the geometric relationships on the eccentric, and is thus to be regarded as known, or it is predetermined according to the application. Different wear states of the friction brake  1  can also be considered. In  FIG. 3 , the curve  3   a  shows the brake without wear, and the curve  3   b  shows the brake with full wear. The stiffness of the friction brake  1  is altered significantly as a result of the wear of the brake pad  3 . Likewise, the temperature influence on the stiffness of the friction brake  1  can also be considered. 
         [0051]    From this pad pressing force F N —rotational angle α diagram, the required input torque T E  of the first transmission  5  can be obtained from the known geometric relationships to achieve the pad pressing forces F N , as shown in  FIG. 4 . Different wear states are again shown here, whereby the curve  4   a  again reflecting the friction brake  1  without wear, and the curve  4   b  the friction brake  1  with full wear. In order to be able to ensure operation of the friction brake  1  over the entire wear state, the input torque T E  must cover the range that is given by the envelope curve (dotted curve  4   c ). This input torque T E  is to be provided by the second transmission element  8 , which is designed accordingly. 
         [0052]    For the electrical actuator  12 , however, it is especially advantageous if the latter can be operated over the entire actuation range with a torque as constant as possible (for example in case of an electric motor) or with a constant force, preferably in a range with high efficiency. Assuming a desired constant torque of the actuator  12 , the input torque T E  or the envelope curve in  FIG. 4  (applied to the input rotational angle of the second transmission element  8 ) directly represents the required torque transmission characteristic (or force transmission characteristic) of the second transmission element  8 . However, since the local torque transmission corresponds to the respective slope of the tangent of the path translation characteristic, the path translation characteristic, and thus the shape of the elevation curve  17 , conversely results as the integral of the torque transmission characteristic, as shown in  FIG. 5 . In  FIG. 5  the curve  5   a  shows the torque transmission characteristic (envelope curve with allowance for wear) and the curve  5   b  the integral of this curve, i.e. the path translation characteristic. The shape of the elevation curve  17  over the rotational angle α (actuation travel) can be derived directly from this in order to achieve a substantially constant torque of the electrical actuator  12 . For this reason, a non-linear second transmission element  8  is preferably used, the elevation curve  17  of which is formed according to the path translation characteristic of the first transmission element  5 . 
         [0053]    For a friction brake with a transmission motor and a first transmission element according to WO 2010/133 463 A1, an actuation time of around 250 ms was measured with a pad pressing force of 40 kN. For a friction brake  1  according to the present invention, the actuation time could be reduced to around 180 ms, which represents a significant improvement. 
         [0054]    In many electrically actuated friction brakes  1 , it is required that they be self-actuating in an energy-free state (electrical actuator  12  without power) and assume an unbraked state without electrical assistance. That can be impossible with high mechanical friction in the drive of the friction brake  1 , because in an electrical actuator  12 , a breakaway torque or a breakaway force, which typically is made up of the mechanical bearing friction and the magnetic “snap” and can amount to 10% of the nominal torque or nominal force, must first be overcome. In addition, with a transmission motor as electrical actuator  12 , for release, cranking against the gear ratio must also be performed with greater torque than present on the motor shaft. In friction brakes  1  with low mechanical drive friction and/or favorable path of actuation force, the friction brake  1  can press itself open by the high pad pressing force n specific ranges. However, this is not possible in all ranges, as for example with a very small pad pressing force (e.g. braking on ice or snow) no adequate force is available for pressing itself open against the breakaway torque. In this state, a non-electrical, storable auxiliary energy must be present for pressing open of the friction brake  1 . These can for example be a release spring, which is tensioned during braking, and which releases the stored energy for pressing open the friction brake  1  when needed. 
         [0055]    When the auxiliary energy is supplied from actuation of the friction brake  1  itself, for example via a release spring, which is tensioned during brake actuation, the total actuation force (or the total actuation torque) is higher by the value of this spring action. Although the energy would not be lost, because it is recovered again no later than on release of the friction brake  1 , it increases the drive torque requirement. Thus, in the simplest case, the release spring would be continuously effective according to their spring characteristic, and thus additionally effective also in the range of large actuation torques, although the release springs in such ranges would be entirely unnecessary for the pressing open of the friction brake  1 . This can be counteracted with a non-linear transmission for the release spring by actuating the release spring by a suitably designed non-linear transmission, for example a release spring  21  that acts via a spring cam  22 , as described below with reference to  FIG. 6 . The non-linear transmission is also driven by the actuation device  10 . 
         [0056]    A spring cam  22  is arranged on an actuation shaft  6  and is co-rotated with the actuation shaft  6 . A spring lever  23  is rotatably mounted at one end. A spring follower element  24 , here for example a rotatably mounted roller, is arranged on the other end of the spring lever  23  and the spring follower element  24  follows the spring cam  22  and rolls thereon. Kinematically speaking, a roller cam follower is therefore implemented again. A release spring  21  acts on the spring lever  23 . If the spring cam  22  is rotated, the spring lever  23  is pivoted by an angle β, and the release spring  21  is thus tensioned. 
         [0057]    However, without the spring cam  22 , the release spring  21  can also act directly on the first transmission element  5  or the second transmission element  8  and release the friction brake  1  and/or support it in actuation. For example, the release spring  21  can pull or press on a lever  16  or the parallelogram drive. Through the selection of the geometry (contact point of the release spring  21  on the actuation device  10  and/or on the friction brake  1 ), the release spring  21  can deliver variable torques to brake actuation, which can also change magnitude and sign during actuation of the friction brake  1 . For example, the return spring torque can become smaller due to the release spring  21  and the geometry when there is an increasing rotational angle α, can change sign and grow larger when there is a further increasing rotational angle α. 
         [0058]    This release spring action, however it is caused exactly (cam, direct action of the release spring  21 , etc.), can also be effected on different positions of the friction brake  1 , not only on the actuation shaft  6  or the lever  16  or the parallelogram, but for example also on the cam disk  11 , the shaft of the electrical actuator  12 , the transmission stages of the electrical actuator  12 , on a separate transmission, etc. In short, at every point of the actuation device  10  via which devices can apply the return effect or actuation effect of the release spring  21 . 
         [0059]    The release spring  21  can also have uncoupling or coupling capabilities, for example, by an electromagnet, in order for example to exert no actuation effect in an unpowered state, for example when the unpowered friction brake  1  must be forcibly moved to the released state. 
         [0060]    The above-described method for obtaining a favorable path transmission characteristic of the second transmission element  8  does not assess the origin of the force (torque). Therefore, the release spring  21 , which is always or occasionally necessary for pressing open the friction brake  1 , can simply be used as an additional force. One thus obtains a total path transmission characteristic including release spring  21  for forming the transmission of the actuation device  10 . The previously described procedure can now be applied to determining the elevation curve of the spring cam  24 . 
         [0061]      FIG. 7  shows the torque that the friction brake  1  exerts from its internal pad pressing force over the actuation range of the electrical actuator  12  on the latter. In the small actuation angle range, the torque is negative, that is, this negative torque is absent in order to release the friction brake  1  automatically. Again, a characteristic diagram over relevant states is used that covers all pad wear states, temperatures, and other influences. Accordingly, the dotted envelope curve  7   a  is the range of the absent release torques and must be supplied by auxiliary energy (for example release spring  21 ). The cam elevation of the spring cam  22  is thus also established by the course of the release torque (envelope curve  7   a ) and the given kinematics. The release spring  21  is thus only tensioned where it is used as release assistance. If the electrical power supply in this rotational angle range fails, the friction brake  1  is reliably opened by the release spring  21 . Outside of this range, the release of the release spring  21  effects support of the electrical actuator  12  for the actuation process of the friction brake. In this way, the otherwise interfering release spring  21  suddenly becomes a support for actuation of the friction brake  1 . 
         [0062]    The result is illustrated in  FIG. 8 , which shows the course of the return torque T F  over the rotational angle of the spring cam  22 . The return spring torque T F  acts for small brake actuation as the internal force from the friction brake  1  to release the friction brake  1 . With strong braking (larger rotational angle), the release spring  21  is again released, in order to support the electrical actuator  12  in brake actuation. 
         [0063]    The transmissions of the actuation device  10  and the release spring  21  mutually influence one another. Therefore, such a friction brake  1  is generally designed in an iterative process in which the optimization steps are repeated until the improvement potential is largely exhausted. One could also proceed in a new design of a friction brake  1  from an already known favorable release spring  21  with transmission or from an already known linear or non-linear transmission of the actuation device  10 . 
         [0064]    The result of such optimization is illustrated in  FIG. 9 , for example. The torque T of the electrical actuator  12  (curve  9   a ) and the return spring torque T F  of the release spring  21  (curve  9   c ) are shown over the actuation range of the electrical actuator. Here, the achieved, substantially constant torque T of the electrical actuator over the actuation range is readily recognized. The curve  9   b  additional allows for self-reinforcement effects of the friction brake  1 , whereby the necessary torque T of the electrical actuator  12  naturally drops. 
         [0065]    The friction brake  1  according to the invention was described above using the example of a brake in which force (torque) must be actively applied in order to press on the brake pads as is required for example in motor vehicles. However, the direction of action of the electrical actuator  12  is insignificant for the invention. The electrical actuator  12  can also prevent the friction brake  1  from actuation with active force (torque), whereby the direction of action would be reversed. The energy for actuation of the friction brake  1  in this case can originate from an auxiliary energy source, such as a spring, for example. Such a friction brake  1  is used, for example, as a railroad brake, elevator brake, crane brake, etc., that has to brake when there is a power loss. The above-described release spring  21  can also be used as an auxiliary energy source for braking, the actuation curve then naturally being designed favorably for the actuation behavior of the brake. For such a friction brake  1 , the kinematics can be designed such that in the range to be kept open, the force (torque) at the electrical actuator  12  is as small as possible or even zero. This can occur similarly to as described above for the parking brake function over a special range of the cam disc, slide, or kinematics. A described detent latch could also be used to hold the friction brake  1  open. 
         [0066]    In friction brakes  1  that are held in the released state by the electrical actuator  12 , for example, in a railroad brake or an elevator brake, a spring, and/or the release spring  12 , can of course conversely be used for actuation of the friction brake  1 . The spring or the kinematics of the actuation device  10  can then also be favorably designed for this reverse actuation behavior. In these spring-actuated friction brakes  1 , the actuation device  10  can be designed advantageously such that, for all cases to be covered (different or no self-reinforcement, different pad states and elasticities, different coefficients of friction, tolerances, return torque of the motor (“cogging”) in different motor states (also unpowered), different friction losses in actuation, temperature, etc.), reliable actuation by the spring is always possible. 
         [0067]    It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.