Abstract:
A brake includes a brake shoe, an actuating element for pressing the brake shoe against a brake disc, and at least one lever disposed such that it increases the braking force applied by the brake shoe to the brake disc by deflecting a tangential force acting on the brake shoe during braking. The actuating element comprises at least one brake disc side part, an actuator side part, and a coupling part disposed between the brake disc side part and the actuator side part, wherein the coupling part can be pivoted relative to the brake disc side part and/or the actuator side part.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to embodiments of a brake having a brake pad, an actuating element for pressing the brake pad against a brake disk and at least one lever arranged such that it increases a braking force imparted by the brake pad to the brake disk by diverting a tangential force that acts on the brake pad during braking. 
     BACKGROUND OF THE INVENTION 
     In conventional brakes, a primary braking force or actuator force is imparted by an actuator to the actuating element such that the brake pad is pressed against the brake disk. When the brake pad comes into contact with the brake disk, a tangential force is generated because the rotating brake disk drags the brake pad with it. This tangential force is diverted by the lever to the actuating element and acts as a secondary braking force or auxiliary force that presses the brake pad against the brake disk to an additional degree. 
     A disadvantage of this known brake is that, at the time at which the brake pad comes into contact with the brake disk, the tangential force is generated abruptly, which abruptly boosts the primary braking force imparted by the actuator. If a small braking force is to be imparted, a situation may arise in which the actuator initially moves the brake pad toward the brake disk, the brake pad then comes into engagement with the brake disk, the tangential force is diverted by the lever and then boosts the brake force to a value considerably higher than the desired braking force. The actuator must thereupon move the brake pad away from the brake disk, the tangential force decreases suddenly and the braking force imparted by the brake pad to the brake disk falls abruptly to a value considerably below the desired braking force. This cycle repeats and leads to a fluctuating braking force. 
     In other words, the function that relates the braking force (x axis) imparted by the brake pad to the brake disk to the primary braking force imparted by the actuator to the actuating element (y axis) has a discontinuity. If the braking force is to be linearly increased, the actuator must at a certain time apply an abruptly changing primary force to the actuating element. In the region of the discontinuity, it is only possible with a great degree of difficulty to regulate the brake such that the comfort of a vehicle equipped with such a brake is not impaired. 
     SUMMARY OF THE INVENTION 
     Generally speaking, it is an object of the present invention to provide a brake that can be regulated more easily. 
     This object can be achieved using a brake in which the actuating element comprises at least one brake-disk-side part, an actuator-side part and a coupling part arranged between the brake-disk-side part and the actuator-side part, with the coupling part being pivotable relative to the brake-disk-side part and/or relative to the actuator-side part. 
     This design advantageously makes it possible for the lever to engage on the coupling part, such that when the tangential force acts on the lever, the lever pivots the coupling part relative to the brake-disk-side part and/or actuator-side part such that the spacing between the brake-disk-side part and the actuator-side part is increased. On account of the increasing spacing, the brake-disk-side part pushes the brake pad further in the direction of the brake disk and thus increases the braking force. 
     Because the coupling part is pivotable, the spacing between the brake-disk-side part and actuator-side part changes only by a very small amount upon the start of engagement between the brake pad and brake disk. This means that the boosting action of the lever at the start of engagement is weakened by the pivoting of the coupling part, and the brake-force-boosting action of the lever first comes into effect gradually with increasing deflection of the lever. If one plots the primary braking force that the actuator must apply to the actuator-side part versus the desired braking force between the brake pad and brake pad, the resulting curve no longer has a discontinuity. As a result, the brake can be controlled or regulated more easily. 
     It is also advantageous that only a small number of additional components are required in order to obtain the advantage of improved regulability. 
     Within the context of the present description, the expressions “brake-disk-side part” and “actuator-side part” refer to the kinematic chain of the transmission of the brake force from an actuator, which exerts a force on the actuator-side part, to the brake pad. It is generally the case that the brake-disk-side part is also situated closer to the brake disk than the actuator-side part, though this is not imperative. 
     The feature whereby the brake-disk-side part, the actuator-side part and the coupling part are pivotably connected to one another should be understood to mean that the design permits a corresponding pivoting movement. For this purpose, it is possible, but not imperative, for the three parts to be connected to one another by means of fixed bearings. It is furthermore expedient for outer regions of the part to be contoured such that the parts are mounted on one another without the need for additional bearings, for example ball bearings. The brake-disk-side part, the actuator-side part and the coupling part may themselves be composed of two or more sub-elements. 
     In a preferred embodiment, the brake-disk-side part, the actuator-side part and the coupling part are connected to one another such that, when the brake pad comes into contact with the brake disk at the start of a braking operation and the lever diverts the tangential force in order to boost the braking force, the coupling part pivots by a small angle relative to the brake-disk-side part and/or relative to the actuator-side part. The pivoting leads to an increase in the spacing between the brake-disk-side part and actuator-side part. 
     In a preferred embodiment, the actuator-side part is guided linearly and the lever engages on the coupling part. In this way, a pivoting of the coupling part does not lead to a pivoting of the actuator-side part, and the actuator is preserved. 
     Furthermore, the brake-disk-side part is preferably mounted such that the coupling part can pivot substantially without the brake-disk-side part pivoting relative to the brake disk. The brake pad is therefore worn uniformly and jamming of the brake is reliably prevented. 
     In a preferred embodiment, the brake-disk-side part, the actuator-side part and the coupling element are coupled to the lever such that a deflection of the lever by a predefined lever pivot angle, for example 1°, out of a zero position leads to a smaller change in a spacing between the brake-disk-side part and the actuator-side part than a deflection by the same lever pivot angle when the lever is already in a deflected position. In other words, the provision of the coupling part has the effect that a movement of the lever boosts the braking force to a particularly great degree when the lever has already been deflected, whereas the braking force is boosted only to a small degree when the lever is situated close to its zero position. The zero position is the position assumed by the lever when no braking force is imparted. 
     The brake-disk-side part, the actuator-side part and the coupling part are preferably coupled to one another such that they are pivotable relative to one another by in each case less than 10°. This results in a particularly rigid design of the brake. 
     To keep production tolerances low, the brake-disk-side part, the actuator-side part and the coupling part can be connected to one another such that they are pivotable relative to one another by more than 0.1° at maximum braking force. 
     The lever is preferably designed such that a primary braking force applied to the actuator-side part, which could also be referred to as the actuator force, is boosted by a secondary braking force, wherein the primary braking force and the secondary braking force add up to give the braking force. The lever then has, for example, a lever ratio selected such that a coefficient of sliding friction of 0.6 between the brake pad and the brake disk leads to a secondary braking force that is lower than twenty times the primary braking force. In this way, a primary braking force must always be imparted to the actuator-side part in order to generate a braking force. A situation therefore cannot arise in which the brake seizes as a result of excessive feedback. 
     In a preferred embodiment, the lever is arranged so as to boost the braking force by diverting the tangential force when the brake disk is rotating relative to the brake pad in a first direction, and a second lever is provided that is arranged so as to boost a braking force imparted by the brake pad to the brake disk by diverting the tangential force when the brake disk is rotating relative to the brake pad in a direction opposite to the first direction. The second lever is preferably of the same design as the first lever, but this is not imperative. 
     Particularly simple mounting is obtained if the lever or the levers have a circular-arc-shaped outer contour in sections and are mounted by means of the contour in a housing of the brake. It is expedient for the brake to be connected to an electric drive such that the brake together with the electric drive forms an electromechanical brake device. 
     Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification. 
     The present invention accordingly comprises the features of construction, combination of elements, and arrangement of parts all as exemplified in the constructions herein set forth, and the scope of the invention will be indicated in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below on the basis of an exemplary embodiment and with reference to the appended drawings, in which: 
         FIG. 1  shows a perspective view of a brake system having a brake in accordance with an embodiment of the present invention, 
         FIG. 2  shows the brake system according to  FIG. 1  in a partially cut-away view, 
         FIG. 3  shows a cross section through the brake according to  FIGS. 1 and 2 , and 
         FIG. 4  shows a further section through the brake. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a brake device  10  having a brake  12  that is actuated by means of an actuator in the form of an electric drive  14 . The brake  12  has a brake pad  16  that can be applied against a brake disk  18 . For this purpose, the electric drive  14  imparts a primary braking force F A , which could also be referred to as the actuator force, to an actuator-side part  20 . The actuator-side part  20  transmits the primary braking force to a coupling part  22 , which in turn transmits the primary braking force to a brake-disk-side part  24 . The actuator-side part  20 , the coupling part  22  and the brake-disk-side part  24  are constituent parts of an actuating element. 
     If the brake disk  18  is rotating at a rotational speed ω and the brake pad  16  comes into contact with the brake disk  18 , then a tangential force F t  is generated. As a result, the brake pad  16  is displaced slightly in the direction of the tangential force F t  and exerts a force on a first lever  26 , which thereupon pivots by a lever pivot angle φ. 
       FIG. 2  shows that the first lever  26  then exerts a force on the coupling part  22 , such that a secondary braking force F H , which could also be referred to as the auxiliary force, is generated. The secondary braking force F H  points in the same direction as the primary braking force F A  and, together, yield the braking force F. The following relationship therefore applies: F A +F H =F. 
       FIG. 3  shows that the coupling part  22  is connected via an outer bearing  28  to the actuator-side part  20 , such that the coupling part  22  can pivot relative to the actuator-side part  20 . If the first lever  26  pivots by a small lever pivot angle φ out of its zero position, then the coupling part  22  pivots relative to the actuator-side part  20  by a small coupling part pivot angle σ, for example of less than 10°. As a result, the coupling part  22  pushes the brake-disk-side part  24  away from itself, such that the brake pad  16  is pressed against the brake disk  18  to an additional degree. 
     The actuator-side part  20  is guided in a linear guide  30  on a housing  32  of the brake  12 , such that no tilting moments act on the electric drive  14 . The outer bearing  28  is formed by a joint head, which is formed on the coupling part  22  and which interacts with a joint socket of the actuator-side part  20 . 
     The coupling part  22  has, on its side facing away from the actuator-side part  20 , a second joint head  34 , which interacts with an associated joint socket  36  of the brake-disk-side part  24  and, with the latter, forms a second outer bearing  38 . If the coupling part  22  pivots by the coupling part pivot angle σ out of its zero position, a spacing A between the actuator-side part  20  and the brake-disk-side part  24  is increased, and as a result, the brake pad  16  is pressed against the brake disk  18  to an additional degree. The first lever  26  thereby, together with the coupling part, leads to a boosting of the primary braking force F A . 
     The coupling part  22  comprises an element  40 , which is variable in length and which can be actuated by the electric drive  14  so as to increase the spacing A between the actuator-side part  20  and the brake-disk-side part  24 , such that wear of the brake pad  16  can be compensated. 
       FIG. 4  shows a cross section through the brake device  10 , which shows a second brake pad  42  that acts on the brake disk  18  on the side facing away from the first brake pad  16 . 
       FIG. 3  also shows a second lever  44  arranged opposite the first lever  26  that, like the first lever  26 , interacts with the coupling part  22 . The second lever  44  has the same function as the first lever  26  and acts when the brake disk  18  is rotating with a rotational speed of −ω (cf.  FIG. 1 ). The brake  12  is of symmetrical design with respect to the plane of symmetry shown in  FIG. 3 . 
     It can be seen that the coupling part  22  has a first leg  48 . 1  and a second leg  48 . 2  that are of mirror-symmetrical design to one another and, with respective head parts, are part of the head bearing  38 . The two legs  48 . 1 ,  48 . 2  are arranged at both sides of a wedge element  46  and can pivot relative to the wedge element  46  by an angle, for example of less than 10°. The two legs  48 . 1 ,  48 . 2  and the wedge element  46  form a rocker that can pivot by a small angle relative to the actuator-side part  20 . 
     The wedge element  46  is arranged relative to the legs  48 . 1 ,  48 . 2  such that a preload force F V  that acts on the brake-disk-side part  20  causes the two legs  48 . 1 ,  48 . 2  to pivot apart slightly. As a result of this pivoting-apart movement, the first lever  26  and the second lever  44  pivot counter to the lever pivot angle γ indicated in  FIG. 3 , such that they bear under preload against the brake-disk-side part  24 . 
     A preload element can be provided for preloading the brake-disk-side part  24  against the coupling part  22  or against the actuator-side part  20  via the coupling part  22 . The preload element can be, for example, a spring. It is sufficient for the spring to impart a preload force of less than 500 N, for example 100 N. Since the brake-disk-side part  24 , the coupling part  22  and the actuator-side part  20  are preloaded against one another and the coupling part  22  preloads the levers  26 ,  44  against the brake-disk-side part  24 , all of the components are in a play-free state. 
     If the actuator-side part  20  is now moved in the direction of the brake disk  18  by the actuator  14 , an air play  50  schematically indicated in  FIG. 3  by a circle is firstly overcome. The air play amounts to between 0.7 mm and 1.5 mm, for example. When the brake pad  16  comes into contact with the brake disk  18 , the tangential force F t  is generated, and on account of the lack of play, a small secondary braking force F H  is generated immediately. The secondary braking force F H  is however small and increases constantly and continuously as the primary braking force F A  increases. In contrast to conventional brakes, therefore, no abrupt boosting of the primary braking force takes place, such that the brake can be controlled or regulated in a particularly effective manner. 
     It will be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween.