Abstract:
An actuating unit for use on an electromechanically actuated disc brake for automotive vehicles including a drive unit or an electric motor, an actuating element for actuating one of two friction linings displaceably arranged in a brake caliper, and a first and a second reducing gear. The first reducing gear is comprised as a ball screw, while a planetary gear is used as the second reducing gear. To increase the efficiency, the present invention discloses a coupling shaft used to transmit forces from the planet cage of the planetary gear to the threaded spindle of the ball screw. The ends of the coupling shaft form universal joints with the planet cage and the threaded spindle.

Description:
TECHNICAL FIELD 
     The present invention generally relates to actuators and more particularly relates to brake calipers relates to an actuating unit. 
     BACKGROUND OF THE INVENTION 
     International patent application WO 99/45292 discloses an electromechanically operating actuating unit of this general type. In the prior-art actuating unit, the force is transmitted from the planet cage to the threaded spindle by means of a positive plug connection that is coupled to the planet cage in a torsion-proof, radially yielding and flexible fashion. 
     What is disadvantageous in the prior-art actuating unit is that the plug coupling has only one degree of freedom so that all disturbances differing from the degree of freedom of the plug coupling are transmitted. This impairs the efficiency that can be achieved. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the above, an object of the present invention is to disclose an actuating unit of the type initially referred to wherein an increase in efficiency can be achieved. 
     According to the present invention, this object is achieved in that the force is transmitted from the planet cage to the threaded spindle by means of a coupling shaft, the ends of which form universal joints with the planet cage and the threaded spindle. Preferably, one end of the coupling shaft is accommodated in a hollow spindle member of the threaded spindle. 
     In another embodiment of the present invention, one end of the coupling shaft is accommodated within the area of the planet cage in an outside ring of a radial bearing that is connected to the planet cage. 
     In one favorable embodiment used for an electromechanically actuated disc brake for automotive vehicles, the said actuating unit being arranged at a brake caliper in which two friction linings that cooperate with each one lateral surface of a brake disc are arranged so as to be displaceable within limits, wherein one of the friction linings is adapted to be moved into engagement with the brake disc by the actuating unit directly by means of the actuating element and the other friction lining is adapted to be moved into engagement with the brake disc by the effect of a reaction force generated by the brake caliper, wherein the actuating unit comprises an electric motor, the first reducing gear is arranged between the electric motor and the actuating element in terms of effect, and the second reducing gear is arranged between the electric motor and a part of the first reducing gear. 
     In another embodiment of the subject matter of the present invention, the threaded nut of the ball screw may have a bipartite design, the first part cooperating with the first friction lining, while the conversion of a rotational movement into translation takes place in the second part. It is particularly favorable when the return area for the balls of the ball screw is provided in the second part. 
     In a design wherein a guide member embracing the threaded nut is provided which is supported on the gearbox case that accommodates the ball screw and on which the threaded spindle is axially supported by means of a radial bead by the intermediary of an axial bearing, it is especially favorable that the rigidity of the radial bead and the area of the guide member opposite the bead are chosen so that the contact surfaces of the axial bearing suffer from an equal deformation during operation. This provision ensures a uniform distribution of the load that acts on the axial bearing, thereby permitting the use of a small bearing that is optimally utilized. 
     In a favorable aspect of the subject matter of the present invention, wherein the guide member includes force-measuring elements, the said guide member contains an axial groove which accommodates conduits associated with the force-measuring elements. In this arrangement, an electric interface or a plug to which the conduits are connected is preferably arranged in the area of the guide member that faces the friction lining. 
     In another embodiment of the subject matter of the present invention, the return movement of the balls is through all threads, and the return area for the balls is designed as a rotation prevention mechanism of the threaded nut in the guide member. Expediently, combining two independent functional means in one component optimizes the mounting space. 
     Besides, it is especially advantageous that the guide member is elastically designed and the threaded nut is arranged in the guide member with a play. It is achieved by this arrangement that the threaded nut is guided only in its rear area by means of the threaded spindle. The disturbances that take effect on the threaded nut are, thus, not supported by way of the sliding friction between the threaded nut and the guide member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an axial cross-sectional view of a design of the electromechanical actuating unit of the present invention. 
     FIG. 2 is a simplified view of the first reducing gear used in the design of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The electromechanical actuating unit of the present invention, as shown in the drawings, is used to actuate a floating-caliper disc brake whose brake caliper (only represented) is displaceably supported in a stationary holder (not shown). A pair of friction linings  4  and  5  is arranged in the brake caliper so that they face the left-hand and right-hand lateral surfaces of a brake disc  6 . 
     In the following, friction lining  4  that is shown on the right in the drawing is referred to as first friction lining, and the other friction lining designated by reference numeral  5  is referred to as second friction lining. While the first friction lining  4  is movable into engagement with the brake disc  6  by the actuating unit directly by means of an actuating element  7 , the second friction lining  5  is urged against the opposite lateral surface of brake disc  6  by the effect of a reaction force generated by the brake caliper when the assembly is actuated. 
     The actuating unit of the present invention which is fitted to the brake caliper by way of securing means (not shown) has a modular design and is generally comprised of three independent subassemblies or modules, namely a drive unit  1 , a first reducing gear  2  that actuates the first friction lining  4 , and a second reducing gear  3  that is interconnected between drive unit  1  and the first reducing gear  2  in terms of effect. 
     The actuating unit  1  mentioned above is comprised of an electric motor  11  which, in the example shown, is a permanent-magnet-energized, electronically commutated motor whose stator  9  is immovably arranged in a motor casing  12  and whose rotor  10  is provided by an annular carrier  13  that carries a plurality of permanent magnet segments  14 . The first reducing gear  2  is interposed between the electric motor  10  and the above-mentioned actuating element  7  in terms of effect and, in the example shown, is configured as a ball screw  16  to  18  accommodated in a gearbox case  19 , which latter may also be of integral design with the above-mentioned brake caliper. In this arrangement, the ball screw comprises a threaded nut  16  and a threaded spindle  17 , with several balls  18  being arranged between the threaded nut  16  and the threaded spindle  17  that circulate upon a rotational movement of the threaded spindle  18  and put the threaded nut  16  into an axial movement or translation. The threaded nut  16  preferably has a bipartite design and is composed of a first part  24  that forms the above-mentioned actuating element  7  and a second part  28  in which a return area or channel  25  for the balls  18  is designed. In the return channel, the balls  18  may run back to the start of the raceway without load. Further, it can be taken from the drawing that the threaded spindle  17  driven by the electric motor  11  by way of the second reducing gear  3  has a three-part design and is comprised of a tubular first spindle member  20  which is in engagement with the threaded nut  16  or  28 , an annular second spindle member  21 , and a third spindle member  22  that interacts with the second reducing gear  3 . The first spindle member  20  confines with the second part  28  of the threaded nut  16  helical screw thread undercuts  23  in which the balls  18  circulate. 
     The arrangement is preferably chosen in such a way that the rotor  10  of electric motor  11  will drive the threaded spindle  17  by the intermediary of the second reducing gear  3 , while the first part  24  of the threaded nut  16  is supported on the first friction lining  4 . Two radial bearings  8 ,  15  are used for the mounting support of the rotor  10 , the said bearings being arranged in the motor casing  12  or in an end plate  35  which is axially supported on the motor casing  12 . 
     In the embodiment of the present invention illustrated in the drawings, the necessary engine torque is reduced by an expedient integration of a planetary gear  30 - 34  forming the above-mentioned second reducing gear  3 . The planetary gear, which is interposed between rotor  10  and threaded spindle  17  in terms of effect, is comprised of a sun wheel  30  which preferably includes an externally toothed area  26  on rotor  10 , a plurality of stepped planet wheels, two of which are shown and have been assigned reference numerals  31  and  32 , and a ring gear  33 . The stepped planet wheels  31 ,  32  accommodated in a planet cage  34  have a first step interacting with the sun wheel  30  and a second step interacting with the ring gear  33 , the first step being formed of toothed wheels  31   a ,  32   a  of large diameter and the second step being formed of toothed wheels  31   b ,  32   b  of small diameter. The ring gear  33  is formed of an internally toothed area of a cover  38  that forms the case of the planetary gear. 
     As can be taken from FIG. 1 in addition, the rotor  10  includes a radial collar  37  carrying components of a position detection system  36  (not shown) with the aid of which the current position of rotor  10  is determined. The information about the position is then determined by means of a Hall sensor or a magneto-resistive element. 
     The above-mentioned threaded nut  16  of the ball screw is preferably arranged with a radial play in a bowl-shaped guide member  29  having a defined elasticity so that it is guided by way of the threaded spindle  17  or  22 . It is achieved thereby that an inclined position of the axis of the ball screw, which is caused by bending up of the brake caliper, is compensated by the elastic deformation of the guide member  29  and the threaded nut  16  which has a play and is not guided. The result is an even contact pressure of the linings  4 ,  5  and thus, a longer service life of the linings. It is especially favorable when the above-mentioned return area  25  of the balls  18  is additionally used as a rotation prevention mechanism of the threaded nut  16  in the guide member  29 . The second annular spindle member or bead  21  is supported on an axial bearing  39  arranged within the guide member  29 . The rigidity values of the bead  21  and an area of the guide member  29  axially opposed to the bead  21  are conformed to one another so that the mentioned parts will be subject to equal deformations during operation of the actuating unit of the present invention, with the result that the inclination of the two parts is equal (cf. FIG. 2 in particular). This provision achieves a uniform distribution of the load over the periphery of the guide member  29  onto the individual roll bodies  50  of the axial bearing  39 , thereby allowing a maximum utilization of the load capacity of the ball screw with the best possible efficiency and an optimal packaging. 
     The third spindle member  22  is preferably connected to the planet cage  34  of the second reducing gear  3  by means of a coupling shaft  40 . It is especially favorable when both ends of the coupling shaft  40  and the areas of the third spindle member  22  and the planet cage  34  in which the said ends are received are so configured that two universal joints  41 ,  42  are provided. The end of the coupling shaft  40  cooperating with the planet cage  34  is preferably received by means of an outside ring  49  of a radial bearing  48  provided in the cover  38 . An elastic seal or sealing sleeve  27  compressed between the first part  24  of the threaded nut  16  and the guide member  29  prevents the ingress of contaminants into the interior of the ball screw. 
     As can be seen in FIG. 2 in particular, measuring elements  43 , e.g. wire strain gauges, are arranged on the surface of the guide member  29  and permit determining the actuating or clamping force that is indirectly measured as an axial deformation (expansion) of the guide member  29 . Conduits  44  that are arranged in grooves  45  provided in the surface of guide member  29  and lead to an electric interface  46  are used for the electrical connection of the wire strain gauges  43 . Interface  46  is preferably configured as a plug that is attached at the guide bowl  29 . The electrical connection to an evaluating electronics (not shown) is established during the final assembly by means of a counter plug  47  integrated in the gearbox case  19 . 
     Of course, various modifications are feasible in the spirit of the present invention. For example, the electric motor that is used as drive unit  1  may be designed as a switched reluctance motor (SR-motor). Other designs of the planetary gear are also possible, such as a two-stepped differential planetary gear or a gear whose planet wheels with their first step are in engagement with a sun wheel and with their second step, by the intermediary of each one spur wheel, are in engagement with a ring gear. Gear units which achieve high reduction ratios due to a deformable toothed ring and an eccentricity are of course also feasible. 
     List of Reference Numerals 
       1  drive unit 
       2  reducing gear 
       3  reducing gear 
       4  friction lining 
       5  friction lining 
       6  brake disc 
       7  actuating element 
       8  radial bearing 
       9  stator 
       10  rotor 
       11  electric motor 
       12  motor casing 
       13  carrier 
       14  permenent magnet segment 
       15  radial bearing 
       16  threaded nut 
       17  threaded spindle 
       18  ball 
       19  gearbox case 
       20  spindle member 
       21  spindle member 
       22  spindle member 
       23  screw thread undercut 
       24  threaded nut part 
       25  return area 
       26  area 
       27  seal 
       28  threaded nut part 
       29  guide member 
       30  sun wheel 
       31  planet wheel 
       31   a  planet wheel 
       31   b  planet wheel 
       32   a  planet wheel 
       32   b  planet wheel 
       33  ring gear 
       34  planet cage 
       35  end plate 
       36  position detection system 
       37  collar 
       38  cover 
       39  axial bearing 
       40  coupling shaft 
       41  universal joint 
       42  universal joint 
       43  measuring element, wire strain gauge 
       44  conduit 
       45  groove 
       46  interface, plug 
       47  counter plug 
       48  radial bearing 
       49  outside ring 
       50  roll body