Abstract:
A brake application for a rail vehicle brake includes a brake actuator for application and release of the rail vehicle brake. Also included is a force converter for converting energy supplied by the brake actuator to a brake application movement. The force converter includes: (1) a shearing force measuring bolt arranged in a power transmission path; (2) at least one measuring sensor measuring breaking force either indirectly or directly; and (3) at least two mutually swivellable force transmission elements having passage openings. The shearing force measuring bolt forms a hinge bolt of a hinge, which hinge bolt penetrates the passage openings.

Description:
BACKGROUND AND SUMMARY 
   The present disclosure relates to a brake application device for a rail vehicle brake. 
   From European Patent Document EP 0 283 947 A2, a brake application device for rail vehicle brakes is known. The brake application device includes a brake actuator for the application and/or release of the brake and a force converter for converting the energy supplied by the brake actuator into a brake application movement. The force converter includes a shearing force measuring bolt arranged in the flow of force and equipped with at least one measuring sensor for the indirect and direct braking force measuring. The shearing force measuring bolt forms a hinge bolt of a hinge projecting through passage openings of at least two force transmission elements of the force converter which can be swivelled with respect to one another. Therefore, a sliding movement takes place at the shearing force measuring bolt under considerable braking forces. As a result, wear gradually occurs at the shearing force measuring bolt which carries the measuring sensor and therefore requires high expenditures for its manufacturing and mounting. This wear leads to an expensive exchange. 
   The present disclosure relates to an electromechanical brake application device in which the shearing force measuring bolt has a longer service life. 
   According to the present disclosure, the brake application device includes a brake actuator for application and release of the rail vehicle brake. Also included is a force converter for converting energy supplied by the brake actuator to a brake application movement. The force converter includes: (1) a shearing force measuring bolt arranged in a power transmission path; (2) at least one measuring sensor measuring breaking force either indirectly or directly; and (3) at least two mutually swivellable force transmission elements having passage openings. The shearing force measuring bolt forms a hinge bolt of a hinge, which hinge bolt penetrates the passage openings. A bushing, having radially interior edge recesses, is arranged radially between at least one of the passage openings and the shearing force measuring bolt. 
   The greatest shearing stress of the shearing force measuring bolt occurs in the area of the abutting planes of the force transmission elements. Axial edge areas of the bushings are subject to bending stress. Because of the radially interior edge recesses, the axial edge areas of the bushings are more flexible than the areas adjoining them, whereby high edge pressures are avoided between the bushings and the shearing force measuring bolt. The resulting evening-out of the tensions has a positive effect on the contact pattern of the sliding pairing which includes the bushing and the shearing force measuring bolt. Also, because of lower edge pressure, the stressing of the shearing force measuring bolt, whose manufacturing and mounting is relatively expensive, is reduced, and its service life is thereby increased. 
   According to an embodiment of the present disclosure, the bushing is non-rotatably held in the passage opening, in which case the bushing forms a sliding pairing with the shearing force measuring bolt. The bushing is constructed such that, with respect to wear conditions, such as hardness, surface roughness, material, etc., the bushing forms the sliding partner which tends to wear out earlier. The material of the bushing can be selected to be relatively soft for this purpose, and the shearing force measuring bolt can be selected to be correspondingly hard. As a result, gradually occurring wear takes place in the less expensive and easily exchangeable bushing instead of at the much more expensive shearing force measuring bolt. 
   According to the present disclosure, a carrying area of a radially exterior circumferential surface of the shearing force measuring bolt is formed by a cylindrically smooth surface without recesses or steps. Because of a lack of notches, this has a favorable effect on the endurance of the shearing force measuring bolt acting as a hinge bolt. As a result, the manufacturing of the shearing force measuring bolt is also easier and less expensive. 
   The shearing force measuring bolt may have an end-side bolt head with an enlarged diameter, in which bolt head an electronic sensor signal analyzing unit is accommodated. The shearing force measuring bolt therefore forms a complete measuring module which can supply signals to a braking force control. As a result, the shearing force measuring bolt can be integrated, as a separate measuring module into a control circuit of brake application devices. Such an arrangement may considerably simplify mounting, exchange or retrofitting. The shearing force measuring bolt may have only one standardized interface which can be connected to a braking force control device by persons not skilled in the field. 
   A measuring sensor, a connection wiring for the electronic sensor signal analyzing unit as well as the electronic sensor signal analyzing unit itself may each be provided redundantly. Thus, an increased reliability of the measuring arrangement may be achieved. In addition, a plausibility check can be carried out by comparing the measuring signals of two or more measuring circuits. 
   Other aspects of the present disclosure will become apparent from the following descriptions when considered in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of an embodiment of a brake application device having an integrated shearing force measuring bolt, according to the present disclosure. 
       FIG. 2  is a sectional view of the shearing force measuring bolt of  FIG. 1  taken along Line II—II. 
   

   DETAILED DESCRIPTION 
   A brake application device, for a rail vehicle is shown in  FIG. 1 . The device  1  may be electromechanical. The device  1  includes a brake actuator  2  having a service brake unit (not separately identified) and an accumulator-type brake unit (not separately identified). The service brake unit includes an electric drive, shown for example, as an electric servomotor  4 , which is accommodated in an actuator housing  6  of the brake actuator  2 . A mechanical force converter  8  is used for converting energy supplied by the brake actuator  2  to a brake application movement. 
   The servomotor  4  causes a coaxial brake spindle  10  to carry out rotations which are converted by the force converter  8  to a brake application movement of brake pads  12  in a direction of a brake disc  14 . Among other things, the force converter  8  comprises a spindle/nut constructional unit  16  with a spindle nut  18  which is rotatably disposed on the brake spindle  10  and which, when the brake spindle  10  is rotated, can carry out linear movements in a direction of a spindle axis  42 . An end of the brake spindle  10  facing away from the servomotor  4  projects into a cylindrical hollow section of a transmission element or connecting rod  20 , which rod  20  is connected in an axially fixed manner with the spindle nut  18 . In addition, the cylindrical hollow section of the connecting rod  20  is held in an axially fixed manner in a sliding sleeve  22  against which at least one pre-loaded spring  24 , which is supported on the actuator housing  6 , is prestressed in a brake release position. The pre-loaded spring  24  is part of the accumulator-type brake unit and is used as an energy accumulator for storing and supplying energy for the application of the brake as a service-type emergency brake. That service-type emergency brake is used in the sense of an underlying safety level in the event of a failure of the service brake unit and/or as a parking brake. The service brake unit as well as the accumulator-type brake unit act upon the connecting rod  20 . The pre-loaded spring  24  is held in the prestressed position by a locking device  26 . 
   A plate-shaped small end  28  of the connecting rod  20  projects out of the sliding sleeve  22  and is provided with a passage opening or connecting rod eye  30 . As illustrated in  FIG. 2 , a hinge bolt  32  penetrates the connecting rod eye  30  as well as passage openings or bores  34  coaxial thereto of cheeks  38 . Cheeks  38  axially reach around the connecting rod eye  30  and are constructed on an end-side fork  35  of a brake lever  36 . The cheeks  38  of the brake lever  36 , the small end  28  of the connecting rod  20  and the hinge bolt  32  together form a hinge  40  of the force converter  8 , whereby one end of the brake lever  36  is linked to the connecting rod  20  perpendicular to the spindle axis  42 . When the brake spindle  10  is driven in the brake application direction or when the locking device  26  of the pre-loaded spring  24  is released, and because of a then axially moving-out connecting rod  20 , the hinge bolt  32 , among other things, is stressed by shearing forces acting upon bolt axis  44  essentially perpendicularly at the same time, the brake lever  36  rotates with respect to the connecting rod  20 . 
   The other end of the brake lever  36  acts upon an eccentric arrangement with an eccentric shaft  46  which is linked to a caliper lever  48  and, together with another caliper lever  50 , forms a caliper  52 . Brake pad holders  54  with brake pads  12  are arranged at one set of ends of the caliper levers  48 ,  50  and are displaceable in a direction of the axis  84  of the brake disc  14 . Ends of the caliper levers  48 ,  50  facing away from the brake pads  12  are connected with one another by a pressure rod actuator  56  which may be electrically operated. The just-described arrangement also forms a part of the force converter  8  which converts move-out motions of the connecting rod  20  caused by the servo motor  4  or by the pre-loaded spring  14  to a brake application movement of the brake pads  12  in the direction of the brake disc  14 . 
   As illustrated in  FIG. 2 , the hinge bolt  32  of the hinge  40  is formed by a shearing force measuring bolt  58 . The shearing force measuring bolt  58  is provided with at least one measuring sensor  60  for the measuring of levels or amount of braking force acting upon the brake pads  12 , which can be derived either indirectly or directly. In an embodiment of the present disclosure, the at least one measuring sensor  60  is formed as load cells of a thin-film method, which are accommodated, for example, in transverse or cross bores  62  extending perpendicular to the bolt axis  44  and may be laser-welded there. The cross bores  62  are situated in an area of radial abutting planes  68  of the small end  28  of the connecting rod  20 . The cross bores  62  extend perpendicular to the bolt axis  44 , with the cheeks  38  of the fork  35  of the brake lever  36 . The cross bores  62  extend in an area of shearing planes of the shearing force measuring bolt  58  stressed by shear by forces in an opposite direction when the brake actuator  2  is operated. Because of elastic shear deformations of the shearing force measuring bolt  58  caused by the shearing forces acting in the opposite directions, the load cells  60  generate proportional signals and supply them to an electronic sensor signal analyzing unit  64 . 
   As an alternative, instead of the load cells  60 , any other type of measuring sensor can be used by which the elastic deformations of the shearing force measuring bolt  58  can be measured. Such measuring sensors can be, for example, pressure-measuring transducers which operate according to a capacitive, piezoelectric or piezoresistive principle. 
   The shearing force measuring bolt  58  has an end-side bolt head  66  whose diameter is enlarged and in which the electronic sensor signal analyzing unit  64  is accommodated. The unit  64  may be cast into the bolt head  66 , whereby a vibration-absorbing or vibration-uncoupling accommodation is obtained. When strain gauges are used as a measuring element  60 , the electronic analyzing unit  64  includes, for example, a strain gauge bridge amplifier circuit. The strain gauges form, for example, a complete or at least half a measuring bridge. A signal of this measuring bridge is amplified and processed by the electronic analyzing unit  64 . The strain gauges maybe held in an axial bore of the shearing force measuring bolt  58 . 
   In a mounted condition, an upper cheek  38  of the brake lever  36  axially impacts on a face-side ring surface of the bolt head  66 . An end of the shearing force measuring bolt  58  pointing away from the bolt head  66  has an outer groove  70  extending transversely to the bolt axis  44 . Outer groove  70  is configured to receive a position-securing snap ring, so that the cheeks  38  of the fork  35  of the brake lever  36  can rest with play on the small end  28  of the connecting rod  20  and relative movements can occur in the abutting planes  68 . In a carrying area  86 , that is, in an area accommodating the cheeks  38  and the connecting rod eye  30 , a radially exterior circumferential surface of the shearing force measuring bolt  58  forms a cylindrically smooth surface without recesses or steps. 
   In the electronic sensor signal analyzing unit  64 , a conversion of shear deformation signals takes place to signals for the actual braking force. The braking force acts upon the brake pads  12 , and the signals are transmitted to a control and regulating device (not shown), in order to be able to adjust a desired braking force by a desired versus actual comparison. Furthermore, the received signals for the actual braking forces are used for monitoring of a force adjustment and operability of the brake application device  1  during safety-relevant brakings. In addition, for a verification of the measuring results, the motor current measured on a drive side by a current sensor can be matched with the signal for the actual braking force. The measuring sensors  60 , a connection wiring  72  for the electronic sensor signal analyzing unit  64  as well as the electronic sensor signal analyzing unit  64  itself are each provided in a redundant construction. Furthermore, the redundantly provided connection wires  72  are each equipped with their own shield. 
   One cylindrical bushing  74 ,  76 ,  78 , respectively, is non-rotatably held in the connecting rod eye  30  of the small end  28  of the connecting rod  20  and in the passage bores  34  of the cheeks  38  of the fork  35  of the brake lever  36 . The bushings  74 ,  76 ,  78  are held, for example, by a pressing-in. Each of the bushings  74 ,  76 ,  78  forms a sliding pairing with the shearing force measuring bolt  58 , with the relative movement taking place at the radially interior circumferential surfaces of the bushing  74 ,  76 ,  78 . The bushings  74 ,  76 ,  78  are constructed such that with respect to wear conditions, such as hardness, surface roughness, material, etc., they form the sliding partner which tends to wear out earlier in comparison to the shearing force measuring bolt  58 . The bushings  74 ,  76 ,  78  may be made of a sintered material, for example, a sintered bronze, and the shearing force measuring bolt  58  may be made of a hardened steel. Such sintered metals can absorb up to 35% of their volume of oil and can lubricate their sliding surface themselves as a result of capillary action. 
   As illustrated in  FIG. 2 , the bushings  74 ,  76 ,  78  essentially have the same length as the passage bores  34  carrying them or as the connecting rod eye  30 . The bushings  74 ,  76 ,  78  include radially interior edge recesses  80  which have, for example, a surroundingly ring-shaped construction and essentially a rectangular cross-section. As an alternative, the edge recesses  80  may have any other shapes. The radially interior edge recesses  80  face one another and are arranged in the area of the two lateral abutting planes  68  of the cheeks  38  with the small end  28  of the connecting rod  20 . The radially interior edge recesses are thus in the planes in which the cross-bores  62  having the measuring sensors  60  are also situated. The greatest shearing stress of the shearing force measuring bolt  58  may exist in the area of the abutting planes  68 , in which case, axial edge areas  82  of the bushings  74 ,  76 ,  78  are subject to bending stress. Because of the radially interior edge recesses  80 , the edge areas  82  of the bushings  74 ,  76 ,  78  are more flexible than adjoining areas, whereby high edge pressures are avoided. A resulting evening-out of tensions has a positive effect on a contact pattern of the sliding pairings that include bushings  74 ,  76 ,  78  and the shearing force measuring bolts. 
   Although the present disclosure has been described and illustrated in detail, it is to be clearly understood that this is done by way of illustration and example only and is not to be taken by way of limitation. The scope of the present disclosure is to be limited only by the terms of the appended claims.