Abstract:
The invention relates to a brake actuator, especially for a rail vehicle brake, comprising a service brake unit with a brake force generator for applying and/or releasing the brake, an accumulator brake unit with an energy accumulator device for accumulating and delivering energy for applying the brake as an operative emergency brake and/or as a parking brake, and a force conversion device for converting the energy that is provided by the brake force generator and/or the energy accumulator device into a brake application movement. The invention provides that the brake actuator has an additional energy accumulator device for accumulating and delivering energy for applying and/or releasing the brake. The additional energy accumulator device and the brake force generator can be designed in such a way that the force required of the brake force generator during a braking operation in order to generate a defined brake application force level that is greater than zero but less than the maximum brake force is zero.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
   State of the Art 
   The invention is based on a brake actuator, particularly for a rail vehicle brake. 
   Essentially, three braking systems are currently used in the rail vehicle field: pneumatic or electro-pneumatic braking systems, hydraulic or electro-hydraulic braking systems as well as mechanical or electro-mechanical braking systems. The braking system may be constructed as an active or passive braking system, depending on whether the force of the brake actuator is to be applied for an engaging (active braking system) or a releasing of the brake (passive braking system). In the event of operating disturbances, in the case of pneumatic systems, an energy accumulation takes place in compressed-air reservoirs; in the case of hydraulic systems, an energy accumulation takes place in hydraulic reservoirs; and in the case of mechanical systems, an energy accumulation takes place in the form of accumulator-type springs. 
   From US Patent Document U.S. Pat. No. 4,546,298, an electromechanical rail vehicle brake is known which has a service brake unit as well as an energy storage brake unit with an energy accumulator. The service brake unit contains a braking force generator for the application and/or release of the brake, for example, in the form of an electric-motor drive. The energy storage brake unit comprises at least one energy accumulator for storing and supplying energy for the application of the brake as an operational emergency brake in the event of a failure of the service brake unit, and/or as a parking brake. The energy storage brake is generally constructed as a spring-loaded brake. An energy converter carries out a conversion of the energy supplied by the braking force generator and/or by the energy accumulator to a brake application movement and comprises, for example, a brake spindle driven by the electric-motor drive. 
   Since the entire braking force or the entire releasing force is applied by the electric-motor drive as the braking force generator, the drive has to be designed for a high output torque. The braking force generator is therefore relatively large and consequently also relatively heavy and expensive. 
   U.S. Patent Document U.S. Pat. No. 4,784,244 describes an electrically operable brake actuator with an accumulator-type spring which, in the event of a service braking, builds up a fraction of the braking force. 
   SUMMARY OF THE INVENTION 
   An additional energy accumulator in the form of the accumulator-type spring and the braking force generator are designed such that the force to be applied by the braking force generator during a braking for generating a defined braking pressure in a defined operating point, which is greater than zero and smaller than the maximal braking force, amounts to zero. Thus the braking force generator does not have to generate an additional braking force in the defined operating point. Rather, the braking force is then generated by the accumulator-type spring alone. For reaching a maximal braking force, the braking force generator assists the accumulator-type spring. For generating lower braking forces, the braking force generator counteracts the force of the accumulator-type spring. The braking force generator therefore acts as only an assisting drive in both load directions for applying the maximal braking force as well as for releasing the brake. The system thereby combines important advantages of a passive braking system with those of an active braking system. However, an accumulator-type spring for the brake application can be smaller than in a purely passive braking system because it does not have to apply the maximal braking force alone but together with the braking force generator. On the other hand, the braking force generator, for example, an electric motor, may also have smaller dimensions than in the case of purely active brake systems because also the braking force generator generates the braking force not alone but together with the accumulator-type spring. 
   The accumulator-type spring can be activated jointly with the one energy accumulator in the event of an emergency and/or parking braking in the brake application direction. Thus, it contributes, not only during service brakings but also during parking and/or emergency brakings, to the generating of braking force. For this reason, not only the braking force generator but also the one energy accumulator may have smaller dimensions. Furthermore, safety is increased because, as a result of the accumulator-type spring as an additional energy accumulator, a redundancy exists in the case of parking and/or emergency brakings. 
   The accumulator-type spring is mechanically connected in parallel with respect to the braking force generator and with respect to an energy accumulator and, in the event of a service braking, can be operated together with the braking force generator in the brake application direction. The accumulator-type spring will then be designed such that, by means of it, when the braking force generator is not active, a defined, preferably a medium, braking force can be generated. 
   Also, the accumulator-type spring is constructed as a radially exterior accumulator-type spring which radially surrounds the interior accumulator-type spring, which forms the energy accumulator, whereby a particularly space-saving arrangement is created. 
   These and other aspects of the present invention will become apparent from the following detailed description of the invention, when considered in conjunction with accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of a preferred embodiment of a brake actuator according to the invention in a release position. 
       FIG. 2  is a view of a brake actuator of  FIG. 1  in a service braking position. 
       FIG. 3  is a view of the brake actuator of  FIG. 1  in an emergency or parking braking position. 
       FIG. 4  is a very schematic view of the brake actuator of FIG.  1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The preferred embodiment of a brake actuator which, as a whole, is marked by reference number  1  in FIG.  1  and is illustrated in a release position, is used as a driving unit of an electro-mechanical brake application device of a rail vehicle. The brake actuator  1  has an essentially hollow-cylindrical actuator housing  2  which in  FIG. 1  is illustrated in a broken-off fashion and which is closed off by a lid section  4  toward an axial end. The lid section  4  has a centered bore  6 . Starting from the lid section  4 , the actuator housing  2  has an essentially double-walled construction. An internal accumulator-type spring  10  and an external accumulator-type spring  12  coaxial thereto are arranged in the space between an interior wall  7  and an exterior wall  8 . The external accumulator-type spring  12  encloses the internal accumulator-type spring  10 . 
   The accumulator-type springs  10 ,  12  are shown as coil springs and are in each case supported by one of their ends at the lid section  4 . The external accumulator-type spring  12  is supported by its other end on a ring collar  14  of an outer sliding sleeve  16 . The internal accumulator-type spring  10  is supported by its other end on a ring collar  18  of an inner sliding sleeve  20 . The inner sliding sleeve  20  is between the outer sliding sleeve  16  and the interior wall  7  of the actuator housing  2 . Furthermore, the inner and the outer sliding sleeve  16 ,  20  are slidably guide in the axial direction on one another. The inner sliding sleeve  20  is slidably guided on a radially interior circumferential surface of the interior wall  7  of the actuator housing  2 . In the release position, the outer sliding sleeve  16  comes to rest on an axial stop  22  of the inner sliding sleeve  20 . Furthermore, the ring collar  14  of the outer sliding sleeve  16  projects over the ring collar  18  of the inner sliding sleeve  20  in the axial and radial direction. 
   On the side facing away from the accumulator-type springs  10 ,  12 , a motor, for example, an SR motor  24  (switched reluctance motor), which can be operated in the four-quadrant operation, is connected to the lid section  4 . An axial ring projection  26  of the motor housing  28  is centered in the bore  6  of the lid section  4 . The SR motor  24  contains a radially exterior housing-fixed stator  30  which encloses a rotor  32 . The rotor  32  can be braked by a blocking brake  34 , for example a permanent-magnet brake, which is closed when it is not energized and opened when it is energized. The rotor  32  is disposed on a hollow shaft  36  which, by way of ball bearings  38 , is rotatably disposed in the motor housing  28 . The shaft  36  is equipped on its radially interior circumferential surface with an axially extending spline toothing  40  in which radially exterior wings  42  of an intermediate sleeve  44  engage which extend in the axial direction. The intermediate sleeve  44  is therefore non-rotatably but axially displaceably guided relative to the hollow shaft  36 . 
   An end-side pin  46  of a brake spindle  48  projects coaxially into an end of the intermediate sleeve  44  facing the accumulator-type springs  10 ,  12  and is held there in a non-rotatable and axially fixed manner. The other end of the brake spindle  48  projects into a cup-shaped section  50  of a connecting rod  52  for an eccentric-shaft lever, which is not shown. For this purpose, the connecting rod  52  has an oblong hole  54  on the end side, into which a load sensing bolt can engage which holds the eccentric-shaft lever. The eccentric-shaft lever acts upon a caliper which is not shown for reasons of scale. The cup-shaped section  50  of the connecting rod  52  is held in the outer sliding sleeve  16  and is connected thereto, for example, by a thread  56 . 
   The brake spindle  48  is rotatably disposed inside the inner sliding sleeve  20  a double-row deep-groove ball bearing  58  which can absorb axial as well as radial forces. An inner race of the ball bearing  58  is tensioned by a nut  60  screwed onto an external thread section of the brake spindle  48  against a shoulder  62  of the brake spindle  48 . As a result, the inner race is non-rotatably and in an axially fixed manner held on the brake spindle  48 . An outer race of the of the deep groove ball bearing  58  is also non-rotatably and in an axially fixed manner held in the inner sliding sleeve  20 . 
   The brake spindle  48  is embraced by a nut/spindle constructional unit  64  which may be constructed as a rolling thread drive, such as a recirculating ball spindle, a threaded roller gear drive or as a planetary rolling thread drive. In this case, the cup-shaped section  50  of the connecting rod  52  is screwed into the outer sliding sleeve  16  to such an extent that the nut  66  of the nut/spindle constructional unit  64  is clamped in between a radially interior projection  68  of the outer sliding sleeve  16  and a face of the cup-shaped section  50  of the connecting rod  52 . Thus, the nut  66  is held in a torsion-proof manner with respect to the latter. During rotations of the brake spindle  48 , the nut  66  is therefore translationally guided along the brake spindle  48  and, in the process, takes along or moves the outer sliding sleeve  16  and the connecting rod  52 . 
   The lid section  4  of the actuator housing  2  includes an annulus  70  housing a gear wheel  74  which is disposed on a locking nut  72 , both of which are received coaxially with respect to the brake spindle  48 . A surface  76  of a radially extending wall  78  of the lid section  4 , which wall  78  bounds the annulus  70  and which surface  76  points away from the annulus  70 , forms the supporting surface for one end respectively of the interior and exterior accumulator-type spring  10 ,  12 . On the other surface of the wall  78  pointing to the annulus  70 , a ring recess is provided in which an axial needle bearing  80  holds the gear wheel  74  axially disposed with respect to the actuator housing  2 . The locking nut  72  is disposed on the other side of the gear wheel  74  pointing away from the axial needle bearing  80 . A radial deep groove ball bearing  82  separates the gear wheel  74  and the actuator housing  2 . An inner race of the deep groove ball bearing  82  is tensioned against a projection  84  of the locking nut  72  by a spring  86  which is secured in its position by a snap ring  88  disposed in the actuator housing  2 . By the effect of the spring  86 , the gear wheel  74  is therefore held in a force-locking manner between the projection  84  of the locking nut  72  and the axial needle bearing  80 . 
   The locking nut  72  engages the inner sliding sleeve  20  and is rotatably disposed thereon by a non-self-locking thread  90 . In addition, a magnetic locking device  92  with a coil  94  and a locking piston  96 , which can be radially operated with respect to the gear wheel  74 , is provided. When the coil  94  is energized, the locking piston  96  extends against the effect of a return spring  98 , viewed in the circumferential direction, between the teeth of the gear wheel  74  and thereby locks it in its rotating position relative to the inner sliding sleeve  20 . In contrast, when the coil  94  is not energized, the locking piston  96  is radially withdrawn by the return spring  98  and permits a free rotation of the gear wheel  74  with respect to the inner sliding sleeve  20 . 
   The SR motor  24  forms a braking force generator; the additional elements of the force transmission path from the SR motor  24  to the caliper form a braking force converting device  100 . However, as an alternative, the braking force generator may also be a hydraulic or pneumatic brake cylinder acting into one or two operating directions, or another unit acting into one or two directions. The locking device  92 , the permanent magnet brake  34  and the SR motor  24  can be controlled by an electronic controlling and regulating device which is not shown. Considering this background, the brake actuator  1  has the following function: 
   In the release position of the brake actuator  1  illustrated in  FIG. 1 , the exterior and the interior accumulator-type spring  10 ,  12  are prestressed. The force of the interior accumulator-type spring  10  is transmitted from the inner sliding sleeve  20  by way of the non-self-locking thread  90  to the locking nut  72  and, from there, by way of the gear wheel  74  to the extended piston  96  of the locking device  92 . As a result of the spring force, a torque is generated in the non-self-locking thread  90 ; that is, the gear wheel  74  wants to rotate together with the locking nut  72 , which, however, is prevented by the extended piston  96  of the locking device  92 . 
   The force of the exterior accumulator-type spring  12  is supported by the outer sliding sleeve  16  on the nut  66  of the nut/spindle constructional unit  64 , although the nut/spindle constructional unit  64  is non-self-locking. The reason is that the torque created because of the force of the exterior accumulator-type spring  12  in the brake spindle  48  is introduced by way of the permanent magnet brake  34 , which is closed in the release position, into the actuator housing  2 . From the nut  66 , the force runs by way of the brake spindle  48  and the double-row deep-groove ball bearing  58  into the inner sliding sleeve  20  and, from there, takes the same path into the gear wheel  74  as the force of the interior accumulator-type spring  10 . This means that, in the release position, the exterior as well as the interior accumulator-type spring  10 ,  12  are held in the tensioned state by the locking device  92 . 
   During the transition from the release position to a service braking, the permanent magnet brake  34  is energized by the electronic controlling and regulating device. This causes the brake to open and permit a rotation of the SR motor  24  which is also supplied with electric energy by the controlling and regulating device. As a result of the rotation of the rotor  32  and of the brake spindle  48 , the nut  66  of the nut/spindle constructional unit  64 , together with the outer sliding sleeve  16  and the connecting rod  52 , is moved into the moved-out service brake position illustrated in FIG.  2 . This moving-out movement of the connecting rod  52  is supported by the exterior accumulator-type spring  12  which, relative to the function, is connected parallel to the SR motor  24 , as schematically illustrated in FIG.  4 . 
   The controlling of the SR motor  24  by the controlling and regulating device and the exterior accumulator-type spring  12  are mutually coordinated such that the exterior accumulator-type spring  12  alone generates a defined braking force value, which is between a minimal and a maximal braking force and defines an operational zero point. In the operational zero point, the SR motor SR  24  is switched currentless. The amount of the braking force acting in the operational zero point is therefore, among other things, a function of the spring rate of the exterior accumulator-type spring  12  and the degree of the prestressing. For achieving the maximal braking force, the SR motor  24  is controlled by the controlling and regulating device in the four-quadrant operation such that it supports the exterior accumulator-type spring  12  by a rotation in the brake application direction and by the supplying of a positive torque, which corresponds, for example, to an operation in the first quadrant. For reaching a braking force lower than in the operational zero point, the SR motor  24  rotates against the brake application direction and supplies a negative torque which, by way of the nut/spindle constructional unit  64 , acts against the exterior accumulator-type spring  12  (operation in the third quadrant). The interior accumulator-type spring  10  does not participate in the generating of the service braking force and remains in the tensioned condition because, as a result of the continuously locked locking device  92 , the gear wheel  74  is in the blocking position. 
   The engaging of the parking brake is initiated by the above-described service braking until a braking force is reached which is approximately 20% lower than the final force to be achieved by means of the parking brake. By means of corresponding control signals of the control device, the SR motor  24  is stopped; by interrupting the power supply, the permanent magnet brake  34  is moved into the braking position; and the locking device  92  is released by switching off the energizing. This situation is illustrated in FIG.  3 . Because of the spring force acting upon the inner sliding sleeve  20  and generated by the interior accumulator-type spring  10 , a torque is generated in the non-self-locking thread  90  between the locking nut  72  and the inner sliding sleeve  20 , which torque is no longer supported by the retracted locking piston  96 . Consequently, the locking nut  72  starts to rotate on the inner sliding sleeve  20 , which then moves into the brake application direction and by way of its axial stop  22 , takes along the outer sliding sleeve  16  with the connecting rod  52 . Simultaneously, because of the spring force of the exterior accumulator-type spring  12 , the unlocked outer sliding sleeve  16  can move in the brake application direction. In this case, it is unimportant whether the permanent magnet brake  34  is opened or closed because the intermediate sleeve  44 , together with the brake spindle  48 , is axially displaced in this process in the spline toothing  40  of the hollow shaft  36  of the rotor  32 , as illustrated in FIG.  3 . In the parking brake position, a total braking force is therefore active which is the result of the sum of the spring forces of the two parallel-acting accumulator-type springs  10 ,  12 . This situation is also illustrated in  FIG. 4 , in which case, after the releasing of the locking device  92  illustrated as a rocker lever, the interior accumulator-type spring  10 , together with the exterior accumulator-type spring  12 , builds up the braking force at the brake shoes. The entire energy supply can then be switched off and the rail vehicle is held by the spring forces of the inner and outer accumulator-type spring  10 ,  12  reliably in the parking brake position. In order to maintain the resulting achieved parking braking force for an extended time period, only a low relaxation may be permitted at the interior and the exterior accumulator-type spring  10 ,  12 . 
   If the power supply of the brake actuator  1  and/or die controlling and regulating device fails during a service braking, the coil  94  of the locking device  92  is no longer energized so that the locking piston  96  releases the gear wheel  74 . The subsequent events are identical to those described with respect to the parking braking, so that, also in the event of an emergency or safety braking, the total braking force is the result of the sum of the spring forces of the two parallel acting accumulator-type springs  10 ,  12 . 
   The release of the brake, starting from the parking braking or emergency braking position takes place in two steps, the interior accumulator-type spring  10  being tensioned first. The permanent magnet brake  34  is energized by the controlling and regulating device and is therefore opened, and the SR motor  24  is driven in the brake application direction. In this case, the rotating brake spindle  48  is supported on the nut  66  of the nut/spindle constructional unit  64  and, together with the inner sliding sleeve  20 , moves in the direction toward the release position. The locking nut  72  rotates on the inner sliding sleeve  20  while the locking device  92  is opened. However, this can also take place when the locking device  92  is closed by means of a free wheel  102  between the locking nut  72  and the gear wheel  74 . The free wheel  102  permits a rotating of the locking nut  72  with respect to the gear wheel  74  when the interior accumulator-type spring  10  is tensioned. A rotating in the opposite direction is not possible. When the tensioned condition of the interior accumulator-type spring  10 , which corresponds to the condition in the release position, has been reached, the SR motor is stopped by the controlling and regulating device and is moved into the locking position by the energizing of the coil  94  of the locking pistons  96 , as shown in FIG.  2 . 
   In another step, the exterior accumulator-type spring  12  in tensioned in that the SR motor  24  is operated in the opposite rotating direction, that is, in the release direction, in which case the brake spindle  48  supported on the locked inner sliding sleeve  20 , as a result of its rotation, screws the nut  66  of the nut/spindle constructional unit  64 , together with the outer sliding sleeve  16 , in the direction of the release position. Then the SR motor  24  is switched off and the permanent magnet brake  34  is moved into the braking position by the interruption of the power supply, as shown in FIG.  1 . 
   Although the present invention 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 invention is to be limited only by the terms of the appended claims.