Abstract:
The invention relates to a brake actuator, especially for a rail vehicle brake, comprising an accumulation brake unit having an energy accumulator for storing and supplying energy for applying the brake, preferably in the event of safety braking and/or park braking, and a locking device for locking and unlocking the energy accumulator. After the release of the locking device, an inertia weight from part of the energy released from the energy accumulator can be subjected to a rotational movement for damping purposes.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
   The invention relates to a brake actuator, particularly for a rail vehicle brake. 
   Currently, three types of wheel braking systems are essentially used in the rail vehicle field: Pneumatic or electro-pneumatic braking systems, hydraulic or electro-hydraulic braking systems as well as mechanical or electromechanical braking systems. The wheel braking system may be constructed as an active or passive braking system, depending on whether the power of the brake actuator has to be applied for the engaging (active braking system) or for the releasing of the brake (passive braking system). In case of operating disturbances, energy is stored in air brake reservoirs if pneumatic systems are used; energy is stored in hydraulic reservoirs if hydraulic systems are used; and energy is accumulated in the form of accumulator-type springs when electromechanical systems are used. 
   From the prior art, electromechanical rail vehicle brakes are known which have a service-type brake unit as well as an accumulator-type brake unit which has an energy accumulator. The service-type brake unit contains a braking power generator for the application and/or release of the brake; for example, in the form of an electric-motor drive. The accumulator-type brake unit comprises at least one energy accumulator for the storage and supply of energy for the application of the brake as a service-type emergency brake when the service-type brake unit fails, and/or as a parking brake. The accumulator-type brake unit is generally constructed as a spring-loaded brake. A power converter provides a conversion of the energy supplied by the braking power 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. 
   When the spring-loaded brake is triggered in the event of a parking braking or an emergency braking, the potential energy stored in the accumulator-type spring is abruptly released and is converted to high kinetic energy of the elements of the power converter which, after the braking position has been reached, are also abruptly decelerated. In this case, the braking system is subjected to high forces which may result in premature wear or damage. 
   In view of the above, the present invention is based on a brake actuator which, when the accumulator-type brake unit is triggered, lower loads will occur, while the braking effect is simultaneously high. Furthermore, this object is to be connected with lower constructional costs and should be able to be implemented in a space-saving manner. 
   Because the potential energy abruptly released when the accumulator-type brake is triggered is, for the most part, converted to rotational energy of the inertia weight, the remaining kinetic energy, by means which the elements of the power converter can be accelerated in the brake application direction, is reduced. For this reason, the shock load acting upon the braking system is reduced, whereby its service life and reliability is increased. The inertia weight is provided in addition to possibly already existing rotational bodies used exclusively for locking the accumulator-type brake unit. The rotational bodies also rotate after the release of the locking device. In particular, the inertia weight has a mass moment of inertia which is sufficient for a noticeable damping of the release of energy abruptly occurring during the release of the locking device. In comparison to linearly moving inertia weights, which require a relatively long acceleration path for generating a significant energy dissipation, less space is required for rotatory inertia weights. In addition, in contrast to oil-pressure-type or gas-pressure-type shock absorbers, the rotational inertia weight can be used independent of the temperature. 
   According to a particularly preferred arrangement, the forces and/or torques generated by the energy accumulator, when the locking device is locked, can be introduced at least by a portion of the inertia weight into a housing of the brake actuator and can be supported there. As a result, the inertia weight forms a component of the locking device and is integrated into its flux of force. The inertia weight therefore has a double function in that, in addition to reducing excess energy, it simultaneously acts as a locking element, whereby a particularly space-saving and light construction is obtained. 
   According to a further development, a transmission gearing with a preferably large gear ratio is arranged between the energy accumulator and the inertia weight. As a result, the forces are reduced which have to be applied for locking the inertia weight, which is simultaneously used as a locking element, in the release position. When the inertia weight is locked, for example, by electromagnetic holding forces, solenoid coils of a lower magnetic force are sufficient, whereby the current consumption and the heating-up of the brake actuator are reduced. Simultaneously, because of the large ratio, the rotational speed of the inertia weight is increased which is entered in a squared manner into the rotational energy, so that a high degree of damping will exist when the accumulator-type brake unit is triggered. 
   The inertia weight is expediently releasably coupled with the energy accumulator by a slipping clutch which is designed such that, after the braking position has been reached, the inertia weight is uncoupled from the energy accumulator. If the inertia weight and the bearing frictions are designed such that the inertia weight continues to rotate after the braking position has been reached, as a result of this arrangement, a gradual reduction of the rotational energy stored in it can take place, which has a positive effect on the service life of the brake actuator. 
   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 the release position. 
       FIG. 2  is a view of the locking device of an accumulator-type brake unit of the brake actuator as an enlarged cutout of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The preferred embodiment of a brake actuator, which as a whole has the reference Number  1  in  FIG. 1  and is illustrated in a release position, is used as the driving unit of an electromechanical brake application device  2  of a rail vehicle. The brake actuator  1  has an essentially hollow-cylindrical actuator housing  3  which is closed off by a lid section  4  toward an axial end. The lid section  4  has an end-side opening  6 . Starting from the lid section  4 , the actuator housing  3  has an essentially double-walled construction. In the space between an interior wall  7  and an exterior wall  8 , an interior accumulator-type spring  10  and an exterior accumulator-type spring  12  coaxial thereto being arranged. The exterior accumulator-type spring  12  encloses the interior accumulator-type spring  10 . 
   The accumulator-type springs  10 ,  12  are preferably constructed as coil springs and are in each case supported by their one end on the actuator housing  3 . The exterior accumulator-type spring  12  is supported by its other end on a ring collar  14  of an exterior sliding sleeve  16 . The interior accumulator-type spring  10  is supported by its other end on a ring collar  18  of an interior sliding sleeve  20 . The interior sliding sleeve  20  is arranged between the exterior sliding sleeve  16  and the interior wall  7  of the actuator housing  3 . Furthermore, the interior and the exterior sliding sleeve  16 ,  20  are displaceably guided in the axial direction on one another, and the interior sliding sleeve  20  is displaceably guided on a radially interior circumferential surface of the interior wall  7  of the actuator housing  3 . In the release position, the exterior sliding sleeve  16  comes to rest on an axial stop  22  of the interior sliding sleeve  20 . In addition, the ring collar  14  of the exterior sliding sleeve  16  projects over the ring collar  18  of the interior sliding sleeve  20  in the axial and radial direction. 
   In the lid section  4 , an SR motor  24  (switched reluctance motor), which can be operated in the four-quadrant operation, is accommodated on the side facing away from the accumulator-type springs  10 ,  12 . The SR motor  24  contains a radially exterior, housing-fixed stator  30  which encloses a rotor  32  which can be braked by a holding brake  34 , preferably a permanent magnet brake, which is closed when it is not energized and open when it is energized. As best illustrated in  FIG. 2 , the rotor  32  is disposed on a hollow shaft  36  which is rotatably disposed by ball bearings  38  in the actuator housing  3 . On its radially interior circumferential surface, the rotor  32  has an axially extending spline toothing  40 , which engages radially exterior wings  42  of an intermediate sleeve  44  which extend in the axial direction. As a result, the intermediate sleeve  44  is 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 lever  53 , as illustrated in  FIG. 1 . The cup-shaped section  50  of the connecting rod  52  is held axially fixed in the exterior sliding sleeve  16  but can also swing out laterally by a universal ball joint. An eye is shaped onto the face of the connecting rod  52  facing away from the accumulator-type springs  10 ,  12 . A pin  55 , which is connected with one end of the eccentric lever  53  of an eccentric arrangement, engages the eye. The eccentric arrangement has an eccentric shaft  56  which is linked to a forked lever  57  which, together with another formed lever  57 ′, forms a caliper. At one end respectively of the calipers  57 ,  57 ′, brake lining holders with brake linings  58  are in each case arranged which are displaceable in the direction of the axis of the brake disk  59 . The ends of the forked levers  57 ,  57 ′ facing away from the brake linings  58  are connected with one another by a plunger rod adjuster  59 ′ which may be electrically operable. 
   As illustrated in  FIG. 2 , the brake spindle  48  is rotatably disposed within the interior sliding sleeve  20 , for example, by a two-row deep groove roller ball bearing  61  which can absorb axial as well as radial forces and by which an interior ring of the bearings  61  is tensioned by a nut  60  against a shoulder  62  of the brake spindle  48 . The nut  60  is screwed onto an external thread section of the brake spindle  48 . As a result, the interior ring is held in a non-rotatable and axially fixed manner on the brake spindle  48 . An exterior ring of the deep groove ball bearing  61  is also held in a non-rotatable and axially fixed manner in the interior sliding sleeve  20 . 
   The brake spindle  48  is surrounded by a nut/spindle constructional unit  64 , which can be constructed as a roller thread drive, such as a circulating ball spindle, a roller thread drive, a thread roller screw drive or as a planetary roller thread drive. The cup-shaped section  50  of the connecting rod  52  is inserted into the exterior sliding sleeve  16  to such an extent that the nut  66  of the nut/spindle constructional unit  64  is clamped between a radially interior projection  68  of the exterior sliding sleeve  16  and a face of the cup-shaped section  50  of the connecting rod  52 , so that it is held with respect to the latter in a manner which protects it against torsion. During rotations of the brake spindle  48 , the nut  66  is therefore translatorily guided along the brake spindle  48  and in the process takes along the exterior sliding sleeve  16  and the connecting rod  52 . 
   In the lid section  4  of the actuator housing  2 , an annulus  70  is constructed in which a ring gear  76  is received coaxially to the brake spindle  48 . The ring gear  76  is in a driving connection with a locking nut  72  by a slipping clutch  74 . The ring gear  76  is disposed on the radially exterior circumferential surface of the locking nut  72  and is non-rotatably connected with the locking nut  72  by the slipping clutch  74  to an upper limit torque. The slipping clutch  74  is preferably formed by axially mutually engaging spur-type serrations  78  on the ring gear  76  and on the locking nut  72 . A diaphragm spring assembly  82  is axially supported on the actuator housing  3  by a snap ring  80  and acts upon a radial deep groove ball bearing  84 , which supports the locking nut  72  relative to the actuator housing  3 . The spring assembly  82  provides the axial force required for a force and form closure of the spur-type serrations  78 . On its side pointing away from the spur-type serrations  78 , the ring gear  76  is axially disposed by an axial needle bearing  86  with respect to the actuator housing  3 . The locking nut  72  encloses and is rotatably disposed on the interior sliding sleeve  20  by a non-self-locking thread  88 . 
   A preferably electromagnetically operable locking device  90  has a housing  92  which is flanged to a radial opening of the annulus  70 . The locking device  90  comprises a shaft  94  on whose radially interior end a bevel gear  96  is arranged and on whose opposite, radially exterior end, a cylindrical inertia weight  98  is arranged. The bevel gear  96  meshes with the toothing of the ring gear  76  and, together with it, forms a bevel gear pair which preferably has a relatively high transmission ratio, which is, for example, in a range of from 3.0 to 8.0. The shaft  94  is rotatably disposed in the housing  92  of the locking device  90  by deep groove ball bearings  100 . The shaft  94  being arranged perpendicular to the brake spindle  48 . 
   The inertia disk  98  has a ring recess  102  for a ring  104  on its face pointing to the brake spindle  48 . The ring  104  is arranged coaxial to the shaft  94  and is displaceably received along pins  106  extending in the axial direction. The ring  104  is non-rotatably connected with the inertia disk  98 . In addition, on its face pointing away from the inertia disk  98 , the ring  104  has a radially external gear rim  108  which is situated opposite another gear rim  108 ′ supported on the housing  92  of the locking device  90 . The gear rim  108  is pushed away from that gear rim  108 ′ by the pressure springs  110 . Furthermore, two solenoid coils  112 ,  112 ′ arranged behind one another in the axial direction in the housing  92  of the locking device  90  are situated opposite the ring  104 . The solenoid coils  112 ,  112 ′ can be energized by an electric connection  114 . The ring  104 , the two gear rims  108 ,  108 ′ and that two solenoid coils  112 ,  112 ′ together form a solenoid cogwheel brake  116 . 
   When the solenoid coils  112 ,  112 ′ are energized, magnetic attraction powers or fields are generated which move the ring  104  against the effect of the pressure springs  110  along the pins  106  in the axial direction toward the solenoid coils  112 ,  112 ′. Thus, the gear rim  108  of the ring  104  comes to engage with the gear rim  108 ′ held on the housing  92  of the locking device  90  and thus enters into a non-rotatable connection therewith. Then, a torque introduced by the ring gear  76  into the locking device  90  can be supported on the housing  92  of the locking device  90 . The flux of force extends through the bevel gear  96 , the shaft  94  and the inertia disk  98 . 
   In the release position of the solenoid cogwheel brake  116 , the solenoid coils  112 ,  112 ′, in contrast, are not energized, so that the gear rim  108  of the ring  104 , as a result of the effect of the pressure springs  110 , becomes disengaged from the gear rim  108 ′ held on the housing  92  of the locking device  90 . The ring gear  76 , together with the bevel gear  96 , the shaft  94  and the inertia disk  98 , can therefore rotate freely with respect to the housing  92  of the locking device  90 . The inertia disk  98 , the ring  104 , the shaft  94  and the bevel gear  96 , together then form an inertia weight or mass  118 , which can be rotated perpendicular to the brake spindle  48  or to the brake application direction and, relative to the slipping clutch  74 , is arranged on the other side of the locking nut  72 . Because of its radius, the inertia disk  98  is the largest portion of the mass moment of inertia of the inertia weight  118 . 
   The SR motor  24  forms a braking power generator; the other elements of the power transmission path from the SR motor  24  to the forked levers  57 ,  57 ′ form a braking power converter  120 . Preferably, an electric motor  24  is used as a braking power generator. However, as an alternative, the braking power generator may also be a hydraulic or pneumatic brake cylinder acting in one or two operating directions, or another unit acting in one or two directions. The locking device  90 , the permanent magnet brake  34  and the SR motor  24  can be controlled by an electronic control and regulating device which is not shown. With 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 preloaded. The force of the interior accumulator-type spring  10  is transmitted from the interior sliding sleeve  20  by the non-self-locking thread  88  to the locking nut  72  and from there by the slipping clutch  74  to the ring gear  76  and the inertia disk  98 . As a result of the spring force of the interior accumulator-type spring  10 , a torque is generated in the non-self-locking thread  88 ; that is, the locking nut  72  wants to rotate together with the inertia weight  118 , which, however, is prevented by the energized and therefore closed solenoid cogwheel brake  116 . 
   The power of the exterior accumulator-type spring  12  is supported by the exterior sliding sleeve  16  on the nut  66  of the nut/spindle constructional unit  64 , although the nut/spindle constructional unit  64  is not self-locking. The reason is that the torque created because of the power of the exterior accumulator-type spring  12  in the brake spindle  48  is introduced by the permanent magnet brake  34  closed in the release position into the actuator housing  3 . From the nut  66 , the power flux extends by the brake spindle  48  and the two-row deep groove ball bearing  61  into the interior sliding sleeve  20  and, from there, takes the same path into the ring gear  76  as the force of the interior accumulator-type spring  10  to the inertia disk  98 . This means that, in the release position, the exterior as well as the interior accumulator-type spring  10 ,  12  are held in the tensioned condition by the locking device  90 . 
   During the transition from the release position to a service-type braking, the permanent magnet brake  34  is energized by the electronic control and regulating device. As a result, the brake  34  opens and permits a rotation of the SR motor  24  which is also supplied with electric energy by the control and regulating device. By means 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 exterior sliding sleeve  16  and the connecting rod  52 , is moved out into the service-type braking position. This moving-out movement of the connecting rod  52  is supported or aided by the exterior accumulator-type spring  12  which, relative to the function, is connected parallel with the SR motor  24 . 
   The controlling of the SR motor  24  by the control 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 power value which is between a minimal and a maximal braking power and defines an operational zero point. In the operational zero point, the SR motor  24  is switched currentless. The amount of the braking power 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 of the degree of the preloading. For achieving the maximal braking power, the SR motor  24  is controlled by the control 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 supplying a positive braking torque, which corresponds, for example, to an operation in the first quadrant. Although for achieving a braking power lower than in the operational zero point, the SR motor  24  rotates in the brake application direction, similar to a generator, it supplies a negative torque which acts by way of the nut/spindle construction unit  64  against the exterior accumulator-type spring  12  (operation in the second quadrant). The interior accumulator-type spring  10  does not participate in the generating of the service-type braking power and remains in the tensioned condition because the locking nut  72  is locked by the still energized solenoid cogwheel brake  116 . 
   The controlled engaging of the parking brake is initiated by the above-described service-type braking until a braking power is reached which is approximately 20% lower than the final power 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; the permanent magnet brake  34  is closed by an interruption of the current supply, and the solenoid cogwheel brake  116  is released by switching off the energization. Because of the spring force acting upon the interior sliding sleeve  20  and generated by the interior accumulator-type spring  10 , a torque is generated in the non-self-locking trapezoidal thread  88  between the locking nut  72  and the interior sliding sleeve  20 , which torque is no longer supported by the now freely rotatable inertia weight  118 . The locking nut  72  therefore begins to rotate on the interior sliding sleeve  20  which then moves into the brake application direction and, by way of its axial stop  22 , takes along the exterior sliding sleeve  16  with the connecting rod  52 . Simultaneously, because of the spring force of the exterior accumulator-type spring  12 , the unlocked exterior sliding sleeve  16  can move into the brake application direction. In this case, it is unimportant whether the permanent magnet brake  34  is open or closed, because the intermediate sleeve  44 , together with the brake spindle  48 , is axially displaced during this operation in the spline toothing  40  of the hollow shaft  36  of the rotor  32 . A total braking power therefore acts in the parking braking position, which total braking power is a result of the sum of the spring forces of the two parallel acting accumulator-type springs  10 ,  12 . 
   During the brake application movement, the rotation of the locking nut  72  is translated by the bevel gear pair  76 ,  96  into a rotation of the inertia weight  118  taking place at a higher rotational speed. Thus a large portion of the potential energy of the relaxing accumulator-type springs  10 ,  12  is converted to rotational energy. When the braking position has been reached, the entire energy supply can be switched off and the rail vehicle is reliably held in the parking braking position by the spring forces of the interior and exterior accumulator-type spring  10 ,  12 . In order to maintain the resulting achieved parking braking power for an extended time period, only a slight relaxation may be permitted in the interior and the exterior accumulator-type spring  10 ,  12 . The two accumulator-type springs  10 ,  12  preferably consist of high-strength silicon spring wire CrS1Va TH-381 HRA of the firm Trefileurope. 
   The rotation of the locking nut  72  stops with the reaching of the braking position. The slipping clutch  74  between the locking nut  72  and the ring gear  76  is designed such that the upper limit torque, starting at which a relative rotation can take place between the spur-type serrations  786 , is exceeded by the torque from the product of the mass moment of inertia of the inertia weight  118  and of the deceleration in the braking end position existing after passing through the brake application stroke. Thus, after the braking end position has been reached, the inertia weight  118  can first continue to rotate and, essentially as a result of the friction taking place between the spur-type serrations  78  of the ring gear  76  and of the locking nut  72 , is slowly caused to come to a stop. As a result, a gradual reduction of the rotational energy accumulated in the inertia weight  118  can take place. 
   If the current supply of the brake actuator  1  and/or the control and regulating device and a higher-ranking vehicle control fail during a service-type braking, the solenoid coils  112 ,  112 ′ of the locking device  90  are no longer energized, so that the pressure springs  110  pull the ring  104  back in the direction of the inertia disk  98  and thereby release the solenoid cogwheel brake  116 . The subsequent events are identical with those described above relative to a parking braking, so that, also in the event of an emergency or safety braking, the total braking power is a result of a sum of the spring forces of the two parallel acting accumulator-type springs  10 ,  12 . 
   The release of the brake starting from the parking or emergency braking position takes place in two steps, in which case the interior accumulator-type spring  10  is tensioned first. The permanent magnet brake  34  is energized by the control and regulating device and is thereby opened, and the SR motor  24  is driven in the brake application direction. The rotating brake spindle  48  is supported on the nut  66  of the nut/spindle constructional unit  64  and moves, together with the interior sliding sleeve  20 , in the direction of the release position. The locking nut  72  moves on the interior sliding sleeve  20  while the locking device  90  is open. When the tensioned condition of the interior accumulator-type spring  10  has been reached, which corresponds to the condition in the release position, the SR motor  24  is stopped by the control and regulating device, and the locking device  90  is changed into the locking position by the energizing of the solenoid coils  112 ,  112 ′. However, the tensioning of the interior accumulator-type spring  10  is also possible when the solenoid coils  112 ,  112 ′ are already energized and the locking device  90  is therefore closed. 
   In an additional step, the exterior accumulator-type spring  12  is tensioned in that the SR motor  24  is operated in the reverse rotating direction; that is, in the release direction. The brake spindle  48 , supported on the locked interior sliding sleeve  20 , as a result of its rotation, screws the nut  66  of the nut/spindle constructional unit  64 , together with the exterior sliding sleeve  16 , in the direction of the release position. Subsequently, the SR motor  24  is switched off and the permanent magnet brake  34  is activated. 
   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.