Patent Publication Number: US-2018038428-A1

Title: Brake actuator

Description:
TECHNICAL FIELD 
     The present invention relates to a brake actuator for brakingly engaging a brake block or pad with a rotating part of a vehicle, comprising spring means creating a linear brake force. The invention also concerns a vehicle comprising such a brake actuator. 
     BACKGROUND 
     Powerful spring means are frequently used in the braking art for creating a parking brake force. The spring means can for example be held compressed by pneumatic or hydraulic pressure. When this pressure is lowered, the spring means are arranged to apply the brakes for parking or at an emergency situation. Such arrangements are often referred to as spring brakes. A spring brake may be combined with a pneumatic or hydraulic service brake actuator. 
     It is also known in the braking art to utilize powerful spring means for service braking. Also in this case the spring means can be held compressed by for example pneumatic or hydraulic pressure. When this pressure is lowered, the spring means are arranged to apply the brakes for lowering the speed of the vehicle, ie for service braking. A service brake of this kind may be called an inverse brake. 
     A problem with such a brake is that the control, normally by pneumatic or hydraulic pressure, of the service brake force generated by the spring can be complicated and not performed with the necessary speed and accuracy. 
     It can also be borne in mind that there is a tendency in the art to employ electricity to an increasing extent for controlling and powering different functions onboard vehicles. 
     WO2004031607A relates to a brake tensioning device, especially for a rail vehicle brake, said device comprising a brake actuator for tensioning and/or releasing the brake, and a force converter for converting the energy outputted by the brake actuator into a brake tensioning movement. The force converter comprises a shearing force measuring bolt which is arranged in the power train and is provided with at least one measuring sensor for directly or indirectly measuring the braking force. The bolt forms an articulated axle of an articulation which penetrates passage openings of at least two force transmission elements of the force converter which can be pivoted in relation to each other. A bushing provided with radially inner edge recesses is radially arranged between at least one opening of a force transmission element and the shearing force measuring bolt. Moreover, a spring means is arranged to apply the brake in case of a failure of braking signals. This spring has, however, no function in ordinary braking situations, which are entirely controlled by the above brake actuator. 
     In U.S. Pat. No. 4,334,711A, a “snow brake” control system for a railway vehicle is described. In the control system, an electronic timing circuit is operative in response to the operator&#39;s brake valve device being moved to its brake release position to provide an output signal that acts through a relay switch to deenergize a magnet valve that normally interrupts communication of “snow brake” control pressure to the system relay valve in order to withhold “snow brake” operation for a predetermined period of time sufficient to allow the vehicle brake units to release the brakes and thereby effect operation of the brake unit slack adjuster mechanism. When the time period expires, the timing circuit output signal disappears and the magnet valve becomes energized to reestablish “snow brake” control pressure during the remainder of the brake release period to maintain a light brake application in effect. The focus of this brake control system is a “snow brake feature”, preventing ice formation on the brake pads. U.S. Pat. No. 4,334,711A is, however, silent on the design of the brake actuator per se, and hence fails to provide information to an artisan desiring to design a brake actuator. 
     CN10321597A discloses a brake arrangement in which a spring is arranged to provide a braking force in the event of a failure of a brake actuator. This document is also silent on the design of the brake actuator per se. 
     DE19617796A describes a brake actuator in which the brake force is created by a trapezoidal thread engagement between two cooperating units, the distance between which may be altered by rotating the trapezoidal thread engagement. 
     DE19851668A discloses a brake actuator which uses a non linear wedge/spring combination to achieve a controllable braking force application. The movements of the wedge are controlled by an electric motor. 
     U.S. Pat. No. 4,175,645A relates to a brake actuator for a vehicle, particularly a rail vehicle, which is automatically applied during a power loss and which is electrically resettable. The brake has an eccentric member which cooperates with a controllable resilient member for actuating the brake force. 
     WO2014189089 describes a brake actuator comprising an combined spring/eccenter mechanism for controlling the delivered brake force by the actuator. 
     SUMMARY 
     An object of the present invention is to mitigate or eliminate the drawbacks discussed above. Hence, the teachings herein are concerned with an inverse service brake, especially for a rail vehicle, in which the compression of the spring means is not directly controlled by pneumatic or hydraulic pressure (which may not even be available onboard the vehicle) and in which the above and other problems are solved or at least reduced. 
     The objects above—as well as other object that will appear from the following description—have now been achieved by the concept set forth in the appended independent claims; preferred embodiments being defined in the related dependent claims. 
     In an aspect, there is provided a brake actuator which comprises an eccentric mechanism in a brake force transmitting chain from the spring means to the brake block or pad; and a motor for controlling the angular position of an eccentric in the eccentric mechanism and thus the brake force transmitted from the spring means. 
     In a further aspect, there is provided a brake actuator for brakingly engaging a brake block or pad with a rotating part of a vehicle. The brake actuator comprises spring means creating a linear brake force, and an eccentric mechanism interconnecting the spring means and the brake block or pad. Furthermore, the brake actuator has a motor for controlling the angular position of an eccentric which controls movements of the eccentric mechanism in the direction of the force generated by the spring means, and thus the brake force transmitted from the spring means to the brake block or pad. 
     The motor is normally an electric rotary motor, but could also be an electric linear motor or even another motor powered by any medium. 
     The purpose of the motor is to control the position of the eccentric mechanism, which means that only limited power is needed and that the speed and accuracy are enhanced. 
     The principles of the concept set forth herein can be used for disc braking or block braking, but in a practical case the brake actuator is employed in a disc brake for a rail vehicle. Here, the arrangement comprises spring means for biasing a drive bridge in a brake application direction, the drive bridge being connected to the brake pad for braking engagement with a brake disc of the vehicle and being controlled in its position in this direction by an eccentric, preferably a cam, which extends through an opening in the drive bridge and is arranged on a control shaft journalled in relation to a housing of the brake actuator and connected to the motor, preferably an electric rotary motor. 
     In this case, the spring means may be compression springs supported by a cover of the housing of the brake actuator, and the control shaft may be journalled in shaft supports of the cover. 
     The function of the motor is primarily to control the position of the eccentric or cam, which means that only a limited rotation thereof is needed. To this end reduction gearing is preferably provided between the electric motor and an outgoing drive pinion thereof. The reduction gearing may comprise a planetary reduction gearing. 
     The drive pinion may be in gear engagement with a gear wheel on the control shaft. For further reduction this gear wheel preferably has a much larger diameter than the drive pinion. 
     In a practical embodiment, the drive bridge may be in connection with a brake head, which in turn may be connected to the brake pad. The brake pad may be attached to a brake pad holder, which is connected to the brake head by a brake lever pivotally attached to the housing. 
     A load cell may be arranged between the drive bridge and the brake head. The purpose of such a load cell is preferably to sense the transmitted brake force and to control the operation of the electric motor for obtaining the desired brake characteristics. 
     The brake actuator may be provided with a built-in slack adjuster device so as to form a so-called brake unit. The purpose of the slack adjuster device is—as is very well known in the art—to compensate for the wear of the brake pad (or brake block) and of the brake disc (or wheel). In the practical embodiment such a slack adjuster device is arranged between the drive bridge and the brake head. 
     In a practical embodiment, the slack adjuster device comprises a nut rod provided with an external threaded nut portion connected to the brake head. The nut portion is in internal thread engagement with a rotatable adjuster tube connected to the drive bridge. The adjuster tube is arranged to be driven by the electric motor via an electromagnetic clutch, a bevel gear wheel and an adjuster tube gear wheel in splines connection with the adjuster tube. 
     In a further aspect, there is provided a vehicle—in particular a rail vehicle—comprising a brake actuator which is configured for brakingly engaging a brake block or pad with a rotating part of the vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teachings herein will be described in further detail below with reference to the accompanying drawings, in which 
         FIG. 1  is an isometric view of an electromechanical disc brake unit, 
         FIG. 2  is a view from above of the same unit with certain portions shown in section, and 
         FIG. 3  is a schematical illustration of a block brake unit embodying the same principles as the disc brake unit of  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIG. 1 , an electromechanical disc brake unit generally comprises a main body  1 , in which a mechanism for converting a rotary movement into a longitudinal movement is contained and to which an electric rotary motor  2  is attached. 
     As is known in the art, such a brake unit is intended for mounting in an under frame of a vehicle, normally a rail vehicle (not shown), in the vicinity of a brake disc D (dotted lines in  FIG. 2 ) which is mounted to a rotating part, normally a wheel axle of the vehicle and with which the brake unit is to brakingly cooperate. 
     A brake disc engaging assembly  3  is connected to the main body  1  in such a manner that minor axial movements of the brake disc D relative to the main body are allowed during service. 
     The design for the mounting of the brake unit in the vehicle does not form a part of the concept set forth herein and is not further illustrated and described. 
     Referring then mainly to  FIG. 2 , the main body  1  has a housing  4  and a cover  5  attached thereto. Also the motor  2  is attached thereto. 
     A first brake pad holder  6 , provided with a replaceable brake pad  7 , is part of the brake disc assembly  3 . A second brake holder  8 , provided with a replaceable brake pad  9 , is slidably arranged on guide rods  10  attached to the first brake pad holder  6 . A brake lever  11  is pivotally connected at its central part to the brake disc assembly  3 . The end to the left in the drawings of the brake lever  11  is pivotally connected to the second brake holder  8 , whereas its end to the right in the drawings is pivotally connected to a brake head  12 . Return springs  13  are arranged around the guide rods  10  between the two brake holders  6 ,  8  for biasing them apart. 
     By this design, a movement downward in  FIG. 10 f    the brake head  12  will cause the second brake pad holder  8  to move in the direction towards the first brake pad holder  6  for effecting a braking engagement of the brake pads  7  and  9  with the brake disc D rotating between these pads. A return movement will then be effected by the return springs  13 . 
     The electric motor  2  has an outgoing, rotating shaft  14  ( FIG. 2 ) in gear engagement with rotatable planet wheels  15 , which at their outer peripheries are in gear engagement with a fixed ring wheel  16 . The planet wheels  15  are journalled in a planet holder  17 , preferably journalled by a radial ball bearing  18  in the main body  1 . The planet holder  17  is provided with an outgoing drive pinion  19 , whose rotational speed is considerably reduced by the described planetary gearing in relation to the rotational speed of the motor  2 . 
     The reducing gear between the motor  2  and the outgoing drive pinion  19  may however be of various designs. 
     A gear wheel  20 , preferably with considerably larger diameter than the drive pinion  19 , is in gear engagement with the drive pinion  19 . A cylindrical control shaft  21  is journalled for rotation in two shaft supports  22  in the cover  5 . 
     A drive bridge  23  is guided by the housing  4  and the cover  5  for longitudinal movements downwards and upwards in  FIG. 2 . Powerful compression springs  24  are arranged between the drive bridge  23  and the cover  5  for exerting—as will appear more clearly below—a brake applying force downwards in  FIG. 2 . 
     The central portion of the control shaft  21  is formed as an eccentric or cam  25  cooperating with an opening in the drive bridge  23  with such a shape that a rotation of the control shaft  21  with its eccentric  25  from the shown rest position with the drive bridge  23  in its uppermost position and the springs  24  compressed will enable the drive bridge  23  to move slightly downwards in  FIG. 2  under the action of the springs  24 . As there is a mechanical connection (to be described) between the drive bridge  23  and the brake head  12 , such a movement can result in a movement downwards of the brake head  12  and a pivotal movement of the brake lever  11  in a brake applying direction. 
     The parts  21 ,  23 ,  25  can together be called an eccentric mechanism. 
     The brake head  12  is provided with a nut rod  26  extending upwards in  FIG. 2 . This nut rod  26  is provided with an external threaded nut portion  26 ′ in internal thread engagement with a rotatable adjuster tube  27 . 
     In an appropriate compartment in the drive bridge  23  there is above the adjuster tube  27  provided a piston  28 , a pressure medium  29 , and a pressure transducer  30 . During operation of the device, the force from the drive bridge  23  is accordingly transmitted to the brake head  12  via the pressure medium  29 , the piston  28 , the adjuster tube  27 , and the nut rod  26  with its nut portion  26 ′. The transmitted force is sensed by the pressure transducer  30  and is used to control the operation of the electric motor  2  for obtaining the desired brake characteristic. 
     The parts  28 - 30  can together be called a load cell. 
     The rotatable adjuster tube  27  (in engagement with the nut portion  26 ′ of the nut rod  26 ) is part of a slack adjuster device now to be described. 
     Selectively connected to the drive pinion  19  over an electromagnetic clutch  31  is a bevel gear wheel  32 , forming a right angle gear with an adjuster tube gear wheel  33 . This letter gear wheel  33  has a splines connection to the adjuster tube  27 , so that rotation of the gear wheel  33  will impart a rotation to the adjuster tube  27  but that relative axial movement is allowed. There is a compression spring  34  biasing the gear wheel  33  downwards in  FIG. 2 . 
     When the rotational movement of the eccentric  25  is indicated to be too long in relation to the desired brake force, which is an indication of worn-off brake pads  7 ,  9 , the electromagnetic clutch  31  will engage, so that rotary motion is transmitted from the drive pinion to the adjuster tube  27  over the right angle gear  32 ,  33 , pushing the nut rod  26  and thus the brake head  12  slightly downwards for compensating for the wear of the brake pads  7 ,  9  and of the brake disc D. 
     The parts  26 ,  26 ′,  27 ,  31 - 34  can together be called a slack adjuster device. 
     An exemplary block brake unit is schematically shown in  FIG. 3 . Shown herein is a housing  40  with an ear  40 ′ for the attachment of the brake unit to a rail vehicle to be braked. In the housing  40  an eccentric mechanism  41  is axially movable, acted on by a powerful spring  42 . Controlled by the eccentric mechanism  41 , as will be described, the force from the spring  42  can be transmitted via a load cell  43  and a slack adjuster device  44  to a brake block  45  to be brakingly applied against a wheel W of the vehicle, on which the brake unit is mounted. 
     The eccentric mechanism  41  has a shaft  46 , which is journalled for rotation in the housing  40  and can be rotated by a motor (not shown). The eccentric mechanism  41  is provided with open sides or axial long-holes for allowing axial movement thereof. The eccentric is here illustrated as a roller  47  contained in a transverse slot  41 ′ in the eccentric mechanism  41 . The roller  47  is connected to a lever  48  which is attached to the shaft  46 . By rotating the shaft  46  an angle α by means of the motor, the eccentric assembly  41  will be allowed to move forward or to left in the drawing under the action of the spring  42 . Also, the roller  47  can itself generate a brake force to the left in the drawing by its engagement with the left side of the slot  41 ′. 
     One or more compression springs  24 ,  42  are used in the two described embodiments, but generally any spring means can be utilized. 
     The means for controlling the eccentric mechanism is shown and described as an electric rotary motor, but generally any motor can be utilized. 
     The teachings herein have been exemplified by a disc brake unit and a schematic block brake unit, but generally the concept can theoretically be embodied in any brake actuator (without load cell and/or slack adjuster device). 
     The electric motor has been described as providing a rotary control movement for the eccentric or cam, but the design is such that the force from the motor can be added as a brake force to the force of the spring means. 
     A favorable aspect of the described embodiments is that thanks to the design with the eccentric mechanism near its equilibrium (as is illustrated in  FIG. 3 ) the great forces from the spring means may be controlled by a small motor.