Abstract:
The brake assembly includes a motor shaft connected to a friction disk assembly. Springs housed in a field cup assembly, frictionally link a clapper plate assembly and friction disk assembly against a mounting plate to activate the brake. To disengage the brake, the field cup assembly magnetically attracts the clapper plate thereto and the friction disk assembly is free to rotate. For manual release, rotation of a lever arm against a reaction plate compresses a wave spring to generate an opposing force which overcomes the springs, thereby forcing the clapper plate assembly away from the friction disk assembly to allow rotation thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/324,812, filed Sep. 24, 2001, which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The subject invention relates to brakes, and more particularly to an improved system for power off brakes with manual releases.  
         BACKGROUND OF THE RELATED ART  
         [0003]    Power-off brakes are known in which electrical current to the brake serves to release the brake, which is otherwise activated. Such power-off brakes may be used when it is desirable that the brake be applied in the event of a power failure. For example, an electric wheelchair would desirably be braked in the event of a power failure to prevent accidental movement. However, subsequent movement of the wheelchair is often desired even though the power is off. Hence, there is a need to have the ability to manually release the power-off brake. U.S. Pat. No. 5,915,507 issued Jun. 29, 1999, which is incorporated herein by reference in its entirety, discloses a power-off brake with manual release. Further exemplary brake and brake-related patents include U.S. Pat. No. 6,161,659, issued Dec. 19, 2000; U.S. Pat. No. 6,125,975, issued Oct. 3, 2000; U.S. Pat. No. 5,979,630, issued Nov. 9, 1999; and U.S. Pat. No. 6,047,805, issued May 11, 2000, each of which is incorporated by reference herein in its entirety. Still further exemplary brake and brake-related patent applications include commonly assigned U.S. patent application Ser. No. 09/528,690, filed Mar. 20, 2000; U.S. patent application Ser. No. 09/841,507 filed Sep. 2, 2001; and U.S. patent application Ser. No. 09/773,722 filed Jan. 31, 2001, each of which is incorporated by reference herein in its entirety.  
           [0004]    There are problems associated with prior art manual release brake mechanisms. Although they recognize the need to alleviate close manufacturing tolerances, and minimize the effects of wear, binding and/or poor release, each of these problems remains prevalent. There is a need, therefore, for an improved manual release mechanism which permits easy operation and assures adequate performance.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the present disclosure to provide a manual release brake mechanism which provides flexible contact to thereby reduce the need for exact manufacturing tolerances and which will minimize component wear.  
           [0006]    It is another object of the present disclosure to provide a manual release mechanism which generates a substantial amount of release pressure compared to the effort required to actuate the mechanism.  
           [0007]    In one embodiment, a brake includes a manual release mechanism. The manual release mechanism has a lever arm for engaging a reaction plate wherein the rotational motion of the lever is translated into axial motion of the reaction plate which then compresses a bias element. The compression of the bias element generates a manual release force which opposes a braking force generated against a brake element by brake springs. When the manual release force overcomes the braking force, the brake element moves toward the lever arm to disengage the brake.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    So that those having ordinary skill in the art to which the disclosed system appertains will more readily understand how to make and use the same, reference may be had to the drawings wherein:  
         [0009]    [0009]FIG. 1 is an exploded front perspective view showing the components of one representative embodiment of a brake assembly constructed in accordance with the subject disclosure.  
         [0010]    [0010]FIG. 2 is an exploded rear perspective view showing the components of the brake assembly of FIG. 1.  
         [0011]    [0011]FIG. 3 is a perspective view of the brake assembly of FIG. 1 in an assembled state.  
         [0012]    [0012]FIG. 4 is a front view of the assembled brake assembly of FIG. 1 in the operational position.  
         [0013]    [0013]FIG. 5 is a cross-sectional view of the brake assembly taken along line  5 - 5  of FIG. 4.  
         [0014]    [0014]FIG. 6 is a cross-sectional view of the brake assembly taken along line  6 - 6  of FIG. 4.  
         [0015]    [0015]FIG. 7 is a front view of the assembled brake assembly of FIG. 1 in the manually released position.  
         [0016]    [0016]FIG. 8 is a cross-sectional view of the brake assembly taken along line  8 - 8  of FIG. 7.  
         [0017]    [0017]FIG. 9 is a cross-sectional view of the brake assembly taken along line  9 - 9  of FIG. 7.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]    The present invention overcomes many of the problems associated with prior art manual release brakes. The advantages, and other features of the system disclosed herein, will become more readily apparent to those having ordinary skill in the art from the following detailed description of certain preferred embodiments taken in conjunction with the drawings which set forth representative embodiments of the present invention and wherein like reference numerals identify similar structural elements.  
         [0019]    Referring to FIGS. 1 and 2, there is shown one representative brake assembly constructed in accordance with the subject disclosure and designated generally by reference numeral  17 . In general, the brake assembly  17  includes a mounting plate assembly  30  housing a plurality of components and mounting the brake  17  to a motor (not shown) as is well known to those of ordinary skill in the pertinent art. In one embodiment, the brake assembly  17  is used on an electrical motor which powers a wheelchair. The mounting plate  30  is preferably a generally cylindrical cup with a rearward opening recess  33 . The rearward opening recess  33  is defined by a bottom portion  34  of the mounting plate  30 . The bottom portion  34  also defines three throughbores  35  for receiving threaded fasteners  37 . Tabs  32  of the mounting plate assembly  30  operatively couple the brake  17  to the motor. Preferably, the mounting plate  30  is die cast aluminum. The mounting plate  30  houses a friction disk assembly  50  adjacent to the bottom portion  34 .  
         [0020]    The friction disc assembly  50  includes a body portion  52  and an annular friction ring  54 . The body portion  52  has a hub  56  with a keyway  58  having two flats  60 . The annular friction ring  54  can be any type of friction material which facilitates frictional linkages as is well known to those of ordinary skill in the pertinent art. Preferably, the annular friction ring  54  is a high coefficient friction material as disclosed in U.S. Pat. No. 6,161,659 which is included herein by reference. Preferably, the body portion  52  of the friction disk  50  is die cast aluminum. The hub  56  which extends at least partially into the recess  33  of the mounting plate  30  couples to the drive shaft of the motor such that the friction disk assembly  50  rotates with the drive shaft but is free to move axially. When the brake  17  engages, the friction disc assembly  50  is biased by a clapper plate assembly  70  against the mounting plate  30  to create a frictional linkage therewith which arrests the drive shaft.  
         [0021]    A field cup assembly  90  selectively pushes the clapper plate  70  into engagement with the friction disk  50 . The field cup assembly  90  includes a front face  92  and a rear face  94 . The front face  92  of the field cup  90  includes tapped holes  96  for bolting the field cup  90  in position, preferably onto the mounting plate  30 . When assembled, the field cup  90  is secured to the mounting plate  30  and the axial distance is set by standoffs  93  with the clapper plate  70  therebetween. The front face  92  of the field cup  90  also comprises three bores  98  to receive three springs  100  (only two shown for simplicity). Each bore  98  is shallower in depth than the height of the spring  100  in order to fix the spring  100  in place while still allowing a portion of the spring  100  to extend out of the bore  98 . Thus, the three springs  100  within the bores apply force to bias the clapper plate  70 . The field cup  90  is presently preferably constructed of steel or other ferromagnetic material in order to conduct magnetic flux.  
         [0022]    Preferably, the field cup  90  is made from lathed magnetic steel. The clapper plate  70  is preferably a stamped steel disk. The clapper plate  70  is free to move axially. The clapper plate assembly  70  is constructed of steel or other ferromagnetic material in order to interact with magnetic flux as is known in the art. The magnetic flux generated by the field cup assembly  90  is at least sufficient to attract the clapper plate  70  to overcome the bias of the three springs  100  when energized. For creating the magnetic field, the field cup  90  includes a redundant coil assembly  102  which creates the magnetic field (see FIG. 5). The coil  102  includes electrical leads  104  for passing current therethrough to create the magnetic field.  
         [0023]    In normal operation, when the brake assembly  17  is engaged, (i.e. deenergized), the clapper plate  70  is frictionally linked to the friction disc assembly  50  by the three springs  100 . When the brake assembly  17  is disengaged, the clapper plate assembly  70  is pulled against the front face  92  of the field cup  90  by the force of the magnetic field generated thereby. In one presently preferred embodiment, cut outs  72  in the clapper plate  70  are provided to allow clearance for the standoffs  93 .  
         [0024]    In addition to the above features, the brake  17  can be manually released, (i.e. released without the use of electrical power to the field cup  90 ). The manual release mechanism, includes a lever arm assembly  110  coupled to the clapper  70  by a shaft  112 . The shaft  112  includes an o-ring  114  to insure a proper fit and a retaining ring  115  for retaining the front end within the clapper  70  and a shoulder  113  formed on the rear end to retain the shaft  112  within a central bore  119  of the lever arm  110 . In another embodiment, the shaft  112  is integral with lever arm assembly  112 .  
         [0025]    The lever arm  110  houses a reaction plate assembly  130  and a wave spring  140  to facilitate the manual release of the brake  17 . The reaction plate  130  is adjacent the lever arm  110  and the wave spring  140  is adjacent the field cup  90 . The reaction plate  130  is a generally spherically shaped disk having a channel in a front side  134  for receiving the wave spring  140 . Preferably, the reaction plate  130  is zinc die cast, powder metal cast or bronze cast. The rear face  94  of the field cup  90  defines an annular channel  106  for locating the wave spring  140 . The rear face  94  also defines a central opening  95  for receiving the shaft  112 .  
         [0026]    The reaction plate  130  forms tabs  136  which are received between bosses  38  mounted on the forward side of the mounting plate  30  to prevent rotation of the reaction plate  130  while still allowing the reaction plate  130  to move axially. In another embodiment, the reaction plate  130  is keyed to the field cup assembly  90  to prevent rotation. Preferably, anti-rattle springs  132  are positioned between the tabs  136  of the reaction plate  130  and the mounting plate  30  to prevent looseness of the reaction plate  130  which may generate undesirable rattle. Preferably, the anti-rattle springs  132  apply light axial pressure to the reaction plate  130  in the direction of the lever arm  110 . The anti-rattle springs  132  ideally have a low spring rate in order to give the lever arm  110  a feel that is not loose and allows for some axial tolerance stack-up without reducing the torque of the brake  17  by greatly opposing the springs  100 .  
         [0027]    The rear side  135  of the reaction plate  130  forms six groups of indentations for interacting with the lever arm assembly  110 . Each group of indentations includes a central major indentation  142  with adjacent minor indentations  144  on each side thereof. The adjacent minor indentations  144  create a positive lock on the manually released position as will be described further below. In another embodiment, there are no adjacent minor indentations. The number of groups of indentation may be varied and still achieve the desired results as would be appreciated by those of ordinary skill in the art upon review of the subject disclosure.  
         [0028]    The lever arm  110  is a generally cup-shaped body  118  having a handle  120  extending radially therefrom. It is envisioned that the handle  120  will be manually activated although it will be appreciated that the handler  120  may also be activated by an apparatus. Six ramps  122  are defined on the rearward inner face  124  of the lever arm  110  for interacting with the groups of indentations of the reaction plate  130 . The ramps  122  extend out radially from a central boss  128  formed on the lever arm  110  about the central opening  119 . The bore  138  of the reaction plate  130  will pivot on the central boss  128  formed for holding the components concentric. Preferably, the lever arm  110  is molded plastic.  
         [0029]    In a preferred embodiment, an electrical board is mounted to the mounting plate  30  with conventional fasteners. The electrical board interfaces with a controller via electrical leads  150  (see FIG. 3) and includes hall effect sensors for determining the position of the lever arm  110 . Magnets (not shown) attached to the lever arm  110  interact with the hall effect sensors to provide a signal indicating the position of the lever arm  110 . The two positions of the lever arm assembly  110  are operational (i.e., not manually released) and manually released. It will be appreciated by those skilled in the art that any suitable sensor such as an optical sensor may be used to determine the location of the lever arm  110 .  
         [0030]    Referring now to FIG. 3, when assembled, the mounting plate  30  and lever arm  110  couple to substantially enclose the components of the brake  17  and prevent inadvertent pinching and maintain cleanliness. The shaft  112  passes through the central opening  119  of the lever arm  110 , the reaction plate  130 , the wave spring  140 , the field cup  90  and the clapper  70 . The shoulder  113  on the shaft  112  retains the shaft  112  in the central opening  119  of the lever arm  110 . The retaining ring  115  secures the rearward end of the shaft  112  to the front side  72  of the clapper plate  70  while allowing each component to move rotationally and axially. The threaded fasteners  37  couple the field cup  90  to the mounting plate  30  which is secured by the tabs  32  to a stationary portion of the apparatus upon which the brake  17  is utilized. The brake  17  is preferably attached to the motor housing. Hub  56  of the friction disk  50  couples to the drive shaft of the motor as would be appreciated by those of ordinary skill in the pertinent art based upon review of the subject disclosure.  
         [0031]    Referring now to FIGS.  4 - 6 , in normal operation, i.e., with the manual release mechanism not affecting operation, the ramps  122  of the lever arm  110  are received within the major indentations  142  of the reaction plate  130 . When no power flows through the coil  102 , the brake  17  is engaged. The springs  100  move the clapper plate  70  towards the friction disc  50 . The clapper plate  70  engages the friction disk  50  to move the friction disk  50  towards the mounting plate  30 . As a result, the friction disc  50  frictionally engages the mounting plate  30  and the clapper plate  70 . The frictional links between the clapper plate  70  and the friction disk assembly  50 , and the friction disk  50  and the mounting plate  30  prevent the friction disc assembly  50  and thereby the drive shaft of the electrical motor from rotating. Under these conditions, the brake assembly  17  is in a static engaged state, i.e. no current passes through the coil  102 . The three springs  100  supply the energy to the clapper plate  70  to hold the friction disc  50  against the mounting plate  30  and thereby the drive shaft of the electrical motor.  
         [0032]    In the static engaged operational state, the ramps  122  of the lever arm  110  remain within the major indentations  142  of the reaction plate  130  to minimize the combined height of these two components. Hence, the compression of the wave spring  140  and resulting force generated by the wave spring  140  is reduced to a level below the force generated by the springs  100 . As a result, the coupling between the lever arm  110  and clapper plate  70  by the shaft  112  does not limit the effect of the springs  100  on the clapper plate  70 .  
         [0033]    To electrically disengage the brake assembly  17 , the controller sends current through the coil  102  of the field cup  90 . The current passing through the coil  102  creates a magnetic field having flux lines. Generally, the flux lines radiate out from the field cup  90 , cross through the clapper plate  70  and return to the field cup assembly  90  to complete a circuit. The magnetic field attracts the clapper plate  70  towards the front face  92  of the field cup  90 . In effect, the field cup  90  acts as a powerful magnet pulling the clapper plate  70  against the front face  92  despite the force of the springs  100 . As a result, the springs  100  become compressed until the clapper plate  70  contacts the front face  92 . When the clapper plate  70  engages the field cup assembly  90  in this manner, a gap is formed between the clapper plate  70  and the friction disk  50 . No frictional linking occurs between the clapper plate  70  and the friction disk  50  because of the gap. As a result, the friction disc assembly  50  is free to rotate with the drive shaft of the electrical motor without mechanical interference.  
         [0034]    To engage the brake  17  again, the controller stops the flow of current to the field cup assembly  90 . The holding power of the magnetic field decreases greatly and the clapper plate assembly  70  is biased towards the friction disk  50  by the springs  100 . Eventually, the magnetic field continues to degrade because of the increased distance from the front face  122  of the field cup assembly  90  and the lack of current to the coil  102  until the magnetic field from the field cup  90  becomes non-existent and the springs  100  bias the clapper plate  70  against the friction disc  50  as described above.  
         [0035]    Referring now to FIGS.  7 - 9 , to manually disengage the brake assembly  17 , the handle  120  of the lever arm  110  is rotated. The rotation may be in either direction because minor indentations  144  are located on both sides of the major indentations  142 . Similarly, in an embodiment with no minor indentations, the rotation may be in either direction. A stop  39  may be secured to the mounting plate  30  to limit the rotation to a single direction. The stop  39  mounts within a hollow  117  formed between bumper features  121  on the lever arm  110  to limit over travel and restrict manual disengagement to only one direction of rotation of the handle  61  of the lever arm assembly  110  as best shown in FIGS. 1 and 2. The stop  39  may be a roll pin, socket head cap screw and the like as would be appreciated by those of ordinary skill in the pertinent art. An additional bore  40  is formed in the mounting plate  30  to allow for varying the selection of the direction of rotation of the lever arm  110  while still allowing restriction of over travel.  
         [0036]    As the handle  120  is rotated, the ramps  122  of the lever arm  110  cam out of the major indentations  142  of the reaction plate  130 . Preferably, a positive lock of the manually release position occurs as the ramps  122  come to rest in the minor indentations  144 . The shallower depth of the minor indentations  144  generates an axial movement of the reaction plate  130  towards the mounting plate  30 . Preferably, the movement of the reaction plate  130  is greater than the axial air gap between the clapper plate  70  and field cup assembly  90  when in the electrically disengaged state.  
         [0037]    The movement of the reaction plate  130  generates an axial force upon the wave spring  140  causing the wave spring  140  to compress. The compression of the wave spring  140  generates a wave spring force. Preferably, the wave spring  140  has a very high spring rate and even a few thousands of compression generates significant force. The wave spring force opposes the force generated by the springs  100  which is at the front portion of the brake  17  applying pressure to the clapper plate  70 . The wave spring force is transmitted to the springs  100  through the reaction plate  130  to the lever arm  110  which is coupled to the clapper plate  70  by the shaft  112  and retaining ring  115 . When the wave spring force exceeds that of the force generated by the springs  100 , the pull on the clapper plate  70  overcomes the springs  100 . As a result, the clapper plate  70  moves toward the lever arm  110 . The springs  100  are compressed and the air gap between the clapper plate  70  and friction disk  50  reforms. Hence, the friction disk  50  and thereby the drive shaft become free to rotate. Further, the compression of the wave spring  140  generates additional clearance which loosens manufacturing tolerances and allows for continued operation after wear of components such as, without limitation, the ramps  122  of the lever arm  110  and indentations  142 ,  144  of the reaction plate  130 .  
         [0038]    The brake  17  generates significantly more force than is nominally required for release. The compression of the springs  100  and wave spring  140  determines the distance of travel and such a distance of travel allows for wear of ramps and, consequently, long life as well as acceptable manufacturing tolerances. The reasonably loose tolerancing of the component parts allows for cost efficient manufacturing. Preferably, the brake assembly does not bottom out when compressing the wave spring  140  or springs  100  and therefore the maximum axial force which the lever arm  110 , shaft  112  or retaining ring  115  endures is equal to the force generated by the wave spring  140  when at maximum compression (i.e. minimum height). By adjusting ramp height and contour of the contact surface as well as adding lubricants, coatings, and proper selection of fabrication materials, extensive life and less forceful operation are obtained. For cost effectiveness, molded parts should be chosen to form features without adding to the part count or requiring additional machining.  
         [0039]    It will be appreciated by those of ordinary skill in the art upon review of the subject disclosure that the cam action of the ramps  122  with the groups of indentations may be done with other features such as, without limitation, a ball bearing-cavity combination. It will be appreciated by those of ordinary skill in the art upon review of the subject disclosure that the springs  100  and wave spring  140  may be substituted by any type of bias element with sufficient spring rate and force such as, without limitation, flexure springs, leaf springs elastomeric or rubber bumpers and the like.  
         [0040]    While the invention has been described with respect to preferred embodiments, those skilled in the art will readily appreciate that various changes and/or modifications can be made to the invention without departing from the spirit or scope of the invention as defined by the appended claims.