Abstract:
A spring-actuated, hydraulically releasable brake has a brake disc extending between first and second brake pads, a spring assembly urging the first pad towards the brake disc, a hydraulic piston and cylinder assembly for causing a brake releasing displacement of the first pad from the brake disc against the action of the spring assembly and a brake wear adjustment mechanism including an adjustable connection between the first brake pad and the piston and cylinder assembly, a force transmitting motion amplifier responsive to the releasing displacement, a rotatably adjustable connection provided between the piston and the first brake pad and operatively controlled by the force transmitting motion amplifier and a lost motion connection and a one-way clutch between the motion amplifier and the adjustable connection.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to brakes and, more particularly, to spring-actuated, hydraulically releasable brakes, including single spring stack sliding caliper brakes and dual spring stack fixed caliper brakes. 
     2. Description of the Related Art 
     Spring-actuated, hydraulically releasable brakes are known which employ actuating springs to urge brake pads against brake discs and hydraulic piston and cylinder assemblies for releasing the brake pads from fictional engagement with the brake discs against the action of the springs. 
     After repeated use, the brake pads become worn and consequently the effectiveness of the brakes is reduced. However, due to the high braking capacities, direct acting functions and small retracted lining clearances of spring-actuated, hydraulically releasable brakes, automatic wear adjusters have not been common in such brakes. Not only does lack of adjustment of the brakes result in reduced braking capacities, but it can also severely reduce the fatigue life of the actuating springs. It has therefore usually been necessary to counteract brake pad or lining wear by manual adjustment of the brakes. However, manual brake adjustment is time-consuming and risky. 
     BRIEF SUMMARY OF THE INVENTION 
     It is, accordingly, an object of the present invention to provide a novel and improved spring-actuated, hydraulically releasable brake which is maintained in proper adjustment, regardless of lining wear and without manual adjustment of the brake. 
     According to the present invention, there is provided a spring-activated, hydraulically releasable brake having first and second brake pads, located at opposite sides of a brake disc, with springs urging the first brake pad against the brake disc, a hydraulic piston and cylinder assembly operable to displace the first pad from the brake disc against the action of the springs, and an automatic brake adjustment mechanism responsive to the amount of the displacement of the first brake pad from the brake disc by the hydraulic piston and cylinder assembly for adjusting the first brake pad toward the brake disc when such displacement exceeds a determined amount. 
     In a preferred embodiment of the invention, the automatic brake adjustment mechanism includes a pivotable member in the path of movement of the piston of the hydraulic piston and cylinder assembly, and a link extending between the pivotable member and a one-way clutch. A lost motion connection is provided between the linkage and the one-way clutch, so that the latter is operated to rotate a shaft extending from the one-way clutch to the piston rod of the piston only when the predetermined amount of the displacement is exceeded. A threaded connection is provided between the shaft and the piston rod, so that rotation of the piston rod shaft causes longitudinal adjustment movement of the piston rod and, therewith, of the first brake pad toward the brake disc. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more readily understood from the following description of preferred embodiments thereof given, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1A shows a view taken in vertical cross-section through a spring-actuated, hydraulically releasable brake embodying the present invention in a released condition; 
     FIG. 1B shows a plan view of the brake as shown in FIG. 1A; 
     FIG. 2B shows a view corresponding to that of FIG. 1A, but with the brake in a spring-actuated condition; 
     FIG. 2B shows a plan view of the brake as shown in FIG. 2B; 
     FIG. 3A shows a view corresponding to that of FIG. 1A, but with the brake out of adjustment; 
     FIG. 3B shows a plan view of the brake as shown in FIG. 3A; 
     FIG. 4 shows a view in perspective of a mechanical motion sensor in perspective; 
     FIG. 5 shows a view in vertical cross-section through a dual spring stack caliper 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1A and 1B there is shown a single spring stack sliding caliper brake indicated generally by reference numeral  10  which has a brake body  12  formed with a downwardly-open cylindrical recess  14  and with an upwardly open cylindrical recess  16 . A piston  18  in the cylindrical recess  16  has a piston rod  20  which extends downwardly from the piston  18  through an intermediate cylindrical boring  22  into the cylindrical recess  14 . 
     The piston rod  20  has a downwardly-open axial opening  24  and is connected to a plunger  26  by an adjustable connection in the form of screw threads  28  formed on the interior of the piston rod  20  and the exterior of the plunger  26 . At its lower end, the plunger  26  has a backing plate  30 , on which is provided a first brake lining or pad  32 . A brake disc  34  extends between the first brake pad  32  and a second brake lining or pad  36  on a caliper arm  38 . 
     A shaft  40 , which is coaxial with the piston rod  20  and the plunger  26 , extends downwardly into an upwardly open recess  42  in the plunger  26  and is longitudinally slidably connected to the plunger  26  by means of a transverse pin  44  extending through the plunger  26  and through a downwardly open slot  46  in the lower end of the shaft  40 . 
     A hexagonal nut  48 , in threaded engagement with the upper end of the shaft  40 , secures a one-way clutch, indicated generally by reference numeral  50 , between the nut  48  and a disc  52  seated on the top of the piston  18 . 
     A mechanical force transmitting motion amplifier, indicated generally by reference numeral  54 , is mounted on the brake body  12 , and is illustrated in greater detail in FIG.  4 . As shown in FIG. 4, the motion amplifier  54  has a pivotable member or block  56 , which is pivotal about a pivot pin  58 , opposite ends of which are secured in a bracket  60  mounted on the brake body  12 . As shown in FIG. 1A, the pivotal block  56  is undercut at its lower side to form a projecting nose  62 , which rests on the top of the piston  18  so that, as the piston  18  is displaced upwardly, the pivotal block  56  pivots in an anticlockwise direction, as viewed in FIG. 1A, about the pivot pin  58 . The pivotal block  56  is biased in a clockwise direction about the pivot pin  58  by a helical compression spring  64  acting between the bracket  60  and the pivotable block  56 , so that the nose  62  is pressed against the top of the piston  18 . 
     The shaft  40  is provided with a projecting adjustment pin  66  which extends into a slot  68  formed in one end of a link  70 , the opposite end of which is secured to a pivot pin  72  extending through the pivotable block  56 . Consequently, the pivotal movement of the pivotable block  56  causes the link  72  move relative to the pin  66 , as described in greater detail below. The pin  66  and the slot  68  form a lost motion connection between the link  70  and the one way clutch  50 . 
     The plunger  26 , and therewith the backing plate  30  and the first brake pad  52 , are urged toward the brake disc  34  by an assembly of disc springs  76  provided in the cylindrical recess  14 , the lower end of this assembly being seated on an annular shoulder  78  on the lower end of the piston rod  20 . 
     The operation of the brake  10  is as follows: 
     When hydraulic fluid is supplied under pressure through a hydraulic port  80  into the cylindrical recess  16 , the piston  18  is displaced upwardly, as viewed in FIG. 1A, and the piston rod  20  and, therewith, the first brake pad  32  are raised against the action of the springs  76  to provide a clearance  82  between the first brake pad  32  and the brake disc  34 . The consequential pivotation of the pivotal block  56  displaces the link  70  to the left, so that the pin  66  becomes located at the right-hand end of the slot  68 . 
     The pivotal block  56  thereby acts as a force transmitting motion amplifying lever, which causes the movement of the link  70  to be amplified with respect to the upward displacement of the piston  18 . Therefore, the relatively small clearance  82  between the first brake pad  32  and the brake disc  34  is amplified by the motion amplifier  54  to an amount which can be better utilized for adjustment of the brake and which makes the adjustment less sensitive to manufacturing clearances and additional clearances between moving parts caused by wear. 
     When the hydraulic pressure is removed, the springs  76  urge the first brake pad  32  against the brake disc  34 , so that the clearance between them is reduced to zero. The link  70  is thereby displaced to the right, as shown in FIG. 2A, so that the pin  66  becomes located at the left-hand end of the slot  68 . The length of the slot  68  is selected to correspond to the amount of the displacement of the link  70  when the brake  10  is properly adjusted. Consequently, when the brake is fully adjusted, no motion is transferred from the link  70  to the adjusting pin  66 . 
     FIG. 3A shows the brake  10  with the hydraulic pressure removed, so that the brake is spring-applied. In this case, the operation of the brake has caused wear of the brake pad  32 , and the brake  10  is therefore out of adjustment by the amount of the wear of the brake pad  32 . This wear causes extra downward displacement of the piston  18 , and consequentially provides movement to the right of the link  70  through a distance greater than the length of the slot  68 , so that the adjusting pin  66  is correspondingly deflected to the right, by the action of the spring  64  acting through the link  70 . The force thereby applied to the link  70  is sufficient to cause rotation of an outer case  86  of the one-way clutch  50 . 
     When the brake  10  is next released, hydraulic pressure is again applied to the piston  18 , thereby returning the pivotal block  56  and the link  70  to the positions in which they are shown in FIGS. 2A and 2B. Although the piston  18  may extend to an out of adjustment condition, it always returns to the same position on release of the brake. 
     The adjusting pin  66  and, thereby, the outer case  86  of the one-way clutch  50  are subsequently deflected in the opposite direction during the motion of the piston  18  on release of the brake  10 , and the one-way clutch  50  is thereby locked, to cause the outer case  86  to be locked to the shaft  40 , so that the shaft  40  is correspondingly rotated until the piston motion is complete. 
     This rotation of the shaft  40  is transmitted through the pin  44  to the plunger  26 , and as a result of the threaded engagement of the screw threads  28  on the plunger  26  and the piston  20 , the plunger  26  is thereby adjusted longitudinally relative to the piston rod  20  toward the brake disc  34 , thereby reducing the amount of the out of adjustment. The piston rod  20  is retained by the action of the springs  76  from rotating with the shaft  40 . 
     This automatic adjustment will continue during the subsequent cycles of operation of the brake until the motion of the link  70  is equal to the length of the slot  68  and, therefore, no further deflection of the adjusting pin  66  occurs. 
     As shown in FIG. 4, a compression spring  90  is provided between the pivotal block  56  and a spring clip  92  at one end of the pivot pin  72 . The compression spring  90  biasses the link  70  axially of the pivot pin  72  towards the one-way clutch  50  to maintain the interengagement of the pin  66  and the slot  68 , and the pivot pin  72  can be manually displaced axially of the pivot pin  72  against the action of the spring  90  to disengage the link  70  from the adjustment pin  66  and thereby to disengage the lost motion connection between the link  70  and the one-way clutch  50 . Manual adjustment of the brake can then be effected by using the hexagonal nut  48  to turn the one-way clutch  50 . Such manual adjustment is required for approximate initial adjustment of the brake and for returning the plunger  26  to a fully retracted position when the brake pads  32  and  36  are replaced. 
     FIG. 5 shows a dual spring stack fixed caliper brake which comprises two brake mechanisms, indicated generally by reference numerals  10 A and  10 B, which as will be readily apparent each correspond to the above-described brake  10 , and in which components identical to those described above with reference to FIG. 1A have, for convenience of illustration, being indicated by reference numerals which correspond to those of FIG. 1A, with the addition of the suffixes A and B. 
     In FIG. 5, the second brake pad  36  and the caliper arm  38  of FIG. 1A are replaced by the brake mechanism  10 B, the brake mechanisms  10 A and  10 B being mounted at opposite sides of the brake disc  34 . 
     As will be apparent to those skilled in the art, other modifications may be made in the above-described invention within the scope of the appended claims.