Abstract:
A slack adjustment system for a disk brake includes a biasing member to adjust slack in a brake system. The biasing member operates independently of pressure applied to a brake actuator. A locking member prevents adjustment when adjustment is not necessary. Release of the locking member allows the biasing member to adjust a resting position of brake pads independent of driver applied brake pressure.

Description:
BACKGROUND OF THE INVENTION 
     This application is a continuation in part of U.S. application Ser. No. 10/355,511, filed on Jan. 31, 2003 now U.S. Pat. No. 6,955,246. 
    
    
     The present invention relates to an adjuster mechanism for a brake. 
     As brake pads or a brake disc wear a gap between the brake pads and brake disc increases. Due to the increase in the gap between the brake pads and the brake disc a brake actuator must travel farther to engage the brake. In other words, there is more slack when the brake is applied, which causes the brakes to become less effective. In order to compensate for slack, a slack adjustment mechanism moves the brake pads closer to the brake disc prior to brake engagement. This adjustment assures a consistent amount of actuator travel in spite of brake pad wear. 
     Conventional brake adjuster mechanisms use relatively complex mechanical assemblies to perform this function. Force from the brake actuator is commonly utilized to drive the adjuster mechanism, which may reduce brake effectiveness and efficiency. 
     In addition, the adjuster mechanism may shift while the brake is not being applied. Shifting may cause undesirable brake pad wear, or further increase slack in the brake system, which may reduce the brake performance. 
     Accordingly, it is desirable to provide an adjuster mechanism which is not effective when the brake is not being utilized. 
     SUMMARY OF THE INVENTION 
     The slack adjustment system according to the present invention provides an adjustment mechanism which utilizes a biasing member to adjust slack in a braking system. The biasing member operates independently of the pressure applied by a brake actuator. A locking mechanism is utilized to secure the adjustment mechanism in place when adjustment is not desired. Additionally, the locking mechanism controls the desired amount of slack. 
     The locking mechanism selectively engages an adjustment gear, or any rotational member engaged with the gear, to prevent the gear from being rotated and undesirably adjusting the gap between the brake pad and the brake disc. The locking mechanism prevents adjustment when the brake is not applied. The locking mechanism includes a latch interfitting with the gear to prevent rotation when engaged with the gear. The latch disengages from the gear after a predetermined amount of movement of the latch. Release of the locking mechanism allows the gear to rotate. The biasing member is mounted to engage and rotate the gear when the locking member is not preventing movement. The biasing member is of a type which applies a rotational force independent of the amount of pressure applied by the brake actuator. The biasing member may be a spring, electric motor, air powered motor or the like. 
     The present invention therefore provides a method of automatically adjusting slack independent of the pressure applied to the brake system. In addition, a locking device prevents undesirable adjustment of slack in the brake system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1  is a sectional side-view of a brake assembly with one embodiment of a slack adjustment system according to the present invention; 
         FIG. 2A  is a sectional plan-view of a brake assembly; 
         FIG. 2B  is a perspective view of one embodiment of the slack adjustment system with the latch engaged on a rotational member; 
         FIG. 3  is a sectional plan-view of the slack adjustment system according to the present invention showing a gear moved forward by a distance equal to the desired amount of slack, with the latch still engaged with the rotational member; 
         FIG. 4  is a sectional plan view of the slack adjustment system according to the present invention showing all components in the brake fully applied position; 
         FIG. 5  is a sectional plan-view of the slack adjustment system according to the present invention shown in the disengaged position; 
         FIG. 6  is a sectional end-view of the rotational member and gear-train showing the preferred directions of rotation; 
         FIG. 7A  is a perspective view of one embodiment of the slack adjustment system of the present invention in a non-braking position; 
         FIG. 7B  is a side view of the  FIG. 7A  embodiment of the slack adjustment system of the present invention in a non-braking position; 
         FIG. 8A  is a perspective view of the  FIG. 7A  embodiment of the slack adjustment system of the present invention in a partial braking position; 
         FIG. 8B  is a side view of the slack adjustment system of  FIG. 8A ; 
         FIG. 9A  is a perspective view of the slack adjustment system of the  FIG. 7A  embodiment of the present invention in a full braking position; 
         FIG. 9B  is a side view of the slack adjustment system of  FIG. 9A ; 
         FIG. 10A  shows another embodiment of the slack adjustment system where a locking mechanism is located adjacent a roller; 
         FIG. 10B  shows the  FIG. 10A  embodiment of the slack adjustment system with a lever and roller having a cam mounted on the end of the roller; 
         FIG. 11  shows an embodiment of the slack adjustment system where the locking mechanism has a latch; 
         FIG. 12A  shows a frame for the brake assembly with the latch and the spring; 
         FIG. 12B  shows a frame for the brake assembly with the latch and the first gear; 
         FIG. 12C  shows a frame for the brake assembly with the latch and the screw within the frame; 
         FIG. 13A  shows the cam engaging the latch when no pressure is applied to the lever; 
         FIG. 13B  shows the lever rotating the cam to drive the latch away from the first gear; 
         FIG. 13C  shows the latch and cam when a sufficient amount slack is in the system to disengage the latch from the first gear; 
         FIG. 13D  shows the cam and latch when the roller is fully rotated; 
         FIG. 14  shows the latch and gear when a sufficient amount slack is in the system to disengage the latch from the first gear; and 
         FIG. 15  shows a biasing member engaging the first gear. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a disc brake assembly  10  that utilizes a slack adjustment system  12  of the present invention. The disc brake assembly  10  has a frame  11 , which encloses the internal components and bears the loads generated by them. As a driver operates a brake (not shown) an input load (illustrated by arrow L) is transferred to a lever  14 , through an opening  16  in the frame  11 . The lever  14  is rotatably supported by the frame  11  through a bearing  18 . Applying the input load L rotates the lever  14  about a lever axis  20 . That is, the lever  14  rotates clockwise about the lever axis  20 , as illustrated in  FIG. 1 . 
     A cylindrical roller  22  is recessed within the base of the lever  14 . The roller  22  is eccentrically centered relative the center of rotation of the lever  14 . That is, the roller  22  rotates about a roller axis  24  that is offset from the lever axis  20 . When the input load L causes the lever  14  to rotate about the lever axis  20  the roller  22  rotates about the roller axis  24 . Because the roller axis  24  is offset from the lever axis  20  the roller  22  moves in an arc relative to the lever axis  20  (the position  15  illustrated in phantom shows the extreme of travel available to the lever  14 ). 
       FIG. 2A  shows a first thrust assembly  26  and a second thrust assembly  28 . The eccentric movement of the roller  22  engages the first thrust assembly  26  and the second thrust assembly  28  and applies a load causing the first and second thrust assemblies  26  and  28  to move perpendicularly away from the lever  14 , guided by a housing  61  that is attached to frame  11  by fasteners  34 , (only one shown in  FIG. 1 ). This motion defines a first thrust axis  27  perpendicular to the lever axis  20  and roller axis  24  along which the first thrust assembly  26  moves. The axial movement of the first thrust assembly  26  along the first thrust axis  27  engages the brake pad  30  by way of a first thrust plate  62 . Similarly, axial movement of the second thrust assembly  28  along a second thrust axis  32  engages the brake pad  30  by way of a second thrust plate  60 . The brake pad  30  then engages the brake disc  29 . 
     When the driver releases the brake, the input load L is reduced and a first return spring  31  and second return spring  33  drive the first and second thrust assemblies  26  and  28  to the original positions. The lever  14  and roller  22  also return to the original positions. The first and second return springs  31  and  33  restrain the first thrust assembly  26 , second thrust assembly  28 , roller  22  and lever  14  in the original positions when no input load L is being applied. 
     As a result of use, brake pad  30  wears away and a gap between the brake pad  30  and the brake disc  29  becomes greater over time. The first and second thrust assemblies  26  and  28  must then travel farther to cause the brake pad  30  to engage the brake disc  29 . To eliminate the need for the brake pad  30  to travel further the first and second thrust assemblies  26  and  28  are lengthened to maintain a constant distance between the brake pad  30  and brake disc  29  over time. The first thrust assembly  26  consists of internally threaded first nut  63  and externally threaded first screw  64 . The first nut  63  is rotationally constrained by the housing  61 , such that when the first screw  64  is rotated, the length of the first thrust assembly  26  along the thrust axis  27  is altered. The second thrust assembly  28  has a similar screw and nut arrangement where the second thrust assembly  28  consists of internally threaded second nut  65  and an externally threaded second screw  67  (shown in  FIG. 2B ). The lengths of the first thrust assembly  26  and second thrust assembly  28  are synchronized by a rotational member  48 , which is permanently engaged with the first and second screws  64  and  67  by way of a gear  68 . If no constraint was in place the rotational member  48  might cause rotation of the first and second screws  64  and  67  lengthening the first and second thrust assemblies  26  and  28  until the brake pad  30  and brake disc  29  were touching. 
       FIG. 2B  shows the slack adjustment system  12  with a locking mechanism  42  that selectively engages the gear  68  to prevent the first screw  64  and second screw  67  from being rotated and undesirably adjusting the gap between the brake pad  30  and the brake disc  29 . The locking mechanism  42  includes a latch  54  mounted to a link  56 , which may be a rod or the like, which is fixed to move with lever  14 . The latch  54  may engage the gear  68  on rotational member  48  preventing rotation of the rotational member  48 . The latch  54  engages the gear  68  when the brake is not applied, and when the brake is applied but the first thrust assembly  26  and second thrust assembly  28  have moved by less than the pre-defined slack such that no adjustment is required. 
     When the brake is not applied, or during normal braking movement, as shown in  FIG. 3 , the locking mechanism  42  is engaged and the rotational member  48  cannot rotate to lengthen the first thrust assembly  26  and second thrust assembly  28 . The axial force applied to first screw  64  and second screw  67  by rotation of lever  14  axially drives the first thrust assembly  26  and second thrust assembly  28  along the first and second thrust axes  27  and  32  toward the brake disc  29 . The locking mechanism  42  and latch  54  driven by the lever  14  via a link  56 , move relative to the gear  68  on the outside of the rotational member  48  (shown in  FIG. 3  to be moving along an axis parallel to the first thrust axis  27 , but alternatively could be moved radially away from the first thrust axis  27  by re-arranging the connecting link  56 ). The link  56  may be rotatably connected to the lever  14  such that when lever  14  is driven forward link  56  rotates to maintain the relative position between latch  54  and gear  68  at an equivalent height. 
     The point at which the latch  54  disengages from the gear  68  is determined by the geometry of the link  56 . The geometry is designed such that when a pre-defined slack between the brake pad  30  and disc  29  has been taken up, the latch  54  disengages from the gear  68 . Simultaneously, load starts to be applied to the first thrust assembly  26  and second thrust assembly  28  via the brake pad  30  that engages the brake disc  29 . This load produces a friction torque between the first nut  63  and first screw  64 , and the second nut  65  and the second screw  67 , preventing any relative rotation and, hence, adjustment when the brake is applied, shown in  FIG. 4 . When the brake is released, all components are returned to their original positions by the return springs  31  and  33 . The latch  54  engages gear  68  again and no adjustment of the length of the first thrust assembly  26  and second thrust assembly  28  takes place. 
     As the brake pad  30  wears, the slack between the brake pad  30  and the brake disc  29  increases, and the first thrust assembly  26  and second thrust assembly  28  must move a greater distance along the thrust axis  27  in order to engage the brake pad  30  with the brake disc  29 . To compensate for the wear on the brake pad  30 , the first and second screws  64  and  67  are adjusted to increase the overall length of the thrust assembly  26 , resulting in a constant distance being maintained between the brake pad  30  and brake disc  29 . 
     Referring to  FIG. 5 , the adjuster system  12  of the present invention is utilized to adjust the slack in the brake assembly  10 . When the locking mechanism  42  is released, as shown, the rotational member  48  and first and second screws  64  and  67  can rotate. The rotational member  48  includes a biasing member  44  and the gear  68  mounted in the housing  61 . The biasing member  44  causes the gear  68  to rotate about a biasing axis  46 . The biasing axis  46  is preferably parallel to and offset from the first thrust axis  27 , but could be in any position or angle inside or outside the frame  11  where the rotational member  48  can still be engaged directly or indirectly to the first and second screws  64  and  67 . The biasing member  44  is preferably a coil spring but may take other forms such as an electric motor, air motor, or the like. The gear  68  is mounted about the biasing member  44  and is driven by the biasing member  44  in a first rotational direction  50  about the biasing axis  46 . The gear  68  engages with the first and second screws  64  and  67  preferably by gear teeth, but other means of engagement may be used. The first and second screws  64  and  67  rotate about the thrust axes  27  and  32  in a second rotational direction  52 . That is, rotational member  48  rotates in a clockwise direction, which rotates the first and second screws  64  and  67  in a counter-clockwise direction, as illustrated in  FIG. 6 . Rotation of the first and second screws  64  and  67  causes the first and second nuts  63  and  65  to move toward the brake pad  30 , thereby lengthening the thrust assemblies  26  and  28 , and decreasing the slack. 
       FIGS. 7A and 7B  show an alternate embodiment. The lever  14  is in a position when no load is being applied. Rotational member  48  is prevented from rotation by latch  54  that engages a first gear  66  on the first screw  64 . First gear  66  meshes with the gear  68  on the rotation member  48 . Latch  54  prevents rotation of first gear  66  and in turn prevents rotation of gear  68 . A second gear meshes with gear  68 , as shown in  FIG. 1 , in a similar manner as the first gear  66 . The second gear  70  is prevented from rotation by gear  68  that also acts to synchronize the first gear  66  with the second gear  70  ensuring that the first thrust assembly  26  and second thrust assembly  28  are adjusted the same length. 
       FIGS. 8A and 8B  show the lever  14  when the brake is applied and the thrust assembly  26  has moved through the pre-defined slack. The latch  54  disengages with first gear  66 . The gear  68  is free to rotate from the torque created by the biasing member  44 . As gear  68  rotates this cause the first gear  66  to rotate, thus rotating the first screw  64 . The first gear  66  is driven in the counter-clockwise direction  52 , lengthening the thrust assembly  26  and reducing the slack. A similar rotation occurs on for the second screw  67  lengthening the second thrust assembly  28  (not shown). 
       FIG. 9A and 9B  show the lever  14 , rotational member  48 , latch  54 , and the first gear  66  on the first screw  64  during a full brake position. The latch  54  has disengaged from the first gear  66 . However, when the brake pad  30  and brake disc  29  are in contact load is applied through the first thrust assembly  26 . The load prevents rotation of the first nut  63  and first screw  64  hence no adjustment occurs. Likewise the second thrust assembly is prevented from rotation. The preferred directions of rotation are shown in  FIG. 6 . 
     When the brake is released, if there is still excess slack when all load is released from the thrust assembly  26 , the rotational member  48  and first screw  64  will be rotated further as shown in  FIGS. 8A and 8B . The first screw  64  will continue to rotate until the travel of the thrust assembly  26  becomes equal to the predefined slack. The second screw  67  (not shown) will also rotate. At this point the latch  54  then re-engages with the first gear  66  preventing any further rotation. 
       FIG. 10A  shows another embodiment slack adjustment system  100  where a locking mechanism  102  is located adjacent the roller  22 . The roller  22  is recessed within the base of the lever  14 . As a driver operates a brake (not shown) an input load (illustrated by arrow L) is transferred to a lever  14 . Applying the input load L rotates the lever  14  causing the roller  22  to rotate (illustrated by arrow R).  FIG. 10B  shows the lever  14  and roller  22  with a cam  108  mounted on the end of the roller  22 . The cam  108  rotates with the roller  22 . 
     Referring to  FIG. 11 , the locking mechanism  102  includes a latch  110  that engages the first gear  66 . A spring  114  drives the latch  110  into the first gear  66  to maintain engagement between the first gear  66  and the latch  110 . 
       FIG. 12A  shows the latch  110  and the spring  114  within a frame  11  for the brake assembly  10 . The spring  114  is within a screw  118  that is threaded into the frame  11 . The screw  118  can be rotated to adjust the force the spring  114  applies to the latch  110 .  FIG. 12B  shows the latch  110  within the frame  11  and contacting the first gear  66 . The cam  108  and screw  118  are not shown so the engagement between the latch  110  and first gear  66  can be seen.  FIG. 12C  shows the locking mechanism  102  including the latch  110  and screw  118  within the frame  11  with the cam  108  and first gear  66 . 
       FIG. 13A  shows the cam  108  engaging the latch  110  when no pressure is applied to the lever  14 . Rotating the lever  14  rotates the cam  108  driving the latch  110  away from the first gear  66  as shown in  FIG. 13B . If there is only a minimal amount of slack in the brake system  10  then the roller  22  will not rotate far enough to disengage the latch  110  from the first gear  66 . Tooth  111  on the latch  110  sits between teeth on the gear  66 , preventing rotation, and hence preventing undesired adjustment. As the slack in the brake system increases the roller  22  must be rotated farther to engage the brakes. The farther the roller  22  rotates the more the cam  108  drives the latch  110  away from the first gear  66 .  FIG. 13C  shows the latch  110  and cam  108  when undesirable slack is in the system and the roller  22  rotates a sufficient amount to disengage the latch  110  from the first gear  66 . As shown a tooth  111  no longer engage between gear teeth on the gear  66 , and no longer preventing the gear  66  from rotating. The position of the first gear  66  and latch  110  at this point are shown in  FIG. 14 . When the latch  110  is disengaged the first gear  66  can rotate freely to lengthen the thrust assemblies  26  and  28  adjusting the slack. 
       FIG. 13D  shows the cam  108  and latch  110  when the roller is fully rotated. The cam  108  is designed such that once the latch  110  has disengaged from the gear  66  the cam  108  will not move the latch  110  further away from the first gear  66 . Thus, the amount of slack in the brake system  10  is controlled by the distance that the cam  108  pushes the latch  110  away from the first gear  66 . 
     A biasing member  120  (not shown) engages the first gear  66  through a gear  122  (shown in  FIG. 15 ). The biasing member  120  is preferably an air motor but may take other forms such as a spring, electric motor, or the like. The biasing member  120  rotates the first gear  66  when the latch  110  is disengaged. Rotation of the first gear  66  causes the thrust assemblies  26  and  28  to lengthen and decreases the slack in the brake system  10 . The force used to adjust the slack adjustment system is  100  is independent of the load L applied to the lever. The biasing member  120  provides the load used to rotate the first gear  66 . By providing an independent source to bias the slack adjustment system  100  the load L applied to the lever is not used, increasing the efficiency of the slack adjustment system  100 . 
     The foregoing description is only illustrative of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specially described. For that reason the following claims should be studied to determine the true scope and content of this invention.