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 device secures the adjustment mechanism in place when adjustment is not necessary. Release of the locking member allows the biasing member to adjust the resting position of brake pads independent of driver applied brake pressure.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an adjuster mechanism for a brake.  
           [0002]    As brake pads or brake disc wear the gap between the pads and brake disc increases. Due to the increase in distance between the brake pads and the brake disc the 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. Adjusting the length of the load bearing components assures a consistent amount of actuator travel in spite of brake pad wear.  
           [0003]    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.  
           [0004]    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.  
           [0005]    Accordingly, it is desirable to provide an adjuster mechanism which does not increase driver effort, and which is securely restrained when the brake is not being utilized.  
         SUMMARY OF THE INVENTION  
         [0006]    The slack adjustment system according to the present invention provides an adjustment mechanism which utilizes a biasing member to adjust slack in a system. The biasing member operates independently of the pressure applied to a brake actuator. A locking mechanism is utilized to secure the adjustment mechanism in place when adjustment is not necessary. Additionally, the locking mechanism controls the desired amount of slack.  
           [0007]    The locking mechanism selectively engages a tappet or any rotational member engaged with said tappet to prevent the tappet from being rotated and unnecessarily adjusting the gap between the brake pad and the brake disc. A latch interfitting with the tappet prevents rotation when engaged with the tappet. The latch disengages from the tappet after a predetermined movement of the tappet. Release of the locking mechanism allows the tappet to rotate. The biasing member is mounted to engage and rotate the tappet when the locking member is not preventing movement. The biasing member is of a type which applies a rotational force to the thrust assembly independent of the amount of pressure applied to the brake actuator. The biasing member may be a spring, electric motor, air powered motor or the like.  
           [0008]    The present invention therefore provides a method of automatically adjusting slack independent of the pressure applied to the brake system by the driver. In addition, a locking device prevents unintentional adjustment of slack in the brake system. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    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:  
         [0010]    [0010]FIG. 1 is a sectional side-view of a brake assembly with a slack adjustment system according to the present invention;  
         [0011]    [0011]FIG. 2 is a sectional plan-view of a brake assembly;  
         [0012]    [0012]FIG. 3 is a sectional plan-view of the slack adjustment system according to the present invention showing the tappet moved forward by a distance equal to the desired amount of slack, with the latch just disengaged from the rotational member;  
         [0013]    [0013]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;  
         [0014]    [0014]FIG. 5 is a sectional plan-view of the slack adjustment system according to the present invention shown in the locked position;  
         [0015]    [0015]FIG. 6 is a sectional end-view of the rotational member and tappet gear-train showing the preferred directions of rotation. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    [0016]FIG. 1 illustrates a disc brake assembly  10  which 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 (schematically illustrated by arrow L) is transferred to a lever  14 , through opening  16  in the frame  11 . The lever  14  is rotatably supported by the frame  11  through a bearing  18 . The lever rotates about a lever axis  20 . That is, the lever  14  rotates clockwise about the lever axis  20 , as illustrated in FIG. 1. The base of the lever  14  is recessed to hold cylindrical roller  22 . The roller  22  is eccentrically centered relative the center of rotation of the lever  14 . That is, the roller axis  24  moves in an arc around the lever axis  20 .  
         [0017]    The input load L causes the lever  14  to rotate about the lever axis  20  and the roller  22  to move in an arc around the lever axis  20  (the position illustrated in phantom shows the extreme of travel available to the lever  14 ). The eccentric movement of the roller  22  engages one or more thrust assemblies  26  and applies a load to the thrust assemblies  26  causing the thrust assemblies  26  to move perpendicularly away from the lever  14 , guided by a housing  61 . The preferred embodiment, shown in FIG. 2, includes two thrust assemblies  26 . This motion defines a thrust axis  27  perpendicular to the lever and roller axes  20 ,  24 . The axial movement of the thrust assemblies  26  along the thrust axis  27  engages the brake pad  28  through the thrust plate  62 . The brake pad  28  engages the brake disc  29 . When the driver releases the brake, actuator input load L is reduced and return spring  31  drives the thrust assemblies  26  to the original position. The lever  14  and roller  22  also return to the original position. The return spring  31  restrains the thrust assemblies  26 , roller  22  and lever  14  in the original position when no input load L is being applied.  
         [0018]    The thrust assembly  26  is guided by a housing  61  that is attached to frame  11  by fasteners  32 , (only one shown). The thrust assemblies  26  consists of internally threaded tappet nuts  63  and externally threaded tappet screws  64 . The tappet nuts  63  are rotationally constrained by the housing  61 , such that when the tappet screws  64  are rotated, the length of the thrust assemblies  26  along the thrust axis  27  is altered. The length of the two thrust assemblies  26  may be synchronized by a rotational member  48 , which is permanently engaged with the two tappet screws  64 .  
         [0019]    Referring to FIG. 2, the locking mechanism  42  selectively engages the gear on the tappet screw  64  to prevent the tappet screw  64  from being rotated and unnecessarily adjusting the gap between the brake pad  28  and the brake disc  29 . A latch  54  intermitting with the rotational member  48  prevents rotation when the brake is not applied, and when the brake is applied but the thrust assemblies  26  have moved by less than the pre-defined slack. The latch  54  is mounted to a link  56 , which may be a rod or the like, which is mounted to lever  14 .  
         [0020]    When the brake is not applied, or during normal braking movement when the thrust assemblies  26  have moved through less than the pre-defined amount of slack and no adjustment is required, the rotational member  48  and tappet screws  64  may be locked from rotation by a locking mechanism  42 . When the locking mechanism  42  is engaged, the rotational member  48  and tappet screws  64  cannot rotate. The force applied to tappet screws  64  by rotation of lever  14  axially drives the thrust assemblies  26  along the thrust axis  27  toward the brake disc  29 . The locking mechanism  42 , consisting of a latch  54  driven by the lever  14  via a link  56 , moves relative to the gear on the outside of the rotational member  48  (shown in FIG. 3 to be moving along an axis parallel to the thrust axis  27 , but alternatively could be moved radially away from the thrust axis  27  by re-arranging the connecting link  56 ). The point at which the latch  54  disengages is determined by the geometry of the link  56 . When the pre-defined slack between the brake pads  28  and disc  29  has been taken up, the latch  54  disengages from the gear on the rotational member  48 . Simultaneously, load starts to be applied to the brake pad  28  via the thrust assemblies  26 . This load produces a friction torque between the tappet nuts  63  and tappet screws  64 , 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 spring  31  with no adjustment of the length of the thrust assemblies  26  having taken place.  
         [0021]    As the brake pad  28  wears away, the slack between the brake pad  28  and the thrust assemblies  26  increases, and the thrust assemblies  26  must move a greater distance along the thrust axis  27  in order to engage the brake pad  28  with the brake disc  29 . To compensate for the wear on the brake pad  28 , the tappet screws  64  are adjusted to increase the overall length of the thrust assembly  26 , resulting in a constant slack being maintained between the brake pad  28  and brake disc  29 .  
         [0022]    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 the rotational member  48  and tappet screws  64  can rotate. A biasing member  44  is mounted in the housing  61 , and applies a biasing torque to the rotational member  48 . A biasing axis  46  is preferably parallel to and offset from the thrust axis  27 , but could be in any position or angle inside or outside the frame  11  where it can still be engaged directly or indirectly to the tappet screws  64 . 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 rotational member  48  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 rotational member  48  engages with the gears on the tappet screws  64  preferably by gears on the tappet, but other means of engagement may be used. The tappet screws  64  rotate about the thrust axis  27  in a second rotational direction  52 . That is, rotational member  48  rotates in a counter-clockwise direction, which rotates the tappet screws  64  in a clockwise direction, as illustrated in FIG. 5. The rotational member  48  is preferably a gear.  
         [0023]    Rotation of the tappet screws  64  causes the tappet nuts  63  to move toward the brake pad  28 , thereby lengthening the thrust assemblies  26  and decreasing the slack.  
         [0024]    When the brake is applied, the latch  54  disengages with the rotational member  48  after the thrust assembly  26  has moved through the pre-defined slack. If there is excess slack, the tappet screw  64  is free to rotate and is driven in the clockwise direction  52 , lengthening the thrust assemblies  26  and reducing the slack. When the thrust assembly  26 , brake pad  28  and brake disc  29  are in contact and load is applied through the thrust assemblies  26 , a friction torque is produced between the tappet nuts  63  and tappet screws  64 , preventing any relative rotation and, hence, adjustment when the brake is applied. The preferred directions of rotation are shown in FIG. 6.  
         [0025]    When the brake is released, if there is still excess slack when all load is released from the thrust assemblies  26 , the rotational member  48  and tappet screws  64  will be rotated further as described in the previous paragraph. It will continue to rotate until the travel of the thrust assembly  26  becomes equal to the predefined slack. The latch  54  then re-engages with the gear on the rotational member  48 , preventing any further rotation and, hence, adjustment of the length of the thrust assemblies  26 .  
         [0026]    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.