Abstract:
A vehicle brake slack adjuster of the type having a housing pivotally connected to a vehicle brake operator and enclosing a slack adjusting mechanism operably coupled to a vehicle brake operating system and a linkage for operably coupling the vehicle brake operator to the slack adjusting mechanism, characterized in that the linkage includes an outer part having inner and outer ends with the outer end being pivotally coupled to the vehicle brake operator and the inner end mounting a gear rack, an inner part having an outer end mounting a gear rack and an inner end coupled to the slack adjuster mechanism and a rotatable gear engaged with each of the gear racks.

Description:
BACKGROUND OF THE INVENTION 
     In my prior U.S. Pat. No. 5,350,043 there is disclosed an improved Automatic Slack Adjuster incorporating a member cooperating with a slack adjuster rotor to determine a reference position for the rotor and to return the rotor to such reference position at the completion of each brake operational cycle, wherein the rotor is additionally coupled to a reciprocating operating link movable by a brake operator for rotating the rotor in a first direction when brakes are applied and a second direction when such brakes are released. Typically, these slack adjusters are designed for use with vehicles having large wheels fitted with brake drums on the order of sixteen and one-half inch diameters. 
     The only problem encountered with this prior slack adjuster is that of installing the adjuster in certain brake installations, such as those used on vehicles using small diameter wheels and associated small brake drums on the order of six and one-half inch diameters, and characterized as not allowing sufficient room for normal operating movements of the slack adjusters. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a modification of the slack adjuster construction disclosed by U.S. Pat. No. 5,350,043, which allows for its installation in confined environments. 
     More specifically, the present invention contemplates a two-fold modification of the structure of the prior slack adjuster disclosed by U.S. Pat. No. 5,350,043, which consists of replacing its one piece operating link with a two part operating link, wherein a first or inner link part is slidably supported by the housing of the slack adjuster and has its inner end shaped in the same manner as an inner end of the one piece link of the prior slack adjuster and a second or outer link part shaped to provide an inner end slidably supported by the housing and an outer end adapted for pivotal coupling to a brake actuator; and a toothed gear is arranged for engagement with a first rack carried by an outer end of the first link part and a second rack carried by the inner end of the second link part. Further, the operating arm of the present housing is inclined relative to the position assumed by the operating arm of the prior slack adjuster. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The nature and mode of operation of the present invention will now be more fully described in the following ailed description taken with the accompanying drawings wherein: 
     FIG. 1 is a side elevational view of an automatic slack adjuster formed in accordance with a preferred form of the present invention; 
     FIG. 2 is a view of the slack adjuster with portions of the slack adjuster housing broken away to show operating elements of the slack adjuster; 
     FIG. 3 is a sectional view taken generally along the line  3 — 3  in FIG. 2 with elements of the slack adjuster shown in brake applied positions thereof; and 
     FIG. 4 is a side elevational view with the housing of the slack adjuster broken away to show positioning of the parts of the operating link in reference to the housing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference is first made to FIG. 1, wherein an automatic slack adjuster of the present invention is generally designated as  10  and shown as being adapted for coupling to a known brake operating system, not shown, via an operating rod  12 , a clevis  14  and a pivot pin  16 ; and to a known brake assembly, not shown, via a cam shaft  18 , rotatably supported within a through opening  20  of a housing  22  of the slack adjuster via a spline connection  24  and worm gear  26 . Housing  22  serves to enclose an automatic slack adjuster mechanism  28 , which is coupled to cam shaft  18  via worm gear  26  and spline connection  24  and to the brake operating system via a linkage  30 . 
     Housing  22  is provided with an integrally formed arm  32  having one or more bore openings  34  sized to slidably receive pivot pin  16  for purposes of coupling the housing to the brake operating system for relative pivotal movement about a first axis  36 , which is disposed parallel to a second axis  38  corresponding to the axis of cam shaft  18  about which housing rotates incident to reciprocating movement of operating rod  12  under the control of the brake operating system. Axes  36  and  38  are arranged in a first plane  40  shown in FIGS. 1 and 4. By reference to FIGS. 1 and 4, it will be understood that second axis  38  also lies in a second plane  44 , which is arranged to bisect housing  22  and form an angle α with the first plane, which is greater than 0° and less than 180°, and preferably less than 90°. 
     Housing  22  is also formed with a first or stepped diameter bore opening  48  extending normal to cam shaft receiving opening  20  and adapted for receipt of slack adjuster mechanism  28 ; second and third bore openings  50  and  52  communicating with bore opening  48 ; a fourth bore opening  54 ; and a fifth bore opening  56  extending normal to bore opening  48  and communicating with bore openings  52  and  54 . 
     Slack adjuster mechanism  28  preferably corresponds to that disclosed by U.S. Pat. No. 5,350,043, which is incorporated by reference herein. However, to facilitate understanding of the present invention, mechanism  28  will be briefly described as including a worm shaft  60  arranged within first bore opening  48  in engagement with worm gear  26  and supported for both rotational and axial movement between a first axial position shown in FIG. 2 and a second position, not shown, in which it is displaced to the left of its first axial position against the return bias of spring  62 . A rotor  64  and a coupling  66  are slidably and rotatably supported on worm shaft  60  by bearing sleeve  60   a  with rotor  64  being normally coupled for rotation with coupling  66  by a one way clutch  68  defined by ratchet teeth  68   a  and  68   b,  and coupling  66  being normally coupled to the worm shaft by a slip device  70  defined by shallow grooves  72   a  and teeth  72   b.  Teeth  68   a  and  68   b  are shaped and arranged to permit uncoupling of rotor  64  relative to coupling  66  when the rotor is driven for rotation about the axis of worm shaft  60  in a first direction, i.e. counterclockwise from a reference position shown in FIG. 3, and to permit coupling  66  to be driven for rotation with rotor  64  when the rotor is driven for rotation in a second direction, i.e. clockwise from an intermediate position, not shown, for return to its reference position. A spring  76  tends to bias ratchet teeth  68   a  into engagement with coupling teeth  68   b  and spring  62  tends to bias worm shaft  60  into its first position shown in FIG. 2, wherein grooves  72   a  and teeth  72   b  engage for purposes of connecting coupling  66  for rotation with the worm shaft. 
     Rotor  64  is shaped to define a radially outwardly projecting lug  80  adapted to project into a transversely extending recess  82  formed in the inner end of linkage  30  and first and second abutments  84  and  86 . 
     Recess  82  is formed with lower and upper surfaces  82   a  and  82   b.  Abutments  84  and  86  are arranged for operable engagement with a member  90 , which is slidably supported within bore opening  50  and biased outwardly thereof by a return spring  92 . Member  90  has a side surface defining a first abutment surface  90   a  and oppositely facing end surfaces defining second and third abutment surfaces  90   b  and  90   c,  respectively. First abutment surface  90   a  is arranged to be engaged with first abutment  84  to define a reference position for rotor  64  shown in FIG. 3; second abutment surface  90   b  is arranged for engagement with by second abutment  86 ; and third abutment surface is arranged for engagement by return spring  92 . 
     In accordance with the present invention, linkage  30  includes a first or inner link part  96 , which is slidably received within third bore opening  52 , and a second or outer link part  98 , which has its inner end slidably received within fourth bore opening  54 , and a toothed gear  100  received within fifth bore opening  56  for rotation about a fourth axis  100   a.  The inner end of inner link part  96  serves to define recess  82  and the outer end of outer link part  98  defines one or more bore openings  102  adapted to slidably receive a pivot pin  104  by which the linkage is coupled to the vehicle brake operating means via a clevis  14  and rod  12  for relative pivotal movement about third axis  106 . The relatively adjacent ends of inner link part  96  and outer link part  98  are formed with gear racks  110  and  112  arranged for engagement with gear  100 , such that the inner link part moves inwardly and outwardly relative to housing  22  incident to like movements of outer link part  98 . 
     By referring to FIGS. 3 and 4, it will be understood that reciprocating movement of outer link part  98  relative to housing  22  occurs along a first path of travel and reciprocating movement of inner link part relative to the housing occurs along a second path of travel, wherein such paths of travel lie in essentially parallel planes  114  and  116 , and form an angle β greater than 0° and less than 180° relative to one another. Additionally, the first path of travel is disposed essentially parallel to first plane  40  and the second path of travel is disposed essentially parallel to second plane  44 . 
     In operation, slack adjuster  10  normally assumes an initial position shown in FIG. 1, wherein the brakes of a vehicle are fully released. In this initial position of the slack adjuster, teeth  68   a  and  68   b  of one way clutch  68  are engaged, and grooves and teeth  72   a  and  72   b  of slip means  70  are engaged, as shown in FIG. 2; and inner link part  96  occupies an initial fully inserted position within housing  22  and rotor  64  occupies its reference position, as shown in FIG. 3, wherein first abutment  84  is engaged with first abutment surface  90   a,  return spring  92  is partially extended and maintains second abutment surface  90   b  in under engagement second abutment  86 , and lug  80  is disposed slightly above lower recess surface  82   a  of the inner link part. 
     Upon application of braking force to the brake operating system, operator shaft  12  is forced to move to the right, as viewed in FIG. 1, and thereby cause housing  22  and worm gear  26  to rotate about axis  38  through some angle until cam shaft  18  has been rotated sufficiently to fully apply the brakes of a vehicle. As an incident to such rotation of housing  22 , link  30  is partially withdrawn from within housing  22 , due to its pivot connection with clevis  14 , until it assumes an extended position, not shown. As link  30  is extended, lower recess surface  82   a  first engages lug  80  and then lifts the lug to thereby impart counterclockwise directed rotation to rotor  64 , as viewed in FIG. 3, until the rotor is moved into its intermediate position, not shown, coincident with the arrival of the link in its extended position. As rotor  64  is rotated from its reference position into its intermediate position, spring  76  permits the rotor to ratchet relative to coupling  66 , and return spring  92  is further compressed as member  90  is forced to slide within recess  50 , due to engagement of second abutment  86  with second abutment surface  90   b.    
     During the whole of the braking operation, worm shaft  60  tends to remain fixed against rotation, and thus worm gear  26  remains essentially rotationally fixed relative to housing  22 , such that both the worm gear and cam shaft  18  are rotated for brake application purposes. On the other hand, as braking force is applied, worm shaft  60  tends to move towards the left, as viewed in FIG. 2, against the bias of spring  62 , due to the axial reaction force created between worm gear  26  and worm shaft  60 . As long as this braking force is below a certain limit, spring  62  will not yield, but when such force overcomes the preload of the spring, worm shaft  60  will be axially displaced until arrested by suitable means. Upon displacement of worm shaft  60  in this manner, grooves and teeth  72   a  and  72   b  tend to become disengaged, such that coupling  66  is free to rotate relative to worm shaft  60 . 
     In order to insure complete disengagement of grooves and teeth  72   a  and  72   b  incident to axial displacement of worm shaft  60  against the bias of spring  62 , there is provided restraining means in the form of a second abutment surface on housing  22 , which is arranged for engagement by coupling  66  and is adapted to limit worm shaft following movement of the coupling to the left, as viewed in FIG. 2, under the bias of spring  76 . 
     Upon release of braking force on the brake operating system, operator shaft  12  is retracted until housing  22  is rotated counterclockwise for return to its initial position shown in FIG. 1, and coincident therewith inner link part  96  is forced to return to its initial contracted position shown in FIG.  3 . As inner link part  96  moves towards its initial position, return spring  92  operating through member  90 , biases rotor  64  for rotation in a clockwise direction for return to its reference position viewed in FIG.  3 . The speed of this clockwise rotation of rotor  64  is limited by the speed at which inner link part  96  is returned to its initial position, since return spring  92  tends to maintain lug  80  in following engagement with link lower surface  82   b.  Further, during rotation of rotor  64  towards its reference position, coupling  66  is coupled for rotation with the rotor, due to the presence of one way clutch  68 . However, coupling  66  remains uncoupled from worm shaft  60 , until such time as axial loading of the worm shaft decreases sufficiently to permit compression spring  62  to force the worm shaft to the right as viewed in FIG. 2 for purposes of reengaging slip means  70 . If re-engagement of slip means  70  does not occur until substantially coincident with the return of rotor  64  to its reference position, no rotational movement will be imparted to worm shaft  60  by the rotor, during the brake operational cycle, and, thus, no adjustment of the vehicle brakes will occur during such cycle and the brakes will remain in properly adjusted condition. On the other hand, if positive re-engagement of slip means  70  should occur before return of rotor  64  to its reference position, rotor  64  will be operable to drive worm shaft  60  for rotation with the result that the worm shaft will drive worm gear  26  and thus rotate cam shaft  18  for rotation relative to housing  22  to take up slack existing in the vehicle brake system. After any such slack adjustment, no further rotation of cam shaft  18  relative to housing  22  will occur during subsequent brake operational cycles, until a subsequent slack condition occurs, due for instance to the further wearing away of brake pads incorporated in the vehicle brake system.