Abstract:
A direct braking of a drive shaft for a tracked vehicle that moves on rotating track(s). A disc brake is connected to the same drive shaft that has sprocket(s) for engaging the track(s). Upon activation by a vehicle driver, opposing pistons engage the disc to retard rotation of the drive shaft. This, in turn, causes slower rotation of the tracks and slower movement of the vehicle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to hydraulically actuated disc brake systems. More particularly, it relates to brake systems for use on tracked vehicles. 
     2. Description of Related Art 
     Tracked vehicles have historically relied on indirect braking systems frequently designed to utilize convex or concave friction braking pads pressed against an inner or outer perimeter of a circular brake drum. Since these tracked vehicles tended to be large and slow, their braking systems were often adapted to operate indirectly, such as on lower torque shafting near the prime mover, rather than directly on the higher torque shafting driving the track. Locating track braking systems near the prime mover also removed brake components from the harsh track operating environment. 
     Newer tracked vehicles include small, lightweight machines that operate at high speeds. These modern tracked vehicles require a lightweight braking solution that operates reliably at high speeds. Suggested by their widespread use on automobiles, disc brakes have been adapted to some modern tracked vehicles. However, these adaptations have lower performance and reliability than state-of-the-art systems typical of modern automobiles. This is because they do not integrate a reliable and cost effective brake system directly on the track drive shaft. 
     Problems associated with brake system design for modern tracked vehicles include providing adequate structure for rigidly mounting the system, space for locating the system, and heat transfer for cooling the system. What is needed is a disc brake system design that solves these problems while remaining economical, lightweight, and reliable. 
     SUMMARY OF THE INVENTION 
     The present invention provides a disc braking apparatus for braking a vehicular track. A rotatable track has a means for engagement with a driver that imparts rotary motion to the track. A typical driver comprises one or more sprockets directly connected to a shaft. The sprockets directly engage the track. The shaft shares a common axis of rotation with the track and is coupled to a rotary prime mover. Shaft braking is provided by a brake disc directly connected to the shaft. A braking assembly incorporates brake actuator pistons for braking the brake disc and anti-friction bearings for supporting the track drive shaft. The assembly may be cooled by convective cooling fins, by liquid cooling, or by other suitable cooling means. A partition supporting the assembly also serves to isolate the brake disc from the track environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described with reference to the accompanying figures. In the figures, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit or digits of a reference number identify the figure in which the reference number first appears. The accompanying figures, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art to make and use the invention. 
         FIG. 1  is a schematic view of a tracked vehicle power train incorporating the braking system of the present invention. 
         FIG. 2  is a fragmentary side view of a first track drive connection of  FIG. 1 . 
         FIG. 3  is a fragmentary side view of a second track drive connection of  FIG. 1 . 
         FIG. 4  is an enlarged cross-sectional view taken along lines  4 — 4  of  FIG. 1 . 
         FIG. 5  is a left end view taken along lines  5 — 5  of  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Introduction: 
     The present invention provides a disc braking system for tracked vehicles. A braking assembly incorporates pistons for applying braking forces and bearings to support a shaft rotating with the brake disc. The integral structure utilizes the stiffness of the shaft to resist yaw between the brake disc and the braking assembly. 
     Braking systems according to the present invention feature shorter piston travel since clearances between the piston and disc are reduced. Formerly, large clearances in the range of 0.05 to 0.15 inches were maintained to accommodate unwanted relative motion between the braking assembly and the disc. The large clearance assured that flexing during operation would not cause disc collisions that knock the piston(s) back into the piston bore(s). Increasing the structural rigidity of the system reduces unwanted relative motion and, therefore, reduces required clearances between the piston(s) and the brake disc. Reduced clearances also reduce piston travel during braking and thereby improve brake responsiveness, reliability, and safety. 
     Braking systems according to the present invention also feature enhanced convective cooling from the brake disc and the braking assembly. Enhanced cooling reduces the heat transfer area required and, consequently, the physical size of these parts. Smaller parts allow for more compact brake system assemblies and facilitate mounting the brake disc directly on the track drive shaft. Direct braking of the track drive shaft eliminates the need for an intermediate shaft and the loss of reliability associated with a belt, chain, or similar drive between an intermediate shaft and the track drive shaft. 
     Brake System: 
       FIG. 1  shows a tracked vehicle power train  100 . The basic elements of the power train include a rotary prime mover  102 , a transmission  104 , a track drive shaft  106 , a brake disc  108 , and a braking assembly  110 . The track drive shaft is, therefore, indirectly driven by the prime mover, and directly braked by the brake disc. 
     Prime mover output shaft  112  connects to an input shaft  114  of transmission  104  by a transmission input coupling depicted schematically by reference  116 . Transmission output shaft  118  is connected to the track drive shaft drive end  120  by a transmission output coupling depicted schematically by reference  123 . Track drive shaft  106 , having centerline  144 , is directly connected to one or more track drive sprockets. The sprocket(s) may be of the tooth insertion type  124  or they may be the tooth abutting type  122 . In either case, one or more sprockets of either type may be employed. 
     Reference is now made to  FIG. 1  showing a first track type  126  and also to  FIG. 2  where a portion of a first track drive connection is shown generally by reference  200 . First track drive shaft sprocket(s)  124  have first teeth  130  that engage track openings  145  in the undersurface  210  of the rotatable first track  126 . The insertion contact points  212  between the first teeth and the walls of the track openings enables forces to be exchanged between the first track and the first teeth. 
     Reference is now made to  FIG. 1  showing a second track type  127  and also to  FIG. 3 , where a portion of a second track drive connection is shown generally by reference  300 . Second track drive shaft sprocket(s)  122  have second teeth  128  that engage track projections  146  on the undersurface  310  of rotatable second track  127 . The abutting contact points  312  between the second teeth and adjacent projections on the second track enables forces to be exchanged between the second track and the second teeth. 
     Referring again to  FIG. 1 , a bearing housing  132  provides rotary support to drive shaft  106  near its free end  134 . The bearing housing, a first cylinder body portion  136 , and a second cylinder body portion  138  form a braking assembly  110 . Brake disc  108  is mounted directly to drive shaft  106  such that cylinder body portions  136  and  138  straddle the brake disc periphery. Track partition  140  or another similar structure supports the braking assembly  110  and may also isolate the brake disc  108  from the track environment  142 . Vehicle structure also includes body part  148  having interconnections (not shown) with the track partition. 
     Referring to  FIGS. 1–3 , forces may be transmitted between the track drive shaft  106  and the track  126 ,  127  as described, or other similar methods may be used. A similar method may transmit force to the track using contact friction between a friction element directly connected to track drive shaft  106  and a feature or surface on the track adapted to a friction drive (not shown). 
     Referring now to  FIG. 4 , the braking system of  FIG. 1  is shown by reference  400  in more detail. The first cylinder body portion  136  has a blind first piston bore  402  with a centerline  404 . A first piston  406  is slidably engaged in the first bore  402 . Similarly, the second cylinder body portion  138  has a blind second piston bore  408  with a centerline  410 . A second piston  412  is slidably engaged in the second bore  408 . The first cylinder body portion  136  is oriented with respect to the second cylinder body portion  138  such that the respective free ends  407 ,  409  of the pistons  406 ,  412  are opposed and spaced-apart with a radial outer portion of the brake disc  108  interposed between them. 
     The first and second body portions  136 ,  138  and the bearing housing  132  may be separate parts held together by fasteners, by welding, or by other suitable means. Alternatively a single casting, forging, or machined piece may form one or more of these parts into a single unit. 
     As one who is skilled in the art will recognize, the opposed cylinder body and piston arrangement discussed above may be replaced with a floating cylinder body design. This alternative floating cylinder body design employs a single cylinder body and piston opposed by a fixed anvil (not shown). Here, an outer radial portion of disc  108  is interposed between the piston free end and a surface of the anvil. 
     Still referring to  FIG. 4 , bearing housing  132  has a bearing bore  414 . One or more bearings are inserted in the bearing bore  414 . A first bearing  416  and a second bearing  418  are shown inserted in the bearing bore. The bearings provide rotatable support for the track drive shaft  106 . The bearings may be anti-friction bearings. A spacer  420  may be used to provide an effective spacing between the bearings thereby creating a significant moment arm to restrain yaw of the track drive shaft relative to the braking assembly  110 . 
     Referring now to  FIG. 5 , a left end view  500  of the braking system of  FIG. 4  is shown. The left end face  502  of the braking assembly  110  has optional convective cooling fins  422 . The braking assembly  110  may be mounted within a bearing assembly cut-out  432  of the track partition(s)  140 . This arrangement exposes the convective cooling fins to the environment  142  where the track  126 ,  127  operates. 
     As one who is skilled in the art will recognize, the cooling fins described above may be replaced by other known cooling means. Alternatives include, for example, liquid cooling means wherein the braking assembly  110  incorporates passages for circulating a liquid coolant (not shown). 
     Referring to a cut-away portion of  FIG. 5 , the brake disc  108  has a plurality of interior airfoils  506  defining generally radial channels  508  between a first disc plate  428  and a corresponding second disc plate  430 . The radial channels may extend from an annular inlet groove  426  in the second disc plate  430  to the peripheral exhausts  510 . Mounting tabs  512  may be located around the perimeter of the braking assembly face  502 . The tabs provide a means for fastening the assembly to the partition(s)  140  or to similar support structures. 
     Operation: 
     In  FIG. 4 , operation of the brake system  400  tends to retard the track drive shaft  106  rotation when the first and second pistons  406 ,  412  press respective friction pads (not shown) against opposing sides of the rotating disc  108 . Rubbing the friction pads on the rotating disc converts the kinetic energy of rotation to frictional heating. Both the disc and the brake assembly  110  become heated thereby during the braking process. 
     Still referring to  FIG. 4 , heat generated by braking increases the temperature of the bearing assembly  110 . Convective heat transfer Q 1  from the cooling fins  422  is enhanced when the surrounding air is stirred by the rotating track and or by vehicle motion. As one who is skilled in the art will recognize, the braking assembly  110  may be cooled by means other than convective cooling fins including coolant circulation as described above. 
     In  FIG. 5 , heat generated by braking increases the temperature of the disc  108 . To enhance heat transfer from the disc the airfoils  506  induce air flow from a common annular inlet groove  426  through radial passages  508  to peripheral exhaust outlets  510 . Relatively cool air flowing through the channels is heated as it cools the hot disc. This ventilated disc design enhances convective heat transfer from the disc, reducing the disc surface area and disc diameter required for a given braking application. 
     Referring again to  FIG. 4 , the disc  108  rotates simultaneously with track drive shaft  106  in a clockwise direction, as indicated by shaft rotation arrow  434 . When braking forces, shown by arrows  436  and  438 , are applied, the overall braking assembly  110  also tends to rotate in the direction of the shaft rotation arrow. This rotation is resisted by the connections between the bearing assembly face  502  and the partition(s)  140 . These and other operational forces may cause yaw moments and resulting side-to-side yaw motions indicated by anti-clockwise yaw arrow  440  and clockwise yaw arrow  446 . Such yaw motions tend to misalign the normally parallel track drive shift axis  144  and the piston bore centerlines  404 ,  410 . Counter forces developed between the track drive shaft and the bearings  416 ,  418  resist these yaw moments and restrain yaw motion. 
     If the yaw moment is anti-clockwise, then the resulting anti-clockwise motion develops resisting first anti-clockwise counter force  442  and second anti-clockwise counter force  444 . These forces restrain further anti-clockwise motion. If the yaw moment is clockwise, then the resulting clockwise motion develops resisting first clockwise counter force  448  and second clockwise counter force  450 . These forces restrain further clockwise motion. Dimension “d1” between transverse bearing centerlines may be selected by varying the dimension “d2” of spacer  420  to produce moment forces sufficient to resist yaw moments. 
     Transferring yaw moments  440  and  446  to track drive shaft  106  adds structural rigidity between the disc  108  and the braking assembly  110 . This added structural rigidity reduces the allowable un-actuated clearances between the pistons  407 ,  409  and the brake disc  108 , enhancing brake performance while avoiding piston knock back. 
     Cooling fins  422  located on the braking assembly and exposed to the increased air flow in the track environment  142  enhance convective cooling of the braking assembly. This feature reduces component size while improving life and reliability. Ventilating the brake disc further improves convective cooling of the disc reducing the required disc surface area and diameter while improving life and reliability. By integrating these desirable new features, the current invention provides a compact, high performance disc braking system that is especially well adapted for use on tracked vehicles. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to those skilled in the art that various changes in form and details can be made without departing from the spirit and scope of the invention. As such, the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and equivalents thereof.