Abstract:
Improvement in a drag brake assembly for a power take-off unit, for use on trucks and the like, including a first reaction member axially located on an output shaft thereon; a brake disc rotatably affixed to and axially movable on the output shaft; a second reaction member forming an inner surface portion of one of the bearing caps; and a spring member interposed between the first reaction member and the brake disc, for normally biasing the brake disc into an engaged position wherein the brake disc engages the second reaction member inner surface portion, with the brake disc including a first frusto-conical outer surface portion and the second reaction member inner surface being provided with a complementary second frusto-conical surface, with the engagement therebetween keeping the output shaft from rotating.

Description:
FIELD OF THE INVENTION 
   The present invention pertains to a power take-off unit, for use on trucks and the like, including a fluid pressure actuated clutch assembly for selectively driving a vehicle accessory from a source of rotational power, such as a prime mover or transmission. More particularly, the invention pertains to an improved drag brake assembly that is automatically engaged when an associated fluid pressure actuated clutch assembly is disengaged, and further that is automatically disengaged when the clutch assembly is engaged. 
   BACKGROUND OF THE INVENTION 
   Power take-off (PTO) units are well known in the art and most commonly used with sources of rotational power, such as engines and transmissions, for rotatably driving an accessory such as a pump which, in turn then operates any number of hydraulically driven devices such as lifting devices, winches, and the like. 
   Frequently, the PTO unit further includes a clutch assembly, generally of the fluid pressure actuated type, for selectively disconnecting the output shaft from the input gear, thus permitting selective and/or intermittent operation of the driven accessory without having to stop the vehicle engine. Thus, when the clutch assembly is engaged, the output shaft is rotatably driven by the input. Conversely, when the clutch assembly is disengaged, the output shaft is decoupled from the input gear and the driven device is not operated by the engine, etc. 
   Since operation of the PTO unit can generate undesirable friction and heat, the PTO unit is generally provided with a considerable quantity of lubricating fluid. However, it has been determined that the relatively viscous nature of the lubricating fluid can cause the output shaft to continue to be at least partially rotatably driven, even though the clutch assembly has been disengaged. This is particularly the case during cold weather operation when the lubricating fluid is cold and viscous, such as when the vehicle is initially started. Naturally, such rotation of the output shaft of the PTO unit, after the clutch assembly has been disconnected, is undesirable. 
   This noted problem has been addressed in the prior art by the addition to the PTO unit output shaft, of a brake system, such as a drag brake assembly. One such prior art device, namely the automatically actuated drag brake assembly set forth in U.S. Pat. No. 6,497,313 B1, to Blalock, which is also assigned to the assignee of the present invention, utilizes a brake piston that is coaxially aligned with an end face of the output shaft and is normally urged into frictional end abutment therewith via a wave spring interposed between one end of the piston and an adjacent bearing end cap, thereby braking the output shaft. A fluid pressure operated clutch, interposed between the input gear and the output shaft, upon actuation, overcomes the bias of the spring and thus couples the output shaft to the input gear. While workable, it has been determined that the available frictional braking surface is not sufficient to ensure complete rotational stoppage of the output shaft under all operating conditions. Thus, the present invention sets forth an improved automatic drag brake for a PTO unit output shaft that overcomes the noted insufficient stopping power of this prior art device. 
   The patent literature includes a large number of PTO unit drag brake devices as well as devices that utilize frictionally engaging cone-type brake members and additionally include: U.S. Pat. No. 3,035,458 to Wickman; U.S. Pat. No. 3,872,954 to Nordstrom et al.; U.S. Pat. No. 4,175,649 to Monks; U.S. Pat. No. 4,310,080 to Jarvis et al.; U.S. Pat. No. 4,567,965 to Woodruff; U.S. Pat. No. 4,706,520 to Sivalingam; U.S. Pat. No. 5,437,355 to Tagaki; U.S. Pat. No. 5,542,306 to Fernandez; and U.S. Pat. No. 6,142,274 to Warner. However, none of these prior art structures, pertains to the use of a cone-type brake, having interacting truncating frusto-conical mating surfaces, where the stationary reaction member, having one of the noted frusto-conical surfaces, is located on the inner surface of the inside diameter of one of the PTO unit bearing end caps. 
   SUMMARY OF THE INVENTION 
   Accordingly, in order to overcome the deficiencies of the prior art devices, the present invention provides an improved drag brake that not only utilized large diameter cone-type interacting brake surfaces, but also utilizes the surface of the inside diameter of one of the bearing end caps as the stationary reaction surface. This construction maximizes the available braking surface, while reducing the space requirement for the brake assembly, as well as reducing the associated manufacturing cost and simplifying the overall structure. 
   Specifically, in terms of structure, in this invention, a power take-off includes: a rigid housing; a first bearing end cap located on one end of the housing; a second bearing end cap located on another end of the housing; an input gear rotatably journalled, relative to the housing, between the end caps; an output shaft, rotably journalled in the end caps, within the housing and extending from one of the end caps; a clutch assembly connected between the input gear and the output shaft, the clutch assembly being operable in either an engaged condition, wherein the input gear is connected to drive the output shaft, or a disengaged condition, wherein the input gear is not connected to drive the output shaft, the clutch assembly being responsive to the application of pressurized fluid for being operated in the engaged condition; a drag brake assembly being operable in either an engaged condition, wherein the drag brake assembly retards rotation of the output shaft, or a disengaged position, wherein the drag brake does not retard rotation of the output shaft, the drag brake assembly being responsive to the application of pressurized fluid for being operated in the disengaged condition; and a conduit for selectively applying pressurized fluid to both the clutch assembly and the drag brake assembly, an improvement in the drag brake assembly comprising:
         a. a first reaction member located on the output shaft;   b. a driven member rotatably affixed but axially movable relative to the output shaft;   c. second reaction member forming a portion of one of the bearing end caps; and   d. spring member, interposed between the first reaction member and the driven member for biasing the driven member into the engaged position wherein the driven member frictionally engages the second reaction member, thereby retarding rotation of the output shaft.       

   In one variation, the driven member is an annular brake disc having a first frusto-conical outer surface portion, wherein said first frusto-conical outer surface portion is preferably continuous. 
   In another variation, the second reaction member takes the form of an inner surface portion of one of the bearing end caps, wherein the inner surface portion is a second frusto-conical inner surface portion, substantially complementary with the first frusto-conical surface portion and preferably continuous. 
   In a further version, the driven member includes a cone-type outer surface portion, wherein the cone-type outer surface portion is preferably continuous. 
   In still another version, the second reaction member takes the form of a cone-type inner surface portion on one of the bearing end caps, said inner surface portion thereof being substantially complementary with said outer surface portion and preferably is continuous. 
   In one version, the second reaction member is located in said first bearing end cap, while in another version the second reaction member is located in the second bearing end cap. 
   In a further version, one of the first and second bearing end caps includes a central aperture, with one end of the output shaft extending therethrough. 
   In still another version, the driven member takes the form of an annular brake disc having a central hub portion that is axially movable relative to the output shaft, with the central hub portion including an axial slot and the output shaft including a radially-extending pin portion, the pin portion freely extending into the slot and thereby coupling the brake disc for conjoint rotation with the output shaft while simultaneously permitting axial movement of said brake disc via axial movement of the slot portion relative to the pin. 
   In yet a different version, the driven member takes the form of an annular brake disc having a cylindrical axial extension on one side thereof which, together with an adjacent portion of the output shaft forms an annular chamber. 
   An added version further includes a generally cylindrical brake piston, having a hub portion located on the output shaft, adapted to move axially with respect thereto while sealingly fitting within the annular chamber, with the brake piston being movable between an engaged position, wherein an annular cavity, between the brake disc and the brake piston, is pressurized, and a disengaged position, wherein the annular cavity is not pressurized. 
   In another version, in the engaged position, the pressurized fluid overcomes the bias of the spring member, thereby axially moving the brake disc out of contact with the second reaction member and thus permitting rotation of the output shaft. 
   In yet a differing version, in the disengaged position, the bias of the spring member overcomes the fluid pressure within the cavity, thereby axially moving the brake disc into contact with the second reaction member and thus retarding rotation of the output shaft. 
   In a further power take-off unit of this invention, including: a rigid housing; a first bearing end cap closing one end of the housing; a second bearing end cap closing an opposing end of the housing; an input member rotatably journalled relative to the housing, intermediate the end caps; an output shaft, within the housing, rotatably journalled in the end caps; a fluid pressure activated clutch assembly, connected between the input member and the output shaft, operative in both an engaged position and a disengaged position, for selectively coupling the input member to the output shaft; a fluid pressure diengaged drag brake assembly, interposed between the output shaft and one of the first and second bearing end caps, for selectively coupling the output shaft to the one bearing end cap; and a conduit, for selectively and simultaneously applying pressurized fluid to both the clutch and brake assemblies; an improvement in the drag brake assembly comprising:
         a. a first reaction member axially located on the output shaft;   b. a brake disc rotatably affixed to and axially movable on the output shaft;   c. second reaction member forming an inner surface portion of one of said bearing end caps; and   d. a spring member, interposed between the first reaction member and the brake disc, for normally biasing the brake disc into an engaged position wherein the brake disc engages the second reaction member, thereby keeping the output shaft from rotating.       

   In a further version, the brake disc includes a first frusto-conical outer surface portion and the noted inner surface portion is provide with a second frusto-conical surface adapted to frictionally engage the first frusto-conical surface portion. Preferably the first and second frusto-conical surface portions are substantially complementary. 
   In yet other versions, the second reaction member forms a part of one of the first and second reaction members, respectively. 
   In a final version, the one bearing end cap is formed of cast iron while the brake disc is formed of heat-treated cast iron. 
   The previously-described advantages and features, as well as other advantages and features, will become readily apparent from the detailed description of the preferred embodiments that follow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional elevational view of the power take-off unit in accordance with this invention, with the clutch assembly being disengaged while the drag brake assembly is engaged; 
       FIG. 2  is a sectional elevational view, similar to that of  FIG. 1 , with the clutch assembly being engaged while the drag brake assembly is disengaged; and 
       FIG. 3  is an exploded view of another embodiment the drag brake assembly of this invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the several drawings, illustrated in  FIG. 1  is a power take-off (PTO) unit, generally indicated at  10 . Since the basic structure, mode of operation and function of PTO unit  10  are well known in the art, in the interest of brevity, only those portions thereof that are necessary for a complete understanding of the invention will be described in detail hereinafter. PTO unit  10  includes a rigid housing  12  that contains a rotatably journalled outside driving gear  14  operatively coupled to an input gear  16 , which in turn is in meshed engagement with an inside drive gear  18  that is rotatably journalled, such as via adjacent needle bearings  22 , on an output shaft  24 . One end of output shaft  24  is rotatably journalled via conventional rolling element bearings  28  located within a recess in a first or closed bearing cap  26  secured to one side of PTO housing  12 , with the other end of output shaft  24  being similarly journalled, via bearing  34  located within a recess formed in a second or open end bearing cap  32  secured to another side of PTO housing  12 . 
   As is well known in the art, outside drive gear  14  is adapted to be operatively connected to a prime mover or a transmission (neither shown) and is rotatably driven in a conventional manner. Output shaft  24  is adapted to be connected to a rotatably driven accessory, such as a hydraulic pump (not shown), in a known manner. 
   PTO unit  10  also includes a known clutch assembly  36  for selectively providing a driving connection between outside drive gear  14  and output shaft  24 . Clutch assembly  36  includes previously-noted inside drive gear  18  which in turn includes an axially-extending hollow cylindrical bell or cup portion  38  having a splined inner surface portion. A plurality of flat annular clutch plates  40  is splined to the inner splined surface portion of bell portion  38  for rotation therewith. Thus, inside drive gear  18  and clutch plates  40  are adapted to be rotatably driven, as a unit, by outside drive gear  14 , via input gear  16 . 
   A further plurality of flat annular friction plates  42  is alternately disposed between clutch plates  40 , with friction plates  42  being splined to an outer surface of an axially extending portion  46  of a clutch member  44  for rotation therewith. Clutch member  44  is, in turn secured, such as via splines, to output shaft  24  for rotation therewith. Thus, friction plates  42 , clutch plates  40 , and output shaft  24  are connected for conjoint rotation, as a unit. Clutch member  44  is restrained from axial movement, in one direction (toward internal drive gear  18 ), by at least one retainer ring  30 , mounted on output shaft  24 . 
   Thus, it should be understood that clutch plates  40 , together with friction plates  42 , form a portion of clutch assembly  36  for PTO unit  10 . A generally annular clutch piston  50  selectively causes clutch plates  40  and friction plates  42  to frictionally inter-engage, thereby actuating clutch assembly  36 . This is accomplished by having clutch piston  50  disposed within a hollow cup-shaped cylindrical clutch cylinder  52 , with one end of clutch piston  50  being disposed within clutch cylinder  52  while the other end thereof extends from an open end of clutch cylinder  52 , adjacent to interleaved clutch plates  40  and friction plates  42 . Both clutch piston  50  and clutch cylinder  52  are supported on output shaft  24 . While clutch piston  50  is axially movable, relative to output shaft  24 , clutch cylinder  52  is restrained from axial movement, in one direction, by at least one retaining ring  54  mounted on output shaft  24 . 
   A coil spring  48 , surrounding output shaft  24 , reacts between clutch piston  50  and clutch member  44  to urge clutch piston  50  toward a disengaging position, adjacent to a closed end of clutch cylinder  52  such that clutch piston  50  does not engage clutch plates  40  and friction plates  42 , resulting in clutch member  44  being disconnected from inside drive gear  18  in a manner well known in the art. 
   An annular clutch chamber  56  is defined between clutch piston  50  and a closed end of clutch cylinder  52 . Clutch chamber  56  communicates, via a radial or transverse passageway  58  and an axial passageway  60 , both of which are located within output shaft  24 , with an annular end chamber  62  formed within a portion of first or closed end bearing cap  26 , with chamber  62  in turn being connected with a pressure port  64 , for a purpose to be explained hereinafter. 
   Turning now to the portion of output shaft  24  extending toward and through second or open end cap  34 , located on shaft  24 , adjacent to inside drive gear  18  and its associated needle bearings  22 , is one embodiment of the improved drag brake assembly  68  of this invention. Drag brake assembly  68  includes a reaction member  70  that is axially affixed, in one direction, by abutting a step  72  on shaft  24 . Also located on shaft  24  and abutting one side of reaction member  70  is a generally annular driven member or brake disc  74  having a central hub portion  76  that is axially movable, relative to shaft  24 , for a distance determined, at least in one direction, by the length of an axial slot  78  in hub portion  76 . A transversely-extending retainer pin  82 , extending from output shaft  24 , rides in slot  78  and couples brake disc  74  to shaft  24  while also permitting the previously-noted axial movement of brake disc  74 . 
   A further coil spring  86 , surrounding output shaft  24 , reacts between reaction member  70  and brake disc  74 , to urge brake disc  74  toward an engaged position, wherein a frusto-conical outer surface portion  80 , of brake disc  74 , frictionally operatively engages a corresponding or complementary frusto-conical inner surface portion  84  of second or open ended bearing end cap  32 , thus acting as a second reaction member, as best seen in  FIG. 1 . 
   Brake disc  74  also includes a cylindrical axial extension  88  on the side thereof opposite from hub portion  76  which, together with output shaft  24 , defines an annular cavity or chamber  90  that serves to house a generally annular brake piston  92  whose hub portion is located on output shaft  24 . The axial movement of brake piston  92 , in at least one direction, is restrained by a retaining ring  94  in output shaft  24 , at rolling element bearing  34 . Terminating into piston cavity  90  is one end of another transverse or radial passageway  96 , in output shaft  24 , whose other end is in communication with output shaft axial passageway  60 . Pressure port  64 , in bearing end cap  26 , is adapted to be connected to a source of pressurized fluid (not shown) in a conventional manner so as to selectively provide pressurized fluid (hydraulic or pneumatic) to first or closed bearing end cap annular end chamber  62  and, by virtue of axial passageway  60  and radial passageways  58  and  96 , to annular clutch chamber  56  and annular brake chamber  90 , respectively. 
   Since PTO unit  10  is normally completely filled with lubricant, which is common in the art, in order to permit the free flow thereof, within PTO unit  10 , brake disc  74  is preferably provided with a plurality of slots  98  (best seen in  FIG. 3 ) through its surface in the region radially intermediate its cylindrical extension  88  and its frusto-conical outer surface portion  80 . Another alternative for achieving the free flow of lubricant within PTO unit  10  is to interrupt the continuity of either frusto-conical inner surface  84  of bearing end cap  32 , or the frusto-conical outer surface  80  of brake disc  74 , with the at least one axial recess or slot (neither shown). Drag brake assembly  68 , together with the frusto-conical inner surface  84  of second or open bearing end cap  32 , are also known as a “cone” friction brake by virtue of its frictionally interacting conical braking or mating surfaces. Bearing caps  32  and  26  are preferably comprised of cast iron while brake disc  74  is preferably comprised of heat-treated cast iron. While generally smooth mating surface finishes are preferred, no additional intermediate friction material layers or coatings are required. 
   Based on the previous description, it should be evident that clutch coil spring  48 , in clutch assembly  36 , serves to normally bias clutch plates  40  and friction plates  42  to a disengaged position or state while brake coil spring  86 , in drag brake assembly  68 , serves to normally bias brake disc  74  to an engaged state or position with end cap  32 , thereby normally or automatically braking PTO unit output shaft  24  while PTO unit  10  is disengaged. 
   The overall operation of PTO unit  10  will now be briefly described. Once the vehicle engine has been started, outside drive gear  14  is rotatably driven, which in turn, via input gear  16 , causes inside drive gear  18  to freely rotate around output shaft  24 . Assuming, that the source of pressurized fluid has not been activated, there is no pressurized fluid in any one of end cap annular chamber  62 , the passageways  58 ,  60  and  96  or within clutch chamber  56  and brake chamber  90 . Therefore, as seen in  FIG. 1 , clutch assembly  36  is maintained in its normally disengaged position under the influence of clutch spring  48 . At the same time, brake disc  74  is urged into its normally engaged position under the influence of brake spring  86 , thereby affirmatively preventing output shaft  24  from rotating. 
   When it is desired to engage PTO unit  10 , in order to operate a driven device (not shown), the source of pressurized fluid is actuated to supply pressurized fluid through pressure port  64 , annular end chamber  62  and conduits or passageways  60 ,  58  and  96  to clutch chamber  56  and brake chamber  90 . When this occurs, as illustrated in  FIG. 2 , the fluid pressure within clutch chamber  56  overcomes the bias or force of clutch spring  48  and moves clutch piston  50  into engagement with interleaved clutch and friction plates  40 ,  42 , respectively, thereby engaging clutch assembly  36  in a known manner and causes output shaft  24  to rotate. Simultaneously, the fluid pressure in brake cavity  90  overcomes the bias or force of brake spring  86  and moves brake disc  74  out of frictional engagement with frusto-conical inner surface  84  of bearing end cap  32 , thereby freeing output shaft  24  to be rotatably driven by outside drive gear  14  in the manner previously described. 
   It should be understood that, if desired, rather than placing or locating cone-type drag brake assembly  68  at open end bearing cap  32 , as is illustrated in  FIGS. 1 and 2 , brake assembly  68 ′ can also be placed or located at closed end bearing cap  26 . This is schematically illustrated in  FIG. 3  which is an exploded view of another embodiment of cone-type brake assembly  68 ′, located at closed end bearing cap  26  instead of open end bearing cap  32 . All brake parts or components remain the same, though reversed relative to  FIGS. 1 and 2 , except that an inner surface portion of bearing cap  26  is now provided with a frusto-conical inner surface portion  84 ′ (not shown), acting as a second reaction member, that mates with frusto-conical brake disc surface portion  80 ′. Clutch assembly  36  (not shown in  FIG. 3 ), is reversed and relocated adjacent to open end bearing cap  34  in a manner well known in the art. The operation of the revised PTO unit of  FIG. 3  remains substantially similar to that of PTO unit  10  illustrated in  FIGS. 1 and 2 . 
   It is deemed that one of ordinary skill in the art will readily recognize that the present invention fills remaining needs in this art and will be able to affect various changes, substitutions of equivalents and various other aspects of the invention as described herein. Thus, it is intended that the protection granted hereon be limited only by the scope of the appended claims and their equivalents.