Abstract:
A telescoping hydraulic hoist which improves stability and rigidity in the extended position without sacrificing the maximum extension length of the hoist and with fewer machined parts which may be dislodged or damaged in operation. The base member has a recess into which intermediate and inner tube stages recede when the hoist is in a fully collapsed position, and a stop-collar on the gland nut bearings overlaps the exposed end of the next broader tube stage, defining a limit of retraction for each intermediate tube stage, so that a tube stage when fully retracted contacts the exposed end of the next broader tube stage, thus dispensing with the need for stop rings.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to hydraulic hoists. In particular, this invention relates to a telescopic hydraulic hoist having a plurality of telescoping tube stages.  
         BACKGROUND OF THE INVENTION  
         [0002]    Telescopic hydraulic hoists are used in many applications. One popular use for telescopic hydraulic hoists is in heavy trucks, for example dump trucks, which require a strong, rigid lifting mechanism to raise the truck&#39;s container or bed for dumping heavy materials such as rubble, dirt, gravel etc.  
           [0003]    U.S. Pat. No. 5,983,778 issued Nov. 16, 1999 to Dawson, entitled “Telescopic Hydraulic Hoist Apparatus,” which is incorporated herein by reference, discloses a telescopic hydraulic hoist formed from a non-corrosive material such as aluminum. The hoist is provided with bearings and hydraulic seals about the bottom portion of each moving stage of the hoist. The bearings and seals are maintained within the hoist, and are thus not exposed to dust or particulate matter from outside the hoist. Air flows into and out of the air spaces between adjacent stages of the hoist through air breathers which are provided in gland nut bearings threadedly engaged to the exposed end of each tube stage.  
           [0004]    The hoist disclosed in U.S. Pat. No. 5,983,778 may also include variable length stroke limiters, which limit the extension of the tube stages to varying degrees, and a cushion member which partially closes off the hydraulic inlet as the innermost stage is fully retracted to slow the hoist motion in the final stages of retraction. However, as is typical in telescopic hoist designs, the retracting movement of the various tube stages in the telescopic hoist is limited by the use of a stop ring inserted near the bottom of the inside diameter of each tube stage, which prevents further retraction of each moving stage once it has reached its fully collapsed position.  
           [0005]    The stop ring may comprise a washer welded to the interior wall or a machined annular insert which is fitted into a groove circumscribing the interior wall of the tube stage. This presents a point of potential weakness in the hoist design, since in the former case the quality of the weld will affect the performance and durability of the tube stage, and in the latter case the groove creates a weak point around the tube wall. Also, the ring can become dislodged from the stage or otherwise distorted, causing a tube stage to fall through the next broader tube stage when the hoist is retracting and resulting in damage to the hoist.  
           [0006]    Furthermore, the differential diameters of the tube stages affects the rigidity or stability of the hoist in the extended position. Given a constant wall thickness, as the diameter of each tube stage decreases, the length of the tube stage which can safely extend beyond the next broader tube stage also decreases. Increasing the wall thickness of the tube stages would enhance the stability of the hoist, but is not a desirable solution because it also increases the weight of the hoist.  
           [0007]    One way to increase the stability of the hoist structure is to increase the overlap between adjacent tube stages of the hoist when the hoist is in its fully extended position. The greater the overlap between one telescopic stage and the next, the more rigid and stable is the structure of the extended hoist. However, increasing the overlap between adjacent tube stages correspondingly decreases the usable length of each tube stage and commensurately limits the maximum extension length of the hoist.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention overcomes these disadvantages by providing a telescopic hydraulic hoist which improves stability and rigidity in the extended position without sacrificing the maximum extension length of the hoist. A hoist according to the invention improves stability by providing greater overlap between tube stages. The invention further eliminates the need for a stop ring, and thus provides a telescopic hydraulic hoist with fewer machined parts which may be dislodged or damaged in operation to thereby extend the life of the hoist, simplify assembly of the hoist, reduce the cost of the hoist components, and eliminate the weak point resulting from the inclusion of a groove or weld used to retain the stop ring in place in a conventional hoist by allowing the wall of the tube stage to be formed to a uniform thickness.  
           [0009]    The invention accomplishes this by providing a base member having a recess into which intermediate and inner tube stages recede when the hoist is in a fully collapsed position. The invention also accomplishes this by providing a stop-collar on the gland nut bearings which defines a limit of retraction for each intermediate tube stage, the collar extending beyond an inner limit of the next broader tube stage so that a tube stage when fully retracted thus contacts the next broader tube stage, dispensing with the need for additional components such as stop rings.  
           [0010]    The present invention thus provides a telescopic multi-stage hydraulic hoist, comprising a hydraulic fluid inlet in communication with an interior of the hoist, an inner tube stage having a contained end and an exposed end, at least one intermediate tube stage having a contained end and an open exposed end and comprising an intermediate gland nut bearing affixed to the exposed end of the at least one intermediate tube stage, the inner tube stage being disposed in the at least one intermediate tube stage in telescoping relation and being extendible through the open end of the at least one intermediate tube stage to an extended position and retractable through the open end of the at least one intermediate tube stage to a collapsed position, an outer tube stage having a first end and a second open end and comprising an outer gland nut bearing affixed to the open end of the outer tube stage and a base member affixed to the first end of the outer tube stage in sealed relation, the at least one intermediate tube stage being spaced from the outer tube stage by the outer gland nut bearing and being extendible through the open end of the outer tube stage to an extended position and retractable through the open end of the outer tube stage to a collapsed position, wherein the exposed end of at least the inner tube stage comprises a stop-collar which overlaps an exposed end of the at least one intermediate tube stage such that the stop-collar contacts the exposed end of the at least one intermediate tube stage when the inner tube stage is in a fully collapsed position.  
           [0011]    The present invention further provides a telescopic multi-stage hydraulic hoist, comprising a hydraulic fluid inlet in communication with an interior of the hoist, an inner tube stage having a contained end and an exposed end, at least one intermediate tube stage having a contained end and an open exposed end and comprising an intermediate gland nut bearing affixed to the exposed end of the at least one intermediate tube stage, the at least one intermediate tube stage being disposed in a next broader tube stage in telescoping relation and being extendible through the open end of the next broader tube stage to an extended position and retractable through the open end of the next broader tube stage to a collapsed position, the inner tube stage being disposed in the at least one intermediate tube stage in telescoping relation and being extendible through the open end of the at least one intermediate tube stage to an extended position and retractable through the open end of the at least one intermediate tube stage to a collapsed position, an outer tube stage having a first end and a second open end and comprising an outer gland nut bearing affixed to the open end of the outer tube stage and a base member affixed to the first end of the outer tube stage in sealed relation, the at least one intermediate tube stage being spaced from the outer tube stage by the outer gland nut bearing and being extendible through the open end of the outer tube stage to an extended position and retractable through the open end of the outer tube stage to a collapsed position, the exposed end of at least the inner tube stage comprises a stop-collar which overlaps the exposed end of the next broader tube stage, wherein when the inner tube stage reaches a fully collapsed position the stop-collar of the inner tube stage contacts the exposed end of the next broader tube stage.  
           [0012]    The present invention further provides a telescopic multi-stage hydraulic hoist, comprising a hydraulic fluid inlet in communication with an interior of the hoist, an outer tube stage having a first end and a second open end and comprising an outer gland nut bearing affixed to the open end of the outer tube stage, at least one intermediate tube stage disposed within the outer tube stage in telescoping relation, the at least one intermediate tube stage having a contained end and an exposed end and comprising an intermediate gland nut bearing affixed to the open end, the intermediate tube stage being extendible through the open end of a next broader intermediate tube stage or the outer tube stage to an extended position and retractable through the open end of the next broader intermediate tube stage or the outer tube stage to a collapsed position, an inner tube stage disposed within the at least one intermediate tube stage in telescoping relation, the inner tube stage having a contained end and an exposed end and being extendible through the open end of the at least one intermediate tube stage to an extended position and retractable through the open end of the at least one intermediate tube stage to a collapsed position, a base member affixed to the first end of the outer tube stage in sealed relation, the base member comprising a recess, and a stop structure for arresting the retraction of the inner tube stage, whereby the contained end of at least the inner tube stage recedes into the recess in the base member when the hoist is in a fully collapsed position.  
           [0013]    In further aspects of the hoist of the invention: the stop-collars project from the gland nut bearings; each stop-collar contacts the gland nut bearing of the next broader tube stage; the gland nut bearings each comprise a wiper and a portion of the stop-collar of one tube stage which contacts the gland nut bearing of the next broader tube stage is provided with an annular recess into which the wiper of the next broader tube stage projects when the one tube stage is in the fully collapsed position; the base member comprises a recess, wherein the contained end of the inner tube stage recedes into the recess in the base member when the hoist is in a fully collapsed position; the hoist comprises a plurality of intermediate tube stages, wherein at least one intermediate tube stage recedes into the recess in the base member when the hoist is in a fully collapsed position; the base member is threadedly engaged to the outer tube stage; the base member comprises a neck bearing threads for engagement to the outer tube stage; and/or at least one of the intermediate tube stages abuts the neck of the base member when in the fully collapsed condition.  
           [0014]    The present invention further provides a telescopic multi-stage hydraulic hoist, comprising a hydraulic fluid inlet in communication with an interior of the hoist, an outer tube stage having a first end and a second open end and comprising an outer gland nut bearing affixed to the open end of the outer tube stage, an inner tube stage disposed within the outer tube stage in telescoping relation, the inner tube stage having a contained end and an exposed end and being extendible through the open end of the outer tube stage to an extended position and retractable through the open end of the outer tube stage to a collapsed position, and a base member affixed to the first end of the outer tube stage in sealed relation, comprising a neck bearing threads for engagement to the outer tube stage, whereby the contained end of the inner tube stage abuts the neck of the base member when the hoist is in the fully collapsed condition.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    In drawings which illustrate by way of example only a preferred embodiment of the invention,  
         [0016]    [0016]FIG. 1A is a partially cutaway perspective view of a telescopic hydraulic hoist according to the invention,  
         [0017]    [0017]FIG. 1B is a partially cutaway perspective view of a telescopic hydraulic hoist of FIG. 1A in a fully collapsed position,  
         [0018]    [0018]FIG. 2 is a cross-sectional elevational view of the hydraulic telescopic hoist of FIG. 1A in a fully extended position,  
         [0019]    [0019]FIG. 3 is a perspective view of a gland nut bearing in the hydraulic telescopic hoist of FIG. 1A having a stop-collar,  
         [0020]    [0020]FIG. 4 is an elevation of the gland nut bearing of FIG. 3,  
         [0021]    [0021]FIG. 5 is a cross-sectional elevation of a rod-eye for the inner tube stage,  
         [0022]    [0022]FIG. 6 is a perspective view of a base member for the hydraulic telescopic hoist of FIG. 1A,  
         [0023]    [0023]FIG. 7 is a perspective view of the base member of FIG. 6 taken from the opposite side,  
         [0024]    [0024]FIG. 8 is a cross-sectional elevation of the base member of FIG. 6, and  
         [0025]    [0025]FIG. 9 is an enlarged elevation of a preferred thread configuration for the hoist of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    [0026]FIG. 1A illustrates a hydraulic hoist  10  in a partially extended position, having an outer tube stage  12 , intermediate tube stages  14 ,  16 ,  18  and  20  and inner tube stage  22 . (For purposes of clarity FIG. 1A shows each tube stage partially extended; in actual operation the tube stages extend one at a time until the hoist is fully extended.) FIG. 1B shows the hydraulic hoist  10  of FIG. 1A in the fully collapsed position.  
         [0027]    Stroke limiters  28  affixed about the contained ends of each intermediate tube stage  14 ,  16 ,  18  and  20  and the inner tube stage  22  define the extension limit of each respective tube stage. The tube stages support bearings  27  (for example comprising wear bands) and seals  33  disposed between the tube stages prevent hydraulic fluid from flowing into air spaces  29  between the tube stages. The stroke limiters  28  may be of varying lengths as described in U.S. Pat. No. 5,983,778 issued Nov. 16, 1999 to Dawson, which is incorporated herein by reference, to allow differential extension lengths which accommodate decreasing strength or stability as the diameter of the tube stages decreases.  
         [0028]    It will be appreciated that the number of stages and their dimensions are a matter of selection for any particular intended use. The hoist of the invention will be described and shown herein as having four intermediate tube stages  14 ,  16 ,  18  and  20  by way of example, however the invention is not intended to be limited thereby.  
         [0029]    Rod eye  26 , shown in FIG. 5, is engaged (preferably threaded) to the exposed end of the inner tube stage  22  for attachment of the hydraulic hoist  10  to a load, for example the bed or frame of a dump truck (not shown), thereby enabling the bed of the dump truck to be elevated. Grease nipple  24  provides a conduit for applying grease to the rod eye  26 , as is known, and air bleeder  25  is in communication with the interior of inner tube stage  22 , allowing air to be bled from the hoist  10  when the hoist  10  is first filled with hydraulic fluid.  
         [0030]    The outer stage  12  comprises a first end and a second open end. A base member  30  is affixed to the first end of the outer stage  12 , in the preferred embodiment comprising a base member  30 , illustrated in FIGS.  6  to  8 . As shown the base member  30  includes a hydraulic fluid inlet  34  for feeding hydraulic fluid into interior of the hoist  10 , and preferably has a threaded portion  36  about the neck  31  for threaded engagement to the first end of the outer tube stage  12 , sealed by an O-ring (not shown). A threaded connection between the base  30  and the outer tube stage  12  is preferred because it is stronger than a conventional weld, reduces the labor required to assemble the hoist  10 , and renders the hoist  10  easier to maintain and repair. As shown in FIG. 9, the preferred thread  31   a  is approximately 6 mm deep and of a ‘saw tooth’ configuration, sloping  2  and 45 degrees, has a pitch of 9 threads per inch, and has a truncated outer edge to reduce interference by grit and other particulate matter.  
         [0031]    Pin hole  38  in base member  30  receives an anchoring pin (not shown) for anchoring the outer stage  12  of the hydraulic hoist  10  to the frame of the truck, and also includes a grease nipple  39 . It will be appreciated that the hoist  10  is invertible, and thus either end can be mounted to the frame or to the load. It will also be appreciated that while it is convenient to provide the hydraulic fluid inlet  34  in the base member  30 , it is also possible to position the hydraulic inlet  34  in another location in communication with the interior of the hoist  10 .  
         [0032]    Base member  30  is further provided with a recess  32 . As can be seen in FIG. 1, in the fully collapsed position a portion of the contained end of each intermediate tube stage  16 ,  18  and  20 , and inner tube stage  22 , recedes into the recess  32  in the base member  30 . This allows the intermediate tube stages  16 ,  18 ,  20  and inner tube stage  22  to be formed longer than the first intermediate stage  14 , without increasing the minimum (fully collapsed) length of the hoist  10 . Thus, when the hoist  10  is fully extended there is a greater overlap between adjacent tube stages, which increases the rigidity and stability of the hoist  10  in operation.  
         [0033]    In the preferred embodiment the broadest intermediate stage  14  in the collapsed position abuts an annular neck  31  about the base member  30 . The neck  31  forms a stop for the intermediate stage  14 , which thus does not recede into the recess  32  in the base member  30 .  
         [0034]    The outer tube stage  12  comprises an outer gland nut bearing  48  affixed to the open end of the outer tube stage  12 . The intermediate tube stages  14 ,  16 ,  18 , and  20  each comprise intermediate gland nut bearing  50  respectively affixed to the exposed ends of intermediate tube stages  14 ,  16 ,  18 , and  20 . The gland nut bearings  48  and  50  provide a bearing surface which maintains each respective next narrower tube stage in concentric spaced relation from the open end of the outer tube stage  12  and the exposed ends of the intermediate tube stages  14 ,  16 ,  18  and  20 . The contained ends of each tube stage  14 ,  16 ,  18  and  20  and the inner tube stage  22  are maintained in concentric spaced relation from the next broader tube stages  12 ,  14 ,  16 ,  18  or  20  by bearings  27  and seals  33 , the bearings comprising for example conventional wear bands disposed in a shallow recess (not shown) about the outer wall of each tube stage  14 ,  16 ,  18 ,  20  and  22 . Each tube stage thus slides through the gland nut bearing  48  or  50  of the next broader tube stage  12 ,  14 ,  16 ,  18  or  20 , and bearings  27  and seals  33  slide along the interior wall of the next broader tube stage  12 ,  14 ,  16 ,  18  or  20 , to thus move the tube stages  14 ,  16 ,  18 ,  20  and  22  in telescoping relation.  
         [0035]    The gland nut bearing  48  has a threaded neck  48   a  for engagement to a threaded portion disposed about the inner wall of the open end of the outer tube stage  12 . As shown in FIGS. 3 and 4, each intermediate gland nut bearing  50  has a threaded neck  52  for engagement to threaded portions respectively disposed about the inner walls of the exposed ends of the tube stages  14 ,  16 ,  18  and  20 , and further comprises a stop-collar  54  which extends radially beyond the interior limit of the next broader tube stage, such that in the collapsed position illustrated in FIG. 1B the stop-collar  54  contacts the exposed end of the next broader tube stage, and in particular abuts against the exposed end of the gland nut bearing  50  (or  48 ) of the next broader tube stage. The rod eye  26  also comprises a stop-collar  54 , which serves as a stop for the inner tube stage  22  by abutting against the exposed end of the gland nut bearing  50  affixed to the narrowest intermediate tube stage  20 .  
         [0036]    The outer gland nut  48  is affixed to the outer stage  12 , which is stationary and therefore does not require a stop-collar. The broadest intermediate tube stage  14  also does not require a stop-collar  54 , because in the embodiment shown the neck  31  forms a stop for the tube stage  14 ; however, the broadest intermediate stage  14  may be provided with a gland nut bearing  50  having a stop-collar  54 , as shown in the drawings, for cosmetic purposes.  
         [0037]    Affixed to the upper portions of gland nut bearings  48  and  50  are annular wipers  60 , made of heavy duty rubber or another suitable material, to prevent dirt and other particulate contaminants from intruding into the spaces between adjacent tube stages. Locking screws (not shown) retain each gland nut bearing  48 ,  50 , base member  30  and rod eye  26  in its respective tube stage  12 ,  14 ,  16 ,  18 ,  20  and  22 , and thereby retain each of the tube stages with respect to the next broader tube stage. Each stop-collar  54  is provided with a shallow annular recess  54   a,  for example {fraction (1/16)} inches deep, which in the collapsed position allows the collar  54  to abut the exposed end of the next broader tube stage (i.e., the exposed face of gland nut  48  or  50 ) without crushing the wiper  60  supported therein. The recess  54   a  also provides a reservoir for the deposit of any dirt pushed up by the wiper  60  of the next broader tube stage.  
         [0038]    As described in U.S. Pat. No. 5,983,778, which is incorporated herein by reference, in the preferred embodiment air breathers  62  are provided for each of hydraulic tube stages  12 ,  14 ,  16 ,  18 , and  20 , illustrated in FIGS. 1 and 2, which allow air to flow out of and into the air spaces  29  between tube stages as the hoist  10  is respectively extended and collapsed. The air breathers  62  are preferably in communication with the respective air spaces  29  through a groove etched along the interior wall of the gland nut bearing  50 , as described in U.S. Pat. No. 5,983,778.  
         [0039]    In operation, with the hoist  10  positioned between the frame and the load, for example the bed and the frame of a dump truck (not shown), and the rod eye  26  and pin hole  38  anchored thereto, pumping hydraulic fluid into the hoist  10  through fluid inlet  34  forces the hydraulic stages  14 ,  16 ,  18 ,  20  and  22  to extend from the collapsed position illustrated in FIG. 1B to the extended position illustrated in FIG. 2. As the hoist  10  extends and the stroke limiters  28  approach the gland nut bearings  48  or  50  of the next broader tube stage, air is forced out of the air spaces  29  between tube stages and egresses through air breathers  62 .  
         [0040]    As each tube stage  14 ,  16 ,  18 ,  20  and  22  reaches the fully extended position illustrated in FIG. 2, its respective stroke limiter  28  contacts the neck  52  of the gland nut bearing  50  of the next adjacent broader tube stage. For example, as the inner tube stage  22  reaches its full extension the stroke limiter  28  affixed around tube stage  22  abuts against the neck  52  of the gland nut bearing  50  affixed to intermediate tube stage  20 ; as the intermediate tube stage  20  reaches its full extension the stroke limiter  28  affixed around tube stage  20  abuts against the neck  52  of the gland nut bearing  50  affixed to intermediate tube stage  18 ; and so on. Thus, in the extended position, the overlap between adjacent tube stages is determined by the axial limits of the stroke limiters  28  and the necks  52  of the gland nut bearings  48  and  50 .  
         [0041]    When the hydraulic pressure is released the hoist  10  collapses from the extended position to the collapsed position shown in FIG. 1B, each intermediate tube stage  14 ,  16 ,  18 ,  20  and inner tube stage  22  is forced to retract by the weight of the truck bed or other load. The volume of the air spaces  29  increases as the stroke limiters  28  recede from their adjacent gland nut bearings  50 , and air is drawn through the air breathers  62  into the air spaces  29 . This prevents air from being drawn through the wipers  62 , which would tend to suck particulate material into the air space  29  between tube stages which could damage the piston seal or the outer surface of the next broader tube stage. The air breathers  62  are preferably provided with filters to clean air as it is drawn into the air spaces  29  and prevent the intrusion of particulate matter between tube stages.  
         [0042]    Because each stop-collar  54  overlaps the gland nut bearing  48  or  50  of the next broader tube stage, as the inner tube stage  22  and intermediate tube stages  16 ,  18  and  20  respectively reach a fully collapsed position the stop-collar  54  of the gland nut bearing  50  mounted on the collapsed tube stage contacts the exposed end of the next broader tube stage, which in the embodiment shown is the exposed end of the gland nut bearing  48  or  50  affixed to the next broader tube stage. Thus, when intermediate tube stage  20  is fully collapsed the stop-collar  54  of the gland nut bearing  50  affixed to tube stage  20  contacts the exposed end surface of the gland nut bearing  50  affixed to intermediate tube stage  18 ; when intermediate tube stage  18  is fully collapsed the stop-collar  54  of the gland nut bearing  50  affixed to intermediate tube stage  18  contacts the exposed end of the gland nut bearing  50  affixed to intermediate tube stage  16 ; and so on. The stop-collar  54  about rod eye  26  similarly extends radially so as to overlap the end of the next broader tube stage  20 , to arrest the retraction of the inner tube stage  22  in like fashion. When the collars  54  of the rod eye  26  and all gland nut bearings  50  abut the respective next broader tube stage, and the contained end of the first intermediate tube stage  14  contacts the neck  31  of the base member  30 , the hoist  10  is in the fully collapsed position.  
         [0043]    As shown in FIG. 1B, in the fully collapsed position the contained ends of inner tube stage  22  and intermediate tube stages  16 ,  18  and  20  recede into the recess  32  formed in base member  30 . In contrast with prior art hoist devices, in which the tube stages rest in staggered fashion on abutting stop rings, this allows the intermediate tube stages  16 ,  18 ,  20  and inner tube stage  22  to be made longer without increasing the length of the outer tube stage  12 , and thus without increasing the length of the hoist  10  in the fully collapsed position. The increased lengths of the intermediate and inner tube stages  16 ,  18 ,  20  and  22  allows for greater overlap between tube stages in the fully extended hoist  10 , and thus provides greater rigidity and stability. Also, the recessed base member  30  weighs considerably less than the solid base casting shown in U.S. Pat. No. 5,983,778.  
         [0044]    It will be appreciated that while the hoist  10  of the invention advantageously comprises intermediate tube stages, the invention also contemplates a two-stage hoist  10  in which an inner tube stage  22  is disposed within the outer tube stage  12  in telescoping relation, extendible through the open end of the outer tube stage  12  to an extended position and retractable to a collapsed position. The base member  30  affixed to the outer tube stage  12  comprises a neck  31  bearing threads for engagement to the outer tube stage  12 , and the contained end of the inner tube stage  22  abuts the neck  31  of the base member  30  when the hoist  10  is in the fully collapsed condition.  
         [0045]    A preferred embodiment of the invention having been thus described by way of example, it will be appreciated by those skilled in the art that various modifications and adaptations may be made without departing from the scope of the invention, as set out in the appended claims. Further, while the invention has been described for purposes of example in the context of a dump truck, the invention may be used in many other applications and is not limited to the specific environment in which it has been so described.