Abstract:
The hand truck brake provides automatic braking for a hand truck as it negotiates a stairway or other uneven surface. The brake is adaptable to various types of hand trucks, including powered stair-climbing trucks. The brake includes two major assemblies. The first is a reciprocating plunger having a distal roller that travels along the surface. When the roller travels over the nose of a stairway tread, the plunger extends to actuate the brake. The second major assembly is a rotary cam rotated by the plunger as it extends. The cam has an extension and a brake shoe, the brake shoe engaging the underlying surface to stop the hand truck when the cam is rotated to its brake-engaging position. The assembly automatically retracts when the hand truck is oriented vertically. Additional controls are provided for the operator to extend or retract the brake mechanism.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/482,499, filed May 4, 2011. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to carts, dollies, hand trucks, and the like, and particularly to a hand truck brake serving to prevent a hand truck from rolling on the tread of a step while negotiating steps or stairways. 
     2. Description of the related art 
     Hand trucks, carts, dollies, and similar articles of equipment are commonly used to transport large and bulky objects (e.g., furniture, office equipment, etc.) over relatively short distances, as to or from a delivery truck or within a building structure. Most such hand trucks and the like are manually operated, i.e., they have no additional motive power (e.g., electric motor, etc.). However, a subclass of such hand trucks is configured or adapted for climbing and descending stairways, most of these devices including some form of motive power. 
     One common need of all such devices, whether powered or non-powered and whether specially adapted for use on stairs or not, is the need to provide some form of braking action to prevent the device from rolling from a step when negotiating steps or stairways. This is conventionally achieved by the operator of the hand truck, who manually holds the truck to prevent it from moving. In practice, this can be difficult at times, depending upon the diameter and relative location of the wheels of the truck, the fore and aft width of the tread of the stairs, whether there is any slope to the stairway tread(s), and other factors. At times, it may require considerable strength to prevent a loaded hand truck from dropping down the stairs if the centers of the wheels are even slightly beyond the nose of the stairway tread. Even when the hand truck is momentarily stable on a stairway tread, it takes only a moment of inattention and slight movement to cause the hand truck to roll beyond the nose of a stairway tread and proceed down the stairway or steps. Even though powered devices configured for negotiating stairways have considerable mechanical advantage limiting the rotation of the wheels when the motor is stopped, they still may roll to some degree against such mechanical advantage, and they may roll freely if the motor and/or driveline are disengaged from the wheels. 
     As a result, a number of braking devices have been developed in the past for the wheels and/or casters of hand trucks, dollies and carts and the like. One example of such is found in German Patent No. 3,934,234, published on Apr. 18, 1991, which describes (according to the drawings and English abstract) a “wheelbarrow” or hand truck having two sets of wheels to assist in drawing the truck up and over the nose of each stairway tread. The wheels have ratcheting brakes that allow rotation in only one direction to prevent them from rolling down a set of steps. The ratchet brakes are controlled by the operator, who actuates a lever at the top of the hand truck frame. 
     Another example of a hand truck or cart configured for negotiating stairways is found in German Patent No. 10,113,635 published on Dec. 5, 2002. This document describes (according to the drawings and English abstract) a “trolley” or hand truck having main wheels in a “star wheel” configuration, i.e., a series of small wheels located at the distal ends of a series of radial arms, the arms and wheels rotating about a common single axis. Manually controlled brakes are provided to prevent rotation of the “star wheel” assembly and of the forwardly disposed casters. 
     Thus, a hand truck brake solving the aforementioned problems is desired. 
     SUMMARY OF THE INVENTION 
     The hand truck brake provides automatic braking action for a hand truck as it negotiates a stairway or uneven sloping terrain. The device may be provided either as a kit or assembly for installation to an existing hand truck, or in combination with a hand truck at the time of manufacture. The device is particularly well suited for installation to an electrically or otherwise powered hand truck adapted for climbing and descending stairs and steps, but may also be applied to any other practicable hand truck configuration. Most preferably, one brake assembly is provided for each wheel in a conventional two-wheel hand truck having a single axle. 
     The hand truck brake comprises two major components. The first is a reciprocating plunger having a roller on its distal end. The plunger acts as a feeler and bears against the underlying surface. When the roller rolls over the nose of a stairway tread, the plunger drops to actuate the brake. The other major component is a rotary cam that is actuated by the movement of the plunger. When the plunger drops, it causes the cam to rotate in order to apply the brake. The brake is a shoe attached to an extension of the cam, the shoe rotating to bear against the underlying surface when the cam rotates due to actuation by the plunger. 
     The above-described operation is entirely automatic, and needs no action or intervention on the part of the operator of the hand truck. Orienting the hand truck to the vertical, i.e., with the toe plate resting upon the surface, pushes the plunger upward to lock it automatically in its retracted position. A control is provided for the operator to deploy the plunger and roller assembly for further braking operation if the system has been disengaged or retracted, and another control is provided for the operator to retract or disengage the brake without orienting the truck to the vertical if the brake has been actuated. The controls are located with the brake assembly and are configured for ease of operation by the foot of the operator to obviate any need for the operator to bend down to access the controls. 
     These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a left side elevation view of a stair-climbing hand truck incorporating a hand truck brake according to the present invention. 
         FIG. 2  is an exploded perspective view of a hand truck brake according to the present invention. 
         FIG. 3  is a detailed left side elevation view in section of a hand truck brake according to the present invention, illustrating various operational details thereof. 
         FIG. 4  is a detailed right side elevation view of the hand truck brake according to the present invention, illustrating further details. 
         FIG. 5  is a partial left side elevation view of the lower end of a hand truck incorporating the hand truck brake according to the present invention, illustrating the deployment of the brake for use. 
         FIG. 6  is a partial left side elevation view of the lower end of a hand truck incorporating the hand truck brake according to the present invention, illustrating the released brake on a level surface. 
         FIG. 7  is a partial left side elevation view of the lower end of a hand truck incorporating the hand truck brake according to the present invention, illustrating actuation of the brake as the feeler passes over the nose of a stair tread. 
         FIG. 8  is a partial left side elevation view in section of the lower end of a stair-climbing hand truck incorporating the hand truck brake according to the present invention, illustrating lifting the hand truck and release of the brake by the stair-climbing mechanism. 
         FIG. 9  is a partial left side elevation view in section of the lower end of a hand truck incorporating the hand truck brake according to the present invention, illustrating automatic retraction of the brake mechanism as the truck is oriented vertically. 
         FIG. 10  is a partial left side elevation view in section of the lower end of a hand truck incorporating the hand truck brake according to the present invention, illustrating retraction of the brake mechanism by the operator. 
     
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The hand truck brake provides automatic braking for a hand truck or the like as it negotiates a flight of steps or other uneven terrain or surface. The brake is particularly well adapted for installation in a motorized, stair-climbing hand truck, but may be adapted to any other practicable hand truck or the like. 
       FIG. 1  of the drawings is an illustration of an exemplary stair-climbing hand truck T. The hand truck brake  10  is shown installed immediately outboard of the left wheel LW of the hand truck T. The hand truck T includes a number of conventional features, i.e., a frame F having an upper end U and opposite lower end L, and conventional left and right wheels LW and RW installed at the lower end L of the frame F. (The right wheel RW is partially illustrated in the elevation view in section of  FIG. 8 .) The illustrated hand truck T represents a model manufactured by the Escalera Company of Yuba City, Calif., and includes a stair climbing and descending mechanism C disposed rearward of the frame F. However, the hand truck brake  10  may be adapted to other types of hand trucks, as noted above. Only a single brake mechanism  10  is shown in the various views of the drawings due to the orientation of the hand truck T and its components in those views. However, it will be understood that two such brake mechanisms  10  are preferably installed on any given hand truck, one brake mechanism  10  being installed adjacent each of the two wheels LW and RW conventionally provided on such hand trucks. 
       FIG. 2  provides an exploded perspective view of the brake mechanism  10 , illustrating its various parts.  FIGS. 3 and 4  respectively provide an elevation view in section through the housing of the mechanism, and an opposite side elevation view of the assembly. The brake mechanism  10  includes a housing  12  having a feeler passage  14  disposed therethrough. An elongate feeler  16  is installed within the feeler passage  14  of the housing  12 . The feeler  16  includes a transverse pin passage  18  therethrough. The housing  12  has an elongate slot  20  therethrough that is aligned with the feeler passage  14 . A feeler retaining and cam engagement pin  22  is installed through the housing slot  20  and the pin passage  18  of the feeler  16  in order to retain the feeler  16  within the passage  14  in the housing  12 . The feeler  16  travels upward and downward in the feeler passage  14  of the housing  12  within the limits defined by the ends of the housing slot  20 , and is urged outward (downward) from the housing  12  by a spring  24  that passes concentrically through the upper portion of the tubular feeler  16  to bear against the feeler retaining and cam engagement pin  22 . The spring  24  is installed through the top of the housing  12  and is retained therein by a retainer plate  26  and spring guide removably installed atop the housing  12 . The feeler  16  is in contact with the surface over which the hand truck T is traveling when the brake mechanism  10  is deployed, and accordingly has a lower distal end  28  having a roller  30  extending therefrom to rotate freely upon the contact surface therebeneath. 
     A cam  32  is pivotally mounted on each axle bolt or shaft A of the hand truck T. The housing  12  is immovably affixed to the structure of the lower portion L of the hand truck frame F, e.g., to the back of the load-carrying platform P. The cam  32  communicates mechanically with the housing  12  and feeler  16  by means of an arcuate slot  34  disposed through or into the cam  32 . The feeler retaining and cam engagement pin  22  extends from the feeler  16 , through the slot  20  of the housing  12 , and into the cam slot  34 . The cam further includes a brake extension  36  extending from its lower portion. A brake shoe  38  is attached to the brake extension  36 . 
       FIG. 5  illustrates the deployment of the brake mechanism  10  by the operator of the hand truck T. The brake mechanism  10  is retractable when not in use, as noted further above. The brake mechanism  10  may be retracted, i.e., the feeler  16  may be drawn upward into the passage  14  within the housing  12 , when braking is not desired. When the operator of the hand truck T wishes to use the brake  10 , he or she may use a foot-operated device to deploy the brake, i.e., to allow the feeler  16  to extend from its passage in the housing  12 . The housing  12  includes a feeler retraction latch  40  extending from the upper rear portion thereof. The latch  40  is disposed directly upon the housing  12  with no additional intervening or remotely actuated mechanisms, and is biased against the back of the housing  12  by a retaining bolt and spring assembly  42 . The housing  12  has a latch pin passage  44  ( FIGS. 2 and 3 ) through the upper rear portion thereof. A latch pin  46  extends from the latch  40  through the latch pin passage  44  in the housing  12 . The feeler  16  includes a latch engagement slot  48  in the rearward side thereof, as shown in  FIGS. 2 and 3 . 
     Normally, the retaining bolt and spring assembly  42  hold the latch  40  securely against the back of the housing  12 , the latch pin  46  being completely seated through the latch pin passage  44  of the housing  12  and extending partially into the feeler passage  14  in the housing  12 . It will be noted that the lower, inboard end of the latch pin  46  is tapered. Thus, if the feeler  16  is pushed upwardly into the passage  14  in the housing  12 , the upper end of the feeler  16  will push the tapered end of the latch pin  46  outward to allow the feeler  16  to retract. As the feeler  16  retracts into its passage  14 , the latch engagement slot  48  in the feeler  16  passes over the tapered inboard end of the latch pin  46 , allowing the retaining bolt and spring  42  to push the latch  40  and the inboard tip of the pin  46  into the latch engagement slot  48  of the feeler  16 . The upper edge of the latch engagement slot  48  in the feeler  16  will catch on the straight upper side of the latch pin  46 , thus holding the feeler  16  in retraction within the housing  12 . However, if the operator of the hand truck T wishes to extend the feeler  16 , he or she need only step on the upper end of the latch  40 , as shown in  FIG. 5 , to draw the latch  40  rearward against the retaining pressure of the spring and bolt assembly  42 , thus withdrawing the latch pin  46  from the latch engagement slot  48  in the feeler  16 . The feeler extension spring  44  then pushes the feeler  16  downward to extend the feeler  16  from the housing  12 . 
       FIGS. 6 ,  7 , and  8  illustrate the operation of the automatic brake mechanism  10  as the hand truck T negotiates a set of steps or stairs. In the example of  FIGS. 6 through 8 , the hand truck T is descending a flight of steps or stairs with the hand truck brake  10  deployed. The upwardly positioned roller R 1  of the stair climbing and descending mechanism C is at or near the top of its travel in  FIG. 6 , after having lowered the two wheels LW and RW of the hand truck T to an intermediate step S of the flight of steps or stairs. The two wheels LW, RW of the hand truck T are free to roll across the surface of the step S in  FIG. 6 , as the brake mechanism  10  has not engaged the surface at this point. This is because the roller  30  of the feeler  16  is also rolling across the surface of the step  5 , the feeler  16  being partially retracted within the housing  12 . The feeler  16  communicates mechanically with the cam  32  by means of the feeler retention and cam engagement pin  22  engaging the arcuate slot  34  of the cam  32 , as shown in  FIG. 4 . This results in the cam  32  rotating clockwise slightly (as viewed in  FIG. 6 , i.e., the opposite side from  FIG. 4 ), thereby lifting the brake shoe  38  forward and upward, away from the surface of the step S, thereby allowing all of the wheels to roll freely. 
     As the hand truck T rolls forward across the surface of the step S, the forwardly disposed roller  30  of the feeler  16  will reach and drop over the edge or nose N of the step S, as shown in  FIG. 7 . When this happens, the feeler  16  extends downward from its housing  12 , the feeler retention and cam engaging pin  22  moving downward as well. The engagement of the pin  22  in the arcuate slot  34  of the cam  22  results in the cam rotating counterclockwise (as seen in  FIG. 7 ), thus dropping the brake shoe  38  onto the surface of the step S to stop any rolling movement of the hand truck T. 
       FIG. 8  illustrates the continuing operation of the stair climbing hand truck T and its brake mechanism  10 . In  FIG. 8  the stair climbing and descending mechanism C has drawn the second roller R 2  counterclockwise around the mechanism by means of its chain drive system. The roller R 2  is shown near (but not quite at) its lowermost position in  FIG. 8 . As the stair climbing and descending mechanism C continues to operate, the second roller R 2  will travel further counterclockwise around its chain driven path, lifting the brake shoe  38  slightly from the surface of the step S. This allows the hand truck T to move forward beyond the nose N of the step S, at which point the hand truck T is supported by the second roller R 2  to descend from the step S to the next lower step. The process repeats with each succeeding step, the feeler  16  being pushed into its housing  12  to rotate the cam  32  and its brake shoe  38  clear of the underlying step surface until the roller  30  of the feeler  16  drops over the nose of the succeeding step to rotate the cam  32  and drop the brake shoe  38  onto the step surface. Actuation of the stair climbing and descending mechanism allows the hand truck T to travel over the nose of that step, and down to the next lower step. The direction of travel of the chain drive of the stair climbing and descending mechanism C is reversed to ascend a set of steps, hand truck brake  10  working as described above. 
     When the steps have been negotiated and the hand truck T is on a level surface, the hand truck brake  10  (or more accurately, the feeler  16 ) may be retracted into the housing  12  to prevent deployment or extension of the feeler  16  and corresponding actuation of the brake show  38 . Two methods are provided for retracting the feeler  16 , as shown in  FIGS. 9 and 10 . 
     The first method of  FIG. 9  occurs essentially automatically when the hand truck T is positioned with its frame F oriented vertically. When this is done, the feeler  16  is pushed upwardly into the housing  12  until the latch engagement slot  48  of the feeler  16  catches on the latch pin  46 , the latch pin  46  then holding the feeler  16  retracted in its housing  12  regardless of the orientation of the hand truck T. This allows the hand truck T to be moved over a surface without the brake shoe  38  extending and dragging on the underlying surface. When the operator of the hand truck T wishes to actuate the brake mechanism  10 , he or she need only use his or her foot top pull the top of the feeler retraction latch  40  back to release the pin  46  and allow the feeler  16  to extend from its housing  12 , generally as shown in  FIG. 5  and described in detail further above. 
     Alternatively, the operator of the hand truck T may retract the feeler  16  by rotating the cam  32 . This procedure is illustrated in  FIG. 10  of the drawings. A brake retraction control is provided on the cam  32  for the operator to actuate when the operator finds that he or she cannot orient the hand truck T vertically on a surface to retract the feeler  16 , as described above and shown in  FIG. 9 . The brake retraction control comprises a control lever bolt  50  (shown clearly in the exploded view of  FIG. 2 ) installed through the upper portion of the cam  32 , and a foot-operated peg  52  installed on the lever bolt  50 . The control lever bolt  50  and its peg  52  are disposed directly upon the cam  32  with no additional intervening or remotely actuated mechanisms. The operator need only step on the peg  52  to push it downward and rearward, thereby rotating the cam  32  clockwise, as shown in  FIG. 10 . This draws the feeler  16  upward in the housing  12 , since the arcuate slot  34  of the cam  32  draws the feeler retention and cam engagement pin  22  upward as the cam  32  rotates. When the feeler  16  is drawn upward in the housing to a sufficient point, the latch pin  46  engages the latch engagement slot  48  of the feeler  16  to hold the feeler  16  in its retracted state. Deployment of the hand truck brake  10 , or more accurately the feeler  16  of the hand truck brake  10 , for operation is accomplished as described further above in the description of the operation shown in  FIG. 5 . 
     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.