Abstract:
The present invention provides a tow bar assembly, which may be retrofitted to a dolly while maintaining convenient space saving properties of permanently fitted tow bars. The novel tow bar assembly includes a tow bar, a shaft and a biasing member, such as a spring, biasing the tow bar towards an upright orientation about an axis of revolution. The shaft has a first end and a second end, which opposes the first end. The shaft connects the tow bar to the dolly from the ends so as to provide rotation of the tow bar in respect to the dolly about the axis of revolution. The shaft features an inner cavity, which extends along the axis of revolution. The biasing member is arranged into the cavity of the shaft and rotationally secured thereto. The shaft also features a first end plug at the first end of the shaft for enclosing the biasing member to the cavity. The first end plug rotationally locks the biasing member to the dolly.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to transporting goods. In particular, the invention relates to dollies, on which parceled goods are transported and stored temporarily. To be precise, the invention relates to a tow bar assembly according to the preamble portion of claim  1  and to a dolly comprising the same. 
       BACKGROUND ART 
       [0002]    There is known a vast variety of different devices used for transporting parceled goods. Typically pieces or stacks thereof are loaded onto a wheeled platform, on which they are conveyed to shop floor or storage. These wheeled platforms are called dollies. Some dollies are equipped with a tow bar for transporting a plurality of dollies in a chained fashion. When the tow bar for pulling the dolly is temporarily not used, it is typically pivoted in an upright position for saving space. U.S. Pat. No. 4,856,810 proposes one solution to providing a space saving tow bar for a dolly. The tow bar known from U.S. Pat. No. 4,856,810 must be manually manipulated into the vertical space saving position. 
         [0003]    A solution for biasing the tow bar to the vertical position is proposed by EP 2278015, which discloses a biasing mechanism, which connects the tow bar to the dolly. The biasing mechanism includes an axle fixed to the dolly and a spring arranged around the axle and tensioned between the tow bar and the chassis of the dolly. The spring biases the tow bar to rotate it about the fixed axle towards an upright position. The biasing mechanism known from EP 2278015 has the additional benefit of assisting coupling between the tow bar and the receiving socket of another dolly. 
         [0004]    The tow bars known from U.S. Pat. No. 4,856,810 and EP 2278015 are both permanently fixed to the dolly. Detachable tow bars are also known for retrofitting a tow bar to a dolly. Such tow bars typically feature a quick coupling between a plug on the tow bar and a corresponding socket, which is to be fixed to the dolly for receiving the tow bar. While detachable tow bars improve modularity of dollies, they lack the benefit of saving space by biasing the tow bar to an upright position. 
         [0005]    It is therefore an aim of the present invention to provide a tow bar assembly, which may be retrofitted to a dolly while maintaining convenient space saving properties of permanently fitted tow bars. 
       SUMMARY 
       [0006]    The aim of the present invention is achieved with aid of a novel tow bar assembly including a tow bar, a shaft and a biasing member, such as a spring, for biasing the tow bar towards an upright orientation about an axis of revolution. The shaft has a first end and a second end, which opposes the first end. The shaft connects the tow bar to the dolly from the opposing ends so as to provide rotation of the tow bar in respect to the dolly about the axis of revolution. The shaft features an inner cavity, which extends along the axis of revolution. The biasing member is arranged into the cavity of the shaft and rotationally secured thereto. The shaft also features a first end plug at the first end of the shaft for enclosing the biasing member to the cavity. The first end plug rotationally locks the biasing member to the dolly. 
         [0007]    More specifically, the tow bar assembly according to the present invention is characterized by the characterizing portion of claim  1 . 
         [0008]    The aim of the present invention is on the other hand achieved with aid of a dolly including such a novel tow bar assembly. 
         [0009]    Considerable benefits are gained with aid of the present invention. The proposed tow bar assembly may be conveniently retrofitted to a dolly thus significantly improving modularity. Because the assembly contains a biasing mechanism, the tow bar will spring to an upright position automatically thus saving space when detached from another dolly without manual user interference. The spring action of the biasing mechanism also aids the coupling of the hitch of the tow bar to the socket of another dolly. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]    In the following, exemplary embodiments of the invention are described in greater detail with reference to the accompanying drawings in which: 
           [0011]      FIG. 1  presents an isometric top view of a dolly with a tow bar assembly according to one embodiment, wherein the castor mount plates have been omitted for illustrative purposes, 
           [0012]      FIG. 2  presents a detailed view of the highlighted section of the tow bar assembly of  FIG. 1 , 
           [0013]      FIG. 3  presents a type E view of  FIG. 2  showing the hidden outlines of internal components of the tow bar assembly, 
           [0014]      FIG. 4  presents a detailed bottom view of the highlighted section of the tow bar assembly of  FIG. 1 , 
           [0015]      FIG. 5  presents a detailed explosion view of the tow bar dolly and tow bar assembly of  FIG. 1 , 
           [0016]      FIG. 6  presents a detailed view of the second end of the shaft, i.e. the proximal end, of the tow bar assembly of  FIG. 5 , and 
           [0017]      FIG. 7  presents a detailed view of the first end of the shaft, i.e. the distal end, of the tow bar assembly of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0018]    As shown in  FIG. 1 , the tow bar assembly  120  may be retrofitted to a dolly  100  having a typical construction including a chassis  110  with two mutually parallel longitudinal peripheral beams  111  and two mutually parallel transversal peripheral beams  112  connected by the longitudinal peripheral beams  111  to form a rectangular frame. Castors  130  are connected to the underside of the rectangular chassis  110  through mount plates, which have been omitted from the drawings for showing details of connecting the tow bar  120  to the dolly  100 . The castors  130  include swivel castors arranged to the front end of the dolly  100 , which features the tow bar assembly  120 , and fixed castors arranged to the rear end of the dolly  100 , which features a female counterpart of a hitch (not shown) for receiving a male counterpart of a hitch of a tow bar of another dolly (not shown). The longitudinal peripheral beams  111  extend in the main travelling direction of the dolly  100 , i.e. in the direction steered to by the fixed castors. Accordingly, the transversal peripheral beams  112  extend in a direction perpendicular to the longitudinal peripheral beams  111  and therefore to the main travelling direction. The chassis  110  also includes at least two mutually parallel longitudinal cross beams  113 , which are distanced from each other in the transversal direction. The longitudinal cross beams  113  extend parallel to the longitudinal peripheral beams  111  and connect the transversal peripheral beams  112  within the rectangular frame of the chassis  110 . 
         [0019]    Turning now to  FIGS. 2 to 4 , which show the relationship between the tow bar assembly  120  and the chassis  110  of the dolly  100 . The longitudinal cross beams  113  contain pivot points for providing an axis of revolution R for the tow bar assembly  120  ( FIG. 2 ). The tow bar assembly  120  contains a tow bar  121  and a shaft  122 , which is fixed thereto. The shaft  122  spans between the longitudinal cross beams  113  within the periphery of the frame of the chassis  110 , whereby the shaft  122  is protected by the frontal transversal peripheral beam  112  ( FIG. 4 ). More specifically, the shaft  122  has a first end  122 A and a second end  122 B, which opposes the first end  122 A, whereby the shaft  122  is connected to the longitudinal cross beams  113  from the ends  122 A,  122 B. The axis of revolution R is therefore formed between and through the first and second end  122 A,  122 B of the shaft  122  ( FIG. 2 ). 
         [0020]      FIGS. 1 and 3  show how the tow bar  121  includes two sections, where the terminal end of a first section features a male counterpart of a hitch and where a second section extends from the first section in an angled manner. The shaft  122  is fixed to said second section of the tow bar  121 . The shaft  122  is used to house the biasing mechanism of the tow bar assembly. The components housed inside the shaft  122  are illustrated by dotted lines in  FIG. 3  and by solid lines in the explosion view of  FIG. 5 . To facilitate the housing of the biasing mechanism the shaft  122  includes an inner cavity, which extends along the axis of revolution R. Firstly, the biasing mechanism includes a biasing member  123 , which is provided to the inner cavity of the shaft  122 . In the embodiment shown in the FIGS. the biasing member  123  is a spring, more specifically a coil spring. 
         [0021]    The biasing mechanism also includes two end plugs  124 ,  125  for closing the ends  122 A,  122 B of the shaft  122  and for enclosing the biasing member  123  to the inner cavity of the shaft  122 . A first end plug  124  is connected to the first end  122 A of the shaft  122  through a sliding fit, whereby rotation between the first end plug  124  and shaft  122  is allowed. 
         [0022]    The first end plug  124  has three functions:
       1. to enclose the biasing member  123  to the inner cavity of the shaft  122 ,   2. to enable pre-tensioning of the biasing member  123  and to   3. to rotationally lock the biasing member  123  to the dolly  100  in the fully assembled state.       
 
         [0026]    The features of the first end plug  124  enabling the three functions are discussed in greater detail hereafter. 
         [0027]    The second end plug  125  is fixed to the second end  122 B of the shaft  122  for enclosing the biasing member  123  to the cavity. The end plugs  124 ,  125  are connected by the biasing member  123 . The first end  122 A of the shaft  122  is rotatable in respect to the dolly  100  by means of the sliding fit between the shaft  122  and the first end plug  124 , which in turn is angularly locked to the dolly  100 . On the other hand the second end  122 B of the shaft  122  may be rotated in respect to the dolly  100  by means of the sliding fit between the dolly  100  and second end plug  125 , which in turn is fixed to the shaft  122 . To facilitate this function the second end plug  125  rotationally locks the biasing member  123  to the shaft  122 . The features of the second end plug  125  enabling the three functions are discussed in greater detail hereafter. It is to be, however, understood that the angular displacement between the first end plug  124 , which is angularly fixed to the dolly  100  but rotatable connected to the shaft  122 , and second end plug  125 , which is rotatably connected to the dolly  100  but angularly fixed to the shaft  122 , causes the biasing member  123  there between to undergo winding. Accordingly, the biasing member  123  preferably contains spring properties to resist winding and more preferably also compression. Such spring properties may be achieved by means of a coil spring. 
         [0028]    Turning now to  FIGS. 5 to 7 , which show the details of the end plugs  124 ,  125  of the shaft  122  and the interface between tow bar assembly  120  and the dolly  100 . As can be seen from  FIG. 5 , the longitudinal cross beams  113  feature pivot points  113   a ,  113   b  for receiving the end plugs  124 ,  125 , respectively. The axis of revolution R passes through the pivot points  113   a ,  113   b  which are aligned accordingly. For providing a rotational lock between the first end  122 A of the shaft  122  and the dolly  100 , the first pivot point  113   a  is formed as a rotationally non-symmetrical opening  113   a . It is to be understood that all references to rotationally symmetrical or non-symmetrical shapes are viewed as rotation about the axis of revolution R, i.e. as rotation about the longitudinal direction of the shaft  122 . The rotationally non-symmetrical opening  113   a  is dimensioned to receive the first end plug  124  in two stages, which are discussed in greater detail hereafter. The second pivot point  113   b  in the opposing longitudinal cross beam  113  is formed as a rotationally symmetrical opening for receiving the second end plug  125  in a rotatable manner. 
         [0029]    In  FIG. 5 , the biasing member  123  is retracted from the inner cavity of the shaft  122  for showing that according to the illustrated embodiment, the biasing member  123  provided in the form of a coil spring terminates at both ends to a straight portion for coupling to the end plugs  124 ,  125 . In other words, according to a particular embodiment, the biasing member  123  is a coil spring, which includes a first coupling portion  123   a . The first coupling portion  123   a  may take the shape of a straight terminal. The other end of the coil spring terminates to a second coupling portion  124   c , which is similar to the first coupling portion  123   a , wherein the first and second coupling portions  123   a ,  123   c  are joined by a spiral section  123   b . In other words, according to one embodiment the biasing member  123  is a flat-ended coil spring. 
         [0030]    The connection between the biasing member  123  and the end plugs  124 ,  125  is provided through cooperating form-locking shapes at the terminal ends of the biasing member and at ends of the end plugs  124 ,  125  proximal to the biasing member  123 . In the illustrated example of  FIG. 5 , the form locking shape  124   d  of the first end plug  124  is a groove for receiving the first coupling portion  123   a  of the biasing member  123 . The second end plug has a similar groove (not shown) for receiving the second coupling portion  123   c  of the biasing member  123 . 
         [0031]    As described above, the second end plug  125  at the second end  122 B of the shaft  122  is fixed thereto to close the second end  122 B of the shaft  122 . The end plug  125  may be welded to the shaft  122 , for example, to ensure strong hold. To facilitate welding, the second end plug  125  includes a rotationally non-symmetrical engagement portion  125   b , such as a racetrack oval shape, for engaging with a wrench or similar tool for maintaining the second end plug  125  in a desired angular position in respect to the shaft  122  during welding. Alternatively, the rotationally non-symmetrical engagement portion  125   b  may be used to dial in the second end plug  125  provided with a male thread (not shown) to the shaft  122  having a receiving female thread in the inner cavity (not shown). 
         [0032]    The terminal end tip  125   a  of the second end plug  125  is rotationally symmetrical for providing rotation in respect to the dolly  100 , more specifically to the second pivot point  113   b  of the longitudinal cross beam  113 . According to the illustrated example of  FIG. 6 , the terminal end tip  125   a  is cylindrical for sturdy rotation in the cylindrical opening of the pivot point  113   b.    
         [0033]    Turning now to  FIG. 7 , which shows the first end plug  124  in greater detail. In essence, the first end plug  124  includes four portions  124   a  to  124   d  shaped to provide the three functions mentioned above. Looking at the surface in closest proximity to the biasing member  123  (see  FIG. 5 ), the first end plug  124  includes a form-locking shape  124   d , such as a groove, for locking the first end plug  124  angularly to the biasing member  123 . The body portion  124   c  of the first end plug  124  extends from the surface proximal to the biasing member  123  along the axis of revolution R. The body portion  124   c  is preferably cylindrical and dimensioned to establish sliding fit in respect to the inner cavity of the shaft  122  for providing rotation there between about the axis of revolution R as well as for axial displacement along the axis of revolution R. 
         [0034]    Extending from the cylindrical body portion  124   c  is a rotationally non-symmetrical shape  124   b . The rotationally non-symmetrical shape  124   b  in the embodiment illustrated in the FIGS. takes the shape of a blunt cam. The rotationally non-symmetrical shape  124   b  may, however, be a different rotationally non-symmetrical shape, such as a quadrangle, triangle, star, oval, etc. According to a preferred embodiment, the rotationally non-symmetrical shape  124   b  is designed to be engaged with a tool, such as a wrench, for rotating the first end plug  124  in respect to the shaft  122  during installation. 
         [0035]    Extending from the rotationally non-symmetrical shape  124   b  along the axis of revolution R is a terminal end tip  124   a , which has a rotationally symmetrical shape. Similarly to the terminal end tip  125   a  of the second end plug  125 , the terminal end tip  124   a  of the first end plug  124   a  is preferably cylindrical for sturdy rotation in the opening of the pivot point  113   a.    
         [0036]    The opening of the pivot point  113   a  as well as the a terminal end tip  124   a  and rotationally non-symmetrical shape  124   b  of the first end plug  124  are dimensioned such that the rotationally non-symmetrical opening  113   a  in the longitudinal cross beam  113  is configured to receive the rotationally symmetrical terminal end tip  124   a  of the first end plug  124  in a rotatable manner in a retracted axial position of the first end plug  124 , and on the other hand to receive the rotationally non-symmetrical shape  124   b  of the first end plug  124  in a non-rotatable manner in an extended axial position of the first end plug  124 . Such a dimensioning principle is due to the intended installation procedure described below. 
         [0037]    The tow bar assembly  120  is intended to be installed to the dolly  100  partially preassembled. The tow bar  121  is preformed to include the mutually angled portions and the hitch at the end of the longer portion. Also, the shaft  122  is attached to the shorter portion of the tow bar  121  and the second end plug  125  is fixed into the inner cavity of the shaft  122  by welding, for example. Dollies which have been designed to receive such a tow bar assembly  120  are ready as is, whereas conventional dollies would be provided with openings  113   a ,  113   b  by drilling and machining or filing suitable holes into the longitudinal cross beams  113 . 
         [0038]    In the installation procedure, the biasing member  123  is firstly inserted into the inner cavity of the shaft  122  so that the second coupling portion  123   c  of the biasing member  123  locks into place to the receiving groove (not shown) on the second end plug  125 . With the biasing member  123  in place, the first end plug  124  is inserted into the inner cavity of the shaft  122  by simply sliding the first end plug  124  in by virtue of the sliding fit there between. The first end plug  124  is rotated in the inner cavity of the shaft  122  so as to lock the first coupling portion  123   a  into place to the receiving form-locking shape  124   d , i.e. groove, in the first end plug  124 . 
         [0039]    With the biasing member  123  enclosed by the shaft  122  and end plugs  124 ,  125 , the biasing member  123  is compressed by pressing the first end plug  124  inward into the inner cavity of the shaft. With the first end plug  124  in the retracted axial position, the tow bar assembly  120  is positioned in respect to the dolly  100  by inserting the terminal tip  125   a  of the second end plug  125  into the receiving opening  113   b  in the longitudinal cross beam  113 . The terminal tip  124   a  of the first end plug  124  is thereafter aligned with the rotationally non-symmetrical opening  113   a  in the opposing longitudinal cross beam  113 . The rotationally non-symmetrical opening  113   a  is dimensioned such that the terminal tip  124   a  of the first end plug  124  may rotate therein. Expelled by the axial spring-back factor of the biasing member  123 , the first end plug  124  is driven outward along the axis of revolution R such that the terminal tip  124   a  is inserted into the rotationally non-symmetrical opening  113   a  along the axial length of the terminal tip  124   a.    
         [0040]    At that stage, the rotationally non-symmetrical shape  124   b  of the first end plug  124  has not yet become recessed into the rotationally non-symmetrical opening  113   a  because it should not be angularly aligned. This matter is preferably taken into consideration in designing the angular position of the second end plug  125  and the coupling portions  123   a ,  123   c  of the biasing member. 
         [0041]    Next, the biasing member  123  is pre-tensioned by rotating the first end plug  124  in respect to the shaft  122 . Since the rotationally non-symmetrical shape  124   b  of the first end plug  124  is not embedded into the opening  113   a , the rotationally non-symmetrical shape  124   b  is engaged with a tool, such as a wrench, and rotated. During the rotation of the first end plug  124 , the biasing member  123 , which is at the other end fixed to the shaft  122  via the second end plug  125 , undergoes winding and thus is pre-tensioned. The first end plug  124  is simultaneously aligned with the rotationally non-symmetrical shape of the opening at the pivot point  113   a  on the longitudinal cross beam  113 . When the rotationally non-symmetrical shape  124   b  of the first end plug  124  is aligned with the rotationally non-symmetrical opening  113   a , the first end plug  124 —driven by the axial spring-back factor of the biasing member  123 —is expelled into the extended axial position, where the first end plug  124  locks into the rotationally non-symmetrical opening  113   a.    
         [0042]    In the fully assembled state, the tow bar assembly  120  may be removed from the dolly  100  by pressing the first end plug  124  inward axially. The first end plug  124  is accessible from underneath the dolly  100 , wherein a thin object, such as a paper clip, may be used to press the terminal tip  124   a  of the first end plug  124 . When the axial spring-back factor of the biasing member  123  is exceeded, the rotationally non-symmetrical shape  124   b  of the first end plug  124  is retracted from the corresponding opening  113   a , where after the tow bar assembly  120  may be dis-assembled in a reverted fashion in respect to assembly. 
         [0043]    Above, only exemplary illustrated embodiments have been described. It is, however, to be understood that the inventive concept may be executed in manners deviating from the above description. For example, the interface between the shaft and the dolly, namely the end plugs, may be inverted such that the longitudinal cross beams have a rotationally symmetrical protrusion and an opposing rotationally non-symmetrical protrusion. The protrusions would be designed to cooperate with respective recessions at the terminal end surfaces of the end plugs of the shaft. Such a tow bar assembly would be installed similarly to the illustrated example with the difference that rotationally non-symmetrical recession in the first end plug of the shaft would lock into place by rotating the end plug for aligning the rotationally non-symmetrical shapes of the end plug and the protrusion of the longitudinal cross beam. 
         [0044]    A skilled person may foresee further deviations from the above description without departing from the invention, which is defined by the appended claims. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 LIST OF REFERENCE NUMBERS. 
               
             
          
           
               
                   
                 Number 
                 Part 
               
               
                   
               
               
                   
                 100 
                 dolly 
               
               
                   
                 110 
                 chassis 
               
               
                   
                 111 
                 longitudinal peripheral beam 
               
               
                   
                 112 
                 transversal peripheral beam 
               
               
                   
                 113 
                 longitudinal cross beam 
               
               
                   
                 113a 
                 pivot point (non-circular opening) 
               
               
                   
                 113b 
                 pivot point (circular opening) 
               
               
                   
                 114 
                 transversal cross beam 
               
               
                   
                 120 
                 tow bar assembly 
               
               
                   
                 121 
                 tow bar 
               
               
                   
                 122 
                 shaft 
               
               
                   
                 122A 
                 first end 
               
               
                   
                 122B 
                 second end 
               
               
                   
                 123 
                 biasing member 
               
               
                   
                 123a 
                 first coupling portion 
               
               
                   
                 123b 
                 spiral section 
               
               
                   
                 123c 
                 second coupling portion 
               
               
                   
                 124 
                 first end plug 
               
               
                   
                 124a 
                 terminal end tip 
               
               
                   
                 124b 
                 rotationally non-symmetrical shape (cam) 
               
               
                   
                 124c 
                 body portion 
               
               
                   
                 124d 
                 form-locking shape (groove) 
               
               
                   
                 125 
                 second end plug 
               
               
                   
                 125a 
                 terminal end tip 
               
               
                   
                 125b 
                 rotationally non-symmetrical engagement portion 
               
               
                   
                 130 
                 castor 
               
               
                   
                 R 
                 axis of revolution