Abstract:
An improved trailer dolly having a fifth wheel and also carrying a ball-type trailer hitch to give the driver the option of towing either type of trailer and having steering means built into the dolly to provide sure and positive steering and control of the towed trailer.

Description:
RELATED APPLICATIONS 
     This application is a Continuation-In-Part of my copending U.S. patent application Ser. No. 09/005,964, filed Jan. 12, 1998, and now abandoned. 
    
    
     FIELD OF INVENTION 
     This invention relates to vehicle trailers and is particularly directed to improved dolly means for attaching trailers to automobiles, pickup trucks and the like. 
     PRIOR ART 
     It is often necessary or desirable to tow trailers behind automobiles, pickup trucks and the like. Unfortunately, these vehicles are not normally equipped for such towing. Some trailers have relatively low attaching tongues which can be attached to ball-type trailer hitches mounted on the rear bumper of the towing vehicle. Other trailers have relatively high attaching tongues and require that a fifth wheel be mounted on the bed of the towing vehicle. Obviously, the latter type of trailers cannot be towed by conventional automobiles, since there is no place to mount the fifth wheel; and, even on pickup trucks, the fifth wheel occupies a significant area within the bed of the pickup which severely limits the load carrying ability of the truck. Also, each of these types of trailer hitch requires that the towing vehicle bear the weight of the trailer, despite the fact that many towing vehicles are not designed for this. Furthermore, no means has been provided heretofore which would enable a vehicle to tow either type of trailer at the driver&#39;s option. Moreover, with either of the prior art types of trailer hitches, reversing or backing up with a trailer has been extremely difficult, if not impossible. Trailer dollies have been known to facilitate connecting trailers to tow vehicles. However, many of the prior art trailer dollies have failed to provide means for steering and control of the trailer. Moreover, none of the prior art trailer dollies have given the driver the option of towing either type of trailer. A search in the United States Patent Office has revealed the following: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 U.S. PAT. NO. 
                 INVENTOR 
                 ISSUED 
               
               
                   
                   
               
             
             
               
                   
                 5,407,221 
                 D. K. Haire et al 
                 Apr. 18, 1995 
               
               
                   
                 3,212,793 
                 D. Petroroia 
                 Oct. 19, 1965 
               
               
                   
                 4,345,775 
                 D. V. Merrifield 
                 Aug. 24, 1982 
               
               
                   
                 5,067,741 
                 J. Ayme 
                 Nov. 26, 1991 
               
               
                   
                 4,033,426 
                 E. J. Williams 
                 Jul.  5, 1977 
               
               
                   
                 3,105,704 
                 A. G. Schramm 
                 Oct.  1, 1963 
               
               
                   
                 1,503,135 
                 W. H. Sargent 
                 Jul. 29, 1924 
               
               
                   
                 4,468,047 
                 J. R. McGhie et al 
                 Aug. 28, 1984 
               
               
                   
                 5,364,117 
                 P. G. Keith 
                 Nov. 15, 1994 
               
               
                   
                 5,348,331 
                 W. H. Hawkins 
                 Sep. 20, 1994 
               
               
                   
                 4,824,135 
                 D. T. McGregor 
                 Apr. 25, 1989 
               
               
                   
                 4,451,058 
                 N. R. Curry 
                 May  29, 1984 
               
               
                   
                   
               
             
          
         
       
     
     Each of these references is subject to the disadvantages discussed above. Thus, none of the prior art trailer dollies have been entirely satisfactory. 
     BRIEF SUMMARY AND OBJECTS OF INVENTION 
     These disadvantages of the prior art are overcome with the present invention and an improved trailer dolly is provided which accommodates both high tongue and low tongue trailers without requiring the towing vehicle to bear the weight of the trailer and which provides cure and positive steering and control of the towed vehicle, even when backing up. 
     These advantages of the present invention are preferably attained by providing an improved trailer dolly having a fifth wheel and also carrying a ball-type trailer hitch to give the driver the option of towing either type of trailer and having steering means built into the dolly to provide sure and positive steering and control of the towed trailer. 
     Accordingly, it is an object of the present invention to provide an improved trailer dolly. 
     Another object of the present invention is to provide an improved trailer dolly which can accommodate either low tongue or high tongue trailers. 
     An additional object of the present invention is to provide an improved trailer dolly which allows the driver the option of towing either low tongue or high tongue trailers. 
     A further object of the present invention is to provide an improved trailer dolly which does not require the towing vehicle to bear the weight of the trailer. 
     Another object of the present invention is to provide an improved trailer dolly having steering means to facilitate steering and control of the dolly. 
     An additional object of the present invention is to provide an improved trailer dolly which provides sure and positive steering and control of the towed trailer, even when backing up. 
     A specific object of the present invention is to provide an improved trailer dolly having a fifth wheel and also carrying a ball-type trailer hitch to give the driver the option of towing either type of trailer and having steering means built into the dolly to provide sure and positive steering and control of the towed trailer. 
     These and other objects and features of the present invention will be apparent from the following detailed description, taken with reference to the figures of the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a rear view of a trailer dolly embodying the present invention; 
     FIG. 2 is a vertical section through the trailer dolly of FIG. 1, taken on the line  2 — 2  of FIG. 1; 
     FIG. 3 is a front view of the trailer dolly of FIG. 1; 
     FIG. 4 is a plan view of the trailer dolly of FIG. 1; 
     FIG. 5 is a diagrammatic representation showing the hydraulic system of the present invention; 
     FIG. 6 is an enlarged side view of the friction bars of the dolly of FIG. 1; and 
     FIG. 7 is a plan view of the friction bars of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In that form of the present invention chosen for purposes of illustration, FIG. 1 shows a trailer dolly, indicated generally at  10 , having a frame  12  supported by springs  14  upon an axle  16  having wheels  18  mounted at each end. As shown, fenders  20  are mounted on the axle  16  and extend above the wheels  18 . The frame  12  supports a fifth wheel  22  and has a lower portion  24  upon which is mounted a ball mount  26 . Also, if desired, an additional ball mount  27  may be located adjacent the fifth wheel  22  to permit connection of a towed vehicle having a gooseneck coupling. The frame  12  has a tongue  28  which projects from the forward edge  30  of the frame  12  and caries suitable coupling means  32  for coupling the tongue  28  to a towing vehicle, as seen at  34  in FIG.  4 . As best seen in FIGS. 6 and 7, the tongue  28  carries a crossbar  36  and  38 , located adjacent the rear end of the tongue  28  and has friction bars  40  connecting the crossbar  36  on each side of the tongue  28  which project forwardly of the coupling means  32  and are attached to the towing vehicle  34  by suitable means, such as U-brackets  37  and bolts  39 . The friction bars  40  have ball joints, not shown, where they enter the U-brackets  37  to permit limited rotation in the roll and pitch planes. Crossbar  36  carries a pair of friction plates  41  flanking each of the friction bars  40 , formed of material similar to that of brake linings, and carries squeeze plates  43  which are urged by bolts  45  and nuts  47  to cause the friction plates  43  to bear against the friction bars  40 . Tightening or loosening nuts  47  serves to adjust the amount of friction applied by the friction plates  41  against the friction bars  40 . This structure serves to restrict vertical movement of the tongue  28  with respect to the towing vehicle  34 . In addition, stabilizer bars  42  and  44 , having ball joints  46  at each end, are connected between brackets  48 , mounted on the front edge  30  of the frame  12  and similar brackets  50  mounted on the rear of the towing vehicle  34 , as seen in FIG.  4 . It is important that the brackets  48  be more closely spaced than the brackets  50  and that the stabilizer bars  42  and  44  be longer than the length of tongue  28 , as this precludes jack-knifing of the dolly  10 . Finally, a pair of hydraulic hoses  52  and  54  are connected to hydraulic ports  56  and  58 , provided on the rear end of the towing vehicle  34 , as best seen in FIG. 4, and are connected to respective ends of a double-acting cylinder  60  mounted on the axle  16  and serving to steer the wheels  18 . A suitable hydraulic reservoir  62  is mounted on the frame  12  and serves to supply hydraulic fluid to cylinder  60  and, thence, to the entire hydraulic system, as best seem in FIG.  5 . 
     As best seen in FIG. 5, the towing vehicle carries a hydraulic cylinder  64  having a piston  66  which is positioned by an arm  68  coupled to pitman arm  70  to the steering box  72  of the towing vehicle  34 . The opposite ends  74  and  76  of the cylinder  64  are connected by hose  78 , which is controlled by valves  88  and petcock  80  to regulate flow between the ends  74  and  76  of the cylinder  64 . End  74  of cylinder  64  is connected by hose  82  to deliver hydraulic fluid to hydraulic port  56 , while end  76  of cylinder  64  is connected by hose  84  to deliver hydraulic fluid to hydraulic port  58 . A ball valve  86  is connected between hydraulic ports  56  and  58  and, when open, allows hydraulic fluid to circulate freely from end  74  of cylinder  64  through hose  82 , valve  86  and hose  84  to end  76  of cylinder  64  and vice versa. When ball valve  86  is closed, the hydraulic fluid is delivered through hydraulic ports  56  and  58  to the towed vehicle. Between cylinder end  74  and valve  86  there is a valve  87  connected to an accumulator  89 . Note that valves  88  must be open or closed in correspondence with valves  86  and  87 . From the hydraulic ports  56  and  58 , the hydraulic fluid passes through hoses  52  and  54  to respective ends  90  and  92  of the double acting cylinder  60 . Cylinder  60  contains a piston  94  which is connected by piston rod  96  to steering arm  98 , which is adjustably connected to control the steering knuckle  100  of axle  16  and, hence, serves to steer the wheels  18 . The fact that steering arm  98  is directly coupled to the steering knuckle  100  causes the dolly to turn simultaneously with the steering mechanism of the towing vehicle  34 . Also, the fact that the steering arm  98  is adjustably connected enables the driver to adjust this connection to cause the dolly  10  to track precisely with the towing vehicle  34 . Ends  90  and  92  of the double-acting cylinder  60  are connected by hoses  102 ,  104  and  106  to the hydraulic reservoir  62  and flow is regulated by valves  107  and  108 . 
     With the hydraulic system of FIG. 5, it will be seen that, when the driver of the towing vehicle  34  turns his steering wheel to turn the front wheels, not shown, of the towing vehicle  34 , this will move the steering box  72 , which will drive pitman arm  70  and piston rod  68  to reposition the piston  66  of hydraulic cylinder  64 . This will cause hydraulic fluid to be discharged from one end  74  or  76  of cylinder  64  and will act, through hoses  82  and  84 , hydraulic ports  56  and  58 , and hoses  52  and  54  to double-acting cylinder  60  and will cause a corresponding repositioning of piston  94 , which will act through piston rod  96  and steering arm  98  to rotate the steering knuckle  100  and, hence, to cause corresponding turning of the wheels  18  of the dolly  10 . Thus, by appropriate adjustment of the connection of steering arm  98  to the steering knuckle  100 , the dolly  10  can be made to always precisely follow the movements of the towing vehicle  34 . This is further ensured by the fact that the stabilizer bars  42  and  44  are connected to the towing vehicle at points  50  which are spaced farther apart than the points  48  at which the stabilizer bars  42  and  44  are attached to the dolly  10  and the stabilizer bars  42  and  44  are longer than the length of the tongue  28 . This connection precludes rotation of the dolly  10  about the vertical yaw axis, while allowing rotation about the longitudinal roll axis and the transverse pitch axis. Consequently, jack-knifing of the dolly  10  is precluded. Also, extreme pitching movement, such as would allow the towing vehicle to flip backward in top of the trailer, is precluded by the fact that the attaching points  46  of the stabilizer bars  42  and  44  with the towing vehicle  34  are not on a common line with the attaching point  32  of the tongue  28 , as clearly seen in FIG.  4 . 
     In use, the user connects the trailer dolly  10  to the towing vehicle  34  by means of coupling means  32  and connects the trailer, not shown, to either the fifth wheel  22  or to the ball mounts  26  and  27 , as appropriate. In this way, the trailer dolly  10  bears the weight of the trailer, rather than the towing vehicle  34 . Also, the trailer dolly  10  enables the towing vehicle  34  to be connected to the trailer regardless of which type of connection the trailer has. Stabilizer bars  42  and  44  are connected between the trailer dolly  10  and the towing vehicle  34  to preclude yawing of the trailer dolly  10  with respect to the towing vehicle  34 , while the hydraulic system of FIG. 5 ensures precise tracking of the dolly  10  with the towing vehicle  34 . Also, friction bars  40  are connected to towing vehicle  34  to restrict vertical movement at coupling means  32 . 
     Obviously, numerous variations and modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the form of the present invention described above and shown in the figures of the accompanying drawing is illustrative only and is not intended to limit the scope of the present invention.