Abstract:
An apparatus and method is described for offsetting a lifting or lowering weight of a tow bar attached to a trailer. The apparatus includes nitrogen accumulators coupled in series to a hydraulic cylinder. The accumulators include volumes of hydraulic fluid and a gas, such as nitrogen, which are preset to have differing nitrogen pressures to accommodate a full range of motion. After initial system pressurization, no separate power source is needed to provide hydraulic support at static conditions, oscillation of the tow bar below horizontal, and lift support from horizontal to a positive angle, allowing the user to lift and position a heavy tow bar several feet with minor user force.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the filing benefit and priority of U.S. Provisional Application Ser. No. 61/429,185 filed Jan. 3, 2011, the contents which are incorporated herein by reference in its entirety. 
    
    
     FEDERAL SPONSORSHIP 
     Not Applicable 
     JOINT RESEARCH AGREEMENT 
     Not Applicable 
     TECHNICAL FIELD 
     This invention pertains generally to the tow bar of a trailer suitable for use in either off-highway or highway travel. This invention also pertains to tow bars coupled to heavy agricultural implements and oversize trailers suitable for on and off highway use to transport overweight and over dimensional loads at low or high speeds. 
     BACKGROUND 
     Generally, trailers for hauling oversize, overweight, and over length loads have previously been described. These heavy loads may include, for example, cranes, agricultural implements, concrete structures, construction equipment, construction materials, oversized vehicles or the like. Prior trailers capable of transporting massive or heavy loads typically include multiple axles and massive tow bars and tongues coupled to the trailer frame. Often, these heavy haul trailers must provide some level of support under the cargo, throughout the length of the cargo, to help reduce the torsional and related forces the cargo may be subjected to during transport and the tow bar must withstand the required towing forces applied to the trailer. Further, sloped and uneven roads may cause additional torsional stress on the cargo and tow bar. These potential applied forces require a tow bar of sufficient strength and mass to withstand these forces. 
     Due to weight of the tongue, prior tow bars are typically difficult to connect out in the field manually without using some sort of additional equipment to lift the heavy tow bar sufficiently high to connect to a hitch of a towing vehicle. Also, when the tow bar is rigidly fixed to the frame of the trailer, lifting the tow bar also requires lifting a proportional weight of the trailer distributed to the tongue or tow bar of the trailer. To reduce the required lifting force, prior tow bars have been hinged with mechanisms coupled to the tow bar to apply an upward force to the tongue to aid the user in lifting the tow bar. However, when lowering a tow bar having these prior mechanisms a user must counteract the force of the mechanism to lower the tow bar. Further, prior tow bars are labor intensive to connect and disconnect. 
     Hence, there is a need for a tow bar capable of use on a trailer system towable over smooth and rough terrains at both low and high speeds. There is also a need for a tow bar that is easily lifted and coupled to a tow vehicle hitch without the need for additional fork lifts, skid loaders or other lift equipment. 
     SUMMARY 
     Embodiments according to the invention include a trailer capable of use on smooth and rough terrains at both low and high speeds. Aspects of the invention include a balanced tow bar that requires minimal force to lift and couple to a tow vehicle. A tow bar of the invention includes a tongue, hydraulic cylinder and first and second accumulators. The tongue has a first end that may couple to a vehicle and a second end adapted to couple to a trailer. The hydraulic cylinder has a first end coupled to the tongue and a second end adapted for coupling to the trailer. The accumulators are pressurized with a gas and are in fluid communication with the hydraulic cylinder. A hydraulic fluid hand pump may be coupled in fluid communication with said hydraulic cylinder to distribute hydraulic fluid into the hydraulic lines and to distribute additional hydraulic fluid into the hydraulic lines as needed. The accumulators may include a gas port to increase or decrease the amount of gas in the accumulators. 
     The accompanying drawings, which are incorporated in and constitute a portion of this specification, illustrate embodiments of the invention and, together with the detailed description, serve to further explain the invention. The embodiments illustrated herein are presently preferred; however, it should be understood, that the invention is not limited to the precise arrangements and instrumentalities shown. For a fuller understanding of the nature and advantages of the invention, reference should be made to the detailed description in conjunction with the accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In the various drawings, which are not necessarily drawn to scale, further description of the inventive aspects of the invention are included and described on the drawings which are incorporated by reference into the description of the invention. Like numerals throughout the figures identify substantially similar components. 
         FIG. 1  is a side elevation view of a vehicle attached to a trailer with a tow bar in accordance with the present invention; 
         FIG. 2  is a top perspective view of a trailer having a tow bar attached to a vehicle in accordance with the present invention; 
         FIG. 3  is a side perspective view of a portion of the tow bar in accordance with the present invention; 
         FIG. 4  is a side perspective view of a portion of the tow bar in accordance with the present invention opposing the side shown in  FIG. 3 ; and 
         FIG. 5  is a top rear perspective view of a portion of the tow bar tongue in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description provides detail of various embodiments of the invention, one or more examples of which are set forth below. Each of these embodiments are provided by way of explanation of the invention, and not intended to be a limitation of the invention. Further, those skilled in the art will appreciate that various modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. By way of example, those skilled in the art will recognize that features illustrated or described as part of one embodiment, may be used in another embodiment to yield a still further embodiment. Thus, it is intended that the present invention also cover such modifications and variations that come within the scope of the appended claims and their equivalents. 
     Prior heavy haul trailer systems typically include a tractor and a trailer combination that can include a front tow vehicle (or tow trailer), connection linkages from front to rear, and a rear dolly (or trailer) system along with provisions made at the top of the front and rear trailers to reduce contact stresses to the cargo. The tow vehicle or tractor can be connected either via a fifth wheel or a tow bar mechanism. Prior platform trailers used for off-highway use are typically equipped with a tow bar, single axles, steering struts, and a platform that allows for placement of larger oversize loads on the jobsite or at other off-highway locations. 
       FIGS. 1 and 2  illustrate a trailer having a tow bar  200  of the present invention used for both on and off highway use. The trailer  210  is shown having a frame or framework  212  including a single carriage or spine with a swivel and hinge  214  coupled to an end of the frame  212 . The tow bar  200  is pivotally attached to the hinge  214 . Those skilled in the art will appreciate that the tow bar  200  of the present invention may be attached to other trailer frameworks without departing from the scope of the present invention. 
     The tow bar system  200  of the present invention is shown in greater detail in  FIGS. 3-5 . The tow bar system includes a tongue  220  that may include a tractor hitch of known suitable construction coupled on one end of the tongue and a hinge  214  coupled to another end of the tongue. The tongue may also include a bolt connected segment interface  222  to allow a user to vary tow bar lengths depending on regulations and performance requirements. The tow bar system also includes a hydraulic cylinder  216  coupled to the tongue  220  and trader frame  212 . In the embodiment shown in  FIG. 3 , an extendable end of a hydraulic support cylinder  216  is mounted to the tongue  220  and the hinge and swivel bar  214  is adapted to receive the other end of the hydraulic support cylinder  216 . By connecting the tow bar  200  to a hinge and swivel, the tow bar may pivot both up and down and side to side. 
     The tow bar  200  system also includes a hydraulic fluid hand pump  218  mounted to the tow bar and coupled in fluid communication with the hydraulic cylinder  216  through hydraulic line  232 . A preferred hand pump of suitable construction possesses a pressure rating in a range of 3,000-10,000 psi, an oil volume per stroke of 0.91 to 0.19 cubic inches, and an oil capacity of 30-70 cubic inches. The hand pump  218  includes a port  250  that allows for initial charge or recharging of the hydraulic lines. The size of the hydraulic cylinder  216  and pressure range of the hydraulic cylinder are dependent upon the tow bar weight, Center Of Gravity (COG) of the tongue  220 , and desired up/down range of motion necessary for tow bar elevation range. The preferred pressure range is between 900 psi &amp; 1,400 psi for the expected range of tongue weights for heavy haul trailers. 
     The tow bar system also includes two accumulators  224  and  226  that are mounted on the tow bar, one on each side of tongue  220 , and that are coupled in series in fluid communication with hydraulic support cylinder  216 . Each hydraulic accumulator  224 ,  226  includes a gas charging port  240  and  242  respectively. The tow bar hydraulic cylinder includes a quick coupler connection  246 , of known suitable construction, that may be used to charge or provide pressure to the system during assembly, a bleed port  252  to evacuate air during internal charging of the system, and a breather  254  on the rod end  217  of the hydraulic cylinder  216 . A closed hydraulic circuit is setup with the hand pump  218 , cylinder  216 , and low/high pressure accumulators  224 / 226 . 
     The accumulators have a fixed volume that may contain both hydraulic fluid and a gas. The accumulators may be pressurized with the gas by charging the accumulators with the gas, nitrogen for example, through the charging ports  240  and  242 . The accumulators are set with differing gas or nitrogen pressures prior to system use. The pressure of the gas within each accumulator applies a force against the hydraulic fluid within the accumulator and through the hydraulic lines  228  and  230  to the hydraulic cylinder  216 . The pressurized hydraulic fluid applies a force against the cylinder rod  217  to force the rod out of the cylinder body. The mass of the tongue counteracts this force but when sufficient pressure is applied to the hydraulic fluid the rod  217  will extend out of the cylinder body. 
     The higher pressure accumulator  226  provides a volume and pre-charge to the hydraulic cylinder  216  so that the tow bar may be balanced at static conditions. The volume of gas within the accumulator  226  also allows for oscillation of the tongue  220  below horizontal to a desired angle, for example, 15 degrees below horizontal. The low pressure accumulator  224  provides sufficient suspension pre-charge to aid in vertical lift, and sufficient accumulator gas volume to provide for adequate hydraulic fluid displacement to ease range of motion. Those skilled in the art will appreciate that since the gas pressure in accumulator  224  is low, a downward force on the tongue will displace hydraulic fluid into the accumulator  224  reducing the volume of gas and increasing the pressure of the gas therein. The range of motion of the tow bar with minimal required force eases displacement in the vertical direction, and eases ability to setup and maneuver manually at the jobsite and connect at the tractor. Essentially, the hydraulic accumulators  224  and  226  provide a “balance” to the tongue so that reduced upward or downward force on the tongue is required to move the tongue respectively upward or downward. 
     After initial system pressurization, no separate power source is needed, other than a slight force on the tongue  220  from a user to actuate the cylinder. Further, the gas or nitrogen pressure within each accumulator  224  and  226  can be adjusted externally to provide more or less force against the cylinder rod. The dissimilar gas pressures within accumulators  224  and  226  further provides an opportunity for the user to balance between tow bar weight, Center Of Gravity (COG) of the tongue, and desired up/down range of motion. 
     During use, a user may charge the accumulators  226  and  224  to a calculated theoretical charge so that the nitrogen pressure from the accumulators will provide the balance and assist range of motion required. For example without limitation intended, a towbar of sufficient weight for heavy hauling may require a charge of 870 psi in the high pressure accumulator  226  and 360 psi in the low pressure accumulator so that the tow bar balances at neutral. The low pressure setting is determined as a function of the desired range of motion of the tow bar above neutral. Once the accumulators  226  and  224  are charged, the user may charge the hydraulic fluid lines  228 ,  230 , and  232  with hydraulic fluid. When the lines are filled with sufficient fluid and air is bled from the lines (bleeder valve  252  and breather port  254  may be utilized), the tongue may be elevated to horizontal and balance itself. The nitrogen charge can be varied in accumulators  226  and  224  to modify amount of assistance and amount of support provided. 
     A user may charge the hydraulic fluid lines  228 ,  230  and  232  with a hydraulic fluid utilizing an external hydraulic supply unit. The nitrogen pressure within accumulator  226  and  224  and the pressure of the hydraulic fluid within the cylinder  216  is of sufficient charge so that the force of the hydraulic fluid against the cylinder rod is of sufficient force to overcome the downward force of the mass of the tongue  220 . Increasing the gas pressure within accumulator  226  will increase the force applied by the hydraulic fluid to the cylinder rod  217 . Once the desired balance is achieved, when the user applies a slight upward or downward force against the tongue, the hydraulic fluid in the lines is displaced and the gas volume within accumulator  224  is either increased or decreased. 
     These and various other aspects and features of the invention are described with the intent to be illustrative, and not restrictive. This invention has been described herein with detail in order to comply with the patent statutes and to provide those skilled in the art with information needed to apply the novel principles and to construct and use such specialized components as are required. It is to be understood, however, that the invention can be carried out by specifically different constructions, and that various modifications, both as to the construction and operating procedures, can be accomplished without departing from the scope of the invention. Further, in the appended claims, the transitional terms comprising and including are used in the open ended sense in that elements in addition to those enumerated may also be present. Other examples will be apparent to those of skill in the art upon reviewing this document.