Abstract:
A method and device for steering a heavy load transport vehicle includes a variable length strut which cooperates with a power steering valve. The length of the variable length strut changes as a function of tow bar rotation. This length variation is mechanically coupled to the power steering valve, which in turn controls an automatic steering system. The present invention permits mechanical steering of the transport vehicle even in the event of failure of the automatic steering system, and does so without placing mechanical stress upon the power steering valve.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the filing benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 60/383,554, filed May 24, 2002, which is included herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to multi-axle transport vehicles for moving heavy loads, and more particularly to a method and apparatus for steering the transport vehicle. 
     BACKGROUND OF THE INVENTION 
     Heavy hauling vehicles for moving transformers, cranes, boats, industrial equipment, and other heavy objects are well known in the art. An example of such a vehicle is shown in U.S. Pat. No. 4,943,078 which discloses a heavy load hauler for traveling on conventional roadways for moving heavy construction equipment such as cranes or the like from one work site to another. The hauler includes a front tractor drawn carriage, a rear carriage, and a load unit between and carried by the carriages. The front carriage is supported upon a multiplicity of independent wheel and axle units. There is a first fifth wheel coupling at the leading end of the front carriage for connecting to the fifth wheel coupling of a tractor. A second fifth wheel coupling is spaced rearwardly. The load carrying rear carriage is also supported upon a multiplicity of independent wheel and axle units. There is a fifth wheel coupling intermediate the leading and trailing ends of the carriage. The load unit has forwardly and rearwardly projecting goosenecks. Each gooseneck has a fifth wheel coupling. The one on the forwardly projecting gooseneck connects to the fifth wheel coupling on the front carriage. The one on the rearwardly projecting gooseneck connects to the fifth wheel coupling on the rear carriage. The load unit may be either the crane itself or a flatbed upon which the crane is carried. At least some of the independent wheel and axle units are steerably mounted on their carriages. Each wheel and axle unit has its wheels supported by a hydraulic suspension. Hydraulic circuitry interconnects all of the suspensions so as to equally distribute the load among all of the wheel units. Steering of the independent wheel and axle units is interphased for the front and rear carriages by a pair of operatively associated interrelated inline valve cylinder units. FIG. 12A shows a valve  718  used in a power steering system which is coupled to a connecting link  703 . 
     Other heavy hauling vehicles are sold by Goldhofer Fahrzeugwerk G.m.b.H. of Memmingen, Germany; Nicolas of Champs Sur Yonne, France; and, Talbert of Renssclaer, Ind. 
     Improved systems having automatic steering at all speeds and suspension systems that respond rapidly to the varying road conditions imposed by higher speeds would greatly reduce the time and effort required to move the vehicle to the load, move the load, and return the vehicle to storage. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method and device for steering a heavy load transport vehicle. The invention combines a conventional hydraulic power steering valve with a variable length strut to effect steering control. The power steering valve is placed in “parallel” across the variable length strut so that as the variable length strut expands and contracts a small distance due to the movement of a tow bar, the power steer valve changes switching states, and though mechanical linkages, causes the transport vehicle to turn in the desired direction. In essence the variable length strut serves as a direction sensor which communicates the desired direction of turn to the power steering valve. 
     The present invention has a distinct advantage over prior art systems in the event of power steering system failure. The variable length strut will turn the steering system without hydraulic power. When this happens, the variable length strut absorbs the mechanical stresses of turning, thereby protecting the power steering valve. This is in contrast to prior art systems where the power steering valve is installed in series with the strut and is thereby exposed to large mechanical stresses if the power steering system fails. 
     Additionally, because of the small displacement of the variable length strut, the present invention provides rapid and continuous steering corrections as the transport vehicle is towed down a highway. 
     In accordance with a preferred embodiment of the invention, a device for steering a transport vehicle having a rotatable tow bar and a front dolly having front wheels is provided and includes: 
     a variable length strut connected between the tow bar and the front dolly, the variable length strut having a first section and a second section, the first and second sections longitudinally movable with respect to one another; 
     a hydraulic power steering valve having a first end and a second end; 
     the first end of the power steering valve connected to the first section of the variable length strut, and the second end of the power steering valve connected to the second section of the variable length strut; and, 
     wherein when the tow bar is rotated, the first and second sections of the variable length strut longitudinally move with respect to one another causing the power steering valve to assume a hydraulic switching state, the switching state including one of (a) a left state which causes the front wheels of the front dolly to turn in a left direction, and (b) a right state which causes the front wheels of the front dolly to turn in a right direction. 
     In accordance with an aspect of the invention, when the rotation of the tow bar is stopped, the power steering valve assumes a neutral hydraulic switching state wherein further turning in a left direction or right direction ceases. 
     In accordance with an aspect of the invention, the first and second sections are longitudinally movable a distance of about 0.13 inches with respect to each other. 
     Other aspects of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a prior art multi-axle transport vehicle for moving heavy loads; 
     FIG. 2 is a top plan view of the vehicle of FIG. 1; 
     FIG. 3 is a side elevation view of a second prior art transport vehicle; 
     FIG. 4 is a partial enlarged top plan view of the vehicle of FIG. 3; 
     FIG. 5 is a top plan view of a multi-axle transport vehicle which includes a system for steering the transport vehicle in accordance with the present invention; 
     FIG. 6 is an enlarged view of area  6  of FIG. 5; 
     FIG. 7 is an enlarged view of area  7  of FIG. 6; 
     FIG. 8 is a top plan view of the transport vehicle turning to the left; 
     FIG. 9 is an enlarged view of area  9  of FIG. 8; 
     FIG. 10 is an enlarged view of the device for steering the vehicle in accordance with the present invention; 
     FIG. 11 is an enlarged partial cross sectional view of area  11  of FIG. 10, showing the device in a neutral state; 
     FIG. 12 is an enlarged partial cross sectional view of area  11  of FIG. 10, showing the device in a turn left state; 
     FIG. 13 is an enlarged partial cross sectional view of area  11  of FIG. 10, showing the device in a turn right state; 
     FIG. 14 is an enlarged view of area  14  of FIG. 11; 
     FIG. 15 is an enlarged view of area  15  of FIG. 12; 
     FIG. 16 is an enlarged view of area  16  of FIG. 13; 
     FIG. 17 is a hydraulic flow diagram with the device in a neutral hydraulic state; 
     FIG. 18 is a hydraulic flow diagram with the device in a turn left hydraulic state; 
     FIG. 19 is a hydraulic flow diagram with the device in a turn right hydraulic state; and, 
     FIG. 20 is a hydraulic flow diagram of a second embodiment with the device in the neutral hydraulic state. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 illustrate side elevation and top plan views, respectively, of a prior art multi-axle transport vehicle  500  for moving heavy loads. The vehicle  500  has a front dolly  502  and a pair of rear dollies  504  upon which a load  506  rests. A towing vehicle  508  such as a tractor pulls transport vehicle  500  using a tow bar  510 . 
     FIGS. 3 and 4 are side elevation and partial enlarged top plan views respectively of a second prior art transport vehicle  600 . Transport vehicle  600  includes a front hauling carriage  602  and a rear hauling carriage  604 . Each hauling carriage has a plurality of dollies  606  (six in the shown embodiment). Each dolly  606  includes two rotatable axles  608  each having four wheels  610 . Axles  608  are rotatably mounted to an axle beam  612 . The dollies  606  are mechanically linked together by turning struts  615  which cause the axles  608  to rotate in a desired manner as transport vehicle  600  turns (refer also to FIG.  8 ). A load bed  614  is attached to two goosenecks  616  which rotatably connect to hubs  618  of hauling carriages  602  and  604 . A heavy load  700  such as a large transformer is carried by load bed  614 . 
     FIG. 5 illustrates a top plan view of a multi-axle transport vehicle  800  which includes a system  20  for steering the transport vehicle  800  in accordance with the present invention. As with FIG. 4, only the front hauling carriage is depicted. System  20  includes a rotatable tow bar  22  which is connected to a towing vehicle  802  and a front dolly  24 . Front dolly  24  includes rotatable axle  25  having wheels  27 . In the shown embodiment, there are both right and left front dollies  24 . A hydraulic cylinder  26  (also refer to FIG. 6) is mechanically connected by a steering crank  28  and a steering strut  30  to front dolly  24 . In the shown embodiment, there are two hydraulic cylinders  26  which are connected in push pull relationship. A variable length strut  32  is connected between tow bar  22  and front dolly  24 . In the shown embodiment, variable length strut  32  is connected to left front dolly  24 . However, it may be appreciated that it could alternatively be connected to right front dolly  24 . Variable length strut  32  has a first section  34  and a second section  36  (refer to FIG.  10 ). First section  34  and second section  36  are longitudinally movable with respect to one another (refer to FIGS.  11 - 16 ). In an embodiment of the invention, first section  34  and second section  36  longitudinally move apart a total distance of about 0.13 inches as variable length strut  32  contracts and expands. 
     A hydraulic power steering valve  38  (also refer to FIG. 10) is coupled along strut  32 . Hydraulic power steering valve  38  has a first end  40  and a second end  42 . Hydraulic power steering valve  38  is of a type available from Garrison Manufacturing of Santa Ana, Calif. First end  40  of power steering valve  38  is connected to first section  34  of variable length strut  32 , and second end  42  of power steering valve  38  is connected to second section  36  of variable length strut  32 . That is, power steering valve  38  is attached in parallel across variable strut  32 . Again referring to FIG. 10, power steering valve  38  is hydraulically connected by hydraulic lines to pair of front hydraulic cylinders  26  and to a hydraulic pump and a hydraulic fluid reservoir (also refer to FIG.  17 ). 
     Now also referring to FIGS. 9,  11 ,  12 , and  13 , when tow bar  22  is rotated, such as when towing vehicle  802  turns, first section  34  and second section  36  of variable length strut  32  longitudinally move with respect to one another causing power steering valve  38  to assume a hydraulic switching state. The hydraulic switching state is communicated to the pair of front hydraulic cylinders  26  which in turn, via steering crank  28  and steering strut  30 , cause front axle  25  and wheels  27  of front dolly  24  to turn in one of (a) a left direction as shown, and (2) a right direction. 
     When the rotation of tow bar  22  is stopped, power steering valve  38  assumes a neutral hydraulic switching state wherein further turning in the left direction or the right direction ceases. That is, the axle  25  and wheels  27  of dolly  24  stop turning (rotationally moving). However, the axle  25  and wheels  27  remain in the turned configuration. FIGS. 17-20 discussed below provide a description of the flow of hydraulic fluid in system  20 . 
     Again referring to FIG. 5, system  20  also has a rear dolly  44  (actually two rear dollies  44 ) which is mechanically linked to front dolly  24  via a series of linkage struts  46  as is well known in the art. A pair of rear hydraulic cylinders  48  are also arranged in push pull relationship, and are mechanically connected to rear dolly  44  via a rear steering crank  50  and rear steering strut  52 . Power steering valve  38  is also hydraulically connected to the pair of rear hydraulic cylinders  48  (refer also to FIG.  20 ). 
     FIG. 6 is an enlarged view of area  6  of FIG. 5 showing various components of steering system  20 . 
     FIG. 7 is an enlarged view of area  7  of FIG. 6 showing pair of hydraulic cylinders  26 , steering crank  28 , and steering struts  30 . It is noted that steering crank  28  pivots about pivot point  31 . Hydraulic cylinders  26  include pistons rods  23  which are driven back and forth by hydraulic pressure exerted upon a piston. 
     FIG. 8 is a top plan view of transport vehicle  800  turning to the left. Through the action of tow bar  22 , variable length strut  32 , power steering valve  38 , hydraulic cylinders  26 , steering crank  28 , and steering struts  30 , axle  25  and wheels  27  of dollies  24  have steered to the left. This steering motion has been coupled to other dolly  24  axles and wheels via linkage struts  46 . Rear hydraulic cylinders  50  have been similarly activated by power steering valve  38  to assist in the turning action. 
     FIG. 9 is an enlarged view of area  9  of FIG. 8 showing various components of steering system  20  in a turned configuration. 
     FIG. 10 is an enlarged view of a device  100  for steering a transport vehicle  800  in accordance with the present invention. Referring also to FIG. 8, transport vehicle  800  has a rotatable tow bar  22  and a front dolly  24 . Device  100  includes a variable length strut  32  which is connected between tow bar  22  and front dolly  24 . Variable length strut  32  has a first elongated section  34  and a second elongated section  36 , wherein first section  34  and second section  36  are longitudinally movable with respect to one another. That is, first section  34  and second section  36  may be longitudinally moved toward one another (contracted, refer to FIG.  12 ), or move away from one another (expanded, refer to FIG.  13 ). Device  100  further includes a hydraulic power steering valve  38  having first end  40  and second end  42 . First end  40  of power steering valve  38  is connected to first section  34  of variable length strut  32 , and second end  42  of power steering valve  38  is connected to second section  36  of variable length strut  32 . Because of this connection, as sections  34  and  36  longitudinally move with respect to one another, their relative position is directly coupled to power steering valve  38 . Power steering valve  38  is hydraulically connected to a pump, a reservoir, and hydraulic cylinders  26  (refer also to FIGS.  17  through  20 ). 
     Referring also to FIG. 9, when tow bar  22  is rotated with respect to transport vehicle  800 , such as when towing vehicle  802  turns, first section  34  and second section  36  of variable length strut  32  longitudinally move with respect to one another. The relative longitudinal movement of first section  34  and second section  36  causes powering steering valve  38  to assume a hydraulic switching state. That state can be one of (a) a left state which causes the front wheels  27  of front dolly  24  to turn (move) in a left direct, (b) a right state which causes the front wheels  27  of front dolly  24  to turn in a right direction, and (c) a neutral state which causes turning motion to cease, but leaves wheels  27  pointing in their last ordered direction. 
     FIG. 11 is an enlarged partial cross sectional view of area  11  of FIG. 10 showing device  100  in a neutral hydraulic switching state (also refer to FIG.  17 ). In this state the first section  34  and second section  36  of variable length strut  32  are neither moved together (contracted) nor moved apart (expanded). This relative longitudinal position of the two sections is mechanically coupled to power steering valve  38  which resultantly assumes a neutral hydraulic switching state. That is, front wheels  25  are neither ordered to turn to the left nor the right. It is noted that in an embodiment of the invention, first section  34  of variable length strut  32  is longitudinally received by second section  36 , and the two sections are connected by a bolt and flange arrangement. Self-lubricating bearings  43  are installed between first section  34  and second section  36  of variable length strut  32 . 
     FIG. 12 is an enlarged partial cross sectional view of area  11  of FIG. 10 showing device  100  in a turn left hydraulic switching state (also refer to FIG.  18 ). Referring also to FIG. 8, tow bar  22  has been rotated to the left as towing vehicle  802  turns left. This motion causes variable length strut  32  to contract. That is, first section  34  and second section  36  move together. This relative longitudinal position of the two sections is mechanically coupled to power steering valve  38  which, through an internal ball stud device, resultantly assumes a left hydraulic switching state which causes front wheels  27  of front dolly  24  to turn in a left direction. 
     FIG. 13 is an enlarged partial cross sectional view of area  11  of FIG. 10 showing device  100  in a turn right hydraulic switching state (also refer to FIG.  19 ). Tow bar  22  is rotated to the right as towing vehicle  802  turns right. This motion causes variable length strut  32  to expand. That is, first section  34  and second section  36  move apart. This relative longitudinal position of the two sections is mechanically coupled to power steering valve  38  which resultantly assumes a right hydraulic switching state which causes front wheels  27  of front dolly  24  to turn in a right direction. 
     FIG. 14 is an enlarged view of area  14  of FIG. 11 showing the relative longitudinal position of first section  34  and second section  36  of variable length strut  32  which results in a neutral hydraulic switching state of power steering valve  38 . Flange  37  of first section  34  and flange  39  of second section  36  are held together by a bolt  41  and reside in a spaced apart relationship wherein a distance D (about 0.065 inches) exists between the two flanges. This spaced relationship of first  34  and second  36  sections is mechanically coupled to power steering valve  38  (refer to FIG.  10 ), and causes power steering valve  38  to assume a neutral hydraulic switching state. Flange  37  has a through hole  51  and flange  39  has threads  53 . Bolt  41  is fed through hole  51  and threaded into flange  39  until proper relative movement of flanges  37  and  39  has been achieved. Then a lock nut  55  is used to retain bolt  41  in a fixed position within threaded flange  39 . 
     FIG. 15 is an enlarged view of area  15  of FIG. 12 showing the relative longitudinal position of first section  34  and second section  36  of variable length strut  32  which results in a turn left hydraulic switching state of power steering valve  38 . As tow bar  22  is turned to the left, variable length strut  32  contracts thereby forcing first section  34  and second section  36  together so that flanges  37  and  39  come into contact. In an embodiment of the invention, the motion between first section  34  and second section  36  is small, being a total distance 2D of about 0.13 inches. That is, the difference between the contracted and expanded lengths of variable length strut  32  is 0.13 inches. The contracted relationship of first section  34  and second section  36  is mechanically coupled to power steering valve  38  (refer to FIG.  10 ), and causes power steering valve  38  to assume a left hydraulic switching state which causes front wheels  27  of front dolly  24  to turn in a left direction. 
     FIG. 16 is an enlarged view of area  16  of FIG. 13 showing the relative longitudinal position of first section  34  and second section  36  of variable length strut  32  which results in a turn right hydraulic switching state of power steering valve  38 . As tow bar  22  is turned to the right, variable length strut  32  expands thereby forcing first section  34  and second section  36  apart. This expanded relationship of first section  34  and second section  36  is mechanically coupled to power steering valve  38  (refer to FIG.  10 ), and causes power steering valve  38  to assume a right hydraulic switching state which causes front wheels  27  of front dolly  24  to turn in a right direction. 
     FIG. 17 is a hydraulic flow diagram with device  100  in a neutral hydraulic state. Hydraulic fluid from a reservoir is pumped via hydraulic lines into power steering valve  38 . In the neutral state, the fluid circulates through power steering valve  38  and is routed back to the reservoir. As has been previously discussed, the neutral hydraulic state of power steering valve  38  is controlled by the relative longitudinal motion of variable length strut  32 . 
     FIG. 18 is a hydraulic flow diagram with device  100  in a turn left hydraulic state. Hydraulic fluid from a reservoir is pumped via hydraulic lines into one side of cylinders  26  and pushes upon a piston within cylinder  26 . It may be appreciated that cylinders  26  are physically arranged so that the piston of one cylinder  26  moves in an opposite direction from the piston in the other cylinder  26 . Fluid from the other side of cylinders  26  is routed back through power steering valve  38  to the reservoir. This turn left hydraulic configuration will be maintained as long as variable length strut  32  is being contracted by the turning action of tow bar  22 . 
     FIG. 19 is a hydraulic flow diagram with device  100  in a turn right hydraulic state. Hydraulic fluid from a reservoir is pumped via hydraulic lines into one side of cylinders  26 . It is noted that the fluid is delivered to the opposite side of cylinders  26  from the left hydraulic state of FIG.  18 . Fluid from the other side of cylinders  26  is routed back through power steering valve  38  to the reservoir. This turn right hydraulic configuration will be maintained as long as variable length strut  32  is being expanded by the turning action of tow bar  22 . 
     FIG. 20 is a hydraulic flow diagram of a second embodiment with device  100  in the neutral hydraulic state. The only difference in this configuration is that hydraulic fluid is also delivered to a second pair of rear cylinders  48  (refer to FIGS.  5  and  8 ). 
     It may be appreciated that the terms left and right can vary depending upon the specific arrangement of the mechanical elements of the present invention. 
     In terms of use, a method for steering a transport vehicle  800 , includes: 
     (a) providing a transport vehicle  800  having a rotatable tow bar  22  and a front dolly  24  having front wheels  25 ; 
     (b) providing a device  100  for steering the transport vehicle  800 , device  100  including: 
     a variable length strut  32  connected between tow bar  22  and front dolly  24 , the variable length strut  32  having a first section  34  and a second section  36 , the first section  34  and second section  36  longitudinally movable with respect to one another; 
     a hydraulic power steering valve  38  having a first end  40  and a second end  42 ; 
     first end  40  of power steering valve  38  connected to first section  34  of variable length strut  32 , and second end  42  of power steering valve  38  connected to second section  36  of variable length strut  32 ; and, 
     (c) rotating tow bar  22  thereby causing first section  34  and second section  36  of variable length strut  32  to longitudinally move with respect to one another, the motion causing power steering valve  38  to assume a hydraulic switching state, the hydraulic switching state including one of (a) a left state which causes front wheels  27  of front dolly  24  to turn in a left direction, and (b) a right state which causes front wheels  27  of front dolly  24  to turn in a right direction. 
     The method may further include: 
     (d) ceasing to rotate tow bar  22  wherein power steering valve  38  assumes a neutral hydraulic switching state and further turning in the left direction or right direction ceases. 
     The method may further include: 
     in step (b), the first section  34  and second section  36  longitudinally movable a distance of about 0.13 inches. 
     The preferred embodiments of the invention described herein are exemplary and numerous modifications, variations, and rearrangements can be readily envisioned to achieve an equivalent result, all of which are intended to be embraced within the scope of the appended claims.