Self-contained steering guidance means
BACKGROUND OF THE INVENTION 
     This invention relates to a vehicle steering mechanism particularly applicable to fork lift truck vehicles. More specifically, this invention is directed to a steering guidance means associated with each steerable wheel of the vehicle which senses the vehicle position with respect to a lateral guide surface and mechanically transmits movement to control the turning of the associated wheel. The invention additionally includes a control means for removing the normal hydraulic power steering means from operation whereby the mechanical guidance mechanism is the sole controller of the vehicle steering. 
     Currently, a real effort is being made to conserve the floor space in storage warehouses by using narrower aisles and accommodating narrow aisle fork lift trucks. Ideally, the width of the narrow aisle should only be slightly greater than the maximum width of the fork lift truck vehicle which travels down the aisles loading and unloading material storage racks arrayed on opposite sides of the aisles. Since it is extremely difficult for an operator to negotiate such narrow aisles without grazing or otherwise hitting the storage racks, guide mechanisms have been developed to guide the vehicle in a precisely determined path within the narrow aisles between rows of storage racks. An additional benefit of these guide means is that they permit the operator to dispense with the function of steering the vehicle and allow him to devote his efforts to other tasks, such as finding the number of the appropriate load space. 
     Illustrative of one of these prior art guidance means is U.S. Pat. No. 3,850,111 to Hansen. With this patent device, a guide plate assembly mounted under the vehicle, such as a fork lift truck vehicle, has a plurality of rollers laterally extending therefrom on oposite sides of the vehicle. The rollers contact accommodating guide rails and the vehicle is slewed to follow a straight line path between the guide rails. This type of device is not entirely satisfactory, however. The principle reason it is not satisfactory is that there is no positive turning of the vehicle steering wheels. Rather, there is no positive control of the vehicle steering wheels exercised by the guide means. A certain amount of tire wear and vehicle shock is also encountered with this type of system since the unit basically slews or drags the vehicle sideways to maintain the correct aisle position. 
     However, with the prior art guide means, very strong floor-mounted guide rails are required because this brute force guidance approach results in such great forces that longitudinal members on the racks cannot be used. Such rails on the floor on each side of the aisle are expensive and interfere with the placing of loads directly on the floor so that a bottom shelf is required. 
     In order to overcome some of these disadvantages a guidance means has been developed to translate the motion of a guidance member contacting the lateral guide surface to the steerable wheels of a vehicle. Examples of this type of device are shown in U.S. Pat. No. 3,858,523 to Allsup, Jr., and U.S. Pat. No. 3,872,794 to Goode. However, while this system which uses the mechanical linkage for translating motion from the guidance member to the wheels of the vehicle is of some improvement, it is nonapplicable to a vehicle wherein the wheels thereof are normally steered by power means such as hydraulic cylinder means. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     It is therefore the primary object of this invention to provide a mechanical guidance mechanism for a vehicle having steerable wheels. 
     It is a further object of this invention to provide such a guidance mechanism having a guidance member positioned to contact a guide surface and direct the vehicle between narrow aisles. 
     It is a further object of this invention to provide such a guidance mechanism including control means for rendering the hydraulic power system normally controlling steering inoperative whereby operation between narrow aisles is accomplished by a mechanical guidance system positioned to contact a guard surface. 
     The invention takes the form of a mechanical guidance mechanism associated with each steerable wheel of the vehicle and having a guidance member in the form of a roller for sensing the vehicle position between guide surfaces on opposite sides of a narrow aisle. The roller is rotatably mounted on a C-shaped slide member which is slidably disposed over a square bar. The square bar is pivotally rigidly affixed to the vehicle intermediate the ends thereof. The other end of the bar is rigidly pivotally affixed to a first lever at one end of the lever. The first lever has a fixed axis from which it pivots intermediate its ends. The other end of said first lever includes an elongated slot. The second lever is pivotally affixed to the vehicle intermediate its ends. A pin is rigidly affixed to one end of the second lever and traverses the slot in the first lever. The other end of the second lever has a spring rigidly mounted thereon which is connected to one end of a third lever. The third lever is also pivotally affixed about the free end thereof. The pivot of the third lever is affixed to the vehicle steering knuckle or king pin so as to turn the associated wheel. In addition, a control valve means is provided for rendering inoperative the double acting hydraulic cylinder normally controlling a pair of steerable wheels. In this manner, control of the steering of the vehicle is accomplished by the mechanical means when the vehicle is in the narrow aisle position. After the vehicle has left the narrow aisle position the control valve may be actuated so as to allow the vehicle hydraulic steering system to regain steering control of the vehicle. 
     Other objects and advantages of the invention will become more apparent from a review of the accompanying drawings and the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a lift truck embodying the instant invention; 
     FIG. 2 is a top plan view of the rear portion of the lift truck of FIG. 1, taken along lines II--II in FIG. 1, and also including a schematic drawing of the hydraulic power steering means; and 
     FIG. 3 is a top quarter isometric view partially cut away of the mechanical guidance means of the instant invention associated with a single steerable wheel. 
    
    
     DETAILED DESCRIPTION 
     Turning to FIG. 1, there is shown generally at 10 a lift truck vehicle having a body 12 which is supported by a plurality of steerable road wheels 14, 16, 18 and 20. Body 12 mounts an operator station generally shown at 22 having an operator seat 24 and an overhead guard protection structure 26 thereover. Pivotally mounted on the front of the vehicle is a mast 28 having a vertically movable carriage 30 mounted thereon. Carriage 30 in turn mounts a plurality of forks 32 for engaging a load. 
     Operator control of the vehicle is accomplished through manual controls mounted on console 34. Steering of the vehicle is accomplished through steering wheel 36 which is connected to a hydraulic power steering means (not shown) within the body of the vehicle. The power for operating this hydraulic power steering means is located within the body of the vehicle at 38. 
     While this description is directed to a lift truck vehicle, it is to be understood that the invention is not to be limited to this application. Rather, other vehicles which may traverse narrow aisles are also contemplated for use with the instant invention. 
     Mechanical guidance means 40, 42, 44, 46 are associated with each steerable wheel of the vehicle as will be more fully hereinafter described. As may be discerned from the subject Figure, the mechanical guidance means are positioned within openings, for example openings 48, 50 in the sides of the vehicle body 12. 
     Turning to FIG. 2, an exemplary showing of the rear wheels 16, 20 is shown. A hydraulic power steering system 52 is comprised of a steering control valve 54 which serves to direct hydraulic fluid from a fluid pressure source 56 by means of a pump 58 and thence to the ends of a steering control cylinder 60 through conduits 62, 64. For controlling the steering of the front wheels (not shown), additional conduits 66, 68 are provided. Thus, when normal power steering of the vehicle is desired, rotation of wheel 36 will selectively direct hydraulic fluid to power, for example, steering cylinder 60. As best seen in FIG. 3, rod end 70 of the cylinder 60 is fixed to axle 72 and the steering links 73 are pivotally affixed to the steering knuckle arms for rotating the knuckle on which the wheel axle is mounted. Axle 72 is rotatable by means of king pin 74 which is journalled into the frame member 76. 
     Turning to FIG. 2, when normal powered steer is desired, valves 78, 80 which intercommunicate the lines leading to opposite sides of the steer cylinders, are, for example, manually closed. In this manner, steer cylinders are effectively in the system and serve to control the steering of the wheels. When it is desired to effectively remove the power steer system from operation, valves 78, 80 are, for example, manually opened and the steer cylinder is effectively bypassed. 
     Each wheel contains an identical mechanical guidance means. Accordingly, for the sake of convenience, a single guidance means will be discussed hereinafter. As shown in FIGS. 2 and 3, such guidance means comprises a guidance member in the form of a roller 81 which is rotatably mounted on a generally C-shaped bar 82 by means of a vertically oriented pin or pivot 86. C-shaped bar or slide member 82 is telescopically disposed over an elongated square bar 88 having end caps 84 affixed thereto. Square bar 88 is pivotally affixed intermediate its end by means of a vertical pivot 90 which is connected to a tab or bracket 92 extending laterally of the bar. An elongated slot correspondingly located on the side of member 82 allows the member to telescope over bracket 92. A first lever 96 is located substantially parallel to bar 88 and is similarly pivotally supported by a pivot 98 located intermediate the ends of the lever. One end of the lever is pivotally connected by a link 100 to square bar 88. The other end of lever 96 includes an elongated slot 102. The second lever 104 is similarly pivotally affixed to the vehicle intermediate its ends by means of a pivot 106. A vertically oriented pin 108 is rigidly affixed to one end of lever 104 and traverses slot 102 within first lever 96. The other end of second lever 104 is connected by means of a spring 110 to the end of the third lever 112 which has its opposite end connected to king pin 74 for rotation thereof. 
     In operation, if the vehicle with which the guidance means is associated crowds too close to a rack on the right side of the aisle within which it is traversing, roller 81 through C-shaped slide member 82, square bar 88, linkage 100, first lever 96 and second lever 104 will extend spring 110 which allows, in cooperation with elongated slot 102, a degree of lost motion. Because the mating springs (not shown) on the opposite wheel will not be as highly extended, the unbalance of forces will steer the end of the lift truck away from the rack. The opposite motion will occur for the opposite direction of lift truck travel. 
     It is to be understood that the foregoing description is merely illustrative of a preferred embodiment of the invention, and that the scope of the invention is not to be limited thereto but is to be determined by the scope of the appended claims.