Abstract:
An attachment for skid steer loaders and the like which combines a forklift mast with width adjustable rolling stabilizer outriggers. The ground engaging rolling stabilizer caster wheels are positioned to each side of the lifted load. The castering wheels bear a large fraction of the weight of the lifted load as well as stabilizing the load while it is in motion over varying terrain. The rolling stabilizer lift dramatically increases the weight lifting capacity and the height to which loads can be lifted beyond that of the loader alone.

Description:
RELATED APPLICATION 
     This application claims the benefit of Provisional Application No. 60/141,074 filed on Jun. 25, 1999, which is incorporated herein in its entirety by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the field of lifting attachments for small power units such as skid steer loaders, Dingoes®, small tractors and “four wheeler” ATVs. More particularly it relates to a forklift attachment with rolling stabilizers for skid steer loaders and the like. 
     BACKGROUND OF THE INVENTION 
     A wide variety of versatile motorized prime movers are used in the construction, maintenance, and grounds upkeep industries. These include skid steer loaders, light tractors, garden tractors, “four wheeler” all terrain vehicles, and many other compact power units. Skid steer loaders, in particular, are widely employed for a variety of material handling, earth moving and transportation tasks. 
     In general, these devices are favored for their compact size, maneuverability and ability to utilize many attachments to accomplish a variety of jobs. The need for these units to be readily transported, generally on a trailer pulled by a pickup truck or other small truck, limits their overall weight. In addition, their high maneuverability is a consequence of their short wheelbase and overall length. 
     Counterweights may be used at the opposite end of the power unit from load lifting attachments to balance the vehicle. In order to balance a massive load, a long moment arm or a heavy counterweight must be used. Consequently, the ability of these units to lift loads is limited by the need to keep the overall length and weight of the power unit relatively small. 
     For example, skid steer loaders used in landscaping may be fitted with fork attachments to move pallets supporting rolls of sod or concrete landscaping materials. An example of such a device is disclosed in U.S. Pat. No. 3,458,069 to Wickberg et al. Fully loaded pallets of landscaping or construction materials are commonly heavy enough to exceed the capacity of the machine to lift them with out raising the rear wheels from the ground. This forces the contractor to use only partially loaded pallets; to employ other machinery at significant expense; or to redistribute at least some of the materials by hand labor. All of these options are inefficient and costly. 
     In addition to lifting loads, compact power units are used to move lifted loads to a variety of locations over many types of terrain. For example, in the construction and landscaping industries, loads are often moved over unpaved surfaces, up, down and across slopes and over generally uneven ground. In order to maintain stability of the vehicles as they currently exist, loads must be kept low and close to the center of gravity of the vehicle. Tall, heavy loads in combination with a slope or uneven ground can cause compact vehicles to be dangerously unstable or even to overturn. 
     The versatility of these already flexible machines would be even greater if their lifting capacity were increased without significantly increasing their weight or reducing maneuverability. Particularly the ability to lift and transport pallets of heavy materials safely over uneven terrain is beneficial. An increase in the height to which loads can be lifted would also be helpful. Additionally, it would be desirable that the stability of the loader, the lifted load and attachment be maximized. 
     SUMMARY OF THE INVENTION 
     The present invention increases the lifting capacity of the power unit it is attached to dramatically beyond that of the power unit alone. It makes practical the safe, stable transport of heavy loads over uneven terrain that cannot be accomplished by the power unit alone. In addition, the invention allows lifting to a greater height than the loader alone is capable of. 
     The present invention is a rolling stabilizer lift attachment that is designed to be manufactured as a product family. Different size ranges of the invention may be manufactured to fulfill different user requirements, the needs of different industries and different pricing categories. The rolling stabilizer lift is adjustable to varying working conditions, providing maximum load stability when desired and offering a compact configuration for operating in restricted spaces. 
     The lift attachment comprises five major components: a mounting plate, a lifting mast, a right rolling stabilizer, a left rolling stabilizer, and lifting forks or other load engaging apparatus. The rolling stabilizer lift may be adapted to attach to a large variety of power units so long as the power unit is sufficiently powerful to move the intended load. 
     The mounting plate may be adapted to accommodate coupling to many different types of power equipment. The mounting plate may be attached to the rest of the assembly by a freely rotating lateral pivot, in order to allow the rolling stabilizers to remain in full contact with the ground despite irregularity of the terrain. The rotation of the pivot may be limited to prevent the rolling stabilizer load from overturning if the ground is dramatically irregular and to allow the attachment to be raised from the ground safely. Additionally, the rotation of the pivot may be restricted from free rotation by a braking mechanism. Some applications may benefit from a non-pivoting attachment. 
     The right and left rolling stabilizers or outriggers each comprise a width adjustable support and a swiveling, caster mounted support wheel and tire. The rolling stabilizers are similar aside from being opposite handed. The rolling stabilizers place the load bearing caster wheels somewhat ahead of and to the sides of the lifting mast. 
     The lifting mast is generally centered between the rolling stabilizers and provides a means for lifting loads. The lifting mast may lift the load via lifting forks however, bale spears, buckets and other load engaging devices may also be utilized. In most cases, the lifting mast will be actuated hydraulically although other actuation approaches may be used. If the power unit connected to the rolling stabilizer lift has a hydraulic power supply, it may be used to operate the lifting mast or a self contained power supply unit may be incorporated on the lift attachment itself. It is preferred that the lifting mast be configured to lift to a height of at least eight feet. 
     In connecting the hydraulic system of the rolling stabilizer lift to the hydraulic pressure supply of the power unit a safety issue arises. It is possible for the operator to disconnect the two systems, intentionally or inadvertently, while a load is still supported by the lifting mast. The power unit may also become disabled or suffer power loss. Upon disconnection of the pressure supply, or if the accidental severance of a hydraulic connection should occur, the load could drop causing damage or injury. Additionally, the release of hydraulic fluid under pressure may be hazardous. A safety device to prevent these occurrences is thus a desirable part of the invention. 
     The safety device comprises a manifold combining a pilot operated check valve with a pressure relief valve. The resulting integrated valve system requires hydraulic pressure to be maintained in the circuit to actuate lift cylinder lowering. If hydraulic pressure is lost, the pilot operated check valve closes holding the lift cylinder in its then current position. The manifold reduces the need for plumbing between individual hydraulic components. 
     In use, the rolling stabilizer lift attachment is attached to a power unit via the mounting plate. The width of separation of the stabilizers may be adjusted as appropriate for the job at hand. The power unit may be driven as usual allowing for the added space requirements of the lift attachment. Power units that have independent lift modules may lift the attachment off the ground to facilitate relocation of the rolling stabilizer lift when the unit is not loaded, for example, to place the rolling stabilizer lift on a truck or trailer for transport. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a right rear perspective view of a rolling stabilizer lift in accordance with the present invention; 
     FIG. 2 is a right front perspective view of the rolling stabilizer lift; 
     FIG. 3 is an exploded right rear perspective view of the rolling stabilizer lift; 
     FIG. 4 is a cross sectional schematic view of a hydraulic manifold for use with the rolling stabilizer lift depicting fluid passageways therein; 
     FIG. 5 is an elevational view of a gravity biased engagement hook for use with the rolling stabilizer lift; 
     FIG. 6 is a schematic view of the hydraulic circuitry of the rolling stabilizer lift; 
     FIGS. 7 a  and  7   b  are schematic representations of forces acting on the rolling stabilizer lift and power unit; 
     FIG. 8 is a graph depicting the summation of forces and design range of the rolling stabilizer lift; and 
     FIG. 9 is a graph depicting the summation of forces and design range of the rolling stabilizer lift for a specific example. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1,  2  and  3 , the rolling stabilizer lift attachment  10  comprises five major components: a mounting plate  12 , a lifting mast  14 , a right rolling stabilizer  16 , a left rolling stabilizer  18 , and a load engaging apparatus  20 . While lifting forks  21  are depicted and described herein, it will be appreciated that many other types of load engaging apparatus  20  may be employed such as bale spears, buckets or grapples, without departing from the spirit and scope of the invention. 
     The mounting plate  12  may be pivotably attached to the lifting mast  14  via a freely pivoting shaft  22 . The shaft is preferably secured into a bushing  24  with a split clamp collar  26  though other securing devices may be used. The pivot  22  may be restrained from perfectly free rotation by a frictional or spring-loaded brake  28  (not shown). Fixed or adjustable stops  30  may be employed. In some applications a non-pivoting or rigid mounting may be preferred. 
     The mounting plate  12  may be adapted to removably attach to a large variety of power units so long as the power unit is sufficiently powerful to move the intended load. Power units may include skid steer loaders, Dingoes®, tractors, garden tractors, “four wheeler” ATVs and others. Dingoes® are small wheeled or tracked skid steer power units manufactured by The Toro Company, 8111 Lyndale Avenue South, Bloomington, Minn. 55420. They are unlike other skid steer loaders in that the operator stands on a platform behind the unit rather than riding on or in it. In discussion here, the power unit will often be referred to as a skid steer loader. This should not be considered as limiting. 
     In the case of power units that have lifting modules of their own, it is important that the rolling stabilizer lift unit be light enough to be lifted by the power unit. In order to fulfill this weight requirement it is preferable that selected parts of the rolling stabilizer lift be constructed of high strength, low alloy steel. 
     The lifting mast  14  of the rolling stabilizer lift  10  is generally similar to that used in a conventional forklift, and comprises a supporting outer mast  32 , a movable inner mast  34  and a movable carriage  36 . The lifting mast  14  is preferably pivotably secured to the mounting plate  12  and is scalable to allow use in concert with many different power units. Preferably a hydraulic cylinder or cylinders  38  provide the lifting force though other means of lifting may be employed. Generally, the lifting cylinder  38  is secured at one end to the base  40  of the outer mast  32 . The piston rod  42  is coupled at its distal end to bracket  43 . Sprockets  44  are rotatably carried by bracket  43  at the upper end thereof. A pair of roller chains (not shown) is connected at one end to the base  40  of the outer mast  32  and at the other end at the base of the carriage  36 . The roller chains (not shown) are positioned so that they travel from the outer mast  32  up and over the sprockets  44  and further down to their connection at the base of the carriage  36 . The carriage  36  is slidably movable within the inner mast  34  and outer mast  32  supported on rollers  46 . The lifting mast  14  preferably has a lifting capacity of at least 1500 pounds and a lifting height of at least eight feet. Other characteristics of the lifting mast  14  are similar in structure to characteristics of conventional forklift masts well known to those skilled in the art. 
     In one embodiment of the invention, the attached power unit may provide hydraulic power for the lifting mast  14  if the power unit has an integral hydraulic power supply. In this case, appropriate hydraulic connections are provided. In the absence of hydraulics on the power unit the rolling stabilizer lift  10  may have a hydraulic power pack (not shown) incorporated thereupon. 
     The load engaging apparatus  20  may comprise lifting forks  21  which are removably attachable to the carriage  36 . Forks  21  may be engaged to the carriage  36  so as to be width adjustable to a plurality of positions. Referring to FIGS. 2 and 5, forks  21  may be engaged to the carriage  36  with the aid of gravity biased engagement hooks  49 . Gravity biased hooks  49  are structured so that when hung from their pivot  51 , gravity tends to force them to an engaged position. Other load engaging apparatus  20  that may be carried by the carriage  36  include: a bale spear, a grapple hook, a clam shell bucket, a dump box, a tilt box, a sod roller, a lifting boom and the like. 
     The rolling stabilizers or outriggers  16 , 18  support position adjustable castering wheel assemblies  50  located to the side and in front of the lifting mast  14 . The rolling stabilizers  16 , 18  are similar, aside from being opposite handed. Each of the rolling stabilizers  16 , 18  comprises a castering wheel assembly  50 , a pivot  52 , a support arm  54 , a slider  56 , a sleeve  58  and a locking device  60 . The sleeve  58  is a hollow polygonal tube secured to the fixed outer mast  32 . The slider  56  is of similar cross sectional shape to the sleeve  58  and is slidably positionable within the sleeve  58 . The distal end of the slider  56  is secured to the support arm  54  which in turn carries a vertical pivot  52  to which the castering wheel assembly  50  is pivotably secured. The rolling stabilizers  16 ,  18  are thus slidably adjustable in separation. Locking device  60  preferably comprises lock pin  62  receivable through apertures  64  in sleeve  58  and through a plurality of mating apertures  66  through slider  56 . The stabilizer arm  54  may be angled down from the horizontal about 10 degrees. The stabilizers  16 , 18  may be linked to be movable simultaneously or unlinked to adjust individually. A pair of rack gears and a pinion (not shown) may link them, for example, to assure symmetrical spacing. The stabilizers  16 , 18  may optionally include a power adjustment mechanism. 
     The hydraulic safety valve manifold  68  depicted in FIGS. 4 and 6 comprises a manifold block  70 , a pilot operating check valve  72  and a pressure reducing valve  74 . 
     The pilot operated check valve  72  preferably has a 3.0:1 valve ratio, requiring a pilot pressure of one-third the load pressure at the cylinder to open the valve. The pressure reducing valve  74  is preferably a direct acting, spool type pressure reducing/relieving valve with internal pilot. 
     Referring to FIG. 4, the manifold block  70  defines a number of ports and connecting fluid passageways. For convenience up, down, right and left will refer to those directions as depicted in FIG.  4 . Beginning at the left side and proceeding clockwise, the down control valve port  76 , is defined in the left side of the manifold block. The top of the block presents the pilot operated check valve port  78 , into which pilot operated check valve  72  may be secured and the down lift cylinder port  80 . The right side of the block presents the pressure reducing valve port  82 , into which pressure reducing valve  74  may be secured. The bottom of the manifold block presents the up cylinder valve port  84  and the up lift cylinder port  86 . First fluid passage  88  interconnects the down control valve port  76  with the pilot operating check valve port  78 . Second fluid passage  90  connects the pilot operated check valve port  78  with the down lift cylinder port  80 . Third fluid passage  92  connects the down lift cylinder port  80  with the pressure reducing valve port  82 . Fourth fluid passage  94  connects the pressure reducing valve port  82  with the up control valve port  84 . Finally, fifth fluid passage  96  connects the up lift cylinder port  86  with the pilot operated check valve port  78 . 
     The schematic diagram of FIG. 6 depicts the hydraulic circuit  98  of the rolling stabilizer lift  10  which employs the above described manifold block. Four way directional control valve  100 , on the power unit  102 , controls whether a lifting circuit or a lowering circuit is active. When four way directional control valve  100  is moved to the right the lifting circuit is active. When it is moved to the left the lowering circuit is activated. 
     The lifting circuit includes a pressure supply  104 , pressure reducing valve  74 , pilot operated check valve  72 , double acting cylinder  106  and fluid return to tank  108 . The lowering circuit includes a pressure supply  104 , a branch to pilot of check valve  110 , double acting cylinder  106 , pilot operated check valve  72  and fluid return to tank  108 . 
     Design factors relating to the rolling stabilizer lift include the relationship between the weight of the power unit, the weight of the rolling stabilizer lift with load, and the positioning of the load bearing wheels. In order to increase the lifting capacity of the power unit, the supporting wheels must be placed appropriately. If the support wheels are placed too near the power unit, too little of the weight of the lift and the load are supported by the arm and wheel assembly, and the load tends to lift the rear wheels of the power unit from the ground, leading to tipping of the power unit. If the wheels are placed too far forward, the weight of the rolling stabilizer lift and load are shifted to the power unit. This negates the benefit of the invention by reducing the load carrying capacity. In addition, moving the supporting wheels farther forward increases the resistance of the lift unit to turning by the power unit. There is a point at which the resistive torque created by friction exceeds the ability of the power unit to apply turning torque to the unit making the power unit and stabilizer lift combination unsteerable. 
     In summary, if the support arms are too short, the combination of rolling stabilizer lift and power unit will tip over in response to a load. If the arms are too long, the combination will be difficult to steer. 
     To understand these design issues in greater detail, reference is made to FIG.  7 . The schematic diagrams of FIGS. 7 a  and  7   b  depict the power unit and the stabilizer lift. The effect of gravity acting upon the power unit creates a force annotated in the drawings as F 1 . Gravity acts upon the lift unit and load creating a force annotated as F 2 . Forces F 1  and F 2  act in opposite directions about a pivot located at the front axle of the power unit. The distance from the pivot point to the center of mass of the power unit is labeled d (x 1 ). The distance from the pivot point to the support wheels is labeled d (x 2 ). The total resistive torque created by friction resisting the turning movement of the assembly labeled M x0  is determined by the equation: 
     
       
         Σ M   0x =0=∫ f[F   1   d ( x   1 )− F   2   d ( x   2 )]  (Eq. 1) 
       
     
     The turning torque available from the power unit is labeled M y0 . The turning torque is a function of the force F 1  and the coefficient of friction μ. This is defined by the equation: 
     
       
         Σ M   y0 =0=ƒ N ( y )  (Eq. 2) 
       
     
     Where N=F 1 μ 
     Tipping load, labeled F t , represents the load that may be carried by the lifting mast before the load exceeds the counterbalance of the mobile power unit and tips the combination of the power unit and rolling stabilizer lift. The tipping load increases as the length of the rolling stabilizer load is lengthened. 
     
       
           F   t   =F   2   d ( x   2 )  (Eq. 3) 
       
     
     The graph of FIG. 8 depicts the relationship of support arm length on the x-axis to the magnitude of tipping load, turning torque and resistive torque on the y-axis. The summation of these three quantities creates a curve with a minimum, where the slope of a tangent to the curve is zero, which represents the optimal rolling stabilizer arm length. There is, of course, a design range X, as identified on the graph, within which the performance of the rolling stabilizer lift is acceptable. This design range is limited to the section of the curve that has a slope slightly less than or greater than zero. 
     The graph depicted in FIG. 9 shows the relationship for a specific example of a 1500 pound Dingo® and a 3250 pound capacity rolling stabilizer lift. The data points used to create the graph are included in Table 1. The design range is limited to the portion of the summation curve where the slope is substantially zero. The optimum arm length is found where the slope equals zero. For this example the optimum arm length is eighteen inches. The exact curve will vary depending upon the design weight of the power unit, the relative position of the power unit and the lift assembly, and the design lift capacity. The design strategy remains the same and can be used to create a family of products. 
     In operation, the rolling stabilizer lift  10  is connected to a power unit. If the power unit is equipped with lift arms and a hydraulic system, such as a skid steer loader, appropriate connections are made. In lifting loads, the rolling stabilizer lift  10  is operated in a fashion generally similar to a forklift, with some differences. 
     The rolling stabilizers  16 , 18 , may be adjusted to a greater width for maximum stability or may be narrowed for narrower loads or to pass through a confined area such as a doorway. This is accomplished by releasing the locking device  60 , sliding the stabilizers  16 , 18  to position and re-engaging the locking device  60 . 
     In moving over uneven ground the pivotably connected attachment plate  12  maintains ground engagement of the castering wheel assembly  50  to support and stabilize the load. In the case of extremely uneven ground or if the rolling stabilizer lift is raised from the ground by a lift arm equipped loader, one of the rotation stops  30  impinges upon the sleeve  58  to prevent the rolling stabilizer lift  10  from rotating so far as to topple the load to the side. For example if one of the castering wheel assemblies  50  drops into a hole the rotation stop  30  will prevent it from dropping to a point that would tip the load. 
     Once a load is lifted it may be pitched backward toward the power unit  102  for additional stability by pitching the lift arms  112  of the power unit  102 , if so equipped. Downward angling of the support arms  54  facilitates this. 
     Two hydraulic circuit paths are employed, one for lifting loads and the other for lowering them. Referring to FIG. 6, for lifting, four way direction control valve  100  is moved to the right. Hydraulic fluid from pressure  104  flows through the up control valve port  84  to pressure reducing valve  74 . If the pressure exceeds the preset value excess fluid is bled off through down lift cylinder port  80 , through down control valve port  76  and returns to tank  108 . The main fluid flow forces open pilot operated check valve  72  and flows to double acting cylinder  106  raising the load. When four way direction control valve  100  is returned to center pressure is removed, pilot operated check valve  72  closes and the load is held in the lifted position. 
     To lower the load, four way direction control valve  100  is moved to the left and fluid flows through down control valve port  76 , pressure is applied to pilot operated check valve  72  via branch  110  opening pilot operated check valve  72  allowing load to lower. The main fluid flow continues on to double acting cylinder  106 , lowering the load. 
     The present invention may be embodied in other specific forms without departing from the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 TURNING 
                   
                 RESISTIVE 
                   
               
               
                 X 
                 D1(X) 
                 TORQUE 
                 D2(X) 
                 TORQUE 
                 Tipping Load L 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 −16 
                 −1136.4 
                 −568.2 
                 5886.4 
                 2943.2 
                 3214.3 
               
               
                 −14 
                 −645.8 
                 −322.9 
                 5395.8 
                 2697.9 
                 3428.6 
               
               
                 −12 
                 −230.8 
                 −115.4 
                 4980.8 
                 2490.4 
                 3642.9 
               
               
                 −10 
                 125.0 
                 62.5 
                 4625.0 
                 2312.5 
                 3857.1 
               
               
                 −8 
                 433.3 
                 216.7 
                 4316.7 
                 2158.3 
                 4071.4 
               
               
                 −6 
                 703.1 
                 351.6 
                 4046.9 
                 2023.4 
                 4285.7 
               
               
                 −4 
                 941.2 
                 470.6 
                 3808.8 
                 1904.4 
                 4500.0 
               
               
                 −2 
                 1152.8 
                 576.4 
                 3597.2 
                 1798.6 
                 4714.3 
               
               
                 0 
                 1342.1 
                 671.1 
                 3407.9 
                 1703.9 
                 4928.6 
               
               
                 2 
                 1512.5 
                 756.3 
                 3237.5 
                 1618.8 
                 5142.9 
               
               
                 4 
                 1666.7 
                 833.3 
                 3083.3 
                 1541.7 
                 5357.1 
               
               
                 6 
                 1806.8 
                 903.4 
                 2943.2 
                 1471.6 
                 5571.4 
               
               
                 8 
                 1934.8 
                 967.4 
                 2815.2 
                 1407.6 
                 5785.7 
               
               
                 10 
                 2052.1 
                 1026.0 
                 2697.9 
                 1349.0 
                 6000.0 
               
               
                 12 
                 2160.0 
                 1080.0 
                 2590.0 
                 1295.0 
                 6214.3 
               
               
                 14 
                 2259.6 
                 1129.8 
                 2490.4 
                 1245.2 
                 6428.6 
               
               
                 16 
                 2351.9 
                 1175.9 
                 2398.1 
                 1199.1 
                 6642.9 
               
               
                 18 
                 2437.5 
                 1218.8 
                 2312.5 
                 1156.3 
                 6857.1 
               
               
                 20 
                 2517.2 
                 1258.6 
                 2232.8 
                 1116.4 
                 7071.4 
               
               
                 22 
                 2591.7 
                 1295.8 
                 2158.3 
                 1079.2 
                 7285.7 
               
               
                 24 
                 2661.3 
                 1330.6 
                 2088.7 
                 1044.4 
                 7500.0 
               
               
                 26 
                 2726.6 
                 1363.3 
                 2023.4 
                 1011.7 
                 7714.3 
               
               
                 28 
                 2787.9 
                 1393.9 
                 1962.1 
                 981.1 
                 7928.6 
               
               
                 30 
                 2845.6 
                 1422.8 
                 1904.4 
                 952.2 
                 8142.9 
               
               
                 32 
                 2900.0 
                 1450.0 
                 1850.0 
                 925.0 
                 8357.1 
               
               
                 34 
                 2951.4 
                 1475.7 
                 1798.6 
                 899.3 
                 8571.4 
               
               
                 36 
                 3000.0 
                 1500.0 
                 1750.0 
                 875.0 
                 8785.7 
               
               
                 38 
                 3046.1 
                 1523.0 
                 1703.9 
                 852.0 
                 9000.0