Abstract:
A friction management system for a traveling crane applies a liquid or solid friction modifier (FM) in precisely controlled quantities to the crane wheels or rail to improve performance and safety during movement of the crane. The friction modifier is applied by a nozzle mounted on a crane truck, which nozzle is opened and closed by a valve. The duration of the valve opening per second, which controls the friction modifier application rate, is approximately proportional to the average current draw, which is detected by current sensors connected to the truck motors.

Description:
CROSS-REFERENCE TO RELATED APPLCIATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/746,605, filed May 5, 2006. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    This invention generally relates to traveling cranes. More particularly, this invention relates to systems for reducing friction during movement of a traveling crane along rails. 
         [0003]    Portal cranes are used extensively in ports to load and unload ships and submarines. These cranes generally have a high load lifting capacity and therefore utilize double flange steel wheel trucks on heavy weight steel rails. The rails have a wide gage (up to 40 ft. or more). Depending on the load lifting capacity, portal cranes have a large number (8 to 16 or more) of two wheel trucks. One-half to one-third of the wheels are powered. Drive motors are generally located on the truck. 
         [0004]      FIGS. 1A and 1B  show a typical diagram of a modern portal crane  1  used by the U.S. Navy. A superstructure of several levels, which levels include a rotating upper works  10  connected to a system of booms, pulleys, hook hoists, steel ropes, etc. collectively designated at  15 , which enables the crane  1  to pick up or lower heavy loads. The particular components of the lifting system or boom  15  will vary according to the intended use of the crane  1 . The upper works  10  and boom  15  are supported by a traveling portal base  16 , which is built on top of a plurality of trucks  11 ,  12 ,  13 ,  14 . The trucks  11 ,  12 ,  13 ,  14  move on heavy rails  37 ,  38  placed with a wide gage  7 . Similar cranes with smaller booms and smaller load lifting capacities are used by commercial services. There are several differences between Navy and commercial cranes but the type of trucks and wheels used in both cranes, collectively referred to herein as traveling cranes, is the same. 
         [0005]    In Navy portal cranes, power is supplied by an on-board engine and generator typically located in the traveling portal base  16 , above the trucks. Many of the other electrical and mechanical systems are located in a chamber-like structural member  28  of the crane  1 . An on-board fuel tank supplies fuel for the engine. The maximum power available is thus limited to the capacity of the engine-generator combination. This power is used for several functions of the crane, including: moving the crane by powering the motors and driving the trucks; rotating the upper works to which the boom is connected; picking up and lowering the load; and changing the height of the boom. 
         [0006]    A major fraction of the total power of both Navy and commercial cranes is used in moving the crane. Portal cranes travel on heavy gage rail track  37 ,  38  which is both tangent and curved in the shipyard. The track has a very wide gage  7  (12 ft to 44 ft and more) and has very sharp curves around the bay in the dock. Commercial cranes typically travel on straight or gently curved tracks. The peak power required to move the cranes depends on the sharpness of the curve. Even on tangent track, portal cranes use much more power with considerable noise and vibration than they need to. 
         [0007]    Typical portal cranes have a large number of two wheel trucks, which operate on sharp curves. This requires some trucks to move laterally by several feet when they are on the curves. This also involves a sharp change of rolling direction of the wheels which are operating on curves. Each truck is free to rotate about its vertical axis, but the rolling direction of the truck wheels is not aligned perfectly when entering a curving rail. As illustrated in  FIG. 2 , the rolling direction  8  of the wheel  17  is different from the direction  9  of the curved rail  18 . The angle  19  between them defines the lateral angle of slip or creep between the wheel  17  and the rail  18 . The wheel  17  must slip laterally by a certain distance every moment in order to stay on the rail  18 . This slip is given by the distance  20 . 
         [0008]    The greater the angle  19 , the larger is the slip  20  and a corresponding lateral friction force, generally designated in  FIG. 3  at  21 . Hence, sharp turns result in the greatest lateral friction force. This lateral friction force  21  is opposed by an equal and opposite force  22  with which one flange  23  of the wheel  17  presses against the rail  18 . It is generally not understood that an angle  19  as small as half a degree can produce lateral forces per wheel of several thousand pounds. 
         [0009]    This force causes significant rail and wheel flange wear and can cause the flange  23  to break in extreme cases. In addition to creating an unsafe condition, replacing a wheel on one of these cranes is an expensive process. In other cases the flange  23  can climb on the rail  18 , resulting in a derailment. Another problem associated with this process is the production of very high levels of noise, which compromises the safety of the workers underneath the crane because of their inability to talk to each other while the crane is moving. Other problems include excessive vibration and shock to both the electrical and mechanical drive trains and to the whole crane. 
         [0010]    Yet another problem is that a major part of the energy of the power plant of the crane is used up in overcoming the wheel-rail contact friction in the lateral direction. At times, such a large part of the generator current is used to overcome this friction, that only one operating function of the crane can be performed at a time, otherwise the electrical system trips and blowouts can occur. For example, crane movement cannot occur simultaneously with the rotation of the upper works  10  or lifting of the load, so the capability of rotating the upper works while traveling around the curve (preferred by the operators) is compromised. Similarly, if the current draw by the truck motors is excessive, the electrical system trips and work is halted until it is fixed. This can happen in the middle of a load lift, leaving the load hanging in the air. Hence, any breakdown of the crane significantly reduces productivity and safety and should be avoided. 
         [0011]    The above problems are only aggravated by the tendency of the wheels to stick as they slip along the rail which, when combined with the associated large lateral friction, causes the whole crane to vibrate and move jerkily. Nothing can be done about the distances slipped because they are defined by the geometry of the wheel and the rail. Therefore, the only way to reduce the detrimental wastage of crane energy is to reduce the friction force  21  between the wheels  17  and the rail  18 . 
         [0012]    Accordingly, a general object and aspect of the present invention is to provide a system whereby the above friction-related problems of prior art traveling cranes are substantially reduced or eliminated. 
         [0013]    Other aspects, objects and advantages of the present invention, including the various features used in various combinations, will be understood from the following description according to preferred embodiments of the present invention, taken in conjunction with the drawings in which certain specific features are shown. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention is designed to solve the above-described problems with traveling cranes that cause them to not perform optimally with respect to: (1) maximum productivity capacity, (2) maximum safety, (3) smooth uninterrupted operation with simultaneous multifunctional ability, and (4) wheel flange/rail wear and durability. The present invention reduces or eliminates the above problems by reducing the root cause of these problems, which is the development of excessive lateral friction between the crane wheel and the rails, by use of an automatic, computer-controlled friction modifier applicator system. 
         [0015]    According to one aspect of the present invention, a friction modifier applicator system for use with a traveling crane has a nozzle mounted on a truck. The nozzle is oriented to spray a friction modifier on the tread and opposing flanges of a wheel and/or on the rail. The friction modifier is supplied to the nozzle by a hose, while a valve controls the release of the friction modifier from the nozzle. A sensor measures a performance value of the truck, which performance value is used by a controller to actuate the valve. 
         [0016]    According to another aspect of the present invention, a friction modifier applicator system for use with a traveling crane has a nozzle mounted on a truck. The nozzle is oriented to spray a friction modifier on a wheel and/or the rail. The friction modifier is supplied to the nozzle by a hose, while a valve controls the release of the friction modifier from the nozzle. A sensor measures current draw of the truck and a controller actuates the valve according to the current draw. 
         [0017]    According to yet another aspect of the present invention, a friction modifier applicator system for use with a traveling crane having four corners includes a nozzle mounted on each corner truck. The nozzles are oriented to spray a friction modifier on the tread and opposing flanges of a wheel of the associated truck. The friction modifier is supplied to the nozzles by hoses, while each nozzle includes a valve that controls the release of the friction modifier. A sensor associated with each truck measures current draw of the truck and a controller uses the average current draw of each truck to actuate the valve associated with that truck. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1A  is a side elevation view of a typical portal crane, showing the essential components. 
           [0019]      FIG. 1B  is an end elevation view of a typical portal crane. 
           [0020]      FIG. 2  is a perspective view of a two-flanged crane wheel on a sharp curved rail, showing the angle of attack. 
           [0021]      FIG. 3  is an end view of a single, double-flanged crane wheel on a curved rail, showing the lateral creep force  21  which produces a large force  22  on the wheel flange. 
           [0022]      FIG. 4  is a perspective view of a friction modifier V-jet spray being applied to the crane wheel on a curved rail. 
           [0023]      FIG. 5  is a side elevation view of the crane lower structure and trucks, with fluid tanks and nozzles of an automatic wheel-rail friction modifier applicator system mounted on corner trucks. 
           [0024]      FIG. 6  is an enlarged, detail view of one corner of the crane, showing a corner truck with a tank and two nozzle placements. 
           [0025]      FIG. 7  is a side elevation view of the lower crane structure, illustrating an alternate embodiment using a central pressurized fluid tank delivering fluid to nozzles on each corner truck. 
           [0026]      FIG. 8  is a diagrammatic side view of a tank with two parts, one carrying the fluid and the other the pumping system. 
           [0027]      FIG. 9  is a side elevation view of a controller box showing the computer, relays and safety locks and related equipment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    This invention is a friction management system for improving productivity, safety and operation of traveling cranes, in particular portal cranes, by applying a liquid or solid friction modifier (FM) in precisely controlled quantities to the wheel tread and flanges of one or more wheels of the lead trucks. This reduces the lateral forces, high current draw trips, and high noise levels and improves productivity through increased capacity for number of lifts with the crane. 
         [0029]      FIG. 4  shows a crane wheel  17  on a curved rail  18 . A friction modifier applicator system, generally designated at  24 , includes a solenoid-controlled valve (not shown) and a V-jet nozzle  25 . The nozzle  25  is placed at an appropriate distance such that that the spray  26  covers the wheel tread  27  and the two flanges  23 . The flat V-shaped spray  26  is applied intermittently by computer control for a specified duration. The FM applied to the wheel  17  transfers to the rail  18  in the region of wheel-rail contact and is then transferred to the tread and flanges of the following wheels. Thus, the contact friction of all wheels with the rail  37 ,  38  at the curved portion  18  is reduced, resulting in the dramatic reduction of both forces  21 ,  22  and of the total energy consumed by the wheels and the crane during movement. While FM application to the wheels is the preferred way to accomplish this task, partial benefits can be obtained by using the present invention to direct the FM application jet on the rail head instead of, or in addition to, the wheels. 
         [0030]    Smooth flowing friction modifier fluid is preferred over solid or slurry because the application rate can be controlled accurately and also because this smooth fluid covers and penetrates the rough surfaces more completely. At least one set of nozzles/applicator is installed on the lead wheel of the lead trucks for FM application to the wheel tread and the two flanges. The pressurized fluid FM is preferably provided to the nozzles  25  equipped with solenoid-controlled valves. Pressure may be developed by a pump, pressurized tank or other means. The FM application is preferably in the form of a V-jet aimed in such a way that the whole tread  27  and both flanges  23  of the wheel  17  are coated by the spray  26 . Other jet types and multiple jets may also be used, although they are not preferred. 
         [0031]    The rate of application of FM may be controlled by changing the duration of the valve opening in each second. For the efficient use of FM, the nozzles  25  may be installed on the lead and trailing trucks. However, nozzles may be installed on each truck without departing from the scope of the present invention. To reduce FM wastage, the trailing truck nozzles may be shut off during forward movement of the crane by using current sensors on truck motor current wires to determine the direction of movement of the crane. The duration of valve opening, which controls the FM application rate, may be increased or decreased as the current draw changes. Fluid tanks, either equipped with pumps or pressurized, may be located above the lead and trailing trucks, as illustrated in  FIGS. 5 and 6 , or at the upper level inside the crane body, as illustrated in  FIG. 7 . 
         [0032]    The application rate control can be achieved in several discrete steps, according to an example described herein, or as a continuous function. By this method, just enough FM is applied for the above benefits to the crane without any loss of traction. 
         [0033]      FIG. 5  shows a side view of the lower crane structure including the trucks supporting the crane. It also shows a preferred placement of the various components of the friction modifier applicator system. The illustrated lead and trailing trucks, generally designated at  32   a  and  32   b  respectively, are equipped with solenoid valve nozzles  33 ,  34 ,  35 ,  36 , which are supplied with the pressurized friction modifier from tanks or containers  31 .  FIG. 5  illustrates two corners of the crane and two corner trucks  32   a ,  32   b , but it will be appreciated that the crane has four corners and is supported by a corner truck at each corner. Preferably, each corner truck is configured according to the following description. 
         [0034]    As illustrated in  FIGS. 5 and 6 , each corner truck preferably includes a pair of nozzles for spraying both wheels of the truck. Hydraulic lines/hoses  30  connect the tanks  31  with the friction modifier to the solenoid valve nozzles  33 ,  34 ,  35 ,  36 . The opening and closing of the solenoid valves is preferably controlled by a controller  39  through electrical lines  29  located in the chamber  28 . A junction box  29   a  may be used in the lines for convenient connection. As noted by the legend in  FIG. 5 , electric lines  29  are indicated in the figure by a triangle and hydraulic lines are denominated by a small circle. 
         [0035]    The direction of motion of the crane is shown by an arrow  43 . For this motion, the nozzles  33 ,  34  of the lead truck  32   a  are activated to apply the friction modifier to the wheels. Preferably, each electrical line supplying power to a truck motor includes a sensor for measuring the current draw and direction of travel of the truck, which are used to determine the amount of FM applied by the nozzles, as described below. The nozzles  35 ,  36  of the trailing truck  32   b  do not operate during forward movement of the crane, i.e., movement in the direction of arrow  43 . The FM applied to the wheels by nozzles  33 ,  34  is then transferred to the rail  37 ,  38 . It then modifies the friction for all the wheels of the trailing trucks. Of course, if the crane is moved in the opposite direction, then truck  32   b  becomes the leading corner truck, in which case its nozzles  35 ,  36  are actuated by the controller  39  and the nozzles  33 ,  34  of the now-trailing corner truck  32   a  are preferably closed to conserve FM. 
         [0036]      FIG. 6  shows an enlarged, detail view of one corner truck  32   b  with preferred tank  31  and nozzle  35 ,  36  placements. Preferably, each of the four corner trucks is configured according to the embodiment of  FIG. 6 . The electrical line  29  connects the solenoid valve nozzles  35 ,  36 , through the connector box  29   a , with the controller  39  of  FIG. 5 . The nozzles  35 ,  36  preferably apply the FM to the wheels  17  of the truck  32   b , which is transferred to the rail  37 ,  38 . A part of the structure  2  of the crane through which the load is transmitted to the trucks is shown at the top of  FIG. 6 . 
         [0037]      FIG. 7  shows an alternative system arrangement using a central pressurized fluid tank instead of four separate smaller tanks  31  located above each corner truck as discussed earlier. One or two larger fluid tanks  41  are placed in the crane, preferably within the upper structure chamber  28 . The fluid tank  41  may be pressurized with compressed air  40  available from the diesel engine-powered compressor of the crane, generally located at the same level  28 . A pressure regulator  42  installed on the tank  41  regulates its pressure. In this arrangement both electrical  29  and hydraulic  30  lines are relatively long, compared to the embodiment of  FIGS. 5 and 6 , starting in the upper chamber  28  and terminating at the nozzles. The rest of the components and their placements are the same as shown in  FIGS. 5 and 6 . 
         [0038]      FIG. 8  is a diagrammatic view of one tank  31  design suitable for placement at each corner of the crane. This shape was found to be suitable for fitting and placing the tank  31  in the space cavity available above the corner trucks of existing cranes. This shape can be changed to fit other crane designs without departing from the scope of the present invention. Two basic chambers need to be present in all such tanks. One chamber  44  carries the FM and the other chamber  45  carries the pumping system. A sight gage  46  is useful for checking the FM level to know when the tank  31  needs filling. Structural support and securing the tank  31  in this design is achieved with slides  49 ,  50  and a tie down  51 , to reduce the vibration. A tank clean out cover  47  and a fill port  48  may be located on top. 
         [0039]      FIG. 9  shows one arrangement of the computer control components. The controller  39  can be provided with different arrangements to suit the requirements of the user. It preferably has several basic components, in addition to electrical power  58  to operate the controller  39  and the components. The first component is a computer  52  with the ability to accurately compute in real time the duration for which the nozzles should apply FM in each second. Preferably, a power supply  55  is included to provide the correct voltage to operate the computer  52  and other components. The controller  39  may also include motor protection modules  54  to protect the motors of the pumping systems. Other preferred components include a sensor interface  56  for the current sensors installed on the crane to measure the current draw by the truck motors, an electrical breaker  53 , and terminal blocks  57  for proper connections. 
         [0040]    The control logic of the invention is as follows. Portal cranes are moved through the dock area at a slow, steady speed typically between 2 and 3 miles per hour. The amount of current draw of the truck motors is directly dependent on the rolling friction of the crane wheels. However, the current draw generally shows fluctuations and oscillations, so it may be preferable to average the current draw. The average current draw of the truck motors is nearly steady and also directly dependent on the rolling friction of the crane wheels. For this reason, the average current draw is a good measure of the energy being consumed in wheel friction. As the amount of FM that needs to be applied to maintain low lateral friction of the wheels on curves is also directly related to the energy consumed in wheel friction, the rate of FM application may be expressed as a function of the average current draw, which can be a linear function or a power function. This will also depend on the characteristics of the FM. 
         [0041]    The control can also be done in steps. This is somewhat preferable when functionality of relationship is not fully established. One example of such a stepwise control function is shown below in Chart 1. 
         [0000]    
       
         
               
               
               
             
           
               
                 CHART 1 
               
               
                   
               
               
                   
                 Total Current Load 
                 Nozzle Open Duration 
               
               
                 Zone 
                 (A1 + A2) AMPS 
                 ms 
               
               
                   
               
             
             
               
                 0 
                  &lt;20 
                 0 (OFF) 
               
               
                 1 (A) 
                 20–40 
                 40 
               
               
                 2 (B) 
                 40–80 
                 80 
               
               
                 3 (C) 
                  80–120 
                 120 
               
               
                 4 (D) 
                 &gt;120 
                 160 
               
               
                   
               
             
          
         
       
     
         [0042]    Chart 1 shows five discrete zones of control in the first column. For each zone there is a corresponding range of total current load (second column), which in this case is the sum of electrical readings from two current sensors reading the current draw of the motors on the front half A 1  and another one for the trailing half A 2  of the motors. The third column shows the nozzle open duration in milliseconds which determines the rate of application of the FM every second. Thus, the amount of FM applied per second increases with the current load on the motors. In a preferred embodiment, the current sensors also determine the direction of movement of the crane and FM is only applied to the wheels of the foremost or leading trucks. In most cases, the operation of the crane will be in the first two zones ( 0  and  1 (A)) and only occasionally will the operation turn to Zone  2  (B). It will be appreciated that actuation of the nozzles may be carried out by a continuous function or a different stepwise function without departing from the scope of the present invention. 
         [0043]    The nozzles of each truck are preferably actuated independently of each other, such that the wheels or rail associated with each truck is treated according to its unique needs. Accordingly, the operation illustrated in Chart 1 is preferably carried out separately for each truck outfitted with a spray nozzle. When properly lubricated, the crane will operate with significantly reduced noise, typically a decrease in the range of 20 decibels, and high current trips will be substantially eliminated, without compromising the traction of the wheels. 
         [0044]    It will be understood that the embodiments of the present invention which have been described are illustrative of some of the applications of the principles of the present invention. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention, including those combinations of features that are individually disclosed or claimed herein. For these reasons, the scope of the invention is not limited to the above description but is as set forth in the following claims.