Abstract:
A variable rate covering system for open top vehicle containers includes a hydraulic actuating system for pivoting arms carrying a roll up cover wherein the fluid flow rates to the hydraulic cylinders are reduced during the initial and final phases of the stroke to reduce acceleration and impact forces on the arms, cover and components, and normal fluid flow rates are provided during central phase movement without significantly affecting overall cycle time. The hydraulic cylinders are provided with metering orifices that reduce fluid flow rates to and from the cylinder pressure chambers for predetermined portions of the stroke length, thereby cushioning the pivoting mechanism at the terminal positions.

Description:
FIELD OF THE INVENTION 
     The present invention relates to apparatus for covering open top vehicle containers, and, in particular, a hydraulically operated pivoting arm covering system having variable rate actuation. 
     BACKGROUND OF THE INVENTION 
     Governmental regulations require many open vehicle containers carrying particulate and waste cargos to limit spillage during transport. Various mechanical, electrical and hydraulic systems have been proposed for covering the load after filling, and uncovering the load at the discharge site. Hydraulic systems have become preferred for larger containers and vehicles carrying a variety of container sizes. 
     Typical hydraulic systems, as disclosed in U.S. Pat. Nos. 4,050,734 and 4,341,416 to Richard, and 4,981,317 to Acosta, employ a pair of pivoting arms that unroll a covering tarp over the container top in movement between an open and closed position. The arms are actuated by a hydraulic cylinders controlled by the operator at the side of the vehicle. For long bed containers or vehicles hauling containers of varying sizes, secondary sets of cylinder actuated extendable linkages are employed as shown representatively in U.S. Pat. Nos. 4,874,196 to Horvath; and Re. 36,135 and 6,237,985 to O&#39;Brian. 
     The hydraulic tarp systems are generally controlled by hydraulic control systems located at the front side of the container behind the vehicle cab. Using two-way valve controls for single actuator sets, or joystick controls for multiple actuator sets, the operator furls or unfurls the cover while maintaining visual contact with its deployment. To minimize deployment time, faster covering rates are preferred by the drivers and the trucking organization. Such speed, however, comes at substantial maintenance costs. The rapid acceleration from the rest condition stresses the cover, the spooling mechanism, and the pivoting arms, and can cause damage to components and misalignments in the system. The impact and sudden deceleration at the end of the cylinder stroke pose similar problems. While slow cylinder rates have been used, the excessive time penalty involved has not been accepted, and accordingly time considerations have prevailed over maintenance preferences. 
     In view of the foregoing, it would-be desirable to provide a container covering system that would reduce maintenance costs while providing acceptable deployment cycles. 
     Accordingly it is an object of the present invention to provide a roll-up cover assembly for truck containers that reduces maintenance costs. 
     Another object of the invention is to provide a hydraulic actuator system for truck container covering apparatus that reduces component damage at the ends of the actuator stroke. 
     A further object of the invention is to provide a hydraulic actuator for a truck container covering system having reduced initial and terminal actuator rates for reducing equipment damage without significantly reducing overall deployment time. 
     Yet another object of the invention is to provide a variable rate covering system for open top containers providing controlled extension and retraction rates form open and closed positions. 
     SUMMARY OF THE INVENTION 
     The foregoing objects are accomplished by a hydraulic actuating system for a pivoting arm container covering system wherein the fluid flow rates to the hydraulic cylinders are reduced during the initial and final phases of the stroke to reduce acceleration and impact forces on the covering system components, and normal fluid flow rates are provided during the central phase, whereby the overall cycle time is not significantly affected. Therein, the hydraulic cylinders are provided with metering orifices that reduce fluid flow rates to and from the cylinder pressure chambers for predetermined portions of the stroke length, thereby cushioning the pivoting mechanism at the terminal positions. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will become apparent upon reading the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematic drawing of a variable rate covering system in accordance with an embodiment of the invention; 
     FIG. 2 is a partial perspective view of a fixed arm covering system illustrating the cover in an intermediate position over an open top container; 
     FIG. 3 is a partial side view of the cover of FIG. 2 in the retracted position; 
     FIG. 4 is a view similar to FIG. 3 of the cover in the extended position; 
     FIG. 5 is a partial side view of an articulated arm cover system illustrating the cover in the retracted position; 
     FIG. 6 is a view similar to FIG. 5 illustrating the cover in an intermediate position; 
     FIG. 7 is a view similar to FIG. 5 illustrating the cover in the extended position; 
     FIG. 8 is a partially sectioned side view of a variable rate hydraulic cylinder for the cover systems; 
     FIG. 9 is an end view of the cylinder taken along line  9 — 9  of FIG. 8; 
     FIG. 10 is an end view of the cylinder taken along line  10 — 10  of FIG. 8; 
     FIG. 11 is a fragmentary partially sectioned cross sectional view of the hydraulic cylinder showing the piston in the retracted position; 
     FIG. 12 is a fragmentary partially sectioned cross sectional view of the hydraulic cylinder showing the piston in the extended position; 
     FIG. 13 is a fragmentary radial sectional view of the metering ring; and 
     FIG. 14 is a fragmentary axial sectional view taken along line  14 — 14  in FIG.  13 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings for the purpose of describing the preferred embodiment and not for limiting same, FIG. 1 schematically illustrates a variable rate covering system  10  for open top containers generally of the types shown in FIGS. 2 through 7. The system  10  includes a pair of variable rate hydraulic cylinders  12   a  and  12   b  attached at a base end  14  to brackets  16  carried on opposed sides of the container and attached at a head end  18  to base arms  20 , which pivot in response to cylinder extension and retraction to move a cover spool  22  between an unfurled open position  24  permitting loading and unloading of an open top container, and a furled closed position  26  enclosing the open top of the container to assist in retaining the container contents. 
     In the preferred embodiment, the cylinders  12   a  and  12   b  are connected in phased relationship from two-way valve  30  by fluid supply lines  32 ,  34 , and  36 . Supply line  32  is connected from valve  30  to extension port  40  on cylinder  12   a . Supply line  34  is connected between retraction port  42  on cylinder  12   a  and extension port  44  on the lower on cylinder  12   b . Supply line  36  is connected between retraction port  46  on cylinder  12   b  and valve  30 . Fluid is supplied from reservoir  48  by a hydraulic pump  50  operated by motor  52 . A relief valve  54  routes fluid to the reservoir  48  under excessive pressure conditions. The cylinders  12   a  and  12   b  are maintained in phase relationship by rephase bypass circuits  56 . As described in greater detail below, the cylinders are provided with a piston assembly having a first metering rings on opposite ends and a central seal assembly. 
     In response to valve  30  actuation, the cylinders provide a variable rate stoke comprising a reduced rate for a distance d e  between the left metering ring and the central seal assembly, a reduced rate for distance d r  between the central seal assembly and the right metering ring, and operational rate for remaining stroke distance d c . 
     The system as above described may be incorporated into various covering systems, including without limitation a fixed arm system of the type shown in FIGS. 2 through 4, or the articulated arm system shown in FIGS. 5 through 7. The system may also be used in covering systems employing other supplemental linkages, such as telescoping outer arms. The cylinders as described above have primary reference to use in conjunction with the lower base arms in such systems and will be hereinafter described with reference thereto. 
     Referring to FIGS. 2 through 4, a fixed arm covering system  110  is used to deploy a cover  112  over an open top container  114 . The cover  112  is mounted on a roll up spool  116  attached at the outer ends of pivoting arms  118  for movement between a retracted position shown in FIG. 3 wherein the cover  112  is furled, through an intermediate position shown in FIG. 2, to an extended position wherein the cover is unfurled and encloses the top end of the container  114 . Movement of the arms  118  is effected by hydraulic cylinders  120 , in accordance with the invention, and operator controlled by lever valve assembly  122  disposed at the front driver side of the container. During movement to and from the retracted position of FIG. 3, the cylinders operate at a reduced rate. During movement to and from the extended position of FIG. 4, the cylinders also operate at a reduced rate. During the intermediate stage shown in FIG. 2, the cylinders operate at a normal rate dependent on conventional operating conditions. 
     For the articulated cover system  200  shown in FIGS. 5 through 7, an arm assembly  202  is pivoted by base cylinders  204  to move a cover  205  over the open upper end of a vehicle mounted container  206 . The arm assembly  202  includes a base arm  210  operated by variable rate hydraulic cylinder  204  in accordance with the invention. An upper secondary arm  214  is attached at the upper end of base arm  210  and operated by secondary hydraulic cylinder  216 . Depending on preference, a multiple rate stroke may be provided by the cylinders  216 . The cover system  200  is moved by cojoint actuation from the cylinders  204  and  216  from the retracted position shown in FIG. 5 at a reduced rate, cojointly by cylinders  204  and  216  during an intermediate distance shown in FIG. 6, and to the extended position shown in FIG. 7 enclosing the top of the container. 
     Referring to FIGS. 8 through 10, the cylinder  12   a , by way of example, for the system described above comprises tube assembly  400  including a cylinder tube  402  carrying a sealed tail  404  having an end ring  406  for mounting on the vehicle at appropriate brackets. A piston assembly  410  including a piston rod  412  is slidably carried in the bore of the tube  402 . The piston rod  412  outwardly terminates with an apertured ring  414  for connection to the pivoting arm of the applicable cover system. The piston rod  412  of the tube assembly  400  is conventionally sealed by packing gland lot  416 . The piston assembly  410  includes a tail metering section  420 , a head metering section  422 , and a center sealing section  424 , axially separated by annular spacer sleeves  426 ,  428 , all of which are carried by the end portion of the piston rod  412  and operatively connected therewith by threaded fastener  429 . Radially extending extension fluid port  430  and retraction fluid port  432  are positioned along the tube  402 . A radially extending rephase port assembly  434  is positioned on the tube  402  intermediate the ports  430  and  432 . The piston sections  420 ,  422 , and  424  have a sliding fit with the inner bore of the tube  402 . The tail metering section  420  includes a circumferential groove carrying a metering ring  440 . The head metering section  422  includes a circumferential groove carrying a metering ring  442 . 
     Referring to FIGS. 11 and 12, the center sealing section  424  includes a zero leakage sealing assembly including an axially spaced series of circumferential grooves carrying a pair of axially spaced, zero leakage bearing rings  444 ,  446  and an intermediate low friction sealing ring  448 . The spacer sleeves  426  and  428  have a reduced diameter establishing annular fluid chambers between the adjacent piston sections. The spacer sleeves have a length for establishing the requisite distance between the adjacent fluid port and the adjacent metering rings for establishing the lengths of the reduced flow rate distances, d e  and d r  as shown in FIG.  1 . The extension fluid port  430  includes a radial passage partially obstructed by the bearing ring  444  in the retracted position. The retraction fluid port  432  includes a radial passage partially obstructed by the bearing ring  446  in the extended position as shown in FIG.  12 . 
     Referring to FIGS. 13 and 14, the metering ring  440  and metering ring  442  are provided with radial slots  460  in the axial end faces and are retained in outwardly opening circumferential grooves  462 . The metering rings have a larger diameter than the base of the groove  462  thereby establishing a flow path between opposed slots. By controlling number, width and depth of the slots, a controlled leakage is established past the metering rings in fluid path between the port and the respective pressure chamber. In a well know manner, the rephase port assembly vents on either side of the seal assembly to allow both pistons to reach a terminal aligned position at the end of each retraction cycle thereby maintaining synchronous aligned movement of the pivoting arms and even deployment of the container cover. 
     In operation, at the commencement of an extension cycle as conditioned by the two-way control valve  30 , the line  32  is pressurized. Initially the flow rate through the extension port is throttled by the bearing ring  444  to limit in a first instance the extension rate. After the extension port is fully open, the flow pressurizes the annular chambers between the piston sections. Flow to the extension pressure chamber is restricted by the metering ring  440  thereby in a second instance providing a second extension rate, which continues until the metering ring passes beyond the extension fluid port  430 . Thereafter, non-restricted flow is applied to the extension pressure chamber effecting a fill extension rate based on system conditions for a center part of the piston stroke. During the center extension stroke, non-restricted fluid flow exits through retraction fluid port  432 . When the head metering section is adjacent the retraction port, the metering ring  442  begins to throttle the exiting fluid flow, thus reducing the extension rate and slowing the pivoting of the arms. As the piston approaches the fully extended position, the retraction port is partially obstructed by the bearing ring  446 , further restricting the exit flow and consequently the terminal extension rate. At the end of the strokes, over pressure conditions resulting from continued valve opening are regulated by the relief valve,  54 , (FIG.  1 ). 
     For the retraction stroke, the reverse conditions apply. The metering ring  442  throttles extension to provide a reduced retraction rate until the metering rings pass the retraction port  432 , at which time a full retraction rate is provided, until the rear metering ring  440  passes the extension fluid port  430 , restricting the exit flow and reducing the retraction rate until the piston is seated at the end of the stroke. 
     Accordingly, it will be appreciated that variable rate cylinders provide reduced acceleration and deceleration conditions at the ends of the piston stroke to lessen loading and impact forces on the cover components at the terminal moments in the open and closed conditions, thereby reducing maintenance cost and extending the operating life of the system. Because of the cushioning features that allow safe seating and removal from the stop positions, a higher flow rate can be used during the center movement thereby increasing the pivoting speed of the arm assemblies and offsetting any increased times occasioned by the slower end rates. Further, the length of the space sleeves may be adjusted to provide ample slow rate motion to allow the operator to safely guide the cover to the stop positions. In many configurations, alignment at the front end of the container is more difficult, particularly in articulated arm designs where various truck and container surfaces must be avoided. Accordingly, it may be preferable to provide an increased slow rate zone during this portion of the traverse. At the rear end of the container, the stowing is more straightforward and a lesser cushioning zone may be sufficient. 
     Having thus described a presently preferred embodiment of the present invention, it will now be appreciated that the objects of the invention have been fully achieved, and it will be understood by those skilled in the art that many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the sprit and scope of the present invention. The disclosures and description herein are intended to be illustrative and are not in any sense limiting of the invention, which is defined solely in accordance with the following claims.