Patent Publication Number: US-2007098494-A1

Title: Hydraulic leveling selection circuit for a work machine

Description:
TECHNICAL FIELD  
      The present disclosure relates to a work machine for the treatment of roadway surfaces, and more particularly to a cold planer for roadway surfacing operations.  
     BACKGROUND  
      Road milling machines, also known as cold planers, may be configured to scarify, remove, mix, or reclaim material from the surface of bituminous, concrete, or asphalt roadways and other surfaces using a rotatable planing tool mounted on a frame. The frame may be mounted on a plurality of tracks/wheels which support and horizontally transport the machine along the working surface.  
      Typically, cold planers may also include a plurality of lifting members positioned near the front and rear of the frame. The lifting members may be adjusted between extended and retracted positions to control the depth and shape of cut by raising or lowering the frame and rotatable planing tool. Actuation of the lifting members may be controlled by a machine operator or other suitable control mechanism.  
      One example of a leveling system for a cold planer is described in U.S. Pat. No. 6,769,836 to Lloyd (“Lloyd”). Lloyd discloses an asphalt recycling machine. The machine includes front and rear axles that are raised and lowered by hydraulic cylinders. In order to stabilize the machine, the front axle&#39;s hydraulic cylinders are hydraulically connected in parallel. The rear axle&#39;s hydraulic cylinders are operated individually to control the height and tilt (slope) of the mainframe of the machine. Individual control of the rear axle&#39;s hydraulic cylinders, together with the front axle&#39;s hydraulic cylinders connected hydraulically, in parallel, form a three-point suspension, allowing the mainframe to ride over uneven surfaces. Also, stability is maintained as the rear wheels of the rear axle operate on a milled to grade surface.  
      The arrangement in Lloyd, wherein the front axle&#39;s hydraulic cylinders are connected while the rear axle&#39;s hydraulic cylinders are individually controlled, limits use of the machine to those job sites/situations in which such an arrangement is desired. For example, assigning individual control to the rear axle&#39;s hydraulic cylinders may be desirable in some instances because the rear axle&#39;s hydraulic cylinders run on the milled to grade surface and may be controlled and adjusted with better accuracy than the front axle&#39;s hydraulic cylinders that may run over uneven surfaces. However, assigning individual control to the front axle&#39;s hydraulic cylinders may be desirable in other situations, such as, for example, when milling/cutting irregularly shaped roadway surfaces or using high digging thicknesses that may cause high drum reaction that may create an upward force on the rear side of the machine. Because the machine in Lloyd only assigns individual control to the rear axle&#39;s hydraulic cylinders, it may not be used in jobs where assigning individual control on the front axle&#39;s hydraulic cylinders is desirable.  
      The disclosed system is directed towards overcoming one or more of the problems set forth above.  
     SUMMARY OF THE INVENTION  
      In one aspect, the present disclosure is directed to a support system for a work machine. The support system may include a front support assembly configured to perform one of stabilization and leveling control, a rear support assembly configured to perform the other of stabilization and leveling control, and a hydraulic circuit configured to selectively switch leveling control between the front and rear support assemblies.  
      In another aspect, the present disclosure is directed to a method of switching leveling control for a work machine. The method may include providing a front support assembly configured to perform one of stabilization and leveling control, providing a rear support assembly configured to perform the other of stabilization and leveling control, and selectively switching leveling control between the front and rear support assemblies.  
      In yet another aspect, the present disclosure may be directed to a work machine configured to perform work on a surface. The work machine may include a frame having a front portion and a rear portion. The work machine may also include a front support assembly including first and second hydraulic cylinders supporting the frame, with the front support assembly being configured to adjust the height of the front portion of the frame relative to the surface. The work machine may further include a rear support assembly including third and fourth hydraulic cylinders supporting the frame, with the rear support assembly being configured to adjust the height of the rear portion of the frame relative to the surface. Additionally, the work machine may include a first valve device operatively connected between the first and second hydraulic cylinders, and a second valve device operatively connected between the third and fourth hydraulic cylinders. When one of the first and second valves is in an open position, the other of the first and second valves is in a closed position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  provides a diagrammatic top view of a work machine according to an exemplary disclosed embodiment.  
       FIG. 2  provides a diagrammatic side view ofthe work machine of  FIG. 1 .  
       FIG. 3  provides a schematic view of a hydraulic system according to an exemplary disclosed embodiment.  
       FIG. 4  provides another schematic view of the hydraulic system of  FIG. 3 .  
       FIG. 5  provides a schematic view of a hydraulic system according to another exemplary disclosed embodiment.  
    
    
     DETAILED DESCRIPTIONS  
      Work machines may be configured to perform work operations at job sites. Examples of work machines may include on and off highway vehicles, construction equipment, and earth-moving equipment. One particular type of work machine is a road milling machine or cold planer  10 , as illustrated in  FIG. 1 . Cold planer  10  may be configured to scarify, remove, mix, or reclaim material from the surface of bituminous, concrete, or asphalt roadways and other surfaces. Elements of cold planer  10  may include a frame  12 , a tool  14 , and front and rear support assemblies  22   a  and  22   b.    
      Front and rear support assemblies  22   a  and  22   b  may be configured to support frame  12  on work surfaces. Front support assembly  22   a  may include right and left front support assemblies  23   a  and  23   b . Similarly, rear support assembly  22   b  may include right and left rear support assemblies  23   c  and  23   d . Furthermore, right front support assembly  23   a  may include a traction device  24   a  and a column  26   a . Traction devices  24   b - 24   d  and columns  26   b - 26   d  may be included in the remaining support assemblies.  
      Traction devices  24   a - 24   d  may perform the function of transporting the cold planer  10  across work surfaces. Traction devices  24   a - 24   d  may include tracks, wheels, and/or other known traction devices suitable for use on mobile work machines. At least one traction device may be powered by a drive assembly (not shown) for forward and rearward movement of cold planer  10 . An example of a drive assembly may include an internal combustion engine or a hydraulic motor. It is further contemplated that traction devices  24   a - 24   d  may be attached to frame  12  by columns  26   a - 26   d.    
      Columns  26   a - 26   d  may be selectively raised and lowered to cause upward, downward, and tilting movement of frame  12 . In one embodiment, columns  26   a - 26   d  may include solid unitary elements that may be driven towards and away from frame  12  of cold planer  10  to raise and lower frame  12  with respect to roadway surface  16 . In another embodiment, columns  26   a - 26   d  may include telescoping portions (not shown), such as, for example, overlapping cylindrical segments adapted to slide inward (retract) or outward (extend) with respect to each other. The inward and outward sliding of the overlapping cylindrical segments may raise and lower frame  12 , and their movement may be actuated by pressurized hydraulic fluid that may be selectively supplied by the machine operator (pilot) and/or by an automated control mechanism.  
      Frame  12  may include one or more structural load carrying members adapted to support and/or protect components of cold planer  10 . Elements of frame  12  may include, for example, housings, beams, and panels. Furthermore, tool  14  may be supported on or within frame  12 .  
      Tool  14 , shown in the side view depicted in  FIG. 2 , may include a rotatable planing tool, such as, for example, a rotatable drum  18  or cylinder. Drum  18  may include a plurality of replaceable bits (not shown) mounted thereon and may be lowered to engage a roadway surface  16 . Upon engagement, the bits may cut and remove material from roadway surface  16 . The removed material may enter conveyor  20  which may transfer the removed material into a dump truck (not shown) for transport off-site. The height of drum  18  relative to the roadway surface  16  may determine the shape and depth of cut made in the roadway surface  16  and may affect the amount of material being removed. Thus, in order to control the shape and depth of cut, drum  18  may be adjusted such that it may vertically move away from, towards, and into roadway surface  16 .  
      An exemplary disclosed embodiment of a hydraulic system  28 , configured to direct pressurized hydraulic fluid, is shown in  FIG. 3 . Hydraulic system  28  may cause movement of columns  26   a - 26   d  using the pressurized hydraulic fluid. Hydraulic system  28  may include a hydraulic circuit  30  for selectively supplying the pressurized hydraulic fluid to different areas of hydraulic system  28 , and hydraulic cylinders  32   a - 32   d  to convert the hydraulic pressure into mechanical motion for actuating columns  26   a - 26   d.    
      Hydraulic circuit  30  may include an assembly of components configured to regulate and control the flow of pressurized hydraulic fluid through hydraulic system  28 . In one embodiment, hydraulic circuit  30  may include a valve manifold  34 , cylinder valves  36   a - 36   d , and two-way valves  38   a  and  38   b . Exemplary sub-components of hydraulic circuit  30  will be discussed below, but it should be understood that hydraulic circuit  30  is not limited to these specific configurations.  
      Valve manifold  34  may be configured to selectively direct pressurized hydraulic fluid from apertures  40   a - 40   f  into the other parts of hydraulic circuit  30 . Valve manifold  34  may include flow conduits  42   a - 42   h , selector valves  44   a - 44   c , a low pressure line  48 , and a two-way valve  50 . It should be understood that valve manifold  34  may include less, more, or different elements from those specified, and the structure of valve manifold  34  may depend on a host of factors, including, for example, the environment of the job site. Also, it should be understood that valve manifold  34  may be replaced by a plurality of valves, such as selector valves  44   a - 44   c , that may be electrically actuated to perform substantially similar functions as those performed by valve manifold  34 .  
      Each of apertures  40   a - 40   f  may be configured to permit pressurized hydraulic fluid to enter into and exit from valve manifold  34 . Flow conduits  42   c  and  42   d , operatively associated with right front support assembly  23   a , may be selectively placed into fluid communication with apertures  40   c - 40   f . Flow conduits  42   a  and  42   b , operatively associated with left front support assembly  23   b , may be selectively placed into fluid communication with apertures  40   a  and  40   b . Flow conduits  42   f  and  42   e , operatively associated with right rear support assembly  23   c , may be selectively placed into fluid communication with apertures  40   e  and  40   f . Flow conduits  42   g  and  42   h , operatively associated with left rear support assembly  23   d , may be selectively placed in fluid communication with apertures  40   c  and  40   d  or  40   a  and  40   b . Flow conduits  42   a ,  42   c ,  42   e , and  42   g  may carry input flow from a fluid source (not shown) into support assemblies  22   a  and  22   b  if colder planer  10  is to be raised, and/or they may carry output flow from support assemblies  22   a  and  22   b  to a tank (not shown) if cold planer  10  is to be lowered. Additionally, input flows from the fluid source (not shown) may pass through flow conduits  42   b ,  42   d ,  42   f , and  42   h , thus allowing these flow conduits to function as pilot lines to actuate cylinder valves  36   a - 36   d.    
      Fluid communication between apertures  40   a - 40   f  and flow conduits  42   a - 42   h  may be determined by selector valves  44   a - 44   c . Selector valves  44   a - 44   c  may each be configured to shift between a first position ( FIG. 3 ) and a second position ( FIG. 4 ). In the first position, selector valve  44   a  may direct the fluid flow from apertures  40   a  and  40   b  towards flow conduits  42   a  and  42   b . In the second position, selector valve  44   a  may direct the fluid flow from apertures  40   a  and  40   b  towards flow conduits  42   g  and  42   h . Similarly, selector valves  44   b  and  44   c  may also selectively direct the fluid flow. Each of selector valves  44   a - 44   c  may be biased by a spring  46   a - 46   c  towards the first position. Actuation of selector valves  44   a - 44   c  against the spring bias from the first position to the second position may be initiated by pressurized hydraulic fluid from low pressure line  48 . Additionally or alternatively, it is also contemplated that selector valves  44   a - 44   c  may be actuated manually or by solenoid actuation upon recognition of an electrical signal.  
      Low pressure line  48  may direct a low pressure hydraulic fluid flow into valve manifold  34  of hydraulic circuit  30  from a tank and pump assembly (not shown). When low pressure line  48  and selector valves  44   a - 44   c  are placed into fluid communication, the low pressure hydraulic fluid flow may physically push each of selector valves  44   a - 44   c  into second position. Fluid communication between low pressure line  48  and selector valves  44   a - 44   c  may occur upon actuation of two-way valve  50 , which may include, for example, a solenoid valve or a two-way pilot valve.  
      Cylinder valves  36   a - 36   d  may be operatively connected to flow conduits  42   a - 42   h  of valve manifold  34 , and may control the fluid flow entering hydraulic cylinders  32   a - 32   d . In one embodiment, cylinder valves  36   a - 36   d  may include counterbalance valves, each counterbalance valve having at least a check valve  52   a - 52   d  and a spring-biased pressure relief valve  54   a - 54   d . Check valves  52   a - 52   d  and pressure relief valves  54   a - 54   d  may be configured to selectively prevent flow, restrict flow, and allow flow to enter into and exit from hydraulic cylinders  32   a - 32   d . Thus, check valves  52   a - 52   d  and pressure relief valves  54   a - 54   d  may be configured to provide braking to hydraulic cylinders  32   a - 32   d  to slow down and/or smooth out their movements. It is also contemplated that cylinder valves  36   a - 36   d  may include double acting counterbalance valves for embodiments that may include double-acting, rather than single-acting, hydraulic cylinders.  
      Hydraulic cylinders  32   a - 32   d  may each include a housing  56   a - 56   d  and a piston  58   a - 58   d  slidably mounted therein. Each of housings  32   a - 32   d  may include a hollow bored interior, and each piston  58   a - 58   d  may include a piston plug  60   a - 60   d  configured to fit closely within the bore and a piston shaft  62   a - 62   d  operatively connected to plugs  60   a - 60   d  and columns  26   a - 26   d . Pistons  58   a - 58   d  may divide their respective cylinder housings  56   a - 56   d  into upper chambers  64   a - 64   d  and lower chambers  66   a - 66   d . Upper chambers  64   a - 64   d  may include outlets  69   a - 69   d  that may direct the pressurized hydraulic fluid out of upper chambers  64   a - 64   d  and into a tank (not shown) or the atmosphere. Lower chambers  66   a - 66   d  may include apertures  68   a - 68   d  to allow the pressurized hydraulic fluid passing through cylinder valves  36   a - 36   d  to enter lower chambers  66   a - 66   d  when extension of hydraulic cylinders  32   a - 32   d  may be desired, and also to allow the pressurized hydraulic fluid within lower chambers  66   a - 66   d  to escape back towards cylinder valves  36   a - 36   d  when retraction of hydraulic cylinders  32   a - 32   d  may be desired. It should be understood that extension and retraction of hydraulic cylinders  32   a - 32   d  may directly result in the raising and lowering of columns  26   a - 26   d.    
      The operation of hydraulic cylinder  32   a  will now be described in more detail. In the state shown in  FIG. 3 , if extension of hydraulic cylinder  32   a  may be desired, pressurized hydraulic fluid supplied from a fluid supply (not shown) may enter flow conduit  42   c  from aperture  40   f . As the pressurized hydraulic fluid travels through flow conduit  42 , it may pass through check valve  52   a , which may create a force on pressure relief valve  54   a  that may drive pressure relief valve  54   a  towards the open position (towards the left) allowing flow to travel through flow conduit  42   c  into aperture  68   a  of lower chamber  66   a  of hydraulic cylinder  32   a . As the pressurized hydraulic fluid builds within lower chamber  66   a , piston  58   a  may be driven upwards to an extended position. Any pressurized hydraulic fluid in upper chamber  64   a  may be forced out through outlet  69   a  by upward motion of piston  58   a . If retraction of hydraulic cylinder  32   a  may be desired, the flow of pressurized hydraulic fluid entering flow conduit  42   c  from aperture  40   f  may cease. Pressurized hydraulic fluid may be supplied from a source (not shown) through inlet  40   e  into flow conduit  42   d , wherein flow conduit  42   d  may act as a pilot line by driving pressure relief valve  54   a  towards the open position (left) allowing pressurized hydraulic fluid within lower chamber  66   a  to exit out through flow conduit  42   c  and aperture  40   f  as the force of gravity on cold planer  10  drives piston  58   a  in a downward direction. Additionally or alternatively, hydraulic cylinder  32  may include a double-acting hydraulic cylinder that may retract and extend in ways known to those skilled in the art. While only the operation of hydraulic cylinder  32   a  has been described in detail, it should be understood that hydraulic cylinders  32   b - 32   d  may be operated in a similar manner.  
      Cylinder valves  36   a  and  36   b  may be selectively placed into fluid communication by two-way valve  38   a , and a similar relationship may exist between cylinder valves  36   c  and  36   d  and two-way valve  38   b . In  FIG. 3 , two-way valve  38   a  is shown in a closed state while two-way valve  38   b  is shown in an open state. In this condition of hydraulic circuit  30 , hydraulic cylinders  32   a  and  32   b  may be individually controlled, while hydraulic cylinders  32   c  and  32   d  may move in unison. In  FIG. 4 , two-way valve  38   a  is shown in an open state, while two-way valve  38   b  is shown in a closed state. In this condition of hydraulic circuit  30 , hydraulic cylinders  32   a  and  32   b  may move unitarily, while hydraulic cylinders  32   c  and  32   d  may move independent of one another. In one embodiment, two-way valves  38   a  and  38   b  may include solenoid valves that may be actuated to move into open and closed positions, wherein if one valve is in open position the other will be in closed position. Additionally, two-way valves  38   a  and  38   b , and any other of the valves described above, may include manually adjustable valves.  
      As shown in  FIG. 5 , it is further contemplated that one or more of the previously described valve devices may be replaced by an electronic controller  70 . Controller may  70  include hardware and software elements adapted to selectively direct the desired amount of flow to hydraulic cylinders  32   a - 32   d  to simulate the function of one or more of the replaced valve devices. In one embodiment, controller  70  may control valve assemblies  72   a - 72   d . Valve assemblies  72   a - 72   d  may include, for example, independent metering valve (“IMV”) assemblies. Each IMV assembly may receive pressurized hydraulic fluid from a hydraulic pump (not shown) and may be in fluid communication with at least one of hydraulic cylinders  32   a - 32   d . An IMV assembly may typically include four independently controllable valves, with one pair of the valves being coupled with a head end (upper chamber) of a hydraulic cylinder and the other pair of controllable valves being coupled with a rod end (lower chamber) of that hydraulic cylinder. Each pair of controllable valves in the IMV assembly may allow flow both to and from its corresponding hydraulic cylinder. The controllable valves may be electronically controlled using controller  70 , depending upon various input signals received from one or more sensors  74   a - 74   d.    
      In operation, controller  70  may monitor position sensors  74   a  and  74   b  associated with hydraulic cylinders  32   a  and  32   b , and using readings from position sensors  74   a  and  74   b  as a reference, the controller may supply equal amounts of flow to hydraulic cylinders  32   a  and  32   b  to simulate the opening of two-way valve  38   a . By simulating the opening of two-way valve  38   a , the controller may assign leveling control to hydraulic cylinders  32   c  and  32   d . Similarly, the controller may simulate the opening of two-way valve  38   b  by supplying equal amounts of flow to hydraulic cylinders  32   c  and  32   d . By simulating the opening of two-way valve  38   b , the controller may assign leveling control to hydraulic cylinders  32   a  and  32   b.    
     INDUSTRIAL APPLICABILITY  
      The disclosed hydraulic system  28  may be used to provide leveling control for work machines. An exemplary disclosed work machine may include, for example, a cold planer  10 .  
      Hydraulic system  28  may provide the benefit of allowing a machine operator to switch leveling control from a front support assembly  22   a  to a rear support assembly  22   b , and vice versa. Front and rear support assemblies  22   a  and  22   b  may include columns  26   a - 26   d  that may be raised and lowered by their respective hydraulic cylinders  32   a - 32   d . In one embodiment, columns  26   a  and  26   b  may act as front columns, and columns  26   c  and  26   d  may act as rear columns. In a front leveling control state shown in  FIG. 3 , each of two-way valves  38   a  and  38   b , two-way valve  50 , and selector valves  44   a - 44   c  may be in a first position. In this first position, selector valves  44   a - 44   c  may direct the fluid flow from apertures  40   a  and  40   b  towards hydraulic cylinder  32   b , and may also direct the fluid flow from apertures  40   e  and  40   f  towards hydraulic cylinder  32   a . Additionally, two-way valve  38   a  may prevent fluid communication between flow conduits  42   a  and  42   c . Thus, front columns  26   a  and  26   b  may be independently driven by fluid flow from apertures  40   e  and  40   f , and  40   a  and  40   b , respectively.  
      Also in the first position, selector valve  44   c  may direct the fluid flow from apertures  40   c  and  40   d  towards hydraulic cylinder  32   d . In addition, two-way valve  38   b  may permit fluid communication between flow conduits  42   g  and  42   e , and thus, hydraulic cylinder  32   c  associated with rear column  26   c  may be driven by the same fluid flow driving rear column  26   d . Accordingly, rear columns  26   c  and  26   d  may move together unitarily or in unison.  
      Independently operated front columns  26   a  and  26   b  may perform leveling by being extended and retracted to control the depth and shape of cut. When equal fluid flow drives both of front columns  26   a  and  26   b , then the front end of frame  12  may raise or lower accordingly. On the other hand, when greater fluid flow drives one of front columns  26   a  and  26   b , then the front end of frame  12  may tilt and/or raise or lower accordingly. At the rear end of frame  12 , operatively connected/linked rear columns  26   c  and  26   d  may provide for a three point machine configuration, with front telescoping columns  26   a  and  26   b  being two points, and rear telescoping columns  26   c  and  26   d  acting together as a third point. The three point machine configuration may provide cold planer  10  with the stability associated with using triangularly arranged support points, may provide both lifting, lowering, and tilting of frame  12 , and may reduce stress in frame  12  as it passes over uneven roadway surface  16 .  
      Switching leveling control from front columns  26   a  and  26   b  to rear columns  26   c  and  26   d  may be accomplished by signaling or actuating each of two-way valves  38   a  and  38   b , into a rear leveling control state corresponding to  FIG. 4 . In this position, two-way valve  50  may allow low pressure fluid to flow through low pressure line  48  to actuate selector valves  44   a - 44   c  into a second position. In this second position, selector valves  44   a - 44   c  may direct the fluid flow from inlet ports  40   a  and  40   b , and  40   e  and  40   f , towards hydraulic cylinders  32   c  and  32   d , respectively. Two-way valve  38   b  may block or prevent fluid communication between fluid conduits  42   e  and  42   g , thus allowing rear columns  26   c  and  26   d  to move independently of one another. Selector valve  44   c  may direct the fluid flow from apertures  40   c  and  40   d  towards hydraulic cylinder  32   a  associated with front column  26   a . Two-way valve  38   a  may permit fluid communication between fluid conduits  42   a  and  42   c , thus linking the fluid flows driving columns  26   a  and  26   b . Accordingly, independently operated rear columns  26   c  and  26   d  may perform leveling, while operatively connected/linked front columns  26   a  and  26   b  may provide for the stable three point machine configuration.  
      The ability to switch leveling control between front and rear support assemblies  22   a  and  22   b , may be advantageous for several reasons. For example, setting leveling control on rear columns  26   c  and  26   d  of rear support assembly  22   b  may allow for a more precise cut in certain situations because traction devices  24   c  and  24   d  associated with rear columns  26   c  and  26   d  may run on a relatively flat (milled) roadway surface  16 . Also, when cold planer  10  mills a small road thickness at high velocity, rear columns  26   c  and  26   d  and/or traction devices  24   c  and  24   d  may be less affected by roadway surface  16  unevenness than front columns  26   a  and  26   b  and/or traction devices  24   a  and  24   b . However, giving leveling control to front columns  26   a  and  26   b  of front support assembly  22   a  may be desirable in other situations. Examples of such situations may include, milling/cutting irregularly shaped roadway surfaces  16 , or using high digging thicknesses that may cause high drum reaction that may create an upward force on the rear side of cold planer  10 . This force may cause leveling control on rear columns  26   c  and  26   d  to become imprecise and/or ineffective. For at least these reasons, the ability to switch leveling control between front support assembly  22   a  and rear support assembly  22   b  may be advantageous, by allowing the machine operator/controller to selectively determine where to assign leveling control based on roadway surface  16  conditions. The result may be an improvement in the flexibility of cold planer  10  because it may be used successfully in a wider variety of situations and job sites.  
      It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed protection system without departing from the scope of the disclosure. Additionally, other embodiments of the disclosed system will be apparent to those skilled in the art from consideration of the specification. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.