Patent Abstract:
A ground engaging work vehicle including a frame, a plurality of tractive elements, a movable extension, a hydraulic fluid using attachment, a hydraulic fluid pump and an accumulator. The plurality of tractive elements are coupled to the frame. The tractive elements engage the ground. The movable extension is connected to the frame. The hydraulic fluid using attachment is coupled to the movable extension. The hydraulic fluid pump is selectively fluidly coupled to the attachment. The accumulator is selectively fluidly coupled to the attachment dependent upon at least one fluid flow requirement of the attachment.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates to vehicles powered by engines, and more particularly to vehicles such as work machines having hydraulic fluid using attachments connected to the vehicle. 
     BACKGROUND OF THE INVENTION 
     The processing of tree trunks, also known as stems involve a harvester head for the delimbing and cutting of a tree. Often the head is utilized to grip an upright tree, cut the tree, after which the tree trunk is delimbed and cut into pieces of a fixed length by way of a sawing device. A harvester head with a feed roller is illustrated in U.S. Patent Publication No. US2007/0125447. A harvester head is particularly connected to the end of a working boom of a work machine. The harvester head includes delimbing portions having blades to delimb the stem as the stem is pulled through the harvester head. The feed rolls press against the trunk and pull the stem therethrough. 
     The vehicle may be a wheeled or tracked vehicle. The harvester vehicle includes an engine for providing power to the operating systems of the vehicle including the electrical and hydraulic systems thereof. 
     What is needed in the art is an efficient way of increasing torque to the motors of the harvester head. 
     SUMMARY OF THE INVENTION 
     The invention one form is directed to a ground engaging work vehicle including a frame, a plurality of tractive elements, a movable extension, a hydraulic fluid using attachment, a hydraulic fluid pump and an accumulator. The plurality of tractive elements are coupled to the frame. The tractive elements engage the ground. The movable extension is connected to the frame. The hydraulic fluid using attachment is coupled to the movable extension. The hydraulic fluid pump is selectively fluidly coupled to the attachment. The accumulator is selectively fluidly coupled to the attachment dependent upon at least one fluid flow requirement of the attachment. 
     The invention in another form is directed to a hydraulic system associated with a ground engaging work vehicle. The system includes a hydraulically driven attachment, a hydraulic fluid pump, and an accumulator. The hydraulic fluid pump is selectively fluidly coupled to the attachment. The accumulator is selectively fluidly coupled to the attachment dependent upon at least one fluid flow requirement of the attachment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustrative vehicle utilizing an embodiment of a hydraulic system of the present invention; 
         FIG. 2  is a schematical block diagram illustrating the hydraulic system of  FIG. 1 ; 
         FIG. 3  is a chart illustrating some of the advantages of the present invention of  FIGS. 1 and 2 ; and 
         FIG. 4  is another chart illustrating further advantages of the invention depicted in  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , there is shown a work vehicle  10  including wheels  12 , a frame  14 , an articulated arm  16 , a cab  18  containing controls  20 , an engine  22  and a hydraulic system  24  driven by engine  22 . Work vehicle  10  may be in the form of a harvester for use in a forest environment. Work vehicle  10  is driven by wheels  12  that are coupled to frame  14 . Wheels  12  are also known as tractive elements  12 , which are depicted here as wheels, yet it is understood that other tractive devices such as tracks may also be used. Articulated arm  16  also known as a movable extension of work vehicle  10  is connected in a movable fashion with frame  14 . 
     An operator sits in cab  18  having access to controls  20  to direct the power of engine  22  and the application of hydraulic fluid from hydraulic system  24 . Attachment  26 , which is also known as a harvester head  26 , is connected to an end of articulated arm  16  and is disposed in a controllable manner about a tree trunk, also known as a tree stem, for the harvesting and processing of a tree. 
     Now, additionally referring to  FIG. 2  there is illustrated, in a schematic form, elements of work vehicle  10 , more specifically hydraulic system  24  and attachment  26 . Hydraulic system  24  includes a hydraulic pump  28 , an accumulator  30 , valves  32 , a controller  34 , a sensor  36  and a sensor  38 . Attachment  26  also known as a harvester head  26  or tree processor  26  includes feed wheels  40 , grab arms  42 , a saw  44  and a measuring device  46 . 
     An operator provides instructions by way of operator controls  20  from cab  18  which are interpreted by controller  34 , which is herein illustrated as a separate stand alone controller, however functions thereof may be included in another controller, typically found on a work vehicle  10 , such as an electronic control unit or even as standalone circuitry. The elements of controller  34  may be carried out by a combination of firmware, software and hardware. Hydraulic pump  28  is hydraulically coupled to valves  32 , which provide a distribution of hydraulic fluid to feed wheels  40 , grab arms  42  and saw  44 . While only a single line is illustrated in  FIG. 2  proceeding from valves  32  to feed wheels  40 , grab arms  42  and saw  44 , it is recognized that more than one hydraulic line may run to each to control different aspects of those items and to provide return flow of the hydraulic fluid. For example, feed wheels  40  may be movable by a hydraulic cylinder, also known as a hydraulic actuator and feed wheels  40  may be rotated with a hydraulic motor for the driving of feed wheels. In a similar fashion saw  44  can have one hydraulic line to provide fluid to the hydraulic motor powering saw  44  as well as fluid to a hydraulic actuator that moves saw  44  so that it engages the stem of the tree to cut the stem at a selected point. 
     In a preferred embodiment of the present invention controller  34  receives a signal from operator controls  20  to initiate an action with at least one part of attachment  26 , such as feed wheels  40 . Controller  34  sends a signal to valves  32  to cause hydraulic flow to be initiated to feed wheels  40 . The hydraulic flow will cause a hydraulic motor that drives feed wheels  40  to rotate thereby moving the stem of a tree through harvester head  26 . To move the stem there is a need for sufficient energy to overcome the inertia of the tree, the drag of limbs on the ground as well as limbs encountering delimbing blades. Controller  34  directs the flow of hydraulic fluid to feed wheels  40  from hydraulic pump  28  and accumulator  30  in a coordinated manner. The fluid flow can be substantially simultaneously supplied from these two sources, or the flow from one of the sources can be delayed relative to the other, as directed by controller  34 . The fluid flow requirement to move wheels  40  can be assumed to be greatest when movement is initiated. Additionally, since measuring device  46  provides positional information and controller  34  would include timing information, the movement of the stem of the tree can be monitored and controller  34  can selectively couple accumulator  30  to the motors of wheels  40  if the stem slows below a predicted or predetermined speed. 
     Since accumulator  30  stores pressurized fluid the flow from accumulator  30  will dissipate over time as it flows to an element of harvester head  26 , and the valve associated with the flow therefrom can then be closed. When fluid flow from hydraulic pump  28  is not being directed elsewhere, controller  34  directs fluid therefrom to accumulator  30  to recharge accumulator  30 . 
     For ease of understanding, system  24  can be considered a passive system without the use of sensors, with accumulator  30  being charged from hydraulic pump  28  whenever flow is not being directed elsewhere by valves  32 . Then a contribution of fluid flow is initiated from accumulator  30  when particular elements are activated, such as when feed wheels  40  are activated. The advantages of this embodiment are discussed below along with those of an alternative embodiment. 
     In an alternative embodiment of the present invention sensors are used to provide further information to controller  34 , such as sensor  36  measures the pressure of hydraulic fluid in accumulator  30  and sensor  38  measures flow rates of hydraulic fluid to the elements of attachment  26 . The information from sensors  36  and  38  are utilized by controller  34 , along with other inputs, to select a time for activating a valve  32  so that pressure from accumulator  30  adds to the hydraulic flow volume and/or pressure coming from hydraulic pump  28  and is sent to a particular element of attachment  26  by way of control signals from controller  34  to valves  32 . The selection of timing and duration of the release of fluid from accumulator  30  is undertaken to supplement power available from hydraulic pump  28 . The varying demands for hydraulic flow for the use of attachment  26  allow controller  34  to selectively use valves  32  to direct pressurized fluid in the system. For example, fluid from hydraulic pump  28  can be used to directly or by way of a hydraulic transformer to increase the pressure in accumulator  30  during times when elements of attachment  26  are not being utilized or the utilization is of an acceptably low volume to allow some of the volume from hydraulic pump  28  to be utilized in accumulating pressurized hydraulic fluid in accumulator  30 . 
     When an operator provides the controlling instructions to controller  34  to activate functions of attachment  26 , controller  34  in selective use of valves  32  can direct flow from hydraulic pump  28  and utilize pressure from accumulator  30  in anticipation of a load that may be encountered by an element of attachment  26 . For example, if saw  44  is going to be powered up, extra hydraulic fluid from accumulator  30  may be released to overcome the starting momentum used to power up saw  44 . In another example, when the stem of a tree is currently in position in harvester head  26  and feed wheels  40  are going to be activated, in anticipation of the fluid flow demand due to the starting of the movement of the substantial mass of the tree stem, which may be compounded by portions of the tree dragging along the ground and when limbs on the tree come against blades which are a part of harvester head  26 . These elements can vary the load as the stem is being processed causing controller  34  to, at various times, supplement the flow of hydraulic fluid to feed wheels  40  by providing a flow from accumulator  30 . 
     Now, additionally referring to  FIGS. 3 and 4 , there are illustrated some of the functional advantages of the embodiments of the present invention. In  FIG. 3  there are two curves with the lower curve showing the movement of the stem of a log through harvester head  26  in quarter second increments with a harvester head  26  without the advantage of the present invention. The upper curve illustrates the log position, hence movement of the log at a faster rate over the same time period utilizing the additional flow from accumulator  30  on a selective basis under the control of controller  34 . 
       FIG. 4  illustrates the acceleration of a log through harvester head  26  and how the acceleration occurs in a much quicker time frame, as illustrated by the curve that peaks further to the left. The curve peaking to the right illustrating the function of harvester head  26  without the advantage of the present invention. The dynamic control of the movement of a log through harvester head  26  improves the throughput of trees due to the present invention. 
     While  FIG. 2  illustrates attachment  26  as being separate from the other elements of hydraulic system  24 , it is to be understood that these elements can be utilized having their position upon attachment  26  or elsewhere on work vehicle  10  without altering the functionality of the present invention. For example, accumulator  30  may exist as a part of harvester head  26  or located elsewhere on vehicle  10 . 
     Information from measuring device  46  can be utilized by controller  34  as an input to show the movement of a stem through harvester head  26  so that controller  34  can selectively release fluid from accumulator  30  in the event the stem slows down, for example when a limb on the log encounters a cutting blade. The fluid flows utilized by the hydraulic motors associated with feed wheels  40 , grab arms  42  and saw  44  can also be utilized as an indication of a need to send additional fluid flow from accumulator  30 . The signal from measuring device  46  includes information on the position of the log, which can then be utilized by controller  34  along with a time stamp measurement associated with the positioning of the log to calculate the acceleration and movement velocity of the log through the system to additionally allow controller  34  to selectively apply or disengage its supply of fluid from accumulator  30 . 
     In the event accumulator  30  is located on harvester head  26 , valves to control the fluid flow from accumulator  30  would be located thereon. In the illustrated reference in  FIG. 2  the use of a single rectangular block to denote valves  32  does not constrain the positioning of the valves to a single location, nor does any of the schematical blocks constrain the location of the particular element or distributed location of multiple elements that may be a part of that particular block. 
     The present invention uses accumulator  30  to store hydraulic fluid at high pressure for use by harvester head  26  as needed to supplement the normal hydraulic fluid flow from hydraulic pump  28 . The additional flow from accumulator  30  is used to provide the high volume oil demanded by harvester head  26  during certain operations including the log feeding, previously discussed, as well as cross-cutting of the log by way of saw  44 . Accumulator  30  is supplied with oil by hydraulic pump  28  during times when the maximum hydraulic pump capacity is not required for use by harvester head  26  or other elements of work vehicle  10 . This advantageously allows high oil flow volumes when needed without requiring the machine to be oversized in regard to a higher horsepower engine or an oversized hydraulic pump. This provides for lower initial cost of components as well as overall operating cost during operation, which increases the engine efficiency, such as the ability to run at a lower horse power without sacrificing head productivity while also reducing heat dissipation requirements of the system. 
     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.

Technology Classification (CPC): 4