Patent Publication Number: US-2011073192-A1

Title: System and method for managing load flow requirements for a tractor single pump hydraulic system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority of U.S. Provisional Patent Application No. 61/228,498 entitled “SYSTEM AND METHOD FOR MANAGING LOAD FLOW REQUIREMENTS FOR A TRACTOR SINGLE PUMP HYDRAULIC SYSTEM,” filed Jul. 24, 2009, the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to land vehicle hydraulic systems generally and more specifically to pipelayer hydraulic assemblies mounted to track-type tractors. 
     BACKGROUND OF THE INVENTION 
     Hydraulic track-type pipelayers consist of a track-type crawler tractor with a pipelayer structure mounted to it, along with the associated hydraulic hook and boom winches, the winch hydraulic-controls, and all the necessary rigging. The track-type crawler tractor provides the power to drive the hydraulic winches, and any other hydraulic system fitted or used to control the crawler tractor. 
     The pipelayer hydraulic system can be driven either directly with a dedicated implement pump supplying only the pipelayer system, or connected in parallel with the tractor hydraulic implement system. The tractor implement system is also arranged in parallel. A parallel system means that when hydraulic functions are actuated simultaneously, hydraulic fluid flow is divided to each function. It is known however, that there will be a greater flow to the path with the least resistance. Due to this fact, the pipelayer is connected to the tractor implement system in parallel, either the tractor implement system or the pipelayer system could be impaired when used simultaneously. This is because the fluid directed to the path of least resistance could leave the other system with insufficient hydraulic pressure to adequately operate that system. This is typically not an issue with the pipelayer system, since all other existing implements—bulldozer cylinders, rippers, tow winches, etc.—are typically either removed or disconnected, or are not used during critical pipelaying operations. The same is not true, however, for essential hydraulic operations such as the tractor steering system. 
     Crawler tractors have two methods for steering control: mechanical steering clutches, or hydraulic differential steering. Mechanical steering clutches are completely separate from the hydraulic implement system, and are unaffected by it. Hydraulic differential steering systems use a hydraulic steering motor to facilitate a change of direction. The hydraulic steering motor can be powered either by its own dedicated pump, separate from the implement system (a two-pump system), or by the tractor implement pump (a single-pump system). 
     In a single pump system, the steering function could be severely compromised unless it is given precedence over the other tractor implement functions. With a pipelayer connected directly to a single-pump system which also services the steering function, the steering of the tractor could be drastically impaired if a load placed by the pipelayer implement consumes hydraulic flow, leaving insufficient flow for the steering function. For example, if the tractor was making a turn while quickly raising an empty hook, the hook winch would have a very low pressure requirement (least resistance) while having a high flow requirement. In this example, the majority of hydraulic fluid would flow through the pipelayer&#39;s hook circuit, leaving significantly less, and potentially insufficient, flow for the steering function. This is an extremely undesirable situation. For this type of reason, single pump differential steering systems have not been successfully implemented on tractors including implements such as pipelayers, and therefore pipelayers have been primarily used on crawler tractors with mechanical steering clutches. A need, therefore, exists for a single pump differential steering system and method for a tractor including hydraulic implement, such as a pipelayer connected in parallel thereto, wherein the tractor steering system, or any other essential hydraulic system, is not affected by the hydraulic flow requirements of the implement (pipelayer). 
     SUMMARY OF THE INVENTION 
     The system of the present disclosure connects an implement hydraulic system to a single-pump, differential steer, crawler tractor&#39;s implement valve in parallel. The present load-flow system and process gives precedence to the tractor&#39;s essential operation which is in hydraulic fluid communication with an implement system (such as a pipelayer), by allowing the hydraulic power (pressure and flow) to be controlled in the essential operation independently of the hydraulic pressure requirements of the implement system. As a result, full control of the essential hydraulic operation is maintained regardless of the implement system demands. A secondary function and sub-process also allow either the tractor&#39;s essential operation, or the implement system, to dictate the implement pump&#39;s supply-pressure output. As used herein, the term essential operation shall include any system of the tractor which relates to its essential operation and function, such as, but not limited to, the steering system. 
     In its general form, the present disclosure includes a process for managing fluid flow for an essential operation and an implement connected in parallel to a single hydraulic pump. The process includes the steps of determining the essential operation fluid pressure requirement; determining the implement fluid pressure requirement; and maintaining said essential operation fluid pressure requirement by providing fluid flow to the essential operation regardless of the implement fluid pressure requirement. 
     In a preferred embodiment, the present disclosure includes a process for managing fluid flow requirements for a steering system and a pipelayer system connection in parallel to a single pump hydraulic system. The process includes the steps of:
         (1) obtaining a steering system fluid pressure requirement from the essential operation system;   (2) obtaining a pipelayer fluid pressure requirement from the pipelayer system;   (3) determining a greatest system pressure requirement;   (4) transmitting the greatest system pressure requirement signal to the single pump hydraulic system;       

     (5) obtaining fluid flow from the single pump hydraulic system to maintain the greatest system pressure requirement; and
         (6) maintaining fluid flow to satisfy the steering system fluid pressure requirement independent of the pipelayer system fluid pressure requirement.       

     Further aspects, features, and advantages of the present invention will be apparent to those of ordinary skill in the art upon examining the accompanying drawings and upon reading the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a schematic diagram of a single pump parallel hydraulic system including the apparatus and process of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The system of the present disclosure in a preferred embodiment connects a pipelayer hydraulic system to a single-pump, differential steer, crawler tractor&#39;s implement valve in parallel. It gives precedence to the tractor&#39;s steering and implement system by allowing the hydraulic power (pressure and flow) to be controlled in the steering system independently of the hydraulic pressure requirements of the pipelayer system. In this way, full steering control is maintained regardless of the pipelayer system demands. A secondary function also allows either the tractor steering and implement system or the pipelayer system to dictate the implement pump&#39;s supply-pressure output. Without the system of the present disclosure installed, steering control of single-pump, differential steer, crawler tractors would be unreliable with a hydraulic pipelayer system installed. 
     With reference to  FIG. 1 , a tractor hydraulic steering system connected to a pipelayer hydraulic system in parallel  10  is disclosed. System  10  includes a tractor single-pump system  20 , the load flow hydraulic fluid flow apparatus of the present disclosure  30 , tractor steering system  40 , pipelayer system  50 , and tractor hydraulic tank  60 . In system  10 , load-flow apparatus  30  and pipelayer system  50  are preferably connected to the implement valve of a crawler tractor in parallel such that the tractor single pump  20  is in fluid communication with load-flow  30 , which is, in turn, in fluid communication with both the tractor steering system  40  and pipelayer system  50 . Tractor single pump  20 , tractor steering system  40 , and pipelayer system  50  are in fluid communication with tractor hydraulic tank  60 . 
     Hydraulic fluid is pumped by tractor single pump  20  from hydraulic tank  60 , shown by flow diagram  22 . Hydraulic fluid is pumped by the tractor single pump  20  into load flow apparatus  30 , as shown at  24 . Load flow apparatus  30  obtains the fluid flow pressure requirements of the tractor steering system and provides hydraulic fluid flow to steering to tractor steering system  40 , as shown at  26 . Load flow apparatus  30  also obtains the fluid flow pressure requirements of pipelayer system  50  and provides fluid flow to pipelayer system  50  at  28 . Load flow apparatus  30  satisfies the fluid flow pressure requirements of tractor steering system  40  regardless and independent of the fluid flow pressure demands of pipelayer system  50 . Fluid is returned by tractor steering system  40  to hydraulic tank  60 , as shown at  32 . Fluid is returned by pipelayer system  50  to hydraulic tank  60 , as shown at  34 . 
     In operation, tractor steering system  40  provides a signal  42  to load flow apparatus  30  regarding the fluid flow pressure required for proper tractor steering system function. Pipelayer system  50  provides a signal  44  to load flow apparatus  30  regarding the fluid pressure requirement necessary for operation of the pipelayer system. From tractor steering pressure requirement signal  42  and pipelayer pressure requirement signal  44 , load flow apparatus  30  determines the greatest system pressure requirement necessary for the proper function of tractor steering system  40  and/or pipelayer system  50 . This is done by comparing the tractor steering system pressure requirement signal  42  with pipelayer pressure requirement signal  44 . Load flow apparatus  30  provides a signal  46  to tractor single pump  20  regarding this greatest system pressure requirement  46 . Load flow apparatus  30  may include a microprocessor for receiving signals  42  and  44  and for determining the greatest system pressure requirement, the microprocessor may also include as an output for providing the greatest system pressure requirement signal  46  to single pump system  20 . 
     In response to the greatest system pressure requirement signal  46 , the tractor single pump system  20  provides the fluid flow required to maintain the signaled greatest system pressure at  52 . Load flow apparatus  30  receives the flow required to maintain the greatest signal system pressure  52  from tractor pump system  20 . Load flow apparatus  30  distributes the fluid flow required by tractor steering system  40  at the required pressure  54 . Load flow apparatus  30  also provides fluid flow to pipelayer system  50 . The fluid flow to pipelayer system  50  from load flow apparatus  30  is the pump flow required to maintain the greatest system signaled pressure  52  less the fluid flow requirements at the required steering pressure  54  required by steering system  40 . In this way, load flow apparatus  30  maintains at all times the required fluid flow to tractor steering system  40  at the required steering fluid pressure, regardless and independent of the pipelayer system  50 . In the event that the pipelayer system pressure requirement (per signal  44 ) of pipelayer system  50  is less than the tractor steering system requirement (per signal  42 ) of tractor steering system  40 , load flow apparatus  30  will provide the necessary fluid flow to tractor steering system  40  required to maintain the tractor steering pressure requirement without a pressure drop due to fluid flow taking the path of least resistance caused by the lower pressure request of pipelayer system  50 . 
     Load flow apparatus  30  may also provide the necessary fluid flow to maintain the required system pressure in either tractor steering system  40  or pipelayer system  50 , depending on which produces the greatest system pressure requirement, which then becomes the greatest system pressure requirement signal  46 . In this way, either the tractor steering system  40  or the pipelayer system  50  may dictate the pump flow  52  required to maintain the greatest system pressure (per signal  46 ). 
     Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those skilled in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the appended claims.