Abstract:
A transfer pump configured to move a hydraulic fluid in a hydraulic fluid management system of a hydraulic system of a vehicle including a transmission. In one embodiment, the transfer pump moves the fluid from a differential case to a hydraulic reservoir coupled to the transmission. The transfer pump is a positive displacement pump including an unloading device, such as a sealing plate, that is resiliently biased against the pump during a normal operation but is moved away from the pump upon the application of a pilot pressure. The result is an open chamber for the pump gears to turn without developing pressure, to thereby reduce parasitic losses.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present invention generally relates to a work vehicle having a fluid management system, and more particularly to a pump for moving fluid through the fluid management system. 
       BACKGROUND 
       [0002]    Agricultural equipment, such as a tractor or a self-propelled combine-harvester, includes a prime mover which generates power to perform work. In the case of a tractor, the prime mover is a gas powered engine or a diesel engine that generates power from a supply of fuel. The engine drives a transmission which moves wheels or treads to propel the tractor, or other work vehicles, across ground or other surfaces. In addition to providing power to wheels through a transmission, tractors often include a power takeoff (PTO) which includes a shaft coupled to the transmission and which is driven by the engine or a hydraulic motor. 
         [0003]    Both gas powered and diesel powered vehicles includes a fluid management system to manage the movement of a hydraulic fluid in the transmission. In different embodiments, the fluid management system manages the movement of fluid to other vehicle systems and components including a differential, a steering system, brakes, the PTO, and various fluid reservoirs and coolers. Other systems and components which use the managed fluid include a suspension, a hitch, a cab suspension, and selective control valves. 
         [0004]    Fluid management systems typically include a positive displacement pump which transfers the fluid between different portions of the fluid management system, for instance between a differential and a hydraulic reservoir. In one known configuration, the hydraulic system and the drivetrain share the hydraulic fluid and the drivetrain system circulates fluid through a fluid cooler. In one embodiment, a transfer pump, typically a gear pump, moves the common fluid from the differential case to the hydraulic reservoir through a hydraulic filter. 
         [0005]    Energy losses occur throughout the drivetrain when the vehicle is moving or standing still. This energy loss, also known as a parasitic loss, is a result of many factors including the movement of oil in the system which exceeds the flow requirements. The excess flow is returned to a reservoir or a transmission sump, and is consequently not converted to perform a function but instead results in lost energy. 
         [0006]    Transfer pumps under different operating conditions can be a source of these parasitic losses, even when the vehicle&#39;s engine is idling. Attempts to reduce the parasitic losses of positive displacement pumps have been provided by the use of additional devices such as expensive clutches, external unloading valves, large unloading valves, piston pumps, and variable displacement mechanisms for vane pumps. These solutions, however, still develop pressure losses. Consequently, what is needed therefore is a transfer pump that further reduces parasitic losses without the use of costly additional devices or the additional complexity associated with such devices. 
       SUMMARY 
       [0007]    A transfer pump is configured to move a hydraulic fluid in a hydraulic fluid management system of a hydraulic system of a vehicle including a transmission. In one embodiment, the transfer pump moves the fluid from a differential case to a hydraulic reservoir coupled to the transmission. The transfer pump is a positive displacement pump including an unloading device, such as a plate, that is resiliently biased in the pump during a normal operation but is moved away from the pumping gears upon the application of a pilot pressure. The result is an open chamber defining a volume for the pump gears to turn without developing pressure, to thereby reduce parasitic losses. In another embodiment, the plate is resiliently biased away from the pump during normal operation, but is move toward the pump upon the application of a pilot pressure. 
         [0008]    In one embodiment, there is provided a fluid transfer pump including a housing defining a first cavity and a passage operatively coupled to a second cavity. The passage is configured to provide fluid transfer into the second cavity. The housing further includes an interior wall disposed in the housing and a fixed side wall disposed at an end of the housing. A movable member is movably disposed within the housing and a bias element is disposed between the wall and the movable member. A fluid applied to the passage into the second cavity changes the bias force of the bias element and the location of the movable member with respect to the interior wall to change a volume of the first cavity. 
         [0009]    In another embodiment, there is provided a fluid transfer pump including a housing defining a cavity and a passage having an inlet disposed at an external portion of the housing. A movable member is disposed within the cavity. The movable member defines a first chamber, wherein the volume of the first chamber is adjustable with movement of the movable member. A gear set is disposed at the first chamber, wherein the first chamber is configured to hold a fluid. A bias element is disposed at the movable member and is configured to adjust the location of the movable member to a first position defining a first volume of the first chamber and to a second position defining a second volume of the first chamber. 
         [0010]    In still another embodiment, there is provided a method of controlling the operation of a fluid transfer pump having a housing, defining a cavity, and including a bearing, located at the cavity. The method includes: biasing an adjustable plate disposed within the cavity at a first location with a bias element; and applying a fluid pressure to the adjustable plate to adjust the bias of the bias element and to move the adjustable plate away from the bearing to a second location. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The above-mentioned aspects of the present invention and the manner of obtaining them will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention, taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a side perspective view of a work vehicle. 
           [0013]      FIG. 2  is a block diagram of a fluid management system of a work vehicle. 
           [0014]      FIG. 3  is a schematic diagram of cross-section of one embodiment of a positive displacement pump in a first condition. 
           [0015]      FIG. 4  is a schematic diagram of a cross-section of one embodiment of a positive displacement pump in a second condition. 
           [0016]      FIG. 5  is a schematic diagram of a cross-section of another embodiment of a positive displacement pump. 
           [0017]      FIG. 6  is a schematic diagram of an exploded view of the embodiment of the positive displacement pump of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    For the purposes of promoting an understanding of the principles of the novel invention, reference will now be made to the embodiments described herein and illustrated in the drawings with specific language used to describe the same. It will nevertheless be understood that no limitation of the scope of the novel invention is intended. Such alterations and further modifications of the illustrated apparatus, assemblies, devices and methods, and such further applications of the principles of the novel invention as illustrated herein, are contemplated as would normally occur to one skilled in the art to which the novel invention relates. 
         [0019]    The present disclosure is not exclusively directed to any type of machine, but rather extends to different types powered vehicles, including work vehicles such as tractors. For exemplary and illustrative purposes, the present disclosure focuses on a utility tractor  100 . In  FIG. 1 , for example, the tractor  100  includes a cab  102  where an operator controls the operation of the tractor  100 . The tractor  100  includes an outer frame  104  to which a front and rear axle (not shown) are connected. The front axle engages a pair of front ground engaging means  106  (e.g., wheels) mounted thereto and the rear axle engages a pair of rear ground engaging means  108  (e.g., wheels) mounted thereto. Operator controls  110 , such as a steering wheel, shift lever, shift buttons, dashboard display, etc., are disposed in the cab  102 . One or more of these operator controls  110  is operably coupled to the machine&#39;s drive train, including a transmission (not shown) for controlling the operation of the machine  100 . A fluid system  200  (see  FIG. 2 ) is supported by the frame  104  and provides a fluid, such as a hydraulic fluid, to provide for the operation of the transmission of the machine  100  as well as a power take off (PTO) not shown. 
         [0020]    As illustrated in  FIG. 2 , the fluid system  200  includes a transmission  202  and a transmission sump  204  operatively connected to the transmission  202 . The sump  204 , in one embodiment, is also coupled to provide fluid to lubricate a front axle, a PTO, and the front brakes. A cooler (not shown) is coupled to the transmission  202 , as is understood by those skilled in the art. 
         [0021]    A fluid reservoir  206  provides for the storage of fluid used in the fluid system  200  and is coupled to steering and brakes  208 . A differential  210  includes a differential case  212  which is coupled to the reservoir  206 . An oil fill  214  is located at the case  212  to provide for filling of the oil of the differential case  212  as necessary. One or more filters  216  are coupled between a port  217 , of the reservoir  206 , and a transfer pump  218 , which is coupled to the differential case  212 . An inlet  220  of the pump  218  is configured to receive filtered oil which moves through the filter  216 . An outlet  222  is coupled to the differential  212 . A bypass solenoid control valve  224  is coupled between the port  217  and the differential case  212 . 
         [0022]    The pump  218 , in one embodiment, is a low pressure gear pump configured to transfer oil between the reservoir  206  and the differential case  212 . The pump&#39;s pressure building capability is controlled by electrohydraulic or hydraulic control of plate movement and an electrical control signal as indicated at  226 . In one embodiment, a solenoid is located at, within, or distant from the pump  218 . The electrical control signal is provided by a controller  230 , through a control line  231  which includes one or more processors which are configured to control the operation of the pump  218 . The electrical control signal controls the solenoid which opens or closes a hydraulic pilot signal to be applied to the pump  218 . 
         [0023]    The controller  230  is configured to execute or otherwise rely upon computer software applications, components, programs, objects, modules, or data structures, etc. Software routines reside in a memory, resident within the controller or at other external memory (not shown), or are provided as firmware, and executed in response to the various signals received and generated as described herein. The executed software includes one or more specific applications, components, programs, objects, modules or sequences of instructions typically referred to as “program code”. The program code includes one or more instructions located in the memory, other storage devices or elsewhere, which executes the control functions of the vehicle  100 . 
         [0024]      FIG. 3  and  FIG. 4  are a schematic diagram of cross-section of one embodiment of pump  218  in a first state and a second state respectively. In the illustrated embodiments, the pump  218  is a positive displacement pump which includes a housing  232  defining a cavity  233  having disposed therein a first shaft  234  and a second shaft  236 . The shaft  236  includes first and second ends, each of which extend externally to the housing  232 . The shaft is configured to be driven by a driver (not shown). A first gear  238  is fixed to and encircles the shaft  234  and a second gear  240 , which engages the first gear  238 , is fixed to and encircles the shaft  236 . 
         [0025]    The first shaft  234  is supported for rotational movement within the cavity by a first bearing  242  and a second bearing  244 . The second shaft  236  is supported for rotational movement by a third bearing  246  and a fourth bearing  248 . The first and third bearings  242  and  246  are disposed next to or at a flange  250  which forms a sidewall  251  of the housing  232 . A casing  252  forms a portion of the housing  232  and is disposed adjacently to the sidewall  251 . The bearings  242  and  246  form fluid tight seals with the shafts  234  and  236  to substantially seal the cavity  233  at the sidewall  251 . 
         [0026]    Each of the second bearing  244  and the fourth bearing  248  are disposed within an end plate  254 , which is movable with respect to the casing  252  along a direction  256 , in either direction. The second and fourth bearings  244  and  248  are fluidically sealed within the end plate  254 . The end plate  254 , which moves in the direction  256 , is fluidically sealed with an end cover  258 , such that the end plate  254  moves between a first position of  FIG. 3  to a second position of  FIG. 4  and at locations between the first and second positions. The end cover  258  provides another sidewall  260  to complete the housing  232 . Fluidic sealing of the end plate  254  with the end cover  258  is made by a plurality of seals  262  each of which is located at an interface of the end plate  254  and the end cover  258 . 
         [0027]    The end cover  258  defines with an aperture  264  with the casing  252 . In the illustrated embodiment, a casing part  266  is a separable part which is fixedly attached to the rest of the casing  252 . In other embodiments, the casing  252  is single piece unitary part. The aperture  264  is fluidically coupled to a solenoid  268  which is controlled by the controller  230  through the line  231 . The aperture  264  is further fluidically coupled to a cavity  269 , the capacity of which varies as a function of end plate  254  moving with respect to the gears  242  and  246 . 
         [0028]    As pilot pressure is applied by the solenoid  268 , the cavity  269  expands as the end plate  254  moves away from the gears  242  and  246  and which forms an inside wall or an inside surface. At the same time, the cavity  233 , which defines a volume, expands as well as the end plate  254  moves away from the gears  242  and  246 . The capacity of the cavity  233  varies as a function of the position of the end plate  254  with respect to the bearings  238  and  240 . 
         [0029]    A first bias element  270  and a second bias element  272  are each located between the end plate  254  and the end cover  258 . In different embodiments, one or more bias elements are included. In one embodiment, the first and second bias elements  270  and  272  are helical springs, each having ends engaging a groove or an aperture in the end plate  254  and the end cover  258 . Each of the bias elements  270  and  272 , in a relatively uncompressed state as illustrated in  FIG. 3 , forces the end plate  254  away from the end cover  258  to reduce the capacity of the cavity  233 . In this position, there is no pilot pressure applied through the aperture  264 . In the absence of pilot fluid pressure being provided at the aperture  264 , the force provided by the bias elements  270  and  272  is sufficient to maintain the position of the end plate  254 , as illustrated, which reduces the size of cavity  233  to a minimum. In addition, a space  274 , located between the end plate  254  and the end cover  258 , is at a maximum. In this condition, the pump  218  moves fluid from an inlet  276  to an outlet  278 , both of which are fluidically coupled to the cavity  233 . A working pressure for the operation of the gears  238  and  240  is therefore developed. With the end cover  258  in the illustrated position, the pressure developed within the cavity  233  enables the shaft  234  to move the fluid from the inlet  276 , through the cavity  233 , through the outlet  278 , and to other locations within the fluid system  100 . The end clearances of each of the components are controlled in order to achieve an acceptable pumping efficiency. 
         [0030]      FIG. 4  illustrates a state of the pump  218  which is provided to reduce the fluid pressure in the cavity  233  and to unload the gears  238  and  240  when no fluid flow and a low energy state are desired. In this condition, power and/or fuel are saved to thereby reduce costs including operating costs and costs of repair or replacement from use. 
         [0031]    To unload the pump  218 , a pilot pressure is applied to the aperture  264  through activation of the solenoid  268  by the controller  230 . Upon application of the pilot pressure, fluid is forced into the cavity  269  defined between the housing casing  252  and the end plate  254 . With sufficient pressure to overcome the bias force of the bias member  270  and  272 , the space  280  fills with fluid to force the end plate  254  to move away from the gears  238  and  240 . This movement reduces the size of the space  274 . 
         [0032]    As the space  274 , of  FIG. 3 , is reduced in size, a space  282 , which is part of the cavity  233 , expands between the gears  238  and  240  and the end plate  254  as the combined structure of the second bearing  244 , the fourth bearing  248 , and the end plate  254 , moves towards the end cover  258 . As the bias elements are compressed to a shorter length, the end clearance of the gear set is increased to a point where the gears  238  and  240  no longer provide sufficient working pressure for moving fluid from the inlet  276  to the outlet  278 . When the pilot pressure is applied, the pressure is trapped between the seals  262  near the aperture  264 , and this pressure is applied to the differential area of the end plate to push against the springs. Consequently, the gears run in the oil filled chamber, the cavity  233 , which now has a larger capacity, and which lacks sufficient pressure to move fluid under pressure from the inlet  276  to the outlet  278 . During this state of operation, the operating pressure of the pump is essentially zero and the only power required is the torque required to turn the gears in an oil bath. 
         [0033]    In this embodiment, should a fault occur, the space  274  remains as depicted in  FIG. 3  and sufficient pressure is applied within the cavity  233  to enable pressurized fluid flow from the inlet  276  to the outlet  278 . Faults can occur under different conditions, including failure of the solenoid  268  to operate or a decoupling of a fluid line from the aperture  264 . 
         [0034]      FIG. 5  illustrates another embodiment of a pump  300  which includes a housing  302  having a case  304  and a cover  306  fixedly located at one end of the case  304 . The case  304  includes a first cavity  308  and a second cavity  310  separated by an inside wall  312 . The first cavity  308  is substantially closed by the cover  306 , inside walls of the case  304 , and one side of the wall  312 , which acts a spring retainer. The wall  312  includes an aperture  314  through which a ring plunger  316  is inserted. 
         [0035]    A bias member  320  is located on a shaft  318  and is captured between a terminating end  322 , which defines a retaining portion at one end of the bias member  320 . A surface of the wall  312  provides another retaining portion at another end of the bias member such that the bias member is captured between the terminating end  322  and the wall  312 . 
         [0036]    The second cavity  310  is further defined by a first surface  324  of the ring plunger  316  which interfaces with a second surface of the wall  312  to define the second cavity  310 . The second cavity  310  includes a variable volume, the volume of which is adjustable as a function of movement of the ring plunger  316  along a direction  326 , in either direction. A body portion  328  of the plunger  316  defines the first surface  324  and a second surface  330 . The second surface  330  defines with adjacent walls of the case  304  a third cavity  332 , which has a generally ring shaped volume extending around the body portion  328 . The third cavity  332  is coupled to an aperture  334  defined by the case  304  which is configured to receive a fitting  336 . The fitting  336  receives a pilot pressure as described above with regard to  FIGS. 3 and 4 . 
         [0037]    In this embodiment, however, the application of a pilot pressure at the aperture  334  moves the ring plunger  316  away from the wall  312  and toward a pump housing  338 , which provides a sidewall for the housing and which is fixedly attached to the case  304 . The pump housing  338  includes a central channel  340  configured to support a gear  342 . Upon application of the pilot pressure at the aperture  334 , the body portion  328  moves toward the pump housing  338  to provide a working fluid pressure to the bias element  342 . In the illustrated state, the application of the pilot pressure collapses the spring  320 . Consequently, to maintain the gear  342  in a working state, the pilot pressure is continuously maintained. 
         [0038]    If however, it is desired to prevent the gear  342  from pumping, the pilot pressure is removed and the spring force of the bias element  320  moves the body portion  328  away from the gear  342  and toward the cover  306 . Fluid pressure is reduced and while the gear  342  may still turn, the fluid pressure is reduced sufficiently to reduce fluid flow being displaced by the pump. 
         [0039]    In this embodiment, should the solenoid providing the pilot pressure fail to operate, the cavity  310  collapses and sufficient pressure is not available to enable the gear  342  to turn as needed. Consequently, as described herein, each of the different embodiments provides a different state of the pump when the pilot pressure is unavailable. The described embodiments, therefore, provide a relatively inexpensive, but extremely effective unloading mechanism for gear pumps when no flow and low energy states are desired, which saves one or both of power and fuel. 
         [0040]    While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.