Abstract:
This invention provides a fluid system for exchanging used hydraulic fluid with fresh hydraulic fluid in an accessed hydraulic circuit. One particular application provides an exchange apparatus for exchanging fluids of the type found in motor vehicle hydraulic circuits. The exchange apparatus may utilize pressurized spent fluid flow as a fluid power medium to activate the auto-replenishing fluid exchanger system to replace the spent fluid with fresh fluid at equalized flow rates. Alternatively, the exchange apparatus may utilize pressurize fresh fluid as a fluid power medium to activate the exchange system. Additional power may be supplied by an external boost pump to supplement the flow of fluid.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority pursuant to 35 U.S.C §119(e)(1) from the provisional patent application filed pursuant to 35 USC §111(b): as Ser. No. 60/083,557 on Apr. 29, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to fluid exchange systems and in particular to those useful in the exchanging of fluids of the types found in motor vehicles and pressurized hydraulic systems. Disclosed herein is a fluid exchange apparatus wherein used hydraulic fluid is exchanged for fresh fluid by interposing the invention in-line with a hydraulic fluid circulation circuit. The exchange apparatus may utilize pressurized spent fluid flow as a fluid power medium to activate the auto-replenishing fluid exchanger system to replace the spent fluid with fresh fluid at equalized flow rates. Alternatively, the exchange apparatus may be externally powered to replace the spent fluid with fresh fluid at equalized flow rates. 
     2 Related Background Art: 
     A variety of hydraulic fluid exchange systems are known to those skilled in the art. One early example is the applicant&#39;s U.S. Pat. No. 190 5,318,080, which featured a pressure vessel divided into two chambers by a flexible diaphragm (See, FIG.  3 ). To refill this exchange system with fresh fluid in preparation for the exchange operation, fresh fluid was introduced into one chamber causing the diaphragm to distend and simultaneously force the spent fluid out of the second chamber. A particular characteristic of this device was the limited volumetric capacity of the pressure vessel, as the capacity of fluid exchange was substantially equal to the volume of the contained fresh fluid prior to the exchange process. If the volume of fresh fluid contained in fresh-fluid charged receiver was less than the desired exchange capacity, one would have to interrupt the exchange process upon discharge of the fresh fluid load, recharge the receiver with fresh fluid, and then reinstate the exchange process until the desired fluid capacity was exchanged. Merely increasing the volumetric capacity of the fluid receiver would concomitantly increase manufacturing costs, fluid friction losses, and the overall size of the exchange apparatus. As a result, the efficiency of such a device was limited by the volume of fresh fluid the device was able to contain. 
     An additional limitation of prior art exchange systems has been the requirement of onboard fluid tanks for holding fresh fluid and used fluid requirements. These tanks increase the overall size and weight of an exchange apparatus, making movement and storage of the fluid exchange apparatus burdensome. 
     SUMMARY OF THE INVENTION 
     The present invention solves many of the problems existent in prior hydraulic fluid exchange systems. The present invention provides a compact fluid exchange system having a fluid receiver which is substantially smaller than the amount of fluid exchanged during the exchange process. As the size of the fluid receiver in the present invention is not related to the volume of ultimately fluid exchanged, the apparatus can be used to service hydraulic fluid systems having a variety of circuit sizes, configurations, etc. 
     Briefly, the invention includes a reciprocating pump assembly having a pair of pumping chambers and a pair of working chambers. The pump assembly operates to receive used fluid from an accessed hydraulic fluid circuit into one of the working chambers, introduce fresh fluid from a pumping chamber into the hydraulic fluid circuit, simultaneously refill the other pumping chamber with fresh fluid, and simultaneously discharge spent fluid from the other working chamber into a spent fluid receptacle. Fluid flow relative to the pump assembly is directed by a control structure. This reciprocating pump assembly cycles until the predetermined exchange volume is satisfied (determined by such means as visual or optical comparison of fluid input and output, sensor devices, etc.). The invention permits connection to both a bulk fresh fluid supply and a floor drain, such as those typically found in vehicle repair facilities. 
     One object of the invention includes a reciprocating pump assembly having a power medium of a pressurized hydraulic fluid, such as used transmission fluid of an operating motor vehicle during a maintenance procedure, or pressurized fresh fluid from an external source. 
     One object of the invention provides a fluid exchange apparatus released from the requirement of having dedicated on-board fluid reservoirs. A remote bulk fresh fluid supply and remote waste fluid receptacle, such as those found in vehicle repair facilities, may be utilized to practice the present invention. In this manner, a smaller, more compact fluid exchange apparatus is provided. 
     One object of the present invention permits an efficient change between different fresh fluids (grades, additive packages, etc.) between or during exchange procedures. The limited volumetric capacity of the pump assembly and associated conduit results in a limited amount of the previous different fresh fluid charge held within the exchange apparatus. 
     Another object of the invention includes a reciprocating pump assembly having an external power source, such as an electric motor, for powering or assisting in the powering of the pump assembly. Additionally, a booster pump assembly may be provided to assist in the exchange procedure for certain hydraulic environments, such as low flow or pressure systems. 
     Yet another object of the invention provides a range of pump assembly structures for practicing the invention. The pump assembly structures may include a linear pump assembly, a displaced piston/crank assembly, and a rotor pump assembly. These and other objects, features and advantages of the present invention will become apparent to one skilled in the art upon analysis of the following detailed description in view of the drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The present invention will be described hereafter in the Detailed Description of Preferred Embodiments, taken in conjunction with the following drawings, in which like reference numerals refer to like elements throughout. 
     FIG. 1 schematically illustrates a fluid exchange system according to the present invention; 
     FIG. 2 schematically illustrates the fluid exchange system of FIG. 1 at a later point in time; 
     FIG. 3 schematically illustrates the fluid exchange system of FIG. 2 at a later point in time; 
     FIG. 4 is an elevational view of particular components of the fluid exchange system of FIG. 1; 
     FIG. 5 is an elevational view of particular components of the fluid exchange system of FIG. 1; 
     FIG. 6 is a perspective view of particular components of the fluid exchange system of FIG. 1; 
     FIG. 7 is a perspective view of particular components of the fluid exchange system of FIG. 1; 
     FIG. 8 schematically illustrates a second embodiment of a fluid exchange system according to the present invention; 
     FIG. 9 schematically illustrates a third embodiment of a fluid exchange system according to the present invention 
     FIG. 10 is an elevational view of particular components of the fluid exchange system of FIG. 9; 
     FIG. 11 is a top plan view of particular components of the fluid exchange system of FIG. 9; 
     FIG. 12 schematically illustrates a fourth embodiment of a fluid exchange system according to the present invention; 
     FIG. 13 schematically illustrates a fifth embodiment of a fluid exchange system according to the present invention; and 
     FIG. 14 is a perspective view of particular components of the fluid exchange system of FIG.  13 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As shown in FIG. 1, the invention of the present application includes a reciprocating pump assembly  10  having a rigid cylinder body  12  and an interiorly-received dual fluid separation structure  14 . In this preferred embodiment the dual fluid separation structure  14  is a dual piston  16 ,  18  assembly. The cylinder body  12  and dual piston assembly  14  together define two pumping chambers  20 ,  22  disposed substantially between the outer piston ends  16 ,  18  of the dual piston assembly  14 . Two working chambers  24 ,  26  are also defined and are disposed away from the pumping chambers  20 ,  22  and within the cylinder body  12 . The working chambers  24 ,  26  receive pressurized fluid from an accessed hydraulic circuit  30 . Fluid flow relative to the pump assembly  10  is controlled by an actuated control valve assembly  28 . The pressurized fluid, used as a power medium to drive the reciprocating pump  10 , may be automatic transmission fluid of an operating vehicle. The pumping chambers  20 ,  22 , on the other hand, simultaneously introduce fresh fluid into the accessed hydraulic circuit  30  (e.g., transmission cooling circuit). The pumping chambers  20 ,  22  are interconnected by a guide bore  32  which passes through the cylinder body  12 . In operation, the volumes of each of the chambers  20 ,  22 ,  24 ,  26  are variable and determined by the relative position of the dual piston assembly  14  within the cylinder assembly  12 . Minimal fluid is lost across the chamber sealing surfaces  34 . Sealing surfaces  34  may include rings or seals as selected by those skilled in the art. In this embodiment, the working chambers  24 ,  26  are coaxial with the pumping chambers  20 ,  22 . It should be appreciated that the working chambers  24 ,  26  and pumping chambers  20 ,  22  are of a substantially cylindrical shape in this preferred embodiment, however, other configurations are possible. Additionally, the dual fluid separation structure  14  could be a dual diaphragm assembly or other structures disclosed hereinafter. 
     As more fully described herein, the pump assembly  10  is interconnected to an accessed hydraulic fluid circuit  30  through quick-connect fluid couplers  40 ,  42 , fluid conduits  44 ,  46 , and associated unidirectional check valves  48 ,  50 . Used hydraulic fluid from the accessed hydraulic circuit  30  enters the exchange apparatus through quick-connect coupler  42  and a fresh hydraulic fluid flows out of the exchange apparatus and through quick-connect coupler  40 . The flow rate of the used and fresh hydraulic fluid is substantially equivalent during the exchange process. The pump assembly  10  is additionally coupled to a bulk fluid reservoir  60  or similar external fresh fluid source through associated fluid conduit  62  and unidirectional check valves  64 ,  66 . The pump assembly  10  is additionally coupled to an external used fluid receptacle  70 , such as an oil drain or external tank of typical vehicle maintenance facilities. A flow alignment device, as illustrated in applicant&#39;s existing U.S. Pat. No. 5,472,064, may be utilized to practice the present invention. This reference is incorporated herein entirety for all purposes. 
     Still referring to FIG. 1, a plurality of orifices  80 ,  82 ,  84 ,  86 ,  87 ,  89  are interconnected to the pump assembly  10  at the pumping chambers  20 ,  22  and the working chambers  24 ,  26 , each of which is adapted to provide fluid communication from or into respective pumping chambers  20 ,  22  or working chambers  24 ,  26 . Working chambers  24 ,  26  are fluidly coupled to receive used hydraulic fluid from the accessed hydraulic circuit  30  through ports  80  and  82 . Working chambers  24 ,  26  are additionally fluidly coupled to permit discharge of the used hydraulic fluid to the external used fluid receptacle  70  through ports  84  and  86 . As described herein, the fluid flow through respective fluid ports  80 ,  82 ,  84 ,  86  is controlled by a spool valve assembly  28 . Depending on the local pressure conditions, pumping chambers  20 ,  22  are fluidly coupled to either the fresh fluid source  60  or the outlet conduit  44 . 
     In FIGS. 1-3, the present invention is illustrated in schematic, cross-sectional views with arrows schematically depicting fluid flow. Disposed within the cylinder block  12  is the dual fluid separation structure  14 , here illustrated as a dual piston structure  16 ,  18 . Alternatively, a dual diaphragm structure (not shown) may be utilized. The diaphragms may be made of a flexible material such as a rubber-like or other conventional material and may be secured or attached by conventional means to the cylinder body  12  in a manner that a seal is formed between the respective working chambers  24 ,  26  and pumping chambers  20 ,  22 . 
     Referring now to FIGS. 4 and 5, the dual piston assembly  14  and a control valve actuation assembly  90  are illustrated. The dual piston structure  14  has a rod  92  interconnecting the two opposed pistons  16 , 18 . The connecting rod  92  is threadedly secured at each end to an associated piston  16 , 18 . The center rod  92  is hollow and interiorly receives a control rod  94  operatively coupled to the control valve assembly  90 . The control rod  94  includes a first end  96  having threads and a second enlarged end  98 . The enlarged second end  98  is sized to be slidingly received into the interior of the connecting rod  92 . A threaded bushing  102  secures the enlarged end  98  of the control rod  94  within the connecting rod  92 . A pair of coil springs  104 ,  106  are also disposed within the connecting rod  92 . The coil springs  104 , 106  are disposed at either side of the enlarged portion  98  of the control rod  94 . In combination, the control rod  94  (and hence, spool valve  120 ) is linearly displaced under forces imparted by either of the coil springs  104 ,  106  as transferred by the dual piston assembly  14 . 
     Referring now to FIGS. 6 and 7, the control valve assembly  28  for directing fluid flow relative to the pumping assembly  10  is illustrated in perspective view. Control valve assembly  28  includes an actuated spool or spool valve  120 , valve body  122  and cap  125 . Valve body  122  includes a plurality of ports  132 ,  134 ,  136 ,  138 ,  140 ,  142 ,  144  providing fluid communication through the valve assembly  28 . Valve body  122  is threadedly secured at a first end  123  to the cylinder body  12  of the pump assembly  10 . Spool valve  120  is slidably received into the valve body  122 . Spool valve  120  includes a plurality of concentric fluid passageways  146 , 148  which permit fluid to communicate between opposed ports  130 - 144  of the valve body  122 . Additionally, spool valve  120  includes a vent passageway  150  for permitting fluid disposed between the upper face of the spool valve  120  and valve body  122  to be discharged to the used fluid receptacle  70 . Alternative venting approaches may be appreciated by those skilled in the art, and include external vents, relief valves, etc. 
     Still referring to FIGS. 6 and 7, spool valve  120  includes a pair of semi-spherical depressions  152 ,  154  sized to receive a portion of an encased ball  156  disposed on the valve body  122 . The encased ball  156  is inwardly biased by a spring  158  to engage the depressions  152 ,  154 . Together in combination the valve depressions  152 ,  154 , encased ball  156 , and spring  158  form a pair of detent stops for limiting the position of the spool valve  120  within the valve body  122 . Linear movement of the spool valve  120  results only upon exceeding a resistive force of the detent stops. Upon overcoming the detent reaction force, the spool valve  120  displaces within the valve body  122  until it reacts at either a top or bottom surface of the valve body  122 . In this manner, the detent stops tend to restrict the relative position of the spool valve  120  within the valve body  122  to one of two majority positions, illustrated either in FIGS. 1 and 2 or in FIG.  3 . Alternative control valve structures may be readily appreciated by those skilled in the relevant arts. One example of a non-piston actuated control structure is described hereinafter with reference to FIG.  8 . 
     Operation of the Embodiment of FIGS. 1-7 
     The closed fluid circulation system of an automatic transmission or other hydraulic fluid circuit  30  is accessed to provide fluid interconnection of the invention such that used fluid can be received from the fluid circuit  30  and fresh fluid can be simultaneously introduced by the invention to thereby replace the spent fluid. Suitable adapters (not shown) terminating in quick connectors are utilized to allow quick and convenient connection of conduit to a spent fluid outlet side of the accessed fluid circuit and to the return line side of the fluid circuit. When the internal fluid pump (which pressurizes the fluid circuit) is rendered operative, spent fluid is received into the pump assembly  10  at one of the working fluid chambers  24 ,  26  selected by the spool valve assembly  28  (based on the existing position of spool valve  120 ). Referring to FIG. 1 (illustrating fluid conditions immediately after spool valve  120  transitioned to the position of FIG. 1 ), used fluid from the transmission circuit  30  is introduced into the lower working fluid chamber  26  through port  82  from conduit  83  through the spool valve assembly  28 . The used fluid cannot be vented out of the used fluid chamber  26  since the spool valve  28  blocks fluid from port  86 . Therefore, as the used fluid enters working fluid chamber  26  through port  82 , piston assembly  14  is forced upward. As piston assembly  14  is upwardly displaced, each of the four fluid chambers  20 ,  22 ,  24 ,  26  simultaneously experience a change in volumetric conditions: the upper working fluid chamber  24  is discharging used fluid to a used fluid receptacle  70 , the upper pumping chamber  20  is receiving a charge of fresh fluid from the fresh fluid reservoir  60 , the lower working chamber  26  is receiving used fluid from the accessed transmission circuit  30 , and the lower pumping chamber  22  is introducing fresh fluid into the accessed transmission circuit  30 . 
     More specifically, used fluid in the upper working chamber  24  is forced out of port  84  and through passageway  148  of the control valve  120  and through conduit  85  to the used fluid receptacle  70 . Fresh fluid is drawn into the upper pumping chamber  20  from the fresh fluid reservoir  60  through conduit  62  and check valve  64 . The lower working pumping chamber  26  is receiving used fluid from the accessed transmission circuit  30  through conduit  46  and passageway  146  of control valve assembly  120 . The lower pumping chamber  22  forces new fluid out of port  87  through conduit  91  through check valve  50  through conduit  44  and into the return line side of the accessed transmission circuit  30 . Check valve  66  prevents fresh fluid from pumping chamber  22  from flowing back into the fresh fluid reservoir  62  through conduit  63 . 
     FIGS. 2 and 3 schematically illustrate the exchange apparatus of FIG. 1 at later points in time. Piston assembly  14  is illustrated in further upwardly displaced position relative to FIG.  1 . Referring to FIG. 2, the control valve assembly  120  remains in its position of FIG. 1, as the second end  98  of the control rod  94  has not yet contacted the lower coil spring  106 . As piston assembly  14  nears the end of its motion upward, the coil spring  106  is contacted and compressed which creates an increasing actuation force on the valve spool  120 . As piston assembly  14  continues to move upwardly, coil spring  106  is further compressed and overcomes the resistive force of the detent assembly. Referring to FIG. 3, once the detent force is exceeded, the control spool  120  transitions to its upper detented position. This reverses the cycle of the pump assembly  10  and causes the piston assembly  14  to downwardly move under pressure of the used fluid (introduced into the upper working fluid chamber  24  through port  80 ) from the accessed transmission circuit  30 . The piston assembly  14  continues to downwardly move until the second end  98  of the control rod  94  reacts against the upper coil spring  104 , biasing the control spool  120  downward back into the position of FIGS. 1 and 2. The cycle illustrated in FIGS. 1-3 thus repeating. This process of utilizing the automatic reversing cycles is repeated until it is determined that the fluid exchange is complete, i.e., upon comparison of the fresh fluid to the used fluid exiting the accessed circuit, exhaustion of fresh fluid reservoir, etc. 
     FIG. 8 illustrates another preferred embodiment of the present invention. Used and fresh fluid flow relative the pump assembly  500  is controlled by a remote controller device and a remote spool valve assembly. A reciprocating pump assembly  500  includes a reciprocating piston assembly  514  disposed within a cylinder body  501 . Cylinder body  501  is sealed with a lower cylinder end plate  503  and an upper cylinder end plate  505 . End plates  503 ,  505  are secured by threaded fasteners  507 . End plates  503 ,  505  are sealed to valve body  501  by a thin neoprene gasket material or other known sealing approaches. Connecting rod  519  is threadedly secured to an upper piston  518  and a lower piston  516 . Connecting rod  519  is slidably received through guide bore  520  with minimal clearance to promote sealing between the pumping chambers  520 ,  522 . Similarly, pistons  516 ,  518  are fitted within the cylinder body  501  with minimal clearance to promote sealing without creating excessive friction drag. 
     Piston  518  defines within the top half of cylinder assembly  501  a working fluid chamber  524  and a pumping fluid chamber  520 . Likewise, piston  516  defines within the bottom half of cylinder assembly  500  a working fluid chamber  526  and a pumping fluid chamber  522 . 
     End plate  505  includes two fluid ports: a used fluid power inlet port  533 , a used fluid discharge port  535 . End plate  505  also includes an access port  528  for receiving a threaded position sensor  527 . Fluid port  533  is coupled to a used fluid inlet conduit  569 . Port  535  is coupled to a used fluid discharge conduit  575 . 
     Opposite end plate  503  includes two fluid ports: a used fluid power inlet port  529 , and a used fluid discharge port  531 . End plate  503  also includes an access port for receiving a threaded position sensor  525 . Fluid port  529  is coupled to a used fluid conduit  571 . Fluid port  531  is coupled to a fluid discharge conduit  573 . 
     A bi-directional fluid channel  537  is provided to the upper half of cylinder body  501  and a bi-directional fluid channel  597  is provided to the lower half of cylinder body  501 . Fluid channel  537  is coupled to a fresh fluid two-way conduit assembly  547  through port  544 . Channel  539  is connected to a fresh fluid two-way conduit assembly  545  through port  543 . 
     A check valve  553  is disposed between conduit  547  and fresh fluid supply conduit  557 . Fresh fluid supply conduit is also connected through check valve  555  to conduit  545 . Conduit  545  is coupled to a fresh fluid discharge conduit  559  by a check valve  549 . Conduit  559  is connected to conduit  547  by check valve  551 . 
     Conduit  559  is coupled at one end to a female quick connector  561 , and a conduit  565  is connected at one end to a female quick connector  563 . Conduit  565  is coupled at another end to an electrically-operated three-way flow direction selector valve assembly  653  through an inlet port  659 . Valve  653  is coupled to conduit  559  through a fluid bypass outlet port  657 . Valve  653  is coupled to a used fluid inlet conduit  577  at an outlet port  655 . Conduit  557  is connected to a fresh fluid supply reservoir  638 . Reservoir  638  includes a float level switch  640  for signaling a low fluid level condition of the reservoir  638 . 
     A control valve assembly  598  includes a multiple ported valve body  599 , and an interiorly-received spool valve  619  maintained between end plates  601 ,  603 . End plates  601 ,  603  are secured to valve body  599  by threaded fasteners  607 . An electric solenoid assembly  626  is disposed relative the valve body  599 . Solenoid assembly  626  includes an electric coil  627 , and a rod  615  for actuating the spool valve  619 . Spool valve  619  includes a circumferential fluid channel  621 , a circumferential fluid channel  623 , and a vent passage way  624 . 
     Used fluid conduit  575  couples control valve assembly  598  at port  597  to the upper working fluid chamber  524 . Used fluid conduit  573  couples control valve assembly  598  at port  595  to the lower working fluid chamber  526 . Fresh fluid conduit  577  couples control valve assembly  598  at ports  591 ,  593  to circuit  530 . Used fluid conduit  569  couples control valve assembly  598  at port  589  to the upper working fluid chamber  524 . Used fluid conduit  571  couples control valve assembly at port  587  to the lower working fluid chamber  504 . A used fluid conduit  579  couples control valve assembly  598  at ports  583 ,  585  to used fluid receptacle  581 . 
     A microprocessor/controller assembly  631  receives signals from an activation switch  633 , position sensors  525 ,  527  and fluid level sensor  640 , and resultantly controls peripheral mechanisms  598 ,  653 . A power supply  635  may be a  12  volt electrical system of the vehicle being serviced. Microprocessor  631  is provided with an LED power-on indicator  647 , an LED exchange-on indicator  649 , and an LED bypass indicator  651 . Switch  633  is shown with three position configurations; a first switch position  641 , a second switch position  643 ; and a third switch position  645 . 
     Valve  653  provides a bypass configuration (fluid conduit  565  coupled to bypass conduit  657 ) for immediately returning used fluid to the accessed hydraulic circuit and an operative configuration (fluid conduit  565  coupled to conduit  577 ) for introducing fluid to the pump assembly  500 . 
     Similar to the before described piston-based reciprocating fluid exchanger, the piston based reciprocating pump assembly  500  and the control valve assembly  598  of the fluid exchanger of FIG. 8 can be constructed of a wide range of materials, including aluminum or magnesium alloys, steel alloys, plastic or polymer, and composite materials. Particular selection of materials for the pump assembly  500  are well within the scope of knowledge possessed by those skilled in the relevant arts. 
     Fresh fluid supply conduit  638  can be connected to a gravity feed tank system or can be connected to a pressurized fluid feed system. An additional feature may include a pump (not shown) to augment the flow of conduits  559  or  565  (preferably  565  since this tends to be more effective by providing more direct augmentation of low flow through the unit  500 ). A pump must be arranged to have proper flow alignment with the fluid conduit  565 , and may require a variable or fixed bypass. A variable pump would be controllable to provide fluid boost no greater than the output available from the fluid circulation circuit without creating cavitation in the internal pumping mechanism(s) of accessed hydraulic system or any other type of damage such as damage to the integrity of any internal sealing. A fixed boost pump would be set to offset the fluid resistance of the exchange unit. 
     Additional features of the microprocessor system may include volume of exchange displays, fluid clarity displays, fluid pressure displays, etc. Fluid clarity of the used fluid relative to the new fluid can be monitored for control purposes. 
     Operation of the microprocessor operated embodiment of FIG. 8 
     Fresh fluid reservoir  638  is filled with fresh fluid to activate float switch  640 . Power supply  635  is activated. Switch  633  is moved from its position  641  (off position) to position  643  which is its automatic operation. Quick connect couplers  561 ,  563  are connected to counterpart adapters which are in turn connected, one each to one side of the accessed fluid circulation circuit  530 , in this case a fluid cooling circuit of an automatic transmission. 
     The engine is started and the transmission is placed in Park, Neutral or Drive to render the transmission operative to circulate fluid into its fluid circulation (cooling) circuit or other accessible fluid circuit. Fresh fluid pumping chamber  522  is filled with fresh fluid from the prior fluid exchange and used fluid working chamber  524  is essentially filled with used fluid from the prior fluid exchange. Chambers  520  and  526  are essentially empty of fluid (the chambers could contain reciprocally corresponding fractions of their capacity depending on where the last fluid exchange left piston assembly  514  relative to the cylinder body  501 ). 
     Position sensors  525 ,  527 , when contacted by the piston  516 ,  518  indicate when each corresponding chamber is depleted of used fluid. Sensor  525  signals to microprocessor  631  that chamber  526  is essentially empty of used fluid. Microprocessor  631  activates or deactivates solenoid coil  627  to bias the spool valve  619  to its lower position under power of its return spring  628  (as shown). Spool valve  619  establishes fluid communication between ports  597  and  583  during the venting/exhausting/discharge of the used fluid contained in chamber  524  into receiver  581 . Spool valve  619  establishes fluid communication between ports  593  and  587  so that used fluid will be pumped under power of the transmission&#39;s fluid circulation pump into chamber  526 , which causes chamber  522  to discharge its fresh fluid into conduit  545 , through checkvalve  549 , conduit  559 , and through quick connect  561  to return to the transmission circuit  530 . Checkvalve  551  prevents that fresh fluid from chamber  522  from entering chamber  520  and vice-versa when the reciprocating cycle is reversed. 
     Simultaneously with the expulsion of fresh fluid from chamber  522 , fresh fluid flows into chamber  520  under the low pressure in chamber  520  caused by the upward movement of piston  518 . 
     Pistons  516 ,  518  upwardly move until piston  518  contacts position indicator  527  to signal the microprocessor  631  that the chamber  524  depletion of used fluid. The microprocessor deactivates/activates the solenoid  627  to raise spool valve  619  to its upper position, reversing the operations of the reciprocating assembly  500 . The timing of this deceleration, stop and reversal of the movement of piston assembly may be dictated by the instructions contained in the memory of microprocessor  631 . This reciprocating cycle is continued until completion of the exchange procedure. 
     FIGS. 9-11 illustrate another preferred embodiment of the present invention. A reciprocator assembly  700  (also shown in Figure B) is includes a rotor assembly  703 , a rotor receiving body  701 , and a cover member  705 . Rotor assembly  703  is received into the body with center aperture  761  of rotor  703  engaging center bearing post  712 . Bearing surface  714  engages bearing surface  758  of the retained rotor assembly  703 . Rotor assembly  703  has magnetic position sensors  717 ,  719  to signal the position of the rotor assembly  703  within the body  701  for control purposes. 
     In combination, the rotor assembly  703 , body  701 , and cover member  705  together define a pair of working (used) fluid chambers  779   a, b  and a pair of pumping (fresh) fluid chambers  777   a, b  as with the earlier-described embodiments, the volumes of the chambers  777 ,  779  vary with the relative reciprocal position of the rotor  703  within the body  701 . 
     Reciprocator body  701  and rotor  703  are constructed with clearances to allow a relatively free movement of rotor  703  reciprocally within the body  701 . In part, sealing between the defined fluid chambers  777 ,  779  of rotor  703  and reciprocator body  701  is accomplished by minimizing the clearances between rotor sliding surfaces  757  and the body  701 . 
     Reciprocator body  701  has four fluid ports, a pair of bi-directional fresh fluid ports  763 ,  767 , and a pair of bi-directional used fluid ports  765 ,  769 . Fresh fluid port  767  is coupled to a bi-directional fresh fluid conduit  741 . Bi-directional used fluid port  769  is coupled to a used fluid conduit  747 . Fresh fluid port  763  is coupled to a bi-directional fresh fluid conduit  739 . Used fluid port  765  connected to a bi-directional used fluid conduit  749 . A fresh fluid reservoir  721  contains a fresh fluid  723 . Tank  721  is connected to a fresh fluid fill conduit  727  which is in turn connected to both a check valve  729  and a check valve  731 . A controlled four way valve  771  is connected to a used fluid inlet delivery hose  743 , a used fluid discharge conduit  751 , a fluid conduit  747  to port  769 , and to fluid conduit  749  to port  765 . Operation of the valve  771  (mechanically or by a control circuit) controls the introduction of used fluid into the appropriate working fluid chamber  779   a  or  779   b.    
     Conduit  751  drains into a used fluid receiver  753 . Conduit  743  terminates at a female quick connect  773  which is coupled to the outlet side of an accessed fluid circulation system by suitable adapter means (not shown). 
     A priority valve assembly  733  includes of a valve body  735  and valve slide  737 . Valve body  735  has two ends ports, an end port  744  which is connected to conduit  741  and an end port  742  which is connected to conduit  739 . Valve body  735  has a side port  746  which is connected to a fresh fluid outlet delivery hose  745  which terminates at a female quick connect  775 . Female quick connect  775  is connected to the return side of the accessed fluid circulation system by suitable adapter means (not shown). The function of the priority valve  733  is to mechanically control the flow of fresh fluid from an appropriate pumping chamber  777  to the output conduit  745 . 
     If desired a boost pump can be used on conduit  743 . An electrical pressure differential switch can be used to control the boost pump to prevent excessive fluid flows of the system. 
     Similar to the operation of the above described exchange structures, the fluid exchange apparatus of FIGS. 9-11 is coupled to an accessed fluid circuit through quick connect couplers  773 ,  775 . Used fluid is introduced into the pump assembly  700  through port  769 , or port  765  as controlled by the valve  771 . The pressurized used fluid from the accessed fluid circuit reacts within the pump assembly to bias rotor  703  with the fluid chambers  777 ,  779  experiencing a resulting volumetric change. 
     Position sensors  717 ,  719 , which may be magnetic sensors or other known sensors, are used to indicate the relative position of the rotor  703  within the body  701 . A controller may receive a position sensor signal to appropriately alter the valve  771  to cyclically direct the pressurized used fluid into the working fluid chambers  779   a, b.    
     Referring now to FIG. 12, another preferred embodiment of the present invention is illustrated. The pump assembly  810  of this embodiment includes a pair of pistons  816 ,  818  reciprocating on a crank assembly  892  within a cylinder housing  812 . Pumping fluid chambers  820 ,  822  are defined between the top faces of the pistons  816 ,  818  and the walls of the cylinder housing  812 . Working fluid chambers  824 ,  826  are defined between the bottom faces of the pistons  816 ,  818  and the walls of the cylinder chamber  812 . Fresh fluid intake into the pumping fluid chambers  820 ,  822  is through fresh fluid conduits  830  from a fresh fluid reservoir  834 . Unidirectional check valves  836   838  control the fluid flow into the pumping fluid chambers  820 ,  822 . Fresh fluid expulsion into the accessed hydraulic fluid circuit is through unidirectional check valves  842 ,  844 , fresh fluid conduits  846  and coupling  847 . Piston  816 ,  818  movement within the cylinder  812  is regulated by the crank assembly  892  so that pistons  816 ,  818  are displaced in opposite directions (one drawing fresh fluid into the pumping chamber and one expelling fresh fluid in an alternate manner). 
     Used fluid from the accessed hydraulic fluid circuit  830  via coupling  849  is directed into one or the other working fluid chambers  824 ,  826  through associated used fluid conduits  848 . Rotary valving  850  may be used to control the timing and flow of used fluid into alternating working fluid chambers. The rotary valving  850  may be replaced with alternative valving as appreciated by those skilled in the relevant arts. It is appreciated that the purpose of the valving is to direct used pressurized fluid into a working fluid chamber  824 ,  826  to drive the associated piston  816 ,  818  upwardly (and as a result of crank  892  action, drive the other piston  816 ,  818  downwardly). In this manner, used fluid is being directed into a first working chamber  824  from the accessed hydraulic circuit  830 , used fluid is being expelled into a used fluid receptacle  881  by the other working chamber  826 , and simultaneously, fresh fluid is alternatively being drawn into the pump assembly  810  into a first pumping chamber  820 , and fresh fluid is being expelled into the accessed hydraulic circuit  830  by a second pumping chamber  822 . The cyclic procedure continuing until interruption by the operator, fresh fluid reservoir depletion, etc. An additional feature of the system may include an auxiliary power supply  860  for assisting in the pumping process. Such a power supply  860  may be an electric motor (constant or variable speed) directly or intentionally coupled to the crank assembly. An electric motor may be controlled via a control system (not shown) or a mechanical clutch system to provide a fluid boost when required. Operation of the auxiliary power supply  860  may thus be limited to particular hydraulic circuit systems requiring boost power to effect the fluid exchange. 
     Yet another embodiment of the present invention is illustrated in FIGS. 13 &amp; 14. The invention of the present application includes a reciprocating pump assembly  900  having a rigid cylinder body  912  and an interiorly-received dual fluid separation structure  914 . In this preferred embodiment the dual fluid separation structure  914  is a dual piston  916 ,  918  assembly. The cylinder body  912  and dual piston assembly  914  together define two fresh fluid working chambers  920 ,  922  disposed substantially between the outer piston ends  916 ,  918  of the dual piston assembly  914 . Two used fluid pumping chambers  924 ,  926  are also defined and are disposed away from the working chambers  920 ,  922  and within the cylinder body  912 . The working chambers  920 ,  922  receive pressurized fluid from a pressurized fresh fluid reservoir  960 . Fluid flow relative to the pump assembly  900  is controlled by an actuated control valve assembly  928 . The pressurized fluid, used as a power medium to drive the reciprocating pump  910 , may be supplied by an external source. The pumping chambers  924 ,  926 , on the other hand, simultaneously expel used fluid into the used fluid receptacle  970  from the circuit  930 . The working chambers  920 ,  922  are interconnected by a guide bore  932  which passes through the cylinder body  912 . In operation, the volumes of each of the chambers  920 ,  922 ,  924 ,  926  are variable and determined by the relative position of the dual piston assembly  914  within the cylinder assembly  912 . In this embodiment, the working chambers  920 ,  922  are coaxial with the pumping chambers  924 ,  926 . It should be appreciated that the working chambers  920 ,  922  and pumping chambers  924 ,  926  are of a substantially cylindrical shape in this preferred embodiment, however, other configurations are possible. 
     The pump assembly  900  is interconnected to an accessed hydraulic fluid circuit  930  through quick-connect fluid couplers  490 ,  942 , and fluid conduits  944 ,  946 . Used hydraulic fluid from the accessed hydraulic circuit  930  enters the exchange apparatus through quick-connect coupler  940  and a fresh hydraulic fluid flows out of the exchange apparatus and through quick-connect coupler  942 . The flow rate of the used and fresh hydraulic fluid is substantially equivalent during the exchange process. The pump assembly  900  is additionally coupled to a bulk fluid reservoir  960  or similar external fresh fluid source through associated fluid conduit  962 . The pump assembly  900  is additionally coupled to an external used fluid receptacle  970 , such as an oil drain or external tank of typical vehicle maintenance facilities. A flow alignment device, as illustrated in applicant&#39;s existing U.S. Pat. No. 5,472,064, may be utilized to practice the present invention. 
     Still referring to FIG. 1, a plurality of orifices  980 ,  982 ,  984 ,  985 ,  986 ,  987 ,  988 ,  989  are interconnected to the pump assembly  900  at the pumping chambers  924 ,  926  and the working chambers  920 ,  922 , each of which is adapted to provide fluid communication from or into respective chambers. Working chambers  920 ,  922  are fluidly coupled to receive fresh hydraulic fluid from the hydraulic source  960  through ports  987  and  989 . Working chambers  920 ,  922  are additionally fluidly coupled to permit discharge of the fresh hydraulic fluid to the accessed hydraulic circuit  930  through ports  986  and  988 . As described herein, the fluid flow through respective fluid ports is controlled by a spool valve assembly  928 . Depending on the local pressure conditions, pumping chambers  924 ,  926  are fluidly coupled to either the used fluid receptacle  970  or the inlet conduit  946 . 
     Control valve assembly  928  includes an actuated spool or spool valve  9120 , valve body  9122  and cap  9125 . Valve body  9122  includes a plurality of ports  9132 ,  9134 ,  9136 ,  9138 ,  9140 ,  9142 ,  9144  providing fluid communication through the valve assembly  928 . Spool valve  9120  is slidably received into the valve body  9122 . Spool valve  9120  includes a plurality of concentric fluid passageways  9146 ,  9147 ,  9148 ,  9149  which permit fluid to communicate between opposed ports of the valve body  9122 . Additionally, spool valve  9120  includes a vent passageway  9150 . 
     The closed fluid circulation system of an automatic transmission or other hydraulic fluid circuit  930  is accessed to provide fluid interconnection of the invention such that used fluid can be received from the fluid circuit  930  and fresh fluid can be simultaneously introduced by the invention to thereby replace the spent fluid. Suitable adapters (not shown) terminating in quick connectors are utilized to allow quick and convenient connection of conduit to a spent fluid outlet side of the accessed fluid circuit and to the return line side of the fluid circuit. Fresh fluid (pump power medium) is received into the pump assembly  910  at one of the working fluid chambers  920 ,  922  selected by the spool valve assembly  928  (based on the existing position of spool valve  9120 ). Referring to FIG. 13, used fluid from the transmission circuit  930  is introduced into the lower pumping fluid chamber  926  through port  985 . The used fluid cannot be vented out of the used fluid chamber  926  since the spool valve  928  blocks fluid from port  982 . As the fresh fluid enters working fluid chamber  920  through port  989 , piston assembly  914  is forced upward (FIG. 13 depicts the condition of the spool valve  928  immediately subsequent to its transition). As piston assembly  914  is upwardly displaced, each of the four fluid chambers  920 ,  922 ,  924 ,  926  simultaneously experience a change in volumetric conditions: the upper pumping fluid chamber  924  is discharging used fluid to a used fluid receptacle  970 , the upper working chamber  920  is receiving a charge of fresh fluid from the fresh fluid reservoir  960 , the lower pumping chamber  926  is receiving used fluid from the accessed transmission circuit  930 , and the lower working chamber  922  is introducing fresh fluid into the accessed transmission circuit  930 . 
     It is understood that even though numerous characteristics and advantages of the present invention have been disclosed in the foregoing description, the disclosure is illustrative only and changes may be made in detail. Other modifications and alterations are within the knowledge of those skilled in the art and are to be included within the scope of the appended claims.