Abstract:
A rotary flow combiner allows flow from multiple pressure compensated hydraulic pumps; with or without load sensing to be combined into a single outlet. The flows are combined in such a way that each input to the rotary flow combiner has equal flow. The flow from each pump is optimized in such a way that the output from the rotary flow combiner can achieve the maximum range of flow and pressure and so that all the pumps in the multiple pump system are supplying fluid flow at all times. A check valve can allow the rotary flow combiner to pull hydraulic fluid direct from a reservoir in parallel to a lower flow pump such that the volume of flow from the lower pump combined with the fluid drawn directly from the reservoir will match the flow from the higher flow pump.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   Provisional application for patent No. 60/405,674 of Aug. 24, 2002 with the same title: “Equalizing Flow From Pressure Compensated Pumps, With or Without Load Sensing, in a Multiple Pump Circuit” which is hereby incorporated by reference. Applicant claims priority pursuant to 35 U.S.C. Par. 119 (e) (I). 

   Statement as to rights to the invention made under federally sponsored research and development: not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to improving the performance of two or more pressure compensated pumps, with or without load sensing, that supply fluid to a single driven circuit. The invention uses a rotary type flow divider operating in reverse to make fluid flow through the pumps at the same rate of flow even when the pumps are limited to different output pressures. 
   2. Background Information 
   It is often necessary to use more than one pressure compensated pump, with or without load sensing, to supply a hydraulic circuit&#39;s highest flow demand. A prior art hydraulic system might use separate pumps, with separate drive motors for each pump, to feed into a common manifold that supplies pressurized hydraulic fluid to a circuit. In such a prior art arrangement there is an attempt to set each pump so that they will operate at the same sensed pressure level such that when there is a need for pressurized flow that both pumps will supply at least part of the flow. The main problem with such a prior art arrangement is that no matter how closely the pumps are set, one pump will almost always start first and the other pump or pumps sensing the increased pressure will not operate. Even when it is possible to set the pumps to supply flow simultaneously, contamination, wear, spring deterioration and other variations will soon change such that one pump will start off supplying flow and the other pump or pumps will not start until the system requirements exceed the capacity of the first pump. The concept can be implemented with two or more pumps. 
   The prior art multiple pump system allows one pump to lead and the other pumps to start flowing when pressure drops due to a flow demand higher than the first pump can supply. One pump starts and the others start as needed. Some pump manufacturers recommend their pumps be set with triggering pressures 100–150 PSI apart so that they will not try to start flowing at the same time. The problem with starting the prior art system pumps at nearly the same pressure is that the first pump can be forced to no flow when the second pump flow reaches the manifold. In this situation the pumps can oscillate on and off so fast that they suffer mechanical damage. 
   Thus it can be seen that there is a need for a multi-pump system that will allow for multiple pumps to supply hydraulic fluid to a single hydraulic circuit. 
   SUMMARY OF THE INVENTION 
   A rotary flow divider is normally used to divide the flow from a single pump to two or more separate circuits. Operating in reverse of normal installation, the rotary flow divider can become a rotary flow combiner, combining two or more flows instead of dividing them. Normally hydraulic fluid from a pump is fed into a single inlet of a rotary flow divider, is ported to two or more identically sized hydraulic motors in the rotary flow divider and flows out two or more outlets to supply hydraulic fluid in equal volume to two or more circuits. The hydraulic motors of the rotary flow divider have a common shaft so they must turn at the same rate and since they are equal in size they pass the same flow. Equal flow leaving each hydraulic motor outlet of the rotary flow divider is sent to devices needing the same flow even though the devices may operate at different pressures. 
   In this invention the rotary flow divider&#39;s normal outlets become inlets for the rotary flow combiner receiving flow from multiple pump sources and combines them into a common flow output. Since the hydraulic motors of the rotary flow combiner perform like pumps when driven it does not matter if the pressure compensating pumps with or without load sensing have exactly the same pressure setting. When the circuit needs flow the pressure drop at the rotary flow combiner outlet also gives a pressure drop at both inlets causing the pump compensators to shift both pumps on flow and to maintain them on flow. With both pumps flowing pressure at the outlet of the flow combiner equalizes. 
   In another aspect of the invention, when the system requires more fluid than the pumps are capable of producing, pressure drops below compensator setting of both pumps and they will go to full flow. If one pump has less flow than required to meet the demand it will see a vacuum at its outlet since the rotary flow combiner acts as a pump, at this point hydraulic fluid will be drawn directly from a reservoir to make up the required flow difference. This differential flow is powered by the pump with the larger flow through the rotary flow combiner. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates the preferred embodiment of the present invention prior to actuation of any actuator in the driven circuit; 
       FIG. 2  illustrates the operation of the preferred embodiment of the present invention when the embodiment is functioning with identical pumps at low pressure; 
       FIG. 3  illustrates the operation of the preferred embodiment of the present invention when the embodiment is operating with pumps of different flows at less than maximum pressure; 
       FIG. 4  illustrates the operation of the preferred embodiment of the present invention when the embodiment is operating with pumps of different flows near maximum pressure; 
       FIG. 5  illustrates the operation of the preferred embodiment of the present invention when the embodiment is operating with pumps at different pressures while an actuator is moving at a pressure higher than the low pressure pump can reach; 
       FIG. 6  illustrates the operation of a second embodiment of the present invention including three input pumps. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates the preferred embodiment of the present invention. As shown in  FIG. 1  a hydraulic system  100  comprises two pressure compensated pumps  1 A and  1 B powered by drives  3  which can be electrical or can be internal combustion engines or a combination of one electrical motor and one engine. The system  100  supplies fluid power to any number of actuators such as fluid driven rotating actuators  12 ,  13  or a fluid driven linear actuator  14  in driven circuit  200 . Three position solenoid controlled valves  8  can be used to control the operation of the rotating actuators  12 ,  13  and linear actuator  14  while the meter out flow controls  9  can set the flow requirements for each actuator  12 ,  13 ,  14 . Filter  10  filters the flow of hydraulic fluid back to reservoir  6 . Anti-cavitation check valves  5 A and  5 B, have 1 PSI springs in them so they can open and keep the rotary flow combiner  7  from starving for hydraulic fluid from a either pump  1 A,  1 B. Flow meters  2  can show the flow of each pump  1 A,  1 B and pressure gauges  24  and  25  can show pressure from the pumps  1 A and  1 B in supply lines  20  and  23 . Pressure gauge  27  shows the pressure in line  26 , which is the outlet of the rotary flow combiner  7  and the supply for the driven circuit  200 . 
     FIG. 2  illustrates the hydraulic system  100  with the hydraulic motor  12  using, for example, 22 gallons per minute (GPM) flow as set by the meter out flow controls  9 . The rotary flow combiner  7  accepts fluid from the first pump  1 B that starts flowing and immediately the operation of the rotary flow combiner  7  will lower the pressure in line  23  enough to trip the pump  1 A making it flow as well. Check valve  5 A connected parallel to pump  1 A, keeps the left rotary motor  7 C of the rotary flow combiner from cavitating by allowing hydraulic fluid to flow to it from the reservoir  6  until pump  1 A produces flow. Pressure on gauges  24 ,  25  and  26  will read at or near the same pressure (750 PSI) while the rotary motors  7 C and  7 D are running. Flow meters  2 A and  2 B will show identical flow when both pumps  1 A and  1 B are operating. Both pumps  1 A and  1 B will give equal flow until reaching set flow of meter out flow control  9 , thus the system makes continual effective use of both pumps  1 A and  1 B. 
   Rotary flow dividers have a characteristic referred to as ‘intensification’ when used in the conventional manner. If there is resistance to flow out of one outlet of a rotary flow divider, then pressure in that outlet will intensify as the rotary flow divider will attempt to maintain the same volume of flow to each outlet. In this invention, with the rotary flow divider reversed to be a rotary flow combiner  7 , fluid entering the inlets  7 A and  7 B is deintensified so if one pump  1 A is at 1000 PSI and the other pump  1 B is at 0 PSI, then the outlet line  26  will be at 500 PSI. (1000+0/2=500). 
     FIG. 3 . Illustrates the hydraulic system  100  of the hydraulic motor actuator  12  using hydraulic fluid at a rate again of 22 GPM as set by meter out flow controls  9 . In this arrangement of the driven circuit  200  the left pump  1 A is set to pump no more than 8 GPM so anti-cavitation check valve  5 A is forced open by atmospheric pressure which pushes an extra 3 GPM into line  23 . The same result would occur if left pump were replaced with a pump only capable of producing 8 GPM flow. Because of the vacuum, gauge  25  will actually read a pressure slightly below zero such as −2 PSI. Pump  1 B is at 11 GPM and 1200 PSI. Note that pump  1 B is actually capable of pumping 15 GPM at 1500 PSI and that pump  1 B provides the extra power that allows the rotary flow combiner  7  to pull additional hydraulic fluid through the check valve  5 A. Since only one pump  1 B is at pressure, hydraulic fluid going to the hydraulic motor actuator  12  is only at half pressure 600 PSI; (1200 psi+0 psi)/2=600 PSI. Flow meter  2 A is showing 8 GPM while flow meter  2 B is showing 11 GPM with the flow through the check valve  5 A making up the rest of the 22 GPM flow. 
     FIG. 4  illustrates the hydraulic system  100  with said driven circuit  200  with the hydraulic motor actuator  12  still requiring hydraulic fluid at the same 22 GPM rate as set by meter out flow control  9 . In this case the left pump  1 A is only capable of pumping 8 GPM and the pressure required to operate the hydraulic motor actuator  12  is higher than half the set pressure of pump  1 B. The pump  1 B will go to full pressure and the flow from pump  1 B will be reduced (a characteristic of pressure compensated pumps). When pump  1 B flow has dropped to 8 GPM, flow from pump  1 A will push into the left inlet  7 A of the rotary flow combiner  7  at 500 PSI and the rotary flow combiner will push 16 GPM at 1000 PSI into the driven circuit  200 . This flow is not enough to meet the full requirements of the driven circuit  200  but will keep the driven circuit  200  working. In all cases, flow into the inlets  7 A and  7 B of the rotary flow combiner  7  will be equal when any flow is present. 
     FIG. 5  illustrates the driven circuit  200  with the hydraulic motor actuator  12  still requiring hydraulic fluid at a rate of 22 GPM as set by meter out flow control  9 . In this case the hydraulic motor actuator can use 22 GPM at a pressure above what the lowest pressure pump  1 A or  1 B can supply. The pump  1 A can produce 15 GPM at 1300 PSI and the pump  1 B can produce 15 GPM at 1500 PSI. The rotary flow combiner  7  in this case will produce output flow of hydraulic fluid to the driven circuit  200  at 22 GPM and 1400 PSI maximum and 15 GPM up to 1500 PSI. Again although pump  1 A is not fully capable of meeting the load requirement both pumps will operate at capacity. Without a rotary flow combiner  7  this combination of pumps, with flows into a manifold, could only produce 15 GPM at pressures above 1300 PSI because the lower pressure pump  1 A would compensate to no flow above this pressure. 
     FIG. 6  illustrates the driven circuit  200  with the hydraulic motor actuator  12  still requiring hydraulic fluid at a rate of 22 GPM as set by meter outflow controls  9 . This hydraulic system  300  for example uses the same driven circuit  200  but uses three pressure compensated pumps without load sensing  1 A,  1 B and  1 C that feed into the inlets  70 A,  70 B,  70 C of a three motor rotary flow combiner  70 . The operation of the three motor rotary flow combiner  70  is similar to that of the two motor rotary flow combiner  7  in that each rotary motor  70 D,  70 E and  70 F must turn at the same speed and allow for the same flow rates from each inlet  70 A,  70 B and  70 C regardless of flow or pressure settings. The rotary motors  70 D,  70 E and  70 F can be gear motors for example sharing a common shaft (not shown) that keeps them rotating at a proportional rotary speed such as the same speed. Fluid from the third pump  1 C is supplied through line  29  to inlet  70 C and gauge  28  can monitor pressure in line  29 . 
   Using a rotary flow combiner with motors having different ratio flows (not shown) would allow different flow rated pumps to use all their flow output at a pressure without restricting the higher flow ones. 
   A specific example of a useful application is when separate internal combustion engines are driving pumps of the same or different volumes at the same or different pressures. Each internal combustion engine would give its required portion of flow and operate at a comparable horsepower rating for any flow requirement. Without the equal flow provided by the rotary flow combiner, one engine would do all the work most of the time, while the other burns fuel and does no useful work. Neither engine would be operating efficiently. Adding the rotary flow combiner  7  as shown above causes both engines to do a significant portion of the work at all times resulting in even wear on the engines and in more efficient operation. 
   A benefit of this invention is that the pumps in a multi-pump system can be set as closely as possible to the same pressure without causing the pumps to override each other. An additional benefit of this invention is that a conventional multiple pressure compensated pump with or without load sensing circuit can have a noticeable pressure drop as the lead pump reaches its maximum flow and the next pump starts flowing. This pressure drop will be at least as much as the pumps pressures are set differently and even more for a short period of time as the lagging pump or pumps respond and start flowing.