Abstract:
A fluid pumping system for an automatic transmission includes a primary pump operable to draw fluid from a sump to a main delivery line to a main hydraulic circuit of the transmission. A main circuit pressure regulator regulates pressure to the main circuit and exhausts excess fluid to a secondary delivery line to a secondary hydraulic circuit of the transmission. A secondary pump operates to draw fluid from the suction line to a discharge line. A check ball valve operates to permit one way flow from the discharge line to the secondary delivery line. A secondary circuit pressure regulator regulates pressure to the secondary circuit and operates to exhaust flow from the discharge line to a return line or from the discharge line and the secondary delivery line wherein the return line is in continuous fluid communication with the suction line to reduce hydraulic horsepower expended by the secondary pump.

Description:
TECHNICAL FIELD 
     The present invention relates to a fluid pumping system for an automatic transmission. 
     BACKGROUND OF THE INVENTION 
     A power transmission has a fluid pumping system, driven by an engine to deliver fluid to a transmission hydraulic system. The hydraulic system distributes pressurized oil for such transmission operations as shifting gears, torque conversion, lubrication, and cooling. During vehicle acceleration from a low engine speed, relatively high pressure is needed to quickly transfer torque through the gears. Therefore the pump of the fluid pumping system draws substantial energy from the engine. The single pump must be sized to accommodate such maximum flow and pressure requirements of the transmission. This also means that the pump produces excess capacity during lower flow demand operating conditions such as when the vehicle is cruising at higher engine speed. The excess fluid is exhausted through a regulator valve and is therefore a power loss in the system. One proposed solution to improve efficiency is to include a second pump in the pumping system, operating to supplement a lower capacity main pump only during maximum flow demand. 
     The transmission hydraulic circuit to which the fluid pumping system supplies pressurized fluid may include both a low pressure circuit and a separate high pressure circuit each having individual pressure and flow requirements. The low pressure circuit may deliver lubrication throughout the transmission, whereas the high pressure circuit may deliver high pressure fluid to quickly activate friction devices such as clutches and bands in the gearing mechanism. Since the pump scavenges energy directly from the engine, it is desireable to reduce the pump energy draw when not needed to meet the requirements of the automatic transmission thereby reducing fuel consumption. 
     SUMMARY OF THE INVENTION 
     The present invention is for a fluid pumping system for an automatic transmission, and particularly to support two independent hydraulic circuits within the transmission hydraulic system. The pressure delivered to each of the independent hydraulic circuits is individually regulated to that particular circuit&#39;s requirements. The fluid pumping system provides this functionality while improving fuel efficiency. 
     The primary pump is in continuous flow communication with the main hydraulic circuit and selectively connected to the secondary circuit through a main circuit regulator. The secondary pump is connected to the secondary circuit via a one-way check ball valve. A secondary circuit regulator regulates pressure delivered to the secondary circuit. 
     As excess pump flow is developed from the primary pump during certain operating conditions, the main circuit regulator may open to route excess primary pump flow directly to the secondary hydraulic circuit. If the flow provided by the primary pump is sufficient to meet the demands of the secondary circuit, then the secondary circuit regulator shifts to re-circulate flow from the secondary pump back to the sump and not to the secondary circuit. Here the secondary pump essentially freewheels as it operates against zero pressure, substantially reducing the horsepower draw, when the engine is operating at high speeds sufficient for the primary pump to meet the flow demands of both circuits or when there is low flow requirements. This mode of operation improves vehicle fuel economy. Further, if the primary pump is delivering more flow than is needed by the secondary circuit, the excess flow from the primary pump may be diverted by the secondary circuit regulator back to the sump. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The FIGURE is a schematic of a fluid pumping system for use in an automatic transmission. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the FIGURE, there is shown a fluid pumping system, generally designated as  10 , to supply fluid to a hydraulic valve body  12  of an automatic transmission. The hydraulic valve body  12  includes two circuits: a high pressure, main circuit  14  and a low pressure, secondary circuit  16 , each of which is delivered fluid from the fluid pumping system  10  individually. The secondary circuit  16  may deliver low pressure fluid for such functions as lubricating the automatic transmission, operating a torque converter valve solenoids, or cooling. The main circuit  14  delivers high pressure fluid to the gearing mechanisms of the transmission such as fluid-operated clutches and brakes or continuously variable units. 
     The fluid pumping system  10  includes a primary pump  18  and a secondary pump  20 . A common sump  22  and filter  24  are in continuous fluid communication with inlets to each pump  18 , 20  by a suction line  26 . Pressurized fluid flows out a primary pump outlet  28  to a high pressure, main delivery line  30 , which is in continuous fluid communication with the main circuit  14  of the transmission valve body  12  for delivering high pressure fluid thereto. The primary pump outlet  28  is also in selective fluid communication with a secondary delivery line  32  to deliver low pressure fluid to the secondary circuit  16  of the transmission valve body  12 . A two-position, main circuit pressure regulator  34  is disposed intermediate the primary pump outlet  28  and the secondary delivery line  32  and includes a feedback line  36  from the main delivery line  30  on one side of the pressure regulator  34  and a main circuit pressure signal  38  on the opposing side (left side in the FIGURE). A spring  40  biases the main circuit regulator valve  34  to the right, as shown, to prevent flow from the primary pump outlet  28  to the secondary delivery line  32 . The main circuit regulator  34  is connected to regulate pump discharge to the main line  30  by exhausting fluid therefrom to the secondary delivery line  32  in response to main line pressure above the main circuit pressure signal  38 . When the main delivery pressure is greater than the main circuit pressure signal  38 , the two-position main circuit pressure regulator  34  shifts to the left, compressing the spring  40 , and opening the flow path from the primary pump outlet  28  to the secondary delivery line  32 . 
     A secondary pump outlet  42  of the secondary pump  20  is in continuous fluid communication with a discharge line  44  which extends to a three-position, secondary circuit pressure regulator  46 . The secondary circuit regulator  46  includes two inputs—the discharge line  44  and the secondary delivery line  32 —and effectively one output to a common return line  48  to the suction line  26 . A secondary feedback line  50  connects the secondary delivery line  32  to one side of the secondary circuit regulator  46 . A secondary circuit signal  52  provides a signal pressure on the opposing side, shown on the left in the FIGURE. The secondary circuit regulator  46  operates to balance the pressures in the secondary delivery line  32  to the secondary circuit pressure signal  52 . 
     Upstream of the secondary circuit regulator  46 , the discharge line  44  is connected to the secondary delivery line  32  via a check ball valve  54 . A pressure differential across the check ball valve  54  operates to move the valve, allowing flow from the discharge line  44  to the secondary delivery line  32 , while not allowing flow from the secondary delivery line to the discharge line. 
     The secondary circuit regulator  46  has three regulating positions of operation. The first position, shown in the FIGURE as  56 , does not exhaust flow through the regulator  46  to the return line  48  as the fluid pressure in the secondary delivery line  32  is less than the secondary circuit signal  52 . A pressure differential operates to move the check ball valve  54 , allowing flow from the secondary pump  20  to be directed to the secondary delivery line  32 . If there is flow in the secondary delivery line  32  from the primary pump  18 , it is added to the flow from the secondary pump  20 . 
     In the second position  58 , shown as the center position in the FIGURE, all or a portion of the flow from the secondary pump  20 , through the discharge line  44  is allowed to flow through the secondary circuit regulator  46  and to the return line  48 . Some of the secondary pump flow may also flow through the check ball valve  54  to the secondary delivery line  32 . In this instance, fluid is re-circulated to the suction line  26  relieving the secondary pump  20  of a portion of the hydraulic work of drawing fluid from the sump  22 . In the second position  58 , any fluid in the secondary delivery line  32  from the primary pump  18  is not exhausted through the secondary circuit regulator  46 , but may flow to the secondary circuit  16 . 
     In the third position  60 , shown as the right position in the FIGURE, continued pressure buildup in the secondary delivery line  32  as compared to the secondary circuit signal  52  necessitates more exhausting through the secondary circuit regulator  46 . A portion of the flow from the primary pump  18  through the secondary delivery line  32  and all the flow from the secondary pump  20  through the discharge line  44  are exhausted through the secondary circuit regulator  46  to the return line  48 . The third position  60  is utilized when limited fluid flow is needed by the secondary circuit  16  and the need is met by the primary pump  18 . 
     Having described the basic operations of the main and secondary circuit pressure regulators  34 , 46 , their role may be better understood by a discussion of their typical operation in serving the transmission valve body  12 . 
     For example, the secondary circuit  16  may receive fluid flow in three alternative ways. First, the primary pump  18  may solely deliver fluid if excess fluid is being diverted through the main circuit regulator  34  to the secondary delivery line  32  because the main delivery line pressure is greater than required by the main circuit  14 . In this case the secondary circuit regulator  46  may be in the second or third position  58 , 60 . Second, the secondary pump  20  may solely deliver fluid if the main circuit regulator  34  is closed to direct all flow from the primary pump  18  to the main circuit  14 . In this case the secondary circuit regulator  46  may be in the first or second position  56 , 58 . If the secondary circuit  16  requires higher flows than either pump can deliver individually, then both pumps  18 , 20  may deliver fluid thereto, assuming the primary pump  18  is producing pressure in excess of the main circuit signal  38 . In this instance, the secondary circuit regulator  46  may be in the first or second position  56 , 58 . 
     As relative pump capacity is increased by either engine input speed displacing more fluid or decreased flow requirements to the secondary circuit  20 , then excess fluid may be re-circulated to the suction line  26  at the pump inlets. All of the flow from the secondary pump  20  to the discharge line  44  may be re-circulated if the primary pump  18  is sufficient to meet the demands of the main and secondary circuits  14 , 16 . Or a portion of the flow from the secondary pump  20  to the secondary delivery line  32  may be exhausted and re-circulated to the suction line  26 . Finally, a portion of the flow from the primary pump  18  to the secondary delivery line  32  may be exhausted and re-circulated to the suction line  26  if the primary pump is supplying greater pressure to the secondary delivery line than the secondary circuit signal  52  indicates is needed. 
     The present invention is for a fluid pumping system  10 , which supplies fluid to two distinct hydraulic circuits  14 , 16 , regulatable at different pressures and flows. The primary pump  18  is a higher pressure pump which supplies regulated flow to a main hydraulic circuit  14 . The secondary pump  20  is a lower pressure pump which may supply a portion or all of the flow needed to support the secondary hydraulic circuit  16 . Excess flow developed by the primary pump  18  may be exhausted to the secondary circuit  16  to supplement or supplant the function of the secondary pump  20 . In such a case, the secondary circuit pressure regulator  46  re-circulates excess flow from the secondary pump  20  to the pump suction line  26 . Therefore the fluid pumping system provides flexibility to the transmission hydraulic system by having two regulatable outputs while reducing pumping losses without sacrificing volumetric efficiency in meeting a broad range of flow requirements in two different output hydraulic circuits. 
     The foregoing description of the preferred embodiment of the invention has been presented for the purpose of illustration and description. It is not intended to be exhaustive, nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiment may be modified in light of the above teachings. The embodiment was chosen to provide an illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, the foregoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the following claims.