Abstract:
A pump system includes a closed-loop fluid circuit and an open-loop fluid circuit. The closed-loop fluid circuit includes a motor for rotating a first component connected to the closed-loop fluid circuit. A closed-loop pump drives the motor up to a first maximum rotational speed. The open-loop fluid circuit includes an open-loop pump for driving a second component connected to the open-loop fluid circuit. A control circuit includes a control valve for switching the outflow from the open-loop pump. The control valve selectively connects the open-loop pump to the closed-loop fluid circuit and simultaneously disconnects the open-loop pump from the open-loop fluid circuit. When the open-loop pump is connected to the closed-loop circuit, the closed-loop pump and the open-loop pump drive the motor at a second rotational speed greater than the first maximum rotational speed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Patent Application Serial No. 61/503,761, filed Jul. 1, 2011, entitled “Transit Mixer with Combination Open- and Closed-Loop Pump System,” the disclosure of which is hereby incorporated by reference herein in its entirety. 
     
    
     INTRODUCTION 
       [0002]    Many vehicle and equipment hydraulic systems use a closed loop to drive a hydraulic motor and an open loop pump to drive hydraulic motors and cylinders. The closed loop pump and motor system may be used to operate a transit mixer drum, drive wheel motors in a gearbox to propel a vehicle, or drive a motor to operate an auxiliary function such as a platform, a head, a conveyor, etc. The closed loop fluid circuit and the open loop fluid circuit usually operate independent of each circuit. 
         [0003]    In one particular example, transit mixers, also known as concrete or cement trucks, are used to move, mix, and pour large quantities of concrete at construction sites. Typically, the hydraulic system to rotate the mixing drum and control the auxiliary equipment includes the two separate fluid circuits described briefly above. The first fluid circuit includes a pump that can rotate the drum at low speed and high speed. Low speed rotation is used to prevent the concrete from hardening once mixed, typically during transit. High speed rotation is used when mixing the concrete or when cleaning out the drum. In that regard, a large pump is typically required to rotate the mixer even though its full capacity is rarely utilized. The second fluid circuit uses a smaller pump (as compared to the first pump) for driving auxiliary equipment on the transit mixer, for example, the tag axle, chute lift, etc. This pump is typically only used at the construction site for delivering the mixed concrete. 
       SUMMARY 
       [0004]    In one aspect, the technology relates to a pump system including: a closed-loop fluid circuit including: a motor for rotating a first component connected to the closed-loop fluid circuit; and a closed-loop pump for driving the motor at a first maximum rotational speed; an open-loop fluid circuit including an open-loop pump for driving a second component connected to the open-loop fluid circuit; and a control circuit including: a control valve for selectively connecting the open-loop pump to the closed-loop fluid circuit while simultaneously disconnecting the open-loop pump from the open-loop fluid circuit, wherein when the open-loop pump is connected to the closed-loop circuit, the closed-loop pump and the open-loop pump drive the motor at a second maximum rotational speed greater than the first maximum rotational speed. In an embodiment, the closed-loop fluid circuit further includes a control spool for controlling a direction of rotation of the closed-loop pump, such that when the control spool is in a first position, an output flow from the closed-loop pump is directed in a first direction through the closed-loop circuit. In another embodiment, the control circuit further includes a shuttle valve system for controlling an output flow from the open-loop pump, such that when the open-loop pump is connected to the closed-loop circuit and when the shuttle valve system is in a first position, the output flow from the open-loop pump is directed in the first direction through the closed-loop circuit. In yet another embodiment, the pump system further includes a charge pump for filling each of the closed-loop fluid circuit and the open-loop fluid circuit with a hydraulic fluid. In still another embodiment, the pump system further includes a common motor for driving each of the open-loop pump, the closed-loop pump, and the charge pump. 
         [0005]    In another embodiment of the above aspect, the shuttle valve system includes a shuttle valve. In another embodiment, the shuttle valve system includes at least one of a plurality of hydraulic piloted valves and a plurality of electronic solenoid operated valves. In certain embodiments, each of the closed-loop pump and the open-loop pump are variable displacement pumps. In other embodiments, a controller is connected to each of the closed-loop variable displacement pump, the open-loop variable displacement pump, the motor, and the control valve. In yet another embodiment, the controller sends a control signal to actuate the control valve so as to connect the open-loop variable displacement pump to the closed-loop fluid circuit when the controller receives a first component speed signal corresponding to a desired first component speed that is in excess of a first component speed produced when the closed-loop variable displacement pump is at the first maximum rotational speed. In still another embodiment, the control valve is a manual valve. 
         [0006]    In another aspect, the technology relates to a transit mixer including the pump system described above, wherein the first component is a drum. 
         [0007]    In another aspect, the technology relates to a method of controlling a pump system having a closed-loop fluid circuit including a closed-loop variable displacement pump, an open-loop fluid circuit including an open-loop variable displacement pump, a control valve, and a controller, the method including: adjusting an output flow of the closed-loop variable displacement pump based on a first desired speed signal received by the controller; and actuating the control valve so as to connect the open-loop variable displacement pump to the closed-loop fluid circuit based on a second desired speed signal received by the controller. In an embodiment, the method includes increasing an output flow of the open-loop variable speed pump based on a third speed signal received by the controller. In another embodiment, the method includes reducing the output flow of the open-loop variable displacement pump based on a fourth desired speed signal received by the controller. In an embodiment, the method includes changing 2Q an output flow direction from the closed-loop variable displacement pump based on a desired direction signal received by the controller. In yet another embodiment, the method includes changing a position of a shuttle valve at an outlet of the open-loop variable displacement pump based on the desired direction signal received by the controller. In still another embodiment, the method includes disengaging an auxiliary function of the open-loop fluid circuit, prior to actuating the control valve. In another embodiment, the method includes charging each of the open-loop fluid circuit and the closed-loop fluid circuit with hydraulic fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    There are shown in the drawings, embodiments which are presently preferred, it being understood, however, that the technology is not limited to the precise arrangements and instrumentalities shown. 
           [0009]      FIG. 1  is a schematic diagram of a pump system for a transit mixer. 
           [0010]      FIG. 2  is a schematic diagram of a combination open-loop and closed-loop pump system for a transit mixer. 
           [0011]      FIG. 3  is a schematic diagram of a combination open-loop and closed-loop pump system for a dual path propel system. 
           [0012]      FIGS. 3A-3B  are enlarged partial schematic diagrams of the system of  FIG. 3 . 
           [0013]      FIG. 4  is a schematic diagram of a combination open-loop and closed-loop pump system for a single path propel circuit. 
           [0014]      FIG. 5  is a schematic diagram of another embodiment of a combination open-loop and closed-loop pump system for a single path propel circuit. 
           [0015]      FIGS. 6A and 6B  depict a method of controlling a combination open-loop and closed-loop pump system for a transit mixer. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Reference will now be made in detail to the exemplary aspects of the present disclosure that are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like structure. In the present application, a combination open- and closed-loop hydraulic system is often described in the context of a transit mixer. The combination systems disclosed herein, however, may be used in a wide variety of vehicles, such as crop sprayers, skid steer loaders, windrowers, and combine harvesters, as well as other types of industrial equipment, such as mixers, batchers, conveyors and other single purpose rotary actuator applications. Other applications of the systems disclosed herein are contemplated and will be apparent to a person of ordinary skill in the art. 
         [0017]      FIG. 1  depicts a schematic diagram of a pump system for a transit mixer  100 . The pump system  100  includes a first pump  102  that drives the drum motor  104  that in turn rotates the drum. A second pump  106  drives one or more auxiliary components or equipment, for example, a vehicle tag axle  108 , a cement chute lift or positioning apparatus  110 , or other auxiliary components  112 . A control manifold  114  and control valve  116  allow selective disconnection of the second pump  106  from the second fluid circuit  118  and, therefore, selective connection of the second pump  106  to the first fluid circuit  120 . In the depicted embodiment, the first fluid circuit  120  is a closed-loop circuit, and the second fluid circuit  118  is an open-loop circuit. In alternative embodiments, however, both circuits may be closed-loop circuits. Since the drum must operate in reverse to discharge its contents during pouring, an open-loop circuit for the first fluid loop is typically not desirable. The control valve  116  and the control manifold  114  allow for selective connection and isolation of the second pump  106  to the two circuits. The control valve  116  may be manually operated or may be actuated by an electronic controller  122 , as depicted. By combining the output of the second pump  106  with the first fluid circuit  120 , drum motor speed may be increased. A speed sensor  124  on the drum motor, along with command input speed, causes the control valve  116  to actuate, thus combining the second pump  106  with the first fluid circuit  120 , as required or desired. If high speed rotation is required, for example, when mixing concrete or cleaning out the drum, the output of the second pump  106  may be diverted to the first fluid circuit  120  so as to allow the increased rotational speed of the drum motor. 
         [0018]    When use of an auxiliary function is required or desired, the control valve  116  actuates again, thus directing flow to the auxiliary component requiring flow. When the second pump  106  is isolated from the first fluid circuit  120 , the drum motor rotates at a lower speed, helping to ensure concrete held in the drum does not harden. As described above, typical auxiliary functions are chute control (lift, rotate, fold, etc.), as well as tag axle pressure control, but other functions may be incorporated. 
         [0019]      FIG. 2  depicts a schematic diagram of a combination open-loop and closed-loop pump system  200  for a transit mixer. The pump system  200  depicted in  FIG. 2  includes an open-loop charge circuit, a variable displacement closed-loop pump system to drive the drum motor, and a variable displacement open-loop pump system to drive the auxiliary components of the transit mixer. A control circuit  280  includes a number of components used to connect and disconnect the open- and closed-loop circuits. 
         [0020]    The charge circuit includes provide a charge pump  202  to charge and control pressure for the closed-loop hydrostatic drive circuit depicted, in part, by side A and side B. The charge pump  202  draws hydraulic fluid from a unit reservoir  204 , via a main suction line. A suction screen or filter  206  prevents debris from the reservoir  204  from being drawn into the system. The charge pump  202  is driven by a power source or motor  208 , typically an internal combustion engine or an electric motor. In the depicted system, a common motor  208  provides power via a through-drive to all of the charge pump  202 , an open-loop pump  210 , and a closed-loop pump  212 . In such an embodiment, the charge pump  202  may be integrated into a single assembly with pump  212  and pump  210 . In other embodiments, a dedicated motor may be used for the charge pump  202 . The displacement of the charge pump  202  may be determined by the specific application requirements or otherwise as desired. In a commercial embodiment however, a pump having a flow rate of about 8 gal/min to about 12 gal/min at high idle engine RPM may be utilized, though other capacities are contemplated. 
         [0021]    A charge relief valve  214  controls a charge pressure setting in the closed-loop circuit that includes the pump  212  and associated control requirements. In addition, this relief valve  214  will be balanced with a low pressure relief valve  216  to provide proper oil flow through the pump case of pump  212  and motor case of motor  218 . The outlet of the charge pump  202  flows through a charge pressure filter  220  to clean the oil that enters the low pressure side of the hydrostatic drive circuit and that enters the control valve that sets pump displacement (the control spool  234  and solenoids  236 ,  238 , as described in more detail below). After filtration, the hydraulic fluid enters the closed fluid circuit on the low pressure side. In the depicted embodiment, the low pressure side of the closed fluid circuit is indicated by A. A check valve  222  allows charge pressure to enter the low pressure side of the circuit. The low pressure side is the return side, proximate the inlet of the pump  212 . A check valve  224  prevents flow from the high pressure side of the closed fluid circuit. If the direction of motor rotation is reserved, side B becomes the low pressure, return side. In this configuration, hydraulic fluid enters the closed circuit via the check valve  222 , while the check valve  224  prevents from of fluid out of the high pressure supply side. Located between check valves  222 ,  224  and the pump  212  are a power limiting valves  226 ,  228 . These are typically set at the maximum allowable pressure in the closed-fluid circuit. In certain embodiments, the valves  226  and  228  actuate at about 5000 to about 6000 PSI. At this pressure, the flow through the power limiting valves  226 ,  228  will reduce the charge pressure in the closed fluid circuit to a point where the pump  212  will destroke due to the springs in pistons  230  or  232 , thus overcoming the reduced charge pressure and forcing the swash plate towards neutral. 
         [0022]    The swash plate pivot angle is in direct relationship to the outlet flow as it affects the total inward and outward movement of the pump pistons. When the swash plate pivots to the neutral position, there is no inward or outward motion of the pump pistons, so the flow decreases to zero output. The swash plate can be controlled to go over the neutral position whereas the output flow is directed out of the second port, causing the driven motor to go in a reverse direction. 
         [0023]    The charge pump  202  also delivers hydraulic fluid to a control spool  234  that is used to port oil to servo pistons  230  or  232  as required to set the flow rate and direction of the closed-loop pump  212 . The control spool  234  includes two control solenoids  236 ,  238  that are controlled by an electronic controller  240 . Each solenoid  236 ,  238  may move the control spool  234 , thereby causing the charge pressure to be open to one of the two servo pistons  230 ,  232 , thus causing the pump  212  to stroke in the desired direction. The servo pistons  230 ,  232  also controls flow rate. The servo piston  230 , when pressurized, moves a swash plate to drive fluid to the A side of the closed fluid loop. Similarly, the servo piston  232 , when pressurized, moves the swash plate to drive fluid to the B side of the closed fluid loop, thus reserving direction of the pump  212  and, therefore, the motor  218 . In another embodiment, a two-position three-way valve may be utilized to direct flow directly to one of the two servo pistons  230 ,  232 . This configuration would eliminate the spool  234  and a feedback link  242 , which is used to move the spool  234  in a manner similar to that of a servo control loop to maintain a set displacement as required by the controller  240 . The set position is determined by the controller  240  based at least in part on the required speed of motor  218  as measured by a speed sensor  244 . 
         [0024]    Additionally, the charge pump  202  also delivers a flow of cooling hydraulic fluid to both closed-loop pump  212  and the hydrostatic motor  218  that drives the drum mixer. Cooling fluid from the closed-loop pump  212  passes through a hydraulic cooler  246  into a reservoir, which may be the unit reservoir  204 . Cooling fluid passes through the case of the motor  218  and to a reservoir, which may also be the unit reservoir  204 . Depending on specific application needs, an optional solenoid  248  may be utilized if further management of the charge flow is required. This will help ensure proper cooling and maximum pressure requirements through the cases of the motor  218  and the closed-loop pump  212 . The solenoid  248  may be controlled by the electronic controller  240 , depending on specific operating conditions. 
         [0025]    The first fluid circuit, in this case, the closed-loop fluid circuit, includes a closed-loop variable displacement pump  212  that, in a first configuration, moves hydraulic fluid from side A (the low pressure or return side) to side B (the high pressure or supply side). As described above, the closed-loop pump  212  is driven by the motor  208  and its output flow may be reversed to rotate hydraulic motor  218  in either a forward or reverse direction as commanded by the controller. In certain commercial embodiments, the closed-loop pump  212  may produce maximum flow rates from about  30  gal/min to about  35  gal/min, though other pumps having other capacities are contemplated. The closed-loop pump  212  directly drives the hydrostatic motor  218  that may be either fixed or variable displacement. The size of the motor  218  may be determined on an application-specific basis. 
         [0026]    A speed sensor  244  measures the rotational speed and direction of the motor output drive shaft  250 . This measured speed is used as an input to the controller  240  that controls both pumps  212  and  210  to provide the proper flow rate to meet the desired rotational speed to rotate shaft  250 . The shaft  250  may be a propel circuit, a transit mixer drum drive circuit, or generally any rotary driven application. A shuttle valve  252  allows excess charge (i.e., fluid) flow to exit the circuit via a charge relief valve  216 . The shuttle valve  252  also allows excess charge to pass through the motor case, thereby cooling and lubricating the internal components of the motor  218 . The charge relief valve  216  is balanced with the charge relief valve  214  to ensure proper flow through the casing of the motor  218 . 
         [0027]    A control orifice or pressure compensated flow regulator  254  may also be utilized, if required or desired, to allow part of the charge flow to bypass the case of the motor  218 . It should be noted that the combining of flows from pump  210  and charge pump  202  results in much higher flow rates than typically encountered in a traditional closed-loop drive system. The flow out of the flow regulator  254  may be directed through the hydraulic cooler  246  or merely run directly to a reservoir, as depicted, depending on system sizing considerations. Alternatively, a dedicated cooler could be installed downstream of the flow regulator  254 . 
         [0028]    The open-fluid circuit is driven by the variable displacement pump  210 , which draws hydraulic fluid from the unit reservoir  204 . The open-circuit pump  210  may be, in one embodiment, a load sense pressure compensating variable displacement pump. The pump  210  includes both pressure limiting  210 A and load sense  210 B feedback controls as typical in any load sense circuit. The displacement of the pump  210  will be determined by the application needs, but in certain commercial embodiments, flow rates up to about 15 gal/min are contemplated. The pump  210  is driven by either the through drive from the motor  208  or by a dedicated motor. Output from the pump  210  flows to a proportional solenoid valve  262  that is controlled by controller  240 . As described below, the controller  240  actuates the solenoid  262  so as to allow fluid flow from pump  210  into the closed-loop circuit, as required based in part by the required speed setting of the motor  218 . When flow is required for a typical tag axle circuit, the controller  240  activates another solenoid valve  256  to cause the pump to go to a pressure limiting state. In other circuits, solenoid valve  256  may not be required and instead a traditional load sense signal can be fed via shuttle valve  258  to cause the pump to stroke to the required flow rate. Flow to the auxiliary circuit may pass through a pressure reducing valve  260 , if required or desired, to protect auxiliary circuit components from excessive pressure. 
         [0029]    When the solenoid  262  is positioned so as to provide flow from the open-circuit pump  210  to the closed fluid loop, the flow passes through a hydraulic shuttle valve  264  to direct flow from pump  210  into the high pressure side of the closed-loop. Other elements of the open fluid circuit include a check valve  266  that allows outlet pump pressure from the pump  210  to be directed back to the load sense feedback spool on the pump  210  and cause the pump  210  to increase flow rate. The position of the proportional solenoid valve  262  will create a pressure margin that the pump  210  will respond to, and generate the required flow rate needed to satisfy the required rotational speed of the motor  218 . The proportional solenoid valve  262  is controlled by the electronic controller  240  to attain the desired output speed of motor  218 . Furthermore, the check valve  266  will prevent any flow from the pump  210  from entering the closed loop system when the pump  210  is required to provide an auxiliary function and not combine with the flow from the closed loop pump  212 . The check valve  268  prevents back flow from the closed-loop hydrostatic drive circuit when the flow from the pump  210  is not required in the closed fluid circuit. A shuttle valve  258  allows either a load sense signal to the pump  210  when combining with the closed-loop pump circuit or the load sense signal from the auxiliary circuit. An orifice and filter  270  drains the load sense signal when pump  210  has no flow requirements. This drain orifice  270  reduces the outlet pressure to the low pressure standby setting, reducing power loss when no functions are required of the pump  210 . 
         [0030]      FIG. 3  is a schematic diagram of a combination open-loop and closed-loop pump system for a dual path propel system  300 . Partial enlarged schematic diagrams are depicted in  FIGS. 3A and 3B . This dual path system  300  includes two combination open- and closed-loop circuits, each of which controls half of the propel function of a dual path machine, which may include self-propelled windrowers, self-propelled forage harvesters, and skid steer loaders. Such a system  300  may be used in any vehicle that utilizes a dual path propel drive hydraulic system. The components utilized in the various circuits are similar in layout and function to those depicted in the system  200  of  FIG. 2 , and accordingly, are not described in further detail herein. However, for clarity, a number of elements are identified below. The system  300  includes two closed-loop pumps  312 ,  312 ′, one for each of the two closed-loop circuits. The closed-loop circuits also each include a motor  318 ,  318 ′. Drives associated with each of these motors  318 ,  318 ′ are not depicted in  FIG. 3  but would operate similar to the drive  250  depicted in  FIG. 2  to provide power to the desired equipment. A charge pump  302 ,  302 ′ is also included in each of the two closed-loop circuits. Each of the open-loop circuits includes an open-loop pump  310 ,  310 ′. A motor  308  drives both of the closed-loop pumps  312 ,  312 ′ and both of the charge pumps  302 ,  302 ′. A separate motor  309  drives both of the open-loop pumps. Of course, a single motor may be used in place of motors  308 ,  309 . 
         [0031]    Control circuits  380 ,  380 ′ allow for isolation and combination of the related open- and closed-loop circuits. The valve configurations in the depicted control circuits  380 ,  380 ′ differ slightly from the embodiment in  FIG. 2 . Specifically, and with reference to control circuit  380 , the hydraulic shuttle valve  264  (depicted in  FIG. 2 ) is replaced with a valve system including a hydraulic shuttle valve  364  and two hydraulic piloted valves  365 A,  365 B. Together, these three valves  364 ,  365 A,  365 B perform the same function as valve  264 . Of course, a single hydraulic control valve such as valve  264  depicted in  FIG. 2  may alternatively be used. A similar valve  364 ′,  365 A′,  365 B′ configuration is utilized in control circuit  380 ′. The common link between the two combination open- and closed-loop circuits is the ground. 
         [0032]      FIG. 4  is a schematic diagram of a combination open-loop and closed-loop pump system for a single path propel circuit  400 . Such a system  400  may be used with a single-purpose rotary actuator. Again, many of the components are described above with regard to the previous figures. For clarity, the depicted system  400  includes a closed-loop pump  412  and a charge pump  402 , both driven by a motor  408 . A separate motor  409  drives an open loop pump  410 . A motor  418  may be powered by the closed-loop circuit, or the open- and closed-loop circuits, in combination. A control circuit  480  includes a hydraulic shuttle valve  464  and two hydraulic piloted valves  465 A,  465 B. 
         [0033]      FIG. 5  is a schematic diagram of another combination open-loop and closed-loop pump system for a single path propel circuit  500 . Such a system  500  may be used with a single-purpose rotary actuator. Again, many of the components are described above with regard to the previous figures. The depicted system  500  includes a closed-loop pump  512  and a charge pump  502 , both driven by a motor  508 . A separate motor  509  drives an open loop pump  510 . A motor  518  may be powered by the closed-loop circuit, or the open- and closed-loop circuits, in combination. A control circuit  580  differs from those described in  FIGS. 2-4  above. Specifically, the control circuit  580  utilizes electric solenoid operated valves  564 A,  564 B to couple the open-loop pump  510  to the closed-loop circuit. 
         [0034]      FIGS. 6A and 6B  depict one method  600  of controlling a pump system for a transit mixer (such as the pump system  200  depicted in  FIG. 2 ), as controlled by the electronic controller  240 . Similar methods are contemplated to control the systems depicted in  FIGS. 3-5  and would be apparent to a person of skill in the art. The method  600  begins with the controller receiving a signal indicating the desired motor  218  direction (operation  602 ). Certain functions are associated with certain required directions of rotation for the motor  218  and, therefore, the drum. For example, mix, clean, and transport functions typically require the drum to rotate in a first direction. A concrete discharge operation typically requires that the drum rotate in a second, opposite direction. In certain embodiments, certain modes (for example, mix) may automatically be programmed with a set speed, but the depicted method contemplates variable speed adjustment for all modes. If the operator-desired direction has changed from a previously-selected direction (operation  604 ) of the operating motor, any operating pumps must be slowed or stopped prior to changing flow direction. First, the output of the open-loop pump  210  should be reduced and stopped completely (operation  606 ), and then the closed-loop pump  212  should be decreased and then stopped (operation  608 ). Once operation of the pump  212  is sufficiently reduced, the position of the control spool  234  is changed (operation  610 ). The shuttle valve  264  also changes position (operation  612 ), typically in response to a change in pressure, but shuttle valves that require actuation based on a signal sent from the electronic controller  240  may also be used. 
         [0035]    After the direction of flow through the circuit is set, a signal indicative of a drum speed setting is received by the electronic controller  240  (operation  614 ). Again, the drum speed setting may be associated with particular operational modes (e.g., mix), but manual operator control may be more desirable. If the speed setting is less than the maximum flow of the closed-loop pump  212  (operation  616 ), the algorithm next determines if the solenoid valve  262  is closed (operation  618 ), thus ensuring that the open-loop pump  210  is isolated from the closed-loop fluid circuit. Thereafter, the closed-loop pump  212  flow is adjusted until it meets the desired speed set point (operation  620 ). Thereafter, the algorithm waits for further adjustment of the speed setting. Alternatively or additionally, the algorithm may await further adjustment of the directional setting. Regardless, further adjustment of either the desired motor direction or the motor speed setting will return the algorithm to the appropriate position to continue control of the pump circuit. 
         [0036]    Returning to the speed determination inquiry (operation  616 ), if the desired speed setting is not in excess of the maximum closed-loop pump  212  flow capability (operation  622 ), the displacement or flow of the closed-loop pump  212  is first adjusted to its maximum setting (operation  624 ). If the closed-loop pump  212  is at its maximum setting (operation  622 ), the algorithm next determines if flow from the open-loop pump  210  is flowing to the auxiliary or open-fluid circuit (operation  626 ). If apparently not, the algorithm first ensures that the solenoid valve  262  is open (operation  628 ) (thus ensuring connection between the open-loop pump  210  and the closed-fluid circuit), then adjusts the open-loop pump  210  output flow to meet the desired speed level (operation  630 ). This output flow control was previously described. If the open-loop pump  210  is delivering fluid to the auxiliary circuit (operation  626 ), the auxiliary fluid circuit is disconnected (operation  632 ) by either closing the solenoid valve  256  or controlling the auxiliary valve functions (not depicted in  FIG. 2 ) to cease operation, prior to opening solenoid valve  262  (operation  628 ) and adjusting the open-loop pump  210  (operation  630 ). Upon adjustment, as above, the algorithm could wait until further speed or direction adjustment is made. 
         [0037]    Other methods of controlling the pump system are contemplated. For example, the above-described method contemplates a two-position shuttle valve  264 . In the system embodiment depicted in  FIG. 2 , the shuttle valve  264  includes three positions, one each to direct the output from to either the A side or the B side of the closed loop circuit, as well as a third, neutral position and is actuated automatically, due to circuit pressure. Valves that require actuation by the electronic controller may also be utilized. While the above-described method indicates that the shuttle valve  264  automatically moves to the appropriate position based on pressure, an alternative embodiment may include a shuttle valve that requires direct actuation and therefore, modification of the algorithm. Also, the closed-loop pump  212  may be a fixed displacement pump, while the open-loop pump  210  may be a variable displacement pump. Accordingly, variable speed adjustment would only be possible beyond the maximum output flow of the fixed displacement pump, which would require slightly different controls. Having two variable displacement pumps, however, allows for greater flexibility and control. For example, the displacement of both pumps may be individually adjusted as required. That is, instead of adjusting the displacement of the open-loop pump  210  once the closed-loop pump  212  has been set to maximum displacement, the displacement of the open-loop pump  210  may be maximized and the displacement of the closed-loop pump  212  may be adjusted as required. This may provide redundancy in the event of pump failure or if one pump is unable to reach maximum speed due to mechanical or electrical problems. Other modifications and control sequences are contemplated. 
         [0038]    The pump system described above may be sold as a kit, either in a single package or in multiple packages. A kit may include a closed-loop pump, an open-loop pump, and a charge pump, along with the necessary or desired sensors and valves, electronic controller, etc. Alternatively, the pumps, through-drive, and power source therefore, may be sold as a single unit, along with the electronic controller. Users may then obtain the various valves and sensors separately from a third party or from the pump supplier. In another embodiment, the components bounded by line P (as depicted in  FIG. 2 ) may be included in a single package, including all valves, sensors, pumps, piping, and other components. If desired, control wiring may be included, although instructions included with the kit may also specific the type of wiring required based on the particular installation. 
         [0039]    Additionally, the electronic controller may be loaded with the necessary software or firmware required for use of the system. In alternative configurations, software may be included on various types of storage media (CDs, DVDs, USB drives, etc.) for upload to a standard PC, if the PC is to be used as the controller, or if the PC is used in conjunction with the pump system as a user or service interface. Additionally, website addresses and passwords may be included in the kit instructions for programs to be downloaded from a website on the internet. 
         [0040]    The control algorithm technology described herein can be realized in hardware, software, or a combination of hardware and software. The technology described herein can be realized in a centralized fashion in one computer system or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suitable. A typical combination of hardware and software can be a general purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein. Since the technology is contemplated to be used on a transit mixer, however, a stand-alone hardware system including the necessary operator interfaces (directional switch, speed selector, etc.) is desirable. 
         [0041]    The technology described herein also can be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry out these methods. Computer program in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form. 
         [0042]    While there have been described herein what are to be considered exemplary and preferred embodiments of the present technology, other modifications of the technology will become apparent to those skilled in the art from the teachings herein. The particular methods of manufacture and geometries disclosed herein are exemplary in nature and are not to be considered limiting. It is therefore desired to be secured in the appended claims all such modifications as fall within the spirit and scope of the technology. Accordingly, what is desired to be secured by Letters Patent is the technology as defined and differentiated in the following claims, and all equivalents.