Patent Publication Number: US-2011056194-A1

Title: Hydraulic system for heavy equipment

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a continuation-in-part of prior U.S. application Ser. No. 12/557,119, filed on Sep. 10, 2009, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to the field of hydraulic systems including hydraulic cylinders and motors. More specifically, the disclosure relates to the systems and methods used to control the workload of components in a hydraulic system so that hydraulic pumps and drive systems can be optimized for the total amount of flow available, and the desired work outcome. The technology disclosed is particularly useful in hydraulic systems for operation with heavy equipment, such as equipment used for mining and excavating. 
     SUMMARY 
     One embodiment relates to heavy equipment. The heavy equipment includes first and second hydraulic pumps, and first and second hydraulic actuators, where the first hydraulic actuator facilitates a first work function of the heavy equipment and the second hydraulic actuator facilitates a second work function of the heavy equipment. The heavy equipment further includes valving and a computerized controller. The valving is configured to allow the first hydraulic pump to be coupled to the first hydraulic actuator and the second hydraulic actuator, and to allow the second hydraulic pump to be coupled to the first hydraulic actuator and the second hydraulic actuator. The computerized controller is coupled to the valving, and has a logic module. The logic module provides instructions to the computerized controller to operate the valving as a function of inputs from an operator command, a sensor input, and prioritization logic associated with the first and second work functions, so as to optimize performance of the work functions facilitated by the hydraulic actuators with respect to available output of the hydraulic pumps. 
     Another embodiment relates to a hydraulic system, which includes a plurality of hydraulic pumps, a plurality of hydraulic actuators, a manifold comprising a plurality of valves, and a computerized controller coupled to the manifold. The plurality of valves control a flow of hydraulic fluid from the plurality of hydraulic pumps to the plurality of hydraulic actuators, where the plurality of valves of the manifold are configured to allow each of the plurality of hydraulic pumps to be coupled to any one of the plurality of hydraulic actuators while not being coupled to the others of the plurality of hydraulic actuators. The computerized controller has a logic module that provides instructions to the computerized controller to operate the plurality of valves of the manifold to distribute hydraulic fluid flowing through the manifold among the plurality of actuators as a function of inputs from an operator command, a sensor input, and prioritization logic associated with work functions facilitated by the plurality of hydraulic actuators, so as to optimize performance of the work functions facilitated by the plurality of hydraulic actuators with respect to available output of the plurality of hydraulic pumps. 
     Yet another embodiment relates to heavy equipment. The heavy equipment includes a body, an articulated arm extending from the body, first and second actuators, a source of pressurized hydraulic fluid, a manifold, and a computerized controller. The first actuator facilitates a first work function of the heavy equipment, which includes raising and lowering the articulated arm. The second actuator facilitates a second work function of the heavy equipment, which includes moving the body of the heavy equipment. The manifold includes a plurality of valves for distributing to the first and second actuators hydraulic fluid received from the source of pressurized hydraulic fluid, and the computerized controller operates the manifold as a function of prioritization logic related to the first and second work functions. The prioritization logic is updated by the computerized controller during operation of the heavy equipment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an excavator according to an exemplary embodiment. 
         FIG. 2  is a schematic diagram of the hydraulic system for the excavator of  FIG. 1  which has a plurality of pumps driven by electric motors. 
         FIG. 3  is a flowchart of a software routine executed by a supervisory control in  FIG. 2  to measure the wear of the motors and pumps in the hydraulic system. 
         FIG. 4  is a software routine executed by the supervisory controller to vary the assignment of the different pumps to the various hydraulic actuators. 
         FIGS. 5-6  are two tables depicting different assignments of the pumps to hydraulic functions of the excavator. 
         FIG. 7  is a perspective view of a power shovel according to an exemplary embodiment. 
         FIG. 8  is a plan view of the power shovel of  FIG. 7 . 
         FIG. 9  is a perspective view of a hydraulic system of the power shovel of  FIG. 7 . 
         FIG. 10  is a schematic diagram of a hydraulic system according to an exemplary embodiment. 
         FIG. 11  is a priority table for different work functions of an excavator according to an exemplary embodiment. 
         FIG. 12  is a flow chart of a logic module according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     With initial reference to  FIG. 1 , an excavator, such as a front power shovel  10 , has a crawler assembly  12  for moving the shovel across the ground. A cab  14  is pivotally mounted on the crawler tractor so as to swing in left and right. A boom  16  is pivotally mounted to the front of the cab  14  and can be raised and lowered by a boom hydraulic actuator  22  in the form of a first double-acting cylinder-piston assembly. An arm  18  is pivotally attached to the end of the boom  16  that is remote from the cab  14 , and can be pivoted with respect to the boom by an arm hydraulic actuator  23  in the form of a second double-acting cylinder-piston assembly. At the remote end of the arm  18  from the boom is attached to a work tool (e.g., work implement), such as a bucket  20 , that faces forward from the cab  14 , hence this type of excavator is referred to as a front power shovel. The bucket  20  is pivoted or “curled” about the end of the arm  18  by a curl hydraulic actuator  24 , in the form of a third double-acting cylinder-piston assembly. According to an exemplary embodiment, the bucket  20  is made up of two sections which can be opened and closed like a clam shell by a clam hydraulic actuator  25  ( FIG. 2 ). The two bucket sections are held closed together during a digging work function and are separated in order to dump material into a truck or onto a pile. 
     With a reference to  FIG. 2 , the hydraulic system  30  for operating the power shovel comprises a set of four pumps  31 ,  32 ,  33 , and  34  which draw fluid from a reservoir or tank  71 . Each pump  31 ,  32 ,  33 , and  34  has a supply outlet that is connected to a separate primary supply lines  45 ,  46 ,  47 , and  48 . The pressurized fluid from the supply outlet of the first pump  31  is fed into a first primary supply line  45 , the second pump  32  feeds a second primary supply line  46 , the third pump  33  feeds a third primary supply line  47 , and the fourth pump  34  feeds a fourth primary supply line  48 . The pumps  31 - 34  have fixed displacement so that the amount of fluid that is pumped is directly proportional to the speed at which the pump is driven (e.g., including piston or plunger pumping mechanisms, gear pumps, etc.). In other contemplated embodiments, one or more pumps (e.g., impeller or centrifugal pumps) may not be positive displacement pumps. 
     According to an exemplary embodiment, each of the four pumps  31 ,  32 ,  33 , and  34  is driven by a separate electric motor  41 ,  42 ,  43  and  44 , respectively. Each motor  41 ,  42 ,  43  and  44  is operated by a variable speed drive  57 ,  58 ,  59 , and  60  which vary the frequency of the alternating current applied to the respective motor in order to operate the motor at a desired speed. Any of several well known variable speed drives can be utilized, such as the one described in U.S. Pat. No. 4,263,535, which description is incorporated herein by reference. Each combination of a pump, motor and variable speed drive forms a drive-motor-pump assembly (DMP)  26 ,  27 ,  28 , and  29 . It should be understood that a hydraulic system according to other embodiments may have a greater or lesser number of DMP&#39;s. Although referred to as a DMP, in contemplated embodiments a motor (e.g., via gearing) or a drive may be coupled to two or more separate pumping mechanisms, or one or more of the motors may be an engine, where the drive is a throttle and a transmission or clutch may be used to control the interaction between the engine and the pumping mechanism. 
     Each pump  31 - 34  has a case drain through which fluid leakage flows from the pump to the reservoir  71 . Each of those case drains is coupled to a reservoir return line  72  by a separate flow meter  35 ,  36 ,  37  and  38  connected to the respective variable speed drive  57 ,  58 ,  59 , and  60 , directly or indirectly, such as by way of a supervisory controller  50 . A separate temperature sensor  61 ,  62 ,  63  and  64  is mounted on each of the motors  41 ,  42 ,  43 , and  44  respectively, to sense the temperature and provide a signal back to the associated variable speed drive  57 ,  58 ,  59 , and  60 . Thus in addition to controlling the speed of the associated motor, each variable speed drive also gathers data about the motor temperature and the pump drain flow. 
     The DMP&#39;s  26 ,  27 ,  28 , and  29 , specifically the variable speed drives  57 ,  58 ,  59 , and  60 , are controlled by the supervisory controller  50  which in some embodiments is a microcomputer based device that responds to control signals from the human operator of the power shovel and other signals to control the hydraulic actuators  22 ,  23 ,  24 , and  25  to operate the shovel as desired. Those signals are received by the supervisory controller  50  over a control network  51 . The supervisory controller responds to those signals by determining the amount of hydraulic fluid necessary to be produced by each pump  31 ,  32 ,  33 , and  34  and accordingly controls the motor  41 ,  42 ,  43 , and  44  that drives the respective pump. 
     The four primary supply lines  45 ,  46 ,  47 , and  48  feed into a distribution manifold  52  which selectively directs the fluid flow from each pump to different ones of the four hydraulic actuators  22 ,  23 ,  24 , and  25 . Specifically, the manifold  52  has a first actuator supply line  66  which feeds a solenoid operated first control valve  80  for the boom hydraulic actuator  22 . The first control valve  80  is a three-position, four-way valve, which directs fluid from the first actuator supply line  66  to one of the chambers of the cylinder of the boom hydraulic actuator  22 , and drains fluid from the other cylinder chamber into the reservoir return line  72  that leads to the reservoir  71 . In other embodiments, other directional control valves may be used. Depending upon the position of the first control valve  80 , the first hydraulic actuator  22  is driven in either of two directions to thereby raise or lower the boom  16 . Similarly, the second, third, and fourth actuator supply lines  67 ,  68 , and  69  from the distribution manifold  52  are connected by similar second, third, and fourth control valves  81 ,  82 , and  83  to the arm hydraulic actuator  23 , the curl hydraulic actuator  24 , and the clam hydraulic actuator  25 , respectively. The four actuator control valves  80 - 83  are independently operated by separate signals from the supervisory controller  50 . Although the present hydraulic system  30  utilizes control valves  80 - 83  between the distribution manifold  52  and the hydraulic actuators  22 - 25 , the control valves could be eliminated by incorporating their functionality into additional valves in the distribution manifold to control flow to and from each cylinder chamber. 
     The present distribution manifold  52  has a matrix of sixteen distribution valves  84 - 99 . Each distribution valve couples one of the primary supply lines  45 ,  46 ,  47 , or  48  to one of the actuator supply lines  66 ,  67 ,  68 , or  69 . Therefore, when a given distribution valve  84 - 99  is electrically operated by a signal from the supervisory controller  50 , a path is opened between the associated primary supply line and actuator supply line, thereby applying pressurized fluid from the pump connected to that primary supply line to the control valve  80 ,  81 ,  82 , or  83  connected to that actuator supply line. For example, when distribution valve  85  is activated, fluid from the first pump  31  flows through the first primary supply line  45  into the second actuator supply line  67  and onward to the second control valve  81 . By selectively operating one or more of the distribution valve  84 - 99 , the output from each pump  31 - 34  can be used to operate each of the four hydraulic actuators  22 ,  23 ,  24 , or  25 . This results is a given pump being assigned to a hydraulic actuator. It should be understood that on a particular power shovel, there may be a greater or lesser number of pumps and a greater or lesser number of hydraulic actuators; in which case the distribution manifold  52  will be configured with a corresponding different number of distribution valves. For example, hydraulic motors may independently drive the left and right tracks of the crawler assembly  12  to propel the power shovel. 
     It also should be understood that the output from two or more pumps can be combined to supply the same hydraulic actuator  22 - 25 . For example, if only the arm hydraulic actuator  23  is active, the output from multiple pumps can be combined so that the arm is driven to dig into the earth with maximum speed and force. When another shovel function is to operate simultaneously with the arm, one or more of the pumps previously connected to the arm function is reassigned to provide fluid so that the other shovel function is to operate simultaneously with the arm. One or more of the pumps previously connected to the arm function is reassigned to provide fluid to the other shovel function, by redirecting the flow through the distribution manifold  52 . Also should DMP  26 - 29  fail, it is deactivated by shutting off the associated variable speed drive and disconnecting the associated pump by closing all the valves in the distribution manifold  52  that are connected to the respective primary supply line. In this case, fluid from the remaining pumps supplied through the distribution manifold to operate the hydraulic actuators. If, however, the output of a particular pump is not required at a given point in time, its variable speed drive is deactivated so that the motor and thus that pump do not operate. 
     For very large power shovels, relatively large forces are encountered by the arm hydraulic actuator  23  and curl hydraulic actuator  24  during a digging operation. In addition, the arm and curl hydraulic actuators  23  and  24  tend to be operated for longer periods of time then that of the other hydraulic actuators. The clam hydraulic actuator  25  associated with the bucket  20  typically is significantly smaller and consumes far less hydraulic fluid. In previous power shovels, a given pump often was dedicated to supplying fluid to one of the hydraulic actuators and thus the different motor-pump combinations performed different levels of work. In other words, because the pumps and motors for the arm and the bucket curl functions perform considerably more work than other pumps and motors in the hydraulic system, those heavily worked components tended to require more maintenance and more frequent replacement than the other motors and pumps. Therefore, the different motor/pump combinations required servicing at different times during which the entire power shovel had to be taken out of service. The resultant downtime adversely affected the power shovel&#39;s overall productivity and economy of operation. 
     Embodiments disclosed herein overcome the problems with such previous systems by dramatically changing the assignment of the DMP&#39;s to the hydraulic actuators so that each motor/pump combination is exposed to substantially the same amount of use and work. As a consequence, all the DMP&#39;s will require maintenance and possible replacement at about the same point in time. Thus, the service and replacement intervals for the DMP&#39;s are synchronized so that the maintenance intervals, mean time to repair, and mean time between failure are optimized and provide a longer mean time between failure for the entire hydraulic system. This reduces the number of service down periods over the life of the excavator and thereby increases productivity. 
     In order to determine the usage of the DMP&#39;s, the supervisory controller  50  gathers data regarding the operation of their motors and pumps, such as electric current and voltage applied to the motor, motor temperature, speed, torque, aggregate operating time, and amount of pump drain flow. The accumulated data is utilized to determine the relative amount of work performed by each DMP  26 ,  27 ,  28 , and  29 . To this end the supervisory controller  50  executes different software routines that gather and analyze the pump and motor data to estimate the remaining anticipated life of those components and the aggregate amount of use that they have provided. The term DMP is being used to refer to performance of the motor/pump combination as well as performance of the individual motor and pump therein. 
     With reference to  FIG. 3 , a DMP life routine  100  is executed periodically on a timed-interrupt basis by the supervisory controller  50 . This software routine commences at step  102  where a finding is made whether at least one actuator  22 - 25  of the power shovel  10  is currently being operated. The execution of the routine loops through this step until one of the hydraulic actuators  22 - 25  begins operating, at which time the process advances to step  104 . At this juncture, the supervisory controller  50  obtains data indicating the magnitudes of the electric current and voltage that each variable speed drive  57 - 60  is applying to is associated motor  41 - 44 . Each variable speed drive contains circuitry for measuring the magnitude of the voltage and current and converting those measurements into digital data for transmission to the supervisory controller  50 . Next, the recorded electrical data are used at step  106  to compute the average RMS power consumed by each motor during a predefined measurement time period. At step  108 , the newly computed RMS power values are compared to the rated value for each respective motor, as specified by the motor manufacturer to determine whether the operation exceeds the rated power for that motor. If so, for each motor the magnitudes that its rated power value is exceeded are integrated at step  110  to derive a value indicative of the aggregate excessive use of the motor. Those excessive use values then are used at step  112  to calculate the life expectancy of each motor  41 - 44 . For example, the greater the amount of time that the rated power is exceeded and the aggregate magnitude of that excess decreases the life of the motor from the nominal life expectancy specified by the motor manufacturer. The nominal life expectancy is based on the rated power level not being exceeded. An empirically derived relationship for the particular type of motor is used to calculate a how much the motor life expectancy has decreased due to the actual duration of excessive power operation and the aggregate magnitude of that excessive power. The duration of excessive power operation is based on the sampling period for the motor electrical values. The decrease in the expected motor life and the nominal life expectancy are used to project a life expectancy for each motor  41 - 43 . That information is then stored in a table within the supervisory controller  50 . 
     Thereafter at step  114 , the DMP life routine  100  enters a section at step  116  in which the present life expectancy of each pump  31 - 34  is estimated. The supervisory controller  50  initially records the speed and torque of the motors  41 - 43 , which information is derived from the electric voltage and current levels applied by the variable speed drives  57 - 60 . Alternatively, the speed and torque data can be measured by sensors attached to the drive shaft linking a motor to a pump. The supervisory controller  50  also obtains the amounts of fluid flow exhausting from the pump case drains. Those flow rates are sensed by the flow meters  35 ,  36 ,  37 , and  38  connected to circuitry in the variable speed drives  57 ,  58 ,  59 , and  60  which relay the case drain flow data to the supervisory controller  50 . In other embodiments, the flow meters  35 ,  36 ,  37 , and  38  are coupled directly to (e.g., wired to) the supervisory controller  50 . Then at step  118 , the amounts of fluid flow and pressure at the supply outlet of each pump  31 - 34  are derived from the respective speed and torque values. Specifically, the flow is the product of the speed and the fixed pump displacement. The torque correlates directly with the pump supply outlet pressure. Alternatively the fluid flow and pressure can be measured directly by sensors at the supply outlet of each pump  31 - 34 . 
     At step  120 , the values for the amounts of supply outlet fluid flow, pump pressure, and the case drain flow are compared with data provided by the manufacturer of the pumps to determine the present point on the life cycle for each pump. Specifically, the leakage of the pump represented by the flow from the pump case drain increases as a pump ages. In other words, the older the pump, the greater the case drain flow, however, the actual case drain flow at any point in time also is a function of the fluid flow and pressure produced at the supply outlet by the pump. That is, the case drain flow increases as the flow and pressure produced by the pump increase. A typical pump manufacturer has correlated the expected pump case drain flow for various pressure and flow amounts at different times during the life cycle of the pump. By comparing the actual fluid flow, pressure and pump case drain flow to manufacturer specification data, the supervisory controller  50  is able to determine the remaining life of each of the pumps  31 - 34 , at step  122 . This determination is stored with the memory of the supervisory controller  50  for display to the pump operator and service personnel, as well as for determining the trends of the pump life cycle to estimate when pump maintenance and replacement will be required. 
     In contemplated embodiments, the determination of remaining life is used as a weight or factor by the supervisory controller when determining the order of pumps to use. As such, a first pump determined to have low remaining life may be passed over for a second pump determined to have greater remaining life despite the second pump having performed a greater cumulative amount of work. In some contemplated embodiments, the cumulative amount of work of each pump is scaled by a factor associated with the life determination, while in other embodiments the cumulative amount of work is offset by an amount associated with the life determination. 
     With reference to  FIG. 4 , the supervisory controller  50  also executes a software DMP assignment routine  130 , that allocates the output of each pump  31 - 34  to one of the hydraulic actuators  22 - 25  based on the accumulated amount of use of each DMP  26 - 29 . As noted previously, the arm and bucket curl hydraulic actuators  23  and  24  operate more frequently and demand a greater amount of force from the hydraulic system than the boom and bucket clam hydraulic actuators  24  and  25 . Therefore, the DMP&#39;s that supply fluid to the arm and bucket curl hydraulic work more intensely than other DMP&#39;s. The DMP assignment routine  130  determines the aggregate amount of work that each motor/pump combination has performed and adjusts the assignment of the DMP&#39;s  26 - 29  to the various hydraulic actuators  22 - 25  to approximately equalize the work being performed. This results in all the motor/pump combinations incurring essentially the same amount of wear so that they should require maintenance and ultimately replacement at the approximately same time. 
     The DMP assignment routine  130  commences at step  132  where a finding is made whether the hydraulic system  30  is currently operating at least one actuator, if so, the routine advances to step  134 . At that point, the present assignments of the four DMP&#39;s  26 ,  27 ,  28  and  29  to the different hydraulic actuators  22 ,  23 ,  24 , and  25  is recorded as a table in the memory of the supervisory controller  50 .  FIG. 5  depicts an exemplary table in which for each hydraulic function one of the DMP&#39;s is designated. That table also is used by the supervisory controller  50  in opening and closing the distribution valve  84 - 99  in the distribution manifold  52  to direct fluid from each pump to the designated hydraulic actuator. The exemplary table, the supervisory controller  50  would open distribution valve  96  to direct the fluid from the fourth pump  34  to the boom supply line  66 , and open distribution valve  85  to direct the fluid from the first pump  31  to the arm supply line  67 . Similarly distribution valve  94  is opened to direct the fluid from the third pump  33  to the curl supply line  68  and distribution valve  91  is opened to direct the fluid from the second pump  32  to the clam supply line  69 . 
     Returning to the DMP assignment routine  130  in  FIG. 4 , the total amount of time that each DMP  26 - 29  has operated when assigned to each hydraulic actuator is determined at step  136 . For each DMP, the supervisory controller  50  implements a separate timer in software that runs whenever the respective DMP is operating. This provides a cumulative record of the total time that each motor  41 - 44  and each pump  31 - 34  has operated. 
     At step  138  the magnitudes of electric voltage and current that the respective variable speed drive  57 ,  58 ,  59 , and  60  applies to the associated motor  41 ,  42 ,  43  and  44  are read by the supervisory controller  50 . Each variable speed drive  57 ,  58 ,  59 , and  60  stores a digitized temperature value resulting from a signal produced by the temperature sensor  61 ,  62 ,  63  or  64  attached to the associated motor  41 ,  42 ,  43 , or  44 , respectively. The temperature values also are read from the variable speed drives and stored within the memory of the supervisory controller  50  at step  140 . 
     At step  142 , the electrical values read for each motor  41 - 44  are used to determine the amount of work that the respective DMP performed. Specifically, the current and voltage levels for a particular motor are multiplied to produce a value denoting the amount of electrical power consumed during the time interval between measurements. Not all consumed input electrical power is converted into mechanical power for driving the pump, because energy is lost as heat produced in the motor. The measured temperature of the respective motor is used to calculate the amount of the electrical power that was consumed in heating that motor, i.e., the heat power loss. Therefore, the mechanical power provided by the associated pump  31 - 34  is calculated by subtracting the heat power loss from the amount of electrical power consumed. The resultant mechanical power value then is integrated over the measurement interval to derive the amount of work that the pump performed. The new amount of work then is added to a sum of similar amount of work calculated previously to provide a measurement of the aggregate amount of work that the pump has performed since its installation. This work computation is performed individually for each of the pumps  31 - 34  and the resultant aggregate amounts of work are stored in the supervisory controller  50 . At step  144 , the DMP&#39;s  26 - 29  are ranked in order of the aggregate amount of work that each has performed. 
     As noted previously, the DMP&#39;s supplying the arm and curl hydraulic actuators  23  and  24  perform a greater amount of work over time than the boom and clam hydraulic actuators  22  and  25 . Thus the DMP&#39;s that control the flow of fluid to the arm and curl hydraulic actuators correspondingly perform a greater amount of work. The purpose of the DMP assignment routine  130  is to equalize the aggregate amounts of work that the motor/pump combinations perform so that they are subjected to substantially equal amount of wear and therefore require maintenance and ultimately replacement at approximately the same time. Doing so reduces how often the power shovel  10  must be taken out of operation. 
     In a standard configuration of the distribution manifold  52 , a separate pump  31 - 34  is connected to feed fluid to a different hydraulic actuator  22 - 25 . Which pump is connected to which hydraulic actuator is determined dynamically in response to the ranking of the DMP&#39;s based on the aggregate amount of work that each performed. The DMP-to-hydraulic-actuator assignments are recorded as a table in the memory of the supervisory controller  50  and  FIG. 5  depicts as exemplary set of those assignments. Therefore at step  146 , the DMP work rankings are inspected to ensure that the DMP&#39;s with the least aggregate amounts of work are assigned to the arm and curl hydraulic actuators  23  and  24 . Assume for example that upon entering step  146 , the DMP to hydraulic actuator assignments are as depicted in  FIG. 5 , the second DMP  27  now has the greatest aggregate amount of work, and the fourth DMP  29  has the least aggregate amount of work. The supervisory controller  50  in this case will reassign the second DMP  27  to the bucket claim hydraulic actuator  25 , the fourth DMP  29  to the arm hydraulic actuator  25  as depicted in  FIG. 6 . The rearrangement of the DMP to hydraulic actuator assignments causes the supervisory controller  50  to change the configuration of open and closed distribution valves  86 - 97  connected to the pumps  31 - 34  in each DMP to the hydraulic actuator  22 - 25  designated in the assignment table. 
     For machines in which the different hydraulic actuators are subjected to substantially equal forces, the assignment of DMP&#39;s can be based on operating time. For example, the DMP that with the lowest aggregate amount of work is assigned to the hydraulic actuator that operates most often. Similarly the DMP that with the greatest aggregate amount of work is assigned to the hydraulic actuator that operates least often. In another variation of the present control technique, when a single hydraulic actuator is operating, the inactive DMP with the lowest aggregate amount of work is assigned to provide fluid that actuator. 
     In another situation, a given hydraulic actuator may have a varying demand for hydraulic fluid depending on the force acting on that actuator. One DMP alone may not be able to meet all demand levels. Therefore at higher demand levels, multiple pumps are used to provide fluid to that given hydraulic actuator. Here the DMP&#39;s are assigned to the given hydraulic actuator in order from the DMP with the lowest aggregate amount of work to the DMP with the greatest aggregate amount of work. Thereafter, when the demand for hydraulic fluid from a hydraulic actuator decreases, the DMP&#39;s are unassigned in the reverse order. Specifically, the DMP with the greatest aggregate amount of work is disconnected first and the DMP with the lowest aggregate amount of work remains connected until fluid no longer is needed. 
     Referring to  FIG. 7 , an excavator, such as a power shovel  210 , has a crawler truck  212  (e.g., transportation system) upon which is mounted a cab  214  (e.g., body) of the power shovel  210 . The power shovel  210  further includes an articulated arm  234 , which includes a boom  216  that connects to the cab  214  by a pivot joint  218 , which enables the boom  216  to move up and down. The boom  216  has a remote end to which an arm  220  is pivotally connected. The arm  220 , in turn, has a remote end to which a work implement, such as a bucket  222 , is pivotally attached. In some embodiments, the bucket  222  may be a clam-type bucket having two pieces that open and close, somewhat like a clam shell (not shown). In other embodiments, another form of work implement (e.g., fork, breaker, wrecking ball) is attached to the articulated arm  234 . Although shown as the power shovel  210  in  FIG. 7 , heavy equipment and hydraulic systems disclosed herein are not limited to power shovels unless expressly recited in the claims. In contemplated embodiments, the disclosure provided herein may be used with a backhoe, a loader bucket, a skid loader, a crane, a drilling rig, or other forms of mobile or immobile heavy equipment and hydraulic systems. 
     During operation of the power shovel  210 , the boom  216 , the arm  220 , and the bucket  222  are moved with respect to each other by separate hydraulic actuators  224 ,  226 ,  228  in the form of cylinder and piston assemblies (i.e., hydraulic cylinders). As such, the hydraulic actuators  224 ,  226 ,  228  facilitate lifting, lowering, crowding, digging, crushing, maneuvering, and other work functions associated with the articulated arm  234  and a work implement associated with the articulated arm  234 , such as the bucket  222  of the power shovel  210 . The crawler truck  212  is moved on tracks  230  driven by actuators in the form of hydraulic or electric motors, which facilitates locomotion of the power shovel  210  (e.g., propel work function, turn work function). Additionally the cab  214  is rotated about the tracks  230  by way of actuators  236  (e.g., slew motors), which may be hydraulic or electric motors, facilitating work functions requiring rotational movement of the power shovel  210 . 
     Referring to  FIGS. 7-9 , the power shovel  210  includes a powerhouse (e.g., power source, generator) supplying electricity to a hydraulic system  240  ( FIGS. 8-9 ). A computerized controller  242  supervises communication of electricity from electric generators  244  of the powerhouse to one or more hydraulic pumps  232  of the hydraulic system  240 . According to an exemplary embodiment, the hydraulic pumps  232  can be selectively activated based on the demand for hydraulic fluid by actuators of the power shovel  210 , such as actuators  224 ,  226 ,  228  ( FIG. 7) and 236  ( FIG. 8 ). 
     According to an exemplary embodiment, each hydraulic pump  232  includes a pumping mechanism  246  ( FIG. 9 ) (e.g., pistons, impeller), a motor  248  ( FIG. 9 ) (e.g., electric motor, engine), and a drive  250  ( FIG. 8 ) (e.g., inverter, clutch) to control interaction between the motor  248  and the pumping mechanism  246  of the hydraulic pump  232 . In some embodiments, the power shovel  210  includes more than one hydraulic pump  232 , including corresponding motors  248 , drives  250 , and pumping mechanisms  246 . The hydraulic pumps  232  of the power shovel  210  may have the same or different capacities relative to each other. During operation of the power shovel  210 , the computerized controller  242  operates the hydraulic pumps  232  via the drive  250  of each pump  232 , in some embodiments. The hydraulic pumps  232  may be controlled independently of each other, allowing different pumps  232  to be run at different speeds. In contemplated embodiments, a pumping mechanism (e.g., piston set) may be driven by more than one motor, or a single motor may drive more than one pumping mechanism. In other contemplated embodiments, a drive may be used to control more than one motor associated with one or more pumping mechanisms. In still other contemplated embodiments different forms of motors may be used, such as engines, to drive one or more pumping mechanisms. 
     In some embodiments, the computerized controller  242  operates the pumps  232  according to techniques described with regard to  FIGS. 3-4 , such as based upon an estimate of the cumulative work performed by each hydraulic pump  232 . In other embodiments, the computerized controller  242  activates and deactivates the hydraulic pumps  232  in a fixed order, regardless of cumulative work performed. In still other contemplated embodiments, the computerized controller  242  activates and deactivates the hydraulic pumps  232  in a random order so that, over time, work performed by the hydraulic pumps  232  will be approximately equal. Random selection may be facilitated by a random number generator, and the selection of hydraulic pumps  232  may be weighted to favor hydraulic pumps  232  that are in better working condition, such as those determined to have greater remaining life or those determined to have performed less cumulative work. In still other embodiments, the hydraulic pumps  232  are operated according to still other systems. 
     From the hydraulic pumps  232 , hydraulic fluid is delivered through plumbing (e.g., a hydraulic circuit) to valving  252  for distributing the hydraulic fluid to hydraulic actuators of the power shovel  210 , such as actuators  224 ,  226 ,  228  ( FIG. 7) and 236  ( FIG. 8 ). According to an exemplary embodiment, the valving  252  is configured to couple at least two of the pumps  232 , to either of at least two different hydraulic actuators. In some embodiments, the valving  252  is configured to allow each pump  232  in a set of two or more pumps  232  to be coupled to each hydraulic actuator in a set of two or more hydraulic actuators. In some embodiments, the valving  252  allows two or more of the pumps  232  to be coupled to the same hydraulic actuator at the same time. In other contemplated embodiments, a pump  232  may be coupled to two or more hydraulic actuators at the same time, where adjustable restrictors or pressure-control valves provide hydraulic fluid from the same pump  232  to two or more actuators at different pressures. 
     According to an exemplary embodiment, the valving  252  is located in or associated with a manifold  254  (e.g., common manifold, central distributor, distribution hub). As such, plumbing from the hydraulic pumps  232  delivers hydraulic fluid to the manifold  254 , which then allocates the hydraulic fluid, via the valving  252 , to particular actuators to perform particular work functions of the power shovel  210 . In some embodiments, the valving  252  of the manifold includes a matrix of solenoid valves, where a single solenoid valve is associated with a coupling between each hydraulic pump  232  in the set of pumps with each actuator in the set of actuators. Operation of valving  252  in the manifold  254  allows flows from different hydraulic pumps  232  to be combined for different work functions at different times in a dig cycle of the excavator. 
     According to an exemplary embodiment, the net hydraulic flow available from the hydraulic pumps  232  is less than the net hydraulic flow demanded to perform all work functions of hydraulic actuators of the power shovel  210 . Combining the flows and pressures of the different hydraulic pumps  232  at different times during the dig cycle allows for optimal or increased-efficiency with the selection of hydraulic pumps  232  for the design and manufacturing of the power shovel  210 . The pumps  232  need not be selected based upon a maximum pumping requirement for each work function of the power shovel  210 . Instead, in some such embodiments pumps  232  may be combined to meet the maximum pumping requirements. Additionally, operation of the manifold  254  allows the computerized controller  242  to combine and use hydraulic pumps  232  so as to equalized utilization of the pumps  232 , to avoid excessive wear on particular pumps  232  and to reduce the associated maintenance and downtime required to fix or replace the pumps  232 . 
     According to an exemplary embodiment, the valving  252  is controlled by a computerized controller  242 . To facilitate a particular work function of the power shovel  210 , the computerized controller  242  operates the valving  252  to supply hydraulic fluid to one or more actuators associated with the work function. By way of example, for a work function involving lifting of the bucket, the computerized controller  242  may operate a valve configured to allow delivery of hydraulic fluid from one or more of the pumps  232  to the hydraulic actuators  224 ,  226 ,  228  ( FIG. 7 ) associated with the articulated arm  234 . For other work functions involving locomotion of the power shovel  210 , the computerized controller  242  may redirect hydraulic fluid from one or more of the same pumps  232  to actuators associated with rotation of the tracks  230 . In some embodiments, the computerized controller  242  further controls the speed of the pumps  232  and the rate of power production from the powerhouse. In some embodiments, the computerized controller  242  includes one or more sub-controllers, which may be in direct or indirect communication with each other. 
     Referring to  FIG. 10 , a hydraulic system  310  for an excavator includes first, second, and third hydraulic pumps  312 ,  314 ,  316 , which each include a variable speed drive  318 ,  320 ,  322 , a motor  324 ,  326 ,  328  operated by the drive  318 ,  320 ,  322 , and a fixed-displacement pumping mechanism  312 ,  314 ,  316  (e.g., piston set). The drives  318 ,  320 ,  322  receive power from an input power bus  336  (e.g., direct current bus), and the hydraulic pumps  312 ,  314 ,  316  are coupled to a common hydraulic manifold  340 , which includes valving for distributing hydraulic fluid provided to the manifold  340  by the pumps  312 ,  314 ,  316 . First, second, third, fourth, and fifth actuators  342 ,  344 ,  346 ,  348 ,  350  are coupled to the common hydraulic manifold  340 , and receive hydraulic fluid from the manifold  340  to perform work functions of the excavator. The hydraulic system  310  further includes a supervisory controller  352  (e.g., computerized controller) in communication with the drives  318 ,  320 ,  322  of the hydraulic pumps  312 ,  314 ,  316  and the common hydraulic manifold  340 . In contemplated embodiments, the common hydraulic manifold  340  may direct hydraulic fluid to the pumps  312 ,  314 ,  316 , functioning as hydraulic motors, which drive the motors  324 ,  326 ,  328 , functioning as electric generators for energy regeneration purposes. 
     In contemplated scenarios, all of the hydraulic pumps  312 ,  314 ,  316  may be operating at full capacity or a desired capacity (e.g., most fuel-efficient speed), where the output of the pumps  312 ,  314 ,  316  is insufficient to fully meet demands to facilitate all on-going work functions of the excavator. In such scenarios, the supervisory controller  352  uses a logic module to allocate, via control of the valving in the common hydraulic manifold  340 , the available hydraulic fluid (e.g., energy) to the actuators  342 ,  344 ,  346 ,  348 ,  350  based, at least in part, upon prioritization logic (e.g., a table, a program, a matrix, an algorithm, etc.) of the work functions performed by the excavator. In some embodiments, additional inputs, such as sensor data, human-to-machine interface commands, and other inputs, are used by the supervisory controller  352  to allocate and reallocate the available hydraulic fluid during operation of the excavator. The logic module may be stored on supervisory controller  352  or elsewhere. Operation of the excavator according to the logic module is intended to provided an optimal compromise between work functions occurring at the same time. 
     According to an exemplary embodiment, the prioritization logic is adaptable (e.g., changeable, updatable); and, in some embodiments, dynamically updates during operation of the excavator. For example, if sensors indicate to the supervisory controller  352  that power supplied to one of the actuators  342 ,  344 ,  346 ,  348 ,  350  facilitating a digging function is insufficient, the supervisory controller  352  may reallocate hydraulic fluid supplied to others of the actuators  342 ,  344 ,  346 ,  348 ,  350  performing other work functions, such as crowding the bucket (see, e.g., bucket  222  as shown in  FIG. 7 ). Alternatively, if an operator of the excavator desires to simultaneously lower the boom and drive the excavator forward, the supervisory controller  352  may reallocate hydraulic fluid to the actuators  342 ,  344 ,  346 ,  348 ,  350  associated with either work function, depending upon the prioritization logic. The supervisory controller  352  may provide reduced speed to one of the actuators  342 ,  344 ,  346 ,  348 ,  350  in exchange for increased torque to another. 
     Referring to  FIG. 11 , a form of prioritization logic includes a priority table, represented in  FIG. 11  as a matrix. The matrix includes excavator functions and resources (e.g., hydraulic pumps) to provide hydraulic flow to perform the excavator functions. In such an embodiment, the computerized controller uses the prioritization logic provided in the matrix to assign different hydraulic pumps to different excavator functions, with different orders of priority. In some embodiments, the order of priority is determined by which functions are most critical to a dig cycle, such as a typical dig cycle or an optimal dig cycle. 
     During operation of the excavator, each function may require more than one hydraulic pump, and the excavator may not have enough hydraulic pumps to perform each function at full capacity. As such, the prioritization logic allows the computerized controller to assign or reassign hydraulic pumps to new or additional functions based upon dynamic variables, such as operator commands and digging conditions. If one or more of the hydraulic pumps fail or are at a reduced capacity, the prioritization logic is dynamically updated by the computerized controller. As different hydraulic pumps become available or are further required to perform particular work functions, the prioritization logic will adapt to provide a current optimal allocation of the resources for operation of the excavator. The allocation may be optimal with respect to fuel efficiency, rate of production, minimization of wear of components, operator preference, safety, mission, and/or other qualitative objectives or quantitative factors. 
     Referring now to  FIG. 12 , a logic flow diagram provides an exemplary application of the priority table. When the excavator is operating, the first priority resource is used to facilitate a first work function. If the first work function is not operating at a desired level, the logic module will use a second resource, if available, which corresponds to the next priority resource identified in the priority table. If the second resource is not available, the logic module determines whether the second resource has a higher priority a second work function, for which the second resource is currently assigned, or for the first work function. If the priority is higher for the first work function, then the second resource is reassigned to the first work function. Whether or not the addition of the second resource is sufficient to allow performance of the first work function at a desired level, the logic module returns to the step of determining whether the first work function is operating at the desired level, and the loop repeats with additional lower-priority resources being added as necessary to perform the first work function, and the remaining work functions in order of their priority. While  FIG. 12  shows the logic flow diagram, in other contemplated embodiments, prioritization logic may be applied by the computerized controller according to a variety of logical algorithms, which may be more or less intricate than the logic flow of  FIG. 12 , and which may be specifically tailored to another arrangement of heavy equipment or hydraulic system. 
     The foregoing description was primarily directed to a preferred embodiment. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the claims and not limited by the above disclosure. 
     The construction and arrangements of the heavy equipment and hydraulic systems, as shown in the various exemplary embodiments, are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. Some elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process, logical algorithm, or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention.