Patent Publication Number: US-11649609-B2

Title: Hydraulic system and methods for an earthmoving machine

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to hydraulic systems and methods, and more particularly, to a hydraulic system and methods for an earthmoving machine. 
     BACKGROUND 
     Earthmoving machines, such as wheel loaders, motor graders, excavators, and dozers, are commonly used in material moving applications, including mining, road maintenance, surface contouring, etc. To effectively accomplish tasks associated with these applications, the vehicles often include hydraulic systems to provide functionality and/or control various aspects of the machines, such as hydraulically-powered articulation joints, hydraulically-powered traction devices, and hydraulically powered implements, such as buckets, shovels, and blades. A prime mover, for example a diesel, gasoline, or gaseous fuel-powered internal combustion engine, drives dedicated steering and implement pumps that provide hydraulic power to the steering components and the implements. 
     These machines often include exhaust gas recirculation (“EGR”), in which emissions from the engine may be reduced by recirculating a portion of the engine&#39;s exhaust gas back to the engine cylinders. EGR may reduce harmful emissions from the machine by reducing the peak combustion temperature of the engine. Many diesel engines are coupled to an after-treatment system, which includes a diesel oxidation catalyst (“DOC”). The DOC may also be used to reduce emissions by controlling diesel particulate emissions and/or as an auxiliary catalyst for a filter in the after-treatment system, for example, a diesel particulate filter (“DPF”). Nevertheless, such systems often develop an accumulation of particulate matter (e.g., soot) on the filter, for example, due to low exhaust temperatures. The accumulation of particulate matter may result in increased back pressure on the prime mover. Accordingly, the drive system requires periodic regeneration, for example, to burn off particulate matter that has accumulated in the drive system. The regeneration may promote oxidation (e.g., burning off) of the particulate matter on the filter with heat from engine exhaust. However, under certain operating conditions (e.g., when environmental temperatures are low, when torque on the engine is low, etc.), an exhaust temperature of the engine may not be hot enough to provide regeneration. As a result, the machine may encounter difficulties in performing the regeneration in cold ambient temperature conditions (e.g., below freezing) and/or when there is a low load on the engine. 
     U.S. Pat. No. 7,467,033, issued to Miller et al. on Dec. 16, 2008 (“the &#39;033 patent), describes a method of controlling an engine to maintain a calibrated minimum load for the engine. The method of the &#39;033 patent involves a minimum engine torque adder that is calibrate as a torque ramp rate to adjust the allowable torque limit that is added to the engine torque if the measured engine load is near the calibrated minimum engine load for a given engine speed. The method of the &#39;033 patent may help to maintain engine fuel combustion stability and avoid undesirable engine exhaust gas temperatures during prolonged engine operation at low load. While the control method of the &#39;033 patent may help maintain a calibrated minimum load on an engine, the added load on the engine via the torque added may not be desirable under certain conditions. 
     The systems and methods of the present disclosure may address or solve one or more of the problems set forth above and/or other problems in the art. The scope of the current disclosure, however, is defined by the attached claims, and not by the ability to solve any specific problem. 
     SUMMARY 
     In one aspect, a hydraulic system for a machine may include an implement pump, a valve, and an implement valve subsystem. The implement pump may include a load sensing control, and the valve may control the flow of hydraulic fluid to the implement pump. The implement valve subsystem may include one or more implement control subsystems to control movement of an implement. The valve may be an electrohydraulic proportional relief valve and may include a solenoid configured to adjust the pressure of hydraulic fluid delivered to the implement pump proportionally to a current delivered through the solenoid. 
     In another aspect, a method of operating a hydraulic system for a machine may include, in response to a regeneration cycle for a particulate filter in an after-treatment system for an engine, detecting one or more of an ambient temperature, a temperature of the exhaust of the engine, or a load demand on the engine. The method may also include, in response to one or more of the ambient temperature, the temperature of the exhaust of the engine, or the load demand on the engine being below respective threshold values, delivering current through a solenoid of an electrohydraulic valve. The electrohydraulic valve may control a flow of hydraulic fluid to an implement pump, and the current through the solenoid may cause the electrohydraulic valve to open and deliver hydraulic fluid to the implement pump to upstroke the implement pump. The implement pump may control an implement and may include a load sensing control configured to increase the pressure demand on the implement pump in response to the delivery of hydraulic fluid. The increase pressure demand on the implement pump may be configured to increase the power demand on the engine. 
     In yet another aspect, an earthmoving machine may include an engine, an implement, and a hydraulic system. The hydraulic system may include an implement pump and an electrohydraulic valve. The implement pump may be powered by the engine and may be configured to drive the implement, and the implement pump may include a load sensing control. The electrohydraulic valve may control the flow of hydraulic fluid to the load sensing control of the implement pump. The electrohydraulic valve may include a solenoid configured to adjust the pressure of hydraulic fluid through the electrohydraulic valve proportionally to a current delivered through the solenoid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various exemplary embodiments and together with the description, serve to explain the principles of the disclosure. 
         FIG.  1    is an illustration of an exemplary machine according to aspects of the disclosure. 
         FIG.  2    is a schematic of an exemplary hydraulic system of the machine of  FIG.  1   . 
         FIG.  3    provides a flow chart depicting an exemplary method for controlling the hydraulic system of the machine. 
         FIG.  4    provides a flow chart depicting an exemplary method for calibrating one or more aspects of the hydraulic system of the machine. 
         FIG.  5    illustrates a graph of the current command and the power command formed during the calibration of one or more aspects of the hydraulic system of the machine. 
     
    
    
     DETAILED DESCRIPTION 
     Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the features, as claimed. As used herein, the terms “comprises,” “comprising,” “having,” “including,” or other variations thereof, are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such a process, method, article, or apparatus. Further, relative terms, such as, for example, “about,” “substantially,” “generally,” “approximately,” and “proximate” are used to indicate a possible variation of ±10% in a stated value. 
       FIG.  1    depicts an exemplary machine, for example, a wheel loader  10 . Although the machine depicted in  FIG.  1    is a wheel loader, wheel loader  10  may be any of the types of machines described above. Wheel loader  10  includes a machine body  12 , which may include an operator station, an engine housing, and a prime mover or an engine  100 . Engine  100  may be a diesel engine, and may be coupled to an after-treatment system  102 . For example, an exhaust line from engine  100  may be coupled to after-treatment system  102 . After-treatment system  102  may include a diesel oxidation catalyst (“DOC”)  104  and a particulate filter  106  (e.g., a diesel particular filter or a DPF). Wheel loader  10  may also include an implement assembly  14 . Implement assembly  14  may include an arm  16 , a linkage  18 , and a bucket  20 . Bucket  20  may be coupled to an end of arm  16 . Although not shown, bucket  20  may also be a different work implement, such as a fork, grapple, etc., and, in some aspects, the work implement may be interchangeable. Linkage  18  may have one or more degrees of freedom. Wheel loader  10  may include ground surface engaging devices, such as wheels  21  that support machine body  12  and are powered by engine  100 . Although a wheeled machine is shown and described, one skilled in the art will appreciate that other machines, including track-type machines, may also be utilized.  FIG.  1    also shows wheel loader  10  with a first, lowered configuration (solid lines) of implement assembly  14  and with a second, raised configuration (dashed lines) of implement assembly  14 . 
     In the example of the machine being wheel loader  12 , movement (e.g., lift) of bucket  20  and/or arm  16  may be powered and controlled by a lift actuator  22 . Lift actuator  22  may include, for example, a hydraulic fluid cylinder actuator or any other type of actuator, as would be apparent to one skilled in the art. One or more lift pressure sensors  24  may be configured to measure forces within the actuator  22 , or on another component of lift actuator  22 , and may be force sensors. The tilt of bucket  16  may be powered and controlled by a tilt actuator  26 . Tilt actuator  26  may include, for example, a hydraulic fluid cylinder actuator or any other type of actuator, as would be apparent to one skilled in the art. One or more tilt pressure sensors  28  may be configured to measure forces within tilt actuator  26 , or on another component of tilt actuator  26 , and may be force sensors. For example, as shown in  FIG.  1   , lift pressure sensors  24  and tilt pressure sensors  28  may be disposed in/on a head end and a rod end of lift actuator  22  and tilt actuator  26 , respectively. Alternatively or additionally, lift pressure sensors  24  and tilt pressure sensors  28  may be disposed in other locations relative to an actuator, such as within a hydraulic circuit associated with an actuator (e.g., one or more of control subsystems  208   a - 208   c ,  FIG.  2   ). Forces acting on lift and/or tilt cylinder  22 ,  26  may include a head-end pressure and/or a rod-end pressure on each side of a piston of the actuator. Lift pressure sensors  24  and tilt pressure sensors  28  may be configured to measure one or both of head-end and rod-end pressures of the lift and tilt cylinders, respectively. Alternatively, lift pressure sensors  24  and tilt pressure sensors  28  may be configured to measure a net force acting on a lift or tilt cylinder, respectively. Lift pressure sensors  24  and tilt pressure sensors  28  may detect pressure of fluid within their respective actuator. Force or pressure information may also be derived from other sources, including other sensors. 
     Additionally, wheel loader  10  may include one or more additional sensors, for example, an arm position sensor  32  and a bucket position sensor  34 . Arm position sensor  32  may gather data indicative of a position of arm  14 , including for example, an angle, a height or an extension of arm  14 . Bucket position sensor  34  may gather data indicative of a position of bucket  16 , including, for example, a height, lateral location, and/or tilt of bucket  16 . Although not shown, wheel loader  10  may include one or more additional sensors, inertial measurement units, etc. 
     The sensors mentioned herein may be coupled, for example, via a wired or wireless connection, to a controller  30 . In these aspects, controller  30  may be in communication with one or more features of wheel loader  10  and receive inputs from and send outputs to, for example, one or more user interfaces in the cab or remote from wheel loader  10 . For example, wheel loader  10  may include electrohydraulic and/or hydro mechanical hydraulic systems, and controller  30  may control one or more electrical switches or valves in order to control one or more hydraulic cylinders, actuators, or electrical elements in order to operate wheel loader  10 . It is understood that controller  30  may include one or more controllers each associated with one or more components or systems of wheel loader  10 . For example, controller  30  may be in communication with a valve  204  and/or an implement pump  206  ( FIG.  2   ) for controlling aspects of valve  204  and/or implement pump  206 , which may control aspects of engine  100  (e.g., a load command, a temperature of the output exhaust, etc.), as further detailed below. 
     Engine  100  may be configured to generate and transmit power to wheels  21 , for example, via a transmission (not shown). Engine  100  may include an internal combustion engine that produces mechanical and/or electrical power output. For example, engine  100  may be a four-stroke diesel engine. In this aspect, engine  100  may be coupled to after-treatment system  102 , which may include diesel oxidation catalyst (“DOC”)  104  and particulate filter  106 . Engine  100  may include one or more subsystems, for example, a fuel system, an air induction system, an exhaust system (coupled to after-treatment system  102 ), a lubrication system, a cooling system, and/or the like. Engine  100  may be configured to produce a torque output directed to a transmission and/or to other parasitic loads (e.g., to hydraulic systems (i.e., implement pump  206 ), electrical systems, cooling systems, etc.) through a range of speeds. 
     As mentioned, engine  100  may be coupled to after-treatment system  102 , which may include DOC  104  and particular filter  106 . DOC  104  may be the first component (i.e., directly downstream from engine  100 ) of after-treatment system  102 . For example, DOC  104  may receive an exhaust flow from engine  100  at an inlet of DOC  104 . DOC  104  may be a flow through filter that includes one or more oxidation devices. The one or more oxidation devices may include one or more precious metals, and may help to initiate an oxidation of hydrocarbons, carbon monoxide, unburned fuel and oil, etc. Particulate filter  106  may be downstream of DOC in after-treatment system  102 . Particulate filter  106  may be a wall-flow filter that helps to trap or otherwise collect soot or other particulate material that was not oxidized by DOC  104 . Particulate filter  106  may be heated by the exhaust flow from engine  100 , thereby thermally aging or oxidizing the particulate matter deposited in particulate filter  106  when the exhaust flow is of a sufficient temperature. In some instances, for example, when environmental temperatures are low, when torque on the engine is low, etc., the heat from the exhaust flow from engine  100  may not be hot enough to oxidize the particulate material collected by particulate filter  106 . In these instances, it may be necessary for wheel loader  10  to perform a regeneration cycle to increase the load command on engine  100  such that engine  100  outputs an exhaust flow that is hot enough to oxidize the particulate material (e.g., approximately 600 degrees Celsius). In some examples, although not shown, after-treatment system  102  may include a selective catalytic reducer (SCR), for example, downstream of particulate filter  106 . 
       FIG.  2    is a schematic illustration of a portion of a hydraulic system  200  that may control the position and/or movement of an implement, for example, bucket  16 . As shown in  FIG.  2   , hydraulic system  200  includes a pilot pressure valve  202 , a valve  204 , an implement pump  206 , and an implement valve subsystem  208 . Hydraulic system  200  may include a relief valve  210 , for example between portions of valve  204  and implement pump  206 . For example, relief valve  210  may be a proportional relief valve, which may allow for the control of the pressure in the hydraulic line connecting a discharge line  206   a  of implement pump  206  to valve  204 . Hydraulic system  200  may also include a resolver  212 , for example, between portions of valve  204 , implement pump  206 , and implement valve subsystem  208 . Resolver  212  may include a hydraulic logic element and may help to maintain consistent pressures between portions, for example, pilot pressure portions, of valve  204 , implement pump  206 , and implement valve subsystem  208  by receiving two pressures and outputting the higher of the two pressures. Hydraulic system  200  may also include a margin relief valve  214 , which may be positioned within implement valve subsystem  208 , and may relieve pressure from implement valve subsystem  208  when the hydraulic fluid exceeds a predetermined pressure. Margin relief valve  214  may help to create resistance to the flow of hydraulic fluid driven by implement pump  206 . Furthermore, hydraulic system  200  may include one or more pressure sensors  216 , which may detect the pressure of the hydraulic fluid at one or more locations in hydraulic system  200 . Moreover, hydraulic system  200  may include one or more outlets  218 , for example, to return hydraulic fluid to a reservoir tank. One or more components of hydraulic system  200 , for example, one or more of pilot pressure valve  202 , implement pump  206 , implement valve subsystem  208 , relief valve  210 , pressure sensor  216 , etc., may be in communication (e.g., via a wired or wireless connection) with controller  30 . 
     Pilot pressure valve  202  may be any suitable pressure valve, such as, for example, a relief valve, a piston valve, a guided-piston relief valve, a differential-piston relief valve, etc. Pilot pressure valve  202  may provide a release of hydraulic fluid when the internal pressure of hydraulic system  200  exceeds a pressure of approximately 2500 kPa to approximately 4000 kPa, for example, approximately 3800 kPa. Additionally, pilot pressure valve  202  may be coupled to one or more reservoirs (not shown) of hydraulic fluid. In one aspect, pilot pressure valve  202  may be configured to ensure an adjustable pilot pressure for hydraulic system  200 , for example, controlled by controller  30 . 
     As shown in  FIG.  2   , valve  204  is a directional valve and includes a solenoid  230 . For example, wheel loader  10  may be an electrohydraulic machine, and valve  204  may be an electrohydraulic proportional valve. Valve  204  may be biased toward a closed configuration, but valve  204  may open when current is delivered through solenoid  230 . Valve  204  may be a proportional valve and solenoid  230  may be a proportional solenoid, for example, such that solenoid  230  adjusts and/or regulates flow of hydraulic fluid through valve  204  based on an intensity of an electrical signal (i.e., current), for example, from controller  30 . Valve  204  may be a control valve associated with pump  206 . Additionally, as shown, valve  204  may be upstream of implement pump  206 , for example, such that output fluid from valve  204  may be delivered to pump  206 , for example, through resolver  212  when the pressure of the hydraulic fluid from valve  204  exceeds the pressure of hydraulic fluid on the opposing side of resolver  212 . 
     Implement pump  206  may be a hydraulic pump and may include an integrated load sensing control  232 . As mentioned, implement pump  206  may be powered by engine  100 . Additionally, implement pump  206  may pressurize hydraulic fluid based on a pressure, volume, flow, etc. of hydraulic fluid received at load sensing control  232 . In this aspect, the pressure command on implement pump  206  may be proportional to the current through solenoid  230 , for example, through the relationship between the current through solenoid  230  and the flow of hydraulic fluid through valve  204 . For example, as discussed below, over one or more ranges, the pressure command on implement pump  206  may be substantially linearly correlated to the current through solenoid  230 . In these aspects, valve  204  and solenoid  230  may be controlled to add load on engine  100 , for example, during a regeneration cycle. Additionally, over the one or more ranges, the power command on engine  100  may be substantially linearly correlated to the current through solenoid  230 . 
     Implement valve subsystem  208  may include one or more subsystems, for example, to control the position of bucket  20 . The one or more subsystems may be controlled based on the relative pressures on respective portions of the subsystems. For example, implement valve subsystem  208  may include a rack/dump control subsystem  208   a , a lift/lower/float control subsystem  208   b , and one or more auxiliary control subsystems  208   c . Additionally, implement valve subsystem  208  may include an implement valve relief valve  220 , which may be connected to an outlet  222 , for example, to return hydraulic fluid to the reservoir. 
       FIG.  3    is a flow chart depicting an exemplary method  300  for controlling hydraulic system  200 . In an optional initial step  302 , wheel loader  10  may perform an operation, for example, moving material from one location to another. 
     Next, in a step  304 , wheel loader  10  may initiate a regeneration cycle or procedure. For example, one or more sensors coupled to controller  30  may detect a build up of particulate material on particulate filter  106  in after-treatment system  102 . Alternatively, the regeneration procedure may be initiated after a predetermined amount of operating time for wheel loader  10  since the previous regeneration procedure. As discussed above, the regeneration procedure includes increasing the load command on engine  100  such that the exhaust temperature is increased to a certain temperature and/or for a certain duration to help burn off the particulate material on particulate filter  106  in after-treatment system  102 . 
     A step  306  may include increasing the load on engine  100  during the regeneration procedure by upstroking implement pump  206 , for example, via one or more components of hydraulic system  200 . In this aspect, controller  30  may signal valve  204  to transition from a closed configuration to a more open configuration, for example, by delivering current to solenoid  230 . As discussed above, this current through solenoid  230  may deliver more hydraulic fluid to implement pump  206 , which in turn causes implement pump  206  to pump hydraulic fluid at a higher pressure. Implement pump  206  pumping the hydraulic fluid at the higher pressure may increase the load demand on engine  100 , as engine  100  powers implement pump  206 . The increased load demand on engine  100  may increase the temperature of the exhaust output by engine  100 , which may help to burn off particulate matter on particulate filter  106  in after-treatment system  102 . The hydraulic fluid pumped at the higher pressure by implement pump  206  is not used, for example, does not drive any components of implement valve subsystem  208 . Instead, as discussed below, the pressurized fluid may be released through one or more valves and return to a hydraulic fluid tank or reservoir (not shown). 
     In one aspect, step  306  may be optional. For example, controller  30  may only signal valve  204  to transition to the more open configuration when the temperature at particulate filter  106  is below a certain threshold temperature. In this aspect, controller  30  may be coupled to a temperature sensor, for example, at an inlet of particulate filter  106 . Alternatively or additionally, controller  30  may only signal valve  204  to transition to the more open configuration when the ambient temperature is below a certain threshold temperature. In this aspect, controller  30  may be coupled to a temperature sensor on a portion of wheel loader  10 . Furthermore, controller  30  may be coupled to one or more of lift pressure sensor  24 , tile pressure sensor  28 , arm position sensor  32 , and/or bucket position sensor  34 . Controller  30  may receive one or more signals from these sensors indicative of a position and/or load of bucket  20 , which may be indicative of a pressure demand on implement pump  206  and/or a power demand on engine  100 . In this aspect, controller  30  may only signal valve  204  to transition to the more open configuration when one or more of the pressure demand on implement pump  206  and/or the power demand on engine  100  are below certain thresholds, for example, indicating low load conditions. 
     Then, a step  308  includes ending the regeneration procedure. If step  306  is performed, step  308  includes signaling valve  204  to transition to a more closed configuration, for example, by delivering a lower current (or no current) through solenoid  230 . 
     Lastly, method  300  includes a step  310 , in which wheel loader  10  returns to performing the operation (e.g., moving material). Step  310  may include indicating to the user that the regeneration procedure is complete. Nevertheless, it is noted that wheel loader  10  may also be operated during the regeneration procedure. 
     Method  300  may also include displaying one or more indications to a user, for example, via a user interface. For example, one or more the indications may indicate to the user that wheel loader  10  is undergoing a regeneration procedure, an estimated duration of the regeneration procedure, when the regeneration procedure is complete or nearing completion, etc. 
       FIG.  4    is a flow chart depicting an exemplary method  400  for calibrating and/or mapping a relationship of components of hydraulic system  200 . For example, method  400  is a method for calibrating and/or mapping a relationship of a signal or current to valve  204  relative to a pressure command on implement pump  206  and, correspondingly, a load command on engine  100 .  FIG.  5    is a graph of portions of the calibration during method  400 . 
     Although not shown, method  400  may include an initial step of entering a calibration mode, for example, automatically and/or based on user input. The initial step of entering the calibration mode may be done after the manufacture of wheel loader  10  and during initial calibration of wheel loader  10 , for example, before shipment to a user. Alternatively or additionally, the initial step of entering the calibration mode may be done while wheel loader  10  is at a work site. In some aspects, various aspects of method  400  may depend on the operational conditions of wheel loader  10  and/or surrounding wheel loader  10 , for example, ambient temperatures, work site elevation, bucket load conditions, engine speeds, etc. A step  402  includes setting engine  100  at a first engine speed, for example, approximately 800 rotations per minute (“rpm”). A step  404  then includes increasing (or ramping up) the current delivered to solenoid  230 , for example, to transition valve  204  to a more open position such that a greater amount of hydraulic fluid and/or a higher pressure of hydraulic fluid is delivered to implement pump  206 . Step  404  may include increasing the current to solenoid  230  until a pump discharge pressure (e.g., as measured by pressure sensor  216 ) changes by a certain amount, for example, by approximately 100 kPa. The change in the pump discharge pressure may be indicative of the start of an active range for valve  204 , which may be a proportional EH valve. Nevertheless, the change in the pump discharge pressure may not yet indicate the active range over which the current to solenoid controls the overall load add control on engine  100 . 
     Method  400  further includes a step  406 , in which the current to solenoid  230  is incrementally increased or ramped up. For example, the current to solenoid  230  may be increased by approximately 0.01 amps to approximately 0.02 amps, and may be held at each current level for a period of time, for example, approximately 5 seconds, approximately 10 seconds, approximately 20 seconds, approximately 30 seconds, etc. In one aspect, the current to solenoid  230  may be increased by approximately 5% to 10% of the previous current value. Each level of current to solenoid may yield a steady state pressure generated by the pump, which may be measured and recorded. The incremental increase in the current to solenoid  230  may be performed until the pressure change between consecutive current levels is less than a certain value (e.g., approximately 50 kPa). A pressure change between consecutive current levels being less than the certain value may be indicative of implement pump  206  reaching a maximum displacement. At the maximum displacement, the current command, the measured average pump pressure, and the actual engine speed may be recorded. 
     The current values and pressure values at the first engine speed may be correlated, for example, graphed, as discussed below with respect to  FIG.  5   . For example, the commanded current, actual average pump pressure while at the commanded current, and an actual average engine speed may all be recorded for each commanded current level to solenoid. Then, the output power (or power command on engine  100 ) may be calculated, for example, using the engine speed and pump pressure. In one aspect, the calculation may assume a pump speed to engine speed ratio and a maximum pump displacement based on various system and/or design parameters. A pump flow may be calculated based on the pump speed times the maximum pump displacement. The pump flow for a given situation may be calculated based on the pressure of hydraulic fluid in discharge line  206   a . For example:
 
Pump Flow=Engine Speed×1.0448×Maximum Pump Displacement
 
     The pump power may be calculated by the pump flow times the average pump pressure. In one example, the maximum pump power may equal the pump displacement of 165 cc/revolution times the average pump pressure of 8,000 kPa. Accordingly, if the engine speed is 800 rpm, the output engine power may calculated to be approximately 18 kW. It is noted that this calculation includes multiplying by 1.667×10 −8  in order to convert to kilowatts. Alternatively, although not shown, instead of calculating pump power by multiplying the flow and pressure, the pump power may calculated by multiplying the torque and the shaft speed. 
     Next, method  400  includes a step  408 , in which engine  100  is set to a second engine speed, for example, approximately 1800 rpm. Then, step  406  may be repeated at the second engine speed as a step  410 . For example, the current to solenoid  230  may be increased until a pump discharge pressure changes by a certain amount, for example, approximately 100 kPa. The change in the pump discharge pressure may be indicative of the start of an active range for valve  204 , which may be a proportional EH valve. Additionally, the current to solenoid  230  may then be incrementally increased or ramped up, and the pump discharge pressure at each level of current to solenoid  230  may yield a steady state pressure generated by the pump, which may be measured and recorded. Again, the maximum pump flow at the second engine speed may be calculated, and then the engine power may be calculated at the second engine speed. 
     As shown in  FIG.  5   , the measurements made during of method  400  may be graphed as a current to power calibration curve. For example, the two sets of solenoid current commands and the calculated engine power commands (at the two different engine speeds) may be plotted on a graph ( FIG.  5   ), and method  400  may extrapolate a line between the two points to create a current to power calibration curve. The current to power calibration curve may be used to correlate a current through solenoid  230  with a power command on engine  100 , and thus a resulting temperature of the exhaust from engine  100 , which may help burn off particulate material on particulate filter  106 . It is noted that the measurements of method  400  and graph of  FIG.  5    assumes a substantially linear relationship between the power of implement pump  206  and the current through solenoid  230 . If other or additional components are used, this relationship may not be substantially linear. In this instance, the steps of method  400  may be repeated, for example, in order to obtain additional data points (e.g., third and fourth data points). The data points on the graph of the current through solenoid  230  and the power of implement pump  206  may then be used to determine the relationship. In this aspect, method  400  may be repeated as many times as necessary to obtain data points and determine the relationship between the current through solenoid  230  and the power of implement pump  206 . 
       FIG.  5    illustrates a graph  500  of an exemplary relationship between the current command (e.g., in amps (“A”)) delivered to solenoid  230  and the power command (i.e., in kilowatts (“kW”)) output by engine  100 , for example, in order to power implement pump  206 . The power command may be an additional power command relative to a baseline power command on engine  100 , for example, under idling conditions. As shown, with 0 A delivered to solenoid  230 , engine  100  outputs a power command of 0 kW. As the current is increased, for example, to approximately 1.160 A, the power command increases, for example, to approximately 0.1 kW. This initial increase in power command relative to the increased current command may include a steep slope, as shown by a portion  502 . 
     As discussed above, portion  502  may correspond to step  404 . Then, as the current is further increased, the increase in power command relative to the increased current command may include a slope that is less steep, as shown by portion  504 . Over portion  504 , at a first engine speed (e.g., 800 rpm), the current command may be increased from approximately 1.160 A to approximately 1.4 A, and the power command on engine  100  may be calculated based on the engine speed and the pressure of hydraulic fluid from implement pump  206 . In this aspect, the power command on engine  100  may be approximately 45 kW. Then, the current command to solenoid  230  may be increased to approximately 1.9 A, and the resulting power command on engine  100  may be approximately 80 kW. However, further increasing the current command may not significantly increase the current through solenoid  230 , and minimally increase the power command, for example, corresponding to the maximum pump flow. For example, as shown in  FIG.  5   , the current command may remain at approximately 1.9 A, and the power command may be approximately 100 kW. This may be indicative of saturation of the current command at a configurable maximum current value, for example, as shown by portion  506  of graph  500 . Alternatively or additionally, this may be indicative that implement pump  206  has reached maximum displacement, and thus that no additional power can be achieved. Furthermore, this may be indicative that the control valve output pressure has saturated or at a maximum value. As discussed above, portions  504  and  506  may correspond to step  406 . 
     Engine  100  may then be set to a second engine speed, for example, a maximum engine speed and/or approximately 1800 rpm, corresponding to step  408 . Then, step  404  may be repeated, for example, as step  410 , and the current delivered to solenoid  230  may be incrementally increased until a pressure change between consecutive current values is less than a certain value. For example, step  410  may include setting the current command at approximately 1.29 A and measuring an engine command of approximately 18 kW. Moreover, setting the current command at approximately 1.56 A may result in a measured engine command of approximately 55.2 kW. These measurements may also be plotted in graph  500 . For example, as shown in  FIG.  5   , portion  504  may be substantially linear, illustrating the relationship between the current applied to solenoid  230  and the power command on engine  100  over this active range, corresponding to step  406  of method  400 . Additionally, graph  500  may be used to extrapolate a resulting power command on engine  100  for one or more current commands for solenoid  230 , which may also be used to increase the load on engine  100 , for example, to help burn off particulate material on particulate filter  106 , to help in general retarding (e.g., when wheel loader  10  is traveling down a hill), to help warm up engine  100  or other components of wheel loader  10 , for example, when starting wheel loader  10  in cold ambient temperatures, etc. Although the above current commands and power commands are discussed as a part of graph  500 , it is noted that additional data points may be used to form graph  500  or otherwise extrapolate a relationship of the current command and resulting power command under additional conditions, for different engine speeds, etc. Then, the calibrated relationship between the current commands and the power commands may be used, for example, in method  300 , to help perform a regeneration procedure. Additionally, as mentioned above, one or more steps of method  400  may be repeated in order to obtain additional measurements of the pressure changes between different current values, for example, in order to more accurately determine a correlation between the current through solenoid  230  and the power of implement pump  206 . 
     Moreover, although not shown, method  400  may be performed, and graph  500  may be formed, in a reverse order. For example, for a first engine speed, a maximum current command may be applied to saturate solenoid  230  with the maximum current, and the actual pump power may be calculated, indicative of portion  506  as discussed above. Then, the current command may be incrementally reduced until the pump pressure decreases by a certain amount. The current command may be reduced further, and the actual pump power may be determined and plotted, as discussed above to form portion  504 . Lastly, the current command may be reduced further (closer to 0 A), until the pump pressure decreases significantly, indicative of portion  502 . Then, these steps may be repeated at a second engine speed. In some instances, the pump pressure decrease may be observed after engine  100  has been set to the second engine speed. The current commands on solenoid and resulting actual pump power on engine  100  may be graphed to form a graph similar to graph  500 . 
     INDUSTRIAL APPLICABILITY 
     The disclosed aspects of hydraulic system  200  of the present disclosure may be used in any wheel loader  10  or other machine having one or more hydraulic systems. Valve  204  may be incorporated into hydraulic system  200  with minimal modifications of existing hydraulic systems. Moreover, the delivery of hydraulic fluid from valve  204  to implement pump  206  causes implement pump  206  to upstroke without a pressure demand from implement valve subsystem  208 . Accordingly, the regeneration command, via implement pump  206 , may require an increased load command on engine  100  (e.g., increasing the temperature of the exhaust from engine  100  to increase the temperature at particulate filter  106 ) without an implement command. 
     As discussed above, valve  204  may be an electrohydraulic valve with solenoid  230 . Using valve  204  to deliver hydraulic fluid to implement pump  206 , for example, by applying current through solenoid  230 , may cause implement pump  206  to upstroke and demand greater power from engine  100 , even though implement pump  206  or implement valve  208  are not otherwise requesting greater power from engine  100 . Additional components of hydraulic system  200 , for example, margin relief valve  214 , help to release or dump hydraulic fluid from hydraulic system  200 , which may help to reduce the overall pressure, generate a flow restriction for hydraulic fluid, and/or increase the pressure on implement pump  206  and the power demand on engine  100 , without inadvertently delivering high pressure hydraulic fluid to implement valve subsystem  208  or individual subsystems  208   a - 208   c . The pressure demand on implement pump  206 , and thus the power demand on engine  100 , may be proportional to the current applied through solenoid  230  of valve  204 . Moreover, the increase power demand on engine  100  may increase the temperature of exhaust from engine  100 , which may help perform or expedite a regeneration cycle to burn off or otherwise remove particulate material on particulate filter  106  of after-treatment system  102 , for example, when wheel loader  10  is in cold ambient temperature conditions and/or there is a low load on engine  100 . Additionally, it is noted that the strategy to increase the power demand on engine  100  discussed herein may also be used in other circumstances. For instance, the strategy to increase the power demand on engine  100  may be used for general retarding, for example, while wheel loader  10  is traversing a steep down grade and additional load on engine  100  is required. Furthermore, the strategy to increase the power demand on engine  100  may be used to help warm up engine  100  and/or other elements (e.g., hydraulic system  200 ) of wheel loader  10 , for example, when starting wheel loader  10  in cold ambient temperature conditions. 
     Furthermore, the calibration methods discussed herein may allow for a user and/or controller  30  to extrapolate a relationship between current commands on solenoid  230  and the resulting power command on engine  100 . For example, as discussed above, within a determined range (i.e., portion  504 ), increasing the current through solenoid  230  increases the flow of hydraulic fluid to implement pump  206 , which proportionally increases a pressure demand on implement pump  206 , creating a proportional power command on engine  100 . As a result, the temperature of exhaust output from engine  100  may be increased without otherwise moving other components of wheel loader  10 . Moreover, this procedure may be performed by controller  30 , thus reducing or eliminating a need for user intervention during a regeneration cycle. For example, controller  30  may determine the range of portion  504 . Controller  30  may then selectively deliver current through solenoid  230  during a regeneration cycle to control the output pressure of implement pump  206 , and thus control the load demand on engine  100  and increase the temperature of exhaust output from engine  100  during the regeneration cycle, for example, when wheel loader  10  is in cold ambient temperature conditions and/or there is a low load on engine  100 . Based on the calibration, controller  30  may deliver an appropriate or necessary amount of current to solenoid  230  to increase the power command on engine  100  as appropriate or needed, for example, in order to increase the temperature of the exhaust from engine  100  and correspondingly increase the temperature at particulate filter  106 . As mentioned, controller  30  may be coupled to one or more temperature sensors, along with lift pressure sensor  24 , tilt pressure sensor  28 , arm position sensor  32 , bucket position sensor  34 , etc., and may thus determine when temperature and/or load conditions necessitate performing method  300  during a regeneration cycle. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system without departing from the scope of the disclosure. Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. For example, hydraulic system  200 , method  300 , and method  400  may be used on any machine having integrated hydraulic systems. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.