Work machine and method for calibrating an electrohydraulic pump in an out

Abstract

The invention relates to a work machine and a method for calibrating an electro-hydraulic pump in an open-center hydraulic system. A work machine having an open-center hydraulic system for controlling actuation of an implement includes an implement control valve, an electrohydraulically controlled pump, a hydraulic circuit coupled to an implement actuator, and a pressure sensor positioned to measure pressure in the hydraulic circuit between the pump and the implement control valve. A calibration system for calibrating a pump includes a controller having a non-transitory computer-readable medium having program instructions for causing a processor to: calibrate a first pump threshold for a pump in a pump flow profile, where the first pump threshold includes a minimum pump control signal for actuating the pump; determining a lag zone in the pump flow curve; and calibrating a second pump threshold for the pump in the pump flow profile, where the second pump threshold includes a maximum pump control signal for actuating the pump below the reduced pressure setpoint.

Description

Technical Field

[0001] The present disclosure relates to a work machine and a method of calibrating an electrohydraulic pump in an open center hydraulic system. Background Art

[0002] In industrial or construction work machinery, systems with hydraulic pumps, valves, and actuators are often used to generate motion for the machine. There are various technologies to manage the control of these hydraulic devices. Systems that mix elements of each available technology can be developed. Some systems rely entirely on fluid mechanical devices that control pumps, valves, and actuators (also commonly referred to as manual or pilot control). However, other systems include electronic devices for control (commonly referred to as electro-hydraulic control). Electro-hydraulic devices can be used to control hydraulic pumps and valves. These devices can take various design forms. One embodiment of an electro-hydraulic control device is to use a solenoid to induce an electromagnetic force on a valve core directly or indirectly by subjecting the solenoid to a given current. The actuation of the valve core by the solenoid is used to generate a given hydraulic pressure, which can then be used to pilot control the main valve core or pump. This provides the ability to electronically control the flow or pressure in a hydraulic circuit, which is ideal for implementation in complex control systems using microcontrollers. Depending on the application of the electro-hydraulic device in a given system, a method of calibrating the components is often required to optimize system performance. The nominal input / output relationship of the device can be determined based on the component design. However, manufacturing tolerances may cause the system to deviate from the theoretical nominal performance from one component to the next. Calibration routines are often developed to account for this variation. Therein lies the opportunity to develop a calibration routine that is optimized to account for variations in pump performance in an open-center hydraulic system. Summary of the invention

[0003] This Summary is provided to introduce some concepts that will be further described in the following Detailed Description and the accompanying drawings. This Summary is not intended to identify key or essential features of the appended claims, nor is it intended to be used as an aid in determining the scope of the appended claims.

[0004] The present disclosure relates to a working machine having a calibration system and a method for calibrating a pump in an open center hydraulic system. The open center hydraulic system controls actuation of an implement. The open center hydraulic system includes an implement control valve configured to control a flow ratio of a fluid through a hydraulic circuit between a reservoir and an implement actuator in response to a valve control signal. The hydraulic system also includes an electrohydraulic control pump for controlling an outlet flow of a fluid through the hydraulic circuit in response to a pump control signal. The hydraulic circuit is coupled to the implement actuator. A pressure sensor is positioned to measure a flow pressure in the hydraulic circuit between the pump and the implement control valve. The calibration system calibrates a pump for controlling an outlet flow of a fluid through the open center hydraulic system. The calibration system includes a controller having a non-transient computer readable medium having program instructions for performing the following steps. The program instructions calibrate a first pump threshold and a second pump threshold in a pump flow curve. A minimum pump control signal for actuating the pump is inferred from the first pump threshold. A maximum pump control signal for actuating the pump below a reduced pressure set point is inferred from the second pump threshold. The program instructions also include controlling actuation of the implement by transmitting a calibrated pump control signal to the electro-hydraulic controlled pump.

[0005] Calibrating a first pump threshold value in a pump flow curve may include: setting the pump at a constant flow; recording the flow pressure; and increasing or decreasing the valve control signal by pump calibration step points until the flow pressure changes by a limit value. The limit value represents a restriction of fluid flow to the reservoir. Calibrating the first pump threshold value also includes: maintaining the valve control signal at a limit setting; eliminating the pump control signal; increasing or decreasing the pump control signal by the pump calibration step points. The program instructions correlate the flow pressure change with the change in the pump control signal to identify a point on the pump flow curve, and iteratively repeat the steps of increasing or decreasing the pump control signal until the flow pressure rises by a target value.

[0006] The program instructions may also include determining a hysteresis band in the pump flow curve. The program instructions include: setting the valve control signal to a limit setting derived from calibrating the first pump threshold; setting the pump control signal to a full pump command; recording the flow pressure; and reducing the valve control signal until the flow pressure drops by a limited value. The program instructions for determining the hysteresis band also include: correlating the flow pressure with the pump control signal to identify a point on the pump flow curve; and iteratively repeating the steps of reducing the pump control signal and correlating the flow pressure with the pump control signal until the flow pressure drops by a second target value.

[0007] Calibrating a second pump threshold for a pump in a pump flow curve may include: setting an adjusted valve control signal indicating that fluid flow to the reservoir is restricted; setting the pump control signal to a full pump command; recording a flow pressure at the full pump command; setting the pump control signal to near a minimum pump control signal; increasing the pump control signal by a calibration step point; and determining whether the flow pressure is within a defined range of the recorded flow pressure at the full pump command. Iteratively repeating the steps of increasing the pump control signal by the calibration step until the flow pressure is within a defined range of the recorded flow pressure at the full pump command.

[0008] The program instructions also include confirming that the fluid is within an operating temperature range before performing a calibration.

[0009] The program instructions also include confirming that the engine speed is within an operating speed range before performing the calibration.

[0010] In another embodiment, program instructions for calibrating a second pump threshold in a pump flow curve include: setting a valve control signal to a limit setting indicating that fluid flow to the reservoir is limited; setting a pump control signal to a full pump command; recording a flow pressure at a full pump command; setting the pump control signal to a value close to a minimum pump control signal; and increasing the pump control signal by a calibration step point. The program instructions also include: determining whether the flow pressure is within a defined range of the recorded flow pressure at a full pump command; and iteratively repeating the step of increasing the pump control signal by a calibration step point until the flow pressure is within a defined range of the recorded flow pressure. Other features and aspects of the present disclosure will become apparent by considering the following detailed description and accompanying drawings.

[0011] A method for calibrating an electro-hydraulic controlled pump on a work machine having an open-center hydraulic system for actuating an implement coupled to the work machine comprises the following steps. In a first step, the method comprises calibrating a first pump threshold value for the pump in a pump flow curve, wherein a minimum pump control signal for actuating the pump is inferred from the first pump threshold value. In a next step, the method comprises calibrating a second pump threshold value for the pump in the pump flow curve, wherein a maximum pump control signal for actuating the pump below a reduced pressure set point is inferred from the second pump threshold value. The method then comprises controlling actuation of an implement actuator by transmitting the calibrated pump control signal to the electro-hydraulic controlled pump.

[0012] Other features and aspects of the disclosure will become apparent by consideration of the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 An embodiment of an open center hydraulic valve system is shown;

[0014] Figure 2An example of a pump flow curve is shown;

[0015] Figure 3 A high level schematic diagram for calibrating a pump is shown;

[0016] Figure 4A shows a schematic diagram for calibrating a first pump threshold;

[0017] Figure 4B is a more detailed schematic diagram of a portion of a flow chart for calibrating a first pump threshold;

[0018] Figure 5A A schematic diagram for calibrating hysteresis is shown;

[0019] Figure 5B is a more detailed schematic diagram of a portion of the flow chart used to calibrate hysteresis;

[0020] Fig. 6A shows a schematic diagram for calibrating the second pump threshold;

[0021] Figure 6B is a more detailed schematic diagram of a portion of a flow chart for calibrating a second pump threshold; and

[0022] Figure 7 It is a method for calibrating the electrohydraulic pump in an open-center hydraulic system. DETAILED DESCRIPTION

[0023] Before explaining any embodiment in detail, it should be understood that the present disclosure is not limited in its application to the details of the construction and arrangement of the components set forth in the following description or shown in the following figures. The present disclosure can support other embodiments and can be practiced or implemented in various ways. In addition, it should be understood that the words and terms used herein are for descriptive purposes and should not be considered as limiting.

[0024] As used herein, unless otherwise limited or modified, a list of elements separated by a conjunction (e.g., "and") and preceded by the phrase "one or more" or "at least one" indicates a configuration or arrangement that may include the individual elements of the list or any combination thereof. For example, "one or more of A, B, and C" or "at least one of A, B, and C" means: only A; only B; only C; or any combination of two or more of A, B, and C (e.g., A and B; B and C; A and C; or A, B, and C).

[0025] As used herein, the term "controller" is a computing device including a processor and memory. A "controller" may be a single device or optionally multiple devices. The controller may further refer, individually or in any combination, to any hardware, software, firmware, electronic control components, processing logic, processing devices, including but not limited to: application specific integrated circuits (ASICs), electronic circuits, processors (shared, dedicated or groups) and memories that execute one or more software or firmware programs, combinational logic circuits, and / or other appropriate components that provide the described functionality.

[0026] The term "processor" is described and illustrated as a single processor. However, depending on the specific needs, expectations, or specific implementations of the controller and the functionality described, two or more processors may be used. The processor may be a component of the controller, a sub-controller for actuation, or part of another device. Generally, the processor may execute program instructions and may manipulate data to perform operations of the controller, including operations using the algorithms, methods, functions, processes, flows, and procedures described in the present disclosure.

[0027] Reference Figure 1 and Figure 2 , the present disclosure relates to a work machine having an open center hydraulic system 110 for calibrating an electrohydraulic pump 105, wherein the system is used to control an implement actuator 115 coupled to the work machine. The electrohydraulic controlled pump 105 outputs an outlet fluid flow (shown as flow from an inlet 125) through a hydraulic circuit in response to a pump control signal 150. Figure 1 In the illustrated embodiment, the system 110 includes an electro-hydraulic controlled main implement control valve 120 coupled to an independent electro-hydraulic controlled pump 105. The implement control valve 120 is configured to control the flow ratio of fluid through the hydraulic circuit between the reservoir 135 and the implement actuator 115 in response to a valve control signal 145. The implement control valve 120 in the system 110 is of an "open heart" type, meaning that when the valve 120 is in a neutral position, the passage is open to allow hydraulic fluid flow to pass freely between the inlet 125 and the reservoir 135. In this system, the pressure in the hydraulic circuit between the pump 105 and the valve 120 is measured by a pressure sensor 140. The pressure sensor 140 is positioned to measure the flow pressure in the hydraulic circuit between the pump 105 and the implement control valve 120. The position of the pump 105 is controlled by the hydraulic pressure introduced from the electro-hydraulic valve 152. The pressure of the pilot control pump 105 is proportional to the current driven to the control solenoid, which is also referred to as the pump control signal 150 below. A minimum pump control signal 205 begins moving the pump, while a maximum pump control signal 210 achieves full actuation of the pump 105. There may be a hysteresis band 212 indicating the difference between an "up ramp" flow curve 215 (shown as a dashed line) and a down ramp flow curve 220 (shown as a solid line). Figure 2The pump control signal 150 is correlated to the pressure 153 measured downstream by the pressure sensor 140, wherein the precise change in flow rate can be identified as a function of the pressure change. The calibration system and method include identifying two calibration points (222a, 222b) and a hysteresis band 212. The two calibration points (222a, 222b) include a first pump threshold 222a for the pump in the pump flow curve 200 and a second pump threshold 222b for the pump 105 in the pump flow curve 200, from which the minimum pump control signal 205 to actuate the pump 105 can be inferred, and from which the maximum pump control signal 210 to actuate the pump 105 can be inferred.

[0028] As one of the working circuit channels opens, the center channel 155 of the open center hydraulic valve 120 is usually closed at a certain rate. The timing of this conversion can vary from valve to valve. Typically, the center channel 155 is not completely closed until the working circuit channel is at least partially open. This ensures that there is always a path for flow, and the ratio of the orifices formed in the center channel 155 and the working circuit channel determines the flow split. However, there is such a point in the spool travel range, where the center channel 155 begins to restrict (usually substantially) before the working circuit channel opens. This restriction setting can be used to create a known restriction path to the reservoir for fluid flow in the hydraulic circuit, which provides a method 300 for calibrating the first pump threshold 222a and the second pump threshold 222b for the pump 105, from which the minimum pump control signal 205 and the maximum pump control signal 210 can be inferred. Pump calibration establishes the area opening downstream of the pump 105. Because the downstream area remains consistent during calibration, the precise change in fluid flow can be identified as a function of the change in the pressure 153 measured by the pressure sensor 140.

[0029] Reference now Figure 3 And continue to refer to Figure 2, schematically illustrates a high-level flow chart for calibrating an electrohydraulic pump 105 in an open center hydraulic system 110. The controller 165 has a non-transient computer readable medium having program instructions that cause the processor to perform the following steps. Some conditions are required to optimize accuracy and / or precision during calibration. In step 305, the condition includes confirming that the engine speed is within the operating speed range before calibration. The engine speed must be set sufficiently to achieve consistent pump flow relative to the pump control signal 150. Based on the design of the program instructions, this may include low idle or wide open throttle. If the minimum engine speed condition is not met (i.e., not within the normal operating range), the program instructions move to step 309 to pause the calibration routine and continue to correct the engine speed in step 307 before repeating step 305. Step 306 discloses another condition that includes confirming that the fluid in the hydraulic circuit is within the operating temperature range before calibration. Typically, the viscosity of fluids outside the normal operating temperature range may be different and may potentially affect the accuracy of the calibration. For example, executing the calibration routine when the fluid temperature is below the normal operating temperature range can produce calibration results that reflect fluid characteristics that are different from normal operating conditions. As shown in steps 309 and 308, the program instructions will need to delay starting the calibration until the fluid is heated to a temperature within the normal operating temperature range. In addition, the program instructions will not necessarily identify the exact minimum pump control signal 205, the maximum pump control signal 210, or the magnitude of the hysteresis band 212 in the pump flow curve 200. However, the program instructions identify calibration points, such as the first pump threshold 222a and the second pump threshold 222b along the pump flow curve 200, from which the minimum pump control signal 205 and the maximum pump control signal 210 can be inferred. Once the engine speed and temperature are within the limited range reflecting normal operating conditions, the program instructions for calibration move forward. In step 310, the method 300 includes generating limit settings. In step 315, the method 300 includes calibrating the first pump threshold 222a for the pump 105 in the pump flow curve 200. In step 320, the method 300 then calibrates the second pump threshold 222b in the pump flow curve 200 for the pump 105. Finally, in step 330, the method 300 may also include determining the hysteresis band 212 in the pump flow curve 200. The calibration of the thresholds and the identification of the hysteresis may be reordered or omitted and need not follow the steps outlined. The calibration is then completed in step 340. In step 350, the work machine may then control actuation of the implement actuator by transmitting the calibrated pump control signal.

[0030] Figure 4A and Figure 4B The program instructions for calibrating the first pump threshold 222a in step 315 are described in detail, wherein: Figure 4B yes Figure 4A Detailed schematic diagram of steps 460 to 480 in FIG. 4. In a first step 410, the program instructions include causing the processor to set the pump control signal 150 to a low flow within the nominal control range. In the next step 420, the flow pressure 153 is recorded. Then, in step 430, the processor gradually increases the valve control signal until the flow pressure 153 changes a limit value, which indicates that the fluid flow to the reservoir is restricted. The pressure sensor 140 will observe a sudden increase in the flow pressure 153, which is reflected by the restriction setting. The program instructions for calibrating the first pump threshold 222a in the pump flow curve 200 (from which the minimum pump control signal 205 can be inferred) further include steps 440 and 450: maintaining the valve control signal 145 at the limit setting and eliminating the pump control signal 150. In one embodiment, for example, elimination can be defined as setting the pump control signal 50 to 0 mA.

[0031] The pressure 153 from the pressure sensor 140 is recorded in step 420. Next, in step 430, the program instructions determine whether the restriction setting has been achieved. Once the restricted path for pump flow is set, the measured value of the flow pressure 153 can be used to derive a relationship that relates the pump control signal 150 to the change in fluid flow. In step 460, the pump control signal is increased or decreased by calibration step points. In one embodiment, the calibration step point can be a step point when the flow pressure 153 changes a defined minimum value. Because the valve 120 has established a restricted path to the reservoir 135, any fluid flow generated by the pump 105 should produce a rise in the flow pressure 153 and a known point on the pump flow curve 200. Step 470 includes causing the change in the flow pressure 153 to be caused by the change in the pump control signal 150. In step 480, the program instructions iteratively repeat the steps of increasing or decreasing the pump control signal 150 until the flow pressure 153 rises to a target value. The target value can be defined by the design of the open-center hydraulic system. The target value must be large enough to ensure that the change in flow rate is equal to the measurable change in flow pressure 153. This can be done using Figure 4BThe "coarse increments" and "fine" increments outlined in are accomplished through the first round. In step 491, the program instructions include setting the pump control signal to a calibration step point. If the flow pressure 153 does not vary within a defined range in step 492, then the pump control signal is increased by 10 mA in step 493. If the flow pressure 153 varies within a defined range, then the pump control signal 150 is set to another calibration step point in step 494. If the flow pressure 153 is not close to or is not within the defined range shown in step 495, then the program instructions use a fine increment such as 1 mA in step 496. If the flow pressure 153 is close to or within the defined range in step 495, then the calibration point of the first pump threshold 222a is found in step 497. The speed of the pump 105 can control the outlet flow of the pump.

[0032] Now turn to Figure 5A and Figure 5B , a hysteresis can be similarly found. This hysteresis is more closely related to the time when the pump servo mechanism is fully actuated. In one embodiment, the program instructions will set or maintain the valve control signal 145 at the limit setting in step 510. Next, in step 520, the pump control signal 150 is set to a full pump command. Due to the limit setting, this situation will produce a considerable pressure drop on both sides of the valve 120. If the valve control signal 145 at the limit setting produces an overflow pressure 153, the safety valve in the hydraulic circuit will open. The processor then records the flow pressure in step 530. In step 540, the program instructions cause the valve control signal 145 to slowly decrease, thereby gradually opening the center channel 155 until the flow pressure 153 begins to drop below the pressure reduction set point. The decrease in flow pressure 153 is representative of a decrease in fluid flow. The observed pressure drop indicates that the flow has begun to decrease, i.e., the hysteresis band 212 for the pump 105. In step 550, the full pump command is eliminated. In step 560, the program instructions include decreasing the pump control signal 150 by a calibrated step point, and in step 570, the program instructions include correlating the flow pressure 153 with the pump control signal 150 to identify a point on the pump flow curve 200. In step 580, the steps of decreasing the pump control signal 150 and correlating the flow pressure 153 with the pump control signal 150 are iteratively repeated until the pressure drops a second target value and continues to map the lower slope 220 of the pump flow curve 200. Similar to the first target value, the second target value is defined by the design of the open center hydraulic system. Figure 5BAn exemplary embodiment of steps 560 through 580 is provided. Once the pump control signal 150 is set to the calibration step point in step 561, the program instructions evaluate whether the flow pressure 153 has dropped by a second target value in step 562. If not, the full pump command is removed in step 563 and the calibration step point is decreased by 10 mA. If this criterion is met, the pump control signal 150 continues to increase the calibration step point by 10 mA in step 564 and decrease in increments of 1 mA using a "fine" adjustment (steps 565-567) until the calibration point is found in step 568.

[0033] Now turn to Fig. 6A and Figure 6B , showing the Figure 3 320 in step 610, wherein the maximum pump control signal 210 is inferred from the second pump threshold value 222b. Calibration of the second pump threshold value 222b includes: setting the adjusted valve control signal 145 in step 610, the adjusted valve control signal indicating that fluid flow to the reservoir 135 is restricted; setting the pump control signal 150 to a full pump command in step 620, and recording the flow pressure 153 in step 630. Next, in step 640, the program instructions include setting the pump control signal to the minimum pump control signal 205, and increasing the pump control signal 150 by a calibration step point in step 650. Then, in step 660, the program instructions determine whether the flow pressure 153 is within a defined range of the flow pressure 153 at the recorded full pump command from step 630. Then, in step 670, the program instructions iteratively repeat the steps of increasing the pump control signal by the calibration step point until the flow pressure 153 is within a defined range of the flow pressure at the recorded full pump command. Similar to the first pump threshold 222a, the program instructions are tuned by "coarse" increments and "fine" increments. Figure 6B An exemplary embodiment of steps 650 to 670 is provided. Once the pump control signal 150 is set to the calibration step point in step 661, the program instructions evaluate whether the flow pressure 153 has risen to the calibration target value in step 663. If not, the pump control signal is set to 0 mA in step 662 and the calibration step point is increased by 10 mA. If this criterion is met, the calibration step point is decreased by 10 mA in step 664 and the pump control signal 150 continues to be gradually increased in increments of 1 mA using "fine" adjustments (steps 665-667) until the calibration point is found in step 668.

[0034] Now turn to Figure 7, a method 700 of calibrating an electro-hydraulic controlled pump 105 on a work machine having an open center hydraulic system 110 is shown. The system is used to actuate an implement coupled to the work machine (i.e., via an implement actuator 115). The open center hydraulic system 110 includes an implement control valve 120 configured to control a flow ratio of a fluid through a hydraulic circuit between a reservoir 135 and the implement actuator 115 in response to a valve control signal 145. The system also includes a pump 105 for controlling an outlet flow of the fluid through the hydraulic circuit in response to a pump control signal 150; and a pressure sensor 140 positioned to measure a flow pressure 153 in the hydraulic circuit between the pump and the implement control valve 120.

[0035] In a first step 710, the method includes calibrating a first pump threshold 222a for the pump 105 in the pump flow curve 200, wherein a minimum pump control signal 205 for actuating the pump 105 may be inferred from the first pump threshold 222a. Then, in step 720, the method 700 may include determining a hysteresis band 212 in the pump flow curve 200. In a next step 730, the method 700 includes calibrating a second pump threshold 222b for the pump 105 in the pump flow curve 200, wherein a maximum pump control signal 210 for actuating the pump 105 below a reduced pressure set point is inferred from the second pump threshold 222b. Finally, in step 740, the method 700 includes controlling actuation of the implement actuator 115 by transmitting the calibrated pump control signal (222a, 222b) to the electro-hydraulic controlled pump 105.

[0036] One or more steps or operations in any method, process, or system discussed herein may be omitted, repeated, or re-ordered and remain within the scope of the present disclosure.

[0037] Although exemplary embodiments of the present disclosure are described above, these descriptions should not be viewed in a limiting or restrictive sense. Rather, several variations and modifications may be made without departing from the scope of the appended claims.

Claims

1. A work machine having an open center hydraulic system for actuating an implement coupled to the work machine, the open center hydraulic system comprising: Hydraulic circuit; an implement control valve configured to control a flow ratio of fluid through the hydraulic circuit between a reservoir and an implement actuator in response to a valve control signal; an electro-hydraulic control pump for controlling an outlet flow of fluid through the hydraulic circuit in response to a pump control signal, the hydraulic circuit being coupled to the implement actuator; a pressure sensor positioned to measure flow pressure in the hydraulic circuit between the pump and the implement control valve; as well as A calibration system for calibrating the pump for controlling an outlet flow of a fluid through the open center hydraulic system, the calibration system comprising a controller having a non-transitory computer readable medium having program instructions for causing a processor to perform the following steps: calibrating a first pump threshold value for the pump in a pump flow curve, wherein a minimum pump control signal for actuating the pump is inferred from the first pump threshold value; calibrating a second pump threshold for the pump in the pump flow curve, wherein a maximum pump control signal for actuating the pump below a reduced pressure set point is inferred from the second pump threshold; and Actuation of the implement actuator is controlled by transmitting a calibrated pump control signal to the electro-hydraulic control pump.

2. The working machine according to claim 1, wherein: The program instructions for calibrating the first pump threshold in the pump flow curve include: setting the pump control signal to a low flow rate; recording the flow pressure; increasing or decreasing the valve control signal by pump calibration step points until the flow pressure changes by a limit value indicating restriction of fluid flow to the reservoir; maintaining the valve control signal at a limit setting; Eliminating the pump control signal; increasing or decreasing the pump control signal by the pump calibration step point; correlating flow pressure changes with changes in the pump control signal to identify a point on the pump flow curve; and The steps of increasing and decreasing the pump control signal are iteratively repeated until the flow pressure rises to a target value.

3. The working machine according to claim 2, wherein: The program instructions further include: Determining a hysteresis band in the pump flow curve, the program instructions for determining the hysteresis band include: setting the valve control signal to the limit setting derived from calibrating the first pump threshold; setting the pump control signal to a full pump command; recording the flow pressure; reducing the valve control signal until the flow pressure drops by a limit value; eliminating the full pump command; causing the pump control signal to decrease by a calibration step point; correlating the flow pressure with the pump control signal to identify a point on the pump flow curve; and The steps of decreasing the pump control signal and correlating the flow pressure to the pump control signal are iteratively repeated until the flow pressure drops by a second target value.

4. The working machine according to claim 3, wherein: The program instructions for calibrating the second pump threshold in the pump flow curve include: setting an adjusted valve control signal, the adjusted valve control signal indicative of restricting fluid flow to the reservoir; setting the pump control signal to a full pump command; recording said flow pressure at full pump command; setting the pump control signal to be close to a minimum pump control signal; increasing the pump control signal by calibrated step points; determining whether the flow pressure is within a defined range of recorded flow pressures at full pump commands; and The step of increasing the pump control signal by calibrated step points is iteratively repeated until the flow pressure is within a defined range of the recorded flow pressure at full pump command.

5. The working machine according to claim 1, wherein: The program instructions further include: Verify that the fluid temperature is within the operating temperature range before calibration.

6. The working machine according to claim 1, wherein: The program instructions further include: Verify that the engine speed is within the operating speed range before calibrating.

7. The working machine according to claim 1, wherein: The program instructions for calibrating the second pump threshold in the pump flow curve include: setting the valve control signal to a restriction setting, the restriction setting indicating restriction of fluid flow to the reservoir; setting the pump control signal to a full pump command; recording said flow pressure at full pump command; setting the pump control signal to be close to a minimum pump control signal; increasing the pump control signal by calibrated step points; determining whether the flow pressure is within a defined range of recorded flow pressures at full pump commands; and The step of increasing the pump control signal by calibrated step points is iteratively repeated until the flow pressure is within a defined range of recorded flow pressures.

8. A computer readable medium for calibrating an electro-hydraulic controlled pump on a work machine having an open center hydraulic system for actuating an implement coupled to the work machine, the open center hydraulic system comprising: an implement control valve configured to control a flow ratio of fluid through a hydraulic circuit between a reservoir and an implement actuator in response to a valve control signal; the pump for controlling an outlet flow of fluid through the hydraulic circuit in response to a pump control signal; a pressure sensor positioned to measure a flow pressure in the hydraulic circuit between the pump and the implement control valve, the computer readable medium comprising program instructions for causing a processor of a controller to perform the following steps: calibrating a first pump threshold value for the pump in a pump flow curve, wherein a minimum pump control signal for actuating the pump is inferred from the first pump threshold value; calibrating a second pump threshold for the pump in the pump flow curve, wherein a maximum pump control signal for actuating the pump below a reduced pressure set point is inferred from the second pump threshold; Actuation of the implement actuator is controlled by transmitting a calibrated pump control signal to the electro-hydraulic control pump.

9. The computer-readable medium of claim 8, wherein: The program instructions for calibrating the first pump threshold in the pump flow curve include: setting the pump control signal to a low flow rate; recording the flow pressure; increasing or decreasing the valve control signal by pump calibration step points; correlating flow pressure changes with the valve control signal to identify a point on the pump flow curve; and The steps of increasing and decreasing the pump control signal are iteratively repeated until the flow pressure rises to a target value.

10. The computer-readable medium of claim 9, wherein: The program instructions further include: Determining a hysteresis band in the pump flow curve, the program instructions for determining the hysteresis band include: setting the valve control signal to a limit setting derived from calibrating the first pump threshold; setting the pump control signal to a full pump command; recording the flow pressure; reducing the valve control signal until the flow pressure drops by a limit value; reducing the pump control signal until the flow pressure changes by the defined value; eliminating the full pump command; causing the pump control signal to decrease by a calibration step point; correlating the flow pressure with the pump control signal to identify a point on the pump flow curve; and The step of calculating an adjustment amount based on repeated decreases in the pump control signal is iteratively repeated until the adjustment amount falls within a defined range.

11. The computer-readable medium of claim 10, wherein: The program instructions for calibrating the second pump threshold in the pump flow curve include: setting an adjusted valve control signal, the adjusted valve control signal indicative of restricting fluid flow to the reservoir; setting the pump control signal to a full pump command; recording said flow pressure at full pump command; setting the pump control signal to be close to a minimum pump control signal; increasing the pump control signal by calibrated step points; determining whether the flow pressure is within a defined range of recorded flow pressures at full pump commands; and The step of increasing the pump control signal by calibrated step points is iteratively repeated until the flow pressure is within a defined range of the recorded flow pressure at full pump command.

12. The computer-readable medium of claim 8, wherein: The program instructions further include: Verify that the fluid temperature is within the operating temperature range before calibration.

13. The computer-readable medium of claim 8, wherein: The program instructions further include: Verify that the engine speed is within the operating speed range before calibrating.

14. The computer-readable medium of claim 8, wherein: The program instructions for calibrating the second pump threshold in the pump flow curve include: setting the valve control signal to a restriction setting, the restriction setting indicating restriction of fluid flow to the reservoir; setting the pump control signal to a full pump command; recording said flow pressure at full pump command; setting the pump control signal to be close to a minimum pump control signal; increasing the pump control signal by calibrated step points; determining whether the flow pressure is within a defined range of recorded flow pressures at full pump commands; and The step of increasing the pump control signal by calibrated step points is iteratively repeated until the flow pressure is within a defined range of recorded flow pressures.

15. A method of calibrating an electro-hydraulic controlled pump on a work machine having an open center hydraulic system for actuating an implement coupled to the work machine, the open center hydraulic system comprising: an implement control valve configured to control a flow ratio of fluid through a hydraulic circuit between a reservoir and an implement actuator in response to a valve control signal; the pump for controlling an outlet flow rate of fluid through the hydraulic circuit in response to a pump control signal; a pressure sensor positioned to measure flow pressure in the hydraulic circuit between the pump and the implement control valve, the method comprising: calibrating a first pump threshold value for the pump in a pump flow curve, wherein a minimum pump control signal for actuating the pump is inferred from the first pump threshold value; calibrating a second pump threshold for the pump in the pump flow curve, wherein a maximum pump control signal for actuating the pump below a reduced pressure set point is inferred from the second pump threshold; and Actuation of the implement actuator is controlled by transmitting a calibrated pump control signal to the electro-hydraulic control pump.

16. The method according to claim 15, wherein: Calibrating the first pump threshold in the pump flow curve comprises: setting the pump control signal to a low flow rate; recording the flow pressure; increasing or decreasing the valve control signal by pump calibration step points until the flow pressure changes by a limit value, the limit value indicating restriction of fluid flow to the reservoir; maintaining the valve control signal at a limit setting; Eliminating the pump control signal; Increase or decrease the pump control signal by the pump calibration step point; correlating flow pressure changes with changes in the pump control signal to identify a point on the pump flow curve; and The steps of increasing and decreasing the pump control signal are iteratively repeated until the flow pressure rises to a target value.

17. The method of claim 16, further comprising determining a hysteresis band in the pump flow curve, wherein: Determining the hysteresis band involves: setting the valve control signal to the limit setting derived from calibrating the first pump threshold; setting the pump control signal to a full pump command; recording the flow pressure; reducing the valve control signal until the flow pressure drops by a limit value; eliminating the full pump command; causing the pump control signal to decrease by a calibration step point; correlating the flow pressure with the pump control signal to identify a point on the pump flow curve; and The steps of decreasing the pump control signal and associating the flow pressure with the pump control signal are iteratively repeated until the flow pressure drops by a second target value.

18. The method according to claim 15, further comprising: Verify that the fluid temperature is within the operating temperature range before calibration.

19. The method according to claim 15, further comprising: Prior to calibration, it is confirmed whether the engine speed of the work machine is within the operating speed range.

20. The method according to claim 15, wherein: Calibrating the second pump threshold in the pump flow curve comprises: setting the valve control signal to a restriction setting, the restriction setting indicating restriction of fluid flow to the reservoir; setting the pump control signal to a full pump command; Record the flow pressure at full pump command; setting the pump control signal to be close to a minimum pump control signal; increasing the pump control signal by calibrated step points; determining whether the flow pressure is within a defined range of recorded flow pressures at full pump commands; and The step of increasing the pump control signal by calibrated step points is iteratively repeated until the flow pressure is within a defined range of recorded flow pressures.

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