Control method for a hydraulic system and hydraulic system

Abstract

The application discloses a control method of a hydraulic system and the hydraulic system. The hydraulic system comprises a hydraulic pump, a displacement control valve, a main valve, a relief valve, an unloading valve and a working oil cylinder. The spool opening of the unloading valve is adjustable to switch the hydraulic system to a calibration state. The control method comprises the following steps: controlling the spool opening of the unloading valve to be at a first opening to enter the calibration state; controlling the input current of the displacement control valve according to a preset current change curve within a set time period; obtaining a pressure change curve of the oil outlet of the hydraulic pump within the set time period according to the pressure of the oil outlet; and obtaining a pressure curve change inflection point according to the pressure change curve, obtaining a current-flow relationship of the hydraulic pump based on the current change curve, the pressure curve change inflection point, the engine speed and the minimum and maximum design displacement values of the hydraulic pump to complete calibration. The hydraulic pump is calibrated based on the pressure signal, without the need of installing an external flow detection device, and efficient calibration of the hydraulic pump is realized.

Description

Technical Field

[0001] This application relates to the field of calibration technology for electro-hydraulic control systems of engineering machinery, and in particular to a control method for a hydraulic system and a hydraulic system. Background Technology

[0002] In construction machinery, with the increasing electrification and energy efficiency of mainframe products, excavators, for example, are gradually adopting electronically controlled multi-way valves and electronically controlled main pumps. As the power component providing hydraulic energy, the electronically controlled main pump directly affects the excavator's overall working efficiency and fuel consumption; therefore, precise control of its flow rate is crucial. Issues such as production consistency during the initial manufacturing process and mechanical wear and aging during later use will affect the current-flow characteristic curve of the electronically controlled main pump, thus impacting the overall machine's working efficiency and fuel consumption.

[0003] It should be noted that the statements in this background section only provide background information relevant to this application and do not necessarily constitute prior art. Summary of the Invention

[0004] This application provides a control method and a hydraulic system for a hydraulic system, so as to make pump calibration more efficient.

[0005] The first aspect of this application provides a control method for a hydraulic system. The hydraulic system includes a hydraulic pump, a displacement control valve, a main valve, a relief valve, an unloading valve, and a working cylinder. The displacement control valve controls the displacement of the hydraulic pump. The outlet of the hydraulic pump is connected to the working cylinder through the main valve. The relief valve is located between the outlet of the hydraulic pump and the oil tank. The outlet of the hydraulic pump is connected to the oil tank through the unloading valve. The valve core opening of the unloading valve is adjustable to switch the hydraulic system between the working state and the calibration state. The control method of the hydraulic system includes the following steps: controlling the valve core opening of the unloading valve to the first opening to put the hydraulic system into the calibration state; controlling the input current of the displacement control valve within a set time period according to a preset current change curve; acquiring the pressure at the outlet of the hydraulic pump in real time and acquiring the pressure change curve of the outlet of the hydraulic pump within the set time period based on the outlet pressure; acquiring the inflection point of the pressure change curve based on the pressure change curve, and acquiring the current-flow relationship of the hydraulic pump based on the current change curve, the inflection point of the pressure curve, the engine speed, and the minimum and maximum design displacement values ​​of the hydraulic pump to complete the calibration of the hydraulic pump.

[0006] In some embodiments, the hydraulic system further includes a pressure sensor. The pressure sensor is located at the outlet of the hydraulic pump. Real-time acquisition of the pressure at the outlet of the hydraulic pump includes detecting the pressure at the outlet in real time using the pressure sensor.

[0007] In some embodiments, controlling the input current of the displacement control valve within a set time period according to a preset current change curve includes increasing the input current to a set value within the set time period to raise the outlet pressure from the minimum pressure to the maximum pressure. Obtaining the inflection point of the pressure curve change based on the pressure change curve and obtaining the current-flow relationship of the hydraulic pump based on the current change curve, the inflection point of the pressure curve change, the engine speed, and the minimum and maximum design displacement values ​​of the hydraulic pump to complete the calibration of the hydraulic pump includes obtaining the minimum pressure time point when the outlet pressure begins to increase and the maximum pressure time point when the outlet pressure rises to the maximum through the pressure change curve; then obtaining the minimum pressure current value corresponding to the minimum pressure time point and the maximum pressure current value corresponding to the maximum pressure time point through the current change curve; and obtaining the current-flow relationship based on the minimum and maximum pressure current values.

[0008] In some embodiments, controlling the input current of the displacement control valve according to a preset current change curve within a set time period includes increasing the input current to a set value over time, maintaining it for a period of time, and then decreasing it. Obtaining the inflection point of the pressure curve change based on the pressure change curve and obtaining the current-flow relationship of the hydraulic pump based on the current change curve, the inflection point of the pressure curve change, the engine speed, and the minimum and maximum design displacement values ​​of the hydraulic pump to complete the calibration of the hydraulic pump includes increasing the outlet pressure from minimum to maximum through the input current, maintaining it for a period of time, and then decreasing it to minimum. Obtaining the first inflection point when the outlet pressure begins to increase, the second inflection point when the outlet pressure reaches its maximum value, the third inflection point when the outlet pressure begins to decrease, and the fourth inflection point when the outlet pressure reaches its minimum value from the pressure change curve, obtaining the corresponding first, second, third, and fourth current values ​​from the current change curve based on these four inflection points, and then obtaining the current-flow relationship based on these four current values.

[0009] In some embodiments, the control method further includes controlling the input current of the displacement control valve according to a preset current change curve during multiple set time periods, obtaining multiple sets of four inflection points corresponding to the multiple set time periods, obtaining multiple sets of four current values ​​based on the multiple sets of four inflection points and the current change curve, and then calculating the error value between the multiple sets of four current values. If the error value exceeds the error setting value, the same input current is re-inputted multiple times until the error value is less than the error setting value, and then the average value of the multiple sets of four current values ​​is taken.

[0010] In some embodiments, the first opening degree ranges from 90% to 100%.

[0011] In some embodiments, the control method further includes controlling the valve core opening of the unloading valve to a second opening to bring the hydraulic system into operation, wherein the second opening ranges from 10% to 90%.

[0012] In some embodiments, the hydraulic system further includes a control valve for controlling the spool opening of the unloading valve. The control method of the hydraulic system further includes controlling the operation of the control valve to make the spool opening of the unloading valve adjustable.

[0013] In some embodiments, the hydraulic system further includes an engine control unit. The engine control unit is connected to the engine drive of the construction machinery. The control method for the hydraulic system further includes adjusting the engine speed to the rated speed via the engine control unit before entering the calibration state.

[0014] A second aspect of this application provides a hydraulic system. The hydraulic system includes a controller, a hydraulic pump, a main valve, a displacement control valve, a relief valve, an unloading valve, and a working cylinder. The outlet of the hydraulic pump is connected to the working cylinder via the main valve. The displacement control valve controls the displacement of the hydraulic pump. The relief valve is located between the outlet of the hydraulic pump and the oil tank. The outlet of the hydraulic pump is connected to the oil tank via the unloading valve. The valve core opening of the unloading valve is adjustable. The controller is configured to execute the control method of the hydraulic system as described above.

[0015] Based on the technical solution provided in this application, the hydraulic system includes a hydraulic pump, a displacement control valve, a main valve, a relief valve, an unloading valve, and a working cylinder. The displacement control valve is used to control the displacement of the hydraulic pump. The outlet of the hydraulic pump is connected to the working cylinder through the main valve. The relief valve is located between the outlet of the hydraulic pump and the oil tank. The outlet of the hydraulic pump is connected to the oil tank through the unloading valve. The valve core opening of the unloading valve is adjustable to switch the hydraulic system between the working state and the calibration state. The control method of the hydraulic system includes the following steps: controlling the valve core opening of the unloading valve to the first opening position. The calibration process involves several steps: first, adjusting the pressure to bring the hydraulic system into calibration mode; second, controlling the input current of the displacement control valve within a set time period based on a preset current change curve; third, acquiring the outlet pressure of the hydraulic pump in real time and obtaining the outlet pressure change curve within the set time period; fourth, identifying the inflection point of the pressure curve; and finally, determining the current-flow relationship of the hydraulic pump based on the current change curve, the inflection point of the pressure curve, engine speed, and the minimum and maximum design displacement values ​​of the hydraulic pump to complete the calibration. Since the hydraulic pump is calibrated based on pressure signals, and pressure detection devices are inherent in all hydraulic systems, there is no need to install or remove external flow detection devices, thus enabling efficient and convenient calibration of the hydraulic pump.

[0016] Other features and advantages of this application will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0018] Figure 1 This is a flowchart of a control method for a hydraulic system according to an embodiment of this application.

[0019] Figure 2 This is a schematic diagram of the input current for the control method of the hydraulic system according to an embodiment of this application.

[0020] Figure 3 This is a schematic diagram of multiple identical input currents in the control method of the hydraulic system according to an embodiment of this application.

[0021] Figure 4 The hysteresis curve obtained by the control method of the hydraulic system according to the embodiments of this application, and the current-flow relationship obtained by fitting the hysteresis curve.

[0022] Figure 5 This diagram illustrates the relationship between the valve core displacement and valve opening area of ​​the unloading valve in the control method of the hydraulic system according to an embodiment of this application.

[0023] Figure 6 This is a schematic diagram of a hydraulic system according to an embodiment of this application.

[0024] In the picture:

[0025] 11. Hydraulic pump; 12. Displacement control valve; 13. Unloading valve; 14. Pressure sensor; 15. Control valve; 16. Engine control unit; 17. Controller; 18. First directional valve; 19. Second directional valve; 110. First working cylinder; 111. Second working cylinder; 112. Relief valve. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0027] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0028] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways, and the spatial relative descriptions used herein will be interpreted accordingly.

[0029] In existing technologies, there are two main methods for calibrating electronically controlled pumps. The first method is based on flow signals; however, this method requires the installation and removal of external equipment to detect the flow, which is not suitable for calibrating large batches of pumps. The second method is based on engine torque; however, this method has certain risks and errors, lower calibration accuracy, and a more cumbersome calibration process.

[0030] To address the shortcomings of existing technologies, this application proposes an efficient and convenient automatic calibration method for electrically controlled pumps. (Reference) Figure 1 and Figure 6The hydraulic system includes a hydraulic pump 11, a displacement control valve 12, a main valve, a relief valve 112, an unloading valve 13, and a working cylinder. The displacement control valve 12 controls the displacement of the hydraulic pump 11. The outlet of the hydraulic pump 11 is connected to the working cylinder via the main valve. The relief valve 112 is located between the outlet of the hydraulic pump 11 and the oil tank. The outlet of the hydraulic pump 11 is connected to the oil tank via the unloading valve 13. The valve opening of the unloading valve 13 is adjustable to switch the hydraulic system between a working state and a calibration state. The control method of this hydraulic system includes the following steps:

[0031] S1, control the valve core opening of the unloading valve 13 to the first opening degree so that the hydraulic system enters the calibration state;

[0032] S2, according to the preset current change curve, control the input current of the displacement control valve 12 within a set time period;

[0033] S3, real-time acquisition of the pressure at the outlet of hydraulic pump 11 and acquisition of the pressure change curve at the outlet of hydraulic pump 11 within a set time period based on the pressure at the outlet; and

[0034] S4. Obtain the inflection point of the pressure curve change based on the pressure change curve, and obtain the current-flow relationship of the hydraulic pump 11 based on the current change curve, the inflection point of the pressure curve change, the engine speed, and the minimum and maximum design displacement values ​​of the hydraulic pump to complete the calibration of the hydraulic pump 11.

[0035] This application calibrates the hydraulic pump based on pressure signals. Since pressure detection devices are present in all hydraulic systems, there is no need to install and remove external flow detection devices, thus enabling efficient and convenient calibration of the hydraulic pump. Furthermore, the hydraulic system in this embodiment can switch from the operating state to the calibration state by adjusting the opening of the unloading valve, without the need for any additional external testing equipment. The calibration process is convenient and quick.

[0036] Specifically, a controller 17 is also provided in this hydraulic system. The current variation curve can be set through the controller 17, and all the above steps are automatically executed by the controller 17. Therefore, this method can achieve automatic and efficient calibration of the hydraulic system. In step S1, the controller 17 first controls the valve core of the unloading valve 13 to a large opening, bringing the entire hydraulic system into the calibration state. In step S2, the controller 17 controls the current input to the displacement control valve 12 according to the preset current variation curve. The valve core opening of the displacement control valve 12 changes based on the magnitude of the input current, thus changing the pressure at its output port. This pressure change at the output port will change the swashplate angle of the hydraulic pump 11, causing a change in the displacement of the hydraulic pump 11. With the rotational speed of the hydraulic pump 11 remaining constant, the flow rate of the hydraulic pump changes due to the change in displacement. As can be seen from the throttle flow formula, a change in flow rate will cause a change in the pressure at its outlet. Therefore, the displacement control valve 12 causes a change in the pressure at the outlet of the hydraulic pump 11. In step S3, the controller 17 acquires the outlet pressure in real time and converts it into a time-dependent pressure variation curve. In step S4, controller 17 obtains the inflection point of the pressure curve change based on the pressure change curve, and fits the current-flow relationship of the hydraulic pump (i.e., current-flow characteristic curve B) based on the current change curve, the inflection point of the pressure curve change, the engine speed, and the minimum and maximum design displacement values ​​of the hydraulic pump. The selection of the inflection point of the pressure curve change and the fitting process of the current-flow characteristic curve B will be described in detail below.

[0037] refer to Figure 6 In some embodiments, the hydraulic system further includes a pressure sensor 14. The pressure sensor 14 is located at the outlet of the hydraulic pump 11. Real-time acquisition of the pressure at the outlet of the hydraulic pump 11 includes real-time detection of the outlet pressure via the pressure sensor 14. Specifically, the pressure sensor 14 is signal-connected to the controller 17. The pressure sensor 14 transmits the detected pressure value to the controller 17. The controller 17 obtains a pressure change curve based on the pressure value.

[0038] In some embodiments, controlling the input current of the displacement control valve 12 within a set time period according to a preset current change curve includes increasing the input current to a set value within the set time period to raise the outlet pressure from the minimum pressure to the maximum pressure. Obtaining the inflection point of the pressure curve change based on the pressure change curve and obtaining the current-flow relationship of the hydraulic pump 11 based on the current change curve, the inflection point of the pressure curve change, the engine speed, and the minimum and maximum design displacement values ​​of the hydraulic pump to complete the calibration of the hydraulic pump 11 includes obtaining the minimum pressure time point when the outlet pressure begins to increase and the maximum pressure time point when the outlet pressure rises to the maximum through the pressure change curve; then obtaining the minimum pressure current value corresponding to the minimum pressure time point and the maximum pressure current value corresponding to the maximum pressure time point through the current change curve; and obtaining the current-flow relationship based on the minimum and maximum pressure current values.

[0039] Specifically, the value of this setting is related to the characteristics of the hydraulic pump. The specific value is not limited here; it is sufficient that the displacement of the hydraulic pump 11 reaches its maximum before the current increases to the set value. The maximum design displacement of the hydraulic pump 11 is set at the factory. The minimum pressure time point is the time when the displacement of the hydraulic pump 11 is at its minimum. The maximum pressure time point is the time when the displacement of the hydraulic pump 11 reaches its maximum. When the controller 17 detects that the pressure at the oil outlet begins to increase, it obtains the minimum pressure current value corresponding to that moment through the current change curve. When the controller 17 detects that the pressure at the oil outlet rises to its maximum, it obtains the maximum pressure current value corresponding to that moment through the current change curve. In other words, the horizontal axis is plotted with the current magnitude, and the horizontal coordinates corresponding to the minimum and maximum pressure current values ​​are determined on the horizontal axis. The vertical axis is plotted with the flow rate, and the vertical coordinates corresponding to the minimum and maximum displacement of the hydraulic pump 11 are determined on the vertical axis. Connecting these two points yields the relationship between current and flow rate.

[0040] In some embodiments, the displacement control valve 12 is a proportional pressure reducing valve. The valve core opening of the proportional pressure reducing valve is related to the magnitude of the current signal sent by the controller 17. That is, the controller 17 can change the outlet pressure of the proportional pressure reducing valve by changing the magnitude of the current signal, thereby adjusting the displacement of the hydraulic pump 11.

[0041] Considering the need to stabilize test data and reduce short-term impact on the hydraulic system, in some embodiments, controlling the input current of the displacement control valve 12 according to a preset current change curve within a set time period includes increasing the input current over time to a set value, maintaining it for a period, and then decreasing it. Obtaining the inflection point of the pressure curve change based on the pressure change curve and acquiring the current-flow relationship of the hydraulic pump 11 based on the current change curve, the inflection point of the pressure curve change, engine speed, and the minimum and maximum design displacement values ​​of the hydraulic pump to complete the calibration of the hydraulic pump 11 includes increasing the outlet pressure from minimum to maximum through the input current, maintaining it for a period, and then decreasing it to minimum. Obtaining the first inflection point when the outlet pressure begins to increase, the second inflection point when the outlet pressure reaches its maximum value, the third inflection point when the outlet pressure begins to decrease, and the fourth inflection point when the outlet pressure reaches its minimum value through the pressure change curve. Based on these four inflection points, obtaining the corresponding first, second, third, and fourth current values ​​from the current change curve, and then obtaining the current-flow relationship based on these four current values. Specifically, the change of the input current over time can be referenced... Figure 2 The solid line in the diagram represents the input current. In other words, this input current allows us to obtain two pairs of the aforementioned minimum pressure current values ​​(i.e.,...). Figure 2 Points 1 and 4) and the maximum pressure current value (i.e. Figure 2 Points 2 and 3 in the diagram are used as the vertical axis. The vertical coordinates corresponding to the minimum and maximum displacements of the hydraulic pump 11 are then determined on the vertical axis. Connecting these four points yields the hysteresis curve of the current versus flow rate. This hysteresis curve is then used to fit the current-flow characteristic curve B (refer to the diagram). Figure 4 The dashed lines in the text make the calibration results more accurate.

[0042] To further improve the accuracy of the fitting results, in some embodiments, the control method further includes controlling the input current of the displacement control valve 12 according to a preset current change curve within multiple set time periods, and obtaining multiple sets of four inflection points corresponding to the multiple set time periods. Multiple sets of four current values ​​are obtained based on the multiple sets of four inflection points and the current change curve, and then the error value between the multiple sets of four current values ​​is calculated. If the error value exceeds the error setting value, the same input current is re-inputted multiple times until the error value is less than the error setting value, and then the average value of the multiple sets of four current values ​​is taken. Specifically, refer to... Figure 3 Repeat the input of three identical sets of input currents to obtain twelve key nodes (e.g. Figure 3The calibration process involves averaging the values ​​at points 1-4, 1'-4', and 1"-4") to improve the accuracy of the calibration results. This process can be completed within fifteen seconds, making this calibration method highly efficient and accurate, suitable for calibrating large batches of electrically controlled pumps. Furthermore, the controller 17 can be connected to an indicator light signal, allowing the user to be notified whether the calibration is complete by controlling the indicator light to remain constantly lit or flash.

[0043] To improve the stability of the hydraulic system and the accuracy of the calibration results, the valve core opening of the unloading valve 13 should be ensured to be sufficiently large during calibration. In some embodiments, the first opening ranges from 90% to 100%. Specifically, refer to... Figure 5 In region ③, the valve core displacement of the unloading valve 13 is 90%–100%, and the valve opening area of ​​the unloading valve 13 increases uniformly with the increase of the valve core displacement, so that most of the hydraulic oil flows back to the oil tank through the unloading valve 13. This reduces the possibility of overflow of the relief valve in the hydraulic system due to excessive flow of the hydraulic pump 11, thus making the calibration results more accurate. Furthermore, compared with the traditional scheme of unloading in the middle position of the valve core of a multi-way valve, the use of the unloading valve 13 in this hydraulic system can reduce the energy loss along the process and in local areas.

[0044] Still referencing Figure 5 In some embodiments, the control method further includes controlling the valve spool opening of the unloading valve 13 to a second opening degree to bring the hydraulic system into operation. The range of the second opening degree is 10% to 90%. When the hydraulic system is operating normally, the valve spool of the unloading valve 13 is at the following position: Figure 5 The second opening shown in region ② indicates that the unloading valve 13 is used for unloading during normal operation of the hydraulic system, and the valve opening area of ​​the unloading valve 13 increases uniformly with the increase of the valve core displacement (the rate at which the valve opening area in region ② increases with the increase of the valve core displacement is less than the corresponding rate in region 3). Furthermore, when the hydraulic system is operating normally with an increased valve core displacement, the valve core displacement of the unloading valve 13 is variable. For example, during the initial stage, the valve core displacement of the unloading valve 13 is set to 80%. As the hydraulic pump 11 gradually supplies oil to the working oil circuit, the valve core displacement of the unloading valve 13 gradually decreases to ensure the stability of the hydraulic oil in the working oil circuit. In some embodiments, the unloading valve 13 also has a third opening (e.g., ...). Figure 5 In region ①), the valve core displacement of unloading valve 13 is 0-10%, indicating that unloading valve 13 is not open. In this region, even if the valve core displacement increases, the valve opening area of ​​unloading valve 13 remains zero, and the hydraulic system is in an unstarted state.

[0045] To facilitate control of the valve core movement of unloading valve 13, refer to Figure 6In some embodiments, the hydraulic system further includes a control valve 15 for controlling the valve spool opening of the unloading valve 13. The control method of the hydraulic system further includes controlling the control valve 15 to make the valve spool opening of the unloading valve 13 adjustable. Specifically, the control valve 15 is signal-connected to the controller 17. When the calibration program is activated, the hydraulic system enters the calibration state. At this time, the controller 17 applies current to the control valve 15 through the PWM2 port. The outlet pressure of the control valve 15 changes according to the applied current, thereby controlling the valve spool of the unloading valve 13 to move to the first opening degree.

[0046] In some embodiments, the hydraulic system further includes an engine control unit 16. The engine control unit 16 is connected to the engine drive of the construction machinery. The control method for the hydraulic system further includes adjusting the engine speed to a rated speed via the engine control unit 16 before entering a calibration state. Specifically, refer to... Figure 6 The controller 17 is connected to the engine control unit 16 via a CAN bus. When the hydraulic pump 11 needs to be calibrated, the engine speed is first adjusted to the rated speed via the controller 17, and then the calibration program is activated. Only when the engine speed is fast enough can the flow rate of the hydraulic pump 11 be large enough to make the calibration results more accurate.

[0047] The process of calibrating the hydraulic pump using the control method of the hydraulic system provided in this application will be described in detail below. First, the engine speed is adjusted to the rated speed. Controller 17 activates the calibration program. Controller 17 sends the same input current three times to the displacement control valve 12 through the PWM1 port according to the preset current change curve within three set time periods. Simultaneously, it loads the maximum current to the control valve 15 through the PWM2 port. The valve core of the unloading valve 13 is at its first opening degree under the action of the control valve 15. Pressure sensor 14 detects the pressure change at the oil outlet and sends the detection result to controller 17 through the AI0 port. Controller 17 acquires the pressure change curve and obtains twelve inflection points from it. Then, based on the twelve inflection points and the three identical input currents, it finds three sets of four current values ​​and calculates whether the error value of the three sets of data is less than the error setting value. If the error value is greater than the error setting value, the same input current is sent again three times and subsequent calculations are performed until the error value of the three sets of data is less than the error setting value. The three sets of data are then averaged to obtain the hysteresis curve of current versus flow rate. Based on this hysteresis curve, the current-flow relationship of the hydraulic pump 11 is fitted (i.e., the current-flow characteristic curve B). The controller 17 then stores this current-flow relationship and uses it for subsequent overall flow control.

[0048] This application also provides a hydraulic system. This hydraulic system can be installed on construction machinery. (Reference) Figure 6The system includes a controller 17, a hydraulic pump 11, a main valve, a displacement control valve 12, a relief valve 112, an unloading valve 13, and a working cylinder. The outlet of the hydraulic pump 11 is connected to the working cylinder via the main valve. The displacement control valve 12 controls the displacement of the hydraulic pump 11. The relief valve 112 is located between the outlet of the hydraulic pump 11 and the oil tank. The outlet of the hydraulic pump 11 is connected to the oil tank via the unloading valve 13. The valve core opening of the unloading valve 13 is adjustable. The controller 17 is configured to execute the control method of the hydraulic system as described above. The hydraulic system has a built-in calibration function; the controller 17 can automatically control the hydraulic system to operate normally or perform calibration, and after calibration, store the calibration results for subsequent flow control during normal operation of the entire machine. The calibration is efficient and accurate, thus enabling precise control of the overall machine power, improving work efficiency, and reducing fuel consumption.

[0049] In some embodiments, the main valve includes a first directional valve 18 and a second directional valve 19, and the working cylinders include a first working cylinder 110 and a second working cylinder 111. The first directional valve 18 and the second directional valve 19 are respectively connected to the first working cylinder 110 and the second working cylinder 111. When the hydraulic system is working normally (without activating the calibration program), the hydraulic pump 11 delivers hydraulic oil to the two working cylinders through the two directional valves in the main valve for normal operation. In calibration mode (with the calibration program activated), the controller 17 executes the above steps to calibrate the hydraulic system. This hydraulic system enables precise and efficient calibration without structural changes, allowing multiple working cylinders to be driven for operation. The hydraulic system has a simple structure and can be installed on various types of engineering machinery, possessing versatility and enabling more accurate flow control in engineering machinery.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them; although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of this application or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of this application, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in this application.

Claims

1. A control method of a hydraulic system, characterized by, The hydraulic system comprises a hydraulic pump (11), a displacement control valve (12) for controlling the displacement of the hydraulic pump (11), a main valve, a relief valve (112), an unloading valve (13) and a working oil cylinder, an oil outlet of the hydraulic pump (11) is connected with the working oil cylinder through the main valve, the relief valve (112) is arranged between the oil outlet of the hydraulic pump (11) and an oil tank, the oil outlet of the hydraulic pump (11) is connected with the oil tank through the unloading valve (13), the opening degree of a valve core of the unloading valve (13) is adjustable to switch the hydraulic system between a working state and a calibration state, and the control method of the hydraulic system comprises the following steps: controlling the opening degree of the valve core of the unloading valve (13) to be at a first opening degree to make the hydraulic system enter the calibration state; controlling the input current of the displacement control valve (12) according to a preset current change curve within a set time period; real-time acquisition of the pressure of the oil outlet of the hydraulic pump (11) and acquisition of a pressure change curve of the oil outlet of the hydraulic pump (11) within the set time period according to the pressure of the oil outlet; and acquisition of a pressure curve change inflection point according to the pressure change curve and acquisition of a current-flow relationship of the hydraulic pump (11) based on the current change curve, the pressure curve change inflection point, the engine speed and minimum and maximum design displacement values of the hydraulic pump to complete calibration of the hydraulic pump (11).

2. The control method of a hydraulic system according to claim 1, characterized by, The hydraulic system further comprises a pressure sensor (14) arranged at the oil outlet of the hydraulic pump (11), and the real-time acquisition of the pressure of the oil outlet of the hydraulic pump (11) comprises real-time detection of the pressure of the oil outlet by the pressure sensor (14).

3. The control method of a hydraulic system according to claim 1, characterized by, The control of the input current of the displacement control valve (12) according to the preset current change curve within the set time period comprises increasing the input current to a set value within the set time period to make the pressure of the oil outlet rise from a minimum pressure to a maximum pressure, the acquisition of the pressure curve change inflection point according to the pressure change curve and the acquisition of the current-flow relationship of the hydraulic pump (11) based on the current change curve, the pressure curve change inflection point, the engine speed and the minimum and maximum design displacement values of the hydraulic pump to complete the calibration of the hydraulic pump (11) comprise acquisition of a minimum pressure time point when the pressure of the oil outlet starts to increase and a maximum pressure time point when the pressure of the oil outlet rises to the maximum by the pressure change curve, then acquisition of a minimum pressure current value corresponding to the minimum pressure time point and a maximum pressure current value corresponding to the maximum pressure time point by the current change curve, and acquisition of the current-flow relationship according to the minimum pressure current value and the maximum pressure current value.

4. The control method of a hydraulic system according to claim 1, characterized by, The input current of the displacement control valve (12) is controlled according to the preset current change curve in the set time period, which includes increasing the input current to a set value first, then keeping it for a period of time and then reducing it, the pressure curve change inflection point is obtained according to the pressure change curve, and the current-flow relationship of the hydraulic pump (11) is obtained based on the current change curve, the pressure curve change inflection point, the engine speed, and the minimum and maximum design displacement values of the hydraulic pump (11) to complete the calibration of the hydraulic pump (11), which includes increasing the pressure of the oil outlet from minimum to maximum and then keeping it for a period of time and then reducing it to minimum through the input current, obtaining the first inflection point when the pressure of the oil outlet starts to increase, the second inflection point when the pressure of the oil outlet rises to the maximum value, the third inflection point when the pressure of the oil outlet starts to decrease, and the fourth inflection point when the pressure of the oil outlet drops to the minimum value through the pressure change curve, and then obtaining the corresponding first, second, third, and fourth current values from the current change curve based on the four inflection points, and then obtaining the current-flow relationship according to the four current values.

5. The control method of a hydraulic system according to claim 4, characterized by The control method further includes controlling the input current of the displacement control valve (12) according to the preset current change curve in a plurality of set time periods, respectively, and obtaining a plurality of sets of the four inflection points corresponding to the plurality of set time periods, obtaining a plurality of sets of the four current values based on the plurality of sets of the four inflection points and the current change curve, and then calculating the error values between the plurality of sets of the four current values, if the error values exceed the error set value, re-inputting the same input current multiple times until the error values are less than the error set value, and then taking the average of the plurality of sets of the four current values.

6. The control method of a hydraulic system according to claim 1, characterized by The range of the first opening degree is 90% to 100%.

7. The control method of a hydraulic system according to claim 1, characterized by The control method further includes controlling the spool opening degree of the unloading valve (13) to be at a second opening degree to make the hydraulic system enter the working state, and the range of the second opening degree is 10% to 90%.

8. The control method of a hydraulic system according to claim 1, characterized by The hydraulic system further includes a control valve (15) for controlling the spool opening degree of the unloading valve (13), and the control method of the hydraulic system further includes controlling the control valve (15) to act to adjust the spool opening degree of the unloading valve (13).

9. The control method of a hydraulic system according to any one of claims 1 to 8, characterized by, The hydraulic system further includes an engine control unit (16) that is drivingly connected with the engine of the engineering machinery, and the control method of the hydraulic system further includes adjusting the speed of the engine to the rated speed through the engine control unit (16) before entering the calibration state.

10. A hydraulic system characterized by, The hydraulic system includes a controller (17), a hydraulic pump (11), a main valve, a displacement control valve (12), a relief valve (112), an unloading valve (13), and a working oil cylinder, an oil outlet of the hydraulic pump (11) is connected with the working oil cylinder through the main valve, the displacement control valve (12) is used for controlling a displacement of the hydraulic pump (11), the relief valve (112) is arranged between the oil outlet of the hydraulic pump (11) and an oil tank, the oil outlet of the hydraulic pump (11) is connected with the oil tank through the unloading valve (13), a spool opening of the unloading valve (13) is adjustable, and the controller (17) is configured to perform the control method of the hydraulic system according to any one of claims 1 to 9.

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