Hydraulic system using variable displacement pump to realize pressure cut-off function

Abstract

A control unit for a hydraulic system is configured to: obtain an actual system pressure detected by a pressure sensor and an action instruction input by an action instruction input element; obtain the action instruction to determine the required displacement corresponding to the pump; determine the pump output difference based on the required displacement and the current output displacement of the pump, and obtain a pressure threshold value based on the determined pump output difference using a simulated overflow valve characteristic; reduce the required displacement based on the actual system pressure and the obtained pressure threshold value, thereby determining the pump output displacement; and control the pump to operate at the determined pump output displacement.

Description

Technical Field

[0001] The present application relates to a hydraulic system, in particular to a hydraulic system of engineering equipment, which has a function of actively cutting off the system pressure. Background Art

[0002] In hydraulic systems, especially those in construction equipment, hydraulic pumps are often used to drive actuators. The output of a hydraulic pump is often equipped with a relief valve. When system pressure rises and exceeds the relief valve's opening pressure, the relief valve opens, reducing the system pressure and thus providing system safety. This function, which prevents excessive system pressure, is often referred to as a pressure cutoff.

[0003] Variable displacement pumps are increasingly being used in hydraulic systems for engineering equipment. The pump's displacement can be adjusted by controlling its control current. This allows the pump's output pressure to be reduced by reducing the pump's displacement, thereby achieving system pressure cutoff through active control without the need for a relief valve. Using a variable displacement pump to achieve pressure cutoff in closed or open hydraulic systems offers numerous advantages. First, it prevents energy loss caused by hydraulic oil flowing through the relief valve into the return line. Furthermore, in some applications, it is necessary to limit the force or torque output by the hydraulic system. Using a variable displacement pump allows this to be achieved by limiting the pressure within the hydraulic system.

[0004] However, in the existing technology of using variable pumps to achieve pressure cutoff, the following problems are often encountered: (1) the pressure cutoff response is fast, which easily causes system pressure fluctuations; (2) if the system pressure is guaranteed to be stable during pressure cutoff, the pressure cutoff response is slow. Summary of the Invention

[0005] An object of the present application is to provide a control solution for a hydraulic system, wherein both pressure cut-off response speed and system stability can be taken into account while using a variable displacement pump to achieve pressure cut-off.

[0006] To achieve this object, the present application provides, in one aspect, a control unit for a hydraulic system, the hydraulic system comprising:

[0007] Power source;

[0008] a pump driven by a power source, wherein the pump is a variable displacement pump;

[0009] Actuators supplied with hydraulic oil by a pump;

[0010] a pressure sensor configured to detect an actual system pressure of the hydraulic system;

[0011] an action instruction input element configured to input a desired actuator action; and

[0012] a control unit storing a pre-built simulated overflow valve characteristic, wherein the simulated overflow valve characteristic represents a corresponding relationship between a pressure threshold and a pump output difference;

[0013] Wherein, the control unit is configured as:

[0014] Acquiring the actual system pressure detected by the pressure sensor and the action instruction input by the action instruction input component;

[0015] Obtaining the action instruction to determine the required displacement corresponding to the pump;

[0016] determining a pump output difference based on the required displacement and the current output displacement of the pump, and obtaining a pressure threshold value from the simulated relief valve characteristic based on the determined pump output difference;

[0017] reducing the required displacement based on the actual system pressure and the retrieved pressure threshold, thereby determining the pump output displacement;

[0018] The pump is controlled to operate at a determined pump output displacement.

[0019] In one embodiment, the pump output difference is a pump output displacement difference, and the simulated overflow valve characteristic represents a corresponding relationship between a pressure threshold and the pump output displacement difference, wherein the pressure threshold and the pump output displacement difference are positively correlated.

[0020] In one embodiment, the simulated overflow valve characteristic represents a corresponding relationship between a pressure threshold and a pump output displacement difference, wherein the pressure threshold and the pump output displacement difference are in a linear relationship or a quadratic curve relationship.

[0021] In one embodiment, the control unit is configured to determine a pump output displacement difference based on the required displacement and the determined pump output displacement, and to retrieve a pressure threshold value from the simulated relief valve characteristic based on the determined pump output displacement difference.

[0022] In one embodiment, the control unit is configured to further obtain the actual pump displacement, determine a pump output displacement difference based on the required displacement and the actual pump displacement, and obtain a pressure threshold from the simulated overflow valve characteristic based on the determined pump output displacement difference.

[0023] In one embodiment, the pump output difference is a pump output flow difference, and the simulated overflow valve characteristic represents a corresponding relationship between a pressure threshold and the pump output flow difference, wherein the pressure threshold and the pump output flow difference are positively correlated.

[0024] In one embodiment, the simulated overflow valve characteristic represents a corresponding relationship between a pressure threshold and a pump output flow difference, wherein the pressure threshold and the pump output flow difference are in a linear relationship or a quadratic curve relationship.

[0025] In one embodiment, the control unit is configured to also obtain the power source speed, and determine the required flow based on the required displacement and the power source speed, determine the pump output flow based on the determined pump output displacement and the power source speed, determine the pump output flow difference based on the required flow and the pump output flow, and obtain the pressure threshold value from the simulated overflow valve characteristic based on the determined pump output flow difference.

[0026] In one embodiment, the control unit is configured to also obtain the power source speed and the actual pump displacement, and determine the required flow based on the required displacement and the power source speed, determine the actual pump flow based on the actual pump displacement and the power source speed, determine the pump output flow difference based on the required flow and the actual pump flow, and obtain the pressure threshold value from the simulated overflow valve characteristic based on the determined pump output flow difference.

[0027] In one embodiment, the control unit is configured to determine the pump output displacement by PID feedback control, wherein the difference between the actual system pressure and the retrieved pressure threshold is used as a negative feedback term in the PID feedback control.

[0028] In one embodiment, the pump is an electric proportional pump, and the control unit is configured to operate the pump at a determined pump output displacement by controlling a control current of the pump.

[0029] On the other hand, the present application provides a hydraulic system, which includes a power source, a pump, an actuator, a pressure sensor, an action instruction input element and the control unit of the present application.

[0030] According to the hydraulic system control scheme of the present application, the problems that easily arise when using a variable pump to achieve pressure cut-off are improved through simple logic, while taking into account the pressure cut-off response speed and system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present application may be further understood by reading the following detailed description with reference to the accompanying drawings, in which:

[0032] Figure 1 is a hydraulic circuit diagram of an exemplary hydraulic system according to the present application;

[0033] Figure 2 is an exemplary relief valve characteristic curve;

[0034] Figure 3 、 Figure 4 are two exemplary simulated overflow valve characteristic curves constructed in this application;

[0035] Figure 5is a schematic block diagram of the control logic of the hydraulic system of the present application;

[0036] Figure 6 is a flow chart of an exemplary control scheme of the hydraulic system of the present application. DETAILED DESCRIPTION

[0037] The present application generally relates to a hydraulic system, which is applicable to various engineering equipment, such as excavators, rotary drilling rigs, aerial work platforms, etc. Figure 1 An exemplary structure of the hydraulic system of the present application is shown in FIG. The hydraulic system includes a variable pump 2, especially an electric proportional pump, driven by a power source (such as an engine, a motor, etc.) 1. The pump 2 supplies hydraulic oil to the actuator 4 through the main valve 3. Figure 1 In the example shown, the actuator 4 is in the form of a hydraulic motor, but it can also be a hydraulic cylinder, etc. Figure 1 In the example shown, the hydraulic system is an open system, that is, the pump 2 draws hydraulic oil from the oil tank 5 and supplies it to the actuator 4, and the hydraulic oil returns to the oil tank 5 after doing work; however, the hydraulic system can also be a closed system, in which the input and output ports of the pump 2 are connected to the output and input ports of the actuator 4, so that the hydraulic oil circulates between the pump 2 and the actuator 4. Figure 1 The open hydraulic system is described in detail, but the present application is also applicable to closed hydraulic systems.

[0038] Pump 2 is a variable displacement pump, whose displacement is defined as the volume of hydraulic oil discharged per revolution. This displacement is adjusted by a variable displacement mechanism (e.g., a swash plate) within pump 2, varying between 0% and 100% displacement. In this application, pump 2 is preferably an electric proportional pump, where the displacement is determined by controlling the amount of control current applied to the pump.

[0039] The hydraulic system is provided with a pressure sensor 6 for detecting the system pressure in the hydraulic system. The pressure sensor 6 can be arranged near the output port of the pump 2.

[0040] The hydraulic system further includes an action command input element 7 and a control unit 8. The action command input element 7 is configured to be manipulated by an operator of the engineering equipment to input an action command. The control unit 8 is capable of receiving the action command from the command input element 7 and, based on the action command, controlling the operation of the power source 1, pump 2, and main valve 3. It is also capable of acquiring detection values ​​from the pressure sensor 6 and operating parameters of the power source 1 and pump 2.

[0041] The control unit of the present application is configured to be able to realize the pressure cut-off function of the hydraulic system by controlling the pump 2. The pressure cut-off function is realized by adding an emulated overflow valve function in the software, so the overflow valve does not need to be set on the output side of the pump 2 in the hydraulic system.

[0042] First, examine the opening characteristics of the overflow valve. Figure 2 The figure shows a conventional adjustable relief valve characteristic curve. The horizontal axis represents the relief valve flow rate Q, and the vertical axis represents the relief pressure P. Each curve in the figure is a relief valve characteristic curve corresponding to different relief valve opening pressures. The intersection of each curve with the vertical axis is the corresponding relief valve opening pressure. The relief valve opening pressure can be adjusted. For each opening pressure, when the system pressure (the pressure on the relief valve opening side) is lower than the relief valve opening pressure, the relief valve remains closed. When the system pressure reaches the relief valve opening pressure, the relief valve opens. When the relief valve is open, the relief pressure P is positively correlated with the relief valve flow rate Q. That is, as the relief pressure P increases, the relief valve flow rate Q increases. The relationship between the two is usually in the form of a curve (non-linear). For hydraulic systems that use a relief valve on the pump output side, the relief valve opening pressure is the hydraulic system's cut-off pressure.

[0043] This application is based on Figure 2 A simulated relief valve characteristic is constructed from the conventional relief valve characteristic curve in [1]. This simulated relief valve characteristic reflects the corresponding relationship between the cut-off pressure of the hydraulic system of this application and the output capacity of pump 2. The output capacity of pump 2 can be expressed in terms of displacement or flow rate. The flow rate is calculated by multiplying the displacement of pump 2 by the rotational speed (rpm).

[0044] The simulated overflow valve characteristics constructed in the present application can be expressed by the overflow pressure-pump displacement relationship, or by the overflow pressure-pump flow relationship.

[0045] Figure 3 The simulated overflow valve characteristic curve constructed by the present application, which is expressed by the overflow pressure-pump displacement relationship, is shown. The horizontal axis in the figure represents the displacement difference Vg of the pump 2. gap (in the form of a percentage of the maximum displacement, its meaning is described later; it can also be expressed as the volume of hydraulic oil discharged per revolution), the vertical axis represents the system pressure threshold (simulated overflow pressure) P thd The oblique line in the figure represents the pump displacement difference Vg gap With the pressure threshold P thd P0 is the simulated opening pressure, which can be set according to the force or torque generated by the hydraulic oil that the actuator in the hydraulic system can withstand. P0 can be set to be adjustable. When the system pressure is lower than P0, the displacement difference Vg gap When the system pressure reaches and exceeds P0, the displacement difference Vg gap Starting from 0 and gradually increasing. Displacement difference Vg gap With the pressure threshold P thd There is a positive correlation between them, that is, as the displacement difference Vg gap Increase, pressure threshold P thdThe displacement difference Vg is also increased, and the increase can simulate a type of overflow valve suitable for this hydraulic system. gap With the pressure threshold P thd The relationship between can be represented by a straight line or a curve.

[0046] Figure 4 The simulated overflow valve characteristic curve constructed by the present application and expressed by the overflow pressure-pump flow relationship is shown. The horizontal axis in the figure represents the flow difference Q of the pump 2. gap (L / min, its meaning is described later), the vertical axis represents the system pressure threshold (simulated overflow pressure) P thd The oblique line in the figure represents the flow difference Q of pump 2 gap With the pressure threshold P thd The relationship between. P0 is the simulated opening pressure, which can be set to be adjustable. When the system pressure is lower than P0, the flow difference Q gap is 0; when the system pressure reaches and exceeds P0, the flow difference Q gap Starting from 0 and gradually increasing. Flow difference Q gap With the pressure threshold P thd There is a positive correlation between them, that is, as the flow difference Q gap Increase, pressure threshold P thd The flow difference Q is also increased, and the increase can simulate a type of overflow valve suitable for this hydraulic system. gap With the pressure threshold P thd The relationship between can be represented by a straight line or a curve.

[0047] It should be pointed out that those skilled in the art can also construct other forms of simulated overflow valve characteristics, as long as they can reflect the overflow valve provided in the hydraulic system to prevent the system pressure from being too high. Regardless of the specific form, the simulated overflow valve characteristics of the present application must be able to reflect the corresponding relationship between the pressure threshold of the hydraulic system and the pump output difference, and the pressure threshold includes a set simulated opening pressure. When the system pressure is lower than the simulated opening pressure, the pump output difference is 0; when the system pressure reaches and exceeds the simulated opening pressure, the pump output difference gradually increases from 0, and the pump output difference is positively correlated with the pressure threshold. The correlation between the pump output difference and the pressure threshold can be expressed in the form of a linear curve (straight line) or a quadratic or even higher order curve.

[0048] although Figure 3 、 Figure 4 The simulated overflow valve characteristic curve is schematically shown in FIG. 1 , but it can be understood that the relationship between the pump output difference and the pressure threshold constructed in the present application is actually stored in the control program of the control unit 8 in the form of a function, a lookup table, etc.

[0049] In addition, the simulated overflow valve characteristic in the present application is a relationship between simulated opening pressure and pump output artificially constructed in the control program, and does not need to truly correspond to the actual physical characteristics of the overflow valve.

[0050] The control logic for the system pressure stage function implemented by the control unit 8 is Figure 5 The control unit 8 receives the action command from the command input element 7 and the detection signal of the pressure sensor 6, that is, the actual system pressure P act The control unit 8 may also receive the speed n of the power source 1 (for example, from a speed sensor in the power source 1), the actual displacement Vg of the pump 2, and the speed of the power source 1. act (For example, from the swash plate angle sensor in the pump 2) and other information. The control unit 8 is based at least on the actual system pressure P act To control the displacement of the pump 2 and realize the system pressure cut-off function, thereby controlling the hydraulic oil supplied by the pump 2 to the actuator 4 to generate an example or torque that does not exceed, or does not exceed for a long time the bearing capacity of the actuator 4.

[0051] The control unit 8 is provided with a pressure cut-off module, which stores a preset simulated overflow valve characteristic and can execute the overall Figure 6 The system pressure cut-off function is shown in the flowchart in FIG. It should be noted that, in specific implementations, the control unit 8 can control the displacement of the pump 2 in various specific ways, depending on the signals collected by the control unit 8. Several specific implementations of the control flow are described below.

[0052] In the first embodiment of the control process, the control unit 8 is based only on the actual system pressure P act Realize the pressure cut-off function.

[0053] like Figure 6 As shown, in step S1 , the control unit 8 activates the pressure cut-off function.

[0054] Next, in step S2 , the pressure cutoff module stands by, waiting for an execution request signal (action command, representing a request for an actuator to operate) from the command input element 7 .

[0055] Next, in step S3, the pressure cutoff module determines whether it has received an execution request signal from the command input element 7. If the determination result is yes, the process goes to step S4; if the determination result is no, the process returns to step S2.

[0056] In step S4, the pressure cut-off module determines the required displacement Vg of the pump 2 corresponding to the execution demand signal. dem Required displacement Vg of pump 2 dem It is usually calculated by the functional module that specifically controls the action of the actuator.

[0057] Next, in step S5, the pressure cut-off module calculates the required displacement Vg dem and the output displacement Vg of pump 2 out The difference between Vg gap :Vg gap =Vg dem -Vg out .

[0058] Next, in step S6, the pressure cut-off module calculates the Vg gap In such Figure 3 Schematic representation of the simulated overflow valve characteristics (pressure threshold P thd -Displacement difference Vg gap Relationship) to find the corresponding pressure threshold P thd .

[0059] Next, in step S7, the pressure cut-off module collects the actual system pressure P act , and based on the required displacement Vg dem , Actual system pressure P act , pressure threshold P thd Determine the output displacement Vg out :

[0060] Vg out =f(Vg dem , P thd , P act )

[0061] Among them, function f reflects P act With P thd The difference between ΔP(=P act -P thd ) Correction (reduction) of the output displacement. The larger the ΔP, the greater the correction value (reduction value) of the output displacement.

[0062] The pressure cutoff module can use PID feedback control or other pressure cutoff methods to achieve correction of the output displacement. For PID feedback control, ΔP serves as the negative feedback term in the control. Other pressure cutoff methods may include, for example, the method disclosed in paragraph 0043 of the specification of US2013000292A1. For example, a pressure decrease ΔV proportional to ΔP can be set, Vg out =Vg dem Other pressure cut-off methods commonly used in the art can also be used here.

[0063] The output displacement Vg determined in step S7 out It is used in step S5 in the next control cycle.

[0064] Next, in step S8, the control unit 8 controls the displacement of the pump 2 to reach the output displacement Vg determined in step S7. out For example, for an electric proportional pump, the control unit 8 determines the output displacement Vg out The corresponding pump control current is used to control the variable mechanism of the pump (for example, the swash plate angle). After that, the program returns to step S2.

[0065] In the second embodiment of the control process, the control unit 8 is based on the actual system pressure P act And the speed n of the power source 1 realizes the pressure cut-off function.

[0066] like Figure 6 As shown, in step S1 , the control unit 8 activates the pressure cut-off function.

[0067] Next, in step S2 , the pressure cutoff module stands by and waits for an execution request signal from the command input element 7 .

[0068] Next, in step S3, the pressure cutoff module determines whether it has received an execution request signal from the command input element 7. If the determination result is yes, the process goes to step S4; if the determination result is no, the process returns to step S2.

[0069] In step S4, the pressure cut-off module determines the required displacement Vg of the pump 2 corresponding to the execution demand signal. dem .

[0070] Next, in step S5, the pressure cut-off module calculates the required flow rate Q dem The output flow rate Q of pump 2 out The difference between:

[0071] Q dem =k*n*Vg dem

[0072] Q out =k*n*Vg out

[0073] Q gap =Q dem -Q out

[0074] Where k is the transmission ratio between the power source 2 and the pump 1.

[0075] Next, in step S6, the pressure cut-off module calculates the Q gap In such Figure 4 Schematic representation of the simulated overflow valve characteristics (pressure threshold P thd -Flow rate difference Q gapRelationship) to find the corresponding pressure threshold P thd .

[0076] Next, in step S7, the pressure cut-off module collects the actual system pressure P act , and based on the required displacement Vg dem , Actual system pressure P act , pressure threshold P thd Determine the output displacement Vg out :

[0077] Vg out =f(Vg dem , P thd , P act )

[0078] Among them, function f reflects P act With P thd The output displacement is corrected (reduced) by the difference ΔP between them. The pressure cut-off module can use PID feedback control or other pressure cut-off methods to correct the output displacement. The output displacement Vg determined in step S7 out It is used in step S5 in the next control cycle.

[0079] Next, in step S8, the control unit 8 controls the displacement of the pump 2 to reach the output displacement Vg determined in step S7. out After that, the program returns to step S2. Other features that are the same as those in the first embodiment of the control flow will not be described again.

[0080] In the third embodiment of the control process, the control unit 8 is based on the actual system pressure P act and the actual displacement Vg of pump 2 act Achieve pressure cut-off function. Actual displacement Vg of pump 2 act It can be determined by the current control parameters of the variable mechanism (such as the control current of the swash plate drive mechanism) or the position parameters (such as the detection value of the swash plate angle sensor).

[0081] like Figure 6 As shown, in step S1 , the control unit 8 activates the pressure cut-off function.

[0082] Next, in step S2 , the pressure cutoff module stands by and waits for an execution request signal from the command input element 7 .

[0083] Next, in step S3, the pressure cutoff module determines whether it has received an execution request signal from the command input element 7. If the determination result is yes, the process goes to step S4; if the determination result is no, the process returns to step S2.

[0084] In step S4, the pressure cut-off module determines the required displacement Vg of the pump 2 corresponding to the execution demand signal. dem .

[0085] Next, in step S5, the pressure cut-off module calculates the required displacement Vg dem The actual displacement Vg of pump 2 act The difference between Vg gap :Vg gap =Vg dem -Vg act .

[0086] Next, in step S6, the pressure cut-off module calculates the Vg gap In such Figure 3 Schematic representation of the simulated overflow valve characteristics (pressure threshold P thd -Displacement difference Vg gap Relationship) to find the corresponding pressure threshold P thd .

[0087] Next, in step S7, the pressure cut-off module collects the actual system pressure P act , and based on the required displacement Vg dem , Actual system pressure P act , pressure threshold P thd Determine the output displacement Vg out :

[0088] Vg out =f(Vg dem , P thd , P act )

[0089] Among them, function f reflects P act With P thd The difference ΔP between them corrects (reduces) the output displacement.

[0090] Next, in step S8, the control unit 8 controls the displacement of the pump 2 to reach the output displacement Vg determined in step S7. out After that, the program returns to step S2. Other features that are the same as those in the first embodiment of the control flow will not be described again.

[0091] In the fourth embodiment of the control process, the control unit 8 is based on the actual system pressure P act , the speed n of power source 1 and the actual displacement Vg of pump 2 act Realize the pressure cut-off function.

[0092] like Figure 6 As shown, in step S1 , the control unit 8 activates the pressure cut-off function.

[0093] Next, in step S2 , the pressure cutoff module stands by and waits for an execution request signal from the command input element 7 .

[0094] Next, in step S3, the pressure cutoff module determines whether it has received an execution request signal from the command input element 7. If the determination result is yes, the process goes to step S4; if the determination result is no, the process returns to step S2.

[0095] In step S4, the pressure cut-off module determines the required displacement Vg of the pump 2 corresponding to the execution demand signal. dem .

[0096] Next, in step S5, the pressure cut-off module calculates the required flow rate Q dem The actual flow rate Q of pump 2 act The difference between:

[0097] Q dem =k*n*Vg dem

[0098] Q act =k*n*Vg act

[0099] Q gap =Q dem -Q act

[0100] Where k is the transmission ratio between the power source 2 and the pump 1.

[0101] Next, in step S6, the pressure cut-off module calculates the Q gap In such Figure 4 Schematic representation of the simulated overflow valve characteristics (pressure threshold P thd -Flow rate difference Q gap Relationship) to find the corresponding pressure threshold P thd .

[0102] Next, in step S7, the pressure cut-off module collects the actual system pressure P act , and based on the required displacement Vg dem , Actual system pressure P act , pressure threshold P thd Determine the output displacement Vg out :

[0103] Vg out =f(Vg dem , P thd , P act )

[0104] Among them, function f reflects P act With Pthd The difference ΔP between the two values ​​will correct (reduce) the output displacement. The pressure cut-off module can use PID feedback control or other pressure cut-off methods to correct the output displacement.

[0105] Next, in step S8, the control unit 8 controls the displacement of the pump 2 to reach the output displacement Vg determined in step S7. out After that, the program returns to step S2. Other features that are the same as those in the first embodiment of the control flow will not be described again.

[0106] Those skilled in the art can make various adaptive modifications to the corresponding process according to specific applications based on the system pressure cut-off principle of the present application.

[0107] The pressure cut-off module in the control unit of the present application operates in parallel with other functional modules, and limits the system pressure by introducing simulated overflow valve characteristics, preventing the system pressure from exceeding the safety limit without the need for an actual overflow valve.

[0108] The present application also includes a hydraulic system, which is generally as described above, including the aforementioned power source, pump, actuator, pressure sensor, action command input element, control unit, etc.

[0109] In this application's control scheme, the pump output capacity is set by subtracting a correction value from the required displacement that could cause the system pressure to exceed the simulated relief pressure. This correction value is determined by the corresponding pressure threshold obtained through the preset simulated relief valve characteristics. The pressure threshold is set based on the difference (reduction) in the pump output. This ensures that the system pressure remains within the set pressure threshold (pressure cutoff value).

[0110] The control scheme of this application is a closed-loop control scheme that uses simple logic to improve the problems that easily arise when using a variable displacement pump to achieve pressure cutoff, while also taking into account the pressure cutoff response speed and system stability. Therefore, while ensuring a fast pressure cutoff response, it prevents the system pressure from swinging back and forth around a set value, and the pump displacement can remain stable, which helps to maintain the stability of the operation of the engineering equipment. In addition, in applications where it is necessary to limit the force or torque provided by the hydraulic system, it can prevent the force or torque provided by the hydraulic system from exceeding the set value for a long time, thereby avoiding damage to the mechanical structure or the disruption of certain balances, and improving the safety of the entire engineering equipment.

[0111] Although the present application is described herein with reference to specific embodiments, the scope of the present application is not limited to the details shown. Various modifications may be made to these details without departing from the basic principles of the present application.

Claims

1. A control unit for a hydraulic system, the hydraulic system comprising: Power source (1); A pump (2) driven by a power source (1), wherein the pump (2) is a variable displacement pump; an actuator (4) supplied with hydraulic oil by a pump (2); The pressure sensor (6) is configured to detect the actual system pressure (P act ); an action instruction input element (7) configured to input a desired actuator action; as well as A control unit (8) stores a pre-built simulated overflow valve characteristic, wherein the simulated overflow valve characteristic represents a pressure threshold value (P thd ) and the corresponding relationship between the pump output difference; Wherein, the control unit (8) is configured as follows: Get the actual system pressure (P act ) and the action instruction input by the action instruction input element (7); Obtain the action instruction to determine the required displacement (Vg) corresponding to the pump (2) dem ); Based on the required displacement (Vg dem ) and the current output displacement of the pump (2) to determine the pump output difference, and based on the determined pump output difference, obtain the pressure threshold value (P thd ); Based on the actual system pressure (P act ) and the pressure threshold (P thd ) Reduce the required displacement (Vg dem ), thereby determining the pump output displacement (Vg out ); Control the pump (2) to determine the pump output displacement (Vg out )operate.

2. The control unit according to claim 1, wherein: The pump output difference is the pump output displacement difference (Vg gap ), the simulated overflow valve characteristic characterizes the pressure threshold (P thd ) and the difference between the pump output displacement (Vg gap ), where the pressure threshold (P thd ) and the difference between the pump output displacement (Vg gap ) are positively correlated.

3. The control unit according to claim 2, wherein: The simulated overflow valve characteristic characterizes the pressure threshold (P thd ) and the difference between the pump output displacement (Vg gap ), where the pressure threshold (P thd ) and the difference between the pump output displacement (Vg gap ) are linearly or quadratically related.

4. The control unit according to claim 2 or 3, wherein: The control unit is configured to determine the displacement based on the required displacement (Vg dem ) and the determined pump output displacement (Vg out ) Determine the pump output displacement difference (Vg gap ), and based on the determined pump output displacement difference (Vg gap ) The pressure threshold (P thd ).

5. The control unit according to claim 2 or 3, wherein: The control unit is configured to also obtain the actual displacement of the pump (Vg act ), based on the required displacement (Vg dem ) and the actual displacement of the pump (Vg act ) Determine the pump output displacement difference (Vg gap ), and based on the determined pump output displacement difference (Vg gap ) The pressure threshold (P thd ).

6. The control unit according to claim 1, wherein: The pump output difference is the pump output flow difference (Q gap ), the simulated overflow valve characteristic characterizes the pressure threshold (P thd ) and the difference between the pump output flow rate (Q gap ), where the pressure threshold (P thd ) and the difference between the pump output flow rate (Q gap ) are positively correlated.

7. The control unit according to claim 6, wherein: The simulated overflow valve characteristic characterizes the pressure threshold (P thd ) and the difference between the pump output flow rate (Q gap ), where the pressure threshold (P thd ) and the difference between the pump output flow rate (Q gap ) are linearly or quadratically related.

8. The control unit according to claim 6 or 7, wherein: The control unit is configured to further obtain the power source speed (n) and based on the required displacement (Vg dem ) and the power source speed (n) to determine the required flow rate (Q dem ), based on the determined pump output displacement (Vg out ) and the power source speed (n) determine the pump output flow rate (Q out ), based on the demand flow (Q dem ) and the pump output flow (Q out ) Determine the pump output flow difference (Q gap ), and based on the determined pump output flow difference (Q gap ) The pressure threshold (P thd ).

9. The control unit according to claim 6 or 7, wherein: The control unit is configured to also obtain the power source speed (n) and the actual pump displacement (Vg act ), and based on the required displacement (Vg dem ) and the power source speed (n) to determine the required flow rate (Q dem ), based on the actual displacement of the pump (Vg act ) and the power source speed (n) to determine the actual pump flow (Q act ), based on the demand flow (Q dem ) and the actual flow rate of the pump (Q act ) Determine the pump output flow difference (Q gap ), and based on the determined pump output flow difference (Q gap ) The pressure threshold (P thd ).

10. The control unit according to any one of claims 1 to 3, wherein: The control unit is configured to determine the pump output displacement (Vg out ), where the actual system pressure (P act ) and the pressure threshold (P thd ) is used as the negative feedback term in PID feedback control.

11. The control unit according to any one of claims 1 to 3, wherein: The pump (2) is an electric proportional pump, and the control unit is configured to control the control current of the pump (2) so that the pump (2) can output a certain pump displacement (Vg out )operate.

12. A hydraulic system comprising: Power source (1); A pump (2) driven by a power source (1), wherein the pump (2) is a variable displacement pump; an actuator (4) supplied with hydraulic oil by a pump (2); a pressure sensor (6) configured to detect an actual system pressure of the hydraulic system; an action instruction input element (7) configured to input a desired actuator action; as well as A control unit (8) as claimed in any one of claims 1 to 11.

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