Digital hydraulic closed pump control system and control method thereof

Abstract

The embodiment of the application provides a kind of digital hydraulic closed pump control system and its control method, it can be applied to hydraulic transmission and control technical field, the system includes: closed hydraulic circuit, with high-pressure side oil circuit and low-pressure side oil circuit;Digital hydraulic valve group includes cartridge valve between high-pressure side oil circuit and low-pressure side oil circuit, cartridge valve has control cavity, the pressure in control cavity is used to control the conduction state of cartridge valve, multiple high-speed switch valve is connected with the control cavity of cartridge valve, for controlling the pressure of control cavity;Controller is configured to: when the pressure gradient of high-pressure side oil circuit exceeds limit value, multiple high-speed switch valve is output first control signal to drive multiple high-speed switch valve to adjust the pressure in control cavity, to make high-pressure side oil circuit and low-pressure side oil circuit at least partially conductive;When the pressure gradient does not exceed limit value, multiple high-speed switch valve is output second control signal to drive multiple high-speed switch valve to make cartridge valve keep closed state.

Description

Technical Field

[0001] This application relates to the field of hydraulic transmission and control technology, and more specifically to a digital hydraulic closed-loop pump control system and its control method. Background Technology

[0002] Engineering machinery such as tunnel boring machine cutterheads, screw conveyors, and chain cutter continuous wall equipment, mining machinery such as tunneling and anchoring machines, agricultural machinery such as cotton harvesters, and special equipment such as snow blowers, all have hydraulic closed-loop drive systems that are susceptible to changes in load, jamming, and start-up conditions during operation.

[0003] Under the aforementioned operating conditions, a transient pressure surge will occur on the high-pressure side of the closed-loop system. In related technologies, solutions using relief valves suffer from slow response and large pressure overshoot; solutions using accumulators increase system volume and reduce the oil's elastic modulus, thus exacerbating the risk of cavitation on the low-pressure side. Neither approach effectively solves the pressure surge problem. Severe surges can easily damage the plunger structure inside the closed-loop pump and motor, affecting the system's service life. Summary of the Invention

[0004] In view of the above problems, this application provides a digital hydraulic closed-loop pump control system and its control method.

[0005] According to a first aspect of this application, a digital hydraulic closed-loop pump control system is provided, comprising: a closed-loop hydraulic circuit having a high-pressure side oil circuit and a low-pressure side oil circuit; a digital hydraulic valve group 3 including a plurality of high-speed switching valves and a cartridge valve 3.8; the cartridge valve 3.8 being connected between the high-pressure side oil circuit and the low-pressure side oil circuit, the cartridge valve 3.8 having a control chamber, the pressure in the control chamber being used to control the conduction state of the cartridge valve 3.8; and a plurality of high-speed switching valves being connected to the control chamber of the cartridge valve 3.8 for controlling the pressure in the control chamber;

[0006] The controller, electrically connected to the plurality of high-speed switching valves, is configured to: when the pressure gradient of the high-pressure side oil circuit exceeds a predetermined value, output a first control signal to the plurality of high-speed switching valves, the first control signal being used to drive the plurality of high-speed switching valves to adjust the pressure in the control chamber so that the high-pressure side oil circuit and the low-pressure side oil circuit are at least partially connected; when the pressure gradient does not exceed the predetermined value, output a second control signal to the plurality of high-speed switching valves, the second control signal being used to drive the plurality of high-speed switching valves to keep the cartridge valve 3.8 in a closed state.

[0007] According to an embodiment of this application, the digital hydraulic valve group 3 further includes: a shuttle valve 3.1, including two inlets and an outlet, the two inlets being connected to the high-pressure side oil circuit and the low-pressure side oil circuit respectively, and the outlet being used to output the oil from the low-pressure side oil circuit; the second control signal is also used to adjust the flushing flow rate through the shuttle valve 3.1.

[0008] According to an embodiment of this application, the cartridge valve 3.8 includes: a valve core 3.85, used to control the conduction state between the first liquid inlet 3.83 and the second liquid inlet 3.84 by moving; a first cavity 3.81 and a second cavity 3.82, the first cavity 3.81 and the second cavity 3.82 being located on both sides of the valve core 3.85 respectively, used to drive the valve core 3.85 to move under the action of a pressure difference, the pressure difference being the pressure difference between the first cavity 3.81 and the second cavity 3.82; the first liquid inlet 3.83 being connected to the high-pressure side oil circuit; and the second liquid inlet 3.84 being connected to the low-pressure side oil circuit.

[0009] According to an embodiment of this application, the plurality of high-speed switching valves include a first group of high-speed switching valves and a second group of high-speed switching valves; the first group of high-speed switching valves is connected to the first cavity 3.81 and is used to form a first hydraulic half-bridge to control the pressure in the first cavity 3.81; the second group of high-speed switching valves is connected to the second cavity 3.82 and is used to form a second hydraulic half-bridge to control the pressure in the second cavity 3.82; the cartridge valve 3.8 includes a valve core 3.85, which is used to generate displacement according to the pressure difference between the first control cavity 3.81 and the second control cavity 3.82.

[0010] According to an embodiment of this application, the controller is further configured to: control the pressure of the first cavity 3.81 by adjusting the duty cycle of the control signal output to the first group of high-speed switching valves, and / or control the pressure of the second cavity 3.82 by adjusting the duty cycle of the control signal output to the second group of high-speed switching valves.

[0011] According to an embodiment of this application, the digital hydraulic valve group 3 further includes: a temperature sensor 3.3, which is disposed on the oil line between the outlet of the shuttle valve 3.1 and the low-pressure side oil line, and is electrically connected to the controller, for detecting the oil temperature in the closed hydraulic circuit; the controller is further configured to: output a third control signal to the plurality of high-speed switching valves according to the oil temperature, so as to change the flushing flow rate through the shuttle valve 3.1.

[0012] According to an embodiment of this application, the digital hydraulic valve group 3 further includes an accumulator 3.2, which is connected to the oil line between the outlet of the shuttle valve 3.1 and the low-pressure side oil line. The accumulator 3.2 is used to maintain the pressure of the low-pressure side oil line within a preset range.

[0013] According to this application, the closed hydraulic circuit includes a closed pump group 2 and a motor 4; the oil outlet of the closed pump group 2 is connected to the oil inlet of the motor 4 to form the high-pressure side oil circuit, and the oil outlet of the motor 4 is connected to the oil inlet of the closed pump group 2 to form the low-pressure side oil circuit.

[0014] According to an embodiment of this application, the controller is further configured to: during the period when the pressure gradient exceeds the limit value, adjust the duty cycle of the first control signal output to the plurality of high-speed switching valves according to the amount of change in the pressure gradient, so as to change the opening degree of the cartridge valve 3.8.

[0015] According to an embodiment of this application, the controller is further configured to: drive the cartridge valve 3.8 to gradually close during the period when the pressure gradient exceeds the limit value.

[0016] According to an embodiment of this application, it further includes: a replenishing pump group 1, which is connected to the closed hydraulic circuit and is used to replenish leaked oil; and a replenishing overflow valve 1.3, which is connected to the replenishing pump group 1 and is used to control the replenishing pressure.

[0017] According to a second aspect of this application, a control method for a digital hydraulic closed-loop pump control system is provided, comprising: monitoring the pressure gradient of the high-pressure side oil circuit in real time through a controller; when the pressure gradient exceeds a limit value, outputting a first control signal to the plurality of high-speed switching valves, the first control signal being used to drive the plurality of high-speed switching valves to adjust the pressure in the control chamber; when the pressure gradient does not exceed the limit value, outputting a second control signal to the plurality of high-speed switching valves, the second control signal being used to drive the plurality of high-speed switching valves to keep the cartridge valve 3.8 in a closed state.

[0018] According to an embodiment of this application, the method further includes: adjusting the duty cycle of the first control signal during the period when the pressure gradient exceeds the limit value, so as to drive the cartridge valve 3.8 to gradually close.

[0019] According to an embodiment of this application, the method further includes: detecting the oil temperature in the closed hydraulic circuit using a temperature sensor 3.3; and outputting a third control signal to the plurality of high-speed switching valves based on the oil temperature to change the flushing flow rate through the shuttle valve 3.1.

[0020] According to an embodiment of this application, it further includes: when the pressure gradient recovers from exceeding the limit value to not exceeding the limit value, outputting the second control signal to the plurality of high-speed switching valves to drive the cartridge valve 3.8 to close completely.

[0021] According to the digital hydraulic closed-loop pump control system provided in this application embodiment, a cartridge valve is set in parallel with the high-pressure side oil circuit and the low-pressure side oil circuit of the closed hydraulic circuit. Multiple high-speed switching valves are used to precisely control the pressure within the control chamber of the cartridge valve. Simultaneously, the controller monitors the pressure gradient of the high-pressure side oil circuit in real time. When the pressure gradient exceeds a limit value, a first control signal is output to drive the high-speed switching valve to adjust the pressure in the control chamber, causing the cartridge valve to open and at least partially connecting the high-pressure side and the low-pressure side. This allows some of the oil in the high-pressure side oil circuit to flow to the low-pressure side oil circuit in a timely manner, thereby directly reducing the peak value of the pressure shock and suppressing the pressure gradient. The rapid increase in pressure gradient avoids damage to the closed-loop pump and motor caused by a sharp rise in high-pressure side pressure. At the same time, because the rate of increase in high-pressure side pressure is effectively controlled, the flow difference required for oil replenishment on the low-pressure side due to the instantaneous decrease in the amount of oil returned by the motor is also significantly reduced. This prevents the low-pressure side pressure from dropping rapidly or even cavitation, thus protecting the closed-loop hydraulic circuit. When the pressure gradient does not exceed the limit value, the controller outputs a second control signal to keep the cartridge valve closed, preventing the creation of an additional conduction channel between the high-pressure side and the low-pressure side. This avoids system heating and energy waste caused by prolonged overflow, extending the system's service life. Attached Figure Description

[0022] The above-mentioned contents, other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0023] Figure 1 A schematic diagram of a digital hydraulic closed-loop pump control system according to an embodiment of this application is shown.

[0024] Figure 2 A schematic diagram of a replenishment pump assembly according to an embodiment of this application is shown.

[0025] Figure 3 A schematic diagram of a closed-loop pump unit according to an embodiment of this application is shown.

[0026] Figure 4 A schematic diagram of a digital hydraulic valve assembly according to an embodiment of this application is shown.

[0027] Figure 5 A schematic diagram of a cartridge valve according to an embodiment of this application is shown.

[0028] Figure 6 A flowchart illustrating a control method for a digital hydraulic closed-loop pump control system according to an embodiment of this application is shown. Detailed Implementation

[0029] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0030] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0031] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0032] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0033] Figure 1 A schematic diagram of a digital hydraulic closed-loop pump control system according to an embodiment of this application is shown.

[0034] like Figure 1 As shown, the digital hydraulic closed-loop pump control system of this embodiment includes a closed hydraulic circuit, a digital hydraulic valve group 3, and a controller (not shown in the figure, but electrically connected to each electronic control component).

[0035] A closed-loop hydraulic circuit has a high-pressure side oil circuit and a low-pressure side oil circuit. The closed-loop hydraulic circuit may include a closed-loop pump unit 2 and a motor 4. The oil outlet of the closed-loop pump unit 2 is connected to the oil inlet of the motor 4 to form the high-pressure side oil circuit, and the oil outlet of the motor 4 is connected to the oil inlet of the closed-loop pump unit 2 to form the low-pressure side oil circuit. The closed-loop pump unit 2 can change the speed and direction of the motor 4 by adjusting its displacement and direction.

[0036] In some embodiments, the closed hydraulic circuit may further include a replenishing pump assembly 1 for performing basic functions such as replenishing oil.

[0037] The digital hydraulic valve group 3 may include multiple high-speed switching valves and cartridge valves 3.8.

[0038] The two oil ports of the cartridge valve 3.8 are connected in parallel to the high-pressure side oil circuit and the low-pressure side oil circuit of the closed hydraulic circuit, respectively.

[0039] The cartridge valve 3.8 may have a control chamber inside, and the pressure in the control chamber can determine the conduction state of the cartridge valve 3.8.

[0040] For example, the conduction state can be fully connected, disconnected, or partially connected. Fully connected means a passage is formed between the first and second inlet ports, allowing oil to flow through; high-pressure oil can flow to the low-pressure side via the cartridge valve. Disconnected means there is no passage between the first and second inlet ports, preventing oil flow and disconnecting the high-pressure and low-pressure sides. Partially connected means a limited passage is formed between the first and second inlet ports, with the flow area between 0 and the maximum opening; some high-pressure oil flows to the low-pressure side, and the flow rate is controllable.

[0041] Multiple high-speed switching valves are connected to the control chamber of cartridge valve 3.8 via hydraulic lines. By controlling the opening and closing states and timing of these high-speed switching valves, the pressure value within the control chamber can be precisely adjusted.

[0042] The controller is electrically connected to multiple high-speed switching valves (the electrical connections are not shown in the figure, but will be understood by those skilled in the art). The controller is configured to detect or acquire the pressure gradient of the high-pressure side oil circuit in real time and compare the pressure gradient with a preset limit value.

[0043] When the pressure gradient in the high-pressure side oil circuit exceeds a certain limit (i.e., the system detects the start of a shock condition), the controller outputs a first control signal to multiple high-speed switching valves. This first control signal drives the high-speed switching valves to adjust the pressure in the control chamber, changing the conduction state of the cartridge valve 3.8, thereby at least partially connecting the high-pressure side oil circuit and the low-pressure side oil circuit. At this time, some oil in the high-pressure side oil circuit can flow to the low-pressure side oil circuit through the cartridge valve 3.8, thereby suppressing the rapid rise in high-pressure side pressure and weakening the pressure shock.

[0044] When the pressure gradient of the high-pressure side oil circuit does not exceed the limit value (i.e., the system is in a stable or non-impact condition), the controller outputs a second control signal to multiple high-speed switching valves. This second control signal maintains or restores the pressure in the control chamber to the point where the cartridge valve 3.8 is closed, and no additional conduction channel is generated between the high-pressure side and the low-pressure side oil circuits, so the system returns to normal closed-loop circulation.

[0045] The first control signal can be a PWM (Pulse Width Modulation) signal. By adjusting the duty cycle of the PWM signal (i.e., the proportion of high-level time in one cycle), the opening and closing state and average opening time of the high-speed switching valve can be changed, thereby precisely controlling the control chamber entering the cartridge valve 3.8.

[0046] According to the embodiments of this application, the digital hydraulic closed-loop pump control system can automatically and quickly realize on-demand conduction between the high-pressure side and the low-pressure side under impact conditions, thereby effectively reducing pressure shocks, while maintaining the structural integrity of the closed loop under normal operating conditions and avoiding unnecessary energy loss.

[0047] Figure 2 A schematic diagram of a replenishment pump assembly according to an embodiment of this application is shown.

[0048] like Figure 2 As shown, the oil replenishment pump assembly 1 in this embodiment includes a motor 1.1, an oil replenishment pump 1.2, and an oil replenishment overflow valve 1.3.

[0049] Motor 1.1 serves as the power source, driving the oil replenishment pump 1.2 to rotate. Oil replenishment pump 1.2, connected to motor 1.1, draws oil from the oil tank and replenishes leaked oil to the closed hydraulic circuit, maintaining the required oil volume and pressure for normal system operation. Oil replenishment relief valve 1.3, connected between the outlet of oil replenishment pump 1.2 and the oil tank, controls the oil replenishment pressure. When the oil replenishment pressure exceeds a set value, excess oil flows back to the oil tank through oil replenishment relief valve 1.3, thus stabilizing the oil replenishment pressure within the preset range.

[0050] During system operation, motor 1.1 is first started, which drives the oil replenishment pump 1.2 to rotate, filling the oil replenishment circuit with oil. The oil replenishment pressure is controlled by the oil replenishment overflow valve 1.3, and excess oil flows back to the oil tank through the oil replenishment overflow valve 1.3. At this time, the initial pressure of the oil circuits on both sides of the closed system is the same as the oil replenishment pressure.

[0051] According to the embodiments of this application, the oil replenishment pump group 1 can be used to replenish the leaked oil in the closed hydraulic circuit, digital hydraulic valve group and motor and other components in the digital hydraulic closed pump control system provided in the embodiments of this application, so as to ensure that the system can maintain a stable low-pressure side oil replenishment capability under various working conditions.

[0052] Figure 3 A schematic diagram of a closed-loop pump unit according to an embodiment of this application is shown.

[0053] like Figure 3 As shown, the closed-loop pump unit of this embodiment includes a motor 2.1, a closed-loop pump 2.2, a check valve 2.3, an overflow valve 2.4, a replenishing check valve 2.5, and a flushing damper 2.6.

[0054] Motor 2.1 serves as the power source for closed-loop pump 2.2, driving its rotation. Closed-loop pump 2.2, driven by motor 2.1, controls the speed and direction of motor 4 connected to it by changing its displacement and direction, thereby driving the working device. Two check valves 2.3 are arranged in pairs in the oil circuits on both sides of closed-loop pump 2.2. Each check valve 2.3 allows oil to flow from one side of closed-loop pump 2.2 to the other, cooperating with relief valve 2.4 to provide an oil return channel during safe overflow. Two relief valves 2.4 are also arranged in pairs in the oil circuits on both sides of closed-loop pump 2.2. Each relief valve 2.4 limits the maximum pressure of the corresponding side oil circuit; when the pressure in that side oil circuit exceeds the safety set value, oil flows to the opposite side oil circuit via the relief valve 2.4 and the check valve 2.3 on the opposite side. Two replenishing check valves 2.5 are arranged in pairs in the oil circuits on both sides of the closed-loop pump 2.2 to ensure that the replenishing flow provided by the replenishing pump group 1 can automatically replenish the lower pressure side of the oil circuits on both sides of the closed-loop system. A flushing damper 2.6 is installed in the flushing oil circuit of the casing of the closed-loop pump 2.2 to control the flushing flow rate of the bearings and casing of the closed-loop pump 2.2.

[0055] During system operation, after starting motor 2.1, motor 2.1 drives closed-loop pump 2.2 to rotate, increasing the displacement of closed-loop pump 2.2 and causing motor 4 to rotate, thus driving the working device. At this time, the oil inflow side of motor 4 becomes the high-pressure side oil circuit due to the load, and the oil outflow side becomes the low-pressure side oil circuit. The overflow valve 2.4 provides safety protection when the pressure on one side is too high, the oil replenishment check valve 2.5 ensures that the low-pressure side oil circuit always receives replenishment oil, and the flushing damper 2.6 controls the flushing flow rate through the closed-loop pump 2.2 to remove the heat and impurities generated during its operation.

[0056] Figure 4 A schematic diagram of a digital hydraulic valve assembly according to an embodiment of this application is shown.

[0057] like Figure 4 As shown, the digital hydraulic valve group of this embodiment includes a flushing shuttle valve 3.1, multiple high-speed switching valves, and a cartridge valve 3.8.

[0058] The flushing shuttle valve 3.1 operates under the pressure difference between the high and low pressure sides, connecting the oil circuit to the low-pressure side oil circuit of the closed system. The flushing shuttle valve 3.1 has two inlets and one outlet. The two inlets connect to the high-pressure and low-pressure sides of the closed hydraulic circuit, respectively, while the outlet is used to output oil from the low-pressure side. The working principle of the flushing shuttle valve 3.1 is as follows: When the system is working, a pressure difference is formed between the high-pressure and low-pressure sides. The valve core inside the shuttle valve 3.1 moves under the action of this pressure difference, automatically connecting the outlet to the low-pressure side oil circuit. This allows a portion of the oil in the low-pressure side oil circuit to flow out through the outlet and eventually return to the oil tank. This outflowing oil is the flushing flow rate, which can remove heat and impurities from the closed circuit.

[0059] In addition to its shock-resistant control function, the controller can also be configured to regulate the flushing flow rate through the flushing shuttle valve 3.1 using a second control signal. Specifically, the second control signal controls the amount of oil flowing out of the outlet of the shuttle valve 3.1 by adjusting the duty cycle of the PWM control signal of the high-speed switching valve, thereby changing the opening and closing state and the opening and closing time ratio of the high-speed switching valve.

[0060] For example, when the system requires a larger flushing flow rate (such as when the oil temperature is high or there are many impurities), the controller outputs a PWM signal with a high duty cycle, which makes the high-speed switching valve open for a longer period of time per unit time, thereby increasing the flushing flow rate.

[0061] For example, when the system requires a smaller flushing flow (such as when the oil temperature is normal or the system is being cleaned), the controller outputs a PWM signal with a low duty cycle to reduce the flushing flow.

[0062] According to the embodiments of this application, through the above method, the second control signal can ensure that the cartridge valve remains closed (i.e., non-impact condition) while also being used for dynamic adjustment of the flushing flow rate, thereby realizing the reuse of control resources and the integration of system functions.

[0063] like Figure 4 As shown, in some embodiments, multiple high-speed switching valves are divided into a first group of high-speed switching valves and a second group of high-speed switching valves.

[0064] The first set of high-speed switching valves may include, for example, high-speed switching valve a3.4 and high-speed switching valve c3.6. These two high-speed switching valves are connected to the first cavity 3.81 of the cartridge valve 3.8 via hydraulic lines and together form a first hydraulic half-bridge.

[0065] The control principle of the first hydraulic half-bridge is as follows: By controlling the opening and closing combination of the two high-speed switching valves in the first group and the PWM duty cycle, the oil pressure entering the first chamber 3.81 can be adjusted to continuously change between the replenishment pressure and the tank pressure. For example, when the high-speed switching valve a3.4 is open and the high-speed switching valve c3.6 is closed, the pressure in the first chamber 3.81 increases; conversely, the pressure decreases.

[0066] The second set of high-speed switching valves includes, for example, high-speed switching valve b3.5 and high-speed switching valve d3.7. These two high-speed switching valves are connected to the second cavity 3.82 of the cartridge valve 3.8 via hydraulic lines, and together they form a second hydraulic half-bridge to control the pressure in the second cavity 3.82 on the same principle as the first hydraulic half-bridge.

[0067] The valve core 3.85 of the cartridge valve 3.8 can be displaced according to the pressure difference between the first cavity 3.81 and the second cavity 3.82. For example, if the pressure in the first cavity 3.81 is 10 bar and the pressure in the second cavity 3.82 is 5 bar, the pressure difference is 5 bar (direction from the first cavity to the second cavity), the valve core 3.85 moves towards the second cavity; if the pressure in the first cavity 3.81 is 5 bar and the pressure in the second cavity 3.82 is 10 bar, the pressure difference is 5 bar, and the valve core 3.85 moves towards the first cavity.

[0068] According to the embodiments of this application, by independently controlling the pressure of the two chambers with two sets of high-speed switching valves, bidirectional precise control of the valve core 3.85 displacement can be achieved, thereby improving the response speed and control flexibility of the cartridge valve 3.8.

[0069] In some embodiments, the controller is configured to control the pressure of the first cavity 3.81 and the second cavity 3.82 respectively by adjusting the duty cycle of the PWM control signal.

[0070] For pressure control in the first chamber 3.81: The controller outputs PWM signals to the first group of high-speed switching valves (e.g., high-speed switching valves a3.4 and c3.6). By adjusting the duty cycle of this group of PWM signals (i.e., the proportion of high-level time within one cycle), the average opening time of the high-speed switching valves can be changed, thereby controlling the flow rate and pressure of the oil entering the first chamber 3.81. For example: when the duty cycle is 100%, the high-speed switching valves are normally open, and the pressure in the first chamber 3.81 is close to the replenishment pressure; when the duty cycle is 0%, the high-speed switching valves are normally closed, and the pressure in the first chamber 3.81 is close to the tank pressure; when the duty cycle is 50%, the pressure is at an intermediate value.

[0071] For pressure control of the second cavity 3.82: the controller outputs PWM signals to the second set of high-speed switching valves (e.g., high-speed switching valve b3.5 and high-speed switching valve d3.7) to independently adjust the pressure of the second cavity 3.82 using the same principle.

[0072] The controller can adjust the pressure of any one of the chambers individually, or it can adjust the pressure of both chambers simultaneously, depending on the control requirements of the system. For example, when only one-way opening of the cartridge valve is required, only the pressure in the second chamber 3.82 can be increased while keeping the pressure in the first chamber 3.81 unchanged; when a rapid response is required, the pressure in the second chamber 3.82 can be increased while the pressure in the first chamber 3.81 is decreased to maximize the pressure difference and valve core movement speed.

[0073] According to the embodiments of this application, the controller achieves digital and high-precision control of the pressure of the two cavities through the above-mentioned duty cycle adjustment method, avoiding the drift and response lag problems under the traditional analog adjustment method.

[0074] like Figure 4 As shown, in some embodiments, the digital hydraulic valve assembly 3 may further include a temperature sensor 3.3. This temperature sensor 3.3 is located in the oil line between the outlet of the flushing shuttle valve 3.1 and the low-pressure side oil line, and is installed inside the valve assembly or on the pipeline to directly contact the oil flowing through it. The temperature sensor 3.3 is electrically connected to the controller to detect the oil temperature in the closed hydraulic circuit in real time and feeds the temperature signal back to the controller.

[0075] Accordingly, the controller is also configured to output a third control signal to multiple high-speed switching valves based on the oil temperature fed back by the temperature sensor 3.3, in order to change the flushing flow rate through the flushing shuttle valve 3.1. The specific form of the third control signal can be a PWM control signal, which controls the opening and closing state and opening time of the high-speed switching valve by adjusting the duty cycle, thereby adjusting the flushing flow rate.

[0076] When the closed-loop pump 2.2 and motor 4 operate under high load for extended periods or experience significant wear after prolonged use, the temperature sensor 3.3 detects a high oil temperature in the closed-loop circuit and increases the control flow rate. For example, when the oil temperature is below the first temperature threshold (e.g., 50°C): the controller outputs a third control signal with a small duty cycle (e.g., 10%) to maintain a low flushing flow rate, thus preventing excessive cold oil from flowing back to the oil tank and wasting energy.

[0077] For example, when the oil temperature is higher than the first temperature threshold but lower than the second temperature threshold (e.g., 50°C to 70°C): the controller outputs a third control signal with a moderate duty cycle (e.g., 50% duty cycle) to appropriately increase the flushing flow rate to remove heat.

[0078] For example, when the oil temperature is higher than the second temperature threshold (e.g., 70°C): the controller outputs a third control signal with a large duty cycle (e.g., 90% or 100%), so that the flushing flow reaches the maximum value and the system temperature is reduced quickly.

[0079] According to the embodiments of this application, through the above-mentioned temperature feedback control, the oil temperature is detected by a temperature sensor, and the flushing flow rate is dynamically adjusted according to the oil temperature, so that the system temperature is always maintained within a reasonable range. This can realize closed-loop dynamic adjustment of the flushing flow rate, avoid the thermal balance temperature loss of closed pumps and motors after long-term high-load operation or wear and tear, and extend the service life of the system and its components.

[0080] It is understandable that the flushing flow usually contains impurities from the closed loop. Since the high-speed switching valve is not sensitive to the cleanliness of the oil, using a high-speed switching valve to regulate the flow through the flushing shuttle valve 3.1 is more advantageous than traditional spool valve control valves such as proportional valves and servo valves that are sensitive to the cleanliness of the oil.

[0081] like Figure 4 As shown, in some embodiments, the digital hydraulic valve assembly 3 may further include an accumulator 3.2. The accumulator 3.2 is connected to the oil line between the outlet of the flushing shuttle valve 3.1 and the low-pressure side oil line, i.e., connected in parallel or in series with the flushing pipeline. The accumulator 3.2 serves to stabilize the pressure, preventing fluctuations in the low-pressure side oil line from causing unstable control of the valve core 3.85.

[0082] The function of accumulator 3.2 is to maintain the pressure of the low-pressure side oil circuit within a preset range. Its working principle is as follows:

[0083] When the system is operating normally, the pressure in the low-pressure side oil circuit is maintained near a basically stable replenishment pressure by the replenishment pump group 1 and the replenishment overflow valve 1.3. The nitrogen chamber and the oil chamber inside the accumulator 3.2 reach a pressure balance.

[0084] When the system is subjected to an impact, the high-pressure side oil flows to the low-pressure side through the cartridge valve 3.8, which may cause a momentary increase in the low-pressure side pressure. At this time, the accumulator 3.2 absorbs the excess pressure fluctuation by compressing the internal nitrogen gas to prevent the low-pressure side pressure from exceeding the safe upper limit.

[0085] When the pressure on the low-pressure side of the system decreases due to insufficient oil replenishment or pressure drop after impact, the compressed nitrogen inside the accumulator 3.2 expands and pushes the stored oil back to the low-pressure side oil circuit to prevent the low-pressure side pressure from becoming too low or even sucking in air.

[0086] For example, the preset range settings include: lower limit of low-pressure side: set slightly higher than atmospheric pressure (e.g., 2 bar) to prevent cavitation; upper limit of low-pressure side: set to 1.2 times the setting value of the oil replenishment relief valve (e.g., if the oil replenishment pressure is 25 bar, then the upper limit is 30 bar) to prevent overpressure.

[0087] The specific type of accumulator 3.2 can be a bladder accumulator, a piston accumulator, or a diaphragm accumulator, selected according to system pressure and volume requirements. By setting the accumulator 3.2, this application can effectively suppress pressure fluctuations in the low-pressure side oil circuit during pressure regulation of the high-speed switching valve and cartridge valve, thereby improving the stability of valve core control and the reliability of the entire closed system.

[0088] The working principle of the shock protection control of this application is described in detail below:

[0089] When a hydraulic closed-loop system encounters an impact condition during operation, the pressure in the high-pressure side oil circuit rises rapidly under a single impact, increasing the pressure gradient. When the pressure gradient exceeds a limit, the pressure in the first chamber 3.81 and the second chamber 3.82 is changed by adjusting high-speed switching valves a3.4, b3.5, c3.6, and d3.7, thereby controlling the up-and-down movement of valve core 3.85. This achieves on-demand connection between the high-pressure and low-pressure side oil circuits of the closed-loop system, allowing some oil from the high-pressure side to flow to the low-pressure side, controlling the pressure gradient in the high-pressure side oil circuit to not exceed the limit, greatly reducing the pressure impact on the high-pressure side oil circuit, and preventing damage to the closed-loop pump and motor under frequent impact conditions, thus affecting their service life.

[0090] As the single impact continues, the pressure in the high-pressure side oil circuit rises at a limited gradient, and the control valve core 3.85 of the active two-way cartridge valve 3.8 gradually closes to prevent prolonged overflow from causing system overheating and energy waste.

[0091] After a single impact ends, the pressure in the high-pressure side oil circuit begins to drop, and the control valve core 3.85 of the active two-way cartridge valve 3.8 is completely closed. The above working process is repeated when the next impact begins.

[0092] In some embodiments, the controller can be configured to execute a more refined control strategy during the entire impact period when the pressure gradient exceeds a predetermined value: dynamically adjusting the duty cycle of the first control signal according to the amount of change in the pressure gradient, thereby changing the opening of the cartridge valve 3.8.

[0093] The change in pressure gradient can refer to the instantaneous change in the rate of change of pressure over time (Δp / Δt) in the high-pressure side oil circuit during the impact process. A larger pressure gradient indicates a more severe impact; a gradually decreasing pressure gradient indicates that the impact is attenuating. The controller acquires pressure signals in real time through pressure sensors and calculates the instantaneous change in pressure gradient.

[0094] For example, suppose the pressure gradient limit is 100 bar / s. When a pressure gradient of 150 bar / s is detected, the controller outputs a first control signal with a 50% duty cycle, causing the cartridge valve to open to 40%.

[0095] For example, when the pressure gradient rises further to 250 bar / s, the controller increases the duty cycle to 80%, increasing the cartridge valve opening to 70%, allowing more high-pressure oil to flow to the low-pressure side to cope with more severe shocks.

[0096] For example, when the pressure gradient drops to 120 bar / s, the controller will reduce the duty cycle to 30%, thereby reducing the cartridge valve opening to 20% and minimizing unnecessary overflow.

[0097] According to the embodiments of this application, by using the control method described above to adjust the duty cycle in real time according to the pressure gradient change, this application realizes continuous, dynamic, and on-demand adjustment of the cartridge valve opening. It can fully conduct during severe impact to absorb impact energy, and can also reduce the opening in time during impact attenuation to avoid excessive overflow and energy waste.

[0098] In some embodiments, the controller is configured to gradually close the cartridge valve 3.8 rather than instantaneously during the later stages of a single impact process, i.e., when the pressure gradient still exceeds a predetermined value but the impact energy has begun to be released and the upward trend of the high-pressure side pressure has slowed down. Gradual closing can be achieved by the controller progressively reducing the duty cycle of the first control signal.

[0099] Understandably, if the cartridge valve closes abruptly after the impact, the passage between the high-pressure and low-pressure sides is suddenly cut off. The residual pressure fluctuations on the high-pressure side may not be released in time, potentially triggering a secondary pressure shock. Gradually closing the valve allows the high-pressure side pressure to drop smoothly, preventing sudden pressure changes from causing new shocks to the system.

[0100] For example, the controller sets a closing time window, such as 500 milliseconds. Starting from the peak impact moment, the controller reduces the duty cycle of the first control signal by 10% every 50 milliseconds, causing the cartridge valve opening to gradually decrease from 100% to 0%, achieving uniform and gradual closing.

[0101] For example, when the pressure gradient decreases from its peak (e.g., 250 bar / s) to near a limit (100 bar / s), the controller initiates a gradual shutdown procedure. A linear mapping is established between the pressure gradient decrease and the duty cycle adjustment: for every 10 bar / s decrease in the pressure gradient, the duty cycle decreases by 5%; when the pressure gradient falls below the limit, the duty cycle drops to 0%. This method achieves synchronous matching between the shutdown speed and the impact decay rate.

[0102] According to the embodiments of this application, by using the above-mentioned gradual closing control strategy, this application avoids the pressure rebound and secondary impact that may be caused by the instantaneous closing of the cartridge valve, so that the high-pressure side pressure can return to the normal value smoothly and safely, further improving the stability of the system and the life of the components.

[0103] The following comparison with conventional closed systems further illustrates the beneficial effects of this application:

[0104] In a conventional closed-loop system, since it lacks a multi-functional digital hydraulic valve group 3, the high-pressure oil from the outlet of the closed-loop pump 2.2 flows through the motor 4 and returns to the inlet of the closed-loop pump 2.2. When the load driven by the motor 4 has low inertia, the output of the motor 4 experiences a sudden load impact, causing the pressure in the high-pressure side of the closed-loop system to rise. Due to the effect of the elastic modulus of the hydraulic system (oil compression, pipeline expansion), the motor speed will decrease instantaneously, and the return oil volume on the low-pressure side of the motor 4 will be less than the oil output volume on the high-pressure side of the closed-loop pump 2.2. When the replenishment flow rate of the replenishment pump group 1 is insufficient to compensate for this flow difference, the low-pressure side pressure of the closed-loop system will drop rapidly or even cavitation will occur, causing damage to the internal plunger structure of the closed-loop pump 2.2 and the motor 4, thus affecting their service life.

[0105] Under a single impact, the difference in flow rate required to replenish the low-pressure side of a closed system can be calculated using the following formula:

[0106]

[0107] In the formula: Q is the flow rate that the system needs to replenish; V is the total volume of oil on the high-pressure side; β e Δp / Δt is the equivalent bulk modulus of the system; Δp / Δt is the rate of increase in system pressure under impact (pressure gradient).

[0108] Once the mechanism is determined, it is difficult to change the total volume of the high-pressure side oil and the equivalent volumetric elastic modulus of the system. At the same time, since a large flow of oil is required only at the moment of impact, if the oil replenishment pump is increased, the flow of the oil replenishment pump will be lost through overflow most of the time, resulting in large energy loss and high cost.

[0109] Under the same circumstances, when the closed system contains a multi-functional digital hydraulic valve group 3, the pressure impact on the high-pressure side oil circuit is greatly weakened, reducing the system pressure increase rate Δp / Δt under impact. This significantly reduces the flow difference that needs to be added to the low-pressure side of the closed system, preventing the low-pressure side pressure of the closed system from dropping rapidly or even sucking in air, thus extending the service life of the system and its components.

[0110] Meanwhile, in a conventional closed system, since it does not contain a multi-functional digital hydraulic valve group 3, the flow rate of the flushing shuttle valve 3.1 cannot be dynamically adjusted according to the working load and service life of the closed pump 2.2 and motor 4, which can easily cause the thermal equilibrium temperature in the closed circuit to be too high, affecting the service life of the system and its components.

[0111] Under the same conditions, when the closed system contains a multi-functional digital hydraulic valve group 3, the temperature sensor 3.3 detects the oil temperature in the closed circuit in real time. By adjusting the duty cycle of the PWM control signals of high-speed switching valves a3.4, b3.5, c3.6, and d3.7, the opening and closing states are changed, thereby adjusting the flow rate through the flushing shuttle valve 3.1. This achieves effective control of the thermal balance temperature in the closed circuit and extends the service life of the system and its components.

[0112] Figure 5 A schematic diagram of a cartridge valve according to an embodiment of this application is shown.

[0113] like Figure 5 As shown, the cartridge valve 3.8 of this embodiment may include a valve core 3.85, a first inlet port 3.83, a second inlet port 3.84, a first cavity 3.81, and a second cavity 3.82. The first inlet port 3.83 is directly connected to the high-pressure side oil circuit of the closed hydraulic circuit. The second inlet port 3.84 is directly connected to the low-pressure side oil circuit of the closed hydraulic circuit. The valve core 3.85 is disposed inside the cartridge valve 3.8 and can move axially within the valve body. The moving position of the valve core 3.85 can determine the conduction area between the first inlet port 3.83 and the second inlet port 3.84, thereby controlling the conduction state between the high-pressure and low-pressure side oil circuits.

[0114] The first cavity 3.81 and the second cavity 3.82 are located on both sides of the valve core 3.85, for example, the first cavity 3.81 is located above the valve core 3.85, and the second cavity 3.82 is located below the valve core 3.85. (See figure) Figure 5 Both cavities are filled with oil and each has an independent pressure value. The direction and amount of movement of the valve core 3.85 are determined by the pressure difference between the first cavity 3.81 and the second cavity 3.82.

[0115] For example, when the pressure in the first cavity 3.81 is greater than the pressure in the second cavity 3.82, the valve core 3.85 moves downward, the conduction area decreases, and the cartridge valve tends to close.

[0116] For example, when the pressure in the first cavity 3.81 is less than the pressure in the second cavity 3.82, the valve core 3.85 moves upward, the conduction area increases, and the cartridge valve tends to open.

[0117] According to the embodiments of this application, precise control of the on-state of cartridge valve 3.8 can be achieved by controlling the pressure difference between the two cavities.

[0118] Figure 6 A flowchart illustrating a control method for a digital hydraulic closed-loop pump control system according to an embodiment of this application is shown.

[0119] like Figure 6 As shown, the control method of the digital hydraulic closed-loop pump control system in this embodiment may include operations S1-S3.

[0120] During operation S1, the pressure gradient of the high-pressure side oil circuit is monitored in real time through the controller.

[0121] The controller can use a pressure sensor installed in the high-pressure side oil circuit to collect the instantaneous pressure value of the high-pressure side oil circuit and calculate the rate of change of pressure over time, i.e., the pressure gradient (Δp / Δt). The magnitude of the pressure gradient reflects the severity of the pressure shock: the larger the pressure gradient, the more violent the shock; the smaller the pressure gradient, the more stable the system operation.

[0122] In operation S2, when the pressure gradient exceeds the limit value, the first control signal is output to multiple high-speed switching valves.

[0123] When the pressure gradient exceeds a preset limit (e.g., a preset limit of 100 bar / s), the controller determines that the system has entered an impact condition. At this time, the controller outputs a first control signal to multiple high-speed switching valves. The first control signal is used to drive the multiple high-speed switching valves to regulate the pressure in the control chamber.

[0124] Changes in the control chamber pressure alter the pressure difference across the valve core 3.85 of cartridge valve 3.8, thereby driving the valve core to move and changing the conduction state of cartridge valve 3.8. Ultimately, the high-pressure side oil circuit and the low-pressure side oil circuit are at least partially connected, allowing some oil from the high-pressure side to flow to the low-pressure side via cartridge valve 3.8, thus suppressing a sharp rise in high-pressure side pressure and reducing pressure shock.

[0125] In operation S3, when the pressure gradient does not exceed the limit value, a second control signal is output to multiple high-speed switching valves.

[0126] When the pressure gradient does not exceed the limit (e.g., a pressure gradient of 50 bar / s, less than 100 bar / s), the controller determines that the system is in a stable or non-impact condition. At this time, the controller outputs a second control signal to multiple high-speed switching valves.

[0127] The second control signal is used to drive multiple high-speed switching valves to keep the cartridge valve 3.8 in the closed state. Specifically, the second control signal maintains the pressure in the control chamber at zero pressure difference between the first chamber 3.81 and the second chamber 3.82 or keeps the valve core 3.85 in the closed position, so that no additional conduction channel is generated between the high-pressure side oil circuit and the low-pressure side oil circuit, and the system maintains normal closed circulation.

[0128] Through the above control method, the embodiments of this application can automatically and quickly realize on-demand conduction between the high-pressure side and the low-pressure side under impact conditions, thereby effectively weakening the pressure impact; at the same time, it maintains the structural integrity of the closed loop under normal operating conditions, avoiding unnecessary energy loss.

[0129] In some embodiments, during the entire impact period when the pressure gradient exceeds a predetermined value, the controller may also perform gradual closing control: adjusting the duty cycle of the first control signal to drive the cartridge valve to close gradually.

[0130] For example, after the peak pressure, the controller reduces the duty cycle by 10% every 50 milliseconds, gradually decreasing the cartridge valve opening from 70% to 0%, achieving a uniform and gradual closing. Alternatively, the duty cycle can be linearly adjusted based on the decrease in pressure gradient: the duty cycle decreases by 5% for every 10 bar / s decrease in pressure gradient.

[0131] The purpose of gradually closing the valve is to prevent the instantaneous closure of the cartridge valve from causing a secondary pressure surge, so that the pressure on the high-pressure side can drop smoothly.

[0132] In some embodiments, the control method further includes thermal balance control: the temperature of the oil in the closed hydraulic circuit is detected by temperature sensor 3.3, and a third control signal is output to multiple high-speed switching valves according to the detected oil temperature to change the flushing flow rate through shuttle valve 3.1.

[0133] For example: when the oil temperature is below 50℃, a third control signal with a duty cycle of 10% is output to maintain a small flushing flow rate and avoid energy waste; when the oil temperature is between 50℃ and 70℃, a third control signal with a duty cycle of 50% is output to appropriately increase the flushing flow rate; when the oil temperature is above 70℃, a third control signal with a duty cycle of 100% is output to maximize the flushing flow rate and quickly cool down the oil.

[0134] Temperature feedback enables closed-loop dynamic adjustment of flushing flow rate, preventing thermal balance temperature loss after prolonged high-load operation of closed-loop pumps and motors, thus extending component lifespan.

[0135] In some embodiments, when the pressure gradient recovers from exceeding a limit value to not exceeding a limit value (i.e., the impact process ends), the controller outputs a second control signal to multiple high-speed switching valves to drive the cartridge valve to close completely.

[0136] For example, during the impact process, the pressure gradient gradually decreases from 250 bar / s to 90 bar / s (below the limit of 100 bar / s). At this time, the controller outputs a second control signal to move the cartridge valve core to the cut-off position, completely disconnecting the high-pressure side from the low-pressure side, and the system returns to normal closed-loop circulation.

[0137] Those skilled in the art will understand that the features described in the various embodiments of this application can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in this application. In particular, the features described in the various embodiments of this application can be combined and / or combined in various ways without departing from the spirit and teachings of this application. All such combinations and / or combinations fall within the scope of this application.

Claims

1. A digital hydraulic closed-loop pump control system, characterized in that, include: A closed hydraulic circuit with a high-pressure side oil circuit and a low-pressure side oil circuit; The digital hydraulic valve assembly (3) includes multiple high-speed switching valves and cartridge valves (3.8). A cartridge valve (3.8) is connected between the high-pressure side oil circuit and the low-pressure side oil circuit. The cartridge valve (3.8) has a control chamber, and the pressure in the control chamber is used to control the conduction state of the cartridge valve (3.8). Multiple high-speed switching valves are connected to the control chamber of the cartridge valve (3.8) to control the pressure in the control chamber; The controller, electrically connected to the plurality of high-speed switching valves, is configured as follows: When the pressure gradient of the high-pressure side oil circuit exceeds a limit value, a first control signal is output to the plurality of high-speed switching valves. The first control signal is used to drive the plurality of high-speed switching valves to adjust the pressure in the control chamber so that the high-pressure side oil circuit and the low-pressure side oil circuit are at least partially connected. When the pressure gradient does not exceed the limit value, the second control signal is output to the plurality of high-speed switching valves. The second control signal is used to drive the plurality of high-speed switching valves to keep the cartridge valve (3.8) in the closed state.

2. The digital hydraulic closed-loop pump control system according to claim 1, characterized in that, The digital hydraulic valve group (3) further includes: a shuttle valve (3.1), which includes two inlets and an outlet. The two inlets are respectively connected to the high-pressure side oil circuit and the low-pressure side oil circuit, and the outlet is used to output the oil from the low-pressure side oil circuit. The second control signal is also used to regulate the flushing flow rate through the shuttle valve (3.1).

3. The digital hydraulic closed-loop pump control system according to claim 1, characterized in that, The cartridge valve (3.8) includes: The valve core (3.85) is used to control the conduction state between the first liquid inlet (3.83) and the second liquid inlet (3.84) by moving it; The first cavity (3.81) and the second cavity (3.82) are located on both sides of the valve core (3.85) and are used to drive the valve core (3.85) to move under the action of pressure difference. The pressure difference is the pressure difference between the first cavity (3.81) and the second cavity (3.82). The first liquid inlet (3.83) is connected to the high-pressure side oil circuit; The second liquid inlet (3.84) is connected to the low-pressure side oil circuit.

4. The digital hydraulic closed-loop pump control system according to claim 3, characterized in that, The plurality of high-speed switching valves includes a first group of high-speed switching valves and a second group of high-speed switching valves. The first set of high-speed switching valves is connected to the first cavity (3.81) to form a first hydraulic half-bridge to control the pressure in the first cavity (3.81); The second set of high-speed switching valves is connected to the second cavity (3.82) to form a second hydraulic half-bridge to control the pressure inside the second cavity (3.82); The cartridge valve (3.8) includes a valve core (3.85) for generating displacement based on the pressure difference between the first control chamber (3.81) and the second control chamber (3.82).

5. The digital hydraulic closed-loop pump control system according to claim 4, characterized in that, The controller is also used to: control the pressure of the first cavity (3.81) by adjusting the duty cycle of the control signal output to the first set of high-speed switching valves, and / or to control the pressure of the second cavity (3.82) by adjusting the duty cycle of the control signal output to the second set of high-speed switching valves.

6. The digital hydraulic closed-loop pump control system according to claim 2, characterized in that, The digital hydraulic valve assembly (3) also includes: A temperature sensor (3.3) is installed on the oil line between the outlet of the shuttle valve (3.1) and the low-pressure side oil line, and is electrically connected to the controller to detect the oil temperature in the closed hydraulic circuit. The controller is also configured to output a third control signal to the plurality of high-speed switching valves according to the oil temperature, so as to change the flushing flow rate through the shuttle valve (3.1).

7. The digital hydraulic closed-loop pump control system according to claim 2, characterized in that, The digital hydraulic valve assembly (3) also includes: An accumulator (3.2) is connected to the oil line between the outlet of the shuttle valve (3.1) and the low-pressure side oil line. The accumulator (3.2) is used to maintain the pressure of the low-pressure side oil line within a preset range.

8. The digital hydraulic closed-loop pump control system according to claim 1, characterized in that, The closed hydraulic circuit includes a closed pump unit (2) and a motor (4). The oil outlet of the closed pump group (2) is connected to the oil inlet of the motor (4) to form the high-pressure side oil circuit, and the oil outlet of the motor (4) is connected to the oil inlet of the closed pump group (2) to form the low-pressure side oil circuit.

9. The digital hydraulic closed-loop pump control system according to claim 1, characterized in that, The controller is also used for: During the period when the pressure gradient exceeds the limit value, the duty cycle of the first control signal output to the plurality of high-speed switching valves is adjusted according to the amount of change in the pressure gradient, so as to change the opening degree of the cartridge valve (3.8).

10. The digital hydraulic closed-loop pump control system according to claim 1, characterized in that, The controller is also used for: During the period when the pressure gradient exceeds the limit value, the cartridge valve (3.8) is driven to gradually close.

11. The digital hydraulic closed-loop pump control system according to claim 1, characterized in that, Also includes: The replenishing pump unit (1) is connected to the closed hydraulic circuit and is used to replenish the leaked oil. The oil replenishment overflow valve (1.3) is connected to the oil replenishment pump group (1) and is used to control the oil replenishment pressure.

12. A control method for a digital hydraulic closed-loop pump control system based on any one of claims 1-11, characterized in that, include: The pressure gradient of the high-pressure side oil circuit is monitored in real time by the controller. When the pressure gradient exceeds a limit value, a first control signal is output to the plurality of high-speed switching valves. The first control signal is used to drive the plurality of high-speed switching valves to adjust the pressure in the control chamber. When the pressure gradient does not exceed the limit value, the second control signal is output to the plurality of high-speed switching valves. The second control signal is used to drive the plurality of high-speed switching valves to keep the cartridge valve (3.8) in the closed state.

13. The control method according to claim 12, characterized in that, Also includes: During the period when the pressure gradient exceeds the limit value, the duty cycle of the first control signal is adjusted to drive the cartridge valve (3.8) to gradually close.

14. The control method according to claim 12, characterized in that, Also includes: The temperature of the oil in the closed hydraulic circuit is detected by a temperature sensor (3.3); Based on the oil temperature, a third control signal is output to the plurality of high-speed switching valves to change the flushing flow rate through the shuttle valve (3.1).

15. The control method according to claim 12, characterized in that, Also includes: When the pressure gradient recovers from exceeding the limit value to not exceeding the limit value, the second control signal is output to the plurality of high-speed switching valves to drive the cartridge valve (3.8) to close completely.

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