Two-stage overflow valve capable of accurately controlling low pressure

Abstract

The invention relates to the technical field of overflow valves, and discloses a two-stage overflow valve capable of accurately controlling low pressure, which comprises an overflow valve assembly, a first-stage air cylinder assembly and a second-stage air cylinder assembly are sequentially arranged on the right side of the overflow valve assembly, the overflow valve assembly comprises a valve body and a valve core, and an oil outlet and an oil inlet which are arranged in a staggered manner are formed in the valve body; a pressure sensor is arranged at the oil inlet, the first-stage air cylinder assembly comprises a first-stage cylinder body and a first-stage piston, the second-stage air cylinder assembly comprises a second-stage cylinder body and a second-stage piston, the valve element, the first-stage piston and the second-stage piston are sequentially connected and coaxially arranged, and air sources are introduced into the left side and the right side of the first-stage piston and the left side and the right side of the second-stage piston to control the valve element to move leftwards and rightwards. And the on-off state between the oil inlet and the oil outlet is switched, and the stress balance state of the left side and the right side of the valve element is achieved. When the double-stage pressure regulating valve is used, the pressure can be regulated from 0 bar, the maximum pressure regulating range can be expanded according to needs, and double-stage precise control over a low-pressure interval and a high-pressure interval is achieved.

Description

Technical Field

[0001] This invention relates to the field of relief valve technology, and more specifically to a two-stage relief valve capable of precisely controlling low pressure. Background Technology

[0002] In hydraulic testing systems, performance testing of oil or water pumps is crucial for ensuring their reliability. This typically requires precise control of the pump's outlet pressure to achieve a full-range pressure test from 0 bar to the rated pressure (20 bar). Based on data from different pressure points, the performance of the tested component is evaluated, and key characteristic curves such as pressure versus flow and pressure versus efficiency are plotted. Simultaneously, adjustable load devices are often required in the testing system to simulate actual operating conditions. Currently, the mainstream technology for adjusting outlet pressure (or load) in testing systems employs an electronically controlled actuator. Pressure signals are collected by a pressure sensor as feedback, and a PID control loop is constructed between this feedback and the actuator's electrical signal to regulate the target pressure load. Within this technical framework, there are two common solutions for setting up the back pressure relief valve:

[0003] One approach is to use a hydraulically controlled proportional relief valve for back pressure regulation. This type of relief valve controls the relief pressure by adjusting the valve core opening through an electronic control signal. However, its pressure regulation characteristics have obvious limitations: as can be seen from the pressure curve of the mainstream hydraulically controlled proportional relief valve, its minimum initial pressure adjustment pressure is usually 3 bar to 5 bar. For the low pressure load control requirements below 3 bar (or 5 bar) that are often required during the test, this approach cannot meet them at all. The pressure adjustment range can only cover the range from 3 bar (or 5 bar) to the rated pressure, resulting in the lack of performance test data for oil pumps or water pumps under low pressure conditions, and making it impossible to fully evaluate the full-condition performance of the test component.

[0004] Another approach is to use an electric proportional ball valve (or electric proportional needle valve), which regulates the flow rate by controlling the valve opening, thereby indirectly adjusting the pressure. However, this approach faces several technical challenges in practical applications: when pump speed changes cause flow rate fluctuations, the matching relationship between valve opening and pressure is broken, and the pressure fluctuates significantly with the flow rate. In this case, the opening of the electric proportional valve needs to be adjusted in real time. However, the adjustment response time of this type of valve is usually between 1.5s and 3s, with a significant response lag. It also cannot automatically adapt to pressure fluctuations caused by load changes, making it difficult to quickly and accurately stabilize the pressure at the target value. Even when using a proportional flow valve (needle valve type) with a relatively fast control speed, the adjustment time from fully open to fully closed still requires 2s to 5s. Furthermore, because the opening is controlled by a cone valve structure, the relationship between the opening and the flow rate is non-linear, resulting in non-linear pressure regulation. In actual operation, it is difficult to stabilize the pressure at a specific value, further affecting the accuracy and stability of the test data.

[0005] In summary, both of the existing mainstream back pressure regulation solutions have significant drawbacks. In test scenarios that require coverage of the entire pressure range starting from 0 bar, especially the need for precise control in the low pressure range and the need for pressure stability when facing flow fluctuations, the existing technologies cannot meet these requirements and it is difficult to achieve high-precision performance testing of oil pumps or water pumps under all operating conditions. Summary of the Invention

[0006] In view of this, the present invention provides a two-stage relief valve that can precisely control low pressure. During use, the pressure can be adjusted from 0 bar, and the maximum pressure adjustment range can be expanded as needed, realizing two-stage precise control of low pressure range and high pressure range.

[0007] To achieve the above objectives, the present invention provides a two-stage relief valve capable of precisely controlling low pressure, comprising a relief valve assembly. A first-stage cylinder assembly and a second-stage cylinder assembly are sequentially arranged on the right side of the relief valve assembly. The relief valve assembly includes a valve body and a valve core slidably connected to the inner cavity of the valve body. An end cap is provided at the right port of the valve body, and the end cap has an exhaust port communicating with the inner cavity of the valve body. An oil outlet and an oil inlet are respectively provided on the upper and lower sides of the valve body, arranged in a staggered manner. The oil outlet is located to the right of the oil inlet, and both are communicating with the inner cavity of the valve body. A pressure sensor is provided at the oil inlet, and the oil inlet is connected to the outlet of the pump under test.

[0008] The first-stage cylinder assembly includes a first-stage cylinder body and a first-stage piston disposed inside the first-stage cylinder body. The second-stage cylinder assembly includes a second-stage cylinder body and a second-stage piston disposed inside the second-stage cylinder body. The valve core, the first-stage piston, and the second-stage piston are sequentially connected and coaxially arranged. The first-stage cylinder body and the second-stage cylinder body are respectively fixedly connected to the right end cover.

[0009] By supplying air to the left and right sides of the first-stage piston and the second-stage piston respectively, the valve core is controlled to move left and right, and the connection and disconnection between the oil inlet and outlet are switched, so as to achieve a force balance state on the left and right sides of the valve core.

[0010] Preferably, when the overflow valve assembly is in the fully open state, the pressure of the pressure sensor is 0, the air source is introduced into the left side of the first-stage piston and the second-stage piston, and the first-stage piston and the second-stage piston are driven by force to move the valve core to the right. When the oil inlet and the oil outlet are connected, the medium is discharged from the pump under test through the oil inlet and directly discharged into the oil tank through the oil outlet.

[0011] Preferably, when the air source is introduced into the right side of the first-stage piston, the overflow valve is in a low-pressure regulation state. The first-stage piston is pushed by force to move the valve core to the left, and the oil outlet tends to close. The flow rate output by the pump under test acts on the left side of the valve core to generate a rightward force F0. The right side of the valve core is pushed by the first-stage piston F1. When F0 and F1 are unbalanced, the valve core will be pushed to move left and right until the forces on both ends of the valve core are equal.

[0012] Preferably, an air source is introduced into the right side of the first-stage piston and the second-stage piston, the overflow valve is in a high-pressure regulation state, the first-stage piston and the second-stage piston are pushed by force to move the valve core to the left, the oil outlet tends to close, the flow rate output by the pump under test acts on the left side of the valve core to generate a rightward force F0, the right side of the valve core is pushed by the first-stage piston and the second-stage piston F1. When F0 and F1 are unbalanced, the valve core will be pushed to move left and right until the forces on both ends of the valve core are equal.

[0013] Preferably, F0 is equal to the pressure at the oil inlet multiplied by the force-bearing area of ​​the valve core.

[0014] Preferably, the left sides of the first-stage piston and the second-stage piston are connected in parallel to one outlet of the two-position five-way directional valve, and the right sides of the first-stage piston and the second-stage piston are connected in parallel to the other outlet of the two-position five-way directional valve. The inlet of the two-position five-way directional valve is connected to a compressed air source.

[0015] Preferably, a proportional pressure reducing valve is installed on the main pipeline connecting the first-stage piston and the second-stage piston in parallel, and an electromagnetic switch valve is installed on the branch pipeline of the second-stage piston.

[0016] Preferably, the two-position five-way directional valve, the pneumatic proportional pressure reducing valve, and the solenoid switch valve are all connected to the controller.

[0017] Preferably, the valve core is connected to the first-stage cylinder assembly and the second-stage cylinder assembly in a floating connection manner, so that the valve core and the valve hole of the relief valve assembly remain coaxial.

[0018] Preferably, the valve core has several pressure equalization grooves on its peripheral wall, allowing the medium to enter and fill the pressure equalization grooves, thereby reducing the resistance when the valve core moves.

[0019] As can be seen from the above technical solution, compared with the prior art, the two-stage relief valve that can accurately control low pressure provided by the present invention has the following beneficial effects:

[0020] 1. This invention establishes a dual-stage pressure regulation core structure by setting an overflow valve assembly and sequentially connecting a primary cylinder assembly and a secondary cylinder assembly, and coaxially connecting the valve core, primary piston, and secondary piston. On the one hand, it overcomes the limitation of existing overflow valves that cannot adjust from 0 bar, achieving full-range coverage of pressure from 0 bar to rated pressure, meeting the testing requirements of oil pumps or water pumps under low-pressure conditions. On the other hand, by introducing air sources to both sides of the piston to control the movement of the valve core, and utilizing the force balance principle on the left and right sides of the valve core, it can automatically adapt to changes in the flow rate of the pump under test, maintaining stable pressure without additional real-time adjustment of the actuator opening. This solves the problem of large pressure fluctuations and difficulty in precise pressure control in existing electric proportional valves, providing a precise pressure control basis for plotting characteristic curves such as pressure-flow rate and pressure-efficiency.

[0021] 2. This invention further improves the targeting and accuracy of pressure regulation by refining the air source control logic under different operating conditions. When the overflow valve assembly is fully open, air supply to the left side of the piston can move the valve core to the right limit, realizing direct connection between the oil inlet and outlet, ensuring that the pressure is stable at 0 bar, and providing a precise benchmark for low-pressure testing. When regulating small pressure, air is only supplied to the right side of the first-stage piston. Through the balance between the thrust of the single-stage cylinder and the pressure on the left side of the valve core, high-precision control in the 0-3 bar low-pressure range is achieved. When regulating large pressure, air is supplied to the right sides of both the first and second-stage pistons. Through the balance between the combined force of the two-stage cylinder and the valve core pressure, the regulation accuracy in the high-pressure range is ensured. Ultimately, it achieves graded and precise control in the low and high pressure ranges, covering the full operating condition testing requirements of the pump under test.

[0022] 3. This invention clarifies that the force F0 on the left side of the valve core is equal to the product of the oil inlet pressure and the force-bearing area of ​​the valve core. This quantified force calculation relationship provides a precise theoretical basis for the force balance between the valve core and the piston. By determining parameters such as the valve core area and the effective cylinder area during the design stage, the proportional relationship of pressure regulation can be pre-calibrated, avoiding the nonlinearity problem of pressure regulation in the prior art. This further improves the accuracy and predictability of pressure control, ensuring that each adjustment can quickly approach and stabilize at the target pressure value.

[0023] 4. This invention connects the left and right sides of the first and second stage pistons in parallel to a two-position five-way directional valve, and installs a gas proportional pressure reducing valve in the main pipeline and an electromagnetic switch valve in the branch pipe of the second stage piston. Simultaneously, all valves are connected to a controller. This achieves integrated control of the air circuit, allowing for rapid switching of pressure conditions (0 bar, low pressure, high pressure) via electrical signals, with a response speed far faster than existing electric proportional valves. Furthermore, the introduction of the gas proportional pressure reducing valve further improves the accuracy of air source pressure regulation. Combined with the controller's PID control, it enables automated and intelligent pressure regulation, reducing human error and improving testing efficiency.

[0024] 5. This invention uses a floating connection to connect the valve core and the cylinder assembly, effectively avoiding misalignment issues between the valve core, valve hole, and piston caused by cylinder installation size errors, and preventing valve core jamming. Simultaneously, a pressure equalization groove is provided on the valve core's peripheral wall, allowing the medium to fill the groove and reducing the valve core's movement resistance. This ensures smooth and uninterrupted movement of the valve core during force balance adjustment, improving the structural reliability and service life of the relief valve. Furthermore, it avoids pressure regulation lag or fluctuations caused by poor valve core movement, further guaranteeing the stability and accuracy of pressure control. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 This is a schematic diagram showing the connection between the two-stage relief valve, which can accurately control low pressure, and the pneumatic control section of the present invention.

[0027] Figure 2 This is a schematic diagram of the overall structure of the two-stage relief valve of the present invention, which can accurately control low pressure.

[0028] Figure 3 This is an enlarged view of the valve core of the present invention;

[0029] Figure 4 This is a diagram showing the force balance relationship of the valve core in this invention;

[0030] Figure 5 This is a small pressure test curve of the present invention.

[0031] Explanation of reference numerals in the attached diagram: 1-Relief valve assembly, 2-Compressed air source, 3-Two-position five-way directional valve, 4-Proportional pressure reducing valve, 5-Solenoid switch valve, 6-Pressure sensor, 7-Pump under test, 8-First-stage cylinder assembly, 9-Second-stage cylinder assembly;

[0032] 1.1-Valve body, 1.2-Oil outlet, 1.3-Valve core, 1.4-Floating connection mounting plate, 1.5-Oil inlet, 1.6-Fixing bolt, 1.7-Fixing bolt sleeve, 1.8-End cap, 1.9-Exhaust port, 1.10-Pressure equalization groove, 2.1-First-stage cylinder, 2.2-First-stage piston, 3.1-Cylinder connecting rod, 3.2-Second-stage cylinder, 3.3-Second-stage piston. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of an exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] Please see the appendix Figure 1-5 The present invention discloses a two-stage relief valve capable of precisely controlling low pressure, comprising five parts: relief valve assembly 1, first-stage cylinder assembly 8, second-stage cylinder assembly 9, air circuit control part, and electrical control part. It adopts force transmission control and performs precise adjustment through the principle of mechanical balance.

[0035] like Figure 1 , Figure 2 As shown, the overflow valve assembly 1 includes a valve body 1.1, a valve core 1.3, and an end cap 1.8.

[0036] The valve core 1.3 is slidably connected to the inside of the valve body 1.1 and is connected to the piston of the cylinder (first-stage cylinder assembly 8, second-stage cylinder assembly 9) in a floating connection form, so that the valve core 1.3 and the overflow valve orifice are kept coaxial, avoiding the misalignment problem between the valve core 1.3, the valve orifice, and the cylinder piston caused by cylinder installation size errors. An end cover 1.8 is provided at the right port of the valve body 1.1. The end cover 1.8 is provided with an exhaust port 1.9 communicating with the inner cavity of the valve body 1.1. An oil inlet 1.5 and an oil outlet 1.2 communicating with the inner cavity of the valve body 1.1 are respectively provided on the side wall of the valve body 1.1. The oil inlet 1.5 and the oil outlet 1.2 are staggered, with the oil inlet 1.5 located to the left of the oil outlet 1.2. A pressure sensor 6 is provided at the oil inlet 1.5, and the oil inlet 1.5 is connected to the outlet of the pump under test 7.

[0037] The first-stage cylinder assembly 8 and the second-stage cylinder assembly 9 are sequentially connected to the right side of the overflow valve assembly 1. The first-stage cylinder assembly 8 includes a first-stage cylinder body 2.1 and a first-stage piston 2.2 disposed inside the first-stage cylinder body 2.1. The second-stage cylinder assembly 9 includes a second-stage cylinder body 3.2 and a second-stage piston 3.3 disposed inside the second-stage cylinder body 3.2. The valve core 1.3, the first-stage piston 2.2 and the second-stage piston 3.3 are sequentially connected and coaxially arranged. The first-stage cylinder body 2.1 and the second-stage cylinder body 3.2 are respectively fixedly connected to the end cover 1.8, wherein the second-stage cylinder body 3.2 is fixedly connected to the end cover 1.8 through the cylinder connector 3.1.

[0038] A floating connection mounting plate 1.4 is provided on the right side of the valve core 1.3. The valve core 1.3 and the first-stage piston 2.2 are connected by the floating connection mounting plate 1.4, as well as the fixing bolts 1.6 and fixing bolt sleeves 1.7.

[0039] The pneumatic control section includes a compressed air source 2, a two-position five-way reversing valve 3, a pneumatic proportional pressure reducing valve 4, and a solenoid switch valve 5. The electrical control section is a controller (PLC), and the control model can be 4-20mA or 0-10mA. The electrical control section is connected to and controls the pneumatic control section.

[0040] The left sides of the first-stage piston 2.2 and the second-stage piston 3.3 are connected in parallel to one outlet of the two-position five-way directional valve 3. The right sides of the first-stage piston 2.2 and the second-stage piston 3.3 are connected in parallel to the other outlet of the two-position five-way directional valve 3. The compressed air source 2 is connected to the inlet of the two-position five-way directional valve 3. The air proportional pressure reducing valve 4 is installed on the main pipe after the first-stage piston 2.2 and the second-stage piston 3.3 are connected in parallel, and the solenoid switch valve 5 is installed on the branch pipe of the second-stage piston 3.3.

[0041] In this embodiment, the pump under test 7 is an oil pump or a water pump. When testing the oil pump, its working efficiency is tested under fixed pressure conditions. By setting a target pressure, the pressure collected by the pressure sensor 6 and the control signal of the gas proportional pressure reducing valve 4 are adjusted by PID, thereby realizing the automatic adjustment of the overflow valve assembly 1.

[0042] like Figure 3 As shown, the valve core 1.3 is provided with several pressure equalization grooves 1.10. The medium can enter and fill the pressure equalization grooves 1.10, reducing the resistance when the valve core 1.3 moves and making the valve core 1.3 and the valve hole more coaxial.

[0043] The working principle of this invention is as follows:

[0044] The system uses primary and secondary cylinders as actuators. The air pressure is adjusted to 0-5 bar (or about 6 bar) by the air proportional pressure reducing valve 4 to push the piston of the cylinder. The piston of the cylinder is mechanically connected to the valve core 1.3 of the overflow valve assembly 1.

[0045] The force F0 on the valve core 1.3 is the product of the outlet pressure of the pump 7 under test and the area of ​​the valve core 1.3. The force F1 (or F1+F2) on the cylinder piston is the product of the air pressure input by the proportional pressure reducing valve 4 and the effective pressure-bearing area of ​​the first-stage piston 2.2 (or the first-stage piston 2.2+second-stage piston 3.3). The two are balanced by F1 and F0.

[0046] When F0 is greater than F1, it will push the valve core 1.3 to move in a direction that tends to open the oil outlet 1.2, making the opening of the oil outlet 1.2 larger, and more fluid will be released from the oil outlet 1.2, thereby reducing the pressure. At this time, F0 will decrease accordingly.

[0047] When F0 is less than F1, the overflow valve core 1.3 will be pushed by the cylinder piston to move towards the closed direction, which will reduce the opening of the oil outlet 1.2 and reduce the flow rate of pressure relief from the oil outlet 1.2, thereby increasing the pressure. Therefore, F0 will increase accordingly.

[0048] Therefore, the force on the valve core 1.3 of the relief valve is always balanced with the force on the cylinder piston. As long as there is an imbalance at both ends, the valve core 1.3 will be pushed to move, and the opening of the oil outlet 1.2 will become larger or smaller, thereby achieving an automatic balance. Therefore, when the output flow of the pump under test 7 changes, as long as the force at the cylinder piston remains unchanged, the outlet pressure of the pump under test 7 will be adaptively adjusted to maintain pressure stability.

[0049] In condition 1, when the pressure is 0, the overflow valve assembly 1 is fully open, the 2-position 5-way directional valve 3 is not energized, and the air source is connected to the left side of the first-stage piston 2.2 and the second-stage piston 3.3. The cylinder drives the piston and valve core 1.3 to move to the right side of the diagram until the limit is reached. The two oil ports (inlet 1.5 and outlet 1.2) of the overflow valve assembly 1 are connected. The medium is discharged from the port of the tested pump 7 through the inlet 1.5 of the overflow valve assembly 1. The overflow valve assembly 1 is fully open and is directly discharged into the oil tank through the outlet 1.2. The pressure is 0.

[0050] In operating condition two, under low pressure regulation: the two-position five-way directional valve 3 is energized, and the pressure air source flows to the proportional pressure reducing valve 6 and the first-stage cylinder assembly 8. The solenoid switch valve 5 is not energized and is in the closed state. The air pressure from the proportional pressure reducing valve 4 flows only to the right side of the first-stage piston 2.2. At this time, the piston of the first-stage cylinder assembly 8 is under force, pushing the valve core 1.3 of the relief valve assembly 1 to move to the left. The oil outlet 1.2 of the relief valve assembly 1 tends to close. Meanwhile, the pump under test 7 continues to output flow, thus causing a certain outlet pressure to build up on the left side of the relief valve assembly 1. The oil outlet pressure multiplied by the area of ​​the valve core 1.3 gives the force F0 on the left side of the valve core 1.3. The right side of the valve core 1.3 is subjected to the thrust F1 of the cylinder. F0 and F1 need to be balanced. If they are not balanced, the valve core 1.3 will be pushed to move left and right until the two ends are equal.

[0051] In operating condition 3, during high pressure regulation: the 2-position 5-way directional valve 3 is energized, and the pressure air source flows to the proportional pressure reducing valve 4 and the first-stage cylinder assembly 8. The solenoid switch valve 5 is energized and in the open state. The air pressure from the proportional pressure reducing valve flows to the right side of the first-stage piston 2.2 and the second-stage piston 3.3. At this time, the piston of the first-stage cylinder assembly 8 is under force, pushing the valve core 1.3 to move to the left. The oil outlet 1.2 of the overflow valve assembly 1 tends to close. Meanwhile, the pump under test 7 continues to output flow, causing a certain outlet pressure to build up on the left side of the overflow valve assembly 1. The oil outlet pressure multiplied by the area of ​​the valve core 1.3 gives the force F0 on the left side of the valve core 1.3. The right side of the valve core is subjected to the thrust F1 of the cylinder. F0 and F1 need to be balanced. If they are not balanced, the valve core 1.3 will be pushed left and right until the two ends are equal.

[0052] The overflow valve provided by this invention features a two-stage pressure regulation method, divided into two adjustment ranges. This allows for higher precision in a small pressure range while ensuring pressure regulation accuracy over a large range. To achieve a more precise regulation effect, this invention employs a pneumatic proportional pressure reducing valve 4 with an accuracy of ±0.5%. Due to its high sensitivity and good linearity, it meets the requirements for pilot control. Its accuracy parameters are shown in Table 1 below:

[0053] Table 1 Parameters of Gas Proportional Pressure Regulator

[0054] linearity Within ±1%FS hysteresis Within 0.5% FS Repeatability Within ±0.5%FS Sensitivity Within 0.2% FS Temperature characteristics Within ±0.12%FS / ℃

[0055] like Figure 4 The diagram illustrates the force balance principle of valve core 1.3. Here, S0 is the force-bearing area of ​​valve core 1.3, P0 is the outlet pressure of the pump 7 under test, F0 is the force exerted by the outlet pressure on valve core 1.3, S1 is the effective area of ​​the first-stage cylinder, P1 is the pressure output by the proportional pressure reducing valve 4, F1 is the force exerted by the first-stage cylinder on its piston, S2 is the effective area of ​​the second-stage cylinder, and F2 is the force exerted by the second-stage cylinder on its piston.

[0056] The force balance relationship of the structure shown in the diagram can be analyzed:

[0057] The valve core is always in a force balance relationship, meaning the force on the left end is balanced with the force on the right end. If it is unbalanced, the valve core will move in response until it reaches balance. The force relationship is: F0 = F1 + F2

[0058] When using a small pressure adjustment range, the piston can be driven by only one-stage cylinder through air path selection, with the balance relationship: P0*S0=P1*S1.

[0059] The relationship between the outlet pressure P0 of the pump under test and the regulating pressure P1 of the proportional valve is: P0 = P1(S1 / S0), which is a direct proportional relationship of a linear function. Its proportionality coefficient is directly related to the size of the valve core and the cylinder diameter of the first-stage cylinder. The relationship of its proportionality coefficient is calculated during the design.

[0060] When adjusting high pressure, a single-stage cylinder is used, and the balance relationship is: P0*S0=P1*S1+P1*S2.

[0061] The relationship between the outlet pressure P0 of the pump under test and the pressure P1 controlled by the proportional valve is: P0 = P1((S1+S2) / S0), which is a direct proportional relationship of a linear function. Its proportionality coefficient is directly related to the size of the valve core and the cylinder diameter of the first-stage and second-stage cylinders. The relationship of its proportionality coefficient is calculated during the design.

[0062] like Figure 5 The figure shows the low-pressure test curve during the experiment. The control air proportional valve pressure changes from 0 bar to 5 bar and back to 0 bar. The green line in the figure is the outlet pressure curve of the tested component, which changes from 0.2 bar to 3 bar and back to 0.2 bar.

[0063] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A two-stage relief valve capable of precisely controlling low pressure, characterized in that, The system includes an overflow valve assembly (1), on the right side of which a first-stage cylinder assembly (8) and a second-stage cylinder assembly (9) are arranged in sequence. The overflow valve assembly (1) includes a valve body (1.1) and a valve core (1.3) slidably connected to the inner cavity of the valve body (1.1). An end cap (1.8) is provided at the right port of the valve body (1.1). An exhaust port (1.9) communicating with the inner cavity of the valve body (1.1) is provided on the end cap (1.8). An oil outlet (1.2) and an oil inlet (1.5) are respectively arranged in a staggered manner on the upper and lower sides of the valve body (1.1). The oil outlet (1.2) is located to the right of the oil inlet (1.5) and both are communicating with the inner cavity of the valve body (1.1). A pressure sensor (6) is provided at the oil inlet (1.5). The oil inlet (1.5) is connected to the outlet of the pump under test (7). The first-stage cylinder assembly (8) includes a first-stage cylinder body (2.1) and a first-stage piston (2.2) disposed inside the first-stage cylinder body (2.1). The second-stage cylinder assembly (9) includes a second-stage cylinder body (3.2) and a second-stage piston (3.3) disposed inside the second-stage cylinder body (3.2). The valve core (1.3), the first-stage piston (2.2) and the second-stage piston (3.3) are sequentially connected and coaxially arranged. The first-stage cylinder body (2.1) and the second-stage cylinder body (3.2) are respectively fixedly connected to the right end cover (1.8). By supplying air to the left and right sides of the first-stage piston (2.2) and the second-stage piston (3.3) respectively, the valve core (1.3) can be moved left and right, and the oil inlet (1.5) and oil outlet (1.2) can be switched to achieve a force balance between the left and right sides of the valve core (1.3).

2. The two-stage relief valve capable of precisely controlling low pressure according to claim 1, characterized in that, When the overflow valve assembly (1) is in the fully open state, the pressure of the pressure sensor (6) is 0. The air source is introduced into the left side of the first-stage piston (2.2) and the second-stage piston (3.3). The first-stage piston (2.2) and the second-stage piston (3.3) are driven by force to move the valve core (1.3) to the right. When the oil inlet (1.5) and the oil outlet (1.2) are connected, the medium is discharged from the pump under test (7) through the oil inlet (1.5) and directly discharged into the oil tank through the oil outlet (1.2).

3. The two-stage relief valve capable of precisely controlling low pressure according to claim 1, characterized in that, When the air source is introduced into the right side of the first-stage piston (2.2), the overflow valve is in a low-pressure regulation state. The first-stage piston (2.2) is pushed by the force to move the valve core (1.3) to the left. The oil outlet (1.2) tends to close. The flow rate output by the pump under test (7) acts on the left side of the valve core (1.3) to generate a force F0 to the right. The right side of the valve core (1.3) is pushed by the first-stage piston (2.2) with a force F1. When F0 and F1 are unbalanced, the valve core (1.3) will be pushed to move left and right until the forces on both ends of the valve core (1.3) are equal.

4. The two-stage relief valve capable of precisely controlling low pressure according to claim 1, characterized in that, Air is supplied to the right side of the first-stage piston (2.2) and the second-stage piston (3.3), and the overflow valve is in a high-pressure regulation state. The first-stage piston (2.2) and the second-stage piston (3.3) are pushed by the force to move the valve core (1.3) to the left, and the oil outlet (1.2) tends to close. The flow rate output by the pump under test (7) acts on the left side of the valve core (1.3) to generate a force F0 to the right. The right side of the valve core (1.3) is pushed by the first-stage piston (2.2) and the second-stage piston (3.3) with a thrust F1. When F0 and F1 are unbalanced, the valve core (1.3) will be pushed to move left and right until the forces on both ends of the valve core (1.3) are equal.

5. The two-stage relief valve capable of precisely controlling low pressure according to claim 3 or 4, characterized in that, The F0 is equal to the pressure at the oil inlet (1.5) multiplied by the force-bearing area of ​​the valve core (1.3).

6. The two-stage relief valve capable of precisely controlling low pressure according to claim 1, characterized in that, The left side of the first-stage piston (2.2) and the second-stage piston (3.3) are connected in parallel to one outlet of the two-position five-way directional valve (3), and the right side of the first-stage piston (2.2) and the second-stage piston (3.3) are connected in parallel to the other outlet of the two-position five-way directional valve (3). The inlet of the two-position five-way directional valve (3) is connected to a compressed air source (2).

7. The two-stage relief valve capable of precisely controlling low pressure according to claim 6, characterized in that, A gas proportional pressure reducing valve (4) is installed on the main pipeline after the first-stage piston (2.2) and the second-stage piston (3.3) are connected in parallel, and an electromagnetic switch valve (5) is installed on the branch pipeline of the second-stage piston (3.3).

8. The two-stage relief valve capable of precisely controlling low pressure according to claim 7, characterized in that, The two-position five-way reversing valve (3), the air proportional pressure reducing valve (4), and the electromagnetic switch valve (5) are all connected to the controller.

9. The two-stage relief valve for precisely controlling low pressure according to claim 1, characterized in that, The valve core (1.3) is connected to the first-stage cylinder assembly (8) and the second-stage cylinder assembly (9) in a floating connection form so that the valve core (1.3) and the valve hole of the overflow valve assembly (1) remain coaxial.

10. The two-stage relief valve capable of precisely controlling low pressure according to claim 9, characterized in that, The valve core (1.3) has several pressure equalization grooves (1.10) on its peripheral wall. The medium can enter and fill the pressure equalization grooves (1.10) to reduce the resistance when the valve core (1.3) moves.

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