Unloading valve and hydraulic system

Abstract

The invention relates to the technical field of hydraulic valves, and provides an unloading valve and a hydraulic system.The unloading valve comprises a valve sleeve, an oil inlet channel, an oil outlet channel and a control channel are formed in the valve sleeve, a valve cavity is formed in the valve sleeve and comprises a first cavity body and a second cavity body, and the inner diameter of the second cavity body is larger than that of the first cavity body; the control channel is communicated to the second cavity, the oil inlet channel and the oil outlet channel are communicated to the first cavity, and the inner diameter of the oil inlet channel is smaller than that of the first cavity; the valve element comprises a first element body and a second element body, the diameter of the second element body is larger than that of the first element body, the first element body is inserted into the first cavity, and the second element body is inserted into the second element body. The diameter of the second core body of the valve core in the unloading valve is larger than that of the first core body, even if the system pressure suddenly rises, the force borne by the first core body is difficult to exceed the force borne by the second core body, the risk that an oil inlet channel and an oil outlet channel are abnormally conducted is greatly reduced, and the state stability of the unloading valve is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic valves, and more specifically, to a relief valve and a hydraulic system. Background Art

[0002] A hydraulic system is a system that uses liquid (usually oil) as a working medium to transfer and control energy through the pressure energy of the liquid. It is widely used in various industrial and engineering fields. An oil motor is a device that uses hydraulic energy to generate mechanical motion. The main function of an oil motor is to convert the pressure energy of the hydraulic system into linear motion or rotational motion to drive mechanical equipment.

[0003] The unloading valve is also an important control element in the hydraulic system. It is mainly used to guide part or all of the hydraulic oil from the high-pressure side back to the oil tank when the system pressure reaches a certain value, so as to reduce the system pressure, prevent overload, and protect other components in the system. Specifically, after the unloading valve is actuated, the valve core moves to allow the pressure oil to enter the lower end of the oil cylinder, and the oil motor can be quickly closed; when the system pressure drops to the preset recovery pressure, the valve core is reset under the action of the spring or solenoid valve, closing the unloading channel, and the system resumes normal operation.

[0004] However, when using a traditional unloading valve, once the system pressure of the oil motor fluctuates, it is very easy to cause insufficient pressure at the valve core of the unloading valve, causing the unloading valve to open, causing the oil motor to shut down, and then causing abnormal operation of the unit. In other words, due to the fluctuation of system pressure, the state of the unloading valve will be extremely unstable, and the unloading valve may open, which will interfere with the stable state of the oil motor and bring serious safety hazards to the operation of the unit.

[0005] Therefore, the existing technology still needs to be improved and developed. Summary of the invention

[0006] The purpose of the present invention is to provide a relief valve and a hydraulic system to solve the technical problem in the prior art that the valve core of the relief valve is easily opened under the influence of system pressure.

[0007] To achieve the above object, a first aspect of the present invention provides a relief valve, the relief valve comprising:

[0008] A valve sleeve, wherein an oil inlet channel, an oil outlet channel and a control channel are provided on the valve sleeve, a valve cavity is provided inside the valve sleeve, and the valve cavity comprises a first cavity and a second cavity which are coaxially arranged, and the inner diameter of the second cavity is larger than the inner diameter of the first cavity; the control channel is connected to the second cavity, and the oil inlet channel and the oil outlet channel are connected to the first cavity, and the inner diameter of the oil inlet channel is smaller than the inner diameter of the first cavity;

[0009] The valve core comprises a first core body and a second core body which are coaxially arranged, wherein the diameter of the second core body is larger than the diameter of the first core body, the first core body is inserted into the first cavity, and the second core body is inserted into the second core body;

[0010] The valve core is suitable for sliding between a first position and a second position, and control oil flows in the control channel, and the control oil is used to push the valve core to slide toward the first position and close the oil inlet channel and the oil outlet channel through the first core body; pressure oil is provided in the oil inlet channel, and the pressure oil is used to push the valve core to slide toward the second position and connect the oil inlet channel and the oil outlet channel.

[0011] Further, a first step surface is formed at the joint of the first cavity and the second cavity, and a second step surface is formed at the joint of the first core and the second core. When the valve core is located at the first position, the second step surface stops at the first step surface.

[0012] Further, the diameter of the first core is equal to the inner diameter of the first cavity, and the diameter of the second core is equal to the inner diameter of the second cavity.

[0013] In some embodiments, the first cavity and the oil inlet passage form a third step surface on their diameters, and when the valve core is located at the first position, the end surface of the first core stops at the third step surface.

[0014] Furthermore, an outer chamfer is provided on the end surface of the first core body along the circumferential direction, and an inner chamfer is provided on the third step surface along the circumferential direction. When the valve core is located at the first position, the outer chamfer abuts against the inner chamfer.

[0015] In some embodiments, the valve sleeve is further provided with an internal leakage channel connected to the valve cavity, and the internal leakage channel is connected to the second cavity.

[0016] Furthermore, it also includes a valve cover, which is connected to the valve sleeve and is used to close the second cavity.

[0017] In some embodiments, a spring is further included which is sleeved on the valve core, and two ends of the spring are respectively fixedly connected to the valve cover and the valve core for resetting the valve core.

[0018] A second aspect of the present invention provides a hydraulic system, the hydraulic system comprising the unloading valve in the above embodiment.

[0019] In some embodiments, the hydraulic system also includes an oil motor, a solenoid valve and a servo valve, the solenoid valve is used to control the oil pressure of the control oil in the control channel, the servo valve is used to control the oil pressure of the pressure oil in the oil inlet channel, the oil outlet channel is connected to the oil cylinder of the oil motor, and the internal leakage channel is connected to an oil return pipeline.

[0020] The unloading valve and hydraulic system provided by the present invention have at least the following beneficial effects:

[0021] When the system pressure suddenly rises unstably, the valve core of the present invention is divided into a first core body and a second core body with different radii. By increasing the end face area on one side of the control oil channel, the stability of the valve core when the valve of the solenoid valve is opened is improved. Since the diameter of the second core body of the valve core in the unloading valve is larger than the diameter of the first core body, even if the system pressure suddenly rises, the force applied to the first core body is unlikely to exceed the force applied to the second core body, thereby greatly reducing the risk of abnormal conduction of the oil inlet and outlet channels, thereby improving the stability of the unloading valve state. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 A schematic diagram of the structure of the unloading valve provided in an embodiment of the present invention when it is in a closed state;

[0024] Figure 2 A schematic diagram of the structure of the unloading valve provided in an embodiment of the present invention when it is in an open state;

[0025] Figure 3 A schematic diagram of the structure of a valve sleeve provided in an embodiment of the present invention;

[0026] Figure 4 A schematic diagram of the structure of a valve core provided in an embodiment of the present invention;

[0027] Figure 5 A schematic structural diagram of a hydraulic system provided in an embodiment of the present invention.

[0028] Among them, the reference numerals in the figure are:

[0029] 1. Valve sleeve; 11. Oil inlet channel; 12. Oil outlet channel; 13. Control channel; 14. Valve cavity; 15. First cavity; 16. Second cavity;

[0030] 2. valve core; 21. first core body; 22. second core body;

[0031] 3. The first step surface;

[0032] 4. The second step surface;

[0033] 5. The third step surface;

[0034] 6. External chamfer;

[0035] 7. Inner chamfer;

[0036] 8. Internal leakage channel;

[0037] 9. Valve cover; 91. Spring;

[0038] 100. Oil motor; 101. Solenoid valve; 102. Servo valve. DETAILED DESCRIPTION

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] It should be noted that when a component is referred to as being "fixed on" or "disposed on" another component, it may be directly or indirectly located on the other component. When a component is referred to as being "connected to" another component, it may be directly or indirectly connected to the other component. The directions or positions indicated by the terms "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the directions or positions shown in the accompanying drawings and are only for the convenience of description and cannot be understood as limitations on the present technical solution. The terms "first" and "second" are only used for the convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0041] A first aspect of an embodiment of the present invention provides a relief valve. The relief valve according to the embodiment of the present invention is described below in conjunction with the accompanying drawings.

[0042] See also Figure 1 and Figure 2 , Figure 1 and Figure 2 The schematic structural diagram of the unloading valve of the present invention is shown. The unloading valve comprises a valve sleeve 1 and a valve core 2 which are installed in cooperation with each other.

[0043] For more details, see Figure 1-Figure 4An oil inlet channel 11, an oil outlet channel 12 and a control channel 13 are provided on the valve sleeve 1. A valve cavity 14 is provided inside the valve sleeve 1. The valve cavity 14 includes a first cavity 15 and a second cavity 16 which are coaxially arranged. The inner diameter of the second cavity 16 is larger than the inner diameter of the first cavity 15. The control channel 13 is connected to the second cavity 16. The oil inlet channel 11 and the oil outlet channel 12 are connected to the first cavity 15. The inner diameter of the oil inlet channel 11 is smaller than the inner diameter of the first cavity 15.

[0044] The valve core 2 includes a first core body 21 and a second core body 22 which are coaxially arranged. The diameter of the second core body 22 is larger than the diameter of the first core body 21. The first core body 21 is inserted into the first cavity 15, and the second core body 22 is inserted into the second core body 22. It can be understood that the first core body 21 and the second core body 22 are cylindrical core bodies with different diameters, and the first core body 21 and the second core body 22 are formed into the valve core 2 in an integral manner.

[0045] Among them, the valve core 2 is suitable for sliding between the first position and the second position, and control oil flows in the control channel 13, and the control oil is used to push the valve core 2 to slide to the first position and close the oil inlet channel 11 and the oil outlet channel 12 through the first core body 21; the oil inlet channel 11 is provided with pressure oil, and the pressure oil is used to push the valve core 2 to slide to the second position and connect the oil inlet channel 11 and the oil outlet channel 12.

[0046] Furthermore, the unloading valve closes or opens the oil inlet channel 11 and the oil outlet channel 12 by moving the valve core 2 in the valve sleeve 1. The valve core 2 is used to control the flow of hydraulic oil. When the system pressure exceeds a preset value, the valve core 2 will move to open the channel and allow the hydraulic oil to flow back to the oil tank.

[0047] The valve sleeve 1 is the main part of the unloading valve, which is used to be sleeved on the outside of the valve core 2. It provides guidance and support for the valve core 2 to ensure that the valve core 2 moves on the correct track. The valve sleeve 1 is a metal shell with multiple holes and channels, which are used to connect the oil inlet, oil outlet and control port, that is, the oil inlet channel 11, the oil outlet channel 12 and the control channel 13 in this embodiment, wherein the control channel 13 is used to connect the solenoid valve 101, and the solenoid valve 101 is controlled to be on and off according to the set pressure.

[0048] The working principle of this unloading valve is:

[0049] When the system pressure is lower than the set pressure of the control channel 13, the valve of the solenoid valve 101 is closed, and the control oil does not enter the oil control channel. At this time, the oil pressure of the valve core 2 at the control oil end is less than the oil pressure at the pressure oil end. The pressure oil pushes the valve core 2 to slide to the second position, the oil inlet channel 11 and the oil outlet channel 12 are connected, and the pressure oil enters the system through the oil inlet channel 11; when the system pressure reaches or exceeds the set pressure of the control channel 13, the valve of the solenoid valve 101 is opened, the control oil enters the oil control channel, and a control pressure is generated on the valve core 2. After the control pressure acts on the valve core 2, it will push the valve core 2 to move to the first position, closing the oil inlet channel 11 and the oil outlet channel 12, and the pressure oil no longer enters the system, and the system pressure drops.

[0050] It can be understood that the movement of the valve core 2 depends on the pressure difference at both ends of the valve core 2. The end face of the valve core 2 close to the oil inlet channel 11 is defined as the first end face, and the end face of the valve core 2 close to the control channel 13 is defined as the second end face. The area of ​​the first end face is S1, the area of ​​the second end face is S, and the cross-sectional area of ​​the oil inlet channel 11 is S2. Since the diameter of the second core body 22 is larger than the diameter of the first core body 21, and the inner diameter of the oil inlet channel 11 is smaller than the inner diameter of the first cavity 15, S>S1>S2. In addition, when the first core body 21 closes the oil inlet channel 11, the first core body 21 will form a circular step surface at the joint of the oil inlet channel 11, and the area of ​​the step surface is (S1-S2).

[0051] When the solenoid valve 101 is closed, the second end face is no longer subjected to the control oil, and the first end face of the valve core 2 is subjected to a force F2 = P*S1, and the second end face of the valve core 2 is subjected to a force F2 = 0. The valve core 2 moves to the second position under the action of the pressure oil, and the oil inlet channel 11 and the oil outlet channel 12 are connected.

[0052] When the valve of the solenoid valve 101 is opened, the control oil acts on the second end face, the oil pressure of the pressure oil on the first end face is P, and the oil pressure of the control oil on the second end face is P1. It should be noted that the control oil is not less than the oil pressure of the pressure oil, that is, in normal use, P≤P1, and the pressure oil acts on the area of ​​the oil inlet channel 11 on the first end face, that is, the pressure oil acts on the S2 area. Of course, the oil outlet channel 12 also has an oil pressure P2 acting on the first end face, and P2 mainly acts on the step surface (S1-S2), and the area of ​​S2 is far greater than that of the step surface (S1-S2). Greater than (S1-S2). It should be noted that, according to usage statistics, the size of P2 is basically the same as the size of P, and P2 will not exceed 1.5 times of P. At this time, the force F1=P*S2+P2*(S1-S2) applied to the first end face of the valve core 2, and the force F2=P1*S applied to the second end face of the valve core 2. By judging the sizes of F1 and F2, the moving direction of the valve core 2 can be determined. Specifically, when F1 is greater than F2, the valve core 2 moves to the second position, and when F1 is less than F2, the valve core 2 moves to the first position.

[0053] When judging the size of F1 and F2, two situations need to be considered. One is when the system pressure is stable, and the other is when the system pressure is unstable, that is, the system pressure will suddenly increase.

[0054] When the system pressure is stable, the size of P2 is basically the same as the size of P, the force F1=P*S2+P2*(S1-S2) exerted on the first end face of the valve core 2 is approximately equal to P*S1, and the force F2=P1*S exerted on the second end face of the valve core 2. It can be found that P≤P1. Even when P=P1, since the area S of the second end face is larger than the area S1 of the first end face, the force F2 exerted on the second end face is always larger than the force F1 exerted on the first end face. The valve core 2 can be maintained in the first position and block the oil inlet channel 11 and the oil outlet channel 12.

[0055] When the system pressure is unstable, that is, P2 suddenly increases, that is, P2=1.5P, the force F1 applied to the first end face of the valve core 2 is F1=P*S2+1.5P*(S1-S2)=1.5P*S1-0.5P*S2. At this time, the force applied to the first end face of the valve core 2 is greater than P*S1. Therefore, when P=P1, if the area S of the second end face is equal to the area S1 of the first end face, then the force F2 applied to the second end face may be smaller than the force F1 applied to the first end face. At this time, the valve core 2 will be pushed to the second position, causing the oil inlet channel 11 and the oil outlet channel 12 to be abnormally conductive. Therefore, the state of the unloading valve at this time is extremely unstable and may be opened, which will interfere with the stable state of the system.

[0056] However, in the present embodiment, the area S of the second end face is larger than the area S1 of the first end face. Therefore, even if the system pressure suddenly increases, it is difficult for the force F1 exerted on the first end face (first core 21) to exceed the force F2 exerted on the second end face (second core 22), thereby greatly reducing the risk of abnormal conduction between the oil inlet channel 11 and the oil outlet channel 12, improving the stability of the unloading valve state, and thereby being able to better maintain the stability of the system.

[0057] It should be noted that the valve core 2 of the conventional unloading valve is set to be cylindrical, that is, the area S of the second end face is equal to the area S1 of the first end face. Therefore, when the system pressure suddenly rises due to instability, the valve core 2 is very likely to be pushed to the second position by the high pressure, that is, the risk of abnormal conduction of the unloading valve will be greatly increased. This embodiment is to reduce the risk of abnormal conduction of the unloading valve, so the valve core 2 is divided into a first core body 21 and a second core body 22 with different radii, and the stability of the valve core 2 when the valve of the solenoid valve 101 is opened is improved by increasing the end face area on one side of the control oil channel.

[0058] In some embodiments, see Figure 1-Figure 4A first step surface 3 is formed at the joint of the first cavity 15 and the second cavity 16 , and a second step surface 4 is formed at the joint of the first core 21 and the second core 22 . When the valve core 2 is located at the first position, the second step surface 4 stops at the first step surface 3 .

[0059] When the valve core 2 is in the first position, it is first ensured that the first end face abuts against the first cavity 15. At this time, the stress on the valve core 2 is concentrated on the first end face, resulting in a large stress on the first end face, which may easily cause damage to the valve core 2. In order to share the stress on the first end face, when the valve core 2 is in the first position, the second step surface 4 abuts against the first step surface 3. In this way, part of the stress on the valve core 2 is divided into the first step surface 3 and the second step surface 4, so that the stress on the valve core 2 is more dispersed, reducing the risk of damage to the valve core 2.

[0060] Furthermore, the diameter of the first core 21 is equal to the inner diameter of the first cavity 15 , and the diameter of the second core 22 is equal to the inner diameter of the second cavity 16 .

[0061] In other words, the valve core 2 and the valve cavity 14 fit tightly together to ensure that the fluid does not leak from the gap between them. If there is a large gap between the valve core 2 and the valve cavity 14 of the valve sleeve 1, the fluid will generate eddy currents and impacts when passing through at high speed, resulting in rapid wear of the valve core 2 and the valve cavity 14. Tight fit can reduce such wear, extend the service life of the unloading valve, and improve the safety of the system.

[0062] In some embodiments, in order to further improve the close fit between the valve core 2 and the valve cavity 14, a third step surface 5 is formed on the diameter of the first cavity 15 and the oil inlet channel 11. When the valve core 2 is in the first position, the end surface of the first core 21 stops at the third step surface 5.

[0063] In some embodiments, see Figure 1-Figure 4 The end surface of the first core body 21 is provided with an outer chamfer 6 along the circumferential direction, and the third step surface 5 is provided with an inner chamfer 7 along the circumferential direction. When the valve core 2 is located at the first position, the outer chamfer 6 abuts against the inner chamfer 7.

[0064] The inner chamfer 7 refers to the chamfering treatment performed on the third step surface 5, which can reduce the risk of stress concentration caused by sharp inner angles, and can ensure that the outer chamfer 6 of the first core 21 can smoothly fit and stop on the third step surface 5, while reducing wear during assembly.

[0065] The outer chamfer 6 refers to the chamfering treatment performed on the outer edge of the first core body 21. The outer chamfer 6 can make the fit between the first core body 21 and the third step surface 5 smoother, reduce the difficulty of assembly, and the design of the outer chamfer 6 can disperse the stress between the first core body 21 and the third step surface 5, thereby extending the service life of the unloading valve and the valve core 2.

[0066] Furthermore, the outer chamfer 6 can be realized by turning, milling or grinding, and the inner chamfer 7 can be processed by using a drill, reamer or lathe with a specific shape.

[0067] In some embodiments, see Figure 1-Figure 3 The valve sleeve 1 is also provided with an internal leakage channel 8 connected to the valve cavity 14 , and the internal leakage channel 8 is connected to the second cavity 16 .

[0068] Furthermore, the internal leakage channel 8 is connected to the oil tank or the bypass channel for discharging the excess fluid (pressure oil and control oil) entering between the valve core 2 and the inner wall of the valve cavity 14 .

[0069] When the system pressure exceeds the set value, the internal leakage channel 8 will open and discharge the excess fluid back to the tank or bypass, thereby reducing the system pressure and protecting the equipment from overpressure damage. In some cases, sudden pressure changes may cause hydraulic shock. The internal leakage channel 8 can respond quickly and release the pressure to reduce the impact of hydraulic shock on the system.

[0070] Further, see Figure 1-Figure 2 The unloading valve further comprises a valve cover 9, which is connected to the valve sleeve 1 and is used to close the second cavity 16. The valve cover 9 is used to close the top of the valve sleeve 1, fix the valve core 2, and ensure the sealing of the entire valve cavity 14.

[0071] Furthermore, the valve cover 9 is a metal cover with threads or flanges, which is fixed to the valve sleeve 1 by bolts or threads. The valve cover 9 uses the same material as the valve sleeve 1 to ensure matching and sealing.

[0072] Further, see Figure 1-Figure 2 The unloading valve also includes a spring 91 sleeved on the valve core 2. The two ends of the spring 91 are fixedly connected to the valve cover 9 and the valve core 2 respectively, and are used to reset the valve core 2.

[0073] The spring 91 is used to set the opening and closing pressure of the unloading valve. When the pressure of the pressure oil exceeds the preset pressure of the spring, the spring will be compressed, causing the valve core 2 to move and open the passage. When the pressure of the pressure oil drops to the recovery pressure, the spring pushes the valve core 2 back to its original position and closes the passage. The spring is a spiral metal spring installed between the valve core 2 and the valve cover 9. The spring uses high-strength spring steel to ensure elasticity and durability.

[0074] A second aspect of the present invention provides a hydraulic system. Figure 5 , including the unloading valve in the above embodiment.

[0075] Further, see Figure 5The hydraulic system also includes an oil motor 100, a solenoid valve 101 and a servo valve 102. The solenoid valve 101 is used to control the oil pressure of the control oil in the control channel 13, and the servo valve 102 is used to control the oil pressure of the pressure oil in the oil inlet channel 11. The oil outlet channel 12 is connected to the oil cylinder of the oil motor 100, and the internal leakage channel 8 is connected to the return oil pipeline.

[0076] By setting up the unloading valve, even when the hydraulic system pressure is unstable, since the area S of the second end face is larger than the area S1 of the first end face, the force F1 exerted on the first core 21 is unlikely to exceed the force F2 exerted on the second core 22, thereby greatly reducing the risk of abnormal conduction between the oil inlet channel 11 and the oil outlet channel 12 and improving the stability of the unloading valve state, thereby better maintaining the stability of the hydraulic system.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A relief valve, characterized in that: include: A valve sleeve, wherein an oil inlet channel, an oil outlet channel and a control channel are provided on the valve sleeve, a valve cavity is provided inside the valve sleeve, and the valve cavity comprises a first cavity and a second cavity which are coaxially arranged, and the inner diameter of the second cavity is larger than the inner diameter of the first cavity; the control channel is connected to the second cavity, and the oil inlet channel and the oil outlet channel are connected to the first cavity, and the inner diameter of the oil inlet channel is smaller than the inner diameter of the first cavity; The valve core comprises a first core body and a second core body which are coaxially arranged, wherein the diameter of the second core body is larger than the diameter of the first core body, the first core body is inserted into the first cavity, and the second core body is inserted into the second core body; The valve core is suitable for sliding between a first position and a second position, and control oil flows in the control channel, and the control oil is used to push the valve core to slide toward the first position and close the oil inlet channel and the oil outlet channel through the first core body; pressure oil is provided in the oil inlet channel, and the pressure oil is used to push the valve core to slide toward the second position and connect the oil inlet channel and the oil outlet channel.

2. The unloading valve according to claim 1, characterized in that: A first step surface is formed at the joint of the first cavity and the second cavity, and a second step surface is formed at the joint of the first core and the second core. When the valve core is located at the first position, the second step surface stops at the first step surface.

3. The unloading valve according to claim 1, characterized in that: The diameter of the first core is equal to the inner diameter of the first cavity, and the diameter of the second core is equal to the inner diameter of the second cavity.

4. The unloading valve according to claim 1, characterized in that: The first cavity and the oil inlet passage form a third step surface on their diameters. When the valve core is located at the first position, the end surface of the first core stops at the third step surface.

5. The unloading valve according to claim 4, characterized in that: The end surface of the first core body is provided with an outer chamfer along the circumferential direction, and the third step surface is provided with an inner chamfer along the circumferential direction. When the valve core is located at the first position, the outer chamfer abuts against the inner chamfer.

6. The unloading valve according to claim 1, characterized in that: The valve sleeve is also provided with an internal leakage channel connected to the valve cavity, and the internal leakage channel is connected to the second cavity.

7. The unloading valve according to claim 1, characterized in that: A valve cover is also included, which is connected to the valve sleeve and is used to close the second cavity.

8. The unloading valve according to claim 7, characterized in that: It also includes a spring sleeved on the valve core, with two ends of the spring fixedly connected to the valve cover and the valve core respectively, for resetting the valve core.

9. A hydraulic system, characterized in that: Comprising a unloading valve as described in any one of claims 1-8.

10. The hydraulic system according to claim 9, characterized in that: The hydraulic system also includes an oil motor, a solenoid valve and a servo valve. The solenoid valve is used to control the oil pressure of the control oil in the control channel. The servo valve is used to control the oil pressure of the pressure oil in the oil inlet channel. The oil outlet channel is connected to the oil cylinder of the oil motor. The internal leakage channel is connected to an oil return pipeline.

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