Bidirectionally driven electro-hydraulic proportional pilot valve

Abstract

The present invention relates to a bidirectionally driven electro-hydraulic proportional pilot valve, comprising a pilot valve sleeve, a pilot valve core, and an electromagnetic drive unit for controlling the bidirectional axial movement of the pilot valve core. When the first electromagnetic coil or the second electromagnetic coil is energized, electromagnetic forces in different directions are generated on the armature to control the movement of the pilot valve core in different directions. The pilot valve core has at least a first position and a second position. In the first position, the oil inlet P is connected to the working oil port B, and the working oil port A is connected to the oil return port T; in the second position, the oil inlet P is connected to the working oil port A, and the working oil port B is connected to the oil return port T. The electromagnetic drive unit employs two sets of electromagnetic coils with different winding directions. By inputting current into the different electromagnetic coils, the axial movement of the pilot valve core in different directions is controlled, thereby achieving bidirectional drive of the pilot valve core and thus realizing on-off control of the pilot pressure of the main valve core. The structure is reasonable, the control is reliable, the response is fast, and the hysteresis loop is small.

Description

Technical Field

[0001] The present invention relates to the field of hydraulic technology, in particular to a bidirectionally driven electro-hydraulic proportional pilot valve. Background Art

[0002] Proportional control technology, developed in the late 1960s, is reliable, inexpensive, and meets the control accuracy and response characteristics required by industrial control systems. The electro-hydraulic proportional valve, the primary power amplifier component in proportional control systems, continuously and proportionally controls hydraulic system parameters such as pressure and flow according to input electrical signals. While its control accuracy lags behind that of servo valves, electro-hydraulic proportional valves offer strong resistance to contamination, reducing operational failures caused by contamination and improving the stability and reliability of hydraulic systems. Furthermore, proportional valves are less expensive than servo valves and have a simpler structure, making them widely used.

[0003] The input element of a proportional valve is an electro-mechanical converter, which converts the input electrical signal into mechanical energy. Common converters include servo motors, stepper motors, voice coil motors, and proportional solenoids. Most commonly used proportional valves utilize proportional solenoids. Proportional solenoids are designed based on electromagnetic principles, generating force, torque, or displacement proportional to the input current signal. In an electro-hydraulic proportional valve, the proportional solenoid generates a corresponding output force or displacement based on the input electrical signal, causing the associated hydraulic valve core to generate a corresponding force or displacement. This changes the valve opening pressure or valve opening, thereby achieving pressure or flow control proportional to the input current.

[0004] Conventional plug-in electro-hydraulic proportional pilot valves utilize a single electromagnet coil, which can only control the movement of the pilot valve core in one direction, providing only a unidirectional driving force. Therefore, a single main valve core requires two electro-proportional pilot valves to achieve directional reversal. Existing technical solutions often utilize a one-piece manufacturing process for the pilot valve, which is difficult, consumes a lot of material, and is costly. Conventional electro-hydraulic proportional pilot valves also exhibit slow response and cannot meet the high-frequency response requirements of the entire system. Furthermore, conventional solutions lack a filtering device, which often results in foreign matter becoming stuck in the pilot valve, causing system failure. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention provides a bidirectionally driven electro-hydraulic proportional pilot valve, in which the electromagnetic drive unit adopts two groups of electromagnetic coils with different winding directions. The axial movement of the pilot valve core is controlled in different directions by inputting current into different electromagnetic coils, thereby realizing bidirectional drive of the pilot valve core and on-off control of the pilot pressure of the main valve core. The valve has a reasonable structure, reliable control, fast response and small hysteresis loop.

[0006] A bidirectionally driven electro-hydraulic proportional pilot valve comprises a pilot valve sleeve, a pilot valve core, and an electromagnetic drive unit for controlling the axial bidirectional movement of the pilot valve core, wherein the electromagnetic drive unit comprises an armature, a first pilot spring, a second pilot spring, a guide sleeve, a permanent magnet, a shell and an end cover, wherein the armature is axially movable in the guide sleeve, the first pilot spring, the pilot valve core, the armature and the second pilot spring are axially pressed in sequence, the permanent magnet is arranged on the outer wall of the guide sleeve, and the first electromagnetic coil and the second electromagnetic coil with different winding directions are respectively arranged on both axial sides of the permanent magnet, the shell cover is arranged on the outside of the first electromagnetic coil, the permanent magnet and the second electromagnetic coil, and the end cover is installed at one end of the shell; the pilot valve core One end face has an oil inlet P, and the pilot valve core is provided with an oil inlet channel along the axial direction from the oil inlet, and the pilot valve core is provided with an oil outlet radially connected to the oil inlet channel, and the pilot valve sleeve is provided with a working oil port A, a working oil port B and an oil return port T; when the first electromagnetic coil is energized or the second electromagnetic coil is energized, electromagnetic forces in different directions are generated on the armature to control the movement of the pilot valve core in different directions, and the pilot valve core has at least a first position and a second position. When in the first position, the oil inlet P is connected to the working oil port B, and the working oil port A is connected to the oil return port T; when in the second position, the oil inlet P is connected to the working oil port A, and the working oil port B is connected to the oil return port T.

[0007] Optionally, the pilot valve core has a first boss and a second boss, the width of the first boss along the axial direction of the pilot valve core is not less than the width of the working oil port A along the axial direction of the pilot valve core, and the width of the second boss along the axial direction of the pilot valve core is not less than the width of the working oil port B along the axial direction of the pilot valve core.

[0008] Optionally, the distance between the first boss and the second boss is equal to the distance between the working oil port A and the working oil port B.

[0009] Optionally, a circumferential oil storage groove is respectively provided on the outer periphery of the first boss and the second boss.

[0010] Optionally, a first magnetic isolation ring and a second magnetic isolation ring are provided on the guide sleeve, and a throat with a reduced diameter is formed inside the guide sleeve. The position of the first magnetic isolation ring corresponds to between the armature and the pilot valve sleeve, and the position of the second magnetic isolation ring corresponds to between the throat and the armature.

[0011] Optionally, the cross-sections of the first magnetic isolation ring and the second magnetic isolation ring are both trapezoidal, and the first magnetic isolation ring and the second magnetic isolation ring are symmetrically distributed along a plane perpendicular to the axis of the armature.

[0012] Optionally, a first magnetic isolation gasket is provided on the end surface of the pilot valve sleeve facing the armature, and a second magnetic isolation gasket is provided on the side surface of the throat facing the armature.

[0013] Optionally, one end of the guide sleeve is sleeved with one end of the pilot valve sleeve with a sealing ring provided therebetween, and the other end of the guide sleeve is provided with a telescopic adjustment member capable of axially pressing against the second pilot spring.

[0014] Optionally, one end of the first pilot spring is positioned inside the pilot valve sleeve by a retaining spring, and the other end abuts against the pilot valve core; one end of the second pilot spring abuts against the armature, and the other end is connected to the guide sleeve or the telescopic adjustment member, and the telescopic adjustment member is threadedly connected to the guide sleeve.

[0015] Optionally, a filter is provided at the oil inlet P.

[0016] Optionally, the outer wall surface of the armature and / or the inner wall surface of the guide sleeve has a coating layer for reducing friction between the armature and the guide sleeve.

[0017] Optionally, the coating layer is SiC or a resin-based composite material.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0019] (1) The bidirectional reversing control of the main valve core can be achieved by a single plug-in electro-hydraulic proportional pilot valve of the present invention, which reduces the volume of the main valve and the supporting cost of the main valve compared with the traditional single electromagnetic coil proportional pilot valve;

[0020] (2) An oil storage tank structure is added to the surface of the pilot valve core to increase lubrication and reduce the friction between the pilot valve core and the pilot valve sleeve, thereby reducing the hysteresis ring of the electro-hydraulic proportional pilot valve and improving the response of the pilot valve;

[0021] (3) The design of the magnetic isolation ring structure at both ends of the armature reduces the time when the pilot valve core cannot be quickly switched due to the attraction between the armature and the guide sleeve, and the armature and the pilot valve sleeve, thereby improving the response time of the electro-hydraulic proportional pilot valve and directly affecting the frequency response of the main valve, thus better meeting the requirements of intelligent and high-speed engineering machinery;

[0022] (4) The pilot valve sleeve and the electromagnet end cover are designed to be split, which reduces the difficulty of one-piece processing in the original technology, saves raw materials, and directly reduces the cost of the electro-hydraulic proportional pilot valve;

[0023] (5) A filter is installed at the oil inlet of the electro-hydraulic proportional pilot valve, which effectively reduces the pilot valve failure caused by oil impurities and improves the reliability of the entire machine;

[0024] (6) The design of the telescopic adjustment piece can adjust the position of the pilot valve core, making it convenient for the electro-hydraulic proportional pilot valve to be adjusted to the center position;

[0025] (7) Adding a coating layer of materials such as SiC or resin-based composite materials to the surface of the armature can reduce the friction between the armature and the guide sleeve, thereby reducing the hysteresis of the electromagnet output force and ultimately reducing the hysteresis of the main valve flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the bidirectionally driven electro-hydraulic proportional pilot valve of the present invention;

[0027] Figure 2 It is a structural schematic diagram of the electromagnetic drive unit in the bidirectionally driven electro-hydraulic proportional pilot valve of the present invention;

[0028] Figure 3 、 Figure 4 It is a schematic diagram of the oil supply path when the pilot valve core of the bidirectionally driven electro-hydraulic proportional pilot valve of the present invention moves in different directions.

[0029] In the accompanying drawings: 1.1-pilot valve sleeve, 1.2-circlip, 1.3-first pilot spring, 1.4-pilot valve core, 1.5-filter, 2.1-end cover, 2.2-first magnetic isolation gasket, 2.3-housing, 2.4-armature, 2.5-second electromagnetic coil, 2.6-guide sleeve, 2.7-telescopic adjustment piece, 2.8-second magnetic isolation gasket, 2.9-second pilot spring, 2.10-second magnetic isolation ring, 2.11-permanent magnet, 2.12-first electromagnetic coil, 2.13-first magnetic isolation ring. DETAILED DESCRIPTION

[0030] The following description of exemplary embodiments of the present invention is made in conjunction with the accompanying drawings, in which various details of the embodiments of the present invention are included to facilitate understanding. These details should be considered as merely exemplary. Therefore, it should be appreciated by those skilled in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present invention. Similarly, for the sake of clarity and conciseness, descriptions of well-known functions and structures are omitted in the following description.

[0031] like Figures 1 to 4As shown, a bidirectionally driven electro-hydraulic proportional pilot valve of the present invention includes a pilot valve sleeve 1.1, a pilot valve core 1.4, and an electromagnetic drive unit for controlling the axial bidirectional movement of the pilot valve core 1.4. The electromagnetic drive unit includes an armature 2.4, a first pilot spring 1.3, a second pilot spring 2.9, a guide sleeve 2.6, a permanent magnet 2.11, a housing 2.3, and an end cover 2.1. The armature 2.4 is axially movable within the guide sleeve 2.6. The first pilot spring 1.3, the pilot valve core 1.4, the armature 2.4, and the second pilot spring 2.9 are axially pressed against each other in sequence. The permanent magnet 2.11 is disposed on the outer wall of the guide sleeve 2.6. A first electromagnetic coil 2.12 and a second electromagnetic coil 2.5 with different winding directions are respectively disposed on either axial side of the permanent magnet 2.11. The housing 2.3 covers the first electromagnetic coil 2.12 and the permanent magnet 2.1. 1 and the outside of the second electromagnetic coil 2.5, the end cover 2.1 is installed at one end of the housing 2.3; one end surface of the pilot valve core 1.4 has an oil inlet P, and an oil inlet channel is opened on the pilot valve core 1.4 along the axial direction from the oil inlet, and an oil outlet is opened in the radial direction on the pilot valve core 1.4 and communicates with the oil inlet channel; the pilot valve sleeve 1.1 is provided with a working oil port A, a working oil port B and an oil return port T; when the first electromagnetic coil 2.12 or the second electromagnetic coil 2.5 is energized, electromagnetic forces in different directions are generated on the armature 2.4 to control the movement of the pilot valve core 1.4 in different directions. The pilot valve core 1.4 has at least a first position and a second position. When in the first position, the oil inlet P is connected to the working oil port B, and the working oil port A is connected to the oil return port T; when in the second position, the oil inlet P is connected to the working oil port A, and the working oil port B is connected to the oil return port T.

[0032] More specifically, the pilot valve core 1.4 has a first boss and a second boss. The width of the first boss along the axial direction of the pilot valve core 1.4 is not less than the width of the working oil port A along the axial direction of the pilot valve core 1.4, and the width of the second boss along the axial direction of the pilot valve core 1.4 is not less than the width of the working oil port B along the axial direction of the pilot valve core 1.4; the distance between the first boss and the second boss is equal to the distance between the working oil port A and the working oil port B, that is, when the first boss blocks the working oil port B, the second boss just blocks the working oil port A.

[0033] In addition, circumferential oil storage grooves are respectively provided on the outer circumferences of the first boss and the second boss for temporarily storing the pilot oil to improve the lubrication of the pilot valve core 1.4 when it moves relative to the pilot valve sleeve 1.1; a first magnetic isolation ring 2.13 and a second magnetic isolation ring 2.10 are provided on the guide sleeve 2.6, and a throat portion with a reduced diameter is formed inside the guide sleeve 2.6. The position of the first magnetic isolation ring 2.13 corresponds to that between the armature 2.4 and the pilot valve sleeve 1.1, and the position of the second magnetic isolation ring 2.10 corresponds to that between the throat portion and the armature 2.4; the cross-sections of the first magnetic isolation ring 2.13 and the second magnetic isolation ring 2.10 are both trapezoidal, and the first magnetic isolation ring 2.13 and the second magnetic isolation ring 2.10 are symmetrically distributed along a plane perpendicular to the axis of the armature 2.4; the pilot valve sleeve 1.1 A first magnetic isolation gasket 2.2 is provided on the end face facing the armature 2.4, and a second magnetic isolation gasket 2.8 is provided on the side of the throat facing the armature 2.4; one end of the guide sleeve 2.6 is sleeved with one end of the pilot valve sleeve 1.1 and a sealing ring is provided between the two, and the other end of the guide sleeve 2.6 is provided with a telescopic adjustment piece 2.7 that can axially press against the second pilot spring 2.9; one end of the first pilot spring 1.3 is positioned inside the pilot valve sleeve 1.1 by a retaining spring 1.2, and the other end abuts against the pilot valve core 1.4; one end of the second pilot spring 2.9 abuts against the armature 2.4, and the other end is connected to the guide sleeve 2.6 or the telescopic adjustment piece 2.7, and the telescopic adjustment piece 2.7 is threadedly connected to the guide sleeve 2.6; a filter screen 1.5 is provided at the oil inlet P.

[0034] Furthermore, the outer surface of the armature has a coating layer to reduce friction generated during relative motion between the outer surface of the armature and the inner surface of the guide sleeve. Specifically, the coating layer can be made of SiC or a resin-based composite material to reduce friction between the armature and the guide sleeve. In other embodiments, the coating layer can be provided on the inner surface of the guide sleeve, or on both the outer surface of the armature and the inner surface of the guide sleeve, also using SiC or a resin-based composite material.

[0035] See also Figure 2 The function of the magnetic isolation ring is to change the distribution of the closed magnetic flux Φ1 inside the electromagnet. Its presence also divides guide sleeve 2.6 into three parts, the left and right parts also called pole shoes. Magnetic flux Φ1 bends along the direction of the magnetic isolation angle α through guide sleeve 2.6 and the front section of the second magnetic isolation ring 2.10, entering radial air gap δ1. It then bends into the front face of armature 2.4, exits at the rear section of armature 2.4, and enters housing 2.3, ultimately forming a closed circuit. Magnetic flux Φ1 acts on armature 2.4, generating an electromagnetic attractive force Fm1 at an angle of magnetic isolation angle α with the axis of armature 2.4. The formula for calculating electromagnetic attractive force Fm1 is:

[0036]

[0037] Among them, N is the number of coil turns, I is the input current, μ0 is the magnetic permeability, δ1 is the magnetic resistance length of the radial gap between the armature 2.4 and the guide sleeve 2.6, which is a constant value; S1 is the magnetic resistance area of ​​the radial gap between the armature 2.4 and the guide sleeve 2.6; α is the magnetic isolation angle, which changes as the armature 2.4 moves left and right.

[0038] Magnetic flux Φ2 enters the interior of armature 2.4 perpendicularly from the front end of guide sleeve 2.6, exits from the rear end of armature 2.4, and enters housing 2.3, finally forming a closed circuit. Magnetic flux Φ2 acts on armature 2.4 to generate electromagnetic attraction Fm2 parallel to the axis of armature 2.4. The calculation formula of electromagnetic attraction Fm2 is:

[0039]

[0040] Where N is the number of coil turns, I is the input current, μ0 is the magnetic permeability, δ2 is the reluctance length of the axial gap between the armature 2.4 and the pole piece, which is a variable that changes with the axial movement of the armature 2.4, and S2 is the cross-sectional area of ​​the inner wall of the guide sleeve 2.6, which is the reluctance area of ​​the axial gap and is a constant.

[0041] The axial reluctance gap δ2, the radial reluctance gap δ1, and the magnetic isolation ring angle α are key factors affecting the magnitude of the electromagnetic force. The electromagnetic attractive forces Fm1 and Fm2 both vary with the axial movement of the armature 2.4. The resultant force of the two in the axial direction constitutes the proportional electromagnet output force Fm. By designing corresponding δ1, δ2, and α, the electromagnet output force Fm varies proportionally with the input command.

[0042] Working process of electro-hydraulic proportional pilot valve:

[0043] See also Figure 1 and Figure 3 When the second electromagnetic coil 2.5 is energized, an electromagnetic force is generated on the armature 2.4 to move to the left. The armature 2.4 moves to the left and compresses the second pilot spring 2.9. The pilot valve core 1.4 also moves to the left under the action of the first pilot spring 1.3. At this time, the pilot oil is supplied from the oil inlet P to the working oil port B. The working oil port A is connected to the oil return port T. For the same principle, see Figure 1 and Figure 4When the first solenoid coil 2.12 is energized, an electromagnetic force is generated on the armature 2.4, causing it to move rightward, compressing the first pilot spring 1.3. Pilot oil is then supplied from the oil inlet P to the working oil port A, connecting the working oil port B to the oil return port T. The command current input by the first solenoid coil 2.12 and the second solenoid coil 2.5 switches the pilot oil circuit. The first and second magnetic isolation washers 2.2 and 2.8 prevent magnetization between the armature 2.4, the guide sleeve 2.6, and the pilot valve sleeve 1.1. This would require a sufficiently large electromagnetic force to open the pilot valve spool 1.4. The design of these magnetic isolation washers shortens the pilot valve's switching time and improves its speed.

[0044] Compared with the prior art, the advantages of the bidirectionally driven electro-hydraulic proportional pilot valve of the present invention are:

[0045] (1) The bidirectional reversing control of the main valve core can be achieved by a single plug-in electro-hydraulic proportional pilot valve of the present invention, which reduces the volume of the main valve and the supporting cost of the main valve compared with the traditional single electromagnetic coil proportional pilot valve;

[0046] (2) An oil storage tank structure is added to the surface of the pilot valve core to increase lubrication and reduce the friction between the pilot valve core and the pilot valve sleeve, thereby reducing the hysteresis ring of the electro-hydraulic proportional pilot valve and improving the response of the pilot valve;

[0047] (3) The design of the magnetic isolation ring structure at both ends of the armature reduces the time when the pilot valve core cannot be quickly switched due to the attraction between the armature and the guide sleeve, and the armature and the pilot valve sleeve, thereby improving the response time of the electro-hydraulic proportional pilot valve and directly affecting the frequency response of the main valve, thus better meeting the requirements of intelligent and high-speed engineering machinery;

[0048] (4) The pilot valve sleeve and the electromagnet end cover are designed to be split, which reduces the difficulty of one-piece processing in the original technology, saves raw materials, and directly reduces the cost of the electro-hydraulic proportional pilot valve;

[0049] (5) A filter is installed at the oil inlet of the electro-hydraulic proportional pilot valve, which effectively reduces the pilot valve failure caused by oil impurities and improves the reliability of the entire machine;

[0050] (6) The design of the telescopic adjustment piece can adjust the position of the pilot valve core, making it convenient for the electro-hydraulic proportional pilot valve to be adjusted to the center position;

[0051] (7) Adding a coating layer of materials such as SiC or resin-based composite materials to the surface of the armature can reduce the friction between the armature and the guide sleeve, thereby reducing the hysteresis of the electromagnet output force and ultimately reducing the hysteresis of the main valve flow.

[0052] The above specific embodiments do not constitute a limitation on the scope of protection of the present invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions may occur depending on design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. Bidirectional driven electro-hydraulic proportional pilot valve, characterized in that: It includes a pilot valve sleeve, a pilot valve core, and an electromagnetic drive unit for controlling the axial and bidirectional movement of the pilot valve core. The electromagnetic drive unit includes an armature, a first pilot spring, a second pilot spring, a guide sleeve, a permanent magnet, a housing, and an end cover. The armature is axially movable in the guide sleeve. The first pilot spring, the pilot valve core, the armature, and the second pilot spring are axially pressed against each other in sequence. The permanent magnet is disposed on the outer wall of the guide sleeve. A first electromagnetic coil and a second electromagnetic coil with different winding directions are respectively disposed on both axial sides of the permanent magnet. The housing cover is disposed outside the first electromagnetic coil, the permanent magnet, and the second electromagnetic coil. The end cover is mounted on one end of the housing. An oil inlet P is formed on one end face of the pilot valve core. An oil inlet passage is formed on the pilot valve core along the axis from the oil inlet. An oil outlet is formed on the pilot valve core in a radial direction and communicates with the oil inlet passage. A working oil port A, a working oil port B and an oil return port T are formed on the pilot valve sleeve. When the first electromagnetic coil or the second electromagnetic coil is energized, electromagnetic forces in different directions are generated on the armature to control the pilot valve core to move in different directions. The pilot valve core has at least a first position and a second position. When in the first position, the oil inlet P is connected to the working oil port B, and the working oil port A is connected to the oil return port T; when in the second position, the oil inlet P is connected to the working oil port A, and the working oil port B is connected to the oil return port T. The guide sleeve is provided with a first magnetic isolation ring and a second magnetic isolation ring. A throat portion with a reduced diameter is formed inside the guide sleeve. The first magnetic isolation ring is located between the armature and the pilot valve sleeve, and the second magnetic isolation ring is located between the throat portion and the armature. The cross-sections of the first magnetic isolation ring and the second magnetic isolation ring are both trapezoidal, and the first magnetic isolation ring and the second magnetic isolation ring are symmetrically distributed along a plane perpendicular to the axis of the armature; The closed magnetic flux Φ1 inside the electromagnet bends along the direction of the magnetic isolation angle α through the guide sleeve and the front section of the second magnetic isolation ring into the radial air gap δ1, then bends into the front end surface of the armature, exits the rear section of the armature and enters the housing, finally forming a closed circuit; the magnetic flux Φ1 acts on the armature to generate an electromagnetic attraction Fm1 with an angle of magnetic isolation angle α with the armature axis. The calculation formula of the electromagnetic attraction Fm1 is: Among them, N is the number of coil turns, I is the input current, μ0 is the magnetic permeability, δ1 is the magnetic resistance length of the radial gap between the armature and the guide sleeve, which is a constant; S1 is the magnetic resistance area of ​​the radial gap between the armature and the guide sleeve; α is the magnetic isolation angle, which changes as the armature moves left and right.

2. The pilot valve according to claim 1, characterized in that The pilot valve core has a first boss and a second boss. The width of the first boss along the axial direction of the pilot valve core is not less than the width of the working oil port A along the axial direction of the pilot valve core, and the width of the second boss along the axial direction of the pilot valve core is not less than the width of the working oil port B along the axial direction of the pilot valve core.

3. The pilot valve according to claim 2, characterized in that The distance between the first boss and the second boss is equal to the distance between the working oil port A and the working oil port B.

4. The pilot valve according to claim 2, wherein: Circumferential oil storage grooves are respectively formed on the outer peripheries of the first boss and the second boss.

5. The pilot valve according to claim 1, wherein: The end surface of the pilot valve sleeve facing the armature is provided with a first magnetic isolation gasket, and the side surface of the throat portion facing the armature is provided with a second magnetic isolation gasket.

6. The pilot valve according to claim 1, wherein: One end of the guide sleeve is sleeved with one end of the pilot valve sleeve with a sealing ring arranged therebetween, and the other end of the guide sleeve is provided with a telescopic adjustment member capable of axially pressing against the second pilot spring.

7. The pilot valve according to claim 6, characterized in that One end of the first pilot spring is positioned inside the pilot valve sleeve by a retaining spring, and the other end abuts against the pilot valve core; one end of the second pilot spring abuts against the armature, and the other end is connected to the guide sleeve or the telescopic adjustment member, and the telescopic adjustment member is threadedly connected to the guide sleeve.

8. The pilot valve according to claim 1, wherein: The oil inlet P is provided with a filter.

9. The pilot valve according to claim 1, wherein: An outer wall surface of the armature and / or an inner wall surface of the guide sleeve has a coating layer for reducing friction between the armature and the guide sleeve.

10. The pilot valve according to claim 9, characterized in that The coating layer is SiC or a resin-based composite material.

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