Electronic expansion valve and manufacturing method

By plating a stainless steel layer on the valve seat of the electronic expansion valve, the problems of uneven solder distribution and internal leakage in the welding sealing parts in the prior art are solved, and higher welding sealing and cost-effectiveness are achieved.

CN120232196APending Publication Date: 2025-07-01ZHEJIANG SANHUA INTELLIGENT CONTROLS CO LTD
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Patent Information

Application Number
CN202311846463.5
Authority / Receiving Office
CN · China
Patent Type
Applications(China)
Current Assignee / Owner
Filing Date
2023-12-28
Publication Date
2025-07-01

AI Technical Summary

Technical Problem

Existing electronic expansion valves have great challenges in the internal leakage of the valve body, especially due to the poor welding process of brass and stainless steel, the solder distribution in the welding sealing parts is uneven and the air holes are present, which increases the risk of leakage in the valve body.

Method used

By plating a stainless steel layer on the inner surface of the valve seat, the welding difficulty with the stainless steel valve core is reduced, and the welding performance between the valve seat and the first connector is ensured through the non-stainless steel coating area, the solder filling of the entire welding surface is denser and the risk of internal leakage is reduced.

Benefits of technology

It effectively optimizes the internal leakage performance of the electronic expansion valve, reduces welding costs, and improves the corrosion resistance and oxidation resistance of the valve body.

✦ Generated by Eureka AI based on patent content.

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Abstract

The electronic expansion valve comprises a valve body used for flow regulation and a coil component used for driving, the valve body comprises a valve seat, a valve element, a valve needle, a first connecting pipe and a second connecting pipe, the valve seat is provided with a first inner hole and a second inner hole, the valve element is welded and fixed to the second inner hole, and the valve element is welded and fixed to the coil component. The valve element is provided with a third inner hole, the valve seat, the first connecting pipe and the second connecting pipe are made of copper, and the valve element and the valve needle are made of stainless steel. A stainless steel coating area and a non-stainless steel coating area are arranged on the hole wall of a second inner hole of the valve seat, and the valve element is connected with the stainless steel coating area in a welded mode. The first connecting pipe is connected with the non-stainless steel coating area in a welded mode, and the upper end face of the first connecting pipe is connected with the lower surface of the valve element in a welded mode. The welding manufacturability and the sealing effect of the valve seat and the valve element are improved, meanwhile, the economical efficiency of welding flux selection is improved, and the effect of improving the inner leakage performance of the valve body at low cost is achieved.
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Description

Technical Field

[0001] The present invention relates to the technical field of valves, in particular to an electronic expansion valve. The present invention also relates to a manufacturing method of the electronic expansion valve. Background Art

[0002] Electronic expansion valves are widely used in air conditioners, refrigeration units, ice-making units, and other refrigeration equipment. The most typical application is the air-conditioning system. The electronic expansion valve can ensure the stable indoor temperature while regulating the refrigerant flow rate, so it plays a very important role in the air-conditioning system.

[0003] According to different driving methods, electronic expansion valves can be divided into direct-acting electronic expansion valves and reduction-type electronic expansion valves. Taking the reduction-type electronic expansion valve as an example, it mainly includes a valve body for flow regulation and a coil component for driving. Among them, the valve body includes core components such as a valve seat, a valve stem, a valve needle, and a bellows. The coil component includes a permanent magnet stepper motor, a gear reduction mechanism with a reduction function, and a screw pair structure for converting the rotary motion of the motor into the vertical motion of the screw rod.

[0004] Reduction-type electronic expansion valves are mostly used in indoor units and have high requirements for internal leakage of the valve body. The total stroke of the up-and-down movement of the valve needle of such expansion valves is relatively short, only 0.7 mm from fully closed to fully open. Therefore, impurities are likely to accumulate at the valve port. When the valve body is in the fully closed state, the extrusion force of the valve needle on the valve port is more than 300 N, and the valve body will be operated to be fully closed when the whole machine is shut down.

[0005] Due to the poor weldability of brass and stainless steel, the solder at the welded seal part is likely to be unevenly distributed and have pores, resulting in an increase in internal leakage of the valve body. Therefore, this structure has high requirements for the fluidity of the solder, and high-silver solder is generally selected, which is expensive.

[0006] In addition, since the valve seat and valve port of the brass material are integrally processed, the valve port is made of brass, and the material is relatively soft, which is easily affected by the accumulation of impurities and the large extrusion force of the stainless steel valve needle. Summary of the Invention

[0007] The purpose of the present invention is to provide an electronic expansion valve to solve the above technical problems.

[0008] Another purpose of the present invention is to provide a manufacturing method of an electronic expansion valve.

[0009] To achieve the above object, the present invention provides an electronic expansion valve, which includes a valve body for flow regulation and a coil component for driving. The valve body includes a valve seat, a valve core, a valve needle, a first nozzle and a second nozzle. A diversion cavity is provided inside the valve seat. A first inner hole is provided in the upper part of the diversion cavity, and a second inner hole is provided in the lower part of the diversion cavity. The valve core is fixedly welded to the second inner hole. The valve core is provided with a third inner hole, and the upper end of the third inner hole forms a valve port. The valve needle passes through the first inner hole and cooperates with the valve port. The valve seat, the first nozzle and the second nozzle are made of copper, and the valve core and the valve needle are made of stainless steel. A stainless steel plating area and a non-stainless steel plating area are provided on the inner wall of the second inner hole of the valve seat. The valve core is welded and connected to the stainless steel plating area through its outer surface. The first nozzle is welded and connected to the non-stainless steel plating area through the outer surface of its insertion end, and the upper end surface of the first nozzle is welded and connected to the lower surface of the valve core.

[0010] Optionally, the valve core includes an integrally formed first ring portion and a second ring portion. The outer diameter of the first ring portion is greater than the outer diameter of the second ring portion, and the height of the second ring portion is greater than the height of the first ring portion. The second inner hole of the valve seat includes a large hole portion and a small hole portion, and a step surface is formed between the large hole portion and the small hole portion. The upper section of the inner wall of the large hole portion is provided with a first stainless steel plating layer, the step surface is provided with a second stainless steel layer, and the inner wall of the small hole portion is provided with a third stainless steel plating layer. The first stainless steel plating layer, the second stainless steel layer and the third stainless steel plating layer form the stainless steel plating area, and the lower section of the inner wall of the large hole portion is the non-stainless steel plating area. The outer peripheral surface of the first ring portion is welded and connected to the first stainless steel plating layer, the upper surface of the first ring portion is welded and connected to the second stainless steel layer, and the outer peripheral surface of the second ring portion is welded and connected to the third stainless steel plating layer.

[0011] Optionally, the thickness of the first stainless steel plating layer, the second stainless steel layer and the third stainless steel plating layer is 2μm - 3μm.

[0012] Optionally, the lower surface of the valve core is provided with a copper plating layer, and is welded and connected to the upper end surface of the first nozzle through the copper plating layer.

[0013] Optionally, the thickness of the copper plating layer on the lower surface of the valve core is 2μm - 3μm.

[0014] Optionally, the valve needle and the inner wall of the first inner hole are slidably matched in the axial direction to guide the valve needle.

[0015] Optionally, a gap is left between the outer peripheral surface of the upper end of the valve core and the hole wall of the upper end of the second inner hole, and at least part of the gap is filled with the melted solder; a chamfer is provided at the outer edge of the upper surface of the first ring portion, and the chamfered area is filled with the melted solder.

[0016] Optionally, the upper end of the valve core includes a cylindrical section with a diameter smaller than that of the second inner hole and a tapered surface transition section.

[0017] Optionally, the valve seat is made of brass, and the first connecting pipe and the second connecting pipe are made of red copper.

[0018] To achieve the above another object, the present invention provides a method for manufacturing an electronic expansion valve, including the following steps:

[0019] Machining a first inner hole, a second inner hole and a diversion cavity on a valve seat made of copper;

[0020] Plating stainless steel on a partial area of the second inner hole of the valve seat to form a stainless steel coating area and a non-stainless steel coating area on the hole wall of the second inner hole;

[0021] Machining the valve core from a stainless steel bar stock, and reserving machining allowance for finish boring the third inner hole during the machining process;

[0022] Installing the valve core into the valve seat so that the valve core is matched with the stainless steel coating area of the valve seat;

[0023] Installing the first connecting pipe made of copper and the second connecting pipe made of copper into the valve seat so that the insertion end of the first connecting pipe is matched with the non-stainless steel coating area of the valve seat;

[0024] Performing tunnel furnace or flame brazing;

[0025] Performing coaxial finish boring on the first inner hole of the valve seat and the third inner hole of the valve core;

[0026] Installing a valve needle made of stainless steel into the first inner hole of the valve seat.

[0027] For the electronic expansion valve provided by the present invention, the valve seat, the first connecting pipe and the second connecting pipe are made of copper, the valve core and the valve needle are made of stainless steel, and a part of the inner surface of the valve seat is plated with a stainless steel layer. According to the characteristic that the closer the materials are, the better the weldability is, after the inner surface of the valve seat is plated with the stainless steel layer, the welding difficulty with the stainless steel valve core can be reduced. At the same time, through the non-stainless steel coating, the welding performance between the valve seat and the first connecting pipe can be ensured, so that the solder filling of the entire welding surface is denser, the risk of internal leakage is reduced, and the internal leakage performance of the electronic expansion valve is optimized; moreover, the valve core is made of stainless steel material, and when it is matched with the valve needle made of the same stainless steel material, the hardness resistance is improved, and the valve port is not easily damaged by the accumulation of impurities and the extrusion force of the valve needle.

[0028] In addition, before welding the valve seat plated with stainless steel to the stainless steel valve core, it can effectively protect the inner surface of the copper valve seat from corrosion and oxidation, enabling better corrosion resistance and oxidation resistance at the weld. In terms of solder selection, the silver content in the solder can be reduced or eliminated, thereby improving the welding economy between the valve seat and the valve core. Brief Description of the Drawings

[0029] Figure 1 FIG. 1 is a schematic structural diagram of an electronic expansion valve provided by an embodiment of the present invention;

[0030] Figure 2 FIG. 2 is a schematic structural diagram of the valve needle cooperating with the valve core;

[0031] Figure 3 FIG. 3 is Figure 1 an axonometric view of the valve core shown in FIG. 1;

[0032] Figure 4 FIG. 4 is Figure 1 an axonometric view of the valve core shown in FIG. 1 from another perspective;

[0033] Figure 5 FIG. 5 is a schematic structural diagram of the valve seat

[0034] Figure 6 FIG. 6 is a schematic structural diagram of the valve core, the first connecting pipe, and the second connecting pipe installed on the valve seat;

[0035] Figure 7 FIG. 7 is Figure 6 a partial enlarged view of part I in FIG. 6;

[0036] Figure 8 FIG. 8 is a process flow chart of a manufacturing method of an electronic expansion valve provided by an embodiment of the present invention.

[0037] In the figures:

[0038] 10 - valve body

[0039] 11 - bellows

[0040] 12 - valve stem

[0041] 13 - valve seat

[0042] 131 - first inner hole

[0043] 132 - second inner hole

[0044] 1321 - large hole part

[0045] 1322 - small hole part

[0046] 1323 - step surface

[0047] 14 - valve needle

[0048] 15 - Valve core

[0049] 151 - First ring part

[0050] 1511 - Cylindrical section

[0051] 1512 - Conical surface transition section

[0052] 152 - Second ring part

[0053] 153 - Third inner hole

[0054] 16 - First connecting pipe

[0055] 17 - Second connecting pipe

[0056] 20 - Coil component Detailed implementation manners

[0057] In order to enable those skilled in the art of this technology to better understand the solution of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0058] In this article, terms such as "upper, lower, inner, outer" are established based on the positional relationship shown in the accompanying drawings. Depending on the different accompanying drawings, the corresponding positional relationship may also change accordingly. Therefore, it cannot be understood as an absolute limitation of the protection scope; moreover, relational terms such as "first" and "second" are only used to distinguish one component with the same name from another, and do not necessarily require or imply any such actual relationship or order between these components.

[0059] Please refer to Figure 1 、 Figure 2 , Figure 1 which is a schematic structural diagram of an electronic expansion valve provided by an embodiment of the present invention; Figure 2 which is a schematic structural diagram of the valve needle cooperating with the valve core.

[0060] In a specific embodiment, the electronic expansion valve provided by the present invention is a speed-reducing electronic expansion valve, which can be widely applied to refrigeration and heating devices or equipment such as air conditioners, heat pump water heaters, chillers, vending machines, ice makers, supermarket freezers, refrigerators, etc.

[0061] This speed-reducing electronic expansion valve mainly consists of two major parts: a valve body 10 and a coil component 20. The valve body 10 is used to regulate the flow rate, and the coil component 20 is used to drive the valve body 10 to perform the action of regulating the flow rate. Among them, the valve body 10 has core components such as a valve seat 13, a valve core 15, a valve stem 12, a valve needle 14, a bellows 11, a first connecting pipe 16, and a second connecting pipe 17. The coil component 20 has a permanent magnet stepper motor, a gear reduction mechanism with a speed-reducing function, and a screw pair structure that converts the rotational motion of the motor into the vertical motion of the lead screw.

[0062] During operation, the stepper motor is driven to rotate by a high-pulse-frequency current, directly driving the gear reducer, and through the transmission of the screw pair and the bellows, the valve needle 14 rises or falls, thereby changing the opening degree of the valve port to automatically regulate the flow rate of the refrigerant and keep the refrigerant circuit system in the best state all the time.

[0063] Please then refer to Figures 3 to 7 , Figure 3 for Figure 1 the axonometric view of the valve core shown in Figure 4 for Figure 1 the axonometric view of the valve core shown in another perspective in Figure 5 is the structural schematic diagram of the valve seat; Figure 6 is the structural schematic diagram of the valve core, the first connecting pipe, and the second connecting pipe installed on the valve seat; Figure 7 for Figure 6 the partial enlarged view of part I in

[0064] The valve seat 13 is made of brass material, and a diversion cavity is provided inside it. A first inner hole 131 is provided at the upper part of the diversion cavity, and a second inner hole 132 is provided at the lower part of the diversion cavity. The first inner hole 131 and the second inner hole 132 are on the same axis. Both the first connecting pipe 16 and the second connecting pipe 17 can be made of copper material. The first connecting pipe 16 is a vertical connecting pipe, and its upper end is inserted into the second inner hole 132 of the valve seat and is welded to both the valve seat 13 and the valve core 15. The second connecting pipe 17 is a horizontal connecting pipe, and one end of it is inserted into the lateral opening of the valve seat 13 and is welded to the valve seat 13.

[0065] The valve core 15 is made of stainless steel material. For example, it can be formed by turning a stainless steel bar. The valve core 15 is welded and fixed to the second inner hole 132 of the valve seat 13. A third inner hole 153 is provided on the valve core 15, and the upper end of the third inner hole 153 forms the valve port. A machining allowance for finish boring is reserved in the third inner hole 153 so that after welding is completed, it can be finish bored coaxially with the first inner hole 131.

[0066] The valve needle 14 is made of stainless steel material. It passes through the first inner hole 131 from top to bottom and is in sliding fit with the inner wall of the first inner hole 131 in the axial direction to guide the valve needle 14. The valve needle 14 realizes the flow rate regulation function by cooperating with the valve port.

[0067] The second inner hole 132 of the valve seat 13 is provided with a stainless steel coating area and a non-stainless steel coating area on the hole wall. The valve core 15 is welded to the stainless steel coating area through its outer surface, and the first connecting pipe 16 is welded to the non-stainless steel coating area through the outer surface of its insertion end. The upper end surface of the first connecting pipe 16 is also welded to the lower surface of the valve core 15.

[0068] The above-mentioned non-stainless steel coating area refers to the area on the inner wall of the valve seat 13 where no stainless steel coating is designed and the copper material is still retained to facilitate welding with the first connecting pipe 16.

[0069] Specifically, the valve core 15 is mainly composed of an integrally formed first ring portion 151 and a second ring portion 152. The outer diameter of the first ring portion 151 is larger than that of the second ring portion 152, and the height of the second ring portion 152 is greater than that of the first ring portion 151. The second inner hole 132 of the valve seat 13 includes a large hole portion 1321 and a small hole portion 1322. A step surface 1323 is formed between the large hole portion 1321 and the small hole portion 1322. The inner wall of the large hole portion 1321 is provided with a first stainless steel coating a in the upper section, the step surface 1323 is provided with a second stainless steel layer b, and the inner wall of the small hole portion 1322 is provided with a third stainless steel coating c. The first stainless steel coating a, the second stainless steel layer b, and the third stainless steel coating c form a stainless steel coating area with a thickness of 2μm - 3μm. The lower section of the inner wall of the large hole portion 1321 is a non-stainless steel coating area d.

[0070] The outer peripheral surface of the first ring portion 151 is welded to the first stainless steel coating a, the upper surface of the first ring portion 151 is welded to the second stainless steel layer b, the outer peripheral surface of the second ring portion 152 is welded to the third stainless steel coating c, and the outer surface of the insertion end of the first connecting pipe 16 is welded to the non-stainless steel coating area d.

[0071] At the same time, the lower surface of the valve core 15 is provided with a copper plating layer e with a thickness of 2μm - 3μm, and the upper end surface of the first connecting pipe 16 is welded to the copper plating layer e of the valve core 15.

[0072] The valve seat 13 can be plated with stainless steel by electroplating or electroless plating, etc. Before plating stainless steel, surface treatment of the copper body is required, including removing oil stains, oxide scales, and copper rust. The types of electroplated stainless steel can be selected from low-carbon steel, high-strength steel, etc. After the valve seat 13, the valve core 15, the first connecting pipe 16, and the second connecting pipe 17 are assembled, tunnel furnace or flame brazing is carried out.

[0073] According to the characteristic that the closer the materials are, the relatively better the weldability, plating a stainless steel layer on the inner surface of the valve seat 13 can reduce the welding difficulty between the valve seat 13 and the stainless steel valve core 15. After the valve seat 13 is plated with stainless steel, before welding with the stainless steel valve core 15, it can effectively protect a part of the inner surface of the brass valve seat 13 from corrosion and oxidation. In terms of solder selection, a solder with a reduced or eliminated silver content in the solder can be used. For example, the valve core 15 can be made of 304 stainless steel. Therefore, solders such as A302 or A304 can be used for welding to improve the welding economy between the valve seat 13 and the valve core 15. Moreover, the process of electroplating the valve seat 13 first and then welding can easily ensure the density of the solder filled in each part and reduce the risk of internal leakage.

[0074] In addition, after the welding of the valve seat 13 component is completed, the first inner hole 131 of the valve seat 13 and the third inner hole 153 of the valve core 15 can be finish-bored to ensure the coaxiality between the valve needle guiding section and the valve port and improve the product operation performance.

[0075] Furthermore, the upper end of the first ring portion 151 has a cylindrical section 1511 and a tapered surface transition section 1512 with a diameter smaller than the diameter of the second inner hole 132. There is a gap between the outer peripheral surfaces of the cylindrical section 1511 and the tapered surface transition section 1512 and the hole wall at the upper end of the second inner hole 132. At least part of this gap is filled with the melted solder. The upper surface of the first ring portion 151 is provided with a chamfer at the outer edge. This chamfer and the right-angle area of the second inner hole 132 form a triangular cavity. After the welding is completed, the inside of the triangular cavity is filled with the melted solder.

[0076] By designing the gap allowance and the triangular cavity, during the welding process, the capillary action can be increased, the solder fluidity can be improved, and after the welding is formed, more solder will accumulate at the positions of the gap allowance and the triangular cavity, providing two welding anchoring points. Moreover, the solder in the gap allowance and the triangular cavity is annular, which is equivalent to providing two locally strengthened sealing parts. Compared with a single-thickness solder layer, a more stable and reliable welding effect can be obtained.

[0077] Please refer to Figure 8 , Figure 8 which is the process flow chart of a method for manufacturing an electronic expansion valve provided by an embodiment of the present invention.

[0078] In addition to the above-mentioned electronic expansion valve, the present invention also provides a method for manufacturing an electronic expansion valve to process and manufacture the electronic expansion valve described above, including the following steps:

[0079] S01: Process the first inner hole 131, the second inner hole 132 and the diversion cavity on the valve seat 13;

[0080] S02: Electroplate a partial area of the second inner hole 132 of the valve seat 13 with stainless steel, so that the hole wall of the second inner hole 132 forms a stainless steel plating area and a non-stainless steel plating area;

[0081] S03: Machine-process the valve core 15 from a stainless steel rod, and reserve machining allowance for finish boring the third inner hole 153 during the machining process;

[0082] S04: Install the valve core 15 into the valve seat 13, so that the valve core 15 is matched with the stainless steel plating area of the valve seat 13;

[0083] S05: Install the first connecting pipe 16 and the second connecting pipe 17 into the valve seat 13, so that the insertion end of the first connecting pipe 16 is matched with the non-stainless steel plating area of the valve seat 13;

[0084] S06: Perform tunnel furnace or flame brazing on the assembled parts;

[0085] S07: Perform coaxial finish boring on the first inner hole 131 of the valve seat 13 and the third inner hole 153 of the valve core 15. Through finish boring, the coaxiality between the valve needle guiding section and the valve port can be ensured, and the action performance of the product can be improved;

[0086] S08: Install the valve needle 14 made of stainless steel into the first inner hole 131 of the valve seat 13.

[0087] The above embodiments are only the preferred solutions of the present invention, and are not specifically limited thereto. On this basis, targeted adjustments can be made according to actual needs to obtain different implementation manners. For example, the above structure and method are not only applicable to the reducing electronic expansion valve, but also applicable to the direct-acting electronic expansion valve, etc. Since there are many possible implementation manners, they will not be exemplified one by one here.

[0088] The present invention improves the welding processability and sealing effect with the stainless steel valve core 15, and at the same time improves the economy of solder selection by plating a stainless steel layer on the surface of the valve seat 13 for mating with the stainless steel valve core 15, achieving the effect of improving the internal leakage performance of the valve body at low cost.

[0089] The above has introduced the electronic expansion valve and manufacturing method provided by the present invention in detail. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An electronic expansion valve, comprising a valve body (10) for flow regulation and a coil component (20) for driving. The valve body (10) includes a valve seat (13), a valve core (15), a valve needle (14), a first connecting pipe (16), and a second connecting pipe (17). A diversion cavity is provided inside the valve seat (13). A first inner hole (131) is provided in the upper part of the diversion cavity, and a second inner hole (132) is provided in the lower part of the diversion cavity. The valve core (15) is fixedly welded to the second inner hole (132). The valve core (15) is provided with a third inner hole (153). The upper end of the third inner hole (153) forms a valve port. The valve needle (14) passes through the first inner hole (131) and cooperates with the valve port. It is characterized in that, The valve seat (13), the first connecting pipe (16) and the second connecting pipe (17) are made of copper, and the valve core (15) and the valve needle (14) are made of stainless steel; on the inner wall of the second inner hole (132) of the valve seat (13), there are a stainless steel plating area and a non-stainless steel plating area. The valve core (15) is welded to the stainless steel plating area through its outer surface; the first connecting pipe (16) is welded to the non-stainless steel plating area through the outer surface of its insertion end, and the upper end surface of the first connecting pipe (16) is welded to the lower surface of the valve core (15).

2. The electronic expansion valve according to claim 1, characterized in that, The valve core (15) includes an integrally formed first ring portion (151) and a second ring portion (152). The outer diameter of the first ring portion (151) is larger than that of the second ring portion (152), and the height of the second ring portion (152) is greater than that of the first ring portion (151); the second inner hole (132) of the valve seat (13) includes a large hole portion (1321) and a small hole portion (1322), and a step surface (1323) is formed between the large hole portion (1321) and the small hole portion (1322); on the upper section of the inner wall of the large hole portion (1321), there is a first stainless steel plating layer (a), the step surface (1323) is provided with a second stainless steel layer (b), and the inner wall of the small hole portion (1322) is provided with a third stainless steel plating layer (c). The first stainless steel plating layer (a), the second stainless steel layer (b) and the third stainless steel plating layer (c) form the stainless steel plating area, and the lower section of the inner wall of the large hole portion (1321) is the non-stainless steel plating area (d); the outer peripheral surface of the first ring portion (151) is welded to the first stainless steel plating layer (a), the upper surface of the first ring portion (151) is welded to the second stainless steel layer (b), and the outer peripheral surface of the second ring portion (152) is welded to the third stainless steel plating layer (c).

3. The electronic expansion valve according to claim 2, wherein The thickness of the first stainless steel plating layer (a), the second stainless steel layer (b) and the third stainless steel plating layer (c) is 2μm - 3μm.

4. The electronic expansion valve according to claim 1, wherein The lower surface of the valve core (15) is provided with a copper plating layer (e), and is welded to the upper end surface of the first connecting pipe (16) through the copper plating layer (e).

5. The electronic expansion valve according to claim 4, wherein, The thickness of the copper plating layer (e) on the lower surface of the valve core (15) is 2μm - 3μm.

6. The electronic expansion valve according to claim 1, characterized in that, The valve needle (14) is in sliding fit with the inner wall of the first inner hole (131) in the axial direction to guide the valve needle (14).

7. The electronic expansion valve according to claim 2, characterized in that, There is a gap between the outer peripheral surface of the upper end of the valve core (15) and the inner wall of the upper end of the second inner hole (132), and at least part of the gap is filled with the melted solder; a chamfer is provided at the outer edge of the upper surface of the first ring portion (151), and the chamfer area is filled with the melted solder.

8. The electronic expansion valve according to claim 7, wherein The upper end of the valve core (15) includes a cylindrical section (1511) with a diameter smaller than the diameter of the second inner hole (132) and a conical surface transition section (1512).

9. The electronic expansion valve according to any one of claims 1 to 8, characterized in that, The valve seat (13) is made of brass, and the first connecting pipe (16) and the second connecting pipe (17) are made of red copper.

10. A method for manufacturing an electronic expansion valve, comprising the following steps: Machining a first inner hole (131), a second inner hole (132) and a diversion cavity on a valve seat (13) made of copper; Plating stainless steel on a partial area of the second inner hole (132) of the valve seat (13) so that the hole wall of the second inner hole (132) forms a stainless steel plating area and a non-stainless steel plating area; Machining and forming a valve core (15) from a stainless steel bar stock, and reserving a machining allowance for finish boring the third inner hole (153) thereon during the machining process; Installing the valve core (15) into the valve seat (13) so that the valve core (15) is matched with the stainless steel plating area of the valve seat (13); Installing a first connecting pipe (16) made of copper and a second connecting pipe (17) made of copper into the valve seat (13) so that the insertion end of the first connecting pipe (16) is matched with the non-stainless steel plating area of the valve seat (13); Performing tunnel furnace or flame brazing on the assembled parts; Performing coaxial finish boring on the first inner hole (131) of the valve seat (13) and the third inner hole (153) of the valve core (15); Inserting a valve needle (14) made of stainless steel into the first inner hole (131) of the valve seat (13).