Integrally-formed spring for engine valve and heat treatment method

Abstract

The invention relates to the technical field of spring heat treatment, in particular to an integrally-formed spring for an engine valve and a heat treatment method.The heat treatment method comprises the steps that a partition compression strategy is adopted for a wound spring, acoustic emission signals and stress values are synchronously collected, and a defect area or a stress concentration area is marked; determining and marking a stress concentration area or judging that initial winding parameter setting is unreasonable; for a defect area or a stress concentration area, pulse magnetic field repairing or double-stage partition induction tempering compensation is triggered; judging whether the initial winding parameters or the preset magnetic field parameters are reasonably set according to the Vickers hardness and the fatigue life attenuation rate, and determining whether to adjust the preset magnetic field parameters; judging whether a penetrating crack or a high-stress belt exists in the spring or not, and determining whether a cladding triggering condition is achieved or not; and extracting the inherent frequency of the spring to determine whether the engine can cause spring resonance in the valve. Inherent defects and heat treatment parameter setting problems are distinguished through compression detection, and the resonance characteristic of the spring is optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of spring heat treatment, and particularly relates to an integrally formed spring for an engine valve and a heat treatment method therefor. Background Art

[0002] The function of the valve is to specifically be responsible for inputting fuel into the engine and discharging exhaust gas. The function of the valve spring is to rely on the tension of its spring to quickly return the opened valve to the closed position, prevent the valve from generating a gap due to inertial force during the movement of the engine, ensure that the valve can be closely attached in the closed state, and also prevent the valve from being damaged due to jumping during vibration and thus destroying the sealing performance.

[0003] Chinese Patent Publication No.: CN114700440A discloses a processing method for an engine valve spring. The processing method includes: inspection of spring wire material → winding → stress relief tempering → induction heating quenching, induction heating tempering → end face grinding → chamfering the inner corner → shot peening → dot painting → hot pressing → full inspection → rust prevention → finished product inspection → packaging; in the step of inspecting the spring wire material, the content of non-metallic inclusions in the spring wire material is controlled to improve the purity of the steel used for the spring wire; in the step of induction heating quenching, the valve spring is first subjected to induction heating and then quenched by rapid oil cooling; in the step of induction heating tempering, the valve spring is first subjected to induction heating and then air-cooled to room temperature. It can be seen that the processing method for the engine valve spring has the following problems: It ignores the possibility that the spring after winding still has inherent defects after quenching and tempering, that is, the structural problems caused by the winding process itself. Summary of the Invention

[0004] For this reason, the present invention provides an integrally formed spring for an engine valve and a heat treatment method therefor, so as to overcome the problem that the spring still has inherent defects after quenching and tempering due to the structural problems caused by the winding process itself in the prior art.

[0005] To achieve the above object, the present invention provides a heat treatment method for an integrally formed spring for an engine valve, including: Selecting high-performance alloy steel wire and winding the wire according to the initial winding parameters, adopting a zone compression strategy for the wound spring, and performing different degrees of compression on the end closely wound area, the middle closely wound area and the two side loosely wound areas of the spring; During the zone compression process, acoustic emission signals and stress values are synchronously collected, and the risk of material defects in the closely wound area or the loosely wound area is judged according to the stress change and acoustic emission energy to mark the defective area, or, the stress concentration area is judged according to the strain gradient of adjacent areas, and the marked stress concentration area or the unreasonable setting of the initial winding parameters is determined according to the determination result of the pitch change; For defect areas or stress concentration areas, different repair strategies are determined according to the acoustic emission energy and stress changes to trigger pulsed magnetic field repair until the acoustic detection requirements are met, or, two-stage zoned induction tempering compensation is carried out according to the preset magnetic field parameters and the stage duration of the second stage is adjusted according to the retained austenite content in the spring; For springs after compression detection or repair tempering, judge whether the initial winding parameters or the preset magnetic field parameter settings are reasonable according to the Vickers hardness and fatigue life attenuation rate, and determine whether to adjust the preset magnetic field parameters in different stages; Judge whether there are through cracks or high stress zones in the spring according to the distribution of defect areas and stress concentration areas, and determine whether the cladding trigger condition is met according to the judgment result and the corresponding strain gradient and acoustic emission signal energy; Detect the spring after heat treatment and extract the natural frequency of the spring to determine whether the operating frequency of the engine will cause resonance of the spring in the valve.

[0006] Further, the process of marking the defect area includes, Calculate the stress change in the closely wound area or the loosely wound area according to the stress values of the closely wound area or the loosely wound area measured before and after the spring is divided into zones and compressed; If the stress change in the closely wound area or the loosely wound area is greater than the first standard value and the acoustic emission energy suddenly increases, it is judged that there is a risk of material defect in the closely wound area or the loosely wound area, and it is marked as a defect area; The judgment process of the sudden increase in the acoustic emission energy is that the acoustic emission signal appears as a burst signal in a fixed frequency band, and the burst signal is an acoustic emission signal whose rise duration, duration and signal amplitude meet the requirements.

[0007] Further, the process of judging the stress concentration area includes, Calculate the strain gradient according to the stress changes at both ends of the area composed of adjacent closely wound areas and loosely wound areas and the length of the area composed of the adjacent closely wound areas and loosely wound areas; If the strain gradient of any area composed of adjacent closely wound areas and loosely wound areas is greater than the second standard value, after judging that the pitch change of the area composed of the adjacent closely wound areas and loosely wound areas is smooth, mark the area of the spring corresponding to the area composed of the adjacent closely wound areas and loosely wound areas as the stress concentration area.

[0008] Further, the process of judging that the pitch change of the area composed of adjacent closely wound areas and loosely wound areas is smooth includes, Detect the radius of curvature of the area composed of adjacent closely wound areas and loosely wound areas. If the radius of curvature is greater than or equal to three times the wire diameter, it is judged that the pitch change of the area composed of the adjacent closely wound areas and loosely wound areas is smooth; If the radius of curvature is less than three times the wire diameter, it is judged that the pitch change of the area composed of adjacent closely wound areas and loosely wound areas is not smooth, and the initial winding parameter setting is unreasonable.

[0009] Further, the process of determining the triggering of pulsed magnetic field repair includes triggering the pulsed magnetic field repair when the energy of the acoustic emission signal continuously exceeds the threshold and the strain grows non-linearly. If the defective area is in the tightly wound area, an axial magnetic field is applied to the defective area until the acoustic detection requirements are met; if the defective area is in the loosely wound areas on both sides, a radial rotating magnetic field is applied to the defective area until the acoustic detection requirements are met. Among them, the acoustic detection requirement is that when performing secondary compression detection, the decrease in acoustic emission energy is greater than the critical value.

[0010] Further, the process of two-stage zoned induction tempering compensation includes Performing zoned induction tempering compensation for the stress concentration area, and applying pulsed magnetic fields in zones according to preset magnetic field parameters for two-stage tempering; Detecting the retained austenite content in the spring, and when the retained austenite content is greater than the target content, extending the stage time of stage two according to the ratio of the retained austenite content to the target content.

[0011] Further, the process of determining whether the initial winding parameters or the preset magnetic field parameters are reasonable includes Performing Vickers hardness test and high-frequency fatigue test on the spring after compression detection or repair tempering, and calculating the fatigue life attenuation rate according to the results of the high-frequency fatigue test; When the Vickers hardness is within the appropriate range and the fatigue life attenuation rate is less than zero, it is determined that the initial winding parameters and the tempering parameters are set reasonably; When the Vickers hardness is not within the appropriate range, it is determined that the tempering parameter setting is unreasonable and the tempering parameter is adjusted, or the initial winding parameter setting is unreasonable according to whether the fatigue life attenuation rate is less than half; Among them, if the Vickers hardness is less than the minimum value of the range, the tempering temperature is reduced by adjusting the preset magnetic field parameter in stage one; if the Vickers hardness is greater than the maximum value of the range, it is determined that the spring toughness is insufficient, and the tempering duration is increased by adjusting the preset magnetic field parameter in stage two.

[0012] Further, after the end tightly wound area, the middle tightly wound area and the loosely wound areas on both sides of the spring are compressed to different degrees; According to whether there are adjacent defective areas or stress concentration areas, it is determined that the wound spring has a through crack or a high stress zone; When the strain gradient in the area composed of adjacent tightly wound areas and loosely wound areas is greater than the third standard value, the energy of the acoustic emission signal continuously exceeds the threshold, and there is a through crack or a high stress zone, the cladding trigger condition is achieved, and laser cladding compensation is performed in the inner measurement area of the spring.

[0013] Further, extract the first six natural frequencies of the spring, If the ratio of any order frequency to the engine operating frequency is not within the resonance range, it is determined that the valve opening frequency avoids the resonance peak. If the ratio of any order frequency to the engine operating frequency falls within the resonance range, it is determined that the design parameters of the spring in the non-uniform pitch spiral structure need to be adjusted, and the design parameters include the lengths and pitches of the closely wound area and the sparsely wound area.

[0014] An integrally formed spring for an engine valve, comprising: The spring is divided into an end closely wound area, a middle closely wound area, and two side sparsely wound areas. The end closely wound areas are located at both ends of the spring, the middle closely wound area is located in the middle of the spring, and the two side sparsely wound areas are located in the areas from both sides of the middle of the spring to the ends; The end closely wound area and the middle closely wound area adopt a close pitch, and the two side sparsely wound areas adopt a sparse pitch.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows. Due to the pitch change of the spring, different potential defects in different regions are targeted and excited through the zoning compression strategy. By combining the acoustic emission signal and stress change analysis, material defects (such as inclusions and microcracks) and process defects (such as pitch mutation and stress concentration) are effectively distinguished, and online non-destructive detection is realized, improving the detection efficiency; the pulsed magnetic field repair is triggered according to the acoustic emission energy grading, realizing non-contact defect repair and avoiding the oxidation risk of traditional heat treatment; the two-stage zoning tempering dynamically adjusts the duration of the second stage according to the retained austenite content, ensuring the balance of hardness and toughness, and improving the service life compared with the traditional tempering process; the Vickers hardness and fatigue life attenuation rate are used as the final inspection indicators to directly feedback the rationality of the initial winding parameters or magnetic field parameters; the cladding trigger condition ensures that local strengthening is only targeted at high-risk regions, reducing material costs and improving production efficiency.

[0016] Furthermore, the present invention realizes the precise identification and positioning of internal defects and stress concentration in the spring through the zoning compression detection method for differential compression strategy and multi-modal signal synchronous acquisition, combines stress changes and acoustic characteristics to sensitively identify the defect areas inside the steel wire, and improves the defect detection rate compared with the traditional uniform compression method; at the same time, due to the pitch difference between the closely wound area and the sparsely wound area of the designed spring, the contact angle during winding needs to change correspondingly, and there may be a high strain gradient area generating geometrically necessary dislocations, resulting in stress concentration areas. This method distinguishes process defects from material defects based on strain gradient calculation and curvature radius verification. When the curvature meets the standard, it clearly determines that the local stress concentration of the spring is not a structural design problem, guides subsequent targeted repair, and improves the accuracy of subsequent heat treatment of the spring.

[0017] Furthermore, applying a magnetic field to the defective area can close microcracks through magneto-induced vibration, and applying a low-frequency gradient magnetic field to the stress area can promote the rearrangement of dislocations. This method repairs defects and performs heat treatment on the spring based on acoustic emission signals and pulsed magnetic fields, accurately identifies material defects through the acoustic emission energy threshold and non-linear growth of strain, and uses magnetic field treatments with different parameters for the densely wound area and the sparsely wound area respectively to match the repair effect with the regional characteristics. Taking the acoustic detection requirement as the repair termination criterion ensures stable repair quality; and promotes the efficient recombination of dislocations through the alternating action of magnetic fields with different intensities, and adjusts the stage duration according to the retained austenite content to improve the adaptability and flexibility of heat treatment.

[0018] Furthermore, when the Vickers hardness is large, it is usually accompanied by a decrease in toughness, which can reflect insufficient tempering in heat treatment. This method determines over-softening or insufficient toughness through the Vickers hardness, combines high-frequency fatigue tests to judge problems in heat treatment or the pre-winding process, can accurately identify and distinguish the fundamental problems existing in the spring, implements a differential adjustment strategy, adjusts the magnetic field parameters to control the tempering temperature to ensure toughness recovery, and avoids over-correction.

[0019] Furthermore, the present invention controls the spring quality based on sectional compression detection. By selective laser melting (SLM), reinforcing materials (ceramic particles) are cladded in local areas of the spring to increase the stiffness of specific parts. The laser power is controlled to decrease from the center to the edge to achieve a continuous change in the particle content from 15% to 0%. The toughness of the matrix is maintained in the low-stress area to form a "rigid-flexible gradient" transition, avoiding the cracking risk of the spring in the engine valve.

[0020] Furthermore, the valve spring is located between the cylinder head and the spring seat at the end of the valve stem. When the working frequency of the valve spring is equal to or an integer multiple of its natural frequency, the valve spring will resonate, increasing the probability of breakage. The present invention uses a variable pitch spring to prevent resonance. By sectional design, the distribution of the natural frequency of the spring is changed, optimizing the resonance characteristics of the spring. By adjusting the ratio of the densely wound area and the sparsely wound area, the dynamic response characteristics of the spring can be precisely controlled; the dense winding design (smaller pitch) in the end dense winding area and the middle dense winding area improves the stiffness and strength at both ends of the spring, enhancing the support stability of the spring during valve operation; the larger pitch is used in the sparsely wound areas on both sides, effectively reducing the stiffness of the middle section of the spring, enabling the spring to better adapt to the high-speed reciprocating motion of the valve; the "dense at both ends and sparse in the middle" sectional structure makes the spring as a whole exhibit a "rigid-flexible combination" mechanical property, ensuring both sufficient supporting force and good buffering performance, effectively avoiding resonance phenomena within the engine operating speed range, and improving the working stability of the valve system. Brief Description of the Drawings

[0021] Figure 1Schematic flowchart of the heat treatment method for the integrally formed spring used for the engine valve in the embodiments of the present invention; Figure 2 Schematic structural diagram of the spring in the embodiments of the present invention; Figure 3 Schematic flowchart for adjusting the preset magnetic field parameters when the preset magnetic field parameters are set unreasonably in the embodiments of the present invention; Figure 4 Schematic flowchart for determining whether the operating frequency of the engine will cause resonance of the valve spring in the embodiments of the present invention. Detailed implementation manners

[0022] In order to make the objectives and advantages of the present invention clearer and more understandable, the present invention will be further described below in conjunction with 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.

[0023] The preferred implementation manners of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these implementation manners are only used to explain the technical principles of the present invention and do not limit the protection scope of the present invention.

[0024] It should be noted that in the description of the present invention, the terms indicating the direction or positional relationship such as "upper", "lower", "left", "right", "inner", "outer", etc. are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0025] In addition, it should also be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0026] Please refer to Figures 1 - 4 as shown Figure 1 Schematic flowchart of the heat treatment method for the integrally formed spring used for the engine valve in the embodiments of the present invention; Figure 2 Schematic structural diagram of the spring in the embodiments of the present invention; Figure 3 Schematic flowchart for adjusting the preset magnetic field parameters when the preset magnetic field parameters are set unreasonably in the embodiments of the present invention; Figure 4 Schematic flowchart for determining whether the operating frequency of the engine will cause resonance of the valve spring in the embodiments of the present invention.

[0027] The present invention provides a heat treatment method for an integrally formed spring for an engine valve, including: Step S1, selecting high-performance alloy steel wire and winding the wire according to initial winding parameters, adopting a zoning compression strategy for the wound spring, and performing different degrees of compression on the end closely wound area, middle closely wound area, and both side loosely wound areas of the spring; Step S2, synchronously collecting acoustic emission signals and stress values during the zoning compression process, judging the material defect risk of the closely wound area or loosely wound area according to the stress change and acoustic emission energy to mark the defect area, or, judging the stress concentration area according to the strain gradient of adjacent areas, and determining whether to mark the stress concentration area or judge that the initial winding parameter setting is unreasonable according to the determination result of the pitch change; Step S3, for the defect area or stress concentration area, determining different repair strategies for triggering pulsed magnetic field repair according to the acoustic emission energy and stress change until the acoustic detection requirements are met, or, performing two-stage zoning induction tempering compensation according to preset magnetic field parameters and adjusting the stage duration of the second stage according to the retained austenite content in the spring; Step S4, judging whether the initial winding parameters or preset magnetic field parameter settings are reasonable for the spring after compression detection or repair tempering, and determining whether to adjust the preset magnetic field parameters in different stages; Step S5, judging whether there are through cracks or high stress zones in the spring according to the distribution of the defect area and stress concentration area, and determining whether the cladding trigger condition is reached according to the determination result and the corresponding strain gradient and acoustic emission signal energy; Step S6, detecting the heat-treated spring, extracting the natural frequency of the spring to determine whether the operating frequency of the engine will cause resonance of the spring in the valve.

[0028] Specifically, the winding process is to wind the high-performance alloy steel wire according to the initial winding parameters by using a spring coiling machine, winding in a right-handed direction, and visually checking for no rust or damage; In this embodiment, the selected high-performance alloy steel wire is high-carbon chromium silicon alloy steel (SAE 9254) or nickel-titanium memory alloy (Ni-Ti); Based on the engine speed spectrum analysis, a non-uniform spiral structure is designed, and the valve spring is divided into a high stress section and a low stress section; The high stress section is located in the end area and middle area of the valve spring, and the low stress section is located in the area from both sides of the middle of the valve spring to the end. A closely wound pitch is adopted in the high stress section, and a loosely wound pitch is adopted in the low stress section; Adopting a zoning compression strategy for the wound spring, and performing different degrees of compression on the end closely wound area, middle closely wound area, and both side loosely wound areas of the spring according to the corresponding compression strategy for different areas of the spring; The compression amount of the end closely wound area accounts for 30% of the free height, the compression amount of the two side loosely wound areas accounts for 50% of the free height, and the compression amount of the middle closely wound area accounts for 20% of the free height.

[0029] Specifically, in the present invention, there is a pitch change in the spring. By means of the zoning compression strategy, potential defects in different regions are targeted to be excited. Combining the analysis of acoustic emission signals and stress changes can effectively distinguish material defects (such as inclusions, microcracks) from process defects (such as pitch mutations, stress concentrations), and realizing online non-destructive detection improves the detection efficiency; the pulsed magnetic field repair is triggered according to the grading of acoustic emission energy, realizing non-contact defect repair and avoiding the oxidation risk of traditional heat treatment; the two-stage zoning tempering dynamically adjusts the duration of the second stage according to the retained austenite content, ensuring the balance between hardness and toughness and improving the service life compared with the traditional tempering process; taking the Vickers hardness and the fatigue life attenuation rate as the final inspection indicators directly reflects the rationality of the initial winding parameters or magnetic field parameters; the cladding triggering conditions ensure that local strengthening is only targeted at high-risk areas, reducing material costs and improving production efficiency.

[0030] During the zoning compression process, stress and acoustic emission signals are synchronously collected. The local strain distribution is measured by a fiber Bragg grating strain sensor, and the acoustic emission signal is captured by an acoustic emission sensor. The acoustic emission signal is a microscopic yield signal. In implementation, the microscopic yield signal emitted by the spring during the compression process within the frequency range of 150 - 500 kHz is captured by an acoustic emission sensor.

[0031] In this embodiment, the two end closely wound areas and one middle closely wound area of the spring are collectively referred to as the closely wound area, and the two side loosely wound areas of the spring are collectively referred to as the loosely wound area.

[0032] Calculate the stress change of the closely wound area or the loosely wound area according to the stress value of the closely wound area or the loosely wound area measured before and after the zoning compression of the spring. If the stress change of the closely wound area or the loosely wound area is greater than the first standard value and the acoustic emission energy suddenly increases, it is determined that there is a risk of material defects in the closely wound area or the loosely wound area, and it is marked as a defect area. Specifically, the determination process of the sudden increase in acoustic emission energy is that a burst signal appears in the 200 - 400 kHz frequency band of the acoustic emission signal. The burst signal is an acoustic emission signal with a rising duration < 1 μs, a duration < 50 μs, and a signal amplitude 20 dB higher than the background noise. In implementation, a broadband sensor is used to capture the original voltage signal V(t). The background noise energy En is calculated by taking the first 100 ms of no-load signal. The acoustic emission signal energy Ea after removing the background noise energy is obtained by integrating the signal within the detection window (t1, t2). During the spring compression detection process, the acoustic emission signal waveform is drawn according to the acoustic emission signal energy Ea. Ea = ; It represents the integral of the instantaneous power captured by the sensor over time within the time window (t1, t2). In the formula, R represents the input impedance of the sensor, which is equal to the equivalent resistance at the output end of the acoustic emission sensor and is used to convert the voltage signal V(t) output by the sensor into a power signal.

[0033] Calculate the strain gradient according to the stress change at both ends of the region composed of adjacent closely wound regions and loosely wound regions and the length of the corresponding region composed of adjacent closely wound regions and loosely wound regions. The strain gradient is equal to the strain difference of the stress change at both ends divided by the length of the corresponding region. If the strain gradient of any region composed of adjacent closely wound regions and loosely wound regions is greater than the second standard value, after determining that the pitch change of the region composed of adjacent closely wound regions and loosely wound regions is smooth, mark the region of the spring corresponding to the region composed of adjacent closely wound regions and loosely wound regions as a stress concentration region. Among them, the first standard value is 0.8%, and the second standard value is 10% / mm.

[0034] The process of determining that the pitch change of the region composed of adjacent closely wound regions and loosely wound regions is smooth includes using an optical instrument curvature radius tester to detect the curvature radius of the region composed of adjacent closely wound regions and loosely wound regions. If the curvature radius is greater than or equal to three times the wire diameter, it is determined that the pitch change of the region composed of adjacent closely wound regions and loosely wound regions is smooth. If the curvature radius is less than three times the wire diameter, it is determined that the pitch change of the region composed of adjacent closely wound regions and loosely wound regions is not smooth, and the initial winding parameters are set unreasonably. The wire diameter is the wire diameter of the high-performance alloy steel wire.

[0035] Specifically, the present invention realizes the accurate identification and positioning of internal defects and stress concentration in the spring through the partition compression detection method for differential compression strategy and multi-modal signal synchronous acquisition, combines stress change and acoustic characteristics to sensitively identify the defect area inside the steel wire, and improves the defect detection rate compared with the traditional uniform compression method; at the same time, due to the pitch difference between the closely wound region and the loosely wound region of the designed spring, the contact angle during winding needs to change correspondingly, and there may be geometrically necessary dislocations in the high strain gradient region, resulting in stress concentration regions. This method distinguishes process defects and material defects based on strain gradient calculation and curvature radius verification, clearly determines local stress concentration in the spring rather than a structural design problem when the curvature meets the standard, guides subsequent targeted repair, and improves the accuracy of subsequent heat treatment of the spring.

[0036] During the compression detection process, in response to the risk of material defects, when the acoustic emission signal energy Ea continuously exceeds the threshold and the strain grows non-linearly, trigger pulsed magnetic field repair. If the defective area is in the tightly wound area, apply an axial magnetic field of 1.2 T to the defective area until the acoustic detection requirements are met; If the defective area is in the loosely wound areas on both sides, apply a radial rotating magnetic field of 0.8 T to the defective area until the acoustic detection requirements are met; When the acoustic detection requirement is secondary compression detection, the decrease in acoustic emission energy is greater than the critical value; Among them, the duration of the continuous exceeding is 5 μs, the threshold is 50 dB, and the critical value is 40%.

[0037] Perform zonal induction tempering compensation for the stress concentration area, apply a pulsed magnetic field for two-stage tempering to promote the rearrangement of dislocations; The spring after compression detection passes through a Helmholtz coil (magnetic field uniformity ±2%); Apply a pulsed magnetic field for two-stage tempering according to the preset magnetic field parameters in zones. The preset magnetic field parameters for the first stage are (1.5 T, 10 Hz), the stage duration is 10 min, and the preset magnetic field parameters for the second stage are (0.5 T, 5 Hz), and the stage duration is 20 min; Specifically, apply the pulsed magnetic field in zones according to the preset magnetic field parameters during the tempering stage, and the magnetic field direction forms an angle of 45 ± 5° with the spring axis; Detect the retained austenite content in the spring by online X-ray diffraction (XRD), and adjust the stage duration of the second stage according to the retained austenite content; Specifically, when the retained austenite content is greater than the target content, extend the stage time of the second stage according to the ratio of the retained austenite content to the target content; Among them, the target content is 3%.

[0038] Specifically, applying a magnetic field to the defective area can close microcracks through magneto-vibration, and applying a low-frequency gradient magnetic field to the stress area can promote the rearrangement of dislocations. This method repairs defects and performs heat treatment on the spring based on acoustic emission signals and pulsed magnetic fields, accurately identifies material defects through the acoustic emission energy threshold and strain non-linear growth, uses magnetic field treatments with different parameters for the tightly wound area and the loosely wound area respectively to match the repair effect with the area characteristics, uses the acoustic detection requirements as the repair termination standard to ensure stable repair quality; and promotes the efficient recombination of dislocations through the alternating action of magnetic fields with different intensities, and adjusts the stage duration according to the retained austenite content to improve the adaptability and flexibility of heat treatment.

[0039] Perform Vickers hardness inspection and high-frequency fatigue test on the spring after compression detection or repair tempering, compare the experimental results with those of the spring without compression detection after winding, and calculate the fatigue life attenuation rate according to the high-frequency fatigue test results; If the Vickers hardness is within the appropriate range and the fatigue life attenuation rate is less than zero, it is determined that the initial winding parameters and the preset magnetic field parameters are reasonably set; If the Vickers hardness is not within the appropriate range, but the fatigue life attenuation rate is less than half (50%), it is determined that the preset magnetic field parameters are unreasonably set, and the preset magnetic field parameters are adjusted; Specifically, if the Vickers hardness HV is less than the minimum value of the range, it is determined that the preset magnetic field parameters are unreasonably set, resulting in excessive softening of the spring, and the tempering temperature is reduced by adjusting the preset magnetic field parameters in the first stage; In implementation, the magnetic field intensity of the preset magnetic field parameters in the first stage is reduced according to the ratio of the Vickers hardness to the minimum value of the range; If the Vickers hardness HV is greater than the maximum value of the range, it is determined that the spring has insufficient toughness, and the tempering duration is increased by adjusting the preset magnetic field parameters in the second stage; In implementation, the stage duration of the second stage is increased according to the ratio of the Vickers hardness to the maximum value of the range; When the Vickers hardness is not within the appropriate range and the fatigue life attenuation rate is greater than half (50%), it is determined that the initial winding parameters are unreasonably set, resulting in a decrease in the fatigue limit of the spring material after winding; Among them, the appropriate range consists of a minimum value of the range and a maximum value of the range. The minimum value of the range is 450, and the maximum value of the range is 500.

[0040] Specifically, when the Vickers hardness is large, it is usually accompanied by a decrease in toughness, which can reflect insufficient tempering in heat treatment. This method determines excessive softening or insufficient toughness through the Vickers hardness, combines high-frequency fatigue tests to judge problems in heat treatment or the pre-winding process, can accurately identify and distinguish the fundamental problems of the spring, implement a differential adjustment strategy, adjust the magnetic field parameters to control the tempering temperature to ensure toughness recovery, and avoid overcorrection.

[0041] After different degrees of compression are performed on the end tightly wound area, the middle tightly wound area, and the two side loosely wound areas of the spring, If there are defect areas in both the adjacent tightly wound area and the loosely wound area, it is determined that the wound spring has a through crack; If there are stress concentration areas in both the adjacent tightly wound area and the loosely wound area, it is determined that the wound spring has a high stress zone at the junction of the transition area and the tightly wound area due to the pitch mutation; When the strain gradient in the area composed of the adjacent tightly wound area and the loosely wound area is greater than the third standard value, the acoustic emission signal energy Ea continuously exceeds the threshold, and there is a through crack or a high stress zone, the cladding trigger condition is achieved, and laser cladding compensation is performed in the inner area of the spring; Nanoscale silicon nitride particles are injected through laser cladding. A galvanometer scanning laser head is used to cladding silicon nitride / metal composite powder within a range of 1.5 turns on the inner side of the spring, and the laser power is controlled to decrease from the center to the edge; During implementation, the volume fraction of nano-silicon nitride particles is 15%, and the power from the laser center to the edge is 1000W - 600W; Among them, the third standard value is 15% / mm.

[0042] Specifically, the present invention controls the spring quality based on zonal compression detection. By selective laser melting (SLM), reinforcing materials (ceramic particles) are cladded in local areas of the spring to enhance the stiffness of specific parts. The laser power is controlled to decrease from the center to the edge to achieve a continuous change in the particle content from 15% to 0%. The low-stress area maintains the toughness of the matrix, forming a "rigid-flexible gradient" transition to avoid the cracking risk of the spring in the engine valve.

[0043] Inspect the springs without material defect risks and stress concentration areas, as well as the springs after repair or tempering or cladding, according to the engine operating parameters to determine whether the engine operating frequency will cause valve spring resonance; Based on the engine speed n (rpm), calculate the valve opening frequency f = n / 120 (Hz). Apply a static load to the spring to simulate the state of the spring being compressed by the valve and conduct modal analysis; During modal analysis, extract the first 6 natural frequencies fn of the spring. The natural frequencies fn include f1 to f6; If the ratio of any order of frequency to the engine operating frequency is not within the resonance range, it is determined that the valve opening frequency f avoids the resonance peak; If the ratio of any order of frequency to the engine operating frequency falls within the resonance range, it is determined that the design parameters of the spring in the non-uniform pitch spiral structure need to be adjusted. The design parameters include the lengths and pitches of the closely wound area and the loosely wound area.

[0044] Among them, the resonance range is 0.9 - 1.1.

[0045] An integrally formed spring for an engine valve, comprising: The spring is divided into an end closely wound area, a middle closely wound area, and two side loosely wound areas. The end closely wound area is located at both ends of the spring, the middle closely wound area is located in the middle of the spring, and the two side loosely wound areas are located in the areas from both sides of the middle of the spring to the ends; The end closely wound area and the middle closely wound area adopt a close pitch, and the two side loosely wound areas adopt a loose pitch.

[0046] Specifically, the valve spring is located between the cylinder head and the spring seat at the end of the valve stem. When the operating frequency of the valve spring is equal to or an integer multiple of its natural frequency, the valve spring will resonate, increasing the probability of breakage. The present invention uses a variable pitch spring to prevent resonance. By means of a partition design, the distribution of the natural frequency of the spring is changed, optimizing the resonance characteristics of the spring. By adjusting the ratio of the closely wound area to the sparsely wound area, the dynamic response characteristics of the spring can be precisely controlled. The closely wound design (with a smaller pitch) in the end closely wound area and the middle closely wound area increases the stiffness and strength at both ends of the spring, enhancing the support stability of the spring during valve operation. The larger pitch in the sparsely wound areas on both sides effectively reduces the stiffness in the middle section of the spring, enabling the spring to better adapt to the high-speed reciprocating motion of the valve. The "closely wound at both ends and sparsely wound in the middle" partition structure gives the spring an overall mechanical property of "combining rigidity and flexibility", ensuring both sufficient supporting force and good buffering performance, effectively avoiding resonance phenomena within the engine operating speed range, and improving the operating stability of the valve system.

[0047] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easily understood by those skilled in the art that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

[0048] The above are only the preferred embodiments of the present invention and are not used to limit the present invention; for those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A heat treatment method for an integrally formed spring for an engine valve, characterized in that, Including, Select high-performance alloy steel wire and wind the wire according to the initial winding parameters to obtain a spring. Adopt a zoning compression strategy for the spring, and compress the end winding area, the middle winding area and the two side sparse winding areas of the spring to different degrees; Synchronously collect acoustic emission signals and stress values during the zoning compression process. Judge the material defect risk of the winding area or the sparse winding area according to the stress change and the acoustic emission energy, mark the defective area, or judge the stress concentration area according to the strain gradient of adjacent areas. Determine and mark the stress concentration area or judge that the initial winding parameters are set unreasonably according to the pitch change determination result; For the defective area or the stress concentration area, determine different repair strategies according to the acoustic emission energy and the stress change to trigger pulse magnetic field repair until the acoustic detection requirements are met, or perform two-stage zoning induction tempering compensation according to the preset magnetic field parameters and adjust the stage duration of the second stage according to the retained austenite content in the spring; For the spring after compression detection or repair tempering, judge whether the initial winding parameters or the preset magnetic field parameters are set reasonably according to the Vickers hardness and the fatigue life attenuation rate, and determine whether to adjust the preset magnetic field parameters in different stages; Judge whether there is a through crack or a high stress zone in the spring according to the distribution of the defective area and the stress concentration area, and determine whether the cladding trigger condition is achieved according to the judgment result and the corresponding strain gradient and acoustic emission signal energy; Detect the spring after heat treatment, extract the natural frequency of the spring to determine whether the working frequency of the engine will cause resonance of the spring in the valve.

2. The heat treatment method of the integrally formed spring for an engine valve according to claim 1, characterized in that, The process of marking the defective area includes, Calculate the stress change in the winding area or the sparse winding area according to the stress values of the winding area or the sparse winding area measured before and after the zoning compression of the spring; If the stress change in the winding area or the sparse winding area is greater than the first standard value and the acoustic emission energy suddenly increases, judge that there is a material defect risk in the winding area or the sparse winding area, and mark it as the defective area; The judgment process of the sudden increase in the acoustic emission energy is that the acoustic emission signal appears as a burst signal in a fixed frequency band, and the burst signal is an acoustic emission signal whose rise time, duration and signal amplitude meet the requirements.

3. The heat treatment method of the integrally formed spring for an engine valve according to claim 2, characterized in that, The process of judging the stress concentration area includes, Calculate the strain gradient according to the stress changes at both ends of the area composed of adjacent winding areas and sparse winding areas and the length of the area composed of the corresponding adjacent winding areas and sparse winding areas; If the strain gradient of any area composed of adjacent winding areas and sparse winding areas is greater than the second standard value, after judging that the pitch change of the area composed of the adjacent winding areas and sparse winding areas is smooth, mark the area of the spring corresponding to the area composed of the adjacent winding areas and sparse winding areas as the stress concentration area.

4. The heat treatment method of the integrally formed spring for an engine valve according to claim 3, characterized in that, The process of judging that the pitch change of the area composed of adjacent winding areas and sparse winding areas is smooth includes, Detect the radius of curvature of the area composed of adjacent winding areas and sparse winding areas, compare the radius of curvature with the wire diameter, and judge whether the pitch change of the area composed of adjacent winding areas and sparse winding areas is smooth; When it is judged that the pitch change of the area composed of adjacent winding areas and sparse winding areas is not smooth, it is determined that the initial winding parameters are set unreasonably.

5. The heat treatment method of the integrally formed spring for an engine valve according to claim 4, characterized in that, The process of determining the triggering of pulsed magnetic field repair includes triggering pulsed magnetic field repair when the energy of the acoustic emission signal continuously exceeds the threshold and the strain grows nonlinearly. If the defective area is in the tightly wound area, apply an axial magnetic field to the defective area until the acoustic detection requirements are met. If the defective area is in the loosely wound areas on both sides, apply a radial rotating magnetic field to the defective area until the acoustic detection requirements are met. Among them, when the acoustic detection requirement is secondary compression detection, the decrease in acoustic emission energy is greater than the critical value.

6. The heat treatment method of the integrally formed spring for an engine valve according to claim 5, characterized in that, The process of two-stage zoned induction tempering compensation includes Conduct zoned induction tempering compensation for the stress concentration area, and apply pulsed magnetic fields in zones according to the preset magnetic field parameters for two-stage tempering. Detect the retained austenite content in the spring. When the retained austenite content is greater than the target content, extend the stage time of stage two according to the ratio of the retained austenite content to the target content.

7. The heat treatment method of the integrally formed spring for an engine valve according to claim 6, characterized in that, The process of judging whether the initial winding parameters or the preset magnetic field parameters are set reasonably includes Conduct Vickers hardness inspection and high-frequency fatigue test on the spring after compression detection or repair tempering, and calculate the fatigue life attenuation rate according to the high-frequency fatigue test results. When the Vickers hardness is within the appropriate range and the fatigue life attenuation rate is less than zero, it is judged that the initial winding parameters and tempering parameters are set reasonably. When the Vickers hardness is not within the appropriate range, determine whether the tempering parameter setting is unreasonable by adjusting the tempering parameter according to whether the fatigue life attenuation rate is less than half, or the initial winding parameter setting is unreasonable. Among them, if the Vickers hardness is less than the minimum value of the range, reduce the tempering temperature by adjusting the preset magnetic field parameter of stage one; if the Vickers hardness is greater than the maximum value of the range, it is judged that the spring toughness is insufficient, and increase the tempering duration by adjusting the preset magnetic field parameter of stage two.

8. The heat treatment method of the integrally formed spring for an engine valve according to claim 7, characterized in that, After compressing the tightly wound area at the end, the tightly wound area in the middle, and the loosely wound areas on both sides of the spring to different degrees; Determine whether there is a through crack or a high stress band in the wound spring according to whether there is an adjacent defective area or stress concentration area. When the strain gradient in the area composed of adjacent tightly wound areas and loosely wound areas is greater than the third standard value, the energy of the acoustic emission signal continuously exceeds the threshold, and there is a through crack or a high stress band, the cladding trigger condition is achieved, and laser cladding compensation is performed in the inner measurement area of the spring.

9. The heat treatment method of the integrally formed spring for an engine valve according to claim 8, characterized in that, Extract the first six natural frequencies of the spring. If the ratio of any order frequency to the engine operating frequency is not within the resonance range, it is judged that the valve opening frequency avoids the resonance peak. If the ratio of any order frequency to the engine operating frequency falls within the resonance range, it is judged that the design parameters of the spring in the non-uniform pitch spiral structure need to be adjusted, and the design parameters include the lengths and pitches of the tightly wound area and the loosely wound area.

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