An integrally formed spring for an engine valve and a heat treatment method

Abstract

The present invention relates to the field of spring heat treatment technology, and in particular to an integrally formed spring for an engine valve and a heat treatment method, comprising: adopting a partitioned compression strategy for the wound spring, synchronously collecting acoustic emission signals and stress values, marking defective areas or stress concentration areas, determining the marked stress concentration areas or judging that the initial winding parameter settings are unreasonable; triggering pulse magnetic field repair or two-stage partitioned induction tempering compensation for the defective areas or stress concentration areas; judging whether the initial winding parameters or preset magnetic field parameters are reasonable based on Vickers hardness and fatigue life decay rate, and determining whether the preset magnetic field parameters are adjusted; judging whether the spring has through cracks or high stress bands, and determining whether the cladding trigger condition is met; and extracting the spring's natural frequency to determine whether the engine will cause spring resonance in the valve. The present invention distinguishes inherent defects from heat treatment parameter setting problems through compression testing, and optimizes the resonance characteristics of the spring.

Description

Technical Field

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

[0002] The valve is responsible for introducing fuel into the engine and expelling exhaust gases. The valve spring's function is to quickly return the open valve to the closed position through its tension. This prevents the valve from gapping due to inertia during engine movement, ensuring a tight fit when closed. It also prevents the valve from vibrating and damaging its seal.

[0003] Chinese Patent Publication No. CN114700440A discloses a method for processing engine valve springs, which includes: spring wire material inspection → winding → stress relief tempering → induction hardening and induction tempering → end face grinding → chamfering → shot blasting → painting → hot pressing → full inspection → rust prevention → finished product inspection → packaging. During the spring wire material inspection step, the non-metallic inclusion content in the spring wire material is controlled to improve the purity of the spring wire steel. During the induction hardening step, the valve spring is first induction heated and then subjected to oil quenching. During the induction tempering step, the valve spring is first induction heated and then air cooled to room temperature. Therefore, the engine valve spring processing method has the following problems:

[0004] The possibility that the coiled spring still has inherent defects after quenching and tempering is ignored, that is, structural problems caused by the coiling process itself. Summary of the Invention

[0005] To this end, the present invention provides an integrally formed spring for an engine valve and a heat treatment method, so as to overcome the problem in the prior art that the winding process itself causes structural problems resulting in inherent defects in the spring after quenching and tempering.

[0006] To achieve the above object, the present invention provides a heat treatment method for an integrally formed spring for an engine valve, comprising:

[0007] High-performance alloy steel wire is selected and wound according to the initial winding parameters. A zone compression strategy is adopted for the wound spring, with different degrees of compression applied to the densely wound area at the end, the densely wound area in the middle, and the sparsely wound areas on both sides of the spring.

[0008] During the zone compression process, acoustic emission signals and stress values are collected synchronously. The material defect risk of the densely wound area or the sparsely wound area is determined based on the stress change and acoustic emission energy, and the defect area is marked. Alternatively, the stress concentration area is determined based on the strain gradient of the adjacent area. The stress concentration area is marked based on the pitch change judgment result, or it is determined that the initial winding parameter setting is unreasonable.

[0009] For defective areas or stress concentration areas, different repair strategies are adopted according to the acoustic emission energy and stress changes to trigger pulse magnetic field repair until the acoustic detection requirements are met. Alternatively, two-stage partitioned induction tempering compensation is performed according to preset magnetic field parameters and the duration of the second stage is adjusted according to the retained austenite content in the spring.

[0010] For springs after compression testing or repair and tempering, determine whether the initial winding parameters or preset magnetic field parameters are reasonable based on Vickers hardness and fatigue life decay rate, and determine whether to adjust the preset magnetic field parameters at different stages;

[0011] Determine whether the spring has through cracks or high stress zones based on the distribution of defect areas and stress concentration areas, and determine whether the cladding trigger conditions are met based on the determination results, the corresponding strain gradient, and the acoustic emission signal energy;

[0012] The heat-treated spring is tested and its natural frequency is extracted to determine whether the engine's operating frequency will cause spring resonance in the valve.

[0013] Furthermore, the process of marking defective areas includes,

[0014] Calculate the stress change of the densely wound area or the sparsely wound area according to the stress values of the densely wound area or the sparsely wound area measured before and after the spring is compressed;

[0015] If the stress change in the dense winding area or the sparse winding area is greater than the first standard value and the acoustic emission energy increases suddenly, it is determined that there is a risk of material defects in the dense winding area or the sparse winding area and it is marked as a defective area;

[0016] The process of judging whether the acoustic emission energy suddenly increases is that a burst signal appears in the acoustic emission 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.

[0017] Furthermore, the process of determining the stress concentration area includes:

[0018] Calculating the strain gradient based on the stress changes at both ends of the region composed of the adjacent densely wound region and the sparsely wound region and the length of the region composed of the corresponding adjacent densely wound region and the sparsely wound region;

[0019] If the strain gradient of any area composed of adjacent dense winding areas and sparse winding areas is greater than the second standard value, after determining that the pitch change of the area composed of adjacent dense winding areas and sparse winding areas is smooth, the area composed of the corresponding adjacent dense winding areas and sparse winding areas of the spring is marked as a stress concentration area.

[0020] Furthermore, the process of determining whether the pitch variation of the region consisting of adjacent dense winding regions and sparse winding regions is smooth includes:

[0021] Detecting the curvature radius of an area composed of adjacent dense winding areas and sparse winding areas, and if the curvature radius is greater than or equal to three times the wire diameter, determining that the pitch change of the area composed of adjacent dense winding areas and sparse winding areas is smooth;

[0022] If the curvature radius is less than three times the wire diameter, it is determined that the pitch variation of the region consisting of the adjacent dense winding region and the sparse winding region is not smooth, and the initial winding parameter setting is unreasonable.

[0023] Furthermore, the process of determining to trigger the pulse magnetic field repair includes triggering the pulse magnetic field repair when the energy of the acoustic emission signal continuously exceeds a threshold value and the strain increases nonlinearly;

[0024] If the defect area is in the dense winding area, an axial magnetic field is applied to the defect area until the acoustic detection requirements are met; if the defect area is in the sparse winding areas on both sides, a radial rotating magnetic field is applied to the defect area until the acoustic detection requirements are met;

[0025] The acoustic detection requirement is that during secondary compression detection, the acoustic emission energy decreases by more than a critical value.

[0026] Furthermore, the process of dual-stage partitioned induction tempering compensation includes:

[0027] Perform zoned induction tempering compensation for stress concentration areas, and apply pulsed magnetic fields in zones according to preset magnetic field parameters for two-stage tempering;

[0028] The retained austenite content in the spring is detected. When the retained austenite content is greater than the target content, the stage time of the second stage is extended according to the ratio of the retained austenite content to the target content.

[0029] Furthermore, the process of determining whether the initial winding parameters or the preset magnetic field parameters are reasonable includes:

[0030] Conduct Vickers hardness test and high-frequency fatigue test on springs after compression testing or repair and tempering, and calculate fatigue life attenuation rate based on the high-frequency fatigue test results;

[0031] When the Vickers hardness is within an appropriate range and the fatigue life decay rate is less than zero, it is judged that the initial winding parameters and tempering parameters are reasonably set;

[0032] When the Vickers hardness is not within the appropriate range, the tempering parameters are determined to be unreasonable and the tempering parameters should be adjusted based on whether the fatigue life decay rate is less than half, or the initial winding parameters are set unreasonable;

[0033] 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 parameters 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 the tempering time is increased by adjusting the preset magnetic field parameters of stage two.

[0034] Furthermore, after the end dense winding area, the middle dense winding area and the two side sparse winding areas of the spring are compressed to different degrees;

[0035] Determine whether there are through cracks or high stress zones in the coiled spring based on whether there are adjacent defective areas or stress concentration areas.

[0036] When the strain gradient of the area composed of adjacent densely wound areas and sparsely wound areas is greater than the third standard value, the energy of the acoustic emission signal continues to exceed the threshold, and there are through-cracks or high-stress zones, the cladding triggering conditions are met and laser cladding compensation is performed in the inner area of the spring.

[0037] Furthermore, the first six natural frequencies of the spring are extracted.

[0038] If the ratio of any order frequency to the engine operating frequency is not within the resonance range, the valve opening frequency is judged to avoid the resonance peak;

[0039] 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-equidistant helical structure need to be adjusted, and the design parameters include the length and pitch of the densely wound area and the sparsely wound area.

[0040] An integrally formed spring for an engine valve, comprising:

[0041] The spring is divided into end dense winding areas, middle dense winding areas and two side sparse winding areas. The end dense winding areas are located at both ends of the spring, the middle dense winding area is located in the middle of the spring, and the two side sparse winding areas are located in the area from both sides of the middle of the spring to the ends.

[0042] The end dense winding area and the middle dense winding area adopt a dense winding pitch, and the two side sparse winding areas adopt a sparse winding pitch.

[0043] Compared with the prior art, the beneficial effect of the present invention lies in that, due to the pitch variation of the spring, the potential defects in different areas are targetedly stimulated through the partition compression strategy, and the material defects (such as inclusions, microcracks) and process defects (such as pitch mutation, stress concentration) are effectively distinguished by combining the acoustic emission signal and stress change analysis, and online non-destructive detection is realized to improve the detection efficiency; the pulsed magnetic field repair is triggered according to the acoustic emission energy level to realize non-contact defect repair and avoid the oxidation risk of traditional heat treatment; the two-stage partition tempering dynamically adjusts the length of the second stage through the retained austenite content to ensure the balance between hardness and toughness, and the service life is improved compared with the traditional tempering process; the Vickers hardness and fatigue life decay 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 areas, reducing material costs and improving production efficiency.

[0044] Furthermore, the present invention uses a partitioned compression detection method to implement differentiated compression strategies and synchronously collect multimodal signals, thereby achieving accurate identification and positioning of internal defects and stress concentration in the spring, and combining stress changes and acoustic characteristics to sensitively identify defective areas inside the steel wire, thereby improving the defect detection rate compared with the traditional uniform compression method; at the same time, due to the difference in pitch between the densely wound area and the sparsely wound area of the designed spring, the contact angle of the winding needs to change accordingly during the winding process, and there may be high strain gradient areas that produce geometrically necessary dislocations, resulting in stress concentration areas. This method distinguishes between process defects and material defects based on strain gradient calculation and curvature radius verification, and clearly determines that the local stress concentration of the spring is not a structural design problem when the curvature meets the standard, guiding subsequent targeted repairs and improving the accuracy of subsequent heat treatment of the spring.

[0045] 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 and heat treats spring defects based on acoustic emission signals and pulsed magnetic fields, accurately identifies material defects through acoustic emission energy thresholds and nonlinear strain growth, and uses magnetic field treatments with different parameters for densely wound areas and sparsely wound areas to match the repair effect with regional characteristics. The acoustic detection requirements are used as the repair termination standard to ensure stable repair quality. The alternating action of magnetic fields of different intensities promotes the efficient recombination of dislocations, and the adaptability and flexibility of heat treatment are improved by adjusting the stage length according to the retained austenite content.

[0046] Furthermore, when the Vickers hardness is high, it is usually accompanied by a decrease in toughness, which can provide feedback on insufficient tempering during heat treatment. This method determines excessive softening or insufficient toughness through Vickers hardness, and combines it with high-frequency fatigue testing to judge whether there are problems with the heat treatment or pre-winding process. It can accurately identify and distinguish the fundamental problems of the spring, implement differentiated adjustment strategies, adjust magnetic field parameters to control the tempering temperature to ensure toughness recovery, and avoid excessive correction.

[0047] Furthermore, the present invention controls the quality of the spring based on zoned compression detection, and uses selective laser melting (SLM) to clad reinforcing materials (ceramic particles) in local areas of the spring to improve the stiffness of specific parts. The laser power is controlled to decrease from the center to the edge to achieve a continuous change in particle content from 15% to 0%. The low-stress area maintains the toughness of the matrix, forming a "rigid-flexible gradual" transition, thereby avoiding the risk of cracking the spring in the engine valve.

[0048] Furthermore, the valve spring is located between the cylinder head and the spring seat at the rear 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. The natural frequency distribution of the spring is modified through a zoning design, thereby optimizing the spring's resonance characteristics. Adjusting the ratio of the dense winding area to the sparse winding area can precisely control the spring's dynamic response characteristics. The dense winding design (with a smaller pitch) of the end and middle dense winding areas increases the stiffness and strength of the spring at both ends, enhancing the spring's support stability during valve operation. The sparse winding areas on both sides use a larger pitch, effectively reducing the stiffness of the spring's middle section, allowing the spring to better adapt to the high-speed reciprocating motion of the valve. The "dense at both ends, sparse in the middle" zoning structure gives the spring a "combined rigidity and flexibility" mechanical property, ensuring sufficient support force while also providing good cushioning performance. This effectively avoids resonance within the engine's operating speed range and improves the operating stability of the valve system. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of a process for heat treatment of an integrally formed spring for an engine valve according to an embodiment of the present invention;

[0050] Figure 2 A schematic structural diagram of a spring in an embodiment of the present invention;

[0051] Figure 3 A schematic diagram of a process for adjusting the preset magnetic field parameters when the preset magnetic field parameters are set unreasonably in an embodiment of the present invention;

[0052] Figure 4 2 is a flow chart of determining whether the operating frequency of an engine will cause valve spring resonance in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to make the objects and advantages of the present invention more clearly understood, the present invention is 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.

[0054] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0055] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside", and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying 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. Therefore, it cannot be understood as a limitation on the present invention.

[0056] Furthermore, it should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0057] See also Figures 1-4 As shown, Figure 1 Schematic diagram of a process for heat treatment of an integrally formed spring for an engine valve according to an embodiment of the present invention; Figure 2 A schematic structural diagram of a spring in an embodiment of the present invention; Figure 3 A schematic diagram of a process for adjusting the preset magnetic field parameters when the preset magnetic field parameters are set unreasonably in an embodiment of the present invention; Figure 4 2 is a flow chart of determining whether the operating frequency of an engine will cause valve spring resonance in an embodiment of the present invention.

[0058] The present invention provides a heat treatment method for an integrally formed spring for an engine valve, comprising:

[0059] Step S1: Select a high-performance alloy steel wire and wind it according to the initial winding parameters. A zone compression strategy is applied to the wound spring, and the densely wound area at the end, the densely wound area in the middle, and the sparsely wound areas on both sides of the spring are compressed to varying degrees.

[0060] Step S2: Acoustic emission signals and stress values are collected synchronously during the partition compression process. The material defect risk of the dense winding area or the sparse winding area is determined based on the stress change and the acoustic emission energy, and the defect area is marked. Alternatively, the stress concentration area is determined based on the strain gradient of the adjacent area. The stress concentration area is marked or the initial winding parameter setting is determined to be unreasonable based on the pitch change determination result.

[0061] Step S3: For defective areas or stress concentration areas, trigger pulse magnetic field repair based on acoustic emission energy and stress changes to adopt different repair strategies until the acoustic detection requirements are met, or perform two-stage partitioned induction tempering compensation according to preset magnetic field parameters and adjust the duration of stage two according to the retained austenite content in the spring;

[0062] Step S4: for the spring after compression testing or repair and tempering, judging whether the initial winding parameters or the preset magnetic field parameters are reasonable based on the Vickers hardness and fatigue life decay rate, and determining whether to adjust the preset magnetic field parameters at different stages;

[0063] Step S5: Determine whether the spring has a through crack or a high stress zone based on the distribution of defect areas and stress concentration areas, and determine whether the cladding trigger condition is met based on the determination result and the corresponding strain gradient and acoustic emission signal energy;

[0064] Step S6: testing the heat-treated spring, extracting the natural frequency of the spring to determine whether the operating frequency of the engine will cause spring resonance in the valve.

[0065] Specifically, the winding process is to use a spring coiling machine to coil the high-performance alloy steel wire according to the initial winding parameters, and the winding is clockwise, and there is no rust or damage visually;

[0066] In this embodiment, the high-performance alloy steel wire selected is high-carbon chromium-silicon alloy steel (SAE 9254) or nickel-titanium shape memory alloy (Ni-Ti);

[0067] Based on the engine speed spectrum analysis, a non-equidistant helical structure is designed to divide the valve spring into high-stress and low-stress sections.

[0068] The high stress section is located in the end area and the middle area of the valve spring, and the low stress section is located in the area from both sides of the middle to the end of the valve spring. A dense winding pitch is used in the high stress section, and a sparse winding pitch is used in the low stress section.

[0069] A zone compression strategy is adopted for the wound spring. Corresponding compression strategies are adopted according to different areas of the spring, and different degrees of compression are applied to the densely wound area at the end, the densely wound area in the middle, and the sparsely wound areas on both sides of the spring.

[0070] The compression of the densely wound area at the end accounts for 30% of the free height, the compression of the sparsely wound area on both sides accounts for 50% of the free height, and the compression of the densely wound area in the middle accounts for 20% of the free height.

[0071] Specifically, the present invention has a spring with pitch changes, and the potential defects in different areas are targetedly stimulated by a partitioned compression strategy. The acoustic emission signal and stress change analysis are combined to effectively distinguish material defects (such as inclusions, microcracks) from process defects (such as pitch mutations, stress concentration), and realize online non-destructive detection to improve detection efficiency; pulsed magnetic field repair is triggered according to the acoustic emission energy level to achieve non-contact defect repair, avoiding the oxidation risk of traditional heat treatment; two-stage partitioned tempering dynamically adjusts the length of the second stage through the retained austenite content to ensure the balance between hardness and toughness, and the service life is improved compared to the traditional tempering process; Vickers hardness and fatigue life decay rate are used as 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 areas, reducing material costs and improving production efficiency.

[0072] During the partition compression process, stress and acoustic emission signals are collected synchronously, local strain distribution is measured by fiber Bragg grating strain sensors, and acoustic emission signals are captured by acoustic emission sensors. The acoustic emission signals are microscopic yield signals.

[0073] In practice, an acoustic emission sensor is used to capture the microscopic yield signal emitted by the spring during the compression process within a frequency range of 150-500 kHz.

[0074] In this embodiment, the two end dense winding areas and one middle dense winding area of the spring are collectively referred to as dense winding areas, and the two side sparse winding areas of the spring are collectively referred to as sparse winding areas.

[0075] Calculate the stress change of the densely wound area or the sparsely wound area according to the stress values of the densely wound area or the sparsely wound area measured before and after the spring is compressed;

[0076] If the stress change in the dense winding area or the sparse winding area is greater than the first standard value and the acoustic emission energy increases suddenly, it is determined that there is a risk of material defects in the dense winding area or the sparse winding area and it is marked as a defective area;

[0077] Specifically, the process for judging the sudden increase in acoustic emission energy is that a burst signal appears in the 200-400kHz frequency band of the acoustic emission signal, wherein the burst signal is an acoustic emission signal with a rise time of less than 1μs, a duration of less than 50μs, and a signal amplitude of more than 20dB higher than the background noise;

[0078] During 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 100ms of the no-load signal. The signal within the detection window (t1, t2) is integrated to obtain the acoustic emission signal energy Ea after removing the background noise energy. During the spring compression test, the acoustic emission signal waveform is plotted based on the acoustic emission signal energy Ea.

[0079] Ea= ; represents the time integral of the instantaneous power captured by the sensor within the time window (t1, t2);

[0080] Where 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.

[0081] Calculating a strain gradient based on stress changes at both ends of a region composed of adjacent densely wound regions and sparsely wound regions and the length of a region composed of corresponding adjacent densely wound regions and sparsely wound regions, wherein the strain gradient is equal to the strain difference of the stress changes at both ends divided by the length of the corresponding region;

[0082] If the strain gradient of any region consisting of adjacent densely wound areas and sparsely wound areas is greater than the second standard value, then after determining that the pitch change of the region consisting of adjacent densely wound areas and sparsely wound areas is smooth, the region of the spring consisting of the corresponding adjacent densely wound areas and sparsely wound areas is marked as a stress concentration region;

[0083] The first standard value is 0.8%, and the second standard value is 10% / mm.

[0084] The process of determining whether the pitch variation of the region composed of the adjacent dense winding region and the sparse winding region is smooth comprises using an optical instrument curvature radius tester to detect the curvature radius of the region composed of the adjacent dense winding region and the sparse winding region;

[0085] If the radius of curvature is greater than or equal to three times the wire diameter, it is determined that the pitch variation of the region consisting of the adjacent dense winding region and the sparse winding region is smooth;

[0086] If the curvature radius is less than three times the wire diameter, it is determined that the pitch change of the area composed of adjacent dense winding areas and sparse winding areas is not smooth, and the initial winding parameter setting is unreasonable;

[0087] The wire diameter is the wire diameter of high-performance alloy steel wire.

[0088] Specifically, the present invention uses a partitioned compression detection method to implement differentiated compression strategies and synchronously collect multimodal signals, thereby achieving accurate identification and positioning of internal defects and stress concentration in the spring, and combining stress changes and acoustic characteristics to sensitively identify defective areas inside the steel wire, thereby improving the defect detection rate compared with the traditional uniform compression method; at the same time, due to the difference in pitch between the densely wound area and the sparsely wound area of the designed spring, the contact angle of the winding needs to change accordingly during the winding process, and there may be high strain gradient areas that produce geometrically necessary dislocations, resulting in stress concentration areas. This method distinguishes between process defects and material defects based on strain gradient calculation and curvature radius verification, and clearly determines that the local stress concentration of the spring is not a structural design problem when the curvature meets the standard, guiding subsequent targeted repairs and improving the accuracy of subsequent heat treatment of the spring.

[0089] During the compression test, in response to the material defect risk, when the acoustic emission signal energy Ea continuously exceeds the threshold and the strain increases nonlinearly, a pulsed magnetic field repair is triggered;

[0090] If the defect area is in the densely wound area, apply a 1.2T axial magnetic field to the defect area until the acoustic detection requirements are met;

[0091] If the defect area is in the sparse winding area on both sides, apply a 0.8T radial rotating magnetic field to the defect area until the acoustic detection requirements are met;

[0092] The acoustic detection requirement is that when the secondary compression detection is performed, the acoustic emission energy decreases by more than a critical value;

[0093] The duration of the continuous exceeding is 5 μs, the threshold is 50 dB, and the critical value is 40%.

[0094] Perform zoned induction tempering compensation for stress concentration areas and apply pulsed magnetic field for double-stage tempering to promote dislocation rearrangement;

[0095] The spring after compression testing passes through the Helmholtz coil (magnetic field uniformity ± 2%).

[0096] A pulsed magnetic field is applied in zones according to the preset magnetic field parameters for two-stage tempering. The preset magnetic field parameters for stage one are (1.5T, 10Hz), and the stage duration is 10 minutes. The preset magnetic field parameters for stage two are (0.5T, 5Hz), and the stage duration is 20 minutes.

[0097] Specifically, during the tempering stage, the pulsed magnetic field is applied in zones according to preset magnetic field parameters, and the direction of the magnetic field forms an angle of 45±5° with the axis of the spring;

[0098] The retained austenite content in the spring is detected by online X-ray diffraction (XRD), and the duration of stage 2 is adjusted according to the retained austenite content;

[0099] Specifically, when the retained austenite content is greater than the target content, the stage time of the second stage is extended according to the ratio of the retained austenite content to the target content;

[0100] Wherein, the target content is 3%.

[0101] Specifically, applying a magnetic field to the defect area can close microcracks through magneto-induced vibration, and applying a low-frequency gradient magnetic field to the stress area can promote dislocation rearrangement. This method repairs and heat treats spring defects based on acoustic emission signals and pulsed magnetic fields, accurately identifies material defects through acoustic emission energy thresholds and strain nonlinear growth, and uses magnetic field treatments with different parameters for densely wound areas and sparsely wound areas to match the repair effect with regional characteristics. The acoustic detection requirements are used as the repair termination standard to ensure stable repair quality. The alternating action of magnetic fields of different intensities promotes efficient reorganization of dislocations, and the adaptability and flexibility of heat treatment are improved by adjusting the stage length according to the retained austenite content.

[0102] Perform Vickers hardness test and high-frequency fatigue test on springs after compression test or repair and tempering, compare the test results of springs without compression test after winding, and calculate fatigue life decay rate based on the high-frequency fatigue test results;

[0103] If the Vickers hardness is within the appropriate range and the fatigue life decay rate is less than zero, it is judged that the initial winding parameters and the preset magnetic field parameters are reasonably set;

[0104] If the Vickers hardness is not within the appropriate range, but the fatigue life decay rate is less than half (50%), it is determined that the preset magnetic field parameters are set improperly and the preset magnetic field parameters are adjusted;

[0105] 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 set unreasonably, resulting in excessive softening of the spring, and the tempering temperature is lowered by adjusting the preset magnetic field parameters in the first stage;

[0106] During implementation, the magnetic field intensity of the preset magnetic field parameters in stage one is reduced according to the ratio of the Vickers hardness to the minimum value of the range;

[0107] If the Vickers hardness HV is greater than the maximum value of the range, it is judged that the spring toughness is insufficient, and the tempering time is increased by adjusting the preset magnetic field parameters in stage 2;

[0108] During implementation, the duration of the second stage is increased according to the ratio of the Vickers hardness to the maximum value of the range;

[0109] When the Vickers hardness is not within the appropriate range and the fatigue life decay rate is greater than half (50%), it is judged that the initial winding parameters are set unreasonably, resulting in a decrease in the fatigue limit of the spring material after winding;

[0110] The appropriate range consists of a range minimum value and a range maximum value, the range minimum value is 450, and the range maximum value is 500.

[0111] Specifically, when the Vickers hardness is high, it is usually accompanied by a decrease in toughness, which can provide feedback on insufficient tempering during heat treatment. This method determines excessive softening or insufficient toughness through Vickers hardness, and combines it with high-frequency fatigue testing to judge whether there are problems with the heat treatment or pre-winding process. It can accurately identify and distinguish the fundamental problems of the spring, implement differentiated adjustment strategies, adjust the magnetic field parameters to control the tempering temperature to ensure toughness recovery, and avoid excessive correction.

[0112] After the spring's end dense winding area, middle dense winding area and both sides sparse winding area are compressed to different degrees,

[0113] If there are defective areas in both the adjacent densely wound area and the sparsely wound area, it is determined that there are through cracks in the wound spring;

[0114] If stress concentration areas exist in both the adjacent densely wound area and the sparsely wound area, it is determined that a high stress zone exists at the junction of the transition area and the densely wound area due to the sudden change in pitch after winding;

[0115] When the strain gradient in the area consisting of adjacent densely wound areas and sparsely wound areas is greater than the third standard value, the acoustic emission signal energy Ea continuously exceeds the threshold, and there are through-cracks or high-stress zones, the cladding triggering conditions are met and laser cladding compensation is performed in the inner area of the spring;

[0116] Nano-silicon nitride particles are injected through laser cladding. A galvanometer scanning laser head is used to clad the silicon nitride / metal composite powder within 1.5 circles inside the spring. The laser power is controlled to decrease from the center to the edge.

[0117] In the implementation, the volume fraction of nano-silicon nitride particles was 15%, and the power from the center to the edge of the laser was 1000W-600W;

[0118] Wherein, the third standard value is 15% / mm.

[0119] Specifically, the present invention controls the quality of the spring based on zoned compression detection, and uses selective laser melting (SLM) to clad reinforcing materials (ceramic particles) in local areas of the spring to improve the stiffness of specific parts. The laser power is controlled to decrease from the center to the edge to achieve a continuous change in particle content from 15% to 0%. The low-stress area maintains the toughness of the matrix, forming a "rigid-flexible gradual" transition, thereby avoiding the risk of cracking the spring in the engine valve.

[0120] Inspect springs that do not have material defect risks or stress concentration areas, as well as springs that have been repaired, tempered, or clad, based on engine operating parameters to determine whether the engine's operating frequency will cause valve spring resonance;

[0121] The valve opening frequency f = n / 120 (Hz) is calculated based on the engine speed n (rpm). A static load is applied to the spring to simulate the state of the spring being compressed by the valve, and modal analysis is performed.

[0122] During modal analysis, the first six natural frequencies fn of the spring are extracted. The natural frequencies fn include f1~f6.

[0123] If the ratio of any order frequency to the engine operating frequency is not within the resonance range, the valve opening frequency f is determined to avoid the resonance peak;

[0124] 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-equidistant helical structure need to be adjusted, and the design parameters include the length and pitch of the densely wound area and the sparsely wound area.

[0125] Wherein, the resonance range is 0.9-1.1.

[0126] An integrally formed spring for an engine valve, comprising:

[0127] The spring is divided into end dense winding areas, middle dense winding areas and two side sparse winding areas. The end dense winding areas are located at both ends of the spring, the middle dense winding area is located in the middle of the spring, and the two side sparse winding areas are located in the area from both sides of the middle of the spring to the ends.

[0128] The end dense winding area and the middle dense winding area adopt a dense winding pitch, and the two side sparse winding areas adopt a sparse winding pitch.

[0129] Specifically, the valve spring is located between the cylinder head and the spring seat at the rear end of the valve stem. When the valve spring's operating frequency is equal to or an integer multiple of its natural frequency, the valve spring will resonate, increasing the chance of breakage. The present invention utilizes a variable-pitch spring to prevent resonance. This zoning design modifies the spring's natural frequency distribution, optimizing its resonance characteristics. Adjusting the ratio of densely wound and sparsely wound areas allows for precise control of the spring's dynamic response. The densely wound design (with a smaller pitch) in the end and middle densely wound areas increases the spring's stiffness and strength at both ends, enhancing its support stability during valve operation. The sparsely wound areas on both sides utilize a larger pitch, effectively reducing the stiffness of the spring's midsection, allowing it to better adapt to the high-speed reciprocating motion of the valve. This "dense at both ends, sparse in the middle" zoning structure creates a spring with both rigidity and flexibility, ensuring sufficient support and excellent cushioning performance. This effectively prevents resonance within the engine's operating speed range and improves the operational stability of the valve system.

[0130] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

[0131] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A heat treatment method for an integrally formed spring for an engine valve, characterized in that: include, A high-performance alloy steel wire is selected and wound according to initial winding parameters to obtain a spring. A zone compression strategy is adopted for the spring, and the densely wound area at the end, the densely wound area in the middle, and the sparsely wound areas on both sides of the spring are compressed to different degrees. During the zone compression process, acoustic emission signals and stress values are collected synchronously. The material defect risk of the densely wound area or the sparsely wound area is determined based on the stress change and acoustic emission energy, and the defect area is marked. Alternatively, the stress concentration area is determined based on the strain gradient of the adjacent area. The stress concentration area is marked based on the pitch change judgment result, or it is determined that the initial winding parameter setting is unreasonable. For defective areas or stress concentration areas, different repair strategies are adopted according to the acoustic emission energy and stress changes to trigger pulse magnetic field repair until the acoustic detection requirements are met. Alternatively, two-stage partitioned induction tempering compensation is performed according to preset magnetic field parameters and the duration of the second stage is adjusted according to the retained austenite content in the spring. For springs after compression testing or repair and tempering, determine whether the initial winding parameters or preset magnetic field parameters are reasonable based on Vickers hardness and fatigue life decay rate, and determine whether to adjust the preset magnetic field parameters at different stages; Determine whether the spring has through cracks or high stress zones based on the distribution of defect areas and stress concentration areas, and determine whether the cladding trigger conditions are met based on the determination results, the corresponding strain gradient, and the acoustic emission signal energy; Test the heat-treated springs and extract their natural frequency to determine if the engine's operating frequency will cause spring resonance in the valve. The process of marking defective areas involves, Calculate the stress change of the densely wound area or the sparsely wound area according to the stress values of the densely wound area or the sparsely wound area measured before and after the spring is compressed; If the stress change in the dense winding area or the sparse winding area is greater than the first standard value and the acoustic emission energy increases suddenly, it is determined that there is a risk of material defects in the dense winding area or the sparse winding area and it is marked as a defective area; The process of judging whether the acoustic emission energy suddenly increases is that a burst signal appears in the acoustic emission 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.

2. The heat treatment method for an integrally formed spring for an engine valve according to claim 1, characterized in that: The process of determining stress concentration areas includes: Calculating the strain gradient based on the stress changes at both ends of the region composed of the adjacent densely wound region and the sparsely wound region and the length of the region composed of the corresponding adjacent densely wound region and the sparsely wound region; If the strain gradient of any area composed of adjacent dense winding areas and sparse winding areas is greater than the second standard value, after determining that the pitch change of the area composed of adjacent dense winding areas and sparse winding areas is smooth, the area composed of the corresponding adjacent dense winding areas and sparse winding areas of the spring is marked as a stress concentration area.

3. The heat treatment method for an integrally formed spring for an engine valve according to claim 2, characterized in that: The process of determining whether the pitch variation of an area consisting of adjacent dense winding areas and sparse winding areas is smooth includes: Detecting the curvature radius of the area composed of adjacent dense winding areas and sparse winding areas, comparing the curvature radius with the wire diameter, and determining whether the pitch change of the area composed of adjacent dense winding areas and sparse winding areas is smooth; When it is determined that the pitch variation of the region consisting of the adjacent dense winding region and the sparse winding region is not smooth, it is determined that the initial winding parameter setting is unreasonable.

4. The heat treatment method for an integrally formed spring for an engine valve according to claim 3, characterized in that: The process of determining the triggering of the pulse magnetic field repair includes triggering the pulse magnetic field repair when the energy of the acoustic emission signal continuously exceeds the threshold value and the strain increases nonlinearly; If the defect area is in the densely wound area, an axial magnetic field is applied to the defect area until the acoustic detection requirements are met; If the defect area is in the sparse winding area on both sides, a radial rotating magnetic field is applied to the defect area until the acoustic detection requirements are met; The acoustic detection requirement is that during secondary compression detection, the acoustic emission energy decreases by more than a critical value.

5. The heat treatment method for an integrally formed spring for an engine valve according to claim 4, characterized in that: The process of two-stage partitioned induction tempering compensation includes: Perform zoned induction tempering compensation for stress concentration areas, and apply pulsed magnetic fields in zones according to preset magnetic field parameters for two-stage tempering; The retained austenite content in the spring is detected. When the retained austenite content is greater than the target content, the stage time of the second stage is extended according to the ratio of the retained austenite content to the target content.

6. The heat treatment method for an integrally formed spring for an engine valve according to claim 5, characterized in that: The process of judging whether the initial winding parameters or the preset magnetic field parameters are reasonable includes: Conduct Vickers hardness test and high-frequency fatigue test on springs after compression testing or repair and tempering, and calculate fatigue life attenuation rate based on the high-frequency fatigue test results; When the Vickers hardness is within an appropriate range and the fatigue life decay rate is less than zero, it is judged that the initial winding parameters and tempering parameters are reasonably set; When the Vickers hardness is not within the appropriate range, the tempering parameters are determined to be unreasonable and the tempering parameters should be adjusted based on whether the fatigue life decay rate is less than half, or the initial winding parameters are set unreasonable; 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 parameters 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 the tempering time is increased by adjusting the preset magnetic field parameters of stage two.

7. The heat treatment method for an integrally formed spring for an engine valve according to claim 6, characterized in that: After the end dense winding area, the middle dense winding area and the sparse winding areas on both sides of the spring are compressed to different degrees; Determine whether there are through cracks or high stress zones in the coiled spring based on whether there are adjacent defective areas or stress concentration areas. When the strain gradient of the area composed of adjacent densely wound areas and sparsely wound areas is greater than the third standard value, the energy of the acoustic emission signal continues to exceed the threshold, and there are through-cracks or high-stress zones, the cladding triggering conditions are met and laser cladding compensation is performed in the inner area of the spring.

8. The heat treatment method for an integrally formed spring for an engine valve according to claim 7, 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, the valve opening frequency is judged to avoid 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-equidistant helical structure need to be adjusted, and the design parameters include the length and pitch of the densely wound area and the sparsely wound area.

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