Method and device for measuring internal hardness of carburized and quenched gear

Abstract

The invention discloses a method and a device for measuring the internal hardness of a carburized and quenched gear. The core of the method is that a segmented measurement strategy is adopted: in a first hardness gradient change area close to the surface, rapid positioning is carried out through a coarse adjustment mode; and in a second gradient change area close to the center, switching to a fine adjustment mode to carry out precise mobile positioning. By measuring hardness values of a series of radial points, a distribution curve is drawn, and the effective hardened layer depth is determined according to a fixed standard value or a calculated value based on the core hardness. The measuring device is provided with a gear shifting mechanism which can drive the duplicate gear to be meshed with the coarse adjustment gear or the fine adjustment gear, switching of different transmission ratios is achieved, and therefore the detection platform is driven to achieve a coarse displacement mode and a fine displacement mode. The problem that efficiency and precision of a traditional measurement method are difficult to consider at the same time is effectively solved, and the reliability of the result is ensured through a systematized anomaly review process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material heat treatment detection, and particularly relates to a measurement method and device for internal hardness of carburized and quenched gears. BACKGROUND

[0002] As a core basic component in mechanical transmission system, the performance of gears directly affects the reliability, durability and service life of the entire equipment. Carburizing and quenching is a key heat treatment process for improving the surface hardness, wear resistance and fatigue strength of gears. This process forms a hardened layer with high hardness and residual compressive stress on the surface of the gear, while maintaining good toughness in the core, thereby imparting excellent comprehensive mechanical properties to the gear.

[0003] Effective hardened layer depth is one of the core technical indicators for evaluating the quality of carburized and quenched gears, which is defined as the vertical distance from the surface of the gear to a specified hardness value. Accurate measurement of the hardness gradient distribution from the surface to the core of the gear and determination of the hardened layer depth based thereon are of great significance for product quality control, process optimization and failure analysis.

[0004] Currently, the internal hardness of carburized and quenched gears is generally measured by using a Vickers hardness tester on the cross section of the gear. The conventional operation method is as follows: the prepared gear sample is fixed on a common platform, the platform is moved by manually rotating the screw drive, and the indenter of the hardness tester is aligned with a series of preset measurement points from the surface to the core in turn for indentation testing, and finally a hardness-depth curve is drawn.

[0005] However, this traditional measurement method has several significant technical defects: Firstly, the entire measurement process relies on manual single-mode displacement adjustment by the operator. In the area close to the surface, the hardness gradient changes sharply, and precise positioning with small steps is required to avoid missing key feature points, which is extremely inefficient for manual operation; while in the area close to the core, the hardness changes tend to be flat, and if small-step movement is still used, a lot of time will be wasted. The single movement mode cannot balance the requirements of measurement efficiency and accuracy.

[0006] Secondly, manual control has large human error and uncertainty, and it is difficult to ensure the accuracy and consistency of each displacement, which is prone to cause distortion of the measurement data due to inaccurate positioning, and ultimately affects the accuracy of the determination of the hardened layer depth.

[0007] Thirdly, when there is abnormal fluctuation of the hardness value, there is a lack of systematic abnormal diagnosis and data processing mechanism, and usually only simple repeated measurement can be performed relying on the experience of the operator, and it is difficult to effectively identify and eliminate the errors caused by equipment, sample or environmental interference, and the reliability of the data is questionable.

[0008] Therefore, there is an urgent need in the art for a high-precision gear internal hardness measurement method and special device that can automatically and intelligently perform segmented precision measurement and effectively handle measurement abnormalities to solve the above-mentioned long-standing technical problems. SUMMARY

[0009] To overcome the above-mentioned defects of the prior art, embodiments of the present application provide a carburized and quenched gear internal hardness measurement method and device.

[0010] To achieve the above-mentioned purposes, the innovative points of the present application are as follows: the method uses a measurement device and includes the following steps: Prepare a gear sample, obtain a section to be measured, and fix the sample on the detection platform of the measurement device; Operate the coarse adjustment knob to drive the detection platform to move so that the hardness tester indenter is aligned with the edge of the section to be measured, defining the initial zero point from the surface; Control the detection platform to move the sample in segments; when approaching the first hardness gradient change zone near the surface: operate the shift mechanism of the measurement device to switch to the coarse adjustment mode, rotate the coarse adjustment knob to quickly move the detection platform to the target measurement area; when approaching the second hardness gradient change zone near the core: switch to the fine adjustment mode, rotate the fine adjustment knob to drive the slider to move precisely with smaller displacement intervals, and sequentially position to a series of preset radial measurement points; Record the hardness values and depth values of the series of measurement points, and draw a hardness distribution curve; Based on the intersection depth of the hardness distribution curve and the preset judgment rule, determine the hardening layer depth of the gear.

[0011] Further, the rule for the above-mentioned segmented movement is: the interval from the surface to a preset depth threshold is defined as the first hardness gradient change zone, and the coarse adjustment movement is performed with a displacement interval of not less than 0.10 mm; the interval after exceeding the preset depth threshold is defined as the second hardness gradient change zone, and the fine adjustment movement is performed with a displacement interval of not more than 0.05 mm; the preset depth threshold is 70%-80% of the designed hardening layer depth of the gear.

[0012] Further, the series of measurement points at least include: 0.05 mm, 0.10 mm from the surface; 80% of the lower limit value of the effective hardening layer depth required by the technical specification; 120% of the upper limit value; and the center point of the gear.

[0013] Further, during the measurement process, when the hardness values of three consecutive measurement points change by more than ±15% of the average hardness value relative to the previous point, an abnormal review process is triggered, including: S1, check the detection platform calibration state; S2, recalibrate the hardness tester reference; S3, three times of repeated measurement are taken to get average value, if the data after repeated measurement is still abnormal, continue to execute S4 and S5 S4, wavelet denoising processing is performed on the abnormal data; S5, system error is eliminated by using linear regression method.

[0014] Further, the standard hardness value is a fixed value HV fixed , which is suitable for the standardized gear products verified by process.

[0015] Further, the standard hardness value is a gear core hardness value HV core , plus a fixed increment ΔHV, wherein ΔHV=K×design hardening layer depth, K is a material coefficient.

[0016] Further, the application provides a measuring device, the measuring device comprises a base, a detection platform is slidably arranged on the base, the inner part of the base is respectively provided with rotatable and mutually parallel input shaft A, input shaft B and input shaft C, the input shaft C is located between the input shaft A and the input shaft B, a coarse adjustment knob is rotatably arranged on the base and connected to one end of the input shaft A, the other end of the input shaft A is provided with a gear A, a fine adjustment knob is rotatably arranged on the base and connected to one end of the input shaft B, the other end of the input shaft B is provided with a gear B, the input shaft C is provided with a double gear that can axially slide, the double gear has coaxially arranged gear C and gear D, the diameter of the gear C is smaller than that of the gear D; the end of the input shaft C is provided with an axially extending lead screw, the bottom of the detection platform is provided with a nut, the lead screw and the nut form a lead screw and nut pair, the gear A and the gear B are arranged in the axial direction of the input shaft C; The pitch circle diameter of the gear B is greater than that of the gear A, and the pitch circle diameter of the gear A is greater than that of the gear D on the double gear; The gear shifting mechanism acts on the double gear, and the double gear is arranged in three clear switching positions on the input shaft C: The first position: the double gear is pushed to the flush position of the gear A along the input shaft C, so that the gear D and the gear A are engaged, forming a first transmission ratio, realizing a coarse adjustment transmission path; The second position: the double gear is located in the middle position of the input shaft C, so that the gear C, the gear D and the gear A, the gear B are not engaged; The third position: the double gear is pushed to the flush position of the gear B along the input shaft C, so that the gear C and the gear B are engaged, forming a second transmission ratio, realizing a fine adjustment transmission path; The first transmission ratio is less than the second transmission ratio, so that the moving speed of the platform in the coarse adjustment mode is greater than that in the fine adjustment mode.

[0017] Further, the body of the base is provided with a guide groove, the length direction of the guide groove is consistent with the moving direction of the detection platform; the connecting plate is fixedly connected with the bottom of the detection platform at the top, and extends to the space inside the base through the guide groove at the lower part; the nut is fixedly installed at the lower end of the connecting plate inside the base; wherein the screw rod and the nut form a screw rod nut pair, and the connecting plate is configured to be slidable along the guide groove.

[0018] Further, the gear shifting mechanism comprises a shifting lever and a shifting fork; the middle part of the shifting lever is hingedly connected to the base through a rotating shaft, and the bottom part is provided with a driving pin; the middle part of the shifting fork is hingedly connected to the base through a fixed pin shaft, one end is provided with an oblong hole matched with the driving pin, and the other end is a fork-shaped part which can be clamped into an annular shifting fork groove, the fork-shaped part has two mutually parallel prongs, and the connecting line of the two prong ends is parallel to the axis of the input shaft C; the double gear is an integral structure, which is arranged between the shaft neck parts of the gear C and the gear D, and is provided with an annular shifting fork groove; the two prongs and the shifting fork groove are gap matched, so that the shifting fork does not interfere with the rotation of the input shaft C when the shifting fork slides axially to drive the double gear.

[0019] Further, the gear shifting mechanism further comprises a positioning assembly, the positioning assembly comprises a spring and a positioning steel ball, one end of the spring is fixed to the base, and the other end abuts against the positioning steel ball; the shifting lever is provided with three recesses corresponding to the first position, the second position and the third position respectively; when the shifting lever is shifted to the corresponding position, the positioning steel ball is clamped into the corresponding recess under the action of the spring, so as to realize accurate positioning of the gear position and hand feeling feedback. The tooth ends of the gear A, the gear B, the gear C and the gear D are all machined with guide chamfers, which are used for guiding the smooth meshing of the tooth profile during gear shifting, reducing impact and wear; The input shaft A, the input shaft B and the input shaft C are all provided with angular contact ball bearings, the angular contact ball bearings are arranged on the base, and the pre-tightening torque of the angular contact ball bearings is 5-8 N·m.

[0020] The beneficial effects of the present application are: 1、The present application fundamentally solves the technical contradiction that efficiency and precision are difficult to be considered in gear hardness gradient measurement through the unique segmented measurement mode and the corresponding mechanical gear shifting transmission device. Specifically, in the first hardness gradient change area close to the surface, coarse adjustment mode and large step fast movement are adopted, which significantly shortens the time-consuming of finding the measurement area and greatly improves the measurement efficiency; in the second hardness gradient change area close to the center, fine adjustment mode and small step precise movement are switched to, which ensures accurate positioning in the area where the hardness value changes gently, effectively avoids data distortion caused by positioning error, and thus realizes the unity of high precision and high efficiency as a whole.

[0021] 2. This invention significantly improves the reliability and consistency of measurement results by introducing a systematic anomaly review and data processing workflow. When abnormal fluctuations are detected in continuous measurement data, a multi-step review process is automatically triggered, including hardware checks, equipment calibration, retesting and verification, and advanced algorithm processing (wavelet denoising, linear regression). This workflow can systematically eliminate interference from equipment failures, random errors, and systematic errors, intelligently correct and verify abnormal data, and ultimately output highly reliable hardness distribution data and hardened layer depth determination results, overcoming the shortcomings of traditional methods that rely excessively on operator experience, have limited processing methods, and suffer from poor reliability. Attached Figure Description

[0022] Figure 1 This is a top view of the interior top of the base of the present invention.

[0023] Figure 2 This is a side view of the connection between the shifting mechanism and the base of the present invention.

[0024] Figure 3 This is a structural diagram showing the relative positions of the positioning component and the recess in this invention.

[0025] Figure 4 This is a structural diagram of the side of the detection platform of the present invention.

[0026] Figure 5 This is a schematic diagram of the hardness distribution curve of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1: Hardness Measurement of Standard Gear Products This embodiment uses a standardized carburized and quenched gear that has undergone process verification as an example to illustrate the implementation process of this method. The designed hardened layer depth (CHD) of this gear is 1.0 mm.

[0029] 1. Sample preparation and installation First, a sample containing the tooth profile is prepared by wire cutting from the gear to be tested. The cross-section of the sample is then ground, polished, and lightly etched to obtain a clear metallographic cross-section. Subsequently, the sample is securely mounted on the testing platform 11 of the measuring device.

[0030] like Figure 1As shown, the measuring device includes a base 1, and the detection platform 11 extends to the inside of the base 1 through the connecting structure of its bottom. The inside of the base 1 is provided with input shaft A12, input shaft B13 and input shaft C14 which are parallel to each other. The coarse adjustment knob 15 is connected to one end of the input shaft A12, and the other end of the input shaft A12 is provided with gear A21. The fine adjustment knob 16 is connected to one end of the input shaft B13, and the other end of the input shaft B13 is provided with gear B22. The input shaft C14 is sleeved with a double gear which can axially slide, and the double gear has coaxially arranged pinion C23 and gear D24. The end of the input shaft C14 is connected with a lead screw 17, and the lead screw 17 and a nut 18 fixed to a connecting plate 41 form a screw-nut pair. The guide groove 4 plays a guiding role for the movement of the detection platform 11.

[0031] As shown in Figure 4 The bottom of the detection platform 11 is fixedly connected with a connecting plate 41. The lower part of the connecting plate 41 passes through the guide groove 4 formed in the base 1 and extends to the inside of the base 1. The nut 18 is fixedly installed at the lower end of the connecting plate 41 inside the base 1. When the lead screw 17 rotates, the nut 18 cooperating with it converts the rotary motion into the linear motion of the connecting plate 41 and the detection platform 11 in the direction of the guide groove 4.

[0032] The core transmission and gear shifting structure of the measuring device is as follows: the power of rotating the coarse adjustment or fine adjustment knob 16 is transmitted through the gear train inside the base 1. The tooth ends of the gear A21, the gear B22, the gear C23 and the gear D24 are all machined with a guide chamfer, which ensures that the gears can smoothly and impact-free mesh when the gear shifting mechanism 5 is operated, significantly reduces the gear shifting resistance and tooth end wear, and improves the operation feeling and service life of the device. The gear shifting mechanism 5 also includes a positioning assembly 7.

[0033] As shown in Figure 3 The positioning assembly 7 includes a spring 71 and a positioning steel ball 72, wherein one end of the spring 71 is fixed to the base 1, and the other end continuously abuts against the positioning steel ball 72. When the lever 51 is moved, the lever 51 itself rotates, and the three recesses 8 thereon will pass through the positioning steel ball 72 in turn. When the lever 51 moves to the "coarse adjustment", "neutral" or "fine adjustment" position, the positioning steel ball 72 will accurately be clamped into the corresponding recess 8 under the pressure of the spring 71, producing a clear "click" sound and a hand feeling pause, thereby providing clear gear feedback for the operator, achieving accurate positioning of the gear, and effectively preventing transmission errors caused by unclear gears 2. Zero and initial positioning The operator manually rotates the coarse adjustment knob 15 on the measuring device, driving the test platform 11 and the sample on it to move. By observing the optical microscope or CCD camera linked to the test platform 11, the diamond indenter of the Vickers hardness tester is precisely aligned with the edge of the section to be tested, i.e., the surface of the gear. This position is defined as the initial zero point (0.00 mm) for depth measurement.

[0034] 3. Segmented movement and measurement point positioning The control and detection platform 11 moves the sample in segments towards the center to locate a series of preset measurement points: First hardness gradient variation zone (coarse adjustment mode): the range from the surface to the preset depth threshold (1.0mm × 80% = 0.8mm in this example). Operate the shift mechanism 5 to switch to coarse adjustment mode. At this time, rotate the coarse adjustment knob 15, and the detection platform 11 moves rapidly in steps of 0.10mm / revolution. Within this area, select points 0.05mm and 0.10mm from the surface to perform hardness indentation tests.

[0035] Second hardness gradient variation zone (fine-tuning mode): the area beyond 0.8mm depth, up to the core. Operate the shift mechanism 5 to switch to fine-tuning mode. At this time, rotate the fine-tuning knob 16, and the detection platform 11 moves in precision steps of 0.02mm / revolution. Within this area, in addition to increasing the density of detection points in areas where the hardness gradient may change significantly, it must also include 80% of the lower limit of the effective hardened layer depth required by the technical specifications (e.g., 0.8mm) (i.e., 0.64mm), 120% of the upper limit (e.g., 1.2mm) (i.e., 1.44mm), and the center point of the gear.

[0036] 4. Hardness testing and data recording At each preset measurement point, the Vickers hardness tester automatically performs an indentation test and records the hardness value (HV) and the corresponding depth value (mm) at that point.

[0037] 5. Data processing and hardened layer depth determination After recording the data for all points, plot the distribution curve of hardness (HV) relative to depth (mm). For example... Figure 5 As shown, the hardness distribution curve starts from the surface and gradually decreases with increasing depth. A horizontal dashed line is drawn on the curve to indicate the point on the curve where the hardness value is the standard hardness value (e.g., 513 HV). The intersection of this horizontal dashed line and the hardness distribution curve represents the effective hardened layer depth (CHD) of the gear. This embodiment uses a standard hardness value determination method, where the standardized product uses a fixed standard value of HV. fixed The hardness value is 513HV. Find the point with a hardness value of 513HV on the plotted curve; the depth corresponding to this point is the effective hardened layer depth of the gear.

[0038] 6. Exception Handling During the measurement process, the control system monitors the data in real time. If an anomaly occurs, i.e., the hardness values ​​at three consecutive points fluctuate by more than ±15% of the average value, the anomaly review process is immediately triggered. First (S1), pause the test and check if the displacement platform is calibrated accurately.

[0039] Then (S2), the hardness tester is recalibrated using a standard hardness block to ensure that the measurement reference is correct.

[0040] Next (S3), the abnormal point and the points before and after it are retested three times, and the average hardness is taken as the final value of the point.

[0041] If significant anomalies (S4) still exist in the data after retesting, wavelet denoising processing is performed on the entire hardness distribution curve data to eliminate random interference.

[0042] Finally (S5), linear regression is used to fit the denoised data to eliminate possible systematic errors and obtain a more accurate hardness distribution curve before the hardened layer depth is determined.

[0043] Example 2: Hardness Measurement of Non-standard Customized Gear Products This embodiment takes a non-standard customized gear made of a new material or using a new process as an example, where the core hardness has a significant impact on the determination of the hardened layer.

[0044] The implementation steps of this embodiment are basically the same as those of Embodiment 1, the main difference being the method of determining the standard hardness value.

[0045] In this embodiment, instead of using a fixed value HV, the hardness value HV of the gear core is measured first. core (For example, the measured value is 380 HV). Then, according to the formula, the standard hardness value = HV core The calculation is performed using +ΔHV. Here, ΔHV = K × designed hardened layer depth. Assuming the coefficient K for the gear material is 150 and the designed hardened layer depth is 1.2 mm, then ΔHV = 150 × 1.2 = 180 HV. Therefore, the standard hardness value used to determine the effective hardened layer depth is 380 + 180 = 560 HV. The depth corresponding to 560 HV can then be found on the hardness distribution curve.

[0046] (III) Working principle of the measuring device The measuring device described in this invention is key to achieving the aforementioned high-precision, segmented measurement method. Its core working principle lies in changing the transmission path through the shifting mechanism 5 to switch between coarse and fine adjustment modes.

[0047] like Figure 2As shown, the shift mechanism 5 includes a shift lever 51 and a shift fork 52. The middle part of the shift lever 51 is hinged to the base 1 by a hinge shaft 6, and the bottom part is provided with a driving pin 61. The middle part of the shift fork 52 is hinged to the base 1 by a fixed pin shaft 62. One end of the shift fork 52 is provided with an oblong hole 63 matched with the driving pin 61, and the other end is a forked part. The two parallel prongs 64 of the forked part are inserted into the annular shift fork groove 65 on the double gear shaft neck, and the two are clearance fit. The shift lever 51 is provided with three arc-shaped recesses 8, and the center of the arc is the hinge point of the shift lever 51.

[0048] Coarse adjustment mode (first position): when the shift lever 51 is pushed to the first position, the shift fork 52 drives the double gear shaft to slide, so that the gear D24 on the double gear shaft is engaged with the gear A21 on the input shaft A12. In this process, the guide chamfer of the gear teeth ensures smooth and smooth engagement. At this time, rotate the coarse adjustment knob 15, and the power is transmitted to the input shaft C14 through the input shaft A12, gear A21→gear D24, and finally converted into large step linear movement of the detection platform 11 through the screw nut pair. This path transmission is relatively small, and the platform moves fast, which is used for fast positioning. When the shift lever 51 is in place, the steel ball in the positioning assembly 7 is clamped into the first recess 8 under the action of the spring 71, providing clear gear confirmation feeling.

[0049] Neutral position (second position): the shift lever 51 is placed in the middle position, and the double gear is not engaged with the gear A21 and the gear B. The positioning steel ball 72 is clamped into the middle recess 8. At this time, rotating the coarse adjustment knob or the fine adjustment knob 16 will not drive the platform, which is convenient for observation and selection of the measurement area.

[0050] Fine adjustment mode (third position): when the shift lever 51 is pushed to the third position, the double gear slides so that the gear C23 on the double gear is engaged with the gear B22 on the input shaft B13. Similarly, rely on the guide chamfer to realize smooth engagement. At this time, rotate the fine adjustment knob 16, and the power is transmitted to the input shaft C14 through the input shaft B13, gear B22→gear C23. This path transmission is relatively large, so the fine adjustment knob 16 rotates several turns, and the input shaft C14 rotates slowly for one turn, which is converted into extremely small precise displacement of the detection platform 11 through the screw nut pair, which is used for accurate alignment of the measurement point. After the shift lever 51 is in place, the positioning steel ball 72 is clamped into the third recess 8.

[0051] The positioning assembly 7 provides clear gear feeling and self-locking function during gear shifting, ensures that the double gear can accurately stay at three preset positions, prevents gear shifting due to vibration and other reasons during work, and ensures the stability of measurement. The guide groove 4 and the connecting plate 41 structure ensure that the detection platform 11 can only move smoothly in the predetermined direction without radial shaking, ensuring the accuracy of the depth measurement value. All input shafts adopt angular contact ball bearings 9 (the pre-tightening torque is set to 6N.m). Further transmission gap is eliminated, high movement accuracy is ensured, and finally the implementation of the entire measurement method is supported.

[0052] Finally, it should be pointed out that: first, in the description of the present application, it should be pointed out that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, which can be mechanical connection or electrical connection, or the communication between two elements, or direct connection, "up", "down", "left", "right" and the like are only used to indicate the relative positional relationship, when the absolute position of the described object changes, the relative positional relationship may change; Secondly: the drawings of the disclosed embodiments of the present application only involve the structures involved in the disclosed embodiments, other structures can refer to the usual design, and in the case of no conflict, the same embodiment and different embodiments of the present application can be combined with each other; Finally: the above only describes the preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method of measuring the internal hardness of a carburized and quenched gear, characterized by, The method comprises the following steps by means of a measuring device: Preparation of a gear sample, obtaining a cross section to be measured, and fixing the sample on a detection platform of the measuring device; Operating a coarse adjustment knob to drive the detection platform to move so that a hardness tester indenter is aligned with the edge of the cross section to be measured, defining an initial zero point of distance from the surface; Controlling the detection platform to move the sample in sections; when approaching a first hardness gradient change zone near the surface: operating a shift mechanism of the measuring device to switch to a coarse adjustment mode, rotating the coarse adjustment knob to quickly move the detection platform to a target measurement area; when approaching a second hardness gradient change zone near the center: switching to a fine adjustment mode, rotating the fine adjustment knob to drive the slider to move precisely with smaller displacement intervals, and sequentially positioning a series of preset radial measurement points; Recording hardness values and depth values of the series of measurement points to draw a hardness distribution curve; Based on the intersection depth of the hardness distribution curve and a preset judgment rule, the hardened layer depth of the gear is determined.

2. A method of measuring the internal hardness of a carburized and quenched gear according to claim 1, characterized in that, The rules of the section movement are: the interval from the surface to a preset depth threshold is defined as the first hardness gradient change zone, and the coarse adjustment movement is performed with a displacement interval of not less than 0.10 mm; the interval beyond the preset depth threshold is defined as the second hardness gradient change zone, and the fine adjustment movement is performed with a displacement interval of not more than 0.05 mm; the preset depth threshold is 70%-80% of the design hardened layer depth of the gear.

3. The method of measuring the internal hardness of a carburized and quenched gear according to claim 1, wherein The series of measurement points at least include: 0.05 mm, 0.10 mm from the surface; 80% of the lower limit value of the effective hardened layer depth required by the technical specification; 120% of the upper limit value; and the center point of the gear.

4. The method of claim 1 wherein, During the measurement process, when the hardness values of three consecutive measurement points change by more than ±15% of the average hardness value relative to the previous point, an abnormal review process is triggered, including: S1, checking the detection platform calibration state; S2, recalibrating the hardness tester reference; S3, performing three repeated measurements and taking the average value, if the data is still abnormal after the repeated measurements, continue to perform S4 and S5 S4, wavelet denoising processing of abnormal data; S5, eliminating system error by linear regression method.

5. The method of measuring the internal hardness of a carburized and quenched gear as set forth in claim 1, wherein, The standard hardness value is a fixed value HV fixed , which is applicable to standardized gear products that have been process verified.

6. The method of measuring the internal hardness of a carburized and quenched gear as set forth in claim 1, wherein, The standard hardness value is the gear core hardness value HV core plus a fixed increment AHV, where AHV = K x design case depth, K being a material coefficient.

7. A measuring apparatus for the carburized and quenched gear hardness measuring method as set forth in claim 1, characterized by The measuring device comprises a base, the detection platform is slidably arranged on the base, the base is internally provided with input shafts A, B and C which are rotatable and parallel to each other, the input shaft C is located between the input shaft A and the input shaft B, the coarse adjustment knob is rotatably arranged on the base and connected to one end of the input shaft A, the other end of the input shaft A is provided with a gear A, the fine adjustment knob is rotatably arranged on the base and connected to one end of the input shaft B, the other end of the input shaft B is provided with a gear B, the input shaft C is provided with a double gear which can axially slide, the double gear has coaxially arranged gears C and D, the diameter of the gear C is smaller than that of the gear D; the end of the input shaft C is provided with an axially extending lead screw, the bottom of the detection platform is provided with a nut, the lead screw and the nut form a lead screw and nut pair, and the gear A and the gear B are arranged in the axial direction of the input shaft C. The pitch circle diameter of the gear B is greater than that of the gear A, and the pitch circle diameter of the gear A is greater than that of the gear D; The shift mechanism acts on the double gear, which is arranged on the input shaft C in three clear switching positions: The first position: the double gear is pushed to the level position of the gear A along the input shaft C, so that the gear D and the gear A are engaged to form the first transmission ratio, realizing the coarse adjustment transmission path; The second position: the double gear is located in the middle position of the input shaft C, so that the gear C, the gear D and the gear A, the gear B are not engaged; The third position: the double gear is pushed to the level position of the gear B along the input shaft C, so that the gear C and the gear B are engaged to form the second transmission ratio, realizing the fine adjustment transmission path; The first transmission ratio is less than the second transmission ratio, so that the platform moving speed in the coarse adjustment mode is greater than that in the fine adjustment mode.

8. A measuring device according to claim 7, characterised in that A guide groove is formed in the body of the base, and the length direction of the guide groove is consistent with the moving direction of the detection platform; a connecting plate is fixedly connected with the bottom of the detection platform at the top, and extends to the space inside the base through the guide groove at the lower part; the nut is fixedly installed at the lower end of the connecting plate inside the base; wherein the screw rod and the nut constitute a screw rod and nut pair, and the connecting plate is configured to slide along the guide groove.

9. A measuring device according to claim 7, characterized in that The shift mechanism includes a shift lever and a shift fork; the middle part of the shift lever is hinged to the base through a rotating shaft, and the bottom is provided with a driving pin; the middle part of the shift fork is hinged to the base through a fixed pin shaft, one end is provided with an oblong hole matched with the driving pin, and the other end is a fork-shaped part which can be clamped into an annular shift fork groove, and the fork-shaped part has two parallel prongs, and the connecting line of the two prong ends is parallel to the axis of the input shaft C; The double gear is an integral structure, which is provided with the annular shift fork groove at the shaft neck part between the gear C and the gear D; the two prongs and the shift fork groove are gap matched, so that the shift fork does not interfere with the rotation of the double gear around the input shaft C when driving the double gear to slide axially.

10. A measuring device according to claim 9, characterized in that The shift mechanism further includes a positioning assembly, the positioning assembly includes a spring and a positioning steel ball, one end of the spring is fixed to the base, and the other end abuts against the positioning steel ball; the shift lever is provided with three pits corresponding to the first position, the second position and the third position respectively; when the shift lever is shifted to the corresponding position, the positioning steel ball is clamped into the corresponding pit under the action of the spring, so as to realize the accurate positioning of the gear and the hand feeling feedback; The gear A, the gear B, the gear C and the gear D are all machined with guide chamfers at the tooth ends, which are used to guide the smooth meshing of the tooth profile during shifting, reduce impact and wear; The input shaft A, the input shaft B and the input shaft C are all provided with angular contact ball bearings, which are arranged on the base, and the pre-tightening torque of the angular contact ball bearing is 5-8 N·m.

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