A method and system for fatigue testing of an outer ball cage retainer of a constant velocity drive shaft

Abstract

The application discloses a constant velocity drive shaft outer ball cage retainer fatigue test method and system. The method comprises the following steps: clamping a constant velocity drive shaft test piece; applying a first alternating torque and a first swing angle periodically fluctuating with time to a second loading end, so that the shaft rod reciprocally swings with the outer ball cage bell-shaped shell axis forming an included angle; applying a first radial load perpendicular to the shaft rod axis to the bell-shaped shell through the first loading end; collecting vibration acceleration signals of the outer ball cage region in real time; performing frequency spectrum analysis on the vibration acceleration signals, extracting the energy value of the retainer characteristic frequency, and determining that the retainer fails when the change rate of the energy value relative to the initial reference value exceeds a preset threshold. Through load coordination control and specific failure determination logic, the application can truly simulate the stress state under the limit working condition, effectively avoid the misjudgment caused by the load change during the running-in period, and realize the accurate identification of the early fatigue failure of the retainer.

Description

Technical Field

[0001] This application relates to the field of automotive transmission system testing technology, and in particular to a fatigue test method and system for the outer ball cage cage of a constant velocity drive shaft. Background Technology

[0002] As a core component of the automotive transmission system, the constant velocity drive shaft is primarily responsible for transmitting power from the transmission or transfer case to the drive wheels, while also accommodating the relative displacement between the wheels and the vehicle body caused by road bumps and steering movements. One of its core components is the outer CV joint, which contains a cage to maintain the uniform distribution of steel balls within the track and transmit torque. Under actual driving conditions, especially when the vehicle is at its limit during cornering, accelerating at high throttle, or driving on complex road surfaces, the outer CV joint must withstand not only the large torque transmitted from the engine but also the large-angle sway caused by suspension movement and the enormous radial force caused by wheel loads. This extreme "bending-torsion-radial" combined load condition can easily lead to stress concentration, wear, and even fatigue fracture of the cage inside the outer CV joint.

[0003] Cage failure is often sudden; once it breaks, it can cause steel balls to scatter, power loss, or even wheel jamming, seriously threatening driving safety. Therefore, it is crucial to conduct precise dynamic fatigue tests on the outer ball cage of the constant velocity drive shaft during the research and development phase.

[0004] Currently, the fatigue testing of external ball cage cages in the industry mainly has the following problems and shortcomings: First, there is distortion in the simulation of operating conditions. Traditional fatigue testing equipment often uses a single degree of freedom loading, such as applying only rotational torque or only static bending moment. However, under actual extreme operating conditions, there is a specific phase relationship between the torque input and the swing angle (for example, when a vehicle makes a sharp turn, the peak torque often lags behind the peak swing angle), and the radial load changes dynamically with the swing angle. Existing technologies struggle to accurately simulate this complex phase lag and dynamically coupled load, resulting in significant deviations between test results and actual road failure modes, failing to effectively expose potential product defects.

[0005] Second, failure monitoring methods are outdated. Current methods for assessing cage fatigue failure largely rely on disassembly and inspection after durability testing, or monitoring the vibration intensity of the assembly on a test bench. However, when the cage develops initial microcracks or slight wear, the overall vibration change of the entire drive shaft is often very small and easily masked by background noise. By the time the overall vibration exceeds acceptable levels, the cage has often already suffered devastating damage, making it impossible to capture early failure characteristics and hindering design improvements and lifespan prediction.

[0006] Third, improper benchmark settings can lead to misjudgments. When conducting fatigue life monitoring based on vibration signals, it is usually necessary to set an initial benchmark value. For tests that require a break-in period, if the low-load vibration data at the beginning of the test (break-in period) is directly used as the benchmark, the vibration energy will rise significantly when the test enters the formal high-load fatigue stage due to the step increase in the load itself, resulting in a false "failure" misjudgment. Conversely, if the benchmark value is not properly selected, it may also lead to the missed detection of true failure signals.

[0007] Therefore, there is an urgent need for a dynamic fatigue test method and system for the outer ball cage of a constant velocity drive shaft that can realistically simulate extreme bending and torsion combined working conditions and accurately identify early failure characteristics, in order to solve the above-mentioned technical problems. Summary of the Invention

[0008] This application provides a fatigue testing method and system for the outer ball cage of a constant velocity drive shaft, aiming to solve the problems of unrealistic working condition simulation, delayed failure monitoring, and easy misjudgment in the prior art.

[0009] To solve the above-mentioned technical problems, one technical solution adopted in this application is: to provide a fatigue test method for the outer ball cage of a constant velocity drive shaft. The method includes: S1: Clamp the constant velocity drive shaft specimen; the constant velocity drive shaft specimen includes an outer ball cage and a shaft rod, the outer ball cage is fixed to the first loading end, and the end of the shaft rod is connected to the second loading end; S2: Apply a first alternating torque to the second loading end, the torque value of the first alternating torque fluctuating periodically with time; S3: Apply a first swing angle to the second loading end so that the axis of the shaft and the axis of the bell-shaped shell of the outer ball cage form an angle and swing back and forth within a preset angle range; S4: Apply a first radial load to the bell-shaped shell of the outer ball cage through the first loading end, wherein the direction of the first radial load is perpendicular to the axis of the shaft; S5: Real-time acquisition of vibration acceleration signals in the outer ball cage area; S6: Perform spectral analysis on the vibration acceleration signal to extract the energy value of the characteristic frequency of the cage inside the outer ball cage. When the rate of change of the energy value relative to the initial reference value exceeds a preset threshold, the cage is determined to be faulty.

[0010] In some embodiments, in step S2, the waveform of the first alternating torque is configured as a sine wave or a trapezoidal wave, and the frequency of the first alternating torque is controlled within the range of 1Hz to 5Hz.

[0011] In some embodiments, in step S3, the oscillation frequency of the first oscillation angle is set to be consistent with the frequency of the first alternating torque.

[0012] In some embodiments, in step S3, the waveform of the first swing angle is configured to lag the waveform of the first alternating torque by a preset phase angle, the preset phase angle being in the range of 30° to 90°, for simulating impact hysteresis under extreme cornering conditions.

[0013] In some embodiments, in step S4, the magnitude of the first radial load is configured to increase as the absolute value of the first swing angle increases.

[0014] In some embodiments, in step S4, the first radial load consists of a constantly applied base load force and an adjusting load force that dynamically changes with the first swing angle, wherein the adjusting load force is linearly positively correlated with the absolute value of the first swing angle.

[0015] In some embodiments, the specific steps for extracting the energy value of the cage characteristic frequency in step S6 include: calculating the root mean square value of the filtered signal at the cage passing frequency and its second harmonic, and using the sum of the root mean square values ​​as the energy value.

[0016] In some embodiments, in step S6, the initial reference value is set as the average energy value collected and calculated within the first preset time period after the torque applied to the second loading end reaches the peak value of the first alternating torque, and the rate of change is calculated based on the ratio of the average energy value within the sliding time window at the current moment to the initial reference value.

[0017] In some embodiments, the method further includes a phased loading step: the test process is sequentially divided into a break-in stage and a formal fatigue stage, wherein the applied peak torque and swing angle amplitude are set to 50% to 70% of those in the formal fatigue stage.

[0018] To solve the above-mentioned technical problems, another technical solution adopted in this application is: providing a fatigue testing system for an outer ball cage of a constant velocity drive shaft. This system includes: a clamping module, comprising a first loading end and a second loading end; the first loading end is configured to fix the outer ball cage of the constant velocity drive shaft and is capable of applying a radial load perpendicular to the shaft axis to the outer ball cage; the second loading end is configured to connect to the end of the shaft of the constant velocity drive shaft; a composite loading module is connected to the second loading end and is used to apply torque and swing angle to the second loading end; a signal acquisition module is used to acquire vibration signals during the test; and a control module is electrically connected to the first loading end, the composite loading module, and the signal acquisition module respectively, and is used to control each module to execute the test method described above.

[0019] The beneficial effects of this application are as follows: Unlike existing technologies, this application provides a fatigue testing method and system for the outer ball cage of a constant velocity drive shaft. This method constructs a highly realistic extreme bending-torsional combined load environment by coordinating the control of torque, oscillation angle, and radial load, and introducing phase lag control, thus solving the problem that traditional single-condition loading cannot reproduce actual failure modes. Simultaneously, by introducing a failure judgment method based on spectrum analysis and specific benchmark selection logic, it achieves accurate identification of early micro-cracks and wear in the cage, avoiding misjudgments caused by load changes during the break-in period or external interference, significantly improving the reliability of the test results and their engineering application value. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a schematic flowchart of an embodiment of the fatigue test method for the outer ball cage of the constant velocity drive shaft provided in this application; Figure 2 This is a schematic diagram of an embodiment of the fatigue testing system for the outer ball cage of the constant velocity drive shaft provided in this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0022] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0023] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0024] To address the problems of limited operating condition simulation, delayed failure monitoring, and unreasonable benchmark settings in existing technologies, this application provides an innovative testing scheme. This scheme not only focuses on the magnitude of the load but also on the coupling relationship between loads (phase and frequency correlation), and introduces an intelligent signal processing algorithm to achieve high-precision testing of the fatigue life of the outer ball cage of a constant velocity drive shaft.

[0025] Specifically, this application provides a fatigue testing method for the outer ball cage cage of a constant velocity drive shaft. (See reference...) Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the testing method provided in this application. The method includes: Step S1: Clamp the constant velocity drive shaft specimen.

[0026] Specifically, the constant velocity drive shaft specimen includes an outer ball cage and a shaft. During clamping, the constant velocity drive shaft specimen needs to be securely mounted on the test bench, ensuring its centerline is aligned with the centerline of the loading system to avoid additional bending moments. Specifically, the outer ball cage of the constant velocity drive shaft is fixed to the first loading end, and the end of the shaft is connected to the second loading end.

[0027] Here, the first loading end mainly serves to fix and apply lateral / radial forces; it is usually fixed or applies force only in a specific direction. The second loading end is the driving end, responsible for driving the axle to rotate, swing, and transmit torque. This layout, with one end fixed and the other driven, simulates the installation posture of an actual vehicle where the outer CV joint connects to the wheel hub, and the axle connects to the differential.

[0028] Step S2: Apply the first alternating torque to the second loading end.

[0029] A first alternating torque is applied to the second loading end. The value of the first alternating torque fluctuates periodically over time. This step is designed to simulate the fluctuation characteristics of engine output torque. For example, during vehicle acceleration, the torque gradually increases; at the moment of gear shift, the torque drops to zero and then quickly recovers.

[0030] In some embodiments, the waveform of the first alternating torque is configured as a sine wave or a trapezoidal wave; a sine wave is suitable for simulating steady-state cyclic conditions, while a trapezoidal wave can more realistically simulate torque shocks during gear shifts or rapid acceleration.

[0031] Furthermore, the frequency of the first alternating torque is controlled within the range of 1Hz to 5Hz. While frequencies that are too low (e.g., <0.1Hz) are close to static conditions, the testing efficiency is extremely low; frequencies that are too high (e.g., >20Hz) are limited by the dynamic response capability of the test bench and introduce high-frequency inertial interference, which does not conform to the failure characteristics of the vehicle's main low-frequency, high-torque components. 1Hz to 5Hz is the typical frequency range for driveshaft stress during vehicle start-up, hill climbing, and rapid acceleration, effectively stimulating the low-cycle fatigue characteristics of the cage.

[0032] Step S3: Apply the first swing angle to the second loading end.

[0033] By swinging, an angle is formed between the axis of the axle and the axis of the bell-shaped shell of the outer CV joint, and the axle swings back and forth within a preset angle range. This step simulates the change in the swing angle of the outer CV joint caused by suspension bounce during vehicle movement.

[0034] In some embodiments, the oscillation frequency of the first oscillation angle is set to be consistent with the frequency of the first alternating torque. By synchronizing the torque fluctuation with the oscillation motion, the resonance condition of a vehicle continuously turning or driving on undulating roads at a specific speed can be simulated, thereby accelerating the fatigue process and shortening the test time.

[0035] In some embodiments, the waveform of the first swing angle is configured to lag the waveform of the first alternating torque by a preset phase angle, the preset phase angle being in the range of 30° to 90°, for simulating the impact hysteresis under extreme cornering conditions.

[0036] In actual vehicle dynamics, when a driver sharply turns the steering wheel into a curve, the peak sway angle is often accompanied by a downshift or engine speed adjustment before high torque is applied to the drive wheels. This time lag (phase difference) causes the steel balls inside the outer CV joint to generate a huge impact load on the cage window. By setting a phase lag of 30° to 90°, this extreme impact condition can be accurately reproduced, exposing the cage's weak points in impact resistance more effectively than traditional in-phase loading.

[0037] By adjusting the hysteresis phase angle to different angles such as 30°, 45°, 60° or 90°, the extreme conditions under the suspension geometry of different vehicle models can be simulated, thereby finding the phase range in which the cage is most prone to failure.

[0038] Step S4: Apply a first radial load to the bell-shaped shell of the outer ball cage through the first loading end.

[0039] The direction of the first radial load is perpendicular to the axis of the shaft. In actual driving, the reaction force of the ground on the tire is transmitted to the outer CV joint through the wheel hub. This force is mainly manifested as a radial force, which is perpendicular to the drive shaft axis. This embodiment simulates this force state by applying a radial load to the bell-shaped shell through the first loading end.

[0040] In some embodiments, the magnitude of the first radial load is configured to increase as the absolute value of the first swing angle increases.

[0041] In vehicle suspension operation, as wheel bounce increases, i.e., the outer CV joint swing angle increases, the lateral force or vertical load transmitted to the outer CV joint usually also increases. This dynamic coupling relationship can more realistically reproduce the stress state of the outer CV joint and avoid unrealistic failure modes caused by applying a constant radial force.

[0042] In some embodiments, to precisely control this dynamic process, the first radial load consists of a constantly applied base load and an adjusting load that dynamically varies with the first swing angle. The base load is used to simulate the preload generated by the vehicle's own weight, while the adjusting load simulates the load increment under dynamic conditions.

[0043] Right now, .in, This is the first radial load; The base load is used to simulate the static load on the vehicle; k is a proportionality coefficient. Adjust the applied force based on the absolute value of the first swing angle. With the first swing angle The absolute values ​​of these values ​​show a linear positive correlation.

[0044] By reading the data from the swing angle sensor in real time, the controller calculates and outputs the command value of the first radial load in real time, thus achieving high-precision dynamic tracking of the first radial load as the first swing angle changes.

[0045] Step S5: Real-time acquisition of vibration acceleration signals in the outer ball cage area.

[0046] Vibration is the most direct manifestation of mechanical failure. High-sensitivity vibration acceleration sensors are typically installed on the exterior of the outer ball cage, usually in sensitive areas of the bell shell, such as directly above or to the side of the cage. These sensors collect vibration acceleration signals in real time and transmit them to a data acquisition system. Because the cage is located inside the outer ball cage, the impact from crack propagation or wear on the cage is transmitted through the steel balls and bell shell, manifesting as high-frequency vibration of the outer shell.

[0047] Step S6: Perform spectrum analysis on the vibration acceleration signal to extract the energy value of the characteristic frequency of the cage inside the outer ball cage. When the rate of change of the energy value relative to the initial reference value exceeds a preset threshold, the cage is determined to be faulty.

[0048] Traditionally, the total effective value (RMS) of vibration is directly considered. However, since the load itself fluctuates significantly in this test, the total vibration RMS will fluctuate drastically with the periodic changes in torque and swing angle, and therefore cannot be directly used to determine failure.

[0049] This application employs frequency domain analysis to specifically extract the energy value of the cage's characteristic frequency. During operation, the cage's rotational speed, shaft speed, and ball rotation speed maintain a fixed kinematic relationship, thus determining the cage's fault characteristic frequency. When the cage cracks or peels off, the energy at this frequency abnormally increases.

[0050] Specifically, in some embodiments, extracting the energy value of the cage characteristic frequency includes: First, the original vibration signal is filtered to remove low-frequency structural noise and high-frequency electrical noise.

[0051] Secondly, a Fast Fourier Transform is performed on the filtered signal to obtain the spectrum.

[0052] Next, calculate the frequency at which the cage passes through in the spectrum. and its second harmonic 2 The root mean square value at that point. The reason for choosing the second harmonic is that early fault signals often have nonlinear characteristics, which will excite harmonic components.

[0053] Finally, it will be through frequency and its second harmonic 2 The sum of the root mean square values ​​at each point is used as the energy value.

[0054] During operation, the characteristic frequency of a cage failure typically manifests as a surge in energy at the passing frequency and its harmonics. Using the root mean square (RMS) value effectively reflects the average power of the signal and exhibits high sensitivity to sudden impact signals. By summing the fundamental and second harmonic energies, the degree of cage wear and cracking can be comprehensively evaluated, improving the accuracy of the assessment.

[0055] In this embodiment, the initial reference value is set as the average value of the energy value collected and calculated within the first preset time period after the torque applied to the second loading end reaches the peak value of the first alternating torque.

[0056] The testing process is typically divided into a break-in phase and a formal fatigue phase. During the break-in phase, the applied peak torque and oscillation angle amplitude are set to 50%–70% of those in the formal fatigue phase. The main purpose of the break-in phase is to allow good contact patterns to form between the raceways inside the outer ball cage and the steel balls and cage windows, eliminate machining burrs, and prevent initial seizure under high loads. After a period of break-in, the formal fatigue phase begins, and life testing is conducted.

[0057] Phased loading can effectively protect the specimen from impact during the initial installation stage, while ensuring that the internal clearance of the outer ball cage reaches an ideal state.

[0058] The test begins at time T0, entering the break-in phase. At this time, the torque is low, for example, 50% of the torque in the formal fatigue phase. The cage fits tightly, and the vibration signal may be unstable and have a low amplitude. If a reference value is selected during the T0-T1 phase, this reference value is very small. When the formal fatigue phase begins at time T1, the torque is instantly loaded to 100%. Even if the cage is intact at this time, the vibration energy will increase exponentially due to the increased load. The calculated rate of change will be very large, causing the system to misjudge as a failure.

[0059] Therefore, in this embodiment, the initial reference value is selected after the torque reaches its peak value. That is, only after the test bench has completed the transition from break-in to formal load, and the load has stabilized at the peak level of the first alternating torque (i.e., the operating level of the formal fatigue stage), does the energy value within the first preset time period begin to be recorded. The preset time period is, for example, 30 seconds, and the average energy value within this preset time period is calculated as the initial reference value. Initial baseline value This represents the vibration level of a constant velocity drive shaft under normal load in a healthy state.

[0060] In subsequent experiments, the average energy value within the sliding time window (e.g., the most recent second) is calculated in real time. The sliding time window can be set to, for example, 1 second, 2 seconds, or 3 seconds, and the rate of change can be calculated. When the rate of change When the value exceeds a preset threshold, such as 1.5, 2.0, or 3.0, it indicates a significant increase in the characteristic frequency energy, indicating that the cage has experienced fatigue failure, and the system automatically shuts down and alarms.

[0061] Since the initial stage of testing often requires a low-load break-in period, directly using the initial signal as a benchmark can lead to misjudgments in the subsequent high-load stage. This solution sets the initial benchmark value selection time after the torque reaches its peak, meaning that the initial benchmark value is based on vibration data under formal fatigue conditions when the specimen is in good condition and operating stably. Subsequently, by calculating the ratio of the current value to the benchmark value through a sliding time window, the absolute value difference caused by load fluctuations can be effectively eliminated, thus truly reflecting the relative energy change caused by fatigue damage.

[0062] Optionally, the initial reference value Alternatively, the values ​​can be calibrated in advance, and the average energy value can be calculated directly during the formal fatigue phase. and rate of change That's all.

[0063] Based on the above method, this application also provides a fatigue testing system for the outer ball cage cage of a constant velocity drive shaft. (See reference...) Figure 2 The constant velocity drive shaft external ball cage dynamic fatigue testing system 100 includes a clamping module 10, a composite loading module 20, a signal acquisition module 30, and a control module 40.

[0064] The clamping module 10 includes a first loading end and a second loading end.

[0065] The first loading end is configured as an outer ball cage with a fixed constant velocity drive shaft and is capable of applying a radial load perpendicular to the shaft axis to the outer ball cage. The first loading end typically includes a radial actuator, such as a hydraulic servo cylinder or an electric cylinder, whose piston rod is connected to a clamp for gripping or holding the bell-shaped shell of the outer ball cage.

[0066] The second loading end is configured to connect to the end of the shaft of the constant velocity drive shaft. The second loading end typically includes a rotating spindle, which integrates a torque loading mechanism and an angle swing mechanism.

[0067] The composite loading module 20 is connected to the second loading end and is used to apply torque signals and swing angle signals to the second loading end to drive the second loading end to execute complex motion trajectories.

[0068] The signal acquisition module 30 is used to acquire vibration acceleration signals during the test. The signal acquisition module 30 may include an acceleration sensor installed near the outer ball cage.

[0069] The control module 40 is electrically connected to the first loading terminal, the composite loading module 20, and the signal acquisition module 30, respectively. The control module 40 can be an industrial computer or a real-time controller, internally running the control algorithm of the aforementioned experimental method. It is responsible for sending instructions to each module, controlling actions according to the set waveforms, phases, and frequencies, while simultaneously receiving data from the signal acquisition module, performing real-time spectrum analysis and logical judgment, and monitoring the experimental status.

[0070] To enable those skilled in the art to better understand the present invention, a specific example of experimental parameters is provided below: Specimen Information: A certain model of new energy vehicle uses a constant velocity drive shaft with a fixed outer ball cage (RF type), containing 6 steel balls, and the shaft length is 600mm.

[0071] Experimental procedures and parameter settings: 1. Clamping (S1): Fix the outer ball cage to the hydraulic chuck at the first loading end, and connect the end of the shaft to the main shaft flange at the second loading end through the flange.

[0072] 2. Break-in phase (preliminary steps): Set the break-in time to 15 minutes. Apply alternating torque with a peak value of ±500 Nm and a frequency of 2 Hz; apply oscillation angle with an amplitude of ±10º, a frequency of 2 Hz, and a phase difference of 0º.

[0073] 3. Formal Loading (S2-S4): Torque control (S2): Set the first alternating torque peak value to ±1000Nm, the waveform to a trapezoidal wave, with the rising edge and falling edge each accounting for 10% of the cycle, and the frequency to 2Hz.

[0074] Angle control (S3): Set the first swing angle amplitude to ±20º and the frequency to 2Hz. Set the phase angle to 45º, meaning the peak value of the angle waveform lags behind the torque waveform by 45 degrees.

[0075] Radial force control (S4): Sets the base load force =500N, set the linear correlation coefficient k = 50N / º.

[0076] When the angle When = 0º, radial force = 500N.

[0077] When the angle At 20º, radial force = 500 + 50×20 = 1500N.

[0078] The controller updates the radial force command in real time at a frequency of 2Hz.

[0079] 4. Signal Acquisition (S5): The sensor is installed above the outer ball cage, and the sampling frequency is set to 20kHz.

[0080] 5. Initial baseline value establishment (S6 precondition): Once the system has been loaded from 500 Nm to 1000 Nm and stabilized, reference sampling is initiated.

[0081] The sampling time is 2.5 seconds, covering 5 cycles.

[0082] Calculated initial reference value = 0.85 m / s 2 (Normalized energy unit).

[0083] 6. Failure Monitoring (S6): Set the sliding window duration to 1 second.

[0084] The preset threshold is set to 3.0, which means an energy increase of 200%.

[0085] When the experiment reached the 500,000th cycle, energy fluctuations were monitored, and the average energy value was... Rise to 1.7 m / s 2 rate of change = 2.0, the system issued a warning.

[0086] When the experiment reached its 520,000th cycle, the average energy value was... It suddenly rose to 3.5 m / s 2 rate of change = 4.11>3.0. The system has been determined to be faulty and has been shut down for protection.

[0087] Disassembly and inspection revealed a clear through-crack at the cage window, verifying the accuracy of the initial assessment.

[0088] Unlike existing technologies, this application provides a fatigue testing method and system for the outer ball cage of a constant velocity drive shaft. This method constructs a highly realistic extreme bending-torsional combined load environment by coordinating the control of torque, oscillation angle, and radial load, and introducing phase lag control. This solves the problem that traditional single-condition loading cannot reproduce actual failure modes. Simultaneously, by introducing a failure determination method based on spectrum analysis and specific benchmark selection logic, it achieves accurate identification of early micro-cracks and wear in the cage, avoiding misjudgments caused by load changes during the break-in period or external interference, significantly improving the reliability of the test results and their engineering application value.

[0089] In summary, this application, through unique methodological design and system integration, achieves precise dynamic fatigue testing of the outer ball cage cage under extreme bending and torsion conditions. By employing dynamic phase control, radial force tracking, and failure determination techniques based on frequency domain characteristics and intelligent benchmark selection, the authenticity and reliability of the test are greatly improved, solving a long-standing technical problem in the industry and possessing extremely high practical value and promotional significance.

[0090] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A fatigue test method for the outer ball cage of a constant velocity drive shaft, characterized in that, include: S1: Clamp the constant velocity drive shaft specimen; the constant velocity drive shaft specimen includes an outer ball cage and a shaft rod, the outer ball cage is fixed to the first loading end, and the end of the shaft rod is connected to the second loading end; S2: Apply a first alternating torque to the second loading end, the torque value of the first alternating torque fluctuating periodically with time; S3: Apply a first swing angle to the second loading end so that the axis of the shaft and the axis of the bell-shaped shell of the outer ball cage form an angle and swing back and forth within a preset angle range; S4: Apply a first radial load to the bell-shaped shell of the outer ball cage through the first loading end, wherein the direction of the first radial load is perpendicular to the axis of the shaft; S5: Real-time acquisition of vibration acceleration signals in the outer ball cage area; S6: Perform spectral analysis on the vibration acceleration signal to extract the energy value of the characteristic frequency of the cage inside the outer ball cage. When the rate of change of the energy value relative to the initial reference value exceeds a preset threshold, the cage is determined to be faulty.

2. The fatigue test method for the outer ball cage of the constant velocity drive shaft according to claim 1, characterized in that, In step S2, the waveform of the first alternating torque is configured as a sine wave or a trapezoidal wave, and the frequency of the first alternating torque is controlled within the range of 1Hz to 5Hz.

3. The fatigue test method for the outer ball cage of the constant velocity drive shaft according to claim 1, characterized in that, In step S3, the swing frequency of the first swing angle is set to be consistent with the frequency of the first alternating torque.

4. The fatigue test method for the outer ball cage of the constant velocity drive shaft according to claim 3, characterized in that, In step S3, the waveform of the first swing angle is configured to lag the waveform of the first alternating torque by a preset phase angle, the preset phase angle being in the range of 30° to 90°, to simulate the impact hysteresis under extreme cornering conditions.

5. The fatigue test method for the outer ball cage of the constant velocity drive shaft according to claim 1, characterized in that, In step S4, the magnitude of the first radial load is configured to increase as the absolute value of the first swing angle increases.

6. The fatigue test method for the outer ball cage of the constant velocity drive shaft according to claim 5, characterized in that, In step S4, the first radial load consists of a constant base load force and an adjustment load force that dynamically changes with the first swing angle, wherein the adjustment load force is linearly positively correlated with the absolute value of the first swing angle.

7. The fatigue test method for the outer ball cage of the constant velocity drive shaft according to claim 1, characterized in that, In step S6, the specific steps for extracting the energy value of the cage characteristic frequency include: calculating the root mean square value of the filtered signal at the cage passing frequency and its second harmonic, and using the sum of the root mean square values ​​as the energy value.

8. The fatigue test method for the outer ball cage of the constant velocity drive shaft according to claim 7, characterized in that, In step S6, the initial reference value is set as the average energy value collected and calculated within the first preset time period after the torque applied to the second loading end reaches the peak value of the first alternating torque. The rate of change is calculated based on the ratio of the average energy value within the sliding time window at the current moment to the initial reference value.

9. The fatigue test method for the outer ball cage of the constant velocity drive shaft according to claim 1, characterized in that, The test process was divided into a break-in stage and a formal fatigue stage. During the break-in stage, the peak torque and oscillation angle amplitude were set to 50% to 70% of those during the formal fatigue stage.

10. A fatigue testing system for an outer ball cage cage of a constant velocity drive shaft, characterized in that, include: The clamping module includes a first loading end and a second loading end; the first loading end is configured to fix the outer ball cage of the constant velocity drive shaft and is capable of applying a radial load perpendicular to the shaft axis to the outer ball cage; the second loading end is configured to connect to the end of the shaft of the constant velocity drive shaft. A composite loading module, connected to the second loading end, is used to apply torque and swing angle to the second loading end; The signal acquisition module is used to acquire vibration acceleration signals during the test. The control module is electrically connected to the first loading end, the composite loading module, and the signal acquisition module, respectively, and is used to control each module to perform the fatigue test method as described in any one of claims 1 to 9.

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