A self-excited vibration test method for a helicopter supercritical floating spline shaft

Abstract

The invention discloses a self-excited vibration test method for a supercritical floating spline shaft of a helicopter. The tester of a bench test is improved, and a simulated installation support is designed to simulate the actual installation structure of the floating spline of a helicopter tail transmission system, so as to meet the self-excited vibration test conditions of the tail shaft. The boundary conditions of the self-excited vibration of the supercritical floating spline shaft can be obtained through the bench test, and the dynamic characteristics of the floating spline supercritical tail shaft can be further clarified. The self-excited vibration boundary is clearer, which provides further safety guarantee for the subsequent iron bird test or field flight test. The test process is operable and predictable. If the problem of self-excited vibration of the tail shaft occurs, the troubleshooting cycle can be greatly shortened and the troubleshooting cost can be reduced. A safe and reliable test process is provided for the self-excited vibration test of the supercritical floating spline shaft of the helicopter.

Description

Technical Field

[0001] The invention relates to the technical field of helicopter transmission system testing and experiment, in particular to a self-excited vibration testing method for a helicopter supercritical floating spline shaft. Background Art

[0002] The main function of the helicopter tail transmission shaft system is to transfer the tail transmission power of the main reducer to the center reducer, and to transfer the output power of the center reducer to the tail reducer. It is an important part of the helicopter transmission system. In recent years, with the further improvement of helicopter tactical indicators, the supercritical tail shaft with floating spline connection structure has become an advanced transmission system design concept. This type of tail shaft has a simple structure, good maintainability and high reliability. The floating spline is grease lubricated, and the front and rear cylindrical surfaces are centered. It generally works for a long time above the first-order critical speed. The structural diagram is shown in Figure 1 As shown. When the floating spline structure of the tail shaft is in an abnormal working state, for example, the spline mating surface or positioning surface is poorly lubricated, the friction force inside the spline increases, inducing the increase of self-excited vibration, thereby aggravating the wear of the spline mating surface, and further aggravating the self-excited vibration. This is repeated, the local temperature of the mating part rises, the grease dries up, and the self-excited vibration gradually diverges, causing the tail shaft to break due to excessive amplitude, seriously affecting the flight safety of the helicopter. Therefore, in order for the helicopter supercritical tail drive shaft to achieve long-term safe operation, one of the main factors affecting the operation safety of the supercritical tail shaft must be solved, that is, the self-excited vibration divergence problem of the supercritical tail shaft containing the floating spline structure.

[0003] At present, the main bench tests for helicopter tail drive shafts include critical speed tests and overtorque tests. The tests are generally carried out on electric power closed testers or mechanical power closed testers. The flanges at both ends of the tail shaft are connected to the test equipment through laminated couplings. The test is carried out at a certain torque and speed. The Bode diagram of the tail shaft is obtained by the vibration test system to determine the operating speed safety margin of the supercritical shaft. At the same time, an overtorque test of a certain number of cycles is carried out at the specified lamination installation angle to verify the structural integrity and durability of the tail shaft. In addition, according to the requirements of the helicopter development specifications, the real ground iron bird test or actual flight test is the most ideal research method, but the iron bird test and flight test are risky, costly, and time-consuming, and cannot be used as test conditions for studying self-excited vibration, so the application of this method is limited. Therefore, whether it is a bench test or an iron bird test, there is no relevant self-excited vibration verification test specified for the supercritical tail shaft with floating splines, and there is no relevant test method to follow.

[0004] However, my country started late in the study of self-excited vibration of supercritical tail shaft with floating spline, the mechanism research is not perfect, and there are few experimental studies in this area. At present, only some simple test devices are used to verify the calculation and simulation results, and mainly simulated test pieces or scaled pieces are used for testing. At the same time, the boundary conditions are simplified and the test conditions are single, which still cannot simulate the test loads under actual boundary conditions. How to effectively carry out the self-excited vibration test research of supercritical shaft, standardize the test methods, and find out the divergence boundary of self-excited vibration is crucial to suppressing the self-excited vibration of supercritical tail shaft. Summary of the invention

[0005] The invention provides a self-excited vibration test method for a supercritical floating spline shaft of a helicopter, so as to solve the technical problem that the boundary conditions of the self-excited vibration of the supercritical floating spline shaft cannot be obtained by the existing test method.

[0006] According to one aspect of the present invention, a self-excited vibration test method for a supercritical floating spline shaft of a helicopter is provided, comprising the following contents:

[0007] Design a simulated mounting bracket for mounting the tail transmission output pinion assembly to simulate the actual mounting structure of the floating spline of the helicopter tail transmission system;

[0008] Connect the simulated mounting support and the supercritical tail shaft in series in the tester;

[0009] Arrange test sensors and set various parameter limit values ​​in the test system of the tester;

[0010] The tail shaft self-excited vibration test was carried out to obtain the boundary conditions of the self-excited vibration of the supercritical floating spline shaft.

[0011] Furthermore, the tail transmission output pinion assembly includes a pinion output shaft, a casing assembly, a roller bearing and a ball bearing. The front end of the pinion output shaft is supported on the roller bearing and the rear end is supported on the ball bearing. The ball bearing is installed on the casing assembly. The simulated mounting support includes a box body, a box cover, a lubricating oil nozzle, an expansion sleeve flange and a sealing end cover. The box body and the box cover are designed as upper and lower parts and are fixedly connected. The roller bearing and the casing assembly are installed between the box body and the box cover, and the casing assembly is fixed to the box body and the rear end surface of the box body. A fixed connection is provided to realize axial fixation of the tail transmission output pinion assembly; the roller bearing is matched with the housing and the housing cover with a small clearance; the lubricating oil nozzle is installed on the housing cover and extends into the cavity enclosed by the housing cover and the housing to lubricate the roller bearing and the ball bearing; an oil return port is provided on the bottom side of the housing to connect with an external lubricating oil system; the outer cylindrical surface of the expansion sleeve flange is interference fit with the inner cylindrical surface of the pinion output shaft to realize friction torque transmission; the sealing end cover is fixedly installed on the front end surface of the housing and the housing cover.

[0012] Furthermore, the process of arranging the test sensor includes the following contents:

[0013] At least two sets of temperature indicating sheets are pasted on the corresponding spline contact positions on the inner cylindrical surface of the tail transmission output flange, three-way vibration sensors are arranged at the simulated mounting support and bearing support, horizontal / vertical laser displacement sensors and speed sensors are arranged at 1 / 2 length of the supercritical tail shaft, and thermocouples are pasted on the outer ring of the support bearing.

[0014] Furthermore, the process of carrying out the tail shaft self-excited vibration test to obtain the boundary conditions of the supercritical floating spline shaft self-excited vibration includes the following contents:

[0015] Conduct modal tests to identify modal parameters, including natural frequency, damping ratio and mode shape;

[0016] Carry out speed commissioning test to verify whether the tail shaft is working normally;

[0017] Conduct running tests according to the test load spectrum to obtain test data of the self-excited vibration of the tail shaft;

[0018] On the basis of the running test, the poor lubrication state test is carried out to quantitatively determine the grease state of the spline when the self-excited vibration suddenly changes;

[0019] Based on the grease state determined by the poor lubrication state test, a durability wear test is conducted to determine the boundary values ​​of acceleration and displacement of the tail shaft self-excited vibration;

[0020] The wear of the spline and the locating section after the durability wear test is checked with a stereoscope, and the matching dimensions of the spline and the locating section are measured to determine the boundary conditions of the self-excited vibration of the tail shaft.

[0021] Furthermore, the process of conducting a modal test to identify modal parameters includes the following:

[0022] The acceleration sensor is arranged at a certain measuring point of the tail shaft, and a pulse force hammer is used to hammer in sequence to generate multi-point excitation. The pulse excitation signal generated by the pulse force hammer and the response signal measured by the acceleration sensor are collected and analyzed to identify the modal parameters.

[0023] Furthermore, the process of carrying out the speed adjustment test to verify whether the tail shaft working state is normal includes the following contents:

[0024] Starting from zero speed, gradually increase to 120% of the rated speed at intervals of 10%. Run stably for 3 minutes in each speed state, and record the simulated installation support vibration fundamental frequency and total amount, tail shaft displacement fundamental frequency and total amount corresponding to each speed state point. If it is within the limit, go to the next step. If it is exceeded, further eliminate the influencing factors that cause excessive vibration and repeat the speed debugging test to ensure normal vibration under the actual simulation state.

[0025] Furthermore, the process of performing the running test according to the test load spectrum to obtain the test data of the tail shaft self-excited vibration includes the following contents:

[0026] The running test is carried out according to the test load spectrum to simulate the speed and load of the tail shaft under the actual working state. Each test state is stable for 3 minutes, and the specific values ​​of the fundamental frequency and self-excited vibration under each test state are recorded. The test is repeated three times, and the maximum value of each test state is taken as the vibration data of the tail shaft under normal operation. At the same time, the bearing temperature change is recorded. After each test, the flange temperature indicator is removed and the highest temperature of the spline part of the whole process is recorded.

[0027] Furthermore, the process of conducting a poor lubrication state test based on the operation test to quantitatively determine the grease state of the spline when the self-excited vibration suddenly changes includes the following:

[0028] Reduce the amount of grease applied on the splines and locating surfaces at intervals of 10% of the total weight, repeat the test procedure of the operating test to perform a poor lubrication condition test, compare the test results of the poor lubrication condition test with the test results of the operating test, and determine whether the self-excited vibration of the tail shaft changes suddenly. If a sudden change occurs, stop the poor lubrication condition test and proceed to the next step. If no sudden change occurs, further reduce the amount of grease applied and repeat the poor lubrication condition test process until a sudden change occurs.

[0029] Furthermore, the process of performing a durability wear test based on the grease state determined by the poor lubrication state test to determine the boundary values ​​of the acceleration and displacement of the self-excited vibration of the tail shaft includes the following:

[0030] The last grease application amount in the poor lubrication state test and multiple test procedures in the load spectrum that induces the sudden change of self-excited vibration are selected as test conditions. The floating spline durability wear test is carried out under the installation angle of the laminated coupling specified in the tail shaft over-torque test. During the test, attention is paid to the tail shaft vibration, displacement, spline and bearing temperature changes. At the same time, the wear of the spline and locating section is detected in each cycle. When the self-excited vibration increases further and exceeds 50% of the sudden change value in the poor lubrication state test, the test is stopped.

[0031] Furthermore, the boundary conditions of the self-excited vibration of the tail shaft include the displacement value and vibration value corresponding to the self-excited vibration when the durability wear test is stopped, and the matching dimension measurement results of the spline and the positioning section after the durability wear test.

[0032] The present invention has the following effects:

[0033] The self-excited vibration test method of the helicopter supercritical floating spline shaft of the present invention can simulate the actual installation structure of the floating spline of the helicopter tail transmission system by designing a simulated installation support for installing the tail transmission output pinion assembly to reliably support the floating spline structure, so as to meet the tail shaft self-excited vibration test conditions. Then, the simulated installation support and the supercritical tail shaft are connected in series in the tester, and the test sensors are arranged to measure the test parameters during the test process, and the limit values ​​of various parameters are set in the tester test system, and finally the tail shaft self-excited vibration test is carried out to obtain the boundary conditions of the self-excited vibration of the supercritical floating spline shaft. The self-excited vibration test method of the present invention improves the test instrument of the bench test, designs a simulated installation support to simulate the actual installation structure of the floating spline of the helicopter tail transmission system, so as to meet the tail shaft self-excited vibration test conditions. The boundary conditions of the self-excited vibration of the supercritical floating spline shaft can be obtained through the bench test, and the dynamic characteristics of the floating spline supercritical tail shaft can be further clarified. The self-excited vibration boundary is clearer, which provides further safety guarantee for the subsequent iron bird test or field flight test, and the test process is operable and predictable. If the tail shaft self-excited vibration problem occurs, the troubleshooting cycle can be greatly shortened and the troubleshooting cost can be reduced, which provides a safe and reliable test process for the self-excited vibration test of the helicopter supercritical floating spline shaft.

[0034] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0036] Figure 1 It is a structural schematic diagram of a floating spline structure.

[0037] Figure 2 It is a flow chart of a self-excited vibration test method for a helicopter supercritical floating spline shaft according to a preferred embodiment of the present invention.

[0038] Figure 3 It is a schematic diagram of the structure in which the tail transmission output pinion assembly is installed on a simulated mounting support in a preferred embodiment of the present invention.

[0039] Figure 4 It is a schematic diagram of the installation structure in which a simulated installation support and a supercritical tail shaft are connected in series in an electric power closed tester in a preferred embodiment of the present invention.

[0040] Figure 5 yes Figure 2 Schematic diagram of a sub-process of step S4 in FIG. DETAILED DESCRIPTION

[0041] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0042] like Figure 2 As shown, a preferred embodiment of the present invention provides a self-excited vibration test method for a supercritical floating spline shaft of a helicopter, comprising the following contents:

[0043] Step S1: designing a simulated mounting bracket for mounting a tail transmission output pinion assembly to simulate an actual mounting structure of a floating spline of a helicopter tail transmission system;

[0044] Step S2: Connecting the simulated mounting support and the supercritical tail shaft in series in the tester;

[0045] Step S3: Arrange test sensors and set various parameter limit values ​​in the test system of the tester;

[0046] Step S4: Conduct a tail shaft self-excited vibration test to obtain boundary conditions for self-excited vibration of the supercritical floating spline shaft.

[0047] It can be understood that the self-excited vibration test method of the helicopter supercritical floating spline shaft of this embodiment can simulate the actual installation structure of the floating spline of the helicopter tail transmission system by designing a simulated installation support for installing the tail transmission output pinion assembly to reliably support the floating spline structure, so as to meet the tail shaft self-excited vibration test conditions. Then, the simulated installation support and the supercritical tail shaft are connected in series in the tester, and the test sensors are arranged to measure the test parameters during the test process, and the limit values ​​of various parameters are set in the tester test system. Finally, the tail shaft self-excited vibration test is carried out to obtain the boundary conditions of the self-excited vibration of the supercritical floating spline shaft. The self-excited vibration test method of the present invention improves the test instrument of the bench test, designs a simulated installation support to simulate the actual installation structure of the floating spline of the helicopter tail transmission system, so as to meet the tail shaft self-excited vibration test conditions. The boundary conditions of the self-excited vibration of the supercritical floating spline shaft can be obtained through the bench test, and the dynamic characteristics of the floating spline supercritical tail shaft can be further clarified. The self-excited vibration boundary is clearer, which provides further safety guarantee for the subsequent iron bird test or field flight test, and the test process is operable and predictable. If the tail shaft self-excited vibration problem occurs, the troubleshooting cycle can be greatly shortened and the troubleshooting cost can be reduced, which provides a safe and reliable test process for the self-excited vibration test of the helicopter supercritical floating spline shaft.

[0048] It can be understood that in step S1, it is necessary to improve the structure of the existing electric power sealing tester or mechanical power sealing tester to meet the tail shaft self-excited vibration test conditions. Figure 3As shown, the tail transmission output pinion assembly includes a pinion output shaft, a casing assembly, a roller bearing and a ball bearing. The front end of the pinion output shaft is supported on the roller bearing and the rear end is supported on the ball bearing. The ball bearing is installed on the casing assembly. The simulated mounting support includes a housing, a casing cover, a lubricating oil nozzle, an expansion sleeve flange and a sealing end cover. The housing and the casing cover are designed to be split up and down and fixedly connected. Specifically, the housing and the casing cover are positioned by locating pins on both sides and are connected and fixed by four M20 bolts. The roller bearing and the casing assembly are installed between the housing and the casing cover, and the casing assembly is fixedly connected to the housing and the rear end face of the housing to achieve axial fixation of the tail transmission output pinion assembly. Specifically, the casing assembly is fixed to the rear end face of the casing cover and the housing by 8 M12 bolts. The roller bearing is matched with the housing and the casing cover with a small clearance to meet the requirements of the bearing manual. The lubricating oil nozzle is installed on the box cover and extends into the cavity formed by the box cover and the box body, and is used to lubricate the roller bearings and ball bearings. The bottom side of the box body is provided with an oil return port, which is used to connect to the external lubricating oil system. After the lubricating oil enters the oil supply port, it is divided into two paths, and the roller bearings and ball bearings are lubricated through the small holes on both sides of the lubricating oil nozzle, and then it is drawn back to the external lubricating oil system through the oil return port. The outer cylindrical surface of the expansion sleeve flange is matched with the inner cylindrical surface of the pinion output shaft. According to the design requirements, a certain torque is applied to a circle of hexagon socket bolts of the expansion sleeve to form an interference fit with the inner hole of the pinion output shaft, thereby realizing friction torque transmission. The sealing end cover is fixedly installed on the front end surface of the box body and the box cover to improve the sealing performance. The rear end of the pinion output shaft is connected to the tail transmission output flange through a floating spline, wherein the rear end of the pinion output shaft is an internal spline, and the tail transmission output flange is an external spline. By improving the tester of the bench test, a simulated mounting bracket was designed to simulate the actual mounting structure of the floating spline of the helicopter tail transmission system to meet the tail shaft self-excited vibration test conditions.

[0049] It can be understood that in step S2, the pinion output shaft is connected to the tail transmission output flange through a floating spline, and the tail transmission output flange is connected to the supercritical tail shaft through a laminated coupling, so that the simulated mounting support and the supercritical tail shaft are connected in series in the tester. Wherein, the tester adopts an electric power closed tester or a mechanical power closed tester. As a preferred embodiment, Figure 4As shown, the simulated mounting support and the supercritical tail shaft are connected in series in the electric power closed tester, and then the whole tester system is installed and aligned. The electric power closed tester uses a drive motor as the power, and adjusts the speed of the supercritical tail shaft by adjusting the output speed of the drive motor through the variable frequency speed regulator. The power of the drive motor is transmitted to the supercritical tail shaft through a front speed-increasing gearbox for testing. The torque load of the tester is applied by the loading motor at the other end. By changing the excitation current of the loading motor, the electric power generated by the loading motor can be adjusted. The electric power output by the loading motor generates a resistance torque on the motor rotor, which can apply a torque load to the supercritical tail shaft. At the same time, the power output by the loading motor can be fed back to the front traction motor or the power grid through the electric power closed system. Among them, the simulated mounting support, the front speed-increasing gearbox, and the rear speed-increasing gearbox are all lubricated by an external lubrication system, and the lubricating system circuit is equipped with a lubricating oil pressure sensor and a lubricating oil temperature sensor.

[0050] It can be understood that the process of arranging the test sensor in step S3 specifically includes the following contents:

[0051] At least two sets of temperature indicating sheets are pasted on the corresponding spline contact positions on the inner cylindrical surface of the tail transmission output flange, three-way vibration sensors are arranged at the simulated mounting support and bearing support, horizontal / vertical laser displacement sensors and speed sensors are arranged at 1 / 2 length of the supercritical tail shaft, and thermocouples are pasted on the outer ring of the support bearing.

[0052] Specifically, at least two sets of temperature indicator sheets (such as Figure 1 As shown in the figure, the temperature of the spline during the test can be measured. By arranging three-way vibration sensors at the simulated mounting support and the bearing support, the vibration values ​​in the horizontal, vertical and axial directions can be measured. By arranging horizontal / vertical laser displacement sensors and speed sensors at 1 / 2 the length of the supercritical tail shaft, the vertical displacement, horizontal displacement and speed of the supercritical tail shaft during the test can be measured. By sticking a thermocouple on the outer ring of the support bearing, the bearing temperature change can be monitored during the test.

[0053] Then, turn on the tester control system and test system, set the limit values ​​of various parameters of the tester, including torque, speed, displacement, vibration, lubricating oil pressure and lubricating oil temperature of the lubrication system, etc., and confirm that all preparatory work before the test has been completed, so that the conditions for safe testing are met.

[0054] It is understandable that Figure 5 Said step S4 specifically includes the following contents:

[0055] Step S41: conducting a modal test to identify modal parameters, where the modal parameters include natural frequency, damping ratio and modal vibration shape;

[0056] Step S42: Carry out a speed adjustment test to verify whether the tail shaft is working normally;

[0057] Step S43: performing an operation test according to the test load spectrum to obtain test data of the self-excited vibration of the tail shaft;

[0058] Step S44: conducting a poor lubrication state test based on the operation test to quantitatively determine the grease state of the spline when the self-excited vibration suddenly changes;

[0059] Step S45: performing a durability wear test based on the grease state determined by the poor lubrication state test to determine the boundary values ​​of the acceleration and displacement of the self-excited vibration of the tail shaft;

[0060] Step S46: Use a stereoscope to check the wear of the spline and the locating section after the durability wear test, and measure the matching dimensions of the spline and the locating section to determine the boundary conditions of the self-excited vibration of the tail shaft.

[0061] It can be understood that in the present invention, firstly, modal parameters including natural frequency, damping ratio and modal vibration shape are identified through modal test, so as to provide a basis for the safe implementation of speed test, and then speed test is carried out to verify whether the working state of tail shaft is normal, to find out the vibration law of tail shaft in the working speed range, and then operation test is carried out to simulate the speed and load of tail shaft in actual working state, to obtain specific test data of self-excited vibration of tail shaft, and then, on the basis of operation test, poor lubrication state test is carried out to verify the sudden change of self-excited vibration, to quantitatively judge the state of spline grease at the time of sudden change, and then, based on the state of grease determined by poor lubrication test, a durability wear test is carried out to further verify the durability and structure of tail shaft. The structural integrity is checked, and the boundary values ​​of the self-excited vibration acceleration and displacement of the tail shaft are determined. Finally, the wear of the spline and the positioning segment after the test is further determined through dimensional detection and stereoscopic inspection. Each test is progressive and mutually verified, and finally the boundary conditions of the self-excited vibration of the tail shaft are obtained. The dynamic characteristics of the floating spline supercritical tail shaft can be further clarified, and the self-excited vibration boundary is clearer, which provides further safety guarantees for the subsequent iron bird test or field flight test. The test process is operational and predictable. If the tail shaft self-excited vibration problem occurs, the troubleshooting cycle can be greatly shortened and the troubleshooting cost can be reduced, which provides a safe and reliable test process for the self-excited vibration test of the helicopter supercritical floating spline shaft.

[0062] It can be understood that the step S41 specifically includes the following contents:

[0063] Modal tests are carried out. Modal test software is used to arrange the acceleration sensor at a measuring point of the tail shaft. A pulse hammer is used to hammer in sequence to generate multi-point excitation. The pulse excitation signal generated by the pulse hammer and the response signal measured by the acceleration sensor are collected for analysis. The analysis process specifically includes FFT analysis, calculation of transfer function, etc., to identify the modal parameters. The modal parameters mainly include natural frequency, damping ratio and modal vibration shape.

[0064] It can be understood that the step S42 specifically includes the following contents:

[0065] Carry out the speed adjustment test, starting from zero speed, gradually increase to 120% rated speed at intervals of 10% rated speed, and run stably for 3 minutes at each speed state, wherein, when it increases to the speed corresponding to the natural frequency obtained in step S41, it passes quickly without stopping, and records the vibration fundamental frequency and total amount of the simulated installation support, the fundamental frequency and total amount of the tail shaft displacement corresponding to each speed state point. If it does not exceed the limit, proceed to the next step. If it exceeds the limit, further eliminate the factors causing excessive vibration and repeat the speed adjustment test to ensure normal vibration under the actual simulation state. Among them, the factors causing excessive vibration include mechanical installation, bolt imbalance, internal negative pressure at the spline fitting, test system and other reasons.

[0066] It can be understood that the step S43 specifically includes the following contents:

[0067] According to the test load spectrum, the running test is carried out to simulate the speed and load of the tail shaft in the actual working state. Each test state is stable for 3 minutes, and the fundamental frequency vibration and self-excited vibration of the tail shaft are paid attention to. The specific values ​​of the fundamental frequency and self-excited vibration in each test state are recorded. The test is repeated three times, and the maximum value of each test state is taken as the vibration data of the tail shaft when it is working normally. At the same time, the bearing temperature change is recorded. After each test, the flange temperature indicator is removed to record the highest temperature of the spline part of the whole process. Among them, the test load spectrum includes test loads of various working states such as starting, ground slow, air slow, level flight, climbing, turning, and descending. Each working state is controlled by the test program.

[0068] It can be understood that the step S44 specifically includes the following contents:

[0069] Reduce the amount of grease applied on the splines and locating surfaces at intervals of 10% of the total weight, repeat the test procedure in step S43 to perform a poor lubrication condition test, compare the test results of the poor lubrication condition test with the test results of the operation test, and determine whether the self-excited vibration of the tail shaft changes suddenly. If a sudden change occurs, stop the poor lubrication condition test and proceed to the next step. If no sudden change occurs, further reduce the amount of grease applied, and repeat step S44 until a sudden change occurs.

[0070] It can be understood that the self-excited vibration of the tail transmission shaft containing floating splines mentioned in the present invention includes the following concepts:

[0071] (1) When the tail drive shaft passes the first critical speed, and certain conditions are met between the external damping and the internal damping (friction on the spline tooth surface and the locating surface), the system may experience self-excited vibration;

[0072] (2) When the tail drive shaft is in a supercritical working state and the internal friction damping is less than the external damping, the drive shaft will self-excite vibration, but at this time the vibration amplitude of the drive shaft is within a certain range and a stable limit cycle can be formed;

[0073] (3) When the tail drive shaft is in a supercritical working state and when the internal friction damping is greater than the external damping, the drive shaft vibration breaks through the limit cycle, the vibration amplitude increases sharply, self-excited vibration divergence occurs, and instability occurs.

[0074] Among them, self-excited vibration means that there is always a subharmonic during the operation of the tail shaft, and its frequency is the same as the first-order natural frequency of the tail shaft, and the corresponding displacement value and vibration acceleration under the self-excited vibration frequency will undergo a sudden change in magnitude, especially the displacement. For example, under a certain load state, the displacement or acceleration corresponding to the self-excited vibration frequency of one or several measuring points of the tail shaft has an order of magnitude change compared with the test result of step S43, such as the displacement changes from 0.1mm to 1mm, and the vibration acceleration changes from 0.03g to 0.3g, then it is determined that the self-excited vibration of the tail shaft has a sudden change.

[0075] It can be understood that the step S45 specifically includes the following contents:

[0076] The last amount of grease applied in step S44 and multiple test procedures in the load spectrum that induces a sudden change in self-excited vibration are selected as test conditions, and a floating spline durability wear test is carried out under the installation angle of the laminated coupling specified in the tail shaft over-torque test. During the test, attention is paid to the tail shaft vibration, displacement, spline and bearing temperature changes. At the same time, the wear of the spline and the locating section is detected in each cycle. When the self-excited vibration increases further and exceeds 50% of the sudden change value in step S44, the test is stopped.

[0077] It can be understood that in step S46, the wear of the spline and the locating section after the durability wear test is checked with a stereoscope, the matching dimensions of the spline and the locating section are measured, and the maximum temperature of the temperature indicator and the thermocouple is recorded, so as to determine the boundary conditions of the self-excited vibration of the tail shaft.

[0078] Optionally, the boundary conditions of the self-excited vibration of the tail shaft are based on the displacement value and vibration value corresponding to the self-excited vibration when the durability wear test is stopped, and the measurement results of the matching dimensions of the spline and the positioning section after the durability wear test. If any parameter exceeds the limit, the test must be stopped immediately for inspection. The results of the stereoscopic inspection, temperature indicator and thermocouple values ​​are only for reference. For example, if the splines and positioning surfaces are found to have obvious scratches, pits or the temperature exceeds the limit value during the stereoscopic inspection, the test can be stopped. The rest will be handled according to the actual situation and will not affect the safety of the test. In the subsequent iron bird test or field flight test, the boundary conditions obtained by the bench test must be strictly referred to to ensure the smooth progress of the whole machine test.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A self-excited vibration test method for a helicopter supercritical floating spline shaft, characterized in that: Includes the following: Design a simulated mounting bracket for mounting the tail transmission output pinion assembly to simulate the actual mounting structure of the floating spline of the helicopter tail transmission system; Connect the simulated mounting support and the supercritical tail shaft in series in the tester; Arrange test sensors and set various parameter limit values ​​in the test system of the tester; Carry out tail shaft self-excited vibration test to obtain the boundary conditions of supercritical floating spline shaft self-excited vibration; The tail transmission output pinion assembly comprises a pinion output shaft, a casing assembly, a roller bearing and a ball bearing. The front end of the pinion output shaft is supported on the roller bearing, and the rear end is supported on the ball bearing. The ball bearing is installed on the casing assembly. The simulated mounting support comprises a casing, a casing cover, a lubricating oil nozzle, an expansion sleeve flange and a sealing end cover. The casing and the casing cover are designed as upper and lower parts and are fixedly connected. The roller bearing and the casing assembly are installed between the casing and the casing cover, and the casing assembly is fixedly connected to the casing and the rear end surface of the casing to achieve axial fixation of the tail transmission output pinion assembly. The roller bearing is matched with the casing and the casing cover with a small clearance. The lubricating oil nozzle is installed on the casing cover and extends into the cavity enclosed by the casing cover and the casing to lubricate the roller bearing and the ball bearing. An oil return port is provided on the bottom side of the casing for connection with an external lubricating oil system. The outer cylindrical surface of the expansion sleeve flange is interference fit with the inner hole cylindrical surface of the pinion output shaft to achieve friction torque transmission. The sealing end cover is fixedly installed on the front end surface of the casing and the casing cover. The process of arranging the test sensor includes the following: At least two sets of temperature-indicating sheets are pasted on the inner cylindrical surface of the tail transmission output flange at the corresponding spline contact positions, three-way vibration sensors are arranged at the simulated mounting support and the bearing support, horizontal / vertical laser displacement sensors and speed sensors are arranged at 1 / 2 of the length of the supercritical tail shaft, and thermocouples are pasted on the outer ring of the support bearing; The process of carrying out the tail shaft self-excited vibration test to obtain the boundary conditions of the supercritical floating spline shaft self-excited vibration includes the following: Conduct modal tests to identify modal parameters, including natural frequency, damping ratio and mode shape; Carry out speed commissioning test to verify whether the tail shaft is working normally; Conduct running tests according to the test load spectrum to obtain test data of the self-excited vibration of the tail shaft; On the basis of the running test, the poor lubrication state test is carried out to quantitatively determine the grease state of the spline when the self-excited vibration suddenly changes; Based on the grease state determined by the poor lubrication state test, a durability wear test is conducted to determine the boundary values ​​of acceleration and displacement of the tail shaft self-excited vibration; The wear of the spline and the locating section after the durability wear test is checked with a stereoscope, and the matching dimensions of the spline and the locating section are measured to determine the boundary conditions of the self-excited vibration of the tail shaft.

2. The self-excited vibration test method of a helicopter supercritical floating spline shaft according to claim 1, characterized in that: The process of conducting modal tests to identify modal parameters includes the following: The acceleration sensor is arranged at a certain measuring point of the tail shaft, and a pulse force hammer is used to hammer in sequence to generate multi-point excitation. The pulse excitation signal generated by the pulse force hammer and the response signal measured by the acceleration sensor are collected and analyzed to identify the modal parameters.

3. The self-excited vibration test method of a helicopter supercritical floating spline shaft according to claim 1, characterized in that: The process of carrying out the speed commissioning test to verify whether the tail shaft is working normally includes the following: Starting from zero speed, gradually increase to 120% of the rated speed at intervals of 10%. Run stably for 3 minutes in each speed state, and record the simulated installation support vibration fundamental frequency and total amount, tail shaft displacement fundamental frequency and total amount corresponding to each speed state point. If it is within the limit, proceed to the next step. If it is exceeded, further eliminate the influencing factors that cause excessive vibration and repeat the speed debugging test to ensure normal vibration under the actual simulation state.

4. The self-excited vibration test method of a helicopter supercritical floating spline shaft according to claim 1, characterized in that: The process of performing the running test according to the test load spectrum to obtain the test data of the tail shaft self-excited vibration includes the following contents: The running test is carried out according to the test load spectrum to simulate the speed and load of the tail shaft under the actual working state. Each test state is stable for 3 minutes, and the specific values ​​of the fundamental frequency and self-excited vibration under each test state are recorded. The test is repeated three times, and the maximum value of each test state is taken as the vibration data of the tail shaft under normal operation. At the same time, the bearing temperature change is recorded. After each test, the flange temperature indicator is removed and the highest temperature of the spline part of the whole process is recorded.

5. The self-excited vibration test method of a helicopter supercritical floating spline shaft according to claim 1, characterized in that: The process of conducting the poor lubrication state test on the basis of the running test to quantitatively determine the grease state of the spline when the self-excited vibration suddenly changes includes the following contents: Reduce the amount of grease applied on the splines and locating surfaces at intervals of 10% of the total weight, repeat the test procedure of the operating test to conduct a poor lubrication condition test, compare the test results of the poor lubrication condition test with the test results of the operating test, and determine whether the self-excited vibration of the tail shaft changes suddenly. If a sudden change occurs, stop the poor lubrication condition test and proceed to the next step. If no sudden change occurs, further reduce the amount of grease applied and repeat the poor lubrication condition test process until a sudden change occurs.

6. The self-excited vibration test method of a helicopter supercritical floating spline shaft according to claim 1, characterized in that: The process of performing a durability wear test based on the grease state determined by the poor lubrication state test to determine the boundary values ​​of the acceleration and displacement of the self-excited vibration of the tail shaft includes the following: The last grease application amount in the poor lubrication state test and multiple test procedures in the load spectrum that induces the sudden change of self-excited vibration are selected as test conditions. The floating spline durability wear test is carried out under the installation angle of the laminated coupling specified in the tail shaft over-torque test. During the test, attention is paid to the tail shaft vibration, displacement, spline and bearing temperature changes. At the same time, the wear of the spline and locating section is detected in each cycle. When the self-excited vibration increases further and exceeds 50% of the sudden change value in the poor lubrication state test, the test is stopped.

7. The self-excited vibration test method of a helicopter supercritical floating spline shaft according to claim 1, characterized in that: The boundary conditions of the self-excited vibration of the tail shaft include the displacement value and vibration value corresponding to the self-excited vibration when the durability wear test is stopped, and the matching dimension measurement results of the spline and the positioning section after the durability wear test.

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