Nonlinear Vibration Characteristics of the Involute Spline Coupling in Aeroengine with the Parallel Misalignment

In order to control the vibration of the involute spline coupling in aeroengine well and reduce the fretting wear, a bending–torsion coupling nonlinear vibration model of the involute spline coupling with the misalignment was proposed, and a dynamic meshing stiffness function with multiteeth engagement was established. Then, the influence of different misalignment, wear, and rotation speeds with different misalignment on the nonlinear vibration characteristics of the involute aviation spline coupling was explored. The result shows that with an increase of the parallel misalignment, the system experienced the state of a single period, a quasiperiod, multiperiod, and chaos but finally only alternated between the quasiperiod and the chaos state. The uneven wear of each tooth of the spline displayed a significant influence on the vibration of the spline coupling, and the influence of the uniform wear was smaller under given conditions here. Furthermore, with an increase of the speed, the larger the misalignment was, the more times the system entered or left the chaos state were. The model proposed here is found to be closer to the actual working conditions, and the analysis results can provide more accurate external load conditions for the prediction of the fretting damage of the spline coupling in aeroengine.

Nonlinear dynamic load analysis of aviation spline coupling with mass eccentricity and misalignment

Most of the time, mass eccentricity, and misalignment exist at the same time with aviation spline coupling working. Therefore, in this paper, the function of dynamic meshing force between multi-teeth and a non-linear dynamic model of involute spline coupling system in aero-engine with mass eccentricity and misalignment were presented. And then, the non-linear dynamic meshing force of spline coupling in aero-engine on different misalignment and mass eccentricity was investigated. The result shows that when the mass eccentricity and the misalignment are both small, the aviation involute spline coupling can run steady. And with the increase of mass eccentricity or misalignment, the dynamic load coefficient of the aviation involute spline coupling gradually increase. At the same time, as the mass eccentricity or misalignment increases, some teeth suffer more load, some teeth suffer less load, and some teeth are out of engagement so that they do not suffer any load. The running state of spline coupling becomes more and more unstable.

Involute spline couplings in aero-engine: Predicting nonlinear dynamic response with mass eccentricity

This work presents a nonlinear dynamic model considering the multi-tooth meshing behaviour and mass eccentricity of an involute spline coupling to tackle the serious problem of involute spline failure, in aviation power transmission systems. The dynamic meshing force is calculated for the same. Based on this, the influence of different mass eccentricities on the nonlinear dynamic response of the spline coupling was investigated in aero-engines. The results show that when the mass eccentricity is small, its impact on the system is insignificant. When the eccentricity reaches a certain value, the quasi-periodic and chaotic state appears alternately. Meanwhile, it can be concluded that the acceleration-frequency spectrum during the multi-periodic phase is an approximation of the working frequency with the accuracy affected by multiple teeth engagements. This was validated by the vibration experiments of the involute spline coupling. The proposed model, which considers the multi-tooth meshing behaviour and the mass eccentricity provides a reference model for the dynamic analysis of similar structures. The nonlinear dynamic response results attained lay a good theoretical foundation for fretting damage analysis and precise designs for involute spline couplings.

Extensive Experimental Study on the Stability of Rotor System With Spline Coupling

Spline couplings which have simple structure, high reliability and can compensate torque transmission error are widely used in rotating machineries, such as aeroengine and gasturbine, etc. Recent efforts show that it is potential to make the rotor system losing its stability. Nevertheless, the experimental study of rotor system with spline coupling is rare and inadequate. This indicates a need to study the factors that affect the stability of rotor system with spline coupling experimentally. In this paper, a specially designed spline connection rotor test rig has been built and used to simulate a multi rotor system of turboshaft engine. The experimental instability characteristics of spline connected rotor system are presented. The instability speed and critical speed under different conditions such as lubrication conditions, external damping, load torque, spline tooth error and fit type of internal and external spline are measured. Based on the above-mentioned results, the effect rules of the influence factors on spline connected rotor system stability are studied. Results show that lubrication can effectively weaken the vibration of the system. The increased external damping makes the stability better when the spline coupling is unlubricated. With the increasing of load, the subharmonic vibration decreases after the system loses its stability, the system stability becomes better. The stability of spline coupled system with larger tooth error is better than that with normal one. Normal fit-up spline coupling improves the system stability under the conditions of lubrication and small external damping. This study may be helpful to get the favorable parameter setting of spline connected rotor system for avoiding instability and reducing vibration.

FEM Design of a Cutting-Edge Support System for Micro-GT

The design of the support system (shaft, bearings, and mechanical coupling devices) of the rotor plays a key role in the development of efficient micro-gas turbines (micro-GTs) for distributed power generation. Foil air bearings are the most widespread technical solution well suited to design a reliable support system, although they cannot withstand a large number of start-stop cycles of the units. In order to overcome such limitation, we have recently proposed an innovative support system that takes advantage of spline couplings and two bearing types (e.g., air and rolling-element bearings). The devised support system employs splines as both convenient coupling systems and actuators for the load partition between the two bearing types. In the present work, the helical spline coupling is studied by means of structural FEM analyses including contact simulation in order to design the support system. Numerical results confirm previous findings in that the load transfer through the spline coupling is mainly a function of the helix angle. In addition, friction factor and structural stiffness cannot be neglected in the accurate design of the spline coupling. Such design parameters are now included in the proposed design procedure, which formerly assumed frictionless contact and rigid bodies.

Wear Characteristics of the Material Specimen and Method of Predicting Wear in Floating Spline Couplings of Aero-Engine

In order to reduce wear and design high-performance spline coupling, the friction coefficient, wear coefficient, and wear depth of 14 groups of material specimens were tested using multifunctional friction and wear tester. The effect of materials, loads, rotation speed, and surface treatment on friction coefficient, wear coefficient, and wear depth was investigated. A method using an Archard’s equation based on the finite element method to calculate the wear depth of 14 groups of material specimens was proposed, and the results were consistent with the experimental results. Then, the wear of a floating involute spline coupling of aero-engine was predicted using this method. It can be concluded that carburizing and silvering can decrease the friction coefficient. The wear and wear coefficient decreased after carburizing. So, it is necessary to take 18CrNi4A with carburization and 32Cr3MoVA with nitridation as the material of the spline coupling in aero-engine to minimize wear. Furthermore, the method presented to predicate the wear of spline coupling in this work provided a good fundament for the fatigue prediction methodology of spline coupling.