Split Torque Research Articles

Full-Scale Gear Tooth Bending Fatigue Tests Obtained Early in the Development of a Rotorcraft Transmission

A new gear testing method is introduced to reduce development cost and time. It allows component-level testing of individual gear meshes and new gear designs. Instrumented gear sets are tested at full load while the rest of gearbox components are still being built. Since the fatigue strength of the gears is determined earlier in the development cycle, design deficiencies are identified and understood earlier. In this new method, an individual gear mesh installed in a stiff facility housing is used to mimic the contact pattern and bending stress demonstrated by the same mesh in an actual aircraft housing. Analytical gear models are used to identify the displacement difference between the stiff test facility and the aircraft housing. The test stand is designed so it can be adjusted accurately to provide gear and pinion positions that are representative of the deflected positions under load in the aircraft housing. A spiral bevel mesh and a split torque double helical reduction stage with multiple meshes are evaluated using the developed method. The contact pattern and strain survey results of the gear meshes are correlated with predicted results.

A novel real-time energy management strategy based on Monte Carlo Tree Search for coupled powertrain platform via vehicle-to-cloud connectivity

To improve the performance and efficiency of the energy management strategy used in electric vehicles equipped with a dual-motor coupled powertrain platform, this study proposes a systematic real-time search approach via vehicle-to-cloud (V2C) connectivity to reduce the battery degradation and electrical consumption by control working mode and split torque. To be specific, the Monte Carlo Tree Search (MCTS) is employed to search for optimal control sequence in the velocity feasible range in the cloud platform, considering battery loss and electric cost. The logic of time and velocity range updating is proposed as the solution for abrupt traffic changes. To evaluate the effectiveness of the proposed method, a rule-based and an online DP (Dynamic Programming) -based strategy is developed as the baseline approach. Meanwhile, the assessment conditions include standard cycles following power noise and real-world driving cycles. Finally, actual vehicle and hardware-in-the-loop (HIL) experimental results demonstrate that the proposed method significantly outperforms other strategies, the average total cost is 0.36 USD/km, and the improvements are 12.9% and 11.4% compared to the rule-based and online DP-based approaches, respectively.

Investigation of Load Sharing and Dynamic Load Characteristics of a Split Torque Transmission System with Double-Helical Gear Modification

A new dynamic model for a two-input two-path split torque transmission system which considers meshing error, time-varying meshing stiffness, and meshing-in impact is proposed. Time-varying meshing stiffness and meshing-in impact of each gear pair are accurately calculated based on tooth contact analysis and loaded tooth contact analysis. Equivalent displacements of eccentricity error and installation error along the meshing line of second- and third-stages gears are derived. The modified tooth surface of a third-stage double-helical gear is obtained by optimizing the amplitude of static loaded transmission error and meshing-in impact via nondominated sorting genetic algorithm-II (NSGA-II). Influence of modification on load sharing and dynamic load characteristics of split torque transmission system is investigated. The results indicate that the system’s dynamic meshing force increases when meshing-in impact is accounted for, which is unfavorable for the transmission. Following the modification of a double-helical gear, the dynamic load characteristics of the split torque transmission system are significantly improved, while its load sharing characteristics are improved to a certain extent.

A New Acoustic Emission Sensor Based Gear Fault Detection Approach

In order to reduce wind energy costs, prognostics and health management (PHM) of wind turbine is needed to reduce operations and maintenance cost of wind turbines. The major cost on wind turbine repairs is due to gearbox failure. Therefore, developing effective gearbox fault detection tools is important in the PHM of wind turbine. PHM system allows less costly maintenance because it can inform operators of needed repairs before a fault causes collateral damage happens to the gearbox. In this paper, a new acoustic emission (AE) sensor based gear fault detection approach is presented. This approach combines a heterodyne based frequency reduction technique with time synchronous average (TSA) and spectral kurtosis (SK) toprocess AE sensor signals and extract features as condition indictors for gear fault detection. Heterodyne techniques commonly used in communication are used to preprocess the AE signals before sampling. By heterodyning, the AE signal frequency is down shifted from MHz to below 50 kHz. This reduced AE signal sampling rate is comparable to that of vibration signals. The presented approach is validated using seeded gear tooth crack fault tests on a notational split torque gearbox. The approach presented in this paper is physics based and the validation results have showed that it could effectively detect the gear faults.

Investigation of nonlinear dynamics and load sharing characteristics of a two-path split torque transmission system

The dynamic responses and load sharing features of a two-path split torque gear transmission system are investigated in this study. The possible combinations of shaft angles to ensure the gear pairs work properly are determined considering the adjacency relationship, concentric relationship, geometrical conditions and installation conditions. A dynamic model of the system considering time-varying mesh stiffness, backlash, static transmission error, stagger angle excitations and gyroscopic effects of gear body and flexible shaft is proposed. The natural characteristics of the system including natural frequencies and critical speeds are obtained. The influences of the shaft angle, asymmetric transmission error excitations and right-to-left stagger angle of double-helical gear teeth on the dynamic transmission error responses and load sharing features of the two-path split torque gear transmission system are investigated. Several references to determine the system parameters to improve the transmission property and load sharing performance of the system are provided based on the numerical simulation results.

Influence of Backlash on Load Sharing and Dynamic Load Characteristics of Twice Split Torque Transmission System

Based on the characteristics of the helicopter main reduction gearbox, and combined with the advantages of face gear and cylindrical gear power dividing, a new configuration of helicopter main gearbox with twice split paths is proposed. A bending–torsional coupled dynamic model of the system is developed through the lumped parameter method, and the influence of stiffness, damping and backlash are considered. The dynamic equation is solved by Runge–Kutta method, and the load sharing and the dynamic load coefficients are obtained, as well as their variation with the backlash. Results show that with the increase of the backlash, the load-sharing coefficient decreases, the dynamic load coefficient increases, but the other drive stages are almost unaffected. Compared with split torque stages and power confluence stages, the load sharing and dynamic load coefficient of power input stages are the most sensitive to the backlash of the power input stage, and the appropriate increase of the backlash can effectively improve the dynamic properties. Therefore, in order to obtain better dynamic performance, it is necessary to allocate the backlash reasonably.

Tooth surface friction and its influence on dynamic transmission error of double power input transmission system

According to the meshing characteristics of spur gears and helical gears, calculation formulas of time varying friction stiffness and friction torque coefficient are derived. Based on the theory of the concentrated parameter, considering the influence of the time-varying coefficient of friction, time-varying meshing stiffness and the integrated error of the integrated, a three-dimensional dynamic model for a double power input transmission system with multi degrees of freedom and variable parameters was developed, including the flexional, torsional and axial motions. The Fourier series method is used to solve the equations by transforming the time varying system into a linear time invariant system, and the total system response of the system is obtained after the superposition of each order excitation response. The change law of friction torque coefficient and friction stiffness is obtained too. The results show that the friction stiffness curve of herringbone gear changes gently without mutations, and the direction is constant which what makes the resultant friction force direction be of the friction no unchanged. The tooth surface roughness has a certain influence on the dynamic transmission error. The first and second harmonic order frequencies of the split torque stage gears have an important influence on the dynamic transmission errors.

Influence of torsional stiffness on load sharing coefficient of a power split drive system

A dynamic model of power split transmission system with face gear and cylindrical gear is established. The factors including time-varying mesh stiffness, torsional stiffness, supporting stiffness, and clearance are considered in the model. The influence of the torsional stiffness of compound gear shaft on the load sharing coefficient is analyzed. The results show that the influence of the torsional stiffness of the compound gear shaft is obvious. Because the torsional stiffness of the output gear components is larger and the torsional stiffness of the input gear is smaller, so the input stage's deformation coordination ability is strong. Therefore, with the increase of the torsional stiffness of the compound gear shaft, the load sharing coefficient of the power input stages is improved, but the load sharing coefficient of the split torque stages and power confluence stages is worse. Hence, the torsional stiffness ratio of the transmission shaft should be rationally allocated under the condition that the torsional stiffness of the compound shaft is small.

Load Sharing Multiobjective Optimization Design of a Split Torque Helicopter Transmission

Split torque designs can offer significant advantages over the traditional planetary designs for helicopter transmissions. However, it has two unique properties, gap and phase differences, which result in the risk of unequal load sharing. Various methods have been proposed to eliminate the effect of gap and promote load sharing to a certain extent. In this paper, system design parameters will be optimized to change the phase difference, thereby further improving load sharing. A nonlinear dynamic model is established to measure the load sharing with dynamic mesh forces quantitatively. Afterwards, a multiobjective optimization of a reference split torque design is conducted with the promoting of load sharing property, lightweight, and safety considered as the objectives. The load sharing property, which is measured by load sharing coefficient, is evaluated under multiple operating conditions with dynamic analysis method. To solve the multiobjective model with NSGA-II, an improvement is done to overcome the problem of time consuming. Finally, a satisfied optimal solution is picked up as the final design from the Pareto optimal front, which achieves improvements in all the three objectives compared with the reference design.

Signal Processing Techniques to Improve an Acoustic Emissions Sensor


 
 
 Acoustic Emissions (AE) are stress waves produced by the sudden internal stress redistribution of material caused by changes in the internal structure of the material. Possible causes of these changes are crack initiation and growth, crack opening/closure, or pitting in monolithic materials (gear/ bearing material). Where as vibration can measure the effect of damage, AE is a direct measure of damage. Unfortunately, AE methodologies suffer from the need of high sample rates (4 to 10 Msps) and relatively immature algorithms for condition indictors (CI). This paper hypothesizes that the AE signature is the result of some forcing function (e.g. periodic motion in the case of rotating machinery). By using analog signal processing to demodulating the AE signature, one can reconstruct the information carried (e.g. modulation) by the AE signature and provide improved diagnostics. As most on-line condition monitoring systems are embedded system, analog signal processing techniques where used which reduce the effective sample rate needed to operate on the AE signal to those similarly found in traditional vibration processing systems. Further, by implementing another signal processing technique, time synchronous averaging, the AE signal is further enhanced. This allowed, for the first time, an AE signal to be used to identify a specific component within gearbox. This processing is tested on a split torque gearbox and results are presented.
 
 

Floating Shaft Load Sharing Method for Face Gear Split Torque Transmission System

In this study, the equivalent gear meshing error principle was used to analysis face gear split torque dynamics modeling, the mathematical model includes stiffness of shaft supporting, position of gears, backlashes, time-varying stiffness, damping, manufacturing error, assembly error. The result shows the floating shaft can achieved load sharing, the support stiffness is an important factor, decreasing the input shaft support stiffness, load sharing performance becomes better and vibration decreases by increasing the displacement of shaft. To study effect of errors, every errors change separately while others’ ideal. Every errors affect load sharing in different way, gear 4 manufacturing error and shaft 2 assembly error affect load sharing most, load sharing cannot achieve by decreasing one error.

Analysis of Split Torque Transmission System Load Sharing

A calculative model for parallel shaft split torque transmission system is presented, the model includes stiffness of shaft supporting, time-varying stiffness, damping, gear eccentric error errors, bearing eccentric errors, gear tooth thickness error, assembly error. Dynamic analytic model is built using the theory of equivalent mesh error and Newton method. The model was solved by variable step size forth/fifth-order Runge-Kutta method. The result shown all error affect load sharing in different way, one error deduced sharply can not improve load sharing obviously.

Gear Fault Location Detection for Split Torque Gearbox Using AE Sensors

In comparison with a traditional planetary gearbox, the split torque gearbox (STG) potentially offers lower weight, increased reliability, and improved efficiency. These benefits have driven helicopter object exchange models (OEMs) to develop products using STG. However, the unique structure of the STG creates a problem on how to locate the gear faults in an STG. As of today, only limited research on STG fault detection using vibration and acoustic emission (AE) sensors has been conducted. In this paper, an effective gear fault location detection methodology using AE sensors for STG is presented. The methodology uses wavelet transform to process AE sensor signals at different locations to determine the arrival time of the AE bursts. By analyzing the arrival time of the AE bursts, the gear fault location can be determined. The parameters of the wavelets are optimized by using an ant colony optimization algorithm. Real seeded gear fault experimental tests on a notional STG are conducted. AE signals at different locations of the gearbox with both healthy and damaged output driving gears are collected simultaneously to determine the location of the damaged gear. Experimental results have shown the effectiveness of the presented methodology.

Load Sharing of Parallel Shaft Split Torque Transmission System

Parallel shaft split torque Transmission system Split torque Load sharing Abstract: The Newton method was applied to develop a system of equations of motion, the mathematical model includes stiffness of shaft supporting, position of gears, backlashes, time-varying stiffness, composite transmission errors, damping. The model was solved by variable step size forth/fifth-order Runge-Kutta method. The load sharing was affected obviously by asymmetry of gear backlashes, stiffness of shaft supporting and gear position

Feasible Geometrical Configurations for Split Torque Gearboxes With Idler Pinions

The split torque gearbox is a practical solution to the transmission of high torques with the lowest possible weight. In this article, we perform the mathematics necessary to calculate possible solutions for the simultaneous meshing of four wheels on the basis of geometric conditioning factors. These calculations will be illustrated by numerical applications. Finally, particular cases of planetary gearboxes and a gearbox with equal idler pinions are studied, with the conclusion that their application is appropriate in specific conditions.

Gear Fault Location Detection for Split Torque Gearbox using AE Sensors


 
 
 In comparison with a traditional planetary gearbox, the split torque gearbox (STG) potentially offers lower weight, increased reliability, and improved efficiency. These benefits have driven helicopter OEMs to develop products using STG. However, the effect of multiple gears meshing simultaneously with the central gear and a large number of synchronous components (gears or bearing) in close proximity creates a problem on how to detect the gear fault location in a STG. As of today, only limited research on STG fault detection using vibration sensors and acoustic emission sensors has been conducted.In this paper, an effective methodology on gear fault location detection using AE sensors for STG is presented. The methodology uses wavelet transform to process the AE sensor signals to determine the arrival time of the AE bursts at different locations. By analyzing the arrival times of the AE bursts, the gear fault location can be determined. The parameters of the wavelet transform are optimized by using an ant colony optimization algorithm. Real seeded gear fault experimental tests on a notational STG are conducted. AE sensor signals at the locations of healthy and damaged output driving gears are collected simultaneously to determine the location of the damaged gear. Experimental results have shown the effectiveness of the presented methodology.
 
 

Quantification of condition indicator performance on a split torque gearbox

The requirement for higher energy density transmissions (lower weight) in helicopters has led to the development of the split torque gearbox (STG) to replace the traditional planetary gearbox by the drive train designer. This may pose a challenge for the current gear analysis methods used in health and usage monitoring systems (HUMS). Gear analysis uses time synchronous averages to separates in frequency gears that are physically close to a sensor. The effect of a large number of synchronous components (gears or bearing) in close proximity may significantly reduce the fault signal (reduce signal to noise ratio) and therefore reduce the effectiveness of current gear analysis algorithms. In this paper, quantification of condition indicator performance on a split torque gearbox is reported. The vibration signatures are processed through a number of gear analysis algorithms to quantify the gear fault performance. The performance metric is separability.

Application of Face-Gear Drives in Helicopter Transmissions

The use of face-gears in helicopter transmissions was explored. A light-weight, split torque transmission design utilizing face-gears was described. Face-gear design is discussed. Topics included basic design geometry, tooth generation, limiting inner and outer radii, and recommendation for the gear ratio. Face-gear experimental studies were also included and the feasibility of face-gears in high-speed, high-load applications such as helicopter transmissions was demonstrated. Torque-split tests were performed and demonstrated an accurate split of torque using the face-gear concept.

Split Torque Transmission Load Sharing

Split torque transmissions are attractive alternatives to conventional planetary designs for helicopter transmissions. The split torque designs can offer lighter weight and fewer parts but have not been used extensively for lack of experience, especially with obtaining proper load sharing. Two split torque designs that use different load-sharing methods have been studied. Precise indexing and alignment of the geartrain to produce acceptable load sharing has been demonstrated. An elastomeric torque splitter that has large torsional compliance and damping produces even better load sharing while reducing dynamic transmission error and noise. However, the elastomeric torque splitter as now configured is not capable over the full range of operating conditions of a fielded system. A thrust balancing load-sharing device was evaluated. Friction forces that oppose the motion of the balance mechanism are significant. A static analysis suggests increasing the helix angle of the input pinion of the thrust balancing design. Also, dynamic analysis of this design predicts good load sharing and a significant torsional response to accumulative pitch errors of the gears.

Split Torque Helicopter Transmissions with Widely Separated Engines

A three-stage helicopter transmission of split torque type is shown to offer advances in a configuration that allows the engine axes to be widely separated and parallel. Three variants of the configuration are examined; one design with separated drive paths and four final-drive pinions is discussed in detail. This design offers 26 per cent less weight and 9 per cent lower losses than current production transmissions. Comparison is made with epicyclic type transmissions of similar rating that have been developed in the past decade.