Main Gearbox Research Articles

A New Mathematical Modeling Method for Four‐Stage Helicopter Main Gearbox and Dynamic Response Optimization

A new mathematical modeling method, namely, the finite element method and the lumped mass method (LMM‐FEM) mixed modeling, is applied to establish the overall multinode dynamic model of a four‐stage helicopter main gearbox. The design of structural parameters of the shaft is the critical link in the four‐stage gearbox; it affects the response of multiple input and output branches; however, only the meshing pairs were frequently shown in the dynamic model in previous research. Therefore, each shaft is also treated as a single node and the shaft parameters are coupled into the dynamic equations in this method, which is more accurate for the transmission chain. The differential equations of the system are solved by the Fourier series method, and the dynamic response of each meshing element is calculated. The sensitivity analysis method and parameter optimization method are applied to obtain the key shaft parameters corresponding to each meshing element. The results show that the magnitude of dynamic response in converging meshing pair and tail output pair is higher than that of other meshing pairs, and the wall thickness has great sensitivity to a rotor shaft. In addition, the sensitivity analysis method can be used to select the corresponding shaft node efficiently and choose parameters appropriately for reducing the system response.

Fatigue crack fault diagnosis and prognosis based on hidden semi‐Markov model

Aiming at the fault diagnosis and remaining useful life (RUL) prediction of fatigue cracks of a helicopter main gearbox planet carrier, this article proposes a hidden semi-Markov model (HSMM) methodology, which introduces the explicit state durational distribution parameters into the traditional hidden Markov model (HMM), thus overcoming the limitation of exponential distribution in HMM, retaining strong pattern recognition and classification ability, and improving the diagnostic and prognostic accuracy, and the effectiveness of the method was verified through experiments.

TYPES OF CONTACT DAMAGES OF GEAR WHEELS OF THE MAIN HELICOPTER GEARBOXES IN OPERATION

Insufficient quality of gear wheels production extensively restricts the improvement of characteristics of helicopter gearboxes. For improvement of production quality of gear wheels of the main helicopter gearboxes, it is necessary to establish main types of their contact damages in operation.

DOUBLE CHEMICAL-THERMAL TREATMENT OF GEAR WHEELS OF HELICOPTER MAIN GEARBOXES

Influence estimation of consecutive stages of chemical-thermal treatment (cementation + nitriding) on the manufacture quality of the gear wheels of helicopter main gearboxes made of 16H3NVFМB-Sh steel.

The Variation of the Forces acting in a Helical Cylindrical Gear according to its operating Modes

The main objective of this paper is a five operating mode comparison case study that reveals the values of the main three force components acting in the contact point where two gears are meshed together. For the determination of this force components, the initial part of the paper will consist in the calculation of the moment of torsion for the output pinion of the gearbox, with the help of the total power of the power turbine that drives the main shaft. This will also conclude that of the total power generated by the 18802,242 [kW] turbine power plant, the power turbine that drives the main shaft through the main gearbox will return the power of 5000 [kW].

Vibration-Based Condition Monitoring of Wind Turbine Gearboxes Based on Cyclostationary Analysis

Wind industry experiences a tremendous growth during the last few decades. As of the end of 2016, the worldwide total installed electricity generation capacity from wind power amounted to 486,790 MW, presenting an increase of 12.5% compared to the previous year. Nowadays wind turbine manufacturers tend to adopt new business models proposing total health monitoring services and solutions, using regular inspections or even embedding sensors and health monitoring systems within each unit. Regularly planned or permanent monitoring ensures a continuous power generation and reduces maintenance costs, prompting specific actions when necessary. The core of wind turbine drivetrain is usually a complicated planetary gearbox. One of the main gearbox components which are commonly responsible for the machinery breakdowns are rolling element bearings. The failure signs of an early bearing damage are usually weak compared to other sources of excitation (e.g., gears). Focusing toward the accurate and early bearing fault detection, a plethora of signal processing methods have been proposed including spectral analysis, synchronous averaging and enveloping. Envelope analysis is based on the extraction of the envelope of the signal, after filtering around a frequency band excited by impacts due to the bearing faults. Kurtogram has been proposed and widely used as an automatic methodology for the selection of the filtering band, being on the other hand sensible in outliers. Recently, an emerging interest has been focused on modeling rotating machinery signals as cyclostationary, which is a particular class of nonstationary stochastic processes. Cyclic spectral correlation and cyclic spectral coherence (CSC) have been presented as powerful tools for condition monitoring of rolling element bearings, exploiting their cyclostationary behavior. In this work, a new diagnostic tool is introduced based on the integration of the cyclic spectral coherence (CSC) along a frequency band that contains the diagnostic information. A special procedure is proposed in order to automatically select the filtering band, maximizing the corresponding fault indicators. The effectiveness of the methodology is validated using the National Renewable Energy Laboratory (NREL) wind turbine gearbox vibration condition monitoring benchmarking dataset which includes various faults with different levels of diagnostic complexity.

Feedback in Automated Clutch Control Circuit for Truck Start-Up Process

The paper presents description of a mechatronic control system for mechanical transmission of a 20-ton truck, as well as its adaptive start-up algorithm, transient process behavior which significantly affects durability of automated power unit elements, vehicle movement smoothness and driver’s comfort when driving. A multidisciplinary model of the mechatronic control system has been developed in the software package Imagine Lab AMESim because its power unit including a diesel engine, a dry frictional two-disc clutch, a main mechanical stepped gearbox and an additional gearbox has electrical components besides mechanical and pneumatic ones. The given model allows to test complex control algorithms and analyze the behavior of intelligent systems in the early designing stages. The research has been carried out on the basis of the test complex at Department “Automobiles”, Automotive and Tractor Faculty, Belarusian National Technical University. Research results confirm an adequacy of the AMESim developed multidisciplinary model. Feedback on the increment of an angular velocity difference between driving and driven parts of the friction clutch has been introduced for precise friction clutch control. Threshold values of a feedback parameter have been determined on the basis of the developed computer model and these values will be used for programming a microprocessor unit when implementing an adaptive algorithm for a truck start-up process

Modular heavy duty truck transmission

The design of a modular gearbox for heavy trucks, which consists of a differential divider, a main gearbox and a differential demultiplicator with an integrated rear gear is described. The proposed design has smaller dimensions, weight and inertial masses of rotating parts, has greater rigidity and speed of the gear shifting process.A vehicle equipped with this transmission will make better use of the engine power and save fuel, which will increase its competitiveness in the market.

Using frequency domain analysis techniques for diagnosis of planetary bearing defect in a CH-46E helicopter aft gearbox

Abstract Condition monitoring for helicopters has always been one of the most critical technologies to guarantee the integrity of the rotorcrafts, enhance operational and personnel safety, and reduce the overall maintenance costs. Over the past decades, health and usage monitoring system (HUMS) has been developed and implemented in helicopters to monitor the health status for the main gearbox (MGB) and other key components of the transmission system, improving condition-based maintenance for helicopters. However, many studies have indicated that current HUMS has a limited sensitivity to MGB planetary bearing defects. To enhance HUMS' performance, this paper presents an approach based on frequency domain analysis techniques to diagnose planetary bearing defects using real helicopter data collected from a CH-46E helicopter aft MGB. Vibration data was processed using signal processing techniques including self-adaptive noise cancellation (SANC), discrete-random separation (DRS), cepstrum editing, kurtogram, envelope analysis and iterative envelope cancellation. Processing results conclude that frequency domain analysis techniques can provide distinct and intuitive indications of the seeded defects at both the inner race and the outer race of the faulty planetary bearing.

Influence of oil film stiffness on natural characteristics of single-rotor three-input helicopter main gearbox

The elastohydrodynamic lubrication (EHL) contact model is established, the oil film stiffness is calculated based on Dowson-Higginson empirical minimum thickness equation. The vibration model of single-rotor three-input helicopter main reducer is proposed by lumped mass method, and nonlinear factors like oil film stiffness, dynamic meshing force are taken into account. The influence of oil film stiffness on system natural frequency is analyzed as well. The results show that oil film stiffness of the internal and external meshing pairs in the planetary gear system have greater impact on the natural frequency, which tends to destabilize the system. Therefore, the planetary gear train is the most crucial branch regarding the system splash lubrication. When all the oil film stiffness in the system are greater than 4×109 N/m, the natural frequencies tend to be stable. This study can provide the theoretical reference for the lubrication characteristics in the single-rotor multi-input helicopter.

Classification and synthesis of three-loop planetary gearboxes

In the transmissions of trucks, agricultural vehicles and tractors, gear boxes with a planetary divider and/or an additional reductor unit which is depending on the traffic conditions of the machine, reduces the speed of rotation or operates on a direct drive are used. The divider and the additional reductor unit are intended for a stepwise changing of the range of the main 3-speed or 4-speed gearbox, consisting of gears with fixed axles, which makes it possible to increase the number of stages realized 4 times. If the planetary train will work in the differential mode, this will allow additionally increase the number of stages in the combined planetary gearboxes and, accordingly, the number of operating modes of the tractor. Consequently, the main gearbox consists of gears with fixed axes of gears can work either separately in a single-flow mode of operation of the planetary train (reductor or in the direct drive mode) or in a two-flow mode - in parallel with other ordinary gears when the planetary train as a differential. When using two planetary trains operating in the differential mode, the number of parallel power flows increases to three, which makes it possible to further improve the functional and power capabilities of multi-flow gearboxes. The purpose of the study is to analyze gearbox schemes consisting of three sets of gears with fixed gearwheel axes and two differential mechanisms forming three parallel power transmission flows. Classification of possible structural schemes of three-flow transmissions is given, a general expression for calculating the number of stages of a three-flow gearbox is obtained. A technique for the synthesis of kinematic schemes of three-flow planetary gearboxes is described, with the using of which new gearbox schemes are obtained for each possible structure, which are characterized by using simple mechanisms, high efficiency and a small number of control elements.

Planetary bearing defect detection in a commercial helicopter main gearbox with vibration and acoustic emission

Helicopter gearboxes significantly differ from other transmission types and exhibit unique behaviours that reduce the effectiveness of traditional fault diagnostics methods. In addition, due to lack of redundancy, helicopter transmission failure can lead to catastrophic accidents. Bearing faults in helicopter gearboxes are difficult to discriminate due to the low signal-to-noise ratio in the presence of gear vibration. In addition, the vibration response from the planet gear bearings must be transmitted via a time-varying path through the ring gear to externally mounted accelerometers, which cause yet further bearing vibration signal suppression. This research programme has resulted in the successful proof of concept of a broadband wireless transmission sensor that incorporates power scavenging while operating within a helicopter gearbox. In addition, this article investigates the application of signal separation techniques in detection of bearing faults within the epicyclic module of a large helicopter (CS-29) main gearbox using vibration and acoustic emissions. It compares their effectiveness for various operating conditions. Three signal processing techniques, including an adaptive filter, spectral kurtosis and envelope analysis, were combined for this investigation. In addition, this research discusses the feasibility of using acoustic emission for helicopter gearbox monitoring.

Vibrodiagnostics Used for Evaluating the Technical Condition of a Mechanical Gearbox

The aim of this article is to evaluate the technical condition of a mechanical four-speed gearbox tightly connected to a mechanical two-speed auxiliary gearbox placed in an off-road vehicle. When observing the technical condition of the mechanical gearbox, we used one of technical diagnostics methods, namely vibrodiagnostics. The mechanical gearbox was monitored during all its life cycle up to failure occurrence. In the article there is a detailed description of the stand where the gearbox technical condition was monitored. When observing vibration signals, we used four tri-axial sensors placed in four selected spots depending on the design arrangement of antifriction bearings. In order to evaluate the measured results, two methods were applied, namely the root mean square gRMS based on the measured acceleration in three axes. The other method used for monitoring the technical condition was the Crest factor. The aim of the experiment was to monitor the technical condition of the mechanical gearbox, mainly its antifriction bearings, therefore the values were measured when the gear was put into fourth position and into overdrive in the auxiliary gearbox. When the gear is put into fourth position, the torque is transmitted from the motor through the main gearbox and the auxiliary gearbox directly. Single gearbox wheels are engaged but not loaded (they do not transmit the torque). At the end of our article we introduced the measured values along with the oral evaluation of the technical condition of the mechanical gearbox and the auxiliary gearbox.

Design challenge of a new monolithic concept for the main landing gear bay of a large passenger aircraft

In this paper, ITEMB team in the contest of the Clean Sky 2 framework, with the scope of a new architecture for the Main Landing Gear of a single isle aircraft type, presents its development in designing the two major item of the Main Landing Gear Bay that are the “roof” and the “rear pressure bulkhead” using pre-preg CFRP material. Typically, a lot of parts (metallic and also composite made) are involved in the two items manufacturing: the research effort has targeted the design of one piece structures consisting in a monolithic “roof” and “monolithic “rear pressure bulkhead”. The assembly of these ones takes advantages from a hole-tohole assembly supported by statistical analysis. The main expected advantages are the reduction of: both non-recurring and recurring cost, the overall flow time and weight saving. The ITEMB (InTEgrated Main landing gear Box) team has worked adapting a bag-to-bag technology to the geometrical and strength capability requirements of the component and outcome of the research (not yet concluded at time of issuing this paper) includes: A design principle supported by stress analysis for strength, stability and local main load introduction; A manufacturing trials campaign to reach the possess of a robust process; A limited coupons test campaign to demonstrate that no specific critical items exists in the design approach. Finally, participants have acquired a new design and manufacturing technique, applicable also to other Aircraft components upgrading their capabilities and European strength in composite structures manufacturing.

Failure Analysis of Cooler Fan Drive Gear System of Helicopter

This paper presents the failure analysis of cooler fan drive gear system of helicopter. The work involves failure analysis of two components of main gear box assembly i.e. intermediate gear and drive fan pinion. The materials of the gears are made up of case carburizing steel. The microstructure of both the components is martensite. The microstructure of un-failed teeth is finer than that of the failed teeth. The crack is observed near the root of the failed teeth. It seems that cracks are formed only at the roots of the teeth and propagated inside the material. It has been observed that the fatigue cracks are formed at the roots of many teeth during service. These cracks have been sharply revealed by etching. The large crack length introduces simultaneous failure of several teeth as observed in intermediate gear while the short crack of drive pinion results in successive failure of the same. Both the teeth of intermediate gear and drive fan pinion fail by bending fatigue due to over/shock loads although the associated mechanisms are quite different.

Failure Analysis of Cooler Fan Drive Gear System of Main Gear Box of Helicopter

This paper presents the failure analysis of cooler fan drive gear system of helicopter. The work involves failure analysis of two components of main gear box assembly i.e. intermediate gear and drive fan pinion. The materials of the gears are made up of case carburizing steel. The microstructure of both the components is tempered martensite. The hardness values measured on the intermediate gear (un-failed and failed) and drive fan pinion show that the hardness of the un-failed intermediate gear teeth is more compared to failed intermediate gear teeth and drive fan pinion. The low hardness value of failed component is likely due to coarsening of microstructure during operation. Fracture surfaces of the failed intermediate gear display the presence of rubbed features, ductile dimples and micro cracks while dive fan pinion exhibit the presence of ductile dimples, striations and intergranular fracture features. The intergranular fracture features observed can be ascribed to improper microstructure resulting from deviation in heat treatment process. Initially, a single tooth of drive fan pinion has broken due to fatigue and subsequently other teeth have broken by transferring load to its immediate neighbour

Experimental and Statistical Energy Analysis of the Structure-borne Noise in a Helicopter Cabin

In this work, the mechanical power transferred from the main gearbox to the cabin of a helicopter is obtained experimentally and used as an input to the vibroacoustic model of the fuselage for interior noise prediction. The estimation of the transmitted mechanical power is based on the experimental evaluation of the coupled mechanical mobility and in-flight accelerations measured at the points connecting the main gearbox to the fuselage, i.e. the antitorque plate and struts. The predicted values, together with the airborne noise sources (upper deck cavity noise and aerodynamic excitation due to the turbulent boundary layer on the fuselage skin) are then fed into the vibroacoustic model of the fuselage/cabin, which is obtained using a Statistical Energy Analysis (SEA) approach. The reliability of the approach is finally demonstrated by comparing the SEA simulation results and in-flight noise measurements in terms of sound pressure level in the passenger cabin compartment.

A study on helicopter main gearbox planetary bearing fault diagnosis

The condition monitoring of helicopter main gearbox (MGB) is crucial for operation safety, flight airworthiness and maintenance scheduling. Currently, the helicopter health and usage monitoring system, HUMS, is installed on helicopters to monitor the health state of their transmission systems and predict remaining useful life of key helicopter components. However, recent helicopter accidents related to MGB failures indicate that HUMS is not sensitive and accurate enough to diagnose MGB planetary bearing defects. To contribute in improving the diagnostic capability of HUMS, diagnosis of a MGB planetary bearing with seeded defect was investigated in this study. A commercial SA330 MGB was adopted for the seeded defect tests. Two test cases are demonstrated in this paper: the MGB at 16,000 rpm input speed with 180 kW load and at 23,000 rpm input speed with 1760 kW load. Vibration data was recorded, and processed using signal processing techniques including self-adaptive noise cancellation (SANC), kurtogram and envelope analysis. Processing results indicate that the seeded planetary bearing defect was successfully detected in both test cases.

Load Sharing Behavior of Star Gearing Reducer for Geared Turbofan Engine

Load sharing behavior is very important for power-split gearing system, star gearing reducer as a new type and special transmission system can be used in many industry fields. However, there is few literature regarding the key multiple-split load sharing issue in main gearbox used in new type geared turbofan engine. Further mechanism analysis are made on load sharing behavior among star gears of star gearing reducer for geared turbofan engine. Comprehensive meshing error analysis are conducted on eccentricity error, gear thickness error, base pitch error, assembly error, and bearing error of star gearing reducer respectively. Floating meshing error resulting from meshing clearance variation caused by the simultaneous floating of sun gear and annular gear are taken into account. A refined mathematical model for load sharing coefficient calculation is established in consideration of different meshing stiffness and supporting stiffness for components. The regular curves of load sharing coefficient under the influence of interactions, single action and single variation of various component errors are obtained. The accurate sensitivity of load sharing coefficient toward different errors is mastered. The load sharing coefficient of star gearing reducer is 1.033 and the maximum meshing force in gear tooth is about 3010 N. This paper provides scientific theory evidences for optimal parameter design and proper tolerance distribution in advanced development and manufacturing process, so as to achieve optimal effects in economy and technology.

Bearing Signal Separation of Commercial Helicopter Main Gearbox

Gears are significant component in a multiplicity of industrial applications such as machine tool and gearboxes. An unforeseen failure of gear may result in significant economic losses. Therefore this research propose fault detection improvement throught series of vibration signal processing techuiques. These techniques have been tested experimentally using vibration data collected from the transmission system of a CS-29 ‘Category A’ helicopter gearbox under different bearing damage severity of the second planetary stage. Results showed successful improvement of bearing fault detection.