Gear Test Rig Research Articles

Product Development Methodology Targeting Efficiency and Acoustics of E-Mobility Gearboxes

This paper presents an approach for physical/virtual coupled product development and validation. A method for studying the influence of tooth geometry on the efficiency and acoustics of an electric vehicle’s powertrain will be presented. To achieve improved acoustic characteristics the micro geometry of the teeth will be optimized. The modified gears were analysed on a gear test rig under load and at high speeds and evaluated with regard to their acoustic properties. Established analytical models are used to describe the influence of profile modifications on the gear stiffness of helical gears. The authors’ approach is to calculate the dynamic system behaviour of the gearbox using a 1D simulation. Based on this, studies of the entire gear box will be performed. For this, the results of the 1D simulation are coupled with 3D FEA analyses. This enables acoustic calculations (structure-borne and airborne sound) to be carried out.

Evaluation of vibration behavior at different sensing positions on gearboxes

Monitoring systems for rolling contacts in machinery are widespread. There are multiple solutions in various applications like Health Usage Monitoring Systems (HUMS) for Helicopters and smart bearings from different manufacturers. The number of solutions and possibilities is rising. This paper outlines how the vibrational behavior depends on the measuring position outside and inside the gearbox. The effect of the sensor location is evaluated by examining different locations close to the main excitation of gearboxes—the loaded tooth contact—as well as positions on the gearbox housing. Based on the results, recommendations for an optimal sensor position for gear vibration monitoring are given by considering the efforts of sensor integration. The results can be used to select sensors with the lowest cost to support the widespread gear vibration monitoring.Important locations for health monitoring are the gear meshes inside the gearbox. Due to the requirement of high power density, a compact design is mandatory. This does not allow for sensor application close to the gear meshes but only on the outside of the gearbox. An impediment of signal quality and less chance of early damage detection is the consequence. Hence, efforts have been made to directly integrate multiple sensors inside the gear body without negatively impacting the package.For the investigation of the vibration transmission behavior, an FZG gear test rig is selected. These standardized test rigs are approved and established all around the world for the creation and evaluation of various gear failure data. The presented test rig has been modified to be able to sense vibration in the gear wheel, at the gear wheel, and on the gearbox housing to evaluate different sensor positions and vibration sensors for their suitability on vibration measurement.

Optimized Compound Layer Design for Highly Loaded Nitrided Gears

AbstractNitriding is a thermochemical surface hardening process, which can be used to improve the performance properties of gears. In particular, the tooth flank and tooth root load-carrying capacity can be significantly increased by nitriding. Previous work has shown that tribological dominated failure modes and limits, such as the micro-pitting and wear load-carrying capacity of gears, can be significantly increased by a suitable compound layer structure. In this work, the relationship between compound layer design and macro-pitting load-carrying capacity of nitrided gears is explored based on experimental investigations. For this purpose, the materials EN31CrMoV9 and EN42CrMo4 were nitrided under varying nitriding conditions to produce compound layers with different structures and properties. The characteristics of the compound layer such as phase composition, compound layer thickness and pore seam were extensively characterized by means of metallographic techniques, XRD, GDOES, and EBSD. Experimental investigations of the macro-pitting load-carrying capacity were carried out on an FZG back-to-back gear test rig with center distance a = 52 mm. It was shown that the pitting load-carrying capacity depends to a large extent on the characteristics of the compound layer, in particular on the formation of the pore seam. A minimum pore seam thickness of CLTP ≥ 1.8 µm has a positive effect on the pitting load-carrying capacity. The test results for the pitting load-carrying capacity are above (σH lim ≥ 1690 N/mm2) or, in some cases, significantly above (σH lim = 1979 N/mm2) the strength values specified in ISO 6336-5:2016 for nitrided nitriding steels (σH lim = 1450 N/mm2; material quality ME) and case-hardened alloy steels (σH lim = 1650 N/mm2; material quality ME).

The influence of shot peening on gear teeth micropitting and contact fatigue failure

Case-hardened gears present a high contact fatigue load capacity in a compact and light mechanical transmission systems but sometimes, micropitting appears. This damage can lead to early contact fatigue failure called macropitting (NF ISO 10825-1). A previous study has demonstrated that an appropriate shot peening treatment could reduce the micropitting phenomenon via tests on a twin disc machine.The aim of this paper is to study the influence of shot peening on the micropitting of case-hardened gears tooth flank and its development to macropitting. Experimental tests are carried out using a back-to-back gear test rig, an interrupted test method is defined in order to monitor the micropitting initiation and its propagation on the tooth flank. Two variants of carburized spur gear specimens are tested. The reference specimen has a case-hardened ground tooth flanks which is a typical gear application. The other specimen has a case-hardened ground tooth flanks with a shot peened finishing process. The fatigue tests are run until the appearance of macropitting. The performed inspections of specimens indicate that shot peening modifies the surface roughness, the surface topography and increases the compressive residual stress. The experimental results show that micropitting occurs on both shot-peened and non-shot-peened gears after approximately the same running time. However, a difference is observed in the propagation of micropitting on the tooth flanks. In comparison to reference gears, shot peening has postponed the apparition of macropitting by more than 60%. An analytical study is also conducted to validate the prediction of micropitting using the ISO/TR 6336-22 by comparing the results with the occurrence of micropitting on the tested gears.

A novel metric-based model with the ability of zero-shot learning for intelligent fault diagnosis

Intelligent fault diagnosis plays an important role in maintaining the safe and reliable operation of rotating machinery. However, the data collected in real engineering scenarios may be severely insufficient, which presents challenges to the intelligent fault diagnosis methods. To address this problem, this paper introduces a metric-based meta learning approach for gear fault diagnosis under zero shot conditions. Firstly, a gear-rotor dynamics model is established to simulate the vibration signals under different fault conditions. And the signals are converted into energy maps through wavelet transformation to provide frequency domain fault features. Secondly, a deep convolutional network is employed as the feature extraction module to construct the prototype representations by calculating the average embedding within each fault class. Then, the distances between the actual signals collected from the gear test rig and the class prototypes are computed. Finally, the softmax is applied to convert these distances into probability distributions for outputting the predicted fault classes. Furthermore, label smoothing technology is introduced to mitigate the probability distribution differences between simulated signals and real signals. The experimental results demonstrate that the average diagnostic accuracy of the proposed model reaches 98.9%, which is better than other models.

A Dual-pronged approach for evaluation of contact stresses in nylon hybrid composite gears under misalignment

Polymer based composite gears have been a subject of intense studies by virtue of their wide gamut of applications. The authors have therefore embarked on developing a polymer-based composite with Graphene oxide (GO) and Tungsten Di-sulphide (TD) as reinforcements specifically for gear-based applications. The work outlined in this paper mainly deals with the fabrication of spur gears with the developed composite and investigating the contact stresses induced in these gears under misalignment of shafts. A dual-pronged approach is adopted in this procedure. The first being simulation studies using ANSYS WORKBENCH, while, the second and the most vital approach is through experimentation. The experimental approach required the design and development of a universal gear test rig (GTR) equipped with Data Acquisition System [DAS], which was successfully accomplished. The GTR was particularly premeditated to accommodate and adjust the alignment of the shaft axes. The experimentation was conducted under radial, axial and angular misalignments and combinations thereof. The composite material developed for this specific application was observed to function effectively in-comparison to the existing gear materials particularly under misalignment. The strains and stresses obtained from analytical and experimental methods were compared and found to be nearly identical under corresponding misalignments. Furthermore, it can be deduced from the studies that the combined effect of radial and yaw misalignments produces the highest strain, which is in fact, almost ten times that of strain in other forms of misalignment. The results of this research work will contribute in enhancing the understanding of nylon composite gear’s performance under misalignment conditions, enabling the best maintenance practices in industries.

Angle domain cepstral comb and notch liftering—A method to separate concurrent gear and bearing faults under variable speed conditions

In recent years, in particular because of the importance of wind turbines in renewable power generation, there is now a demand for signal processing techniques to cope with the variable speed. It is also important to distinguish between gear and bearing faults which are both critical in wind turbine monitoring. This paper describes a pair of interrelated techniques, which make use of the fundamental differences between gear and bearing fault signals to separately diagnose them, even when both are present at the same time, andfor speed variations up to ± 20%. The signals are order tracked to the (rotation) angle domain, after which the real cepstrum is calculated. The deterministic gear signals appear only at discrete quefrencies, which can be extracted by comb liftering, which results in signals virtually independent of speed and speed variation, and which are very close to the static transmission error (STE) of each gear. For bearing faults, the discrete quefrency components are instead removed by a comb notch lifter, leaving a signal dominated by the bearing fault information. The paper gives numerous examples from gear test rigs with concurrent gear faults (root crack and developing pitting) and bearing faults, separating and diagnosing the two types of fault sources while excluding background noise.

Limitations of the Check Calculation for Tooth Deformation of Plastic Gears According to Gear Design Guideline VDI 2736.

An in situ gear test rig has been developed at the Institute of Polymer Technology (LKT) to characterize the deformation of plastic gears during operation. It analyses timing differences between following index pulses of rotary encoders on the input and output shaft. This measurement principle enables the continuous measurement of the elastic tooth deformation and permanent deformations and wear at operating speed by switching between a high and low torque. Gear tests using a steel-polybutylene terephthalate (PBT) gear set were performed at different rotational speeds and tooth temperatures to analyze the tooth deformation during operation. The results were compared to the calculated deformation according to gear design guideline VDI 2736. Moreover, the results of the gear tests were correlated with the results of a dynamomechanical analysis (DMA). Both, the DMA and the in situ gear tests show that the effect of temperature on deformation is much higher than the effect of frequency or rotational speed. However, the experimentally measured tooth deformation is significantly higher (up to 50%) than the calculated at lower speed. Thus, the check calculation according to VDI 2736 underestimates the actual tooth deformation at lower speeds. Therefore, the guideline should be adjusted in the future.

Contact fatigue performance and failure mechanisms of Fe-based small-module gears fabricated using powder metallurgy technique

Gears fabricated using powder metallurgy technique (PMT) have the potential to replace traditional wrought gears due to their very high forming efficiency and relatively low cost. However, their practical applications are restricted due to the lack of understanding of their fatigue properties and failure mechanisms. This work investigates the contact fatigue performance and corresponding failure mechanism of a typical Fe-based small-module gears fabricated by PMT. The fatigue tests were conducted under grease lubrication condition, using a power-opened small-module gear testing rig. The experimental results show that the current PMT fabricated small-module gears exhibit contact fatigue properties comparable to those of traditional wrought steel gears. It has been found that the subsurface cracks induced from pores are the dominant cause of spalling of PMT fabricated small-module gears during rolling contact. The cracks tend to propagate between adjacent pores, playing a vital role in the overall fatigue life. Thus, this study suggests that PMT can be a successful method for fabricating Fe-based small-module gears with excellent contact fatigue property if formation of pores during fabrication is well inhibited.

The effects of cooling rate (mould temperature) on HDPE gears produced through injection moulding

The effects of mould temperature (cooling temperature) on molten HDPE (Hostalen GC 7260) during manufacture, is evaluated in this paper. HDPE gears were produced at varying mould temperatures using Injection Moulding. Optimised injection values for melt temperature, injection volume, hold pressure, and hold time were obtained, and then held constant while the mould temperature was altered.Analysis on how the mould temperature affected peak melting points and crystallinity were then carried out using differential scanning calorimetry (DSC). These revealed that crystallinity improved as the mould temperature was increased from 22 °C to 65 °C. Gears produced at similar cooling temperatures were then meshed on a gear test rig and run at 1000 rpm, using different torque loadings. Their wear rates, and modes of failure were then analysed, and comparisons were made to ascertain how the differing mould temperatures employed during the injection moulding manufacturing process affected their wear characteristics. Topographical analysis of worn gear teeth was performed using scanning electron microscopy (SEM). It was noted that gear tooth wear and failure was dependent on the mould temperature employed during the manufacturing process. Gears produced at 65 °C showed improved tooth surface wear resistance at lower loads (0.5 Nm and 1 Nm) compared to those produced at 22 °C, but were more likely to fail through tooth fracture at the pitch line due to excessive material removal. Gears produced at lower mould temperatures, on the other hand, exhibited better wear resistance for higher loads (3 Nm and 4 Nm), compared to those produced at higher mould temperatures, and were more likely to fail due to material flow. The results show a correlation between mould temperature, crystallinity, and gear performance. Based on wear rate responses of gears produced at differing mould temperatures to the application of varying torque loadings, a Mould Temperature to Torque Reference Chart for HDPE is presented.

Kalorimetrische Messung der Ver- zahnungsverlustleistung im Bereich hoher Umfangsgeschwindigkeiten

Gear damage, e.g. scuffing, reacts sensitively to the local dissipation of frictional heat during a full gear mesh. Several empirical friction models have been established in relevant literature. These can be used to calculate the gear friction locally or averaged over a mesh. For calibration purpose, experimental data from twin disc machines with stationary contact conditions are mostly used. However, the assignment of the model as well as the consideration of topographical, rheological and geometrical effects is often subject to uncertainties. In this paper, a method is presented to measure the power losses of high-speed spur gears up to vt = 100 m/s. The measurement principle uses the calorimetric properties of the circulating lubricant. The implementation of the measurement setup in a highspeed gear test rig reduces thermal interferences from sealings and bearings. Analysis regarding the measurement quality show that the measurement method delivers reproducible results with a high measurement resolution over a wide range of operating conditions.

Artificial intelligence of things based approach for anomaly detection in rotating machines

In the present era of Industry 4.0, Artificial Intelligence (AI) and Internet of Things (IoT) are revitalizing the predictive maintenance systems for industrial rotating machines through real-time approaches. In this work, an Artificial Intelligence of Things (AIoT) based framework is developed and implemented for anomaly detection in rotating machines through vibration monitoring. Signals are captured using a low-cost MPU6050 accelerometer with Raspberry Pi 4B as an edge device. The edge-centric mechanism is based on Support Vector Machine (SVM) for effective implementation on the edge device. A dedicated web-based platform is designed to communicate with the edge device for real-time decisions. The developed framework is validated on three rotating machines, including gear test rig, bearing test rig, and induction motor. The results demonstrate the robustness of the proposed method for anomaly detection on different machines. Also, the developed framework has the capability to remotely monitor and control the machines in real-time.

Test Rig for the In Situ Measurement of the Elastic Tooth Deflection of Plastic Gears

A new steel-plastic gear set testing methodology has been developed at the Institute of Polymer Technology (LKT). The in situ gear test rig analyses the timing differences between the index pulses of rotary encoders on the input and output shaft. This measurement principle enables the continuous measurement of the elastic tooth deflection on the one hand and permanent deformations and wear on the other hand by switching between a high loading torque and a low measuring torque. However, the elastic tooth deflection measurement using this principle has not yet been validated. Therefore, in situ gear tests using polybutylene terephthalate (PBT) gears were performed to evaluate the elastic tooth deflection of the plastic gear during operation. The results were compared to the results of pulsator tests. The comparison shows a very good correlation between the results of the newly developed in situ gear test rig and the well-established pulsator test rig. However, it has been shown that the test rig design creates a measuring offset due to angular displacements of the shafts due to torsion of test rig components.

Numerical investigation on meshing temperature of multicomponent nylon gears by incorporating viscoelasticity

This study concerns a numerical analysis of the meshing temperature for a multicomponent nylon gear by incorporating typical viscoelastic responses of polymers. Firstly, the generalized Maxwell model parameters were calibrated by the dynamic mechanical analysis to capture the viscoelasticity of polyamide 66. Next, the finite element model predicting the meshing temperature was established, including the heat generation analysis model, which calculates the generation of the frictional and hysteretic heat, and the heat propagation analysis model, which simulates the heat transmission. Different material models were used for polyamide 66 to investigate the influences of temperature dependence, strain rate dependence, and hysteretic effect. The effect of the iteration sequence on the meshing temperature calculation was also analyzed, i.e., how the heat generation should be updated as the loading cycles increase. A reasonable iteration scheme was determined by balancing the computational precision and consumption. It is noteworthy that the evolution of the ambient temperature around the gear and the worm within the housing was also considered. Finally, the accuracy of such meshing temperature analysis was validated on a self-developed gear test rig, in terms of the peak temperature evolution on the gear side surface. The experimental results and the simulation with the ambient temperature correction match well and the maximum error is 5 °C.

Fault tracing of gear systems: An in-situ measurement-based transfer path analysis method

A transfer path analysis method based on the in-situ measurement is proposed for the fault tracing of parallel axis gear systems. A virtual decoupling technique is used to achieve the in-situ measurement of the decoupled frequency response function (FRF) between bearing positions and measuring points on housing, avoiding the tedious test procedure and non-representative assembly conditions caused by the physical decoupling. Based on the decoupled FRF and the responses of the gearbox housing, the bearing force is identified using the Tikhonov regularization theory. Then the frequency-dependent path contribution, which will be used to perform the transfer path analysis, is obtained by multiplying the decoupled FRF and the bearing force. Finally, the fault-specific path rank order is determined using the path contribution within the resonant frequency band. This band is located by the spectral kurtosis algorithm. Based on the proposed in-situ path analysis, fault tracing is conducted by determining the dominant transfer path. The effectiveness of the proposed path analysis method is verified both numerically and experimentally. A two-stage parallel axis gear test rig with localized defects is utilized to demonstrate the efficacy of the proposed fault tracing strategy. Moreover, based on the path analysis, a physically-interpretable signal decomposition method is proposed to enhance the fault feature. Through this decomposition method, the fault indicator of the weakest fault type (chipped tooth) can be magnified by 204%. The proposed transfer path analysis method provides a feasible strategy for fault tracing, feature enhancement and incipient fault diagnosis of parallel axis gear systems.

Sound intensity analysis of straight bevel gears finished by using AFF process

This article reports using the Abrasive flow finishing (AFF) process to finish straight bevel gears (SBG) to improve their microgeometry errors and surface characteristics. Microgeometry errors, surface roughness parameters, and dual flank roll testing parameters was compared for unfinished and the AFF finished SBG. An indigenously developed bevel gear test rig was used for the sound intensity measurement and experiments were conducted by varying speeds at four levels. Finishing of SBG by the AFF process reduced their microgeometry errors, surface roughness, and improved functional performance parameters, resulting in reduced sound power generation. This study proves the potential of the AFF process to improve gear quality and help to establish it as a cost-effective, productive, and sustainable non-traditional solution for high-quality gear finishing.

Temperature measurement and error analysis of the transverse plane of oil-jet-lubrication herringbone gear with infrared pyrometers.

Frictional power losses of high-speed and heavy-load herringbone gearboxes increase the temperature of the gearbox. Thus, real-time surface temperature measurement is significant for evaluating the gearbox lubrication design. A rotating gear test rig with an infrared pyrometer is developed in this paper to conduct real-time and accurate temperature measurements of the transverse plane of the oil-jet-lubrication herringbone gear. First, the influencing factors and measuring errors of surface temperature are analyzed using the infrared pyrometer. The emissivity of the measured surface of a gear tooth painted with matte black is experimentally calibrated. Second, the temperature measurement tests of the oil-jet-lubrication herringbone gear under different conditions are carried out. Measurement errors resulting from purge air pressure, purge air temperature, and oil-jet temperature are also experimentally studied. The results indicate that the purge gas flow can reduce the measurement errors of the infrared pyrometer resulting from oil mist with an appropriate purge air pressure and purge air temperature. Finally, a mathematical curve-fitting of the measurement results between the infrared pyrometer and thermocouple is carried out. The calculated temperatures by the curve-fitting formula are compared with the measured thermocouple temperature, with the relative differences being less than 1 °C. Thus, the curve-fitting formula is credible for the real-time measurement of surface temperature, while the relevant measuring method is also valuable for engineering applications of high-speed gear systems under oil-jet-lubrication conditions.

Experimental Investigation on the Wear Performance of Nano-Additives on Degraded Gear Lubricant

This study investigates the degradation of a commercially available gear lubricant and the potential of nano-additives to mitigate such degradation. Initially, we performed an experimental study on the chemical degradation of commercially available API GL-4 EP90 gear lubricant by mixing the different concentrations of aqueous hydrochloric acid (aqueous HCl) varying from 0.0005% v/v up to 0.0025% v/v, while maintaining overall water content in the oil below the prescribed limits. The degradation was monitored using the pH value, total acid number (TAN) value, and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analysis. The experiments were performed on a developed gear test rig using conventional gear oil as well as chemically aged gear oil, and the corresponding results of pH value and wear debris were recorded. Based on the results, an empirical regression model between the concentration of aqueous HCl and lubricant aging time has been established. Under chemically aged lubricant, severe wear of gear was observed, which motivated us to explore suitable nano-additive to minimize the gear wear. Initially, three nano-additives—graphite, graphene, and “graphene oxide functionalized with silicon oxide (GO@SiO2)”—were chosen. A series of tests were conducted using the design of experiments method (L8 and L16 orthogonal array) to investigate the effect of nano-additives and to find the optimum additive for wear performance. Finally, experiments were conducted on gear setup using the degraded lubricant optimized with nano-additive. Overall results indicate a very significant contribution of nano-additives in decreasing gear wear.

Load-bearing analysis of polymer nanocomposite gears using a temperature-based step loading technique: Experimental and numerical study

The load-bearing characteristic of polyoxymethylene (POM)/carbon black (CB)/CaCO3 ternary nanocomposite gears were assessed using a temperature-based step loading approach. An online temperature measuring system was integrated into the gear test rig to continuously measure the gears’ bulk temperature. Dynamic mechanical thermal analysis (DMTA) was performed to explore a correlation between the viscoelastic characteristics, failure, and wear behavior of nanocomposite gears. The step loading test results showed that the load-bearing capacity was incremented from 7 Nm for pure POM to 10 Nm for POM/CB/3CaCO3 ternary nanocomposite gear. The finite element analysis of gears indicated that the maximum contact stress was different for those with similar critical torque. It was suggested that the maximum contact stress could complement the step loading technique in defining the load-carrying capacity of polymer-based gears. The failure analysis indicated the impediment of tooth cracking and thermal bending in ternary nanocomposite gears. The scanning electron microscopy (SEM) micrographs showed a much smoother tooth worn surface with minor traces of surface cracks and plastic flow for ternary nanocomposites, assigned to the promoted wear resistance, elastic response, and lower hysteretic self-heating due to the synergetic reinforcing effects of CB and nano-CaCO3.

In Situ Measured Tooth Flank Wear of Plastic Gears under Spectrum Loading

The wear behaviour of PBT-steel gear sets under temporarily changed load has been investigated using an in situ gear test rig developed at the LKT. The in situ test method is based on analysing the timing differences between the index pulses of rotary encoders on the input and output shaft of the test rig. The loading torque was varied between two levels and compared to the permanently applied equivalent average load in terms of the resulting tooth flank wear. Moreover, the number of load changes has been varied to analyse the influence of load changes on the gear wear. The results show that the applied load spectrum determines the resulting tooth flank wear even if the average applied load is the same. Moreover, it could be shown that the sequence of the applied load, i.e., the load history, plays an important role, since the applied load and the duration of the applied load within the run-in-stage disproportionately affect the wear behaviour over time.