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With the continuous improvement of the operating temperature of aero transmission under the high-speed and high load, gear scuffing failure has become a key factor restricting the performance of aircrafts. To efficiently predict the operating temperature of aero gears, a sequential coupling numerical analysis method of the gear temperature is proposed for an aero engine gear, which simulates the bulk temperature and flash temperature under different working conditions, considering factors such as solid-liquid-gas multi-state flow heat exchange and heat dissipation coefficients of different tooth surfaces. The simulated gear contact temperature is compared with calculation results of ISO/TS 6336-20 and shows consistency, the largest deviation between which under different working conditions is controlled within 10%. When the input speed is 22 400 r/min and the torque is 119.4 N∙m, the split large gear contact temperature reaches 242.6 ℃, the scuffing safety factor is 1.22, and there is a risk of scuffing failure. The proposed simulation analysis method can effectively predict the operating temperature of aero high-speed gears, and provide an efficient and reliable method for assessing the risk of aero gear scuffing failure.

For co-rotating twin-screw gear transmissions, due to the complexity of the design process, multiple parameters as well as model iterations, cumbersome process and manifold work are needed. It is essential to develop a design and analysis software to improve the designing effect and efficiency. In this work a design and optimization model for co-rotating twin-screw gear transmission is established to develop a professional design and analysis software. The software development is based on the C++ programing language and the Qt application framework. Combining engineering practice cases, the operability, effect of optimization, and reliability of the developed software have been verified. The results show that the mass of the gear transmission is reduced by 7.98% compared to engineering applications. Optimization results can achieve stable convergence with a convergence accuracy of 99.02%, and the gear safety factor can be controlled within 8%. The developed software is expected to promote the transformation and upgrading of industrial design methods.

Ingot processing affects gear fatigue performance, which remains to be studied and becomes an important bottleneck problem limiting gear anti-fatigue design and cost saving. Surface integrity measurements of 18CrNiMo7-6 gears with mold ingots, continuous casting billet and electro-slag ingots are carried out, and tooth root residual stress, surface roughness and hardness gradient of these gears are studied. Based on GB/T 14230—2021 Test method of tooth bending strength for gear load capacity, gear bending fatigue tests are conducted with the staircase method. The bending fatigue limits under different reliabilities are obtained, and the influence of ingot processing on the bending fatigue performance is explored. The gear bending fatigue limit is also evaluated with the effective Locati method, and is compared with results of the lifting method. It provides some references for fundamental data construction of gear fatigue and anti-fatigue design in China.

Aiming at the problem that the conventional oil-immersed lubrication condition cannot truly reflect the operating environment of gear oil-injection lubrication, referring to the FZG A/8.3/90 gear scuffing load capacity test method and using oil injection lubrication gear fatigue test bench, the scuffing load capacity test of 18CrNiMo7-6 carburized gears is carried out based on oil injection lubrication condition with 4106 aviation lubricant. Based on the two-parameter Weibull distribution theory, the gear scuffing performance is evaluated under different reliabilities. Furthermore, based on Python language and database SQLite, a gear scuffing test data management system is developed to realize the effective management and efficient utilization of scuffing test data. The results show that under the same working and process condition, the gear scuffing failure FZG load level has 2-3 degree dispersity. Based on GB/Z 6413.1—2003 flash temperature method, it is found that under the condition of 4106 aviation lubricant injection lubrication, for 50%, 90% and 99% reliability, the gear scuffing temperature of shot peening process is 212.55 ℃, 183.22 ℃ and 152.24 ℃ respectively, improving by 1.51%, 7.31%, 14.99% respectively compared with the grinding process state. The developed data management system realizes scuffing test data flow management. Through the fitting function of two-parameter Weibull distribution, the gear scuffing temperature under different reliability can be obtained, which provides an efficient tool for the evaluation of gear scuffing load capacity.

The high-end transmission equipment such as the new generation of aero-engines faces the challenge of extreme service environments such as high speed, high temperature and heavy load. Scuffing failure is one of the main failure modes of gears, which seriously affects life and reliability. The common Chinese gear scuffing design standards include GB/Z 6413—2003 and HB/Z 84.4—1984. However, the calculation results of these standards for the scuffing loading capacity of gears are different, and difference exists in the application scope of these formulae. Thus, a comparative study of the cylindrical involute gear scuffing capacity standards based on GB/Z 6413 and HB/Z 84.4 is carried out from three aspects: theoretical analysis, parameter comparison and case studies. For FZG A type gears, dozens of case groups have been calculated. The results show that the calculated average friction coefficient of HB/Z 84.4 is higher than that of GB/Z 6413.2, and the calculated results of HB/Z 84.4 are conservative. It is found that calculation results of the surface temperature of GB/Z 6413.1 and GB/Z 6413.2 are consistent in a large range of torque, oil temperature, and speed. However, the difference in the tooth surface temperature of the two methods becomes larger as the tooth module decreases. The temperature results are generally consistent with each other as the tooth module lies within the range of 4-7 mm.

Planetary roller screw mechanism (PRSM) is a new type of heavy duty transmission devices. Rated static load is a key indicator to reflect its carrying capacity. Aiming at the problems of inconsistent calculation methods of PRSM rated static load and large difference between calculation results at present, four calculation methods of PRSM rated static load based on ball screw, rolling bearings, yield limit and elastic-plastic linear strengthening are expounded and corresponding calculation models are established; the PRSM elastic-plastic finite element contact analysis model is established, and the accuracy of the four calculation methods is compared and verified; an improved PRSM rated static load calculation method based on rolling bearing standards is proposed. The results show that the calculated results of the rated static load based on rolling bearings agree well with the finite element results. The improved calculation method reduces the average error from 17.03% to 8.90%, which can accurately calculate the rated static load of PRSM. It provides theoretical support for the design and selection of planetary roller screw mechanism.

Scuffing failure in high-speed aviation gears is a critical issue that hinders the improvement of operating performance and reliability in modern aviation equipment. The unclear failure mechanism limits the effective design of anti-scuffing measures. In this study, a scuffing test method was designed for high-speed aviation gears to investigate the effects of tooth profiles and surface treatment on the gear scuffing performance. The results indicate that both the pressure angle and surface treatment significantly affect gear scuffing behavior. Under different geometric treatment states, the range of the Ryder load stages at which gear scuffing initiated was between 5 and 13. The 25° pressure angle gear with barrel finishing treatment exhibited the optimal anti-scuffing performance. Compared to the ground state, barrel finishing increases gear scuffing loading capacity by 30% to 33%. Tooth profile optimization based on pressure angle changes improves gear loading capacity by 56.9%. This work provides an exploration of the anti-scuffing design of high-speed gears. [ABSTRACT FROM AUTHOR]

PEEK was a high-strength, heat-resistant engineering polymer, but the absence of basic data of PEEK contact fatigue restricted the reliable and long-life applications under heavy-duty conditions. PEEK rolling contact fatigue tests and gear contact fatigue tests under oil injection lubrication were conducted herein, and the S-N curves were obtained. It is found that the PEEK rolling contact fatigue limit is 14% higher than gear contact fatigue limit, and the rolling contact fatigue life of rollers under the contact pressure of 135 MPa is 58% higher than gear fatigue life. And then, the conversion formula of PEEK roller-gear contact fatigue life was further proposed. [ABSTRACT FROM AUTHOR]

Gear-manufacturing quality affects the load sharing between the meshing gears as well as the load distribution along the width of the tooth. This study aims to investigate the effect of gear-manufacturing quality on the mechanical and thermal states of polymer-gear pairs and consequently on their lifetime. The deviations of the geometric quality parameters, i.e. the lead profile and pitch, were found to have a substantial effect on the stress (root and flank) state of the gear. The effect of the lead deviation was found to be most pronounced for the quality grades Q12 to Q10, where depending on the load, a 30–80% stress reduction was observed when improving the gear quality from Q12 to Q10. Improving the quality from Q10 to Q8 did not lead to a substantial improvement in the load distribution and the observed stress reduction was in range of 5–20%. Similar trends were found for the pitch deviation, where again the most pronounced stress reduction was seen when improving the quality grade from Q12 to Q10. The study reveals where the most effective changes, leading to an increased gear-life, can be achieved. Improving the gear quality grade from Q12 to Q11 proved to have a much more substantial effect than improving the gear quality from Q9 to Q8. Considering that improving the gear quality from Q12 to Q11 or even Q10 can be achieved by a proper tool design and corrective iterations with the right process parameters, while improving the quality from Q9 to Q8 is by far more challenging. A novel methodology is proposed to assess the effect of the gear's quality on the generation of heat and the resulting operational temperature. The proposed methodology enables more accurate prediction of the gear pair's operating temperature. [ABSTRACT FROM AUTHOR]