Meshing impact is an important factor that affects gear vibration and noise. Therefore, it is of great theoretical and practical significance to study the characteristics of offline meshing impact to reduce the vibration caused by meshing impact. Currently, a single-pair gear is the research goal, ignoring complex coupling relationships between systems, and the established numerical solution formula of the meshing impact cannot be verified. By using Hilbert demodulation and instantaneous frequency, this study obtained the meshing impact signal from the dynamic transmission error signal of the experiment and obtained the maximum deformation caused by the meshing impact. The meshing stiffness of a single tooth was obtained by loaded tooth contact analysis and tooth contact analysis, and the meshing impact force was calculated. The dynamic model of the meshing impact considering the contact ratio was established to compare with the obtained force in the experiment. The method of measuring the meshing impact signal from experiments has not been reported in relevant literature. The method has the advantages of being extensive, accurate and convenient, and it is not affected by the complexity of the system. At the same time, this method can be used to determine the gear teeth with meshing impact in the course of operation and provide a basis for real-time shape modification and design. Therefore, it is of great significance.
The meshing impact on transmission system and internal meshing gear pair and its impact on the load sharing and dynamic characteristics of the system are not well understood yet. In this paper, the meshing impact models of internal gear pairs and planetary transmission system were successfully constructed, and the meshing impact point, meshing impact time and meshing impact force were accurately obtained. Meshing impact in gear transmission system is obviously affected by eccentricity error, installation error, and other errors. Due to the difference in error of each component, the internal and external gears of each branch lead to different meshing positions, which causes the constant change in meshing impact point, meshing impact time and meshing impact force. This creates difficulties in the analysis of meshing impact characteristics of gear transmission system. Load Tooth Contact Analysis (LTCA) method can be used to accurately analyse the change in position of gear tooth under load condition. Through the dynamic model of planetary transmission system, the influence in component errors on the contact position of tooth surface is obtained. Combining the loaded transmission error of the tooth surface under load and the geometric transmission errors under the influence of component errors, the model of meshing impact for accurately solving the system is deduced, and the influence of meshing impact on the system's load sharing coefficient and dynamic load factor coefficient is analysed. By comparing the planetary transmission system before and after considering the meshing impact of the system, it is found that the system's load-sharing coefficient increases slightly, dynamic load factor coefficient fluctuates significantly, and meshing force becomes more clutter after considering meshing impact.
Considering flexibility of the support shafts as well as bearing supports, the effect of meshing impact force and meshing stiffness on the dynamic behavior of a gear transmission system in electric vehicle is investigated in this paper using the proposed hybrid user-defined element method. First, a structured grid generation method is introduced to establish accurate mesh models of the pinion and gear teeth. Second, coupling the tooth mesh models and the flexible shafts as well as bearings, two finite element models are, respectively, constructed for the two helical gear pairs of the electric vehicle reduction unit to calculate the meshing impact force. Next, the basic mechanism of meshing impact is explained in detail according to the finite element results, and the impact force is determined as one of the main internal excitations substituted into the dynamic model established by the hybrid user-defined element method. Under 50 N m input torque and 12,010 r/min rotational speed of the input shaft, the simulation results by the hybrid user-defined element method indicate that the example system reaches a steady state and the vibrations primarily occur at the meshing frequencies. With an increment of 600 r/min of the input rotational speed, it is also concluded from the results that (1) the calculated impact force approximately presents linear growth with the increase of the input shaft rotational speed and (2) the root mean square values of the vibration acceleration generally grow with the increase of the speed.
MR Elastography is a new technique using conventional MRI system to assess the elastic properties of tissues. When using pneumatic driver, usually one driver was put at one place of tissue. But the shear wave generated by one pneumatic driver cannot illuminate the large area due to the attenuation. So we use two pneumatic drivers driven synchronously to generate interference shear wave in our experiments. The results from the phantom study show the interference wave pattern generated by the twin pneumatic drivers can compensate the attenuation of the shear wave when propagating in phantom. Also, a finite element modeling was used to simulate twin pneumatic driver datasets. It is hoped that by twin pneumatic drivers, we can illuminate the whole brain; the liver and large areas in-vivo. Further study will be conducted with the twin pneumatic drivers in ex-vivo and in-vivo studies.
As a key part of vibration generation and transmission of planetary gear transmissions, thin-walled inner ring gear deforms under the influence of meshing excitation and seriously affects the reliability and fatigue life of the transmission system. The effect of the flexibility of the inner ring gear on the transmission system is ignored in the calculation of making the inner ring gear as a rigid body in the lumped parameter model, while the calculation amount of the finite element model is too large. Therefore, it is very important to establish an accurate and reasonable model to solve the flexibility of the inner ring gear. In this paper, according to the supporting mode, supporting quantity, thickness, and sectional shape of the inner ring gear, the inner ring gear is reasonably separated into the form of multisection curved beam. The displacement of the gear teeth in the meshing line caused by the flexibility of the inner ring gear is obtained rapidly and accurately. It lays an important theoretical foundation for the dynamic analysis of planetary gear transmission.
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