Recent Patents on Mechanical Engineering - Volume 15, Issue 3, 2022

Background: In the face of the development trend of high-end manufacturing servitization, the reliability standard of manufacturing products gradually increases. Objective: In order to accurately predict the product life cycle, the accelerated degradation evaluation technology could be applied to significantly shorten the experiment duration. As the technologies of intelligent manufacturing and industrial big data develop, the theory of accelerated degradation evolves as well. Methods: Based on the scientific knowledge mapping, co-author network and co-existence network, 22283 pertinent articles since the year 2010 have been collected to conduct a bibliometric study. Results: The results show that the accelerated degradation reliability assessment spans over many research fields, and achieves great development in the mathematical modeling and experiment verification. Conclusion: To further the study, more efforts are expected in the areas such as building effective evaluation systems and enhancing the credibility of the assessment outcomes, as more advanced sensory data and wireless communication technologies become available.

Aim: The article presents an analysis of the feasibility of R1234yf and R448A, two new low GWP refrigerants, as alternatives to R404A in the refrigeration system of small high and lowtemperature test equipment. Methods: The physical properties of R448A and R404A are similar. Compared with R404A, the GWP of R1234yf and R448A reduced by 99.9% and 67.7%, respectively. The analysis is based on an experimental comparison of R404A with R448A and R1234yf, comparing the compressor discharge temperature, COP, cooling capacity, and the cooling rate of three refrigeration systems at different ambient temperatures. Results: The experimental results show that the cooling capacity of R448A is better than R404A at a higher condensing temperature. Conclusion: When the charging volume is 230g, and the ambient temperature is 25°C, the COP of the R448A system is increased by about 24.63% compared with the R404A system.

Aim: This study aimed to predict the mechanical product maintenance time in the absence of a physical prototype or similar product statistics throughout the design stage. Methods: According to the theory of time accumulative estimation method, a product maintenance time prediction method framework based on a virtual prototype was constructed, which described the prediction process. The virtual maintenance environment containing virtual prototype, virtual human, and maintenance tools was developed. The virtual human’s position and posture information during the maintenance process was obtained by implementing VBScript language. Results: Basic maintenance motions that constitute the whole maintenance process were classified into 4 categories: body movement, upper limb movement, grasp/replace, and operation. Based on MODAPTS (modular arrangement of predetermined time standard) method and virtual maintenance simulation, corresponding time prediction methods for each categories were proposed. Conclusion: Taking a maintenance dissassembly and assembly task of engine as an example, through the comparison between the measured actual maintenance time and predicted time of several methods, feasibility and effectiveness of proposed method are verified.

Background: The global energy consumption problem is becoming more serious, therefore, it is a hot trend to improve energy efficiency and choose environmentally friendly alternative working fluids. Objective: The main thermophysical parameters of the refrigerant mixture, which blended HCFO 1224yd(Z) and HFO1336mzz(Z) in the high-temperature heat pump cycle, were theoretically studied to replace HFC245fa. The theoretical cycle model of refrigerant mixtures of high-temperature heat pumps was established. Methods: In this paper, a theoretical cycle model of the mixed refrigerant high-temperature heat pump is established, and the cycle performance of the mixed refrigerant in the high-temperature heat pump system under different working conditions is compared. Results: It was found that HFO1336mzz(Z) could reduce the exhaust temperature of the compressor and increase the heat pump coefficient COPh, and HCFO1224yd(Z) could improve the problem of excessive suction specific volume in high-temperature heat pump systems. Conclusion: The result shows that the refrigerant mixture with 0.6/0.4 HCFO1224yd(Z)/HFO1336 mzz(Z) has the best cycle performance when the condensing temperature is 150 °C, and the cycle temperature rise ranges from 50 to 70°C.When the cycle temperature rise is 70°C, and the condensing temperature ranges from 110 °C to 150°C, the coefficient of performance value of the refrigerant mixture with 0.2/0.8 HCFO1224yd(Z)/HFO1336mzz(Z) reaches the maximum of 3.11.

Background: The Vibration Isolation Platform (VIP) can greatly reduce the risk of damage to dynamic equipment caused by external vibration interference and provide the most stable and reliable working environment for dynamic equipment. Objective: Aiming at the problems of small vibration isolation dimension, low bearing capacity, serious motion coupling, and narrow vibration isolation bandwidth in the field of vibration isolation of dynamic load equipment, a hydraulic redundant six degrees of freedom parallel vibration isolation platform (PVIP) with active and passive composite vibration isolation support is proposed. Methods: The dynamic coupling model of active and Passive Hybrid Vibration Isolation (APHVI) of redundant PVIP is established, and the matrix diagonal decoupling control strategy and fuzzy PI control theory are combined. Analysis of passive vibration isolation performance and APHVI performance of VIP is done. Results: The simulation results show that the effect of APHVI based on fuzzy PI decoupling control is better than that of passive vibration isolation and matrix diagonal decoupling control. Conclusion: Fuzzy PI control can effectively attenuate more than 98 % of the disturbance, significantly improve the vibration isolation performance and decoupling effect of the platform, and expand the effective vibration isolation bandwidth.

Aim: The Internal Combustion Engine (ICE) based vehicles must follow strict regulations regarding noise levels, especially in the racing competition. The noise level is typically gauged as per two different scenarios: stationary engine revolution and maximum achievable revolution. One cannot reach the required noise level by deploying just reactive or resistive muffler type separately. This research recommends a novel mix of reactive and resistive mufflers in a single package solution. For assessing the noise level, three different types of mufflers are devised and studied by means of a computational approach. The new exhaust design in this study becomes a novelty of the proposed article. In analyzing the acoustic capability of the muffler, up to now it has not been able to dampen in various frequency ranges. Methods: In this paper, the author wants to perform a computational analysis of 3 muffler models that combine several methods of attenuation that are effective at different specific frequency ranges with different configurations in order to obtain a good combined attenuation capability in various frequency ranges. Muffler 1 uses simple reactive and dissipative techniques like standard mufflers, while muffler 2 combines the dissipative technique with a Helmholtz resonator acting as the reactive part. Muffler 3 has a multi-chamber system that uses a combination of several advanced techniques. The three mufflers are evaluated on the basis of their capacity to decrease noise level. This noise level is assessed by considering both transmission and insertion loss through mathematical calculations in the frequency range of 200 Hz to 6400 Hz with the help of pressure acoustic, frequency domain (ACPR) simulation. Apart from noise evaluation, this study also examines flow parameters to estimate the pressure drop for the proposed muffler. Results: Comsol simulation provided both Insertion Loss (IL) and Transmission Loss (TL) with different trends. Muffler 3 had broadband response compared to its counterparts. Verifiying the finite element simulation results, electroacoustic models of each muffler were simulated using Matlab Simulink to get frequency response. Both finite element and electroacoustic modeling results have a good agreement. Pressure distribution of each model was also evaluated in terms of isosurface total pressure. Conclusion: It is demonstrated that the proposed muffler having a multi-chamber setup provides the best performances showing both superior and consistent noise reduction throughout the 200-6400 Hz frequency range and good airflow that does not create backpressure due to noise suppression efforts.

Background: Compared with other types of compressors, although the scroll compressor has a simple structure and low noise, due to the limitation of the structure, it has defects such as excessively high discharge temperature, and has extremely high requirements on the machining accuracy of parts. The oil-free scroll compressor is a new type of scroll machine, which does not contain oil during the working process; it can be applied to cases with low displacement requirements and a high-pressure ratio. Objective: Taking a scroll compressor with a rated displacement of 0.6 m³/min as the research object, the analysis and research of the working performance parameters of the scroll compressor in actual work provide a certain theoretical basis for the improvement and optimization of the test prototype. Methods: The thermodynamic model of the scroll compressor in the actual working process is established by the variable-mass system thermodynamics and the control volume method. Based on the CFD method, a three-dimensional unsteady-state numerical simulation of the flow characteristics of the working fluid in the scroll compressor's working chamber is carried out in order to verify the thermodynamic model. Considering the accuracy of numerical simulation, a test platform with air as the working fluid is set up. Results: Through the thermodynamic model and numerical simulation, the changes of temperature, pressure and velocity in the working chamber of the scroll compressor with the orbiting angle of the main shaft as well as the gas force and torque acting on the orbiting scroll tooth are obtained. Through experiments, the law of volume flow and shaft power of the scroll compressor with the speed of change, and the law of the change of discharge temperature with pressure at different speeds are obtained. Conclusion: At the same time, the thermodynamic model established by considering heat transfer and leakage is more in line with the actual working process of the compressor; the mass exchange between adjacent working chambers of the scroll compressor has a greater impact on the temperature and pressure in the working chamber. Due to internal leakage and irreversible loss, such as heat transmission, there is a deviation between the theoretical volume flow and the actual volume flow.

Background: The employment of Phase Change Materials (PCMs) provides a potential selection for heat dissipation and energy storage. The main reason that hinders the wide application is the low thermal conductivity of PCMs. Combining the proper metal fin and copper foam, the fin/composite phase change material (Fin-CPCM) structure with good performance could be obtained. However, the flow resistance of liquid paraffin among the porous structure has seldom been reported, which will significantly affect the thermal performance inside the metal foam. Furthermore, the presence of porous metal foam is primarily helpful for enhancing the heat transfer process from the bottom heat source. The heat transfer rate is slow due to the one-dimensional heat transfer from the bottom. It should be beneficial for improving the heat transfer performance by adding external fins. Therefore, in the present study, a modified structure by combining the metal fin and copper foam is proposed to further accelerate the melting process and improve the temperature uniformity of the composite. Objective: The purpose of this study is to research the differences in the heat transfer performance among pure paraffin, Composite Phase Change Materials (CPCM) and Fin/Composite Phase Change Material (Fin-CPCM) under different heating conditions, and the flow resistance of melting paraffin in copper foam. Methods: To experimentally research the differences in the heat transfer performance among pure paraffin, CPCM and Fin-CPCM under different heating conditions, a visual experimental platform was set up, and the flow resistance of melting paraffin in copper foam was also analyzed. In order to probe into the limits of the heat transfer capability of composite phase change materials, the temperature distribution of PCMs under constant heat fluxes and constant temperature conditions was studied. In addition, the evolution of the temperature distributions was visualized by using the infrared thermal imager at specific points during the melting process. Results: The experimental results showed that the maximum temperature of Fin-CPCM decreased by 21°C under the heat flux of 1500W/m² compared with pure paraffin. At constant temperature heating conditions, the melting time of Fin-CPCM at a temperature of 75°C is about 2600s, which is 65% less than that of pure paraffin. Due to the presence of the external fins, which brings the advantage of improving the heat transfer rate, the experimental result exhibited the most uniform temperature distribution. Conclusion: The addition of copper foam can accelerate the melting process. The addition of external fins brings the advantage of improving the heat transfer rate, and can make the temperature distribution more uniform.

Background: Dexterity is an important index for evaluating the motion performance of a robot. The size of the robot connecting rods directly affects the performance of flexibility. Objective: The purpose of this study is to provide an overview of optimal design methods from many pieces of literature and patents, and propose a new optimal design method for ensuring the robot completes its tasks flexibly and efficiently under workspace constraints. Methods: The kinematics and working space of the robot are analyzed to determine the range of motion of each joint. Then, a dexterity index is established based on the mean value of the global spatial condition number. Finally, an improved cuckoo algorithm is proposed, which changes the step size control factor with the number of iterations. Taking the dexterity index as the objective optimization function and the working radius as the constraint condition, the improved cuckoo search algorithm is used to optimize the size of the robot rod. Results: The improved cuckoo algorithm and proposed rod size optimized method are fully evaluated by experiments and comparative studies. The optimization design process shows that the proposed method has better solution accuracy and faster convergence speed. The optimized design results show that the robot's dexterity index has increased by 26.1%. Conclusion: The proposed method has better solution accuracy and faster convergence speed. The method was suitable for optimizing the rod parameters of the robot, and it was very meaningful to improve the motion performance of the robot.