This paper focuses on the discrete sliding mode control (SMC) method adopted in the permanent magnet synchronous motor (PMSM) current loop control system. Based on the predefined-time terminal sliding mode (PTSM) method, a discrete PTSM and its sufficient conditions for convergence are proposed. Considering that the PMSM current loop control system can be rewritten as a typical discrete first-order multiple-input multiple-output (MIMO) system in practical applications, a discrete PTSM law is further proposed. The effectiveness of the proposed discrete PTSM controller is verified through numerical simulations and experiments on a PMSM drive control test bench. Experiments are conducted to compare different current loop control schemes, which fully demonstrates that the discrete PTSM method proposed in this paper can achieve better dynamic performance of discrete state variables during the convergence sliding process.

In this paper, a second-order predefined-time terminal sliding mode (SPTSM) is proposed, which is investigated for the practical applications of the speed regulation system of a permanent magnet synchronous motor (PMSM) by using predefined-time stability theory and Lyapunov stability theory. At first, we propose the SPTSM, which involves the controller’s design by using the novel reaching law with predefined-time terminal sliding mode (PTSM) and the novel sliding mode surface with PTSM. Second, we derive the novel SPTSM controller for the universal second-order nonlinear single-input single-output (SISO) system and the practical applications of the speed regulation system of the PMSM separately. Then, numerical simulation results of the speed regulation system of the PMSM are also included to check the effect of the theoretical results and the corresponding parameters on the convergence rates, so that the results can be guidance for the selection of SPTSM controller parameters. Finally, the dynamic responsiveness and robustness of the system are validated through numerical simulations and experimental results. It has been observed that the robust SPTSM controller, which is designed with the PTSM-PTSM, referring to the sliding mode that involves a reaching law with PTSM and a sliding mode surface with PTSM, exhibits superior performance.

In rotating machinery, unbalanced mass is one of the most common causes of system vibration. This paper presents an experimental investigation of the unbalance response of a gas foil bearing-rotor system, based on a 30 kW-rated commercial hydrogen fuel cell vehicle air compressor. The study examines the response of the system to varying unbalanced masses at different rotational speeds. Experimental results show that, after adding unbalanced mass, subsynchronous vibration of the rotor is relatively slight, while synchronous vibration is the main source of vibration; when unbalanced mass is added to one side of the rotor, the synchronous vibration on that side initially decreases and then increases with speed, while synchronous vibration on the opposite side continuously increases with speed; when unbalanced mass is added to both sides, the synchronous vibration on each side increases with the phase difference of the unbalanced mass at low speed, while the opposite trend occurs at high speed. The analysis of the gas foil bearing-rotor system dynamics model established based on the dynamic coefficient of the bearing shows that the bending of the rotor offsets the displacement caused by the unbalanced mass, which is the primary reason for the nonlinear behavior of the synchronous vibration of the rotor. These findings contribute to an improved understanding of GFB-rotor interactions under unbalanced conditions and provide practical guidance for optimizing dynamic balancing strategies in hydrogen fuel cell vehicle compressors.

Gas film thickness significantly influences the performance prediction of Gas Foil Thrust Bearings (GFTB). However, the Classical Model (CM) for GFTBs exhibits inaccuracies in describing gas film thickness. In this paper, we explore the differences in the details of gas film thickness modeling and propose a Parallel Segmentation Model (PSM), which fixes the errors of the CM in describing the gas film thickness in the ramp section, and a Full-Ramp Model (FRM), to which a more realistic description of the gas film in the flat section is also added. Comparative analysis, utilizing a publicly available test dataset based on the open-source GFTB structure, establishes that the FRM surpasses the CM and PSM in accurately predicting load capacity. In-depth analysis shows that the location of the minimum gas film thickness for determining the load capacity is located at the innermost circle of the free end of the top foil, whereas the FRM is subjected to the same load with a larger film thickness at this location, which may be due to the unique geometry of the top foil of the FRM. Subsequently, employing the FRM, a parametric study explores load capacity in GFTB, considering variables such as ramp height, top foil thickness, bump foil stiffness, ramp section extent, and top foil area. The results demonstrate that GFTB load capacity exhibits a linear increase with the expansion of the top foil area. Moreover, the load capacity increases with augmented top foil thickness and bump foil stiffness, albeit at a decreasing rate. Additionally, an increase in ramp section extent initially enhances load capacity, reaching a maximum value before declining. Similarly, an increase in ramp height initially augments load capacity, attaining a maximum before subsequent diminution.

The dynamic pressure mechanical seal stator needs the ability of axial sliding and angular swing. The O-ring in the sliding interface plays the role of sealing and compensation. The quality of its design is very important to the stable operation of the seal. Therefore, the finite element model of the fretting compensation structure was established, and the pre-compression amount of the two typical compensation structures of the O-ring integral groove and the split groove in the smooth micro compensation condition and the vibration disturbance micro compensation condition were analyzed respectively. The effects of medium pressure and wire diameter on the sealing performance and compensation characteristics of O-rings were tested and verified. The analysis results showed that the most important factors affecting the compensation performance of the static ring were the compression amount of the O-ring and the interface friction coefficient. The split groove compensation structure had better followability in the compensation process, more suitable for high-speed, and stronger vibration conditions. The friction force and the degree of fluctuation was smaller. The analysis results were verified by experiments, and the optimal compensation structure parameters of the O-ring were obtained. During the start-up stage of the dynamic pressure mechanical seal, the friction of the O-ring was the largest.Reducing the compression amount and improving the lubrication state of the compensation interface can effectively reduce the fluctuation of the friction force. To improve the compensation performance, good lubrication can effectively reduce the frictional force fluctuation by more than 20%. The research results provide a reference for the design of the micro compensation structure of the high-speed dynamic pressure mechanical seal.

The critical speed is a crucial factor that impacts the stability of high-speed compressors. However, limited research has simultaneously considered the influence of gas foil bearings (GFBs), labyrinth seals, and impellers on critical speed. In this study, we develop a rotordynamic model that incorporates the aerodynamic forces of GFBs, labyrinth seals, and impellers to explore the effects of each component on the critical speed. To validate the developed model, experimental tests are conducted on a centrifugal compressor test bed, and the results exhibit a high level of agreement with the model calculations. By comparing the model calculations that include different components, we comprehensively analyze the influence of each component on the critical speed. The findings reveal that, for centrifugal compressors used in fuel cell vehicles, the rotordynamic coefficients resulting from GFBs are significantly larger than those resulting from impellers and labyrinth seals. Thus, it is reasonable to disregard the aerodynamic forces caused by impellers and labyrinth seals when calculating the critical speed. Furthermore, substituting rigid gas bearings for GFBs as a means to simplify the calculations has only a very slight impact on the results. This study aims to optimize the design process of centrifugal compressors for fuel cell vehicles and offers valuable insights for designing compressors of similar sizes.

Reducing costs and improving durability are essential factors for commercializing gas foil bearings, crucial components of fuel cell vehicle air compressors. In this paper, a two-pad gas foil bearing is proposed. By reducing the number of top foils, adopting a symmetrical design, and eliminating the welding step, the cost of processing and assembly is reduced, and the potential source of failure caused by welding is eliminated. The feasibility of the two-pad gas foil bearing was verified through testing on a commercial fuel cell vehicle air compressor. Then, durability testing was performed in accordance with fuel cell vehicle usage requirements, including an accelerated random vibration test equivalent to 6,000 h of on-board operation and a 200,000-cycle start-stop test. These tests simulated the damage caused to the bearings during fuel cell vehicle operation and start-stop periods, respectively. The durability test results indicated that the two-pad gas foil bearing provides good start-stop durability but insufficient durability against on-board random vibration. The failure causes were analyzed, and improvement measures were proposed. Our findings can be utilized to guide the manufacturing of low-cost and highly durable gas foil bearings.

This paper aims to investigate the predefined-time synchronization analysis for two different multiple-input-multiple-output systems. Firstly, based on the definition of predefined-time synchronization, we propose a novel Lyapunov function and a novel fast terminal sliding mode, each having corresponding sufficient conditions for predefined-time synchronization. Second, we respectively derive the novel fast terminal sliding mode controllers for synchronization schemes with and without taking into account the uncertainty. The desired convergence time can be obtained by setting predefined-time parameters Tpi in advance. Finally, the controllers and the corresponding parameters designed for comparison are applied to predefined-time synchronization of two chaotic systems. The efficacy and robustness of the obtained results are demonstrated by numerical simulations.

重型车辆的整车排放测试是国Ⅵ排放法规的重要测试项目之一.以满足国Ⅵ排放法规的重型天然气发动机为研究对象,分别进行发动机台架WHTC循环和整车实际道路排放PEMS测试,并将发动机运行工况、排放测试结果进行对比分析.研究发现,两种排放测试方法发动机运行工况有一定的相似性,但是WHTC循环测试时发动机排温上升较快且过量空气系数波动较小,三元催化器的催化转化效率较高.两种测试方法下污染物排放均满足国Ⅵ排放限值,但是由于发动机运行工况及外界条件的变化,两者之间的排放存在着一定的差异,发动机台架WHTC循环排放值较低,NOx的比排放值相差16.41％,CO排放相差20.2％,THC排放相差15.8％.发动机在进行开发标定时需要兼顾两种工况,对排放留出更宽裕度.

With the shortage of traditional fossil energy and the aggravation of global warming, the demand for transformation from traditional fossil energy to renewable energy becomes more and more urgent. Compressed air energy storage technology is a guaranteed technology to overcome the time limit of renewable energy and achieve sustainable, efficient and large-scale application of renewable resources. In order to solve the traditional compressed air energy storage technology energy output variety is single, there is low grade energy waste defects. This paper presents a compressed air energy storage system based on intermediate cooling. Through the intercooler, the system adjusts the inlet temperature of the expander, improves the output cooling quality, and realizes the coupling operation of refrigeration and energy storage. This paper establishes a thermodynamic model of the system, analyzes the effects of ambient air temperature and inlet temperature of expander on system performance, and compares the energy efficiency ratio of the system with that of compressed air refrigeration system. The simulation results show that the system can adjust the inlet temperature of expander to increase the net power consumption and achieve high quality cooling output.

为探究旋转式密封圈脱开全过程的密封性能参数变化,借助非线性有限元软件ANSYS,建立三维的"超弹性体"的两参数Mooney-Rivlin橡胶模型、弹簧和"刚体"的静止轴模型,研究传统唇型密封圈和2种新型唇形密封圈(G形与S形)在脱开过程中接触压力、接触宽度、摩擦力的变化规律,分析入口压力、过盈量、弹簧力、橡胶密度对脱开转速的影响.结果表明:3种旋转式密封圈的接触压力、接触宽度均随转速增加而减少且减少的速率相同,摩擦力随转速的增加先增大再减少;3种旋转式密封圈的最大接触压力均发生在唇口靠近空气侧,空气侧与介质侧的接触宽度之比为2:1,从唇口到空气侧的0.6 mm内,接触压力均趋近于最高值;入口压力对脱开转速影响最大,橡胶密度对脱开转速的影响也较大,而过盈量和弹簧力的影响较小;G形和S形唇形密封结构的脱开转速比传统密封结构低40％左右,证明了环形弹簧的离心力能够加速唇口的脱开.采用压力监控的实验精确地测定开启转速,实验结果与数值分析结果相差较小,证明了数值分析的准确性.

Frosting of the evaporators is inevitable during system operation. As such, defrosting must be conducted peri-odically to ensure stable and efficient operation of the system. However, the current control methods often cause ?mal-defrosting " due to the complexity and randomness of frosting. To improve the defrosting accuracy of the system a new detection method for the amount of frost was proposed based on the image processing gray scale image theory. Further, the theory of combining the frosting characteristic parameter St with gray contrast C of the frosting image to forecast the critical defrosting time t of the system was established. Through experiments, the best defrosting times (t(best1) and t(best2)) of the system were determined, compared with t. Additionally, a frosting error factor (FEF) was identified, compared with the St value of times(t(best1),t(best2) and t). The results show that there was a defrost lag in the defrost time determined by the existing defrost control method,the average time error TEF was by 177.25 s and 321 s. Finally, in view of the illumination effect, the influence of illumination intensity on the accuracy of the proposed method was explored. After changing the illumination intensity,new defrost control method still offers high control accuracy, TEF was by 64 s and 324 s. Overall, from the perspective of engineering applications, the proposed method can reduce the influence of illumination intensity on frosting image recognition, allowing the system to accurately judge the defrosting start point, thereby realising accurate defrosting.

考虑热与变形对油气两相动压密封自振稳定性的影响,建立基于油气两相动压密封自振稳定性数学模型,采用流固热耦合有限元方法,研究油气比、转速、压差和O形圈阻尼等参数对油气两相动压密封受干扰后的轴向、角向自振稳定性能的影响.结果表明:转速较低时轴向自振稳定性较好而角向自振稳定性较差,转速高时两者相反,O形圈阻尼较低时轴向自振稳定性较差而角向自振稳定性较好,O形圈阻尼高时两者相反,因此在极端转速和取极端O形圈阻尼的情况下轴向或角向临界频率较小,不利于油气两相动压密封自振稳定;压差越大轴向临界频率越大,轴向自振稳定性越好,但角向临界频率越小,角向自振稳定性越差;随着两相介质油气比的增大,轴向临界频率减小而轴向临界质量增大,油气比在0.1～0.15时临界频率、质量以及转动惯量较大,密封综合自振稳定性能较好.

针对高速高压高温/低温工况下动压密封变形问题,以动压密封的典型结构为研究对象,考虑动环的支撑和约束,建立热固耦合分析模型,研究热载荷、力载荷和约束对动环端面微变形的影响,并提出动环端面微变形改善方法.结果表明:多载荷共同作用时,温差对动环端面微变形影响最大,其次是转速和压力;在2种情况下,动环端面微变形受温度值的影响很小,主要与温差有关;相比低温,动环端面微变形更易受高温的影响,单位温差的变形变化量为3～4倍;动环形心距旋转中心越远,动环端面微变形受转速影响越大,且呈抛物线关系;动环端面微变形与压差呈线性关系.对高速高压宽温域的动压密封,控制动环端面微变形,首先,应降低动环的温差;其次,若转速够高,应适当增加动环厚度,通过扩大形心变化区域能增加86％的动环端面微变形范围,若转速不够高,通过合理的结构设计约束动环内表面以控制动环翻转,最大能降低65.2％的动环端面微变形;最后,合理设计的轴向压紧力能进一步确保动环端面微变形维持在极小范围内.

在含有颗粒介质的工作环境中下,硬质材料配对机械密封环的热力耦合变形和摩擦磨损对机械密封的泄漏和使用寿命起着至关重要的作用.考虑动静环和颗粒介质的摩擦,试验测定了摩擦系数,建立了动静环热力耦合的有限元计算模型,研究了 WC-Co硬质合金和无压烧结碳化硅(SSiC)陶瓷两种硬质材料密封的温度场和端面变形规律,分析了不同工况下的密封间隙变化规律.试验测试分析了密封环温度、磨损前后的泄漏及表面粗糙度,讨论了端面的磨损机理,验证了计算模型的准确性.结果表明:考虑动环磨粒摩擦热的有限元模型能准确地预测密封的温度和端面变形;耦合作用下动静环端面呈现外径脱离、内径贴合的变形,且变形差异程度随压差和转速的增大而加剧;变形导致端面磨痕分布不均匀,内径磨痕较严重.WC-Co硬质合金配对密封环的端面变形小、泄漏量小,高硬度WC颗粒对Co基体能产生很好的"阴影效应",具有良好的耐磨粒磨损性能.SSiC陶瓷材料韧性差,易产生片状磨屑,形成过渡型磨粒磨损,材料耐磨性较差,泄漏量增加明显.在磨粒工况下,WC-Co硬质合金机械密封具有泄漏小、耐磨性强的特点.研究结果为颗粒介质中机械密封的材料应用及设计优化提供了参考.

针对密封端面参数结构选取不当导致密封高速旋转时动静环烧毁的问题,对螺旋槽泵出型动压密封端面参数进行了优化.基于气相流体控制方程,采用了流固热耦合有限元分析方法,考虑动静环变形以及热变形对流体的影响,研究了螺旋角、槽数、槽堰比、槽坝比、槽深等端面参数对开启力、泄漏量、摩擦功耗以及气膜刚度等密封性能的影响,提出了螺旋槽泵出型动压密封设计优化方案;采用试验研究方法,验证了计算模型的准确性;对比了运转前后密封端面微观形貌图,发现试验密封端面几乎无摩擦磨损,验证了密封可行性.研究结果表明:螺旋角在15°～20°、槽数在12个～16个、槽堰比在0.5 ～0.6、槽坝比在0.65～0.75、槽深在7μm～10μm时,密封开启力、气膜刚度较大,泄漏率、摩擦功耗较小,密封综合性能最佳.

为提高发动机启动性能,改善汽车启动时蓄电池电流过大的问题,研究了超级电容-蓄电池组成的串联式和并联式复合电源.超级电容通过控制器与汽车蓄电池串联形成串联式复合电源,通过与汽车蓄电池并联形成并联式复合电源.在某1.5 L汽油机上进行启动实验,实验结果表明,复合电源能有效降低蓄电池峰值电流,明显降低铅蓄电池的电压降,同时启动时间明显降低.与串联复合电源相比,并联式复合电源在改善蓄电池电流过大方面更明显.

The characteristics of urea injection and NOx conversion efficiency are closely related.A SCR test bench was built based on V2O5-WO3/TiO2 catalyst,and NO,NH3 and O2 feed streams were dosed by mass flow controllers.The effect of normalized stoichiometric ratio (NSR) and catalyst temperature on ammonia storage,ammonia slip and NOx conversion efficiency was studied.The results show that the influence of NSR and temperature on ammonia storage,ammonia slip and NOx conversion efficiency is obvious.The time of ammonia storage will be shorten with the increase of NSR,then the improving speed of NOx conversion efficiency is high.The NSR fix 2.2,the NOx reduction efficiency increase from 0 to 4.3％ within 15 s,and the NOx reduction efficiency increase from 0 to 8.7％ within 15 s when NSR set 3.0.The time of ammonia slip and ammonia storage are closely related,the time of ammonia slip will be shorten with the increase of NSR.The method of NSR from larger to the smaller can increase ammonia storage rate and optimize NOx conversion efficiency.Using this injection method to carry out the European transient cycle (ETC) test,the brake specific emission of NOx reduce from 8.26 g/(kW · h) to 1.91 g/(kW · h),and the average and peak value of ammonia are 5×10-6 and 18×10-6,the NOx can reach the National V emission regulations.

根据共轨喷油器的驱动要求,设计了基于智能电磁阀驱动芯片MC33816的智能电控共轨喷油器驱动单元,开发了相应的软件控制策略.该单元包括DC-DC升压模块、高低边驱动模块和电流波形反馈控制模块,实现了Peak& Hold驱动方式.试验表明,该智能驱动电路性能优异、响应迅速、运行可靠,达到了精确控制喷油量和喷油定时的目的.