不同模数下圆柱直齿轮成形的数值模拟及分析

论述了在直齿轮分度圆直径为定值时，变形程度与模数的关系。通过对三种不同模数的齿轮在特定的条件下温挤压成形数值模拟，结果及分析表明，随着齿轮模数的增大，变形程度也增大，金属向齿顶及周围流动就相对较多，齿形就容易充满，但齿轮头部内凹与头的齿部凸肚现象就越厉害。     

STEYR转向节模锻成形工艺研究

针对转向节的外形特点，从即能满足尺寸精度要求，又能使模具有足够高的强度和寿命的角度出发，论述了模锻工艺的合理选择，模具的合理化设计以及提高模具寿命的研究情况。     

混合动力矿用车再生制动能量回收系统控制策略

在传统的矿用车液压制动系统理论基础上,在安全情况下,基于混合动力矿用车再生制动能量回收最大化,提出了一种后轮并联混合矿用车再生制动力分配与再生制动控制策略。主要考虑电机发电效率、电池的SOC值及制动力分配等综合因素对再生制动能量回收的影响,运用ADVISOR进行整车建模和典型矿山制动工况下仿真。结果表明:制动初速度为15 km/h,制动强度Z分别为0.1、0.3、0.5的最大再生制动能量回收效率分别为65.01%、55.99%、46.41%。采用后驱并联混合矿用车再生制动控制策略解决制动安全性能问题,并实现最大化再生制动回收效率。     

Precognitive control: open- and closed-loop steering in a lane-change manoeuvre

Abstract

This paper presents two experiments in which steering a lane-change manoeuvre is analysed as a precognitive control task. The suggestion that the dependence on instantaneous visual feedback is low during such a task was tested by analysing steering performance under conditions both with and without visual occlusion. Steering force served as the main independent variable in experiment I, which was performed in a fixed-base driving simulator. A 1 s visual occlusion period during the initial steering-wheel movement to the left was given every other manoeuvre. The results indicate that steering force reduces steering-wheel amplitude variability, this effect also being reflected in the maximum heading angle variability.

Steering-wheel angle amplitude was the main independent variable in experiment II, which was carried out in the instrumented car. In this experiment the duration of the occlusion period was 3 s, i.e. covering the complete pull-out phase of the manoeuvre. The results show that variability in steering-wheel movement amplitude increases about linearly with the amplitude: standard deviations are about 9% of the amplitude. For both experiments I and II the results correspond quite well with those of an earlier reproduction experiment. Regarding the withdrawal of visual feedback it appears that occlusion affects the mutual tuning of steering amplitude and timing, rather than affecting these quantities separately. The vehicle-motion effects resulting from occlusion are relatively small and it can be concluded therefore that a temporary withdrawal of visual feedback has no dramatic effects in the pre-programmed task considered here.     

Efficient driver drowsiness detection at moderate levels of drowsiness

Previous research on driver drowsiness detection has focused primarily on lane deviation metrics and high levels of fatigue. The present research sought to develop a method for detecting driver drowsiness at more moderate levels of fatigue, well before accident risk is imminent. Eighty-seven different driver drowsiness detection metrics proposed in the literature were evaluated in two simulated shift work studies with high-fidelity simulator driving in a controlled laboratory environment. Twenty-nine participants were subjected to a night shift condition, which resulted in moderate levels of fatigue; 12 participants were in a day shift condition, which served as control. Ten simulated work days in the study design each included four 30-min driving sessions, during which participants drove a standardized scenario of rural highways. Ten straight and uneventful road segments in each driving session were designated to extract the 87 different driving metrics being evaluated. The dimensionality of the overall data set across all participants, all driving sessions and all road segments was reduced with principal component analysis, which revealed that there were two dominant dimensions: measures of steering wheel variability and measures of lateral lane position variability. The latter correlated most with an independent measure of fatigue, namely performance on a psychomotor vigilance test administered prior to each drive. We replicated our findings across eight curved road segments used for validation in each driving session. Furthermore, we showed that lateral lane position variability could be derived from measured changes in steering wheel angle through a transfer function, reflecting how steering wheel movements change vehicle heading in accordance with the forces acting on the vehicle and the road. This is important given that traditional video-based lane tracking technology is prone to data loss when lane markers are missing, when weather conditions are bad, or in darkness. Our research findings indicated that steering wheel variability provides a basis for developing a cost-effective and easy-to-install alternative technology for in-vehicle driver drowsiness detection at moderate levels of fatigue.     

基于非线性方程法的齿轮钢淬透性计算模型

采用非线性回归方程计算方法，结合实际生产的齿轮钢淬透性数据对数学模型进行修正。在此基础上，开发了齿轮钢淬透性的计算预报平台，实现根据成分和预设的晶粒度级别预报任意端淬距离的淬透性值。模型预测精度高于传统的多元线性回归方法。     

Exploring the roles of portfolio steering committees in project portfolio governance

Governing project portfolios engages different actors in organizations including portfolio managers, portfolio officers, top managers, and others who may team up as portfolio steering committees. While portfolio steering committees play a regular role in project portfolio governance, their role is still unclear. Through an in-depth multiple case study in three Danish companies, the roles of portfolio steering committees were explored. The results showed that portfolio committees may play three distinct roles in portfolio governance: a) communication and consolidation role, b) negotiation role, and c) decision making role. The results challenged the notion that portfolio committee meetings are the place and time to make collective decisions on the portfolio, rather, portfolio steering committees might unintentionally become or intentionally be used for other purposes than decision making. The empirical evidence of the study proposes that these three roles might be related to two governance design factors: frequency and duration of committee meetings.     

成形铣齿切削载荷与加工精度的分析

错齿盘铣刀可用于齿轮的成形铣齿加工,具有多刃断续切削和变切屑厚度等特点,属于非自由强力铣削。切削载荷、加工精度逐渐成为切削机制的主要内容。通过试验方法,测量获得铣齿加工的典型载荷,可知切入、切中、切出三个阶段具有不同的特征。通过三坐标测量加工精度,分析得出齿向呈现了倒锥形的结果。其中切中阶段,加工精度为正并逐渐提高;而切出阶段,加工精度为负。基于对三向切削载荷及机床主轴箱体的悬伸对加工精度的直接影响分析,解释了"收口"现象的主要原因。该类实时的切削数据可用于现场分析与控制,进而实现精度补偿。     

磁力传动齿轮泵结构设计及分析

针对系统要求,为使齿轮泵达到高可靠性、零泄漏的要求,设计一种特殊的齿轮泵结构。采用磁力传动使齿轮泵和电机以非接触式进行连接,取消了传统结构上的轴封,摩擦力小,使电机的输入功率减少;将动密封转换为静密封,使该齿轮泵实现零泄漏的指标。     

A new fault diagnosis algorithm for helical gears rotating at low speed using an optical encoder

Helical gears are widely used in gearboxes due to its low noise and high load carrying capacity, but it is difficult to diagnose their early faults based on the signals produced by condition monitoring systems, particularly when the gears rotate at low speed. In this paper, a new concept of Root Mean Square (RMS) value calculation using angle domain signals within small angular ranges is proposed. With this concept, a new diagnosis algorithm based on the time pulses of an encoder is developed to overcome the difficulty of fault diagnosis for helical gears at low rotational speeds. In this proposed algorithm, both acceleration signals and encoder impulse signal are acquired at the same time. The sampling rate and data length in angular domain are determined based on the rotational speed and size of the gear. The vibration signals in angular domain are obtained by re-sampling the vibration signal of the gear in the time domain according to the encoder pulse signal. The fault features of the helical gear at low rotational speed are then obtained with reference to the RMS values in small angular ranges and the order tracking spectrum following the Angular Domain Synchronous Average processing (ADSA). The new algorithm is not only able to reduce the noise and improves the signal to noise ratio by the ADSA method, but also extracts the features of helical gear fault from the meshing position of the faulty gear teeth, hence overcoming the difficulty of fault diagnosis of helical gears rotating at low speed. The experimental results have shown that the new algorithm is more effective than traditional diagnosis methods. The paper concludes that the proposed helical gear fault diagnosis method based on time pulses of encoder algorithm provides a new means of helical gear fault detection and diagnosis.