Abstract:To improve the safety of lateral obstacle avoidance for an intelligent vehicle with a shared driving control between human driver and autonomous driving system, a robust control strategy based on dynamic obstacle avoidance warning is proposed. Considering the dynamic changes of acceleration and speed of the vehicle ahead, the longitudinal safety distance model is established, and a multi-level warning algorithm based on the fusion and complementation of the critical longitudinal safety distance and the reciprocal of collision time is proposed. According to the different warning status and dynamic intervention of the driver, relative controls are put up for the vehicle so as to achieve the safety of the intelligent vehicle. Meanwhile, to realize the precise control of trajectory tracking, the robust control strategy of lateral obstacle avoidance based on parameter perturbation is proposed. Finally, the simulation platform of Carsim and Simulink is constructed, and the proposed control strategy is verified. The results indicate that the proposed control strategy can obtain different warning levels and can dynamically adjust warning states with dynamic intervention of the driver. If the driver does not respond to the warning until the fourth level warning, the control strategy automatically takes over the intelligent vehicle and carries out the lateral obstacle avoidance control, improving the safety and yaw stability of the intelligent vehicle.

Abstract:The single-zone heat-release rate algorithm is widely used in combustion heat-release diagnosis in gasoline engine. However, it is difficult to reasonably estimate the specific heat ratio and heat transfer, which affects the reliability of the analysis results. Based on the single-zone heat-release rate model, a specific-heat-ratio estimation method considering the influence of heat transfer is proposed, which calculates the polytropic exponent during compression and expansion, and interpolates it based on the gas temperature in the combustion interval to obtain the variable specific heat ratio for the calculation of the total heat release. From the perspectives of the energy released during the cycle and the combustion control parameters, the proposed method is compared with the existing method by using the experimental data of the gasoline engine. The results show that the total cumulative heat release calculated by this method is more accurate, the combustion end point is advanced, and the correlation between the combustion control parameters is significantly improved, indicating that this algorithm can describe the combustion history in the cylinder more accurately.

Abstract:In order to investigate the impact of driving behavior on real driving emissions (RDE) of heavy-duty diesel vehicles, a total of 9 times of smooth driving, normal driving and rough driving were carried out on three vehicles using the portable emissions measurement system (PMES). The dynamic parameters v·a_pos[95] and emission factors of the urban, rural, motorway section and total travel distance of each vehicle were calculated before and after the three tests, and the dynamic parameters v·a_pos[95] were used to analyze the effects of pollutant emission characteristics. The results show that compared with smooth driving, the NO_x emission factors of the three vehicles under normal driving and rough driving behavior increase by 33.73%-621.10% and the PN emission factors increase by 21.26%-122.40%. At the same time, the correlation between CO emission factors and the dynamic parameters v·a_pos[95] is not obvious, but the NO_x emission factors and PN emission factors of suburbs and high-speed sections have a strong correlation with the dynamics parameters v·a_pos[95]. It can be seen that the impact of driving styles on vehicle emissions cannot be ignored.

Abstract:To improve the economy of a multi-axle electric vehicle, an optimal driving force distribution control strategy is proposed in this paper. The drive torque distribution is optimized offline to achieve optimal efficiency of the drive system, and then a drive mode table for online application is generated. Through table interpolation, the number of active driving axles and the specific driving axles to be activated is determined based on the instantaneous axle loads so as to make full use of the ground adhesion. A backward simulation model is established using MATLAB/Simulink, and simulation analyses are carried out under the adapted world transient vehicle cycle working condition. The simulation results show that the proposed optimal driving force distribution control strategy improves energy consumption by 9.18% compared with the average torque distribution control strategy and by 6.12% compared with the axle load ratio based control strategy.

Abstract:Aiming at the problem of insufficient real-time recognition capabilities of existing vehicle recognition methods, a single shot multibox detector(SSD) algorithm based on improved depthwise separable convolution is proposed for vehicle type recognition. Firstly, this paper proposes to extract the features using depthwise separable convolution network, and introduces the inverted residuals module to solve the problem of reduced accuracy due to the small number of channels and feature compression. Secondly, based on the rigid body characteristics of the vehicles, the region candidate frame is redesigned to reduce the amount of model parameter calculation. Finally, ablation experiments are performed on the BIT-Vehicle dataset to compare the performance differences of different network models. The results show that the improved depthwise separable convolution SSD vehicle type recognition method can achieve a recognition accuracy of 96.12%, and the detection speed increases to 0.078 s/frame.

Abstract:In order to more accurately detect the vehicle stopping in highway tunnels, this paper proposes a new methodology that combines the traditional image processing technology with deep learning. Firstly, the foreground moving targets are extracted using the background difference method based on Gaussian mixture model (GMM). Then the meanshift algorithm is applied to track these foreground moving targets. By calculating the speed of the moving targets and the correlation of the moving targets between the neighboring video frames, and comparing the results with the speed threshold and correlation threshold, the static target is detected. Finally, combined with the convolutional neural network (CNN) classification model, whether the static target is vehicle is identified. The method proposed in this paper is validated using the real highway tunnel vehicle stopping video and achieves an accuracy of at least 84%. Compared with the traditional image processing method without CNN, our method improves at least 63% accuracy.

Abstract:The calculation and design of geometric parameters of a double-circular-arc gear-shaper cutter and the analysis of its tooth profile error are one of the challenges in harmonic drive manufacturing. In order to study the calculation method of geometric parameters and the distribution of tooth profile errors, a mathematical model of the tooth profile and tooth surface of the double-circular-arc gear-shaper cutter is established by kinematics method. Based on the model, the influence of the back angle of the top edge of double-circular-arc gear-shaper cutter on the grindable length of the gear-shaper cutter is studied; the calculation methods of the geometric parameters, such as the back angle of the side edge and the front angle of the side edge, are put forward, and the influential factors of these parameters and the change law from the top of the tooth to the root of the tooth are studied; the influence of the front angle and the back angle of the top edge on the tooth profile error of the double-circular-arc gear-shaper cutter is analyzed; and the design method of the rake angle of the gear-shaper cutter is given by an example. The conclusions are drawn as follows. 1) The grindable length of the gear-shaper cutter decreases with the increase of the back angle of the top edge. 2) The back angle of the side edge is related to the radius of the point and the pressure angle and increases with the increase of the back angle of the top edge. 3) The front angle of the side edge increases with the increase of the front angle of the top edge and the back angle of the top edge, and the front angle of the top edge has a greater influence on the front angle of the side edge. 4) Both the front angle and the back angle of the top edge have a great influence on the tooth shape error of the gear shaper. In short, when selecting the parameters, a larger front angle and a smaller back angle should be selected under the condition of ensuring the accuracy of tooth profile.

Abstract:In order to analyze the influences of assembly errors on the contact of roller enveloping worm gearing, an interference analysis model of the roller enveloping worm was build based on the theory of gear meshing and differential geometry, considering four assembly errors: center distance error, worm axial error, worm gear axial error, and shaft intersection angle error. The quantitative evaluation index and its numerical calculation method of the transmission pair under two kinds of interference conditions were put forward. The correctness of the mathematical model was verified by the example calculation. The results suggest that the theoretical contact line of the roller enveloping hourglass worm gearing is a space cylindrical spiral curve near the middle plane. Among the components of the assembly error, the axial error of the worm has the greatest influence on the contact interference, while the axial error of the worm gear has the least influence.

Abstract:The reliability and service life of the heavy-duty and high-speed gear transmission system are severely affected by the large impact load of the system. The objective of this study is to reduce the impact load of the cutting transmission system by optimizing the motion parameters during the operation of the shearer. Taking a coal mining machine gear transmission system as an example, an electromechanical coupling model of the power transmission system of the shearer including the dynamic model of the motor and the dynamic model of the coupled gear train and the planetary gear train was established. The simulation results show that under sudden load changes, the dynamic optimization of the motion parameters reduces the impact load in the cutting transmission system. An experimental bench for the cutting power transmission system was set up to study the effects of motion parameter optimization on the impact load of the cutting transmission system. The trend of the impact load of the transmission system and the speed adjustment duration obtained from experiments and simulations are in good agreement, verifying the effectiveness of the motion parameter optimization.

Abstract:In order to study the theoretical basis of Mn(Ⅱ) removal in water by alkali modified pomelo peel biochar, the dynamic adsorption of Mn(Ⅱ) in a fixed bed was investigated. Using flow rate, bed height, and initial concentration of Mn(Ⅱ) as variables, the effects of these three operating conditions on the adsorption of Mn(Ⅱ) in a fixed bed of alkali-modified pomelo peel biochar were studied, and the data were fitted by varying models. The results show that the alkali-modified pomelo peel biochar has a certain buffering effect on the adsorption of Mn(Ⅱ). The fixed bed operation time is prolonged with the decrease of flow rate and Mn(Ⅱ) initial concentration, as well as the increase of bed height. The highest adsorption capacity of alkali modified pomelo peel biochar for Mn(Ⅱ) is observed(25.59 mg/g) when the flow rate is 1 mL/min, Mn(Ⅱ) initial concentration is 150 mg/L and bed height is 2 cm. The Thomas model indicates that internal and external diffusion are not control procedures in the process of adsorption; the Adams-Bohart model suggests that the adsorption preliminary kinetics in the fixed bed is controlled by external mass transfer, and its linear expression (the BDST model) relatively accurately predicts the operation time of effluent Mn(Ⅱ) concentration reaching 70% of influent Mn(Ⅱ) concentration under each initial condition; the modified dose-response model accurately describes the shape of the Mn(Ⅱ) breakthrough curve.

Abstract:With the engineering background of Urumqi region’s solar water heating system for floor heating, this paper analyzed the fluid flow and heat transfer processes inside three thermal storage tanks with different top or obstacle structures numerically in order to make full use of solar energy and improve the comprehensive efficiency of solar energy system. The alternate operation mode of each water tank is also discussed. The results show that it is feasible to use the multi-tank alternate operation mode at different times. According to the thermal stratification evaluation results of the water tank, at three typical moments(11:30, 15:00 and 18:00) when the outdoor temperature during the typical day is relatively stable in the region, the reasonable operation mode of the water tank is: at 11:30, 3# water tank (spherical top and obstacle inside the tank with single round hole) is preferentially operated, followed by 2# water tank (conical top and obstacle inside the tank with five round holes) or 1# water tank (conical top and obstacle inside the tank with single round hole); at 15:00 and 18:00, 3# water tank should be preferentially operated while 1# and 2# water tanks can be used as backup for each other. For users with higher water temperature requirements but less water consumption, it is suggested that 3# water tank is preferentially operated, followed by the 1# water tank. When users generate a lot of backwater and need hot water with higher temperature, the operation of 2# water tank is preferred. It is of great engineering guiding significance to operate appropriate hot water storage tank in a timely manner and adjust the fluid parameters according to the local meteorological conditions so as to make full use of solar energy resources and improve the reliability of the solar heating system.

Abstract:BiVO₄ and BiVO₄/sepiolite were prepared by hydrothermal method, and Ag/BiVO₄/sepiolite composite photocatalysts with different Ag loadings were prepared under the light using AgNO₃ as a precursor reagent. XRD, SEM, TEM, XPS and DRS were used to characterize the photocatalysts. Using rhodamine B as a model pollutant, the effects of different Ag loadings on the performance of Ag/BiVO₄/sepiolite composite photocatalysts were investigated. The results show that when the loading of Ag reaches 60%, the composite photocatalyst has the best decolorization effect on rhodamine B, and the rhodamine B can be completely decolorized within 10 minutes. At the same time, the 0.6Ag/BiVO₄/sepiolite sample shows substantial recyclability and cycling stability.

Abstract:The mechanical properties of FGH96 superalloy after long-term aging were studied with tensile tests, stress rupture tests, and creep tests. The microstructure and precipitation phases were investigated by optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Results show that at the condition of aging temperature of 550 ℃ and 650 ℃, aging time from 100 h to 7 500 h, the grain size, morphology of γ' phase, fraction of MC plus M₃B₂ phases, tensile properties, and rupture strength of the FGH96 superalloy after long-term aging keep nearly the same with those before long-term aging. The factions of γ' phase and Cr₂₃C₆ phase increase with increasing aging time at 650 ℃ while they remain almost unchanged at 550 ℃, which leads to the increasing residual strain of creep deformation for the 650 ℃ aged FGH96 superalloy.