﻿ 基于双模式驱动的飞行汽车起飞阶段动力匹配分析<sup>*</sup>
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Power matching of flying cars during takeoff stage based on dual-mode driving
XU Bin, TIAN Fugang
School of Transportation Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100083, China
Received: 2017-05-05; Accepted: 2017-06-30; Published online: 2017-09-13 11:46
Corresponding author. XU Bin, E-mail: xbacb@buaa.edu.cn
Abstract: To solve power-matching problem during takeoff stage of folding wing flying car, the basic dynamic control strategy was studied.The dual-mode driving characteristics during takeoff stage were analyzed through theoretical calculation, and the concept of the optimal switching time was proposed.Based on the basic parameters and results of power-matching calculation of the concept car, the driving state simulation models under different working conditions were established in Simulink. According to the driving state simulation mo-dels, the simulation analyses on driving state during takeoff stage were conducted, and the dual-mode driver selection principle and optimum matching scheme of switching time were obtained.The calculation results show that the takeoff acceleration time is reduced by 22% and the takeoff distance is shortened by 13% based on dual-mode driving.The optimization analyses on transmission and vehicle parameters and variation of output characteristics were further conducted, from which the effect of the parameters on power performance during takeoff stage was obtained.
Key words: flying car     dual-mode driving     optimal switching time     Simulink simulation     parameter analysis

1 双模式驱动与最佳切换时刻的定义 1.1 双模式驱动

1.2 最佳切换时刻

2 动力学分析 2.1 双模式驱动行驶状态的分类

1) 地面运行。机翼不展开，此时的受力情况与普通的汽车类似，发动机的扭矩通过轮胎转变为驱动车辆前进的驱动力。

2) 起飞阶段。轮胎驱动，机翼展开，与地面运行状态的主要区别在于升力，主要出现在起飞滑跑的前半段。

3) 螺旋桨驱动。机翼展开，受力情况与普通飞机类似，应用在起飞阶段及飞行阶段。

 图 1 飞行汽车起飞阶段受力示意图[6-7] Fig. 1 Force diagram of flying car during takeoff stage[6-7]

1) 认为前后轮载荷平均分配，忽略由于质心不平分轴距带来的一系列影响，该影响包括但不限于：后轮载荷所决定的附着力的限制、前后轮滚动阻力的大小、起飞过程中整车姿态变化导致的升阻力特性变化等。

2) 不针对力矩做分析，将车速达到起飞车速(升力、重力相平衡)作为分析的终点。

3) 不考虑爬坡阻力Fi的影响，认为在起飞过程中沿着水平路面行驶。

2.2 飞行汽车动力学建模

 (1a)

 (1b)

 (2)

1) 地面运行。

 (3)

FL在这一阶段忽略。

2) 起飞阶段。纯轮胎驱动。

 (4)

3) 螺旋桨驱动。

 (5)
3 动力匹配计算

 参数 数值 载荷W/N 6500 起飞速度/(km·h-1) 110 升阻比K 10 迎风面积A/m2 2 车轮半径r/m 0.52 螺旋桨传动比i 2.43 螺旋桨直径D/m 1.8 机翼投影面积Al/m2 9

3.1 发动机选型计算

 (6)

 (7)

 图 2 发动机外特性曲线 Fig. 2 External characteristic curves of engine
3.2 传动比计算

3.2.1 主减速器传动比

 (8)

3.2.2 一挡传动比

 (9)

3.2.3 中间挡传动比

4 双模式驱动行驶状态仿真

 (10)

5 双模式驱动控制及最佳切换时刻分析 5.1 最佳切换时刻的选取

2.1节进行受力分析时提到，起飞阶段驱动与地面运行最大的区别在于升力的影响，升力随车速的提高而增大，受此影响轮胎与地面的附着力减小，轮胎能提供的驱动力也逐渐变小。当车速增大到某一值时，达到轮胎的打滑界限，如图 3所示。

 图 3 起飞阶段轮胎驱动力与对应发动机转速下螺旋桨驱动力 Fig. 3 Wheel driving force and propeller driving force under the same engine speed during takeoff stage

5.2 双模式驱动与纯螺旋桨驱动对比

 图 4 起飞过程加速曲线 Fig. 4 Accelerating curves during takeoff stage

 驱动方式 加速时间/s 起飞滑跑距离/m 纯螺旋桨驱动 16.87 276 双模式驱动 13.15 240 优化率/% 22.05 13.04

5.3 双模式驱动下各参数对起飞性能的影响

5.3.1 传动比

 图 5 传动比对起飞滑跑距离的影响 Fig. 5 Influence of transmission ratio on takeoff running distance

5.3.2 换挡转速

 图 6 换挡转速对加速时间和起飞滑跑距离的影响 Fig. 6 Influence of shifting speed on acceleration time and takeoff running distance

5.3.3 整车设计参数

 图 7 整车质量对加速时间和起飞滑跑距离的影响 Fig. 7 Influence of vehicle quality on acceleration time and takeoff running distance

 图 8 滚动阻力和迎风阻力与车速的关系 Fig. 8 Relationship between wheel and windward resistance and vehicle speed

 图 9 阻力系数对加速时间和起飞滑跑距离的影响 Fig. 9 Influence of drag coefficient on acceleration time and takeoff running distance
5.4 发动机特性对起飞性能的影响

 图 10 不同发动机转矩特性曲线 Fig. 10 Different engine torque characteristic curves

 图 11 发动机适应性系数对切换时间和总加速时间的影响 Fig. 11 Influence of engine adaptability coefficient on switching time and take-off acceleration time
 图 12 发动机适应性系数对切换时刻行驶距离和总起飞滑跑距离的影响 Fig. 12 Influence of engine adaptability coefficient on running distance at switching time and running distance of take-off stage

6 结论

1) 本文采用双模式的驱动策略，相比纯螺旋桨驱动，能有效提升起飞阶段的动力性能，缩短起飞滑跑阶段的时间和距离。

2) 最佳切换时刻出现在轮胎驱动力和螺旋桨驱动力相等的位置；考虑到换挡产生的驱动力变化，以换挡点作为切换点有利于改善行驶稳定性。

3) 在进行传动系统参数的选取时，应以起飞阶段轮胎驱动工况作为对象进行匹配和优化设计，尤其要注意的是，因为升力的影响，在进行挡位和换挡策略的设计时，要以避免车轮打滑作为边界条件。

4) 对于飞行汽车，空气动力性能的影响较一般汽车而言更加明显，迎风阻力在起飞阶段成为主要阻力源。

5) 与飞行汽车相匹配的发动机，适应性系数应根据起飞阶段发动机常用工况进行选取；与车用发动机不同，较大的适应性系数，不仅对提高起飞动力性无益，还会使飞行阶段工作恶化。

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#### 文章信息

XU Bin, TIAN Fugang

Power matching of flying cars during takeoff stage based on dual-mode driving

Journal of Beijing University of Aeronautics and Astronsutics, 2018, 44(4): 662-669
http://dx.doi.org/10.13700/j.bh.1001-5965.2017.0279