摘要
直升机具有垂直起降、悬停和低空机动飞行的独特优势,在军用和民用航空领域发挥着重要作用,然而低速、高油耗、短续航和高噪声等不足制约了其应用市场拓展。根据飞行工况变化动态调整旋翼转速的变旋翼转速技术能较大程度上克服上述不足,提升直升机的综合性能,因而成为当前直升机领域重要的研究课题。目前,在变旋翼转速对直升机具体性能的影响、变旋翼转速的优化与控制、因使用变旋翼转速技术衍生的控制和变旋翼转速的实现等问题的研究仍面临着诸多挑战。基于此,文中综合了国内外变旋翼转速技术的研究成果,着重从变旋翼转速对直升机性能的影响、变旋翼转速的优化与控制、变旋翼转速技术的实现3个方面阐述了变旋翼转速技术的研究发展现状,并对其进行归纳和展望,旨在为高性能直升机变旋翼转速技术的发展提供有价值的参考。
直升机自20世纪40年代面世以来,因能实现垂直起降、空中悬停、近空低速平飞等独特功能,且相较于固定翼飞机具有起降方便灵活、低空机动性好等优点,被广泛应用于军用和民用航空领域。然而,受限于构
目前,针对变旋翼转速技术的研究已取得了长足的进步,但在对直升机性能影响的分析、变旋翼转速的优化与控制,以及变旋翼转速的设计实现等方面的研究仍存在诸多待解决的问题。对变旋翼转速研究进行系统综述的文献较少。韩东
1)变旋翼转速对直升机性能方面的影响;
2)变旋翼转速的优化与控制问题研究;
3)变旋翼转速技术的具体实现方案。
文中介绍了变旋翼转速技术的定义及其特点,综述了旋翼变转速对直升机性能的影响研究,系统论述了变旋翼转速和变旋翼转速过程中的优化与控制问题的研究现状,并从发动机和传动系统的角度综述了变旋翼转速实现的代表性研究。最后,总结和展望了未来变旋翼转速技术的研究发展,以期为后续发展提供有益参考。
考虑到涡轴发动机的最优转速区间较窄、旋翼转速变化会引起机身共
A160“蜂鸟”直升机(

图1 典型变旋翼转速直升机
Fig. 1 Classic types of variable rotor speed helicopter
开展旋翼变转速对直升机性能影响的分析研究来探明旋翼转速与直升机性能参数的关系是变旋翼转速技术走向工程应用的前提条件和首要任务。
直升机的飞行性能主要包括需用功率、悬停性能、巡航性能和机动性能等。Kare

图2 需用功率随转速变化曲
Fig. 2 Rotor power vs rotor spee
Han
部分学者还研究了旋翼转速变化对悬停和续航性能的影响。尹崇
旋翼转速变化对直升机的配平、操纵性能和稳定性能也有重要影响。文献[

图3 配平操纵量随旋翼转速变化曲
Fig. 3 Variation curve of operation variable with rotor spee
旋翼转速变化对直升机的振动、噪声等方面性能的影响也很明显。旋翼转速的变化会使旋翼各阶载荷频率靠近甚至跨越机体的固有频率从而引发较严重的共振问
变旋翼转速对直升机性能影响分析有力地推进了后续变旋翼转速相关技术,尤其是变旋翼转速优化与控制技术的研究与发展。本节从变旋翼转速的优化与控制和由变旋翼转速衍生的控制问题两方面切入,综述目前国内外的相关文献,以期厘清关键点和难点,为后续研究提供参考。

图4 涡轴发动机特性曲线图(自由转速
Fig. 4 Characteristic curves of turboshaft engine (power turbine with variable speed
早期的变旋翼转速优化与控制研究仅针对旋翼或发动机单独研究,忽略了两者之间的高度耦合性和非线性时变性。仅针对旋翼端独立开展变旋翼转速研究,将需用功率最低等效为发动机燃油消耗最小,求解最优旋翼转速。由
部分学者以直升机/发动机综合系统为研究对象,开展了相关的转速优化与控制研究。在变旋翼转速条件下,旋翼需用功率是由旋翼转速和旋翼操纵量共同决定的。姚文荣
。 | (1) |
式中:Nmr为最优旋翼转速;Np为动力涡轮转速;ni为第一级减速齿轮传动比;ncvt为无级变速装置传动比;nf为最后一级减速齿轮传动比。
汪勇
。 | (2) |
宁景
变旋翼转速带来一系列的问题,如:转速跳变导致传动系统功率损失、变旋翼转速过程中的动力涡轮转速超调、下垂抑制和动态响应延迟等,这些问题亟待解决。本部分主要介绍变旋翼转速衍生的控制问题及其解决方法。
Litt

图5 双发配置下的扭矩序列转移控制示意图
Fig. 5 Schematic diagram of torque sequence transfer control in dual engine configuration
以上控制策略与直接采用无级变速转速控制相比更繁琐。姚文荣
当前基于发动机/直升机综合系统实现变旋翼转速控制还需要解决变转速带来的强扭矩扰动造成的转速超调/下垂、功率跟随迟缓和振动载荷增大等问题。恒转速控制过程中同样存在动力涡轮转速超调/下垂问题,为解决该问题先后产生了串级PID(proportional integral derivative)、总距/扭矩前馈控制、自抗扰控制(active disturbance rejection control,ADRC)和非线性模型预测控制(nonlinear model predictive control,NMPC)等方法。其中,ADRC最早由韩京
优化与控制问题关乎变旋翼转速技术能否实现预期功能,而实现变旋翼转速的结构设计才是其能否走向工程应用的关键所在。随着直升机设计水平的提升,变旋翼转速已经具备技术上的可行性,
类型 | 公司 | 机型 | 变旋翼转速方案 |
---|---|---|---|
常规直升机 | Sikosky | H-5(最早) | 传动系统变速 |
Eurocopter | EC135、EC145 | 发动机变速 | |
复合直升机 | Lockheed Martin | 夏延AH-56 |
发动机变 |
Eurocopter | X3 | 传动系统变速 | |
复合直升机-共轴双旋翼直升机 | Sikosky | XH-59、X2、S-97“侵袭者” | 发动机变速+传动系统变速 |
Sikosky -Boeing | SB>1“挑战者” | 发动机变速+传动系统变速 | |
复合直升机-最优旋翼转速直升机 | Boeing | A160“蜂鸟”无人直升机 | 传动系统变速 |
倾转旋翼机 | Bell | XV-15 | 传动系统变速 |
Bell-Lockheed Martin | V-280 | 传动系统变速 | |
Bell-Boeing | V-22“鱼鹰” | 发动机变速+传动系统变速 | |
Leonardo/Agusta Westland | AW609 | 发动机变速 |
发动机变速(动力涡轮变转速),即通过调节发动机输出轴转速来改变主旋翼输出转速,能够避免传动系统质量增加,同时实现主旋翼转速的连续可调,是变旋翼转速的理想实现方案。然而,常规的动力涡轮设计通常只能在较窄范围内保证发动机的高效运
目前变转速动力涡轮的研究难点仍然是涡轮效率问题,要求在实现变转速的同时还要保证涡轮高效稳定的功率输出,而涡轮效率主要与涡轮载荷、叶型攻角、雷诺数有关,因此在以下方面还面临关键技术难题。
1)涡轮载荷较大问题:涡轮转速降低造成的级载荷增加是巡航工况下涡轮效率降低的主因。增加涡轮级数可以有效降低级载荷,但会造成叶型攻角变化过大而导致气动损
2)叶型攻角变化较大问题:随涡轮转速降低叶型攻角会偏离设计值,导致气动性能恶化,涡轮效率降低。宽攻角适应性叶型设计和可变导叶与动叶设计能有效解决叶型攻角损失,但是会造成间隙泄漏、增加重量和控制复杂度等问
3)低雷诺数问题:低雷诺数问题使得前2个问题造成的气动问题更加突出。将动力涡轮设计点设置在巡航速度附近能够弥补部分效率损失,但是并没有根本上解决低雷诺数环境下高负荷大叶型攻角造成的效率降低问
传动系统变速技术既可以实现50%~100%宽范围的转速调节,又具有较高的技术成熟度,因此成为发动机变速的理想替代方案。目前变速传动系统构型主要有两级变速传动构型和无级变速传动构型2种。本节整理归纳了在传动系统变速构型方面的研究,以期为未来研究提供参考。
吴裕平
行星轮系因为传动效率高、传动比范围大、负载能力强、结构紧凑等优点在变速传动系统中应用广
a)定轴行星齿轮构

图6 定轴行星齿轮构型
Fig. 6 Two-speed transmission configuration with fixed-axis planetary gear
b)改进型定轴行星齿轮构
定轴双星惰轮构型(

图7 定轴双星惰轮构型
Fig. 7 Two-speed configuration with fixed-axis planetary and idler gear
反向定轴双星构型(

图8 反向定轴双星构
Fig. 8 Two-speed configuration with reversing and fixed-axis double planetary gea
定轴行星齿轮-面齿轮构型(

图9 定轴行星齿轮-面齿轮构
Fig. 9 Two-speed transmission configuration with fixed axis planetary gear-face gea
该构型(

图10 偏置复合齿轮构型
Fig. 10 Two-speed transmission configuration with offset compound gear
西科斯基公司和贝尔公司的专利中都包含此种构型(

图11 离合器-超越齿轮构
Fig. 11 Two-speed configuration with clutch-free gea
差动轮系能够实现大传动比范围的平稳传动,且具有体积小、承载能力强的特点,常用于变速机构的设计

图12 离合器-差动轮系构
Fig. 12 Two-speed configuration with clutch-differential gear-trai
对于单离合器-差动轮系构型,摩擦离合器分离时,自由轮锁死,动力直接从输出轴到太阳轮6,然后经行星齿轮5、齿圈4和行星架高速输出;摩擦离合器接合时,自由轮放松,动力分2路传递,一路经齿轮1、齿轮2、摩擦离合器、齿轮3和齿圈4传递,一路直接到太阳轮6,2路动力汇总后由行星架低速输出。该构型结构简单、可行性高,但是传动受配齿精度影响明显。双离合器-差动轮系构型实质上就是用超越离合器替换自由轮,然后再对称布置一个摩擦离合器,动力传递过程类似。配齿困难、制造精度要求高、安装困难是两者的共性问题,而后者还存在控制复杂、对称部位均载难以保证的问题。
此外,还存在一种双离合两级变速传动构

图13 双离合两级变速传动构型
Fig. 13 Double clutch two-stage variable speed transmission configuration
两级变速主要针对直升机悬停和巡航工况,在高、低速切换过程中会发生转速跳变和不同步现象,导致振动冲击和功率损失,而无级变速传动则能够轻易实现连续、平稳的转速调整,因而更适合最优旋翼转速直升机,但由于设计复杂度较高,目前整体上仍处于概念研究阶段。
无级变速来源于Torotrak公司的专利,2003年SAE年会正式提出无级变速的概念。目前,无级变速传动主要应用于风机领域和汽车传动领域。NASA Glenn Research Center在其专利中最早提出双输入差动轮系无级变速传动构

图15 双输入差动轮系无级变速传动构
Fig. 15 Continuously variable transmission configuration with dual input differential gear trai
综上,两级变速传动构型和无极变速传动构型均能满足基本的变旋翼转速需求,但两者在结构设计、功能实现、适用性等多方面存在差别,同时也存在一些共性问题,归结如下。
1) 结构设计:两级变速只需针对悬停和巡航状态在两个速度设计点进行切换,结构相对简单,而无级变速需要连续调节转速,因而其结构设计更加复杂。
2) 功能实现:两级变速只能在高低2个设计速度点实现效率最优,在高、低转速切换过程中还存在转速跳转和功率损失问题,离合器长时间接合还会导致摩擦发
3) 适用性:无级变速更适合飞行状态变化频繁的最优转速旋翼直升机,而两级变速与长期处于悬停和巡航2种工况的倾转旋翼机更适配。
4) 共性问题:与固定传动比传动构型相比,均不同程度地增加了传动系统的重量和结构复杂性,降低了机械传动效率,这一定程度上抵消了变旋翼转速带来的能耗减少。此外,两级变速主要通过离合器进行高、低转速的切换,无级变速通过转速控制装置实现连续变速,均存在可靠性降低的问题。
变旋翼转速直升机在提高飞行速度、减少燃油消耗、延长续航里程和续航时间及改善噪声等方面优势明显,同时也存在着共振风险增高、自转安全性下降,以及结构设计和控制复杂等问题。当前,变旋翼转速对直升机性能的影响研究较多且较成熟,这为变旋翼转速技术的深入研究和工程应用提供了理论基础;基于发动机/直升机综合系统对变旋翼转速进行优化与控制有利于提升发动机/直升机这一高耦合系统的整体效率;针对变旋翼转速过程中的转速超调、跳变、动态响应品质变差和系统鲁棒性降低等问题的研究进一步提升了直升机的综合性能;变旋翼转速的结构实现(变转速动力涡轮技术和变速传动系统构型设计)问题的研究,极大地加快了变旋翼转速技术工程应用的步伐。然而,以上方面的研究仍存在诸多不足,面临较多的理论和技术难题。文中从4个方面对变旋翼转速技术进行总结并展望其未来发展,内容如下。
1)更普适、全面、详尽和准确的直升机性能参数采集、计算和分析。目前大部分关于变旋翼转速直升机性能分析的研究是基于模型计算分析或将风洞测试数据经性能分析软件处理得出主要性能参数的变化规律,模型精度、实验室测试与真实飞行工况的符合程度均会影响结论的准确可靠性。此外,大部分研究仅针对特定机型和定常稳定飞行场景,并未验证结论在其他机型和极端非定常场景(高速、大载荷、高海拔等)的适用性。基于以上研究得出的理论性成果用于指导实际变旋翼转速设计可能存在一定偏差。因此,未来还需要通过更精确的计算模型、贴近真实工况的测试、更丰富的机型和更完备的性能参数评价指标进一步展开变旋翼转速对直升机性能的影响研究。
2)变旋翼转速综合建模、优化与控制的研究有待加强。限于研究条件,当前多数研究采用近似简化模型,如采用简化旋翼模型代替直升机模型、采用的模型缺乏飞行控制模块、采用理想变速传动模型等,忽略了模型精度和各子系统间耦合性的影响。当前的研究更多地专注于挖掘发动机/直升机系统的功率/能耗性能来优化和控制旋翼转速,而较少考虑最大飞行速度、最大航程和航时、机动性、稳定性和声学特性等性能指标实现更综合的优化与控制。此外,如何解决变旋翼转速过程中的衍生问题,提升直升机的综合性能和控制品质,同样值得深入研究。因此,未来有必要建立更精确、更完整和更综合的变旋翼转速优化控制模型,实现直升机性能的综合优化和改善控制品质。
3)变转速动力涡轮和变速传动系统构型的设计问题有待深入研究。变转速动力涡轮需要在保证宽转速调节范围的同时保证高效率,如何通过结构设计和优化有效解决高载荷、低雷诺数、叶型攻角变化较大等影响动力涡轮效率的问题亟待继续深入研究。两级变速传动是目前成熟度较高的方案,但难以实现连续调速,如何通过设计和控制实现准连续调速值得深入研究;无级变速传动能实现宽范围连续转速调节,工况适应性更好,是较为理想的方案,但目前技术可行性较低,结构设计研究亟待加强。此外,质量增加、结构复杂、可靠性降低、传动效率下降和齿轮加工困难等是变速传动系统设计的共同难题,也是未来变速传动研究的重点。
4)真实飞行工况下的测试验证和工程应用有待落实。目前多数研究仅从理论研究和数字仿真试验或半物理仿真试验来展开变旋翼转速的研究,理论的准确性和方法的可靠性亟待实物测试验证。虽然部分变转速动力涡轮和变速传动系统构型设计已经应用于少量机型,但多数方案仍停留在专利或文献中,亟待工程化。因此,有必要进一步完善设计和解决工程中的应用难题。
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