范例翻译

A SIMPLE MECHANICAL TRANSMISSION SYSTEM FOR

HYBRID VEHICLES INCORPORATING A FLYWHEEL U. Diego-Ayala (a), P. Martinez-Gonzalez (b), KR. Pullen (c)

（a）Electronic Variable Technologies（EVT），Barcelona，Spain，08028，https://www.360docs.net/doc/1011683548.html,

（b）Department of Mechanical Engineering,Imperial College,London,SW7 2BX,p.martinez05@https://www.360docs.net/doc/1011683548.html, （c）Department of Mechanical Engineering, City University, Northampton Square,London, EC1V 0HB,

Keith.Pullen. 1 https://www.360docs.net/doc/1011683548.html,

Abstract : In recent years it has been proven that hybrid forms of powertrains in vehicles can lead to substantial reductions in fuel consumption and emissions. In particular, the advent of

commercial Hybrid Electric Vehicles proved that improved performance has been achieved by implementing a secondary energy source in a vehicle powertrain. However, the only secondary energy source implemented to date is based on electrochemical batteries, which suffer from technical and economic disadvantages. To overcome this, a novel powertrain based in both mechanical power transmission and mechanical energy storage is proposed. This article presents a brief explanation of flywheel technology as it applies to hybrid vehicles and a qualitative comparison with existing energy storage technologies is also presented. Finally computational simulations will show that the implementation of this powertrain in a vehicle leads to important reductions in fuel consumption while requmng only mechanical components in the system, instead

of batteries, motors, generators and power electronics

Keywords: Regenerative energy, flywheel, hybrid vehicle, epicyclic gearbox, CVT.

1 Introduction

During recent years there has been a growing concern about the effect of automotive tail pipe emissions on the environment, particularly regarding their contribution to climate change. Since the last decade, the European Union has introduced a set of standards to limit pollutant emissions of new vehicles, including NOx, HC, CO, and particulate matter emissions. These limits have become gradually more restrictive, with Euro 5 [1] being the latest standard which will affect vehicles introduced in 2009. The European Parliament has also promised to introduce binding legislation to limit CO2 emissions for the average new car fleet to 120 g CO2/km by 2012 [2], of which vehicle propulsion technology is expected to achieve a target of 130 g C02ikm on its own and the remaining 10 g C02ikm to come from use of different fuels and tyres, improved efficiency of air-conditioning systems and changes in driving strategies. The Automotive industry, through the European Automobile Manufacturers Association has met with scepticism the approach of the proposed legislation, since they claim that relying heavily on vehicle technology to meet these demands would not be costeffective and the targets would not be met within the proposed time

frame [3]. It is evident that if these targets are to be met, an entirely new vehicle powertrain design must be introduced at a marginal cost increase.

Foreseeing this scenario, novel types of vehicles with improved powertrains, termed Hybrid Electric Vehicles (HEV), have been successfully developed and introduced, the most successful commercial example being the Toyota Prius. Although HEVs have demonstrated considerable reductions in fuel consumption and emissions, their reliance on batteries presents considerable drawbacks, including low power and energy to weight ratio, lifetime severely affected by power rate demand, and increased cost of vehicle due to the motor and its controller. To overcome this, vehicles with hybrid powertrains that avoid the use of batteries and motors have been proposed, but only by a few authors [4-8]. These systems have the characteristic of having an energy system storage which is purely mechanical: a flywheel. Despite the great advantages shown by the flywheel with respect to batteries; up to date there is no powertrain technology sufficiently mature to fully replace batteries with flywheels as energy storage units for hybrids. Apart of the technical challenge of using the flywheel, providing a continuous variation of the ratio between the vehicle and the flywheel is a major challenge. To overcome such limitations, new types of CVTs are under research and being development. For example, the company Electronic Variable Technologies (EVT) is currently developing a state of the art CVT based on the utilization of epicyclic gearboxes, combined with small motors to control the speed [9, 10]. Given the characteristics of this transmission, the system has the potential to be used in the future to propulsive hybrid vehicles using flywheels as a secondary energy source.

The system presented here provides a different approach. With a simpler powertrain designed to function as a bolt-in system. The complete conceptual design of the system and its potential performance are presented. The operating principle, a scale physical model and its computational model are also described. The findings into the operation of the proposed system are discussed. Results of numerical simulations of a full size hybrid vehicle using the hybrid system are also presented.

2 Flywheel Technology

The majority of hybrid vehicles in production and research are based around the use of an electrochemical battery for the secondary energy storage unit. Batteries have been in development for over two centuries and sold as commercial products for nearly as long. And with advances in battery technology during the past few decades, driven in part by portable consumer products, it is not surprising that they would be seen as the first choice for hybrid vehicles by the generally conservative automotive industry. This is currently partnered with the internal combustion engine

(ICE), a robust and low cost technology.

HEV technology is undoubtedly the most mature hybrid powertrain technology available; however it suffers from fundamental technical drawbacks that may hinder its standard introduction in new vehicles at a massive scale, and ultimately their long term survival. One of the main problems with HEVs is associated with the electromechanical batteries sensitivity to internal and external conditions that affect battery performance. The amount of power a battery can deliver and the rate at which they accept charge is greatly affected by their state of charge (SOC) and temperature conditions. This is particularly a problem when regenerative braking, given the high peaks of power that must be accepted by the batteries in a short period of time. Since charge acceptance is best at partial SOC (PSOC), batteries must be able to withstand prolonged PSOC [11]. Furthermore, current automotive batteries do not deliver the reliability required in the industry (i.e. six-sigma), and must be replaced several times during the vehicle's life [12].

Some of the shortcomings of HEVs may be overcome with the inclusion of supercapacitors, which can sustain very high power densities in the range of 5,000 W/kg over a wide temperature range. They also have very long shelf life and high cycle efficiency [13]. Their excellent power capabilities make supercapacitors a very attractive option for their integration in HEVs, particularly to boost regenerative braking capabilities and acceleration. However, their high cost is one of the main problems hampering their introduction in most HEV applications, and the potential for cost reduction is controversial [13]. Furthermore, as their voltage varies with SOC, electronic control and switching equipment is needed [12], adding to its price tag. As the system is electrical, hybrid vehicles with supercapacitors still carry a penalty for transforming energy.

The high-speed flywheel is proposed as an alternative to batteries, which offers an efficient, low cost complement to the ICE. The characteristics of the flywheel are decoupled such that the maximum power depends only on the transmission whereas the quantity of energy storage is related to the size and speed of the flywheel. Advanced flywheels exhibit energy storage densities comparable to that of batteries, but with much higher power densities (essentially determined by the rating of the transmission system).Figure 1 presents a Ragone plot with the energy and power densities of different energy storage technologies.

Figure 1. Ragone plot of energy storage technologies, showing their power and energy densities. Taken from:

Science & Technology Review [14]

In contrast with batteries, the power capabilities of flywheels are independent on the amount of energy stored and on temperature, and its service lifetime is quoted in ranges of 105 to 107 full-cycles [15]. In fact, the energy characteristics and longevity of flywheels are unaffected by deep cycling, which on a battery is highly detrimental [16]. Another useful characteristic is the ease by which, unlike batteries, the state of charge of the flywheel can be readily determined, simple by measuring its rotating velocity.

The type of energy stored is kinetic hence energy which can be transmitted in the mechanical form thus avoiding inefficient energy transformations. The round-trip energy efficiency is thus typically quoted above 90%, but it is time dependant. For short-term storage, it can reach levels close to 100%, but aerodynamic and bearing losses causes it to decrease for medium and long term storage. It is essential thus that the flywheel operates in a vacuum environment and that high efficiency bearings are used [17].

In all, these characteristics make the flywheel particularly suited for applications were power surges are common. This suggests their applicability in hybrid vehicles, particularly for regenerative braking and assisted acceleration for city driving conditions, where a high speed flywheel has the potential to offer improved energy efficiency over the batteries and supercapacitors alternatives and potentially at a fraction of the cost.

3 The Mechanical Energy Storage System and Mechanical Hybrid Vehicle

Flywheel based hybrid vehicle transmissions are far less developed than battery based systems and, as such, there is considerable opportunities for innovation and a need for basic research to be carried out. Some of the major challenges are:

?The design of the flywheel rotor, seal, bearings and containment.

?The design of an infinitely variable transmission

Although solutions do exist for both of the above, greater effort needs to be devoted to understanding and developing cost -effective solutions, without the introduction of too many unknown variables at one time. One way to overcome such drawbacks is with a system of reduced complexity and based around mature technology. The proposal presented in this article is based on these premises. It is an arrangement with a purely mechanical transmission. It is a bolt-on system, which can be added in parallel onto a conventional vehicle powertrain as opposed to requiring a complete re-design of the transmission. Because of this, the benefits in fuel economy are not as substantial as can be gained by a more complex system.

3.1 Description of the Mechanical Energy Storage System

The mechanical energy storage system consists of a flywheel, a planetary gear set (PGS), a brake (located at the ring gear of the PGS) and a small continuously variable transmission unit, CVT, as shown in Figure 2. The PGS provides the continuous and wide range of ratios necessary to operate the hybrid system under the driving conditions where the use of the system is most attractive (braking and decelerating both at low and high speeds). The PGS is an attractive alternative to directly using a continuously variable transmission (CVT) as a mechanical link, as this would require a CVT with an impractically wide ratio, a limited power capability, and a likely low efficiency and costs that would offset the economical benefits of a purely mechanical hybrid system.

Figure 2. The CVT -Brake Mechanical Hybrid Powertrain.

Using this configuration, the mechanical hybrid powertrain uses either the CVT or a frictional brake at the ring gear of the robust PGS to control power flow between the vehicle (carrier branch) and the flywheel (sun branch). This provides a low-cost powertrain with a relatively simple control system able to provide regenerative braking and to assist acceleration with power transmitted via direct mechanical means.

Power flow through the hybrid transmission is better understood by examining the torque equilibrium and kinematic relationships of the PGS. Given a known torque in the carrier (Tc), the torque in the ring (TR) and sun (Ts) are given by [18]:

C AT -=R T (1)

C S BT T -= (2)

)

)(()()(112222221R S R S R S R S R A ++++= (3) A R S R S S S B -=++=1)

)((221121 (4) and R and S are the number of teeth of the sun and ring gears of the PGS and the subscripts refer to the stage of the PGS. The kinematics of the PGS is more complex though, as the speed of a branch is dependent on the current speed of the other two branches, as shown in the next equation:

S R C B A ωωω+= (5)

Where we, W R and W5 refer to the angular speeds of the carrier, ring and sun branches of the PGS respectively.

5 Conclusions

A novel hybrid powertrain able to store and provide energy from a flywheel by mechanical means has been presented in this article. A description of the operation and the control strategy of the hybrid vehicle were provided, including a computational analysis of the operation of the hybrid vehicle under realistic driving patterns. The results, obtained with ADVISOR, showed improvements in fuel economy up to 26% for the conditions tested. It has also been found that the implementation of such a hybrid system is better suited for a heavily congested traffic, since continuous stops/starts are advantageous for the recovery and re-utilisation of energy.The results of this study suggest that mechanical hybrid vehicles could become an option should the mechanical components be designed and optimised to operate within the grounds explained in this study.

一种带有飞轮的混合动力车辆机械传输系统

U. Diego-Ayala (a) P. Martinez-Gonzalez (b), K.R. Pullen (c)

(a) 电子可变电技术（EVT ）, 巴塞罗那, 西班牙, 08028, udiego@https://www.360docs.net/doc/1011683548.html,

(b)伦敦帝国理工大学，机械工程系，SW7 2BX, p.martinez05@https://www.360docs.net/doc/1011683548.html,

(c) 机械工程学院城市学院，北安普顿广场，伦敦，ECI V OHB, Keith.Pullen.l@https://www.360docs.net/doc/1011683548.html,

摘要:近几年来的研究表明，混合动力汽车的动力总成可以大大减少能源的损耗和尾气的排放。尤其是商业混合动力电动车的出现证明了：在汽车的动力总成中添加辅助能量源可以提高车辆的性能。然而，迄今为止所有的辅助能量源都来自于受到科技和价格局限的电化学电池。为了克服这个缺陷，提出了基于机械传动和机械能量储存的动力总成。本文简明介绍了运用于混合动力汽车的飞轮技术并且将其与现有的能量储存技术做了一个本质的对比。最终计算机模型证明了在汽车中装备这个动力总成会使得能源损耗大幅降低，而且这个系统只需要机械元件，

不需要电池、发动机、发电机或者电力电子。

关键字：可再生能源，飞轮，混合动力汽车，行星齿轮，无极变速齿轮。

1 引言

近年来，人们越来越关注汽车尾气排放对环境和气候的影响。在过去的十年里，欧盟引进了一系列关于新上市汽车排放物的标准，这个标准涉及了NOX，HC,CO和颗粒排放物。欧洲汽车尾气排放标准将会影响到2009年生产的汽车，而且这些限制也逐渐变得越来越严厉，欧盟会议还承诺将会通过立法来改善这一现状。到2012年每辆新车的平均二氧化碳排放量的将被限制到120g C02/km，其中汽车推进技术本身有望实现130g C02/km的排放量目标，其余的10g C02/km 排放量的减少来自于不同的燃料和轮胎的使用，空调系统效率的提升以及驾驶策略的改变。然而汽车行业通过欧洲汽车制造商协会对该行为表示质疑。他们声称过多的依赖科技来解决这些要求将会使得成本效益丧失，而且在所给出的时间框架内这个目标是实现不了的。有证据表明，如果想实现这些目标就必须在边际成本增加的条件之下设计一个全新的动力总成。

这种被称为混合动力电动车并且装备了改良过的动力总成的全新车型已经被提出并且研制，这其中最成功的商业例子就是丰田普锐斯。尽管混合电动车已经证明了它大大降低了能源消耗和排放量，但是它们对电池的依赖依旧是一个很大的缺点，这包括较低的功率和能量重量比，寿命被功率负荷严重影响以及由于发电机机器控制器的存在而增加的成本。为了克服这些缺点，一小部分人提了出了不使用发电机和电池的混合动力汽车。这些车的特点是有一个纯机械的能量储存系统：飞轮。尽管和电池相比飞轮显示出了巨大的优势，但是还没有足够成熟的动力总成技术使得飞轮可以作为混合动力的能量储存单元来代替电池。为了突破这些局限性，新型的无级变速齿轮正在被研究和开发。例如，EVT公司正在研制最先进的无级变速齿轮，这种无级变速齿轮基于对行星齿轮的运用，并且还结合了小型发动机来控制速度。考虑到这个传动装置的这些特性，该系统可以运用于使用飞轮作为辅助能量源的混合动力汽车并且具有推进这种混合动力车发展的潜力。

本文提供了一个不同的方案，一个更简单的螺旋式系统动力总成。系统完整的概念设计和潜在的性能已经呈现了出来。本文将介绍一个成比例的物理模型和计算机模型以及它的工作原理。并且对这个系统操作的研究结果进行了讨论。也对使用了这种混合系统的全尺寸混合动力汽车进行了数字模拟分析。

2 飞轮技术

大多数正在生产和研究的混合动力汽车都是以电化学电池作为能量储存单元为基础的。对于电池的研究已经超过了两个世纪而且电池作为商业产品被销售也差不多有这么长时间了。受便携式消费产品的驱使，在过去的几十年里，电池的技术有了很大的进步，所以对于保守的汽车行业把电池作为混合动力汽车能量储存单元的首选也就不足为奇了。这就是最近汽车行业和有着物美价廉技术的国际内燃机组织合作的原因。

混合动力电动汽车无疑是具有最成熟的动力总成技术；但是却受到了基本技术缺陷的制约，而这可能会阻碍到大规模地引进新车型，而且还会影响到混合动力电动车的长期存在。混合电动汽车面对的一个主要问题是电化学电池对内部外部条件的敏感，而这些内外部条件将会影响到电池的性能。电池能传递的功率和充电的速度会很大程度上受到荷电状态和温度的影响。当进行可再生能制动时，很高的功率峰值必须在短时间内被电池吸收，这是个相当大的难题。由于电池的充电转换率最高是在局部处于荷电状态时最好，因此电池必须可以承受长期局部荷电状态。此外，现有的电池不能提供行业所需的可靠性，所以在汽车的使用过程中中必须更换多次。

混合电动汽车的一些缺点可以被超级电容克服，它可以在很宽的温度范围内保持很高的功率密度范围，即5000W/kg。他们也具有很长的保质期和很高的循环效率。出色的能量容量使得超级电容成为了整合混合电动车的一个非常具有吸引力的选择，特别是在推动再生能制动和辅助加速方面。但是高成本成为了阻碍超级电容进入混合电动汽车应用领域的一个主要原因，而且对于超级电容的成本

图表1.储能技术的能量曲线，表明了能量和功率密度

可控性仍然存在争议。此外超级电容的电压是随着荷电状态而变化的，所以需要电子控制和转换设备，而这会增加它的价格。鉴于系统是电子的，配备了超

级电容的混合动力汽车需要有能量转换装置。

因此高速飞轮作为电池的替代品被提了出来，它是内燃机高效低成本的辅助设备。飞轮的特性是不耦合的，诸如最大的传输功率只和变速器有关，但是能量储存的大小和飞轮的大小却和速度有关。先进的飞轮展现出能和电池媲美的能量储存密度，而且有更高的功率密度（本质上是有变速器系统的速率决定的）。图表一给出的能量比较图呈现出不同能量存储技术的能量和功率密度。

与电池相比，飞轮储存能量的能力是独立于存储容量的多少和温度，其使用寿命是105到107完整工作周期。事实上，飞轮的能量特性和长寿命是不受对电池非常不利的充放电循环总数影响的。不同于电池，飞轮的另一个有益的特性是它的荷电状态容易确定，只要通过检测它的转速就可以了。

能量的储存形式是可以通过机械能传播的动能，从而避免了低效率的能量转换。因此双程的能源效率通常在90%以上，但它和时间有关。对于短期存储，效率可以达到接近100％，但空气动力损耗和轴承损耗导致其中期和长期储存的效率降低。因此使飞轮工作在真空环境和使用高效率的轴承是非常重要的。

总之，这些特性使得飞轮运用于非常合适的电涌应用变得很常见。这表明它适合运用于混合动力汽车，特别是在城市驾驶条件下的再生能制动和辅助加速，并且在城市驾驶条件下作为电池和超级电容的替代品，高速飞轮具有以低成本提供更高的能量效率的潜力。

3 机械能储存系统和机械混合动力汽车

基于混合动力汽车变速器的飞轮远远不如系统的电池技术成熟，然而正因如此，有相当大的机会对此展开创新性研究和基础研究。一下列出一些主要的挑战：?飞轮转子，密封圈，轴承和外壳的设计

?无级变速器的设计

尽管存在可以同时解决以上两个挑战的方案，但是仍需在不引入过多未知变量的条件下节约成本。一个基于成熟技术而且复杂性降低的系统可以克服这些缺陷。这篇文章提出的建议是基于这些前提的。它是个纯粹的机械变速器装置，一个附加系统，这套系统可以并行装备在现有的汽车动力总成上，不需要重新设计完整额变速系统。正因如此，在燃料经济性方面的益处不像通过一套更为复杂的系统可以获得那么大。

3.1机械能储存系统的描述

这个机械能储存系统的组成包括飞轮，行星齿轮组，制动装置（安装在行星齿轮组的行星轮），小型无级变速器单元，还有一个恒压变压器，正如图表2中

展示。行星齿轮组提供了较宽的连续速比范围，而这对在高速和低速下的刹车和减速的驾驶条件下操作混合动力汽车是很重要的。对直接使用恒压变压器作为机械连结来说，行星齿轮组是一个具有吸引力的可替代选择，这是因为所需的恒压变压器需要有不切实际的宽比率和有限的能量容量，以及可能存在的低效率，更何况成本的增加会抵消纯机械混合动力系统带来的经济效益。

使用这个配置，机械混合动力总成既可以使用恒压变压器又可以使用安装在强健的行星齿轮组行星轮的摩擦制动装置来控制汽车和飞轮之间的能量流。这个具有相当简单的控制系统的低成本动力总成可以实现可再生能制动和辅助加速，其中能量是通过机械元件直接传递的。

图2.机械无级变速制动混合动力总成

通过力矩平衡和行星齿轮组的动力学关系可以更好的理解在混合动力变速器中的能量流。给定负载一个未知的力矩Tc ，行星轮的力矩为Tr ，太阳轮的力矩为Ts ，则有：

C AT -=R T (1)

C S BT T -= (2)

)

)(()()(112222221R S R S R S R S R A ++++= (3) A R S R S S S B -=++=

1))((221121 (4) 其中R 和S 分别代表行星齿轮组中太阳轮和行星轮的齿数，其下标是代表行星齿轮组的级数。然而，行星齿轮组的运动更为复杂，因为，其中一个支路的速度和由另外两个支路的现有速度有关，正如下一个公式所示：

S R C B A ωωω+= (5)

其中ωC ，ωR 和ωS 代表行星齿轮组系统的负载，行星轮和太阳轮支路各自的角速度。

结论

本文提出了一种可以使用飞轮通过机械传动方式来储存和释放能量的全新混合动力总成，并描述了混合动力汽车的操纵和控制策略，其中包括在真实驾驶条件下对混合动力汽车操作的计算机分析。在导师指导下得出的结论表明，在测试条件下该动力总成可以节约的燃料高达26%。由于连续不断的启动和停车对能量的回收再利用非常有利，因此装配这种混合动力系统对交通拥堵地段行驶的车辆更为有用。研究结果表明机械混合动力车辆可以成为人们的一个新选择，其中的机械元件需要通过本文阐述的理由来进行设计优化。