3.5　Flywheels

Text（课文）

The flywheel is the kind of energy supply unit that stores energy in mechanical form.Flywheels store kinetic energy within a rotating wheel-like rotor or disk made of composite materials.Flywheels have a long history of usage in automobiles，being routinely used in all of today's IC engines to store energy and smooth the power delivered by abrupt pulses of the engine.However，the amount of energy storage required in flywheels of IC engines is small and is limited by the need of the vehicle to accelerate rapidly.The flywheel is currently being looked into for use in a number of different capacities.Flywheels can be used in HEVs with a standard IC engine as a power assist device.Alternatively，flywheels can be used to replace chemical batteries in EVs to serve as the primary energy source or could be used in conjunction with batteries.However，technological breakthroughs in increasing the specific energy of flywheels are necessary before they can be considered as the energy source for EVs and HEVs.The flywheels of today are quite complex，large and heavy.Safety is also a concern with flywheels.

The flywheel design objective is to maximize energy density.The material to be used in a flywheel must be lightweight with high tensile strength conditions that are satisfied by composite materials.

Flywheels have several advantages as an energy source，the most important of which is the high specific power.Theoretically，specific power of flywheels has been shown to be of the order of 5 to 10 kW/kg，with a specific power of 2 kW/kg being easily achievable without exceeding safe working stresses.Other performance features that make flywheels attractive can be attributed to their mechanical nature.Flywheels are not affected by temperature extremes.There are no concerns with toxic chemical processing and disposal of waste materials，making flywheels environmentally friendlier than chemical batteries.Flywheel energy storage is reliable in that it possesses excellent controllability and repeatability characteristics.The state of charge in flywheels is precisely known at all times through measurement of the rotational speed.The energy conversion process to and from a flywheel approaches 98%，compared to 75% to 80% of batteries.The service life of a flywheel is many times that of a battery，with little maintenance required.The charging of flywheels is a fraction of that required by batteries and can be less than 10 min for full recharge in a flywheel charging station.The ability to absorb or release a high amount of power in a short period of time also aids the regenerative braking process.

Despite several advantages，there are still a number of significant drawbacks with flywheels.The major difficulty in implementing a flywheel energy storage system is in the extra equipment needed to operate and contain the device.The extras are particularly difficult in EV and HEV applications，where the extra weight and expense make a big difference.

New words and expressions（单词和短语）

1.New words（单词）

2.Expressions（短语）

Notes to the text（难点解析）

★1.However，technological breakthroughs in increasing the specific energy of flywheels are necessary before they can be considered as the energy source for EVs and HEVs.然而，在飞轮成为电动汽车或者混合动力汽车的能量源之前，需要突破的技术方面的问题是增加飞轮的比能量。

★2.The material to be used in a flywheel must be lightweight with high tensile strength conditions that are satisfied by composite materials.在飞轮中使用的材料必须具有重量轻、拉伸强度高的特点，而复合材料能很好地满足这样的条件。

Exercises（练习）

◆1.Translate the following passages（expressions）into Chinese（英译汉）

（1）Safety is also a concern with flywheels.

（2）The flywheels of today are quite complex，large and heavy.

（3）power assist device（4）charging station

◆2.Translate the following passages（expressions）into English（汉译英）

（1）能量供给单元

（2）复合材料

（3）飞轮可在很短的时间内吸收或释放很多的能量，这将有助于再生制动。

◆3.Directions:Answer the following questions briefly according to the text

What is the principle of the flywheel？

Reading material（阅读材料）

The use of flywheels for storing energy in mechanical form is not a new concept.More than 25 years ago，the Oerlikon Engineering Company in Switzerland made the first passenger bus solely powered by a massive flywheel.This flywheel，weighing 1，500 kg and operating at 3，000 r/min，was recharged by electricity at each bus stop.The traditional flywheel is a massive steel rotor with hundreds of kilograms that spins on the order of ten hundred of r/min.On the contrary，the advanced flywheel is a lightweight composite rotor with tens of kilograms and rotates on the order of ten thousand of r/min；it is the so-called ultra-high-speed flywheel.

The concept of ultra-high-speed flywheels appears to be a feasible means for fulfilling the stringent energy storage requirements for EV and HEV applications，namely high specific energy，high specific power，long cycle life，high energy efficiency，quick recharge，maintenance-free characteristics，cost effectiveness，and environmental friendliness.