自 1947 年推出 Tama 电动车到最近展示的 ZEV BladeGlider 先进电动跑车概念原型，日产 (Nissan) 对电动动力系统研发从未停歇。这家汽车制造商一直在不断改良电动推进系统解决方案，而电动汽车技术的研发仍有很长一段路要走。

继 2010 年推出世界上首款现代纯电动乘用车后，日产 (Nissan) 一直将自身定位为零排放汽车(ZEV)技术领导者。据了解，第二代聆风 (Leaf) 将在今年 9 月上市。

目前，日产欧洲公司 (Nissan Europe) 正带领一个英国研究团队开展“高能量密度电池 (HEDB) 项目”(High Energy Density Battery - HEDB)，联手研发下一代高能量密度电池，为电动车和混合电动车提供高性能的多功能电池系统。目前，日产的电动汽车电池组生产仍在英国的桑德兰工厂进行。

简单来说，该研究团队将通过多项具体试点项目，实现电池产品的多样化和工艺改进。作为项目的核心成员之一，Hyperdrive Innovation 公司创始人、常务执行董事 Stephen Irish 最近接受了《国际汽车工程》的采访。 Irish 指出，尽管电池化学领域在最近几年中已经取得了大量进展，“但并未出现可以显著优化电池密度的‘神奇’解决方案。”然而，Irish 认为，凭借“高能量密度电池”项目取得的电池组级优化成果及 Hyperdrive 公司的电池管理系统 (BMS)，电动汽车电池的使用寿命和能效均能得到保证，并可以支持“机会充电”(opportunity charging)。

电池开发工作的重点在于深刻理解特定车型的占空比，并时时权衡成本。Irish 表示：“如何才能取得最大价值？车辆或设备的使用频率如何？如何进行充电？能源又从哪里来？我们总是不断问自己这些问题。”此外，电池的开发也不能忽视车辆重量、电子元件及其工作方式的相互影响。

尽管 Hyperdrive 公司的主要任务是电池管理系统的开发，但创新的化学解决方案也是公司需要投入精力的地方。这家公司最近已经开始进行锂硫电池的相关研发。理论上讲，锂硫电池的能量密度可以达到锂离子电池的 5 倍。不过，Irish 透露，锂硫电池目前仍处于研发阶段，且在真实世界中也可能无法达到理想能量密度。

“我们虽然不是化学家，但也必须了解电池化学领域的最新进展，并将其充分融入至我们的技术研发和产品设计中。”Irish 解释说，“与OEM一样，我们也需要清晰的产品上市路线。”

电池尺寸很重要

Irish 说，由于电池市场中存在一些“极端用户”，要解决的问题有时会变得更加复杂。其中一部分极端用户并不关心电池寿命，一心只想着最大程度地延长电池工作时长、提高电池储能容量以及缩短电池充电时间；而另一部分极端用户则最看重电池及其相关电子系统的使用寿命，以及在电池产品的完整生命周期中实现电池价值最大化。

Irish 表示，“我个人倾向于尽量缩小电池体积，只要可以满足车主的日常通勤需求即可，这可以同时降低重量和成本。大多数人开车也只是上上班而已，并不会像自己以为的那样，会经常进行长距离驾驶。”然而，值得注意的是，最终用户总是希望获得更长的续航里程，这也是我们需要面对的市场壁垒以及必须克服的挑战。”

Irish 指出，在放电率维持在 80% 的情况下，典型电动汽车电池的使用寿命通常在 5000 到 6000 次充放之间。但如果放电率达到 100%，电池的使用寿命则将缩短三分之二。此外，一些二级再用系统的应用，也将有助于电池取得最高能效。

降低电池和电池管理系统的成本是一场持久战，其中通用化设计可以实现的规模经济效益非常显著。Irish 解释说，“如果我们选择定制系统，则必须重复支付一次性工程费用（NRE），而考虑到研发工具和验证测试需求，这笔开支可能非常庞大。”对比之下，Hyperdrive 公司打造的一系列标准模块化产品不但可以降低成本，而且还能缩短产品上市时间。

此外，Hyperdrive 公司还设计了一款适用于商用车辆和部分非公路设备的模块化电池系统。此外，Hyperdrive 公司还联手德事隆(Textron) 旗下 Douglas Equipment 公司，设计了一款后推式轻度混合牵引器。

低温运行技术研究

低温运行是电动汽车研发工作中最值得关注的领域之一。为了积累相关经验，Hyperdrive 还联手英国南极科考队，共同开展联合项目。一些低电流应用主要采用非牵引型电池，该项目的研究目的是尽量了解电池及其相关系统在接近零下 50°C的极端低温下的性能。一般来说，内燃机在极端低温下的性能很差，通常需要通宵预热发动机。

Irish 对电动汽车在低温（尽管不是极端低温）下的表现非常有信心。他说，“由于电动汽车通常需要在夜间充电，因此早上的车舱环境将会较为温暖舒适，挡风玻璃也不会结霜。”

Irish 表示，Hyperdrive 公司在进行电池管理系统研发时已经考虑了温度的要求，该系统将通过主动控制电池充放电，尽量避免对电池的损害。然而，一些应用场景仍离不开热管理系统。

Irish 的工作经验非常丰富，曾多次参与捷豹路虎 (JaguarLand Rover) 和 NSK转向系统 (NSK Steering Systems) 的开发项目。Irish 在 5 年前成立 Hyperdrive公司，目前与日产的合作包括在各类电动车中安装采用日产电池技术的高性能系统和电池储能系统。另外，日产欧洲联合研究团队中的其他成员包括：华威制造集团 (Warwick Manufacturing Group)、华威大学 (University of Warwick)、纽卡斯尔大学 (Newcastle University)、零碳未来公司 (Zero CarbonFutures) 等。

It’s been a long road for Nissan from its 1947 Tama EV to its advanced prototype ZEV BladeGlider sports car, but that road still stretches to—and far beyond—the technology horizon, as it continues to refine electric propulsion solutions.

The company claims world leadership in ZEV technology following the 2010 introduction of the Leaf EV, the first modern-era battery-electric passenger car. The second generation Leaf will make its premiere in September.

As previously reported in Automotive Engineeering (http://articles.sae.org/14604/), Nissan Europe  is leading a U.K. consortium to research and develop future generation batteries via the High Energy Density Battery (HEDB) project. Its aim is to deliver multifunctional battery systems for EVs and HEVs. Nissan manufactures EV battery packs at its Sunderland, U.K. plant.

The consortium will embrace pilot projects, product diversification and process improvement. A key member is Hyperdrive Innovation, whose founder and Commercial Managing Director, Stephen Irish, spoke recently with AE. He noted that while substantial improvements in cell chemistry have been made in recent years, "there is no magic solution regarding enhancing energy density." However, he sees potential for pack-level improvements through the consortium as well as the Battery Management Systems (BMS) developed by Hyperdrive to ensure cell longevity and efficiency while accommodating "opportunity charging.”

Vital to battery development work is understanding the duty cycles of specific vehicle types as well as cost, said Irish: “We ask ourselves where best value will be achieved—how, and how frequently, a vehicle or machine is to be used, how it’s charged, where the energy comes from." Making that energy go further concerns vehicle weight and power electronics and how they work.

While Hyperdrive’s focus is BMS development, novel chemistry solutions need to be considered, too. The company has recently worked with lithium sulfur which, in theory, can deliver specific energy density that is five times that of lithium-ion. However, Li-S is still in development "and in the real world it could be less," Irish said.

"We are not chemists but we do need to know about these developments to spot trends and to be able to develop our technologies and absorb them into our products," he explained. "For us, just as for an OEM, there has to be a clear route to market.”

Battery size matters

Sometimes, that market is complicated by what Irish terms “extreme outliers”—users who care less about a battery’s life and just want to max up-time and extract as much energy as possible from it and also charge it as quickly as possible. The other extreme concerns users who require optimal longevity for the battery and its associated electronic systems, to achieve best possible value over time.

“Personally, I would argue for the smallest battery possible for a daily commuting vehicle, saving weight and cost. Most people do not drive as far in a week or month as they think they do," Irish said. "However, it is still the market barrier of increased range that end-users want. It has to be overcome.”

Typical EV battery life expectancy is 5000 to 6000 cycles at consistent 80% discharge rates, Irish noted. Taking it to 100% discharge cuts its life by two-thirds, he said, adding that secondary re-use applications will help harvest maximum value from the cells.

Getting battery and BMS costs down is a constant battle. Achieving economies of scale is significant; supporting this is designing for commonality. “If we do bespoke systems we have to pass on non-recurring engineering (NRE) costs, which can be substantial in terms of tooling and validation testing," Irish explained. A more standard suite of products, as Hyperdrive has created, allows on-costs to be reduced while enabling faster time-to-market.

Hyperdrive also has designed a modular universal battery suitable for commercial vehicles and some off-highway applications. Together with Douglas Equipment, part of Textron, the company has developed a push-back mild hybrid tractor.

Low-temperature research

A particular area of concern for EVs is low-temperature operation. To gain experience, Hyperdrive carried out a project with the British Antarctic Survey team. Batteries were non-traction types with low current applications. The research aim was to learn as much as possible about battery and associated systems’ performance at temperature extremes of around -50°C. ICEs have problems at very low temperatures and need overnight engine heating.

Irish is confident of EV performance meeting low temperature challenges, albeit not down to extreme levels. “And an electric vehicle charging overnight will be warm in the morning with comfortable cabin and clear windshield.”

Hyperdrive's BMS has been developed to take account of temperature; it actively controls charge and discharge of the battery cells to obviate potential damage but thermal management would be needed in some applications, said Irish.

Following a broad range of engineering experience, including development projects at Jaguar Land Rover and NSK Steering Systems, Irish established Hyperdrive five years ago. Its partnership with Nissan includes installation of high performance systems incorporating Nisan cell technology into various EV and battery energy storage systems. Other consortium members are: Warwick Manufacturing Group, University of Warwick; Newcastle University; and Zero Carbon Futures.

Author: Stuart Birch
Source: SAE Automotive Engineering Magazine