故事的开始于壳牌(Shell)、Gordon Murray Design公司（下简称GMD公司）、Geo Technology和一个想法。

这个想法就是打造一款具有超强经济性的小型汽油机，用于三座超紧凑城市车T25M。 这辆车将更加轻质高效，最高时速可达130 km/h（80 mph），综合油耗将达到2.8 L/100 km （84 mpg）甚至更低。T25M的空气动力学性能也会更好，车辆将装配一块可以向前敞开的单面遮蓬，在行驶时可实现零宽度摇摆。

为了实现这一目标，多方合作伙伴在2015年4月发起了M项目（M为英文Mobility的首字母，意为车“辆动力”），达成共识：“让进步开始吧！”

这一进程最早始于GMD的T25M研发项目，而如今参与各方确实都取得了进展，有越来越多的技术保密信息开始展示给公众。在位于德国汉堡的壳牌技术中心，合作各方的多名高管对项目的未来前景进行了展望。

壳牌创新润滑油技术经理Bob Mainwaring表示：“2010年，壳牌公司曾为GMD的T25城市汽车项目供应润滑油（http://articles.sae.org/10006/），使T25的燃油经济性在欧洲城市循环测试中提升了6.5%，在综合循环测试中则提高了4.7%。这些成绩让合作各方开始思考，如果要在2025年实现能源效率翻倍的目标，是否可以联手打造一款效率极高的发动机，并以在此基础上开发一种全面综合的解决方案？”

而这个问题的答案已开始慢慢成形。获得突破的关键之处在于采用先进的润滑油解决方案，并大量使用类金刚石碳涂层（DLC），降低发动机中几乎所有活动部件的摩擦。

Mainwaring强调，公司之间的通力合作非常必要，这样才能将硬件设计与降低摩擦相结合。他指出，虽然大家都知道要合作，但实施起来并不容易。

“一方面，我们想通过降低油品粘度来减少阻力和摩擦，但另一方面，如果油品粘度太低，部件之间形成的油膜就会变薄，这会使硬件更容易磨损，”他解释道。“这两个方面之间进行平衡非常重要，我们将需要达到的状态描述为‘安全的最边缘’。”

这里的“安全”是指在保证硬件处于合理磨损范围内的情况下，尽最大可能降低润滑剂的粘度。壳牌的工程师对润滑油的配方进行了调整，使其在所需的范围内尽可能降低润滑油的低温粘度，从而防止部件表面直接接触，加速磨损，特别是凸轮-挺杆和活塞环-气缸套等关键接触面。

在这些接触面涂上保护用的DLC（类金刚石复合物）涂层后，壳牌团队得以确信润滑油与磨损的关键接触点正是在凸轮轴和滑动轴承之间。

Mainwaring解释道，这个关键点的抗磨性能是由润滑油和添加剂粘度决定的，换言之，我们要知道，根据曲轴所承受的负载，润滑油粘度最低可降至多少？

实现这一平衡的关键在于要将润滑油视为一个设计元件：“需要不断改变硬件来适应润滑油，也需要不断调整润滑油来适应硬件要求，这样才能取得最佳的燃油经济性，”他对《汽车工程杂志》如是说。

M项目所用的润滑油配方原型属于SAE 0W-12级，而非常见的5W-30级油品。但润滑油行业通常既不认可0W-12级，也不认可粘度更高的0W-16级油品。在与Geo Technology共同进行的发动机及其润滑油研发过程中，壳牌的工程师决定放下常规，致力于设计一款粘度极低而又满足项目要求的发动机油。他们计划采用钼盐等摩擦改进剂，以达到这一目标。

这款定制的润滑油已经用于首辆T25M展示车型所搭载的660 cm3的三菱3缸基础发动机。Geo Technology的工程主管Hidehito Ikebe表示，与同等体积的机型相比，这台基础发动机拥有极高的转速，而且功率强劲（在转速为7500rpm时功率可达55 kW/73hp），但为了满足本项目的需求，这款发动机的功率已调整到转速5500 rpm时36 kW（48 hp），而压缩比则从10.8:1提升到了12.4:1。

Geo Technology还设计了一些新的部件，使用“beehive(蜂窝式)”阀门弹簧、钛金属气门、以及DLC涂层等技术来降低发动机的摩擦。

Ikebe表示，活塞是降低摩擦的关键。除了活塞顶之外，T25M的整个活塞都是全新设计的。活塞环从3个减为2个，而铁箍的数量也减少了40%。连杆延长了9%，活塞重量降低了40%。通过这些变化，活塞的惯性质量减少了30%。

T25M目前还没有制定上市计划。M项目的本质是进行可行性试验，但参与项目的各方都希望它能为未来提升量产发动机的效率打下坚实的基础。他们都表示从项目中获得了一些“灵感”。

T25M项目由壳牌公司资助，但具体预算尚未公布。

T25M的官方发布时间已从2015年11月推迟至2016年第2季度，原因有二——一方面这个项目“雄心勃勃”，希望能够尽善尽美，另一方面，项目需要先行收集所有数据，并与其他三款车辆原型进行能量与燃耗比较，这也需要更长的时间。

空气动力性能和材料研发也是M项目的重要组成部分。很多人可能认为，空气动力性能对城市车来说可能并不是那么重要，但GMD的设计总监Andy Jones强调说，对一辆载有3名乘客（95%的情况下是成年人）的城市汽车而言，不到0,30 Cd的风阻系数已经很不错了。这款车高度为1.6 m（5.2英尺），相对较高，但却可以轻松停入2.65长、1.35宽（8.7 x 4.4英尺）的空间，一般来说在一个标准的停车位上，可以停泊3辆T25M。

Jones解释道，实现相对较低的风阻系数意义重大，因为城市车不仅仅在市中心行驶，也会前往郊区，而车辆在这里的行驶速度相对较高。由于车辆设计的最高时速高达128km/h，因此空气动力性能可以产生巨大影响。

Jones表示，在T25M“奋力降低车辆驱动能源”的努力中，“超越传统架构”的轻量化理念也颇为重要，因此项目的另一大重点内容是使用先进材料，以及对车身主体结构进行重新思考。

T25M项目对于新材料的需求，推动GMD开发了iStream Carbon这一创新产品，这一成果已在2015年东京车展上展出。这一底盘技术已在雅马哈Sports Ride概念跑车中得到应用。

作者：Stuart Birch
来源：SAE《汽车工程杂志》
翻译：SAE上海办公室

Low-friction techniques push advanced city-car project toward 84-mpg target

In the beginning there were Shell, Gordon Murray Design (GMD), Geo Technology, and an idea.

The idea was to create a very small gasoline engine that demonstrated super efficiency to provide a 3-seat, aerodynamic, lightweight and ultra-compact city car having forward opening single canopy access with zero-width swing. The car would have a combined fuel consumption of 2.8 L/100 km (84 mpg equivalent) or less, and a top speed of around 130 km/h (80 mph).

To achieve it, in April 2015 Project M (for mobility) was initiated and the partners agreed: “Let progress commence.”

It did, with R&D development of the Gordon Murray T25M. Now, as the project continues, the cloak of confidentiality has been partially pulled aside. At Shell’s Hamburg [Germany] Technical Center, senior executives of the companies involved revealed the shape of graphs to come.

Bob Mainwaring, Shell Lubricants Technology Manager for Innovation, said: “Shell supplied lubricants for Gordon Murray Design’s T25 city car program (http://articles.sae.org/10006/) in 2010, with the result that fuel consumption improved by 6.5% in the European urban cycle and 4.7% in the combined cycle. Those results seeded the thinking that with energy consumption set to double by 2050, what would be the result if we worked together on an holistic, co-engineered approach with a new engine design to achieve a very high level of engine efficiency?”

The answer is emerging, with a major advance centering on reducing the friction of almost all moving parts of that engine using advanced lubrication solutions complemented by extensive use of Diamond-like Carbon Coatings (DLC).

Mainwaring emphasized the need for companies to collaborate and to link hardware design with programs to reduce friction. That is well enough known but achieving it can be tough, he acknowledged.

“On one hand we want to reduce viscosity to lower drag forces and lower friction but on the other hand reducing viscosity, oil thicknesses within a component are likely to drop, making the hardware more vulnerable to wear," he noted. "Balancing the two is very important and we call that being ‘close to the edge but safe’.”

"Safe" in this context means pushing the limits of viscosity while achieving acceptable wear. Shell engineers adjusted the lubricant's formulation to give as low viscosity as possible at low temperature, while keeping it as high as it needs to be (which might be a low value at high temperature) to stop surfaces touching and wearing, he said, noting critical interfaces such as the cam-to-tappet and piston ring-to-cylinder liner.

By coating these surfaces with DLC (Diamond-like Compound), the Shell team was able to protect these and ensure that the lubricant-vs.-wear pinch point is the crankshaft and its journal bearings.

That pinch-point is in the control of the viscosity of the lubricant and the additives, Mainwaring explained, adding a simple summation: How low can the viscosity be for the loads that are imposed on the crankshaft?

An essential element of achieving this balance is to consider the lubricant as a design component: “Changing the hardware to match the lubricant and the lubricant to match the hardware will give the best fuel economy,” he toldAutomotive Engineering.

The prototype formulation for Project M is in the SAE 0W-12 range compared to the typical 5W-30 grade. Industry specifications do not recognize either 0W-12 or thicker 0W-16. In working with Geo Technology to co-engineer the engine and its oil, Shell engineers are essentially throwing away the specification book and the compromises it forces. Their aim instead is to design an engine oil that delivers the very low friction results that it is targeting. Use of friction modifiers, some containing elements such as molybdenum will be used.

It is this bespoke approach that has been applied to the base 660-cm³ Mitsubishi3-cylinder engine that will power the one-off technology demonstrator T25M. The base engine is high revving and powerful (55 kW/73-hp at 7500 rpm) for its size, but Hidehito Ikebe, Director of Engineering at Geo Technology, said that to support the project’s criteria, this has been reduced to 36 kW (48 hp) at 5500 rpm. Compression ratio was raised from 10.8:1 to 12.4:1.

The company has designed some new parts, introduced "beehive" type valve springs, titanium valves, and incorporated DLC solutions to reduce friction in several areas.

Ikebe said the piston is the most significant area for reducing friction. Except for the crown, piston design for the T25M is all new. Two rings instead of the normal three are used, and the number of strakes reduced by 40%. The connecting rods were extended by 9%, and piston weight reduced by 40%. Collectively these changes produce a 30% reduction in inertial mass, he explained.

There is no intention at present of bringing the T25M to market. Project M is a capability analysis exercise only, but all those involved in it clearly hope that it will represent a building block for future advances in efficiency for series produced engines. Certainly some “insights of value” have emerged, agree the participants.

The project is being funded by Shell, although no specific details of its budget have been released.

The timing of getting the T25M to its unveiling stage (moved from an officially announced November 2015 to Q2 of 2016) is due both to the project being “very ambitious” and for the decision to first gather all the data needed and compare it against three vehicle archetypes on an energy and fuel consumption basis.

Aerodynamics and materials also are a significant part of Project M. With regard to aerodynamic efficiency, it might be thought that it is not of paramount importance for a city car. But Andy Jones, GMD’s Design Director, emphasized that for a car carrying three, 95th-percentile adults, its sub-0,30 Cd figure is good. The vehicle is relatively high at 1.6 m/5.2 ft, but very short for “nose-in” parking at 2.65-m long and 1.35-m wide (8.7 x 4.4 ft) to permit three of the type to park in a standard parking space.

Achieving the relatively low Cd is significant, Jones explained, because city cars are often driven not just in central areas but into and around urban areas where speeds reached can be relatively high. The car's designated 128 km/h (80 mph) Vmax capability makes aerodynamics significant.

Jones said that application of advanced materials and rethink of the vehicle’s primary structure is the second major element of the T25M’s “fight to reduce vehicle drive energy,” with a lightweighting philosophy "that goes beyond conventional architectures.”

The T25M contains the materials evolution that has led to GMD’s iStream Carbon, shown for the first time at the 2015 Tokyo Motor Show. It is the chassis technology used for the Yamaha Sports Ride Concept.

Author: Stuart Birch
Source: SAE Automotive Engineering Magazine