在介绍公司技术时，梅赛德斯-奔驰（Mercedes-Benz）一向没有夸口的习惯，因此当这家公司的工程师表示将开展 “史上最大的战略性发动机计划” 时，这绝对值得大家的关注，而电气化正是其中最引人关注的部分。

梅赛德斯-奔驰旗下全新4缸2.0L柴油发动机为公司的“闪电战”拉开了帷幕，目前这款发动机已经在梅赛德斯-奔驰E级桥车上采用。2017年，公司还将继续推出一款用于S级轿车的全新4.0L V8双涡轮汽油发动机、采用48V技术的新型6缸汽油/柴油发动机，以及另外一款同样采用48V电气系统为辅助功能供电的2.0L 4缸汽油发动机。由于梅赛德斯-奔驰的工程师认为，如果要搭配48V电气系统，直列式发动机的优势更大，因此上述6缸发动机均采用了直列设计，并不是“V”型气缸排列。

与现行版本相比，新一代8缸发动机的排量缩小了0.7L，应用了气缸钝化技术，可在负载较低的巡航状态下进入4缸模式。据了解，这款发动机的官方数据非常亮眼，功率输出 “超过” 350kW (469hp)，峰值扭矩可达 “大约” 700 N·m (516lb·ft)，已经吸引了梅赛德斯-奔驰高性能分部AMG调优专家的目光。

目前，一些高档汽车制造商倾向于通过减少发动机的气缸数量，来达到相关燃耗和排放要求。举例而言，正在奋力跻身于豪车品牌之列的沃尔沃（Volvo）就为旗下绝大部分车型配备了4缸发动机。然而，尽管梅赛德斯-奔驰旗下也拥有不少4缸车型，但却并没有被一头扎进“降低排量”的热潮之中。相反，这家德国汽车厂商决定采用更多的先进辅助技术，来满足政策对清洁、经济发动机的要求，并同时保证用户对公司中高级车型的性能和优化预期。

除了48V系统以外，公司还将应用更多辅助技术进行发动机优化，包括一款集成启动器发电机（ISG）和一款电动辅助涡轮增压压缩机（eZV），可协助车辆废气涡轮压缩机的运转。

为了继续保持最大效率的系统衔接，梅塞德斯-奔驰专门在公司的Sindelfingen工厂中设置了一个新的传动系统整合中心（AIZ）。

全新I6问世，将取代V6发动机

戴姆勒集团与梅赛德斯的汽车开发组织研究工作负责人Thomas Weber博士教授在谈及公司的“战略性发动机计划”时表示，“我们在设计高科技发动机时必须综合考虑所有当下和未来的需求，而我们也正是这么做的。为了实现这一目标，关键的成功因素之一就是广泛推进动力系统的电气化。”

在所有新型发动机之中，最受关注的就是这款3.0L直列6缸发动机。其中，汽油版M256“据称”可以输出300kW（402hp）的马力和超过500N·m（369 lb·ft）的峰值扭矩。梅赛德斯-奔驰在多个场合介绍发动机的新架构时均采用了这样的说法，这意味着公司要么是对这些数据信心不足，要么就是日后还准备了更大的惊喜。与新款4缸柴油发动机相同，汽油版发动机的单缸体积也在500立方厘米。

这款6缸直列汽油发动机（明年将登陆S级豪华轿车）采用了48V电气系统和增压进气技术，增加了ISG发电机为能量回收系统等混动功能供电。

1998年，为了满足车辆的正向碰撞预防需求，梅赛德斯-奔驰首款6缸V型发动机M112正式问世，取代了公司经典的系列I6直列汽油发动机。2017年，梅赛德斯-奔驰又重回“I”时代，直列发动机再次焕发新生。梅赛德斯-奔驰的工程师称，这款发动机的性能与8缸发动机相仿，将给明年的S级轿车带来特别惊喜。此外，这款发动机减少了系统对前端辅助带动的需求，从而可以为工程师的设计带来更多可能性，有助于控制车辆的总长度。

梅赛德斯-奔驰的工程师表示，针对少量热量损失的“类发动机”废气再处理系统也有助于降低排放。48V电气系统可以为水泵、空调和ISG等“用电大户”供电。与现行V6发动机相比，这种设计可以大约减排15%。

全新I4发动机，应用48V技术

全新I6系列中的OM656发动机采用了Camtronic公司的可变气门正时系统，应用了钢制分级活塞和2级涡轮增压技术。

梅赛德斯-奔驰的工程师称，分级活塞可以给燃烧过程带来积极影响，比如活塞关键区域的热负载及减少烟尘进入机油方面。与之前的“欧米伽”燃烧室相比，新发动机的燃烧率更高，因此效率也有所提升。在新设计中，工程师们专门综合优化了燃烧室形状、空气流动和喷油器的设计，从而提高空气的使用效率，支持发动机在高空气顺差状态下的运行。这意味着，这款发动机可以将尾气中的微粒排放控制在一个相当低的水平。

发动机机体采用铝制材料，缸体也采用了“改进”的Nanoslide涂层。此外，这款发动机也采用了“类发动机”尾气处理系统和Camtronic的可切换排气凸轮轴。

这款发动机的功率输出 “超过” 230kW (308 hp)，可以称得上是梅赛德斯-奔驰史上最强劲的乘用车柴油发动机，最大扭矩 “超过” 650 N·m (479lb·ft)。

目前，4.0L V8汽油版M176是本系列中最强劲的发动机，据称可以强势输出350kW（469hp）的马力，2,000转时的扭矩输出在700 Nm（516 lb·ft）左右。

这款发动机也支持气缸钝化，可在轻负载时通过Camtronic进行切换，进入4缸模式。为了增加效率，工程师将发动机的2个涡轮增压器放置在两排气缸之间的位置。

尽管看起来不如6缸和8缸发动机那么“光鲜亮丽”，但梅赛德斯-奔驰的2.0L 4缸发动机M264对公司一些“走量”的车型有重要意义。M264又称Toptype，采用了“降型/适型化”设计，可提供100 kW/L（134hp/L）的单位输出。这款发动机采用了大量先进技术，比如双涡旋涡轮增压器、48V带动启动器发电机和48V水泵等。据称，能量回收表现可达12.5kW（17hp）左右。

M264支持熄火滑行，进气侧采用了Camtronic系统。另外，梅赛德斯-奔驰还计划扩大颗粒过滤器在汽油发动机产品中的应用。

M256--“专为电气化设计”

Weber教授强调了进行持续研发，从而在同时期内提供更多动力系统选择的重要性：“无论是高效、清洁的汽油机、柴油机、插电式混动机、纯电池，还是氢燃料发动机，这些动力系统都有自身存在的理由，也有各自的发展前景。M256是梅赛德斯-奔驰首款从一开始就为电气化专门设计的发动机。”

他补充说，发动机内的ISG系统可为车辆的混合动力、增压和能量回收系统供电，并同时节省之前高压混动系统所消耗的燃料。“另外，M256的电动辅助压缩机也取得了令人印象深刻的提升，此时大型涡轮增压器可以更快进入最佳工作状态。”

Weber教授在谈及公司的发动机战略时总是在说“适型化”，而不是“小型化”。他指出，“为了实现上述性能和输出优化，除了从一开始就简单减少气缸的数量外，我们还有一些更加智慧的解决方案。”他称，M176 V8发动机可在转速3,600rmp之下时关闭部分气缸，变身为一个特别高效的4缸发动机。之后，随着需求的增加，更多气缸可逐步切入为发动机提供更多输出，而用户在整个过程中不会感到任何不便。

梅赛德斯-奔驰的全新“动力系统集成中心”拥有10个测试平台，可直接进行高精度的扭矩测试。该中心将以发动机和变速器为研究重心，主要是为了优化车辆的舒适度、动力性能、整体灵活性，从本质上说也就是车辆的驾乘和操作性能。另外，该中心还拥有一个海拔环境测试舱和全自动汽车测力计。

梅赛德斯-奔驰正在准备建设一个汽车安全、电子部件和计算机技术研发中心。另外，公司刚刚发布了旗下的EQ纯电动SUV概念车，这款车的前后轴均安装了电机，可支持四轮驱动，动态分配前后轮的扭矩。车辆电池则位于前后轴之间的中间位置。

梅赛德斯-奔驰曾表示，这款概念车的最大功率输出为300 kW（402 hp），最大扭矩为700-N·m，续航里程可达500 km。

Mercedes-Benz is not generally given to hyperbole to detail its technology, so when company engineers describe a program as “the biggest strategic engine initiative” in the automaker's long history, it is worth taking notice. And electrification is very much to the fore.

The company's latest propulsion blitz opened with the new 4-cylinder 2.0-L diesel now used in the E-Class. It will continue in 2017 with the appearance of a new gasoline 4.0-L V8 biturbo for the S-Class, new 6-cylinder units in gasoline and diesel forms with 48V technology, and a 2.0-L 4-cylinder gasoline which also uses 48V to power auxiliaries. The sixes are inline, not "vee"-arranged, because Mercedes’ engineers reckon in combination with 48V electric systems, the return to the hallowed inline-six layout delivers meaningful packaging advantages.

The V8 has capacity reduced by about 0.7-L from the outgoing V8 and gets cylinder deactivation, becoming a "four-pot" unit under light loads while cruising. With a claimed output of  “over” 350 kW (469 hp) with “about” 700 N·m (516 lb·ft) peak torque, the engine has received attention from Mercedes’ AMG tuning specialists.

Some premium car makers are fixated on reduction of cylinder count—for example Volvo, with its aim of being accepted by the market as a premium producer, reckoning four cylinders is the maximum for all its models—to achieve required fuel consumption and emissions targets. Mercedes, though, while demonstrating what can be achieved with four cylinders on many models, is not being seduced by the prospect of drastic cubic-capacity reduction. Instead, it is using advanced complementary technology to meet the unremitting demands for cleaner, more-frugal engines while maintaining the level of performance and refinement expected of its powertrains in their higher-level models.

As well as 48V, those complementary technologies also include an integrated starter generator (ISG) and electric auxiliary turbocharger compressor (eZV) to assist the exhaust-driven compressor.

To help continue maximum efficiency systems cohesion, Mercedes has opened a new powertrain integration center (AIZ) at its Sindelfingen assembly complex.

All-new I6 replaces V6

Prof. Dr. Thomas Weber, responsible for group research for Daimler AG and Mercedes cars’ development, says of the strategic power unit initiative: “Our high-tech engines need to be (and are) designed with a view to all current and future requirements. A key success factor is the extensive electrification of the powertrain."

Of the new engines, it is the 3.0-L inline sixes that are the real attention-grabbers. The gasoline version (M256) produces a claimed 300 kW (402 hp) and delivers maximum torque of “more than” 500 N·m (369 lb·ft)—the qualifying words, which the company uses extensively in its initial talk about the new engine architectures, shows either a caution about claims or a plan to surprise later. Mercedes has chosen 500 cm³ per cylinder as the optimum swept volume, the same as that for the new 4-cylinder diesel.

The gasoline inline 6-cylinder (the S-Class gets that too, next year) uses a 48V system and forced air via an eZV and has an ISG to look after hybrid aspects, including energy recovery.

Mercedes' first V6, the M112, was introduced in 1998 as a response to new frontal-crash requirements, replacing the company's classic gasoline I6 family. For the move back to inline cylinders for 2017, Mercedes engineers cite performance akin to an 8-cylinder, which should make next year’s S-Class something very special. It also brings design opportunities, such as eliminating the need for a front-end accessory belt drive, that help reduce overall length.

Near-engine exhaust aftertreatment for low heat loss helps reduce emissions. The 48V system looks after the high-power demands of the water pump and air-conditioning compressor and the ISG. With this setup, emissions are down some 15% against the outgoing V6, engineers claim.

48V with new I4

The diesel version (OM656) of the new I6 family incorporates the Camtronic variable valve timing, with steel stepped-bowl pistons and 2-stage turbocharging.

The stepped-bowl piston has a positive effect on the combustion process, engineers explain, in terms of thermal loading of critical areas of the pistons and the introduction of soot into the engine oil. Efficiency is increased by the higher burn rate in comparison with the previous "omega" combustion bowl. The characteristic feature of the specifically configured combination of bowl shape, air movement and injector is its very efficient utilization of air, which allows operation with high air surplus. This means that particulate emissions can be reduced to an especially low level, engineers said.

The engine’s block is aluminum and what is described as “improved” Nanoslide coating is used to line the cylinders. The engine also uses near-engine exhaust treatment. A Camtronic switchable exhaust camshaft is integrated.

Output is “over” 230 kW (308 hp) to make it the most powerful passenger-car diesel in Mercedes-Benz history. Maximum torque is “over” 650 N·m (479 lb·ft).

Topping the muscle chart for the new engine group is the M176 gasoline V8 4.0-L, claimed to deliver a hefty 350 kW (469 hp) and “around 700 Nm (516 lb·ft) from 2000 rpm.

Cylinder shut-off via Camtronic at part load effectively creates a V4. For added efficiency, the engine’s two turbochargers are placed between the cylinder banks.

Less glamorous than the sixes and V8 but very significant for Mercedes’ higher-volume models is the new gasoline 2.0-L 4-cylinder (M264). Also known as the Toptype, it follows downsizing/rightsizing philosophy by offering a specific output of 100 kW (134 hp) per liter. It is technology-dense with a twin-scroll turbocharger, belt-driven 48V starter-generator and 48V water pump. Energy recovery capability is claimed to be some 12.5 kW (17 hp).

The design enables engine-off coasting and Camtronic is used on the intake side. And Mercedes plans to expand its application of particulate filters across its gasoline engine range.

M256 "designed for electrification"

Prof. Weber underlined the importance of Mercedes continuing to develop and offer a wide range of co-existing drive systems: “Efficient and clean gasoline engines, diesels, plug-in hybrids, battery and hydrogen drives—each has its justification and future prospects. The M256 is the first engine that we have systematically designed for electrification from the outset.”

The ISG, responsible for hybrid functions, achieves boost or energy recovery while allowing fuel savings that were previously reserved for high-voltage hybrid technology, he added: “And the electric auxiliary compressor makes for an impressive step-off with the M256, bridging the time lag before the large exhaust turbocharger cuts in to full effect.”

Weber always talks of “rightsizing” rather than downsizing. “Instead of trimming the number of cylinders from the outset, thereby foregoing refinement and output, there are much more intelligent solutions," he noted. The M176 V8 uses cylinder shutoff; at part-load up to 3600 rpm it is an especially efficient 4-cylinder, he claims. Then, imperceptibly for the vehicle’s occupants, cylinders 2, 3, 5 and 8 cut in.

Mercedes’ new Powertrain Integration Center houses 10 test rigs fitted with high-precision torque measurement directly at the wheels. Integration covers engine and transmission, comfort, dynamics and overall agility—essentially ride and handling. The center includes a climatic altitude chamber and fully automatic operation of the vehicle on a dynamometer.

Mercedes is just starting work on a vehicle safety, electronics, and computer technology center. Just revealed is Mercedes EQ pure electric SUV coupe concept, with motors on front and rear axles to give all-wheel drive and front/rear variable torque distribution. A battery is positioned between the axles in the car's floor.

Mercedes has talked of a maximum 300-kW (402-hp) output and up to 700-N·m for the concept, and a potential 500-km (310 mi) range.

Author: Stuart Birch
Source: SAE Automotive Engineering Magazine