无论何时，新款发动机的问世一定是大新闻，而采用新的设计流程的新发动机诞生，则更是重大新闻。美国万国卡车公司（International Truck）最近公布了旗下主要适用于重型8级卡车应用的全新发动机设计International A26。此外，万国卡车还同时介绍了公司的α发动机研发项目。该项目召集了一小批精英人马，专门致力于为发动机研发提供新的方向。

万国卡车公司的先进工程研发副总裁Darren Gosbee表示，“A26经过全新设计，可以提供行业最领先的正常运行时间、耐用性和可靠性。”具体来说，这款12.4L的A26重型卡车发动机采用了一款来自公司合作伙伴大众汽车（Volkswagen Group）的MAN D26直列6缸曲轴箱，并围绕D26采用了大量创新组件设计，可以优化A26的四项关键指标：正常运行时间、燃油效率、重量和NVH性能（噪音、振动和不平顺性）。

A26发动机的重量仅为2,299磅（1,043公斤），比纳威司达（Navistar）的N13发动机轻55磅（25公斤）；比传统的15L大缸径发动机轻600到700磅（272到318公斤）。尽管重量有所减轻，但A26仍然可以输出最高475 hp（354kW）的功率和1,750 lb·ft（2,373 N·m）的扭矩。

为了提供最长的正常运行时间，“简洁”一直是万国卡车公司的设计关注点之一。Gosbee表示，“A26可以说是现代发动机的极简设计代表，从设计、校准到测试，我们在研发的每一个环节都时刻谨记要为客户提供最长的正常运行时间。”此外，公司还采用了更大的活塞销、连杆和衬套，从而实现更好的负载分配；更小的活塞冷却喷流系统，可以提高油压并将换油服务周期延长至70,000英里（112,654公里）。

此外，A26的一些其他优化也为这款发动机带来了5%的燃料经济性提升，包括博格华纳（BorgWarner）的全新单级可变几何形状涡轮增压器搭配一款简化空气管理系统；博世（Bosch）的2,500-bar（36,259- psi）高压共轨燃油系统和新款气缸盖加冷却剂通道设计也有助于同时降低A26的燃耗和排放。

除了部件材料方面的选择，简化设计还有助于保证A26发动机“重量轻”的优势。具体来说，万国卡车为这款A26发动机采用了1款钛材料压缩机轮（而非原来的铝制机轮），从而保证更长的正常运行时间并减轻重量。复合材料阀门和铝制飞轮外壳也进一步为A26降低了重量。

为了优化NVH性能，A26还采用了全新的曲轴箱、独立油盘及橡胶垫设计，以便吸收震动。公司还决定放弃之前的11叶片设计，转而采用了1款6叶风扇，可以提供更加安静的运转表现及更低的功耗。此外，A26的发动机校准也经过专门编程，可以降低发动机噪音。

皆可博车辆系统（Jacobs Vehicle Systems）与纳威司达（Navistar）的工程师联手为这款A26发动机提供了一款原厂压缩释放式发动机制动器。雅各布斯公司表示，“通过采用这款全新可变几何涡轮，A26发动机在较低转速和较高海拔地区的制动性能取得了67%的提升。”此外，这款涡轮增压器还可以减少所需降速档位的数量，并提供更好的NVH性能。

α项目推动研发加速进行

作为万国卡车公司的全新发动机研发计划，α项目旨在从各个方面优化公司的发动机设计。卡车及零部件总裁Bill Kozek表示，“α项目已经从根本上改变了我们的柴油发动机设计。”具体来说，α项目的参与团队人员安排非常精简，这可以保证更快的响应和决策速度。此外，团队成员在进行决定时还被赋予了更大的自主权，不仅要达到2017年的排放规定，还要从四项关键指标入手，对发动机产品进行最全面的整体优化。

α项目达成的共识之一是利用行业成熟技术，而非利用客户来试验新的产品。重型发动机产品线营销经理Jim Nachtman简单表示，公司的策略是“留下最好的，优化其他的。”A26的曲轴、主轴承和连杆轴承、EGR冷却器与阀门、汽油和燃油滤清器、空气压缩机、飞轮外壳等多项其他部件均沿用了纳威司达N13发动机的设计。不过，为了将A26发动机的压缩比提升至18.5:1，许多往复式部件的设计均进行了改变，比如连杆、活塞销和活塞等。此外，为了优化燃料经济性而不同时增加过多复杂度，公司决定采用一款速度较慢的单速水泵，而非变速泵设计。

α团队已经对A26发动机进行了成千上万小时的测功器试验，各个发动机转速和各级别负载均有覆盖。Kozek说，“A26发动机进行了极端测试，B10寿命达到了前所未有的120万英里（192万公里）。”由于采用了热疲劳性能更好的CGI-紧密石墨铸铁材料曲柄箱（相较于之前的传统灰口铸铁材料），A26的极限工作温度可低至-40°F(-40°C)。

A26发动机将会首先搭载于万国LT系列卡车。万国卡车公司还将为A26提供为期2年的不限里程保修。A26发动机是万国卡车公司新一代发动机中的第一款，未来定将携手α项目带领公司走向一个新的开始。

Any time a new engine is announced, it is major news. Pairing a new engine with a new approach to engine development is even bigger news. International Truck recently unveiled its all-new engine for the Class 8 market called the International A26. Along with that came news of an initiative called Project Alpha, which brought together a small team of powertrain engineers dedicated to a new perspective on engine development.

"The A26 was designed from the ground up to deliver industry-leading uptime, durability and reliability," said Darren Gosbee, vice president of advanced engineering. The 12.4-L A26 sources a MAN D26 inline 6-cylinder crankcase from their partnership with the Volkswagen Group and surrounds it with numerous all-new components to optimize four key criteria: uptime, fuel efficiency, weight and NVH (noise, vibration and harshness).

The engine weighs only 2299 lb (1043 kg), which is 55 lb (25 kg) less than the Navistar N13 engine it replaces and 600-700 lb (272-318 kg) lighter than traditional 15-L big bore engines. Despite the reduction in weight, the engine can still produce up to 475 hp (354 kW) and 1750 lb·ft (2373 N·m).

Simplicity was one of the focal points of the engine design to deliver maximum uptime. “The A26 is as simple as a modern engine can be, and we’ve built uptime into every part of the development process, from design to calibration to testing,” said Gosbee. Larger piston pins, connecting rods and bushings are used for better load distribution. Smaller piston cooling jets have increased oil pressure and help extend oil change service intervals up to 70,000 mi (112,654 km).

Other improvements across engine systems have helped deliver up to a 5% increase in fuel economy. The new BorgWarner single-stage variable geometry turbocharger leads off a simplified air management system. The Bosch 2500-bar (36,259-psi) high pressure common rail fuel system and new cylinder head with coolant passages that are 50% less restrictive help reduce both fuel consumption and emissions.

Simplification also helped lead to keeping the International A26 light weight, in addition to component material choices. A titanium compressor wheel was used instead of aluminum for improved fatigue life while continuing to reduce weight. Composite valve covers and an aluminum flywheel housing provided additional weight savings.

To improve NVH, the A26 has been given a new sculpted crankcase with an isolated oil pan and rubber gasket designed to absorb vibrations. A six-blade fan was decided over the previous eleven-blade, which allows for quieter operation in addition to reducing power consumption. The engine calibration is also programmed for reduced engine noise.

Jacobs Vehicle Systems collaborated with Navistar engineers to provide a factory-installed compression release engine brake for the A26 engine. “By leveraging the benefits of the new variable geometry turbo, the A26 engine brake performance increased up to 67% at lower engine speeds and higher altitudes,” according to Jacobs. Other stated benefits include a reduction in the need for downshifting and improved NVH.

Project Alpha initiative speeds development

All of these improvements were the goal of Project Alpha, a brand-new initiative by International for this engine’s development. “Project Alpha has fundamentally changed how we design diesel engines,” says Bill Kozek, president of Truck and Parts. The group was formed using fewer members to speed up and focus engine design decisions. They were also given more autonomy in their decision making to not only meet the 2017 emissions regulations but improve the overall product performance in those four key areas.

One of the mandates Project Alpha decided on was to leverage proven industry technologies over testing new ones on customers. “Keep the best and improve the rest,” was a mantra for Jim Nachtman, marketing manager of Heavy-Duty Product Line. The crankshaft, main and rod bearings, EGR cooler and valves, oil and fuel filters, air compressors and flywheel housing along with several other components were carried over from the Navistar N13 engine. However, many of the reciprocating components like the connecting rods, piston pins and pistons were replaced to increase the compression ratio up to 18.5:1. A slower, single-speed water pump was decided over a variable speed pump to improve the fuel economy without the complexity.

The Project Alpha team put the A26 engine through hundreds of thousands of hours of dynamometer testing at severe engine speeds and loads. “It’s been tested to extremes and meets a demanding B10 design life standard for an unprecedented 1.2 million miles,” said Kozek. The engine was temperature tested as low as -40°F (-40°C), which was aided by a switch to Compact Graphite Iron (CGI) for the crankcase which has better thermal fatigue than previous traditional gray iron.

The A26 will now be available in the International LT Series trucks. International is backing the engine with a two-year, unlimited mile warranty. It is the first of a new wave of engines for International trucks. The Project Alpha team and A26 engine are a new beginning for the brand.

Author: Matthew Borst
Source: SAE Automotive Engineering Magazine