無論何時，新款發動機的問世一定是大新聞，而采用新的設計流程的新發動機誕生，則更是重大新聞。美國萬國卡車公司（International Truck）最近公布了旗下主要適用于重型8級卡車應用的全新發動機設計International A26。此外，萬國卡車還同時介紹了公司的α發動機研發項目。該項目召集了一小批精英人馬，專門致力于為發動機研發提供新的方向。
萬國卡車公司的先進工程研發副總裁Darren Gosbee表示，“A26經過全新設計，可以提供行業最領先的正常運行時間、耐用性和可靠性。”具體來說，這款12.4L的A26重型卡車發動機采用了一款來自公司合作伙伴大眾汽車（Volkswagen Group）的MAN D26直列6缸曲軸箱，并圍繞D26采用了大量創新組件設計，可以優化A26的四項關鍵指標：正常運行時間、燃油效率、重量和NVH性能（噪音、振動和不平順性）。
A26發動機的重量僅為2,299磅（1,043公斤），比納威司達（Navistar）的N13發動機輕55磅（25公斤）；比傳統的15L大缸徑發動機輕600到700磅（272到318公斤）。盡管重量有所減輕，但A26仍然可以輸出最高475 hp（354kW）的功率和1,750 lb·ft（2,373 N·m）的扭矩。
為了提供最長的正常運行時間，“簡潔”一直是萬國卡車公司的設計關注點之一。Gosbee表示，“A26可以說是現代發動機的極簡設計代表，從設計、校準到測試，我們在研發的每一個環節都時刻謹記要為客戶提供最長的正常運行時間。”此外，公司還采用了更大的活塞銷、連桿和襯套，從而實現更好的負載分配；更小的活塞冷卻噴流系統，可以提高油壓并將換油服務周期延長至70,000英里（112,654公里）。
此外，A26的一些其他優化也為這款發動機帶來了5%的燃料經濟性提升，包括博格華納（BorgWarner）的全新單級可變幾何形狀渦輪增壓器搭配一款簡化空氣管理系統；博世（Bosch）的2,500-bar（36,259- psi）高壓共軌燃油系統和新款氣缸蓋加冷卻劑通道設計也有助于同時降低A26的燃耗和排放。
除了部件材料方面的選擇，簡化設計還有助于保證A26發動機“重量輕”的優勢。具體來說，萬國卡車為這款A26發動機采用了1款鈦材料壓縮機輪（而非原來的鋁制機輪），從而保證更長的正常運行時間并減輕重量。復合材料閥門和鋁制飛輪外殼也進一步為A26降低了重量。
為了優化NVH性能，A26還采用了全新的曲軸箱、獨立油盤及橡膠墊設計，以便吸收震動。公司還決定放棄之前的11葉片設計，轉而采用了1款6葉風扇，可以提供更加安靜的運轉表現及更低的功耗。此外，A26的發動機校準也經過專門編程，可以降低發動機噪音。
皆可博車輛系統（Jacobs Vehicle Systems）與納威司達（Navistar）的工程師聯手為這款A26發動機提供了一款原廠壓縮釋放式發動機制動器。雅各布斯公司表示，“通過采用這款全新可變幾何渦輪，A26發動機在較低轉速和較高海拔地區的制動性能取得了67%的提升。”此外，這款渦輪增壓器還可以減少所需降速檔位的數量，并提供更好的NVH性能。
α項目推動研發加速進行
作為萬國卡車公司的全新發動機研發計劃，α項目旨在從各個方面優化公司的發動機設計。卡車及零部件總裁Bill Kozek表示，“α項目已經從根本上改變了我們的柴油發動機設計。”具體來說，α項目的參與團隊人員安排非常精簡，這可以保證更快的響應和決策速度。此外，團隊成員在進行決定時還被賦予了更大的自主權，不僅要達到2017年的排放規定，還要從四項關鍵指標入手，對發動機產品進行最全面的整體優化。
α項目達成的共識之一是利用行業成熟技術，而非利用客戶來試驗新的產品。重型發動機產品線營銷經理Jim Nachtman簡單表示，公司的策略是“留下最好的，優化其他的。”A26的曲軸、主軸承和連桿軸承、EGR冷卻器與閥門、汽油和燃油濾清器、空氣壓縮機、飛輪外殼等多項其他部件均沿用了納威司達N13發動機的設計。不過，為了將A26發動機的壓縮比提升至18.5:1，許多往復式部件的設計均進行了改變，比如連桿、活塞銷和活塞等。此外，為了優化燃料經濟性而不同時增加過多復雜度，公司決定采用一款速度較慢的單速水泵，而非變速泵設計。
α團隊已經對A26發動機進行了成千上萬小時的測功器試驗，各個發動機轉速和各級別負載均有覆蓋。Kozek說，“A26發動機進行了極端測試，B10壽命達到了前所未有的120萬英里（192萬公里）。”由于采用了熱疲勞性能更好的CGI-緊密石墨鑄鐵材料曲柄箱（相較于之前的傳統灰口鑄鐵材料），A26的極限工作溫度可低至-40°F(-40°C)。
A26發動機將會首先搭載于萬國LT系列卡車。萬國卡車公司還將為A26提供為期2年的不限里程保修。A26發動機是萬國卡車公司新一代發動機中的第一款，未來定將攜手α項目帶領公司走向一個新的開始。
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
萬國卡車（International Truck）公司決定放棄之前的11葉片設計，轉而為這款A26發動機搭配了1款6葉風扇，可以實現更加安靜的運行表現，及更低的功耗。
萬國卡車A26發動機采用了Jacobs(皆可博)的發動機制動系統。Jacobs (皆可博)和萬國卡車通過為A26搭配一款新型可變幾何形狀渦輪，最高可將這款發動機的低速運轉制動性能提升67%。
為了將壓縮比提升至18.5:1，A26發動機的許多往復式部件均進行了一些改變，比如連桿、活塞銷和活塞等。
A26發動機將會首先搭載于萬國LT系列卡車。