Lexus 2-Liter Engine ArchitectureThe Lexus in-line, four-cylinder, two-liter engine in the 2015 NX 200t includes a balance shaft with resin gearing. It uses a twin scroll turbocharger. The engine also has an air to liquid intercooler. Fuel is delivered to the engine by both port and also direct injection. The VVT-iW cam and valve timing system can allow the engine to operate in both the Otto and also Atkinson cycles. The exhaust manifold is built into the cylinder head and is cooled to keep exhaust gases from causing too much strain on this super-hot area of the engine. Let’s dive deep into this engine design now and take a closer look at every aspect of what could be the most important Toyota/Lexus engine in a decade.
Lexus 2.0-Liter Engine Turbocharger DetailsTurbochargers compress the intake charge to aid in combustion. The twin-scroll turbocharger on the Lexus 2015 NX 200t is different in many key ways from competitors’ turbos. The first unique aspect is that Lexus is making its own turbo. Most automakers don’t make turbos. They source them from companies outside. This slows development; means automakers are fitting a standard part to their engine, rather than making it a custom fit, and the quality program now involves two corporations. Lexus takes ownership of this turbo and it was designed entirely in-house by Lexus and manufactured in the Miyoshi plant. Lexus controls its turbocharger from raw material processing to installation in its vehicle.
Most automakers are using twin scroll turbos now with aim of reducing complexity (compared to twin turbos), space, and of course turbo-lag. Lexus’ design focused on not just power, but also fuel efficiency and emissions. Lexus and Toyota live and die by QDR, quality, durability, and reliability. By making this turbocharger themselves Lexus controls its own QDR destiny.
Lexus’ new turbo design has a focus on reduced friction, efficiency optimized turbine blades, and a reduction in noise, vibration, and harshness (NVH). This focus on reduced NVH is apparent when one stands outside the car while it runs. The engine is silent. Stand next a BMW 2.0 liter turbo, such as that in the BMW X3 28i and you will immediately sense the difference in Lexus’ reduced NVH.
Lexus’ turbo impeller is forged to near its final shape which helps control distortion. The impeller wheel is electron beam welded to continue this attention to dimensional accuracy. The turbo housing itself is a new cast-steel material with reduced nickel content Lexus says helps the casing deal with and resist heat distortion and wear.
Lexus 2.0 Turbo Intercooler DetailsIntercoolers remove heat from the compression of the air by the turbo and aid in combustion. A cooler air intake charge is more dense, and thus has more oxygen for combustion (PV=nRT). Lexus mounted its intercooler downstream of the turbo (of course), behind the engine and low in the engine bay. This has many advantages including lower center of gravity (radiators are heavy) and to move the weight back toward the centerline of the vehicle.
Lexus Cam and Valvetrain Details Lexus uses an ultra-lightweight valvetrain with sodium filled valves. The variable valve timing (VVT) system now used by Lexus is called VVT-iW. The i stands for intelligent, and the W stands for wide. The upshot of the new system is that it operates over a wider segment of the intake timing. The system can advance and retard timing so much that the engine actually operates at times in the Otto cycle, and at times in the Atkinson cycle. Say goodbye to the debate over whether to use Otto (more power overall) or Atkinson (better fuel efficiency in some circumstances).
Lexus Exhaust Manifold DetailsThe Lexus exhaust manifold is a 4-pipe to 2-pipe to 1-pipe system that is integrated directly into the cylinder head. Lexus uses engine coolant to remove heat from this critical part to prolong life. It also prolongs the range that the engine can be operated in with the optimum air-fuel ratio. Lexus designed the exhaust manifold to work with the turbocharger to reduce exhaust gas pulsing.
http://www.torquenews.com/1083/2015-nx-200t-lexus-2-liter-turbo-engine-companys-most-important-decade
文章有点长，亮点有点多，我着重介绍几个吧：
1）发动机型号是8AR-FTS。
2）双涡管涡轮增压器。和其它厂商不同，这台涡轮增压器是完全自己生产的。雷克萨斯宣称各种高大上的技术运用使得增压器的NVH控制的更好，发热控制的更好，磨损更小。
3）电喷+直喷。压缩比10:1。被黄金动力组合长期讥笑的VVT-i这次多了个字母变身VVT-iW, W等于wide，表示进气正时的控制范围更加宽，可以在低负荷时变成阿特金森循环（虽然这个技术也不新鲜了）。
4）4-2-1排气歧管直接与气缸连接（区别于其他发动机用螺栓紧固？），歧管由发动机冷却液冷却以减少整个引擎舱的发热量（这个很重要大家都知道。。。）。雷克萨斯宣称针对涡轮增压引擎的排气脉冲做了针对性设计。
5）中冷器被放在了发动机的后面，为了改善前后配重（会不会降低冷却效率？毕竟放在前面更容易吃到风）。中冷器尽量靠下是为了降低车辆重心（会不会更容易被打坏？）。
6）最大功率235匹@4800-5600rpm。最大扭矩350牛米@1650-4000rpm。放进四驱的NX里0—96kmph用时7秒。雷克萨斯宣称综合百公里油耗10L。
从各种参数看来这台发动机明年放到国产汉兰达里是用来取代现在的3.5V6的（大概也是被排量税给逼的。。。），而且据胖哥杨力说会匹配现在3.5上的那台5速手自一体。。。