豐田油電混動普銳斯所搭載的先進(jìn)電驅(qū)動技術(shù)在業(yè)界聞名遐邇，但一直以來，豐田都沒有放棄對內(nèi)燃機(jī)技術(shù)的探索。
在2018年的日內(nèi)瓦車展上，豐田正式推出了全新“Dynamic Force”2.0 L四缸發(fā)動機(jī)系列。該系列將首推兩款發(fā)動機(jī)：內(nèi)燃機(jī)版和阿特金森循環(huán)混動升級版。豐田宣稱，傳統(tǒng)版和混動版的最高熱效率將分別達(dá)到40%和41%。該發(fā)動機(jī)的詳細(xì)信息及技術(shù)參數(shù)，您可查閱由豐田工程師在于2018年全球汽車年會（WCX2018）發(fā)表的相關(guān)論文，相關(guān)論文信息，請至正文最下方。
這兩款發(fā)動機(jī)是豐田汽油機(jī)系列的最新力作。為使汽油機(jī)的制動熱效率足以媲美輕型柴油機(jī)，豐田一直在積極探索，此前在2015年版的普銳斯上搭載了連續(xù)可變氣門正時（VVT）1.8 L發(fā)動機(jī)和大容量廢氣再循環(huán)（EGR）系統(tǒng)，隨后又在凱美瑞混動版中使用了2.5L四缸發(fā)動機(jī)。
與此同時，現(xiàn)代宣布伊蘭特Eco車型所搭載的1.4L Kappa阿特金森循環(huán)四缸發(fā)動機(jī)和Ioniq混動版所搭載的1.6LKappa系列發(fā)動機(jī)的熱效率也都達(dá)到了40%。
熱發(fā)動機(jī)的熱效率，指的是設(shè)備的有效輸出能量和輸入能量之比。以百分比計，熱效率一定是在0%到100%之間。由于摩擦、熱損失等原因，實(shí)際熱效率通常遠(yuǎn)低于100%，汽車汽油機(jī)的熱效率一般在25%左右。
此次豐田的成功并非得益于像馬自達(dá)壓燃SpCCI（火花控制壓縮點(diǎn)火）發(fā)動機(jī)這樣的突破性技術(shù)，而應(yīng)該歸功于豐田對消除一切不必要能源損失的執(zhí)著。
一個重大的技術(shù)提升是新型發(fā)動機(jī)采用了全新激光熔覆閥座（laser-clad valve seat）。閥座和氣閥表面無縫貼合，從而減少了閥座對進(jìn)氣直流的干擾，進(jìn)而增強(qiáng)了燃燒室內(nèi)的渦流。
為了匹配長沖程小孔徑的設(shè)計（80.5 x 97.6mm），全新2.0 L四缸發(fā)動機(jī)增寬了氣閥夾角，同時采用越來越普遍的四缸內(nèi)燃機(jī)的氣缸排量規(guī)格——496.5cc。
為使發(fā)動機(jī)的效率不受負(fù)荷和速度的影響，2.0L發(fā)動機(jī)搭載了雷克薩斯發(fā)動機(jī)的缸內(nèi)直噴和進(jìn)氣道噴射相結(jié)合的雙噴系統(tǒng)。
此外，新款發(fā)動機(jī)還采用了類似于馬自達(dá)新一代高效直噴創(chuàng)馳藍(lán)天汽油發(fā)動機(jī)（Skyactic-V）的超高壓縮比，傳統(tǒng)內(nèi)燃機(jī)版為13:1，混動版為14:1。豐田表示，高壓縮比、改進(jìn)的高滾流進(jìn)氣口、雙噴系統(tǒng)以及長沖程帶來的高速進(jìn)氣，顯著提高了Dynamic Force 發(fā)動機(jī)的燃燒速度。
新款發(fā)動機(jī)沿用了雷克薩斯發(fā)動機(jī)的設(shè)計，以電子相位器取代了進(jìn)氣凸輪軸的液壓執(zhí)行器，進(jìn)一步提高了可變氣門正時系統(tǒng)的精準(zhǔn)性。豐田研發(fā)副總Gerald Killman表示，“這樣做的好處是發(fā)動機(jī)的響應(yīng)會更快，特別是在寒冷的環(huán)境下。”汽油的黏性在低溫下會升高，影響可變氣門正時系統(tǒng)的響應(yīng)速度。因此，電子進(jìn)氣凸輪相位器必不可少。”
Killman還表示，由于快速正時調(diào)校對排氣的影響較小，因此排氣凸輪作動器仍沿用液壓式，“電子凸輪相位器成本更高，如果不能帶來明顯的效益，那為什么還要替換呢？”
為降低摩擦，新款發(fā)動機(jī)的活塞采用了樹脂涂覆的激光菱形花紋側(cè)裙設(shè)計。此外還搭載了可在各類環(huán)境下精準(zhǔn)高效地控制冷卻劑溫度的電子調(diào)溫器，以及只在需要的時候轉(zhuǎn)動的電子水泵。
Killman表示，“暖機(jī)時不能有水流。”因此，和皮帶驅(qū)動的水泵不同，當(dāng)發(fā)動機(jī)溫度較低時，電子水泵會自動關(guān)閉。
雖然油泵是機(jī)械驅(qū)動式，但其容量可變，因而可以減少寄生負(fù)荷。Killman強(qiáng)調(diào)，“我們需要改善每一個零部件。”
2.0L混動版在6600rpm時額定功率為126kW（170hp），在4800rpm時扭矩為 205 N·m（151磅英尺）。2.0L傳統(tǒng)版發(fā)動機(jī)在6000rpm時額定功率為107kW（143hp），在4400rpm時扭矩為 205 N·m（151磅英尺）。
近來，豐田又推出了匹配新款發(fā)動機(jī)的全新CVT。該款由愛信精機(jī)生產(chǎn)的全新變速箱在車輛起步時采用齒輪傳動，起步后改用皮帶，傳動比切換速度加快，更適合高速行駛。
Killman表示，這樣的設(shè)計使CVT齒輪變速箱的響應(yīng)速度更接近線性輸出的齒輪傳動，進(jìn)一步增加了效率、提升了客戶滿意度，“新款CVT的設(shè)計初衷是希望在提高能效的同時帶來更多駕駛樂趣。”
Killman還說，新款CVT傳動皮帶的角度由之前的11°收窄到了9°，換擋速度提升了20%，起步齒輪的應(yīng)用使整體傳動速度提升了15%。
Toyota is well-regarded for its advances in electric drive technology with its hybrid-electric Prius models, but the company also continues to make progress with internal combustion engine technology.
At the 2018 Geneva Motor Show, Toyota engineers unveiled a new 2.0-L four-cylinder gasoline engine family it dubs “Dynamic Force.” There will be two versions initially—one for purely ICE-powered vehicles and a revised Atkinson-cycle version for hybrid-electric applications. Toyota claims the conventional version will achieve 40% peak thermal efficiency and the hybrid engine will reach 41%. Toyota engineers will explain the engines in further detail in an SAE Technical Paper to be presented at WCX 2018.
These are the latest Toyota gasoline ICEs to offer levels of brake thermal efficiency (BTE) approaching that of light-duty diesels. They follow a 1.8L VVT in the 2015 Prius that used a large-volume exhaust gas recirculation (EGR) system, and the 2.5-L four used in the Camry Hybrid.
Hyundai also claims 40% BTE for its Kappa-family 1.4-L Atkinson cycle four used in the Elantra Eco and the 1.6L Kappa used in the Ioniq hybrid.
A heat engine’s thermal efficiency is the ratio between the useful output of a device and the input, in energy terms. The thermal efficiency must be between 0% and 100% when expressed as a percentage. Due to factors including friction, heat loss, etc., thermal efficiencies typically are much less than 100%. A typical automotive gasoline ICE operates at around 25%.
Toyota’s recent success is achieved, not by breakthrough like Mazda’s gasoline-compression-ignition SpCCI engine, but by relentless nibbling away at waste.
A significant improvement is the use of a new laser-clad valve seat that shrinks the seat to the absolute minimum of the contact surface with the valve face. This reduces the seat’s interference with the intake port’s straight shot into the combustion chamber, which contributes to intake charge swirl inside the combustion chamber.
The valves in the new 2.0-L four also are arranged in a wider included angle to fit within the smaller diameter of the undersquare (80.5 x 97.6-mm) bore and stroke design. Each cylinder measures 496.5cc, increasingly typical for current generation 4-cylinder ICEs.
The engine features a dual fuel injection system, as seen previously on the Lexus-brand engines, with both direct injectors and port injectors to provide the best efficiency under all loads and engine speeds.
Very high compression ratios—13:1 for the conventional engine and 14:1 for the hybrid—are similar to those used by Mazda for its Skyactiv-G. Combined with the revised tumble-inducing intake ports, and dual-injection scheme and high intake charge velocity associated with long-stroke designs, the Dynamic Force Engine boasts much faster combustion, according to the company.
Increased variable-valve-timing control precision is provided by electronic phasers for the intake camshafts. These replace hydraulic actuators, as Toyota has also done on Lexus engines. “The advantage is that it is faster, especially in cold conditions,” explained Gerald Killman, vice president of research and development. Cold, thick oil leads to sluggish variable valve timing, so the electric intake cam phasers are critical.
Exhaust cam actuators remain hydraulic because the exhaust side is less sensitive to rapid timing adjustments, he continued. “[Electric cam phasers] cost more, so if there isn’t a clear benefit, why bother?” Killman asked.
Low-friction pistons feature laser-crosshatching in their resin-coated skirts for reduced friction. Other technologies aimed at higher efficiency include the use of an electronic thermostat to precisely control the coolant temperature for efficiency under all conditions, and an electric water pump ensures that the water pump only spins quickly when it needs to.
“In the warm up, you want to avoid any water flow,” said Killman. So unlike a belt-driven pump, the electric pump just turns off when the engine is cold.
The oil pump is mechanically driven, but it is variable capacity, so its parasitic load is reduced. “We need improvement in every single item,” Killman emphasized.
Power ratings for the conventional 2.0-L engine are 126 kW (170 hp) at 6600 rpm and 205 N·m (151 lb·ft) at 4800 rpm. The new hybrid engine is rated at 107 kW (143 hp) at 6000 rpm and 180 N·m (132 lb·ft) at 4400 rpm.
Toyota also recently announced an innovation for the CVT to be matched to the engine. This Aisin AW-supplied transmission will employ a conventional first gear ratio for launch, then switch to the CVT when it upshifts from first gear. This lets the CVT shift its ratios to higher-speed driving.
The result is improved efficiency and better customer satisfaction because the response is more like the familiar linearity of a geared transmission, reported Killman. “This new CVT was designed looking to driving pleasure as well as efficiency,” he said.
Shift speed is a claimed 20% quicker because the CVT’s belt angle is 9° rather than the previous 11°, and the transmission’s overall ratio spread is 15% greater thanks to the addition of the launch gear, Killman explained.
Author: Dan Carney
Source: SAE Automotive Engineering Magazine
豐田新款2.0L四缸汽油機(jī)的傳統(tǒng)版的制動熱效率高達(dá)40%，阿特金森循環(huán)混動版更是達(dá)到了41%。（豐田）
豐田2.0L發(fā)動機(jī)剖面圖展示了激光熔覆閥座的增強(qiáng)進(jìn)氣渦流的功能和GDI噴嘴的位置。（豐田）
為降低摩擦，豐田進(jìn)一步優(yōu)化了全新2.0L 四缸汽油機(jī)的活塞。（豐田）