日產的新VC-Turbo引擎：值得努力嗎？https://www.sae.org/news/2018/05/2019-infiniti-qx-50-w-vc-turbo-review
2018-05-24 RON SESSIONS

在2016年巴黎車展上宣布，日產的新型可變壓縮比發動機 - 被稱為VC Turbo--至少暫時推動暫停按鈕，推動公司走向完全電動汽車未來。作為KR20DDET全面生產，2.0升VC Turbo首次亮相全新2019款英菲尼迪QX50緊湊型豪華SUV。它將在其第二次公佈的2019年日產Altima應用中獲得相當大的生產規模。

詳見SAE技術論文2018-01-0371，“採用世界首個可變壓縮比技術開發新型2L汽油VC-Turbo發動機”（https://www.sae.org/publications/technical-papers/content / 2018-01-0371 /），VC Turbo可以無限制地改變其活塞行程和有效壓縮比在8：1和14：1之間。低壓縮模式適用於高功率需求和高道路負載條件以及用於巡航和輕載的高壓縮模式。

一些汽車製造商已經探索了VC技術，但卻被成本，複雜性和可靠性的障礙所挫敗。日產是第一個將其推向道路的人，這是二十年工作的高潮。根據首席動力總成工程師Shinichi Kiga的說法，僅靠風險投資運營所獲得的燃油效率為8％。

作為完整的道路到屋頂重做的一部分，新的QX50轉向了一個全新的平台。它降低了之前實用程序的後輪驅動佈局，橫向安裝的VC Turbo取代了縱向安裝的3.7升V6和7速自動變速箱。 VC Turbo與日產JATCO提供的Xtronic無級變速自動變速箱相匹配。前輪驅動和按需全輪驅動均可提供。

橫向動力傳動系統比以前從FM平台G35轎車獲得的縱向動力傳動系統更節省空間。新款QX50與前一版本相比，前後尾部縮短了8.1英寸（206毫米），同時獲得了後座腿部空間和貨艙空間。

汽車工程公司在洛杉磯城市街道，地區高速公路和蜿蜒的馬里布峽谷道路上行駛了一台配備VC渦輪增壓的2019 QX50飛越大約160英里（257公里）。在洛杉磯大部分地區的道路上，小型豪華SUV和盜賊一樣厚，QX50絕對是其中的元素。清晰的油門響應在那裡非常珍貴 - 高度的巴爾乾化道路突然合併，消失的車道，隱藏的交叉路口和整體交通混亂。在額定功率為268馬力（200千瓦）時，新款QX50的峰值輸出比去年的V6降低了59馬力（44千瓦）。但在紅綠燈阻力賽中，扭矩是王道。與奧迪，寶馬，雷克薩斯等競爭對手的渦輪增壓四驅車一樣，新款VC渦輪驅動的QX50在低轉速（1600轉/分鐘）時達到了280磅·英尺（283牛·米）的峰值。它保持在扭矩曲線的脂肪部分達到4800轉/分鐘，從而使其具有健康的中頻和部分油門響應。

0-60英里/小時（0-97公里/小時）的衝刺現在需要大約6.5秒，比去年的模型低約半秒。不是說你覺得被騙了。加速仍然接近2.0升渦輪增壓X3和Q5。 KR20DDET閥芯快速而CVT雖然有時表現出“彈性”質量，但可以毫不拖延地改變比率。發動機在低壓縮模式和高壓縮模式之間的過渡是無縫且透明的。即使您在發動機以高壓縮（動力）或低壓縮（Eco）模式運行時顯示的speedo和tach之間的大部分裝飾性數字儀表，也不會發出任何聲音或觸覺感覺。

然而，當從休息狀態沖壓油門時，存在一瞬間察覺到的渦輪遲滯。感覺可能是CVT皮帶衝到錐體上的正確位置，或者是對油門圖的牽引力控制干預。
新款VC Turbo的聲音與去年的V6咆哮聲不同，雙排氣管（去年的型號只有一個排氣管）的排氣音高一點，並且在上限範圍內。它唱的歌幾乎是意大利語。 2019年型號通過音頻揚聲器實現主動降噪功能，在高速公路上以低轉速巡航時可消除不必要的隆隆聲，並有效增強聲音以強調正面音符。
換擋撥片允許駕駛員在CVT中召喚八個模擬的固定齒輪比。四種可選的駕駛模式 - 標準，運動，生態和個人 - 定製油門和傳動比圖。

效率大提高

為什麼日產會遇到增加壓縮引擎成本和復雜性的麻煩？燃油經濟性。該公司預計，與之前的3.7升V6相比，VC Turbo的QX50燃油經濟性將增長27-30％。本文發佈時尚未提供最終EPA數據，但英菲尼迪估計2019年QX50與AWD將達到24英里/加侖/ 30英里/加侖公路/ 26英里/加侖綜合評級。
26英里/加侖的合計數字僅比美國環保署的總和估計值高出1英里/加侖

Nissan’s new VCR engine: worth the effort?

2018-05-24 RON SESSIONS

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Announced at the 2016 Paris Motor Show, Nissan’s new Variable Compression Ratio engine—known as the VC Turbo—pushes the pause button, at least momentarily, on the company’s journey to a completely electrified-vehicle future. Fully productionized as the KR20DDET, the 2.0-L VC Turbo debuts in the all-new 2019 Infiniti QX50 compact luxury SUV. It will gain considerable production scale in its second announced application, the 2019 Nissan Altima.

As detailed in SAE Technical Paper 2018-01-0371, “Development of a New 2L Gasoline VC-Turbo Engine with the World’s First Variable Compression Ratio Technology” (https://www.sae.org/publications/technical-papers/content/2018-01-0371/), the VC Turbo can infinitely vary its piston stroke and effective compression ratio between 8:1 and 14:1. The low-compression mode is for high power demand and high-road-load conditions and the high-compression mode for cruising and light loads.

Several carmakers have explored VC technology, only to be thwarted by the hurdles of cost, complexity and reliability. Nissan is the first to put it on the road, a culmination of two decades of work. The fuel efficiency gained from VC operation alone is 8%, according to Shinichi Kiga, the Chief Powertrain Engineer.

Crossover showcase

As part of a complete road-to-roof redo, the new QX50 moves to an all-new platform. It drops the previous utility’s rear-drive layout and the transverse-mounted VC Turbo replaces the longitudinally mounted 3.7-L V6 and 7-speed automatic. The VC Turbo is matched to Nissan’s JATCO-supplied Xtronic continuously variable automatic transmission. Both front-drive and on-demand all-wheel drive are available.

The transverse powertrain is more space-efficient than the previous longitudinal one derived from the FM-platform G35 sedan. The new QX50 is 8.1 in (206 mm) shorter nose-to-tail than the previous version, yet gains rear seat legroom and cargo space.

Automotive Engineering piloted a VC Turbo-equipped 2019 QX50 over about 160 miles (257 km) of Los Angeles city streets, area freeways and winding Malibu canyon roads. Small luxury SUVs are as thick as thieves on most LA-area roads and the QX50 was definitely in its element. Crisp throttle response is highly prized there—highly Balkanized roads make for sudden merges, disappearing lanes, hidden intersections and overall traffic chaos. At a rated 268 hp (200 kW), peak output for the new QX50 is down by 59 hp (44 kW) from last year’s V6. But in stoplight drag races, torque is king. And as with competitive turbo fours from Audi, BMW, Lexus and others, the new VC Turbo-powered QX50 reaches its peak advertised 280 lb·ft (283 N·m) at a low (1600) rpm. It stays in the fat part of the torque curve to 4800 rpm, giving it healthy midrange and part-throttle responses.

A 0-60 mph (0-97 km/h) sprint now takes about 6.5 seconds, around a half-second down from last year’s model. Not that you feel cheated. Acceleration is still close to 2.0-L turbo-powered X3s and Q5s. The KR20DDET spools quickly and the CVT, although sometimes exhibiting a ‘springy’ quality, changes ratios without delay. The engine’s transitions between low and high compression modes are seamless and transparent. Even if you peek at the largely decorative digital meter between the speedo and tach that displays when the engine is operating in high compression (Power) or low-compression (Eco) modes, there’s no audible or tactile sensation of anything occurring under the hood.

There is, however, a split second of perceived turbo lag when punching the throttle from rest. The sensation could be a CVT belt rushing to the right place on the cone, or a traction control intervention to the throttle map.
The new VC Turbo has a different voice than last year’s V6 growl, with an exhaust note from the dual pipes (last year’s model had a single exhaust) a bit higher pitched and in the upper rev range. The song it sings is almost Italianate. The 2019 model sports both active noise cancellation working through the audio speakers to nullify unwanted rumbles when cruising at highway speeds at low rpm and active sound enhancement to emphasize the positive notes.
There are paddle shifters that allow the driver to summon eight simulated fixed gear ratios in the CVT. Four selectable driving modes--standard, sport, eco and personal—tailor the throttle and transmission ratio maps.

Big efficiency gain

Why did Nissan go to the trouble of the increased costs and complexity of the variable-compression engine? Fuel economy. The company is anticipating a 27-30% jump in QX50 fuel economy with the VC Turbo compared with that of the previous 3.7-L V6. Final EPA numbers were not yet available when this article was posted but Infiniti estimates that the 2019 QX50 with AWD will achieve a 24 mpg city/30 mpg highway/26 mpg combined rating.
The 26-mpg-combined number is just 1-mpg better than the combined EPA estimates for the 2018 BMW X3 xDrive30i and Audi Q5 and is 2-mpg more efficient than for the AWD 2018 Lexus NX300. Those competitors use turbocharged 4-cylinder engines but without variable compression.

In 100+ miles (161 km) of L.A. metropolitan driving, the 3952-lb (1793-kg) QX50 delivered 24 mpg, mostly operating in the high-load/low-compression mode. So, the real question: How much of the QX50’s fuel-economy improvement is due to downsizing to a 2.0-L 4-cylinder turbo and how much of it is attributable to the variable-compression feature?

While Kiga-san maintained that the VC feature alone is good for an 8% fuel-economy gain, other factors include the move to a CVT and overall vehicle weight savings of about 100 lb (45 kg).
Challenges in optimizing the VC mechanism included machining the central cantilever/actuators that vary the piston stroke, Kiga said. Tolerances are critical, he continued, and that’s one of the reasons the VC Turbo 4-cylinder is assembled at the same Yokohama plant that makes the high-performance Nissan GT-R V6.

The VC Turbo engine requires premium-octane fuel—a surprise to some who might think that the ability to switch to low-compression mode under higher road loads would permit the use of lower-octane ratings.
With Infiniti stating that its products will be electrified from 2021 forward, where does that leave an elegant and complicated mechanical solution to improved fuel economy such as the VC Turbo? It’s a shame buyers can’t see the fascinating workings within this machine that took Nissan engineers so long to perfect. Then again, how many luxury SUV buyers are apt to look under the hood at all?