大眾汽車 (Volkswagen) 的暢銷產(chǎn)品EA888 4 缸汽油發(fā)動(dòng)機(jī)系列新添又一明星產(chǎn)品——全新 B 循環(huán)發(fā)動(dòng)機(jī) EA888 Gen3B。盡管沒有明確說(shuō)明，但大眾汽車似乎有意讓這款發(fā)動(dòng)機(jī)接替未來(lái)將退出北美市場(chǎng)的高效柴油發(fā)動(dòng)機(jī)。
大眾汽車將全新EA888發(fā)動(dòng)機(jī)第三代稱為“B 循環(huán)”架構(gòu)，是因?yàn)锽 代表大眾汽車先進(jìn)動(dòng)力系統(tǒng)研發(fā)工程師 Ralf Budack 的姓氏首字母。多年以來(lái)，Budack 一直在努力研究如何結(jié)合目前越來(lái)越受歡迎的阿特金森循環(huán)和米勒循環(huán)燃燒過程，通過延遲關(guān)閉進(jìn)氣門縮短壓縮行程，增長(zhǎng)膨脹行程。
在此背景之下，這款 2.0L EA888 Gen3B 發(fā)動(dòng)機(jī)應(yīng)運(yùn)而生。大眾汽車表示，與 1.8LTSI 發(fā)動(dòng)機(jī)相比， Gen3B 可以取得與前者相同的功率水平，但燃料經(jīng)濟(jì)性可以實(shí)現(xiàn) 8% 的提升，幾乎與小型 1.4L 發(fā)動(dòng)機(jī)持平。因此，購(gòu)車者除了享受到 2.0L發(fā)動(dòng)機(jī)比目前的1.8L發(fā)動(dòng)機(jī)更大的排量之外，還可以同時(shí)獲得 1.4L 小型發(fā)動(dòng)機(jī)才能達(dá)到的燃油效率。EA888 Gen3B 發(fā)動(dòng)機(jī)將率先采用于 2018 款全新途觀 (Tiguan) 緊湊型跨界車，而后將陸續(xù)用于帕薩特 (Passat)、捷達(dá) (Jetta)、高爾夫 (Golf) 和甲殼蟲 (Beetle) 等車型。
新型氣缸蓋與花式凸輪軸設(shè)計(jì)
在最近一次的媒體見面會(huì)上，大眾汽車動(dòng)力系統(tǒng)工程師 Marcel Zirwes 詳細(xì)介紹了這款發(fā)動(dòng)機(jī)的開發(fā)細(xì)節(jié)。Zirwes 表示，雖然新款 B 循環(huán)發(fā)動(dòng)機(jī)保留了 EA888 的鑄鐵缸體，但氣缸蓋設(shè)計(jì)幾乎已經(jīng)完全不同了。
這款 EA888 Gen3B 發(fā)動(dòng)機(jī)的核心技術(shù)在于兩步式進(jìn)氣凸輪軸設(shè)計(jì)。具體來(lái)講，新設(shè)計(jì)采用了一款滑動(dòng)鈍齒，可以實(shí)現(xiàn)可變氣門正時(shí)：發(fā)動(dòng)機(jī)可以在需要最大功率時(shí)保持正常進(jìn)氣門開啟設(shè)置，也可以在部分負(fù)載條件下，利用凸輪凸角提前關(guān)閉進(jìn)氣門，從而實(shí)現(xiàn)更長(zhǎng)的膨脹行程，這也就是 B 循環(huán)的意義所在。
Zirwes 表示，B 循環(huán)發(fā)動(dòng)機(jī)的進(jìn)氣門機(jī)制不僅可以縮短進(jìn)氣門的開啟時(shí)間，開合幅度也有縮小。
EA888 Gen3B 發(fā)動(dòng)機(jī)的全新鋁質(zhì)活塞采用了一種獨(dú)特的活塞頂和活塞碗設(shè)計(jì)，可以實(shí)現(xiàn) 11.7:1 的高壓縮比（相較之下，EA888 Gen3 標(biāo)準(zhǔn) 4缸發(fā)動(dòng)機(jī)的壓縮比僅為 9.6:1）。這款 B 循環(huán)發(fā)動(dòng)機(jī)搭配了一款響應(yīng)速度更快的渦輪增壓器，使用常規(guī)汽油即可取得最大功率和扭矩。與普通的 2.0L 發(fā)動(dòng)機(jī)相比，新款 B 循環(huán)發(fā)動(dòng)機(jī)還調(diào)整了噴嘴的位置，每個(gè)燃燒周期中最多可以實(shí)現(xiàn) 3 次噴射。
由于采用了張力更低的活塞環(huán)設(shè)計(jì)，新款發(fā)動(dòng)機(jī)的摩擦減少了 8% 左右；這種設(shè)計(jì)在完全負(fù)載條件下的平均有效制動(dòng)壓力 (BMEP) 更低，這意味著工程師可以縮小車輛曲柄的主軸承尺寸，以及2 條平衡軸之間的傳動(dòng)鏈尺寸，進(jìn)而實(shí)現(xiàn)小型化設(shè)計(jì)。
目前，B 循環(huán)發(fā)動(dòng)機(jī)為新款途觀的唯一發(fā)動(dòng)機(jī)配置，4,400 轉(zhuǎn)時(shí)可提供 184 hp 馬力，與前身 2.0L 發(fā)動(dòng)機(jī)相比，可在更低轉(zhuǎn)速時(shí)輸出峰值功率。具體來(lái)說(shuō)，該款發(fā)動(dòng)機(jī)在 1,600轉(zhuǎn)時(shí)即可輸出最大扭矩 221 lb·ft (300 N·m)，并持續(xù)保持至4,000 轉(zhuǎn)左右，這與柴油機(jī)的水平相仿。盡管與途觀目前采用的 2.0L TSI 發(fā)動(dòng)機(jī)相比，新款 B 循環(huán)發(fā)動(dòng)機(jī)的功率輸出降低了 200 hp，但扭矩卻出人意料地實(shí)現(xiàn)了 14 lb·ft (19 N·m) 的提升。
對(duì) 2018 款途觀而言，目前這款 B 循環(huán)發(fā)動(dòng)機(jī)僅可搭配大眾汽車的 8 速自動(dòng)變速器。盡管新途觀采用了大眾汽車的暢銷 MQB 汽車架構(gòu)，但與該架構(gòu)車型通常搭配的 DSG 手動(dòng)變速器不同，為了提供更加流暢的駕駛性能，面向北美市場(chǎng)的途觀特別采用了傳統(tǒng)的自動(dòng)扭矩轉(zhuǎn)換器設(shè)計(jì)。
Volkswagen’s not saying it directly, but the company’s unique new twist on its well-established EA888 gasoline 4-cylinder engine family looks to be a potentially effective high-efficiency surrogate for the diesel engines it no longer will sell in North America.
The company calls the new third-generation variant of the AE888 engine architecture “B-Cycle,” so named for its developer, VW group advanced-powertrain engineer Ralf Budack, who for years envisioned this melding of the increasingly popular Atkinson- and Miller-cycle combustion processes that seek to use a truncated compression ratio—via late closing of the intake valves—to achieve an effectively longer expansion ratio.
Resulting is a 2.0-L engine that VW said has the power of the 1.8-L TSI it replaces, but roughly 8% better fuel economy—generating efficiency one might expect from a smaller 1.4-L engine. So in effect, buyers who get the new B-Cycle engine—first in the all-new 2018 Tiguan compact crossover and then the Passat, Jetta and Golf and Beetle—will enjoy 2.0-L displacement in place of today’s 1.8-L, with the added bonus of 1.4-L-like efficiency.
New cylinder head, fancy cam
Although the EA888’s iron cylinder block remains, the new B-Cycle variant has what amounts to an almost entirely new cylinder head design, said Marcel Zirwes, a VW powertrain engineer who detailed the engine’s development during a recent media program.
The central technology for the B-Cycle variant is a two-step intake camshaft that employs a sliding cog to locate the cam on one of two discrete timing regimes: a normal intake-valve opening setup when maximum power is required, or the partial-load setting that angles the cam lobes for the early intake-valve closing that delivers the B-Cycle effects. Zirwes said the B-Cycle intake-valve regime brings not only more-brief initial valve-opening duration, but also a smaller opening.
A new alloy piston has a unique crown and bowl shape that enables the higher 11.7:1 compression ratio (the standard third-generation EA888 4-cylinder engines have just a 9.6:1 compression ratio)—but the B-Cycle engine’s optimized interplay of engine operation, along with a new, faster-responding turbocharger, means the engine can develop full power and torque on regular-grade gasoline. The direct-injection system has relocated injectors compared with the standard 2.0-L engine and enables up to three injection events per combustion cycle.
The new engine’s friction is reduced by some 8% with lower-tension piston rings; the design’s lower full-load brake mean effective pressure (BMEP) also means that the crankshaft main-bearing diameter could be reduced and the size of the chain driving the twin balance shafts is smaller.
The B-Cycle is the only engine offering in the new Tiguan and develops 184 hp at 4,400 rpm, the power peak coming slightly sooner than with the previous 2.0-L engine. Maximum torque is 221 lb·ft (300 N·m), arriving at a low, almost diesel-like 1,600 rpm and holding to almost 4000 rpm. The hp figure does represent a reduction from the 200 hp available from the outgoing Tiguan’s 2.0-L TSI engine, but the more-economical B-Cycle engine surprisingly makes 14 lb·ft (19 N·m) more torque.
For the 2018 Tiguan, the B-Cycle engine is available exclusively with VW’s 8-speed automatic transmission. Although the new Tiguan is based on the company’s widespread MQB vehicle architecture that sees most engines coupled with the direct-shift gearbox (DSG) automated-manual transmission, VW said the conventional torque-converter automatic was specified for the Tiguan in the U.S. because of its smoother driving characteristics.
Author: Bill Visnic
Source: SAE Automotive Engineering Magazine
大眾汽車推出 EA888 Gen3B 全新發(fā)動(dòng)機(jī)。其中，B 代表大眾汽車先進(jìn)動(dòng)力系統(tǒng)研發(fā)工程師 Ralf Budack 的姓氏首字母。
目前，大眾汽車廣泛使用的EA888 渦輪增壓直噴 4 缸發(fā)動(dòng)機(jī)系列又新增了一款明星產(chǎn)品——第三代 B 循環(huán)發(fā)動(dòng)機(jī) EA888 Gen3B。
EA888 Gen3B 發(fā)動(dòng)機(jī)的獨(dú)特凸輪軸調(diào)整機(jī)制，可以延遲關(guān)閉進(jìn)氣門，這也是 B 循環(huán)概念的核心。
EA888 Gen3B 發(fā)動(dòng)機(jī)的氣缸蓋設(shè)計(jì)幾乎與 EA888標(biāo)準(zhǔn) 2.0L 發(fā)動(dòng)機(jī)沒有任何相似之處。
大眾的 EA888 Gen3B 發(fā)動(dòng)機(jī)實(shí)現(xiàn)了“駕駛員”時(shí)速范圍內(nèi)的能效提升。