從最近的情況來看，汽車制造商似乎并未叫停對內燃發(fā)動機的投資。舉個例子，通用汽車 (General Motors) 旗下豪車品牌凱迪拉克 (Cadillac) 即耗時 4 年時間，隆重推出了一款全新 V8 發(fā)動機。按照計劃，凱迪拉克旗艦車型運動版 CT6 將自 2019 年上半年起，獨家使用該款 4.2 升 DOHC V8 雙渦輪增壓發(fā)動機。然而，我們不難想象，未來通用汽車將勢必還有至少一款關鍵車型也采用這款 V8 發(fā)動機。
凱迪拉克 V8 發(fā)動機首席工程師 Jordan Lee 向少數(shù)媒體展示了公司最新 V8 發(fā)動機的架構。Lee 表示，這款發(fā)動機繼承了凱迪拉克品牌對與眾不同和卓越性能的一貫追求，完美地將精致與性能融為一體。升級后的 2019 款 CT6 產品線將為客戶帶來兩種搭配不同配置 V8 發(fā)動機的版本，其中一款專為運動車型設計，5,700 轉時可輸出 550 hp 馬力，3200 到 4000 轉時可取得 627 lb·ft（850 N·m）的峰值扭矩。
這款全新鋁制 V8 的標準版本預計可在 5,000 到 5,200 轉時輸出 500 hp 馬力，并在 2,600 到 4,600 轉時輸出 553 lb·ft (700 N·m) 扭矩。這款發(fā)動機的副總工程師 John Rydzewski 表示，發(fā)動機達到這些數(shù)據(jù)的前提是使用優(yōu)質的無鉛汽油。這款發(fā)動機采用了高壓 (5,076-psi) 直噴系統(tǒng)，壓縮比為 9.8:1。對此，通用工程師告訴《汽車工程》，直噴系統(tǒng)的壓力相對較高，這意味著不必采用目前非常流行的“直噴+進氣口噴射”的組合設計。
別具一格的 V 型設計
這款全新 4.2 L V8 發(fā)動機的標志性特征也許就是“逆向”開口設計：排氣口位于發(fā)動機 90 度 V形結構的內側，而進氣口則將從 V形結構的外側將空氣輸送進入氣缸。
事實上，這并非通用汽車的首款量產 V8 發(fā)動機，但卻是凱迪拉克發(fā)動機首次將這一概念發(fā)展到新的極致：公司不僅將雙渦管渦輪增壓器安裝至發(fā)動機的 V 形結構中（作為排氣歧管的整體組成部分之一），而且還將定容催化轉換器也安裝在此處，重新定義了催化過程中的“緊耦合(close-couple)”概念。車輛的催化轉化器為了方便氧氣傳感器的安裝而鉆了孔，名副其實地“坐”在發(fā)動機之上。這意味著，尾氣一旦離開轉化器，則將在此后通往后保杠雙排氣管路的道路上暢通無阻，不受任何組件的限制。
Rydzewski 表示，“Hot V”設計是“最有效的優(yōu)化系統(tǒng)渦輪響應速度的方法”。
緊湊型雙渦管渦輪增壓器由三菱重工 (MHI) 提供，且具有電子廢氣門控制功能；通用汽車表示，這款渦輪增壓器采用了鋁鈦合金材料，重量只有鉻鎳鐵合金同類設計的一半，最高轉速可達 170,000 轉。渦輪增壓器的最大增壓范圍為 20 psi，液化中冷器的設計則最多可以協(xié)助每個氣缸組抑制 20 kW 的散發(fā)熱量，據(jù)稱最高可使進氣溫度降低 130 華氏度（54 攝氏度）。
Lee 補充說，在全新 V8 的研發(fā)中，協(xié)助發(fā)動機渦輪排出所產生的巨大熱量是最具挑戰(zhàn)性的任務之一。Lee 表示，“從一張白紙完全開始新的設計”可以讓我們采用新的熱量管理解決方案，讓 V8 一直維持在可接受的溫度范圍之內，特別是在發(fā)動機已經(jīng)關閉但渦輪增壓器和催化器中仍存在大量熱量的一段時間內。Lee 表示，當發(fā)動機停止后，車輛的前冷卻風機將繼續(xù)循環(huán)發(fā)動機周圍的空氣，而可變流量水泵也將繼續(xù)泵送冷卻液，直至車輛的冷卻需求完全得到滿足。
緊湊安裝
Lee 表示，凱迪拉克新款 V8 發(fā)動機各氣缸之間的間距僅為 10 毫米（0.4 英寸），因此盡管排量達 4.2 L，但安裝尺寸卻比之前版本短 50 毫米（2 英寸）。各氣缸的內徑為 86 毫米，沖程為 90.2 毫米；Lee 表示，各氣缸間相對狹窄的安裝位置并不會限制氣缸本身的內徑。
這款 V8 的六螺栓主軸承氣缸體采用了 A319 鋁材料搭配壓入式鐵質內襯的設計，氣缸蓋采用了 Rotocast 的 356 鋁材，帶有 36 毫米進氣閥和 29 毫米的鈉填充排氣閥，曲軸和連桿均采用了鍛鋼材料。
節(jié)油措施
盡管 4.2 L V8 發(fā)動機項目的主要目標時優(yōu)化性能，但這款發(fā)動機也采用了多種節(jié)能技術。
其中，最重要的是首次采用了一款專為通用 DOHC V8 發(fā)動機設計的主動燃料管理系統(tǒng)。在合適的條件下，該系統(tǒng)可以實現(xiàn)氣缸鈍化功能，即關閉發(fā)動機一側氣缸靠外的 2 個汽缸和另一側氣缸靠內的 2 個汽缸。在可變氣門正時系統(tǒng)中，排氣門最大張合角度為 55 度，進氣門的最大張合角度則為 70 度。此外，新型V8 還采用了一款新型 E86 發(fā)動機管理控制器，對各種發(fā)動機運行參數(shù)進行管理。
這款新發(fā)動機還采用了啟停裝置以提高節(jié)油效果，但 Lee 表示現(xiàn)在公布發(fā)動機的燃油經(jīng)濟性數(shù)據(jù)還為時過早。
對于 2019 款 CT6 而言，無論采用何種版本的 V8 發(fā)動機，車輛均將配備通用汽車的 Hydra-Matic 10 速自動變速器、性能先決換擋/加速系統(tǒng) (PAS / PAL) 及方向盤換檔控制系統(tǒng)。車輛采用了電子中控臺選擇器設計，不再使用傳統(tǒng)的物理連接，因此可以騰出更大車內空間。
此外，這款 CT6 還會標配全輪驅動系統(tǒng) (AWD)，更好地發(fā)揮 V8 發(fā)動機的強勁性能。AWD 分動箱將與發(fā)動機的鑄鋁油底殼進行整體安裝。
肯塔基州手工打造
凱迪拉克的最新 4.2 L V8 發(fā)動機將在通用汽車位于肯塔基州 Bowling Green 市的高性能生產中心 (Performance Build Center) 手工裝配而成。值得一提的是，這里也是雪佛蘭 Corvette 及其搭配的多款手工打造發(fā)動機的組裝場地。
事實上，業(yè)內一直有傳言稱新一代 Corvette 可能會轉而采用全新的 V8 發(fā)動機，而非該車型長期使用的小型 OHV V8 發(fā)動機，甚至還有可能增加或直接轉向一種新的先進中型發(fā)動機車輛架構。新款凱迪拉克 V8 發(fā)動機的動力和扭矩“潛力”顯而易見，且對生產場地的安排也讓人充滿遐想——這款新型發(fā)動機是否會最終登陸雪佛蘭 Corvette 或其他凱迪拉克車型？
正如大家所料，通用汽車的動力總成工程師并未直接回應這種猜測，但的確表示新的凱迪拉克V8“可能是未來公司多個其他項目的基礎”，這意味著通用總工程師并未一口否認這種可能性。
In the latest signal that automakers aren’t shutting off investment in internal-combustion just yet, General Motors’ Cadillac premium-vehicle brand unwrapped an all-new V8 roughly four years in the making. Cadillac will begin with exclusive use of the twin-turbocharged 4.2-L DOHC V8 starting in the first half of 2019 with a high-performance V-Sport variant of the CT6 flagship sedan—but it’s easy to speculate the V8 could be earmarked for future use by at least one other important GM model.
Revealing the new V8 architecture to a small media group, Jordan Lee, chief engineer for Cadillac V8 engines, said the engine is intended to underscore the Cadillac brand’s exclusivity and performance heritage and deliver an appropriate blend of high performance and refinement. The updated 2019 CT6 lineup will offer two variants of the new V8: a high-output version for the V-Sport model that generates an estimated 550 hp at 5,700 rpm and peak torque of 627 lb·ft (850 N·m) from 3,200-4,000 rpm.
The standard variant of the all-aluminum V8 is projected to produce 500 hp at 5,000-5,200 rpm and 553 lb·ft (700 N·m) from 2,600-4,600 rpm. Assistant chief engineer John Rydzewski said premium-unleaded fuel is required to achieve those output figures. The fueling system is a high-pressure (5,076-psi) direct-injection system and compression ratio is 9.8:1. Engineers told Automotive Engineering that the comparatively high pressure of the DI system meant they could forego the current trend of coupling direct- and port-injection fuelling systems.
The “Hot V” difference
Perhaps the new 4.2-L V8’s signature design feature is “reverse” porting that sees the exhaust ports on the inside of the engine’s 90-degree vee, with intake charge entering the cylinders from ports on the outside of the vee.
This is not a first for production-vehicle V8s, but the Cadillac engine takes the concept to a new extreme, locating not only both twin-scroll turbochargers in the engine vee (as integral parts of each exhaust manifold), but also the single-volume catalytic converters, bringing a new definition to the term “close-coupled” in relation to the catalysts. The catalytic converters, drilled for inclusion of an oxygen sensor, literally sit atop the engine and all but inside its valley. Once the exhaust leaves the converter, there are no other components or restrictions on the route to the dual exhaust tips at the rear bumper.
Rydzewski said the “Hot V” design is “the most effective way to optimize the turbo responsiveness of the system.”
The compact twin-scroll turbochargers are supplied by Mitsubishi Heavy Industries (MHI) and feature electronic wastegate control; the titanium-aluminide turbines can spin at up to 170,000 rpm and are half the weight of a similar design in Inconel material, GM said. Maximum boost pressure is 20 psi and the air-to-liquid intercooler design can reject up to 20 kW of heat per cylinder bank, dropping intake-charge temperature by as much as 130 deg (74 C), Cadillac said.
Extracting the immense heat developed in the engine vee was one of the most challenging aspects of the new V8’s development, added Lee. He said the clean-sheet design allowed new thermal-management solutions to assure the V8 maintains acceptable temperatures, particularly after the engine is shut down and the turbochargers and catalysts retain immense amounts of heat. Lee said the single front cooling fan continues to circulate ambient air over and around the engine, while the variable-flow water pump also circulates coolant for whatever time is required after engine shut-down.
Compact packaging
With cylinder bores just 10 mm (0.4 in) apart, Cadillac’s new V8 packages its 4.2 liters of displacement in a footprint that’s about 50 mm (2 in) shorter than usual, said Lee. Bore is 86 mm and stroke is 90.2 mm; Lee said the tight spacing between bores did not dictate a limitation on bore size.
The V8’s 6-bolt main-bearing cylinder block is A319 aluminum with pressed-in iron liners and the cylinder heads are Rotocast-supplied 356 aluminum, with 36 mm intake valves and sodium-filled 29-mm exhaust valves. The crankshaft is forged steel, as are the connecting rods.
Fuel-saving measures
Performance and refinement were paramount design targets for the 4.2-L V8, but the architecture includes several fuel-saving technologies.
Most significant is Active Fuel Management in its first use for a GM-made DOHC V8. The setup operates the engine in 4-cyl. mode when appropriate, shutting down the outboard two cylinders of one bank and the inner two cylinders of the other engine bank. The variable valve timing allows for 55 deg of authority for exhaust valves and 70 deg of authority for intake. This and other engine-operating parameters are governed by a new E86 engine-management controller.
The new engine also incorporates start-stop for increased fuel saving, although Lee said it remains too early to release projected fuel-economy figures.
For the 2019 CT6, either variant of the new V8 will be coupled with the GM Hydra-Matic 10-speed automatic transmission with GM’s Performance Algorithm Shifting/Performance Algorithm Liftfoot (PAS/PAL) and steering-wheel paddle shift control. An electronic console selector frees interior space by eliminating mechanical linkages.
Additionally, the CT6 applications will include all-wheel-drive as standard fitment with the new V8. The AWD transfer case is mounted integrally with the engine’s cast-aluminum oil pan.
Hand-made in Kentucky
Cadillac’s new 4.2-L V8 will be hand-assembled at GM’s Performance Build Center in Bowling Green, Kentucky. This is the site of assembly for Chevrolet’s Corvette and certain hand-built engines for that model.
It has long been rumoured that the next-generation Corvette could be powered by a new V8 engine—other than its longstanding small-block OHV V8—in addition to the possibility of either adding or wholly moving to an advanced mid-engine vehicle architecture. With the obvious power and torque “headroom” of the new Cadillac V8 and its new assembly location in the same plant where the Corvette and special Corvette engines are built, many will find it logical to speculate that Cadillac’s new V8 architecture is foreshadowing its eventual use for the Corvette—or other Cadillac models.
The company’s powertrain engineers of course aren’t directly addressing that speculation, but Lee didn’t exactly throw cold water when telling the media that the new Cadillac V8 “could be the basis for a lot of other things going forward.”
Author: Bill Visnic
Source: SAE Automotive Engineering Magazine
凱迪拉克推出全新4.2 升 V8 發(fā)動機，專為2019 款 CT6 系列設計。為了滿足運動版CT6 對性能的高要求，這款雙渦輪增壓 DOHC V8 發(fā)動機的功率輸出高達 550 hp，扭矩輸出則達 627 lb·ft。（圖片來源：通用汽車）
重新設計的2019款凱迪拉克CT6 V-Sport 采用了Escala概念車的設計理念，并將采用全新設計的4.2L V8高性能版發(fā)動機。