當(dāng)大眾汽車（Volkswagen）埋頭專注于滿足美國(guó)與歐洲的燃油排放標(biāo)準(zhǔn)要求時(shí)，通用汽車在就已經(jīng)將發(fā)展重心轉(zhuǎn)移到了小型渦輪增壓柴油機(jī)乘用車市場(chǎng)。當(dāng)馬自達(dá)（Mazda）正在驗(yàn)證其2.2升Skyactiv-D發(fā)動(dòng)機(jī)，為CX-5（預(yù)計(jì)2018年春發(fā)布的新款）做準(zhǔn)備時(shí)，通用汽車（GM）也同樣希望能夠填補(bǔ)這一市場(chǎng)空白。事實(shí)上，作為2018款雪佛蘭Cruze and Equinox所選用的發(fā)動(dòng)機(jī)，這款造價(jià)2,200美元的1.6升渦輪增壓柴油機(jī)4年前就在意大利完成了設(shè)計(jì)，之前還曾在底特律進(jìn)行校準(zhǔn)，而目前則正在匈牙利進(jìn)行制造。
低油耗是柴油動(dòng)力系統(tǒng)的一大優(yōu)勢(shì)，這在公路行駛工況下尤為明顯。根據(jù)美國(guó)環(huán)保署（EPA）公路測(cè)試標(biāo)準(zhǔn)，在搭載通用與福特合資的9T50 9級(jí)自動(dòng)變速箱時(shí)，Cruze柴油機(jī)的油耗為52mpg(4.52L/100km)。兩輪驅(qū)動(dòng)的6級(jí)自動(dòng)變速Equinox油耗為39mpg(6.03L/100km)，而該車型的四輪驅(qū)動(dòng)版油耗則為38mpg(6.19L/100km)。由于Equinox整備質(zhì)量?jī)?yōu)勢(shì)明顯，在真實(shí)駕駛工況下，9級(jí)變速相對(duì)于6級(jí)變速的燃油經(jīng)濟(jì)性優(yōu)勢(shì)并不明顯。
獲得SAE認(rèn)證的“flüsterdiesel 安靜發(fā)動(dòng)機(jī)”
這臺(tái)SAE認(rèn)證的功率為102千瓦（合137馬力）的發(fā)動(dòng)機(jī)，是通用全球MDE家族的一員。發(fā)動(dòng)機(jī)轉(zhuǎn)速在每分鐘1500至3250轉(zhuǎn)之間時(shí)，可達(dá)到理論峰值扭矩的90%，即325牛·米（合240磅·英尺）。在《汽車工程》雜志（Automotive Engineering）的道路測(cè)試中發(fā)現(xiàn)，這臺(tái)發(fā)動(dòng)機(jī)的噪音非常小。德國(guó)汽車行業(yè)的撰稿人率先給它起了個(gè)別名叫做“der flüsterdiesel”，翻譯過(guò)來(lái)就是“安靜的發(fā)動(dòng)機(jī)”。當(dāng)你站在怠速狀態(tài)的發(fā)動(dòng)機(jī)旁時(shí)，幾乎聽不到任何的震顫聲。
這款發(fā)動(dòng)機(jī)的汽缸蓋、汽缸體和汽缸座都是鋁制的，壓縮比為16:1，采用固定氣門正時(shí)技術(shù)。發(fā)動(dòng)機(jī)的性能和排放表現(xiàn)都有明顯提升，這主要?dú)w功于位于發(fā)動(dòng)機(jī)軸上的旋轉(zhuǎn)蝶閥。通過(guò)從這一裝置，每個(gè)汽缸都能增加一次進(jìn)氣。博格華納的可變形渦輪增壓量最高可達(dá)290千帕（合42 psi），采用空氣對(duì)空氣的冷卻方式，可讓加速更順暢。同大多數(shù)柴油機(jī)一樣，這款發(fā)動(dòng)機(jī)在快速空轉(zhuǎn)時(shí)可以實(shí)現(xiàn)最大扭矩，使汽車啟動(dòng)時(shí)體驗(yàn)良好。
盡管頂部蓋有一層吸音棉，噴油器和共軌裝置也覆有吸音棉，并采用了翻蓋式歧管，但要最終要成就這樣一款低噪音發(fā)動(dòng)機(jī)，還是要依靠?jī)?yōu)秀的工程設(shè)計(jì)。這臺(tái)1.6升的發(fā)動(dòng)機(jī)里，裝有10步螺線管噴油器（每個(gè)噴油器有8個(gè)孔），定時(shí)齒輪和定時(shí)鏈的位置都靠后，這樣鐘型外殼和傳動(dòng)軸就能夠吸收定時(shí)齒輪或定時(shí)鏈帶來(lái)的噪音。
通用全球推進(jìn)系統(tǒng)區(qū)域總工程師Mike Siegrist表示，該款多重噴油器更趨近于壓電式噴油器。不過(guò)，他也透露，如果真的采用壓電式噴油器的話，那么在1.5升基本款的燃油發(fā)動(dòng)機(jī)里，每個(gè)孔的造價(jià)都要再貴上30美元。這款新一代螺線管噴油器的脈動(dòng)頻率可以達(dá)到之前的2倍，當(dāng)系統(tǒng)在2,000 bar（合29,000 psi）的壓強(qiáng)下工作時(shí)，性能可以接近壓電式噴油器。
螺線管噴油器的多次脈沖噴油方式
螺線管噴油器起初進(jìn)行預(yù)燃燒噴油，接下來(lái)會(huì)進(jìn)行很多次高頻預(yù)點(diǎn)火嘗試，以縮短延遲時(shí)間，之后才是燃燒噴油。這些措施可減少氮氧化物的生成，并降低噪音或振動(dòng)。接下來(lái)則是燃燒—點(diǎn)火脈沖，之后是燃燒后脈沖，用以控制蒸汽溫度，盡可能多地充分燃燒微粒，并進(jìn)一步減少尾氣排放。最多可達(dá)十次的脈沖過(guò)程，最終可以實(shí)現(xiàn)以上所說(shuō)的結(jié)果。
Siegrist解釋說(shuō)，廢氣再循環(huán)（EGR）系統(tǒng)包含液體冷卻，盡管柴油發(fā)動(dòng)機(jī)一般是在非節(jié)流狀態(tài)下運(yùn)轉(zhuǎn)的，1.6升的Ecotec發(fā)動(dòng)機(jī)里卻裝有一個(gè)電子節(jié)流閥以此來(lái)提升歧管的壓力，以增加EGR空氣流動(dòng)，成為發(fā)動(dòng)機(jī)控制系統(tǒng)的一部分。該系統(tǒng)將后燃燒選擇性催化還原（SCR）與尿素噴射合在一起，進(jìn)一步控制氮氧化物的排放。此外，這一系統(tǒng)里還包括了一種氧化催化劑和帶有再生功能的顆粒捕集器。很明顯，通用正在不遺余力地進(jìn)行研發(fā)，以期達(dá)到美國(guó)對(duì)于該類發(fā)動(dòng)機(jī)的認(rèn)證標(biāo)準(zhǔn)要求，確保低排放。
搭載這款發(fā)動(dòng)機(jī)的汽車都有一個(gè)18.5升（合4.9加侖）的容器來(lái)存放尿素溶液（也稱為“柴油發(fā)動(dòng)機(jī)排放處理液”）。盡管制造商試圖將處理液更換的里程數(shù)調(diào)整到12,000公里以上（合7,500英里），使之接近發(fā)動(dòng)機(jī)油的換油期，然而Siegrist還是略顯保守地表示，根據(jù)最終校準(zhǔn)結(jié)果來(lái)看，1.6升的Ecotec發(fā)動(dòng)機(jī)更有可能在行駛8,000至9,600公里（5000~6000英里）左右后就需要補(bǔ)充尿素溶液，因?yàn)樵谶@個(gè)里程數(shù)下，尿素箱檢測(cè)系統(tǒng)曾多次通過(guò)儀表盤發(fā)出補(bǔ)充處理液的警告。
怠速啟停也是這款發(fā)動(dòng)機(jī)的一大優(yōu)勢(shì)，而根據(jù)《汽車工程》的道路測(cè)試顯示，發(fā)動(dòng)機(jī)的再次啟動(dòng)迅捷而輕巧，甚至讓人幾乎感覺(jué)不到。
When Volkswagen fell afoul of U.S. and European emissions rules, it effectively stripped the U.S. car market of small turbodiesels for passenger vehicles. While Mazda is still certifying its 2.2-L Skyactiv-D for the CX-5 (now expected on sale in spring 2018), General Motors is also eager to fill the void. Its new 1.6-L turbodiesel, a $2,200 option for the 2018 Chevrolet Cruze and Equinox, was engineered four years ago in Italy, is built in Hungary, and was calibrated in Detroit for the hitherto-abandoned market.
Fuel economy, with highway numbers particularly impressive, are diesel strong points. The Cruze diesel is EPA highway-rated at 52 mpg with the GM-Ford joint venture 9T50 9-speed automatic. The Equinox is rated at 39 mpg for 2WD, 38 mpg for 4WD with the 6-speed automatic. Equinox’ greater curb weight precludes any real-world economy advantage for the 9-speed vs. the 6-speed.
SAE-certified "flüsterdiesel"
The engine, part of GM's global MDE family, SAE-certified at 137 hp (102 kW). GM claims 90% of the 240 lb·ft (325 N·m) peak torque is available from 1500 to 3250 rpm. The engine proved extremely quiet during an Automotive Engineering road test. German autowriters first dubbed it der flüsterdiesel, or "whisper diesel." We heard no audible chatter while standing next to the car with the engine idling.
Featuring an aluminum cylinder head, block and bedplate, the engine has a 16:1 compression ratio and fixed valve timing. Performance and emissions are improved by variable intake air swirl from a shaft-mounted lineup of pivoting butterfly valves for one of each cylinder’s two intakes. The BorgWarner variable-geometry turbo machine, with peak boost of 42 psi (290 kPA), uses air-to-air intercooling which smoothes acceleration. Like most diesels, peak torque is at fast idle, providing pleasing launch.
Although there’s an acoustic foam top cover, acoustic foam-covered injectors and common rail; and clamshell manifold cover, quiet design also is engineered-in. The 1.6-L incorporates 10-step solenoid fuel injectors (each with eight holes), and rear location of timing gears and chains, where the bell housing and transaxle absorb gear/chain noise.
That level of multi-injection would be more typical of piezo injectors, admitted Mike Siegrist, GM Global Propulsion's Regional Chief Engineer. But piezo units would add an intolerable “$30 per hole” over the 1.5-L base gasoline engine, he revealed. This new generation of solenoid injectors, with twice the previous pulsation rate, he said, provides near-piezo performance with the system operating at 29,000 psi (2000 bar).
Multi-pulse solenoid strategy
Solenoids start with pre-combustion pilot injection, and follow with a varying number of rapid pre-ignition “shots” for a shortened delay before the combustion injection. These reduce NOx generation and lower noise/vibration. The combustion-ignition pulse follows, and then post combustion pulses to control exhaust gas temperature, burn off maximum amount of particulate and further lower emissions. It’s the up-to-10 pulses that produce the total results.
The EGR (exhaust gas recirculation) system incorporates liquid cooling and although a diesel normally runs unthrottled, the Ecotec 1.6 L has an electronic throttle to raise manifold pressure, to increase EGR flow as part of the engine control system, Siegrist explained.
The system incorporates post-combustion SCR (selective catalyst reduction) with urea injection for further NOx control. There is also an oxidation catalyst and particulate filter with regeneration. GM clearly approached U.S. certification of this engine aggressively to ensure low emissions.
The vehicles have an 18.5-L (4.9 gal) tank of “diesel emission fluid” urea solution. Although manufacturers try to calibrate for a 7500-mi-plus (12,000 km) range to coincide with the oil change interval, Siegrist conceded that with the final calibrations the 1.6-L Ecotec is more likely to need a tank refill in the 5000-6000 mi (8000-9600 km) range. He explained that the urea tank monitoring system provides continuous instrument panel warnings in plenty of time for a refill.
Idle stop-start is incorporated with both automatics, and AE's road testing showed it’s barely perceptible, with restarts quick and gentle.
Author: Paul Weissler
Source: SAE Automotive Engineering Magazine
1.6升渦輪增壓柴油機(jī)與1.5升基本款渦輪增壓汽油機(jī)的扭矩對(duì)比曲線圖。（數(shù)據(jù)來(lái)源：通用汽車）
著名剖面圖畫家David Kimble筆下的通用汽車1.6升渦輪增壓柴油發(fā)動(dòng)機(jī)。（插圖：David Kimble/通用）
通用1.6升渦輪增壓柴油機(jī)的后視圖里，可以看到定時(shí)鏈驅(qū)動(dòng)裝置。（圖片來(lái)源：Paul Weissler）
博格華納（BorgWarner）的可變形渦輪是通用1.6升渦輪增壓柴油機(jī)的一大特點(diǎn)，它和氧化催化劑裝置緊挨在一起。（圖片來(lái)源：通用）