為了實(shí)現(xiàn)每車平均碳排放不超過95克/公里的目標(biāo)，以達(dá)到歐盟6d CO2排放標(biāo)準(zhǔn)，發(fā)動(dòng)機(jī)制造商不斷發(fā)出號召，希望供應(yīng)商和專業(yè)研發(fā)公司能夠給予他們技術(shù)支持。
專業(yè)材料研發(fā)公司Materion正在研究的就是這一問題。就已經(jīng)透露的一些細(xì)節(jié)可知，Materion將通過實(shí)測研發(fā)一款新的硅金屬強(qiáng)化銅合金，以增強(qiáng)壓縮機(jī)活塞環(huán)的工效。這一技術(shù)被稱為PerforMet，適用對象是小型增壓發(fā)動(dòng)機(jī)，使之同自然吸氣式發(fā)動(dòng)機(jī)相比，能夠應(yīng)對更加高溫高壓的作業(yè)環(huán)境。
Materion業(yè)務(wù)發(fā)展部總監(jiān)David Krus指出，讓更小的發(fā)動(dòng)機(jī)輸出和以往相同的動(dòng)力和扭矩，同時(shí)也會對鋁合金活塞用料產(chǎn)生磨損和疲勞等負(fù)面作用，影響耐用性。
“這會帶來可靠性方面的問題。”Krus在接受SAE《汽車工程》雜志采訪時(shí)談到，“隨著活塞頂部溫度不斷升高，早燃（敲缸）的可能性也會不斷增加，影響發(fā)動(dòng)機(jī)性能。”
Krus表示，在大大提升了導(dǎo)熱性之后，PerforMet活塞環(huán)的研發(fā)已經(jīng)取得了很大進(jìn)展。他補(bǔ)充說，“這使得無效熱量可以盡可能被帶離活塞，導(dǎo)入發(fā)動(dòng)機(jī)體和冷卻套管。”
那么為何之前一直沒有嘗試這一技術(shù)呢？Krus解釋說，這是因?yàn)镸aterion這一特殊合金無法直接澆筑成近凈環(huán)形狀（near-netring shapes）。同時(shí)，其他一些生產(chǎn)環(huán)狀金屬件的常用工藝，如異型鋼絲，也很難應(yīng)用到這一合金上。因此，這一想法只能等到相應(yīng)技術(shù)成熟時(shí)，才能付諸實(shí)踐。
英國技術(shù)咨詢公司GE精密工程及當(dāng)時(shí)公司的技術(shù)總監(jiān)Scott Bredda參與了同Materion的合作。Bredda建議使用這一新的合金技術(shù)來加工熱傳導(dǎo)活塞環(huán)。
Krus解釋說：“最初，我們的想法是用這一技術(shù)來加工閥門座和閥門導(dǎo)管。然后才產(chǎn)生了用其加工活塞環(huán)的想法。我們都覺得這主意實(shí)在太棒了！我們把它放到熱學(xué)模型中（這一模型原本是用在Ultraboost項(xiàng)目上的，希望能在2.0升的I4增壓發(fā)動(dòng)機(jī)上實(shí)現(xiàn)5.0升V8發(fā)動(dòng)機(jī)的性能），然后看到溫度降低了很多。因此我們猜想這個(gè)方向應(yīng)該是正確的，于是開始著手研發(fā)這一活塞環(huán)。”
據(jù)Materion稱，合金活塞環(huán)的效能最高可達(dá)普通鐵基活塞環(huán)的4倍，不僅活塞溫度可以比以往最多降低25°C，活塞頂部溫度也能最多降低30°C，既增強(qiáng)了活塞的抗疲勞能力，也提升了燃燒效能。
PerforMet成功問世后，發(fā)動(dòng)機(jī)制造商也將有更多新的方案可供選擇，其中就包括把活塞頂環(huán)的位置上移，以縮小活塞環(huán)和活塞頂之間的空腔，使積聚在未點(diǎn)燃部位的燃料有所減少，從而降低燃燒不充分而造成的尾氣排放。
Materion宣布，PerforMet環(huán)已在內(nèi)燃機(jī)汽車上進(jìn)行實(shí)測，以了解其耐用性、使用壽命以及抗磨損等具體特性。同時(shí)公司還表示，有兩家“全球性大型汽車制造商”正計(jì)劃于今年晚些時(shí)候，在多汽缸發(fā)動(dòng)機(jī)上測試PerforMet活塞環(huán)。
Krus說，Materion期待PerforMet環(huán)能率先進(jìn)入歐洲市場，以幫助汽車廠商達(dá)到2020年法規(guī)要求。而要打入北美市場，則有可能要借助賽車賽事上的宣傳推廣。
To meet Euro 6d CO2 emissions targets calling for a fleet average emissions limit of 95g/km, engine OEMs increasingly are calling on suppliers and research specialists for technical help.
Materials development specialist Materion Corp. is doing just that, revealing details of a real-world test program to develop a new metal-silicide-strengthened bronze alloy for enhancing piston compression ring efficiency. The technology, called PerforMet, is aimed particularly at downsized, boosted engines that need to cope with higher pressures and temperatures compared to naturally-aspirated units.
David Krus, Materion’s Director of Business Development, noted that producing equivalent power and torque from smaller engines impacts wear and fatigue resistance characteristics of aluminum alloys used to make pistons.
"This raises reliability issues," he told Automotive Engineering, "and as the piston crown gets hotter, the tendency for premature combustion (knock) increases which affects performance.”
Krus said PerforMet piston rings have been developed having significantly improved thermal conductivity. “They allow unwanted heat to conduct effectively away from the pistons into the engine block and cooling jackets,” he added.
Why wasn’t it tried before? Krus explained that his company's unique alloy cannot be poured directly into near-net ring shapes. Nor is it particularly amenable to the other common process for manufacture of rings—using profiled steel wire. So the idea had to wait for new technology to allow it to be achieved.
Working with Materion was U.K. consultancy GE Precision Engineering and its then Technical Director Scott Bredda, who suggested using that technology for a conductive piston ring.
Explained Krus: “Originally, we had been looking at using the technology for valve seats and guides. Then came the piston ring idea and we said, ‘Great!’. We put it into our thermal model [from the Ultraboost project designed to achieve 5.0-L V8 performance from a boosted 2.0-L I4] and saw temperatures dropping very significantly. So we reckoned we were onto something good and are now developing the wire product."
The improvement is claimed by Materion to be up to four times greater than that of typical iron-based piston rings. This equates to average piston temperatures being reduced by up to 25°C and piston crown temperatures by up to 30ºC, increasing both fatigue resistance of the piston and its combustion efficiency.
The use of PerforMet has been designed to allow engine makers to introduce new solutions, including raising the piston top ring land to a higher location to reduce the cavity between the ring and the crown. Shrinking this crevice volume reduces the amount of fuel that gathers in the space that is not ignited, thus reducing emissions of unburned fuel.
Materion has announced that the PerforMet rings are now being evaluated in real-world ICEs for durability, longevity and wear characteristics. The company announced that two "high volume global car manufacturers" are planning to test PerforMet piston rings in multi-cylinder engines later this year.
Materion expects PerforMet to be used initially in the European market to meet the 2020 legislation. Its North American introduction is likely to be via racing, Krus said.
Author: Stuart Birch
Source: SAE Automotive Engineering Magazine
圖中展示的是Materion全新活塞環(huán)技術(shù)的效果。該技術(shù)正在進(jìn)行真實(shí)工況測試。（圖例來源：Materion集團(tuán)）
David Krus說，他希望PerforMet環(huán)能首先登陸歐洲的OEM市場。（圖片來源：Materion集團(tuán)）
