為了實現每車平均碳排放不超過95克/公里的目標，以達到歐盟6d CO2排放標準，發動機制造商不斷發出號召，希望供應商和專業研發公司能夠給予他們技術支持。
專業材料研發公司Materion正在研究的就是這一問題。就已經透露的一些細節可知，Materion將通過實測研發一款新的硅金屬強化銅合金，以增強壓縮機活塞環的工效。這一技術被稱為PerforMet，適用對象是小型增壓發動機，使之同自然吸氣式發動機相比，能夠應對更加高溫高壓的作業環境。
Materion業務發展部總監David Krus指出，讓更小的發動機輸出和以往相同的動力和扭矩，同時也會對鋁合金活塞用料產生磨損和疲勞等負面作用，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，影響發動機性能。”
Krus表示，在大大提升了導熱性之后，PerforMet活塞環的研發已經取得了很大進展。他補充說，“這使得無效熱量可以盡可能被帶離活塞，導入發動機體和冷卻套管。”
那么為何之前一直沒有嘗試這一技術呢？Krus解釋說，這是因為Materion這一特殊合金無法直接澆筑成近凈環形狀（near-netring shapes）。同時，其他一些生產環狀金屬件的常用工藝，如異型鋼絲，也很難應用到這一合金上。因此，這一想法只能等到相應技術成熟時，才能付諸實踐。
英國技術咨詢公司GE精密工程及當時公司的技術總監Scott Bredda參與了同Materion的合作。Bredda建議使用這一新的合金技術來加工熱傳導活塞環。
Krus解釋說：“最初，我們的想法是用這一技術來加工閥門座和閥門導管。然后才產生了用其加工活塞環的想法。我們都覺得這主意實在太棒了！我們把它放到熱學模型中（這一模型原本是用在Ultraboost項目上的，希望能在2.0升的I4增壓發動機上實現5.0升V8發動機的性能），然后看到溫度降低了很多。因此我們猜想這個方向應該是正確的，于是開始著手研發這一活塞環。”
據Materion稱，合金活塞環的效能最高可達普通鐵基活塞環的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，既增強了活塞的抗疲勞能力，也提升了燃燒效能。
PerforMet成功問世后，發動機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的位置上移，以縮小活塞環和活塞頂之間的空腔，使積聚在未點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環已在內燃機汽車上進行實測，以了解其耐用性、使用壽命以及抗磨損等具體特性。同時公司還表示，有兩家“全球性大型汽車制造商”正計劃于今年晚些時候，在多汽缸發動機上測試PerforMet活塞環。
Krus說，Materion期待PerforMet環能率先進入歐洲市場，以幫助汽車廠商達到2020年法規要求。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全新活塞環技術的效果。該技術正在進行真實工況測試。（圖例來源：Materion集團）
David Krus說，他希望PerforMet環能首先登陸歐洲的OEM市場。（圖片來源：Materion集團）
