在汽車行業(yè)中，塑料一直都是一種很理想的減重材料，長期以來都在大量廣泛地應(yīng)用于汽車的各個(gè)部分，比如車身面板、內(nèi)飾材料和發(fā)動(dòng)機(jī)艙部件等，但從未想過要把變速箱外殼和齒輪組也改為塑料。
不過，這種情況可能要發(fā)生改變了。最近，有兩家歐洲公司正在進(jìn)行聯(lián)合研究工作，旨在顯著擴(kuò)大塑料復(fù)合材料在汽車傳動(dòng)系統(tǒng)中的應(yīng)用，而且他們還計(jì)劃借助電動(dòng)車研究進(jìn)行技術(shù)改良。
這對(duì)合作伙伴分別為英國變速器設(shè)計(jì)工程咨詢公司Drive System Design(DSD)，以及廣泛活躍在汽車、航空、能源和環(huán)境等領(lǐng)域的布魯塞爾國際化學(xué)集團(tuán)Solvay。
為了優(yōu)化未來純電動(dòng)車的NVH特性（噪聲、振動(dòng)和不平順性），這兩家公司開始聯(lián)手研發(fā)塑料材質(zhì)的變速器外殼，并同時(shí)探索通過這種材料提高齒輪嚙合效率的可能性?？紤]到噪聲問題，使用金屬材料的可能性基本可以被直接排除在外。
DSD公司總經(jīng)理Mark Findlay解釋說：“利用塑料替代傳統(tǒng)的金屬鑄件不但可以立刻獲得減重效益，而且還有潛力實(shí)現(xiàn)效率的提升。聚合材料的固有阻尼特性允許廠商設(shè)計(jì)更多的有效檔位，比如采用更小的螺旋升角或正齒輪等。由于產(chǎn)生的噪聲過大，這種設(shè)計(jì)根本無法應(yīng)用在傳統(tǒng)材料的變速箱外殼中。而采用更小的輪齒可以減少滑動(dòng)、增加滾動(dòng)，從而提高齒輪組的效率。”
Findlay認(rèn)為，機(jī)軸、套管和液壓閥體均有希望被納入塑料復(fù)合材料（或增強(qiáng)塑料復(fù)合材料）的應(yīng)用范圍。對(duì)常規(guī)乘用車變速器而言，如果完全使用塑料材料則最高可獲得45%的減重效益。即使在為了保證車輛NVH特性而為車輛增加一層“皮膚”之后，使用塑料材料的減重比例仍可達(dá)到25%。此外，由于采用了塑料材料，每次齒輪嚙合過程中的動(dòng)能損耗最高可以減少0.5%。
事實(shí)上，這兩家公司的合作，并不是汽車行業(yè)第一次試圖拓展塑料復(fù)合材料在基礎(chǔ)動(dòng)力系統(tǒng)中的應(yīng)用，但理想變?yōu)楝F(xiàn)實(shí)總是不那么容易。
早在20世紀(jì)60年代末，通用汽車就開始進(jìn)行復(fù)合材料變速箱的研究，并成功打造了一個(gè)原型。F1方程式和航空航天行業(yè)也開展了類似的研發(fā)項(xiàng)目，探索復(fù)合材料帶來的更多可能性。
20世紀(jì)80年代，復(fù)合材料應(yīng)用的發(fā)展開始停滯不前，當(dāng)時(shí)的復(fù)合技術(shù)無法滿足管套和輪齒等變速器元件的高容量需求，但如今的技術(shù)可能會(huì)實(shí)現(xiàn)改變了。
Findlay對(duì)塑料材料可能應(yīng)用范圍的看法相當(dāng)務(wù)實(shí)。他強(qiáng)調(diào)，為了協(xié)助提升車輛的NVH表現(xiàn)，這種技術(shù)可能最先在頂級(jí)電動(dòng)車領(lǐng)域發(fā)揮作用。“由于電動(dòng)車并不使用內(nèi)燃機(jī)，因此傳動(dòng)系統(tǒng)的任何NVH問題均會(huì)更容易暴露在相對(duì)安靜的車艙之中，這對(duì)能夠發(fā)揮自身固有阻尼優(yōu)勢的塑料變速器外殼來說非常有利。”
此外，由于電動(dòng)車行駛時(shí)的溫度也比傳統(tǒng)內(nèi)燃機(jī)車更低，因此也能更好地適應(yīng)低成本聚合材料120°C(248°F)左右的溫度極限。Findlay的一個(gè)觀點(diǎn)非常有趣，他認(rèn)為由于現(xiàn)階段電動(dòng)車的產(chǎn)量遠(yuǎn)遠(yuǎn)低于內(nèi)燃機(jī)車，剛好可以給相關(guān)制造技術(shù)一定的發(fā)展時(shí)間，逐步從原型制造階段進(jìn)化至量產(chǎn)階段。
Findlay認(rèn)為現(xiàn)在的挑戰(zhàn)是：“汽車行業(yè)對(duì)很多新材料的機(jī)械屬性并不熟悉，很容易掉入一些‘陷阱’之中，而且由于這些材料的非線性特性，隨著溫度變化，其屬性發(fā)生改變的程度高達(dá)50%。舉例而言，聚合物在到達(dá)玻璃化溫度(glass transition temperature)后會(huì)逐漸變軟，這會(huì)極大地影響該材料的機(jī)械屬性，有時(shí)甚至吸點(diǎn)水也會(huì)影響聚合物的屬性。通常來講，在設(shè)計(jì)研發(fā)過程中尋求與材料供應(yīng)商的合作，是個(gè)不錯(cuò)的做法，但如果設(shè)計(jì)研發(fā)的對(duì)象是聚合物這類屬性多變的材料，那么與材料供應(yīng)商的合作就是必不可少的了。”
DSD公司和Solvay集團(tuán)正是為了實(shí)現(xiàn)這樣的強(qiáng)強(qiáng)聯(lián)手，開始了他們的復(fù)合變速器外殼聯(lián)合研發(fā)項(xiàng)目。
考慮到結(jié)構(gòu)性功能和量產(chǎn)制造的成本，這兩家公司在塑料變速器研發(fā)中引入了低成本的復(fù)合技術(shù)。DSD公司認(rèn)為，如果按照目前$10/kg的平均行業(yè)減重補(bǔ)貼計(jì)算，塑料復(fù)合材料變速器外殼的成本完全可以與現(xiàn)有的鋁制產(chǎn)品競爭。
Solvay集團(tuán)表示，通過高效的FE（有限元）分析技術(shù)，結(jié)合使用現(xiàn)有的機(jī)械屬性數(shù)據(jù)，以及模流特性和纖維定向等參數(shù)，針對(duì)復(fù)合材料耐久性的預(yù)測水平可以得到大幅提升。一般而言，純塑料元件的回收相當(dāng)簡單明了，而且關(guān)于復(fù)合材料回收的相關(guān)研究也在不斷進(jìn)行之中，所有材料廠商都要面對(duì)回收塑料材料的問題。這些都可以成為塑料傳動(dòng)系統(tǒng)的研發(fā)的推動(dòng)力。
Findlay表示：“我們比較傾向于設(shè)計(jì)一種復(fù)合結(jié)構(gòu)的變速器外殼，具體是在結(jié)構(gòu)性框架周圍注塑聚合材料，從而形成一層連續(xù)的屏障，防止由于機(jī)油侵入造成內(nèi)嵌與外層聚合材料之間的結(jié)合強(qiáng)度減弱。
DSD公司和Solvay集團(tuán)正在與多家汽車廠商探討適用于各種未來變速器和傳動(dòng)系統(tǒng)的潛在替代材料。目前，復(fù)合材料變速器技術(shù)仍處于研發(fā)階段，仍需繼續(xù)尋找最合適的材料和工藝，必須經(jīng)過進(jìn)一步的優(yōu)化后才能進(jìn)入接近量產(chǎn)的階段。
DSP公司和Solvay集團(tuán)預(yù)測，復(fù)合變速器外殼可能會(huì)在未來5到10年內(nèi)進(jìn)在市場上推出。
Solvay集團(tuán)全球汽車市場經(jīng)理Mark Wright強(qiáng)調(diào)，必須通過提供一系列解決方案，不斷爭取新的潛在客戶，這點(diǎn)非常重要：“每個(gè)客戶都有不同方面的需求，比如減重、NVH優(yōu)化或能效提升等。我們必須針對(duì)每家客戶的特定要求，為他們提供最合適的解決方案。”
他解釋說，Solvay集團(tuán)積極參與了“多項(xiàng)”具有很高知名度的項(xiàng)目，z展示公司在材料科學(xué)方面的潛力：“目前，Solar Impulse正在進(jìn)行環(huán)球飛行挑戰(zhàn)，我們?yōu)檫@駕實(shí)驗(yàn)性零碳太陽能飛行器提供了15種我們自己的產(chǎn)品；我們還為Polimotor 2全塑料賽車發(fā)動(dòng)機(jī)項(xiàng)目提供了多種熱塑材料。”
Polimotor 2項(xiàng)目大量采用復(fù)合材料，還將利用Solvay公司的高級(jí)聚合技術(shù)研發(fā)至多10種發(fā)動(dòng)機(jī)零部件，包括水泵、油泵、進(jìn)水口/出水口、節(jié)氣門、油軌等多種高性能部件。目前，Solvay集團(tuán)可以提供的材料包括Amodel聚鄰苯二甲酰胺(PPA)、AvaSpire聚芳基甲酮(PAEK)、Radel聚亞苯基砜(PPSU)、Ryton聚苯基硫醚(PPS)、Torlon聚酰胺酰亞胺(PAI)，以及Tecnoflon VPL氟橡膠等。
作者：Stuart Birch
來源：SAE《汽車工程》雜志
翻譯：SAE上海辦公室
DSD, Solvay 'sink their teeth' into plastic transmission advances
For the automotive industry, plastics have long been a weight-saving material of choice, with a wide range of high-volume applications from body panels to interiors and underhood components—but transmission housings and gears are not among them.
Now that may change. Two European companies are collaborating in a study to achieve solutions that could herald a much wider role for plastic composites across transmission applications, and they are using electric vehicle (EV) research to help refine the technology.
The companies are U.K.-based Drive System Design (DSD), an engineering consultancy specializing in transmission design, development, and control, and Brussels-headquartered Solvay, an international chemicals group operating in sectors that include automotive, aerospace, energy, and the environment.
Based on their joint initiative to create a plastic transmission housing to improve NVH characteristics of a future pure EV, both companies are also exploring the possibility of using the material to improve the efficiency of meshing gears via tooth. In terms of noise, that would rule out using metals.
DSD Managing Director Mark Findlay explained: “There is an immediate weight saving from substituting plastic materials for conventional metal castings, but equally important is the potential for improved efficiency. The inherent damping provided by polymeric materials permits the use of much more efficient gears, such as reduced helix angles or spur gears, that would have unacceptable noise characteristics in a conventional casing. By using shorter teeth, typical tooth profiles for higher efficiency would have reduced sliding and increased rolling.”
He believes there is potential for shafts, casings, and hydraulic valve bodies to be made from plastic (suitably reinforced where appropriate), and states that full implementation could produce savings of up to 45% in casing weight for a typical passenger car transmission. With an NVH “skin” added, the saving would still reach 25%. A reduction in transmission losses would be “up to 0.5% per gear mesh.”
There is nothing new in wanting to extrapolate plastic’s roles into fundamental powertrain technology, but wanting and achieving are not the same things.
In the late 1960s, General Motors considered composite gearboxes and created prototypes. Formula One and aerospace industries have also embraced R&D programs that looked at possibilities.
In the 1980s, when such advances were seriously mooted, contemporary composites’ technology could not deliver radical powertrain application solutions such as casings and gear teeth for high-volume requirements; now it may be able to.
Findlay is pragmatic about these possible developments and stresses that it is in the premium EV category that the technology is likely to find its first application to help counter NVH: “The low cabin noise levels in a vehicle without an IC engine expose any NVH issues arising from the driveline, making the inherent damping of a plastic housing advantageous.”
Temperatures encountered in an EV are lower than an IC engine powertrain, so are more compatible with lower cost polymer temperature limits of around 120°C (248°F). An interesting point made by Findlay is that current production EV production volumes are hugely lower than those of conventional vehicles, making it easier for manufacturing technology eventually to migrate from prototype quantities to series production levels.
There are challenges, he said: “New and unfamiliar materials bring pitfalls for the unwary because of the subtleties of the mechanical properties, which can change by up to 50% over the operating temperature range due to non-linear behavior. Polymers soften above their glass transition temperature, which can significantly affect mechanical properties; even the moisture absorption of polymers can influence properties. It’s always good practice to work with a material supplier from the earliest stage of design but, when the material properties are as different as polymers and metals, it is absolutely essential.”
That is why DSD and Solvay are busy cooperating to meld their individual specialist capabilities.
For the plastic transmission study, low-cost composite technology is being incorporated from the outset to combine structural capability with volume-feasible manufacturing costs. Including the typical industry allowance for weight reduction at $10/kg saved, DSD believes composite transmission casings can be engineered to be competitive in price with existing aluminum products.
Solvay states that durability prediction has been greatly enhanced by effective finite element (FE) analysis, backed by proven data on mechanical properties and appreciation of the influence of parameters such as mold flow characteristics and fiber orientation (for composites). The recycling of plastic-only components is regarded as being straightforward, and research into composite recycling is ongoing; an issue that is common to all material manufacturers. All this is germane to the possible drivetrain developments.
Said Findlay: “Our preferred approach for a transmission casing is composite construction involving overmolding a polymer around a structural frame to provide a continuous barrier against any ingress of oil, which could otherwise infiltrate and weaken the bond between the inserts and the polymer.”
DSD and Solvay are currently discussing with vehicle manufacturers the areas within transmission and driveline systems that offer the best potential for material substitution in the future. Currently, the technology is in the development phase to optimize and prepare the most suitable materials and processes in a near-production-ready state.
DSD and Solvay anticipate a five- to 10-year timescale before the first applications come to market.
Solvay’s Global Automotive Marketing Manager, Mark Wright, underlines that it is important to approach potential customers with a range of alternative ideas: “Each customer has individual priorities, whether for weight reduction, NVH improvement, or increased efficiency. We have to reflect that by presenting the most appropriate options for their particular case.”
He explained that Solvay has taken part in “a number” of high-profile projects to demonstrate the potential of its materials: “We supply the Solar Impulse—an experimental zero-carbon, solar-powered aircraft attempting to fly around the world—with 15 different Solvay products, and also support the Polimotor 2 race engine program by providing several different thermoplastic materials.”
Polimotor 2 is composites intensive and will use Solvay’s advanced polymer technology to develop up to 10 engine parts, including a water pump, oil pump, water inlet/outlet, throttle body, fuel rail, and other high-performance components. Solvay materials targeted for use encompass Amodel polyphthalamide (PPA), AvaSpire polyaryletherketone (PAEK), Radel polyphenylsulfone (PPSU), Ryton polyphenylene sulfide (PPS), Torlon polyamide-imide (PAI), and Tecnoflon VPL fluoroelastomers.
Author: Stuart Birch
Source: SAE Automotive Engineering Magazine
DSD公司和Solvay集團(tuán)正在進(jìn)行復(fù)合材料設(shè)計(jì)改良，從而尋找適合變速器應(yīng)用的解決方案，比如圖中的塑料變速器外殼。 
工程咨詢公司DSD總經(jīng)理MarkFindlay相信，塑料很有潛力成為一種變速器替代材料。
Solvay集團(tuán)的復(fù)合材料可用于制造鏈輪。
DSD公司復(fù)合材料變速器外殼設(shè)計(jì)細(xì)節(jié)圖。
Solvay集團(tuán)正在與DSD公司合作研發(fā)動(dòng)力系統(tǒng)中的復(fù)合材料應(yīng)用，圖為該集團(tuán)全球汽車市場部經(jīng)理Mark Wright。