CA1050汽車驅(qū)動(dòng)橋主減速器設(shè)計(jì)[雙曲面錐齒輪式單級(jí)] 基于5t的輕型載貨 貨車,雙曲面錐齒輪式單級(jí),CA1050汽車驅(qū)動(dòng)橋主減速器設(shè)計(jì)[雙曲面錐齒輪式單級(jí)],基于5t的輕型載貨,貨車,CA1050,汽車,驅(qū)動(dòng),減速器,設(shè)計(jì),雙曲面,齒輪,式單級(jí),基于,輕型,載貨 ULTRALIGHT-HYBRID VEHICLE DESIGN: OVERCOMING THE BARRIERS TO USING ADVANCED COMPOSITES IN THE AUTOMOTIVE INDUSTRY 1. INTRODUCTION Advanced polymeric composites have several advantagesincluding parts consolidation, high specific strength and energy absorption, styling flexibility, good noise/vibration/harshness (NVH) characteristics, and excellent corrosion resistancethat suit them to automobiles. Furthermore, technological advances in processing and materials appear to make advanced composites suitable for high-volume applications: low-pressure fabrication processes such as resin transfer molding (RTM) could require very low investment costs and, depending on the choice of resin and tooling material, offer fast cycle times, while new versions of resins and fibers promise low cost and high performance. In addition, recent developments in automotive design drive the need for what is potentially advanced composites biggest advantage: mass reduction. Ultralight-hybrid vehicle designs, such as Rocky Mountain Institutes “hypercar” concept, necessitate stringent mass-optimization particularly for the body-in-white1, the automotive term for the unfinished body and its frame or chassis. Advanced composite bodies-in-white have the potential to be up to 67% lighter than a conventional steel unibody for equivalent size and safety. However, a quick look at the use of advanced composites in the automotive industry raises an obvious question: If advanced composites are such wonderful materials, why are they not being used? Aside from a few specialty components for niche vehicles, such as one part in the Dodge Viper, and even fewer whole-system applications such GMs 1991 Ultralite concept car, the auto industry has shunned the use of advanced composites. Even regular structural composites, using low- performance reinforcements in quasi-isotropic arrangements, are being applied in lower-than- expected quantities. In response, organizations targeting the automotive industry, such as the Automotive Composites Consortium (ACC), and composite producers, including some in NISTs Advanced Technology Program (ATP), are ambitiously implementing strategies to speed the integration of structural and advanced composites into the automobile. But the ACCs focus on component applications such as a composite pickup truck box, like the ATPs funding of manufacturing process improvements without accompanying design changes, indicate a strategy of evolutionary integration. While an evolutionary approach minimizes risk in the short term, it may not be the optimal long-term strategy to overcome the barriers to putting advanced composites into cars. Just as the combination of an ultralight body with a hybrid driveline provides a “l(fā)eapfrog” approach to increasing fuel efficiency and decreasing emissions, so the whole-system application of composites to an ultralight monocoque BIW is the best way for the advanced materials and automotive industries to “tunnel through” the barriers to large-scale implementation. To an automaker, a leapfrog approach to composite integration could provide benefits far out-weighing the risks and uncertainties of working with unfamiliar materials and technologies. To an advanced materials supplier, a leapfrog approach can prevent the “set up to fail” scenario experienced in many automotive component applications by optimally exploiting the new materials intrinsic advantages. In addition, a leapfrog approach could potentially expand the advanced materials market by severalfold or more, achieving volumes which could lower their products costs. Thus an advanced materials push into the BIW should not be simply an issue of material substitution one part at a time: it needs to substitute materials using a whole-platform design that maximizes the materials benefits while minimizingand potentially 1 eliminatingmany of their costs. 2. TECHNOLOGIES FOR VOLUME PRODUCTION How could polymeric composite BIWs be competitively made in high volume? There is no definitive answer; the slate of potential technologies for fabricating and assembling an advanced- materials-based BIW is large and growing rapidly. The diversity of technological options adds both uncertainty and robustness. Also, while advanced polymeric composites require sophisticated design to take advantage of unique properties such as anisotropy, their high-volume manufacturing and assembly techniques are conceptually simple. The most promising off-the-shelf or near-term technologies for BIW manufacturing are briefly listed next; a fuller survey is in. 2.1 Raw Materials Polymeric composites incorporate fibrous reinforcement in a resin matrix. Issues important for raw material selection include cost, compatibility with fabrication technologies, mechanical and environmental performance, and recyclability. 2.2Molding In the various molding operations, the intermediate fiber form and resin, combined either previously or directly in the mold, are shaped and hardened into the form of the molding cavity. For an all-composite BIW, liquid composite molding (LCM)either resin transfer molding (RTM) or structural reaction-injection molding (SRIM)is generally considered to be the most promising process . Both RTM and SRIM utilize thermoset resins because of their low viscosity, although cyclic thermoplastics may be adaptable. LCM requires a preform, which can comprise a variety of intermediate fiber forms. As mentioned above, an advanced-composite BIW would probably use a more complex preform with higher-performance fibers. Compression molding, normally done with Sheet Molding Compound (SMC), is a high-pressure process with a lower cycle time and generally a better surface finish than LCM, suiting it to BIW applications within the current steel infrastructure. However, like glass, a fully compression-molded BIW, due to its weight, may not be able to reap adequate synergies with a hybrid drive, nor have adequate crashworthiness. BIW designs, less mature but higher-performance manufacturing technologies such as RTM or SRIM appear to be more applicable to an all-composite BIW. 2.3 Technological Barriers Unlike the overall design strategy for composite BIWs, none of the composite technologies listed above require fundamental advances to permit volume BIW manufacturing. Each needs varying degrees of refinement but seems to face no intractable technological barriers: implementation requires technology optimization and integration rather than invention. Some of the key techno-economic barriers are described next. 2.3.1 Carbon-Fiber Cost The cost of carbon fiber is often cited as the most formidable barrier to commercial applications for carbon-fiber composites. For PAN-based carbon fiber, the combination of expensive precursor and low-volume, specialized equipment has led to its high cost. However, two enterprising domestic manufacturers, Zoltek and Akzo Nobel, offer low-cost, hightow commodity-grade carbon fiber. Bulk creel prices for their continuous fiber are currently as low as $17.60/kg. Central to further decreases in price are cheaper versions of the precursor, which has “no cost controlling differences” from the commodity-grade acrylic fiber that costs$3.00/kg. to produce .In addition, higher volumes of production are needed to lower unit capital and labor costs. High-volume manufacturing could soon be realized: Zoltek and Akzo plan near-term expansion. Their strategy could overcome the cost barrier for advanced 2 composites with a supply-push of low-cost fiber into the transportation market. 2.3.2 Preforming The difficulty of producing complex preforms at reasonable cost is cited almost as often as carbon-fiber cost as the chief technical barrier to high-volume advanced composites manufacturing. Princetons Conference on Basic Research Needs for Vehicles of the Future recently gave preforming the highest priority among needed research and innovation .Currently, automakers favor quasi-isotropic chopped or continuous mat preforms of glass fiber, which, as was mentioned above, are too weak, isotropic, and hence heavy for a mass-optimized BIW. The anisotropic strategies common in aerospace applications, such as prepreg tapes and hand lay-up with autoclaving, are too slow and costly for cars. Fortunately, the problem of creating low-cost complex preforms may not be intractable: several innovative technologies could permit the rapid and inexpensive fabrication of complex, net-shape preforms. Fabrics such as COTECH are non-crimp, stitch-bonded layers of unidirectional continuous fiber that, according to their manufacturer, can be cheaper than random mat yet perform about as well as unidirectional tape. A stitch-bonding process can inexpensively create complex preforms by combining a quasi-isotropic base of fabric with strategically placed inserts of unidirectional fabric or roving at maximum load points. Alternatively, the CompForm process claims even cheaper and faster complex preforming potential, substituting UV-curable binders for fabric stitchesalthough this process cannot be used with a carbon-intensive preform. For creating net-shape preforms, fast ultrasonic cutting, using nesting patterns to minimize waste, could be a good complement to stitch-bonding. Obviously, complex preforms require heavy front-end engineering to avoid resin flow problems such as racetracking and unexpected fiber movements. Nevertheless, these processes have real-world validity: both UV stitching and ultrasonic cutting were used to create a complex preform for a Buick Riviera bumper beam. 2.3.4 Surface Quality Because composite monocoques require structural composites with Class A surfaces, a significant barrier is producing components with both high fiber-volume fractions and smooth, porosity-free exteriors. If soft tooling is used to capture strategic advantages or to ensure compatibility with E-beam curing for cycle-time reductions, the challenge of obtaining Class A surfaces becomes more complex and important. While Class A surfaces could be difficult for structural composites, they are by no means impossible. The stitch-bonded fabric described above for complex preforms wets out easily and has a surprisingly smooth surface, as it is made up of unidirectional layers, so subject to resin consistency and tooling surface quality, it could simply be surface-finished with a Class A mold and painted, saving the investment and operation costs of conventional steel finishing prerequisite to painting exterior BIW parts. An even simpler approach could also avoid painting by applying one of several proprietary lay-in-the-mold Class A colorcoat polymer products, or perhaps inject a thermoplastic colorcoat into a Class A mold and then lay in the structural elements behind it using a compatible resin system. 3. OVERCOMING THE BARRIERS The results of these surveys led one set of interviewers to conclude that since “the adoption of structural composites faces multiple barriers, no one simple quick fix will rapidly accelerate their deployment.” Yet despite complex implementation details, there is a relatively simpleif un- expectedconceptual framework to integrate advanced composites into automaking. The most effective way to overcome the barriers appears to be replacing todays dominant strategy of incremental, part-by-part materials substitution with a whole-system-designed, all-advanced- composite BIW. This “l(fā)eapfrog” approach integrates a clean-sheet design, high-performance raw materials, 3 existing manufacturing methods, and a radically simpler and smaller assembly process. It holds promise of bypassing many barriers and of changing automakers attitude toward advanced composites from a “necessary evil” or indefinitely postponable inconvenience into a prompt and lucrative opportunity. Ways to circumvent major barriers are surveyed next. 3.1 Cost Component-by-component substitution of composites for steel cannot occur until market-determined material prices justify substitution on a single-part basis, either through cheaper manufacturing or through saved gasoline, with little if any credit for mass decompoundingand even for the saved steel itself. The substituted materials remain costly, however, because only small volumes are being bought. Credit should be, but is not always, taken for the modest reductions in parts count; as a result, thinking in component terms-makes it hard or impossible to quantify saved assembly costs. Finally, integration of a composite component within a steel BIW can raise overall assembly costs, especially if the composite parts cycle times are longer or their dimensions and other properties are more variable. As a result, integration requirements often economically favor compression molding over RTM, leading to parts with suboptimal performance for demanding structural applications. In contrast, clean-sheet whole-platform redesign can yield radical reductions in parts count, size, and complexity: the typical BIW would have only a few parts, and assembly effort would drop by an order of magnitude. Buying the special materials in bulk should yield discounts and, through increasing production volumes, cut market prices .Production volumes could be optimized for convenience and market demand, rather than artificially inflated to meet amortization requirements for steel tools and presses. Production flexibility could be retained not only in volume but also in styling. Finally, savings could accumulate “downstream” from BIW manufacturing through a much smaller and simpler driveline and other components, shorter product cycle times, and greater production flexibility. 3.2 Safety Advanced composites have fundamentally different energy absorption characteristics and failure modes than steel. They fit uncomfortably into the traditional safety-design paradigm, especially when applied by steel-oriented designers who treat advanced composites as “black steel”. Inadequate redesign can yield suspect composite parts, creating an impression of poor safety. However, clean-sheet design of an all-composite BIW can take advantage of these materials unique properties, including, in proper shapes, specific energy absorption five times that of steel. Equivalent safety for an ultralight, using superior materials and design to compensate for light mass, requires a new design approach implementable only at the system level, not in isolated components alone. To explicate the design paradigm for an all-composite BIW, RMI is currently preparing a primer on ultralight composite-based car safety principles and praxis. 3.3Risk Less widely perceived than the risk of leapfrogging to an all-composite BIW is the inherent and often ruinous risk of the present BIW manufacturing infrastructure. Its inherently high fixed costs and low variable costs make profits extremely sensitive to sales volumes, endangering income whenever demand falters. Furthermore, the high fixed costs impel large production runs, which shrink model variety and focus more risk on the market success of each model. Long product cycles, too, make new models lag behind dynamic public tastes, further heightening the risk of disastrous ventures. Conventional component-based use of composites, forced into the same paradigm, could carry similar risks. In contrast, soft-tooled, net-shape advanced-composite monocoques could offer strategic advantages with a precisely opposite risk profile. The tooling could be cheaply fabricated with few parts, 4 inexpensive materials, and only one die set per part. Presses could be inexpensive and low pressure; assembly, drastically simplified; tolerances, tens of microns or better. The resulting production process could have inherently low fixed costs and higher variable costs. The low fixed costs could permit and encourage many small runs of highly differentiated products that diversify the market-risk portfolio. The extremely short tooling cycles and frequent tool replacement or refurbishment could foster continuous improvement and very rapid market-matching evolution. Successes could then be quickly identified and capitalized upon, putting slow-cycle competitors at a significant strategic disadvantage. 4. CONCLUSIONS The technology needed for the competitive mass production of automotive BIWs as advanced-composite monocoques is essentially at hand. Optimizing the technology suite requires further development, but as part of normal industrial evolution: the techniques required to progress from adequate to optimal manufacturing are a neednot a significant barrier. The real barrier is automakers cultural reluctance, for understandable reasons such as their unfamiliarity with advanced composites, to adopt a leapfrog design approach that reveals advanced composites major advantages in this high-volume application. An incremental strategy may lower short-term risk but could lead to “set-up-to-fail” ventures because of advanced composites awkward fit into the steel infrastructure. While understanding the value of whole-system design for advanced composites may be simple, overcoming the cultural inertia of incrementalism will involve a complex, detailed multi-tiered strategy. Key steps could include, but are not limited to, educating automakers on advanced materials benefits and design strategies; establishing a common materials, process, and testing database to facilitate standardization and integrate technologies; collaboration among firms in the advanced materials industry, potentially to develop manufacturable, optimized BIW designs such as AISIs ULSAB; coordinated, long-term cooperation between the auto and advanced composites industries along the lines of the RTM partnership between Dodge and APX for the Viper; refocusing projects from strategic organizations such as the ACC and ATP from component-specific to whole-BIW designs; and establishing futures markets to stabilize material prices. Overall, the potential for rapid market emergence of ultralight-hybrid “hypercars” provides a powerful driver for the development of mass-optimized, all-advanced-composite BIWs. Moreover, the potentially decisive competitive manufacturing and marketing advantages of whole-systems design and net-shape, flexible, and fast-cycle manufacturing make the production of ultralight BIWs attractive without external driversand could even allow them to go full-circle and motivate ultralight-hybrid production. Although adopting a clean-sheet approach to design and materials selection involves an admittedly high level of uncertainty in the short run, those adopting an incremental strategy could be at much greater risk as time passes: failure to lead, let alone quickly emulate, competitors leapfrogs could be a “bet-your-company” strategy. The wreckage of the mainframe computer industry should have taught everyone the importance of killing ones own products with better new ones before someone else does. Automakers are especially at risk in this case because many of their potential competitors may not yet have appeared on the radar: smart, hungry aerospace engineers in Southern California, Seattle, Switzerland, or Singapore may be the automotive version of the next Apple or Xerox. Yet past innovations such as the GM Ultralite and Impact, the Ford Composite Intensive Vehicle, and the Chrysler Patriot and Viper4 confirm that with vision and will, a leapfrog design strategy combined with the right technologies can be turned into rapid learning and successful products. America happens to lead (or at least tie) in all the capabilities needed to do this with advanced materials and hypercars. Visionary leaders in the U.S. advanced materials and auto industry are starting to 5 understand the importance of strong and prompt actions to capture that new high ground first. This may well become the central challenge of the late 1990s and beyond for the nations best materials and process engineers. REFERENCES 1. N.A. Gjostein, “Technology Needs Beyond PNGV,” Basic Research Needs for Veh