如今，無處不在的12V電池可能會迎來一個新伙伴：48V。最近，工程師開始逐步掃清48V電氣系統中存在的種種問題，預計該架構將在未來幾年實現井噴式發展。
“現在我們關心的是48V系統的普及速度，”全球市場調研公司Strategy Analytics汽車電子高級分析師Kevin Mak表示，“技術問題并不是問題，廠商的產品周期才是。現階段，48V系統在美國要面臨的唯一問題在于如何在提升燃料經濟性的同時控制成本預算。”
現階段，較高電壓電系可以為啟停系統等“用電大戶”供電，日后還可能驅動空調和電加熱催化器等更多車上應用。與電氣傳動系統上采用的高電壓電系相比，48V系統的關鍵優勢之一在于可在相對簡潔的設計下提供更多能量，從而提升車輛的燃料經濟性。
“從成本方面來看，48V系統的優勢之一在于廠商并不需要為服務人員和急救人員提供高壓隔離保護系統，而60V以上電氣系統就必須配備了。”IAV汽車工程商業部總監Jason McConnell表示，“典型的12V系統最高僅能輸出3kW功率，而48V的功率輸出則可達12kW，是前者的4倍。”
封裝挑戰
支持者認為，憑借種種優勢，48V除了可以按照最初設計為啟停系統供電外，未來還可以扮演更多角色。比如，再生制動系統可以節約能源，車輛可以關掉空調等“用電大戶”節省能量。另外，48V的組件（包括電機）和布線也更加節省空間。
“要讓12V的設備輸出6kW功率，你的電流必須達到500A。”Richardo公司混動和電動系統工程運營部經理Tomasz Salamon表示，“連續輸送這么大的電流，你肯定需要非常粗的電線。但當你升到48V電系時，同樣輸出6kW只需要125A電流，這樣你就可以大幅縮減電線等零部件的尺寸。最終，我們將逐漸看到越來越多的組件開始選擇48V系統，這可以節省安裝尺寸、提高能效，還能提供更大的功率。”
如何平衡成本是48V所要面臨的真正挑戰。大多數開發人員表示，為了發揮48V的所有優勢，我們必須仔細審視所有的細微之處。另外，系統的優化必須從全局入手，我們必須整體考慮多種系統和參數的影響。
德爾福汽車工程副總裁Mary Gustanski表示，“如果你不關注車輛架構優化和能源管理系統，就一定會錯過很多東西。”
盡管48V的實施并不復雜，但一些細節問題很有可能讓整個設計“功虧一簣”。首先，第一個問題是找到安裝硬件設備的空間，現今車輛的前蓋下方、座椅下面和后備箱里基本都沒有什么剩余空間。
“現在的主要挑戰在于組件整合，為DC-DC逆變器和電池尋找一個‘容身之地’。”大陸汽車動力技術與創新主管Brian McKay表示，“封裝和機械集成非常重要。”
尺寸更小的12V電池?
雖然汽車領域會出現新的電源，但基本電力架構并不會發生巨大改變。一般來說，傳統的交流發電機將被皮帶式啟動器發電機所取代，由后者負責通過DC-DC逆變器為電池充電。未來較長一段時間內，很多現有車輛組件仍將由鉛酸電池供電。
江森自控（Johnson Controls Power Solutions）動力系統技術研究員Tom Watson表示，“我們預計，短期來看，采用48V系統的車輛仍將保留12V的發動機冷啟動啟動器，而48V電機則主要負責發動機熱起來之后的二次啟動任務。”
“這意味著12V電池仍需承擔冷啟動負載。”Watson表示，“隨著架構和技術的不斷成熟，未來48V電機可能會成為發動機的唯一電源。這樣一來，12V電池的任務量將有所減輕，廠商也因此可以采用尺寸和容量更小的12V電池。”
高壓電氣系統架構的設計和實現需要大量關注細節。雖然，對于這些高電壓混動和電動車而言，安全并不是最需要擔心的問題，但的確仍存在一些需要考慮的地方。
德國FEV公司電氣動力系統研發與測試經理Soumendu Chanda表示，“如何應對48V系統固有電弧作用帶來的風險，以及如何保證車輛的再生制動系統可以滿足所有的扭矩安全需求，這些都是汽車廠商在廣泛采用48V之前必須考慮的問題。”
不過，通常這些高電壓系統均可適用于多條汽車產品線，這是開發人員值得高興的事。另外，對于這些必須嚴格執行預算的工程師來說，封裝絕對算的上最大的設計挑戰之一。
“人們希望實現技術集成，把電池以及換流器與逆變器中的電子元件統統放進一個盒子里，因此你必須減少布線。”McConnell表示，“48V適用于大量車型，絕大部分設計都很容易實現重用和擴展。”
未來架構
隨著一些技術開始從豪車向主流車型下滲，成本方面的考慮開始變得更加重要。未來，預計與歐洲地區“熱火朝天”的場面相比，48V系統在美國的推廣可能要暗淡很多，這主要是因為節省燃油對北美用戶并沒有這么重要。
“我們最大的障礙是如何在預算之內提供具有吸引力的靈活解決方案。”Salamon表示，“48V系統仍需要一定時間，直到組件價格下落到一定水平才能登陸更多平價車型。”
也許，性能比價格問題更加重要。早期啟停系統一直由于重啟過程動靜太大而備受指責。如今，大多數設計團隊均專注于確保電機和發動機的順利配合，盡量減少整個過程對駕駛員的影響。
“校準必須非常精準——你必須確保客戶可以接受發動機從‘滑行’進入‘重啟’階段的響應延遲。”McKay表示，“皮帶式啟動器發電機的啟動延遲不能超過400毫秒。”
對于系統設計師來說，如何保證電池的充電也是一個關鍵問題。設計師在權衡設計時必須考慮到再生制動系統的需求。許多開發人員認為，隨著電系的不斷演進，啟動器發電機也將不斷發展，并最終在降低風阻的同時回收更多能量。
“當前的48V系統一般會將發電機集成在傳動帶上。”Watson表示，“如果采用皮帶式發電機，則發動機必須一刻不停的運轉，驅動發動機的轉動。這意味研發人員必須在發動機通過“航行”或“滑行”狀態節省的燃料與車輛制動回收系統造成的發動機摩擦之間做出平衡。”
Watson表示，“隨著時間的推移，車輛發電機可能會直接整合在傳動或動力系統內，這樣一來，無論發動機處于何種狀態，系統隨時都可以進行制動回收。”
作者：Terry Costlow
來源：SAE《汽車工程》雜志
翻譯：SAE中國辦公室
Design simplicity is key to new 48-V systems
The ubiquitous 12-volt battery may soon have a partner. Engineers are ironing out the kinks in 48-volt architectures being employed to power demanding systems, sparking expectations that deployment will skyrocket over the next few years.
“This is mainly a question of how rapidly it will be adopted,” said Kevin Mak, a Senior Analyst for Automotive Electronics at Strategy Analytics. “It’s not much of a technical issue, it’s more the OEM product cycles. The only issue in the U.S. is that it’s difficult to justify the cost premium for additional fuel economy.”
Higher voltage systems enable power-hungry functions like start-stop, with potential to drive many more like air conditioning and electrically heated catalysts. A key benefit is that the extra energy, which can be used to help fuel economy, comes with far fewer design challenges compared to high voltage systems found on today’s electrified powertrains.
“One significant benefit on the cost side is that this is below the 60-V threshold for isolation and protection for service personnel and first responders,” said Jason McConnell, Business Unit Director at IAV Automotive Engineering. “A typical 12-V system is limited to a maximum of around 3 kilowatts, when you go to 48-V, power increases by a factor of four to around 12 kW.”
Packaging challenges
Proponents say the technology’s benefits extend beyond its initial role of powering start-stop systems. Regenerative braking conserves energy. High power systems like air conditioning can be turned off, conserving energy. 48-V components including motors and wiring can be smaller.
“To get six kW from a 12-V machine, you need around 500 amps,” said Tomasz Salamon, Engineering Operations Manager for Hybrid and Electric Systems atRicardo. “That’s a lot of current, you need very thick wires for continuous operation. When you upscale to 48 V, 500 amps becomes 125 amps, so you can significantly reduce the size of components. Eventually we’ll see more components going to 48-V, which gives you smaller and more-efficient electrical components—and more power capability.”
Getting the biggest bang for the buck can be a real challenge. Most developers say that many subtleties must be examined to gain all the available benefits. Optimization requires taking a broad view that includes many different systems and parameters.
“If you don’t focus on vehicle architecture optimization and an energy management system, you’re leaving a lot on the table,” said Mary Gustanski, Vice President of Engineering at Delphi Automotive.
While the complexity of implementing a 48-V system may be comparatively minor, the devil’s in the details. One of the first hurdles is figuring out where to put all the hardware. There’s not much room under the hood, under seats or in the trunk.
“The main challenge is integrating components, finding space for the dc-dc converter and the battery,” said Brian McKay, Head of Powertrain Technology and Innovation at Continental Automotive. “Packaging and mechanical integration are very important.”
Smaller 12-V batteries?
Although there will be a new power source, the basic power architecture won’t change dramatically. Conventional alternators will typically be replaced by a belt-starter-generator that will recharge both batteries via the dc-dc converter. Many existing components will be powered by lead acid batteries—for a while.
“We expect near term 48-V vehicles to retain the 12-V starter for cold engine cranking while the 48-V motor/generator will manage the restarts with a warm engine,” said Tom Watson, Technical Fellow, Powertrain, at Johnson Controls Power Solutions.
“This means the 12-V battery still needs to meet cold-crank loads as well," Watson said. "As the architecture and technology matures, the 48-V motor/generator may become the sole source of cranking the engine in all conditions, in which case the 12-V battery may reduce in capacity and size.”
Devising and implementing these architectures requires plenty of attention to detail. Though safety concerns are nowhere near those for high voltage hybrids and electric vehicles, some issues must be examined.
“The increased risk of arcing inherent in a 48-V system, and ensuring that a regenerative braking strategy meets all torque safety requirements, are some of the safety considerations that should be addressed before widespread adoption of 48-V systems,” said Soumendu Chanda, Manager, Electrified Powertrain Development & Testing at FEV.
One bright spot for development teams is that systems can often be used on a range of vehicle lines. Packaging will be among the design challenges facing engineers who are striving to meet stringent pricing goals.
“People are looking to integrate technologies, putting the battery, power electronics from the inverter and the dc-dc converter in one box so you’ve got less cabling,” McConnell said. “48V technologies can be adopted over a large number of vehicles; there’s definitely reusability and scalability in most designs.”
Future architectures
Cost considerations will become more important as the technology migrates from luxury to mainstream vehicles. Projected U.S. adoption has paled compared to Europe, largely because the fuel savings are less important in North America.
“The biggest hurdle is making feasible solutions at price points that are appealing to customers,” Salamon said. “It will take time until components hit lower prices so they’re accessible to lower price vehicles.”
Performance is perhaps more critical than pricing. Early start-stop systems drew plenty of criticism for rough, noticeable restarts. Most design teams are focused on making sure that electric motors and engines work smoothly together so drivers barely notice transitions.
“Calibration needs to be precise—you need to get dialed in to ensure that customers are pleased with the response times when they go from engine-off coasting to restarting the engine,” McKay said. “There can’t be more than a 400-millisecond delay for the belt- starter-generator to turn on.”
Keeping the batteries charged is another important parameter for system designers. Regenerative braking is an important factor when engineers are making design tradeoffs. Many developers feel that as power architectures evolve, the starter generator may migrate to a spot that regains more energy while reducing drag.
“Current 48-V systems typically integrate the motor/generator on the belt,” Watson said. “With a belt-driven motor/generator, the engine will always need to spin to drive the motor/generator. This means a tradeoff is needed between the fuel savings of 'sailing' or coasting and regen braking which will inherently bring with it engine friction even if the engine is not running.
"You may see a shift over time to motor/generators that are embedded in the transmission or driveline so that regen braking can be performed no matter what the engine state is,” he observed.
Author: Terry Costlow
Source: SAE Automotive Engineering Magazine
在大陸（Continental）的48V架構中啟動發電機將取代交流發電機