經(jīng)德爾福測算，48V輕混系統(tǒng)能夠以30%的成本達成純電動汽車二氧化碳減排目標的70%。
德爾福認為48V輕型混合動力系統(tǒng)可以顯著降低二氧化碳的排放量，造福未來的汽車行業(yè)。在2015年法蘭克福車展上，德爾福全球先進電氣與電子架構(gòu)總監(jiān)Christian Schäfer告訴《汽車工程雜志》，現(xiàn)在的許多技術(shù)驅(qū)動力都是在最近15年出現(xiàn)的。
“最主要的動力來自歐盟的規(guī)定，歐盟各國必須在2021年前讓平均車隊二氧化碳排放量降至95 g/km，”他表示。“我們的想法是，既然我們已經(jīng)有一種輕混系統(tǒng)，那么就不必在所有車輛上安裝高壓電機了，因為這種方案造價太高。我們可以在較低的車型級別里使用48V系統(tǒng)，甚至是C級車。如果車輛沒有后驅(qū)裝置，那么我們可以用一種皮帶驅(qū)動的啟動器/交流發(fā)電機作為電機增壓設(shè)備，也就是說，用交流發(fā)電機來提高內(nèi)燃機的功率。”
德爾福認為，汽車啟動后的最初100 米（328英尺）內(nèi)可以用電力驅(qū)動。
Schäfer強調(diào)，再生制動技術(shù)將成為降低二氧化碳排放的主要方式。
“從我們的經(jīng)驗以及和歐洲各OEM的討論結(jié)果來看，目前標稱功率在10-12 kW之間的測試車隊在搭載了48V交流發(fā)電機之后，二氧化碳排放量下降了7-10%。下一代驅(qū)動系統(tǒng)的輸出功率將上升至20 kW，我們預(yù)測二氧化碳可以減少15%。”
德爾福認為，除了可以降低二氧化碳排放之外，將低壓轉(zhuǎn)換成高壓還有別的好處。某些系統(tǒng)（如動態(tài)底盤控制）帶來的車輛功率負載更高。“電流峰值將會很高，因此不能使用12V系統(tǒng)，” Schäfer表示。
此外，Schäfer表示，許多OEM的目標是取消發(fā)動機中的所有皮帶驅(qū)動附件，但交流發(fā)電機除外。這意味著HVAC壓縮器、動力轉(zhuǎn)向泵和冷卻劑泵等系統(tǒng)都將由這個48V系統(tǒng)來驅(qū)動。
48V系統(tǒng)可將皮帶驅(qū)動的附件精簡至一臺啟動器/交流發(fā)電機，并為自動駕駛汽車提供失效保護系統(tǒng)的供電。
“有皮帶，就意味著將會產(chǎn)生很多摩擦，比如在高速公路上，動力轉(zhuǎn)向泵是處于最高速度的，但其實并不需要這么高，” Schäfer表示。因此可以將動力轉(zhuǎn)向泵做成一種“按需提供速度的”電力驅(qū)動系統(tǒng)。“這是另一種可以降低少量CO2排放的方法。”
對那些無法滿足2021年歐盟CO2排放標準的汽車制造商而言，在安裝了一個48V系統(tǒng)后，至少可以將排放水平降至處罰線之下。德爾福在和多家OEM的討論中發(fā)現(xiàn)，20-70%的混合動力車都將配置一個48V的輕型混合動力系統(tǒng)。德爾福認為，純電動汽車的銷量增長情況并沒有達到2009年和2010年時人們做出的預(yù)期，這種情況就是其原因之一。“你現(xiàn)在可以用30%左右的成本實現(xiàn)60-70%的目標，” Schäfer說。
現(xiàn)在德爾福正在研發(fā)48V系統(tǒng)所需的電氣部件，其中包括一個3kW的DC/DC48-12 V轉(zhuǎn)換器。
“最重要的是，這是一個雙向裝置。交流發(fā)電機所在的48V端在產(chǎn)生了3kW的功率后，將其傳向12V端，為電池、乘員舒適性功能、照明系統(tǒng)和傳統(tǒng)設(shè)備等供電，” Schäfer解釋道，“但是為了讓一輛12V的車升至48V，我們也配備了一個增壓模式，將1kW標稱功率從12V轉(zhuǎn)換至48V。” 德爾福的這一設(shè)備將推出氣冷和液冷兩種選項。
該設(shè)施的其他部件還包括符合最高防水標準與抗震標準的48V 電氣連接器。此外，德爾福還計劃為48V系統(tǒng)設(shè)計一個警示色碼，用以提醒用戶這不是一個12V系統(tǒng)。目前認為48V應(yīng)該標成藍色。
德爾福預(yù)計在2016年開始生產(chǎn)48V電氣分配器，輸出電流為40安培。另外公司還在研發(fā)一款采用一種名為MOSFET的半導(dǎo)體熔線的智能48V分配器，預(yù)計于2017年投產(chǎn)。
“智能熔斷是能夠檢測48V電板和12V電板上所有故障模式的唯一方法，” Schäfer稱。它采用的原理是電弧檢測，因為傳統(tǒng)電氣熔斷絲太危險了。
德爾福使用一種算法來檢測電弧。“我們必須區(qū)分‘好的電弧’和‘壞的電弧’”，Schäfer說，“好的電弧是繼電器電弧。如果繼電器處于斷開狀態(tài)，那么會電弧將一直保持著2毫秒。如果時間超過10毫秒，那我們就會關(guān)閉開關(guān)，但只關(guān)掉特定線路而非整個48V分配器。”
12-48V變電系統(tǒng)也會為未來的自動駕駛系統(tǒng)提供一定程度的電力冗余，以便配備失效保護系統(tǒng)。
作者：John Kendall
來源：SAE《汽車工程雜志》
翻譯：SAE 上海辦公室
Delphi says 48-volt mild-hybrid systems could offer 15% CO2 reductions
48-volt mild hybrids could offer 70% of the CO2 reduction benefits of battery electric vehicles at 30% of the cost, reckons Delphi.
Delphi believes that 48-volt mild hybrids could offer significant CO2 reductions and driver benefits for cars in the future. Speaking at the IAA 2015 (Frankfurt Motor Show), Christian Schäfer, Global Director of Advanced Electrical and Electronic Architectures at Delphi, told Automotive Engineering that there are several drivers for the technology that were not present 15 years ago.
“The main driver is the carbon dioxide threshold of 95 g/km fleet average in 2021 across the European Union," he said. "The idea is that we have a mild hybrid, so we don’t need high-voltage on all cars because it is too expensive to implement. We would have 48-volts, especially in the low segment, up to C-segment cars. Then we could have a belt-driven starter/alternator and can use it as an e-boost if you don’t have a rear drive unit, so the alternator is an electrical machine to boost the combustion engine.”
Delphi envisages that the car would start with electric propulsion for the first 100 m (328 ft) of movement.
Regenerative braking would be the main path to reduce CO2 emissions, reckons Schäfer.
“From our experience and our discussions with European OEMs, we have seen between 7 and 10 percent reductions in CO2 emissions from the current test fleet with today’s 48-volt alternators, which have a nominal power of between 10 and 12 kW. For the next generation with up to 20 kW, we expect that we could increase the CO2 reduction to 15%.”
Besides the CO2 reduction potential of 48-volt systems, Delphi sees other reasons to switch to the higher voltage electrical architecture. Some systems, such as dynamic chassis control, would impose a high power load on the car. “You would have high current peaks, so you can’t do it with a 12-volt system,” said Schäfer.
In addition, the aim of many vehicle OEMs, according to Schäfer, is to remove all belt-driven ancillaries from the engine with the exception of the alternator. This would mean that all these systems—such as the HVAC compressor, power steering pump, and coolant pump—would be driven electrically from the 48-volt system.
A 48-volt system could reduce belt-driven ancillaries to the starter/alternator and offer a fail-safe electrical architecture for autonomous driving.
“With the belt, you have a lot of friction; for instance on the highway, you have the highest speed on the power steering pump, but you don’t need it,” said Schäfer. Then power steering could be an “on-demand” electrically driven system. “That’s another way you can reduce CO2 emissions by a small amount.”
The penalty charges that would be imposed on manufacturers who might struggle to comply with the 2021 EU CO2 emissions average could at least be offset by fitting a 48-volt system. From the discussions that Delphi has already had, between 20 and 70 percent of all hybrids will be produced with a 48-volt mild-hybrid system. The company thinks that it is a reason why the growth in battery-electric vehicles is not as strong as was expected in 2009 and 2010. “You can reach about 60 to 70 percent of the targets with around 30 percent of the cost,” said Schäfer.
Delphi is already working on the electrical components that would be required for a 48-volt architecture. This includes a 3-kW DC/DC 48/12-volt converter.
“The important thing is that it is a bi-directional device, producing 3 kW from 48 volts where the alternator is, to the 12-volt side to support the battery and all the comfort functions, bulbs, and traditional equipment,” explained Schäfer, “But to make a jump start possible from a 12-volt car to a 48-volt car, we have a boost mode as well to transform 1 kW nominal power from 12- to 48-volts.” Delphi will produce the device with both air and liquid cooling options.
Other components include waterproof 48-volt electrical connectors that meet the highest waterproof and vibration-resistant standards. Delphi also plans to introduce color-coding for 48-volt systems to warn users that this is not a 12-volt system. The suggestion is that 48-volt systems should be coded blue.
Delphi expects to begin production of a 48-volt electrical distributor in 2016 that will provide a 40-amp output. A smart 48-volt distributor, incorporating a semi-conductor MOSFET fuse, is already in development, with production planned for 2017.
“Smart fusing is the only chance to detect all failure modes which could occur on a 48-volt and 12-volt board,” said Schäfer. This would include electrical arc detection, because it could be too dangerous to use conventional electrical melting fuses.
An algorithm is used to detect arcing. “We have to distinguish [between] 'good arcs' and 'bad arcs,'” said Schäfer, “The good arcs are the relays. If a relay is open, there is always an arc for around 2 ms. If we have more than 10 ms, we would switch off and then only the dedicated path and not the complete 48-volt system.”
A 48-volt architecture in combination with 12-volt system also offers a level of electrical redundancy for future autonomous driving systems, where a failsafe system would be required.
Author: John Kendall
Source: SAE Automotive Engineering Magazine
