隨著北美汽車市場(chǎng)對(duì)啟停系統(tǒng)的接受程度日益增加，各家廠商開(kāi)始考慮借助鋰離子電池、超級(jí)電容、48V“輕混”系統(tǒng)等一系列技術(shù)，應(yīng)對(duì)相當(dāng)車輛頻繁啟停，通常每天多達(dá)超過(guò)20次的工況。簡(jiǎn)單來(lái)說(shuō)，啟停系統(tǒng)的工作原理是通過(guò)減少發(fā)動(dòng)機(jī)空轉(zhuǎn)，達(dá)到降低車輛燃料消耗和排放的目的。
即使是最不可撼動(dòng)的鉛酸電池也開(kāi)始進(jìn)化了。如今，過(guò)去幾十年來(lái)最常用的傳統(tǒng)電池正逐漸被支持深度循環(huán)(deep-cycling)功能的增強(qiáng)型富液式蓄電池（Enhanced Flooded Battery，下簡(jiǎn)稱EFB）和吸附式玻璃纖維隔板（Absorbent Glass Mat，下簡(jiǎn)稱AGM）電池所取代。雖然電子元件的快速普及也是一個(gè)因素，但造成這一趨勢(shì)的關(guān)鍵原因還是在于啟停系統(tǒng)的崛起，而啟停系統(tǒng)會(huì)對(duì)電池的快充功能和使用壽命提出更高要求。
“一般而言，較大的12V AGM電池的使用壽命是傳統(tǒng)電池的4倍，這對(duì)汽車啟停系統(tǒng)目前的推廣非常重要。”通用汽車(GM)啟停系統(tǒng)全球總監(jiān)Kathi Walker表示，“鋰離子電池的應(yīng)用可在近期成為現(xiàn)實(shí)。”
雖然鋰離子電池可能終有一日會(huì)成大氣候，但目前由于其過(guò)于高昂的價(jià)格，并不適合用作車輛啟動(dòng)、照明和打火供電的主要電源。不過(guò)，鋰離子電池仍然可以在動(dòng)力系統(tǒng)之外發(fā)揮作用。
“如果要綜合考量性能與成本，鉛酸蓄電池和高級(jí)鉛酸電池仍是世界上最適合內(nèi)燃機(jī)汽車的電源技術(shù)，而且這一情況在未來(lái)10年內(nèi)不會(huì)改變。”全球最大的鉛酸蓄電池供應(yīng)商江森自控(Johnson Controls)動(dòng)力解決方案部高級(jí)市場(chǎng)&技術(shù)戰(zhàn)略師Craig Rigby表示，“這就是說(shuō)，我們可以通過(guò)新增鋰離子電池等技術(shù)，提高鉛酸電池的燃料經(jīng)濟(jì)性，以支持制動(dòng)動(dòng)能回收等更多的車內(nèi)電動(dòng)功能。”
目前，啟停系統(tǒng)正是驅(qū)動(dòng)汽車電池領(lǐng)域轉(zhuǎn)型的主要推力。美國(guó)阿崗國(guó)家實(shí)驗(yàn)室曾在2015年發(fā)布了一份研究報(bào)告，分析啟停系統(tǒng)對(duì)車輛啟動(dòng)系統(tǒng)元件壽命的影響，其中也包括電池。研究顯示，傳統(tǒng)富液式鉛酸啟動(dòng)器電池的使用壽命與很多因素有關(guān)，其中受車輛啟動(dòng)次數(shù)的影響最小。事實(shí)上，真正影響電池使用壽命的因素，是發(fā)動(dòng)機(jī)頻繁啟停時(shí)不能充分為蓄電池充電，以及發(fā)動(dòng)機(jī)在停止?fàn)顟B(tài)下的過(guò)度放電。由于放電深度的影響，每次發(fā)動(dòng)機(jī)熄火時(shí)，車內(nèi)輔助設(shè)備的耗電對(duì)電池使用壽命的影響最大，也最直接。如果電池可以在發(fā)動(dòng)機(jī)兩次啟動(dòng)之間充分充電，上述的耗電對(duì)電池的影響幾乎可以忽略不計(jì)，甚至可以認(rèn)為根本就不會(huì)產(chǎn)生影響。
與此形成對(duì)比的是，阿崗國(guó)家實(shí)驗(yàn)室的研究結(jié)果顯示，無(wú)論發(fā)動(dòng)機(jī)的啟動(dòng)次數(shù)如何，如果車輛的電池一直無(wú)法達(dá)到滿充狀態(tài)，電池就會(huì)更快發(fā)生故障。研究同時(shí)發(fā)現(xiàn)，由于交流發(fā)電機(jī)的功率輸出較低，發(fā)動(dòng)機(jī)怠速時(shí)并不能為電池進(jìn)行有效充電，而駕駛過(guò)程中的充電效果最佳。（詳見(jiàn)以下鏈接http://www.anl.gov/energy-systems/publication/stop-and-restart-effects-modern-vehicle-starting-system-components。）
對(duì)于電氣系統(tǒng)設(shè)計(jì)師而言，為頻繁重新啟動(dòng)的發(fā)動(dòng)機(jī)提供電力僅是需要面對(duì)的挑戰(zhàn)之一。為了讓消費(fèi)者接受帶有啟停系統(tǒng)的車型，保證車內(nèi)音響和照明功能處于恒定狀態(tài)非常重要，這就需要12V電池所扮演的“緩沖”角色。
“在啟動(dòng)時(shí)，車輛的電系會(huì)經(jīng)歷一次電壓驟降，從而導(dǎo)致車內(nèi)照明變暗等狀況。”Walker表示，“為了保證車內(nèi)照明等功能的穩(wěn)定性，車輛可以采用多種技術(shù)，保護(hù)車內(nèi)元件不受電壓驟降的影響，從而在車輛啟動(dòng)過(guò)程中保證消費(fèi)者的滿意度。這些技術(shù)包括雙電池設(shè)計(jì)、DC/DC轉(zhuǎn)換器和超級(jí)電容等。”
目前，市面上已經(jīng)出現(xiàn)了多款采用雙電池系統(tǒng)的車型，這種設(shè)計(jì)可以支持車內(nèi)大量的耗電功能與應(yīng)用。由于如今的車輛不僅采用了很多復(fù)雜的節(jié)能技術(shù)，而且還應(yīng)用了多種多樣的安全功能，這種雙電池的設(shè)計(jì)也將日益普遍。
舉例而言，2016款2.5L雪佛蘭邁銳寶的啟停系統(tǒng)正是采用了雙電池設(shè)計(jì)：一塊12V電池位于發(fā)動(dòng)機(jī)蓋之下，另一塊則安裝在車尾。系統(tǒng)（為了加快啟動(dòng)速度而搭配了一個(gè)串聯(lián)螺線圈啟動(dòng)器）經(jīng)過(guò)特別校準(zhǔn)，當(dāng)車輛內(nèi)燃機(jī)停止工作時(shí)，第二塊電池可以接收信號(hào)立刻接管車內(nèi)的輔助系統(tǒng)供電負(fù)載，比如照明、空調(diào)、音響、車窗和門鎖的功能。此外，即使發(fā)動(dòng)機(jī)停止工作，車輛的空調(diào)此時(shí)仍然可以正常運(yùn)行，只不過(guò)會(huì)轉(zhuǎn)換為低功率模式。
“雙電池系統(tǒng)可以在多個(gè)方面體現(xiàn)自己的價(jià)值，未來(lái)這種設(shè)計(jì)將越來(lái)越普遍，”Rigby表示，“兩塊電池可以在車輛的啟停過(guò)程中提供更穩(wěn)定的電壓，還能為高級(jí)安全系統(tǒng)提供高級(jí)別的可靠性冗余。此外，這種雙電池、雙化學(xué)系統(tǒng)的設(shè)計(jì)也是性能和成本之間的最佳平衡，可以為汽車生產(chǎn)商和消費(fèi)者提供最大的價(jià)值。”
通常來(lái)說(shuō)，車輛的第二塊電池多為48V系統(tǒng)。系統(tǒng)的電壓更高，驅(qū)動(dòng)停車攝像頭和整合式傳感器等功能就越容易。雖然48V系統(tǒng)優(yōu)勢(shì)多多，但專家稱汽車行業(yè)未來(lái)可能仍會(huì)沿用12V系統(tǒng)。不過(guò)，起亞(Kia)公司曾在2016年芝加哥車展上發(fā)布了2017款Niro混動(dòng)多功能車，這款CUV并未搭配12V鉛酸電池，而是直接通過(guò)48V鋰電池組為車輛頭燈、擋風(fēng)窗雨刷等功能供電，而這些功能通常是由傳統(tǒng)的12V鉛酸電池支持的（見(jiàn)http://articles.sae.org/14614/）。
“更高的電壓可以降低系統(tǒng)的峰值電流。”德州儀器(Texas Instruments)商業(yè)發(fā)展經(jīng)理Stefano Zanella表示，“電池對(duì)其在特定安培小時(shí)內(nèi)釋放的容量和負(fù)載電流非常敏感，充分利用電池的這一特點(diǎn)，可以有效延長(zhǎng)電池使用壽命、減少電纜尺寸，從而降低成本，并減輕重量。”
Zanella解釋說(shuō)，48V系統(tǒng)必須搭配DC/DC轉(zhuǎn)換器或第二塊12V電池工作，這是由于目前的汽車采用了大量成本非常低的12V元件，汽車生產(chǎn)商一時(shí)很難將這些元件全部替換為48V元件。
除了48V系統(tǒng)，一些開(kāi)發(fā)者還選擇使用超級(jí)電容為車輛的啟停系統(tǒng)供電。這些超級(jí)電容可以在發(fā)動(dòng)機(jī)關(guān)閉期間提供電力，不會(huì)給電池造成任何負(fù)擔(dān)。
“由于超級(jí)電容在放電時(shí)并不涉及化學(xué)反應(yīng)，因此放電速度非?？?。”通用汽車的Walker表示，“2016款凱迪拉克ATS和CTS均采用了超級(jí)電容的設(shè)計(jì)，可以在車輛啟動(dòng)時(shí)提供更快的能量提升。這種能量流可以加快發(fā)動(dòng)機(jī)的啟動(dòng)速度，有助于為駕駛員提供更加流暢的再啟動(dòng)體驗(yàn)。”
這種設(shè)計(jì)可以延長(zhǎng)鉛酸電池的使用壽命。在凱迪拉克系統(tǒng)的設(shè)計(jì)過(guò)程中，通用公司與大陸集團(tuán)(Continental)合作，采用了麥克斯威科技公司(Maxwell Technologies)的超級(jí)電容，有力補(bǔ)充了車輛的電池電源，但目前高性能版ATS-V和CTS-V尚未采用超級(jí)電容的設(shè)計(jì)。
“增加一個(gè)超級(jí)電容可以顯著降低電池的啟動(dòng)電流，從而延緩電池化學(xué)材料的損耗。”麥克斯威高級(jí)產(chǎn)品營(yíng)銷經(jīng)理Jens Keiser表示，“此外，這種設(shè)計(jì)還能降低電池的峰值電流需求。”
作者：Terry Costlow
來(lái)源：SAE 《汽車工程雜志》
翻譯：SAE 上海辦公室
Powering up the new stop-start systems
As stop-start systems gain acceptance in North America, a range of technologies including lithium ion batteries, ultracapacitors, and 48-V "mild hybrid" systems are under consideration to handle the aggressive start cycles, typically more than 20 per day, that are required of these systems. Stop-start is aimed at reducing vehicle fuel consumption and emissions by reducing engine idling.
Even the venerable lead acid battery is evolving. Enhanced flooded batteries and absorbent glass mat (AGM) technologies with deep-cycling capability are slowly displacing batteries used for several decades. While the rapid expansion of electronics overall is a factor, a key reason is the rise of stop-start, which requires quick recharging and long lifetimes.
“Larger 12-volt AGM batteries, which deliver up to four times the typical life cycle of a conventional battery, are important to the current implementation of stop-start,” said Kathi Walker, GM Global Engineering Lead for Stop-Start Systems. “Lithium-ion batteries could be used in the near future.”
While Li-ion batteries may someday take over, they’re currently too expensive to displace the primary storage source for starting, lighting and ignition. However, Li-ion may expand beyond its role in electrified powertrains.
“Lead-acid and advanced lead-acid batteries continue to be the best technology for internal combustion vehicles in terms of performance and cost, and this will continue well into the next decade,” said Craig Rigby, Advanced Market & Technology Strategist at Johnson Controls Power Solutions, the largest global supplier of lead-acid batteries. “That said, fuel efficiency can be found by supplementing the lead-acid battery with other technologies such as Li-ion to deliver brake regeneration and support more electrified functions in the vehicle.”
At present, stop-start is the driving force for these changes. Research published in 2015 by Argonne National Laboratory examined the impact of stop-start systems on vehicle starter system component life, including the battery. The study revealed that the expected lifespan of a conventional flooded lead-acid starter battery is impacted minimally from the number of starting events. Rather, battery life is mostly impacted by limited charge times between frequent engine start events and from excessive discharge during engine-off events from accessory loads. The length of and the cumulative accessory power draw during each engine shutdown event has a direct and strong effect on battery longevity because of the depth of discharge. If the battery is returned to a full charge between engine starts, the effect on battery life is negligible or nonexistent.
Conversely, the ANL research showed that battery failure will occur more quickly if a full charge is never reached regardless of the number of engine start cycles. Also, idling was determined to not be an effective method of recharging the battery because of low alternator power output; driving is best. (See http://www.anl.gov/energy-systems/publication/stop-and-restart-effects-modern-vehicle-starting-system-components.)
Simply providing the power to regularly restart engines is just one challenge for electrical system designers. Keeping radios and interior lights at constant levels—a "buffering" role played by the 12V battery—is a critical factor for consumer acceptance of stop-start vehicles.
“During an auto start, there is a voltage dip in the vehicle’s electrical system,” Walker said. “In order to maintain functionality of cabin systems such as interior lights, there are technologies that can be added to a vehicle to protect the components against a voltage dip and maintain customer satisfaction during an auto start. These technologies include dual batteries, DC/DC converters and ultracapacitors.”
A handful of vehicles already use dual battery systems to support large numbers of power-hungry features and functions. It may become more common as more safety critical technologies are combined on vehicles that use complex fuel-saving techniques.
The 2016 Chevrolet Malibu 2.5-L's stop-start system, for example, uses two batteries: a 12-V battery under the hood and a second one mounted in the rear. The system (equipped with a tandem-solenoid starter for faster starts) is calibrated so that when the ICE shuts off, the second battery is signaled to handle the car's hotel loads—i.e., power the lights, climate control, audio, windows and door locks. Also, with the engine off the car's climate control remains on, albeit operating on reduced power.
“Dual battery systems will become more common as they provide value in several ways,” Rigby said. “Having two batteries provides better voltage stability during start-stop events as well as redundancy to support the high degree of reliability necessary with advanced safety systems. In addition, a dual battery, dual chemistry system allows the optimization of performance and cost to deliver the best value for automakers and consumers.”
Often, the second battery is a 48-V system. Engineering higher-voltage systems can make it simpler to power functions such as parking cameras and integrated sensors. Though going to 48V is beneficial, experts said the industry trend has been to retain the 12V systems. But at the 2016 Chicago auto show, Kia unveiled its 2017 Niro hybrid CUV, which uses its lithium battery pack to provide power for the headlights, windshield wipers, and other traditional tasks of the 12-V lead-acid battery, which has been eliminated (see http://articles.sae.org/14614/).
“Higher voltages help keeping the peak amperage down,” explained Stefano Zanella, Business Development Manager at Texas Instruments. “Batteries are sensitive to the ratio of their capacity expressed in amp hours and the load current, increasing their lifetime and reducing cable size, making them cheaper and lighter."
A 48V rail will require a DC/DC converter or a second 12V battery, he explained, because there are just too many 12V components in a car that are very cheap and cannot be effectively replaced by 48V components.
Some developers are turning to ultracapacitors to provide quick boosts for stop-start systems. They can provide power to turn the engine over without straining the battery.
“Since ultracapacitors do not rely on a chemical reaction to supply their energy, ultracapacitors can discharge their stored energy very quickly,” GM's Walker said. “The 2016 Cadillac ATS and CTS take advantage of ultracapacitors to provide a quick energy boost during the auto start. This burst of energy allows the engine to start faster and helps in providing a more seamless restart for the driver.”
This design technique can extend the lifetimes of lead acid batteries. The Cadillac system, co-developed with Continental, uses Maxwell Technologies ultracaps to augment battery power. It is not available on the ATS-V and CTS-V performance versions.
“Adding an ultracapacitor lets the battery deliver significantly lower starting currents, which leads to less degradation of the battery chemistry,” said Jens Keiser, Maxwell's senior product marketing manager. “Also, the battery sees fewer high-current peak demands.”
Author: Terry Costlow
Source: SAE Automotive Engineering
江森自控正在不斷提高AGM電池的產(chǎn)量，以滿足北美市場(chǎng)對(duì)啟停系統(tǒng)的需求。 
基礎(chǔ)款2.5L邁銳寶啟停系統(tǒng)的示意圖，其中1代表12V AGM主電池；2代表雙電池隔離模塊；3代表為了保證車輛配重平衡而安裝在車尾的12V AGM輔助電池。