啟停系統(tǒng)在歐洲已非常成功，但著重于美國(guó)市場(chǎng)的研發(fā)團(tuán)隊(duì)仍致力于達(dá)到最佳燃油效率和舒適性。在消費(fèi)者滿意度評(píng)級(jí)方面，順暢的再啟動(dòng)和對(duì)調(diào)頻廣播音量的影響也位列最大挑戰(zhàn)之中。
啟停系統(tǒng)在歐洲和日本的應(yīng)用已十分普遍，但北美市場(chǎng)的接受度仍然有限。由于油價(jià)較低，4-10%的燃油節(jié)約量并非很有吸引力，并且啟停系統(tǒng)的噪聲較大，重啟時(shí)有抖動(dòng)現(xiàn)象，也影響了其推廣。但隨著法規(guī)的落實(shí)，以及系統(tǒng)越來越精密，這些情況可能會(huì)有所改變。
“系統(tǒng)使用率比2007-08年的預(yù)測(cè)值低很多，但隨著燃油使用效率標(biāo)準(zhǔn)（CAFE）的制定，使用率應(yīng)該會(huì)快速提升，”IHS汽車動(dòng)力系統(tǒng)預(yù)測(cè)總監(jiān)Devin Lindsay表示。“系統(tǒng)已經(jīng)降低發(fā)動(dòng)機(jī)運(yùn)行的噪聲和抖動(dòng)感了，今后很多系統(tǒng)會(huì)設(shè)計(jì)一個(gè)按鈕，駕駛員可以選擇關(guān)閉這個(gè)功能。”
美國(guó)的汽車制造商正在努力為消費(fèi)者提供更多選擇。啟停系統(tǒng)將成為通用汽車多款2016凱迪拉克車型的標(biāo)配?？蛻糁R(shí)普及和技術(shù)進(jìn)步將成為影響啟停系統(tǒng)發(fā)展的兩個(gè)非常重要的因素。
“啟停技術(shù)發(fā)展的最大難題就是進(jìn)行客戶知識(shí)普及，我們需要讓客戶了解系統(tǒng)的工作方式，這樣他們才會(huì)更認(rèn)可這種技術(shù)，”通用汽車啟停系統(tǒng)全球工程主管Kathi Walker表示。“從設(shè)計(jì)的角度來說，保持整個(gè)汽車平臺(tái)的快速、無縫的自動(dòng)啟動(dòng)是非常有挑戰(zhàn)性的。”
通用汽車使用了大陸公司（Continental Automotive Systems）的電壓穩(wěn)定系統(tǒng)，該系統(tǒng)配置了麥克斯威科技公司（Maxwell Technologies）的超級(jí)電容器，有助于穩(wěn)定電流，并在啟動(dòng)器開始發(fā)動(dòng)時(shí)保證廣播和空調(diào)正常運(yùn)行。此外，超級(jí)電容器也可以減輕發(fā)動(dòng)機(jī)的振動(dòng)，使重啟更加順暢，并且可以降低影響電池壽命的重復(fù)循環(huán)次數(shù)。
超級(jí)電容器也有助于通用汽車達(dá)到一系列低溫環(huán)境的技術(shù)要求。相關(guān)部件配有等效串聯(lián)電阻（ESR），因此車輛的冬季操作性能得以優(yōu)化。
“在低溫環(huán)境中，電池的ESR有所增高，因此啟動(dòng)器所需的啟動(dòng)功率低于正常重啟操作的要求，” Maxwell高級(jí)產(chǎn)品營(yíng)銷經(jīng)理Jens Keiser表示。“超級(jí)電容器的ESR在-40攝氏度以上的環(huán)境中都很穩(wěn)定。”
不論在何種溫度環(huán)境中，發(fā)動(dòng)機(jī)啟動(dòng)時(shí)，電壓通常會(huì)下降到4-6 V左右。一些對(duì)電壓、電流有較高要求的系統(tǒng)會(huì)受此影響，比如娛樂信息節(jié)目系統(tǒng)，與其他數(shù)字裝置不同，該系統(tǒng)的很多部件不能在3.3 V或1.8 V的低壓環(huán)境中運(yùn)行。
“比較棘手的領(lǐng)域之一是音頻系統(tǒng)，”意法半導(dǎo)體公司（STMicroelectronics）市場(chǎng)研發(fā)部的首席工程師Bill Cleaver表示。“音頻系統(tǒng)的很多敏感模擬部件需要在5V的電壓環(huán)境中操作，比如AM/FM調(diào)諧器和功率放大器，這些部件有固定阻坑，需要用高電壓維持聲級(jí)。如果音樂太響，音量會(huì)下降，除非功率系統(tǒng)中有增壓支持裝置。”
為了解決這些問題，通用公司將超級(jí)電容器裝配到凱迪拉克系統(tǒng)中，有助于減小電池尺寸，并降低重量。
“車輛啟動(dòng)時(shí)，能量需求是很低的，但功率需求卻非常高，所以必須增加電池尺寸，以便滿足這些高功率要求，” Keiser表示。“通過添加超級(jí)電容器滿足高功率要求，可以減小電池尺寸，并著重滿足能量需求。超級(jí)電容器的功率密度約為常規(guī)鉛酸蓄電池的六到十倍。”
最大的挑戰(zhàn)來自主流的美國(guó)市場(chǎng)，也就是自動(dòng)檔的內(nèi)燃機(jī)車型。我們需要確保在這種車型上系統(tǒng)可以順暢地順暢，并且要保證合理的成本。
“所有混合動(dòng)力車都有控制元件，所以很容易實(shí)現(xiàn)系統(tǒng)順暢運(yùn)行，” 意法半導(dǎo)體公司汽車產(chǎn)品部（APG）MCU營(yíng)銷高級(jí)總監(jiān)Roger Forchhammer表示。“但如果不是混合動(dòng)力車，成本會(huì)劇增。”
許多電池制造商正在竭力實(shí)現(xiàn)穩(wěn)健增長(zhǎng)。在城市，車輛在行駛中重啟發(fā)動(dòng)機(jī)的情況，要求電池壽命更長(zhǎng)，充電速度更快。據(jù)預(yù)計(jì)，在配有啟停系統(tǒng)的車輛中，吸附式玻璃纖維隔板電池（AGM）和增強(qiáng)型富液式電池（EFB）技術(shù)的應(yīng)用將穩(wěn)健增長(zhǎng)。
“我們預(yù)計(jì)，到2020年，啟停系統(tǒng)將覆蓋40%的新車，江森自控（Johnson Controls Power Solutions）的高級(jí)市場(chǎng)技術(shù)策略師Craig Rigby表示。“主流汽車制造商紛紛表示要大力發(fā)展啟停系統(tǒng)，并將其作為新的動(dòng)力傳動(dòng)基本策略。我們已經(jīng)開始努力擴(kuò)大AGM和EFB電池的容量，以便滿足日益增長(zhǎng)的需求。”
作者：Terry Costlow
來源：SAE《汽車工程雜志》
翻譯：SAE上海辦公室
Can turning off the engine turn customers on?
Stop-start systems have seen success in Europe, but development teams focused on the U.S. market are still working to get the right combination of fuel efficiency and comfort. Smooth restarts and radio volume are among for biggest challenges for garnering desired customer satisfaction ratings.
Stop-start is common in Europe and Japan, but acceptance in North America has been limited. The 4-10% fuel savings hasn’t been a big lure given fairly low fuel prices and noticeable noise and shuddering during restarts. That may change as regulations take hold and systems become more sophisticated.
“Adoption has been much slower than people anticipated back in 2007-08, but it should go forward quicker because of the CAFE credits available,” said Devin Lindsay, Powertrain Forecasting Director at IHS Automotive. “Systems have reduced the feeling when the engine engages, and many will have a button that lets the driver turn the function off.”
U.S. carmakers are increasing their offerings. General Motors is making stop-start a standard feature on many 2016 Cadillac models. Customer education and technology are both critical factors in the future of the technology.
“The most challenging part of the stop-start technology is educating the customers so they understand how the system works and they become more accepting/comfortable with the technology,” said Kathi Walker, GM Global Engineering Lead for Stop/Start Systems. “From a design perspective, repeatability of quick and seamless auto starts across vehicle platforms is very challenging.”
GM uses Continental Automotive Systems’ voltage stabilization system, which employs Maxwell Technologies’ ultracapacitors. The ultracapacitor helps maintain current to keep radios and air conditioners running when the starter is cranking. It also lessens engine vibration to smooth out restarts while reducing repeated cycling that can shorten battery life.
The ultracapacitor also helps GM meet requirements in cold environments. These components have equivalent series resistance (ESR) capabilities that give them better winter performance.
“In cold temperatures, the battery ESR is increasing and therefore, cranking power for the starter is below what is required for a reliable restart,” said Jens Keiser, Senior Product Marketing Manager at Maxwell. “The ESR of ultracapacitors is stable until -40 degrees Celsius.”
Regardless of the temperature, voltage levels often fall to around 4-6 V when the engine is started. That can impact systems that have higher voltage and current requirements such as infotainment, where some components don’t have the low 3.3 or 1.8 V levels of many digital devices.
“One of the trickiest areas is the audio system,” said Bill Cleaver, Principal Engineer, Market Development at STMicroelectronics. “A lot of sensitive analog parts in the audio systems operate at 5V—things like the AM-FM tuner and power amps, which have a fixed impedance so they need higher voltages to maintain sound levels. If music is loud, volume will be reduced unless you have boost support built into the power system.”
Concerns like these prompted GM to include ultracapacitors in the Cadillac system. That helps reduce battery size and weight.
“The energy demand of a cranking event is very low, but the power demand is very high, therefore the battery has to be oversized to meet these high power requirements,” Keiser said. “By adding an ultracapacitor to address the high power requirements, the battery can be downsized and focus on the energy demands. Ultracapacitors have approximately six to 10 times the power density of the typical lead-acid battery.”
The challenges are greatest in the mainstream of the U.S. market: internal combustion engines with automatic transmissions. The systems needed to ensure that restarts occur smoothly are a fair cost-adder.
“Any hybrid vehicle has the controls, so it’s easy to keep everything running,” said Roger Forchhammer, Senior Manager, Automotive Product Group (APG) MCU Marketing at STMicroelectronics. “If it’s not a hybrid, there’s a significant cost bump.”
Some battery makers are ramping up for solid growth. Restarting engines during city driving will require longer lifetimes and quicker recharging. Absorbent glass mat and enhanced flooded battery technologies are expected to see solid growth in vehicles with stop-start.
We expect it to reach 40% of new vehicle production by 2020,” said Craig Rigby, Advanced Market & Technology Strategist at Johnson Controls Power Solutions. “All the major automakers have indicated the move to start-stop as the new baseline powertrain strategy. We have already committed to expanding the capacity for AGM and EFB batteries to meet the increasing demand.”
Author: Terry Costlow
Source: SAE Automotive Engineering Magazine
Maxwell的超級(jí)電容器有助于通用汽車和其他整車商設(shè)計(jì)啟停系統(tǒng)，可實(shí)現(xiàn)順暢啟動(dòng)，而無需降低廣播音量。