對于美國的大部分地區來說2019年的冬天是一個非常難熬的冬天。北極寒流極地渦旋夾帶著驟強暴風雪橫掃了美國中西部地區，甚至在通常氣候溫和的圣迭戈、洛杉磯以及拉斯維加斯氣溫也創下了歷史新低。這對于越來越多的電動汽車擁有者來說絕對是一個壞消息，因為他們已經發現在極端溫度下電動汽車的續航里程及充電時長都會受到不同程度的影響。
Henry Payne是一名底特律新聞的汽車評論家，他有一輛Tesla Model 3，Henry表示：“在寒冷的日子里，Model 3的續航里程至少減少了30%。”當然這不僅僅是他感受到了這種變化，Timothy Grewe 通用汽車電動推進實驗室的首席工程師也感受到了，他有一輛全新的雪佛蘭Bolt電動車，他說：“通常情況下，Bolt在充滿電的情況下跑個270英里（432公里）是沒有問題的，但是溫度掉到負數時只能跑170英里（272公里）”
純電動汽車在寒冷天氣的續航里程問題，一直以來都是用戶所關注的問題，也是在社交媒體上的常見話題。因此一些新的研究正試圖量化這些影響。結果顯示，當氣溫低于冰點時部分車輛的續航里程損失達到50%以上，但如果駕駛者關閉座艙加熱系統的話情況會相對好一點。
AAA 美國汽車協會研究
最近的兩項研究之一，同樣也研究了高環境溫度對續航里程的影響，我們發現熱量也會影響續航但不會達到在寒冷天氣時的那種程度。但即便如此，續航里程的降低不僅對車主造成了嚴重的影響，同樣對于那些在未來的數年里準備向市場推出數十款電動化新車型的汽車制造商來說問題也一樣嚴重。他們已經在這上面投資了數百億美元，任何可能讓消費者降低對電池技術吸引力的事情，都可能使得收回這些投資變得更加困難。
“我們發現溫度對于電動汽車的影響遠遠超出我們的預期，”AAA汽車工程總監Greg Brannon說，“對于所有計劃部署推出電動汽車的制造商來說，這是他們必須要處理的事情。”AAA總共測試了BMW i3，雪佛蘭Bolt EV，日產Leaf，特斯拉 Model S和大眾電動高爾夫這五款來自不同品牌的電動車型。AAA的工程師對每輛車分別進行了20°F（約零下6.7°C）以及95°F（35°C）的環境下的測試。
Brannon表示，事實證明這些車輛對熱條件的反應非常相似，當室外溫度在20°F（約零下6.7°C）且未開啟座艙加熱系統的情況下續航里程平均減少12%，這個下降幅度還是在可接受范圍之內。但是一旦啟動空調系統，續航里程則會平均下降41%，換句話說EPA核定范圍為200英里（380公里）續航里程的純電動汽車在這種情景下只能行駛118英里（188.8公里）。
這些數字還不能完全反映潛在的續航里程損失，這里還沒有考慮在冬季通勤時還會打開座椅或者方向盤加熱或是打開前照燈的情況，駕駛者可以切實體會到這些影響，此外不僅僅是續航里程減少他們會還支出更多的費用。根據AAA估計，一位典型的美國純電動汽車車主每1,000英里（1,600公里）可能需要多支出24.27美元（約合165元人民幣）。該研究團隊同樣還進行了在極熱天氣下的實驗測試，當氣溫達到95°F（35°C），如果駕駛員愿意忍受酷暑，那么續航里程僅下降4%，但是一旦開啟空調將直線下降17%。
(以電耗為例，美國EPA組織一直以能耗作為一輛汽車的重要指標，并設定了“MPG”值作為考量標準，而在新能源汽車“MPGe”的計算上，“e”代表的是每加侖汽油能行駛的英里數。將“汽油”轉換為了“電”，換算后就變成每“33.7度”電可以行駛多少英里。)
消費者聯盟研究
消費者報告雜志的出版商消費者聯盟（Consumers Union）也進行類似的測試，其報告對AAA的調查作出了相同的回應。消費者聯盟挑選了2款電動車進行了測試，一輛是特斯拉Model 3 EPA核定續航里程310英里（496公里），另一輛是日產的Leaf EPA核定續航里程151英里（241.6公里）。本次測試時室外平均氣溫在0-10°F（約零下17.8 ~零下12°C）的情況下進行。
當特斯拉實際行駛了64英里（102.4公里）后，續航里程表顯示減少了121英里（204.8公里），剩余電量大概還可以行駛189英里（302公里）。而日產的表現更差，實際行駛了64英里（102.4公里）后，續航里程表顯示“燒了”141英里（225.6公里），當測試結束時其續航里程表上顯示僅剩10英里（16公里）。
電池適宜溫度
AAA的Brannon表示，部分問題在于“鋰離子電池和我們喜歡同樣的溫度，大約是70°F（21°C）左右。”如果外部溫度遠低于此，那么用于儲存能量的化學物質會遇到各種問題。通用汽車的Grewe解釋說，除此之外，電池組件還會產生越來越大的阻力，從而限制了它們可以承受的功率，以及電池組的充放電速度。
我們針對現代汽車 Kona做了一次明顯不科學的測試，在底特律室外溫度20°F（零下6.7°C）的一天，我們使用SAE L3級50-kW充電器對它進行充電測試，45分鐘后里程表顯示僅從31英里（49.6公里）充到了110英里（176公里），這幾乎是汽車制造商在理想條件下承諾的一半。
在AAA進行研究測試的5個品牌中僅有特斯拉對結果表示異議，其發言人表示：“根據我們車隊獲得的實際數據顯示，Model S在室外溫度20°F（零下6.7°C）的情況下沒有消費者反應續航里程發生減少的情況發生，而在95°F（35°C）的情況下也僅減少1%。”但是來自日產Leaf項目的高管Carl Phillips表示：“毫無疑問溫度會對電動汽車的續航里程有所影響，且所有的電動車在寒冷天氣中表現都很相似。”
行業專家表示，電動車主可以通過很多種方式避免續航里程的減少。大多數純電動車輛在插入充電器時可以“預先調節”，比如駕駛員可以利用電網電能，在出門用車前使用智能手機應用程序或是信息娛樂系統的內置軟件啟動座艙加熱系統給車輛升溫。同時汽車制造商還鼓勵駕駛員在冬季里，可以使用座椅和方向盤加熱系統減少對空調系統的依賴。
AAA方法論
AAA與洛杉磯南加州汽車研究中心（ARC）的汽車俱樂部合作，針對在使用和不使用HVAC系統的情況下，環境溫度對電動車行駛里程的影響進行了初步研究。本次測試使用到了以下設備：安培小時計，OBD-II掃描工具和測力計。
在選擇本次測試車輛時預先設立了一套標準，比如該車型需要在全美國都有銷售，EPA核定續航里程不少于100英里（160公里）。為防止單一品牌的過度代表，每家制造商僅可有一輛車參與測試。
It’s been a tough winter in much of the U.S. When the Midwest hasn’t been dealing with a Polar Vortex it been smacked by a “bombogenesis.” But even normally temperate seasonal regions like San Diego, Los Angeles and Las Vegas have been hit with harsh and, in some cases, record cold this year. That’s particular bad news for the growing number of owners of battery-electric vehicles who have discovered the impact extreme temperatures can have on both range and charging times.
“I’m consistently seeing a 30% degradation” in range on cold days, said Henry Payne, an automotive reviewer for The Detroit News and owner of a Tesla Model 3. He’s by no means alone. “I can get 270 miles [range] no problem,” from his Chevrolet Bolt EV with a fresh and fully charged battery, said Timothy Grewe, chief engineer at General Motors’ electric propulsion lab. But Grewe notes that when temperatures fell into negative territory, “I got around 170.”
The issue of cold-weather range has been a subject of concern among BEV owners for some time, and a frequent topic on social media. But several new studies have attempted to quantify the effects. The results are significant, showing that some vehicles lose more than 50% of their range in sub-freezing temperatures, though drivers can mitigate the losses if they’re willing to limit their use of cabin heating.
AAA study
One of the two recent studies also looked at the impact of high ambient temperatures and found that heat, too, can draw down range, though not to nearly the extend that cold does. Even then, degradation of range poses potentially serious problems not only for EV owners but for the automakers who are rushing dozens of new electrified offerings to market over the next few years. They’re investing tens of billions of dollars and anything that could reduce the appeal of battery-based technology could make it more difficult to recover those investments.
“We found that the impact of temperature on EVs is significantly more than we expected,” said Greg Brannon, AAA’s director of automotive engineering. “It’s something all automakers are going to have to deal with as they push for further EV deployment because it’s something that could surprise consumers.” The organization tested five separate models: the BMW i3, the Chevrolet Bolt EV, the Nissan Leaf, the Tesla Model S and the Volkswagen e-Golf. AAA engineers subjecting each car to both 20-degree F cold and 95-degree F heat.
The vehicles proved surprisingly similar in their response to the thermal conditions, said Brannon. He noted that, on average, they lost about 12% of their range on the cold side. That was a relatively modest decline, but it did not include the use of any form of cabin heating. When HVAC systems were activated, the range degradation averaged 41%. In other words, a BEV with an EPA-rated range of 200 miles would get only 118 miles between charges.
And those numbers don’t fully reflect potential range loss, as they don’t factor in the use of seat or steering wheel heaters or headlights during winter commutes. The impact is felt by motorists in various ways. Not only can they travel less per charge, but they also pay more. AAA estimated a typical American BEV owner would pay an extra $24.27 per 1,000 miles. The group’s study also examined what happens on extremely hot days. At 96 degrees F, range dipped 4%--if the driver was willing to sweat it out. With the HVAC turned on, range degradation climbed to 17%.
Consumers Union study
The AAA findings were largely echoed by a separate study conducted by Consumers Union, the publisher of Consumer Reports magazine. It focused on two EVs—the Tesla Model 3 with a 310-mile EPA rating, and the 151-mile version of the Nissan Leaf. Testing was conducted at the CU track on days when the outside temperature averaged between 0 to 10 degrees F.
The Tesla used up the equivalent of 121 miles to cover 64 actual miles of driving, leaving it with a displayed range remaining of 189 miles. The Nissan fared even worse, “burning” 141 miles of stated range to travel those 64 miles. At the end of the test, the second-generation Leaf had only 10 miles showing on its range display.
Electric habitable zone
Part of the problem, said the AAA’s Brannon, is that “lithium-ion batteries like the same sort of temperatures that we do, around 70 degrees.” Much below that and the chemistry used to store energy runs into various problems. Among other things, battery components develop increased resistance that limits how much power they can hold, as well as how fast a battery pack can be charged or discharged, explained GM’s Grewe.
A decidedly unscientific test of a Hyundai Kona on a 20-degree F day in Detroit found it was only able to go from 31 to 110 displayed miles after being plugged in for 45-minutes to a 50-kW SAE Level 3 charger. That’s barely half what the automaker normally promises under ideal conditions.
Of the five brands included in the AAA range study, only Tesla raised any real concerns with the results. “Based on real-world data from our fleet,” said a spokesperson, “the average Model S customer doesn’t experience anywhere near that decrease in range at 20 degrees Fahrenheit, and the decrease in range at 95 degrees Fahrenheit is roughly 1%.” That said, Carl Phillips, a Nissan executive working on the Leaf program, said there is no question, “temperature has an impact” on range, adding that “all EVs perform similarly in cold weather.”
There are some ways that an owner can reduce range degradation, according to industry experts. Most battery-electric vehicles can be “pre-conditioned” when they are plugged into a charger. That means a motorist can use a smartphone app or software built into the infotainment system to start warming the vehicle’s cabin up before they leave home, office or store, using grid energy. Automakers also encourage drivers to reduce their winter reliance on the HVAC system and stay warm using seat and steering wheel.
Percent change in cost for 1000 miles of combined urban/highway driving relative to 75°F
AAA methodology
AAA conducted primary research in partnership with the Automotive Club of Southern California’s Automotive Research Center (ARC) in Los Angeles to understand impacts of ambient temperature on electric vehicle driving range with and without the use of the HVAC system. Testing was conducted using the following equipment: ampere-hour meter, OBD-II scan tool and dynamometer.
Test vehicles were selected using a pre-determined set of criteria such as availability for sale throughout the United States with a minimum EPA estimated driving range of 100 miles. One vehicle per manufacturer was tested to prevent overrepresentation of a single brand. Additional information on methodology can be found in the full report.
Author: PAUL A. EISENSTEIN
Source: SAE Automotive Engineering Magazine
在溫差75°F（約41.7°C）且關閉空調的情況下測試，續航里程百分比變化。(圖片來源：AAA)
在溫差75°F（約41.7°C）且關閉空調的情況下測試，，MPGe百分比變化。(圖片來源：AAA)
在溫差75°F（約41.7°C）開啟空調的情況下測試，續航里程百分比變化。(圖片來源：AAA)
在溫差75°F（約41.7°C）開啟空調的情況下測試，MPGe百分比變化。(圖片來源：AAA)
在溫差75°F（約41.7°C）情況下測試，1,000英里（1,600公里）城市及高速公路綜合工況下成本變化百分比。