現代摩比斯的阿爾耶普盧格測試基地的最高平均溫度為-7℃。基地內有一汪冰湖，占地160萬平方米，是多種汽車性能的測試場所。
- By Sebastian Blanco
SAE《汽車工程》雜志記者也趕到這里，見證全新Nexo 燃料電池版、Kona電動版及現代自主研發的HVAC關鍵系統的冬季測試。
瑞典阿爾耶普盧格市距北極圈約57公里。數十年來，這座邊遠小城已成為了一個熱鬧的汽車工業中心。自從1973年的第一場冬季測試以來，這座城市已經成為了數十家整車企業和供應商的冬季駐地。這里的冬季平均最高溫度約為19°F（-7℃），最低為3°F（-16℃）。每逢冬季，這座小城就成了工程師的天下。
當地居民將住宅出租給涌進的汽車大軍，自己搬到別人家，或是和鎮上的親朋好友一起住露營車，這種臨時生活方式是汽車動力綠色化進程必然導致的一個副效應。
在這些車企中，現代汽車（Hyundai）選擇寒冷地帶開展測試的動力尤為強烈。現代希望在2025前成為全球環保車輛市場的龍頭企業，實現這一目標的關鍵是發展純電動車和燃料電池車。而鑒于這兩種車型在低溫下的獨特性能，保證HVAC（暖通空調）系統擁有卓越的低溫性能就成為了現代的首要任務。
阿爾耶普盧格市也就這樣成為了現代功能汽車研發部主管Gunther Frank的第二故鄉。今年年初，《汽車工程》雜志受邀前往Frank團隊的冬季駐地，當時他們正在籌備全新Nexo燃料電池版和Kona電動版的量產。
FATC研發
現代HVAC系統的基礎研發主要是在韓國南陽技術研究中心的氣候室內完成。然后車輛被運到瑞典，進行場地測試和現場調校。Frank表示，低溫測試通常會持續一到兩周，接著進行同樣時長的高溫測試。而常溫測試的時間最長，可能需要三到四周，因為FATC（全自動溫度控制）系統很難實現常溫下的精確調整。
“不論是從制冷或制熱的角度來看，還是就FATC的控制而言，常溫情況都要復雜很多，”Frank表示，“當我們在一個小時內從海拔2500米（8202英尺）、氣溫很低的阿爾卑斯山區開到22-23℃（72-73°F）的山谷，控制器需要感知到溫度的變化，并做出反應。”
現代希望將FATC用于旗下所有車型，無論其采用何種動力類型。其基本構想是，駕駛員設好溫度、按下“自動調節”按鈕后，再也無需考慮開暖氣還是冷氣的問題。
“這當然是最理想的情況，但是人和人之間的差別很大，”Frank說道，“你今天的心情和另一天的心情相比，差別也會很大，我們無法創造出一個適用于所有情況的控制算法。這是一個很好的性能，但是你要確保用戶可以修改系統，因為最終一切取決于用戶的要求。”
不過對于在阿爾耶普盧格的Frank團隊而言，更重要的挑戰在于，如何在沒有傳統內燃機車輛所產生余熱的條件下，獲得穩定的熱能。現代的全新燃料電池車和純電動車均使用了高壓電子壓縮機。和舊版壓縮機不同，電子壓縮機可以獨立運轉，無需靠發動機帶動，在座艙溫度穩定之后可以關閉，進而降低能耗、提升效率。
由于高壓系統無需等暖機后再運轉，因此，和內燃機車型相比，它的制熱速度更快。“從HVAC的角度看，新型車的情況比過去好太多了，”Frank說道，“如果沒有電子制熱設備，發動機啟動后，座艙制熱要花很長的時間。有了高壓系統，我們可以讓座艙馬上變暖。”
Nexo 燃料電池版制熱系統
Nexo 是現代計劃于2018年推出的第二代燃料電池車型，和上一代途勝燃料電池版相比，Nexo電池堆棧的效率和性能都有了提升，而且所有零部件都經過了重新研發。Nexo的燃料電池系統實現了60%的效率，途勝為55%。此外Nexo還擴大了儲氫容量，目前配備三個儲氫罐，每罐容量為6.3千克（13.9磅）。這使得Nexo的續航里程在NEDC城市工況下達到了800公里（497英里），在美標工況下超過了370英里（595公里）。
雖然這些數字都只是初步測試成果，但是Nexo高級工程師Sang Ho Yoon表示，Nexo的續航里程應該比途勝燃料電池版高35%左右，后者的美標測試結果為256英里（426公里）。
Nexo的驅動和制熱都是靠同一種能源，因此研發出一個高效的HVAC系統成為了實現長續航的關鍵。電堆在冷卻時也會產生一些余熱供Nexo的HVAC系統使用，這一點和傳統內燃機車有些相似，但就整體過程而言，兩者的差別還是很大。好消息是這種差別并沒有影響Nexo的HVAC系統性能。
Frank在一個室外溫度只有-23℃（-9.4°F）的日子成功證明了Nexo的快速制熱性能，這讓他很高興。在短短三分鐘之后，一個與駕駛員胸部位置持平的溫度感應器顯示車內溫度已經達到了15°C（59°F）。
“我們的內部目標是，當環境溫度為-20℃（-4°F）時，座艙的平均溫度可以在開車后20分鐘內達到18℃（64°F），”Frank說道，“相信我，對小型內燃機車來說，要達到這個目標非常困難。而對我們的純電動和燃料電池車型而言，這將輕而易舉。”
Frank還說道，車內搭載的3.7 kW Air Side PTC（正溫度系數）熱敏電阻也是快速制熱的一大功臣。早在90年代，人們就開始研究使用PTC熱敏電阻作為車載加熱器。有些汽油車也采用了PTC熱敏電阻，例如一些三缸歐系車搭載的1Kw PTC單元。而在替代能源車輛上，PTC才真正有了用武之地。
他解釋道，“要加熱燃料電池車的座艙，第一步是加熱電堆的冷卻系統。然后，PTC就會開始為Nexo的座艙快速提供熱量。電堆溫度升高后，余熱產生，PTC的功率下降。在瑞士，我們發現PTC功率可以一直降到零。”
“當車輛狀態穩定后，制熱過程就和內燃機車很相似了。制熱系統的運行不需要額外的電能，”Frank說道，“在穩定狀態下，續航里程不會受到影響。”
現代為Nexo內部研發了一款全新的膜電組件和3D多孔流場。Yonn表示，“3D多孔流場是為Nexo電堆制定的全新概念，它可以提升能量密度，改善電堆性能。”他還說道，Nexo采用了全球最小的汽車供氫系統，因為Nexo摒棄了途勝燃料電池版的氫氣循環泵，僅靠噴嘴為電池堆的電化學反應提供氫氣。
此外，Nexo的全新熱管理系統采用了一個雙向閥門和一個四向閥門，從而改善了電堆制冷劑溫度控制的響應性。Yoon表示，這是首次在電動汽車上使用四向閥門，它可以改善Nexo的冷啟動性能。冷啟動是燃料電池汽車的硬傷，但Nexo可以達到現代旗下所有內燃機車必須通過的標準，即在-30℃（-22°F）下啟動。
而且這不是唯一Nexo可以和內燃機車相媲美的地方。據Yoon介紹，由于Nexo采用了一種全新的高度耐用膜、一種全新的電池堆鉑金催化劑以及一項全新的操控技術，因此其動力總成的額定使用壽命和現代內燃機車一樣，都是10年16萬公里（10萬英里）。
Nexo動力總成的最大輸出功率為120kW、最大扭矩為395N·m。據稱，這將使Nexo的最高時速在途勝燃料電池版的基礎上提升10%，加速性能提升25%。
Kona電動版的制熱系統
Kona電動版分為兩款。第一款的電池容量為64 kWh，續航里程為470公里（292英里），（這里所有續航里程都只是基于WLTP“世界協調車輛排放試驗規程”制定的目標數據。）功率為204hp，百公里加速7.6秒。第二款的電池容量為39kWh，續航里程為300公里（186英里），電機功率為135 hp，百公里加速9.3秒。兩款的最大扭矩都是395N·m。如果使用100kW的快充器，第一款車可在不到一個小時內充滿80%的電量，但如果使用7.2 kW Level 2充電器，充電時間將長達近10小時。
電動汽車面臨的一大難題就是根據座艙溫度調節電池溫度。Kona 電動版采用了Ionia和起亞Soul電動款的氣冷電池組，但加大了尺寸。Kona電池組的最高工作溫度為40℃（104℉）。為防止過熱，電動版采用了一個主動液冷系統和一個散熱器。如果還不能滿足要求，也可以使用座艙的空調系統來冷卻電池組。
和Nexo一樣，Kona 電動版也采用了Air Side PTC熱敏電阻，功率為5kW，此外還有一個2.7kW的熱泵。之所以采用比Nexo更強勁的PTC，是因為Kona電動版沒有燃料電池堆的余熱可供座艙制熱。不過，Kona還是可以汲取電機等其它電子零部件的熱能。
Frank說，“我們可以傳遞其它熱能來加熱座艙，這樣的話，整體加熱系統的效率都能得到提升。”
Kona熱泵系統的理想工作溫度為0℃（32℉）以上，使用空氣中的熱能來驅動AC。Frank表示，當環境溫度為0℃（32℉）、座艙溫度為23℃（73℉）時，“和關閉加熱器相比，PTC系統的熱能損失多了近40%，但由于熱泵系統可以產生超過20%的額外能量，因此整體能效會更高。”
為了讓新能源車型的用戶滿意，這些都是現代冬季測試工程師必須達成的目標。如果PTC、FATC等HVAC組成部件能在阿爾耶普盧格運作，那么其它地方就應該不是問題。要是不行，那就再回到這片嚴寒之中做更多的測試。
Kona純電動和Nexo的冰湖趣味
一輛早期原型車的駕駛體驗，往往只能幫助我們粗略猜想未來量產車的性能表現，但是在瑞典北部，開著全新的現代Nexo氫燃料電池版和Kona電動版在冰湖上疾馳，卻向我們證明了一點——環保車的調校方式不止一種。
幾乎可以肯定地說，Nexo的價格會高出Kona，這似乎是理所當然的。Nexo的懸掛更靈活，穩定控制系統更強，即使在現代的冰湖賽道上，也極少會失去抓地力。節氣門和轉向響應性雖然受到了極大的限制，但是系統可以進行迅速且強力的干預，這對于量產車型的安全性能來說是個良好的開端。車輛沒有發生太多的過度轉向，而至于轉向不足的情況，在冰面上自然是會出現的。
相比之下，Kona電動版離量產還有更長的距離。在嚴寒極限下，車輛后部噪聲十分明顯。安全控制策略的調校也有所不同，車輛可以在冰面上適度漂移。因此，在廣闊的冰面賽道的安全范圍內，駕駛電動版更有意思，這也意味著兩種車型中，電動版可能是更有樂趣的一款。
Kona電動版的重心低，駕駛穩定性好，這要感謝安裝在底板下的電池組。在濕滑路面，很難測試電動版的最快加速度。但在冰面上，當車速達到100km/h （62mph）時，車輛的扭矩表現仍十分出色，不過一旦碰到濕滑路段，就算將油門踩到底，加速效果也十分微弱。
這兩款零排放車型都采用了防滑輪胎，駕駛穩定性很好。Kona采用的是大陸215-55 R 17 V XL WinterContact TS 850P 輪胎，Nexo則選用了韓泰Winter I-cept Evo2 245/45R19 102V M+S輪胎。
AE goes way north for an inside look at Hyundai’s winter testing of the new Nexo FCV and Kona EV and their unique and critical HVAC systems.
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Arjeplog, Sweden sits around 35 miles (57 km) below the Arctic Circle, but this remote city has been a bustling hub for the automotive industry for decades. Since the first winter tests were conducted here in the 1973, the area has become a second home to a dozen OEMs and suppliers during the brutally cold winter months. Engineers take over the small town every winter when average high temperatures hover around 19°F (-7 C) and the average low is a brisk 3°F (-16 C).
To make room for the influx, residents rent out their homes to the auto industry, moving into guest rooms or in campers parked with relatives or friends in other parts of town. These temporary living situations are required as the automotive industry pushes forward to greener powertrains.
Hyundai has a particular impetus to test where it's cold. Battery EVs and fuel-cell vehicles (FCV) have unique cold-climate operating characteristics, and those propulsion types will play a major role in the company's aim to vie for the global eco-car sales lead by 2025. Ensuring optimum HVAC system cold-climate performance for EVs and FCVs is paramount.
Arjeplog, then, has become like a second home to engineer Gunther Frank, Hyundai’s head of Functional Vehicle Development. Automotive Engineering was invited to join Frank and his team in their winter lair in early 2018 as they prepared the new Nexo fuel cell vehicle and the Kona EV for production.
Developing FATC
Hyundai does most basic HVAC development work using a climate chamber at its Namyang Technology Research Center in Korea. Then the cars come to Sweden for on-site field tests and fine tuning. Frank said a car typically spends one to two weeks in cold weather testing, and the same amount of time in hot weather. It's the in-between climate that actually takes longer, maybe three or four weeks, because it's difficult to get the full automatic temperature control (FATC) system just right.
"Mild climate conditions are much, much more complex, not from the performance point of view in terms of cooling or heating, but from the control point of view of the FATC," Frank said. "In alpine regions, when we are at a height of 2,500 meters (8,202 feet) where it is quite cool, and we are driving within an hour down to the valley where we see temperatures of 22 or 23 °C (72-73°F), the controller has to be aware of the changing conditions and react."
FATC is Hyundai's end goal for all of its vehicles, no matter what powertrain they use. The basic idea is that the driver can set a temperature, push the "auto" button, and then never think of the heating or cooling settings again.
"This would be the ideal situation, having just the 'auto' button, but human beings are so different," Frank said. "The way you feel one day in comparison to the other is also so different and you are never going to be able to create a control algorithm which will fit all of them. It's a very nice feature, but you have to make sure that the customer has the possibility to overwrite the system, because finally it's up to them."
The more important challenge for Frank and his team in Arjeplog, though, is getting consistent heat without the waste heat from a traditional ICE. Both of Hyundai's new fuel cell and all-electric vehicles use high-voltage electronic compressors. Unlike older compressors, which needed to run off of engine RPM, the electronic compressors can be run independently. They can also be turned off when the cabin climate is stable, which then reduces the load on the energy source and thus leads to increased efficiency.
The high-voltage systems can also heat up the cabin faster than an ICE, since they don't need a warm engine to work. "From the HVAC point of view, it's a much, much better situation than in the olden days," Frank noted. "If you don't have an electronic heating device, when you start your engine, it takes a very long time until the cabin becomes warm. With our high-voltage systems, we have the possibility to immediately warm up the cabin."
Heating the Nexo FCV
The Nexo is the Hyundai's second-gen fuel-cell vehicle, arriving some time in 2018. It follows the Tucson FCV and has increased fuel cell stack efficiency and performance. All of its components are newly developed. In fact, the Nexo achieves 60% fuel cell system efficiency, compared to the Tucson's 55%. Based on this improvement, along with an increase in the hydrogen storage available on board (three tanks that each hold 6.3 kg (13.9 lb) of hydrogen, the Nexo's driving range could reach over 800 km (497 mi) in NEDC city mode, and over 370 miles on the U.S. test cycle.
These numbers are preliminary, but Nexo senior engineer Sang Ho Yoon said the driving range would be around a 35% increase over the Tucson fuel cell. That vehicle is rated at 265 miles in the U.S.
The same energy used to move the car is needed to heat it, so developing an efficient HVAC system is important to achieving long range. While there are similarities between the HVAC system in the Nexo and a standard ICE vehicle – there is some free heat energy available because the stack needs to be cooled down – the overall process is quite different. The good news is that different also works.
Frank happily proved the Nexo's rapid heating power on a day when the outside ambient temperature was -23°C (-9.4 F). After just three minutes in the prototype, a breast-level temperate sensor showed it was 15°C (59 F) in the car.
"We have an internal target that with an ambient temperature of -20 C (-4 F), the average cabin temperature should reach an average of 18°C (64 F) after 20 minutes of driving," Frank said. "Believe me, it's quite tough to fulfill that with low-capacity internal combustion engine cars. With our full EV cars or with our fuel cell car, we are able to reach that target much, much faster."
Part of that quick heat comes from a 3.7-kW Air Side positive temperature coefficient (PTC) thermistor. The use of PTC thermistors as heaters in cars has been studied since at least the 1990s and they are used today in some gas cars, especially 1-kW units in 3-cylinder European vehicles. With alternative powertrain models, PTCs have really come into their own, Frank explained.
The first step to warming a fuel cell car's cabin, Frank explained, is to heat up the cooling system of the stack. While this happens, the PTC offers quick heat in the Nexo's cabin. Once the stack is warmed up and able to provide some excess heat, the PTC's power is reduced, even down to zero in the conditions we experienced in Sweden.
"When the car is in a stable condition, it's similar to internal combustion engine cars and we don't need additional electronic power to run the heating system," he said. "In stable conditions, there is no influence on driving range."
Hyundai developed a new membrane electrode assembly and 3D porous flow field in house for the Nexo. "The 3D porous flow field is a new concept for the Nexo stack," Yoon said. "It can improve the stack performance for power density." Yoon said the Nexo uses the world's smallest hydrogen supply system for automotive use because it does away with the hydrogen recirculating pump required in the Tucson fuel cell and only uses an ejector to supply hydrogen for the electrochemical reaction within the fuel cell stack.
A new thermal management system means improved response time to control the coolant temperature of the stack thanks to a two-way and a four-way valve. The four-way valve is a world's first for electric vehicles, Yoon said, and it improves the Nexo's cold-start ability. Cold starts are traditionally difficult for fuel cell vehicles, but the Nexo can start at ambient temperatures of -30°C (-22 F), the same threshold the company's ICE vehicles must pass.
That's not the only way the Nexo will function like an ICE. Thanks to a new, highly durable membrane, a new platinum catalyst in the stack, and a new operating control technology, Yoon said the durability rating for the new fuel cell powertrain warranty will cover 160,000 km (100,000 mi) and 10 years, just like the company's ICE vehicles.
The Nexo's powertrain has a maximum power output of 120 kW and 395 N·m. This will improve top speed by a claimed 10% and acceleration performance by 25%, compared to the Tucson FCEV.
Heating the Kona EV
The Kona EV will come in two flavors, a 64-kW·h model with up to 470 km (292 mi) of range (all range numbers here are just targets, and are based on WLTP homologation). This model offers 204 hp and a 0-100 km/h (0-62 mph) time of 7.6 seconds. The 39-kW·h model will get up to almost 300 km (186 mi) on a charge with a motor that generates 135 hp and hits 100 km/h in 9.3 seconds. Both powertrain versions deliver 395 N·m. On a 100-kW fast charger, the 64-kW·h battery can be charged to 80% in less than one hour. A 7.2-kW, Level 2 charger will take almost 10 hours to fully charge the larger pack.
One challenge with electric vehicles is that the battery temperature needs to be moderated along with the cabin. The Kona EV uses battery packs that are bigger than the ones used in Hyundai's Ioniq and Kia Soul EVs, which are air-cooled. The Kona's battery pack shouldn't get hotter than 40°C (104 F), which is why the battery in the Kona EV uses an active liquid cooling system in combination with a radiator to keep it from overheating. If this is not sufficient, the cabin's AC system can be used to cool down the battery as well.
Like the Nexo, the Kona EV prototype uses an AirSide PTC – this time a 5-kW unit – along with a 2.7-kW heat pump. A more powerful PTC is needed because there's no waste heat from a fuel cell stack to help warm the cabin. The Kona EV does manage to siphon some heat energy off of the electronic components, including the motor.
"We are able to transfer it and use that energy to warm up the cabin and to increase the efficiency of the overall heating system," Frank noted.
The heat pump system uses some heat energy from the air, ideally at ambient temperatures above 0°C (32 F), which then runs the AC drive cycle. At an ambient temperature of 0°C (32 F) and a cabin setting of 23°C (73F), "we are losing about 40% in comparison to heater off when we have a PTC system, but we are able to create 20% more energy with the heat pump system and therefore to increase the efficiency," Frank said.
Those are the numbers that Hyundai's winter test engineers have to crunch to keep drivers of their new powertrain vehicles happy. If the PTC and the FATC and all the rest can work in Arjeplog, chances are they will work in other parts of the world. If not, it's back to the cold for more testing.
Frozen-lake driving in a fuel cell car
Driving an early prototype gives only a hint of what the finished vehicle will act like, but spinning the upcoming Hyundai Nexo hydrogen fuel cell and the Kona EV around a frozen lake in northern Sweden prove there's more than one way to tune an eco car.
The Nexo, as seems appropriate for what will almost certainly be the more expensive of the two models, has a softer suspension and an aggressive stability control system that prevented the FCEV from ever really losing its footing, even when speeding around Hyundai's circular ice track. Throttle and steering response were dramatically limited and the system's interventions were early and substantial, which bodes well for the safety of the eventual production vehicle. There was not a lot of oversteer and there wasn't much to do about the understeer in the icy circumstances.
The Kona EV, on the other hand, felt further from production ready, with plenty of noise coming from the back when pushed to the frozen limits. The safety control strategy is also tuned different here, allowing us to mildly drift the car on the lake. This meant more fun on the safe confines of the expansive ice track, and it means the EV might be the more fun of the two models.
Thankfully, the Kona EV's floor-mounted battery creates a low center of gravity that helps keep the car firm locked onto the track. It was difficult to test out the EV's flat-our acceleration on the slippery surfaces, but the impressive torque got the tires spinning on the ice, even when we were already at 100 km/h (62 mph). Even so, pushing the accelerator pedal all the way to the floor didn't do much once the system detected slippery conditions and neutered our input.
Thanks in part to their grippy tires, both zero-emission vehicles kept their composure. The Kona rode on Continental 215-55 R 17 V XL WinterContact TS 850P tires, while the Next wore Hankook’s Winter I-cept Evo2 245/45R19 102V M+S.
Author: Sebastian Blanco
Source: SAE Automotive Engineering Magazine
SAE《汽車工程》雜志記者也趕到這里，見證全新Nexo 燃料電池版、Kona電動版及現代自主研發的HVAC關鍵系統的冬季測試。
阿爾耶普盧格的一個溫暖的木屋里，工程師們正在檢查當天的數據。
上圖為Nexo燃料電池電堆，下圖為Nexo的空氣處理系統。中間帶有棱紋的是加濕器/空冷器模塊。其右側中間紫色部分是離心氣泵。
燃料電池版的電堆能量加熱使用循環：第一步，COD（陰極氧消耗）加熱器加熱電堆制冷劑；第二步，PTC加熱器提供主要熱能；第三步，隨著制冷劑溫度的升高，PTC加熱器功率下降，達到節能效果；第四步，當制冷劑加熱器溫度足夠提供熱量后，關閉PTC加熱器。
Nexo熱能管理系統首次使用了使用四向閥門，它可以改善電堆制冷劑溫度控制的響應性。