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伊頓和BAE系統(tǒng)公司（BAE Systems）合作研發(fā)了一款配備BAE電子組件和伊頓四速變速箱的電動(dòng)動(dòng)力總成。

長(zhǎng)期以來(lái)，OEM一直大力宣傳純電動(dòng)車無(wú)需使用變速箱等部件，因?yàn)殡姍C(jī)提供了足夠的瞬時(shí)扭矩，不再需要使用其他設(shè)備在選定減速比的基礎(chǔ)上提供更多的扭矩增益。然而，汽車行業(yè)發(fā)現(xiàn)這一概念在特定的應(yīng)用場(chǎng)景中存在局限性。

在連續(xù)坡道或高速公路上運(yùn)載重物時(shí)，純電動(dòng)車的直驅(qū)電機(jī)的效率和續(xù)航里程可能會(huì)迅速降低。雖然可以通過(guò)增加電池和電機(jī)尺寸來(lái)提升負(fù)載能力，但這會(huì)增加車輛的成本和重量，導(dǎo)致問(wèn)題變得更加嚴(yán)重。

為解決這一問(wèn)題，伊頓和BAE系統(tǒng)公司共同研發(fā)了一種解決方案，該方案不僅為純電動(dòng)卡車提供了更大的靈活性，還可以使用尺寸較小電池組和電機(jī)，并同時(shí)實(shí)現(xiàn)與同等燃油卡車相當(dāng)?shù)男阅堋?/span>

Webb總結(jié)，“許多部件都可能出現(xiàn)故障，不僅會(huì)增加成本和復(fù)雜性，還會(huì)增加制造難度。我們盡可能集成和應(yīng)用多種先進(jìn)的商業(yè)化材料技術(shù)，以提高產(chǎn)品散熱性能和工作效率，從而簡(jiǎn)化產(chǎn)品的制造、安裝和服務(wù)過(guò)程。”

伊頓集成到測(cè)試卡車上的變速箱只有四個(gè)檔位，這比常見(jiàn)內(nèi)燃機(jī)卡車和輕型車輛的檔位數(shù)量要少得多。Hopkins解釋道，“因?yàn)殡姍C(jī)的運(yùn)行范圍比發(fā)動(dòng)機(jī)廣得多，因此無(wú)需那么多檔位。總之，我們已經(jīng)找到了滿足市場(chǎng)需求的最佳解決方案。”

Webb繼續(xù)說(shuō)，“這樣一來(lái)，一個(gè)核心模塊就可以服務(wù)于多個(gè)市場(chǎng)，這不僅提升了所有核心功能的通用性，還降低了非重復(fù)性工程成本（NRE），從而使OEM和最終用戶都能受益。考慮到平臺(tái)電氣化成本高昂，通用性核心功能將惠及整個(gè)行業(yè)。”

在伊頓試驗(yàn)場(chǎng)特意建造的土路上進(jìn)行坡道測(cè)試時(shí)，該卡車也展現(xiàn)出穩(wěn)定的性能，沒(méi)有出現(xiàn)塵土飛揚(yáng)的情況。不過(guò)，由于車輛在完全停止的狀態(tài)下也能將扭矩拉滿，因此即使掛在一檔上，開(kāi)足馬力仍會(huì)令車輪在低摩擦系數(shù)路面上打滑。但這輛原型車的電門(mén)經(jīng)過(guò)了精心校準(zhǔn)，因此后輪打滑不會(huì)引起嚴(yán)重的揚(yáng)塵。

One of the advantages that OEMs have long touted for battery-electric vehicles (BEVs) has been the elimination of components like the transmission. The instant torque that an electric motor can supply often mitigates the need for any sort of torque multiplication beyond what the chosen axle ratio can provide. However, what the industry has found is that this concept has its limitations in certain use cases.

When asked to haul heavy loads over sustained grades or at freeway speeds, a direct drive BEV powertrain rapidly begins losing efficiency and range. Of course, batteries and motors can be scaled up to handle heavier loads, but these methods add both cost and weight to vehicles for which these specs are already major concerns.

To that end, Eaton and BAE Systems have teamed up to create a solution that not only provides greater flexibility for battery-electric trucks, but also enables smaller scale battery packs and motors while still matching the performance of an equivalent internal combustion engine (ICE) truck.

SAE Media was invited to a ride-and-drive event demonstrating their collaborative creation, where we experienced their test truck from behind the wheel and learned how all the systems work together to reduce overall complexity.

Gearing up

Eaton is not new to providing transmissions for heavy-duty trucks. The company formed an E-Powertrain division several years ago specifically for developing EV-centric components and systems. “What we do is focus on the mechanical components of an electrified powertrain such as differentials, reduction gears and full transmission systems,” said Justin Hopkins, product director, E-Powertrain, Eaton.

BAE is Eaton’s partner on the electrical side of the powertrain, providing motors, inverters and power electronics. Tom Webb, director of business development and strategy, BAE Systems, outlined where the electrified truck market is in BAE’s view and where the highest adoption rates seem to be among the various sectors of the trucking and commercial vehicle industry.

“In terms of market segments where EVs are actually capturing market share, we’re seeing a lot of transit bus, school bus and materials handling,” Webb said. “That may be due to incentives for the first two, but for the third it’s actually now become economically sustainable. Those are all good duty cycles for BEVs, but for some segments the infrastructure isn’t there yet. Obviously, there’s still a lot of challenges ahead with electrification, and we’re not going to tell you that it’s all ready for primetime. But in some market segments, it’s really getting there.”

“We seek to consolidate and simplify because of experience,” Webb continued. “On the trucking side, a lot of this technology is new with a lot of OEMs rushing to get products to market and tick that box. A lot of them are taking a very distributed approach to the architecture with a lot of boxes, wires and interconnects. It does make the product electrified, but it’s probably not the best way.

“There are too many things that can break, add cost and complexity and are not easy to manufacture. What we’re trying to do is integrate and use as many advanced commercial technologies as possible in terms of materials to get heat out, get efficiency up and ultimately make things easier to manufacture, install and service.”

Hitting the spot

Hopkins detailed why adding a gearbox to an electrified powertrain provides greater flexibility not only in design but also in overall performance. “For transit, most of the buses we see do not travel above 45 mph (72 kph). Now there are buses that do have to drive up steep hills like in San Fransisco,” he said. “But in the truck space, a gearbox helps significantly because you have to be able to do 70 mph (112 kph) and also climb some serious grades. Which is why we realized right away that going to a gearbox would be a big advantage over a direct drive architecture.”

There are other advantages too, such as downsizing the motor and power electronics. “The truck market is not as subsidized, it is more TCO and cost sensitive,” Hopkins said. “Because you need the combination of excellent startability, we have to ask, ‘what is the steepest grade I can start on with a full load?’ You also have to look at cruising efficiency.”

“It’s very difficult to get that out of a direct drive solution because your motor is being asked to do two different things: run at high speed very efficiently or produce a ton of low-end torque,” Hopkins continued. “So, it’s a lot easier once you have multiple speeds to be able to have a standard motor that doesn’t [require] extreme high-end torque and can be more optimized to operate at a more moderate speed in the sweet spot of a motor’s efficiency.”

An electric motor’s efficiency map is “a lot wider and more expansive than an ICE sweet spot in terms of peak efficiency,” Hopkins noted. “But you’re still trying to optimize that motor for peak efficiency where you’re doing the most amount of miles. So, when you get that multiplication for both those demands, it’s very helpful to have the gearbox.”

Hopkins also explained how introducing a transmission can reduce overall cost of an electrified powertrain. “Copper is expensive, and you also have various motor types that use rare earth metals. Scaling these motors up also adds weight. By introducing a transmission, you’re reducing overall weight and reducing overall motor costs,” he said.

The transmission that Eaton has integrated into the test truck has only four speeds, which is a fraction of what has become customary not only in trucks, but also light vehicles. “Because the motor has a much larger range of operation, you don’t need as many speeds,” Hopkins explained. “We really landed on as where we think the market sweet spot is.”

Cutting complexity

The test bed for Eaton’s EV transmission is a reworked 2018 Freightliner M2 crew cab equipped with a Meritor rear axle geared at 3.9:1. While this is still a test mule that began its life running on liquid gold rather than electrons, the overall installation and integration of its adopted powertrain is noticeably simple. It’s what you don’t notice under the hood that catches your eye.

“There’s a lot of current generation-one EV trucks that you see at various tradeshows that have a lot of ‘stuff’ in them. A lot of these generation-one EVs have a very distributed architecture [and] when you remove petroleum, you have to power all your accessories with electrons,” BAE’s Webb said. “So, what we’ve done is build a six-in-one architecture where we’ve integrated a lot of different functions.”

Indeed, the simplicity of the installation makes the test truck in question look much closer to a production-ready product rather than a rolling laboratory. “Our system isn’t just highly integrated, it’s also modular,” Webb said. “So, each of these functions are like slices that can come together or be removed so we can expand and contract them. We wanted to have the ability to support different platforms and duty cycles so that we didn’t constantly have to go back and start from scratch.”

“This allows us to service multiple markets with a core building block,” Webb continued. “That drives commonality between all the core functions, but also benefits the OEM and end user in terms of reducing NRE [non-recurring engineering]. It’s expensive to electrify each platform, so if there’s commonality that carries over, that helps the industry.”

Take a ride

SAE Media was permitted to take Eaton/BAE’s test mule for an extended test drive around Eaton’s proving grounds in Marshall, Michigan. The facility features an oval test track, an off-road course and several paved and unpaved grades ranging from 5- to 25-percent.

As noted by Hopkins, the transmission really does not shift much on level surfaces and below freeway speeds. However, we were able to verify his claim that above 62 mph (100 km/h), the transmission did indeed grab fourth and operate as a direct drive unit would mechanically even with a load in the back.

We also tackled various grades in the truck, which provided an opportunity to show off a few of the truck’s party tricks. The powertrain has a hill hold function that works much like an ICE vehicle would. Even on grades as steep as 25%, one could lift their foot off the accelerator and the truck would hold itself on the grade for a short period before freerolling again.

The steeper grades also provided an opportunity to demonstrate the shift logic of the transmission when more torque is required to make a hill. Like an ICE vehicle, the truck will usually not give a downshift command under full acceleration. However, if the driver feels the truck slowing while on a steep grade, a lift off the accelerator at a low enough speed would signal the transmission to engage first so that the truck could continue climbing.

The off-road grades also demonstrated the truck’s capability to not turn the manicured dirt roads of Eaton’s proving grounds into the starting line of a WRC stage. Naturally, because full torque is available from a dead stop, full power in first gear would likely spin tires in low mu situations. However, the throttle calibration is refined enough even in this prototype that its rear tires won’t suddenly turn into gravel machine guns.

Final thoughts

What Eaton and BAE have collaborated to create is quite impressive. By reintroducing a transmission to a BEV powertrain, they have demonstrated that an electrified powertrain can be even more flexible for truck applications while also reducing the overall weight of the motor and battery packs, which is still a major sticking point for pure electric vehicles.

Eaton and BAE are not the first to put a gearbox in a battery-powered truck. Volvo, for example, uses a two-speed gearbox in its VNR Electric. But their approach demonstrates that not only can electrified powertrains become more flexible in operation, they also can be far more simplified in terms of installation and overall architecture while still providing the necessary performance that fleet owners demand.