Five years ago, few predicted the high level of fragmentation in powertrains, drivelines and fuels that exists in 2017. Nearly everyone now agrees, however, that Hybridization of all types is essential to meeting the latest European, North American and Asian emissions regulations and in bridging toward the long-term electric future—whenever that comes.
“We see it as a ‘spectrum of electrification’ from stop-start systems all the way to pure EV—and everything’s in play,” observed John Barlage, Director of Product Strategy, of BorgWarner PowerDrive Systems. Like other Tier 1 powertrain systems planners, he sees “very large volumes” of 48V hybrid applications coming in the next (2019-2021) cycle.
Already arriving in Europe from Audi and other German OEMs, the 48V systems provide greater on-board electrical power for CO2-reducing features such as e-boosting, and for ADAS (automated driver assistance systems) sensor suites which can gobble up to 3 kW.
“We’re going to see North America adopt 48V because it has such interesting economics,” Barlage asserted. The technology is often described as delivering about 70% of the performance of a conventional [powersplit-type] dedicated hybrid for about 30% of the cost. BorgWarner engineers also considered system architecture and packaging in developing a broad new portfolio of 48V and higher voltage hybrid-power modules aimed at P2 (position 2) applications.
In the so-called P2 location, the electric motor is located between the combustion engine and transmission; see diagram. The other industry-recognized hybrid positions include (starting from the front of the vehicle) P0 (belt-alternator-starter ‘BAS’); P1 (such as Honda’s IMA in the flywheel position); P3 has the motor on the transmission output shaft ahead of the final drive, and P4 (electric rear axle drives) often called ‘through the road’ AWD hybrids. The latter also offers torque-vectoring capability.
“P2 offers a lot of very interesting driveline opportunities,” Barlage observed, “including paired with dual-clutch (DCT) and even automated-clutch manuals [see http://articles.sae.org/15576/]. It also presents a very nice combination for plug-in hybrids. A P2 with PHEV capability actually delivers better overall efficiency in pure electric mode than a powersplit type does. If you want to go on the autobahn in electrically, or want to electrify a truck, you want a P2 type hybrid.”
On- and off-axis
“P-Zero ‘BAS’ systems were the starting point of our development with the same 48-V motor module used in the other positions,” explained Joel Maguire, BorgWarner’s Technical Fellow, Advanced Engineering. The engineering strategy “has economies of scale by applying a common electric machine across the locations.”
The product development team designed what Maguire calls “a nice, compact motor-generator ‘form factor’ based on a broad set of OEM vehicle-packaging requirements,” optimizing use of the e-motor’s magnetic material for P2, P3 or P4 applications, depending on what the OEM needs. “Some [competitors’] powersplit and even P2 architectures have had to compromise because their hardware wasn’t so ‘comfortable’ in terms of its flexibility with the existing vehicle package,” he told Automotive Engineering.
BorgWarner’s P2 module features an axial length of 6.57 in (167 mm). Rated peak torque is greater than 330 N·m (243 lb·ft). Peak power is greater than 80 kW (107 hp), according to the company. It is engineered for both on-axis (meaning located on the same axis as the transmission input shaft, engine crankshaft and torsional damper) and off-axis fitments. The latter, mounted piggyback on the transaxle case, is a chain-driven solution designed for the tight packaging needs of smaller transverse-engine/front drive vehicles.
“The key savings is the space from wheel to wheel; it avoids potential tear up, with zero length in axial growth,” Maguire explained. “You eliminate the alternator and can integrate the AC compressor on the same chain drive and can still run the compressor off the 48V when the engine is off.”
Both P2 modules include a disconnect clutch nested within the e-motor and an integrated dual-mass flywheel, enabling integration with popular transmissions: planetary step-type automatics, DCTs, continuously variable (CVTs) and automated manuals. The BorgWarner engineers note another P2 advantage: re-use of the existing engine and transmission.
“With P2 you’re dropping a module in between the engine and trans. For sure, it’s not a perfectly ‘clean’ addition,” Barlage said. “But compared with a dedicated hybrid transmission it’s still less expensive and requires a lot less modification. And it’s scalable.” Engineered into a DCT, the P2 unit becomes a triple-clutch arrangement or what BorgWarner calls ‘K-Zero’ with the disconnect clutch connected to the e-motor and the K1 and K2 clutches handling the shifting between the two gear clusters.
“Our strategy is to play in all architectures, from P-Zero to P4, so as we see OEM movement into any of the hybrid positions, we’ve got a system engineered for them all,” Maguire noted.