On Monday, Audi announced its next-generation mild hybrid system. Called MHEV Plus, this fuel-saving, performance-boosting technology will be offered in the A5 and Q5 models that ride atop the automaker’s Premium Platform Combustion (PPC) vehicle architecture. Given the modularity and compact design of this new powertrain system, it wouldn’t be surprising to see MHEV Plus added to other model lines in the four-ring brand’s product portfolio.
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PTG, The Heart Of MHEV Plus
Audi’s new mild-hybrid drivetrain system is comprised of three main components. There’s a Powertrain Generator (PTG) that provides assistive driving force and regenerative braking capability, there’s a belt-driven alternator-starter (BAS) and then a lithium iron-phosphate battery pack that stores and releases energy as needed. MHEV Plus helps bolster the combustion engine, though it also allows a vehicle to drive short distances purely on electric power.
In a media release shared by the automaker, Geoffrey Bouquot, member of the board of management for technical development at Audi said, “This [technology] will strengthen our product portfolio of all-electric models, plug-in hybrids, and vehicles with efficient combustion engines.”
The heart of this system, and what really sets it apart from Audi’s previous mild hybrid designs, is the PTG, which is mounted on the output shaft of the transmission, a clean and compact location. This unit, which is liquid-cooled for optimal performance and longevity in a wide range of temperatures also contains its own power electronics. Augmenting the combustion engine, the PTG provides up to 24 horsepower (18 kW) and 170 pound-feet of torque (230 Nm). Recuperating energy that would normally be lost, the PTG also provides up to 25 kW of regenerative braking capability, working to slow the vehicle down right to a stop.
In drive, that full 24 hp is available when the accelerator pedal is pressed to roughly the 80 percent point or if the driver hits the kickdown switch. If S mode is selected, you get the whole megillah at much lower pedal application points for a more dynamic feel.
Overall, the output shaft can spin at up to 5,550 rpm, allowing the PTG to support a vehicle’s engine at speeds between roughly 81 and 87 mph (130 to 140 km/h) depending on application. Beyond those speeds, a dog clutch allows the PTG to automatically disengage. A clever bit of engineering, Audi’s new powertrain generator weighs just about 46 pounds (21 kg) and, thanks to its compact design, can fit in a wide range of vehicles with minimal modifications required. Adding even more flexibility, this setup also works with both front-wheel drive and Audi’s famed Quattro all-wheel-drive system.
BAS + LFP FTW!
Audi
Of course, the PTG isn’t the only part of MHEV Plus. There’s also the best-driven alternator starter and the all-important battery pack. Like previous mild hybrid systems, the BAS is designed to more smoothly and quietly start the combustion engine than a conventional, pinion-type starter can. This helps the system feel refined and, hopefully, seamless.
As for the battery pack, it should operate at 48 volts, has a gross capacity of 1.7 kilowatt-hours and uses the reliable and oftentimes more affordable lithium iron-phosphate chemistry (LFP), the first time Audi has put a battery of this type in a mild hybrid. Just like the PTG, this energy reservoir is liquid-cooled for improved performance and reliability in a wide range of operating conditions.
How much fuel can all this technology save? Well, according to Audi, a conventional vehicle with a 3.0-liter V6 and Quattro all-wheel drive might have a combined fuel consumption rating of between 8.0 and 7.4 liters per 100 km in WLTP testing. The automaker’s MHEV Plus system could save up to 0.74 l/100 km on the same drive cycle, a not-insignificant amount.
But, Now A Bit Of Bad News
Audi
There seems to be a lot to like about Audi’s new mild hybrid system, but it’s not all good news. According to the automaker, this technology will not be offered in the U.S. “due to differing customer needs,” which is a real shame. Many drivers still prefer combustion-powered cars and trucks over EVs, and sensible, relatively simple electrification like this can dramatically improve a vehicle’s fuel efficiency.
