Volvo's Tricks of the EV Trade

Why Volvo uses starter-generators and raised tunnels for its electrified vehicles.

The Volvo XC60 T8 PHEV chassis – similar in design to its XC90 T8 brother – features a center-tunnel battery pack enabled by a crankshaft-mounted ISG that eliminates a conventional driveshaft. (Volvo)

Volvo first demonstrated its Integrated Starter Generator (ISG) at the 2001 Frankfurt Motor Show. Replacing the starter-motor and alternator with the ISG allows a gas engine to shut off at will — mainly to prevent idling at a stop. For the company, it was a logical first step for fuel savings. But Volvo engineers at the time could hardly have predicted how useful an ISG would become, decades later, in the electric era.

The XC90 T8 is the only seven-seat PHEV currently on the market. That was made possible by Volvo’s propulsion system architecture. (Volvo)

As Automotive Engineering discovered on our recent drive of the 2020 Volvo XC90 T8 plug-in hybrid during its media launch, an integrated crankshaft generator doesn’t merely allow stop-start or mild-hybrid propulsion. While piloting the XC90 T8 along the Trans-Canada Highway in August, we were able to keep the three-row, full-size SUV in pure electric mode for its first 21 miles (34 km).

For that distance, we strictly used the 87-hp (65-kW) electric motor sitting on the rear axle. When extra power is needed, or the plug-in hybrid’s 11.4-kW-h pack is depleted, the ISG wakes up the XC90 T8’s 2.0-L gasoline engine. That adds a wallop of 313 more horsepower (233 kW) and 295 lb-ft (400 Nm) to the vehicle via the front wheels. The electric motor is still providing service because the ISG and sophisticated control system ensures that the XC90 T8 is an all-wheel-drive vehicle all of the time.

“What the ISG is doing is shutting off the gas engine, and it can bring it back up seamlessly,” said Jim Nichols, senior manager of product and technology communications. “It’s more about managing the gas engine than the electric motors.”

Human intervention helped manage the electric side of things. By putting the vehicle in “Pure Eco” mode, and keeping a steady touch on the accelerator pedal, I was able to keep the 4,993-lb (2,265-kg) vehicle in pure EV mode. This was graphically represented in the dashboard display by a lightning bolt. The digital display showed me when I was approaching the switchover to gasoline. At those moments, I gently eased off the accelerator and thereby refrained from internal combustion.

The “Pure” mode is not governed to a fixed maximum speed. For those 21 all-electric miles, I consistently traveled near 70 mph (113 km-h). Granted, that leg of the trip was flat or slightly downhill. Nichols said there are two goals with the T8 plug-in hybrid. “One is to extend miles per gallon,” he said. “And the other is to get a little bit of a performance kick.” The system creates a constant charge going to the battery, just enough juice to allow the electrically motivated rear wheels to combine with the engine for combined 400 hp (298 kW).

The Volvo XC90 T8 plug-in hybrid first went on sale in the United States in 2015, as a 2016 model vehicle. Nichols said the XC90 has been “continuously improved” since then. The current iteration, now on sale, boosts the battery size to 11.6 kW-h — a 14% increase that represents a corresponding improvement in EV range. Volvo also improved the smoothness of the brake-pedal feel by replacing the previous vacuum brake system with a hydraulic module from Continental. The 2020 XC90 also comes with aesthetic updates, such as an attractive concave front grille and crystal gear shifter.

Packaging benefits

In the long run, Volvo’s ongoing use of the ISG might is a matter of vehicle packaging. “The XC90 is a seven-seater and a plug-in hybrid at the same time,” said Anders Robertson, product manager for Volvo Cars USA. “That’s totally unique. Nobody else can do that.” Nichols explained that the design of a rear electric motor and front gas engine eliminates the need for a driveshaft. The leaves room for the battery pack in the central tunnel — from about the A-pillar to a foot in front of the second-row seats.

For at least a few decades, automakers have extolled the virtues of using a “skateboard,” the layout pioneered by GM on various concepts that puts EV batteries flat in the floor, under the cabin. But that approach creates a dilemma for platforms that serve multiple purposes, including adaptation from pure internal combustion to a plug-in hybrid. Robertson explained that competitors often use valuable passenger and cargo space to store a battery pack. “We package the batteries in the center tunnel so we can still have a seven-seater,” he said. (The 2020 XC90 T8 is also available in a six-seat configuration.)

Nichols said that Volvo started building the Scalable Product Architecture (SPA) platform soon after splitting from Ford in 2010. “We built SPA from the ground up to handle electrification,” said Nichols. “With a tunnel, there’s more flexibility to do plug-in hybrids. And that’s what we did with the XC90, S90, and XC60.” Volvo’s CMA architecture was similarly used for smaller vehicles, such as the XC40 crossover. Volvo’s first full battery-electric vehicle is expected to be the XC40. “The CMA platform already has the packing for more battery cells,” he said. Of course, a pure electric car doesn’t have a gas engine and therefore doesn’t require an ISG to shut down internal combustion.

The XC90 T8 rides on Volvo's scalable SCA architecture. (Volvo)

Keep in mind that Volvo and Polestar, its electric/performance division, share vehicle platforms. While they operate as separate companies, the two entities communicate about plans. “Polestar will squeeze everything they can out of electrification,” said Volvo’s Nichols. “It then comes to Volvo when it has been worked out on the Polestar side.”

Hans Pehrson, head of electric propulsion strategy at Polestar, told us that he thinks the raised tunnel is a good concept. We spoke with him at the debut of the 78-kW-h Polestar, at the 2019 Geneva Motor Show. “We use the tunnel for a good packaging purpose. It’s not air in there,” he said. “We don’t think it’s a compromise.”

In effect, the space created when removing the driveshaft was reclaimed to store batteries for both plug-in hybrids and EVs. The ISG approach ultimately became a boon for a safety-focused brand like Volvo. “The center of the car is the safest place to put the battery,” said Nichols. “If you have impacts from the side or front or wherever, it’s not going to breach the battery pack.”