Swedespeed

For the Volvo Enthusiast

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22 October 2018

Volvo’s latest Twin-Engine T8 powertrain offers up impressive performance. Up to 415 hp in the Polestar Engineered S60, with massive swaths of torque to go with it. We said that “it pulls you back into your seat in a way that makes drivers giggle and passengers clutch any available handles.” Even better, if offers up a 21-mile or so electric-only range. Though with a touch less power on the EV side. So how does Volvo do it? And what are the twin engines at play?

The Twin Engine T8 setup launched in the XC90 back in 2015. It gave that big seven-seat crossover a 14-mile electric range in the EPA cycle. More impressively it gave it a 53 mpge fuel economy figure. Massive for an SUV, and even more impressive for one that offered up 400 hp and 472 lb-ft of torque.

So how exactly does having twin engines make this more fuel efficient? Well, there aren’t actually two engines, for a start. There is actually one engine and two motors.

The first is Volvo’s 2.0L twin-charged four-cylinder. We’ve already detailed how that one uses a turbo and an electrically-coupled supercharger to make an impressive 318 hp from such a small engine.

Volvo S60 T8 Plug-in Hybrid Chassis

Between that engine and the gearbox is a small electric motor. That one works as a motor to send 46 hp to the gearbox along with 110 lb-ft of torque. It also helps start the engine, power the accessories, and provide regenerative braking.

The second electric motor is the twin part. It’s mounted in the rear and provides all of the drive to the rear wheels. It adds 82 hp and 177 lb-ft to the thrust equation. It also handles the back portion of the all-wheel drive. So since there’s not a physical connection between the front and rear, it can never send all the power back there. But that’s not a bad thing. The lack of driveshaft makes it simpler and cheaper to adapt the powertrain between sedan, SUV, and whatever other body styles (or wheelbase) they want to put it in.

With a conventional AWD system, you need to mount a transfer case and a rear differential. Plus a center driveshaft. Put them into a different car, even on the same platform, and yuo need to find new places to mount those parts. Plus if the car is shorter you need a shorter driveshaft. With the T8’s rear electric motor driving the rear wheels directly, none of those components are needed. Just mount the motor, add stub axles, and run some wire. Want to make the car 2-inches longer next week? Run two more inches of wire. Easy as pie.

So it’s not really twin-engine, but Twin Engine makes for better branding than “Two Electric Motors and a Gas Engine.” Or “Två Elmotorer och en Gasmotor” if Google Translate has sent me in the right direction. We’ll just count the front driveline as one engine and the rear motor as the second. And call them paternal twins.

If you’re doing the math on those power figures, you’ve probably noticed they don’t quite add up. That’s because peak power from each source arrives at a different RPM. But that’s good for performance too. When one power source isn’t at its peak, another one is. More area under the power curve on the dyno means more acceleration.

Volvo has taken advantage of the lack of driveshaft in other ways. While many plug-in hybrids lose a big chunk of their trunk to batteries, Volvo has taken a different path. Where a driveshaft might go in a conventional AWD vehicle, they’ve installed batteries. 9.2 kWh worth of them. Mounted low they don’t hurt handling and they stay out of the cargo area.

Since the batteries can be charged from the wall, and not just the gas engine and regeneration, Volvo has added a few ways to control the system. Pure keeps the vehicle in electric-only mode. It can drive at speeds up to 74 mph without using any gasoline. The range varies depending on if you’re in an SUV or a car, since the vehicle weight can change massively. Hybrid mode drives much like any other hybrid. The computer figures out how much gas and how much electric to use for optimal efficiency.

Then there’s the fun mode. Power. All systems are go and damn the torpedoes. It will give you all the power available from all three drive systems, whenever you ask for it.

So what about the T5 Twin Engine? That’s the one destined for the XC40 and other 40-series vehicles. It’s got some innovative differences. For a start, there’s only one gas engine and one electric motor. No rear-drive. And the electric motor doesn’t go between the engine and gearbox.

Instead, it makes use of a quirk of the dual-clutch gearbox. See, dual-clutch gearboxes have two input shafts. One operated by each clutch. Gears 1,3,5, and 7 are mounted to one shaft, 2, 4, and 6 the other. We won’t get into how it all works this time, so for now, just call it magic.

Volvo connects the electric motor to the 2,4, and 6 shaft. So when the gas engine is off, the T5 drivetrain really only uses those three gears. It can’t power the others. But the gas engine can either power the odd-numbered gears at the same time as the electric motor turns the other ones (they all connect again at the back of the transmission) or they can both power the same even-gear shaft. It’s a very innovative solution that’s probably less complicated in operation than it sounds. That one uses a 1.5L turbo four and gets a total of 247 hp and 295 lb-ft. Impressive for a 1.5.

So that’s how Volvo’s two motors, and engine, and a pizza place lithium-ion battery work together to give more power and more efficiency in the same package. And how that package can fit in multiple vehicles.

 

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