Volvo’s Drive-E: Environmentally Efficient—& Clever—Powertrains
Although Al Gore may not have invented the Internet, the former U.S. vice president and 2007 Nobel Prize-winner did have a signal effect on the development of a family of engines developed in Sweden. No, it was not predicated on his visiting Scandinavia to pick up his medal. Rather, his 2006 book, An Inconvenient Truth: The Planetary Emergency of Global Warming and What We Can Do About It, had an effect on the thinking of the powertrain engineers at Volvo, says Jan-Erik Larsson, director, Powertrain, Volvo Car Corporation.
Larsson explains that the genesis was the issue of CO2 emissions, which Gore’s book calls attention to. “How can we solve the emissions, the CO2 problem? That was the starting point,” Larsson says.
In addition to which, there is the European Union emissions regulations instituted in 2009 that Volvo and other European manufacturers have to meet. Step one is for a fleet average of all new cars to have CO2 emissions of 130 g/km by 2015. Then it is 95 g/km in 2020. And back in 2007, the average was 158.7 g/km. Certainly inconvenient so far as then-existing powertrains went.
There was another driving issue. Back in 2000, Volvo Group sold Volvo Car to Ford. But around 2007, Larsson recalls, “It started to leak out from Ford that they were going to sell us.” At that time, Ford had created the “Premier Automotive Group.” It consisted of Lincoln, Volvo, Jaguar, Land Rover, and Aston-Martin.” Aston-Martin was sold off in 2007. Jaguar Land Rover went in 2008. And the shoe dropped for Volvo in 2010, when Ford sold Volvo Car to Geely Automobile.
The then-rumored sale had a direct effect on Larsson and his colleagues beyond who was going to be cutting their paychecks: “Ford was our main supplier of engines. We needed a stand-alone scenario.”
So, with those factors, they set out to create new engines, and they did so on a fast track. The strategy was accomplished in 2007, design concept work in 2008, and the first engines were tested in 2009. And now with the launch of 2015 XC60, V60 and S60 (and with the anticipation of the forthcoming XC90, with the new Volvo scalable architecture underpinning it), the new engines are under the hoods and will be the bases for all future Volvo engines.
While the company still produces an I5, it will be phased out of production. Which leaves Volvo with the in-line four cylinder architecture that it developed, as well as a three-cylinder engine. Volvo, Larsson says, will not be going bigger than four cylinders and ~two liters of displacement.
Larsson recalls that the starting point for the development was addressing how they could meet the 2020 low CO2 levels. “You soon realize that you need to do downsizing, down-speeding. We said to reach that level of CO2, four cylinders could do it.” That’s only part of it. “Our customers demand performance and power from the engines.” So that part of the equation had to be figured, as well.
So in order to meet their requirements, they developed two gasoline engine variants and one diesel variant. While it might seem that the two types—ignition combustion and compression combustion—would be widely different, Larsson says that the engine architecture is one that facilitates significant sharing. He enumerates, “There is huge commonality between the petrol and the diesel engines. We have 25% totally identical parts—the same part number. There is 50% from the same concept, but with small adaptations. Twenty-five percent are unique.” So in the case of the first-named, there are things like the crankshaft, bedplate, and alternator. For the second, there are the engine block and balancer module. And for the completely unique, there are the cylinder heads.
It is also important to note that the “Drive-E” powertrain architecture (the “E” stands for “environmental,” not “electrical”) will lend itself to a total of four gasoline engines and four diesels. This doesn’t include another variation, which would be the hybridization of the powertrain, but that is accounted for in the basic design, as there is a spacer between the engine and the Aisin Warner eight-speed automatic transmission (used throughout the lineup) which, Larsson says, is available for integrating an integrated starter generator, which he describes as being the “first step to a mild hybrid.” Then to go full-hybrid, there is the possibility of putting an electric motor on the rear axle. So while there are three powertrain variants now (with only the gasoline T5 and T6 gasoline versions being made available in the U.S. market), there are plenty more to come. It is worth noting, however, that all Drive-E engines feature start-stop and brake regeneration. Brake pressure measurement is used to determine when to stop and start the engine. To assure seamless operation, there is an electric oil pump and an improved starter motor.
There is also a driver-selectable ECO+ button that, when engaged, not only performs stop-start when the vehicle is stopped, but also provides “ECO-coast,” which disengages the engine brake when the driver lifts from the accelerator, thereby putting engine speed down to idle speed, but which also initiates “ECO-climate,” which disconnects the air conditioning compressor (given the temperatures in Sweden, this is probably a reasonable thing; know that it can be overridden by pressing the AC button).
Volvo has made a $300-million invest-ment in its plant in Sköve, Sweden, with flexible manufacturing equipment that permits the engine variations to be readily handled in production.
The T5 engine produces 240 hp and 258 lb-ft of torque. The T6 engine produces 302 hp and 295 lb-ft of torque. The difference between the two? The T5 features an integrated sheet steel manifold turbocharger. The T6 not only has the turbocharger, but a supercharger, as well. Larsson explains that they opted to go with the turbocharger and the supercharger rather than twin turbochargers because with a four cylinder engine, that would mean that there would be two cylinders each for the turbos, which wouldn’t provide high output especially at the low end. If there were serial turbochargers, then they could run to a problem with high backpressure, which would lead to performance problems.
So for the T6, the clutchable roots-type supercharger is geared to provide low-end torque. Then, when sufficient speed is reached, the supercharger is disengaged and the turbocharger is deployed to improve performance. “The biggest struggle,” Larsson admits, “was to make them work together with the control software.”
So what about the CO2?
The Drive-E powertrains are available in three Volvo vehicles in the U.S. at present: The S60 sedan, the V60 wagon (T5 only), and the XC60 crossover. According to certification under the New European Driving Cycle, the S60 with a T6 has CO2 emissions of 149 g/km. With the 240-hp, T5 engine, it is rated at 137 g/km. (In case you are wondering about miles per gallon, the S60 T6 provides 24/35 mpg and the T5 25/37 mpg).
In the development of these powertrains, Volvo engineers worked hard at providing all manner of improvements to achieve their goals. For example, the cast-in cast-iron cylinder liners are sprayed with eutectic aluminium to improve the bonding of the liners to the block. The pistons have reduced friction thanks to a PVD coating on the top ring and new honing specifications. Piston pins are coated with diamond-like coating (DLC). An electric water pump is used in the gas engines to reduce friction losses and to facilitate fast engine warm-up. And on it goes.
Larsson explains that when Ford purchased Volvo, powertrain engineering was something that became of reduced importance in Sweden, given that Ford was to become the predominant supplier of engines. But as the sale of Volvo to another company started to take shape, the powertrain engineering ranks were bolstered. And with the ownership by Geely, which is making an $11-billion investment in Volvo’s technology, powertrain developments are back to the fore. And it is clear that Larsson and his colleagues are excited about what they’ve developed.
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