An innovative form of plug-in hybrid, described as three cars in one, was exhibited by Volvo at the North American International Auto Show in Detroit Jan. 9. The gasoline-engine car, based on the S60, is officially a concept car, but it is really a prototype, and a version with a diesel engine is expected to be on sale later this year in Europe. The car was introduced at the show by Stefan Jacoby, President and CEO of Volvo Car Corp.
The "three cars in one" description is based on a sophisticated control system that leads to a three-button control panel with "Pure," "Hybrid," and "Power" choices. "Pure" refers to pure electric vehicle (EV) operation. "Hybrid" is gasoline-electric hybrid operation, which is the default mode. Although the car moves from a stop on electric power, it immediately reverts to hybrid operation. "Power" is a combination of maximum performance from the engine and a 52 kW electric motor.
The engine is an all-new 2.0-L four-cylinder turbo rated at 280 hp (209 kW), which is higher than any mass-production turbo four of this displacement currently available in the U.S. The turbocharger itself is just a single scroll with a wastegate peak of 15 psi (1.03 bar), but it is a large unit and the engine itself has a flat torque curve from 1800 to 4500 rpm. This has permitted tuning for the high performance level, according to Olle Odsell, Technical Project Leader for Volvo hybrids.
The Volvo is equipped with a 12-kW·h lithium-ion battery pack (rectangular pouch type from LG Chem's Korean plant). It is rated for a 600-mi (960-km) range from the combination of 35 mi (56 km) electric drive and the remainder from hybrid operation with the fuel from its 14-gal (53-L) tank. Fuel economy in hybrid drive is approximately 39 mpg, according to Odsell. Combined U.S. EPA fuel economy is projected to be 50 mpg. On the NEDC (New European Drive Cycle), based on carbon dioxide emissions of just 53 g/km, the car would be rated at over 100 mpg.
The electric drive system is in the rear. The electric motor will be supplied by a joint venture operation between Volvo and Siemens. The 35-mi pure EV range is based on a 30% depletion of the battery's 12 kW·h, or just over 8 kW·h, Odsell said. The rear axle with its electric motor provides side impact protection for the battery pack, which sits above, in a high-strength steel compartment just under the luggage area floor. Odsell said Volvo has confidence in the safety of the location, which includes the chassis' rear-end impact protection, which was heavily modified to provide extra protection. The battery pack also is protected by a complex electronic safety system, and in cases of battery failure any battery gasses that escape would be safely ducted away.
The battery pack, including the steel compartment, weighs approximately 80 kg (176 lb). But Odsell said that perhaps half the added weight of the pack is saved by the use of the four-cylinder turbo vs. a six-cylinder, or even more vs. a V8 of an equivalent peak performance.
The gasoline powertrain, which is transverse-mounted in front, includes a virtually conventional eight-speed automatic transmission and an integrated starter generator (ISG) designed for the hybrid. The ISG charges the batteries when braking and under some other conditions, and as a motor it is rated at 34 kW. So there are modes under which it even can contribute to acceleration, Odsell said. A production supplier for the ISG has not yet been designated, he added.
The preferred battery charge method is plug-in to 110-V/12-A (7.5 h) or 220-V/12-A (3.5 h) household or charging station current. However, the Volvo system also incorporates a "save" function for cars that are driven in areas that legally mandate or provide incentives for pure EV operation. If the driver anticipates the EV need well in advance and activates "save," the system will simply switch to hybrid operation and leave enough EV capacity in the battery pack for up to 20 mi (32 km). If the driver makes a late decision to travel to (and then through) the EV area sometime during a trip, the "save" function will use the gasoline engine to charge the battery pack to provide up to a 20-mi range for the legally required EV drive.
In the luxury car field in which Volvo competes, performance also is important. In the Power mode, the car can accelerate from 0-60 mph (97 km/h) in 5.8 s. This is from the combination of the peak engine performance (including a torque figure of 280 lb·ft/380 N·m) and the electric motor's 52 kW and 148 lb·ft (201 N·m). The totals are 350 hp (261 kW) and 428 lb·ft (580 N·m).
Volvo also noted that it would be testing a flywheel energy system (Flywheel Kinetic Energy Recovery System) on public roads later this year. The system, which can rev the flywheel up to 60,000 rpm on braking and store energy in the rotating mass, can effectively add up to 80 hp (60 kW), so a four-cylinder would perform like a six-cylinder. Volvo estimates that a flywheel system has the potential for improving fuel economy in some driving modes up to 20%.