Squeezing full-hybrid fuel savings out of mild-hybrid hardware
The general consensus among just about everybody tasked with engineering cars to meet the ever tightening Corporate Average Fuel Economy standards is that doing so is going to require some sort of electrification. And those electrification cognoscenti are increasingly bullish on low-voltage, lower cost, mild-hybridization using sophisticated starter/alternator devices. By low voltage, we mean anything under 60 volts, which is the threshold for risking grave bodily harm if a human accidentally contacts a hot circuit. These days that means quadrupling the tried and true 12-volt architecture to 48 volts. Such systems have been on our radar for several years, but Continental has just come up with a new design that greatly increases the potential fuel/CO2 savings.
Developed in conjunction with Schaeffler and deployed on a Ford Focus 1.0-liter EcoBoost engine, the biggest trick is moving the belt that connects the starter/alternator to the driveline to a point between the engine and transaxle, with electronically controlled clutches on either side of the belt drive. This permits several new fuel-sipper operating modes: Open the clutch on the engine side and the motor can launch the vehicle electrically while the engine restarts, or propel it electrically at low speeds in stop-and-go traffic, or permit frequent coasting or sailing, with the e-motor providing the modest thrust needed to maintain a low cruising speed. In this mode, the 48-volt system can recuperate far more energy than similar 12-volt mild-hybrid systems are able to, especially since there’s no engine braking effect robbing the electric system of precious deceleration. Open the other clutch and the e-motor can power the A/C at a standstill with the engine off, because the compressor is driven by the starter/alternator’s belt. This allows the cabin to stay cool for far longer during all of these engine-off periods, the only limitation now being the energy stored in the 0.5-kilowatt-hour, 48-volt lithium-ion battery.
Other upgrades on this so-called “Gasoline Technology Car II” relative to 2014’s “GTC I” include an improved baseline 1.0-liter EcoBoost I-3 (compression ratio increased from 10.0:1 to 12.0:1, Continental’s new semi-radial/semi-axial “RAAX” turbine turbocharger that reduces the rotational inertia of the turbine by 40 percent for improved responsiveness), an electric vacuum pump to power the brakes during engine-off operation, an advanced thermal management unit with electrically driven coolant pumps (so no accessory drive is needed on the front of the engine), and an electric catalyst heater. The latter, an especially fast-acting unit powered by the 48-volt battery, accounts for 3.5-g CO2 savings alone relative to the fuel enrichment that would otherwise be dedicated to catalyst light-off.
What’s the total claimed fuel consumption benefit? Better than 25 percent relative to the base Focus 1.0-liter. Icing on the cake: We’re told the price for all this hardware should not exceed that of the last-generation Malibu mild-hybrid belt-alternator-starter system. Continental isn’t saying when or where we’ll see this technology deployed first, but it spent a week intensively demonstrating its new GTC II prototype to automakers before showing it to the press.