Less than a year after announcing the Multiair valve control technology for its 1.4-L inline four-cylinder gasoline engine, Fiat at the Geneva Show unveiled its first engine series designed from a clean sheet to operate with the electro-hydraulic Multiair valve gear.
The new engine is a parallel twin-cylinder unit displacing 875 cm3. Fiat is no stranger to the parallel-twin configuration, having first employed a 579-cm3 twin in the 1957 Nuova 500, followed by larger-displacement successors. The new engine, known internally as the SGE (Small Gasoline Engine) program, is not based on any existing Fiat powerplant. It will launch in September and is slated to power a variety of A- and B-segment vehicles.
All SGE variants will feature four valves per cylinder with dual overhead camshafts equipped with the Multiair hardware and controls operating on the inlet camshaft. The system can vary valve closure to suit operating conditions and control air flow without using the throttle to reduce pumping losses. (For more on Multiair, see AEI June 2009, p. 48.)
The first Twin-Air engine to enter production will be a turbocharged variant rated at 63 kW (85 hp) and 195 N·m (144 lb·ft), with 90% of peak torque available from 1750 rpm, according to Fiat engineers. Carbon dioxide emissions of 95 g/km at the tailpipe are expected when paired with Fiat's automated manual transmission, and 98 g/km with a fully manual gearbox. All Twin-Air engines will be equipped with automatic stop/start systems.
The engine features a 360° crankshaft—both pistons rise and fall together, with one cylinder firing each revolution of the crankshaft. This arrangement is widely used in motorcycle engines and is prone to excessive vibration when employed without countermeasures—either counter-rotating Lanchester shafts or isolating engine mounts.
Giovanni Mastrangelo, Platform Manager – Small Gasoline Engines at Fiat Powertrain Technologies told AEI, “All the engines are equipped with a counterbalance shaft – very important in terms of NVH and to reduce frequencies of the first order. The engine block is cast iron, the oil pan is a structural feature – also important in terms of NVH and the engine block has a deep skirt."
He explained that during development everything was optimized to reduce internal friction, including very-low-friction piston rings. Mastrangelo also noted that the water pump drive is taken from the counterbalance shaft via an intermediate gear drive between the crankshaft and counterbalance shaft.
Compared with Fiat’s 1.2-L eight-valve inline four-cylinder, the turbocharged twin uses 15% less fuel, yet delivers 25% more power, according to the company. Compared with the 1.4-L 16-valve engine, it consumes 30% less fuel and offers similar performance. In addition, it offers significant package benefits vs. an inline four of similar performance and could be around 10% lighter.
Fiat plans to produce a dual-fuel version as well, designed to operate on gasoline or natural gas. These versions will be equipped with a second set of injectors on the intake manifold. In time, the range of Twin-Air engines will offer power outputs between 65-105 hp (48-78 kW).
Fiat has also developed the Twin-Air for use in hybrid drivetrains and suggests that it is well suited to powering a motor/generator fitted between the engine and gearbox.
The engine will be built at the automaker's Bielsko Biala plant in southeastern Poland.