In the automotive dictionary of downsizing, the words “one” and “three” are becoming increasingly interlinked; “one” representing the engine capacity expressed in liters and “three” the number of cylinders necessary to achieve it.
General Motors Europe is the latest company to be cited in that definition. At the 2013 Frankfurt International Motor Show (Sept. 10-22), GME will unveil its 1.0-L, three-cylinder turbocharged gasoline engine. Known as SGE (Small Gasoline Engine), the direct-injected unit will be used to power the 2014 Opel/Vauxhall Adam city car, among other applications. It's a modular design which, in 1.0-L form, will deliver 84.6 kW (113.4 hp) and 166 N·m (122 lb·ft) from 1800 to 4700 rpm.
The new triple will drive through a new 6-speed gearbox, a combination aimed at good performance with low fuel consumption and emissions. Built at GM's new Szentgotthard, Hungary, plant on a line shared with diesel production, the 1.0-L is the initial member of a modular family of three- and four-cylinder units ranging up to 1.6-L, a portfolio that mirrors Ford's EcoBoost family.
Although the engine is new for GME, the concept is not. In 1996, the Opel Corsa was offered with a 1.0-L gasoline triple rated at just 40 kW (53.6 hp) and 82 N·m (60.5 hp). This AEI editor can attest that it was memorably breathless and not much fun to drive. A more powerful Twin Port version came in 2003, part of GME’s “O” family that heralded the current modular strategy.
Attention to NVH
Dr. Mathias Alt, Chief Engineer, Small Gasoline Engines at GME, said: “In developing this small engine, we not only set out to minimize fuel consumption and CO2 emissions, we also wanted to demonstrate that three cylinders can be just as refined as four or more.”
He explained that his development teams successfully focused on the traditional challenges of three-cylinder engines: balance, noise, and vibration. “This is a very lively and refined three-cylinder engine which doesn’t compromise driving fun,” he said.
Dr. Alt regards the new engine, designated 1.0-L SIDI (Spark Ignition Direct Injection) Turbo, as establishing a refinement benchmark for triples, with NVH characteristics superior to many four-cylinder units. Fuel consumption is claimed to be some 20% better than that of the 1.6-L naturally aspirated engine used in the company’s Astra models.
As well as DI, continuously variable valve timing and a lightweight aluminum cylinder-block are central to the engine’s efficiency. GME engineers expect the new engine family to deliver CO2 emissions significantly lower than 100g/km.
The die-cast aluminum cylinder block is designed to reduce radiated and structure-borne engine noise, as well as cutting weight. The high-pressure fuel rail and injectors are isolated from the cylinder head to minimize the transmission of pulsing, while the fuel pump and fuel line are acoustically treated.
An expected component for a modern triple is the use of a balancer shaft in the oil sump. For the 1.0-L SIDI Turbo, the shaft is driven by a chain with inverted teeth for quieter running. It spins at crankshaft speed and is mass-optimized to offset inherent three-cylinder vibrations.
The list of GME’s items necessary for quieter, smoother operation, include acoustically optimized covers for the top and front of the engine, the intake manifold, and camshaft housings; crankshaft isolation with iron main bearing inserts; inverted teeth for camshaft drive chains; a low-hiss turbo compressor; and a lower oil pan in steel.
During bench testing at WOT, the new triple demonstrates lower noise levels across the rpm range than similarly powerful gasoline turbos up to 1.6-L, GME engineers claim. Because of this, the level of additional in-car sound insulation is significantly reduced, and complex engine mountings and subframes are not required.
All-new 6-speed manual
Precision engineering is used in the integration of the exhaust manifold inside the aluminum cylinder head, which is bolted directly to the low-inertia, water-cooled turbocharger. The compact installation has been configured to help deliver a fast boost charge to optimize low-end torque. Maximum torque at 1800 rpm is almost 30% up on the 1.6-L Astra engine at the same rpm.
Six-hole fuel injectors are centrally located above each piston, and dual cam-phasing enables variable valve timing for required levels of engine breathing efficiency. Fuel consumption is further aided by use of a twin displacement oil pump and a switchable water pump. The latter is disengaged when the engine coolant is cold to facilitate faster warm-up.
The 1.0-L SIDI engine is allied to a new, 6-speed manual gearbox designed for medium torque applications. Its 37-kg (81.5-lb) dry weight is some 30% less than GM's incumbent 6-speed, and its compact design provides a measurement of 375 mm (14.7 in) along its axis.
The transmission incorporates refinements recently introduced on GME’s next-generation gearboxes, including gears with wide, asymmetrically cut dog teeth and triple-cone synchronizers for first/second gear with double cones for third/fourth. Reverse gear is also synchronized.
The new gearbox will be used in a range of small and subcompact Opel and Vauxhall models with engines rated at up to 220 N·m. (162 lb·ft). The matrix of gearing choices comprises 12 sets of gear ratios and seven final drives.
The 1.0-L SIDI Turbo and its new 6-speed gearbox mark the latest step in a program for the renewal of GME's powertrain portfolio, which will include three new engine families and 13 new engines introduced between 2012 and 2016, plus several new transmissions.
That program began with the launch of the first engines in new midsize gasoline and diesel families. These 1.6-litre turbo units will be joined by the 1.0-L SIDI Turbo, as the first example of a new, small displacement engine family being built at Szentgotthard. There, gasoline and diesel engines are produced on a shared assembly line.