Opel revealed details of its new three-cylinder gasoline engine at the Aachen Colloquium in Germany. Clean, smooth and quiet: Opel’s all-new 1.0-liter SIDI Turbo will raise the bar for three-cylinder engine refinement when it makes its debut in the Opel ADAM next year. It is not only economical and more friendly to the climate, it is also silky smooth to drive, with noise and vibration characteristics superior to many four-cylinder engines.
This pocket powerhouse belies its diminutive size by developing 85 kW/115 hp, together with strong torque of 166 Nm all the way from 1,800 to 4,700 rpm. It therefore enables better acceleration at low rpm than larger engines with similar horsepower, together with much lower fuel consumption and CO2 emissions. For example, compared to Opel’s current 1.6-liter naturally-aspirated engine, the new 1.0 SIDI Turbo (Spark Ignition Direct Injection) offers the same maximum power output, while delivering 30 percent more torque and 20 percent better fuel economy.
State-of-the-art technologies include high-pressure direct fuel injection, an ultra-compact turbocharging system, continuously variable valve timing and a lightweight aluminum construction with a cylinder head-integrated exhaust manifold. Numerous ‘sound engineering’ measures which contribute to the engine’s benchmark refinement include an acoustically-developed cylinder block; a sump-mounted balancer shaft; structural isolation of the fuel injection system and crankshaft; drive chains with inverted teeth and engine covers designed for acoustic attenuation.
The 1.0 SIDI Turbo is the first in a new, modular family of three and four-cylinder gasoline engines in the sub-1.6-liter class which are engineered to meet customer demand for strong, downsized engine performance. It makes its debut in the Opel ADAM next year, together with an all-new, six-speed manual gearbox. All vehicle applications of the 1.0 SIDI Turbo are designed to operate with Start/Stop functionality and are expected to deliver combined cycle CO2 emissions significantly lower than 100 g/km.
“In developing this small engine, we not only set out to minimize fuel consumption and CO2 emissions, but also wanted to demonstrate that three cylinders can be just as refined as four or more,” says Dr. Matthias Alt, Opel’s Chief Engineer, Small Gasoline Engines.
“We tackled at source the various balance, noise and vibration issues typical of conventional three-cylinder engines, and we’re confident customers will be pleasantly surprised by the results. This is a very lively and refined three-cylinder engine, which doesn’t compromise on driving fun. Put simply, it’s big on refinement and performance but small on fuel consumption.”
German engineering for class-leading refinement
Starting with a clean sheet of paper, Opel and GM global engineering teams leveraged their combined expertise to eliminate the harsh, ‘off-beat’ running characteristics, which have traditionally been a downside to the economical driving appeal of three-cylinder engines. As a result, the 1.0 SIDI Turbo boasts a four cylinder-like ‘soundtrack’, which clearly positions it as the new benchmark for refinement among three-cylinder engines.
Throughout the development process, the prevention and mitigation of vibration and harshness was achieved through extensive modeling work, as well as component hardware and whole-engine validation on the test bench. The scope of the work also included the development of engine management functions and the in-vehicle integration of the entire powertrain.
The engine’s all-aluminum architecture was acoustically designed to reduce both airborne and structure-borne operating noise, as well as to save weight. Its inherent refinement is so good, the need to mask the transfer of engine noise with in-car sound insulation, or complex engine and sub-frame mountings, is significantly reduced. The persistent reduction of unwelcome engine sounds also gives engineers greater freedom in fine-tuning the sound of induction and exhaust systems to meet the requirements of specific vehicle applications.
As a result of this intense focus on refinement, the 1.0 SIDI Turbo not only runs more smoothly than similar three-cylinder engines, but also more quietly than many four-cylinder units. For example, during development in laboratory bench testing at full throttle, it emitted lower sounds levels across all engine speeds than gasoline turbos up to 1.6 liters in displacement.
Other specific features that contribute to the engine’s impressive refinement include:
A small balance-shaft mounted longitudinally in the oil sump. Driven by a chain with inverted teeth for quiet running, this counter-rotating shaft revolves at crankshaft speed and is mass-optimized to off-set the inherent vibrations from a three cylinder operation.
The high-pressure fuel rail and injectors are isolated from the cylinder head. This ensures there is no metal-to-metal contact and prevents the transmission of pulsing energy through the engine structure. The fuel pump and fuel line are also acoustically optimized.
Camshaft drive-chain optimized for low sound levels through an inverted-tooth design. The entire chain architecture, including its tensioning, wrap and guides, is designed for reduced overall noise radiation and the elimination of any perceived abnormal sounds.
The integration of a stamped steel plate in the oil pan at the bottom of the aluminum sump also reduces noise radiation.
Further noise attenuation measures are: acoustically-optimized covers for the top and front of the engine, the design of the intake manifold and camshaft housings, crankshaft isolation with iron main bearing inserts, and the use of a low-hiss compressor in the turbocharger.
Lightweight all-aluminum architecture
The core engine-architecture is focused on saving weight and consists of an aluminum, high pressure, die-cast cylinder block, cylinder head and crankshaft bedplate. The combined block/bedplate weight is just 15.5 kg, while the complete engine offers a ten percent weight saving compared to Opel’s current 1.6 naturally-aspirated engine of similar power.
The ‘long-stroke’ cylinder layout supports superior torque characteristics, with the piston stroke of 77.4 mm exceeding its diameter of 74.0 mm. For high power, a compression ratio of 10.5:1 is combined with turbocharging and high-pressure direct fuel injection.
The cylinder head features a water-cooled exhaust manifold integrated within the aluminum casting. This single-piece concept provides a number of benefits: it contributes to fast engine warm-up, and enhances durability by eliminating the need for gasket sealing around the exhaust ports, as well as offering under-hood packaging advantages.
For structural stiffness, the block has cast-in-place iron cylinder liners, with aluminum cast over the top surfaces to optimize cylinder head gasket sealing. The bedplate bulkheads also contain cast-in, nodular iron inserts for localized structural stiffness. Additional structural strength is contributed by the die-cast aluminum sump.
A six-counterweight, forged steel crankshaft transfers the high specific output of the 1.0 SIDI Turbo to the driveline with a minimum of vibration. The upper front main bearings are polymer coated for enhanced durability, particularly under Start/Stop conditions.
The steel con-rods are forged from Powder Metal (PM), which provides equivalent or improved strength compared to a standard forging, while ensuring reduced mass variation. An oil-retaining groove, in combination with an optimized taper angle at the small end, reduces bushing wear. Under-skirt oil jets cool the aluminium pistons and provide additional bore lubrication, which also reduces engine sound during cold starts.
Dual overhead camshafts, operating four valves per cylinder with low-friction, hydraulic roller finger followers, are hollow in section to save weight, and driven by a timing chain with life-long automatic hydraulic tensioning. Aluminum cam phasers enable variable timing for the opening and closing of the inlet and exhaust valves, giving best possible fuel consumption, performance and low emissions under all engine load conditions.
Direct fuel injection delivers more power and greater fuel economy
The 1.0 SIDI Turbo packs a punch, generating 30 percent more torque than Opel’s current 1.6-liter, naturally-aspirated engine, as well as the same 85 kW/115 hp maximum power output. Peak torque of 166 Nm is available across a wide plateau from 1,800 rpm to 4,700 rpm, while maximum power is delivered at just 5,200 rpm. This is an engine that is small in size but big in performance.
The 1.0 SIDI Turbo is also extremely frugal, delivering a 20 percent improvement in fuel economy compared to the 1.6-liter engine. In the Opel ADAM, it will give CO2 emissions of well under 100 g/km, as well as combined cycle fuel consumption approaching 4.0 l/100 km.
Key to both power and frugality is a high-pressure, direct fuel injection system, which helps extract as much energy from the fuel as possible. The six-hole, SIDI injectors, operating at a maximum pressure of 200 bar, are ideally positioned over the center of the combustion chamber and deliver a fine, homogenous spray without wasteful wetting of the inlet valves or port walls. The fuel flow rate at the injectors supports the metering of small, multiple injections.
There is no metal-to-metal contact between the cylinder head and the fuel rail or the injectors. This careful isolation eliminates a major, structure-borne path for operating noise from the injection system. The fuel rail is decoupled by a rubber/steel damper and the injectors are isolated in the combustion chamber by carbon-filled Teflon seals. Acoustics are further enhanced by software algorithms suppressing noises generated from a high pressure fuel pump needle and a foam outer shell.
The longer firing intervals of a three-cylinder enable the use of wider cam profiles than possible with a four-cylinder engine, which extends the duration of the valve opening times to give better cylinder scavenging (gas exchange) for more complete combustion.
To further improve fuel economy and engine operating efficiency, oil is circulated by a two-stage, variable displacement oil pump. This supplies high or low pressure as required by running conditions and includes on-off control of the under-skirt piston cooling jets. A switchable water pump, which is disengaged when the engine is cold in order to give a faster warm-up, also contributes to low fuel consumption.
The Front End Accessory Drive (FEAD) – a five-rib belt connecting the water pump, the alternator and the air conditioning compressor – features a mechanical isolator to remove the effect of crankshaft oscillations. In addition to refinement benefits, this also allows a reduction in tensioning force to reduce friction levels and improve efficiency.
Ultra-compact, fast boost turbocharging system
While high-pressure, direct injection fills the engine’s combustion chambers with a fine mist of fuel, an ultra-compact turbocharging system packs its cylinders with air. Leveraging the design advantages of the cylinder head-integrated exhaust manifold, the 1.0 SIDI’s turbocharger is more closely coupled to the engine than on any other power unit – giving the driver a fast and strong throttle response.
The integration of the water-cooled exhaust manifold within the cylinder head, and the design of the tiny, low-inertia turbocharger, which is also water-cooled, is an exercise in jewel-like, precision engineering.
The sizing of the turbocharger is key to achieving a fine balance between the need for strong low-end torque, fast throttle response, reduced fuel consumption and high maximum power. A single stage, single scroll turbocharger generating maximum boost pressure of 1.5 bar with an intercooler and pressure-operated wastegate was selected as the best configuration. The diameter of the turbine wheel is just 35 mm, while the low-hiss compressor measures only 40 mm across. This combination delivers an excellent transient throttle response, generating 90 percent of maximum torque within 1.5 seconds from just 1,500 rpm. That entails a six-fold increase in cylinder pressure, with the turbo shaft spinning at up to 250,000 rpm.
Water-cooling of the exhaust reduces temperatures for improved emissions control, while also reducing heat build-up around the turbine. This allows the use of an Inconel turbine wheel and a medium grade austenitic steel turbine housing. The gasket to the cylinder head is integrated in one of the heat shields, and V-band clamps and a weight-optimized design all contribute to the turbocharger's lightweight construction.
The turbo feeds the engine through high tumble intake ports, which facilitate early combustion phasing, a short burn duration and good combustion stability. Running turbocharged engines at high loads usually requires retardation of the spark timing to avoid ‘knocking’ or harmful pre-ignition of the intake charge. A high tumble port minimizes the need for this measure.
Meeting current and future needs
The launch of the 1.0 SIDI Turbo is the latest step in the substantial renewal of Opel’s powertrain portfolio, which will see 13 new engines introduced between 2012 and 2016, plus a host of new transmissions.
The program has already begun with the launch of the first 1.6-liter turbo engines from new medium displacement gasoline and diesel families. Now the 1.0 SIDI Turbo arrives as the first example of a new, modular small displacement gasoline engine family, comprising three and four-cylinder engines of less than 1.6 liters displacement. All variants of these new engine families are built at Opel’s state-of-the-art plant in Szentgotthard, Hungary, where gasoline and diesel engines are produced on a shared assembly line.
While the 1.0 SIDI Turbo makes its debut next year in the small ADAM, it can also be used globally in a range of GM applications including larger vehicles, in combination with manual or automatic transmissions.
Like all new-generation Opel power plants, the 1.0 SIDI Turbo is successfully focused on meeting a growing customer demand for ‘downsized’ engines which are able to deliver reduced fuel consumption and CO2 emissions, as well as the power and refinement typical of larger displacement engines.