Tuesday 6 November 2012

Active Cylinder Technology (ACT) Fuel saving cylinder deactivation technology

New engine family.

The 1.4 TSI of the Polo BlueGT is the top engine of the entirely new series of petrol engines that has been developed. The engine range consists of 1.0, 1.2 and 1.4 litre engines. The efficient 1.0-litre three-cylinder engines are used to drive such cars as the new up!. The 1.2- and 1.4-litre four-cylinder engines were each designed as charged direct fuel injection engines (TSI).
The outstanding technical aspect of the engine is its active cylinder management (ACT). Volkswagen is the first carmaker to implement this fuel saving cylinder deactivation technology on four-cylinder engines, as it was previously the preserve of large eight or 12 cylinder engines. Shutting down the second and third cylinders during low and medium load states reduces fuel consumption in the EU driving cycle by about 0.4 l/60 miles. For urban driving it saves as much as 1.0 l/60 miles. Even while driving at 70 km/h in fifth gear, fuel consumption of the Polo BlueGT is reduced by 0.7 l/60 miles.

Active cylinder Technology (ACT) mode of operation.

ACT is active over an engine speed range between 1,400 and 4,000 rpm and torque outputs between 25 and approx. 100 Nm – a range that covers nearly 70 per cent of all driving states in the EU driving cycle! If the driver presses the accelerator pedal hard, both cylinders begin to work again without a noticeable transition. The high efficiency of the system has no negative effects on smooth running: even with two cylinders the excellently balanced the 1.4 TSI engine of the Polo BlueGT runs very quietly and with low vibration.
All mechanical switchover processes take place within one-half of a camshaft rotation; depending on engine speed this takes between just 13 and 36 milliseconds. Accompanying interventions in ignition and throttle valve processes smooth the transitions. What’s more, thanks to an accelerator pedal sensor and intelligent monitoring software, the system can also detect irregular driving profiles – such as during a drive through a roundabout or in sporty shifting on a highway. In such cases, cylinder shut-off is deactivated. The driver is aware of whether two or four cylinders are active by a related indicator in the multifunction display between the speedometer and tachometer.

ACT components.

Altogether, the components of active cylinder management weigh just three kilogrammes. Their actuators, the camshafts and their bearing frames are integrated in the cylinder head; two low-friction bearings reduce friction of the shafts. It is only with the TSI concept – petrol direct injection plus turbocharging – that a cylinder deactivation is even conceivable in its form today.

Aluminium block reduces weight.

Thanks to an ultra-rigid aluminium die-cast crankcase, the new petrol engines are especially light with a maximum weight of 114 kg. The 1.4 TSI of the new Polo BlueGT is 22 kg lighter than its counterpart of the previous engine series. The meticulously practised lightweight construction for which Volkswagen is renowned extends to the smallest of details: for example, engine developers reduced the crankshaft main bearing diameter of the 1.4 TSI from 54 to 48 mm; the crankshaft itself was lightened by 20 per cent, while the weight of the connecting rods was even reduced by 25 per cent. The rod bearing pins are hollow bored, and the aluminium pistons (now with flat piston crowns) have also been weight-optimised.

Exhaust manifold in the cylinder head.

Particular importance was also paid to the whole issue of thermal management. To use optimally the thermal energy of the exhaust in the hot running phase, and to cool it more effectively at high loads, the exhaust manifold of the new engines was integrated in the cylinder head and was provided with its own cooling jacket.

Small turbocharger, big effects.

By means of the innovative construction of the exhaust manifold, Volkswagen was also able to use a very narrow single-scroll compressor in turbocharger selection. This also reduced the engine’s weight. In the new engine, the intercooler was integrated in the induction pipe which is made of injection-moulded plastic, allowing significantly accelerated pressure build-up. This has resulted in very responsive downsized engines.

Toothed belt in the valve drive.

In the new generation of engines, Volkswagen was also able to make further significant reductions in internal friction. Take the example of the overhead camshafts (DOHC): the drive here is not by chain, rather by a single-stage, low-friction toothed belt drive with a 20 mm wide belt and load-reducing profiled belt wheels. Thanks to its high-end material specification, this toothed belt’s service life reliably spans the life of the entire vehicle. Actuation of the valve drive via roller cam followers and an anti-friction bearing for the high loads of the first camshaft bearing also lead to reduced friction resistances.
To ensure that the engine takes up as little mounting space as possible, ancillary components such as the water pump, air conditioning compressor and alternator are screwed directly to the engine and the oil sump without additional brackets, and they are driven by a single-track toothed belt with a permanent tension roller.

Variable camshaft for more torque.

To reduce emissions and fuel consumption further, and to improve torque in the lower rev range, the intake camshaft on the engines was designed to be adjustable over a crankshaft angle range of 50 degrees– on the 140 PS 1.4 TSI of the new Polo BlueGT an exhaust camshaft adjuster is added. It permits the desired spread of control times, enabling even more spontaneous response from low revs; at the same time, torque is improved at high revs.

200 bar injection pressure.

The maximum injection pressure of the new TSI versions (direct fuel injection) is 200 bar. State-of-the-art five-hole injection nozzles deliver up to three individual injections to each of the cylinders via a stainless steel distributor bar with extreme precision. In designing the combustion chamber, Volkswagen also paid particular attention to achieving minimal wetting of the combustion chamber walls with fuel and to optimised flame propagation.

Article source: www.volkswagen.co.uk

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