VW's 1.5L TSI Engine Touts Diesel Efficiency without the Cost
Sometimes it seems like Europe gets all the cool cars. Case in point, the 1.5L-equipped Volkswagen Golf. The Miller-Cycle engine found in this innovative VDub is capable of diesel-like efficiency without the cost.
An alternate engine cycle and turbocharging
According to VW, its TSI ACT BlueMotion Miller-Cycle engine is 10% more efficient than comparable engines. Specs given for the 1.5L TSI's output and consumption are 128 hp and 49 mpg.
This increase in efficiency results from pairing VW's TSI (Turbocharged Stratified Injection) with the efficient Miller-cycle. In most ways, the Miller-Cycle is similar to the traditional, Otto-cycle. The main difference is Miller engines have either early or late intake valve timing.
In the case of VW's new engine, the intake valves are open for a shorter period of time. The valves are closed when the piston is still on its way up during the intake stroke. This helps reduce pumping loses under partial load. It also allows for a high, 12.5:1 compression ratio.
Then there's the variable geometry turbocharger (VGT). The VGT aids the Miller-Cycle engine by filling the cylinders with boost pressure. This helps compensate for the early intake valve timing. The VGT design features adjustable vanes that allow for variable boost. Not only is this design more efficient and precise, but it also eliminates the need for a turbo wastegate.
Micro-hybrid cylinder deactivation
Another trick the Golf has up its sleeve is cylinder deactivation. Depending on driving conditions, VW's Active Cylinder Management (ACT) has the ability to turn off either two cylinders, or all cylinders. When power demand is low, the system turns off the two inner cylinders. The driver is notified by a "2-Cylinder Mode" notification on the dash.
Paired with the automatic transmission, the engine is capable of entering eco-coasting mode. When the vehicle is allowed to coast, the engine control system turns off the engine and uses a clutch to disengage it from the drivetrain. This is a form of micro-hybrid system that harvests the vehicle's kinetic energy. A compact lithium-ion battery provides the vehicle with power when the engine is off.
The good news is, Volkswagen plans on implementing technology derived from the TSI ACT BlueMotion on future models. If we're lucky, we may even get some of that tech here in the states.
Source: Green Car Congress
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