Nissan’s Infiniti division will present its first Variable Compression-Turbocharged (VC-T) engine at the Paris Motor Show. This technology took them more than two decades to perfect. The QX50’s 2.0-liter turbo engine from Infiniti makes 268 horsepower and 288 pound-feet of torque while having up to 27 percent better fuel economy.
Here’s how it works. Instead of having the pistons connected to the crankshaft, Infiniti‘s engine has a pivot arm with a connection on each end. One end connects to the piston, the other connects to a second lower shaft, which is controlled by an actuator arm. At any given time the engine’s pistons move up and down according to the lobes on the crankshaft. But the actuator arm can change the angle of the pivot arm up and down. That is, the pistons still move in the same motion with the same stroke, but phase the entire stroke up or down. Move the pivot up and there’s less room at the top, which means a higher compression ratio. Move the pivot down and the compression ratio goes down, too. As an added bonus, the lower shaft eliminates the need for counter-rotating balance shafts.
Infiniti says this system works constantly and can vary the compression ratio to any number between 8:1 and 14:1. It also uses electronic variable valve timing on the intake valves to switch into Atkinson-cycle combustion for greater efficiency. The exhaust valve uses a more common oil pressure-based cam phaser. Other features include a cylinder head with integrated exhaust manifold, electronic wastegate control for the turbo, and a variable-displacement oil pump. Both port and direct fuel injection are used as well.
Infiniti says that the variable-compression-ratio technology can be scaled to other sizes of four-cylinder engines, but it is impractical for V6 and V8 engines. We expect the VC-T to be paired with a CVT in the QX50. The VC-T in the QX50 will be mounted transverse but offer some form of all-wheel drive. The transverse setup guarantees more widespread adoption. For the near future, the VC-T will be exclusive to the QX50, production of which starts in 2017.