This disclosure relates to powertrain systems and, more particularly, to cylinder deactivation powertrain systems.
Conventionally, applying cylinder deactivation on piston engine powertrains provides improved fuel economy over a combination of speeds and loads limited by excessive torque pulses. However, the limited speed-load range of those piston engine powertrains, where cylinder deactivation can be used, reduce the overall improvement in fuel economy to such a degree that few production vehicles employ cylinder deactivation. When cylinder deactivation is employed, one or more cylinders are fired and then skipped, or deactivated, and a time lapse occurs until the next cylinder fires. The resulting time lapse translates into roughness that can become a customer dissatisfier. This irregular or staggered torque output reduces the fuel economy efficiency otherwise available from cylinder deactivation. In addition, the exhaust emissions generally increase due to the inconsistent fuel delivery and combustion.
Accordingly, there exists a need to selectively fire cylinders without causing objectionable torque pulses and increasing emissions.
The drawbacks and disadvantages of the prior art are overcome by the embodiments of the powertrain system described herein. The powertrain system comprises an engine coupled to a drive shaft, and a torque-smoothing device that is configured to sometimes assist the drive shaft by adding energy, and at other times to move energy from the drive shaft to the energy storage device. The engine is also equipped with a cylinder deactivation system configured to deactivate one or more engine cylinders, and a direct cylinder injection system configured to deliver fuel to firing cylinders. An engine management system is configured to provide control, diagnostic and maintenance operations for the powertrain system.
The method for operating the internal combustion engine comprises activating the engine, and deactivating one or more engine cylinders. When the engine generates an inconsistent torque output, a torque-smoothing system is activated to smooth the torque output of the engine.