Abstract: A combine harvester (102) drive system switches between a first isochronous operating curve (622) and a second isochronous operating curve (628) of an isochronously governed engine (126) when a load on the combine harvester engine (126) reaches one or more threshold load conditions.

Abstract: A grass treatment device is provided, which comprises a motor configured to provide a power, a grass treatment tool configured to interact with and treat a grass surface, a drive mechanism configured to propel the device relative to the grass surface and a transmission operably positioned between the motor, the tool and the drive mechanism. The transmission is configured to transmit power from the motor independently to the tool and to the drive mechanism. The transmission is further configured to transform a constant output from the motor into independent variable powering of the tool and the drive mechanism.