Hybrid drive system for a harvester

A method of operating a hybrid drive system comprising a main drive, a reservoir of hydraulic fluid, a hydraulic power storage for storing hydraulic fluid at a pressure higher than that of the reservoir, a main hydraulic power unit mechanically connected to the main drive and hydraulically connected to the hydraulic power storage and to the reservoir, wherein the main hydraulic power unit comprises a plurality of hydraulic power storage units, an intermittent auxiliary drive configured to be powered intermittently by the main drive during an operating period such that the main drive powers the intermittent auxiliary drive during an activated time period and the main drive does not power the intermittent auxiliary drive during a deactivated time period and a power exchange control system coupled to the hydraulic power unit and the hydraulic power storage;

• the method comprising the steps of:
• receiving with the power exchange control system an input signal representative of an intermittent operation of the intermittent auxiliary drive during the operation period;
• determining an output signal with the power exchange control system from this input signal as a function of a desired bidirectional power exchange between the main drive and the hydraulic power storage during the operating period, wherein the output signal is configured for selectively connecting a first subset and at least one different, other subset of one or more of the hydraulic power storage units to the hydraulic auxiliary power unit;
• providing the output signal to the hydraulic power storage with the power exchange control system;
• determining for the activated time period using the power exchange control system:
• a peak load time period during which shell an average power required by the intermittent auxiliary load is higher than the average power required by the intermittent auxiliary load during the activated time period;
• and
• a nominal load time period during a remaining part of the activated time period;
• determining for the deactivated time period an initial deactivated time period followed by a subsequent deactivated time period with the power exchange control system;
• providing an output signal for connecting the first subset during the peak load time period and during the initial deactivated time period with the power exchange control system;
• providing an output signal for connecting the at least one other subset during the nominal load time period and during the subsequent deactivated time period with the power exchange control system.