Hydraulic hybrid vehicle with large-ratio shift transmission and method of operation thereof

A drive system for a hybrid vehicle, comprising:

• a first power source, including a first pump/motor having a first driveshaft;
• a second power source, including a second pump/motor having a second driveshaft rotationally coupled to the first driveshaft so as to rotate at a common rate with the first driveshaft;
• a third pump/motor configured to be powered to pressurize fluid for driving the first and second pump/motors;
• a mechanical transmission having an input and an output, the input operatively coupled to the first and second driveshafts, the transmission including a neutral setting, at which the first and second pump/motors are disengaged from the output;
• a third power source capable of providing motive power to the vehicle independent of the first and second power sources.

A method for operating a hybrid vehicle, comprising:

• accelerating the hybrid vehicle by applying high-pressure fluid to a hydraulic machine coupled to apply torque to a drive axle of the vehicle;
• removing torque applied by the hydraulic machine by reducing a fluid displacement of the machine;
• following the removing torque, changing from a first gear ratio to a second gear ratio of a transmission interposed between the hydraulic machine and the drive axle, a difference in ratio between the first gear ratio and the second gear ratio being at least 2:1;
• and
• following the changing from a first gear ratio to a second gear ratio, restoring torque applied by the hydraulic machine by increasing the fluid displacement of the machine.