Energy recovery system for work vehicle including hydraulic drive circuit and method of recovering energy

An energy-recovering hydraulic drive system for a work vehicle, comprising:

• an internal combustion engine;
• a drive wheel;
• a gas-charged hydraulic fluid accumulator;
• a hydraulic reservoir;
• and
• a closed loop hydrostatic drive circuit, including a pump, a drive motor, a first conduit, a second conduit and a valve assembly,
• the drive pump being drivingly coupled to the engine and including first and second pump ports, each of the first and second pump ports functioning as both a hydraulic fluid inlet and a hydraulic fluid outlet,
• the drive motor including first and second motor ports, each of the first and second motor ports functioning as both a hydraulic fluid inlet and a hydraulic fluid outlet,
• the drive motor being coupled to the drive wheel to drive the work vehicle over the ground,
• the first conduit being in fluid communication with the first pump port and the first motor port,
• the second conduit being in fluid communication with second pump port and the second motor port, and
• the valve assembly being in selectively changeable between (1) a first configuration in which a first portion of hydraulic fluid leaving the first pump port is directed into the accumulator and simultaneously an amount of hydraulic fluid is directed from the reservoir into the first motor port;
• and (2) a second configuration in which a second portion of hydraulic fluid leaving the second port of the motor is directed into the reservoir and simultaneously an amount of hydraulic fluid is directed from the accumulator into the second port of the pump.