Engine assist by recovering swing kinetic energy

A method for recovering swing kinetic energy in a hydraulic system of a machine, comprising:

• providing pressurized fluid to a swing motor with a pump of the machine to cause the swing motor to swing a work tool of the machine about a vertical axis;
• sensing a fluid pressure from the swing motor at a swing charge valve;
• opening the swing charge valve to fluidly connect the swing motor to a first accumulator in response to a sensed fluid pressure from the swing motor being greater than or equal to a charge set pressure of the swing charge valve and causing the swing charge valve to move from a normally closed position toward an open position;
• selectively fluidly connecting the first accumulator to an assist motor via a discharge valve, wherein the assist motor is operatively connected to a power source of the machine;
• determining a power demand on the power source for output power;
• and
• causing the discharge valve to fluidly connect the first accumulator with the assist motor in response determining that the power demand on the power source for output power is greater than a minimum assisted power demand.

An energy recovery system for a machine having a work tool movable through segments of an excavation cycle, a swing motor configured to swing the work tool about a vertical axis, a pump selectively fluidly connected to the swing motor to provide pressurized fluid to cause the swing motor to swing the work tool, a power source operatively connected to the pump to output power to drive the pump, and a controller, the energy recovery system comprising:

• a first accumulator;
• a swing charge valve having a normally closed position, an open position, and a charge set pressure, the swing charge valve being positioned to selectively fluidly connect the swing motor to the first accumulator, wherein the swing charge valve moves from the normally closed position to the open position and fluidly connects the swing motor to the first accumulator when a swing motor fluid pressure communicated to the swing charge valve from the swing motor is greater than the charge set pressure;
• an assist motor operatively connected to the power source;
• and
• a discharge valve having a normally closed position and an open position, the discharge valve being positioned to selectively fluidly connect the first accumulator to the assist motor,
• wherein the controller is configured to determine a power demand on the power source to output power, and to cause the discharge valve to move from the normally closed position to the open position to fluidly connect the first accumulator with the assist motor in response determining that the power demand on the power source is greater than a minimum assisted power demand.