Abstract: A hybrid swing drive system (1) of a hydraulic construction machine includes a variable displacement hydraulic swing pump (3) operable by a prime mover (2); a hydraulic swing motor (16) for performing a swing function of the machine; an accumulator (10); a controller (244); a swing control valve assembly (15) disposed in a first hydraulic path extending from the swing pump to the swing motor, the swing control valve assembly having a first position fluidly connecting the swing pump to a first side of the swing motor and a second position fluidly connecting the swing pump to a second side of the swing motor; and an accumulator control valve (12) having an open position fluidly connecting the accumulator to the first hydraulic path at an accumulator control valve connection point and a closed position fluidly isolating the accumulator from the first hydraulic path.

Abstract: A load sense open center hydraulic system provides efficiency and operator feedback and includes one or more constant flow-open center valves (218); respective one or more parallel power cores (238) operatively coupled to the one or more constant flow-open center valves; a variable capacity pump (246) directly fluidly connected to the one or more parallel power cores; and a pressure compensated flow control fluidly connected between the variable capacity pump and the one or more constant flow-open center valves. The one or more constant flow-open center valves are not fluidly coupled to a fixed capacity pump.

Abstract: A hybrid swing drive system (1) of a hydraulic construction machine includes a variable displacement hydraulic swing pump (3) operable by a prime mover (2); a hydraulic swing motor (16) for performing a swing function of the machine; an accumulator (10); a controller (244); a swing control valve assembly (15) disposed in a first hydraulic path extending from the swing pump to the swing motor, the swing control valve assembly having a first position fluidly connecting the swing pump to a first side of the swing motor and a second position fluidly connecting the swing pump to a second side of the swing motor; and an accumulator control valve (12) having an open position fluidly connecting the accumulator to the first hydraulic path at an accumulator control valve connection point and a closed position fluidly isolating the accumulator from the first hydraulic path.

Abstract: A load sense open center hydraulic system provides efficiency and operator feedback and includes one or more constant flow-open center valves (218); respective one or more parallel power cores (238) operatively coupled to the one or more constant flow-open center valves; a variable capacity pump (246) directly fluidly connected to the one or more parallel power cores; and a pressure compensated flow control fluidly connected between the variable capacity pump and the one or more constant flow-open center valves. The one or more constant flow-open center valves are not fluidly coupled to a fixed capacity pump.