US Patent 7234298 Hybrid hydraulic system and work machine using same

A hydraulic system and work machine are provided, the hydraulic system including at least one hydraulic cylinder with a first port and a second port connected by a first fluid passage. A first pump, which is a bi-directional hydraulic pump is positioned within the first fluid passage, and a second pump is positioned in parallel with the first pump and disposed within a second fluid passage. An accumulator fluidly connects with the second fluid passage.