| 摘要 |
PROBLEM TO BE SOLVED: To achieve reduction of pump noises and vibrations, in a configuration of multiple-port pumps having three or more ports, in a pump for closed-circuit configuration.SOLUTION: A multiple-port pump unit 70 is rotatably arranged in a casing 108, and includes a cylinder block 112 having a plurality of cylinders 122, and a plurality of ports formed on a valve plate 116 fixed to the casing 108. Some ports are connected to a pressure chamber of a boom cylinder, the remaining ports are connected to an oil tank. A notch which becomes gradually smaller as coming nearer toward the tip is provided, at the end of the same side as a rotational direction of the cylinder block 112 of an opening end of each port. A notch provided at top dead center position of piston, and a notch provided at bottom dead center position of piston are made larger, while a notch provided at a middle position between the top dead center position and the bottom dead center position of piston are made smaller. |
