HYDRAULIC TRANSMISSION FOR CONSTRUCTION MACHINE

摘要

PROBLEM TO BE SOLVED: To enable the present invention to be adapted for both of an attachment requiring a large flow rate and an attachment requiring a small flow rate without requiring a replacement and reform of a control valve and limiting a pilot pressure changing-over a direction changing over valve for the attachment.SOLUTION: A hydraulic transmission of this invention is installed at a mini-shovel, for example, and it has a selector valve device 34 for changing over a flow rate supplied to a direction changing-over valve 6 acting as a direction changing-over valve for an attachment to any one of a large flow rate merging hydraulic oil of a second hydraulic pump P2 and hydraulic oil of a third hydraulic pump P3 and a small flow rate corresponding to hydraulic oil of only the second hydraulic pump P2. The selector valve device 34 is disposed outside a control valve 2 and enables a supply of the hydraulic oil of the third hydraulic pump P3 to the control valve 2 and a discharge thereof to a tank T in response to the instruction positions H and L of a flow rate changing-over switch 33 to be selectively carried out.