Patent ID: 7320217

Claim:
A load controller provided in a hydrostatic transmission for a work vehicle, wherein power supplied from an engine is branched to drive an implement system and a traveling system, and a hydrostatic transmission is provided in the traveling system; the hydrostatic transmission connecting, in an oil-hydraulic closed circuit, an oil-hydraulic pump driven by the engine and an oil-hydraulic motor driven by the oil-hydraulic pump; the load controller comprising: a bypass oil line for bypassing an oil line that has high pressure during forward movement in the oil-hydraulic closed circuit to reach an oil line that has low pressure during forward movement or an oil tank; a first opening/closing valve for opening or closing the bypass oil line; an opening/closing valve controller that detects a load applied to the engine while traveling during working and opens the first opening/closing valve when the load exceeds a predetermined level; a second opening/closing valve on the valve-outlet side of the first opening/closing valve that opens or closes the bypass oil line by external operation; and a flow control valve between the first opening/closing valve and the second opening/closing valve.