PROBLEM TO BE SOLVED: To provide a hydraulic circuit that changes the lifting speed of a reaping part, controls a variation caused by a load applied to the reaping part at a lifting speed in a low-speed lifting, lifts the reaping part at the low-speed rotation of an engine and yet is safely matched to a combine harvester machine in the low-speed lifting.SOLUTION: The hydraulic circuit drives a hydraulic cylinder 2 for lifting and lowering the reaping part of a combine harvester, by a pressurized oil sent from an oil tank 3 through a hydraulic pump 4, includes a feed oil path for feeding a pressurized oil from the hydraulic pump 4 to the hydraulic cylinder 2, a drain oil path that is connected to the feed oil path and selectively changes a plurality of oil paths passing through throttles for restricting drain flow rates having different cross-section areas of flow channel and a pressure control valve 16 that is connected to the feed oil path and controls the hydraulic pressure of the feed oil path to a fixed pressure. The feed oil path includes an openable and closable switching valve 7 and a throttle 9 that is connected to the switching valve 7 in parallel and restricts a feed oil amount.COPYRIGHT: (C)2010,JPO&INPIT【課題】 刈取部の昇降速度を変速可能な油圧回路であって、低速上昇時の上昇速度において刈取部にかかる負荷によって生じる変動を抑制することができ、エンジンの低速回転時にも刈取部の低速上昇が可能であり、しかも、低速昇降に関してコンバイン本機へのマッチングが容易な、油圧回路を提供する。【解決手段】 コンバインの刈取部を昇降させる油圧シリンダー2を、オイルタンク3から油圧ポンプ4を介して送られる圧力油によって駆動するための油圧回路であって、油圧ポンプ4から油圧シリンダー2に圧力油を供給するための供給油路と、供給油路に接続され、流路断面積の異なるドレン流量制限用絞りを通る複数の油路を切り換え選択可能なドレン油路と、供給油路に接続され、該供給油路の油圧を所定圧力に制御するための圧力制御弁16と、を有し、前記供給油路は、開閉可能な切換弁7と、切換弁7と並列に接続された供給油量制限用絞り9とを有する。【選択図】 図2
