PROBLEM TO BE SOLVED: To make the lift control of the reaping device smooth by improving the hydraulic control circuit even in the overloaded reaping operation.SOLUTION: In the hydraulic control circuit of a combine harvester, a reaping hoisting valve (12) controls pressurized oil sent to a reaping hoisting cylinder (11) which raises and lowers a reaping device (10), and a pilot nonreturn valve (65), which stops pressurized oil returning from the reaping hoisting cylinder (11), is installed to the reaping hoisting valve (12). In the hydraulic control circuit, a manual reaping lowering means (A) which compulsorily opens the pilot nonreturn valve (65) and releases the nonreturn condition is installed. Moreover, after the pressurized oil supply to the pilot nonreturn valve (65) is stopped, the nonreturn condition is composed to be released by the manual reaping lowering means (A) which opens the pilot nonreturn valve (65). In addition, the manual reaping lowering means (A) is a push pin (84) of the pilot nonreturn valve (65) to be pushed to the direction to which the pilot nonreturn valve (65) is opened by manual operation.COPYRIGHT: (C)2013,JPO&INPIT【課題】油圧制御回路を改良することで、過負荷の刈り取り作業中であっても刈取装置の昇降制御をスムースに行えるようにする。【解決手段】刈取装置(10)を昇降する刈取昇降シリンダ(11)に送る圧油を制御する刈取昇降バルブ(12)に、刈取昇降シリンダ(11)からの戻り圧油を止めるパイロット逆止バルブ(65)を設けたコンバインの油圧制御回路において、パイロット逆止バルブ(65)を強制的に開放して逆止状態を解除する手動刈取降下手段(A)を設ける。また、パイロット逆止バルブ(65)への圧油供給を停止した後に、手動刈取降下手段(A)によってパイロット逆止バルブ(65)を開放して逆止状態を解除する構成とする。また、手動刈取降下手段(A)を、手動操作でパイロット逆止バルブ(65)のパイロット逆止バルブ(65)を開放する方向に押すプッシュピン(84)とする。【選択図】図8
