| 摘要 |
<p>1512668 Hydraulic control circuits CATERPILLAR TRACTOR CO 11 Aug 1975 [12 Aug 1974] 33429/75 Heading F1P An hydraulic control system having lift cylinders 17, and a pilot operated directional control valve 16 for the cylinders comprises a pump 13, which supplies pilot fluid to a pilot valve 56 for operating the control valve 16, and a shuttle valve 79, which allows fluid to flow from the load side of the cylinders 17 to the pilot valve when the pump 13 is inoperative due to engine failure, and normally closes the connection to the pilot valve when the pump 13 is operating. Thus, if the engine fails when the piston-rods of the cylinders 17 are extended and under load, the shuttle 79 is moved downwards by a spring 81 from the position in which it is normally held by fluid pressure, and this connects line 83 to line 82 so that pressurized fluid is supplied to the pilot valve 56 so that the control valve 16 can be moved to the "lower" position. Any residual pressure below the pistons in the cylinders 17 is exhausted through a bore 85 in the pilot valve. A pump 12 supplies fluid to the control valve 16.</p> |
