| 摘要 |
A steering arrangement includes four hydraulic pressure chambers 31-34, the first and third of which are selectively operable to steer in a first direction and the second and fourth being selectively operable to steer in a second direction. Pistons 38, 42, cylinders 37, 41, double acting rams and a ratio changeover valve 26 are provided. A pump system (52A, 52B see fig 5A) supplies pressurised fluid to the chambers via a steering system which has a first mode wherein pressurised fluid is simultaneously supplied to a selected pair of the chambers 31-34 depending on the steering direction. In a second mode, the fluid is supplied by an automatic steering system to one of the pressure chambers depending on the steering direction. In automatic mode a pump (52B) supplies pressurised hydraulic fluid to a GPS steering valve 122. The invention is usable with agricultural vehicles where a quick change of direction is needed or when GPS and automatic steering are used when accuracy of ploughing or spraying direction is required. The arrangement is also operable following pump failure. |
