| 摘要 |
<p>1422273 Fluid-pressure control systems CATERPILLAR TRACTOR CO 22 March 1973 [23 March 1972] 13921/73 Heading G3P [Also in Division F2] A pilot valve 10 comprises a housing 12 in which are reciprocally mounted identical spools 16, 16 having passages to control the flow of positioning liquid through lines 74, 76 to the main valve 72 of a servomotor. The spool 16 has a central land 36 in alignment with an inlet passage 18 from pump 20. Slight axial movement, say to the right, of spool 16 from its neutral position causes liquid to flow from inlet 18 into a transverse spool slot 50 and thence through axial port 46 into annular groove 32 in communication with line 74. A leak-off from groove 32 to drain 22 via a port 58 in land 42 ensures that the pressure in line 74 is less than in inlet 18. The control spool 82 of main valve 72 is thus caused to move rapidly to the right, through its dead band range, against the action of a low rate centering spring until contact is made with a high rate spring. Further rightwards movement of pilot spool 16 places an axial, variable section, slot 54 in parallel with the now fully effective port 46 so as to increase the control pressure in line 74. A further rapid increase in the latter occurs when spool 16 has moved to such extent that leak-off port 58 is blocked. Fig. 3 (not shown) illustrates the relationship between spool travel and control pressure spool 16 includes an identical set of ports &c. on the opposite side of central land 36 to control pressure in line 76, a dowel 66 to prevent rotation of the spool, and biasing springs 70.</p> |
