| 摘要 |
<p>PURPOSE:To accurately perform detection of speed and displacement of a spool to improve responsiveness by providing a spool speed detector and a displacement detector on both end parts of the spool driven directly by means of a force motor. CONSTITUTION:When a coil 4 wound round the big bobbin 3 of a force motor A is electrified, axial force is generated on said bobbin 3 by means of a magnetic circuit formed by a big yoke 1 and a big permanent magnet 2. By means of the axial force, a spool 8 is axially moved in a sleeve 7 through a plate spring 5 to change over oil pressure ports 14a-14c. At this time, speed of the spool 8 is detected by means of a speed detector 11 formed by a small permanent magnet 11b in a small yoke 11a and a small bobbin 11c, which is formed by winding a coil 11d, while displacement of the spool 8 is detected by means of a displacement detector 9 formed by a magnetic-resistant element piece 9c piercing between magnets 9a and 9b. The servo valves concerned are subjected to feedback control in compliance with output of the detectors 11, 9.</p> |
