Hydraulic servo-drive device and variable turbo-supercharger using the same

A variable geometry turbocharger, comprising:

• exhaust inlet walls provided facing to each other at a nozzle at an outer side of a turbine wheel;
• a plurality of nozzle vanes disposed between the exhaust inlet walls at a predetermined interval along a circumferential direction of the turbine wheel;
• a slide mechanism that advances and retracts, in a facing direction, one of the exhaust inlet walls relative to the other of the exhaust inlet walls;
• and
• a hydraulic servo drive device for driving the slide mechanism, the hydraulic servo drive device comprising:
• a pilot spool that is slid by a pilot pressure and switches between supply and shutoff of oil;
• a biasing unit that biases the pilot spool;
• a servo piston that is slid in accordance with the pilot spool;
• a detector that detects a displacement of the servo piston;
• a pump hydraulic chamber into which oil for moving the servo piston is flowed;
• a pump port to which oil from a pump is supplied;
• a piston oil path that communicates the pump port with the pump hydraulic chamber;
• a discharge circulating oil path that communicates the pump hydraulic chamber supplied with the oil with a drain port when the pump port and the pump hydraulic chamber are communicated with each other and the oil from the pump is supplied to the pump hydraulic chamber via the piston oil path;
• and
• a housing that houses the servo piston;
• wherein:
• the detector includes:
• a stator that is provided on the housing, and a movable member that is attached on an end of the servo piston via an attachment member to move with the servo piston, wherein the movable member generates a magnetic field that is detectable by the stator;
• the pump hydraulic chamber is formed, in the housing, between the movable member provided on the servo piston and the stator provided on the housing;
• a center hole penetrating along a sliding direction and housing the pilot spool is formed in the servo piston;
• and
• a pilot hydraulic chamber in which the pilot pressure works is formed between an end of the pilot spool and the movable member provided on the servo piston in the center hole of the servo piston.