Patent ID: 8029395
Filing Date: 2011-10-04
Classification: F16H

Abstract:
1. A hydraulic actuator for a belt type continuously variable transmission which has a pulley that includes a fixed sheave formed integrally with a pulley shaft and a movable sheave disposed opposite to said fixed sheave to be capable of moving in an axial direction, a driving belt wound around said pulley, and a hydraulic actuator for moving said movable sheave in said axial direction, and which performs a speed shift by having said hydraulic actuator move said movable sheave such that a ratio of an effective winding diameter of said driving belt relative to said pulley is varied, comprising: a first cylinder that projects from a back surface of said movable sheave; a drum in which a first drum portion covering said first cylinder, a second drum portion having an inner end that is fitted slidably to an outer peripheral surface of a boss portion of said movable sheave, and a back surface portion connecting an end portion of said first drum portion and an end portion of said second drum portion are formed continuously; a first plunger having an outer periphery that is fitted slidably to an inner peripheral surface of said first cylinder and an inner periphery that contacts a projection formed on a peripheral surface of said second drum portion such that a first hydraulic chamber is formed between said first plunger and said back surface of said movable sheave; a second plunger having an inner periphery that is fitted slidably to said first plunger and an outer periphery that is fitted slidably to said first drum portion such that a second hydraulic chamber is formed between said second plunger and said back surface portion of said drum; a second cylinder formed with a base portion that is fixed to said pulley shaft and a cylinder portion that increases in diameter from said base portion and has an end that contacts said back surface portion of said drum; and a third plunger having an outer periphery that is fitted slidably to said cylinder portion of said second cylinder and an inner periphery that is fixed to said boss portion of said movable sheave such that a third hydraulic chamber is formed between said third plunger and said cylinder portion of said second cylinder, wherein an oil passage that connects said first hydraulic chamber and said second hydraulic chamber is formed by a gap between said second drum portion and said first plunger, which are fitted together via said projection.