Hydraulic booster device

Abstract

In this invention, an idea is adopted in which the pressure at a forward portion and a backward portion of valve device is steppingly dropped twice. The valve device of the present invention includes, on the axis of a spool 600, a first valve 710 located nearer an inlet port and a second valve 720 located nearer an outlet port. A throttling area made by the second valve 720 is larger than a throttling area made by the first valve 710. For example, of all the pressure difference equal to 120 kg/cm.sup.2 or more required at the forward and backward portions of the valve device, a portion in the range where the problem of an occurrence of a foreign noise is not encountered (for example, a portion ranging from 100 to 120 kg/cm.sup.2) is undertaken by the first valve 710, and the remaining portion ranging from 20 to 30 kg/cm.sup.2 is undertaken by the second valve 720. By doing so, there can be eliminated such a pressure difference where a generation of a noise before and after an actual throttling (including a primary throttling made by the first valve 710 and a secondary throttling made by the second valve 720) can become a problem.

Dependencies are inferred from the claim text.