Modulator in anti-skid system

Claim 1

A modulator for use in an anti-skid system for automotive vehicles wherein the volume of the fluid under pressure during braking varies by the slide movement of a plunger disposed so that the brake action is controlled thereby, comprising a first valve member disposed in a fluid passage of larger diameter in the path of fluid under pressure from a master cylinder to a wheel cylinder, a second valve member communicating with said master cylinder through a fluid flow restricting passage of small diameter in said path of fluid under pressure, a first spring normally biasing said first valve member toward an associated valve seat, and a second spring normally biasing said second valve member toward an associated valve seat, wherein said first and second valve members are in the open and closed positions respectively in the initial stage of fluid pressure application to said wheel cylinder without any control, while in the stage of fluid pressure control following said initial stage, said first and second valve members are urged to the closed and open positions respectively in response to a predetermined pressure difference between the fluid pressure at the side of said master cylinder and the fluid pressure at the side of said wheel cylinder, said second valve member being afterwards urged to the closed and open positions by the sliding movement of said plunger in combination with said second spring so that the fluid under pressure can be supplied at a controlled rate through said fluid flow restricting passage when necessary.