Valve assembly for brake fluid pressure control

A valve assembly for brake fluid pressure control in a system having a brake master cylinder and a wheel brake cylinder, comprising:

• a body having an inlet port connected to the brake master cylinder, an outlet port connected to the wheel brake cylinder, and a cylinder bore communicating the inlet and outlet ports;
• a first seat member having an axially extending bore and a seat surface and fitted securely in the cylinder bore in sealed relation with respect to a wall surface of the cylinder bore;
• a second seat member having an axially extending bore and a seat surface and fitted securely in the cylinder bore in sealed relation with respect to the wall surface of the cylinder bore and adjacent to said first seat member;
• a third seat member having a seat surface, a first end portion fitted into the bore of said first seat member in sealed relation therewith and a second end portion fitted into the bore of said second seat member in sealed relation therewith for forming first and second valve chambers inside said first and second seat member, respectively;
• first and second valve elements accommodated in said first and second valve chambers, respectively;
• first and second passageway means arranged in parallel each for connecting the inlet port to the outlet port through the first and second valve chambers in secession;
• a spring for urging the first valve element to contact with the seat surface of said first seat member to cut off said first passageway means, and for urging the second valve element to separate from the seat surface of said third seat member to open said second passageway means and bring said second valve element into contact with the seat surface of said second seat member for cutting off said first passageway means;
• a pressure reducing piston for separating the first valve body from the seat surface of said first seat member against said spring;
• and
• a by-pass piston for separating the second valve element from the seat surface of said second seat member and bringing said second valve element into contact with the seat surface of said third seat member against said spring;
• said third seat member having an outer diameter smaller than an inner diameter of said first and second seat members and being provided with first and second annular grooves formed in its outer periphery and fitted with seal rings for providing a seal between the outer periphery of said third seat member and wall surfaces of the axially extending bores of said first and second seat members, respectively;
• first and second passages constituting said first passageway means being formed respectively in said first and second seat members, said first and second passages extending axially of said first and second seat members and being offset by equal distances from a central axis thereof;
• said first and second seat members being further provided with respective first and second holes opposing each other at relative angular positions when said first and second passages are in communication with each other;
• said first and second seat members being joined to each other by a pin press fitted into said first and second holes, said first, second and third seat members, said first and second valve elements and said spring constituting a unitary assembly by means of said pin.