Master cylinder with improved piston guidance

A master cylinder comprising:

• a casing structure defining a bore, an annular groove in surrounding relation to the bore between forward and rearward ends of the bore, and a reservoir port opening in the groove and communicating with a reservoir for containing hydraulic fluid;
• a piston mounted for sliding stroking movement in the bore between rearwardly retracted and forwardly extended positions and adapted for connection at a rearward end thereof to a piston rod;
• an annular seal positioned in the annular groove forwardly of the reservoir port;
• an annular bearing member positioned in the annular groove forwardly of the seal for guiding a forward end of the piston during stroking movement of the piston in the bore;
• the bearing member including a main body annular portion seated against an annular shoulder defining the forward end of the annular groove and an annular lip portion extending rearwardly from the main body portion and having a crenellated configuration;
• and
• the seal including a flexible annular lip portion positioned in annular surrounding relation to the bearing lip and movable in response to fluid pressure variations between an outwardly flexed position in which it blocks communication between the reservoir and the bore and an inwardly flexed position in which it allows communication between the reservoir and the bore through the bearing lip crenelation.

A master cylinder comprising a casing structure defining a bore, an annular groove in surrounding relation to the bore between forward and rearward ends of the bore, and a reservoir port opening in the groove and communicating with a reservoir for containing hydraulic fluid;

• and a piston mounted for sliding, stroking movement in the bore between rearwardly retracted and forwardly extended positions and adapted for connection at a rearward end thereof to a piston rod, characterized in that:
• the casing structure comprises a molded plastic structure;
• the bore includes a forward portion forwardly of the annular groove having a draft angle with the bore diameter forwardly decreasing;
• and
• the master cylinder further includes an annular bearing member positioned at the forward end of the annular groove and having an internal cylindrical bearing surface for receiving and guiding the piston having a diameter approximating the diameter of the piston and greater than the diameter of the forward portion of the bore at the juncture of the forward bore portion with the forward end of the annular groove.

A master cylinder assembly including a molded front part defining a forward bore, a molded rear part defining a rear bore, coacting means on the front and rear parts fixedly coupling the parts together with the forward bore and the rearward bore aligned, and a piston mounted for reciprocal stroking movement in the aligned bores between retracted and extended positions, characterized in that:

• the front part is molded with an annular groove positioned radially outwardly of the forward bore;
• the forward bore extends forwardly from the groove to a location proximate a front end of the front part and is molded with a draft angle with the diameter maximized at the groove and decreasing in a forward direction;
• and
• the master cylinder assembly further includes an annular bearing seated in the groove and having a cylindrical inner diameter conforming generally to the diameter of the piston and greater than the diameter of the forward bore portion at the groove whereby to provide bearing support for a front end of the piston as the front end of the piston moves forwardly into the draft angle forward bore.