Anti lock brake system

Claim 1

A vehicle anti-lock brake system, of the type including one or more wheel brakes and corresponding wheel cylinders therefore, a brake pedal operated master cylinder having a hydraulic connection to said wheel cylinders for operating said wheel brakes by pressurized hydraulic fluid and a reservoir containing hydraulic fluid under atmospheric pressure, and said reservoir in communication with said master cylinder to supply hydraulic fluid to said master cylinder pressurized hydraulic fluid applied to said wheel cylinders by discharge of said pressurized hydraulic fluid including one or more outlet valves in a return line, a controllably activated pump, said pump having a working chamber, a suction chamber, and an output pressure chamber, means hydraulically connecting said output pressure chamber to one or more of said wheel cylinders including one or more inlet valves and connecting pressure lines; a suction line communicating with said reservoir and flow passage means connecting said return line to said suction chamber, to receive discharge from said wheel cylinder, said flow passage means including a reducing area region causing a sub-atmospheric pressure to develop in said discharge flow, and means placing said suction line in communication with said suction chamber via said sub-atmospheric pressure region of said flow passage means, whereby hydraulic fluid flow from said return line into said suction chamber causes suction of hydraulic fluid out of said reservoir and into said suction chamber to precharge said suction chamber with hydraulic fluid preparatory to re-pressurization of said one or more wheel cylinders.