Master cylinder

This invention relates to a master cylinder wherein a piston assembly has first and smaller second surface areas that are combined to define a first effective area while the smaller second surface area defines a second effective area in a first chamber and where operational pressurized hydraulic fluid presented to the first chamber is directly communicated to wheel brakes in a first brake circuit and acts on the first effective area to pressurize fluid in a second chamber that is communicated to wheel brakes in a second brake circuit to effect a first brake application in response to movement of an input member by a force applied to a brake pedal and where movement of the input member by a manual force, in an absence of the presence of operational pressurized hydraulic fluid in the first chamber, moves the second effective area into the second chamber to pressurize fluid therein that is communicated to the wheel brakes in the second brake circuit. A master cylinder () including a housing () with a bore () for retaining a piston assembly () to define a first chamber () that is connected to wheel brakes (′) in a first brake circuit and a second chamber () that is connected to wheel brakes (′) in a second brake circuit. The piston assembly () includes a sleeve () and a concentric cylindrical body () whose respective first and second end surface areas define a first effective area (D) while the second end surface area of the cylindrical body () defines a second effective area (D) within the bore (). A valve () activated by axial movement of an input member () allows operational hydraulic fluid to be simultaneously communicated to the wheel brakes (′) and the first chamber () where the operational hydraulic fluid acts on the first effective area (D) to move the piston assembly () and pressurize fluid in the second chamber () to develop pressurized fluid that is communicated to wheel brakes (′) to complete a first brake application. In an absence of operational hydraulic fluid in the first chamber (), a manual input acts on the cylindrical (body ) to move the second effective area (D) into the second chamber () and pressurize fluid therein to initiate a second brake application.