Motor vehicle master cylinder with device for detecting actuation of a braking system

A master cylinder (1) for a motor vehicle braking system, comprising:

• a body (2) made of non-magnetic material;
• a bore (3) located in the body (2) of the master cylinder;
• a variable-volume pressure chamber (5) within the bore (3);
• a piston (34) located in the bore that slides therein for varying the volume of the pressure chamber (5);
• and
• a detection device (9) fixed to the body (2) of the master cylinder and facing the bore for detecting actuation of the braking system corresponding to movement of the piston, said detection device having first circuit and a second circuit that are opened or closed by a magnetic piece (19) carried by the piston (4), characterized in that said first magnetic circuit is defined by a first pole piece (29) having a first gap (26) formed with the magnetic piece (19), a second pole piece (30) having a second gap (27) formed with the magnetic piece (19) and a magnet (32) located between the first and second pole pieces such that when said piston is in a rest position a residual magnetic flux flows in said first magnetic circuit by way of said first and second air gaps and said second magnetic circuit is defined by a third pole piece (31) having a third gap (25) formed with the magnetic piece (19) and a fourth gap (24) formed between said first pole piece (29) and said third pole piece (31) and a magnetic-field-variation sensor (28) that is isolated from said residual magnetic flux flow in said first magnetic circuit by said third gap and said fourth gap when the piston (34) is in the rest position and only when the piston moves is the magnetic-field-variation sensor (28) closed and magnetic flux flow occurs in the second magnetic circuit to provide an indication of the movement of the piston (34).