# US 7,018,002 B2 · Motor vehicle master cylinder with device for detecting actuation of a braking system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,018,002 B2 - Document ID: US7018002B2 - Status: Granted - Kind: B2 - Application number: 10/780,326 - Filed: 2004-02-17 - Published: 2004-08-26 - Granted: 2006-03-28 - Earliest claimed: 2003-02-21 - Assignees: Robert Bosch GmbH - Inventors: Olivier Masson; Jean Fourcade - Web page: https://patentgrep.com/patent/US7018002B2 ## CPC - B60Q 1/441: {Electric switches operable by the driver's pedals} - B60T 7/042: {by electrical means, e.g. using travel or force sensors} - B60T 11/16: Master control, e.g. master cylinders (master cylinders associated with vacuum boosters B60T13/565) - B60T 17/22: Devices for monitoring or checking brake systems; Signal devices - F15B 15/2807: {Position switches, i.e. means for sensing of discrete positions only, e.g. limit switches} - G01D 5/147: {influenced by the movement of a third element, the position of Hall device and the source of magnetic field being fixed in respect to each other} - G01D 5/2515: {with magnetically controlled switches, e.g. by movement of a magnet} - H01H 36/002: {Actuation by moving ferromagnetic material, switch and magnet being fixed} - H01H 36/0046: {Limit switches, also fail-safe operation or anti-tamper considerations} - B60Q: ARRANGEMENT OF SIGNALLING OR LIGHTING DEVICES, THE MOUNTING OR SUPPORTING THEREOF OR CIRCUITS THEREFOR, FOR VEHICLES IN GENERAL - B60T: VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL (electrodynamic brake systems for vehicle, in general B60L; brakes per se, i.e. devices where braking effect occurs, including ultimate brake actuators, F16D); ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES - F15B: SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR - G01D: MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR - H01H: ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES (contact cables H01B7/10; electrolytic self-interrupters H01G9/18; emergency protective circuit arrangements H02H; switching by electronic means without contact-making H03K17/00) ## Abstract The invention proposes a master cylinder 1 with a device for detecting actuation of a braking system. The detection device is fixed to a body 2 of the master cylinder 1 at a pressure chamber 5. The detection device comprises a magnetic circuit 9 able to be opened and closed by a moving magnetic piece 19. The moving magnetic piece 19 is, for example, fixed to a piston 4 of the master cylinder 1. Actuation of a brake pedal causes the piston 4 and the moving piece 19 to advance in the master cylinder 1. The magnetic circuit 9 therefore changes state (opened or closed). The change in state of the magnetic field switches the brake lights on and off. ## Claims ### Claim 1 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). ### Claim 2 (depends on 1) The master cylinder according to claim 1, characterized in that said first pole piece (29), said second pole piece (30) and said third pole piece (31) are mutually parallel and are perpendicular to a forward travel of the piston (34). ### Claim 3 (depends on 2) The master cylinder according to claim 2, characterized in that a sum of the first air gap (26) and second air gap (27) is less than a sum of the first gap (26), third air gap (25) and fourth air gap (24) and as a result said second magnetic circuit is initially isolated from said first magnetic circuit. ### Claim 4 (depends on 3) The master cylinder according to claim 3, characterized in that the magnetic piece (19) is a sleeve tube (19) having a length equal to a working stroke of the piston (34) such that when the piston (34) is in the rest position the first and second magnetic circuits are open and on movement of said piston said first and second magnetic circuit remains are sequentially closed. ### Claim 5 (depends on 4) The master cylinder according to claim 4, characterized in that the magnetic-field-variation sensor is a reed switch. ### Claim 6 (depends on 4) The master cylinder according to claim 4 wherein said movement of said magnetic piece (19) a signal is derived from said first magnetic circuit to provide a continuous visual indication of a brake application.