# US 8,539,766 B2 · Master cylinder with flow groove > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,539,766 B2 - Document ID: US8539766B2 - Status: Granted - Kind: B2 - Application number: 12/819,633 - Filed: 2010-06-21 - Published: 2011-12-22 - Granted: 2013-09-24 - Earliest claimed: 2010-06-21 - Assignees: Robert Bosch GmbH - Applicants: Andrew Paul Wasson - Inventors: Andrew Paul Wasson - Web page: https://patentgrep.com/patent/US8539766B2 ## CPC - B60T 11/232: Recuperation valves - B60T 11/236: Piston sealing arrangements - 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 ## Abstract A master cylinder includes a cylinder bore, a first piston positioned within the cylinder bore, a second piston positioned within the bore and located forwardly of the first piston, a first pressure chamber within the cylinder bore and defined in part by a rear portion of the second piston and a forward portion of the first piston, a first pressure chamber seal extending radially outwardly from the rear portion of the second piston, a first reservoir inlet configured to provide fluid communication between a reservoir and the cylinder bore at a location forwardly of the first pressure chamber seal, and a first groove extending axially along the cylinder bore and positioned such that (i) when the second piston is in a released position, the first groove is located directly outwardly of the first pressure chamber seal and the reservoir is in fluid communication with the first pressure chamber through the first groove, and (ii) when the second piston is in an activated position, the first pressure chamber seal isolates the reservoir from the first pressure chamber at a location forwardly of the first groove. ## Claims ### Claim 1 A master cylinder comprising: a cylinder bore; a first piston positioned within the cylinder bore; a second piston positioned within the bore and located forwardly of the first piston; a first pressure chamber within the cylinder bore and defined in part by a rear portion of the second piston and a forward portion of the first piston; a first pressure chamber seal extending radially outwardly from the rear portion of the second piston; a first reservoir inlet configured to provide fluid communication between a reservoir and the cylinder bore at a location forwardly of the first pressure chamber seal; and a first groove extending axially along the cylinder bore and positioned such that (i) when the second piston is in a released position, the first groove is located directly outwardly of the first pressure chamber seal and the reservoir is in fluid communication with the first pressure chamber through the first groove, and (ii) when the second piston is in an activated position, the first pressure chamber seal isolates the reservoir from the first pressure chamber at a location forwardly of the first groove. ### Claim 2 (depends on 1) The master cylinder of claim 1, wherein the first groove is one of a plurality of grooves, each of the plurality of grooves extending axially along the cylinder bore and positioned such that when the second piston is in the released position, each of the plurality of grooves is located directly outwardly of the first pressure chamber seal. ### Claim 3 (depends on 1) The master cylinder of claim 1, wherein the first groove extends radially completely about the cylinder bore. ### Claim 4 (depends on 1) The master cylinder of claim 1, further comprising: a second pressure chamber within the cylinder bore and defined in part by a forward portion of the second piston. ### Claim 5 (depends on 4) The master cylinder of claim 4, further comprising: a second reservoir inlet configured to provide fluid communication between the reservoir and the cylinder bore at a location forwardly of the first pressure chamber seal; and a second seal extending radially outwardly from the second piston, the second seal defining a rearward portion of the second pressure chamber and a forward portion of a low pressure area, the low pressure area extending between the second seal and the first pressure chamber seal. ### Claim 6 (depends on 5) The master cylinder of claim 5, further comprising: a release path extending between the low pressure area and a rearward face of the second piston; and a first poppet assembly configured to sealingly engage the rearward face of the second piston. ### Claim 7 (depends on 6) The master cylinder of claim 6, further comprising: a second poppet assembly configured to isolate the second pressure chamber from the reservoir. ### Claim 8 A braking system comprising: a master cylinder including an inner wall defining a portion of a bore; a primary piston positioned within the bore; a secondary piston positioned within the bore and located forwardly of the primary piston; a primary pressure chamber within the bore and defined in part by a rear portion of the secondary piston and a forward portion of the primary piston; a secondary pressure chamber within the bore and defined in part by a forward portion of the secondary piston; a first seal extending radially outwardly from the second piston, the first seal isolating the secondary pressure chamber from a low pressure secondary area; a second seal extending radially outwardly from the second piston, the second seal positioned between the low pressure secondary area and the primary pressure chamber; a reservoir in fluid communication with the low pressure secondary area; and a first groove extending axially along the bore and positioned such that (i) when the secondary piston is in a released position, the first groove is located directly outwardly of the second seal and the reservoir is in fluid communication with the primary pressure chamber through the first groove, and (ii) when the secondary piston is in an activated position, the second seal sealingly engages the inner wall to isolate the reservoir from the primary pressure chamber. ### Claim 9 (depends on 8) The braking system of claim 8, wherein the first groove is one of a plurality of grooves, each of the plurality of grooves extending axially along the bore and positioned such that when the secondary piston is in the released position, each of the plurality of grooves is located directly outwardly of the second seal. ### Claim 10 (depends on 8) The braking system of claim 8, wherein the first groove extends radially completely about the bore. ### Claim 11 (depends on 8) The braking system of claim 8, wherein the reservoir is in fluid communication with a secondary pressure chamber inlet. ### Claim 12 (depends on 11) The braking system of claim 11, further comprising: a release path extending between the low pressure secondary area and a rearward face of the secondary piston; and a first poppet assembly configured to sealingly engage the rearward face of the secondary piston. ### Claim 13 (depends on 12) The braking system of claim of claim 12, further comprising: a second poppet assembly configured to isolate the secondary pressure chamber from the reservoir.