Brake warning switch with bypass

Claim 2

In a dual hydraulic system having first and second lines normally subject to substantially equal pressures, a sensing unit connected to said first and second lines to produce a signal responsive to a predetermined pressure differential between said lines and a pressure changing device in one of said lines for changing the pressure in said one line, the improvement comprising said sensing unit including a housing, a first member axially movable in said housing responsive to said predetermined pressure differential and having a neutral position when said pressures are balanced, a second member in said housing, said first and second members being constructed and arranged to provide relative movement between said first and second members by said predetermined pressure differential, cooperating valve means carried by said first and second members and operable by said axial movement of said first member from said neutral position to render said pressure changing device inoperable to change said pressure in said one line, said cooperating valve means including an internal axial passage extending from an end face of one of said members and a poppet axially sealingly engaging a portion of said end face surrounding said passage when said first member is in said neutral position, and said poppet being axially separated from said portion of said end face surrounding said passage by said axial movement of said first member from said neutral position to open said axial passage.

Claim 3

A device as set forth in claim 1 including spring means operable in said neutral position to axially bias said cooperating valve means into axially sealing engagement.

Claim 4

A device as set forth in claim 1 wherein said internal axial passage is in said first member.

Claim 5

A device as set forth in claim 1 including spring means operable in said neutral position to axially bias said poppet against said portion of said end face surrounding said passage when said first member is in said neutral position.

Claim 6

A device as set forth in claim 4 including stop means for limiting axial movement of said poppet toward said portion of said end face surrounding said passage to permit said separation of said poppet from said portion of said end face surrounding said passage by said axial movement of said first member from said neutral position.

Claim 7

A combination hydraulic brake warning device for use in dual brake systems including a housing, an axial bore in said housing, piston means slidably mounted in said axial bore and making sealing engagement with the walls thereof, signal sensing means operable by axial movement of said piston means in said bore in either direction from a neutral position, passage means at one end of said axial bore to admit fluid pressure therein, from a first brake line, a chamber at the other end of said axial bore at the other end of said piston means whereby said piston means is normally held in the centered position by a balanced fluid pressure at said passage means and said chamber, an inlet to said chamber connected to a second brake line, said chamber having an outlet passage, a pressure changing valve having an inlet and an outlet, said valve inlet being connected to said chamber outlet passage, a port in said housing intermediate the ends of said piston means, said port being connected to the outlet from said pressure changing valve and to the brake actuators, an internal axially extending passage in said piston means extending from an end face of said piston means in said chamber to said port, and a valve poppet in said chamber operable to axially engage a portion of said end face surrounding said passage to close said passage when said piston means is in a centered position, and said axial movement of said piston means in one direction away from said centered position axially separating said poppet from said portion of said end face surrounding said passage to open said passage to bypass said pressure changing valve.

Claim 8

A combination hydraulic brake warning device for use in dual brake systems including a housing, an axial bore in said housing, piston means slidably mounted in said axial bore and making sealing engagement with the walls thereof, signal sensing means operable by axial movement of said piston means in said bore in either direction from a neutral position, passage means at one end of said axial bore to admit fluid pressure therein, from a first brake line, a chamber at the other end of said axial bore at the other end of said piston means whereby said piston means is normally held in the centered position by a balanced fluid pressure at said passage means and said chamber, an inlet to said chamber connected to a second brake line, said chamber having an outlet passage, a pressure changing valve having an inlet and an outlet, said valve inlet being connected to said chamber outlet passage, a port in said housing intermediate the ends of said piston means, said port being connected to the outlet from said pressure changing valve and to the brake actuators, an internal axially extending passage in said piston means extending from an end face of said piston means in said chamber to said port, and a valve poppet in said chamber operable to axially engage a portion of said end face surrounding said passage to close said passage when said piston means is in a centered position, and said axial movement of said piston means in one direction away from said centered position axially separating said poppet from said portion of said end face surrounding said passage to open said passage to bypass said pressure changing valve.

Claim 9

A brake warning device as set forth in claim 6 including stop means for limiting axial movement of said poppet toward said portion of said end face surrounding said passage to permit said separation of said poppet from said portion of said end face surrounding said passage by said axial movement of said first member from said neutral position.

Claim 10

A brake warning device as set forth in claim 7 wherein said device includes a first spring at said one end of said axial bore biasing said piston means toward said chamber and a second spring in said chamber biasing said piston means away from said chamber, whereby both of said springs bias said piston means toward said centered position, said second spring also engaging said poppet to hold said poppet in axial engagement with said portion of said end face surrounding said piston means when said piston means is in said centered position.

Claim 11

A brake warning device as set forth in claim 8 wherein said stop means is an annular shoulder in said housing engageable by said poppet to limit movement of said poppet away from said chamber.

Claim 12

A brake warning device as set forth in claim 9 wherein said poppet comprises a rigid carrier in said chamber adapted to engage saId annular shoulder to limit movement of said poppet away from said chamber and an elastomeric poppet member secured to said carrier and adapted to make axial sealing engagement with said portion of said end face surrounding said piston means.