Abstract A first piston is displaceable in a housing and has a first piston portion having a larger effective surface and movable in one direction. A second piston portion normally disengaged from the first piston portion has a smaller effective surface and is moveable in an opposite direction into operative engagement with the first piston portion. The second piston is spaced from and defines with the first piston portion a chamber. A first inlet communicates with this chamber and is at the pressure prevailing in a first hydraulic brake circuit. A second inlet communicates with a smaller effective surface of the second piston portion and is at the pressure prevailing in a second hydraulic brake circuit. A biasing arrangement biases the second piston portion in the aforementioned one direction until the pressure upon the smaller effective surface exceeds the biasing force so that the second piston portion moves in the opposite direction into operative engagement with the first piston portion, with the result that the force acting upon the first piston portion urging the same in the one direction is reduced to the differential of the forces acting upon the effective surfaces of the two piston portions. A third inlet is subject to the pressure prevailing in a trailer brake circuit, and a third feed-back piston is connected with the second piston to resist movement thereof in the opposite direction and has a reaction surface exposed to the pressure of the third inlet and so dimensioned that the force acting upon it is substantially equal to the aforementioned differential.
In a trailer brake control valve actuated by dual pneumatic brake circuits of road vehicles, a combination comprising a housing; a first piston displaceable in said housing and comprising a first piston portion having a larger effective surface and being movable in one direction, and a second piston portion normally disengaged from said first piston portion and having a smaller effective surface, said second piston portion being movable in an opposite direction into operative engagement with said first piston portion; a second piston spaced from and defining with said first piston portion a chamber, said second piston being movable in said opposite direction; a first inlet communicating with said chamber and being under pressure prevailing in a first hydraulic brake circuit; a second inlet communicating with said smaller effective surface of said second piston portion and being under the pressure prevailing in a second hydraulic brake circuit; biasing means biasing said second piston portion in said one direction until pressure upon said smaller effective surface exceeds the biasing force of said biasing means so that said second piston portion moves in said opposite direction into operative engagement with said first piston portion, so that the forcE acting upon said first piston portion and urging the same in said one direction is reduced to the differential of the forces acting upon said effective surfaces; a third inlet subject to the pressure prevailing in a trailer brake circuit; and a third feed-back piston connected with said second piston to resist movement thereof in said opposite direction and having a reaction surface which is exposed to said pressure in said third inlet and so dimensioned that the force acting upon it substantially equals said differential.
Claim 2
Dependent Claim
282 words
In a trailer brake control valve actuated by dual pneumatic brake circuits of road vehicles, a combination comprising a housing; a first piston displaceable in said housing and comprising a first piston portion having a larger effective surface and being movable in one direction, and a second piston portion normally disengaged from said first piston portion and having a smaller effective surface, said second piston portion being movable in an opposite direction into operative engagement with said first piston portion; a second piston spaced from and defining with said first piston portion a chamber, said second piston being movable in said opposite direction; a first inlet communicating with said chamber and being under pressure prevailing in a first hydraulic brake circuit; a second inlet communicating with said smaller effective surface of said second piston portion and being under the pressure prevailing in a second hydraulic brake circuit; biasing means biasing said second piston portion in said one direction until pressure upon said smaller effective surface exceeds the biasing force of said biasing means so that said second piston portion moves in said opposite direction into operative engagement with said first piston portion, so that the forcE acting upon said first piston portion and urging the same in said one direction is reduced to the differential of the forces acting upon said effective surfaces; a third inlet subject to the pressure prevailing in a trailer brake circuit; and a third feed-back piston connected with said second piston to resist movement thereof in said opposite direction and having a reaction surface which is exposed to said pressure in said third inlet and so dimensioned that the force acting upon it substantially equals said differential.
Claim 3
Dependent Claim
74 words
A combination as defined in claim 1; and further comprising mounting means connected and movable with said first piston portion and mounting said second piston portion for movement relative to said first piston portion in said opposite direction through a predetermined distance, and including abutment means engaged by said second piston portion upon movement of the same through said distance so that said second piston portion becomes operatively engaged with said first piston portion.
Claim 4
Dependent Claim
15 words
A combination as defined in claim 2; and further comprising means for varying said distance.
Claim 5
Dependent Claim
55 words
A combination as defined in claim 1; further comprising a tubular member connected and movable with said third piston; and a piston member surrounding said tubular member and having a first and an oppositely directed second piston member surface which are respectively exposed to the pressure of a hydraulic-fluid reservior and of a safety-brake circuit.
Claim 6
Dependent Claim
48 words
A combination as defined in claim 4; and further comprising means preventing movement of said piston member relative to said tubular member in direction from said first toward said second piston member surface, but permitting such movement in direction from said second toward said first piston member surface.