US 4,118,076 AGranted

Control valve having reduced crack-open pressure

AssigneeWagner Electric Corporation

InventorWilliam M. Mild

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Abstract

A control valve having relay and proportioning pistons has an intermediate piston which controls air pressure access to a blind flow chamber. At a relatively low value of control air pressure, the intermediate piston is shuttled into a position which closes and traps the existing value of control air pressure in the blind flow chamber. The trapped constant value of air pressure in the blind flow chamber operates on a larger area piston whose force is added to the forces derived from further increases in control air pressure to provide a first region of output air pressure having incremental increases smaller than the input. When the input air pressure reaches a certain value, a second region of output air pressure is reached where further increases in input air pressure cause metered addition to the air pressure in the blind flow chamber and thus produces incremental output increases greater than incremental input increases. At a high value of input air pressure, a third region is reached in which output and input air pressures become and remain equal.

Claims15

Dependent claims

A control valve comprising:

(a) a housing;
(b) said housing being adapted to receive control fluid pressure at a first inlet, fluid pressure at a second inlet and providing brake fluid pressure at an outlet thereof;
(c) control valve means moveable in said housing for controlling the application therethrough of fluid pressure from said second inlet to said outlet upon receipt at said first inlet of control fluid pressure;
(d) differential piston means within said housing, said differential piston means having larger and smaller piston areas in sealing contact with larger and smaller bores in said housing;
(e) means for freely communicating control fluid pressure to said larger piston area at fluid pressures between atmospheric pressure and a first level of control fluid pressure greater than atmospheric pressure;
(f) means for isolating said larger piston area from said control fluid pressure upon the occurrence of said first level of control fluid pressure, whereby a fixed value of fluid pressure equal to said first level is trapped between said larger and smaller piston areas;
(g) means for providing brake fluid pressure in a first predetermined ratio to said control fluid pressure for control fluid pressure between said first and a second, higher level of control fluid pressure;
and
(h) means for admitting control fluid pressure in metered amounts between said larger and smaller piston areas at greater than said second level of control fluid pressure higher than said first level of control fluid pressure, whereby brake fluid pressure is provided in a second predetermined ratio higher than said first predetermined ratio.

6 more elements

A control valve comprising:

(a) a housing;
(b) said housing being adapted to receive control fluid pressure at a first inlet, fluid pressure at a second inlet and providing brake fluid pressure at an outlet thereof;
(c) control valve means moveable in said housing for controlling the application therethrough of fluid pressure from said second inlet to said outlet upon receipt at said first inlet of control fluid pressure;
(d) differential piston means within said housing, said differential piston means having larger and smaller piston areas in sealing contact with larger and smaller bores in said housing;
(e) means for admitting control fluid pressure to said larger piston area at fluid pressure between atmospheric pressure and a first level of control fluid pressure greater than atmospheric pressure;
(f) means for isolating said larger piston area from said control fluid pressure upon the occurrence of said first level of control fluid pressure, whereby a fixed value of fluid pressure equal to said first level is trapped between said larger and smaller piston areas;
(g) means for providing brake fluid pressure in a first predetermined ratio to said control fluid pressure for control fluid pressure between said first and a second, higher level of control fluid pressure;
and
(h) means for admitting control fluid pressure in metered amounts between said larger and smaller piston areas at greater than said second level of control fluid pressure higher than said first level of control fluid pressure, whereby brake fluid pressure is provided in a second predetermined ratio higher than said first predetermined ratio, said means for isolating comprises:
(i) an intermediate bore within said differential piston means;
(ii) an intermediate piston in sealing relationship within said intermediate bore;
(iii) upper and lower flow passage means in bypass relationship to said smaller piston area;
(iv) first valve means on said differential piston means between said upper and lower flow passages;
(v) second valve means on said intermediate piston, said second valve means being axially aligned with said first valve means;
(vi) said intermediate piston having first and second positions;
(vii) a spring urging said intermediate piston into its first position;
(viii) said intermediate piston being urged into its second position by the force of fluid pressure across the effective area of the intermediate piston;
and
(ix) said first and second valve means being in sealing contact when said intermediate piston is in its second position;
whereby said upper and lower flow passages are isolated from each other.

17 more elements

Dependencies are inferred from the claim text.