Secondary air pressure control valve

Abstract

A pressure control valve for venting excess air pressure in a secondary air supply conduit opening to an exhaust system of an internal combustion engine has a relief valve member to close a vent port through which excess air pressure in the secondary air supply conduit is vented. The valve member is directly operable in response to excess pressure in the secondary air supply conduit. This valve member is fixedly secured to one end of a stem slidably extending through a spring seat. The stem has at its opposite end a flange and a coil spring is compressed between the spring seat and the flange to urge the relief valve to its vent port closing position. The spring seat is spring biased in a direction toward the flange to increase compression of the coil spring and it is also moved in the opposite direction in response to intake manifold vacuum by means of a vacuum servo to reduce compression of the coil spring. When the intake manifold is higher than a predetermined magnitude, as during deceleration of the engine, the vacuum servo causes the valve member to remain opened, so that substantially all air in the secondary air supply conduit may be vented. The vacuum servo has a diaphragm dividing an enclosing casing into first and second chambers, respectively, on the opposite sides thereof, the first chamber being exposed to ambient atmospheric air, the second chamber being connected to the intake system. The spring seat is disposed in the second chamber and is fixed to the diaphragm. The vacuum servo has also a spring disposed in the second chamber to bias the diaphragm to urge the spring seat in a direction toward the flange to cause an increase compression of the coil spring.