Road load modulated exhaust gas recirculation system

Claim 1

An exhaust gas recirculating system for an internal combustion engine, having a throttle valve controlling flow through a carburetor induction passage, comprising, a duct connecting the exhaust gases to the engine intake manifold, a spring closed exhaust gas recirculation (EGR) valve normally closing the duct to prevent recirculation and movable to an open position by a signal vacuum connected thereto, the induction passage containing an exhaust gas recirculating (EGR) port located relative to the throttle valve so as to be at essentially atmospheric pressure at closed throttle positions with decreases in pressure level in proportion to the progressive opening of the throttle valve until EGR port vacuum reaches the level of manifold vacuum, conduit means operatively connecting the EGR port signal vacuum to the valve to move the same, and vacuum signal control means in the conduit means for at times reducing the EGR flow by reducing the level of the EGR vacuum signal at the EGR valve to a value below the value at the EGR vacuum port, and below the level necessary to maintain the EGR valve open, the control means including an air bleed means responsive to a predetermined mode of operation of the engine for bleeding air into the conduit means, the conduit means including first and second flow restrictors in series flow arrangement with each other, the conduit means connection to the EGR valve being between the flow restrictors, and the air bleed means being located downstream of the restrictor furthest from the EGR port.