Diesel engine exhaust gas recirculation system with greater atmospheric pressure compensation at low engine load

Claim 1

An exhaust gas recirculation system for a diesel engine for a vehicle utilizing an air intake system and an exhaust system, comprising: (a) an exhaust gas recirculation passage a downstream end of which is connected to said exhaust system and an upstream end of which is connected to said air intake system, so as to recirculate exhaust gas from said exhaust system to said air intake system; (b) an exhaust gas recirculation control valve comprising a pressure chamber, which regulates flow resistance of said exhaust gas recirculation passage according to an amount by which the pressure in said pressure chamber is lower than ambient atmospheric pressure, so as to regulate a flow amount of said recirculation of exhaust gas from said exhaust system to said air intake system; (c) means for providing a supply of low pressure; (d) an absolute pressure control valve, comprising an input port and an output port, which receives supply of low pressure from said means for providing low pressure at said input port, and which provides a supply of pressure at said output port the absolute pressure value of which is substantially fixed; (e) a regulator valve comprising an input port and an output port, said regulator valve receiving at said input port a supply of said pressure at said output port of said absolute pressure control valve the absolute pressure value of which is substantially fixed, and producing at said output port an output pressure value which depends upon engine load; and (f) a vacuum control valve comprising a pressure regulating chamber which receives a supply of pressure from said means for providing low pressure and an output port opening from said pressure regulating chamber, and in accordance with increasing engine load increasing an absolute pressure value at and below which pressure in said pressure regulating chamber is bled to atmosphere, and further comprising a control chamber which receives supply of said output pressure value from said output port of said regulator valve and which controls the bleeding of said pressure regulating chamber to atmosphere according to the pressure therein by altering said certain pressure value, and said output port of said vacuum control valve being communicated to said pressure chamber of said exhaust gas recirculation control valve.