This invention relates to an improvement of a carburetor with an exhaust gas recirculation system for internal combustion engines.
For reduction of noxious substances in an exhaust gas and consumption of fuel, it is necessary to make a fuel-air mixture produced by a carburetor lean to the extent within which operation performance of the engine is not lost, which follows protection of a catalyst used for the reduction of the noxious substances, because by the lean fuel-air mixture it is possible to avoid abnormal elevation of temperature adjacent to or at the catalyst. In an internal combustion engine employing the exhaust gas recirculation system for reduction of nitrogen oxides (NO.sub.x), it is impossible to make the fuel-air mixture lean over all the scope of operation of the engine, because during the recirculation of an exhaust gas from the engine, the fuel-air mixture is further made lean, so that the operation performance of the engine comes to be extremely bad.
As measures for preventing the fuel-air mixture from being made lean, a vacuum-responsive fuel compensation device supplying fuel into a main fuel passage during running of the engine under a low output is known. The device is provided with a solenoid valve which is driven by a gear switch and suction vacuum detecting switch, and close or open an vacuum passage, so that fuel jetted from the main fuel passage is compensated to produce rich fuel-air mixture. The device, however, closes or opens a fuel compensation valve by making use of a vacuum change and compensates fuel through the main fuel passage the nozzle portion of which is provided in a Venturi portion, so that the quantity of compensated fuel is approximately constant and even if the device is used for the exhaust gas recirculation system, it is difficult to effect the compensation of fuel corresponding to a rate of the recirculation of the exhaust gas. Therefore, the reduction of the fuel consumption and the noxious substances in the exhaust gas is not necessarily sufficient.