In the Patent Specification Serial No. 482,881 of the June 25, 1974, there was described a device for correcting the air-fuel dose of internal combustion engines comprising at least one auxiliary air inlet connected to the induction manifold of the engine downstream of the member determining the dosing of the air-fuel-mixture, at least one control valve controlling the said auxiliary air inlet or inlets, the said control valve being controlled by the negative pressure prevailing in the throat of the venturi of the dosing device by means of a capsule whose diaphragm, elastically preloaded, is subjected to the said negative pressure by way of a conduit opening into the said body, the said negative pressure being itself modified by an electromagnetic valve, the opening of which is controlled by a probe arranged in the exhaust manifold and adapted to deliver an electrical current adapted to be varied in accordance with the composition of the burned gases.
The applicants have found that the device thus described is directly applicable to internal combustion engines using a gas fuel, or internal combustion engines combining the use of two fuels by using the auxiliary air inlet as a fuel gas inlet.
When the fuel is only gas, the carburettor can be dispensed with, and in that case there only remains in the induction pipe the venturi making it possible to take the dynamic negative pressure prevailing in the induction pipe, followed by the butterfly valve for regulating the air intake, the gas inlet conduit opening downstream of the said butterfly valve.
When the carburettor is retained, it is regulated so as to provide a lean mixture and the probe ensures the automatic regulation of the additional fuel gas.