Automatic device for controlling the pressure of the intake air of an I.C. engine as its operating altitude varies

An I.C. engine particularly for motor vehicles, provided with carburetion means for forming the in-drawn air and fuel mixture, provided with means for adjusting the mixture flow under different conditions of engine use and also provided with an automatic device for controlling the pressure of the air drawn in as the engine operating altitude varies, said device comprising first valve means adapted to induce in the air flow reaching the engine carburetion means a fall in pressure variable between a maximum value at zero altitude and a minimum value at a predetermined altitude so as to keep the pressure downstream of said valve means substantially constant and equal to the external pressure corresponding to said predetermined altitude independently of the altitude of operation of the engine, and also comprising first actuator means which control said first valve means and are operated by an operating pressure which, as the altitude of operation of the engine increases, assumes intermediate values between the external atmospheric pressure and the pressure existing downstream of said first valve means, at said predetermined altitude the operating pressure assuming a value equal to the substantially constant value existing downstream of said first valve means, and the device also comprising second valve means controlled by second actuator means sensitive to an absolute pressure which is a function of the external atmospheric pressure, said valve means controlled by said second actuator means modulating the operating pressure reaching said first actuator means.