Electro-pneumatic device for regulating the supply of air to an internal combustion engine

In an electro-pneumatic device for controlling the supply of additional air to an internal combustion engine to regulate the richness of the combustible mixture in said engine, said device including a suction-controlled valve, an electrically-operated valve operatively connected to said suction-controlled valve, a sensor for sensing the composition of exhaust gases from said engine and an electronic device, which is responsive to engine speed and to signals from said sensor, operatively connected to said electrically-operated valve, said suction-controlled valve being arranged to deliver extra air at predetermined rates of flow to said engine downstream of a carburettor of said engine, the improvement wherein said electro-pneumatic device further comprises:

• a. pneumatic regulator valve means, said valve means including an upstream stage in which, in operation, air pressure decreases from atmospheric pressure to an intermediate pressure, and a downstream stage in which, in operation, air pressure decreases from said intermediate pressure to a mixture delivery pressure at which combustible mixture is aspirated by said engine, each of said stages including a slide valve and at least one diaphragm actuating said slide valve, means defining a passage controlled by said downstream stage, said downstream stage opening said passage by an amount proportional to the difference between a command pressure and said mixture delivery pressure, and said upstream stage controlling the difference between said intermediate pressure and said mixture delivery pressure to maintain said difference substantially constant or proportional to said mixture delivery pressure;
• b. a command valve system including means defining a chamber in which said command pressure is generated, first passage means communicating said chamber with a source of said intermediate pressure or with atmosphere, second passage means communicating said chamber with a source of said mixture delivery pressure, and means alternately connecting said chamber through said first passage means for a first period to said source of said intermediate pressure or to atmosphere and during a second period through said second passage means to said source of said mixture delivery pressure;
• and
• c. an electronic system operative to produce an electric signal having a square wave form and means for applying said signal to said command valve system, said signal having a square wave form, the mark/space ratio of which is constant and the mark period of which is a function of the speed of said engine as indicated by the ignition frequency of said engine and a function of a signal delivered by said exhaust gas composition sensor, said function being such that the rate of flow of said additional air supply is at least substantially proportional to the rate of flow of a main stream of air aspirated by said engine, said mark/space ratio and the cross-sections of said first and second passage means satisfying requirements imposed by the constancy of parameters imposed by said pneumatic regulator valve and the requirements that each mark period is less than the time taken for said chamber in which said command pressure is generated to fill completely or empty completely, and that emptying preponderates over filling.