Air-fuel ratio sensor

Claim 1

An air-fuel-ratio sensor, comprising a mounting body; a sensor unit extending away from a top of the mounting body and having an oxygen pump with a wall means formed at an extended tip of the sensor unit, said oxygen pump having an oxygen-ion-conductive solid electrolyte plate with a pair of electrodes secured to opposite surfaces thereof, said wall means facing one of said electrodes and being parallel thereto and spaced therefrom at a small spacing so as to define a diffusion-restricting narrow gap therebetween; and a cup-shaped protector having a closed end and a side wall, said protector being secured to said mounting body to enclose said sensor unit therein, said side wall of said cup-shaped protector having at least two rows of holes extending therethrough, said rows spaced axially along the longitudinal axis of said cup-shaped protector, and deflectors secured to the edges of the holes and extending inwardly of the protector at acute angles relative to the inner surface of the side wall of the protector, the angles of said deflectors in each row being greater than the angles of the deflectors in a preceding row in a direction along the longitudinal axis of said protector and toward said closed end, wherein said holes and said deflectors are such that gas outside the protector flows into the protector through said holes in a swirling motion, and the amount of said swirling gas in the protector increases with the axial distance from the mounting body.