Patent ID: 8398836

Claim:
A sensor element of a gas sensor for detecting a predetermined gas component in a measurement gas, comprising: a solid electrolyte body formed mainly of an oxygen ion conductive solid electrolyte; a gas inlet open to an external space for introducing the measurement gas from said external space to inside of said sensor element, said gas inlet formed on a front end surface of said sensor element in a longitudinal direction thereof; a first diffusion-controlling part, a second diffusion-controlling part, and a third diffusion-controlling part, each provided as two long horizontal slits; an inner space including a first inner space and a second inner space, said first inner space communicating with said gas inlet under a predetermined diffusion resistance applied by said first diffusion-controlling part and said second diffusion-controlling part, and said second inner space communicating with said first inner space under a predetermined diffusion resistance applied by said third diffusion-controlling part; a main pump cell for pumping oxygen out of said first inner space by applying a predetermined voltage between a first electrode and a second electrode, said first electrode being formed on a surface of said first inner space and said second electrode being formed in a space different from said inner space; and an auxiliary pump cell for pumping oxygen out of said second inner space by applying a predetermined voltage between an auxiliary first electrode and said second electrode, said auxiliary first electrode being formed on a surface of said first inner space, wherein said gas inlet, said first diffusion-controlling part, said second diffusion-controlling part, said first inner space, said third diffusion-controlling part, and said second inner space are arranged in this order in said longitudinal direction of said sensor element, and wherein the length of said first inner space in a short-side direction of said sensor element as viewed from the front end portion side thereof is x 1 and the length of said first inner space in said longitudinal direction thereof is x 2 , 0.05 ≦x 1/ x 2≦0.25.