Patent claim: A gas sensor comprising a sensor element an inner protective cover having a bottomed cylindrical shape the inner protective cover having at least one first inner gas hole and at least one second inner gas hole formed therein and covering a free end of the sensor element and an outer protective cover having a bottomed cylindrical shape the outer protective cover having a plurality of outer gas holes formed therein and covering the inner protective cover wherein the first inner gas hole is located so as to be closer to a base end of the sensor element than the second inner gas hole and wherein a ratio A2A1 defined by a ratio of an opening area A1 per first inner gas hole and an opening area A2 per second inner gas hole is higher than or equal to 0.9 and lower than or equal to 3.8 wherein the outer protective cover is a cover having a side surface and a bottom surface and wherein each of the outer gas holes is formed in a boundary portion between the side surface and the bottom surface of the outer protective cover and wherein an angle 1 formed by an external opening plane of the outer gas hole and the bottom surface of the outerprotective cover is in the range from 10 to 80.

Related passage: A gas concentration detection sensor 800 shown in Fig.19 was fabricated.The gas concentration detection sensor 800 included a protective cover 820 having a triplelayered structure namely including an inner protection cover 830 covering over the free end of the sensor element 110 and having a thickness of 0.3 mm an intermediate protection cover 840 covering over the inner protection cover 830 and having a thickness of 0.3 mm and an outer protection cover 850 covering over the intermediate protection cover 840 and having a thickness of 0.4 mm.The inner protection cover 830 had an outer circumferential face that was in contact with a metal main clamp 802 and included a cylindrical largediameter section 832 having an axial length of 5.5 mm and an inner diameter of 6.8 mm and a bottomed cylindrical edge section 834 having an axial length of 13.9 mm and an innerdiameter of 6.4 mm.Twelve inner gas apertures 834a each having an inner diameter of 1.5 mm were arranged around a side face of the edge section 834.A gas passing aperture 834b having an inner diameter of 5 mm was disposed at the center of a bottom face of the edge section 834.The outer opening plane of the gas passing aperture 834b formed an angle of 0 degree with the bottom face of the edge section 834.The inner gas apertures 834a were arranged at equal intervals such that they were axially vertically in Fig.19 staggered in two levels.The intermediate protection cover 840 had an inner circumferential face that was in contact with the metal main clamp 802 and included a largediameter section 842 having an axial length of 1.8 mm and an inner diameter of 13.9 mm a cylindrical stem section 844 having an axial length of 8.4 mm and an inner diameter of 9.1 mm and a bottomed cylindrical edge section 846 having an axial length of 5.5 mm and an inner diameter of 6.9 mm.The largediameter section 842 was connected to the stem section 844 through a step element 843.The stem section 844 was also connected to the edge section 846 through a step.In the step element 843 as shown in Fig.20 six first intermediate gas apertures 843a each shaped in a 40degree arc of a circle having a diameter of 11.6 mm and each having a width of 1 mm were arranged at equal intervals.A second intermediate gas aperture 846a having an inner diameter of 1.1 mm was formed at the center of a bottom face of the edge section 846.The outer protection cover 850 had an inner circumferential face that was in contactwith the metal main clamp 802 and included a cylindrical largediameter section 852 having an axial length of 5.6 mm and an inner diameter of 14.4 mm and a bottomed cylindrical edge section 854 having an axial length of 18.2 mm and an inner diameter of 13.8 mm Six outer gas apertures 854a each having an inner diameter of 2 mm were formed around a side face of the edge section 854.The edge section 834 of the inner protection cover 830 was in contact with the edge section 846 of the intermediate protection cover 840 such that a space defined by the inner protection cover 830 and the intermediate protection cover 840 was divided into an upper chamber 822 and a lower chamber 824.