Oxygen sensor protected against contaminants

Claim 1

An oxygen sensor comprising: an oxygen detecting element in a tubular form of a solid electrolyte which is closed at a lower end and opened at the other upper end and which has a conductive layer deposited on both outer and inner surfaces; an output terminal, one end of which is retained at an upper portion of the open end of said oxygen detecting element; a first tube which surrounds and protects said oxygen detecting element and said output terminal; a second tube having a lower end portion surrounding an upper end portion of said first tube, vertical air flow passages being provided between said first and second tubes and extending to the uppermost end of said first tube so that the length of said air flow passage is maximized; and air-permeable, water- and oil-impermeable spacer means having a lower end abutting against an uppermost end of said first tube and having an upper end fitted into an upper end of said second tube, said spacer means circumscribing said output terminal for insulating said output terminal and covering uppermost ends of said vertical air flow passages, for permitting atmospheric air to flow therethrough while blocking oil and water, said spacer means being molded from a mixture of an inorganic fiber and a thermal plastic resin.