A gas sensor element includes a main body having a solid electrolyte body on which a measurement gas-side electrode and a reference gas-side electrode are provided, a trap layer covering an outer peripheral surface of the main body to trap poisoning substances contained in a measurement gas, and a waterproof protective layer covering an outer peripheral surface of the trap layer. In the protective layer, there is formed at least one measurement gas introduction port for introducing the measurement gas to the measurement gas-side electrode via the trap layer.

A connector has a fixing hole in an intermediate portion of a terminal member, and has an engagement portion projecting downward in a thickness direction, at an end portion at a front end side of the fixing hole. Therefore, when the terminal member is attached to a housing, movement of the terminal member toward a rear end side can be restricted by fitting a projection portion of the housing into the fixing hole. Furthermore, since the engagement portion is provided to the terminal member, movement of the terminal member toward the rear end side can be restricted by engaging the engagement portion with a front end surface of a protrusion portion of the housing.

A connector has a fixing hole in an intermediate portion of a terminal member, and has an engagement portion projecting downward in a thickness direction, at an end portion at a front end side of the fixing hole. Therefore, when the terminal member is attached to a housing, movement of the terminal member toward a rear end side can be restricted by fitting a projection portion of the housing into the fixing hole. Furthermore, since the engagement portion is provided to the terminal member, movement of the terminal member toward the rear end side can be restricted by engaging the engagement portion with a front end surface of a protrusion portion of the housing.

The sensor control unit is used for a gas sensor disposed in an exhaust pipe in an engine as an internal combustion engine of a vehicle. The gas sensor includes a sensor cell having an exhaust gas electrode, an atmosphere side electrode and a solid electrolyte, and a heater that heats the sensor cell. The sensor control unit includes a heater control unit that controls a heater to heat a sensor cell. The heater control unit heats the sensor cell to be at an operation control temperature during the combustion operation of the engine and heats the sensor cell to be at an operation stop control temperature which is higher than the operation control temperature.

A gas concentration detection device for detecting a gas concentration using a limiting current type gas concentration sensor. In an application voltage line set to pass through a plurality of limiting current regions for different values of gas concentration, the voltage set by the application voltage line is an identical first voltage value used when an air/fuel ratio corresponding to the gas concentration is in a predetermined first range, is an identical second voltage value different from the first voltage value used when the air/fuel ratio is in a second range adjacent to the first range, and the first voltage value and the second voltage value are switched between the first range and the second range.

A gas concentration detection device for detecting a gas concentration using a limiting current type gas concentration sensor. In an application voltage line set to pass through a plurality of limiting current regions for different values of gas concentration, the voltage set by the application voltage line is an identical first voltage value used when an air/fuel ratio corresponding to the gas concentration is in a predetermined first range, is an identical second voltage value different from the first voltage value used when the air/fuel ratio is in a second range adjacent to the first range, and the first voltage value and the second voltage value are switched between the first range and the second range.

A sensor element according to the present invention includes an element body having a measurement-object gas flow section into which an exhaust gas is introduced, an adjustment pump cell including a measurement-object-gas-side electrode disposed in a portion exposed to the exhaust gas on an outer side of the element body, the adjustment pump cell being configured to adjust an oxygen concentration in an oxygen concentration adjustment chamber included in the measurement-object gas flow section, a measurement electrode disposed in a measurement chamber located downstream of the oxygen concentration adjustment chamber, and a reference electrode into which a reference gas is introduced. The measurement-object-gas-side electrode has an Au/(Pt+Au) ratio (=an area of a portion where Au is exposed/an area of a portion where Au and Pt are exposed) 0.2-0.7, the Au/(Pt+Au) ratio being measured by using XPS.

A sensor element according to the present invention includes an element body having a measurement-object gas flow section into which an exhaust gas is introduced, an adjustment pump cell including a measurement-object-gas-side electrode disposed in a portion exposed to the exhaust gas on an outer side of the element body, the adjustment pump cell being configured to adjust an oxygen concentration in an oxygen concentration adjustment chamber included in the measurement-object gas flow section, a measurement electrode disposed in a measurement chamber located downstream of the oxygen concentration adjustment chamber, and a reference electrode into which a reference gas is introduced. The measurement-object-gas-side electrode has an Au/(Pt+Au) ratio (=an area of a portion where Au is exposed/an area of a portion where Au and Pt are exposed) 0.2-0.7, the Au/(Pt+Au) ratio being measured by using XPS.

A gas sensor includes a sensor element and a contact metal fitting. The sensor element has an element body having an oxygen-ion-conductive solid electrolyte layer; an upper connector electrode disposed outside the element body; a lead disposed outside the element body and electrically conductive to the upper connector electrode; and a first protection layer that covers the lead, where a thickness T1 of a portion covering the lead is 2 .Math.m or more, a porosity P1 is 20% or less, and a height difference D1 relative to the upper connector electrode is 22 .Math.m or less. The contact metal fitting has: a conduction member that projects to the upper connector electrode and is in contact with and electrically conducted to the upper connector electrode; and a support member that projects toward the lead and is in contact with the first protection layer.

A gas sensor includes a sensor element and a contact metal fitting. The sensor element has an element body having an oxygen-ion-conductive solid electrolyte layer; an upper connector electrode disposed outside the element body; a lead disposed outside the element body and electrically conductive to the upper connector electrode; and a first protection layer that covers the lead, where a thickness T1 of a portion covering the lead is 2 .Math.m or more, a porosity P1 is 20% or less, and a height difference D1 relative to the upper connector electrode is 22 .Math.m or less. The contact metal fitting has: a conduction member that projects to the upper connector electrode and is in contact with and electrically conducted to the upper connector electrode; and a support member that projects toward the lead and is in contact with the first protection layer.