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.

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.

In a sensor element, a reference gas regulation pump cell pumps in oxygen to the periphery of a reference electrode in which a reference gas is introduced, by the flow of a control current Ip3 between the reference electrode and an outer pump electrode located in a region exposed to a measurement-object gas. An average current density of the reference electrode under the flow of the control current Ip3 is higher than 0 μA/mm.sup.2 and lower than 400 μA/mm.sup.2. The average current density is preferably not higher than 170 μA/mm.sup.2. An average value of the control current Ip3 is preferably higher than 1 μA. The outer pump electrode as a measurement-object gas side electrode of the reference gas regulation pump cell may be provided on an outer surface of a layered body (or more specifically, on a second solid electrolyte layer).

In a sensor element, a reference gas regulation pump cell pumps in oxygen to the periphery of a reference electrode in which a reference gas is introduced, by the flow of a control current Ip3 between the reference electrode and an outer pump electrode located in a region exposed to a measurement-object gas. An average current density of the reference electrode under the flow of the control current Ip3 is higher than 0 μA/mm.sup.2 and lower than 400 μA/mm.sup.2. The average current density is preferably not higher than 170 μA/mm.sup.2. An average value of the control current Ip3 is preferably higher than 1 μA. The outer pump electrode as a measurement-object gas side electrode of the reference gas regulation pump cell may be provided on an outer surface of a layered body (or more specifically, on a second solid electrolyte layer).

An insulating separator of a gas sensor is formed to be dividable into a forward separator having a terminal disposition hole, and a rear separator having four terminal disposition holes. The insulating separator has a ventilation path formed between the forward separator and the rear separator. As a result, moisture and the like which enter the insulating separator from a forward side of the forward separator through the terminal disposition hole can be discharged outward of the insulating separator through the ventilation path. As a result, corrosion of metal terminals caused by entry of moisture can be reduced, whereby transmission of a sensor signal and application of current or voltage through the metal terminals can be appropriately implemented.

An insulating separator of a gas sensor is formed to be dividable into a forward separator having a terminal disposition hole, and a rear separator having four terminal disposition holes. The insulating separator has a ventilation path formed between the forward separator and the rear separator. As a result, moisture and the like which enter the insulating separator from a forward side of the forward separator through the terminal disposition hole can be discharged outward of the insulating separator through the ventilation path. As a result, corrosion of metal terminals caused by entry of moisture can be reduced, whereby transmission of a sensor signal and application of current or voltage through the metal terminals can be appropriately implemented.

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, a ratio for lean is set as a ratio of change in current with respect to a change in voltage when an air/fuel ratio corresponding to the gas concentration is lean, and a ratio of rich different from the ratio for lean is set when the air/fuel ratio is rich.

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, a ratio for lean is set as a ratio of change in current with respect to a change in voltage when an air/fuel ratio corresponding to the gas concentration is lean, and a ratio of rich different from the ratio for lean is set when the air/fuel ratio is rich.

A gas sensor includes a main pump cell, a storage unit that stores information about a zero point in a first correspondence relationship, where the first correspondence relationship is a linear correspondence relationship between the oxygen concentration in a measurement-object gas and the main pump current, an oxygen-concentration-detecting unit that detects the oxygen concentration in a measurement-object gas, based on a measured value p of the main pump current and the information about the zero point, and a measured-value-obtaining unit that performs a second control process and that obtains a measured value b1 at a measurement point B1 at which a known value of the oxygen concentration and the main pump current are relevant to each other with a measurement timing. The oxygen-concentration-detecting unit makes zero point correction such that a divergence of the zero point from the first correspondence relationship is corrected based on the measured value b1.

A gas sensor includes a main pump cell, a storage unit that stores information about a zero point in a first correspondence relationship, where the first correspondence relationship is a linear correspondence relationship between the oxygen concentration in a measurement-object gas and the main pump current, an oxygen-concentration-detecting unit that detects the oxygen concentration in a measurement-object gas, based on a measured value p of the main pump current and the information about the zero point, and a measured-value-obtaining unit that performs a second control process and that obtains a measured value b1 at a measurement point B1 at which a known value of the oxygen concentration and the main pump current are relevant to each other with a measurement timing. The oxygen-concentration-detecting unit makes zero point correction such that a divergence of the zero point from the first correspondence relationship is corrected based on the measured value b1.