Gas sensor and method of controlling gas sensor

1. A gas sensor comprising:

a sensor element including a structural body made up from a solid electrolyte that exhibits at least oxygen ion conductivity, a gas introduction port formed in the structural body and into which a gas to be measured is introduced, an oxygen concentration adjustment chamber communicating with the gas introduction port, a measurement chamber communicating with the oxygen concentration adjustment chamber, and a preliminary adjustment chamber disposed between the gas introduction port and the oxygen concentration adjustment chamber, and communicating with the gas introduction port;

an oxygen concentration control unit configured to control an oxygen concentration in the oxygen concentration adjustment chamber;

a temperature control unit configured to control a temperature of the sensor element;

a specified component measurement unit configured to measure a concentration of a specified component inside the measurement chamber;

a preliminary oxygen concentration control unit having the solid electrolyte and two electrodes formed on both sides of the solid electrolyte, and which is configured to control the oxygen concentration in the preliminary adjustment chamber;

a drive control unit configured to control the preliminary oxygen concentration control unit; and

a target component acquisition unit configured to acquire concentrations of a first target component and a second target component, on basis of a difference between a sensor output from the specified component measurement unit at a time of a first operation of the preliminary oxygen concentration control unit, and a sensor output from the specified component measurement unit at a time of a second operation of the preliminary oxygen concentration control unit, and one of the respective sensor outputs;

wherein an inequality Voff<Va<Vb is satisfied, where Va is a first voltage applied to the preliminary oxygen concentration control unit during the first operation thereof, Vb is a second voltage applied to the preliminary oxygen concentration control unit during the second operation thereof, and Voff is a voltage applied thereto at a time when the preliminary oxygen concentration control unit is stopped.

2. The gas sensor according to claim 1 , wherein:

when a range of a voltage applied to the preliminary oxygen concentration control unit, which is a voltage range in which, while the second target component while remaining in a form of the second target component passes through the preliminary adjustment chamber and reaches an interior of the oxygen concentration adjustment chamber, and while the first target component while remaining in a form of the first target component passes through the preliminary adjustment chamber and reaches the interior of the oxygen concentration adjustment chamber, defines a first voltage range; and

when a range of the voltage applied to the preliminary oxygen concentration control unit, which is a voltage range in which, while the second target component is changed into the first target component in the preliminary adjustment chamber and reaches the interior of the oxygen concentration adjustment chamber, and while the first target component while remaining in the form of the first target component passes through the preliminary adjustment chamber and reaches the interior of the oxygen concentration adjustment chamber, defines a second voltage range;

the first voltage Va is included within the first voltage range, and the second voltage Vb is included within the second voltage range.

3. The gas sensor according to claim 2 , wherein:

under an environment in which there is supplied a first gas to be measured, which contains the first target component and does not contain the second target component, a sensor output when the voltage Voff is applied to the preliminary oxygen concentration control unit is represented by Ip 3 off( 1 ), a sensor output when the first voltage Va is applied to the preliminary oxygen concentration control unit is represented by Ip 3 va ( 1 ), and a sensor output when the second voltage Vb is applied to the preliminary oxygen concentration control unit is represented by Ip 3 vb ( 1 ); and

under an environment in which there is supplied a second gas to be measured, which contains the second target component and does not contain the first target component, a sensor output when the voltage Voff is applied to the preliminary oxygen concentration control unit is represented by Ip 3 off( 2 ), a sensor output when the first voltage Va is applied to the preliminary oxygen concentration control unit is represented by Ip 3 va ( 2 ), and a sensor output when the second voltage Vb is applied to the preliminary oxygen concentration control unit is represented by Ip 3 vb ( 2 );

equations Ip 3 off( 1 )−Ip 3 va ( 1 )=ΔIp 3 ( 1 ) and Ip 3 off( 2 )−Ip 3 vb ( 2 )=ΔIp 3 ( 2 ) are defined; and

assuming that |ΔIp 3 ( 1 )−ΔIp 3 ( 2 )| defines a standard difference when the second voltage Vb is applied to the preliminary oxygen concentration control unit at the time of the second operation;

then |ΔIp 3 ( 1 )−ΔIp 3 ( 2 )| when the first voltage Va is applied to the preliminary oxygen concentration control unit at the time of the first operation is less than or equal to one half of the standard difference.

4. The gas sensor according to claim 2 , wherein:

under an environment in which there is supplied a first gas to be measured, which contains the first target component and does not contain the second target component, a sensor output when the voltage Voff is applied to the preliminary oxygen concentration control unit is represented by Ip 3 off( 1 ), a sensor output when the first voltage Va is applied to the preliminary oxygen concentration control unit is represented by Ip 3 va ( 1 ), and a sensor output when the second voltage Vb is applied to the preliminary oxygen concentration control unit is represented by Ip 3 vb ( 1 );

under an environment in which there is supplied a second gas to be measured, which contains the second target component and does not contain the first target component, a sensor output when the voltage Voff is applied to the preliminary oxygen concentration control unit is represented by Ip 3 off( 2 ), a sensor output when the first voltage Va is applied to the preliminary oxygen concentration control unit is represented by Ip 3 va ( 2 ), and a sensor output when the second voltage Vb is applied to the preliminary oxygen concentration control unit is represented by Ip 3 vb ( 2 ); and

assuming that Ip 3 off( 1 )−Ip 3 va ( 1 )=ΔIp 3 ( 1 ) and Ip 3 off( 2 )−Ip 3 vb ( 2 )=ΔIp 3 ( 2 );

then |ΔIp 3 ( 1 )−ΔIp 3 ( 2 )| when the first voltage Va is applied to the preliminary oxygen concentration control unit at the time of the first operation is less than or equal to 0.05 μA.

5. The gas sensor according to claim 1 , wherein the specified component is NO, the first target component is NO, and the second target component is NH 3 .

6. A method of controlling a gas sensor, wherein the gas sensor includes:

a sensor element including a structural body made up from a solid electrolyte that exhibits at least oxygen ion conductivity, a gas introduction port formed in the structural body and into which a gas to be measured is introduced, an oxygen concentration adjustment chamber communicating with the gas introduction port, a measurement chamber communicating with the oxygen concentration adjustment chamber, and a preliminary adjustment chamber disposed between the gas introduction port and the oxygen concentration adjustment chamber, and communicating with the gas introduction port;

an oxygen concentration control unit configured to control an oxygen concentration in the oxygen concentration adjustment chamber;

a temperature control unit configured to control a temperature of the sensor element;

a specified component measurement unit configured to measure a concentration of a specified component inside the measurement chamber;

a preliminary oxygen concentration control unit having the solid electrolyte and two electrodes formed on both sides of the solid electrolyte, and which is configured to control the oxygen concentration in the preliminary adjustment chamber;

a drive control unit configured to control the preliminary oxygen concentration control unit; and

a target component acquisition unit configured to acquire concentrations of a first target component and a second target component, on basis of a difference between a sensor output from the specified component measurement unit at a time of a first operation of the preliminary oxygen concentration control unit, and a sensor output from the specified component measurement unit at a time of a second operation of the preliminary oxygen concentration control unit, and one of the respective sensor outputs;

wherein, upon execution of the method, an inequality Voff<Va<Vb is satisfied, where Va is a first voltage applied to the preliminary oxygen concentration control unit during the first operation thereof, Vb is a second voltage applied to the preliminary oxygen concentration control unit during the second operation thereof, and Voff is a voltage applied thereto at a time when the preliminary oxygen concentration control unit is stopped.

7. The method of controlling the gas sensor according to claim 6 , wherein:

when a range of a voltage applied to the preliminary oxygen concentration control unit, which is a voltage range in which, while the second target component while remaining in a form of the second target component passes through the preliminary adjustment chamber and reaches an interior of the oxygen concentration adjustment chamber, and while the first target component while remaining in a form of the first target component passes through the preliminary adjustment chamber and reaches the interior of the oxygen concentration adjustment chamber, defines a first voltage range; and

when a range of the voltage applied to the preliminary oxygen concentration control unit, which is a voltage range in which, while the second target component is changed into the first target component in the preliminary adjustment chamber and reaches the interior of the oxygen concentration adjustment chamber, and while the first target component while remaining in the form of the first target component passes through the preliminary adjustment chamber and reaches the interior of the oxygen concentration adjustment chamber, defines a second voltage range;

the first voltage Va is set from within the first voltage range, and the second voltage Vb is set from within the second voltage range.

8. The method of controlling the gas sensor according to claim 7 , wherein:

under an environment in which there is supplied a first gas to be measured, which contains the first target component and does not contain the second target component, a sensor output when the voltage Voff is applied to the preliminary oxygen concentration control unit is represented by Ip 3 off( 1 ), a sensor output when the first voltage Va is applied to the preliminary oxygen concentration control unit is represented by Ip 3 va ( 1 ), and a sensor output when the second voltage Vb is applied to the preliminary oxygen concentration control unit is represented by Ip 3 vb ( 1 ); and

under an environment in which there is supplied a second gas to be measured, which contains the second target component and does not contain the first target component, a sensor output when the voltage Voff is applied to the preliminary oxygen concentration control unit is represented by Ip 3 off( 2 ), a sensor output when the first voltage Va is applied to the preliminary oxygen concentration control unit is represented by Ip 3 va ( 2 ), and a sensor output when the second voltage Vb is applied to the preliminary oxygen concentration control unit is represented by Ip 3 vb ( 2 );

equations Ip 3 off( 1 )−Ip 3 va ( 1 )=ΔIp 3 ( 1 ) and Ip 3 off( 2 )−Ip 3 vb ( 2 )=ΔIp 3 ( 2 ) are defined; and

assuming that |Ip 3 ( 1 )−ΔIp 3 ( 2 )| defines a standard difference when the second voltage Vb is applied to the preliminary oxygen concentration control unit at the time of the second operation;

then |ΔIp 3 ( 1 )−ΔIp 3 ( 2 )| when the first voltage Va is applied to the preliminary oxygen concentration control unit at the time of the first operation is set to be less than or equal to one half of the standard difference.

9. The method of controlling the gas sensor according to claim 7 , wherein:

under an environment in which there is supplied a first gas to be measured, which contains the first target component and does not contain the second target component, a sensor output when the voltage Voff is applied to the preliminary oxygen concentration control unit is represented by Ip 3 off( 1 ), a sensor output when the first voltage Va is applied to the preliminary oxygen concentration control unit is represented by Ip 3 va ( 1 ), and a sensor output when the second voltage Vb is applied to the preliminary oxygen concentration control unit is represented by Ip 3 vb ( 1 );

under an environment in which there is supplied a second gas to be measured, which contains the second target component and does not contain the first target component, a sensor output when the voltage Voff is applied to the preliminary oxygen concentration control unit is represented by Ip 3 off( 2 ), a sensor output when the first voltage Va is applied to the preliminary oxygen concentration control unit is represented by Ip 3 va ( 2 ), and a sensor output when the second voltage Vb is applied to the preliminary oxygen concentration control unit is represented by Ip 3 vb ( 2 ); and

assuming that Ip 3 off( 1 )−Ip 3 va ( 1 )=ΔIp 3 ( 1 ) and Ip 3 off( 2 )−Ip 3 vb ( 2 )=ΔIp 3 ( 2 );

then |ΔIp 3 ( 1 )−ΔIp 3 ( 2 )| when the first voltage Va is applied to the preliminary oxygen concentration control unit at the time of the first operation is set to be less than or equal to 0.05 μA.

10. The method of controlling the gas sensor according to claim 6 , wherein the specified component is NO, the first target component is NO, and the second target component is NH 3 .