US-12618799-B2 - Gas sensor and method of identifying deviation of reference potential of the same

US12618799B2US 12618799 B2US12618799 B2US 12618799B2US-12618799-B2

Abstract

A gas sensor includes a sensor element and a control device, and detects a specific gas concentration that is a concentration of a specific gas in a measurement-object gas. The sensor element includes an element body including an oxygen-ion-conductive solid electrolyte layer and provided with a measurement-object gas flow portion therein, the measurement-object gas flow portion introducing the measurement-object gas and causing the measurement-object gas to flow therethrough; a measurement electrode disposed in a measurement chamber of the measurement-object gas flow portion; and a reference electrode disposed inside the element body to come into contact with a reference gas that serves as a reference for detection of the specific gas concentration. The control device measures a voltage across the ground and the reference electrode, and identifies a deviation of the reference potential that is the electrical potential of the reference electrode based on the measured voltage.

Inventors

Shingo Tanaka
Yusuke Watanabe
Ryo Hashikawa

Assignees

NGK INSULATORS, LTD.

Dates

Publication Date: 20260505
Application Date: 20230726
Priority Date: 20220805

Claims (7)

1 . A gas sensor comprising a sensor element and a control device, and being configured to detect a specific gas concentration which is a concentration of a specific gas in a measurement-object gas, the sensor element including: an element body including an oxygen-ion-conductive solid electrolyte layer and provided with a measurement-object gas flow portion therein, the measurement-object gas flow portion being configured to introduce the measurement-object gas and cause the measurement-object gas to flow therethrough; a measurement electrode disposed in a measurement chamber of the measurement-object gas flow portion; and a reference electrode disposed inside the element body to come into contact with a reference gas that serves as a reference for detection of the specific gas concentration, wherein the control device is configured to measure a voltage across a ground and the reference electrode, and identify a deviation of a reference potential that is an electrical potential of the reference electrode by performing one or more of magnitude relationship comparison of the measurement value with a normal value, calculation of a difference or a ratio between the measurement value and the normal value, comparison of the measurement value with a predetermined acceptable range, and determination as to whether a measurement value is in the predetermined acceptable range.
2 . The gas sensor according to claim 1 , wherein the sensor element includes a reference-gas adjustment pump cell including a measurement-object-gas side electrode and the reference electrode, the measurement-object-gas side electrode being provided in the element body to come into contact with the measurement-object gas, and when the measured voltage is higher than a predetermined acceptable range, the control device controls the reference-gas adjustment pump cell so that oxygen is pumped out from a periphery of the reference electrode into a periphery of the measurement-object-gas side electrode, and when the measured voltage is lower than the predetermined acceptable range, the control device controls the reference-gas adjustment pump cell so that oxygen is pumped into the periphery of the reference electrode from the periphery of the measurement-object-gas side electrode.
3 . The gas sensor according to claim 1 , wherein the sensor element includes a measurement pump cell including an outer measurement electrode and the measurement electrode, the outer measurement electrode being provided outside the element body to come into contact with the measurement-object gas, the control device being configured to perform a measurement pump control process for controlling the measurement pump cell so that a measurement voltage that is a voltage across the measurement electrode and the reference electrode reaches a measurement voltage target value, and to detect the specific gas concentration in the measurement-object gas based on a pump current which flows through the measurement pump cell by the measurement pump control process, and the control device being configured to correct control of the measurement pump cell in the measurement pump control process based on the identified deviation of the reference potential.
4 . The gas sensor according to claim 3 , wherein the sensor element includes an adjustment pump cell including an inner adjustment electrode and adjusts an oxygen concentration in an oxygen concentration adjustment chamber, the inner adjustment electrode being disposed in the oxygen concentration adjustment chamber located upstream of the measurement chamber of the measurement-object gas flow portion, the control device being configured to perform an adjustment pump control process for adjusting the oxygen concentration in the oxygen concentration adjustment chamber by controlling the adjustment pump cell so that an adjustment voltage that is a voltage across the inner adjustment electrode and the reference electrode reaches an adjustment voltage target value, and the control device being configured to correct control of the adjustment pump cell in the adjustment pump control process based on the identified deviation of the reference potential.
5 . The gas sensor according to claim 1 , wherein the sensor element includes a ground terminal connected to the ground, and the control device measures a voltage across the ground terminal and the reference electrode as a voltage across the ground and the reference electrode.
6 . The gas sensor according to claim 5 , wherein the sensor element includes a heater that heats the element body, and the ground terminal is a terminal of the heater.
7 . A method of identifying a deviation of a reference potential of a gas sensor that detects a specific gas concentration which is a concentration of a specific gas in a measurement-object gas, the gas sensor including a sensor element having: an element body including an oxygen-ion-conductive solid electrolyte layer and provided with a measurement-object gas flow portion therein, the measurement-object gas flow portion introducing the measurement-object gas and causing the measurement-object gas to flow therethrough; a measurement electrode disposed in the measurement-object gas flow portion; and a reference electrode disposed inside the element body to come into contact with a reference gas that serves as a reference for detection of the specific gas concentration, the method including a step of measuring a voltage across a ground and the reference electrode, and identify a deviation of the reference potential that is an electrical potential of the reference electrode by performing one or more of magnitude relationship comparison of the measurement value with a normal value, calculation of a difference or a ratio between the measurement value and the normal value, comparison of the measurement value with a predetermined acceptable range, and determination as to whether a measurement value is in the predetermined acceptable range.

Description

The present application claims priority from Japanese Patent Application No. 2022-125272 filed on Aug. 5, 2022, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor and a method of identifying the deviation of reference potential of the gas sensor. 2. Description of the Related Art A known gas sensor in related art detects the concentration of a specific gas such as NOx in a measurement-object gas such as an exhaust gas of an automobile. For example, the sensor element of the gas sensor described in Patent Literature 1 includes: a layered body having a plurality of oxygen-ion-conductive solid electrolyte layers and provided therein with a measurement-object gas flow portion that introduces a measurement-object gas and causes the measurement-object gas to flow therethrough; a measurement electrode disposed in the measurement-object gas flow portion; a measurement-object-gas side electrode disposed in a part of the layered body to be exposed to the measurement-object gas; a reference electrode disposed inside the layered body; and a porous reference-gas introduction layer that introduces a reference gas (e.g., an atmospheric gas) serving as a reference for detection of a specific gas concentration in the measurement-object gas and causes the reference gas to flow to the reference electrode. This gas sensor detects the specific gas concentration in the measurement-object gas based on the electromotive force generated between the reference electrode and the measurement electrode. In addition, the gas sensor includes a reference gas adjustment device that pumps oxygen into the periphery of the reference electrode by passing a control current between the reference electrode and the measurement-object-gas side electrode. Patent Literature 1 states that when the oxygen concentration in the reference gas in the periphery of the reference electrode temporarily reduces, the reduction in the oxygen concentration can be compensated by the reference gas adjustment device that pumps oxygen into the periphery of the reference electrode, thus a decrease in the accuracy of detection of the specific gas concentration can be prevented. CITATION LIST Patent Literature PTL 1: JP 2018-173320 A SUMMARY OF THE INVENTION Even when oxygen is pumped into the periphery of the reference electrode using the reference gas adjustment device as in the gas sensor described in Patent Literature 1, it is difficult to maintain the oxygen concentration in the periphery of the reference electrode at a constant value completely. When the oxygen concentration in the periphery of the reference electrode changes, the electrical potential of the reference electrode changes and the accuracy of detection of the specific gas concentration decreases. Thus, there has been a demand for identifying a deviation of the electrical potential of the reference electrode. The present invention has been made to solve the aforementioned problems, and a main object thereof is to identify a deviation of the reference potential. In order to achieve the aforementioned main object, the present invention employs the following solutions. [1] A gas sensor of the present invention is a gas sensor including a sensor element and a control device and being configured to detect a specific gas concentration which is a concentration of a specific gas in a measurement-object gas, the sensor element including: an element body including an oxygen-ion-conductive solid electrolyte layer and provided with a measurement-object gas flow portion therein, the measurement-object gas flow portion introducing the measurement-object gas and causing the measurement-object gas to flow therethrough; a measurement electrode disposed in a measurement chamber of the measurement-object gas flow portion; and a reference electrode disposed inside the element body to come into contact with a reference gas that serves as a reference for detection of the specific gas concentration. The control device measures a voltage across a ground and the reference electrode, and identifies a deviation of a reference potential that is an electrical potential of the reference electrode based on the measured voltage. In this gas sensor, the control device measures the voltage across the ground and the reference electrode. The voltage varies with change in the oxygen concentration in the periphery of the reference electrode, in other words, change in the reference potential that is the electrical potential of the reference electrode, thus it is possible to identify the deviation of the reference potential based on the voltage. In this case, the control device may identify the deviation of the reference potential by comparing a measurement value of the voltage across the ground and the reference electrode with a normal value or an acceptable range. As specific examples of identifying the reference potential, com