Ngk Insulators, Inc.

Yasuhiko Hamada

Nobuhide Kato

Nobuyuki Kokune

Nobukazu Ikoma

Hiroshi Ishikawa

Tsunenori Yoshimura

Atsushi Iino

Hiroshi Nagata

Disclosed is a gas sensor for controlling a concentration of oxygen and/or measuring NOx by allowing a current to flow through an ion-conductive member for conducting oxygen ion, by the aid of a current supply circuit, wherein the current, which is outputted from the current supply circuit, has a pulse waveform (current signal) having a constant crest value, and the current supply circuit comprises a rectangular wave-generating circuit for controlling a frequency of the current signal on the basis of an electromotive force generated in the ion-conductive member to which the current signal is supplied. Accordingly, it is possible to highly accurately measure the predetermined gas component while scarcely being affected by the electric noise or the like.

Gas sensor and method for controlling the same

A total of a most adjacent spacing distance in an axial direction between an outer gas-introducing hole of an outer protective cover and a slit provided at a flange of an intermediate protective cover and a most adjacent spacing distance in the axial direction between the slit of the intermediate protective cover and an inner gas-introducing hole of an inner protective cover is at least not less than 10 mm. Gaps for avoiding accumulation of water due to boundary tension are provided in a radial direction between the outer protective cover and the intermediate protective cover and in the radial direction between the outer protective cover and the inner protective cover.

Gas sensor

A gas sensor comprises a main pumping cell for pumping-processing oxygen contained in a first chamber, a feedback control system for comparing a partial pressure of oxygen in the first chamber with a first reference value to control the main pumping cell so that the partial pressure of oxygen has a predetermined value at which NO is not decomposable, an auxiliary pumping cell for pumping-processing oxygen in the second chamber, and a measuring pumping cell for pumping-processing oxygen produced by decomposition of NOx. The gas sensor further comprises a correcting control system for correcting and controlling the feedback control system on the basis of a difference between a second reference value and a value of a pumping current flowing through the auxiliary pumping cell to give a constant oxygen concentration in the second chamber, and a self-diagnosis unit for comparing the value of the pumping current with a prescribed range and Judging whether or not any trouble occurs, on the basis of an obtained result of comparison. Accordingly, it is possible to provide the gas sensor having a self-diagnosis function capable of quickly and reliably detecting whether or not any trouble occurs.

Disclosed is a method for controlling a gas sensor comprising the steps of pumping-processing oxygen contained in a measurement gas introduced from external space into a first chamber by using a main pumping cell so that a partial pressure of oxygen in the first chamber is controlled to have a predetermined value at which a predetermined gas component as a measurement objective is not decomposable; decomposing the predetermined gas component contained in the measurement gas in a second chamber by the aid of a catalytic action and/or electrolysis by using a detecting pumping cell to pumping-process oxygen produced during the decomposition; and measuring the predetermined gas component contained in the measurement gas on the basis of a pumping current which flows during the pumping process; wherein the oxygen to be pumped out by the detecting pumping cell is pumped out toward an inner pumping electrode which is fixed to have a base electric potential (ground electric potential), of the main pumping cell. Accordingly, it is possible to facilitate miniaturization of a control circuit system of the gas sensor and reduction of the weight thereof.

Gas sensor and method for controlling gas sensor

Disclosed is a gas sensor for measuring a NOx concentration comprising a main pumping cell and a detecting electrode, the main pumping cell including an electrode (an inner pumping electrode and an outer pumping electrode) having no decomposing/reducing ability for NOx or a low decomposing/reducing ability for NOx, to be used so that an oxygen concentration in a first chamber is controlled to have a predetermined value at which NO is not substantially decomposable, and the detecting electrode having a certain decomposing/reducing ability for NOx or a high decomposing/reducing ability for NOx, to be used so that NOx is decomposed to measure the NOx concentration by measuring an amount of oxygen produced during this process, wherein a buffering space is provided between a gas-introducing port and the first chamber. Accordingly, it is possible to avoid any influence of exhaust gas pressure pulsation generated in a measurement gas and improve the measurement accuracy on the detecting electrode.

Disclosed is a gas sensor comprising a main pumping cell for pumping-processing oxygen in a first chamber; an auxiliary pumping cell for pumping-processing oxygen in a second chamber; and a measuring pumping cell for pumping-processing oxygen in a measurement gas introduced through a third diffusion rate-determining section; wherein a NOx component contained in the measurement gas is measured on the basis of a pumping current flowing through the measuring pumping cell. The gas sensor further comprises a heater for heating at least the main pumping cell, the auxiliary pumping cell, and the measuring pumping cell to predetermined temperatures; an impedance-detecting circuit for detecting an impedance between an inner pumping electrode and an auxiliary pumping electrode; and a self-diagnosis unit for comparing an impedance value detected by the impedance-detecting circuit with a prescribed value to decide whether or not any trouble occurs, on the basis of a result of comparison. Accordingly, it is possible to provide the gas sensor which has a self-diagnosis function capable of quickly and reliably detecting whether or not the gas sensor has any trouble.

Disclosed is a gas sensor comprising a main pumping cell for pumping-processing oxygen contained in a measurement gas introduced into a first chamber, an auxiliary pumping cell for pumping-processing oxygen contained in the measurement gas introduced into a second chamber, a measuring pumping cell for pumping-processing oxygen in the measurement gas introduced via a third diffusion rate-determining section, an ammeter for detecting a pumping current generated depending on an amount of oxygen pumping-processed by the measuring pumping cell, a heater for heating at least the main pumping cell, the auxiliary pumping cell, and the measuring pumping cell to a predetermined temperature, an impedance-detecting circuit for detecting an impedance between an inner pumping electrode and an auxiliary pumping electrode, and a heater control circuit for controlling electric power application to the heater on the basis of a value of the impedance detected by the impedance-detecting circuit. Accordingly, it is possible to realize suppression of variation in detection output which would be otherwise caused depending on the measurement gas temperature and a high S/N ratio of detection output.

A gas sensor comprises a main pumping cell for pumping-processing oxygen contained in a first chamber, a feedback control system for comparing a partial pressure of oxygen in the first chamber with a first reference value to control the main pumping cell so that the partial pressure of oxygen has a predetermined value at which NO is not decomposable, an auxiliary pumping cell for pumping-processing oxygen in the second chamber, and a measuring pumping cell for pumping-processing oxygen produced by decomposition of NOx. The gas sensor further comprises a correcting control system for correcting and controlling the feedback control system on the basis of a difference between a second reference value and a value of a pumping current flowing through the auxiliary pumping cell to give a constant oxygen concentration in the second chamber, and a self-diagnosis unit for comparing the value of the pumping current with a prescribed range and judging whether or not any trouble occurs, on the basis of an obtained result of comparison. Accordingly, it is possible to provide the gas sensor having a self-diagnosis function capable of quickly and reliably detecting whether or not any trouble occurs.

Disclosed is a gas sensor comprising a main pumping cell including a solid electrolyte layer contacting with an external space, and an inner pumping electrode and an outer pumping electrode formed on inner and outer surfaces of the solid electrolyte layer, for pumping-processing oxygen contained in a measurement gas introduced from the external space on the basis of a control voltage applied between the electrodes; a feedback control system for adjusting the control voltage to give a predetermined level of a voltage between the inner pumping electrode and a reference electrode disposed at a reference gas-introducing space; and a heater for heating at least the main pumping cell to a predetermined temperature; wherein the outer pumping electrode is connected to a negative side lead wire of the heater. Accordingly, the control operation in the feedback control system, which is performed to constantly control the concentration of a predetermined gas component in the measurement gas by the aid of the pumping operation, is not affected by the heater leak current, the length of the heater lead wire, and the heater current (heater output). Thus, it is possible to accurately control the concentration of the predetermined gas component.

Gas sensor having a function for minimizing heater leak current

Disclosed is a gas sensor comprising a sensor element for measuring a predetermined gas component contained in an introduced measurement gas, and a protective cover arranged to surround a forward end of the sensor element; the gas sensor including the sensor element having a gas-introducing port which is disposed at a forward end surface thereof for introducing the measurement gas thereinto; and the protective cover comprising an inner protective cover and an outer protective cover. The inner protective cover is provided with an opening section which makes communication with the gas-introducing port. An inner protective cover space, which is formed between the inner protective cover and the sensor element, is isolated from a communication passage which makes communication from the opening section of the inner protective cover to the gas-introducing port of the sensor element so that the measurement gas principally diffuses and flows from the opening section into the gas-introducing port of the sensor element. Accordingly, it is possible to simultaneously solve the element temperature drop and the crack formation caused by condensed water, and highly accurately measure the predetermined gas component.

A carbon monoxide sensor (40) has a substrate arranged with other adjacent or overlaid layers attached thereon (41) defining a first space (43a) into which a unknown gas or gas mixture is introduced into and a second space (43b) communicating with the first space. A carbon monoxide adsorbent (61) is disposed in the second space, and an electrode (56) detects a partial pressure of oxygen in the carbon monoxide adsorbent. A pump cell includes the cell part (42), made of a solid electrolyte conducting oxygen ion, and a pair of electrodes (51, 52). The pump cell substantially removes oxygen from a gas in the first space (43a) while carbon monoxide in the gas is adsorbed onto the carbon monoxide adsorbent (61). Then, the pump cell introduces oxygen into the first space (43a), and a time is measured that the oxygen diffuses from the first space (43a) to the first detecting electrode (56) through the adsorbent (61). Only after an initial flow of the oxygen reacts with the carbon monoxide on the adsorbent (61), the oxygen reaches the first detecting electrode (56). Therefore, the time of transit across the adsorbent relates to an amount of the carbon monoxide in the gas. The carbon monoxide sensor is not affected by the concentration of oxygen in the gas, thereby improving accuracy in measuring the carbon monoxide concentration.

Carbon monoxide sensor

A bottomed, inner cylindrical member 21 is placed around a sensor element 2, and a bottomed, outer cylindrical member 24 is located around this inner cylinder 21. The inner cylinder 21 includes a hole 21a at a location opposite to the electrode of sensor element 2, and the outer cylinder 24 includes holes 24a and 24b at locations that are not opposite to the hole 21a. Between the inner and outer cylinders 21 and 24, there is a gap wide enough to prevent water from staying therebetween due to surface tension. Water entering the sensor assembly through the holes 24a and 24b in the outer cylinder 24 is immediately discharged out of the holes 24a and 24b through the gap between the outer and inner cylinders 24 and 21. Water, even when entering the outer cylinder 24, is unlikely to impinge directly on the sensor element 2 built in the inner cylinder 21.

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Nagoya, Japan

Yasuhiko Hamada