Ngk Insulators, Inc.

Nobuhide Kato

Yasuhiko Hamada

Kunihiko Nakagaki

Takao Murase

Hiroshi Kurachi

Masanori Katsu

Noriyuki Ina

Nobukazu Ikoma

Satoshi Nishikawa

Atsushi Iino

Takeya Miyashita

Nobuyuki Kokune

Yuji Katsuda

Tomonori Takahashi

Toshihiro Yoshida

Hiroshi Ishikawa

Fujio Ishiguro

Hitoshi Nishizawa

Toshihiko Suzuki

Yasushi Watanabe

Makoto Noda

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 gas sensor for measuring an amount of a measurement gas component, including a solid electrolyte having an internal space, a gas-introducing port for introducing measurement gas from an external space into the internal space, diffusion rate-determining means between the internal space and the gas-introducing port, and inner and outer pumping electrodes for pumping-processing oxygen contained in the measurement gas. The diffusion rate-determining means includes slits each having, when viewed in a plane substantially perpendicular to a longitudinal extension axis thereof, two dimensions, with at least one dimension of each slit being not more than 10 microns.

Gas sensor and nitrogen oxide sensor

A NOx sensor for measuring NOx concentration including a main pumping cell and a detecting electrode, the main pumping cell-including an electrode having no decomposing/reducing ability for NOx or a low decomposing/reducing ability for NOx, to be used to control oxygen concentration in a measurement gas 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 cermet electrode composed of a Pt&mdash;Rh alloy and a ceramic component is used as the detecting electrode. Accordingly, it is possible to suppress the oxidation of Rh and the reconversion into the metal contained in the detecting electrode, stabilize the impedance, and stabilize the sensitivity to NOx.

NOx concentration-measuring apparatus

One of a pair of temperature sensor sections in a combustible gas sensor is covered with porous oxidizing catalytic layers ( ) for oxidizing a combustible gas, and the other is not covered with the oxidizing catalyst layers. The temperature sensor sections each have temperature sensitive portions ( ) made of a dense ceramic material, resistors ( ) buried therein and having a positive resistance temperature coefficient, current leads ( ) and voltage leads ( ). A method for detecting the deterioration of a catalyst which intends to eliminate the combustible gas, by the use of this combustible gas sensor is further disclosed. When a difference between temperatures of the pair of resistors or a difference between powers fed to the pair of resistors is in excess of a predetermined value, it is judged that the catalyst has been deteriorated.

Method for detecting deterioration of catalyst

An NOx removal system has a combustion apparatus for applying energy to a load based on a predetermined combustion control process, an NOx remover for reacting NOx emitted from the combustion apparatus with NH to produce N and H O, an NH and/or urea introducing apparatus connected upstream of the NOx remover, for introducing NH and/or urea into a gas passage extending from the combustion apparatus to the NOx remover, and sensor, which is also sensitive connected downstream of the NOx remover, for generating a detected signal based on NH and NOx contained in a gas discharged from the NOx remover. A controller controls a rate at which NH and/or urea is introduced into the gas passage by the NH and/or urea introducing apparatus while repeatedly increasing and reducing the rate, in response to the detected signal generated by the NOx sensor. The NOx removal system, which employs NH and/or urea as a reducing agent, is capable of accurately controlling the rate at which NH and/or urea is introduced into the gas passage through a simple arrangement, and minimizing the discharge of NH and NOx.

System for removing NOx from exhaust gases

Disclosed is a NOx 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 measurement gas 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 cermet electrode composed of a Pt&mdash;Rh alloy and a ceramic component is used as the detecting electrode. Accordingly, it is possible to suppress the oxidation of Rh and the reconversion into the metal contained in the detecting electrode, stabilize the impedance, and stabilize the sensitivity to NOx.

NOx concentration-measuring method

Disclosed are a gas sensor and a nitrogen oxide sensor each comprising a first diffusion rate-determining section for giving a predetermined diffusion resistance to a measurement gas to be introduced into a first chamber, the first diffusion rate-determining section being formed with a slit having a laterally extending aperture formed at a front end portion of a second spacer layer to make contact with the lower surface of a second solid electrolyte layer in which the aperture is formed to extend with an identical aperture width up to the first chamber, and a slit having a laterally extending aperture formed at a front end portion of the second spacer layer to make contact with the upper surface of a first solid electrolyte layer in which the aperture is formed to extend with an identical aperture width up to the first chamber. The slits have a substantially identical cross-sectional configuration, in which the length in the vertical direction is not more than 10 &mgr;m, and the length in the lateral direction is about 2 mm. Accordingly, it is possible to avoid the influence of the pulsation of the exhaust gas pressure generated in the measurement gas, and it is possible to improve the measurement accuracy obtained on the detecting electrode.

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

It is intended to avoid invasion of oxygen through any route except for an introducing port for a measurement gas so that the amount of oxide or inflammable gas contained in the measurement gas may be measured highly accurately. Insulative layers are provided for respective lead wires at positions corresponding to portions at which the temperature of the oxygen ion-conductive solid electrolyte is increased due to heat generation effected by a heater. Each of the insulative layers is formed to have a pattern in which one end is exposed to a first chamber or a second chamber, and the other end terminates at a position separated by a predetermined distance from a corresponding through-hole. At least the lead wires, which lead to an auxiliary pumping electrode and a detecting electrode, are densified. Preferably, the insulative layers for these lead wires are also densified.

A sensor for measuring nitrogen oxide (NOx) in a gas by decomposing NOx in the gas and measuring an amount of oxygen generated by the decomposition includes: means for introducing the gas to a first inner space under a first diffusion resistance and connected with an external space, means for controlling an oxygen partial pressure in an atmosphere in the first inner space to be a predetermined low value at which NO is not decomposed substantially by a main pump means, means for introducing a controlled atmosphere of the first inner space into a second inner space which is connected with the first inner space and which is under a second diffusion resistance, and means for converting the atmosphere into an electric signal corresponding to the quantity of oxygen generated by decomposition or reduction of NOx contained in the atmosphere by an electric signal conversion means. A first oxygen concentration detecting means is disposed for detecting an oxygen partial pressure in the second inner space, and a control voltage to be applied to the main pump means is adjusted on the basis of an output of the first oxygen concentration detecting means.

Sensor for measuring nitrogen oxide

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.

Growing community of inventors

Ama-gun, Japan

Nobuhide Kato