Ford Motor Company Limited

Stanley R Merchant

Wells L Green

Michael J Cermak

Michael J Esper

Elmer T Heiney, Iii

Charles M Wells

An exhaust gas sensor electrical circuit is improved by the provision of circuit means for inhibiting reduction in the magnitude of the change in voltage signal produced in the sensor circuitry. The reduction in magnitude change would otherwise result from prolonged exposure of the sensor ceramic elements to exhaust gases produced by combustion of a rich air/fuel mixture or a lean air/fuel mixture. The sensor has a titania or other exhaust gas sensing element responsive to temperature and to the partial pressure of oxygen. A second metal oxide ceramic element also is responsive to exhaust gas sensor temperature, but is more slowly responsive to the partial pressure of oxygen in the exhaust gases. Prolonged exposure of the second element in the sensor to rich-mixture exhaust gases or to lean-mixture exhaust gases can lead to a temporary but substantial loss of output signal magnitude from the sensor in the absence of the inhibiting means of the improved circuitry.

Exhaust gas sensor electrical circuit improvement

An improved sensor having a ceramic element that undergoes a change in an electrical characteristic in response to a change in the partial pressure of oxygen in a mixture of gases to which the ceramic element is exposed. Sensors of this type are used to detect the air/fuel ratio of mixtures supplied to internal combustion engines. Prior art sensors are characterized by little change in their respective electrical characteristics at low operating temperatures. A charge transfer material, platinum or platinum/rhodium is applied to the ceramic element to facilitate or make possible the electron transfers required for sensor operation at low temperatures. Platinum/rhodium alloy is the currently preferred charge transfer material. This alloy, which preferably is 90% platinum and 10% rhodium, reduces the minimum temperature of operation for the sensor as taught herein, and it also substantially eliminates vaporization loss of the charge transfer material.

Exhaust gas sensor having porous, metal-impregnated ceramic element

An improved exhaust gas sensor of the type having first and second titania ceramic elements which have electrical resistances varying as a function of both the temperature and the composition of exhaust gases from internal combustion engines to which the elements are exposed. The first and second titania elements are connected in series circuit in the utilization of the sensor and the resistance of the second element over the operating temperature range of the exhaust gas sensor compensates the signal of the first titania element in a manner that produces a desired signal. The desired signal is a result of variation of the second titania element resistance values when exhaust gases cycle between lean-mixture and rich-mixture compositions. The resistance values of the second titania element are intermediate the corresponding resistances of the first titania element over the temperature range. The second titania element is more dense than the first titania element. It has a density in the range from 3.2 g/cm.sup.3 to 3.8 g/cm.sup.3, i.e., between about 76% and 90% of theoretical density.

Exhaust gas sensor having two titania ceramic elements

A high temperature thermistor and its method of fabrication are disclosed. The thermistor is fabricated from titanium dioxide ceramic forming material and is fabricated to achieve a high degree of densification approaching 100% of theoretical density. At elevated temperatures in the range of from about 700.degree. F. to about 1500.degree. F. densified titania ceramic material behaves as a semiconductor having a resistance which is responsive principally to the temperature of the thermistor element. The thermistor is fabricated by processing titania powder which includes a substantial majority of rutile phase material. The titania powder is processed to achieve a thermistor chip or member which demonstrates a high degree of density.

Titania thermistor and method of fabricating

A pair of ceramic chips, formed of similar metal oxide ceramic materials which are semiconductors at elevated temperature, are connected electrically in series and are arranged for exposure to the hot gaseous combustion by-products produced by an internal combustion engine. The chips are positioned in the exhaust gas conduit by a ceramic insulator having a plurality of longitudinal passages extending therethrough. A plurality of electrical terminal members are received within the rear of the longitudinal passages. Electrical leads extend from the chips to the terminal members through the plurality of passages and support the chips while providing electrical communication between the chips and the electrical terminals. The electrical terminals are adapted for communication to electronic and/or electrical utilization means. One of the pair of chips is processed to exhibit a rapid change in an electrical property responsive to differences in the exhaust gas chemistry and differences in exhaust gas temperature. The other of the chips is processed to exhibit a rapid change in an electrical property responsive to differences in exhaust gas temperature only. The preferred material is titania. For temperatures in the range of from about 700.degree. F. to about 1500.degree. F., the application of a reference voltage across the series connected chips will produce a substantially temperature independent voltage variation across either chip in response to changes in exhaust gas chemistry and which is relatively insensitive to changes in the exhaust gas temperature.

Temperature compensated resistive exhaust gas sensor construction

A stoichiometric air/fuel ratio exhaust gas sensor construction particularly useful with variable resistance partial pressure of oxygen responsive sensor material is disclosed. A generally cylindrical mounting body, formed of corrosion resistant material, is arranged for receipt within the exhaust system of an internal combustion engine and is provided with a two-part ceramic insert member for support of a wafer of variable resistance sensor material. The ceramic insert member is comprised of a first portion having a slotted tip for receipt and support of the wafer of partial pressure of oxygen responsive ceramic sensor material. The ceramic insert member is arranged to position the wafer within a perforated shield member at a remote free end of the cylindrical housing body. The wafer includes a pair of extending high temperature resistant electrical conductors which are received within bores provided therefor in the ceramic insert member. The extending leads are electrically connected, proximate to the interface of the two-part ceramic insert member, to a pair of relatively flexible, electrically low resistance, high temperature resistant extending lead wires which are received within the second portion of the ceramic insert member.

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Garden City, MI, United States of America

Stanley R Merchant