Abstract: An apparatus and method using a two-serial space sensor (having first and second internal spaces 2,3) for accurately measuring NOx concentration in gas, e.g., exhausted from an internal combustion engine. Both NOx (nitrogen oxide) and oxygen are forced to be partially dissociated in the first space 2 to an oxygen concentration level of 2×10−7 to 2×10−10 atm by pumping out oxygen from the first space 2. The NOx concentration is determined based on the second current measured in the second space 4 and based on the NO dissociation percentage in the first chamber which is 0.5-50%, or preferably 2-20%. The NOx measurement accuracy is further improved when the above oxygen concentration level is maintained from 2×10−8 to 2×10−9 and the temperature drift of the sensor is maintained within ±5° C. under a sensor temperature range of 700-900° C.

Abstract: A constant current Iconst is applied to an electromotive force cell which is interposed between a gap (measurement chamber) of a fixed atmosphere and an oxygen reference chamber of a constant oxygen content, for measurement of a resistance value of the electromotive force cell, whereby the resistance value can be measured accurately irrespective of an oxygen content in an atmosphere to be measured by an oxygen sensor element or cell unit. The resistance value of the electromotive force cell is measured at a predetermined timing T2 after application of a current is started, so that a measure resistance value is free of a variation of a resistance value due to deterioration of porous electrodes of an electromotive force cell, such a variation being included in the measured resistance value in case the measurement is done by using an AC current, and therefore accurate measurement can be attained.

Abstract: A method of detecting a deteriorated condition of a wide range air-fuel ratio sensor is provided. Firstly, a current is applied to an electromotive force cell to detect a voltage Vs0 across electrodes on opposite side surfaces of the cell. Application of the current is suspended, and a voltage drop Vsd1 across the electrodes is detected after lapse of a time ranging from 10 .mu.s to 1 ms after the application of the current is suspended. Based on the voltage drop Vsd1 is detected a first resistance value Rvs1 equated to the temperature of the electromotive force cell. Further, after lapse of a time ranging from 10 ms to 50 ms after the application of the current to the electromotive force cell is suspended, a voltage drop Vsd2 across the electrodes of the electromotive force cell is detected. Based on the voltage drop Vsd2 is detected a second resistance value Rvs2 equated to an internal resistance of the electromotive force cell including a resistance component resulting from deterioration.

Abstract: A branch metal terminal has a branch lead terminal portion with a branch wire connected to this terminal portion through a branch female metal terminal. The branch wire is connected to a female-side wire connected to a mold-type electronic part.

Abstract: A method of detecting an activated condition of a wide range air-fuel ratio sensor is provided. With this method, application of a current to a heater is started idiately after an engine is started (S00). Then, a current Icp for pumping is passed through an electromotive force cell (S10). A lapse of a predetermined time Tin is waited for (S18). After a lapse of time Tin, a voltage Vs across both electrodes of the electromotive force cell is detected (S20) and labeled as Vs0 (S22). Then, application of Icp is suspended (S30) and a routine is held on standby until a time of 25 ms elapses (S35). At the point of time when the time of 25 ms has elapsed, the voltage across the electrodes on the opposite sides of the electromotive force cell is detected (S40) and labeled as Vs1 (S45). A resistance value Rs1 is calculated from Vs0, Vs1 and Icp (S50).

Abstract: An oxygen sensor according to the present invention has battery element and a pump element in each of which porous electrodes are disposed on both faces of a solid electrolyte substrate. A minute current is supplied to the battery element after the start of energizing a heater and the activation of the sensor elements are judged on the basis of an interelectrode voltage generated at this energizing. A heater voltage is set to be 12V at the start of energizing. When the time period necessary for the interelectrode voltage to reach a predetermined voltage is short, the applied voltage is lowered to 11V. As a result, the time period necessary for judging the sensor elements to be activated can be made substantially constant irrespective of variations in sensor characteristics. After the activation judgment, the variation of the temperature of the sensor element is monitored on the basis of the interelectrode voltage.

Abstract: Activation treatment for a zirconia oxygen sensor is performed by applying alternately a treating voltage, which can make an oxygen partial pressure at the electrode-zirconia interface of a sensor equal to or higher than a critical oxygen partial pressure value (10.sup.-34 atm) not to cause blackening, between a pair of electrodes of the sensor at temperatures of 500.degree. to 800.degree. C. As a result, the treatment current flowing through the sensor can always be held below the critical level, whereby the sensor can be activated without causing blackening and other physical structural changes to occur in the zirconia sensing element. If the sensor is to be used in an A/F ratio control or the like on an internal combustion engine, it can be rendered active at all times by the activation treatment during or before or after the control.

Abstract: The invention provides a method for accurately and precisely detecting deterioration of a catalyst and measuring a conversion efficiency of a catalyst for HC/CO/NOx by using an oxygen sensor and an air/fuel ratio sensor disposed on the upstream and downstream sides of the catalyst, respectively. The catalyst is determined to be deteriorating when an output amplitude of the air/fuel ratio sensor becomes greater than a predetermined value. The conversion efficiency of the catalyst is determined based on a predetermined relationship between the output amplitude and the mean converted rate of HC/CO/NOx.

Abstract: An oxygen sensor including, at least, a) an oxygen pump element having a solid electrolyte plate and two porous electrodes, one on each surface of the solid electrolyte plate, b) a gas diffusion chamber facing one of the porous electrodes, and c) a gas diffusion path connecting the gas diffusion chamber and the ambience of the oxygen sensor, is defined its thickness between 0.7 to 1.25 mm, and its width between 2.8 to 4.0 mm. The restricted size renders higher resistance against repeated thermal shocks, and shorter warming-up time, which leads to greater accuracy and higher responsiveness in the oxygen content measurement.

Abstract: The invention provides an air/fuel ratio sensor, including an electrochemical sensor cell and an electrochemical pump cell, which shows both a quick response and a stable limiting current. This is realized by limiting the ratio of the area a of a region A to the area b of a region B on the inner electrode of the electrochemical sensor within a specified range, 0<a/b.ltoreq.0.1. Here, the region A corresponds to a region C within a 0.5 mm distance from the end of the gas diffusion hole except on the 0.5 mm distance line on the inner electrode of the electrochemical pump cell, and the region B corresponds to a region D or the complement of the region C on the inner electrode of the electrochemical pump cell.

Abstract: A control system has a controlled element, such as an element for sensing an air/fuel ratio of an internal combustion engine, having a high order lag, a controller element connected with the controlled element to form a closed path, and a third element connected with the controlled element and controller element for modifying an output signal of the controlled element in accordance with an output signal of the controller element so that a phase angle in a frequency response of a loop transfer function of the controlled and controller elements does not reach -180.degree..

Abstract: A method of controlling an oxygen concentration sensor of the type having oxygen pump and sensor cell elements spaced from each other to form a gap or a restricted region both of which are to be placed in some gases containing an oxygen component, and a heater element for heating said oxygen pump and sensor cell elements under energization of a heater current supplied thereto.A pump current is supplied to the oxygen pump element as long as the heater current is supplied to the heater element. However, the initiation of the supply of the pump current is somewhat delayed at the initial stage of the supply of the heater current in order to avoid incorrect operation due to the unstable cool state of the sensor, and to present possible flow of excessive pump current through the pump element which would cause deterioration of the oxygen pump element.