Abstract: A method of treating a porous body in a gas concentration sensor to regulate the gas diffusion. The porous body is impregnated with a impregnant containing a component that adheres to or binds with the pore surfaces. The component may be a metal salt, examples of which are Al(NO.sub.3).sub.3, CaCl.sub.2 and H.sub.2 PtCl.sub.2. A colloidal solution may be used.

Abstract: A torque detecting apparatus comprises an annular bobbinless sensor coil disposed on a rotatable shaft, and a position adjustable, non-ferromagnetic metal core member disposed adjacent the sensor coil. When the shaft is twisted, the core member moves in a hollow space defined by the sensor coil to thereby change inductance thereof in accordance with angular displacement between the sensor coil and the core member. A detecting part is disposed in opposition to a solenoid coil wound on the shaft with a gap therebetween for detecting the angular displacement in terms of a change in an oscillation frequency. A sensor set is constituted by the sensor coil and the metal core. A pair of sensor sets may be disposed, wherein one sensor set is so connected that inductance of the associated sensor coil is decreased while the other sensor set is so connected that inductance of the associated sensor coil is increased. Difference or ratio between the two oscillation frequencies may be inputted to a resonance circuit.

Abstract: An air-fuel ratio sensor in which the temperature dependence as well as the pressure dependence of a detection signal obtained by the air-fuel ratio sensor are suppressed to thereby improve the accuracy in air-fuel ratio by the air-fuel ratio sensor, which is not influenced by deposits in an exhaust gas and which is high in durability. The suppression is achieved by using a gas-diffusion limiting portion having such critical parameters as 10-30% porosity, 1-3 micrometers mean pore size and 200-1000 micrometers thickness. Alternatively the parameters may be 15-25% porosity, 0.1-7 micrometers pore size and 400-800 micrometers thickness.

Abstract: At least one of center and ground electrodes of a spark plug has a thin layer formed by bonding noble metal powder on a discharge-related surface area of the electrode stock of said at least one of said center and ground electrodes in accordance with ultrasonic bonding. Instead of the thin layer, a discharge tip may be formed there by boring a hole in the electrode stock, filling noble metal powder, which has been obtained by coating spherical or flaky metal particles with a corresponding noble metal or noble metal alloy, in the hole and then bonding the thus-filled noble metal powder in accordance with ultrasonic bonding. As a further alternative, a tip made of a noble metal or an alloy thereof may be bonded by ultrasonic bonding or resistance welding in the hole with a layer of metal powder of a metal having good high-temperature erosion resistance or an alloy thereof interposed therebetween. The spark plug enjoys a long operating life.

Abstract: An air/fuel ratio sensor having an unambiguous output with respect to both the fuel-rich and the fuel-lean regions and which does not require the introduction of atmospheric air. The sensor is composed of first and second elements, each having porous electrodes formed on opposite sides of an oxygen-ion-conductive electrolyte plate. The two elements are arranged to define between them a gas compartment communicating with the atmosphere to be detected via one or more diffusion limiting portions. One of the elements serves as an oxygen concentration differential electrochemical cell and the other one as an oxygen pump. An internal reference oxygen source is formed on the side of one of the elements opposite the gas compartment, and a small current is caused to flow the first element so as to transfer oxygens from the gas compartment to the oxygen source.

Abstract: At least one of center and ground electrodes of a spark plug has a thin layer formed by bonding noble metal powder on a discharge-related surface area of the electrode stock of said at least one of said center and ground electrodes in accordance with ultrasonic bonding. Instead of the thin layer, a discharge tip may be formed there by boring a hole in the electrode stock, filling noble metal powder, which has been obtained by coating spherical or flaky metal particles with a corresponding noble metal or noble metal alloy, in the hole and then bonding the thus-filled noble metal powder in accordance with ultrasonic bonding. As a further alternative, a tip made of a noble metal or an alloy thereof may be bonded by ultrasonic bonding or resistance welding in the hole with a layer or metal powder of a metal having good high-temperature erosion resistance or an alloy thereof interposed therebetween. The spark plug enjoys a long operating life.

Abstract: An air/fuel ratio sensor having two units of probe is disclosed each of which comprises two sensing elements, each having a pair of porous electrodes on oppostie sides of an oxygen ion-conductive solid electrolyte; a gas compartment which is formed in contact with one porous electrode for each sensing element and which communicates with the gaseous atmosphere of interest by way of a gas diffusion limiting portion; and an internal reference oxygen source which is formed in contact with one sensing element on the porous electrode side which is opposite the side where said gas compartment is provided. The oxygen source communicates with the outside by way of a leakage resisting portion. The gas compartment in the first unit of probe communicates directly with the gaseous atmosphere of interest by way of a first gas diffusion limiting portion while the gas compartment in the second unit of probe communicates with the gas in the first unit of probe by way of a second gas diffusion limiting portion.

Abstract: The invention relates to a gas sensor having first and second solid electrolyte cells each of which has a solid electrolyte plate, e.g. a zirconia plate, and a pair of porous electrode layers formed on the opposite surfaces of the plate, spacing means to hold the first and second cells in a narrowly spaced, opposite and parallel arrangement and to define a gas chamber, which admits a gas atmosphere subject to measurement, within the gap between the two cells such that the inner electrode layers of the two cells face each other across the gas chamber and means to appropriately restrict diffusion of the gas atmosphere into the gas chamber. Usually one of the two solid electrolyte cells is used as a concentration cell and the other as an ion pump.

Abstract: A spark plug having a center electrode comprises a ceramic insulator whose leg portion is shaped at the tip in a bag form so as to close the insulator bore. A firing tip is provided at the bag-shaped tip in a face-to-face relation with a side electrode by fixing an electrode element made of a sinter of a ceramic powder containing particles of a size between 10 and 200 .mu.m which are coated with a noble metal to a thickness of 0.1-20 .mu.m. An electrode axis extends from the top end of the plug and is inserted through the insulator bore.