Abstract: A damped piezoelectric ceramic resonator. The resonator is a thin flat plate of piezoelectric ceramic material which has parallel major planar surfaces and is polarized in one direction in such a way that said direction is at an angle of from 0.degree. to 60.degree. with respect to said major surfaces, the thickness dimension of said plate being such as to impart thereto a resonance of vibrations in a thickness-shear mode at a particularly selected frequency higher than one megacycle. Operating electrodes are applied to said major planar surfaces. Vibration damping means is attached tightly to the contour of the edge of said flat plate so as to suppress unwanted resonance vibrations in said flat plate during operating. The vibration damping means is a ring of a rubber material having a hardness from 20 to 70 on the Shore A Scale and is under a tension of 20-500 gm/cm.

Abstract: An air-fuel ratio sensing device for an air-fuel ratio control system of an internal combustion engine, which device includes a sensing element exposed to exhaust gases passing through an exhaust gas passageway. A housing surrounding the sensing element has a plurality of openings to admit the exhaust gases into the housing, and a plurality of temperature responsive valves associated with the openings, respectively, which are closed when the exhaust gases exceed an excessively high temperature to prevent the sensing element from being deteriorated due to excessively high temperature of the exhaust gases.

Abstract: Gas recirculation into engine combustion chambers is controlled to a constant ratio with respect to the amount of induction air despite wide variations in manifold vacuum.

Abstract: An exhaust gas recirculation system comprises an exhaust gas flow control valve; a vacuum actuator for operation of the flow control valve; and a control apparatus constructed and arranged such that an output vacuum of the control apparatus applied to the vacuum actuator is an amplification of the venturi vacuum modified by the intake manifold vacuum.

Abstract: This invention provides a surface elastic wave device constituted by a unitary body of a piezoelectric plate having a pair of transducers thereon, which unitary body is embedded in a casing, and wherein the wave propagation of a surface elastic wave generated on the surface of the piezoelectric plate during excitation of the device is prevented from being transferred to the casing by a thin film inserted between the casing and the wave propagation surface of the piezoelectric plate or by using as the casing a roll of flexible sheet which has the same function of wave propagation prevention as that of the thin film. This device is advantageous because it has a low spurious signal level without incrementing insertion loss, is easy to manufacture and is inexpensive. This invention also provides an effective method of making the device.

Abstract: An electronically controlled exhaust gas purifying system for use with an internal combustion engine of a motor vehicle including not only a catalytic converter but also an auxiliary thermal reactor which is located upstream of the catalytic converter and by which exhaust gases emitted from the engine is re-combusted to the extent that the catalytic converter is not destroyed or damaged by the residual unconsumed compounds in exhaust gases discharged from the thermal reactor. The system is provided with an electronic control means for shutting off the flow of secondary air to be mixed with the exhaust gases emitted from the engine both when at least one of the temperatures of the catalytic converter and the thermal reactor rises above a critical value at which they would be destroyed or damaged, and when the engine is under cranking operation. The electronic control means retards the spark in order to heat the exhaust gases when the temperature of the reactor falls to its reaction commencement temperature.

Abstract: A frequency discriminating apparatus is constituted by a piezoelectric ceramic resonator, a reference capacitor, a pre-amplifier including a broad tuning circuit, a pair of amplitude detectors, and a differential amplitude limiter. The piezoelectric ceramic resonator is made of a piezoelectric lead titanate ceramic plate having a pair of electrodes covering the entire area of the major surfaces thereof, and the plate is poled with a poling field of not less than 50 kV/cm in the thickness direction. The thickness of the plate is chosen so as to cause the plate to vibrate in the thickness-extensional vibration of the 3rd harmonic overtone at a preselected frequency when an electrical signal is applied to the pair of electrodes. The differential amplitude limiter differentially adds the two signals detected by the two amplitude detectors and limits the peak output voltage amplitudes to a predetermined amplitude.

Abstract: An auxiliary flow control valve is disposed in an exhaust gas recirculation passageway at a location upstream of a main flow control valve controlling the flow rate of exhaust gases recirculated into an intake system. Two conduits communicating with an intake manifold communicate with a vacuum chamber of a servo motor controlling the main flow control valve. One of the conduits has formed therein a restriction to limit the flow rate of fluid therethrough. A check valve is disposed in the other conduit to close the same when the vacuum in the intake manifold is increased and constant and to open the other conduit when the vacuum in the intake manifold is reduced.

Abstract: Flow of secondary air into the exhaust system is regulated by diaphragm assembly controlled valves between an air supply and the exhaust system. The diaphragm assemblies respond to vacuum in the intake air system of the engine.

Abstract: A valve responsive to both venturi vacuum and intake manifold vacuum operates a recirculation valve by means of vacuum amplification.

Abstract: A plurality of pump elements is progressively increasing the pressure of air to respectively supply air at various pressures into portions in an exhaust gas purifying system requiring secondary air.

Abstract: A valve disposed in the central space of the manifold normally divides the space into two halves to avoid mutual interference of exhaust gas flows. At low engine speeds, the valve causes the exhaust gas flows from all branches to be disturbed and to mix with each other, to promote oxidation of HC and CO.