Abstract: Disclosed is an exchange system having an originating call restriction function comprising a unit for counting originating calls, a unit for counting incoming calls, a storage unit for storing a number (N.sub.o) or originating calls that can be accepted from accommodated subscribers (111) within a predetermined period, storage unit for storing a number (N.sub.i) of incoming calls that can be accepted within a predetermined period, and a unit for correcting the number of calls that can be accepted. The correction of the number of calls that can be accepted is effected by comparing the number (N.sub.i) of incoming calls that can be accepted and a number (N.sub.ai) of accepted incoming calls. When the difference between the number (N.sub.i) of incoming calls that can be accepted and the number (N.sub.ai) of accepted incoming calls is decreased below a predetermined value, the number (N.sub.o) of originating calls that can be accepted is decreased by a predetermined correcting value (.alpha.), and the number (N.

Abstract: A spark plug for an internal combustion engine including a center electrode, an earth electrode, a metal tip joined by welding to an ignition section of at least one of the center electrode and the earth electrode, and an alloy layer located at a welding portion between the metal tip and the at least one electrode. The metal tip is formed of material highly resistant to heat and wear which is distinct in the coefficient of thermal expansion from the material of the electrodes. The alloy layer is formed to have a thickness of at least about 10.mu., so as to avoid the rupture of the metal tip along the surface thereof adjacent to the welding portion.

Abstract: A spark plug for internal-combustion engines has a spark discharge gap defined between at least two electrodes opposing to each other, and a platinum-containing wear-resistant discharging layer provided on one of the electrodes. The spark plug has a thermal stress relieving layer disposed between the discharging layer and the base metal constituting the one eletrode. The thermal stress relieving layer is made of a platinum base alloy containing nickel, which constitutes the base metal. The discharging layer may be made of a material consisting essentially of 70 to 90 wt % platinum and 30 to 10 wt % iridium. The thermal stress relieving layer may be made of a material consisting essentially of 5 to 95 wt % platinum and 95 to 5 wt % nickel. Another platinum-containing wear-resistant layer may be provided on the other electrode, the wear-resistant layer being made of a material consisting essentially of 5 to 60 wt % nickel and 95 to 40 wt % platinum.

Abstract: An ignition plug of extended durability which reduces crack formation in noble metal layer on the center electrode and the ground electrode by joining a noblemental layer consisting of 85 to 70% by weight of Pt and 15 to 30% by weight of Ir to the spark discharge portion of the center electrode and also another noble metal layer consisting of 90 to 70% by weight of Pt and 10 to 30% by weight of Ni to the spark discharge portion of the ground electrode.

Abstract: A spark plug for an internal combustion engine comprises (a) an insulator surrounding a central electrode and (b) a housing having a grounded electrode and disposed on the periphery of the insulator. A taper-nose portion of the insulator, which is designed to be exposed to unburnt carbon in combustion gases of a combustion chamber, is modified to facilitate carbon removal from the taper-nose portion and to maintain excellent electrical insulation. The modification comprises a coating of a mixture of vanadium oxide and zirconium oxide in the form of a porous layer or a sponge-like porous layer having an irregularly-shaped structure with pores; it is fixed to the exposed surface of the taper-nose portion to improve the self-cleaning ability of the spark plug without decreasing the degree of electrical insulation provided by the insulator.

Abstract: A spark plug, wherein a central electrode is electrically insulated from an uter electrically-conductive casing (ground to an internal combustion engine when in use) by an insulator sealed in the casing, separating the central electrode from the casing and having a taper-nose portion which is designed to be exposed to unburnt carbon in combustion gases of a combustion chamber, is modified to facilitate carbon removal from the taper-nose portion. Discrete isolated particles or isolated aggregates of particles of vanadium oxide are adhered over the exposed surface of the taper-nose portion to improve the self-cleaning ability of the spark plug without decreasing the degree of electrical insulation provided by the insulator. The particles of vanadium oxide are formed from a suspension which is applied to the surface of the taper-nose portion of the spark plug. The resulting coating is then dried in situ.

Abstract: A spark plug for an internal combustion engine including a center electrode, an earth electrode, a metal tip joined by welding to an ignition section of at least one of the center electrode and the earth electrode, and an alloy layer located at a welding portion between the metal tip and the at least one electrode. The metal tip is formed of material highly resistant to heat and wear which is distinct in the coefficient of thermal expansion from the material of the electrodes. The alloy layer is formed to have a thickness of at least about 10.mu., so as to avoid the rupture of the metal tip along the surface thereof adjacent to the welding portion.