Glow plug for engine

Proposed is a sheathed-element glow plug (10) designed to be fitted in the combustion chamber of air compression type internal combustion engines. As with prior art devices of this kind, the glow plug contains a resistor (17) inside the sheath (13), the resistor (17) being made up of two coils (20, 21) connected in series. While the coil (20) nearest the combustion chamber is a heating coil with substantially constant resistance at all operating temperatures, the resistance-wire coil (21) remote from the combustion chamber, which acts as a control element, has a high coefficient temperature-resistance. The invention calls for the resistance coil (21) acting as the control element to consist of a cobalt/iron alloy whose structure is not destroyed when the alloy is exposed to the temperatures occurring in an internal combustion engine. According to the invention, this alloy is chosen so that it retains a face-centered cubic structure in all operating conditions of the glow plug (10). The iron content of the alloy lies between 6 and 18 % by wt., preferably 12 to 14 % by wt. The coil resistor (17) is embedded, as in prior art devices, in an electrically insulating material (18) which is a good thermal conductor.