Glow plug structure

US4200077A · kind A · utility

Assignee

• Robert Bosch GmbH · DE

Inventors

• Gunther Kauhl · Marbach am Neckar, DE
• Hannes Pflug · Gerlingen, DE
• Leo Steinke · Waiblingen, DE

Key dates

• Filing date: Sep 13, 1978
• Grant date: Apr 29, 1980
• Expiry date: Sep 13, 1998

Classification

• Technology area (CPC Y): Emerging Cross-Sectional Technologies
• CPC primary: Y10T29/49085
• WIPO field: Thermal processes and apparatus
• WIPO sector: Mechanical engineering

Abstract

To prevent damage to the heating wire of an electrically heated glow plug due to non-uniform expansion of materials within the glow plug upon heating thereof, and particularly due to excessive expansion of filler material surrounding a spiraled heating wire, the filler material is made in two sections, one being located within the spiral of the heater wire and comprising a material of a thermal conductivity of expansion approximately matching that of the heater wire, typically high-temperature annealed aluminum oxide, magnesium aluminum spinel, silicon nitride, boron nitride, silicon carbide, or the like, the outer section between the heater wire and the inner wall of the glow tube being of a material of good heat conductivity, such as magnesium oxide. In manufacture, the first material is introduced into the heater wire spiral in the form of a compacted rod which, after assembly to the tube and introduction of the second material, is crushed by diametrical reduction of the tube after closing thereof, for example by hammering, rolling or swaging.