Robert Boschgmbh

Gunther Kauhl

Leo Steinke

Hannes Pflug

Helmut Weyl

Heinz Krauss

Jens Glauner

To heat the glow plug for an internal combustion engine, a spiral band or ribbon is wound in an essentially co-planar spiral about a central bolt secured to the bottom of the glow plug, the outer terminal of the spiral being connected to a lead-in with highly positive temperature coefficient of resistance to provide for self-limiting current flow upon heating of the glow plug. All free spaces in the glow plug are filled with a highly heat-conductive insulating material, for example magnesium oxide.

Glow plug arrangement

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.

Glow plug structure

To permit use of a standard starting switch customary in Otto engines to start automotive-type Diesel engines requiring energization of a glow plug, the 'start' position of the control switch is unstable, for example spring-loaded, and returns the switch to 'on' position upon release. The ON position also simultaneously forms the pre-heat switch position. The system includes a first relay having its connecting contacts connected to the glow plug and to a source of power, and a second relay forming a transfer switch with one terminal set connected as a self-holding circuit. The coil of the first relay is connected through the other set of transfer contacts of the second relay to the ON terminal of the switch to form the pre-heat circuit when the second relay is de-energized. The 'start' position connects the starting motor. The coil of the second relay is energized from a common transfer junction either when the switch is in the 'start' position or when a heater switch, included in the circuit of the glow plugs, has sufficient current flowing therethrough which also causes the glow plugs to become hot.

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Affalterbach, Germany

Gunther Kauhl