A current technical debate concerns means for reducing the fuel consumption of motor vehicles. This technical debate is part of the wider economic and ecological debate about reducing the associated carbon-dioxide emissions. Suppliers in the various sectors of automotive technology, too, consequently feel challenged to call existing technical concepts into question.
One approach by automobile manufacturers to addressing the problem of carbon-dioxide emissions consists in reducing (‘downsizing’) the stroke volume of engines while preserving or even increasing their power. This approach has virtually reached the technological limits of current mechanical solutions. To obtain the best possible results within these limits of engine technology, sensors are used for monitoring and control purposes even in situations where they were not used previously, for example in surroundings with operating temperatures in excess of 150° C.
The electronic components currently used have operating temperature limits of around 150° C. and, in the new applications, come very close to those limits. A possible remedy to this is to adopt measures for cooling and protecting the sensors, but such measures are elaborate and costly.
Even coils used for inductive sensors are approaching the limits of their operating temperatures, since for geometrical reasons such sensor arrays and their electronic components have to be positioned very close to the moving signal-emitters in order to be able, reliably, to transmit not only large signal variations but small ones as well.
To improve the sensitivity or signal range of an inductive sensor, those with knowledge of the subject can increase the number of turns in the coil. In the prior art multilayer circuit-carriers are known, which can be used to multiply the number of turns of an initially monolayer sensor. For example, in a four-layer circuit-carrier the number of turns is multiplied fourfold and in a six-layer circuit-carrier the number of turns is multiplied sixfold. FIG. 1 illustrates the operating principle of a known coil of this type with a plurality of windings; FIG. 1 also shows the distribution of the magnetic field produced by this coil. Thus, the windings extend over several layer planes.
Against this background the invention starts from circuit-carriers or printed circuit boards as known, for example, from DE 20 2004 019 489 U1. Both the upper side and the lower side of this circuit-carrier or this inductive sensor unit carry coils, i.e. a plurality of coils are accommodated in more than one layer of the printed circuit. In the prior art two, three or four layers of this flat type are known.