Abstract: A heating device for use in motor vehicles to rapidly heat combustion chambers, exhaust gas sensors, catalyzers and other associated apparatus. A resistive heating element is connected in series with a low-impedance measuring resistor and a switch across a power source, while a resistance bridge is formed with the aid of two further resistors. The diagonal bridge voltages are compared in a comparator whose output actuates a control circuit which operates the heater switch. The heater switch also provides the power for the comparator. In a first interval, constant current is applied to the heating element, while the current is pulsed during a second time interval. The switch control pulses may be provided by a free-running oscillator or one whose pulses are synchronized with the undulations of the engine starter current.

Abstract: Safety apparatus for a motor vehicle electric consumer having a temperature-dependent internal resistance, which includes a temperature indicating circuit for providing a signal which accurately indicates the consumer temperature to a threshold switch which actuates a switching device to interrupt current flow through the consumer whenever the consumer temperature exceeds a predetermined maximum value. The temperature indicating circuit either may be a consumer resistance measuring circuit such as a bridge circuit including the consumer in one leg thereof, or may be a consumer temperature replicating circuit, connected in parallel with the consumer, such as a special RC network. The switching device either may be a switch connected in series with the consumer, or a switch connected in parallel with the consumer, in which case the apparatus also includes an overcurrent device connected in series with the parallel combination of the switch and the consumer.

Abstract: A heating device for use in motor vehicles to rapidly heat combustion chambers, exhaust gas sensors, catalyzers and other associated apparatus. A resistive heating element is connected in series with a low-impedance measuring resistor and a switch across a power source, while a resistance bridge is formed with the aid of two further resistors. The diagonal bridge voltages are compared in a comparator whose output actuates a control circuit which operates the heater switch. The heater switch also provides the power for the comparator. In a first interval, constant current is applied to the heating element, while the current is pulsed during a second time interval. The switch control pulses may be provided by a free-running oscillator or one whose pulses are synchronized with the undulations of the engine starter current.