Electric heating – Heating devices – With power supply and voltage or current regulation or...
Patent
1991-01-09
1994-02-22
Paschall, Mark H.
Electric heating
Heating devices
With power supply and voltage or current regulation or...
219202, 219497, 219528, H05B 102, H05B 334
Patent
active
052889742
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heating arrangement and more particularly relates to a heating arrangement suitable for use in heating the seat in a motor vehicle.
2. Description of the Related Art
It has been proposed previously to provide a heater integrated into the seat of a motor vehicle in order to heat the seat. Of course, it is necessary to provide some type of thermostatic control for such a heater.
It has been proposed to utilise an electromechanical relay, to effect such thermostatic control. However, such a relay, because it operates in a mechanical manner, cannot make a very large number of different "makes" and "breaks". Consequently such a relay must be adapted to operate with a relatively large hysteresis loop, for example, making at 15.degree. C. and breaking at 35.degree. C. Whilst such a relay may comprise a switch operated by relay coils in response to signals from a temperature sensing arrangement, another example of this type of arrangement is a bi-metallic thermostat switch, in which both the temperature sensor function and the switching function are embodied in the same device. Such a device does not need a control circuit, and is therefore very cheap. However, the big hysteresis loop that is necessary proves to be a disadvantage.
Other types of temperature sensors have been proposed for use in such an application, for example a thermistor, which is a resistor having a negative temperature dependence, or the base-emitter voltage of a transistor. However, if temperature sensors of this type are utilised a control circuit is needed to actuate the relay. This requires a control box or circuit which is located outside the seat squab, while the sensor is placed in the seat squab.
It would, of course, be possible to utilise a heating wire which has a positive, but very small, temperature dependence as the temperature sensor. In such an arrangement the resistance of the heating wire is monitored to provide the necessary control. However, this requires the provision of a complicated, and thus expensive, control circuit.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved heating arrangement.
According to one aspect of this invention there is provided a heating arrangement for heating a seat, said arrangement comprising electrical heating means embedded in the seat, and temperature responsive means and control means for controlling the supply of electrical current to the heating means, also embedded in the seat, wherein the temperature responsive means and the control means are comprised by components mounted on a flexible printed circuit board, embedded in the seat.
Conveniently, the temperature responsive means comprise means adapted to provide an output control signal whenever the temperature sensed by the temperature responsive means is below a pre-determined limit, and the control means comprise a power transistor.
Advantageously said transistor comprises a field effect transistor.
Conveniently the control means comprises a differential amplifier, means to provide a substantially constant pre-determined potential to a first terminal thereof, and means to provide a potential to a second terminal thereof, which include a temperature sensitive component so that the potential supplied to the second terminal of the differential amplifier depends upon the temperature sensed by the temperature sensitive component.
Preferably the first terminal of the differential amplifier is connected to a node between two resistors connected in series between an earth rail, and a rail carrying a substantially pre-determined potential, and the second terminal of the differential amplifier is connected to a node between a series connection of a resistor and a thermistor, connected in series between earth and said rail carrying said predetermined potential.
Advantageously the control arrangement is connected to enable the operation of the transistor and to disable the operation of the transistor.
Preferably an oscillator is emp
REFERENCES:
patent: 2698893 (1955-01-01), Ballard
patent: 3423574 (1969-01-01), Shomphe et al.
patent: 3586829 (1971-06-01), Farmer et al.
patent: 4464564 (1984-08-01), Zimmermann et al.
patent: 4633061 (1986-12-01), Arikawa
patent: 4736091 (1988-04-01), Moe
Paschall Mark H.
Plantron AB
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