Electrical heating arrangement.

The invention relates to an electric heater for heating a plate with the aid of a flat PTC resistor.

Such heaters have been known, for example, for heating external mirrors of motor vehicles, comp. The published documents of the German utility model DE-GM 79 19 839 and DE-GM 7929 548. There is a PTC resistor as self-regulating heating member with a terminal electrode on a heat spreader plate soldered. The local heat distribution plate is connected via a solder joint with an electric line, which is, for example, to the body (mass) of the motor vehicle in connection. The other terminal electrode is also connected by soldering to an electric wire leading to the switch, which connects the heating circuit to the power supply of the motor vehicle. The installation of this PTC resistor and its connections is very costly due to the solder joints. The connections must be done carefully we len, to achieve the lowest possible electrical and thermal contact resistance. In addition, it may in the long run come in the solder to heat stress cracks.

further still hollow cylindrical PTC resistors with power supply electrodes on both end surfaces in the prior art can be seen, comp. the published German patent application DE-OS 14 65 439. Also disc springs for contacting a flat circular PTC resistor within a housing are known , compare the published German patent application DE-OS 25 40 029. here, however, the contact forces are dependent on the dimensions of the housing.

The invention has for its object to provide an electric heater of the type mentioned, whose PTC resistor fast and secure - that is, without large electrical and thermal resistances - can be mounted.

The invention solves this object in that the PTC resistor is formed as a flat cylindrical ring, the outer ring surfaces form the terminal electrodes, that in the area to be heated plate has a through opening is arranged such that the PTC resistor having its first terminal electrode around the opening rests on the plate and that a fastening member is pushed through the opening of the PTC resistor and through the opening of the plate, which presses the PTC resistor onto the plate.

The second connection electrode may be contacted, that the fastening member presses an annular electrical contact member onto the second connection electrode of the PTC resistor.

An improved heat distribution at the PTC resistor is achieved in that the fastening member presses a perforated heat distribution plate to the second terminal electrode. In this case, the contact part may be either itself designed as a heat distribution plate or the contact part is disposed between the PTC resistor and the heat spreader plate.

The fastening part may be formed in several parts and for example consist of a T-shaped spring member with a pin and of a self-locking, slotted spring washer, said spring washer with the interposition of the plate, the PTC resistor and, if the heat distribution plate and / or of the contact part on the pin is pushed and the deferred parts are pressed against each other.

To increase the elastic pressing force may be between the deferred parts on the one hand and the spring washer on the other hand, an elastic corrugated ring be disposed. The invention does not require solder connections for connecting the electrical leads to the electrodes of the PTC resistor or for the thermal contact between the PTC-resistor and the plate to be heated. Installation can be done largely by machine. Quite substantial tolerances in the dimensions, for example in the thicknesses of the components involved can be easily compensated for, so that always sufficient pressure between the PTC resistor and to the heated plate or the electrical connection members is present.

In the drawing, an embodiment of the invention is shown, which is described in more detail below. Figure 1 shows the individual parts of a heating device, as they are placed before the assembly between a lower and an upper punch of a mounting press.

Figure 2 shows the fully assembled heater of Figure 1 .:

The to be heated plate 1 may be a thin aluminum sheet and serve for example in a known manner for heating a motor vehicle exterior mirror. The plate 1 has a round through-hole 2, and a Stekkerzunge 3 for connection to the power supply. On the annular surface 4 around the hole 2 thermal compound 5 is applied. In the thermal paste 5 of the flat annular PTC-resistor 6 is placed which comprises a about a central through hole 7 extending annular body eighth The PTC-resistor 6 is located with a ring-shaped connection electrode 9 on the thermal compound fifth On the other annular terminal electrode 10 a ring-shaped contact portion 11 is placed in the form of a brass disc with a male tongue 12th The contact part 11 may be flat - as shown - or as the PTC resistor overarching dome, see 11 'dash-dot indicated in Figure 2. In order to secure sufficient spring forces a corrugated ring 13 is provided.

The actual fastening device is composed of a cross-sectionally T-shaped spring member 14 and a slotted cooperating therewith spring washer 15, which is known as a "Snap". The spring member 14 is made of a heat-resistant plastic, for example glass fiber-reinforced polycarbonate. It includes a flat annular 14b pressing part 14a and a hollow pin. The hollow pin 14b is stepped and formed with a conical transition 14c and a front chamfer 14d. The slotted spring washer 15 is made of spring steel plate-shaped and has a central through-hole 15a and more, at an acute angle to the disk plane extending, on the inner periphery distributed locking finger 15b.

It is mounted by the spring member 14 with its pressing part 14a placed on a lower die 16 or other firm surface. now on the pin 14b, the parts 1, 5, 6, 11 and 13 are attached. Then the spring washer 15 is placed on the chamfer 14d of the pin 14b; because the central opening 15a of the spring washer 15 is slightly smaller than the diameter of the pin 14b is formed in the region between the locking fingers 15b. Then the spring washer 15 is pushed by means of the upper punch 17 on the pin 14b. Here, the locking finger bend 15b and the corrugated ring 13 is compressed. After the desired contact pressure is achieved, the punch 17 is moved back. The locking finger 15b now snagging in the pin 14b, so that the parts 1, 5, 6, 11 and 13 are held together. The consequence of this is good thermal and electrical contact of this said parts, see FIG. 2