Heating device

Abstract

Heating device with a plate-shaped PTC resistor (3) having a thickness, a front (31), a back (32) and narrow sides (33, 34), wherein the distance from the front (31) to the back (32) is the thickness, and a first contact element (4) and a second contact element (4) that electrically contact the PTC resistor (3), wherein the PTC resistor (3) is electrically contacted by the contact elements (4) on opposite narrow sides (33, 34), characterized in that the electrical contact elements (4) are strips of sheet metal.

Description

[0001] The invention relates to a heating device according to the preamble of claim 1, as known from US 4,072,848 A. Similar heating devices are known, for example, from DE 10 2015 107 316 A1, DE 10 2012 107 113 A1 or DE 39 42 266 A1.

[0002] Heating devices for vehicles, such as those used to heat the passenger compartment, typically contain plate-shaped ceramic PTC resistors to generate heat. This is because PTC resistors are inherently protected from overheating by exhibiting a significant increase in electrical resistance at a critical temperature. The electrical resistance of PTC resistors at lower temperatures is relatively low, which causes significant inrush currents, especially when multiple PTC resistors are connected in parallel.

[0003] From DE 197 24 734 A1 a heating device for motor vehicles is known which contains more cost-effective and less moisture-sensitive silicon heating elements instead of PTC resistors, which are contacted on their respective narrow sides.

[0004] Plate-shaped PTC resistors based on barium titanate were developed for heating vehicles with an electrical system voltage of 12 V or 24 V. When such PTC resistors are used in heating devices for vehicles with an electrical system voltage of 48 V or even more than 100 V, care must be taken to ensure that the current does not become too high.

[0005] Transforming a high on-board voltage into a lower voltage of 12 V or 24 V is relatively complex and not economical.

[0006] Current levels can be reduced by connecting several resistors in series. German patent DE 10 2015 107 316 A1 discloses a heating device in which an NTC resistor is connected in series with PTC resistors. Although current levels can be significantly reduced in this way, the series connection considerably increases manufacturing costs.

[0007] The object of the present invention is to show a way in which a heating device for vehicles with an on-board voltage of 48 V or even more than 100 V can be economically implemented using conventional PTC resistors.

[0008] This problem is solved by a heating device according to claim 1. Advantageous embodiments of the invention are the subject of dependent claims.

[0009] A plate-shaped PTC resistor has a front, a back, and narrow sides that connect the front and back. The distance from the front to the back is the thickness of the plate-shaped PTC resistor. The distance between opposite narrow sides is the width or length of the plate-shaped PTC resistor. In conventional heating devices, such as those disclosed in DE 10 2015 107 316 A1, DE 10 2012 107 113 A1, or DE 39 42 266 A1, the PTC resistors are electrically contacted at their front and back. In contrast, the PTC resistor(s) of a heating device according to the invention are electrically contacted at opposite narrow sides. The electrical resistance of the PTC resistor in a device according to the invention is therefore significantly higher, so that even at considerably higher voltages of 100 V or more, currents remain within an acceptable range.

[0010] A heating device according to the present invention can contain several plate-shaped PTC resistors that are electrically contacted by contact elements on opposite narrow sides. Several PTC resistors can be connected in parallel and arranged between the same two contact elements. In this way, a rod-shaped heating device can be manufactured economically.

[0011] An advantageous embodiment of the invention provides an electrically insulating frame that holds the ceramic PTC resistor(s) and the contact elements. The contact elements can be embedded in the frame, for example by overmolding the contact elements in a plastic frame.

[0012] A further advantageous embodiment of the invention provides that the contact elements bear a spring against the PTC resistors. For example, the contact elements can form springs that press against the PTC resistors. The contact elements can be designed as leaf springs, in particular as curved leaf springs.

[0013] Spring forces can be used to clamp the PTC resistor(s) in the frame. For example, the electrical contact elements can be designed as sheet metal strips. An edge of such a strip can be bent so that the contact element can spring against the PTC resistor(s). The bent edges act like a curved leaf spring.

[0014] A further advantageous embodiment of the invention provides a tube in which the ceramic PTC resistor(s) and the contact elements are arranged. Such a tube can be made of metal and electrically insulated by layers of ceramic material or another insulator covering the front and back of the PTC resistor(s).

[0015] The invention can, for example, be designed as an air heater containing several rod-shaped heating devices arranged side by side, with cooling fins arranged between adjacent heating devices.

[0016] Further details and advantages of the invention are explained using an exemplary embodiment of the invention with reference to the accompanying drawings. These show: Fig. 1 an electric heating device; Fig. 2 a frame that holds contact elements and several PTC resistors; Fig. 3. Another view on Fig. 2; Fig. 4 a detailed view of Fig. 3; and Fig. 5 a sectional view of Fig. 3.

[0017] Fig. Figure 1 shows a heating device for heating the interior of a vehicle's passenger compartment. The in Fig. The heating device shown in Figure 1 is an air heater with several heating elements 1 and cooling fins 2 connected to the heating elements 1. The heating elements 1 are arranged side by side, and the cooling fins 2 are positioned between them. The ends of the heating elements 1 are held by brackets 8 and 9.

[0018] The heating elements 1 can have tubes, e.g., flat tubes, in which plate-shaped PTC resistors made of a barium titanate-based ceramic are arranged. The tubes of the heating elements can be made of metal, e.g., an aluminum-based alloy. Fig. 2 and Fig. Figure 3 shows an embodiment of an insulating frame 6 which holds several plate-shaped PTC resistors 3 and electrical contact elements 4. Fig. 4 shows a detailed view of Fig. 3, namely one end of the frame 6 and the contact elements 4 together with one of the PTC resistors 3. Fig. Figure 5 shows a sectional view of the frame 6 with contact elements 4 and PTC resistor 3.

[0019] The plate-shaped PTC resistors 3 have a front 31, a back 32, and narrow sides 33, 34. The distance from the front 31 to the back 32 is the thickness of the plate-shaped PTC resistor 3. The distance between opposite narrow sides 33, 34 is the width of the plate-shaped PTC resistor 3.

[0020] The plate-shaped PTC resistors 3 are electrically contacted by the contact elements 4 on opposite narrow sides 33, 34. Heating current thus flows through the PTC resistors 3 in the plane defined by the plate-shaped PTC resistors 3 across the width of the PTC resistor 3. Compared to conventional designs where the heating current flows from a front to a back side of a plate-shaped PTC resistor in the thickness direction of the plate-shaped PTC resistor, the electrical resistance provided by the PTC resistor 3 contacted at opposite narrow sides is much greater. Heating currents are therefore advantageously reduced, even when high voltage is applied to the contact elements 4.

[0021] The contact elements 4 are embedded in the frame 6, for example by overmolding. The contact elements 4 can be sheet metal strips, so that each contact element 4 electrically contacts several plate-shaped PTC resistors 3, which are arranged in a row and held by the frame 6.

[0022] The PTC resistors 3 can be clamped between the contact elements 4. For example, the contact elements can be sheet metal strips with bent edge regions 41 that spring against the narrow sides of the PTC resistors 3, forming contact tongues. Clamping forces can be reduced as required by cutting out portions of the bent edge regions 41.

[0023] The narrow sides 33, 34 of the PTC resistors 3, which are contacted by the contact elements 4, can bear a metal layer to improve the electrical contact between the contact elements 4 and the PTC resistors 3.

[0024] Heat generated by the PTC resistors 3 is transferred to a tube of the heating element 1 via the front and back surfaces 31, 32 of the PTC resistors 3. The PTC resistors 3 can be electrically insulated from a surrounding tube by insulating layers covering the front and back surfaces 31, 32, e.g., by layers of ceramic material such as aluminum oxide. Flat tubes can be compressed to improve thermal coupling after the frame 6 containing the PTC resistors 3, contact elements 4, and insulating layers has been arranged within it. Compressing the flat tubes makes them flatter and exerts pressure on the front and back surfaces 31, 32 of the PTC resistors 3. Reference symbol list 1 heating element 2 cooling fins 3 PTC resistors 4 contact element 6 frames 8 bracket 9 bracket 31 Front 32 Back 33 Narrow side 34 Narrow side 41 Bent hand area

Claims

[1] Heating device with a plate-shaped PTC resistor (3) having a thickness, a front (31), a back (32) and narrow sides (33, 34), wherein the distance from the front (31) to the back (32) is the thickness, and a first contact element (4) and a second contact element (4) that electrically contact the PTC resistor (3), wherein the PTC resistor (3) is electrically contacted by the contact elements (4) on opposite narrow sides (33, 34), characterized by , that the electrical contact elements (4) are strips of sheet metal. [2] Heating device according to claim 1, characterized by an electrically insulating frame (6) that holds the PTC resistor (3) and the contact elements (4). [3] Heating device according to claim 2, characterized by that the contact elements (4) are embedded in the frame (6), preferably by overmolding. [4] Heating device according to one of the preceding claims, characterized by , that it contains several plate-shaped ceramic PTC resistors (3) arranged in a row and electrically contacted on opposite narrow sides (33, 34). [5] Heating device according to one of the preceding claims, characterized by a tube in which the ceramic PTC resistor (3) or the resistors and the contact elements (4) are arranged. [6] Heating device according to one of the preceding claims, characterized by , that the contact elements (4) contact the PTC resistors (3) with bent edge areas (41). [7] Heating device according to one of the preceding claims, characterized by , that the electrical contact elements (4) spring against the narrow sides (33, 34) of the PTC resistor or PTC resistors. [8] Heating device according to one of the preceding claims, characterized by, that the narrow sides (33, 34) of the PTC resistor or PTC resistors are covered by a metal layer. [9] Air heater with several rod-shaped heating devices according to one of the preceding claims, characterized by , that the rod-shaped heating devices (1) are arranged next to each other and cooling fins (2) are arranged between adjacent rod-shaped heating devices (1).

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