Air heating device and heating assembly

Abstract: Air heating device comprising a frame (11), a plurality of box sections (16) and PTC-tablets (25). The PTC-tablets (25) are positioned between the box sections (16), functioning as heat sinks. The box sections (16) are extruded from aluminum or aluminum alloys and these extrusions are provided with fins (19,20). The PTC-tablets are connected to the box sections by a conductive adhesive. The invention also relates to an air heating assembly comprising several air heating devices.

Description: The invention relates to an air heating device according to the preamble of claim 1. Such a device is known from EP-A-0 350 528. Such a device can be used in cars for heating of ventilation air which has to be supplied to the front screen during the time that the engine is not sufficiently heated to take over air heating through the normal heater radiator. It is an advantage that cold air can be electrically heated without sophisticated control mechanisms whilst the temperature cannot exceed a certain value determined by the properties of the PTC-material. With the known device the heat sinks comprise separate metal strips and the fins are connected to the heat sinks by brazing. The PTC-tablets are positioned flat against the heat sinks without being adhered thereto. Because of that corrosion can result at the contact surfaces between pills and heat sinks giving a deterioriated electric contact. Two of the four frame ledges comprise two strips, being displacable relative to each other, in between which a undulated resilient belt is placed, pressing the inner strip to an adjacent metal heat sink strip and in this way the assembly comprising separate heat sinks, fins and non adhered PTC-tablets are clamped within the frame. Furthermore the pills are maintained in their position by an extra plastic holder. Separate production of heat sink strips and fins, brazing of the fins and assembling to a unit results in a costly structure. To also obtain a good contact between the PTC-tablets and the heat sinks these have to adjoin to each other exactly flat; the tolerance limits are small which also has a price raising effect. The invention aims to obviate these drawbacks. According to the invention this is realized with a air heating device as described above with the characterizing features of claim 1. Through the use of adhesive corrosion on the electrical contact face between heat sinks and pills is prevented. To prevent that short circuiting results from current conducting adhesive, used to adhere the PTC-tablets to the heat sinks, the heat sinks are provided with protrusions realized extruding for positioning of the PTC-tablets and the PTC-tablets project all over their circumference beyond the circumference edges of the protrusions. Surplus adhesive will flow in the space between the projecting edges of the PTC-tablets and the related heat sink. Short circuit by other causes can be prevented by covering the box profiles with a heat-proof electric isolating coating. To prevent the PTC-tablets from loosening because of non-uniform temperature expansion, one of the heat sinks of each box section is provided with a dilatation gap during extruding, and each PTC-pill is connected at one face by stiff quality adhesive and at the other face by a yielding quality adhesive. To locally interrupt the current if short circuiting occurs, without putting all of the heating device out of operation, in a thickened wall portion of each box section an opening is realized during extruding, in which opening a fuse holder comprising a stainless steel sleeve is pressed, resulting in a reliable electric contact with aluminum by excluding of oxygen. The sleeves are connected at the position of adjacent box sections after each other in one position through a fuse and a contact spring to one current rail and in the other position through a contact spring to the other current rail. All sub assemblies of box sections and sleeves are identical and cheap. The device can be easily assembled if the frame comprises two parts clamped to each other, wherein the clamping face extends over the circumference of the frame and when the assembly of box sections and PTC-tablet is enclosed within the frame by a compression spring. The frame gives both thermal and electrical insulation. The air heating device according to the invention is particular well suited to be connected to the casing of a standard cooling water radiator of a car. It is remarked that from the French patent application FR-A-2 404 985 a liquid heating device is known comprising two box section-like reservoirs having ribs and a disk placed between said reservoirs. The material of the disk conducts at low temperature more current than at higher temperature. Only two box sections are provided not being extruded and not introduced into a frame. Furthermore it is remarked that in EP-A-0 243 077 (Ford Motor Company) a electrical air heating device is disclosed being positioned in the ventilation channel of a car and comprising a casing from an insulating material wherein two sets of heat conducting channels are provided, wherein between the channels of each set an undulated rib strip is positioned and between the channels facing each other of the two sets PTC-tablets are positioned. Also in this structure rib strips are brazed to the heat conducting channels, such that no extruded sections, each having two heat sinks and fins extending between these heat sinks and also being extruded, are provided. It is advantage of this heating device not being realized by extrusion that the ribs can be provided with louvres to increase heat transfer to air. In the device according to the subject invention heat transfer to air can be increased by positioning the fins nearer to each other and/or to increase the air flow path within the heating device. Furthermore from DE-A-3,119,302 several embodiments of an air heating device are known, wherein between two heat sinks, being embodied as separate flat strips, PTC-material is provided and to the heat sinks fins are connected being realized as elements e.g. from aluminum being cast in an ingot or bent with an undulated shape from a panel. Extrusion is only used with the PTC-element. Using of extruded box sections comprising both two heat sinks and fins extending inbetween is not disclosed in this specification. The invention also relates to a heating assembly comprising at least two heating devices as described above as well as a frame work enclosing said heating devices. In this way by means of modules a heating assembly can be realized according to the subject need. E.g. in countries where lower temperatures are normal more heating devices can be incorporated in a heating assembly as with heating assemblies used in e.g. cars driven in warmer countries. To obtain a well defined positioning of the several heating devices within a heating assembly, according to a preferred embodiment each heating device being positioned during use adjacent to another heating device is providded with resilient pressure means such as resilient tabs. The invention will be further elucidated referring to preferred embodiments shown in the drawing, wherein: Fig. 1 shows a schematical view of a heating radiator of a car and an electric air heating device according to the invention connected thereto; Fig. 2 perspectively shows a part of the electric air heating device according to Fig. 1; Fig. 3 shows a side view of the device according to Fig. 2; Fig. 4 shows a box section to be used for realizing the electric heating device according to Fig. 2; Fig. 5 shows a further embodiment of the heating device according to the invention to be used in a heating assembly; Fig.6 shows a heating assembly comprising several heating devices according to Fig. 5; and Fig. 7 shows a detail of Fig. 6. The usual radiator of a car, schematically shown in Fig. 1, comprises a casing 1 having a cooling water supply 2 and a cooling water discharge 3, a cooling water tube 4 extending between this supply and discharge, and an air intake opening 5. Heat exchange strips 7 are connected to tube 4 and extend in the flow direction of air, indicated by an arrow. Insulation material 8 is provided to the inner surface of casing 1. Inside of housing 1 downflow of tube 4 a frame 11 is provided and inside this frame 11 an electrical heating device 12 is provided, which will be further described below. A header 13 is connected to casing 1 through a flange connection 14. From this header air hoses 15 extend to the interior of the car. In fig. 2-4 the structure of the electrical heating device is shown. Inside frame 11 a number of box sections 16 is provided. These are realized from aluminum or an aluminum alloy by extrusion and comprise two heat sinks 17, 18 and fins 19 extending between these heat sinks and shorter fins 20. On the heat sinks protrusions 21 are realized during extruding. One side of the box section is provided over a part of its height with a thickened wall 22 in which a hole 23 is recessed. In this hole a stainless steel sleeve 24 is pressed functioning as fuse holder and providing a reliable contact aluminum-stainless steel. On the projections 21 tablets 25 from a material having a positive temperature coefficient (PTC) are connected by a heat and current conducting adhesive (e.g. epoxy glue filled by silver particles). One of the heat sinks 18 of each box section is provided with a dilatation gap 26 realized during extruding. As shown in fig. 2 the box sections 16 are spaced from each other by the PTC-tablets. Each PTC-tablet is adhered with its two faces to a projection 21. The tablet is adhered to the one projection by means of a plastic adhesive and to the other projection by means of a hard adhesive. Because of that the tablet will not get loose during temperature expansions and contractions. The dilatation gap 26 in each box section allows these movements. A resilient clip 29 encloses the assembly of box sections and PTC-tablets in the frame 11 and compensates for thermical expansion between the stack of heat sinks and the frame. In frame portion 11a two channels 30a,30b respectively are recessed and in each of said channels a voltage rail 31a, 31b is provided. Alternating with each box section 16 the voltage rail 31b is connected with the bottom of the related sleeve 24 introduced by pressing and so with the related box section 16, through a contact spring 32 and a fuse 34. The voltage rail 31 is connected to the other box sections 16 through the contact spring 32 and sleeve 24. If the voltage rail 31a is electrically positive and the voltage rail 31b is electrically negative, an electric current will flow through rail 31a, fuses 34, fuse holders 24 to the related box sections and from there through the PTC-tablets 25, the other box sections, the fuse holders 24 (without fuse) to rail 31b. The PTC-tablets are heated to a temperature depending from their material and release their heat to the box sections, through which air flows being rapidly brought to the desired temperature. As soon as the engine is heated, air will be sufficiently heated in the usual radiator, such that the electric heating member can be switched off by a thermostatt. Under very cold circumstances and with very efficient engines, emitting less heat, it is possible that the electric heating device is in continuous use during driving. It is essential for the invention that in the electric heating device extruded box sections having two heat sinks and fins in between are used. To prevent short circuit the following measures have been taken: The box sections 16 are covered with a heat-resistent current insulating coating and the PTC-tablets 25 extend near their circumference beyond the projections 21, such that superfluous conducting adhesive can flow in the space 35 between projecting peripheral edges of the tablets and the related heat sink and cannot contact the adjacent heat sink by flowing. Because of the described electric connection the box profiles are alternately positive and negative. However, other positioning of the connections are possible. In figures 5-7 a further embodiment of the invention is shown. In fig. 6 a heating assembly is generally indicated by reference number 40. This heating assembly is constructed from heating devices indicated by 41 one of which is shown in fig. 5. Each heating device or module comprises several box sections 42 between which PTC-elements 43 are provided. Box sections 42 and PTC-elements 43 are enclosed by frame 44 comprising a base plate 45, side walls 46, 47 and a rear wall 48. Side wall 47 is provided with protruding resilient tabs 58. In side wall 46 dents 56 are provided which in combination with tabs 48 ensure that box sections 42 and PTC's 43 will always be resiliently enclosed by frame 44. Tab 48 being inside frame 44 functions to press the box sections 42 and PTC-elements 43 against each other and is comparable with clip 29 of fig. 2. Tab 48 extending outwardly from wall 47 functions (as is shown in fig. 6) to pressure several heating devices 41 against each other within frame work 49. In both the base plate and the rear wall openings (not shown) are provided adjacent the contact area between the base plate and the box profile and between the rear wall and the box profile respectively. Frame work 49 is provided at its rear wall 50 with cams 60 protruding through every second opening in rear wall 58 of each heating device. Near its front wall 51 cams 52 project to the related opening in base plate 45. During use current will flow from cam 52 through the contacted box section 42, PTC 43 and from there to the adjacent box section and cam 60. Short circuiting projecting is realized by fuse and fuse holder assembly 53 shown more detailed in fig. 7 (the fuse itself is not shown). The voltage is supplied to rear wall 50 through voltage rail 54. At the front side voltage is supplied through rail 55. As indicated in the figures several layers of insulation are provided to prevent short circuiting. Because several heating devices 41 are incorporated in heating assembly 40 it is sufficient to use only one fuse for each heating device further lowering the costs of such a device. By using the arrangement according to figures 5-7 the failure of one or more PTC's will have a less detrimental effect on the heating capacity of each heating device compared with the device according to figures 1-4. The invention cannot only be used for cars but also for electric heaters and similar devices.

Claims: Air heating device comprising a number of panel strip like heat sinks (17,18), being arranged parallel in a frame (11), a number of PTC-tablets (25), a large number of heat conducting fins (19,20) extending perpendicular to the heat sinks, and electrical connection means, characterized in that , box sections (16) extruded from aluminum or an aluminum alloy are used, each having two heat sinks (17,18) and fins (19,20) extending in between, in that the PCT-tablets (25) are connected by a current conducting adhesive to the heat sinks and in that the assembly of box sections (16) and PTC-tablets (25) is enclosed within the frame (11) by a pressure spring (29). Air heating device according to claim 1, wherein the heat sinks (17,18) are provided with projections (21) for the PCT-tablets (25), the projections being extruded together with the heat sinks. Air heating device according to claim 2, wherein the PTC-tablets (25) protrude at their circumference at all sides along the circumferential edges of the protrusions (21). Air heating device according to one of the preceding claims, wherein one of the heat sinks of each box section (16) is provided with a dilatation slit (26), each PTC-tablet at one face being fixed by a hard adhesive and at the other face by a plastic adhesive. Air heating device according to one of the preceding claims, wherein in one of the frame portions of the plastic frame (11) extending perpendicular to the heat sinks (17,18) two channels (30a,30b) are provided, each of the channels being provided with a voltage rail (31a,31b respectively) wherein one box section of successive box sections (16) is connected to one voltage rail and the other box section to the other voltage rail. Air heating device according to claim 5, wherein an opening (23) is made during the extrusion in a thickened wall portion (22) of each box section (16), in which openings a fuse holder (24) embodied as a stainless steel bush, is pressed, said bushes at the position of the adjacent box sections are alternately connected through a fuse (34) and a contact spring (32) with one voltage rail (31a) and through a contact spring (33) with the other voltage rail (31b). Air heating device according to one of the preceding claims wherein the frame (11) consists of two portions (11a, 11b) clamped to each other, the clamping plane extending along the circumference of the frame. Air heating device according to one of the preceding claims, wherein the box sections (16) are coated with a heat resistant electrically isolating material. Air heating device according to one of the preceding claims, wherein the frame of the electrical air heating device is connected to the housing of a usual radiator heated by the cooling water of a motor of a car so that ventilation air flows subsequently through the radiator and the electrical heating device. Air heating assembly comprising at least two air heating devices according to one of the preceding claims, as well as a frame work enclosing said heating devices. Air heating assembly according to claim 10, wherein the portion of the frame of each heating device being in the position of use adjacent another heating device, is provided with resilient pressure means.

Inventors: GOLBACH ERIK JOHANNES MARIA, VAN DEN ELST FREDERIK MANNES N, VAN DER PLOEG ARIE, GOLBACH, ERIK JOHANNES MARIA, VAN DEN ELST, FREDERIK MANNES NICOLAAS, VAN DER PLOEG, ARIE
Applicants: TEXAS INSTRUMENTS HOLLAND, TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS HOLLAND B.V., TEXAS INSTRUMENTS INCORPORATED
Application year: 1991
Main classification: F24H3
IPC codes: H05B3, F24H3