Electric Heating Device

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric heating device with a housing, a first heating chamber through which a medium to be heated can flow, an electric heating device that is thermally coupled to the first heating chamber, and a control device for controlling the electric heating device.

2. Background of the Invention

Such an electric heating device usually has a metal housing part that separates the heating chamber from the electric heating device. The thermal conductivity properties of the metal housing part promote heat transfer from the electric heating device to the medium to be heated.

In the present invention, as in the prior art, this medium can be a liquid or a gaseous medium. In addition, the metal housing part has upright walls which can surround the electrical heating device or the control device and thus provide electromagnetic shielding.

The electrical heating device of the present invention is used in particular in a motor vehicle. Here, it is particularly important to ensure that the switching of the power current of the electrical heating device by the control device installed therein does not cause electromagnetic interference within the vehicle. The relevant components are completely surrounded by the upright wall of the housing part. These can usually form a circumferential edge provided with a groove, which interacts with a metallic housing cover and is sealed in the groove so that moisture and dirt cannot enter the housing.

SUMMARY

Based on this, the present invention is based on the task of specifying an electric heating device that can be produced more economically without losing the basic functionality of the electric heating device and its suitability for installation in a vehicle.

In view of this, it is proposed that the housing has a metal support plate that delimits the heating chamber and interacts with a housing cover. The housing cover is sealed to the support plate to form a control housing in which the control device is shielded. For this purpose, it is advantageous to form the housing cover from a sheet metal material. The housing cover is usually trough-shaped with upright walls and a cover surface from which the upright walls protrude. These upright walls are usually sealed to the support plate.

The support plate may have a substantially flat extension. In contrast to the prior art and the housing base part provided therein, the support plate has no surrounding walls that create a receptacle for a control device or a heating device of the electrical heating device. Insofar as upright walls protrude from the support plate, these serve primarily, if not exclusively, for the mounting of plug housings. Usually, one plug housing is provided for the power current and one plug housing for the control signals.

The support plate is usually the only thick-walled metal component. A thick-walled component is defined as a component with a wall thickness of at least 2 mm. In contrast, the housing cover is usually made of thin-walled sheet metal with a wall thickness of at least 0.5 mm. The housing cover is usually formed by reshaping a sheet metal. This allows the electrical heating device to be manufactured in a relatively weight-saving and thus cost-saving manner. In addition, the housing cover follows the shape of the components underneath, which results in volumetric installation space advantages compared to a cuboid housing with a closing cover.

As mentioned above, the support plate may have no upright walls surrounding a chamber. In the case of an upright wall that is part of the support plate and serves to mount the plug housings, such a wall is usually limited to no more than 30% of the circumference of the support plate. Such a wall may be limited to one end face. The end face is the end face of a rectangular support plate in plan view that is smaller than the long side surface. This upright wall may extend to a certain extent onto the adjacent long side surfaces. However, the majority of these longitudinal side surfaces and at least 70% of the extension of the longitudinal side surface are usually free of an upright wall. The opposite end surface has no upright wall.

In addition to the aforementioned connections for the plug housings, the support plate also may form a connection for a grounding bolt, which is screwed or pressed into the support plate. The support plate usually forms all mechanical and/or electrical connections for the electrical heating device. The aforementioned plug housings can also be mounted in the plane of the support plate. The plug housings are usually screwed to the support plate. The support plate also may have a receptacle for feeding the plug contacts from the outside into the housing of the electrical heating device. The support plate may also have a thread or a hole for attaching a grounding bolt. The electrical heating device is usually electrically grounded via this grounding bolt. The support plate may form a surface that delimits the heating chamber. The remaining surfaces, in particular those of the heating chamber, may be formed by a plastic housing that interacts with the support plate in a sealed manner. The support plate can be thermally conductive connected to the electrical heating device and form a contact surface for the thermally conductive device of the electrical heating device. This electrical heating device can be a PTC heating device comprising at least one ceramic PTC element and conductor tracks connected to it with different polarities. With regard to symmetrical heat extraction, there is usually a further heating chamber on the opposite side and extending parallel to the support plate, which can be thermally coupled to the PTC heating device with the interposition of a flat sheet metal and/or an insulating layer. The support plate accordingly forms a contact surface for the electrical heating device, whereby electrical insulation may also be provided between the electrical heating device and the surface of the support plate forming the contact surface. The support plate may also form a contact surface for coupling out power loss from a power transistor of the control device. The aforementioned surfaces usually extend parallel to the main direction of extension of the support plate. The fastening means necessary for fastening or thermally conducting contact of the corresponding components, for example in the form of bores, threaded bores, blind holes or screws of the electrical heating device, are all provided on the support plate. The components connected to the support plate may extend beyond the support plate by at least 60%, and more typically at least 67%, of the circumference of the support plate.

The remaining parts of the housing may be designed as plastic or metal trays that interact with the support plate in a sealing manner, for which purpose the support plate can form circumferential grooves.

The height of the support plate is usually no more than 15 mm. In addition to securing all components inside the electric heating device and the housing, the plate may form all necessary mounting points for fixing the electric heating device in a motor vehicle.

The trough-shaped housing part or parts may extend transversely to the main direction of extension of the support plate, which is at least 1.5 times greater than the corresponding extension of the support plate.

This outlines the essential features of a substantially flat, two-dimensional support plate according to the present invention. These features may be implemented individually or in combination.

The housing cover, which is usually made of sheet metal, can enclose the electric heating device.

In particular, the control housing can enclose a flow housing that interacts thermally with the electric heating device and may also interact in a sealed manner with the support plate to form the heating chamber.

This heating chamber may be one of two heating chambers. The other heating chamber may be provided on the side opposite the first heating chamber in a thermally conductive manner and may be coupled to an electrical heating device. In this further development, the electrical heating device is usually located between the two heating chambers and rests on one side against the support plate.

The second heating chamber may comprise a sheet metal base connected thermally to the electric heating device. This sheet metal base may interact with the support plate in a sealed manner to seal the electric heating device from the environment. A plastic cover surrounding the second heating chamber can also be sealed to the sheet metal base, so that the second heating chamber is formed between the sheet metal base and the walls of the plastic cover. The connection between the plastic cover and the sheet metal base can be made by gluing or sealed with an insert gasket. The first heating chamber can be formed between the support plate and the electrical heating device. In this case, the electrical heating device does not necessarily have direct electrical contact with the support plate. Instead, at least one power transistor of the control device can be thermally conductive on the side of the heating device opposite the support plate in order to cool it via the first heating chamber. On the side of the support plate opposite the housing cover, a heating chamber cover made of sheet metal and cooperating with the support plate may be provided, which covers the first heating chamber, if necessary together with the electrical heating device. This heating chamber cover does not necessarily form the corresponding heating chamber itself. Rather, it may be formed only between the electrical heating device and the support plate, whereby the electrical heating device interacts with the support plate in a sealed manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of the following invention are apparent from the following description of embodiments in conjunction with the drawing. This shows:

FIG. 1 is a schematic cross-sectional view of a first embodiment of the present invention;

FIG. 2 is a schematic sectional view of a second embodiment of the present invention;

FIG. 3 is a schematic sectional view of a first variant for sealing a cover against a support plate;

FIG. 4 is a schematic cross-sectional view of a second variant for sealing a cover against a support plate;

FIG. 5 is a perspective side view of a third embodiment of the present invention;

FIG. 6 is a perspective top view of the support plate of the embodiment shown in FIG. 5;

FIG. 7 is a view according to FIG. 6 after assembly of further components of the electrical heating device of the embodiment according to FIGS. 5 and 6;

FIG. 8 is a perspective top view approximately according to FIG. 7 for the opposite main side surface of the support plate; and

FIG. 9 is a perspective front view for an embodiment modified from the embodiment shown in FIGS. 5 to 8.

DETAILED DESCRIPTION

In the figures, reference numeral 2 denotes an electric heating device and reference numeral 4 denotes a housing thereof.

In the embodiment shown in FIG. 1, a first heating chamber 6 is formed between a support plate 8 and a shell-shaped flow housing 10, against which, on a side opposite the support plate 8, a control device 12 and specially provided circuit breakers 14 are thermally conductive. Thus, the heating chamber 6 is heated on one side by the power dissipation of the power switches 14 and on the opposite side by a heating device 16, which is a PTC heating device and rests against a contact surface 17 formed by the support plate 8 on the side opposite the heating chamber 6. Opposite the support plate 8, a sheet metal base 18 is in heat-conducting contact with the electrical heating device 16, which delimits a second heating chamber 20 opposite the heating device 16 and is sealed by a plastic housing cover, referred to as plastic cover 22. The housing cover 22 is sealed against the sheet metal base 18 by gluing, welding, or a sealing ring/ring gasket. The plastic cover 22 forms connections 24 for the inlet and outlet of the medium to be heated.

The flow housing 10 provided on the opposite side is usually a cover formed from sheet metal material, which in the present case is provided sealed against the support plate 8 with the interposition of a schematically indicated seal 26, for example in the form of a ring or a sealing compound, into which the edge of the flow housing 10 is immersed. The heating chamber 6 formed in this way is referred to below as the first heating chamber. On the opposite side, the second heating chamber 20 is formed between the sheet metal base 18 and the plastic cover 22. While the housing cover 10 also serves to ensure good heat transfer from the power switch 14 to the medium to be heated in the first heating chamber 6, this is not the case for the plastic cover 22, which is therefore produced from plastic material that is lighter and more cost-effectively processed, even in complex final contours.

The flow housing 10 is covered by a housing cover 30 made of sheet metal, which interacts with the support plate 8 in the manner mentioned above to form a seal, thereby creating a control housing 32 which also encloses the first heating chamber 6 and thus the flow housing 10 between itself and the support plate 8. This housing cover 30 shields the control device 12 from the outside and creates a sealed enclosure for the control device 12.

Reference numeral 34 schematically indicates connector housings for the power current and for control signals, which are processed in the control device 12 to control the power current. Reference numeral 36 indicates a flow connection recessed in the support plate 8 between the second heating chamber 20 and the first heating chamber 6, of which there are two. One of the flow connections 36 transfers liquid medium introduced through a nozzle 24 directly into the first heating chamber 6, essentially bypassing the second heating chamber 20. The other flow connection 36 returns this partial flow from the first heating chamber 6 back to the nozzle 24 for discharge of the flow. Thus, the two partial flows in the first heating chamber 6 and in the second heating chamber 20 flow parallel to each other.

In FIG. 2, identical components are marked with the same reference symbols. In this embodiment, the first heating chamber 6 is formed between the support plate 8 and the electric heating device 16, which in this case is a thick-film heating device. The first heating chamber 6 is sealed from the electric heating device 16, which interacts with the support plate 8 in a sealed manner. This can be achieved by inserting a seal or by bonding the heating device to the support plate 8. The housing cover 30 is provided on the side of the support plate 8 opposite the heating device 16 and interacts with the support plate 8 in a sealed manner to enclose the control device 12. As in the embodiment shown in FIG. 1, connector housings 34 for the power current and for control signals are connected to the support plate 8. In the schematic embodiment shown in FIG. 2, these connector housings 34 are located on the side of the support plate 8 on which the control device 12 is also located. However, the connector housings 34 may also be provided wholly or partly on the opposite side. In this embodiment, the heating device 16 is closed with a heating chamber cover 40 and cooperates in a sealed manner with the support plate 8, so that the electrical heating device 16 is sealed off from the environment in the housing 4. In the embodiment shown in FIG. 2, the covers 30 and 40 can be made of plastic or sheet metal. The connectors 24 are separate components, which may be made of plastic, which are screwed to the support plate 8 together with a seal and screw connection. This allows the connectors 24 to be adapted to different interface requirements in a relatively flexible and cost-effective manner.

FIGS. 3 and 4 illustrate further developments for sealing the covers 30, 40 in a sealing groove 42, which is formed by the support plate 12 and into which a sealing compound 44 is introduced. An edge of the cover 30, 40 marked with reference numeral 46 is received in the sealing groove 42. At least one boundary wall 48 bounding the sealing groove 42 laterally forms a widened groove opening 50. In FIG. 3, the two boundary walls 48 are each flared outwards in a funnel shape; in FIG. 4, only the outer edge 46 is flared. These funnel-shaped designs facilitate the insertion of the circumferential edge 46 into the sealing groove 42. FIG. 4 in particular enables original producing without undercuts.

FIG. 6 shows a perspective top view of an embodiment of a support plate 8 which forms passages 52 for the material to be heated, forming the flow connections 36 to the first heating chamber 6. This first heating chamber 6 is circumferentially bounded by a first boundary groove 54, in which the circumferential edge of the flow housing 10 is sealed. Outside this is a further circumferential cover groove 56, which can interact in a sealed manner with the housing cover 30. The first heating chamber 6 has flow fins 58 formed by the support plate 8, which define flow channels for the medium to be heated within the first heating chamber 6. These flow ribs 58 can protrude into a fastening plane in which support domes 60 end and are each provided with a blind hole or internal thread.

In FIG. 6, a feed-through 62 for contact tongues 64, which can be seen in FIG. 7, can be seen to the side of the first heating chamber 6. These contact tongues serve to electrically contact a control device (not shown in FIG. 5) whose power transistors are thermally conductive against the flow housing 10.

FIG. 7 shows the inner ends of the plug housings 32a for the control signals and 32b for the power current. Corresponding to the position of the support domes 60 and the threaded holes provided therefor within the support plate 8, the flow housing 10 has holes 66 so that fastening screws can pass through the control housing 10 and be connected to the support plate 8 in a sealed manner.

FIG. 7 shows the support plate 8 from the opposite side. An electrical heating device 16 is provided there, which is electrically connected to the control device via its contact tongues 62 and is to be closed with a sheet metal base (not shown) to be sealed against the support plate 8, whereby a base of the second heating chamber can be formed, which is closed by the plastic cover 22 shown in FIGS. 5 and 7, which forms the connection nozzles 24 for the inlet and outlet of the flow.

As the figures reproduced above illustrate, the support plate 8 is essentially flat. It only has contours that are slightly raised from the plane essentially contained in the support plate 8, which serve to guide the flow and seal other housing parts, in particular the housing covers, against the support plate 8. The support plate 8 forms all the fastening means acting in a material, force, and/or form-fitting manner for fastening the other components of the heating device 2 to the housing 4, including fastening means for screwing the plug housings 34 and fastening means for the respective covers 18, 22, 30.

A support plate 8 within the meaning of the following invention is also realized by the embodiment illustrated in FIG. 9, in which the support plate 8 forms a raised wall 70 at its front end, which is provided with bores and through-openings for the two plug housings 34a and 34b. Otherwise, however, the support plate 8 is flat and, like the embodiment discussed above, has no upright walls.