Patent Application
20230008619
This application claims the benefit of priority under 35 U.S.C. § 119 to European Patent Application No.: 21184584.7, filed Jul. 8, 2021, the contents of which is incorporated herein by reference in its entirety.
The invention relates to an electric heating device, in particular for a motor vehicle.
The statements in this section merely provide background information related to the present disclosure and several definitions for terms used in the present disclosure and may not constitute prior art.
In motor vehicles with purely electric drive, the waste heat generated by an internal combustion engine during operation is not available. Heat—for example to heat the interior of the motor vehicle—must therefore be generated by other means. Electrical heating devices, in particular so-called positive temperature coefficient (PTC) heaters, are known. Such PTC heaters have an electrical resistance that also increases with increasing temperature. The increase in electrical resistance is accompanied by a decrease in electrical current through the heater. The PTC property of the heater thus has a self-regulating effect and prevents the PTC heater from heating up too much. However, this limits the maximum temperature that can be reached by the PTC heater. Typical maximum heating temperatures are about 200° C.
It is therefore known from the prior art to use so-called thick film technology (“TFR”). This means that a film with a certain film thickness made of a so-called thick film material is applied to a substrate—such as a printed circuit board or the like—and forms an electrical conduction path that can be electrically energized. The so-called thick-film materials that are suitable for this purpose also have an electrical resistance that increases with increasing temperature. However, thick-film materials lack the self-regulating property mentioned above for PTEC heaters, so that these materials can reach much higher temperatures—up to 400° C., for example. A heater using TFR technology thus achieves significantly higher heating powers than a pure PTC heater.
However, a disadvantage associated with TFR technology is that local “hotspots”, i.e. local zones with particularly high temperatures, can occur in the conduction path formed by the thick film. In practice, these hotspots occur particularly frequently at points in the conductive path where it is curved or has a kink or a curved contour. In extreme cases, a too high temperature in these zones can result in damage or even destruction of the thick film, so that the electrical conduction path is interrupted and, as a result, heating power can no longer be generated.
The objective of the present disclosure is to provide an improved embodiment for an electrical heating device in which the above-described problem(s) no longer occur. This objective is achieved with an electric heating device that comprises a substrate on which an electrical conduction path is arranged, which extends from a first electrical conduction path terminal to a second electrical conduction path terminal, the conduction path being formed from an electrically conductive thick-film material (DFM) at least in a thick-film conduction path section, the at least one thick-film conduction path section extending rectilinearly in a plan view of the substrate. The objective is further achieved by various advantageous forms of the electrical heating device as described above and further defined herein.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawing, in which:
The drawings are provided herewith for purely illustrative purposes and are not intended to limit the scope of the present invention.
The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. It should be understood that throughout the description, corresponding reference numerals indicate identical, similar or functionally equivalent parts and features.
Within this specification, embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein.
The present disclosure is based on the general concept of realizing that the electrical conduction path of the electrical heating device described at the beginning only in conduction path sections with the aid of thick-film technology, in which the electrical conduction path has a straight-line contour. In contrast, in sections of the conductive path in which the conductive path is not straight, i.e. curved or curved or with a kink, it can be designed in the convention-al manner, i.e. using a conventional electrically conductive material. In this way, the undesirable formation of hot spots mentioned above can be avoided.
In accordance with the general concept of the present disclosure the electrical heating device, in particular for use in an electric vehicle, i.e. a vehicle with a purely electric drive, comprises a substrate on which an electrical conduction path is arranged which can be electrically energized and for this purpose extends on the substrate from a first electrical conduction path terminal to a second electrical conduction path terminal. The substrate is electrically insulating and may be made of an electrically insulating material for this purpose. The two electrical conduction path terminals can be electrically connected to an electrical voltage or current source, so that in this way the electrical conduction path can be electrically energized. With the aid of the two conductive path terminals, temperature measurement is also possible by measuring the electrical resistance of the conductive path. If the electrical resistance of the thick film material is known as a function of temperature, i.e. the R-T dependence, the instantaneous temperature of the electrical conduction path can be determined. In this way, the proper functioning—especially with regard to the occurrence of excessive temperatures—of the heating device can be monitored.
According to one aspect of the present disclosure, the conductive path has at least one thick-film conductive path section made of an electrically conductive thick-film material, the at least one thick-film conductive path section extending in a straight line in a plan view of the substrate, i.e. in particular not in a curved manner and in particular not curved and in particular without kinks.
According to another aspect of the present disclosure, no thick-film conductive path section is provided with non-rectilinear extension. In this way, the formation of undesirable “hot spots” is particularly effectively counteracted.
In one embodiment of the present disclosure, as the thick film material, a material may be used which is known to the person skilled in the art under the designation “ESL29130”. The at least one thick film conductive path section may have a film thickness that is between 20 and 30 micrometers, preferably around 25 micrometers (μm).
According to another embodiment, the heating device comprises an electrical temperature sensor, in particular a positive temperature coefficient (PTC) or negative temperature coefficient (NTC) temperature sensor, arranged on the substrate for determining an instantaneous temperature of the electrical conduction path. Thus, an additional monitoring of the temperature of the heating device is possible.
According to another aspect of the present disclosure, the electrical conduction path has at least one non-thick-film conduction path section in which the electrical conduction path is formed from an electrically conductive non-thick-film material different from a thick-film material. Preferably, the non-thick film material may be a silver-palladium conductor, which is known to the person skilled in the art under the designation “ESL9695”.
In this way, an electric power path with a large number of thick film conductive path sections can be realized on the surface of the substrate, so that a high electric heating power is provided overall. In particular, a high heating power per unit area is achieved by means of this embodiment.
According to yet another aspect of the present disclosure, in the top view of the substrate, the electrical conduction path in the non-thick-film conduction path section can have a straight-line or non-straight-line extension, in particular a curved or curvilinear extension or an extension having a kink or an angle. Also in this way, an electrical power path with a large number of conduction path sections can be realized, so that a high electrical heating power is provided overall.
In one embodiment, it may be advantageous if all thick-film conduction path sections and all non-thick-film conduction path sections are electrically connected in series with each other. This electrical interconnection variant proves to be particularly easy to manufacture. In addition, the occurrence of even a single “hotspot” is particularly easy to detect, since even a single hotspot causes an increase in the electrical resistance of the entire electrical conduction path.
In another embodiment, it may be advantageous if the electrical conduction path has a meandering geometry at least in sections in the top view of the substrate, whereby the existing thick-film conduction path sections are also straight in this device. Alternatively, two adjacent thick-film conductive path sections can each be interconnected by means of a non-thick-film conductive path section extending transversely to the two adjacent thick-film conductive path sections. This variant requires particularly little installation space.
In yet another embodiment it may be advantageous for at least two thick film conductive path sections and at least two non-thick film conductive path sections to alternate along an extension of the conductive path. In this way, the installation space available on the substrate for the electrical conduction path can be optimally utilized.
According to another embodiment it may be advantageous if the electrical conduction path has at least two, preferably several, thick-film conduction path sections that are electrically connected in parallel with one another. In this way, a redundancy of thick-film conduction path sections is created, the functional reliability of the electrical heating device is improved, and in the event of a functional failure of one thick-film conduction path section, the electrical current can flow through the electrical conduction path through the parallel-connected further thick-film conduction path section.
Alternatively, the electrically parallel-connected thick film conduction path sections may be electrically disposed between at least one first non-thick film conduction path section and at least one second non-thick film conduction path section. This variant makes optimal use of the available installation space on the substrate.
Alternatively, the at least two thick film conduction path sections may each have a longitudinal geometry when viewed from above the substrate and may each extend along a longitudinal direction, preferably a common longitudinal direction, and may be spaced apart from one another transversely to the longitudinal direction.
According to another aspect of the present disclosure, at least one thick-film conductive path section has, in the plan view of the substrate, the geometry of a rectangle with two mutually opposite narrow sides and two mutually opposite broad sides, In this embodiment, the thick-film conductive path section merges at the two narrow sides or broad sides in each case into a non-thick-film conductive path section. Alternatively, a ratio of the length of the broad sides to the length of the narrow sides is at most 3:1, preferably at most 2:1, most preferably 1.5:1. In this way, a two-dimensional and thus homogeneous heating of electrical conduction path or of the substrate and thus of the electrical heating device is achieved. Alternatively, the electrical resistance of the thick-film material increases with increasing temperature of the thick-film material.
In another advantageous embodiment, the non-thick film material may be a positive temperature coefficient (PTC) material. Such a PTC material has a self-regulating effect in the manner of a control loop, i.e., due to the increasing electrical resistance with increasing temperature, the electrical current through the PTC material decreases so that the temperature of the PTC material does not increase indefinitely.
The substrate may have a T-shaped geometry in plan view with a T-base and a T-roof. Here, the two electrical conduction path terminals are arranged in an area of the T-base facing away from the T-roof, and the at least one thick-film conduction path section is arranged in the T-roof. This variant requires little installation space and, in particular, allows a simple electrical connection of the electrical conduction path an electrical voltage source or electrical current source.
When desirable, the temperature sensor may extend along the T-base. In this way, the temperature in a central area of the heating device can be determined. The temperature sensor may have first and second sensor terminals and comprise an electrical conduction path of an electrically conductive PTC material electrically connecting the first sensor terminal to the second sensor terminal. Thus, the instantaneous temperature of the heater can be determined by determining the electrical resistance of this conductive path given a known resistance-temperature relationship.
Alternatively, the first and second sensor connections can both be arranged between the two line path connections. Also this variant allows a space saving electrical connection of the temperature sensor to a device for determining the temperature.
According to another aspect of the present disclosure an electric vehicle is provided with a purely electric drive and a heating device as described above and further defined herein. The advantages of the heating device according to the present disclosure as explained above therefore also apply to the electric vehicle without exceeding the scope of the present disclosure.
Further important features and advantages of the electric heating device of the present disclosure will be apparent from the drawing and from the accompanying figure description based on the drawings. It is understood that the features mentioned above and those to be explained below can be used not only in the combination indicated in each case, but also in other combinations or on their own, without departing from the scope of the present disclosure.
Referring to
In the example of
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As can be seen from
In addition, the electrical conduction path 3 has a plurality of non-thick film conduction path portions 8 in which the electrical conduction path 5 is formed of an electrically conductive non-thick film material N-DFM different from the thick film material DFM. In the top view D of the substrate 2 shown, the electrical conduction path 5 has a meandering geometry in a main section 17, which is located in the region of the T-roof 13. Thus, the thick film conduction path sections 5 and also the non-thick film conduction path sections 8 are arranged in the T-roof 13. In the top view D of the substrate 2 shown, the electrical conduction path 3 in the non-thick-film conduction path section 8 can each have a contour with a kink or an angle as shown. However, it is also possible in principle—in an analogous manner to the thick-film conduction path sections 5—to have a straight-line contour course in each case (not shown). Instead of a non-rectilinear contour with the angle or kink shown, a non-rectilinear, in particular curved or curvilinear contour (not shown in
In the example of
In the plan view D of the substrate 2, the thick-film conductive path sections 5 each have a longitudinal geometry and each extend along a common longitudinal direction L. Furthermore, the thick-film conductive path sections 5 are arranged side by side at a distance transverse to the longitudinal direction L. The non-thick-film conductive path sections 8 also have a longitudinal geometry, each non-thick-film conductive path section 8 interconnecting two adjacent thick-film conductive path sections 5. The thick-film conduction path sections 5 and the non-thick-film conduction path sections 8 preferably have the same path width—measured transversely to a flow direction of the electrical charge carriers through the electrical conduction path 3.
As
Referring now to
In the example of
Referring now to
In a simplified variant of
The specific examples provided in this disclosure are given to illustrate various embodiments of the invention and should not be construed to limit the scope of the disclosure. The embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein.
The foregoing description of various forms of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications or variations are possible in light of the above teachings. The forms discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various forms and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21184584.7 | Jul 2021 | EP | regional |
