Patent Application
20190166653
This application claims priority to European Application No. EP 17203815.0, filed on Nov. 27, 2017, the contents of which are hereby incorporated by reference in its entirety.
The invention relates to a PTC heater comprising at least one PTC heating element.
Modern motor vehicles are increasingly optimized for consumption and less and less waste heat is available for conventionally heating the interior. In particular when cold starting the motor vehicle and in the case of low outside temperatures, the interior can be additionally heated for example by means of a PTC (Positive Temperature Coefficient) heater. PTC heaters are already known from the prior art and are made of typically ceramic PTCs, which are characterized by an electrical resistance, which increases as the temperature increases. The PTC heater is throttled by its own behavior and the heating surfaces of the PTC heater have an even temperature distribution. The temperature of the heating surfaces is in particular independent of boundary conditions—such as for example of the applied voltage, the resistance of the PTC or the air quantity above the PTC heater. The PTC heater is cost-efficient, can be installed in air ducts of the air conditioning system in a space-saving manner and quickly converts the electrical energy into the heat.
In hybrid or electric vehicles, a PTC heater has a particularly high significance, because no waste heat or only a small amount of waste heat is produced in a hybrid or electric vehicle, and can be used for heating. For an effective heating in a hybrid or electric vehicle, the PTC heater needs to partially convert a wattage of more than 3 kW into heat. This is why the PTC heater is operated at a high voltage in order to keep the current as low as possible. The voltages are thereby above 60 V and partially above 300 V. To rule out exposure of the passengers during operation of the PTC heater, the PTC heater needs to also be touch-protected and flashover-protected. Voltage conducting components of the PTC heater need to furthermore be encapsulated in a dust-tight and water-tight manner. To meet the increasing demands on the touch protection, the voltage conducting components are electrically insulated to the outside to an increasing extent. The heat release of the PTC heater to the outside, which causes an unwanted throttling of the PTC heater, is also reduced thereby. The wattage, which the PTC heater can convert into the heat, is also reduced accordingly.
It is thus the object of the invention to specify an improved or at least alternative embodiment for a PTC heater of the generic type, in the case of which the described disadvantages are overcome.
According to the invention, this object is solved by the subject matter of the independent claim(s). Advantageous further embodiments are the subject matter of the dependent claim(s).
The invention at hand is based on the general idea of improving the heat release to the outside in a PTC heater comprising at least one PTC heating element and to thus prevent an unwanted throttling of the PTC heater. The at least one PTC heating element thereby has a heating layer of a PTC material, which is arranged between two electrode plates and which is electrically contacted therewith. The PTC heater further has a housing, in which the at least one PTC heating element is arranged. The electrode plates of the at least one PTC heating element are thereby fixed to the housing so as to transfer heat and so as to be electrically insulated. According to the invention, at least one electrically insulated heat conducting layer divides the heating layer and is fixed to the divided heating layer so as to transfer heat. Advantageously, the at least one heat conducting layer has a heat conductivity, which is higher as compared to the heating layer, and dissipates the heat generated in the heating layer to the outside. Advantageously, an unwanted throttling of the PTC heating element is thus prevented. The heat conducting layer is electrically insulated from the heating layer, so that the heat conducting layer does not influence electrical properties of the PTC heating element.
Advantageously, the heating layer can be made of the sintered PTC material, which preferably has barium titanate or consists thereof. The heating layer of sintered barium titanate has a heat conductivity of approximately 2 W/mK. The at least one heat conducting layer can for example consist of a sintered ceramic, which preferably has aluminum nitride or boron nitride, or consists thereof. In the case of the sintered aluminum nitride, the heat conducting layer has a heat conductivity of approximately 130 W/mK and in the case of the sintered boron nitride a heat conductivity of approximately 60 W/mK. The heat conducting layer of one of these materials can effectively dissipate the heat generated in the heating layer to the outside and can thus prevent an unwanted throttling of the PTC heating element and of the PTC heater. In the alternative, the at least one heat conducting layer can be a metal plate, which is electrically insulated from the divided heating layer by means of an insulating coating. The insulating coating is preferably an oxide layer or a varnish or an insulating film.
In the case of an advantageous embodiment of the PTC heater according to the invention, provision is made for the at least one heat conducting layer to extend from the one electrode plate to the other electrode plate and to divide the heating layer vertically to the electrode plates. The at least one heat conducting layer thereby abuts on both sides of the divided heating layer so as to transfer heat and can dissipate the heat generated in the heating layer via the electrode plates. On both sides of the housing, the electrodes plates arranged on the housing and electrically insulated therefrom in each case form a heating surface, at which the heat generated in the heating layer is released into the surrounding area. The heat can be released more effectively to the electrode plates and to the respective heating surfaces of the housing by means of the at least one heat conducting layer.
The heating layer can in particular be divided into a plurality of individual heating part layers, wherein the respective heating part layers and the respective heat conducting layers are arranged so as to alternate and vertically to the electrode plates. The heat generated in the heating layer can be dissipated evenly from the PTC heating element in this way and an unwanted throttling of the PTC heating element and of the PTC heater can be prevented thereby in an advantageous manner. The respective heat conducting layer is thereby electrically insulated from the divided heating layer and the electrode plates, so that electrical properties of the PTC heating element and of the PTC heater are not influenced.
In the case of an advantageous further development of the PTC heater according to the invention, provision is made for at least one heat conducting layer to extend in parallel to the electrode plates and to divide the heating layer in parallel to the electrode plates. The at least one heat conducting layer can dissipate the heat, which is only dissipated slowly via the heating layer itself, from a middle area of the heating layer. An unwanted throttling of the PTC heating element and of the PTC heater can be prevented in an advantageous manner thereby. The at least one heat conducting layer is electrically insulated from the divided heating layer and the electrode plates and does not influences electrical properties of the PTC heating element and of the PTC heater in this way.
To effectively dissipate the heat from the at least one heat conducting layer to the outside, a heat distribution body of the PTC heating element can be fixed to the at least one heat conducting layer on one side and to the housing on the other side so as to transfer heat. The heat distribution body can consist for example of a sintered ceramic, which is preferably an aluminum nitride or a boron nitride. The heat distribution body dissipates the heat from the at least one heat conducting layer to the housing, to which the heat distribution body is fixed so as to transfer heat, and thus forms at least one body heating surface of the PTC heater. The heating surface is expanded in an advantageous manner by means of the body heating surface and the heat generated in the PTC heating element can be released into the surrounding area in a large-scale and even manner.
Provision can advantageously be made for an electrically insulating insulating plate to be arranged in each case between the electrode plates and the housing. The respective insulating plate is fixed to the housing so as to transfer heat and electrically insulates the electrode plates from the housing. The PTC heater is protected against touch and flashover in this way. The respective insulating plate can additionally be connected to the heat distribution body of the PTC heating element so as to transfer heat, in order to be able to effectively release the heat generated in the PTC heating element to the heating surface and to the body heating surface. Advantageously, the respective insulating plate can consist of an aluminum oxide or a sintered ceramic, preferably an aluminum nitride or a boron nitride.
As a whole, the heat generated in the heating layer is dissipated to the outside in an improved manner and an unwanted throttling of the PTC heating element is thereby prevented in an advantageous manner by means of the PTC heater according to the invention. Furthermore, the heat output of the PTC heating element and of the PTC heater is increased thereby.
Further important features and advantages of the invention follow from the subclaims, from the drawings, and from the corresponding figure description by means of the drawings.
It goes without saying that the above-mentioned features and the features, which will be explained below, cannot only be used in the respective specified combination, but also in other combinations or alone, without leaving the scope of the invention at hand.
Preferred exemplary embodiments of the invention are illustrated in the drawings and will be explained in more detail in the description below, whereby identical reference numerals refer to identical or similar or functionally identical components.
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As a whole, the heat generated in the PTC heater 1 according to the invention in the heating layer 3 can be effectively dissipated to the outside and an unwanted throttling of the PTC heating element 2 can be prevented in an advantageous manner thereby. Furthermore, the heat output of the PTC heating element 2 and of the PTC heater 1 is increased thereby.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17203815.0 | Nov 2017 | EP | regional |
