PTC heating element

Abstract

The invention relates to a PTC heating element (1) with a three-dimensional base body (2) having at least two opposing main surfaces (3, 4), wherein the distance of the base body (2) between the main surfaces (3, 4) is the thickness D of the base body (2), and wherein the electrical resistance R of the PTC heating element (1) has a minimum at higher temperatures and a resistance characteristic that increases further at even higher temperatures, wherein the reference temperature Tref is the temperature at which the electrical resistance has twice the value at its minimum at Tmin, and wherein the power potential LP of the PTC heating element (1) is determined according to the following formula: LP = ( Uop / D ) * tref with Uop = the maximum operating voltage of the PTC heating element (1), where: 65000 (V / mm) °C <= LP Uop >= 480 V D <= 2.5 mm Tref < = 175 ° C .

Description

[0001] The invention relates to a PTC heating element, in particular for an electric heater, especially for a motor vehicle, which is operated in an 800 V operating voltage class.

[0002] PTC heating elements are well-known in the prior art. They typically consist of a ceramic material, which is pressed into a cuboid, for example. This cuboid typically has two essentially parallel surfaces that serve for electrical contact. The thickness of the PTC element determines, among other things, its electrical resistance, heat dissipation, and the reference temperature, which is the temperature at which the reference resistance is reached. This reference resistance is twice the minimum resistance of the resistance curve as a function of temperature.

[0003] Such PTC heating elements are typically used in electrically operated heaters, i.e., electric heaters.

[0004] For electric vehicles or hybrid vehicles in the passenger car or commercial vehicle sector, electric heating or auxiliary heating is particularly important, as there is little or no waste heat from a combustion engine. In electrically powered vehicles, an electric heater is a systemically simple way to heat a fluid, such as air, water, or coolant.

[0005] The electric heater is not only of great importance during the start-up phase, as with a conventional combustion engine, but also during driving, in order to ensure the maintenance of the cabin interior temperature in cold ambient temperatures.

[0006] In principle, an electric heater can be designed as an air-side heater or a coolant-side electric heater, especially as a high-voltage heater (HV).

[0007] Since the electric high-voltage heaters are powered by the vehicle's traction battery on both the air and coolant sides, nominal voltage ranges of 220–850 V are currently provided. The maximum operating voltage is 480 V in the 400 V voltage class and 940 V to 1250 V in the 800 V voltage class. The respective power output of these electric heaters is approximately 5 to 10 kW.

[0008] The PTC heating element exhibits electrical resistance as a function of temperature, i.e., a resistance-temperature characteristic curve. This characteristic decreases approximately linearly from low to high temperatures until a minimum is reached, after which the resistance increases sharply again with further temperature increases. The reference temperature is the temperature at which the resistance is twice as high as the minimum resistance at a temperature higher than the minimum.

[0009] The resistance-temperature characteristic curve of PTC heating elements can be shifted to a certain extent in both the vertical and horizontal directions. This shift can be achieved by influencing various factors of the PTC heating element, such as the ceramic composition, the addition of lead, the thickness of the PTC heating element, etc.

[0010] Shifting the curve vertically changes the electrical resistance. However, in steady-state operation, only as much electrical power can be generated and delivered as can be thermally transferred to the fluid being heated. Therefore, if the curve is shifted further downwards vertically, the power output in steady-state operation often does not increase, but the maximum switching current when passing through the minimum resistance value Rmin does.

[0011] Shifting the curve horizontally alters the reference temperature to lower or higher values. Adding lead, among other materials, to the ceramic material shifts the curve to the right towards higher temperatures. This makes the PTC heating element, and consequently the high-voltage heater, more efficient from a purely thermal perspective, as there is a greater driving temperature gradient from the PTC heating element to the fluid being heated. However, this also shifts the operating range of the PTC heating element to higher temperatures. As a result, all components of the high-voltage heater and surrounding components are subjected to higher temperatures. While the PTC high-voltage heater does regulate itself under critical conditions, this occurs at excessively high temperatures. Furthermore, shifting the characteristic curve to higher temperatures makes the PTC heating element less stable and increases the risk of stress breakdown through the sintered ceramic PTC material.The reduced specific dielectric strength can be remedied by increasing the material thickness of the PTC heating element. However, this in turn reduces the performance of the PTC heating element.

[0012] Higher temperatures at the PTC heating element also increase the risk that its characteristics will change over its lifetime. With increasing temperature, the PTC heating element exhibits an increase in its catalytic behavior, for example, when it absorbs moisture. This alters the behavior of the PTC heating element, further reducing its dielectric strength.

[0013] The operating range of the PTC heating element adjusts itself so that the electrical energy always equals the thermal energy output, i.e., Eelectrical = Ethermal. At a fixed operating voltage U, the PTC heating element generates as much energy as is transferred, or can be transferred, to the fluid being heated via the heat exchanger.

[0014] The greater the mass flow rate of the fluid and / or the driving temperature gradient between the PTC heating element surface and the temperature of the fluid, the more power can be delivered.

[0015] For example, if the mass flow rate of the fluid to be heated is reduced, the fluid will become warmer at a given power / voltage. However, this also causes the PTC heating element to heat up. Due to the increased heating of the PTC heating element, its electrical resistance increases along the RT curve, and the power output decreases until an equilibrium between electrical and thermal power is automatically re-established.

[0016] Currently used PTC heating elements in series production for high-voltage applications in the 800-volt operating voltage class have a material thickness between 3.0 mm and 3.5 mm, with a continuing upward trend. A disadvantage of these PTC heating elements is their low thermal conductivity. The thermal conductivity is only about 2 W / (mK). As a result, the PTC heating element is not uniformly warm during operation, but rather hottest in the center core and significantly cooler at the surface. The reference temperature (Tref) of typical, well-known PTC heating elements is generally between 190 and 230 °C and higher.

[0017] This illustrates a current trend for PTC heating elements in the high-voltage range (800 V operating voltage class) towards ever greater material thicknesses of up to 3.5 mm and more, with the addition of lead being deemed necessary to shift the operating range to higher temperatures. This results in the aforementioned disadvantages. In particular, the addition of lead must be mentioned, as its use should be reduced or avoided due to the associated environmental impact.

[0018] The task is therefore to create a PTC heating element that is improved compared to the state of the art, improves or avoids the disadvantages of the state of the art, operates at lower temperatures, and reduces or avoids the lead content.

[0019] This problem is solved using the features of claim 1.

[0020] One embodiment of the PTC heating element according to the invention relates to a PTC heating element with a three-dimensional base body having at least two opposing main surfaces, wherein the distance of the base body between the main surfaces is the thickness D of the base body, and wherein the electrical resistance R of the PTC heating element has a minimum at higher temperatures and a resistance characteristic that increases further at even higher temperatures, wherein the reference temperature Tref is the temperature at which the electrical resistance has twice the value of the minimum at Tmin, and wherein the power potential LP of the PTC heating element is determined according to the following formula: LP=(Uop / D)*Tref with Uop = the maximum operating voltage of the PTC heating element, where: 65000(V / mm)°C<=LP, Uop>=480 V, D<=2.5 mm and Target <= 175 °C.

[0021] This creates a PTC heating element which has a higher power potential LP than the PTC heating elements according to the state of the art, whereby the thickness D is significantly smaller than in the state of the art and the reference temperature Tref is also significantly lower than in the state of the art.

[0022] This results in improved heating performance due to the reduced thickness D, because the heat from the PTC heating element is dissipated more efficiently in thinner elements, even though the thermal conductivity of the PTC material is relatively low. Since the PTC element heats up more internally due to its low thermal conductivity, the external temperature is higher in thinner PTC heating elements. Furthermore, the reference temperature does not need to be increased, which can be particularly beneficial for the environment if lead or lead oxide can be avoided. This also improves the dielectric strength because the reference temperature Tref is reduced. Due to the reduced reference temperature Tref, the dielectric strength can be achieved even with a reduced thickness D. The resulting power potential LP is then 65,000 (V / mm)°C or significantly higher.

[0023] It is also advantageous if the PTC heating element is designed for an operating voltage class of 800 V or higher. This allows the PTC heating element to be used at operating voltages up to 1000 V or higher.

[0024] It is particularly advantageous if the following applies: 70000(V / mm)°C<=LP, in particular 80000(V / mm)°C<=LP, further in particular 100000(V / mm)°C<=LP.

[0025] With these values ​​for the power potential LP, the conductivity of the heating element is significantly improved compared to the state of the art, because the thickness of the PTC heating element is reduced instead of increasing, contrary to the trend of the state of the art.

[0026] It is also advantageous if the following applies to the PTC heating element: D<=2.0 mm, in particular D<=1.5 mm, further in particular D<=1.0 mm, further in particular D<=0.8 mm, further in particular D<=0.5 mm.

[0027] These reduced thickness values ​​(D) result in improved heating performance of the PTC element and the electric heater, a significant reduction in lead use, a lower reference temperature, better aging resistance due to the lower component temperature, higher power potential, etc. (see also above). Furthermore, a smaller installation space is achieved for the electric heater because the heating element as a whole requires less space due to the thinner PTC heating elements.

[0028] It is also advantageous if the following applies: Reef <= 170 °C, in particular Reef <= 160 °C, further in particular Reef <= 140 °C, further in particular Meeting <= 130 °C, further in particular Meeting temperature <= 120 °C.

[0029] The lower the Tref value, the better the heating performance and the better the resistance to aging due to the lower temperature of the components.

[0030] It is also advantageous if the following applies: Uop>=600 V, in particular Uop>=800 V, further in particular Uop>=920 V, further in particular Uop>=940 V.

[0031] The values ​​for Uop define the maximum operating voltage, as required, for example, by the vehicle manufacturer, in order to use such a PTC heating element in a heater configured in this way.

[0032] It is particularly advantageous if the three-dimensional basic body with at least two opposing main surfaces is designed as a cuboid or a cylinder, especially as a flat cuboid or a flat cylinder, in which the extent in the plane of the main surfaces is at least five times or more greater than the thickness D. This achieves a suitable design for the available installation space.

[0033] It is also advantageous if the base body is made of a ceramic material, in particular sintered barium titanate, optionally with the addition of other additives and / or unavoidable impurities. This achieves the typical electrical PTC resistance curves as a function of temperature, resulting in an increasing resistance with rising temperature for self-regulation.

[0034] It is also advantageous if the base material is manufactured without the addition of lead and / or lead oxide. This reduces or eliminates environmental pollution caused by this substance.

[0035] It is also advantageous if at least one or both main surfaces of the base body are provided with an electrically conductive coating, in particular a metallic coating such as a silver or aluminum coating. This improves the contact of the PTC heating element, for example by means of contact plates on the main surfaces of the PTC heating element.

[0036] It is also advantageous when the PTC heating element is used in an electrically operated heater for the circulation and heating of air, such as in an air conditioning unit for the interior of a motor vehicle. By reducing the reference temperature of the PTC heating elements, the risk of overheating of adjacent components and assemblies is avoided, in particular overheating of plastic parts of the air conditioning system, thus reducing the risk of fire or damage.

[0037] The invention is explained in more detail below based on exemplary embodiments and the figures in the drawings.

[0038] They show: Fig. 1 a schematic view of an embodiment of a PTC heating element according to the invention, Fig. 2 another view of the PTC heating element after Fig. 1, Fig. 3 another view of the PTC heating element after Fig. 1, Fig. 4 a resistance characteristic R vs. T of a PTC heating element, Fig. 5 a resistance characteristic R vs. T of a PTC heating element, Fig. 6. A resistance characteristic R vs. T of a PTC heating element, Fig. 7 a diagram of the power potential LP vs. the thickness D of the PTC heating element, and Fig. 8 a diagram of the power potential LP vs. reference temperature Tref of the PTC heating element.

[0039] The Fig. 1, Fig. 2, and Fig. Figure 3 shows a schematic representation of a PTC heating element 1 with a three-dimensional base body 2 having at least two opposing main surfaces 3, 4. The distance of the base body 2 between the main surfaces 3, 4 is the thickness D of the base body 2.

[0040] In an advantageous example, the PTC heating element 1 with its three-dimensional base body 2 with the at least two opposing main surfaces 3, 4 is designed as a cuboid or as a cylinder, in particular as a flat cuboid or as a flat cylinder, in which the extent in the plane of the main surfaces 3, 4 is at least five times or more greater than the thickness D.

[0041] Preferably, the base body 2 of the PTC heating element 1 is made of a ceramic material, in particular of sintered barium titanate, optionally with the addition of further additives and / or unavoidable impurities. The additives can, for example, also influence the positioning of the resistance characteristic curve in the diagram.

[0042] For example, the base body 2 can also be produced without the addition of lead and / or lead oxide, which significantly improves environmental compatibility.

[0043] Furthermore, at least one main surface 3, 4 of the base body 2, or both main surfaces 3, 4 of the base body 2, can be provided with an electrically conductive coating, in particular with a metallic coating, such as a silver or aluminum coating. This improves the electrical contact with an adjacent contact plate of a heater.

[0044] The electrical resistance R of the PTC heating element 1 is shown in the Fig. 4, Fig. 5 to Fig. 6, starting at low temperatures and progressing to higher temperatures, exhibits a minimum resistance and a resistance characteristic that continues to increase at further higher temperatures, where the reference temperature Tref is the temperature at which the electrical resistance Rref has twice the value of the minimum at Tmin, i.e., Rref = 2*Rmin.

[0045] The resistance characteristic can be shifted both horizontally and vertically in the diagram by influencing the choice of material and the thickness of the PTC heating element 1, as shown in the Fig. 5 and Fig. 6 is indicated. In Fig. 6 shows the working area in an oval-shaped area, which is located on the rising branch of the resistance characteristic.

[0046] The power potential LP of the PTC heating element 1, which is a characteristic parameter for the PTC heating element 1 according to the invention, is determined according to the following formula: LP=(Uop / D)*Tref with Uop = the maximum operating voltage of the PTC heating element 1, where: 65000(V / mm)°C<=LP Uop>=480 V D<=2.5 mm Target <= 175 °C.

[0047] In the present embodiment, this applies to a PTC heating element 1 designed for an operating voltage class of 800 V.

[0048] Regarding performance potential: 70000(V / mm)°C<=LP, in particular 80000(V / mm)°C<=LP, further in particular 100000(V / mm)°C<=LP.

[0049] The following also applies: D<=2.0 mm, in particular D<=1.5 mm, further in particular D<=1.0 mm, further in particular D<=0.8 mm, further in particular D<=0.5 mm.

[0050] Preferably, the following also applies: Reef <= 170 °C in particular Reef <= 160 °C, further in particular Reef <= 140 °C further in particular Meeting <= 130 °C further in particular Meeting <= 120 °C

[0051] The following also applies preferably: Uop>=600 V, in particular Uop>=800 V, further in particular Uop>=920 V, further in particular Uop>=940 V.

[0052] The following two tables are explained to illustrate the invention and to compare it with the prior art.

[0053] Table 1 presents data and measured values ​​for state-of-the-art PTC heating elements used in air conditioning systems for heating the vehicle interior in production vehicles. The operating voltage class for all PTC heating elements is 800 V, and the maximum operating voltage is between 800 V and 940 V.

[0054] The material thickness D is 3.0 mm and 3.5 mm, with the more modern vehicles having the larger thickness D.

[0055] The reference temperature Tref for the PTC heating elements according to the state of the art is between 188 °C and 227 °C, which is already very unfavorable because it could damage the surrounding materials and assemblies, especially in the event of a failed airflow in an electric heater.

[0056] The maximum operating voltage Uop divided by the thickness D, i.e. Uop / D, is in the range of 229 and 313 V / mm, with a focus towards higher values.

[0057] The power potential LP ranges from 42971 to 71127 (V / mm)°C.

[0058] Table 2 shows a representation of data and measured values ​​of PTC heating elements 1 according to the invention. The operating voltage class for all PTC heating elements 1 is 800 V and the maximum operating voltage is 940 V.

[0059] The material thickness D is significantly lower compared to the state of the art and is in the range of 2.5 mm to 0.5 mm, thus significantly lower than in the state of the art, and the values ​​tend towards smaller thicknesses D.

[0060] The reference temperature Tref for the PTC heating elements 1 according to the invention lies between 175 °C and 115 °C, which is very low, thus largely reducing the risk of damage, ignition, and fires. This also significantly increases the thermal performance of the PTC heating element 1.

[0061] The maximum operating voltage Uop divided by the thickness D, i.e. Uop / D, is in the range of 376 and 940 V / mm with a tendency towards even higher values.

[0062] The performance potential LP ranges from 65800 to 108100 (V / mm)°C.

[0063] It is evident that significant improvements can be achieved with the thinner PTC heating elements 1, whereby the use of lead can also be significantly reduced or avoided, because the problems of the thick PTC heating elements 1 do not exist with the thin PTC heating elements 1, so that lead can be reduced or avoided.

[0064] The Fig. 7 and Fig. Figure 8 shows these values ​​in a graphical representation. The power potential LP is plotted against the material thickness D. Fig. 7 and the power potential LP above the reference temperature Tref for Fig. Figure 8 is shown. It can be seen in both representations that the measured values ​​of the examples according to the invention lie in the upper left quadrant above the angle bisector and tend towards lower thicknesses D and lower reference temperatures Tref, in each case with increasing power potential LP.

[0065] The measured values ​​of the PTC heating elements 1, in accordance with the state of the art, lie below the angle bisector and, on the other hand, tend towards higher thicknesses and higher reference temperatures at lower LP.

[0066] The design of the PTC heating elements 1 according to the invention, contrary to the trend of the prior art, offers significant advantages in PTC heating elements of the 800 V operating voltage class, resulting in smaller thicknesses D and lower reference temperatures. Reference symbol list 1 PTC heating element 2 basic shapes 3 Main area 4 Main area

Claims

[1] PTC heating element (1) with a three-dimensional base body (2) having at least two opposing main surfaces (3, 4), wherein the distance of the base body (2) between the main surfaces (3, 4) is the thickness D of the base body (2), and wherein the electrical resistance R of the PTC heating element (1) exhibits a minimum at higher temperatures and a resistance characteristic that increases further at higher temperatures, wherein the reference temperature Tref is the temperature at which the electrical resistance has twice the value at its minimum at Tmin, and wherein the power potential LP of the PTC heating element (1) is determined according to the following formula: LP = (Uop / D)*Tref with Uop = the maximum operating voltage of the PTC heating element (1), where: 65000(V / mm)°C<=LP Uop>=480 V D<=2.5 mm Target <= 175 °C. [2] PTC heating element (1) according to claim 1, characterized bythat it is designed for the operating voltage class of 800 V. [3] PTC heating element (1) according to claim 1 or 2, characterized by , that is true: 70000(V / mm)°C<=LP, in particular 80000(V / mm)°C<=LP, further in particular 100000(V / mm)°C<=LP. [4] PTC heating element (1) according to any one of the preceding claims, characterized by , that is true: D<=2.0 mm, in particular D<=1.5 mm, further in particular D<=1.0 mm, further in particular D<=0.8 mm, further in particular D<=0.5 mm. [5] PTC heating element (1) according to any one of the preceding claims, characterized by , that is true: Reef <= 170 °C, in particular Reef <= 160 °C, further in particular Reef <= 140 °C, further in particular Meeting <= 130 °C, further in particular Thref<120 °C. [6] PTC heating element (1) according to any one of the preceding claims, characterized by , that is true: Uop >= 600 V, in particular Uop >= 800 V, further in particular Uop >= 920 V, further in particular Uop >= 940 V. [7] PTC heating element (1) according to any one of the preceding claims, characterized by , that the three-dimensional basic body (2) with the at least two opposing principal surfaces (3, 4) is designed as a cuboid or as a cylinder, in particular as a flat cuboid or as a flat cylinder, in which the extent in the plane of the principal surfaces (3, 4) is at least five times or more greater than the thickness D. [8] PTC heating element (1) according to any one of the preceding claims, characterized by, that the base body (2) is made of a ceramic material, in particular of a sintered barium titanate, optionally with the addition of further additives and / or unavoidable impurities. [9] PTC heating element (1) according to claim 8, characterized by , that the base body (2) is produced without the addition of lead and / or lead oxide. [10] PTC heating element (1) according to any one of the preceding claims, characterized by , that at least one main surface (3, 4) of the base body (2) or both main surfaces (3, 4) of the base body (2) is provided with an electrically conductive coating, in particular with a metallic coating, such as a silver or aluminum coating. [11] PTC heating element (1) according to one of the preceding claims, which is used in an electrically operated heater for the flow and heating of air, which heater is arranged in an air conditioning unit for the air conditioning of the interior of a motor vehicle.

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