PTC heating element

Abstract

The invention relates to a PTC heating element (1) having a three-dimensional main body (2) with at least two main surfaces (3, 4) facing away from each other, the distance of the main body (2) between the main surfaces (3, 4) being the thickness D of the main body (2), and wherein the resistance R of the PTC heating element (1) has a minimum value first as the temperature increases and has a resistance characteristic that continues to increase as the temperature continues to increase, the reference temperature Tref is a temperature at which the resistance has a value twice the minimum value Rmin, and wherein the performance potential LP of the PTC heating element (1) is determined according to the following formula: LP = (Uop / D) Tref wherein Uop = the maximum operating voltage of the PTC heating element (1), where applicable: 65000 (V / mm) DEG C < = LP, Uop > = 480 V, D < = 2.5 mm, Tref < = 175 DEG C.

Description

Technical Field

[0001] This invention relates to PTC heating elements, particularly PTC heating elements for electric heaters, especially PTC heating elements for electric heaters of motor vehicles, which operate at an operating voltage level of 800 V. Background Technology

[0002] PTC heating elements are known in various forms in the prior art. They are typically made of ceramic materials, for example, pressed into cuboids, which typically have two substantially parallel faces used for electrical contact. The thickness of the PTC element, in particular, determines the resistance, heat dissipation, and reference temperature, which is the temperature at which a reference resistance is reached, and the reference resistance is twice the minimum resistance of the resistance curve as a function of temperature.

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

[0004] In the case of electric or hybrid vehicles in the passenger or commercial vehicle sector, the settings for electric heating or auxiliary heating are particularly important because there is little or no waste heat from the internal combustion engine. In electrically powered vehicles, electric heaters are a simple and feasible solution for heating systems that supply fluids such as air, water, or cooling water.

[0005] Here, the electric heater is crucial not only during the start-up phase (as in a conventional internal combustion engine) but also during driving to ensure that the interior temperature of the vehicle is maintained in cold ambient temperatures.

[0006] In principle, electric heaters provide the possibility of constituting an air-side heater or a coolant-side electric heater, especially as a high-volt (HV) heater.

[0007] Since both the air-side and coolant-side electric HV heaters are powered by the vehicle's drive battery, the current rated voltage range is set at 220 V to 850 V. The maximum operating voltage is 480 V at the 400 V voltage rating. At the 800 V voltage rating, the maximum operating voltage is 940 V to 1250 V. The respective power ratings of these electric heaters are approximately in the range of 5 kW to 10 kW.

[0008] PTC heating elements have resistance as a function of temperature, known as the resistance-temperature characteristic line. This characteristic line decreases approximately linearly from lower to higher temperatures until it reaches a minimum value, and then the resistance rises sharply again as the temperature continues to increase. The reference temperature here is the temperature at which the resistance is at its minimum value, and is greater than the temperature at which the resistance is at its minimum value.

[0009] In a PTC heating element, the resistance temperature characteristic curve can shift to some extent along both the vertical and horizontal directions. This shift is achieved by various factors that influence the PTC heating element, such as ceramic composition, lead addition, and the thickness of the PTC heating element.

[0010] The vertical movement of the curve causes a change in resistance. However, in steady-state operation, the electrical power generated and released is only as much as the thermal power that can be released to the fluid to be heated. Therefore, if the curve continues to move downwards in the vertical direction, the power will not typically increase in steady-state conditions, but the maximum operating current will increase when the minimum resistance Rmin is crossed.

[0011] A horizontal shift in the curve causes the reference temperature to change towards lower or higher temperature values. Adding lead, particularly to the ceramic material, shifts the curve to the right towards higher temperatures. From a purely thermal perspective, this improves the performance of the PTC heating element and, consequently, the HV heater, due to the larger driving temperature difference between the PTC heating element and the fluid being heated. However, this shifts the operating range of the PTC heating element to higher temperatures. Consequently, all components of the HV heater and its surrounding structural elements will be subjected to higher temperature loads. Although the PTC-HV heater is tuned to be limited under critical boundary conditions, the temperature becomes excessively high. Similarly, the shift of the characteristic line towards higher temperatures makes the PTC heating element more unstable and increases the risk of voltage breakdown through the sintered ceramic PTC material. Increasing the material thickness of the PTC heating element remedies the reduced specific dielectric strength. However, this, in turn, reduces the performance of the PTC heating element.

[0012] Higher temperatures on PTC heating elements also increase the risk of changes in their properties over their lifespan. As temperatures increase, the catalytic behavior of the PTC heating element improves, for example, in the case of moisture absorption. This behavior alters the PTC heating element's behavior, which in turn further reduces its dielectric strength.

[0013] The operating range of a PTC heating element is such that electrical energy is always equal to the released heat energy, i.e., Eelectric = Eheat. At the specified operating voltage U, the energy generated at the PTC heating element is therefore equal to the energy released through the heat exchanger or capable of being released to the fluid to be heated.

[0014] The greater the mass flow rate of the fluid and / or the greater the driving temperature difference between the surface of the PTC heating element and the fluid temperature, the more power is released.

[0015] For example, if the mass flow rate of the fluid to be heated decreases, the fluid becomes hotter at the set power / voltage. However, this will cause the PTC heating element to also become hotter. As the PTC heating element is heated more intensely, the resistance increases along the RT curve, while the power decreases until the electrical power and thermal power are automatically rebalanced.

[0016] Currently, PTC heating elements used in HV applications operating at 800 volts in the prior art have a material thickness between 3.0 mm and 3.5 mm, and this thickness is trending upwards. A disadvantage of these PTC heating elements is their low thermal conductivity, which is only about 2 W / (mK). This results in uneven temperature distribution during operation—the core is the hottest part, while the surface is significantly cooler. The reference temperature (Tref) of commonly known PTC heating elements is generally between 190°C and 230°C, and higher.

[0017] This indicates that current development of PTC heating elements for high-voltage applications at 800 volts is moving towards increasing material thickness to 3.5 mm and above, where lead contamination is considered necessary to extend the operating range to higher temperatures. This leads to the aforementioned drawbacks. However, it should be particularly noted that lead contamination should be reduced or avoided due to the associated environmental burden. Summary of the Invention

[0018] Therefore, the objective of this invention is to provide an improved PTC heating element compared to the prior art, which improves or avoids the disadvantages of the prior art, operates at a lower operating temperature, and reduces or avoids the lead content.

[0019] This task is solved by the features of claim 1.

[0020] An embodiment of the PTC heating element according to the present invention relates to a PTC heating element having a three-dimensional substrate having at least two main surfaces facing away from each other, wherein the spacing between the main surfaces of the substrate is the thickness D of the substrate, and wherein the resistance R of the PTC heating element first has a minimum value as the temperature rises, and has a resistance characteristic that continues to increase as the temperature continues to rise, wherein the reference temperature Tref is the temperature at which the resistance has twice the minimum value Rmin, and wherein the performance potential LP of the PTC heating element is determined by the following formula: LP = (Uop / D)×Tref Where Uop = the maximum operating voltage of the PTC heating element, and the applicable voltage is: 65000 (V / mm)℃ ≤ LP Uop ≥ 480 V, D ≤ 2.5 mm, and Tref ≤ 175℃.

[0021] This provides a PTC heating element with a higher performance potential LP than that of PTC heating elements according to the prior art, wherein the thickness D is significantly smaller than that in the prior art, and the reference temperature Tref is also significantly lower than that in the prior art.

[0022] This achieves improved heating power due to a smaller thickness D, because despite the relatively low thermal conductivity of PTC material, a thinner PTC heating element can better dissipate heat. The lower thermal conductivity allows the PTC element to be heated more thoroughly internally, resulting in a higher external surface temperature even with a thinner PTC heating element. Furthermore, the reference temperature does not need to be increased, and eliminating lead or lead oxide would be particularly beneficial to the environment. This also improves dielectric strength by lowering the reference temperature Tref. The lower reference temperature Tref allows for good dielectric strength even with a thinner thickness D. The resulting performance potential LP is 65000 (V / mm)℃ or significantly higher.

[0023] It is also appropriate that the PTC heating element is configured here for operating voltage levels of 800 V or higher. Thus, the PTC heating element can be used at operating voltages up to 1000 V or higher.

[0024] It is particularly advantageous that the following applies: 70000 (V / mm)℃ ≤ LP Especially 80000 (V / mm)℃ ≤ LP More especially 100000 (V / mm)℃ ≤ LP.

[0025] With respect to these values ​​of performance potential LP, the conductivity of the heating element is significantly improved compared to the prior art because, contrary to the trend of the prior art, the thickness of the PTC heating element is reduced.

[0026] It is also advantageous that PTC heating elements are suitable for the following: D ≤ 2.0 mm, Especially D ≤ 1.5 mm, More especially D ≤ 1.0 mm, More especially D ≤ 0.8 mm, More especially D ≤ 0.5 mm.

[0027] These reduced thickness values ​​(D) were used to improve the heating power of PTC elements and electric heaters, significantly reduce the use of lead, lower the reference temperature, improve aging resistance due to lower component temperatures, and achieve higher performance potentials, as mentioned above. Furthermore, a smaller structural space for the electric heater was achieved because the thinner PTC heating element resulted in a smaller overall structural space required for the heating regulator.

[0028] It is also advantageous that the following applies: Tref ≤ 170 ℃, Especially Tref ≤ 160 ℃, More especially Tref ≤ 140 ℃, More especially Tref ≤ 130 ℃, More especially Tref ≤ 120 ℃.

[0029] The lower the Tref, the better the heating power, and the better the aging resistance due to the lower temperature of the component.

[0030] It is also advantageous that the following applies: Uop ≥ 600 V, Especially Uop ≥ 800 V, More especially Uop ≥ 920 V, More especially Uop ≥ 940 V.

[0031] The value of Uop defines the maximum operating voltage, which may be required by the vehicle manufacturer to enable the use of such a PTC heating element in a heater configured in this way.

[0032] Of particular advantage is that the three-dimensional base having at least two back-to-back main faces is constructed as a cuboid or a prism, especially as a flattened cuboid or a flattened prism, wherein the extension in the plane of the main face is at least five times or more the thickness D. This achieves a shape suitable for usable spaces.

[0033] Advantageously, the matrix is ​​made of ceramic materials, particularly sintered barium titanate, optionally mixed with additional additives and / or unavoidable impurities. This allows for the realization of a typical electrical PTC resistance variation curve as a function of temperature, so as to obtain an increased resistance at rising temperatures for autonomous tuning.

[0034] Another advantage is that the matrix is ​​manufactured without the addition of lead and / or lead oxide. Therefore, the environmental burden caused by this substance can be reduced or avoided.

[0035] It is also advantageous that at least one or both main surfaces of the substrate are provided with a conductive coating, especially a metallic coating, such as a silver or aluminum coating. This is used to improve, for example, contact between the PTC heating element and the PTC heating element via contact pads.

[0036] It is also suitable to use PTC heating elements in electrically operated heaters that circulate and heat air, which are arranged in air conditioning systems used to regulate the air inside a motor vehicle. This reduces the risk of fire or damage by lowering the reference temperature of the PTC heating element, thus preventing overheating of adjacent components and structural assemblies, particularly the plastic parts of the air conditioning system. Attached Figure Description

[0037] The present invention will now be explained in detail with reference to the accompanying drawings and embodiments.

[0038] in:

[0039] Figure 1 A schematic view of an embodiment of the PTC heating element according to the present invention is shown;

[0040] Figure 2 It shows that according to Figure 1 Another view of the PTC heating element;

[0041] Figure 3 It shows that according to Figure 1 Another view of the PTC heating element;

[0042] Figure 4 The relationship between the resistance characteristics R and T of the PTC heating element is shown;

[0043] Figure 5The relationship between the resistance characteristics R and T of the PTC heating element is shown;

[0044] Figure 6 The relationship between the resistance characteristics R and T of the PTC heating element is shown;

[0045] Figure 7 A graph showing the relationship between the performance potential LP of a PTC heating element and its thickness D is presented.

[0046] Figure 8 A graph showing the relationship between the performance potential LP of the PTC heating element and the reference temperature Tref is presented. Detailed Implementation

[0047] Figure 1 , Figure 2 and Figure 3 A schematic diagram of a PTC heating element 1 is shown. The PTC element has a three-dimensional substrate 2 with at least two main surfaces 3 and 4 facing away from each other. The distance between the main surfaces 3 and 4 of the substrate 2 is the thickness D of the substrate 2.

[0048] In an advantageous example, the PTC heating element 1 is constructed as a cuboid or prism, particularly as a flat cuboid or flat prism, of its three-dimensional base 2 having at least two back-to-back main faces 3, 4, wherein the extension in the plane of the main faces 3, 4 is at least five times or more the thickness D.

[0049] Preferably, the substrate 2 of the PTC heating element 1 is made of ceramic material, particularly sintered barium titanate, optionally mixed with additional additives and / or unavoidable impurities. This mixing can, for example, affect the positioning of the resistance characteristic lines in the graph.

[0050] Here, matrix 2 can also be manufactured without the addition of lead and / or lead oxide, which significantly improves environmental compatibility.

[0051] Furthermore, at least one main surface 3, 4, or both main surfaces 3, 4 of the substrate 2 may be provided with a conductive coating, especially a metallic coating, such as a silver coating or an aluminum coating. This improves the electrical contact with the contact piece that abuts the heater.

[0052] The resistance R of PTC heating element 1, see [reference]. Figures 4 to 6 Starting from a low temperature, the resistance first reaches a minimum value as the temperature rises, and then continues to increase as the temperature continues to rise. The reference temperature Tref is the temperature at which the resistance Rref has twice the minimum value Rmin, i.e., Rref = 2 × Rmin.

[0053] The resistance characteristics are affected by the material selection and thickness of the PTC heating element 1, such as in Figure 5and Figure 6 The indicated location, for example, allows for both horizontal and vertical movement within a chart. Figure 6 The working range is shown in the elliptical region, which is arranged on the rising branch of the resistance characteristic.

[0054] As a characteristic parameter of the PTC heating element 1 according to the present invention, the performance potential LP of the PTC heating element 1 is determined according to the following formula: LP = (Uop / D)×Tref Where, Uop = the maximum operating voltage of PTC heating element 1 The applicable ones are: 65000 (V / mm)℃ ≤ LP Uop ≥ 480 V, D ≤ 2.5 mm, Tref ≤ 175℃.

[0055] In this embodiment, this applies to a PTC heating element 1 configured for an operating voltage rating of 800 V.

[0056] For performance potentials, the applicable terms are: 70000 (V / mm)℃ ≤ LP Especially 80000 (V / mm)℃ ≤ LP More especially 100000 (V / mm)℃ ≤ LP.

[0057] In addition, the following applies: D ≤ 2.0 mm, Especially D ≤ 1.5 mm, More especially D ≤ 1.0 mm, More especially D ≤ 0.8 mm, More especially D ≤ 0.5 mm.

[0058] In particular, the following also applies: Tref ≤ 170 ℃, Especially Tref ≤ 160 ℃, More especially Tref ≤ 140 ℃, More especially Tref ≤ 130 ℃, More especially Tref ≤ 120 ℃.

[0059] The preferred option also applies to: Uop ≥ 600 V, Especially Uop ≥ 800 V, More especially Uop ≥ 920 V, More especially Uop ≥ 940 V.

[0060] To explain the present invention and to compare it with the prior art, the two tables attached below are explained.

[0061] Table 1 shows a graph of data and measurements for PTC heating elements used in air conditioning systems for heating the interior space of motor vehicles, according to the prior art. These PTC elements are applied to the interior spaces of mass-produced vehicles. Here, the operating voltage rating for all PTC heating elements is 800 V, and the maximum operating voltage is between 800 V and 940 V.

[0062] The material thickness D is 3.0 mm and 3.5 mm, with the newer vehicles having a larger thickness D.

[0063] According to existing technology, the reference temperature Tref of the PTC heating element is between 188°C and 227°C, which is very unfavorable because it may damage the surrounding materials and the unit, especially in the event of an interruption of airflow in the electric heater.

[0064] The maximum operating voltage Uop divided by the thickness D, i.e., Uop / D, ranges from 229 V / mm to 313 V / mm, with a predominance of higher values.

[0065] The performance potential LP ranges from 42971 (V / mm)℃ to 71127 (V / mm)℃.

[0066] Table 2 shows a graph of data and measurements for the PTC heating element 1 according to the present invention. All PTC heating elements 1 have an operating voltage rating of 800 V and a maximum operating voltage of 940 V.

[0067] The material thickness D is significantly smaller than that of the prior art, and is significantly smaller in the range of 2.5 mm to 0.5 mm, with the value tending towards a smaller thickness D.

[0068] The reference temperature Tref of the PTC heating element 1 according to the present invention is between 175°C and 115°C, which is quite low, greatly reducing the risk of damage, ignition, and fire. Furthermore, this significantly improves the thermal performance of the PTC heating element 1.

[0069] The maximum operating voltage Uop divided by the thickness D, i.e., Uop / D, ranges from 376 V / mm to 940 V / mm, and tends to increase towards higher values.

[0070] The performance potential LP is between 65800 (V / mm)℃ and 108100 (V / mm)℃.

[0071] It has been shown that significant improvements can be achieved with thinner PTC heating elements 1, in which the use of lead can also be significantly limited or avoided, because the problems of thick PTC heating elements do not exist in these thin PTC heating elements, thereby reducing or avoiding lead.

[0072] Figure 7 and Figure 8 These values ​​are presented in the form of a graph or chart. Here, Figure 7 The relationship between the performance potential LP and the material thickness D was plotted, and Figure 8 The relationship between the performance potential LP and the reference temperature Tref was plotted. From these two graphs, it can be seen that the measurements according to the example of the present invention are above the angle bisector in the upper left quadrant, and with an increase in the performance potential LP, both tend towards a lower thickness D and a lower reference temperature Tref.

[0073] The measured values ​​of the existing PTC heating element 1 are located below the angle bisector, and conversely, tend to be higher in terms of thickness and higher reference temperature when LP is lower.

[0074] In PTC heating elements operating at 800V, the design of the PTC heating element 1 according to the present invention has the significant advantages of smaller thickness D and lower reference temperature, contrary to the trend of the prior art.

[0075] List of reference numerals

[0076] 1 PTC heating element

[0077] 2. Matrix

[0078] 3 Main side

[0079] 4 Main side

[0080] Table 1

[0081] Table 2

Claims

1. PTC heating element (1) having a three-dimensional base body (2) with at least two mutually opposing main faces (3, 4), wherein The distance of the base body (2) between the main faces (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 value at first and a resistance characteristic which continues to increase with a continued increase in temperature, wherein the reference temperature Tref is the temperature at which the electrical resistance has a value which is twice the minimum value Rmin, and wherein the performance potential LP of the PTC heating element (1) is determined as follows: LP = (Uop / D) x Tref wherein Uop = the maximum operating voltage of the PTC heating element (1), wherein it applies that: 65000 (V / mm)°C ≤ LP, Uop ≥ 480 V, D ≤ 2.5 mm, Tref ≤ 175°C.

2. The PTC heating element (1) according to claim 1, characterized in that The PTC heating element is configured for an operating voltage class of 800 V.

3. The PTC heating element (1) according to claim 1 or 2, characterized in that It applies that: 70000 (V / mm)°C ≤ LP, In particular 80000 (V / mm)°C ≤ LP, More particularly 100000 (V / mm)°C ≤ LP.

4. The PTC heating element (1) according to any of the preceding claims, characterized in that It applies that: D ≤ 2.0 mm, In particular D ≤ 1.5 mm, More particularly D ≤ 1.0 mm, More particularly D ≤ 0.8 mm, More particularly D ≤ 0.5 mm.

5. The PTC heating element (1) according to any of the preceding claims, characterized in that It applies that: Tref ≤ 170 °C, In particular Tref ≤ 160 °C, More particularly Tref ≤ 140 °C, More particularly Tref ≤ 130 °C, More particularly Tref ≤ 120 °C.

6. The PTC heating element (1) according to any of the preceding claims, characterized in that It applies that: Uop ≥ 600 V, In particular Uop ≥ 800 V, More particularly Uop ≥ 920 V, More particularly Uop ≥ 940 V.

7. The PTC heating element (1) according to any of the preceding claims, characterized in that The three-dimensional base body (2) having at least two mutually opposing main faces (3, 4) is configured as a cuboid or as a cylinder, in particular as a flat cuboid or a flat cylinder, in which the extent in the plane of the main faces (3, 4) is at least five times greater than the thickness D.

8. The PTC heating element (1) according to any of the preceding claims, characterized in that The base body (2) is made of a ceramic material, in particular of sintered barium titanate, optionally mixed with further additives and / or unavoidable impurities.

9. The PTC heating element (1) according to claim 8, characterized in that The base body (2) is produced without the addition of lead and / or lead oxide.

10. The PTC heating element (1) according to any of the preceding claims, characterized in that At least one main face (3, 4) of the base body (2) or both main faces (3, 4) of the base body (2) are each provided with an electrically conductive coating, in particular a metal coating, such as a silver coating or an aluminum coating.

11. The PTC heating element (1) according to any one of the preceding claims, which is used in an electrically operated heater through which air flows and is warmed, which heater is arranged in an air conditioning device for air conditioning an interior space of a motor vehicle.

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