Heating device for installation in a vehicle tank for reducing agents and vehicle tank
The heating device with a heat distribution element and conductive materials addresses uncontrollable heat release issues, ensuring reliable and rapid heating of reducing agents with uniform output.
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- SCHAEFFLER TECHNOLOGIES AG & CO KG
- Filing Date
- 2018-10-02
- Publication Date
- 2026-06-11
AI Technical Summary
Existing heating devices for vehicle tanks storing reducing agents used in exhaust aftertreatment systems face issues with uncontrollable heat release, leading to reduced heating power or shutdown of PTC heating elements due to excessive temperature, especially when the reducing agent level is low.
A heating device with a heat distribution element and a heat conducting device made of materials with varying thermal conductivities, designed to distribute heat uniformly and efficiently within the heat distribution body, preventing excessive temperature rise and ensuring consistent heating power.
Ensures reliable and rapid heating of reducing agents with uniform output, independent of the fill level, by maintaining consistent heat flow and preventing PTC heating element shutdown.
Smart Images
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Abstract
Description
Technical field
[0001] The invention relates to a heating device for installation in a vehicle tank for reducing agents, which can be introduced into the exhaust system of a motor vehicle for exhaust aftertreatment, comprising at least one electric heating element and a heat distribution element, wherein the at least one electric heating element comprises a PTC heating element arranged in thermally conductive contact with the heat distribution element. The heat distribution element is formed from a first material having a first thermal conductivity, and the heat distribution element is configured to transport and dissipate heat generated by the PTC heating element. The invention further relates to a vehicle tank for a motor vehicle, which is designed to store a reducing agent that can be introduced into the exhaust system of the motor vehicle for exhaust aftertreatment, comprising such a heating device. State of the art
[0002] It is known that to reduce nitrogen oxide emissions from motor vehicles with internal combustion engines, a liquid reducing agent is injected into the exhaust stream using the selective catalytic reduction (SCR) process. This process converts the nitrogen oxides (NOx) contained in the exhaust stream into harmless components such as nitrogen (N2) and water (H2O) by means of a catalyst. Ammonia (NH3) and / or a reducing agent precursor such as urea (CH4N2O) or a urea-water solution are typically used as the reducing agent. A 32.5% urea-water solution, available under the trade name AdBlue®, is a proven reducing agent precursor.
[0003] A tank is provided for storing the liquid reducing agent, which interacts with a pumping unit to enable the reducing agent to be pumped from the tank to the exhaust stream. When pumping and storing liquid reducing agent, it must be taken into account that the liquid reducing agent, especially an aqueous urea solution, can freeze, at least partially. For example, the freezing point of the reducing agent precursor AdBlue® is typically around -11 °C.
[0004] This leads to the problem that, especially during cold starts or restarts, there is little to no liquid reducing agent available to supply the exhaust system. Nevertheless, it must be ensured that nitrogen oxides in the exhaust stream are reduced even at very low temperatures in the vicinity of the vehicle. Therefore, measures are required to reduce freezing and / or enable rapid thawing of frozen reducing agent in the tank. For this purpose, the tank used to store the reducing agent is typically equipped with a heating device to keep at least some of the reducing agent in the tank liquid or to liquefy it at low temperatures, thus allowing it to continue being introduced into the exhaust stream.
[0005] Such a heating device typically includes a PTC heating element (PTC = positive temperature coefficient). This type of thermistor, also known as a negative temperature coefficient thermistor, converts electrical current into heat and exhibits a specific temperature-dependent dependence of its electrical resistance. At low temperatures, the PTC heating element has low electrical resistance, which increases exponentially when a defined switching temperature is exceeded. This property makes the PTC heating element self-regulating: at low temperatures, a high current flows, causing the PTC heating element to heat up quickly and generate high heating power. Once the switching temperature is reached, the current through the PTC element decreases, preventing the temperature from rising significantly above the switching temperature, and the heating power is reduced accordingly.
[0006] A heating device and a vehicle tank of the type mentioned above are disclosed, for example, in DE 10 2006 027 487 A1. The heating device is arranged in the vehicle tank for a liquid reducing agent and comprises a flat aluminum body designed as a heat distribution element, in which several electrical heating elements are integrated. The electrical heating elements are PTC heating elements, which transfer heat to the flat aluminum body. The heat is then dissipated to the reducing agent via the aluminum body. This heating device is intended to enable the thawing of frozen reducing agent, so that liquid reducing agent is available even at low temperatures, which can be supplied to the exhaust system via a conveying module.
[0007] Furthermore, DE 10 2007 059 848 A1 describes a heating device that can be installed in a tank for AdBlue®. The heating device has a heating resistor with a positive temperature coefficient, which is surrounded by a ribbed aluminum body.
[0008] From EP 1 767 417 A1, a tank for a urea solution with a heating device arranged in the tank is also known. The heating device has a rod-shaped PTC heating element which is thermally connected to a heat distribution element. The heat distribution element has a fused sleeve with several plate-shaped de-icing surfaces. During operation, heat is conducted from the PTC heating element via the fused sleeve to the de-icing surfaces of the heat distribution element, so that heat is transferred to the urea solution frozen in the tank essentially via the de-icing surfaces.
[0009] WO 2014 / 198 870 A1 discloses a module for the metered supply of a liquid, comprising a chamber having a chamber wall that at least partially encloses a chamber space of the chamber, wherein the chamber is at least partially surrounded by a hood, wherein at least one cavity is present between the hood and the separated chamber, and wherein the hood is heatable.
[0010] A particular disadvantage of such heating devices is that the heat generated by the PTC heating element and transferred to the heat distribution body is essentially released uncontrollably into the environment and / or the reducing agent. This can result, especially when the reducing agent level in the vehicle tank is low, in the PTC heating element transferring more heat to the heat distribution body per unit of time than the heat distribution body can dissipate and release. This causes the temperature of the PTC heating element, in particular, to rise, ultimately leading to a reduction in heating power or even the PTC heating element switching off. In such a case, at least temporarily, only reduced or no heating power is available to warm the reducing agent. Description of the invention, problem, solution, advantages
[0011] Therefore, a first object of the invention is to provide a heating device for installation in a liquid tank for reducing agents, which can be introduced into the exhaust system of a motor vehicle for exhaust aftertreatment, and which ensures the most reliable and rapid heating of the reducing agent with the most uniform heating output possible. Furthermore, the second object of the invention is to provide a vehicle tank for a motor vehicle, which is designed to store a reducing agent that can be introduced into the exhaust system of a motor vehicle for exhaust aftertreatment, with a heating device in which the most reliable and rapid heating of the reducing agent with the most uniform heating output possible is ensured.
[0012] The first problem is solved according to the invention by the features of claim 1. Advantageous embodiments and further developments are set out in the dependent claims and the following description.
[0013] Accordingly, a heating device for installation in a vehicle tank for reducing agents, which can be introduced into the exhaust system of a motor vehicle, comprises, in a known manner, at least one electric heating element and a heat distribution element, wherein the at least one electric heating element comprises a PTC heating element arranged in thermally conductive contact with the heat distribution element. The heat distribution element is formed from a first material having a first thermal conductivity, and the heat distribution element is configured to transport and dissipate heat generated by the PTC heating element.
[0014] According to the invention, a heat conducting device is arranged on and / or in the heat distribution body, which is formed from a second material having a second thermal conductivity different from the first thermal conductivity, wherein the heat conducting device is designed to distribute heat from the PTC heating element in a targeted manner within the heat distribution body, wherein the heat conducting device comprises at least one heat conducting element which is arranged at least partially within the heat distribution body, wherein the heat conducting element is designed to prevent or at least reduce the emission of heat to the environment of the heat distribution body.The invention is based on the premise that particularly efficient heating of the reducing agent in a vehicle tank is achieved when the heating power of a PTC heating element is as uniform and high as possible, without a significant increase in the temperature of the PTC heating element, in particular an increase to or above the switching temperature of the PTC heating element. Furthermore, the invention is based on the premise that reliable and rapid heating of the reducing agent with a uniform heating power is further promoted by ensuring that as much of the heat distribution element as possible is heated, particularly regardless of the fill level of the reducing agent in the vehicle tank.Therefore, the invention provides that the heat distribution body has a heat conduction device arranged on and / or in the heat distribution body, which is made of a second material having a thermal conductivity different from that of the first material of the heat distribution body, and which is designed to distribute heat from the PTC heating element in a targeted manner within the heat distribution body. This allows the heat conduction through the heat distribution body to be influenced in such a way that the heat conduction extends, in particular, over the entire heat distribution body, thus ensuring the most complete possible heating of the heat distribution body and, in principle, making the largest possible surface area of the heat distribution body available for heat dissipation.This helps to ensure that the heat flow introduced into the heating device by the PTC heating element is approximately equal to the heat flow that can be dissipated to the environment and / or the reducing agent by the heat distribution body, thereby significantly reducing the risk of the PTC heating element "switching off" due to excessive temperature and enabling efficient heating of the reducing agent largely independent of the fill level in the vehicle tank.
[0015] The embodiment according to the invention has the advantage that it provides a heating device in which, in particular, a significant heat flow is established within the heat distribution body and which ensures the most reliable and rapid heating of the reducing agent with the most uniform heating output possible.
[0016] The term reducing agent used includes both a reducing agent, in particular ammonia, and a reducing agent solution, a reducing agent precursor, in particular urea, and a reducing agent precursor solution, in particular AdBlue®.
[0017] The heat distribution body is specifically designed to transport or conduct the heat generated by the PTC heating element and transferred to the heat distribution body to areas further away from the PTC heating element and to release heat to the reducing agent and / or the environment.
[0018] The heat-conducting element influences the heat conduction within the heat distribution body in such a way that heat is not released to the environment in the area of the heat-conducting element, or only to a reduced extent, but remains primarily within the heat distribution body and can be conducted within it. The size and / or arrangement of the heat-conducting element can be adapted to the desired heat conduction behavior in the heat distribution body. Preferably, the heat-conducting device comprises several such heat-conducting elements. For example, the heat-conducting element can be made of a second material, particularly a metallic one, which has a higher thermal conductivity than the first, so that it conducts heat particularly well within the heat distribution body.The heat-conducting element can be positioned as far inside the heat distribution body as possible, maximizing the distance between the element and the surface. Alternatively, the element can be made of a second material with a lower thermal conductivity than the first, thus reducing or preventing heat conduction. In this case, the element can be positioned as close as possible to the surface of the heat distribution body, creating thermal insulation within the body. Advantageously, the heat-conducting medium is cast into the heat distribution body.
[0019] The heat distribution body can be in direct contact with the PTC heating element. In an advantageous embodiment of the invention, the heat distribution body has a contact surface against which the PTC heating element rests, at least partially. The heat conduction device comprises a coupling element that is arranged directly between a side surface of the PTC heating element facing the contact surface and the contact surface. The second material of the coupling element has a higher thermal conductivity than the first. In this way, particularly good thermal coupling of the PTC heating element to the heat distribution body and the most targeted possible introduction of heat into the heat distribution body can be achieved.Preferably, the coupling element is designed to have a larger surface area than the side surface of the PTC heating element facing the contact surface, so that the largest possible contact area is formed between the contact surface of the heat conducting device and the coupling element, through which heat can be dissipated from the coupling element to the heat distribution body.
[0020] The coupling element is advantageously made of a second material that exhibits a significantly higher thermal conductivity than the first. A metal body, preferably a metal foil or sheet, is particularly advantageous for the coupling element. Metals generally have high thermal conductivity. Using a metal foil or sheet provides a lightweight coupling element that also requires little installation space.
[0021] In a further advantageous embodiment, the heat-conducting device comprises at least one thermal insulation layer, which is arranged at least partially on the surface of the heat distribution body. The second material of the at least one thermal insulation layer has a lower thermal conductivity than the first. This ensures that the heat generated by the PTC heating element and transferred to the heat distribution body is not, or only to a reduced extent, released to the environment, at least in the area of the surface of the heat distribution body where the thermal insulation layer is located, but rather remains primarily within the heat distribution body and can be conducted within it. The size and / or arrangement of the thermal insulation layer can be tailored to the desired heat conduction behavior within the heat distribution body.Preferably, the heat-conducting device comprises several such thermal insulation layers. In particular, the entire area adjacent to the PTC heating element can be provided with one or more thermal insulation layers. Advantageously, the thermal insulation layer is made of a second material that has a significantly lower thermal conductivity than the first, preferably a second material that has a significantly lower thermal conductivity than metal.
[0022] The heat distribution body can, for example, be made of a metallic first material. In an advantageous embodiment, the first material is aluminum. Aluminum has a particularly high thermal conductivity and thus promotes heat conduction and heat distribution within the heat distribution body.
[0023] In a further advantageous embodiment, the heat distribution element is essentially pot-shaped. Such a heat distribution element can be inserted, in particular from below, into a bottom opening of the vehicle tank and, when installed, extends with its essentially circular cylindrical wall and base from the bottom of the vehicle tank into the interior of the tank. This design enables a particularly large heat distribution area and thus a large heat flow to the reducing agent, thereby further contributing to reliable and rapid heating of the reducing agent.
[0024] The second problem is solved according to the invention by the features of claim 8.
[0025] The vehicle tank according to the invention for a motor vehicle is designed to store a reducing agent which can be introduced into an exhaust stream of the motor vehicle for exhaust aftertreatment. The vehicle tank has a heating device according to the invention.
[0026] The advantages and preferred embodiments described for the heating device according to the invention also apply accordingly to the vehicle tank according to the invention. Brief description of the drawings
[0027] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 in a schematic sectional view a heating device, and Fig. 2 in a schematic sectional view a vehicle tank with a heating device in an alternative embodiment.
[0028] Corresponding parts in all figures are always marked with the same reference symbols.
[0029] In Fig. Figure 1 shows a schematic sectional view of an embodiment of a heating device 1. The heating device 1 comprises an electric heating element 2, which contains a PTC heating element 3, and a heat distribution body 4 made of aluminum. The PTC heating element 3 is in thermal contact with a contact surface 5 of the heat distribution body 4.
[0030] The PTC heating element 3 can be accessed via the Fig. The electrical connection (not shown) is supplied with electrical energy and converts electrical energy into heat during operation. The PTC heating element 3 exhibits a particular dependence of its electrical resistance on temperature. At low temperatures, the PTC heating element 3 has a low electrical resistance, which increases exponentially when a defined switching temperature is exceeded. Upon reaching the switching temperature, the current through the PTC element 3 is reduced, and the heating power is correspondingly decreased.
[0031] The heat distribution body 4 has a heat conducting device 6, which is arranged on and in the heat distribution body 4. The heat conducting device 6 is made of a second material that has a second thermal conductivity different from that of aluminum and is designed to distribute heat generated by the PTC heating element 3 in a targeted manner within the heat distribution body 4.
[0032] For this purpose, a coupling element 8 is arranged between a side surface 7 of the PTC heating element 3 facing the contact surface 5 and the contact surface 5. The coupling element 8 is designed as a metal sheet with a higher thermal conductivity than aluminum. Furthermore, the coupling element 8 has a larger surface area than the side surface 7 of the PTC heating element 3 facing the contact surface 5, so that a large contact area is formed between the contact surface 5 of the heat distribution body 4 and the coupling element 8, through which heat can be transferred from the coupling element 8 to the heat distribution body 4. This ensures particularly good thermal coupling of the PTC heating element 3 to the heat distribution body 4 and allows for the most targeted possible introduction of heat into the heat distribution body 4. Additionally, a thermal insulation layer 9a is arranged in certain areas on the surface of the heat distribution body 4.The thermal insulation layer 9a is made of a second material that has a lower thermal conductivity than aluminum. This ensures that the heat generated by the PTC heating element 3 and transferred to the heat distribution body 4 is not released to the environment, or only to a reduced extent, at least in the area of the surface of the heat distribution body 4 where the thermal insulation layer 9a is located, but remains primarily within the heat distribution body 4 and can be conducted within it.
[0033] Furthermore, a heat-conducting element 10 is arranged in a region near the surface of the heat distribution body 4. The heat-conducting element 10 is designed to prevent or at least reduce the transfer of heat to the surroundings of the heat distribution body 4. The heat-conducting element 10 thus also influences the heat conduction within the heat distribution body 4 in such a way that heat is not transferred to the surroundings in the area of the heat-conducting element 10, or only to a reduced extent, but remains primarily within the heat distribution body 4 and can be conducted within it. The heat-conducting element 10 is made of a second material that has a lower thermal conductivity than aluminum, so that heat conduction through the heat-conducting element 10 is prevented or reduced.
[0034] The targeted distribution of heat within the heat distribution body 4, influenced by the heat conduction device 6, ensures that heat conduction extends across the entire heat distribution body, thus enabling the most complete heating of the heat distribution body 4 possible. This maximizes the surface area of the heat distribution body 4 available for heat dissipation. Consequently, the heat flow introduced into the heat distribution body 4 by the PTC heating element 3 closely matches the heat flow that the heat distribution body 4 can dissipate to the environment and / or the reducing agent. This significantly reduces the risk of the PTC heating element 3 shutting down due to excessive temperature and ensures the most reliable and uniform heating performance possible.
[0035] Fig. Figure 2 shows a schematic sectional view of a vehicle fuel tank 11 with a heating device 1 in an alternative embodiment. The heating device 1 essentially corresponds to the one shown in Figure 2. Fig. 1 heating device 1 shown, wherein the heat distribution body 4 is essentially pot-shaped.
[0036] Reducing agent 14 is located in an inner compartment 12 of the vehicle tank housing 13. An opening 16 is provided in the area of the bottom 15 of the vehicle tank 11, through which the heating device 1 is positioned, projecting into the inner compartment 12 of the vehicle tank 11. The heat distribution element 4 has a circumferential, collar-like contact section 17, which is arranged to seal against the bottom 15 of the vehicle tank 11 on the outside. The heat distribution element 4 thus separates a drying chamber 18 from the inner compartment 12 of the vehicle tank 11, which is filled with reducing agent 14. A conveying module (not shown) for conveying the reducing agent 14 can be accommodated in this drying chamber 18.
[0037] The heat conduction device 6 of the heat distribution body 4 comprises the coupling element 8, which is arranged directly between the PTC heating element 3 and the heat distribution body 4, as well as two thermal insulation layers 9b, 9c of different sizes, which are arranged in certain areas on the surface of the heat distribution body 4. One thermal insulation layer 9b is arranged on the surface of the heat distribution body 4 facing the inner area 12 of the vehicle tank 11, and the other thermal insulation layer 9c is arranged on the surface of the heat distribution body 4 facing the drying chamber 18.
[0038] The pot-shaped design of the heat distribution body 4 enables a large surface area heat transfer and thus a relatively large heat flow to the reducing agent 13, thereby further contributing to a reliable and rapid heating of the reducing agent 13.
[0039] The different features of the individual embodiments can also be combined with one another. The embodiments of Fig. 1 and Fig. 2 in particular do not have a restrictive character and serve to clarify the inventive idea.
Claims
[1] Heating device (1) for installation in a vehicle tank (11) for reducing agent (14), which can be introduced into an exhaust system of a motor vehicle for exhaust aftertreatment, comprising at least one electric heating element (2) and a heat distribution body (4), wherein the at least one electric heating element (2) comprises a PTC heating element (3) arranged in thermally conductive contact with the heat distribution body (4), wherein the heat distribution body (4) is formed from a first material having a first thermal conductivity, and wherein the heat distribution body (4) is configured to transport and release heat generated by the PTC heating element (3), wherein a heat conducting device (6) is arranged on and / or in the heat distribution body (4), which is formed from a second material having a second thermal conductivity different from the first, and wherein the heat conducting device (6) is configured toto distribute heat from the PTC heating element (3) in a targeted manner within the heat distribution body (4), , characterized by , that the heat conducting device (6) comprises at least one heat conducting element (10) which is arranged at least partially within the heat distribution body (4), wherein the heat conducting element (10) is designed to prevent or at least reduce the emission of heat to the environment of the heat distribution body (4). [2] Heating device (1) according to claim 1, characterized by , that the heat distribution body (4) has a contact surface (5) on which the PTC heating element (3) is at least partially in contact, wherein the heat conducting device (6) comprises a coupling element (8) which is arranged directly between a side surface (7) of the PTC heating element (3) facing the contact surface and the contact surface (5), and wherein the second material of the coupling element (8) has a higher second thermal conductivity than the first. [3] Heating device (1) according to claim 2, characterized by , that coupling element (8) is a metal body, preferably a metal foil or a metal sheet. [4] Heating device (1) according to one of the preceding claims, characterized by , that the heat conducting device (6) comprises at least one thermal insulation layer (9a, 9b, 9c) which is arranged at least partially on the surface of the heat distribution body (4), wherein the second material of the at least one thermal insulation layer (9a, 9b, 9c) has a second thermal conductivity that is lower than the first thermal conductivity. [5] Heating device (1) according to any one of the preceding claims, characterized by that the first material is aluminum. [6] Heating device (1) according to any one of the preceding claims, characterized by , that the heat distribution body (4) is essentially pot-shaped. [7] Vehicle tank (11) for a motor vehicle, which is designed to store a reducing agent (14) which can be introduced into an exhaust stream of the motor vehicle for exhaust aftertreatment, with a heating device (1) according to one of claims 1 to 6.